Ex Parte Ryu et alDownload PDFPatent Trial and Appeal BoardSep 29, 201411331325 (P.T.A.B. Sep. 29, 2014) Copy Citation UNITED STATES PATENT AND TRADEMARK OFFICE ____________________ BEFORE THE PATENT TRIAL AND APPEAL BOARD ____________________ Ex parte SEI-HYUNG RYU, ANANT K. AGARWAL, and ALLAN WARD ____________________ Appeal 2012-007912 Application 11/331,325 Technology Center 2800 ____________________ Before ADRIENE LEPIANE HANLON, CATHERINE Q. TIMM, and JAMES C. HOUSEL, Administrative Patent Judges. TIMM, Administrative Patent Judge. DECISION ON APPEAL STATEMENT OF CASE Appellants seek review of the Examiner’s decision to reject claims 1– 8, 10, and 12–19 under 35 U.S.C. § 103(a) as obvious over Hideyuki1 in view of Kinoshita2 and Havemann3 and claim 6 over those references further 1 JP3147331, pub. June 24, 1991. We rely upon the English Abstract and Figures. Appellants state that they attached a machine translation of Hideyuki (Appeal Br. 5), but the document attached to the Appeal Brief does not appear to correspond to Hideyuki. Therefore, we do not rely upon that document. 2 US 6,831,345 B2, patented Dec. 14, 2004. Appeal 2012-007912 Application 11/331,325 2 in view of Akiyama.4 We have jurisdiction under 35 U.S.C. §§ 6(b) and 134(a). We AFFIRM. The claims are directed to an edge termination structure for a silicon carbide semiconductor device (see claims 1 and 13). Figure 14 illustrates one embodiment of the device and is reproduced below: Figure 14 is a cross-sectional illustration of a SiC Schottky diode having an edge termination according to some embodiments of the invention To further illustrate the invention and emphasize the limitations of the claim at issue in the appeal, we reproduce claim 1 with reference numerals from Figure 14, and important limitations italicized. 1. An edge termination structure for a silicon carbide semiconductor device, comprising: a plurality of spaced apart concentric floating guard rings [34] in a silicon carbide layer [30], the plurality of spaced apart 3 US 5,565,384, patented Oct. 15, 1996. 4 US 5,994,189, patented Nov. 30, 1999. Appeal 2012-007912 Application 11/331,325 3 concentric floating guard rings [34] at least partially surrounding a silicon carbide-based junction [52]; an insulating structure [56, 66] on a surface of the silicon carbide layer [30]; and a silicon carbide surface charge compensation region [38] between the floating guard rings [34] and adjacent the surface of the silicon carbide layer [30], wherein the surface charge compensation region [38] has a dopant concentration such that the surface charge compensation region [38] is substantially depleted by surface charges of the insulating structure [56, 66] and the surface charge compensation region [38] is fully depleted when a reverse bias lower than the blocking voltage of the device is applied to the device; wherein the insulating structure [56, 66] comprises a silicon nitride layer [56] on the silicon carbide layer [30], and an organic protective layer [66] on the silicon nitride layer [56], wherein the silicon nitride layer [56] is between the organic protective layer [66] and the silicon carbide layer [30], and wherein the organic protective layer [66] does not contact the silicon carbide layer [30]. (Claims Appendix at Appeal Br. 10 (emphasis added).) OPINION As a first matter, with respect to the rejection of all the claims over Hideyuki in view of Kinoshita and Havemann, Appellants do not argue any claim apart from the others. Therefore, for that rejection we select claim 1 as representative to decide the issue on appeal. The issue on appeal is: Have Appellants identified a reversible error in the Examiner’s determination that one of ordinary skill in the art would have constructed an edge termination structure including a silicon surface charge compensation Appeal 2012-007912 Application 11/331,325 4 region having the dopant concentration required by claim 1 when following the teachings of Hideyuki? The Examiner relies upon Hideyuki’s Figure 2 as depicting the edge termination structure. Figure 2 is reproduced below: Figure 2 of Hideyuki is a cross-sectional view of a high-breakdown-strength semiconductor device Hideyuki discloses the device as having a substrate 1 of N- conductivity, a first region 2 and second region (guard rings) 3 both having P+ conductivity, and a third region 8 of P- conductivity. The English Abstract of Hideyuki does not identify the composition of layer 7, but given the similarities of Hideyuki’s device to other devices with guard rings that have high breakdown strength, it was reasonable for the Examiner to find that Hideyuki would have suggested to one of ordinary skill in the art a device including an insulating layer at 7 (compare Hideyuki, Fig. 2 with Appellants’ Figure 1A and with Kinoshita, Fig. 21 (showing Appeal 2012-007912 Application 11/331,325 5 oxide layer 106 above guard rings 108 as explained in col. 1, l. 49 to col. 2, l. 27)). Hideyuki discloses forming the third region 8, i.e., the region between first region 2 and the second region (guard rings) 3, by a diffusion process (Hideyuki, Abstract). The third region 8 has an impurity concentration lower than that of the first region, i.e., region 2.5 Hideyuki states that “[b]y this structure, a breakdown strength can be improved.” (Hideyuki, Abstract.) Other than to say that the impurity (dopant) concentration is lower than that of the first region 2, Hideyuki does not identify the level of concentration of the dopant; nor does Hideyuki specifically state the concentration results in the depletions recited in claim 1. But the Examiner concludes that it would have been obvious to one of ordinary skill in the art at the time of the invention to obtain the concentration as recited in claim “in order to improve the device characteristics when operating the device.” (Ans. 7.) The basis for the conclusion: The concentration level is a mere matter of performing routine experimentation to optimize it for a desired result (id.). Indeed, parameters such as concentration are normally the type of variable one of ordinary skill in the art would be expected to optimize through routine experimentation. See In re Aller, 220 F.2d 454, 456 (CCPA 1955) (“Normally, it is to be expected that a change in temperature, or in concentration, or in both, would be an unpatentable modification . . . where 5 At one location within the English Abstract, Hideyuki identifies the third region with reference numeral 6; that is clearly a typographical error given the third region connects the first region 2 and second region 3. It is region 8 that so connects first region 2 and second region 3. Appeal 2012-007912 Application 11/331,325 6 the general conditions of a claim are disclosed in the prior art, it is not inventive to discover the optimum or workable ranges by routine experimentation.”) In the context of Hideyuki, one of ordinary skill in the art would have performed routine experimentation to find the optimal or workable concentrations that would result in a semiconductor device with the high breakdown strength and excellent switching characteristics Hideyuki desires (Hideyuki, Abstract). It appears that the low impurity concentrations suggested by Hideyuki are in-line with the dopant concentrations sought by Appellants to obtain the results they recite in claim 1 (compare Hideyuki, Abstract (concentrations lower than that of the first region in a device with guard rings) with Spec. ¶ 59 (concentration small enough so that the surface charge compensation regions can be completely depleted at a lower voltage, which may be required for the guard rings to function properly)). A preponderance of the evidence supports the Examiner’s determination that the dopant concentration required by claim 1 would have been arrived at through routine experimentation by one of ordinary skill in the art following the teachings of Hideyuki. This is sufficient to support a prima facie case of obviousness and shift the burden to Appellants to show that the concentration recited in the claim represents a range that is critical for obtaining an unexpected result. See In re Boesch, 617 F.2d 272, 276 (CCPA 1980); In re Woodruff, 919 F.2d 1575, 1578 (Fed. Cir. 1990); Aller, 220 F.2d at 456. Appellants present no convincing evidence of unexpected results on this record. Appeal 2012-007912 Application 11/331,325 7 Appellants present no persuasive arguments directed to the rejection of claim 6 over Hideyuki, Kinoshita, Havemann, and Akiyama. We sustain that rejection for the reasons presented above. CONCLUSION We sustain the Examiner’s rejections. DECISION The Examiner’s decision is affirmed. TIME PERIOD FOR RESPONSE No time period for taking any subsequent action in connection with this appeal may be extended under 37 C.F.R. § 1.136(a)(1). AFFIRMED cdc Copy with citationCopy as parenthetical citation