New interface definition for lithography equipment

Abstract

Disclosed herein is a method for representing control parameter data for controlling a lithographic apparatus during scanning exposure of an exposure field on a substrate, the method comprising obtaining a set of periodic basis functions, each basis function in the set of periodic basis functions having a different frequency and a period smaller than a dimension associated with the exposure field over which the lithographic apparatus needs to be controlled, obtaining control parameter data, and determining a representation of the control parameter data using the set of periodic basis functions.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application Publication No. 21159201.9, filed February 25, 2021, and European Patent Application Publication No. 21162871.4, filed March 16, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to control interfaces, and in particular to control interface parameters associated with corresponding basis functions for expressing a control profile for controlling a lithographic apparatus during a scanning (exposure) operation. [Background technology]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, patterning devices, also known as masks or reticles, can be used to generate the circuit patterns formed on individual layers of the ICs. This pattern can be transferred onto a target portion (e.g., part of a die, one die, or several dies, the target portion being often referred to as a "field" or "exposure field") on the 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. Each target portion is typically exposed by the lithographic apparatus in a scanning manner (e.g., the reticle and the substrate are moved during exposure so that one complete exposure field is exposed in one scanning motion).

[0004] In lithography processes, it is important to control the actuators of the lithography apparatus, in particular the position of the substrate stage and the imaging characteristics of the projection lens used to transfer a pattern onto a target portion during a scanning movement. For example, to enable overlay control, state-of-the-art lithography apparatuses are provided with control interfaces based on a polynomial definition of the distribution of a desired parameter (typically, pattern overlay or positioning) across the field. A well-known example of such a polynomial definition is the so-called k-parameter-based interface, where each k-parameter corresponds to a combination of polynomials associated with a particular geometric transformation (e.g., magnification, pincushion, etc.). As modern lithography apparatuses are increasingly capable of control at higher resolutions (e.g., smaller spatial scales), the control interface definitions of modern lithography apparatuses have also had to adapt to this higher resolution control. Until now, this has been achieved by incorporating increasingly higher-order polynomial terms to accommodate the enhanced control capabilities. For example, the set of available k-parameters has been significantly expanded over the past decade. However, the use of high-order (HO) polynomials has a clear drawback in control: when these HO polynomials are used to represent or fit (overlay) parameter data, the parameter values ​​at the edge of the field may become unstable (blow up), an effect often referred to as the "Runge effect." Summary of the Invention

[0005]

[0005] The object of the present invention is to provide a control interface definition that is better suited to representing parameter data at high resolution (e.g., small spatial scales) while at the same time being less susceptible to unstable behavior at the edges of the field in which the parameter data is distributed.

[0006]

[0006] According to a first aspect of the present invention, there is provided a method for representing control parameter data for controlling a lithographic apparatus during scanning exposure of an exposure field on a substrate, the method comprising obtaining a set of periodic basis functions, each basis function of the set having a different frequency and a period smaller than a dimension associated with the exposure field over which the lithographic apparatus needs to be controlled, obtaining control parameter data, and determining a representation of the control parameter data using the set of periodic basis functions.

[0007]

[0007] By representing the control parameter data using periodic functions with different periods and / or frequencies, with all periods smaller than the dimensions of the field, a high resolution control interface is provided that is less susceptible to the Runge effect.

[0008] Optionally, the representation of the control parameter data may further be used to configure or control the lithographic apparatus.

[0009]

[0009] Preferably, the method further includes obtaining a set of polynomial basis functions, each polynomial basis function having a lower degree than required to represent the control parameter data, and further using the set of polynomial basis functions together with the set of periodic basis functions in determining the representation of the control parameter data.

[0010] Preferably, the set of periodic basis functions are all based on sine functions defined over the exposure field of the substrate.

[0011] Preferably, a set of periodic basis functions is defined as a two-dimensional function in a first coordinate (X) and a second coordinate (Y) of the exposure field on the substrate.

[0012] Preferably, the set of polynomial basis functions is associated with a combination of polynomials associated with the k parameter.

[0013]

[0013] Preferably, the set of periodic basis functions includes at least a first sine function having a period at a first coordinate that is half the dimension of the exposure field at the first coordinate and a period at a second coordinate that is 40% of the dimension of the exposure field at the second coordinate.

[0014]

[0014] Preferably, the set of periodic basis functions includes at least a second sine function having a period at a first coordinate that is one-quarter of the dimension of the exposure field at the first coordinate and a period at a second coordinate that is approximately 30% of the dimension of the exposure field at the second coordinate.

[0015] Preferably, the set of polynomial basis functions has a maximum degree of 4 in the first coordinate and a maximum degree of 5 in the second coordinate.

[0016] Preferably, the combined set f(x) of periodic basis functions and polynomial basis functions associated with the first coordinate is expressed by the following equation: f(x)=c0+c1x 1 +c2x 2 +c3x 3 +c4x 4 -c5sin(2π(1-x))-c6sin(2.5π(1-x))-c7sin(3π(1-x))-c8sin(3.5π(1-x))-c9sin(4π(1-x)) In the above formula, c0 to c9 are the control interface parameters associated with the first coordinate.

[0017] Preferably, the combined set f(y) of periodic basis functions and polynomial basis functions associated with the second coordinate is expressed by the following equation: f(y)=c'0+c'1y 1 +c'2y 2 +c'3y 3 +c'4y 4 +c'5y5 -c'6sin(2.5π(1-y))- -c'7sin(3π(1-y))-c'8sin(3.5π(1-x)) In the above formula, c'0 to c'8 are control interface parameters related to the second coordinate.

[0018]

[0017] According to a second aspect of the present invention, there is provided a device manufacturing method comprising expressing control parameter data in accordance with the method of the first aspect and then using the expression of the control parameter data to control a lithographic apparatus when patterning an exposure field on a substrate.

[0019] According to a third aspect of the present invention there is provided a computer program which, when executed by a computing system, causes the computing system to perform the method of the first aspect.

[0020] According to a fourth aspect of the present invention, there is provided a computer readable medium carrying instructions which, when executed by a computing system, cause the computing system to perform the method of the first aspect.

[0021] According to a fifth aspect of the present invention, there is provided a lithographic apparatus configured to perform the method of the first aspect.

[0022]

[0021] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows a lithographic apparatus together with other equipment that forms a semiconductor device production facility. [Figure 2] 1 shows a representation of control parameter data. [Figure 3] 1 illustrates an exemplary matrix of values ​​associated with control parameter representations according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Before describing embodiments of the present invention in detail, it is beneficial to present an exemplary environment in which embodiments of the present invention may be implemented.

[0025]

[0023] Figure 1 shows a typical layout of a semiconductor manufacturing facility. A lithographic apparatus 100 applies a desired pattern to a substrate. Lithographic apparatus are used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device MA, also called a mask or reticle, provides a circuit pattern of features (often referred to as "product features") to be formed on an individual layer of the IC. This pattern is transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate "W" (e.g. a silicon wafer) via exposure 104 of the patterning device 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.

[0026] Known lithographic apparatus irradiate each target portion of the substrate by illuminating the patterning device while synchronously positioning the target portion at the imaging area of ​​the patterning device. The illuminated target portion of the substrate is called an "exposure field" or simply a "field". The layout of the field on the substrate is typically a network of adjacent rectangles aligned according to a two-dimensional Cartesian coordinate system (e.g. aligned along mutually orthogonal X and Y axes).

[0027]

[0025] A lithographic apparatus is required to accurately reproduce a desired pattern on a substrate. The positions and dimensions of the applied product features must be within certain tolerances. Position errors can occur due to overlay errors (often called "overlay"). Overlay is the error in placing a first product feature in a first layer relative to a second product feature in a second layer. Lithographic apparatus minimize overlay errors by precisely aligning each wafer with a reference before patterning. This is done by measuring the positions of alignment marks applied to the substrate. To prevent overlay errors, the substrate position is controlled during the patterning process based on the alignment measurements.

[0028] If the applied dose associated with exposure 104 is not within specifications, errors in the critical dimension (CD) of the product features may occur. For this reason, lithographic apparatus 100 must be able to accurately control the dose of radiation applied to the substrate. CD errors can also occur if the substrate is not correctly positioned with respect to the focal plane associated with the pattern image. Focus position errors are generally related to non-planarity of the substrate surface. Lithographic apparatus minimize these focus position errors by measuring the surface topography of the substrate using a level sensor before patterning. Subsequent substrate height corrections are applied during patterning to ensure accurate imaging (focusing) of the patterning device onto the substrate.

[0029]

[0027] To verify overlay and CD errors associated with the lithography process, the patterned substrate is inspected by a metrology tool 140. A common example of a metrology tool is a scatterometer. Scatterometers traditionally measure properties of dedicated metrology targets. These metrology targets represent product features, except that their dimensions are typically larger to enable accurate measurements. Scatterometers measure overlay by detecting asymmetries in the diffraction pattern associated with the overlay metrology target. Critical dimensions are measured by analysis of the diffraction pattern associated with the CD metrology target. Another example of a metrology tool is an electron beam (E-beam)-based inspection tool, such as a scanning electron microscope (SEM).

[0030] Within a semiconductor manufacturing facility, the lithography apparatus 100 and metrology apparatus 140 form part of a "lithocell" or "lithocluster." The lithocluster also includes a coating apparatus 108 for applying a photosensitive resist to a substrate W, a baking apparatus 110, a developer apparatus 112 for developing an exposed pattern into a physical resist pattern, an etching station 122, an apparatus 124 for performing a post-etch annealing step, and possibly further processing equipment 126. The metrology apparatus is configured to inspect the substrate after development (112) or after further processing (e.g., etching). The various apparatus within the lithocell are controlled by a supervisory control system SCS, which issues control signals 166 (indicated by arrows emanating from the SCS in FIG. 1 ) to control the lithography apparatus via a lithography apparatus control unit LACU 106 to execute a recipe R. The SCS enables the various apparatus to be operated to maximize throughput and product yield. An important control mechanism is the feedback 146 of the metrology tool 140 (via the SCS) to various tools, particularly the lithography tool 100. Based on the characteristics of the metrology feedback, corrective actions are determined to improve the processing quality of subsequent substrates.

[0031]

[0029] The performance of lithography equipment is conventionally controlled and corrected by methods such as advanced process control (APC), as described in, for example, U.S. Patent Application Publication No. 2012 / 008127A1. Advanced process control techniques use measurements of metrology targets applied to the substrate. A manufacturing execution system (MES) schedules the APC measurements and communicates the measurement results to a data processing unit. The data processing unit converts the characteristics of the measurement data into a recipe containing instructions for the lithography equipment. This method is highly effective in suppressing drift phenomena associated with lithography equipment.

[0032] The APC process applies corrections in a feedback loop. The APC corrections are a set of k parameters defined for each substrate, i.e., wafer, field in a lot. The k parameters are related to polynomial basis functions that parameterize the imaging distortion across each substrate field. For example, each k parameter may describe a particular image distortion component, such as one or more of scaling error, barrel distortion, pincushion distortion, etc.

[0033] The k parameter is also used as an input to the lithography system (scanner) to correct for distortion. Wafer_1 (field_1: k1~kn, field_2: k1~kn, etc.), Wafer_2 (field_1: k1~kn, field_2: k1~kn, etc.), etc.

[0034] Each k parameter is communicated to the control interface of the scanner and is then used to control / configure the relevant part of the scanner (eg, lens, wafer stage, reticle stage).

[0035] In known systems, the control interface is purely based on a polynomial basis function-based representation of the control parameter data (such as overlay data and alignment data). However, for high frequency control parameter data, it is necessary to use (very) high order polynomial basis functions (e.g., those with order greater than 5 across the field), which leads to large oscillations in the basis function representation of the control parameter data at locations where no data is available. This oscillatory behavior is often referred to as the "Runge effect" and prevents the use of high order polynomial basis functions to represent data at small spatial scales (high resolution).

[0036]

[0034] In such cases, it has been found to be beneficial to utilize periodic basis functions: Representing the control parameter data using periodic functions with different periods, all smaller than the dimensions of the field, provides a high-resolution control interface that is less susceptible to the Runge effect.

[0037]

[0035] Instead of using increasingly higher order polynomial basis functions to accommodate increasingly higher resolution control interface requirements, periodic basis functions are preferably combined with lower order polynomial basis functions to represent control parameter data.

[0038]

[0036] Typically, both polynomial and periodic basis functions are functions of the X and Y coordinates, which are related to the dimensions of the field. The dimensions of the field are usually different in X and Y, and the control characteristics of the lithographic apparatus are also different in the two coordinates. In view of the latter, the periodic and polynomial basis functions used may have different periods / frequencies and polynomial orders with respect to the X coordinate and the corresponding Y coordinate. For example, the maximum order may be 4 in X and 5 in Y, and the number of periods related to the period of the periodic basis function may vary from 2 to 4 in X and from 3 to 5 in Y. Naturally, the exact settings of the maximum and minimum orders of the polynomials and the periods / frequencies may be adapted to the field dimensions and / or control characteristics of the lithographic apparatus.

[0039]

[0037] In Figure 2, an example of an embodiment of the present invention is shown. A distortion control parameter "disto" data set is obtained, and the "disto" parameter is measured as a function of the x-coordinate (parallel to the slit projected onto the substrate by the lithography apparatus). A conventional representation of the "disto" parameter using high-order polynomial basis functions (related to the k-parameter) is shown by curve 201, and the oscillatory behavior between the measurement points can be clearly seen. Curve 202 shows the resulting representation of the "disto" parameter when using a combined set of periodic (sinusoidal) and polynomial (low-order) basis functions. Clearly, representation 202 follows the measurement points very well, yet does not exhibit any oscillatory behavior (Runge effect).

[0040]

[0038] In one embodiment, there is provided a method for representing control parameter data for controlling a lithographic apparatus, the method comprising obtaining a set of periodic basis functions, each basis function of the set having a different frequency and a period smaller than a dimension associated with an exposure field of a substrate over which the lithographic apparatus needs to be controlled; obtaining control parameter data; and determining a representation of the control parameter data using the set of periodic basis functions.

[0041]

[0039] By expressing the control parameter data using periodic functions with different periods and / or frequencies, with the period being smaller than the dimensions of the field, a high resolution control interface is provided that is less susceptible to the Runge effect.

[0042]

[0040] In one embodiment, the representation of the control parameter data can be further used to configure or control the lithographic apparatus, for example by generating a control recipe that includes coefficients by which each of a set of periodic basis functions and polynomial basis functions needs to be multiplied in order to accurately represent the control parameter data.

[0043]

[0041] In one embodiment, the method further includes obtaining a set of polynomial basis functions, each polynomial basis function having a lower degree than required to represent the control parameter data, and further using the set of polynomial basis functions together with the set of periodic basis functions in determining the representation of the control parameter data.

[0044] In one embodiment, the set of periodic basis functions are all based on sine functions defined over the exposure field of the substrate.

[0045] In one embodiment, a set of polynomial basis functions is associated with a combination of polynomials associated with the k parameter.

[0046] FIG. 3 illustrates an example matrix of values ​​associated with a control interface according to an embodiment of the present invention. For example, control parameters may be overlaid in the X or Y direction, with each control parameter having its own control interface parameters associated with a corresponding set of periodic and polynomial-based functions used to represent the control parameter data. FIG. 3 shows that for the overlay X, one set of polynomial basis functions is of order 4 in the X coordinate and order 5 in the Y coordinate, and the periodic basis functions have a repetition frequency of 2-4 cycles per field in the X coordinate and 2.5-3.5 cycles per field in the Y coordinate. For the overlay Y coordinate, a different control interface parameterization is selected for the definition of the periodic basis functions to accommodate different field dimensions and / or control characteristics of the lithography apparatus in the Y direction (scan direction) compared to the X direction (slit direction).

[0047] In one embodiment, a set of periodic basis functions is defined as a two-dimensional function in a first coordinate (X) and a second coordinate (Y) of the exposure field on the substrate.

[0048]

[0046] In one embodiment, a set of periodic basis functions includes at least a first sine function having a period at a first coordinate that is half the dimension of the exposure field at the first coordinate and a period at a second coordinate that is 40% of the dimension of the exposure field at the second coordinate.

[0049]

[0047] In one embodiment, a set of periodic basis functions includes at least a second sine function having a period at a first coordinate that is one-quarter of the dimension of the exposure field at the first coordinate and a period at a second coordinate that is approximately 30% of the dimension of the exposure field at the second coordinate.

[0050] In one embodiment, a set of polynomial basis functions has a maximum degree of 4 in the first coordinate and a maximum degree of 5 in the second coordinate.

[0051] In one embodiment, the combined set of periodic and polynomial basis functions f(x) associated with the first coordinate is expressed by: f(x)=c0+c1x 1 +c2x 2 +c3x 3 +c4x 4 -c5sin(2π(1-x))-c6sin(2.5π(1-x))-c7sin(3π(1-x))-c8sin(3.5π(1-x))-c9sin(4π(1-x)) where c0 through c9 are the control interface parameters associated with the first coordinate. The first coordinate "x" is normalized to the range [-1, 1] across the entire dimension of the field along the first coordinate.

[0052] In one embodiment, the combined set of periodic and polynomial basis functions f(y) associated with the second coordinate is expressed by: f(y)=c'0+c'1y 1 +c'2y 2 +c'3y 3 +c'4y 4 +c'5y 5-c'6sin(2.5π(1-y))- -c'7sin(3π(1-y))-c'8sin(3.5π(1-x)) where c'0 through c'8 are the control interface parameters associated with the second coordinate. The second coordinate "y" is normalized to the range [-1,1] across the entire dimension of the field along the second coordinate.

[0053] Typically, the first coordinate "x" relates to a direction perpendicular to the direction of scanning performed by the lithographic apparatus, and the second coordinate "y" relates to the direction of scanning.

[0054]

[0052] In one embodiment, a device manufacturing method is provided that includes expressing control parameter data according to a method described in any one of the preceding embodiments, and then controlling a lithographic apparatus when patterning an exposure field on a substrate using the expression of the control parameter data.

[0055] In one embodiment, there is provided a computer program which, when executed by a computing system, causes the computing system to perform the method according to any one of the preceding embodiments.

[0056] In one embodiment, a computer readable medium is provided that carries instructions that, when executed by a computing system, cause the computing system to perform the method of any one of the preceding embodiments.

[0057] In an embodiment, there is provided a lithographic apparatus configured to perform a method according to any one of the preceding embodiments.

[0058] As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 1 to 100 nm), as well as particle beams such as ion beams or electron beams. Implementations of scatterometers and other inspection devices can be made at UV and EUV wavelengths using appropriate light sources, and the present disclosure is in no way limited to systems using IR and visible radiation.

[0059] The term "lens", where applicable in context, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components. In devices operating in the UV and / or EUV range, reflective components may be used.

[0060]

[0058] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. 1. A method for representing control parameter data for controlling a lithographic apparatus during a scanning exposure of an exposure field on a substrate, said method comprising: obtaining a set of periodic basis functions, each basis function in the set having a different frequency and a period that is smaller than a dimension associated with the exposure field over which the lithographic apparatus needs to be controlled; obtaining the control parameter data; determining a representation of the control parameter data using the set of periodic basis functions; and A method comprising:

2. The method of claim 1 , wherein the representation of the control parameter data is further used to configure or control the lithographic apparatus.

3. 2. The method of claim 1, further comprising obtaining a set of polynomial basis functions, each polynomial basis function having a lower degree than required to represent the control parameter data, and further using the set of polynomial basis functions together with the set of periodic basis functions in determining the representation of the control parameter data.

4. 2. The method of claim 1, wherein said set of periodic basis functions are all based on sine functions defined over said exposure field.

5. 2. The method of claim 1, wherein the set of periodic basis functions is defined as a two-dimensional function in a first coordinate (X) and a second coordinate (Y) of the exposure field on the substrate.

6. The method of claim 3 , wherein the set of polynomial basis functions is associated with a k parameter.

7. 6. The method of claim 5, wherein the set of periodic basis functions includes at least a first sine function having a period at the first coordinate that is half the dimension of the exposure field at the first coordinate and a period at the second coordinate that is 40% of the dimension of the exposure field at the second coordinate.

8. 6. The method of claim 5, wherein the set of periodic basis functions includes at least a second sine function having a period at the first coordinate that is one-quarter of the dimension of the exposure field at the first coordinate and a period at the second coordinate that is approximately 30% of the dimension of the exposure field at the second coordinate.

9. The method of claim 3 , wherein the set of polynomial basis functions has a maximum degree of 4 in the first coordinate and a maximum degree of 5 in the second coordinate.

10. A combined set of periodic basis functions and polynomial basis functions f(x) associated with the first coordinate is expressed by the following equation: f(x)=c ０ +c １ x １ +c ２ x ２ +c ３ x ３ +c ４ x ４ -c ５ sin(2π(1-x))-c ６ sin(2.5π(1-x))-c ７ sin(3π(1-x))-c ８ sin(3.5π(1-x))-c ９ sin(4π(1-x)) In the above formula, c ０ ~c ９ 6. The method of claim 5, wherein x is a control interface parameter associated with the first coordinate, and x is a value normalized to the range [-1, 1] across the entire dimension of the field along the first coordinate.

11. A combined set of periodic basis functions and polynomial basis functions f(y) associated with the second coordinate is expressed by the following equation: f(y)c' ０ c' １ y １ c' ２ y ２ c' ３ y ３ c' ４ y ４ c' ５ y ５ c' ６ ()) ７ sin(3π(1-y))-c' ８ p In the above formula, c' ０ ~c' ８ 6. The method of claim 5, wherein y is a control interface parameter associated with the second coordinate, and y is a value normalized to the range [-1, 1] across the entire dimension of the field along the second coordinate.

12. 1. A device manufacturing method, the method comprising: representing said control parameter data according to the method of claim 1; then using the representation of the control parameter data to control the lithographic apparatus in patterning the exposure field of the substrate; A device manufacturing method comprising:

13. A computer program which, when executed by a computing system, causes said computing system to carry out the method of any one of claims 1 to 6.

14. 10. A computer-readable medium bearing instructions that, when executed by a computing system, cause the computing system to perform the method of claim 1.

15. A lithographic apparatus configured to perform the method of claim 1.

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