JPS59198649A - Electron beam device - Google Patents

Abstract

PURPOSE:To express the near end of a cathode life by monitoring the changing degree of a parameter setting an instruction signal controlling a beam current, from the initial value immediately after cathode renewal. CONSTITUTION:Bias voltage control circuits 5 and 6 feedback-controlling the bias voltage to be impressed on an electron gun and beam current control devices 56 and 31 correcting a bias voltage setting signal Vg while comparing effective value Iba of the beam current in the constant state after beam irradiation with the current set value Ibc are provided. A cathode life can be known by checking the changing degree from the initial value, after cathode renewal, of the parameter setting said bias voltage setting signal Vg and a filament can be renewed in a mass production line , while selecting timing not causing trouble to production, thus bringing industrial big advantage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam apparatus that irradiates a workpiece with a high-speed electron beam to perform processing such as drilling, welding, melting, and heat treatment.

This glaze is used in child beam devices to generally control the beam current to perform the desired processing, but in order to uniformly process a large number of workpieces one after another, it is necessary to maintain good consistency and reproducibility of the beam current. be. Therefore, an automatic beam current control circuit is often used that detects the value of the beam current, compares it with a set value, and performs feedback control so that the deviation is eliminated.

However, in electron beam processing equipment, the cathode (or filament) generally has a lifespan of only several tens to hundreds of hours, and must be replaced from time to time.

By using an automatic beam current control circuit, the beam current is automatically corrected so that it does not change even though the cathode gradually wears out, and at some point suddenly (due to a filament breakage, etc.), the set beam current is obtained. It often becomes impossible to do so. Now that the cathode has reached the end of its lifespan, the cathode must be replaced. If there is some way to know when the cathode is nearing the end of its lifespan, the user can start replacing the cathode at a time convenient for him, which would have the advantage of not disrupting the pace of production. .

This invention is equipped with a relatively inexpensive and highly reliable beam current control device that is capable of rapidly increasing and decreasing the beam current, and can indicate that the cathode life is nearing its end. The present invention provides an electron beam device. Another purpose of this invention is to prevent an electron beam device that has good beam current accuracy and reproducibility and is suitable for repeatedly processing many workpieces of the same type from suddenly becoming unable to process due to cathode life. It is said that

Therefore, in the electron beam device of the present invention, after the beam current rises, the value of the beam current is detected during a part of the period during which the steady state is maintained, and the detected value is compared with the beam current setting value to generate a correction signal. A beam current control device is used in which a command signal is generated and applied to a command signal generating section that controls the beam current, and a comparator 68 monitors the degree to which the parameter defining the command signal changes from the initial value immediately after the cathode update.

The content of this invention will be described below using figures.

FIG. 1 is an explanatory diagram of a main part of an embodiment of an electron beam device according to the invention. One way to control the beam current in an electron beam device is to use the grid-cathode voltage (grid bias voltage) of an electron beam source, that is, an electron gun consisting of a cathode or filament 51, a grid 52, and an anode 53. . 34 is an accelerating power source; 55 is an object to be irradiated; and 54 is an electron beam. A voltage waveform similar to that of the autotransformer 1 which provides the input to the rectifying and smoothing circuit 58 is applied to the feedback transformer 2, and a DC voltage approximately proportional to the digrid bias voltage is outputted by the rectifying and smoothing circuit IM3. It compares with the signal waveform 4 from the voltage setting circuit 31 and performs foot-knock control so as to follow it. FIG. 3 shows a detailed explanation of the bias voltage setting circuit 31 described here. In the figure, 61 is a bias voltage calculation circuit, and the beam current target value Ib is given from the outside. Based on the accelerating voltage Vp, the preset electron gun μ, and the coefficient K, the bias voltage is calculated by the formula for the triode beam current: and the bias voltage setting signal ■
Get 2o. Reference numeral 62 denotes a bias voltage correction circuit that corrects the value of K in equation (1) used in the arithmetic circuit 61.

That is, before the beam starts up, the voltage of the generator 65 is selected by the selector switch 66 to a preset value of coefficient 1, and the calculation circuit 61 calculates 2 KOs. The value of K may change slightly due to changes in the characteristics of the K. Therefore, the voltage Vgo output to the four bias control circuits (deviation amplifier 5 and thyristor circuit 6) and the detection resistor 35 are actually used as bias voltage setting signals. After the actual beam current rises, the beam current command signal generator is activated during a part of the period during which the steady state is maintained - 11, 12...13 in Figure 2. A sample and hold booster 59 output from 56 causes the sample and hold circuit 63 to set the value of K to 1.
', and set a flip-flop 64 to store whether there is data in the sample and hold circuit (
(with memory), and then press the changeover switch 66 to K. 1' from the side
Switch to the side. In this case, the arithmetic circuit 61 is -Kl'
The calculation is slightly revised to eliminate the difference between the beam current command value Ibc and the actual value Iba.

Note that the data held by the sample hold is held until the fifth-order sample signal 59 is input or a reset 67 is input. If the variable width of the beam current is wide and it is not possible to cover the entire beam current range with one-to-one data due to the non-linear characteristics of the electron gun, divide the variable width of the beam current into several equal parts and A correction circuit 62 for providing one K for each variable range. Sample hold 63. Selector switch 66° flip-flop 64. Preset value generator 6
A number of 5'z equal parts are prepared and used selectively (not shown). Here, at the filament exchange completion signal 71,
A comparator 68 outputs the initial value of the parameter stored in the data hold circuit 70 and the updated value of the parameter.
If the monitor L and K values are outside a certain range (for example, ±15%) 10 times in a row, alarm 69 will be issued, which will prevent a decrease in the filament heating current or a poor electron gun setting. Please take appropriate measures under all headings.
If these defects are not found, it can be determined that the filament is wearing out and will soon reach the end of its life. The deviation amplifier 5 and the SiRisk circuit 6 are placed in a feedback loop that updates the value of 1 from time to time as described here.

The thyristor circuit 6 is supplied with power from a commercial frequency AC power source 7. In this way, the grid bias voltage of the electron guns (51 to 53) can be controlled to be approximately similar to No. 16 waveform 4.

In this case, a beam current waveform that changes over time as shown in FIG. 2 is obtained. As mentioned above, the full value of the beam current is detected in parts 11, 12 and 13 of the period when the beam current reaches a steady value. value, or a value sampled in synchronization with the ripple frequency to reduce the influence of AC ripple, or a value sampled multiple times to remove noise due to discharge, etc., and has a significant difference from the previous and subsequent values. uses a combination of methods to extract values obtained by processing the data to remove them. As shown above, feedback control is performed in the form of sampling only in the steady state, and open loop control is performed during the beam rise/fall period. There are no automatic shoots or undersheets that tend to occur due to discontinuity of the feedback signal, and the electron beam processing has good reproducibility and can be repeated many times.

Furthermore, since the bias voltage feed sub-loop shown in Figure 1 is not affected by the high voltage section, it exhibits sufficiently fast response and can prevent rapid beam current rise without increasing the frequency of the high voltage circuit input power supply. enable.

As described above, you can know in advance that the cathode (filament) is nearing its end before it reaches its end.
When the uninvented electron beam device is used in mass production lines, it is possible to renew the filament at a time that does not disrupt production, which provides great industrial advantages.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the main parts of an embodiment of the beam current control circuit for an electron beam device according to the invention, FIG. 2 is a waveform diagram showing constant temporal changes in the beam current, and FIG. FIG. 3 is a diagram illustrating in detail the bias voltage addition circuit 31 shown in the figure. 1...Single-turn transformer, 2...Transformer, 3...
- Rectification and smoothing circuit, 4... Signal waveform, 5...
Deviation amplifier, 6... Thyristor circuit, 8, 9.
10... Period when the beam current reaches a steady value, 11,1
2, 13, 8° 1 within the period of steady value shown in 9.10
Part period, 56... Beam current command signal generator, 5
7...Bias transformer, 58...Bias rectifier% 51...Filament, 52...
Grid% 53... Anode, 54...
・Electron beam, 55... Kameko beam irradiated object, 3
4... Accelerating voltage source, 35... Beam current detection resistor, 31... Bias voltage setting device, 59...
...Sample hold signal, 67...Sample hold reset signal, 61...Bias' compaction calculation circuit, 62...Bias voltage correction circuit,
63...Sample hold circuit, 64...
...Flip-flop, 65...Initial value K for the proportional coefficient of the electron gun.

Claims (1)

[Claims] (1) Based on the bias voltage setting signal from the command signal generator (bias voltage setting circuit), the bias voltage applied between the grid and cand of the electron gun is compared with the detection signal from the bias voltage detector, and feedback is provided. After the beam irradiation starts and the beam current rises, the actual value of the beam current is detected during a part of the period during which the steady state is maintained, and the actual value of the beam current is detected. A beam current control device for an electron beam device is configured to correct a bias voltage setting signal by comparing a value with a beam current setting value, and a beam current control device for an electron beam device is configured to correct a bias voltage setting signal by comparing a beam current setting value with a beam current setting value. An electron beam device that checks the degree of change and indicates when to replace the cathode. 2) Feedback control is performed by comparing the bias voltage applied between the grid and cand of the electron gun at the start of beam irradiation with the detection signal from the bias voltage detector based on the setting signal from the bias voltage setting circuit. A bias voltage setting signal is supplied to the bias voltage control circuit, and the bias voltage setting circuit is used to obtain a required beam current from a beam current target value and an accelerating voltage detection value from an accelerating voltage detector. is calculated according to the characteristics of the electron gun, and after the beam irradiation starts and the beam current rises, the actual value of the beam current is detected during a part of the period during which the steady state is maintained. , a correction circuit that compares the actual value with the bias voltage setting value and generates a bias voltage correction signal, and corrects the bias voltage setting signal so that the desired beam current value is always obtained. The beam current control device has a beam current control device equipped with a bias signal setting signal, and checks the degree of change from the initial value immediately after the cathode update of the parameter adding the bias signal setting signal, and instructs when to replace the cathode. Beam device.