Use of an Excimer Lamp for Photochemical Resistless Etching of Thermal Silicon Oxide Substrate
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ABSTRACT Photochemical resistless etching was carried out by using a Xe 2* excimer lamp and a KrF excimer laser. The decomposition method with Xe 2* excimer lamp increases the decomposition efficiency by 100 times than that of using ArF excimer laser and etchant gas, CHCIF 2 . Xe 2* excimer lamp irradiation allowed decomposition of CHCIF 2 gas to produce CF 2 radical with a small quantity of gas. The CF 2 radical was polymerized to form fluorocarbon layer on the Si0 2 substrate. Simultaneously, circuit patterned KrF excimer laser was vertically irradiated the fluorocarbon layer on the substrate for resistless etching. The etching depth was about 1,000A. INTRODUCTION Fabrication of an insulating layer and its patterned etching are indispensable for Si semi-conductor manufacturing. The insulating layer, SiO 2, has been etched by plasma such as electron cyclotron resonance (ECR) or inductively coupled plasma (ICP) [1-3]. This is dry process etching and can make a line width smaller than wet process etching. It also makes possible anisotropic etching. However, it has disadvantages such as charge-up and damage to substrates[4]. Furthermore, pattern etching requires to do lithography, including resist application, exposure and development. In the process, it requires exposure of a circuit pattern after applying a resist to a Si wafer, using a Hg lamp, i-ray or KrF excimer laser. Recently, to answer to the demand for minute pattern etching, exposure by ArF excimer laser and synchrotron X-radiation (SR) have been studied. Using these light sources, resist application is still unavoidable [5-6]. A part of resist unexposed is removed by a developing solution after exposure, and then a part of Si0 2 uncovered by a resist layer is etched. In order to simplify resist application and development procedures, we have studied on photochemical etching [7-9] by using Freon as an etchant and ArF and KrF excimer lasers that have different wavelength [10-1 I]. In a reaction system, a resist layer was formed on Si0 2 substrate and was simultaneously irradiated with KrF laser of circuit pattern. CF 2* of the resist, which was simultaneously excited, removed 0 atom from the Si0 2 substrate of the Linder layer of the resist photochemically to etch. In etching method, a polymerized layer of CF 2* generated by photodecomposition of Freon is very important. We, therefore, have studied using CFC-12 (CCi 2F2 ) that has an strong absorption in the wavelength of ArF laser. However, as CFC-12 is prohibited to use effective January 1, 1996, we started using HCFC-22 (CHCIF 2) as a substitute Freon. This gas has a poor absorption in the ArF laser, whose photo-decomposition efficiency is low. In this study, thus, we used Xe 2* excimer lamp [12] light (172nm), which has a strong absorption to CHCIF 2; we 543 Mat. Res. Soc. Symp. Proc. Vol.
397 01996
Materials Research Society
performed a highly effective etching of Si0 2. The etching depth was 1000A. We successfully demonstrated a completely dry etching by simultaneous processing of resist applicati
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