薄矽晶片在長波長紅外光的平均放射率之測量

Measurement of the average emissivity of thin silicon wafers in long wavelength Infrared

張宏瑋(Hung-Wei Chang)

指導教授 ： 林登松

國立清華大學/理學院/物理學系/碩士(2015年)

摘要

以紅外線熱像儀量測溫度時，實用上放射率(ε)是唯一可調整的參數，ε是一般光學特性吸收率(α’)、穿透率(Tr*)、反射率(R*) 之函數。從Kirchhoff’s law of Radiation中可以知道在熱平衡時ε等於α’，而α’、Tr*、R*之和為1，對於矽晶片樣品而言，R*、α’在長波長紅外光基本上與和樣品厚度(d)無關，而Tr*則和樣品厚度相關，在以往的文獻中，只關注在參雜濃度對於放射率的影響，而近年來發現的超薄材料如石墨烯以及矽烯，可以用來製作超快電晶體，而在電晶體製作上經常使用到熱製程，如果能夠了解厚度與放射率間的關係，在量測超薄樣品時會有很大的幫助。
傳統量測放射率的方法，是將樣品與近似黑體放入定溫爐內，同時比較兩者的光強度藉此得到放射率，但是在量測薄樣品時會有背景輻射影響的疑慮，因此我們提出一個新的研究方法量測放射率，利用光電子能譜學(XPS)探測氣體是否從矽晶片表面上脫附，並且結合熱電偶(Thermocouple)以及紅外線熱像儀(IR camera)來研究長波長紅外光波段(8-13μm)中，超薄矽晶片的平均放射率，而此方法可以去除背景熱輻射的影響。
藉由實驗以及理論計算結果，可以將放射率與厚度的關係整理成線性區、過渡區、常數區，分別有不同的適用條件。實驗結果顯示在矽晶片溫度為732 K時，厚度20μm的矽晶片平均放射率為0.08±0.02，而厚度550μm的矽晶片平均放射率為0.68±0.02，但是當矽晶片的溫度為1067 K時，厚度20μm的矽晶片平均放射率為0.61±0.01，而厚度550μm的矽晶片平均放射率為0.68±0.01。

關鍵字

矽晶片 ； 放射率 ； 紅外線熱像儀

並列摘要

The long wavelength infrared (LWIR) refers to the wave length ranging from 8-13 m. This wavelength range is often used in thermopile-based infrared pyrometers, which are commonly used to non-contact temperature measurement of Si wafers. Emissivity is, in practical, the only adjustable parameter for infrared pyrometers. From Kirchhoff’s law of radiation, at thermal equilibrium, emissivity is equal to absorptivity; the sum of absorptivity, reflectivity and transmissivity is one. The reflectivity of silicon in LWIR is independent of wafer thickness (d), while transmissivity does depend on d and absorption coefficient. In the literature, much has been studied on the effect of doping concentration to emissivity. Less has been known about the relation between thickness and emissivity. Recently, ultrathin material like silicene and graphene have been discovered and triggered many possible applications. The measurement and control of temperature of these ultrathin materials are important for their processing in device fabrication. If the emissivity of thin films can be precisely determined, then we can measure the temperature of silicene and graphene by pyrometers.
The traditional method to calibrate emissivity is to put a sample and a nearly-perfect blackbody in a temperature-controlled furnace for comparative measurement of their radiance. However, the thermal radiation from the background furnace cannot be fully eliminated for thin samples in this method. In this study, we have proposed a new approach to obtain the average emissivity of ultrathin silicon wafer in LWIR by employing a combination of techniques XPS, thermocouples and pyrometers. In our method, the effect of background thermal radiation can be ignored.
The experiment results show that the emissivity of silicon wafers decreases with their thickness, in agreement with theoretical predictions. At 732 K, the average emissivity is 0.08±0.02 for Si wafers of 20 μm in thickness; 0.68±0.02 for 550 μm. However, at temperatures higher than ~1067 K, the emissivity changes little for wafers with thickness >~20 um. The measured average emissivity for 20-μm-thick wafers is 0.61±0.01 and 0.68±0.01 for 550 μm.

並列關鍵字

Silicon wafer ； Emissivity ； Thermal camera

參考文獻

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