A High Sensitivity and Compact Real Time Gas Concentration Sensor for Semiconductor and Electronic Device Manufacturing Process
Authors: Ishii Hidekazu , Nagase Masaaki , Ikeda Nobukazu , Shiba Yoshinobu , Shirai Yasuyuki , Kuroda Rihito , Sugawa Shigetoshi 
Published: February 2020

Various metal-organic(MO) gases are used in manufacturing processes of electronic device such as semiconductors, power devices, LEDs and displays. These MO gas are generally supplied with bubbling, and the in-line concentration sensor is used to control their concentration [1]. However, due to diversification of semiconductor processes, adaptation to various MO gas, high sensitivity and high speed sampling are required [2]. Various MO gases have the light absorption in the ultraviolet light wavelength region of 400 nm or less, and we developed a concentration sensor by measuring ultraviolet absorbance. Fig. 1 shows the developed concentration sensor unit. A small gas cell with a good sealing performance against reactive gases was prepared, and a detection circuit section was fabricated by adopting a charge amplifier method to obtain high sensitivity, instead of the commonly-used transimpedance amplifier method. So far, we demonstrated that highly sensitivity to commonly used MO gases such as Bis(cyclopentadienyl)magnesium[Cp2Mg] with the response speed of 400 msec or less could be realized using the developed sensor [3]. In this abstract, we report on the possibility of measuring the concentration of Zr and Hf MO gases that are commonly used in semiconductor High-k process.
The measurement was carried out by heating the gas cell with an optical path length of 50 mm at 50 ° C. In the measurement, the LED with a wavelength λ of 360 nm and the LED with λ of 255 nm were switched and irradiated alternatively. The output voltage difference of the two wavelength LEDs according to concentration was taken into the PC with 16bit output and data processing was performed. The sampling period was 400 msec. For Zr MO gas, Tetrakis(ethylmethylamino)zirconium[TEMAZ] and Tris(dimethylamino)cyclopentadienylzirconium[ZAC] were evaluated and for the Hf MO gas, and Tetrakis (ethylmethylamino)hafnium[TEMAH] was evaluated for the Hf MO gas. Fig.2 shows the evaluation results for TEMAZ. Fig. 2 (a) shows the output of the concentration sensor unit when 41.5ppm-TEMAZ and 100%-Ar are switched at intervals of about 5 min by the valve operation. Good repeatability for the output signals were obtained for each gases in each periods. Fig. 2 (b) shows a calibration curve for TEMAZ, where the output signal as a function of the TEMAZ concentration is shown. The calibration curve was superior in linearity. Also, because the charge amplifier method was adopted, we confirmed that very small minimum detection sensitivity of 95 ppb could be achieved by taking into account of 5 σ of circuit noise. Similarly, we found that the minimum detection sensitivities of ZAC and TEMAH were 141 ppb and 80 ppb, respectively. The results demonstrated that the developed concentration sensor is very useful for realizing the precise measurement of various MO gases in semiconductor manufacturing.
[1] T. W. Woods et al., ECS Transactions, 3 (7) 215-217, 2006.
[2] V. Miikkulainen et al., J. Appl. Phys. 113, 021301 (2013)
[3] H. Ishii et al., IEEE Sensors 2016 (IEEE), 877-879, 2016.

Figure 1