Piezoelectric Effect on Plasma Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films
- PDF / 278,462 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 25 Downloads / 218 Views
PIEZOELECTRIC EFFECT ON PLASMA CHEMICAL VAPOR DEPOSITION OF HYDROGENATED AMORPHOUS SILICON FILMS Masashi KAWASAKI, Masatomo SUMIYA, and Hideomi KOINUMA Research Laboratory of Engineering Materials, Tokyo Institute of Technology 4259 Nagatsuta Midori-ku Yokohama 227, Japan
ABSTRACT As a potential method for controlling the surface reaction of plasma CVD, mechanical vibration generated by a piezoelectric device was applied on the substrate during glow discharge decomposition of SiH 4 . The application of 2MHz vibration dramatically improved 0 the photoconductivity of a-Si:H films prepared at a substrate temperature of 12 'C. IR and CPM spectra for the films revealed that the piezoelectric vibration remarkably modulated 14 the amorphous network structure and reduced the defect density to 4.3x10 cm-3, which is the best among the values ever reported. INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) films deposited by the glow-discharge plasma have been used in a variety of devices. The improvement in quality and reliability of a-Si:H films has been desired for higher performances in the devices. Since the surface reaction dominates the structure of a-Si:H, it should be most important to control the surface reaction during the film deposition. Knight proposed the improvement of a-Si:H properties by enhancing the mobility of silicon-containing species (precursors) at the growing surface[l], but he did not provide any specific ideas to achieve the purpose. The Monte Carlo simulation of film growth process suggested that the surface migration of precursors had the most significant effect on the final film structure [2]. For modifying the surface reaction of plasma CVD, a variety of techniques, such as UV laser irradiation[3] and low energy ion irradiation[4], have been reported. However, these additional excitation sources provide very high energy quanta (UV laser -5eV, ion -50eV), compared with the activation energy (E.-0.2eV) for the hopping migration process of precursors adsorbed on the surface. Recently, Ganguly et al. reported that the thermal energy of about 40meV (substrate temperature of 450'C), which is much lower than E., could enhance the surface migration [5]. If one could provide a low energy excitation source which selectively enhance the surface migration process, it should be possible to modulate the surface reaction and thereby the amorphous network and defect density in the resulting film. As a promising candidate of such an excitation source, we propose ultrasonic vibration and have investigated its effects on the plasma CVD growth of a-Si:H Mat. Res. Soc. Symp. Proc. Vol. 297. ©1993 Materials Research Society
140
film. EXPERIMENTAL A lead zirconium titanium oxide (PZT) disk (diameter 30mm, thickness 2mm, with Ag electrodes plated on the both sides) was used as a mechanical vibration generator with a resonance frequency of 2MHz. As shown in Fig. 1,a substrate (glass or c-Si) was glued on the PZT with indium and a part of the top electrode on the PZT was isolated to form a reference electrode. 2M
Data Loading...
