Charged particle beam device

Abstract

Provided is a charged particle beam device capable of reducing the distortion of an observation image of a sample irradiated with a plurality of charged particle beams. The charged particle beam device includes: a charged particle beam source that emits a plurality of charged particle beams toward a sample; a detector that detects signal electrons emitted from the sample by irradiation with each of the charged particle beams and outputs a detection signal; a lens that focuses the signal electrons on the detector; and a control unit that generates an observation image on the basis of the detection signal and controls each unit. The charged particle beam device is characterized in that: the control unit acquires observation images in different frames for an observation sample to be observed, measures a feature amount in each of the observation images, and sets a condition of the lens on the basis of a difference value between the measured feature amounts.

Description

Charged particle beam device

[0001] The present invention relates to a charged particle beam device that irradiates a sample with a plurality of charged particle beams to generate an observation image.

[0002] For observing a semiconductor device with increasing miniaturization, a charged particle beam device is used that irradiates a sample with a charged particle beam such as an electron beam and generates an observation image of the sample by detecting electrons emitted from the sample. The sample irradiated with the charged particle beam may be charged, and the charging of the sample causes distortion in the observation image. Also, the sample may be deformed by the irradiation of the charged particle beam, causing distortion in the observation image.

[0003] Patent Document 1 discloses obtaining a plurality of images with different scanning directions at the same position and using the difference in feature amounts obtained from each image to identify the cause of distortion in the observation image or to detect device conditions for suppressing the occurrence of distortion.

[0004] Japanese Patent Application Laid-Open No. 2012-053989

[0005] However, in Patent Document 1, consideration for charging when a plurality of charged particle beams are irradiated onto the sample is insufficient. In a charged particle beam device that improves inspection efficiency by irradiating a sample with a plurality of charged particle beams, since a plurality of regions are charged, the distortion generated in the observation image becomes large.

[0006] Therefore, an object of the present invention is to provide a charged particle beam device capable of reducing distortion in an observation image of a sample irradiated with a plurality of charged particle beams.

[0007] To achieve the above object, the present invention provides a charged particle beam device including a charged particle beam source that emits a plurality of charged particle beams toward a sample, a detector that detects signal electrons emitted from the sample by each irradiation of the charged particle beam and outputs a detection signal, a lens that focuses the signal electrons onto the detector, and a control unit that generates an observation image based on the detection signal and controls each part. The control unit acquires an observation image of an observation sample, which is an observation target, in different frames, measures feature amounts in each observation image, and sets the conditions of the lens based on the difference value of the measured feature amounts.

[0008] According to the present invention, it is possible to provide a charged particle beam apparatus that can reduce distortion of the observed image of a sample irradiated with multiple charged particle beams.

[0009] Figure 1 shows an example of the overall configuration of the charged particle beam apparatus in Example 1. Figure 2 shows an example of the relationship between the charge potential of the sample and the irradiation time. Figure 3 shows an example of the distribution of distortion of the observed image when the scanning direction is the X direction. Figure 4 shows an example of the distribution of distortion of the observed image when the scanning direction is the Y direction. Figure 5 shows an example of the relationship between the average value of the distortion in each direction and the charge potential. Figure 6 shows the process flow for creating a database in which the difference values ​​of the feature quantities of the observed image are associated with the conditions of the secondary optical lens. Figure 7 shows the process flow for setting the conditions of the secondary optical lens for the observed sample. Figure 8 shows an example of the GUI of Example 1.

[0010] Hereinafter, an embodiment of the charged particle beam apparatus according to the present invention will be described with reference to the attached drawings. The charged particle beam apparatus is a device that detects electrons emitted by irradiating a sample with a charged particle beam and generates an observation image of the sample.

[0011] The charged particle beam apparatus of Example 1 will be described using Figure 1. The charged particle beam apparatus illustrated in Figure 1 is a scanning electron microscope (SEM) in which the charged particle beam irradiated onto the sample 110 is a multi-beam 105 containing multiple electron beams, and comprises a microscope body 100 and a control unit 120. The microscope body 100 comprises an electron gun 101, a primary optical lens 103, a multi-beam forming unit 104, a multi-detector 106, a beam separator 107, a deflector 108, a stage 109, and a secondary optical lens 112. Each part will be described below.

[0012] Stage 109 holds the sample 110. A voltage may also be applied to stage 109.

[0013] The electron gun 101 emits an electron beam 102. The primary optical lens 103 focuses the electron beam 102 emitted from the electron gun 101. The multi-beam forming unit 104 forms a multi-beam 105 from the electron beam 102. Figure 1 illustrates a multi-beam 105 containing three electron beams. In other words, in Figure 1, a single electron gun 101 and a multi-beam forming unit 104 constitute a charged particle source that emits three electron beams toward the sample 110. Note that the number of electron beams included in the multi-beam 105 is not limited to three. Also, instead of a single electron gun 101 and a multi-beam forming unit 104, a charged particle source may be configured with multiple electron guns 101.

[0014] The deflector 108 deflects the multibeam 105 so as to scan the sample 110. When the sample 110 is irradiated with the multibeam 105 deflected by the deflector 108, signal electrons 111, such as secondary electrons and backscattered electrons, are emitted. The beam separator 107 is, for example, a Wien filter, which changes the trajectory of the signal electrons 111 without changing the trajectory of the multibeam 105, and causes the signal electrons 111 to be incident on the multidetector 106.

[0015] The multi-detector 106 detects the signal electrons 111 and outputs the detection signal to the control unit 120. The multi-detector 106 is equipped with the same number of detection elements as the electron beams contained in the multi-beam 105. The secondary optical lens 112 is a lens placed between the sample 110 and the multi-detector 106, and focuses the signal electrons 111 onto the multi-detector 106. The secondary optical lens 112 may also have a function to adjust the shift, rotation, or shear of the position into which the signal electrons 111 are incident.

[0016] The control unit 120 is a device that controls the operation of each part of the microscope body 100, and is, for example, a general-purpose computer. The control unit 120 also generates an SEM image as an observation image of the sample 110 based on the detection signal output from the multi-detector 106. The control unit 120 is connected to a display unit 121 that displays the observation image and other data, and a storage unit 122 that stores the observation image and various other data.

[0017] Incidentally, the sample 110 becomes charged in accordance with the difference between the amount of incident electrons and the amount of emitted electrons. For example, if the amount of emitted signal electrons 111 and electrons flowing out through the stage 109 is greater than the amount of electrons contained in the irradiated multibeam 105, the sample 110 becomes positively charged. As illustrated in Figure 2, the charge potential of the sample 110 increases with the increase in the number of frames of the observation image, i.e., the irradiation time, and saturates at a predetermined value. That is, the difference in charge potential between frames is maximum between the first and second frames. Furthermore, the charging of the sample 110 causes the multibeam 105 to be deflected, resulting in distortion of the observation image. For example, when the sample 110 is positively charged, the electron beam is deflected inward, causing distortion in the observation image where the distance between patterns on the sample 110 increases, hindering the observation of the sample 110.

[0018] Figures 3A and 3B illustrate the distortion of the observed image when the sample 110 is scanned by the multibeam 105. Figure 3A shows the distortion distribution when the scanning direction of the multibeam 105 is in the X direction, and Figure 3B shows the distortion distribution when the scanning direction of the multibeam 105 is in the Y direction. The sample 110 is irradiated with a 3x3 arrangement of multibeams 105, and the squares in each figure represent the scanning range of each of the nine electron beams.

[0019] In Figure 3A, the distortion in the Y direction is greater than the distortion in the X direction, and the magnitude of the distortion in the Y direction varies depending on the position in the Y direction. Similarly, in Figure 3B, the distortion in the X direction is greater than the distortion in the Y direction, and the magnitude of the distortion in the X direction varies depending on the position in the X direction. In other words, the distortion in the direction perpendicular to the scanning direction is greater than the distortion in the same direction as the scanning direction, and the magnitude of the distortion varies depending on the position in the direction perpendicular to the scanning direction. The average value of the distortion in each direction increases as the charge potential increases, as illustrated in Figure 4.

[0020] Although distortion of the observed image can be reduced by adjusting the conditions of the secondary optical lens 112, this adjustment takes time. Therefore, by creating a database in advance that associates the difference values ​​of the observed image features with the conditions of the secondary optical lens 112, the time required to adjust the conditions of the secondary optical lens 112 can be shortened.

[0021] Using Figure 5, we will explain step by step the process of creating a database that associates the difference values ​​of the features of the observed image with the conditions of the secondary optical lens 112.

[0022] (S501) A known sample, which has a known shape, is placed on the stage 109.

[0023] (S502) Imaging conditions are set. The imaging conditions include the acceleration voltage and current of the electron beam 102, scanning direction, scanning speed, etc.

[0024] (S503) The control unit 120 measures the characteristic quantities of the observed image of the known sample. The characteristic quantities of the observed image are, for example, the distance between patterns and the size of the patterns. In S503, the characteristic quantities of the known sample before it is charged are measured.

[0025] (S504) The control unit 120 applies a voltage to the stage 109. The applied voltage to the stage 109 causes the known sample to become charged.

[0026] (S505) The control unit 120 measures the characteristic quantities of the observed image of the charged known sample. The characteristic quantities measured in S505 are the same physical quantities as the characteristic quantities measured in S503. Since the characteristic quantities after the known sample has been charged are measured in S505, the measured characteristic quantities include the distortion of the observed image due to charging. In other words, the distortion of the observed image is quantified by the difference between the characteristic quantities measured in S503 and the characteristic quantities measured in S505.

[0027] (S506) The control unit 120 searches for conditions for the secondary optical lens 112 such that the distortion of the observed image is below a predetermined threshold. That is, the conditions of the secondary optical lens 112 are changed, the feature quantities are measured, and the difference value of the feature quantities is calculated, and this process is repeated until the difference value is below the threshold. The conditions of the secondary optical lens 112 are, for example, the current supplied to the secondary optical lens 112 and the voltage applied to it.

[0028] (S507) The control unit 120 associates the difference in feature values ​​measured in S503 and S505 with the conditions of the secondary optical lens 112 searched in S506 and creates a database.

[0029] (S508) The control unit 120 determines whether or not to terminate the creation of the database. If the creation of the database is not terminated, the process is returned to S504 via S509; if it is terminated, the process flow ends. Whether or not to terminate the creation of the database is determined, for example, by whether or not the number of correspondences between the difference values ​​of the feature quantities and the conditions of the secondary optical lens 112 exceeds a predetermined number. That is, if the number of correspondences exceeds a predetermined number, the creation of the database is terminated.

[0030] (S509) The control unit 120 initializes the conditions of the secondary optical lens 112. After the conditions of the secondary optical lens 112 are initialized, the charging of the known sample is performed in S504, the measurement of feature quantities is performed in S505, the condition search is performed in S506, and the database is created in S507.

[0031] As explained using Figure 5, a database is created that associates the difference values ​​of the features of the observed image with the conditions of the secondary optical lens 112. The created database is stored in the storage unit 122 and used to set the conditions of the secondary optical lens 112 when observing the observation sample. The database may also be created for each imaging condition and sample material. By creating a database for each imaging condition and sample material, the conditions of the secondary optical lens 112 can be set more precisely.

[0032] Using Figure 6, the process of setting the conditions for the secondary optical lens 112 for the observation sample will be explained step by step.

[0033] (S601) The observation sample, which is the sample to be observed, is placed on the stage 109.

[0034] (S602) Imaging conditions are set.

[0035] (S603) The control unit 120 acquires observation images from different frames and measures the feature quantities of each observation image. For example, the observation image from the first frame and the observation image from the second frame are acquired, and the distance between patterns is measured in each observation image.

[0036] (S604) The control unit 120 calculates the difference value of the feature quantities measured in S603. Even if the distance between patterns of the observed sample deviates from the design value, the deviation from the design value is resolved by calculating the difference value of the feature quantities measured in different frames.

[0037] (S605) The control unit 120 sets the conditions for the secondary optical lens 112 based on the difference value of the feature quantities calculated in S604. That is, the conditions for the secondary optical lens 112 are set by comparing the difference value of the feature quantities calculated in S604 with the database stored in the storage unit 122.

[0038] As explained using Figure 6, the conditions for the secondary optical lens 112 for the observation sample are quickly set, and an observation image with reduced distortion can be obtained. The set conditions for the secondary optical lens 112 may also be displayed on the display unit 121.

[0039] An example of a GUI (Graphical User Interface) that displays the conditions of the secondary optical lens 112 set for the observation sample will be explained using Figure 7. The GUI exemplified in Figure 7 includes an observation position input unit 701, an imaging condition input unit 702, an application button 703, a brightness distribution display unit 704, a lens condition display unit 705, and an observation image display unit 706.

[0040] The observation position input unit 701 receives the center coordinates of the observation area. The imaging condition input unit 702 receives the imaging conditions. The imaging conditions include the electron beam acceleration voltage and current, scanning direction, number of pixels, scanning speed, etc. The imaging conditions may be set for each frame. The apply button 703 is pressed when the observation position and imaging conditions entered in the observation position input unit 701 and the imaging condition input unit 702 are applied.

[0041] The luminance distribution display unit 704 displays a graph showing the luminance value distribution for each frame. In the "FOV NUM" column, one of multiple fields of view is selected, and the difference value of the feature quantities in the selected field of view is displayed in the "Y Magnification" column. The lens condition display unit 705 displays the conditions of the secondary optical lens 112, which are set based on the difference value of the feature quantities between frames. The observation image display unit 706 displays the SEM image acquired using the set conditions of the secondary optical lens 112.

[0042] Furthermore, reducing distortion in the observed image is not limited to the settings of the secondary optical lens 112. For example, the irradiation conditions of the multi-beam 105 may be adjusted based on the difference in feature quantities calculated between observed images of the sample in different frames. By adjusting the irradiation conditions of the multi-beam 105, the charging of the observed sample is suppressed and distortion of the observed image is reduced. Alternatively, image processing may be applied to the observed image based on the difference in feature quantities calculated between observed images of the sample in different frames. By applying image processing, distortion of the observed image is reduced.

[0043] The embodiments of the present invention have been described above. The present invention is not limited to the embodiments described above, and the components can be modified and implemented without departing from the spirit of the invention. Furthermore, the multiple components disclosed in the above embodiments may be combined as appropriate. In addition, some components may be deleted from all the components shown in the above embodiments.

[0044] Microscope body 100, electron gun 101, electron beam 102, primary optical lens 103, multi-beam forming unit 104, multi-beam 105, multi-detector 106, beam separator 107, deflector 108, stage 109, sample 110, signal electron 111, secondary optical lens 112, control unit 120, display unit 121, memory unit 122, observation position input unit 701, imaging condition input unit 702, application button 703, brightness distribution display unit 704, lens condition display unit 705, observation image display unit 706.

Claims

1. A charged particle beam apparatus comprising a charged particle beam source that emits multiple charged particle beams toward a sample, a detector that detects signal electrons emitted from the sample by irradiation with each of the charged particle beams and outputs a detection signal, a lens that focuses the signal electrons toward the detector, and a control unit that generates an observation image based on the detection signal and controls each part, wherein the control unit acquires observation images of the observation sample, which is the object of observation, in different frames, measures the feature quantities in each observation image, and sets the conditions of the lens based on the difference value of the measured feature quantities.

2. A charged particle beam apparatus according to claim 1, further comprising a storage unit that stores a database relating the difference in feature quantities in each observation image of a known sample having a known shape before and after charging, and the conditions of the lens when the distortion in the observation image of the known sample after charging is below a threshold, wherein the control unit sets the conditions of the lens by comparing the difference in feature quantities measured for the observation sample with the database.

3. A charged particle beam apparatus according to claim 2, wherein the control unit compares the difference between the feature quantity in the first frame of the observed image and the feature quantity in the second frame of the observed image with the database.

4. A charged particle beam apparatus according to claim 2, wherein the database is created for each imaging condition.

5. A charged particle beam apparatus according to claim 2, wherein the database is created for each known sample material.

Images