JPS6119044A - Stereoscanning-type electron microscope - Google Patents

Abstract

PURPOSE:To enable the three-dimensional structure of the sample to be quantitatively grasped through observation on the spot by scanning is primary electron beam to branch it into two beams which are then obliquely irradiated upon one spot on the sample. CONSTITUTION:An electron beam passing through an objective diaphragm 25 is scanned by a primary scanning coil 26, which is located under the objective diaphragm 25, at a scanning frequency sufficiently lower than that of a secondary scanning coil 28 to branch the electron beam into two beams. The thus branched electron beams are then focused upon one sport on a sample 29. In this stereoscanning-type electron microcsope, one detector 30 is used and it is connected to CRTs 32 and 33 thereby displaying the signal from the left amplifying system on the CRT32 and that from the right amplifying system on the CRT33. Therefore, it is possible to produce a three-dimensional image of the sample surface by simultaneously observing the image screens of the CRTs 32 and 33. Consequently, it is possible to quantitatively grasp the three-dimensional structure of the sample 29 through observation on the spot.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a scanning secondary electron microscope that enables observation of the three-dimensional structure of a sample substance by "in-situ observation".

(Prior Art and its Problems) Conventionally, when observing the surface structure of a conductive substance, ie, a semiconductor metal, etc., a scanning secondary electron microscope has been frequently used. A scanning secondary electron microscope (hereinafter abbreviated as 8BM) is carried out using a suitable vacuum thread (~10 Torr).
FIG. 1 shows a primary electron beam thread provided in a standard 8EM, in which a sample is irradiated with an electron beam at an accelerating voltage of about 0KV to 5QKV. The electron beam emitted from the electron mirror section 11 passes through a focusing lens aperture 12 and is then focused by a focusing lens 13. The electron flow density is determined by the relationship between the focusing lens 13 and the focusing lens aperture 12. Furthermore, the electron beam
The light is focused by the objective lens 14 so as to focus on the upper E, passes through the objective lens diaphragm 15, is scanned left and right by the scanning coil 16, and is irradiated onto the sample 17.

Secondary electrons generated from substances have low kinetic energy, so
Detection #r184 is pulled in by the accelerating electric field. What should be noted here is that the obtained image is observed with the observer's naked eye placed on the electronic mirror 11 side and the illumination placed on the detector 18 side.

The depth of focus of the SEM is much deeper than that of an optical microscope, and since the resolution is largely determined by the diameter of the electron beam, with the development of fine electron beams, spatial resolution of several tens of times has been obtained. Since it can be controlled by electronic circuits, it has become an indispensable device for observing the surface of microscopic samples.

When observing a surface, knowing its unevenness is a very frequently encountered requirement. For example, to determine whether the surface defects observed are dents, chips, or holes, raised ridges, or ridges, or whether linear scratches are depressed or raised. It is almost impossible to observe the sample from one direction. This is possible only when there is a part with known irregularities on the sample.

In order to meet these demands, the conventional method was to tilt the sample stage to the left and right by several degrees with respect to the direction of the incident electron beam, take a pair of left and right images, and then observe the left and right pair of photographs simultaneously using an optical stereo microscope. I was getting 3D information. To perform this method, I would like to know more than anything that it is necessary to set the sample stage placed in the vacuum chamber at appropriate angles to the left and right, and that determining the appropriate angles requires skill. The drawback was that "on-the-spot observation" was not possible.

(Objective of the Invention) The present invention eliminates these conventional drawbacks and provides an 88M device that can determine the unevenness of the sample surface through "in-situ observation" and quantitatively evaluate the depth of the unevenness. It is about providing.

(Summary of the Invention) According to the present invention, the scanning point of the primary electron beam is not one point directly above the sample, but two points on the left and right of the scanning point, and the primary electron beam is irradiated obliquely from the two points to one point on the sample. and an SEM characterized in that the two series of primary electron beam threads are operated in a time-division manner, and a period signal is given to the secondary electron amplification thread to give separate images to two CRTs. .

The present invention achieves the above-mentioned configuration in accordance with 1) of the prior art.
It is not possible to evaluate unevenness by “in-situ observation”. 2) Quantitative evaluation of the depth of unevenness is difficult. This problem was solved.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention, showing a primary electron beam irradiation system and a secondary electron detection thread.

Ion mirror 21, focusing lens aperture 22, focusing lens 23,
The primary electron beam system including the objective lens 24 and the objective lens aperture 25 is the same as the conventional 8BM shown in FIG.

In the present invention, the first scanning coil 2 is placed under the objective lens aperture 25.
6 is placed, and a second scanning coil 28 (described below) is used to scan a sample 29 with an appropriate curvature diameter using an electrostatic field lens 27.
It is set to focus on one point. Here, the voltage of the electrostatic field lens 27 is controlled so that the light is incident on one point of the sample 29 at an equal angle θ. Further, after exiting the electrostatic field lens 27, the two beams are each scanned by a second scanning coil 28 at an appropriate frequency, and the amplitude thereof is also determined according to the magnification ratio of the image.

As mentioned above, in order to realize images observed on the sample surface from two directions of ±θ, it is necessary to use the electron beam with two incident directions as in the present invention, and the angle of the detection thread must be set in two directions. This cannot be achieved by setting it. Although there is only one detector 30, its amplification thread 31. The CRTs 32 and 33 are divided into two series. The periodic signal sent from the first scanning coil 26 is used to operate either one of the amplification threads 31. That is, in Figure 2, the secondary electron signal from the beam divided on the left is shown in CI (Ta2), and the secondary electron signal from the beam divided on the right is shown in 0RT33. Both screens are viewed simultaneously with a stereo microscope. By observing, it is possible to "in-situ observe" a three-dimensional image of the sample surface.

Since OIt T 32 and 33 are images from two directions, the measured distance of each part is slightly different. This difference and the angle of incidence θ.

By combining the working distance l, the depth of each unevenness can be calculated, which can be processed by a computer and displayed digitally or graphically.

(Effect of the invention) As explained above, according to the present invention, the three-dimensional structure of the sample is
This can be quantitatively understood through on-the-spot observation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional 8EM, and FIG. 2 is a block diagram of a stereo 8EM according to the present invention. In the figure,

Claims (1)

[Claims] The sample material is irradiated with a primary electron beam accelerated by a high electric field,
In a so-called scanning secondary electron microscope that observes secondary electrons generated, there is a primary electron beam system that irradiates a sample with a primary electron beam from two directions, and a time-based system that detects secondary electrons generated from each irradiation direction. Split into two O's on the left and right
A stereo scanning electron microscope characterized by comprising at least a secondary electron detection system for displaying on RT.