Continuity and reliability assessment of a scalable 3×50μm and 2×40μm via-middle TSV module

Abstract

An advanced TSV metallization scheme, featuring a high conformal ALD oxide liner, a thermal ALD WN barrier, an electroless NiB platable seed and a high throughput copper ECD filling is presented. Because of the high conformality of the WN barrier and NiB seed, very thin layers can be deposited, reducing the manufacturing cost significantly, while still guaranteeing continuous barrier/seed layers all along the TSV sidewall to the bottom of the TSV. 3 × 50μm via-middle wafers, processed with this metallization scheme, are further processed through the thinning module, by using temporary bonded carriers, the backside passivation module and a copper RDL module by using a semi-additive process. The TSV resistance is measured between the 5μm thick RDL copper layer at the back side and the METPASS aluminum layer at the wafer front side. Low spread and high yield is obtained on the resistance data distribution of both single kelvin and daisy chain structures. The same metallization scheme is successfully scaled to a 2μm diameter and 40μm deep via-middle module. The conformal deposition of the barrier and the seed layer enables further scaling down to aspect ratio 20:1 through silicon via's with 5μm pitch, still ensuring the void-free bottom up copper fill by electroplating. The integrity of the liner/barrier system against Cu diffusion from TSV to silicon has been verified using the established controlled I-V method. Field acceleration factors, extracted in both copper-confined and copper-driven regime, indicate good TDDB reliability of this advanced 2 × 40μm TSV middle module.