Photo enhanced CVD

In this section we will describe two forms of LCVD using laser beams. The deposition rate enhancement can be by  

Deutsch and Rathman193 showed that using an ArF laser beam parallel to the substrate, tungsten depositions can be obtained in a H2/WF6 gas mixture at 8 Torr. The substrate temperature was varied between 200 and 440°C. At 440°C, the bulk resistivity was about 17 /rOcm. However, below 350°C, high resistivity (100-300 /iflcm) /3-W is obtained. By a heat treatment at 650°C in H2 the /3-W phase can be converted into the a-W phase. The activation energy found for the photo reaction was 40.7 kJ/mole. 

Tsuzuku et al.195 also used an ArF laser with the beam parallel to the substrate (10 mm above). While varying the substrate temperature between 350 and 450°C, tungsten depositions were obtained in a H2/WF6 mixture. In their case no /3-W was reported. The reaction orders obtained were one for hydrogen and 1/2 for WF6 according to the rate expression  

The activation energy for the photo enhanced reaction is 35 kJ/mole which is similar to the value obtained by Deutsch and Rathman. The authors note that this is close to the activation energy of atomic hydrogen diffusion on a tungsten surface (40 kJ/mole). Tsuzuku ct al. come to the following proposal for the reaction route  

Only depositions of tungsten on Si substrates were obtained. No tungsten was found on thermal oxide. A complication found was that the tungsten lines were partially silicided in the center. 

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