Patterning capability and limitations by pattern collapse in 45nm and below node photo mask production

Abstract

As the industry approaches to 45nm and below lithography, resolution and pattern collapse of SRAF (Sub Resolution Assistant Feature) on photoresist is becoming critical issues on photomask industry. The collapse of photoresist pattern has been become a serious problem in manufacturing of fine patterns in wafer and mask industries. The presumed causes of the resist pattern collapse are capillary forces acting on the patterns and adhesion property of the patterns. The use of thinner resist thickness has been known as one of the most effective method among reported literatures. However, etching resistance of present resist is still bad. Therefore it is difficult to reduce the photoresist thickness, though the pattern size is very small. In this paper, the available limits of resist thickness for FEP171 were calculated for several kinds of common absorber layers as considering current dry etch capability. We focused on pattern design and collapse window for SRAF. FEP171 resist performance especially for resolution and collapse window were evaluated for both 2000Å and 3000Å thickness with line, space, and length focused on sub 100nm features. Radial position effect and drying conditions were studied herein.