The use of an excimer laser for exposing the inorganic resist system Ag2Se/GeSe2 was recently reported (Ref. 1). One of the startling findings of that work was the dramatic (60-fold) decrease in the required dose as the pulse energy was increased; the required dose can be as low as 5 mJ/cm2. One of the questions arising out of that work was whether the high contrast and resolution of this resist system could be maintained under this form of exposure; the work reported in this paper indicates that these desirable quantities are indeed maintained. The value of contrast measured exceeded 10 (i.e., extremely high). By way of demonstrating this high value we exposed, using a KrF excimer laser operating at 249 nm, a film of Ag2Se/GeSe2 in the proximity printing mode with a Cr-on-quartz mask and observed the resulting Fresnel fringes at feature edges. Fringes with a half-period of 0.25 μm and aerial modulation of only 10% were resolved, thus indicating that even under pulsed laser beam exposure this material enjoys very desirable imaging properties both in terms of contrast and resolution. Another aspect which must be considered before the material can be regarded as practical for IC fabrication is that of possible contamination of the workpiece by the resist components—particularly silver. Experiments are currently underway involving both C–V measurements and Rutherford backscattering to determine the extent and the effect of such contaminants; preliminary results suggest that there is no significant contamination.

Over the past several years a class of silver-doped GeSex materials has received attention as a high gamma, negative resist. The columnar structure of the GeSex films is believed to be linked to some of the lithographic properties of the resist. However, the mechanism of Ag incorporation is not well understood. In this paper we report secondary ion mass spectroscopy (SIMS) observations of the Ag migration in GeSe2 films. Furthermore, we have found evidence for a fast Ag diffusion effect in GeSe2. These findings are consistent with a columnar GeSe2 structure. The Ag concentration depth profile in 3000- and 6000-Å-thick films of GeSe2 on substrates consisting of 300 Å of Ta on silicon wafers has been studied by SIMS. An O+2 primary beam was used in the SIMS analysis, with the bombardment energy reduced to 3 keV to minimize possible beam-induced effects and to increase the depth resolution. The Ag2Se/GeSe2 resist was exposed by an unfiltered mercury arc source and received doses ranging from 0 to 2 J/cm2. The unreacted Ag2Se was stripped prior to the SIMS analysis. The Ag incorporation was found to increase rapidly with exposure first, and then saturate about 1 J/cm2. But instead of Ag being uniformly distributed through the GeSe2 films, its concentration peaks both near the top surface and at the substrate interface. The anomalous Ag peak at the substrate interface indicates that Ag diffuses far beyond the penetration depth of the radiation and presumably piles up in front of the Ta diffusion barrier. Moreover, with the same exposure, the anomalous Ag peaks are identical in both the 3000- and 6000-Å-thick films. These results are consistent with the model of Ag diffusion through the columnar structure of GeSe2, an extremely fast path in regions between the columns extending through the film, and a slower diffusion component in the denser regions within the columns.

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This paper examines the performance of a specific family of dyed resists. The effect of dye concentration 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.

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