Scanning electron microscope system, pattern measurement method using same, and scanning electron microscope

In order to allow detecting backscattered electrons (BSEs) generated from the bottom of a hole for determining whether a hole with a super high aspect ratio is opened or for inspecting and measuring the ratio of the top diameter to the bottom diameter of a hole, which are typified in 3D-NAND processes of opening a hole, a primary electron beam accelerated at a high accelerating voltage is applied to a sample. Backscattered electrons (BSEs) at a low angle (e.g. a zenith angle of five degrees or more) are detected. Thus, the bottom of a hole is observed using “penetrating BSEs” having been emitted from the bottom of the hole and penetrated the side wall. Using the characteristics in which a penetrating distance is relatively prolonged through a deep hole and the amount of penetrating BSEs is decreased to cause a dark image, a calibration curve expressing the relationship between a hole depth and the brightness is given to measure the hole depth.

TECHNICAL FIELD

The present invention relates to a dimension measurement method for patterns formed on a semiconductor wafer, and more specifically to a scanning electron microscope system for dimension measurement of hole patterns and groove patterns with a high aspect ratio, a pattern measurement method using the same, and a scanning electron microscope.

BACKGROUND ART

For pattern dimension management in semiconductor manufacturing processes, a critical dimension scanning electron microscope (SEM) is widely used, in which an SEM is specialized only to semiconductors.FIG. 2Ais the basic configuration of a previously existing critical dimension SEM. A primary electron beam102emitted from an electron gun101is narrowly focused at a capacitor lens103, and two-dimensionally scanned over a sample107by a deflector104. Typically, a relatively low accelerating voltage of about one kV is used for an accelerating voltage. Secondary electrons120generated from the sample107by applying the electron beam are captured at a detector121, and thus a secondary electron beam image is obtained. On the secondary electron beam image, pattern edges are bright on the image due to a tilt angle effect or edge effect. Thus, the locations of the edges are detected by image processing methods to determine dimensions.

Reductions in the costs of semiconductor devices are achieved by decreasing chip areas by downscaling. However, increases in manufacturing costs such as lithography cancel the merits of the costs obtained by decreasing chip areas. In NAND flash memories, which are new schemes for cost reductions, the development of a technique (3D-NAND) is accelerating, in which memory cell arrays are stacked to form a three-dimensional memory cell array.

3D-NAND is formed through process steps in which after an electrode film and an insulating film are alternately stacked, a hole penetrated from a topmost layer to a lowermost layer is opened at one time (seeFIG. 3A), a memory film is formed on the side surface of the hole, and then a columnar electrode is buried. The process steps of opening a hole determine the success or failure of this process. The key point is to provide a hole that is penetrated to the lowermost layer in proper diameter. Requests are to manage whether a hole is opened or not or manage the ratio of the top diameter to the bottom diameter of a hole.

For a technique of observing whether a hole is opened or not or observing the ratio of the top diameter to the bottom diameter of a hole, Patent Literature 1, for example, describes a scanning electron microscope. The scanning electron microscope provides high energy primary electrons with energy enough to cause the primary electrons to reflect off the side wall or bottom face of a groove or hole of a sample and penetrate the inside of the sample for escaping from the surface of the sample or for generating tertiary electrons on the surface of the sample. The scanning electron microscope applies these primary electrons to the sample for observing a hole pattern having an aspect ratio of around three. Patent Literature 1 shows exemplary accelerating voltages of 100 kV and 200 kV for primary electrons.

Patent Literature 1 describes a configuration in which reflected electrons are disposed between an objective lens and a sample and detected by a scintillator, and tertiary electrons having passed through the center hollow portion of the objective lens are extracted using an extraction electric field and detected by the scintillator.

On the other hand, in Patent Literature 2, an electron beam accelerated at a voltage of 50 kV or more is applied to a sample using a scanning electron microscope, and secondary electrons or tertiary electrons generated from the sample are detected by a scintillator for observing the inside of a hole or groove. Similarly to Patent Literature 1, a configuration is described in which reflected electrons are disposed between an objective lens and a sample and are detected by a scintillator, and tertiary electrons having passed through the center hollow portion of the objective lens are extracted using an extraction electric field, and detected by the scintillator.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. Hei4(1992)-149944

Patent Literature 2: Japanese Unexamined Patent Application Publication No. Hei6(1994)-310075

SUMMARY OF INVENTION

Technical Problem

In order to manage the process steps of opening a hole, it is necessary to inspect and measure a hole with a considerably high aspect ratio in which the diameter of the hole is about 50 nm and the depth is 2 μm or more. However, as illustrated inFIG. 2B, a previously existing critical dimension SEM has a problem, which is that secondary electrons generated in the inside of a hole collide against the inner wall and are lost before escaping to the outside; thus, signals from the bottom of the hole are hardly obtained, and the bottom diameter of the hole, which is specifically important, fails to be measured.

According to a method described in Patent Literature 1, a configuration is described in which reflected electrons of high energy generated from the bottom of the hole are separated from tertiary electrons generated from the reflected electrons of high energy having passed the side wall of the hole using a suction electrode, and the reflected electrons and the tertiary electrons are detected. However, the level of tertiary signals generated from a sample formed with a narrow, deep hole with a large aspect ratio is typically low. Therefore, in the configuration described in Patent Literature 1 in which tertiary electrons are sucked using the suction electrode for detection, only some of tertiary electrons generated from the sample can be detected. In the case where a narrow, deep hole with a large aspect ratio is observed, it is difficult to reliably provide a sufficient level of the detection signals of tertiary electrons.

In the configuration described in Patent Literature 1 in which reflected electrons are detected using the scintillator disposed between the objective lens and the sample and tertiary electrons having passed through the center hollow portion of the objective lens are extracted using an extraction electric field and detected by the scintillator, in tertiary electrons generated from the sample, only some of tertiary electrons having passed through the center hollow portion of the objective lens can be detected, and it is difficult to reliably provide a sufficient level of detection signals of tertiary electrons. In reflected electrons generated from the bottom of a deep hole with a large aspect ratio, most of the components of reflected electrons emitted from the hole opening to the outside travel in the direction along the center axis of the hole. Thus, the scintillator disposed around the objective lens is difficult to detect tertiary electrons except tertiary electrons having passed through the center hollow portion of the objective lens. On the other hand, also in the scanning electron microscope system described in Patent Literature 2, only some of tertiary electrons generated from the sample can be detected by the disclosed scintillator, and it is difficult to reliably provide a sufficient level of the detection signals of tertiary electrons. In addition, most of the components of reflected electrons generated from the bottom of a deep hole with a large aspect ratio travel in the direction along the center axis of the hole. Thus, the scintillator disposed around the objective lens is difficult to detect tertiary electrons except tertiary electrons having passed through the center hollow portion of the objective lens.

The present invention is to solve the problems of the above-described previously existing techniques and to provide a scanning electron microscope system that can measure a hole diameter or a groove width with a high aspect ratio, a pattern measurement method using the same, and a scanning electron microscope.

Solution to Problem

In order to solve the problems, in the present invention, a scanning electron microscope system that measures a hole pattern or a groove pattern formed on a substrate is configured to include: a primary electron beam application unit that scans and applies a primary electron beam to a pattern formed on the substrate; a backscattered electron detection unit that detects backscattered electrons having penetrated a side wall of the hole pattern or the groove pattern among backscattered electrons emitted from the substrate to which a primary electron beam is applied by the primary electron beam application unit; an electron beam image generation unit that generates an electron beam image corresponding to a distribution of intensity of the backscattered electrons detected by the backscattered electron detection unit; and an image processing unit that determines a boundary region between a dark region and a bright region, the dark region being present in the bright region on the electron beam image generated by the electron beam image generation unit, and detects the determined boundary region as a location of an edge of the hole pattern or the groove pattern.

In order to solve the problems, in the present invention, a scanning electron microscope system that measures a hole pattern or a groove pattern formed on a substrate is configured to include: a primary electron beam application unit that scans and applies a primary electron beam to a pattern formed on the substrate; a backscattered electron detection unit that detects backscattered electrons having penetrated a side wall of the hole pattern or the groove pattern among backscattered electrons emitted from the substrate to which a primary electron beam is applied by the primary electron beam application unit; an electron beam image generation unit that generates an electron beam image corresponding to a distribution of intensity of the backscattered electrons detected by the backscattered electron detection unit; and a depth estimation unit that determines a boundary region between a dark region and a bright region, the dark region being present in the bright region on the electron beam image generated by the electron beam image generation unit, and estimates a depth of the hole pattern or the groove pattern from information about brightness of the dark region in the determined boundary region.

In order to solve the problems, in the present invention, a scanning electron microscope system that measures a hole pattern or a groove pattern formed on a substrate is configured to include: a primary electron beam application unit that scans and applies a primary electron beam to a pattern formed on the substrate; a backscattered electron detection unit that detects backscattered electrons having penetrated a side wall of the hole pattern or the groove pattern among backscattered electrons emitted from the substrate to which a primary electron beam is applied by the primary electron beam application unit; an electron beam image generation unit that generates an electron beam image corresponding to a distribution of intensity of the backscattered electrons detected by the backscattered electron detection unit; an image processing unit that determines a boundary region between a dark region and a bright region, the dark region being present in the bright region on the electron beam image generated by the electron beam image generation unit, and detects the determined boundary region as a location of an edge of the hole pattern or the groove pattern; and a depth estimation unit that determines a boundary region between a dark region and a bright region, the dark region being present in the bright region on the electron beam image generated by the electron beam image generation unit, and estimates a depth of the hole pattern or the groove pattern from information about brightness of the dark region in the determined boundary region.

In order to solve the problems, in the present invention, in a pattern measurement method for a hole pattern or a groove pattern formed on a substrate using a scanning electron microscope system, the method includes: scanning and applying a primary electron beam to a hole pattern or a groove pattern formed on a substrate using an electron microscope; detecting backscattered electrons having penetrated a side wall of the hole pattern or the groove pattern among backscattered electrons emitted from the substrate to which the primary electron beam is applied; generating an electron beam image corresponding to a distribution of intensity of the detected backscattered electrons; determining a boundary region between a dark region and a bright region, the dark region being present in the bright region on the generated electron beam image; and detecting the determined boundary region as a location of an edge of the hole pattern or the groove pattern, and/or estimating a depth of the hole pattern or the groove pattern from information about brightness of the dark region in the determined boundary region.

In order to solve the problems, in the present invention, an electron microscope that measures a hole pattern or a groove pattern formed on a substrate is configured to include: a primary electron beam application unit that scans and applies a primary electron beam to a pattern formed on the substrate; a backscattered electron detection unit that detects backscattered electrons having penetrated a side wall of the hole pattern or the groove pattern among backscattered electrons emitted from the substrate to which a primary electron beam is applied by the primary electron beam application unit; and an electron beam image generation unit that generates an electron beam image corresponding to a distribution of intensity of the backscattered electrons detected by the backscattered electron detection unit.

Advantageous Effects of Invention

According to the present invention, the diameter of a hole with a high aspect ratio can be measured, as well as the depth of a hole can be measured.

DESCRIPTION OF EMBODIMENTS

In the present invention, an electron beam at a high accelerating voltage is applied to a sample, and backscattered electrons (BSEs) at a low angle (e.g. a zenith angle of five degrees or more) are detected. Thus, the bottom of a hole is observed using “penetrating BSEs”, which are emitted from the bottom of the hole and penetrate the side wall. In the present specification, the zenith angle is defined as an angle formed of the normal direction of the surface of a sample, which is a measurement target, and the emission direction of emitted electrons.

With the use of the characteristics in which a penetrating distance is relatively prolonged through a deep hole and the amount of penetrating BSEs is decreased to cause a dark image, a calibration curve expressing the relationship between the depth of a hole and the brightness is given, and the depth of the hole is measured.

In the following, embodiments will be described with reference to the drawings.

First Embodiment

FIG. 1Ais the basic configuration of a scanning electron microscope system100to which the present invention is applied. The electron microscope system100is configured of an imaging optical system001, a control unit021, an operating unit022, a storage unit023, an input/output unit024, and other components. The imaging optical system001generates a primary electron beam102at a high accelerating voltage (e.g. a voltage of 30 kV or more) from an electron gun101, focuses the primary electron beam102at a capacitor lens103, passes the primary electron beam102through an objective lens105, and then focuses the primary electron beam102on the surface of a sample200.

The primary electron beam102is two-dimensionally scanned over the sample200by a deflector104. Backscattered electrons110in a low angle direction emitted from the sample200are received at an annular yttrium aluminium garnet (YAG) scintillator106(seeFIG. 1B), and converted into optical signals. The optical signals are guided to a high electron multiplier112by an optical fiber111, and a digital image is generated by an image generating unit113. In the processes, brightness correction is typically performed in order that the image has correct brightness. The obtained image is stored on the storage unit023. A stage108is moved to allow capturing images at given positions on the sample.

The control unit021controls voltages applied to regions around the electron gun101, the adjustment of the focal positions of the capacitor lens104and the objective lens105, the movement of the stage108, and the operation timing of the image generating unit113, for example. The operating unit022performs a dimension measurement process using the obtained image. The input/output unit024inputs sample information and the imaging conditions, and outputs the measured result of dimensions, for example.

With the use of the configuration as illustrated inFIG. 1A, a primary electron beam of high energy (a high accelerating voltage) is applied to the sample200, and backscattered electrons (BSEs) of high energy are emitted from the sample200. As illustrated inFIG. 1C, the emitted BSEs penetrate the side wall of a hole210formed on the sample200, and reach the annular scintillator106. Thus, the bottom of the hole can be observed.

Also in the case of the previously existing techniques, applying primary electrons to the bottom of a hole emits BSEs. However, the primary electrons have low energy (at a low accelerating voltage). Thus, the energy of BSEs is also low. Therefore, most of BSEs lose energy while traveling through the inside of the side wall, and fail to penetrate the side wall (seeFIG. 2B).

In the present invention, a high accelerating voltage is combined with low angle BSEs (BSEs generated in the direction in which an angle formed of the normal direction on the surface of the sample200and the BSEs is relatively large) for allowing the observation of the bottom of a hole based on the detection principle, which is referred to as “penetrating BSEs”, unlike the previously existing detection principle.

For the detection of low angle BSEs, an annular semiconductor detector or a Robinson detector may be used in addition to the YAG scintillator106. Instead of the annular scintillator, a configuration may be possible in which detectors are disposed in multiple directions.

FIGS. 4A to 4Dare the results confirming the effectiveness of the present invention by electron beam simulation (Monte Carlo simulation).FIG. 4Ais the cross sectional topology of a hole411formed on a sample401in which a top diameter td1is 70 nm, a bottom diameter bd1is 70 nm, and a hole depth hd1is 3.2 μm (in the following, referred to as a hole t70b70).FIG. 4Bis the cross sectional topology of a hole412formed on a sample402in which a top diameter td2is 70 nm, a bottom diameter bd2is 30 nm, and a hole depth hd2is 3.2 μm (in the following, referred to as a hole t70b30). The accelerating voltage was set to 30 kV. A secondary electron image (SE image) was obtained under the conditions in which electrons having energy of 50 eV or less were detected. A low angle BSE image was obtained under the conditions in which emitted electrons having an energy of 5,000 eV or greater at a zenith angle of 15 to 65 degrees were detected (In the present specification, the zenith angle is defined as an angle formed of the normal direction on the surface of the sample200and the emission direction of emitted electrons.).

FIG. 4Cis the signal waveforms of SE images detected when the primary electron beam102is applied to the samples401and402formed with the holes411and412having different cross sectional topologies illustrated inFIGS. 4A and 4B.FIG. 4Dis the signal waveforms of low angle BSE images. The horizontal axis in each ofFIGS. 4C and 4Dexpresses the distance from the center of the hole411or412. In the hole t70b70, x=35 nm corresponds to the bottom edge of the hole. In the hole t70b30, x=15 nm corresponds to the bottom edge. The vertical axis in each ofFIGS. 4C and 4Dexpresses the detected signal strength (Yield).

As illustrated inFIG. 4C, in the case of the SE images, in a signal waveform421of the SE image detected from the sample401formed with the hole t70b70(the hole411inFIG. 4A) and a signal waveform422of the low angle SE image detected from the sample402formed with the hole t70b30(the hole412inFIG. 4B), the signal strength from the bottom part of the hole is very small, and it is difficult to detect the location of the bottom edge from this signal waveform.

On the other hand, as illustrated inFIG. 4D, in the case of the low angle BSE images, the location of the rising edge of the signal waveform of a low angle BSE image431detected from the sample401formed with the hole t70b70(the hole411inFIG. 4A) is located near x=35 nm, and the location of the rising edge of the signal waveform of a low angle BSE image432detected from the sample402formed with the hole t70b30(the hole412inFIG. 4B) is located near x=15 nm. It is revealed that the low angle BSE images are more suitable for the detection of the location of the bottom edge of the hole than the SE images.

FIGS. 5A to 5Care a specific detection method for the location of the bottom edge of a hole. As illustrated inFIG. 5A, a low angle BSE image501of a hole pattern is an image in which a hole inner region502is dark and a hole outer region503is bright. In the case where the side wall of a hole is steep, the image has a sharp edge. In the case where the side wall of a hole is tapered, the image has a blur edge. A signal waveform510inFIG. 5Band a signal waveform520inFIG. 5Care sliced waveforms taken along line A-A crossing the hole502inFIG. 5A. As illustrated inFIG. 4D, the bottom edge expresses the location of the rising edge of the signal waveform. Thus, as illustrated inFIG. 5B, a bottom line511and a slope line512are fit to the bottom region and slope region of the signal waveform, respectively. Their intersection points are detected as bottom edges513, and then a bottom diameter514is determined. Alternatively, as illustrated inFIG. 5C, a method may be possible in which a threshold that internally divides a maximum value521and a minimum value522of the signal waveform in a given ratio and the intersection points of the threshold with the signal waveform are edge points. In the process, a method may be possible in which a large threshold and a small threshold (th1:523and a th2:524) are given and then a first hole diameter525and a second hole diameter526are determined. The difference between the first hole diameter525and the second hole diameter526(the first hole diameter−the second hole diameter) is taken as a side wall tilt angle index value. The sizes of the taper of the side wall can be monitored according to the sizes of the side wall tilt angle index value.

As described above, the first embodiment is the basic configuration of the present invention. According to the embodiment, the diameter of a hole with a high aspect ratio can be measured, which is not allowed to be measured by the previously existing techniques.

Second Embodiment

In this embodiment, a method is provided for measuring the diameter of a hole as well as the depth of a hole.

The present invention implements the observation of the bottom of a hole by detecting BSEs having penetrated the side wall. However, a deep hole with a large aspect ratio prolongs a distance required for electrons having been emitted from the bottom of the hole to penetrate the side wall and reach the surface. Thus, the ratio of electrons that consume energy in the midway and fail to penetrate the surface is increased. In other words, on the obtained image, the depth of a hole can be measured (estimated) using the relationship in which a deeper hole has a darker hole part.

In the following, in order to implement the measurement of the depth of a hole, necessary conditions for the configuration will be shown. The configuration of a scanning electron microscope system used in the embodiment is the same as the configuration of the scanning electron microscope system100described in the first embodiment and illustrated inFIG. 1A.

FIG. 6Ais a graph610of the comparison of a signal waveform611from a hole with a depth of 2.0 μm with a signal waveform612from a hole with a depth of 3.2 μm on low angle BSE images. The waveforms are detected when a primary electron beam is applied to these holes formed on samples. In both of the holes, the top diameter of the hole pattern formed on the sample (corresponding to td2inFIG. 4B) is 70 nm, and the bottom diameter (corresponding to bd2inFIG. 4B) is 30 nm. The accelerating voltage and other conditions are the same as the conditions for the simulation described inFIGS. 4A to 4D. A signal6111of a signal waveform611is detected from BSEs emitted from the portion corresponding to the bottom of the hole in the case where the hole depth of the hole pattern (corresponding to hd2inFIG. 4B) is 2.0 μm. A signal6121of a signal waveform612is detected from BSEs emitted from the portion corresponding to the bottom of the hole in the case where the depth of the hole is 3.2 μm. It is revealed that the signal strength of the signal6121is clearly smaller than the signal strength of the signal6111. This is the characteristics greatly different from the previously existing techniques that detect SEs.

FIG. 6Bis a graph620of the relationships between the hole depths of hole patterns formed on a sample and signal strengths (yields)621,622, and623of signals detected from BSEs emitted from the portion corresponding to the bottom part of the hole (corresponding to the signals6111and6121inFIG. 6A) under the conditions in which the accelerating voltages of primary electrons applied to the sample are 15 kV, 30 kV, and 45 kV. The signal strength is great when the accelerating voltage is high because BSEs have large energy and the number of electrons penetrating the side wall and reaching the topmost surface of the sample is great. In the case where the bottom of a deep hole is observed, the application of primary electrons to a sample at a high accelerating voltage is advantageous. In the case where a hole has a depth of 3 μm or more (a hole with an aspect ratio of more than 40) and a target of the present invention, the accelerating voltage of primary electrons is desirably 30 kV or more. Since the accelerating voltage in the previously existing techniques is about 1 kV, it is difficult to detect penetrating BSEs having energy that causes the BSEs to penetrate the side wall of a hole formed on a sample.

FIGS. 7A and 7Bare the results of simulation performed in order to clear the range of a zenith angle (seeFIG. 7A) suited to the detection of penetrating BSEs. Similarly to the cases described inFIGS. 6A and 6B, a top diameter td3of a hole pattern formed on a sample was set to 70 nm, and a bottom diameter bd3was set to 30 nm. A graph710inFIG. 7Bis the distribution of the signal strength to the zenith angle in the case where a hole depth hd3is 0.1 μm, 0.6 μm, and 1.2 μm.

In the simulation described inFIGS. 4A to 4D, the range of a zenith angle703, in which emitted electrons are detected, is set to an angle of 15 to 65 degrees, assuming the annular scintillator106as illustrated inFIG. 1B. In simulation inFIGS. 7A and 7B, the entire zenith angle is detected. As illustrated inFIGS. 7A and 7B, at a zenith angle of five degrees or less, the signal strength is almost the same even though the depths of the holes are different. The reason is that emitted electrons include many electrons that have been emitted from the bottom of the hole and have escaped from the opening of the hole to the hole outer region (Changes in the signal strength caused by the depth of the hole depend on differences in the distance of electrons having passed the inside of the side wall. Thus, in the case of electrons that do not pass the side wall, no difference is observed in the signal strength caused by the depth of the hole.). For the measurement of the depth of the hole, it is revealed that low angle BSEs at a zenith angle of five degrees or more are desirably detected.

In the embodiment, the annular scintillator106is used for detecting BSEs, which is provided between the sample200and the objective lens105(seeFIG. 1). Thus, high angle BSEs pass through a hole1061in the center of the scintillator106. Therefore, high angle BSEs (having a small zenith angle703) which have passed through the hole1061in the center of the scintillator106are not detected at the scintillator106. Consequently, the necessary conditions are satisfied.

On the other hand, in order to reliably provide the signal amount of BSE detection signals, a wide cover range of the zenith angle for detecting BSEs using the scintillator106is advantageous. From the relationship between the zenith angle and the BSE signal strength illustrated in the graph710inFIG. 7B, desirably, at least a range of a zenith angle of 20 to 60 degrees is covered, in which the signal strength of BSE detection signals is large. In the embodiment, the necessary conditions can be satisfied by adjusting the diameter of the scintillator106and the distance from the scintillator106to the sample200.

FIG. 8Ais a flowchart of a flow of the process of measuring the depth of a hole. From the input unit024of the scanning electron microscope system100illustrated inFIG. 1A, imaging conditions, such as the imaging magnification and the accelerating voltage, are inputted (S801). Subsequently, the imaging optical system001acquires the image of the sample200based on the conditions inputted in S801(S802). Image signals obtained by imaging the sample200at the imaging optical system001are inputted to the operating unit022(S803).

As illustrated in the image810, at the operating unit022, average brightness B0of a hole part811is calculated (S8031). Based on a beam current Ip in imaging and a brightness correction value (Brightness, Contrast) applied in generating the image, a transformation B1=f (B0, Ip, brightness, constant) is used, and the average brightness of the hole part811is converted into B1(S8032). Subsequently, reference is made to a calibration curve821expressing the relationship between the depth of a hole and the brightness of the hole as illustrated in a graph820, and then the depth of the hole is determined (S8033).

In S8032, the brightness of the hole is converted from B0to B1. The reason is that the brightness of the hole on the image is also changed depending on the beam current value or the brightness correction value. Thus, making reference to the calibration curve has no meaning without the conversion of the brightness under the reference conditions. In other words, the calibration curve821is necessary to have the relationship between the depth of the hole and the brightness of the hole under the reference conditions as illustrated in a wafer map830inFIG. 8B.

Referring toFIGS. 9A to 9C, the calibration curve will be additionally described. A graph910inFIG. 9Ais an atom number dependence911of the intensity of reflected electrons, in the relationship in which the intensity of reflected electrons (yield) is higher as the atom number (the mean atomic number in the case of a compound) is greater. Typical materials used in semiconductor processes are plotted on the graph. The mean atomic number is written in parentheses. For example, SiO2 and Si are used for materials for film stacks (201and202inFIG. 3A). SiGe is used for a stopper film (205inFIG. 3A). The intensity of penetrating BSEs is also changed in proportion to the intensity of reflected electrons. Thus, the calibration curve is necessary to have data of accelerating voltages for individual materials. As illustrated inFIG. 6B, the intensity of penetrating BSEs is also varied depending on the accelerating voltage of the primary electron beam102applied to the sample200. Therefore, as illustrated in a graph920inFIG. 9Band a graph930inFIG. 9C, the calibration curve is necessary to have data individually for materials and accelerating voltages.

In the case where it is possible to generate a standard sample in which the depth of a hole is changed step by step, data for the calibration curve only has to be generated by actually measuring the brightness of the hole. However, it is sometimes difficult to generate such a standard sample. As illustrated inFIG. 10, in this case, a calibration curve1040may be obtained as below. One or two points in actually measured data (1010), in which the depths of holes are known, are interpolated (1030) based on a result (1020) of simulation. Such data1041for the calibration curve only has to be determined for each of accelerating voltages.

As described above, the basic configuration of hardware according to the second embodiment is the same as that of the first embodiment. With the use of the calibration curve expressing the relationship between the depth of a hole and the brightness of the hole with the satisfaction of the necessary conditions in which the accelerating voltage is 30 kV or more and the zenith angle is five degrees or more, the depth of the hole can be measured.

The first and the second embodiments have the same hardware configuration. Thus, the first and the second embodiments can be implemented with the same system configuration.

Third Embodiment

FIG. 11Ais the basic configuration of an imaging optical system002according to a third embodiment of the present invention. The difference from the imaging optical system001described in the first embodiment (seeFIG. 1A) lies in that a detector121that detects secondary electrons120emitted from a sample200is additionally provided.

As illustrated inFIG. 2B, orFIGS. 4C and 4D, secondary electrons (SEs) emitted from the bottom of a hole formed on the sample fail to escape to the hole outer region. However, as illustrated inFIG. 11B, secondary electrons130emitted from near a top edge131of the hole are detected at the detector121.

As the schematic diagram1310illustrated inFIG. 12A, secondary electrons (130inFIG. 11B) emitted from near a top edge1312of a hole1311have a bright peak on the image by the edge effect. Thus, these electrons are suited to the measurement of the top diameter of a hole. As illustrated inFIG. 12B, the detection of peaks1321and1322of a signal waveform1320allows the determination of a top diameter1323of the hole.

As illustrated inFIG. 12C, the combination of the first embodiment with the second embodiment and the third embodiment determines a top diameter d1(1331), a hole depth h (1333), and a bottom diameter d2(1332) of a hole133. Thus, it is possible to acquire information necessary to manage the ratio of the top diameter to the bottom diameter of a hole, which is a problem of measurement described at the beginning.

With the use of the imaging optical system002illustrated inFIG. 11A, a low angle BSE image from the detector106and an SE image from the detector121are acquired at the same time. This provides merits below.FIG. 13Ais a schematic diagram1410of an SE image.FIG. 13Bis a schematic diagram1420of a BSE image. As a hole1411on the schematic diagram1410of the SE image inFIG. 13Aand a hole1421on the schematic diagram1420of the BSE image inFIG. 13B, the displacement of the centers of the holes on the SE image and the BSE image suggests that a hole expressed by the holes1411and1421is not provided perpendicularly.

In the case where the SE image and the BSE image are not acquired at the same time, the positional displacement in acquiring the images fails to be distinguished from the eccentricity of the hole pattern. However, this problem does not arise in the case where the SE image and the BSE image are acquired at the same time. Thus, with the comparison of the same hole pattern between the SE image and the BSE image, the degree of eccentricity of the hole pattern can be determined more accurately.

According to the embodiment, with the combined use of the low angle BSE image and the SE image detected at the same time, the top diameter of a hole can be more accurately measured, as well as information effective for managing the perpendicularity of a hole can be obtained.

Fourth Embodiment

FIG. 14Ais the basic configuration of an imaging optical system003according to a fourth embodiment of the present invention. The difference from the imaging optical system001described in the first embodiment (seeFIG. 1) lies in that the imaging optical system003is additionally provided with a detector151that detects high angle BSEs150(BSEs150emitted in the direction in which an angle from the surface of the sample107is relatively large) emitted from the sample107and an image generating unit152that generates a high angle BSE image.

As illustrated inFIG. 14B, the detector151detects high angle BSEs130that have been nearly upwardly emitted from a bottom hole1503of a hole1501formed on the sample107, have passed through an opening1502of the hole1501, and then have traveled to the hole outer region. Output signals from the detector151having detected the high angle BSEs130are inputted to the image generating unit152that generates a high angle BSE image. A digital image is generated, and inputted to the operating unit022. InFIG. 7B, it is described that the high angle BSE image has no sensitivity to the depth of a hole. In other words, the high angle BSE image has information about the intensity of reflected electrons from the bottom of a hole material regardless of the depth of the hole.

As illustrated inFIGS. 3B and 3C, in the case where holes206to209are not normally formed, the material of the hole bottom is usually unknown. In the case of a low angle BSE image detected at the scintillator106, the signal amount is also varied depending on changes in the depth of the hole as well as the difference of the material of the hole bottom. Thus, distinguishing between the depth and the material fails. On the other hand, a high angle BSE image detected at the detector151has no sensitivity to the depth of a hole. Thus, it is possible to estimate the hole bottom material from the signal strength.

FIG. 15is a process flow of the operating unit022in the case where the high angle BSE image is also used. First, the brightness of the hole bottom is calculated from a high angle BSE image inputted from the image generating unit152that generates a high angle BSE image (S160). From the brightness, the material of the hole bottom is estimated. Although not illustrated in the drawing, in the process, similarly, it is necessary to provide the step corresponding to the conversion of the brightness in the case of the low angle BSE image (S8032inFIG. 8). In the case where the hole bottom material fails to be determined, the process is ended because the measurement of the depth of the hole using the low angle BSE image has no meaning. In the case where the determination of the hole bottom material is enabled, the brightness of the hole bottom is calculated using the low angle BSE image inputted from the image generating unit113that generates a low angle BSE image (S162). After the brightness is converted (S163), reference is made to the calibration curves for materials and accelerating voltages, and then the depth of the hole is calculated (S164).

As described above, according to the embodiment, the depth of a hole can be measured even in the case where the material of the hole bottom is unknown.

Fifth Embodiment

A fifth embodiment is a user interface for implementing the present invention. In order to automatically perform measurement described in the first to fourth embodiments, it is necessary to generate a recipe that specifies various conditions in advance. In addition to a measurement box1710that specifies a pattern1711to be measured as illustrated inFIG. 16A, on the screen of the input/output unit024, the recipe displays a material specifying box1720that specifies a side wall film material1721and a hole bottom material1722illustrated inFIG. 16Band a condition setting box1730that sets the optical conditions for selecting BSEs and SEs as illustrated inFIG. 16Cand the output content of an output information display unit1735.

According to the embodiment, it is possible to specify items that need user input for implementing the present invention.

Sixth Embodiment

FIG. 18Ais the basic configuration of an imaging optical system according to a sixth embodiment of the present invention. The configurations according to the first to fourth embodiments are mainly targeted for measuring hole patterns. The embodiment is targeted for a groove pattern with a high aspect ratio (180inFIG. 17). For example, this corresponds to the process of forming the slit of a word line in the 3D-NAND processes. In the embodiment, a detector180split in azimuth angle directions to detect low angle BSEs is used in the imaging optical system004as the detector180to detect low angle BSEs.

In the case where a measurement target is a groove pattern, BSEs emitted in the longitudinal direction of the groove are not penetrating BSEs. Thus, the detector180does not detect BSEs emitted in the longitudinal direction, and detects only penetrating BSEs emitted in the transverse direction of the groove. This is a detector180, which is split in orientation directions, including four detecting devices180ato180das illustrated inFIG. 18B. Depending on the direction of the groove, the output from which one of the detecting devices in the orientations is selected.

With the use of the imaging optical system004as illustrated inFIG. 18A, the depth or groove width of the groove pattern180formed on the sample200as illustrated inFIG. 17can be measured, as well as the depth or diameter of the hole pattern as described in the first and the second embodiments can be measured.

According to the embodiment, the detection of penetrating BSEs, which is the present invention, is applicable to the measurement of a groove pattern with a high aspect ratio.

REFERENCE SIGNS LIST