Tatsuo Matsudo

Observation of oscillating behavior in the reflectance difference spectra of oxidized Si(001) surfaces

Layer-by-layer oxidation of Si(001)-(2×1) surfaces was observed using the reflectance difference (RD) spectroscopy. Distinctive features in the RD spectra appeared near the E1 (3.3 eV) and E2 (4.2 eV) transition energies of Si. The polarity of these features was repeatedly reversed as the oxide thickness was increased to 4 monolayers (MLs). Oscillation of the RD amplitude near the E1 transition energy was observed in real time during the oxidation process. A half period of the oscillation corresponds to the oxidation of 1 ML. These results demonstrate the possibility of in situ counting and control of the number of oxidized layers.

Low-Coherence Interferometry-Based Non-Contact Temperature Monitoring of a Silicon Wafer and Chamber Parts during Plasma Etching

We performed real-time non-contact monitoring of temperatures of a silicon wafer and chamber parts in plasma etching processes using optical fiber-based low-coherence interferometry. The measurements were performed in dual-frequency capacitively coupled Ar/C4F8/O2 plasma processes. The temperature of a 780-µm-thick Si wafer was measured with a deviation of 0.11 K. Comparison between in-situ measurement results of an on-wafer temperature sensor and an optical-fiber type fluorescence temperature sensor confirmed that the low-coherence interferometry had superior performance in monitoring the temperature of the Si wafer in real-time. This method will enable better control of etching performance with improved process reproducibility.

Simultaneous In situ Measurement of Silicon Substrate Temperature and Silicon Dioxide Film Thickness during Plasma Etching of Silicon Dioxide Using Low-Coherence Interferometry

We have successfully performed real-time noncontact monitoring of substrate temperature and thin film thickness during plasma etching using optical-fiber-based low-coherence interferometry. The simultaneous measurement of the silicon (Si) substrate temperature and the etching depth of the silicon dioxide (SiO2) thin film on this substrate was performed in a dual-frequency capacitively coupled Ar/C4F8/O2 plasma. The SiO2 film thickness was deduced from the ratio of the interference intensity at the SiO2/Si interface to that at the Si/air interface. The measurement error in the SiO2 film thickness was less than 11 nm. The temperature variation of the Si wafer was derived from the temperature change of its optical path length. The temperature measurement error, caused by the shift in optical path length due to the change in SiO2 film thickness, was reduced from 7.5 to 0.6 °C by compensating for the shift using the SiO2 thickness data. This method enables precise control of etching performance and improves process reproducibility.