JP6237048B2 - Pattern measuring method and apparatus - Google Patents

Description

  The present invention relates to a pattern measurement method for observing and measuring a sample by irradiating a sample such as a pattern with an electron beam, and a pattern measurement apparatus for executing the method.

  As semiconductor devices such as large-scale integrated circuits (LSIs) are highly integrated, circuit patterns of semiconductor devices tend to be miniaturized and complicated. In order to form fine circuit patterns, photomasks and reticles (hereinafter collectively referred to as masks) as high-precision original image patterns are required, and pattern position accuracy and dimensional accuracy are becoming increasingly severe. ing.

  At present, an exposure method of transferring a pattern onto a wafer by an optical projection exposure apparatus using an ArF excimer laser is mainly used. However, in order to realize finer pattern transfer, a wavelength of 13 is used as exposure light. 2. Description of the Related Art Lithography (hereinafter referred to as EUV lithography) technology using extreme ultra-violet (EUV) light in the vicinity of 5 nm is drawing attention. This EUV lithography needs to be performed in a vacuum due to the characteristics of the light source wavelength. In the EUV wavelength region, the refractive index of most substances is slightly smaller than “1”, and the light absorption is very high. For this reason, in EUV lithography, the refractive optical system conventionally used cannot be used, but becomes a reflection optical system. Therefore, the EUV mask is not a conventional transmission type but a reflection type.

  As described above, since the EUV mask is a reflection type, it is important to measure and manage the side wall angle of the pattern. In addition, as a defect peculiar to the EUV mask, there is a multilayer film defect caused by pits, bumps, foreign matters, etc. on the substrate. If these foreign substances are present, the period of the multilayer film is disturbed to cause a phase difference from the normal part, resulting in a so-called phase defect. Therefore, phase defect inspection is important. The phase defect affects pattern transfer onto the wafer, and three-dimensional information such as the width and height of the defect is necessary to accurately grasp the influence. Thus, in the EUV mask, in addition to the conventional two-dimensional measurement, the need for three-dimensional measurement is increasing.

  As a pattern dimension measuring method, measurement using a scanning electron microscope (hereinafter referred to as SEM) is performed. In SEM, incident electrons are irradiated while scanning within the electron beam scanning range, secondary electrons emitted from the sample are acquired through a scintillator, and the amount of acquired electrons is converted into luminance and displayed on a display device. doing. The amount of secondary electrons emitted from the sample depends on the unevenness of the pattern surface, and a large amount of secondary electrons are emitted from an inclined portion such as a pattern edge. Therefore, an image having a bright brightness at the pattern edge is obtained, the image is converted into a signal profile, and the pattern dimension is measured by a threshold method or a differential gradient method.

  Examples of the pattern three-dimensional measurement apparatus include an atomic force microscope (hereinafter referred to as AFM), scatterometry, a cross-sectional observation SEM, and a pattern measurement SEM. As a three-dimensional measurement method in the SEM for pattern measurement, a method of observing by tilting the electron beam, or by arranging a plurality of secondary electron detectors and using secondary electron signals captured by each detector, the pattern tertiary There is a method of performing original measurement (for example, see Patent Document 1).

JP 2013-2872 A

  However, in the SEM, an electron beam is irradiated when observing and measuring a sample, and a phenomenon occurs in which the sample surface is charged by the electron beam. That is, the irradiation surface is positively or negatively charged depending on the difference between the charge of charged particles incident on the sample and the charge of discharged charged particles. With the charged potential of the sample surface, the emitted secondary electrons are accelerated or pulled back to the sample, and the secondary electron emission efficiency changes. As a result, there is a problem that the amount of secondary electrons detected becomes unstable.

  One of the phenomena caused by the charging of the sample is a drift phenomenon. The drift phenomenon is a phenomenon in which a pattern image moves during observation of a sample (during electron beam irradiation). This is considered to occur when the trajectory of the electron beam is bent by the electric field distribution formed on the surface of the sample or in the space on the sample, and it is desirable to eliminate it as much as possible during pattern observation and measurement. When the sample is irradiated with the electron beam trajectory bent, a pattern image is generated at a position deviated from the design coordinates of the pattern, which affects the position accuracy of pattern measurement and cannot be measured accurately. There is a problem.

  Such an electric field distribution also affects the trajectory of secondary electrons emitted from the sample. In Patent Document 1, a method related to three-dimensional measurement of a pattern is described. This method is a method of arranging a plurality of secondary electron detectors around the electron beam axis and adding or subtracting the acquired signals to measure, but the trajectory of the secondary electrons is bent by the electric field distribution, If the secondary electrons are biased to the detector on one side, the subtracted signal shape will be affected, and accurate measurement and observation will not be possible. Therefore, it is not suitable as a measurement method using a mask that is likely to be charged.

  In the EUV mask, when a circuit pattern is transferred onto a semiconductor substrate, if chips are arranged at a high density in order to improve productivity, there are areas where multiple exposure is performed multiple times between adjacent chips. In the multiple exposure area, there is a problem that the transfer size changes, and in order to solve this, a groove (light-shielding frame) is formed in the outer periphery of the substrate from the absorption layer to the multilayer reflection layer, and the wavelength of the exposure light source An EUV mask having a high light shielding property has been proposed.

  However, since the above EUV mask with a light shielding frame has an electrically insulated structure inside and outside the light shielding frame, charging is likely to occur during measurement by SEM using an electron beam, and the above-described adverse effects are caused. For this reason, a method for measuring with high accuracy is desired.

  The present invention has been made in view of the above circumstances. In particular, even in a sample such as a mask that is easily charged by electron beam irradiation, the trajectory of secondary electrons is deflected by the effect of sample charging caused by electron beam irradiation. It is an object of the present invention to provide a method and an apparatus method capable of preventing a phenomenon and performing highly accurate pattern measurement.

  A first aspect of the present invention for solving the above problems includes a step of irradiating a pattern on a mask with an electron beam, a step of detecting secondary electrons emitted from the pattern irradiated with the electron beam, A step of controlling the trajectory of the secondary electrons by the electrode, a step of generating image data based on the detection signal detected in the step of detecting, a step of generating a signal profile of a pattern from the image data, and the signal profile And a step of measuring the side wall angle and the three-dimensional shape of the pattern based on the above.

In the above-described detecting step, a technique of detecting secondary electrons by a plurality of electron detectors provided symmetrically with respect to the axis of the electron beam can be applied.
Further, in the above-described controlling step, the difference between the luminance values of the images acquired by the left and right electron detectors provided symmetrically with respect to the electron beam axis, or the current measured by the left and right electron detectors A method of controlling the trajectory of the secondary electrons by changing the voltage value applied to the electrode based on one of the value differences can be applied. Preferably, a plurality of electrodes for controlling the trajectories of secondary electrons are provided between the electron detector and the mask.

In addition, a second aspect of the present invention for solving the above-described problems includes a means for irradiating the pattern on the mask with an electron beam, and a means for detecting secondary electrons emitted from the pattern irradiated with the electron beam. A means for controlling the trajectory of the secondary electrons by the electrode, a means for generating image data based on the detection signal detected by the means for detecting, a means for generating a signal profile of the pattern from the image data, and a signal profile A pattern measuring device on a mask comprising: means for measuring a side wall angle and a three-dimensional shape of a pattern based on the mask. In the control means described above, the difference between the luminance values of the images acquired by the left and right electron detectors provided symmetrically with respect to the axis of the electron beam, or the current value measured by the left and right electron detectors. A method of controlling the trajectory of the secondary electrons by changing the voltage value applied to the electrode based on one of the differences can be applied.

  According to the present invention, the phenomenon of secondary electron trajectory deflection due to the influence of mask (sample) charging caused by electron beam irradiation can be prevented, so the side wall angle measurement and three-dimensional shape measurement of the pattern on the mask can be performed. It is possible to carry out with high accuracy.

Schematic configuration diagram of a scanning electron microscope apparatus which is an example of a pattern measuring apparatus of the present invention The figure which shows the relationship between the luminance value difference of the image between electron detectors, and the applied voltage to an electrode The flowchart which shows the procedure of the pattern measurement method which concerns on 1st Embodiment. The figure explaining the trajectory control of the secondary electron by the pattern measurement method concerning a 1st embodiment The figure which shows the structural example which provided the current measurement means in the electron detector The figure which shows the relationship between the electric current value difference between electron detectors, and the applied voltage to an electrode The flowchart which shows the procedure of the pattern measurement method which concerns on 2nd Embodiment. The figure which shows the structural example of the scanning electron microscope apparatus which provided the some electrode The figure which shows the reflective mask of an Example The figure which shows the result at the time of applying the measuring method of a prior art to the reflective mask of FIG. The figure which shows the relationship between the luminance value difference of the image between the electron detectors in this Example, and the applied voltage to an electrode. The figure which shows the result at the time of applying the pattern measuring method of this invention to the reflective mask of FIG.

  Hereinafter, a pattern measurement method and apparatus according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating the configuration of a scanning electron microscope that is an example of an apparatus that executes the pattern measurement method of the present invention. The scanning electron microscope shown in FIG. 1 is for observing and measuring a sample by irradiating the sample with an electron beam, and includes an electron column 10, a control calculation unit 20, a display 21, an electrode control unit 22, and a signal processing unit. 23, a data calculation unit 24, and an output unit 25. The electron column 10 includes an electron gun 11, an extraction electrode 13, a condenser lens 14, a deflector 15, an objective lens 16, and an electron detector 18. A stage 26 on which a pattern 17 that is a sample is placed is arranged below the electron column 10 (in the direction of electron beam irradiation).

  Inside the electron column 10, the electron gun 11 generates electrons. Electrons generated from the electron gun 11 are extracted by the extraction electrode 13 and focused by the condenser lens 14 to become an electron beam (primary electron beam) 12. After the irradiation direction is determined by the deflector 15, the electron beam 12 is irradiated on the pattern 17 placed on the stage 26 through focusing by the objective lens 16. The deflector 15 deflects the electron beam 12 so that the electron beam 12 is scanned and irradiated on the pattern 17, and outputs a signal corresponding to the deflection to the control calculation unit 20.

  An electron detector 18 for detecting secondary electrons emitted from the pattern 17 when irradiated with the electron beam 12 is provided in the vicinity of the irradiation port of the electron beam 12 facing the electron gun 11 of the electron column 10. Yes. A plurality of electron detectors 18 are provided at positions symmetrical with respect to the axis of the electron beam 12 (irradiation center axis). As the electron detector of the electron detector 18, for example, a scintillator and a photomultiplier tube can be used. By applying a positive voltage to the scintillator, secondary electrons emitted from the pattern 17 are accelerated simultaneously with the electron detector 18 and collide with the scintillator. The light emitted from the scintillator is amplified by a photomultiplier tube and detected as a signal from the electron detector 18. The detected signal is output to the control calculation unit 20.

  The control calculation unit 20 inputs a deflection signal from the deflector 15 and a detection signal from the electron detector 18. Then, the control calculation unit 20 synchronizes the deflection position of the electron beam 12 obtained from the deflection signal and the amount of secondary electrons obtained from the detection signal, and generates image data (SEM image). Display as an electronic image.

  Further, the image data (SEM image) generated by the control calculation unit 20 is signal-processed by the signal processing unit 23, and the data calculation unit 24 performs each processing according to the side wall angle measurement or the three-dimensional shape measurement of the pattern 17, etc. An arithmetic process (addition, subtraction, differentiation, integration, etc.) of the signal acquired by the electron detector 18 is performed. These calculations are performed by a conventionally known measurement method. The measurement result obtained by the calculation is output via the output unit 25.

  The feature of the above-described pattern measurement apparatus (scanning electron microscope) of the present invention is that secondary electrons emitted from the pattern 17 irradiated with the electron beam 12 between the electron detector 18 and the pattern 17 as the sample. An electrode 19 for controlling the trajectory is provided. The electrode 19 is optimally controlled by the electrode controller 22.

Hereinafter, the pattern measurement method realized by the pattern measurement apparatus of the present invention having the above-described configuration will be described mainly with respect to the method for controlling the electrode 19 by the electrode control unit 22.
For ease of explanation, the plurality of electron detectors 18 provided at positions symmetrical with respect to the axis of the electron beam 12 are referred to as “left-side electron detector 18” or “right-side electron detector 12”. This is appropriately expressed as “electronic detector 18” or the like. The plurality of electrodes 19 are also appropriately expressed as “the left electrode 19 or the“ right electrode 19 ”or the like as in the electron detector 18.

(First embodiment)
In the pattern measurement method according to the first embodiment of the present invention, the electrode control unit 22 controls the electrode 19 according to the luminance of the image based on the amount of secondary electrons detected by the electron detector 18. Do. Specifically, the electrode control unit 22 controls the trajectory of secondary electrons emitted from the pattern 17 by changing the voltage value applied to the electrode 19.

  For example, when a force that bends secondary electrons to the left with respect to the axis of the primary electron beam (electron beam 12) due to the electric field distribution generated by charging the sample (pattern 17), the primary electron beam (electron) Many secondary electrons are incident on the left detector (electron detector 18) installed on the left side with respect to the axis of the line 12). Therefore, the brightness of the image of the left detector is displayed brightly. On the other hand, the brightness of the image of the right detector (electron detector 18) installed on the right side with respect to the axis of the primary electron beam (electron beam 12) becomes dark. Therefore, the luminance of the image is digitized, and when the difference between the luminance values of the left and right images exceeds a certain threshold value, a predetermined voltage is applied to the left and right electrodes (electrode 19).

  FIG. 2 is a graph showing the relationship between the luminance value difference of the image between the left and right electron detectors 18 and the voltage value applied to the electrode 19. As described above, the voltage applied to the electrode 19 is controlled to be higher as the luminance value difference between the left and right images is larger. The magnitude of the brightness value difference is proportional to the amount of deflection of the secondary electron orbit, and the larger the brightness value difference, the more the secondary electrons are biased toward the electron detector 18 on one side. Even if the pattern 17 is not charged and the trajectory of the secondary electrons is not deflected, a slight luminance value difference may occur between the images of the left and right electron detectors 18. Since a slight characteristic difference between the pattern 17 to be observed and the photomultiplier tube provided in the electron detector 18 may occur, it is preferable to set a threshold value for the luminance value difference in advance. In this way, the luminance value difference is monitored and feedback control is performed on the electrode 19 to change the trajectory of the secondary electrons, and the pattern 17 is not affected by the electric field distribution formed by the charging of the pattern 17. The signal it has can be acquired.

  Next, the pattern measurement method according to the first embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing the procedure of the pattern measurement method according to the first embodiment of the present invention.

  First, the electron beam 12 is irradiated to the pattern 17 (step S100). When the electron beam 12 is applied to the pattern 17, the left and right electron detectors 18 respectively detect secondary electrons emitted from the surface of the pattern 17, and based on the detected amount of secondary electrons. The image and its luminance value are calculated respectively (step S101). Once the luminance value is calculated, the electrode control unit 22 then calculates a luminance value difference between the luminance value calculated by the left electron detector 18 and the luminance value calculated by the right electron detector 18. Calculate (step S102). Then, the electrode control unit 22 compares the calculated luminance value difference with a predetermined threshold value of the luminance value difference (step S103).

  As a result of the comparison in step S103, when the calculated luminance value difference is larger than the threshold value (step S103: No), the electrode control unit 22 applies a predetermined voltage to the left and right electrodes 19 (step S104). Specifically, a negative voltage is applied to the electrode 19 provided on the same side as the electron detector 18 having the larger luminance value, and the electrode 19 provided on the same side as the electron detector having the smaller luminance value is applied. Apply a positive voltage. Note that the negative voltage and the positive voltage to be applied may have the same or different absolute values. As a result, as shown in FIG. 4, the trajectory of the secondary electrons emitted from the pattern 17 and deflected in one direction (right side in the example of FIG. 4) under the influence of the electric field distribution formed by the electrode 19 And secondary electrons can be guided to the electron detector 18 in a balanced manner.

  The processes from step S101 to S104 are repeated until the luminance value difference becomes equal to or smaller than the threshold value. That is, the luminance values of the images acquired by the left and right electron detectors 18 are calculated in real time at regular intervals or at predetermined intervals (steps S101 and S102), and the luminance between the left and right electron detectors 18 and 18 is calculated. The voltage value applied to the electrode 19 is increased stepwise (the negative voltage increases the absolute value) until the value difference becomes equal to or less than the threshold value (steps S103 and S104). Then, as a result of the comparison in step S103, when the luminance value difference is equal to or smaller than the threshold value (step S103: Yes), the process is terminated.

(Second Embodiment)
In the pattern measurement method according to the second embodiment of the present invention, the electrode control unit 22 controls the electrode 19 according to the difference in the current value detected by the electron detector 18. Specifically, the electrode control unit 22 controls the trajectory of secondary electrons emitted from the pattern 17 by changing the voltage value applied to the electrode 19. The current value can be detected, for example, by monitoring the current value of the current measuring means installed in the electronic detector 18. FIG. 5 is a diagram showing an example in which the current measuring means 66 is installed in the electron detector 18.

  For example, when a force that bends secondary electrons to the left with respect to the axis of the primary electron beam (electron beam 12) due to the electric field distribution generated by charging the sample (pattern 17), the primary electron beam (electron) Many secondary electrons are incident on the left detector (electron detector 18) installed on the left side with respect to the axis of the line 12). Therefore, the current value of the ammeter (current measuring means 66) installed in the left detector (electronic detector 18) increases. On the other hand, the current value of the ammeter (current measuring means 66) installed in the right detector (electron detector 18) installed on the right side with respect to the axis of the primary electron beam (electron beam 12) becomes small. Therefore, when the current value difference of the ammeter (current measuring means 66) of the left and right detectors exceeds a certain threshold value, a voltage is applied to the left and right electrodes (electrode 19).

  FIG. 6 is a graph showing the relationship between the current value difference of the current measuring means 66 installed between the left and right electron detectors 18 and the voltage value applied to the electrode 19. As described above, the voltage applied to the electrode 19 is controlled to be higher as the current value difference is larger. The magnitude of the current value difference is proportional to the amount of deflection of the secondary electron orbit, and the larger the current value difference, the more the secondary electrons are biased toward the electron detector 18 on one side. The current value of the current measuring means 66 of each electron detector 18 is monitored, and the voltage value applied to the electrode 19 is controlled so that the current value difference becomes small. As described above, the current value is monitored and feedback control is performed on the electrode 19 to change the trajectory of the secondary electrons, and the pattern 17 originally has no influence of the electric field distribution formed by the charging of the pattern 17. A signal can be acquired.

  Next, a pattern measurement method according to the second embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing the procedure of the pattern measurement method according to the second embodiment of the present invention.

  First, the electron beam 12 is irradiated to the pattern 17 (step S200). When the pattern 17 is irradiated with the electron beam 12, the left and right electron detectors 18 respectively detect secondary electrons emitted from the surface of the pattern 17 (step S201), and the detected secondary electrons. The left and right current measuring means 66 respectively measure current values (step S202). When the current value is measured, the electrode control unit 22 is then installed in the current value measured by the left current measuring means 66 installed in the left electron detector 18 and in the right electron detector 18. A current value difference from the current value measured by the current measuring means 66 on the right side is calculated (step S203). Then, the electrode control unit 22 compares the calculated current value difference with a predetermined current value difference threshold value (step S204).

  As a result of the comparison in step S204, when the calculated current value difference is larger than the threshold (step S204: No), the electrode control unit 22 applies a predetermined voltage to the left and right electrodes 19 (step S205). Specifically, a negative voltage is applied to the electrode 19 provided on the same side as the electron detector 18 having the larger current value, and the electrode 19 provided on the same side as the electron detector 18 having the smaller current value. Apply a positive voltage to Note that the negative voltage and the positive voltage to be applied may have the same or different absolute values. Thus, similarly to the first embodiment described above, the trajectory of the secondary electrons emitted from the pattern 17 and deflected in one direction under the influence of the electric field distribution formed by the electrode 19 can be controlled. It becomes possible.

  The processes from step S201 to S205 are repeatedly performed until the current value difference becomes equal to or smaller than the threshold value. That is, the current values of the current measuring means 66 installed in the left and right electron detectors 18 are monitored in real time constantly or at predetermined intervals (steps S201 to S203), and the left current measuring means 66 and the right current measuring means 66 are monitored. The voltage value applied to the electrode 19 is increased stepwise (the negative voltage increases the absolute value) until the current value difference between and becomes lower than the threshold value (steps S204 and S205). Then, as a result of the comparison in step S204, when the current value difference becomes equal to or smaller than the threshold value (step S204: Yes), the process is terminated.

  As shown in FIG. 8, the electrodes 19 for controlling the trajectories of secondary electrons emitted from the pattern 17 are not a pair at positions symmetrical with respect to the axis of the electron beam 12, but the axis of the electron beam 12. A plurality may be installed in the direction. By arranging a plurality of electrodes 19 and selectively selecting the electrodes that control the trajectory of the secondary electrons, it is possible to control the influence of the electric field distribution formed by charging the pattern 17 with higher accuracy. Become.

  Specific examples of the pattern measurement method of the present invention will be described below. In addition, in order to clarify the effect by a present Example, the measurement by the measuring method of a prior art was also performed and both measurement results were compared.

  A reflective mask blank shown in FIG. 9A was prepared. This mask blank is a 40-pair multilayer made of molybdenum (Mo) having a thickness of 2.8 nm and silicon (Si) having a thickness of 4.2 nm on an optically polished synthetic quartz substrate 1 having a size of 6 inches square. The reflective layer 2 is laminated, the ruthenium (Ru) protective layer 3 having a thickness of 2.5 nm is laminated on the multilayer reflective layer 2, and the tantalum boron nitride (TaBN) and tantalum having a thickness of 70 nm are laminated on the protective layer 3. In this structure, an absorption layer 4 made of an oxide (TaO) is stacked. A conductive layer 5 made of chromium nitride (CrN) is formed on the back surface.

  An electron beam resist is applied to the mask blanks, a pattern is drawn with an electron beam drawing apparatus, and developed to form a resist pattern. Then, the absorption layer 4 is dry-etched with a mixed gas of chlorine and oxygen, and a resist is formed. A reflective mask having the pattern shown in FIG. 9B was produced by peeling and cleaning.

  Next, a light shielding frame 6 was formed on the outer periphery of the reflective mask. First, an i-line resist is applied to a reflective mask, the pattern of the light shielding frame 6 is drawn by an i-line drawing machine, developed to form a resist pattern, and then dry-etched to absorb the absorption layer 4, the protective layer 3, and the multilayer A reflective mask provided with a light shielding frame 6 shown in FIG. 9C was manufactured by etching the reflective layer 2 and removing and cleaning the resist.

First, the result when the measurement method of the prior art is applied to the reflective mask with the light shielding frame 6 is shown.
Pattern side wall angle measurement and three-dimensional shape measurement of the reflective mask with the light shielding frame 6 were performed. When the side wall angle of a line pattern having a design dimension of 200 nm was measured, the left edge of the line pattern was measured to be 80.2 degrees and the right edge was measured to be 88.6 degrees, and the angle difference between the left and right edges was remarkable. Separately, when the side wall angle of this line pattern was measured using an AFM (not shown), the left edge was measured as 85.8 degrees and the right edge was measured as 86.1 degrees, and the side wall angles of the left and right edges were almost equal. . For this reason, it was found that the measurement by the SEM was not accurately performed due to the charging caused by the electron beam irradiation.

  FIG. 10A shows signal shapes acquired by the left and right electron detectors 18 at the time of line pattern measurement. In the signal of the left electron detector 18, there is almost no difference in the magnitudes of the two peaks P1 and P2 corresponding to the left and right edges of the line pattern. In general, since many secondary electrons are incident on the electron detector facing the edge (in this embodiment, many secondary electrons emitted from the left edge of the line pattern enter the left electron detector 18). There is a clear difference in the peak size of the left and right edges of the pattern. However, since the secondary electrons are deflected due to the influence of the charging of the pattern 17, the signal shape of FIG. 10A does not become as described above. Further, the overall signal intensity of the right electron detector 18 is lower than that of the left electron detector 18, and the secondary electron trajectory is biased toward the left electron detector 18. I understand.

  FIG. 10B shows a signal obtained by integrating the difference signal obtained by subtracting the signal of the right electron detector 18 from the signal of the left electron detector 18. Since the influence of the pattern 17 composition is offset in the difference signal and only the surface irregularity signal is extracted, a signal profile corresponding to the cross-sectional shape of the pattern 17 is obtained by integrating the above-described difference signal. However, FIG. 10B is completely different from the cross-sectional shape of the pattern 17.

Next, the result when the pattern measurement method of the present invention is applied to the reflective mask with the light shielding frame 6 will be described.
When the image luminance value of the left and right electron detectors 18 is calculated by irradiating an electron beam onto a line pattern having a design dimension of 200 nm, the luminance value of the left electron detector 18 is 73.3 and the right electron detector 18 has a luminance value. The luminance value was 30.1 and the luminance value difference was 43.2. A voltage was applied to the electrode 19 because the luminance value difference was larger than the preset threshold value of luminance value (3.5). A negative voltage was applied to the left electrode 19 provided on the same side as the left electron detector 18, and a positive voltage was applied to the right electrode 19 provided on the same side as the right electron detector 18. The luminance value of the image of each electron detector 18 was calculated in real time, and the voltage value applied to the electrode 19 was increased until the difference in luminance value between the left and right electron detectors 18 was equal to or less than the threshold value. The relationship between the luminance value difference and the voltage applied to the electrode 19 is shown in FIG. As the voltage value of the electrode 19 is increased, the luminance value difference is decreased. When the applied voltage reaches 87V, the luminance value difference is equal to or less than the threshold value, and thus the adjustment of the secondary electron trajectory by the electrode 19 is completed.

  Next, when the side wall angle of the line pattern was measured in this state, the left edge of the line pattern was measured as 85.7 degrees, the right edge was measured as 85.9 degrees, and the side wall angles of the left and right edges were substantially equal. Moreover, it was confirmed that the measurement value of AFM almost coincides with the measurement value with high accuracy.

  FIG. 12A shows signal shapes of the left and right electron detectors 18. In the signal from the left electron detector 18, the size of the peak P3 corresponding to the left edge of the line pattern is larger than the size of the peak P4 corresponding to the right edge. The signal from the right electron detector 18 is reversed. In general, since many secondary electrons are incident on the electron detector facing the edge, it can be said that this signal shape is normally measured. Further, it was found that the signal strengths of the left and right electron detectors 18 are substantially equal, and secondary electrons are emitted uniformly in the left-right direction.

  FIG. 12B shows a signal obtained by integrating the difference signal obtained by subtracting the signal of the right electron detector 18 from the signal of the left electron detector 18. The cross-sectional shape of the line pattern is accurately reproduced.

  As shown in this embodiment, the trajectory of secondary electrons emitted from the pattern 17 is controlled by the electrode 19 so that the pattern side wall angle and the three-dimensional shape inherent to the pattern 17 can be measured. . Therefore, it was confirmed that by applying the present invention, it is possible to measure with high accuracy even for a mask that cannot be measured with high accuracy due to charging of the pattern 17.

  The pattern measurement method and apparatus of the present invention prevents the phenomenon of secondary electron trajectory deflection due to the influence of sample charging caused by electron beam irradiation, and can accurately perform pattern side wall angle measurement and three-dimensional shape measurement. It is expected to be used in fields where high-precision pattern measurement is required.

DESCRIPTION OF SYMBOLS 1 Synthetic quartz substrate 2 Multilayer reflection layer 3 Protective layer 4 Absorption layer 5 Conductive layer 6 Shading frame 10 Electron barrel 11 Electron gun 12 Electron beam 13 Extraction electrode 14 Condenser lens 15 Deflector 16 Objective lens 17 Pattern 18 Electron detector 19 Electrode DESCRIPTION OF SYMBOLS 20 Control calculating part 21 Display 22 Electrode control part 23 Signal processing part 24 Data calculating part 25 Output part 26 Stage 66 Current measurement means

Claims (6)

A pattern measurement method on a mask,
Irradiating the pattern on the mask with an electron beam;
Detecting secondary electrons emitted from the pattern irradiated with the electron beam;
Controlling the trajectory of the secondary electrons with an electrode;
Generating image data based on the detection signal detected in the detecting step;
Generating a signal profile of the pattern from the image data;
Measuring the side wall angle and three-dimensional shape of the pattern based on the signal profile ,
In the controlling step, a voltage value applied to the electrode is changed based on a difference in luminance value of an image acquired by left and right electron detectors arranged symmetrically with respect to the axis of the electron beam. A pattern measuring method , wherein the trajectory of the secondary electrons is controlled . A pattern measurement method on a mask,
Irradiating the pattern on the mask with an electron beam;
Detecting secondary electrons emitted from the pattern irradiated with the electron beam;
Controlling the trajectory of the secondary electrons with an electrode;
Generating image data based on the detection signal detected in the detecting step;
Generating a signal profile of the pattern from the image data;
Measuring the side wall angle and three-dimensional shape of the pattern based on the signal profile,
In the controlling step, by changing a voltage value applied to the electrode based on a difference between current values measured by left and right electron detectors arranged symmetrically with respect to the axis of the electron beam, A pattern measuring method, wherein the trajectory of secondary electrons is controlled. In the detecting step, by the electron detector multiple, and detects the secondary electrons, the pattern measuring method according to claim 1 or 2. In the step of the control, and controlling the trajectory of the secondary electrons with the electrode provided plurality in between said electron detector mask any of claims 1 to 3 The pattern measurement method according to claim 1. A pattern measuring device on a mask,
Means for irradiating the pattern on the mask with an electron beam;
Means for detecting secondary electrons emitted from the pattern irradiated with the electron beam;
Means for controlling the trajectory of the secondary electrons by an electrode;
Means for generating image data based on a detection signal detected by the detecting means;
Means for generating a signal profile of a pattern from the image data;
Means for measuring a sidewall angle and a three-dimensional shape of the pattern based on the signal profile ;
In the control means, a voltage value applied to the electrode is changed based on a difference in luminance value of an image acquired by left and right electron detectors arranged symmetrically with respect to the electron beam axis. A pattern measuring apparatus for controlling the trajectory of the secondary electrons . A pattern measuring device on a mask,
Means for irradiating the pattern on the mask with an electron beam;
Means for detecting secondary electrons emitted from the pattern irradiated with the electron beam;
Means for controlling the trajectory of the secondary electrons by an electrode;
Means for generating image data based on a detection signal detected by the detecting means;
Means for generating a signal profile of a pattern from the image data;
Means for measuring a sidewall angle and a three-dimensional shape of the pattern based on the signal profile;
In the controlling means, by changing a voltage value applied to the electrode based on a difference between current values measured by left and right electron detectors arranged symmetrically with respect to the axis of the electron beam, A pattern measuring apparatus for controlling the trajectory of secondary electrons.

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