REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION INTENSITY OSCILLATIONS DURING MOLECULAR-BEAM EPITAXY ON ROTATING SUBSTRATES

We report the gated detection of reflection high-energy electron diffr action (RHEED) signal intensity oscillations during molecular-beam epi taxy (MBE) while the wafer is being rotated at high speed (>100 rpm). In general, a larger number of oscillation periods are observed with t his technique than during stationary measurement because of the very h igh growth rate uniformity across the sample. We found that the averag e over all azimuths of the RHEED specular spot intensity shows the sam e growth induced oscillations. This allowed us to replace the gated de tection by an averaging detection method: a low-pass filter suppresses fast variations due to rapid changes in azimuth, while passing low-fr equency (<1 Hz) growth related oscillations. This simplifies the detec tion system and at the same time reduces noise related to wafer motion , 60 Hz, etc. These techniques have potential use for in situ monitori ng of thickness and composition of device wafers.