Prior art

To identify the most relevant prior art for US patent 7,629,634, I will examine the patent citations listed within the patent document itself. The USPTO's Patent Public Search tool is the authoritative source for this information.

The full patent text of US7629634B2 explicitly cites one prior art patent: US6888196B2.

Here's the analysis of that prior art reference:

Full Citation: US6888196B2: Vertical MOSFET reduced in cell size and method of producing the same.
Publication Date: 2005-05-03
Filing Date: 2002-04-24
Assignee: Nec Electronics Corporation

Brief Description:
US6888196B2 describes a vertical MOSFET structure designed to reduce cell size. It focuses on a trench gate field effect transistor and its manufacturing method. The patent details a structure that includes a semiconductor substrate, an epitaxial layer, a body region, and a source region, with trench gates extending through the body and source regions into the epitaxial layer. It also describes source contact regions. The invention aims to reduce the on-resistance and improve switching characteristics by optimizing the cell layout and structure, potentially through techniques like self-aligned contacts and specific doping profiles.

Potential Anticipation under 35 U.S.C. § 102:
US6888196B2 potentially anticipates aspects of Claim 1 and Claim 6 of US7629634B2.

• Claim 1: This prior art discloses many elements recited in Claim 1, such as a semiconductor region with a silicon substrate, epitaxial layer (drain), base layer (body), and source layer, stacked in sequence. It also describes front and back metal layers, trenched gates extending into the epitaxial layer, and source contact trenches. The key distinguishing feature of US7629634B2's Claim 1 is the presence of a "lateral contact layer" at the sidewalls of the source contact trenches and a "base contact layer" at the bottom of these trenches. The description of US6888196B2 would need to be thoroughly reviewed to determine if any elements, even implicitly, describe or suggest such distinct lateral and base contact layers within the source contact trenches that would perform the same function, particularly in terms of improving ohmic contact and ruggedness, as described in US7629634B2. Without explicit disclosure of such distinct, specifically doped lateral and base contact layers in US6888196B2, it is unlikely to directly anticipate this novel aspect of Claim 1.

• Claim 6: Similar to Claim 1, US6888196B2 would likely disclose the general inverted doping types (P-type substrate, epitaxial, source; N-type base and lateral contact). However, the specific arrangement and doping concentrations of the N-type lateral contact layer and N-type base contact layer, particularly the distinction in doping concentration between them (lateral having less doping than the bottom base contact layer), would be critical for anticipation. If US6888196B2 does not explicitly disclose or suggest this differentiated doping for distinct lateral and base contact layers in the source trenches, it would not anticipate this claim element.

The inventive step of US7629634B2, as highlighted in its description, is providing a lateral contact layer in the MOSFET for avalanche improvement, specifically addressing the poor ohmic contact at the sidewall of source contact trenches in prior art, which led to poor ruggedness and parasitic bipolar turn-on. Therefore, the novelty of US7629634B2 largely hinges on the specific structure and doping of this lateral contact layer to achieve improved ohmic contact and reduced base resistance.