Laser Crystallization for Polycrystalline Silicon Device Applications

Abstract

Pulsed excimer-laser processing of amorphous silicon on non-crystalline substrates is an important processing technology for large-area polysilicon electronics, such as flat-panel displays and two-dimensional imaging arrays. The technique allows for the creation of CMOS polysilicon on glass substrates, the integration of polysilicon silicon and amorphous devices on the same glass substrate, and the fabrication of self-aligned amorphous silicon thin-film transistors via laser doping. Materials studies show that laser-crystallized polysilicon contains larger grains with fewer defects than polysilicon prepared by other techniques and exhibits large lateral grain growth in a narrow range of excimer laser energy density, with a corresponding peak in the electron mobility. This interesting materials phenomenon provides the opportunity to create excellent polysilicon for device applications, using an appropriate region of parameter space to avoid a non-uniform grain-size distribution and large surface roughness. Also, laser-processing enhancements, such as laser doping and fabrication of self-aligned transistors, provide additional tools to fabricate unique devices. These materials and device processing issues are described, and the device results are presented. For the devices, emphasis is placed on homogeneity and stability as well as on important performance parameters, such as thin-film transistor mobility and leakage currents.