Comparison of step coverage and other aspects of the H2/WF6 and SiH4/WF6 reduction schemes used in blanket LPCVD of tungsten

In contemporary LPCVD of tungsten (for contact fill) the tungsten source is exclusively WF/sub 6/. H/sub 2/, SiH/sub 4/ or a combination of these gases are typically used as the reducing agents. In the H/sub 2/ case the growth rate is generally a factor of 5 lower than in the corresponding SiH/sub 4/ case (provided that other process parameters are comparable). Since there is a clear trend in tungsten CVD towards single wafer equipment (because of thickness uniformity requirements, increasing wafer diameter and automatic wafer handling) a high growth rate (i.e. high wafer throughput) is desirable, while maintaining good stepcoverage. Hence, it is appropriate to investigate more closely the stepcoverage properties of the H/sub 2//WF/sub 6/ and SiH/sub 4//WF/sub 6/ chemistries. Important parameters which determine the conformality are surface migration and sticking coefficients. These parameters, however, are difficult to quantify under real deposition conditions. Nevertheless, valuable data can be obtained from a systematic exploration of conformality as a function of parameters like the identify of the reduction agent, gas flow, total pressure and temperature. In this study the authors present preliminary data concerning conformality of the H/sub //WF/sub 6/ and SiH/sub 4//WF/sub 6/ chemistries. Although experimental data are still limited, some trends can be analyzed. In addition some kinetic data on the SiH/sub 4//WF/sub 6/ chemistry are presented