How Lam Research is Tackling 3D NAND Scaling Challenges to 1,000 Layers

Traditional NAND flash memory relies on shrinking transistors in a two-dimensional plane, which is reaching its physical limits.

Introduction

The rise of AI applications is placing unprecedented demands on NAND storage, necessitating higher capacities to support memory-intensive processing and AI training models. While much focus has been placed on compute and new memory types like high-bandwidth memory (HBM), the scaling of 3D NAND remains a critical area of development.

The main reason why 3D NAND scaling remains critical despite the focus on compute and new memory types like HBM for AI applications boils down to two key factors:

Cost-Effectiveness: 3D NAND offers a very cost-effective way to store vast amounts of data. While HBM offers faster processing speeds, it’s significantly more expensive per unit of storage compared to 3D NAND. For storing the massive datasets and training models used in AI, 3D NAND with its high capacity and lower cost remains the more practical solution.

Cold Storage Needs: AI applications often use large datasets that aren’t accessed constantly but still need to be readily available. 3D NAND’s high density makes it ideal for efficiently archiving data in “cold storage,” where it can be retrieved when needed. HBM, which focuses on speed, better suits actively processed data.

The challenge for 3D NAND manufacturers is to continue increasing density and capacity while maintaining cost efficiency.

Recent breakthroughs in etch technology are proving essential to overcoming these challenges and pushing the boundaries towards 1,000-layer 3D NAND.

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Understanding the Scaling Challenge

As the industry progresses towards the 1,000-layer roadmap, the complexity of scaling increases significantly. This challenge is compounded by the need for precise high-aspect ratio (HAR) etching.

Traditional NAND flash memory relies on shrinking transistors in a two-dimensional plane, which is reaching its physical limits. 3D NAND overcomes this by stacking layers of memory cells on top of each other, allowing for higher density. However, this creates new challenges in the manufacturing process, particularly in the etching stage.

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Here’s how etch breakthroughs are addressing 3D NAND scaling challenges:

  • High Aspect Ratio (HAR) Etching: This is the most critical step, as it involves creating tiny holes (channels) through numerous layers to define the memory cells. Uniformity across all these layers is crucial. Advancements include pulsed power plasma technology that uses very short, high-power bursts to achieve precise etching.
  • Maintaining Profile, Selectivity, and Critical Dimension (CD): Etching needs to achieve the desired channel shape (profile) while not damaging surrounding materials (selectivity) and ensuring all channels are the same size (CD). This becomes tougher with more layers.

By tackling these etching hurdles, manufacturers can pave the way for 3D NAND with hundreds or even thousands of layers, significantly increasing storage capacity.

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An Analogy to Understand this

Imagine you’re building a high-rise apartment building to house more people (data) in the same amount of space (chip size). Regular NAND flash memory would be like a single floor building. 3D NAND is like a building with many floors stacked on top of each other.

The etching process is like carving out individual apartments in this multi-floor building. The challenges become:

  • High Aspect Ratio: Drilling perfectly straight and deep holes throughout all floors to create the rooms. Imagine drilling these holes so thin and deep that they could reach 4 times the height of the Burj Khalifa without wobbling!
  • Maintaining Design and Consistency: Making sure all the rooms across all floors are the same size and shape, and that drilling doesn’t damage the hallways or support beams (other materials on the chip). It’s like having a cookie cutter that can precisely cut identical rooms on every floor without affecting the building’s structure.

Etch breakthroughs are like developing new drilling techniques and tools to address these challenges. This allows us to build even taller buildings (more NAND layers) with perfectly designed and uniform apartments (memory cells), ultimately housing a much larger population (data) in the same amount of space.

Innovations in Etch Technology

Lam Research, a leader in etch technology, has been pivotal in addressing these challenges. With over 20 years as the dry plasma etch market leader and extensive experience in NAND HAR etching, Lam has etched more than 100 million NAND wafers.

Dr. Harmeet Singh, Group Vice President and General Manager of the Etch Product Group at Lam Research, emphasizes the importance of achieving near-perfect hole profiles for 1,000-layer 3D NAND.

Pulsed Power Plasma Technology

One of Lam’s solutions is pulsed power plasma technology, which uses high power in short bursts to increase ion energy while keeping average power constant.

Imagine etching those tiny channels in the 3D NAND like using a sandblaster to carve out delicate shapes in a block of wood. A regular sandblaster uses a continuous stream of sand particles, which can be too harsh and damage the wood around the desired design.

Pulsed power plasma technology is like using a more controlled sandblaster. Here’s how:

  • Regular Plasma Etching: This is like using a constant stream of sand particles. The etching process relies on ions (charged particles) in the plasma to remove material. However, with a constant flow, the ions can have too much energy, which can etch too quickly or damage surrounding areas.
  • Pulsed Power Plasma: This is like using short bursts of high-pressure air to propel the sand. Instead of a constant stream, the plasma delivers very brief, high-powered pulses. These short bursts allow for:
    • Increased Ion Energy: During the pulse, the ions are briefly accelerated to a higher energy, allowing them to etch the material more efficiently.
    • Lower Average Power: Since the pulses are short, the overall power used is lower. This helps to reduce heat generation and minimizes damage to unwanted areas. Think of it like using short, powerful blasts of air instead of a continuous stream, giving the wood a chance to rest in between.

By using these controlled bursts, pulsed power plasma technology allows for more precise etching, achieving the desired profile (shape) of the channels in the 3D NAND while minimizing damage to surrounding materials. It’s like having a more delicate sandblasting technique that can create intricate designs without ruining the overall structure.

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Cryogenic Etching

Lam has also developed cryogenic etching, using a special mixture of etch gases at temperatures below 0°C.

This process shifts from chemisorption to physisorption, increasing etching rates and enabling precise profile control without polymerizing gases.

Cryogenic etching delivers 2.5 times faster etch rates and double the profile precision compared to conventional HAR etching.

Understanding Cryogenic Etching

In the analogy of building a high-rise with tiny apartments (channels), Lam’s cryogenic etching is like using a special technique with cooler temperatures to achieve cleaner and more precise etching. Here’s a breakdown:

  • Regular Etching (Chemisorption): Imagine etching the channels is like gluing (chemisorption) tiny particles onto the material and then scraping them off. This can be messy because the glue might leave a residue or damage nearby areas if not controlled perfectly.
  • Cryogenic Etching (Physisorption): Cryogenic etching works differently. By using a special gas mixture at very cold temperatures (below 0°C), it changes the interaction between the gas and the material. Here’s what happens:
    • Colder Temperature: The cooler temperature reduces the “stickiness” of the gas molecules. Instead of forming strong chemical bonds (chemisorption) with the material, they create weaker physical bonds (physisorption).
    • Think of Velcro vs. Super Glue: Imagine switching from super glue (chemisorption) to Velcro (physisorption). Velcro holds things together, but it’s much easier to attach and detach without leaving a residue.

Real-World Impact and Future Prospects

Since its introduction into high-volume production in 2019, Lam’s cryogenic HAR etching technology has etched over five million wafers.

This technology is instrumental in transitioning NAND from 2D to 3D and scaling 3D NAND to new heights. With more than 7,500 HAR dielectric etch chambers in production, Lam continues to lead the way in etch innovation.

Why This Matters

The demand for higher capacity NAND storage is driven by advancements in AI and other data-intensive applications.

As technology evolves, the need for faster, more efficient, and higher-density storage solutions becomes crucial. Innovations in etch technology are essential for meeting these demands.

By overcoming the challenges of scaling 3D NAND to 1,000 layers, manufacturers can deliver storage solutions that support the growing needs of modern applications.

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Why It Is Important

  1. Meeting Industry Demands: Higher capacity and faster NAND storage are vital for supporting AI, 5G, and advanced computing. Innovations in etch technology ensure that storage solutions keep pace with these rapidly growing fields.
  2. Driving Technological Advancements: The ability to scale 3D NAND to 1,000 layers unlocks new possibilities for technology development, enabling more powerful and efficient devices. This drives progress in various sectors, including consumer electronics, telecommunications, and automotive technologies.
  3. Economic Impact: Efficient and scalable NAND storage contributes to the overall health of the semiconductor industry. It supports a wide range of applications, from everyday consumer devices to critical infrastructure, impacting global economies and industries.
  4. Sustainability and Cost Efficiency: As NAND technology scales, cost efficiency becomes increasingly important. Innovations that improve etching precision and efficiency help reduce production costs, making advanced storage solutions more accessible and sustainable.

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Conclusion

The journey towards 1,000-layer 3D NAND is marked by significant challenges and breakthroughs in etch technology. Lam Research’s advancements in pulsed power plasma and cryogenic etching are critical to achieving the necessary precision and efficiency for high-aspect ratio etching.

As the demand for higher capacity NAND storage grows, these innovations will play a crucial role in meeting the needs of AI applications and beyond.

Continued innovation in etch technology is key to enabling the future of 3D NAND, ensuring that the semiconductor industry can keep pace with the increasing demands of advanced computing applications.

Kumar Priyadarshi
Kumar Priyadarshi

Kumar Joined IISER Pune after qualifying IIT-JEE in 2012. In his 5th year, he travelled to Singapore for his master’s thesis which yielded a Research Paper in ACS Nano. Kumar Joined Global Foundries as a process Engineer in Singapore working at 40 nm Process node. Working as a scientist at IIT Bombay as Senior Scientist, Kumar Led the team which built India’s 1st Memory Chip with Semiconductor Lab (SCL).

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