As the semiconductor feature size continues to shrink, the high NA lithography has become a reality. Coupling with high NA lithography, both the critical dimension control and the insufficient resist thickness for etch mask are becoming major challenges for lithographers. Hence two things are highly desired, one is an effective anti-reflective coating (ARC) strategy to maintain low reflectance for good critical dimension (CD) uniformity (CDU) control, and the other is combined ARC and hard-mask concept to satisfy both lithography and etch performance needs for feature patterning.In this study, a dual dielectric anti-reflective coating (dual-DARC) was first demonstrated as an effective ARC for contact application with high NA lithography. The ordinary single DARC is very sensitive to the thickness variation of underlying films, resulting in a >45nm contact CD variation at interlayer dielectric (ILD) thickness variation of ±150nm induced by CMP process. Unlike the single DARC, the dual-DARC performs a less CD variation of ~5nm at the same film thickness variation. By extending the dual-DARC concept to combined ARC/hard-mask application to contact and poly patterning, several ARC/hard-mask schemes were compared by reflectance control, CD uniformity control and etch hard-mask performance. Apart from the good reflectance and CD uniformity control of dual-DARC-like schemes, the most attractive is that the proper use of dual-DARC concept to hard-mask application, the tight thickness control is not necessary for the bottom layer and you can just tailor the bottom layer's thickness to meet the individual process needs.

As semiconductor technologies move toward 0.18um and below, it is difficult to get high pattern fidelity by 248-nm wavelength exposure. To reduce proximity effect, a lot of resolution enhancement technologies (RET) such as OPC, assistant feature, and double exposure technologies (DET) have been introduced. In this paper, random contact holes with low proximity effect were delivered by using 248-nm exposure tool in conjunction with double exposure technology. A low proximity resist patterns were formed by a well-designed Pack-mask. Then ion implantation treatment produced a solvent proof skin on the developed resist. The second lithography process was performed over the post-implanted resist layer. Resist coating as well as exposure perfectly transfer the patterns from Cover-mask. After etch, random holes with low proximity effect were easily achieved. In addition, higher energy association with higher dosages is able to maintain good critical dimension even if wafers went through three rework processes.Keywords: low proximity effect, double exposure, ion implantation, resist hardening, random contact hole INTRODUCTIONKrF lithography is now widely used for critical layers printing, however, getting usable common window for isolated and dense holes with size of 0.18um and below by KrF tools is still very challenging. To address the insufficient common process window issue, several commercial tools are available to correct the optical proximity effect while enabling low proximity printing by these tools makes mask cost expensive.In our approach, instead of OPC, pack-and-cover masks in combination with double exposure [1] were used. The first exposure will serve two purposes of improving the DoF (depth of focus) and reducing the proximity effect. To reduce the proximity effect, we pack up the contact holes to single pitch with dummy holes in a 6% half tone mask called pack-mask. As for improving the DoF, Quasar illumination mode with NA=0.7, σi/σo =0.55/0.85 was selected for first exposure. Before the second resist coating on the first resist, the first layer resist was treated by Ar + implantation to be insoluble to solvent [2]. After first resist patterned and implanted, second resist patterning selectively opens up the desired contact holes by a binary mask with larger random hole layout. The implanted first resist not only delineates the desired contact hole size but also serves contact etching resistant barrier. Accordingly desired contact hole patterns with low proximity can be achieved after contact etch.

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