Photomask Cr–MoSi etching

Abstract

Studies on photomask Cr and MoSi etch processes were carried out and etch kinetics and modeling were performed. The photomasks were etched using two different etch tools and metrology to support theoretical suppositions and process characterization was performed using profilometry and critical dimension (CD) scanning electron microscopy. A 50 keV electron-beam writing system employing positive chemically amplified resist was used for pattern creation. Loading-etch rate equations were theoretically proposed and experimentally tested. It was found that the calculated Cr and MoSi etch rates agreed well with experimental results. Local etch rates versus local loading on one photomask were studied and kinetic equations were proposed showing excellent agreement with experimental results. Cr and MoSi etch CD movements versus local load on one photomask were also investigated. It was found that load effects on Cr and MoSi etch CD movements could be controlled in opposite directions leading to a compensation strategy proposal for MoSi optimization, instead of using a point-to-point 3σ as the optimization parameter (objective function). By using this compensation method, the final MoSi CD uniformity of 100–110 nm technology node photomasks (∼30% load) was in the range of 8.5–10.1 nm (3σ). This final CD uniformity was obtained on both of the photomask etch tools tested.