Fabrication and Thermal Stability of W‐Si Ohmic Contacts

W‐Si ohmic contacts have been fabricated using rf‐sputtered W and bulk‐doped n‐ and p‐type Si. The investigated doping range is for B (p‐type) and for As (n‐type); with corresponding contact resistance ranging as and , respectively. Steam‐grown and deposited oxide were used as the mask to study the effect of impurity redistribution during steam oxidation on contact resistance. Chemical (100:1 buffered ) and sputter etch cleaning were used to remove the native oxide from contact windows before W deposition. Metallurgical and electrical stability of these contacts was studied up to ∼830°C. The unannealed contacts (using steam oxide mask) are ohmic if the Si has >10¹⁹/cm³ As but the minimum B needed is ∼10²⁰/cm³. This difference stems from two reasons: (i) B is lost from Si during steam oxidation whereas As concentrates in Si; (ii) the native oxide growing on p‐Si seems to be electrically quite different from that on n‐Si. Contacts improve with anealing up to ∼800°C (1 hr treatments), but if higher temperatures are used high resistance or "opens" may occur. Sputter etching is found to be more effective in cleaning the contact windows than the chemical cleaning.