Amine gradient process for 157-nm lithography

Abstract

To accomplish minimizing feature size to sub 7Onm, 157nm photolithography becomes a strong candidate as a new lithographic technology. However, there is a strong need for new photoresists, which are transparent to 157nm light sources. To have a transparency for 157nm light source, fluorinated organic polymers are studied intensively. As a result, there are some ofpolymers that have absorbance of 2//tm. However, in spite ofthis low absorbance of 2//tm, resist profile simulation tells us bulk slope problems. To obtain more than 85 degree of resist pattern profile, the absorbance of resist must be 1 .2/Pm. The absorbance of 1.2/Pm is very difficult target to accomplish. To overcome this light absorption problem, we have developed "amine gradient resist process (AGRP)" which gives an amine gradient in photoresist and can make a vertical profile though the resist has poor transparency to light source. By adding chromophore that absorbs 193nm wavelength, we made model ArF resists of which absorbances were from 1.2//mi to 4 Pm. By patterning experiment using these model resists and 193nm scanner, we could confirm that the resist absorbance should be lower than 1.2/Pm to obtain vertical profile pattern at the resist thickness of l5Onm. But if we use AGRP, the absorbance of 2.5/11111 willbe enough value for the vertical profile pattern. So we could conclude that by combining 157nm resists and amine gradient process, resist absorbance problem in 157nm photolithography could be solved. We also studied for the resist properties that were suitable for AGRR