Study of local stress using stress-absorbing Si diaphragm

A methodology was developed to study the residual stress distribution of th in-film patterns residing on a silicon wafer. The Si underlying the pattern s studied was thinned down so that the deformation caused by residual stres s in the microstructure could be detected by a Twyman-Green interferometer. A procedure called "numerical etching" was implemented to simulate the Si etching process, which linked the stress state of the microstructure on a r egular wafer to that on a Si diaphragm. An initial stress field on the patt ern was assumed, and its effect on the bending of the Si diaphragm beneath was calculated and compared to the measured value. The discrepancy between them was used to modify the initially assumed stress field and repeated unt il a satisfactory match was achieved. We believe that the approximated stre ss field sufficiently reflects the real stress distribution in the patterne d structure under investigation. The stress distribution in an electroless Ni pad residing on Si for a flip-chip packaging application is used as an e xample. (C) 1999 American Vacuum Society.