JP2004362883A - Secondary electron detector and charged particle beam inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance a collection rate of secondary electrons to enhance detection efficiency of the secondary electrons. <P>SOLUTION: This secondary electron detector 1 is provided with: a scintillator 3 for converting the secondary electrons to a light signal; an electron collecting electrode 2 for guiding and collecting the secondary electrons to the scintillator 3 by an electric field; and a photoelectron multiplier 6 for converting the light signal to an electric signal. The collecting electrode 2 is divided into a grid electrode 2a and an auxiliary electrode 2b. The grid electrode 2a is installed in the front part of the scintillator 3; the auxiliary electrode 2b surrounds a side part and a rear part of the scintillator 3; and voltages are allowed to be individually applied to the grid electrode 2a and the auxiliary electrode 2b. By separating the grid electrode 2a from the auxiliary electrode 2b and by respectively applying the different voltages to them, the electric field for guiding and collecting the secondary electrons to the scintillator 3 is formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a secondary electron detector that detects secondary electrons excited by irradiation with a charged particle beam, and a charged particle beam inspection device that inspects a sample using the secondary electron detector.
[0002]
[Prior art]
2. Description of the Related Art A charged particle beam inspection device that inspects a sample by irradiating a sample with a charged particle beam such as an electron beam and detecting secondary electrons excited and emitted by the charged particle beam is known.
[0003]
For example, the potential of each TFT cell is measured by irradiating the TFT cell of the thin film transistor array substrate (TFT array substrate) with an electron beam and detecting the intensity of the generated secondary electrons, and the measured signal of the TFT cell is estimated. There is known a TFT array inspection apparatus for inspecting whether a TFT cell includes a defect such as a short circuit by determining whether the signal is a signal to be output. For example, Patent Document 1 is known as such an apparatus.
[0004]
Such a charged particle beam inspection apparatus includes a secondary electron detector as a detecting means for detecting secondary electrons. As the secondary electron detector, a detector that converts a secondary electron into an optical signal using a scintillator and detects the signal is known. FIG. 4 is a schematic configuration diagram of a conventional secondary electron detector (for example, Patent Document 2). When the electron beam 110 is condensed and irradiated on the sample 111 by the objective lens 112, secondary electrons are excited by the electron beam and emitted from the sample 111.
[0005]
The secondary electron detector 101 includes a scintillator 103, a collector 102 provided in front of the scintillator 103, and a light guide 105 for guiding light converted by the scintillator 103 to a photomultiplier tube 106. A voltage V1 (for example, 200 V) is applied to the collector 102 to attract secondary electrons emitted from the sample 111. Also, a high voltage V2 (for example, 10 kV) is applied to the scintillator 103, and the secondary electrons that have passed through the grid of the collector 102 are taken in. In the scintillator 103, secondary electrons are converted into light, and the light reaches the cathode 107 of the photomultiplier tube 106 by the light guide 105. A voltage V3 (for example, 500 to 1000 V) is applied to the cathode. Photoelectrons struck out of the cathode 107 by light are multiplied by a large number of secondary electron multipliers 108 and then captured by the anode 109. From the anode 109, a signal corresponding to the amount of secondary electrons collected by the scintillator 103 is output.
[0006]
[Patent Document 1]
Japanese Patent Application No. 11-25247 (paragraph numbers 0040 and 0041, FIG. 1)
[0007]
[Patent Document 2]
JP-A-9-82260 (paragraph number 0002 to paragraph number 0004, FIG. 3)
[0008]
[Problems to be solved by the invention]
In a sample inspection using a detection signal obtained by detecting secondary electrons emitted from a sample, such as measurement of a sample potential by a TFT inspection device, in order to improve the accuracy of inspection such as defect determination, the S of the detection signal is required. It is required to increase the / N ratio. In order to improve the S / N ratio, it is necessary to increase the secondary electron detection efficiency in the secondary electron detector.
[0009]
Conventional secondary electron detectors cannot be said to sufficiently efficiently collect secondary electrons emitted from a sample, and secondary electrons that do not reach the scintillator remain. If the uncollected secondary electrons can be collected, it is expected that the detection efficiency of the secondary electrons will increase.
[0010]
Accordingly, it is an object of the present invention to solve the above-mentioned conventional problems and to increase the collection rate of secondary electrons and increase the efficiency of detecting secondary electrons.
[0011]
[Means for Solving the Problems]
A secondary electron detector of the present invention includes a scintillator for converting secondary electrons into an optical signal, an electron collecting electrode for attracting and collecting secondary electrons to the scintillator by an electric field, and a photoelectron for converting an optical signal into an electric signal. A multiplying tube for separating the electron collecting electrode into a grid electrode and an auxiliary electrode. The grid electrode is provided at the front of the scintillator, and the auxiliary electrode surrounds the side and the rear of the scintillator so that a voltage can be individually applied to the grid electrode and the auxiliary electrode. By separating the grid electrode and the auxiliary electrode and applying different voltages to each other, an electric field for attracting and collecting secondary electrons in the scintillator is formed. Here, the voltage applied to the auxiliary electrode is lower than the voltage applied to the grid electrode.
[0012]
Further, the charged particle beam inspection device of the present invention is an inspection device for detecting secondary electrons excited by irradiating a sample with a charged particle beam and inspecting the sample, and includes a secondary electron detector of the present invention. The voltage applied to the auxiliary electrode is lower than the voltage applied to the grid electrode.
[0013]
The charged particle beam inspection apparatus can measure a sample potential with secondary electrons and inspect the sample with the measured potential. This charged particle beam inspection apparatus can be applied to a TFT array inspection apparatus in which an inspection target is a TFT cell, and a secondary electron excited by irradiating the TFT cell with an electron beam is detected by a secondary electron detector. The potential of the TFT cell is measured by the detected secondary electrons, and the TFT array can be inspected by the measured potential.
[0014]
By using the secondary electron detector of the present invention, the collection efficiency of secondary electrons is increased, the S / N ratio of a detection signal is improved, and the inspection accuracy of a sample such as a TFT array is increased.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 is a schematic diagram for explaining a secondary electron detector of the present invention. In FIG. 1, a secondary electron detector 1 includes a scintillator 3 for converting secondary electrons emitted from a sample (not shown) into an optical signal, and an electron collecting device for causing the scintillator 3 to collect secondary electrons. The apparatus includes an electrode 2, a photomultiplier tube 6 for converting an optical signal converted by the scintillator 3 into an electric signal, and a light guide 5 for connecting the sample and the photomultiplier tube 6 and transmitting the optical signal.
[0017]
The scintillator 3 has one end of a light guide 5 connected to the surface opposite to the surface for collecting secondary electrons, and is fixed by a scintillator fixture 4.
[0018]
The electron collecting electrode 2 of the present invention is configured by being divided into two electrodes, a grid electrode 2a disposed in front of the scintillator 3 and an auxiliary electrode 2b disposed so as to surround the side and rear of the scintillator 3. The grid electrode 2a and the auxiliary electrode 2b are electrically separated by, for example, an insulating member 2c.
[0019]
In the configuration shown in the drawing, the auxiliary electrode 2 b is provided so as to surround the side and rear of the scintillator 3 except for the front and the scintillator fixture 4. Although not shown, an opening is provided in the auxiliary electrode 2b in front of the scintillator 3, so that secondary electrons passing through the grid electrode 2a reach the scintillator 3. An opening for passing the light guide 5 is formed in a part of the auxiliary electrode 2b. The opening through which the light guide 5 passes is not limited to the rear part of the auxiliary electrode 2b as shown in FIG. 1, but may be provided on the side part of the auxiliary electrode 2b.
[0020]
A power supply 7 and a power supply 8 are connected to the grid electrode 2a and the auxiliary electrode 2b, respectively, and a power supply 9 is connected to the scintillator 3.
[0021]
Different voltages can be applied to the grid electrode 2a and the auxiliary electrode 2b by the power supply 7 and the power supply 8, respectively. For example, a voltage of about +300 V to 700 V is applied to the grid electrode 2 a by the power supply 7, and a voltage lower than the voltage applied to the grid electrode 2 a is applied to the auxiliary electrode 2 b by the power supply 8. Further, a voltage of, for example, about +8000 V is applied to the scintillator 3 by the power supply 9. The voltage applied to the auxiliary electrode 2b may be a negative voltage.
[0022]
When a voltage is applied to the grid electrode 2a and the auxiliary electrode 2b, an electric field is formed around the secondary electron collecting electrode 2. This electric field attracts secondary electrons emitted from the sample and spread over a wide area toward the secondary electron collecting electrode 2. At this time, by making the voltage applied to the auxiliary electrode 2b lower than the voltage applied to the grid electrode 2a, the attracted secondary electrons are collected more on the grid electrode 2a side than on the auxiliary electrode 2b. Secondary electrons that have passed through the grid electrode 2a are collected by the scintillator 3 applied to a higher voltage, and are converted into optical signals.
[0023]
FIG. 1A shows a configuration example in which a power supply 8 is connected to the auxiliary electrode 2b, and FIG. 1B shows a configuration example in which the auxiliary electrode 2b is at 0 V or ground. The auxiliary electrode can be grounded by short-circuiting it to a chamber or the like of a device provided with a secondary electron detector.
[0024]
Note that the configuration of the photomultiplier tube 6 can be the same as the configuration shown in FIG. 4, and a description thereof will be omitted.
[0025]
FIG. 2 is a diagram showing an example of the output of the secondary electron detector with respect to the voltage applied to the auxiliary electrode in the secondary electron detector of the present invention. In this example, a case is shown in which +500 V is applied to the grid electrode 2a and fixed, and +300 V and 0 V are applied to the auxiliary electrode 2b (indicated by a triangle in the figure).
[0026]
The secondary electron detector output (indicated by the symbol “■” in the figure) obtained when the voltage applied to the auxiliary electrode 2b is lower than the voltage applied to the grid electrode 2a, and the area around the scintillator without the auxiliary electrode Is compared with the secondary electron detector output (shown by a black circle in the figure) obtained when the same voltage is applied to the electrodes surrounding the electrodes, the secondary electron detector when a low voltage is applied to the auxiliary electrode 2b The output is larger than the output of the secondary electron detector without the auxiliary electrode, and it is confirmed that the secondary electron detection efficiency is improved. The detection efficiency is improved by about 20% when compared with the output of the secondary electron detector.
[0027]
In the secondary electron detector of the present invention, the electrode for collecting electrons is separated into a grid electrode for collecting secondary electrons and passing the scintillator and an auxiliary electrode surrounding the side and rear of the scintillator, and a voltage applied to the auxiliary electrode. Is lower than the voltage applied to the grid electrode, thereby forming an electric field distribution that attracts more secondary electrons toward the grid electrode. According to the electric field formed on the electron collecting electrode of the secondary electron detector of the present invention, the secondary electrons that have been drawn to a portion other than the grid electrode in the related art can be collected by the grid electrode. Secondary electrons can be collected to improve the detection efficiency of secondary electrons.
[0028]
Next, an example of a charged particle inspection apparatus using the secondary electron detector of the present invention will be described. The example shown in FIG. 3 is a configuration example of an electron beam inspection apparatus such as a TFT array inspection apparatus. The TFT array inspection apparatus uses an electron beam as a charged particle beam, irradiates the TFT cell with an electron beam, measures the intensity of secondary electrons generated, and measures the potential of the TFT cell. Is determined.
[0029]
3, the electron beam inspection apparatus 10 is a configuration example of an electron gun / secondary electron detection system including an extraction electrode and an energy filter. The electron gun / secondary electron detection system is provided in a chamber 12.
[0030]
An electron beam (not shown) emitted from the electron gun 11 irradiates the sample 16 after passing through the energy filter 14 and the extraction grid electrode 15. Secondary electrons are excited in the sample 16 by the irradiation of the electron beam, and the excited secondary electrons are emitted to the outside of the sample 16. The secondary electron detector 1 collects emitted secondary electrons (not shown), and performs a sample inspection by measuring the intensity of the generated secondary electrons. In the case of inspecting a TFT cell, the potential of the TFT cell is measured from the intensity of the detected secondary electrons, and the measured potential is compared with a predetermined potential to perform inspection such as defect determination of the TFT cell. Do.
[0031]
In order to suppress secondary electrons emitted from the sample from colliding with a wall surface or the like to generate secondary electrons, the recoil secondary electron suppression grid 13 is provided with the above-described electron gun / secondary electron detection system. It is provided around.
[0032]
The secondary electron detector 1 of the present invention improves the S / N ratio by increasing the detection efficiency of the secondary electrons emitted from the sample 16, thereby improving the inspection accuracy of the electron beam inspection apparatus 10. it can.
[0033]
【The invention's effect】
As described above, according to the present invention, the collection rate of secondary electrons can be increased, and the detection efficiency of secondary electrons can be increased.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a secondary electron detector of the present invention.
FIG. 2 is a diagram showing an example of a secondary electron detector output with respect to a voltage applied to an auxiliary electrode in the secondary electron detector of the present invention.
FIG. 3 is a configuration example of an electron beam inspection apparatus.
FIG. 4 is a schematic configuration diagram of a conventional secondary electron detector.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Secondary electron detector, 2 ... Electron collection electrode, 2a ... Grid electrode, 2b ... Auxiliary electrode, 3 ... Scintillator, 4 ... Scintillator fixture, 5 ... Light guide, 6 ... Photomultiplier tube, 7, 8 Reference numeral 9 power supply 10 electron beam inspection device 11 electron gun 12 chamber 13 recoil secondary electron suppression grid 14 energy filter 15 extraction grid 16 sample 101 101 secondary Electron detector, 102, collector, 103, scintillator, 105, light guide, 106, photomultiplier, 107, cathode, 108, secondary electron multiplier, 109, anode, 110, electron beam, 111, sample, 112 Objective lens.

Claims (5)

A scintillator for converting secondary electrons into optical signals,
An electron collection electrode for attracting and collecting secondary electrons to the scintillator by an electric field;
A photomultiplier tube for converting an optical signal into an electric signal,
The electron collecting electrode is separated into a grid electrode provided at the front of the scintillator and an auxiliary electrode surrounding the side and the rear of the scintillator, and a voltage can be individually applied to the grid electrode and the auxiliary electrode. ,
A secondary electron detector, wherein an electric field for attracting and collecting secondary electrons is formed in the scintillator by applying different voltages to the grid electrode and the auxiliary electrode. The secondary electron detector according to claim 1, wherein a voltage applied to the auxiliary electrode is lower than a voltage applied to the grid electrode. A microbeam inspection apparatus comprising the secondary electron detector according to claim 1, wherein a secondary electron excited by irradiating the sample with a charged particle beam is detected by the secondary electron detector to inspect the sample. So,
The voltage applied to the auxiliary electrode is lower than the voltage applied to the grid electrode. The charged particle beam inspection apparatus according to claim 3, wherein a sample potential is measured by the secondary electrons, and the sample is inspected by the potential. Secondary electrons excited by irradiating the TFT cell with an electron beam are detected by the secondary electron detector, the potential of the TFT cell is measured by the secondary electrons, and the TFT array is inspected by the potential. The charged particle beam inspection apparatus according to claim 4, wherein

Images