Resolution Of Optical Lithography Research Articles

Resolution and linewidth tolerances in electron beam and optical projection lithography

In order to understand the practical limits of electron beam direct-write and optical projection lithography techniques in device fabrication with micrometer and submicrometer geometries, we have exercised two computer simulation programs to estimate resolution limits and linewidth control. Latent image contrast and developed resist thickness contrast were calculated as a function of line-array spatial frequency. The linewidth tolerances were calculated by varying exposure, development time, focusing, line/space Pattern, resist thickness, etc. These simulation results indicate that the lithographic performance of the two techniques using state-of-the-art exposure tools are comparable at 1-µm dimensions. Some relevant experimental data also are presented.

Recent developments in two-level resist technology

High resolution optical lithography requires a sophisticated photoresist technology. In the micron and submicron linewidth regime, the shallow depth of focus characteristic of optical systems gives rise to the need for multilevel resists. Recent work in this area has concentrated on both two-and three-level systems. An example is a two-layer resist (TLR) technique 1 which uses a thin top layer of positive resist over a thick layer of PMMA. The pattern formed in the thin top layer serves as a mask for a deep UV blanket exposure of the thick PMMA bottom layer. Recently a new deep UV source 2 was described for use with this technology. This paper will describe the exposure/development characteristics of the thick PMMA layer for the combination of this novel UV source and a new development chemistry. The paper will compare the complexity of several multilevel resist processes to point up the advantages of simplicity that the TLR technique provides. A comparison of the step coverage ability of this particular TLR technology with that of conventional positive resists is also made. Using the new development chemistry and lamp, (PMMA) structures of 0.4 μ width having 3.5:1 vertical: horizontal aspect ratios have been fabricated.