Environment influence on Ti diffusion and layer degradation of a SiC/Ni2Si/TiW/Au contact structure

X-ray diffraction, x-ray photoelectron spectroscopy, and “in situ” sheet resistance measurements were used to study the thermal stability of TiW films as diffusion barriers between a gold overlay and the Ni2Si/SiC ohmic contact. The degradation phenomenon is totally different in the O2 environment as compared to the vacuum ambient. The sheet resistance shows an anomalous behavior with thermal annealing in vacuum from 300 to 580 °C, which is correlated to the Ti diffusion through the Au layer. In particular, Ti diffuses through Au grain boundaries at 315 °C forming TiOx on the sample surface, while at 400 °C, Ti bulk diffusion occurs. The activation energy for titanium diffusion in gold layers is 1.9±0.2 eV, a typical value for the volume diffusion in a metal layer. Thermal annealing performed in an oxygen environment prevented the Ti grain boundary diffusion at low temperature (until 450 °C) while at higher temperatures (higher than 500  °C) a complete degradation of the diffusion barrier occurs.

[1]  Thomas Gessner,et al.  A High Temperature Stable Metallization Scheme for SiC-Technology Operating at 400°C in Air , 1997 .

[2]  R. Schmid-Fetzer,et al.  Metals on 6H-SiC: contact formation from the materials science point of view , 1997 .

[3]  L. Vegard,et al.  Die Konstitution der Mischkristalle und die Raumfüllung der Atome , 1921 .

[4]  Y. Shapira,et al.  Thermal stability of a Ti-Si-N diffusion barrier in contact with a Ti adhesion layer for Au metallization , 1999 .

[5]  L. Calcagno,et al.  Improvement of high temperature stability of nickel contacts on n-type 6H-SiC , 2001 .

[6]  B. Odekirk,et al.  Tantalum carbide ohmic contacts to n-type silicon carbide , 1999 .

[7]  T. Tisone,et al.  Diffusion in Thin Film Ti–Au, Ti–Pd, and Ti–Pt Couples , 1972 .

[8]  M. Bozack,et al.  High‐temperature ohmic contact to n‐type 6H‐SiC using nickel , 1995 .

[9]  H. Okumura,et al.  Scanning tunneling microscopy studies of formation of 8×5 reconstructed structure of Ga on the Si(001) surface , 1999 .

[10]  P. Neudeck,et al.  High-temperature electronics - a role for wide bandgap semiconductors? , 2002, Proc. IEEE.

[11]  Zhanpeng Jin,et al.  Thermodynamic assessment of the Au-Ti system , 2001 .

[12]  Frank W. Gayle,et al.  Free-surface solidification habit and point group symmetry of a faceted, icosahedral Al-Li-Cu phase , 1987 .

[13]  S. Bass,et al.  Constituent quarks and g1 , 1999, hep-ph/9902280.

[14]  John R. Williams,et al.  The Physics of Ohmic Contacts to SiC , 1997 .

[15]  P. A. Turner,et al.  Thin‐film interdiffusion. I. Au‐Pd, Pd‐Au, Ti‐Pd, Ti‐Au, Ti‐Pd‐Au, and Ti‐Au‐Pd , 1975 .

[16]  T. Uemoto.  Reduction of Ohmic Contact Resistance on n-Type 6H-SiC by Heavy Doping , 1995 .