STMicroelectronics Inc v. Ocean Semiconductor LLC

1. Case Identification

• Case #: IPR2021-01349
• Patent #: 6,420,097
• Filed: August 20, 2021
• Petitioner(s): STMicroelectronics, Inc.
• Patent Owner(s): Ocean Semiconductor LLC
• Challenged Claims: 1-17

2. Patent Overview

• Title: Method for Trimming a Hardmask for Semiconductor Fabrication
• Brief Description: The ’097 patent discloses a method for fabricating semiconductor circuit features, such as gate lines, with linewidths smaller than what conventional lithography can achieve. The invention uses an intermediate hardmask layer positioned between a photoresist layer and a device layer, which is isotropically etched (trimmed) to be narrower than the overlying photoresist mask before being used to pattern the underlying device layer.

3. Grounds for Unpatentability

Ground 1: Obviousness over Chapman in view of AAPA or Hause - Claims 1-9 and 16-17 are obvious over Chapman in view of AAPA or Hause.

• Prior Art Relied Upon: Chapman (5,976,769), Applicant Admitted Prior Art (“AAPA”), and Hause (5,885,887).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Chapman taught the core inventive concept of the ’097 patent: a three-step etching process for creating sub-lithographic patterns. This process includes (i) an anisotropic etch of an intermediate hardmask layer, (ii) a timed isotropic etch to laterally trim the hardmask, making it narrower than the overlying resist, and (iii) an anisotropic etch of an underlying device layer using the trimmed hardmask. This mapping addresses the primary limitations of independent claim 1.
  • Motivation to Combine (for 35 U.S.C. §103 grounds): Petitioner asserted that the ’097 patent itself, through its AAPA disclosures, acknowledged that ultra-thin resist (UTR) layers were well known for achieving better pattern resolution. A POSITA would combine Chapman’s trimming process with a UTR layer, as also taught by Hause, to gain the known and predictable benefits of improved patterning accuracy and better process control. Hause specifically explained that thicker resist layers, like the one in Chapman, could inaccurately replicate image patterns, providing a clear reason to substitute a thinner UTR layer.
  • Expectation of Success (for §103 grounds): A POSITA would have reasonably expected success in using a UTR layer with Chapman’s process, as it was a known technique for improving the very type of lithographic patterning Chapman addressed.

Ground 2: Obviousness over Laaksonen in view of AAPA or Hause - Claims 1-2, 4-9, 12-15, and 17 are obvious over Laaksonen in view of AAPA or Hause.

• Prior Art Relied Upon: Laaksonen (6,362,111), AAPA, and Hause (5,885,887).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner presented Laaksonen as an alternative primary reference that also disclosed the key features of the ’097 patent. Laaksonen taught a process for forming polysilicon lines with linewidths below lithography limits by using a hardmask (a bottom anti-reflective coating, or BARC) between resist and polysilicon layers. Laaksonen’s process involved an anisotropic etch of the BARC followed by an isotropic overetch that introduces a "horizontal component" to reduce the hardmask’s width, which is then used to etch the underlying polysilicon.
  • Motivation to Combine (for §103 grounds): The motivation to combine Laaksonen with a UTR layer from Hause or AAPA was argued to be the same as in Ground 1. A POSITA would seek to improve the patterning accuracy of Laaksonen’s process by replacing its conventional resist layer with a UTR layer, thereby achieving more precise replication of the image pattern, a known benefit of using UTRs.
  • Expectation of Success (for §103 grounds): The combination was argued to be a predictable substitution of one known element (a standard resist) with another (a UTR) to obtain expected improvements in lithographic accuracy.

Ground 3: Obviousness over Core References and Secondary Art - Claims 10-15 are obvious over Chapman, AAPA or Hause, in view of additional references.

• Prior Art Relied Upon: The combination from Ground 1, plus Becker (a 1999 SPIE proceeding paper), Jeoung (6,358,672), Wong (6,319,655), Lin (a 1999 SPIE proceeding paper), or Cirelli (a 1996 journal article).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground built upon the Chapman/Hause combination to address dependent claims reciting specific resist treatments and hardmask structures. For claims 10-11, which require treating the resist to "enhance selectivity," Petitioner pointed to Becker, Jeoung, and Wong, which taught using UV baking or electron beam curing to stabilize resist and improve its etch resistance. For claims 12-15, which require a multi-layer hardmask, Petitioner cited Lin and Cirelli, which taught using multi-layer anti-reflective coatings with underlying etch-stop layers.
  • Motivation to Combine (for §103 grounds): A POSITA would combine these secondary references to solve known problems or achieve predictable benefits. Applying resist stabilization techniques from Becker would predictably improve the resist's performance during the hardmask etch. Similarly, incorporating a multi-layer hardmask from Lin or Cirelli would provide the known benefits of an etch-stop function and simplified manufacturing control.
• Additional Grounds: Petitioner asserted additional obviousness challenges based on combinations of Laaksonen with Chapman and the secondary references (Becker, Jeoung, Wong) to address the remaining claims.

4. Arguments Regarding Discretionary Denial

• Petitioner argued against discretionary denial under 35 U.S.C. §325(d), asserting that the primary references central to its petition—Chapman and Laaksonen—were never presented to or considered by the PTO during the original prosecution. Petitioner contended these references teach the exact three-step etching process that the examiner found to be missing from the art of record.
• Petitioner also argued against discretionary denial under Fintiv, stating that the co-pending district court case is in an early phase with a target trial date that is uncertain and likely to slip past the IPR’s statutory deadline for a Final Written Decision. Further, Petitioner argued that the IPR is more comprehensive, challenging all 17 patent claims while only claims 1-14 and 17 are asserted in the litigation, making the IPR a more efficient vehicle for resolving the patentability dispute.

5. Relief Requested

• Petitioner requests the institution of an inter partes review and the cancellation of claims 1-17 of Patent 6,420,097 as unpatentable.