The opinion of the court was delivered by: Conner, Senior D. J.
In these two actions, plaintiff Gertrude Neumark Rothschild charges defendants Cree, Inc. ("Cree") and Philips Lumileds Lighting U.S. LLC ("Lumileds") respectively with infringement of her following United States patents on methods of producing light emitting diodes:
No. 4,904,618, entitled Process for Doping Crystals of Wide Band Gap Semiconductors issued February 27, 1990 on an application filed August 22,1988 ("the '618 patent"); and
No. 5,252,499, entitled Wide Band Gap Semiconductors Having Low Bipolar Resistivity and Method of Formation, issued October 12, 1993 on an application filed August 15, 1988 ('the '499 patent").
A joint Markman hearing*fn1 was conducted in the two actions on March 19, 2007 to determine the proper construction of a number of disputed terms in the claims of the two patents. This opinion incorporates the Court's conclusions as to the proper construction of the claim terms in question.
Claim Construction Principles
In Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005), the Court prescribed the proper procedure for determining the meaning of patent claims. The terms of the claims are generally given their customary meaning to a person of ordinary skill in the art at the time of the invention, who is deemed to read the terms not only in the context of the particular claim in which they appear but in the context of the entire patent, including the other claims, the specification and drawing and, if needed, its prosecution history. If, after consideration of such intrinsic evidence, the meaning of a claim term is still uncertain, the Court may look to such extrinsic evidence as expert and inventor testimony, dictionaries and learned treatises. However, the patentee is permitted to be her own lexicographer so that if in the specification she clearly gives a claim term a special definition, that definition controls. (Id. at 1316.)
Light emitting diodes, or LEDs, are used by the billions in a multitude of applications, including instrument panels, alphanumeric displays, billboards, traffic lights and as an energy-efficient substitute for incandescent bulbs. LEDs are essentially p-n junctions of wide band gap semiconductor materials. Semiconductors are materials having an electrical conductivity in an intermediate range between insulators and conductors. When an element from Group II of the periodic table, such as zinc (Zn) or cadmium (Cd), having two electrons in its outer shell, is combined with an element from Group VI, such as selenium (Se) or tellurium (Te), having six electrons in its outer shell, a compound having a normal eight electrons in its outer shell, such as zinc selenide (ZnSe), is formed. Likewise such compounds may be formed by combining an element from Group III, such as gallium (Ga), with an element from Group V, such as arsenic (As). The first group of compounds are known as II-VI compounds and the latter group as III-V compounds. If a dopant, or impurity, is incorporated into a crystal of one of these compounds, either during or after crystal growth, the electrical properties of the compound may be changed in a useful manner. For example, if a II-VI compound such as zinc selenide is doped with an element from Group V of the periodic table, such as nitrogen (N), having five electrons in its outer shell, its atoms displace some of the selenium atoms in the crystal lattice, thereby creating electron acceptors or "holes" in the crystal, making it a "p-type" material. If the dopant is an element from Group III, such as gallium (Ga), having three electrons in its outer shell, its atoms displace some of the zinc atoms in the lattice, creating a excess of electrons in the crystal, making it an n-type material. When a junction is formed between a p-type and an n-type material, and a voltage is applied across the junction, electrons will move from the n-type material to fill the holes in the p-type material and, as they do so, the energy they lose in dropping from the conduction band to the valence band is released in the form of light whose wavelength or color depends on the width of the gap between those bands in the particular material. For example, if the band gap is between 1.65 and 2.00 electron volts ("eV"), red light is produced; if it is below 1.65 eV, invisible infrared light or heat is produced. If the band gap is between 2.51 and 2.76 eV, blue light is produced; if it is above that range, violet or ultraviolet light is produced.
Semiconductor materials with wide band gaps are more difficult to dope because they more readily become "compensated," meaning that impurities in the material supply electrons to fill the holes in p-type material or acceptors to receive the electrons in n-type material. This reduces incorporation of the dopants into the crystal lattice and unacceptably increases the resistivity of the semiconductor. Therefore red LEDs are much more easily produced and more commonly used than blue LEDs, which have been called "the long-sought Holy Grail of LED technology." (Puri Decl., Ex. 4.) The patents in suit concern methods for doping wide band gap semiconductor materials to make LEDs which emit shorter wavelength (green or blue) light.
In the Abstract section of the specification, the invention is summarized as follows:
Non-equilibrium impurity incorporation is used to dope hard-to-dope crystals of wide band gap semiconductors, such as zinc selenide and zinc telluride. This involves incorporating into the crystal a compensating pair of primary and secondary dopants, thereby to increase the solubility of either dopant alone in the crystals. Thereafter, the secondary more mobile dopant is removed preferentially, leaving the primary dopant predominant. This technique is used to dope zinc selenide p-type by the use of nitrogen as the primary dopant and lithium as the secondary dopant.
Plaintiff charges both defendants with infringement of Claims 1, 4 and 5 of the '618 patent. Claims 1 and 5 are the only independent claims of the patent; Claim 4 is dependent on Claim 1 and contains no additional disputed terms. Claims 1 and 5 read as follows:
1. A process for the non-equilibrium incorporation of a dopant into a crystal of a wide band gap semiconductor comprising the steps of treating the crystal in the presence of first and second compensating dopants of different mobilities for introducing substantially equal amounts of the two dopants into at least a portion of the crystal such that the concentration of the less mobile of the two dopants in said portion of the crystal is in excess of the solubility therein of the less mobile dopant in the absence of the more mobile of the two dopants and then heating the crystal to remove therefrom preferentially the more mobile of the two dopants, whereby there is left a non-equilibrium concentration of the less mobile dopant in said portion of the crystal.
5. The process of forming a p-n junction diode in a crystal of a wide band gap semiconductor comprising the steps of preparing a crystal of the semiconductor of one conductivity type and growing on a surface of the crystal an epitaxial layer that includes a compensating pair of primary and secondary dopants in substantially equal amounts, such that the concentration of the primary dopant in the layer is in excess of the solubility of the primary dopant in the layer in the absence of the secondary dopant, where the primary dopant is characteristic of the conductivity type opposite that of said crystal and is less mobile than the secondary dopant, and removing selectively the secondary dopant from the layer to leave it of the opposite conductivity type, where the dopant remaining in the layer is predominantly the primary dopant in a non-equilibrium concentration.
The parties do not dispute the indicated construction of the following terms of the claims of the'618 patent:
"dopant" means an impurity added to a semiconductor material to alter its electronic properties;
"non-equilibrium incorporation" means incorporation of a dopant in excess of its equilibrium solubility at a particular temperature and concentration of compensating species;
"wide band gap" means a band gap of at least 1.4 eV; "compensating dopant" means a dopant which provides either donors in p-type material or acceptors in n-type material;
"substantially equal amounts" means approximately equal molar quantities; and "in excess of the solubility" means that the concentration of the less mobile dopant is greater than it would have been in the absence of the more mobile dopant.
The construction of the following terms of the '618 patent claims is in dispute:
This term appears in Claim 1 and, by reference, in Claim 4, which is dependent on it. Claim 5 uses a different term, "preparing a crystal," which will be discussed separately.
Plaintiff contends that this term should be defined as "subjecting the crystal to a process," a definition which includes incorporation of dopant into a crystal during its growth. (Pl. Op. Br. at 15.)*fn2 Defendants contend that it should be defined as " treating a pre-existing crystal."
The phrase "treating the crystal" does not appear in the specification of the '618 patent. However, in support of her proposed construction of the term, plaintiff points out that the specification of her contemporaneously filed '499 patent (at 2:39-42) states: "There are three conventional, non-esoteric methods for introducing dopants into the substrate: by diffusion, by implantation and during growth." Then, as examples of introduction of dopants during crystal growth, plaintiff refers to the specification of the '618 patent (at 2:50-52; 3:43-47; 4:19-25). These disclosures would clearly support a claim specifically calling for incorporation of dopants into a crystal of a semiconductor during growth of the crystal. However, merely because a procedure is disclosed in the specification does not mean that all of the claims of the patent should be construed so that their language covers that procedure as a step of the process claimed, particularly where there are other claims clearly covering a process which includes that step.
Cree points out that Claim 5 of the '618 patent calls for "preparing a crystal . . . and growing on a surface of the crystal an epitaxial layer that includes a compensating pair of primary and secondary dopants . . . ," and asserts that the "plain and ordinary meaning of this language requires that a substrate is first formed and then an epitaxial layer is grown on a surface of the substrate." (Cree Op. Br. at 34-35.) The Court agrees. But that does not mean that Claim 1 should also be so limited. It does not contain language similar to the quoted portion of Claim 5.
Lumileds points out (Lum. Op. Mem. at 12) that, in prosecuting in the European Patent Office ("EPO") a patent application based on and claiming priority from the applications for the two patents here in suit, plaintiff's attorney, in a letter to the EPO dated 21 February 1997 (id., Ex. I), stated:
Thus, the dopants may be introduced into an existing crystal or may be introduced during its growth. However, since the reference in existing claim 1 to "treating the crystal . . ." could be construed as implying that the dopants are necessarily introduced into an otherwise fully formed crystal, this language has been removed from claim 1 so that this claim refers simply to "introducing into."
No such change was made in the corresponding Claim 1 of the U.S. '618 patent.
The statement of the patentee's attorney that the claim term in question "could be construed as implying" that the dopants are introduced into a fully formed crystal is merely a recognition of the obvious fact that the claim term is sufficiently ambiguous that it might be interpreted to require incorporation of the dopants into a pre-existing crystal. But it is not a concession that the claim term should be or would normally be interpreted to exclude introduction of the dopants during growth of the crystal. Indeed, defendants' argument is a two-edged sword: this clarification of the corresponding claim of the EPO application can also be viewed as evidence that plaintiff considered that the method of her invention contemplated incorporation of the dopants into a crystal during its growth.
The specification of the '618 patent resolves the issue. In the Detailed Description of the Invention, it describes only two illustrative examples of the patented method. At column 3, lines 16-62, there is described a method which involves growing on an n-type slice of zinc selenide an epitaxial p-type layer which is "grown by LPE [liquid phase epitaxy] to include both lithium and nitrogen." At column 4, lines 10-45, there is described an "alternative embodiment" which involves growing on a p-type slice of zinc telluride an n-type epitaxial layer which is grown by MOCVD (metal-organo-chemical vapor deposition) to incorporate chlorine as the primary dopant and lithium as the secondary dopant. Thus, in both of the two exemplary methods, the dopants are introduced into the epitaxial crystal during its growth. More significantly, there is no detailed description of a method in which the dopants are introduced into a pre-existing crystal, although the specification (at 5:1-2) briefly mentions that "other techniques are feasible including molecular beam epitaxy." Therefore, if, as defendants urge, the term in question were construed to require treatment of a pre-existing crystal, a serious question would be raised about the validity of Claim 1 under 35 U.S.C. §112, first paragraph, based on lack of an enabling disclosure. See Nat'l Recovery Techs. v. Magnetic Separation Sys., Inc., 166 F.3d 1190 (Fed. Cir. 1999).
The Court concludes that a person of ordinary skill in the art, reading the '618 patent specification and seeing that, in both of the only detailed examples described, the dopants are incorporated during crystal growth, would understand that the term "treating the crystal" was meant to cover that alternative.
The Court therefore construes the term "treating the crystal" to mean: subjecting the crystal to a process which may occur during its growth.
Plaintiff contends that this term, which appears in both Claims 1 and 5, should be construed to mean "taking away." Plaintiff adds that the term really needs no construction by the Court, but if it does, it should be construed to mean taking away "an effective amount of the . . . more mobile dopant." (Pl. Op. Br. at 14.)
Lumileds states that plaintiff's proposed definition hardly clarifies the term, and that it "can only mean either partial or complete 'taking away'." (Lum. Opp. Mem. at 5.)
Cree contends that the term should be construed to require that the more mobile dopant be removed "so that it is no longer within the semiconductor," in other words, "not just moving the dopant to other locations within the crystal/layer." (Cree Op. Br. at 36-37.) The Court agrees that the definition should make clear that the portion of the more mobile dopant which is removed is taken entirely out of the crystal and not merely moved within it. Such a meaning is indicated not only by the choice of the word "remove" instead of "move" but also by the language in Claim 1 which calls for "heating the crystal to remove therefrom preferentially the more mobile of the two dopants . . ." (emphasis added). The specification contains similar language; in the Detailed Description of the first illustrative method at column 3, lines 51-52, it is stated ". . . the lithium is preferentially removed from the epitaxial layer." (emphasis added). This concept is probably expressed adequately by the words "taking away" proposed by plaintiff and accepted by Lumileds. But to avoid any possibility of misconstruction, the words "from the crystal" should be added. The Court also believes that the definition should make it clear ...