JPH02117061A - Secondary electron detector and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a good observation image without intruding na external light into a light guide and free from appearance of background in a display image by providing a light shielding film formed with a prescribed thickness of conductive material which efficiently transmits an incident electron, but hardly transmits light. CONSTITUTION:A transparent conductive film 2 is formed on the surface of the head chip 1 of a cylindrical light guide, and a fluorescent material layer 3 is formed thereon, and further, a light shielding film 4 made up of Al with a film thickness of 500A is formed closely attached to the upper part of the fluorescent material layer 4. A secondary electron which falls on the surface of the film 4 transmits the film 4, and falls on the surface of the fluorescent material layer 3 to stimulate it; and it emits fluorescence. Then, the inside of a sample chamber is bright, but the light there is screened by the light shielding film 4, so that external light does not intrude into the light guide and no background appears in a display image. Thereby, it is possible to obtain a good observation image.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a secondary electron detector such as a scanning electron microscope.

2. Description of the Related Art An example of a conventional secondary electron detector such as a scanning electron microscope or an electron beam tester is shown in FIG. FIG. 5 shows an enlarged cross-sectional view of the scintillator portion at the tip, and FIG. 6 shows a further enlarged cross-sectional view of the phosphor layer. An electron beam 52 emerging from an electron optical system 51 is irradiated onto a sample 53, and secondary electrons 54 are emitted. The secondary electrons 54 are
The light is accelerated toward the scintillator 55 to which a positive DC bias potential of about 1 okV is applied, and is captured. That is, the secondary electrons 54 pass through the metal back 56 and enter the phosphor layer 57, stimulating it. Phosphor F! 57 emits fluorescence. This fluorescence passes through a light guide 58 and a photomultiplier tube 59
incident on . In the photomultiplier tube 59, the incident light signal is converted into electrons again by the external photoelectric effect, amplified, and sent as an electric signal to a subsequent amplifier. To the north is the secondary electron detection mechanism. Usually, the photoelectric conversion section consisting of the metal back 56, the phosphor layer 57, etc. is called the scintillator 55, and the scintillator 55 that amplifies and converts the secondary electron signal into an electric signal, and the photomultiplier tube 59 are collectively called the scintillator 55. It is called a detector 60.

Problems to be Solved by the Invention For example, in recent years, there have been attempts to apply scanning electron microscopes to detect defective pixels in TFT arrays for liquid crystal televisions (for example, Japanese Patent Application No. 193321/1983).
, This captures the potential difference between a defective pixel and a normal pixel as a contrast difference between secondary electron images. With this device, TF
At the T-array stage, it has become possible to detect many defective pixels caused by TFT arrays. However, there are some defective pixels in an actual liquid crystal panel that cannot be detected when the TFT array is observed using the above-mentioned apparatus. This is because the actual driving state and the driving state of the device described above are not completely equal. One of the reasons is
In actual driving conditions, defective pixels may be induced by leakage light from a backlight or the like that enters the transistor portion of the TPT. On the other hand, in the conventional secondary electron detector using a scintillator as described above, even if an attempt is made to capture a secondary electron image in bright conditions, the metal back 56 transmits the light, so the photomultiplier tube 59 does not receive the light. is incident and appears on the displayed image as a background,
It was impossible to observe the image. This means that
Metal back 56 used in conventional scintillators
Usually, Al is deposited on a phosphor N57 at an amount of several tens of OA, and as shown in FIG. 6, there are numerous pinholes and cracks on the surface, through which light enters. Therefore, in the past, it was not even possible to know whether or not there was a photo-induced defect.

In addition to the above examples, SEM with the sample irradiated with light
Even if you want to observe the image or observe the SEM image of the light emitter itself, it is not possible with conventional scintillators.

The present invention aims to solve these problems of conventional scintillators.

Means for Solving the Problems The scintillator of the secondary electron detector of the present invention is held in close contact with or with a predetermined space above the phosphor layer, so that at least incident electrons are efficiently transmitted and almost no light is transmitted. The light shielding film is made of a predetermined conductive material and has a predetermined thickness. The light-shielding film is produced by forming a base layer on a substrate smoothly, which is soluble in a predetermined solvent, and then forming a thin film for the light-shielding film to a predetermined thickness. Then, the thin film is peeled off by immersing it in the solvent to dissolve and remove the base layer, and then the peeled off thin film is installed at a predetermined position.

The light shielding film is a thin film of metal or alloy containing at least one of C, Be, AI, and other metal elements.

The present invention according to claim 3 provides a secondary electron detector set to a predetermined electron beam current amount and a predetermined scintillator bias potential, wherein light emitted from a phosphor layer by electrons transmitted through the light shielding film is detected. The signal strength at the output stage of the photomultiplier tube is at least 2 @ relative to other noise levels.
This is a light shielding film having an electron transmittance as high as the above.

The present invention according to claim 4 is characterized in that the intensity of the optical signal from the light emission of the phosphor layer due to the electrons transmitted through the light shielding film is reduced to the noise level due to the light transmitted through the light shielding film at the output stage of the photomultiplier tube. On the other hand, a light shielding film having at least twice the number of light shielding films is used.

Operation: First, a base layer that can be dissolved in a predetermined solvent is smoothly formed on a substrate, and then a thin film for the light shielding film is formed to a predetermined thickness, and then the base layer is immersed in the solvent. By the method of peeling off the thin film by dissolving and removing it, a smooth light-shielding thin film with almost no pinholes can be obtained. After that, by installing this peeled thin film in a predetermined place that can block light, even when capturing a secondary electron image in bright conditions, external light will no longer enter the light guide, and the displayed image will be No background appears and a good observation image can be obtained.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a cross-sectional view showing one embodiment of the scintillator of the secondary electron detector of the present invention. A transparent conductive film 2 is formed on the surface of a cylindrical light guide tip l having a diameter of 10 mm, and a phosphor layer 3 is formed thereon. In this example, a film of 500A thick Al! ! A light shielding film 4 is formed.

The secondary electrons incident from above pass through the light shielding film 4, enter the phosphor layer 3, and stimulate it. The phosphor layer 3 emits fluorescence. This fluorescence enters the photomultiplier tube 59 from the light guide tip l through the light guide below it. At this time, by simply providing the light shielding film 4, even if the inside of the sample chamber is bright, the light is blocked by the light shielding film 4, so that external light no longer enters the light guide, and the displayed image No background appears and a good observation image can be obtained.

The light guide tip 1 is made of glass, and both end faces and side surfaces are polished and smooth to improve light transmission efficiency. This may be an acrylic resin or the like, depending on the case. The transparent conductive film 2 thereon is provided to prevent charge-up of the phosphor layer 3. This is also indium-
It is desirable to use a material with high light transmittance for fluorescence from the phosphor layer 3, such as tin oxide (hereinafter abbreviated as ITO).

In this example, an ITO vapor-deposited film having a thickness of 200 to 400 Å was used. Sheet resistance is lk/mouth, wavelength 400nm ~ 7
The visible light transmittance at 00 nm was 90%. Phosphor layer 3
P47 was used as the phosphor powder. The phosphor layer 3 is formed by a normal precipitation method using isopropanol as a dispersant.
The layer was formed to have a thickness of about lθ to 20 am.

Next, a method for manufacturing the AI light shielding film 4 will be explained based on FIG. 2. First, glass substrate 5 (20mm
Spin code the gelatin onto the 20 mm).

As the gelatin, a 50% aqueous solution of RX12 manufactured by Nitta Gelatin was used. 1.2 drops of this was dropped onto the glass substrate 5J using a dropper and rotated in a spinner for 30 seconds at a rotation speed of 2000 rpm to form a smooth gelatin film 6 with a thickness of 2000 Å. On top of this, 8l'PJc7 was deposited. The vapor-deposited AI film 7 is heated to 45 to 55°C along with the glass substrate 5.
Soak in moderately warm water. Since gelatin is water-soluble, water gradually penetrates into the gelatin layer from the edges, and the Al film is peeled off in 10 to 15 minutes. The AI film exhibits the property of floating on the water surface and becoming taut (see Figure 2(e)). This is thought to be due to the effects of a very small amount of fat remaining on the membrane surface.

Note that the water temperature may be room temperature, but the gelatin will dissolve faster if the water temperature is slightly higher. However, when the water temperature reaches 60°C or higher, the AI film becomes transparent.

This is considered to be because the Al film was oxidized. In order to prevent the film from turning over and breaking during peeling, the depth of water on the substrate surface is preferably about 5 mm.

Furthermore, if one or two drops of an aqueous ethanol solution diluted to 50% or less is dropped onto the surface of the membrane floating on the water surface using a dropper, wrinkles can be smoothed out by the diffusing power of the ethanol. Next, as shown in Fig. 2(f), scoop the At film stretched on the water surface from below onto the light guide tip IJ: with the phosphor N3 formed thereon. An Al film 7 is placed on the layer 3. At that time, be careful not to leave any wrinkles as much as possible. If there are wrinkles, moisture will remain there, and when the pressure is reduced, it will evaporate and break the membrane.

In the method of this embodiment, a small amount of residual moisture may evaporate and create small holes in the membrane, but as will be described later, there is no problem in practice. In addition, we also attempted to stack two Al films by drying the moisture in the air and repeating the process shown in FIG. 2 for another film. The purpose of this is to almost eliminate pinholes by overlapping them. Through the above operations, the light shielding film 4 with almost no pinholes could be formed using either method.

The scintillator 10 created as described above is set on the upper end of the light guide 58 using the corona ring 61. The gap between the side edge of the corona ring 61 and the periphery of the light shielding film 4 is filled with Ag paste. This is to prevent discharge and to shield the peripheral area from light.
For two reasons. After assembly, apply a -degree vacuum and check that the gas remaining between the eyebrows does not expand and break the Al film.

Note that the side surface of the light guide 58 was shielded from light with black acrylic paint.

The performance of this scintillator was evaluated by trying it on the secondary electron detector of the defective pixel inspection device described above. As a result, the acceleration voltage of the electron beam 52 is 10 kV, and the beam current amount is 500 kV.
9A, when the bias potential of the scintillator 55 was OkV, the total optimal film thickness of the AI light shielding film was 40OA to 100OA regardless of whether it was a single layer or a multilayer. It was confirmed that with the above film thickness, there are 3 to 5 pinholes in the film in a single layer, and 0 to 1 in the case of two layers. Regarding light shielding properties, in the defective pixel inspection device described above, no background appears in the image even when the sample surface illuminance is 20,001 ux, and in terms of sensitivity, the potential resolution is exactly the same as that of the conventional example, and the S/ A good secondary electron image of N could be obtained. The bias potential of the scintillator of a normal scanning electron microscope, such as the defective pixel inspection device mentioned above, is about lokV, so if the film thickness becomes 200 OA or more,
The transmittance of secondary electrons decreased, resulting in a decrease in sensitivity.

Of course, either raise the bias potential of the scintillator 10 to more than lokV or increase the beam current amount of the electron beam 52 to 5009
If it is increased above A, the energy density of the secondary electrons incident on the phosphor layer 3 will increase accordingly, and even if the thickness of the light shielding film 4 is 200 OA or more, the amount of fluorescence will increase and the sensitivity will be increased. be able to. However, if the beam current amount is increased beyond this level, charge-up will become noticeable in the case of insulator samples, and the bias potential of the scintillator will be increased from 12 to
If you try to raise the scintillator to 131 cV or higher, the withstand voltage of the scintillator will no longer hold, and it will be necessary to change the structure to a new one with a higher withstand voltage. Normally, it is desirable that the thickness of the light shielding film 4 is 2000^ or less, which is appropriate under the above-mentioned general usage conditions. On the other hand, if the thickness of a single layer is 300
It was found that even if an attempt was made to make the At film below A, the At film would be destroyed when attempting to peel it off in water.

In this embodiment, AI was used as the light-shielding film material of the scintillator of the present invention, but other materials may be used as long as they have light-shielding properties, appropriate conductivity, and high electron transmittance.

For example, a thin film made of a light metal element such as Be or an alloy thereof, or a thin film made of a compound containing C or other metal elements can have similar effects.

Furthermore, in this example, gelatin was used as the intermediate film and water was used as the solvent when peeling the Al film.
Combinations such as cellophane-organic solvent, paraffin-organic solvent, polyvinyl chloride-organic solvent, and polyvinyl alcohol-water may be used, respectively.

Next, FIG. 3 shows another embodiment of the configuration of the present invention. In this example, the light shielding film 4 is not brought into close contact with the phosphor layer 3 as in the previous example, but as shown in the figure.
It is arranged with a space maintained between it and the phosphor layer 3. The light shielding film 4 is very thin at 400 to 100 OA, so it is easily torn. Therefore, as shown in the figure, a mesh 11 was provided inside the cylinder of the corona ring 12, and this was used as a support for the light shielding film 4. The mesh 11 has a pitch of 0.5 to 3+aa+,
A mesh having a diameter of 20 to 10,071 m was used. The manufacturing method used was the same as in the example of the manufacturing method described above. During depressurization, the space between the light shielding film 4 and the phosphor layer 3 is made to have the same atmospheric pressure as the outside through the exhaust hole 13 so that the light shielding film 4 is not torn due to the pressure difference. Even if the scintillator of this example is used, no background will appear in the image even when the sample surface illuminance is 20001 ux in the defective pixel inspection apparatus described above, and the sensitivity will also be
It was possible to obtain a secondary electron image with a potential resolution completely equivalent to that of the conventional example and a good S/N ratio.

A TFT array for a liquid crystal television was observed using the aforementioned defective pixel inspection apparatus equipped with the scintillator of the present invention. Although it is a defective pixel in an actual liquid crystal panel, when observing the TFT array with the above device, in a dark state,
Some of the defective pixels that cannot be detected emit visible white light to T
It was discovered that when observed while irradiating an FT array, it appears as a defective pixel. This is considered to be because, for some reason, only the transistor of the relevant pixel exhibited greater photoconduction than that of the normal pixel, and the charges accumulated in the pixel electrode were discharged. As described above, according to the present invention, the existence of photo-induced defective pixels has been revealed for the first time.

By observing the secondary electron image while irradiated with light, it was possible to improve the detection ability of the defective pixel inspection apparatus described above.

Effects of the Invention As described above, by realizing the light-shielding scintillator of the present invention, the existence of photo-induced defective pixels became clear for the first time. This can provide new guidelines for failure analysis of T F T l-transistors. and,
By observing the secondary electron image while irradiated with light, it was possible to improve the detection ability of the defective pixel inspection apparatus described above. In addition, in many cases other than those mentioned above, the scintillator of the present invention makes it possible for the first time to observe a SEM image of a sample while being irradiated with light, or to observe an SEM image of the light emitting body itself. It means that. In other words, new possibilities for electron beam testing have expanded.
In particular, the present invention has great significance in terms of its application to material analysis, operation analysis of electronic devices, and the like.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an embodiment of a scintillator for a secondary electron detector of the present invention, FIG. 2 is a process diagram showing an embodiment of a method for manufacturing the scintillator, and FIG. FIG. 4 is a cross-sectional view showing another embodiment of the present invention, and FIG. 4 is a cross-sectional view showing how a conventional scintillator is attached to a scanning electron microscope. FIG. 5 is a cross-sectional view of a conventional scintillator, and FIG. The figure is a cross-sectional view of the vicinity of the phosphor layer of the same scintillator. 2... Transparent conductive film, 3... Phosphor layer, 4... Light shielding film, 6... Gelatin film, 7... AI film, 8...
Water, 10...Scintillator, 11...Mesh, 1
3... Name of exhaust vent agent Patent attorney Shigetaka Awano (1 person) Figure 1] Light force "id tip" diagram Figure 3 Figure 58 Nine power side diagram Figure 5 Figure 63 The light is id tip teff.

Claims (1)

[Scope of Claims] (1) Secondary electron detection comprising a scintillator equipped with a phosphor layer that emits light when secondary electrons from a sample are incident thereon, and a photomultiplier tube that converts the emitted light into an electrical signal and amplifies it. In the device, the scintillator is made of a predetermined film made of a predetermined conductive material that is held in close contact with or with a predetermined space above the phosphor layer, and that transmits at least incident electrons efficiently but hardly transmits light. A secondary electron detector characterized by having a thick light shielding film. (2) The secondary electron detector according to claim 1, characterized in that the light shielding film consists of a plurality of sheets. (3) A secondary electron detector set to a predetermined electron beam current amount and a predetermined scintillator bias potential, wherein the optical signal intensity from light emission of the phosphor layer by electrons transmitted through the light shielding film is The secondary electron according to claim 1 or 2, characterized in that the light shielding film has an electron transmittance at least twice that of other noise levels at the output stage of a photomultiplier tube. Detector. (4) The optical signal intensity from the light emission of the phosphor layer due to the electrons transmitted through the light shielding film is at least 2 times higher than the noise level due to the light transmitted through the light shielding film at the output stage of the photomultiplier tube. The secondary electron detector according to claim 1 or 2, characterized in that a light shielding film having a light shielding film that is at least twice as large as the light shielding film is used. (5) The light shielding film is at least a single layer or multiple layers of Al.
3. The secondary electron detector according to claim 1, wherein the secondary electron detector is made of a thin film and has a total thickness of 2000A or less. (6) To make a scintillator, first, a base layer that can be dissolved in a predetermined solvent is smoothly formed on a substrate, and then a thin film for the light shielding film is formed to a predetermined thickness, and then a base layer that can be dissolved in a predetermined solvent is formed on the substrate. peel off the thin film by soaking, dissolving and removing the underlying layer,
6. The method of manufacturing a secondary electron detector according to claim 1, wherein the secondary electron detector is manufactured by subsequently installing the peeled thin film at a predetermined position. (7) The method for manufacturing a secondary electron detector according to claim 6, characterized in that water is used as the solvent and gelatin is used as the underlayer.