Influence of Surface Organic Contamination on the Incubation Time in Low-Pressure Chemical Vapor Deposition of Silicon N
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ABSTRACT Trace organic contaminants adsorbing on silicon surfaces during transportation of wafers to a reaction chamber in an air ambient cause incubation before film growth starts in low-pressure chemical vapor deposition (LPCVD) of silicon nitride film on silicon substrates. The incubation time for wafers either exposed to cleanroom air for a long period without being stored in a box or stored in an outgassing plastic box prior to LPCVD is longer than that for wafers transported to the CVD reactor immediately after the previous step. It has been found that the longer incubation time is attributed to not only extraneous oxide grown on the silicon surface but also organic contaminants adsorbed on the surface. INTRODUCTION Not only particulate and metallic contaminants but also trace organic contaminants adsorbing on the surface of silicon wafers have been found to have an increasingly detrimental impact on the performance and yield of semiconductor products. When silicon wafers are exposed, after wet cleaning and drying, to the atmosphere in a conventional cleanroom, gaseous organic molecules in the air easily adsorb onto the wafer surfaces in a short period[l]. In fact, polymeric materials are found almost everywhere in cleanrooms[2]. To avoid the adsorption of airborne organics on silicon surfaces, wafers should be stored in plastic boxes, usually made of polypropylene and/or polycarbonate materials. However, while wafers are stored in such boxes to protect them from airbome contaminants, organic gases vaporized from the boxes'plastic materiel adsorb onto the wafer surfaces [2,3]. Recently, it has been shown that major organic contaminants on the surface of silicon wafers stored in plastic boxes are organic additives for plastic material [3]. It has also been reported that organic contaminants degrade the gate oxide integrity (GOI) [4,5]. However this is strongly dependent on the atmosphere where the wafers are inserted into the oxidation fumace. The GOI of contaminated wafers loaded into the furnace in a nitrogen atmosphere can be degraded. In contrast, the GOI of contaminated wafers loaded in an oxygen-containing ambient will not be degraded. This shows organic contaminants will reside on the surface as carbon contaminants in an oxygen-free ambient[4,6], while they are oxidatively degraded and evaporated during wafer loading in an oxygen-containing ambient[7]. It has not been reported but organic contaminants would also give deleterious effects in the CVD step where the employment of an oxidizing ambient is prohibited for prevention of oxide film growth. Therefore, it is required that the influence of surface organic contamination on CVD of silicon nitride on silicon substrates, where wafer loading into a CVD reactor in an oxygen-containing ambient cannot be allowed, be investigated. As dynamic-random-access memories (DRAMs) increasingly become highly integrated, thinner capacitor dielectric films are required to reduce capacitor areas [8]. Oxidized nitride (ON) films have frequently been used as dielectric fil
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