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 said 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, the light source and detector being arranged in suitable locations with regard to the substrate such that light impinging on the substrate from the source is substantially reflected directly towards the detector,

• said substrate being periodically rotated about an axis substantially normal to the growing plane within said reaction chamber to ensure uniform deposition of said substance thereon,
• said reaction chamber being provided with operable shutter means disposed between an opening in said reaction chamber and said light source to permit light through said shutter and opening when said shutter is open but preventing such when closed,
• characterized in that the 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.