6.152J3.155J Czochralski growth of single crystals: stress, dislocations 6.12J/3.155J Microelectronic processing Dead boundary layer For large temperature gradients, e.g. dT/a w 1000C/cm and given a=2.6 x 10-6/C, then AV- aAT=> strains of 0.6%6 which exceeds the yield stress of Si,-> dislocations N。v.26,2003 Line defects: dislocations Dislocations originate in shear strains, mostly induced by thermal gradients during growt A couple of dislocations/wafer is typical Why so few? 1)"Tang"(neck at beginning of xtl allows dislocations to move to surface 2)Large number of atoms are involved in a dislocation = high energy, U Dislocation has low entropy(most atoms are in unique place = TS is very positive larg small Nov.26,20036.152J/3.155J 10 19 Nov.26 , 2003 6.12J / 3.155J Microelectronic processing dT/dx § 1000C/cm Seed Melt Dead boundary layer Czochralski growth of single crystals: stress, dislocations For large temperature gradients, e.g. dT/dx § 1000C/cm., and given a = 2.6 x 10-6/0C, then Dl/l = aDT => strains of 0.6%, which exceeds the yield stress of Si, => dislocations 20 Nov.26 , 2003 6.12J / 3.155J Microelectronic processing Dislocations originate in shear strains, mostly induced by thermal gradients during growth. Line defects: dislocations A couple of dislocations/wafer is typical. Why so few? 1) “Tang” (neck at beginning of xtl) allows dislocations to move to surface 2) Large number of atoms are involved in a dislocation, => high energy, U Dislocation has low entropy (most atoms are in unique place) G = H - TS is very positive large small