A study of plasma etching of filament evaporated Ti, in a radial flow reactor, using Pd (Au) as a mask is described. This work was prompted by recurrent problems with etch-out of Ti from contact windows during wet chemical patterning of Ti for the Ti-Pd-Au metallization process. CF4, CClF3, and CBrF3 plasmas were investigated. Details of some of the plasma chemistry and interaction of these plasmas with Au are given. Only CBrF3 plasmas were found to provide suitable selectivity for etching Ti in the presence of Au. CBrF3 tends to produce an unstable plasma. However, a stable, uniform plasma can be formed by the addition of a sufficient quantity of He. Oxygen was also added to enhance the amount of atomic bromine formed in the plasma since this was thought to be the active species for Ti etching. The optimum gas mixture was determined to be 63% CBrF3, 25% He, and 12% O-2. A relatively strong Arrhenius-type temperature dependence of the etch rate was measured with an activation energy of similar to 0.2 eV for this gas mixture. The range of process parameters (power, pressure, temperature) for which acceptable etching could be achieved was found to be quite broad and working conditions were chosen mainly on the basis of an arbitrary etch time of 4 min to clear 1000 angstrom of Ti from a 3 in. wafer. These conditions are: 200W rf power, 0.35 Torr of the CBrF3-He-O-2 mixture, 150 degrees C wafer platen temperature, and a 4.4 cm electrode spacing. No measurable etching of Au or Pd occurs, using these conditions, While the etch rate for CVD Si3N4 is,similar to 25 angstrom/rain. Undercutting of Ti is negligible even with a 100% overetch. No change in MOS characteristics was observed after plasma exposure.
