Ken Aihara

Enhanced nucleation of oxide precipitates during Czochralski silicon crystal growth with nitrogen doping

Thermal stability of oxide precipitate nuclei has been investigated for Czochralski silicon crystals with nitrogen doping. The experimental result indicates that generation of the grown-in oxide precipitate nuclei stable over 800 °C is enhanced by nitrogen doping. On the other hand, even though we confirmed this existence, doped nitrogen shows no influence on further oxide precipitate nucleation during the isothermal annealing at 600 °C after an epitaxial silicon growth process. Thus, it is found that the nitrogen doping only enhances the oxide precipitate nucleation at higher temperature during crystal cooling. The enhanced precipitate nucleation during the cooling is considered to be through excess vacancies which are suppressed to agglomerate by nitrogen.

Creation of Bonded SOI Substrates with CZ Silicon Higher than 1000 Ωcm in Resistivity

1,. Introduction RF devices to create wireless communication systems require semiconductor material higher than 1.000 Qcm in resistivity in order to minimize energy loss due to eddy current in signal propagation. Since the concept of system LSIs has been widely spread, RF devices are designed as a part of LSI so that highly functional devices are proposed(l). Thus, ideal material for them is bonded SOI with base silicon (Si) wafers higher than 1000 Qcm in resistivity, as shown in Fig. L. Strong dernands of larger diarneter Si wafers have made us develop CZ wafers with such high resistivity instead of FZwaf.ers whose high resistivity is easily obtained. Usually CZ wafers are available in resistivity range lower than 100 Qcm. It is true when tight tolerance in resistivity is required. However, since wafers are used for base wafers in bonded SOI structure, the target to develop is just resistivity higher than 1000 Qcrn By controlling impurities effective to conductivity in source material such as poly-Si, CZ wafers with several thousand Qcm in resistivity were actually obtained. However, the other issue for high resistivity is oxygen donors. Oxygen donors are generated by the change of interstitial oxygen (Oi) in silicon when annealed at 450C(2). 450C annealing is common for aluminum sintering at the very end of device processes. The rate of resistivity drop by these donors depends on the arnount of Oi as well as annealing time at 450C. We have studied the effect of Oi donors on resistivity by using CZ wafers with several thousand Qcm in resistivity. This paper reports these results and will propose silicon wafers available for base wafers in bonded SOI.