Physical and electrical properties of W/MN_x/poly-Si_1-xGe_x (x = 0, 0.2, 0.6) gates stack with post-thermal process

We investigated the physical and electrical properties of a W/WN_x/poly-Si_1-xGe_x gates stack with a post-thermal process for use in the high performance complementary metal oxide semiconductor field effect transistor. Under the same annealing conditions, the crystallinity of the W films degraded, and the sheet resistance of the W/WN_x/poly-Si_1-xGe_x films increased with increasing Ge content of the poly-Si_1-xGe_x films. These results are attributed to the increase in surface roughness of the poly-Si_1-xGe_x films, which suppressed grain growth in the W films as the Ge content of poly Si_1-xGe_x increased. After high temperature annealing, the grain size of the W films increased, and the crystallinity of the W films was enhanced due to a reduction of the uniform strain. The elimination of uniform strain in W films and the increase in grain size led to a decrease in the sheet resistance of the W/WN_x/poly-Si_1-xGe_x structure. In addition, no evidence of the formation of WSi_x was observed even after annealing at 900°C for 30 min due to the WN_x barrier between the W film and the poly-Si_1-xGe_x film. However, the N content of the WN_x films decreased by about 61% of the initial amount and accumulated below the WN_x layer, suggesting an interfacial reaction between the WN_x film and the poly-Si_1-xGe_x film. As the annealing temperature increased, the amount of dopant in the poly Si_1-xGe_x films of the W/WN_x/poly-Si_1-xGe_x system also decreased due to boron accumulation and the formation of a boron compound (BN).