Southampton Nanofabrication Centre
Southampton Nanofabrication Centre

Growth of silicon dioxide is performed using thermal oxidation, either in a dry or a wet ambient. For the highest quality oxides, such as gate oxides, dry oxidation is preferred. Advantages are a slow oxidation rate, good control of the oxide thickness in thin oxides and high values of breakdown field. For thicker oxides, such as a field oxide in CMOS technology, wet oxidation is preferred. The main advantage is a fast oxidation rate, so that a thick oxide (around 0.5 micron) can be produced in a reasonable period of time (around an hour). The main disadvantage of oxidation is that a high temperature is required of typically 900C or above. For applications requiring a silicon dioxide layer produced at a lower temperature, plasma enhanced chemical vapour deposition can be used.

Tempress Oxidation Furnaces

For silicon and other clean processes, several oxidation furnaces are available, including a 200mm dry oxidation furnace, a 150mm dry oxidation furnace and a 150mm wet oxidation furnace. For other processes, a 150mm dry oxidation furnace is available. These furnaces allow automated loading of up to 25 wafers in a quartz boat and provide oxidations at temperatures between 600 and 1150C. Temperature accuracy can be controlled to better than ±1C.

Jipelec Jetfirst 200

Where very thin silicon dioxide layers are required, rapid thermal oxidation can be used. Rapid thermal oxidation is a technique that provides a short (typically 30 seconds) oxidation at a high temperature using fast lamp heaters. Two Jipelec Jetfirst 200 rapid thermal oxidation systems are available in the clean room, one for clean silicon processing and one for general use. Temperatures between 400 and 1200C can be reached and the oxidation time can be varied from 5 seconds to 10 minutes, with a ramp-up rate of 150C/s. Absolute temperature can be controlled to within ±5C. Temperature is generally measured using a pyrometer, but a thermocouple can also be used