Polysilane bilayer applications

One application of polysilanes is in a bilayer construction, as shown in Figure 10. To cover existing topography on the wafer, a thin planarizing layer of a nonphotoactive polymer is deposited, followed by a very thin photoresist layer, about 0.5 to 0.2 pm in thickness. The wafer is exposed through a mask. 

Because of their desirable properties and radiation sensitivity, polysilanes have been used in a variety of microlithographic applications as (1) mid-UV contrast-enhancing materials, (2) imaging layers in a variety of bilayer lithographic processes, and (3) new resist materials for ionizing radiation. 

The conventional bilayer resist systems in which the top imaging layer (typically organosilicon polymer) also serves as an etch mask was first proposed by Hatzakis et al. in 1981, ostensibly for electron-beam lithography. Since then, a number of organosilicon resists for bilayer resist systems have been reported for use in near-UV, DUV, mid-UV, electron-beam, and x-ray applications, a good review of which has been provided by Ohnishi et al. In recent times, negative-tone resist systems and processes based on silicon-backbone polymers such as polysilanes,polysilynes, and plasma-deposited polymers have been developed for 193-nm lithography. 

---