Contact resistivity between tungsten and impurity (P and B)-doped Si1-x-yGexCy epitaxial layer

Contact resistivity between tungsten and in situ impurity (P and B)-doped Si1-x-yGexCy films with 0≤x≤0.7, 0≤y≤0.02 has been investigated. In the case of the P-doped Si1-x-yGexCy films, the contact resistivity decreases with increasing the carrier concentration, independently of the Ge and C fraction. Because P atoms become electrically inactive with increasing the Ge and C fractions, lower Ge and C fractions are necessary to reduce the contact resistivity. By growing the multi-layer P-doped epitaxial Si with a high carrier concentration of 4x1020 cm-3 at a very low temperature of 450 deg. C on the P-doped Si1-x-yGexCy film, very low contact resistivity of 6.5x10-8 Ω cm2 is achieved. On the other hand, in the case of the B-doped Si1-x-yGexCy films, the contact resistivity decreases with increasing the Ge fraction and scarcely depends on C fraction at a specified carrier concentration, and is typically 25 and 57% lower for x=0.44 and 0.7 than that for Si, respectively. For the B-doped Si0.56Ge0.44 films with a high carrier concentration of 6x1020 cm-3, very low contact resistivity is obtained to be 3.8x10-8 Ω cm2. These results demonstrate that low contact resistivity is caused by the lowering of schottky barrier height between metal and the B-doped film, due to the valence band shift