DEPTH PROFILES FOR HYDROGEN-ENHANCED THERMAL DONOR FORMATION IN SILICON - SPREADING RESISTANCE PROBE MEASUREMENTS

Hydrogen enhancement of formation rates for oxygen-related thermal don ors in Si has been investigated for dependence on the source of hydrog en, hydrogen isotope, and exposure time and temperature. Hydrogen inje ction efficiency is an important variable and depth profiles are depen dent upon the surface preparation of samples exposed in an electron cy clotron resonance plasma where ion energies are less than or equal to 35 eV. Formation rates up to 2 x 10(16) cm(-1)/h at 400 degrees C have been observed. A sublinear dependence of the donor formation rate on beam current under 50 keV ion implantation is interpreted as a competi tion between oxygen-hydrogen and hydrogen-hydrogen interactions. Depen dence on isotope mass and on exposure time in the plasma indicates hyd rogen is the diffusing species that determines the penetration depth f or the enhanced donor formation. Peculiar box-like depth profiles and high formation rates near the advancing front produced in RF plasma ex posures are suggestive of hydrogen accumulation near the advancing fro nt. The temperature dependence for the penetration depth gives an acti vation energy of 1.5 +/- 0.2 eV. This energy is attributed to trap-lim ited diffusion wherein hydrogen lowers the energy barrier for the oxyg en motion necessary to form thermal donors.