Ion milling device, holder, and cross-section milling processing method

Abstract

The present invention comprises: a mask sample table unit 113 comprising a holder 111 to which a sample 112 is adhered; a sample unit base 106 on which the mask sample table unit is mounted; and an ion source 103 that irradiates the sample with a non-focused ion beam 104. The holder comprises first to third surfaces. A first surface 201 and a second surface 203 to which the sample is adhered are connected by a third surface 202. The angle formed by the first surface and the third surface is a right angle, and the angle formed by the first surface and the second surface is an acute angle. When the mask sample table unit is mounted on the sample unit base so as to directly face the ion source, the first surface of the holder is perpendicular to an ion beam center of the ion beam.

Description

Technical Field

[0001] The present invention relates to an ion milling apparatus, a holder, and a cross-sectional milling method.

Background Art

[0002] There is known an ion milling apparatus that irradiates a non-focused ion beam to expose a cross-section in order to observe the internal structure of a sample. Patent Document 1 discloses an ion milling apparatus that performs cross-sectional milling in which a part of the ion beam is shielded by a mask (shielding plate) disposed above the sample, and the cross-section of the sample is exposed along the end face of the mask. Further, in the ion milling apparatus of Patent Document 1, it is possible to slide the sample mask unit to form a cross-section wider than the ion beam width or to perform processing at a plurality of points.

[0003] On the other hand, there is known a FIB-SEM that processes a sample with a focused ion beam (FIB: Focused Ion Beam) and performs observation and measurement with a scanning electron microscope. Patent Document 2 discloses that an inclined cross-section is exposed to a sample including a circuit element by irradiation with a focused ion beam, and measurement in the depth direction of the pattern is performed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When exposing an inclined cross-section of a sample, it is difficult to obtain an inclined cross-section with a desired angle by controlling the inclination angle in the ion milling apparatus of Patent Document 1. On the other hand, in the focused ion beam apparatus of Patent Document 2, an inclined cross-section can be processed only in a narrow region with a width and depth of about several hundred micrometers.

[0006] An object of the present invention is to provide an ion milling apparatus capable of producing a wide-area and precisely controlled inclined cross-section of a laminated structure such as a coating film or a functional thin film or a three-dimensional device such as MEMS.

Means for Solving the Problems

[0007] An ion milling apparatus according to an embodiment of the present invention includes a mask sample stage unit including a holder to which a sample is adhered, a sample unit base on which the mask sample stage unit is mounted, and an ion source that irradiates a non-focused ion beam onto the sample. The holder includes a first surface to a third surface. The first surface and the second surface to which the sample is adhered are connected by the third surface. The angle formed by the first surface and the third surface is a right angle, and the angle formed by the first surface and the second surface is an acute angle. When the mask sample stage unit is mounted on the sample unit base so as to face the ion source, the first surface of the holder is perpendicular to the ion beam center of the ion beam.

Effects of the Invention

[0008] An ion milling apparatus capable of producing a precisely controlled inclined cross-section is provided. Other problems and novel features will become apparent from the description of this specification and the accompanying drawings.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 6A

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Figure 6C

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Figure 7B

Figure 8

Embodiments for Carrying Out the Invention

[0010] FIG. 1 shows a configuration example of an ion milling apparatus 101. The ion milling apparatus 101 mainly includes a vacuum chamber 102, an ion source 103 attached to the vacuum chamber 102, a sample stage 105 attached to a surface different from that of the ion source 103, a sample unit base 106 extending from the sample stage 105, a mask sample stage unit 113 placed on the sample unit base 106 and on which a sample 112 to be subjected to cross-section milling processing is placed, a vacuum exhaust system 109 for exhausting the inside of the vacuum chamber 102, and a linear guide 110 provided on the surface of the vacuum chamber 102 to which the sample stage 105 is attached.

[0011] The sample stage 105 is attached to a flange 102f that also serves as a part of the container wall of the vacuum chamber 102. By pulling out the flange 102f along the linear guide 110, the vacuum chamber 102 can be opened to the atmosphere. At this time, together with the sample unit base 106, it is pulled out to the outside of the vacuum chamber 102. In this way, the sample stage pulling mechanism is configured.

[0012] The mask sample stage unit 113 is assembled by stacking the fine movement mechanism 107, the connecting member 108, and the holder 111 in order. A sample 112 is adhesively fixed on the holder 111. The holder 111 is a mask sample stage integrated holder that has a function as a sample stage for placing the sample 112 and a function as a mask for masking the sample 112. Driven by the drive source provided in the sample stage 105, the mask sample stage unit 113 swings around a swing axis S perpendicular to the center (ion beam center) B of the ion beam 104. In FIG. 1, the ion beam center B is parallel to the Z axis, the swing axis S is parallel to the Y axis, the ion source 103 and the mask sample stage unit 113 face each other, and the state where the boundary (edge) between the holder 111 and the sample 112 is parallel to the X axis is shown. By the swinging operation, the mask sample stage unit 113 is rotationally driven within a range where the angle formed by the edge and the X-axis direction is ±θ.

[0013] The fine movement mechanism 107 that constitutes the mask sample stage unit 113 is configured to be movable in two axes in the plane perpendicular to the ion beam center B, that is, in the X-axis direction and the Y-axis direction in the state of FIG. 1, and is used to adjust the relative position between the ion beam center B and the mask sample stage unit 113. The details of the adjustment will be described later. The connecting member 108 serves as a base for placing the holder 111 on the fine movement mechanism 107.

[0014] The shape of the holder 111 is shown in FIGS. 2A to 2C. FIG. 2A is a bird's-eye view, FIG. 2B is a top view, and FIG. 2C is a side view. FIGS. 2B and 2C show the coordinate axes corresponding to the coordinate axes in FIG. 1. The holder 111 includes a mask surface (first surface) 201 facing the ion source 103 and a sample placement surface (second surface) 203 to which the sample 112 is adhesively fixed when the mask sample stage unit 113 is facing the ion source 103. The mask surface 201 and the sample placement surface 203 are connected by a sample protection surface (third surface) 202. The sample protection surface 202 is provided so that portions other than the target processing position (the position where the cross-section is desired to be exposed) of the sample 112 are not cut by ion beam irradiation. In order to minimize the amount of the holder 111 cut by ion beam irradiation, it is desirable that the material be titanium, graphite carbon, etc., which have high ion beam resistance.

[0015] Since the mask surface 201 is a plane parallel to the XY plane and the sample protection surface 202 is a plane parallel to the XZ plane, the angle formed between the mask surface 201 and the sample protection surface 202 is a right angle. Also, the sample placement surface 203 is inclined in the Z direction, and the angle formed between the mask surface 201 and the sample placement surface 203 is an acute angle. Also, the intersection line between the mask surface 201 and the sample protection surface 202 and the intersection line between the sample protection surface 202 and the sample placement surface 203 are parallel.

[0016] Using FIG. 3, the procedure for producing an inclined cross-section of the sample 112 placed on the mask sample stage unit 113 by the ion milling apparatus 101 will be described.

[0017] S301: The user adhesively fixes the sample 112 to the sample placement surface 203 of the holder 111. As shown in FIG. 1, the portion of the sample 112 protruding from the intersection line between the sample protection surface 202 and the sample placement surface 203 of the holder 111 becomes the portion to be subjected to cross-section milling treatment by the ion beam 104. Therefore, when fixing the sample 112 to the holder 111, the protruding amount is adjusted using the adjustment table 205 so that the target processing position of the sample 112 is located on the intersection line between the sample protection surface 202 and the sample placement surface 203. FIG. 4 shows a state in which the holder 111 is placed on the adjustment table 205 and the protruding amount of the sample 112 is adjusted.

[0018] The adjustment table 205 is a table for adjusting the protrusion amount of the sample 112, which is manufactured according to the holder 111. The adjustment table 205 is provided with a triangular groove for mounting the holder 111. The adjustment of the protrusion amount is performed in a state where the bottom surface of the holder 111 contacts the placement surface 206, which is one side surface of the triangular groove, and the mask surface 201 of the holder 111 contacts the adjustment surface 207, which is the other side surface of the triangular groove, when the holder 111 is placed on the adjustment table 205.

[0019] In order to precisely adjust the protrusion amount, the adjustment table 205 is provided with a protrusion amount adjusting jig 204. The triangular groove is formed such that when the sample 112 is placed on the sample placement surface 203 of the holder 111, the sample 112 slides down toward the sample protection surface 202 due to its own weight. The sample 112 is held on the sample placement surface 203 by the protrusion amount adjusting jig 204, and the sample protrusion amount can be set by sliding the protrusion amount adjustment bar 208 in the direction of the arrow. By using a precise screw mechanism such as that used in a micrometer for the protrusion amount adjustment bar 208, the protrusion amount of the sample can be precisely adjusted. When the desired protrusion amount is reached, the sample 112 is adhesively fixed to the sample placement surface 203.

[0020] The protrusion amount is set based on the distance from the tip of the trimmed sample 112 to the target processing position when the sample 112 is trimmed. When the processing is at an arbitrary location where the target processing position is not specified, it is desirable to set the protrusion amount to about 50 μm. For fixing the sample 112 to the sample placement surface 203, adhesives such as carbon paste, hot wax, and nail polish can be used. When the sample 112 is fixed, the holder 111 is removed from the adjustment table 205 and attached to the fine movement mechanism 107 via the connecting member 108.

[0021] S302: Adjust so that the ion beam center B of the ion beam 104 emitted from the ion source 103 comes to the center of the end of the sample protection surface 202 of the holder 111. An example of the adjustment method will be described with reference to FIGS. 5A - B.

[0022] Since the relative position between the ion beam center B and the mask sample stage unit 113 needs to be precisely adjusted, it is performed using an optical microscope. The optical microscope is provided with a fixing stage that reproducibly places the mask sample stage unit 113 at a fixed position on the observation stage of the optical microscope. Prior to performing the adjustment in step S302, the field of view of the optical microscope is adjusted so that the ion beam center B is at the center of the field of view of the optical microscope. This adjustment is performed at the timing of maintenance and does not need to be performed each time the sample is placed on the holder.

[0023] The adjustment of the field of view of the optical microscope will be described with reference to FIG. 5A. The fine movement mechanism 107 is set to the standard position (X-axis direction = 0, Y-axis direction = 0), a photosensitive paper, silver foil, etc. is attached to the mask surface 201 of the holder 111, and the field of view of the optical microscope is moved so that the mark formed by irradiating the ion beam 104, that is, the ion beam center 502, comes to the center of the field of view 501 of the optical microscope.

[0024] FIG. 5B shows the field of view 503 of the optical microscope when the mask sample stage unit 113 on which the sample 112 is placed in step S302 is installed on the fixing stage of the optical microscope. When the fine movement mechanism 107 is in the standard position (X-axis direction = 0, Y-axis direction = 0), the image of the sample 112 is the sample image 112I1, and the image of the mask surface 201 is the mask surface image 201I1. Since the ion beam center is at the center of the field of view 503, the position X3 in the X-axis direction and the position Y3 in the Y-axis direction of the fine movement mechanism 107 are adjusted so that the processing target position, and thus the center of the end of the sample protection surface 202 of the holder 111, comes to the center of the field of view 503. Thereby, the sample protection surface 202 of the holder is adjusted to be positioned along the ion beam center of the ion beam. After the adjustment by the fine movement mechanism 107, the image of the sample 112 is the sample image 112I2, and the image of the mask surface 201 is the mask surface image 201I2.

[0025] S303: Attach the mask sample stage unit 113 to the sample unit base 106. The mask sample stage unit attachment position of the sample unit base 106 is fixed. As shown in FIG. 1, the mask surface 201 of the holder 111 is fixed so as to face the ion source 103.

[0026] S304: Irradiate the ion beam 104 toward the sample 112 to perform cross-sectional milling. If the irradiation direction of the ion beam 104 is concentrated in one direction, machining streaks will appear on the cross-section of the sample. To prevent the occurrence of such cross-sectional disturbances, swing machining is performed in which the mask sample stage unit 113 is swung around the swing axis S while performing the milling process.

[0027] As described above, the protruding region of the sample 112 adhesively fixed to the sample placement surface 203 is milled by ion beam irradiation.

[0028] Figures 6A to 6C show the states of the holder 111 and the sample 112 after the cross-sectional milling process. As shown in Figure 6A, the cross-section 601 of the sample 112 is exposed along the sample protection surface 202 of the holder 111. The cross-section 601 is an inclined cross-section with an inclined cut according to the inclination of the sample placement surface 203 of the holder 111.

[0029] As shown in Figure 1, during the milling process, since the ion beam 104 is adjusted to be emitted so that the ion beam center B is along the sample protection surface 202, the sample protection surface 202 of the holder 111 will also be shaved by the irradiation of the ion beam 104 together with the sample 112. This situation is shown in Figure 6B. At this time, for the milling region 602 of the sample protection surface 202, the length shaved in the extension direction (Z-axis direction) of the ion beam center B is defined as the machining depth D, and the length of the milling region 602 at the end of the sample protection surface 202 is defined as the machining width W.

[0030] The length L of the sample protection surface 202 in the Z-axis direction affects the accuracy of the milling process. If the length L is too short, for example, L < 0.1 mm, the milling area 602 will reach the sample placement surface 203 before the machining is completed, and a cross-section along the sample protection surface 202 cannot be obtained. On the other hand, if the length L is too long, for example, L > 10 mm, the position of the sample 112 relative to the ion source 103 becomes farther, resulting in a decrease in the intensity of the non-focused ion beam 104. As a result, the machining rate decreases. The increase in machining time due to the decrease in the machining rate makes the influence of heating associated with sputtering of the sample 112 and the holder 111 by the ion beam 104 more prominent. Specifically, since the sample 112 and the holder 111 have different coefficients of thermal expansion, the adhesion between the holder 111 and the sample 112 decreases during the milling process, and problems such as sputter particles entering the gap will occur. As a result, a decrease in machining accuracy such as the curvature of the cross-section 601 occurs. To avoid such problems, it is desirable that the length L of the sample protection surface 202 in the Z-axis direction is 0.1 mm or more and 10 mm or less, preferably 0.5 mm or more and 3 mm or less, and particularly 2 mm or less.

[0031] FIG. 6C schematically shows a state in which the cross-section 601 of the obtained sample 112 is observed with a scanning electron microscope. The sample 112 has a structure in which a semiconductor layer and an insulating film layer are laminated on a semiconductor substrate. Since the cross-section 601 is obtained as a flat surface without curvature, it becomes possible to observe the boundary of the parallel laminated films without distortion.

[0032] The inclination angle α of the sample placement surface 203 of the holder 111 can be changed by remaking the holder 111 according to the sample 112 to be placed, and can be customized within the range of several degrees to 70 degrees or less. FIG. 7A shows the holder 111 with the inclination angle α = 10°, and FIG. 7B shows the holder 111 with the inclination angle α = 70°. Only the inclination angle α is changed, and the other sizes are the same. It is possible to fabricate the holder 111 with the optimal inclination angle α according to the type of the sample 112 to be placed and the purpose of observation / measurement.

[0033] FIG. 8 shows an example in which the mask sample stage unit 113 is mounted on the sample unit base 106 via the slide movement mechanism 801. The slide movement mechanism 801 is a mechanism for realizing wide-area milling processing or multi-point milling processing. The slide movement mechanism 801 includes a drive source and reciprocates the mask sample stage unit 113 in the direction of the intersection line between the sample protection surface 202 and the sample placement surface 203 of the holder 111, here in the X-axis direction. The wide-area milling processing is a process of performing processing on an area wider than the width of the ion beam 104, and the multi-point milling processing is a process of performing processing on a plurality of processing target positions of the sample.

[0034] When performing wide-area milling processing, the milling processing may be performed while performing both the reciprocating motion by the slide movement mechanism 801 and the swinging motion centered on the swing axis S. Further, when performing multi-point milling processing, the milling processing may be performed on a plurality of processing target positions by moving the irradiation position of the ion beam 104 by the slide movement mechanism 801.

[0035] Note that the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for a part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

Explanation of Reference Numerals

[0036] 101: Ion milling device, 102: Vacuum chamber, 102f: Flange, 103: Ion source, 104: Ion beam, 105: Sample stage, 106: Sample unit base, 107: Micromotion mechanism, 108: Connecting member, 109: Vacuum exhaust system, 110: Linear guide, 111: Holder, 112: Sample, 113: Mask sample stage unit, 201: Mask surface, 202: Sample protection surface, 203: Sample placement surface, 204: Protrusion amount adjusting jig, 205: Adjusting table, 206: Placement surface, 207: Adjusting surface, 208: Protrusion amount adjustment bar, 501, 503: Field of view, 502: Ion beam center, 601: Cross section, 602: Milling region, 801: Slide movement mechanism.

Claims

1. A mask sample stage unit including a holder to which a sample is adhered, a sample unit base on which the mask sample stage unit is mounted, and an ion source that irradiates the sample with a non-focused ion beam. The holder includes a first surface to a third surface, the first surface and the second surface to which the sample is adhered are connected by the third surface, the angle formed by the first surface and the third surface is a right angle, and the angle formed by the first surface and the second surface is an acute angle. An ion milling apparatus, wherein when the mask sample stage unit is mounted on the sample unit base so as to face the ion source, the first surface of the holder is perpendicular to the ion beam center of the ion beam.

2. In Claim 1, the sample is adhered to the second surface such that the amount of protrusion from the intersection line of the second surface and the third surface of the holder is a predetermined amount of protrusion.

3. In Claim 1, the distance between the intersection line of the first surface and the third surface of the holder and the intersection line of the second surface and the third surface is 0.1 mm or more and 10 mm or less.

4. In Claim 1, the mask sample stage unit includes a fine movement mechanism, the fine movement mechanism is configured to be able to move the sample unit base within a plane perpendicular to the ion beam center of the ion beam in a state where the mask sample stage unit faces the ion source, and the fine movement mechanism is characterized in that the third surface of the holder is adjusted to be positioned along the ion beam center of the ion beam.

5. In Claim 1, it has a sample stage that rotationally drives the mask sample stage unit via the sample unit base, and the sample stage is characterized in that the mask sample stage unit is swung about a swing axis orthogonal to the ion beam center of the ion beam and the intersection line of the second surface and the third surface of the holder.

6. In Claim 5, the mask sample stage unit is mounted on the sample unit base via a slide movement mechanism, and the slide movement mechanism is characterized in that the mask sample stage unit is reciprocally moved in the direction of the intersection line of the second surface and the third surface of the holder.

7. A holder to which a sample for performing cross-sectional milling processing with a non-clustered ion beam is adhered, having a first surface to a third surface, the first surface and the second surface to which the sample is adhered are connected by the third surface, the angle formed by the first surface and the third surface is a right angle, and the angle formed by the first surface and the second surface is an acute angle, the ion beam is irradiated onto the sample from the direction of the first surface, and the holder is characterized in that.

8. In claim 7, the sample is adhered to the second surface so as to have a predetermined protruding amount from the intersection line of the second surface and the third surface of the holder, and the holder is characterized in that.

9. In claim 7, the distance between the intersection line of the first surface and the third surface and the intersection line of the second surface and the third surface is 0.1 mm or more and 10 mm or less, and the holder is characterized in that.

10. In claim 7, a holder made of titanium or graphite carbon.

11. A cross-sectional milling processing method using an ion milling apparatus including a mask sample stage unit including a holder, a sample unit base on which the mask sample stage unit is mounted, and an ion source, the holder includes a first surface to a third surface, the first surface and the second surface are connected by the third surface, the angle formed by the first surface and the third surface is a right angle, and the angle formed by the first surface and the second surface is an acute angle, adhere the sample to the second surface of the holder so that the protruding amount from the intersection line of the second surface and the third surface of the holder becomes a predetermined protruding amount, irradiate a non-clustered ion beam from the ion source onto the sample from the direction of the first surface of the holder, and the cross-sectional milling processing method is characterized in that.

12. In claim 11, the mask sample stage unit includes a fine movement mechanism, the fine movement mechanism is configured to be able to move the sample unit base in a plane perpendicular to the ion beam center of the ion beam in a state where the mask sample stage unit faces the ion source, the fine movement mechanism is adjusted so that the third surface of the holder is positioned along the ion beam center of the ion beam, and the cross-sectional milling processing method is characterized in that.

13. In claim 11, the ion milling apparatus includes a sample stage for rotationally driving the mask sample stage unit via the sample unit base, During the period when the ion source irradiates the sample with the ion beam, the sample stage swings the mask sample stage unit about a swing axis perpendicular to the ion beam center of the ion beam and the intersection line between the second surface and the third surface of the holder. A cross-sectional milling method characterized by this.

14. In claim 13, The mask sample stage unit is mounted on the sample unit base via a slide movement mechanism. During the period when the ion source irradiates the sample with the ion beam, the slide movement mechanism reciprocates the mask sample stage unit in the direction of the intersection line between the second surface and the third surface of the holder. A cross-sectional milling method characterized by this.

15. In claim 14, The sample is characterized in that a region having a width wider than the width of the ion beam is processed, or a plurality of processing target positions are processed. A cross-sectional milling method characterized by this.

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