TSV Wafer+Patterning of Sub 1µm CD TSV and Bond Pad for Fine-pitch 2.5D/3D hybrid bonding Applications

This study investigates sub-micron lithography and etching for through-silicon vias (TSVs) and bond pads targeting fine-pitch 2.5D/3D hybrid bonding in advanced packaging. The authors aim to push i-line stepper lithography beyond its nominal 1 µm resolution limit by optimizing photoresist type, thickness, and exposure parameters. Two resists were evaluated: a chemically amplified resist (CAR, ZR8800) and a Novolac resist (PFI26A).

Key findings include:

1. Critical dimension (CD) achievement: Using optimized stepper exposure and development conditions, TSV features below 1 µm CD were achieved across multiple pitches (2.5 µm, 10 µm, 50 µm), with PFI26A achieving ~650 nm for 2.5 µm pitch and ZR8800 achieving ~890 nm for 50 µm pitch (page 4, Figures 5–7). Post-etch CD reduction further improved profiles by ~15%, achieving straight sidewalls and high aspect ratios (~17) for 14 µm deep TSVs (page 4, Figure 10).

2. Resist performance:

• CAR ZR8800: Enables finer patterning with sharp edges and straight profiles, but highly sensitive to environmental factors and post-exposure delay (PED), causing CD variations of 60–80 nm over a wafer batch.

• Novolac PFI26A: Exhibits environmental stability and minimal PED sensitivity, providing consistent CD uniformity (CDU) but requires higher exposure energy and longer development. PFI26A consistently yielded superior CDU for small pitches post-etch (pages 2–3, Figures 2–4).

3. Process optimization: Key factors for sub-micron patterning included resist thickness tuning, exposure energy adjustment, and dry etch passivation, allowing uniform pattern transfer even at isolated TSV pitches. Post-lithography and post-etch inspections demonstrated reliable CD control and improved top CD uniformity (FICD) (pages 3–4, Figures 6–9).

The study demonstrates that conventional stepper lithography can be extended to sub-micron TSVs and bond pads, supporting fine-pitch 2.5D/3D hybrid bonding with high aspect ratio TSVs while balancing throughput, CD control, and process stability. These results highlight a cost-effective pathway for advanced packaging without requiring extreme-resolution tools (page 4, Conclusion).