Determination of stress profile and optimization of stress gradient in PECVD poly-SiGe films

This paper presents a method to determine the stress profile in PECVD poly-SiGe layers. Poly-SiGe films are thinned down by successive plasma etching to obtain different thicknesses. Stress gradient values are obtained for each thickness. These values are fitted to the best possible function. The relative stress profile is obtained from this function. The average stress value for the film is obtained by measuring wafer curvature before and after film deposition. Using the average overall stress value, the stress profile is determined completely. This method is applied to a 10\mu m thick PECVD poly-SiGe film. This procedure was repeated for another layer with a stress compensation layer on the top. It was demonstrated that it is possible to calculate the required thickness of this compensation top layer such that the film has a zero stress gradient.