Charged particle beam device, sample cooling mechanism, and continuous cross-sectional processing observation method

Abstract

The present invention provides a charged particle beam device comprising: a base frame; a sample chamber supported by the base frame; a contact member that is supported by the sample chamber and contacts the sample inside the sample chamber; and a cooling source container that accommodates a cooling source. The cooling source container is supported by the sample chamber or the base frame outside the sample chamber. The contact member is not in contact with the cooling source container, and is configured such that a portion thereof is inserted into the cooling source container and contacts the cooling source.

Description

Charged particle beam device, specimen cooling mechanism, and continuous cross-section processing and observation method

[0001] The present invention relates to a charged particle beam device such as an FIB-SEM, a sample cooling mechanism used in the charged particle beam device, and a method for continuous cross-sectional processing and observation of a sample using the charged particle beam device.

[0002] A focused ion beam (FIB) device is a type of charged particle beam device that processes samples by scanning the surface of a sample with a focused ion beam and generates microscopic images by detecting secondary electrons generated on the sample surface. When processing or observing a sample with this focused ion beam device, the sample heats up due to irradiation with the FIB, and depending on the type of sample, the original state may not be maintained, which may affect structural analysis.

[0003] Therefore, some charged particle beam devices such as FIB devices are equipped with a sample cooling mechanism that cools a sample while it is being irradiated with a charged particle beam such as an FIB, as described in Patent Documents 1 and 2. In the sample cooling mechanisms described in these documents, a cooling source container containing a cooling source (e.g., liquid nitrogen) is attached to a holder that holds the sample, and the holder and the cooling source are in contact inside the cooling source container. This allows heat to be transferred between the sample and the cooling source via the holder, thereby cooling the sample.

[0004] JP 2010-55988 A JP 2014-10965 A

[0005] For example, in three-dimensional structural analysis (Cut and See) using an FIB-SEM device, sample processing and image acquisition are repeated to obtain successive cross-sectional images of the sample. This type of three-dimensional structural analysis requires the sample to be cooled for a long period of time because the sample processing and image acquisition are repeated. Therefore, the remaining amount of cooling source in the cooling source container decreases significantly during the three-dimensional structural analysis, and in some cases, the cooling source needs to be replenished during the three-dimensional structural analysis.

[0006] In the sample cooling mechanisms described in Patent Documents 1 and 2, a cooling-source container is attached to a holder, and the cooling-source container is supported by the cooling holder. Therefore, the load applied to the holder by the cooling-source container varies greatly depending on the remaining amount of cooling source. The holder may be displaced due to the load fluctuation, which may cause the sample to change position. Furthermore, when the cooling source container is replenished with liquid nitrogen or other cooling source liquid as its remaining amount decreases, the boiling of the cooling source liquid when it is poured into the cooling-source container causes vibrations in the cooling-source container, which are then transmitted to the holder.

[0007] An object of the present invention is to provide a charged particle beam device, a sample cooling mechanism, and a method for continuous cross-section processing and observation that can cool a sample over a long period of time while suppressing changes in the position of the sample during irradiation with a charged particle beam.

[0008] In order to achieve the above-mentioned object, the present invention provides a charged particle beam device comprising: a base frame; a sample chamber supported by the base frame; a contact member supported by the sample chamber and in contact with the sample inside the sample chamber; and a cooling source container that houses a cooling source, wherein the cooling source container is supported by the sample chamber or the base frame outside the sample chamber, and the contact member is not in contact with the cooling source container and is configured such that a portion of the contact member is inserted into the cooling source container and comes into contact with the cooling source.

[0009] According to the present invention, it is possible to cool a sample for a long period of time while suppressing changes in the position of the sample during irradiation with a charged particle beam.

[0010] 1 is a schematic diagram of a charged particle beam device according to an embodiment of the present invention; 2 is a schematic diagram of a sample cooling mechanism provided in the charged particle beam device according to an embodiment of the present invention; 3 is a flowchart showing a procedure for continuous cross-section processing and observation using the charged particle beam device according to an embodiment of the present invention; 4 is a diagram showing a state of continuous cross-section processing and observation using the charged particle beam device according to an embodiment of the present invention;

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] -Charged particle beam device- Figure 1 is a schematic diagram of a charged particle beam device according to one embodiment of the present invention. The charged particle beam device 1 illustrated in Figure 1 is an FIB-SEM, which is capable of processing a sample S using an FIB (focused ion beam) and observing the sample S using an EB (electron beam). The sample S is, for example, a sample piece cut out from a relatively large semiconductor wafer (e.g., 300 mm in diameter), or a relatively small sample (e.g., approximately 10 mm). The charged particle beam device 1 is capable of acquiring continuous cross-sectional images of the sample S, which can be used for three-dimensional structural analysis of the sample S.

[0013] The charged particle beam device 1 illustrated in FIG. 1 includes a base frame 2, a sample chamber 3 supported by the base frame 2, an FIB column 4 that emits an FIB, an EB column 5 that emits an EB, a detector 6 that detects secondary electrons generated in the sample S when irradiated with the EB from the EB column 5, and a sample cooling mechanism 7 that cools the sample S inside the vacuum sample chamber 3.

[0014] The sample chamber 3, together with the FIB column 4 and the EB column 5, is maintained at a high vacuum during processing or observation of the sample S. A holder 21 for holding the sample S is disposed inside the sample chamber 3.

[0015] The FIB column 4 processes the sample S held in the holder section 21 by irradiating the sample S with an FIB extracted from the ion source by an extraction electrode. While Fig. 1 illustrates a configuration in which the FIB column 4 is installed in the sample chamber 3 in a state inclined relative to the vertical, the FIB column 4 may also be installed in the sample chamber 3 in a vertical position. The FIB column 4 is controlled by a control device 10.

[0016] The EB column 5 scans the sample S held in the holder section 21 with EB extracted from the electron source by an extraction electrode. While Fig. 1 illustrates a configuration in which the EB column 5 is installed vertically in the sample chamber 3, the EB column 5 may also be installed in an inclined position in the sample chamber 3. The EB column 5 is controlled by a control device 10.

[0017] The control device 10 is a computer having an arithmetic unit (e.g., CPU) and a storage device (e.g., RAM, ROM, HDD, SSD), which detects secondary charged particles (e.g., secondary electrons) from the sample S, captures signals input from the detector 6 in synchronization with the EB scanning signal, and generates image data of an observation image (SEM image) of the sample S. The generated image data is stored in a storage device and appropriately displayed on a display device 11 (e.g., monitor). In addition to the display device 11, an input device 12 (e.g., keyboard) is connected to the control device 10, and, for example, items and conditions related to processing and observation are input through the input device 12 to instruct the control device 10. The control device 10 executes a program stored in the storage device, and, in accordance with the instructions, irradiates the sample S with an EB to obtain an observation image of the sample S, or irradiates the sample S with an FIB to process the sample S. Note that the detector 6 may detect secondary charged particles generated by irradiating the sample S with the FIB, thereby generating an observation image (SIM image) of the sample S.

[0018] 2 is a schematic diagram of the sample cooling mechanism 7. The sample cooling mechanism 7 is a mechanism for cooling the sample S inside the sample chamber 3, which is in a high vacuum state. The sample cooling mechanism 7 includes a contact member 20 and a cooling source container 30.

[0019] The cooling-source container 30 is a container that contains a cooling source C (e.g., liquid nitrogen). The cooling-source container 30 is placed on a base 2a that is provided as a predetermined installation position on the base frame 2 outside the sample chamber 3, and is thereby supported by the base frame 2. The shape of the cooling-source container 30 is not particularly limited, and in addition to a cylindrical bucket-type container as exemplified in Fig. 1, for example, a rectangular box-type container can be appropriately adopted.

[0020] Cooling-Source Container The cooling-source container 30 is configured so as not to come into direct contact with the contact member 20. Specifically, the cooling-source container 30 has a wide insertion hole 31 for inserting the contact member 20. When set on the base 30, a portion of the contact member 20 is inserted into the cooling-source container 30 through the insertion hole 31. The opening size of the insertion hole 31 is set so that a gap G is maintained between the contact member 20 inserted into the cooling-source container 30 and the inner wall of the insertion hole 31. Only the atmosphere exists in the gap G, and no structure such as a sealing member is interposed. Furthermore, to prevent leakage of the cooling source C from this gap G, the insertion hole 31 is positioned entirely above the maximum liquid level L of the cooling source C in the cooling-source container 30. FIG. 2 illustrates a state in which the cooling-source container 30 is filled with the cooling source C up to the maximum liquid level L. A mark X indicating the maximum liquid level L is preferably provided on the cooling-source container 30.

[0021] 2 illustrates a configuration in which the insertion hole 31 is provided on the top surface of the cooling-source container 20, but the insertion hole 31 may be configured to open on the side surface (e.g., the upper part of the side surface) of the cooling-source container 20. Even in this case, the entire insertion hole 31 is configured to be higher than the maximum liquid level L (marked X). Also, while FIG. 2 illustrates a configuration in which the cooling-source container 30 is directly supported on the base frame 2 (base portion 2a), in order to avoid direct contact between the cooling-source container 30 and the contact member 20, for example, the cooling-source container 30 may be supported on the sample chamber 3.

[0022] Contact member The contact member 20 is supported by the wall of the sample chamber 3 and contacts the sample S inside the sample chamber 3, but as described above, it is not in contact with the cooling source container 30 and a portion of it is inserted into the cooling source container 30 to contact the cooling source C.

[0023] In this embodiment, the contact member 20 is a sample holder that holds the sample S being processed or observed by FIB or EB. The contact member 20 as a sample holder includes a holder portion 21, a heat conduction portion 22, and a cooling fin 23.

[0024] The holder part 21 is a long, thin, arm-like member arranged inside the sample chamber 3, with the sample S set at its tip and supporting the sample S inside the sample chamber 3. The holder part 21 has a double-tube structure, for example, with an outer cylinder made of aluminum material and a core made of copper material (e.g., phosphor bronze), and a vacuum is maintained between the outer cylinder and the core. The sample S is held by the copper material core exposed at the tip. The holder part 21 can rotate around its center line, allowing the held sample S to be tilted.

[0025] The heat conductive portion 22 is a member for dissipating heat from the sample S, and is supported by the wall of the sample chamber 3 and penetrates the wall. The heat conductive portion 22 also has a double-tube structure similar to the holder portion 21. In the example of FIG. 2 , the contact member 20 is configured such that the heat conductive portion 22 engages with and is supported by the sample chamber 3, but it may also be configured such that the holder portion 21 is supported by the sample chamber 3. The heat conductive portion 22 is an L-shaped member, and the holder portion 21 is attached to the portion of the heat conductive portion 22 facing the inside of the sample chamber 3, and the portion that slopes down outside the sample chamber 3 is inserted into the cooling-source container 30 through the insertion hole 31. However, the heat conductive portion 22 does not necessarily have to be L-shaped, and the shape can be appropriately designed depending on the connection with the cooling-source container 30 and the sample chamber 3.

[0026] The cooling fins 23 are components for increasing the contact area between the heat conduction unit 22 and the cooling source C, and are provided at the tip of the portion of the heat conduction unit 22 that is inserted into the cooling source container 30 and contacts the cooling source C. The cooling fins 23 are provided at the lower end of the core of the heat conduction unit 22 so that the cooling fins 23 remain in contact with the cooling source C even when the liquid level of the cooling source C drops. The cooling fins 23 are made of the same copper-based material as the holder unit 21 and the core of the heat conduction unit 22. The configuration of the cooling fins 23 is not limited, and may be, for example, a configuration in which multiple pin fins protrude from the surface of the heat conduction unit 22. However, in this embodiment, a configuration in which multiple disk-shaped fins are arranged at predetermined intervals is adopted. The disk-shaped cooling fins 23 are easy to process, which has the advantage of ensuring ease of manufacturing the cooling fins 23. The tip (lower end) of the heat conduction portion 22, including the cooling fin 23, is separated from the bottom surface of the cooling source container 30 (the upward-facing inner wall surface inside the cooling source container 30), ensuring a non-contact state between the contact member 20 and the cooling source container 30.

[0027] With the above configuration, heat is transferred between the sample S, the holder 6, the heat conducting portion 22, and the cooling fin 23 through their respective contact portions. The cooling fin 23 is immersed in and comes into contact with the cooling source C filled in the cooling source container 30, and the temperature of the cooling source C is transferred from the cooling fin 23, thereby cooling the heat conducting portion 22, the holder 6, and the sample S.

[0028] As shown in FIG. 1 , the sample chamber 3 is equipped with a probe 8. The probe 8 is driven by a manipulator (not shown) and transports the sample S attached to its tip. The probe 8 is used when setting the sample S in the holder portion 21 of the contact member 20, for example. The probe 8 is also a contact member that is supported by the sample chamber 3 and comes into contact with the sample S inside the sample chamber 3, and like the sample holder, can be used to cool the sample S by inserting a portion of it into the cooling source container 30 (or another cooling source container) and bringing it into contact with the cooling source C.

[0029] 3 is a flowchart showing the steps of continuous cross-section processing and observation using the charged particle beam device 1 of this embodiment. In the continuous cross-section processing and observation method using the charged particle beam device 1, a slicing step S12 and an SEM image acquisition step S13 are repeatedly performed in parallel with a cooling step S11. The cooling step S11 is a step of cooling the sample S via the sample holder, which is the contact member 20. The slicing step S12 is a step of irradiating the sample S held by the sample holder with an FIB (focused ion beam) to slice the sample S. The SEM image acquisition step S13 is a step of irradiating the cross-section of the sample S exposed by the slicing step S12 with an EB (electron beam) to acquire an SEM image of the cross-section of the sample S.

[0030] For example, when the flow of FIG. 3 is started, the sample S held in the holder 21 is cooled by heat transfer between the sample S and the cooling source C via the contact member 20 (cooling step S11). In this state, the sample S is irradiated with an FIB to slice the sample S by a predetermined thickness, exposing a cross-section of the target observation region of the sample S (slicing step S12). Once the cross-section of the target observation region of the sample S is exposed, the exposed cross-section is scanned with an EB to acquire an SEM image of the cross-section (SEM image acquisition step S13). After acquiring the SEM image of the cross-section of the target region, it is determined whether acquisition of consecutive cross-sections of the target region has been completed (step S14). If the desired number of SEM images has not yet been acquired, the slicing step S12 and the SEM image acquisition step S13 are performed again. Once the desired number of SEM images have been acquired, the consecutive cross-section processing and observation is terminated.

[0031] FIG. 4 illustrates the continuous cross-section processing and observation using the charged particle beam device 1 of this embodiment. Although the holder 21 is not shown in FIG. 4 , the sample S is held by the holder 21. The holder 21 is rotated to tilt the sample S so that the top surface of the sample S faces the FIB. The sample S is, for example, a sample piece cut from a semiconductor wafer and has a microdevice structure, defects, etc., inside it. In the continuous cross-section processing and observation, a cross-section observation image of a desired observation target, such as a device structure or defects, inside the sample S is acquired and used for three-dimensional structural analysis of the observation target. Specifically, an FIB is irradiated near a position where the observation target is expected to exist in the sample S to form a processed groove V by etching, and a cross-section processing area is set so that the processed groove V widens toward the position where the observation target is expected to exist. In the following description, the direction in which the processed groove V widens is referred to as direction PD.

[0032] In the continuous cross-section processing and observation, processing areas A1, A2, A3, etc., which are aligned in the direction PD, are sequentially etched with an FIB, widening the processing groove V in the direction PD. During this process, each time processing of a processing area A1, A2, A3, etc. is completed, the cross-sections (observation surfaces) B1, B2, B3, etc., exposed by the processing are scanned with an EB, and SEM observation images and EDS maps of each cross-section B1, B2, B3, etc. are sequentially acquired. By repeating this cross-section processing and cross-section observation (Cut & See), SEM images of multiple cross-sections of the sample S, including the observation target, are acquired along the direction PD. Then, image processing is performed by the control device 10 to sequentially superimpose these multiple SEM images, thereby obtaining a three-dimensional image of a predetermined area of ​​the sample S, including the observation target.

[0033] -Effects- (1) In this embodiment, by inserting a portion of the contact member 20 that contacts the sample S inside the sample chamber 3 into the cooling-source container 30 and bringing it into contact with the cooling source C, heat transfer occurs between the cooling source C and the sample S via the contact member 20, and the sample S can be cooled. In addition, by making the contact member 20 non-contact with the cooling-source container 30, even if the cooling source C decreases and the weight of the cooling source C changes significantly during processing or observation of the sample S, the external force applied to the contact member 20 can be prevented from changing accordingly, and the positional change of the sample S held by the contact member 20 can be prevented.

[0034] Because weight changes in the cooling source C are tolerated during processing or observation of the sample S, even if the remaining amount of cooling source C changes significantly during processing of the sample S or acquisition of observation images, the processing position accuracy and the position accuracy of the observation image relative to the sample S can be maintained. For example, in the above-mentioned continuous cross-section processing and observation, processing and acquisition of observation images are repeated over a long period of time, so changes in the remaining amount of cooling source C are unavoidable during operation. In contrast, in this embodiment, if a sufficient amount of cooling source C is pre-filled in the cooling-source container 30, even long-term processes such as continuous cross-section processing and observation can be completed without refilling the cooling source C. Furthermore, vibration transmission from the cooling-source container 30 to the contact member 20 can be suppressed. Therefore, even if the cooling source C is replenished during continuous cross-section processing and observation, displacement of the sample S due to vibrations in the cooling-source container 30 caused by boiling of the cooling source C when it is introduced into the cooling-source container 30 can be suppressed. In other words, the cooling source C can be replenished even while processing the sample S or acquiring observation images of the sample S. In addition, because significant weight changes in the cooling source C are tolerated, the cooling-source container 30 can be made larger.

[0035] As described above, according to this embodiment, the sample S can be cooled for a long period of time while suppressing changes in position during irradiation with a charged particle beam such as an FIB.

[0036] Furthermore, the above-mentioned effect can be obtained by making the contact member 20 and the cooling-source container 30 non-contact. Therefore, for example, it is possible to remove the cooling-source container from an existing sample holder or the like to which the cooling-source container is attached, and use this sample holder as the contact member 20 without any unnecessary modifications. Therefore, it is easy to configure the sample cooling mechanism 7 by utilizing an existing sample holder or the like. It is also easy to replace the sample cooling mechanism 7 with one of an existing structure.

[0037] (2) The insertion hole 31 into which the contact member 20 of the cooling-source container 30 is inserted is formed so as to secure a gap G between the contact member 20 inserted into the cooling-source container 30. This prevents contact between the contact member 20 and the cooling-source container 30, and prevents changes in the weight of the cooling-source container 30 and vibrations of the cooling-source container 30 due to changes in the remaining amount of cooling source C from being transmitted to the contact member 20.

[0038] (3) If the contact member 20 is inserted into the lower part (near the bottom) of the cooling-source container 30, the insertion hole 31 will be located at a position lower than the liquid level of the cooling source C. Therefore, in order to prevent leakage of the cooling source C, it is necessary to seal the gap between the insertion hole 31 and the contact member 20, resulting in a structure in which the contact member 20 contacts the cooling-source container 30 via a sealing member. In this case, vibrations of the cooling-source container 30 will be transmitted to the contact member 20.

[0039] In contrast, in this embodiment, the insertion hole 31 is provided at a position higher than the maximum liquid level L of the cooling source C in the cooling-source container 30. Therefore, a gap G is allowed between the insertion hole 31 and the contact member 20, and leakage of the cooling source C from this gap G can be suppressed.

[0040] (4) The contact member 20 is provided with the cooling fins 23 at the portion that contacts the cooling source C, which increases the contact area between the contact member 20 and the cooling source C and allows for efficient cooling of the sample S. The provision of the cooling fins 23 makes it possible to make the cooling capacity less susceptible to changes even if the liquid level of the cooling source C changes significantly. This is also advantageous in terms of enlarging the cooling source container 30.

[0041] (5) By using the contact member 20 as the sample holder of the FIB-SEM device, the sample S can be stably cooled during continuous cross-sectional processing and observation as described above, and the accuracy of the processing position and observation position can be improved.

[0042] -Modifications- The present invention is not limited to the above-described embodiments and may include various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. For example, it is possible to replace some of the configurations with other configurations. It is also possible to delete some of the configurations of the embodiments or add other configurations.

[0043] For example, FIG. 1 illustrates a charged particle beam device 1 for processing or observing a sample piece cut from a relatively large (e.g., 300 mm diameter) semiconductor wafer or a relatively small (e.g., approximately 10 mm) sample S. However, the present invention is also applicable to charged particle beam devices for processing or observing relatively large (e.g., 300 mm diameter) semiconductor wafers. The present invention is also applicable to FIB devices that do not have an EB column, and electron microscopes such as SEMs and STEMs that do not have an FIB column. As mentioned above, the contact member 20 of the sample cooling mechanism 7 may be any element that can contact the sample S inside the sample chamber 3 and transfer heat between the sample S and the contact member 20, and may be a probe 8 or other element, rather than a sample holder.

[0044] 1...Charged particle beam device, 2...Base frame, 3...Sample chamber, 4...Focused ion beam column, 5...Electron beam column, 6...Detector, 7...Sample cooling mechanism, 20...Contact member, 23...Cooling fin, 30...Cooling source container, 31...Insertion hole, B1-B3...Sample cross section, EB...Electron beam, FIB...Focused ion beam, G...Gap, L...Maximum liquid level, S...Sample, S11...Cooling process, S12...Slicing process, S13...SEM image acquisition process

Claims

1. A charged particle beam apparatus comprising a base frame, a sample chamber supported by the base frame, a contact member supported by the sample chamber and contacting the sample inside the sample chamber, and a cooling source container housing a cooling source, wherein the cooling source container is supported by the sample chamber or the base frame outside the sample chamber, and the contact member is non-contact with the cooling source container and is configured such that a part thereof is inserted into the cooling source container and contacts the cooling source.

2. The charged particle beam apparatus according to claim 1, wherein the cooling source container has an insertion hole for inserting the contact member, and the insertion hole is formed such that a gap is secured between the cooling source container and the contact member inserted therein.

3. The charged particle beam apparatus according to claim 2, wherein the insertion hole is provided at a position higher than the maximum liquid level of the cooling source in the cooling source container.

4. The charged particle beam apparatus according to claim 1, wherein the contact member includes cooling fins at a portion contacting the cooling source.

5. The charged particle beam apparatus according to claim 1, wherein the contact member is a sample holder for holding the sample.

6. The charged particle beam apparatus according to claim 5, further comprising a focused ion beam column for emitting a focused ion beam, an electron beam column for emitting an electron beam, and a detector for detecting electrons.

7. A sample cooling mechanism used in a charged particle beam apparatus comprising a base frame and a sample chamber supported by the base frame, the sample cooling mechanism including a contact member supported by the sample chamber and contacting the sample inside the sample chamber, and a cooling source container housing a cooling source, wherein the cooling source container is supported by the sample chamber or the base frame outside the sample chamber, and the contact member is non-contact with the cooling source container and is configured such that a part thereof is inserted into the cooling source container and contacts the cooling source.

8. Using the charged particle beam apparatus according to claim 6, while cooling the sample through the sample holder, a slicing step of irradiating a focused ion beam onto the sample held by the sample holder to slice the sample, and an SEM image acquisition step of irradiating an electron beam onto the sample cross-section exposed by the slicing and acquiring an SEM image of the sample cross-section are repeatedly performed. A continuous cross-section processing observation method characterized by this.

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