JPS5990347A - Saddle type deflection coil - Google Patents

Abstract

PURPOSE:To reduce deflective distortion even during large angle deflection by setting a winding angle (estimated angle from the axis of electron beam) theta of a coil which is parallel to the axis of electron beam to the value near the specific value. CONSTITUTION:A winding angle (estimated angle from the axis of electron beam) theta of the coil 1a, which is parallel to the axis of electron beam, of the saddle type deflection coil 1 which is placed coaxially with the axis of electron beam and is composed of the coil 1a parallel to the axis of electron beam and the coil 1b along the circle about the axis of electron beam, it set to an angle near 103 degrees. Thereby, distortion can be kept small even when the electron beam is deflected by a large angle and a sample picture can be observed without distortion up to ultralow-multiplication factor by fully utilizing the merits in application of saddle type coil.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a saddle-shaped deflection coil used for electron beam scanning in a scanning electron microscope or the like.

Toroidal windings are the mainstream deflection coil for electron beam scanning used in scanning electron microscopes. The toroidal-wound deflection coil is a coil wound at a fixed angle on a core made of ferromagnetic material such as ferrite, and has the advantage of being simple in structure and easy to install within the device. In addition to the magnetic field required to deflect the electron beam, a magnetic field leaks to the outside of the coil and flows into the yoke of the objective lens, etc., causing the following problems.

1 > When a high-speed scanning current such as TV scanning is applied,
Due to the poor frequency characteristics of the pure iron yoke of the objective lens, the magnetic field used to deflect the electron beam is distorted, which ultimately causes distortion in the image obtained by the cathode ray tube.

2) Since the pure iron yoke of the objective lens has hysteresis, the irradiation position of the electron beam shifts when the magnification of the scanning electron microscope is changed.

3) li! Since there is a lot of i flux leakage, the deflection magnetic field is not effectively introduced into the electron beam path, and the electron beam deflection characteristics are not good.

On the other hand, saddle-shaped coils have significantly better deflection characteristics than the toroidal coils because there is less leakage of the magnetic field to the outside of the coil, but when the electron beam is stopped significantly (deflection angle of 10° or more), the magnetic flux becomes distorted. This causes deflection distortion. Since this deflection distortion is proportional to the cube of the angular deviation, it becomes a problem in low (or extremely low magnification) observation in a scanning electron microscope.

Figures 1 and 2 show a general saddle-shaped supine coil;
The figure is a perspective view of only the coil portion, and FIG. 2 is a cross-sectional view including the ferromagnetic core. Reference numeral 1 denotes a coil, which consists of a part 1a parallel to the electron beam axis and a part 1h along a circle centered on the electron beam axis. Of the two coil parts, the part 1a parallel to the electron beam axis generates a magnetic field that contributes to the deflection of the electron beam, and a magnetic flux as shown by the symbol 3 in Fig. 2 flows.Actual device In this case, the coil is not single but X, Y
The same coils for both sardines and several coils for axis alignment are stacked 3 times.
- rolled. In FIG. 2, θ is the winding angle, which is the viewing angle from the electron beam axis of both ends of the coil portion 18 parallel to the electron beam axis. Conventionally, it was considered that the best winding angle θ was 120 degrees, but according to the inventor's experiments, at such a large deflection angle, 120 degrees winding causes deflection distortion to be as large as 3% to 7%, resulting in low It was found that magnification or very low magnification observation was not practical.

The purpose of the present invention is to provide a saddle-shaped deflection coil with small deflection distortion even when deflecting at a large angle, and its configuration is such that the electron beam axis 4. In a saddle-shaped deflection coil that is placed coaxially with the electron beam and consists of a coil portion that runs parallel to the electron beam 11 and a coil portion that runs along a circle centered on the electron beam axis, the winding of the coil portion that is parallel to the electron beam axis is The saddle-shaped deflection coil has a turning angle (angle of view from the electron beam axis) θ set around 103 degrees.

The present inventor conducted various experiments regarding the relationship between the saddle-shaped coil 111 angle and deflection distortion, and obtained results as shown in the curve of FIG. 3. Experiment 1. Using a high-precision cathode ray tube with distortion in the tl direction of 4-h°11°,
On Trial 1, the electron beam was scanned over an area of 10 mm x 10 mm, and the distortion was measured from the image on the cathode ray tube at 10x observation magnification. The vertical axis is the winding angle θ, and the horizontal axis is the deflection distortion. This is an indication. A positive deflection distortion indicates a barrel distortion, and a positive deflection distortion indicates a pincushion distortion.

As can be seen from the figure, when the deflection is made at a large angle, the deflection distortion depends on the winding angle, and the curve (A) shows a positive/negative reversal when the winding angle is around 1031f, so a winding angle around this area should be used. It can be immediately determined that the deflection distortion is extremely small. In fact, we succeeded in setting the winding angle to 103 degrees and suppressing the deflection distortion to TJo and 3% or less. At extremely low observation magnifications of around 10x, it is acceptable even if there is some distortion in the image, and assuming that the distortion is around 1.5%, the area surrounded by the dotted line in Figure 3 is the practical winding. angle range. That is, the winding angle O is 97
Within a range of about 110 degrees from the normal angle, it is possible to observe the sample image with almost no deflection distortion, regardless of the large angle of deflection.

Note that the above-mentioned curve is not always in the shape shown in FIG. 3, and some differences may occur depending on the shape, size, winding method, etc. of the coil. However, the tendency shown in FIG. 3, especially when the winding angle θ is 103
There is no change in the tendency for the sign to change around the degree.

When incorporating into an actual device, the coil is not a single coil, but ×
The coils for direction scanning, Y direction scanning, X, Y fine shift, etc. are wound in an overlapping manner, but if each coil is set within the above angle range, the deflection distortion of the electron beam caused by each coil can be made very small.

As explained above, by setting the winding angle θ to around 103 degrees, it is possible to suppress the distortion force within h\1.5% even when the electron beam is placed at a large angle within 1.5%. By taking advantage of the advantages of using a molded coil, it is possible to observe a sample image at extremely low igre without distortion.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the main parts of a general saddle-type deflection coil, Figure 2
The figure is a sectional view of the saddle-shaped deflection coil, and FIG. 3 is an explanatory diagram of the present invention. 1: Saddle 411 Coil 1a: Coil portion parallel to the electron beam axis ib: fi Coil portion along the circle centered on the electron beam axis 2゛Ferromagnetic core 3: Magnetic flux Patent applicant JEOL Ltd. Representative 9 Fuji - husband

Claims (1)

[Scope of Claims] 1. A saddle-shaped deflection coil that is placed coaxially with the electron beam axis and includes a coil portion in a direction parallel to the electron beam axis and a coil portion along a circle centered on the electron beam axis, wherein the electron A saddle-shaped deflection coil characterized in that the winding angle (angle of view from the electron beam axis) θ of the coil portion parallel to the wire axis is set to around i03 degrees. 2. The saddle-shaped deflection coil according to claim 1, wherein the winding angle θ is set in a range of 97 degrees to 110 degrees. 3. A saddle-shaped deflection coil according to claim 1 or 2, wherein a plurality of coils are wound one on top of the other at substantially the same winding angle. 4. The saddle-shaped deflection coil according to any one of claims 1 to 3, wherein a ferromagnetic core is arranged outside the coil.