HWAHAK KONGHAK, Vol.37, No.1, 64-71, February, 1999
폴리이미드 박막의 잔류 응력과 응력 완화 현상
Residual Stresses and Relaxation Behaviors of Polyimides Thin Films
초록
Poly(p-phenylene pyromellitimide)(PMDA-PDA)와 poly(4,4'-oxydiphenylene pyromellitimide)(PMDA-ODA)를 각각의 poly(amic acid) 및 poly(amic diethyl ester)전구체로부터 제조하였다. 이들 박막에 대하여, Thin Film Stress Analyzer (TFSA)를 이용하여 폴리이미드 박막의 잔류 응력거동은 공정온도(25-400 ℃) 하에서 전구체의 열적 이미드화에 따라 실시간으로 측정되었고, 수분 흡수에 따른 응력 완화 현상은 25 ℃와 100 %상대 습도하에서 수정된 Fick's law를 적용하여 모사하였다. 또한, 전구체의 종류에 따른 모폴로지와 잔류 응력거동과 관계는 WAXD을 이용하여 조사되었다. 폴리이미드 박막의 잔류 응력은 PMDA-ODA(PAA)-PMDA-ODA(PAE)>PMDA-PDA(PAE)>PMDA-PDA(PAA) 순이었고, 박막 내부로의 수분 확산 속도는 PMDA-ODA(PAA)>PMDA-ODA(PAE)>PMDA-PDA(PAE)>PMDA-PDA(PAA) 순이었다. 결과적으로, 폴리이미드 박막의 잔류 응력과 박막내로의 수분 흡수에 의한 응력 완화 거동은 전구체 종류와 이미드화 과정에 따른 폴리이미드의 모폴로지(사슬 강직도, 질서도, 배향도) 변화와 관련성이 있게 나타났다. 또한, 100 % 습도에서 측정된 폴리이미드 박막에 대한 응력 완화 계수는 전자 미세 저울로 측정한 수분 확산도와 일치하는 경향을 나타내었다.
Poly(p-phenylene pyromellitimide) (PMDA-PDA) and poly(4,4'-oxydiphenylene pyromellitimide) (PMDA-ODA) films were prepared from their poly(amic acid) (PAA) and poly(amic diethyl ester) (PAE) precursors. For these thin films, residual stresses were detected in-situ during thermal imidization of the polyimide precursors as a function of processing temperature over the range 25-400 ℃ using thin film stress analyzer, whereas moisture-induced stress relaxation was simulated as a function of time in 100 % relative humidity at 25 ℃ by a modified Fick's law. In addition, their relationship between morphological structures and residual stress behaviors depending on precursor origins were investigated by X-ray diffraction. In comparison, the residual stress was in the increasing order PMDA-ODA(PAA)-PMDA-ODA(PAE) >PMDA-PDA(PAE)>PMDA-PDA(PAA) and coefficient of water diffusion into thin films was in the increasing order PMDA-ODA(PAA)>PMDA-ODA(PAE)>PMDA-PDA(PAE) >PMDA-PDA(PAA). Conclusively, the residual stress and the stress relaxation behaviors induced by water diffusion kinetics were strongly affected by the morphology nature (chain rigidity, chain order, orientation) depending on the precursor origins and imidization step. In addition, stress relaxation coefficients for these polyimide films measured at 100 % relative humidity show consistent trend with water diffusivity of polyimide thin films measured by electro-microbalance.
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