Resolving the mechanisms of current gain increase under forward current stress in poly emitter n-p-n transistors

The mechanisms behind moderate bias current gain ( beta ) increase of n-p-n transistors under forward current stress are investigated in polysilicon emitter transistors processed with different dopant impurities and concentrations, and with different amounts of hydrogen plasma treatment. The results suggest that transport of atomic hydrogen toward the poly/monosilicon interface region and its subsequent passivation of dangling bonds at both poly grain boundaries and the poly/monosilicon interface are responsible for the moderate bias beta increase. To alleviate the beta instability, elimination of hydrogen involvement and/or a higher doping concentration inside the poly emitter in the back-end-of-line (BEOL) processes are/is recommended.<<ETX>>

[1]  E. Hackbarth,et al.  On the very-high-current degradations on Si n-p-n transistors , 1990 .

[2]  D. Greve,et al.  Minority-carrier hole diffusion length in heavily-doped polysilicon and its influence on polysilicon-emitter transistors , 1988 .

[3]  J. Zhao,et al.  On the effects of hydrogen in p-n-p transistors under forward current stress in a C-BiCMOS technology , 1993, IEEE Electron Device Letters.

[4]  Hydrogen in crystalline semiconductors , 1987 .

[5]  G. Patton,et al.  Physics, technology, and modeling of polysilicon emitter contacts for VLSI bipolar transistors , 1986, IEEE Transactions on Electron Devices.

[6]  K. Saraswat,et al.  A model for conduction in polycrystalline silicon—Part I: Theory , 1981, IEEE Transactions on Electron Devices.

[7]  C. Kaya,et al.  Reliability analysis of self-aligned bipolar transistor under forward active current stress , 1986, 1986 International Electron Devices Meeting.

[8]  D.D. Tang,et al.  Metal migration into polysilicon emitter after very high current stress , 1992, IEEE Electron Device Letters.

[9]  K. Saraswat,et al.  A model for conduction in polycrystalline silicon—Part II: Comparison of theory and experiment , 1981, IEEE Transactions on Electron Devices.

[10]  Surface recombination current with a nonideality factor greater than 2 , 1989, IEEE Electron Device Letters.

[11]  R. A. Wachnik,et al.  Degradation of bipolar transistors under high current stress at 300 K , 1988 .

[12]  David S. Ginley,et al.  Passivation of grain boundaries in polycrystalline silicon , 1979 .