Inspection method and apparatus lithographic apparatus, lithographic processing cell, device manufacturing method and distance measuring system
AssigneeASML Netherlands B.V.
InventorsJohan Maria Van Boxmeer, Henricus Petrus Maria Pellemans, Robert Franken
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Abstract
A scatterometer has a focus sensor arranged to detect whether the target being measured is in a correct focal plane. A modulation is applied to a component of the focus sensor or the scatterometer such that a defocus as measured by the focus sensor varies according to a certain function. From knowledge of the modulation, the gain of the sensor can be calibrated.
Claims21
An inspection apparatus configured to measure a property of a substrate, the apparatus comprising:
- a focus sensor arranged to generate a focus error signal indicative of a position of the substrate relative to an optimum focal plane;
- a modulator arranged to impose an alternating signal on the focus error signal;
- and
- a gain determination circuit arranged to calculate a gain of the focus sensor from the focus error signal on which the alternating signal has been imposed.
A method of measuring a property of a substrate, the method comprising:
- generating a focus error signal indicative of a position of the substrate relative to an optimum focal plane using a focus sensor;
- imposing an alternating signal on the focus error signal;
- and
- calculating a gain of the focus sensor from the focus error signal on which the alternating signal has been imposed.
A lithographic apparatus, comprising:
- an illumination optical system arranged to illuminate a pattern;
- a projection optical system arranged to project an image of the pattern on to a substrate;
- and
- an inspection apparatus configured to measure a property of a substrate, the apparatus comprising:
- a focus sensor arranged to generate a focus error signal indicative of a position of the substrate relative to an optimum focal plane;
- a modulator arranged to impose an alternating signal on the focus error signal;
- and
- a gain determination circuit arranged to calculate a gain of the focus sensor from the focus error signal on which the alternating signal has been imposed.
A lithographic cell comprising:
- a coater arranged to coat a substrate with a radiation sensitive layer;
- a lithographic apparatus arranged to expose an image onto the radiation sensitive layer of the substrate coated by the coater;
- a developer arranged to develop an image exposed by the lithographic apparatus;
- and
- an inspection apparatus configured to measure a property of a substrate, the apparatus comprising:
- a focus sensor arranged to generate a focus error signal indicative of a position of the substrate relative to an optimum focal plane;
- a modulator arranged to impose an alternating signal on the focus error signal;
- and
- a gain determination circuit arranged to calculate a gain of the focus sensor from the focus error signal on which the alternating signal has been imposed.
A device manufacturing method comprising:
- using a lithographic apparatus to form a pattern on a substrate;
- and
- determining a value related to a parameter of the formed pattern by:
- generating a focus error signal indicative of a position of the substrate relative to an optimum focal plane using a focus sensor;
- imposing an alternating signal on the focus error signal;
- and
- calculating a gain of the focus sensor from the focus error signal on which the alternating signal has been imposed.
A distance measuring system arranged to measure a distance between a target and a reference, the system comprising:
- a sensor arranged to output a signal having a value indicative of the distance;
- a modulator arranged to vary the distance as measured by the sensor according to a known cyclic function;
- and
- a signal processor arranged to, responsive to the signal output by the sensor and the known cyclic function, determine therefrom a relationship between the value of the signal and the actual distance between the target and the reference.
Dependencies are inferred from the claim text.