Coordinate measuring stage and coordinate measuring instrument

Details Coordinate measuring stage and coordinate measuring instrument Coordinate measuring stage and coordinate measuring instrument

2002-08-20

2004-08-17

Fuller, Rodney (Department: 2851)

Photocopying

Projection printing and copying cameras

Detailed holder for photosensitive paper

C355S053000, C355S075000

Reexamination Certificate

active

06778260

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority of the German patent application 101 40 174.4 which is incorporated by reference herein.
FIELD OF THE INVENTION
The invention concerns a coordinate measuring stage with interferometric position determination, as well as a coordinate measuring instrument for high-accuracy measurement of the coordinates of the edges of a pattern element on a substrate
BACKGROUND OF THE INVENTION
Coordinate measuring stages of the kind cited above are used in high-accuracy coordinate measuring instruments of the kind cited above. One such coordinate measuring instrument is described in the article “Maskenmetrologie mit der LEICA LMS IPRO für die Halbleiterproduktion” [Mask metrology using the LEICA LMS IPRO for semiconductor production] by K. -D. Röth and K. Rinn, Mitteilungen für Wissenschaft und Technik Vol. XI, No. 5, pp. 130-135, October 1997. This measuring instrument is used for high-accuracy measurement of the coordinates of the edges of a pattern element on a substrate, e.g. a mask and a wafer.
The coordinate measuring instrument comprises a measuring stage of the kind cited above which is horizontally displaceable in the X direction and the Y direction. It serves to receive the substrates having features whose edge coordinates are to be measured. In addition, a separate interferometer measurement beam path is associated with each coordinate axis (X, Y) of the measuring stage. Mounted on two mutually perpendicular sides of the measuring stage are measurement mirrors that are located at the ends of the two interferometer measurement beam paths. By means of the two measurement mirrors, the position of the measuring stage can be determined interferometrically.
The coordinate measuring instrument furthermore possesses an incident-light illumination device having an optical axis; an imaging device (for example, a microscope objective); and a detector device (for example, a high-resolution digital camera or a position-sensitive detector) for the imaged features. The measured coordinates of an edge of a feature to be measured are obtained from the interferometrically measured present position of the measuring stage and the distance (relative to the optical axis) of the feature to be measured. The positioning accuracy with which the interferometric measurement of the measuring stage position is acquired therefore directly influences the determination of the coordinates of the edges on the features on the substrates. Because an optimum measurement result requires that optical sensing occur in an accurately defined focal plane (called the Abbé{acute over ( )} plane), deviations in vertical running accuracy from that ideal plane also contribute error components to the measurement results.
Coordinate measuring instruments of the aforesaid kind serve for the determination of coordinates with a reproducibility in the range of less than 5 nm. Since this measurement accuracy depends very substantially on the X-Y positioning accuracy and the vertical running accuracy of the measuring stage, the requirements in terms of the construction of the measuring stage are extremely high.
A coordinate measuring stage of the coordinate measuring instrument described above comprises the following elements arranged one above another:
a stationary base part having a linear X guidance element;
above that, a center part, movable slidingly along the linear X guidance element, which has a first drive element associated with it and is rigidly joined to a linear Y guidance element;
above that, an X-Y-positionable stage body which is movable slidingly along the Y guidance element and has a second drive element associated with it.
The X guidance element is configured on the center of the base part, for example as a recessed groove on which the center part is guided. The wide center part is arranged transversely to the X guidance element and forms, with the X guidance element, a movable cross. This stage construction is therefore commonly known to those skilled in the art as a “cross-slide stage.” The center part carries the Y guidance element on its center axis, and is supported on the surface of the base part, on either side of the X guidance element, with a total of three support air bearings. The result is a stable three-point support.
The stage body is guided in its motion by the Y guidance element, and spans over the center part. It is supported on the surface of the base part, on either side of the X guidance element, with a total of four support air bearings, i.e. with two support air bearings on each side of the X guidance element. Since a bearing system having four support surfaces is redundant, one of the four support air bearings is configured as a resilient support air bearing in order to compensate for irregularities on the surface of the base part.
Since the coordinate measuring machine must be operated at a constant ambient temperature in order to achieve optimum measurement results, it is set up in a climate-controlled chamber. In individual factories, different ambient temperatures are required in the climate-controlled chambers. The instruments are thus operated, depending on the temperature selected, in a temperature range between 20 and 23° Celsius. These temperature differences result in different material elongations at the individual components of the coordinate measuring machine. This in turn changes the air gaps of the air bearings. Some of the guidance air bearings were therefore also designed to be resilient. For example, on each guidance element the guidance air bearings on one side of the guidance element are designed to be resilient, and the guidance air bearings on the opposite side are designed to be rigid.
Both the support air bearings and the guidance air bearings were selected with very small air gaps (on the order of 3 to 4 &mgr;m). Adaptation to irregularities of the particular guidance surface is performed by way of the respective resiliently mounted support or guidance air bearings. The narrow air gap heights are highly tolerance-sensitive and must therefore be aligned.
The resilient air bearings have proven to be problematic in practice, however, since they permit a slight tilting and therefore warping of the stage body upon displacement of the measurement stage and with different substrate weights. In addition, they can transfer the vertical orientation inaccuracies of the center part, caused by the irregularity of the base part surface, via the Y guidance element to the stage body. This results in a change in the interferometric position measurement as a function of the X-Y position that is arrived at, and thus has direct repercussions on measurement accuracy.
A further disadvantage of this measurement stage is the fact that transmitted-light illumination of the substrate is not possible, since the center part extends, with the Y-guide, in the center of the stage. The known measurement stage is also suitable only for substrates up to a maximum size of 220 mm. Any enlargement of the individual elements of the measurement stage for the purpose of adaptation to larger substrates would simply aggravate the vibration problem.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to describe a coordinate measuring stage that is suitable for both incident-light and transmitted-light measurements, that is suitable for future even larger and heavier substrates (with diameters of 300 mm and more) and at the same time exhibits greatly improved X-Y running accuracy and improved vertical running accuracy.
This object is achieved by a coordinate measuring stage with interferometric position determination that comprises:
a) a stationary base part having a linear X guidance element;
b) a center part placed above said stationary base part, wherein said center part is movable slidingly along the linear X guidance element, which has a first drive element associated with it and is rigidly joined to a linear Y guidance element;
c) an X-Y-positionable stage body placed above said center part, wherein sai

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