Purified Silicon Film Formation from Metallurgical-Grade Silicon by Hydrogen-Plasma-Induced Chemical Transport

Abstract

A purified Si film is prepared directly from metallurgical-grade (MG) Si by chemical transport using sub-atmospheric pressure H 2 plasma. The purification mechanism is based on the selective etching of Si using atomic H. It is demonstrated that the concentrations of most metal impurities (e.g., Fe, Cr, Ni, Ti, and Mn) in the prepared Si film are in the acceptable range for solar-grade Si material, or below the determination limit of the several impurity measuring methods employed in this study. From the infrared absorption measurements of the etching product produced by the reaction between H 2 plasma and MG-Si, it is found that the main etching product is SiH 4 . Therefore, a remote-type chemical transport process is developed to produce SiH 4 gas directly from MG-Si. Using other purifying principles (such as a pyrolysis filter in combination with this process), it is demonstrated that purified Si films about B, P and metal atoms can be produced from metallurgical-grade Si (<98% purity).

Effects of Surface Temperature on High-Rate Etching of Silicon by Narrow-Gap Microwave Hydrogen Plasma

“…On the efficient production of SiH 4 gas using this method, control of Si surface temperature in the hydrogen plasma etching is very important, because the etch rate is dependent on temperature. In our previous study, we showed that the etch rate remarkably decreases with increasing substrate temperature from 100 to 400 C. 3,5) Such decrease in etch rate has been also reported in some literatures, [10][11][12] and the behavior has been explained from a viewpoint of H 2 desorption from the etching surface. However, the detail on the etching characteristics is still not fully understood.…”

“…Based on the Si etching reaction with hydrogen (H), we have proposed a method to produce the high-purity SiH 4 gas directly from metallurgical-grade Si (MG-Si) materials. [1][2][3] This method is based on two important technologies. One is the utilization of narrow-gap microwave plasma system.…”

“…This system can supply high-density atomic H to Si substrate, which leads to the etching at high rate. 3,4) The other is the selective etching of Si. In this method, the difference in hydrogenation reaction of Si and metals is utilized as one of the key technologies to obtain the purified SiH 4 gas.…”

“…In this method, the difference in hydrogenation reaction of Si and metals is utilized as one of the key technologies to obtain the purified SiH 4 gas. 3,5,6) MG-Si includes some metal impurities such as Fe, Ti, and Cr and so on. But, most of these metal hydrides except B, P, and C do not volatilize easily near room temperature, compared with Si hydrides.…”

Selective Boron Elimination from B2H6–SiH4Gas Mixtures for Purifying Si

“…Our proposed method is based on the direct hydrogenation of MG-Si with hydrogen plasma. 16,17 The atomic hydrogen generated in the plasma can selectively etch Si atoms by the following reaction:…”