Correlation of G sub m degradation with refractive index of capping materials.

Five different plasma-deposited silicon nitride films were evaluated for use as a cap for polysilicon gate MOSFETs. The films were (1) a-SiN:H deposited in NS-AL; (2) Applied Materials a SiN:H process B; (3) Applied Materials a-SiN:H process D; (4) silicon oxynitride, a SiON:H deposited at NS-RD; and (5) fluorinated silicon nitride, a-SiNF:H deposited at MH. The films with the lowest refractive index (a-SiON:H and a-SiNF:H) were on devices that aged the least as measured by transconductance degradation. This result is interpreted in terms of the Meyer- Fair model if the lower refractive index films are more porous to H leaving the device than the higher refractive index films. Our results also show that films with low H content and low absolute value of stress age the least.