JP4848310B2 - Microscope with probe and probe driving method - Google Patents

Description

  The present invention relates to a microscope with a probe.

  In the process of manufacturing semiconductor integrated circuits such as microprocessors and semiconductor memories, measurement of wiring dimensions using an electron microscope and detection of foreign matter / defects on a wiring pattern are performed to investigate product characteristics. A scanning electron microscope (SEM) apparatus may be used for inspecting abnormal electrical characteristics of individual transistors constituting a semiconductor sample. At the time of inspection by SEM, a semiconductor sample is shaved in advance, one electrode of the transistor is exposed, and a fine probe (probe) having a tip radius of about 50 nm is brought into direct contact with the electrode of the transistor.

  In order to measure the electrical characteristics of each transistor using a probe, the positional relationship between the probe tip and the sample part to be contacted with the probe tip is grasped from the electron microscope image, and the probe is driven until the probe contacts the sample. To do. That is, the probe is brought close to the sample or the sample fixing base, and the movement of the probe is stopped as soon as it is detected that the probe has contacted the sample or the sample fixing base.

  What should be noted when bringing the probe close to or in contact with the sample or the sample stage is to set the probe speed and detect the contact. Conventionally, the probe speed is set by an operator viewing an electron microscope image. As a method for detecting contact, there are a method for detecting contact from an electrical signal such as a change in contact resistance and a change in current flowing through the probe, and a method for detecting contact by detecting a contrast change in an electron microscope image.

JP 2005-167146 A JP-A-5-299048

  As a result of intensive studies by the inventor, it has been found that when the operator sets the probe speed by visually observing an electron microscope image, it is difficult to determine the probe speed unless the distance between the probe and the sample is known. If the probe speed is set high even though the distance between the probe and the sample is short, the probe or sample piece may rapidly approach the sample or sample stage and the probe or sample piece may be damaged. . In addition, if the probe speed is set to be slow although the distance between the probe and the sample is long, the time until contact becomes too long. For this reason, it is necessary to drive the probe at a desired speed in accordance with the distance between the probe and the sample.

  Contact detection using a change in contact resistance or a change in current becomes very difficult when the sample or sample piece is an insulator. Further, the contact detection based on the contrast change from the electron microscope image is ambiguous because the operator visually determines the contact by visually checking the electron microscope image. If the probe is continuously driven without noticing contact, the probe and the sample piece may be damaged.

  An object of the present invention relates to providing a microscope with a probe that can quickly bring a probe tip into contact with a sample without fear of damaging the probe or the sample.

  The microscope with a probe of the present invention calculates the distance from the probe to the sample by recognizing the image obtained from the microscope while the probe is approaching the sample direction and calculating the probe area in the recognition region. To do.

  According to the present invention, there is no fear of damaging the probe or the sample, and the tip of the probe can be brought into contact with the sample quickly.

  Embodiments of the present invention will be described below with reference to the drawings. In order to facilitate understanding, the same reference numerals are given to the same members in the following drawings. The position and number of the probes are arbitrary, but in the following description, in order to simplify the description, the number of probes will be described as one. In each embodiment, it is assumed that a scanning electron microscope (SEM) is used as a microscope, for example.

  FIG. 1 is a conceptual diagram showing an example of a microscope with a probe. The microscope with a probe includes a scanning electron microscope 1, a probe 2, a signal detector 3, an analog signal line 4, an A / D converter 8, an image display 9, a magnification changing unit 10, and image processing. Unit 11, length measurement processing unit 12, length measurement data processing unit 13, storage unit 14, probe drive controller 15, probe drive mechanism 16, and sample stage 17.

  The sample 5 is mounted on the sample stage 17 and is movable. As shown in FIG. 1, the microscope is positioned in a direction perpendicular to the sample surface (Z direction). A method of bringing the tip of the probe 2 into contact with the part 6 of the sample 5 will be described. The operation of bringing the tip of the probe 2 into contact with the portion 6 of the sample 5 is performed by bringing the probe 2 closer to the sample 5 from above in the vertical direction. That is, in the microscope with a probe of this example, the direction in which the probe 2 is moved when the probe 2 is brought into contact with the sample 5 (Z-axis direction) coincides with the optical axis of the microscope.

  Analog information such as secondary electrons and reflected electrons obtained by the signal detector 3 using the scanning electron microscope 1 is transmitted to the A / D converter 8 via the analog signal line 4 and is digitally converted. The digitally converted data is transmitted to the image display 9 and displayed as a two-dimensional image. This image is hereinafter referred to as an SEM image. The SEM image displayed on the image display 9 can be enlarged or reduced by the magnification changing unit 10.

  In the microscope with a probe, using the SEM image, the sample 5 or the probe 2 is moved so that the tip 7 of the probe 2 is directly above the portion 6 of the sample 5 to be brought into contact with the tip 7 of the probe 2, and then the SEM While calculating the distance from the tip 7 of the probe 2 to the sample site 6 using the image, the probe 2 is driven downward and brought into contact with the sample site 6. In calculating the distance from the tip 7 of the probe 2 to the sample region 6, the SEM image obtained by the image display 9 is analyzed by the image processing unit 11, and the length measurement processing unit 12 and the length measurement data are calculated based on the analysis result. This is performed by the processing unit 13 and stored in the storage unit 14. The probe speed is determined by the probe drive controller 15 based on the analysis result, and the probe drive mechanism 16 drives the probe 2 in the Z-axis direction at the probe drive speed.

  Before the probe is driven, the part 6 of the sample 5 with which the tip 7 of the probe 2 is brought into contact is found and surrounded by an image recognition area frame 18 as shown in FIG.

  The operation of bringing the probe tip into contact with the sample site in the microscope with a probe of the present invention will be described below with reference to the flowchart of FIG. First, in step S101, as shown in FIG. 2B, the image processing unit 11 recognizes the SEM image and adjusts the sample position and the microscope so that the sample region 6 comes to the image center 19. As a result, the SEM image displayed by the image display unit 9 is such that, as shown in FIG. 2 (a), for example, the sample region 6 that has been out of the image center 19 is first displayed as shown in FIG. 2 (b). 19 is located. By this operation, the sample site 6 where the probe tip 7 is to be brought into contact with the image center 19 of the microscope is always positioned regardless of whether the magnification of the microscope is enlarged or reduced.

  Next, in step S102, the length measurement processing unit 12 focuses on the sample region 6 and detects the Z-axis information WD0 of the sample region 7. The Z-axis information WD0 is a working distance that is a distance from the objective lens of the microscope 1 to the sample portion 7. Next, in step S <b> 103, an image of the sample region 6 in a state where the probe 2 is not contained is acquired and stored in the storage unit 14.

  Next, in step S103, if one of the movement axes (Y ′ axis) of the sample stage 17 or the probe 2 is the image center direction as shown in FIG. The sample 5 or the probe 2 is moved in the other movement axis (X′-axis direction), and as shown in FIG. 4B, the probe tip 7 shows the direction of the image center 19 on the Y′-axis. To do. In step S <b> 104, the image processing unit 18 confirms whether the probe tip 7 has reached the image center 19. If not, in step S105, the sample position or the probe 2 is moved in the Y'-axis direction. This movement and confirmation are performed, for example, every few milliseconds. When the probe tip 7 reaches the image center 19, in step S107, the image processing unit 11 acquires an image of the sample region 6 in which the probe 2 is contained and stores the image in the storage unit 14. In step S108, the image processing unit 11 compares the image of the sample part 6 in the state without the probe 2 acquired in step S103 with the image of the sample part 6 in the state of the probe 2 acquired in step S107. Then, the difference is taken, the difference image is recognized as the probe 2, and the luminance of the probe 2 is stored in the storage unit 14. Thereafter, the process proceeds to the flowchart of FIG.

  Next, a description will be given below with reference to the flowchart of FIG. In step S <b> 201, the image processing unit 11 determines whether the region having the luminance of the probe 2 in the image recognition region 18, that is, the probe 2 is 20% or more of the image recognition region 18. This is to improve the calculation accuracy because the distance between the probe tip 7 and the sample part 6 is calculated based on the area occupied by the probe 2 in the image recognition region 18 as described below. If it is 20% or more, in step S207, the image processing unit 11 performs focus synthesis, and an image in a state in which both the probe tip 7 and the sample region 6 are focused is displayed on the image display 11. Thereafter, the process proceeds to the flowchart of FIG.

  In step S201, if it is less than 20% as shown in FIG. 6A, it is determined in step S202 whether the current magnification of the microscope 1 is the maximum magnification. If it is not the maximum magnification, the magnification is enlarged by the magnification changing unit 10 in step S203. For example, as shown in FIG. 6B, the image is enlarged from 1000 times to 3000 times. Next, in step S204, the autofocus function is used to focus on the height of the probe tip 7, and the process returns to step S201. The region having the brightness of the probe 2 in the image recognition region 18 is again the image recognition region. Whether 20% or more of 18 is determined. If the current magnification of the microscope is the maximum magnification in step S202, it is determined in step S205 whether the current image recognition area 18 is 1/64 of the initial area. If it is not 1/64, the area of the image recognition area 18 is halved in step S206, the process returns to step S201, and the area having the brightness of the probe 2 in the image recognition area 18 is again the image recognition area. Whether 20% or more of 18 is determined. In step S205, when the current image recognition area 18 is 1/64 of the initial area, the area having the brightness of the probe 2 in the image recognition area 18 is given up to be 20% or more of the image recognition area 18, Proceed to step S207.

  Next, a description will be given below with reference to the flowchart of FIG. In the microscope with a probe of the present invention, the distance between the probe tip 7 and the sample portion 6 is calculated based on the area occupied by the probe 2 in the image recognition region 18 to determine the probe driving speed. FIG. 8 is a diagram for explaining the positional relationship between the probe tip 7 and the sample portion 6. This will be described below with reference to this figure.

  First, in a state where the probe 2 shown in FIG. 8A is not driven in the Z-axis direction, the length measurement processing unit 12 focuses on the probe tip 7 and detects the Z-axis information WD1 of the probe tip 7. WD 1 is a working distance of the probe tip 7. This can be obtained from a current value necessary for focusing on a predetermined position in the focus function provided in the scanning electron microscope. Then, a difference from the working distance WD0 of the sample part 6 stored in the storage unit 14 is obtained to obtain a distance Z1 between the probe tip 7 and the sample part 6.

  Next, in step S <b> 302, the image processing unit 11 measures an area A <b> 1 occupied by the probe 2 (region having the luminance of the probe 2) in the image recognition region 18. In step S303, the probe drive controller 15 sends a probe drive speed v1 corresponding to the distance Z1 to the probe drive mechanism 16, and the probe drive mechanism 16 drives the probe 2 downward in the Z-axis direction at a speed v1 for a predetermined time T seconds. Let At this time, information on the probe driving speed is also sent to the length measurement data processing unit 13.

  Next, in step S304, the area Ai occupied by the probe 2 in the image recognition region 18 after driving the probe is measured. In step S305, the length measurement data processing unit 13 calculates the distance between the probe tip 7 and the sample region 6 from the change in the area Ai. Hereinafter, such a calculation method will be described with reference to FIG.

FIG. 8A shows a state before the probe is driven, a plan view displayed on the image display 9 is shown on the left, and a cross-sectional view along the line aa ′ in the plan view is shown on the right. In the cross-sectional view of FIG. 8A, a line segment connecting the end of the cross section of the probe 2 and a reference point (for example, an objective lens of a microscope) of the Z-axis information is lowered from the reference point to the sample region 6 (that is, Z The relationship between the angle θ1 formed by the perpendicular line (parallel to the axis) and the distance between the reference point and the probe tip 7, that is, the working distance WD1 of the probe tip 7 is obtained by the following equation (1).
θ1 = tan ⁻¹ ((L / 2) WD1) (1)
Here, L represents the thickness of the probe 2 at the end of the image recognition area 18.

FIG. 8B shows a state after the probe is driven. As in FIG. 8A, the left side is a plan view displayed on the image display 9, and the right side is along the aa ′ line of the plan view. FIG. In the cross-sectional view of FIG. 8B, a line segment connecting the end of the cross section of the probe 2 and a reference point (for example, an objective lens of a microscope) of the Z-axis information is lowered from the reference point to the sample region 6 (that is, Z The relationship between the angle θi formed by the perpendicular line (parallel to the axis) and the distance between the reference point and the probe tip 7, that is, the working distance Wi of the probe tip 7 is obtained as in the following equation (2).
θi = tan ⁻¹ ((L / 2) WDi) (2)

Here, A is an area occupied by the probe 2 in the image recognition region 18, and φ is a solid angle when the probe is viewed from the electron gun.
A∝φ (3)
In addition, θ is an angle formed by a line segment connecting the end of the cross-sectional view of the probe 2 and the reference point of the Z-axis information, and a perpendicular drawn from the reference point of the Z-axis information to the sample part 6; When the probe 2 is approximated by a circle,
φ = α × 2π (1-cos θ) (4)
There is a relationship. Here, α is a constant.

Therefore, the area occupied by the probe 2 in the image recognition region 18 in the state before the probe driving in FIG. 8A is A1, and the probe 2 is in the image recognition region 18 in the state after the probe driving in FIG. If the area occupied is Ai, the following relationship can be derived.
A1 = β × 2π (1-cos θ1) (5)
Ai = β × 2π (1-cos θi) (6)
Here, β is a proportionality constant.

Therefore, from the equations (1) to (6),
WDi = (L / 2) / tan (cos ⁻¹ (1- (Ai / A1) (1-cos (tan ⁻¹ ((L / 2) / WD1)))) (7)
The relationship can be guided.
Further, the distance Zi between the probe tip 7 and the sample portion 6 in the state of FIG. 8B is obtained as in the following equation (8).
Zi = WD0-WDi (8)
Therefore, the value of the distance Zi between the probe tip 7 and the sample portion 6 can be obtained from the area occupied by the probe 2 in the image recognition region 18 using the equations (7) and (8).

  Returning to the flowchart of FIG. In step S305, the length measurement data processing unit 13 calculates Zi as described above and sends it to the probe drive controller 15. In step S306, the probe drive controller 15 determines the probe drive speed vi corresponding to the distance Zi and sends it to the probe drive mechanism 16 and the length measurement data processing unit 12. In step S307, the probe drive mechanism 16 drives the probe 2 downward in the Z-axis direction at a speed vi for a predetermined time T seconds.

  In step S308, the length measurement data processing unit 13 determines whether the probe drive speed vi is the minimum speed vmin. In the case of the minimum speed, the process proceeds to the flowchart of FIG. If it is not the minimum speed, the image processing unit 11 confirms the position of the probe tip 7 in step S309, and if it is deviated from the center of the observation image as shown in FIG. 9A, as shown in FIG. 9B. The sample position and the horizontal position of the microscope and the probe 2 are adjusted so as to come to the image center 19. Thereafter, i is incremented by 1 in step S320, and the process returns to step S304.

  Next, description will be made below with reference to the flowchart of FIG. When the probe drive speed reaches the minimum speed vmin, the length measurement data processing unit 13 detects the contact between the probe tip 7 and the sample portion 6 based on the area occupied by the probe 2 in the image recognition region 18. In step S401, i is incremented by 1. In step S402, the image processing unit 11 measures the area Ai occupied by the probe 2 in the image recognition region 18. In step 403, the length measurement data processing unit 13 determines whether the area Ai is smaller than the area A (i-1) occupied by the probe 2 in the image recognition region 18 measured last time. When the area is small, it means that the probe 2 has moved downward in the Z-axis direction and the probe tip 7 is not yet in contact with the sample site 6. The probe 2 is driven downward at a speed vmin for a predetermined time T seconds in the Z-axis direction, and the process returns to step S401. In step S403, if the area is the same as or larger than the previous time, it is determined that the probe tip 7 is in contact with the sample region 6 and the probe 2 does not move further downward in the Z-axis direction. In S405, the driving of the probe 2 is finished, and the operation of bringing the probe tip 7 into contact with the sample region 6 is finished. Such automatic contact detection makes it possible to bring the tip of the probe into contact with the sample site with minimal damage to the sample and the probe.

  In combination with the contact detection method based on area changes as described above, contact detection such as measurement of contact resistance, which has been used for detecting contact between the probe and the sample, and current flowing from the sample to the probe is performed. Also good.

  The present invention can be used for a microscope with a probe.

It is a block diagram which shows an example of a structure of a microscope with a probe. (A) And (b) is a schematic diagram explaining designation | designated of an image recognition area | region and a movement to the image center. It is a flowchart explaining the operation | movement which contacts a probe front-end | tip to a sample site | part. (A) thru | or (c) is a schematic diagram explaining the operation | movement which moves a probe front-end | tip just above a sample site | part. FIG. 4 is a flowchart for explaining an operation of bringing a probe tip into contact with a sample site following the flowchart of FIG. (A) And (b) is a schematic diagram explaining the operation | movement which adjusts the area which the probe in an image recognition area occupies. FIG. 6 is a flowchart for explaining an operation of bringing a probe tip into contact with a sample site following the flowchart of FIG. 5. It is a figure explaining the positional relationship of a probe front-end | tip and a sample site | part, (a) is a top view, (b) is sectional drawing. (A) And (b) is a schematic diagram explaining the operation | movement which corrects the shift | offset | difference of a probe position. FIG. 8 is a flowchart for explaining the operation of bringing the probe tip into contact with the sample site following the flowchart of FIG. 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scanning electron microscope 2 Probe 3 Signal detector 4 Analog signal line 5 Sample 6 Sample part 7 Probe tip 8 A / D converter 9 Image display 10 Magnification change part 11 Image processing part 12 Length measurement part 13 Length measurement data Processing unit 14 Storage unit 15 Probe drive controller 16 Probe drive mechanism 17 Sample stage 18 Image recognition area 19 Image center

Claims (9)

A sample stage on which the sample is placed;
A microscope for observing the sample;
A probe,
Probe driving means for driving the probe;
Image processing means for processing an image observed by the microscope and measuring an area occupied by the probe in a predetermined image recognition region;
A length measurement processing means for measuring a distance from a reference position to each of the tip of the probe and each of the sample parts in the image recognition area based on a focus condition;
Based on the change of the area occupied by the probe in the image recognition region due to the driving of the probe and the distance from the reference position to the tip of the probe and each of the sample parts in the image recognition region, A microscope with a probe, comprising: a length measurement data processing means for calculating a distance between a tip and a sample part in the image recognition region.   The probe driving means switches a plurality of speeds stepwise according to the distance between the probe tip and the sample part so that the drive speed becomes slower as the probe tip approaches the sample part. 2. The microscope with a probe according to claim 1, wherein the probe is driven in a direction approaching the sample portion.   The probe is driven in a direction approaching the sample region, and when the area occupied by the probe in the image recognition region measured at a predetermined time interval does not change, the driving of the probe is stopped. The microscope with a probe according to claim 1. A sample stage on which the sample is placed;
A microscope for observing the sample;
A probe,
A probe driving mechanism for driving the probe;
Process the observation image by the microscope, calculate the area occupied by the probe in a predetermined image recognition region,
Calculate the distance from the reference position to the tip of the probe and each of the sample parts in the image recognition area based on the focus condition,
Based on the change of the area occupied by the probe in the image recognition region due to the driving of the probe and the distance from the reference position to the tip of the probe and each of the sample parts in the image recognition region, A microscope with a probe, comprising: an arithmetic unit that calculates a distance between a tip and a sample portion in the image recognition region.   The probe driving mechanism switches a plurality of speeds stepwise according to the distance between the probe tip and the sample part so that the drive speed becomes slower as the probe tip approaches the sample part. The probe-equipped microscope according to claim 4, wherein the probe is driven in a direction approaching the sample portion.   The probe is driven in a direction approaching the sample region, and when the area occupied by the probe in the image recognition region measured at a predetermined time interval does not change, the driving of the probe is stopped. The microscope with a probe according to claim 4. Measure the position in a direction perpendicular to the microscope image of a predetermined part of the sample selected as the image recognition area in the microscope image based on the focus condition,
Place the tip of the probe directly above the image recognition area,
Measure the position of the probe tip in the direction perpendicular to the microscope image based on the focus condition,
Driving the probe in a direction in which the probe approaches the sample site;
Measure the area occupied by the probe in the image recognition region in the microscope image,
The distance between the tip of the probe and the sample part based on the change in the area occupied by the probe in the image recognition region due to the driving of the probe and the vertical position of the probe tip and the sample part A probe driving method characterized by:   In driving the probe, a plurality of speeds are stepped according to the calculated distance between the tip of the probe and the sample portion so that the driving speed becomes slower as the tip of the probe approaches the sample portion. The probe driving method according to claim 7, wherein the probe is driven in such a direction that the probe is driven in a direction approaching the sample region.   8. The probe according to claim 7, wherein when the probe occupies the area occupied by the probe in the image recognition region measured at a predetermined time interval, the probe is stopped. Driving method.

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