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 (φ) varying from 3 μm to 30 μm 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 φ = 3 μm 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 (∼200 MPa) than for the TSV with SiO₂ liner (∼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 °C. We obtained the resistance value of as low as 18 mΩ per 10 μm-width TSV with 500 nm-thick PI liner fabricated on 12-inch wafer.