Growth characteristics of photolytic laser-induced chemical vapor deposition of tungsten from WF6

Abstract

ArF laser induced chemical vapor deposition (CVD) of W onto (100)Si from a WF6/H2/Ar mixture and with the laser beam in parallel to the substrate surface was studied. The influence of substrate temperature on the deposition rate was investigated in a broad range (25–450 °C) for both focused and unfocused beam conditions and compared with thermal CVD data. Above the threshold temperature for the thermal process, 250 °C, a combined thermal and photolytic process takes place. Below 250 °C the laser induced photolytic process yields deposition with a nearly temperature independent deposition rate of about 100 Å/min when a focused beam is used. For an unfocused beam a slightly lower deposition rate was observed. The distance between the laser beam and the substrate surface had only a slight influence on the deposition rate. For the focused beam conditions the deposition rate was only reduced by roughly 10% when the distance was increased from 0 to 8 mm. For the unfocused case the deposition rate increased, without reaching the focused beam values, upon increasing the beam to substrate distance in the range 0–8 mm. The substrate temperature had a strong influence on the resistivity of the deposited films for both laser-induced and thermal processes. For obtaining a low resistivity value, 8 μΩ cm, a substrate temperature above 350 °C was required. This was mainly due to the fact that the high-resistivity β phase was formed at lower temperatures. The influence of H2 concentration on the growth rate was investigated by replacing H2 with Ar. A small amount of H2 was enough to increase the deposition rate considerably. Use of Ar diluted gas resulted also in a higher deposition rate. Finally, the deposition rate increased linearly with increased total pressure.