REAL-TIME EXTRACTION OF GROWTH-RATES FROM ROTATING SUBSTRATES DURING MOLECULAR-BEAM EPITAXY

We present a method for measuring molecular-beam epitaxy growth rates in near real-time on rotating substrates. This is done by digitizing a video image of the reflection high-energy electron diffraction screen , automatically tracking and measuring the specular spot width, and us ing numerical techniques to filter the resulting signal. The digitizat ion and image and signal processing take approximately 0.4 a to accomp lish, so this technique offers the molecular-beam epitaxy grower the a bility to actively adjust growth times in order to deposit a desired l ayer thickness: The measurement has a demonstrated precision of approx imately 2%, which is sufficient to allow active control of epilayer th ickness by counting monolayers as they are deposited. When postgrowth techniques, such as frequency domain analysis, are also used, the refl ection high-energy electron diffraction measurement of layer thickness on rotating substrates improves to a precision of better than 1%. Sin ce all of the components in the system described are commercially avai lable, duplication is straightforward. (C) 1995 American Vacuum Societ y.