Process-induced transfer pattern in Si epitaxy using pocket susceptor

The vapor-phase epitaxial growth of silicon epwafers using pocket susceptor is studied. Characteristic transfer patterns are frequently observed on the backside wafer surface. The pattern has the shape of tree-rings extending from the wafer edge. The size and shape of the transfer pattern is sensitive to the growth sequence and the process condition such as growth temperature. The pattern is attributed to the chemical transfer of the coating from the pocket to the sagging front of the wafer. It is discovered that the tree-ring pattern is a true record of the process history. Each ring can be assigned to a particular growth step and vise versa. A close examination of the ring pattern provides valuable insight on wafer sagging in response to the process change. The result of pattern transfer is compared with that using a flat susceptor.