JPH04147549A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To obtain a good-contrast image of a scanning electron microscope which has a sail dia. and a deep hole shape at the bottom and the opening by converting the brightness level of secondary electron or reflection electron detected signals in accordance with a preset conversion table to enhance the brightness level based on the hole bottom. CONSTITUTION:Secondary electrons arising from the irradiation of electron beams are detected by a detector 6. Relative signals are amplified by an amplifier 7 and converted by an A-D converter 8 into digital signals which are supplied to the brightness conversion section 9, when the brightness of input signals is converted in accordance with a conversion table stored in a brightness conversion table storage 12. The brightness conversion table allows the output of output brightness 0 for input brightness 1 so that the output brightness in the area of the input brightness to brightness B1 is almost equal to that in the area of the input brightness from brightness B2. The signals of the brightness conversion section 9 are converted by a D-A converter 10 into analog signals which are then supplied to a cathode ray tube 11. The strength of secondary electron signals from the bottom of a contact hole is made equal to the strength of secondary electron signals from the periphery of the contact hole to observe both the edge and the bottom of the contact hole in good contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a scanning electron microscope and a method for photographing secondary electron images or backscattered electron images, which are suitable for use in inspecting the manufacturing process of ultra-LS1 circuits.

(Prior Art) One of the inspections in the manufacturing process of the LS1 circuit is the visual inspection of contact holes in the resist using a scanning electron microscope. In general, observing the inside or bottom of a hole with a small diameter is the weakest point of a scanning electron microscope.
As the degree of integration increases, the diameter of the contact hole becomes smaller, making it increasingly difficult to observe with a scanning electron microscope. On the other hand, there are times when a contact hole is so minute that a request is made to observe it with a scanning electron microscope. Is this contact hole an electrode hole for connecting the lower element and upper electrode, or does it penetrate through the bottom, that is, the part that contacts the element, or in the correct shape?
The object of inspection is to see if there is any residue left behind from the renst that results in an incorrect shape.

(Problem to be solved by the invention) As a method of detecting secondary electrons generated through a small-diameter, deep contact hole, a secondary electron detector is placed above the objective lens, and the objective lens is excited with a strong magnetic field. There is a type of scanning electron microscope that traps secondary electrons in a magnetic field and pulls them up, and it has become possible to observe contact holes quite well.

However, in this type of scanning electron microscope, the hole diameter of the objective lens must be made large in order to capture the secondary electrons, so it is necessary to use a bottom-face (the surface facing the sample) or a flat objective lens. As a result, there is a drawback that the sample cannot be tilted.

In a scanning electron microscope, which has a conical objective lens that allows for a large tilt angle of the sample, and a secondary electron detector is placed between the sample and the objective lens, the electric field of the secondary electron detector is transmitted to the bottom of the contact hole. If penetration is difficult, the intensity of the secondary electron signal from the bottom becomes significantly weaker, and the contrast difference between the top and bottom of the hole becomes extreme. Therefore, when trying to optimize the contrast of the bottom to observe the bottom, the area around the hole becomes pure white, causing halation. Conversely, if the upper part of the hole is adjusted to the optimum brightness, the bottom part will be completely black, making it impossible to observe the bottom part.

As described above, it is extremely difficult to find the optimal contrast that allows the top and bottom of the contact hole to be observed simultaneously because the contrast difference is too large. In the invention disclosed in the earlier application (Japanese Unexamined Patent Publication No. 64-43470), a signal obtained by adding the secondary electron signal and the absorbed current of the sample is used, or the absorbed current is the current flowing in the sample. There is a problem that a time delay occurs in the detection signal in order to detect the Applicable only when speed is slow.

The present invention has been made in view of these points, and its purpose is to obtain a scanning electron microscope image of the bottom and opening of a small and deep hole shape such as a contact hole with good contrast. The goal is to realize a scanning electron microscope.

(Means for Solving the Problems) A scanning electron microscope based on the present invention includes a focusing means for focusing an electron beam on a sample, a scanning means for two-dimensionally scanning the electron beam on the sample, and a scanning electron microscope for focusing an electron beam on a sample. a detector that detects secondary electrons or reflected electrons generated based on irradiation with an electron beam; a brightness converter that converts the brightness level of a detection signal from the detector based on a predetermined conversion table; and a brightness converter It is characterized by comprising an image display means to which a signal whose luminance has been converted is supplied.

(Function) In the scanning electron microscope based on the present invention, the brightness level of the secondary electron or backscattered electron detection signal is converted based on a predetermined conversion table to increase the signal brightness based on the bottom of the hole.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention, where 1 is an electron gun. An electron beam generated from the electron gun 1 is narrowly focused onto a sample 3 by an objective lens 2. The sample 3
The upper electron beam irradiation position is changed according to a signal supplied to the deflection coil 4. A scanning signal is supplied to the deflection coil 4 from a scanning signal generating circuit 5. The sample 3
The secondary electrons generated by the electron beam irradiation are 2
It is detected by the secondary electron detector 6. The signal detected by the detector 6 is amplified by an amplifier 7, and then
The signal is supplied to the AD converter 8.

The digital signal from the AD converter 8 is supplied to the luminance converter 9, and the output signal of the luminance converter 9 is supplied to the DA converter 10.
and converted into an analog signal. DA converter 1
The output signal of 0 is supplied as a luminance signal to the cathode ray tube 11 to which the scanning signal is supplied from the scanning signal generating circuit 5. Note that the brightness conversion section 9 converts the human input signal based on a conversion table stored in the brightness conversion table storage means 12. The operation of the scanning electron microscope having such a configuration is as follows.

A scanning signal for two-dimensionally scanning a specific range on the sample 3 is supplied from the scanning signal generation circuit 5 to the deflection coil 4, and as a result, the area including the contact hole provided on the sample 3 is exposed to the electron beam. scanned by Figure 2 (a
) shows a contact hole H provided in sample 3, in which a resist R is coated on a substrate S made of silicon, and a hole is made in a part of it by etching.
A contact hole H is formed. When the contact hole H is linearly scanned with an electron beam, secondary electrons generated by the electron beam irradiation are detected by the detector 6. Figure 2(b) shows this detected 2
The next electronic signal is shown.

This signal is amplified by an amplifier 7, converted into a digital signal by an AD converter 8, and supplied to a luminance converter 9. In the brightness conversion section 9, the brightness of the input signal is converted based on a conversion table stored in the brightness conversion table storage means 12.

As this brightness conversion table, a table having the relationship as shown in FIG. 3 is used. In the example shown in Fig. 3, output brightness O is output for human power brightness I, but the human power brightness range up to brightness B1 and the human power brightness range from brightness B2 are approximately the same as the output brightness. It is like that.

Therefore, among the human input signals shown in FIG. 2(b), the signal level up to the brightness level B1 is increased and is made to be equal to the signal level of the brightness level 82 or higher, and from this brightness converter 9, the signal level up to the brightness level B1 is The signal shown in (C) is generated.

The signal shown in FIG. 2(c) is converted into an analog signal by the DA converter 10, and then supplied from the scanning signal generation circuit 5 to the cathode ray tube 12, which is co-supplied with the scanning signal 1J or 1. A secondary electron image is displayed on the cathode ray tube 12. In this secondary electron image, as shown in FIG. 2(f), the intensity of the secondary electron signal from the bottom of the contact hole is approximately equal to the intensity of the secondary electron signal from the periphery of the contact hole. This allows both the edge and bottom of the contact hole to be observed with appropriate contrast. Note that the conversion table stored in the brightness conversion table storage means 12 is not limited to the one shown in FIG. 3, but may also be a table with a relation that inverts the signal in the weak brightness range up to B1, as shown in FIG. May be used. Of course, 82 or more signals may be inverted.

FIG. 3 shows the configuration of a signal processing section in another embodiment of the present invention, and the same parts as in FIG. 1 are given the same numbers. In this embodiment, the conversion table for converting the brightness in the brightness converter 9 can be arbitrarily set by manual operation, and also can be set automatically according to a human input signal. . In the figure, A
The output signal of the D converter 8 is also supplied to the level determination section 13, and the signal from the level determination section 13 is sent to the switch 1.
4 to the brightness conversion table generation unit 15.

The switch 14 switches between the signal from the level determination section 13 and the manual setting signal to generate the brightness conversion table generation section 1.
Supply to 5. The operation of the second configuration is as follows.

First, when setting the conversion table manually, the switch 14 is switched to the state shown by the dotted line in the figure, and the level B, . supply the signal.

The brightness conversion table generation unit 15 generates a conversion table having the relationship shown in FIG. 3 or 4 based on the input level, stores it in an internal storage means, and calculates the brightness based on this stored table. Controls the converter 9.

Next, if you want to automatically generate a table, switch 14
can be switched as shown by the solid line in the figure. At this time, the level determination unit 13 generates a brightness distribution histogram based on the secondary electron exposure (No. 8), and automatically determines the B, 82 level based on this histogram. The determined B, , B2 level signals are supplied to the brightness conversion table generation section 15 via the switch 14, and this generation section generates a conversion table having the relationship as shown in FIGS. 3 and 4.

Note that although B and B2 are described here as separate levels, they may coincide.

(Effects of the Invention) As explained above, in the scanning electron microscope based on the present invention, since the sample image is displayed based on the signal, It is possible to simultaneously observe scanning electron microscope images of both the periphery and the surrounding area with good contrast. Also,
Since a secondary electron or reflected electron detection signal is used, the signal detection response is fast, and it can sufficiently cope with high-speed electron beam scanning such as TV scanning speed.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a scanning electron microscope based on the present invention, FIG. 2 is a signal waveform diagram for explaining the present invention in detail, and FIGS. 3 and 4 are input luminance in the luminance conversion section. FIG. 5 is a diagram showing the relationship between output brightness and output brightness, and is a diagram showing another embodiment of the present invention. 1. Electron gun 2. Objective lens 3. Sample
4... Deflection coil 5... Scanning signal generation circuit 6... Detector 7... Amplifier 8... AD converter 9... Brightness converter 10... DA converter
11...Cathode ray tube 12...Brightness conversion table storage means 13...Level judgment unit 14...Switch]5...Brightness conversion table generation unit

Claims (1)

[Claims] A focusing means for focusing the electron beam on the sample, a scanning means for two-dimensionally scanning the electron beam on the sample, and detecting secondary electrons or reflected electrons generated based on the irradiation of the electron beam onto the sample. a brightness converter that converts the brightness level of a detection signal from the detector based on a predetermined conversion table; and an image display means to which a signal whose brightness has been converted by the brightness converter is supplied. electronic microscope.