JP2012068227A - Ion milling device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion milling device and method capable of directly cooling a surface of a sample irradiated with an ion beam at the time of milling by irradiating the sample with the ion beam.SOLUTION: An ion milling device comprises; a sampling stage 1 where a sample S is placed; an ion source 2 for generating an ion beam with which the sample S is irradiated; a sample chamber 3 maintaining a storage space of the sampling stage 1 as a predetermined vacuum; and refrigerant supplying means 5 for supplying a gaseous refrigerant to cool the sample S inside the sample chamber 3. A surface of the sample irradiated with the ion beam can be directly cooled by the gaseous refrigerant by supplying the gaseous refrigerant inside the sample chamber.

Description

  The present invention relates to an ion milling apparatus and an ion milling method that can suppress a temperature rise of a sample when the sample is milled by an ion beam.

  An ion milling device is known as a device for producing a specimen for SEM observation or performing microfabrication of a semiconductor or the like. This apparatus is an apparatus that removes a sample surface by irradiating a sample placed on a sample stage in a sample chamber with an ion beam. Since the sample irradiated with the ion beam is accompanied by a temperature rise reaching, for example, 100 ° C. or more, the sample may be thermally deteriorated when the sample includes a material having low heat resistance. In that case, the form and structure of the sample change, and there is a possibility that accurate sample information cannot be obtained even if the sample is observed with a microscope, or desired fine processing cannot be performed. As a countermeasure against the temperature rise of the sample, Patent Document 1 discloses a sample cross-section preparation apparatus provided with a sample cooling mechanism. Specifically, a first shielding material that partially covers the sample and partially shields the ion beam, a second shielding material that is in close contact with the sample and the sample support member and serves as a cooling unit, and both shielding materials And a heat conduction braided wire that is cooled by liquid nitrogen or the like is attached to the second shielding material. According to this apparatus, the irradiation range of the ion beam to the sample is restricted by the first shielding material to suppress the temperature rise of the sample, and the heat of the sample is passed through the second shielding material and the braided wire for cooling conduction. It is said that heat deterioration of the sample can be suppressed by radiating heat.

JP 2009-145050

  However, the above prior art has the following problems.

(1) The irradiation surface of the sample with the ion beam cannot be directly cooled.
A portion of the sample where thermal degradation is desired to be suppressed is an irradiation surface on which milling is performed by ion beam irradiation. However, since this irradiation surface itself cannot be covered with the second shielding material, the second shielding material is brought into contact with a surface other than the irradiation surface of the sample, and the sample is cooled by heat conduction through the contact surface. become. For this reason, the irradiated surface of the sample cannot be efficiently cooled. In particular, since a resin-embedded sample used as one of SEM observation samples is covered with a resin having low thermal conductivity, cooling the irradiated surface through the contact surface has low cooling efficiency. .

(2) It takes time to cool the sample and return to room temperature.
In the cooling by heat conduction using the second shielding material and the braided wire for cooling conduction, the sample stage is cooled to, for example, about −120 ° C. using liquid nitrogen or the like. Therefore, it takes about 1 hour from setting the sample on the sample stage to starting milling. On the other hand, after milling is completed, it takes about 30 minutes to return the sample and its surroundings to room temperature to prevent condensation when the sample chamber is released to the atmosphere.

(3) It is difficult to uniformly cool the entire large sample.
When preparing a sample for a microscope, a large resin-embedded sample may be placed on the sample stage, and the sample stage is as large as about 50 mmφ. For this reason, it is difficult to uniformly cool the entire surface of the sample table, and it is also difficult to uniformly cool the sample mounted on the sample table.

(4) It is difficult to cope with the rotation and inclination of the sample stage.
Since the sample stage of the ion milling apparatus uniformly mills a wide range of the sample, it can usually be rotated with the sample tilted. However, in the above cooling mechanism, it is necessary to secure the solid-solid contact between the sample and the second shielding material or the solid-solid contact between the second shielding material and the braided wire for cooling conduction. Difficult to do.

  The present invention has been made in view of the above circumstances, and one of the purposes thereof is an ion that can directly cool an irradiation surface of an ion beam on a sample when the sample is irradiated with an ion beam for milling. It is to provide a milling apparatus and an ion milling method.

  Another object of the present invention is to provide an ion milling apparatus and an ion milling method that can quickly cool a sample and return it to room temperature.

  Another object of the present invention is to provide an ion milling apparatus and an ion milling method that can easily cool the entire sample uniformly.

  Still another object of the present invention is to provide an ion milling apparatus and an ion milling method capable of easily cooling even a sample placed on a rotating sample stage.

  The inventors changed the idea by cooling the sample using heat conduction by contact between solids, and used the gas refrigerant as a transport medium for moving the heat from the sample to the outside of the sample chamber. As a result, the present invention has been completed.

  The ion milling apparatus of the present invention includes a sample stage on which a sample is placed, an ion source that generates an ion beam that irradiates the sample, a sample chamber that holds a storage space of the sample stage in a predetermined vacuum, and the sample And a refrigerant supply means for supplying a gaseous refrigerant for cooling the sample into the sample chamber.

  According to this configuration, by supplying the gaseous refrigerant into the sample chamber, the irradiation surface of the ion beam in the sample can be directly cooled by the gaseous refrigerant. For this reason, it is possible to efficiently cool the most desired part of the sample and to avoid excessive cooling of the sample easily by adjusting the type of gas refrigerant and supply conditions, and introducing and milling the sample into the sample chamber. A series of operations such as start / end of sample and removal of sample can be performed smoothly. In addition, cooling according to the size and shape of the sample can be easily realized by adjusting the type of gas refrigerant and supply conditions. Furthermore, since the cooling of the sample does not depend on the heat conduction caused by the contact between the solids, the sample can be cooled without being affected by the driving of the sample stage such as rotation and tilt.

  As one form of this invention apparatus, the said refrigerant | coolant supply means is provided with the nozzle arrange | positioned so that a gaseous refrigerant | coolant may be injected into a sample in the said sample chamber.

  In the apparatus of the present invention, the supply path is not particularly limited as long as the gaseous refrigerant can be supplied into the sample chamber. However, if a nozzle for injecting a gaseous refrigerant to the sample is provided in the sample chamber, the sample can be more locally and efficiently compared to a case where an inlet for the gaseous refrigerant is provided in the sample chamber to cool the entire chamber. The irradiated surface can be cooled.

  As an aspect of the apparatus of the present invention, when the nozzle is provided, the refrigerant supply means may include a nozzle variable mechanism that adjusts the jet direction of the gas refrigerant and the distance to the sample.

  By including the variable mechanism of the nozzle, the nozzle can be arranged at an appropriate position according to the size and shape of the sample, and the sample can be cooled more efficiently and reliably.

  As one form of the device of the present invention, the gas refrigerant is preferably an inert gas.

  When the gaseous refrigerant is an inert gas, the gaseous refrigerant does not react with the sample, and the sample can be cooled without causing alteration of the sample.

  One aspect of the apparatus of the present invention further includes a switching unit that switches between irradiation of the sample with the ion beam and supply of the gaseous refrigerant into the sample chamber.

  By switching the irradiation of the ion beam to the sample and the supply of the gaseous refrigerant into the sample chamber by this switching means, the sample can be switched between milling and cooling, and excessive heating and cooling of the sample can be suppressed. Can do. Further, even when the degree of vacuum necessary for generating the ion beam and the degree of vacuum in the sample chamber necessary for cooling the sample are different, different degrees of vacuum appropriate for each of the sample milling and cooling can be easily realized.

  When the switching unit is provided as an aspect of the present invention device, the switching unit stores a switching condition set in advance, and irradiation of the ion beam based on the switching condition read from the storage unit. It is preferable to include a switching control means for switching the supply of the gaseous refrigerant.

  According to this configuration, the milling and cooling of the sample can be automatically switched under a desired switching condition, and the ion milling apparatus can be easily operated.

  As an aspect of the apparatus of the present invention, the ion source may include a plasma chamber that communicates with the sample chamber and holds the ion beam generation space in a predetermined vacuum. In that case, it is preferable that the ion milling apparatus further includes a differential evacuation mechanism that holds the sample chamber and the plasma chamber at different degrees of vacuum.

  By providing a differential pumping mechanism, the plasma chamber can be set to a high vacuum suitable for the generation of ions, and the sample chamber can be set to a low vacuum suitable for heat dissipation of the sample by introducing a gas refrigerant. The sample can be cooled at the same time. Therefore, a series of operations such as introduction of the sample into the sample chamber, start / end of milling, and removal of the sample can be performed particularly smoothly.

  As one form of this invention apparatus, providing further the cooling mechanism which cools the said gaseous refrigerant is mentioned.

  The gas refrigerant can be cooled to a predetermined temperature by the cooling mechanism, and the sample can be cooled more efficiently by supplying the low-temperature refrigerant into the sample chamber.

On the other hand, the first ion milling method of the present invention includes the following steps.
Ion milling process: The surface of the sample is removed by irradiating the sample with an ion beam generated in the plasma chamber.
Cooling step: The sample is cooled by supplying a gaseous refrigerant into the sample chamber that communicates with the plasma chamber and stores the sample.
Then, the ion milling process and the cooling process are switched and performed.

  By switching between the ion milling process and the cooling process, excessive heating and cooling of the sample can be suppressed. Also, different degrees of vacuum suitable for each of sample milling and cooling can be easily realized.

The second ion milling method of the present invention includes the following steps.
Ion milling process: The surface of the sample is removed by irradiating the sample with an ion beam generated in the plasma chamber.
Cooling step: The sample is cooled by supplying a gaseous refrigerant into the sample chamber that communicates with the plasma chamber and stores the sample.
The plasma chamber and the sample chamber are differentially evacuated, and the ion milling process and the cooling process are performed simultaneously.

  According to this method, the ion milling process and the cooling process can be performed simultaneously, and a series of operations such as introduction of the sample into the sample chamber, start / end of milling, and removal of the sample can be performed particularly smoothly.

  As one form of the first and second methods of the present invention, the cooling step may be performed by directly injecting a gaseous refrigerant from a nozzle provided in the sample chamber.

  By jetting the gaseous refrigerant directly from the nozzle onto the sample, only the sample can be cooled more specifically and efficiently.

  According to the ion milling apparatus and the ion milling method of the present invention, when performing the milling by irradiating the sample with the ion beam, the temperature rise of the sample can be suppressed. Therefore, even if the sample is vulnerable to heat, thermal degradation of the sample can be suppressed as much as possible.

1 is a functional block diagram of an ion milling apparatus according to Embodiment 1. FIG. 6 is a functional block diagram of an ion milling apparatus according to Embodiment 2. FIG. 6 is a flowchart illustrating an operation procedure of the apparatus according to the second embodiment. It is a functional block diagram of an ion milling apparatus according to Embodiment 3. 6 is a graph showing test results of Test Example 1. 10 is a graph showing test results of Test Example 2. 10 is a graph showing test results of Test Example 3. 10 is a graph showing test results of Test Example 4. It is a graph which shows the test result of Test Example 5-1. It is a graph which shows the test result of test example 5-2. 10 is a photomicrograph showing the imaging result of Test Example 6.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, an embodiment of the present invention will be described by taking an ion milling apparatus for producing a sample of an electron microscope such as an SEM as an example.

Embodiment 1
(overall structure)
The ion milling apparatus shown in FIG. 1 accommodates a sample stage 1 on which a sample S is mounted, an ion source 2 that generates an ion beam that irradiates the sample S, and the sample stage 1 to create a predetermined atmosphere around the sample. A sample chamber 3 for maintaining a degree of vacuum and a computer 4 for controlling operations such as ion beam irradiation are provided. The main feature of the apparatus of the present invention is that the sample chamber 3 is provided with a refrigerant supply means 5 for supplying a gaseous refrigerant. Hereinafter, the configuration of each unit will be described in more detail.

(Sample stage)
The sample stage 1 is a stage on which the sample S is mounted. This sample stage 1 is configured to be able to rotate with the installation surface of the sample S inclined. By rotating in this inclined state, the wide range of the sample S can be uniformly milled. In particular, the sample stage 1 having a eucentric function can be preferably used. By providing the eucentric function, the sample S can be tilted and rotated with reference to the point of interest of the sample S. In each test example to be described later, in order to measure the temperature of the surface (irradiation surface) irradiated with the ion beam of the simulated sample, a thermometer 11 connected to a thermocouple (not shown) and its measurement data are acquired. A data logger 13 is provided. The thermocouple is introduced into the sample chamber 3 through a field through flange (not shown) of the ion milling device.

(Ion source)
The ion source 2 is a plasma chamber 21 that maintains a space for ionizing a gas at a predetermined degree of vacuum, ionizes the gas in the chamber 21 to generate ions, and accelerates the ions as a beam. A beam generator 23 is provided. Various known configurations can be used for the ion source 2 itself.

<Plasma chamber>
The plasma chamber 21 is a vacuum container for keeping the inside at a pressure suitable for generating an ion beam by the beam generator 23. A flow rate adjusting valve such as a mass flow controller 21B is connected to the plasma chamber 21, and a gas for generating ions, such as argon gas, is introduced into the plasma chamber 21 via the flow rate adjusting valve. The gas introduced into the plasma chamber 21 is not limited to argon. A preferable pressure in the plasma chamber 21 for generating the ion beam is about 0.02 to 0.08 Pa.

<Beam generator>
The beam generating unit 23 includes an anode and a cathode (discharge electrode: not shown) for ionizing the gas introduced into the plasma chamber 21, and further includes an acceleration electrode 23E for accelerating ions generated by ionizing the gas. Prepare. A predetermined discharge voltage can be applied between the anode and the cathode, and the gas is converted into plasma by the discharge. Then, a predetermined accelerating voltage is applied to the accelerating electrode 23E, and the energy to be incident on the sample chamber 3 side is adjusted using ions in the plasma chamber 21 as a beam.

(Sample chamber)
The sample chamber 3 is a container that stores the sample stage 1 and holds the internal space in a predetermined vacuum. The sample chamber 3 communicates with the plasma chamber 21 of the ion source 2 described above, and can irradiate an ion beam from the ion source 2 toward the sample stage 1.

  As an exhaust system, a turbo molecular pump 31 for high vacuum exhaust, a solenoid valve for vacuum exhaust control 32, and an electromagnetic valve 33 for introducing air are sequentially connected in series to the sample chamber 3, and both solenoid valves 32, A rotary pump 34 for low vacuum exhaust is connected between 33. By using these exhaust systems, the pressure in the sample chamber 3 and the above-described plasma chamber 21 can be adjusted to a predetermined degree of vacuum or returned to normal pressure. This degree of vacuum is measured by a high vacuum pressure gauge 35 and a low vacuum pressure gauge 36.

  When a gaseous refrigerant is introduced into the sample chamber 3 by the refrigerant supply means 5 described later, the pressure in the chamber 3 increases (the degree of vacuum decreases). In this case, the gas refrigerant can be effectively used as a heat transfer medium from the sample S by setting the pressure to a predetermined lower limit value or more. Conversely, by setting this pressure to be equal to or lower than the predetermined upper limit value, the influence on the pressure in the plasma chamber 21 communicating with the sample chamber 3 can be suppressed, and the ion beam can be generated reliably. A preferable pressure in the sample chamber 3 for cooling the sample S is about 0.1 Pa to about 35 Pa.

(Refrigerant supply means)
The refrigerant supply means 5 is typically connected to a refrigerant supply source 51 for storing a gaseous refrigerant, a refrigerant supply path 53 connected from the supply source 51 into the sample chamber 3, and a tip of the refrigerant supply path 53. A nozzle 55 directed against the sample S in the sample chamber 3.

<Refrigerant supply source>
A typical example of the refrigerant supply source 51 is a tank. As the kind of the gas refrigerant stored in the tank, dry gas can be used suitably. This is because if the gas refrigerant contains moisture, it takes time to reach a predetermined degree of vacuum when the sample chamber 3 is exhausted. In particular, a gas containing no oxygen is suitable. This is because if the dry gas contains oxygen, it tends to contain moisture and the sample may be oxidized. More specifically, an inert gas such as helium, nitrogen, or argon can be suitably used as the gas refrigerant. Among them, helium has a high thermal conductivity and is preferable as a heat transfer medium from the sample S in consideration of efficient cooling of the sample. On the other hand, nitrogen and argon have lower thermal conductivity than helium, but are preferable in that they can be obtained at low cost.

  The temperature of the gaseous refrigerant is not particularly limited as long as the temperature of the sample S can be lowered. A gaseous refrigerant at normal temperature is preferable because it can be easily handled. When importance is attached to the cooling ability of the sample S, the temperature of the gaseous refrigerant may be cooled to room temperature or lower as necessary. For this cooling, gas refrigerant cooling means 57 (shown by broken lines) may be provided in the middle of the refrigerant supply source 51 or the refrigerant supply path 53 described below. As the cooling means 57, a known refrigerator or cooler can be used.

<Refrigerant supply path>
The refrigerant supply path 53 is a pipe line that guides the gaseous refrigerant from the tank into the sample chamber 3. Usually, a flow rate adjusting valve such as a mass flow controller 53B is provided in the middle of the pipeline. Examples of the introduction of the refrigerant supply path 53 into the sample chamber 3 include introduction of a pipe line from an opening / closing door of the sample chamber 3 or introduction of a pipe line from a location other than the opening / closing door of the sample chamber 3. In the apparatus of FIG. 1, the former configuration is adopted, and a refrigerant supply path 53 is introduced into the sample chamber 3 via a field through flange (not shown). However, in the latter case, it is often easier to increase the degree of freedom of the arrangement position of the nozzle 55 described below.

<Nozzle>
The nozzle 55 is an injection port for supplying a gaseous refrigerant into the sample chamber 3. By injecting the gaseous refrigerant from the nozzle 55, the sample, particularly the irradiation surface of the ion beam, is effectively cooled.

  Examples of the arrangement form of the nozzle 55 in the sample chamber 3 include forming an opening serving as the nozzle 55 on the wall surface of the sample chamber 3 or projecting a tubular nozzle into the space in the chamber 3. In the former case, the entire sample chamber 3 can be cooled. In the latter case, it is possible to specifically cool the sample S by injecting the gaseous refrigerant directly onto the sample S by adjusting the direction of the nozzle 55. In the latter case in particular, the arrangement of the nozzle 55 is preferably set at a position that does not interfere with the ion beam irradiation field. With this arrangement, it is possible to prevent the nozzle 55 from being milled by the ion beam or electromagnetically attracting the ion beam. Usually, there are many apparatuses in which the ion source 2 is positioned upward and the sample stage 1 is positioned downward, and the ion beam is irradiated from above to below. In that case, the nozzle 55 can be disposed without interfering with the ion beam by disposing the nozzle 55 so as to be directed obliquely from below to the inclined sample mounting surface of the sample stage 1. However, in the apparatus of FIG. 1, the nozzles 55 are arranged from obliquely upward to obliquely downward of the sample stage 1.

  Examples of the shape of the nozzle 55 include a single tube, a nozzle whose tip is branched into a plurality, and a nozzle having a flat opening at the tip. One tubular nozzle 55 has the simplest configuration. The nozzle having the tip branched into a plurality of portions can inject the gas refrigerant simultaneously to a plurality of locations of the sample by injecting the gas refrigerant from each branch pipe, and is suitable for cooling a wide range of the sample. A flat nozzle can also inject a gaseous refrigerant over a wide range in its wide direction, and is also suitable for cooling a wide range of the sample.

  The installation position of the nozzle 55 in the sample chamber 3 may be fixed or variable. When this installation position is fixed, if the tip of the nozzle 55 is arranged so as to face the center of the sample stage 1, the sample S is cooled almost uniformly even if there is a slight difference in the size or shape of the sample S. be able to. When making the installation position of the nozzle 55 variable, it is preferable to provide a variable mechanism in the nozzle 55 to adjust the position of the nozzle tip. There are manual and automatic variable mechanisms. Examples of the manual variable mechanism include a tubular nozzle that can be bent at a plurality of bent portions, and a nozzle made of a flexible tube that can bend the entire nozzle into a snake shape. As the automatic variable mechanism, there is a drive variable mechanism that drives the nozzle in the X-Y-Z direction or the like in the sample chamber by an actuator such as a motor. If these variable mechanisms are provided, the gas refrigerant can be injected to an appropriate position regardless of the size and shape of the sample S. When the installation position of the nozzle 55 is variable, it is preferable to install the nozzle so that the nozzle 55 faces a position within about 1 cm from the eucentric center of the sample (sample stage).

  As the constituent material of the nozzle 55, various plastics, rubber, metal, or ceramics can be used. Since plastic and rubber are excellent in moldability, the degree of freedom of the shape of the nozzle 55 is high. Metals and ceramics are easy to configure a nozzle having high rigidity and high durability. Furthermore, it is good also as a nozzle which consists of a composite material of each of these materials.

(Computer)
The operation of each part of the ion milling apparatus described above is performed under the control of the computer 4. The computer 4 includes a control means 41 having a CPU, RAM, ROM (not shown), a signal output unit 44 that outputs a control signal to each unit, a signal input unit 45 that inputs a signal from each unit, a keyboard, and the like Input means 46 and display means 47 such as a display are provided. The signal output unit 44 includes, for example, a turbo molecular pump 31, an evacuation control solenoid valve 32, an atmosphere introduction solenoid valve 33, an operation signal of the rotary pump 34, an operation signal of the mass flow controller 21B, a discharge voltage between the anode and the cathode, The control signal of the acceleration voltage of the acceleration electrode 23E is output. For example, measurement signals from the high vacuum pressure gauge 35 and the low vacuum pressure gauge 36 are input to the signal input unit 45. In addition, the computer 1 includes switching means 48α that can switch between irradiation of the sample S with the ion beam and injection of the gaseous refrigerant from the nozzle 55. This switching means 48α stops one of the operations currently being executed out of the operations of irradiation of the sample S with the ion beam and jetting of the gaseous refrigerant from the nozzle 55, and starts the other operation that is currently stopped. Command to output. For example, the switching operation may be executed by inputting a switching command from the input means 46, or a separate switch dedicated to switching may be provided to execute the switching operation.

(Use procedure and operation of ion milling equipment)
First, the sample S is set on the sample stage 1, and if necessary, the sample stage 1 is rotated while being held in a predetermined inclined state. In this state, the sample is irradiated with an ion beam from the ion source 2. At that time, a gas is introduced into the plasma chamber 21 to maintain a predetermined degree of vacuum, and ions are generated by ionizing the gas by applying a voltage to the discharge electrode of the beam generator 23. Then, a predetermined acceleration voltage is applied to the acceleration electrode 23E to accelerate the ions into a beam.

  When milling due to ion beam irradiation proceeds to some extent, a switching command is input to the computer 4 before the sample S becomes so hot that the sample S deteriorates, ion beam irradiation is stopped, and gaseous refrigerant is supplied to the sample chamber 3 To start. While the gaseous refrigerant is supplied, the inside of the sample chamber 3 is maintained at a vacuum suitable for cooling the sample S. The introduction of the gas refrigerant may cause the plasma chamber 21 to have a low degree of vacuum that is not suitable for generating an ion beam. However, since the ion beam is not irradiated when the gas refrigerant is introduced, there is no particular problem.

  The start of the supply of the gas refrigerant, that is, the stop of the irradiation of the ion beam, by previously setting a thermocouple electrode on the simulated sample, and obtaining the relationship between the irradiation time of the ion beam and the temperature of the irradiation surface of the sample S It is preferable to determine the irradiation time of the ion beam that can bring the sample to a temperature at which the sample does not deteriorate. Similarly, as for the supply time of the gas refrigerant, an appropriate supply time during which the sample S is not excessively cooled can be selected by obtaining a correlation with the temperature of the irradiation surface of the simulated sample in advance. In addition, the temperature of the irradiation surface of the sample S is measured with a non-contact type thermometer or the like, and when the temperature of the irradiation surface reaches a predetermined upper limit value or lower limit value, the switching means 48α may perform the switching operation. Good. When the supply of the gaseous refrigerant is started, the gaseous refrigerant ejected from the nozzle 55 is directly blown onto the irradiation surface of the sample S.

  When the gaseous refrigerant is supplied for a predetermined time, the switching command is input to the computer 4 again, the supply of the gaseous refrigerant is stopped, and the ion beam irradiation is resumed. At that time, the inside of the plasma chamber 21 has a low degree of vacuum suitable for cooling the sample S and not a high degree of vacuum suitable for generating the ion beam. Is quickly exhausted by an exhaust system to switch to a predetermined high vacuum. Then, the inside of the plasma chamber 21 is set to a predetermined high vacuum, and the sample S is irradiated again with an ion beam.

  Similarly, the sample S may be ion milled by repeatedly switching between irradiation of the sample S with the ion beam and supply of the gaseous refrigerant into the sample chamber 3.

(Function and effect)
According to the above ion milling device of the present invention, the following effects can be obtained.

  (1) By supplying the gaseous refrigerant into the sample chamber, the irradiation surface of the sample irradiated with the ion beam can be directly cooled with the gaseous refrigerant. Therefore, ion milling can be started promptly after the sample is mounted on the sample stage while suppressing thermal degradation of the sample.

  (2) By switching the irradiation of the sample with the ion beam and the supply of the gaseous refrigerant into the sample chamber, the sample is not excessively heated or cooled. Therefore, the sample cooled after the ion milling can be quickly returned to normal temperature.

  (3) By spraying a gas refrigerant directly on the sample itself, particularly on the irradiated surface, even a large sample can be uniformly cooled throughout. In particular, even for a sample embedded with a resin having low thermal conductivity, the entire irradiated surface can be specifically and efficiently cooled.

  (4) Since the cooling of the sample is performed by spraying a gaseous refrigerant, it is not heat dissipation utilizing contact between solids of the sample and another solid material. Therefore, even if the sample stage is tilted and rotated, the sample can be cooled without any additional structural change particularly in the ion milling apparatus.

[Embodiment 2]
In the first embodiment, an apparatus has been described in which a switching command is input to a computer to switch between irradiation of an ion beam onto a sample and supply of a gaseous refrigerant into the sample chamber. In this example, an ion milling apparatus that can automatically perform the switching by causing the computer to program the switching conditions in advance will be described with reference to FIGS. The following description will be focused on differences from the first embodiment, and description of common points will be omitted.

(Device configuration)
In this example, as shown in FIG. 2, the computer 4 includes switching means 48β, and the switching means 48β further includes storage means 48M and switching control means 48C. The storage means 48M stores the switching condition between the irradiation of the ion beam onto the sample S and the supply of the gaseous refrigerant into the sample chamber 3, and the switching control means 48C reads the switching read out from the storage means 48M. Switching between ion beam irradiation and gas refrigerant supply is executed based on the conditions. As a specific example of the switching condition, the ratio of the supply time of the gas refrigerant in one minute is used as a cooling rate, and switching between ion beam irradiation and gas refrigerant supply is performed at a preset cooling rate. For example, when an ion beam is irradiated for 15 seconds per minute and gas refrigerant is supplied for 45 seconds, the cooling rate is 75%. Conversely, when an ion beam is irradiated for 45 seconds per minute and gas refrigerant is supplied for 15 seconds. The cooling rate will be 25%. A plurality of switching conditions are stored so that several patterns of such cooling rates can be selected so that appropriate cooling can be performed according to the material, size, and shape of the sample.

  In addition, a non-contact type thermometer (not shown) is installed in the sample chamber 3, and the temperature of the irradiated surface of the sample is measured with the thermometer, and when the measurement result reaches a predetermined upper limit value, It is also possible to stop the irradiation and start the supply of the gas refrigerant, and when the lower limit is reached, conversely start the irradiation of the ion beam and stop the supply of the gas refrigerant. For example, as shown in FIG. 3, first, the temperature T of the irradiated surface of the sample is acquired (step S1). Next, it is determined whether the temperature T is equal to or higher than a predetermined lower limit value LL and lower than an upper limit value UL (step S2). The lower limit value LL may be set to a temperature at which the sample is not excessively cooled, and the upper limit value UL may be set to a temperature at which the sample is not excessively heated. If this determination is Yes, the operations of ion beam irradiation and gaseous refrigerant supply are maintained as they are (step S3). Conversely, if the above determination is No, it is further determined whether or not T exceeds the upper limit value (step S4). If this determination is Yes, since the temperature of the sample is becoming too high, a gaseous refrigerant is supplied into the sample chamber (step S5), and the sample is cooled. On the contrary, if the above determination is No, the temperature T is less than the lower limit value LL, so the irradiation of the sample with the ion beam is started and the supply of the gaseous refrigerant into the sample chamber is stopped. Then, it is determined whether or not to end the milling based on whether or not the total irradiation time of the ion beam has reached a predetermined time (step S7). If this determination is Yes, the process ends. The processing after step S1 is repeated again.

  It is preferable to examine the correlation between the cooling rate and the temperature of the irradiation surface of the sample in advance for each type of gas refrigerant using a simulation sample similar to the actual sample S to determine the appropriate switching conditions.

(Function and effect)
In any case, according to the ion milling apparatus of this example, it is possible to automatically switch between irradiation of the ion beam to the sample and supply of the gaseous refrigerant into the sample chamber. Therefore, a series of operations from the introduction of the sample into the sample chamber to the end of milling can be performed smoothly.

[Embodiment 3]
In the first and second embodiments, an apparatus that switches between irradiation of an ion beam onto a sample and supply of a gaseous refrigerant into the sample chamber has been described. In this example, an ion milling apparatus capable of simultaneously performing irradiation of the sample with an ion beam and supply of a gaseous refrigerant into the sample chamber will be described with reference to FIG. The following description will be focused on differences from the first and second embodiments, and description of common points will be omitted.

(Device configuration)
As described in the first and second embodiments, it is preferable to adjust the plasma chamber to a high degree of vacuum suitable for generating an ion beam and the sample chamber to a low degree of vacuum suitable for cooling a sample. Therefore, as shown in FIG. 4, the degree of vacuum in each of the chambers 21 and 3 can be independently controlled by providing a differential exhaust mechanism. More specifically, for example, the plasma chamber 21 and the sample chamber 3 are communicated with each other through the orifice 21H, and an exhaust system is provided for each of the chambers 21 and 3, thereby maintaining the chambers 21 and 3 at different degrees of vacuum. Can do. As an exhaust system for the plasma chamber 21, a turbo molecular pump 22P for high vacuum exhaust, a solenoid valve for vacuum exhaust control 24P, and an electromagnetic valve for air introduction 26P are sequentially connected in series to the chamber 21. A rotary pump 28P for low vacuum exhaust is connected between 24P and 26P. In the apparatus of this example, the apparatus similar to Embodiments 1 and 2 can be used for other configurations except that the differential exhaust mechanism is provided.

(Function and effect)
According to the ion milling apparatus of this example, the plasma chamber and the sample chamber can be maintained at independent vacuum degrees by differential evacuation. Therefore, the plasma chamber can be adjusted to a high degree of vacuum suitable for generating an ion beam, and the sample chamber can be adjusted to a low degree of vacuum suitable for cooling a sample, and the ion beam can be supplied while supplying a gaseous refrigerant into the sample chamber. The sample can be irradiated without any trouble. Therefore, it is not necessary to switch between irradiation of the ion beam to the sample and supply of the gaseous refrigerant into the sample chamber, and efficient sample milling can be realized.

[Test Example 1: Difference in acceleration voltage]
Using an ion milling device SVM-730 manufactured by Sanyu Denshi Co., Ltd. as a base configuration, we examined how the temperature of the irradiated surface of the sample changes depending on the acceleration voltage. As a sample, a resin block (32 mmφ) corresponding to a resin-embedded sample is used. A junction point of a K-type thermocouple is arranged on the irradiation surface of the sample, and the irradiation surface is irradiated with an ion beam while changing the acceleration voltage, and the temperature measurement result with the thermocouple is obtained.

  The result is shown in FIG. As is apparent from this graph, the higher the acceleration voltage, the greater the temperature rise on the sample surface. More specifically, when the acceleration voltage is about 2 kV, the temperature of the irradiated surface hardly increases. On the other hand, when the acceleration voltage is 4 kV, the temperature rises sharply in several tens of seconds after the ion beam irradiation, and after that, the temperature of the irradiated surface is kept up to about 50 ° C. As the acceleration voltage rises, the temperature reached increases, and at 6 kV, the temperature of the irradiated surface reaches 120 ° C or higher. From these results, it can be seen that when the acceleration voltage is about 4 kV or more, it is effective to supply the gaseous refrigerant to the sample chamber to cool the sample.

[Test Example 2: Difference in gaseous refrigerant]
Next, with the same equipment, the acceleration voltage was set to 6 kV, and the simulated sample was irradiated with an ion beam for about 10 seconds. Various gaseous refrigerants were introduced into the sample chamber from the time when the temperature of the irradiated surface became around 80 ° C. The temperature change of the irradiated surface with the passage of time from the start of the supply was examined. The gaseous refrigerant used here is argon, helium, nitrogen, and the atmosphere. In any gaseous refrigerant, the refrigerant temperature was normal temperature and the pressure in the sample chamber was 10 Pa.

  The result is shown in FIG. As can be seen from this graph, when the gaseous refrigerant is helium, the temperature of the irradiated surface starts to decrease sharply after the gaseous refrigerant is supplied into the sample chamber. This is presumably because the thermal conductivity of helium is larger than that of other gaseous refrigerants. With other gaseous refrigerants, nitrogen and the atmosphere have almost the same cooling curve, and argon has the slowest cooling rate until about 25 seconds from the start of cooling, but after that it exceeds the cooling rate of the atmosphere and nitrogen, and 50% The temperature of the irradiated surface that reaches after 2 seconds is the second lowest after helium. From the above results, it can be seen that helium is preferable as the gaseous refrigerant when priority is given to the cooling efficiency of the sample. In addition, when air is introduced into the sample chamber, since it contains moisture, it takes a longer time to exhaust and reach a predetermined degree of vacuum than other gas refrigerants. Therefore, it is considered that an inert gas other than the atmosphere is preferable in order to switch the irradiation of the ion beam to the sample and the supply of the gaseous refrigerant to the sample chamber.

[Test Example 3: Difference in injection mode of gaseous refrigerant]
Furthermore, with the same device, install a nozzle so that the gaseous refrigerant can be injected from diagonally below the sample irradiation surface, set the acceleration voltage to 6 kV, and irradiate the simulated sample with an ion beam for about 10 seconds. A gas refrigerant consisting of nitrogen was supplied to the sample chamber for 50 seconds from the time when the temperature of the sample became about 80 ° C., and the temperature change of the irradiated surface with the passage of time from the start of supply was examined. The tilt angle of the sample stage is 90 ° (vertical surface), and there is no rotation of the sample. At that time, as one injection mode, the irradiation surface is cooled by direct injection with the tip of the nozzle directed to the junction of the thermocouple on the irradiation surface of the sample, and as the other injection mode, the tip of the nozzle is sealed. At the same time, the gas refrigerant was jetted in the left-right direction substantially orthogonal to the longitudinal direction of the nozzle, and the irradiation surface was cooled so that the gas refrigerant was not directly blown onto the irradiation surface. The pressure in the sample chamber when supplying the gaseous refrigerant is 10 Pa.

  The result is shown in FIG. In the figure, “Direct” indicates that the gaseous refrigerant is directly sprayed on the sample, and “Shower” indicates that the gaseous refrigerant is introduced into the sample chamber without blowing the gaseous refrigerant directly on the sample. As is clear from this graph, “Direct” is cooled more quickly than “Shower”, and the temperature reached after 50 seconds is slightly lower in “Direct”. From this, it can be said that the cooling capability is higher when the gaseous refrigerant is sprayed directly on the sample.

[Test Example 4: Difference in pressure in sample chamber]
Next, with the same equipment, the acceleration voltage was set to 6 kV, and the simulated sample was irradiated with the ion beam for about 10 seconds, and the nitrogen pressure was changed into the sample chamber from the time when the temperature of the irradiated surface became around 80 ° C. The temperature change of the irradiated surface with the lapse of time from the start of the supply was examined. In any case, the supplied refrigerant temperature is normal temperature.

  The result is shown in FIG. As is clear from this graph, it can be seen that the higher the pressure in the sample chamber, the faster the sample can be cooled. Specifically, it is preferable to set the pressure to 1 Pa or higher, more preferably about 7.5 Pa or higher in terms of efficiently cooling the sample. On the other hand, when the pressure in the sample chamber is 0.1 Pa or less, the cooling rate of the sample is moderate. Considering that the preferable pressure for generating plasma in the plasma chamber is about 0.05 Pa, it is difficult to irradiate the ion beam while keeping the sample chamber communicating with the plasma chamber at 1 Pa or more. In other words, when the differential pumping mechanism is not used, it is understood that it is preferable to switch between irradiation of the ion beam and supply of the gaseous refrigerant into the sample chamber.

[Test Example 5-1: Alternate switching << Difference in cooling rate >>]
Next, the ion beam irradiation on the sample and the injection of the gas refrigerant to the sample are switched using the same device, and the sample is alternately milled and cooled to measure the temperature change of the irradiated surface of the sample. did. At that time, the sample was cooled at different cooling rates. The cooling rate is the ratio of the cooling time in 1 minute, that is, the time during which the gaseous refrigerant is jetted onto the sample. In this example, three cooling rates of 25%, 50%, and 75% were used. For example, if the cooling rate is 25%, it means that the sample was irradiated with an ion beam for 45 seconds and the gaseous refrigerant was injected into the sample for 15 seconds. The ion milling condition is that the acceleration voltage is 6 kV, and the gas refrigerant supply condition is that the gas refrigerant is nitrogen, and the pressure in the sample chamber when the gas refrigerant is supplied is 10 Pa. The total time for ion milling and cooling of the sample is about 10 minutes.

  The result is shown in FIG. As shown in this graph, it can be seen that the higher the cooling rate, the lower the upper limit temperature of the sample. Specifically, when the cooling rate is 75%, the upper limit temperature of the sample is about 60 ° C., 50% is less than 70 ° C., and 25% is more than 80 ° C. It can also be seen that the upper limit value in each cycle of ion milling and cooling falls within a substantially constant value at any cooling rate. Therefore, it can be expected that ion milling without thermal degradation of the sample is possible by selecting an appropriate cooling rate according to the thermal degradation temperature of the sample.

[Test Example 5-2: Alternating switching << difference in gas refrigerant >>
Next, using the same apparatus, the sample was alternately subjected to ion milling and cooling in the same manner as in Test Example 5-1, changing the type of gaseous refrigerant, and the temperature change of the irradiated surface of the sample was measured. There are four types of gaseous refrigerants: argon, helium, nitrogen, and air. The ion milling conditions are an acceleration voltage of 6 kV, the gas refrigerant supply conditions are a cooling rate of 75%, and the pressure of the sample chamber when the gas refrigerant is supplied is 10 Pa.

  The result is shown in FIG. As can be seen from this graph, even when ion milling and cooling of the sample are performed alternately, the cooling rate of helium is still high and the lower limit cooling temperature is low. That is, if the total time for irradiating the sample with the ion beam is the same, the total time for ion milling and cooling of the sample can be shortened by using helium as the gas refrigerant as compared with other gas refrigerants.

[Test Example 6: Observation of solder sample by SEM]
Next, with a similar apparatus, a resin-embedded sample at a soldering location with tin and lead-containing solder was ion milled to form a cross section, and the cross section was observed with an SEM. A sample was prepared by mirror-polishing a resin-embedded sample by mechanical polishing, and further performing ion milling by “alternate switching” as in Test Example 5-1 (Example 1). The ion beam irradiation conditions are: acceleration voltage: 4 kV, irradiation current: 65 to 75 μA, sample tilt angle: 85 °, eccentricity: 0 mm, sample rotation: yes, and total ion beam irradiation time: 20 minutes. On the other hand, the supply conditions of the gas refrigerant are gas refrigerant: nitrogen, cooling rate: 75%, and pressure of the sample chamber at the time of gas refrigerant supply: 10 Pa. In addition, for comparison, a sample (Comparative Example 1) that was observed while being mirror-polished and a sample (Comparative Example 2) that was ion-milled without cooling with a gaseous refrigerant were also observed by SEM. The ion beam irradiation conditions of Comparative Example 2 are the same as those of Example 1 except that the total ion beam irradiation time is 15 minutes.

  The result is shown in FIG. In the figure, the left is an observation photograph of each sample of Comparative Example 1 in which only mirror polishing is performed, the center is in Comparative Example 2 in which ion milling is performed without cooling with a gas refrigerant, and the right is in Example 1 in which ion milling is performed with cooling with a gas refrigerant. The upper row has a magnification of 3000 times and the lower row has a magnification of 10000 times. In any of the photographs, the light gray region presenting in an island shape is the lead portion of the solder, the darker gray region surrounding the periphery is the tin portion of the solder, and the black spots are voids.

  In the comparative example 1, it turns out that many space | gap exists in the surface of a sample cross section. In Comparative Example 2, the presence of voids is much less than in Comparative Example 1, but a considerable amount of voids remain in the vicinity of the grain boundaries in the lead portion. In contrast to these comparative examples, Example 1 can be said to be substantially free of voids, and it can be seen that there is almost no change in the cross section during the preparation of the sample.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, it can be expected that the cooling efficiency of the sample is improved by cooling the sample chamber itself with an appropriate cooling means. Further, even when switching between irradiation of an ion beam to a sample and supply of a gaseous refrigerant into the sample chamber, the differential exhaust described in the third embodiment may be performed. In this case, since the plasma chamber and the sample chamber can be maintained at different vacuum degrees, it is only necessary to irradiate / stop the ion beam to the sample and supply / stop the gaseous refrigerant into the sample chamber. It is not necessary to adjust the degree of vacuum every time the operation is switched.

  The ion milling apparatus and the ion milling method of the present invention can be suitably used in the field of performing various kinds of fine processing such as production of a sample for a microscope such as SEM and TEM, and manufacture of a semiconductor device and a storage medium.

1 Sample stage
11 Thermometer 13 Data logger
2 Ion source
21 Plasma chamber 21B Mass flow controller 21H Orifice
22P Turbo molecular pump 23 Beam generator 23E Accelerating electrode
24P Solenoid valve for vacuum exhaust control 26P Solenoid valve for air introduction
28P Rotary pump
3 Sample chamber
31 (31S) Turbo molecular pump 32 (32S) Vacuum exhaust control solenoid valve
33 (33S) Air introduction solenoid valve 34 (34S) Rotary pump
35 High vacuum pressure gauge 36 Low vacuum pressure gauge
4 computer
41 Control means 44 Signal output section 45 Signal input section
46 Input means 47 Display means 48α, 48β Switching means
48M storage means 48C switching control means
5 Refrigerant supply means
51 Refrigerant supply source 53 Refrigerant supply path 53B Mass flow controller
55 Nozzle 57 Cooling means
S sample

Claims (11)

A sample stage on which the sample is installed;
An ion source for generating an ion beam for irradiating the sample;
A sample chamber for holding the storage space of the sample stage in a predetermined vacuum;
An ion milling apparatus comprising: a refrigerant supply means for supplying a gaseous refrigerant for cooling the sample into the sample chamber.   2. The ion milling device according to claim 1, wherein the refrigerant supply means includes a nozzle arranged to inject a gaseous refrigerant onto the sample in the sample chamber.   3. The ion milling apparatus according to claim 2, wherein the refrigerant supply means includes a nozzle variable mechanism that adjusts a jet direction of the gas refrigerant and a distance to the sample.   4. The ion milling device according to claim 1, wherein the gaseous refrigerant is an inert gas.   5. The ion milling according to claim 1, further comprising switching means for switching between irradiation of the sample with the ion beam and supply of the gaseous refrigerant into the sample chamber. apparatus. The switching means is
Storage means for storing preset switching conditions;
6. The ion milling apparatus according to claim 5, further comprising switching control means for switching the irradiation of the ion beam and the supply of the gaseous refrigerant based on the switching condition read from the storage means. The ion source includes a plasma chamber that communicates with the sample chamber and holds a generation space of the ion beam in a predetermined vacuum,
7. The ion milling apparatus according to claim 1, further comprising a differential evacuation mechanism that holds the sample chamber and the plasma chamber at different degrees of vacuum.   8. The ion milling device according to claim 1, further comprising a cooling mechanism that cools the gaseous refrigerant. An ion milling process for removing the surface of the sample by irradiating the sample with an ion beam generated in the plasma chamber;
A cooling step of cooling the sample by supplying a gaseous refrigerant into a sample chamber that communicates with the plasma chamber and stores the sample,
An ion milling method, wherein the ion milling step and the cooling step are switched. An ion milling process for removing the surface of the sample by irradiating the sample with an ion beam generated in the plasma chamber;
A cooling step of cooling the sample by supplying a gaseous refrigerant into a sample chamber that communicates with the plasma chamber and stores the sample,
An ion milling method, wherein the plasma chamber and the sample chamber are differentially evacuated to perform the ion milling step and the cooling step simultaneously.   11. The ion milling method according to claim 9, wherein the cooling step is performed by injecting a gaseous refrigerant directly onto the sample from a nozzle provided in the sample chamber.