Method for fabricating semiconductor device with deposition cycles of chemical vapor deposition process to form 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, wherein the adhesive layer includes a bottom portion disposed on the substrate and a sidewall portion disposed on the first dielectric layer, and a thickness of the bottom portion of the adhesive layer is greater than a thickness of the sidewall portion of the adhesive layer, wherein a thickness of the sidewall portion of the adhesive layer gradually decreases from bottom ends of the expanded hole towards top ends of the expanded hole, wherein the adhesive layer is formed of titanium, titanium nitride, or tantalum, tantalum nitride;
• conformally forming a first conductive layer on the adhesive layer by a second chemical vapor deposition process, wherein the first conductive layer includes a bottom portion disposed on the bottom portion of the adhesive layer and a sidewall portion disposed on the sidewall portion of the adhesive layer, and a thickness of the bottom portion of the first conductive layer gradually decreases from the bottom ends of the expanded hole towards the top ends of the expanded hole;
• 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 one deposition cycle of the deposition cycles of the second chemical vapor deposition process comprises exposing the adhesive layer to a pulse of a silicon-containing reducing agent and then exposing the adhesive layer to a pulse of a tungsten-containing precursor after the exposure to the pulse of the silicon-containing reducing agent;
• wherein the post-treatment comprises introducing diborane pulses to the first conductive layer.