Contact resistivity between tungsten and impurity (P and B)-doped Si _1-x-y Ge _x C _y epitaxial layer

Contact resistivity between tungsten and in situ impurity (P and B)-doped Si _1-x-y Ge _x C _y films with 0 ≤ x ≤ 0.7, 0 ≤ y ≤ 0.02 has been investigated. In the case of the P-doped Si _1-x-y Ge _x C _y 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 × 10 ²⁰ cm ^-3 at a very low temperature of 450 °C on the P-doped Si _1-x-y Ge _x C _y film, very low contact resistivity of 6.5 × 10 ^-8 Ω cm ² is achieved. On the other hand, in the case of the B-doped Si _1-x-y Ge _x C _y 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 Si _0.56 Ge _0.44 films with a high carrier concentration of 6 × 10 ²⁰ cm ^-3 , very low contact resistivity is obtained to be 3.8 × 10 ^-8 Ω cm ² . 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.