JP2011243540A - Selected area aperture plate of transmission electron microscope, manufacturing method of selected area aperture plate, and observing method of selected area electron diffraction image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a selected area aperture plate, a manufacturing method of the same and the like, in which a fine pore can be formed while maintaining mechanical strength, and which is suitable for observing a selected area electron diffraction image of a TEM.SOLUTION: The manufacturing method of a selected area aperture plate includes: forming a preliminary fabrication region 16 (2 μm or less) by FIB fabrication in an aperture plate 11 composed of a single material such as tantalum or molybdenum with a depth of tens μm or more whose mechanical strength is secured and which screens an electron beam; and next, forming a fine pore 15 of 1 μm or less. Since a side wall portion of this fine pore 15 is formed with a sharp cutting edge and a non-taper shape, an outer periphery outside the fine pore 15 does not transmit even a high energy electron beam of 200 keV to 300 keV.

Description

  The present invention relates to a limited field stop plate used for observation of a limited field electron diffraction image of a transmission electron microscope (TEM), a manufacturing method thereof, and a method for observing a limited field electron diffraction image.

  The limited-field electron diffraction method of TEM is a method of obtaining an electron diffraction image in a state where an observation field is limited by inserting a stop on the real image surface of an objective lens. The observation field area at this time can be limited by the hole diameter of the limited field stop, and the observation field diameter is the product of the reciprocal of the magnification of the objective lens and the hole diameter. For example, when the objective lens is made 100 times, a diaphragm having a hole diameter of 1 μm or less is required to obtain an electron diffraction image from a limited field of view of 10 nm or less. A limited field stop of TEM is often used with a plurality of holes on the axis of a single metal plate of molybdenum, tantalum, etc. with a thickness of several tens of μm. In some cases, the same hole diameter may be provided.

  In addition, the TEM has a moving mechanism for selecting each aperture and an adjustment mechanism for aligning the center of the aperture with the optical axis of the electron beam, so that the aperture can be selected according to the observation purpose. Yes.

  Up to now, as a technique for forming an aperture or aperture with a small hole, an etching method (Patent Document 1) or a focused ion beam (FIB) method (Patent Document 1) applying machining or semiconductor process technology (Patent Document) 2) is known. In the etching method, as a method of forming an aperture of 20 nm in diameter by repeating the bonding of different materials such as the base layer Si, the coating layer SiO2, the coating layer Pt and the dry / wet etching process a plurality of times, the FIB method It is known as a method of forming a hole in a circular plate and mounting it on a holder, and a method of directly forming a hole in a diaphragm base.

JP 2008-204675 A JP 2007-329043

  Here, the diaphragm plate described in the above-mentioned patent document and the problems in manufacturing the plate will be described. The limited field stop used in the TEM limited field observation is a stop for selecting the observation field with high positional accuracy, and therefore, it is necessary that electron beam transmission does not occur in the stop part other than the fine hole portion.

In the diaphragm plate manufactured by the etching method, the material of the sheet layer in which the diaphragm hole is formed is composed of light element SiO ₂ , and the thickness of the sheet layer including the periphery of the diaphragm hole is as thin as about 1 μm, so 200 keV to 300 keV The high energy electron beam passes through the periphery of the hole, and the selected position accuracy of the observation field is remarkably lowered. Moreover, since the shape of the hole sidewall produced by etching lacks sharpness, it is difficult to apply it to a limited field stop.

In addition, even if a Pt film of about 0.3 μm is formed on the surface to prevent transmission of an electron beam through a SiO ₂ sheet layer having a thickness of about 1 μm, transmission of a low energy electron beam of about several keV is blocked. It is effective to do this, but with a high acceleration electron beam, the electron beam passes through the sheet layer and the Pt film. When the Pt film thickness is increased to prevent electron beam transmission, the inner wall of the aperture hole is coated with Pt, and the inner wall of the aperture hole becomes uneven, making it impossible to select a field-of-view restriction region with high positional accuracy. .

  Furthermore, when the base layer has an Si thickness of about 200 μm, the mechanical strength when mounted on the limited field stop holder cannot be ensured, causing a problem that the stop is curved and deformed. Furthermore, the residual resist used during etching causes charging and contamination during TEM observation.

  FIG. 12 is a conceptual diagram when the metal plate 2 is sputtered by the ion beam 1, and FIG. 13 shows an example of the aperture hole manufactured at that time. When the metal plate 2 is processed with the ion beam 1, as the processing depth increases, the sputtered material 3 is not discharged onto the surface of the metal plate 2, but accumulates on the wall surface of the hole, and the shape of the processed hole 4 changes in the depth direction. Tapered. In particular, with a metal plate of several tens of μm, it is difficult to penetrate fine holes (metal plate having an aspect ratio of 10 or more) of about 1 μm at a time by the FIB method.

  In addition, even if a thin metal plate diaphragm base with a thickness of several μm is used to make a fine hole by the FIB method, the mechanical strength cannot be secured when mounted on the TEM limited field diaphragm holder, and the metal plate 2 Bends and the micropores are deformed.

The present invention has been made in view of the recent problems described above, and its main purpose is as follows.
It is an object of the present invention to provide a limited field stop plate that can form fine holes while maintaining mechanical strength, and is suitable for observing a limited field electron diffraction image of a TEM, and a method for manufacturing the same.

  Another object of the present invention is to provide a method for observing a limited field electron diffraction image using the limited field stop plate.

  The feature of the limited field stop plate in the present invention for achieving the main object is that a preliminary processing region thinner than the thickness of the limited field stop plate main body is formed, and a fine hole is formed in the preliminary processing region.

  More specifically, a preliminary processing region having a thickness of about 2 μm is formed on a plate having a thickness of several tens of μm or more, and micropores having a diameter of about 1 μm are provided in the preliminary processing region. This will be described in detail in the embodiment to be described.

  The feature of the limited field stop plate manufacturing method of the present invention that achieves the main object is that a preliminary processing region having a diameter larger than that of the fine hole is first formed, and then the fine hole is penetrated into the preliminary processing region. .

  More specifically, by inputting the FIB processing coefficient parameter, the end point position of the set processing depth is controlled to form the preliminary processing region, and then the fine hole is provided in this FIB, thereby restricting the field-of-view diaphragm plate. It is in the place where it was made to manufacture.

  The feature of the present invention for achieving the other object is that the restricted field stop plate constructed or manufactured as described above is inserted into the real image surface of the objective lens of the transmission electron microscope, and the observation field is limited. It is to observe an electron diffraction image. More specifically, a sample with a limited field electron diffraction image corresponding to electron beam irradiation with a diameter of 10 nm or less is used using a limited field stop plate having a micropore diameter of 1 μm or less. The local lattice distortion is observed.

  According to the present invention, it is possible to easily obtain a limited field stop plate suitable for TEM limited field electron diffraction image observation. By using the limited field stop plate of the present invention, limited field electron diffraction from a minute region is achieved. An image can be observed with high positional accuracy.

Schematic diagram of the FIB device for manufacturing the diaphragm plate of the present invention Schematic diagram of a limited field stop plate for TEM according to one embodiment of the present invention Sectional view of the limited field stop plate of FIG. Schematic diagram of TEM limited field stop plate with machined holes at specific locations Cross-sectional view of a diaphragm plate for explaining the micropore manufacturing procedure according to the present invention Schematic diagram for explaining the limited field of view observation region of TEM The schematic diagram explaining the processing method of the side wall part of the processing hole which concerns on one Example of this invention. Schematic diagram of a limited field stop plate according to another embodiment of the present invention The figure which shows the optical system of the transmission electron microscope to which this invention is applied Cross-sectional view of Si substrate in lattice strain measurement to which the present invention is applied Cross-sectional view of Si substrate in lattice strain measurement to which the present invention is applied Conceptual diagram when sputtering metal plate with focused ion beam Cross-sectional view of the throttle hole when processed in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the illustrated examples. In the embodiments described below, in addition to the objects and features of the present invention, tantalum, molybdenum, etc. having a thickness of several tens of μm or more that shield high-energy electron beams of 200 keV to 300 keV while ensuring mechanical strength. Using a single metal plate, a plurality of fine holes of 1 μm or less are provided on the plate axis, and the side walls of the fine holes are sharp and non-tapered so that electron beam transmission does not occur around the fine holes. Of course, the present invention is not limited to these examples.

  FIG. 1 shows the configuration of an FIB apparatus for manufacturing a limited field stop plate according to the present invention. This FIB apparatus includes an ion source 5, an ion optical system 6, a deflector 7 for deflecting a beam, and a control device 9 for controlling these. In an actual apparatus, a sample chamber in which a diaphragm plate 10 to be processed is mounted is provided, but is omitted in the drawing. By forming a plurality of fine holes of 1 μm or less in a metal plate plate made of a single material such as tantalum or molybdenum having a thickness of several tens of μm or more by the FIB method using such an FIB apparatus, The limited field stop plate is manufactured.

  FIG. 2 shows the configuration of the limited field stop plate 11 according to an embodiment of the present invention, which is a stop made of a single material in which fine holes and the like are formed in the existing TEM limited field stop 11 by the FIB method. Screw holes 12 for mounting and fixing to the TEM diaphragm holder are installed at the end of the plate. In TEM limited field of view observation, the operation of changing the aperture according to the observation purpose occurs, so even if the aperture is changed, it is observed that the microscopic holes are always arranged on the electron beam optical axis. Is desirable. Therefore, the plurality of micro holes are arranged at the same interval on the straight line in the long axis direction on the plate, and are arranged in the central part in the short axis direction in the short axis direction so that the aperture from the optical axis accompanying the change operation of the aperture hole is reduced. The aperture configuration is such that no hole displacement occurs. A hole 13 serving as a mark is formed by machining in order to process a fine hole at a predetermined position on the plate.

  FIG. 3 is a cross-sectional view (A-B cross section of FIG. 2) showing the fine holes and the like of the aperture plate 11. The inner wall shape is sharp and is composed of a non-tapered micro hole 15 of about 1 μm parallel to the electron beam incident direction and a pre-processed region 14 in which a micro hole processing portion 16 having a diameter larger than the micro hole is left at about 2 μm . The fine hole processed portion 16 has a thickness of about 2 μm. However, since the material is made of heavy metal such as molybdenum or tantalum, transmission does not occur even with a high energy electron beam of 200 keV to 300 keV.

  Next, a manufacturing method of the limited field stop plate according to the present invention will be described. FIG. 4 shows the configuration of the existing TEM limited field stop 11. A screw hole 12 for mounting and fixing to the TEM diaphragm holder and a machined mark hole 13 for machining a micro hole are provided at a predetermined position on the plate 11. The specified position 18 indicates a position where no deviation of the aperture from the electron beam optical axis caused by the aperture changing operation occurs. Fine hole production to a specified position with high position accuracy is possible by controlling the sample stage of the FIB device. The processing to the specified position by the sample stage control is performed by moving the sample stage about 3 mm in the long axis direction from the position of the machined hole 13, creating a fine hole, and further moving the 3 mm sample stage. This is a method of producing a minute hole at a position.

  FIG. 5 shows the steps (a), (b) and (c) for producing micropores according to the present invention using the FIB method. First, a method for processing the preliminary processing region 14 having a diameter larger than that of the fine hole 15 will be described (FIG. 5A). Preliminary processing is a pre-processing for opening micro holes with high accuracy, and it is a path for electron beams to pass through the aperture, and it is not necessary to sharpen the shape of the processing side wall, so processing time is reduced. In order to shorten the time, it is preferable to increase the ion beam current amount.

In the FIB processing apparatus, the processing depth can be controlled using the spatter rate specific to the material as a parameter. For example, the processing factor of molybdenum is about 0.1 μm ³ / nA · s. For example, in the large current ion beam mode of about 50 nA, the processing time required for processing a volume of processing width 15 μm × 15 μm, depth 36, and 8 μm is calculated as about 6 minutes, and the processing is automatically terminated.

  Thus, in FIB processing, FIB processing can be performed with depth designation by inputting a processing coefficient parameter, and positioning of the processing end depth can be easily performed with high accuracy. Further, when the initial thickness of the metal plate is large, it is possible to perform sputtering step by step while controlling the depth direction.

  By the above method, the fine hole processed part 16 remaining in a thickness of about 2 μm can be easily produced, and at the same time, the fine hole processed part 16 having an arbitrary thickness can be produced with high accuracy. FIG. 5 (b) shows a cross-sectional view of a diaphragm plate in which micro holes having a diameter of 1 μm or less are processed in the micro hole processing portion 16 remaining in a thickness of about 2 μm. The ion beam current amount is made smaller than the FIB processing conditions at the time of preliminary processing region processing to reduce the ion beam diameter to improve the processing position accuracy, and the shape of the hole side wall 17 is sharpened and flattened.

  However, by making the fine hole processed portion 16 thinner, it is possible to reduce the taper shape of the processed hole due to the reattachment of the sputtered material to the processed hole side wall portion 17. The processed hole side wall portion 17 of the hole processed portion 16 is processed into a wedge shape, and a processed side wall portion 17 in which transmission of an electron beam occurs around the processed hole is formed.

  The TEM limited visual field observation region in the case of the aperture shape of FIG. 5B will be described with reference to FIG. A region 19 limited by the penetrating hole 15, that is, a limited visual field through which an electron beam is observed through a 1 μm-diameter fine hole, and at the same time, a processing hole side wall 17 (area thinner than 2 μm) having a tapered shape. Due to the influence of the transmitted electron beam, a region 20 in which the limited visual field shift occurs is further added to the outside, and an error occurs in the region selected by the limited visual field stop of the fine hole.

  Therefore, as shown in FIG. 7, the ion optical system 6 and the deflection system 7 of the FIB apparatus are controlled so that the ion beam 8 is scanned while being inclined in accordance with the taper angle of the processing hole side wall portion 17 to thereby form a tapered processing hole. The above problem can be solved by finishing the side wall portion 17 flat. In this way, by tilting the ion beam, a fine hole having a non-tapered shape in which the inner wall shape 17 of the fine hole is sharp and parallel to the electron beam incident direction as shown in FIG. An aperture that does not cause a shift can be obtained.

  Since this limited visual field shift is a problem with the tapered side wall, the aspect ratio can be made as small as possible if the thickness of the micro-hole processed portion left in the preliminary processing is 2 μm or less and processed to a thickness that does not transmit electron beams. In addition, the tapered shape of the processed hole side wall portion 17 caused by the influence of the ion beam flare can be reduced. Processing depth control at this time can be easily performed by processing end point management of the FIB processing apparatus.

  By mounting the aperture plate 11 produced as described above on a TEM and performing limited field of view observation, an electron diffraction image can be selectively observed only from the region that has passed through the aperture hole. Therefore, by inserting a limited field stop according to the shape of the sample selected in the limited field of view of the TEM observation sample, an electron diffraction image that does not include information other than the limited field observation point can be acquired. For example, when the target observation field of view is a quadrangular shape, as shown in FIG. 8, the observation target region is mounted by mounting a shape in which the fine hole is matched to the observation target region, here, a rectangular aperture. It becomes possible to select with high spatial resolution.

  In this case, the method for FIB processing of the quadrangular hole can be performed by the same procedure as the method for processing the circular hole described above. In addition, the shape of the fine holes is not limited to a rectangular shape, and it is possible to observe a diffraction image using only necessary electron diffraction information by forming a polygon according to the shape of the sample or the observation target region. Become.

  FIG. 9 shows an optical system of a transmission electron microscope to which the present invention is applied. In particular, an electron beam optical path in an electron diffraction mode by limited field observation is shown here. The figure shows an electron optical path in a vacuum, but a configuration such as a vacuum exhaust system is omitted.

  The electron beam 26 emitted from the electron gun 25 is cut only into a portion having uniform brightness by a converging lens stop 27 having a hole diameter of several hundred μm or more. The electron beam 26 that has passed through the converging lens diaphragm 27 is spread in parallel by the irradiation lens 28 and then irradiated onto the sample 29.

  The limited field stop plate 30 according to the present invention is installed on the real image plane of the objective lens 31. The limited field observation of the TEM is a field 33 corresponding to the hole of the limited field stop 30 installed on the real image plane of the objective lens 31, that is, the region that intersects the sample when the electron beam passing through the hole of the stop is traced in reverse. 34 is obtained, and an electron beam path equivalent to that when the electron beam is irradiated only to the region 34 is obtained.

  In the electron diffraction image mode in the limited field observation, the object point position of the intermediate lens 35 becomes the back focal plane 37 of the objective lens 31, so the electron diffraction image of the objective lens rear focal plane is finally obtained by the intermediate lens 35 and the projection lens 36. Magnified on screen 38. Therefore, if the limited field stop 30 is inserted with the real image of the objective lens 31 to limit the field of view, an electron diffraction image from the target region of the sample can be acquired, and the irradiation region setting at that time is set to the hole diameter of the limited field stop 30. It can be done by selection. The movement control of the limited field stop is performed by the control device 32.

  Next, an observation example using an electron diffraction image from an area limited to 10 nm or less by a limited field stop having a fine pore diameter of 1 μm or less will be described. It can be applied to local strain measurement of semiconductor devices.

  For miniaturized semiconductor devices, research is being carried out to improve the device characteristics by effectively utilizing strain. The strain distribution in the channel region of the device is being designed and developed so as to greatly affect the device performance, and in order to control these distortions, accurate strain evaluation is required, and the micro-diameter limited visual field This is achieved by electron diffraction images using a stop.

  An example of observation and measurement of lattice distortion will be described with reference to schematic cross-sectional views of the Si substrate shown in FIGS. Lattice strain measurement using electron diffraction is performed by directly measuring the distance between the diffraction spot centers of the electron diffraction pattern of the strained region 21 and the unstrained region 22 (reference) on the Si substrate 24, and measuring the distance between the diffraction spots. This method is known as a method of comparing changes and calculating the relative distortion rate with the reference region 22. Here, the device structure 23 is a material embedded on the Si substrate 24 in order to introduce strain, and the selection of the observation field of view of the strain regions 21 and the unstrained regions 22 at a plurality of locations is an electrical control device. In step 32, the limited field stop is moved.

  In this distortion observation, it is important that the acquired diffraction spot shape has a sharp and highly symmetric intensity distribution in order to specify the spot center position with high accuracy and improve the measurement accuracy.

  In the limited-field electron diffraction of the present invention, a diaphragm with a smaller hole diameter than that of the current diaphragm can be produced. Therefore, the limited-field electron beam corresponding to electron beam irradiation with a diameter of 10 nm or less with improved parallelism of the incident electron beam. The diffraction image can be observed, and it can be applied to highly accurate lattice distortion measurement of about 0.1%.

  In addition, when obtaining the strain distribution from the entire sample, as shown in FIG. 11, a rectangular aperture is used rather than acquiring strain data from a plurality of regions using a circular aperture as shown in FIG. It is desirable to measure the entire strain distribution measurement region while eliminating the unevenness of the measurement region using the, and maintaining the resolution of the region limited by the diaphragm.

DESCRIPTION OF SYMBOLS 1,8 ... Ion beam 2 ... Metal plate 3 ... Sputtered material 4 ... Processing hole 5 ... Ion source 6 ... Ion optical system 7 ... Deflector 9 ... Control Apparatus 10 ... Diaphragm plate 11 ... Restricted field diaphragm plate 12 ... Screw hole 13 ... Machined hole 14 ... Pre-machined region 15 ... Micro hole 16 ... Micro hole processed part 17 ·········································································································································· • Strain region 23 ... Device structure 24 ... Si substrate 25 ... Electron gun 26 ... Electron beam 27 ... Converging lens stop 28 ... Irradiation lens 29 ... Sample 30 ... Restriction Field stop 31 ... Objective lens
32 ... Control device 33 ... Field of view 34 corresponding to hole of limited field stop ... Area 35 intersecting sample 35 ... Intermediate lens 36 ... Projection lens

Claims (10)

  A limited field stop plate that is inserted into the real image surface of an objective lens of a transmission electron microscope and obtains an electron diffraction image in a state in which the observation field is limited, and is provided with a preliminary processing region that is thinner than the thickness of the plate body. A limited field stop plate of a transmission electron microscope, characterized in that a fine hole for a field stop is formed in a processing region.   The limited field stop plate according to claim 1, which is made of a single metal material such as molybdenum or tantalum having a thickness of several tens of μm.   3. The limited field stop plate of a transmission electron microscope according to claim 1, wherein a thickness of the preliminary processing region is equivalent to 2 μm and a diameter of the fine hole is 1 μm or less.   2. The limited field stop plate of a transmission electron microscope according to claim 1, wherein a side wall shape of the fine hole is a non-tapered shape parallel to an electron beam incident direction.   2. The limited field stop plate of a transmission electron microscope according to claim 1, wherein a plurality of fine holes are formed along a major axis direction of the stop plate.   2. The limited field stop plate of a transmission electron microscope according to claim 1, wherein the fine hole has a polygonal shape.   In a manufacturing method of a limited field diaphragm plate that is inserted into a real image surface of an objective lens of a transmission electron microscope and obtains an electron diffraction image in a state where an observation field is limited, a preliminary processing region thinner than the thickness of the plate body is obtained by FIB processing. A method of manufacturing a limited field stop plate for a transmission electron microscope, which is formed and then penetrates through a fine hole with the FIB at a specific position in the preliminary processing region.   8. The limited field stop of a transmission electron microscope according to claim 7, wherein the preliminary processing region is formed by controlling an end point position of a set reaching processing depth by inputting a coefficient parameter in the FIB processing. Plate manufacturing method.   A limited field electron of a transmission electron microscope, wherein the limited field stop plate according to claim 1 is inserted into a real image surface of an objective lens of a transmission electron microscope, and an electron diffraction image of the sample is observed in a state where the observation field is limited. Observation method of diffraction image.   10. The method for observing a limited field electron diffraction image according to claim 9, wherein the sample is obtained with a limited field electron diffraction image corresponding to electron beam irradiation having a diameter of 10 nm or less using a limited field diaphragm plate having a diameter of the micropore of 1 μm or less. To observe a limited-field electron diffraction image of a transmission electron microscope for observing local lattice distortions of the transmission electron microscope.

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