CN109863573B

CN109863573B - Method of inspecting a substrate and computer readable medium having instructions stored thereon

Info

Publication number: CN109863573B
Application number: CN201680090320.8A
Authority: CN
Inventors: 伯纳德·G·穆勒; 张雪娜; 彼得·努南; 库普雷特·辛格·维迪
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2016-12-12
Filing date: 2016-12-12
Publication date: 2021-10-15
Anticipated expiration: 2036-12-12
Also published as: TW201837865A; KR102260984B1; CN109863573A; KR20190052121A; TWI734875B; WO2018108239A1

Abstract

A method for inspecting a substrate is described. The method comprises the following steps: providing a substrate in a vacuum chamber, the substrate being a large area substrate, wherein the substrate has a thin film having a grain structure deposited on the substrate; generating a primary charged particle beam with an imaging charged particle beam microscope, wherein the primary charged particle beam impinges on the substrate in the vacuum chamber; and generating one or more images from signal particles released from the substrate upon impact by the primary charged particle beam, wherein the one or more images are topographical images.

Description

Method of inspecting a substrate and computer readable medium having instructions stored thereon

Technical Field

The present disclosure relates to LTPS layer authentication and a method of inspecting a substrate. More particularly, embodiments described herein relate to a method for inspecting a substrate for display manufacturing, and more particularly, to a large area substrate for display manufacturing.

Background

In many applications, it is desirable to deposit a thin layer on a substrate, for example a glass substrate. Conventionally, substrates are coated in different chambers of a coating apparatus. For some applications, the substrate is coated in vacuum using vapor deposition techniques. Over the past few years, the price of electronic devices, and in particular optoelectronic devices, has decreased dramatically. Furthermore, the pixel density in displays is increasing. For TFT displays, high density TFT integration is required. However, even if the number of Thin Film Transistors (TFTs) within the device increases, it is desirable to increase the yield and reduce the manufacturing cost as much as possible.

One aspect of increasing the pixel density is the use of LTPS-TFTs (low temperature polysilicon) which may be used, for example, in LCD or AMOLED displays. During the fabrication of the LTPS-TFT, the gate electrode may be used as a mask to dope the contact regions of the active layer towards the source and drain of the transistor. The quality of this self-aligned doping can determine the yield of the manufacturing process. Therefore, there is a need to improve and control such processes. However, other self-aligned doping applications, i.e. applications other than the process of LTPS-TFTs, may also benefit from the improved process.

For these processes, it is beneficial to inspect the substrate to monitor the quality of the substrate (i.e., the quality of the deposited layer, particularly the LTPS layer). For example, glass substrates having a layer of coating material deposited thereon are manufactured for the display market. Displays are typically fabricated on large area substrates of ever increasing size. In addition, displays such as TFT displays are also undergoing constant improvement. For example, Low Temperature Polysilicon (LTPS) is one development in which low power consumption and improved characteristics may be achieved with respect to backlights.

The inspection of the substrate may be performed by, for example, an optical system. However, LTPS grain structure, grain size, and grain morphology of grains at grain boundaries are particularly difficult to review with optical systems because grain size may be below optical resolution, making the grains invisible to the optical system. Inspection of small portions of substrates has also been performed using charged particle beam devices in combination with surface etching. Surface etching can enhance contrast, e.g., grain boundaries, but causes damage to the glass substrate such that small portions of the substrate are inspected rather than the entirety of the substrate. Therefore, after inspecting the substrate, it is impossible to continue processing the substrate, for example, to inspect the influence of the grain structure on the final product.

Therefore, in view of the increasing demands on the quality of displays on large area substrates, for example, an improved method for inspecting large area substrates is needed.

Disclosure of Invention

A method of inspecting a substrate and an apparatus using the same are provided. Various aspects, benefits and features of the disclosure may be apparent from the claims, description and drawings.

According to one embodiment, a method for inspecting a substrate is provided. The method comprises the following steps: providing a substrate in a vacuum chamber, the substrate being a large area substrate, wherein the substrate has a thin film having a grain structure deposited on the substrate; generating a primary charged particle beam with an imaging charged particle beam microscope, wherein the primary charged particle beam impinges on the substrate in the vacuum chamber; and generating one or more images from signal particles released from the substrate upon primary charged particle beam impingement, wherein the one or more images are topographical images.

In some embodiments, the inventive methods described herein may be embodied in a computer-readable medium. The computer readable medium has instructions stored thereon that, when executed, cause a charged particle beam microscope to perform a method for inspecting a substrate as any of the methods described herein.

Drawings

A full and enabling disclosure to one of ordinary skill in the art is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein:

FIG. 1 shows a side view of an imaging charged particle beam microscope for use in embodiments described herein.

Fig. 2 shows a detection arrangement comprising a segmented scintillator (scintillator) for embodiments described herein.

Fig. 3A shows a topographical image according to an embodiment of the present disclosure.

Fig. 3B illustrates a combined image combined from multiple topographical images according to an embodiment of the present disclosure.

Fig. 4 shows an image of a prior art air SEM measurement in which an etched sample surface is measured.

Fig. 5 shows a flow diagram illustrating a method according to embodiments described herein, in particular a method for inspecting large area substrates.

Fig. 6 shows a flow diagram illustrating a further method according to embodiments described herein, in particular a method for calibrating and inspecting a large area substrate, for example for display manufacturing.

Detailed Description

Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in the figures. The various examples are provided by way of illustration and are not intended as limitations. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. The present disclosure is intended to embrace such modifications and variations.

In the following description of the drawings, like reference numerals refer to like parts. Only the differences of the respective embodiments will be described. The structures shown in the drawings are not necessarily shown to true scale but rather serve to better understand the embodiments.

The term "substrate" as used herein encompasses both non-flexible substrates (e.g., glass substrates or glass sheets) and flexible substrates (e.g., webs (webs) and foils). The substrate may be a coated substrate, wherein one or more layers of material are coated or deposited on the substrate, for example by a Physical Vapor Deposition (PVD) process or a Chemical Vapor Deposition (CVD) process.

Embodiments described herein relate to large area substrates, particularly large area substrates for the display market. According to some embodiments, the large area substrate or the corresponding substrate support may have at least 1m²The size of (c). The size may be from about 1.375m²(1100 mm. times.1250 mm-passage 5) to about 9m²More particularly from about 2m²To about 9m²Or even up to 12m². The substrate or substrate receiving area provided according to the structures, apparatus and methods of some embodiments described herein may be a large area substrate as described herein. For example, the large area substrate or carrier may be: generation 5 (GEN 5), which corresponds to about 1.375m²The substrate (1.1m × 1.25 m); generation 7.5 (GEN 7.5), which corresponds to about 4.39m²The substrate (1.95m × 2.25 m); generation 8.5 (GEN 8.5), which corresponds to up to about 5.7m²A substrate (2.2m × 2.5 m); or generation 10 (GEN10) which corresponds to about 9m²The substrate (2.88m × 3130 m). Even higher generations, such as generation 11 (GEN 11) and generation 12 (GEN 12) and their corresponding substrate areas may be similarly implemented.

Without limiting the scope of protection of the present application, in the following, a charged particle beam device, such as a charged particle beam microscope or a component thereof, will be exemplarily referred to as a charged particle beam device, which comprises the detection of secondary or backscattered particles (such as electrons). Embodiments may still be applied to apparatus and components for detecting particles (corpuscles), such as secondary and/or backscattered charged particles in the form of electrons or ions, photons, X-rays or other signals, in order to obtain an image of a sample. When referring to particles, a particle is understood to be an optical signal, where a particle is a photon as well as a particle (where a particle is an ion, atom, electron or other particle). As described herein, the discussion and description of detection is exemplary with respect to electrons in a scanning electron microscope. Other types of charged particles, such as positive ions, may be used in the apparatus of various instruments.

According to embodiments herein, which may be combined with other embodiments, the signal (charged particle) beam or the signal (charged particle) sub-beam (beamlet) is referred to as a secondary and/or backscattered particle beam. Typically, the signal beam or secondary beam is generated by impinging a primary beam or a primary sub-beam on the sample. A primary charged particle beam or a primary charged particle beamlet is generated by a particle beam source and is directed and deflected over a sample to be examined or imaged.

FIG. 1 shows a charged particle beam device or a charged particle beam microscope100. An electron beam (not shown) may be generated by the electron beam source 112. Additional beam shaping means (beam shaping means) such as baffles, extractors and/or anodes may be disposed within the bore chamber 110. The beam may be aligned with a beam limiting aperture (beam limiting aperture) that is sized to shape the beam, i.e., block a portion of the beam. The electron beam source chamber includes a TFE emitter. The bore chamber may be evacuated to 10 deg.f^-8Mbar to 10^-9Pressure in mbar.

A condenser lens (condenser lens) may be provided in the further vacuum chamber 120 of the column of the charged particle beam microscope 100. For example, the condenser lens may include a pole piece 122 and a coil 124. In which further vacuum chamber further electron-optical elements 126 may be arranged. The further electron-optical element 126 may be selected from the group consisting of: an stigmator, a correction element for chromatic and/or spherical aberration, and an alignment deflector for aligning the primary charged particle beam with the optical axis of an objective lens (objective lens) 140.

The primary electron beam may be focused on the substrate 10 by the objective lens 140. The substrate 10 is positioned at a substrate location on the substrate support 150. When the electron beam impinges on the substrate 10, signal electrons (e.g., secondary and/or backscattered electrons) and/or x-rays are released from the substrate 10 and may be detected by the detector 139.

In the exemplary embodiment described with reference to fig. 1, a condenser lens 123 is provided. A two-stage deflection system (not shown) may be arranged between the condenser lens and, for example, a beam limiting aperture (e.g., a beam shaping aperture) for directing the beam towards the aperture. As shown in fig. 1, objective lens 140 has a magnetic lens component with

pole pieces

142 and 146 and with a coil 144. The objective lens focuses the primary electron beam on the substrate 10. Further, the upper electrode 152 and the lower electrode 154 form an electrostatic lens component of the objective lens 140.

In addition, a scanning deflector assembly 170 may be provided. The scanning deflector component 170 can be, for example, a magnetic component, but is preferably an electrostatic scanning deflector component, which is configured to achieve high pixel rates. The scan deflector assembly 170 may be a single stage assembly as shown in fig. 1. In addition, two-stage deflector assemblies or even three-stage deflector assemblies may be provided for scanning. The stages (stages) are arranged at different positions along the optical axis.

The lower electrode 154 is connected to a voltage source (not shown). The lower electrode of the objective lens, which is the deceleration electrode of the immersion lens component, i.e. the deceleration field lens component, is typically at a potential that provides a landing energy of charged particles on the substrate that is equal to or less than 2keV, e.g. 500V or 1 keV. As exemplarily shown in fig. 1, the substrate support 150 may be set to ground potential, according to some embodiments. Thus, the lower electrode 154 may have a positive voltage of about 200V to 1kV, for example, to produce landing energies of 200eV to 1 keV.

According to some embodiments, which can be combined with other embodiments described herein, the primary charged particle beam near the substrate 10 (e.g. within the objective lens, behind the objective lens, or a combination thereof) can be decelerated. The deceleration may be provided by the lower electrodes 154, i.e., the deceleration field lenses, respectively. Deceleration may be provided, for example, by electrostatic lens components of the objective lens. For example, additionally or alternatively, a retarding bias voltage may be applied to the substrate 10 and/or the substrate support in order to provide a retarding field lens component according to embodiments described herein. The objective lens may be an electrostatic-magnetic compound lens having, for example, an axial gap or a radial gap, or the objective lens may be an electrostatic retarding field lens.

According to some embodiments, which can be combined with other embodiments described herein, the distance between the lower portion or edge of the objective lens (e.g., the lower electrode 154) and the substrate or substrate support can be 1 millimeter (mm) to 3 mm, e.g., 1.5 mm. The resolution of images measured on large area substrates (e.g., substrates having an area equal to or greater than 1 square meter, such as equal to or greater than 1.5 square meters) is less than 15 nanometers, such as 3 nanometers to 12 nanometers, such as about 10 nanometers. The resolution is mainly defined by the size of the substrate support for large area substrates and the vibrations and motions caused by the size of the substrate support.

An advantage of having a landing energy equal to or less than 2keV, in particular equal to or less than 1keV, is that the primary electron beam impinging on the substrate produces a stronger signal than a high energy electron beam. Since the layers deposited on the substrate, such as the LTPS layer, are thin and since high energy electrons penetrate deep into the substrate, i.e. below the layer, only a small number of electrons may generate a detector signal that covers information about the deposited layer. In contrast, low energy electrons, e.g., electrons having landing energies equal to or less than 2keV, penetrate only into shallow regions of the substrate, thus providing more information about the deposited layer. Thus, even when the substrate is not subjected to surface etching as provided by the embodiments described herein, an improved image, for example, an improved image of grain boundaries, may be provided. Further, embodiments described herein provide electron microscope images under vacuum conditions on large area substrates (i.e., substrates having an area equal to or greater than 1 square meter). Providing electron microscope images under vacuum allows for low landing energies, e.g., equal to or less than 2keV (e.g., equal to or less than 1 keV).

For high resolution applications it is beneficial to provide landing energies, e.g. equal to or less than 2keV (e.g. equal to or less than 1keV) and to have high charged particle beam energies in the column, e.g. beam energies equal to or greater than 10keV, such as equal to or greater than 30 keV. Embodiments may include a deceleration before the substrate 10 (e.g., within the objective lens and/or between the objective lens and the substrate 10) with a factor equal to or greater than 5 (e.g., equal to or greater than 10). For other applications, low landing energies, e.g. equal to or less than 2keV, can also be provided without deceleration, e.g. in case the beam energy within the column is not higher than 2 keV.

According to embodiments described herein, which may be combined with other embodiments, an electron microscope image of a thin film having grains is provided. For example, a scanning electron microscope image of a portion of a thin film deposited on a large area substrate is provided. The image is provided under vacuum conditions that allow low energy imaging, wherein the landing energy of the electron beam on the thin film is equal to or less than 2keV, for example about 1 keV. Thus, embodiments of the present disclosure with respect to low energy imaging provide non-destructive imaging compared to high energy electron beam imaging (<7keV) with AIR SEM, for example. Thus, electron beam viewing may be provided during the fabrication of optoelectronic devices, such as displays fabricated on large area substrates.

The charged particle beam microscope 100 as shown in fig. 1 comprises a detector 139 located in the detection vacuum region 130. While the detector 139 shown in fig. 2 includes the scintillator device 136. The scintillator arrangement 136 has an opening 201, for example an opening in the center of the scintillator arrangement. The aperture 201 is used to route the primary charged particle beam through the detector 139.

The scintillator arrangement 136 is segmented to have two or more scintillator segments 236. According to some embodiments, which can be combined with other embodiments described herein, four scintillator segments, i.e. four segment detectors (Quad detectors), can be provided. The four segments allow the appearance of topographical images in two dimensions x and y of the substrate plane. The respective images are shown in fig. 3A.

Light guide 134 is connected to each scintillator segment 236. Further, a photo multiplier (photo multiplier) or another signal detection component 132 may be provided for each light guide. Accordingly, some embodiments that may be combined with other embodiments herein include an efflet-sohnery (Everhart-Thornley) detector arrangement as the detector 139. Some embodiments may also use avalanche photodiodes (avalanche photodiodes) as signal detection components or as microchannel plates.

According to embodiments described herein, which can be combined with other embodiments, the scintillator arrangement can be manufactured from a low noise scintillator having a lower bandwidth, which results in a better signal-to-noise ratio, which can be further improved by averaging multiple segments of the scintillator arrangement 136. For example, the scintillator may have a decay time of 50 nanoseconds to 100 nanoseconds, such as about 60 nanoseconds. Measurements according to embodiments of the present disclosure may have a pixel rate of 3MHz to 10MHz, for example about 5 MHz.

In some embodiments, which can be combined with other embodiments described herein, the primary charged particle beam can be tilted such that the primary charged particle beam impinges on the substrate at a predetermined tilted beam landing angle. For example, the tilted primary charged particle beam may have an inclination (with respect to the normal on the substrate), i.e. an angle of incidence of more than 5 °, e.g. 10 ° to 20 °, e.g. about 15 °. The untilted primary charged particle beam may have an angle of incidence of less than 3 °. According to embodiments described herein, an imaging charged particle beam microscope as described herein may be used for imaging using one or more tilted beams. Thus, 3D imaging, imaging of stairs and imaging of other height structures may be improved.

According to one embodiment, the beam tilt (beam tilt) with tilt angle may be generated by a pre-lens deflection unit (pre-lens deflection unit), which may comprise two deflection coils (deflection coils) to deflect the beam away from the optical axis. In view of such two stages (stages), the beam can be deflected to appear to occur from a point coincident with the apparent position of the charged particle beam source. The pre-lens deflection unit may be arranged between the charged particle source and the objective lens. The in-lens deflection unit may be arranged within the field of the objective lens such that the fields overlap. The in-lens deflection unit may be a two-stage unit comprising two deflection coils. The in-lens deflection unit may redirect the beam such that the beam passes through the center of the objective lens, i.e. the center of the focusing action, at the optical axis. Redirecting refers to causing a charged particle beam to impinge the surface of the substrate from a direction substantially opposite to the direction in which no beam passes through the optical axis. The combined action of the in-lens deflection unit and the objective lens directs the primary charged particle beam back to the optical axis so that the primary charged particle beam hits the sample at a predetermined tilted beam landing angle.

According to another embodiment, the beam tilt may be generated by a deflection unit comprising two deflectors to deflect the beam away from the optical axis. In view of such two stages (stages), the beam can be deflected to appear to occur from a point coincident with the apparent position of the charged particle beam source. The pre-lens deflection unit may be arranged between the charged particle source and the objective lens. Above the pre-lens deflection unit, a Wien filter (Wien filter) generating a cross electromagnetic field may be disposed. An off-axis path of the charged particle beam through the objective lens causes a first chromatic aberration. The energy dispersion effect of the wien filter introduces a second color difference of the same kind as the first color difference. By appropriately selecting the strength of the electric field E and the magnetic field B of the wien filter, the second color difference can be adjusted to have the same magnitude as the first color difference but to have the opposite direction to the first color difference. In effect, the second color difference substantially compensates the first color difference in the plane of the substrate surface. The primary charged particle beam is tilted by traveling off-axis through the objective lens and the focusing action of the objective lens.

According to further embodiments, which may additionally or alternatively be applied, the beam tilt may also be introduced by mechanically tilting the lens barrel (i.e. with respect to the optical axis of the substrate). Tilting the charged particle beam by providing a tilted beam path within the column provides for faster switching between several beam angles and reduces the introduction of vibrations compared to mechanical movements.

According to some embodiments, an apparatus for inspecting a substrate, in particular for display manufacturing, is provided. This device comprises a vacuum chamber as described herein. This apparatus further includes a substrate support disposed in the vacuum chamber as described herein. This apparatus further comprises a first imaging charged particle beam microscope and optionally a second imaging charged particle beam microscope as described herein. The second imaged charged particle beam microscope is separated from the first imaged charged particle beam microscope by a distance of at least 5 cm to 60 cm, for example about 25 cm to 35 cm.

The images shown in fig. 3A are images of four segments of the detector 139 of the grain structure of low temperature polysilicon. Technologies for fabricating TFTs on a glass substrate include an amorphous silicon (a-Si) process and a Low Temperature Polysilicon (LTPS) process. The main difference between the amorphous silicon process and the low temperature polysilicon process is the electrical characteristics of the device and the complexity of the process. Low temperature poly-silicon (LTPS) TFTs have higher mobility, but the process of fabricating low temperature poly-silicon TFTs is more complicated. Although the amorphous silicon TFT has a low mobility, a process of manufacturing the amorphous silicon TFT is simple. According to embodiments described herein, a low temperature polysilicon TFT process may be improved and process control is beneficial. A low temperature polysilicon TFT process is one example of a use for which the embodiments described herein may be beneficial. To fabricate the low temperature polysilicon TFT, the deposited layer is locally melted due to laser irradiation. For example, the laser radiation may have a width of about 60 centimeters. Thus, a distance of about 30 cm between the charged particle beam microscopes may be sufficient in this region to provide an analysis of the process.

A method of inspecting a substrate is provided that includes generating a primary charged particle beam in a vacuum chamber and generating one or more images from the signal particles, wherein the one or more images are topographic images. As shown in fig. 3A, for example, four topographical images may be provided by imaging a portion of a thin film having a grain structure with a segmented detector, such as a Quad detector (Quad detector), having four segments. The topographic images of fig. 3A may be combined into a combined-perspective secondary electron image as shown in fig. 3B. According to embodiments described herein, the images described herein may be compared to optical images having two or more illumination angles (e.g., four illumination angles) of a light source, wherein the optical images may be obtained from shadows of the imaging grain structure's illumination angle values. This is different from measuring with an oblique beam, which corresponds to a stereoscopic optical image.

In fig. 3B, an algorithm has been provided to highlight the grain boundaries of the grains of the LTPS film. The topographical image as shown in fig. 3A or the combined image as shown in fig. 3B may be used to inspect LTPS layers (e.g., in the display industry), or other thin film layers having a grain structure. The electron beam observed according to the methods described herein can image a thin film having a grain structure (e.g., an LTPS layer having multiple viewing angles). Improved topographical information may be provided. This allows a more accurate assessment of the grain structure.

For comparison, fig. 4 shows the measurement results of the prior art. Fig. 4 shows an image of a destructive measurement in which the LTPS layer has been etched and imaged with a high energy electron beam. The image surface may present a large portion of line 42 and may identify a peak corresponding to point 44. It is apparent that one or more images as shown in fig. 3A or a combined image as shown in fig. 3B provide improved topographical information and are therefore used for a better assessment of the grain structure. Further, the obtained images as shown in fig. 3A and 3B are non-destructive. Thus, the imaged thin film or corresponding substrate as shown in fig. 3A and 3B may be further processed according to embodiments described herein.

According to embodiments described herein, the grain structure may be described by the size of the grains, the shape of the grains, the distribution of the grains, the area of the grains, and the like. Such parameters may be evaluated via statistical analysis methods for one or more of the parameters described above. For example, the characteristics of the grains of the grain structure may be determined as an arithmetic mean, a quadratic mean, a weighted mean, and/or a median.

According to embodiments described herein, which may be combined with other embodiments, the topographical information may be used by software algorithms, for example, for detecting and analyzing the grain structure (e.g., in LTPS grain structure). The computation of the grain structure characteristics may also include a watershed algorithm (watershed algorithm). The computation based on one or more images (i.e., a topographic image or a combined image of topographic images) may provide at least one characteristic of grains of a grain structure selected from the group consisting of: the area of the crystal grains of the crystal grain structure, the perimeter of the crystal grains of the crystal grain structure, the minimum size of the crystal grains of the crystal grain structure, the maximum size of the crystal grains of the crystal grain structure, the size of the crystal grains of the crystal grain structure in a predetermined direction, and the peak height of the grain boundary of the crystal grains of the crystal grain structure. For example, a two-channel or multi-channel detector (e.g., a four-channel detector) is used to image the LTPS topography from quasi-illumination sources (four illumination sources) at two or more (e.g., four) respective viewing angles in the top-down SEM image. These two or more (e.g., four) viewing angles give surface information for detecting and evaluating the size, uniformity, local distribution, and all statistical data used to describe the parameters of a thin film with a grain structure (i.e., LTPS layer).

According to some embodiments, which can be combined with other embodiments described herein, statistical data of the characteristics of the grain structure and/or parameters of the grain structure can be used to verify process parameters of the manufacturing method of the deposited thin film. A process for feedback to a film having a grain structure may be provided. For example, a Low Temperature Polysilicon (LTPS) TFT process may be controlled by Electron Beam Review (EBR) according to embodiments described herein.

According to some embodiments, which can be combined with other embodiments described herein, an algorithm for identifying statistical data of characteristics of the grain structure or parameters of the grain structure of the thin film can be applied to the combined image as shown in fig. 3B. It has been found that it may be beneficial to apply these algorithms to the individual topography images shown in fig. 3A, and combine the values produced by these algorithms into a combined value for use in evaluating the grain structure.

According to embodiments described herein, the area of a grain in the grain structure, the perimeter of a grain in the grain structure, and one or more dimensions of a grain in the grain structure may be measured. For example, grains having a size of about 100 nm to 500 nm may be measured. According to some embodiments, which can be combined with other embodiments described herein, the field of view, which can be measured by scanning the primary electron beam over the substrate, can have a size of up to 10 micrometers (μm).

The grains are typically surrounded by grain boundaries having peaks, which may have a peak height equal to or less than 50 nanometers. According to embodiments, which can be combined with other embodiments described herein, the normal operation of the charged particle beam microscope is to use a non-tilted beam, i.e. the beam may have an angle of incidence on the substrate equal to or less than 3 °. The height of the peak may be determined based on the length of the shadow of one or more of the topographical images. The length of the shadow can be calibrated to the measured peak height.

For calibration, the primary charged particle beam may be tilted to an angle equal to or greater than 5 °, for example, about 15 °. The height of the height profile, i.e., the grain boundaries of the grains, may be measured using the tilted beam image or using two or more tilted beam images. The above-described tilted beam image or two or more tilted beam images may be obtained on a thin film having a grain structure, such as a Low Temperature Polysilicon (LTPS) layer, or on a substrate having artificial alignment properties. The height of the grain boundaries of the grain structure or the absolute value of the artificial calibration characteristics can be obtained from the measurement using the oblique beam. After removing the tilt and providing a normal operating angle of incidence (e.g., a tilt of less than 3 °, such as a tilt of 0 °), then the topographical image can be measured and the length of the shadow can be calibrated to the previous measured height.

According to some embodiments, an apparatus for inspecting large area substrates for display manufacturing may be an in-line apparatus, i.e., an apparatus that may include a load lock to load and unload a substrate imaged using an imaging charged particle beam microscope (e.g., a Scanning Electron Microscope (SEM)) in a vacuum chamber may be provided linearly with another previous test or process and linearly with yet another subsequent test or process. Since the charged particle beam for imaging on the substrate has a low energy equal to or less than 2kV, the structure provided on the substrate is not damaged. Thus, the substrate may be provided for further processing in a display manufacturing plant. As understood herein, the number of substrates to be tested may be 10% to 100% of the total number of substrates in a display manufacturing plant. Therefore, even if an apparatus for inspection including an imaging charged particle beam microscope can be provided as an in-line tool, it is not necessary to test 100% of substrates in a production line.

The vacuum chamber may comprise one or more valves that may connect the vacuum chamber with another chamber, particularly when the apparatus is an in-line apparatus. The one or more valves may be closed after the substrate is introduced into the vacuum chamber. Thus, the gas atmosphere in the vacuum chamber can be controlled by creating a technical vacuum (e.g. using one or more vacuum pumps). One benefit of inspecting a substrate in a vacuum chamber is that vacuum conditions can facilitate inspection of the substrate using a low energy charged particle beam, as compared to, for example, inspection at atmospheric pressure. For example, the low energy charged particle beam may have a landing energy equal to or less than 2keV, in particular equal to or less than 1keV, for example 100eV to 800 eV. The low-energy beam does not penetrate deep inside the substrate compared to the high-energy beam, and thus can provide excellent information on, for example, a coating layer on the substrate.

Fig. 5 shows a flow chart of a method of inspecting a substrate, such as a substrate used in display manufacturing. As shown in block 502, a large area substrate is provided in a vacuum chamber, wherein the large area substrate has a thin film with a grain structure deposited on the substrate. The substrate can be measured as part of a conventional process, i.e., without the need for sample preparation for similar etching. Furthermore, the measurement steps shown below are non-destructive, and the substrate may be further processed after electron beam observation. A primary charged particle beam is generated and impinges a thin film on a large area substrate under vacuum conditions, as shown in block 504. The vacuum condition allows for low energy landing energy on the substrate. For example, energy equal to or less than 2keV, such as energy of about 1keV, can be provided. Block 506 in fig. 5 indicates generating one or more topographical images. According to embodiments described herein, the topographical image is generated with a non-tilted beam. The non-tilted beam is beneficial for easy control of the electron beam microscope and thus the throughput. The topography image may be provided by a segmented detector such that multiple views of the non-tilted beam may be obtained via one measurement. The topographical image may be used to determine one or more characteristics or parameters of a grain structure (e.g., a grain structure in an LTPS layer).

Fig. 6 shows a flow chart of another method of inspecting a substrate. For calibration of the shadow length of the topography image measured at a non-tilted beam angle, the primary charged particle beam may be tilted to an angle of incidence equal to or greater than 5 °, such as 10 ° to 20 °. This is indicated in block 602. At block 604, one or more images of the region with the oblique beams are generated. As shown in block 606, the height of the structure or feature is measured from one or more images with the tilted beams. In block 608, features are measured for the same area and/or at the same structure with the non-tilted beam, wherein one or more topographical images, such as test images, are generated. The height measured in absolute value from one or more topographical images as indicated in block 606 is calibrated to the length of the shadow of the image measured in block 608. In block 608, the test image is measured with a non-tilted beam so that the length of the shadow can be calibrated to the measurement height in absolute value. The calibration is shown in block 610. In block 612, the height of the peak of the grain boundary of the grain structure is measured using calibration and based on the shadow length. The process shown at block 612 may be repeated multiple times based on the calibrations generated at blocks 602 through 610, according to embodiments described herein. Thus, the calibration may be provided once or regularly at predetermined time intervals. Measurements may be made during inspection of a substrate in a manufacturing process with a non-tilted beam. From the calibration done previously, the calibration can be used to determine the height of the grain boundaries of the grain structure. This is advantageous for increasing the measurement speed and thus the throughput. For example, the calibration needs to be performed once, and the check can be performed, for example, once a week or even once a month or even on a longer time scale, with measurements being taken continuously.

While the foregoing is directed to embodiments, other and further embodiments of the invention may be devised without departing from the scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A method for inspecting a substrate, the method comprising:

providing the substrate in a vacuum chamber, the substrate being a large area substrate, wherein the substrate has a thin film having a grain structure deposited on the substrate;

generating a primary charged particle beam with an imaging charged particle beam microscope, wherein the primary charged particle beam impinges on the substrate in the vacuum chamber;

generating one or more images from signal particles released from the substrate upon impact by the primary charged particle beam, wherein the one or more images are topographic images; and

calculating at least one characteristic of grains of the grain structure from the one or more images, the at least one characteristic of grains of the grain structure including a peak height of grain boundaries of grains of the grain structure based on a previously completed calibration.

2. The method of claim 1, wherein a landing energy of the primary charged particle beam when impinging on the substrate is equal to or less than 2 keV.

3. The method of claim 1, wherein the one or more images are generated with a segmented detector.

4. The method of claim 2, wherein the one or more images are generated with a segmented detector.

5. The method of claim 3, wherein the one or more images are generated with a Quad detector (Quad detector) having four segments.

6. The method of claim 3, wherein the one or more images are produced at a tilt angle of the primary charged particle beam equal to or less than 3 °.

7. The method of claim 4, wherein the one or more images are produced at a tilt angle of the primary charged particle beam equal to or less than 3 °.

8. The method of claim 1, wherein the at least one characteristic of a grain of the grain structure is determined as: at least one of an arithmetic mean, a quadratic mean, a weighted mean, a minimum, a maximum, and/or a median.

9. The method of claim 1, wherein the computing uses a watershed algorithm (watershed algorithm).

10. The method of claim 1, wherein two or more of the one or more images are combined to form a combined image, and the computing is performed using the combined image.

11. The method of claim 7, wherein the calculating is performed using the one or more images to form one or more corresponding calculated values, and wherein the one or more corresponding calculated values are combined.

12. The method of claim 7, further comprising:

verifying process parameters of a manufacturing method of the thin film by the at least one characteristic of the grains of the grain structure.

13. The method of any of the preceding claims, further comprising:

tilting the primary charged particle beam to an angle equal to or greater than 5 °;

measuring the height of the height profile;

tilting the primary charged particle beam back to a normal operating angle;

generating one or more test images from signal particles released from the substrate when the primary charged particle beam impinges at the angle of normal operation, wherein the one or more test images are topographic images; and

calibrating the length of the shadow of the one or more images as a topographical image using the measured height.

14. The method of any one of claims 1 to 7, wherein the inspection method is an intermediate process of a manufacturing method of a display.

15. The method of any of claims 1 to 7, further comprising:

generating a further primary charged particle beam with a further imaging charged particle beam microscope, wherein the further primary charged particle beam impinges on the substrate in the vacuum chamber; and

generating one or more further images from further signal particles released from the substrate upon impact of the further primary charged particle beam, wherein the one or more further images are topographical images.

16. The method of claim 15, wherein the primary charged particle beam and the further primary charged particle beam have a distance of 5 cm to 60 cm at the location of impingement on the substrate.

17. A computer readable medium having stored thereon instructions that, when executed, cause a charged particle beam microscope to perform a method for inspecting a substrate, the method being as claimed in any one of claims 1 to 7.

18. The computer-readable medium of claim 17, wherein the method further comprises:

calculating from the one or more images at least one further characteristic of grains of the grain structure, the at least one further characteristic of grains of the grain structure being selected from: an area of a grain of the grain structure, a perimeter of a grain of the grain structure, a minimum size of a grain of the grain structure, a maximum size of a grain of the grain structure, and a size of a grain of the grain structure in a predetermined direction.