Effect of process parameters on the structural characteristics of laterally grown, laser-annealed polycrystalline silicon films

Abstract

In this work, we have conducted a systematic study aiming at assessing the effects of process parameters on the microstructural characteristics of laterally grown polycrystalline silicon (poly-Si) films. Poly-Si films were formed by the sequential lateral solidification (SLS) method. The Si film thickness was found to affect significantly the quality of the poly-Si microstructure, manifested by a decreased crystal-growth defect density and increased subboundary spacing in thicker films. A weak (100) texture was observed in the lateral growth direction, except for very thin films (<30 nm) where (110) texture was observed. No specific texture was identified in the normal and transverse directions. Lateral crystallization proceeds by seeded, lateral epitaxial growth at an advancing pitch. We investigated the quality of lateral growth as a function of the advancing, substrate pitch. We found that an optimum pitch range exists, bound on the low end by the detailed shape of the beam-edge profile and on the high end by the quality of crystal formed under deep, interfacial undercooling. In that sense, only a fraction of the laser beamlet can be effectively used for lateral growth and the process should be tuned towards maximizing this fraction. Thin film transistor data were used to further refine the considerations driving the selection of optimum process parameters for SLS lateral crystallization providing the least sensitivity to process-induced variations.

Effects of mechanical strain on laser crystallized polysilicon thin film transistors and ring oscillators fabricated on stainless steel foil

“…It is important to note that the inverter stages of all the ring oscillators in a same group are identical. SLS crystallized polysilicon material with the film thickness of greater than 50 nm shows a strong crystallographic orientation along the direction of lateral growth [4]. Superior TFT performance can be obtained by orienting its channel to the same direction.…”

“…To electrically isolate and mechanically balance the steel substrate, 3 lm SiO 2 passivation layer was coated on both sides of the wafer using plasma enhanced chemical vapor deposition (PECVD) system. The semiconducting active layer consisted of 50 nm of polycrystalline silicon film, deposited initially in the amorphous phase by PECVD and then laser crystallized using the sequential lateral solidification (SLS) technology [3,4]. The SLS method results in elongated polysilicon grains which have a high quality microstructure.…”

A flash analog to digital converter on stainless steel foil substrate

“…As it was mentioned before, the accuracy of the ADC, beside its dependence to the linearity of the comparators, is also related to the matching level of the series connected resistors. We have previously experimented with resistor ladders using laser crystallized polysilicon technology to develop a 3-bit and 5-bit Rail to Rail Digital to Analog Converter (DAC) [9] and great linearity was obtained due to good resistor matching (R = 1 kX ± 50 X). Therefore we have incorporated the same resistor elements which were made out of n-type, non-silicided polysilicon active material to develop the resistor ladder of the flash ADC.…”

Performance and reliability of SLS ELA polysilicon TFTs fabricated with novel crystallization techniques

“…High reliability should also be achieved for the fabrication of commercial products to be possible. With the recent polysilicon crystallization process breakthroughs, using various excimer laser anneal (ELA) methods such as sequential lateral solidification (SLS), the TFT performance has substantially increased [2][3][4][5][6]. The several variations of the SLS technique allow the manufacturing of polysilicon films with excellent intragrain quality and grains of different geometry.…”