Forming a crystalline semiconductor film on a glass substrate

Abstract

A method of crystallizing amorphous silicon on a glass substrate relies on deliberately heating the glass substrate above its strain point during processing, making low temperature glasses, such as soda lime glasses, ideal for such use. Since the glass is plastic above this temperature while the silicon remains elastic, the glass is forced to conform to the shape defined by the silicon once this temperature is exceeded. This process relaxes any stresses which might otherwise be created in the glass or film, as long as the glass temperature is above the strain point. As the glass temperature is reduced back below the strain point, the glass becomes progressively more rigid and stresses will begin to build up in the film and glass. When cooled slowly, the stress in the film and the glass can be controlled by appropriate selection of a thermal expansion coefficient of the glass relative to that of silicon, particularly those with linear expansion coefficients in the range 4-10 ppm/° C. below the strain point.