JPS60231579A - Convergence detecting device of electron beam - Google Patents

Abstract

PURPOSE:To eliminate differences between individual workers and detect convergence of electron beam at high accuracy by giving different potential to an electron collector divided into plural pieces, and separating and detecting various electron beams emitted from an object. CONSTITUTION:An electron beam EB is irradiated on a work WK and current of a convergent lens 12 is changed. In this case, spot diameter of the electron beam on the surface of the work WK is stopped down with time from fuzzy, enlarged state, and becomes minimum when converged on the work WK, and with further lapse of time, becomes again fuzzy, enlarged state. Output signals from each part of an electron collector 14 are stored in a waveform storing device 20 together with diagram of current fluctuation of the convergent lens 12. Then signal processing of stored data is made by an operation processing device 24, and current value of the lens at which the electron beam is converged on the work WK is determined. Thus, convergence of the electron beam EB is detected easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a device for detecting that an electron beam is focused on a workpiece in an electron beam processing machine.

[Prior art]

The conventional focus position adjustment method for electron beam processing machines is as follows:
A common method is to irradiate the workpiece or a block made of tungsten, copper, etc. with an electron beam and visually observe the resulting molten pool, or to adjust the current of the focusing lens while directly observing the electron beam. be. However, this method has the problem of individual differences in focal position judgment among workers. Particularly in welding work, the position of the elongation point of the electron beam greatly influences the shape of the melt penetration.

10 to 12 show the focal position of this electron beam and the shape of the melt penetration. The focal positions of the electron beams are shown in FIGS. 10 to 12 (A), respectively.

Assuming that the distance between the focusing lens and the intervention position is ll, the state shown in FIG. 10 is a case where ab=1, and the focal position of the electron beam (EB) is
K). At this time, the shape of the welding will be desirable as shown in Figure 10 (B).
The state shown in the figure is a case where ab<1, and the focal position of the electron beam (EB) is within the workpiece (W K ). Also, the state shown in Figure 12 is a
This is the case where b>1, and the focal position of the electron beam (EB) is above the surface of the workpiece (WK). The shape of the melt penetration in these cases of ab(1° a b ) 1 is not preferable as shown in FIGS. 11(B) and 12(B), respectively. In this way, the shape of the melt penetration changes greatly depending on the adjustment of the focal point position. In the conventional visual inspection method, it is difficult to accurately determine the pointless position, and as a result, it is often not possible to obtain a desirable weld penetration shape.

An example of a method for improving this problem is disclosed in Japanese Patent Laid-Open No. 48-339.

According to this invention, instead of visually observing the molten pool produced by electron beam irradiation, the light generated from the electron beam irradiated part of the workpiece is detected and this change is displayed on the indicator, so that the indicator Focusing of the electron beam will be adjusted while looking at the display. Although this improves accuracy compared to visual inspection of the molten pool, it cannot prevent the problem of variations due to individual differences among workers.

[Summary of the invention]

The present invention has been made to solve these problems, and its purpose is to detect the focusing of an electron beam with high precision, excluding individual differences among workers.For this purpose, The present invention moves the beam static point position while irradiating the object with an electron beam, irradiates the object with the electron beam, and thereby divides the various electron beams emitted from the object into a plurality of beams, each with a different potential. is received by a given collector, and the collector separates and detects the electron beam,
Furthermore, this is introduced into the signal change, and this is used to guide the focal point of the electron beam onto the surface of the workpiece, thereby minimizing the spot diameter (hereinafter referred to as focusing). be.

[Embodiments of the invention]

FIG. 1 is a block diagram showing an embodiment of the present invention. 1st
In the figure, an electron beam (EB) is emitted from an electron gun 00 toward a workpiece (WK).

In the path of this electron beam (EB), two focusing lenses α and an electron collector α♦ are arranged. By passing a variable current through the focusing lens 02, the electron beam (E
B) makes it possible to vary the degree of focusing. The time-dependent change in the current of this focusing lens a
As shown in the figure. The width of this change is set so that the point of the electron beam (EB) is located on the workpiece (WK) no matter where the workpiece (WK) is placed in the processing chamber (not shown). be done. The electron collector α→ is for detecting an electron beam, and in this embodiment, it is divided into a member (A) and a member (B′) as shown in FIG. Next, in FIG. 1, a power source a is connected between the electron collector α4 and the workpiece (WK). The power source (1 yuzu is for giving a potential difference between each part of the divided members (A) and (B) of the electron collector α4 and the workpiece (WK). 3 to the workpiece (WK) When the electron beam (EB) is irradiated, a radiation electron beam (RB) is generated from the workpiece (W K ). Figure 4 shows the potential of the electron collector α◆ and the detection of the radiation electron beam (, RB ). This shows the relationship between the amount of emitted electrons and the amount of emitted electrons.According to this, the detected amount of emitted electron beams changes suddenly near the area where the potential of the electron collector changes from positive to negative, but this is related to the energy distribution of various types of emitted electron beams. Figure 5 shows the energy distribution of various types of radiation electron beams.
A) is a thermal electron, (B) is a secondary electron, and (C) is a reflected electron. Therefore, the part of the electron collector that is given a negative potential has some of the electrons contained in the emitted electron beam (RB). , only reflected electrons with high energy reach the area, and conversely, secondary electrons and thermal electrons with low energy reach the part to which a positive potential is applied in addition to the reflected electrons. These radiation electron beams (RB)
An electrical signal due to the arrival of is output from the electronic collector o4. These signals therefore change with the focusing state of the electron beam (EB). Next, the current of the focusing lens (6) and the output signal of the electron collector ←◆ are input to a waveform storage device. This waveform storage device has a function of temporarily storing and accumulating the waveform of an input signal. The waveform storage device q is connected to a calculation processing device (c).

This calculation processing device QIO analyzes the signal waveform stored in the waveform storage device and detects beam convergence.

The present invention has the above-mentioned configuration, and its operation will be explained as follows7. First, the 5th order focusing lens (6 ) is changed as shown in Figure 2. In this case, the workpiece (WK)
The spot diameter of the electron beam (BB) on the surface of the electron beam (BB) is narrowed down over time from an enlarged state where the electric point is shifted, and becomes the minimum when it is focused on the workpiece (WK), and as time passes, the focus shifts again. It will be in an expanded state. When the electron beam (EB) is focused on the workpiece (WK), the density of the electron beam (EB) increases, causing minute melting and evaporation on the workpiece (WK). Figure 6 shows the intensity of the emitted electron beam (RB) when the current of the focusing lens (b) is changed as shown in Figure 2, that is, the electron collector (1
The changes in output from each part of 4 are shown. In FIG. 6, (A) indicates the workpiece (
WK) shows an example of the output from a portion to which a positive potential is applied, and (B) shows an example of the output from a portion to which a negative potential is applied. As mentioned in Reference 1, reflected electrons, secondary electrons, and thermoelectrons reach the part of the electron collector α to which a positive potential is applied as radiated electrons #Il (Rr-1), but in this case, the electron beam (EB ) are focused on the surface of the workpiece (WK) and melting occurs, resulting in an increase in thermoelectrons. Therefore, a maximum value as shown in FIG. 6(A) occurs. When this maximum value is shown, the current value flowing through the focusing lens (6) based on the diagram shown in Figure 2 is the electron beam (EB).
This corresponds to the convergence of High-energy reflected electrons arrive at the portion of the electron collector 04 to which a negative potential is applied as a radiation electron beam (RB). In this case, the quadruplet beam (
EB) is focused on the surface of the workpiece (WK) and the workpiece (WK) is
Melting and evaporation of W K ) occur, so that the electron beam (EB) falls from the surface of the workpiece (WK) into the interior, resulting in a minimum value as shown in FIG. 6(B).

Based on the diagram shown in FIG. 2 at the time of this minimum value, the current value applied to the focusing lens (6) corresponds to the focusing of the electron beam (EB). Furthermore, accurate detection of the focusing of this electron beam (EB) is uncertain if only one output signal is used. The reason for this is that when the current value of the electron beam (EB) for focused detection is small, the melting and evaporation of the workpiece (V% (K) is small, so the radiation electron beam (R, The change in the signal of (B) becomes small, making it difficult to detect the focus using the peak value in Figure 6 (C).On the contrary, the electron beam for focus detection (
If the current value of EB) is large, the thermal electrons in Figure 6 (
The peak of A) may lack sharpness, making accurate focusing detection difficult.

Therefore, all the output signals from each part of the electron collector 0.9 are stored in the waveform storage device along with a diagram of the current change of the focusing lens. Next, the calculation processing device Q4 performs signal processing on the stored data to determine the lens current value at which the electron beam (E B ) is focused on the workpiece (VwK). Although FIGS. 6(A) and (B) show the case where the signal has a simple peak, according to the embodiment, there may be cases where the signal shows a minimum value when the signal increases, as shown in FIG. 7(A), or may show a maximum value when the signal decreases, as shown in Figure 7 (B), but even in such cases, it is easy to focus the electron beam (EB) by using a computer processing device. can be detected.

In the above embodiment, the electronic collector α fathom was divided into two concentrically as shown in FIG.
Furthermore, it is divided concentrically into six or more parts, and a different potential is applied to each part to perform even more detailed analysis using a calculation processing device (c).
By performing this, it is also possible to detect the focusing of the electron beam (EB) more accurately.

In addition, when the workpiece (WK) is tilted or moved, each type of radiation electron beam shows a characteristic distribution, but in this case, the electron collector a4 is divided radially as shown in Fig. 8. This makes it possible to efficiently separate various types of electron beams.

Furthermore, in the above embodiments, the direct workpiece (WK)
Although the focus of the beam is detected by irradiating the electron beam (EB) onto the workpiece (WK), an appropriate focus detection member may be placed at the position of the workpiece (WK). This is effective in cases where it is unacceptable to form minute scratches on the surface of the workpiece (WK). Note that the focusing lens a2
In addition to changing the current as shown in Figure 2,
It is also possible to reverse the change as shown in FIG.

〔Effect of the invention〕

As explained above, the present invention applies different potentials to each divided electron collector and separately detects various electron beams emitted from an object. The convergence of the electron beam can be detected with high accuracy, and processing can be performed satisfactorily. Furthermore, the beam corner position adjustment can be automated.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the focusing detection device according to the present invention, Figs. 2 and 9 are diagrams showing changes in current of the focusing lens, and Figs. 6 and 8 are diagrams showing states of division of the electron collector. Figure 4 is a diagram showing the relationship between the potential of the electron collector and the detected amount of radiation electron beam, Figure 5 is an energy distribution diagram of various radiation electron beams, and Figure 6 and Figure 7 are radiation electron beam intensity. FIG. 10, FIG. 11, and FIG. 12 are explanatory diagrams showing the focal position of the electron beam and the shape of the melt penetration. 1 shown in the diagram
2 is a focusing lens, 14 is an electron collector, EB is an electron beam, RB is a radiation electron beam, and WK is a workpiece. In addition,
The same reference numerals in the figures indicate the same or corresponding parts. Agent Patent Attorney Sanro Kimura Figure 1 Figure 2 Figure 3 Figure 4 Left Figure 5 1 (I cut = 12 4qE) Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 (B) (8) (8J'

Claims (4)

[Claims] (1) When irradiating an object with an electron beam and changing the current of the focusing lens to move the beam focal point, place a collector divided into multiple parts above the object and apply different potentials to each one; An electron beam focusing detection device is characterized in that it separately detects various electron beams emitted from an object and detects beam focusing from changes in each signal. (2) A negative potential is applied to a certain part of the collector to detect only high-energy electron beams, and a positive potential is applied to another part of the collector to detect low-energy electron beams as well. Focused detection device as described in . (3) The focusing detection device according to claim 1 or 2, wherein the collector is divided into concentric circles. (4) The focusing detection device according to claim 1 or 2, wherein the collector is radially divided.