Substrate curvature measurement system

Mechanical stress on wafer substrates is a problem of growing importance in the microelectronics industry due to the demand for reduced device dimensions. This ultimately leads to stress in interconnections during the manufacture of very large scale integrated devices (VLSI). Differences in thermal expansions between film and substrate lead to stresses introduced by temperature changes after film deposition, which results in spherical deformation of the substrate. Several one-dimensional measurement techniques (1-10) are available to measure the spherical deformation of substrates, with the most recent technique being a combination of a laser beam deflection and light scattering techniques (5). In this paper we describe a novel technique for substrate curvature measurement. It makes use of a 2-dimensional low power optical scanning technique with few moving components, and has an error voltage correction scheme for the reduction of position inaccuracy. This system has been built and tested and the results are discussed below.