Ar + Implantation Effects on Polycrystalline Thin Films
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J.H. LEE, C.W. HWANG, J.E. SHIN, YS. JIN, and S.B. MAH LCD R&D 2,8 Samsung Electronics Co., Kiheung, Yongin-Gun, Kyungki-Do, 449-900, Korea ABSTRACT The solid phase crystallization behavior of argon ion (Ar) implanted very thin Poly-Si films of 500A polycrystalline silicon (poly-Si) films has been investigated. thickness were deposited at 6251C by low pressure chemical vapor deposition (LPCVD). The films were amorphized by Ar' implantation with 7 ° tilt angle. The amount of ions implanted was varied from 2.0 x 10'3 cm-2 to 1.2 x 10I' cm*2 and the acceleration voltages from 40KeV to 120KeV. The films were recrystallized by furnace annealing at 5801C for 48 hours in N 2 atmosphere, followed by 1000oC annealing The crystallinity of the recrystallized Si films and the distribution of the argon atoms in the film were investigated. It was found that the crystallinity strongly depended on the Ar" implantation dose. The average grain size of Ar' implanted film was about 0.25pn , which was smaller than that of Si' implanted film of the same dose, 0.45pm. Ar atoms retarded the grain growth rate during the annealing process and the excess Ar atoms in Si films were segregated at the surface of silicon films after 10001C annealing Poly-Si thin film transistors (TFTs) were fabricated at high temperature using Ar' implantation technique. Remarkable electrical characteristics (IdsVgs) were obtained such as an electron mobility of 35 canN.s, which was attributed to the enhancement of crystallinity by Ar' implantation. But, segregated Ar atoms near the interface would give rise to structural deformation and crystalline defects which can act as the scattering and' trapping centers for carriers. INTRODUCTION Poly-Si TFTs have attracted considerable interest for larga-area electronics, and application to three dimensional integrated circuits. In poly-Si TFT, grain boundaries degrade carrier transport and exert a strong influence on
device characteristics[l]. One method to reduce the disadvantageous effects from the grain boundaries is to enlarge the grain size by silicon ion implantation prior to crystallization anneal. The technique called seed selection through ion channeling has been demonstrated in grain size enhancement for poly-Si films[2]. Kung et al.,[3] have presented the technique to modify crystallographic orientations of poly-Si films by varying implant angle. Noguchi et al., [4][5] have demonstrated a silicon ion (Si) implantation method to amorphize poly-Si films as thin as 300A and subsequent recrystallization for grain size enhancement. Generally, SiF 4 is used for source gas in the method of seed selection through ion channeling But in the case of using SiF 4 for source gas, one of the major problems is the generation of particles coming from the residuum during SiV implantation, which causes frequent maintenance of implantation equipment. Therefore, we studied the mechanism of a technique with an argon ion (Ar) source. Ar is an inert gas and does not affect the resistivity of the poly-Si film. Ar ion has a similar io
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