WO2005017997A1

WO2005017997A1 - Charged particle beam inspection

Info

Publication number: WO2005017997A1
Application number: PCT/US2004/006634
Authority: WO
Inventors: Youval Nehmadi; Zamir Abraham; Gil Sod-Moriah; Yair Eran; Chen Ofek; Yaron Cohen
Original assignee: Applied Materials Israel Ltd; Applied Materials Inc
Current assignee: Applied Materials Israel Ltd; Applied Materials Inc
Priority date: 2003-08-01
Filing date: 2004-03-04
Publication date: 2005-02-24
Anticipated expiration: 2006-02-01
Also published as: US20080092088A1; US7587700B2

Abstract

The invention provides a method and a measurement system. The system includes: (i) a scanner for scanning an area that comprises multiple structural elements with a beam of charged particles; (ii) a detector (16), positioned to receive charged particles resulting from an interaction between the area and the beam of charged particles and to provide multiple detection signals; and (iii) a processor (102), adapted to process detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements.

Description

CHARGED PARTICLE BEAM INSPECTION

RELATED APPLICATIONS

[001] This application claims the priority of U.S provisional application serial number 60/491,799 filed August 1, 2003 titled "auto retrieve targets from images and/or designs".

HELD OF THE INVENTION

[002] This invention relates to metrology systems and methods in determimng features of sub- micron structural elements such as lines, contacts, trenches and the like, of measure structural elements such as but not limited to semiconductors wafers, reticles.

BACKGROUND OF THE INVENTION

[003] Integrated circuits are very complex devices that include multiple layers. Each layer may include conductive material, isolating material while other layers may include semi-conductive materials. These various materials are arranged in patterns, usually in accordance with the expected functionality of the integrated circuit. The patterns also reflect the manufacturing process of the integrated circuits.

[004] Integrated circuits are manufactured by complex multi-staged manufacturing processes. During this multi-staged process resistive material is (i) deposited on a substrate/ layer, (ii) exposed by a photolithographic process, and (iii) developed to produce a pattern that defines some areas to be later etched.

[005] Various metrology, inspection and failure analysis techniques evolved for inspecting integrated circuits both during the fabrication stages, between consecutive manufacturing stages, either in combination with the manufacturing process (also termed "in line" inspection techniques) or not (also termed "offline" inspection techniques). Various optical as well as charged particle beam inspection tools and review tools are known in the art, such as the NeraSEM™, Compluss™ and SEMVision™ of Applied Materials Inc. of Santa Clara, California.

[006] Manufacturing failures may affect the electrical characteristics of the integrated circuits. Some of these failures result from unwanted deviations from the required dimensions of the patterns. A "critical dimension" is usually the width of a patterned line, the distance between two patterned lines, the width of a contact and the like.

[007] One of the goals of metrology is to determine whether the inspected structural elements include deviations from these critical dimensions. This inspection is usually done by charged particles beam imaging that provide the high resolution required to measure said deviations.

[008] A typical measured structural element is a line that has two opposing sidewalls. The measurement of the bottom width of the line involves measuring the top width of the line as well as measuring its sidewalls. Another typical measured structural element is a contact or a hole to be filled with conductive materials. Said structural element is also referred to as via.

SUMMARY OF THE INVENTION

[009] The invention provides a method that include the stages of: scanning an area that comprises multiple structural elements with a beam of charged particles to receive multiple detection signals; and processing detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements.

[0010] The invention provides a method that includes the stages of scanning an area that comprises multiple structural elements with a beam of charged particles to receive multiple detection signals; and processing detection signals associated with multiple ideally identical structural elements to provide a result representative of a relationship between at least two of said ideally identical structural elements.

[0011] The invention provides a method that includes the stages of: scanning a repetitive arrangement of multiple ideally identical structural elements with a beam of charged particles to receive multiple detection signals; and processing detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements.

[0012] The invention provides a measurement system that includes: a scanner for scanning an area that comprises multiple structural elements with a beam of charged particles; a detector, positioned to receive charged particles resulting from an interaction between the area and the beam of charged particles and to provide multiple detection signals; and a processor, adapted to process detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements. The invention provides a measurement tool that includes : a scanner for scanning an area that includes multiple structural elements with abeam of charged particles; a detector, positioned to receive charged particles resulting from an interaction between the area and the beam of charged particles and to provide multiple detection signals; and a processor, adapted to process detection signals associated with multiple ideally identical structural elements to provide a result representative of a relationship between at least two ideally identical structural elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0014] Figure 1 is a schematic illustration of a critical dimension scanning electron microscope, in accordance with an embodiment of the invention;

[0015] Figures 2, 12 and 13 are flow charts of methods, according to various embodiments of the invention;

[0016] Figure 3 is an exemplary image of a scanned area;

[0017] Figure 4 is a three dimensional graph representative of CD changes across the area of figure 3;

[0018] Figures 5-8, and 16-17 illustrate various inter-feature measurements that can be used to define various structural element features;

[0019] Figures 9 and 10 illustrate an image and a CAD representation, respectively, of an area to be scanned

[0020] Figure 11 illustrates a stacking technique according to an embodiment of the invention; and

[0021] Figures 14-15 illustrate a set of signals, as well as their FFT transformation, according to an embodiment of the invention. DETAILED DESCRIPTION OF THE DRAWINGS

[0022] A typical CD-SEM includes an electron gun, for generating an electron beam, deflection and tilt units as well as focusing lens, for enabling scanning of a specimen with an electron beam, that may be in a certain tilt condition, while reducing various aberrations and misalignments. Electrons, such as secondary electrons that are omitted as result of an interaction between the specimen and the electron beam are attracted to a detector that provides detection signals that are processed by a processing unit. The detection signals may be used to determine various features of the specimen, as well as form images of the inspected specimen.

[0023] The invention may be implemented on CD-SEMs of various architectures that may differ from each other by the amount of their parts as well as the arrangement of said parts. For example the amount of deflection units, as well as the exact structure of each unit may vary. The CD-SEM may include in-lens as well as out of lens detectors or a combination of both.

[0024] According to an embodiment of the invention the measurement of multiple measurement targets allows to reduce the total^' exposure of the scanned area. This may allow reducing the electron-beam to material interactions that may appear in various forms such as shrinking effects - commonly known to exist in the 193nm resist used in advanced icrolithography processes, charging effects and the like.

[0025] A measurement system such as CD-SEM 100 is illustrated in Figure 1. The CD-SEM 100 includes: (i) a scanner, such as scanning deflection unit 102, for scanning an area that comprises multiple structural elements with a beam of charged particles; (ii) a detector, such as in-lens detector 16, positioned to receive charged particles resulting from an interaction between the area and the beam of charged particles and to provide multiple detection signals; and (iii) a processor, such as processor 102, that is adapted to process detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements.

[0026] CD-SEM 100 further includes: (a) an electron gun 103 emitting an electron beam 101 , which is extracted by the anode 104, (b) an objective lens 112 that focuses the electron beam on a surface 105a of an inspected object 105, (c) deflection units 108-111, and (d) a stage 101 for introducing a relative mechanical movement between the object 105 and the objective lens 112.

[0027] The beam is scanned over the specimen using the scanning deflection unit 102. An alignment of the beam to the aperture 106 or a desired optical axis respectively can be achieved by the deflection units 108 to 111. As a deflection unit coils, electrostatic modules in the form of charged plates or a combination of coils and electrostatic deflectors can be used.

[0028] In-lens detector 16 is able to detect secondary electrons that escape from the object 105 at a variety of angles with relatively low energy (3 to 50 eN). Measurements of scattered or secondary corpuscles from a specimen can be conducted with detectors in the form of scintiflators connected to photomultiplier tubes or the like. Since the way of measuring the signals does not influence the inventive idea in general, this is not to be understood as limiting the invention. It is noted that the CD-SEM may include, additionally or alternatively, at least one out-of lens detector.

[0029] Detection signals are processed by processor 102 that may also be adapted to control the parts of CD-SEM 100 and coordinate their operation. Conveniently, processor 102 has image processing capabilities and is able to process the detection signals in various manners. A typical processing scheme includes generating a waveform that reflects the amplitude of the detection signal versus the scan direction. The waveform is further processed to generate an image, to determine locations of at least one edge, and other cross sectional features of inspected structural elements.

[0030] The different parts of the system are connected to corresponding supply units (such as high voltage supply unit 21) that are controlled by various control units, most of them are omitted from the figure for simplifying the explanation. The control units may determine the current supplied to a certain part, as well as the voltage.

[0031] CD-SEM 100 includes a double deflection system that includes deflection units llO and 111. Thus, the beam tilt introduced in the first deflection unit 110, can be corrected for in the second deflection unit 111. Due to this double deflection system, the electron beam can be shifted in one direction without introducing a beam tilt of the electron beam with respect to the optical axis.

[0032] Modem CD-SEMs are able to measure structural elements that have cross sections that have sub-micron dimensions, with an accuracy of several nanometers. The size of these cross sections is expected to reduce in the future, as manufacturing and inspection processes continue to improve.

[0033] Various features of the cross section may be of interest. These feature may include, for example: the shape of the cross section, the shape of one or more sections of the cross section, the width and/or height and/or angular orientation of the cross section sections, as well as the relationship between cross section sections. The feature can reflect typical values, as well as maximal and/or minimal values. Typically the width of the bottom of a line is of interest, but this is not necessarily so and other features may be of interest. [0034] Figure 2 is a flow chart of method 200 that includes staged 210-240, according to an embodiment of the invention.

[0035] Stage 220 includes scanning an area that includes multiple structural elements with a beam of charged particles to receive multiple detection signals. Conveniently, the area is scanned without introducing a substantial mechanically movement between the beam of charged particles and the area. Preferably, the area is defined by a field of view of a measurement tool. For convenience of explanation it is assumed that the beam of charged particles is electron beam 101 (of Figure 1), the detection signals are received by in-lens detector 16 (of Figure 1) and that the area is area 300 (of Figure 3) that includes multiple structural elements such as contacts 302.

[0036] Stage 220 is followed by stage 230 of processing detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements. Referring to the previous assumption it can be assumed that the ideally identical structural elements are contacts 302 and that the processing is implemented by a processing unit that is part of controller 33.

[0037] According to an embodiment of the invention method 200 also includes stage 240 of displaying the results. The results can be displayed in various manners known in the art. In addition, stage 240 may include displaying a relationship between a location of a structural element and a result representative of a feature of said structural element. Such a display is illustrated in Figure 4 that provides a three dimensional illustration of the change of critical dimensions of contacts 320 across area 300. The X-axis 410 and the Y-axis 420 describe a location of a contact 302 while the Z- axis 430 describes a change in the critical dimension.

[0038] According to an embodiment of the invention the method 200 can make use of the arrangement of the ideally identical structural elements. If for example, they are arranged in a substantially repetitive arrangement then stage 230 of processing can include determining a spatial relationship between at least two ideally identical structural elements.

[0039] According to an embodiment of the invention method 200 can also determine, conveniently during stage 230, features of a certain structural element in response to inter-features measurements. Figures 5-8 illustrate various measurements of inter-feature measurements that can be used to define various structural element features.

[0040] According to an embodiment of the invention stage 230 includes sorting detection signals associated with multiple ideally identical structural elements out of the received multiple detection signals. This is usually done after an image of the area is generated and the signals that are associated with a certain structural element form an image of said structural element. In such a case the processing may include applying image-processing operations to provide the result. Typically images of multiple ideally identical structural elements are located and are processed to provide the result. For example in Figure 3 the signals that are scattered from a contact 302 are processed to generate an image of said contact.

[0041] According to an embodiment of the invention stage 230 include measuring the structural elements that are located within the area and then determining which structural elements can be defined as ideally identical. The measurement may include measuring at least two dimensions of a structural element, measuring CD fro two different angles and the like. In some cases the measurement is applied in response to information representative of an expected shape of the structural element.

[0042] According to an embodiment of the invention said measurements can assist in sorting structural elements that are located within the area. For example, if circular shaped structural elements and ellipse shaped structural elements are positioned at the area they may be separated from each other by measuring the horizontal as well as the vertical cross section of each shape.

[0043] According to various embodiments of the invention stage 230 includes applying at least one statistical operation to provide the result. The statistical operation may include averaging, weighted averaging, standard deviation, distribution skewness, and the like.

[0044] According to another aspect of the invention stage 230 includes processing a set of detection signals, such as detection signals associated with an imaginary line that interacts with at least two ideally identical structural objects arranged at a repetitive pattern. This set of detection signals is processed by applying a frequency transformation such as a FFT transform, and processing the results. Such an example is illustrated at Figures 14-15. Referring to Figure 14, a curve 1430 represents the relationship between an intensity of a detection signal (Y-axis 1420) and the timing (location) of said signal (X-axis 1410). Referring to Figure 15, a curve 1530 represents the relationship between an spatial intensity of a FFT converted detection signal (Y-axis 1520) and the spatial frequency X-axis 1510).

[0045] According another embodiment of the invention the method 200 can cope with areas that include both ideally identical structural elements as well as other structural elements. The area can also include multiple different types of ideally identical structural elements. For example a certain area can include a first group of small contact holes as well as a medium sized contact holes. In order to process only signals associated the same (ideally) stmctural elements the stage of processing includes sorting the signals. This is usually done after an image of the area is generated and various image processing techniques can be applied to sort the appropriate signals.

[0046] According to another embodiment of the invention method 200 may include calculating a measurement result relating to a first group of ideally identical structural elements, providing another result representative of a second group of ideally identical structures that differ from the members of the first group. Optionally, the result may reflect a relationship between these two measurement results. It is also noted that more than two groups can be processed at the same manner.

[0047] According to other embodiments of the invention the features of multiple stmctural elements can be combined/manipulated to provide an image of a representative structural element, as illustrated in Figure 12. This manipulation is also referred to as stacking.

[0048] Method 200 usually includes stage 210 of dete-mining the area to be scanned. The determination may involve processing EDA files such as CAD file representative of portions of at least one layer of the inspected object. Figure 9 and 10 illustrate an image 900 of an area, as well as a CAD representation 1000 of said area. The area includes an array 910 of ideally identical contacts 912. This array can be located by processing the CAD representation, by received coordinates of the array from a client or from an operator and the like.

[0049] According to an embodiment of the invention stage 210 may include receiving a description of certain features of interest (for example, contact holes of a certain volume, contact holes of a certain diameter, distance between lines, edges or contact holes and the like) and processing CAD files until said features are found. The processing can be responsive to certain location, to user or operator definitions and the like.

[0050] According to an embodiment of the inventions stage 230 of processing may processing various features in order to provide a certain result, such as the area of a contact holes, their diameter.

[0051] Conveniently, stage 220 includes a single scan but according to other embodiments of the invention this is not necessarily so. The result may be provided in response to images acquired during multiple scans. [0052] According to an embodiment of the invention multiple features and even the relationship between these features can be determined in response to the scanning of stage 220.

[0053] Figure 12 illustrated a method 1200 according to an embodiment of the invention. Figure 12 starts by stage 1210 of defining a certain area that includes multiple ideally identical structural elements. For example, said area may be area 300 of Figure 3.

[0054] Stage 1210 is followed by stage 1220 of scanning an area that includes multiple structural elements with a beam of charged particles to receive multiple detection signals. This stage or stage 1210 may include locating the area which usually includes introducing a mechanical movement such as to roughly align the scanner with the area, generating an image if a vicinity of the area and locating the area by applying image processing operations. The mechanical movement can include moving the object by an X-Y stage an or moving the column. This location stage is known in the art and does not require additional explanations. Typically, the location of such an area is responsive to a measurement recipe fed by the measurement tool operator.

[0055] Stage 1220 is followed by stage 1230 of processing detection signals associated with multiple ideally identical structural elements to provide a result representative of a relationship between at least two of said ideally identical structural elements. The relationship may include distance, spatial distribution of the ideally identical structural elements, alignment and the like. Typically this stage includes inter-structural element measurements, some of which are illustrated in figures 5-8, and 16 - 17.

[0056] Figure 5 is an image of an array of ideally identical contact holes 502. Figure 6 illustrates various inter-feature measurements, such as the distance (dl 506) between two adjacent contact holes 506(1) and 506(2) of array 500, as well as the distance (d2504) between the centers of said adjacent contact holes. The relationship between dl and d2 can reflect the measurements of the contact holes themselves (especially when more than two adjacent features, for example feature on both sides of a certain contact hole, are measured).

[0057] Figure 7 is an image of two vertical lines 701 and 703 and multiple contact holes 702 that are positioned between these lines. Figure 8 illustrates various inter-feature measurements such as the distance (d4706) between line 701 and contact hole 702(3), the vertical displacement (dl 704) between adjacent contact holes 702(3) and 702(2), the distance (d2710) between lines 701 and 703 and the distance (d3 708) between line 703 and the contact hole 702(1). [0058] Figure 16 is an image 1600 of an array that include pairs of a circular shaped contact hole 1604 as well as an ellipse shaped contact hole 1602. Figure 17 illustrates various measurements of the contact holes (vertical and horizontal size of each features - rl 1703 and r2 1704 of ellipse shaped contact hole 1602, r3 1713 and r4 1714 of circular shaped contact hole 1604, as various inter-feature measurements such as the distance (dl 1701) between adjacent contact holes 1602 and 1604, and the distance (d2 1702) between the centers of these shapes 1602 and 1604.

[0059] Figure 13 illustrates method 1300 according to an embodiment of the invention. Method 1300 includes stage 1320 of scanning a repetitive arrangement of multiple ideally identical structural elements with abeam of charged particles to receive multiple detection signals. Stage 1320 is followed by stage 1330 of processing detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements.

[0060] The present invention can be practiced by employing conventional tools, methodology and components. Accordingly, the details of such tools, component and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as shapes of cross sections of typical lines, amount of deflection units, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention might be practiced without resorting to the details specifically set forth.

[0061 ] Only exemplary embodiments of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

Claims

WE CLAIM

1. A method, comprising: scanning an area that comprises multiple structural elements with a beam of charged particles to receive multiple detection signals; and processing detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements.

2. The method of claim 1 wherein the area is scanned without introducing a substantial mechanically movement between the beam of charged particles and the area.

3. The method of claim 1 wherein the area is defined by a field of view of a measurement tool.

4. The method of claim 1 wherein the ideally identical structural elements are arranged at a substantially repetitive arrangement.

5. The method of claim 4 wherein the stage of processing comprising determining a spatial relationship between at least two ideally identical structural elements.

6. The method of claim 1 wherein the processing comprising sorting detection signals associated with multiple ideally identical structural elements out of the received multiple detection signals.

7. The method of claim 1 wherein the area comprises multiple first structural elements and multiple second structural elements, whereas the first structural elements differ from the second structural elements and wherein the first structural elements are ideally identical to each other.

8. The method of claim 7 wherein the stage of processing comprising selecting detection signals representative of the first structural elements.

9. The method of claim 1 wherein the stage of processing further comprises generating an image of at least a portion of the area.

10. The method of claim 9 wherein the stage of processing further comprises applying image processing operations to provide the result.

11. The method of claim 9 wherein the image comprises multiple structural element images and wherein the stage of processing further comprises locating at least two structural element images.

12. The method of claim 1 wherein the stage of scanning comprising scanning the area with a low intensity beam of charged particle beams.

13. The method of claim 1 further comprising determining the area.

14. The method of claim 13 wherein said area comprises a portion of a layer of an integrated circuit and whereas the determination is responsive to a representation of said portion of a layer.

15. The method of claim 1 wherein the stage of processing comprises applying at least one statistical operation to provide the result.

16. The method of claim 1 wherein the stage of processing comprises determining a spatial relationship between at least two ideally identical structural elements.

17. The method of claim 1 wherein the stage of processing comprises applying a frequency transformation operation on multiple detection signals.

18. The method of claim 1 further comprising displaying a relationship between a location of a structural element and a result representative of a feature of said structural element.

19. The method of claim 1 wherein the processing comprising measuring structural elements located within the area.

20. The method of claim 19 further comprising sorting structural elements in response to the measurements.

21. The method of claim 1 further comprising determining a relationship between non- ideally identical structural elements.

22. A method, comprising: scanning an area that comprises multiple structural elements with a beam of charged particles to receive multiple detection signals; and processing detection signals associated with multiple ideally identical stmctural elements to provide a result representative of a relationship between at least two of said ideally identical structural elements.

23. The method of claim 21 wherein the relationship between two ideally identical stmctural elements is a distance between adjacent structural elements.

24. The method of claim 21 wherein the ideally identical structural elements are arranged at a substantially repetitive pattern.

25. The method of claim 23 further comprising selecting the repetitive arrangement out of multiple repetitive arrangements.

26. A method, comprising: scanning a repetitive arrangement of multiple ideally identical structural elements with a beam of charged particles to receive multiple detection signals; and processing detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical structural elements.

27. A measurement system comprising: a scanner for scanning an area that comprises multiple structural elements with a beam of charged particles; a detector, positioned to receive charged particles resulting from an interaction between the area and the beam of charged particles and to provide multiple detection signals; and a processor, adapted to process detection signals associated with multiple ideally identical structural elements to provide a result representative of at least one feature of at least one of said ideally identical stmctural elements.

28. A measurement system comprising: a scanner for scanning an area that comprises multiple structural elements with a beam of charged particles; a detector, positioned to receive charged particles resulting from an interaction between the area and the beam of charged particles and to provide multiple detection signals; and a processor, adapted to process detection signals associated with multiple ideally identical stmctural elements to provide a result representative of a relationsliip between at least two ideally identical structural elements.