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A9.6.1

Effect of the hydrogen content in the optical properties and etching of silicon nitride films deposited by PECVD for uncooled microbolometers R. Ambrosio, A. Torres, A. Kosarev, M. Landa and A. Heredia. Instituto Nacional de Astrofísica, Óptica y Electrónica, INAOE, Apdo. P. 51 and 216, P.O. Box. 72000 , Puebla, Mexico. ABSTRACT We have studied silicon nitride films a-SiN:H deposited at a substrate temperature of 350°C by means of the Low frequency (LF) PECVD from silane and nitrogen as stock gases. Film properties as hydrogen bonding and content, nitrogen content, refractive index and etch rate are reported and analyzed. Our deposited films show physical properties similar to those that are obtained deposition temperatures of 700ºC by the low pressure chemical vapor deposition (LPCVD) technique. An investigation of bonding structures for the deposited films was performed, and quantitative results for hydrogen bonding based on Fourier Transform Infrared (FTIR) analysis are presented. It was observed that low hydrogen content in the films is in good correlation with low etch rate in 10% buffered HF solution, therefore these films present a material with good etch selectivity in respect to others materials (as phosphosilicate glass PSG, Al etc). Selectivity which makes these films very promising in surface micromachining for fabrication of sensors and device structures, e.g. microbolometers. Additionally, the Si-N bond at 830-840cm-1 was analyzed because of its big absorption produced at 12µm; therefore these films can be used as absorber layers in uncooled microbolometres. INTRODUCTION Silicon nitride films are widely used in microelectronics as passivation layers and insulators in integrated circuits manufacturing. On the other hand, silicon nitride has gained interest in the field of MEMS technology, because of its mechanical properties, which are suitable for the fabrication of micromechanical sensors and actuators [1]. Additionally, in recent years this material has been studied as potential material for integrated optics due to its low absorption losses in both visible and near infrared range [2]. These films can be deposited either by plasma enhanced chemical vapor deposition (PECVD) or LPCVD. Silicon nitride deposited by LPCVD at temperatures above 700ºC result stoichiometric (Si3N4) and has high resistivity, low porosity and low etch rate [3]. Silicon nitride films obtained by PECVD have been used as gate dielectric with the advantage of low deposition temperature in thin films transistors. Standard LPCVD silicon nitride has a hydrogen concentration below 5 at.% [3], whereas in PECVD deposited silicon nitride H2 concentrations up to 25 at. % have been achieved, where silane and ammonia or ammonia/nitrogen mixtures have been used as source gases [3]. The PECVD deposited films from ammonia and nitrogen generally result nitrogen rich and contain a large amount of hydrogen, 20-35 at. %, with a large fraction bound in N-H groups. Low hydrogen content films have been deposited using fluorinated ammonia [4],