CN117129499A

CN117129499A - Method for analysing the surface of a sample by means of grazing incidence X-ray scattering and device for analysing a sample

Info

Publication number: CN117129499A
Application number: CN202310582754.1A
Authority: CN
Inventors: 路新慧; 秦敏超; 陈博锋
Original assignee: Chinese University of Hong Kong CUHK
Current assignee: Chinese University of Hong Kong CUHK
Priority date: 2022-05-26
Filing date: 2023-05-23
Publication date: 2023-11-28

Abstract

Methods and apparatus for analyzing a surface of a sample by grazing incidence X-ray scattering (GIXS) are provided. The method comprises the following steps: propagating the X-ray beam onto a surface of the sample to produce a scattered wave; collecting scattered waves by a two-dimensional detector; performing a GIXS mapping on the collected scattered waves; and determining one or more characteristics of the sample based on the obtained GIXS map. The step of performing the GIXS mapping includes performing a longitudinal X-ray scan and a transverse X-ray scan of the surface of the sample. The sample may be a large area polycrystalline film. Determining one or more characteristics of the sample includes: the location of defects in the sample, the crystallinity at a plurality of different locations of the sample, or the crystallinity at a plurality of different depths of the sample is determined.

Description

Method for analysing the surface of a sample by means of grazing incidence X-ray scattering and device for analysing a sample

Technical Field

The present application relates to a method and apparatus for analysing the surface of a sample, in particular by grazing incidence X-ray scattering.

Background

Large area polycrystalline thin films (LPTF) composed of semiconductors, metal oxides, and metals have been widely used in commercial solar cells, detectors, light emitting diodes, memristors, and transistors. The performance and stability of these devices are closely related to the film quality of the LPTF, so rapid quality inspection is a necessary step in optimizing the device fabrication. To investigate the quality of thin films, the market has developed a variety of techniques including coplanar X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, and Scanning Electron Microscopy (SEM). However, these conventional techniques are limited to detecting a local area of a few square micrometers in the film, making it difficult to detect a large area of the entire film due to low scan speeds and high operating costs. The performance of the film produced in large area is more easily affected by the quality unevenness and defects, so the development of a rapid defect detection method suitable for the film with large area is particularly important for the industrial production of LPTF.

Disclosure of Invention

There remains a need in the art for improved designs and techniques for analyzing the quality of large area polycrystalline thin films (LPTF). The present application provides a method for analyzing LPTF surfaces by grazing incidence X-ray scattering (GIXS). The method comprises the following steps: irradiating an X-ray beam onto a surface of a thin film sample to generate a scattered wave; collecting scattered waves by a two-dimensional detector; thereafter, GIXS mapping is performed on the collected scattered waves; and determining one or more characteristics of the sample based on the obtained GIXS map. The X-ray beam is generated by a synchrotron light source or a Cu/Mg/Al target. The sample may be a large area polycrystalline thin film (LPTF), such as an area greater than 1cm ² Is a polycrystalline perovskite thin film. The LPTF materials include, but are not limited to, semiconductors, metal oxides, or metals. Semiconductors include, but are not limited to, silicon, copper indium gallium selenide, copper zinc tin sulfide, and metal halide perovskite. The metal oxides include, but are not limited to, tin oxides, zinc oxides, indium oxides, titanium oxides, and aluminum oxides. Metals include, but are not limited to, gold, silver, aluminum, copper, zinc, lead, and tin. Further, the steps of performing GIXS mapping include, but are not limited to: performing grazing incidence small angle X-ray powderEmission (GISAXS), grazing incidence wide angle X-ray scattering (GIWAXS), or grazing incidence transmission small angle X-ray scattering (GTSAXS). The step of determining one or more characteristics of the sample includes determining a location of a defect of the sample, detecting crystallinity at a plurality of different locations and depths of the sample. The step of determining the crystallinity at a plurality of different depths of the sample comprises: GIXS mapping is performed by adjusting an incident angle of an X-ray beam to control an X-ray penetration depth. Furthermore, the step of performing the GIXS mapping includes performing a longitudinal X-ray scan and a transverse X-ray scan of the sample surface. Performing a longitudinal X-ray scan includes: adjusting the incidence angle of the X-rays to adjust the coverage length (footprint) of the X-rays is adjustable, performing a transverse X-ray scan includes: the sample is moved in a direction orthogonal to the plane of incidence of the X-rays. The X-ray footprint of the sample is a function of the size of the X-ray beam and the angle of incidence of the X-ray beam, and the resolution of the longitudinal scan can be determined by the distance between the sample and the two-dimensional detector and the pixel size of the two-dimensional detector.

The present application contemplates an apparatus for analyzing a sample. The device comprises: an X-ray source configured to generate an incident X-ray beam and direct the incident X-ray beam onto a surface of a sample; an adjustable sample stage configured to be operable to adjust an angle between an incident X-ray beam and a surface of a sample and to move the sample in three dimensions; a two-dimensional (2D) detector configured to collect X-ray beam signals scattered from a sample surface; and a processor configured to receive the collected signals, perform a GIXS mapping on the collected signals, and determine one or more characteristics of the sample based on the obtained GIXS mapping. The X-ray source may be a synchrotron light source or an X-ray source with a Cu/Mg/Al target, and one or more features of the sample may reflect the location of sample defects.

Drawings

FIG. 1 is a flow chart of a method for analyzing large area polycrystalline thin film sample characteristics based on grazing incidence X-ray scattering (GIXS) measurements in an embodiment in accordance with the present application.

FIG. 2 is a schematic illustration of an apparatus setup for analyzing large area polycrystalline thin film sample properties based on GIXS measurements, in accordance with an embodiment of the present application.

FIG. 3 is a schematic diagram showing scattering geometry of the GIXS measurement apparatus and method in which wave vectors are used in an embodiment of the present applicationAt a shallow angle of incidence alpha _i Hit the sample, producing an angle of emergence alpha relative to the sample surface _f Is>The exit plane has an azimuth angle +_with respect to the entrance plane>The direct beam is directed to the origin of the reciprocal space, and the polar angle χ is q _z Axis and scattering wave vector->At q _r -q _z The angle between the projections on the plane, and the polar angle θ _B Corresponds to the smallest detectable fraction χ.

FIG. 4 is a schematic diagram showing defect detection using GIXS techniques in an embodiment of the present application, wherein the X-ray coverage of the sample is a function of beam size d and angle of incidence θ.

Fig. 5 is a schematic diagram showing localization of defects in the LPTF by q values obtained by a two-dimensional detector in an embodiment of the present application.

Fig. 6 is a GIXS plot showing perovskite films obtained based on long X-ray coverage in an embodiment of the application.

FIG. 7 is a plot showing the integration of characteristic GIXS peaks obtained from a long X-ray coverage area simulated in an embodiment of the present application.

Fig. 8 is a graph showing simulated GIXS plots from uniform LPTF in an embodiment of the present application.

FIG. 9 is a graph showing simulated GIXS mapping results obtained from non-uniform LPTF in an embodiment of the present application.

FIG. 10 shows the practice of the present applicationIn embodiments, the X-ray penetration depth and the incident angle alpha _i And critical angle alpha _c Is a schematic diagram of the relationship of (a).

Fig. 11 is a graph showing estimated X-ray penetration depth in a perovskite film versus angle of incidence in an embodiment of the application.

Detailed Description

Embodiments of the present application relate to a method and apparatus for rapidly detecting defects of large area polycrystalline thin films (LPTF) widely used in commercial solar cells, light emitting diodes, detectors, memory resistors and transistors. The application adopts a nondestructive grazing incidence X-ray scattering (GIXS) technology to detect the crystal state of the film, and accurately determines the accurate position of the LPTF defect based on the relationship between the defect position of the LPTF and the wave vector obtained by measurement, thereby finding the problem of the film early in the large-scale device production of the LPTF so as to improve the final yield of film deposition.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well as the singular forms as well, unless the context clearly indicates otherwise. The terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

Unless defined otherwise, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Furthermore, the meanings of terms such as those defined in the general dictionary should be consistent with their meanings in the relevant art and herein, and should not be interpreted as idealized or overly formal meanings unless expressly so defined herein.

When the term "about" is used herein in connection with a numerical value, it is understood that the value may range from 90% of the value to 110% of the value, i.e., the value may be +/-10% of the value. For example, "about 1kg" means 0.90kg to 1.1kg.

In describing the present application, it should be understood that various techniques and steps are disclosed. Each technology has individual advantages, and each technology may also be used with one or more, and in some cases even all, of the other disclosed technologies. Thus, for the sake of clarity, this description will avoid repeating each and every possible combination of steps in an unnecessary fashion. However, it is to be understood that combinations of these are fully within the scope of the application and claims when read from the specification and claims.

Referring to fig. 1, a method of analyzing the surface of a sample by grazing incidence X-ray scattering (GIXS) is illustrated. First, in step S110, an X-ray beam is irradiated onto a surface of a sample for analysis to generate a scattered wave. Then, in step S120, the scattered wave is collected by the two-dimensional detector. Next, in step S130, a GIXS drawing is performed based on the collected scattered waves. Then, at step S140, one or more characteristics of the sample are determined based on the generated GIXS map.

Fig. 2 shows an apparatus for performing sample analysis. The apparatus 200 comprises: an X-ray source 210 configured to generate an X-ray beam and direct the X-ray beam onto a surface of a sample; a sample stage 220 configured to be operable to adjust an angle between an incident X-ray beam and a sample surface and to move the sample in three dimensions; a two-dimensional (2D) detector 230 configured to collect X-ray beam signals scattered from a surface of the sample; and a processor 240 configured to receive the collected signals, perform a GIXS mapping on the collected signals, and determine one or more characteristics of the sample based on the generated GIXS mapping.

Fig. 3 shows the scattering geometry of the GIXS measurement apparatus and the GIXS measurement method in more detail. With initial wave vectorIs at glancing angle alpha _i Irradiation of the sample to be measuredOn the surface, an exit angle alpha is generated relative to the sample surface _f Is>Scattered wave->Collected by a two-dimensional area detector (e.g., pilatus 300K). The exit plane has an azimuth angle +_ relative to the entrance plane>The direct beam is directed to the origin of the reciprocal space, and the polar angle χ is q _z Axis and scattered wave vectorAt q _r -q _z The angle between the projections on the plane, and the polar angle θ _B Corresponding to the smallest detectable χ. Scattered wave vector->Can be represented by the following equations (1) - (4):

wherein,along the out-of-plane (OOP) direction relative to the sample surface, and +.>And->Both are in the in-plane (IP) direction, < ->And->Parallel to the plane of incidence and perpendicular to the plane of incidence, respectively.

Fig. 4 illustrates the defect detection of LPTF by GIXS technique in both longitudinal and transverse X-ray scans, wherein the X-ray footprint of the sample is a function of beam size d and angle of incidence θ, in an embodiment of the present application. By utilizing a high intensity X-ray beam (e.g., synchrotron-based X-ray beam), the above-described method can achieve a single exposure in milliseconds due to the elongated X-ray coverage area. The X-ray beam size (d) is typically in the range between tens of micrometers and millimeters. The angle of incidence (θ) of the corresponding X-ray beam is approximately in the range of 0.01 ° to 5 °. Due to geometrical distortions of the X-ray beam, the X-ray coverage area may span several millimeters to tens of meters, sufficient to cover the entire length of the LPTF for longitudinal X-ray scanning.

As shown in fig. 5, when the two-dimensional detector receives the scattered signal from the longitudinal scan, the distance of the sample from the detector can be obtained by calculating the q value of the corresponding characteristic signal, thereby calculating the position of the defect in the LPTF.

In one embodiment, the two-dimensional detector is a Pilatus3R300K two-dimensional detector comprising 487×619 pixels, with a pixel size of 0.172×0.172 μm.

The relationship between the defect location and the corresponding q value can be represented by equation (5):

wherein (d) ₁ -d ₀ ) And (q) ₁ -q ₀ ) The sample length and the scattering peak width, respectively, d 'represent the position of the defect offset from the initial position, and q' is the corresponding scattering signal position of the defect.

In one example, a polycrystalline perovskite thin film was used as a sample for analysis to demonstrate the utility of the present application for defect detection by the GIXS technique. Referring to fig. 6, the GIXS pattern of the large-area perovskite film is obtained based on the long X-ray coverage so that a plurality of scattering peaks are superimposed, appearing as one widened plateau (plateau) instead of a distinct gaussian peak.

Nonetheless, as shown in fig. 7, non-uniform perovskite films can cause uneven plateau at certain q values. By measuring the q value of the recess position on the mesa, the position where the trap region exists in the large-area perovskite film can be determined according to equation (5). The resolution of the longitudinal scan is determined by the distance of the sample from the detector and the pixel size in the two-dimensional detector.

Then, as shown in fig. 4, the sample stage can be moved in a direction orthogonal to the plane of incidence of the X-rays to achieve a lateral scan. The lateral scan resolution is determined by the step size (e.g., 5 mm) of each movement. Thus, by integrating the results of the longitudinal X-ray scan and the transverse X-ray scan, a GIXS map may be obtained.

Fig. 8 shows a simulated GIXS plot obtained from a uniform LPTF, which shows a uniform scattering intensity distribution. In contrast, as shown in fig. 9, an LPTF containing defects may result in a scattering intensity with higher or lower intensity at some points. Such an uneven distribution may identify the defect locations of the LPTF. Furthermore, the crystal structure along the out-of-plane direction, i.e. depth profile, can also be determined by adjusting the angle of incidence of the X-ray beam, the X-ray penetration depth will correspondingly vary. FIG. 10 shows the X-ray penetration depth and the X-ray incidence angle alpha _i And critical angle alpha _c Is a relationship of (3). When incident angle alpha _i Less than critical angle alpha _c In the time-course of which the first and second contact surfaces,total external reflection of the X-ray beam occurs. Therefore, only the surface structure information of a film thickness of a few nanometers is detected. When the angle of incidence is increased to near or slightly above the critical angle, the crystal structure of the film within a certain depth can be measured due to the partial penetration of the X-rays. By gradually increasing the angle of incidence until a signal from the substrate beneath the sample is observed, reflecting the complete penetration of the X-rays into the whole film, average structural information is provided throughout the whole film.

In one embodiment, perovskite films are used as the sample analysis. By observing the signal from the substrate under the sample and the thickness of the film, the corresponding critical angle of the film detected by the X-rays of a certain energy can be estimated based on the angle of incidence. Fig. 11 shows a polycrystalline three-dimensional perovskite film having a critical angle of 0.15 ° at 10keV, which simulates the relationship between penetration depth and different angles of incidence. When the angle of incidence is less than the critical angle, the X-rays penetrate only a few nanometers of the surface of the film; whereas at incident angles greater than a critical angle (such as 1 deg.), the X-rays penetrate completely into the film. Thus, GIXS measurements can be performed at different angles of incidence to determine the vertical uniformity of the film.

Because conventional techniques generally detect only a limited area (e.g., a few square micrometers), they are time consuming and costly to operate, and it is difficult to achieve detection of large areas of thin films.

In contrast, embodiments of the present application utilize the geometric distortion of the X-ray beam in the GIXS technique to detect films up to several meters wide through a single X-ray exposure in a few seconds. Analysis of the GIXS plot, combined with lateral movement of the sample, yields overall information including film quality. Thus, by analyzing the difference in scattering intensity at different q values, film uniformity can be checked and defects of the LPTF can be precisely located.

With a combination of longitudinal and transverse X-ray scans, a GIXS mapping of the LPTF can be achieved, so that the defect location of the LPTF can be precisely located. Longitudinal scanning is achieved in a single exposure in the millisecond order by utilizing a steerable X-ray footprint caused by geometric distortions of the X-ray beam, and lateral scanning is performed by moving the sample during scanning. Furthermore, by adjusting the incident angle of the incident beam to control the X-ray penetration depth, the GIXS measurement can reflect the depth profile of the crystal structure in the LPTF.

In general, the resolution of a longitudinal scan is determined by the distance of the sample from the detector and the pixel size in the two-dimensional detector, while the resolution of a transverse scan is determined by the step size (e.g., 5 mm) of each movement of the sample stage.

Embodiments of the present application may enable a rapid determination of film quality within a few seconds, allowing for rapid screening of poor quality LPTF prior to deposition of subsequent layers, thereby improving yield of LPTF and saving cost for mass production.

In addition, the accuracy of the embodiment of the application can be further improved by optimizing the relationship between the q value and the defect position of the film. The long X-ray coverage causes a broadening of the scattering peaks, which may lead to an overlap between the different peaks. Embodiments of the present application may separate out overlapping regions prior to analyzing the scattering intensity distribution. Since various LPTF may have different crystal structures and interplanar spacings, embodiments of the present application are suitable for detecting and analyzing different types of LPTF.

All patents, patent applications, provisional applications, and publications, including all charts, cited or cited herein are fully incorporated by reference so long as they do not inconsistent with the explicit reference in the present specification. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application. In addition, any element or limitation of any application disclosed herein or embodiments thereof may be combined with any and/or all other elements or limitations disclosed herein (alone or in any combination) or any other application or embodiments thereof, and all such combinations are contemplated as being within the scope of the present application without being limited thereto.

Claims

1. A method of analyzing a surface of a sample by grazing incidence X-ray scattering, comprising:

irradiating an X-ray beam onto a surface of a sample to generate a scattered wave;

adjusting the position of the sample through a sample table;

collecting the scattered waves by a two-dimensional detector;

performing a grazing incidence X-ray scatter plot on the collected scattered waves; and

one or more characteristics of the sample are determined based on the obtained grazing incidence X-ray scatter plot.

2. The method of claim 1, wherein the X-ray beam is generated by a synchrotron light source or a Cu/Mg/Al target.

3. The method of claim 1, wherein the sample is a large area polycrystalline film.

4. A method according to claim 3, wherein the large area polycrystalline thin film is a polycrystalline perovskite thin film.

5. A method according to claim 3, wherein said surface of said large area polycrystalline film has a thickness of greater than 1cm ² Is a part of the area of the substrate.

6. A method according to claim 3, wherein the large area polycrystalline thin film is made of one of a semiconductor, a metal oxide and a metal.

7. The method of claim 6, wherein the semiconductor is one of silicon, copper indium gallium selenide, copper zinc tin sulfide, and metal halide perovskite.

8. The method of claim 6, wherein the metal oxide is one of tin oxide, zinc oxide, indium oxide, titanium oxide, and aluminum oxide.

9. The method of claim 6, wherein the metal is one of gold, silver, aluminum, copper, zinc, lead, and tin.

10. The method of claim 1, wherein performing grazing incidence X-ray scatter mapping comprises: grazing incidence low angle X-ray scattering, grazing incidence wide angle X-ray scattering or grazing incidence transmissive low angle X-ray scattering is performed.

11. The method of claim 1, wherein determining one or more characteristics of the sample comprises: determining the location of the sample defect.

12. The method of claim 1, wherein determining one or more characteristics of the sample comprises: crystallinity is determined at a plurality of different locations of the sample.

13. The method of claim 1, wherein determining one or more characteristics of the sample comprises: crystallinity is determined at a plurality of different depths of the sample.

14. The method of claim 13, wherein determining the crystallinity at a plurality of different depths of the sample comprises: the grazing incidence X-ray scatter plot is performed by adjusting an angle of incidence of the X-ray beam to control an X-ray penetration depth.

15. The method of claim 1, wherein performing grazing incidence X-ray scatter mapping comprises: a longitudinal X-ray scan and a transverse X-ray scan of the surface of the sample are performed.

16. The method of claim 15, wherein performing the longitudinal X-ray scan comprises: a single exposure of the steerable X-ray footprint caused by geometrical distortion of the X-ray beam is performed.

17. The method of claim 16, wherein the X-ray footprint of the sample is a function of the size of the X-ray beam and the angle of incidence of the X-ray beam.

18. The method of claim 15, wherein the resolution of the longitudinal X-ray scan is determined by the distance between the sample and the two-dimensional detector and the pixel size of the two-dimensional detector.

19. The method of claim 15, wherein performing the transverse X-ray scan comprises: the sample is moved in a direction orthogonal to the plane of incidence of the X-rays.

20. An apparatus for analyzing a sample, comprising:

an X-ray source configured to generate an incident X-ray beam and direct the incident X-ray beam onto a surface of a sample;

a sample stage configured to be operable to adjust an angle between the incident X-ray beam and the surface of the sample and to move the sample in three dimensions;

a two-dimensional detector configured to collect signals of X-ray beams scattered from the surface of the sample; and

a processor configured to receive the collected signals, perform a grazing incidence X-ray scatter plot on the collected signals, and determine one or more characteristics of the sample based on the obtained grazing incidence X-ray scatter plot.

21. The apparatus of claim 20, wherein the X-ray source comprises a synchrotron light source or an X-ray source with a Cu/Mg/Al target.

22. The apparatus of claim 20, wherein the one or more characteristics of the sample comprise a location of the sample defect.