PTAB

IPR2017-00919

GlobalFoundries U.S. Inc. v. Godo Kaisha IP Bridge 1

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1. Case Identification

2. Patent Overview

  • Title: Semiconductor Integrated Circuit with Copper Wiring Layer
  • Brief Description: The ’324 patent discloses a semiconductor integrated circuit with a two-layer diffusion-barrier film designed to prevent copper from a wiring layer from diffusing into underlying layers. The barrier is comprised of a first crystalline metal film containing nitrogen for adhesion to the copper and a second amorphous metal nitride film for superior diffusion blocking.

3. Grounds for Unpatentability

Ground 1: Claims 1-3, 5-7, and 9 are obvious over Ding in view of Zhang

  • Prior Art Relied Upon: Ding (Patent 6,887,353) and Zhang (Patent 5,893,752).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner asserted that Ding teaches nearly all elements of the challenged claims, including a two-layer TaNx/Ta barrier structure for use with copper interconnects. In Ding, a bottom amorphous tantalum nitride (TaNx) layer provides diffusion blocking, and an overlying top crystalline tantalum (Ta) layer provides good adhesion to a subsequent copper layer. Petitioner argued that the only element not explicitly disclosed in Ding is the presence of nitrogen in the top crystalline layer. This element, Petitioner contended, is supplied by Zhang. Zhang teaches a similar two-layer, tantalum-based diffusion barrier where a top "tantalum-rich tantalum nitride film" has a lower nitrogen content than the bottom film and is used for adhesion. Petitioner argued that a person of ordinary skill in the art (POSITA) would find it obvious to modify Ding’s structure with the teachings of Zhang. For dependent claims 2 and 3, which recite thickness ranges for the barrier films, Petitioner argued that Ding discloses broader or overlapping ranges. Selecting a specific thickness within those known ranges was presented as an obvious design choice for a POSITA balancing well-understood performance trade-offs like diffusion blocking, adhesion, and film stress.
    • Motivation to Combine: A POSITA would combine the teachings of Ding and Zhang to incorporate a small amount of nitrogen into Ding's top tantalum layer to achieve predictable and well-known technical benefits. Petitioner identified three primary motivations for this combination:
      • (1) Improved Polishing: Zhang taught that pure tantalum films are difficult to remove using chemical mechanical polishing (CMP). Adding nitrogen, as suggested by Zhang's "tantalum-rich nitride film," would make the top layer easier to polish, reducing the "dishing effect" and processing time.
      • (2) Enhanced Barrier Properties: It was known that nitrogen added to tantalum segregates at grain boundaries, which obstructs the fast diffusion paths for copper. A POSITA would be motivated to add nitrogen to Ding’s top layer to improve its overall performance as a diffusion barrier without significantly degrading adhesion.
      • (3) Reduced Resistivity: A POSITA would be motivated to add a small amount of nitrogen to the tantalum layer to reduce its electrical resistivity, thereby minimizing power consumption and RC delays in the final device, a known benefit in the art.
    • Expectation of Success: A POSITA would have had a high expectation of success in making this combination. The proposal involved applying known sputter-deposition techniques to well-understood materials to solve a known problem in semiconductor manufacturing. The result would be a predictable improvement, yielding a barrier with both the strong diffusion-blocking properties of Ding's amorphous layer and the enhanced adhesion and barrier performance of the nitrogen-containing crystalline layer suggested by Zhang. The art, including Zhang, confirmed that adding a small amount of nitrogen would not prevent the top layer from remaining crystalline, ensuring its primary function for adhesion was maintained.

4. Key Technical Contentions

  • Petitioner's central technical argument was that the sputter-deposition process described in both Ding and Zhang would inherently result in the claimed structure. Petitioner argued that a POSITA would understand that fabricating the barrier layers in a single vacuum cycle—where nitrogen gas is used for the first layer and then shut off for the second—would inevitably leave residual nitrogen in the chamber. This residual nitrogen would necessarily be incorporated into the subsequently deposited top tantalum layer. Therefore, even if not explicitly stated, Ding’s top tantalum layer would inherently contain nitrogen, making the claimed invention an obvious and unavoidable result of a known manufacturing process.

5. Arguments Regarding Discretionary Denial

  • Petitioner argued that the Board should not exercise discretionary denial based on redundancy with other concurrently filed or pending petitions (e.g., IPR2016-01249). The petition asserted that its invalidity ground (Ding in view of Zhang) is substantively different and not cumulative of grounds in other petitions that might assert obviousness based on Zhang in view of Ding. Petitioner maintained that because each ground starts with a different primary reference, relies on different disclosures to establish the claim elements, and presents distinct motivations to combine, they represent "equally compelling" but separate lines of reasoning that warrant independent consideration by the Board.

6. Relief Requested

  • Petitioner requested the institution of an inter partes review and the cancellation of claims 1-3, 5-7, and 9 of Patent 6,538,324 as unpatentable under 35 U.S.C. §103.