Growth rate, thickness and morphology by multiple wavelength reflectance
For epitaxial growth, as with all other thin-film growth processes, it is essential to have real-time information about the actual growth rate and film thickness. Optical reflectance is usually the method of choice because it gives direct access to the growing layers and can be implemented through a single normal incidence viewport. However, the information gained by reflectance measurements is not limited to growth rate alone.
Different wavelengths for different layers
Reflectance makes it possible to monitor multiple essential properties of the growing layers. Usually, these three wavelengths are measured:
- 950 nm: correction of emissivity changes (True Temperature); growth rate and thickness analysis for high growth rate and IR transparent materials
- 633 nm - for GaN buffer layers: growth rate and thickness analysis of materials transparent at 633 nm
- 405 nm: comparison of quantum wells (MQW)- growth rate of thin layers, interface quality, roughness, growth rate of thin oxide layers, materials transparent at 405 nm.
- Other wavelengths are available on request.