JP2008218259A - Inspection method and inspection apparatus - Google Patents

Abstract

A charged particle beam apparatus matching method capable of accurately measuring and inspecting a line width, a defect, and the like of a sample is provided.
In a matching method using a charged particle beam apparatus that performs pattern matching between an SEM image obtained by an electron microscope and design data of a sample, and measures a line width, inspection of a defect, etc., a calibration mark or a mark attached thereto is provided. The sample is placed on the stage, multiple SEM images are acquired by changing the height, the position distortion of the SEM image is matched with the design position distortion data, and the calibration is performed when the height is changed A first step of creating correction data for inspection, a second step of acquiring an inspection SEM image by focusing, and using the correction data for calibration of the first step based on the focus height value, the inspection SEM The third step of correcting the positional distortion of the image, the SEM image subjected to the positional distortion correction, and the design data are matched to measure or inspect the sample. And a fourth step of performing.
[Selection] Figure 1

Description

  The present invention relates to a matching method using a charged particle beam apparatus and a charged particle beam apparatus using the method, and for example, acquires a wide range of SEM images of a sample such as a wafer by changing the focus, and distorts the design data of the sample. Charged particle beam apparatus, such as an electron microscope, a scanning electron microscope, a CD-SEM, etc., which prepares calibration data for generating a defect, compares each SEM image with the corrected design data, and inspects line width, defects, etc. And an inspection apparatus such as a charged particle beam apparatus using the method.

  Conventionally, for example, an image correcting unit that receives CAD design data and generates a corrected layout image through predetermined image processing, a matching unit that is an image comparison unit that performs matching between the corrected layout image and an SEM image, There is known an inspection apparatus including an image collation unit including a memory (paragraph 0018 of FIG. 1 and FIG. 1).

  Further, for example, in paragraph 0006 of Patent Document 2, all conditions necessary for inspection are created from design information such as CAD data to shooting conditions, points to be measured, and length measurement algorithms. To realize an operator-free, fully automated semiconductor inspection system that performs a matching process with a SEM image using design data as a template in the system, which can perform a stable matching process with a high correlation value A system is disclosed.

Further, for example, in paragraph 0010 of Patent Document 3, in an SEM image or the like, an imaging recipe for measuring a pattern shape by measuring various dimension values such as a wiring width of a pattern from an observation image (coordinates of each imaging point, An imaging recipe creation device and a method thereof are disclosed in which an imaging condition and an image template information) are automatically generated by analysis using a CAD image converted from CAD data to shorten the generation time.
JP 2000-266706 A JP 2002-328015 A JP 2006-351746 A

  In general, wide field SEM images are technically difficult. When a wide field of view is used, the positional distortion of the image due to the Scan system increases. Since distortion is proportional to the cube of the angle of view, the degree of distortion increases toward the periphery. In particular, in an apparatus for creating an imaging recipe as shown in Patent Document 3 above, when performing defect inspection by matching with design data of a sample such as a wafer over the entire field of view, the positional distortion increases the accuracy of defect detection. It was getting worse.

  Accordingly, the present invention acquires a wide range of SEM images of a sample such as a wafer by changing the focus of a plurality of sheets, prepares calibration data that causes distortion in the design data of the sample, and corrects each SEM image. Compare with design data, and if necessary, the height value on the sample surface is added to the correction data to accurately measure and inspect the sample line width, defects, etc. It is an object of the present invention to provide an inspection method using a matching method of a charged particle beam apparatus such as a microscope and a CD-SEM, and an inspection apparatus such as a charged particle beam apparatus using the method.

  Examples of the solution of the present invention are as described in the claims.

  Calibration data (distortion error map) that generates distortion in the design data of the sample even if positional distortion occurs in the image of a wide-field SEM image of a sample such as a wafer and the degree of distortion increases toward the periphery. ) Or reproducible positional distortion data, each SEM image can be matched with the corrected design data, and can be compared accurately, so the line width and defects of the sample can be accurately measured. Can be measured and inspected. Since it corresponds also to the change of the focus position on the sample surface (change of the focus position), it is possible to perform matching with the SEM image with high definition of the sample.

  The best mode of the present invention will be described below.

  In the preferred embodiment of the present invention, a wide range of SEM images of a sample such as a wafer are acquired by changing the position of multiple focus, especially autofocus (in-focus), and distortion is generated in advance in the design data of the sample. Calibration data (distortion error map, Distortion Error Map) or reproducible positional distortion data is prepared, and a wide range of SEM images and sample design data of wafers taken by changing the in-focus position are prepared. Calibration data in which distortion is generated in advance or reproducible positional distortion data is compared by a pattern matching method. By the comparison, distortion correction data necessary for correcting distortion, for example, magnification correction (MagX, MagY) in the X-axis direction and Y-axis direction, rotation correction around the X-axis (RotX, RotY), and X-axis direction A table of correction data such as shift variation (ShiftX, ShiftY), residue map (Residual map), and the like is created.

The strain data is not necessarily limited to the strain data in which the design data is distorted, which is proportional to the cube of the angle of view, but also to other irradiation conditions such as a charged particle beam (sample height, This includes strain data reproduced when the same RFC, acceleration voltage, etc.) are obtained, for example, statically measured 20 times on a sample such as a wafer, and the average is obtained. The distortion data is called reproducible positional distortion data.

In addition, when a sample such as a wafer is carried into a predetermined sample stage of the inspection apparatus, a height sensor (a sensor for detecting the height by irradiating the sample with laser light) or a capacitance sensor (electrostatic capacity of the sample). The height of the sample (such as the height of the sample surface of several nanometers caused by bending of the sample surface, etc.) is known in advance by a sensor that detects the volume and detects the height. If the focus position (auto focus position) is aligned with the area (including the following ultra-small area), the area to be inspected next (including the ultra-small area) is higher than the area previously inspected. Since it is only necessary to adjust the in-focus position according to the difference, it is not necessary to perform autofocus every time. Therefore, it is possible to acquire the SEM image for inspection by performing autofocus only once. It is not necessary to perform autofocus every time, and work efficiency can be improved.

  The created table (table) is stored in the storage means of the charged particle beam device, and when an image of a sample such as a wafer is acquired by the charged particle beam device, the correction data of the table (table) is taken into account, An accurate image without distortion of a sample such as a wafer is acquired. And it compares with design data, such as a wafer, using a pattern matching method. At that time, since a change in the focus position on the sample surface (change in the focus position) is accompanied, the change in the focus position (change in the focus position), that is, the height value on the sample surface is also included in the correction data. It is taken into account.

  The SEM image of a sample such as a wafer captures an accurate sample image without distortion. Therefore, when comparing the design data of a wafer or the like with the pattern matching method, a sample defect is mistakenly caused by the influence of distortion or the like. Therefore, it is possible to obtain accurate information such as the line width of the sample. Conversely, even when a defect is overlooked due to distortion, a defect can be newly found by acquiring an SEM image without distortion.

  When matching the SEM image without distortion or reduced with the design data of the sample by the pattern matching method, for example, it is divided into ultra-fine regions (sub-fields, sub fields) of several nanometers, for example. It can also be compared.

  When the SEM image without distortion and the design data of the sample are matched by the pattern matching method for each ultra-fine region (subfield, Sub Field), for example, the line width of the sample in the ultra-fine region of several nanometers, Defects can be measured and inspected.

  Embodiments of the present invention will be described with reference to the drawings.

  In FIG. 1, a wafer 11 with a calibration mark 10 (calibration mark) for distortion correction is placed on a stage (not shown) of a charged particle beam apparatus (not shown). In FIG. 1, the calibration mark 10 is formed as a known figure or the like. However, the calibration mark 10 is not limited to this, and the calibration mark 10 may be provided directly on a stage (sample stage) (not shown), and is used for calibration of a three-dimensional shape with a three-dimensional height difference. It may be a mark.

  In the example shown in FIG. 1, a charged particle beam such as an electron beam is irradiated from a charged particle beam device onto a wafer 11 with a calibration mark 10, and the generated charged particles such as secondary electrons are not shown. Detected by a secondary electron detector, led to an image display device such as an imaging tube or a monitor, and an SEM image is displayed.

  A negative voltage is applied to the wafer 11 with the calibration mark 10 to variably reduce the acceleration voltage of the irradiated charged particle beam, and the electric field state (retarding) is the same as that of an actual charged particle beam apparatus. )It has become.

  In general, the surface of a sample such as a wafer with a calibration mark 10 is slightly bent when placed on a stage. Therefore, if the irradiation position of the charged particle beam on the mask surface changes, the alignment is changed. The focal position changes. Therefore, the sample (mask) on the stage is moved in the Z direction which is a direction perpendicular to the sample such as the wafer 11 to automatically adjust the focus position (focus position). For this purpose, an electrostrictive element 12 (PZT, piezo element, etc.) constituting a part of the moving means in the Z direction is used.

  As shown in FIG. 2, in order to capture a plurality of SEM images 21 to 24, the above-described Z-direction moving means (electrostrictive element 12 or the like) is used, and an automatic operation is performed according to the deflection variation of the surface of the sample such as the wafer 11. Focusing is performed, the in-focus position is changed, and a plurality of SEM images 21 to 24 are captured. Here, the step of acquiring the SEM image for inspection by applying autofocus does not need to be applied every time the SEM image is acquired. For example, when a wafer as a sample is carried into the apparatus, a height map of the wafer (a height of about several nanometers on the surface of the wafer generated by the deflection of the wafer surface, etc.) is obtained by a plurality of height sensors or capacitance sensors. If a map showing the entire surface of the wafer, etc.) is prepared, the height in another inspection area can be obtained by applying autofocus at the time of the first SEM image acquisition. The focus (height) position may be adjusted according to the height map.

  Although not shown in the figure, a change in the SEM image due to the electric charge charged on the sample such as the wafer 11 is obtained by capturing the SEM images 21 to 24 at a certain time. Can also be recorded.

  The plurality of SEM images 21 to 24 are recorded in a memory (storage means) of a charged particle beam apparatus (not shown). Pattern matching between the recorded SEM image and calibration data 30 (refer to the distortion error map in FIG. 3) recorded in the memory (storage means) and generated in advance in the design data of the sample such as the wafer 11 Match by law.

  The calibration data 30 is a distortion error map, for example, design data of a sample such as the wafer 11 in order to correspond to the magnitude of optical distortion that cannot be removed by linear correction by software. This design data can be created in advance by applying an optical distortion of about several nanometers to several tens of nanometers.

  A wide range of SEM images 21 to 24 of a sample such as a wafer 11 taken by changing the in-focus (focus) position and calibration data 30 in which distortion is generated in advance in the design data of the sample are compared by a pattern matching method. To do. In that case, the images may be compared one by one, or the captured SEM images 21 to 24 are weighted and averaged for each predetermined number, and the averaged SEM image and calibration data 30 in which distortion has been generated in advance. May be compared.

  When the distortion correction value is taken on the vertical axis and the magnification fluctuation, rotation fluctuation and shift fluctuation are taken on the horizontal axis, the correlation is obtained as shown in FIG.

  By such comparison, distortion correction data necessary for correcting distortion, for example, magnification correction (MagX, MagY) in the X-axis direction and Y-axis direction, rotation correction around the X axis (RotX, RotY), X axis A table (table) of correction data such as shift variation in the direction (ShiftX, ShiftY) and residue map (Residual Map) is created as illustrated in FIG. This is based on the correlation shown in FIG. 4, and from this, the correction data (Scan correction data) can be summarized as a table (Scan correction table) as shown in FIG.

  When the created table (table, see FIG. 5) is stored in the memory (storage means) of the charged particle beam apparatus and the image of the sample such as the wafer 11 is acquired by the charged particle beam apparatus, the table (table, In consideration of the correction data (see FIG. 5), an accurate image without distortion of the sample such as the wafer 11 is acquired, and a new SEM image and design data of the wafer or the like are compared using a pattern matching method. In addition, since there is a change in focus position on the sample surface (change in focus position), the change in focus position (change in focus position), that is, the height value on the sample surface is also taken into account in the correction data. Is preferred.

  According to the above, accurate sample images without distortion (or with reduced distortion) are captured in the SEM images 21 to 24 of the sample such as the wafer 11. Therefore, when comparing SEM images and design data such as wafers by the pattern matching method, it is not erroneously mistaken for a sample defect due to distortion or the like. Information can be obtained. Conversely, even when a defect is overlooked due to distortion, a defect can be newly found by acquiring an SEM image without distortion.

  Moreover, since it corresponds also to the change of the focus position on a sample surface (change of a focus position), it can match by the SEM image with the high sharpness of a sample.

  As shown in FIG. 6, when matching the above-described SEM image 60 (inspection image) without distortion and design data 61 of a sample such as a wafer by a pattern matching method, for example, an ultra-fine region 60a in units of several nm. , 61a (subfield, Sub Field) can be divided and compared.

  When the SEM image 60 that is not distorted and the design data 61 of the sample are matched by the pattern matching method for each of the ultrafine regions 60a and 61a (subfield, Sub Field), for example, in the ultrafine regions 60a and 61a in units of several nm. Measurement of the line width (CD, critical dimension) of the sample, inspection of a defect of the sample, and the like can be performed.

  It is preferable to perform inspection / CD measurement after performing matching or linear correction for each of the ultrafine regions 60a and 61a.

A state in which a sample with a calibration mark is arranged and distortion correction data is acquired is shown. A mode that a plurality of SEM images are acquired is shown. 3 shows calibration data (a distortion error map) in which distortion is generated in advance in design data of a sample such as a wafer. The graph showing the relationship between a distortion correction value and each of magnification fluctuation, rotation fluctuation, and shift fluctuation. The table | surface (table) of distortion correction data required in order to correct | amend distortion is shown. A state in which an SEM image (inspection image) is compared with design data of a sample divided for each ultra-fine region (subfield, Sub Field) of, for example, several nanometers by a matching method is shown.

Explanation of symbols

10 Calibration mark 11 Wafer (sample)
12 Electrostrictive element 21-24 SEM image 30 Calibration data (distortion error map)

Claims (9)

In the inspection method for matching the SEM image captured by the electron microscope and the design data of the sample by pattern matching, and performing line width measurement, defect inspection, etc.
Place a calibration mark or a sample with the calibration mark on the stage, change the height, acquire multiple SEM images, position distortion of the SEM image and design position distortion data or reproducibility A first step of matching with certain positional distortion data and creating correction data for calibration when the height is changed;
A second step of acquiring an SEM image for inspection with auto-focusing;
A third step of correcting the positional distortion of the inspection SEM image using the calibration correction data of the first step from the height value of the autofocus;
An inspection method comprising: a fourth step of matching the SEM image subjected to the positional distortion correction with design data and measuring or inspecting the sample. In the inspection method for matching the SEM image captured by the electron microscope and the design data of the sample by pattern matching, and performing line width measurement, defect inspection, etc.
Place a calibration mark or a sample with the calibration mark on the stage, change the height, acquire multiple SEM images, position distortion of the SEM image and design position distortion data or reproducibility A first step of matching with certain positional distortion data and creating correction data for calibration when the height is changed;
A second step of acquiring an SEM image for inspection by applying autofocus only when acquiring the first SEM image;
A third step of correcting the positional distortion of the inspection SEM image using the calibration correction data of the first step from the height value of the autofocus;
An inspection method comprising: a fourth step of matching the SEM image subjected to the positional distortion correction with design data and measuring or inspecting the sample. In the inspection method for matching the SEM image captured by the electron microscope and the design data of the sample by pattern matching, and measuring the line width and inspecting the defect,
Place a calibration mark or a sample with the calibration mark on the stage, change the height, take multiple SEM images, position distortion of the SEM image and design position distortion data or reproducible position A first step (preprocessing 1) for performing calibration with distortion data and creating calibration correction data for magnification and rotation when the height is changed;
A second step of acquiring an SEM image for inspection by autofocusing on the sample, (this processing),
A third step of correcting the positional distortion of the inspection SEM image using the calibration correction data of the first step (preprocessing 1) from the height value of the autofocus;
And a fourth step of matching the SEM image subjected to the positional distortion correction with the design data of the sample and measuring the line width or the like or inspecting the defect of the sample. .   4. The inspection method according to claim 1, wherein matching between the SEM image subjected to positional distortion correction and the design data of the sample is performed by subfield (Sub Field) obtained by dividing the field of view of the SEM image into a plurality of fields. ) Inspection method characterized by being performed every time.   The inspection method according to any one of claims 1 to 4, wherein the calibration mark or the sample to which the calibration mark is attached is mounted on a stage at a single or a plurality of heights. Method.   6. The inspection method according to claim 5, wherein the stage is moved in the Z direction using an electrostrictive element. In the inspection method for matching the SEM image captured by the electron microscope and the design data of the sample by pattern matching, and performing line width measurement, defect inspection, etc.
A calibration mark or a sample to which the calibration mark is attached is placed on the stage, and a voltage can be applied to the calibration mark. A plurality of SEM images are taken by changing the voltage, and positional distortion of the SEM image is performed. First step of creating calibration correction data for magnification and rotation when voltage is changed by matching position distortion data with design or position distortion data with reproducibility (step 2) When,
Applying a bias voltage (RFC) to the test sample to obtain a test SEM image (this process);
A third step of correcting positional distortion of the inspection SEM image from the value of the bias voltage (RFC) using the calibration correction data of the first step (preprocessing 2);
A fourth step of performing matching between the SEM image subjected to the positional distortion correction and the design data of the sample and measuring a line width or the like or inspecting a defect of the sample.   8. The inspection method according to claim 7, wherein matching between the SEM image subjected to positional distortion correction and the design data is performed for each subfield (Sub Field) obtained by dividing the field of view of the SEM image into a plurality of subfields. Inspection method.   An inspection apparatus configured to measure a line width or the like or inspect a defect of a sample by the inspection method according to any one of claims 1 to 8.

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