Gravitational stress-induced dislocations in large-diameter silicon wafers studied by X-ray topography and computer simulation

Dislocations in slip bands introduced under gravitational stress in 200 mm diam Czochralski-grown silicon wafers were characterized by X-ray topography, and slip band initiation was estimated by computer simulation for 300 mm diam wafers. Surface scratching on the wafer back by contact with the jig forms an amorphous region, resulting in a collective motion of dislocations during annealing at 1473 K under gravitational stress. The occurrence of slip bands along the <110> directions was observed with a length of several centimeters from the contact area of the wafer-supporting jigs. Burgers Vectors and slip planes of the gravitational stress-induced dislocations were determined to extend along the [(1) over bar 10] direction in the (111) or (<(11)over bar>1) plane, terminating at the surface with screw-type in character. Three types of half loop of dislocations were identified with Burgers vectors of [011] in (<(11)over bar>1), [101] in (<(11)over bar>1), and [011] in (11(1) over bar) planes. By the reaction a/2[011] + a/2[101] = a/2[110], Lomer-type edge dislocations were found to be created. The gravitational stress in a 300 mm diam wafer was computed by a finite element method. By comparing the gravitational stress with the critical stress to multiply slip dislocations previously obtained, conditions for suppressing slip bands are predicted for wafers larger than 300 mm diam.