Laser reflectometry for in-situ monitoring of the epitaxial growth of thin films

摘要

Abstract: Laser reflectometry is a simple technique, which is readily applied to real-time monitoring epitaxial growth of thin semiconductor films. It can be applied with a probe laser of low power to monitor normal and assisted semiconductor growth or with high power lasers to 'self monitor' laser assisted growth, for example during selective area epitaxy. In normal growth, laser reflectometry is most suitable for monitoring films having a thickness $GREQ $lambda@/4 where $lambda is the monitoring wavelength, although, having monolayer sensitivity, it can be used to monitor much thinner film growth. Examples of a Bragg reflector grown with the aid of laser reflectometry and a 6 nm AlGaAs/GaAs superlattice are given. Both growth rate and chemical composition of alloy semiconductors can be obtained in real-time for films of the above thickness and this is illustrated by reference to the AlGaAs system. Its high sensitivity to chemical composition has enabled the chemical beam epitaxial growth of carbon doped GaAs films to be monitored: results of a recent study of such films are presented and discussed. By aligning a low power probe laser along an excimer laser beam the assisted growth can be monitored. In addition to giving instantaneous information on the growth rate, the monitoring also provides a check on the developing surface morphology. In selective area epitaxy, via Ar$+$PLU$/ laser assistance, the reflected signal contains growth information relating exactly to the laser footprint. Results of 'self-monitoring' Ar$+$PLU$/ assisted CBE grown GaAs are discussed in terms of the mechanisms involved in the laser assistance.!24