JP4609992B2 - Drift correction method and apparatus for automatic FIB machining - Google Patents

Description

  The present invention relates to a drift correction method and apparatus during FIB automatic machining.

  When beam irradiation is performed to finely process a sample surface with a FIB apparatus (focused ion beam apparatus), if the beam irradiation time becomes longer, the stage system or electric system on which the sample is placed drifts with time, so Beam writing may not be obtained. In particular, the positional accuracy required for microfabrication has become 100 nm or less due to the reduction in the design rules of semiconductor devices. In order to realize such position accuracy, the drift amount that the irradiation position moves during microfabrication is required to be 1 / 10th of 10 nm or less. For this reason, a unique mark is provided on the sample, and beam irradiation correction by drift is performed based on the positional deviation of the mark (see, for example, Patent Document 1).

  In addition, straight line processing is performed in the direction parallel to the cross section of the sample to be created, and the straight line position limited to the direction perpendicular to the straight line is processed as a measurement value for drift correction with reference to this straight line processing region A technique for correcting the position is known (see, for example, Patent Document 2).

In this type of conventional FIB apparatus, a highly accurate pulse motor is used, or stage movement is performed using stage marks. Therefore, after the stage position is determined, machining is started and position correction is performed. That is, drift correction is performed after the start of machining.
JP-A-9-274879 (paragraphs 0009 to 0011, FIG. 1) JP 2003-331775 A (paragraph 0017 to paragraph 0031, FIG. 1)

  In the above-described conventional technique, in the case where automatic processing with stage movement is performed at the position of the ion beam, the stage movement due to a certain mark is corrected. The purpose of the FIB apparatus is to automatically process a sample. However, since a plurality of processing positions are processed, it is difficult to accurately reproduce the stage position with mechanical accuracy. For this reason, the mechanical accuracy of the stage has been increased, or a unique mark has been added and corrected by moving the stage.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a drift correction method and apparatus during automatic FIB processing that can quickly perform sample positioning and FIB processing.

(1) According to the first aspect of the present invention, at the time of FIB processing on a sample, a step of providing at least one reference image region having a large reference image acquisition region and a smaller reference image acquisition region on the sample, and processing The stage movement before the start includes a scan image of the larger reference image acquisition area acquired before the stage movement, and a direction of image shift from the scan image of the larger reference image acquisition area acquired after the stage movement. The amount is obtained by calculation, the step of positioning the stage based on the direction and amount of image shift obtained by the calculation, and at the time of ion beam processing , acquired before FIB scanning for processing in the FIB processing region Scan image of the smaller reference image acquisition area and acquired after FIB scan for processing in the FIB processing area Obtained by calculation the direction and amount of deviation of an image from the scanned image of the reference image acquisition area towards the small step to adjust the bi chromatography beam deflection system based on the direction and amount of deviation of the image obtained by the calculation It is comprised by these.

(2) The invention described in claim 2 is characterized in that Fourier transform is used as means for obtaining the direction and amount of image shift.
(3) The invention described in claim 3 is characterized in that an image shift direction and amount are obtained by using image processing other than Fourier transform .

(4) The invention described in claim 4 is a reference image setting for setting at least one reference image area having a large reference image acquisition area and a smaller reference image acquisition area on the sample at the time of FIB processing on the sample. Means, an image reading means for reading an image of the reference image area at the time of FIB processing, an arithmetic control means for receiving the output of the image reading means and performing the following processing (a) and (b):
(A) For the stage movement before the start of processing, the scan image of the larger reference image acquisition area acquired before the stage movement and the scan image of the larger reference image acquisition area acquired after the stage movement are used. Find the direction and amount of displacement by calculation
(B) At the time of ion beam processing, a scan image of the smaller reference image acquisition region acquired before performing the FIB scan for processing into the FIB processing region and acquired after performing an FIB scan for processing into the FIB processing region The direction and amount of image shift are obtained by calculation from the scanned image of the smaller reference image acquisition region.
Based on the direction and amount of image shift obtained by the process (a) of the arithmetic control means, the means for positioning the stage, and the process (b) of the arithmetic control means Beam deflection system adjustment means for correcting the beam deflection system based on the direction and amount of image shift is provided .

  (1) According to the invention described in claim 1, for stage movement before the start of beam processing, stage positioning is performed using the larger reference image, and drift correction is performed using the smaller reference image during beam processing. Therefore, the positioning of the sample and the FIB processing can be performed quickly.

  (2) According to the second aspect of the present invention, the direction and amount of image shift can be obtained from the pre-ion beam irradiation image and the post-irradiation image using a small reference image by using Fourier transform, and quick drift is achieved. Correction can be performed.

(3) According to the invention described in claim 3, the direction and amount of image shift can be obtained from a small reference image using image processing other than Fourier transform .

(4) According to the invention described in claim 4 , for stage movement before the start of beam processing, stage positioning is performed using the larger reference image, and drift correction is performed using the smaller reference image during beam processing. Therefore, the positioning of the sample and the FIB processing can be performed quickly .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the main part of the present invention. In the figure, reference numeral 1 denotes an ion source that emits ions, 2 denotes an optical system that converges the ion beam emitted from the ion source 1, and 3 denotes a deflector as a beam deflection system adjusting unit that deflects the ion beam. A processing setting screen 10 includes a processing area and a reference image area. In the processing setting screen 10, 11 is a reference image region, 12 is a first processing region (processing 1 region), and 13 is a second processing region (processing 2 region).

  FIG. 2 is a diagram showing a processing setting screen. The processing setting screen shown in the figure corresponds to the region of the sample scanned with the ion beam, and the drawing shows the case where two processing setting screens 10A and 10B are provided, but the present invention is not limited to this. Absent. These processing setting screens are given by reference image setting means (not shown). Of the reference image areas 11A and 11B, 1A and 1B are larger reference images, and 2A and 2B are smaller reference images. The larger reference images 1A and 1B are used for positioning by moving the stage before the start of processing, and the smaller reference images 2A and 2B are used for drift correction during FIB processing. The reference images 1A, 2A, 1B, and 2B may be any images that include some structure.

  The first processing region (processing 1 region) 12A, 12B and the second processing region (processing 2 region) 13A, 13B are regions where etching or the like is actually performed by irradiating an ion beam. 14A and 14B are regions sandwiched between the processing 1 region and the processing 2 region, and are thin films. That is, by etching the sample separately into the processing 1 region and the processing 2 region, a region sandwiched between these two regions is formed and used as a thin film. The thin films 14A and 14B are observed with an SEM (scanning electron microscope) or a TEM (transmission electron microscope).

  Returning again to the description of FIG. Reference numeral 20 denotes image reading means for reading the images in the reference image areas 11A and 11B. Specifically, the reference image regions 11A and 11B are scanned with an ion beam, and a reflected particle signal reflected from the reference image region is detected by a detector and converted into an electrical signal. As the image reading means 20, for example, a PMT is used. 21 is an image before drift, and 22 is an image after drift. Reference numeral 30 denotes arithmetic control means for receiving the image information read from the image reading means 20 and calculating the direction and amount of image shift from the images before and after the ion beam irradiation. As the arithmetic control means 30, for example, a computer is used.

  The arithmetic control means 30 obtains a position correction amount from the direction and amount of the deviation and gives it to the deflector 3 as a deflection correction amount. Specifically, the correction amount signals in the x and y directions output from the arithmetic control unit 30 are amplified by the amplifiers 4 and 5 via the amplifiers 4 and 5 and then given to the deflector 3. The operation of the apparatus configured as described above will be described as follows.

  First, the processing setting screens 10A and 10B are set. The processing setting screens 10A and 10B are set by the operator setting an appropriate region of the sample. When the processing setting screens 10A and 10B are set, the operator determines one of the reference image areas 11A and 11B using reference image setting means (not shown). In the reference image regions 11A and 11B, the most appropriate portion is used for calculating the direction and amount of image shift before and after ion beam irradiation. If there is only one reference image area, the direction and amount of image shift can be obtained.

  Next, the machining 1 regions 12A and 12B and the machining 2 regions 13A and 13B are determined. The processing 1 regions 12A and 12B and the processing 2 regions 13A and 13B are regions necessary for creating the thin pieces 14A and 14B to be observed with a TEM or the like. From this, the area etched by the ion beam and the distance between the processing 1 regions 12A and 13A and the processing 2 regions 12B and 13B are determined. The distance between the processing 1 regions 12A and 12B and the processing 2 regions 13A and 13B is not limited to the thickness of the thin pieces 14A and 14B. The images read by the image reading means 20 in the reference image areas 11A, 11B, the processed 1 areas 12A, 13A, and the processed 2 areas 13A, 13B determined in this manner are stored in a memory (not shown) attached to the arithmetic control means 30. ).

  When the reference image areas 11A and 11B, the processing 1 areas 12A and 12B, and the processing 2 areas 13A and 13B are determined in this way, the operator starts the operation of the apparatus. The arithmetic control unit 30 scans the reference image areas 11A and 11B with the deflector 3 based on the image data of the reference image areas 11A and 11B stored in the attached memory, and reads the image data 21 before drift. The read image data 21 is stored in a memory attached to the arithmetic control unit 30.

  Here, when moving the processing setting screen 10A to a predetermined position by moving the stage, the arithmetic control unit 30 positions the stage using the larger reference image 1A. Specifically, the processing setting screen 10A is read by the image reading means 20, and Fourier transform is performed between the image stored in the memory in advance using the arithmetic control means 30, and image shift for position correction is performed. Find the amount. Then, the stage is moved in such a direction that the image shift is eliminated from the image shift and amount. As described above, according to the present invention, when the stage is not positioned, the stage can be positioned using the reference image 1A which is a larger image.

This positioning can also be used when moving the stage from the machining setting screen 10A to the machining setting screen 10B.
When the positioning of the sample is completed in this way, this time, the smaller reference image 2A is used to calculate the deviation and amount of the image due to drift, and drift correction is performed. First, the arithmetic control means 30 scans the deflector 3 to scan the machining 1 area. This scan is repeated until the sample is etched to a predetermined depth. For example, when the entire scanning of the processing 1 area is performed five times, the scanning operation of the apparatus is stopped and an operation for correcting the image shift is performed. Specifically, the reference image 2A is scanned to obtain image information. Then, the image shift direction and amount are detected by performing Fourier transform between the image information obtained in this way and the image information before drift stored in the memory. Specifically, the arithmetic control unit 30 detects the image shift and the amount of change by performing Fourier transform between the image information before drift and the image information after five scans. A technique for obtaining an image shift using Fourier transform is well known (for example, see Japanese Patent Laid-Open No. 9-43173). If the Fourier transform is used, the direction and amount of image shift can be accurately obtained. The number of scans 5 described above is not limited to this, and an arbitrary number can be set.

  When the image drift correction amount is obtained in this way, the arithmetic control means 30 amplifies the rotation correction amount by the amplifiers 4 and 5, and then scans the first processing region 12A in addition to the deflector 3. When the entire surface is scanned five times with the same rotation correction amount, the operation of the apparatus is stopped again, and the rotation is corrected. When such an operation is repeated, the region to be processed 1 is gradually displaced (etched), and the depth of the concave portion is increased.

  When the processing 1 region is etched to a predetermined depth, the processing region 2 is scanned by operating the apparatus. Even in this case, a scan image of the reference image region 11A is obtained, and the image control unit 30 obtains the image shift and amount from the obtained scan image and the image information before drift, and is based on the image shift and amount. The correction amount is amplified by the amplifiers 4 and 5 and then applied to the deflector 3. In this way, the machining 2 area is scanned in a state where the rotation is corrected.

  When the five full scans are completed, the apparatus is stopped, rotation correction is performed again, and five full scans are performed. When such a process is repeated and the depth of the concave portion of the sample becomes the same as the depth of the processing 1 region, the operation of the apparatus is stopped. As a result, a thin film as shown in 14A of FIG. 2 is formed, and the thin film can be used to observe the sample by TEM or the like. The above operation is exactly the same on the processing setting screen 10B side.

  As described above in detail, according to the present invention, stage movement is performed using the larger reference image for stage movement before the start of beam processing, and drift is performed using the smaller reference image during beam processing. Since correction is performed, sample positioning and FIB processing can be performed promptly.

  In the above description, the case where an area where some structure exists in the sample is used is taken as an example of the reference image. However, some samples have almost no structure. In such a case, it is necessary to use a specific mark. Hereinafter, the formation of the mark will be described. FIG. 3 is an explanatory diagram of a mark forming method. In the figure, 10 is a processing setting screen. Reference numeral 15 denotes a vapor deposition region (depot region), and 16 denotes a hole formed by etching near the center of the vapor deposition region 15.

  When forming the mark, the vapor deposition region 15 is first formed, and then the hole 16 is formed in the central portion of the vapor deposition region 15 by etching. In this way, an image with a clear image structure can be created as a reference image. If a region including such a mark is used as a reference image, it is possible to more accurately determine the image shift and amount.

  In the above-described embodiment, the case where Fourier transform is used to obtain the direction and amount of image shift is taken as an example. However, the present invention is not limited to this. If the direction and amount of image shift can be obtained, the direction and amount of image shift can be determined using an image processing technique other than Fourier transform. it can.

It is a block diagram which shows one embodiment of the principal part of this invention. It is a figure which shows a process setting screen. It is explanatory drawing of the formation method of a mark.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ion gun 2 Optical system 3 Deflector 4 Amplifier 5 Amplifier 10 Processing setting screen 11 Reference image area 12 Processing area 13 Processing area 20 Image reading means 21 Image before drift 22 Image after drift 30 Calculation control means

Claims (4)

Providing at least one reference image region having a large reference image acquisition region and a smaller reference image acquisition region on the sample during FIB processing on the sample; and
The stage movement before the start of processing includes the scan image of the larger reference image acquisition area acquired before the stage movement and the direction of image shift from the scan image of the larger reference image acquisition area acquired after the stage movement. And calculating the amount, and positioning the stage based on the direction and amount of image shift obtained by the calculation,
At the time of ion beam processing, the scan image of the smaller reference image acquisition region acquired before performing the FIB scan for processing in the FIB processing region and the smaller one acquired after performing the FIB scan for processing in the FIB processing region Determination by calculation direction and amount of deviation from the scanned image image of the reference image acquisition area, and performing the adjustment of the bi chromatography beam deflection system based on the direction and amount of deviation of the image obtained by the calculation,
The drift correction method at the time of FIB automatic processing comprised by this .   2. The drift correction method during FIB automatic machining according to claim 1, wherein Fourier transform is used as means for obtaining the direction and amount of image shift. 2. The drift correction method during FIB automatic processing according to claim 1, wherein the direction and amount of image shift are obtained using image processing other than Fourier transform . A reference image setting means for setting at least one reference image area having a large reference image acquisition area and a smaller reference image acquisition area on the sample at the time of FIB processing on the sample;
Image reading means for reading an image of the reference image area at the time of FIB processing;
Arithmetic control means for receiving the output of the image reading means and performing the following processes (a) and (b);
(A) For the stage movement before the start of processing, the scan image of the larger reference image acquisition area acquired before the stage movement and the scan image of the larger reference image acquisition area acquired after the stage movement are used. Find the direction and amount of displacement by calculation
(B) At the time of ion beam processing, a scan image of the smaller reference image acquisition region acquired before performing the FIB scan for processing into the FIB processing region and acquired after performing an FIB scan for processing into the FIB processing region The direction and amount of image shift are obtained by calculation from the scanned image of the smaller reference image acquisition region.
Means for positioning the stage based on the direction and amount of image shift obtained by the processing (a) of the arithmetic control means;
Beam deflection system adjusting means for correcting the beam deflection system based on the direction and amount of image shift obtained by the process (b) of the arithmetic control means;
Drift correction apparatus during FIB automatic machining, characterized in that it comprises a.

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