This paper examines improvement in post-etching gate critical dimension (CD) uniformity by post exposure bake
(PEB) temperature control. Although intra-wafer and inter-wafer resist CD uniformity is improved by PEB temperature
optimization, intra-wafer gate CD uniformity after etching could not be improved due to etcher-attributed factors. To
improve these factors, we carried out two-step optimization that combines lithography CD optimization with etching CD
optimization. By using this method, the optimization strategy can clarify the targets of optimization in each step. PEB
temperature optimization was performed by two step optimization in which etcher-attributed CD variations were
canceled out, leading to 66% improvement of gate etching CD uniformity successfully. Without any changes in
modification parameter, this PEB temperature optimization proved to be applicable to several reticle patterns with
different pattern density. Moreover, this optimization method proved the applicability to the gate process for a 55nm
node logic device for the duration of five months without modification. The result proved its long-term stability and
practicality.
We have investigated relationship between immersion topcoats and water, and between topcoats and ArF resist films for
the use in ArF immersion lithography from the stand point of the work of adhesion characteristics. We evaluated surface
free energy of topcoat films and resist films each from the contact angle measurement. From values of measured free
energy, we obtained work of adhesion between topcoats and water, and between topcoats and resist films. In addition,
we calculated an interfacial free energy between topcoats and resist films, which is related to the interface stability. As a
result of evaluation of the interfacial free energy of four different kinds of topcoats, the topcoat which has lower surface
free energy was found to have lower work of adhesion between topcoat and water, and lower interfacial free energy
between a topcoat and a resist. These results indicate that the topcoat which has lower surface free energy has more less
interaction between water and topcoat and stabile interface between a topcoat and a resist film.
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