PBS resist profile studies for submicron mask lithography

Robert L. Dean; Homer Y. Lem; Charles A. Sauer; Hong Chang

doi:10.1117/12.195807

7 December 1994 PBS resist profile studies for submicron mask lithography

Robert L. Dean, Homer Y. Lem, Charles A. Sauer, Hong Chang

Proceedings Volume 2322, 14th Annual BACUS Symposium on Photomask Technology and Management; (1994) https://doi.org/10.1117/12.195807
Event: 14th Annual BACUS Symposium on Photomask Technology and Management, 1994, Santa Clara, CA, United States

Abstract

Design rules for 250 nm devices and optical proximity correction (OPC) enhancement techniques require improved resolution. Resolution requirements for these applications extend into the 500 nm realm. The most widely used resist for e-beam generated masks is PBS. Difficulties have been reported when using PBS for features smaller than 2.0 micrometers . These have included poor resolution and CD linearity anomalies at <EQ 1.5 micrometers . Methods were investigated to improve the resolution and CD linearity of PBS resist. The investigation included a study of resist profiles. Results show that resist wall angles improve with increases in dose. At a nominal dose of 1.0 (mu) C/cm², angles can range from 40 to 60 degrees, depending on the type of feature. A significant improvement in wall angle is noted at 2.0 (mu) C/cm², and the angles continue to improve with higher doses until they approach 90 degrees at 4.0 (mu) C/cm². The symmetry of resist lines improves when a puddle process is used instead of the standard spin-spray process. Fluid flowing across the resist during spin-spray processing creates asymmetries, especially with submicron features. This flow asymmetry is eliminated with a puddle process. Postdevelop baking is critical for both resolution and CD linearity. Resist baked at the standard 120 degree(s)C shows degradation of wall angles, asymmetry of resist profiles, and loss of unexposed resist at feature edges. Poor CD linearity is caused by postbaking at temperatures that are too high. A postbake of 98 degree(s) to 102 degree(s)C maintains sharp wall angles and prevents line edge roughness. Experiments show good resolution at 0.7 micrometers for all features, including contacts in both tones, with good CD linearity, CD control, and CD uniformity. The changes made in PBS processing described in this paper can result in acceptable processing of features down to 0.5 micrometers for most mask layers, without relying on the use of proximity effect correction.

Citation Download Citation

Robert L. Dean, Homer Y. Lem, Charles A. Sauer, and Hong Chang "PBS resist profile studies for submicron mask lithography", Proc. SPIE 2322, 14th Annual BACUS Symposium on Photomask Technology and Management, (7 December 1994); https://doi.org/10.1117/12.195807

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