Subscriber
Index
Nikon vs. ASML, Part II| thinfilmmfg.com
Subscriber
Index
Nikon vs. ASML, Part II |
As Part I of this article explained, Nikon is fighting its patent infringement battle with ASML on two fronts. A complaint before the International Trade Commission alleges infringement of seven patents, related to illumination, stage design, and system engineering. A parallel suit in the Federal District Court of California alleges infringement of four additional patents. Nikon declined to discuss legal strategy, so it's not clear how the company chose which patents to litigate in which venue.
The four patents at issue in the federal case are US Patents #5,528,118; #5,982,128; #6,034,378; and #6,242,754. They fall into two broad groups, dealing with stage design and with position detection.
The two stage design patents, US Patents #5,528,118 and #5,982,128, derive from the same initial patent application. Both describe a guideless stage, isolated from the rest of the system within a reaction frame. The frame keeps reaction forces due to the stage movement from affecting the rest of the system, while helping to isolate the stage from external vibrations.
The '118 patent describes a "Guideless stage with isolated reaction stage." The reaction frame support structure is independent of the wafer stage base. Two follower frames slide on the reaction frame in orthogonal directions. The wafer stage slides between these follower frames. Moments of force due to the frame drive elements sum to zero at the center of gravity of the wafer stage.
The '128 patent, titled "Lithography apparatus with movable stage and mechanical isolation of stage drive," places this stage design in the context of the lithography system. Isolation blocks mount to the support structure for the projection lens. The wafer stage base rests on these isolation blocks.
Meanwhile, the reaction frame rests on a completely independent foundation. The stage drive mechanism consists of several coil-and-magnet elements. One piece of each coil/magnet pair is attached to an arm of the reaction frame, while the other is attached to the stage. In this way, magnetic forces move the stage on air bearings without making physical contact. Together, these two patents underpin the more complex stage designs discussed in Part I.
Vibration-free stage movement is only part of the puzzle. The control system also has to know precisely where the stage is. The other patents at issue in the federal case, US Patents #6,034,378 and #6,242,754, deal with precise measurement of the substrate position. Both patents rely on diffraction of coherent light from a step structure.
Diffraction from a grating depends on the wavelength of the incident light, the angle of incidence, and the spacing of the grating. Both the angle of incidence and the apparent spacing can change with the relative positions of the step structure and the light source.
The '378 patent exploits this behavior by irradiating the grating mask with three or more coherent beams having slightly different wavelengths. A photoelectric sensor detects the intensity of the diffracted beams in a specific direction. The signal changes as the substrate moves.
The '754 patent refines this idea. It describes a system for illuminating the grating with two coherent beams at symmetrical angles of incidence. Two photodetectors collect the diffracted light at different angles. Software described in the patent calculates the substrate position from the diffracted beams.
Between the ITC complaint and the federal infringement case, Nikon is clearly mounting a broad attack on ASML's step-and-scan technology. If ASML's equipment is found to infringe these patents, the company's US market position could suffer a severe blow. (ASML did not respond to requests for comment.)
The final outcome of the suits is likely several years in the future. Initial rulings from both the ITC and the District Court will require 12-18 months. Both sides are sure to appeal any adverse result. ASML's lawyers are probably reviewing the company's patent portfolio with an eye to possible countersuits as well.
To read the full text of these patents, visit Delphion's patent database.
| This site is Copyright ©2001-2002 by Thin Film Manufacturing. All Rights Reserved |