CH₄ concentration distribution in a semiconductor process chamber measured by the CT-TDLAS

We measured methane (CH4) concentration distribution in a semiconductor process chamber by using the computed tomography-tunable diode laser spectroscopy (CT-TDLAS). We designed the CT-TDLAS measurement system with a 32-laser-path. The CH₄ concentration distribution was measured by the CT-TDLAS based on the 32 absorption spectra which were collected by scanning the laser wavelength around the CH₄ absorption peak of 1653.7 nm. We checked linearity of the measurement, validity of the algorithm, and resolution of the computed tomography (CT) reconstructed distribution. In the algorithm check, we measured a simple concentration distribution generated in a five-fold concentric cylinder. Next, we designed a semiconductor process chamber in which the 32-laser-path was installed. After quantitative evaluations of the CT reconstructed distributions by comparing the simulated results of computational fluid dynamics, we actually measured the CH₄ concentration distribution in the chamber when we streamed 10% CH₄ from one of four inlet ports and nitrogen from other three ports into the chamber. The measured distributions were obviously different in accordance with the CH₄ inlet location, although all the inlet ports were located cyclic-symmetrically. Those results indicated that the flow impedances of the four exhaust holes on the susceptor were different depending their locations.