Deep-UV (240-250 nm) lithography is of one the most promising new lithographic techniques for patterning devices with 0.35-0.5 μm structures. Chemically amplified resists have been reported to meet the necessary requirements of both excimer laser and Hg source-based exposure tools. The chemistry of one family of these materials involves the photogeneration of organic acid catalysts from 2,6-dinitrobenzyl esters, which, upon mild heating, effect the removal of a t-butoxy carbonyl protecting group from poly(t-butoxycarbonyloxy-α-methylstyrene), [poly(t-BOC-α-methylstyrene)]. The thermal behavior of the esters has been examined, and the quantum yield determined for selected examples. A lithographic evaluation of resists based upon several organic ester acid precursors and poly(t-BOC-α-methylstyrene) has been made. Sensitivities ranging from 2 to 100 mJ/cm² in the deep-UV region have been observed, and 0.5 μm resolution has been demonstrated, using a contact printer equipped with a 248 nm laser source.

Poly(p-t-butoxycarbonyloxystyrene) (PBOCST) and poly(t-butyl p-vinylbenzoate) (PTBVB) provide sensitive, negative tone, electron beam resist systems when sensitized with "onium salt" acid generators. The sensitivity is high (0.5-2.5μC/cm² at 20 keV) owing to chemical amplification. The resolution and contrast are also high owing to the polarity change incorporated in the design. Development with an organic solvent provides sub-half-micrometer resolution.

Photolithography using KrF excimer laser (248 nm) is the most exciting technology which has the capability of resolution below 0.5 pm. However good profiles of resist patterns are not obtained by the KrF excimer laser lithography because of strong absorption of conventional deep UV resist such as naphtoquinonediazide-novolac resin type. In order to resolve this problem, a new positive resist (STAR-P) for KrF excimer laser lithography has been developed. This resist is composed of 2-diazo-1,3-dicarbonyl compounds for a sensitizer, which is an alkaline dissolution inhibitor for base polymer, poly (stylene-co-maleic acid half ester) as a base polymer, and diethylene glycol dimethyl ester as a coating solvent. 2-diazo-1,3-dicarbonyl compounds have a strong absorption peak at around 248nm, and are effectively bleached by KrF excimer laser exposure. Moreover, the transmittance of base polymer at 1.0pm thickness is 70% at 248nm. In this study, the photobleachability, thermal stability and inhibition of these sensitizers were evaluated on several 2-diazo-1,3-dicarbonyl compounds which had different substuents. The resolution of these resists were evaluated by a KrF excimer laser stepper system (NA:0.36). The new resist with 1,7-bis(3-chlorosulfony1-4-methyl phenyl)-4-diazo-3,5-heptanedione as sensitizer (STAR-P2) shows the best results. Strong photobleaching occurred at around. 248 nm by KrF excimer laser exposure. The loss of resist thickness at unexposed regions after developing was hardly observed. It was found that chlorosulfonyl groups have a superior capacity for alkaline inhibition. Gamma (γ) value was 2.71, and it was much higher than that of conventional positive resist of naphtoquinonediazide-novolac resin type (1.05). High aspect ratio sub-micron patterns were obtained in spite of the 1.Oμm resist thickness. In conclusion, a new positive resist for KrF excimer laser lithography has been developed. As STAR-P2 has excellent photobleachability for the KrF excimer laser exposure, high aspect ratio patterns can be attained at 1pm thickness. A new single-layer-resist system for KrF excimer laser lithography is realized by using this new resist (STAR-P2).

This paper describes the development of deep UV resist materials based on chemically amplified crosslinking systems for use in excimer laser photolithography at the KrF lasing wavelength of 248 nm. This work will describe the use of a transparent resin, polyp-vinyl)phenol, which has excellent plasma etch resistance and demonstrates high resolution (sub half-micron line-space pairs for a 1.0 micron thick film) when used in an Advanced Negative Resist (ANR) formulation, XP-8843. Under 140C post-exposure bake conditions, XP-8843 exhibits fast photospeed (15 mJ/cm²), high contrast (4.1), vertical sidewalls, and good process latitude.

The dissolution inhibition effect and alkaline solubility were investigated for naphthoquinone diazides like 1,2-naphthoquinone diazide (NQD), its 5-sulfonylchloride (NQD-C) and 5-sulfonyloxybenzene (DAM), and for other compounds like sulfonylchlorides, sulfonyl esters, sulfones and a ketone which do not contain a naphthoquinone diazide moiety. As a result, it has turned out that the dissolution inhibition effect does not depend on the specific structure; namely, the naphthoquinone diazide moiety itself, but largely on the alkaline solubility of the compounds added to a novolak resin. An XPS study for the films consisting of a novolak resin and a dissolution inhibitor indicates a formation of an inhibitor-rich protective thin layer on the film surface after immersion of the film in an alkaline developer. In this paper is proposed a new third dissolution inhibition mechanism in addition to the previously reported chemical crosslinking and dipolar interaction; i.e., the alkaline insoluble protective layer inhibits the dissolution of novolak resin at the interface between the film and the developer. A new three-component type deep-UV resist has been also developed as an application of the new mechanism. The resist consists of a novolak resin, 5-diazo Meldrum's acid and a new dissolution inhibitors like phenyltosylate and p-phenylene ditosylate, which successfully improve the residual resist thickness.

A new simple photoresist process for contrast enhancement of pattern profiles was published in 1987's SPIE symposium. This process, which is called REL (Resolution Enhanced Lithography), consists of conventional novolak positive photoresist process steps and a deep UV flood exposure step between image exposure and development. The effect of REL process is caused by the reduction of the solubility rate in alkaline developer in the exposed areas. In this paper, we describe the influence of the flood exposure light wavelength on profiles of photoresist and a chemical formation reaction of the insoluble layer in alkaline developer. In the experiments, three types of light sources were used which had maximum intensities at wavelengths of 254nm, 313nm, and 365nm, respectively. The resist profiles depend on the wavelength of the deep UV flood exposure light. A good resist profile with rectangular cross section was obtained with the 365nm light source. In this case, the flood exposure light reaches the internal region of the resist and the dissolution rate reduction occurs not only at the surface but also in the bulk of the resist. The chemical formation reaction of insoluble layer in alkaline developer was studied, using Differential Scanning Chromatography (DSC), Thermogravimetric analysis (TGA), Gel Permeation Chromatography (GPC), and Fourier Transform Infrared Spectroscopy (FT-IR). From the results of these analyses, it is concluded that the formation of the insoluble layer results from the esterification reaction under the deep UV flood exposure between novolak resin and unphotoreacted PAC in the exposed areas.

The ion beam interaction with very thin films (0.5 μm thickness) of a fundamental polymer, polystyrene, was investigated by means of radiation chemistry. Radiation effects on solubility of spin-coated polystyrene films were measured for hydrogen, helium and nitrogen ion beams (0.4 - 3.3 MeV). Measurements were also carried out for 20 keV electrons. By using ion beam pulse radiolysis system, the transient phenomena excited by energetic ion beams were investigated. The time profiles of the excimer fluorescence from ion irradiated polystyrene thin film were measured for hydrogen, helium and nitrogen ions (0.6 - 2.8 MeV). The results for energetic ions were compared with those for low LET radiation, such as fast electron or gamma-ray. Very large differences in radiation effects on solubility and some differences in transient phenomena were found and discussed from the view point of high density electronic excitation.

A molecular mechanism for the dissolution of novolac is proposed, based on the idea of a critical degree of deprotonation as being the condition for the transfer of polymer into solution. The rate at which the critical deprotonation condition is achieved is controlled by the supply of developer into a thin penetration zone, and depends in particular on the rate of diffusion of the base cations which are the developer component with the lowest mobility. The penetration zone contains phenolate ions and ion-bound water, but it retains the structure of a rigid polymer membrane, as evidenced by the diffusion coefficient of cations in the pene;tration zone which is several orders of magnitude slower than in an open gel of the same material. When the critical degree of deprotonation is reached, the membrane structure unravels and all subsequent events, chain rearrangement and transfer into solution, occur rapidly. The supralinear dependence of dissolution rate on base concentration and the effect of the size of the base cation are plausibly interpreted by the model. The diffusion of developer components is assumed to occur preferentially via hydrophilic sites in the polymer matrix. These sites define a diffusion path which acts like a hydrophilic diffusion channel. Suitably designed hydrophobic molecules can block some of the channels and in this way alter the dissolution rate. They reduce in effect the diffusion crossect ion of the material. Hydrophilic additives, on the other hand, introduce additional channels into the system and promote dissolution. The concept of diffusion channels appears to provide a unified interpretation for a number of common observations.

The role of resin structure, molecular weight and glass transition temperature, Tg, on the thermal performance of positive photoresists were investigated. The novolak resins in these resists have structures with progressively higher order of regularity, stiffness and intermolecular hydrogen bonding, yet of sufficient molecular weight to be functional. We have found good correlation between resist thermal performance and the novolak resin chemical composition and structure. Cresylic formaldehyde resins provide almost identical hardbake deformation temperature, HBDT, regardless of the resin Tg, structure, monomer ratio and resist solvent. Resistance to thermal flow increases as the resin stiffness, aromatic character and intermolecular hydrogen bonding are increased. Photoresist resolution, however, is dependent on the type of solvent used, resin molecular weight, chemical composition and structure. Photoresist compositions which exhibit the higher HBDT, generally, have poor resolution capability. By properly balancing the resin structure and composition, positive photoresists were developed showing high resolution capability and resistance to thermal flow, in the range of 145 to 190°C.

This paper describes the effect of elevated softbake temperatures, up to 150°C, on the behavior of diazoquinone/novolac high resolution positive photoresists. The advantages of higher softbakes include improved thermal stablity, contrast and process latitude. For a standard g-line photoresist using a 2,1,5-diazo/THBP PAC (EPA-914-27, MacDermid Inc.), it was found that by increasing the softbake from 110° to 130°C, gamma increased from 2.4 to 3.8 and the thermal stability (the start of image rounding) increased from 120° to 130°C; while the required exposure energy increased by only about 30%. UV absorption revealed that about 90% (compared to 110°C softbake) of the diazo is retained at 130°C, and about 55% at 150°C. GPC analysis showed that resin/PAC reactions occurred to some extent at a softbake of 130°C, and extensively at 150°C. These resin/PAC interactions appear to be the source of the improved properties observed with higher softbake temperatures. Similar results were not found with 2,1,4-type resin. Several other systems were also investigated to further understand the photoresist chemistry.

The use of controlled absorption by the addition of organic dyes to photoresists has improved notching control over topography on reflective substrates. However, the majority of dyes commonly used have a side effect of significant photospeed loss. Earlier work by Bohland et all has shown the dissolution effect of either coumarin 6 or coumarin 314 dye in photoresist to play a greater role in changing energy required to expose the resist than the optical effects of the dyes. Curcumin dye was found to minimize photospeed loss in novolak-based positive photoresist while maintaining control of reflective notching. Preliminary base solubility investigations of curcumin and coumarin 314 revealed striking differences between the two dyes. Curcumin is freely soluble in metal ion bearing developers as well as in metal ion free developers; coumarin 314 is sparingly soluble at best in both developer types. Curcumin owes its absorption at 436 nm to extended conjugation of its enolic tautomer, which is more acidic than its keto counterpart. This increased acidity is conjectured to be the main cause of curcumin's enhanced solubility in base, as compared to coumarin 314. The effect of these differences on photoresist lithographic performance is the subject of this paper. Using Bohland's methodology, the Dill optical and dissolution rate constants were combined in turn to partition the optical and the dissolution contributions of both dyes to the resulting simulated image. SAMPLE and DRM-PROSIM simulations were conducted. Dissolution rates of dyed, unsensitized polymers were measured as a function of both dye loading and type. Additionally, unexposed dissolution rates of both curcumin- and coumarin 314-dyed Shipley Microposit^® S1400-31^TM photoresists were measured as a function of their respective dye loadings.

Fundamentals and mechanism of a direct image reversal process, which switches the tone of a resist from positive to negative without added bases are presented. A sulfonic acid generated photochemically from an aryl naphthoquinonediazide-sulfonate catalyzes the crosslinking of exposed resist areas. Based on this principle, a concept for a new naphthoquinonediazide with sufficient absorptivity at g-line and preserved acid generating capability was developed. The desired functionality of the PAC, prepared in a multistep synthesis, is proven. Guidelines for optimization of the most important process parameters are established for the newly formulated g-line image reversal resist. Lithographic results include 0.6 μm equal lines and spaces with nearly vertical side walls using a 0.35 NA g-line stepper.

This paper studies the chemistry of image reversal resists composed of diazonaphthoquinone/novolac resins and varying amounts of aliphatic and aromatic amines. Special emphasis is placed on understanding the mechanism of decarboxylation as impacted by 2,1,4- vs. 2,1,5-diazonaphthoquinone esters. It is shown that the electron-withdrawing effect of the sulfonyl group in the 4- position of the diazo is much stronger compared to the same effect of the same group in the 5- position. The 2,1,4-type resists are therefore more effective in image reversal, requiring lower amine concentrations to be operative. The impact of the weaker electron-withdrawing effect in the 2,1,5-type sensitizer can be compensated for by increasing the concentration of the amine. Higher basicity of the amine allows lower concentrations for satisfactory image reversal performance. Unlike image reversal systems based on acid-catalyzed, heat-induced crosslinking, which tend to favor negative slopes, sidewall profiles of the systems studied here can be controlled from negative, to vertical, to positive, by changing the diazo content of the resist and the PEB temperature. It has also been found that some of the decarboxylation type, image reversal formulations display shelf-life stabilities greater than six months, making them viable production products.

Physical bombardment plays a dominant role in the O₂ reactive ion etching (RIE) pattern transfer step in multilevel lithography. Statistical mechanical models of sheath collision processes relate the flux, energy, and angular distribution of particles bombarding the surface to the pressure, sheath thickness, and voltage drop across the sheath. The estimated flux of bombarding particles allows measured etching rates to be converted into yields. We find that the trends for the etching rate as a function of pressure, bias voltage, frequency and other system variables reflect a single trend for the yield as a function of the average bombardment energy. Organic polymer etching yields are proportional to bombardment energy while there is a threshold energy in organosilicon polymer etching; consequently the selectivity in bilevel lithography increases as the bombardment energy decreases. Etching profiles and process latitudes are determined by the yield weighted angular distribution, and by the etching rate relative to the mask erosion rate. The angular distributions are determined by the dimensionless sheath thickness in units of the mean free path for momentum transfer collisions. Mask erosion is not significant in trilevel lithography where the etching mask is Si0₂, however, depending on the selectivity and the wall angle, mask erosion may significantly affect profiles and latitudes in bilevel lithography. The etching rate at each point on the polymer interface is proportional to an energy flux vector that is calculated by performing a double integral of the energy weighted angular distribution function over the field of view accessible to that point on the interface. The resulting interface evolution equation is mathematically equivalent to a free surface evolution equation for a two phase hydro-dynamic system, where the energy flux vector plays the role of the fluid velocity vector in the hydrodynamic system. This convective partial differential equation is reduced to a coupled set of ordinary differential equations via the method of characteristics (or rays) and solved numerically. The predicted etching profiles are in good agreement with observed profiles over a wide range of etching conditions. Simulated process latitude trends in multilevel lithography are presented.

Steady-state etching rates and initial film losses were measured for two types of silicon-containing polymers (polysiloxanes and polysilyistyrenes) under a variety of oxygen plasma conditions. While steady state behavior was observed for most conditions, the silylstyrene resists showed higher etch rates than predicted from recent models. The deviations were explained by the fact that the oxidized layer formed from silylstyrene polymers has a large residual carbon content, and thus sputters at a rate higher than predicted for a stoichiometric SiO₂ layer. The siloxane material showed good agreement with the model under all conditions and was determined to form a more SiO₂-like oxidized layer. XPS analysis was used to monitor the conversion of carbon-bound silicon to oxidized species for the polysilylstyrenes. Conversion was more rapid and more complete when etching with higher ion energies. Polysilylmethylstyrene reached a steady-state oxide thickness between 3.4 and 5.8 nm, depending on etching conditions. A copolymer of this material with chloromethylstyrene showed a comparable thickness when etched at high ion energies, but did not reach a steady state when etched at conditions where the average ion energy was below 110 eV.

Novel Polysiloxanes with a phenol pendant group were synthesized and applied to bilayer photoresists for g-line and deep-UV (248 nm) lithography. These polymers had adequate aqueous-base solubility and oxygen-RIE resistance to serve as the base resin component for top imaging resists in bilayer resist systems. One of these polysiloxanes was synthesized from chlorodiethoxyphenylsilane and m-trimethylsiloxychlobenzene. Others were synthesized from dichlorophenylsilane and phenol and phenols with a double bond moiety (eugenol, isoeugenol and m-isopropenylphenol). These polysiloxanes had from 9.8 wt.% to 13.1 wt.X Si content and displayed an oxygen-RIE resistance 10 times greater than novolak resin. The m.p. values for these polymers ranged from 30°C to 90°C. The UV transmittance value (at 248 nm, 1 micron thickness) were from 7 % to 76 X. Resists were prepared from these polysiloxanes and sensitizers. In g-line lithography, the sensitizer was naphthoquinonediazide. In deep-UV (248 nm) lithography, the sensitizer was selected from naphtoquinonediazide, diazide and diazo compounds. 0.5 micron line and space patterns were obtained, when the resist was exposed using a g-line stepper, and using a tetramethylammonium hydroxide solution (ca. 1.3 %). 0.4 micron line and space patterns were resolved, when the resist was exposed using a KrF excimer laser stepper, and developed using the same solution. The top layer pattern could be transferred to the bottom layer (hard baked positive resist OFPR-5000) using oxygen-RIE. The etching rate for the silicon containing resist was 35 nm/min, while that for OFPR-5000 was 555 nm/min. These polysiloxanes make it possible to obtain the fine pattern resolution required in VLSI processing.

The concept is attained that controlling of the dissolution rate ratio between completely exposed and unexposed resist areas is useful for obtaining steeper resist profiles and higher resolution when resists have high absorbance. Its usefulness is confirmed by experiments. Using 0.4 μm thick SPP with absorbance of 0.4, the linear relation between mask and resist pattern line widths is maintained to 0.40 μm line and space patterns. 0.36 μm line and space patterns with vertical walls are obtained in 0.4 μm thick SNP with absorbance of 1.2.

Peroxo-polytungstic acid (HPA) is investigated as a spin-coatable inorganic resist material for excimer laser lithography. HPA is synthesized by dissolving metallic tungsten into an H₂O₂ solution. It is possible to form an amorphous and microstructure-free film by spin-coating a water-based solution. The sensitivity characteristics of the film were determined for KrF (248 nm) and XeC1 (308 nm) excimer lasers. Absorption coefficients at 248 nm and 308 nm are 7μm^-1 and 2μm^-1, respectively. Solubility of the film is reduced by laser beam irradiation. Sensitivity for KrF is nine times higher than for XeC1 owing to the difference in laser beam absorbance. Moreover, sensitivity is enhanced by niobium doping to HPA. The best sensitivity is 100 mJ/cm² at 248 nm, which is almost the same value as that for a typical novolak-based organic resist. The effects of reciprocity failure are small in laser pulse energy less than 16 mJ/cm²-pulse. Reduction projection of KrF excimer laser was performed using a stepper with a lens NA of 0.35. A good profile sub-half micron pattern with an aspect ratio of 3 was successfully fabricated through the two-layer resist process.

A novel dry-developed single-layer resist scheme has been used to form submicrometer patterns in thick (>1 μm) polymer films exposed with deep-UV light. Hydrophobic polymers such as halogenated or chloromethylated polystyrenes or analogous poly(vinylbiphenyls) undergo oxidation to form hydroxyl and carbonyl groups when exposed in air with 248.4 or 193 nm light. The hydrophilic hydroxyl and carbonyl groups in the exposed regions bind water to the polymer surface via hydrogen bonding. In contrast, the unexposed hydrophobic regions that lack equivalent hydrogen bonding functionalities do not bind water at the polymer surface. Treatment of the patterned (exposed) films with TiCI4 converts the adsorbed water on the exposed regions into TiO2 which protects the underlying organic film from oxidative removal during a subsequent oxygen reactive ion etching step, thus affording negative tone images. The sensitivity of the polymer depends on the type, amount and the position of halogen on the aromatic group. Optimum results were obtained for chlorinated polystyrenes exposed at 193 nm where absorbance is very high (sensitivity 6-32 mJ/cm², γ > 2.0). Patterns having submicrometer features were made with 193 and 248.4 nm light, but results obtained from 193 nm exposure were somewhat inferior than expected because of the exposure tool limitations. Exposure of the same polymers at 248.4 nm using a deep-UV stepper has provided patterns with ~0.4 μm resolution in 1.2 μm thick films (sensitivity 200 - 300 mJ/cm², γ > 1.5) in spite of their very weak absorption at 248 nm (ε <200 I/mole-cm). Patterns made this way presently have some line-edge roughness and background residue.

The silylation behavior of some positive resists has been investigated using 248nm KrF Excimer laser expo-sure. In particular we have studied novolac-based mid-UV (i-line) positive resists and also variants which use an image reversal scheme. Both types of resist were found to produce selectivities in etch rate of 10-15. The etch rate was slower in the exposed regions in the positive case, and slower in the flood-exposed areas in the image reversal schemes. We have compared our results to the mechanisms for silylation selectivity suggested in the literature and find them to be consistent with models that propose cross-linking as a diffusion inhibitor. The nature of the cross-linking however is not the same in all cases, and depends on the chemistry and processing parameters of the resist system.

In this paper various single level resist systems are presented that combine gas phase silylation with dry development. For novolak-diazoquinone type resists it is shown that the photoselectivity of the silylation process is determined, to a large extent, by the presence of hydrogen bonds between the resin and the un-exposed sensitizer. Upon irradiation these physical crosslinks are replaced by weaker hydrogen bonds between the resin and the indene-carboxylic acid. The effect of the presilylation bake temperature and decarboxylation are discussed. Also the influence of decomposition of the photoactive compound on the selectivity is shown. Other systems presented in this paper are based on chemical crosslinking of the resist. SUPER (SUbmicron Positive dry Etch Resist) is based on the combination of acid-catalyzed crosslinking and gas phase silylation. Because of the chemistry that is used, SUPER can be an interesting candidate for DUV-lithography. Crosslinking of, novolak-diazoquinone type photoresists is another possibility to create a selectivity for the silylation process. A system based on electron beam lithography is presented. Sub-half-micron features, without problems with the proximity effect, are shown.

Double layer resist process using fatty acid and Al was proposed for fine pattern fabrication. Oriented thin films of stearic acid and w-tricosenoic acid were formed on an Al evaporated substrate by evaporation using a furnace with an orifice of a few mm diameter. Electron beam exposure characteristics of the films were studied and 2um L/S pattern was successfully developed by heating the substrate and C12 etching of Al.

Optical lithography is reflection limited within the limits of the image contrast provided by the exposure tool. The introduction of antireflection layers (ARLs) enables the use of high contrast resists which reproduce the optical image within the theoretically maximum possible range. If such resists are available, the need for multilayer resist techniques is appreciably reduced. This work reviews the known lithographic tools that counteract the reflection problem especially in the case of Al-layers, and extends the application of ARLs to silicide, poly-Si and dielectric layers on Si. The results are based on simulations performed with SAMPLE and experimental work on submicron devices.

Ultrathin (0.9 nm - 15.3 nm) poly(methylmethacrylate) (PMMA) films prepared by the Langmuir-Blodgett (LB) technique have been explored as high-resolution electron beam resists. One-eighth micron lines-and-spaces patterns have been achieved by using a Perkin Elmer MEBES I pattern generation system as the exposure tool. The etch resistance of films with thicknesses greater than 4.5 nm is sufficient to allow patterning of chromium film suitable for photomask fabrication. Monolayer PMMA films containing 5 mol% pyrenedodecanoic acid (PDA) as a probe were prepared by transfer to the substrate at different surface pressures and characterized by fluorescence spectroscopy. The ratio of excimer to monomer emission intensity (Ie/Im) has a maximum value at ~ 10 dyn/cm, which may be related to a structural rearrangement in the film. Intrinsic bilayer LB PMMA films prepared at 1 and 19 dyn/cm have also been examined by transmission electron microscopy (TEM). The wrinkle-like surface topography observed in the 19 dyn/cm sample and not in the 1 dyn/cm sample suggests that the structure of the LB PMMA film depends on the transfer pressure.

A general approach to the modeling and simulation of advanced resist systems that rely on transitions between multiple chemical states is presented. The SAMPLE program has been extended to include multiple chemical states that occur during post-exposure baking steps. The bake simulation routine uses reaction kinetics to convert a user specified system of chemical reactions to a system of nonlinear first order differential equations. The system of differential equations is solved numerically for the local concentration of each chemical state throughout the resist as a function of time. The general modeling approach and simulation capability are demonstrated for Shipley XP-8798 chemical amplification resist. The exposure is modeled through resist bleaching measurements. Infrared spectroscopy is used to determine reaction rate coefficients for the acid catalyzed cross-linking reaction that occurs during the post-exposure bake. The development rate is related to the state of the resist following the bake. The models for the exposure, baking and development of the resist are combined to simulate a resist development profile. Experimental results are used in conjunction with simulation to determine the effect of increased sensitivity on resolution.

Picosecond electron-beam and synchrotron radiation pulse radiolysis are powerful method to study the reaction mechanism in irradiated electron beam and X-ray resists. The primary processes can be detected spectroscopically by using both pulse radiolysis systems. The details of the pulse radiolysis systems and a typical exsample of pulse radiolysis studies on the resists are introduced.

A versatile system designed specifically for experimental automated photoresist characterization has been constructed utilizing an excimer laser source for exposure at 248nm. The system was assembled, as much as possible, from commercially available components in order to facilitate its replication. The software and hardware are completely documented in a University of California-Berkeley Engineering Research Lab Memo. An IBM PC-AT compatible computer controls an excimer laser, operates a Fourier Transform Infrared (FTIR) Spectrometer, measures and records the energy of each laser pulse (incident, reflected, and transmitted), opens and closes shutters, and operates two linear stages for sample movement. All operations (except FTIR data reduction) are managed by a control program written in the "C" language. The system is capable of measuring total exposure dose, performing bleaching measurements, creating and recording exposure pulse sequences, and generating exposure patterns suitable for multiple channel monitoring of the development. The total exposure energy, energy per pulse, and pulse rate are selectable over a wide range. The system contains an in-situ Fourier Transform Infrared Spectrometer for qualitative and quantitative analysis of the photoresist baking and exposure processes (baking is not done in-situ). FIIR may be performed in transmission or reflection. The FTIR data will form the basis of comprehensive multi-state resist models. The system's versatility facilitates the development of new automated and repeatable experiments. Simple controlling software, utilizing the provided interface sub-routines, can be written to control new experiments and collect data.

The advantages of using polydimethylglutarimide (PMGI) as an underlayer for a "Portable Conformable Mask" (PCM) process have been demonstrated by Shipley Company and Rohm and Haas. Here we describe an optimized PMGI formulation coupled with an advanced bilayer resist process. This paper reports on material studies involving PMGI composition, dye additives, and a casting solvent and their relationship to PCM process control. The use of different Deep UV flood expose wavelengths during the image transfer step has an effect on image profile and exposure time. Wavelengths between 240 nm and 280 nm are preferred. For submicron imaging, a dyed Novolak resist can be used to increase the masking efficiency of the imaging layer. A PCM process using a Novolak resist imaging layer and a dyed PMGI planarizing layer controls standing wave effects and reflective notching and provides thick resist patterns for etching and lift-off applications. Excellent linewidth control and process latitude can be achieved on g-line steppers.

New pattern transfer technology for G-line lithography has been developed. G-line lithography using steppers have become the main tool in the production of submicron design rule VLSI. To adapt G-line lithography for half-micron design rule VLSI production, we have developed new and simple pattern transfer technology. High contrast patterns and resolution were obtained in this technology. This was achieved by using a soak process to treat the resist surface before exposure in the conventional resist process. The surface treatment was done by dipping the wafer in a solution of tetramethyl ammonium hydroxide(TMAH) rather than a chlorobenzene solution. And also, we combined with new pattern transfer technology with CEL (contrast enhanced lithography) to control the aerial image. The resists were imaged by using G-line steppers with NA value of 0.54 and 0.45. The positive photoresists used were S1400(Shipley), TSMR-Vl(Tokyo Ohka) and TSMR-CRB2(Tokyo Ohka dyed resist). A conventional developer for positive photoresist was used for the surface treatment by TMAH alkaline solution. In this process, we have evaluated the baking step either before or after the image exposure in the conventional process in order to compare pattern profiles.

Dry-developable single layer resist process using plasma polymerized film was investigated. For the process, the selective fixation of Si-containing organic monomer to base polymer at the exposed part was applied. Plasma polymerized film was formed by an inductively coupled gas flow type reactor. Si-containing monomer was diffused to a base polymer in the sealed reactor under the pressure of several Torr at RT. The contrast of Si-containing monomer between the exposed and unexposed parts was attained by expelling the unreacted monomer at the unexposed part after pattering exposure. The pattern formation was performed through the process using SR as a pattering source. The 1-1.5um pattern was obtained by O₂ RIE. An investigation about the diffusion level of Si-containing monomer was conducted by IR and ESCA depth-profile.

A statistically developed process is described that uses the unique advantages of the AZ* 5200 reversible tone resist to produce severe retrograde slopes and accommodate a sputtered liftoff patterning. Precision thin film resistors were used in the development to measure the variability and repeatability of the process. The single level liftoff technique offers cost and processing advantages over more complicated systems.

Fourier transform infrared (FUR) spectroscopy was used to study the effects of various resist process variables on the photospeed. Resist components which are responsible for photospeed changes were identified. The doublet peak around 2100 cm^-1 , which corresponds to the diazo group of photoactime compound (PAC), was used for a quantitative measurement of PAC content. The peak at 1700 cm^-1, which corresponds to the acetyl group of the solvent used in the resist, was used to measure the solvent content. The PAC is stable at low temperatures, but begins to decompose at 120°C. This temperature is called critical temperature. It was found that below the critical temperature, the solvent content and the resist-thickness-induced changes in reflectivity are the main factors affecting the photospeed. Above the critical temperature, PAC content is the main factor that affects photospeed. The above described technique was also used to study the kinetics of photochemical reactions during resist exposure, and the effect of fluorescent light on resist in a typical manufacturing area. The effects were found to be negligible for wafers in a black cassette and oriented parallel to the light rays, even when exposed for several hours.

Surface composition of aluminized substrates after exposure to sodium silicate buffered and non-buffered alkaline developers is described. Variable angle x-ray photoelectron scattering (XPS) reveals that sodium silicate buffered alkaline developers form a protective aluminosilicate film on the wafer surface which inhibits aluminum erosion. The elemental composition and possible mechanisms of film formation are presented. Aluminum-copper alloy sputtered wafers are more susceptible to etch by non-buffered alkaline developers than non-alloyed aluminum sputtered wafers.

Along with the increase in the integrations of IC's, the process dimensions of photolithography is proceeding to more and more fine patterns. In the fabrication of 16 Mega bit DRAM which is the next generation device, the photolithography will be required to have a technology close to half micron geometry work. The role to be played by photoresists in such geometry work is extremely large and important. Under such circumstance, we have developed ultrahigh resolution positive working photoresist, TSMR-V3 which can cope with a half micron photolithography.

There are particular polymeric materials having acid labile groups pendant to the polymer backbone which can be used to produce resist structures having autodecomposition temperatures greater than 160°C. The increase in autodecomposition temperature of the resist is achieved by selecting acid labile groups which upon acid catalyzed deprotection generate less stable intermediate carbonium ions than the t-butyl carbonium ion. Acid labile groups that provide increased autodecomposition stability include those capable of forming secondary aliphatic and deactivated secondary benzylic carbonium ion intermediates. There must be a hydrogen on a carbon adjacent to the carbonium ion in order for elimination of an alkene and a proton to occur and continue the chemical amplification process. The acid labile pendant groups can be part of a polystyrene homopolymer or part of copolymers containing styrene and maleimide units.

In this study the influence of polyPAC structure was determined by examining the dissolution characteristics of various experimental photoresists. The PACs in these materials have structures in which the PAC chromophores are deployed at low and high density but otherwise have the same functionality, with three diazoquinone (DAQ) moieties per PAC molecule. Our studies indicate that the greatest degree of dissolution inhibition is obtained when the DAQ groups are spread broadly across the same molecule. Furthermore, those PACs which showed the strongest inhibition in unexposed and lightly exposed resists exhibited the least dissolution rate enhancement in exposed resists. Resists made with PACs whose DAQ moieties are widely separated exhibit an extraordinary supralinear relationship between the dissolution rate and the exposure energy. Energy reaction orders for these materials have values much greater than the expected value of three predicted by polyphotolysis theory. A possible mechanism for this phenomenon is proposed. In addition, the lithographic implications of the dissolution characteristics of these experimental resists are discussed as they relate to resist optimization.

Activated phenolic monomers modified with hydroxymethyl groups were used to prepare a number of novolak resins described in this paper. In most cases the starting repeat units and final novolaks were prepared in situ from their corresponding methylolated phenols. The synthesis and characterization of four specific novolak structures are presented. The resist performance based on one novolak system was investigated as a function of the novolak composition. Repeat units produced by the condensation of 3,5-dimethyl phenol and 4-hydroxybenzyl alcohol provided the basis for this novolak structure. FT-IR spectroscopy was used to investigate the types of hydrogen bonds and their interactions within this system.

Model cresol novolac resins and photoactive compounds (PAC) based on polyhydroxybenzophenones were prepared according to known procedures. The components and resists formulated from them were exposed to X-rays from Aladdin, the electron storage ring at the University of Wisconsin. The loss of azide functionality and the conversion of PAC to acid or ester was monitored by FTIR difference spectrometry. The energy dependence of the sensitivity of conversion of diazonaphthoquinone to ketene was followed by monitoring the loss of diazide when exposed to synchrotron radiation. The effect of PAC functionality on the sensitivity and chemical pathways was studied. The relationship of structure and photon energy to lithographic performance are explored. We discuss the applicability of synchrotron radiation as an exposure source and FTIR as an analytical tool for the study of X-ray resist mechanisms.

Polyimides have many desirable properties for use in the microelectronics industry, including ease of application, excellent planarization capability, and good electrical insulating properties. A polyamic acid that is also an imagable resist simplifies processing by eliminating the need for separate resist application and removal steps. Negative-working polyimide resists are quite common, but there are very few examples of positive-working polyimide-based resists. In this paper, we describe a positive polyimide resist which is based upon a diazonaphthoquinone dissolution inhibitor that is standard in the resist industry. The positive polyimide resist described here has high resolution, high heat resistance, and excellent dielectric properties.

The chemistry of Photochemical Image Enhancement with anthracene photooxiidation is described in detail, emphasizing materials properties needed to avoid reciprocity failure due to oxygen depletion. The application of new materials, including dianthrylethanes and methacrylate-siloxane graft copolymers, is described; these are capable of providing exposure times of less than 1 sec, with the possibility of further improvements. The performance characteristics of existing materials have been compared to those of CEL by use of a simple analytical formula. Data are also presented on behavior in the deep UV, with a view toward application as CEL and PIE materials for DUV lithography.

The standard Rayleigh relation for the resolution of an optical system states that the resolution is proportional to the exposure wavelength divided by the numerical aperture of the system. The constant of proportionality "k" is directly effected by processing techniques and may be reduced depending on the chosen photoitsist process. Reducing the "k" factor directly impacts the manufacturing of advanced integrated circuits since it implies the ability to resolve finer features without the ever larger capital expenditures required for new exposure tools. It also allows the execution of current processes with increased processing latitude. This paper reports on the results obtained using a surface imaging technique to reduce the "k" factor for standard and advanced processing applications.

Surface imaging using silylation treatment is explored with the aim of understanding the size of the process window for submicron lithography. The influences of resist materials and process temperature were investigated. Resist material strongly influenced the quality of imaging. However, the optimum processing conditions for the conventional diazoquinone/novolac resist and specially formulated dry develop resist were similar. Soft bake temperature, presilylation bake temperature, and silylation bake temperature strongly influenced critical dimension (CD) control in the temperature regimes investigated. The large effect of presilylation bake and silylation bake temperature on CD control can probably be overcome by driving the diazoquinone induced cross linking reaction to completion. However, it is unclear whether a similar scheme will control the 0.025μm per degree centigrade line width variation with soft bake temperature. Considering both the depth of focus and exposure latitude data, the dry develop process appears to conservatively extend the manufacturable resolution to a k of about 0.65 in the Rayleigh resolution equation. At this resolution, our data indicate a depth of focus of about 1.5μ to 2.0μ and an exposure latitude of about 30% (for 0.6μ lines/spaces printed with a 0.40 NA i-line stepper).

By using PLASMASK(*) resist in the DESIRE(*) process, multilayer resist performances can be achieved on a single layer. The aim of this paper is to show , for each step of DESIRE process , the influence of the different parameters on lithographic performances , and finally the use of such process on critical levels for 0.6μm CMOS technology . Exposure experiment have been performed on an I-line ASM stepper ( NA = 0.4 ) A modified HMDS vapor prime from SVG has been used for resist silylation . Silicon depth profi-les in PLASMASK resist versus dose, time and temperature of silylation have been measured by RBS method. Statistical Experimental Designs (S.E.D.) have allowed the determination of process parameters influence as well as the identification of their interactions on lithographic performances . The resulting optimized process will be demonstrated on a metal 1, 0.64μm CMOS technology. * PLASMASK and DESIRE are trademarks from UCB Electronics.

As far as double metal technology is concerned the performances of multilayer resist processes are well known. In an industrial context the results provided by steppers are now guaranteed : focus, resolution alignment accuracy, even for grainy reflective substrates with severe topographies. Through the development of new processes it is now possible to industrially use single layer resist systems. Using the DESIRE (Diffusion Enhanced Silylation Resist Exposed) process is a good example of this, not only with regard to lithography but also to etching, electrical results and C.D. stability. For each of the above, the same results will be shown as for multilayer processes. We will briefly describe the DESIRE process as well as the equipment. The C.D. evaluation and resolution depending on resist thickness, exposure and soft bake will be presented. The behaviour of the resist during an oxygen and chlorine plasma etching will be discussed. The yields on test strutures will be presented.

A new silyl ether of resorcinol novolak resin (SERN) and a new photoactive compound (S-55NQ) have been developed for a bilayer resist system. The SERN resin is an addition-condensation type terpolymer from resorcinol, hexamethylenetetramine, and phenyl silyl ether (PSE), which is a reaction product of resorcinol and chlorosilane, under acid catalyzed condition. The S-55NQ sensitizer is a sulfonate ester of spiroglycol and naphthoquinone diazide. This alkaline soluble Si-containing resist, useful in the mid-UV region, shows high dry etching resistance to O₂ plasma and O₂ RIE. An etching rate ratio of 4.5 or higher based on HPR-204 as the bottom layer is obtained.

We are investigating the structure and homogeneity of thin, multi-component resists prepared by spin casting and Langmuir Blodgett film formation technologies. Fluorescence spectroscopy has been used to evaluate various casting solvents for spin casting of multi-component films. Films of novolac containing pyrene as a small molecule probe were cast from various ethers and ether alcohols. The small molecules aggregated less when the dipole moment of the solvent closely matched that of the polymer. Langmuir-Blodgett techniques were used to create very thin (40 nm) films of novolac/diazoquinone. Images down to 1 jim were developed in these films and transferred into 50 nm of chrome. These very thin resist films could have various applications in advanced resist technologies, including mask making and deep UV lithography.

This paper studies the requirements for, and the performance of, a developer suitable for spray puddle develop processes. The surface tension of the developer has to be lowered, by adding a surfactant, to avoid "pullback" of the developer during puddling. It is shown that this develop process is sensitive to a variety of parameters due to the effect of resist loading on the surface tension of the developer. Optimization of a spray puddle develop process has been done for AZ1500, AZ1300, AZP4000 and AZ5200 resists. Results include dose requirements, exposure latitude and across wafer linewidth uniformity for the optimized develop cycle. A response surface analysis on the exposure and focus latitudes in spray puddle develop mode has been done. It has been observed that the developer also affects the thermal characteristics of a photoresist. This study shows that the surfactant added does not degrade the thermal stability or any other performance parameters of resists and does not cause reticulation of the resist during plasma etch. This developer can be used in spray and batch mode too.

A 3-dimensional multiple state molecular-scale model is described for simulating the exposure and development of positive diazonaphthoquinone/novolac-type photoresist. Resist composition and properties of the individual components are specified; development proceeds through percolational approach. A second macro-scale simulator then uses the dose/response information generated by the molecular scale model to simulate exposure and development of resist profiles in three dimensions. Simulation results are presented to describe the effects of varying the PAC/resin ratio, resin dissolution rate, and the number of photoactive groups per molecule in terms of lithographically relevant properties such as contrast, energy reaction order and resist profile appearance.

The least action principle algorithm is extended to model the development of a three dimensional latent image in an exposed resist The photoactive compound (PAC) concentration is determined in a model resist film from the exact solution of Dill's equations for the exposure-bleaching process for the case of a matched substrate. The procedure is valid for all mask shapes and is illustrated with an elliptical symmetry imposed upon the incident light intensity. Utilizing these PAC gradients, the three dimensional least action principle algorithm is employed to compute developed resist profiles.

A study is presented of the performance of a Novolak-resin naphtoquinone-diazide sensitized resist exposed in the deep-UV. The material under study is PR-1024MB-600, designed for exposure in the UV (280-340 nm) range, including the i-line and h-line as well as deep UV (248 nm). The A, B, C exposure parameters of the photoresist have been measured at 248 nm. Classical bleaching characteristics are observed at low energy; the photoresist transmittance increases with dose. At higher doses the photoresist transmittance decreases, suggesting UV radiation effects on the resin. A model for the behavior and the associated parameter-extraction method for the UV transmittance versus dose in the presence of a variable resin absorbence are proposed. The development characteristics of the photoresist exposed at 248 nm are meas-ured and the results for exposure with less than 5 mJ/cm²/pulse and total dose less than 1 f/cm² show normal positive pho-toresist characteristics. Higher total dose, with low energy per pulse yields a negative tone mode. This tone reversal behavior suggests UV-induced cross-linking. Exposure using high pulse energies (> 25 mlicm² per pulse) also yields a negative tone response. Thermal calculations suggest a heating effect. The image reversal performance of the PR-1024MB resist with addition of low-volatility amines is also demonstrated. Under similar conditions the image reversal process is 10-20 times more sensitive than in positive tone operation. In image reversal the deep-UV photoresist contrast exceeds 2, larger than the value observed in the normal mode.

This paper examines the performance of a specific family of dyed resists. The effect of dye con-centration on the line profiles of a homologous series of positive photoresists is studied. Usable images are obtained with dye concentrations of 0%, 0.4%, and 0.6% (percentage of the formulation). Both standard softbake or a softbake plus post-exposure bake (PEB) processes are used. Resist linewidths and cross-sections are measured on substrates that are representative of those encountered on integrated circuits. Optical exposure and develop simulation parameters (two developers) for this family of resists are also extracted.

Film curvature effects are characterized for positive resist films patterned on topography. The radius of curvature (ROC) of resist contours is measured for different film thicknesses and step heights. Estimates of exposure dose and linewidth variations are obtained from this data. On reflective substrates the reflected light ray contributes to longer effective path lengths and greater linewidth changes for a given percent dose change. From film curvature effects alone linewidth deviations can be as large as 0.4 to 0.5 microns. The presence of these effects accounts for the reduction in reflective notching observed with dyed resists. An experimental verification of this result is also presented using water soluble, transparent overcoats. These overcoats effectively eliminate film curvature effects without introducing any exposure dose, wall profile, or development time penalities.

The application of a new organic anti-reflective coating layer, "ARC-XL" from Brewer Science Inc. is described for high resolution metallisation lithography. The "ARC-XL" is soluble in positive resist developer and is removed in the same process step as the exposed resist so that particular attention is paid to "ARC-XL" bake conditions. The enhanced process latitude to be gained using "ARC-XL" with a high temperature resist is compared to latitude without "ARC-XL" by both electron microscopy and electrical linewidth measurement. "PROLITH" simulations confirm the enhanced process latitude to be gained using "ARC-XL". Further modelling shows resist sidewall profiles with and without "ARC-XL" as a function of stepper focus and exposure.

Lift-off technology provides an alternate metal patterning technology to that of subtractive etching. In this paper, we characterize a trilayer resist process which provides a practical means for producing the stencils which are required for successful lift-off in a 1.6 μm metal pitch CMOS process, with biasing for nominal mask design rule or wider metal interconnections. The trilayer structure we describe consists of a planarization layer of polydimethylglutarimide (PMGI), a spin-on organosilicon polymer intermediate layer, and a positive novolac photo-imaging layer. All three layers can be coated and cured sequentially in automated equipment, and the intermediate and planarization layers can be etched in-situ, minimizing wafer handling and contamination. The rationale for use of lifted off metal interconnections and requirements for liftoff stencils are described. In this paper, we characterize dimension biasing and proximity effects for the photoresist layer, organosilicon layer, and PMGI layer, as well as the final lifted off metal interconnections. Minimal proximity effects and differential biasing due to feature size variations are shown for feature sizes ranging from 0.7 - 2.0 μm, with biasing in favor of wider metal interconnections.

A new statistical analysis technique will be shown for process comparisons and optimization in production photolithography. The experimental layout proposed allows for efficient collection of data off-line for calculation of a process index relating the 6 sigma repeatability to assumed specification limits for each experimental cell of a full factorial experiment. Appropriate blocking of the experiment and number of repeats used allows the process index to be compared to the process capability calculations in popular use throughout the semiconductor industry.

Continuous Improvements In Optical Imaging And Photoresist Technology Have Pushed Optical Lithography To Submicron Resolution. Photoresist Image Reversal (I.R.) Processing Has Evolved As An Alternative To More Complicated Resist Schemes (Contrast Enhancement Or Multilayer Resist) To Enhance The Resolution Of An Optical Exposure Tool.There Are Several Published Processing Methods And Resist Chemistries For Image Reversal Of Positive Working Resist In The Literature . We Have Investigated An Image Reversal Process For I-Line (365 Nm Wavelength) Lithography To Improve Resolution And Exposure Latitude Compared To A Standard I-Line Resist System. In This Reversal Process, The Resist Is Exposed Through A Mask, Baked After The Exposure, Flood Exposed, And Finally Developed In A Dilute Aqueous Base Solution To Generate A High Quality, Negative Tone Image Of The Mask. In This Paper , We Report Our Study Of I-Line Image Reversal Processing To Push The Resolution Limit Of Our Optical Exposure Tool To Half Micron Sizes. The Effects Of Various Resist Processing Variables On Linewidth, Resolution And Mask Bias Will Be Discussed.

Image reversal of a positive photoresist is capable of improving resolution, sidewall angles, and process latitude. Another advantage of an image reversible system is that it produces a negative image by aqueous development. Using novolac resists, we have developed new chemistry which is based on "blocked" reactive agents. The reactive agent can be thermally liberated from the resin, or it can be photochemically generated. After generation, it reacts with the indene carboxylic acid groups in the exposed area to render this area insoluble. After postbake, the resist is flood exposed to convert the remaining photoactive compound in the resist layer; development then gives a negative image of the mask. In one practice of this chemistry, the reactive agent and indene carboxylic acids groups are co-photogenerated. As a result of crosslinking between these two species during processing, the contrast of the photoresist is improved. We call this concept Dual-PAC imaging. Because the crosslinking is a second order reaction based on two photogenerated species, the concentration gradients in the film are sharper than a single-PAC system which follows first order kinetics. The result is an improvement in resolution, cleanout and process latitude as well as contrast.

With advances in new semiconductor IC manufacturing techniques and more complex process flows, the processing environment that a wafer is exposed to has become a critical issue. New CMOS process flows with shallow junction regions and thin gate oxides are susceptible to damage by free electrons and charged ionic species found in plasma processing environments. The following article presents data to quantify device damage due to various photoresist removal techniques. A dry chemical, ozone based ashing process is compared with more conventional wet chemical and plasma resist stripping methods. In this study, several ashers were compared with wet stripping and with traditional barrel ashing to quantify damage to thin gate oxides. Systems tested included two "downstream" RF plasma ashers, two "downstream" microwave plasma ashers and the non-plasma ozone ashing system. Tests were conducted to detect damage to gate oxides using CV (capacitance-voltage) and TDDB (time-dependent-dielectric-breakdown) measurements. Only the ozone asher did not cause measurable damage to 250Å gate oxides. The major source of damage appearing to be charge build up across capacitors during plasma ashing after poly etch.

A program for simulating latent image formation in a photoresist for complex photolithographical systems is described. For a number of new photolithographic systems, which use more than one exposure and several different chemical reactions, the concentration profiles of the chemical components of the resist can be calculated with this program. Some results for positive imaging, Image Reversal, Built In Mask and ImRe with two pattern-wise exposures are given.