1. INTRODUCTION
 
  In Japan, whether or not a claimed invention has an inventive step is determined based on whether or not those skilled in the art would have easily arrived at the invention from prior arts (e.g., publicly known prior arts, publicly worked prior arts, and prior arts disclosed in a distributed publication) as of the reference date, i.e., before filing of the patent application.

  In detail, the determination of inventive step is made as following steps: (1) specifying the claimed invention and a primary cited prior art; (2) comparing the configuration of the claimed invention with the primary cited prior art to specify identical features and differences therebetween; and (3) determining whether or not those skilled in the art would have easily arrived at the differences, and if this determination result is YES, the inventive step is denied, on the other hand, if NO, the inventive step is affirmed.

  According to the Japanese practice, in some cases, whether or not a configuration related to the difference is a well-known art may be disputed in the step (3), and how the well-known art is specified may have a great influence on the determination of the inventive step.

  Thus, grasping points to note in specifying the well-known art is very useful in the determination of the inventive step.

  In this News Letter, we introduce a court case of which one of disputed issues is whether or not the specification of a well-known art is appropriate in the determination of inventive step.

2. COURT CASE
(Decision of the Intellectual Property High Court made on March 19, 2020 (2019 [administrative litigation case, the first instance] No. 10100))

2-1. Outline of Case
  The Plaintiff is the patentee of JP6,252,092B titled "Nitride Semiconductor Layered Body and LED Using the Same" (hereinafter, referred to as the "Patent").

  A non-party filed an opposition to the grant of the Patent.  The Japan Patent Office examined the opposition, and determined to revoke the patent related to all the claims of the Patent (hereinafter, referred to as "Determination of Revocation").

  The Plaintiff filed a litigation rescinding the Determination of Revocation, and the IP High Court rendered a decision dismissing the Determination of Revocation.

2-2. Outline of the Determination of Revocation
(1) The invention recited in claim 1 of the Patent (Invention 1)
The Invention 1 specified in the Determination of Revocation is as follows:

[Claim 1]
  A nitride semiconductor layered body, comprising:
  a template substrate comprised of an underground substrate having a c plane on an upper surface thereof and made of sapphire, and a buffer layer formed in contact with the upper surface of the underground substrate and made of aluminum nitride in a thickness of 2 µm to 4 µm;
  a superlattice layer formed in contact with the upper surface of the template substrate by alternately stacking an aluminum gallium nitride layer and an aluminum nitride layer;
  a first compositionally graded layer formed in contact with the upper surface of the superlattice layer and made of undoped aluminum gallium nitride, the undoped aluminum gallium nitride having an aluminum ratio mAl1 decreasing from the superlattice layer side to the upper side;
  a second compositionally graded layer formed in contact with the upper surface of the first compositionally graded layer and made of n-type impurity doped aluminum gallium nitride, the n-type impurity doped aluminum gallium nitride having an aluminum ratio m_Al2 decreasing from the first compositionally graded layer side to the upper side;
  an active layer formed in contact with the upper surface of the second compositionally graded layer, made of a Group Ⅲ nitride semiconductor, and having a luminescent layer emitting a deep ultraviolet light; and
  a p-side layer formed in contact with the upper surface of the active layer.

(2) Differences between the Invention 1 and the cited prior art

The Determination of Revocation specifies the following differences.
(Difference 1)

    The first layer in the Invention 1 is "a first compositionally graded layer…having an aluminum ratio m_Al1 decreasing from the superlattice layer side to the upper side," while the first layer in the cited prior art is not such a layer.

(Difference 2)

    The second layer in the Invention 1 is "a second compositionally graded layer …having an aluminum ratio m_Al2 decreasing from the first compositionally graded layer side to the upper side," while the second layer in the cited prior art is not such a layer.

(3) Reason for Revocation
    The Determination of Revocation holds that those skilled in the art would have easily arrived at the Invention 1 based on the cited prior art and the well-known art disclosed in the cited references 4-6.

(4) Recognition of Well-Known Art

The Determination of Revocation judges on the well-known art as follows:

"Cited Reference 4 describes in paragraph [0006] [sic, actually [0007]]: ‘…also has an increased drive voltage of 5.3V, which results in the element life of 35 hours, that is, a practical life (5,000 hours or above) cannot be achieved,' and also describes in paragraphs [0044] to [0046]: ‘after the layers up to the n-type AlGaN cladding layer 202 were formed by the same process as in Example 2, the n-type guide layer 203 was … a compositionally graded layer with a thickness of 0.15 µm, which was doped with 9×10¹⁷cm^-3 of Si and in which the Al mixed crystal ratio gradually decreased from Al_0.2Ga_0.8N to GaN in the growing direction …(omitted)… Moreover, further lower current and longer lifetime were achieved as compared with Example 2.  This is an effect caused by applying compositionally graded layers as the n-type guide layer 203 and the p-type guide layer 208 and thus the crystal lattice distortion in the n-side buffer layer 204 and the p-side buffer layer 206 and the active layer 205 with a quantum well structure was reduced.'
    Moreover, Cited Reference 5 describes in paragraph [0042]: ‘as a method of changing the AlN molar fraction and the thickness of the AlGaN cladding layer and the AlGaN contact layer, it is also possible to form these layers as compositionally graded AlGaN layers in which the AlN molar fraction varies linearly or parabolically.  It is expected to reduce the heterogap, resulting in a lower element resistance.'  This paragraph also describes: ‘a method of realizing a laser element having a sufficiently low drive voltage is also provided.'
    Further, Cited Reference 6 describes in paragraph [0006]: ‘In such a semiconductor multilayer film reflecting mirror, since a compositionally graded layer in which the composition of the layer varies so that the band gap continuously approaches from one semiconductor to the other semiconductor is provided at the interface between the first and second semiconductors, the band discontinuity between the semiconductors is reduced and thus the electric resistance is reduced, which decreases the drive voltage of an LED, etc. and prevents loss of its element life due to the heat generation.'
    According to the above descriptions of Cited References 4-6, it is recognized that in the technology of semiconductor light-emitting elements it was a well-known art, before the filing of the subject application, to employ a compositionally graded layer in which the Al ratio of the AlGaN layer is graded in order to reduce a drive voltage.
    Moreover, it is apparent that a lower drive voltage is also desirable in the cited prior art."

 
2-3. Judgment of IP High Court
    Regarding whether or not the well-known art was appropriately specified, the IP High Court judges as follows:

"The light-emitting elements disclosed in Cited References 4-6 all apply a compositionally graded layer as the AlGaN layer or AlGaAs layer.  In Cited Reference 4, for reducing the crystal lattice distortion in the buffer layers and the active layer, the compositionally graded layer is applied as the guide layers adjacent to the buffer layers.  In Cited Reference 5, for reducing the heterogap between two adjacent layers (contact layer and cladding layer), the compositionally graded layer is applied as the two layers.  In Cited Reference 6, for reducing the heterogap between two adjacent semiconductor layers, a compositionally graded layer is newly provided between the two layers.  As seen, it is recognized that Cited References 4-6 indicated by the Defendant apply the art of the compositionally graded layer for different technical significances as a part of the specified semiconductor layer structure constituting the respective elements.  Thus, the Defendant disregards the structure of the semiconductor layered body and the technical significance, and interprets in a broader sense the disclosure of the cited references to arrive at applying the compositionally graded layer in which the Al ratio of the AlGaN layer is graded (the art of the Invention) in order to reduce the drive voltage in the technical field of semiconductor light-emitting elements.  This should be considered as an argument based on hindsight.  Therefore, the art of the Invention cannot be recognized as a well-known art."

    To an extent of applying a compositionally graded layer as two adjacent layers for reducing the heterogap between the two layers to reduce the drive voltage, the IP High Court also states that there may be a room for recognizing the art of the Invention as a well-known art (based on the evidence filed by the Defendant (author's note: it describes that, in the technical field of semiconductor light-emitting elements with AlGaN, heterojunction is one of causes of an excess drive voltage and heterojunction barrier resistance can be reduced by applying compositional grading in the heterojunction interface) and Cited Reference 5).  However, regarding the existence of motivation, the IP High Court judges as follows:

"In the cited prior art (author's note: ‘Cited Prior Art A' in the decision), both the undoped layer and the doped layer are made of Al0.6Ga0.4N, and it is considered that there is no heterogap between them.  Further, even focusing on the heterogap between the superlattice buffer and the undoped layer, in the cited prior art, the n-side electrode is formed in the doped layer which is the contact layer, or the undoped layer.  Thus, it is considered that the heterogap with the superlattice buffer which is further lower (at the opposite side to the p-side electrode) has little influence on the drive voltage.
    Thus, regarding the undoped layer of the cited prior art, both in the relation with the adjacent doped layer and in the relation with the superlattice buffer, it cannot be recognized that there is motivation of applying a compositionally graded layer in order to reduce the heterogap for reducing the drive voltage.  Therefore, even if the above art was well known, at least the configuration related to the Difference 1 would not have been easily arrived."

 
(the underline added by the author)
 
3. DISCUSSION
 
    In determination of the inventive step, the Decision holds that, while recognizing that a plurality of cited references describe a configuration related to the differences between the Invention and the primary cited prior art, such a configuration is applied for different technical significances (in other words, for solving different problems), and thus, it is based on a hindsight to regard the Invention as a well-known art by only considering the configuration in a broader sense while disregarding the technical significances.  Thus, the Decision denies the judgment on the recognition of the well-known art in the Determination of Revocation.
    Therefore, in determination of the inventive step, if a configuration related to a difference was a well-known art and the well-known art is specified based on a plurality of cited references, it is necessary to judge whether the well-known art is specified appropriately, while paying attention to the technical significance of applying the configuration disclosed in each cited reference.
    We hope that the foregoing is helpful for you in determination of the inventive step in Japan.
    Please be free to contact us if you have any question or need further information.