Lithographic apparatus and device manufacturing method utilizing data filtering

• US 7,403,265 B2
• Filed: 03/30/2005
• Issued: 07/22/2008
• Est. Priority Date: 03/30/2005
• Status: Expired due to Fees

• 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
• Primary Examiner(s): Mathews; Alan A
• Application Number:
  US11/093,259
• Publication Number:
  US 20060221322A1
• Time in Patent Office: 1,210 Days
• Field of Search: 355/53, 355/67, 355/77
• US Class Current: 355/67
• 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 comprise 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 of radiation. The patterning device modulates the sub-beams of radiation 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 for pattern sharpening, image log slope control, and/or CD biasing can also be used.

Claims

1. A lithography apparatus, comprising:

a projection system that projects a beam of radiation onto a substrate as an array of sub-beams of radiation;

a patterning device that modulates 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 low-pass filter that operates on pattern data derived from the requested dose pattern in order to form a frequency-clipped target dose pattern that predominantly comprises only spatial frequency components below a selected threshold frequency; and

a data manipulation device that 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.

2. The lithographic apparatus of claim 1, wherein the threshold frequency is chosen so that a difference between a dose received at a point on the substrate and the requested dose at the point is independent of a position of the point relative to grid positions associated with the array of spot exposures.

3. The lithographic apparatus of claim 1, wherein the threshold frequency is substantially equal to π

/p, wherein p is a spot exposure pitch.

4. The lithographic apparatus of claim 3, wherein the array of spot exposures has a rectangular form.

5. The lithographic apparatus of claim 1, wherein the threshold frequency is substantially equal to 4π

/3p, wherein p is a spot exposure pitch.

6. The lithographic apparatus of claim 5, wherein the array of spot exposures has one of a hexagonal form or a quasi-hexagonal form.

7. The lithographic apparatus of claim 1, wherein the filter has an amplitude-frequency response substantially equal to that of the array of spot exposures.

8. The lithographic apparatus of claim 1, further comprising:

a sharpening filter that sharpens a target product feature to be formed.

9. The lithographic apparatus of claim 8, wherein the sharpening filter is defined as a mathematical function with a spatial Fourier transform, {tilde over (F)}_{sharp filter}, defined as follows:

${\tilde{F}}_{\mathrm{sharp}<br><br><br><br>\mathrm{filter}}=\left(\begin{array}{cc}<br><br>1/\tilde{H}<br><br>\left(\mathrm{\omega <br><br>}\right)<br><br>& \mathrm{when}<br><br><br><br>\mathrm{\omega <br><br>}\le <br><br>{\mathrm{\omega <br><br>}}_M\\ <br><br>1/\tilde{H}<br><br>\left(\mathrm{\omega <br><br>}={\mathrm{\omega <br><br>}}_M\right)<br><br>& \mathrm{when}<br><br><br><br>\mathrm{\omega <br><br>}><br><br>{\mathrm{\omega <br><br>}}_M\end{array}\right)$

wherein {tilde over (H)}(ω

) is a Fourier transform of the target product feature, ω

=√

{square root over ((k_x²+k_y²),)}ω

_M is a selected threshold spatial frequency, and k_x and k_y are spatial frequency components corresponding respectively to perpendicular axes x and y lying in a plane of the substrate.

10. The lithographic apparatus of claim 9, wherein ω

_M=π

/p and p is a pitch of the array of spot exposures.

11. The lithographic apparatus of claim 8, wherein an application of the sharpening filter is defined as the following multiplication in the Fourier domain:

{tilde over (D)}_{sharp filtered}={tilde over (F)}_{sharp filter}·

{tilde over (F)}_{low-pass filter}·

{tilde over (D)}_unfiltered,

wherein {tilde over (D)}_unfiltered is a Fourier domain representation of the pattern data derived from the requested dose pattern, {tilde over (F)}_{low-pass filter} is a Fourier domain representation of the low-pass filter, {tilde over (F)}_{sharp filter} is a Fourier domain representation of the sharpening filter, and {tilde over (D)}_{sharp filtered} is a Fourier domain representation of the pattern data derived from the requested dose pattern after filtering by the sharpening filter and the low-pass filter.

12. The lithographic apparatus of claim 1, further comprising:

an image log slope filter that controls an image log slope of the pattern to be formed on the substrate.

13. The lithographic apparatus of claim 12, wherein the image log slope filter is defined as the following mathematical function in the spatial domain:

$F_{\mathrm{slope}}=\{\begin{array}{cc}\frac{1}{\mathrm{\pi <br><br>}·<br><br>R_{\mathrm{slope}}^2}& \mathrm{when}<br><br><br><br>\sqrt{x^2+y^2}\le <br><br>R_{\mathrm{slope}}\\ 0& \mathrm{when}<br><br><br><br>\sqrt{x^2+y^2}><br><br>R_{\mathrm{slope}}\end{array}$

where x and y are position coordinates defined relative to axes lying in a plane of the substrate, and R_slope is a variable control parameter useable to control the image log slope.

14. The lithographic apparatus of claim 12, wherein an application of the image log slope filter is defined as the following multiplication in the Fourier domain:

{tilde over (D)}_{slope filtered}={tilde over (F)}_{slope filter}·

{tilde over (F)}_{low-pass filter}·

{tilde over (D)}_unfiltered

wherein {tilde over (D)}_unfiltered is a Fourier domain representation of the pattern data derived from the requested dose pattern, {tilde over (F)}_{low-pass filter} is a Fourier domain representation of the low-pass filter, {tilde over (F)}_{slope filter} is a Fourier domain representation of the image log slope filter, and {tilde over (D)}_{slope filtered} is a Fourier domain representation of the pattern data derived from the requested dose pattern after filtering by the log slope filter and the low-pass filter.

15. The lithographic apparatus of claim 1, further comprising:

a combined filter that operates on the pattern data derived from the requested dose pattern in order to control an image log slope of the pattern to be formed on the substrate and sharpen a target product feature in the pattern data derived from the requested dose pattern.

16. The lithographic apparatus of claim 15, wherein the application of the combined filter is defined as the following multiplication in the Fourier domain:

{tilde over (D)}_{combined filtered}={tilde over (F)}_{combined filter}·

{tilde over (D)}_unfiltered=({tilde over (F)}_{slope filter}·

{tilde over (F)}_{sharp filter}·

{tilde over (F)}_{low-pass filter})·

{tilde over (D)}_unfiltered

wherein {tilde over (D)}_unfiltered is a Fourier domain representation of the pattern data derived from the requested dose pattern, {tilde over (F)}_{low-pass filter} is a Fourier domain representation of the low-pass filter, {tilde over (F)}_{sharp filter} is a Fourier domain representation of a sharpening filter, {tilde over (F)}_{slope filter} is a Fourier domain representation of a image log slope filter, {tilde over (F)}_{combined filter} is a Fourier domain representation of a combined filter comprising the operations of {tilde over (F)}_{slope filter}, {tilde over (F)}_{sharp filter} and {tilde over (F)}_{low-pass filter}, and {tilde over (D)}_{combined filtered} is a Fourier domain representation of the pattern data derived from the requested dose pattern after filtering by the image log slope filter, the sharpening filter and the low-pass filter.

17. A device manufacturing 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 one 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;

filtering 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; and

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 the frequency-clipped target dose pattern.