Segregation and drift of arsenic in SiO₂ under the influence of a temperature gradient

We have found that arsenic implanted into SiO₂ segregates at high temperatures into As-rich spherical inclusions of 50-500 Å in diameter, provided that there is no free oxygen in the SiO₂ and the initial As concentration exceeds 1 at. %. The phase separation suppresses the diffusion of arsenic, even at temperatures as high as 1400°C. We have discovered, however, that the As-rich inclusions can be easily moved in a temperature gradient. They migrate towards the heat source at a rate of 2300 Å/h in a gradient of 0.14°C/μm, at 1405°C, permitting their efficient removal from the oxide and into silicon.