K. R. Ryan

A model of the chemical processes occurring in CF4/O2 discharges used in plasma etching

A model has been developed in an attempt to explain the chemistry which occurs in plasmas produced in mixtures of CF4 and O2. Emphasis is placed on gas-phase free radical reactions, and the predictions of the model are compared with experimental results. Dissociation rates following electron impact are deduced mainly from experimental observations although relative dissociation rates have been calculated. An important assumption of the model is that CF2 can be produced as a primary dissociation product following electron impact. Furthermore, this process is favored over that producing CF3 by more than a factor of 2. Experimental evidence is presented to support this assumption. Although the model agrees well with experiment on the total amount of fluorine produced, some discrepancy exists between the predicted and measured values of [F2]. It is suggested that the higher concentrations detected in the experiments resulted from recombination of F atoms in the sampling region. The agreement for concentrations of CO2, CO, and COF2 is generally better than a factor of 2 over a wide range of experimental conditions.

A model for the etching of Si in CF4 plasmas: comparison with experimental measurements

A model has been developed to describe the chemistry which occurs in CF4 plasmas and the etching of Si both in the plasma and downstream. One very important feature of this model is that for discharge residence times which vary by more than an order of magnitude, the amount of CF4 consumed is low and relatively constant. This is because the gas-phase combination reactions between F and both CF3 and CF2 lead to the rapid reforming of CF4. The model predicts that CF2 is a major species in the gas phase and that the [F] detected as a sample point downstream is a very sensitive function of [CF2]/[F] in the discharge. Even though the calculations show that [F] in the discharge varies only slightly over the wide range of experimental conditions considered, large variations in [F] at the sample point occur because the [CF2]/[F] ratio in the discharge changes. The concentrations of C2F6 and SiF4 are predicted to within a factor of 2 over a very wide range of experimental conditions. This confirms the importance of gas-phase free radical reactions in the etching of Si.

Gas-phase reactions of CF2 with O(3P) to produce COF: Their significance in plasma processing

AbstractReactions between CF2 and O(3P) have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. The major reaction for CF2 has been found to be

Gas-phase reactions of CF3 and CF2 with atomic and molecular fluorine: their significance in plasma etching

CF_2 + O \to COF + F

Gas-phase reactions of SF5, SF2 and SOF with O(3P): their significance in plasma processing

with

Gas-phase combination reactions of SF4 and SF5 with F in plasmas of SF6

CF_2 + O \to CO + 2F(F_2 )