Lithographic Apparatus and Device Manufacturing Method Utilizing Data Filtering

• US 20090011345A1
• Filed: 07/02/2008
• Published: 01/08/2009
• Est. Priority Date: 03/30/2005
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Tinnemans, Patricius Aloysius Jacobus, Baselmans, Johannes Jacobus Matheus
• Granted Patent: US 7,864,295 B2
• Time in Patent Office: Days
• US Class Current: 430/30
• CPC Class Codes: G03F 7/70191 Optical correction elements, filters or phase plates for controlling intensity, wavelength, polarisation, phase or the like
• CPC Class Codes: G03F 7/70291 Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices
• CPC Class Codes: G03F 7/70433 Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors
• CPC Class Codes: G03F 7/70508 Data handling in all parts of the microlithographic apparatus, e.g. handling pattern data for addressable masks or data transfer to or from different components within the exposure apparatus

Abstract

An apparatus and method are used to form patterns on a substrate. The apparatus comprises a projection system, a patterning device, a low-pass filter, and a data manipulation device. The projection system projects a beam of radiation onto the substrate as an array of sub-beams. The patterning device modulates the sub-beams to substantially produce a requested dose pattern on the substrate. The low-pass filter operates on pattern data derived from the requested dose pattern in order to form a frequency-clipped target dose pattern that comprises only spatial frequency components below a selected threshold frequency. The data manipulation device produces a control signal comprising spot exposure intensities to be produced by the patterning device, based on a direct algebraic least-squares fit of the spot exposure intensities to the frequency-clipped target dose pattern. In various examples, filters can also be used.

Claims

1. A lithography apparatus, comprising:

a projection system configured to project a beam of radiation onto a substrate as an array of sub-beams of radiation;

a patterning device configured to modulate the sub-beams of radiation to substantially produce a requested dose pattern on the substrate, the dose pattern being built up from an array of spot exposures in which at least neighboring ones of the spot exposures are imaged incoherently with respect to each other and each of the spot exposures is produced by one of the sub-beams of radiation at a particular time;

a data manipulation device configured to produce a control signal comprising spot exposure intensities to be produced by the patterning device based on a direct algebraic least-squares fit of spot exposure intensities to data derived from the requested dose pattern, wherein the least-squares fit is performed by multiplying a pseudo-inverted form of a point-spread function matrix by a column vector representing the pattern data derived from the requested dose pattern, the point-spread function matrix comprising information about a shape and relative position of the point-spread function of each spot to be exposed on the substrate by one of the sub-beams of radiation at a given time; and

a low-pass filter configured to remove spatial frequency components of a signal above a selected threshold frequency, incorporated offline into the pseudo-inverted form of the point-spread-function matrix, ready for the least-squares fit, by the following operation;

[K]⁺_filtered=F_{low-pass filter}[K]⁺,

wherein [K]⁺ and [K]⁺_filtered are the pseudo-inverted form of the point-spread function matrix respectively before and after filtering, and

wherein F_{low-pass filter} is a mathematical definition of the low-pass filter in a spatial domain.

2. The lithography apparatus of claim 1, further comprising:

a sharpening filter configured to sharpen a target product feature to be formed, defined in a spatial domain by mathematical function F_{sharp filter}, wherein the sharpening filter and the low-pass filter are incorporated offline into the pseudo-inverted form of the point-spread function matrix [K]⁺ to form a filtered point-spread function matrix [K]⁺_filtered via the following operation;

[K]⁺_filtered=F_{combined filter}[K]⁺=(F_{low-pass filter}F_{sharp filter})[K]⁺,

wherein F_{combined filter} is a mathematical definition of the combined action of the low-pass filter and the sharpening filter in the spatial domain.

3. The lithography apparatus of claim 1, further comprising:

an image log slope filter configured to control an image log slope of the pattern to be formed on the substrate, defined in the spatial domain by mathematical function F_{slope filter}, wherein the image log slope filter and the low-pass filter are incorporated offline into the point-spread function matrix [K]⁺ to form a filtered point-spread function matrix [K]⁺_filtered via the following operation;

[K]⁺_filtered=F_{combined filter}[K]⁺=(F_{low-pass filter}F_{slope filter})[K]⁺,

wherein F_{combined filter} is a mathematical definition of the combined action of the low-pass filter and the sharpening filter in the spatial domain.

4. The lithography apparatus of claim 1, further comprising:

a sharpening filter configured to sharpen a target product feature to be formed, defined in a spatial domain by mathematical function F_{sharp filter}; and

an image log slope filter configured to control an image log slope of the pattern to be formed on the substrate, defined in the spatial domain by mathematical function F_{slope filter}, wherein the sharpening filter, the image log slope filter, and the low-pass filter are incorporated offline into the point-spread function matrix [K]⁺ to form a filtered point-spread function matrix [K]⁺_filtered via the following operation;

[K]⁺_filtered=F_{combined filter}[K]⁺=(F_{low-pass filter}F_{sharp filter}F_{slope filter})[K]⁺,

wherein F_{combined filter} is a mathematical definition of the combined action of the low-pass filter, the sharpening filter, and the image log slope filter in the spatial domain.

5. A lithography apparatus, comprising:

a projection system configured to project a beam of radiation onto a substrate as an array of sub-beams of radiation;

an array of individually controllable elements configured to modulate the sub-beams of radiation to substantially form a requested dose pattern on the substrate, the requested dose pattern being built up over time from an array of spot exposures, each of the spot exposures being produced by one of the sub-beams of radiation at a given time;

a rasterizer device configured to convert data defining the requested dose pattern to a sequence of data representing the requested dose at a corresponding sequence of points within the pattern;

a data manipulation device configured to receive the sequence of data and generates a control signal therefrom, the control signal being used to control the array of individually controllable elements; and

a focus determination unit configured to measure a position of at least a portion of the substrate relative to a plane of best focus, wherein the data manipulation device comprises a focus compensation unit that changes the control signal based on measured deviations of the at least a portion of the substrate relative to the plane of best focus.

6. The lithography apparatus of claim 5, wherein the focus determination unit comprises:

at least one ultrasonic transducer and receiver, rigidly connected to the projection system and configured to measure the position of the substrate surface relative to the projection system, at one or more points, by measuring travel time of reflected ultrasonic waves.

7. A lithography apparatus, comprising:

a patterning device configured to modulate a beam of radiation;

a projection system configured to project the modulated beam of radiation onto a substrate; and

a CD-biasing filter configured to operate on pattern data derived from a requested dose pattern to be transmitted to the patterning device, which controls critical dimension characteristics of a radiation dose pattern produced by the patterning device.

8. The lithography apparatus of claim 7, wherein the CD-biasing filter is configured to adjust a magnification of at least a portion of the dose pattern without adjusting a position of the portion relative to other portions of the dose pattern.

9. The lithography apparatus of claim 7, wherein the CD-biasing filter is configured to adjust a critical dimension of multiple regions of the dose pattern independently.

10. The lithography apparatus of claim 7, wherein the CD-biasing filter is configured to adjust a critical dimension parallel to a first axis in a plane of the dose pattern independently of a critical dimension parallel to a second non-parallel axis in the plane of the dose pattern.

11. A lithography apparatus, comprising:

an illumination system configured to condition a beam of radiation;

a projection system configured to project the beam of radiation onto the substrate as an array of sub-beams of radiation;

a patterning device configured to modulate the sub-beams of radiation to substantially produce a requested dose pattern on the substrate, the dose pattern being built up from an array of spot exposures, each of the spot exposure being produced by one of the sub-beams of radiation at a particular time, wherein the radiation intensity of a given sub-beam of radiation is controlled according to an activation state of a corresponding portion of the patterning device; and

a data manipulation device configured to transform a signal comprising spot exposure radiation doses derived from the requested dose pattern to a control signal representing activation states of the patterning device to produce the requested dose pattern, wherein the transformation corrects for intensity variations caused by at least one of components of the projection system, components of the illumination system, radiation sources for the illumination system, and components of the patterning device.

12. The lithography apparatus of claim 11, wherein the data manipulation device comprises:

a memory device configured to store a lookup table, the data manipulation device accessing the lookup table to convert from an activation state for a particular portion of the patterning device to a corresponding control voltage to produce the activation state for that portion, wherein the transformation is performed by changing at least a subset of values in the lookup table.

13. The lithography apparatus of claim 11, wherein the data manipulation device comprises:

a multiplier configured to convert a spot exposure radiation dose produced by a particular portion of the patterning device to an activation state for that portion, wherein the transformation is performed by changing a gain characteristic of the multiplier.

14. A method, comprising:

projecting a beam of radiation onto a substrate as an array of sub-beams of radiation;

modulating the sub-beams of radiation to substantially produce a requested dose pattern on the substrate, the dose pattern being built up from an array of spot exposures in which at least neighboring ones of the spot exposures are imaged incoherently with respect to each other and each of the spot exposures is produced by one of the sub-beams of radiation at a particular time;

producing a control signal comprising spot exposure intensities to be produced by the modulating based on a direct algebraic least-squares fit of the spot exposure intensities to data derived from the requested dose pattern, wherein the least-squares fit is performed by multiplying a pseudo-inverted form of a point-spread function matrix by a column vector representing the pattern data derived from the requested dose pattern, the point-spread function matrix comprising information about the shape and relative position of the point-spread function of each spot to be exposed on the substrate by one of the sub-beams of radiation at a given time; and

filtering to remove spatial frequency components of a signal above a selected threshold frequency, incorporated offline into the pseudo-inverted form of the point-spread-function matrix, ready for the least-squares fit, by the following operation;

[K]⁺_filtered=F_{low-pass filter}[K]⁺,

wherein [K]⁺ and [K]⁺_filtered are the pseudo-inverted form of the point-spread function matrix respectively before and after filtering, and where F_{low-pass filter} represents a mathematical definition of the filtering in the spatial domain.

15. A method, comprising:

projecting a beam of radiation onto a substrate as an array of sub-beams of radiation;

modulating the sub-beams of radiation to substantially form a requested dose pattern on the substrate, the requested dose pattern being built up over time from an array of spot exposures, each of the spot exposures being produced by one of the sub-beams of radiation at a given time;

converting data defining the requested dose pattern to a sequence of data representing the requested dose at a corresponding sequence of points within the pattern;

generating a control signal from the sequence of data that is used to control the modulating;

measuring the position of at least a portion of the substrate relative to a plane of best focus; and

modifying the control signal based on measured deviations of the at least a portion of the substrate relative to the plane of best focus.

16. A method, comprising:

modulating a beam of radiation;

projecting the modulated beam of radiation onto a substrate; and

CD-biasing filtering the pattern data derived from a requested dose pattern, which is used to perform the modulating, in order to control critical dimension characteristics of a radiation dose pattern produced by the modulating.

17. A method, comprising:

conditioning a beam of radiation;

projecting the beam of radiation onto the substrate as an array of sub-beams of radiation;

modulating the sub-beams of radiation to substantially produce a requested dose pattern on the substrate, the dose pattern being built up from an array of spot exposures, each of the spot exposures being produced by one of the sub-beams of radiation at a particular time;

controlling radiation intensity of a given one of the sub-beams of radiation according to an activation state of a corresponding portion of a patterning device that performs the modulating;

transforming a signal comprising spot exposure radiation doses derived from the requested dose pattern to a control signal representing activation states of the patterning device to substantially produce the requested dose pattern; and

modifying the transforming step to correct for intensity variations caused by at least one of components of the projection system, components of the illumination system, radiation sources for the illumination system, and components of the patterning device.