O2 플라즈마 전처리 및 후속 열처리 조건이 Ti 박막과 WPR 절연층 사이의 계면 접착력에 미치는 영향
Effects of O2 Plasma Pre-treatment and Post-annealing Conditions on the Interfacial Adhesion Between Ti Thin Film and WPR Dielectric
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Fan-out wafer level packaging (FOWLP) 재배선 적용을 위한 Ti 박막과 WPR 절연층 사이의 계면 신뢰성을평가하기 위해, O2 플라즈마 전처리 및 후속 열처리 시간에 따라 90° 필 테스트를 진행하였다. O2 플라즈마 전처리 시간이 증가 할수록 계면 접착력이 감소하다가 유지되는 거동을 보였으며, 이는 과도한 O2 플라즈마 전처리가 WPR 절연층내의 C-O-C 또는 C=O 결합을 끊어 WPR 표면이 손상을 받아 계면 접착력이 저하된 것으로 판단된다. 또한 O2 플라즈마 전처리를 30초 진행한 시편을 150oC 후속 열처리 진행한 결과, 계면 접착력이 0시간에서 24시간까지는 감소하였으나, 100시간까지 유지되는 거동을 보였다. 이는 고온에 취약한 WPR 절연층이 과도한 열처리로 인해 손상되어 계면 접착력이 급격히 감소하다가 유지되는 것으로 판단된다. 따라서, 절연층 소재에 대한 최적의 플라즈마 전처리 조건을 확보하는 것이 FOWLP 재배선의 계면신뢰성 향상을 위한 핵심요소임을 알 수 있다.
Abstract
The effects of O2 plasma pre-treatment and post-annealing conditions on the interfacial adhesion of Ti thin film and WPR dielectric were investigated using 90o peel test for fan-out wafer level packaging (FOWLP) redistribution layer (RDL) applications. Peel strength between Ti film and WPR dielectric decreased from 8.9±1.3 g/mm to 2.7±0.9 g/ mm for variation of O2 plasma pre-treatment time from 30s to 300s, which is closely related to C-O-C or C=O bonds breakage at the WPR dielectric surface due to excessive plasma pre-treatment conditions. During post-annealing at 150oC, the peel strength abruptly decreased from 0 h to 24 h, and then maintained constant until 100 h, which is also mainly due to the damage of WPR dielectric which is weak to high temperature. Therefore, the optimum plasma pre-treatment conditions on the surface of dielectric is essential to interfacial reliability of FOWLP RDL.
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