Northern Telecom Limited v. Samsung Electronics

• Citation: 215 F.3d 1281,55 USPQ2d 1065
• Parties: (Fed. Cir. 2000) NORTHERN TELECOM LIMITED, Plaintiff-Appellant, v. SAMSUNG ELECTRONICS CO., LTD. and SAMSUNG SEMICONDUCTOR, INC., Defendants-Cross Appellants. 99-1208, -1227 DECIDED:
• Decision Date: 13 June 2000
• Court: United States Courts of Appeals. United States Court of Appeals for the Federal Circuit

Page 1281

215 F.3d 1281 (Fed. Cir. 2000)

NORTHERN TELECOM LIMITED, Plaintiff-Appellant, v. SAMSUNG ELECTRONICS CO., LTD. and SAMSUNG SEMICONDUCTOR, INC., Defendants-Cross Appellants.

99-1208, -1227

United States Court of Appeals for the Federal Circuit

DECIDED: June 13, 2000

Appealed from: U.S. District Court for the Northern District of California Judge Martin J. Jenkins

[Copyrighted Material Omitted] Donald R. Dunner, Finnegan, Henderson, Farrabow, Garrett & Dunner, L.L.P., of Washington, DC, argued for plaintiff-appellant. With him on the briefs were Thomas H. Jenkins, of Washington, DC, and R. Bruce Bower, of Atlanta, Georgia.

David E. Monahan, Gray Cary Ware & Freidenrich LLP, of San Diego, California, argued for defendants-cross appellants. With him on the briefs was Cathy Ann Bencivengo. Of counsel on the brief were Alan H. MacPherson, Edward V. Anderson, Craig J. Bristol, and Steven M. Levitan, Skjerven, Morrill, MacPherson, Franklin & Friel, of San Jose, California. Of counsel was Edward C. Kwok.

Before MICHEL, Circuit Judge, ARCHER, Senior Circuit Judge, and CLEVENGER, Circuit Judge.

CLEVENGER, Circuit Judge.

Northern Telecom Limited ("Northern Telecom") appeals from the United States District Court for the Northern District of California, which granted summary judgment invalidating Northern Telecom's United States Patent No. 4,030,967 ("the '967 patent") for failure to disclose the best mode contemplated by the inventor of carrying out the invention. See Northern Telecom Ltd. v. Samsung Elec. Co., Ltd., No. C-95-449, slip op. at 1 (N.D. Cal. Sep. 17, 1996). Samsung Electronics Co., Ltd., and Samsung Semiconductor, Inc. (collectively "Samsung") cross-appeal the district court's grant of summary judgment in favor of Northern Telecom on claim construction and its finding that Samsung literally infringed the '967 patent. Because we disagree with the district court's conclusion that the inventors of the '967 patent failed to disclose the best mode of carrying out their invention, we reverse the court's grant of summary judgment of invalidity and remand for further proceedings. We affirm, however, the district court's rulings on claim construction and literal infringement.

I

Northern Telecom owns the '967 patent, titled "Gaseous Plasma Etching Of Aluminum And Aluminum Oxide." The '967 patent contains one independent claim: "A process for gaseous etching of aluminum and aluminum oxide, including an initial step of plasma etching in the presence of a gaseous trihalide comprising at least in part, a boron trihalide."

Aluminum etching is used in the manufacture of integrated circuit semiconductor devices to create conductive lines of aluminum or aluminum alloy between various electronic devices on a silicon substrate. A typical manufacturing process begins with a silicon wafer coated with a conductive layer of aluminum or aluminum alloy. The manufacturer first covers the conductive layer with a mask of nonetchable material. Next, an aluminum etching process is applied to remove portions of the conductive film not protected by the mask. Finally, the manufacturer removes the masking material, leaving the desired pattern on the surface of the semiconductor substrate.

Until the mid 1970's, most integrated circuit manufacturers used wet chemicals to remove aluminum from the silicon substrate during the etching process. However, because wet etching tended to "undercut" desirable aluminum beneath the mask, this technique caused poor pattern definition and limited attempts to reduce conductive line widths. Wet etching also involved the use of toxic chemicals which were expensive and environmentally damaging. Dry etching offered an alternative to wet etching that would potentially avoid the undercutting problem and the costs associated with using and disposing of toxic chemicals.

In 1975-76, Northern Telecom undertook a research and development project for the United States Army Electronic Command to develop a new etching technique that would permit smaller semiconductor devices. The Northern Telecom researchers focused on plasma etching, a type of dry etching. Previous attempts to plasma etch aluminum had failed due to the presence of a naturally-occurring layer of aluminum oxide that forms on the surface of aluminum when exposed to air. These failures occurred because chlorine and bromine-based gases would not etch through the aluminum oxide layer. The '967 inventors discovered that certain etch gases-- specifically boron trihalides--would remove the oxide layer and permit etching of the aluminum underneath. The use of boron trihalides in plasma etching enabled etching of aluminum line widths below 2 microns, a significant advance in the miniaturization of semiconductor devices.

There are three types of dry etching techniques important to this case: (1) sputter etching; (2) plasma etching; and (3) reactive ion etching. Sputter etching is essentially a mechanical process whereby the metal being etched is bombarded with energetic ions that physically dislodge atoms from the exposed metal. There are no chemical reactions involved in sputter etching. Although sputter etching was known at the time of the '967 invention, it was considered a very slow process and, thus, undesirable.

Plasma etching utilizes a gas plasma, which is created by applying voltage to a low pressure gas. The gas plasma comprises a mixture of particles: reactive neutrals, excited neutrals, electrons, positively charged chemical species, and negatively charged chemical species. Plasma etching is primarily a chemical process in which a reaction occurs between an active species in the plasma and the metal surface. The parties dispute whether plasma etching, in the context of the '967 patent, necessarily excludes the presence of charged ions that mechanically dislodge atoms from the exposed metal, as occurs in the sputter etching process. The district court held that "plasma etching refers to a chemical process without excluding the non-chemical process of ion bombardment."

Reactive ion etching combines the mechanical ion bombardment of sputter etching with the chemical process of plasma etching. In this technique, the metal surface to be etched is intentionally charged with a negative voltage, which causes positively charged ions in the gas plasma to accelerate toward the metal surface, bombarding the surface with enough energy to dislodge exposed metal atoms. Simultaneously, active radicals in the gas plasma chemically react with the metal surface to form volatile compounds that are then removed from the metal surface.

The final step in manufacturing an integrated circuit semiconductor device is typically to heat or "sinter" the etched product at temperatures above 400oC. Sintering improves the contact between the conductive lines and the silicon substrate. However, during sintering, a phenomenon known as "spearing" may occur, which results in tiny metal protrusions extending downward from the bottom of the aluminum layer into the silicon substrate. Spearing occurs because elevated temperatures cause silicon to diffuse upward into the aluminum layer, allowing aluminum to fill the spaces vacated by the silicon. Spearing is undesirable because it may cause short circuits between multiple conductive layers in an integrated circuit semiconductor device.

One solution to the spearing problem is to use an aluminum silicon alloy as the metallic layer rather than pure aluminum. If the silicon content of the aluminum alloy exceeds the solid solubility limit for silicon in aluminum at the sintering temperature, then no diffusion of silicon from the substrate will occur and, thus, spearing will be prevented. It is undisputed that the inventors of the '967 patent knew that aluminum silicon alloy could be used in this manner and, indeed, believed that the use of aluminum silicon alloy was necessary to manufacture semiconductors below 2 microns.

Northern Telecom's infringement action against Samsung, originally filed in the United States District Court for the Northern District of Texas, was transferred to the District Court for the Northern District of California in February 1995. On September 17, 1996, the district court issued an opinion setting forth its interpretation of two disputed claim elements, "plasma etching" and "aluminum and aluminum oxide." The district court construed "plasma etching" to be a chemical process, but one that does not necessarily exclude the mechanical process of ion bombardment. It construed "aluminum and aluminum oxide" to refer solely to pure aluminum and its native layer of aluminum oxide, and not to alloys such as aluminum silicon.

Samsung's accused reactive ion etching process employs a boron trichloride plasma, which chemically reacts with and removes metal surface atoms. In addition, the metal surface is negatively charged, which causes positively charged ions in the plasma to accelerate toward the surface and mechanically remove some metal atoms. Samsung described this process as "synergistically combin[ing] energetic ion bombardment with chemically active radicals to achieve an etch rate far in excess of what would be achieved by plasma etching or sputter etching alone." Notwithstanding the additional element of ion bombardment, the district court found that, because Samsung's process included boron trihalide plasma etching, it fell within the literal scope of the '967 patent. In addition, the court found that, although the '967 patent specifically claims a method of plasma etching pure aluminum and aluminum oxide, Samsung's use of an aluminum silicon alloy did not avoid this limitation because pure aluminum is present within the aluminum silicon alloy.

After discovery, Samsung moved for summary judgment of invalidity of the '967 patent under 35 U.S.C. § 112, which requires an inventor to set forth in the patent specification "the best mode contemplated by the inventor of carrying out his...