Temperature gradient zone melting process employing a buffer layer

In the process for fabricating a semiconductor device by thermal gradient zone melting wherein said process comprises the steps of:

• selecting a wafer body of suitable semiconductor material which is of one type of conductivity, said body having two major generally parallel opposed surfaces, said opposed surfaces being respectively the top and bottom surfaces;
• depositing an array of droplets in solid form on said top surface, said droplets comprising suitable metal-rich conductive material which is of an opposite type of conductivity;
• heating said wafer body and said droplets to a sufficient temperature for simultaneously
• (a) establishing a thermal gradient through said wafer body wherein said bottom surface is at a higher temperature than said top surface, and
• (b) melting said droplets to enable migration of said droplets through said wafer body toward said bottom surface;
• and
• removing heat from said top surface to enhance the establishment of said thermal gradient, whereby said droplets form column-like paths the conductivity of which is opposite to the conductivity of said wafer body, the improvement which comprises:
• applying a layer of suitable buffer material on the entire area of said bottom surface, said buffer layer having the characteristic of being insoluble with said droplets;
• and
• placing said wafer body on a generally planar surface of heating means with the entire area of said bottom surface having said buffer layer thereon directly on said heating surface,
• whereby said buffer layer terminates said migration of said droplets to prevent alloying of said droplets with said heating surface.