Highly Beneficial Organic Liner with Extremely Low Thermal Stress for Fine Cu-TSV in 3D-Integration

The constructive role played by the Thermal-chemical vapor deposited (CVD) organic polyimide (PI) liner in the Cu-TSVs with diameter or width (phi) varying from 3 mu m to 30 mu m has been studied meticulously for its thermal stability, leakage current (LC), capacitance, TSV-chain resistance, stress absorbing ability, and the Si-lattice distortion arising from thermo-mechanical stress (TMS). The measured LC values for the CVD deposited PI liner is in the order of 10(-13) to 10(-15) A, which is on par with the value obtained for the conventional SiO2 liner. The extremely low modulus value of PI liner helps not only to reduce the amount of Cu extrusion, but also maintain an uniform Cu-extrusion. We were able to achieve a conformal deposition of PI liner even in phi = 3 mu m via having the aspect ratio of 10 with the step coverage values of more than 0.8 (80%) at the TSV bottom corner. It was found that the d-space changing and thus the lattice stress is nearly five times smaller for the TSV with PI liner (similar to 200 MPa) than for the TSV with SiO2 liner (similar to 1000 MPa). Nearly zero-degradation of PI liner was confirmed from C1s, O1s, and N1s core-level x-ray photoelectron spectra taken before and after annealing at 400 degrees C. We obtained the resistance value of as low as 18 m Omega per 10 mu m-width TSV with 500 nm-thick PI liner fabricated on 12-inch wafer.