Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
2000-10-10
2002-05-21
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S053000, C355S067000
Reexamination Certificate
active
06392738
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to contamination detection means. More particularly, the invention relates to contamination detection means in a lithographic projection apparatus comprising:
an illumination system for supplying a projection beam of radiation;
a first object table for holding a mask;
a second object table provided with a support surface for supporting and holding a substrate at its backside surface; and
a projection system for imaging an irradiated portion of the mask onto a target portion of the substrate.
2. Description of the Related Art
An apparatus of this type 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 then be imaged onto a target portion comprising one or more dies on a substrate (silicon wafer) that has been coated with a layer of radiation sensitive material (resist) on its top surface. In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated through the reticle, one at a time. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire reticle pattern onto the target portion at once; such an apparatus is commonly referred to as a waferstepper. In an alternative apparatus—which is commonly referred to as a step-and-scan apparatus—each target portion 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.
In general, apparatus of this type contained a single first object (mask) table and a single second object (substrate) table. However, machines are becoming available in which there are at least two independently movable substrate tables; see, for example, the multi-stage apparatus described in International Patent Applications WO 98/28665 and WO 98/40791. The basic operating principle behind such multi-stage apparatus is that, while a first substrate table is underneath the projection system so as to allow exposure of a first substrate located on that table, a second substrate table can run to a loading position, discharge an exposed substrate, pick up a new substrate, perform some initial metrology steps on the new substrate, and then stand by to transfer this new substrate to the exposure position underneath the projection system as soon as exposure of the first substrate is completed, whence the cycle repeats itself; in this manner, it is possible to achieve a substantially increased machine throughput, which in turn improves the cost of ownership of the machine.
Lithographic apparatus may employ various types of projection radiation, such as ultra-violet light (UV), extreme UV, X-rays, ion beams or electron beams, for example. Depending on the type of radiation used and the particular design requirements of the apparatus, the projection system may be refractive, reflective or catadioptric, for example, and may comprise vitreous components, grazing-incidence mirrors, selective multi-layer coatings, magnetic and/or electrostatic field lenses, etc; for simplicity, such components may be loosely referred to in this text, either singly or collectively, as a “lens”. The apparatus may comprise components that are operated in vacuum, and are correspondingly vacuum-compatible.
When a substrate is loaded onto the support surface of the substrate table, the substrate may be sucked against the support surface applying a vacuum to a space between the support surface and the backside surface of the substrate. Using this method the substrate will take a form determined by the support surface. The support surface may be provided with a matrix arrangement of protrusions, substantially perpendicular to the support surface whereby the backside of the substrate is lying on a contact surface represented by a top part of the protrusions. The form of the substrate will then be determined by the contact surfaces that are all located in the same plane. If contamination particles are present in between the support surface and the backside surface of the substrate the form of the substrate is not determined only by the form of the support surface but also by the contamination particles. The contamination could cause an unacceptable deformation of the substrate, which may result in focus and overlay errors during imaging of the pattern in the mask onto a top surface of the substrate. The errors may result in a rejection of manufactured substrates and thus in a lower throughput of the lithographic apparatus, which leads to an increase in the cost of ownership.
SUMMARY OF THE INVENTION
It is an object of the invention to prevent focus and overlay errors caused by contamination particles present in between the support surface and the substrate backside surface. These and other objects are achieved in an apparatus as specified in the opening paragraph, characterized in that the apparatus comprises contamination detection means constructed and arranged to detect the presence of contamination on one or both of the support surface and the substrate backside surface.
By detecting the presence of contamination on the support surface one may initiate cleaning of the support surface such that focus and overlay errors caused by said contamination are anticipated. By detecting the presence of contamination on the backside surface of the substrate one may choose to reject contaminated substrates such that the contamination will not reach the support surface. In both manners fewer manufactured substrates will be rejected and the cost of ownership of the apparatus will be improved.
In a first embodiment of the invention, said contamination detection means comprises:
level sensing means constructed and arranged to detect a surface figure of a substrate positioned upon said support surface;
data storage means for storing surface figures of at least two substrates; and
processing means adapted to compare surface figures of at least two substrates stored in said data storage means so as to recognize a recurring deformation in the surface figures of said substrates at a similar location indicating the presence of contamination at that location on the support surface.
In this way level sensing means already present in the apparatus may be used for the detection of contamination present at the support surface. Such level sensing means may detect the surface figure of a substrate positioned upon said support surface and said surface figure may be used during exposure to adjust the height and tilt of the substrate such that the substrate will be positioned within the focal plane of the projection system. In case the surface figure of more than one substrate comprises a deformation at a similar location, said deformation indicates contamination of the support surface on said location because said contamination will deform every substrate positioned upon that support surface.
In a further embodiment of the invention, the contamination detection means is adapted to detect a location of contamination on said support surface and said apparatus comprises a cleaning tool adapted to move with respect to said support surface to said location and to clean said location. In this manner contamination detected on a particular location on said support surface may be cleaned in situ by the cleaning tool and a throughput penalty is avoided because opening, inspecting, cleaning and closing of the apparatus, which may cost a lot of time in which the apparatus is not operative, is
Klaassen Franciscus A. G.
van de Pasch Engelbertus A. F.
van Meer Aschwin L. H. J.
Adams Russell
ASML Netherlands B.V.
Nguyen Henry Hung
Pillsbury & Winthrop LLP
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