Apparatus for measuring semiconductor physical characteristics

Reflectometry apparatus for gathering meaningful reflectance data indicative of one or more characteristics of a substance being grown within a reaction chamber in real time during growth, said apparatus including a light source disposed to the outside of the reaction chamber which includes a substantially horizontal substrate on which the substance growth occurs, and a detector being capable of converting light into electrical signals which are subsequently subjected to computer processing, said light source and detector being arranged in suitable locations with regard to the substrate such that light entering an opening in the reaction chamber and impinging on the substrate from said source is substantially reflected back through the opening and directly towards said detector,

• the substrate being periodically rotated about an axis substantially normal to the growing plane within the reaction chamber to ensure uniform deposition of the substance thereon,
• said apparatus being provided with a shutter arranged to permit light through said shutter when said shutter is open but preventing such when closed,
• characterized in that said shutter is caused to open in synchronicity with the speed of revolution of the substrate such that substantially the same discrete area of the substance growing on the substrate is illuminated so as to eliminate the effects of precession on the measurements.