WO2012081428A1 - 走査電子顕微鏡及びそれを用いた測長方法 - Google Patents
走査電子顕微鏡及びそれを用いた測長方法 Download PDFInfo
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- WO2012081428A1 WO2012081428A1 PCT/JP2011/078013 JP2011078013W WO2012081428A1 WO 2012081428 A1 WO2012081428 A1 WO 2012081428A1 JP 2011078013 W JP2011078013 W JP 2011078013W WO 2012081428 A1 WO2012081428 A1 WO 2012081428A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
- H01J37/05—Electron or ion-optical arrangements for separating electrons or ions according to their energy or mass
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B15/00—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
- H01J37/10—Lenses
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/244—Detectors; Associated components or circuits therefor
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/04—Means for controlling the discharge
- H01J2237/047—Changing particle velocity
- H01J2237/0473—Changing particle velocity accelerating
- H01J2237/04735—Changing particle velocity accelerating with electrostatic means
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/24485—Energy spectrometers
Definitions
- the present invention relates to a scanning electron microscope (hereinafter referred to as SEM) and a length measuring method using the same.
- Non-Patent Document 1 there is a method of energy discrimination of signal electrons detected in the SEM (for example, Non-Patent Document 1).
- Signal electrons detected in SEM are classified as secondary electrons, reflected electrons, and Auger electrons. Discrimination of the signal electrons is expected to be effective in measuring the dimensions of a three-dimensional device and performing local elemental analysis.
- the reflected electrons have high energy, they can escape from the bottom of the three-dimensional device and are expected to be useful for observing the bottom.
- Auger electrons have an energy inherent to the element and are generated only on the surface of the sample, local elemental analysis can be performed by detecting Auger electrons.
- secondary electrons are electrons generally used for image formation in a scanning electron microscope and are generated from the surface of the sample, so that information reflecting the shape of the sample can be obtained.
- an energy filter for discriminating signal electrons a voltage is applied to a metal grid, etc., and a deceleration electric field type that allows only electrons with energy higher than the applied voltage to pass through. Electrons are deflected by an electromagnetic field and discriminated by differences in electron trajectories. Two types of deflection type are often used.
- a thin-film transmission type energy filter has been devised that utilizes the fact that the penetration depth into a substance varies depending on the energy of electrons.
- the thin film transmission type has a problem that the energy of signal electrons that can be transmitted is determined by the thickness of the thin film, so that arbitrary energy discrimination cannot be performed.
- the deceleration electric field type energy filter transmits all electrons having energy equal to or higher than the threshold value, and thus is superior to the deflection type in terms of signal intensity, and is superior to the thin film transmission type in that the user can freely determine the threshold value. On the other hand, there is a problem that the energy resolution is inferior to the deflection type.
- the deceleration electric field type energy filter includes a conductor grid 201 and an energy filter power source 126 connected to the grid as shown in FIG.
- a negative voltage VF is applied to the conductor grid 201 by the energy filter power source 126, a potential barrier as shown by an equipotential line (equipotential surface) 202 is formed.
- signal electrons 139 including secondary electrons, reflected electrons, and Auger electrons are emitted from the wafer 113. Thereafter, only the electrons having energy exceeding the potential barrier among the signal electrons 139 incident on the energy filter pass through the energy filter and are detected.
- a retarding method in which a negative voltage Vr of several kV is applied to the wafer 113 by the retarding power source 121 and the primary electrons 138 are decelerated immediately before the wafer is often employed.
- the retarding method is characterized in that the signal electrons 139 emitted from the wafer 113 are accelerated by a negative voltage Vr of several kV applied to the wafer 113. Therefore, when the retarding method and the deceleration electric field type energy filter are used together, the signal electrons 139 enter the energy filter 108 with energy of several keV. In this case, in order to discriminate the signal electrons 139 from energy, it is necessary to apply a voltage of ⁇ several kV to the energy filter power supply 126.
- the potential at the center of the grid is lower than the voltage VF applied to the conductor grid 201.
- An object of the present invention is to provide a scanning electron microscope including a decelerating electric field type energy filter capable of obtaining high energy resolution even when a retarding optical system is provided, and a length measuring method using the same.
- an electron source, a deflector for deflecting a primary electron beam emitted from the electron source, and the primary electron beam deflected by the deflector are converged.
- a scanning electron microscope comprising: a decelerating electric field type energy filter that discriminates energy of the signal electrons, wherein the decelerating electric field type energy filter includes a conductor thin film for energy discrimination of the signal electrons. Use a microscope.
- FIG. 4 is a graph of the number of electrons passing through a filter (S curve) with respect to a voltage applied to a grid, for explaining a difference in energy resolution between the energy filters shown in FIGS. 2 and 3. It is a graph of the number of signal electrons with respect to the energy of signal electrons detected by the energy filter shown in FIGS. 2 and 3.
- a conductive thin film having a thickness of 100 mm to 500 mm (10 nm to 50 nm) is pasted on a grid of a conventional deceleration electric field type energy filter, and a negative voltage is applied to the grid to discriminate energy of signal electrons. It is characterized by performing.
- the present embodiment in the SEM using the retarding method, it is possible to obtain energy resolution superior to that of the conventional decelerating electric field type energy filter. The reason why an energy resolution better than that of the conventional deceleration electric field type energy filter can be obtained by using the conductive thin film will be described below.
- the potential at the center of the grid is lower than the voltage VF ( ⁇ 0) applied to the conductor grid 201 (FIG. 2). Due to the influence of this potential drop, even electrons having an energy lower than ⁇ VF can pass through the energy filter, and the energy resolution is lowered.
- a conductor thin film 304 is attached to a conductor grid 302 to which a voltage is applied (FIG. 3).
- the equipotential lines 202 are formed substantially parallel to the conductor thin film 304 as shown in FIG.
- the equipotential lines 202 are formed more parallel to the conductor thin film 304 on the signal electron incident side.
- the potential drop at the center of the grid caused by the conventional decelerating electric field type energy filter (FIG. 2) is eliminated, and a substantially uniform potential barrier of the applied voltage VF is formed.
- FIG. 4 shows how the number of electrons passing through the filter changes with respect to the voltage VF applied to the conductor grids 201 and 302 at this time.
- the curve shown in FIG. 4 is called an S curve.
- the S curve shows a behavior close to a step function (solid line in FIG. 4), and the energy resolution is larger than that of the conventional energy filter. improves.
- the energy resolution is defined by the rising width of the S curve, and the energy resolution is better as the width is smaller.
- the deceleration electric field type energy filter is a so-called high-pass filter having a characteristic of allowing all electrons having energy that can pass through a potential barrier formed by a voltage applied to the grid to pass.
- the energy dependence of the number of signal electrons emitted from the sample is generally represented in FIG.
- the signal electrons those having an energy of 0 to 50 eV are called secondary electrons 501, and those having an energy of 50 eV or more are called reflected electrons 502.
- the Auger electron 503 is an electron emitted due to excitation of the inner core electron of the atom, and its energy is unique to the atom.
- a scanning image is formed only with the secondary electrons 501, an image reflecting the shape of the sample surface is obtained, and when a scanning image is formed only with the reflected electrons 502, an image reflecting the inside of the sample and the difference in element numbers is obtained. It is done.
- a deceleration electric field type energy filter using a conductive thin film makes it possible to detect only electrons having energy higher than the voltage applied to the filter. This effect is effective, for example, when detecting reflected electrons having energy in the vicinity of V0, or detecting secondary electrons having energy of ⁇ 10 eV or more.
- the conductor 602 is connected to a retarding power source 121 for applying a potential Vr ( ⁇ 0) for decelerating the primary electrons 138 immediately before the sample.
- the insulator 601 When the insulator 601 is irradiated with the primary electrons 138, the insulator 601 is charged, and whether the charge is positive or negative is determined by the secondary electron generation efficiency defined by (secondary electron amount) / (primary electron amount).
- the insulator 601 is negatively charged if the secondary electron generation efficiency is smaller than 1.0, and positively charged if it is larger than 1.0.
- the secondary electron generation efficiency is determined by the energy when the primary electrons 138 are incident, and the secondary electron generation efficiency of an insulator generally used in a semiconductor device exceeds 1.0 from 500 eV to 1000 eV.
- FIG. 7 is a diagram showing an example of energy distribution of signal electrons emitted from the conductor pattern and the insulator pattern.
- the deceleration electric field type energy filter is a high-pass filter that passes all electrons having energy equal to or higher than a certain threshold. However, a differential image of two images obtained by applying two different set voltages to the filter grid is used. When formed, it is possible to form an image created by signal electrons in an arbitrary energy range.
- a scanned image 1 After applying a first set voltage VF1 to the grid of the filter at the same location of the sample using a decelerating electric field type energy filter using a conductive thin film, a scanned image 1 is acquired, and then a second set voltage VF2 ( After applying ⁇ VF1), a scanned image 2 is acquired.
- the difference image between the scanned images 1 and 2 is an image formed by signal electrons in the energy range from ⁇ VF1 to ⁇ VF2 as indicated by the hatched portion in FIG.
- the deceleration electric field type energy filter using a conductive thin film has better energy resolution than a conventional filter, for example, an image can be formed only from Auger electrons. Since the energy of Auger electrons is unique to an element, the spatial distribution of a minute region of an arbitrary element can be visualized by forming a scanning image from Auger electrons.
- FIG. 1 is a schematic overall configuration diagram of a scanning electron microscope (SEM type length measuring device) provided with a deceleration electric field type energy filter using a conductive thin film according to the present embodiment.
- SEM type length measuring device scanning electron microscope
- the SEM type length measuring device is roughly divided into a SEM casing 103, a sample chamber 117, a SEM system control unit 136, a vacuum exhaust system unit 112, an image forming unit 129, and a length measurement system control unit 137.
- the SEM casing 103 and the sample chamber 117 are scanned by a vacuum exhaust system unit 112 having a vacuum exhaust device such as a rotary pump, a dry pump, and a turbo molecular pump and a mechanism for controlling them. It is evacuated so that a sufficient degree of vacuum is maintained.
- the evacuation system unit 112 controls opening and closing of the valve (A) 141 and the valve (B) 142 that connect the evacuation apparatus, the SEM housing 103 and the sample chamber 117.
- the SEM housing 103 includes an irradiation system that irradiates a sample with primary electrons 138 and a detection system, and includes an electron source 102, a condenser lens 104, a diaphragm 105, a reflector 128, a detector 127, an E ⁇ B deflector 107, An energy filter 108, deflectors 109 and 110, a booster electrode 125, an objective lens (converging lens) 111, and a trap plate electrode 123 are included.
- a decelerating electric field type energy filter 108 using a conductive thin film which will be described later, is directly under the E ⁇ B deflector 107, and a negative voltage is applied from the energy filter power supply 126 to the conductive thin film in order to decelerate the signal electrons 139. Applied and functions as an energy filter.
- the primary electrons 138 emitted from the electron source 102 are converged by the condenser lens 104, pass through the aperture 105 for controlling the current of the primary electrons 138 incident on the wafer (sample) 113, and the holes and energy of the reflector 128. After passing through a shield pipe (details will be described later) of the filter 108 and being deflected by the deflectors 109 and 110, it is narrowed down by the objective lens (convergence lens) 111 and enters the sample.
- Signal electrons 139 (secondary electrons, reflected electrons, Auger electrons) generated by irradiating the wafer 113 with the primary electrons 138 are negative voltage applied to the wafer holder 114 by the retarding power source 121, and trap plate electrodes. 123 and the booster electrode 125 are accelerated by the potential difference, converged by the objective lens (convergence lens) 111, deflected by the deflectors 109 and 110, pass through the energy filter 108, and collide with the reflector 128.
- the objective lens convergence lens
- Electrons 140 (tertiary electrons) generated from the reflecting plate 128 due to the signal electrons 139 colliding with the reflecting plate 128 are drawn into the detector 127 by the E ⁇ B deflector 107.
- a configuration for detecting electrons 140 (tertiary electrons) generated from the reflector 128 will be described.
- a detector capable of directly detecting the signal electrons 139 at the reflector 128 position such as a semiconductor detector or a microchannel plate, is provided. Even if installed, the effect of the present invention can be obtained.
- the signal electrons 139 can be lifted to the reflector 128 side.
- the same voltage as the retarding voltage is applied to the trap plate electrode 123 from the trap plate power source 122 in order to prevent the potential of the booster electrode 125 from leaking onto the wafer 113 and to equalize the charge of the wafer 113 to be charged. To do.
- the sample chamber 117 includes a stage 116, an insulating material 115, and a wafer holder 114 on which the wafer 113 is placed.
- the wafer holder 114 and the stage 116 grounded are electrically insulated by the insulating material 115.
- a voltage can be applied to the wafer holder 114 from the outside by a retarding power source 121.
- the wafer 113 and the wafer holder 114 are in contact with each other, and the wafer 113 and the wafer holder 114 are at the same potential.
- a negative voltage can be applied to the other sample from the retarding power source 121 and observed.
- the stage 116 can be driven in a plane perpendicular to the central axis of the SEM casing 103. That is, if the central axis of the SEM casing 103 is the z axis, the stage 116 can move in the x, y plane.
- the wafer holder 114 is fixed to the stage 116 via an insulating material 115, and the wafer holder 114 can be moved by driving the stage 116.
- the movement of the stage 116 is controlled by the stage controller 119 and the stage driving unit 120 in the stage control unit 118.
- the SEM system control unit 136 includes an electron gun power source 101 that controls the acceleration voltage of the primary electrons 138 emitted from the electron source 102, a condenser lens 104, an E ⁇ B deflector 107, deflectors 109 and 110, and an objective lens (converging lens).
- the device is connected to an energy filter power source 126 that controls a voltage applied to the conductive thin film of the filter 108, an evacuation system unit 112, an image forming unit 129, and an image display unit 135, and controls the above apparatus by sending a signal.
- the current of the primary electrons 138 passing through the diaphragm 105 is controlled by controlling the current flowing through the coil constituting the condenser lens 104 by the electron optical system control power source 106. Further, by controlling the current of the coil constituting the E ⁇ B deflector 107 and the voltage of the electrodes by the electron optical system control power source 106, the primary electrons 138 are not deflected by the E ⁇ B deflector 107, and the tertiary The electrons 140 can be drawn into the detector 127. Further, the primary electron 138 is scanned on the wafer 113 by controlling the current flowing in the coils constituting the deflectors 109 and 110 by the electron optical system control power source 106.
- the current flowing through the coils constituting the objective lens 111 is controlled by the electron optical system control power source 106. This control is performed by the electron gun power source 101, the booster power source 124, the trap plate power source. 122.
- the retarding power supply 121 changes, the primary electrons 138 are always focused on the wafer 113.
- the energy of the primary electrons 138 incident on the wafer 113 is determined by the difference between the acceleration voltage set by the electron gun power supply 101 and the voltage (retarding voltage) applied to the wafer holder 114 by the retarding power supply 121, and by changing the retarding voltage.
- the energy of the primary electrons 138 incident on the wafer 113 can be changed.
- Detector and image forming unit In order to form a scanning image, the primary electrons 138 are deflected by the deflectors 109 and 110 so that the primary electrons 138 scan on the wafer 113, and the signals of the tertiary electrons 140 captured by the detector 127 are converted into signal amplifiers.
- the signal After being amplified at 130, the signal is converted into a digital signal by the AD converter unit 131 and sent to the image processing unit 132.
- the image processing unit 132 forms a scanned image as a map of tertiary electron signals synchronized with the scanning signal.
- the formed scanned image is stored in the image memory unit 133.
- the amplification of the signal amplifier 130 is performed so that the maximum gradation value and the minimum gradation value of the formed scanning image fall within the range from the lowest value to the highest value assigned to one pixel of the image. Rate and offset are adjusted automatically. The amplification factor and offset can also be set by the user.
- the detector 127 is floated at a positive high voltage.
- the difference processing unit 134 has a function of forming a difference image between any two scanned images stored in the image memory unit 133. As will be described later, the difference processing unit 134 is used when forming an image using signal electrons in an arbitrary energy range.
- the length measuring system control unit 137 has the pattern and process information of the wafer 113 to be measured, process information, observation conditions, length measuring region, so that optimum length measurement is always performed.
- An algorithm used for length measurement is stored and connected to the SEM system control unit 136, and the entire apparatus is managed and controlled via the SEM system control unit 136.
- the SEM type length measuring device is capable of measuring the length of the wafer 113 regardless of the presence or absence of an operator and monitoring the length measurement result.
- Structure of a deceleration electric field type energy filter using a conductive thin film Next, the structure of the deceleration electric field type energy filter 108 using a conductive thin film will be described in detail with reference to FIGS.
- FIG. 10 is a schematic sectional view of a deceleration electric field type energy filter using a conductive thin film used in the scanning electron microscope according to the present embodiment, and FIG. 18 is a perspective view thereof.
- the energy filter 108 mounted on the SEM type length measuring device is composed of conductor grids 301, 302, and 303.
- the pitch of the conductor grids 301, 302, and 303 is such that the conductor thin film is not torn and is stuck loosely, for example, ⁇ 1 mm.
- conductor thin film 304 is attached only to the conductor grid 302
- a conductor thin film similar to the conductor thin film 304 can be attached to both or one of the conductor grids 301 and 303 in addition to the conductor grid 302.
- the conductor grid 302 is connected to an energy filter power supply 126 capable of applying a negative voltage through a feedthrough (not shown) capable of maintaining a vacuum. Further, in order to avoid discharge, the conductor grid 302 is separated from the conductor grids 301 and 303 and the shield pipe 1001 by ⁇ 1 mm or more.
- the conductive thin film 304 has conductivity, and as the conductive material, for example, a conductor such as Al, Au, Cu, W, C, or stainless steel, or an insulating thin film such as SiN on which the above-described conductor is deposited is used. be able to. These may be used alone or in combination.
- graphene can be used as a conductor instead of a conductor such as Al, Au, Cu, W, C, and stainless steel.
- the thickness of the conductor thin film 304 is 3 mm or more and 30 mm or less (0.3 nm or more and 3 nm or less), and by reducing the thickness of the conductor thin film 304, secondary electrons having energy to be transmitted are scattered in the thin film. This makes it possible to reduce the phenomenon that is difficult to detect. Furthermore, an improvement in the S / N ratio of the SEM image can be obtained by improving the transmittance of the thin film.
- the conductor thin film 304 preferably has an opening of about several ⁇ m for allowing the signal electrons 139 to pass through.
- the conductive thin film 304 there is a microgrid that is commercially available as a sample holder in a transmission electron microscope. Even when the conductor thin film 304 has an opening of about .mu.m, the uniformity of the potential barrier formed on the conductor grid 302 is sufficiently maintained.
- an aperture ratio of 80% and an energy filter having a size of 10 cm ⁇ were used. However, it is not limited to this. It is desirable that the aperture ratio be as high as possible within a range in which an equal electric field is formed in parallel with the conductor thin film.
- an example of a method of attaching the conductor thin film 304 to the conductor grid 302 will be described.
- An organic film such as collodion is attached to the conductor grid 302, and a conductor such as Al, Au, Cu, W, or stainless steel is deposited on the above-described organic film in a thickness of 100 to 500 mm, and then heated to burn off the organic film.
- a conductor such as Al, Au, Cu, W, or stainless steel is deposited on the above-described organic film in a thickness of 100 to 500 mm, and then heated to burn off the organic film.
- the conductor thin film which has C as a main component is produced by heating the said organic film single-piece
- the graphene produced on a metal substrate such as Cu or Ni is transferred to a resist such as polymethyl methacrylate (PMMA), and then the PMMA to which the graphene is transferred is attached to the conductor grid 302.
- PMMA polymethyl methacrylate
- the conductor thin film 304 can be obtained by removing only PMMA with a resist stripper.
- a negative voltage can be applied from the energy filter power supply 126 to the conductor grid 302 to which the conductive thin film 304 is attached, and a potential barrier is formed by the applied voltage, and only the signal electrons 139 having energy higher than the potential barrier can pass the energy filter 108. I can pass.
- the orbit of the primary electrons 138 becomes approximately 0V, Even if a voltage is applied to the energy filter, the primary electrons 138 can pass through the energy filter 108 with little influence.
- the diameter of the shield pipe is about 1 mm (1 ⁇ 0.5 mm).
- the above-described shield pipe 1001 is connected to both of the conductor grids 301 and 303, but can be connected to only one of the conductor grids 301 and 303.
- the conductive thin film is used for the deceleration electric field type energy filter, so that the energy resolution of the small electric field type filter with a large signal amount is greatly improved, and the retarding optical system is provided. Even if it is a case, the scanning electron microscope provided with the deceleration electric field type
- the automatic length measurement is divided into an “recipe creation process” by an operator and an “automatic length measurement process” using a recipe.
- the recipe creation of the present embodiment is executed on the SEM type length measuring apparatus shown in FIG. 1, and each of the recipe creation process or the automatic length measurement process is entirely performed by the length measurement system control unit 137. It is governed.
- an external server is connected to the length measuring system control unit 137 or the image display unit 135, and the recipe Information with a large data size, such as information, is stored in an external server.
- the length measurement system control unit 137 or the image display unit 135 is provided with a communication function depending on whether or not connection to the server is possible.
- the communication function means, for example, software for controlling communication processing, a computer for executing software, or a terminal for connecting to a communication line.
- communication processing software The realized function may be referred to as a communication function.
- “Recipe creation process” The recipe creation procedure will be described with reference to FIG. (Sample Basic Information Input Step S1100) An operator who wants to measure a sample first inputs information on the sample to be measured. For example, the device operator inputs information while viewing the input screen displayed on the image display unit 135.
- the type of wafer and the name of the manufacturing process correspond to the information described above, and these pieces of information input by the operator are used to classify and manage a plurality of recipes.
- Optical condition selection step S1101 Select the optical conditions to be used when measuring.
- the parameters of the optical conditions are the probe current incident on the sample, the field of view at the time of imaging, the incident energy, and the electric field strength formed on the sample.
- the SEM image the SEM is acquired by multiple image acquisition such as frame addition. "Deterioration of image quality” and "abnormal contrast such as unevenness of brightness, which is a detrimental effect during measurement,” are determined not to occur.
- the operator may arbitrarily select the optical conditions, or the manufacturer may determine recommended conditions at the time of shipping the apparatus and use them.
- Temporal registration step S1102 for alignment In a sample on which a pattern such as a semiconductor wafer is formed, it is necessary to accurately measure the positional relationship between the coordinates of the stage 116 that moves the sample and the coordinates of the pattern formed on the sample. In this embodiment, the process of measuring this positional relationship is referred to as an alignment process.
- the image of the pattern on the sample that can be recognized on the optical image and the SEM image is registered in the external server as a template.
- a template may be registered by connecting an external storage device to the length measurement system control unit 137.
- optical image template is used in the first alignment step
- SEM image template is used in the second alignment step.
- the second alignment step with high accuracy is performed.
- the registration work is executed by, for example, selecting an optical image and an SEM image displayed on the image display unit 135 by the apparatus operator.
- Registration position registration step S1103 In order to accurately correct the positional relationship between the coordinates of the stage 116 and the coordinates of the pattern formed on the sample, it is necessary to perform an alignment process in at least two places. Here, the location where alignment is performed is registered.
- the registration is executed, for example, when the apparatus operator selects an appropriate position on the SEM image displayed on the image display unit 135.
- Alignment execution step S1104 Here, the positional relationship between the coordinates of the stage 116 and the coordinates of the sample pattern is measured from an image comparison between the template and the optical image and SEM image captured at the location registered above.
- a position search template for searching for a place to be measured is registered in the vicinity of the pattern to be measured.
- the template for measuring position search is stored in an external server like the template for alignment, but the template may be registered by connecting an external storage device to the length measurement system control unit 137.
- the registration operation itself is performed in the same manner as when the alignment template is registered.
- Information registered as a template is a low-magnification SEM image and stage coordinates.
- a low-magnification SEM image is taken, and the position is determined by performing pattern matching with the registered image.
- the template for the part to be measured is registered in the external server.
- the image registered as the template an image having the same magnification as the imaging magnification of the SEM when measuring the dimension of the pattern is registered.
- the work performed at the time of registration is the same as the work of registering the alignment template and the measurement position search template.
- Step S1107 of necessity of energy filter If it is necessary to use an energy filter for the sample to be measured, set the energy filter according to the following procedure. If it is not necessary to use the energy filter, the process jumps to the image acquisition process (execution of length measurement) in step S1109 shown in FIG. Although it is possible for the operator to determine whether or not to use the energy filter, it can be set freely. However, the apparatus may automatically determine whether or not it is necessary to use the energy filter from the basic information of the sample described above.
- the device automatically determines There are two types of methods that the device automatically determines.
- One is a method in which an apparatus determines whether or not it is necessary to use an energy filter by referring to a recipe created in the past.
- the recipe is stored in the external server, but an external storage device different from the server may be connected to the length measurement system control unit 137.
- a storage unit such as a memory may be provided in the length measurement system control unit 137 or another device element to store the recipe.
- the length measurement system control unit 137 calls a recipe from an external server or an external storage device and refers to it according to the basic information of the sample input by the apparatus operator.
- the device manufacturer stores a correspondence table on the necessity of using the energy filter in the device, and the device judges whether or not the energy filter is necessary based on the correspondence table. It is a method. For example, when the sample is a semiconductor wafer, the structure and material on the wafer surface are reflected in the process name, and a correspondence table of energy filter usage conditions recommended by the manufacturer is created for each name and stored in the apparatus.
- an external storage device is connected to the length measurement system control unit 137 to store a correspondence table.
- the length measurement system control unit 137 refers to the correspondence table using the name of the manufacturing process input by the apparatus operator as a reference key, and determines whether or not the use of an energy filter is necessary for the sample manufactured by the manufacturing process.
- the correspondence table can be updated only by exchanging the recording medium when the correspondence table is updated, the updating operation is facilitated.
- the entire length measurement system is configured such that a new correspondence table is stored in an external server and can be downloaded from the server when the correspondence table is updated, the work of updating the correspondence table is further facilitated.
- the “length measuring system” means a system constituted by an SEM type length measuring device, an external server, and a communication line, and includes other system elements within a range related to length measurement.
- the type of sample to be measured is selected from the choices by pressing the button (A) 1202 that can select information stored in the apparatus by a pull-down function (S1302).
- the length measurement system control unit 137 calls an energy-dependent spectrum of the number of signal electrons (secondary electrons, reflected electrons, Auger electrons) from an external server or an external storage device in accordance with the type of sample input by the apparatus operator. (S1303).
- the spectrum of the energy dependence of the number of signal electrons for a typical sample is recorded by the manufacturer on an external server or an external storage device, but for a sample that is not recorded, the user can add it later.
- the spectrum can be directly registered in the external server or the external storage device by the user as numerical data, but can also be measured by the SEM type length measuring device shown in FIG.
- the S curve measured from the signal electrons generated from the sample is a convolution of the energy dependence spectrum of the number of signal electrons and the transmission function of the energy filter 108.
- the S curve is obtained by observing the sample while changing the voltage applied to the energy filter 108.
- the transmission function of the energy filter 108 is, for example, that the same voltage as the voltage for accelerating the primary electrons 138 by the electron source 102 is applied to the wafer (sample) 113, and the primary electrons 138 are rebounded immediately above the wafer 113. Can be determined by measuring the change in the number of electrons reaching the detector 127 with respect to the voltage applied to the energy filter 108.
- the transmission function can be measured by the user, but the manufacturer may record it in advance on an external server or an external storage device.
- the S curve and the transmission function are obtained, the energy dependence spectrum of the target number of signal electrons can be obtained by deconvolution of both.
- This calculation and processing can be executed by the length measurement system control unit 137, and the result is stored in an external server or an external storage device connected to the length measurement system control unit 137.
- the detected energy range is displayed as a hatched portion on the spectrum of the GUI 1201. (S1305).
- a method of inputting the energy range of signal electrons on the GUI 1201 will be described, but the same result can be obtained even if the user inputs the energy range using a slide bar or the like.
- the input range of the detection lower limit energy (E1) is 0 ⁇ E1 ⁇ Vin (Vin: incident energy of the primary electrons to the wafer), and the input range of the detection upper limit energy (E2) is E1 ⁇ E2 ⁇ Vin.
- E2 Vin in step S1306, the first set voltage VF1 of the energy filter is set to Vr ⁇ E1 (Vr: retarding voltage in the first embodiment), and the second set voltage VF2 of the energy filter is set to 0.
- the setting is made (S1307).
- an image by signal electrons in the energy range from E1 to E2 (hatched portion on the spectrum of the GUI 1201) is displayed on the scanning image display unit 1205 on the GUI 1201 at any time.
- the imaging method and the total number of images to be displayed are selected from the options by pressing a button (B) 1206 and a button (C) 1207 that can select information stored in the apparatus by a pull-down function.
- the user can change the energy range of the signal electrons to be detected in synchronization with the operation of changing the energy range of the detected signal electrons.
- An image to be formed can be observed on the GUI 1201. Thereby, the user can determine the optimum energy range in a short time.
- the process proceeds to “image acquisition process” in FIG. (Step S1109 of image acquisition / processing) Details of processing performed in “image acquisition / processing” will be described with reference to a flowchart (FIG. 14). This flowchart corresponds to steps S1107 to S1109 in FIG.
- step S1401 of necessity of energy filter when the energy filter is not used, a scanning image is acquired under the conditions determined in the selection of the optical conditions (FIG. 11, step S1101), and the “execution of length measurement” step S1409 is performed.
- step S1401 when the energy filter is used, first, the first set voltage VF1 is applied to the grid of the energy filter (S1402), and the scanned image 1 at that time is acquired (S1403). If the set value of VF2 is 0 in step S1404, the scanning image 1 is used to perform “measurement” in FIG. If the set value of VF2 is not 0 in step S1404, the scanned image 1 is stored in the image memory unit (S1405), the second set voltage VF2 is applied to the energy filter grid (S1406), and the scanned image 2 is acquired. (S1407).
- a difference image between the scanned image 1 and the scanned image 2 is formed (S1408), and the formed difference image is used after “execution of length measurement (step S1409)” in FIG.
- Length measurement is performed on the image obtained in step S1109 of “image acquisition / processing”, and the apparatus stores the result.
- the information stored here may be only the measured dimension, but an SEM image may be attached and stored.
- Recipe file saving step S1110) If the length is properly measured, the recipe file is saved (step S1110). If the length cannot be measured appropriately, the process returns to “Optical condition selection (step S1101)” and the same operation as above is repeated.
- “Automatic length measurement process” Next, the procedure of automatic length measurement using a recipe is shown using FIG.
- Step S1501 At the start of this step, first, the operator inputs basic information of the sample to be measured.
- the apparatus reads an appropriate recipe from an external server based on the input basic information, and starts automatic length measurement. Since the process after the input of the basic information is automatically executed based on the recipe by the length measuring SEM, the operator's hand is not bothered.
- Alignment is performed based on the alignment point information recorded in the recipe, and the positional relationship between the stage coordinates and the coordinates of the sample pattern is corrected.
- Transfer to measurement position Step S1503 Next, a location to be measured is searched based on the coordinates recorded as the measurement position search template and the low-magnification image of the SEM.
- the SEM system control unit 136 moves the stage 116 via the stage control unit 118 so that the measurement site on the sample is located in the irradiation region of the primary electron beam 138.
- the information on the necessity of using the energy filter recorded in the recipe is read, and if the energy filter needs to be used, the energy filter condition recorded in the recipe is set (S1505), and the image acquisition / processing step ( Move to S1506). If it is not necessary to use the energy filter, the process proceeds to the image acquisition / processing step (S1506) without setting the energy filter.
- Step S1506 of image acquisition / processing Image acquisition and difference processing are performed under the conditions recorded in the recipe.
- the obtained image is used in the length measurement step.
- Measurement step S1507 Length measurement is performed on the image obtained in the image acquisition / processing step.
- the result may be stored only in the measured dimension as in the above (execution of length measurement), but may be stored with an image attached. Further, the result can be confirmed by displaying it on the image display unit 135 (S1508).
- the stage 116 moves the sample to the next length measurement point, and performs the length measurement in the same procedure as described above.
- length measurement with the use of an energy filter can be realized.
- unnecessary energy filter operations can be omitted from the entire length measurement process. This is effective in improving the measurement throughput, and is particularly effective when a measurement SEM is provided in a mass production line for manufacturing semiconductor devices.
- energy filter control software is stored in the length measurement system control unit 137 by providing a memory or other external storage device.
- a dedicated chip for executing the steps shown in FIGS. 11 and 15 may be incorporated in the length measurement system control unit.
- a high-precision pattern dimension can be obtained by using a scanning electron microscope equipped with a deceleration electric field type energy filter having a conductive thin film.
- a length measurement method capable of measurement can be provided.
- FIG. 16 is a schematic configuration diagram of an essential part of the SEM type length measuring apparatus according to the present embodiment.
- the conductive thin film 304 is used. It is necessary to remove the attached contamination or replace the conductive thin film 304. When exchanging the conductive thin film with contamination, it is necessary to disassemble the SEM casing 103, which is a heavy burden on the operator.
- a method of automatically removing the contaminants adhering to the conductive thin film 304 of the energy filter 108 part and using the apparatus for the SEM type length measuring apparatus (FIG. 1) shown in the first embodiment without maintenance. provide.
- This embodiment can be realized only by adding the gas supply unit 1601 shown in FIG. 16 to the SEM type length measuring device (FIG. 1) shown in the first embodiment.
- a method for removing carbon as a contaminant attached to the conductive thin film will be described with reference to FIG.
- the contamination removal method described below is set in the length measurement system control unit 137 so that it is automatically performed when the usage time of the apparatus exceeds a certain time (for example, 1000 hours). The user can also manually select to remove contamination.
- valve (A) 141 and the valve (B) 142 connecting the SEM housing 103 and the sample chamber 117 and the vacuum exhaust unit 112 are closed.
- ozone gas is introduced from the gas supply unit 1601. Carbon, the main component of ozone and contamination, C + O 3 ⁇ CO + O 2 As shown in FIG.
- Embodiments 1 and 2 the same effects as those of Embodiments 1 and 2 can be obtained.
- a maintenance-free scanning electron microscope and a length measurement method using the same can be provided.
- FIG. 17 shows a schematic overall configuration diagram of a scanning electron microscope (SEM type length measuring device) according to the present embodiment.
- the detector (B) 1709 is provided below the energy filter 108, so that the tertiary electrons (B) 1704 generated by the signal electrons 139 colliding with the energy filter 108 are obtained. It is possible to detect.
- the above-mentioned tertiary electrons have been lost without being detected by the SEM type length measuring apparatus shown in FIG. 1, and secondary electrons are mainly generated among the signal electrons colliding with the filter. Therefore, in the SEM type length measuring device described in this embodiment, signal electrons that have passed through an energy filter to which a negative voltage is applied, for example, both reflected electrons and secondary electrons that have collided with the filter are simultaneously detected and imaged. Can do.
- the SEM type length measuring device is roughly divided into a SEM casing 103, a sample chamber 117, a SEM system control unit 136, a vacuum exhaust system unit 112, an image forming unit 129, and a length measurement system control unit 137.
- the SEM housing 103 includes an irradiation system that irradiates a sample with primary electrons 138 and a detection system.
- the SEM housing 103 includes an electron source 102, a condenser lens 104, a diaphragm 105, a reflector 128, a detector (A) 1705, and a detector (B 1709, E ⁇ B deflector (A) 1701, E ⁇ B deflector (B) 1702, energy filter 108, deflectors 109 and 110, booster electrode 125, objective lens 111, and trap plate electrode 123.
- the primary electrons 138 emitted from the electron source 102 are converged by the condenser lens 104, pass through the aperture 105 for controlling the current of the primary electrons 138 incident on the wafer 113, the holes of the reflector 128, and the energy filter 108. After passing through the shield pipe and being deflected by the deflectors 109 and 110, it is narrowed down by the objective lens 111 and enters the sample.
- an E ⁇ B deflector (A) 1701 and a detector (A) 1705 are installed on the reflector side of the energy filter 108, and the E ⁇ B is positioned on the objective lens 111 side of the energy filter 108.
- a B deflector (B) 1702 and a detector (B) 1709 are installed.
- Signal electrons 139 (secondary electrons, reflected electrons, Auger electrons) generated by irradiating the wafer 113 with the primary electrons 138 are negative voltage applied to the wafer holder 114 by the retarding power source 121, and trap plate electrodes. 123 and the booster electrode 125 are accelerated by the potential difference, converged by the objective lens 111, deflected by the deflectors 109 and 110, pass through the energy filter 108, and collide with the reflector 128.
- Electrons (tertiary electrons (A) 1703) generated from the reflector 128 due to the signal electrons 139 colliding with the reflector 128 are drawn into the detector (A) 1705 by the E ⁇ B deflector (A) 1701. .
- Electrons (tertiary electrons (B) 1704) generated from the energy filter 108 due to the signal electrons 139 colliding with the energy filter 108 are drawn into the detector (B) 1709 by the E ⁇ B deflector (B) 1702.
- the signal electrons 139 can be lifted to the reflector 128 side. Further, in order to prevent the potential of the booster electrode 125 from leaking onto the wafer (sample) 113 and to make the charging of the wafer 113 to be charged uniform, the trap plate electrode 123 is supplied with the same voltage as the retarding voltage. Applied from 122. (Electronic optical system control power supply) The current of the primary electrons 138 passing through the diaphragm 105 is controlled by controlling the current flowing through the coil constituting the condenser lens 104 by the electron optical system control power source 106.
- the primary electrons 138 are Without being deflected by the E ⁇ B deflector (A) 1701 and the E ⁇ B deflector (B) 1702, the tertiary electron (A) 1703 and the tertiary electron (B) 1704 are detected by the detector (A) 1705, the detector ( B) Can be pulled into 1709. Further, the primary electron 138 is scanned on the wafer 113 by controlling the current flowing through the coils constituting the deflectors 109 and 110 by the electron optical system control power source 106.
- the current flowing through the coils constituting the objective lens 111 is controlled by the electron optical system control power source 106. This control is performed by the electron gun power source 101, the booster power source 124, the trap plate power source. 122.
- the retarding power supply 121 changes, the primary electrons 138 are always focused on the wafer 113.
- the energy of the primary electrons 138 incident on the wafer 113 is determined by the difference between the acceleration voltage set by the electron gun power supply 101 and the voltage (retarding voltage) applied to the wafer holder 114 by the retarding power supply 121, and by changing the retarding voltage.
- the energy of the primary electrons 138 incident on the wafer 113 can be changed.
- Detector and image forming unit In order to form a scanning image by signal electrons detected by the detector (A) 1705, the deflectors 109 and 110 deflect the primary electrons 138 so that the primary electrons 138 scan on the wafer 113, and the detector ( A)
- the signal of the tertiary electrons (A) 1703 taken in by 1705 is amplified by the signal amplifier (A) 1706, and then converted into a digital signal by the AD converter (A) 1707, and then sent to the image processor (A) 1708.
- An image processing unit (A) 1708 forms a scanned image as a map of tertiary electron signals synchronized with the scanning signal.
- the formed scanned image is stored in the image memory unit 133.
- the deflectors 109 and 110 deflect the primary electrons 138 so that the primary electrons 138 scan on the wafer 113, and
- the signal of the tertiary electrons (B) 1704 captured by the detector (B) 1709 is amplified by the signal amplifier (B) 1710, and then converted into a digital signal by the AD converter unit (B) 1711, and the image processing unit (B ) Send a signal to 1712.
- the image processing unit (B) 1712 forms a scanned image as a map of tertiary electron signals synchronized with the scanning signal.
- the formed scanned image is stored in the image memory unit 133.
- the detector (A) 1705 and the detector (B) 1709 are floated to a positive high voltage.
- the difference / combination processing unit 1713 has a function of forming a difference image and a composite image of any two scanned images stored in the image memory unit 133. As described in the second embodiment, the difference / combination processing unit 1713 detects the detector (A) 1705 to the image processing unit (A) 1708 when the first set voltage VF1 ( ⁇ 0) is applied to the energy filter 108. When the second set voltage VF2 ( ⁇ 0) is applied, a difference image between the scan image A1 obtained in step S1 and the scan image A2 obtained in the image processing unit (A) 1708 can be created. This difference image is formed by signal electrons having energies from -VF1 to -VF2.
- the scanned image A obtained by the detector (A) 1705 to the image processing unit (A) 1708 and the detector (B) 1709 to the image processing unit (B) 1712 are obtained.
- a composite image of the scanned image B can be created. This is effective when no voltage is applied to the energy filter 108. This is because, even when no voltage is applied to the energy filter 108, a certain percentage of signal electrons collide with the conductor meshes (grids) 301, 302, 303 and the conductor thin film 304, so that the electrons that can reach the reflector 128 are This is because there are few compared with the case where the energy filter 108 is not mounted. As a result, when using the SEM type length measuring device with the energy filter 108 mounted but without applying a voltage, the S / N of the image is deteriorated, leading to deterioration of length measurement reproducibility and reduction of throughput.
- the energy filter is detected by detecting the tertiary electrons (B) 1704 generated by colliding with the energy filter 108 by the E ⁇ B deflector (B) 1702 and the detector (B) 1709. Even when the SEM type length measuring device is used without applying a voltage to 108, the S / N equivalent to that of the SEM type length measuring device without the energy filter 108 can be maintained.
- the user can confirm the scanned image stored in the image memory unit 133 and the difference image and the synthesized image formed by the difference / combination processing unit 1713 at any time via the SEM system control unit 136.
- this invention is not limited to the above-mentioned Example, Various modifications are included.
- the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.
- a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment.
- SYMBOLS 101 Electron gun power supply, 102 ... Electron source, 103 ... SEM housing, 104 ... Condenser lens, 105 ... Aperture, 106 ... Electron optical system control power supply, 107 ... ExB deflector, 108 ... Energy filter, 109 ... Deflection (A), 110 ... deflector (B), 111 ... objective lens, 112 ... evacuation system section, 113 ... wafer, 114 ... wafer holder, 115 ... insulating material, 116 ... stage, 117 ... sample chamber, 118 ... stage Control unit, 119 ... stage controller, 120 ... stage drive unit, 121 ... retarding power supply, 122 ...
- Conductor grid 2 303 ... Conductor grid 3, 304 ... Conductor thin film, 501 ... Secondary electrons, 502 ... Reflected electrons, 503 ... Auger electrons, 601 ... insulator, 602 ... conductor, 603 ... secondary electrons emitted from the insulator, 604 ... secondary electrons emitted from the conductor, 701 ... energy dependence of the number of secondary electrons emitted from the conductor, 702 ... energy dependence of the number of secondary electrons emitted from the insulator, 1001 ... Shield pipe, 1201 ... GUI, 1202 ... Button (A), 1203 ... Detection lower limit energy input section, 1204 ... Detection upper limit energy input section, 1205 ...
- Scanned image display section 1206 ... Button (B), 1207 ... Button (C), 1601 ... Gas supply unit, 1701 ... ExB deflector (A), 1702 ... ExB deflector (B), 1703 ... tertiary electron (A), 1704 ... tertiary electron (B), 1705 ... detector (A), 1706 ... signal amplifier (A), 1707 ... AD converter section (A), 1708 ... image forming section (A), 1709 ... detector (B), 1710 ... signal amplifier (B), 1711 ... AD converter section (B), 1712 ... image Forming unit (B), 1713... Difference / combination processing unit.
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Abstract
Description
本実施の形態では、従来の減速電界型エネルギーフィルタのグリッドに、厚さが100Å以上500Å以下(10nm以上50nm以下)の導体薄膜を張り付け、グリッドに負電圧を印加することで信号電子のエネルギー弁別を行うことを特徴とする。本実施の形態により、リターディング法を用いたSEMにおいて、従来の減速電界型エネルギーフィルタよりも優れたエネルギー分解能を得ることができる。導体薄膜を用いることで、従来の減速電界型エネルギーフィルタよりも良いエネルギー分解能を得ることができる理由について以下に述べる。
(SEM筐体および試料室)
SEM筐体103は、試料に対して一次電子138を照射する照射系と検出系からなり、電子源102、コンデンサレンズ104、絞り105、反射板128、検出器127、E×B偏向器107、エネルギーフィルタ108、偏向器109、110、ブースタ電極125、対物レンズ(収束レンズ)111、トラップ板電極123で構成される。
(SEMシステム制御部)
SEMシステム制御部136は、電子源102から出射する一次電子138の加速電圧を制御する電子銃電源101、コンデンサレンズ104、E×B偏向器107、偏向器109、110、対物レンズ(収束レンズ)111を制御する電子光学系制御電源106、ブースタ電極125の電圧を制御するブースタ電源124、トラップ板電極123の電圧を制御するトラップ板電源122、ウェハホルダ114の電圧を制御するリターディング電源121、エネルギーフィルタ108の導体薄膜に印加する電圧を制御するエネルギーフィルタ電源126、真空排気システム部112、画像形成部129、画像表示部135と接続されており、信号を送ることで上記の装置を制御する。
(電子光学系制御電源)
電子光学系制御電源106により、コンデンサレンズ104を構成するコイルに流れる電流を制御することで、絞り105を通過する一次電子138の電流を制御する。さらに、電子光学系制御電源106により、E×B偏向器107を構成するコイルの電流、および電極の電圧を制御することで、一次電子138はE×B偏向器107において偏向させること無く、三次電子140を検出器127に引き込むことができる。さらに、電子光学系制御電源106により、偏向器109、110を構成するコイルに流れる電流を制御することで、一次電子138をウェハ113上で走査する。
(検出器及び画像形成部)
走査像を形成するためには、一次電子138がウェハ113上を走査するように偏向器109、110で一次電子138を偏向し、検出器127で取り込まれた三次電子140の信号を、信号増幅器130で増幅した後、ADコンバータ部131でデジタル信号に変換し、画像処理部132へ信号を送る。画像処理部132では走査信号と同期した3次電子信号のマップとして走査像を形成する。形成された走査像は画像メモリ部133に保存される。
(測長システム制御部)
本実施例に示したSEM式測長装置では、常に最適な測長が行なわれるよう、測長システム制御部137が、測長するウェハ113のパターンおよびプロセスの情報、観察条件、測長領域、測長に用いるアルゴリズム等を記憶し、かつSEMシステム制御部136と接続されており、SEMシステム制御部136を介して装置全体を管理及び制御する。
(導体薄膜を用いた減速電界型エネルギーフィルタの構造)
次に、導体薄膜を用いた減速電界型エネルギーフィルタ108の構造について図10、図18を用いて詳細に説明する。図10は本実施例に係る走査電子顕微鏡で用いる導体薄膜を用いた減速電界型エネルギーフィルタの概略構成断面図であり、図18はその斜視図である。
また、Al,Au,Cu,W,C,ステンレスなどの導体に代わる導体として、グラフェンを用いることも可能である。この場合、導体薄膜304の厚さは3Å以上30Å以下(0.3nm以上3nm以下)となり、導体薄膜304の厚さを薄くすることで、透過すべきエネルギーを持った二次電子が薄膜に散乱されて検出されにくくなる現象を低減することが可能となる。さらに、薄膜の透過率が向上することで、SEM画像のSN比が向上する効果も得られる。
また、導体として、グラフェンを用いる場合は、Cu,Niなどの金属基板上に作製したグラフェンをポリメチルメタクリレート(PMMA)などのレジストに転写した後、グラフェンを転写したPMMAを導体グリッド302に貼り付け、レジスト剥離剤によりPMMAのみ除去することで導体薄膜304を得ることができる。
「レシピ作成の工程」
図11を用いてレシピの作成手順を示す。
(試料の基本情報の入力ステップS1100)
試料の測長を行おうとするオペレータは、まず、測長する試料の情報を入力する。装置オペレータは、例えば、画像表示部135に示される入力画面を見ながら、情報を入力する。ここで、試料が例えば半導体ウェハの場合は、ウェハの品種、製造工程の名称が前述の情報に相当し、オペレータが入力したこれらの情報は複数存在するレシピを分類し管理するために用いられる。
(光学条件の選定ステップS1101)
測長を行う際に用いる光学条件を選定する。光学条件のパラメータは、試料に入射するプローブ電流、撮像時の視野、入射エネルギー、試料上に形成される電界強度であり、SEM画像の取得で、「フレーム加算等の複数回の画像取得でSEMの画質が劣化」「測長時の弊害となる明るさムラ等の異常コントラスト」が発生しないよう決められる。この作業は、オペレータが光学条件を任意に選んでも良いし、装置出荷時に製造元が推奨条件を決め、それを用いても良い。
(アライメント用のテンプレート登録ステップS1102)
半導体ウェハ等のパターンが形成された試料では、試料を動かすステージ116の座標と試料上に形成されたパターンの座標との位置関係を正確に計測する必要がある。本実施例では、この位置関係を計測する工程をアライメント工程とする。ここでは、光学画像上及びSEM画像上で認識可能な試料上のパターンの画像を、テンプレートとして外部サーバに登録する。測長システム制御部137に外部記憶装置を接続してテンプレートを登録しても良い。
(アライメント位置の登録ステップS1103)
ステージ116の座標と試料上に形成されたパターンの座標との位置関係を正確に補正するためには最低2つの場所でアライメント工程を行う必要がある。
ここではアライメントを行う場所の登録を行う。登録は、例えば、画像表示部135に表示されるSEM画像上での適当な位置を、装置オペレータが選択することにより実行される。
(アライメントの実行ステップS1104)
ここでは、テンプレートと上記で登録した場所で撮像した光学画像及びSEM画像の画像比較からステージ116の座標と試料のパターンの座標の位置関係を計測する。
(測定位置検索用のテンプレート登録ステップS1105)
次に、測長するパターンの近傍に測定する場所を探すための位置検索用テンプレートを登録する。測定位置検索用のテンプレートは、アライメント用のテンプレートと同様、外部サーバに記憶されるが、測長システム制御部137に外部記憶装置を接続してテンプレートを登録しても良い。
(測長点のテンプレートを登録S1106)
前記の測定位置検索用のテンプレートを登録後、測長する箇所のテンプレートを外部サーバに登録する。ここで、テンプレートとして登録される画像はパターンの寸法を測定するときの、SEMの撮像倍率とほぼ同じ倍率の画像を登録する。登録時に実行する作業は、アライメント用のテンプレート及び測定位置検索用のテンプレートの登録作業と同じである。
(エネルギーフィルタ要否の判定ステップS1107)
測長する試料にエネルギーフィルタの使用が必要な場合は、以下の手順でエネルギーフィルタの設定を行う。エネルギーフィルタの使用が不要の場合、図11に示されるステップS1109の画像取得処理(測長の実施)に飛ぶ。エネルギーフィルタ使用の要不要は、オペレータが判断し、自由に設定することも可能だが、先に記述した試料の基本情報から、装置が自動的にエネルギーフィルタ使用の要不要を判断しても良い。
(エネルギーフィルタの設定ステップS1108)
エネルギーフィルタの使用条件の設定方法について図12に示すGUI1201と、図13に示すフローチャートを用いて説明する。エネルギーフィルタを使用する場合、図12に示すGUI1201が新たに画像表示部135に表示される(S1301)。
(画像取得・処理のステップS1109)
「画像取得・処理」で行う処理の詳細についてフローチャート(図14)を用いて説明する。本フローチャートは、図11のステップS1107~ステップS1109に対応する。
(レシピファイルの保存ステップS1110)
適切に測長が行なわれている場合は、レシピのファイルの保存を行う(ステップS1110)。適切に測長ができない場合は、「光学条件の選定(ステップS1101)」まで戻り、上記と同じ作業を繰り返す。
「自動測長の工程」
次に図15を用いてレシピを用いた自動測長の手順を示す。
(レシピファイルの読み出しステップS1501)
本ステップの開始に当たって、まず、オペレータは測長する試料の基本情報を入力する。装置は入力された基本情報を元に、外部サーバより適切なレシピを読み出し、自動測長を開始する。基本情報の入力以降の処理は、測長SEMがレシピを元に自動的に実行するため、オペレータの手を煩わせることはない。
(アライメントステップS1502)
レシピに記録されているアライメント点の情報を元にアライメントを行い、ステージ座標と試料のパターンの座標との位置関係を補正する。
(測定位置への移動ステップステップS1503)
次に、測定位置検索用テンプレートとして記録される座標とSEMの低倍画像を元に測長する場所を探す。測長箇所の位置座標が判明すると、SEMシステム制御部136はステージ制御部118を介して、試料上の測長箇所が一次電子線138の照射領域に位置するようにステージ116を移動する。
(エネルギーフィルタ要否の判定ステップS1504)~(エネルギーフィルタの設定ステップS1505))
レシピに記録されているエネルギーフィルタ使用の要否の情報を読み出し、エネルギーフィルタの使用が必要な場合は、レシピに記録されたエネルギーフィルタの条件に設定し(S1505)、画像取得・処理のステップ(S1506)に移動する。エネルギーフィルタの使用が不要の場合は、エネルギーフィルタの設定は行わずに画像取得・処理のステップ(S1506)に移動する。
(画像取得・処理のステップS1506)
レシピに記録された条件で、画像の取得および差分処理を行う。得られた画像は測長のステップで使用する。
(測長のステップS1507)
画像取得・処理のステップで得られた画像に対して測長を実施する。結果は前記の(測長の実施)と同様、測長した寸法のみ記憶しても良いが、画像を添付して保存しても良い。また、結果は画像表示部135に表示することにより確認することができる(S1508)。
C+O3 →CO+O2
の通りに反応し、導体薄膜304表面より離脱する。
(SEM筐体および試料室)
SEM筐体103は、試料に対して一次電子138を照射する照射系と検出系からなり、電子源102、コンデンサレンズ104、絞り105、反射板128、検出器(A)1705、検出器(B)1709、E×B偏向器(A)1701、E×B偏向器(B)1702、エネルギーフィルタ108、偏向器109、110、ブースタ電極125、対物レンズ111、トラップ板電極123で構成される。
(電子光学系制御電源)
電子光学系制御電源106により、コンデンサレンズ104を構成するコイルに流れる電流を制御することで、絞り105を通過する一次電子138の電流を制御する。さらに、電子光学系制御電源106により、E×B偏向器(A)1701、E×B偏向器(B)1702を構成するコイルの電流、および電極の電圧を制御する事で、一次電子138はE×B偏向器(A)1701、E×B偏向器(B)1702において偏向されること無く、三次電子(A)1703、三次電子(B)1704を検出器(A)1705、検出器(B)1709に引き込むことができる。さらに、電子光学系制御電源106により、偏向器109、110を構成するコイルに流れる電流を制御する事で、一次電子138をウェハ113上で走査する。
(検出器及び画像形成部)
検出器(A)1705で検出される信号電子による走査像を形成するためには、一次電子138がウェハ113上を走査するように偏向器109、110で一次電子138を偏向し、検出器(A)1705で取り込まれた三次電子(A)1703の信号を、信号増幅器(A)1706で増幅した後、ADコンバータ部(A)1707でデジタル信号に変換し、画像処理部(A)1708へ信号を送る。画像処理部(A)1708では走査信号と同期した3次電子信号のマップとして走査像を形成する。形成された走査像は画像メモリ部133に保存される。
201…導体グリッド、202…等電位線、
301…導体グリッド1、302…導体グリッド2、303…導体グリッド3、304…導体薄膜、
501…二次電子、502…反射電子、503…オージェ電子、
601…絶縁体、602…導体、603…絶縁体から放出された二次電子、604…導体から放出された二次電子、
701…導体から放出された二次電子数のエネルギー依存性、702…絶縁体から放出された二次電子数のエネルギー依存性、
1001…シールドパイプ、
1201…GUI、1202…ボタン(A)、1203…検出下限エネルギー入力部、1204…検出上限エネルギー入力部、1205…走査像表示部、1206…ボタン(B)、1207…ボタン(C)、
1601…ガス供給部、
1701…E×B偏向器(A)、1702…E×B偏向器(B)、1703…三次電子(A)、1704…三次電子(B)、1705…検出器(A)、1706…信号増幅器(A)、1707…ADコンバータ部(A)、1708…画像形成部(A)、1709…検出器(B)、1710…信号増幅器(B)、1711…ADコンバータ部(B)、1712…画像形成部(B)、1713…差分・合成処理部。
Claims (16)
- 電子源と、前記電子源から放出される一次電子線を偏向するための偏向器と、前記偏向器によって偏向された前記一次電子線を収束するための収束レンズと、前記収束レンズによって収束された前記一次電子線の試料への照射に起因して放出される信号電子を検出する電子検出器と、前記電子検出器よりも前記試料側に配置され前記信号電子のエネルギーを弁別する減速電界型エネルギーフィルタと、を備えた走査電子顕微鏡において、
前記減速電界型エネルギーフィルタは、前記信号電子のエネルギー弁別用の導体薄膜を有することを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
更に、前記試料に照射される前記一次電子線を減速するための減速手段を備えることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記導体薄膜は、少なくともC,グラフェン,Al,Au,Cu,Wのいずれかを有し、厚みが0.3nm以上50nm以下の範囲であることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記導体薄膜は絶縁体と導体との多層膜であり、厚みが0.3nm以上50nm以下の範囲であることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記導体薄膜は穴を多数有しており、
多数の前記穴は前記試料から放出された前記信号電子が通過するものであることを特徴とする走査電子顕微鏡。 - 請求項5に記載の走査電子顕微鏡において、
多数の前記穴は10μm以下の直径を有することを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記導体薄膜は開口部を少なくとも一つ有しており、
前記開口部は前記一次電子線が通過するものであることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記開口部は1±0.5mmの直径を有することを特徴とする走査電子顕微鏡。 - 請求項7に記載の走査電子顕微鏡において、
前記開口部の内部には前記一次電子線が通過するシールドパイプが配置され、
前記シールドパイプは接地されていることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
更に、前記導体薄膜に印加する設定電圧を入力するためのユーザインターフェースを備えたことを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記導体薄膜に第一の設定電圧を印加した状態で得られる第一の走査像と、
前記導体薄膜に第二の設定電圧を印加した状態で得られる第二の走査像との差分画像を形成する画像処理回路を備えたことを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
更に、前記導体薄膜よりも前記試料側に第2の電子検出器を備え、
前記第2の電子検出器は、前記試料より放出された前記信号電子が前記導体薄膜へ衝突することに起因して放出される電子を検出するものであることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
更に、前記導体薄膜の表面に付着する汚染物を除去するためのオゾンもしくは活性酸素のガス供給システムを備え、
前記ガス供給システムは前記電子検出器と前記試料との間に配置されることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記減速電界型エネルギーフィルタは、前記導体薄膜を挟んで設けられた第1と第2の導体グリッドとを有し、
前記第1と第2の導体グリッドは接地されていることを特徴とする走査電子顕微鏡。 - 請求項1に記載の走査電子顕微鏡において、
前記導体薄膜は導体グリッドの試料側端部に配置されていることを特徴とする走査電子顕微鏡。 - 請求項11に記載の走査電子顕微鏡を用いた測長方法であって、
前記導体薄膜に第一の電圧を印加し、前記信号電子が前記第一の電圧でエネルギー弁別された電子に基づいて第一の画像を得る工程と、
前記導体薄膜に第二の電圧を印加し、前記信号電子が前記第二の電圧でエネルギー弁別された電子に基づいて第二の画像を得る工程と、
前記第一の画像と前記第二の画像の差分画像を形成する工程と、
前記差分画像より前記試料のパターン寸法を計測する工程とを含み、
前記差分画像が前記試料のオージェ電子によって形成されることを特徴とする測長方法。
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JP5771628B2 (ja) | 2015-09-02 |
JPWO2012081428A1 (ja) | 2014-05-22 |
US20130292568A1 (en) | 2013-11-07 |
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