JP2015220130A - Optical microscopy device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To capture the optical image at a part, irradiated with a charged particle beam and a microscopic image is taken in, clearly and brightly without moving a sample.SOLUTION: An optical microscopy device 10 is provided, in a vacuum vessel 12, with an electron beam irradiation system 21 having the vacuum vessel 12 where a stage 13 is provided in a sample chamber 11, and irradiating the observation part of a sample W with an electron beam, and an electron beam detector 26 for detecting the microscopic image by the secondary electron beam from the observation part. An optical imaging system 31 for capturing the optical image of the observation part is provided in the vacuum vessel 12, and a light source 36 for illumination, illuminating the observation part, is arranged in the sample chamber 11. The observation part is irradiated directly with the illumination light from the light source for illumination.

Description

  The present invention relates to an optical microscope for use in a charged particle beam apparatus that obtains a microscopic image of a sample, that is, an observation image, by irradiating the sample with a charged particle beam and captures an optical image of the sample surface.

  Examples of the charged particle beam apparatus that obtains an observation image based on a signal obtained by irradiating a sample with a charged particle beam include a scanning electron microscope (SEM) using an electron beam and a scanning transmission electron microscope (STEM). . A scanning electron microscope is used to obtain a microscopic image of a sample surface by detecting secondary electrons and reflected electrons generated when an electron beam is irradiated on a sample to be observed. Is used to obtain a microscopic image inside the sample based on electrons scattered and diffracted in the sample by transmitting an electron beam while scanning the sample. All electron microscopes have a high magnification of several tens of thousands of times.

  In such a charged particle beam apparatus, since it is necessary to confirm which part or region of the microscopic image obtained by electron beam irradiation is in the sample, an optical microscope with a lower magnification than the charged particle beam apparatus Is attached. The magnification observation apparatus described in Patent Document 1 includes a vacuum vessel provided with a sample chamber, that is, a body as a chamber, and a high-magnification electron beam imaging device for acquiring a microscopic image of the sample in the sample chamber; A low-magnification optical imaging device that captures an optical image of the sample is provided on the body, and an objective lens of the optical imaging device faces a portion where the sample is irradiated with an electron beam.

  The inspection and measurement apparatus described in Patent Document 2 has a chamber as a vacuum container provided with a sample chamber, and a wafer holder that is movable in two X- and Y-axis directions is disposed in the sample chamber. In the chamber, an electron optical system that irradiates an electron beam toward the sample, a detector that detects a secondary electron beam, and an optical microscope unit are provided in the chamber. The sample to be observed is moved by the stage to a position where the electron beam is irradiated and a position facing the optical microscope unit.

  Patent Document 3 describes a charged particle beam mapping projection optical system. This optical system has a chamber as a vacuum container provided with a sample chamber, and a sample is arranged so as to be movable in two axial directions of X and Y provided in the sample chamber. A primary column provided with an irradiation optical system for irradiating a sample with a charged particle beam for irradiation, and a secondary column provided with a mapping projection optical system for irradiating an electron beam detector with an observation charged particle beam emitted from the sample. A column is provided in the chamber. In order to capture an optical image of a microscopic image, an objective lens of an optical microscope is incorporated in the secondary column. The sample to be observed is moved by the stage to the position where the electron beam is irradiated and the position facing the objective lens of the optical microscope, as in the inspection and measurement apparatus described in Patent Document 2.

JP 2012-15027 A JP 2013-33739 A JP 2000-3692 A

  As described in Patent Document 1, when the objective lens of the optical imaging device is arranged to face a portion irradiated with an electron beam, a microscopic image is captured and an optical image is simultaneously captured without moving the sample. Can do. On the other hand, as described in Patent Documents 2 and 3, the stage is moved to the target visual field after confirming the irradiation region of the electron beam in advance by the optical microscope, but what is necessary to move the stage mechanically? Some fine adjustments are required. Thus, it takes time to search for a field of view. In order to move the stage to the field of view, a microscopic image and an optical image could not be obtained simultaneously.

  In the conventional charged particle beam apparatus described above, a light source is disposed outside the charged particle beam apparatus in order to irradiate light on a portion of a microscopic image and capture an optical image with an optical microscope. In the magnifying observation apparatus described in Patent Document 1, illumination light is irradiated onto a sample stage from an illumination unit connected to a light source by a fiber. Moreover, the optical microscope part described in Patent Document 2 has a CCD camera arranged in a chamber, and light from a light source attached to the chamber is irradiated to a part imaged by the CCD camera. Furthermore, in the mapping projection optical system described in Patent Document 3, light from an externally arranged light source is irradiated onto the sample through a fiber.

  As described above, in the method in which the light source and the objective lens are arranged outside the chamber as a vacuum vessel, the illumination light irradiated on the sample and reflected from the sample does not sufficiently enter the objective lens of the optical imaging device, and a bright optical image is obtained. There is a problem that imaging cannot be performed. In particular, when the optical imaging device is opposed to the part to which the electron beam is irradiated, the distance between the electron beam imaging device and the sample is narrow. Therefore, in the structure where the light source is arranged outside, the illumination light is sufficiently irradiated to the sample. There is a problem that is not done.

  An object of the present invention is to make it possible to take a clear and bright image of an optical image of a site where a microscopic image is captured by irradiation with a charged particle beam without moving the sample.

  The optical microscope of the present invention has a sample chamber regulated to a pressure equal to or lower than atmospheric pressure, a vacuum vessel in which a sample stage is provided in the sample chamber, a vacuum vessel provided in the vacuum vessel, and disposed on the sample stand A particle beam irradiation system for irradiating the sample with a charged particle beam, a microscopic image detection system for detecting a microscopic image with a secondary particle beam from the observation site irradiated with the particle beam, and the vacuum facing the observation site An optical imaging system that is provided in the container and captures an optical image of the observation site; and an illumination light source that is disposed in the sample chamber and illuminates the observation site.

  An optical imaging system is arranged opposite to an observation site for obtaining a microscopic image of the sample arranged in the vacuum vessel, and the optical image of the microscopic image is directly taken by the optical imaging system. Since the observation site is directly irradiated with the light from the illumination light source disposed in the vacuum vessel, a clear and bright optical image can be captured by the optical imaging system.

It is the schematic which shows one Embodiment of an optical microscope. It is the schematic which shows the imaging optical path in an example of the optical imaging system shown in FIG. (A) is an observation region image showing a test pattern of a sample, and (B) to (D) are optical images of the image formation surface when the incidence angle of the image formation surface is changed. It is the schematic which shows the specific structure of the optical imaging system which forms an optical image. It is a characteristic diagram of LED as a light source for illumination which illuminates the observation site | part of a sample. It is the schematic which shows the other specific example of an optical imaging system. It is the schematic which shows the other specific example of an optical imaging system.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the optical microscope 10 has a chamber in which a sample chamber 11 is provided, that is, a vacuum vessel 12, and the sample chamber 11 has a pressure lower than atmospheric pressure, that is, a vacuum pressure by a vacuum pump (not shown). Pressure is adjusted. The vacuum vessel 12 is provided with a sample stage 13 on which a sample W such as a wafer is placed. The sample stage 13 supports the sample W so as to be movable in the horizontal plane, that is, in the horizontal X and Y 2 axis directions.

  The vacuum vessel 12 is provided with an electron beam irradiation system 21 as a particle beam irradiation system. The electron beam irradiation system 21 includes a column 22, and an electron beam source 23 that irradiates an electron beam as a charged particle is provided at the base end portion of the column 22. In the column 22, a condenser lens 24, a scanning deflector 25, and the like are provided, and an electron beam irradiation system 21 is configured by these, and the electron beam emitted from the electron beam source 23 is the sample W The observation site is scanned and irradiated.

  In order to detect the secondary particle beam emitted from the sample, that is, the secondary electron beam by irradiating the observation site with the electron beam, the vacuum vessel 12 is provided with an electron beam detector 26. The electron beam detector 26 constitutes a microscopic image detection system for detecting a microscopic image of the observation site, and a high-magnification microscopic image is obtained based on the detection signal from the electron beam detector 26.

  In order to capture an optical image of the observation region of the sample W, the vacuum container 12 is provided with an optical imaging system 31. The optical imaging system 31 has a first optical element 32 arranged to face the observation site of the sample W, and the first optical element 32 is adjusted to a vacuum pressure in the sample chamber 11 of the vacuum vessel 12. Is provided. The vacuum container 12 is provided with a viewing window 33 made of a translucent member. The viewing window 33 transmits the image light from the first optical element 32 and closes the vacuum container 12 to reduce the vacuum pressure. The sample chamber 11 and the outside of the vacuum vessel 12 that are regulated to each other are closed.

  An imaging device 34 that captures an optical image of the observation site is provided outside the vacuum vessel 12, and image light from the first optical element 32 is captured between the imaging device 34 and the viewing window 33. A second optical element 35 that forms an image on the imaging surface of the vessel 34 is provided. Based on the detection signal from the imager 34, an optical image with a lower magnification than the microscopic image is obtained. The optical axis O of the optical imaging system 31 intersects the electron beam axis S of the electron beam irradiation system 21, and can directly capture an optical image of the observation site of the sample W irradiated with the electron beam.

  The tip of the column 22 is close to the sample W, and the electron beam axis S is substantially perpendicular to the sample W, whereas the optical axis O is used to avoid interference with the tip of the column 22. The surface is inclined at an angle θ. In order to capture a clear and bright optical image by the optical imaging system 31, an illumination light source 36 is disposed in the sample chamber 11 in the vacuum container 12. The illumination light source 36 is an LED, and is arranged in the sample chamber 11 close to the sample stage 13, that is, on the microscopic image detection system side, that is, on the column 22 side constituting the microscopic image detection system. The number of LEDs as the illumination light source 36 may be one or plural. As shown in FIG. 1, when the illumination light source 36 is disposed in the sample chamber 11, the illumination light source 36 can be brought close to the sample W, so that the observation site can be illuminated brightly.

  The optical microscope 10 has a control unit 41, and power is supplied from the control unit 41 to the electron beam source 23 and power is supplied to the illumination light source 36. A detection signal from the electron beam detector 26 is sent to the control unit 41, and a detection signal from the imager 34 is sent to the control unit 41. The control unit 41 is connected to a microscopic image display unit 42 that displays a microscopic image and an optical image display unit 43 that displays an optical image. The control unit 41 includes a microprocessor that calculates a detection signal and a memory that stores an operator, map data, and the like, and based on the detection signal from the electron beam detector 26, a high-magnification microscopic image. The calculated microscopic image is displayed on the microscopic image display unit 42. Further, the control unit 41 calculates an optical image having a magnification lower than that of the microscopic image based on the detection signal from the imaging device 34, and the calculated optical image is displayed on the optical image display unit 43.

  When the microscopic image display unit 42 and the optical image display unit 43 are displayed on separate displays arranged adjacent to each other, or when both images are displayed on the same display, the microscopic image and the optical image are displayed simultaneously. Both images can be compared. Therefore, when positioning the observation site to be irradiated with the electron beam, the operator moves the sample stage 13 while visually observing the optical image displayed on the optical image display unit 43, thereby observing the observation site. The position can be set easily. In order to obtain a microscopic image of the positioned observation site, the electron beam source 23 irradiates the sample W with the electron beam, and the secondary electron beam is detected by the electron beam detector 26. A microscopic image is displayed on the microscopic image display unit 42 based on the detected signal. The operator can compare both the display unit of the microscopic image and the optical image, and can easily change the observation site.

  2 is a schematic diagram showing an imaging optical path in an example of the optical imaging system 31 shown in FIG. 1, and FIG. 4 is a schematic showing a specific structure of the optical imaging system 31 forming the imaging optical path shown in FIG. FIG.

  In the optical imaging system 31 shown in FIG. 2, the first optical element 32 and the second optical element 35 are both constituted by lenses. The image light reflected from the observation region of the sample W passes through the first lens 32 a serving as an objective lens disposed in the sample chamber 11, and then is narrowed down by the aperture 37 and passes through the viewing window 33. The image light transmitted through the viewing window 33 forms an optical image on the imaging surface 38 of the imaging device 34 by the second lens 35a as an imaging lens disposed outside the vacuum vessel 12, that is, in the atmosphere. . Since the first lens 32a is exposed to the sample chamber 11 that is in a vacuum state, it is preferably formed by a single lens. Since the second lens 35a is exposed to atmospheric pressure, it can be formed by a compound lens.

  As shown by the arrow in FIG. 2, the image pickup device 34 is swingable, and the incident angle α of the image light with respect to the imaging plane 38 is variable. The optical axis O of the first lens 32a as the objective lens is inclined at an angle θ with respect to the sample W, and the image light from the first lens 32a becomes an image from a direction in which the observation site is inclined. Yes. Accordingly, when the imaging plane 38 is perpendicular to the optical axis O, an image of the observation site from the inclined direction is formed on the imaging plane 38, but the image light on the imaging plane 38 is imaged. By changing the incident angle, an optical image substantially corresponding to the observation site observed from the front side is formed on the imaging plane 38.

  FIG. 3A shows an observation site image as a test pattern formed on the observation site of the sample W. FIG. 3 (B) shows an incident angle α with respect to the optical axis O of 90 °, FIG. 3 (C) shows an incident angle α of 45 °, and FIG. 3 (D) shows an image formed when the incident angle α is 21 °. An optical image of the surface is shown.

  When the incident angle α is 90 °, that is, when the imaging plane 38 is perpendicular to the optical axis O, an optical image is obtained by observing the observation site from an inclined direction, but the test of the observation site shown in FIG. The optical image is crushed in the vertical direction in FIG. 3 rather than the pattern image. In addition, in FIGS. 3B and 3C, the test pattern lines on the upper and lower ends are blurred images.

  On the other hand, when the incident angle α is set to 21 °, as shown in FIG. 3D, the entire image comes into focus, and the optical image is enlarged more than the observation site image of the test pattern. In this way, by changing the incident angle α, an optical image is formed on the imaging surface 38 as a kind of zooming action. When the incident angle α at which this magnified image is obtained is within a range of ± 5 ° with reference to 21 °, it has been found that an image enlargement effect can be obtained without blurring the focus of the test pattern of the observed region image. . When the enlargement effect is obtained in this way, the optical image is for observing the presence / absence of the observation site, so that the observation site can be easily detected.

  As the LED used as the illumination light source 36, a white LED, a blue LED, a red LED, or the like can be used, and an LED having an optimal color is selected according to the type of the observation image of the sample W or the like. The LED as the illumination light source is movably mounted on a holder (not shown) so that the irradiation angle can be changed with respect to the observation site or the distance to the observation site can be changed.

  The optical imaging system 31 shown in FIG. 4 has a lens barrel 39. A first lens 32a and an aperture 37 are incorporated in the distal end portion of the lens barrel 39, and a second lens 35a is incorporated in the proximal end portion. It has been incorporated. A viewing window 33 is incorporated in the lens barrel 39, and the proximal end side and the distal end side of the lens barrel 39 are closed or sealed by the viewing window 33. The lens barrel 39 is attached to the vacuum vessel 12 at a portion close to the viewing window 33, and the space between the lens barrel 39 and the vacuum vessel 12 is sealed by a sealing member.

  The front end portion of the lens barrel 39 communicates with the sample chamber 11 of the vacuum vessel 12 through a communication hole, and the first lens 32a is exposed to the pressure in the sample chamber 11 that is regulated to atmospheric pressure or less. In contrast, the second lens 35a is exposed to the external atmospheric pressure. For this reason, when the structure between the first lens 32a and the second lens 35a in the lens barrel 39 is sealed and the observation window 33 is not used, the lens barrel 39 and the vacuum container 12 in the atmospheric pressure state are connected to each other. Although the optical axis O may be displaced from the lens barrel 39 in the attached state, as described above, when the first lens 32 a is exposed to the vacuum in the sample chamber 11, the optical axis O. Therefore, a clear optical image can be taken.

  FIG. 5 is a characteristic diagram of an LED serving as an illumination light source 36 that illuminates the observation site of the sample. In FIG. 5, the horizontal axis indicates the elapsed time since the start of LED emission, and the vertical axis indicates the LED. The temperature change of the support stand for supporting is shown. Since the illumination light source 36 is arranged in the sample chamber 11 in a vacuum state that is depressurized from the atmospheric pressure, when the LED generates heat, the heat is not released using air as a heat transfer medium, and the LED is in an overheated state. It was thought to be. However, as shown in FIG. 5, until the time a has elapsed from the start of lighting, the support base has greatly increased to the temperature T2, but thereafter there has been no significant temperature increase, and the normal continuous use time b has elapsed. It was found that the steady temperature T1 can be substantially maintained. At the steady temperature, there was no change in the light emission characteristics of the LED, that is, the light emission illuminance, and the same was true for the LED emitting any color such as red and blue.

  Therefore, even if an LED is arranged as the illumination light source 36 in the sample chamber 11 that is kept in a vacuum state when an image is detected, the LED is not heated excessively, and has a desired illuminance from the vicinity of the sample W. The observation site of the sample W could be directly irradiated with the LED. Since the observation site can be directly illuminated, a clear and bright optical image can be captured by the optical imaging system 31.

  FIG. 6 is a schematic diagram showing another specific example of the optical imaging system 31. This optical imaging system 31 has a lens barrel portion 51 that is integrally attached to the vacuum vessel 12, and an observation window 33 made of a transparent material is attached to an opening 52 provided in the lens barrel portion 51. The inside and outside of the lens barrel 51 are closed by the viewing window 33. A lens barrel portion 53 having a smaller diameter than the lens barrel portion 51 is mounted inside the lens barrel portion 51, and the first lens 32 a and the aperture 37 are attached to the lens barrel portion 53. The optical imaging system 31 shown in FIG. 6 is similar to the case shown in FIGS. 2 and 4 when looking at the structure of the lens barrel portions 51 and 53.

  FIG. 7 is a schematic view showing still another specific example of the optical imaging system. The optical imaging system 31 includes a first reflection mirror 32b and a second reflection mirror 32c. The first reflection mirror 32b faces the observation site of the sample W, and the second reflection mirror 32c The reflected light from the first reflecting mirror 32 b is reflected to the second lens 35 a through the viewing window 33. The first optical element 32 is constituted by both the reflection mirrors 32b and 32c. In particular, a toroidal mirror is used for the first reflecting mirror 32b in order to reduce astigmatism. Even in this type of mirror-type optical imaging system, when the incident angle α is set in a range of 21 ° ± 5 °, an optical image in focus can be obtained while enlarging the image of the observation site.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. In the embodiment, the sample is irradiated with an electron beam to obtain a microscopic image of the observation site. However, the optical microscope of the present invention uses an ion beam as a charged particle beam to observe or inspect the sample observation site. The present invention can also be applied to a charged particle beam apparatus for performing the above. Further, the present invention can be applied not only to SEM but also to STEM.

DESCRIPTION OF SYMBOLS 10 Optical microscope 11 Sample chamber 12 Vacuum container 13 Sample stand 21 Electron beam irradiation system 22 Column 23 Electron beam source 24 Condenser lens 25 Scan deflector 26 Electron beam detector 31 Optical imaging system 32 1st optical element 32a 1st Lens 32b First reflecting mirror 32c Second reflecting mirror 33 Viewing window 34 Imager 35 Second optical element 35a Second lens 36 Illumination light source 37 Aperture 38 Imaging surface 39 Lens barrel 41 Control unit 42 Microscopic image Display unit 43 Optical image display unit 51 Lens barrel unit 52 Opening 53 Lens barrel unit O Optical axis S Electron beam axis W Sample

Claims (8)

A vacuum chamber having a sample chamber regulated to a pressure equal to or lower than atmospheric pressure, and a sample stage provided in the sample chamber;
A particle beam irradiation system for irradiating a charged particle beam to a sample provided in the vacuum vessel and disposed on the sample stage;
A microscopic image detection system for detecting a microscopic image by a secondary particle beam from an observation site irradiated with the particle beam;
An optical imaging system that is provided in the vacuum container so as to face the observation site and captures an optical image of the observation site;
An illumination light source disposed in the sample chamber and illuminating the observation site;
Having
Optical microscope.   2. The optical microscope according to claim 1, wherein the illumination light source is an LED, and the LED is arranged closer to the microscope image detection system than the sample table and disposed in the sample chamber. The optical microscope according to claim 1 or 2,
The optical imaging system is
A first optical element disposed in the sample chamber so as to face the observation site;
A viewing window that transmits image light from the first optical element and closes the vacuum vessel;
An imager that is disposed outside the vacuum vessel and captures the optical image of the observation site;
A second optical element that is disposed outside the vacuum vessel and forms an image of the image light from the first optical element on an imaging surface of the imaging device;
Having
Optical microscope.   4. The optical microscope according to claim 3, wherein the first optical element is an objective lens and the second optical element is an imaging lens.   4. The optical microscope according to claim 3, wherein the first optical element has a first reflection mirror facing the observation site, and reflected light from the first reflection mirror is directed toward the second optical element. An optical microscope, which is a second reflecting mirror that reflects.   The optical microscope apparatus according to any one of claims 3 to 5, wherein the imaging device is swingable so that an incident angle of the image light with respect to the imaging plane is variable.   The optical microscope according to claim 6, wherein the incident angle is in a range of 21 ° ± 5 °.   8. The optical microscope apparatus according to claim 1, wherein a microscopic image display unit that displays the microscopic image and an optical image that is provided adjacent to the microscopic image display unit and displays the optical image. An optical microscope apparatus that includes a display unit and displays the microscopic image and the optical image in comparison with each other.

Images