Optical feedback control of epitaxial growth

Increasing complexity, more stringent tolerances on layer compositions and thicknesses, the trend toward chemical deposition methods, and the need to maintain satisfactory yields despite increasing economic pressures are creating genuine needs for obtaining real-time information about epitaxial growth. While the ultimate goal is closed-loop feedback control, even the more modest objective of monitoring can already provide substantial benefits by allowing conditions to be modified on-line to meet composition and thickness specifications, and by providing records by which causes of downstream failures of complex devices can be identified and eliminated. Optical probes are attractive because they are noninvasive and can be used in any transparent ambient, including the high pressure ambients used for organometallic chemical vapor deposition (OMCVD). Traditional difficulties regarding surface sensitivity have been overcome by the invention of new and improvements of existing techniques, and sample-driven closed-loop feedback control of epitaxial growth has now been achieved