Slow Growth of Oxide
Thermal Oxide or SiO2 is one of the “building block” films used in making both simple and complex semiconductor devices. If grown correctly using a high purity, low defect silicon substrate, it can be an excellent dielectric (insulating) thin film. It is normally found on a device as “field oxide” electrically isolating polysilicon, metal, or other conductive thin film(s) from the silicon substrate or “bulk” of the device. It is also found on the device as a “gate oxide”.
Silicon wafers are oxidized in furnaces ranging from 800°C to 1050°C. The furnaces consist of a quartz tube in which the wafers are placed on a carrier made of quartz glass. The quartz glass has a very high melting point (above 1500°C) providing a stable carrier for high temperature processes. To prevent cracks and/or warping, the quartz tube is heated slowly (e.g. +10°C per minute). Individual heating zones provide optimal tempering throughout the tube.
Dry Oxidation Characteristics:
Si + O2 → SiO2
Wet Oxidation Characteristics:
Si + 2H2O → SiO2 + 2H2
NanoSILICON, Inc. provides wet and dry thermal oxide processing capabilities starting from 500Å. Both processes use ultra-high purity sources of steam and/or oxygen. The purified steam and oxygen produces batch thickness uniformity of ±5% and typical within wafer uniformity of ±3%.
Thickness uniformity is verified by our Nanometrics 210. This tool uses a technique called white light reflection in which data is taken with normal incidence reflection of white light (480nm – 850nm) from the surface and spectral data is captured through a spectrometer attached to the camera port of the microscope. The data is modeled and the optical parameters are adjusted to give a best least-squared fit to the data. Refractive index can be manually entered or used as a parameter in the fitting routine. Thicknesses of films is measured in spots down to approximately 10µm, allowing for measurement of thin films at various points in the processing.
Thermal Oxide Specifications
| Dry Thermal Oxide | |
|---|---|
| Thickness | 500Å – 2,000Å |
| Thickness Variation | Target Thickness ±5% |
| Process Temperature | 800°C – 1050°C |
| Gases | O2 |
| Furnace Type | Horizontal Furnace |
| Wet Thermal Oxide | |
|---|---|
| Thickness | 2,000Å – 100,000Å |
| Thickness Variation | Target Thickness ±5% |
| Process Temperature | 800°C – 1050°C |
| Gases | Steam |
| Furnace Type | Horizontal Furnace |