OXYGEN ISOTOPIC EXCHANGE DURING THE ANNEALING OF LOW-ENERGY SIMOX LAYERS

To follow the mass transport during annealing of SIMOX structure four <100> single crystal silicon wafers were implanted at 680-degrees-C wi th 90 keV or 70 keV O-18+ in order to understand and quantify the effe cts of the SiO2 capping layer on the growing buried SiO2 layer. After implantation pieces of the implanted wafers were capped with approxima tely 500-1000 nm natural SiO2 cap by plasma sputtering, and then annea led at 1360-degrees-C for 6 h in a quart silica tube in flowing nitrog en. For the 90 keV wafers (1) 3.5, (2) 4.0, and (3) 4.3 x 10(17 O-18+/ cm2 the anneal results in continuous oxide layers with some silicon is lands and pin holes, and a constant number (approximately 1.8 X 10(17) /cm2) of implanted O-18 has exchanged with O-16 atoms in the cap. The O-18 distributions within the cap for the three annealed samples are v ery similar. The lowest dose (1 X 10(17) O-18+/cm2, 70 keV) used for w afer 4 is only about one third of the critical dose (PHI(c)A) required to form a continuous oxide layer after implantation and annealing. Af ter the anneal, unlike what was found at the higher doses, it is found that all of the implanted O-18 has moved to the cap, with no buried o xide precipitate layer being observed. It is proposed that the diffusi onal exchange of O-16 and O-18 is thought to be via thermal vacancies. The self-diffusion coefficient of O-18 in the SiO2 cap has been estim ated to be between 3.5 X 10(-15) and 3.4 X 10(-14) cm2/s, at 1360-degr ees-C.