Photoenhanced Deposition of Silicon Oxide Thin Films Using an Internal Nitrogen Discharge Lamp
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PHOTOENHANCED DEPOSITION OF SILICON OXIDE THIN FILMS USING NITROGEN DISCHARGE LAMP
AN INTERNAL
Paul A. Robertson and W.I. Milne Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 IPZ, ENGLAND
ABSTRACT This paper describes the optical and electrical properties of silicon oxide thin films produced using a novel photoenhanced deposition technique. Since there is no damage to the growing film surface from energetic ions, this process has the potential to produce better semiconductor/insulator interfaces than those grown using conventional RF glow discharge techniques. The deposition system is comprised of a windowless nitrogen discharge lamp contained within the reaction vessel. This unified approach allows the low wavelength UV light from the lamp to couple directly into the reaction gases without attenuation by a window material or the need for mercury sensitisation. Thin films of silicon oxide have been deposited onto single crystal silicon wafer substrates from a nitrous oxide/monosilane reaction gas mixture. The deposition rate and physical properties of films produced in this way are comparable to those of high quality insulator films deposited by plasma enhanced CVD techniques. The results of electrical tests indicate that this material could be used as a low temperature deposited insulator for thin film devices. INTRODUCTION There has recently been interest in the low temperature deposition of silicon oxide and silicon nitride insulator thin films [1,2]. In contrast to conventional RF glow discharge techniques, the photoenhanced deposition process does not have highly energetic species bombarding the growing film surface. The absence of these charged particles from the film growth region should enable the production of cleaner semiconductor/insulator interfaces. Several groups have deposited silicon oxide thin films from the photoenhanced reaction of oxygen with monosilane or disilane [3,4] using a deuterium or mercury discharge lamp as the ultra-violet light source. The UV radiation is transmitted through a fused silica window into the reaction vessel where it is absorbed by the oxygen molecules. The molecules dissociate into oxygen atoms which are required in the reaction chain leading to polymeric silicon oxide films. However, the use of oxygen gas results in high film porosity due to gas phase reactions between the molecular oxygen and silane. In addition to this problem, the UV radiation is attenuated by the presence of a window material between the lamp and reaction gases. Boyer et al. [5] have produced nearly stoichiometric silicon dioxide thin films using a nitrous oxide/monosilane reaction gas mixture, excited by UV radiation from an ArF laser. Although the film porosity is likely to be less in this case, there are much higher costs and maintenance requirements associated with running a laser than an incoherent light source. In this paper, we describe the optical and electrical properties of silicon oxide thin films produced in a novel deposition system using a reaction g
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