Selective Etching of Silicon Dioxide Using Reactive Ion Etching with CF-H

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 i