US-12619161-B2 - Method for inferring a processing parameter such as focus and associated apparatuses and manufacturing method

US12619161B2US 12619161 B2US12619161 B2US 12619161B2US-12619161-B2

Abstract

A method of inferring a value for a first processing parameter of a lithographic process, the first processing parameter being subject to a coupled dependency of a second processing parameter. The method includes determining a first metric and a second metric from measurement data, each of the first metric and second metric being dependent on both the first processing parameter and second processing parameter The first metric shows a stronger dependence to the first processing parameter than the second processing parameter and the second metric shows a stronger dependence to the second processing parameter than the first processing parameter. The value for the first processing parameter is inferred from the first and second metrics.

Inventors

Frank Staals

Assignees

ASML NETHERLANDS B.V.

Dates

Publication Date: 20260505
Application Date: 20200907
Priority Date: 20190926

Claims (20)

1 . A method of inferring a value for a first processing parameter and a value for a second processing parameter of a lithographic process, the method comprising: determining a first metric and a second metric from measurement data relating to at least one structure on a substrate formed using the lithographic process, each of the first metric and second metric being dependent on both the first processing parameter and the second processing parameter, the first metric having a different dependence on the first processing parameter than the second processing parameter and the second metric having a different dependence on the second processing parameter than the first processing parameter; and inferring the value for the first processing parameter and the value for the second processing parameter based on a relationship of the first metric against the second metric, or vice versa.
2 . The method as claimed in claim 1 , wherein the first metric has a stronger dependence on the first processing parameter than the second processing parameter.
3 . The method as claimed in claim 1 , wherein the second metric has a stronger dependence on the second processing parameter than the first processing parameter.
4 . The method as claimed in claim 1 , wherein the first metric comprises an asymmetry metric based on a difference in intensity of complementary diffraction orders from diffraction of measurement radiation following measurement of the at least one structure.
5 . The method as claimed in claim 4 , wherein the second metric comprises a sum metric based on a sum of the intensities of the complementary diffraction orders.
6 . The method as claimed in claim 1 , wherein the at least one structure comprises a target having been formed with a focus dependent asymmetry, and the first processing parameter comprises focus during formation of the target.
7 . The method as claimed in claim 1 , wherein the second processing parameter comprises effective dose during formation of the target.
8 . The method as claimed in claim 1 , wherein the inferring comprises referring to a calibration relationship describing the relationship of the first metric against the second metric for different values of the first processing parameter and the second processing parameter.
9 . A metrology apparatus for measuring a parameter of a lithographic process, the metrology apparatus configured to perform the method of claim 1 .
10 . A lithographic system comprising: a lithographic apparatus comprising a projection optical system arranged to project an image of a pattern onto a substrate; and the metrology apparatus according to claim 9 , wherein the lithographic apparatus is arranged to use the inferred value for the first processing parameter or for the second processing parameter in determining a control correction when applying the pattern to further substrates.
11 . A computer program product comprising a non-transitory computer-readable medium having processor readable instructions therein, the instructions, when run on a suitable processor controlled apparatus, are configured to cause the processor controlled apparatus to perform the method of claim 1 .
12 . A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including: using the method of claim 1 to monitor the first processing parameter or second processing parameter, and controlling the lithographic process for later substrates in accordance with the inferred value for the first processing parameter or second processing parameter.
13 . A method of inferring a focus value from a target having been formed with a focus dependent asymmetry, relating to focus during formation of the target in a lithographic process, and inferring a value of effective dose during formation of the target, the method comprising: determining an asymmetry metric and a sum metric from measurement data, the asymmetry metric being based on a difference in intensity of complementary diffraction orders from diffraction of measurement radiation following measurement of the target, and the sum metric is based on a sum of the intensities of the complementary diffraction orders; and inferring the focus value and the value of effective dose from a relationship of the asymmetry metric against the sum metric, or vice versa.
14 . A computer program product comprising a non-transitory computer-readable medium having processor readable instructions therein, the instructions, when run on a suitable processor controlled apparatus, are configured to cause the processor controlled apparatus to perform the method of claim 13 .
15 . A metrology apparatus for measuring a parameter of a lithographic process, the metrology apparatus configured to perform the method of claim 13 .
16 . A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including: using the method of claim 13 to monitor the focus value or the value of effective dose, and controlling the lithographic process for later substrates in accordance with the inferred focus value or inferred value of effective dose.
17 . A method comprising: determining a calibration relationship based on calibration measurements relating to at least one structure on a substrate formed using a lithographic process at different values for a first processing parameter and a second processing parameter, the calibration relationship describing a relationship of a first metric against a second metric for different values of the first processing parameter and the second processing parameter, wherein each of the first metric and second metric is dependent on both the first processing parameter and second processing parameter, the first metric having a stronger dependence on the first processing parameter than the second processing parameter and the second metric having a stronger dependence on the second processing parameter than the first processing parameter; and fitting a calibration plane for performing a calibration in the lithographic process to a constant value for the second processing parameter.
18 . A computer program product comprising a non-transitory computer-readable medium having processor readable instructions therein, the instructions, when run on a suitable processor controlled apparatus, are configured to cause the processor controlled apparatus to perform the method of claim 17 .
19 . A metrology apparatus for measuring a parameter of a lithographic process, the metrology apparatus configured to perform the method of claim 17 .
20 . The method as claimed in claim 17 , wherein the first processing parameter comprises focus during applying of a pattern using the lithographic process or the second processing parameter comprises effective dose during applying of a pattern using the lithographic process.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is the U.S. national phase entry of PCT Patent Application No. PCT/EP2020/074900 which was filed on Sep. 7, 2020, which claims the benefit of priority of European Patent Application No. 19199804.6 which was filed on Sep. 26, 2019 and which is incorporated herein in its entirety by reference. BACKGROUND Field of the Invention The present invention relates to a metrology apparatus and methods usable, for example, to perform metrology in the manufacture of devices by lithographic techniques. The invention further relates to such methods for monitoring a focus parameter in a lithographic process. Background Art A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. In lithographic processes, it is desirable frequently to make measurements of the structures created, e.g., for process control and verification. Various tools for making such measurements are known, including scanning electron microscopes, which are often used to measure critical dimension (CD), and specialized tools to measure overlay, the accuracy of alignment of two layers in a device. Recently, various forms of scatterometers have been developed for use in the lithographic field. These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation—e.g., intensity at a single angle of reflection as a function of wavelength; intensity at one or more wavelengths as a function of reflected angle; or polarization as a function of reflected angle—to obtain a diffraction “spectrum” from which a property of interest of the target can be determined. Examples of known scatterometers include angle-resolved scatterometers of the type described in US2006033921A1 and US2010201963A1. The targets used by such scatterometers are relatively large, e.g., 40 μm by 40 μm, gratings and the measurement beam generates a spot that is smaller than the grating (i.e., the grating is underfilled). Examples of dark field imaging metrology can be found in international patent applications US20100328655A1 and US2011069292A1 which documents are hereby incorporated by reference in their entirety. Further developments of the technique have been described in published patent publications US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A and WO2013178422A1. These targets can be smaller than the illumination spot and may be surrounded by product structures on a wafer. Multiple gratings can be measured in one image, using a composite grating target. The contents of all these applications are also incorporated herein by reference. One important parameter of a lithographic process which requires monitoring is focus. There is a desire to integrate an ever-increasing number of electronic components in an IC. To realize this, it is necessary to decrease the size of the components and therefore to increase the resolution of the projection system, so that increasingly smaller details, or line widths, can be projected on a target portion of the substrate. As the critical dimension (CD) in lithography shrinks, consistency of focus, both across a substrate and between substrates, becomes increasingly important. CD is the dimension of a feature or features (such as the gate width of a transistor) for which variations will cause undesirable variation in physical properties of the feature. Traditionally, optimal settings were determined by “send-ahead wafers” i.e. substrates that are exposed, developed and measured in advance of a production run. In the send-ahead wafers, test structures were exposed in a so-called focus exposure matrix (FEM) and the best focus and energy settings were determined from examination of those test structures. Focus and dose are cross-linked terms, and therefore focus inference is affected by any variation of effective dose from assumed dose. SUMMARY OF THE INVENTION The present invention aims to address the issue of the effect of dose on focus inference. The invention in a first aspect provides a method of inferring a value for a first processing parameter of a lithographic process, the method comprising: determining a first metric and a second metric from measurem