Abstract
The advent of 193 nm ArF lithography opened new era of sub-90 nm patterning in DRAM industry. ArF lithography in single layer scheme, however, has limitation in the substrate fabrication of sub-90 nm L/S due to the decreased physical thickness of resist less than 3000Å and weak chemical structure of resist. Bi-layer scheme, composed of Si-containing top layer and thick organic bottom layer, is gaining attention for its capability of patterning and control of resist thickness as a substitute for single layer. Several resists were evaluated for bi-layer process in terms of resolution, dry development, bottom layer durability and SEM induced CD shrinkage. Resolution down to 80 nm was achieved with Si content ranging from 8 to 9%. Etch selectivity in the dry development was a strong function of Si content and chemical structure of top layer with pitch size dependence based on O2/N2 gas chemistry in dual frequency plasma tool. Profile control after dry development was subject to change depending on the gas ratio (O2/N2) and power. Resist structure was proved to be a key factor in bottom resist durability at the substrate etch condition. Best combination of top and bottom resists in bi-layer scheme will be discussed.
