Ion milling device

Abstract

When a remaining amount of liquid nitrogen 10 stored in a dewar 102 is reduced, liquid nitrogen 10 is automatically supplied to the dewar 102. An ion milling device 100 comprises: a dewar 102; a sensor 112 provided inside the dewar 102; a tank 103; piping 104 for connecting the inside of the dewar 102 and the inside of the tank 103; a valve 105 provided in the piping 104; and a control unit 140 that controls the sensor 112 and the valve 105. When the liquid nitrogen 10 is not detected by the sensor 112, liquid nitrogen 10 is supplied from the inside of the tank 103 into the dewar 102 through the piping 104 by opening the valve 105.

Description

Ion milling equipment

[0001] The present invention relates to an ion milling apparatus, and more particularly to an ion milling apparatus equipped with a dewar for storing liquid nitrogen.

[0002] In an ion milling device, a sample to be observed with an electron microscope is processed by irradiating it with an unfocused ion beam. This type of processing is called ion milling. The sputtering phenomenon causes atoms on the surface of the sample to be ejected, polishing the surface of the sample without stress and exposing the internal structure of the sample. The polished surface or the exposed internal structure of the sample becomes the observation surface for scanning electron microscopes and transmission electron microscopes.

[0003] Irradiation with an ion beam can sometimes cause a temperature rise in the sample. In such cases, the temperature rise can be reduced by performing ion milling while indirectly cooling the sample with a cooling solution such as liquid nitrogen. This type of processing is called cooled ion milling.

[0004] Patent Document 1 discloses a means for supplying liquid helium from an insulated container to an insulated tank, but does not describe a means for returning the supplied liquid helium to the insulated container after use of the device.

[0005] Japanese Unexamined Patent Publication No. 8-15397

[0006] Cold ion milling is performed in an ion milling apparatus equipped with an insulated container called a Dewar. In the ion milling apparatus, the sample is returned to room temperature after cold ion milling to prevent condensation from forming on the sample, and then the sample is removed. Since it is preferable that the heat capacity of the heated area is small when returning to room temperature, the capacity of the Dewar is made as small as possible, for example, 200 ml to 800 ml. If a large-capacity Dewar is used and the interior of the Dewar is pressurized, there is a risk of excessive liquid nitrogen being supplied, so it is desirable to consider a supply method other than pressurization.

[0007] The dewar connected to the outer wall of the sample chamber has a double structure, so when the inside of the sample chamber is evacuated, a high vacuum is created between the inner and outer walls of the dewar, allowing liquid nitrogen to be held for a long time. A metal support that extends into the inside of the dewar is connected to the inner wall of the dewar, and when liquid nitrogen is injected into the dewar, the support is cooled. If this support is connected to the sample with a copper wire, the sample can be indirectly cooled.

[0008] The cooling time of the sample depends on the amount of liquid nitrogen remaining inside the Dewar. Therefore, the Dewar must be constantly filled with liquid nitrogen while the sample is being cooled. However, when the sample is irradiated with an ion beam, the temperature of the entire holder, including the sample, rises, resulting in increased liquid nitrogen consumption. Therefore, it is necessary to ensure a sufficient amount of liquid nitrogen, for example by using a larger-capacity Dewar. However, increasing the capacity of the Dewar will tilt the center of gravity of the entire ion milling system, raising concerns about it tipping over. Therefore, a means of supplying liquid nitrogen from outside the Dewar must be considered.

[0009] The main object of the present application is to provide an ion milling apparatus that can automatically supply liquid nitrogen from a tank provided outside the dewar to the dewar when the remaining amount of liquid nitrogen stored in the dewar becomes low. Another object of the present application is to provide an ion milling apparatus that can automatically discharge liquid nitrogen from inside the dewar to the tank when sample processing is completed.

[0010] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0011] A brief summary of a representative embodiment of the present invention will be given below.

[0012] An ion milling apparatus according to one embodiment includes a dewar for storing liquid nitrogen, a first sensor provided inside the dewar and capable of detecting the liquid nitrogen inside the dewar, a tank for storing the liquid nitrogen to be supplied into the dewar, a first pipe connecting the inside of the dewar to the inside of the tank, a first valve provided on the first pipe, and a control unit for controlling the first sensor and the first valve. When the first sensor does not detect the liquid nitrogen, the first valve is opened so that the liquid nitrogen is supplied from the inside of the tank to the inside of the dewar via the first pipe.

[0013] According to one embodiment, an ion milling apparatus can be provided that can automatically supply liquid nitrogen from a tank provided outside the dewar to the dewar when the remaining amount of liquid nitrogen stored in the dewar becomes low, and can also be provided that can automatically discharge liquid nitrogen from inside the dewar to the tank when sample processing is completed.

[0014] FIG. 1 is a schematic diagram showing an ion milling apparatus according to embodiment 1. FIG. 2 is a schematic diagram showing a sensor according to embodiment 1. FIG. 3 is an explanatory diagram for explaining the principle of the sensor according to embodiment 1. FIG. 4 is a schematic diagram showing a system of the ion milling apparatus according to embodiment 1. FIG. 5 is a flowchart showing a method for supplying liquid nitrogen according to embodiment 1. FIG. 6 is a schematic diagram showing the ion milling apparatus during supply of liquid nitrogen according to embodiment 1. FIG. 7 is a flowchart showing a method for discharging liquid nitrogen according to embodiment 1. FIG. 8 is a schematic diagram showing the ion milling apparatus during discharge of liquid nitrogen according to embodiment 1.

[0015] Hereinafter, embodiments will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. In the following embodiments, explanations of the same or similar parts will not be repeated unless particularly necessary.

[0016] First Embodiment <Structure of Ion Milling Apparatus> An ion milling apparatus 100 according to a first embodiment will be described below with reference to FIGS. 1 to 4. FIG.

[0017] As shown in FIG. 1 , the ion milling apparatus 100 mainly comprises a sample chamber 101, a dewar 102, a tank 103, piping 104, a valve 105, a release valve 106, a safety valve 107, piping 108, a valve 109, a heater 110, an upper stage sensor 111, a middle stage sensor 112, a lower stage sensor 113, a pressure gauge 114, a release valve 115, a safety valve 116, piping 117, a valve 118, a heater 119, an upper stage sensor 120, a lower stage sensor 121, a pressure gauge 122, a movable mechanism 123, piping 124, a valve 125, piping 126, a valve 127, a heater 128, a release valve 129, a fixing part 130, and a cooling cable fixing part 131.

[0018] The dewar 102 is provided for storing liquid nitrogen 10. The tank 103 is provided for storing the liquid nitrogen 10 to be supplied into the dewar 102. The interior of the dewar 102 and the interior of the tank 103 are connected by a pipe 104. A valve 105 is provided on the pipe 104. With the valve 105 open, the liquid nitrogen 10 is supplied from the interior of the tank 103 to the interior of the dewar 102 via the pipe 104. The capacity of the dewar 102 is, for example, 100 ml or more and 200 ml or less. The capacity of the tank 103 is sufficiently larger than the capacity of the dewar 102, for example, 4000 ml or more and 8000 ml or less.

[0019] The interior of the dewar 102 and the interior of the tank 103 are connected by a pipe 124. The pipe 124 is provided on the bottom surface of the dewar 102 and at the bottom of the tank 103. A valve 125 is provided on the pipe 124. With the valve 125 open, the liquid nitrogen 10 is discharged from the interior of the dewar 102 to the interior of the tank 103 through the pipe 124.

[0020] The dewar 102 is provided with a release valve 106, a safety valve 107, and a pressure gauge 114. By closing the release valve 106 or the safety valve 107, the inside of the dewar 102 is made airtight. By opening the release valve 106 or the safety valve 107, the inside of the dewar 102 is opened to the atmosphere. The pressure gauge 114 can measure the air pressure inside the dewar 102.

[0021] A heater 110 is provided outside the dewar 102. The inside of the dewar 102 and the heater 110 are connected by a pipe 108. A valve 109 is provided to the pipe 108. By driving the heater 110 with the valve 109 open, the heat from the heater 110 can be transferred to the inside of the dewar 102 via the pipe 108.

[0022] An upper level sensor 111, a middle level sensor 112, and a lower level sensor 113 are provided inside the dewar 102. Inside the dewar 102, the upper level sensor 111 is provided above the middle level sensor 112, and the lower level sensor 113 is provided below the middle level sensor 112. The upper level sensor 111, the middle level sensor, and the lower level sensor 113 are each liquid level sensors that can detect the liquid nitrogen 10 inside the dewar 102.

[0023] The tank 103 is provided with a release valve 115, a safety valve 116, and a pressure gauge 122. By closing the release valve 115 or the safety valve 116, the inside of the tank 103 is made airtight. By opening the release valve 115 or the safety valve 116, the inside of the tank 103 is opened to the atmosphere. The pressure gauge 122 can measure the air pressure inside the tank 103.

[0024] A heater 119 is provided outside the tank 103. The inside of the tank 103 and the heater 119 are connected by a pipe 117. A valve 118 is provided to the pipe 117. By driving the heater 119 with the valve 118 open, the heat from the heater 119 can be transferred to the inside of the tank 103 via the pipe 117.

[0025] An upper level sensor 120 and a lower level sensor 121 are provided inside the tank 103. Inside the tank 103, the upper level sensor 120 is provided above the lower level sensor 121. The upper level sensor 120 and the lower level sensor 121 are each liquid level sensors and can detect the liquid nitrogen 10 inside the tank 103.

[0026] A movable mechanism 123 is provided below the tank 103. The movable mechanism 123 is provided to move the tank 103 in the vertical direction. The vertical position of the tank 103 is adjusted by the movable mechanism 123.

[0027] The inside of the sample chamber 101 and the inside of the dewar 102 are connected by a cooling passage piping 126. The piping 126 is fixed by a fixing part 130 provided on the outer wall of the sample chamber 101 and is connected to a cooling cable fixing part 131 provided inside the sample chamber 101.

[0028] Furthermore, in order to reduce the amount of evaporation of the liquid nitrogen 10 in the pipe 126, the pipe 126 and the dewar 102 have a double structure with an inner wall and an outer wall. When the inside of the sample chamber 101 is evacuated, a high vacuum is created between the inner and outer walls, allowing the liquid nitrogen 10 to be held for a long period of time.

[0029] A valve 127 is provided on the pipe 126. When a sample is being processed inside the sample chamber 101, the valve 127 is opened to supply liquid nitrogen 10 from inside the dewar 102 to inside the sample chamber 101 via the pipe 126.

[0030] The heater 128 is provided adjacent to the pipe 126 and between the valve 127 and the sample chamber 101. By driving the heater 128, the heat from the heater 128 can be transferred to the inside of the pipe 126. In addition, an open valve 129 is provided in the pipe 126 located between the valve 127 and the sample chamber 101. By closing the open valve 129, the inside of the pipe 126 is made airtight. By opening the open valve 129, the inside of the pipe 126 is opened to the atmosphere.

[0031] A sample to be observed by an electron microscope such as a scanning electron microscope or a transmission electron microscope is processed inside the sample chamber 101. Although not shown here, an ion gun capable of irradiating an unfocused ion beam is provided inside the sample chamber 101. The sample is processed while held in a holder.

[0032] The sample may be, for example, a metal, semiconductor, glass, ceramic, or thermoplastic resin. In particular, when the sample is a thermoplastic resin or a metallic material such as solder that undergoes a phase transformation at low temperatures, it is desirable to perform cooled ion milling. In cooled ion milling, liquid nitrogen 10 is supplied from inside the Dewar 102 to the inside of the sample chamber 101 during ion milling, sufficiently cooling the cooling cable fixing part 131. The holder holding the sample is fixed to a copper wire extended from the cooling cable fixing part 131. Therefore, the sample is indirectly cooled by the liquid nitrogen 10 supplied from the Dewar 102.

[0033] 2 and 3, the upper sensor 111, the middle sensor 112, the lower sensor 113, the upper sensor 120, and the lower sensor 121 will be described below. Note that the upper sensor 111, the middle sensor 112, the lower sensor 113, the upper sensor 120, and the lower sensor 121 are sensors with the same structure, so the upper sensor 111 will be described below as a representative.

[0034] 2, the upper sensor 111 includes a resistive element 132. Both ends of the resistive element 132 are electrically connected to a power source 133. The operating principle of the upper sensor 111 will be described with reference to FIG.

[0035] When the upper sensor 111 is in contact with the liquid nitrogen 10, the temperature is T ０ , the resistance value of the resistor element 132 is R Ｔ０ , the resistance temperature coefficient is α Ｔ０ When the upper sensor 111 is separated from the liquid nitrogen 10, the temperature is set to T and the resistance value of the resistance element 132 is set to R Ｔ This resistance value R Ｔ is expressed by the formula shown in FIG. Ｔ０ >0 relationship and T-T ０It is essential that the relationship of .gtoreq.0 is satisfied.

[0036] As the temperature decreases, the resistance value of the resistor element 132 decreases, and the amount of current flowing through the resistor element 132 increases. On the other hand, as the temperature increases, the resistance value of the resistor element 132 increases, and the amount of current flowing through the resistor element 132 decreases. The upper sensor 111 determines whether or not liquid nitrogen 10 is present based on the amount of current flowing through the resistor element 132. Note that the amount of current described here is measured in units of "A."

[0037] That is, if the amount of current flowing through the resistance element 132 is greater than a predetermined value, it is determined that the upper sensor 111 is in contact with the liquid nitrogen 10 and can detect the liquid nitrogen 10. Therefore, it can be determined that the liquid nitrogen level is located above the upper sensor 111 and that there is a sufficient amount of liquid nitrogen 10 remaining.

[0038] On the other hand, if the amount of current flowing through the resistance element 132 becomes smaller than the predetermined value, the upper sensor 111 determines that it is far from the liquid nitrogen 10 and cannot detect the liquid nitrogen 10. Therefore, it can be determined that the liquid level of the liquid nitrogen 10 is located below the upper sensor 111 and that the remaining amount of liquid nitrogen 10 is insufficient.

[0039] 4, the ion milling apparatus 100 includes a control unit 140. The control unit 140 is a processing unit including a semiconductor device such as a CPU. The control unit 140 is electrically connected to and controls the valves, relief valves, pressure gauges, heater drive and movable mechanisms, sensors, and ion gun.

[0040] That is, in each step performed in each supply method and discharge method described below, the opening and closing operations of valves 105, 109, 118, 125, and 127, the opening and closing operations of release valves 106, 115, and 129, the opening and closing operations of safety valves 107 and 116, the measurement operations of pressure gauges 114 and 122, the driving of heaters 110, 119, and 128, the adjustment operation of movable mechanism 123, the detection operations of sensors 111, 112, 113, 120, and 121, and the ion beam irradiation of the ion gun in sample chamber 101 are controlled by control unit 140.

[0041] 1, during normal cooling ion milling, the inside of the dewar 102 is filled with liquid nitrogen 10 so that the liquid level of the liquid nitrogen 10 is positioned at least above the middle sensor 112, and preferably above the upper sensor 111. Also, valves 105, 109, 118, and 125, safety valves 107 and 116, and release valve 129 are closed so as not to encourage the movement of the liquid nitrogen 10. Also, release valves 106 and 115 are open.

[0042] When a sample is being processed inside the sample chamber 101 , liquid nitrogen 10 is supplied from inside the dewar 102 to inside the sample chamber 101 via the pipe 126 by opening the valve 127 .

[0043] <Method of Supplying Liquid Nitrogen to the Inside of the Dewar> A method of supplying liquid nitrogen 10 from the inside of the tank 103 to the inside of the dewar 102 when the remaining amount of liquid nitrogen 10 stored inside the dewar 102 is low will be described below using Figures 5 to 7. The following explanation will basically be made using the flowchart in Figure 5 and the schematic diagram in Figure 6, but the schematic diagram in Figure 7 will also be used as necessary.

[0044] The liquid nitrogen 10 is supplied from the inside of the tank 103 to the inside of the dewar 102 by using the siphon effect. Therefore, the inside of the pipe 104 is filled with the liquid nitrogen 10.

[0045] The amount of liquid nitrogen 10 remaining in the dewar 102 decreases depending on the time required for cooling ion milling. Therefore, it is necessary to replenish the dewar 102 with liquid nitrogen 10 from the tank 103.

[0046] In step S1, the liquid nitrogen 10 is detected by the middle stage sensor 112 in the dewar 102. Step S1 is the starting point for the supply of liquid nitrogen 10 to the dewar 102. When the liquid level of the liquid nitrogen 10 is below the interruption sensor 112 and the middle stage sensor 112 does not detect the liquid nitrogen 10, steps S2 and S3 are performed.

[0047] In step S2, the release valve 115 for the tank 103 is closed, thereby making the inside of the tank 103 airtight.

[0048] In step S3, the supply valve 105 is opened, which allows the liquid nitrogen 10 to pass through the inside of the pipe 104.

[0049] In step S4, after steps S2 and S3, the supply of liquid nitrogen 10 is started. Liquid nitrogen 10 is supplied from the inside of tank 103 to the inside of dewar 102 via pipe 104 by the siphon effect.

[0050] In step S5, the vertical position of the tank 103 is adjusted by the movable mechanism 123 so that the tank 103 rises as the supply of liquid nitrogen 10 begins. Since the potential energy of the liquid nitrogen 10 inside the tank 103 increases, the supply by the siphon effect is promoted. Preferably, the vertical position of the tank 103 is adjusted so that the liquid level of the liquid nitrogen 10 inside the tank 103 is higher than the liquid level of the liquid nitrogen 10 inside the dewar 102.

[0051] In step S6, the upper sensor 120 of the tank 103 detects the liquid nitrogen 10. If the upper sensor 120 does not detect the liquid nitrogen 10 (NO), steps S7 and S8 are performed. If the upper sensor 120 detects the liquid nitrogen 10 (YES), step S9 is performed.

[0052] That is, when the amount of liquid nitrogen 10 stored inside the tank 103 becomes low, there is a risk that the supply of liquid nitrogen 10 to the dewar 102 cannot be fully compensated for by the siphon effect alone. Therefore, by performing steps S7 and S8, the air pressure inside the tank 103 can be increased to or above the vapor pressure of the liquid nitrogen 10.

[0053] 7 shows steps S7 and S8. In step S7, after it is confirmed that the release valve 115 for the tank 103 is closed, the pressurizing valve 118 is opened.

[0054] In step S8, the pressurizing heater 119 is driven. As a result, the liquid nitrogen 10 inside the tank 103 is vaporized by the heat from the heater 119, the air pressure inside the tank 103 increases, and a pressure difference occurs between the inside of the tank 103 and the inside of the dewar 102. This pressure difference promotes the supply of liquid nitrogen 10 from the inside of the tank 103 to the inside of the dewar 102.

[0055] Here, in order to increase the potential energy even a little, it is preferable to raise the position of the tank 103 to the maximum by the movable mechanism 123 .

[0056] If the air pressure inside the tank 103 rises too much, the tank 103 is opened to the atmosphere by the safety valve 116. That is, when the pressure gauge 122 measures that the air pressure inside the tank 103 has reached a predetermined value or higher, the valve 118 is closed, the heater 119 is stopped, and the safety valve 116 is opened.

[0057] In step S9, the upper sensor 111 in the dewar 102 detects the liquid nitrogen 10. When the upper sensor 111 detects the liquid nitrogen 10, it means that a sufficient amount of liquid nitrogen 10 has been supplied to the dewar 102. Steps S10 and onward are steps for stopping the supply of liquid nitrogen 10.

[0058] In step S10, the upper sensor 120 of the tank 103 detects the liquid nitrogen 10. If the upper sensor 120 does not detect the liquid nitrogen 10 (NO), steps S11 and S12 are performed. If the upper sensor 120 detects the liquid nitrogen 10 (YES), step S13 is performed.

[0059] At this point, if the upper sensor 120 does not detect the liquid nitrogen 10, it means that the heater 119 is being driven in step S8. Therefore, in step S11, the heater 119 is stopped, and in step S12, the valve 118 is closed.

[0060] In step S13, the valve 105 is closed. In step S14, the release valve 115 for the tank 103 is opened. In step S15, the supply of liquid nitrogen 10 from the inside of the tank 103 to the inside of the dewar 102 is terminated.

[0061] As described above, according to the ion milling apparatus 100 of the first embodiment, when the remaining amount of liquid nitrogen 10 stored in the dewar 102 becomes low, liquid nitrogen 10 can be automatically supplied from the tank 103 to the dewar 102. Therefore, there is no need to manually resupply liquid nitrogen 10 into the dewar 102, and the processing time for cold ion milling can be extended. Furthermore, the remaining amount of liquid nitrogen 10 during cold ion milling can be ensured without increasing the capacity of the dewar 102.

[0062] When the liquid nitrogen 10 in the tank 103 is about to run out, the lower sensor 121 of the tank 103 will no longer detect the liquid nitrogen 10. In this case, the control unit 140 performs feedback control, and an instruction to replenish the liquid nitrogen 10 is displayed on the monitor of the ion milling apparatus 100. The user can then replenish the liquid nitrogen 10 into the tank 103.

[0063] <Method of Discharging Liquid Nitrogen> A method of discharging liquid nitrogen 10 from inside the dewar 102 to inside the tank 103 will be described below with reference to FIGS. 8 and 9. FIG.

[0064] In step S21, processing of the sample is completed inside the sample chamber 101. At this point, the valve 105 is closed, and the supply of liquid nitrogen 10 from the inside of the tank 103 to the inside of the dewar 102 is stopped. In step S22 and thereafter, a discharge operation is performed to discharge the liquid nitrogen 10 from the inside of the dewar 102 to the inside of the tank 103 via the pipe 124.

[0065] In step S22, the valve 127 for the cooling passage is closed, thereby stopping the supply of liquid nitrogen 10 from the inside of the dewar 102 to the inside of the sample chamber 101.

[0066] In step S23, the open valve 129 for the cooling passage is opened, which allows the liquid nitrogen 10 remaining in the pipe 124 to be discharged.

[0067] In step S24, the release valve 106 of the dewar 102 is closed, thereby making the inside of the dewar 102 airtight.

[0068] In step S25, the discharge valve 125 is opened, which starts discharging the liquid nitrogen 10 from the inside of the dewar 102 to the inside of the tank 103 via the pipe 124.

[0069] In step S26, the vertical position of the tank 103 is adjusted by the movable mechanism 123 so that the tank 103 descends. As a result, gravity acts, making it easier for the liquid nitrogen 10 to move from inside the dewar 102 to inside the tank 103.

[0070] In step S27, the pressurizing valve 109 for the dewar 102 is opened. In step S28, the heater 110 for pressurizing the dewar 102 is driven. As a result, the liquid nitrogen 10 inside the dewar 102 is vaporized by the heat from the heater 110, the air pressure inside the dewar 102 increases, and a pressure difference occurs between the inside of the dewar 102 and the inside of the tank 103. This pressure difference promotes the discharge of the liquid nitrogen 10 from the inside of the dewar 102 to the inside of the tank 103.

[0071] If the air pressure inside the dewar 102 rises too much, the dewar 102 is opened to the atmosphere by the safety valve 107. That is, when the pressure gauge 114 measures that the air pressure inside the dewar 102 has reached a predetermined value or higher, the valve 109 is closed, the heater 110 is stopped, and the safety valve 107 is opened.

[0072] In step S29, the heater 128 for the cooling passage is driven. As a result, the liquid nitrogen 10 remaining in the pipe 126 located between the sample chamber 101 and the valve 127 is vaporized by the heat from the heater 128 and discharged from the release valve 129.

[0073] Furthermore, the temperatures of the cooling passage fixing part 130 and the cooling cable fixing part 131 rise due to heat conduction through the piping 126. This causes the temperature of the copper wire extended from the cooling cable fixing part 131 to rise, and the temperature of the holder fixed to the copper wire also rises. Therefore, the temperature of the sample held in the holder also rises, and the sample can be removed after the sample has been brought to a state where condensation does not form.

[0074] In step S30, the lower sensor 113 of the dewar 102 detects the liquid nitrogen 10. If the lower sensor 113 does not detect the liquid nitrogen 10, it means that the liquid nitrogen 10 has been sufficiently discharged from the inside of the dewar 102. Steps S31 and onward are steps for stopping the discharge operation of the liquid nitrogen 10.

[0075] In step S31, the cooling passage heater 128 is stopped. In step S32, the pressurizing heater 110 is stopped. In step S33, the pressurizing valve 109 is closed. In step S34, the exhaust valve 125 is closed. In step S35, the release valve 106 of the dewar 102 is opened. In step S36, the cooling passage release valve 129 is closed.

[0076] This completes the operation of discharging the liquid nitrogen 10 from the inside of the dewar 102 to the inside of the tank 103.

[0077] In this way, according to the ion milling apparatus 100 of the first embodiment, the liquid nitrogen 10 inside the dewar 102 can be automatically discharged into the tank 103 when the processing of the sample is completed.

[0078] Before starting ion milling again, it is necessary to prepare a state in which liquid nitrogen 10 can be supplied from the inside of the tank 103 to the inside of the dewar 102 by the siphon effect. For example, the supply valve 105 is opened, the release valve 115 of the tank 103 is closed, the pressurizing valve 118 is opened, and the pressurizing heater 119 is driven. This increases the air pressure inside the tank 103, creating a pressure difference between the inside of the tank 103 and the inside of the dewar 102. This pressure difference causes liquid nitrogen 10 to move from the inside of the tank 103 to the inside of the pipe 104, filling the inside of the pipe 104 with liquid nitrogen 10, thereby achieving the siphon effect.

[0079] The present invention has been specifically described above based on the form for implementing the present invention, but the present invention is not limited to the above-described embodiment and can be modified in various ways without departing from the spirit of the present invention.

[0080] For example, the heater 119 of the tank 103 and the heater 110 of the dewar 102 may not be provided. In that case, the pressurization pipe 108 provided in the dewar 102 and the pressurization pipe 117 provided in the tank 103 do not have a double vacuum structure, and the pressurization valve 109 provided in the dewar 102 and the pressurization valve 118 provided in the tank 103 are opened while the liquid nitrogen in the pipes is constantly being encouraged to vaporize. This allows the vaporized liquid nitrogen to flow into the container, increasing the pressure in the dewar 102 and the tank 103.

[0081] 10 Liquid nitrogen 100 Ion milling apparatus 101 Sample chamber 102 Dewar 103 Tank 104 Supply piping 105 Supply valve 106 Dewar release valve 107 Dewar safety valve 108 Pressurization piping 109 Pressurization valve 110 Pressurization heater 111 Dewar upper sensor 112 Dewar middle sensor 113 Dewar lower sensor 114 Dewar pressure gauge 115 Tank release valve 116 Tank safety valve 117 Pressurization piping 118 Pressurization valve 119 Pressurization heater 120 Tank upper sensor 121 Tank lower sensor 122 Tank pressure gauge 123 Tank movable mechanism 124 Discharge piping 125 Discharge valve 126 Cooling passage piping 127 Valve for cooling passage 128 Heater for cooling passage 129 Open valve for cooling passage 130 Fixing part for cooling passage 131 Cooling cable fixing part 132 Resistance element 133 Power supply 140 Control unit

Claims

1. a dewar for storing liquid nitrogen; a first sensor provided inside the dewar and capable of detecting the liquid nitrogen inside the dewar; a second sensor provided inside the dewar above the first sensor and capable of detecting the liquid nitrogen inside the dewar; a tank for storing the liquid nitrogen to be supplied to the interior of the dewar; a first pipe connecting the inside of the dewar and the inside of the tank; a first valve provided in the first pipe; a control unit for controlling the first sensor, the second sensor, and the first valve; Equipped with When the first sensor does not detect the liquid nitrogen, the first valve is opened to supply the liquid nitrogen from inside the tank to inside the dewar through the first pipe, When the second sensor detects the liquid nitrogen, the first valve is closed, thereby stopping the supply of the liquid nitrogen from inside the tank to inside the dewar.

2. 2. The ion milling apparatus according to claim 1, the first sensor includes a resistive element; The amount of current flowing through the resistor element varies with temperature, The first sensor determines whether or not the liquid nitrogen is present based on the amount of the current.

3. (delete)

4. 2. The ion milling apparatus according to claim 1, Further, a movable mechanism for moving the tank in a vertical direction is provided, the movable mechanism is controlled by the control unit; When the first sensor does not detect the liquid nitrogen, the movable mechanism adjusts the vertical position of the tank so that the liquid nitrogen level inside the tank is higher than the liquid nitrogen level inside the Dewar.

5. 2. The ion milling apparatus according to claim 1, a third sensor provided inside the tank and capable of detecting the liquid nitrogen inside the tank; a first heater provided outside the tank; a second pipe connecting the inside of the tank and the first heater; a second valve provided in the second pipe; a first open valve provided in the tank; a first pressure gauge provided in the tank for measuring air pressure inside the tank; Further provided with the third sensor, the first heater, the second valve, the first release valve, and the first pressure gauge are controlled by the control unit; When the third sensor does not detect the liquid nitrogen, the first open valve is closed, the second valve is opened, and the first heater is driven, whereby the heat from the first heater causes the liquid nitrogen inside the tank to evaporate, the air pressure inside the tank increases, and the air pressure difference between the inside of the tank and the inside of the dewar promotes the supply of the liquid nitrogen from the inside of the tank to the inside of the dewar.

6. 6. The ion milling apparatus according to claim 5, When the second sensor detects the liquid nitrogen, the operation of the first heater is stopped, the second valve is closed, and the first valve is closed, thereby stopping the supply of the liquid nitrogen from inside the tank to inside the Dewar.

7. 6. The ion milling apparatus according to claim 5, Further, a first safety valve is provided in the tank, the first safety valve is controlled by the control unit; an ion milling apparatus that, when the first pressure gauge measures that the air pressure inside the tank has reached a predetermined value or higher, closes the first valve, stops the first heater, and opens the first safety valve.

8. 2. The ion milling apparatus according to claim 1, a third pipe connecting the inside of the dewar and the inside of the tank; a third valve provided in the third pipe; Further provided with the third valve is controlled by the control unit; an ion milling apparatus, wherein the first valve is closed and the third valve is opened when the liquid nitrogen is discharged from the inside of the dewar to the inside of the tank through the third pipe;

9. 9. The ion milling apparatus according to claim 8, a fourth sensor provided inside the dewar below the first sensor and capable of detecting the liquid nitrogen inside the dewar; the fourth sensor is controlled by the control unit; An ion milling apparatus, wherein when the fourth sensor does not detect the liquid nitrogen, the third valve is closed, thereby stopping the discharge of the liquid nitrogen from inside the dewar to inside the tank.

10. 9. The ion milling apparatus according to claim 8, Further, a movable mechanism for moving the tank in a vertical direction is provided, the movable mechanism is controlled by the control unit; an ion milling apparatus, wherein the movable mechanism adjusts the vertical position of the tank so that the tank descends when the liquid nitrogen is discharged from inside the dewar to inside the tank through the third pipe.

11. 9. The ion milling apparatus according to claim 8, a second heater provided outside the dewar; a fourth pipe connecting the inside of the dewar and the second heater; a fourth valve provided in the fourth pipe; a second release valve provided in the dewar; a second pressure gauge provided in the dewar for measuring the air pressure inside the dewar; Further provided with the second heater, the fourth valve, the second release valve, and the second pressure gauge are controlled by the control unit; An ion milling apparatus in which, when discharging the liquid nitrogen from inside the dewar to inside the tank through the third piping, the second open valve is closed, the fourth valve is opened, and the second heater is driven, so that the heat from the second heater causes the liquid nitrogen inside the dewar to vaporize, the air pressure inside the dewar increases, and the air pressure difference between the inside of the dewar and the inside of the tank promotes the discharge of the liquid nitrogen from inside the dewar to inside the tank.

12. The ion milling apparatus according to claim 11, Further comprising a second safety valve provided in the dewar; the second relief valve is controlled by the control unit; an ion milling apparatus, wherein when the second pressure gauge measures that the air pressure inside the dewar has reached a predetermined value or higher, the fourth valve is closed, the second heater is stopped, and the second safety valve is opened.

13. 9. The ion milling apparatus according to claim 8, a sample chamber for processing the sample; a fifth pipe connecting the inside of the dewar and the inside of the sample chamber; a fifth valve provided in the fifth pipe; Further provided with the fifth valve is controlled by the control unit; An ion milling apparatus in which, when the sample is being processed inside the sample chamber, the fifth valve is opened so that the liquid nitrogen is supplied from inside the Dewar to inside the sample chamber via the fifth piping.

14. The ion milling apparatus according to claim 13, a third heater provided adjacent to the fifth pipe and between the fifth valve and the sample chamber; a third open valve provided in the fifth pipe located between the fifth valve and the sample chamber; Further provided with the third heater and the third release valve are controlled by the control unit; an ion milling apparatus in which, after the processing of the sample is completed, when the liquid nitrogen is discharged from inside the Dewar to inside the tank through the third piping, the fifth valve is closed, the third open valve is opened, and the third heater is driven, so that the liquid nitrogen remaining in the fifth piping is vaporized by the heat from the third heater and discharged from the third open valve.