Piezoresistive microcantilevers for <i>in situ</i> stress measurements during thin film deposition

Abstract

Conventional thin film stress measurements detect the physical deflection of a cantilever substrate induced by the stress in a deposited film. We have developed an electrical technique for in situ stress measurement that detects the piezoresistive response of resistors fabricated within the surface of a 20-μm-thick Si microcantilever substrate. By using Si cantilevers fabricated from (110) wafers, boron-implanted resistors oriented along ⟨110⟩ in-plane directions, which have a large piezoresistive response, were used for sensing the biaxial stress in the substrate surface resulting from the stress that developed in a deposited film. Resistors oriented along ⟨001⟩ in-plane directions, which have the least sensitive piezoresistive response and a temperature-dependent resistivity, were used to monitor the substrate temperature during deposition. Intrinsic stresses related to the thin film formation process, excluding thermal stresses, were measured for Cu during deposition as a function of film thickness and as a function of time during interruptions of growth. The piezocantilever’s insensitivity to both mechanical vibration and substrate alignment, good signal-to-noise ratio, and the potential for stress measurement during chemical vapor deposition are improvements over conventional thin film stress measurement techniques.