Sequential lateral solidification processing for polycrystalline Si TFTs

The sequential lateral solidification (SLS) process is an excimer-laser projection-based scheme for crystallization of thin films on amorphous substrates. This method can be used to readily produce a wide range of microstructures through manipulation of grain boundary placement within the crystallized material. In this paper, we focus on the 2-shot SLS process for crystallization of thin Si films for thin-film transistor (TFT) applications. We have investigated the effect of process parameter variation on the resulting microstructure, as well as on the performance of TFTs fabricated on the material. The 2-shot SLS microstructure was further engineered to reduce anisotropy of the TFT performance relative to the lateral growth direction using additional laser scans. Through this method, we were able to improve the mobility directionality ratio between devices with majority carrier flow parallel and perpendicular to the lateral growth direction, respectively, from 0.3 to over 0.7. Post-SLS process thinning and planarization of the Si surface was used to improve the uniformity and performance of the TFT devices.

I. Introduction

Low-Temperature-Compatible (LT) crystallization schemes for producing large-grained polycrystalline Si films on high-temperature-incompatible amorphous substrates have been studied extensively in the past decade [1]– [3]. These materials are important for integration of driver circuitry into large-area microelectronic applications such as active matrix liquid crystal displays (AMLCDs) or organic light-emitting diodes (OLEDs) that reside on substrates such as glass or plastic. High-performance thin-film transistor (TFT) devices fabricated using these materials for the active region are desirable, as they can enable integration of various driver components directly onto the substrate in order to reduce manufacturing costs, and to increase the functionality of large-area microelectronics.