Estimated approach development and experimental validation of residual stress-induced warpage under the SiNx PECVD coating process

Abstract

Depositing silicon nitride (SiNx) coating by utilizing the plasma-enhanced chemical vapor deposition (PECVD) procedure is currently an important approach in the semiconductor industry because SiNx coating has several excellent application functions, such as passivation layer and oxygen/vapor barrier. However, residual stress occurs in the thin film resulted from the coefficient of thermal expansion (CTE) mismatch, lattice mismatch, defects, and impurities during the PECVD process. The SiNx-coated wafer would induce harsh warpage generated by coating film's residual stress. Aforementioned issue might generate the defects in the products, thus resulting in disrupted process and reliability problems. Such warpage is also unfavorable to the high flatness requirement for subsequent fabrication with the continuous scaling of advanced-technology devices. Accordingly, this study presents a novel process-oriented simulation methodology integrated with fluid dynamics-mechanical coupling responses to estimate its induced warpage magnitude affected by the pressure and temperature distributions during PECVD process and the initial intrinsic stress of SiNx coating. Under the consideration of the abovementioned loadings, the resultant stress and warpage after force balance for depositing SiNx coatings are obtained through process-oriented layer-by-layer simulation. On the basis of the simulated results and the data of experimental measurements, an intrinsic stress surface for SiNx is established by the radio frequency power, ammonia, and silane gas flow rate. Accordingly, the warpage magnitude and intrinsic stress of PECVD SiNx thin coating prior to actual processing can be immediately and accurately judged by the simulation methodology and SiNx intrinsic stress surface presented in this investigation.