Improved Characteristics of Rainbow Defects with Novel Wafer Edge Exposure Technique

摘要

The demand for manufacturing integrated circuit with high circuit speed and high packing density requires reduced feature sizes in ULSI structures. As the device feature size shrinks below sub-130 nm it needs the tight control of defect reduction in lithography process. Especially, resist peeling at the wafer edge is one of the major sources for particle generation. The WEE (Wafer Edge Exposure) process removes resist up to a width of a few mm from the wafer edge in order to prevent particle generation in succeeding process. The defect induced from wafer edge after WEE has given the critical damage to electrical properties and device yield. In this paper, we have applied novel WEE kit to reduce the rainbow bandwidth caused by WEE step in wafer edge. The novel WEE kit consists of chrome slit and lens assembly to minimize the scattering of UV beam from the optic fiber in comparison with the conventional WEE kit using condensing lens only. And we have investigated the influence of rainbow bandwidth for the different resist thickness, UV intensity, exposure time and then presented the experimental results obtained by using novel WEE kit. The change of rainbow bandwidth was also characterized by OM (Optical Microscope) and SEM (Scanning Electron Microscope). With the novel WEE kit the bandwidth of rainbow is reduced to 5 μm, while the conventional WEE kit has been induced 20 μm of bandwidth on bare silicon wafer. In the case of patterned wafer, the bandwidth of rainbow is reduced to 60 μm for the novel WEE kit, while the conventional WEE kit has induced 230μm of bandwidth. Therefore, it is confirmed that the application of novel WEE kit for patterned process makes less rainbow defect and finally increases the device yield for mass production.