The use of spectroscopic ellipsometry and spectral reflectance to measure surface properties of a semiconductor wafer is well-known. Both of these methods involve the detection of light reflected from the surface of the wafer to determine the spectral characteristics of the light, such as intensity and polarization at various wavelengths. These measurements are usually taken in real-time during the performance of a process affecting surface properties, such as epitaxial growth. The spectral characteristics of the reflected light are compared to the spectral characteristics of known materials to determine the surface properties of the wafer such as composition, surface roughness and epilayer thickness.
In the mass production of integrated circuit chips, it is often desirable to produce a plurality of identical wafers. One step in the efficient production of such wafers involves simultaneous epitaxial growth on a plurality of wafers in a single reactor chamber. To accomplish this, the wafers are typically mounted around the perimeter of a flat wafer holder, which rotates the wafers around a vertical rotation axis during epitaxial growth to ensure an even distribution of the source material.
Although spectroscopic ellipsometry and spectral reflectance are well-suited for the measurement of surface properties for a single, stationary wafer, known spectroscopic measurement systems are not suitable for use with multiple-wafer epitaxial growth chambers, due to the constant motion of the wafers into and out of alignment with the measurement apparatus.