This PDF file contains the editorial “Is There a Future in Microlithography?” for JM3 Vol. 2 Issue 01

To realize high productivity at the 100-nm node, ASML developed the TWINSCAN^TM AT:1100B. This dual-stage 193-nm lithography system combines high throughput TWINSCAN^TM technology for 300-mm wafers, excellent dynamical performance, and low-aberration 0.75-NA Starlith^TM 1100 projection optics. The system is equipped with a 20-W 4-kHz ArF laser and the AERIAL^TM II illuminator, enabling high intensity off-axis and multipole QUASAR^TM illumination. Important process control requirements for the 100-nm technology node are CD variation across the chip and across the wafer. Full wafer leveling, including dies on the edge of the wafer, and CD uniformity performance on 300-mm wafers with and without topology are presented, showing full wafer CD uniformity numbers as low as 6.3 nm 3σ for 100-nm isolated lines with assisting features. Imaging performance of dense, fully isolated lines plus dense and isolated contact holes is shown. Also, printing of critical customer structures is discussed. With these results it is demonstrated that the TWINSCAN^TM AT:1100B 300-mm ArF Step & Scan system meets the requirements for the 100-nm node.

We present the methodology and recent results on the long-term evaluation of optical materials for 157-nm lithographic applications. We review the unique metrology capabilities that have been developed for accurately assessing optical properties of samples both online and offline, utilizing VUV spectrophotometry with in situ lamp-based cleaning. We describe ultraclean marathon testing chambers that have been designed to decouple effects of intrinsic material degradation from extrinsic ambient effects. We review our experience with lithography-grade 157-nm lasers and detector durability. We review the current status of bulk materials for lenses, such as CaF₂ and BaF₂, and durability results of antireflectance coatings. Finally, we discuss the current state of laser durability of organic pellicles.

Off-axis incident light produces shadowing and an imbalance in the diffracted light. Shadowing causes a change in the critical dimension (CD) and a shift in the position of patterns due to the multiple interference of the absorber and buffer layers. In addition, the imbalance in the diffracted light influences the optical proximity-effect correction (OPC) of actual patterns with a process factor k1 below 0.6. In this study, the main factors influencing OPC were investigated. These include asymmetric aberrations and optical proximity effects (OPE) in line patterns. OPC was then applied to a T-shaped pattern. It is found that the mask error factor (MEF) in low-contrast regions of a layout is an important consideration in OPC.

Recent studies have shown the utility of ion projection lithography (IPL) for the manufacturing of integrated circuits. In addition, ion projection direct structuring (IPDS) can be used for resistless, noncontact modification of materials. In cooperation with IBM Storage Technology Division, ion projection patterning of magnetic media layers has been demonstrated. With masked ion beam proximity techniques, unique capabilities for lithography on nonplanar (curved) surfaces are outlined. Designs are presented for a masked ion beam proximity lithography (MIBL) and masked ion beam direct structuring (MIBS) tool with sub-20-nm resolution capability within 88-mm exposure fields. The possibility of extremely high reduction ratios (200:1) for high-volume projection maskless lithography (projection-ML2) is discussed. In the case of projection-ML2 there are advantages of using electrons instead of ions. Including gray scaling, an improved concept for a ≤50-nm projection-ML2 system is presented with the potential to meet a throughput of 20 wafers per hour (300 mm).

We present an extension to the ray-transfer matrix method, which is often used to characterize optical systems. The main purpose of the extended method is to model micro-optical-bench systems that are usually manufactured using surface micromachining and other microfabrication technologies. Using a homogeneous coordinate system to extend standard ray-transfer matrices allows the matrix notation to account for manufacturing tolerances. As an example of this method's usefulness, we calculate the coupling losses in a surface micromachined fiber-optic switch.

Studies on MoSi etch processes were carried out using a design-of-experiments (DOE) methodology. Data was gathered using profilometers and optical critical dimension (CD) measurement systems. MoSi etch chemical kinetics was studied and a kinetic equation was developed showing that MoSi etch rate has a linear relationship with inductively coupled plasma (ICP) power, and an exponential relationship with the negative inverse of the DC bias electrode voltage. The reaction orders of the MoSi etch were 0.2 to SF₆ concentration (molar fraction) and 0.5 to O₂ concentration, and the activation energy was found to be 1350 kJ/mol. A dimensionless number method was used for results analysis and a calculable dimensionless number was defined. This number was found to be proportional to the isolated/dense etch bias. Etcher performance was also analyzed using a matrix transformation method and it was found that matrix-analysis-calculated etch results agreed with those obtained by experimental measurement. The optimal MoSi etch process window was expressed graphically.

We give the proof of principle of a new experimental method to determine the aberrations of an optical system in the field. The measurement is based on the observation of the intensity point-spread function of the lens. To analyze and interpret the measurement, use is made of an analytical method, the so-called extended Nijboer-Zernike approach. The new method is applicable to lithographic projection lenses, but also to EUV mirror systems or microscopes such as the objective lens of an optical mask inspection tool. Phase retrieval is demonstrated both analytically and experimentally. The extension of the method to the case of a medium-to-large hole sized test object is presented. Theory and experimental results are given. In addition we present the extension to the case of aberrations comprising both phase and amplitude errors.

New imaging techniques in atomic force microscopy have been developed to suppress bending of the sharpened probe during scanning. After analyzing the bending of the probe, it is clear that the bending is caused by response of servo control and slip of the probe on the slope. It is essential that we do not scan the probe under contact on a sample surface and we approach the surface at a contact force of <10 nN for slip-free operation. The technique controls the probe such that approaching and gap-controlling are done without scanning after the probe has been stepped from pixel to pixel, and the step movement is done after lifting the probe up from the sample surface without servo controlling. This technique permits us to use a very sharpened and slim probe so that we can observe a steep structure, such as a dry-etched groove and hole, and a photoresist pattern with a high aspect ratio faithfully. We clarify that it is possible to apply this technique to monitoring the steep structures with an inline process monitor in the large scale integration process without cracking the wafer.

The process of shifting from human after develop inspection (ADI) to automatic detection, classification, and review of macro defects in the photolithography process is overviewed. The experiences and improvements from integration of automated macro defect detection and classification systems in a full-volume, state-of-the-art production fab is described. As the semiconductor industry moves toward adoption of integrated metrology solutions, the increased use of commercially available macro automated defect detection and classification systems provide multiple benefits for today's sub-half micron chip manufacturers. Such systems impact the yield by achieving substantial defect detection, classification accuracy, and reporting consistency. The system not only minimizes the time to detect and to fix manufacturing and processing problems but also simplifies process flow. Identification of process problems is increased considerably by providing 100% detection and review of all wafers in a lot using both stand-alone and inline integrated defect metrology. In order for the system to be utilized with the full capacity, the system has to be set up easily and quickly. Furthermore, programming and optimizing recipes used by the system should be flexible enough to identify for new defect types as they appear or when a different set of classification criteria is needed to focus on specific process problems. These systems are more effectively utilized in the production environment when tool-to-tool matching not only among inline-integrated units, but also between inline integrated and standalone units is available. Defect management methods that help increase process yield at a lower cost are becoming more important than ever in today's competitive semiconductor market. The most important task in defect management is to identify defects and their possible causes as early as possible. Early detection and diagnosis eliminates engineering time focused on existing bad wafers/dies. Another benefit is to correct the faulty processes to avoid producing additional bad wafers/dies. Early detection of photo problems can significantly increase process yield because the wafers can be reworked.