PTAB

IPR2016-00635

Ricoh Americas Corp. v. Round Rock Research

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1. Case Identification

2. Patent Overview

  • Title: Semiconductor Device with Mixed Metal Silicide/Nitride Contact
  • Brief Description: The ’405 patent discloses a semiconductor device featuring a conductive contact for a component, such as a MOSFET. The invention centers on a contact composed of a metal silicide (e.g., titanium silicide) with a metal nitride (e.g., titanium nitride) interspersed throughout the silicide, including specifically at the interface with the silicon substrate.

3. Grounds for Unpatentability

Ground 1: Claims 1-3 are obvious over Byun 1996.

  • Prior Art Relied Upon: Byun (Journal of the Electrochemical Society, Jun. 1996).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Byun 1996 teaches all limitations of the challenged claims. Byun describes forming titanium silicide (TiSi2) contacts on silicon substrates for CMOS devices by annealing a titanium nitride (TiNx) film. Petitioner contended that Byun’s analytical results, particularly AES depth profiles (Fig. 2(d), 10(d)), XTEM images (Fig. 7, 17A), and HREM images (Fig. 8A), demonstrate that titanium nitride (TiN) precipitates are formed and interspersed throughout the resulting TiSi2 layer. Crucially, Petitioner asserted these figures show TiN is present at the boundary with the silicon substrate, thus teaching the key limitation of "metal nitride... including at a substrate-silicide interface."
    • Key Aspects: Petitioner emphasized that while the examiner considered Byun during prosecution, the examiner apparently overlooked these specific figures and the detailed structural analysis they provide. Petitioner framed its argument as presenting "new aspects" of Byun that were not previously addressed.

Ground 2: Claims 1-3 are obvious over Iwata.

  • Prior Art Relied Upon: Iwata (Patent 5,849,634).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner contended that Iwata teaches fabricating semiconductor transistors with a contact layer where TiN is intentionally formed between crystal grains of TiSi2. This is done to improve the film's heat resistance and prevent agglomeration during high-temperature processing. Petitioner argued that Iwata’s disclosure of TiN existing "in the grain boundaries of the formed silicide film" meets the claim limitation of a metal nitride being "interspersed with" and "throughout" the metal silicide. Because these grain boundaries exist throughout the film, they necessarily extend to the substrate-silicide interface, thereby disclosing all limitations of claim 1.

Ground 3: Claims 1-3 are obvious over Byun 1996 in combination with Iwata and Ogawa.

  • Prior Art Relied Upon: Byun (Journal of the Electrochemical Society, Jun. 1996), Iwata (Patent 5,849,634), and Ogawa (Japanese Application # JP 2-96374).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner asserted that Byun and Iwata independently teach the formation of TiSi2 contacts containing interspersed TiN. Ogawa was presented as reinforcing and extending these teachings. Ogawa explicitly discloses that introducing impurities like nitrogen into a silicide film prevents surface degradation, inhibits undesirable grain growth, and increases conductivity. Ogawa demonstrates these benefits even with low nitrogen concentrations (e.g., 0.05%) and provides data showing significantly improved sheet resistance compared to a nitrogen-free film.
    • Motivation to Combine: A POSITA would combine these references as they all address the same well-known problem in semiconductor manufacturing: improving the performance (i.e., electrical resistance and thermal stability) of silicide contacts. The references provide known, alternative, and mutually reinforcing solutions to this problem. Ogawa’s clear teaching on the benefits of adding nitrogen would motivate a POSITA to apply its principles to the contact formation processes described in Byun or Iwata.
    • Expectation of Success: A POSITA would have a high expectation of success, as combining the teachings involves the application of established techniques (adding nitrogen) to well-understood materials (titanium silicide) to achieve the predictable results of improved stability and conductivity, as explicitly taught by all three references.

  • Additional Grounds: Petitioner asserted an additional obviousness challenge against claims 1-3 based on the combination of Byun 1996 and Iwata. The arguments for this ground relied on the same rationale that both references provide known, alternative solutions to improve silicide contacts, making their combination obvious to a POSITA.

4. Key Claim Construction Positions

  • "substrate-silicide interface": Petitioner argued this term must be construed as "the boundary between the silicon substrate and the silicide." This construction was based on the patent's specification and statements made during prosecution. The position was critical to the invalidity arguments, as Petitioner's central contention was that the prior art disclosed metal nitride precisely at this boundary, which was the limitation added to secure allowance of the claims.
  • "contact comprising metal silicide interspersed with metal nitride...": Petitioner asserted that the open-ended term "comprising" means the contact can include other materials besides metal silicide and metal nitride. This construction was used to argue that the structures shown in the prior art, which may not be pure, fall within the scope of the claims.

5. Arguments Regarding Discretionary Denial

  • Petitioner preemptively argued against discretionary denial under 35 U.S.C. §325(d), which allows the Board to reject a petition that relies on art previously presented to the Office. While acknowledging that Byun 1996 was before the examiner, Petitioner contended that the examiner failed to appreciate the significance of specific figures (e.g., 7, 8A, 17A) showing the physical structure of the resulting contact. Petitioner argued that its analysis of these "new aspects" of Byun constituted substantially different arguments than those considered during prosecution, making a new review by the Board appropriate.

6. Relief Requested

  • Petitioner requested institution of an inter partes review and cancellation of claims 1-3 of Patent 6,147,405 as unpatentable under 35 U.S.C. §103.