Ex Parte Zwieback et al

Patent Trial and Appeal Board

Jan 13, 2015

12067258 (P.T.A.B. Jan. 13, 2015)

UNITED STATES PATENT AND TRADEMARK OFFICE
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BEFORE
THE PATENT TRIAL AND APPEAL BOARD
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Ex parte ILYA ZWIEBACK,1
Donovan L. Barrett, and Avinash K. Gupta
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Appeal 2013-004298
Application 12/067,258
Technology Center 1700
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Before PETER F. KRATZ, MARK NAGUMO, and
N. WHITNEY WILSON, Administrative Patent Judges.

NAGUMO, Administrative Patent Judge.

DECISION ON APPEAL
Ilya Zwieback, Donovan L. Barrett, and Avinash K. Gupta
(“Zwieback”) timely appeal under 35 U.S.C. § 134(a) from a non-final
rejection2 of claims 1–8, which are all of the pending claims. We have
jurisdiction under 35 U.S.C. § 6. We reverse.

1 The real party in interest is listed as II-VI Incorporated. (Appeal Brief,
filed 9 October 2012 (“Br.”), 2.)
2 Office action mailed 9 May 2012 (“Office Action”; cited as “OA”),
following a Request for Continued Examination filed 27 February 2012.
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OPINION
A. Introduction3
The subject matter on appeal relates to processes of growing crystals
(claims 1–7), and to a crystal made by that process (claim 8). Although the
claims are not so limited, the ʼ258 Specification teaches that the process is
aimed at making semiconducting silicon carbide (“SiC”) wafers doped with
very low concentrations of nitrogen atoms, i.e., less than 1016 nitrogen
atoms/cm3. (Spec. 1 [0001].) Such substrates are said to be prepared by
physical vapor transport by sublimation at temperatures in excess of 2000°C,
followed by condensation on a seed crystal. (Id. at [0002].) The resulting
substrates are said to be useful for microwave devices. (Id. at [0001].)
According to the Specification, a major problem is that many
components in the growth chamber, including the susceptor (a material that
absorbs electromagnetic radiation and re-emits that energy as heat), the
crucible (that holds the SiC material to be sublimated), heat shields, and
thermal insulation, are made of graphite, which is very porous and capable
of absorbing large amounts of gas, including nitrogen, the main constituent
of the ambient atmosphere. (Id. at [0003].) Thus, graphite is said to be the
principal source of nitrogen contamination in the growth of SiC crystals.
(Id.) Even after known methods of removing nitrogen, SiC crystals grown

3 Application 12/067,258, Intra-cavity gettering of nitrogen in SiC crystal
growth, filed 20 August 2008, as the national stage of PCT/US06/37968,
filed 27 September 2006, claiming the benefit of a provisional application
filed 28 September 2005. We refer to the “ʼ258 Specification,” which we
cite as “Spec.”
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under these conditions are said to contain undesirable levels of nitrogen.
(Id. at [0004].)
The Specification teaches a three-step method culminating in in situ
gettering that exploits the ability of graphite to absorb preferentially nitrogen
from a mixture of nitrogen and an inert gas such as argon to remove residual
nitrogen from the chamber during crystal growth. (Spec. 3 [0016].)
In the first step, the fully loaded growth chamber and its contents are
degassed by evacuating the chamber to a pressure of 10−5 to 10−7 torr (1 torr
is 1/760 atmospheric pressure) (“first pressure,” or “P1”) and then heating
to ~1200°C (“first temperature,” or “T1”) for a period of 12 to 18 hours.
(Id. at [0018]–[0019].)
In the second step the graphite is activated—still more nitrogen is
removed—by filling the chamber with an inert gas such as argon to a
pressure of 500–600 torr (“second pressure,” or “P2”), and then heating to a
temperature (“second temperature,” or “T2”) that is 50°C to 150°C greater
than the desired sublimation temperature, which is typically between 2000
and 2400°C. (Id. at 3–4 [0021].) In the words of the Specification,
“[p]urging growth chamber 2 with the flow of inert gas reduces the nitrogen
content in the atmosphere of growth chamber 2 while the gas pressure of the
inert gas in growth chamber 2 avoids vapor transport from source
material 10 to seed crystal 12.” (Id. at 4 [0021].) That is, during this second
stage of heating at relatively high inert gas pressure, the SiC sublimates, but
few of the SiC gas molecules reach the seed crystal substrate due to the flow
of the inert gas.
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In the third step, the pressure in the growth chamber is reduced to
typical growth conditions of 1 to 100 torr of inert gas (“third pressure,”
or “P3”), and the temperature is reduced by 50 to 150°C to the desired
growth temperature (“third temperature,” or “T3”). (Id. at [0023].) Under
these conditions, vapor transport of SiC from the source to the seed crystal
can occur, while any residual nitrogen that contacts the activated graphite is
adsorbed preferentially. (Id.) The Specification teaches that “[t]his results
in a reduction of the nitrogen partial pressure in the chamber and,
accordingly, a reduction of nitrogen in the growing crystal.” (Id.)
Claim 1 is representative of the dispositive issues and reads:
A method of growing a crystal inside a crystal growth
chamber, said method comprising:
(a) providing a crystal growth chamber having therein
at least one component formed of a material that
absorbs at least one gas that is a donor impurity in the
growth of crystals in the chamber,
said chamber further including therein a source
material and a seed crystal;
(b) heating the interior of the chamber to a first, elevated
temperature in the presence of a first pressure whereupon
the combination of the first temperature and the first
pressure is sufficient to degas the at least one gas from the
component;
(c) exposing the interior of the chamber to an inert gas at a
second, elevated temperature in the presence of a second
pressure, wherein
the second temperature is higher than the first
temperature and higher than a third, desired crystal
growth temperature which is also higher than the first
temperature, and
the second pressure is greater than the first pressure;
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(d) reducing the inert gas pressure in the chamber to a third
pressure that is between the first pressure and the second
pressure; and
(e) lowering the temperature inside the chamber to the
third, desired crystal growth temperature whereupon the
source material sublimates (changes from a solid into a
vapor) and the vapor from said sublimation deposits on the
seed crystal,
wherein each of the first, second and third temperatures is
established by controlled heating of the interior of the
chamber.
(Claims App., Br. 13; some indentation, paragraphing, and emphasis added.)
Thus, the relative values of the pressures are P1 < P3 < P2, and the
relative values of the temperatures are T1 < T3 < T2.
The Examiner maintains the following grounds of rejection:4
A. Claims 1–7 stand rejected under 35 U.S.C. § 103(a) in view
of the combined teachings of Barrett,5 Tsvetkov,6 and
Winter.7
A2. Claim 8 stands rejected under 35 U.S.C. § 102(b) in view of
Barrett.

4 Examiner’s Answer mailed 4 December 2012 (“Ans.”).
5 Donovan L. Barrett et al., Method of making a low resistivity silicon
carbide boule, U.S. Patent No. 5,937,317 (1999). (Mr. Barrett is listed as an
inventor of the application in this appeal. Co-inventor Richard H. Hopkins
has submitted a declaration in this appeal: see page 6, n.8, infra).
6 Valeri F. Tsvetkov and David P. Malta, Method and apparatus for the
production of silicon carbide crystals, U.S. Patent Application Publication
2006/0254505 A1 (2006).
7 Charles H. Winter and T. Suren Lewkebandara, Process for coating with
single source precursors, U.S. Patent No. 5,425,966 (1995).
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B. Discussion
Findings of fact throughout this Opinion are supported by a
preponderance of the evidence of record.
Initially, we find that Zwieback devotes all substantive arguments for
patentability to claim 1. Accordingly, we focus our attention on those
arguments.
Briefly, the Examiner finds that Barrett describes an SiC crystal
growth process in which (using Zwieback’s notation):
P1 < P3 < P2
but that Barrett does not describe expressly the corresponding
temperatures, T1, T2, and T3. (OA 5–6.) The Examiner finds that Barrett
teaches that crystal “growth takes place only in the third step related to [P3]
and [T3],” and reasons that “hence, growth does not take place in the steps
of [T1] and [T2].” (Id. at 6, ll. 7–9.) The Examiner finds that Winter
illustrates that it is well-known “that sublimation temperature varies with the
pressure,” (id. at ll. 12–13) and concludes that it would have been obvious to
a person having ordinary skill in the art that, “for [the sublimation of] SiC,
temperature and pressure have a correlative relationship” (id. at ll. 14–15).
Applying these principles to the teachings of Zwieback, the Examiner
concludes that it would have been obvious “to adjust [P2] and [T2],
including wherein [T2] is higher than [T3], to the point at that will not
sustain crystal growth.” (Id. at 7, ll. 4–5.) The motivation to do so would
have been, the Examiner explains, to optimize degassing temperatures and
pressures; and “the determination of a workable or optimal range is routinely
practiced in the art.” (Id. at ll. 5–13.)
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The flaw in the Examiner’s findings, as Zwieback points out and as
supported by the declaration of Dr. Hopkins,8 is that a “correlative relation”
between temperature and pressure exists only in a closed system in
equilibrium where the ideal gas law is directly applicable, and the systems
taught by Barrett and by Winter are open, not closed. (Hopkins Decl. 6,
¶ 37.) Thus, rather than having a “correlated relationship,” the temperatures
and pressures (T1, P1), (T2, P2), and (T3, P3) are “completely independent
variables that are realized independently to achieve optimal process speed
and best quality crystal/coating.” (Id. at 5, ¶ 33.) The Examiner has not
directed our attention to substantial evidence of record that supports the
findings that the temperatures and pressures described by Barrett are
correlated in the manner found by the Examiner.
We therefore reverse the rejections for obviousness.
The Examiner relies on the conclusion that a product [an SiC crystal]
“that was made by the process as recited” in appealed claim 1 anticipates
product-by-process claim 8. (OA 3, ll. 1–3.)
As the premise that the process would have been obvious—or that it
has been described—has been shown to be faulty, and as the Examiner has

8 Declaration of Richard H. Hopkins, Ph.D., filed 27 February 2012
(“Hopkins Decl.”), during examination, and included in the Evidence
Appendix to the Brief. Dr. Hopkins is listed as a co-inventor on the Barrett
patent. Dr, Hopkins testifies regarding his extensive credentials as an expert
in the arts relevant to this application.
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not offered any other explanation of anticipation, we reverse the rejection of
claim 8 for anticipation.9
C. Order
We reverse the rejections of claims 1–8.
REVERSED

cdc

9 We have not overlooked the breadth of the appealed claims, which are not
limited as to the nature of the substrate, the composition of components of
the reactor, the inert gas, or the sublimated material. But broad claims are
not always obvious or anticipated by similar prior art. Rather, sufficiently
similar prior art must be identified and analyzed to demonstrate that the
differences between what is claimed and the prior art are such that the
claimed invention would have been obvious as of the date of invention.
35 U.S.C. § 103(a) [Pre-AIA]. Alternatively, a basis must be established
that a prior art material is sufficiently similar to the claimed material that the
burden is transferred to the Applicant to show that the reference material is,
more likely than not, not within the scope of the claimed material. In re
Best, 562 F.2d 1252, 1255 (CCPA 1977).