JPH0326901B2

JPH0326901B2 -

Info

Publication number: JPH0326901B2
Application number: JP59256958A
Authority: JP
Inventors: Motosuke Myoshi
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1984-12-05
Filing date: 1984-12-05
Publication date: 1991-04-12
Also published as: JPS61135035A

Description

[Brief explanation of the drawing]

第１図は本発明に係る電子ビームテスタ用表面
電位測定装置の一実施例を示す構成説明図、第２
図は同じく他の実施例を示す構成説明図、第３図
ａ，ｂは各対応して第１図、第２図におけるエネ
ルギフイルタの特性を示す特性図、第４図は表面
電位測定装置の測定原理を説明するために示す二
次電子エネルギ分布を示す図、第５図は従来の表
面電位測定装置を示す構成説明図である。１０……リング状シンチレータ、１１……高電
圧面、２０……バツフアグリツド、５０……試
料、５１……半球状阻止電場型エネルギフイル
タ、５３……フイルタグリツド。 FIG. 1 is a configuration explanatory diagram showing one embodiment of a surface potential measuring device for an electron beam tester according to the present invention, and FIG.
The figure is a configuration explanatory diagram showing another embodiment, FIGS. 3a and 3b are characteristic diagrams showing the characteristics of the energy filters in FIGS. 1 and 2, respectively, and FIG. 4 is a diagram showing the characteristics of the energy filter in FIGS. FIG. 5 is a diagram showing a secondary electron energy distribution for explaining the measurement principle, and is a configuration explanatory diagram showing a conventional surface potential measuring device. DESCRIPTION OF SYMBOLS 10... Ring-shaped scintillator, 11... High voltage surface, 20... Buffer grid, 50... Sample, 51... Hemispherical blocking electric field type energy filter, 53... Filter grid.

Claims

[Claims] 1. Secondary electrons having a hemispherical blocking electric field type energy filter installed approximately at the position of the sample to which the electron beam is irradiated, and a ring-shaped scintillator installed around this energy filter. 1. A surface potential measuring device for an electron beam tester, comprising: a detector. 2. A surface potential for an electron beam tester according to claim 1, characterized in that a buffer grid is disposed between the filter grid of the energy filter and the scintillator, and the buffer grid is biased with a positive potential. measuring device. ** Theory [Technical Field of the Invention] The present invention relates to a surface potential measuring device used in an electron beam tester, and more particularly to a secondary electron detection unit. [Technical background of the invention] An electron beam tester uses an electron beam to
This is a device that measures the surface potential of semiconductor wafer circuits such as LSI using a non-contact method. In this case, an energy filter (energy analyzer) is generally used to measure the surface potential of the sample using an electron beam, and the principle of surface potential measurement is based on a blocking field type energy filter and a secondary electron detector. is used in combination to detect secondary electrons with energy above a certain threshold, which are discriminated by an energy filter. FIG. 4 shows the energy distribution of secondary electrons emitted from the sample surface when the sample surface is irradiated with an electron beam. This energy distribution shifts when the surface potential of the sample changes, so by measuring the amount of shift, it is possible to know the change in surface potential. FIG. 5 shows a conventional surface potential measuring device, in which a hemispherical blocking field type energy filter 51 has a double grid (the inner side is the extraction voltage generation grid) provided so as to cover the front of the sample 50 in a hemispherical manner. 52, with a filter grid 53 on the outside), and a secondary electron detector 54 (consisting of a scintillator 55 and a photomultiplier tube 56) is disposed at one location on the outside. There is. The above-mentioned extraction voltage generation grid 52
is for efficiently making secondary electrons 58 emitted from the sample surface when the sample 50 is irradiated with an electron beam 57 enter the filter grid 53, and generates a voltage of about 100 to 1000V. A suitable voltage is applied to the filter grid 53, which forms a potential barrier against the secondary electrons 58. The secondary electron detector 54 detects the total amount of secondary electrons reaching the potential barrier, and measures the change _in the detection current Is to determine the surface potential _Vs of the sample 50. You can notice changes. The scintillator 55 of the secondary electron detector 54 is a type of phosphor and has a metal film (usually a thin film of aluminum) deposited on its surface.
High voltage (8 to 10kV) is applied,
The incoming secondary electrons are accelerated and hit the phosphor, causing it to emit light. This light emission output is detected by a photomultiplier tube 56 and converted into an electrical signal. In the surface potential measuring device described above, in order to increase the measurement sensitivity, it is effective to install the secondary electron detector 54 close to the filter grid 53 to increase the secondary electron detection efficiency. [Problems with Background Art] However, the above-described conventional surface potential measuring device has a drawback in that measurement accuracy is poor because measurement results vary depending on the installation position of the secondary electron detector 54. The reason is that the hemispherical energy filter 51 uniformly and efficiently transfers secondary electrons emitted in all directions forward from the secondary electron emission source (sample 50) located at the approximate center of the hemisphere to the filter grid 53. Since it can be made incident,
This is because, although it has excellent characteristics, the secondary electron detector 54 is installed only in one of the above directions, so it can only detect secondary electrons emitted in this one direction. . In other words, the hemispherical energy filter 5 can capture secondary electrons in all directions.
The advantages of the method No. 1 are not fully utilized, and the measurement results will vary depending on the direction in which the secondary electron detector 54 is installed. [Object of the invention] The present invention has been made in view of the above circumstances, and
The present invention provides a surface potential measuring device for an electron beam tester that can improve measurement sensitivity and measurement accuracy. [Summary of the Invention] That is, in the surface potential measuring device for an electron beam tester of the present invention, a hemispherical blocking electric field type energy filter is installed approximately at the center of the sample irradiated with the electron beam, and a hemispherical blocking electric field type energy filter is installed around the energy filter. It is characterized by being provided with a secondary electron detector having a ring-shaped scintillator installed therein. As a result, secondary electrons emitted from the sample are detected by the secondary electron detector in all directions, improving measurement sensitivity and measurement accuracy. [Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The surface potential measuring device shown in FIG. 1 is the same as the one in FIG. 5, except that the configuration of the secondary electron detector is different from the conventional surface potential measuring device described above with reference to FIG. 5. Reference numerals are given and explanations thereof are omitted. The secondary electron detector includes a ring-shaped scintillator 10 and a photomultiplier tube (not shown),
The inside of the ring-shaped scintillator 10 is a high voltage surface 11, and the scintillator 10 is installed around the filter grid 53 with this high voltage surface 11 facing the filter grid 53 side. According to the above configuration, the secondary electrons 58 emitted from the surface of the sample 50 in all forward directions are uniformly and efficiently incident on the filter grid 53 in all directions by the extraction voltage generating grid 52, and the potential caused by the filter grid 53 is All secondary electrons that have crossed the barrier are detected by the ring-shaped scintillator 10. By using the ring-shaped scintillator 10 in this way, there is no directionality regarding secondary electron detection, so compared to the case where secondary electron detection is performed in one direction as shown in the conventional example, the secondary electron Detection efficiency (measurement sensitivity) and measurement accuracy are improved. In addition, in order to efficiently detect secondary electrons,
It is better to install the scintillator 10 as close to the filter grid 53 as possible. The reason for this is
As the scintillator 10 is moved away from the filter grid 53, extra space is required, and as a result, the focal length of the objective lens for the electron beam must be increased, which is a major cause of a decrease in spatial resolution and stability of the electron beam. This is because, of course, the detection efficiency also decreases. On the other hand, the scintillator 10 is attached to the filter grid 5.
3, the high voltage of the scintillator 10 will affect the filter potential surface formed by the filter grid 53, deteriorating the characteristics of the energy filter. To improve this, a hemispherical buffer grid 20 is provided between the filter grid 53 and the scintillator 10 as shown in FIG. What is necessary is to remove the influence of the filter on the filter potential surface. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. Here, in order to explain the effect of the buffer grid 20 mentioned above, the characteristic curve of an energy filter without a buffer grid (see FIG. 1) is shown in FIG. The characteristic curve (see FIG. 2) is shown in FIG. 3b. The characteristic curves of these energy filters are determined when the sample surface potential V _s is fixed and the filter grid 53 is
Secondary electron detection current I _s when changing the voltage V _f
It represents the change in the integral curve (generally S
(referred to as a curve). This S-shaped curve shifts when the sample surface potential V _s changes, and by detecting this shift amount, the amount of change in the surface potential can be determined. Ideally, the S-shaped curve moves in parallel, and the amount of movement ΔV _f matches the amount of change in surface potential ΔV _s ,
ΔV _f =ΔV _s . In this case, in the S-curve shown in Figure 3a obtained without a buffer grid, the shape of characteristic A when V _s = 0V and characteristic A' when V _s = 5V are different. In the S-curve shown in Figure 3b obtained when a buffer grid is used, the shapes of characteristic B when V _s = 0V and characteristic B' when V _s = 5V are almost the same, and the characteristics due to the buffer grid are It can be seen that an improvement effect can be obtained. [Effects of the Invention] As described above, the surface potential measuring device for an electron beam tester of the present invention uses a secondary electron detector having a ring-shaped scintillator, so that secondary electrons can be detected in all directions including the secondary electron emission direction. Since electronic detection is performed, both measurement sensitivity and measurement accuracy are improved, and it is possible to precisely measure the surface potential of VLSI circuit patterns, etc.