Hybrid Bonding Technology: Revolutionizing Semiconductor Design with Ultra-Dense 3D Connections

Hybrid Bonding Technology: Revolutionizing Semiconductor Design with Ultra-Dense 3D Connections

Introduction to Hybrid Bonding Technology

As semiconductor manufacturers continue to push the boundaries of miniaturization, a new technology known as hybrid bonding is emerging as a pivotal development. Unlike traditional methods that focus on shrinking transistor sizes, hybrid bonding stacks multiple chips within a single package, potentially offsetting the slowdown in Moore’s Law. This approach promises significant advancements in transistor density and overall chip performance.

Hybrid Bonding: A Game-Changer for Semiconductors

At the IEEE Electronic Components and Technology Conference (ECTC) held in Denver this May, various research groups unveiled advancements in hybrid bonding technology. This technique enables the creation of extremely high-density connections between stacked chips, with some developments achieving up to 7 million links per square millimeter. These dense connections are essential for maintaining efficient communication between different silicon pieces within a chip package.

The Evolution of Moore’s Law and System Technology Co-Optimization

According to Intel’s Yi Shi, Moore’s Law is now driven by System Technology Co-Optimization (STCO). This concept involves fabricating different chip functions—such as cache memory and logic—separately and then assembling them using advanced packaging technologies like hybrid bonding. This approach allows chips to benefit from the best manufacturing processes available for each function while maintaining high-density connections between them.

Market Growth and Importance of Hybrid Bonding

Hybrid bonding is rapidly becoming the leading segment of the advanced-packaging industry. Gabriella Pereira of Yole Group notes that while hybrid bonding currently represents a small portion of the market, it is expected to constitute about half of the $38 billion market by 2029. This growth is attributed to hybrid bonding’s ability to provide the highest density of vertical connections compared to other advanced-packaging technologies.

How Hybrid Bonding Works

How Hybrid bonding works 

Image credit: IMEC

Hybrid bonding involves several critical steps:

1. Preparation: Wafers or chips are prepared with oxide insulation and recessed copper pads.
2. Initial Bonding: The wafers are pressed together, forming a preliminary bond between the oxides.
3. Heating: The stacked wafers are heated slowly, which causes the copper to expand and create a solid electrical connection.
4. Surface Flattening: Engineers work to flatten the oxide surfaces to ensure robust connections, addressing issues such as warping or bulging.
5. Copper Control: Precise control over copper levels is necessary to ensure successful bonding without gaps or misalignment.
6. Bond Strength: Initially, weak hydrogen bonds are formed, which are strengthened into covalent bonds through annealing.
7. Temperature and Time Optimization: Researchers are exploring ways to reduce the temperature and duration required for the final bonding process.
8. Copper Grain Formation: Efforts are being made to improve the continuity of copper grains across boundaries to enhance electrical performance.

Advances in Wafer-on-Wafer and Chip-on-Wafer Technologies

Recent research has shown impressive improvements in wafer-on-wafer (WoW) bonding, achieving pitches as tight as 360 to 500 nanometers. This requires extreme precision in wafer flatness and surface preparation. Hybrid bonding technology is also critical for chip-on-wafer (CoW) applications, which are used in high-end processors and memory chips. While CoW presents additional challenges, advancements continue to improve its effectiveness and reliability.

Imec used plasma etching to dice up chips and give them chamfered corners. The technique relieves mechanical stress that could interfere with bonding
Image credit: IMEC

Future Directions and Emerging Technologies

Looking ahead, researchers are optimistic about further reductions in bond pitches, potentially down to 200 nanometers. Technologies like backside power delivery are expected to enhance the efficiency of these connections. Additionally, hybrid bonding may expand beyond silicon, with potential applications in gallium nitride, glass wafers, and even quantum computing chips.

Hybrid bonding represents a major leap forward in semiconductor technology, promising to revolutionize chip design and performance in the coming years.