Reactant supply in reactive ion etching

In reactive ion etching, the etch rate may be reactant limited, so that a measurement of reactant supply is neccessary to understand the details of the etching process. A quantitative determination of reactant supply can be obtained by measuring the total dissociation of the etching gas. In particular, this paper reports the total dissociation of CF₄ as a function of input power and pressure in a diode system. A quadrupole mass spectrometer measuring the CF₃⁺ peak indicates the presence of CF₄ as well as other molecules containing the (CF₃) radical. A transient technique is used to separate the contributions of the other molecules from CF₄ so that the total CF₄ number density can be calculated. The production of reactant by the dissociation of Cf₄ causes etching of silicon and SiO₂ on the cathode of the system. Possible reaction sequences of these etching processes are modelled by using the known supply of reactant. The partial pressures of the etching products are calculated and correlated with the etch rates and the rise in total pressure.