PTAB

IPR2021-00177

Microchip Technology Inc v. Bell Semiconductor LLC

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Method for Forming a Silicide Block
  • Brief Description: The ’669 patent describes a method for fabricating semiconductor devices, specifically a dual-layer "salicide block" process to selectively prevent silicidation on certain areas like resistors. The method uses a thin oxide film as a precise etch stop beneath a block dielectric layer (e.g., Si3N4 or SiON) to provide improved control over conventional single-layer, timed-etch processes.

3. Grounds for Unpatentability

Ground 1: Obviousness over Wu - Claims 1-3, 5-9, and 13-19 are obvious over Wu.

  • Prior Art Relied Upon: Wu (Patent 6,586,311).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Wu disclosed all elements of independent claims 1 and 16 except for one specific process sequence. Wu taught a nearly identical salicide block method, including disposing an oxide buffer layer on a wafer, depositing a silicon nitride dielectric layer over the oxide, using a patterned photomask to protect a passive resistor region, and etching the nitride layer using the oxide as an etch stop. However, Wu did not explicitly state the order of removing the photomask relative to removing the exposed oxide film before the final silicidation step.
    • Motivation to Combine (for §103 grounds): Not applicable (single reference). However, for the missing step, Petitioner argued that removing the mask before or after the oxide cleaning dip were the only two viable options. A person of ordinary skill in the art (POSITA), motivated by the known need to improve fabrication processes, would have found it obvious to try both simple, predictable sequences.
    • Expectation of Success (for §103 grounds): A POSITA would have had a clear expectation of success in trying either removal sequence, as both would predictably result in either a hard mask process or a protected photoresist process, both of which were well-understood techniques.

Ground 2: Obviousness over Wu and Pradeep - Claims 1-3, 5-9, and 13-15 are obvious over Wu in view of Pradeep.

  • Prior Art Relied Upon: Wu (Patent 6,586,311), Pradeep (Patent 6,277,683).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground asserted that Wu taught all limitations of independent claim 1, except for the explicit sequence of removing the block mask before removing the exposed portions of the oxide film. Petitioner introduced Pradeep to supply this missing element. Pradeep was cited for its express teaching of a process where a photoresist mask is removed (via plasma ashing or wet strip) before a subsequent wet etch is performed to remove the exposed underlying oxide layer.
    • Motivation to Combine (for §103 grounds): A POSITA would combine Wu and Pradeep because both patents address the same problem of improving selective salicide formation by using a multi-layer blocking structure. Pradeep’s clear teaching of the mask-then-oxide removal sequence provided a known, predictable, and finite solution to complete the process disclosed in Wu.
    • Expectation of Success (for §103 grounds): Petitioner contended that a POSITA would have a high expectation of success, as incorporating Pradeep's conventional process step into Wu's highly similar fabrication framework would predictably expose the desired silicon areas for silicidation without altering the function of either process.

Ground 5: Obviousness over Wu and Lee - Claims 16-19 are obvious over Wu in view of Lee.

  • Prior Art Relied Upon: Wu (Patent 6,586,311), Lee (Patent 6,586,332).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground challenged independent claim 16, which recites a method for protecting a resistor that "projects above the surface of the semiconductor substrate." While Petitioner argued Wu taught the core elements, Lee was introduced to provide stronger and more explicit teachings. Lee expressly disclosed forming a discrete polysilicon resistor that projects above a substrate surface and then forming a multi-layer blocking structure over it, directly mapping to limitations 16[a] and 16[b]. Further, Lee taught that its selectively etched blocking layer (SiC) could function as a hard mask, satisfying the "create a hard mask" limitation of 16[e].
    • Motivation to Combine (for §103 grounds): A POSITA would have been motivated to combine the references, as both provide solutions for protecting semiconductor elements during silicidation. Petitioner argued it would have been a simple and obvious substitution to use Lee's well-defined discrete poly resistor in place of Wu's more generalized epitaxial layer resistor, while still using Wu’s effective dual-layer blocking process for protection.
    • Expectation of Success (for §103 grounds): The combination was argued to be predictable. A POSITA would understand that Wu's two-layer (oxide/nitride) salicide block process would be equally effective at protecting Lee's discrete resistor as it was for its own, as the underlying materials and fabrication principles are fundamentally the same.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including combinations of Wu, Pradeep, and Lee for claims 3-4 (distinguishing poly vs. island resistors); Wu, Pradeep, and Chou for claims 10-12 (adding endpoint detection); and separate challenges based on Pradeep and Lee as the primary combination.

4. Arguments Regarding Discretionary Denial

  • Petitioner argued that discretionary denial under the Fintiv factors was unwarranted. The petition asserted that the parallel district court proceeding was in its infancy, with a trial date that was not firm and was likely to occur after a Final Written Decision in the IPR. Petitioner also stipulated not to pursue in district court any invalidity ground raised or that could have been reasonably raised in the IPR, thereby preventing duplicative efforts and overlap between the proceedings.

5. Relief Requested

  • Petitioner requested institution of an inter partes review and cancellation of claims 1-19 of Patent 6,743,669 as unpatentable under 35 U.S.C. §103.