Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2000-03-06
2004-01-06
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S053000
Reexamination Certificate
active
06674510
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to height detection and levelling, for example of the substrate and/or mask, in lithographic apparatus. More particularly, the invention relates to a system for off-axis levelling in lithographic projection apparatus comprising:
a radiation system for supplying a projection beam of radiation;
a first object table provided with a mask holder for holding a mask;
a second, movable object table provided with a substrate holder for holding a substrate;
a projection system for imaging an irradiated portion of the mask onto a target portion of the substrate; and
a positioning system for moving said second object table between an exposure position, at which said projection system can image said mask portion onto said substrate, and a measurement position.
SUMMARY OF THE INVENTION
For the sake of simplicity, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection systems, including refractive optics, reflective optics, catadioptric systems, and charged particle optics, for example. The radiation system may also include elements operating according to any of these principles for directing, shaping or controlling the projection beam, and such elements may also be referred to below, collectively or singularly, as a “lens”. In addition, the first and second object tables may be referred to as the “mask table” and the “substrate table”, respectively. Further, the lithographic apparatus may be of a type having two or more mask tables and/or two or more substrate tables. In such “multiple stage” devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the mask (reticle) may contain a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto an exposure area (die) on a substrate (silicon wafer) which has been coated with a layer of photosensitive material (resist). In general, a single wafer will contain a whole network of adjacent dies which are successively irradiated via the reticle, one at a time. In one type of lithographic project apparatus, each die is irradiated by exposing the entire reticle pattern onto the die at once, such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus—which is commonly referred to as a step-and-scan apparatus—each die is irradiated by progressively scanning the reticle pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the wafer table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally <1), the speed V at which the wafer table is scanned will be a factor M times that at which the reticle table is scanned. More information with regard to lithographic devices as here described can be gleaned from International Patent Application WO 97/33205, for example.
Until very recently, lithographic apparatus contained a single mask table and a single substrate table. However, machines are now becoming available in which there are at least two independently moveable substrate tables; see, for example, the multi-stage apparatus described in International Patent Applications WO98/28665 and WO98/40791. The basic operating principle behind such multi-stage apparatus is that, while a first substrate table is at the exposure position underneath the projection system for exposure of a first substrate located on that table, a second substrate table can run to a loading position, discharge a previously exposed substrate, pick up a new substrate, perform some initial measurements on the new substrate and then stand ready to transfer the new substrate to the exposure position underneath the projection system as soon as exposure of the first substrate is completed; the cycle then repeats. In this manner it is possible to increase substantially the machine throughput, which in turn improves the cost of ownership of the machine. It should be understood that the same principle could be used with just one substrate table which is moved between exposure and measurement positions.
The measurements performed on the substrate at the measurement position may, for example, include a determination of the spatial relationship (in X & Y directions) between various contemplated exposure areas on the substrate (“dies”), reference markers on the substrate and at least one reference marker (e.g. fiducial) located on the substrate table outside the area of the substrate. Such information can subsequently be employed at the exposure position to perform a fast and accurate X and Y positioning of the exposure areas with respect to the projection beam; for more information see WO 99/32940 (P-0079), for example. This document also describes the preparation at the measurement position of a height map relating the Z position of the substrate surface at various points to a reference plane of the substrate holder. However the reference plane is defined by a Z-interferometer at the measurement position and a different Z-interferometer is used at the exposure position. It is therefore necessary to know accurately the relationship between the origins of the two Z-interferometers.
An object of the present invention is to provide a system for off-axis levelling a substrate in a lithographic projection apparatus that avoids the need to relate the origins of two interferometer systems and enables additional improvements in positioning of the exposure areas during exposure processes.
According to the present invention there is provided a lithographic projection apparatus comprising:
a radiation system for supplying a projection beam of radiation;
a first object table provided with a mask holder for holding a mask;
a second, movable object table provided with a substrate holder for holding a substrate;
a projection system for imaging an irradiated portion of the mask onto a target portion of the substrate; and
a positioning system for moving said second object table between an exposure station, at which said projection system can image said mask portion onto said substrate, and a measurement station; characterized in that
said second object table has a physical reference surface fixed thereto;
and by:
height mapping means located at said measurement station and constructed and arranged to measure the height, relative to said physical reference surface, of a plurality of points on the surface of a substrate held on said substrate holder and to create a height map thereof;
position measuring means located at said exposure station for measuring the position of said physical reference surface in a first direction substantially perpendicular to said substrate surface, after movement of said second object table to said exposure station; and
control means constructed and arranged to control the position of said second object table in at least said first direction, during exposure of said target portion, in accordance with said height map and said position measured by said position measuring means.
According to a further aspect of the present invention there is provided a method of manufacturing a device using a lithographic projection apparatus comprising:
a radiation system for supplying a projection beam of radiation;
a first object table provided with a mask holder for holding a mask;
a second, movable object table provided with a substrate holder for holding a substrate; and
a projection system for imaging irradiated portions of the mask onto target portions of the substrate at an exposure station; the method comprising the steps of:
providing a mask bearing a pattern to said first object table;
providing a substrate having a radiation-sensitive layer to said second object table; and
imaging said
Boonman Marcus E. J.
Castenmiller Thomas J. M.
Du Croo de Jongh Richard J. H.
Gemen Jacobus
Heuts Frederik T. E.
Adams Russell
ASML Netherlands B.V.
Kim Peter B.
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