Recent developments in two-level resist technology

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Abstract
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 source2 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.

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