Drift of arsenic in SiO sub 2 in a lamp furnace with a built- in temperature gradient.

We have found that arsenic implanted into SiO sub 2 segregates at high temperatures in an oxygen-free ambient into spherical, As-rich inclusions of 50 to 500angstroms in diameter. The phase separation prevents diffusion of arsenic, even at temperatures as high as 1400C. However, the As-rich inclusions or droplets can be easily moved in a temperature gradient. They migrate towards the heat source at a rate of 2300angstroms/hour in a gradient of 0.14C /micron, at 1405C, permitting their efficient removal from the oxide and into silicon. We propose a model to explain the dependence of droplet velocity on their size.