The authors describe the enhancement of the area-selective chemical vapor deposition of cobalt films on one oxide surface over another from the precursor Co2(CO)8 by addition of the nucleation inhibitor ammonia (NH3). In the absence of an NH3 coflow, the Co2(CO)8 precursor exhibits a weak intrinsic selectivity: at 70 °C, Co nucleates quickly on Al2O3 but more slowly on SiO2. The addition of an NH3 coflow, however, greatly amplifies the selectivity between different oxide surfaces. Thus, NH3 significantly inhibits nucleation on acidic oxides such as SiO2 and WO3 but has little effect on more basic oxides such as Al2O3, HfO2, and MgO. Comparison of growth on fully hydroxylated and dehydroxylated SiO2 suggests that hydroxyl groups are the nucleation sites that are affected by the addition of NH3. The mechanism of nucleation appears to be disproportionation of Co2(CO)8 to Co2+ (the intermediate that leads to nucleation) and Co(CO)4-: this disproportionation occurs readily on basic oxides but not on acidic oxides. The addition of NH3 has little effect on Co nucleation on basic oxides, probably because ammonia binds poorly to such surfaces, but NH3 greatly retards nucleation on acidic oxides such as SiO2; the authors propose that the latter result is either a site blocking effect or the result of conversion of Co2+ to inactive Co(NH3)x2+ species. Nucleation of cobalt is facile on gold (a very unreactive metal) even in the presence of NH3. The authors have found, however, that the deposition of Co on tungsten can be inhibited by exposing the surface briefly to ozone; no deposition occurs on the resulting thin tungsten oxide overlayer from Co2(CO)8 in the presence of NH3. In other words, this thin oxide overlayer affords the same selective inhibition behavior as seen on bulk WO3. In this way, both metal-on-metal and metal-on-oxide selectivity can be achieved. Cobalt films grown in the absence and presence of ammonia have resistivities of 11-20 and 15-25 μω cm, respectively.
|Original language||English (US)|
|Journal||Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films|
|State||Published - May 1 2020|
ASJC Scopus subject areas
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films