Nitridation of fine grain chemical vapor deposited tungsten film as diffusion barrier for aluminum metallization

Abstract

A novel tungsten nitride (WNx) film for diffusion barrier applications has been prepared by nitridation of a fine grain chemical vapor deposited tungsten (CVD-W) film. The fine grain CVD-W is deposited at 300 degrees C in a low pressure chemical vapor deposition reactor with a SiH4/WF6 flow rate of 12.5/5 seem under a total gas pressure of 100 mTorr. The subsequent nitridation process is executed in nitrogen plasma at 300 degrees C without breaking vacuum. The thickness of WN, layer as examined by secondary ion mass spectroscopy is 50 nm after 5 min exposure to nitrogen plasma. X-ray photoelectron spectroscopy spectra shows that the atomic ratio of tungsten to nitrogen in WNx, layer is 2:1. According to the analysis by Auger electron spectroscopy and the measurement of n(+)p junction leakage current, the Al/WNx/W/Si multilayer maintains excellent interfacial stability after furnace annealing at 575 degrees C for 30 min. The effectiveness of W2N barrier is attributed to stuffing grain boundaries with nitrogen atoms which eliminates the rapid diffusion paths in fine grain CVD-W films. (C) 1997 American Institute of Physics.