JPH06325718A - Scanning type electron microscope - Google Patents

Abstract

PURPOSE:To obtain a technique to set automatically an optimum beam current which gives no damage to a sample during the sample observation. CONSTITUTION:The electron beam emitted by an electron gun 1 is radiated on a sample 5, a signal generated from the surface of the sample is converted into an electric signal by a detector 6, and it is stored in an image processing device 10. In the device 10, an image to be the standard stored beforehand, and the image stored this time are compared, and when the device 10 decides they are not the same images, a beam current converting instruction is output from a control unit 15 to an HV control unit 17. This process is repeated until the images are judged the same (until the beam current becomes an optimum value). Consequently, an optimum beam current can be set without depending on the experience and the technique of an operator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope equipped with an image processing device.

[0002]

2. Description of the Related Art In a scanning electron microscope, a person judges and sets a beam current value with which a sample is irradiated by an image displayed on an image display device. The following are phenomena that occur when the beam current value is not appropriate.

A) The surface of the insulator sample is charged, making it difficult to observe an image.

B) When the beam current value is larger than an appropriate value, the sample is damaged and accurate surface information cannot be obtained.

Conventionally, humans have set the beam current value by judging the problems a) and b) from the image on the image display device. Further, as a solution only for a), Japanese Patent Laid-Open No.
As described in Japanese Patent No. 15144, a method of applying a DC voltage to the sample holder to neutralize the electrostatic charge is used.

[0006]

However, the method in which a person makes a judgment based on an image and sets a beam current is a method in which a large number of operators are present in one scanning electron microscope, so that the individual sense of Judgment cannot set clear standards.

It is an object of the present invention to provide a scanning electron microscope which avoids charge-up and sets the optimum beam current for a sample to be observed, regardless of the type of sample to be observed regardless of operator experience.

[0008]

To this end, the present invention is directed to irradiating a sample placed in a sample chamber with an electron beam from an electron beam generator and observing at least two or more identical materials and identical patterns. In the target scanning electron microscope, using an image processing device, it was judged whether or not the reference image and the image of the sample to be used for observation were equivalent, and a means for changing the beam current until they were equivalent was provided. It is characterized by

[0009]

According to the present invention, an image processing apparatus having a function of storing a plurality of images in the image processing apparatus and having a function of comparing the stored images can be compared by an operator with a reference image for image comparison. Remember. What is a reference image?
It is an image stored in the image processing apparatus by determining one point on the sample to be observed as a measurement reference point for setting the optimum beam current and at that point the optimum beam current.

[0010]

Embodiments Embodiments will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of an image processing apparatus.

The electron beam emitted and accelerated by the electron gun 1 is narrowed down by the objective lens 4 and irradiated on the observation sample 5. The deflection coil 3 is excited by the deflection amplifier 7, and the electron beam 2 is two-dimensionally scanned on the observation sample 5. Further, the secondary electron signal generated by the electron beam incident on the observation sample 5 is converted into an electric signal by the detector 6, and the A / D
The converter 9 converts the analog signal into a digital signal and stores it in the image processing apparatus 10. Further, the control unit 15 can read all or part of the image data in the image processing apparatus 10.

With the above arrangement, the present invention performs the following processing.

First, a place for setting the beam current value is selected on the observation sample, the optimum beam current value is judged and set in the image displayed on the image display device and stored in the image processing device 10. In this process, the stored image is used as the reference image. The process of storing the reference image may be performed once as long as the shape on the sample to be observed does not differ from the shape of the observed sample on which the process of storing the reference image is different.

Next, the optimum beam current value setting process for the observation sample will be described with reference to FIG.

In the image processing apparatus, the reference image is processed by a) passing a filter, b) binarizing, and c) differentiating. The image subjected to this processing is referred to as A image. Further, the image of the point defined as the reference on the observation sample desired to be observed with the optimum beam current at present is stored in the image processing apparatus, and the above a),
b), c) processing is performed. The image subjected to this processing is referred to as B image. In the image processing apparatus, if the A image and the B image are compared and the image processing apparatus determines that they are different images, the beam current value is changed as shown in FIG. 3 (a signal is issued from the control unit 15 and the HV control unit 17 The beam current value is changed to the current beam current value in the + direction or in the − direction.) The image after the change is subjected to the above a), b), and c) processing, and the processed image is newly set as the B image. The image and the B image are compared. This process is repeated until the image processing apparatus determines that the A image and the B image are equivalent. The fact that the A image and the B image are the same means that the beam current value is the optimum condition in the sample (FIG. 3).

[0017]

The present invention is as described above. According to the present invention, it is possible to have a clear reference value in image quality by creating a reference image in observing a sample with an electron microscope or the like.

Further, according to the present invention, it is possible to automatically set the beam current value, which was influenced by the experience of an operator such as an electron microscope.

[Brief description of drawings]

FIG. 1 is a block diagram of a scanning electron microscope showing an embodiment of the present invention.

FIG. 2 is a PAD diagram for setting a beam current.

FIG. 3 is a flowchart for setting a beam current value.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron beam, 3 ... Deflection coil, 4 ... Objective lens, 5 ... Sample, 6 ... Detector, 7 ... Deflection amplifier, 8
Deflection signal generator, 9 ... A / D converter, 10 ... Image processing device, 11 ... D / A converter, 12 ... Deflection amplifier, 13 ...
Deflection coil, 14 ... Deflection signal generator, 15 ... Control unit, 16 ... D / A converter, 17 ... HV control unit.

Claims (1)

[Claims] 1. A sample placed in a sample chamber is irradiated with an electron beam from an electron beam generator in the mirror body, and the same material,
In a scanning electron microscope for the purpose of observing at least two samples with the same pattern, it has the function of holding multiple data in the image memory and the function to judge whether or not the data are equivalent. A scanning electron microscope characterized by automatically setting an optimum beam current for a sample by using an image processing device having a.