The step coverage of undoped and phosphorus-doped SiO2 glass films

The step coverage of undoped and phosphorous-doped SiO2 glass films has been studied. Various parameters which play a role in determining the quality of the step coverage are briefly discussed. The step coverage capability of various deposition processes is evaluated. The processes compared are: atmospheric-pressure CVD, low-temperature, low-pressure CVD (Silox), mid-temperature, low-pressure CVD (TEOS) and plasma-enhanced CVD. The parametric dependence of the step coverage obtained in the deposition of undoped glass by use of the mid-temperature low-pressure technique is reported. It is demonstrated that the quality of the step coverage is strongly dependent on the deposition conditions. It improved with increasing TEOS flow rate and molecular residence time in the reactor. Addition of nitrogen, oxygen, or phosphine/nitrogen mixture to the TEOS causes a deterioration in the step coverage capability of the deposition process. The step coverage of this particular process is independent of the deposition temperature in the range 650–780 °C.