PHOTO-STIMULATED CVD OF SINX FOR GAAS IC APPLICATIONS

The characteristics of silicon nitride deposited by a photo-enhanced CVD process have been investigated. The nitride films are used as inter metal insulator in GaAs ICs. For this application the step coverage is the most crucial aspect. The photo-CVD of SiN//x proves to be a surface determined deposition process, even in the case of undercutted structures. The insulation between first and second metallization was measured on a contact test structure with 1800 cross-overs. The insulating resistance in this structure is in the G OMEGA range even if the nitride is only 300 nm thick. A thickness uniformity of 4% for a batch of six 3 inch wafers and a reproducibility of 5% were obtained for 300 nm thick films, the intrinsic tensile stress being as small as 10**7 to 10**8 dyn/cm**2. The threshold voltage shift due to deposition was only minus 25 mv for MESFETs in GaAs ICs.