F.A. Vollenbroek

A study of catalytically transformed negative X-ray resists, based on aqueous base developable resin, an acid generator and a crosslinker

Abstract Negative working X-ray resists, based on phenolic resin, an acid generator and a crosslinker are described. First the sensitivities of various activators are compared by using a proton scavenger, that produces a colour upon protonation. Although diphenyliodonium hexafluorophosphate and chlorinated triazine derivatives appear to be the most sensitive ones, the difference with naphthoquinone diazides and CBr4 is not very pronounced. Subsequently it is shown that those activators that produce strong acids can induce acid catalyzed condensation reactions in resist films that consist of a phenolic resin and polyfunctional alkylating agents. As only very small amounts of acid are needed to render the phenolic resin insoluble in aqueous base developer, a very high sensitivity can be reached. Preliminary results with some experimental resists show a sensitivity of 20 mJ/cm2.

Built in mask (BIM): a new way to a submicron process with high resolution and good latitude

Abstract The performance of the Image Reversal (ImRe) process can be improved considerably by formation of a dye in the patternwise irradiated, insolubilized, areas. The dye is generated during the reversal bake and acts as a (built in) mask during the blanket exposure. The resulting intensity distribution is self-aligned to the intensity distribution of the first exposure and thus leads to a better defined mask edge in the latent image. Simulation results obtained with the newly developed program SLIM (Simulation of Latent Image Manipulation) and some chemical routes for dye formation are presented.

An optimized image reversal process for half-micron lithograhy

Abstract Resist profile and linewidth control of a previously defined 0.5 μm Image Reversal process for I-line exposure tools have been investigated. The slope of the resist profiles is mainly determined by the penetration depth of the imaging light, defocus, the flood exposure dose, and the resist composition, whereas the linewidth is determined by the patternwise exposure dose and the development time. The post exposure bake is a parameter that influences both slope and linewidth. The trends seen in results of simulated latent images for influences of the flood exposure dose and Dills B-parameter are found to be consistent with experiment. Development rate measurements show that the contrast curve of AZ5214-E in Image Reversal mode shows high contrast (γ = 9) combined with high thickness loss. It was found that linewidth decreases with higher prebake temperatures. This indicates that the mobility during the post exposure bake, and hence the crosslinking efficiency, is lower if higher prebakes are applied. Linewidth variation caused by thin film interference effects is within 0.08 μm on silicon for 0.5 μm features.

Towards an optimized image reversal process for half micron lithography

Abstract A 0.5 μm process was developed based on image reversal technology, using AZ5214-E, followed by l-line exposure, post exposure bake, flood exposure and track development. Starting with a prebake temperature of 90 °C, several problems were encountered. One problem was that only 0.6 μm lines and spaces could be resolved. Another problem was distortion at the line ends, which was accompanied by a relatively large corner radius in larger features. However, using a prebake of 130 °C, 0.5 μm lines and spaces were resolved with good latitudes for dose, post exposure bake temperature and develop time. The focus latitude for 0.5 μm features is acceptable. Moreover, both the distortion at the line ends is diminished and the corner radius is reduced. Patterns in the range 0.5–2.0 μm can be reproduced without using a mask bias. The results are interpreted in terms of the physical chemistry of the process.

High resolution optical lithography by formation of a Built On Mask (BOM)

Abstract By means of a U.V. induced shift in absorption from 360 to 435 nm an image is formed in a photosensitive layers on top of a positive photoresist. Upon heating this image becomes fixed. The resulting mask, which we call a Built On Mask (B.O.M.), is transferred into the photoresist by means of a flood exposure. Then the top layer is stripped and the photoresist developed. A positive resist image results when the flood exposure is done with 365 nm and a negative image results with a 435 nm flood exposure. Experiments with the BOM system show a resolution capability which lies below 0.8 μm and also a large process latitude.

Resist profile control of image reversal process in contact lithography

Abstract Image reversal with AZ 5214 resist is characterized by contact lithography, using a statistical experimental approach. Overhanging and quasi vertical profiles which are of particular interest in GaAs technology (lift-off and anisotropic etching processing) are obtained simply by varying the UV3 exposure dose and submicron features are achieved with a low dispersion (3 σ = 0.12 μm) using a thick resist.