Rapid thermal oxidation is a technique that provides a short (typically 30 seconds) anneal at a high temperature using fast lamp heaters. The Nanofabrication facility houses two Jipelec Jetfirst200 rapid thermal annealers, one for clean silicon processing and one for general use.
Temperatures between 400°C - 1200°C can be reached and there is the capability to vary the anneal time from 5 seconds to 10 minutes, with a ramp-up rate of 150°C/s. Absolute temperature can be controlled to within +/-5°C. Temperature is generally measured using a pyrometer, but a thermocouple can also be used. Some typical high temperature applications are dopant activation after implantation or crystal healing.
For silicon and other clean processes, several anneal furnaces are available, including a 200 mm anneal furnace and a 150 mm anneal furnace. For general processes, a 150 mm anneal furnace is available.
These furnaces allow automated loading of up to 25 wafers in a quartz boat and provide oxidations at temperatures between 600°C and 1000°C. Temperature accuracy can be controlled to within +/-1°C or less.
For alloying of metal contacts, a low temperature anneal furnace is available which uses forming gas (a mixture of hydrogen and nitrogen). An alloy anneal is typically performed at 420°C for about 15 minutes and has the dual functions of providing a low resistance ohmic contact and of hydrogen passivation of the interface between silicon dioxide and silicon.
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.