TGV (Through Glass Via) Process

TGV (Through Glass Via) is an advanced packaging technology that creates vertically through microvias in ultra-thin glass substrates and metallizes them to enable vertical interconnection between chips. Featuring low loss at high frequencies, low thermal stress, and cost advantages, TGV is regarded as one of the key solutions for 2.5D/3D packaging and Chiplet integration.

Core Principle

The TGV process involves fabricating micron-scale through holes, typically 10–50 μm in diameter, in 100–700 μm ultra-thin glass substrates such as borosilicate glass or quartz. These vias are then filled with copper by electroplating to form vertical conductive channels, serving as an alternative to traditional TSV silicon interposers.

Standard Process Flow

1. Substrate Pretreatment

The glass substrate is cleaned, dried, and coated with photoresist, followed by photolithography to remove contaminants and define the via patterns.

2. Laser Via Formation

This is the core step of the TGV process. An ultrafast laser, such as a picosecond or femtosecond laser, is focused inside the glass to induce microcracks or modified regions, forming high-aspect-ratio via channels. The aspect ratio can reach up to 150:1, with via diameters as small as 3 μm and hole-to-hole uniformity exceeding 95% across millions of vias.

3. Wet Etching / Via Enlargement / Cleaning

HF or BHF etching is used to remove the laser-modified regions, smooth the via sidewalls, and precisely control the final via diameter. The substrate is then thoroughly cleaned to remove residual impurities.

4. Metallization

Seed Layer Deposition:
A Ti/Cu or AlN/Cu seed layer is deposited by sputtering to ensure strong adhesion to the via sidewalls.

Copper Electroplating:
Pulse or DC electroplating is used to achieve complete, void-free copper filling inside the vias.

Surface Treatment:
CMP is performed to planarize the surface, followed by anti-oxidation coating if required.

5. RDL Formation / Bumping

A redistribution layer is fabricated with fine line/space capability, typically ≤2 μm, followed by solder ball placement or copper pillar formation for subsequent chip bonding.

6. Testing / Dicing

Electrical testing is performed, followed by wafer dicing and final product inspection.

Summary

With its advantages of high-frequency low-loss performance, low thermal stress, and competitive cost, TGV has become a key technology for 3D interconnection in the post-Moore era. Its core technical breakthroughs lie in laser via formation and void-free copper electroplating. As the technology moves toward mass production in 2026, it is expected to play an important role in AI computing, 5G/6G RF devices, advanced packaging, and Chiplet integration.