Process Integration and Testing of TSV Si Interposers for 3D Integration Applications

Two 3D Si interposer demonstration vehicles containing through-Si vias (TSVs) were successfully fabricated using integration of two different TSV formation and multilevel metallization (MLM) process modules. The first Si interposer vehicles were made with a dual damascene front-side MLM (5 levels), backside TSV (unfilled, vias-last), and backside metallization (2 levels) process sequence on standard thickness 6 '' wafers. The front-side MLM was comprised of 4 metal routing layers (2 mu m Cu with 2 mu m oxide interlayer dielectric) and 1 metal pad layer. Electrical yield as high as 100% was obtained on contact chain test structures containing 26,400 vias between the front-side MLM layers, while the average contact resistance between the dual damascene levels was < 4 m Omega per via. TSV dimensions of 100 and 80 mu m diameter and 6:1 aspect ratio were investigated. DRIE bottom clear process conditions were optimized for each via dimension to produce 100% yield on TSV contact chains with up to 540 vias. The optimized DRIE conditions also resulted in TSV resistance below 30 m Omega and sufficient TSV isolation resistance (> 100M Omega/via at 3.3V) for the target application. Functional testing of two die (4 cm x 3.7 cm die size) showed that 99% of the functional circuit path nets had acceptable continuity and isolation. The second Si interposer vehicles were fabricated using a vias-first TSV (filled, blind vias), wafer-level packaging (WLP) front-side MLM (2 levels), wafer thinning (via reveal), and WLP-MLM (1 level) process sequence on stock 6 '' wafers. Via dimensions for the vias-first interposers were 50 mu m diameter x 315 mu m depth or 80 mu m diameter x 315 mu m depth (6:1 or 4:1 aspect ratios). The front and backside MLM was formed with a 2 mu m Cu routing layer and one of two spin-on dielectrics (polyimide or ALX) for evaluation of polymer dielectric process compatibility with Cu-filled TSVs and thinned wafer processing. Details of the process modules and process integration required to realize the TSV Si interposers are described.