We have previously shown that location-controlled single-crystal regions can be obtained by implementing a version of the sequential lateral solidification process referred to as dot-SLS. Performed on an amorphous Si precursor, however, the process results in regions having an apparently random surface crystal-orientation distribution that may negatively impact the uniformity of resulting devices. In this paper, we demonstrate one approach to control the surface orientation of dot-SLS processed regions. We accomplish this in a simple manner by performing the process on textured polycrystalline Si precursor films that were, in turn, obtained using laser processing of as-deposited amorphous Si films. This hybrid approach is possible and effective because the dot-SLS process allows for preserving the original texture of the "seed" crystals, while successfully removing all random high-angle grain boundaries within the laterally solidified regions. We identify and utilize two specific and well-known laser-processing techniques for obtaining highly (100) or (111) surface textured polycrystalline Si films. The results from dot-SLS experiments performed on (100) textured films- obtained through "mixed-phase" zone-melting recrystallization using a continuous-wave laser - were found to be particularly significant as the growth from {100} surface-oriented seeds resulted in single-crystal regions that were predominantly free of any planar defects.
Formation of TFTs inside location-controlled large Si grains with a low temperature process is an attractive approach for realizing system-circuit integration with displays on a large glass substrate. Local structural variations of the substrate using photolithography allows an accurate location-control of the large Si grains in excimer-laser crystallization. Single-crystalline Si (c-Si) TFTs was formed inside a location-controlled large (6 μm) grain by μ-Czochraski process of a-Si film. The c-Si TFTs showed field effect mobility of 450 cm2/Vs on average. Crystallization characteristics, spread of the TFT characteristics and effects of process parameters
will be reviewed and discussed.
This paper reviews advanced excimer-laser crystallization techniques and its application to crystal-Si thin film transistors (TFTs). Combined microstructure and time- resolved optical reflectivity investigations during conventional excimer-laser crystallization showed that explosive crystallization occurs during excimer-laser irradiation. Two methods enabling location-control of large silicon islands will be reviewed. One of the methods uses local thermal relief by modifying locally the heat extraction rate towards the substrate. A small unmolten region remains at the center of high heat extraction part which then acts as a seed for radially grown Si grain with a diameter of 6 micrometers . One of the other methods use geometric selection through a vertical narrow constriction. In this method, upon laser irradiation, a small unmolten Si region remains at the bottom of narrow holes etched in the underlying isolation layer. During vertical regrowth, a single grain is filtered out which subsequently seeds the lateral growth of large grains. We will also discuss the performance of crystal-silicon TFTs that are formed in the location-controlled Si grains. The field-effect mobility for electrons is 450 cm2Vs, which is very close to that of TFTs made with silicon-on-insulator wafers.
Conference Committee Involvement (1)
Laser Applications in Microelectronic and Optoelectronic Manufacturing XII
22 January 2007 | San Jose, California, United States
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