Thick Thermal Oxides
For optical wave guide applications thick (>10 µm) silicon dioxide films of excellent thickness and index of refraction uniformity are required. Tystar Corporation has been offering process technology for these applications for several years. In semiconductor applications the most frequently used technology is based on a pyrogenic process, using the combustion of H2 and O2 in either an external heater or an internal furnace torch to generate the steam for the thermal oxidation process. Typical oxidation temperatures are in excess of 1,100 °C and oxidation times from several days to weeks to achieve the desired oxide thickness. Tystar's preferred approach is using a continuous D.I. water feed system in combination with a liquid flow controller and a flash vaporizer. The liquid flow controller has a flow range of up to 10 cm3 per minute. With a 4 cm3 per minute H2O flow, the system generates about 5-slpm steam.
The following wafer parameters for thick oxides (approximately 15 μm) grown in a TYTAN 2000 furnace system for up to 8"/200 mm wafers have been obtained:
- Thickness Uniformity: < 1%, 2σ, within wafer, Wafer-to-Wafer, Run-to-Run
- Refractive Index Uniformity: Better than 1 × 10-4, 2σ
- Particle Density: 2 > 0.25 mm for a 5 hour process.