Correlation between etching and optical properties of organic films for multilayer resist

Abstract

The correlation between the amount and rate of etching and various properties of organic film for multi-layer resist (MLR) was investigated. The etching critical dimension (CD) of 140-nm pitch interconnects is controlled by the etching conditions as well as by the properties of the organic film used as the bottom layer resist. Six organic films were tested that had different densities, hardness values, refractive indexes, and FT-IR peaks. Patterned samples of these films were exposed using electron projection lithography. The results showed amount of side etching, which effects the etching CD of interconnects, of the bottom layer depended on the etching rate of the film. In turn, the etching rate depended on a film's hardness and refractive index, but not on its density. The etching rate decreased with increasing hardness and with increasing refractive index in the visible wavelength spectrum. Consequently, the etching CD of interconnects can be better controlled by using an organic film as the bottom layer resist when the film has appropriate properties.