Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
Claim(s) 1-2 is/are rejected under 35 U.S.C. 103 as being unpatentable over Yamaguchi (hereinafter Yamaguchi, US 2018/0269278) in view of Hutzler et al. (hereinafter Hutzler, US 2024/0128329) and Hamada et al. (hereinafter Hamada, US 2019/0148485).
In regards to independent claim 1, Yamaguchi teaches a semiconductor device, comprising:
a semiconductor substrate of a first semiconductor type, the semiconductor substrate having a main surface (Yamaguchi, Fig. 8, Item 4, 21, “an n+-type semiconductor substrate”);
a drift layer of the first semiconductor type, provided at the main surface of the semiconductor substrate (Yamaguchi, Fig. 8, Item 22, “n−-type drift layer”);
a base layer of a second conductivity type, provided at a surface layer of the drift layer (Yamaguchi, Fig. 8, Item 7, “on a p-type base layer 7 ”);
an active region through which a main current flows (Yamaguchi, Fig. 8, Item 20, “an active region 20”), the active region having
a source region of the first semiconductor type, selectively provided in a surface layer of the base layer (Yamaguchi, Fig. 8, Item 8, “ n-type source region 8”),
a trench (Yamaguchi, Fig. 8, Item 51, “In the active region 20, a trench 51”), and
a gate electrode provided in the trench via a gate insulating film (Yamaguchi, Fig. 8, Item 6, 5, “the gate electrode 6 containing poly-silicon is embedded in the trench 51, via the gate insulating film 5”) and; and
a termination region surrounding a periphery of the active region (Yamaguchi, Fig. 8, Item 30, “edge termination region 30”), , the termination region having
a conductive film electrically connected to the gate electrode (Yamaguchi, Fig. 8, Item 15,6, “The gate wiring 15 is connected with the gate electrode 6”),
a field oxide film that insulates the conductive film and the drift layer from each other (Yamaguchi, Fig. 8, Item 16, “a LOCOS oxide film 16”),,
and
a contact hole that penetrates through the conductive film and reaches the field oxide film (Yamaguchi, Fig. 8, Item 53, “trench 53 is provided penetrating the interlayer insulating film 9 and the gate wiring 15”), wherein
the contact hole is embedded in the field oxide film such that a thickness of the field oxide film below the contact hole is thinner than a thickness of the field oxide film outside the contact hole (Yamaguchi, Fig. 8, Item C, [0037], “For example, the thickness of the part under the bottom of the gate contact C (the bottom of the trench 53) is 3 to 15% thinner than a thickness of the part where the gate contact C is not provided (a thickness of the LOCOS oxide film 16)”).
Yamaguchi fails to explicitly teach a trench reaching the drift layer from a surface of the source region. Hutzler teaches a trench reaching the drift layer from a surface of the source region (Hutzler, Fig. 4A Item 35 from Item 34 to 32). It would have been obvious to one of ordinary skill in the art, having the teachings of Yamaguchi and Hutzler before him before the effective filing date of the claimed invention, to modify the trench gate MOSFET taught by Yamaguchi to include the elongated trench of Hutzler in order to obtain a trench gate MOSFET whose trench reaches the drift layer. One would have been motivated to make such a combination because a deeper trenched can increase the channel length thereby reducing the on-resistance.
Yamaguchi fails to explicitly teaches the contact hole is 54 nm to 85 nm thinner than a thickness of the field oxide film outside the contact hole. Yamaguchi teaches the field oxide is 3 to 15% thinner than a thickness of the part where the gate contact C is not provided (Yamaguchi, [0037]). Hamada teaches the field oxide thickness is desirably in a range of 500 nm to 5 μm (Hamada, [0058]). It would have been obvious to one of ordinary skill in the art, having the teachings of Yamaguchi and Hamada before him before the effective filing date of the claimed invention, to modify the trench gate MOSFET taught by Yamaguchi to include the field oxide that is 500 nm to 5 μm of Hamada in order to obtain a trench gate MOSFET whose field oxide that is 15-750nm thinner in the contact hole. One would have been motivated to make such a combination because the field oxide thickness provided would reduce parasitic capacitive effects between the drift region and the conductive layer.
In regards to dependent claim 2, Yamaguchi teaches the semiconductor device according to claim 1, further comprising
a barrier metal covering sidewalls and a bottom of the contact hole (Yamaguchi, barrier metal, [0050]); and
a contact plug disposed in the contact hole on the barrier metal (Yamaguchi, tungsten plug, [0050]).
Allowable Subject Matter
Claims 3-9 are allowed.
The following is an examiner’s statement of reasons for allowance: The prior art fails to disclose or teach an obvious combination of the following limitations when taken with the claim as a whole:
Claim 3:
performing a heat treatment, thereby, forming an oxide film in the first contact hole in the active region and in the second contact hole in the termination region;
performing etching, thereby, removing the oxide film; and
forming a source electrode at the first contact hole in the active region and forming a gate metal electrode at the second contact hole in the termination region, wherein
the heat treatment is performed using a first gas containing oxygen only at a beginning of the heat treatment and during a period thereafter, the oxygen is cut.
Claim 4-9 depend upon and allowable claim; therefore, they are allowable.
Any comments considered necessary by applicant must be submitted no later than the payment of the issue fee and, to avoid processing delays, should preferably accompany the issue fee. Such submissions should be clearly labeled “Comments on Statement of Reasons for Allowance.”
Conclusion
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/WILLIAM C TRAPANESE/Primary Examiner, Art Unit 2812