The deformation of silicon at high temperatures and strain rates

Abstract

Polycrystalline and 〈100〉 single crystalline semiconductor grade silicon samples have been subjected to uniaxial compression at strain rates from 10−5 to 12 s−1 at temperatures ranging from 1100 to 1380 °C. Both intrinsic and p-type polycrystalline material and p-type single crystalline material were tested. Except at the highest temperature and lowest strain rate, no steady state deformation was observed for the polycrystalline material. In all other cases strain hardening was observed which increased with increasing strain rates. The polycrystalline material could be compressed by as much as 50 pct at 1380 °C and a strain rate of 7 s−1 without cracking. An axial stress of approximately 170 MPa produces a strain rate of 5 s−1 at 1380 °C. The stress necessary to produce a given strain rate increases rapidly with decreasing temperature while the ductility rapidly decreases. A preliminary forming limit diagram has also been determined for the polycrystalline material at 1380 °C. The deformation rate-controlling process in the polycrystalline material at high stresses could be the production of vacancies on jogged dislocations.