With the rapid expansion of capacity to transmit and process information, devices for visually displaying information have become increasingly important. Lightweight, flat visual display devices are particularly needed for portable computers and wireless communications instruments.
One promising approach to providing flat-panel displays is the active matrix liquid crystal device (AMLCD). In essence the AMLCD comprises an array of thin film transistors, capacitors and electrodes formed on a transparent substrate and incorporated in an LCD display. Each thin film transistor controls an electrode which, in turn, polarizes a pixel-size region of liquid crystal. Typically the transistors are comprised of thin films of amorphous silicon. One difficulty with these devices, however, is that amorphous silicon lacks sufficient electron mobility to be used for drivers and registers in the display. Hence a hybrid structure combining amorphous silicon on glass and a crystalline silicon chip is required.
Polysilicon has higher electron mobility than amorphous silicon, and if polysilicon can be substituted for amorphous silicon in AMLCD devices, the entire display--complete with drivers--can be integrated on the substrate. However, few transparent materials can withstand the high temperatures, typically in excess of 600.degree. C., required to grow polysilicon. Consequently efforts to make polysilicon based displays have required substrates of high temperature glass, such as fused quartz which are expensive, heavy, and fragile. Moreover typical thin films of polysilicon have randomly oriented grains producing random distribution of defect densities and non-uniform etching and oxidation characteristics. Accordingly, there is a need for a method for low temperature growth of silicon of enhanced electron mobility and reduced grain structure (hereafter "epitaxial silicon") which can utilize a wider variety of substrate materials.