JPH01134943A - Inspecting device - Google Patents

Abstract

PURPOSE:To prevent a reduction in a resolution for the image of a matter to be tested and an electrification by a method wherein, with electron beams scanned at high speed in an X direction in a TV scanning mode, electron beams are scanned at low speed in a Y direction in a slow scanning mode synchronized with the frequency of a power supply. CONSTITUTION:When saw-tooth wave currents synchronized with each other are made to flow from a scanning power supply D3 to deflecting coils C1 and C2, electron beams in a main body S1 and electron beams in a CRT 11 are scanned in X and Y directions to intersect orthogonally. The frequencies of the saw-tooth currents, which are made to flow from the power supply D3, are synchronized with the frequency of a commercial AC power supply and the electron beams in the Y direction in the main body S1 and the CRT 11 are scanned at low speed in a slow scanning mode synchronized with the frequency of this power supply, while the electron beams in the X direction in the main body S1 and the CRT 11 are scanned at high speed in a TV scanning mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a technique that is effective when applied to an inspection technique using a scanning electron microscope.

[Conventional technology]

Regarding the inspection technology of semiconductor wafers (hereinafter referred to as wafers) using a scanning electron microscope, for example, Nikkei McGraw-Hill, published October 1, 1985, [Nikkei Microchip October issue JP123-P134] There is.

The above document describes measures such as changing the accelerating voltage of the electron beam depending on the type of object to be inspected in order to reduce damage to the wafer due to electron beam irradiation and prevent charge-up phenomenon caused by charging of the insulator part. The outline of the various inspection devices used is explained.

By the way, an inspection device using a scanning electron microscope uses an electron beam to scan an inspection area of an object in the XY force direction, captures secondary electrons and reflected electrons generated from the inspection area, and uses the electron beam to A predetermined examination is performed by displaying an enlarged image of the examination area on a connected CRT in synchronization with the scanning.

Electron beam scanning methods include TV scanning, which scans in the XY force direction at high speed by synchronizing the frequency of the sawtooth wave current flowing from the scanning power supply with the high frequency of the internal clock, and the frequency of the commercial AC power supply (50/60Hz). There is a slow scan in which scanning is performed in the XY force direction at low speed in synchronization with the scanning speed.The former is mainly used when observing a still image of an object to be inspected, and the latter is used when taking a photograph.

[Problem that the invention seeks to solve]

TVTV scan method, in order to scan the electron beam at high speed,
Although this has the advantage that charge-up phenomenon due to charging of the insulator part of the object to be inspected is less likely to occur, the scanning speed is not synchronized with the frequency of the commercial AC power supply, which is the main component of external magnetic fields and external vibrations, so each frame A drawback is that the resolution when superimposing images is reduced due to fluctuations in the frequency of the commercial AC power source.

In addition, in the TV scan method, since the S/N ratio of secondary electrons and reflected electrons captured by the -frame is low, the object to be inspected is repeatedly scanned with an electron beam. If it is easily charged, a charge-up phenomenon may occur.

On the other hand, the slow scan method, which scans in synchronization with the frequency of the commercial AC power supply, has the advantage of less degradation of resolution caused by external magnetic fields and external vibrations, but the Since there is a large amount of electricity, the insulator part is easily charged, and the charge-up phenomenon is unavoidable.

The present invention has been made focusing on the above problems,
The purpose is to provide a technique that can effectively prevent a decrease in the resolution of an image of an object to be inspected and prevent charging.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, a sawtooth wave current synchronized with the power supply frequency is passed from the scanning power source to the deflection coil of the main body and the deflection coil of the CRT, and the electron beam inside the main body and the electron beam inside the CRT are
High-speed scanning is performed in the direction by TV scan, and low-speed scanning is performed in the Y direction by slow scan synchronized with the above power supply frequency. This is an inspection device that performs a predetermined inspection based on an image of an object to be inspected obtained by detecting electrons.

[Effect]

According to the above-mentioned means, by synchronizing the frequency of the sawtooth wave current with the frequency of the commercial AC power supply, it is possible to reliably prevent the resolution of the image of the object to be inspected from decreasing due to the influence of the external magnetic field or the power frequency component of external vibration. It can be prevented.

In addition, by scanning the electron beam in the X direction at high speed with a TV scan and scanning the electron beam in the Y direction with a slow scan, blanking of the electron beam occurs between each scanning line, which reduces the charging of the object to be inspected. This can be reliably prevented.

〔Example〕

FIG. 1 is a block diagram showing the main parts of an inspection device according to an embodiment of the present invention, and FIG. 2 is a time chart showing the waveform of a sawtooth wave current in this inspection device.

The main parts of the inspection apparatus 1 of this embodiment are composed of a main body S1 and an electric system S2 that controls the main body S1.

A sample stage 3 is installed inside a vacuum chamber 2 provided in the main body S, and a desired part of a wafer (object to be inspected) 4 placed on this sample stage 3 is vertically placed above the vacuum chamber 2. The lens barrel 5 is positioned on the axis of the lens barrel 5.

An exhaust port 6 is provided below the sample stage 3, and an exhaust system (not shown) such as an exhaust pump connected to the exhaust port 6 evacuates the right side of the vacuum chamber 2 and the inside of the lens barrel 5 to a desired degree of vacuum. It has become so.

An acceleration type 1IIN D + for high voltage acceleration is connected to an electron gun 7 installed vertically downward at the upper end of the lens barrel 5, and thermoelectrons focused and accelerated inside the electron gun 7 are emitted as an electron beam. It looks like this.

In the path of the electron beam, an electron optical system consisting of a focusing lens L1, an objective lens L2, etc. is arranged above and below the deflection coil C+, and the image is determined by a signal from a lens power source D2 connected to the focusing lens L1. Focusing, the amount of electron beam irradiated onto the wafer 4, etc. are controlled.

A detector 8 that captures secondary electrons generated from the wafer 4 is installed near the sample stage 3, and an amplifier A.

The electrical signal amplified by the image forming section 9 and the image processing section 1
0, and further, the brightness is modulated by a CRT II for still image observation, and the image is displayed as a predetermined image.

Between the deflection coil C8 of the main body S1 and the deflection coil C2 of the CRT II, a magnification setting device 12, an X deflection amplifier A2,
-Y deflection amplifier As, X scanning signal generator 13, Y scanning signal generator 14, blanking circuit 15, drive amplifier A4. The scanning type RDs consisting of As are connected, and the mutually synchronized sawtooth wave currents are connected to the scanning power source D.
3 to the deflection coils C1 and C2, the main body Sl
The electron beam inside the CRTII and the electron beam inside the CRTII are scanned in orthogonal XY directions.

The frequency of the sawtooth wave current flowing from the scanning power supply was synchronized to the frequency of the commercial AC power supply (50/60Hz), and the electron beams in each Y direction inside the main body SI and inside the CRT II were synchronized to this power supply frequency. The image is scanned at low speed in slow scan mode.

On the other hand, the electron beams in each X direction inside the main body S and inside the CRTII are scanned at high speed by TV scanning.

Next, an inspection method using this inspection device 1 will be explained.

When the wafer 4 is positioned on the sample stage 3 and the inside of the vacuum chamber 2 and lens barrel 5 are evacuated to a predetermined degree of vacuum, the second
A sawtooth wave current with a waveform as shown in the figure is applied to the scanning power supply D.
3 X scanning signal generator 13 and Y scanning signal generator 1
The electron beams flow from the electron beams 4 to the deflection coils C1 and C2, sweep into the main body S and into the CRT II, and the inspection region of the wafer 4 is scanned by the synchronized electron beams.

At this time, the time interval of each scanning line is the reciprocal of the frequency of the commercial AC power supply (1150 seconds or 1/60 seconds), but the X direction is a TV scan synchronized with the internal clock high frequency of 25000H2, for example. In this case, the speed of the electron beam scanned in the X direction is 1/
The period is 25,000 seconds, and until the start of the next scanning line, the electron beam emission is blanked by a pulse signal from the blanking circuit 15 (FIG. 2).

When such an electron beam is irradiated onto a predetermined inspection area of the wafer 4, the secondary electrons generated from the inspection area are captured by the detector 8, and the light emitted by the secondary electrons that collide with the scintillator inside the detector 8 is converted into electricity. The signal is converted into a signal and input to the image forming section 9, and a one-frame image of the inspection site is formed.

The images of each frame formed by the image forming section 9 are input to the image memory built in the image processing section 10 and superimposed, and are displayed on the CRT II as a still image. By observing this, for example, the wafer 4 The appearance and dimensions of the resist pattern deposited on the substrate are inspected.

As described above, according to this embodiment, the following effects can be obtained.

(1) From the scanning power source D3 to the deflection coil C of the main body S1
By synchronizing the frequency of the sawtooth wave current flowing through the deflection coil C2 of the + and CRT II with the frequency of the commercial AC power supply, a decrease in the resolution of the image of the examination area due to the influence of the power supply frequency component of external magnetic fields and external vibrations is prevented. ,
In addition, by scanning the electron beam in the X direction at high speed with a TV scan and blanking the electron beam radiation until the beginning of the next scanning line, the photoresist etc. deposited on the wafer 4 can be charged. Therefore, a still image with high resolution can be obtained by TV scanning.

(2) According to (1) above, the inspection accuracy of the wafer 4 is improved, so that the yield of the wafer manufacturing process is improved and a highly reliable semiconductor device can be obtained.

As above, the invention made by the present inventor has been specifically explained based on Examples, but it should be noted that the present invention is not limited to the Examples and can be modified in various ways without departing from the gist thereof. Not even.

For example, the present invention can be applied to an inspection device that performs inspection by displaying an image on a CRT with afterglow properties.

Further, the present invention can also be applied to an inspection apparatus that detects reflected electrons generated from an inspection part of a wafer.

The above explanation has mainly been about the application of the invention made by the present inventor to wafer inspection technology, which is the background field of application, but it is not limited to this and is widely applicable to general inspection technology. Can be applied.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, a sawtooth wave current synchronized with the power supply frequency is passed from the scanning power source to the deflection coil of the main body and the deflection coil of the CRT, and the electron beam inside the main body and the electron beam inside the CRT are
By performing high-speed scanning with TV scan in the direction, and low-speed scanning with slow scan synchronized to the above power frequency in the Y direction, the resolution of the image of the inspected object due to the influence of the external magnetic field and the power frequency component of external vibration can be improved. As a result of reliably preventing deterioration and reliably preventing charging of the object to be inspected, the inspection accuracy of the object to be inspected is improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of an inspection device according to an embodiment of the present invention, and FIG. 2 is a time chart showing the waveform of a sawtooth wave current in this inspection device. DESCRIPTION OF SYMBOLS 1... Inspection device, 2... Vacuum chamber, 3... Sample stage, 4... Semiconductor wafer (inspected object), 5... Lens barrel, 6... Exhaust port, 7... - Electron gun, 8... Detector, 9... Image forming section, 10... Image processing section, 11...
・CRT, 12...Magnification setting device, 13...X scanning signal generator, 14...Y scanning signal generator, 15...Blanking circuit, A1...Amplifier, A2...X
Deflection amplifier, As...Y deflection amplifier, As,
As...Drive amplifier, CI l C2.
... Deflection coil, D+ ... Acceleration power supply for high voltage acceleration,
D2...Lens power supply, D,...Scanning power supply, L+
...Focusing lens, L2 ...Objective lens, S
I: Main body, S2: Electrical system.

Claims (1)

[Claims] 1. Sawtooth wave currents synchronized with each other are passed from a scanning power source to the deflection coil of the main body and the deflection coil of the CRT, so that the electron beam in the main body and the electron beam in the CRT are orthogonal to each other. An inspection device that scans in the X and Y directions and performs a predetermined inspection based on the image of the inspected object obtained by detecting secondary electrons or reflected electrons generated from the inspected object irradiated with the electron beam in the main body. The frequency of the sawtooth wave current is synchronized with the power supply frequency, and the electron beam in the X direction is scanned at high speed by TV scan, and the electron beam in the Y direction is scanned at low speed by slow scan synchronized with the power supply frequency. An inspection device characterized by: 2. The inspection device according to claim 1, wherein a still image obtained by superimposing images of each frame is displayed on a CRT.