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 20 0 mm diam Czochralski-grown silicon wafers were characterized by X-ray topography, and slip band initiation was estimated by computer simula tion for 300 mm diam wafers. Surface scratching on the wafer back by c ontact with the jig forms an amorphous region, resulting in a collecti ve motion of dislocations during annealing at 1473 K under gravitation al stress. The occurrence of slip bands along the <110> directions was observed with a length of several centimeters from the contact area o f the wafer-supporting jigs. Burgers Vectors and slip planes of the gr avitational stress-induced dislocations were determined to extend alon g the [(1) over bar 10] direction in the (111) or (<(11)over bar>1) pl ane, terminating at the surface with screw-type in character. Three ty pes 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] i n (11(1) over bar) planes. By the reaction a/2[011] + a/2[101] = a/2[1 10], Lomer-type edge dislocations were found to be created. The gravit ational stress in a 300 mm diam wafer was computed by a finite element method. By comparing the gravitational stress with the critical stres s to multiply slip dislocations previously obtained, conditions for su ppressing slip bands are predicted for wafers larger than 300 mm diam.