Method for fabricating semiconductor device with composite contact structure

A method for fabricating a semiconductor device, comprising:

• forming a first dielectric layer on a substrate;
• forming an expanded hole in the first dielectric layer;
• conformally forming an adhesive layer in the expanded hole by a first chemical vapor deposition process;
• conformally forming a first conductive layer on the adhesive layer by a second chemical vapor deposition process;
• performing a post-treatment to the first conductive layer;
• forming a first conductive structure on the first conductive layer by a third chemical vapor deposition process;
• wherein the adhesive layer, the first conductive layer, and the first conductive structure together configure a composite contact structure;
• wherein the second chemical vapor deposition process comprises an initial deposition step and subsequent deposition cycles repeated until the first conductive layer is formed to a predetermined thickness;
• wherein the post-treatment comprises introducing diborane pulses to the first conductive layer.