EMI Group N America v. Cypress Semiconductor

• Decision Date: 21 September 2001
• Citation: 60 USPQ2d 1423,268 F.3d 1342
• Parties: (Fed. Cir. 2001) EMI GROUP NORTH AMERICA, INC., Plaintiff-Appellant, v. CYPRESS SEMICONDUCTOR CORPORATION, Defendant-Appellee. 00-1508 DECIDED:
• Court: U.S. Court of Appeals — Federal Circuit

Page 1342

268 F.3d 1342 (Fed. Cir. 2001)

EMI GROUP NORTH AMERICA, INC., Plaintiff-Appellant, v. CYPRESS SEMICONDUCTOR CORPORATION, Defendant-Appellee.

00-1508

United States Court of Appeals for the Federal Circuit

DECIDED: September 21, 2001

Appealed from:United States District Court for the District of Delaware Judge Roderick R. McKelvie

James P. Bradley, Sidley & Austin, of Dallas, Texas, argued for plaintiff-appellant. With him on the brief were Kathi A. Cover and William D. McSpadden. Of counsel were Ivan S. Kavrukov, Cooper & Dunham LLP, of New York, New York; and Donald F. Parsons, Jr., Morris, Nichols, Arsht and Tunnell, of Wilmington, Delaware.

C. Randall Bain, Brown & Bain, P.A., of Phoenix, Arizona, argued for defendant-appellee. With him on the brief were C. Mark Kittredge and Roger A. Denning.

Before RADER, Circuit Judge, PLAGER, Senior Circuit Judge, and DYK, Circuit Judge.

RADER, Circuit Judge.

After a jury verdict, the United States District Court for the District of Delaware denied EMI Group North America, Inc.'s motion for a new trial. EMI Group N. Am., Inc. v. Cypress Semiconductor Corp., 104 F. Supp. 2d 370 (D. Del. 2000). Because the district court did not abuse its discretion in determining that the jury verdicts were consistent, this court affirms.

EMI also sought a judgment as a matter of law (JMOL) that United States Patent Nos. 4,826,785 (the '785 patent) and 4,935,801 (the '801 patent) are not invalid. The district court denied the motion in part. Because a reasonable jury could conclude on this record that claim 1 of the '785 patent and claims 1 and 5 of the '801 patent are impossible, this court affirms the district court's denial of EMI's motion for JMOL.

The district court granted in-part EMI's motion for JMOL that the '785 and '801 patents are not invalid for obviousness or anticipation. Because the district court erred in finding that the mechanism recited in the asserted claims is not inherent, this court reverses the district court's partial grant of EMI's motion for JMOL.

The district court also denied in-part EMI's motion for JMOL that Cypress Semiconductor Corp. infringed the asserted claims of the '785 and '801 patents. Because we find that the claims of the '785 and '801 patents are invalid, this court does not reach the issue of infringement.

I.

The present case features metallic fuses for semiconductor chips. Due to manufacturing complexities, semiconductor chips typically have redundant circuitry. Manufacturers test each chip to determine whether portions of the chip are dysfunctional. Manufacturers then disconnect the dysfunctional portions and the redundant circuitry takes over the function. With this method, the manufacturing process yields a greater percentage of viable chips.

Interconnects, called links or fuses, typically connect sections of a chip. To disconnect a dysfunctional portion of the semiconductor chip, manufacturers sever the fuses that connect the dysfunctional portion to the rest of the chip. A laser beam performs this disconnecting function by melting or "blowing" a portion of the fuse. EMI owns the '801 patent, which claims a structure for a metallic fuse with an optically absorptive upper layer, and the '785 patent, which claims a method for fabricating and blowing such a fuse. The '801 patent is a divisional of the application that led to the '785 patent.

Originally, the semiconductor industry made fuses of polysilicon. A laser easily blew these fuses without damaging the surrounding structures of the chip. Because metal produced a more efficient and reliable circuit, manufacturers began switching to metal fuses in the 1980s. Metal fuses, however, presented a significant manufacturing problem because they do not melt without a high energy laser blast. This high laser energy damages the underlying silicon substrate and surrounding polysilicon structures of the chip.

In 1986, Dr. Robert Jones, Jr. and Mr. Paul McClure, both scientists with INMOS Corp.,¹ developed a metallic fuse structure that would melt under a low energy laser. The fuse structure 24, as disclosed in both the '785 and '801 patents, has metal interconnect layers, typically made of a material such as aluminum, underneath a cap 22. The cap is an optically absorptive refractory material, such as tungsten or titanium. This optically absorptive refractory material has a higher boiling point than underlying metal layers and absorbs low energy laser radiation that the underlying metal layers would typically reflect. In some of the embodiments disclosed in both patents, the cap 22 is further covered with a glass passivation layer 26.

[Tabular or Graphical Material Omitted]

The specification of both patents describes the theoretical mechanism for blowing the disclosed metallic fuse. According to the specifications, as the transition metal layer absorbs laser energy, it causes "the rest of the underlying metallic fuse portion to heat up and eventually melt" while it remains solid. '785 patent, Col. 2, ll. 44-45; '801 patent, Col. 2, ll. 50-51. The underlying metallic portion eventually evaporates and the fuse quickly accumulates vapor pressure under the transition metal layer. This vapor pressure, in theory, causes the melted fuse material to explode, thus removing the fuse from the chip. '785 patent, Col. 2, ll. 45-50; '801 patent, Col. 2, ll. 51-56. This entire fuse explosion sequence occurs within nanoseconds.

Thus, according to both the '785 and '801 patents: "The use of the thin, high-temperature optically absorptive coating on top of the interconnect member forming the fuse portion acts as a cap to prevent evaporation until the vapor pressure of the material below the cap is very high." '785 patent, Col. 2, ll. 50-54; '801 patent, Col. 2, ll. 56-60. Dr. Jones and Mr. McClure did not, however, practice or observe the actual severance of the fuse by this method. Rather the disclosed and claimed explosive mechanism is theoretical. Claim 1, the only independent claim of the '785 patent, recites:

1.A method of fabricating on a substrate surface a fuse forming an integral part of a metallic interconnect line joining elements in an integrated circuit, the method comprising:

forming a metal interconnect layer above the substrate surface;

forming a layer of an optically absorptive refractory transition metal above said metal interconnect layer, said refractory metal having a higher boiling point than said metal interconnect layer;

defining said metal interconnect layer and said optically absorptive layer into a patterned metallic interconnect for the integrated circuit including a fuse portion therein, said refractory metal forming a cap to prevent evaporation of said fuse portion when said fuse portion is exposed to a directed energy source to increase the vapor pressure under the cap to produce an explosive removal of said fuse portion; and

removing said fuse portion from said interconnect line by exposing said optically absorptive refractory metal to directed energy source that explosively removes said fuse portion without damaging the substrate.

(Emphasis added.) Claims 1 and 5, the only independent claims of the '801 patent, recite:

1.A fuse for a metallic interconnect line that joins elements of an integrated circuit formed on and in a silicon substrate wherein the fuse comprises

a layered interconnect structure having an upper layer of an optically absorptive material and a lower layer of metal below said upper layer,

said optically absorptive material having a higher boiling temperature than that of said metal, said upper layer forming an explosion-inducing cap,

said layered interconnect configured such that a laser light directed on said upper layer is absorbed thereby and causes said lower layer to vaporize before said upper layer vaporizes thereby inducing an explosion which substantially removes said layered interconnect structure, disconnecting the previously joined elements of the integrated circuit.

5.A fuse for metallic interconnect line that joins elements of an integrated circuit formed on and in a silicon substrate wherein the fuse comprisesi [sic]

a layered interconnect structure having an explosion-inducing cap which includes an upper layer of an optically absorptive material,

said layered interconnect structure further including a lower layer of metal below said upper layer, said optically absorptive material having a higher boiling temperature relative to said metal,

said layered interconnect structure being responsive to a laser light having a circular Gaussian energy distribution output on said upper layer, such that when said layered interconnect structure is exposed to said laser light, said upper layer absorbs said laser light and transmits heat to said lower layer, said lower layer vaporizes before said upper layer causing an explosion, said explosion forming an opening between said elements on said integrated circuit.

(Emphasis added.)

EMI sued Cypress in 1998 for infringement of the '785 and '801 patents by fuses manufactured by Cypress' RAM 3, RAM 4, and RAM 5 processes. Cypress' accused fuses feature an aluminum layer capped by a tungsten-titanium alloy layer and further covered by a glass passivation layer. In September 1999, the district court held a Markman hearing and issued an order construing the asserted claims.

During the ensuing trial, EMI's expert witness, Dr. Fair, testified about the accuracy of the claimed theoretical vapor-induced explosion mechanism. Cypress' expert witness, Dr. Bernstein, testified that the explosion mechanism recited in the asserted claims is impossible. He explained that before the fuse temperature becomes hot enough to vaporize the metal layer, the metal expands under the heat causing any passivation layer to crack at the corners of the fuse. Melted metal then ejects through the cracks. According to Dr. Bernstein, the metal layers of a fuse cannot vaporize under a transition metal cap...