CN114270259A

CN114270259A - Apparatus and method for reticle identification in a lithographic apparatus

Info

Publication number: CN114270259A
Application number: CN202080056946.3A
Authority: CN
Inventors: Y·弗拉迪米斯基; M·阿里夫; J·H·瓦尔什
Original assignee: ASML Holding NV
Current assignee: ASML Holding NV
Priority date: 2019-08-12
Filing date: 2020-08-05
Publication date: 2022-04-01
Also published as: TWI878333B; WO2021028296A1; TW202113470A

Abstract

A code mark for a reticle, such as a reticle, wherein individual elements of the mark comprise a diffraction grating such that the apparent brightness of an element depends on whether light from the element is diffracted into or out of the numerical aperture of a lens of a reader.

Description

Apparatus and method for reticle identification in a lithographic apparatus

Cross Reference to Related Applications

This application claims priority to U.S. application 62/885,561 filed on 12.8.2019, which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a method and system for identifying a substrate (such as a reticle or wafer within a lithographic apparatus) in a lithographic apparatus.

Background

A lithographic apparatus is a machine that applies a desired pattern onto a substrate, such as a wafer of semiconductor material, usually onto a target portion of the substrate. A reticle (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 a wafer. The transfer of the pattern is typically achieved by imaging onto a layer of radiation-sensitive material (resist) provided on the wafer. Typically, a single wafer will contain adjacent target portions that are successively patterned.

A lithography system employs some form of reticle that is imaged onto a beam used to illuminate a wafer. A "reticle" as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. Reticles in DUV and EUV lithography systems employ barcode readers to identify the reticle by reading a barcode printed thereon. The most advanced bar code readers in lithography systems rely on bar code target contrast formed by reticle coatings with different transmission and/or reflection, including bar code patterns.

The properties of the coatings used in the lithography system are designed for and controlled by lithography performance requirements, offering very limited (if any) possibilities in the optimization of specular reflection and/or transmission properties suitable for the reliable performance of barcode readers. The stringent lithographic optical requirements for reduced Critical Dimension (CD) imaging of semiconductor circuit features by advanced reticle coatings result in attenuated barcode contrast, thus preventing reliable barcode reading. In many cases, the bar code contrast value is as low as a few percent, resulting in bar code reader failure.

Disclosure of Invention

The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

According to one aspect of an embodiment, a reticle is disclosed that includes a pattern and a code mark, the code mark including a plurality of cells, a subset of the cells in the plurality of cells each including a diffraction grating. The plurality of cells may be arranged as a cell array. The array may be a regular array. The array may be a rectangular array. The diffraction grating may comprise a two-dimensional diffraction grating. The diffraction grating may comprise a rectangular grid of diffraction elements. The rectangular grid includes aligned rows and columns of diffractive elements. The rectangular grid may comprise offset rows and columns of diffractive elements. The diffractive element may be displaced from the precise periodic position spaced by a distance d by an amount on the order of d multiplied by the numerical aperture of a lens arranged to receive light from the grid.

According to another aspect of an embodiment, a lithographic apparatus is disclosed for transferring a pattern from a reticle onto a substrate, the lithographic apparatus comprising a reticle having a code mark, the code mark comprising a plurality of cells, a subset of the cells in the plurality of cells each comprising a diffraction grating. The plurality of cells may be arranged as a cell array. The array may be a regular array. The array may be a rectangular array. The diffraction grating may comprise a two-dimensional diffraction grating. The diffraction grating may comprise a rectangular grid of diffraction elements. The rectangular grid includes aligned rows and columns of diffractive elements. The rectangular grid may comprise offset rows and columns of diffractive elements. The diffractive element may be displaced from the precise periodic position spaced by a distance d by an amount on the order of d multiplied by the numerical aperture of a lens arranged to receive light from the grid.

According to another aspect of the embodiments, there is disclosed a device manufacturing method comprising: identifying a reticle using a code mark comprising a plurality of cells, a subset of the cells in the plurality of cells each comprising a diffraction grating; and transferring the pattern on the reticle to a substrate.

Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to the specific embodiments described herein. These embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

Drawings

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.

FIG. 1 is a non-to-scale diagram of a reticle according to an embodiment of the invention.

FIG. 2 is a diagram of a bar code pattern in accordance with an aspect of an embodiment of the present invention.

Fig. 3 is a non-to-scale diagram of a reflective barcode reading arrangement with on-axis illumination in accordance with an aspect of an embodiment.

Fig. 4 is a non-to-scale diagram of a reflective barcode reading arrangement with off-axis illumination in accordance with an aspect of an embodiment.

Fig. 5 is a non-to-scale diagram of a transmissive barcode reading arrangement with on-axis illumination in accordance with an aspect of an embodiment.

Fig. 6 is a non-to-scale diagram of a transmissive barcode reading arrangement with off-axis illumination in accordance with an aspect of an embodiment.

The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.

Detailed Description

This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the appended claims.

Reference in the described embodiment(s) and specification to "one embodiment," "an example embodiment," etc., indicates that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Aspects of embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include: read Only Memory (ROM); random Access Memory (RAM); a magnetic disk storage medium; an optical storage medium; a flash memory device; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

Fig. 1 shows a reticle MA. The reticle may be transmissive or reflective. Examples of reticles include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Reticle MA may be aligned to the substrate using reticle alignment marks M1, M2. The reticle MA may also include code marks BC for identifying the reticle. As used herein, the term code mark refers to any one-or two-dimensional pattern placed on a mask to provide information that can be read by a lithographic apparatus to identify the mask. As such, the term code indicia is wide enough to encompass bar codes, QR codes, and patterns of encoded information. Barcodes are used in the examples described herein, but it should be understood that the concepts involved herein apply to patterns other than those traditionally understood as barcodes.

As mentioned above, typically, the coded indicia employ a contrast between lighter and darker areas to create a pattern of coded information. These regions may be referred to as fields, pixels, or cells. Increasing the constraints on the properties of the coating that can be placed on the surface of the reticle reduces the amount of available contrast and thus hinders the ability of the camera to read the mark (i.e., distinguish between bright and dark fields). Therefore, there is a need to be able to encode readable information in a pattern without relying on the relative brightness of the cells.

In accordance with one aspect of the embodiment, a two-dimensional code label 10 is shown in FIG. 2. The illustrated example of code label 1O includes pixel array 12. The array pixels 12 are used to encode an identifier for the reticle and/or any other desired information. In the illustrated embodiment, the array is a binary system in which each pixel can be in one of two states. Of course, more or fewer pixels may be used depending on the amount of information to be encoded. The pixel array need not be square, but can be any convenient shape, even a linear array or an irregular shape. FIG. 2 depicts a two-dimensional barcode and a "square" grating, by way of example only. It should be understood that one-dimensional (linear) barcodes and other types of patterns are within the scope of the present disclosure.

Two examples of two-dimensional diffraction gratings that make up each pixel or cell of code mark 10 are also shown in fig. 2. The two-dimensional diffraction grating 14 is a square grid of elements having a pitch d. The two-dimensional diffraction grating 16 is a grid of diffraction elements arranged in a staggered or "checkerboard" arrangement. These diffraction gratings diffract incident light into various diffraction orders. Figure 2 depicts a "square" grating, by way of example only. It should be understood that other types of dense two-dimensional gratings, such as hexagonal (and other) patterns, are also within the scope of the present disclosure.

Thus, the surface under the barcode pattern is modified to increase the contrast of the barcode pattern. This may be accomplished by modulating the area under the barcode pattern produced by diffraction from the reflective and/or transmissive surfaces to enhance scattering, thereby facilitating formation of a barcode image in a conventional manner. This may potentially reduce or even eliminate readability problems associated with low contrast barcode patterns formed by specular reflection in retroreflective or transilluminated image forming modes.

Bar code targets are designed to diffract light in a 2D scattering pattern or diffraction grating, as described in the diffraction equations

d(sinθ_m+sinθ_i)＝mλ

Wherein theta is_mAnd theta_iIncident angle and m-order diffraction, respectively, λ is the imaging wavelength and d is the effective grating period, as shown in figure 2.

Incident light beam theta_i＝θ₁Directing either 0 or the first order diffracted beam perpendicularly to the object plane θ_m＝θ₁0 diffraction equation becomes

d sin(θ_i)＝λ

When diffracted light does not appear at the lens numerical aperture, i.e., when (NA) sin (θ)₁) At > N, the cells with the grating will appear dark in the image received by the barcode reader camera. In the case where the diffracted light is directed into the lens numerical aperture, the features with the grating will appear "bright" in the image. In order to fill the imaging lens NA effectively, the grating elements may deviate slightly and randomly from the ideal position. The magnitude of the displacement δ can be evaluated as a fraction of the grating period and the numerical aperture.

±δ/d≈NA

Fig. 3 shows an arrangement in which imaging of the code pattern 10 is performed using retro-reflection. The coaxial illuminator 20 directs a beam 26 of spatially coherent light through a lens 24 onto the bar code pattern 10 on a reticle 26. The cells of the bar code 10 that do not have a diffraction pattern will reflect light in the beam 28 back into the lens 24 to reach the bar code reader camera 30. The cells will appear bright. The portion of the bar code 10 having the diffraction pattern will diffract light outside the numerical aperture of the lens 24 into two

beams

32 and 34. The light does not reach the camera 30 and therefore the fields will appear dark.

Fig. 3 depicts an arrangement in which coaxial illumination is used. Fig. 4 depicts a retroreflective arrangement in which off-axis illumination is used. In fig. 4 and the remaining figures, similar elements are given the same reference numerals as in fig. 3. In the arrangement of fig. 4, first illuminator 40 directs a beam 44 of spatially coherent light to bar code 10 on reticle 26. Second illuminator 42 directs a beam 46 of spatially coherent light to bar code 10 on reticle 26. The beam 44 is reflected by areas of the bar code 10 that do not have a diffraction grating into a beam 48 that is outside the numerical aperture of the lens 24. Thus, these areas will appear dark to the camera 30. Similarly, the beam 46 will be reflected into the beam 50 by areas of the bar code 10 that do not have a diffraction pattern. The area with the diffraction pattern will direct first order diffracted light 52 through lens 24 to reach camera 30. These areas will appear bright.

The arrangement of fig. 3 and 4 is for a reflective reticle. For transmissive reticles, the arrangements of fig. 5 and 6 may be used. In the arrangement of FIG. 5, illuminator 60 provides on-axis illumination with a beam 62 of spatially coherent light, which beam 62 of spatially coherent light passes through reticle 26 and bar code 10 thereon. The areas of the bar code 10 without the diffraction grating will allow light to pass through the lens 20 in the form of a beam 64 to reach the camera 30. These areas will appear bright. The areas of the bar code 10 having the diffraction pattern diffract light into a beam 66 and a beam 68. These areas will appear dark.

Fig. 6 shows an arrangement in which off-axis illumination is used with a transmissive reticle. In the arrangement of fig. 6, there is a first illuminator 70 that generates a beam 72 and a second illuminator 74 that generates a beam 76. The areas of the bar code 10 on the reticle 26 that do not have a diffraction grating will allow the beam 72 of spatially coherent light to pass through the reticle 26 into the beam 78. Similarly, areas of the bar code 10 on the reticle 26 that do not have a diffraction grating will allow the beam 76 of spatially coherent light to pass through to the beam 80. Both beam 78 and beam 80 are outside the numerical aperture of lens 20 so that the areas in bar code 10 without the diffraction grating will appear dark to camera 30. The areas of the bar code 10 on the reticle 26 having the diffraction grating diffract the

beams

72 and 76 into a combined beam 82. The light beam 82 passes through the lens 28 and reaches the camera 30. Thus, the areas on the bar code 10 on the reticle 26 having the diffraction grating will appear bright.

The size of the pixels may be selected depending on the particular application, and will generally be the result of a trade-off between readability and availability of space on the reticle.

The information encoded in the tag 10 may be a simple identification number or may include other information such as a time and date stamp. To encode this information, techniques known from the communication arts may be used. For example, the code may include an error detection and/or correction scheme, such as parity bits or a cyclic redundancy code. The encoding need not use the entire symbol space provided by the tag 10, but only a subset of the possible signals that are less likely to be confused in the event of a read error or a tag corruption.

In one embodiment, a simple camera CA may be employed for reading the indicia. The camera may have a suitable magnifying lens and autofocus capability. Pattern recognition software may be used to decode the image of the marker 10.

These embodiments may be further described using the following clauses:

1. a reticle, comprising:

a pattern; and

a code mark comprising a plurality of cells, a subset of the cells in the plurality of cells each comprising a diffraction grating.

2. The reticle according to clause 1, wherein the plurality of cells are arranged as an array of cells.

3. The reticle of clause 2, wherein the array is a regular array.

4. The reticle according to clause 2 or 3, wherein the array is a rectangular array.

5. The reticle according to any one of clauses 1-4, wherein the diffraction grating comprises a two-dimensional diffraction grating.

6. The reticle according to clause 5, wherein the diffraction grating comprises a rectangular grid of diffractive elements.

7. The reticle of clause 6, wherein the rectangular grid comprises aligned rows and columns of diffractive elements.

8. The reticle of clause 6, wherein the rectangular grid comprises offset rows and columns of diffractive elements.

9. The reticle according to clause 6, wherein the diffractive element is displaced from the precise periodic position spaced by a distance d by an amount on the order of d multiplied by a numerical aperture of a lens arranged to receive light from the grid.

10. A lithographic apparatus for transferring a pattern from a reticle onto a substrate, the lithographic apparatus comprising:

a reticle having a code mark, the code mark comprising a plurality of cells, a subset of the cells in the plurality of cells each comprising a diffraction grating.

11. The lithographic apparatus according to clause 10, wherein the plurality of cells is arranged as an array of cells.

12. The lithographic apparatus according to clause 11, wherein the array is a regular array.

13. The lithographic apparatus according to clause 11 or 12, wherein the array is a rectangular array.

14. The lithographic apparatus according to any of clauses 11-13, wherein the diffraction grating comprises a two-dimensional diffraction grating.

15. The lithographic apparatus according to clause 14, wherein the diffraction grating comprises a rectangular grid of diffractive elements.

16. The reticle of clause 15, wherein the rectangular grid comprises aligned rows and columns of diffractive elements.

17. The reticle of clause 15, wherein the rectangular grid comprises offset rows and columns of diffractive elements.

18. The reticle according to clause 15, wherein the diffractive element is displaced from the precise periodic position spaced by a distance d by an amount on the order of d multiplied by a numerical aperture of a lens arranged to receive light from the grid.

19. The lithographic apparatus of any of clauses 11-18, further comprising: an illumination source arranged to illuminate the code marks, and a reader having a lens arranged to receive light from the code marks.

20. The lithographic apparatus of clause 19, wherein the illumination source is arranged to illuminate the code mark coaxially with respect to the optical axis of the lens.

21. The lithographic apparatus of clause 19, wherein the illumination source is arranged to illuminate the code mark off-axis with respect to the optical axis of the lens.

22. A device manufacturing method, comprising:

identifying a reticle using a code mark comprising a plurality of cells, a subset of the cells in the plurality of cells each comprising a diffraction grating; and

the pattern on the reticle is transferred to a substrate.

Although the above describes an embodiment using a two-dimensional code as an example, it is obvious to those skilled in the art that the concepts disclosed herein are equally applicable to a one-dimensional code.

Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered as synonymous with the more general terms "substrate" or "target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography, a topography in a reticle defines a pattern produced on a substrate. The topography of the reticle may be pressed into a resist layer provided to the substrate, and the resist subsequently cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the reticle is removed from the resist to leave a pattern therein.

The terms "light", "radiation" and "beam" as used herein include all types of electromagnetic radiation. In particular, the term "light" may be used, although it is understood that the radiation described using this term may not be in the visible portion of the spectrum.

The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not restrictive. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

It should be understood that the detailed description, and not the summary and abstract sections, is intended to be used to interpret the claims. The summary and abstract sections may set forth one or more, but not all exemplary embodiments of the present invention as contemplated by the inventors, and are therefore not intended to limit the present invention and the appended claims in any way.

The invention has been described above with the aid of functional building blocks illustrating the implementation of specific functions and relationships thereof. Boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries may be defined so long as the specified functions and relationships thereof are appropriately performed.

The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

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 appended hereto and their equivalents.

Claims

1. A reticle comprising:

pattern; and

A code mark comprising a plurality of cells, a subset of the cells of the plurality of cells each comprising a diffraction grating.

2. The reticle of claim 1, wherein the plurality of cells are arranged in a cell array.

3. The reticle of claim 2, wherein the array is a regular array.

4. The reticle of claim 2 or 3, wherein the array is a rectangular array.

5. The reticle of any of claims 1-4, wherein the diffraction grating comprises a two-dimensional diffraction grating.

6. The reticle of claim 5, wherein the diffraction grating comprises a rectangular grid of diffractive elements.

7. The reticle of claim 6, wherein the rectangular grid comprises aligned rows and columns of diffractive elements.

8. The reticle of claim 6, wherein the rectangular grid includes shifted rows and columns of diffractive elements.

9. The reticle of claim 6, wherein the diffractive elements are displaced from precise periodic positions separated by a distance d by an amount on the order of the product of d and the numerical aperture of the lens, the lens. is arranged to receive light from the grid.

10. A lithographic apparatus for transferring a pattern from a reticle to a substrate, the lithographic apparatus comprising:

A reticle having a code mark comprising a plurality of cells, a subset of the cells of the plurality of cells each comprising a diffraction grating.

11. The lithographic apparatus of claim 10, wherein the plurality of cells are arranged in a cell array.

12. The lithographic apparatus of claim 11, wherein the array is a regular array.

13. The lithographic apparatus of claim 11 or 12, wherein the array is a rectangular array.

14. The lithographic apparatus of any of claims 11-13, wherein the diffraction grating comprises a two-dimensional diffraction grating.

15. The lithographic apparatus of claim 14, wherein the diffraction grating comprises a rectangular grid of diffractive elements.