Micron Technology Inc v. Yangtze Memory Technologies Co Ltd

1. Case Identification

• Case #: IPR2024-00790
• Patent #: 10,868,031
• Filed: April 18, 2024
• Petitioner(s): Micron Technology, Inc.
• Patent Owner(s): Yangtze Memory Technologies Company, Ltd.
• Challenged Claims: 1-5

2. Patent Overview

• Title: Multiple-Stack Three-Dimensional Memory Device and Fabrication Method Thereof
• Brief Description: The ’031 patent relates to multi-stack 3D NAND memory devices. The purported invention is a device structure that includes supporting pillars with aligned sidewalls and semiconductor channel structures with unaligned sidewalls, allegedly created by distinct one-step and two-step etch processes, respectively, to improve fabrication efficiency.

3. Grounds for Unpatentability

Ground 1: Claims 1-4 are obvious over Kim

• Prior Art Relied Upon: Kim (Patent 10,381,369).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Kim, which was not considered during prosecution, discloses all limitations of independent claim 1. Kim teaches a multi-stack 3D NAND device with a staircase structure, a surrounding filling structure, and both semiconductor channels and supporting "dummy structures." Critically, Petitioner asserted that Kim explicitly teaches that its channels are formed via a two-step etch process (one etch per stack), resulting in a "stepped profile" or unaligned sidewalls at the stack interface. In contrast, Kim teaches that its supporting pillars are formed via a single etch process after both stacks are formed, resulting in a "planar profile" or aligned sidewalls.
  • Motivation to Combine (for §103 grounds): As a single-reference ground, this section is not applicable. The argument was that Kim inherently discloses the claimed features, making them obvious.
  • Expectation of Success (for §103 grounds): This section is not applicable for a single-reference ground.

Ground 2: Claims 1-2 and 4-5 are obvious over Tessariol

• Prior Art Relied Upon: Tessariol (Application # 2019/0081061).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner contended that Tessariol, also not before the examiner, teaches all elements of the challenged claims. Tessariol discloses a multi-stack 3D NAND device featuring channel structures and supporting pillars (dummy structures and operative vias). Petitioner argued that Tessariol's figures and description show that the channel structures are formed by a two-step etch process, which inherently creates unaligned sidewalls due to etch tapering in each step. Conversely, Tessariol describes forming the supporting pillars via a single masking and etch step through both stacks, which would be understood by a Person of Ordinary Skill in the Art (POSITA) to produce aligned sidewalls.
  • Motivation to Combine (for §103 grounds): This section is not applicable for a single-reference ground.
  • Expectation of Success (for §103 grounds): This section is not applicable for a single-reference ground.

Ground 3: Claims 1-2 and 4-5 are obvious over Tessariol in view of Kim

• Prior Art Relied Upon: Tessariol (Application # 2019/0081061) and Kim (Patent 10,381,369).

• Core Argument for this Ground:

  • Prior Art Mapping: This ground used Kim to supplement Tessariol's disclosures. Petitioner argued that to the extent Tessariol's disclosure of certain features is implicit, Kim's express teachings make the combination obvious. Specifically, Petitioner asserted that a POSITA would look to Kim’s more efficient staircase structure to improve upon Tessariol’s design. Kim’s explicit disclosure that a two-step etch process results in misaligned channel sidewalls and a one-step etch process results in aligned pillar sidewalls would confirm the structures that are inherent in, but not explicitly stated by, Tessariol.
  • Motivation to Combine (for §103 grounds): A POSITA would combine Kim with Tessariol to improve Tessariol's design and better understand its structures. Petitioner argued a POSITA would be motivated to use Kim's more efficient staircase region, apply Kim's clear teachings on etch profiles to the same structures in Tessariol, and use Kim's conventional filling techniques.
  • Expectation of Success (for §103 grounds): A POSITA would have a reasonable expectation of success because both references describe the same fundamental 3D NAND structures, and the proposed modifications involved applying well-understood fabrication techniques from one device to a highly similar device.

• Additional Grounds: Petitioner asserted an additional obviousness challenge for claim 4 over Kim in view of Tessariol, arguing a POSITA would be motivated to modify Kim’s supporting pillars to use a conductive core and insulating liner as taught by Tessariol for improved structural support and dual-role (support and interconnect) functionality.

4. Key Technical Contentions (Beyond Claim Construction)

• Etch Process vs. Sidewall Profile: A central technical premise of the petition is that the sidewall alignment of a vertical structure in a multi-stack device is a direct and predictable result of the manufacturing process. Petitioner consistently argued that a two-step etch process (etching one stack, depositing the next, then etching the second) inherently results in "unaligned" or stepped sidewalls at the interface, while a single etch process through all stacks results in "aligned" or planar sidewalls.

5. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial under Fintiv is unwarranted. The scheduled trial date in the parallel district court litigation (December 1, 2025) is distant, ensuring the Final Written Decision (FWD) would issue well in advance. Investment in the parallel case was asserted to be minimal, with discovery in its infancy.
• Petitioner stipulated that, if the inter partes review (IPR) is instituted, it will not advance in the district court any invalidity ground that was raised or could have been reasonably raised in the petition, mitigating concerns of issue overlap.
• Petitioner also argued against denial under 35 U.S.C. §325(d), emphasizing that the primary references (Kim and Tessariol) are new and were never considered by the examiner. These references were argued to be highly material, as they directly teach the alleged point of novelty—unaligned channels and aligned pillars—that was the basis for allowance.

6. Relief Requested

• Petitioner requested institution of an IPR and cancellation of claims 1-5 of the ’031 patent as unpatentable under 35 U.S.C. §103.