Epi-film thickness measurements using emission Fourier transform infrared spectroscopy. I. Sensor characterization

This paper reports the measurement of epitaxial silicon film thickness using a Fourier transform infrared spectrometer. The implementation and characteristics of emission Fourier transform infrared spectroscopy (E/FT-IR) for film thickness measurement are described. The limitation and robustness of the E/FT-IR technique, and its comparison to conventional FT-IR are reported in detail. Issues such as E/FT-IR´s repeatability, reproducibility, the effect of vacuum window material and its coating, and the effect of wafer rotation, are evaluated. We find that good repeatability and reproducibility of the E/FT-IR technique can be achieved. The repeatability of the E/FT-IR technique in terms of standard deviation is 0.01 μm, in terms of coefficient of variation is about 0.1% for all wafer temperatures (550°C, 610°C, and 660°C). The window material, window stress, and its coatings do not affect the film thickness measurement as long as sufficient light intensity reaches the FT-IR detector. Additionally, when FT-IR thickness measurements are performed on a rotating wafer (with speeds up to 55 rpm), we find that only a small amount of noise is introduced, and a good measurement repeatability can still be maintained