Charge carrier beam device

Abstract

Charge carrier beam device, comprising: a charge carrier source (111) that emits a charge carrier beam (112); a gain electrode (113) arranged between the charge carrier source (111) and a sample (103) to form a path for the charge carrier beam (112) and to accelerate and decelerate the charge carrier beam (112); a first pole piece (115) that covers the amplifying electrode (113); a second pole piece (116) that covers the first pole piece (115); a first lens coil (117) arranged outside the first pole piece (115) and inside the second pole piece (116) to form a first lens (119); and a second lens coil (118) arranged outside the second pole piece (116) to form a second lens (120); characterized by a control electrode (114) formed between a distal end section of the first pole piece (115) and a distal end section of the second pole piece (116) to control an electric field (130, 131) formed between the sample (103) and the distal end section of the second pole piece (116).

Description

Technical field

[0001] The present invention relates to a charge carrier beam device. State of the art

[0002] A technique for using an intensifying magnetic field lens superimposed with an electric field lens in a charge carrier beam device (see patent reference 1) is disclosed. An advantage of an objective lens from patent reference 1 is, for example, the high resolution for low-energy observation using an electrostatic retardation field. Patent reference 2 shows an objective lens arrangement comprising a first, second, and third pole piece, each substantially rotationally symmetric. The first, second, and third pole pieces are arranged on the same side of an object plane. One end of the first pole piece is separated from one end of the second pole piece to form a first slit, and one end of the third pole piece is separated from one end of the second pole piece to form a second slit.A first excitation coil generates a focusing magnetic field in the first slit, and a second excitation coil generates a compensating magnetic field in the second slit. A first and a second power source supply current to the first and second excitation coils, respectively. A magnetic flux generated in the second pole piece is oriented in the same direction as a magnetic flux generated in the second pole piece.

[0003] Patent literature 3 describes a scanning electron microscope in which an objective lens has an upper, a lower, and an outer magnetic pole piece. The bore diameter of the lower magnetic pole piece is smaller than that of the upper and outer magnetic pole pieces. The lens field between the upper and lower magnetic pole pieces is generated for observing a large sample located at a large working distance. The lens field between the lower and outer magnetic pole pieces is generated to obtain an image of the sample.

[0004] Patent reference 4 shows a scanning electron microscope in which a tubular yoke is formed around another yoke. A magnetic pole is attached to the lower end of the yoke. An excitation coil is wound between the aforementioned yokes to form the lens field between the lower magnetic pole and the upper magnetic pole. The excitation current is supplied to the excitation coils from a DC power source. Literature on the state of the art Patent literature PTL1: JP H012 - 98 633 A PTL2: WO 2007 / 060 017 A2 PTL3: US 4 419 581 A PTL4: JP S57-118357A Brief description of the invention: Technical problem

[0005] According to patent literature 1, the resolution can deteriorate depending on the condition of a sample. For example, if a sample surface has irregularities or if the sample is inclined with respect to an optical axis through which a charge carrier beam travels, the electric field lens formed on the sample is distorted and the performance of the objective lens is degraded.

[0006] It is therefore an object of the invention to provide a charge carrier beam device that is capable of realizing high-resolution observations by preventing distortion of the electric field lens. Solution to the problem

[0007] A charge carrier beam device according to one aspect of the invention comprises: a charge carrier source emitting a charge carrier beam; a gain electrode arranged between the charge carrier source and a sample to form a path for the charge carrier beam and to accelerate and decelerate the charge carrier beam; a first pole piece covering the gain electrode; a second pole piece covering the first pole piece; a first lens coil arranged outside the first pole piece and inside the second pole piece to form a first lens; a second lens coil arranged outside the second pole piece to form a second lens; and a control electrode formed between a distal end section of the first pole piece and a distal end section of the second pole piece to control an electric field formed between the sample and the distal end section of the second pole piece. Beneficial effect

[0008] According to the invention, it is possible to provide a charge carrier beam device that is capable of realizing high-resolution observations by preventing the distortion of an electric field lens. Brief description of the drawings [ Fig. 1] Fig. Figure 1 is a schematic representation of a REM. [ Fig. 2] Fig. Figure 2 is a detailed view of the REM. [ Fig. 3] The Fig. Figures 3A to 3C are schematic views of an electric delay field. [ Fig. 4] The Fig. 4A to 4C are cross-sectional views of a division unit made up of various components that form a lens. [ Fig. 5] Fig. Figure 5 is a cross-sectional view of an in-housing detector mounted on a split position. [ Fig. 6] The Fig. Figures 6A to 6D are schematic views of methods for fastening the division unit. [ Fig. 7] The Fig. Figures 7A to 7B are schematic views of methods for introducing a voltage into a control electrode. [ Fig. 8] Fig. Figure 8 is a schematic representation of a FIB-REM. Description of embodiments

[0009] The following embodiments describe a scanning electron microscope (hereinafter referred to as "SEM") as an example of a charge carrier beam device; however, the invention is not limited thereto and can be applied to an ion fine beam scanning electron microscope (hereinafter referred to as "FIB-SEM"), a scanning transmission electron microscope (RTEM), and the like. First embodiment

[0010] Fig. Figure 1 is a schematic representation of the SEM. The SEM comprises an SEM housing 102, which irradiates a sample 103 with a primary charge carrier beam (here a primary electron beam), a sample chamber 101 on which the housing 102 is mounted and which holds the sample during observation, a base frame 100 on which the sample chamber 101 is mounted, a monitor (display unit) 104, which displays an image, and a control unit 105, which controls a system of the entire SEM.

[0011] Fig. Figure 2 is a detailed view of the SEM. The SEM housing 102 comprises an electron source 111 that emits a primary electron beam 112, an objective lens that focuses the primary electron beam 112 onto the sample 103, a gain electrode 113 and a control electrode 114 that accelerate the primary electron beam 112 from directly below the electron source 110 to a distal end of the objective lens in order to pass through the objective lens in a high-energy state, and detectors 122 and 123 that detect signal electrons 121 generated from the sample 103 by irradiation with the primary electron beam 112. When the primary electron beam 112 is accelerated by the amplification electrode 113 and the control electrode 114, the energy of the primary electron beam 112 is increased when receiving a focusing effect through the objective lens, and accordingly the lens error is reduced and the resolution is improved.

[0012] The objective lens is a type of magnetic field lens 119 superimposed with an electric field and featuring two modes. One is a non-immersion magnetic field lens 119 (immersion-free mode) without magnetic field transmission to the sample; the other is an immersion magnetic field lens 120 (immersion mode) that generates a magnetic field on the sample. The former is suitable for analysis without the influence of a magnetic field and for observing a magnetic sample, as there is no magnetic field transmission to the sample. The latter is suitable for high-resolution observation by shortening the lens focal length through the generation of a magnetic field on the sample. In this way, it is possible to perform a wide range of analyses by selectively using the lens mode of the magnetic field lens according to the application.

[0013] The non-immersion magnetic lens 119 (first lens) is formed between a first pole piece 115 and a second pole piece 116 by supplying current to a first lens coil 117 located outside the first pole piece 115 and inside the second pole piece 116. Conversely, the immersion magnetic field lens 120 (second lens) is formed between the second pole piece 116 and the sample 103 by causing a current to flow through a second lens coil 118 located outside the second pole piece 116. The intensity of these magnetic field lenses can be controlled by the control unit 105, which regulates the currents flowing through the coils to focus the primary electron beam 112 onto the sample 103.

[0014] The first pole piece 115 and the second pole piece 116 have an axially symmetrical hollow cone shape and are formed from a soft magnetic material, such as pure iron or Permendur. Furthermore, the open hole of the second pole piece 116 on the sample side is smaller than the open hole of the first pole piece 115 on the sample side.

[0015] The first pole piece 115 and the second pole piece 116 are arranged between the electron source 111 and the sample 103, and the second pole piece 116 is arranged outside the first pole piece 115. A sample-side distal end section of the second pole piece 116 is arranged closer to the sample than a sample-side distal end section of the first pole piece.

[0016] The detectors that detect signal electrons include the housing-internal detectors 122 mounted in the SEM housing 102 and the sample chamber detector 123 mounted in the sample chamber 101. For example, a detector with a scintillator or a detector with a semiconductor is used.

[0017] The Fig. Figures 3A to 3C are schematic views of an electric delay field, wherein Fig. 3A shows a second electric delay field that is formed on the sample, Fig. 3B shows a second electric delay field at the time of sample inclination and Fig. 3C shows a reduced second electrical delay field.

[0018] The amplification electrode 113 has a hollow cylindrical shape which is axially symmetric with respect to an optical axis 110 and is arranged within the first pole piece 115 from directly below the electron source to below a distal end of the first pole piece 115 on the sample side.

[0019] The control electrode 114 has a hollow cone shape, which is axially symmetric with respect to the optical axis 110 and is arranged between the amplifying electrode 113 and the second pole piece 116.

[0020] A positive voltage is applied to the amplifying electrode 113, and a voltage lower than that of the amplifying electrode 113 and higher than that of the sample 103 is applied to the control electrode 114. When the voltage values ​​of the amplifying electrode 113 and the control electrode 114 are different, a first electric retardation field 130, which retards the primary electron beam 112, is formed by a potential difference, and a second electric retardation field 131, which retards the primary electron beam 112, is formed by a potential difference between the control electrode 114 and the second pole piece 116 and the sample 103. Here, the distance between the distal end section of the second pole piece 116 and the sample 103, as well as the voltage applied to the control electrode 114, is adjusted to a suitable value.In this way, the second electric delay field 131 is mainly formed by the potential difference between the control electrode 114 and the second pole piece 116, and the discharge of the electric field onto the sample 103 can be prevented.

[0021] That is, the amplifying electrode 113, the control electrode 114, the second pole piece 116 and the probe 103 are arranged electrically independently of each other and V s ≤ V c ≤ V b is fulfilled if the voltage applied to sample 103 is expressed as V s The voltage applied to the control electrode 114 is defined as V c is defined and the voltage applied to the amplification electrode 113 is defined as V b is defined.

[0022] For example, if the distance between the distal end section of the second pole piece 116 and the sample 103 is 4 mm, the scattering loss of the electric field at the sample can be prevented if the voltage value of the control electrode 114 is approximately 100 V relative to the grounded sample. Therefore, it is possible to prevent the distortion of the second electric delay field 131, which is generated depending on the sample shape, such as irregularities on the sample surface and the sample inclination, and to prevent a deterioration of the lens performance caused by the sample shape.

[0023] Furthermore, the voltage values ​​of the amplification electrode 113 and the control electrode 114 can be changed at will via a GUI (display unit 104) that operates the SEM. This makes it easy to change the voltage values ​​of the electrodes under the observation conditions.

[0024] By setting the voltage of the amplification electrode 113 to a constant value at the time of switching the mode of the objective lens and by changing only the voltage value of the control electrode, it is possible to use the objective lens independently of the change in the optical condition that accompanies the change in the voltage value of the amplification electrode 113.

[0025] Next, a working principle of the SEM is described. The primary electron beam 112, emitted by the electron source 111, moves at high speed within the cylinder of the gain electrode 113. In non-immersion mode, the primary electron beam 112 is focused by the non-immersion magnetic field lens 119, decelerated by the first electric deceleration field 130 and the second electric deceleration field 131, and then directed onto the sample 103. Conversely, in immersion mode, the primary electron beam 112 is focused by the immersion magnetic field lens 120 after being decelerated by the first electric deceleration field 130, then by the second electric deceleration field 131 generated on the sample 103, and finally directed onto the sample 103.In this way, the primary electron beam 112 receives high energy through acceleration by the amplifying electrode 113 and is then focused by the magnetic field lens. Accordingly, it is possible to reduce the imaging error of the primary electron beam 112 that is generated when passing through the magnetic field lens.

[0026] The primary electron beam 112, focused by the lens effect, scans the sample by means of a deflection effect of a scanning coil. When the sample 103 is irradiated with the primary electron beam 112, signal electrons 121 are emitted. The signal electrons 121 are detected by the internal detectors 122 or the sample chamber detector 123.

[0027] The delay effect of the first electric delay field 130 and the second electric delay field 131 can be controlled by controlling the voltage applied to the control electrode 114. For example, if it is desired to reduce the second electric delay field 131 on the sample by tilting the sample relative to a sample having a surface shape that is not axially symmetric to the optical axis 110 or to the optical axis, the potential of the control electrode 114 can be controlled so that it is close to the sample potential.

[0028] If it is desired to increase the resolution of the immersion-type magnetic field lens 120, the voltage value of the control electrode 114 is high to strengthen the second electric delay field 131. Furthermore, if it is desired to observe an inclined sample or a sample with surface irregularities while increasing the resolution of the non-immersion-type magnetic lens 119, the voltage value of the control electrode 114 is close to the potential of the second pole piece and the sample to weaken the second electric delay field 131.

[0029] In this way, high-resolution observation is possible in every mode of the objective lens, regardless of the sample shape. This means that distortion of the electrical delay field on the sample, which poses a problem with objective lens gain, can be prevented by the control electrode 114.

[0030] If the signal electrons 121 are secondary electrons with a low energy of approximately 50 eV, they are absorbed into the SEM housing 102 by the second electric retardation field 131. In contrast, backscattered electrons, compared to secondary electrons with relatively high energy, move in a straight line without being focused by the second electric retardation field 131. Therefore, secondary electrons and backscattered electrons can be distinguished by the intensity of the first and second electric retardation fields 131 and the arrangement of the detectors.

[0031] The Fig. Figures 4A to 4C are cross-sectional views of a division unit of 141 different components that form the objective lens. Fig. Figure 4A shows a state in which the division unit 141 is disconnected from the SEM. The division unit 141 in Fig. 4B consists of the sample-side distal end section of the amplifying electrode, the control electrode, the sample-side distal end section of the first pole piece and the sample-side distal end section of the second pole piece. Fig. Figure 4C shows an example where the sample-side distal end section of the first pole piece is not included in the division unit 141. This allows various components to be separated from the SEM if necessary. This facilitates easy repair if an electrode or pole piece forming the objective lens becomes contaminated by impurities, gas adsorption, or the like, or is damaged by a foreign substance, thus improving maintainability.

[0032] Fig. Figure 5 shows a cross-sectional view of an in-house detector 22 mounted on a splitting position. In this case, repairs are simplified if the generation of signal electrons is reduced by contamination of the detection area or if the detector fails. In addition to the in-house detector 22, a deflection element for deflecting the electron beam or a throttle hole for differential extraction can also be mounted in the splitting position. Therefore, the use of the splitting unit 141 has the advantage of simplifying the insertion of other components into the splitting position.

[0033] In the division unit 141, the reinforcing electrode, the control electrode, the first pole piece and the second pole piece are attached by means of an insulating element 140 (resin material, ceramic material or the like), since they must be electrically independent of each other.

[0034] The Fig. Figures 6A to 6D are schematic views of methods for fastening the division unit, wherein Fig. 6A shows a method for directly attaching the division unit to an upper second pole piece 116a with a screw, Fig. Figure 6B shows a method for directly attaching a lower second pole piece 116b to a screw cut into the upper second pole piece 116a and the Fig. 6C and Fig. Figure 6D shows a method for attaching the division unit using insulators, such as a resin material and a ceramic material. The lower second pole piece is in Fig. 6C at the upper second pole piece and in Fig. 6D is attached to the first pole piece. In any case, it is assumed that the end faces of the upper and lower second pole pieces are connected without gaps. Furthermore, a fastening method involving resin application and magnetic adsorption is possible.

[0035] To achieve the desired performance of the objective lens, it is necessary to align the central axes of the magnetic field lens and the electric field lens. This means that the mounting accuracy of the positions of the first and second pole pieces, which form the magnetic field lens, and the gain electrode and control electrode, which form the electric field lens, is crucial. In the present embodiment, the advantage lies in the fact that assembly efficiency can be improved through downsizing, and the module can be provided as a consumable by assembling the components requiring precise mounting accuracy as the module itself.

[0036] The Fig. 7A and Fig. Figure 7B shows schematic views of methods for introducing a voltage into the control electrode, wherein Fig. 7A shows a method for introducing a voltage from the division position of the second pole piece, and Fig. Figure 7B shows a method for introducing a voltage from a hole formed in the side face of the second pole piece. It is preferable to provide two to four holes in axial symmetry. The method for introducing a voltage into the lower amplifying electrode 113b can be a method for connecting it to the upper amplifying electrode 113a at the division position, or a method for introducing a voltage from outside the second pole piece in the same way as for the control electrode. Possible connection methods include connecting by means of a spring, connecting by means of a cable, and the like.

[0037] According to the first embodiment, by adding a control electrode in addition to the amplification electrode for accelerating the charge carrier beam, it is possible to achieve high-resolution observation by superimposing an electric field, independent of the mode of the objective lens. Furthermore, it is also possible to

[0038] To provide a charge carrier beam device that enables both high-resolution and electromagnetic field-free observation of a sample. Furthermore, by forming the sample-side distal end section of the pole piece and the electrode in modular units and designing them as a detachable structure, it is possible to ensure stable operation while improving assembly and maintainability. Second embodiment

[0039] Fig.Figure 8 is a schematic representation of the FIB-SEM (Focused Ion Beam, also known as a combined charge carrier beam device). In the FIB-SEM, an FIB housing 170 is mounted facing a sample, and the sample is processed by the FIB. Generally, the sample in the FIB-SEM is tilted so that it is orthogonal to the central axis of the FIB housing 170 during processing, and the processing is carried out by an ion beam. Therefore, if an electric delay field is formed between an objective lens and the sample, the electric field will be distorted by the sample's tilt, and this can lead to a deterioration of the lens performance, as can occur with a primary electron beam irradiation position on the sample, and thus to a deterioration of the SEM's resolution.In a device that tilts a sample relative to the SEM housing 102, such as the FIB-SEM, controlling the electrical delay field formed between the objective lens and the sample is important. In the present embodiment, controlling the electrical delay field between the objective lens and the sample via the control electrode achieves an effect of improved resolution through amplification, even for a tilted sample.

[0040] Furthermore, using the distal end of the objective lens of the FIB-SEM is also effective as a division unit. When the sample is processed by the FIB, atomized particles (atoms and molecules) are ejected from the sample. If these atomized particles adhere to the distal end of the objective lens, problems such as discharges can occur, resulting from degradation of the performance of an in-house detector and a deterioration of the insulation between the electrodes. Therefore, a detachable structure that uses the sample-side distal end of the pole pieces and an electrode as the division unit has the advantage that these components can be easily replaced if a problem arises with the in-house detector or the electrode. Reference symbol list 100 base frames 101 Sample chamber 102 SEM housings 103 Sample 104 Monitor 105 Control unit 110 Optical axis 111 Electron source 112 Primary electron beam 113 Amplification electrode 113a upper amplifying electrode 113b lower amplification electrode 114 Control electrode 115 first pole piece 116 second pole piece 116a upper second pole piece 116b lower second pole piece 117 first lens coil 118 second lens coil 119 Non-immersion magnetic field lens 120 immersion-type magnetic field lenses 121 signal electrons 122 internal detector 123 Sample chamber detector 130 first electric delay field 131 second electric delay field 132 inclined sample 140 Electrode mounting component 141 division unit 150 division unit mounting screw 151 Division unit fastening component 160 Voltage supply line 161 One-piece voltage entry 170 FIB enclosures

Claims

[1] Charge carrier beam device comprising: a charge carrier source (111) that emits a charge carrier beam (112); a gain electrode (113) arranged between the charge carrier source (111) and a sample (103) to form a path for the charge carrier beam (112) and to accelerate and decelerate the charge carrier beam (112); a first pole piece (115) that covers the amplifying electrode (113); a second pole piece (116) that covers the first pole piece (115); a first lens coil (117) arranged outside the first pole piece (115) and inside the second pole piece (116) to form a first lens (119); and a second lens coil (118) arranged outside the second pole piece (116) to form a second lens (120); characterized by a control electrode (114) formed between a distal end section of the first pole piece (115) and a distal end section of the second pole piece (116) to control an electric field (130, 131) formed between the sample (103) and the distal end section of the second pole piece (116). [2] Charge carrier beam device according to claim 1, wherein the first lens (119) is a non-immersion lens and the second lens (120) is an immersion lens. [3] Charge carrier beam device according to claim 1, further comprising: a division unit (141) which is detachably formed on the charge carrier beam device, wherein the division unit (141) comprises a distal end section of the second pole piece (116) on the sample side. [4] Charge carrier beam device according to claim 3, wherein the division unit (141) further comprises the control electrode (114) and a distal end section of the amplification electrode (113) on the sample side. [5] Charge carrier beam device according to claim 3, wherein a component can be inserted into the charge carrier beam device from a division position between the division unit (141) and the charge carrier beam device. [6] Charge carrier beam device according to claim 5, wherein the component is a detector (122) that detects charged particles generated from the sample (103). [7] Charge carrier beam device according to claim 5, wherein the component is a throttle hole for differential vacuum extraction. [8] The charge carrier beam device according to claim 5, wherein the component is a deflection element that deflects a charge carrier beam (112). [9] Charge carrier beam device according to claim 1, wherein the second pole piece (116) comprises two to four through holes which are axially symmetric on a side surface of the second pole piece (116) and which introduce a voltage into the control electrode (114). [10] Charge carrier beam device according to claim 1, wherein the amplifying electrode (113), the control electrode (114), the second pole piece (116) and the sample (103) are arranged electrically independently of each other and V s ≤ V c ≤ V b is fulfilled if a voltage applied to the sample (113) is expressed as V s is defined as a voltage applied to the control electrode (114) as V c is defined and a voltage applied to the amplification electrode (113) is defined as V b is defined. [11] The charge carrier beam device according to claim 1, wherein the distal end sections of the first and second pole pieces (115, 116) on the sample side and the distal end sections of the amplification electrode (113) and the control electrode (114) on the sample side have an axially symmetrical hollow cone shape, the distal end section of the amplification electrode (113) on the sample side is located between the distal end section of the first pole piece (115) on the sample side and the distal end section of the second pole piece (116) on the sample side, and the distal end section of the control electrode (114) on the sample side is located between the distal end section of the amplification electrode (113) on the sample side and the distal end section of the second pole piece (116) on the sample side. [12] Charge carrier beam device according to claim 1, wherein a voltage applied to the amplifying electrode (113) when a first lens coil (117) is excited and a voltage applied to the amplifying electrode (113) when a second lens coil (118) is excited are set to the same potential.

Images