JP2004361138A - Fib device for tem sample processing equipped with function for automatically recognizing bending - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of TEM sample automatic finishing by being equipped with a function for recognizing automatically a bending phenomenon generated in TEM sample processing by an FIB device. <P>SOLUTION: In a bending automatic recognition method in the TEM sample processing, secondary electron detection is performed by a secondary charged particle detector at a thinning time of the TEM sample, and the sample is determined to be bent when detecting a sudden change in a detection signal. In a TEM sample processing method, the secondary electron detection is performed by the secondary charged particle detector at the thinning time of the TEM sample, and the sample is determined to be bent when detecting the sudden change in the detection signal, and thinning is discontinued. Cutting by the FIB is performed to straighten the bending, and thinning is proceeded in this state. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for automatically recognizing bending distortion generated in the process of thinning a sample such as a transmission electron microscope (TEM) using a focused ion beam (FIB).
[0002]
[Prior art]
The cross-sectional sample for TEM observation needs to be thinned until it is thin enough to allow transmission of an electron beam by specifying a desired observation position of a large sample. It is well known to make such a sample by thinning using an FIB apparatus. A method of cutting a small piece mechanically from a wafer-like sample and processing it, and etching the wafer as it is to obtain a thin piece There is known a method of taking out a sample that has been converted into a solid. As shown in FIG. 6A, the former processing method requires a machining process in which a small block having a width of 500 μm to 2 mm and a length of 3 mm is first cut from a sample wafer, and the upper portion is further cut to 50 μm or less. As shown in FIG. 6B, a raw material gas such as W (CO) ₆ is sprayed onto the processing portion by a gas gun as shown in FIG. 6B, and a protective film is formed by deposition. After that, as shown in FIG. 6-C, FIB is irradiated to produce a sample by slicing to the target finish width, and as shown in FIG. 4-D, the electron beam is transmitted and used as a cross-sectional sample for TEM observation. Used. In the latter processing method, focused ion beam processing is executed directly from the wafer without machining, and a protective film is first formed on the processing portion by deposition using FIB as shown in FIG. A focused ion beam is irradiated from above the surface, and both sides of the observation cross section are cut off by etching, and a square hole is formed on both sides of the observation cross section with a focused ion beam device. Etching is performed by scanning the FIB from both sides, and thinning is performed to the target finish width. The bottom cut, side cut and cut are made in the peripheral part of the thinned sample, and finally the thin sample is held by a glass probe operated by a manipulator, and is moved and adhered to a sample fixing table such as an organic thin film. To complete the TEM observation sample.
[0003]
Regardless of the method for producing a cross-sectional sample for TEM observation, there is a process called thinning processing by FIB in the processing process. In this case, if the sample is made thinner, the thin wall portion of the sample may be distorted and curved as if the celluloid underlay was pressed and bent from both sides. In such a state, even if the ion beam is scanned linearly, the sample is deformed, so that it is impossible to perform planar processing with a uniform thickness. As shown in FIG. 4-A, when the slicing process proceeds and the final finishing process is started, the slab portion has a dimension on the order of submicron, and is easily deformed by bending when subjected to compositional structural stress. FIG. 4-B shows a state where the stress is small and there is no deformation, and FIG. 4-C is a diagram schematically showing a state where the stress is large and the curve is deformed. If processing of linear scanning by FIB is continued in such a curved state, the observation surface will be cut and the precious sample will be destroyed. Conventionally, in such a case, the sample block has to be replaced and the operation has to be performed again from the beginning. However, when the sample is the same type of element, the compositional and structural conditions are the same, and thus a sample that is easily deformed often gives the same result. However, if the processing is interrupted at the stage of thickness before deformation occurs, the electron transmittance is low, or mismatched portions remain on the images on both sides, which is unsatisfactory as a TEM sample. In order to solve this problem, the present applicant previously presented Patent Document 1. In view of the fact that the bending strain of the sample generated is caused by the concentration of stress in the sample material, FIG. 4-D is a plan view showing the upper portion of the processed cross section, and FIG. 4-E is a perspective view. As shown in the drawing, a non-patterned portion that does not affect the observation in the cross-sectional portion is subjected to a cutting process, and the necessary processing is advanced by releasing the stress and correcting the curvature. However, it is impossible to predict when and when this bending due to stress will occur. If the processing is continued without recognizing this bending, the thin piece portion of the processed TEM sample may be processed and cannot be used as the TEM sample. Although the technique of Patent Document 1 presents a technique for correcting the bending, it does not present a technique for early detection of the bending phenomenon. It is important to detect the bending phenomenon at an early stage in order not to destroy the TEM sample. For this purpose, processing must be performed while frequently observing with a scanning electron microscope (SEM) attached to the FIB apparatus. I had to. In the case of a sample with a large stress, special attention is required, and this problem cannot be dealt with by the TEM sample automatic finishing using a recipe.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-35391 “Method for Removing Sample Distortion During Thinning” Published on Feb. 2, 2000, paragraph number [0006] FIG.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a technique that enables automatic finishing of a TEM sample by providing a function of automatically recognizing a bending phenomenon that occurs in TEM sample processing by an FIB apparatus.
[0006]
[Means for Solving the Problems]
In the TEM sample processing automatic bending method of the present invention, the secondary charged particle detector performs secondary electron detection at the time of thinning the TEM sample, and the sample is curved when a sudden change is detected in the detection signal. I decided to judge. In the TEM sample processing method of the present invention, secondary electron detection is performed with a secondary charged particle detector during thinning processing of the TEM sample, and when a sudden change is detected in the detection signal, it is determined that the sample is curved. Then, the thinning process was interrupted, the cutting process using FIB was performed to correct the bending, and the thinning process was advanced in that state.
[0007]
Further, the FIB apparatus for processing a TEM sample having an automatic bending recognition function according to the present invention is a means for detecting secondary electrons emitted from a sample during finishing processing of a thin section with a secondary charged particle detector, and this detection. Means for detecting the curvature of the sample from the change of the signal, and means for interrupting the FIB processing by the output when the detection means detects the curvature of the sample, the means for detecting the curvature When the differential value of the secondary charged particle detection signal is determined by comparing with the threshold value, the difference signal with the secondary charged particle detection level at the starting point of the scanning line is calculated, and the calculated value exceeds the threshold value. This is realized by determining, or by determining the secondary charged particle detection level as a graph corresponding to the scanning position, and determining that the sample is bent when the graph cannot be linearly approximated.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
When the bending phenomenon occurring at the time of processing the TEM sample is monitored as a scanning ion microscope (SIM) image, when the bending of the thin piece portion is processed, a sharply bright portion appears in the scanning line image of the processed portion. I discovered that. In that case, the thin piece portion is cut in a short time, making it unusable as a TEM sample. Considering this phenomenon, if the thin sample is flat as shown by a solid line in FIG. 1-A, the FIB is scanned along its surface in a shallow contact state as shown in FIG. 1-B. The observation SIM image at that time is displayed as a uniform linear image as a whole. On the other hand, when the thin sample is bent as shown by the wavy line in FIG. 1-A, the FIB is shallow at the fixed portion at both ends and deeply hits at the convex warped portion as shown in FIG. 1-C. Since it is scanned linearly, the observation SIM image at that time is displayed as a straight line with a bright central portion and high luminance, and both ends with low luminance. When the sample piece is curved in this way, the area subjected to FIB irradiation is widened, so that it is understood that the SIM image is observed with high brightness. By the way, the curve when a strong stress is applied is not always convex on the processed surface, and may be curved so as to be concave. In that case, since the FIB does not cut into the sample surface, there is no problem. However, when the opposite surface to be performed next is processed, the processed surface becomes convex as described above, and can be detected at that time.
[0009]
The present invention pays attention to a phenomenon in which a bright portion suddenly appears when the thin piece portion is bent, and it is conceived that the bending at the time of sample preparation can be detected in real time by monitoring this change in luminance. Since the luminance change at that time corresponds to the detection signal level of the secondary charged particles (secondary electrons), the output signal may be used as the detection signal. When the processing area is set and the processing is started, the FIB hits the sample deeply at the beginning, so a bright scanning line is displayed on the whole, and as the processing proceeds, the FIB hit becomes shallower. It will be displayed. Therefore, it is difficult to detect a bend only by the detection signal level (brightness) of secondary charged particles, and when a bend occurs, the change in brightness occurs within the same scan, so the change in brightness within the same scan is determined. This makes it possible to detect bending. In order to determine this sudden change in luminance, for example, (1) a method of detecting the change rate (differential value) of the detection signal by comparing it with a threshold, and (2) graphing the luminance level in correspondence with the scanning position, linear approximation (3) A method for determining that the sample is bent when it is no longer possible, and (3) calculating the difference signal between the luminance level at each position of the scanning line and the luminance level at the starting point of the scanning line and detecting that the value exceeds the threshold The method to do can be adopted. If the bending is detected, the FIB processing is immediately interrupted, and then the FIB is irradiated to the portion that does not interfere with the observation of the TEM specimen thin piece portion to perform the slit processing, and the bending stress is released. If the thinning process is resumed after repair, the sample can be prevented from being damaged.
[0010]
An outline of the FIB apparatus that performs these processes will be described with reference to FIG. 1 is an ion source, 2 is an ion beam, 3 is an ion optical system, 4 is a deflector, 9 is a sample, and 5 is a sample stage. 6 is a gas gun, 7 is a secondary charged particle detector, 8 is not essential, but is a charge neutralizer that neutralizes the charge of the sample, 10 is a computer that functions as a controller of the apparatus, 11 is a scanning ion microscope (SIM) ) And a control panel, and 12 is an input operation unit. In addition, a vacuum device that puts the sample chamber in a vacuum state and a drive mechanism for setting the sample stage 5 to a desired position angle are provided as equipment not shown. The drive mechanism is generally X. Y. Z, T, R direction displacement, ion beam axis rotation, and angle adjustment with respect to the ion beam axis can be performed. Further, the computer 10 outputs various control signals such as an acceleration voltage, an ion optical system setting signal, a stage drive signal, a deflector scanning signal to the deflector, and a gas gun or charge neutralizer operation signal. The above configuration is a basic configuration of a conventional FIB apparatus. In addition to the above basic configuration, the FIB apparatus for processing a TEM sample having an automatic bending recognition function according to the present invention uses a secondary charged particle detector 7 to emit secondary electrons emitted from the sample during the finishing process of thinning. It is necessary to have a means for detecting, a means for detecting the curvature of the sample from the change of the detection signal, and a function for interrupting the FIB processing by the output when the detecting means detects the curvature of the sample. As means for judging the bending state of the sample from the change in detection of secondary charged particles, (1) a method of detecting the change rate (differential value) of the secondary charged particle detection signal by comparing it with a threshold value, or (3) When a method of detecting the difference signal between the luminance level at each position of the scanning line and the luminance level at the starting point of the scanning line and detecting that the value exceeds the threshold, a comparator should be installed in hardware. However, although it is realizable, the structure which determines as data processing by software within the computer 10 is simple. Also, (2) graphing the luminance level in correspondence with the scanning position, and adopting a method of determining that the sample is bent when linear approximation cannot be performed, the graph line is overlapped with the line of the allowable width and protrudes from the width. It can be implemented by providing means for determining whether or not. Of course, a configuration in which this is also determined as data processing in software in the computer 10 is adopted. One feature of the apparatus of the present invention is that the computer 10 has such a function of detecting the bending of the sample.
[0011]
The operation of the sample when the sample is processed using the FIB apparatus of the present invention will be described with reference to the flowchart of FIG. 3 while monitoring the curve of the sample. In the sample preparation process in step 1, when entering the finishing stage of the thinning process, as shown in step 2, the FIB under conditions for performing the finishing process is scanned along the sample surface. In step 3, the detection signal from the secondary charged particle detector is input to the signal processing unit. In step 4, the sample processing unit automatically performs a sample bending recognition process and monitors whether there is an abnormality. In step 5, it is determined whether an abnormality has been detected in the signal processing unit. If no abnormality is detected, it is confirmed in step 6 whether the processing has been completed. If the processing has been completed, the process proceeds to step 7 and the FIB irradiation is stopped. However, if the machining is in progress, the process returns to step 4 to continue the machining. The abnormality detection method is implemented in various forms as described above. If an abnormality is detected in step 5, FIB irradiation is immediately stopped in step 8 and the machining is interrupted. In step 9, a microscope image obtained by SEM or SIM is obtained and the curved state is observed, a portion where there is no problem even if the cutting process is performed is specified, and a cutting process using FIB is executed in step 10. In step 11, it is confirmed whether or not the curvature of the sample has been corrected. If it has not been corrected yet, the process returns to step 10 to proceed with the cutting process. When it is confirmed that the problem has been corrected, the process returns to step 2 to start the FIB investigation and resume the finishing process.
[0012]
The automatic bending recognition method in TEM sample processing according to the present invention performs secondary electron detection with a secondary charged particle detector during thinning processing of a TEM sample, and detects a sudden change in the detection signal. Since it automatically determines that the sample is curved, it is possible to detect the curvature of the sample quickly and reliably without burdening the operator, and without requiring skilled skills, and support for creating a TEM sample with a high yield. it can.
In the TEM sample processing method of the present invention, secondary electron detection is performed with a secondary charged particle detector during thinning processing of the TEM sample, and when a sudden change is detected in the detection signal, it is determined that the sample is curved. Therefore, the thinning process is interrupted, the cutting process is performed by FIB, the bend is corrected, and the thinning process is advanced in that state, so that it does not ruin the precious specimen like before. This is not a time-consuming process such as often interrupting the process during the process and proceeding while confirming the state, but increases the possibility of highly reliable automatic processing. Therefore, it is particularly effective when making a valuable sample without replacement.
[0013]
The FIB apparatus for processing a TEM sample according to the present invention is a means for detecting secondary electrons emitted from a sample during the finishing process of thinning with a secondary charged particle detector, and detects the curvature of the sample from the change of the detection signal. And means for interrupting the FIB processing by the output when the detection means detects the curvature of the sample, so that the curvature of the sample is automatically recognized and the thinning process is interrupted. It is possible not to mess up the precious sample like before with the conventional equipment, and it is not time-consuming processing that often interrupts the processing and confirms the state while proceeding. This increases the possibility of highly reliable automatic processing.
In addition, as a means for detecting the curvature of the sample, the differential value of the secondary charged particle detection signal is determined by comparing with a threshold value, and the difference signal from the secondary charged particle detection level at the starting point of the scanning line is calculated, The present invention is to determine when the calculated value exceeds a threshold value, or to determine that the sample is bent when the secondary charged particle detection level is graphed in correspondence with the scanning position and the graph cannot be linearly approximated. The FIB apparatus for processing a TEM sample can be easily realized by software as signal processing in a computer without requiring a special hardware member.
[0014]
When the TEM sample processing is continuously performed until the finishing processing, the bending due to the stress may ruin the sample, which has been a great obstacle to automatic processing of only one sample. However, when this method is used, even in the case of a stressed sample, it is not necessary for the operator to constantly monitor the processing screen, and TEM sample automatic finishing using a recipe can be performed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a phenomenon focused on by the present invention.
FIG. 2 is a diagram showing a basic configuration of an FIB apparatus used in the present invention.
FIG. 3 is a flowchart for explaining the operation of a TEM sample processing FIB apparatus having an automatic bending recognition function according to the present invention.
FIG. 4 is a diagram for explaining a bending phenomenon of a thin piece sample, which is a premise of the present invention, and a method for correcting the bending.
FIG. 5 is a diagram for explaining a method of creating a TEM sample by directly processing a large sample with an FIB apparatus.
FIG. 6 is a diagram for explaining a method of mechanically cutting out a small piece from a large sample and processing it with an FIB apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ion source 7 Secondary charged particle detector 2 Ion beam 8 Charge neutralizer 3 Ion optical system 9 Sample 4 Deflector 10 Computer 5 Sample stage 11 Display 6 Gas gun 12 Input operation part

Claims (7)

Secondary charged particle detection is performed with a secondary charged particle detector at the time of thinning of a TEM sample, and when a sudden change is detected in the detection signal at the time of finishing processing, it is determined that the sample is curved. Automatic bending in TEM sample processing Recognition method. When the TEM sample is thinned, the secondary charged particle detector detects the secondary charged particles, and when a sudden change is detected in the detection signal during finishing, the sample is judged to be curved and the thinning process is interrupted. And TEM sample processing method for protecting the sample. When the TEM sample is thinned, the secondary charged particle detector detects the secondary charged particles, and when a sudden change is detected in the detection signal during finishing, the sample is judged to be curved and the thinning process is interrupted. Then, a TEM sample processing method in which cutting is performed by FIB under a predesignated condition to correct the bending, and the thinning process is advanced in that state. Means for detecting secondary charged particles released from the sample during the thinning process with a secondary charged particle detector, means for detecting the curvature of the sample from a change in the detection signal, and means for detecting the curvature of the sample A FIB apparatus for processing a TEM sample, which has a function of automatically recognizing a bend, and a means for interrupting the FIB processing according to the output of the detected FIB. 5. The FIB apparatus for processing a TEM sample according to claim 3 or 4, wherein the means for detecting the curvature of the sample is determined by comparing a differential value of the secondary charged particle detection signal with a threshold value. The means for detecting the curvature of the sample calculates a difference signal from the detection level of the secondary charged particles at the starting point of the scanning line, and determines that the calculated value exceeds a threshold value. FIB apparatus for TEM sample processing as described. The means for detecting the curvature of the sample is a graph in which the secondary charged particle detection level is correlated with the scanning position, and when the graph cannot be linearly approximated, it is determined that the sample is bent. FIB equipment for TEM sample processing.

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