JP7770583B2 - Ion milling device, cross-sectional milling method, and cross-sectional milling holder - Google Patents

Description

The present invention relates to an ion milling apparatus, a cross-section milling method, and a cross-section milling holder.

An ion milling device irradiates the surface or cross section of a sample (e.g., metal, semiconductor, glass, ceramic, etc.) with an unfocused ion beam (e.g., Ar ions) accelerated to several kV, sputtering atoms off the sample surface without stress, thereby obtaining a smooth, machined surface. This is an excellent characteristic for smoothing the surface or cross section of a sample for observation using an electron microscope, such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

Patent Document 1 discloses a method for preparing a cross-section observation sample in which the top of a workpiece is covered with a shielding plate, and the portion protruding from the shielding plate is irradiated with an ion beam to etch the sample, thereby mirror-polishing the portion of the sample along the edge of the shielding plate. According to the disclosure of Patent Document 1, by irradiating the ion beam while moving the shielding plate by the reciprocating motion of a rod fixed to one side of the shielding plate, it is possible to reduce the depth of a depression formed in the shielding plate by ion beam irradiation during processing of a sample, and to extend the life of the shielding plate.

JP 2012-2740 A

In order to obtain a clean cross section by cross-section milling using an ion milling device, it is necessary to bring the shielding plate and the sample into close contact with each other to prevent ions from entering between them. As disclosed in Patent Document 1, if the shielding plate is moved while the shielding plate and the sample are in close contact with each other, friction between the shielding plate and the sample may cause the position of the sample sandwiched between the shielding plate and the sample stage to shift. Therefore, the ion beam irradiation is performed with the contact between the shielding plate and the sample reduced.

The technology disclosed in Patent Document 1 can minimize damage to the shielding plate caused by ion beam irradiation, and is therefore considered effective even when performing long-term cross-section milling, such as when exposing the cross-section of a thick sample. However, performing long-term ion beam irradiation while reducing the adhesion between the shielding plate and the sample can lead to a decrease in the accuracy of the cross-section. In order to distribute the damage to the shielding plate caused by ion beam irradiation without reducing the accuracy of the cross-section, it is necessary to control the adhesion between the sample and the shielding plate so that an appropriate degree of adhesion is obtained when processing the sample and when moving the shielding plate.

An ion milling apparatus according to one embodiment of the present invention comprises a sample stage on which a cross-sectional milling holder for holding a sample and a shielding plate is mounted, an ion gun for emitting an unfocused ion beam toward the sample, and a shielding plate driving unit for changing the adhesion between the sample and the shielding plate and the position of the shielding plate relative to the sample in the edge direction along the boundary between the sample held in the cross-sectional milling holder and the shielding plate.

The processing range in the depth direction in cross-sectional milling processing can be expanded. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

FIG. 1 is a diagram showing the overall configuration of an ion milling apparatus. FIG. 10 is a diagram showing the state of the shielding plate and the sample after cross-section milling processing. FIG. 10 is a diagram showing the adhesion between the sample and the shielding plate. FIG. 10 is a diagram showing the adhesion between the sample and the shielding plate. FIG. 2 is a front view of the cross-sectional milling holder. FIG. 1 is a side view of a cross-sectional milling holder. 10A and 10B are schematic diagrams showing the movement of the shielding plate. FIG. 10 is a schematic diagram showing the state in which the cross-section milling holder is attached to the motor unit. 10 is a flowchart of a cross-section milling process involving a moving operation of a shielding plate.

FIG. 1 shows the overall configuration of an ion milling apparatus. A sample 1 is placed on a sample stage 2, and an ion beam is irradiated onto the sample 1 from an ion gun 4. The ion gun 4 employs a Penning system, which is effective for miniaturizing the structure. In a Penning system ion gun, argon ions are generated by colliding electrons generated by a Penning discharge with argon gas inside the ion gun, and the generated argon ions are accelerated and emitted as an ion beam. To this end, a discharge voltage for generating a Penning discharge and an acceleration voltage for accelerating the argon ions are applied to the ion gun 4 from a high-voltage power supply 5a, and argon gas is supplied, the flow rate of which is controlled by an MFC (Mass Flow Controller) 5b.

A shielding plate 3 is placed above the sample 1 to shield the ion beam irradiated onto the sample 1 from the ion gun 4. The exposed portion of the sample 1 protruding from the edge of the shielding plate 3 is milled with the ion beam (cross-section milling). The sample stage 2 is driven by a stage driver 9 during the cross-section milling process. For example, the stage driver 9 controls the sample stage 2 to perform a swing motion about a swing axis S (Y direction) that is set perpendicular to the ion beam center B of the ion beam, and a sliding motion along the edge direction along the boundary between the sample 1 and the shielding plate 3 (in the case where the sample 1 faces the ion gun 4, a direction (X direction) perpendicular to the ion beam center B and the swing axis S). The swing motion, which swings the sample 1 around the swing axis S within a predetermined angular range (swing angle), can smooth the processed surface. Furthermore, the sliding motion, which moves the sample 1 back and forth in the edge direction around the ion beam center B, can widen the processing width in the edge direction. The ion milling process is performed in a sample chamber 6 evacuated by an exhaust system 10. Furthermore, the ion milling apparatus of this embodiment is equipped with a shielding plate driver 8 that moves the shielding plate 3 in the edge direction relative to the sample 1. Although the shielding plate driver 8 and stage driver 9 are shown in FIG. 1 as being outside the sample chamber 6, this merely shows the existence of the drivers and does not limit the location of the drivers. Furthermore, while FIG. 1 simply shows the sample 1 as if it were directly placed on the sample stage 2, as will be described later, the sample 1 and shielding plate 3 are held by a cross-section milling holder, and the cross-section milling holder is mounted on the sample stage 2.

The ion milling apparatus is controlled by a computer 12 and a controller 11, which are sometimes collectively referred to as a control unit. The computer 12 sets the ion milling conditions set by the user in the controller 11, and the controller 11 controls each component of the ion milling apparatus (the ion gun 4, the sample stage 2, the shielding plate 3, the exhaust system 10, etc.) based on the set control values.

FIG. 2 shows the state of the shielding plate 3 and the sample 1 when cross-section milling is performed without moving the shielding plate 3. It can be seen that the upper end of the shielding plate 3 is gradually milled away as the processing time passes. If the upper end of the shielding plate 3 is deeply milled away by the ion beam, the ions will collide with the sample 1 unevenly, which may cause irregularities such as bumps on the cross-section of the sample 1 being cross-section milled. Therefore, the shielding plate driving unit 8 of this embodiment moves the shielding plate 3 in the edge direction relative to the sample 1, thereby dispersing the influence of the ion beam irradiating the shielding plate 3 over a wide area during the cross-section milling process and preventing deep damage to a portion of the shielding plate 3 and affecting the cross-section of the sample 1.

During cross-section milling, it is desirable to maintain strong adhesion between the sample 1 and the shielding plate 3. This is because ions may enter the gap between the sample 1 and the shielding plate 3, causing distortion of the cross-section of the sample 1. On the other hand, if the shielding plate 3 is moved relative to the sample 1 while the adhesion is strong, friction between the sample 1 and the shielding plate 3 may cause the sample 1 to shift position. Figures 3A and 3B are diagrams showing the adhesion between the sample 1 and the shielding plate 3. The sample 1 in this example is a Si plate. Figure 3A shows the state in which the sample 1 is being processed, with the sample 1 and the shielding plate 3 fixed without any gap. On the other hand, Figure 3B shows the state in which the shielding plate 3 is being moved toward the edge, with a gap 31 formed between the sample 1 and the shielding plate 3. This prevents the sample 1 from moving on the sample holder due to the movement of the shielding plate 3.

The structure of the cross-section milling holder 40 for fixing the shielding plate 3 to the sample 1 will be described using Figures 4A and 4B. Figure 4A is a front view (viewed from the ion gun 4), and Figure 4B is a side view. The shielding plate 3 is fixed to a shielding plate holder 43 with fixing screws 44. The shielding plate holder 43 is fixed to the sample holder 41 with shielding plate fixing screws 42. The shielding plate holder 43 functions to adjust the adhesion between the shielding plate 3 and the sample 1. Tightening the shielding plate fixing screws 42 increases the adhesion, and loosening the shielding plate fixing screws 42 decreases the adhesion. The shielding plate holder 43 is preferably made of a metal with spring properties, such as phosphor bronze. Tightening the shielding plate fixing screws 42 applies force in the Z direction, achieving high adhesion between the shielding plate 3 and the sample 1.

The shield plate fixing screws 42 are fixed to the sample holder 41 through grooves 45 in the shield plate holder 43. The grooves 45 have a length in the vertical direction (Y direction) that matches the diameter of the shield plate fixing screws 42, while being elongated in the horizontal direction (edge direction). This allows the shield plate 3 to be moved in the X direction relative to the sample 1 by changing the position of the shield plate fixing screws 42 in the longitudinal direction (edge direction) of the grooves 45.

FIG. 4C is a schematic diagram showing the movement of the shielding plate 3 in the cross-section milling holder 40. In the cross-section milling holder 40a, the shielding plate fixing screw 42 is located at the longitudinal center of the groove 45. In the cross-section milling holder 40b, the shielding plate fixing screw 42 is located to the right of the longitudinal center of the groove 45 as viewed from the ion gun. In the cross-section milling holder 40c, the shielding plate fixing screw 42 is located to the left of the longitudinal center of the groove 45 as viewed from the ion gun. In FIG. 4C, a center line 47 is shown to clearly show the relative positional relationship of the movement of the shielding plate 3. In this way, by moving the shielding plate holder 43 to which the shielding plate 3 is fixed in the edge direction (left and right) relative to the sample holder 41, the shielding plate 3 can be moved in the edge direction (left and right) relative to the sample 1. When moving the shielding plate holder 43, the shielding plate fixing screw 42 must be loosened to prevent the sample 1 from being misaligned.

The shielding plate 3 is electrically controlled to move during the cross-section milling process. Figure 5 shows a schematic diagram (top view) of the detailed configuration of the shielding plate drive unit 8 that moves the shielding plate 3. The shielding plate drive unit 8 includes a motor unit 50 attached to the back surface of the cross-section milling holder 40, a rotor 51 rotated by the motor unit 50, a shielding plate moving mechanism 52, and a power cable 53 that supplies power to the motor unit 50. The motor unit 50 rotates the rotor 51 under the control of the controller 11. The rotor 51 can switch its rotation direction between clockwise and counterclockwise. The shielding plate moving mechanism 52 uses the rotation of the rotor 51 as a drive source for rotating the shielding plate fixing screw 42 and for moving the position of the shielding plate fixing screw 42 within the groove 45.

FIG. 6 shows a flowchart of the cross-section milling process accompanied by the movement of the shielding plate 3.

Step 101: The user places the sample 1 to be subjected to cross-section milling processing on the ion milling apparatus, sets the processing conditions for the sample 1 in the ion milling apparatus from the computer 12, and then sends a processing start command.

Step 102: The control unit causes the ion gun 4 to irradiate the sample 1 with an ion beam for a predetermined time, thereby performing processing (cross-section milling processing) on the sample 1. Depending on the processing conditions, the control unit also causes a swing operation and a slide operation to be performed.

Step 103: The control unit temporarily stops the processing of the sample 1.

Step 104: The shielding plate driving unit 8 loosens the shielding plate fixing screws 42 of the cross-section milling holder 40 to weaken the adhesion between the sample 1 and the shielding plate 3.

Step 105: With the contact between the sample 1 and the shielding plate 3 weakened, the shielding plate driving unit 8 moves the shielding plate 3 by a certain amount in the edge direction relative to the sample 1.

Step 106: The shielding plate driving unit 8 tightens the shielding plate fixing screws 42 of the cross-section milling holder 40 to strengthen the adhesion between the sample 1 and the shielding plate 3.

Step 107: The control unit restarts the machining and transitions to step 102.

The predetermined time for performing the processing in step 102 and the amount of movement of the shielding plate 3 in step 105 may be dynamically adjusted depending on the processing conditions set in step 101 .

The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to make the present invention easier to understand, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be implemented in software, with a processor interpreting and executing a program that implements each function. Information such as the program, table, and file that implements each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, memory card, optical recording medium, or magnetic recording medium.

1: sample, 2: sample stage, 3: shielding plate, 4: ion gun, 5a: high-voltage power supply, 5b: MFC, 6: sample chamber, 8: shielding plate drive unit, 9: stage drive unit, 10: exhaust system, 11: controller, 12: computer, 31: gap, 40: cross-section milling holder, 41: sample holder, 42: shielding plate fixing screw, 43: shielding plate holder, 44: fixing screw, 45: groove, 47: center line, 50: motor unit, 51: rotating body, 52: shielding plate moving mechanism, 53: power cable.

Claims (12)

a sample stage on which a cross-section milling holder for holding a sample and a shielding plate is mounted;
an ion gun that emits an unfocused ion beam toward the sample;
An ion milling apparatus having a shielding plate driving unit that changes the adhesion between the sample and the shielding plate and the position of the shielding plate relative to the sample in the edge direction along the boundary between the sample held in the cross-section milling holder and the shielding plate. In claim 1,
a control unit for controlling the cross-section milling process of the sample;
The control unit stops the irradiation of the ion beam from the ion gun onto the sample, weakens the adhesion between the sample and the shielding plate using the shielding plate driving unit, moves the position of the shielding plate relative to the sample in the edge direction, and after strengthening the adhesion between the sample and the shielding plate, resumes the irradiation of the ion beam from the ion gun onto the sample. In claim 2,
The control unit is an ion milling apparatus that repeatedly performs irradiation of the ion beam from the ion gun to the sample for a predetermined time and movement of the position of the shielding plate relative to the sample in the edge direction. In claim 1,
an ion milling apparatus having a stage driving unit that causes the sample stage to perform a swing motion about a swing axis that is set perpendicular to the center of the ion beam of the ion beam, and a slide motion that moves the sample in the edge direction. In claim 2,
the cross-section milling holder comprises a shield plate holder to which the shield plate is fixed, a sample holder that sandwiches the shield plate and the sample, and a shield plate fixing screw that fixes the shield plate holder to the sample holder;
The shield plate fixing screw passes through a groove provided in the shield plate holder and having a longitudinal direction in the edge direction, thereby fixing the shield plate holder to the sample holder. In claim 5,
The shielding plate driving unit moves the position where the shielding plate fixing screw passes through the groove of the shielding plate holder in the ion milling apparatus. In claim 5,
The shielding plate driving unit is an ion milling apparatus that includes a motor unit, a rotating body that is rotated by the motor unit, and a shielding plate driving mechanism that uses the rotation of the rotating body as a driving source to rotate or move the shielding plate fixing screw. In claim 5,
An ion milling apparatus in which the material of the shielding plate holder is phosphor bronze. A cross-section milling method using an ion milling apparatus, comprising:
the ion milling apparatus comprises a sample stage on which a cross-section milling holder for holding a sample and a shielding plate is mounted, an ion gun for emitting an unfocused ion beam toward the sample, and a shielding plate driving unit for changing the adhesion between the sample and the shielding plate and the position of the shielding plate relative to the sample in an edge direction along the boundary between the sample held by the cross-section milling holder and the shielding plate;
the ion gun stops irradiating the sample with the ion beam after a predetermined time has elapsed;
the shielding plate driving unit weakens the adhesion between the sample and the shielding plate to move the position of the shielding plate relative to the sample in the edge direction, and then strengthens the adhesion between the sample and the shielding plate again;
The ion gun resumes irradiating the sample with the ion beam. In claim 9,
A cross-section milling method that repeatedly performs irradiation of the ion beam from the ion gun onto the sample for a predetermined time and movement of the position of the shielding plate relative to the sample in the edge direction. A cross-section milling holder for holding a sample and a shielding plate for cross-section milling processing by an ion milling apparatus,
a shielding plate holder to which the shielding plate is fixed;
a sample holder that sandwiches the shielding plate and the sample;
a shield plate fixing screw for fixing the shield plate holder to the sample holder;
The shield plate fixing screw is provided in the shield plate holder and passes through a groove having a longitudinal direction in the edge direction along the boundary between the sample and the shield plate to fix the shield plate holder to the sample holder. In claim 11,
The material of the shielding plate holder is phosphor bronze.