Electroplating Cu on ALD $\text{TiN}$ for Small Size TSV

Si interposer with TSV technology plays a key role in 2.5D and 3D system integration. Via filling with smaller size is becoming more and more challenge. Atomic Layer Deposition (ALD) can fabricate diffusion barrier layer with better step coverage, film uniformity and controllable thickness in small size TSV. TiN thin film deposited by ALD can serve as diffusion barrier layer and seed layer for TSV structure simultaneously. In this paper, by optimizing ALD process parameters, a continuous TiN layer has been successfully deposited on TSV sidewall. Different pre-wetting solutions and different concentration ratios between accelerator(A) and suppressor(B) in electroplating solution has been examined to obtain the optimal parameters for electroplating Cu. The results show that ~30nm thick TiN films with resistivity of below 200 µΩ.cm can satisfy the basic function of diffusion barrier layer and seed layer for TSV structure. Pre-wetting solution-deionized water with added suppressor and additives B: A ranging from 6.5 to 7 are superior to other conditions for obtaining high-quality void-free Cu TSV. As concluded, ALD TiN can work as diffusion barrier layer and seed layer for small size TSV structure. Cu filling TSVs with diameter of 5-6µm, pitch of 15µm and aspect ratio ranging from 7 to 10 have been successfully demonstrated.