Influence of low-dose ion-beam mixing on CoSi2 formation

In this study, the critical dose for ion-beam mixing of Co and Si with Ge ions which results in homogenous CoSi2 formation after rapid thermal annealing was found. For this purpose, Co was deposited by sputtering on chemically cleaned (100)- oriented Si and subsequently mixed with Ge ions at doses in the range of 2x10high14 to 1x10high15 cmhighminus2. Silicidation was performed in a rapid thermal annealing (RTA) system at temperatures between 700 degree C and 1000 degree C. Rutherford backscattering measurements showed that annealing at 700 degree C results in an uncomplete reaction when ion-beam mixing at a dose of 2x10high14 cmhighminus2 or no ion-beam mixing were performed. After annealing at 1000 degree C, TEM samples revealed an inhomogenous CoSi2 film consisting of large grains embedded in the Si. Mixing at doses at or above equal or bigger than 5x10high14 cmhighminus2 and subsequent RTA at 700 degree C resulted in uniform CoSi2 layers. Higher annealing temperatures cause larger grains and resistivity values as low as 18 MyOmegacm. Therefore, we demonstrated that the critical dose leading to complete formation of smooth CoSi2 films with abrupt interfaces is 5x10high14 cmhighminus2 which is nearly the same value as the amorphization dose of Ge in Si