JP2011180153A - Charged particle beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a downsized charged beam inspection apparatus, saving on a space, reducing a cost, preventing vibration, accelerating the speed, and having a high reliability of inspection, and large effects, especially for the case of a wafer having a large diameter, in a device for inspecting defects of a sample. <P>SOLUTION: A charged beam particle device is equipped with: a rotating stage on which a sample is placed; a uniaxial mobile stage that moves the rotating stage along a uniaxial direction; a vacuum chamber containing the uniaxial mobile stage; a first column for detecting a defect on the sample by irradiating the sample with light or a charged particle beam; and a second column for re-detecting the defect by irradiating the sample with a charged particle beam on the basis of the coordinates of the defect detected by the first column. A detector for detecting the defect has its detector plane facing toward the center of each column. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a charged particle beam apparatus that observes and processes a sample using a charged particle beam such as an electron beam or an ion beam.

  Among the observation targets of charged particle beam devices, in particular, semiconductor devices are attracting attention for inspection methods and processing methods using charged particle beams in addition to increasing the sensitivity of optical systems by miniaturizing circuit patterns to be formed. . In the inspection, an inspection apparatus using a scanning electron microscope (SEM) has been developed. In the inspection of a semiconductor wafer on which a semiconductor device is formed, a defect detection by an optical image or a charged particle beam scanning image, a review SEM for observing and classifying the defect, and a length measurement SEM for inspecting a pattern dimension are used. In addition, various techniques have been developed, such as processing of a defect portion using a focused ion beam apparatus (FIB), tilt observation of a sample using an SEM, and X-ray analysis. Due to the complexity of the structure and materials of semiconductor devices, it has become common to organize inspection data using a mixture of multiple inspection methods, and a technique for combining multiple inspection functions into a single device is also proposed. (For example, refer to Patent Document 1). On the other hand, the diameter of semiconductor wafers is increasing, and in particular, the charged particle beam method requires a vacuum vessel, so the apparatus must be enlarged. The above situation has lowered even the most important inspection reliability by nature, such as a decrease in throughput due to an increase in the cost and size of the inspection system, and an increase in the risk of foreign matter adhesion due to wafer transfer between complicated inspection processes. In particular, in an electron beam or ion beam apparatus, an increase in driving resistance and residual vibration due to an increase in the size of the positioning stage causes a decrease in throughput due to an increase in evacuation time in addition to a decrease in accuracy and an increase in movement time. Moreover, it has become a large cost burden for the user of the apparatus to install an inspection apparatus that requires a large vacuum container in an expensive clean room.

JP 2006-294482 A

  The present invention can reduce the size of an apparatus for inspecting a defect of a sample, and can save space, reduce cost, suppress vibration and increase the speed, and provide inspection reliability, and is particularly effective for a wafer having a large diameter. The purpose is to obtain a large charged beam inspection apparatus.

  In order to solve the above-mentioned problems, an embodiment of the present invention includes a plurality of inspection mechanisms that perform at least one inspection by a charged beam mechanism, and each inspection mechanism is arranged in a common vacuum container that is arranged substantially on one axis. A uniaxial movement mechanism that moves uniaxially between each of the inspection mechanisms provided, a rotary stage that places a sample and has a rotation axis on the uniaxial movement mechanism, and moves the sample between the inspection mechanisms by a uniaxial movement mechanism, In addition, the inspection position of the sample is adjusted to the inspection mechanism with the rotary stage, and the sample is inspected by the inspection mechanism.

  As described above, according to the embodiments of the present invention, the apparatus can be miniaturized, and space saving, cost reduction, vibration suppression and high speed, inspection reliability can be obtained, especially in the case of a wafer having a large diameter. A charged beam inspection apparatus having a large effect can be obtained.

The longitudinal cross-sectional view which shows schematic structure of a charged particle beam apparatus. The longitudinal cross-sectional view which shows schematic structure of a charged particle beam apparatus. The longitudinal cross-sectional view which shows schematic structure of a charged particle beam apparatus. The longitudinal cross-sectional view which shows schematic structure of a charged particle beam apparatus. FIG. 2 is a plan sectional view showing a schematic configuration of the charged particle beam apparatus. The top view explaining the movement state of the wafer on a stage. The top view of a wafer. The top view and side view which expanded the observation object on a wafer.

  An embodiment of the present invention will be described below. In order to cope with an increase in the diameter of a semiconductor wafer and a combination of inspection processes, a plurality of inspection mechanisms are provided in the same vacuum vessel, and a rotary stage and a uniaxial stage moving mechanism system are used for moving a sample. That is, the sample is moved between the inspection mechanisms by the uniaxial movement mechanism, and the inspection positioning on the sample wafer is performed by using the rotary stage and the uniaxial movement stage in common. As a result, the vacuum container is made half the size of the conventional XY moving stage, the increase in the weight of the movable part can be suppressed, and the size can be reduced. Thus, there are effects of space saving and cost reduction. Further, by bringing the two devices together, it is possible to prevent adhesion of foreign matters when the wafer moves between the devices. Furthermore, since unnecessary vibrations can be suppressed by the rotary stage, high-speed positioning is possible. In addition, the image information of each inspection mechanism and the accompanying information such as defect coordinates, height, size, and image contrast are shared to improve the reliability and operability of defect inspection and dimension measurement. The effect is particularly remarkable in the case of a large-diameter wafer having an outer diameter of 450 mm.

  FIG. 1 is a longitudinal sectional view showing a schematic configuration of a charged particle beam apparatus. Two charged particle beam columns are provided for one vacuum vessel 12 in which a wafer 8 as a sample is placed. One is a defect inspection SEM that irradiates the wafer 8 with an electron beam and detects a secondary signal generated on the wafer 8 to detect a defect. The other is an enlarged image of the defect detected by the inspection SEM. It is a defect review SEM classified based on feature quantities. The wafer 8 is first positioned under the column of the defect inspection SEM by the rotary stage 10 and the uniaxial moving stage 11 in the vacuum vessel 12.

  In the defect inspection SEM, although the spot size of the electron beam is small, the entire surface of the wafer 8 is to be inspected, so that the number of scans of the electron beam for constituting one screen is reduced and the speed is increased. The wafer 8 is irradiated with a high-current electron beam. The electrons emitted from the high-current electron source 1b are narrowed down by the first irradiation lens 2b and the limiting diaphragm 3b. Further, the convergence angle of the electron beam is adjusted by the second irradiation lens 4b and finally imaged on the wafer 8 by the objective lens 7b. Here, beam scanning is performed by the deflector 6b, an image signal is obtained by the detector 5b, and defect information on the sample surface is obtained. In the defect inspection SEM, a control electrode 13 for controlling the charging of the sample surface and the emitted electron trajectory is installed, and is detected with a predetermined sensitivity such as potential contrast due to charging, insulation state, foreign matter, pattern abnormality, and the like.

  Next, the wafer 8 that has been inspected is transported together with the rotary stage 10 under the defect review SEM in the vacuum vessel 12 with the uniaxial moving stage 11 being driven by the drive system 9. Defect information such as defect coordinates, size, and image contrast obtained by the defect inspection SEM is stored in a storage device (not shown), and is used as search information when a defect is searched for by the defect review SEM.

  The defect review SEM narrows down the electrons emitted from the electron source 1a with the first irradiation lens 2a and the limiting diaphragm 3a. Further, the electronic opening angle is adjusted by the second irradiation lens 4a, and finally the image is formed on the wafer 8 by the objective lens 7a, scanned by the deflector 6a, and a scanned image is obtained by the detector 5a. The defect review SEM searches for the defect based on the defect coordinates based on the defect information acquired by the defect inspection SEM, and captures an enlarged image when the defect is found. Based on the defect image, the defect type is classified by an arithmetic device (not shown). Based on the information on the defect, the user can specify the process in which the defect has occurred and investigate the cause of the defect.

  As described above, according to the configuration shown in FIG. 1, a series of operations from defect detection to defect classification of the wafer 8 can be realized at high speed and with low risk without waste. Further, in the defect inspection SEM, since a defect is extracted by a comparison process that takes a difference between a reference image having no defect and an inspection image, pixels that are not defective may be detected as a defect due to image noise or the like. Therefore, it is possible to easily inspect the defect coordinates that cannot be extracted by the defect review SEM by the defect inspection SEM.

  FIG. 2 is a longitudinal sectional view showing a schematic configuration of the charged particle beam apparatus, in which a defect review SEM and a tilted image observation SEM are provided in one vacuum vessel 12. The defect review SEM on the left side of FIG. 2 has the same configuration and function as those shown in FIG. In the right-side tilt image observation SEM, the electrons emitted from the electron source 1c are narrowed down by the first irradiation lens 2c and the limiting diaphragm 3c. Further, the opening angle of the electron beam is adjusted by the second irradiation lens 4c, and finally the image is formed on the wafer 8 by the objective lens 7c, the electron beam is scanned by the deflector 6c, and the scanning image signal is obtained by the detector 5c. obtain. In addition to the detector 5c, an X-ray detector can be used to analyze the material of the sample surface defect.

  In the inspection process, first, the upper wafer 8 is scanned with an electron beam at high speed by the deflector 6a of the defect review SEM, and the defect type is classified and displayed based on the obtained defect image. The wafer 8 that has completed the defect review is moved under the tilted image observation SEM by the movement of the rotary stage 10 on the uniaxial moving stage 11. Further, defect information such as the defect size, coordinates, and image contrast obtained by the defect review SEM is sent to a control device (not shown) of the tilted image observation SEM. The tilted image observation SEM irradiates the wafer 8 with a tilted electron beam, analyzes the defect unevenness and analyzes the components, and obtains detailed information. Since defects such as peeling are likely to occur at the peripheral edge of the wafer 8, the inclined image observation SEM can observe the peripheral edge of the wafer 8 in addition to the observation of the inclined image of the defect.

  FIG. 3 is a longitudinal sectional view showing a schematic configuration of the charged particle beam apparatus. A defect review SEM is provided on the left side and a focused ion beam apparatus (FIB) is provided on one vacuum container 12 on the right side. The defect review SEM has the same configuration and function as those shown in FIG. The FIB narrows ions emitted from the ion source 1d by the electrostatic irradiation lens 2d and the ion current limiting diaphragm 3d. Further, the ion beam is imaged on the wafer 8 by the electrostatic objective lens 7d, scanned by the deflector 6d, and an image signal is obtained by the ion emission electron detector 5d.

  In the inspection process, the type of defect of the wafer 8 on the rotary stage 10 is classified based on the defect image obtained by the defect review SEM. The wafer 8 that has completed the defect review is moved under the FIB by the movement of the rotary stage 10 on the uniaxial moving stage 11. Also, defect information such as defect size, coordinates, and image contrast obtained by the defect review SEM is sent to a control device (not shown) of the FIB. In FIB, a defect occurrence site is cut out and observed by a three-dimensional structure or X-ray analysis of the defect site.

  FIG. 4 is a longitudinal sectional view showing a schematic configuration of the charged particle beam apparatus, in which a defect review SEM and an optical inspection apparatus are provided in one vacuum vessel 12. In the optical inspection apparatus on the right side of FIG. 4, the light emitted from the light source 1e is imaged on the wafer 8 by the limiting aperture 3e and the optical microscope 14, and an image signal is obtained by the photodetector 5e. Since the optical inspection apparatus has a lower magnification than the defect review SEM, the entire surface of the wafer 8 is first inspected by the optical inspection apparatus, and the defect is enlarged by the defect review SEM based on the coordinates of the detected defect. Take an image and make a detailed observation. The configuration of the optical inspection apparatus includes a bright field method and a dark field method. In the dark field method, a laser beam is used as a light source. In addition, in the defect inspection of the wafer 8 before the pattern is formed, when the optical inspection apparatus and the defect review SEM are separate apparatuses, the correction accuracy of coordinates between the both apparatuses is low, and the optical inspection apparatus Although it is difficult to redetect the detected defect with the defect review SEM, in this apparatus, since both the optical inspection device and the defect review SEM are provided in one vacuum vessel 12, and the stage is shared, The problem of coordinate error is eliminated, and the defect detected by the optical inspection apparatus can be easily redetected by the defect review SEM.

  FIG. 5 is a plan sectional view showing a schematic configuration of the charged particle beam apparatus according to the present invention. The plan sectional view of the configuration shown in FIG. 1 is taken as an example, and a detector 5a and a deflector 6a of a defect review SEM are shown. The detector 5b and the deflector 6b of the inspection SEM are shown. The planar shape inside the vacuum vessel 12 has a short side with a dimension obtained by adding an allowance to the outer shape of the wafer 8, and a long side with a dimension obtained by adding the allowance to twice the outer shape of the wafer 8. The wafer 8 is moved in the longitudinal direction by a uniaxial moving stage 11 (not shown) inside the vacuum vessel and is rotated by a rotating stage 10 (not shown). The computer 19 controls both the control of the electron beam and the processing of the obtained image. Digital deflection control data is generated by the deflection control circuit 17 from the digital deflection data of the electron beam sent from the computer 19, converted into an analog deflection control signal by the deflection drive circuit 18, and sent to the deflector 6a or deflector 6b. . The computer 19 sends stage control data to the stage control circuit 20, and a stage drive signal is sent from the stage control circuit 20 to the stage drive circuit 21, so that the rotary stage 10 (not shown) and the uniaxial moving stage 11 (not shown) are driven. The

  First, the defect inspection of the wafer 8 is performed by the defect inspection SEM, and the signal detected by the detector 5b of the defect inspection SEM is converted from an analog signal to a digital signal by the signal processing circuit 16 and imaged by the image processing circuit 15. The defect is detected by comparison with a reference image having no defect, and the resulting data is sent to the computer 19 and stored in a storage device (not shown). Next, the wafer 8 is moved to the defect review SEM, and the wafer 8 is positioned so that the defect is found at the position of the coordinates of the stored defect. A signal detected by the detector 5a is imaged by the image processing circuit 15 and compared with a reference image having no defect to detect a defect. Alternatively, the defect is detected by comparing with the stored image of the defect inspection SEM. If the image processing circuit 15 cannot correct the positional deviation of the defect due to a mechanical error during the movement of the stage, the deflection control circuit 17 adjusts the deflection of the electron beam, or the stage control circuit 20 adjusts the position of the wafer 8. Adjust to correct. When a defect is detected, the defect review SEM changes the enlargement magnification, takes a high-magnification image, and stores the image in a storage device (not shown) of the computer 19. The computer 19 calculates feature quantities such as the size and shape of the defect from the high-magnification image, and classifies the defect. This step is repeated for the number of defects or the number of specified conditions. As for the positional deviation of defects, a plurality of positional deviation information is stored as wafer positional distortion information in a storage device (not shown) of the computer 19 and can be corrected with high accuracy by techniques such as polynomial approximation and interpolation calculation of memory mapping values. It is. Further, the computer 19 controls the focusing of the electron beam of the defect review SEM based on the information of the focusing of the electron beam when acquiring the image of the defect inspection SEM.

  The movement of the uniaxial moving stage 11 shown in FIG. 1 is detected by a known laser interferometer (not shown), and the rotation of the rotary stage 10 is detected by a known angle scale reading device (not shown), and includes a position vibration. Correction and rotation angle correction are performed by the stage control circuit 20.

  The circuit configuration shown in FIG. 5 shares the image processing circuit 15, signal processing circuit 16, deflection control circuit 17, and deflection drive circuit 18 of the defect inspection SEM and defect review SEM, but by providing two systems, The control algorithm can be simplified and speeded up, and in the event of a failure, it can be substituted.

  FIG. 6 is a plan view for explaining the movement state of the wafer on the stage. The distance L is the distance between the center positions of the two SEM columns, and the position when the wafer 8 is positioned at the extreme end when the uniaxial movement in the vacuum apparatus 12 is indicated by a broken line. A great advantage of the rotary stage system according to the present invention is that, if it is small and light and has a strict rotational symmetry, there is no vibration in principle due to the moment of movement during movement. Instead, as shown in FIG. 6, rotation of the coordinate system occurs at the observation position. Therefore, processing for obtaining an erect image is required.

  It is assumed that the orthogonal coordinates on the wafer are X and Y, the polar coordinates are r and θ, and the wafer 8 is at the observation position in FIG. The relationship between orthogonal coordinates (X, Y) and polar coordinates (r, θ) is given below.

X = r cos θ
Y = rsinθ
The stage movement amount of the rotating system with reference to the reference orthogonal coordinates (X ′, Y ′) on the stage is given as follows.

X ′ = r
θ ′ = π−θ
Using the above equations, the defect coordinates are corrected.

  FIG. 7 is a plan view of a wafer and shows an example of an image capturing process in consideration of the rotation of the wafer. The pattern 22 on the wafer is imaged in the deflection range 23 of the electron beam at polar coordinates (r, θ). Since the image obtained by imaging the pattern 22 with the orthogonal coordinates (X, Y) in the defect inspection SEM is in the direction shown in FIG. 7C, even in the case of the defect review SEM shown in FIG. In order to obtain an erect image of the imaging range 24 as shown in (c), it is necessary to rotate the image by the following size.

θ ″ = π + θ
Accordingly, as shown in FIG. 7B, an image is obtained with the deflection range 23 having a size including the imaging range 24, and rotated as shown in FIG. 7C. As the image rotation method, a method of changing the scanning direction of the electron beam and a method of rotating by image processing are possible.

  FIG. 8 is an enlarged plan view and side view of the observation target on the wafer. As shown in FIG. 8A, the image detected by the SEM is shaded on the observation object 25. Therefore, the defect inspection SEM using the non-rotating XY stage and the defect review SEM have a detector XY for defects. It is necessary to match the directions on the plane so that the shadows are generated in the same way. When capturing high-angle electrons in a three-dimensional observation target, the light and darkness and shadow direction rotate, and it may be important as information when the unevenness of the observation target is classified. Caution must be taken. As shown in the side view of FIG. 8B, when the convex observation object 25 in the imaging range 24 on the wafer 8 is imaged by the detector 5b, as shown in the plan view of FIG. An image in which the observation object 25 is shaded is obtained. In the configuration of the present invention, as shown in FIG. 5, since the directions of the detectors 5a and 5b coincide with the centers of the respective columns indicated by the alternate long and short dash line, the observation that occurs in the image between the respective columns. The shadow direction of the subject is not different.

  As described above, according to the embodiments of the present invention, it is possible to reduce the size of the apparatus, save space, reduce costs, suppress vibrations, and achieve high reliability by reducing foreign matter, and in particular, a charged beam inspection apparatus for a wafer having a large diameter. The effect is remarkable.

1a, 1b, 1c Electron source 1d Ion source 1e Light sources 2a, 2b, 2c First irradiation lens 2d Electrostatic irradiation lenses 3a, 3b, 3c, 3e Limiting aperture 3d Ion current limiting apertures 4a, 4b, 4c Second irradiation lens 5a , 5b, 5c detector 5d ion emission electron detector 5e photodetectors 6a, 6b, 6c, 6d deflectors 7a, 7b, 7c objective lens 7d electrostatic objective lens 8 wafer 9 drive system 10 rotating stage 11 uniaxial moving stage 12 Vacuum container 13 Control electrode 14 Optical microscope 15 Image processing circuit 16 Signal processing circuit 17 Deflection control circuit 18 Deflection drive circuit 19 Computer 20 Stage control circuit 21 Stage drive circuit 22 Pattern 23 Deflection range 24 Imaging range 25 Observation object

Claims (3)

A rotating stage on which the sample is mounted;
A single axis moving stage for moving the rotary stage in a single axis direction;
A vacuum chamber containing the uniaxial moving stage;
A first column for detecting defects on the sample by irradiating the sample with light or a charged particle beam;
A second column that re-detects the defect by irradiating the sample with a charged particle beam based on the coordinates of the defect detected in the first column;
The charged particle beam apparatus according to claim 1, wherein the direction of the detection surface of the detector for detecting the defect is directed to the center of each column. A vacuum container for storing the sample;
A first column that irradiates the sample with light or a charged particle beam and images the sample based on an image signal from a first detector;
A second image is obtained by irradiating the sample with a charged particle beam based on the image of the sample imaged in the first column and re-imaging or processing the image at the imaging position based on an image signal from a second detector. A charged particle beam device comprising a column,
A rotary stage provided in the vacuum vessel and on which the sample is placed;
A uniaxial movement mechanism provided in the vacuum vessel and uniaxially moving the rotary stage;
The direction of the detection surface of the first detector is toward the center of the first column,
The charged particle beam device according to claim 1, wherein the direction of the detection surface of the second detector is directed to the center of the second column. In the description of claim 1 or claim 2,
The charged particle beam apparatus according to claim 1, wherein a convex shape is formed on the observation target surface of the sample.

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