Thermal Stability of Pt and C-Doped NiSi Films

The thermal stability of Pt and C doped Ni-silicide films was studied. For Ni(Pt)Si layers the addition of e.g. 10% of Pt to the Ni sputtering target results in an improvement of the thermal stability of the Ni(Pt)Si up to 750degC (30 s). Recently, it was discovered that the addition of C to the NiSi film has an even larger effect. The end result is a C-doped NiSi film with a remarkable thermal stability to temperatures exceeding ~850degC (30 s). When heated to even higher temperatures, the NiSirC degrades via conversion to NiSi₂. A detailed analysis has been given on the crystal structure (TEM) of films that have undergone various types of anneals. It has been shown that the percentage of substitutional C has a large impact on the sheet resistance (Rs) of the as-silicided NiSi:C film, whereas it has little or no effect on the termal stability of such films at higher temperatures (850degC, 30 s). Further, it was found that films with 1.7 at.% C or higher can withstand a 30 min. anneal at 750degC. This enhanced thermal stability makes this type of silicide compatible with planarization techniques that are currently in use in e.g. memory fabrication (and that are not compatible with pure or Pt-doped NiSi).