Deposition of highly conductive n⁺ silicon film for a-Si:H thin film transistor

Plasma enhanced chemical vapor deposition of phosphorus-doped n+ silicon film over a wide range of process conditions has been studied. The deposited films were characterized with SIMS, Raman, and XRD. An unusually abrupt change of resistivity over a small SiH4 (1% PH3) flow rate has been observed and was correlated to the variation of the film's morphology from amorphous to microcrystalline. The grains are less than 50 angstroms in size and has strong 〈111〉 orientation. Amorphous silicon thin film transistors with microcrystalline n+ source and drain contacts have consistently good device characteristics. However, the contact resistance is comparable to the channel resistance when the channel length approaches 1 micrometer.