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

Abstract

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 4×1020cm−3 at a very low temperature of 450°C on the P-doped Si1−x−yGexCy film, very low contact resistivity of 6.5×10−8Ωcm2 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 6×1020cm−3, very low contact resistivity is obtained to be 3.8×10−8Ωcm2. 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.