Temperature Dependent Emissivity of Multilayers on Silicon
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INTRODUCTION On the verge of the twenty first century, the demand for larger wafers and scaling of device dimensions seem to be more stringent than ever. Along with that, process uniformity and repeatability are critical issues. It appears that cluster-based single-wafer tools will be the manufacturing approach taken by the silicon industry. Some examples of these processes will be Rapid Thermal Processing (RTP) and Chemical Vapor Deposition (CVD). Inthese semiconductor processes and especially in RTP, knowledge of radiative properties, optical properties and the temperature control to ±10C are of great importance. In an RTP chamber, the wafer is not in thermal equilibrium with its surroundings. Therefore, traditional temperature measurement techniques such as thermocouples cannot be applied, unless the thermocouple is embedded inside the wafer. From this point of view, pyrometry has established itself as the instrument of choice for in-situ temperature measurements. While the conventional pyrometers enjoy the benefits of non-contact, realtime, and fast thermal response, they however, are seriously limited by their operating wavelengths and spatial resolution due to the limited number of sensors, and more so by their extreme sensitivity to any change of the wafer emissivity which may occur during the process.
69 Mat. Res. Soc. Symp. Proc. Vol. 470 ©1997 Materials Research Society
In this paper, a detailed study ofemissivity of various silicon related materials are presented. A mathematical model, proposed by Flory [11, has been utilized extensively to Investigate the acquired high temperature emlssivity data. EXPERIMENTAL DETAILS The schematic of the spectral emissometer Is presented In Fig.1 [2]. It consists of a heml-ellipsoldal mirror providing two foci, one for the exciting source Inthe form of a diffuse radiating near-blackbody source and the other for the sample under Investigation. A microprocessor controlled motorized chopper facilitates In simultaneous measurement of sample spectral properties such as radiance, reflectance and transmittance. A carefully adjusted set of five mirrors provide the optical path for measurement of the optical properties. The source of heating of the samples Is provided by oxy-acetylene/propane torch. However, because of safety considerations and potential sample contamination, various alternatives to heat the samples, uniformly In a controlled environment, are being Investigated. The spectral emissometer consists of three GaAs lasers to facilitate In aligning the sample at the appropriate focus. A high resolution Bomem FTIR, consisting of Ge and HgCdTe detectors, Interfaced with a Pentium processor, permits data acquisition of the measured optical properties. Further, this On-Une computer enables the user to flip the mirrors to acquire transmission/reflection spectra via software tools such as Spectra Calc and GRAMS. The system, acquired by NJIT from On-Une Technologies through a research grant from the Defense Advanced Research Projects Agency (DARPA), Is the third of its ki
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