Sachiko Yabe

Control of acidity of the substrate for precise pattern fabrication using a chemically amplified resist

The chemically amplified (CA) resist has been widely and generally used for sub-quarter micron device fabrication using a KrF excimer laser stepper. However many problems have been revealed and laborious efforts have been seriously undertaken to solve them. Among these issues, we have been examining the dependence of the resist characteristics on the substrate properties. In order to control and minimize the fluctuation of the critical dimension, we have been evaluating the relation between the cleanliness of the substrate materials and the CA resist patterning characteristics, especially, we have been focusing on the effect of a wet cleaning process-step which is a necessary and important process-step for actual device manufacturing. Among the several materials which we evaluated, we found that the characteristics of an amorphous carbon(a-C) film used as an anti-reflective coating were significantly affected and changed by the sulfuric acid and hydroperoxide mixture (SPM) cleaning. For the other materials, no characteristic changes in the cause of this SPM cleaning were observed, and this cleaning method was effective and applicable to almost materials except the a-C film. In case of the a-C film, the acidic residue remained after the cleaning, and this contamination changed the acidity of the film. The resist patterning characteristics fabricated on the contaminated film were drastically changed, and pattern collapse occurred. In order to diminish this remaining contamination and control the acidity of the contaminated substrate, we tried to apply a high temperature treatment, an alkaline treatment and a UV cure treatment.

Thin resist process having high dry-etching resistance in 0.13-μm KrF lithography

The dependence of resists materials nd process conditions on dry etching resistance was examined for polysilicon, silicon oxide and metal etch applications. Thin resist process is a simple and cost-effective technique for resolution enhancement, and it enlarges the process margin because of reduction of the resist pattern aspect ratio and improved film transparency. However, to use thin resist process in manufacturing, sufficient etch selectivity is required for function of the etching mask. The high dry etching resistance resist process or the hard mask process was one of the solutions. In this study, we evaluated the dry etching rate of KrF resist materials such as a positive photoresist (acetal type and ESCAP type) and a negative photoresist, and the effect of process conditions such as baking temperature and electron beam (EB) exposure. Under polysilicon and metal etching conditions, the etch rate dependence or resist materials such as ESCAP and the negative resist indicated high dry etching resistance compared with the acetal-type resist. However, under silicon oxide etching conditions, etch rate dependence on the kind of resist polymer was small. These data indicated that the etch rate dependence on resist polymer is strongly governed by the etching conditions. High-temperature baking and EB curing processes were effective for improving etch selectivity. Regarding the influence of baking temperature, although etch rates were strongly dependent on etching conditions, the effect of etch rate change ratio by baking was not dependent on the etching conditions. The EB curing process is the effective in improving etching resistance, but it also shows dependence on the etching conditions. The EB curing process was quite effective in improving etching resistance, but it also shows dependence on the etching conditions. The EB curing process was quite effective in the case of polysilicon and metal etch processing. Therefore, the dry etching resistance for thin-layer application was improved by the resist process, although it strongly depended on the etch process conditions. Form the analysis of resists polymer and residual solvent by FR-IR, GC-MS and DSC, it seemed that the effect of etch resistance improvement by EB curing is mainly caused by the resins structural change. On the other hand, the effect of baking conditions was mainly due to the solvent in the resist. Finally, we confirmed the lithographic and etching performance by using the EB curing process for three types of resists with 130nm node gate, contact and metal layers.

Fabrication of isolated gates by negative-tone process and resolution enhancement technology

Interesting characteristics of a negative-tone process have been reported: enlargement of photolithographic margins of isolated line, reduction of optical proximity effect, greater dry etching selectivity. A possibility of fabrication of isolated gates of 0.13micrometers class logic device by the combination of negative-tone process and resolution enhancement technology (RET), was investigated in the KrF lithography. Photolithographic margins of 0.13micrometers isolated line were evaluated by simulation and experiment as well. Parameters are mask type, the transparency of attenuated PSM, mask-pattern size, and coherence factor. The condition defined by the optimal combination of attenuated PSM, mask-pattern size, and coherence factor. The condition defined by the optimal combination of attenuated PSM and a small coherence factor value at NA equals 0.60 increased the photolithographic margins of 0.13 micrometers isolated line. The margins evaluate under the optimal condition exceeded either of the values obtained in the negative-tone process without RET, and in positive-tone process with attenuated PSM and annular illumination. The effect of residue could be neglected in the isolate line under the optimal condition. The common window of 0.13micrometers isolate line and 0.18micrometers L/S, and that of 0.13micrometers isolated line and 0.20micrometers L/S, both increased under the optimal condition. The margins of 0.13micrometers isolated line further increased when NA was 0.68.