트랜치 구조에서의 레이저 유기 충격파 세정 방향에 따른 입자 제거 효과

Abstract

Dry cleaning has been studied to control the removal force on pattern wafers as device feature sizes decrease to below 100 nm. Laser shock wave cleaning (LSC) has been introduced to remove particles on patterned wafers. In this method particles are removed by shock wave which generated by a focused laser beam having biconvex lens. LSC can be applied to BEOL, local cleaning of wafer and extreme ultraviolet (EUV) lithography mask. For the application of LSC to EUV mask cleaning or any BEOL cleaning process, the questions have been raised how the particles behave when patterns exist. For example, EUV lithography mask contains various layers with their topographies. This topography might create ¨shadow effect〃 during cleaning process. In this paper, the effect of pattern topography on the particle removal was investigated on trench patterns using LSC. A laser shock wave was generated by a Q-switched Nd:YAG laser (IMT, Korea) with a maximum pulse energy of 1800 mJ at a wavelength of 1064 nm. To characterize the topographical effect on LSC, samples with trench patterns were aligned for and against the shockwave propagation direction. The pattern width and aspect ratio were 5 ??m and 0.25, respectively. PSL microspheres (500 nm red fluorescence, Duke Scientific, USA) were used as the particulate contaminant source and were deposited on the STI patterned wafers by dipping them into the IPA solution which contained PSL microspheres. Cleaning performances such as PRE and cleaning area were analyzed by a fluorescence microscope (LV-150, Nikon, Japan). The topographical effect was characterized as a function of laser shock wave propagation direction. PRE was lower in case of vertical direction when compared to horizontal direction. It means that the topography of a trench is critical in removing particles. It could be observed that LSC in vertical direction left more particles than horizontal and also in both cases the remained particles were present at the trench side wall. Based on these results, it could be concluded that LSC in horizontal direction has more PRE than in vertical direction and hence topography is an important consideration during LSC.