The silicon etching rate by chlorine trifluoride gas is systematically studied using a reactor having a very small cross section above the silicon substrate and achieving a very high efficiency of etchant gas consumption and very large etching rate, larger than 20 m min Ϫ1 . The silicon etching rate is shown to be proportional to the flow rate of the chlorine trifluoride gas. However, this rate is, for the first time, found to be independent of the initial silicon substrate temperature. This study shows that the silicon substrate is automatically heated to the temperature determined by the balance of the reaction heat and the heat transport in the reactor. Since this temperature increment processes an extremely large-surface chemical reaction rate, the etching rate is governed by the transport rate of the chlorine trifluoride gas. This study concludes that a high efficiency silicon etching by chlorine trifluoride gas is possible without any supplemental heating.Chlorine trifluoride (ClF 3 ) gas has a very high reactivity for various materials. 1-5 This gas is especially suitable for plasmaless etching 2,6-10 near room temperature at atmospheric and reduced pressures. In silicon crystal technology, chlorine trifluoride gas has been known to be used for the in situ cleaning 2,11,12 of a chemical vapor deposition ͑CVD͒ reactor in order to remove any polysilicon film deposited on the susceptor and on the inner wall of the chamber.For the further development of new industrial etching and cleaning processes using chlorine trifluoride gas, its chemical reaction should be systematically studied. For this purpose, our previous study 13 reported the chemical reaction between a silicon surface and chlorine trifluoride gas in ambient nitrogen at atmospheric pressure. It also reported that chlorine trifluoride gas has been shown to work as a source of active fluorine atoms to form inorganic fluorides, for example, silicon tetrafluoride for silicon etching. However, this previous study was performed only to evaluate the overall chemical reaction and the produced gas species. The other fundamental properties of the chemical reaction by chlorine trifluoride gas, such as the etching rate and the rate-determining parameters, have, unfortunately, not been studied.Therefore, in this study using the chlorine trifluoride gas in the CVD reactor designed for achieving the industrially applicable highperformance process, the silicon etching rate and its ratedetermining parameters are experimentally evaluated. ExperimentalIn order to etch silicon by chlorine trifluoride gas, the horizontal cold-wall CVD reactor shown in Fig. 1 was used. This reactor consists of a gas supply system, a quartz chamber, and infrared lamps. A 30 ϫ 50 mm silicon substrate is horizontally held on the bottom wall of the quartz chamber. The silicon substrate is cut from the n-type ͑100͒ 200 mm diam semiconductor silicon wafer, which was grown using the Chzochralski method.The silicon substrate is heated by infrared rays from the infrared lamps through the transpar...

The mechanism causing the behavior of the silicon etch rate using chlorine trifluoride gas, which appears to be independent of the substrate temperature in a horizontal cold-wall reactor, is clarified by means of numerical calculations taking into account the surface chemical reaction rate on the silicon substrate surface and the transport phenomena in the entire reactor. The activation energy of the overall rate constant of its surface chemical reaction is evaluated, for the first time, to be 6000 J mol Ϫ1 , which can reproduce the etch rate and its behavior obtained by the measurement. With increasing substrate temperature in the reactor, the effect of a moderate increase in both the diffusivity of chlorine trifluoride gas and the overall rate constant is considered to be compensated by the decrease in the chlorine trifluoride gas concentration due to the gas volume expansion in the gas phase above the substrate. Therefore, the etch rate can be independent of the substrate temperature.Chlorine trifluoride (ClF 3 ) gas has very high reactivity, particularly for plasmaless fluorination, for etching and surface modification of various materials at low temperatures. 1-17 For further development and advance of its industrial applications, the rate and the behavior of the chemical reaction should be systematically studied. For this purpose, the authors studied 15,16 the chemical reaction of chlorine trifluoride gas with silicon, which is an important semiconductor material for manufacturing electronic devices for information technology. In these previous reports, the etch rate of silicon in nitrogen ambient at atmospheric pressure was shown to be independent of the substrate temperature using a horizontal cold-wall reactor designed for obtaining a high etchant consumption rate. Because this behavior is different from those reported by other researchers 1,13 and because the etch rate behavior is important for designing the process and the reactor using chlorine trifluoride gas, the mechanism causing this temperature-independent etch rate behavior should be clarified. For this kind of study, the entire phenomena in the reactor, such as transport phenomena and surface chemical reactions, should be evaluated and clarified. Here, the rate constant of the surface chemical reaction should be obtained as necessary information.Therefore, in this study using chlorine trifluoride gas for etching a silicon surface in a horizontal cold-wall reactor, the overall surface chemical reaction rate constant for silicon etching is evaluated by numerical calculations taking into account the transport phenomena in the entire reactor. Additionally, the mechanism causing the temperature-independent etch rate behavior is studied from the viewpoint of the transport phenomena linked with the surface chemical reaction. ExperimentalHere the experimental conditions for etching the silicon substrate surface using the chlorine trifluoride gas are briefly described, following our previous study. 16 To etch a semiconductor silicon surface using chlori...