PTAB

IPR2025-01433

ExCelLiance MOS Corp v. Force MOS Technology Co Ltd

Key Events

Petition

petition

Title: Trenched MOSFET with Trenched Source Contact
Brief Description: The ’634 patent relates to a trenched Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) structure designed to improve ohmic contact and reduce base resistance. The patent asserts its novelty lies in adding a distinct "lateral contact layer" along the sidewalls of the source contact trench, in addition to a conventional base contact layer at the trench bottom.

Prior Art Relied Upon: Hshieh (Application # 2006/0273384).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner argued that Hshieh discloses a nearly identical trenched MOSFET structure that meets every limitation of the challenged claims. Hshieh’s P+-doped region (128/228) is described as "surrounding" its source-body contact trench, which Petitioner contended necessarily covers both the trench sidewalls and the bottom. This single region in Hshieh corresponds to the claimed “lateral contact layer” (on the sidewalls) and “base contact layer” (at the bottom). For dependent claims, Petitioner asserted the doping concentration gradient of claim 2 is an inherent result of Hshieh’s disclosed fabrication process, where ion implantation onto sloped trench walls naturally results in lower doping than on the perpendicular trench bottom. Other dependent claims reciting features like Ti/TiN barrier layers and tungsten plugs were also argued to be expressly disclosed by Hshieh.
- Motivation to Combine (for §103 grounds): Not applicable as this is a single-reference ground. Petitioner argued Hshieh itself renders the claims obvious.
- Expectation of Success (for §103 grounds): Not applicable.

Prior Art Relied Upon: Uno (Patent 6,984,864).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner argued that Uno discloses a trench MISFET (a type of MOSFET) with all the structural features of the challenged claims. Uno’s P+-semiconductor region (23), described as a "back gate contact region," extends along the sidewalls and bottom of the source contact trench, thereby disclosing both the "lateral contact layer" and "base contact layer." As with Hshieh, Petitioner contended that the doping gradient required by dependent claim 2 is an inherent physical consequence of Uno’s disclosed use of ion implantation with its described trench geometry. Petitioner further argued that substituting industry-standard tungsten for Uno's disclosed aluminum contact plugs would have been an obvious design choice for a person of ordinary skill in the art (POSITA).
- Motivation to Combine (for §103 grounds): Not applicable as this is a single-reference ground. Petitioner argued Uno itself renders the claims obvious.
- Expectation of Success (for §103 grounds): Not applicable.

Prior Art Relied Upon: Hshieh (Application # 2006/0273384) and Uno (Patent 6,984,864).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner contended that Hshieh and Uno each independently render the claims obvious. Alternatively, if the Board were to find any limitation missing from one reference, the other would supply it. For example, if Hshieh were found not to teach a bottom metal layer, a POSITA would look to Uno’s explicit disclosure of a bottom drain electrode (35) to complete the structure. Both references disclose all other key features, including the layered MOSFET structure and a doped region surrounding the source contact trench.
- Motivation to Combine (for §103 grounds): A POSITA would combine Hshieh and Uno because both address the same technical field of vertical trench MOSFETs and disclose conventional, interchangeable components. The combination would involve the predictable application of known elements (e.g., Uno’s backside contact) to a known structure (Hshieh’s MOSFET) to achieve the well-understood goal of creating a functional device with low resistance.
- Expectation of Success (for §103 grounds): A POSITA would have had a high expectation of success, as the combination relies on implementing well-established silicon fabrication techniques common to both references.

"the bottom base of said trenches..." and "the sidewalls of said trenches...": Petitioner proposed that these terms be construed based on their spatial relationship, defined by a horizontal plane intersecting the lowest point of the trenches. Under this construction, the "sidewalls" are the portions of the trench within the base layer above this plane, and the "bottom base" is the region at or below this plane.
Importance: This construction is critical to the invalidity arguments. It allows Petitioner to argue that a single, continuous doped region in the prior art that "surrounds" a trench inherently discloses two distinct claimed elements: the "lateral contact layer" on the sidewalls and the "base contact layer" at the bottom.

Inherent Doping Gradient from Ion Implantation: A central technical contention was that the doping concentration gradient recited in claims 2 and 6 is an inherent and obvious result of the fabrication methods disclosed in Hshieh and Uno. Petitioner argued that the physics of perpendicular ion implantation into a trench with sloped sidewalls necessarily causes the flat bottom to receive a higher dopant dose than the angled sidewalls. This well-known physical principle, supported by expert testimony and simulations, allegedly renders the claimed doping relationship obvious even if not explicitly stated in the prior art.

Petitioner requests institution of an inter partes review and cancellation of claims 1-9 of the ’634 patent as unpatentable.