Abstract: The present invention provides for an apparatus for measuring a curvature of a surface of a wafer in a multi-wafer epitaxial reactor.

Abstract: A flat light emitting plate, a method for calibrating a pyrometer and a method for determining the temperature of a semiconducting wafer inside a processing chamber by said pyrometer. The invention provides a method for calibrating a pyrometer by means of a cold source which is also applicable to processing chambers with a narrow slit. According to the invention, a flat light emitting plate for simulating thermal radiation is provided, comprising a main body made of a transparent material, a light emission area located on an upper surface of the light emitting plate for emitting light, at least one light source located on a lateral surface of the light emitting plate, at least one detector located on a lateral surface of the light emitting plate, and a regulating circuit for adjusting the intensity of light emitted by the light sources.