Machining method and charged particle beam device

Abstract

This machining method for exposing a specific layer from a sample in which a plurality of layers including the specific layer are laminated includes a marking step for machining a plurality of marks across the plurality of layers in a cross-section of the sample, a focused ion beam image generation step for irradiating the sample with a focused ion beam to generate a focused ion beam image of the cross-section of the sample, a focused ion beam length measurement step for measuring the distance between the plurality of marks in the specific layer on the basis of the focused ion beam image, a machining step for irradiating the sample with the focused ion beam to machine the cross-section of the sample by a prescribed amount, an electron beam image generation step for irradiating the sample with an electron beam to generate an electron beam image of the sample after the machining step is completed, an electron beam length measurement step for measuring the distance between the plurality of marks on the basis of the electron beam image, and a specific layer determination step for determining whether the specific layer is exposed on the basis of the results of the focused ion beam length measurement step and the electron beam length measurement step.

Description

Processing method and charged particle beam device

[0001] The present invention relates to a processing method and a charged particle beam device.

[0002] When observing a sample using a transmission electron microscope (TEM) or the like, it is known to use a charged particle beam device to etch the sample into a shape suitable for observation (see, for example, Patent Document 1). Furthermore, when observing a specific layer (hereinafter referred to as a "specific layer") in a layered sample, the specific layer must be exposed. Therefore, a method for accurately detecting the exposure of a specific layer of a sample is known (see, for example, Patent Document 2).

[0003] JP 2013-120714 A JP 2021-51878 A

[0004] However, as samples become increasingly miniaturized, it becomes more difficult to detect a specific layer based on an observation image of the exposed layer. The present invention has been made in view of these circumstances, and its purpose is to accurately detect and process a specific layer even in a very small sample.

[0005] An example of a processing method according to the present invention is a processing method for exposing a specific layer from a sample having a plurality of stacked layers including the specific layer, the method comprising: a marking step for processing a plurality of marks spanning the plurality of layers on a cross section of the sample; a focused ion beam image generating step for irradiating the sample with a focused ion beam to generate a focused ion beam image of the cross section of the sample; a focused ion beam measurement step for measuring distances between the plurality of marks in the specific layer based on the focused ion beam image; a processing step for irradiating the sample with a focused ion beam to process the cross section of the sample by a predetermined amount; an electron beam image generating step for irradiating the sample with an electron beam to generate an electron beam image of the sample after the processing step is completed; an electron beam measurement step for measuring distances between the plurality of marks based on the electron beam image; and a specific layer determination step for determining whether the specific layer is exposed or not based on results of the focused ion beam measurement step and the electron beam measurement step.

[0006] An example of a charged particle beam apparatus according to the present invention is a charged particle beam apparatus that exposes a specific layer from a sample having a plurality of layers stacked thereon, including the specific layer, the charged particle beam apparatus executing the following steps: a marking step that processes a plurality of marks spanning the plurality of layers on a cross section of the sample; a focused ion beam image generating step that irradiates the sample with a focused ion beam to generate a focused ion beam image of the cross section of the sample; a focused ion beam measurement step that measures distances between the plurality of marks in the specific layer based on the focused ion beam image; a processing step that irradiates the sample with a focused ion beam to process the cross section of the sample by a predetermined amount; an electron beam image generating step that irradiates the sample with an electron beam to generate an electron beam image of the sample after the processing step is completed; an electron beam measurement step that measures the distances between the plurality of marks based on the electron beam image; and a specific layer determination step that determines whether the specific layer is exposed or not based on results of the focused ion beam measurement step and the electron beam measurement step.

[0007] According to the present invention, a specific layer can be accurately detected and processed even in a minute sample.

[0008] FIG. 1 is a diagram showing a schematic configuration of a charged particle beam device according to Example 1. FIG. 2 is a diagram showing a schematic configuration of a control unit according to Example 1. FIG. 3 is a flow diagram of an exposure processing method for a charged particle beam device according to Example 1. FIG. 4 is a diagram showing a state in which a plurality of marks have been processed on a cross section of a sample. FIG. 5 is a diagram showing a state after step S105 has been completed. FIG. 6 is a diagram showing a state in which a specific layer has been exposed as a result of repeated slicing. FIG. 7 is a flow diagram of an exposure processing method for a charged particle beam device according to Example 2.

[0009] The present invention will be described in detail below with reference to the accompanying drawings, in which: [Embodiment 1] A charged particle beam device according to this embodiment can expose a specific layer from a sample having multiple layers, including the specific layer, stacked thereon, by executing the processing method described below.

[0010] Charged particle beam devices generate focused ion beam images and process cross sections of samples by irradiating a focused ion beam onto a sample made up of multiple stacked layers.

[0011] For example, when a specific layer (particular layer) of a sample having multiple layers stacked thereon is to be observed using an SEM or TEM, it is necessary to process the cross section of the sample to expose the specific layer. In this case, the charged particle beam device processes the sample to expose the specific layer and determines whether or not the specific layer has been exposed from a cross-sectional image of the sample.

[0012] However, depending on the material of the sample, the difference in contrast between the images is small, making it difficult to determine whether a specific layer is exposed from the cross-sectional image.Furthermore, with the miniaturization of samples, there is a demand for processing even layers with thicknesses in the nanometer range.

[0013] One of the features of this embodiment is that by measuring the distance between multiple marks made on the sample, it is possible to accurately detect and process specific layers even in very small samples.

[0014] The exposure of the specific layer may mean that the specific layer is completely exposed or that only a part of the specific layer is exposed. That is, the detection of the specific layer may mean detecting that the specific layer is exposed in a part of the region where the specific layer is present when viewed from the stacking direction, or may mean detecting that the specific layer is exposed in the entire region.

[0015] Detecting the partial exposure of a specific layer may be detecting a change from a certain layer to a specific layer. For example, if a specific layer that was not exposed at all until then becomes partially exposed after a certain processing treatment, it can be considered that a change from a certain layer to a specific layer has been detected.

[0016] The layer direction is the in-plane direction of a plane parallel to each layer. The stacking direction is the direction in which each layer is stacked, for example, the normal direction of a plane parallel to each layer. Furthermore, a focused ion beam image is an observation image that can be obtained by irradiating a sample with a focused ion beam, and an electron beam image is an observation image that can be obtained by irradiating a sample with an electron beam.

[0017] The sample is a sample in which multiple layers, including a specific layer, are stacked in a predetermined stacking direction. The specific layer is a layer composed of a substance to be observed (e.g., a semiconductor, etc.). The sample may also have multiple specific layers and one or more layers not to be observed stacked in the stacking direction. The layers not to be observed are layers composed of a substance not to be observed (e.g., a metal conductor used as a transmission path for power or signals, etc.). For example, the sample is a 3D-NAND type flash memory, etc.

[0018] The stacking direction may be any direction. For example, the stacking direction of the samples accommodated in the sample chamber may be the vertical direction or the horizontal direction.

[0019] More specific examples of this embodiment will be described below.

[0020] First Embodiment The configuration of a charged particle beam system 1 according to a first embodiment will be described below.

[0021] Fig. 1 is a diagram showing a schematic configuration of a charged particle beam system 1 according to Example 1. As shown in Fig. 1 , the charged particle beam system 1 includes a sample chamber 10, a focused ion beam column 11, an electron beam column 12, a secondary charged particle detector 13, a transmitted electron detector 14, a sample stage 15, a driving mechanism 16, an input unit 17, a display unit 18, and a control device 19.

[0022] The sample chamber 10 is formed of a pressure-resistant housing with an airtight structure that can maintain a desired reduced pressure state. The inside of the sample chamber 10 can be evacuated by an exhaust device (not shown) until the desired reduced pressure state is reached.

[0023] The focused ion beam column 11 irradiates a focused ion beam (FIB) onto a sample 40 placed inside the sample chamber 10. This processes the cross section of the sample 40. Hereinafter, processing the sample 40 with a focused ion beam may be referred to as "FIB processing." Hereinafter, in this embodiment, as an example, FIB processing is performed parallel to the layer of the sample (i.e., so that the processing surface is parallel to the layer).

[0024] The electron beam column 12 irradiates a sample 40 placed inside the sample chamber 10 with an electron beam (EB), which is an example of a charged particle beam.

[0025] The secondary charged particle detector 13 detects secondary electrons generated from the sample 40 by irradiation with the electron beam or focused ion beam. The secondary charged particle detector 13 transmits the detection result of the secondary electrons to the control device 19.

[0026] The transmission electron detector 14 detects the transmission electrons that have passed through the sample 40 and the electron beam that has not been incident on the sample 40 as a result of irradiating the sample 40 with the electron beam. The transmission electron detector 14 transmits the detection results to the control device 19. In this embodiment, the transmission electron detector 14 may be omitted.

[0027] The sample stage 15 holds the sample 40 and is disposed inside the sample chamber 10. The sample stage 15 is driven by a driving mechanism 16.

[0028] The driving mechanism 16 translates and rotates the sample stage 15 three-dimensionally. The driving mechanism 16 translates the sample stage 15, for example, along each of the X-axis, Y-axis, and Z-axis directions in three-dimensional space. The Z-axis is, for example, the up-down direction and is perpendicular to the plane formed by the X-axis and Y-axis (XY plane). The driving mechanism 16 also includes, for example, a tilt mechanism that rotates the sample stage 15 around the X-axis or Y-axis, and a rotation mechanism that rotates the sample stage 15 around the Z-axis. Hereinafter, the angle by which the tilt mechanism rotates the sample stage 15 is referred to as the tilt angle.

[0029] The input unit 17 is, for example, a mouse and a keyboard that output signals in response to input operations by an operator.

[0030] The display unit 18 includes a display device such as a liquid crystal display, etc. The display unit 18 displays various information about the charged particle beam device 1, image data generated from signals output from the secondary charged particle detector 13 (and the transmitted electron detector 14 in some cases), and a screen for performing operations such as enlarging, reducing, moving, and rotating the image data.

[0031] The control device 19 comprehensively controls the operation of the charged particle beam device 1. The control device 19 has, for example, a hardware configuration as a known computer, and includes, for example, a calculation means and a storage means. The calculation means includes, for example, a processor, and the storage means includes, for example, a storage medium such as a semiconductor memory device or a magnetic disk device. Some or all of the storage medium may be non-transitory storage media.

[0032] The storage means may store a program, and the processor may execute the program, causing the control device 19 to perform the functions described in this embodiment.

[0033] The control device 19 includes an EB control unit 20 , an FIB control unit 21 , an image forming unit 22 , a sample stage control unit 23 , and a control unit 24 .

[0034] The EB control unit 20 outputs an irradiation signal to the electron beam column 12 based on a signal from the control unit 24, causing the electron beam column 12 to irradiate the electron beam.

[0035] The FIB control unit 21 outputs an irradiation signal to the focused ion beam column 11 based on a signal from the control unit 24, causing the focused ion beam to be irradiated from the focused ion beam column 11. The FIB control unit 21 can adjust the irradiation direction of the focused ion beam irradiated from the focused ion beam column 11 based on the signal from the control unit 24.

[0036] The image forming unit 22 forms data of an observation image (for example, a focused ion beam image and an electron beam image) of the sample 40 based on a signal of secondary electrons generated from the sample 40 and detected by the secondary charged particle detector 13. Furthermore, the image forming unit 22 may generate a transmission image of the sample 40 based on a signal of transmitted electrons detected by the transmitted electron detector 14.

[0037] The sample stage control unit 23 controls the driving of the drive mechanism 16 based on a signal from the control unit 24, and outputs a drive signal to the drive mechanism 16 to drive the sample stage 15, thereby allowing the sample stage 15 to be translated or the tilt angle to be changed.

[0038] 2 is a diagram illustrating a schematic configuration of the control unit 24 according to Example 1. The control unit 24 includes a display control unit 30, a layer count unit 31, a length measurement unit 32, and a determination unit 33.

[0039] The display control unit 30 causes the display unit 18 to display the above-mentioned transmission image and SEM image.

[0040] The layer counting unit 31 determines the number and positions of layers of the sample 40 based on the focused ion beam image generated by the image forming unit 22 .

[0041] The length measurement unit 32 measures the distances between the multiple marks based on the focused ion beam image and the electron beam image generated by the image formation unit 22 .

[0042] The determination unit 33 determines whether or not a specific layer is exposed among the multiple layers of the sample 40, based on the measurement results of the length measurement unit 32. For example, as will be described later, the determination unit 33 determines that the specific layer is exposed when the distance between marks in the focused ion beam image measured by the length measurement unit 32 is equal to the distance between marks in the electron beam image measured by the length measurement unit 32.

[0043] The following describes a processing method (hereinafter referred to as "exposure processing method") in which the charged particle beam device 1 exposes a specific layer from a sample in which a plurality of layers including the specific layer are stacked.

[0044] FIG. 3 is a flow diagram of an exposure processing method of the charged particle beam apparatus 1 according to the first embodiment.

[0045] [Exposure Processing Method] The charged particle beam device 1 irradiates a focused ion beam to generate a focused ion beam image of the sample 40. The charged particle beam device 1 or its user adjusts the position of the sample stage based on this image (step S101: sample stage adjustment step).

[0046] The charged particle beam device 1 irradiates the sample 40 with a focused ion beam to generate a focused ion beam image of the sample 40, and determines the position of each layer based on the image (step S102: layer counting step). For example, a focused ion beam image of a cross section of the sample 40 including cross sections of multiple layers can be used. For example, the layer counting unit 31 creates a brightness profile from the focused ion beam image, and determines the position of each layer based on the magnitude of brightness.

[0047] The charged particle beam device 1 irradiates a focused ion beam to process multiple marks across multiple layers of the sample 40 (step S103: marking step), as shown in Fig. 4. Fig. 4 shows the state in which multiple marks have been processed on the cross section of the sample 40. In Fig. 4, the boundaries between layers are indicated by dotted lines, and a specific layer 41 is indicated by a dotted pattern. Each mark can be formed, for example, as a groove.

[0048] 4, the multiple marks include a first mark 51 and a second mark 52. The first mark 51 and the second mark 52 are processed so as not to be parallel to each other. In this manner, the charged particle beam device 1 processes multiple marks across multiple layers on the cross section of the sample 40.

[0049] The charged particle beam device 1 irradiates a focused ion beam onto a sample 40 to generate a focused ion beam image of a cross section of the sample 40 (focused ion beam image generation step of step S104), and measures the distance L1 between the first mark 51 and the second mark 52 in the specific layer 41 based on the image (focused ion beam measurement step of step S104).

[0050] The focused ion beam image is, for example, as shown in Fig. 4. For example, in the focused ion beam image obtained in the focused ion beam image generating step, the length measuring unit 32 measures the distances between a plurality of marks overlapping the specific layer 41 based on the positions of each layer obtained in the layer counting step.

[0051] 4, the thickness of the specific layer 41 is exaggerated, so the distance L1 varies depending on the depth position of the specific layer 41, but in an actual sample, such a change is considered to be within the allowable error range. Alternatively, the first mark 51 and the second mark 52 can be processed at appropriate positions so that the distance L1 is large enough to ignore the change in the distance L1 depending on the depth position.

[0052] The charged particle beam device 1 irradiates the sample 40 with a focused ion beam to process (e.g., slice) the cross section of the sample 40 by a predetermined amount to form a new cross section (step S105: processing step). Figure 5 shows the state after step S105 is completed.

[0053] After step S105 is completed, the charged particle beam device 1 irradiates the sample 40 with an electron beam to generate an electron beam image of the sample 40 (electron beam image generation step of step S106), and measures the distance L2 between the first mark 51 and the second mark 52 based on the image (electron beam measurement step of step S106). For example, the distance measurement unit 32 measures the distance between multiple marks from the electron beam image.

[0054] 5, the distance L2 can be measured based on the portion exposed on the processed surface of the sample 40. In other words, it is not necessary to use a cross section of the sample 40 to measure the distance L2, and the distance L2 can be measured using an electron beam image, which can be generated more easily than a focused ion beam image (although a cross section can also be used).

[0055] The charged particle beam device 1 determines whether or not a specific layer 41 among the multiple layers is exposed based on the results of step S104 (particularly, the focused ion beam length measurement step) and step S106 (particularly, the electron beam length measurement step) (step S107: mark distance determination step). This step S107 functions as a specific layer determination step.

[0056] For example, the determination unit 33 compares the measurement result (distance L1) obtained in step S104 with the measurement result (distance L2) obtained in step S106 to determine whether they match. If the measurement result obtained in step S104 and the measurement result obtained in step S106 do not match (this corresponds to the state in FIG. 5), the determination unit 33 determines that the specific layer is not exposed, and returns to the processing of step S105 so that slicing is performed again.

[0057] 6 shows a state in which a specific layer 41 is exposed as a result of repeated slicing. If the measurement result (distance L1) obtained in step S104 and the measurement result (distance L2) obtained in step S106 match (this corresponds to the state in FIG. 6), the determination unit 33 determines that the specific layer is exposed. Here, "match" does not only mean a strict match, but may also include a match within a predetermined tolerance range. If the determination unit 33 determines that the specific layer is exposed, the charged particle beam device 1 ends the series of processes shown in FIG. 3.

[0058] In this way, the charged particle beam device 1 of this embodiment performs the marking step and the length measurement step using a focused ion beam, and further performs the length measurement step using an electron beam. This allows the charged particle beam device 1 to determine the exposure of a specific layer by using the length measurement results. As a result, the charged particle beam device 1 can accurately detect and process a specific layer even in a minute sample.

[0059] In particular, the charged particle beam device 1 sets up a processing step (S105), an electron beam image generating step and electron beam length measuring step (S106), and a specific layer determining step (S107), and repeatedly executes this set until it is determined in the specific layer determining step (S107) that the specific layer 41 is exposed. By repeating this set, it is possible to more reliably detect the exposure of the specific layer.

[0060] Example 2 Example 2 is an example in which a correction step for correcting the scanning direction of the focused ion beam is added to the above-described Example 1. Hereinafter, a description of parts common to Example 1 may be omitted.

[0061] 7 is a flow chart of an exposure processing method for a charged particle beam apparatus according to Example 2. Steps S101 to S107 can be performed in the same manner as in Example 1.

[0062] If it is determined in step S107 that the distance L1 and the distance L2 do not match, the charged particle beam device determines whether the position of the first mark 51 in a certain electron beam image (first electron beam image; for example, the electron beam image in the last executed set) matches the position of the first mark 51 in an electron beam image (second electron beam image; for example, the electron beam image in the previously executed set) generated before (for example, just before) that electron beam image (step S108: first mark position determination step).

[0063] If the position of the first mark 51 in the first electron beam image matches the position of the first mark 51 in the second electron beam image, the process returns to step S105, as in the first embodiment.

[0064] On the other hand, if the positions of the first marks 51 are different, the charged particle beam device corrects the scanning direction of the focused ion beam in the processing step (step S109: correction step).

[0065] This correction of the scanning direction is performed so that the position of the first mark 51 always remains the same in electron beam images generated thereafter. In other words, the charged particle beam device corrects the scanning direction of the focused ion beam so that the processing surface in the processing step performed after the correction becomes parallel to the layer of the sample 40. Alternatively, the charged particle beam device may correct the scanning direction of the focused ion beam so that the processing surface in the processing step performed after the correction becomes perpendicular to the imaging direction of the electron beam image. Such a correction can be performed based on the positions of the first mark 51 in each of the first electron beam image and the second electron beam image.

[0066] Such a correction stabilizes the position of the first mark 51 in the electron beam image, thereby improving the measurement accuracy of the distance L2 in step S106. Furthermore, since the position of the first mark 51 does not change, there is no need to expand the imaging range of the electron beam image during repeated slicing.

[0067] In this Example 2, if the first mark 51 is processed so that it extends in a direction perpendicular to the layer of the sample 40, the processing direction and the imaging direction can be appropriately aligned, particularly when the imaging direction of the electron beam image is perpendicular to the layer. As described above, the second mark 52 is processed so that it extends at an angle to the first mark 51, i.e., in a direction that is not perpendicular to the layer of the sample 40, and therefore the distance L2 changes as the slicing process is repeated.

[0068] In the second embodiment described above, the scanning direction of the focused ion beam is corrected in S109. However, instead of or in addition to this, the imaging direction of the electron beam image in the electron beam measurement step (S106) may be corrected in S109. The imaging direction is corrected so that the position of the first mark 51 is always the same in electron beam images generated thereafter. Such a correction can be performed based on the positions of the first mark 51 in each of the first electron beam image and the second electron beam image. This configuration also improves the measurement accuracy of the distance L2.

[0069] DESCRIPTION OF SYMBOLS 1...Charged particle beam device 10...Sample chamber 11...Focused ion beam column 12...Electron beam column 13...Secondary charged particle detector 14...Transmission electron detector 15...Sample stage 16...Drive mechanism 17...Input unit 18...Display unit 19...Control device 20...EB control unit 21...FIB control unit 22...Image formation unit 23...Sample stage control unit 24...Control unit 30...Display control unit 31...Layer count unit 32...Measurement unit 33...Determination unit 40...Sample 41...Specific layer 51...First mark (mark) 52...Second mark (mark) L1, L2...Distance between multiple marks S101...Sample stage adjustment step S102...Layer count step S103...Marking step S104...Focused ion beam image generation step and focused ion beam measurement step S105...Processing step S106: Electron beam image generation step and electron beam length measurement step S107: Mark-to-mark distance determination step S108: First mark position determination step S109: Correction step

Claims

1. A processing method for exposing a specific layer from a sample having a plurality of laminated layers including a specific layer, comprising: a marking step for processing a plurality of marks spanning the plurality of layers on a cross section of the sample; a focused ion beam image generating step for irradiating the sample with a focused ion beam to generate a focused ion beam image of the cross section of the sample; a focused ion beam measurement step for measuring a distance between the plurality of marks in the specific layer based on the focused ion beam image; a processing step for irradiating the sample with a focused ion beam to process the cross section of the sample by a predetermined amount; an electron beam image generating step for irradiating the sample with an electron beam after the processing step is completed to generate an electron beam image of the sample; an electron beam measurement step for measuring the distance between the plurality of marks based on the electron beam image; and a specific layer determination step for determining whether or not the specific layer is exposed based on results of the focused ion beam measurement step and the electron beam measurement step.

2. The processing method according to claim 1, wherein the processing step, the electron beam image generating step, the electron beam length measuring step, and the specific layer determining step are set as a set, and the set is repeatedly executed until it is determined in the specific layer determining step that the specific layer has been exposed.

3. The processing method according to claim 1, wherein the plurality of marks include: a first mark extending in a direction perpendicular to a layer of the sample; and a second mark extending at an angle to the first mark.

4. The processing method according to claim 3, further comprising a correction step of correcting the scanning direction of the focused ion beam in the processing step when the position of the first mark in the first electron beam image differs from the position of the first mark in a second electron beam image generated before the first electron beam image.

5. The processing method described in claim 3, further comprising a correction step of correcting the imaging direction of the electron beam image in the electron beam measurement step when the position of the first mark in the first electron beam image differs from the position of the first mark in a second electron beam image generated before the first electron beam image.

6. A charged particle beam apparatus for exposing a specific layer from a sample having a plurality of laminated layers including a specific layer, the charged particle beam apparatus executing the following steps: a marking step for processing a plurality of marks spanning the plurality of layers on a cross section of the sample; a focused ion beam image generating step for irradiating the sample with a focused ion beam to generate a focused ion beam image of the cross section of the sample; a focused ion beam measurement step for measuring a distance between the plurality of marks in the specific layer based on the focused ion beam image; a processing step for irradiating the sample with a focused ion beam to process the cross section of the sample by a predetermined amount; an electron beam image generating step for irradiating the sample with an electron beam after the processing step is completed, the electron beam measurement step for irradiating the sample with an electron beam to generate an electron beam image of the sample; an electron beam measurement step for measuring the distance between the plurality of marks based on the electron beam image; and a specific layer determination step for determining whether the specific layer is exposed or not based on results of the focused ion beam measurement step and the electron beam measurement step.

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