Ex Parte Frohberg et alDownload PDFPatent Trial and Appeal BoardSep 26, 201412359839 (P.T.A.B. Sep. 26, 2014) Copy Citation UNITED STATES PATENT AND TRADEMARK OFFICE ____________________ BEFORE THE PATENT TRIAL AND APPEAL BOARD ____________________ Ex parte KAI FROHBERG, VOLKER GRIMM, HEIKE SALZ, and HEIKE BERTHOLD ____________________ Appeal 2012-007144 Application 12/359,839 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– 3, 5–12, and 24–34. We have jurisdiction under 35 U.S.C. §§ 6(b) and 134(a). We REVERSE. Representative claim 1, with the limitation at issue italicized, is reproduced below: 1. A method, comprising: Appeal 2012-007144 Application 12/359,839 2 forming a dielectric layer stack above a first transistor and a second transistor, said dielectric layer stack comprising a first stress-inducing layer and an etch control layer formed above said first stress-inducing layer; performing an etch sequence for selectively removing a portion of said dielectric layer stack from above said second transistor; concurrently recessing metal silicide regions in the second transistor and reducing a size of a sidewall spacer structure formed on sidewalls of a gate electrode structure of said second transistor, while maintaining a sidewall spacer structure formed on sidewalls of a gate electrode structure of said first transistor; forming a second stress-inducing layer above said first and second transistors; and removing a portion of said second stress-inducing layer from above said first transistor by using said etch control layer as an etch stop material. (Claims Appendix at Appeal Br. A-1 (emphasis added).) Claim 24, the only other independent claim on appeal, similarly requires “said reducing being concurrent with forming recesses in metal silicide regions in the first transistor.” (Claims Appendix at Appeal Br. A-3.) The Examiner rejects claims 1 and 24, along with various dependent claims, under 35 U.S.C. § 103(a) as obvious over Yang1 in view of Smith2 (Ans. 4–6). The Examiner further refers to Choi3 in responding to Appellants’ arguments (Ans. 9–10). 1 Yang et al., US 2007/0108525 A1, pub. May 17, 2007. 2 Smith, US 6,255,180 B1, patented July 3, 2001. 3 Choi et al., US 6,437,411 B1, patented Aug. 20, 2002. Although the Examiner did not include Choi in the statement of the rejection, Appellants’ arguments evince an understanding of the Examiner’s reliance upon Choi. Appeal 2012-007144 Application 12/359,839 3 The Examiner finds that Yang teaches a method including the claimed steps of forming, performing, forming and removing, and further finds that Yang teaches reducing the size of a sidewall spacer structure formed on sidewalls of the gate electrode structure of the second transistor as also required by claim 1 (Ans. 5). There is no question that Yang does not expressly disclose recessing metal silicide regions in the second transistor concurrently with the step of reducing the size of the sidewall spacer structure (Ans. 5). Rather, the Examiner finds this recessing step to be inherent in the process of Yang in view of Smith (Ans. 5–6). The Examiner’s inherency finding is based upon the fact that Yang teaches reducing the size of the sidewall spacer structure by etching with CHF3 (Ans. 5, citing Yang ¶ 59). According to the Examiner, Smith teaches that a plasma provided with CHF3 can be used (Ans. 5). The Examiner concludes that it would have been obvious to one of ordinary skill in the art at the time the invention was made to reduce the size of the nitride sidewall spacer structure of Yang by etching with plasma provided with CHF3 as taught by Smith and so etching would concurrently recess the metal silicide regions of Yang at least to a certain degree (Ans. 5–6). To support the inherent nature of the metal silicide etching, the Examiner also points out that Choi teaches using a plasma etching technique with, for instance, CHF3 gas, to etch a metal silicide layer (Ans. 9). In general, a limitation is inherent “if it is the ‘natural result flowing from’ the explicit disclosure of the prior art.” Schering Corp. v. Geneva Pharms., 339 F.3d 1373, 1379 (Fed. Cir. 2003) (quoting Eli Lilly & Co. v. Because the Examiner’s error was harmless, we consider Choi in rendering our Decision. Appeal 2012-007144 Application 12/359,839 4 Barr Labs., Inc., 251 F.3d 955, 970 (Fed. Cir. 2001)). “Inherency ... may not be established by probabilities or possibilities. The mere fact that a certain thing may result from a given set of circumstances is not sufficient.” MEHL/Biophile Int’l Corp. v. Milgraum, 192 F.3d 1362, 1365 (Fed. Cir. 1999) (quoting In re Oelrich, 666 F.2d 578, 581 (CCPA 1981)). This is not to say that the step of recessing must always occur in every embodiment of the method taught by Yang in order to be inherent; it is possible to establish inherency by establishing that it would have been obvious to select plasma etching using CHF3 as taught by Smith, but the Examiner must establish that once this selection is made, recessing the metal silicide regions will always occur. See Hewlett-Packard Co. v. Mustek Sys., Inc., 340 F.3d 1314, 1326 (Fed. Cir. 2003) (the fact that changing one setting on a prior art scanner would cause the scanner to behave in a different manner than claimed did not defeat a finding of inherency given there was no dispute that another setting resulted in the claimed operation). Yang is particularly concerned with the effects of etching with chemicals such as CHF3 on the metal silicide contact 28. According to Yang, some damage may take place within silicide contact 28 when etching away the nitride stress inducing liner 30 using etching chemicals such as CHF3 (Yang ¶ 58). According to Yang, this damage consists of at least some part, particularly a surface region, of the silicide becoming amorphorized (id.). As pointed out by Appellants, amorphorization involves a change in phase from crystalline to amorphous (Appeal Br. 6). The Examiner provides no evidence that such a phase transition results in recessing of the metal silicide regions. Appeal 2012-007144 Application 12/359,839 5 Even though Yang points out a concern with damaging the metal silicide contact, and further teaches a step of etching the nitride spacers with similar etchants as used to etch the nitride liner 30, Yang is completely silent with regard to any etching or recessing of the silicide contact (Yang ¶¶ 58– 59). This is some evidence that recessing it not necessarily occurring, but not a level of evidence that indicates the Examiner’s inherency finding is unreasonable. More importantly, the evidence as a whole supports Appellants’ argument that recessing does not necessarily occur when plasma etching a nitride spacer with CHF3 as taught by Smith because the ability of an etching process to remove one type of material, and the selectivity of the etching process to this type of material in relation to other types of material, is determined by the parameters of the etching process such as the type of etchant, the flow rate of the etching gas, the temperature, and the pressure. (Appeal Br. 7.) Yang is not specific as to the type of etching used to etch the spacers, but discloses a number of chemicals typically used when the spacer is comprised of a nitride (Yang ¶ 59). Specifically, Yang lists CH2F2, CHF3, CH3F, and O2 (id.). Again, Yang does not disclose any removal or recessing of the metal silicide contact (id.). Smith teaches anisotropic etching a nitride layer to form sidewall spacers using a plasma provided with a carbon-containing species, e.g., CHF3, C2H2F4, and/or a fluorocarbon, e.g., C2F6 (Smith, col. 6, ll. 53–57). Smith also is silent with respect to any etching of metal silicide. Appeal 2012-007144 Application 12/359,839 6 Choi teaches an isotropic dry etching of a metal silicide layer by a plasma etching technique used with at least one of CF4, C2F6, CHF3, CO, Ar, O2, N2, and He-O2 gas in, for instance, a transformer coupled plasma source type apparatus or a decoupled plasma source type apparatus (Choi, col. 13, ll. 3–8). Choi discloses specific gas mixtures, flow rates, temperatures, and pressures and sets conditions to obtain specific etching rates in lateral and vertical directions (Choi, col. 13, ll. 9–23). Given that Yang selects the etching parameters to etch the nitride of the spacers and is silent with respect to any etching of the silicide, it follows that one of ordinary skill in the art would have selected the etching parameters to etch the nitride rather than the silicide and Smith and Choi do not provide evidence that, despite those efforts to limit etching to the nitride, etching of the silicide would still occur. We cannot say that the Examiner has provided the level of evidence required to support the finding of inherency. The Examiner applies further prior art references to reject other dependent claims, but the Examiner does not rely upon those references in a way that overcomes the deficiency discussed above. Therefore, we do not sustain the Examiner’s rejections. DECISION The Examiner’s decision is reversed. REVERSED cdc Copy with citationCopy as parenthetical citation