JP2008257914A - Beam apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a beam apparatus acquiring a sample image sufficiently reflecting composition information of the observed sample by efficiently detecting reflected electrons. <P>SOLUTION: A beam apparatus has a beam source 1, an objective lens 4 focusing a primary beam 2 onto the sample 5, and a diaphragm 7 mounted between the beam source 1 and the objective lens 4. In addition, the beam apparatus is provided with; a detector 15 detecting particles to be detected generated from the diaphragm 7 by having the reflected electrons 10 generated from the sample 5 in response to radiation of the primary beam 2, a hollow shaped electrode 14 with a central axis positioned on an optical axis of the primary beam 2 with an opening provided on a side surface facing the detector 15. The particles to be detected are moved from the diaphragm 7 to the detector side 15 through the opening due to the effect of an electric field formed by the electrode 14 and the moved particles passed through the diaphragm 7 to be detected are detected by the detector 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a beam apparatus using a beam such as a scanning electron microscope.

  FIG. 1 is a diagram showing a configuration of an electron optical system in a scanning electron microscope. Here, the scanning deflector is omitted in FIG.

  The primary electron beam 2 emitted from the electron source 1 is accelerated to a predetermined acceleration voltage and then shaped into a perfect circle by the beam shaping diaphragm 7. Then, the electron beam 2 is focused by the objective lens 4 so that the focal point of the electron beam 2 is positioned on the sample surface of the observation sample 5. In this state, a scanning deflector (not shown) scans the electron beam 2 on the sample surface of the observation sample 5, thereby detecting secondary signals (secondary electrons, reflected electrons, etc.) generated from the sample surface. . Based on the detection result, a scanned image (sample image) of the sample surface is created.

  Usually, the beam shaping diaphragm 7 has a beam current limiting function, and the beam current is increased or decreased by changing the excitation intensity of a condenser lens (not shown) between the beam shaping diaphragm 7 and the electron source 1. It is possible to make it. When such control is performed to increase or decrease the beam current, the position of the virtual light source viewed from the objective lens 4 changes, and the objective lens 4 cannot control the appropriate focusing angle (the opening angle of the electron beam 2). Here, the resolution of the scanned image depends on the beam diameter on the observation sample 5, and the beam diameter greatly depends on the focusing angle.

  The smallest beam diameter is obtained at the optimum focusing angle, and the resolution of the scanned image is maximized. Therefore, by using the focusing lens 3, it is possible to correct the change in the virtual light source position and thereby focus the electron beam 2 on the sample surface at an appropriate focusing angle.

  A method for detecting a secondary signal in the prior art is shown in FIGS. FIG. 2 is a diagram showing a trajectory of secondary electrons generated from the observation sample 5. FIG. 3 is a diagram showing the trajectory of the reflected electrons generated from the observation sample 5. 2 and 3, a charged particle detector 8 is provided between the focusing lens 3 and the objective lens 4.

  The secondary electrons 10 emitted from the observation sample 5 have various directions and energies, but fly in a certain orbit according to the field of the objective lens 4 and the field of the surrounding structure. Here, it is possible to fly the secondary electrons 10 in the direction of the charged particle detector 8 by appropriately designing the objective lens 4 and surrounding structures.

  In FIG. 2, since the secondary electrons 10 have lower energy than the primary electron beam 2, they receive a large focusing action in the magnetic field of the objective lens 4 and make zero or more crossovers. If the trajectory of the secondary electrons 10 when diverging through the magnetic field is in the direction of divergence, the charged particle detector 8 is reached. A scanning image is formed based on the detection result of the secondary electrons 10 detected by the charged particle detector 8. Usually, the position where the detection efficiency of secondary electrons is the best is determined by electron optical simulation or experiment, and the charged particle detector 8 is arranged at the position.

  In FIG. 3, since the reflected electrons 9 have many components having substantially the same energy as the primary electron beam 2, the focusing effect on the reflected electrons 9 by the magnetic field of the objective lens 4 is not large. Therefore, the reflected electrons 9 reach the charged particle detector 8 without making a crossover. The charged particle detector 8 has a hole through which the primary electron beam 2 passes. When the diameter of the orbital range of the reflected electrons 9 is larger than the diameter of the holes, the reflected electrons 9 can be detected by the charged particle detector 8. The detection result is also added to form a scanned image.

  However, when the diameter of the orbital range of the reflected electrons 9 is smaller than the hole diameter, the reflected electrons 9 cannot be detected by the charged particle detector 8.

  Here, the difference between secondary electrons and reflected electrons will be described. Since the secondary electrons have low energy and only those generated on the extreme surface of the observation sample are emitted to the outside of the observation sample, they are suitable for capturing an image of the surface of the observation sample. On the other hand, since reflected electrons have higher energy than secondary electrons, they have information from the back side of the observation sample, and are suitable for capturing the composition of the observation sample.

  This type of conventional device has a source side detector and a sample side detector on the optical axis, and these detectors detect almost all of the secondary electrons emitted from the sample. A technique is known (see Patent Document 1).

  An apparatus having a first detector and a second detector is known for detecting secondary electrons or reflected electrons generated based on the interaction between the primary electron beam and the sample. (See Patent Document 2).

  Furthermore, there is known an apparatus that can separate and detect secondary electrons and reflected electrons from a sample with an apparatus having a simple structure (see Patent Document 3).

  A first detector for detecting secondary electrons emitted from the sample; and a second detector for detecting secondary electrons that have passed through the holes of the first detector. An apparatus is known in which secondary electrons can be detected by synthesizing or separating outputs (see Patent Document 4).

JP 2000-30654 A Japanese Patent Application Laid-Open No. 2004-221089 JP 2000-299078 A JP-A-9-219170

  In the prior art, the diameter of the hole that becomes the path of the primary electron beam 2 of the charged particle detector 8 is set larger than the diameter of the orbital range of the reflected electrons 9. Therefore, it is difficult to detect the reflected electrons 9 emitted from the observation sample 5.

  Specifically, the beam diameter of the reflected electrons 9 is about several hundred μm, whereas the path (hole) of the primary electron beam 2 in the charged particle detector 8 is at least about 500 μm to 1 mm unless the primary electron beam is opened. 2 is affected by scattering or the like.

  Here, in the beam shaping diaphragm 7 disposed between the electron source 1 and the focusing lens 3, the diameter (diaphragm diameter) of the hole through which the primary electron beam 2 passes is about 30 μm. Therefore, if a signal based on the reflected electrons that have reached the beam shaping diaphragm 7 can be detected efficiently, the reflected electrons can be detected efficiently as a result.

  The present invention has been made in view of the above points, and provides a beam apparatus that can efficiently detect reflected electrons and thereby obtain a sample image in which composition information of an observation sample is sufficiently reflected. The purpose is to provide.

  A beam apparatus according to the present invention is disposed between a beam source that emits a primary beam, an objective lens that focuses and irradiates a primary beam emitted from the beam source on a sample, and the beam source and the objective lens. In a beam device having an aperture, secondary particles generated secondary from the sample in response to irradiation of the primary beam reach the aperture, thereby detecting a detected particle generated from the aperture, and a beam source A hollow electrode having a central axis located on the optical axis of the primary beam and having an opening provided on a side surface facing the detector, and is detected from the diaphragm by the action of an electric field formed by the electrode. The particles move to the detector side through the opening, and the detected particles thus moved are detected by the detector.

  In the present invention, a secondary particle secondarily generated from the sample in response to the irradiation of the primary beam reaches the stop, thereby providing a detector for detecting detected particles generated from the stop, and from the beam source. A hollow electrode having a central axis located on the optical axis of the primary beam and having an opening provided on a side surface facing the detector is provided, and particles to be detected from the diaphragm are caused by the action of an electric field formed by the electrode. The particles to be detected move to the detector side through the opening, and the detected particles are detected by the detector.

  Thereby, the said to-be-detected particle can be attracted | sucked to the detector side by the effect | action of the electric field formed by the said electrode. Therefore, it is possible to efficiently detect a signal (the detected particle) based on the secondary particles that have reached the aperture from the sample, and as a result, the secondary particles can be detected efficiently.

  Therefore, when the secondary particle is a reflected electron, a signal based on the reflected electron can be detected efficiently, and as a result, the reflected electron can be detected efficiently.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a schematic configuration diagram showing a beam apparatus according to the present invention.

  This beam apparatus includes an electron source (beam source) 1, an objective lens 4 that focuses and irradiates a primary electron beam (primary beam) 2 generated from the electron source 1 onto an observation sample 5, and the electron source 1 and the objective lens. 4, a focusing lens 3 disposed between 4, a beam shaping diaphragm (diaphragm) 7 disposed between the electron source 1 and the focusing lens 3, and a scanning deflector (not shown), and a scanning electron microscope It has the composition of.

  The beam shaping diaphragm 7 is provided with a hole through which the primary electron beam 2 passes. The diameter of the hole is set to about 30 μm, which is sufficiently smaller than the diameter of the orbital range of the reflected electrons generated from the observation sample 5.

  An electron detector (detector) 15 is disposed on the observation sample 5 side of the beam shaping diaphragm 7 and in the vicinity of the beam shaping diaphragm 7. In the electron detector 15, reflected electrons (secondary particles) 10 that are secondarily generated from the observation sample 5 in response to the irradiation of the primary electron beam 2 reach the beam shaping diaphragm 7, and thereby the beam shaping diaphragm 7. This is for detecting the detected electrons generated from. Here, the detected electrons are secondary electrons. Note that a charged particle detector, which is disposed between the focusing lens 3 and the objective lens 4 and detects secondary electrons generated from the observation sample 5 in response to the irradiation of the primary electron beam 2, is not shown. .

  An electrode 14 is disposed between the beam shaping diaphragm 7 and the focusing lens 3. As shown in FIG. 5, the electrode 14 has a central axis located on the optical axis of the primary electron beam 2 from the electron source 1, and an opening 18 is formed on a side surface 14 of the electrode 14 facing the electron detector 15. It consists of a provided hollow-shaped annular electrode.

  Further, the beam shaping diaphragm 7 is movable in a direction orthogonal to the optical axis of the primary electron beam 2, and two slits 17 a and 17 b through which the beam shaping diaphragm 7 can pass during the movement are side surfaces of the electrode 14. 14a. Here, the two slits 17a and 17b are formed at positions facing each other. An intermediate portion of the slit 17a located on the electron detector 15 side is connected to an upper end portion of the opening 18 formed therebelow.

  A flange 14b is provided at the lower end of the electrode 14 (the end located on the observation sample 5 side). The flange 14b is connected to a flange of a liner tube (not shown).

  The electrode 14 is made of phosphor bronze or aluminum. This is because phosphor bronze and aluminum are non-magnetic materials and have electrical conductivity. If the electrode 14 is configured using a material made of a magnetic material, an unnecessary deflection action is exerted on the primary electron beam 2, which is not preferable.

  In addition, a potential that is a predetermined negative potential is applied to the electrode 14 by the power source 16 with respect to the beam shaping diaphragm 7. This potential is set in a range between −10 V and less than OV. The beam shaping diaphragm 7 is at a ground potential (ground potential).

  Here, as a reference, FIG. 6 shows a perspective view (bird's eye view) when the electrode 14 is viewed from the electron detector 15 side. In the drawing, the thickness of each part of the electrode 14 is not shown.

  The operation of the beam apparatus of the present invention having such a configuration will be described.

  The primary electron beam 2 emitted from the electron source 1 is accelerated to a predetermined acceleration voltage and then shaped into a perfect circle by the beam shaping diaphragm 7. Then, the electron beam 2 is focused by the objective lens 4 so that the focal point of the electron beam 2 is positioned on the sample surface of the observation sample 5. In this state, the electron beam 2 is scanned on the sample surface of the observation sample 5 by a deflection scanner (not shown). Thereby, the electron beam 2 is irradiated on the sample surface of the observation sample 5.

  The reflected electrons 10 generated from the observation sample 5 in response to the irradiation of the electron beam 2 include the objective lens 4, a charged particle detector (not shown) for detecting secondary electrons from the observation sample 5, and the focusing lens 3. Passes and reaches the beam shaping stop 7.

  Here, as described above, the hole provided in the beam shaping diaphragm 7 has a diameter sufficiently smaller than the diameter of the orbital range of the reflected electrons 10. Therefore, the reflected electrons 10 that have reached the beam shaping diaphragm 7 collide with the peripheral portion of the hole.

  In this way, secondary electrons 18 serving as particles to be detected are generated from the portion of the beam shaping diaphragm 7 where the reflected electrons 10 collide (see FIG. 5).

  Here, the above-described negative potential is applied to the electrode 14 shown in FIG. 5 by the power source 16 with respect to the beam shaping diaphragm 7 set to the ground potential. Thus, an electric field is formed inside the electrode 14 to which the negative potential is applied.

  An opening 18 is formed in a portion of the side surface 14 a of the electrode 14 facing the electron detector 15. Due to the presence of the opening 18, the optical axis (beam axis) of the primary electron beam 2 in the electrode 14. The nearby electric field is asymmetric. As a result, the electric field becomes a deflection electric field that attracts the secondary electrons 11 to the electron detector 15 side through the opening 18.

  Thereby, the secondary electrons 11 generated from the beam shaping diaphragm 7 can be efficiently detected by the electron detector 15.

  Here, FIG. 7 shows a simulation result when a voltage that is negative with respect to the ground potential of the beam shaping diaphragm 7 is applied to the electrode 14 by the power source 16.

  The detection efficiency of the secondary electrons 11 by the electron detector 15 was about 6% when the voltage applied to the electrode 14 was 0 V (the same potential as the beam shaping aperture 7).

  On the other hand, when the voltage applied to the electrode 14 was −3 V, the detection efficiency was improved to 80%.

  Therefore, it is effective to apply a negative potential to the electrode 14 with respect to the potential of the beam shaping aperture 7. As the negative potential applied to the electrode 14, a negative potential set in a range between −10 V and 0 V (less than 0 V) is preferable.

  The magnitude of the deflection electric field formed in the electrode 14 when a negative potential in the range is applied to the electrode 14 is substantially in the trajectory of the primary electron beam 2 having energy of several hundred eV to several keV. It is so small that it has no effect. Therefore, the detection efficiency of the secondary electrons 11 by the electron detector 15 can be improved without increasing the deflection aberration of the primary electron beam 2. Here, when the electric potential is further lower than −10 V, in order to attract the secondary electrons 11 to the electron detector 15, the attracting electric field generated from the tip of the electron detector 15 is affected. The detection efficiency of the secondary electrons 11 is deteriorated. Accordingly, the setting range of the potential is desirably −10V to less than 0V.

  Here, FIG. 7 shows a liner tube 33 connected to a focusing lens and an objective lens (not shown) located on the rear stage side. The flange 14b of the electrode 14 is fixed to the flange 24 of the liner tube 33 with a bolt or the like.

  Next, a first modification of the present invention will be described with reference to FIG. In this modification, the basic configuration is the same as that of the above-described embodiment, except that an energy filter 19 is disposed between the focusing lens 3 and the objective lens 4.

  The operation of this modification is the same as that of the above embodiment. Here, the secondary particles 10 generated from the observation sample 5 and reaching the beam shaping aperture 7 actually include reflected electrons including elastic backscattered electrons and multiple scattered electrons having lower energy than that, In some cases, secondary electron components may be included. Elastic backscattered electrons are electrons having substantially the same energy as that of the primary beam among reflected electrons.

  In such a case, for example, only the elastic backscattered electrons are extracted and detected from the secondary particles 10 mainly composed of reflected electrons, and a scanning image based on the elastic backscattered electrons is formed. Only the elastic backscattered electrons 10a are extracted by passing the secondary particles 10 generated from the energy through the energy filter 19.

  Then, the extracted elastic backscattered electrons 10 a reach the beam shaping aperture 7. Secondary electrons 11 are generated from the beam shaping diaphragm 7 where the elastic backscattered electrons 10 a have reached, and the secondary electrons 11 are detected by the electron detector 15.

  Thereby, the scanning image based on the elastic backscattered electrons 10a can be acquired. This elastic backscattered electron 10a is a secondary signal that largely reflects the information of the composition contrast (composition difference) of the observation sample 5, and the scanned image obtained based on the elastic backscattered electron 10a is the composition contrast. Becomes a clearly displayed scanning image.

  Here, since the energy of the elastic backscattered electrons 10a is substantially the same as the energy of the primary electron beam 2, the intensity of the energy filter 19 is such that the secondary particles 10 having an energy lower than the energy of the primary electron beam 2 are subjected to beam shaping. What is necessary is just to set it as the intensity | strength which can be deflected so that it may not reach the aperture_diaphragm | restriction 7. FIG.

  As the configuration of the energy filter 19, for example, the configuration of a Wien filter can be used. Further, instead of this configuration, an electric field deflector or a magnetic field deflector can be used.

  Next, a second modification of the present invention will be described with reference to FIG. In this modification, instead of the energy filter used in the first modification, a lens pair including a deceleration lens 31 and an acceleration lens 32 is provided.

  In the figure, a decelerating lens 31 is provided between the objective lens 4 and the observation sample 5. An acceleration lens 32 is provided between the focusing lens 3 and the objective lens 4.

  In such a configuration, the secondary electron focusing action of the acceleration lens 32 produces the same action as the energy filter.

  Therefore, also in this configuration, only the elastic backscattered electrons 10 a can be extracted from the secondary particles 10, and only the elastic backscattered electrons 10 a can reach the beam shaping aperture 7. Secondary electrons 11 are generated from the beam shaping diaphragm 7 where the elastic backscattered electrons 10a have arrived, and the secondary electrons 11 are detected by the electron detector 15 to obtain a scanning image based on the elastic backscattered electrons 10a. Can do.

  The beam apparatus of the present invention includes a beam source 1 that emits a primary beam 2, an objective lens 4 that focuses and irradiates a primary beam 2 emitted from the beam source 1 onto a sample 5, and the beam source 1 and the objective lens 4. In the beam apparatus having the diaphragm 7 disposed between the secondary particles 10, secondary particles 10 that are secondarily generated from the sample 5 in response to the irradiation of the primary beam 2 reach the diaphragm 7, and are thereby generated from the diaphragm 7. A hollow electrode having a detector 15 for detecting the detected particle 11 and a central axis positioned on the optical axis of the primary beam 2 from the beam source 1 and having an opening 18 on a side surface 14a facing the detector 15. 14, and the detected particle 11 from the diaphragm 7 moves to the detector 15 side through the opening 18 by the action of the electric field formed by the electrode 14, and the detected particle 11 thus moved becomes the detector 15. Detected by

Here, the diaphragm 7 is movable in a direction perpendicular to the optical axis, and the electrode 14 is formed with a slit 17 through which the diaphragm 7 passes, and is located on the sample 5 side of the electrode 14. A flange 14 b is provided at the end. Further, a potential set in a range between −10 V and less than 0 V with respect to the potential of the diaphragm 7 is applied to the electrode 14.

  The electrode 14 is made of phosphor bronze or aluminum.

  The secondary particles 10 are reflected electrons, and the detected particles 11 are secondary electrons.

  Furthermore, an energy filter 19 may be provided between the diaphragm 7 and the sample 5, and specific secondary particles extracted by the energy filter 19 may reach the diaphragm 7.

  Further, a decelerating lens 31 is provided between the objective lens 4 and the sample 5, and an accelerating lens 32 is provided between the focusing lens 3 and the objective lens 4, and extraction is performed by a lens pair including the decelerating lens 31 and the accelerating lens 32. The specified secondary particles may reach the diaphragm 7.

  Here, the specific secondary particles to be extracted can be elastic backscattered electrons.

  As described above, in the present invention, the secondary particles 10 that are secondarily generated from the sample 5 in response to the irradiation of the primary beam 2 reach the diaphragm 7, thereby detecting the detected particles 11 generated from the diaphragm 7. A detector 15 is provided, and a hollow electrode 14 having a central axis located on the optical axis of the primary beam 2 from the beam source 1 and having an opening 18 on a side surface 14a facing the detector 15 is provided. Due to the action of the electric field formed by 14, the detected particle 11 from the diaphragm 7 moves to the detector 15 side through the opening 18, and the detected particle 11 thus moved is detected by the detector 15.

  Thereby, the to-be-detected particle | grains 11 can be attracted | sucked to the detector 15 side by the effect | action of the electric field formed by the electrode 14. FIG. Therefore, a signal (detected particle 11) based on the secondary particles 10 reaching the diaphragm 7 from the sample 5 can be detected efficiently, and as a result, the secondary particles 10 can be detected efficiently.

  Therefore, when the secondary particle 10 is a reflected electron, a signal based on the reflected electron can be detected efficiently, and as a result, the reflected electron can be detected efficiently.

It is a figure which shows the structure of the scanning electron microscope in a prior art. It is a figure which shows the trajectory of the secondary electron which generate | occur | produced from the observation sample. It is a figure which shows the track | orbit of the reflected electron which generate | occur | produced from the observation sample. It is a schematic block diagram which shows the beam apparatus in this invention. It is sectional drawing which shows the structure of the electrode in this invention. It is a perspective view which shows the structure of the electrode in this invention. It is a figure which shows the simulation in this invention. It is a schematic block diagram which shows the 1st modification in this invention. It is a schematic block diagram which shows the 2nd modification in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron source (beam source), 2 ... Primary electron beam (primary beam), 3 ... Condensing lens, 4 ... Objective lens, 5 ... Observation sample (sample), 7 ... Beam shaping stop (stop), 10 ... Reflected electron (Secondary particles), 11 ... detected particles (secondary electrons), 14 ... electrodes, 14a ... side surfaces, 15 ... electron detector (detector)

Claims (10)

In a beam apparatus comprising: a beam source that emits a primary beam; an objective lens that focuses and irradiates the primary beam emitted from the beam source onto a sample; and a diaphragm disposed between the beam source and the objective lens. The secondary particles generated secondarily from the sample in response to the irradiation of the primary beam reach the stop, thereby detecting the detected particles generated from the stop, and on the optical axis of the primary beam from the beam source. It has a hollow electrode with a central axis located and an opening provided on the side facing the detector, and the detected particles from the diaphragm are detected through the opening by the action of the electric field formed by the electrode. A beam device characterized in that the detected particles moved to the detector side and moved thereby are detected by the detector. The beam apparatus according to claim 1, wherein the diaphragm is movable in a direction orthogonal to the optical axis, and a slit through which the diaphragm is formed is formed in the electrode. The beam apparatus according to claim 1 or 2, wherein a flange is provided at an end portion of the electrode located on the sample side. The electric potential set in the range between -10V or more and less than 0V is applied to the electrode with respect to the electric potential of the diaphragm when the detection target particle is detected by the detector. Item 4. The beam device according to any one of Items 1 to 3. 5. The beam apparatus according to claim 1, wherein the electrode is made of phosphor bronze or aluminum. 6. The beam apparatus according to claim 1, wherein the secondary particles are reflected electrons. The beam apparatus according to claim 1, wherein the detected particles are secondary electrons. 8. The energy filter is provided between the diaphragm and the sample, and specific secondary particles extracted by the energy filter reach the diaphragm. 9. Beam device. A decelerating lens is provided between the objective lens and the sample, and an accelerating lens is provided between the stop and the objective lens, and extraction is performed by a lens pair including the decelerating lens and the accelerating lens. The beam device according to any one of claims 1 to 7, wherein the specified secondary particles reach the diaphragm. The beam device according to claim 8 or 9, wherein the specific secondary particles to be extracted are elastic backscattered electrons.

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