JP6165110B2 - Charged particle beam system - Google Patents

Description

  The present disclosure relates to charged particle beam systems, charged particle sources for charged particle beam systems, in particular gas field ion sources and methods of operating charged particle beam systems.

  Charged particle sources, charged particle systems, and methods of operating charged particle systems and charged particle sources can be used for a variety of applications, including sample property measurement or identification, or for sample preparation. A charged particle source typically generates charged particles that can be directed to be incident on a sample by components of a charged particle beam system. By detecting a product resulting from the interaction between the sample and the charged particle beam, a sample image can be generated or the sample characteristics can be identified.

The following documents contain prior art that has some relevance to the present disclosure.

European Patent Application No. 2088613 European Patent Application Publication No. 2218542 US Patent Application Publication No. 2012119086 European Patent Application No. 2068343 European Patent Application No. 2110843 US Patent Application Publication No. 2012132802 US Patent Application Publication No. 2012199758 International Publication No. 2007067310 Pamphlet International Publication No. 08152132 Pamphlet

  According to a first aspect, the present disclosure is directed to a charged particle beam system. The charged particle beam system includes a charged particle beam source, a charged particle column, a sample chamber, a plurality of electric devices disposed in or inside the charged particle column, the charged particle beam source and the sample chamber, And at least one first converter for converting an electrical AC voltage force into an electrical DC voltage. The first transducer is disposed at a distance from any one of the charged particle beam source, the charged particle column, and the charged particle chamber, and all the elements of the plurality of electric devices are operated while the charged particle beam source is operating. When operated, the power supply is configured exclusively by a DC voltage supplied from the converter.

  In one embodiment, the shortest distance between the first transducer and each of the charged particle beam source, charged particle column, and sample chamber is at least 2 meters.

  In a further embodiment, the system further comprises a second transducer. The second converter is configured to provide a high voltage applied to the charged particle source, and the second converter converts the output DC voltage of the first converter to the high voltage.

  In still further embodiments, the charged particle beam system further includes a first barrier between the sample chamber, the high mass table on which the sample chamber is located, and the table and the floor on which the table is located. And a second vibration isolation system disposed between the table and the sample chamber. The first mechanical vacuum pump can be disposed on the table and can be connected to the first vacuum region via at least one flexible bellows.

  In still further embodiments, the at least one flexible bellows includes a first flexible bellows portion, a second flexible bellows portion, and a rigid tube or flange between the first flexible bellows portion and the second flexible bellows portion. .

  In a still further embodiment, the table has a stone or concrete plate.

  In still further embodiments, the particle source comprises a gas field ion source.

  In still further embodiments, the charged particle beam source is a noble gas field ion beam source, and the charged particle beam system further includes a housing defining a first vacuum region and a second vacuum region. A noble gas field ion beam source is disposed in the first vacuum region. The first mechanical vacuum pump is functionally connected to the first vacuum region. The ion getter pump can be connected to the charged particle beam column, and the gas supply system can be connected to the first vacuum region. The gas supply system can be configured to supply a rare gas to a rare gas field ion beam source.

  In yet further embodiments, the charged particle beam column is located between the first vacuum region and the sample chamber adjacent to the first vacuum region.

  In a further embodiment, the charged particle beam system further comprises a controller configured to switch off the ion getter pump when the noble gas field ion beam source generates the ion beam.

  In still further embodiments, the controller is further configured to switch on the ion getter pump only when the pressure in the first vacuum region falls below a specified pressure value.

  In still further embodiments, the charged particle beam system further comprises a heater and a controller. The controller is configured to heat the heater to release noble gas atoms from the ion getter pump.

  In yet a further embodiment, the charged particle beam system further includes a flange in which the ion getter pump is connected to the charged particle beam system, and the ion getter pump is disposed between the ion getter pump and the charged particle beam column in the flange. And have a valve.

  In still further embodiments, the charged particle beam further has a first housing. In the first housing, a charged particle beam source, a sample stage movably arranged inside the sample chamber, an ion optical system and an aperture plate arranged between the charged particle beam source and the sample stage are arranged. . The first housing can be directly attached to the tubular portion of the sample chamber, and the tubular portion can form an integral part of the sample chamber. The ion optical system and the aperture plate can be attached to the inside of the tubular portion.

  In still further embodiments, the charged particle beam system further comprises a first housing having a charged particle source disposed therein. The first housing has a second housing having a first portion of the tiltable mount and a charged particle optic defining an optical axis. The second housing has a second portion of the tiltable mount. The second portion is configured to accommodate the first portion of the tiltable mount to allow the first housing to tilt relative to the second housing. The first and second portions of the tiltable mount can be configured to form an air bearing. A motor drive can be provided that allows the first housing to tilt relative to the second housing. It can also be equipped with a controller that can be configured to control motor drive and air supply to the air bearing.

In still further embodiments, the charged particle beam system further comprises a measurement device. The measuring device is configured to measure and store the tilt position of the first housing relative to the second housing.

Also in a further embodiment of the charged particle beam system, the controller can be configured to control the tilting movement of the first housing driven by a motor and to reduce the holder to a previously stored tilt position.

  In a further embodiment of the charged particle beam system, the controller is further configured to stop the air supply to the air bearing when the measurement device provides a signal that a pre-stored tilt position has been reached. Is possible.

  In yet further embodiments, the charged particle beam system further comprises a movable peg configured to be motor driven. The receptacle is connectable to the first housing and the peg is configured to contact the receptacle. The controller can be further configured to drive the motor drive in a direction that releases the contact between the peg and the receptacle when the air supply to the air bearing is switched off.

  In yet further embodiments, the charged particle beam system further comprises a gas supply system that supplies one or more gases to the charged particle beam source. The gas supply system has a leak valve, and a constant gas flow rate is provided through the leak valve. Actuates a leak valve and can be equipped with an actuator configured to change a constant gas flow rate through the leak valve, and measures the gas pressure in the charged particle beam source and generates an output signal Can be equipped. The controller can be configured to control the movement of the actuator and change the gas flow rate based on the output signal of the sensor via a leak valve. The controller can also be configured to control the movement of the actuator only after a specific user interaction.

  Another aspect of the present invention relates to a charged particle beam system, the charged particle beam system having a charged particle beam source, a charged particle beam column, a sample chamber, a high mass on which the sample chamber is located, a table, and At least one of a first anti-vibration system between the table on which the table is located, a second anti-vibration system disposed between the table and the sample chamber, a sample chamber, a charged particle source and a charged particle column; Having at least one vacuum pump operatively connected to one. At least one vacuum pump can be disposed on the table. The vacuum pump is connectable to at least one of the sample chamber, charged particle source, and charged particle column via at least one flexible bellows.

  Another aspect of the present invention relates to a charged particle beam system, the charged particle beam system including a charged particle beam source, a first housing in which the charged particle source is mounted, a sample chamber having a second housing, and an interior of the sample chamber. A sample stage movably arranged, an ion optical system positioned between the charged particle beam source and the sample stage, and an aperture plate are included. The first housing can be directly attached to the tubular portion of the second housing, and the tubular portion can form an integral part of the second housing. The ion optical system and the aperture plate can be attached to the inside of the tubular portion.

  Another aspect of the present invention relates to a charged particle beam system, the charged particle beam system having a conductive tip having a tip apex and a holder for holding the conductive tip. The holder can have a first portion of a tiltable mount. The housing with the charged particle optic defining the optical axis can have a second portion of the tiltable mount. The second portion is configured to correspond to the first portion of the tiltable mount so that the holder can be tilted with respect to the housing. The first and second portions of the tiltable mount can be configured to form an air bearing. The motor drive configured to provide the holder with a tilting motion with respect to the housing can also be equipped with a controller configured to control the motor drive and the air supply to the air bearing.

  Another aspect of the present invention relates to a gas field ion source, which includes a housing, a conductive chip disposed within the housing, and a gas supply system for supplying one or more gases to the housing. The gas supply system has a leak valve, and a constant gas flow rate is provided through the leak valve. Furthermore, an actuator configured to act on the leak valve and change a constant gas flow rate through the leak valve can be provided. Furthermore, a sensor configured to measure the gas pressure in the housing and generate an output signal, and configured to control the movement of the actuator to change the gas flow rate based on the output signal of the sensor via a leak valve Can be equipped. The controller can be configured to control the movement of the actuator only after a specific user interaction.

  Embodiments are described in detail below with reference to the accompanying drawings.

It is sectional drawing which shows the mechanical structure of a charged particle beam system. It is an expanded sectional view of the particle | grain chamber of the charged particle beam system of FIG. It is an expanded sectional view of a gas field ion source. 1 is a schematic diagram of a charged particle beam system including a vacuum system. It is a three-dimensional representation of the external housing of the gas field ion source. FIG. 6 is a flow chart illustrating various steps in a cleaning process for a gas field ion source operated with a noble gas such as neon. It is a flowchart which shows adjustment of a chip | tip vertex part. It is a perspective view of a leak valve operated by a motor. 6 is a flow chart relating to adjustment of air flow for a gas field ion source. It is a figure which shows the principle of the gas field ion beam system provided with the electrical configuration. A and B are diagrams showing images of an emitter tip of a gas field ion source. It is sectional drawing of a gas field ion source provided with a heat shield. It is the schematic which shows embodiment of the heat shield which can exchange gas. It is the schematic which shows embodiment of the heat shield which can exchange gas.

  The charged particle beam system 1 of FIG. 1 has a sample chamber 10 mounted on a heavy and sturdy table 5. The table 5 can be a stone plate or a concrete plate. The table 5 itself is placed on a plurality of first legs 3a and 3b, and two of the first legs 3a and 3b are shown in FIG. The first legs 3a, 3b are designed to be located on the floor 2. Each first leg 3a, 3b includes or supports a first vibration isolator 4a, 4b in order to avoid vibration transmission from the floor to the table 5.

  The sample chamber 10 is placed on the table 5 via a plurality of second legs 18a, 18b. Each second leg 18a, 18b also includes or supports a second vibration isolator 9a, 9b. These vibration damping materials 9a and 9b serve to reduce or prevent vibration transmission from the table 5 to the sample chamber. Such vibrations of the table 5 may originate from a mechanical vacuum pump 17, such as a turbo pump that is fixedly connected to or attached to the table 5, for example. Since the table 5 has a large mass, the vibration amplitude generated by the mechanical pump 17 is greatly reduced.

  A mechanical pump 17 is functionally connected to the sample chamber 10. For this functional connection, the inlet of the pump 17 is connected to the rigid tube 7 via two flexible bellows 6, 8 or to a compact vacuum flange between the two flexible bellows, and the sample chamber Up to 10. The complete line from the pump 17 to the sample chamber forms a series of “flexible bellows-rigid tube-flexible bellows” arrangement. This arrangement further damps vibration energy and serves to reduce vibration transmitted from the table to the chamber. Chamber vibration can be further reduced when the mass of the intermediate tube is large, and can be further reduced when there is an energy absorber in contact with the bellows or tube. Chamber vibration can be further reduced if there is a mechanical resonance in the tube and bellows, and this mechanical resonance preferentially absorbs and dissipates vibration energy at frequencies due to the pump 17.

  In the particular embodiment described below, the charged particle beam system can have more than one mechanical pump, in particular two turbomolecular pumps. As a means of reducing the effects of vibration on image quality, both turbomolecular pumps (or all if more than two turbomolecular pumps) are connected to the charged particle beam system by successive pairs of flexible bellows. . The charged particle beam system can have two turbomolecular pumps, one for the chamber and one for the gun.

  The double bellows arrangement prevents vibrations associated with the rotational frequency of the pump (eg 900 Hz or 1 kHz and its harmonics) from being transmitted to the microscope. The turbo pump itself is fixedly attached to a huge stone platform (table 5) selected because of its large mass and the damping capacity provided. This stone platform serves to reduce the measurable vibrations on the stone to the nanometer or sub-nanometer level. Vibration transmission to the microscope is further reduced by two successive bellows arrangements with a rigid tube in between. Turbo vibration measured in the sample chamber 10 or charged particle source is typically at the sub-nanometer or sub-angstrom level. In this way, an appropriate pumping speed (eg, a vacuum pumping speed of 200 liters per second or more) can be achieved without adversely degrading image quality.

  The sample chamber 10 has a vacuum tight housing 19. The tubular extension 11 is fixedly and non-separably attached to the housing 19 of the sample chamber 10. The tubular extension 11 can be formed by a metal tube welded to the remainder of the housing 19 that surrounds the sample chamber 10. Alternatively, the tubular extension can be an integral part of the chamber housing itself.

  A charged particle column 12 is attached inside the tubular extension 11. Thus, the charged particle column 12 has a lens, a diaphragm, and a beam scanning system not shown in FIG. By attaching the components of the charged particle column 12 directly inside the tubular extension of the housing 19 of the sample chamber 10, the components between the charged particle column and the sample stage 20 disposed inside the sample chamber 10 Mechanical vibration can be avoided or at least reduced.

  Connected to the tubular extension 11 of the sample chamber housing 19 is a module containing a charged particle source. The module has a lower housing part 16 having an upper spherical surface. The upper spherical surface forms part of a biaxial tilt mount. Furthermore, the source module has an upper housing 15 in which a charged particle emitter is mounted. In the case shown, the charged particle source is a gas field ion source and the charged particle emitter 14 is a conductive tip. The upper housing 15 also has a spherical surface portion that forms the second portion of the biaxial tilt mount. With the help of this tilting mount, the upper housing part 15 holding the charged particle emitter 14 can be tilted with respect to the charged particle column 12 about two axes and the emission axis of the charged particles emitted by the charged particle emitter 14 can be adjusted. And aligned with the optical axis defined by the charged particle components disposed within the charged particle column 12.

  The tilt mount can be designed as an air shaft, the spherical surface of the upper housing 15 or the spherical surface of the lower housing 16 has a small channel (not shown) through which air flow can be provided, The flow lifts the upper housing, and the upper housing is designed to be easily movable relative to the lower housing. By stopping the air flow, the upper housing and the lower housing are gripped together by a strong frictional force between the upper housing and the lower housing.

  In FIG. 2, the housing 19 of the sample chamber 10 with a tubular extension is shown in detail. The charged particle column 12 mounted in the tubular portion 11 has a plurality of diaphragms 22, a deflection system 23, and an objective lens 21. The objective lens 21 allows the charged particle beam to be focused on a sample that can be positioned on a sample stage (not shown) inside the sample chamber 10, and the entire sample can be scanned. If the charged particle beam system is a gas field ion beam system, the lens 21 and the deflection system 23 are electrostatic components that act on the ions with electrostatic forces due to different electrostatic potentials applied to the system components. Furthermore, the charged particle column 12 has a first pressure limiting opening 24 and a second pressure limiting opening 25, which are intermediate vacuum regions (intermediate column regions 70) between the vacuum region in which the emitter tip 14 and the sample chamber 10 are located. Form. The component of the charged particle column 12 in the vicinity of the emitter of the gas field ion source is an electrode 26 that forms part of the condenser lens that follows the deflector 27. In this case, the deflector 27 aligns the beam from the gas field ion source with the optical axis defined by the charged particle optic that continues downward in the direction of beam propagation into the sample chamber 10.

  FIG. 3 shows a compact gas field ion source design. This gas field ion source is designed with doubly nested insulators. This provides a compact design while still providing a high voltage and variable beam energy and gas containment. The design consists of multiple parts. The first part is a thermally conductive (eg copper) base platform 31. The base platform 31 is grounded and directly connected to the cryogenic cooling system 52 and is thermally connected to the cryogenic cooling system 52 by a flexible thermal conductor 32 such as a copper ribbon or copper braided wire. Due to the elasticity of the thermal conductor 32, the entire gas field ion source can be tilted and any vibration transmission can be minimized. Due to the thermal conductivity of the braided wire, the gas field ion source can also be heated as a routine maintenance procedure.

  The cryogenic cooling system can be a dewar filled with liquid nitrogen and / or solid nitrogen. Alternatively, the cryogenic cooling system can be a dewar filled with solid nitrogen. The dewar has a heater 73c, and the dewar and the base platform 31 can be heated by the heater 73c. Alternatively, the cryogenic cooling system can be a mechanical refrigeration device.

  A central tubular high voltage insulator 33 is connected to the grounded base platform 31. The central tubular high voltage insulator 33 is made of alumina or sapphire, for example, and mechanically supports a conductive tip 34 forming a gas field ion emitter. The central tubular insulator 33 provides electrical insulation above 30 kV with respect to the base platform 31. The central insulator 33 has one or more open portions for connecting the high voltage lead wires 35 and 36, and the high voltage lead wires 35 and 36 need to be connected to the conductive chip 34. The conductive tip 34 provides the high voltage necessary to operate the tip 34 as a gas field ion source and also provides a heating current for heating the tip 34.

  An external tubular and cylindrical insulator 37 is also connected to the base platform 31, and the external tubular and cylindrical insulator 37 surrounds the central insulator 33. The outer tubular insulator 37 mechanically supports the extraction electrode 38 and also provides electrical insulation above (and beyond) 30 kV.

  The extraction electrode 38 is designed with a small hole 39 (for example, a diameter of 1 mm, 3 mm, 5 mm), and the small hole 39 is designed to be a small distance (for example, 1 mm, 3 mm, 5 mm). The base platform 31, the central insulator 33, the outer cylindrical insulator 37 and the extraction electrode 38 jointly define the inner gas containment vessel 41. The vacuum induction or pumping rate through the extraction electrode hole 39 is relatively small to support a higher pressure in the region of the conductive tip 34 compared to the outer region of the internal gas containment vessel 41. The only paths through which gas exits are the aforementioned extraction holes, gas delivery path 40 and pumping valve 42. The gas delivery path 40 passes through a narrow tube 40 that extends from the bottom of the supply to the internal gas containment container 41 through the grounded base platform 31. The pumping valve 42 can be mounted on the base platform 31 or can be incorporated into the gas delivery path 40.

  All the above-mentioned components of the charged particle source are supported on a base platform 31, which is mechanically supported by a rigid but thermally non-conductive bearing structure (not shown). The support structure is attached to the upper part of the external vacuum vessel (15 in FIG. 1). The upper part of the external vacuum vessel can be tilted by the contact surface of the concave spherical surface at a small angle of up to 5 degrees, and the concave spherical surface corresponds to the convex spherical surface of the lower part of the external vacuum housing (16 in FIG. 1). To do.

  An ion getter 45 is disposed inside the internal gas containment vessel. In order to improve the vacuum in the internal gas containment vessel, a chemical getter agent 45 is included inside the gas containment vessel 41. These chemical getter agents 45 are activated when baking the gas field ion source. The heater 73b is provided to heat the chemical getter agent 45. While the chemical getter 45 is heated to about 200 ° C. for 2 hours and when these components are cooled, the chemical getter 45 leaves many chemical activators such as Zr, V, Fe and Ti remaining. These serve to effectively pump out many unnecessary gas species with a pump. The getter agent can be coated directly on the existing part, for example the surface of the outer cylindrical insulator 37, or can be adhered as a ribbon-like material to the inner surface forming the inner gas containment vessel. Among possible impurities, pumping rate of chemical getter agent for hydrogen is important because hydrogen is not cryopumped effectively by cryogenic cooling surfaces. The chemical getter agent 45 in the internal gas containment vessel 41 is also very effective against further impurities of the transported helium and neon gases. The noble gases helium and neon are not affected, but all impurities are effectively pumped out. While these are periodically regenerated, the generated gas can be exhausted by the pump in an improved manner by opening the bypass valve 42 (flapper type valve) created for the purpose. The internal gas containment container 41 is connected to the external gas storage container 81.

  As will be described in detail below, the gas supply pipe 40 can have a heater 73a. The inner gas containment vessel 41 can be surrounded by a radiation shield that minimizes radiant heat transfer from the outer vessel wall (room temperature) to the ion source. The internal gas containment vessel 41 can also have an optically transparent window that allows the emitter chip 34 to be viewed directly from the outside of the internal vacuum vessel. Since the windows are aligned in the external vacuum vessel, the emitter tip of the gas field ion source can be observed with a camera or a thermometer. With such a camera, the source can be inspected and the source temperature monitored during routine maintenance. One or both of these windows can be leaded glass, minimizing X-ray radiation transfer from the inside to the outside. The base platform 31 is also ideal for temperature sensors such as thermocouples due to its high thermal conductivity.

  The gas field ion source is operated with a voltage established based on the geometry of the emitter tip 34. The geometric shape includes elements such as the average cone angle and average radius of curvature of the emitter tip 34.

  The above design has the advantage of low mass and volume. The low mass and volume speeds up heat circulation, reduces the cooling load, and reduces cost and complexity. Furthermore, because of the compact design, the noble gas that operates the gas field ion source can be quickly replaced. In particular, since the internal gas containment vessel 41 has a compact design, the operation of the gas field ion source with helium and the operation with neon can be quickly changed.

  Under ideal operating conditions, the apex of the emitter tip 34 is generally spherical (eg, 50, 100, or 200 nm in diameter). A spherical surface is actually better described as a series of facets, and these series of facets approximate a spherical surface. In the vicinity of the apex of the emitter tip 34, the end shape is more preferably approximated by three facets. These facets intersect at one vertex to form a three-sided pyramid. The pyramid end can be at a relatively shallow angle (eg, 70 or 80 degrees with respect to the emitter axis). The pyramid ridges and vertices are slightly rounded at the atomic level, with no single atom ridges or no single atoms at the vertices.

Under ideal operating conditions, three atoms of emitter material are present at the apex to form an equilateral triangle. These three atoms (hereafter referred to as “trimers”) are the most prominent, so they generate the largest electric field when a positive voltage (eg 20 kV, 30 kV, 40 kV) is applied to the extraction electrode. To do. In the presence of helium or neon gas, neutral atoms can be field ionized directly above these three atoms. At relatively high gas pressures (10 ^-2 Torr or 10 ^-3 Torr at local pressure), ionization is possible at a rate of 10 ⁶ or 10 ⁷ or 10 ⁸ ions per second. Under ideal circumstances, this stable flow of ions is constant over time and lasts indefinitely.

In practice, under typical conditions when operating with helium, ion emission can exhibit an emission current of 100 pA, which can continue for more than 10 consecutive days, 0.5 ms on a millisecond or earlier time scale. Fluctuates up and down by about%. The gradual loss of emission current can proceed at a rate of 10% per day if not corrected. The performance of helium (or the performance of operation with helium) is somewhat affected by the purity of the gas. Gas purity can be 99.9990% or 99.9999% or better, and the basic vacuum quality in the absence of helium is typically 2 x ^10-9 Torr, 1 x ^10-9 Torr, 5 x 10 ^-10 Torr or above.

  As used herein, the range of Torr units can be replaced by mbar units.

When a gas field ion source is operated with neon, there are some complications compared to the situation when operated with helium. For one thing, neon ions are much larger and can therefore sputter at a rate 50 times that of helium. When neon ions strike near the surface, the sputtered atoms are negatively charged (for example, negative secondary ions), and these atoms may accelerate back to the emitter 34, causing damage to the emitter 34. Is caused. On the other hand, neon gas having the same level as that of commercially available helium gas (for example, purity 99.9999%) is not commercially available. The effect of these purity will be described later. Most notably, however, when emitter 34 is activated by neon, emitter 34 needs to operate at a somewhat reduced voltage. For example, if 40 kV is optimal for helium, the same emitter tip will generate an optimal neon emission current at 30 kV. When the voltage is reduced in this manner, the electric field is similarly reduced, and unnecessary atoms (residual gas due to incomplete vacuum or impurities in the gas supply) can reach the emitter 34 at a higher rate. If the field strength is reduced by only 25%, an exponentially higher number of these unwanted atoms (not helium or neon) can reach the emitter. These unwanted atoms (eg, H ₂ , N ₂ , O ₂ , CO, CO ₂ , H ₂ O, etc.) can hinder the reach of neon to the tip of the gas field ion source, and therefore short-term And release instability on both long time scales. In addition, unnecessary atoms promote the corrosion of the emitter material and gradually change the shape of the emitter with time, so that the ion emission current may be gradually reduced and the optimum operating voltage may be gradually reduced. Also, unwanted atoms can more easily cause field evaporation of one or more atoms in the emitter tip 34 and cause a sudden drop in emission.

In order to generate a stable neon beam or a beam of rare gas ions having atoms with a mass greater than that of neon, the composition of the extraction electrode is very important, in particular the surface facing the emitter. The tip 34 of the gas field ion source is configured to be very close to the adjacent extraction electrode 38 provided with a small hole 39. The tip of the ion source 34 and the extraction electrode 38 have a voltage applied to them. The voltage difference causes an extremely large electric field in the vicinity of the apex of the emitter tip 34. The component of the extraction electrode 38 is a material that is not sputtered to the extent that it can be detected by a neon beam, and is made of a material such as carbon, iron, molybdenum, titanium, vanadium, and tantalum that does not form negative ions. Further, the component on the surface of the extraction electrode 38 facing the tip 34 is made of a material (for example, stainless steel or oxygen-free copper) that can be easily cleaned and has a low gas release rate in ultra-high vacuum. Also, the surface can be smoothed (realized by mechanical polishing or electrolytic polishing) and has a mirror finish. In particular, the surface closest to the emitter tip 34 has a mirror finish. Also, the material of the surface of the extraction electrode 38 facing the emitter tip 34 can have a very low negative secondary ion sputtering yield (eg gold, other materials not containing oxides, nickel, etc.). A low negative secondary ion sputter yield reduces the frequency with which negative secondary ions are generated that are accelerated and return to the emitter to cause (or cause impact to break) the emitter. The secondary electron yield can be as low as 10 ^-5 for each incident neon ion.

In order to generate a stable neon beam, it is very important for several reasons to make the shape of the extraction electrode 38 accurate. In particular, the shape of the extraction hole 39 is important. There are several design criteria for the holes in the extraction electrode, and the optimal shape depends on a balance of conflicting needs. First, to make the pores relatively small and contain the ionized gas (helium or neon), the noble gas is allowed to reach the apex of the emitter tip 34 at a relatively high pressure in the range between 10 ⁻² Torr and 10 ⁻³ Torr. It is held in the internal gas containment container 41 in the vicinity of the portion, and the pressure can be remarkably lowered to the range between 10 ⁻⁵ Torr and 10 ⁻⁷ Torr outside the internal gas containment container 41. Reducing the pressure outside the inner gas containment vessel 41 is important to minimize the rate at which desired high energy ions are scattered by low energy neutral gas atoms. Scattering causes unwanted beam tails and causes some ions to even become neutral. Therefore, the vacuum conductance of the hole 39 in the extraction electrode 38 is important. The vacuum conductance is measured in liters per second and is a reference scale that determines how the pressure drops from one side of the hole 39 (inside) to the other side of the hole 39 (outside).

  Also, if the hole 39 in the extraction electrode 38 is too large, the emitter tip 34 of the gas field ion source is exposed radiatively to a higher temperature surface. The emitter tip 34 and extraction electrode 38 of the gas field ion source are held at a cryogenic temperature in the range between -210 ° C and -190 ° C. If the hole 39 in the extraction electrode 38 is too large, the emitter tip 34 of the gas field ion source is not cooled to cryogenic temperature, but rather is warmed to a larger surface area that is at room temperature (eg, + 20 ° C.). Usually, a cryogenic cooling surface effectively traps unwanted gas atoms, while a warm surface cannot effectively trap gas atoms.

  However, there is an opposite reason for requiring that the hole 39 of the extraction electrode 38 not be too small. For example, if the hole 39 is too small, it can be challenging to produce the hole and keep it clean at the level necessary to support the high vacuum and high electric field at which the hole should function. . Also, the emitter tip 34 should be centered within 10% of the diameter of the extraction hole 39 relative to the hole 39 in the extraction electrode 38. Therefore, if the hole is too small, it will be difficult to position it symmetrically with respect to the tip 34 of the emitter.

  Also, the angular spread of the extraction hole should not be too small with respect to the apex of the tip 34 of the ion emitter. In other words, the solid angle of the extraction hole 39 viewed from the emitter tip 34 is of a certain size. This requirement stems from the pattern of ion release. The emitter tip 34 itself is a fairly narrow cone and emits ions with a half cone angle of 2 degrees. However, it is normal that there is a significantly larger angle of unwanted emission, and due to the nature of the emitter shape, the unwanted emission as high as 20 degrees with respect to the emitter axis is quite natural. In order to avoid damage to the extraction electrode 38 and generation of negative secondary ions that may damage the emitter tip 34, it is desirable that these emitted ions do not strike the extraction electrode 38. Unwanted ion emission can also serve to desorb any adsorbate that can migrate to the emitter and destabilize ion emission from the emitter tip. Accordingly, the angular spread of the hole 39 in the extraction electrode 38 and the distance between the emitter tip 34 and the extraction electrode 38 are selected such that the hole angle is about 20 degrees or more.

The internal gas containment vessel 41 has a very good basic vacuum, or similarly unwanted adsorbed atoms (eg atoms and molecules other than the desired working noble gas such as helium or neon) in the internal gas containment vessel 41 There is some importance in the absence of. Such unnecessary atoms and molecules include H ₂ , N ₂ , H ₂ O, O ₂ , CO, NO, CO _{2 and the} like. By way of illustration, the basic vacuum pressure in the internal gas containment vessel 41 is the pressure measured inside the internal gas containment vessel when the gas supply to the internal gas containment vessel, particularly the supply of helium and neon gas, is stopped. is there. The desired pressure will be 10- ¹⁰ Torr or better pressure than that. If the background gas pressure is low at the same time at a pressure of 4 x 10 ^-10 Torr, the time required for the originally clean surface to be covered with unwanted adsorbed atoms to a single monolayer thickness would be about 1 hour. . These adsorbed atoms cause instability of the ion source and are therefore intended to achieve the maximum possible basic vacuum. To achieve this goal, the entire housing of the gas field ion source is configured to be cleaned with ultra high vacuum (UHV) means. The internal gas containment vessel 41 in which the gas field ion source chip 34 is accommodated is constructed and prepared for UHV service.

  FIG. 4 shows a gas field ion microscope. The gas field ion microscope can be operated with two different noble gases for the ion beam, and in this special case is operated with helium or neon. The gas field ion microscope has three vacuum regions inside the microscope housing 19. The first vacuum region is the sample chamber 10, the second vacuum region is the intermediate column region 70, and the third vacuum region is the external vacuum storage container 81, and the gas field ion source is accommodated in the external vacuum storage container 81. The intermediate column region 70 is located between the external gas storage container 81 and the sample chamber 10.

  As previously mentioned, the sample chamber is evacuated by the turbomolecular pump 17, which is mounted on the table 5 (not shown in FIG. 4). The external gas storage container 81 is also exhausted by the mechanical pump 60. The mechanical pump 60 can also be a turbomolecular pump that can also be mounted on the table 5. The connection between the mechanical pump 60 evacuating the external gas containment 81 can be designed like a connection between the pump 17 and the sample chamber, i.e. the connection between the pump 60 and the external gas containment 81 is also It is possible to have two flexible bellows with a rigid tube or a compact vacuum flange between the flexible bellows.

  The intermediate column region 70 is separated from the external gas storage container 81 by the first pressure limiting opening 54. In a similar manner, the intermediate column region 70 is separated from the sample chamber 10 by the second pressure limiting opening 55. The intermediate column region 70 is evacuated by the ion getter pump 56. This has the advantage that the ion getter pump 56 does not generate any vibration.

  The ion getter pump 56 is connected to the control unit 59 and controlled. The controller 59 turns the ion getter pump 56 so that the ion getter pump 56 is always switched off when the gas field ion source is activated and / or noble gas is supplied to the internal gas containment vessel 41. Operate.

  An ion getter pump 56 that exhausts the intermediate column region 70 is connected to the intermediate column region via a flange 72. The flange 72 is provided with a valve 57 that may need to be replaced or otherwise serviced, or that the ion getter pump is switched off or the ion getter pump is in the middle column region 70. It can be closed when the air must not be exhausted. In this way. Replacement or maintenance of the ion getter pump 56 is possible without the intermediate column region 70 being in the atmosphere.

  The ion getter pump 56 has a heater 58, and the heater 58 is also connected to the control unit 59 and controlled. The ion getter pump 56 can be heated by the heater 58, and the rare gas and other adsorbed substances are discharged from the ion getter pump 56 to purify the ion getter pump 56.

  The external gas storage container 81 has a pressure measuring device 82. The pressure measuring device 82 is also connected to the control unit 59. For example, when the internal pressure of the external gas storage container 81 falls below a predetermined pressure value, that is, the output signal of the pressure measuring device 82 indicates that the pressure in the external gas storage container 81 has a predetermined pressure value. Only when it is shown that it has fallen below, it is constituted by a computer having a software program for switching on the ion getter pump 56. In this way, the life of the ion getter pump 56 can be extended.

  As already described above with reference to FIG. 3, a gas field ion source is disposed inside the external gas storage container 81. In FIG. 4, only the components of the gas field ion source forming the inner gas containment vessel 41, ie, the extraction electrode 38 with the base platform 31, the outer tubular insulator 37 and the extraction hole 39 are shown. As shown in FIG. 4, the getter 45 is inside the internal gas containment vessel 41.

  FIG. 4 also shows a flapper valve 42 having a drive device 43. The driving device 43 is also connected to the control unit 59 and controlled. The flapper type valve 42 can be used for gas field ions, for example, between an operation with helium that generates a helium ion beam and an operation with neon that generates a neon ion beam, when it is required to quickly evacuate the internal gas containment vessel 41. The flapper type valve 42 can be opened when a change in source operation is required.

The gas field ion microscope has a cooling device such as an emitter tip, a gas supply pipe 40 and a dewar 52 for cooling the base platform 31. FIG. 4 does not show the thermal connection between the dewar 52 and the components to be cooled, such as the base platform 31 or the gas supply line 40. The dewar 52 has a vacuum jacket that insulates the internal chamber of the dewar that is configured to be filled with cryogen from the outside. The dewar jacket is connected to the sample chamber 10 via a dewar jacket valve and a vacuum line. In this way, the vacuum in the vacuum jacket can be maintained at the pressure of the sample chamber. The dewar jacket valve can be closed in the following cases. That is, any process gas is supplied to the sample in the sample chamber, the chamber is atmospheric, or generally the chamber pressure exceeds a predetermined pressure value, eg, 10 ⁻⁶ Torr. By closing the dewar jacket valve, it is possible to prevent the condensation gas from accumulating in the dewar jacket.

  The gas supply system of the gas field ion beam system shown in FIG. 4 has two gas containers 61 and 62, one container containing helium and the other container containing neon. Both gas containers have a pressure regulator and ensure a constant gas pressure in the gas supply line after the pressure regulator. Each gas supply line has leak valves 63 and 64 following both gas supply lines after the pressure regulator. The leak valves 63, 64 ensure a constant gas flow of the corresponding noble gas from the gas containers 61, 62 to the pipe 40, thereby providing a constant gas flow of the corresponding noble gas into the internal gas containment vessel 41. Secure.

  Both gas supply lines are connected in the direction of gas flow from the gas containers 61, 62 to the pipe 40. Following the direction of gas flow, a purifier 65 and a gas valve 68 follow in a combined gas supply line, which is then connected to a tube 40 that terminates in an internal gas containment vessel 41.

  The gas supply line has a bypass line 66 including a bypass valve 67 that directly connects the gas supply line to the vacuum chamber 10.

  Further, a heater 73a is provided on the gas supply pipe 40, and the gas supply pipe 40 can be heated by the heater 73a.

If the gas field ion beam system is operated with a high helium or neon gas flow for several days, the operation of the gas field ion source is a cryopumping surface, i.e., base platform 31, gas supply tube 40, extraction electrode 38, insulator 33, It is possible to include a step that can warm up 37 and emitter tip 34 for a short time. As a result of this warming up, the accumulated low-temperature adsorbed atoms can be desorbed and then exhausted through the turbo molecular pumps 17 and 60. The gas delivery pipe 40 that supplies a rare gas such as helium or neon gas from the external gas supply containers 61 and 62 to the vicinity of the emitter tip 34 can also be cooled to a cryogenic temperature. As a result, impurities such as H ₂ O, CO, CO ₂ , N ₂ , and O ₂ can be cryopumped on the surface of the tube 40, and the supplied gas is purified. In order to clean the surface of the gas supply pipe 40, the gas supply pipe 40 is similar to the other cryopumping surfaces being heated to at least 100 ° C, more preferably 150 ° C or even 200 ° C. The heater 73 can be periodically heated to a high temperature, and these accumulated adsorbates can be discharged, and can be exhausted through the turbo pumps 60 and 17.

  The gas delivery tube 40 has an inner diameter between 1 mm and 6 mm. The gas delivery pipe 40 connects the external gas delivery system to the internal gas containment container 41 through the wall surface of the external gas storage container 81. The gas delivery pipe 40 has a bypass valve 67 and promotes exhaust of desorbed gas. The bypass valve 67 prevents the desorbed gas from being trapped on a large scale in the internal gas containment vessel 41. The bypass valve 67 can be located completely outside the vacuum housing or is integrated within the internal gas containment vessel 41.

  It has proven effective to periodically remove adsorbed atoms from the emitter tip by one of three techniques. One of the three techniques is to periodically heat the emitter tip 34, for example, at 300 ° C. or higher for 1 minute or longer, while keeping the components forming the internal gas containment vessel 41 at a cryogenic temperature. By heating the emitter tip 34 in this manner, the accumulated adsorbed atoms are thermally excited, and these adsorbed atoms are desorbed and moved to a surrounding surface of lower importance. Such a surface is primarily the cooling surface of the extraction electrode 38, holding adsorbed atoms and reducing the possibility of moving back to the emitter tip 34.

  Alternatively, instead of heating the emitter tip 34, an intense light beam focused on the emitter tip is used to desorb the accumulated adsorbed atoms, thereby making the emitter tip 34 clean and stable ion emission. It is possible to leave it in a suitable state.

  Further alternatively, the adsorbed atoms accumulated by the electric field can be desorbed by increasing the voltage difference between the emitter tip 34 and the extraction electrode 38. For example, if the voltage difference between the emitter tip 34 and the extraction electrode is typically 30 kV for neon emission during operation of the gas field ion source, the electric field is 32 kV, more preferably 35 kV or 40 kV. Can be increased to cause the release of adsorbate.

  The need for one of these three above-mentioned techniques can be assessed by observing the release pattern and looking at the effects of individual adsorbates. The need for one of these three techniques can also be assessed by observing how unstable the emission from the emitter tip 34 is.

  Images of each field ion microscope of the emitter tip are shown in FIGS. 11a and 11b. FIG. 11a shows the central trimer release pattern. Trimeric atoms are brightest, but non-trimeric atom emission sites are also visible. Typically, the gun tilt is adjusted so that one of these three central emission beams is directed to the lower ion column. During ideal operation, the release pattern is very stable and constant over time. However, if the vacuum or gas purity is not ideal, unwanted atoms or molecules may be adsorbed onto the emitter, which is shown as a larger bright spot in FIG. 11b. These emission patterns can be monitored periodically to await these adsorbed molecule or atom changes. Undesirable adsorbed atoms may be located on trimer atoms, on one of the non-trimer primitives, or at different sites. The emission current from the trimer is reduced by the influence of the adsorbate, or the emission current increases at the same time as the adsorbate remains there. Thus, the described technique can be applied until the adsorbate is removed and the release pattern takes on the original desired appearance.

  As described above, even if a small amount of unwanted gas atoms reach the emitter tip of the gas field ion source, the intensity of the emitted beam may fluctuate up or down, or may gradually and progressively weaken. These effects can be reduced by the gas manifold (or gas delivery system). The gas manifold is designed for performance optimization purposes and operating procedures. The gas delivery system includes a bypass valve. The bypass valve allows the gas delivery line to be evacuated as a purification process in the preparatory stage of using the gas delivery line with helium or neon gas. Gas delivery hardware is prepared with materials and methods established for UHV services. The gas delivery system includes an integrated heater. The integrated heater can heat the gas manifold to temperatures as high as 150 ° C, 200 ° C, or even 400 ° C for as long as 8 hours, 12 hours, or even 16 hours, and remove any vacuum contaminants. Also promote separation. During this heating time, the valve 68 in the line to the internal gas containment vessel 41 is closed and the bypass valve 67 in the tube 66 leading to the sample chamber 10 is opened. As a result, the generated gas is exhausted by the pump to the sample chamber 10 where the influence of the generated gas is not so remarkable. The baking process can be repeated after the gas manifold has been exposed to the atmosphere (e.g., after maintenance activities such as container or valve replacement) or when it is necessary to improve the emission stability level. A chemically active purifier 65 can also be incorporated as part of the gas manifold to reduce common impurities. The purifier can be operated by being heated to a high temperature of 100 ° C, 200 ° C or even 300 ° C, room temperature or any desired temperature by a heater dedicated to the purifier. The heater of the purifier can be powered by a DC power supply and does not receive any interference from a 60 Hz or 50 Hz magnetic field. The gas manifold can also have a pressure gauge 58 to monitor the pressure before the gas is transferred to the internal gas containment vessel, although downstream from the precision leak valve.

  The internal gas containment vessel of the gas field ion source has a built-in valve, “flapper type valve” 42. When the flapper type valve is opened, the internal gas containment vessel 41 is connected to the external gas containment vessel 81, and the volume pumping speed of the internal gas containment vessel is 1 liter per second (open only through the extraction hole 39). To 22 liters per second when the additional valve is opened. By using this valve, it is possible to promote the achievement of a low basal pressure, and it is possible to promote a stable neon release by a low basal pressure. Using this valve can reduce the time required to purge one gas (eg, helium) before switching to another gas (eg, neon). The valve can be attached directly to the internal gas containment vessel or can be located further away. The valve can also be incorporated into the gas delivery line 40.

  A cryogenic connection that serves as a gas delivery tube from the gas supply vessel to the internal gas containment vessel can also be provided. As an advantage, the connection to the internal gas containment vessel is reduced, making it easier to connect and disconnect in operation. Another advantage is that the gas path is properly cooled to cryopump any impurities in the helium or neon gas. Another advantage is that when the dewar is heated, the gas delivery tube 40 is properly heated to desorb impurities.

  The internal gas containment vessel can be heated and cooled via a flexible heat conducting element 32 (shown in FIG. 3). The end of the flexible heat conducting element is a heater 73c attached to the cryogenic cooler. When the dewar is filled with cryogen, the dewar serves to keep the gas field ion source cool. When the dewar is not filled with cryogen, the heater can be powered and heats both the dewar and the components that form the internal gas containment vessel. Such a design is particularly suitable because the dewar and the internal gas containment are in a thermally tight relationship and achieving a temperature difference between them is not a simple matter. During baking of both parts, the required power is about 25 watts, and the temperature achieved is 130 ° C. on the dewar and 110 ° C. for the components forming the internal gas containment vessel 41.

  To reduce disturbance due to charge in the image due to specimen charging, it is possible to have a flood gun that supplies an electron beam, the flood gun is in the range above 1 keV, above 1.5 keV or even above 2 keV Of relatively high energy. Higher energy is desirable to reduce charge disturbances in multiple samples.

  One means of reducing the effects of vibration on image quality is to replace one or more turbomolecular pumps with ion getter pumps. Turbomolecular pumps are generally expensive. Further, since the rotating part is included inside, the charged particle beam system is vibrated by the turbo molecular part, and the image quality tends to be deteriorated. One way to reduce costs and eliminate turbo vibration is to select a getter ion pump (aka ion pump) and replace one or more turbo molecular pumps. Getter ion pumps (or ion getter pumps) are based on two pumping mechanisms. The first method is chemical gettering in which scientifically active species are pumped out. The second method directly embeds atoms. The second method works for any gas molecule, including noble gas atoms. On the other hand, the first method does not work for rare gas atoms because the rare gas atoms are chemically inert. The gettering effect is achieved by the binding of the active species to the reactants and is usually a combination of titanium or tantalum that is freshly evaporated by a getter ion pump. It is possible to directly fill the atoms by ionizing the molecules (by electron impact) and accelerating the resulting ions with large electric fields up to 3 keV or 5 keV or 10 keV energies. Thereafter, the ions strike adjacent surfaces (titanium or tantalum) and are implanted to a typical depth of 10 to 100 nm. Once embedded, the gas species can no longer return to the vacuum vessel. Direct filling is accompanied by a sputtering effect. In the sputtering effect, chemically unreacted titanium or tantalum molecules are sputtered, allowing subsequent chemical gettering. However, ion pumps are known to have limited pumping rates for noble gases such as helium and neon. The reasons are: (1) Helium and neon are chemically relatively inert and are therefore most effectively evacuated by the pump by direct filling. (2) Since helium and neon have high ionization energy, they are not easily ionized. And (3) Because of its mobility, helium and neon can be gradually dissipated from the buried state, and surface corrosion proceeds. To overcome the shortcomings of limited life of ion getter pumps in rare gas environments, switch ion getter pumps when the gas present is primarily rare gases, such as when a gas field ion source is operating. It can be turned off. Alternatively, the getter ion pump can be operated in combination with a turbo pump, in which case the ion getter pump evacuates only a small intermediate vacuum space in the charged particle beam column and the gas load on the ion getter pump is limited by throttling. Limited.

  When baking out a gas field ion source to achieve a desired vacuum level, it is beneficial to follow a specific time sequence as described with respect to FIG. In the first step 610, the outer vacuum housing, the inner gas containment vessel 41 and the emitter tip of the gas field ion source are all at least 100 ° C, more preferably 150 ° C or even more preferably 200 ° C. Heated to high temperature. This heating can be performed on all components at the same time. However, if the heating process is first completed at step 611, the external vacuum housing can be cooled to room temperature. During the time that the external vacuum vessel cools down, internal components such as the internal gas containment vessel 41 and the emitter tip of the gas field ion source are continuously heated. Then, after the outer vacuum housing has been cooled down to room temperature in step 612, the components forming the inner gas containment vessel are cooled to cryogenic temperatures, while heating of the gas field ion source tip 34 is still continued. Thereafter, in step 613, after the components forming the internal gas containment vessel have been cooled to cryogenic temperatures, the ion emitter heating is discontinued and the gas field ion source tip 34 is held at cryogenic temperatures. In other temperature versus time schemes, gas field ion source tips can cause material adsorption. This is because these materials are detached from the surrounding surface.

  The control unit 59 is configured to control various heaters 73a, 73b, 73c, 58, for example, by corresponding software codes, and to reliably execute the heating and cooling plans described above by using the heating current through the emitter chip supply line. Is possible.

  Beam landing errors that can appear as image vibrations can be reduced, for example, by removing the time to change the magnetic and electric fields that cause the ion beam to land in the wrong location. Typically, ion and electron microscopes are powered by standard 60 Hz and 50 Hz power systems. These “alternating current” power supplies can accidentally generate small ripple voltages on the control electronics, and these ripple voltages can cause unwanted beam landing errors. For example, the occurrence of 60 ripple of 5 mV on the beam handle electrode will cause the beam to deviate from the desired target in a time-varying manner. Alternatively, an “alternating current” power supply can generate a magnetic field that can exert a force directly on the charged particle beam, again causing a time-varying landing error. For example, a 50 Hz magnetic field with an amplitude of 5 milligauss can cause a time-varying landing error exceeding 1 nm. In general, these “alternating current” power supplies provide power to the individual components that are included and supported in the microscope. Examples of components include turbo pump, ion pump, vacuum gauge, heater, mechanical stage motor, high voltage supply system, filament heater, pico ammeter, chamber illumination, detector, electronic flood gun, camera, DC low voltage Includes supply systems. Most of these systems cannot be used without an AC power input. In other words, an equivalent that uses a DC power source that functions equally as a power source is generally not commercially available. However, it has been desirable to design a gas field ion microscope that does not have a component source (50 Hz or 60 Hz) powered by an AC power source within 3 meters. This can be achieved in the following two ways. First, all components located within 3 meters of the microscope can be designed, specified or modified so that they can only be operated by a DC power supply or a pneumatic actuator. Second, a small number of components that require an AC power source and have no replacement (eg, DC power source) can be placed at a distance of at least 2 meters, more preferably more than 3 meters from the microscope. . For example, a gas field ion microscope can have a high voltage generated locally from a direct current by a direct current transformer. Some heating elements are operated by a DC power source. There is also an AC heater that can be used if the AC heater can be stopped when the microscope is operated. The customer can choose to place the console (with a dedicated AC power computer and monitor) near or far from the microscope according to his / her preference.

  The sample stage 20 inside the sample chamber 10 is a 5-axis motor control stage with high repeatability (less than 2 microns), low drift (less than 10 nm per minute) and low vibration (<1 nm). The axes of the stage (in order from the chamber mounting surface 19 to the sample) are the tilt axis, the X axis, the Y axis, the rotation axis, and the Z axis. Tilt axis tilts the sample from the limit of -5 degrees to 0 degrees (gas field ion source beam strikes the sample in the orthogonal direction), +54 degrees (gallium beam strikes the sample in the orthogonal direction), and the limit of +56 degrees Is possible. In order to achieve this wide range of tilt with the full weight of all upper shafts, a considerable torque with minimal net force is required. The tilt axis is driven by a DC motor or stepper motor with a hermetic rotary feedthrough outside the conventional vacuum region. All upper shafts are actuated by piezoceramic actuators, which have very high rigidity (to reduce vibrations) and inherent blocking performance when not powered.

  As shown in FIG. 5, the gas field ion source can be tilted by a motor drive mechanism. The mechanism is configured to disconnect the drive mechanism when movement is complete to reduce vibration. By way of illustration, a gas field ion source can be tilted by a small angle (typically 1, 2 or 3 degrees in the X or Y direction), tilting the ion source relative to the column. For one, this tilt is required when the exact shape of the emitter cannot be easily controlled. For one thing, such tilting can be required because usually three ion beams are emitted from the apex of the emitter with a separation angle of about 1 degree. One of the emitted ion beams can be directed down to the axis of the ion column and provides the best performance. By tilting the gas field ion source, the selected ion beam can be directed in this way. As mentioned above, and also shown in FIG. 5, the gas field ion source housing has two parts, an upper part 15 and a lower part 16. The upper portion 15 of the housing is forced to tilt by a concave spherical surface that mates with the convex spherical surface of the lower portion 16 fixed to the corresponding housing. The center of the spherical surface coincides with the position of the apex of the emitter tip and is therefore arranged to take a tilting motion sharing the center with the apex of the emitter tip. The contact surfaces of the upper and lower spherical surfaces provide sufficient frictional forces and the two parts are mechanically extremely hard and free from any measurable relative vibration.

  In the system shown in FIG. 5, the upper housing 15 is tilted relative to the lower housing 16 by a motor driven tilt mechanism. The tilt drive mechanism is constituted by a gantry 701 fixed to the lower housing 16, and the lower housing 16 moves a peg that fits inside the receptacle in the upper portion 15 of the housing. Since the peg is moved by two orthogonal axes of the motors 702 and 703 (for X tilt and Y tilt), the peg contacts the edge of the receptacle and the upper housing 15 moves in a desired direction. The relative inclination of the two spherical surfaces is also possible by the action of an air bearing. After the desired tilt is achieved, the air bearing is disabled and the peg moves backward and no longer contacts the edge of the receptacle. In this way, when movement is no longer desired, the motor drive shaft (and any vibration that the shaft may introduce) is completely disconnected. Thus, the motors 702, 703 provide a tilt effect when desired, but the motors 702, 703 are disconnected when service is complete. It is also worthy to note that the upper housing 15 (inclined portion) is equipped with an inclinometer 705 and the inclinometer 705 measures the inclination of the upper housing 15 with respect to the direction of gravity. The inclinometer provides tilt angles in two directions (X direction and Y direction) to the controller that controls the operator and the gun tilt motor. This allows the upper housing to tilt and allows the tilting movement of the ion gun to move from one position to another and back again accordingly. The inclinometer 705 also prevents excessive tilt angles (eg +3 degrees in the X direction and +3 degrees in the Y direction) that can break the interior (can be limited to a total tilt of just 4 degrees from the vertical). . In addition, the upper housing 15 can return to the standard tilt angle when periodic source maintenance needs to be performed based on the line of sight of the fixed camera and the fixed electrical contacts.

  The process of adjusting the inclination of the upper housing will be described with reference to FIG. In the first step 801, the inclination position actually adjusted with respect to the direction of gravity of the upper housing 15 is stored by reading out the actual measurement value provided by the inclinometer 705. In the next step 802, the control unit 59 switches on the air supply to the air bearing between the two spherical surfaces between the upper housing 15 and the lower housing 16. This is followed by step 803 in which the tilt drive 702; 703 is activated, at the same time until the inclinometer 705 provides the desired readout output for the newly adjusted tilt position of the upper housing 15 relative to the lower housing 16. Reading of the actual measurement value by 705 is continued. When the new position is reached, air supply to the air bearing between the upper housing 15 and the lower housing 16 is stopped in step 804. In step 805, the drives 702, 703 are controlled to move in the opposite direction as compared to the movement required to reach the new tilt position until the peg disconnects from the receptacle. The gas field ion beam system can then be actuated by the upper housing 15 at step 806, which is in a new tilted position with respect to the lower housing.

  Since the old tilt position is remembered, if desired, the new process described above is repeated until the inclinometer 705 provides an output signal indicating that the old tilt position has been reached again, but the drives 702, 703. Can be moved in the opposite direction and readjusted to the old tilt position. This process can be used in rebuilding the tip of a gas field ion source. Typically, tip reconstruction is performed with a different emitter tip orientation than when operating the system to record an image of the sample or to process the sample.

As an illustration, the gas field ion beam system can generate sample images by detecting particles leaving the sample due to impinging ion beams, and can manipulate and modify these samples with sub-nanometer accuracy It is. Therefore, it is important to be able to operate the ion microscope so that there is no error at the intended arrival position of the focused ion beam. These landing errors can be very small (eg, less than 100 nm, less than 10 nm, or even less than 1 nm), but even if small, they still have a negative impact on instrument operation. In order to stably operate the gas field ion beam system, an appropriate amount of rare gas for gas ionization in the vicinity of the emitter tip should be secured. In order to ensure proper noble gas pressure, the gas supply system has leak valves 63, 64 (shown in FIG. 4 and in detail in FIG. 8). The leak valves 63 and 64 are manually adjusted by an operator or adjusted by a motor-driven control system. In either case, adjustments are established based on pre-established table values. The table value is associated with mechanically adjusting the working gas pressure to the target value (eg, manually rotating knob 902 or motor position). As shown in FIG. 9, the gas pressure can be evaluated by a meter 82 located in the external gas containment vessel 81 or a meter 69 located in the gas manifold (gas delivery system shown in FIG. 4). Either way, the adjustment can be postponed until the microscope has reached maximum accuracy. In other words, a normal control loop can be interrupted during precision work. For example, if the gas pressure exceeds an acceptable range, the controller 59 can display 906 to the operator via the computer interface (eg, a message “Gas pressure is out of target”) or can change from green to red. A simple light indicator can be provided. The operator can then determine if the current microscope operation allows a corrective action or if this action should be postponed. Taking for reference, normal gas pressure in the microscope operation is read in the range of the pressure gauge 82 from 2.0 x10- ⁶ Torr to 2.1 x 10 ^-6 Torr. If the pressure goes outside this range, it may affect the identity or consistency of the ongoing process. However, corrective actions can have a more serious impact on the replication fidelity of ongoing work. Thus, as shown in FIG. 9, the controller 59, at step 908, only after having received a user interaction 907 that confirms that a modification of gas flow through the needle valve 63 or 64 is desired at that time, the motor 904. Configured to operate.

  The leak valve in the proper position can be a commercially available manual precision leak valve and is incorporated into the gas field ion beam system. As described above in connection with FIG. 3, one leak valve 63 can be equipped for the helium gas delivery system and one leak valve 64 can be equipped for the neon gas delivery system. Leak valves 63, 64 are manually operated without further modification and are provided with a calibration table. The calibration table generally indicates the desired gas pressure and the corresponding knob rotation to achieve these pressures. An alternative embodiment of a motor driven leak valve is shown in FIG. This motor driven leak valve is based on commercially available manual leak valves 63,64. A drive motor 904 having a spindle 905 is connected to the housing portion 903 of the leak valve. The spindle 905 operates on a manual adjustment knob 902 of the manual leak valve.

  Alternatively, the manual leak valve knob mechanism can be dispensed with entirely, and a piezoceramic actuator can be substituted. Alternatively, or alternatively, a manual leak valve knob mechanism can be dispensed with, and a cam drive mechanism can be substituted.

  FIG. 10 shows the electrical configuration of an embodiment of a gas field ion beam system. As described above, the charged particle beam system has a charged particle source with an ion emitter. The ion emitter has a conductive tip 34, an extraction electrode 38, and a deceleration or acceleration electrode 110. A beam deflection system 112 continues downward in the direction of beam propagation. By the beam deflection system, the ion beam can be deflected in a direction perpendicular to its propagation direction, and the ion beam is scanned over the entire surface of the sample located on the sample stage 20. Furthermore, the charged particle beam system has an objective lens. The objective lens has several electrodes 107, 108 and 109 and focuses the ion beam onto the surface of the sample located on the stage 20.

  In order to position the sample with respect to the optical axis 125 defined by the symmetry of the electrodes 107, 108, 109 of the objective lens, the sample stage 20 is movable along several axes and / or around several axes. Typically, the sample stage 20 has four or five free axes for movement. These five axes are typically linear movement perpendicular to the optical axis 125, linear movement along the optical axis 125, tilt or rotation about an axis perpendicular to the optical axis 125, and rotation around the optical axis 125. In order to drive the movement, a corresponding number of motor drives are arranged on the stage 20, of which the drives 105, 106 are shown in FIG.

  In addition to the electric motors 105, 106, the system includes a plurality of additional electric configurations, including an actuator 115 for a leak valve, an actuator 116 for a flapper valve, a vacuum pump 17, an ion getter pump 56, heaters 73a, 73b, 73c, etc. Have parts. These motorized devices are powered by the output power of the AC to DC converter 114 to power all of these drives that may need to operate during operation of the charged particle beam system. The AC / DC converter 114 itself is powered by a normal 50 Hz or 60 Hz power supply 113. The AC / DC converter 114 is configured to be located a few meters, for example at least 2 meters away from the ion optical components of the closest charged particle beam system. Thus, all of the motorized components that are attached in or directly to the charged particle beam system and are operable during conventional operation of the charged particle beam system are powered to the DC output of the AC to DC converter 114. Configured to In addition, a DC / DC voltage converter 118 is provided to generate a high voltage to be applied to the emitter 34, extraction electrode 38, acceleration and deceleration electrode 110, lens electrodes 107, 108 and deflection system 112. The DC / DC voltage converter 118 is configured to generate several different high voltages from the input DC voltage output of the AC / DC converter 114. The various output signals of the DC / DC converter 118 are directed to corresponding electrodes of the charged particle beam system by corresponding supply cables or power supply lines 119-124.

  The electrical concept described above avoids electrical devices that are in close proximity to the charged particle beam system and are driven with an alternating voltage and need to be activated during operation of the charged particle beam system. This electrical concept can greatly reduce the obstacles associated with the 50 Hz or 60 Hz frequency of the AC power supply.

  FIG. 12 is a cross-sectional view of a gas field ion source that includes a radiation shield 803. The design of the gas field ion source is very similar to the gas field ion source described above in connection with FIG. Further, in this case, the source has an inner cylindrical insulator 33 that holds the emitter tip 34 and an outer cylindrical insulator 37 that surrounds the inner insulator 33 and holds the extraction electrode 38 having the hole 39. The space between the external vacuum wall 801 and the external cylindrical electrode 37 forms an external gas storage container 81, and the space surrounded by the external cylindrical electrode forms an internal gas containment container 41. In order to minimize radiant heat transfer from room temperature components such as the external vacuum wall 801, the outer cylindrical electrode 37 and the extraction electrode 38 are surrounded by a radiation shield 803. The radiation shield 803 can usually be formed by a cover 810 and a cylindrical tube having a base 812 on the base side of the cylinder. The radiation shield is plated with polished gold to minimize radiation absorption. Since the radiation shield is connected to the base plate 801, the radiation shield is also cooled to a very low temperature. Alternatively, the radiation shield can also have a dedicated cooling connection to a cooling system such as Dewar. However, a can-shaped radiation shield is less useful when gas transfer is required between the area surrounded by the radiation shield and the area outside the radiation shield.

  Figures 13a and 13b show cross-sectional views of the heat shield. The heat shield can achieve gas exchange between areas inside and outside the radiation shield. In FIG. 13a, the radiation shield has concentric cylinders 805, 806, both made of metal with a high radiation reflective outer surface. Both cylinders have a plurality of holes 807,808. The hole 807 in the inner cylinder 806 is arranged offset in the rotational direction with respect to the hole 808 in the outer cylinder 805. The width of the hole, the distance between the cylinders 805 and 806, and the offset angle between the holes in both cylinders are selected so that the inside of the inner cylinder 806 cannot be seen directly from the outside of the outer cylinder 805. Thus, any radiation that passes through the holes in the outer cylinder 805 impinges on the remaining material portion of the inner cylinder 806.

  The embodiment of FIG. 13 b has a plurality of slabs 809. The slabs 809 are arranged in a cylindrical shape, and each slab is inclined at an angle different from 0 degrees and 90 degrees in the radial direction from the cylinder shaft 811. Also in this embodiment, the direct view of radiation from the outside to the inside of the cylindrical region surrounded by the slab 809 is nearly or minimal.

  In both the embodiments of FIGS. 13a and 13b, gas can flow from the inside of the heat shield to the outside of the heat shield, or in the opposite direction, between the holes 807, 808 or the slab 809, at the same time by the heat shield. Radiative heat transfer from outside the enclosed area into the area is strongly reduced by the heat shield.

The above disclosure can be summarized as follows.
In some embodiments of the process for operating a gas field ion source, the gas field ion source can be initially heated before any voltage is applied to the ion source to desorb any undesired atoms and molecules. To do. In operation, the gas field ion source is cooled to a very low temperature (eg, less than 90 Kelvin), thereby removing large quantities of atoms and molecules. Heating can be as short as, for example, a few seconds, but should be at a temperature of, for example, 500 Kelvin or several hundred Kelvin above.
In some embodiments of the process for operating the gas field ion source, the gas field ion source is applied between the emitter tip and the extraction electrode if the source is not required to operate at an optimum operating voltage. It is possible to operate at the maximum allowable voltage. This “standby voltage” can typically be just below the voltage that causes field evaporation of the emitter tip. This can serve to maximize the polarization of the adsorbed atoms and thus minimize the mobility of the adsorbed atoms. As a result, the opportunity for adsorbed atoms to move toward the apex of the emitter tip is reduced.
In some embodiments, the gas field ion source may be most susceptible to unwanted atoms. As such, the gas field ion source can be surrounded by a cryogenic cooling surface, minimizing the possibility of thermal desorption of any adsorbed atoms that could otherwise reach the emitter of the gas field of the ion source.
In some embodiments of the process for operating a gas field ion source, the cryogenic cooling surface can be periodically heated or photostimulated to desorb adsorbed atoms or molecules. During the heating process, the gas field ion source should be closed by strongly reducing the voltage between the emitter tip and the extraction electrode.
In some embodiments of the process of operating a gas field ion source, as a preparatory step, the vacuum vessel and gas delivery system can be heated to high temperatures to facilitate degassing and to mobilize surface and volume contamination. This can be done under partial vacuum combined with other volatile gases.
In some embodiments of the process for operating a gas field ion source, as a preparatory step, the vacuum vessel and gas delivery system can be electropolished to minimize surface area.
In some embodiments of the gas field ion source, the gun region can be equipped with a chemical getter agent, such as, for example, a commercially available SAES getter agent, providing high exhaust performance for undesired gas species. This chemical getter agent is very effective when the desired gas species is a noble gas. This is because the rare gas is not exhausted by the pump. Chemical getter agents are also very effective for pumping out hydrogen with a pump. This is because this gas species is not effectively exhausted by the pump by the cryogenic method. When the getter agent is chemically active, the gas field ion source is usually heated and the gas field ion source can be disabled.
In some embodiments of the gas field ion source, the gas delivery tube can pass through a cryogenic trap, causing the condensation of impurities. In some embodiments, such portions of the gas delivery system can have a valve, allowing purge.
In some embodiments of the gas field ion source, the gas delivery system can have a purifier. The purifier contains a chemical getter agent that is heated or not heated, and chemically traps any unwanted atoms or molecules.
In some embodiments of the gas field ion source, the gas delivery system has a bypass and the contents containing unwanted atoms and molecules can be purged into a container other than the final gun region.
In some embodiments of the gas field ion source, the region of the gas field ion source can be equipped with an ion pump to pump out undesired gas atoms. Also, the ion pump can be disabled when the desired gas is transported and can be enabled during the gas supply standby.
In some embodiments of the gas field ion source, the vacuum vessel can be equipped with a non-evaporable getter agent conformal coating similar to the SAES getter agent.
In some embodiments of the gas field ion source, the vacuum vessel can be equipped with a hydrogen pump getter, such as a titanium sublimation pump.
In some embodiments of the process of operating the gas field ion source, the gas field ion source is operable during conditions or to prepare the surface. Under conditioned conditions, the ion source can purge adsorbed gas atoms via energetic and highly polarized neutral atom bombardments. Also during conditioning, the extraction electrode, suppressor electrode, lens electrode and other surfaces on which the ion beam can collide during operation of the gas field ion source remove adsorbed atoms or chemically attached atoms. It is washable. The conditioning step can be performed with heavier gas species if acceleration of the process is desired.

  In the above description, features of different aspects of the invention are disclosed in combination. It is to be understood that the scope of the present invention is not intended to be limited to such a combination of features, but is defined solely by the following claims.

Claims (3)

A charged particle beam system,
A charged particle beam source;
A charged particle column;
A sample chamber, the charged particle column, the charged particle beam source, and a plurality of electric devices arranged inside or any one of the sample chamber;
At least one first converter for converting an electrical AC voltage force into an electrical DC voltage;
The plurality of electric devices include at least one device selected from the group consisting of an ion getter pump and a turbo pump,
The first transducer is disposed at a distance from any of the charged particle beam source, the charged particle column and the sample chamber;
All elements of the plurality of motorized devices are configured to be powered solely by the DC voltage supplied from the first converter when activated while the charged particle beam source is in operation. Charged particle beam system.   The charged particle beam system of claim 1, wherein the shortest distance between the first transducer and each of the charged particle beam source, the charged particle column, and the sample chamber is at least 2 meters. Particle beam system. 3. The charged particle beam system according to claim 1 or 2, further comprising a second transducer, the second transducer being configured to provide a high voltage applied to the charged particle beam source. And the second converter converts the output DC voltage of the first converter into the high voltage.