Photo-Induced Growth of Low Dielectric Constant Porous Silica Film at Room Temperature
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a) E-mail [email protected], Tel: +44 (0) 20 7419 3196, Fax: +44 (0) 20 7388 9325 Photo-induced growth of low dielectric constant porous silica film at room temperature Jun-Ying Zhanga) and Ian W. Boyd Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK ABSTRACT We report low temperature (25-200°C) photo-assisted sol-gel processing for the formation of porous silicon dioxide films on Si (100) substrates using 172 nm radiation from an excimer lamp. The effects of substrate temperature and irriadation time on the properties of the films formed have been studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), and electrical measurements. The FTIR spectra revealed the presence of a Si-O-Si stretching vibration peak at 1070 cm-1 after UV irradiation at 200°C. This is similar to that recorded for oxides grown by thermally oxidation of silicon at temperatures between 600-1000°C. Capacitance measurements indicated that the dielectric constant values of the films, found to be between 1.7-3.3, strongly depended on the substrate temperature during irradiation. Dielectric constant values as low as 1.7 were readily achievable at room temperature. These results show that the photochemical induced effects initiated by the UV radiation enable both reduced processing times and reduced processing temperatures to be used. PACS: 42.78.Hk, 61.80.Ba, 81.60.Cp, 85.50.Na Keywords: Photo-assisted sol-gel processing, excimer lamp, porous SiO2 film, low dielectric constant 1. Introduction As microelectronic device densities increase and chip dimensions shrink, propagation delay, crosstalk noise, and power dissipation become significant due to resistance-capacitance (RC) coupling. Integration of low-dielectric-constant (k) materials, as means of reducing these RC time delays, has been identified for 0.1 µm technology and beyond. Current low-k commercialization emphasizes spin-on glasses (SOGs) and fluorinated SiO2 with k>3, and a number of polymers are under development with k values in the range of 2-3 [1-3]. These suffer from potential problems including thermal stability, mechanical and electrical properties, low thermal conductivity, and reliability. However, low-k dielectric nanoporous silica with tuned k values from 1-4 have the advantage of facilitating manufacture of higher performance integrated-circuit (IC) devices because of compatibility with standard microelectronic processing and the ability to tune k over a wide range [4-6]. Low temperature deposition has been required for nanoporous SiO2, because thermal stress degrades device characteristics and reliability of interconnection. Low temperature growth techniques, such as plasma-enhanced chemical vapor deposition (PECVD) [7], atmospheric pressure CVD (APCVD) [8], and electron cyclotron resonance (ECR) CVD [9], have been investigated. However, these cannot reduce the deposition temperature sufficiently, because substrate temperatures above 300°C are required to initiate dehydration and dissociation
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