Low Temperature Annealing of LPCVD Silicon Films
- PDF / 802,837 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 79 Downloads / 260 Views
LOWTEMPERATURE ANNEALING OF LPCVD SILICON FILMS T. Aoyama. N. Konishi, T. Suzuki, and K. Miyata Hitachi Research Laboratory, 4026 Kuji-cho, Hitachi,
Ibaraki 319-12 Japan
ABSTRACT Low temperature, 600°C annealing of LPCVD films was investigated by x-ray diffraction, ESR, TEM,and carrier mobility measurements. An optimum deposition temperature of about 550*C was found to yield good crystallinity and large electron mobility for annealed films; large grain sizes, a maximum crystallite size, and a maximum electron spin density were also observed for films deposited at the optimum temperature. Electron spin density for as-deposited films correlated with the crystalline volume by x-ray diffraction measurements on the films after annealing. This implys that only those amorphous components with high electron spin density can be converted into the crystalline phase by 6O0°C annealing.
INTRODUCTION Active matrix thin film transistors (TFT's) have attracted attention for their applications to liquid crystal (LC) TV's and displays (1). With the requirement of monolithic drivers' integration around display panels (2), polycrystalline silicon instead of amorphous silicon is becoming important due to its high carrier mobility of more than 30 cm2 /Vs. In either materials, however, the process temperature should be lower than about 600°C to allow use of glass substrates. So far, polysilicon films deposited by the LPCVD technique over a wide range of temperatures have been investigated. Kamins (3) reported the structure of polysilicon,especially, the preferred orientation of the films . High temperature annealing at about 1000"C was investigated by Harbeke et al.(4) and Yoon et al.(5); amorphous films were shown advantageous to obtain high crystallinity after annealing. Low temperature annealing at 600C was performed by Bisaro et al.(6) and the effect of both deposition temperature and pressure was examined. High deposition pressure was preferable for obtaining high crystallinity after annealing. Solid phase crystallization, focusing on low temperature annealing, was investigated by Narayan(7),Germain et al.(8), and Bisaro et al.(9) and the crystallization rate was shown to relate to the crystal orientation and the electron spin density (charged dangling bonds) of the film. Electrical properties, including mobility and conductivity for poly or amorphous silicon have been investigated by a number of authers (10-12). Recently polysilicon TFT's were fabricated in different ways (2,13-15) and it was suggested that the deposition temperature should be as low as possible to obtain high carrier mobility(15). However, low temperature annealing of polysilicon films is not fully understood yet from the viewpoint of the annealing mechanism. In this paper we investigated the low temperature annealing of LPCVD films below the process temperature of about 600°C by using x-ray diffraction, electron spin resonance (ESR), transmission electron microscopy (TEM), and TFT's. An optimum temperature was found which yielded high crystallinity and high e
Data Loading...
