(Invited) Millisecond Annealing by Atmospheric Pressure Thermal Plasma Jet and Direct Imaging of Temperature Distribution Using Optical Interference Contactless Thermometry (OICT)

Abstract

A non-contact temperature measurement technique on the basis of optical interference has been developed [1,2]. In Optical Interference Contactless Thermometry (OICT), the transient reflectivity of a substrate during rapid annealing is measured and reproduced by thermal simulation and optical analysis, whereupon the temperature profile is obtained from the simulation results. This method allows us to obtain a temperature distribution inside the wafer because it has depth resolution, unlike other interferometric methods. The time resolution of OICT is dependent on the photodetector, therefore, a millisecond detection of temperature variation is possible. By introducing a proper probe laser, this method can be applied to various substrates such as silicon, silicon carbide, glass, and so on [3-5]. OICT is useful to monitor transient temperature variation during rapid thermal processing. This helps us to correlate the annealing history to the characteristics of annealed samples. For instance, we have demonstrated the direct measurement of crystallization temperature of amorphous silicon, the role of heating and cooling speed on the yield of impurity activation in shallow junction, and the densification of gate SiO2 films and its effect on reliability of transistors under operation [6-9]. In this study, OICT has been extended to temperature field imaging. The principle is the same, and a high-speed camera replaced the photodetector to capture the 2-dimensional interference contour images. The images are analyzed to transfer them to temperature distributions. In the experiment, semiconductor wafers were annealed by atmospheric-pressure thermal plasma jet (TPJ) and the optical measurement was performed from the backside of the wafers. Probe lasers with the wavelengths of 1310nm for silicon wafers, and 633nm for silicon carbide wafers, were used. The laser lights went through a beam expander and irradiated the samples via a beam splitter and the reflected lights were introduce to high-speed cameras. Clear contour movies were obtained, where the contour lines correspond to isothermal lines. This temperature imaging method enables fast analysis of temperature, which can be used for the feedback to the annealing conditions as the real-time monitoring technique.[1] T. Okada, Jpn. J. Appl. Phys., 45 (2006) 4355.[2] T. Okada, Thin Solid Films, 515 (2007) 4897.[3] H. Furukawa, ECS Trans., 13 (1) (2008) 31.[4] K. Maruyama, Jpn. J. Appl. Phys., 54 (2015) 06GC01-1.[5] A. Kameda, J. Appl. Phys., 127 (2020) 203302-1.[6] Y. Mizukawa, Appl. Phys. Express, 13 (2020) 015507-1.[7] K. Matsumoto, Jpn. J. Appl. Phys., 49 (2010) 04DA02-1.[8] K. Matsumoto, Jpn. J. Appl. Phys., 50 (2011) 04DA07-1.[9] S. Higashi, Jpn. J. Appl. Phys., 50 (2011) 03CB10-1.