“Hybrid bonding expected to be introduced after HBM4E… needs to happen faster”
There is a view that hybrid bonding technology, known as a next-generation packaging technology for high-bandwidth memory (HBM), will be introduced after the 7th-generation HBM4E. The basis is that hybrid bonding equipment is costly and difficult to localize domestically, and that the existing thermo-compression (TC) bonding technology can still cope for now.
On the 7th, Joo Seung-hwan, a professor at Inha University’s Graduate School of Manufacturing Innovation, said, “The introduction and application of hybrid bonding equipment will take place around HBM4E or HBM5,” adding, “Equipment makers are making similar predictions.”
Professor Joo said, “The biggest reason hybrid bonding is not applied now is cost,” adding, “Besi, the leader in the bonding equipment industry, has developed hybrid bonding equipment with Applied Materials and is supplying it to TSMC, but the equipment price is quite expensive.” He added, “Domestic equipment companies are trying to localize at a relatively lower price range, but the technology is not yet ready.” In October, Besi and Applied Materials completed development of the die-to-wafer hybrid bonding equipment “KineX Bonding System.” The price of this equipment is said to be in the range of KRW 15–20 billion.
Professor Joo said, “Moreover, the industry believes that even with TC bonding alone, HBM can be stacked up to 33 layers,” adding, “Since HBM4/4E as well as the 8th-generation HBM5 are at the 20–24-high level, there is no compelling reason to use hybrid bonding.” According to data from market research firm Yole Group, HBM manufacturing is expected to move from the currently used TC bonding to fluxless TC bonding that uses no chemicals/adhesives (flux). It will then go through a Cu-Cu direct approach that connects copper to copper and move into hybrid bonding.
Professor Joo said, “The main reason for adopting hybrid bonding for HBM is heat,” noting, “If you manufacture HBM with hybrid bonding, thermal efficiency improves by about 100 times.” He continued, “Because HBM stacks multiple memory chips vertically, the more chips there are, the greater the heat problem,” and emphasized, “As the HBM stack height increases and the number of through-silicon vias (TSVs) rises, the likelihood of applying hybrid bonding grows.”
TSVs are the channels that vertically connect DRAM. An increase in the number of TSVs means these interconnect channels become denser. In the TC bonding method, these channels are connected with tiny metal spheres (micro-bumps). Hybrid bonding directly connects the copper wiring and dielectrics of the chips without micro-bumps, allowing the TSV pitch to be reduced to below a few micrometers (μm).
Professor Joo said, “Up to 16-high HBM, I believe heat can be managed even with TC bonding,” while adding, “When HBM goes from 20–24-high to 24–28-high and the number of TSVs doubles, hybrid bonding will be unavoidable.” He further noted, “According to Besi’s materials, hybrid bonding can improve HBM speed by 11.9 times and connection density by 15 times compared to conventional TC bonding.”
SK hynix Executive Vice President Kang-wook Lee also stated at an academic event hosted by the Korean Institute of Electronics Engineers last April that “hybrid bonding will be applied starting with next-generation HBM that stacks DRAM to 20-high.”
Professor Joo said, “Both SK hynix and Samsung Electronics have tried hybrid bonding,” adding, “SK hynix will continue using TC bonding as a strategy to maximize its current advantages, and the latecomer Samsung Electronics is expected to be the first to apply hybrid bonding.” In 2017, SK hynix co-developed the “Dual TC Bonder Tiger” equipment with Hanmi Semiconductor, and has stabilized process speed and yield with the mass-reflow molded underfill (MR-MUF) method. This is known to offer better productivity than Samsung Electronics’ non-thermal compression–conductive adhesive film (TC-NCF) method.
Samsung Electronics subsidiary SEMES is currently developing hybrid bonding equipment. Hanwha Semitek is preparing a second-generation hybrid bonding tool targeted for early next year. However, Hanmi Semiconductor’s launch timing for hybrid bonding equipment is said to be continuously pushed back. Recently, it announced a wide TC bonder with a fluxless function and plans to release it next year.
Inha University is also currently carrying out, together with LG Electronics, a project worth a total of KRW 7.5 billion titled “Development of innovative equipment technology for ultra-high-density hybrid-bonded stacking equipment for high-performance HBM semiconductors.” The project targets performance similar to Besi’s existing die-to-wafer hybrid bonding tool “Ultra Plus AC.”
Professor Joo stressed, “On the Chinese side as well, hybrid bonding equipment is being developed and introduced,” adding, “Domestic companies must develop technologies and equipment more aggressively to maintain their status as leading nations in HBM.”