CHARACTERIZATION OF BOROPHOSPHOSILICATE AND GERMANOPHOSPHOSILICATE GLASSES FOR VLSI APPLICATIONS.

Phosphosilicate glass (PSG) films deposited by LPCVD low pressure chemical vapor deposition are widely used in the fabrication of VLSI circuits. These films typically undergo two high temperature processing steps (i. e. , flow and reflow) to smoothen the topography and drive-in the junctions. The ability of PSG to flow at a given temperature is primarily a function of the phosphorus content in the glass. Although a reduction in the thermal cycle to minimize dopant redistribution is possible by increasing the P content in PSG, such films become hygroscopic and may corrode the Al metallization. In this study, we examine a series of glass compositions prepared by bulk fusion of a PSG matrix to which oxides of B or Ge are added for the purpose of evaluating the contributory effect of these additions on the viscous properties of the matrix. Thermal expansion measurements were conducted on numerous glass compositions to determine changes in the glass transition temperature and the associated changes in the viscosity of these systems.