JPH0518720Y2 - - Google Patents

Description

[Detailed Description of the Invention] (A) Technical Field This invention relates to an improvement of an electron beam scanning mechanism in a scanning electron beam irradiation device having a double channel window.

An electron beam irradiation device generates an electron beam in a high vacuum, accelerates it, scans it, takes it out into the atmosphere,
It irradiates the object to be treated.

(a) Prior Art FIG. 5 is a schematic front view of only a portion of a scanning electron beam irradiation device.

The scanning tube 1 is a narrow container in the shape of an isosceles trapezoid with a wide bottom. A scanning coil (magnet) is installed to scan the electron beam from side to side.

In the scanning tube 1, electrons are flying vertically downward, but are swung left and right by the Lorentz force caused by the scanning coil.

FIG. 6 is a partial vertical sectional view of the lower end of the scanning tube.

At the lower end of the scan tube 1 is a scan tube flange 2 . A window foil 5 is supported between this and the window foil pressing flange 3. This is the part from which the electron beam comes out, and is called the irradiation window 4.

The object to be processed 6 passes under the irradiation window 4.

The object to be processed 6 is sent in a direction (x direction) perpendicular to the longitudinal direction (y direction) of the irradiation window 4 .

The object to be processed 6 is under atmospheric pressure. The interior of the scanning tube 1 is under high vacuum. Therefore, the window foil 5 becomes the boundary between the vacuum and the atmosphere.

The entire atmospheric pressure is applied to the window foil 5. If the area of the window 4 is large, the tension acting on the window foil 5 is also large. Thicker is better to withstand strong tension. However, in order to allow electron beams to pass through it better, the thinner the material, the better.

Even if the electron beam has high energy, it has a charge, so it is easily scattered and cannot easily pass through even thin metal foil.

Therefore, for example, Ti foil is used with a thickness of 15 to 50 μm, and Al foil is used with a thickness of 30 to 150 μm. Since many electrons lose energy when they hit the window foil, the window foil is heated strongly.

Therefore, the window foil 5 is cooled by the water cooling pipe 10, cooling air, or the like.

In the case of the scanning type, if the window foil is exposed to too much electron beam, it will break, so the energy of the electron beam that can be applied to the window foil is limited. To increase processing capacity, it is necessary to increase the electron beam current. However, there is a limit to the electron beam current that can be applied per unit time and unit area of the window foil.

If so, the only way to increase processing capacity is to widen the window foil. If the irradiation window is simply made wider, the tension due to the difference in pressure between the inside and outside increases, and the foil is likely to break.

Therefore, two irradiation windows may be used. This is called a double channel type window or double window type. What is shown in FIGS. 5 and 6 is a double channel type window. There is a crosspiece and water cooling pipe in the middle, and the irradiation window is divided into two. Although there is only one window foil, there is a crosspiece and water cooling pipe in the middle, which reduces the tension by almost half.

To scan the double window with an electron beam, the irradiation windows 4, 4 are scanned in opposite directions in the longitudinal direction.
When the two irradiation windows are called window I and window, window I is scanned from right to left, the electron beam is transferred to the window, and this is scanned from left to right. In other words, it scans in a rectangular trajectory.

However, the inventor realized that this was not actually the case.

In reality, as shown in FIG. 3, scanning is performed in a parallelogram.

This results in parallelogram scanning rather than rectangular scanning. Scan in the Y direction called HI in window I,
Scanning in the X direction causes a movement called IJ. In the window, start from J and scan in the Y direction of JK.

The X direction is the short side direction, and the Y direction is the longitudinal direction.

As shown in FIG. 4, the X-direction scanning waveform is a rectangular wave, and the Y-direction scanning waveform is a triangular wave. Scanning is performed by generating a magnetic field using a magnet. The electron trajectory is bent by the Lorentz force. The electron beam bends in proportion to the coil current.

Since a triangular wave is used, Y direction scanning is performed continuously in JK and HI directions. The X-direction scan is instantaneously performed by short scans of KH and IJ. Keep the coil current in the X direction constant during Y scanning of JK and HI.

Both have waveforms of several hundred Hz and are synchronized with each other.

However, in reality, IJ and KH are not perpendicular to the Y axis.

Therefore, at both ends, there are quite a few areas where electron beam irradiation is low. The dose distribution is shown at the bottom of Figure 3.

There are 1, 1 areas with insufficient dose on both sides, 2l
It will exist. This means that only the central portion L can receive uniform electron beam irradiation.

The effective irradiation area becomes narrower, which is wasteful.
Note that the portion l where the dose is insufficient is, for example, about 10 cm to more than 10 cm.
It is several tens of cm.

This is because although the Y-direction scanning and the X-direction scanning are synchronized, strictly speaking, their phases do not match correctly. The Y direction scan is slightly delayed compared to the change in the X direction scan. This results in parallelogram scanning.

The opposite may be true. This is exactly the case when the scanning locus is reversed. This is because the X direction scan is delayed.

Even if there is a delay in the X direction or a delay in scanning in the Y direction,
Areas of low dose occur on both sides.

If the X-direction scanning were performed instantaneously, such difficulties would not arise. However, scanning in the X direction also takes a finite amount of time.

If scanning in one direction is switched in synchronization with a change in scanning in another direction, a finite delay will always occur. It has to be a parallelogram.

(c) Configuration In the present invention, hexagonal scanning is performed as shown in FIG.

Perform a Y direction scan AB in window I.
At point B, scanning in the X direction is started while continuing scanning in the Y direction, and at point C, the scanning in the Y direction is reversed. Then, the window reaches point D, which is the starting point of the window.

Y-direction scanning is switched between BDs. Point D or B
It cannot be switched at a point.

In the window, scan DE in the Y direction.
While continuing the Y-direction scan at point E, the X-direction scan is started and the Y-direction scan is reversed at the F point. Then, the starting point A of window I is reached.

In this way, a hexagonal scanning trajectory is created. The missing dose on both sides is shortened to l/2. 1st
The dose distribution is shown at the bottom of the figure. The length at which a uniform dose can be obtained is (L+l). This means that the length l of this part has expanded.

FIG. 2 shows Y-direction and X-direction scanning waveforms for executing the scan shown in FIG. 1. Since this invention was made with an eye to the fact that scanning in the X direction takes a finite amount of time, the scanning in the X direction is not made into a complete rectangular wave. It is a falling and rising edge with a finite slope.

The vicinity of the upper vertex of the Y-direction scan corresponds to points E, F, and A. The upper vertex is F. The vicinity of the bottom point is B,
Corresponds to points C and D. The bottom point is C.

The rising edges of the X-direction scan are E, F, and A, and the midpoint is F. The falling edges are B, C, and D, and the midpoint is point C.

The changing points of such a scanning waveform are C and F for Y-direction scanning, and A and F for X-direction scanning.
D or B,E.

Such a waveform cannot be obtained even if the change is made mainly in the X-direction scan and the Y-direction scan is followed (synchronized) with this.

Even if the change is made mainly in the Y direction scan and the X direction scan is followed (synchronized) with this, such a waveform cannot be obtained.

However, the scanning period is fixed. for example,
It has been confirmed as 200Hz.

If so, instead of deciding which one is the main one and which one is the subordinate one, you should set up another timing circuit to control the Y direction and X direction.
The timings E, F, A, B, C, and D of direction scanning may be given.

This is simple. Since one period is 5 msec, the rise and fall times of the X-direction scan are considered as τ. Starting from point A, set the timing as follows: A...0 B...2.5msec-τ C...2.5msec-τ/2 D...2.5msec E...5msec-τ F...5msec-τ/2 All you have to do is decide. Then, the X direction scanning is switched at points E and B. Switch the Y direction scanning at points F and C.

With such a timing circuit, it is possible to perform control such as synchronizing to either one without specifying the time. This is possible if the X-direction scanning time τ is known.

That is, the Y direction is scanned in synchronization with the switching times B and E of the X direction scan. However, the Y-direction scanning is switched τ/2 after the X-direction switching times B and E. It is sufficient to perform delay synchronization by τ/2.

(d) Effects In a double channel window type electron beam irradiation device, the X-direction scanning time τ is known, and the Y-direction scanning is switched τ/2 after the X-direction scanning switching time. As a result, the scanning locus of the electron beam in the double window becomes a hexagon rather than a parallelogram. The insufficient dose area at both ends of the irradiation window is reduced by approximately half. The intermediate uniform dose region increases.

Therefore, it becomes possible to process larger objects.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a double window electron beam scanning trajectory by the scanning mechanism of the present invention. FIG. 2 is a Y-direction and X-direction scanning waveform diagram for generating such a scanning locus. a is the Y-direction scanning waveform, and b is the X-direction scanning waveform. FIG. 3 is a plan view showing a conventional double window electron beam scanning locus. FIG. 4 is a Y-direction and X-direction scanning waveform chart for generating the scanning locus shown in FIG. 3. Fifth
The figure is a front view of only the upper part of the scanning electron beam irradiation device.
FIG. 6 is a sectional view of the irradiation window at the bottom of the scanning tube. 1... Scan tube, 2... Scan tube flange, 3...
Window foil pressing flange, 4... Irradiation window, 5... Window foil,
6...Object to be treated, 10...Water cooling pipe.

Claims (1)

[Scope of utility model registration request] An electron beam is generated in a high vacuum, it is accelerated, and the electron beam is scanned in the y direction, which is the longitudinal direction, and the x direction, which is perpendicular to this, in the scanning tube that expands below. The electron beam is ejected into the atmosphere through the window foil of the two irradiation windows at the bottom, and irradiates the object to be processed. For scanning in the y direction and in the x direction, a triangular wave is applied to the magnet coil installed at the top of the scanning tube. , in an electron beam irradiation device that uses rectangular waves to flow synchronously, the time required for x-direction scanning is τ, and from the switching time of x-direction scanning, τ/
After 2, the electron beam irradiation device was changed to scan in the y direction.