Fabrication of Silicon Window for Low-price Thermal Imaging System Sung, Byung Mok; Jung, Dong Geon; Bang, Soon Jae; Baek, Sun Min; Kong, Seong Ho;
An infrared (IR) bolometer measures the change of resistance by absorbing incident IR radiation and generates a signal as a function of the radiation intensity. Since a bolometer requires temperature stabilization and light filtering except for the infrared rays, it is essential for the device to be packaged meeting conditions that above mentioned. Minimization of heat loss is needed in order to stabilize temperature of bolometer. Heat loss by conduction or convection requires a medium, so the heat loss will be minimized if the medium is a vacuum. Therefore, vacuum packaging for bolometer is necessary. Another important element in bolometer packaging is germanium (Ge) window, which transmits IR radiation to heat the bolometer. To ensure a complete transmittance of IR light, anti-reflection (AR) coatings are deposited on both sides of the window. Although the transmittance of Ge window is high for IR rays, it is difficult to use frequently in low-price IR bolometer because of its high price. In this paper, we fabricated IR window by utilizing silicon (Si) substrate instead of Ge in order to reduce the cost of bolometer packaging. To enhance the IR transmittance through Si substrate, it is textured using Reactive Ion Etching (RIE). The texturing process of Si substrate is performed along with the change of experimental conditions such as gas ratio, pressure, etching time and RF power.
K. N. Chair, Y. B. Gianchandani, Katsuo Kurabayashi, and K. D. Wise, "Vacuum and Hermetic Packaging of MEMS Using Solder", Warren Cornelius Welch III, 2008.
J. H. Lau, C. K. Lee, C. S. Premachandran, and Yu Aibin, "Advanced MEMS Packaging", Electronic Engineering, McGraw-Hill, New York, 2010.
X. He, G. Karunasiri, T. Mei, W. J. Zeng, P. Neuzil, and U. Sridhar, "Performance of Microbolometer Focal Plane Arrays Under Varying Pressure", IEEE Electron Device Lett, vol. 21, no. 5, 2000.
T. Glaser, A. Ihring, W. Morgenroth, N. Seifert, S. Schroter, and V. Baier, "High Temperature Resistant Antireflective Moth-eye Structures for Infrared Radiation Sensors", Microsyst. Technol, Vol. 11 No. 2-3, pp. 86-90, 2005.
A. Ghosh, P. Kant, P. K. Bandyopadhyay, P. Chandra, and O. P. Nijhawan, "Antireflection Coating on Germanium for Dual Channel (3-5 and 7.5-10.6 um) Thermal Imagers", Infrared Phys. Technol, Vol. 40, pp. 49-53, 1999.
A. Ghosh and A. S. Upadhyaya, "Broad Band Anti-reflection Coating on Zinc Sulphide Simultaneously Effective in SWIR,MWIR and LWIR Regions", Infrared Phys. Technol, Vol. 52, pp. 109-112, 2009.
C. Q. Hu, W. T. Zheng, J. J. Li, Q. Jiang, H. W. Tian, et al, "Ge1-xCx double-layer anti-reflection and protection coatings", Appl. Surf. Sci, Vol. 252, No. 23, pp. 8135-8138, 2006.
H. F. W. Dekkers, F. Duerinckx, J. Szlufcik, et al, "Silicon Surface Texturing by Reactive Ion Etching", OPTO-Electron. Rev, Vol. 8, No. 4, pp. 311-316, 2000.
H. Zou, "Anisotropic Si Deep Beam Etching with Profile Control using SF6/O2 Plasma", Microsyst. Technol, vol. 10, no.8, pp. 603-607, 2004.
Rob Legtenberg, Henri Jansen, Meint de Boer, and Miko Elwenspoek, "Anisotrapic Reactive Ion Etching of Silicon Using SF6/O2/CHF3 Gas Mixtures", J. Electrochem. Sac, Vol. 142, No. 6, pp. 2020-2028, 1995.
A. Burtsev, Y. X. Li, H. W. Zeijl, and C. I. M. Beenakker, "An Anisotropic U-shaped SF6-based Plasma Silicon Trench Etching Investigation", Microelectron. Eng, vol. 40, pp. 85-97, 1998.
Henri Janseny, Han Gardeniers, Meint de Boer, Miko Elwenspoek, and Jan Fluitman, "A Survey on the Reactive Ion Etching of Silicon in Micro Technology", J. Micromech. Microeng, Vol. 6, No. 1, pp. 14-28, 1996.