Court: Court of Appeals for the Federal Circuit; March 29, 2004; Federal Appellate Court
Ultratech Stepper, Inc. appeals the summary judgment of non-infringement granted by the U.S. District Court for the Northern District of California in favor of ASM Lithography, Inc. Ultratech claimed that ASML's imaging systems, produced abroad and imported for U.S. customers, infringed several claims of its U.S. Patent No. 5,281,996 related to photolithographic reduction imaging (PRI) processes used in semiconductor manufacturing. The appellate court disagrees with the district court's interpretation of the patent claims, reversing the summary judgment and remanding the case for further examination of the infringement issue.
The ’996 patent describes an innovation in PRI processes, which are essential for creating semiconductor integrated circuits on silicon wafers. Traditional PRI methods involve projecting patterns from a larger etched mask onto a wafer using a lens, but lens size limits the image field diameter, constraining the size of the projected image. Previous methods to increase image size typically involved enlarging the lens, which is costly and may reduce image detail.
The ’996 patent introduces a method to enlarge the projected pattern without altering lens dimensions. It involves incrementally moving the mask across the lens's viewing field while simultaneously moving the wafer, allowing for the exposure of smaller areas of the wafer in successive increments. This technique enables the total image area on the wafer to exceed the lens's maximum image field diameter, thus addressing the limitations of conventional PRI methods.
The method described in the ’996 patent involves transferring a mask pattern onto a wafer, creating an imaged area larger than the lens's image field, thereby avoiding the need for larger lenses and utilizing existing photolithography apparatuses. The patent presents two embodiments: an extended field image version and a scanning version. Ultratech filed a lawsuit against ASML on March 3, 2000, in the Eastern District of Virginia, claiming infringement of specific patent claims, with the case later moved to the Northern District of California. Claim 1 outlines a method for imaging a large microcircuit device with specific parameters related to lens and mask movement.
The term "microcircuit device" was a point of contention, with Ultratech defining it as one or more die created by superimposing photolithographic patterns, while ASML argued it should refer only to integrated circuits formed from a single die. The district court ultimately sided with a modified definition from ASML, stating that a microcircuit device refers to a single imaged layer on a single die with a diagonal exceeding the lens's image field diameter.
ASML's accused method, which allegedly mirrors the scanning embodiment of the ’996 patent, produces a single large image on the wafer containing multiple circuit patterns. Although each individual circuit is smaller than the lens's image field, the collective pattern is larger. ASML emphasized its process as part of fabricating multiple dies rather than a single die. The district court ruled that ASML’s method did not fulfill the microcircuit device limitation as defined, determining that the exposure field consisting of multiple circuit patterns differed from the claimed microcircuit device.
The court ruled that ASML’s accused process, which produces a single imaged layer on multiple dies, is substantially different from the ’996 patented method that results in a single imaged layer on a single die. The court emphasized the purpose of the ’996 patent—creating larger single circuits—as a basis for rejecting Ultratech’s doctrine of equivalents claim. Consequently, summary judgment was granted against Ultratech for both infringement theories, leading to the current appeal.
Resolution of an infringement claim involves a two-step analysis: first, the trial court must determine the meaning of disputed claim terms, which is a legal matter subject to de novo review; second, the court compares the properly construed claims to the allegedly infringing device to assess whether all limitations of at least one claim are present, either literally or equivalently. A district court's decision based on improper claim construction receives no deference if that construction is pivotal to the infringement issue.
Ultratech seeks to overturn the district court's claim construction by arguing that the single die limitation should be removed. It contends that the term "microcircuit device" pertains to the mask patterns projected onto the wafer, irrespective of the number of die images. ASML, however, supports the district court’s construction. Claim construction focuses on the language of the claims, as defined by the patentee, beginning with the language used in the claims themselves. The preamble of claim 1 refers to a method for imaging a large microcircuit device, and there is ambiguity regarding whether the mask pattern or the image on the wafer should be considered the microcircuit device.
Microcircuit device can either refer to the underlying pattern on the mask or wafer, or specifically to the image on the wafer itself. The correct interpretation is that it pertains to the image on the wafer, as evidenced by the first limitation of claim 1, which stipulates that the diagonal of the microcircuit device must exceed the lens's image field diameter. In both traditional and patented processes, the mask pattern's diagonal exceeds the lens image field diameter, making the first limitation meaningless if interpreted otherwise. The ’996 patent emphasizes that the focus is on imaging the pattern on the wafer, which is used to create functioning circuitry, distinguishing it from the mask pattern. The specification contrasts the exposed square image on the wafer with the pattern on the mask, reinforcing that the microcircuit device is the exposed pattern on the wafer. The claims indicate that the method results in a pattern on the wafer that mirrors the mask's pattern, thus defining the microcircuit device as the complete exposed pattern on the wafer. This understanding does not necessitate examination of the mask pattern's specific contents. A broader interpretation aligns with Ultratech's suggestion that the microcircuit device includes the mask patterns exposed onto the wafer. The term "microcircuit" is generally defined as an integrated circuit or small electrical circuit, while "device" can refer to a mechanism or tool designed for specific functions. The district court's definition describes it as an electric element that cannot be divided without losing its function.
Definitions proposed by both parties regarding "microcircuit device" are rejected as they impose unnecessary functionality requirements inconsistent with the claims of the ’996 patent. The term refers merely to the pattern on the mask to be transferred to the wafer, serving as a design for a potential functioning device rather than having an immediate specific use or purpose. The district court erred by framing its claim construction in terms of the ultimate product, a die, which cannot be created solely through the patented process. The analysis should focus on the claimed process, with the subsequent use of the wafer being irrelevant to the method's scope. The patent specification emphasizes the critical feature of projecting and joining image portions on the wafer to create a single large image or microcircuit device. The process described involves forming reduced images on the wafer through coordinated movement of the mask and wafer, ultimately creating a larger microcircuit device. While ASML argues that the invention's purpose necessitates limiting "microcircuit device" to a single circuit, the inventors’ interchangeable use of "microcircuit device" and "circuit" in various contexts does not impact the imaging method itself. The operational functionality of the invention remains focused on the imaging process, regardless of whether the outcome contributes to one or multiple die.
Inventors of the ’996 patent exclusively claimed a method for image transfer without including any circuitry aspects. The mask pattern's content does not affect the method's execution by skilled practitioners, so claim construction should focus on the claimed method of transferring a pattern from the mask to the wafer. In the context of the patent, the term "microcircuit device" is defined as the pattern developed on the wafer's photo-resist, which corresponds to the mask pattern. A "large microcircuit device" is characterized by a pattern on the wafer that exceeds the diameter of the reduction lens's image field when measured diagonally. The district court mistakenly interpreted a microcircuit device as a single imaged layer on one die, a misunderstanding stemming from the trial court's focus on individual dies. The court's thoughtful analysis might have led to a different conclusion had the parties directed it accordingly. Consequently, the prior summary judgment of non-infringement favoring ASML is reversed, and the case is remanded for an infringement determination based on the correct definition of "microcircuit device." Each party will bear its own costs. The ’996 patent clarifies distinctions between the viewing field and image field of the relevant lens, emphasizing that prior art required fixed masks, whereas the ’996 patent allows mask movement relative to the lens. Additionally, while the term "mask" is used singularly in the opinion, it does not preclude the use of multiple movable masks for imaging large patterns on the wafer.
