Compact purifier for silane gas

Abstract

A purifier for silane was constructed for use in silicon film epitaxy and CVD processes. The purification is realized with 1 kg of a newly developed molecular sieve (K6Zn3) -A zeolite by selectively sorbing phosphine, which is a main impurity in commercially available tanked silane gas. The column of absorbent is continuously cooled to −20 °C, and the flow rate of gas treated ranges is between 0.1 and 3.0 l/min. The effectiveness of the purifier was investigated by using a test gas, a mixture of silane and hydrogen at a volume ratio of 5:95 containing 0.1 ppm of phosphine. An epitaxial film with a resistivity of 0.7 Ω-cm at room temperature was produced from untreated test gas, while one of 3000 Ω-cm was produced from gas treated with the purifier. An estimated life of the absorbent is about 10 000 h, under the condition that the above test gas is passed at a flow rate of 1 l/min. It is further expected that films with much higher resistivities can be produced, if carrier-free silane is used as a raw material gas in place of the present test gas.