JP4472861B2 - Predetermined location access method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily accessing a predetermined predetermined location such as a semiconductor device using an electron beam apparatus or a focused ion beam apparatus, and more particularly to a predetermined location access method suitable for defect analysis of a memory having a repeated pattern. About.
[0002]
[Prior art]
In the technology of semiconductor device evaluation and analysis and defect correction using an electron beam apparatus or a focused ion beam apparatus, the positioning of a specific location is a very important matter and is a time-consuming and troublesome operation. Even if the position information of a specific location is known, it is not easy to capture this within the field of view of the electron beam apparatus or the focused ion beam apparatus. Conventionally, this is done by making full use of a technique such as pattern matching while controlling the position of the sample stage on which the sample is placed in the above apparatus. However, in a normal high-precision stage, the positioning accuracy is 1 to 2 μm, and in particular, access to a specific location is extremely time-consuming and troublesome work as ultra-fine semiconductor devices in recent years and the arrangement structure of the same pattern progress. It has become. The pattern matching method is ineffective for the same repetitive pattern in principle, and recent memories have several hundred or more identical repetitive patterns per μm, and the sample stage can be driven in this order. In order to achieve this, it is necessary to use an ultra-high accuracy stage using a laser interferor or the like. However, this laser interferor itself is expensive, and it is necessary to drive the laser system together with a 5-axis drive stage, which makes it extremely difficult to adopt an ultra-high precision stage. is there.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide an electronic device that allows easy access to a specific location even for a sample having hundreds or more of the same repetitive pattern in μm units without using an expensive ultra-high precision stage. An object of the present invention is to provide a positioning method in a beam apparatus or a focused ion beam apparatus.
[0004]
[Means for Solving the Problems]
In the present invention, in an electron beam apparatus or a focused ion beam apparatus, a first reference point as an origin is imprinted on a sample surface, and this is positioned at a corner opposite to the direction in which the target point exists in the microscope field of view as a reference. A specific point around the end in the direction in which the target point exists in the microscope field is marked as a second reference point, and the end in the microscope field in the direction in which the target point exists using the second reference point as a new reference A specific point in the periphery is engraved as the next reference point, and this is repeated until the target point enters the microscope field of view. When the target point enters the microscope field of view, the target position is within the field of view based on the reference point. I tried to access with.
According to the present invention, in a sample having an array structure in which a plurality of cells are arrayed, a first reference point is formed by etching or deposition with a beam of an electron beam apparatus or a focused ion beam apparatus on a corner cell of the array structure including a target cell. A step of marking the second reference point on a cell around the edge of the microscope image in the direction in which the target cell is present in the microscope image including the first reference point, and the position of the second reference point is the microscope A sample moving step of moving the sample so as to overlap the position of the first reference point in the image;
An image acquisition step for acquiring a new microscope image including the second reference point, and a reference for marking a new reference point on a cell around the end of the new microscope image in the direction in which the target cell exists in the new microscope image A dot marking process.
In the sample moving process, the first reference point and the second reference point are pattern-matched.
Further, the reference point marking step, the sample moving step, and the image acquisition step are repeatedly performed.
Further, the cursor is moved to the target cell on the microscope image, and the target cell is moved to the center of the image.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
For example, if a tester can identify a defective cell in a memory in which cells with the same pattern are arranged in the column direction and the row direction in the order of several hundreds, and want to observe a cross section with a scanning ion microscope, the position information of the defective cell can be obtained from the corner cell. It becomes the origin P1, that is, the coordinate reference (1, 1) and becomes the known coordinate information (m, n). FIG. 3 is a schematic diagram of the memory, in which A is an overall view and B is an enlarged partial view thereof. FIG. 4 is a scanning ion microscope image of 64MDRAM, where A is a planar image of the arranged cell group, and B is a cross-sectional observation view of the specific cell. However, as described above, it is not always easy to capture the defective cell in the microscope field of view. The origin was confirmed by the microscopic field as the position information of the defective cell (m, n) is, for example, a (125,220), it is extremely difficult to access counted in rows and columns direction. The specified observation cell position must be counted while moving the field of view, not the range that can be captured in the same microscope field of view together with the origin at a magnification that can be recognized by each cell. However, since counting while moving the visual field is easy to make a mistake and actually difficult, it is easier to specify and access the position by moving the sample stage. However, the movement information of this general sample stage has low accuracy as described above, and is not useful for specifying a cell of a recent miniaturized memory. Therefore, the present invention has come up with the idea that the position information is determined on an accurate observation screen without using any method.
[0006]
First the location of the origin cell P ₁ begin to grasp in the microscope image. When the surface of the sample 1 (device) is covered with the protective film 2 as shown in FIG. 1A, ions are placed near the origin 1 of the corner using a focused ion beam device as shown in FIG. open the window 3 by irradiating a beam (FIB), and can be observed a plurality of cell groups including the origin cell P ₁ to expose the device surface to confirm the position of the origin cell P ₁ under a microscope image. If the distance between the cells is known, this is not necessary, but if the distance is unknown, the distance between the origin and the target defective cell is calculated by measuring the row interval and the column interval with a microscope image. The magnification of the observation image is set to a field of view around 100 μm × 100 μm where the cell can be observed, and the origin cell P ₁ is positioned at the corner of the field of view. And stamping a second reference point P ₂ selects a predetermined position in the direction of the defective cell 4 as viewed from the origin cell P _1. The second selection of the reference point P ₂ is a point as close as possible to the defective cell 4 within the observation field of view, i.e. it is advantageous for fast access to select a surrounding image region on the opposite side of the origin cell P ₁ . It is advantageous in terms of work to specify coordinates that are easily cut in units of cells or lengths that can be easily handled as position information. In addition, when the surface of the device is a sample whose surface is covered with the protective film 2, the mark is etched by etching, and when the surface is exposed, the mark is attached by deposition. And it is advantageous that this mark is easy to identify.
[0007]
Second reference point P ₂ Positioning but moves the sample stage of the focused ion beam device if it is engraved, the second reference point P ₂ as positioned at the corners in observation of the origin cell P ₁ previously viewing the corner portion of the field of view To do. What is important here is to position the second reference point P ₂ to the new origin position by using a pattern matching technique. Although the position accuracy of the high-precision sample stage driving mechanism is at most 1 to 2 μm, the position information of the second reference point P ₂ which is secured with high accuracy by measuring in the microscope image with respect to the origin cell P ₁ is The pattern matching technology can secure positioning accuracy of 0.1 μm or less without depending on the position accuracy of the high-precision sample stage drive mechanism. To perform the tasks that are stamped selects a third reference point P ₃ where that could position the second reference point P _2. The third selection of the reference point P ₃ is the same as the selection of the previous second reference point P _2, to select a point easily handled as the position information in the peripheral region of the screen close to the defective cell as a target in the observation field. Selected third reference point P ₃ Serves as a reference point in the next observation field is stamped similarly to the second reference point P ₂ of the first. This operation is repeated until the target defective cell 4 is captured within the observation field. Although depending on the size of the sample 1 and the position of the defective cell 4, in general, the target can be captured in the microscope field by several operations. From the final reference point _Pf , the x-direction position and the y-direction position can be measured in the observation field to determine the defective cell 4 at the target point, and the position accuracy can be secured to about 0.1 μm. Therefore, in the case of a device whose surface is covered with a protective film, the target defective cell 4 can be identified and exposed by irradiating the focused ion beam to the region centered on the position.
[0008]
When the target defective cell 4 can be captured in the observation visual field, the position of the defective cell 4 is not necessarily in the central portion in the observation visual field. In that case, it is effective to apply the cursor function of the focused ion beam apparatus. If combined with x-coordinate position and the y-coordinate position of the cursor 5 to the final reference point P _f as shown in A of FIG. 2, the intersection of the cursor 5 on the final reference point P _f be moved sample stage appropriate Since it is linked, the target defective cell 4 is not lost. As shown in FIG. 2B, even if the defective cell 4 is moved to the vicinity of the center in the observation field, the final reference point P _f specified by the cursor 5 is determined. On the other hand, since the position of the target defective cell 4 is 1 cell interval in the x direction and 6 cell intervals in the y direction does not change, it can be easily determined from the cursor position without following the movement. When the sample is in the form of a repeated pattern, it is easy to lose sight of the target by moving the observation field of view, but this concern can be avoided by using this cursor function. The position to set the cursor 5 is not necessarily limited to the last reference point P _f, for example, may be combined from the target point at a distance several cell intervals in the x and y directions. In short, it is only necessary to determine a specific point from which the target point can be immediately determined at a position close to the same field of view.
[0009]
[Example 1]
Now, a case where a defective cell of a 64MDRAM device in which cells having the same pattern as shown in FIG. 4 are arranged in a matrix is found by a test by a tester, and there is a request to observe a cross-sectional image of the cell. The present invention will now be described. Further, it is known that the position of this defective cell is the 125th cell in the x direction and the 220th cell in the y direction counting from the origin cell as shown in FIG.
Since the sample 1 is covered with the protective film 2 as shown in FIG. 1, it drives the sample stage mounted with the sample 1 is set so as to be irradiated with the focused ion beam to the origin cell P ₁ neighborhood. As shown in FIG. 1B, the region near the origin cell P ₁ is irradiated with an ion beam to remove the protective film 2 by etching and open the window 3. The window 3 is processed so that a plurality of cells can be observed in the window from the microscope image. Since the cell group including the origin cell P ₁ from the window 3, as shown in C of FIG. 1 is exposed, the magnification such as a microscope image at this time can be determined by individual cells, i.e., image width is about 100μm Set the observation field of view. From this microscope image, the x-direction (column) interval and the y-direction (row) interval of each cell are measured and stored. Then operating the sample stage so that a corner portion first reference point on the screen to match the origin on the viewing screen to indicate the origin cell P ₁ of the sample 1 in D of FIG.
[0010]
This is to stamp the origin cell P ₁ manageable position identifies a second reference point P ₂ in the direction of the screen edge peripheral area of the defective cell 4 with respect to in the microscopic field, in this example the origin cell P ₁ As a reference, the position of the 100th cell in the x direction and the 100th cell in the y direction was selected. This position is calculated by calculating the design information or the distance between cells measured and stored previously × 100, specifying the position on the microscope screen, irradiating with a focused ion beam, and performing sputter etching. A letter-shaped engraving was added. Next, as shown in E of FIG. 1, this second reference point P ₂ is the origin cell P _{1 that} is the opposite of the diagonal line on the microscope screen. The sample stage is driven to coincide with the position where the position is positioned. In accordance with the reference position in the pattern-matching technique using a cross engraved with second reference point P ₂ identified in the reference position in the observation field of view for positioning when the determining its position. Since the position of the defective cell 4 with respect to the second reference point P ₂ is in there y-direction to the cell position of 25 th in the x-direction has been found that 120 th cell, 25 th cell in the x-direction If it is specified, the target position has been reached. However, in the y direction, even if there are 100 full points in the field of view that are 100 cells apart, they still have not reached 20 cells. Thus, since the observed defective cell 4 is still the target point in the visual field is not captured, it will be stamped to identify the third reference point P ₃ followed. Here stamped to identify the third reference point P ₃ to the 100th cell position in the 25 th y-direction in the x direction with respect to the second reference point P ₂ as illustrated in E.
[0011]
When the following observation field can be regarded goals defective cell 4 when shifted y-direction component, the third reference point P ₃ is in this example a final reference point P _f. Third end in the y direction at a position where the central portion on a microscope image to the x-direction as shown in F of FIG. 1 is not necessary to position the corner portion as a reference point P ₃ of the previous reference point Positioning at the part position is reasonable because the target defective cell 4 can be caught at the center part. It is measured and specified on the screen that the position of the 20-cell interval in the y direction is the position of the target defective cell 4. A focused ion beam is irradiated around this position to expose the target defective cell 4 from the protective film 4. Processing unit a position of the defective cell 4 is identified using the cursor 5 points appropriate defective cell 4 near the third reference point P ₃ or goal if you are biased in the y direction at the time of this work, It is advisable to operate the sample stage with care so as not to lose sight of the position.
In order to process a desired observation cross section, a known cross section process may be performed. However, a drilling process is performed before the cross section to expose the cross section. First, if the beam current is increased and rough digging is performed to form a hole for observation, the observation cross section is sharpened and processed by polishing with the beam current suppressed. When the processing is completed, the sample stage is tilted to obtain a cross-sectional microscopic image.
[0012]
【The invention's effect】
In recent progress in ultra-fine semiconductor devices, access to specific locations from the same pattern arrangement structure has become a very time-consuming and troublesome task. In the beam system, the first reference point that is the origin is imprinted on the sample surface, and it is used as a reference by positioning it at the corner opposite to the direction in which the target point exists in the microscope field. The target point exists in the microscope field. The specific point around the end in the direction to be engraved as a second reference point, and the specific point around the end in the microscope field in the direction in which the target point exists with the second reference point as a new reference This is repeated until the target point enters the microscope visual field, and when the target point enters the microscope visual field, the target position is accessed in the visual field based on the reference point. because there is In particular, it is not necessary to use an ultra-high-precision stage using an expensive laser interferor, etc., and it is possible to access the target point easily and accurately based on the length measurement technology on a precise microscope screen. It became.
[0013]
In addition, since the method of applying the marking to the reference point to the sample by etching or deposition is adopted, it is not necessary to provide a special means, and it can be performed immediately using a normal focused ion beam apparatus.
In addition, since a highly accurate pattern matching technique is applied to the positioning of the engraved reference point, even when shifting to the next microscope field of view, high-accuracy position information can be obtained regardless of the position control accuracy of the sample stage. It can be secured.
If the cursor is placed at the final reference point or a specific point near the target point and linked to the movement of the sample stage, the sample stage is moved by appropriately operating the sample stage when processing the sample. However, there is no such thing as losing sight of the target point.
[Brief description of the drawings]
FIG. 1 is a diagram conceptually illustrating a method for accessing a predetermined position of a semiconductor device according to the present invention, wherein A, B, and C are forms of a semiconductor device as a sample, and D, E, and F are operations in a microscope image. It is the figure which showed the form.
FIG. 2 is a diagram for explaining a method of not losing sight of a target point using a linkage function between a sample stage and a cursor in the present invention.
FIG. 3 is a diagram schematically showing a memory device in which the same pattern as the object of the present invention is arranged in a matrix, and A is an overall view and B is a partially enlarged view thereof.
FIG. 4 is a memory device microscope image in which the same pattern as the object of the present invention is arranged in a matrix, A is a planar image, and B is a specific cross-sectional image thereof.
[Explanation of symbols]
1 Sample P ₁ Origin cell 2 Protective film P ₂ Second reference point 3 Window P ₃ Third reference point 4 Defective cell P _f Final reference point

Claims (4)

In a sample having an array structure in which a plurality of cells are arrayed ,
Marking a first reference point by etching or deposition with a beam of an electron beam apparatus or a focused ion beam apparatus on a corner cell of the array structure including a target cell ;
Marking a second reference point on a cell around an edge of the microscope image in a direction in which the target cell exists in a microscope image including the first reference point ;
A sample moving step of moving the sample so that the position of the second reference point overlaps the position of the first reference point in the microscope image;
An image acquisition step of acquiring a new microscopic image including the second reference point;
A reference point marking step of marking as a new reference point to the end periphery of the cell in the direction of the new microscope image the new cell of the target in the microscopic image is present,
A predetermined location access method . The predetermined position access method according to claim 1, wherein in the sample moving step, pattern matching is performed between the first reference point and the second reference point . The predetermined position access method according to claim 1 or 2, wherein the reference point marking step, the sample moving step, and the image acquisition step are repeatedly performed . The predetermined position access method according to any one of claims 1 to 3, wherein a cursor is moved to the target cell on a microscope image, and the target cell is moved to the center of the image .

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