JP2013145748A - Electron beam apparatus and sample observation method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron beam device which allows a primary optical system to have a precharge function and controls a region and an amount of the precharge to a sample.SOLUTION: An electron beam apparatus includes: a stage 30 on which a sample S is placed and including a moving mechanism; a primary optical system 10 generating an electronic beam having a predetermined radiation region and radiating the electronic beam to the sample S; a secondary optical system 20 detecting an electron obtaining structural information of the sample S and obtaining an image of the sample S for a predetermined visual region; and radiation region change means 13, 14 which change a position of the predetermined radiation region relative to the predetermined visual region. The radiation region change means 13, 14 change the visual region along the moving direction of the sample.

Description

  The present invention relates to an electron beam apparatus using an electron beam and a sample observation method using the same.

  Conventionally, it has a primary optical system for irradiating a semiconductor wafer with an electron beam and a secondary optical system for detecting secondary electrons or reflected electrons emitted from the semiconductor wafer and generating image data from the detection signals. An inspection apparatus for inspecting a defect of a semiconductor wafer is known.

  In such a wafer inspection apparatus using an electron beam, in order to make the charged state of the wafer surface uniform when observing a semiconductor wafer, a processing method called pre-dose or pre-charge that irradiates the semiconductor wafer with charged particles before observation is known. (For example, refer to Patent Document 1).

  In order to perform such pre-dose or pre-charge processing, a pre-charge unit is provided adjacent to a lens barrel as an electron beam source, and charged particles are applied from the pre-charge unit to the semiconductor wafer before observing the wafer by irradiating the electron beam. Irradiate to eliminate uneven charging. Thereby, the charged state on the surface of the conductor wafer becomes uniform, and a uniform image with little image unevenness can be obtained.

International Publication WO2002 / 001596

  However, in the configuration described in Patent Document 1 described above, the irradiation region for irradiating the charged particles by the precharge unit is set to be significantly wider than the visual field that is the detection region of the detector of the secondary optical system. Accordingly, since the precharge irradiation area is large, the region other than the portion to be observed is also charged up, and the elements on the wafer may be destroyed by repeating the precharge.

  Further, the optimum amount of precharge varies depending on the wiring material and insulating material of the wafer, but there is a problem that the dose amount of the charged particles irradiated from the precharge unit cannot be precisely controlled.

  Furthermore, since the precharge unit is provided in addition to the lens barrel as the electron beam source, there is a problem that the exchange of the electron source becomes complicated. In addition, the wafer inspection by the electron beam is performed in a vacuum atmosphere, but it is necessary to perform evacuation for the precharge installation area.

  Therefore, the present invention allows the primary optical system to have a precharge function so that the precharge unit can be omitted, and the precharge region and the amount of the sample are controlled so that the optimum precharge according to the sample is performed. An object of the present invention is to provide an electron beam apparatus that can be used.

In order to achieve the above object, an electron beam apparatus according to a first invention includes a stage on which a sample is placed,
A primary optical system for generating an electron beam having a predetermined irradiation region and irradiating the electron beam toward the sample;
A secondary optical system that detects electrons generated by irradiation of the sample with the electron beam and obtained structural information of the sample, and acquires an image of the sample for a predetermined field of view;
Irradiation area changing means capable of changing the position of the predetermined irradiation area with respect to the predetermined visual field area.

  Thereby, according to the sample, the positional relationship between the position of the irradiation region and the visual field region can be optimized.

A second invention is the electron beam apparatus according to the first invention,
The stage includes a moving mechanism for moving the sample,
The irradiation region changing means changes the position of the predetermined irradiation region with respect to the predetermined visual field region with respect to a relative movement direction of the predetermined irradiation region with respect to the sample. Thereby, it can be set as the electron beam apparatus which can utilize the difference in the kind of generated electron by the difference in the irradiation time of an electron beam.

A third invention is the electron beam apparatus according to the second invention, wherein
The irradiation area changing means changes the position of the predetermined irradiation area so that the predetermined irradiation area precedes the predetermined visual field area in the moving direction of the sample. Thus, the electron beam generated from the primary optical system can also function as a precharge unit, and the charged state of the sample surface can be made uniform without providing a precharge unit.

4th invention is the electron beam apparatus which concerns on 2nd or 3rd invention,
The predetermined irradiation area has an area larger than the predetermined visual field area;
The irradiation area changing means changes the position of the predetermined irradiation area so that the center of the predetermined irradiation area matches the center of the predetermined visual field area. As a result, the precharge amount can be controlled to be small.

According to a fifth invention, in the electron beam apparatus according to any one of the first to fourth inventions,
The sample is a semiconductor wafer;
The secondary optical system is characterized by detecting a short circuit or a conduction failure in a wiring in the semiconductor wafer by acquiring a voltage contrast image of the semiconductor wafer. As a result, it can be used as a wafer defect detection device that detects wiring defects in a semiconductor wafer from a voltage contrast image.

6th invention is the electron beam apparatus which concerns on 2nd invention,
The irradiation region changing means changes the position of the predetermined irradiation region so that the predetermined field of view precedes the predetermined irradiation region with respect to the moving direction of the sample. Thereby, the missing plug defect of the sample can be detected by effectively using the reflected electrons.

7th invention is the electron beam apparatus which concerns on 6th invention,
The sample is a semiconductor wafer;
The secondary optical system detects a pattern defect of the semiconductor wafer by acquiring a surface image of the semiconductor wafer. Thereby, the defect of the wiring pattern in the semiconductor wafer can be detected.

An eighth invention is a sample observation method for observing a sample based on an acquired image,
A sample placing process for placing the sample on the stage;
An electron beam irradiation step of generating an electron beam having a predetermined irradiation region and irradiating the electron beam toward the sample;
Detecting an electron generated by the electron beam irradiation step and obtaining the structural information of the sample, and obtaining an image of the sample for a predetermined visual field region; and
An irradiation region changing step of changing the position of the predetermined irradiation region with respect to the predetermined visual field region.

  Thereby, according to a sample, it can set to the positional relationship of an appropriate irradiation area | region and visual field area | region, and can observe a sample.

A ninth invention is the sample observation method according to the eighth invention,
A sample moving step of moving the stage and moving the placed sample;
The irradiation region changing step is characterized in that the position of the predetermined irradiation region is changed in a direction in which the predetermined irradiation region moves relative to the sample. Thereby, an irradiation dose amount is adjusted using an electron beam irradiation process, and an appropriate sample observation method can be set using a difference between irradiation time and generated electrons.

A tenth invention is the sample observation method according to the ninth invention,
In the irradiation region changing step, the position of the predetermined irradiation region is changed so that the predetermined irradiation region precedes the predetermined visual field region with respect to the moving direction of the sample. As a result, the same effect as the precharge can be obtained in the electron beam irradiation process without using the precharge unit, and the labor required for the precharge process can be eliminated.

An eleventh invention is the sample observation method according to the ninth or tenth invention,
The predetermined irradiation region has an area larger than the predetermined visual field region;
In the irradiation region changing step, the position of the predetermined irradiation region is changed so that the center of the predetermined irradiation region and the predetermined visual field region coincide with each other. Thereby, it is possible to perform sample observation while controlling the precharge amount to be small.

A twelfth invention is the sample observation method according to any one of the ninth to eleventh inventions,
The sample is a semiconductor wafer;
The image acquisition step is characterized by detecting a short circuit or a conduction failure in a wiring in the semiconductor wafer by acquiring a voltage contrast image of the semiconductor wafer. Thereby, it can utilize as a wafer defect inspection method which detects the wiring defect in a semiconductor wafer by a voltage contrast image.

A thirteenth invention is the electron beam apparatus according to the tenth invention, wherein
In the irradiation area changing step, the position of the predetermined irradiation area is changed so that the predetermined visual field area precedes the predetermined irradiation area in the moving direction of the sample. Thereby, a reflected electron can be detected reliably, and it can be set as the sample observation method which can detect a plug defect etc. using a reflected electron.

A fourteenth aspect of the invention is the electron beam apparatus according to the thirteenth aspect of the invention,
The sample is a semiconductor wafer;
The image acquiring step is characterized in that a pattern defect of the semiconductor wafer is detected by acquiring a surface image of the semiconductor wafer. Thereby, it can utilize as a wafer pattern defect inspection method.

  According to the present invention, the charged state of the sample surface can be made uniform without separately providing a precharge unit.

1 is an overall configuration diagram of an electron beam apparatus 100 according to an embodiment to which the present invention is applied. FIG. 4 is an aspect diagram of a positional relationship between an electron beam irradiation region 15 and a visual field region 25 of the secondary optical system 20. FIG. 2A is a diagram illustrating a mode in which the irradiation region precedes the visual field region. FIG. 2B is a diagram showing a mode in which the precharge region 16 is small. FIG. 2C is a diagram showing a mode in which the visual field region 25 precedes the irradiation region 15. It is the figure which showed the amount of electrons which reached the detector 22, and the kind of the electron over time. FIG. 3A is a diagram showing the relationship between the surface potential of the sample S and the number of electrons reaching the detector. FIG. 3B is a diagram showing the relationship between the electron beam irradiation time on the sample S and the number of electrons reaching the detector. It is a relationship diagram between the number of electrons reaching the detector from the wafer and the landing energy. 6 is a diagram for explaining an example of defect detection according to the first embodiment. FIG. 5A is a diagram showing a cross-sectional view in which the ground plug 91 and the open plug 94 are formed on the wafer W. FIG. FIG. 5B is a diagram showing a change in the surface potential of the wafer W when the electron beam is irradiated. 6 is a diagram showing the surface potential dependence of the number of electrons reaching the detector 22 of electrons emitted from the ground plug 91 and the open plug 94 in the wafer W shown in FIG. It is the figure which showed the relationship between electron beam irradiation time and the number of detector arrival electrons per unit time. It is the figure which showed the aspect of the detection method which detects an electron continuously from a reflected electron. FIG. 8A is a diagram showing the total number of electrons reaching the detector in the backscattered electron emission region of the open plug 94. FIG. 8B is a diagram showing the total number of electrons reaching the detector up to the secondary electron detection region of the open plug 94. FIG. 8C is a diagram showing the total number of electrons reaching the detector up to the mirror electron generation region of the open plug 94. It is the figure which showed the aspect which detects the open plug 94, without detecting a reflected electron from the open plug 94. FIG. FIG. 9A is a diagram showing the total number of electrons reaching the detector in the secondary electron emission region of the open plug 94. FIG. 9B is a diagram showing the total number of electrons reaching the detector in a region where secondary electrons and mirror electrons are detected from the open plug 94. It is the figure which showed the total detector arrival electron number in a mirror electron generation area. It is explanatory drawing of the aspect of the open defect inspection method about the wafer W in which the n ^<+> -p plug was formed based on Example 2. FIG. FIG. 11A is a cross-sectional view of the wafer W on which the n ⁺ -p plug 92 is formed. FIG. 11B is a diagram showing the time change of the surface potential when the wafer W is irradiated with an electron beam. It is the figure which showed the surface potential dependence of the number of detector arrival electrons about the wafer shown to Fig.11 (a). It is the figure which showed the relationship between the electron beam irradiation time when the electron beam was irradiated to the n ^<+> -p plug 92 and the open plug 94, and the number of detector arrival electrons per unit time. It is explanatory drawing of the test | inspection method which detects an electron from the time of generation | occurrence | production of a reflected electron, and detects the open plug 94. FIG. 14A is a diagram showing the total number of electrons reaching the detector in the backscattered electron detection region of the open plug 94. FIG. 14B is a diagram showing the total number of electrons reaching the detector in the secondary electron detection region of the open plug 94. FIG. 14C is a diagram showing the total number of electrons reaching the detector in the mirror electron detection region of the open plug 94. It is explanatory drawing of the aspect which concerns on the test | inspection method when not detecting the reflected electron of the open plug. FIG. 15A is a diagram showing the total number of electrons reaching the detector when the open plug 94 is in the secondary electron detection region. FIG. 15B is a diagram showing the total number of electrons reaching the detector when the open plug 94 is in the mirror electron detection region. It is a figure for demonstrating the aspect which detects the open plug 94 in the mirror electron detection area | region of the open plug 94. FIG. 6 is a diagram for explaining a wafer W to be inspected in Example 3. FIG. FIG. 17A is a view showing a cross-sectional structure of the wafer W on which the p ⁺ -n plug is formed. FIG. 17B is a relationship diagram between the electron irradiation time and the surface potential when the wafer W is irradiated with an electron beam. It is the figure which showed the surface potential dependence of the number of electrons reaching | attaining a detector about the electron which generate | occur | produced by irradiation of the electron beam to the wafer W which concerns on Example 3. FIG. FIG. 6 is a relationship diagram between an electron beam irradiation time of a wafer and the number of electrons reaching a detector according to Example 3. It is explanatory drawing of the aspect which detects a reflected electron and detects the open plug 94 about the wafer which concerns on Example 3. FIG. FIG. 20A is a diagram showing the total number of electrons reaching the detector in the backscattered electron detection region of the open plug 94. FIG. 20B is a diagram showing the total number of electrons reaching the detector in the secondary electron detection region of the open plug 94. FIG. 20C is a diagram showing the total number of electrons reaching the detector in the mirror electron detection region of the open plug 94. It is explanatory drawing of the aspect which detects the open plug 94 about the p ^<+>- n plug 93 and the open plug 94, without using a reflected electron. FIG. 21A is a diagram showing the total number of electrons reaching the detector in the secondary electron detection region of the open plug 94. FIG. 21B is a diagram showing the total number of electrons reaching the detector in the mirror electron detection region of the open plug 94. It is a mode explanatory view of a detection method for detecting an open plug 94 using a mirror electron detection region of the open plug 94. FIG. It is the figure which showed the example of the test | inspection image about the test | inspection method using a mirror electron. FIG. 23A1 shows the surface of the wafer W. FIG. FIGS. 24B1 to 24B3 are diagrams illustrating detected images in the dark image mode. It is the figure which showed the example which detects the surface defect of the wafer W using a reflected electron. 24A1 to 24A3 are views showing the surface of the wafer W. FIG. FIGS. 24B1 to 24B3 are diagrams showing detected images in the bright image mode. It is an example of the wiring of VC-TEG. FIG. 25A is a diagram illustrating an example of a normal VC-TEG. FIG. 25B is a diagram illustrating an example of a defective VC-TEG. It is the aspect diagram which test | inspected the wiring of VC-TEG using only mirror electrons. FIG. 26A is a diagram illustrating a detection image in a normal case. FIG. 26B is a diagram showing a detection image when there is a defect.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall configuration diagram of an electron beam apparatus 100 according to an embodiment to which the present invention is applied. In FIG. 1, an electron beam apparatus 100 according to the present embodiment includes a primary optical system 10, a stage 30, and a secondary optical system 20.

  The primary optical system 10 is an optical system for generating a primary electron beam (primary electron beam) and irradiating it toward the sample S. Since the primary optical system according to the present embodiment is an optical system using an electron beam (electron beam), it may be called a primary electron optical system. The primary optical system 10 may include an electron gun 11 that generates a primary electron beam, an aperture 12 that shapes the generated primary electron beam, and a primary lens system 13 that focuses the primary electron beam. These may be provided in the vacuum vessel 51. Although the details will be described later, the primary lens system 13 can adjust the irradiation direction of the primary electron beam, so that the position of the irradiation region of the primary electron beam can be changed. Therefore, the primary lens system 13 also serves as means for changing the irradiation region of the primary electron beam. In addition, since the primary lens system 13 can relatively move the irradiation region of the primary electron beam on the sample S, the primary lens system 13 also serves as a mechanism for moving the primary electron beam. Note that the irradiation region of the primary electron beam may be referred to as an illumination field.

  The primary optical system 10 may further include a Wien filter 14 and an objective lens system 18. The E × B separator 14 may be called a Wien filter, which changes the direction of the primary electron beam by an electric field and a magnetic field orthogonal to each other on a plane, and causes the primary electron beam incident obliquely downward in the vertical direction in which the sample S is present. To go to. And when the electron which obtained the structural information of the sample S generate | occur | produces, those electrons are sent to the upper direction as it is by the Lorentz force of an electric field and a magnetic field. The objective lens system 18 is a lens for finely adjusting the incidence of the primary electron beam on the last sample S.

  The E × B separator 14 can change the irradiation region of the primary electron beam by adjusting the voltage application conditions. Therefore, the role as the irradiation region changing means may be played in the same manner as the primary lens system 13 of the primary optical system 10.

  Further, an electrode (not shown) having a shape of an axial object with respect to the irradiation optical axis of the primary electron beam may be disposed between the objective lens system 15 and the sample S, and voltage control may be performed by a power supply voltage. . Thereby, the landing energy or the like at which the electron beam enters the sample S may be adjusted.

  The stage 30 is a sample stage on which the sample S is placed. The stage 30 may include a moving mechanism such as a motor or a driving mechanism, and may be configured as an XY stage that can move two-dimensionally in the XY direction on a horizontal plane. Further, the stage 30 may be provided in the main housing 60, and may be further provided and supported on the vibration isolation table 32 in the main housing 60. The main housing 60 defines a work chamber as a processing chamber for inspecting the sample S and the like. Further, the vibration isolator 32 has a role of blocking vibration from the floor as a vibration blocking device, and prevents vibration on the bottom wall of the main housing 60 from being transmitted to the stage 30.

  The stage 30 uses, for example, a plurality of tables, a Y table (not shown) that moves in the Y direction on a fixed table (not shown), and an X table that moves in the X direction on the Y table. (Not shown) may be provided so as to be movable in the XY direction by a combination of these movements. Further, a rotatable table (not shown) may be provided on the X table, the holder 31 may be arranged on the rotatable table, and the sample S may be fixed and held on the sample placement surface of the holder 31. The holder 31 may be configured such that the sample S such as a wafer is fixedly held by a mechanical or electrostatic chuck method and can be opened when inspection or the like is completed.

  The stage 30 is moved to the holder 31 on the mounting surface by operating, for example, a plurality of tables as described above, using a moving mechanism such as a servo motor or driving means, an encoder, and various sensors (not shown). You may comprise so that the supported sample S can be positioned with high precision with respect to the irradiated electron beam. Positioning control may be performed by the stage control unit 33. For example, the positioning may be performed in the X direction, the Y direction, the Z direction, and the rotation direction (θ direction) around the axis perpendicular to the support surface of the sample. For positioning in the Z direction, for example, the reference position of the mounting surface on the holder 31 is detected by a position measuring device (laser interference distance measuring device using the principle of an interferometer) using a fine diameter laser, and the position is controlled by a stage. You may make it control by the feedback circuit (not shown) in the unit 33. FIG. For example, when the sample S is a semiconductor wafer, the position of the notch or the orientation flat of the semiconductor wafer is measured to detect the planar position and the rotational position of the wafer with respect to the electron beam, and a rotary table (not shown). May be controlled by being rotated by a stepping motor or the like capable of controlling a minute angle. It is possible to standardize the signals obtained by inputting the rotation position of the wafer with respect to the electron beam and the X and Y positions in advance to a signal detection system or image processing system described later.

  The secondary optical system 20 obtains an image related to the structure of the sample S by detecting electrons obtained from the irradiation of the electron beam toward the sample S by the primary optical system 10 and obtaining information on the sample structure of the sample S. It is means of. Here, the electrons obtained from the sample structure information of the sample S include both electrons emitted from the sample S due to incidence of the electron beam on the sample S and electrons reflected immediately before entering the sample S. Good. The electrons emitted from the sample S include, for example, reflected electrons that are reflected by elastic scattering due to the incidence of the electron beam on the sample S and have reflected energy having substantially the same reflected energy, and secondary energy that is smaller in energy than the incident electron beam. In addition to electrons, backscattered electrons and the like may be included. Also, the electrons reflected without entering the sample S immediately before entering the sample S may include mirror electrons. The mirror electrons can be generated, for example, when the surface potential of the sample S is as large as the acceleration voltage of the electron gun 11. Similarly to the electrons emitted from the sample S, the mirror electrons can acquire information on the structure of the sample S. Based on this, an image of the sample structure of the sample S can be obtained.

  The secondary optical system 20 includes a secondary lens system 21 and a detector 22. The secondary lens system 21 is a lens for passing secondary electrons separated from the primary optical system 10 by the E × B separator 14, and may be composed of, for example, an electrostatic lens. This lens system also functions as a magnifying lens that magnifies an image obtained from electrons passing through the secondary optical system 20. The detector 22 is a means for detecting electrons that have passed through the secondary lens system 21 and acquiring an image of the sample structure of the sample S. The detection surface is disposed on the imaging surface of the secondary lens system 21. It is preferable.

  As the detector 22, a two-dimensional detector having a plurality of pixels on the detection surface is used. Accordingly, the detector 22 detects the electrons obtained from the structure information of the sample S with each pixel of the detection surface, and forms an image on the detection surface. Unlike the scanning electron microscope in which the electron beam apparatus 100 according to the present embodiment detects only the signal intensity of detected electrons one pixel at a time and combines them later to obtain an image, an image is obtained for a predetermined detection region. Since it is projected, it is also called a map projection type. The detector 22 of the electron beam apparatus 100 according to this embodiment includes, for example, a CCD (Charge Coupled Device), a TDI (Time Delay Integration) -CCD or an EB-CCD, an EB-TDI, or other two-dimensional pixels. A detector with can be applied. Since the CCD and the TDI-CCD detect light signals, the detector 22 includes an MCP (Micro-Channel Plate) that amplifies the amount of electrons and a fluorescent plate that converts the electrons into light. It's okay. Further, since the EB-CCD and the EB-TDI can directly detect electrons on the detection surface, they may be applied to the detector 22 as they are when they are used.

  The detection region of the detector 22 is also called a visual field, and will be referred to as a visual field region in the claims, the specification, or the drawings. Since the visual field area of the detector 22 is determined by the arrangement and configuration of the secondary lens system 21 of the secondary optical system 20, the arrangement of the detector 22, and the like, if these are fixed, the visual field area is fixed.

  In addition to the detection unit having a detection surface, the detector 22 may include an image processing unit (not shown), and electrons detected on the detection surface of the detection unit are subjected to image processing in the image processing unit, Image electronic data regarding the sample structure of the sample S may be acquired.

  The storage device 23 is means for storing image electronic data acquired by the image processing unit of the detector 22, and a commonly used memory or the like may be applied thereto.

  The computer 40 includes a display 41 and displays a sample structure image of the sample S stored in the storage unit 23. Further, the state analysis of the sample S may be performed based on the sample structure image, and the stage control unit 33 may be controlled based on the result, for example.

  Next, components related to the electron beam apparatus 100 according to the present embodiment in FIG. 1 will be described. Components related to the electron beam apparatus 100 according to the present embodiment include an optical microscope (not shown), a gate valve 61, a spare environment chamber (mini-environment chamber) 70, a pre-aligner 72, and a hoop. 73, a turbo molecular pump 74, and a dry pump 75.

  First, although not shown, the electron beam apparatus 100 according to the present embodiment may further include an optical microscope that constitutes an alignment control apparatus for positioning the sample S on the stage 30. Since the primary optical system and the secondary optical system, which have been described so far, are set to a high magnification, the magnification may be too high for rough alignment of the sample S. In such a case, a low-magnification optical microscope may be provided, and rough alignment may be performed first using the optical microscope, and then precise alignment may be performed using the electron optical system.

  The gate valve 61 is disposed between the main housing 60 and the spare environment chamber 70, and is a valve that controls communication between both chambers and sealing. By opening the gate valve 61, the sample S is transported between the main housing 60 and the preliminary environment chamber 70, and by closing the gate valve 61, individual pressures in the main housing 60 and the preliminary environment chamber 70 are obtained. Control (vacuum control) becomes possible.

  The preliminary environment chamber 70 includes a housing 71 that defines a mini-environment space whose atmosphere is controlled, and a gas circulation device (not shown) for controlling the atmosphere by circulating a gas such as clean air in the mini-environment space. And a discharge device (not shown) that collects and discharges part of the air supplied into the mini-environment space, and a substrate and a wafer that are disposed in the mini-environment space and are to be inspected A pre-aligner 72 for roughly positioning the sample S such as the above is provided. In addition, a sensor for observing the cleanliness may be provided in the mini-environment space so that the preliminary environment chamber 70 can be shut down when the cleanliness deteriorates.

  For example, when the sample S is a wafer, the pre-aligner 72 arranged in the mini-environment space is an orientation flat (orientation flat) formed on the wafer, or one or a plurality of V-types formed on the outer periphery of the wafer. A notch (notch) may be detected optically or mechanically, and the rotational position around the axis of the wafer may be pre-positioned with an accuracy of about ± 1 degree. The pre-aligner 72 is in charge of coarse positioning of the inspection object.

  The FOUP 73 is a cassette holder that holds a plurality of cassettes (not shown) in which a plurality of samples, for example, about 25 wafers S or the like are stored in a state of being arranged in parallel in the vertical direction. When the target sample S is a semiconductor wafer, the wafer stored in the cassette is a wafer to be inspected, and the inspection is performed after the process of processing the wafer in the semiconductor manufacturing process or during the process. Done. Specifically, for example, a wafer that has been subjected to a film forming process, a CMP (Chemical Mechanical Polishing) process, an ion implantation process, or the like, a wafer having a wiring pattern formed on the surface, or a wafer in which a wiring pattern has not yet been formed. It is stored in the cassette.

  The turbo molecular pump 74 and the dry pump 75 are vacuum pumps for evacuating the inside of the preliminary environment chamber 70. In the atmospheric pressure and low vacuum regions, the dry pump 75 is first operated, and at a stage where a certain degree of vacuum is obtained, the turbo molecular pump 74 is further operated in order to further increase the degree of vacuum and achieve a high vacuum. Thereby, the inside of the reserve environment chamber 70 can be made into a vacuum state.

  Although the vacuum pump is not shown in the primary optical system of the electron beam apparatus 100 according to the present embodiment, a separate vacuum pump is provided to provide the primary optical system 10, the main housing 60, and the secondary optical system. You may comprise so that the inside of 20 may be kept in a vacuum. Further, the turbo molecular pump 74 and the dry pump 75 may also be used for evacuation of the electron beam apparatus 100.

  Next, an aspect in which the position of the electron beam irradiation area is changed with respect to the visual field area in the electron beam apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating a positional relationship between the irradiation region 15 of the primary electron beam and the visual field region 25 of the secondary optical system 20.

  FIG. 2A is a diagram illustrating a mode in which the irradiation region precedes the visual field region. 2A, the mode (A-1) shows a mode in which the position of the electron beam irradiation region 15 is moved in the −Y direction on the lower side of the drawing with respect to the visual field region 25. FIG. In the aspect (A-1), the sample S moves in the + Y direction on the upper side of the paper, and the electron beam irradiation region 15 and the visual field region 25 are relatively located on the lower side (−Y side) of the sample S. It shall move. Hereinafter, it is assumed that the moving direction of the sample S is also the + Y direction and the relative moving direction of the electron beam on the sample S is the -Y direction for all the modes shown in FIG.

  In the mode (A-1), the irradiation region 15 precedes the visual field region 25 by the precharge region 16 with respect to the moving direction (+ Y) of the sample S, and the irradiation region 15 is located above the visual field region 25. The state which has the non-irradiation area | region 26 which does not cover a part of area | region is shown. This is because the area of the irradiation region 15 is set to a standard area and the position of the irradiation region 15 is moved in the −Y direction as it is, so that a portion that cannot be irradiated in the irradiation region 15 is generated. The irradiation region 15 and the visual field region 25 relatively move on the sample S while maintaining this state.

  If there is such a positional relationship between the irradiation region 15 and the visual field region 25, the irradiation region 15 always precedes the movement direction of the sample S by the precharge region 16 relative to the visual field region 25. become. Therefore, the sample S can obtain the same effect as the precharge of the precharge region 16 before the visual field region 25 is inspected, and the surface charge of the sample S can be made uniform. it can. Further, regarding the non-irradiated region 26, in the state of (A-1), electrons that obtain the structural information of the sample S are not generated from the non-irradiated region 26, and the structural information of the sample S cannot be obtained. Since the sample S moves in the irradiation region 15 by moving in the + Y direction, the structure information can be obtained immediately for the non-irradiation region 26 in a series of inspection operations, so that no problem occurs. .

  Note that the position of the irradiation region 15 may be changed by adjusting the irradiation direction of the primary electron beam by the primary lens system 13 of the primary optical system 10, and the primary lens system 13 may change the irradiation region. May serve as a means. Alternatively, the position of the irradiation region 15 may be changed by changing the voltage application condition of the E × B separator 14, or the E × B separator 14 may serve as irradiation region changing means. Good. Furthermore, the width of the precharge region 16 can be controlled by these irradiation region changing means. Therefore, by preliminarily considering the current density of the primary electron beam, the moving speed of the sample S, and the like, the precharge region 16 is determined, so that precise control of the precharge amount can be easily performed.

  As described above, according to the aspect (A-1), the irradiation region 15 is moved so as to precede the visual field region 25, so that only the primary electron beam is precharged without providing a precharge unit. The same effect as that performed can be obtained. In addition, by controlling the precharge region 16, the dose required for precharge can be precisely controlled.

  In the mode (A-2), the center of the irradiation region 15 and the visual field region 25 coincide, but the area of the irradiation region 15 in the mode (A-1) is enlarged, and the entire visual field region 25 is replaced by the irradiation region 15. It is intended to cover. The precharge region 16 that precedes the moving direction (+ Y) of the sample S functions as a precharge with respect to the visual field region 25, as in the case of (A-1).

  According to the aspect (A-2), the non-irradiated region 26 is not formed in the visual field region 25, and electrons with uniform sample structure information can be generated from the entire visual field region 25. A few uniform images can be acquired.

  In the mode (A-3), the magnification of the irradiation region 15 is made lower than that in the mode (A-2), and the center of the irradiation region 15 precedes the visual field region 25, and the entire visual field region 25 is formed. This is an aspect covered with the irradiation region 15.

  According to the aspect (A-3), since the precharge region 16 is set to be as large as possible in a range in which the irradiation region 15 can cover the entire visual field region 25, the image unevenness of the acquired image of the secondary optical system 20 Since the precharge region 16 is made as large as possible, the maximum precharge effect can be obtained in the limited primary electron beam irradiation region 15.

  Next, the aspect of FIG. 2 (B) is demonstrated. FIG. 2B is a diagram showing the relationship between the irradiation region 15 and the visual field region 25 when precharge is small.

  In the mode (B-1), the center of the visual field region 25 and the irradiation region 15 coincide with each other, and the irradiation region 15 covers the visual field region 25 in a state where the precharge region 16 is not so much. When a large amount of precharge is not required, a mode as shown in (B-1) may be adopted.

  According to the aspect of (B-1), by setting the visual field area 25 and the irradiation area 15 to be close to each other and setting the precharge area 16 to be small, only the necessary precharge amount is consumed without consuming unnecessary energy. It can be obtained efficiently.

  Next, the aspect of FIG. 2C will be described. FIG. 2C is a diagram showing an aspect in which the visual field region 25 precedes the irradiation region 15 with respect to the moving direction (+ Y) of the sample S.

  In the aspect of (C-1), the area of the irradiation region 15 is set to a standard size, and the irradiation region 15 is delayed with respect to the moving direction (+ Y) of the sample S so that the visual field region 25 precedes the irradiation region 15. The change is made to move the position 15 in the upper (+ Y) direction of the drawing.

  As will be described in detail later, reflected electrons due to elastic scattering are emitted from the sample S for a predetermined period after irradiation with the electron beam. Therefore, when it is desired to inspect the structure of the sample S by effectively utilizing the reflected electrons, the mode (C-1) is suitable. In the mode (C-1) as well, the non-irradiation region 26 is generated in the visual field region 25, but the non-irradiation region 26 is sequentially irradiated with the electron beam by the movement of the sample S by the stage 30. Therefore, no problem arises in acquiring the image of the sample structure.

  In the mode (C-2), the centers of the visual field region 25 and the irradiation region 15 coincide with each other, but the irradiation region 15 is reduced as compared with the mode (C-1), and the moving direction of the sample S (± Y direction) ) Is a mode in which the visual field region 25 is wider than the irradiation region 15.

  According to the aspect (C-2), it is possible to perform an inspection or the like that effectively uses the reflected electrons with a small energy without irradiating the sample S with a useless primary electron beam.

  The mode (C-3) is a mode in which a spot-like spot beam is scanned in the X direction as an electron beam irradiation means. Thus, by scanning the visual field region 25 with a spot beam perpendicularly to the moving direction of the sample S, reflected electrons can be generated from the sample S, and an inspection using this can be performed.

  The mode (C-4) shows a mode in which a part of the visual field region 25 is irradiated using a thin linear beam for one pixel in the Y direction. This is an intermediate mode between (C-2) and (C-3), and as shown in (C-3), when the X direction is scanned with a spot beam, a time lag occurs in the X direction. This is a mode that makes it possible to generate reflected electrons with the minimum irradiation region 15 while removing.

  Next, a phenomenon in which the amount of electrons and the type of electrons received by the detector 22 of the secondary optical system 20 change with the precharge amount of the wafer will be described with reference to FIG. The inventor of the present application finds this phenomenon and proposes an electron beam apparatus 100 according to the present embodiment and a sample observation method using the same by utilizing this phenomenon.

  FIG. 3 is a diagram showing the amount of electrons reaching the detector 22 and the type of electrons over time. FIG. 3A is a diagram showing the relationship between the surface potential of the sample S and the number of electrons reaching the detector 22 per unit time, the horizontal axis is the surface potential of the sample S, and the vertical axis is the unit time ( Second) indicates the number of electrons that have reached the detector 22.

  In FIG. 3A, in the low landing energy region up to about 20 eV, reflected electrons are detected in the early stage of precharge. Since the amount of the reflected electrons is smaller than that of the irradiated electrons, the electron beam irradiation region 15 is negatively charged over time.

  As negative charging progresses, the surface potential of the irradiated region increases negatively, and the effective landing energy of incident electrons by the electron beam decreases relative to the potential of the irradiated region. Therefore, it becomes difficult for incident electrons to be reflected. At this stage, secondary electrons are generated and emitted from the wafer. Thereafter, when the effective landing energy of the incident electrons by the electron beam is larger than the potential energy of the surface, the landing of the electrons continues, and finally the potential energy of the wafer surface becomes the same as the landing energy of the electrons. Then, the incident electrons do not enter the irradiation region 15 and are reflected immediately before the wafer surface without contacting the wafer surface. This is called mirror electrons.

  FIG. 3A shows that when mirror electrons are generated, the surface potential of the wafer is constant because electrons are no longer incident, and the number of electrons reaching the detector 22 per unit time is also constant. Yes.

  In FIG. 3A, when the potential on the wafer surface is fixed, reflected electrons are always generated when the surface potential energy is smaller than the landing energy of the incident electrons. Therefore, for example, when there is a ground electrode on the wafer surface, reflected electrons are always emitted from that portion.

  FIG. 3B is a diagram showing the relationship between the electron beam irradiation time on the sample S and the number of electrons reached per unit time on the detector 22, where the horizontal axis represents the electron beam irradiation time and the vertical axis represents the electron beam irradiation time. The number of electrons that have reached the detector 22 in unit time (seconds) is shown. 3B is different from FIG. 3A in that the horizontal axis of FIG. 3A is changed from the surface potential to the electron beam irradiation time.

  In FIG. 3 (b), as the precharge progresses and the electron beam irradiation time elapses, the dose amount on the wafer surface increases, and from the wafer, reflected electrons are generated first, then secondary electrons are generated, Finally, it is shown that mirror electrons are generated. In the region where mirror electrons are generated, the number of electrons per unit time reaching the detector 22 is constant even when the electron beam irradiation time is increased.

  FIG. 4 is a diagram showing the relationship between the number of electrons generated from the tungsten region of the wafer and reaching the detector 22 and the landing energy of the incident primary electrons. In FIG. 4, the horizontal axis represents primary electron landing energy (eV), and the vertical axis represents the number of electrons reaching the detector.

  In FIG. 4, as can be seen by comparing the graph curves of the reflected electrons and the secondary electrons, the number of electrons that reach the detector 22 in the low landing energy region up to about 20 eV compared to the secondary electrons. There are overwhelmingly many. This is considered to be due to the difference in the electron transmittance from the wafer to the detector 22 in the projection type electron beam apparatus 100 according to the present embodiment due to the difference in the distribution of the emission directions of the respective electrons. Here, the electron transmittance refers to the ratio of electrons generated from the wafer that can reach the detector 22 through the secondary optical system 20.

  The secondary electrons have a distribution in the emission direction called the so-called “cosine law”, and are distributed not in the vertical direction from the plane formed by the wafer but in an oblique direction having an angle with the vertical axis. Therefore, in general, in the projection type electron beam apparatus employed in the electron beam apparatus 100 according to the present embodiment, the electron transmittance is not so large.

  On the other hand, the reflected electrons are emitted from the wafer so as to be relatively aligned with the direction in which the incident direction of primary electrons is reversed by 180 degrees. Therefore, the electron transmittance of the electron beam apparatus 100 adopting the mapping projection type electron beam apparatus according to the present embodiment is also increased, and the number of electrons reaching the detector 22 is increased by orders of magnitude compared to the secondary electrons. It is thought that.

  In other words, when the reflected electrons are used for the inspection, the number of electrons reaching the detector 22 is remarkably increased as compared with the case where the conventional secondary electrons are used, so that it is necessary for the detector 22 to obtain the same signal intensity. The number of primary electrons can be greatly reduced. For this reason, it is possible to reduce the charging of the wafer and realize an inspection with little damage.

  The relationship between the type of electrons in the low landing energy region and the number of electrons reaching the detector 22 in FIG. 4 is denoted by the diagram shown in FIG.

Returning to FIG. 3, in both FIGS. 3A and 3B, focusing on the number of electrons reaching the detector irradiating the wafer with the primary electron beam and reaching the detector 22, in the initial state, constant electrons The quantity is shown (first state). Next, when the wafer surface reaches a predetermined potential V1, the amount (number) of electrons reaching the detector 22 decreases (second state). If the wafer is further charged up, the amount of electrons reaching the detector 22 rapidly increases at the predetermined potential V2 (third state). Here, the reflected electrons reach the detector in the first state, and the secondary electrons reach the detector 22 in the second state. Further, in the third state, the primary electron beam cannot reach the wafer surface due to an increase in the charge amount of the wafer, and a so-called mirror electron state is reflected immediately before the wafer surface. Here, for example, the dose amount in the first state is 0 to 1.
(ΜC / cm ² ), the dose in the second state is 0.5 to 5 (μC / cm ² ), and the dose in the third state is 3 to 10 (μC / cm ² ). It may be.

  The state change described in FIG. 3 is based on the premise that the portion irradiated with the electron beam is charged up. Therefore, as described above, no charge-up occurs in the portion where the potential is fixed by grounding or the like. That is, in a portion that is in a floating state due to an open defect or the like of wiring, reflected electrons are always generated when the surface potential energy is smaller than the landing energy of incident electrons. By utilizing this phenomenon, it becomes possible to detect a defect by so-called voltage contrast, which detects an open defect or a short defect of a wiring formed on a wafer.

  Next, various examples of detecting a wafer defect using the electron beam apparatus 100 according to the present embodiment will be described.

[Example 1]
As Example 1, an example of detecting an open defect in a wafer on which a ground plug is formed will be described.

  FIG. 5 is a diagram for explaining an example of defect detection according to the first embodiment. FIG. 5A is a diagram showing a cross-sectional view in which the ground plug 91 and the open plug 94 are formed on the wafer W. FIG.

In FIG. 5A, a wafer W uses a p-type silicon substrate 80 as a support substrate, and a p + high concentration impurity region 82 is laminated thereon. A SiO ₂ oxide film layer 84 is formed thereon, and a ground plug 91 is provided in the groove 85 in the oxide film layer 84, and is connected to the conductive type p + high concentration impurity region 81. The ground plug 91 may be formed of tungsten or the like, for example. Since the ground plug 91 is connected to the conductive type p + high concentration impurity region 81, it has the same potential as the p-type silicon substrate 80. On the other hand, the open plug 94 which is a defective plug is not connected to the conductive type p + high-concentration impurity region 81 and is in a floating state.

  FIG. 5B is a diagram showing a change in the surface potential of the wafer W when the wafer W having the configuration shown in FIG. 5A is irradiated with a primary electron beam having a low landing energy. In FIG. 5B, even if the electron irradiation time is increased, the potential of the ground plug 91 does not change. However, since electrons are accumulated in the open plug 94, the potential increases negatively with the passage of time.

  FIG. 6 shows the surface potential dependence of the number of electrons reaching the detector 22 for the electrons emitted from the ground plug 91 and the open plug 94 by the irradiation of the primary electron beam in the wafer W shown in FIG. It is the figure which showed sex.

  In FIG. 6, since the potential of the ground plug 91 is fixed to the ground potential, reflected electrons are always detected. On the other hand, the open plug 94 is negatively charged with time, and the surface potential increases negatively. Therefore, reflected electrons are detected first, but then secondary electrons and finally mirror electrons are detected. Is done. According to experiments, when an appropriate value is selected for the landing energy of the primary electron beam, as shown in FIG. 6, the detected amount of mirror electrons can be made larger than the detected amount of reflected electrons. . In an embodiment to which the present invention is applied, it is assumed that such an appropriate energy is selected as the landing energy of the primary electron beam.

  FIG. 7 is a diagram in which the same data as in FIG. 6 is displayed with the horizontal axis changed to the electron beam irradiation time. The vertical axis indicates the number of electrons per unit time (seconds) reaching the detector 22.

  In FIG. 7, reflected electrons are always detected from the ground plug 91, but from the open plug 94, the types of electrons detected are different with time and the number of electrons reaching the detector is also different. It is shown. In the inspection mode according to the present embodiment, the wafer W is inspected by paying attention to the difference in the number of electrons reaching the detector over time.

  Next, an open plug detection method according to the first embodiment will be described with reference to FIG. FIG. 8 is a diagram illustrating an aspect of a detection method in which electrons are continuously detected from the reflected electrons first detected in the secondary optical system 20.

  FIG. 8A is a diagram comparing the total number of electrons emitted from the open plug 94 and the ground plug 91 and reaching the detector 22 in the reflected electron emission region of the open plug 94. In FIG. 8A, in the backscattered electron detection region, both backscattered electrons are emitted from the open plug 94 and the ground plug 91, so there is no difference in the total number of electrons reaching the detector. Therefore, the backscattered electron detection area is not used for inspection because there is no difference in the acquired images of the open plug 94 and the ground plug 91.

  FIG. 8B is a diagram comparing the total number of electrons emitted from the open plug 94 up to the secondary electron detection region of the open plug 94 and the ground plug 91 and reaching the detector 22. While reflected electrons continue to be emitted from the ground plug 91, the open plug 94 passes through the region that emits reflected electrons and enters the region that emits secondary electrons, as described in FIG. The number of electrons reaching the detector is greatly reduced. Therefore, as shown in FIG. 8B, the total number of electrons reaching the detector of the open plug 94 is smaller than the total number of electrons reaching the detector of the ground plug 91, and the difference becomes clear. Therefore, the acquired image of the wafer W acquired by the secondary optical system 20 has a difference in brightness and an electrical difference can be detected, so that the open plug 94 can be detected. Therefore, the mode of FIG. 8B can be used for the inspection of the open plug 94.

  In order to execute the mode shown in FIG. 8B, detection is performed from the reflected electrons generated in the first stage of electron beam irradiation, so the mode shown in FIG. That's fine. The position of the irradiation region 15 is changed backward (in the + Y direction in FIG. 2) so that the visual field region 25 precedes the electron beam irradiation region 15 with respect to the moving direction of the wafer W. As a result, the irradiation region 15 of the electron beam is entirely detected by the secondary optical system 20 from the beginning, so that the open plug 94 can be detected when the open plug 94 enters the region where secondary electrons are emitted. it can.

  FIG. 8C is a diagram showing a comparison of the total number of electrons reaching the detector generated from the open plug 94 and the ground plug 91 in the mirror electron generation region where the open plug 94 generates mirror electrons. As shown in FIG. 8C, when the mirror electron region is entered, the amount of mirror electrons generated is larger than the amount of reflected electrons generated, so that the electrons generated from the open plug 94 catch up with the electrons generated by the ground plug 91. start. Then, the difference in the total number of electrons reaching the detector between the open plug 94 and the ground plug 91 becomes an uncertain state in which various cases can be considered as time passes, and the difference between the two becomes unclear. Therefore, the mode of FIG. 8C is not suitable for detecting the open plug 94.

  Thus, as described in FIG. 8, only the mode of FIG. 8B is suitable for detecting the open plug 94. Therefore, in an embodiment in which the open plug 94 is detected using reflected electrons, an image of the wafer is acquired when the open plug 94 is in the secondary electron emission region, and a distinction from the ground plug 91 is found. The open plug 94 is detected. In this case, the position of the irradiation region 15 is changed so that the visual field region 25 precedes the irradiation region 15.

  FIG. 9 is a diagram showing a mode in which secondary electrons and mirror electrons are detected from the open plug 94 without detecting reflected electrons, and the open plug 94 is detected based on the detected secondary electrons and mirror electrons.

  FIG. 9A shows the total number of electrons reaching the detector from the open plug 94 and the ground plug 91 in the secondary electron emission region of the open plug 94 in FIG. In FIG. 9A, only secondary electrons are detected from the open plug 94, and only reflected electrons are detected from the ground plug 91. The difference in the amount of electrons reaching the total detector of both is large, and therefore, the difference between the two can be detected from the acquired image with high contrast. The embodiment shown in FIG. 9A is a preferred embodiment for detecting an electrical difference.

  In order to execute such an inspection method for detecting secondary electrons without detecting reflected electrons, an irradiation region with respect to the movement of the wafer W shown in FIGS. The inspection is performed in the arrangement relationship 15 precedes the visual field region 25. If the reflected electrons are emitted from the open plug 94 in the precharge region 16 and only the secondary electrons are set to be detected in the visual field region 25, the inspection method according to FIG. 9A is executed. can do.

  FIG. 9B is a diagram comparing the total number of electrons reaching the detector from the open plug 94 and the ground plug 91 in a region where secondary electrons and mirror electrons are detected from the open plug 94.

  In FIG. 9B, only reflected electrons are detected from the ground plug 91, but both secondary electrons and mirror electrons are detected in the open plug 94. As described in FIG. 7, the amount of reflected electrons generated is larger than the amount of reflected electrons and secondary electrons generated. When the amount of reflected electrons and mirror electrons is compared, the amount of mirror electrons generated is larger. The total number of electrons reaching the detector of the open plug 94 and the ground plug 91 of 9 (b) is such that the number of detected electrons from the open plug 94 catches up with the number of detected electrons from the ground plug 91 with time, and overtakes it. is there. Therefore, the difference between the total number of electrons reaching the total detector is an uncertain magnitude that changes over time. Therefore, the inspection method according to FIG. 9B is not suitable for detecting the open plug 94.

  However, also in the embodiment of FIG. 9B, at the initial stage where mirror electrons start to be generated from the open plug 94, the number of electrons detected from the open plug 94 is larger than the number of electrons detected from the ground plug 91. Since it is clearly less, the acquired image will be dark and it is possible to distinguish them. Conversely, if it takes time until a large amount of mirror electrons are generated from the open plug 94, the number of electrons detected from the open plug 94 is more than the number of electrons detected from the ground plug 91. Thus, the acquired image is brighter with the open plug 94. Therefore, if the electron beam irradiation time (dose amount) can be controlled appropriately, the open plug 94 and the grounding plug 91 are distinguished from each other and the acquired image is differentiated by using the embodiment according to FIG. Can be detected. However, since this method requires precise control of the electron beam irradiation time or dose, the embodiment according to FIG. 9A is more suitable for open plug detection.

  FIG. 10 is a diagram comparing the total number of electrons reaching the detector from the open plug 94 and the ground plug 91 in the region where the open plug 94 generates mirror electrons.

  In FIG. 10, only mirror electrons are detected from the open plug 94, and only reflected electrons are detected from the ground plug 91. As described with reference to FIG. 7, the amount of mirror electrons generated is larger than the amount of reflected electrons generated. Therefore, the total number of mirror electrons generated by the open plug 94 reaches the detector than the reflected electrons emitted from the ground plug 91. There are many clearly. Therefore, the acquired image of the open plug 94 is brighter than the acquired image of the ground plug 91, and the two can be distinguished from each other by the difference in brightness.

  In order to execute the inspection method according to FIG. 10, the irradiation region 15 with respect to the moving direction of the wafer W is used by using the relationship between the irradiation region 15 and the visual field region 25 of FIGS. The irradiation area is changed so as to precede the visual field area 25. In the precharge region 16 in FIGS. 2A and 2B, the reflected electrons and secondary electrons of the open plug 94 are emitted, and the viewing region 25 is set so that only mirror electrons can be detected. In this case, since reflected electrons and secondary electrons are emitted in the precharge region 16, it is desirable that the precharge region be larger than the mode employed in FIG. 9A, and in particular, (A-1) in FIG. ) Or (A-3) may be suitably applied.

  As described so far, in the inspection method according to the first embodiment, the inspection method according to FIGS. 8B, 9A, and 10 is suitable for detecting the open plug 94. According to these aspects, the open plug 94 can be detected from the ground plug 91 by utilizing the voltage contrast of the wafer surface potential. These inspection modes can be easily applied to various modes by changing the position of the irradiation region 15 of the primary electron beam 15 with respect to the visual field region 25. For example, if it is the aspect of FIG.8 (b), you may apply the aspect (C-1)-(C-4) of the visual field precedence type which concerns on FIG.2 (C). If it is the aspect of Fig.9 (a), you may apply the irradiation area | region advance type | mold which concerns on FIG. 2 (A) and (B). Further, the irradiation region preceding type according to FIGS. 2A and 2B may also be applied to the embodiment according to FIG. 10, and in particular, (A-1) in FIG. Or the aspect of (A-3) is suitable.

  On the other hand, the modes according to FIGS. 8A, 8C and 9B are suitable for observing defects on the surface of the pattern because the difference in brightness between the defective portion and the normal portion is small. Yes. If an image of the pattern surface of the wafer is acquired instead of detecting a specific defect and observed to find a pattern abnormality, it can be used as a general pattern defect inspection. In order to execute these inspection modes, the position of the irradiation region 15 of the electron beam with respect to the visual field region 25 may be changed. For example, in the mode according to FIGS. The mode according to FIG. 2C is preferably applied, and the mode according to FIGS. 2A and 2B of the irradiation region preceding type is preferably applied to the mode according to FIG. 9B.

  As described above, in the electron beam apparatus 100 according to the present embodiment shown in FIG. 1, various inspection modes shown in Example 1 are obtained by variously changing the position of the irradiation region 15 of the electron beam with respect to the visual field region 25. Can be executed.

[Example 2]
Next, as Example 2, an example in which an open defect is detected for a wafer W on which an n ⁺ -p plug is formed will be described.

FIG. 11 is a diagram for explaining an aspect of an inspection method for detecting an open defect for a wafer W on which an n ⁺ -p plug is formed.

FIG. 11A is a cross-sectional view of the wafer W on which the n ⁺ -p plug 92 is formed. In FIG. 11A, an n ⁺ high concentration impurity region 83 of the opposite conductivity type is provided on the surface of a p-type silicon substrate 80. A SiO ₂ oxide film layer 84 is laminated on the p-type silicon substrate 80, and an n ⁺ -p plug 92 is formed in the groove 85 of the SiO ₂ oxide film layer 84. The n ⁺ -p plug 92 is electrically connected to the p-type silicon substrate 80 via the n ⁺ high concentration impurity region 83. The n ⁺ -p plug 92 may be made of a metal such as tungsten, for example. In the oxide film layer 84, there are open plugs 94 in a floating state. In the present embodiment, an aspect of an inspection method for detecting such an open plug defect will be described.

When the wafer W having the cross-sectional structure of FIG. 11A is irradiated with an electron beam, the surface potential of the portion where the n ⁺ -p plug 92 is formed reaches several V of about −1 to −2V. From, a minute current flows through the p-type silicon substrate 80. This is because when the n ⁺ high concentration impurity region 83 and the p-type silicon substrate 80 are connected via a depletion layer (not shown) and an electron beam is injected, the n ⁺ high concentration impurity region 83 and the p-type silicon substrate 80 are connected. This is because electrons are accumulated until reaching a predetermined number V because they are forward-connected, but when the predetermined number V is reached, electrons flow into the p-type silicon substrate 80 as current.

FIG. 11B is a diagram showing the change over time of the surface potential of the wafer W when the wafer W having the configuration shown in FIG. 11A is irradiated with an electron beam having a low landing energy. In FIG. 11B, the n ⁺ -p plug 92 has a surface potential that increases negatively until reaching a predetermined number V (for example, about −1 to −2 V) as described above. Reaches the p-type silicon substrate 80, a constant value is obtained. On the other hand, since the open plug 94 accumulates electrons as the electron irradiation time elapses, the surface potential increases negatively in proportion to the electron irradiation time.

FIG. 12 is a diagram showing the surface potential dependence of the number of electrons reaching the detector among the electrons generated for each of the n ⁺ -p plug 92 and the open plug 94 shown in FIG. . In FIG. 12, in the open plug 94, similar to the description in the first embodiment, the type of generated electrons changes from reflected electrons, secondary electrons, and mirror electrons in accordance with the change in surface potential. On the other hand, the n ⁺ -p plug 92 detects reflected electrons at a stage where the surface potential is low. However, if the n ⁺ -p plug 92 enters the secondary electron generation region beyond the reflected electron generation region, the surface potential becomes constant along the way. The number of reaching electrons will also be constant. As described with reference to FIG. 11B, in the case of the n ⁺ -p plug 92, the surface potential is constant, for example, about −1 to −2V, and does not increase further negatively. This is because the number of occurrences per unit time becomes constant. Therefore, when the landing energy of the primary electron beam is selected to be several eV or more larger than the surface potential potential fluctuation amount (for example, about −1 to −2 V) of the wafer W, as shown in FIG. It is possible to create a state where secondary electrons are detected but mirror electrons are not detected.

FIG. 13 is a diagram showing the relationship between the electron beam irradiation time and the number of electrons reaching the detector per unit time when the n ⁺ -p plug 92 and the open plug 94 are irradiated with an electron beam. In FIG. 13, the horizontal axis in FIG. 12 is changed from the surface potential to the electron beam irradiation time.

In FIG. 13, the same number of reflected electrons and secondary electrons are detected from both the n ⁺ -p plug 92 and the open plug 94 in the reflected electron detection region and the secondary electron detection region of the open plug 94. However, in the mirror electron detection region of the open plug 94, mirror electrons are detected from the open plug 94, but secondary electrons are continuously detected from the n ⁺ -p plug 92 as they are. As described with reference to FIG. 13, the surface potential of the n ⁺ -p plug 92 becomes constant at a predetermined number V of the secondary electron emission region, so that even if the electron beam is continuously irradiated thereafter. This is because only constant secondary electrons are emitted per unit time.

Figure 14 utilizes the relationship described in Figure 11 to 13 are diagrams for detecting electrons from the occurrence of reflected electrons describing an inspection method for detecting the open plug 94, n ⁺ -p plug It is the figure which compared and showed the total detector arrival electron number of 92 and the open plug 94. FIG.

FIG. 14A is a diagram comparing the total number of electrons reaching the detector detected from the open plug 94 and the n ⁺ -p plug 92 in the backscattered electron detection region of the open plug 94. In FIG. 14A, since only the same number of reflected electrons are detected in both the open plug 94 and the n ⁺ -p plug 92, there is no difference in brightness between the acquired images. Is unsuitable.

FIG. 14B is a diagram comparing the total number of electrons reaching the detector from the open plug 94 and the n ⁺ -p plug 92 so far in the secondary electron detection region of the open plug 94. In FIG. 14B, the same number of reflected electrons and secondary electrons are detected in both the open plug 94 and the n ⁺ -p plug 92, and there is no difference in the total number of electrons reaching the detector. Therefore, the mode of FIG. 14B is not suitable for detecting the open plug 94.

FIG. 14C is a diagram comparing the total number of electrons reaching the detector from the open plug 94 and the n ⁺ -p plug 92 so far in the mirror electron detection region of the open plug 94. In FIG. 14 (c), the open plug 94 detects all types of electrons including reflected electrons, secondary electrons, and mirror electrons, but the n ⁺ -p plug 92 has only reflected electrons and secondary electrons. Is detected. As shown in FIG. 13, in the mirror electron detection region of the open plug 94, the mirror electron detection amount from the open plug 94 greatly exceeds the secondary electron detection amount from the n ⁺ -p plug 92. . Therefore, also in FIG. 14 (c), the open mirror electrons detected amount of the plug 94 is obviously greater than ^{n +} -p plug 92, also in the total electrons arriving at the detector number, open plug 94 is ^{n +} -p plug 92 Is significantly above. Therefore, in the embodiment of FIG. 14C, the acquired image of the open plug 94 becomes brighter than the acquired image of the n ⁺ -p plug 92, and the open plug 94 can be detected by the brightness difference. This aspect can be said to be a preferable aspect for detecting an electrical difference by voltage contrast.

  In order to execute the mode shown in FIG. 14C, the generated electron is detected from the stage where the initial reflected electrons are generated by the irradiation of the wafer W with the primary electron beam. , 14 changes the position of the irradiation region 15 so as to be the visual field region preceding type in FIG. Thereby, all the electrons generated from the wafer W from the generation stage of the reflected electrons in the visual field region 25 can be detected, and this aspect can be executed. This also applies to the embodiments shown in FIGS. 14A and 14B, which are inappropriate for the detection of the open plug 94, and these also detect electrons generated from the wafer W from the generation stage of the reflected electrons. Therefore, the irradiation region changing mode of the visual field region leading type shown in FIG. 2C is applied.

  FIG. 15 is a diagram for explaining an aspect related to an inspection method in the case of detecting electrons after generation of secondary electrons without detecting electrons in the reflected electron detection region of the open plug 94.

FIG. 15A is a diagram comparing the total number of electrons reaching the detector from the open plug 94 and the n ⁺ -p plug 92 when the open plug 94 is in the secondary electron detection region. In FIG. 15A, the same number of secondary electrons are detected in both the open plug 94 and the n ⁺ -p plug 92. Therefore, there is no difference in brightness between the acquired images, and this aspect is not suitable for detecting the open plug 94.

FIG. 15B is a diagram comparing the total number of electrons reaching the detector from the open plug 94 and the n ⁺ -p plug 92 when the open plug 94 is in the mirror electron detection region. In FIG. 15B, the n ⁺ -p plug 92 detects only secondary electrons, whereas the open plug 94 detects mirror electrons after detecting secondary electrons. As shown in FIG. 15B, the detection amount of the mirror electrons of the open plug 94 is significantly larger than the detection amount of the secondary electrons of the n ⁺ -p plug 92, and the total detector reaching electrons In terms of number, the open plug 94 is clearly larger. Therefore, the acquired image in the secondary optical system 20 of the open plug 94 becomes brighter than the acquired image of the n ⁺ -p plug 92, and it is possible to give a difference in brightness to the image by the difference in surface potential between the two. . Therefore, the mode of FIG. 15B is a preferable test mode for detecting an electrical difference such as detection of the open plug 94.

In order to execute the inspection mode according to FIG. 15, the irradiation region changing means 13, 14 changes the position of the irradiation region 15 with respect to the field region 25 of the electron beam to the irradiation regions shown in FIGS. Change to the preceding type. 2A and 2B, the setting is made so that the reflected electrons are emitted in the precharge region 16, and the field region 25 detects electrons generated after the secondary electron detection region of the open plug 94. If so, the modes of FIGS. 15A and 15B can be executed.

FIG. 16 is a diagram for describing a mode in which the open plug 94 is detected when the mirror electrons are in the region where mirror electrons are detected from the open plug 94. FIG. 16 is a diagram comparing the total number of electrons reaching the detector of the open plug 94 and the n ⁺ -p plug 92 when the open plug 94 is in the mirror electron detection region. In FIG. 16, only mirror electrons are detected from the open plug 94, and only secondary electrons are detected from the n ⁺ -p plug 92. This is because only the secondary electrons are detected from the n ⁺ -p plug 92 in the mirror electron detection region of the open plug 94 as described in FIG. Therefore, in the total number of electrons reaching the detector, the number of detected electrons of the open plug 94 greatly exceeds the number of detected electrons of the n ⁺ -p plug 92, and the acquired image of the open plug 94 is greater than that of the n ⁺ -p plug 92. It becomes brighter than the acquired image and can be distinguished. Therefore, the embodiment of FIG. 16 is preferable for detecting mainly electrical differences of the wafer W.

  In order to execute the embodiment of FIG. 16, only the mirror electron detection region of the open plug 94 is used and the reflected electrons and secondary electrons are not detected. Therefore, the irradiation region changing means 13 and 14 are configured as shown in FIG. The irradiation region 15 is changed so as to apply the irradiation region preceding type of (B). Since both the reflected electrons and the secondary electrons are generated in the precharge region 16 and the field of view region 25 is changed to detect only the mirror electrons, the precharge region 16 is preferably set to a sufficiently large change. The mode of (A-1) or (A-3) in FIG. 2 (A) may be applied.

  As described so far, in the second embodiment, the inspection method shown in FIGS. 14C, 15B, and 16 is suitable for open defect detection using voltage contrast. Also in the second embodiment, as in the first embodiment, in order to execute each mode, the irradiation region changing means 13 and 14 appropriately change the position of the irradiation region 15 with respect to the visual field region 25. For example, in the case of FIG. 14C, detection is performed from reflected electrons, so that the position of the irradiation region 15 is changed so as to be the view-preceding type of FIG. If it is an aspect, the position of the irradiation area 15 is changed so as to be the irradiation area preceding type in FIGS. 2A and 2B, and the emission of the reflected electrons is terminated by the electron beam irradiation of the precharge area 16. Set to do. Further, in the case of FIG. 16, the position of the irradiation region 15 is changed so that the irradiation region preceding type of FIG. 2A and FIG. It is set so that the emission of the next electron ends. As described above, by changing the position of the irradiation region 15 of the electron beam suitable for each inspection mode by the irradiation region changing means 13 and 14, inspection according to the type of the wafer W or the like can be performed.

  14A, 14B, and 15A, which are not suitable for detection of open defects, are not voltage contrast because the difference in brightness between the acquired images of the defective part and the normal part is small. The image of the wafer surface can be acquired and used to inspect defects in the wiring pattern based on the acquired image. Also in this case, it is preferable to change the irradiation position appropriately by the irradiation position changing means 13.

Example 3
Next, as Example 3, an aspect of an inspection method for detecting an open plug defect in a wafer W on which p ⁺ -n plugs are formed will be described.

FIG. 17 is a diagram for explaining the properties of the wafer W to be inspected in the third embodiment. FIG. 17A is a view showing a cross-sectional structure of the wafer W on which the p ⁺ -n plug is formed.

In FIG. 17A, a wafer W to be inspected is provided with an n-type silicon substrate 81 as a support substrate, and a p + high concentration impurity region 82 of the opposite conductivity type is provided on the surface thereof. An SiO ₂ oxide film layer 84 is formed on the n-type silicon substrate, and ap ⁺ -n plug 93 is formed in the groove 85 in the oxide film layer 84. The p ⁺ -n plug 93 is electrically connected to the n-type silicon substrate 81 through the p + high concentration impurity region 83. In the oxide film layer 84, there are open plugs 94 in a floating state. In the present embodiment, an aspect of an inspection method for detecting such an open plug defect will be described.

In FIG. 17A, when the p ⁺ -n plug 93 is irradiated with an electron beam, a reverse voltage is gradually applied to the p + high-concentration impurity region 83 and the n-type silicon substrate 81 to the diode. It will be the same. Therefore, electrons are accumulated in the p ⁺ -n plug 93 until a certain negative potential. However, when the certain negative potential is exceeded, a reverse current flows from the p ⁺ -n plug 93 to the n-type silicon substrate. A phenomenon occurs in which the potential of the p ⁺ -n plug 93 does not increase negatively after starting to flow.

Next, with reference to FIG. 17B, a change in state when the electron beam is irradiated to the p ⁺ -n plug 93 and the open plug 94 in the wafer W having the structure shown in FIG. 17A will be described. FIG. 17B is a diagram showing the relationship between the electron irradiation time and the surface potential when the p ⁺ -n plug 93 and the open plug 94 are irradiated with an electron beam.

In FIG. 17B, since the open plug 94 is in a floating state, electrons accumulate on the surface with the irradiation of the electron beam, and the surface potential increases negatively in proportion to the passage of time. On the other hand, as described in FIG. 17A, the surface potential of the p ⁺ -n plug 93 increases negatively in proportion to the electron beam irradiation up to a predetermined negative potential. When the value is reached, the surface potential remains constant. As described above, this is the same phenomenon as when a reverse voltage is applied to the diode and a reverse current starts to flow when the diode reaches a predetermined voltage. Therefore, the constant value is, for example, an absolute value of 5 V or less. In many cases, the value is about -5 V or more. This value is different for each device, but is clearly larger than the predetermined value (for example, about −1 to −2 V) shown in FIG. 11 according to the second embodiment.

As described above, in the inspection method according to the third embodiment for the wafer W on which the p ⁺ -n plug 93 is formed, the relationship between the electron irradiation time and the surface potential is the same as that of the n ⁺ -p plug 92 according to the second embodiment. Although the same characteristics as those of the formed wafer W are exhibited, the constant values indicated by the normal wiring plugs are different.

FIG. 18 shows the number of electrons reaching the detector among the electrons generated by the electron beam irradiation for the p ⁺ -n plug 93 and the open plug 94 formed on the wafer W shown in FIG. It is the figure which showed the surface potential dependence.

In FIG. 18, in the open plug 94, the kind of electrons generated as reflected electrons, secondary electrons, and mirror electrons changes as the surface potential increases negatively as in the above description. On the other hand, the p ⁺ -n plug 93 generates reflected electrons when the surface potential is low, like the open plug 94, and then generates secondary electrons as the surface potential increases negatively. The surface potential becomes constant in the middle of the generation of secondary electrons, and mirror electrons are not generated. The potential at the point where the surface potential becomes constant is larger on the negative side than the constant potential shown in FIG. 12 described in the second embodiment. Even in the case of the p ⁺ -n plug 93, as shown in FIG. 17B, the value is constant at a value of about −5 V or more, but this value is the same as that in the case of the n ⁺ -p plug 92. Since the value is larger on the negative side than about −1 to −2 V, it is constant at a point closer to the negative side than FIG. On the other hand, the value at which mirror electrons start to be generated is a value that does not reach the mirror electron detection region because the surface electrons are values of −10V and −20V.

FIG. 19 is a diagram showing the relationship between the electron beam irradiation time and the number of electrons reaching the detector per unit time for the p ⁺ -n plug 93 and the open plug 94. The horizontal axis in FIG. 18 is changed from the surface potential to the electron beam irradiation time.

From FIG. 19, the open plug 94 changes its generation electrons to reflected electrons, secondary electrons, and mirror electrons as the electron beam irradiation time elapses, but the p ⁺ -n plug 93 exceeds the reflected electron detection region. When the secondary electron detection region is entered, it can be seen that the secondary electron generation continues without reaching the mirror electron detection region.

FIG. 20 is a diagram for explaining an aspect of detecting the open plug 94 by detecting generated electrons from the reflected electrons for the p ⁺ -n plug 93 and the open plug 94.

FIG. 20A is a diagram comparing the total number of electrons reaching the detector detected from the open plug 94 and the p ⁺ -n plug 93 in the backscattered electron detection region of the open plug 94. In FIG. 20A, since the same number of reflected electrons are detected in both the open plug 94 and the p ⁺ -n plug 93, there is no difference in brightness between these acquired images. Therefore, this aspect is not suitable for detecting the open plug 94.

FIG. 20B is a diagram showing the total number of electrons reaching the detectors detected so far from the open plug 94 and the p ⁺ -n plug 93 in the secondary electron detection region of the open plug 94. . In FIG. 20B, both the open plug 94 and the p ⁺ -n plug 93 detect the same number of reflected electrons and secondary electrons, and the total number of electrons reaching the total detector is the same. There is no difference. Therefore, this aspect is not suitable for detecting the open plug 94.

FIG. 20 (c) is a diagram showing a comparison of the total number of electrons reaching the detector detected from the open plug 94 and the p ⁺ -n plug 93 so far in the mirror electron detection region of the open plug 94. In FIG. 20 (c), the number of mirror electrons detected by the open plug 94 is greatly increased, but the increase of secondary electrons of the p ⁺ -n plug 93 is small. However, the open plug 94 significantly exceeds the p ⁺ -n plug 93. Therefore, in this aspect, a difference in brightness occurs between the acquired images of the open plug 94 and the p ⁺ -n plug 93, and the open plug 94 can be detected by the voltage contrast. Therefore, this aspect is suitable for detecting an electrical difference of the open plug 94 or the like.

  Note that in order to execute the detection method shown in FIGS. 20A to 20C, it is necessary to detect reflected electrons, so any one of the field-preceding modes according to FIG. 2C is applied. To do. You may perform by changing the position of the irradiation area | region 15 using the irradiation area | region change means 13 and 14 so that the irradiation area | region 15 follows the visual field area | region 25. FIG.

FIG. 21 is a diagram for explaining a mode in which the open plug 94 is detected without using reflected electrons for the p ⁺ -n plug 93 and the open plug 94.

FIG. 21A is a diagram comparing the total number of electrons reaching the detector of the open plug 94 and the p ⁺ -n plug 93 in the secondary electron detection region of the open plug 94. In FIG. 21A, since only the same number of secondary electrons are detected from both the open plug 94 and the p ⁺ -n plug 93, there is no difference in brightness between the acquired images. Therefore, this aspect is not suitable for detecting the open plug 94.

FIG. 21B is a diagram comparing the total number of electrons reaching the detector of the open plug 94 and the p ⁺ -n plug 93 in the mirror electron detection region of the open plug 94. In FIG. 21B, secondary electrons and mirror electrons are detected by the open plug 94, and only secondary electrons are detected by the p ⁺ -n plug 93. The number of detected electrons of the mirror electrons is much larger than the number of detected electrons of the secondary electrons. Therefore, the total number of electrons reaching the detector of the open plug 94 is the total number of electrons reaching the detector of the p ⁺ -n plug 93. Is significantly above. Therefore, the acquired image of the open plug 94 in the secondary optical system 20 is an image brighter than the p ⁺ -n plug 93, and the open plug 94 can be detected from the voltage contrast of both. Therefore, this aspect is a preferable aspect for detecting an electrical difference.

  The aspect of the inspection method shown in FIG. 21 is achieved by changing the irradiation region 15 to the irradiation region preceding type shown in FIGS. 2A and 2B by the irradiation region changing means 13 and 14. . Setting is made so that the reflected electrons are emitted from the wafer W in the precharge area 16 so that the reflected electrons are not detected in the visual field area 25.

FIG. 22 is a diagram for explaining an aspect of a detection method for detecting the open plug 94 using the mirror electron detection region of the open plug 94 for the p ⁺ -n plug 93 and the open plug 94. FIG. 22 is a diagram comparing the total number of electrons reaching the detector of the open plug 94 and the p ⁺ -n plug 93 in the mirror electron detection region of the open plug 94. In FIG. 22, only mirror electrons are detected from the open plug 94, and only secondary electrons are detected from the p ⁺ -n plug 93. Since the total number of electrons reaching the detector of the mirror electrons is significantly larger than the total number of electrons reaching the detector of the secondary electrons, the acquired image of the open plug 94 becomes brighter than the acquired image of the p ⁺ -n plug 93. The open plug 94 can be detected from the voltage contrast. Therefore, this aspect is suitable for detecting an electrical difference.

  In order to execute the embodiment according to FIG. 22, only the mirror electron detection region is used without using the backscattered electron detection region and the secondary electron detection region of the open plug 94. It is preferable to apply the irradiation region preceding type of (B). The irradiation region is changed by the irradiation region changing means 13 and 14 so that the reflected electrons and secondary electrons of the open plug 94 can be emitted in the precharge region 16.

As described above, in order to detect an open defect of the wafer W on which the p ⁺ -n plug 93 according to the third embodiment is formed, the aspect of the inspection method of FIGS. 20C, 21B, and 22 is used. Is suitable.

  On the other hand, the modes shown in FIGS. 20A, 20B, and 21A are not suitable for applications in which an electrical difference is detected based on voltage contrast because the difference in brightness is small. It is suitable for use in acquiring and inspecting pattern defects.

  In order to execute these various modes, the irradiation region changing means 13 and 14 select the mode of changing the position of the irradiation region 15 with respect to the visual field region 25 shown in FIGS. 2 (A), (B), and (C). Thus, it is possible to apply inspection modes according to the inspection object.

  FIG. 23 is a diagram showing an example of an inspection image for the inspection method using the mirror electrons shown in FIGS. 9, 10, 15, 16, 21 and 22 in the defect inspection of the open plug 94.

  23, (a1) to (a3) show the surface of the wafer W on which the ground plug 91 is formed, and (b1) to (b3) show acquired images corresponding to the respective wafer W surfaces. . In FIG. 23 (a1), the irradiation region 15 is larger than the visual field region 25, and the irradiation region 15 has a positional relationship preceding the visual field region 25. The arrow in the −Y direction in FIG. 23 indicates the relative movement direction of the irradiation region 15 and the visual field region 25. In practice, the stage 30 moves in the + Y direction.

  FIG. 23 (b1) is a detection image on the detection surface of the detector 22 corresponding to FIG. 23 (a1). In FIG. 23 (a1), reflected electrons are detected at the moment when the electron beam is irradiated, and the entire visual field region is detected.

  Next, the stage 30 scans in the + Y direction or the electron beam in the −Y direction, and the irradiation region 15 and the visual field region 25 move in the inspection region while maintaining the positional relationship of FIG. As shown in (a2), when the open plug 94 is included, only that portion shines brightly as shown in FIG. 23 (b2). Then, mirror electrons are not detected from a normal plug.

  As described above, in the embodiment shown in FIG. 23, in order to increase the detected electrons from the defective portion (open plug 94), the condition is set such that mirror electrons are detected only by the open plug 94 portion. And it is set so that mirror electrons are not detected from other normal plugs. This is called the dark image mode. In the embodiment of FIG. 23, the mirror electrons have a sufficiently large surface potential compared to the reflected electrons and secondary electrons, so that only the defective plug 94 shines brightly in a dark image. Detection is easy.

  As shown in FIG. 23 (a3), when the stage 30 or the electron beam is further scanned and enters the visual field region 25 where the open plug 94 is not present, as shown in FIG. 23 (b3), in the dark image mode. The image becomes dark.

  Thus, the open plug 94 can be easily detected using the dark image mode.

  FIG. 24 is a diagram showing an example of detecting surface defects of the wafer W by selectively using reflected electrons.

  FIG. 24A1 is a diagram showing the positional relationship among the electron beam irradiation region 15, the visual field region 25, and the plug 91. FIG. In FIG. 24A1, the visual field region 25 has an arrangement relationship that precedes the irradiation region 15. Similarly to FIG. 23, the stage 30 moves in the + Y direction or the electron beam moves in the -Y direction, and the inspection area moves. Accordingly, in FIG. 24A1, the irradiation region 15 is changed to a position where the visual field region 25 precedes the irradiation region 15 with respect to the moving direction of the stage 30. Therefore, in the visual field region 25, it is possible to continue to detect electrons at the timing when the electron beam is irradiated on the wafer W for the first time. Therefore, the reflected electrons generated at the first stage of the electron beam irradiation are continuously detected. Therefore, in this case, the detection image on the detection surface of the detector 22 corresponding to FIG. 24 (a1) is as shown in FIG. 24 (b1), and the reflected electrons of all the plugs 91 in the visual field region 25 are detected. An image is formed.

  Next, the stage 30 or the electron beam moves to irradiate the area shown in FIG. 24A2, and the reflected electrons are detected also in this area. In the initial stage, all reflected electrons are detected whether they are grounded or open (floating). Therefore, if no missing plug exists in the pattern of FIG. 24A2, all the images of the plugs 91 are acquired as corresponding detection images as shown in FIG. 24B2.

  Next, the stage 30 or the electron beam further moves to inspect the region of FIG. 24 (a3). In FIG. 24 (a3), it is assumed that a missing plug 95 exists. At this time, the corresponding detected image is as shown in FIG. 24B3, and the missing plug 95 is an image in which no plug is detected.

  In this way, by using reflected electrons, it is possible to easily detect a missing plug by utilizing the property that an image of a reflected electron is captured if there is a metal in the initial stage.

As described above, in the first to third embodiments, the aspect of the method for detecting the open plug 94 when the ground plug 91, the n ⁺ -p plug 92, and the p ⁺ -n plug 93 are formed on the wafer W has been described. However, in the actual wafer W manufacturing process, the above three types of ground plug 91, n ⁺ -p plug 92 and p ⁺ -n plug 93 are usually formed in the same wafer W. Therefore, in the first to third embodiments, it is preferable to adopt a mode in which the open plug 94 can be detected in common. 8 (b), FIG. 9 (b) and FIG. 10 in Example 1, FIG. 14 (c), FIG. 15 (b) and FIG. 16 in Example 2, and FIG. (C), FIG. 21 (b), and FIG. 22 and the embodiment of FIG. 9 (b), FIG. 15 (b), and FIG. This is common in the embodiments of FIGS. 10, 16 and 22 that use only mirror electrons. Therefore, using these detection method aspects, the open plug 94 of the wafer W can be detected using the electron beam apparatus 100 according to the present embodiment. Thereby, the open plug 94 can be detected with minimum energy without using a precharge unit.

Example 4
Next, as Example 4, an aspect of an inspection method for detecting an electrical defect of a VC-TEG will be described. Here, the VC-TEG is a test element group in the voltage contrast inspection. In order to know the structural dimension margin from the viewpoint of the anti-corrosion property, a plurality of test sets with different line widths and wiring spaces are used. Refers to an element group.

  In order to detect an electrical defect by VC-TEG, a secondary electron detection region without detecting the reflected electrons of the open plug 94 shown in FIG. 9A or the inspection method using only mirror electrons of FIG. An inspection method for detecting the generated electrons at is suitable. Since the VC-TEG is basically the same in structure as the wafer W having a pattern having the ground plug 91, the aspect of the inspection method applicable in the first embodiment can be suitably used. In this regard, the inspection method using only mirror electrons in FIG. 10 and the inspection method for detecting generated electrons in the secondary electron detection region of the open plug 94 shown in FIG. 9A clearly generate voltage contrast. I was able to. Further, the inspection method for detecting reflected electrons and secondary electrons in FIG. 8B is also applicable.

  On the other hand, the inspection method for detecting all the reflected electrons to mirror electrons in FIG. 8C and the inspection method for detecting secondary electrons and mirror electrons without detecting the reflected electrons in FIG. 9B are also applicable. There are few margins to differentiate, and it is difficult to set conditions. In addition, the inspection method using only the reflected electrons in FIG. 8A has almost no difference in brightness and darkness, and it is difficult to detect an electrical defect and is difficult to apply.

  Here, when using the inspection methods of FIGS. 10, 9A, and 9B, it is preferable to use the irradiation area advance type shown in FIGS. 2A and 2B as the irradiation area change mode. . In addition, when using the inspection method of the embodiment shown in FIGS. 8B and 8C, it is preferable to use the visual field region leading type shown in FIG.

  FIG. 25 is an example of a VC-TEG wiring. FIG. 25A is a diagram illustrating an example of a normal VC-TEG, and FIG. 25B is a diagram illustrating an example of a VC-TEG when there is a defect.

  Consider the case where the inspection method of FIG. 9A is applied to FIG. The inspection method in FIG. 9A is a method for detecting generated electrons in the secondary electron detection region of the open plug 94. According to this inspection method, reflected electrons are always detected in the ground wiring portion, and secondary electrons are detected in the floating wiring portion 94. Taking the case where the plug is tungsten as an example, the number of reflected electrons detected by reflected electrons and secondary electrons is overwhelmingly large, so that the ground wiring 91 is bright and the floating wiring portion 94 is dark.

  FIG. 26 is a diagram showing an aspect in which the same VC-TEG wiring as in FIG. 25 is inspected by the inspection method using only mirror electrons according to FIG. FIG. 26A is a diagram illustrating a detection image in a normal case. FIG. 26B is a diagram showing a detection image when there is a defect.

  In FIG. 26, when the generated electrons in the mirror electron detection region are used, reflected electrons are detected in the ground wiring portion 91 and mirror electrons are detected in the floating 94 portion. If the landing energy of the primary electron beam is set so that the amount of mirror electrons generated is larger than that of the reflected electrons, the ground wiring 91 becomes dark and the floating wiring portion 94 becomes bright.

  Thus, according to the aspect of the fourth embodiment, not only the wafer W but also the wiring of the VC-TEG can be inspected.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

DESCRIPTION OF SYMBOLS 10 Primary optical system 11 Electron gun 12 Aperture 13 Primary lens system (irradiation area change means)
14 E × B separator (irradiation area changing means)
DESCRIPTION OF SYMBOLS 15 Irradiation area 16 Precharge area 18 Objective lens system 20 Secondary optical system 21 Secondary lens system 22 Detector 23 Storage device 25 Field of view area 26 Non-irradiation area 30 Stage 31 Holder 32 Anti-vibration stand 33 Stage control unit 40 Computer 41 Display 51, 52 Vacuum vessel 60 Main housing 61 Gate valve 70 Spare environment chamber (mini-environment chamber)
71 Housing 72 Pre-aligner 73 Hoop 74 Turbo molecular pump 75 Dry pump 80 p-type silicon substrate 81 n-type silicon substrate 82 p + high concentration impurity region 83 n + high concentration impurity region 84 oxide film layer 85 groove 91 ground plug 92 n ⁺ -p Plug 93 p ⁺ -n plug 94 Open plug

In order to achieve the above object, an electron beam apparatus according to a first aspect of the invention includes a stage having a moving mechanism for placing a sample and moving the sample ,
A primary optical system for generating an electron beam having a predetermined irradiation region and irradiating the electron beam toward the sample;
A secondary optical system that detects electrons generated by irradiation of the sample with the electron beam and obtained structural information of the sample, and acquires an image of the sample for a predetermined field of view;
An irradiation area changing means capable of changing the position of the predetermined irradiation area with respect to the predetermined visual field area ;
The irradiation area changing means changes the position of the predetermined irradiation area with respect to the predetermined visual field area in the direction in which the sample is moved,
The secondary optical system includes a detector, and the detector is a two-dimensional detector having a plurality of pixels on a detection surface, and each electron on the detection surface receives electrons obtained from the structure information of the sample. It detects with the pixel of .

Claims (1)

A stage having a moving mechanism for placing the sample and moving the sample;
A primary optical system for generating an electron beam having a predetermined irradiation region and irradiating the electron beam toward the sample;
A secondary optical system that detects electrons generated by irradiation of the sample with the electron beam and obtained structural information of the sample, and acquires an image of the sample for a predetermined field of view;
An irradiation area changing means capable of changing the position of the predetermined irradiation area with respect to the predetermined visual field area;
The irradiation region changing means is an electron beam apparatus that changes the position of the predetermined irradiation region with respect to the predetermined visual field region in a direction in which the sample is moved.

Images