JP2010182596A - Charged particle beam apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to detect charged particles discharged along on an optical axis. <P>SOLUTION: The charged particle beam apparatus is provided with an acceleration tube electrode 30 for accelerating primary electron beams 1 from an electron gun, a magnetic field lens 2 converging the primary electron beams on a test piece 3, a speed-reduction electrode 6 for speed-reducing the primary electron beams, a scanning coil 4 for scanning on the testpiece by the primary electron beams, a detection system for detecting secondary electrons generated from the test piece 3, and a display unit 13 for displaying a secondary electron image based on the detected secondary electrons. Between the electron gun and the acceleration tube electrode 30, there are arranged a reflection electrode 34 of a doughnut shape to which a negative voltage is impressed and an Einzel lens 32 for focusing the secondary electrons from the test piece 3 on the optical axis in the tube before the reflection electrode 34 in the tube of the acceleration tube electrode 30, respectively, and the detection system is composed of a first detecting unit which has an open port through which the primary electron beams from the electron gun are passed and detects the secondary electrons from the test piece 3 and a second detecting unit which has an open port through which the primary electron beams from the electron gun are passed and detects the secondary electrons which are sent back by the reflection electrode 34 in the test piece direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charged particle beam apparatus including a detector that detects charged particles from a sample.

  In recent years, scanning electron microscopes have been used for inspection of circuit patterns in semiconductor integrated circuits.

  In such a scanning electron microscope, for example, the primary electron beam is controlled in focus in a state in which the influence of chromatic aberration is reduced by maintaining high energy in the acceleration field, and the primary electrons incident on the sample in the deceleration field. There is a technique for observing a sample with a low acceleration voltage and a high resolution by reducing the beam energy.

  FIG. 1 shows a schematic example of such a scanning electron microscope.

  In the figure, 1 is an electron beam (primary electron beam) emitted from an electron gun (not shown), 2 is a magnetic lens that forms a magnetic field for focusing the primary electron beam on the sample 3, and 4 is the primary electron. A scanning coil for forming a deflection field for scanning the sample 3 with the beam 1 in the X and Y directions, respectively, and a cylindrical acceleration tube 5 for forming an electric field for accelerating the primary electron beam 1 in the sample direction An electrode is provided along the scanning coil 4 and the magnetic lens 2.

  Reference numeral 6 denotes a conical deceleration electrode that forms a deceleration field for decelerating the accelerated primary electron beam 1 immediately before the sample, and 7 is a sample stage on which the sample 3 is placed.

  8 is a control device that performs various commands and calculations, 9 is a scanning control device that creates a scanning signal based on the command from the control device, and sends the scanning signal to the scanning coil 4. 10 is a command from the control device 8 The magnetic field lens control device sends an exciting current to the magnetic field lens 2 based on the above.

  Reference numerals 11a and 11b denote secondary electron detectors that respectively detect secondary electrons 12a and 12b emitted from the sample 3 by scanning with the primary electron beam 1, and are provided along the optical axis O. Each secondary electron detector is connected to the control device 8 via an amplifier (not shown) and an AD converter (not shown).

  Reference numeral 13 denotes a display device that displays a secondary electron image and the like regarding the observation region on the sample 3 based on the secondary electron signal sent to the control device 8.

  14 is a variable power source that applies a positive voltage to the acceleration tube electrode 5 based on a command from the control device 8, and 15 is a variable power source that applies a positive voltage to the deceleration electrode 6 based on a command from the control device 8. It is. O is the optical axis (electron optical central axis).

  In the scanning electron microscope having such a configuration, the primary electron beam 1 from an electron gun (not shown) energized with an acceleration voltage of, for example, +1 KV is applied to the acceleration field of the acceleration tube electrode 5 to which, for example, +5 KV is applied. Thus, the energy is energized at +6 KV. For example, the decelerating electrode 6 to which +5 KV is applied passes in the same energy energized state. Such a primary electron beam is decelerated by the decelerating lens L formed between the decelerating electrode and the sample at the ground potential, and the sample 3 is energized with an acceleration voltage of +1 KV. Will be incident on. At this time, the primary electron beam 1 is focused on the sample 3 by the magnetic lens 2, and a predetermined region on the sample is scanned by the scanning coil 4.

  The secondary electrons emitted from the sample 3 by such scanning act as an acceleration lens L (acceleration field L for the primary electron beam 1) formed between the sample 3 and the deceleration electrode 6. The decelerating lens L acts as an accelerating lens when viewed from the secondary electrons from the sample) and enters the accelerating tube electrode 5 through the opening of the decelerating electrode.

  Then, the light is once focused by the magnetic field of the magnetic lens 2 and then diverges. Secondary electrons 12a having a large divergence angle are transmitted to the secondary electron detector 11a, and secondary electrons 12b having a small divergence angle are converted to the secondary electrons. Each is detected by the electron detector 11b.

  The output signals from the secondary electron detectors 11a and 11b are sent to the control device 8 via an amplifier (not shown) and an AD converter (not shown), respectively. And according to the command from the control device, a secondary electron image of the sample based on each secondary electron signal is displayed on the display screen of the display device 12. The secondary electron signals may be added and an image based on the added signal may be displayed.

Japanese Patent Application Laid-Open No. 2004-221089

Now, the amount of secondary electrons emitted from the sample 3 has direction dependency.
FIG. 2 shows each emission angle θ when the primary electron beam 1 is perpendicularly incident on the surface of the sample 3 (0 degree on the primary electron beam and +90 on the sample surface when the angle is increased clockwise). In contrast, the amount of secondary electrons emitted with respect to the sample surface when the angle is increased counterclockwise is assumed to be −90 degrees). The smaller the absolute value of the emission angle θ, the smaller the secondary electrons. The amount of emission is large, and the amount of secondary electron emission decreases as the absolute value of the emission angle increases.

  In consideration of the direction dependency of the amount of secondary electron emission, the scanning electron microscope shown in FIG. 1 has secondary electron detectors 11a and 11b arranged vertically along the optical axis O, and the sample. Among the secondary electrons emitted from 3, those having a relatively large emission angle (with a relatively large divergence angle) 12 a are converted into those having a relatively small emission angle (with a divergence angle of 12) by the secondary electron detector 11 a at the lower stage. (Relatively small) 12b is detected by the upper secondary electron detector 11b.

  However, secondary electrons emitted along the vicinity of the optical axis O (secondary electrons emitted along the vicinity of the optical axis O), that is, the absolute value of the emission angle is extremely small (divergence angle). Secondary electrons (which are extremely small) cannot be detected by any of the secondary electron detectors 11a and 11b.

  However, the amount of such secondary electrons having an extremely small absolute value of the emission angle is extremely large as shown in FIG.

  For this reason, the amount of secondary electron signals contributing to the secondary electron image display of the display device 13 is not sufficient, and the image quality is deteriorated.

  The present invention has been made to solve such problems, and an object thereof is to provide a novel charged particle beam apparatus.

  The charged particle beam apparatus of the present invention includes a charged particle beam generation source, a tubular acceleration lens system for accelerating the charged particle beam from the charged particle beam source, and focuses the charged particle beam from the charged particle beam source onto a sample. A focusing lens system for accelerating and decelerating the focused charged particle beam, a scanning lens system for scanning the sample with the charged particle beam, and secondary charged particles generated from the sample by the scanning. In a charged particle beam apparatus comprising a detection system for detecting and a display means for displaying a secondary charged particle image of the sample based on the detected secondary charged particles, the charged particle beam source and the acceleration lens system, A donut-shaped reflective electrode to which a voltage for repelling secondary charged particles from the sample in the direction of the sample is applied between the sample and the sample in the tube of the acceleration lens system. A second focusing lens system for focusing the next charged particles on the optical axis in the tube in front of the reflecting electrode is disposed, and the detection system has an opening through which the charged particle beam from the charged particle beam source passes. And a second detector that detects secondary charged particles from the sample and an aperture through which the charged particle beam from the charged particle beam source passes, and is returned to the sample by the reflective electrode. And a second detector for detecting charged particles.

  According to the present invention, secondary electrons emitted along the vicinity of the optical axis O with a large amount of emission (secondary electrons emitted along the vicinity of the optical axis O), that is, the absolute value of the emission angle. Can be detected efficiently even for secondary electrons having a very small (a very small divergence angle). Therefore, a high quality sample image can be obtained.

It is a figure which shows the example of 1 structure of the conventional scanning electron microscope. It is a figure which shows an example of the distribution which showed the direction dependence of the amount of secondary electron emission. It is a figure which shows the example of 1 structure of the scanning electron microscope which is an example of the charged particle beam apparatus of this invention. It is a figure which shows the other structural example of the scanning electron microscope which is an example of the charged particle beam apparatus of this invention. It is a figure which shows the other structural example of the scanning electron microscope which is an example of the charged particle beam apparatus of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 3 shows a schematic example of a scanning electron microscope which is an example of the charged particle beam apparatus of the present invention. In the figure, the same reference numerals as those used in FIG. 1 denote the same components.

  In the figure, reference numeral 30 denotes a cylindrical acceleration tube electrode, and a donut-shaped electrode 31 is attached to the upper end facing an electron gun (not shown), and both the donuts are located near the center of the side wall in the acceleration tube electrode. The electrodes on both outer sides of the Einzel lens 32 made up of three shaped electrodes are attached. A control voltage is applied to the central electrode 32c of the Einzel lens from a variable power source 33 that operates based on a command from the control device 8.

  Reference numeral 34 denotes a donut-shaped reflective electrode to which a negative voltage is applied from a variable power source 35 that operates based on a command from the control device 8.

  In the figure, reference numeral 40 denotes a secondary electron detection unit, which includes light guides 36a and 36b, a donut-shaped reflecting plate 37 whose both surfaces (upper and lower surfaces) form a reflecting surface, donut-shaped scintillators 38a and 38b, a through tube 39, and photoelectrons. It consists of multipliers 40a and 40b. The configuration will be described in detail below.

  The light guides 36a (hereinafter referred to as the first ride guide) and 36b (hereinafter referred to as the second ride guide) are both cut at an oblique angle of 45 degrees, and both the cut surfaces sandwich the light reflecting plate 37. The other end of each is attached to the acceleration electrode tube wall so as to penetrate the wall of the acceleration electrode tube 30. In addition, a hole is formed in the center of the tip portion of the light guides 36a and 36b abutted with each other with the light reflection plate 37 interposed therebetween.

  A scintillator 38a (hereinafter referred to as a first scintillator) having an electron detection surface facing the sample side is provided on the lower surface of the front end portion of the first light guide 36a, and is located above the front end portion of the second light guide 36b. A scintillator 38b (hereinafter referred to as a second scintillator) having an electron detection surface facing the electron gun (not shown) is attached to the surface. A hole is formed in the center of each scintillator.

  Further, it follows the hole in the center of the first scintillator 38a, the hole in the center of the abutting surface of the first light guide 36a and the second light guide 36b, and the hole in the center of the second scintillator 38b. The through pipe 39 is fitted into the hole.

  The photomultiplier tubes 40a and 40b are provided at the other ends of the first and second light guides 36a and 36b, respectively. Each photomultiplier tube is connected to the control device 8 via an amplifier (not shown) and AD conversion (not shown).

  In the scanning electron microscope thus configured, for example, the primary electron beam 1 from an electron gun (not shown) energized with an acceleration voltage of +1 KV is applied to the acceleration tube electrode 30 to which, for example, +5 KV is applied. The energy is energized at +6 KV in the acceleration field, and, for example, passes through the deceleration electrode 6 to which +5 KV is applied in the same energy energized state. Such a primary electron beam is decelerated by the decelerating lens L formed between the decelerating electrode and the sample at the ground potential, and the sample 3 is energized with an acceleration voltage of +1 KV. Will be incident on. At this time, the primary electron beam 1 is focused on the sample 3 by the magnetic lens 2, and a predetermined region on the sample is scanned by the scanning coil 4.

  For example, secondary electrons of several eV to several tens eV emitted from the sample 3 by such scanning are accelerated by an acceleration lens L of an acceleration field formed between the sample 3 and the deceleration electrode 6. , And enters the acceleration tube electrode 5 through the opening of the deceleration electrode. At this time, the secondary electrons are energized at +5 KV in the acceleration field of the deceleration electrode 6 and the acceleration tube electrode 30 and once converged by the magnetic field of the magnetic lens 2 and then diverge.

  Of the emitted secondary electrons, secondary electrons 60a having a relatively large divergence angle (relatively large emission angle) hit the first scintillator 38a, and the scintillator corresponds to the amount of secondary electrons. Generating light. The light is reflected by the reflecting plate 37 and is detected by the first photomultiplier tube 40a through the first light guide 36a. The photomultiplier tube converts the detected light into an electrical signal and sends it to the control device 8 via an amplifier (not shown) and an AD converter (not shown). The control device sends a command to the display device 13, and a secondary electron image of the sample based on the secondary electron signal is displayed on the display screen of the display device 13.

  On the other hand, among the scattered secondary electrons, secondary electrons 60b that diverge along the very vicinity of the optical axis including secondary electrons having a relatively small divergence angle (small emission angle) and the optical axis O are It passes through the through pipe 39 and reaches the Einzel lens 32. Among the secondary electrons having a relatively small divergence angle, some of the relatively large divergence angles do not enter the through tube 39. In order to put such a thing into the through-tube 39, the voltage applied to the deceleration electrode 6 may be changed to change the trajectory of the secondary electrons.

  A positive or negative voltage is applied to the central electrode 32 c of the Einzel lens 32 from the variable power source 33 in accordance with a command from the control device 8. Therefore, the secondary electrons approaching the Einzel lens 32 are focused on the optical axis O in the acceleration tube electrode 30 by the lens action of the Einzel lens.

  The secondary electrons once focused in this manner diverge and rise thereafter, and pass through the hole of the electrode 31 attached to the tip of the acceleration tube electrode.

  At this time, the reflective electrode 34 is minus in consideration of the maximum energy value of secondary electrons (several eV to several 10 eV) at the time of sample emission from the variable power source 35 based on the command of the control device 8. Several tens of volts are applied.

  Then, the secondary electrons that have passed through the hole of the electrode 31 are decelerated by the action of the deceleration lens W formed between the electrode and the reflective electrode 34, and the energy of the secondary electrons when the sample is emitted. It is decelerated to a value (several eV to several tens eV) and approaches the reflective electrode 34.

  The secondary electrons approaching the reflective electrode 34 in this way are repulsed in the direction of the sample 3 by the reflective electrode, and at the same time, the acceleration lens W ( The deceleration lens W acting as a deceleration field for the secondary electrons acts as an acceleration lens when viewed from the secondary electrons repelled by the reflective electrode 34) and passes through the hole of the electrode 31. It enters the accelerator tube electrode 30 and is energized at +5 KV by the acceleration field of the accelerator tube electrode.

  The secondary electrons hit the first scintillator 38b, and the scintillator generates an amount of light corresponding to the amount of secondary electrons. The light is reflected by the reflection plate 37, passes through the second light guide 36b, and is detected by the second photomultiplier tube 40b. The photomultiplier tube converts the detected light into an electrical signal and sends it to the control device 8 via an amplifier (not shown) and an AD converter (not shown). The control device sends a command to the display device 13, and a secondary electron image of the sample based on the secondary electron signal is displayed on the display screen of the display device 13.

  Thus, in the present embodiment, secondary electrons emitted along the vicinity of the optical axis O (secondary electrons emitted along the vicinity of the optical axis O) are also detected by the secondary electron detector. Since it can be detected, a high-quality secondary electron image can be obtained.

  A secondary electron image based on a secondary electron signal from the photomultiplier tube 40a (a signal based on a secondary electron having a relatively large divergence angle (a large emission angle)) and a secondary electron image from the photomultiplier tube 40b. Secondary electron images based on secondary electron signals (secondary electrons having a relatively small divergence angle (small emission angle) and secondary electrons radiating along the vicinity of the optical axis including the optical axis O) are separately displayed. However, the secondary electron signals may be added and a secondary electron image based on the added signal may be displayed.

  Further, a minus several tens of volts in consideration of the maximum energy value of secondary electrons (several eV to several tens of eV) at the time of sample emission is applied to the reflective electrode 34, and various energy coming toward the reflective electrode is applied. Although all the secondary electrons are repelled by the reflective electrode, the negative voltage value applied to the reflective electrode may be varied in consideration of the secondary electrons in the energy value range to be obtained. For example, if a secondary electron having an energy value in the range of AeV to BeV is to be obtained, a negative A′V is applied to the reflective electrode 34 to obtain a secondary electron having an energy value equal to or lower than AeV. After applying negative B′V to the reflective electrode 34 to obtain secondary electrons having an energy value of BeV or less, the difference between the latter secondary electrons and the former secondary electrons may be obtained.

  In the example shown in FIG. 3, the obliquely cut end surfaces of the first light guide 36a and the second light guide 36b are abutted with each other via a light reflecting plate 37 that forms a double-side reflecting surface, and the first scintillator 38a. The through-tube 39 in the hole so as to be along the hole in the center of the first light guide 36a and the hole in the center of the butted surface of the second light guide 36b and the hole in the center of the second scintillator 38b. The first light guide 36a and the first light guide 36a are arranged as shown in FIG. 4 (in the figure, the same reference numerals as those used in FIG. 3 indicate the same components). The first light guide 36a 'may be disposed below and the second light guide 36b' may be disposed above the Einzel lens 32 with the respective end surfaces of the second light guide 36b not being in contact with each other. . In this case, the light reflecting plate 37a having a reflecting surface on the side facing the sample 3 and the reflecting plate 37b having a reflecting surface on the side facing the electron gun (not shown) are respectively the first and second lights. As shown in the drawing, through-tubes 39a and 39b, which are provided on the front end surface of the guide in an oblique cut shape and are apparently divided, are provided at the front end portions of the first and second light guides.

  In the apparatus having such a configuration, a signal based on the secondary electrons 60a having a relatively large divergence angle (a large emission angle) is transmitted through the first scintillator 38a, the reflector 37a, and the first light guide 36a ′. Based on secondary electrons 60b obtained by a single photomultiplier tube 40a and including secondary electrons that diverge along the vicinity of the optical axis including the optical axis O and have a relatively small divergence angle (small emission angle). The signal is obtained in the second photomultiplier tube 40b through the through tubes 39a and 39b, the reflective electrode 34, the second scintillator 38b, the reflective plate 37b, and the second light guide 36b ′.

  Further, the scintillators 38a and 38b, the light guides 36a and 36b, the light reflecting plate 37, and the photomultiplier tubes 40a and 40b are not used. Instead, as shown in FIG. The same reference numerals as those shown in FIG. 1 indicate the same components), and an annular electronic detection amplifier 200a (referred to as a first electronic detection amplifier) and 200b (referred to as a second electronic detection amplifier) such as a microchannel plate. Alternatively, the through-tube 201 may be fitted into the central space, and may be arranged vertically on the optical axis O below the Einzel lens 32. In this case, the electronic detection amplifiers 200a and 200b are connected to the control device 8 via amplifiers (not shown), current-voltage converters (not shown), and AD converters (not shown). .

  In the apparatus having such a configuration, a signal based on the secondary electrons 60a having a relatively large divergence angle (a large emission angle) is obtained by the first electron detection amplifier 200a and includes the optical axis O including the optical axis O. A signal based on a secondary electron 60b having a relatively small divergence angle (a small emission angle) including secondary electrons diverging along the vicinity is transmitted through the through-tube 201 and the reflective electrode 34 to the second electron detection amplifier 200b. can get.

  A magnetic field coil that is a rotationally symmetric lens may be provided instead of the Einzel lens 32 in the above example.

  In the above example, the stage 7 is grounded to the ground and the sample 3 is set to the ground potential. However, a voltage is applied to the stage, and a deceleration lens is provided between the acceleration tube electrode 30 and the sample. (Acceleration lens) may be formed.

  In the above example, the secondary electrons are detected to display the secondary electron image of the sample. However, the reflected electrons may be detected to display the reflected electron image of the sample.

  In the above example, a scanning electron microscope is shown as an example of the charged particle beam apparatus of the present invention. However, the present invention can also be applied to other charged particle beam apparatuses such as a focused ion beam.

  When applied to a focused ion beam apparatus, secondary ions from the sample may be detected and a secondary ion image of the sample may be displayed. In this case, a positive voltage is applied to the reflective electrode 34 in order to drive back secondary ions (usually positive secondary ions) from the sample toward the sample. As a matter of course, a secondary ion detector is used in the detection system in place of the secondary electron detector or the backscattered electron detector.

DESCRIPTION OF SYMBOLS 1 Primary electron beam 2 Magnetic lens 3 Sample 4 Scan coil 5, 30 Acceleration tube electrode 6 Deceleration electrode 7 Stage 8 Controller 9 Scan controller
DESCRIPTION OF SYMBOLS 10 Magnetic lens control apparatus 11a, 11b Secondary electron detector 12a, 12b Secondary electron 13 Display apparatus 14, 15 Variable power supply 31 Electrode 32 Einzel lens 33 Variable power supply 34 Reflective electrode 35 Secondary electron detection unit 36a, 36b, 36a ', 36b' Light guide
37, 37a, 37b Reflector
38a, 38b scintillator
39, 39a, 39b Through pipe
40a, 40b Photomultiplier tubes 60a, 60b Secondary electrons 200a, 200b Electron detection amplifier 201 Through tube

Claims (6)

  Charged particle beam generation source, tubular acceleration lens system for accelerating the charged particle beam from the charged particle beam source, focusing lens system for focusing the charged particle beam from the charged particle beam source onto the sample, the acceleration and focusing A decelerating lens system for decelerating the charged particle beam, a scanning lens system for scanning the sample with the charged particle beam, a detection system for detecting secondary charged particles generated from the sample by the scanning, and the detection In a charged particle beam apparatus having display means for displaying a secondary charged particle image of the sample based on the secondary charged particles, a secondary particle from the sample is interposed between the charged particle beam source and an acceleration lens system. A doughnut-shaped reflective electrode to which a voltage for repelling secondary charged particles in the direction of the sample is applied, and secondary charged particles from the sample are placed in the tube of the acceleration lens system. A second focusing lens system for focusing on the optical axis of the tube, and an aperture through which the charged particle beam from the charged particle beam source passes, and the secondary charging from the sample. A first detector for detecting particles, and a second detector for detecting secondary charged particles repelled in the direction of the sample by the reflective electrode, having an aperture through which the charged particle beam from the charged particle beam source passes. A charged particle beam system consisting of   The first detector includes a first light guide whose tip is cut obliquely and a doughnut-shaped scintillator is attached to the lower surface of the tip, and a photomultiplier tube that converts an optical signal from the light guide into an electric signal. The second detector includes a second light guide whose tip is cut obliquely and a donut-shaped scintillator is attached to the top of the tip, and a photomultiplier tube that converts an optical signal from the light guide into an electrical signal. The charged particle beam device according to claim 1, wherein the tip surfaces of the light guides are abutted via a donut-shaped light reflecting plate.   The first detector includes a first light guide having a tip cut obliquely, a doughnut-shaped scintillator attached to the lower surface of the tip, and a donut-shaped light reflecting plate attached to the cut surface. The second detector comprises a photomultiplier tube for converting an optical signal into an electrical signal. The second detector has a tip cut obliquely, a donut-shaped scintillator attached to the top surface of the tip, and a donut-shaped light on the cut surface. The second light guide is provided with a reflector and a photomultiplier tube for converting an optical signal from the light guide into an electric signal. The former is the acceleration on the sample side with the second focusing lens system in between. The charged particle beam apparatus according to claim 1, wherein the latter is disposed in a tube of the system, and the latter is disposed in the tube of the acceleration system on the reflective electrode side.   The first detector and the second detector are both composed of an electronic amplifier. The former electronic amplifier is placed in the tube of the acceleration system on the sample side, and the latter electronic amplifier is placed in the tube of the acceleration system on the reflective electrode side. 2. The charged particle beam apparatus according to claim 1, wherein each of the charged particle beam apparatuses is arranged.   The charged particle beam apparatus according to claim 1, wherein the second focusing lens system comprises an Einzel lens. The charged particle beam apparatus according to claim 4, wherein the electronic amplifier is a microchannel plate.

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