Sample preparation procedure and setup

Abstract

Sample preparation procedure, which includes: in the course of displaying an observational image of a cross-section, which is a first cross-section, of a sample (7) under scanning electron microscope observation on a display screen, subjecting the first cross-section to an etching process by scanning and irradiation by a focused ion beam (9), thereby exposing a second cross-section of the sample (7); and During the display of an observation image of the second cross-section under scanning electron microscope observation on the display screen, changing the scanning direction of the focused ion beam (9) while the scanning and irradiation by the focused ion beam (9) are carried out, and subjecting the second cross-section to etching by scanning and irradiation by the focused ion beam (9) which has the changed scanning direction, thereby exposing a desired cross-section of the sample (7), wherein the sample (7) has a periodically arranged device pattern (32) and wherein the change in the scanning direction of the focused ion beam (9) includes such a change in the scanning direction by rotating the scanning direction of the focused ion beam (9) in the plane of the surface of the sample (7) that it is parallel to an arrangement direction of the device pattern (32) of the sample (7), while the focused ion beam (9) continuously scans and irradiates the sample (7).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a sample preparation method and apparatus for preparing a sample by etching processing using a focused ion beam. 2. Description of the state of the art

[0002] As a method for analyzing internal structures and defects in a semiconductor device or the like, a cross-sectional processing and observation method is known in which a focused ion beam is used for cross-sectional processing of a sample to expose a cross-section containing a desired structure or defect, and a scanning electron microscope is used to observe the cross-section. According to this method, a desired observation target can be exposed within the sample with high accuracy, and thus the structure or defect can be quickly observed.

[0003] As a method for exposing a desired observation target, a method of repeatedly performing cross-sectional processing and cross-sectional observation is disclosed, and the cross-sectional processing is terminated at the time an observation target appears in a cross-sectional observation image (see JP 2009-204480 A). According to this method, a cross-section containing a desired observation target can be accurately exposed.

[0004] JP 2005-122 909 A also shows a method for cross-sectional machining with ion beams, which minimizes rotation-related displacements.

[0005] Another known analytical method is a method for preparing a sample containing a desired observation target from a sample using a focused ion beam and observing the sample through a transmission electron microscope. According to this method, an observation target can be observed with high resolution through the transmission electron microscope.

[0006] In the case of using a focused ion beam to expose a cross section of a semiconductor device or prepare a sample piece, it is important to process a cross section along an arrangement direction of a device pattern in a semiconductor wafer.

[0007] In the cross-sectional processing and observation method, the structure or defects are observed from an observation image of a cross-section containing a device pattern, and therefore, it is necessary to expose the cross-section along the arrangement direction of the device pattern. Furthermore, during sample preparation, the internal structure of the sample is analyzed by transmission electron microscope (TEM) observation, and therefore, it is necessary to prepare a sample having a desired internal structure and aligned along the arrangement direction of the device pattern.

[0008] However, in recent years, the device pattern has become finer along with the densification and reduction in the size of semiconductor devices. Thus, it has become difficult for the conventional method to verify the arrangement direction of the device pattern by observation and to form the cross-section along the arrangement direction of the device pattern. OUTLINE OF THE INVENTION

[0009] Representative aspects of the present invention provide a sample preparation method and apparatus for preparing a sample along an arrangement direction of a fine device pattern.

[0010] (1) According to the invention, there is provided a sample preparation method which includes: in the course of displaying an observation image of a cross section, which is a first cross section, of a sample under scanning electron microscope observation on a display screen, subjecting the first cross section to etching processing by scanning and irradiation by a focused ion beam, thereby exposing a second cross section of the sample;and, in the course of displaying an observation image of the second cross section under scanning electron microscope observation on the display screen, changing a scanning direction of the focused ion beam while performing the scanning and irradiation by the focused ion beam, and subjecting the second cross section to etching processing by the scanning and irradiation by the focused ion beam having the changed scanning direction, thereby exposing a desired cross section of the sample, the sample having a periodically arranged device pattern, and wherein the change in the scanning direction of the focused ion beam comprises such changing of the scanning direction by rotating the scanning direction of the ; focused ion beam in the plane of the surface of the sample such that it is parallel to an arrangement direction of the device pattern of the sample, while the focused ion beam continuously scans and irradiates the sample.

[0011] With this setup, a cross-section of the sample can be exposed along the arrangement direction of an internal device pattern. The scanning direction of the focused ion beam can be adjusted while observing the sample in real time through a scanning electron microscope. Thus, even in a device pattern in which devices are arranged at a pitch of several tens of nanometers, the formation direction of the cross-section and the arrangement direction of the device pattern can be precisely aligned.

[0012] (2) According to another aspect of the present invention, there is provided a sample preparation device including: a sample stage configured to place a sample thereon; a focused ion beam column configured to scan and irradiate the sample with a focused ion beam to expose a cross section of the sample; an electron beam column configured to scan and irradiate the cross section with an electron beam; a charged particle detector configured to detect a charged particle emitted from the cross section by irradiation with the electron beam; a display section configured to display an observation image of the cross section formed by a detection signal of the charged particle detector;an input section configured to receive an input of a rotation angle of a scanning direction of the focused ion beam; and a scanning direction control section configured to change the scanning direction of the focused ion beam during the processing and observation of the cross-section based on the rotation angle input via the input section; wherein the scanning direction control section is configured to change the scanning direction of the focused ion beam by rotating the scanning direction of the focused ion beam in the plane of the sample surface so that it is parallel to an arrangement direction of the device pattern of the sample while the focused ion beam column continuously scans and irradiates the sample with the focused ion beam.

[0013] With this structure, the scanning direction of the focused ion beam can be adjusted while looking at an observation image of the cross section under processing displayed on the display section.

[0014] According to the sample preparation apparatus and method of the present invention, even in the case of a sample having a fine device pattern, the cross section can be formed along the arrangement direction of the device pattern, and thus a sample for analyzing the fine internal structure or defects can be prepared. SHORT DESCRIPTION OF THE DRAWING

[0015] The accompanying drawing shows as follows: Fig. 1 is a structural diagram of a sample preparation device according to an embodiment of the present invention; Fig. 2A and Fig. 2B are explanatory diagrams of a sample surface and a sample cross section, respectively, according to a first example of the present invention; Fig. 3A to 3D are explanatory diagrams of a processing method according to the first example of the present invention; Fig. 4 is a structural diagram of a display screen according to the first example of the present invention; Fig. 5A to 5C are explanatory diagrams of a preparation of a sample for TEM observation according to a second example of the present invention; and Fig. 6 is an explanatory diagram of the sample for TEM observation according to the second example of the present invention. DETAILED DESCRIPTION

[0016] A sample preparation device and a method according to an embodiment of the present invention are described below.

[0017] As in Fig. 1, the sample preparation device in this embodiment includes an EB column 1, an FIB column 2, and a sample chamber 3. The EB column 1 and the FIB column 2 each irradiate a sample 7, which is accommodated in the sample chamber 3, with an electron beam 8 and an ion beam 9.

[0018] The sample preparation device further includes a secondary electron detector 4 and a backscattered electron detector 5 as a charged particle detector. The secondary electron detector 4 is capable of detecting secondary electrons generated from the sample 7 by irradiation with the electron beam 8 or the ion beam 9. The backscattered electron detector 5 is provided within the EB column 1. The backscattered electron detector 5 is capable of detecting backscattered electrons reflected by the sample 7 as a result of the irradiation of the electron beam 8 onto the sample 7.

[0019] The sample preparation device further includes a sample platform 6 for placing the sample 7 thereon. The sample platform 6 can be tilted to change an angle of incidence of the ion beam 9 onto the sample 7. The tilt of the sample platform 6 is controlled by a sample platform control section 16.

[0020] The sample preparation device further includes an EB control section 12, an FIB control section 13, an image generation section 14, and a display section 17. The EB control section 12 transmits an irradiation signal to the EB column 1 to control the EB column 1 to radiate the electron beam 8. The FIB control section 13 transmits an irradiation signal to the FIB column 2 to control the FIB column 2 to radiate the ion beam 9. The image generation section 14 generates a backscattered electron image based on a signal for scanning the electron beam 8, which is sent from the EB control section 12, and a signal of the backscattered electrons detected by the backscattered electron detector 5. The display section 17 is capable of displaying the backscattered electron image.The image forming section 14 forms data of an SEM image based on the signal for scanning by the electron beam 8, which is sent from the EB control section 12, and a signal of the secondary electrons detected by the secondary electron detector 4. The display section 17 is capable of displaying the SEM image. Further, the image forming section 14 forms data of an SIM image based on a signal for scanning by the ion beam 9, which is sent from the FIB control section 13, and a signal of the secondary electrons detected by the secondary electron detector 4. The display section 17 is capable of displaying the SIM image.

[0021] The sample preparation device further includes an input section 10 and a control section 11. An operator inputs conditions via the device controller, such as a beam irradiation condition, into the input section 10. The input section 10 transmits the input information to the control section 11. The control section 11 transmits a control signal to the EB control section 12, the FIB control section 13, the image generation section 14, the sample stage control section 16, or the display section 17, thereby controlling the operation of the sample preparation device.

[0022] A description will be given of the control of the device. For example, the operator sets an irradiation area of ​​the ion beam 9 based on an observation image displayed on the display section 17, such as the backscattered electron image, the SEM image, or the SIM image. The operator inputs a processing frame for setting the irradiation area on the observation image displayed on the display section 17 via the input section 10. The processing frame, as used herein, is a frame indicating a boundary between a region to be irradiated by the ion beam 9 and a region not to be irradiated by the ion beam 9.When the operator inputs an instruction to start processing via the input section 10, a signal indicating the irradiation area and a signal indicating the start of processing are transmitted from the control section 11 to the FIB control section 13, and the FIB control section 13 irradiates the ion beam 9 onto the specified irradiation area of ​​the sample 7. In this way, the irradiation area input by the operator can be irradiated by the ion beam 9.

[0023] A scanning direction control section 15 generates a signal for changing the scanning direction of the ion beam 9 based on a scanning direction of the ion beam 9 input via the input section 10, and transmits the signal to the FIB control section 13. The FIB control section 13 transmits a control signal to the FIB column 2 for changing the scanning direction of the ion beam 9 irradiated from the FIB column 2. Incidentally, the scanning direction control section 15 is configured to change the scanning direction of the ion beam 9 even in the state where the sample 7 is scanned and irradiated by the electron beam 8 and the ion beam 9 from the EB column 1 and the FIB column 2, respectively. (First example)

[0024] Referring to Fig. 2A to 4, a description will be given about a sample preparation method according to this example, which relates to cross-sectional processing and observation for analyzing an internal structure of a sample having a device pattern.

[0025] Fig. 2A is a diagram of sample 7 viewed from a surface 7a. First, sample 7 is scanned and irradiated by the ion beam 9 from the surface 7a to form a processing groove 21 in a portion of the surface 7a. Fig. Figure 2B is a diagram taken along the cross section bb of Fig. 2A. To observe a cross section 7b exposed by preparing the processing groove 21, the cross section 7b is scanned and irradiated by an electron beam 8a. In this way, an SEM image of the cross section 7b is displayed on the display section 17.

[0026] To expose a defect present within sample 7, cross-sectional processing is performed by ion beam 9. In this case, to inspect the defect, the cross-sectional sections undergoing cross-sectional processing are continuously observed by a scanning electron microscope. In other words, during processing to expose cross-sectional sections 7c, 7d, and 7e by ion beams 9a, 9b, and 9c, respectively, the cross-sectional sections 7c, 7d, and 7e are irradiated with electron beams 8b, 8c, and 8d to display respective SEM images of the cross-sectional sections 7c, 7d, and 7e in real time. SEM images are also displayed in real time during the exposing of the cross-sectional sections.

[0027] In this case, a distance t1 between the cross section 7b and the cross section 7c formed by the ion beam 9a is equal to a distance between the cross section 7c and the cross section 7d formed by the ion beam 9b, and a distance between the cross section 7d and the cross section 7e formed by the ion beam 9c. In this example, the distance t1 is set to 1 nm, and after the ion beam 9 is scanned once in the scanning direction, the ion beam 9 is moved by 1 nm in a sub-scanning direction perpendicular to the scanning direction of the ion beam 9, and the ion beam 9 is then scanned once again in the scanning direction. In this way, the scanning by the ion beam 9 in the scanning direction and the movement of the ion beam 9 in the sub-scanning direction are repeatedly performed.

[0028] As described above, the cross sections are observed in real time during processing, and thus the cross section processing can be completed when a defect appears as an observation target in an SEM image, and the defect can be analyzed by observing the cross section containing the defect.

[0029] Furthermore, when analyzing the structure of a sample with a device pattern, it is necessary to expose a cross-section along the arrangement direction of the device pattern. This is because the device structure can only be analyzed by observing a cross-section image in which the original shape of the device pattern appears.

[0030] Fig. Fig. 3B is a diagram of the sample 7 viewed from its surface. In a case where an arrangement direction 33 of a device pattern 32 is not parallel to a scanning direction 31a of the ion beam 9 for exposing the cross section 7b by irradiation, as shown in an SEM image of the cross section 7b of Fig. As shown in Figure 3A, device assemblies 32a, 32b, and 32c in cross section 7b are exposed as assemblies having different widths. When the device assemblies are analyzed from the SEM image of cross section 7b, device assemblies 32a, 32b, and 32c are erroneously determined as device assemblies having different widths.

[0031] To solve this problem, the scanning direction 31a of the ion beam 9 is reversed in the plane of the surface 7a of the sample 7 so that the scanning direction 31a can be parallel to the arrangement direction 33 of the device pattern 32. As shown in Fig. 3D, the scanning direction 31b of the ion beam 9 is reversed to be parallel to the arrangement direction 33 of the device pattern 32, and the sample 7 is processed by the ion beam 9 to expose a cross section 7f. Fig. Figure 3C is an SEM image of cross-section 7f. This SEM image reflects the original device structures of the device pattern 32, in which the device structures 32a, 32b, and 32c, which have the same width, are displayed. In this way, a precise structure analysis can be performed based on the SEM image of the cross-section.

[0032] A description will now be given of a method for changing the scanning direction of the ion beam 9.

[0033] Fig. 4 is a configuration diagram of a display screen of the display section 17. The sample preparation device in this example is capable of scanning and irradiating the electron beam 8 and the ion beam 9 independently of each other, and controlling the start and end of irradiation of the respective beams by operations of an electron beam irradiation button 43 and an ion beam irradiation button 44 via the input section 10. In the case where the sample 7 is irradiated by both the electron beam 8 and the ion beam 9, respective observation images of an SEM image 41 and an SIM image 42 can be displayed on the display screen in real time.

[0034] When a rotation angle of the ion beam 9 is input via the input section 10, the rotation angle is displayed in a rotation angle display section 45 of the display screen. Based on the rotation angle, the scanning direction control section 15 reverses the scanning direction of the ion beam 9. The rotation angle as used here refers to a rotation angle in the plane of the surface 7a of the sample 7 with reference to the scanning direction. In this example, the rotation angle is input in 0.01 degree increments to change the scanning direction.

[0035] The scanning direction control section 15 is configured to reverse the scanning direction during the scanning and irradiation by the ion beam 9. Thus, it is unnecessary to suspend the processing by the ion beam 9 for rotational adjustment of the scanning direction, resulting in the function and effect that the cross-sectional processing can be performed efficiently.

[0036] The scanning direction control section 15 is also capable of reversing the scanning direction of the ion beam 9 during scanning electron microscope observation. In this way, the scanning direction of the ion beam 9 can be adjusted while observing the cross section under processing, and thus even fine adjustment of the rotation angle can be accurately performed. In addition, the scanning direction can be reversed without stopping the scanning and irradiation of the ion beam 9 and without stopping the scanning electron microscope observation, thus significantly shortening the time period required for cross-section processing.

[0037] Furthermore, the cross section reflecting the original shape of the device pattern can be exposed, and thus this example provides the noticeable function and effect as well in the case of analyzing the device pattern structure.

[0038] Although the SEM image is used in the description in the above-mentioned example, a backscattered electron image may be used instead of the SEM image. (Second example)

[0039] Referring to Fig. 5A to 5C and Fig. 6, a description will be given of a sample preparation method according to this example, which relates to a sample for TEM observation.

[0040] Fig. 5A is a diagram of a sample 7 as a semiconductor wafer. To prepare a sample for TEM observation, processing is performed to cut out a strip-shaped sample 51 as a part of the sample 7 from the sample 7 by the ion beam 9. Fig. Fig. 5B is an enlarged diagram of the strip-shaped sample 51 and its surroundings. Processing grooves 52 are formed on both sides of the strip-shaped sample 51 by the ion beam 9. Then, as shown in Fig. 5C, further, a thinning processing is performed such that the strip-shaped sample 51 can have a desired thickness, thus preparing the strip-shaped sample 51 for TEM observation.

[0041] Fig.Figure 6 is an explanatory diagram of the strip-shaped sample 51 for TEM observation. The strip-shaped sample 51 has a structure in which devices 54a and 54b are periodically arranged. The devices 54a and 54b are divided by element isolation (STI) regions 53a, 53b, and 53c, which are provided for device isolation, and are placed in regions sandwiched by the element isolation (STI) regions.

[0042] In thinning processing, the strip-shaped sample 51 is processed such that a desired device structure can remain within the strip-shaped sample 51. For example, in the case of preparing a strip-shaped sample having only one device, the strip-shaped sample 51 is subjected to etching processing by the ion beam 9 such that only the element isolation (STI) region 53b, the element isolation (STI) region 53c, and the device 54b sandwiched by the element isolation (STI) region 53b and the element isolation (STI) region 53c can remain. The distance between the devices is on the order of several tens of nanometers, and thus the final thickness of the strip-shaped sample 51 having only one device is particularly small.In a dilution processing method for preparing such a stripe-shaped sample, it is important to scan and irradiate the sample with the ion beam 9 along the arrangement direction of the device pattern.

[0043] In the thinning processing method, the method described in the first example is used to reverse the scanning direction of the ion beam 9 so that it is parallel to an arrangement direction 55 of the device pattern. In other words, in the state where a cross section 51a is scanned and irradiated by the electron beam 8 to perform scanning electron microscope observation, etching processing is performed by the ion beam 9 such that the thickness of the stripe-shaped sample 51 is reduced. By observing an SEM image of the cross section 51a through the scanning electron microscope observation under the etching processing, the scanning direction of the ion beam 9 is reversed such that the widths of the plurality of element isolation (STI) regions 53a exposed in the cross section 51a can be uniform.In addition, similar etching processing is also performed on a cross section on the opposite side of the cross section 51a of the strip-shaped sample 51. Then, the internal device structure of the strip-shaped sample 51 is estimated based on the device pattern exposed in the cross section and the thickness of the strip-shaped sample 51. The processing by the ion beam 9 is completed when only the element isolation (STI) region 53b, the element isolation (STI) region 53c, and the device 54b sandwiched by the element isolation (STI) region 53b and the element isolation (STI) region 53c remain in the strip-shaped sample 51. In this way, a desired strip-shaped sample 51 can be prepared.

[0044] According to the dilution processing method described above, even in the case of a sample for TEM observation having a particularly fine device pattern, the scanning direction of the ion beam 9 can be reversed while the sample is being observed in real time by scanning electron microscopy. Thus, a desired stripe-shaped sample can be accurately prepared. Furthermore, the scanning direction of the ion beam 9 can be reversed without interrupting the scanning and irradiation of the ion beam 9, and thus a desired stripe-shaped sample can be prepared within a short period of time.

Claims

[1] Sample preparation procedure, which includes: in the course of displaying an observation image of a cross section, which is a first cross section, of a sample (7) under scanning electron microscope observation on a display screen, subjecting the first cross section to etching processing by scanning and irradiation by a focused ion beam (9), thereby exposing a second cross section of the sample (7); and in the course of displaying an observation image of the second cross section under scanning electron microscope observation on the display screen, changing a scanning direction of the focused ion beam (9) while performing scanning and irradiation by the focused ion beam (9), and subjecting the second cross section to etching processing by scanning and irradiation by the focused ion beam (9) having the changed scanning direction, thereby exposing a desired cross section of the sample (7), wherein the sample (7) has a periodically arranged device pattern (32) and wherein changing the scanning direction of the focused ion beam (9) includes changing the scanning direction by rotating the scanning direction of the focused ion beam (9) in the plane of the surface of the sample (7) so that it is parallel to an arrangement direction of the device pattern (32) of the sample (7) while the focused ion beam (9) continuously scans and irradiates the sample (7). [2] A sample preparation method for preparing a strip-shaped sample having a desired cross section formed by the sample preparation method according to claim 1. [3] Sample preparation device containing: a sample platform (6) adapted to place a sample (7) having a periodically arranged device pattern (32) thereon; a focused ion beam column (9) configured to scan and irradiate the sample (7) with a focused ion beam (9) to expose a cross-section of the sample (7); an electron beam column (8) designed to scan and irradiate the cross section with an electron beam (8); a charged particle detector configured to detect a charged particle emitted from the cross section by irradiation by the electron beam (8); a display section (17) configured to display an observation image of the cross section formed by a detection signal of the charged particle detector; an input section (10) configured to receive an input of a rotation angle from a scanning direction of the focused ion beam (9); and a scanning direction control section (15) which is designed to change the scanning direction of the focused ion beam (9) in the course of processing and observing the cross section, based on the rotation angle received by the input section (10), wherein the scanning direction control section (15) is adapted to change the scanning direction of the focused ion beam (9) by rotating the scanning direction of the focused ion beam (9) in the plane of the surface of the sample (7) such that it is parallel to an arrangement direction of the device pattern (32) of the sample, while the column of the focused ion beam (9) continuously scans and irradiates the sample (7) with the focused ion beam (9). [4] Sample preparation device according to claim 3, in which the display section (17) is designed to display: an SEM image or a retroreflected electron microscope image of the cross-section; a SIM image of the sample (7); a focused ion beam display section (9) for instructing a start and a stop of irradiation by the focused ion beam (9); an electron beam display section (8) for instructing a start and a termination of the irradiation by the electron beam (8); and a rotation angle display section (45) for entering the rotation angle. [5] A sample preparation device according to claim 3 or 4, wherein the charged particle detector comprises a backscattered electron detector (5) or a secondary electron detector (4).

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