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

Abstract

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.

Temperature Measurement of Si Substrate Using Optical-Fiber-Type Low-Coherence Interferometry Employing Supercontinuum Light

“…On the other hand, the optical path length and the temperature in the case of SLD were 0.13 m and AE1:0 C, respectively. In our previous study, the accuracy of temperature measurement using SLD for the 780-m-thick Si substrate was estimated to be 0.11 K. 13) The vibrational noise was thoroughly suppressed in the etching chamber because the Si substrate was tightly held by the electrostatic chuck to the substrate holder and the collimation lens for incident SLD light was rigidly fixed to the chamber. In this study, however, the substrate and the collimation lens were not rigidly fixed because of their setting limitation in the furnace, so the measurement accuracy became less than that in the previous study.…”

“…We previously demonstrated the noncontact measurement of the temperature of a silicon (Si) substrate by lowcoherence interferometry (LCI) during silicon dioxide (SiO 2 ) plasma etching in a dual-frequency capacitively coupled Ar/C 4 F 8 /O 2 plasma. 13) The Si temperature is determined from the change in the optical path length between the interference waveforms of the front and back surfaces, since the optical path length is changed by thermal expansion and variation in the refractive index depending on the Si substrate temperature. LCI has many advantages such as temperature measurement of the substrate itself, real-time response, wide measurement range, widely applicable plasma conditions, and high measurement accuracy.…”

Noncontact measurement of substrate temperature by optical low-coherence interferometry in high-power pulsed magnetron sputtering

“…To solve this problem, we have developed a noncontact temperature measurement method based on optical low-coherence interferometry (LCI) and reported the accurate substrate temperature measurement in the plasma etching process. [16][17][18][19][20][21] It is necessary to evaluate the repeatability of the temperature measurement by replacing the plasma-treated substrate with new one. In addition, there are no reports on the application of LCI to the measurement of the substrate temperature in deposition processes.…”

Robust characteristics of semiconductor-substrate temperature measurement by autocorrelation-type frequency-domain low-coherence interferometry

“…In our previous studies, we developed a noncontact substrate temperature measurement technique using a timedomain low-coherence interferometry (TD-LCI) system. [18][19][20] The system resolved issues of size, working temperature range, and measurement accuracy for silicon wafers. The time resolution was, however, limited to the second time scale because the system uses a mechanically scanned mirror to obtain an interferogram for the substrate temperature.…”