The Critical Shear Stress for Slip Generation due to Scratches in Silicon Wafers

Abstract

The relationship between slip dislocations generation due to scratches on silicon wafers and oxygen concentration has been investigated by three-point bending tests at high temperatures from 973 to 1123 K. We have measured the critical shear stresses for slip initiation caused by surface scratches as the onset of dislocation motions. In addition to the locking effect by oxygen atoms of dislocations, it was found that strain rate also has an important role on the value of the critical stress for slip generation caused by scratch. In order to take into account the effect of the strain rate, a new empirical equation as a function of strain rate for the estimation of critical shear stress was developed using the results with the three-point bending in this study. The equation obtained in this work indicates that ramp rates in the thermal process of wafer have a crucial effect on the slip dislocation generation. The estimation of critical shear stress of slip dislocation using this equation shows a good agreement with the experimental results of a heat treatment process.

Effect of Surface Oxygen Concentration on Wafer Strength in Floating Zone Si Wafers

“…Effect of interstitial oxygen atoms on critical shear stress.-It is well known that oxygen atoms affect critical shear stress through locking effect. 5,10,19,20,[28][29][30][31][32] The locking stress can be expressed by the following;…”

“…The indent depth with the force of 0.98 N was close to the depth of scratches, which was observed by using TEM. 20 Under the same load, Vickers indents were introduced at 61-points on the specimen at a pitch of 0.5 mm, as shown in Fig. 1.…”

“…Stress analysis.-Similar to previous studies, 10,20 the hightemperature three-point bending test was carried out using a Shimadzu AG-X universal testing machine equipped with a thermal treatment furnace. The specimen in the thermal treatment furnace was bent by a rod with a load cell.…”

“…We have previously formulated the critical shear stress of slip generation associated with scratches for a CZ wafer using the high-temperature three-point bending test method. 20 In that report, it was shown that the critical shear stress is dependent on temperature, oxygen concentration, and strain rate.…”

“…The cleaved specimens were pre-annealed at 1373 and 1423 K for 30 min, 2 h and 5 h, after which indents were introduced with a 10,20 Specimen width b is 14 mm and the distance between support pins L is 30 mm. Indents introduced by Vickers hardness tester on the specimen surface are placed at 0.5 mm pitch.…”