Composition, oxidation, and optical properties of fluorinated silicon nitride film by inductively coupled plasma enhance
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Composition, oxidation, and optical properties of fluorinated silicon nitride film by inductively coupled plasma enhanced chemical vapor deposition Byung-Hyuk Jun, Joon Sung Lee, and Dae-Weon Kim Department of Materials Science & Engineering, Korea Advanced Institute of Science and Technology, Kusung-Dong, Yusung-Gu, Taejon, 305-701, Korea
Tae-Hyun Sung Center for Advanced Studies in Energy and Environment, Korea Electric Power Research Institute, Munji-Dong, Yusung-Gu, Taejon, 305-380, Korea
Byeong-Soo Bae and Kwangsoo No Department of Materials Science & Engineering, Korea Advanced Institute of Science and Technology, Kusung-Dong, Yusung-Gu, Taejon, 305-701, Korea (Received 30 March 1998; accepted 24 June 1998)
Amorphous fluorinated silicon nitride films have been deposited with the variation of NF3 flow rate using SiH4 , N2 , Ar, and NF3 gases by inductively coupled plasma enhanced chemical vapor deposition for the first time, and the absolute composition, oxidation mechanism, and optical properties were investigated. The absolute composition including hydrogen was performed by means of elastic recoil detection time of flight. It was found that the oxygen and fluorine contents in the film dramatically increased, but the hydrogen content decreased to below 4 at.% as the NF3 flow rate increased. The oxidation mechanism could be explained in terms of the incorporation of the activated residual oxygen species in the chamber into the film with unstable open structure by the fluorine-added plasma. It was shown that the density and optical properties such as refractive index, absorption coefficient, and optical energy gap depended on the film composition. The variations of the above properties for fluorinated silicon nitride film could be interpreted by the contents of fluorine and oxygen with high electronegativity.
I. INTRODUCTION
Many studies of the silicon nitride films in microelectronics have been made for applications such as a passivation layer, intermetal dielectric, and gate insulator for semiconductor technology. Although these films are called silicon nitride, they are not stoichiometric compound Si3 N4 but amorphous hydrogenated silicon nitride (a-SiNx : H) films. Conventionally, a-SiNx : H films are prepared at a relatively low temperature of 300 ±C by plasma enhanced chemical vapor deposition (PECVD) using SiH4yNH3 or SiH4yNH3yN2 gas mixtures. These films usually contain as much as 25–35% of hydrogen1 which is incorporated in the network structure in the form of Si–H and N–H bonds. The impurities can produce localized states in the band gap of the dielectrics which are electrically active as deep trapping or recombination centers. Therefore, these a-SiNx : H films exhibit inferior electrical properties as well as poor resistance to chemical attack. Many attempts have been made to optimize the hydrogen content and the local bonding configurations in a-SiNx : H films.2–5 Among the studies, one approach is to substitute the stronger Si–F bond (116 kcalymol)
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