JP2678059B2 - Electron beam equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] An electron beam apparatus for irradiating an internal wiring of a semiconductor integrated circuit with an electron beam and analyzing the energy of secondary electrons emitted from an irradiation point to measure the voltage of the internal wiring, For the purpose of improving the measurement accuracy and performing the measurement at high speed, the electron beam is converged by the objective lens to irradiate the sample, and the energy of secondary electrons emitted from the sample is provided in the objective lens. In the electron beam apparatus for measuring the voltage of each part of the sample by detecting with the secondary electron detector after the analysis with the secondary energy detector, the analysis of the energy analyzer is provided between the energy analyzer and the secondary electron detector. It has an anode-free microchannel plate which is arranged so as to face the grid and outputs secondary electrons by multiplying the secondary electrons multiplied by the microchannel plate. Nchireta and configured to detect the secondary electron detector formed of photo-multiplier.

[Industrial applications]

The present invention relates to an electron beam apparatus, and more particularly to an electron beam apparatus that irradiates an internal beam of a semiconductor integrated circuit with an electron beam and analyzes the energy of secondary electrons emitted from the irradiation point to measure the voltage of the internal line. .

In recent years, voltage waveform measurement technology using electron beams has been widely used in fields such as LSI diagnosis. The principle of the voltage measurement is to use the physical phenomenon that the energy changes linearly with the change of the potential of the sample that emits the secondary electrons. The energy distribution of the secondary electrons is measured and the energy shift is measured. The amount is calculated and converted into voltage.

Therefore, the measurement accuracy depends on the energy analysis accuracy, and especially when the sample has a fine and complicated structure such as a semiconductor integrated circuit (LSI), the superiority or inferiority becomes remarkable. One of the factors that influence the accuracy of the energy analyzer is the detection efficiency of electrons that have passed through the analyzer (that is, electrons that have passed through the analysis grid). The characteristics required for an ideal analyzer are that the detection efficiency is as large as possible and always constant, that is, it does not change depending on the sample voltage or the analysis voltage.

[Conventional technology]

 FIG. 5 and FIG. 6 are structural views of each example of the conventional device.

In FIG. 5, the electron beam is a magnetic field type objective lens 10.
Are converged by and are irradiated onto the sample 11 such as an LSI. Sample 11
The secondary electrons emitted from are accelerated toward the objective lens 10 by the extraction voltage V _E of the extraction grid 12 which constitutes the energy analyzer provided in the objective lens 10 and analyzed by the buffer voltage V _B of the buffer grid 13. The orbit is controlled so that the light enters the grid 14 substantially vertically. Analysis grid
Only the secondary electrons that exceed the analysis voltage V _R of 14 are the analysis grid 14
After passing through, the light is collected and incident on the scintillator 16 by the reflector 20 and the collector 15. When secondary electrons collide with the scintillator 16, it is converted into an optical signal by the scintillator 16, and this optical signal is guided by a light guide 17 to a photomultiplier (photomultiplier tube) 18, where it is amplified as a current signal. This current signal is supplied from the terminal 19 to the preamplifier at the next stage.

6, those parts which are the same as those corresponding parts in FIG. 5 are designated by the same reference numerals, and a description thereof will be omitted. In FIG. 6, the secondary electrons that have passed through the analysis grid 14 are incident on the microchannel plate 26 having the anode 25, where the electrons are multiplied. The multiplied electrons output from the microchannel plate 26 enter the anode 25, and a current flows in the anode 25 according to the amount of the electrons, and is supplied as a current signal from the terminal 27 to the preamplifier in the next stage.

In FIGS. 5 and 6, the hatched portion is a metallic material, and the matte portion is an insulating material such as ceramic.

[Problems to be solved by the invention]

In the apparatus shown in FIG. 5, the energy VSE from the sample 11 of voltage Vs
The secondary electron emitted at O [eV] has energy of VSEO + V _E −Vs [eV] when passing through the extraction grid 12,
When passing through the buffer grid 13, VSEO + V _B −Vs [e
It has energy of V] and has VSEO + V _B −Vs [eV], and takes a secondary electron orbit as schematically shown in FIG. 7 in the energy analyzer.

That is, the energy of the secondary electrons at the position R passing through the analysis grid 14 changes according to the sample voltage Vs and the analysis voltage V _R. Therefore, if the analysis voltage V _R is changed to perform measurement, the trajectory of the secondary voltage changes, and the secondary electrons do not reach the scintillator 16, which also changes the detection efficiency.

Therefore, the level of the detection signal SE when the analysis voltage V _R is varied with the sample voltages of 0 V and 5 V, that is, the analysis curve, is moved in parallel along the analysis voltage axis as shown by the solid lines I a and I b in FIG. Although the relationship is ideal, in reality, the shape greatly changes with the movement along the analysis voltage axis with respect to the change in the sample voltage Vs as indicated by the broken lines IIa and IIb. Therefore, there is a problem in that the amount of movement of the analysis curve cannot be accurately obtained, and a voltage measurement error occurs.

In the device of FIG. 6, the detection efficiency can be improved by bringing the microchannel plate 26 close to the analysis grid 14. However, in the device of FIG. Has a large capacitance, making it difficult to speed up the preamplifier in the next stage.
Since the current signal at 27 is biased to a high voltage of several 100V, a circuit for isolating the high voltage from the signal current is required, and from this point as well, there is a problem that it is difficult to increase the speed.

The present invention has been made in view of the above points, and an object of the present invention is to provide an electron beam apparatus that improves measurement accuracy and performs measurement at high speed.

[Means for solving the problem]

In the electron beam apparatus of the present invention, the electron beam is converged by the objective lens to irradiate the sample, the energy of the secondary electrons emitted from the sample is analyzed by an energy analyzer provided in the objective lens, and then the secondary electron is emitted. In an electron beam device that detects the voltage of each part of the sample by detecting with a detector, it is placed between the energy analyzer and the secondary electron detector so as to face the analysis grid of the energy analyzer and multiply the secondary electrons. The secondary electron multiplied by the microchannel plate is detected by a secondary electron detector including a scintillator and a photomultiplier.

[Operation] In the present invention, the secondary electrons passing through the analysis grid are multiplied by the anode-free microchannel plate and output as constant energy, and the multiplied secondary electrons are formed by the scintillator and the photomultiplier. Detect with electronic detector. Therefore, the orbits of the multiplied secondary electrons are not affected by the sample voltage and the analysis voltage, the detection efficiency is constant, the measurement accuracy is improved, and the capacitance of the secondary electron detector is small and the output current is small. It enables high speed measurement of signals.

〔Example〕

FIG. 1 shows a structural diagram of an embodiment of the device of the present invention. 5, the same parts as those in FIG. 5 are denoted by the same reference numerals, and the description thereof will be omitted. Further, in FIG. 1, the hatched portion is a metallic material,
The satin portion is an insulating material such as a ceramic material.

In FIG. 1, an extraction grid 12, a buffer grid 13, an analysis grid 14, and an anode-free microchannel plate 30 are provided in the objective lens 10 in order from the sample 11 side along the electron beam axis.

As shown in FIG. 2, the anode-free microchannel plate 30 has, for example, Fe on both sides of a plate material (for example, glass) 30c provided with innumerable minute through holes (channels) 30b substantially along the passage holes 30a for the electron beam to be irradiated. It is provided with an input electrode 30d and an output electrode 30e formed by vapor deposition of -Cr, and is coated with a substance that emits secondary electrons and causes electron multiplication when electrons enter the inner peripheral surface of each fine through hole 30b. ing. A voltage of about +50 to 100V (for example, + 100V) is applied to the input electrode 30d, and a voltage of about +500 to 1000V (for example, + 500V) is applied to the output electrode 30e.

The input electrode 30d is an accelerating electrode for accelerating the electrons to be detected that have passed through the analysis grid 14 to collide with the inner wall near the entrance of the fine through hole 30b. Therefore, the through hole 30b is arranged so as to be inclined with respect to the incident direction of the detected electrons.

The output electrode 30e further accelerates the secondary electrons emitted from the inner wall of the through hole 30b, and in order to obtain a high secondary electron emission efficiency at the next collision, an acceleration electric field along the hole in the through hole 30b is obtained. It is an electrode for generating.

Returning to FIG. 1, the secondary electrons emitted from the sample 11 irradiated with the electron beam pass through the extraction grid 12 and the buffer grid 13 and enter the analysis grid 14,
The secondary electrons that have passed through this are electron-multiplied by the anode-free microchannel plate 30. The electrons multiplied by the anode-free microchannel plate 30 and output are collected by the reflector 20 and the collector 15 and incident on the scintillator 16, and a current signal is output from the terminal 19.

Here, the energy VSEO [eV] from the sample 11 of the voltage Vs
The secondary electrons emitted at have energy of VSEO + V _E −Vs [eV] when passing through the extraction grid 12, have energy of V SEO + V _B −Vs [eV] when passing through the buffer grid 13, and pass through the analysis grid 14. VSEO + V when passing
_It has an energy of _R- Vs [eV], and the energy of the secondary electrons varies depending on the sample voltage Vs and the analysis voltage VR.

However, since the anode-free microchannel plate 30 is provided at a position several mm from the analysis grid 14, the change in the orbit due to the energy fluctuation of the secondary electrons at the position of the anode-free microchannel plate 30 is small and can be almost ignored. And the energy of the multiplied electrons output from the output electrode 30e of the microchannel plate 30 without an anode is always several tens of ev because it is a secondary electron from the material inside the microchannel plate.
And the voltage of the output electrode is constant at 500V. Therefore, the orbits of the multiplied electrons are determined by the electric field distribution of the reflector 20, the collector 15, etc., and the sample voltage Vs and the analysis voltage V _R
Not affected by. That is, the detection efficiency is also constant, and the fourth
An ideal analysis curve is obtained as shown in the figure. Highly accurate voltage measurement is possible. In the figure, solid lines IIIa and IIIb show analysis curves at sample voltages of 0V and 5V, respectively.

In addition, scintillator 16, light guide 17, photomaru 18
Since the electron detector configured in is used, the terminal is
Since the capacitance in 19 is small and the current signal is not biased to a high voltage, the preamplifier in the next stage is sped up and the measurement can be performed at high speed.

〔The invention's effect〕

As described above, according to the electron beam apparatus of the present invention, the measurement accuracy of the sample voltage can be improved and the measurement can be performed at high speed, which is extremely useful in practice.

[Brief description of the drawings]

FIG. 1 is a structural diagram of an embodiment of the device of the present invention, FIG. 2 is a configuration diagram of an embodiment of a microchannel plate without an anode, and FIG. 3 is a diagram schematically showing electron trajectories of the device of the present invention. FIG. 4 is a diagram showing an analysis curve of the device of the present invention, FIGS. 5 and 6 are structural diagrams of each example of the conventional device, FIG. 7 is a diagram schematically showing electron trajectories of the conventional device, and FIG. It is a figure which shows the analysis curve of a conventional apparatus. In the figure, 11 is a sample, 12 is a drawing grid, 13 is a buffer grid, 14 is an analytical grid, 16 is a scintillator, 17 is a light guide, 18 is a photomul, and 30 is a microchannel plate without an anode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Soichi Hama 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Takayuki Abe 1015, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited ( 56) References JP-A-63-231855 (JP, A) JP-A-63-293847 (JP, A) JP-A-61-97575 (JP, A)

Claims (1)

(57) [Claims] 1. An electron beam is converged by an objective lens (10) to irradiate a sample (11), and energy of secondary electrons emitted from the sample (10) is provided in the objective lens (10). In the electron beam apparatus for measuring the voltage of each part of the sample (10) after being analyzed by the energy analyzer and detected by the secondary electron detector, the energy analysis is performed between the energy analyzer and the secondary electron detector. And an anode-free microchannel plate (30) for multiplying and outputting secondary electrons, the microchannel plate (30) being arranged so as to face the analysis grid (14) of the vessel and being multiplied by the microchannel plate (30). An electron beam device characterized by being configured to detect a secondary electron by a secondary electron detector composed of a scintillator (16) and a photomultiplier (18).