George E. Keller

Separation of hydrogen from silane via membranes: A step in the production of ultra-high-purity silicon

Ultra-high-purity silicon (Si) is an important material for the electronics industry. Most of this Si is produced by thermal decomposition of trichlorosilane (SiHCl3). A second route is through decomposition of silane (SiH4). Since the conversion per pass in this process is not complete, the hydrogen which is co-produced can be separated from the gaseous SiH4 and purged so that the SiH4 can be recovered and reused. Three different separation schemes for accomplishing this separation, including absorption, cold box and membranes, were proposed and the relatives merits of these three were studied. The results of this study show that the separation by membranes is the preferred one because of its simplicity in equipment and its low cost in energy. To define the process for the separation of SiH4 and H2 by membranes, three aspects were investigated: (1) permeability measurement, (2) comparison of the mixture performance with the predictions of a design model, and (3) chemical stability of the permeator in the presence of SiH4. The results of permeation of a mixture of the two gases agree well with predictions by the design model using the pure-component permeabilities. The permeator is stable in the presence of SiH4. Thus, a solid data base was obtained for design of a full-scale unit.