JP2019138748A - Pattern measuring method - Google Patents

Abstract

To provide a pattern measuring method with which it is possible to achieve the required accuracy of measurement with high throughput.SOLUTION: A pattern measuring method includes: moving a stage 121 having a sample 124 placed thereon to a prescribed position and acquiring the data of mechanical vibration due to the movement of the stage 121; calculating the vibration index value of a pattern on the basis of the pattern shape information acquired from pattern design data, the scanning condition of a scanning electron microscope 100 and the data of mechanical vibration; repeating the acquisition of the data of mechanical vibration and the calculation of the vibration index value until the vibration index value decreases to or below a permissible value; generating an image of pattern of the sample 124 on the stage 121 by the scanning electron microscope 100 after the vibration index value decreases to or below the permissible value; and measuring the dimension of a pattern on the basis of the image of the pattern.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method for measuring a pattern of a semiconductor integrated circuit using a scanning electron microscope. More specifically, the present invention relates to a size of a pattern constituting a semiconductor integrated circuit (LSI) or a liquid crystal panel manufactured based on design data. It relates to a measuring method.

  With the miniaturization of semiconductor integrated circuits, the demand for measurement accuracy required for pattern dimension measurement has become stricter. Accordingly, pattern dimension measurement using a scanning electron microscope having higher resolution than that of an optical microscope used in conventional pattern dimension measurement has been performed. In recent years, it has been required to measure finely formed pattern dimensions on the order of nanometers. To that end, it is necessary to reduce the pixel size of the observed image and obtain a secondary electron image with less vibration due to stage movement. is important.

  As a factor of the vibration accompanying the stage movement, there are vibration of the XY stage mechanism supporting the wafer and vibration of the electron beam. This is influenced by floor vibrations and sound vibrations due to the installation environment of the scanning electron microscope, and vibrations generated from column and chamber shaking.

  As a countermeasure for the vibration accompanying the stage movement, a method of measuring the vibration of the stage at the time of imaging and correcting the irradiation position of the electron beam based on the amount of variation of the stage, or as disclosed in Patent Document 1, a certain set time Two types of countermeasures are the main methods of taking an image after waiting for the vibration to attenuate.

  However, in the above method of correcting the electron beam irradiation position based on the stage fluctuation amount, the electron beam irradiation position is corrected correctly when the column or chamber vibrates or when the stage fluctuation amount is too large. There is a problem that can not be.

  In the method disclosed in Patent Document 1, there is a problem that high resolution cannot be obtained when the vibration is not attenuated even after waiting for a set time, and the throughput is reduced when the vibration decay time is shorter than the set time. .

  As a solution of Patent Document 1, a technique described in Patent Document 2 has been proposed. This technique is a method in which the apparatus waits for imaging until the vibration of the observation target region is attenuated to a predetermined vibration or less. However, this method inevitably increases the waiting time, resulting in a reduction in throughput.

JP-A-10-135288 JP2015-170539A

  Accordingly, an object of the present invention is to provide a pattern measurement method that can achieve the required measurement accuracy with higher throughput.

  One aspect of the present invention is a method of measuring a dimension of a pattern formed on the surface of a sample using a scanning electron microscope, and moving the stage on which the sample is placed to a predetermined position. Acquire mechanical vibration data, and based on the pattern shape information acquired from the pattern design data, scanning conditions of the scanning electron microscope, and the mechanical vibration data, the vibration index value of the pattern Until the vibration index value falls below the allowable value, and repeats the acquisition of the mechanical vibration data and the calculation of the vibration index value, and after the vibration index value falls below the allowable value, An image of the pattern of the sample is generated by the scanning electron microscope, and the dimension of the pattern is measured based on the image of the pattern.

The step of calculating the vibration index value includes the time required for the scanning electron microscope to scan the pattern based on the pattern shape information, the scanning conditions of the scanning electron microscope, and the mechanical vibration data. And calculating a vibration index value indicating an estimated magnitude of the vibration of the pattern at the calculated time.
The shape information of the pattern includes the size of the pattern, and the scanning conditions of the scanning electron microscope include a scanning range, a scanning speed, a scanning direction with respect to the pattern, and the number of times of scanning.

The mechanical vibration data is calculated from the vibration of the image generated by the scanning electron microscope. By calculating the mechanical vibration data from the vibration of the image generated by the scanning electron microscope, the mechanical vibration data can be acquired with higher accuracy.
The image used for calculation of the mechanical vibration data is an image of an area away from the pattern. As the reason for using an image of a region away from the pattern as the image used for calculating the mechanical vibration data, for example, when an electron beam is irradiated on the surface made of resist, the pattern contracts due to charging, and the pattern It is mentioned that the measured value of a dimension changes.
The mechanical vibration data is obtained by measuring the vibration of the scanning electron microscope. By using the measurement value of the vibration of the scanning electron microscope as the mechanical vibration data, the mechanical vibration data can be acquired without irradiating the wafer with the electron beam. Therefore, pattern shrinkage due to charging can be prevented.
The vibration of the scanning electron microscope includes the vibration of the column housing the electron gun or the vibration of the stage.
The mechanical vibration data is selected from a mechanical vibration database storing past mechanical vibration data calculated or measured in advance. By selecting from the machine vibration database storing the past machine vibration data calculated or measured in advance as the machine vibration data, the time for calculating or measuring the machine vibration can be reduced.

  According to the present invention, the imaging waiting time of the scanning electron microscope is dynamically changed according to the shape information of the pattern to be measured and the scanning conditions of the scanning electron microscope, so that a higher throughput can be achieved with a desired measurement accuracy. It is possible to measure the dimensions of the pattern.

It is a mimetic diagram showing one embodiment of a pattern measuring device provided with a scanning electron microscope. It is a figure which shows an example of a line pattern. It is a graph showing the mechanical vibration accompanying the movement of an XY stage. It is a figure which shows an example of a hole pattern. It is a flowchart explaining the sequence which measures a pattern dimension. It is a figure which shows an example of a line pattern.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram illustrating an embodiment of a pattern measuring apparatus including a scanning electron microscope. As shown in FIG. 1, the pattern measurement apparatus includes a scanning electron microscope 100 and a computer 150 that controls the operation of the scanning electron microscope. The scanning electron microscope 100 includes an electron gun 111 that emits an electron beam composed of primary electrons (charged particles), a focusing lens 112 that focuses the electron beam emitted from the electron gun 111, and deflects the electron beam in the X direction. An X deflector 113, a Y deflector 114 that deflects an electron beam in a Y direction orthogonal to the X direction, and an objective lens 115 that focuses the electron beam onto a wafer 124 that is a sample are provided.

  The electron gun 111, the focusing lens 112, the X deflector 113, the Y deflector 114, and the objective lens 115 are arranged in the column 110. The lower end of the column 110 is fixed to the sample chamber 120. An accelerometer 126 is fixed to the column 110. The accelerometer 126 is provided to measure the acceleration of the column 110 when vibrating. The accelerometer 126 is connected to the acceleration signal processing device 127. The acceleration signal output from the accelerometer 126 is sent to the acceleration signal processing device 127. The acceleration signal processing device 127 is configured to calculate the vibration of the column 110 (vibration amplitude, vibration frequency, vibration direction) by processing the acceleration signal. In the present embodiment, the accelerometer 126 and the acceleration signal processing device 127 constitute a vibration measuring instrument that measures the vibration of the column 110. The acceleration signal processing device 127 is connected to the computer 150. The vibration data (vibration amplitude, vibration frequency, vibration direction) of the column 110 calculated by the acceleration signal processing device 127 is sent to the computer 150.

  The focusing lens 112 and the objective lens 115 are connected to a lens control device 116, and the operations of the focusing lens 112 and the objective lens 115 are controlled by the lens control device 116. This lens control device 116 is connected to a computer 150. The X deflector 113 and the Y deflector 114 are connected to a deflection control device 117, and the deflection operations of the X deflector 113 and the Y deflector 114 are controlled by the deflection control device 117. This deflection control device 117 is also connected to the computer 150 in the same manner. The secondary electron detector 130 and the backscattered electron detector 131 are connected to the image acquisition device 118. The image acquisition device 118 is configured to convert the output signals of the secondary electron detector 130 and the backscattered electron detector 131 into an image. This image acquisition device 118 is similarly connected to the computer 150.

  An XY stage 121 disposed in the sample chamber 120 is connected to a stage control device 122. The XY stage 121 is an example of a stage on which a wafer 124 as a sample is placed. The position of the XY stage 121 is controlled by the stage controller 122. This stage control device 122 is connected to a computer 150. The wafer transfer device 140 is configured to place the wafer 124 on the XY stage 121 in the sample chamber 120. Similarly, the wafer transfer device 140 is connected to the computer 150. The computer 150 includes a storage device 162 in which a design database 161 and a recipe database 165 are stored, an input device 163 such as a keyboard and a mouse that accepts input, and a display device 164.

  A displacement detector 125 is fixed to the XY stage 121. The displacement detector 125 measures the displacement of the XY stage 121. A laser interferometer (interferometer) can be used for the displacement detector 125. The displacement detector 125 is connected to the displacement signal processing device 128. The displacement signal output from the displacement detector 125 is sent to the displacement signal processing device 128. The displacement signal processing device 128 is configured to calculate the vibration (vibration amplitude, vibration frequency, vibration direction) of the XY stage 121 by processing the displacement signal. In the present embodiment, the displacement detector 125 and the displacement signal processing device 128 constitute a vibration measuring device that measures the vibration of the XY stage 121. The displacement signal processing device 128 is connected to the computer 150. The vibration data (vibration amplitude, vibration frequency, vibration direction) of the XY stage 121 calculated by the displacement signal processing device 128 is sent to the computer 150.

  The electron beam emitted from the electron gun 111 is focused by the focusing lens 112, is then focused by the objective lens 115 while being deflected by the X deflector 113 and the Y deflector 114, and is irradiated onto the surface of the wafer 124. When the wafer 124 is irradiated with primary electrons of an electron beam, secondary electrons and reflected electrons are emitted from the wafer 124. Secondary electrons are detected by the secondary electron detector 130. The reflected electrons are detected by the reflected electron detector 131. The detected secondary electron signal and reflected electron signal are input to the image acquisition device 118 and converted into image data by the image acquisition device 118. The image data is transmitted to the computer 150 by the image acquisition device 118. An image of the wafer 124 based on the image data transmitted to the computer 150 is displayed on the display device 164 of the computer 150.

  Design data of the wafer 124 (including design information such as pattern shape, dimensions, and position) is stored in the design database 161 in advance. In addition, information necessary to perform pattern dimension measurement is stored in advance in the recipe database 165 as a recipe. The pattern measuring device operates according to this recipe. The recipe includes an allowable value that represents an error in pattern dimension measurement allowed in the pattern inspection.

  After the XY stage 121 reaches the pattern measurement position specified in the recipe, the computer 150 acquires data on mechanical vibrations associated with the movement of the XY stage 121. Specifically, the computer 150 calculates data of mechanical vibration accompanying the stage movement from the image of the wafer 124 received from the image acquisition device 118. The mechanical vibration accompanying the stage movement includes vibration of the XY stage 121 and / or vibration of the column 110. The mechanical vibration data includes vibration amplitude and vibration frequency.

  The computer 150 can calculate mechanical vibration data by performing Fourier transform or fast Fourier transform on the vibration of the image of the wafer 124. As described above, the computer 150 can acquire the data of the mechanical vibration accompanying the stage movement with higher accuracy from the image acquired at the pattern measurement position.

  In one embodiment, the X deflector 113 and the Y deflector 114 deflect the electron beam from the pattern to be measured, and the mechanical vibration data may be calculated from the vibration of the image in the area away from the pattern to be measured. . The reason for using an image of a region away from the pattern is that when the surface made of resist is irradiated with an electron beam, the pattern contracts due to charging and the measured value of the pattern dimension changes.

  Instead of image vibration, mechanical vibration data may be acquired by measuring vibration of the scanning electron microscope 100. In one embodiment, the vibration data of the column 110 calculated by the vibration measuring instrument configured from the accelerometer 126 and the acceleration signal processing device 127 described above may be used as the mechanical vibration data. Furthermore, in one embodiment, the vibration data of the XY stage 121 calculated by the vibration measuring device configured from the displacement detector 125 and the displacement signal processing device 128 described above may be used as the mechanical vibration data. According to these embodiments, mechanical vibration data can be acquired without irradiating the wafer with an electron beam. Therefore, pattern shrinkage due to charging can be prevented.

  In addition, the above embodiment for calculating mechanical vibration data from image vibration, the above embodiment for measuring mechanical vibration data from column 110 vibration, and the above embodiment for measuring mechanical vibration data from vibration of the XY stage 121. The mechanical vibration data may be acquired by appropriately combining the forms.

  The computer 150 uses the pattern shape information described in the pattern design data of the wafer 124, the calculated or measured mechanical vibration data, and the scanning conditions of the scanning electron microscope 100 to determine the vibration index of the pattern of the wafer 124. Calculate the value. The vibration index value is a numerical value indicating the estimated magnitude of the pattern vibration that may occur due to the mechanical vibration accompanying the movement of the XY stage 121. The pattern shape information includes the pattern shape, size, and position. The scanning conditions of the scanning electron microscope 100 include a scanning range, a scanning speed, a scanning angle, and the number of times of scanning. The scanning range is the size (that is, the field of view) of an image generated by the scanning electron microscope 100. The scanning angle is an angle with respect to a certain reference direction. The reference direction is, for example, the direction of the X axis that is one of the movement axes of the XY stage 121. The cumulative number of scans is the number of times the same position of the pattern is scanned.

  The degree of the influence of mechanical vibration on the pattern measurement accuracy accompanying the movement of the XY stage 121 is that the pattern measurement direction is close to the vertical direction with respect to the scanning direction, the pattern size is large, the scanning range is wide, and the scanning speed is slow. The vibration becomes larger as the direction of vibration is closer to the direction perpendicular to the scanning direction and the number of times of scanning is increased. Pattern size, scan range, and scan speed are related to pattern scan time. That is, the longer the pattern scanning time, the greater the degree of influence of mechanical vibration on the pattern measurement accuracy.

  Next, an example of calculating the vibration index value of the pattern of the wafer 124 will be described. FIG. 2 is a diagram illustrating an example of a line pattern. The measurement target pattern is a line pattern 201 having a width of 20 nm. The shape information of the line pattern 201 can be acquired from design data stored in the design database 161. The scanning condition of the scanning electron microscope 100 is that the pixel size is 1 nm / pixel, the scanning speed per pixel is 100 MHz, the number of times of scanning is one, the scanning angle is 0 degree, and the scanning range is 1000 pixels × 1000 pixels. The direction of pattern dimension measurement is the same as the scanning direction. In this example, the time required to scan the line pattern 201 for measuring the dimension of the line pattern 201 is 20 pixels / 100 MHz × the number of integrations 1 = 0.2 μsec.

  When the mechanical vibration amplitude is 150 nm and the frequency is 100 Hz, the line pattern 201 can be displaced by 150 nm in 0.0025 seconds as shown in FIG. Therefore, the vibration index value indicating the estimated magnitude of the vibration of the line pattern 201 while scanning one line pattern 201 is determined as 150 nm × 0.2 μsec / 0.0025 seconds = 0.012 nm. . A pattern dimension measurement error allowed in pattern inspection, that is, an allowable value is stored in the recipe database 165 in advance. When the allowable value is 0.1 nm, since the vibration index value 0.012 nm is smaller than the allowable value 0.1 nm, the computer 150 causes the scanning electron microscope 100 to image the wafer 124.

  FIG. 4 is a diagram illustrating an example of a hole pattern. The measurement target pattern is a hole pattern 301 having a diameter of 20 nm. The shape information of the hole pattern 301 can be acquired from design data stored in the design database 161. The scanning condition of the scanning electron microscope 100 is that the pixel size is 1 nm / pixel, the scanning speed per pixel is 100 MHz, the number of times of scanning is one, the scanning angle is 0 degree, and the scanning range is 1000 pixels × 1000 pixels. The direction of pattern dimension measurement is perpendicular to the scanning direction.

  In this example, the time required to scan the hole pattern 301 for dimension measurement of the hole pattern 301 is 20 pixels × 1000 pixels / 100 MHz × the number of integrations 1 = 0.2 milliseconds. When the mechanical vibration amplitude is 150 nm and the frequency is 100 Hz, the vibration index value is determined to be 150 nm × 0.2 milliseconds / 0.0025 seconds = 12 nm. Since the vibration index value 12 nm is larger than the allowable value 0.1 nm, the computer 150 does not cause the scanning electron microscope 100 to image the wafer 124.

  The computer 150 obtains mechanical vibration data again, and calculates the vibration index value again. Then, the computer 150 compares the vibration index value with an allowable value. The computer 150 repeats acquisition of mechanical vibration data and calculation of the vibration index value until the vibration index value becomes equal to or less than the allowable value. Then, after the vibration index value becomes equal to or less than the allowable value, the computer 150 issues a command to the scanning electron microscope 100 to generate an image of the hole pattern 301.

  Thus, pattern dimension measurement can be performed with higher throughput by starting imaging before the XY stage 121 completely stops. In particular, the vibration index value can vary depending on not only the mechanical vibration but also the pattern shape and scanning conditions. Therefore, the imaging waiting time dynamically changes depending on the pattern, and the pattern imaging can be performed at a timing suitable for the pattern shape and scanning conditions.

  FIG. 5 is a flowchart illustrating a sequence for measuring pattern dimensions. In step 1, the XY stage 121 that supports the wafer 124 moves to the pattern measurement position. In step 2, the computer 150 acquires data on mechanical vibration accompanying the movement of the XY stage 121. The mechanical vibration data is calculated or measured from the vibration of the image of the wafer 124, the vibration of the column 110, the vibration of the XY stage 121, or a combination thereof. In step 3, the computer 150 calculates the vibration index value of the pattern of the wafer 124 based on the pattern shape information, the mechanical vibration data, and the scanning conditions of the scanning electron microscope 100.

  In step 4, the computer 150 compares the vibration index value with an allowable value. When the vibration index value is larger than the allowable value, the computer 150 acquires the mechanical vibration data in Step 2 again after a predetermined waiting time has elapsed. If the vibration index value is less than or equal to the allowable value, the computer 150 issues a command to the scanning electron microscope 100 in step 5 to generate an image of the pattern of the wafer 124 on the XY stage 121. In step 6, the computer 150 measures the dimension of the pattern from the pattern image. The process of measuring the dimension of the pattern from the image can be performed using a known technique. When the vibration index value is larger than the allowable value in step 4, the computer 150 may proceed to step 2 and acquire the mechanical vibration data again without waiting for a predetermined waiting time.

  In one embodiment, the data of mechanical vibration accompanying the movement of the XY stage 121 may be selected from a mechanical vibration database 167 (see FIG. 1) that stores data of past mechanical vibration calculated or measured in advance. The mechanical vibration database 167 is composed of mechanical vibration data calculated or measured for each pattern measurement position, moving direction, and moving speed of the XY stage 121. The machine vibration database 167 is stored in the storage device 162 of the computer 150. The past mechanical vibration data constituting the mechanical vibration database 167 may be mechanical vibration data calculated or measured during past pattern dimension measurement.

  The computer 150 selects, from the mechanical vibration database 167, mechanical vibration data calculated or measured under the conditions closest to the pattern dimension measurement conditions of the wafer 124 to be measured. Then, the computer 150 calculates a vibration index value of the pattern of the wafer 124 based on the selected mechanical vibration data, pattern shape information, and scanning conditions of the electron microscope 100. According to such an embodiment, time for calculating or measuring mechanical vibration can be reduced.

  The computer 150 determines whether patterns having different sizes are included in the scanning range. Then, when patterns having different sizes are included in the scanning range, the computer 150 calculates a vibration index value based on the pattern having the largest size. For example, as shown in FIG. 6, when a line pattern 401 with a width of 20 nm and a line pattern 402 with a width of 50 nm exist within the scanning range, the time required to scan the line pattern 402 is that the line pattern 401 is scanned. Longer than required. Therefore, the estimated magnitude of the vibration of the line pattern 402 is expected to exceed the estimated magnitude of the vibration of the line pattern 401. Therefore, the computer 150 calculates the time required to scan the line pattern 402 having a larger width, and calculates the vibration index value indicating the estimated magnitude of the vibration of the line pattern 402 at the calculated time. Then, after the vibration index value becomes equal to or less than the allowable value, the electron microscope 100 generates images of the line patterns 401 and 402. As a result, the computer 150 can accurately measure the dimensions of both the line pattern 401 and the line pattern 402 from the image.

  The embodiment described above is described for the purpose of enabling the person having ordinary knowledge in the technical field to which the present invention belongs to implement the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Accordingly, the present invention is not limited to the described embodiments, but is to be construed in the widest scope according to the technical idea defined by the claims.

100 scanning electron microscope 111 electron gun 112 focusing lens 113 X deflector 114 Y deflector 115 objective lens 116 lens control device 117 deflection control device 118 image acquisition device 120 sample chamber 121 XY stage 122 stage control device 124 wafer 125 displacement detector 126 Accelerometer 127 Acceleration signal processor 128 Displacement signal processor 130 Secondary electron detector 131 Backscattered electron detector 140 Wafer transfer device 150 Computer 161 Design database 162 Storage device 163 Input device 164 Display device 165 Recipe database 167 Mechanical vibration database

Claims (8)

A method for measuring a dimension of a pattern formed on a surface of a sample using a scanning electron microscope,
Move the stage on which the sample is placed to a predetermined position,
Acquire data of mechanical vibration accompanying the movement of the stage,
Based on the pattern shape information obtained from the pattern design data, the scanning conditions of the scanning electron microscope, and the mechanical vibration data, the vibration index value of the pattern is calculated,
Until the vibration index value is less than or equal to an allowable value, the acquisition of the mechanical vibration data and the calculation of the vibration index value are repeated,
After the vibration index value is less than or equal to the allowable value, an image of the pattern of the sample on the stage is generated with the scanning electron microscope,
A method of measuring a dimension of the pattern based on an image of the pattern.   The step of calculating the vibration index value includes the time required for the scanning electron microscope to scan the pattern based on the pattern shape information, the scanning conditions of the scanning electron microscope, and the mechanical vibration data. The method according to claim 1, further comprising: calculating a vibration index value indicating an estimated magnitude of vibration of the pattern at the calculated time. The shape information of the pattern includes the size of the pattern,
The method according to claim 1, wherein the scanning conditions of the scanning electron microscope include a scanning range, a scanning speed, a scanning direction with respect to the pattern, and the number of times of scanning.   The method of claim 1, wherein the mechanical vibration data is calculated from vibrations of an image generated by the scanning electron microscope.   The method according to claim 4, wherein the image used for calculating the mechanical vibration data is an image of an area away from the pattern.   The method according to claim 1, wherein the mechanical vibration data is acquired by measuring vibration of the scanning electron microscope.   The method according to claim 6, wherein the vibration of the scanning electron microscope includes vibration of a column housing an electron gun or vibration of the stage.   The method of claim 1, wherein the mechanical vibration data is selected from a mechanical vibration database that stores previously calculated or measured past mechanical vibration data.

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