Lithographic apparatus and method for determining Z position errors/variations and substrate table flatness

Abstract

The invention pertains to a measurement system for measuring displacement of a moveable object relative to a base in at least a first direction of measurement, the moveable object having at least one reference part that is moveable in a plane of movement relative to the base, the actual movements of the reference part being within an area of said plane of movement that is bounded by a closed contour having a shape. The measurement system comprises a sensor head that operatively communicates with a planar element. The sensor head is mounted onto the base and the planar element being mounted onto the reference part of the moveable object or the other way around, wherein the planar element has a shape that is essentially identical to the shape of the closed contour.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a lithographic apparatus, device manufacturing method, and a measurement system. [0003] 2. Description of the Related Art [0004] A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). [0005] In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradia...

AI Technical Summary

Benefits of technology

[0010] By giving the planar element the same shape as the shape of the closed contour, the face of the planar element cooperating with the sensor head is used efficiently as no parts of the planar element remain unused.

[0011] In a preferred embodiment, the first direction of measurement lies within a plane that is at least substantially parallel to the plane of movement. In that case, preferably the sensor head is an encoder head and the planar element is a ruler, which ruler comprises a grating. By using an encoder system comprising an encoder head and a grating, an accuracy comparable to the accuracy of an interferometer can be achieved, without having the disadvantages of an interferometer.

Problems solved by technology

Interferometers are used for their accuracy, but are very expensive equipment.

The mirrors also have to be arranged under various angles, which makes the moveable object even more complex to produce.

Capacitive sensors, on the other hand, have a small range over which they can used, and their accuracy is not always sufficient.

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