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Crystal Growth of Laser Annealed Polycrystalline Silicon As a Function of Hydrogen Content of Precursors Takuo Tamura, Kiyoshi Ogata, Michiko Takahashi1, Kenkichi Suzuki1, Hironaru Yamaguchi, and Satoru Todoroki Production Engineering Research Laboratory, Hitachi Ltd. 292 Yoshida-cho, Totsuka-ku, Yokohama 244-0817, Japan 1 Image-related Device Development Center, Displays, Hitachi Ltd. 3300 Hayano, Mobara, Chiba 297-8622, Japan

ABSTRACT

The influence of hydrogen in a precursor on excimer laser crystallization behavior was investigated. The crystal orientation and lattice constant of polycrystalline silicon films were analyzed by X-ray diffraction measurement. An intensity ratio of 111 to 220 was used as an index of the (111) preferred orientation. A randomly oriented film with an index of 2 at lower energy density changed to the highly (111) oriented phase with an index of more than 15 at higher energy density. It was observed in the PE-CVD films that increasing the hydrogen in the precursor films decreased the orientation index. The lattice constant of the laser-annealed PECVD silicon was found to be larger than that of the PVD silicon and to decrease with an increase in laser energy density. The network structure of as-deposited PVD film with less hydrogen content was denser than that of as-deposited PE-CVD. The network structure of the precursor strongly affected the crystal growth, and the structure of the ELC poly-Si was still affected by the precursors, even though the hydrogen content decreased after laser annealing.

INTRODUCTION

Low-temperature polycrystalline silicon (LTPS) is attractive for many manufacturers of flat panel displays because it has higher electrical performance and can be cheaply produced1). Display technologies have been based on a-Si thin film transistor (TFT), however higher performance of the LTPS TFTs is necessary for next-generation LCD applications. In the LTPS process, an excimer laser crystallization (ELC) technique is used to crystallize precursor amorphous silicon films. The crystallographic features of the LTPS films strongly correspond to electrical characteristics, such as the field-effect mobility and threshold voltage of the TFT2-3). Precursors and ELC conditions can vary the crystallinity of the LTPS films, however the mechanism of the ELC had not been thoroughly revealed. Kuriyama et al. reported that the grain growth phenomenon caused by excimer laser crystallization was strongly affected by precursors4). The authors reported that higher hydrogen concentration in precursor film caused an ablation or pinhole in the ELC film5). Detailed investigations of such crystallization mechanisms and the influences of hydrogen concentration are necessary for the industrialization of LTPS technologies.

Q9.5.1 Downloaded from https://www.cambridge.org/core. La Trobe University, on 18 Mar 2019 at 02:23:25, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-621-Q9.5.1

EXPERIMENTAL

Two kinds of silicon films wer