Correlation of Gm degradation of submicrometer MOSFETs with refractive index and mechanical stress of encapsulation materials

Evaluations of five different plasma-deposited silicon nitride films for use as an encapsulation material for polysilicon-gate MOSFETs are discussed. The films were (1) a-SiN:H; (2) Applied Materials a-SiN:H process B; (3) Applied Materials a-SiN:H process D; (4) silicon oxynitride, a-SiON:H; and (5) fluorinated silicon nitride, a-SiNF:H. Submicrometer MOSFET devices that aged the least as measured by transconductance degradation were encapsulated with films having the lowest refractive index (a-SiON:H and a-SiNF:H). The results show that films with low refractive index and low absolute value of mechanical stress age the least. The results are interpreted in terms of the Meyer-Fair model where the lower refractive index films are more porous to H leaving the device than the higher refractive index films