Selective Etching of Silicon Dioxide Using Reactive Ion Etching with  CF 4 ‐  H 2

Abstract

Highly selective tching of silicon dioxide relative to both silicon and resist has been obtained by reactive ion etching substrates which are loaded onto an rf cathode and exposed to a low pressure discharge of a CF4-H2 etching gas mixture. Silicon dioxide-to-sil icon etch rate ratios as high as 35 to 1 have been measured and silicon dioxide-to-resist e ch rate ratios have been found to exceed 10 to 1. The use of reactive ion etching is imPortant in achieving these high etch ratios; the low operating pressure of between 2.7 and 5.3 Pa and the exposure of substrates to bombardment by energetic ions tend to in-hibit polymerization on the substrates. As a result, it is possible to use the greater I-I2 concentrations which are required for high etch rate ratios. One of the limitations common to the several dry etching configurations that are in use has been a lack of etch selectivity, especially of silicon dioxide relative to resist and silicon. Heinecke has reported that a sili-con dioxide-to-sil icon etch rate ratio of 5 to 1 can be obtained using a C3Fs discharge (1). Higher ratios, between 10 and 15 to 1, were reported by Heinecke using CHFs and CF4-H2 discharges, but the use of these gases was not considered practical because of the high concentration of HF that was produced at the operating pressure of 40 Pa. More recently, a silicon dioxide-to-sil icon etch rate ratio of 10 to 1 was re-ported using a C2H2-CF4 discharge (2). In the latter work, loading the substrates onto a Teflon target con-tr ibuted to the etch rate ratio. In this work, a silicon dioxide-to-sil icon etch rate ratio of 35 to 1 has been achieved by combining the use of the reactive ion etching configuration and a CF4-H2 etching gas mixture. Problems associated with the production of HF have not been observed at the low operating pressure of 4.7 Pa. Exper imenta l Apparatus The reactive ion etching system in this work is