JP3986032B2 - electronic microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is an electron microscope that displays a shape of a through-hole by scanning a sample with a through-hole formed with an electron beam, and a stencil mask that serves as a master when an IC or LSI circuit is printed on a wafer by exposure The present invention relates to an electron microscope that efficiently performs dimensional measurement and defect inspection of fine patterns using an electron beam.
[0002]
[Prior art]
In recent years, the degree of integration of LSI has been steadily improved, but conventional exposure technology using light has reached the limit in the LSI manufacturing process, and ArF photo-excimer laser, X-ray, electron beam exposure technology Are listed as the next candidates. Among them, measurement with light of a stencil mask serving as a master for exposure with an electron beam is impossible for length measurement and defect inspection, and only the surface shape is measured with a scanning electron microscope.
[0003]
In order to observe the shape near the back surface, the sample is turned over and the same measurement is performed. A conventional length measuring machine using a scanning electron microscope scans a sample while irradiating a narrowly focused beam, detects secondary electrons and reflected electrons emitted from the sample at that time by a secondary electron detector, and an amplifier. In order to display the image on the display device.
[0004]
[Problems to be solved by the invention]
However, the stencil mask has a thickness, and the conventional scanning electron microscope cannot obtain information in the depth direction. For this reason, there is a problem that there is no other way but to find a defect on the stencil mask from the actually drawn pattern.
[0005]
Moreover, it is necessary to perform defect detection on the entire surface of the stencil mask, and an efficient detection method is required.
In order to solve these problems, the present invention includes means for detecting electrons passing through a sample having a through-hole such as a stencil mask, and realizes defect detection not only at the surface but also at the center or the like by a passing electron signal. At the same time, the object is to efficiently detect defects on the entire surface of the stencil mask and the like.
[0006]
[Means for Solving the Problems]
Means for solving the problem will be described with reference to FIG.
In FIG. 1, beam deflectors 7 and 8 are for deflecting an electron beam and scanning the sample 1.
[0007]
The secondary electron detector 9 detects secondary electrons and reflected electrons emitted upward of the sample 1.
The passing electron detector 10 detects electrons that have passed through the through hole of the sample 1, secondary electrons emitted from the inner wall of the through hole, and reflected electrons reflected by the inner wall of the through hole.
[0008]
Next, the configuration and operation will be described.
The beam deflectors 7 and 8 scan an electron beam on the sample 1 having a through hole, and the secondary electrons emitted upward and the reflected reflected electrons are detected by the secondary electron detector 9. Electrons that have passed through the through-hole of the sample 1, secondary electrons emitted from the inner wall of the through-hole, and reflected electrons reflected by the inner wall of the through-hole are detected by the passing electron detector 10, and either one of these detected signals is detected. Alternatively, both images are displayed on a display device (not shown).
[0009]
At this time, a bias voltage is applied between the sample 1 and the passing electron detector 10 as the second detector, and secondary electrons emitted from the inner wall of the sample 1 are extracted to detect efficiently. Yes.
[0010]
In addition, each signal detected by the secondary electron detector 9 as the first detector and the passing electron detector 10 as the second detector is operated (for example, OR operation, addition, subtraction, etc.). An image is displayed.
[0011]
In addition, on the image displayed based on the signal of the secondary electron detector 9 which is the first detector and / or the passing electron detector 10 which is the second detector, the designated region is a beam deflector. Reference numerals 7 and 8 perform scanning control with an electron beam to enlarge and display a designated area.
[0012]
Further, the signals from the secondary electron detector 9 as the first detector and the passing electron detector 10 as the second detector are displayed by OR operation, addition or subtraction, and the electron beam in the through hole of the sample 1 The shape of the inlet and the shape inside the through hole are displayed in a superimposed manner.
[0013]
Accordingly, in a stencil mask or the like in which the sample 1 has a through hole, it is possible to easily detect not only the surface but also the center and the outlet at the exit by the passing electron signal, and the through hole of the stencil mask or the like can be detected. It becomes possible to efficiently detect defects on the entire surface of a certain sample 1.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, the embodiment and operation of the present invention will be sequentially described in detail with reference to FIG.
FIG. 1 shows a system configuration diagram of the present invention.
[0015]
In FIG. 1, a sample 1 detects a secondary electron and a reflected electron emitted by irradiating a narrowed primary electron beam, displays an image, or passes through a through hole of a stencil mask that is the sample 1. This is a target sample for displaying an image by detecting detected electrons and secondary electrons and reflected electrons emitted by irradiating the inner wall of the through hole with a primary electron beam. In particular, it is an object to be subjected to various defect inspections and pattern length measurement including dust adhering to the wall surface (inner wall) of the pattern hole vacated in the sample 1 and is held by the stage 19.
[0016]
The objective lens 2 irradiates the sample 1 with a narrowed primary electron beam.
The condenser lens 3 focuses the primary electron beam emitted from the electron gun 4.
[0017]
The electron gun 4 generates a primary electron beam.
The primary electron beam 5 is a primary electron beam generated and emitted by the electron gun 4.
[0018]
The diaphragm 6 is for giving a predetermined opening angle when the primary electron beam emitted from the electron gun 4 is focused by the condenser lens 3.
The beam deflectors 7 and 8 are deflectors (deflection coils or deflection electrodes) for scanning the sample 1 by deflecting the primary electron beam by two stages.
[0019]
The secondary electron detector 9 detects secondary electrons 14 emitted from the sample 1 when the sample 1 is irradiated with a primary electron beam, and further detects reflected electrons reflected from the sample 1. It is. In the illustrated secondary electron detector 9, since the opening angle when viewed from the reflected electrons reflected from the sample 1 is small and the sensitivity to the reflected electrons is low, the objective lens 2 is not shown for high sensitivity. In the portion facing the sample 1, a backscattered electron detector having a semiconductor disk-like shape with a hole through which primary electrons pass is arranged so that the backscattered electrons reflected from the sample 1 can be detected with high sensitivity. May be. Further, in order to generate an image of absorbed electrons other than the reflected electrons, a signal of the primary electron beam absorbed by the sample 1 is taken out, and an absorbed electron image is displayed instead of the reflected electron image by this signal. Good.
[0020]
In the detection electrode 10, secondary electrons that are emitted from the sample 1 and accelerated upward while rotating in a spiral shape on the optical axis by the magnetic field of the objective lens 2 pass through the center of the secondary electron detector 9. Further, the electric field is applied so as to reach the secondary electron detector 9 with good light collection efficiency while avoiding going upward.
[0021]
The passing electron detector 11 detects the passing electrons 15 that have passed through the pattern hole (through hole) of the sample 1, the secondary electrons emitted by irradiating the inner wall of the pattern hole with the primary electrons, and the reflected electrons that have been reflected. These passing electrons, secondary electrons, and reflected electrons are directly detected, or secondary electrons generated by hitting a specific substance are indirectly detected.
[0022]
The detection electrode 12 is configured so that the passing electrons that pass downward from the pattern hole of the sample 1, the secondary electrons emitted by irradiating the inner wall with the primary electrons, and the reflected reflected electrons are efficiently passed by the passing electron detector 11. An electric field is applied so as to be detected.
[0023]
The bias voltage 16 is a bias voltage applied to the sample 1, and an electric field is applied so that secondary electrons emitted from the sample 1 are efficiently collected by the secondary electron detector 9 and the passing electron detector 11. To be applied.
[0024]
The amplifier 17 amplifies the signal detected by the passing electron detector 11.
The amplifier 18 amplifies the signal detected by the secondary electron detector 9.
[0025]
The stage 19 fixes the sample 1 and moves it in the X direction, the Y direction, and if necessary, the Z direction.
Next, the configuration and operation will be described.
[0026]
(1) The primary electron beam generated by the electron gun 4 is focused by the condenser lens 3, further focused by the objective lens 2, and irradiated on the sample 1 with a thin primary electron beam. In this state, the beam deflector 7 , 8 to deflect the primary electron beam on the sample 1 in the X direction and the Y direction.
[0027]
(2) Secondary electrons emitted upward from the sample 1 in the state of (1) are efficiently collected by the secondary electron detector 9 provided on the objective lens 2 to output a signal, The backscattered electrons are also detected by the secondary electron detector 9 to output a signal, or the backscattered electrons are detected by a thin donut-shaped backscattered electron detector having a hole in the optical axis portion on the lower surface of the objective lens 2 (not shown). Output a signal.
[0028]
(3) Passing electrons (primary electrons) that have passed through the pattern hole of the sample 1 in the state of (1), and secondary electrons emitted when the primary electron beam is irradiated on the inner wall or dust of the pattern hole, The reflected electrons that are reflected are detected by the passing electron detector 11 and a signal is output. At this time, the bias voltage 16 is applied to the sample 1 and secondary electrons generated on the inner wall of the pattern hole of the sample 1 are efficiently extracted and detected in the direction of the passing electron detector 11 to detect the defect portion of the pattern hole. (Image) is obtained with a good S / N ratio.
[0029]
(4) The signals output in (2) and (3) are amplified and displayed on the display device, or both signals are operated (OR operation, addition, subtraction) and displayed on the display device. The information on the upper side of the sample 1 and the information on the inner wall of the pattern hole of the sample 1 are easy to see and displayed at the same position.
[0030]
As described above, the sample 1 is irradiated with the primary electron beam and scanned, and the secondary electron image and the reflection of the surface when viewed from above the pattern shape of the sample 1 by the secondary electrons and the reflected electrons emitted upward. An electron image can be displayed. Further, a passing electron image of passing electrons passing through the pattern hole of the sample 1, a secondary electron image of secondary electrons emitted from the inner wall of the pattern hole, and a reflected electron image of reflected electrons can be displayed. In addition, the secondary electron image and the reflected electron image viewed from above the sample 1 can be displayed and the secondary electron image and the reflected electron image of the inner wall of the pattern hole and the passing electron image passed through can be displayed. In addition, information such as the upper side of the pattern hole and the inner wall can be displayed at once to facilitate inspection (inspection of pattern hole diameter, dust on the inner wall, shape of the pattern hole being wide and narrow below) Can be done. Hereinafter, the pattern hole defect inspection will be described in detail.
[0031]
(1) A primary electron beam is irradiated over a wide range of the sample 1 (for example, the entire surface or a range obtained by dividing the entire surface by a predetermined number) and a low-magnification passing electron image (primary electrons (passing electrons passing through the pattern hole of the sample 1). ) Is displayed.
[0032]
(2) Among the pattern holes on the passing electron image displayed in (1), a pattern hole in which dust adheres to the pattern hole or the diameter of the pattern hole is smaller than the inspection value is extracted.
(3) A passing electron image in which the pattern hole is enlarged is displayed by reducing the current supplied to the beam deflectors 7 and 8 so that the pattern hole extracted in (2) is displayed on the entire surface.
[0033]
(4) The diameter of the pattern hole and the adhesion of dust are inspected based on the passing electron image enlarged in (3). Furthermore, the secondary electron image and the reflected electron image emitted upward of the sample 1 described above, and the secondary electron image and the reflected electron image emitted from the inner wall of the pattern hole are displayed in a superimposed manner. Based on the shape of the upper surface, the secondary electron image or the reflected electron image inside the pattern hole, and the passing electron image, it is possible to easily inspect which shape is abnormal (for example, The secondary electron image in the upward direction, the reflected electron image, the secondary electron image on the inner wall, the reflected electron image, and the passing electron image are color-coded and displayed as a line drawing in a superimposed manner, making it easy to identify which location is abnormal Can be inspected).
[0034]
(5) In addition, the dimensions of the pattern holes of the enlarged secondary electron image and the passing electron image can be respectively measured to determine whether each is a predetermined inspection allowable range, and even if the pattern hole has a so-called C shape, The inclination of the hole (for example, the taper angle in the stencil mask) can be obtained (the upper dimension is measured by the secondary electron image in the upper direction, and the dimension of the narrowest part of the pattern hole is measured by the transmission electron image. Slope can be determined).
[0035]
【The invention's effect】
As described above, according to the present invention, the specimen 1 having the through hole is irradiated with the primary electron beam, the secondary electron image in the upward direction, the reflected electron image, and the passing electron image that has passed through the through hole. Since the secondary electron image emitted from the inner wall of the hole and the reflected electron image reflected by the inner wall of the through hole are displayed,
(1) A passing electron image of passing electrons that have passed through a holed pattern can be displayed on the sample 1, and projections attached to the entire inner surface of the hole can be observed.
[0036]
(2) A bias voltage is applied to the sample 1 to extract secondary electrons emitted from the inner wall of the through hole of the sample 1 to display a secondary electron image, and the shape of the protrusion on the inner wall of the through hole is changed to a high S / It can be displayed and observed in N ratio.
[0037]
(3) The upper secondary electron image, the reflected electron image of the sample 1, the secondary electron image of the inner wall of the through hole of the sample 1, the reflected electron image, and the passing electron image that has passed through the through hole are displayed together. The upper surface of the hole and the shape of the inner wall of the through hole can be displayed at the same time, so that the shape can be inspected three-dimensionally.
[0038]
(4) Thus, when the through-hole is thick, the shape of the inner wall of the hole of the stencil mask, which has been difficult to inspect only with the conventional secondary electron image in the upward direction, can be easily obtained by the present invention. It became possible to inspect.
[0039]
(5) Further, after displaying the entire image of the sample 1, only a part of the sample 1 is enlarged and the shape of the through hole and dust attached to the inside can be easily observed and inspected.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of the present invention.
[Explanation of symbols]
1: Sample 2: Objective lens 3: Condenser lens 4: Electron gun 7, 8: Beam deflector 9: Secondary electron detector 11: Transmission electron detector 16: Bias voltage 19: Stage

Claims (4)

In an electron microscope that outputs a two-dimensional image of a through-hole by scanning a sample with a through-hole two-dimensionally with an electron beam,
Scanning means for two-dimensionally scanning the sample on which the through hole is formed with an electron beam;
A first detector provided on the side irradiated with the electron beam to detect the secondary electrons or reflected electrons emitted from the sample;
Provided on the opposite side of the sample from the electron beam irradiation to detect electrons passing through the through hole of the sample, secondary electrons emitted from the inner wall of the through hole, or reflected electrons reflected from the inner wall of the through hole A second detector;
An image of the shape of the upper hole of the through-hole formed in the sample and a signal detected by the second detector, generated from the signal detected by the first detector, and formed on the sample. Means for synthesizing and outputting or displaying both the transmission shape of the hole when the electron beam is transmitted through the through-hole and the image of the shape of the foreign matter including the unevenness of the inner wall of the hole in one image
Electron microscope, comprising the. An image obtained by combining the two into one is output or displayed, and one or both of the first detector image and the second detector image are output or displayed together. The electron microscope according to claim 1. The signal detected by the first detector is a secondary electron signal detected by the first detector, and the signal detected by the second detector is a transmitted electron detected by the second detector. claim 1 or claim 2, wherein the electron microscope is characterized in that a signal. Output or display any one or more of the combined image, the image of the first detector, or the image of the second detector, and a designated area on the output or displayed image 4. The electron microscope according to claim 1, wherein the scanning means includes means for scanning the electron beam to enlarge and output or display the designated area.

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