Ion milling device

Provided is an ion milling device capable of improving the reproducibility of an ion distribution. An ion milling device includes: an ion source (1); a sample stage (2) on which a sample (4) to be processed by being irradiated with an unfocused ion beam from the ion source (1) is placed; and a drive unit (8) configured to be arranged between the ion source (1) and the sample stage (2), and to move a linear ion beam measuring member (7) extending in a first direction to a second direction orthogonal to the first direction, in which the drive unit (8) moves the ion beam measuring member (7) within an emission range of the ion beam in a state where the ion beam is outputted from the ion source (1) under a first emission condition, and an ion beam current flowing through the ion beam measuring member (7) is measured by irradiating the ion beam measuring member (7) with the ion beam.

TECHNICAL FIELD

The present invention relates to an ion milling device.

BACKGROUND ART

JP-A-2002-216653 (PTL 1) discloses an ion milling device that extracts an ion by generating plasma in an ion source, and that performs processing on a substrate by emitting the extracted ion. It is disclosed that since the ion milling device performs processing on, for example, a 4-inch (Φ100) substrate, and obtains an ion beam of a large diameter having a uniform or desired distribution, the ion milling device controls a distribution of the extracted ion beam by electrically controlling a plasma distribution in the ion source. As an example of a control method, it is disclosed that a distribution state of the ion beam is measured by using a Faraday cup and a voltage applied to a plasma control electrode is adjusted based upon a measurement result.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

An ion milling device is a device for polishing a surface of a sample or a cross section thereof by irradiating the sample (for example, metal, semiconductor, glass, and ceramic) with an unfocused ion beam and flicking an atom on the surface of the sample without stress by a sputtering phenomenon. The ion milling device is used as a pretreatment device for observing the surface of the sample or the cross section thereof by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). An effective penning method for miniaturizing a structure is often adopted for an ion generation source of the above-described pretreatment device.

Since an ion beam from a penning type ion source is emitted to the sample in a state where the ion beam is not focused, an ion distribution in the vicinity of an ion beam emission point of the sample has a characteristic that ion density is the highest at a center portion of the ion distribution and the ion density becomes lower toward the outside from the center portion thereof. On the other hand, particularly, in the case of surface observation with an electron microscope, it is necessary to polish the sample surface smoothly in order to accurately observe the structure and composition. Therefore, the ion beam is emitted to the sample at a low incident angle while rotating the sample. Accordingly, it is possible to obtain a wide and smooth processed surface in a peripheral area including a portion to be observed. Since the ion density is directly linked to a processing speed (milling rate) of the sample, the characteristic of the ion distribution significantly affects a processed shape of the processed surface of the sample.

It is known that the ion generated and emitted from a structure of the penning type ion source wears an internal component. As a result of processing the sample, a fine particle that is generated from the processed surface and that floats particularly adheres to an ion emission port of the ion generation source, and causes dirt. Due to such factors, when the ion milling device is continuously used, a characteristic of the ion beam may change, and reproducibility of the processed shape of the processed surface of the sample may deteriorate. When the observation with the electron microscope is performed for the purpose of mass production process control, it is required to perform the same processing on a large number of samples, such that the deterioration in the reproducibility of the processed shape of the ion milling device may lead to deterioration in defect detection accuracy.

Considering the above-described problems, the present invention provides a method for adjusting an ion beam, which is suitable for an ion milling device that performs a pretreatment process of observing a surface of a sample or a cross section thereof, and an ion milling device capable of adjusting an emission condition of the ion beam.

Solution to Problem

An ion milling device according to an embodiment of the present invention includes: an ion source; a sample stage on which a sample to be processed by being irradiated with an unfocused ion beam from the ion source is placed; a drive unit configured to be arranged between the ion source and the sample stage, and to move a linear ion beam measuring member extending in a first direction to a second direction orthogonal to the first direction; and a control unit, in which the control unit moves the ion beam measuring member within an emission range of the ion beam by the drive unit in a state where the ion beam is outputted from the ion source under a first emission condition, and measures an ion beam current flowing through the ion beam measuring member by irradiating the ion beam measuring member with the ion beam.

An ion milling device according to another embodiment of the present invention includes: a sample chamber; an ion source position adjusting mechanism installed in the sample chamber; an ion source attached to the sample chamber via the ion source position adjusting mechanism; a sample stage on which a sample to be processed by being irradiated with an unfocused ion beam from the ion source is placed; and a control unit, in which the control unit obtains an adjustment value of a first emission condition based upon an ion distribution when the sample is irradiated with the ion beam from the ion source under the first emission condition, the ion source is a penning type ion source, and the control unit includes at least one of a discharge voltage of the ion source, a gas flow rate of the ion source, and a distance between the ion source and the sample as a parameter for obtaining the adjustment value of the first emission condition.

Advantageous Effects of Invention

It is possible to improve the reproducibility of an ion distribution of an ion milling device.

Other subjects and novel features will become apparent from the description and accompanying drawings in the specification.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a diagram (schematic diagram) illustrating a main part of an ion milling device according to an embodiment of the present invention from above (a vertical direction is defined as a Y direction). A sample chamber6capable of maintaining a vacuum state includes: an ion source1; a sample stage2where a sample4which is a target to be processed is installed; a sample stage rotation drive source3that rotates the sample stage2in an R direction around a rotation center R0; an ion beam measuring member7which is arranged close to a sample placing surface of the sample stage2; a drive unit8that drives the ion beam measuring member7back and forth in an X direction; and a sample protecting shutter9installed between the ion beam measuring member7and the sample placing surface of the sample stage2.

An ion beam from the ion source1is emitted to the sample4placed on the sample placing surface of the sample stage2in a state of radially spreading around an ion beam center B0. When the sample4is processed, it is necessary to adjust the rotation center R0and the ion beam center B0to coincide with each other. In order to easily perform the above-described adjustment, the ion source1is mounted on the sample chamber6via an ion source position adjusting mechanism5that adjusts a position of the ion source1in the X direction, the Y direction, and a Z direction. As a result, a position of the ion beam center B0of the ion source1, specifically, a position on an XY plane (plane including the X direction and the Y direction) and an operating distance (position in the Z direction, specifically, a distance from an ion beam emission position of the ion source1to the sample stage2) can be adjusted.

The sample stage2has the rotation center R0extending in the Z direction and a tilt axis T0extending in the X direction and intersecting with the rotation center R0on the sample placing surface of the sample stage2, and the sample stage2can be tilted around the tilt axis T0. The drawing illustrates a state in which the sample placing surface of the sample stage2and the ion source1face each other, and here, the ion beam measuring member7and the drive unit8are installed immediately before the sample placing surface of the sample stage2when viewed from the ion source. The ion beam measuring member7and the drive unit8may be arranged between the ion source1and the sample stage2, and it is desirable that the ion beam measuring member7and the drive unit8are placed to the sample4as close as possible in order to more accurately estimate a state of the ion beam acting on the sample4.

The ion beam measuring member7which will be described in detail later is a conductive member, leads an ion beam current flowing therethrough by irradiating the ion beam measuring member7with the ion beam from the ion source1to a control unit outside the sample chamber6by an ion beam current detecting wiring37, and detects an ion distribution emitted from the ion source1as a current amount.

In the drawing, the respective drive unit8and sample protecting shutter9are shown as separate mechanisms from the sample stage2, and both or either one of the drive unit8and the sample protecting shutter9can be mounted thereon as a mechanism of the sample stage2.

FIG. 2illustrates a configuration example of the ion source1used in the ion milling device. Here, a penning type ion source is used as the ion source1. The penning type ion source includes: an anode12which is arranged in the ion source and to which a discharge voltage is applied; and a first cathode10and a second cathode11that generate a potential difference with the anode12, in which an electron is generated by the potential difference between the anode and the cathode. The generated electron floats and stays inside the ion source1under the action of a magnetic field generated by a permanent magnet13. On the other hand, the ion source1includes a gas introduction hole14for introducing an inert gas from the outside, and for example, argon gas is introduced as the inert gas. When the argon gas is introduced into the ion source in which the electron is generated, an argon ion is generated by collision between an argon atom and the electron. The argon ion is attracted to an acceleration electrode15to which an acceleration voltage is applied, passes through anion emission port16from the inside of the ion source, and is emitted toward a target to be processed.

When the sample is processed with the penning type ion source, a component inside the ion source is worn and a fine particle scattered from the sample adheres to the ion emission port16, thereby changing the ion distribution emitted from the ion source. Although it is possible to eliminate the wear and dirt of the component inside the ion source by regularly replacing and cleaning the component, the ion distribution of the ion beam emitted from the ion source is not guaranteed to be in the same state as that before maintenance. When high-precision reproducibility is required for a processed shape of the sample by the ion milling device, with respect to the ion distribution of the ion beam after the replacement work of the component and the cleaning work thereof, it is necessary to confirm whether the desired ion distribution is reproduced, and to adjust an emission condition of the ion source1based upon a confirmation result.

Therefore, in the ion milling device of the embodiment, the ion beam measuring member7is installed in the sample stage2or in the vicinity of the sample stage2, and the ion beam current is measured while the ion beam measuring member7is driven in the X direction by the drive unit8, thereby estimating the ion distribution of an unfocused ion beam to be emitted from the ion source1toward the sample.

FIG. 3illustrates a configuration example of the drive unit8that drives the ion beam measuring member7. The drawing shows a top view of the drive unit8and a cross-sectional view in a state where the ion beam measuring member7is fixed to a base35of the drive unit8. The ion beam measuring member7is fixed to the drive unit8by a fixing member36of the base35. The fixing member36is an insulator, and the ion beam measuring member7and the ion beam current detecting wiring37are insulated from other components by the fixing member36. The base35can be reciprocated in the X direction by a drive mechanism. The drive mechanism of the embodiment includes a motor30, a bevel gear31, a gear32, and a rail member33. The base35can be reciprocated in the X direction by transmitting the drive to the rail member33provided along a movement direction (X direction) of the base35by the bevel gear31and the gear32provided on a drive shaft of the motor30. The motor30is not required to be provided exclusively for the drive unit8, and can also be used as the sample stage rotation drive source3for rotating the sample stage2.

The ion beam measuring member7is in a processed state by being irradiated with the ion beam from the ion source1during the measurement of the ion beam current. Since the ion beam measuring member7is worn out every time the measurement is performed, it is desirable to use a member having a low sputtering yield, which is difficult to be processed by the ion. A linear member is used as the ion beam measuring member7, and the ion beam measuring member7moves in an unfocused ion beam emission range, thereby grasping the ion distribution. Therefore, a diameter of the ion beam measuring member7determines a spatial resolution of the measurable ion distribution. Therefore, it is desirable that the diameter of the ion beam measuring member7is smaller than a half value width of the ion beam during the processing. For example, a linear material of graphite carbon having a diameter of 0.2 mm or more and 0.5 mm or less can be used. It is desirable that a cross-sectional shape of the ion beam measuring member7is a circular shape in order to prevent an irregular behavior of the ion caused by the collision of the ion with the ion beam measuring member7. In addition to the linear material of graphite carbon, a linear material of tungsten can also be used. The ion beam measuring member7is detachable from the drive unit8, and when the ion beam measuring member7is worn out by the ion beam, the consumed ion beam measuring member7is replaced with a new ion beam measuring member.

FIG. 4is a schematic diagram (top view) illustrating a state of ion beam current measurement in the ion milling device of the embodiment. The ion source1, and the sample stage2and the ion beam measuring member7that face the ion source1are illustrated. Since the ion beam to be emitted from the ion source1is unfocused, the unfocused ion beam advances while spreading radially in an area41indicated by a broken line. The ion beam measuring member7moves along the sample placing surface40of the sample stage2over the whole ion beam emission range in the X direction, for example, from a coordinate X0to a coordinate X5, while measuring the ion beam current. The embodiment illustrates an example in which the ion beam measuring member7moves in the X direction, and since the ion beam emitted from the ion source1spreads in the X direction and the Y direction around the ion beam center B0, a longitudinal direction of the ion beam measuring member7is defined as the X direction and the drive unit is configured so that the ion beam measuring member7moves along the sample placing surface40of the sample stage2over the whole ion beam emission range in the Y direction while measuring the ion beam current, such that it is also possible to measure the ion beam current.

FIG. 5Aillustrates a result of measuring the ion beam current by using the ion beam measuring member7from the coordinates X0to X5(refer toFIG. 4) in the ion milling device of the embodiment. A relationship between a beam measurement position and an ion beam current amount (here, referred to as an “ion beam current profile”) illustrated in the drawing can be regarded as the ion distribution emitted from the ion source1to the sample4. (A) is a measurement result of the ion beam current amount at a distance D1 between the ion source and the sample, and (B) is a measurement result of the ion beam current amount at a distance D2 (D2>D1) between the ion source and the sample. A plurality of ion beam current profiles in (A) and (B) are measurement results measured by changing a discharge voltage of the ion source1(the discharge voltage is changed in the same manner for both (A) and (B) to perform the measurement). A vertical axis represents the ion beam current amount, and both (A) and (B) are shown as values normalized by a common reference.

As such, the ion distribution changes by changing the distance from the ion source1to the sample. Even though the distance from the ion source1to the sample is the same, the ion distribution changes by changing the discharge voltage.

A graph illustrated inFIG. 5Bis a graph in which the two graphs illustrated asFIG. 5Aare superimposed and displayed, and an area50is an area sandwiched between a maximum value and a minimum value of all the profiles included in the two graphs. That is, it can be said that the area50is an area where the ion distribution can be adjusted by adjusting two parameters such as the distance D between the ion source and the sample and the discharge voltage. In the embodiment, the ion distribution emitted from the ion source1to the sample4is grasped by the ion beam current profile measured by using the ion beam measuring member7, and the emission condition of the ion source1is adjusted so that a shape of the ion beam current profile approaches a desired state, thereby improving the reproducibility of the processed shape of the sample by the ion milling device. Specifically, among the emission conditions of the ion source1, the distance from the ion source to the sample, the discharge voltage, and a gas flow rate are adjusted.

FIG. 6illustrates a block diagram related to ion distribution adjustment of an ion beam. As the ion source1, the penning type ion source illustrated inFIG. 2is used. Argon gas is introduced into the ion source1via a pipe17, and an argon ion is generated for performing processing.

A discharge voltage Vdand an acceleration voltage Vaapplied to the ion source1are generated by a power supply unit60. The power supply unit60includes ammeters, in which an ammeter61measures a discharge current, and an ammeter62measures an ion beam current flowing by collision of the ion from the ion source1with the ion beam measuring member7. Values of the discharge voltage Vdand the acceleration voltage Vaare set by a control unit63.

The ion source1is fixed to the ion source position adjusting mechanism5, and the position of the ion source1can move independently in the X direction, the Y direction, and the Z direction.

The sample protecting shutter9is arranged between the drive unit8and the sample4, and is configured to be movable vertically in the Y direction by the control of the control unit63. As a drive source for the sample protecting shutter9, a motor and a solenoid can be used, and in order to perform movement control, it is desirable to include a sensor that detects a vertical movement position of the shutter. The sample protecting shutter9is provided to not irradiate the sample4with an unnecessary ion beam when the acquisition of the ion beam current profile is performed in a state where the sample4is placed on the sample stage2.

The power supply unit60, the ion source position adjusting mechanism5, the drive unit8, the sample protecting shutter9, the sample stage2, and the sample stage rotation drive source3are connected to the control unit63, and the control unit63acquires the ion beam current profile, adjusts the ion beam emission condition, and processes the sample. The control unit63is connected to a display unit64, and the display unit64functions as a user interface from an operator with respect to the control unit63, and displays sensing data indicating an operating state of the ion milling device collected by the control unit63. For example, the sensing data displayed on the display unit64includes the discharge voltage value Vd, the discharge current value, the acceleration voltage value Va, and the ion beam current value from the power supply unit60.

A method for acquiring the ion beam current profile and adjusting the ion beam emission condition performed by the control unit63in the ion milling device illustrated inFIG. 6will be described with reference toFIG. 7.

Step S701: The control unit63controls the drive unit8and moves the ion beam measuring member7to an origin position in the X direction. Here, for the simplicity of description, the origin position in the X direction is determined to coincide with an outermost position of the ion beam emission range. A method for taking the origin position is not limited thereto.

Step S702: The control unit63controls the movement of the sample protecting shutter9, and moves the sample protecting shutter9to a beam shielding position.

Step S703: The control unit63controls the power supply unit60, and outputs an ion beam from the ion source1according to an ion beam emission condition stored as a current setting. The current setting refers to the ion beam emission condition determined as a processing condition of the sample4. Generally, an acceleration voltage, a discharge voltage, and a gas flow rate of the ion source1when processing the sample4are determined.

Step S704: After starting the output of the ion beam therefrom, the control unit63controls the drive unit8to start the movement of the ion beam measuring member7in the X direction. As described with reference toFIG. 4, a movement direction is a direction from the outermost position of the ion beam emission range (origin position in the X direction) toward an end portion of the other ion beam emission range. The control unit63manages a current position of the moving ion beam measuring member7in the X direction.

Step S705: When the ion beam measuring member7is irradiated with the ion beam from the ion source1, the ammeter62starts to measure an ion beam current flowing through the ion beam measuring member7and the ion beam current detecting wiring37. The control unit63acquires and stores an ion beam current detection value digitized by the ammeter62.

Step S706: The control unit63displays the acquired ion beam current value on the display unit64as a current detection result. A display format is desirably the beam measurement position-ion beam current amount graph (ion beam current profile) illustrated inFIG. 5A. The current detection result may be displayed on a host PC connected to the ion milling device via LAN or a serial circuit which is not illustrated.

Step S707: The control unit63confirms the current position in the X direction of the ion beam measuring member7moved by the drive unit8, and when the movement of the ion beam measuring member7is not completed, the control unit63repeatedly executes steps S704to S706until the ion beam measuring member7completes the movement over the whole ion beam emission range.

Step S708: When confirming that the ion beam measuring member7completes the movement over the whole ion beam emission range in step S707, the control unit63ends the movement of the ion beam measuring member7.

Step S709: The control unit63calculates an adjustment amount from an ion beam current measurement result. As a comparison target of the adjustment amount, the ion beam current measurement result stored in the control unit63by performing the same measurement when determining a processing condition applied to the processing of the sample4is used, or the previously measured ion beam current measurement result is used. An operator can set in advance which comparison target is to be used. When a reference ion beam current profile (reference ion distribution) which becomes the comparison target and an ion beam current profile (ion distribution) obtained as an ion beam current measurement result measured this time are ideally equal to each other, or when the ion beam emission condition can be adjusted so that the reference ion beam current profile and the ion beam current profile are similar to each other, it is possible to improve the reproducibility of the processed shape of the sample by the ion milling device. A degree of approximation may be determined depending on a degree of the reproducibility of a processed shape of a required sample.

However, in the embodiment, since the ion distribution is observed only by the ion beam current, the acceleration voltage Vaamong the adjustable parameters of the ion source1is not changed. The reason is that when the acceleration voltage Vais changed, a processing speed (milling rate) of the sample significantly changes even though the ion beam current is the same. That is, in the adjustment of the embodiment, it is assumed that processing time of the sample is not an adjustment target.

FIG. 8illustrates a schematic diagram of the ion beam current profile. As a simple method for matching the shapes of the ion beam current profiles, a method for adjusting a peak value P of a representative value of the shape of the ion beam current profile and a half value width HW thereof (spread of the ion beam current profile in which the ion beam current amount becomes half of the peak value P) to be equal to each other will be described. The reason is that when the two values match, the shapes of the ion beam current profiles can be evaluated as approximately equal to each other. The parameters of the ion beam emission condition to be adjusted are the discharge voltage of the ion source1, the gas flow rate thereof, and the distance D between the ion source1and the sample4(or the sample placing surface of the sample stage2, using the sample4as a representative).

The distance between the ion source1and the sample4is changed, thereby making it possible to mainly adjust the value of the peak value P as illustrated inFIG. 5A. The discharge voltage Vdincreases, thereby making it possible to prevent the spread of the argon ion generated inside the ion source1, and as a result, a size of the half value width HW can be adjusted. In the same manner, when the gas flow rate increases, the spread of the argon ion generated inside the ion source1can be prevented, and as a result, the size of the half value width HW can be adjusted. As such, the distance between the ion source1and the sample4and the value of at least one of the discharge voltage Vdand the gas flow rate are adjusted, thereby making it possible to allow the ion beam current profile to be closer to a desired shape. As illustrated inFIG. 5B, it can be seen that a wide adjustment area can be obtained only by adjusting the distance between the ion source1and the sample4and the discharge voltage Vd.

Here, an example of obtaining the adjustment amount by using the peak value P of the ion beam current profile and the half value width HW thereof will be described, and feature amounts of a large number of profile shapes may be extracted and adjusted. For example, a feature amount related to symmetry of the profile shape may be extracted and adjusted.

Step S710: The emission condition of the ion beam is adjusted based upon the adjustment amount calculated in step S709. Specifically, the control unit63executes one or a plurality of controls among the adjustment of the distance between the ion source1and the sample4by the control of the ion source position adjusting mechanism5, the control of the discharge voltage Vdof the ion source1by the control of the power supply unit60, and the control of the gas flow rate supplied to the ion source1by the control of a gas supply mechanism (not illustrated), based upon the calculation result in step S709.

Step S711: After the adjustment according to step S710is performed, when the ion beam current profile is remeasured, the processing is executed again from step S701, and when the ion beam current profile is not remeasured, the adjustment is completed.

Step S712: The control unit63moves the sample protecting shutter9to a beam non-shielding position, and ends the adjustment.

The flowchart ofFIG. 7is an example, and various modifications can be performed. For example, in step S706, the ion beam current measurement result and the reference ion beam current profile which becomes the comparison target of the adjustment amount may be superimposed and displayed. When the operator determines that the adjustment is unnecessary by the superimposed display, a step of stopping the adjustment of the ion beam may be added. In step S710, the control unit63controls the distance between the ion source1and the sample4, and for example, the distance therebetween may be adjusted in a manner that a control amount is displayed on the display unit64, and the operator manually moves the position of the ion source1by the ion source position adjusting mechanism5.

While the invention made by the present inventor has been specifically described above based upon the embodiments, the present invention is not limited to the described embodiments, and various modifications can be made without departing from the gist thereof. For example, the configuration ofFIG. 1is provided with the sample protecting shutter for preventing the sample from being irradiated with the ion beam when the ion beam current profile is acquired, and when irradiation of the sample with the ion beam can be ignored during the period of acquiring the ion beam current profile, the sample protecting shutter9may not be provided. The embodiment describes the ion milling device for performing plane milling processing as an example, and the present invention is also applicable to an ion milling device for performing cross-section milling processing. In the case of the cross-section milling processing, there is a difference that a rotation axis (swing axis) of the sample stage2is arranged to extend in the Y direction, and the emission condition of the ion beam can be adjusted by the same structure.

REFERENCE SIGNS LIST