A methodology was developed in order to characterize the deprotection mechanisms implied in 193nm chemically
amplified (CA) resists. This method is based on resist outgassing measurements as a function of exposure dose and bake
temperature using Thermal Desorption-Gas Chromatography - Mass Spectrometry / Flame Ionization Detector (TDGCMS/
FID) technique. This approach allows both quantitative and qualitative studies of the outgassing behaviour and
was validated from a 193nm model resist representative of CA formulations. In so doing, the identification of outgassed
by-products respectively coming from the PAG, from the polymer as well as from the solvent is made possible. In
parallel, quantitative results as a function of exposure dose and temperature allowed us to monitor the deprotection
process and the solvent evaporation. The quantitative results obtained by this technique were in good agreement with
Thermo-Gravimetric Analysis (TGA) results. Such a methodology can be used not only to characterise 193nm resist
outgassing during exposure, but also be extended to monitor resist behaviour during implant, thermal treatment, e-beam
exposure.
KEYWORDS: Diffusion, Lithography, Temperature metrology, Chemically amplified resists, Photoresist processing, Glasses, Line edge roughness, Systems modeling, Thermal analysis, Complex systems
Chemically Amplified resists are complex systems. If the main mechanisms implied have already been described, the
challenge to even better control and model these formulations remains important as performance requirements become
more and more stringent and critical dimensions get smaller and smaller. This paper tries to assess and deconvolute some
of the main potential mechanisms involved during the process of a 193 nm chemically amplified resist, before correlating
them with the final lithographic results obtained.
A formulation was selected in order to offer a large range of film physical properties, thus allowing the resist film to switch from non-annealing to annealing conditions. The use of thermal analysis as the main characterization technique allowed correlation between the variations in physico-chemical properties and process conditions. This investigation also included a study of the behavior of some additives during bake steps. In so doing, it became possible to correlate the variations of the resist properties under different bake conditions to the changes in its final lithographic performance, i.e. contrast, sensitivity and line edge roughness.
Resolution and accuracy needs for the most advanced nodes, as well as fab capacities management are requirements that
encourage the use of ArF resists for post-gate implant levels.
In this paper, we investigate several key integration criteria that an ArF resist needs to fulfill to be used for implant
applications. Outgassing level is followed during the first seconds of the implantation step and is systematically found
under the chamber pressure limit. As well, stopping power efficiency is evaluated. SIMS analysis and simulation tests
with SRIM software are performed to define the minimum resist thickness that prevents ions to penetrate the layers
underneath. Data indicate that both experimental and simulation tests are in good agreement and that at low energies the
stopping layer thickness is found to be in the order or lower than 80 nm. Finally, the impact of implantation step on
patterned wafers is carried out. Features of interest are dense and isolated lines with a nominal CD of 130 nm. We
control the CD and profile with a standard CD SEM and a CD AFM in order to get access to additional information such
as height of the feature, top rounding and the CD through height. Results underline that our patterned resist doesn't show
significant degradation under our implant conditions.
In this paper we investigate an in situ measurement of polymer and lithographic resist film mechanical properties on a silicon substrate, with a Dynamical Mechanical Analysis tool (DMA).
This technique allows the measure of the glass transition temperature (Tg) of the resist film (thickness range: several μm to few nm) and its elastic and viscous modulus variations with a high
precision and reproducibility. Indeed, DMA appears to be more sensitive than other thermal analysis methods like Differential Scanning Calorimetry (DSC), to monitor Tg variations induced by film
thickness reduction.
First we will discuss the performance of the tool and present the variations of the glass transition
temperature of a PMMA (PolyMethylMethAcrylate) layer as a function of its thickness: we observe a shift towards higher temperatures up to 30°C when the film thickness decreases from one
micrometer to 10nm. This behavior highlights the importance of surface properties versus bulk. We will also discuss the interest of the DMA technique applied to more complex chemistries, as it is the
case for lithographic resist formulations, i.e. a blend of polymer with grafted functionalities, photoactive compounds and various additives. We successfully applied this technique to
characterize different resist film thicknesses and we observed the effect of the thickness on the thermal events. Such kind of change is important to take into account in the optimization of material
performance for thin film applications. This material understanding allows to better define the process conditions and can be applied to different microelectronic topics such as: thermal flow
treatment of positive tone photo resists, hot-embossing nanoimprint, cross linking reactions with negative tone resists or so called "hardening" processes.
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