As semiconductor manufacturing processes evolve more gradually, 3D packaging emerges as an effective means of prolonging Moore’s Law and enhancing the computational prowess of ICs. Within the realm of 3D stacking technology, the Interuniversity Microelectronics Centre (imec) based in Belgium categorizes 3D integration technologies into four distinct types, each determined by different partitioning locations within a chip: 3D-SIP, 3D-SIC, 3D-SOC, and 3D-IC. Based on our previous discussion of 3D-SIP and 3D-SIC stacking, this article places a spotlight on the other two technologies: 3D-SOC and 3D-IC.

Related Article: Differences Between 3D-SIP and 3D-SIC: Why Are TSMC, Intel, and Samsung All Actively Involved?

3D-SOC

A System on Chip (SOC) involves the redesign of several different chips, all fabricated using the same manufacturing process, and integrates them onto a single chip. 3D-SOC takes this concept to new heights by stacking multiple SOC chips vertically. The image below illustrates the transformation of a 2D System on Chip (2D-SOC), where circuits are redivided into blocks, and then stacked to form a 3D System on Chip (3D-SOC).

Source: imec

imec’s research team previously published a paper on IEEE, outlining the advantages of 3D-SOC and backside interconnects. This technology aims to achieve the integration of diverse chips in a heterogeneous system. By intelligently partitioning circuits, it significantly reduces power consumption and boosts computational performance. In comparison to the trending chiplet technology, 3D-SOC holds a competitive edge.

Eric Beyne, IMEC’s Vice President of Research and Project Director for 3D System Integration, pointed out, “Chiplets involve separately designed and processed chiplet dies. A well-known example are high-bandwidth memories (HBMs) – stacks of dynamic random access memory (DRAM) chips. This memory stack connects to a processor chip through interface buses, which limit their use to latency-tolerant applications. As such, the chiplet concept will never allow for fast access between logic and first and intermediate level cache memories.”

However, it’s essential to acknowledge that 3D-SOC technology comes with apparent drawbacks, primarily higher research and development costs and a longer development timeline compared to 3D-SIP technology. Nevertheless, as applications like AIGC, AR/VR, 8K, and others continue to drive the need for high-speed computing, chips are relentlessly progressing towards higher efficiency, lower power consumption, and smaller size. In this context, 3D-SOC technology will maintain its place in advanced packaging.

Backside Power Delivery Network (BSPDN)

The technology of Backside Power Delivery Network (BSPDN) represents a pivotal development in semiconductor manufacturing, offering several advantages, including more flexible circuit design, shorter metal wire lengths, and higher chip utilization. After transforming a 2D System on Chip (2D-SOC) into a 3D-SOC through layered stacking, the original back sides of the chips become the outer sides of the 3D-SOC. At this stage, the “freed-up” backside of the chips can be utilized for signal routing or as power lines for transistors, in contrast to traditional processes where wiring and power lines are designed on the front side of the wafer.

In the past, backside chips were merely used as carriers, but BSPDN technology allows for more space to be used for logic wafer design. According to simulation results, the transmission efficiency of backside PDN is seven times higher than traditional front-side PDN. Intel has also announced the introduction of this technology in the 20Å and 18Å processes.

To achieve BSPDN, a dedicated wafer thinning process (reducing it to a few hundred nanometers) is required, along with nanoscale through-silicon vias (nTSV) to connect backside power to the front-side logic chip.

Another key technology for BSPDN is the Buried Power Rail (BPR), a miniaturization technique that embeds wires beneath the transistors, with some inside the silicon substrate and others in shallow trench isolation oxide layers. BPR replaces power lines and ground lines under standard cells in traditional processes and further reduces the width of standard cells, mitigating IR voltage drop issues.

The diagram below illustrates BSPDN, where backside PDN’s metal wiring is connected to Buried Power Rails (BPR), and the backside of the chip (BS) is connected to the front side of the logic chip (FS).

Source: imec

3D-IC

The final category, 3D-IC, employs new 3D sequential technology (S3D) or Monolithic technology to vertically stack n-type and p-type transistors, forming a Complementary Field-Effect Transistor (CFET). This technology enables two transistors to be stacked and integrated into the size of a single transistor. This not only significantly increases transistor density but also simplifies the layout of CMOS logic circuits, enhancing design efficiency. As seen in the diagram below, n-type and p-type transistors are integrated vertically to form a CFET.

Source: imec

Nevertheless, the key challenge lies in how to vertically integrate each minuscule transistor and address heat dissipation issues under high-speed computing. Major manufacturers are still in the development phase, but the technology’s biggest advantage lies in achieving the highest component density and the smallest node width, even without nodes. With the continuous increase in demand for high-speed computing, 3D-IC technology is set to become a focal point in the industry’s development.

3D Stacking Leading the Global Semiconductor Advancement

imec has outlined a roadmap for 3D stacking, aiming to reduce pitch spacings and increase point density within unit areas. However, imec also emphasizes that the development of 3D packaging technologies does not follow a linear timeline, as depicted in the figure above, as there is no single packaging technology that can cater to all requirements.

With the rapid development of applications such as AIGC, AR/VR, 8K, 5G, and others, a significant demand for computing power is expected to persist. To overcome the bottlenecks in semiconductor process technology, countries worldwide are fully engaged in advanced packaging research, and 3D stacking undoubtedly takes the center stage as the elixir for Moore’s Law continuation.

Explore More

• An In-Depth Explanation of Advanced Packaging Technology: CoWoS
• Intel and Samsung Join TSMC in Fierce Advanced Packaging Race
• Continuing Moore’s Law: Advanced Packaging Enters the 3D Stacked CPU/GPU Era
• Understanding Chiplets, SoC, and SiP: Why TSMC, Intel, Samsung Invest?

(Image: Samsung)

In recent developments, Samsung Foundry, a subsidiary of Samsung Electronics, has disclosed that it has initiated discussions with major chip clients, gearing up to provide services utilizing 1.4nm and 2nm processes.

It’s been said that Samsung being ahead in the production of 3nm GAA (gate-all-around) process, yet not as favored by major clients as TSMC. In response to the comment, Ki-tae Jeong, the CTO of Samsung Foundry, had share his insights at Semiconductor Expo 2023 in South Korea.

According to the Chosun Ilboon’s report, Jeong pointed out that in the semiconductor foundry industry, it typically takes approximately 3 years for major clients to make their final purchasing decisions. Samsung is actively engaging with prominent clients, and results may become evident in the coming years. Also, the company is currently discussing future processes such as 2nm and 1.4nm with major clients.

How are advanced semiconductor processes progressing?

Compared to mature processes, advanced processes are better suited for applications that demand high performance and low power consumption. With emerging technologies like AI and high-performance computing driving the industry, the demand for advanced processes continues to rise. Leading semiconductor companies are committed to developing new technologies, with chip advanced processes evolving from 5nm to 4nm and now down to 3nm, while looking ahead to the possibility of reaching 2nm and 1.4nm.

Current progress from major players:

Samsung
Samsung has already commenced mass production of its second-generation 3nm chips and aims to introduce the 2nm process by the end of 2025, with the 1.4nm process expected by the end of 2027.

TSMC
TSMC is planning to start production for N3P in the latter half of 2024, with N3X and the 2nm process set to enter mass production in 2025. TSMC will introduce Gate-all-around FETs (GAAFET) transistors for the first time at the 2nm process node, offering a 15% speed increase at the same power consumption and up to a 30% reduction in power consumption at the same speed, all while increasing chip density by more than 15%.

Intel
Intel is diligently pursuing its “Four Years, Five Nodes” plan. Presently, Intel 7 and Intel 4 are in mass production, and the Intel 3 process is expected to enter the readiness for production stage in the latter half of this year. Subsequently, Intel 20A and 18A processes are planned to enter the readiness for production stage in the first and second halves of 2024, respectively.

Moreover, industry experts believe that in the near term, Intel will focus on the Intel 3 process as its flagship offering in the advanced process semiconductor foundry sector to compete with TSMC, Samsung, and other players.

ASE Holdings conducted an earning conference on October 26th to unveil its Q3 financial results and offer insights into future business prospects. All eyes are on ASE’s progress in CoWoS advanced packaging. Joseph Tung, the Chief Financial Officer (CFO) of ASE, expressed confidence in AI and ongoing investments in advanced packaging, expecting a twofold increase in revenue share for advanced packaging in the coming year.

The market’s attention is keenly focused on wafer bank (a storage system used in semiconductor manufacturing to keep semiconductor wafers on hand for production, helping to streamline the manufacturing process) levels and inventory management. Tung mentioned that wafer bank levels are consistently declining and will further reduce Q4. With consumer electronics and computer clients gearing up to launch new products, inventory levels are expected to be maintained at a certain level. Overall, inventory reduction is nearing completion.

Tung emphasized that the real challenge lies not in inventory reduction but in the timing of the recovery in consumer demands and the impact of inflation. ASE remains cautious in its outlook for the upcoming year.

As for AI-related developments, Tung is optimistic about the expansion of CoWoS advanced packaging capacity through TSMC. ASE is also set to boost its production capacity for advanced packaging to cater to urgent customer demands. Next year, it is expected that revenue in advanced packaging will double. Tung emphasized that the AI era has already arrived and expects AI to extend to more terminal devices over the next few years. ASE has also invested in the development of Co-Packaged Optics (CPO) technology, ready to meet customer demands when the market is prepared.

To seize opportunities in advanced packaging, ASE previously introduced an Integrated Design Ecosystem (IDE) to optimize collaborative design tools through a platform, systematically enhancing advanced packaging architecture. This initiative has the potential to reduce design cycles by approximately 50%.

Tung pointed out that there are signs of a recovery in PC-related chip testing and packaging, and this year’s performance in automotive chip testing and packaging is expected to outperform other segments.

Looking ahead to future market conditions, Tung believes that the global semiconductor industry’s environment in the coming year will be more favorable than the current year.

(Image: ASE)

GlobalWafers has achieved a milestone by successfully advancing silicon carbide (SiC) crystal growth to 8-inch wafers, aligning with major international players in the industry. The company foresees the commencement of small-scale shipments of 8-inch SiC products in Q4 2024, with substantial growth expected in 2025, surpassing the proportion of 6-inch wafers by 2026.

Accourding to CTEE, Doris Hsu, Chairwoman of GlobalWafers, shared that the yield for 8-inch SiC crystal growth has been excellent, with ample room for further expansion, currently exceeding 50%.

The company emphasizes its readiness with 8-inch SiC crystal growth, cutting, grinding, and polishing capabilities, with sample deliveries set for the first half of next year.

Hsu highlighted customers’ eagerness for GlobalWafers to expedite the transition from 6-inch to 8-inch SiC production, aiming for an “8-inch dominant, 6-inch secondary” approach. The increasing demand for 8-inch SiC is primarily driven by automotive customers.

In terms of technology, SiC is moving from 6-inch to 8-inch wafers due to increased demand. TrendForce’s insights indicated, “Currently, the silicon carbide industry is mostly using 6-inch wafers, accounting for nearly 80% of the market share, while 8-inch wafers make up less than 1%. Expanding the wafer size to 8 inches is considered crucial for further reducing the cost of silicon carbide devices.”

From a cost perspective, 8-inch wafers indeed offer substantial advantages, but the challenge of yield has consistently plagued SiC. TrendForce’s earlier research suggests that, when it reaches maturity, an 8-inch wafer’s selling price is approximately 1.5 times that of a 6-inch wafer, and the number of die an 8-inch wafer can produce is about 1.8 times that of a 6-inch SiC wafer, significantly improving wafer utilization.

While GlobalWafers currently manufactures SiC substrates in Taiwan, the future SiC epitaxy will take place in the United States, with plans to expand with two additional substrate and two additional epitaxy facilities.

The production of SiC crystals involves high-temperature and closed-environment growth, which demands meticulous furnace design and crucible material selection, adding complexity to equipment and operations.

GlobalWafers has designed and developed specialized SiC crystal growth furnaces, enhancing material quality control and lowering crystal growth costs. SiC’s high hardness and brittleness make wafer processing challenging, but GlobalWafers employs higher process accuracy and more efficient wafer handling methods to achieve ultra-thin SiC wafer processing.

(Image: GlobalWafers)

According to Reuter’s report, the merger negotiations between Western Digital and Japan’s Kioxia Holdings have been terminated as the two companies could not reach an agreement on the terms. This potential merger aimed to create one of the largest memory chip manufacturers globally but faced obstacles in its path.

Notably, South Korea’s SK Hynix, a significant investor in Kioxia, expressed its opposition to the deal, citing concerns about its impact on investment asset value.

TrendForce’s Insights:

While the merger talks between Western Digital and Kioxia faced obstacles, primarily involving a major shareholder, SK Hynix, and disagreements over the acquisition price, it is still anticipated that such acquisitions will eventually materialize. This expectation is rooted in the broader context of the NAND Flash industry.

NAND Flash global demand has seen a decline in its growth rate, shifting from approximately 30% before 2020 to around 20% in recent years. Furthermore, TrendForce’s data reveals that in 2023, all NAND Flash suppliers have experienced their most significant operating losses since 2014. Given these challenges, NAND Flash suppliers are compelled to explore strategies to sustain their competitiveness in a changing industry landscape.

Explore more:

• After a Low Base Year in 2023, DRAM and NAND Flash Bit Demand Expected to Increase by 13% and 16% Respectively in 2024, Says TrendForce