JPS647360B2 - - Google Patents

Description

Detailed Description of the Invention The present invention detects when an abnormal discharge occurs in a charged particle beam generator in a processing device that performs processing by irradiating a charged particle beam, and forcibly stops the discharge. The latter relates to an apparatus that eliminates the occurrence of defects in workpieces by recovering the accelerating voltage of a charged particle beam as quickly as possible.

In charged particle beam processing equipment in which electron beams, ion beams, etc. are accelerated at high voltage and irradiated onto the workpiece, steam and occluded gas molecules from the workpiece may enter the charged particle beam generator. In addition, charge may accumulate locally, increasing the electric field strength and causing discharge within the charged particle beam generator, and these discharges are sudden and unpredictable due to their cause. It is.

When such a discharge occurs, unless it is shut off in a short time, the discharge will grow to a large extent and there is a risk of a major accident destroying the charged particle beam generator and the high-voltage power supply. If discharge occurs, it is necessary to shut off the power supply circuit, but usually the primary side, that is, the input side of the high-voltage power supply is shut off, which is easy to operate. However, since a high-voltage power supply usually includes a step-up transformer, a rectifier circuit, and a smoothing circuit, it has a fairly large time constant as a whole, so it takes a considerable amount of time to shut it off and restore it, so when a discharge occurs, Sufficient protection and rapid recovery when the discharge is stopped cannot be expected, and during these periods, the charged particle beam for machining is stopped, resulting in machining defects in the workpiece. A method has also been proposed in which a switching element such as a vacuum tube is inserted in series on the output side of a high-voltage power supply, and the switching element is placed in a cut-off state to cut off the accelerating voltage when discharge occurs. Figure 1 shows a configuration diagram of the device taken into consideration in this way, and shows a high voltage power supply 1.
is supplied with power from an AC power supply 2 and supplies its output to a charged particle beam generator 4 via a switching element 3 connected in series. The beam current flowing through the charged particle beam generator 4 is grounded via a current detector 5 and returned to the high voltage power supply 1. Output e _b of current detector 5
is compared with the reference signal e _r by the comparator 6. Here, the reference signal e _r is set to a value somewhat larger than the maximum value of the signal generated by the beam current flowing through the current detector 5 during normal processing. When the output e _b of the current detector 5 is smaller than the reference signal e _r , the output of the comparator 6 supplies, for example, a positive constant voltage signal to the switching element 3 to make it conductive; When a discharge occurs inside and the current increases so that e _b > e _r , a constant negative voltage signal is output to turn the switching element into a cut-off state.

Here, current detector 5 comparator 6 and reference signal e _r
constitutes an abnormal discharge detector.

Note that 7 is a beam control device that instructs the high voltage power supply 1 and the charged particle beam generator 4 to control the acceleration voltage value, the beam current value, and the irradiation and stop of the beam current, respectively.

In the conventional device described above, the accelerating voltage is cut off by a series switching element on its output side, which enables high-speed cut-off and fast recovery, unlike when switching is performed on the primary side, but the power loss of the switching element inserted in series is ignored. It is necessary not only to set a value that is impossible, but also to provide a sufficient margin for the withstand voltage.

For example, when a vacuum tube is used as a series switching element, the internal voltage drop is 100 to several hundred volts, resulting in a power loss of several hundred watts even during normal welding, making it necessary to use an extremely large vacuum tube as the switching element. It is necessary to use it. It seems that these problems can be solved by using semiconductor switching devices such as transistors with low internal voltage drop, but these semiconductor devices inherently have extremely low overload resistance and can be permanently destroyed by a slight overcurrent or overvoltage. This is well known.

In the device shown in Fig. 1, not only is a normal machining current flowing through the series switching element 3, but also a large current during an abnormal discharge that occurs as a sudden accident can be safely passed through without damaging the element. It is an absolute necessity to do so. Further, when a discharge occurs, a large current caused by the discharge is rapidly cut off, so a large induced voltage caused by the inductance of the circuit is generated across the element. The value of this induced voltage becomes larger as the current cutoff speed becomes faster, and it becomes necessary to use an element having a wide margin in both current capacity and withstand voltage. Furthermore, the biggest drawback of this device is that when a semiconductor element is destroyed by overload, it becomes completely conductive and does not function as a protection device at all.

In the present invention, the high-voltage accelerating power supply normally has a considerable internal impedance, and can sufficiently withstand even if the output side is almost short-circuited for a short period of time. Focusing on the fact that most discharges are stopped by shutting off the high-voltage power supply for several milliseconds to several tens of milliseconds, we installed a switching element or an analog control element on the output side of the high-voltage power supply with a charged particle beam. Connected in parallel with the charged particle beam generator, these parallel elements are made conductive only when abnormal discharge occurs within the charged particle beam generator, thereby limiting the supply of high-voltage accelerating voltage to the charged particle beam generator. The present invention provides a device that can quickly stop the discharge and quickly restore the accelerating voltage after the discharge has stopped.

FIG. 2 is a block diagram showing an embodiment of the present invention, and parts having the same functions as those in FIG. 1 are given the same reference numerals. Further, 8 is a voltage limiter connected in parallel with the charged particle beam generator 4 on the output side of the high-voltage power supply 7, and is a switching element or an analog control element that has the ability to conduct the short-circuit current of the high-voltage power supply 1 for a very short time. is used. Here, as in FIG. 1, the current detector 5, comparator 6, and reference signal e _r constitute an abnormal discharge detector. In the device shown in Fig. 2, when normal, the output e _b of the beam current detector 5 is
is smaller than the reference signal e _r, and at this time, the comparator 6 outputs, for example, a negative voltage signal, contrary to the case in FIG. 1, and keeps the voltage limiter 8 in the cut-off state. When an abnormal discharge occurs in the charged particle beam generator 4, the discharge current returns to the high voltage power supply 1 via the current detector 5, so the output e _b of the current detector 5 rapidly increases and becomes larger than e _r . The output of the voltage regulator 6 is inverted and becomes a positive voltage signal, causing the voltage limiter 8 to conduct and grounding the output of the high voltage power supply 1. As a result, the accelerating voltage of the charged particle beam generator 4 drops instantaneously, and the discharge generated inside can no longer be maintained and disappears. When the discharge stops, the output e _b of the current detector 5 decreases, the output of the comparator 6 is inverted again, and the voltage limiter 8 stops conducting.
As a result, the accelerating voltage is applied to the charged particle beam generator 4 again, the beam is generated as before, and processing is restarted. The time from the occurrence of discharge until the accelerating voltage recovers and machining is restarted is determined only by the response speed of the voltage limiter 8 and is completely unrelated to the internal time constant of the high voltage power supply, so it can be as short as several tens of milliseconds. It's time. In this case, the recovery time of the accelerating voltage can be further shortened by setting the amount of conduction of the voltage limiter 8 to the minimum amount of conduction necessary to stop the abnormal discharge instead of making it completely conductive.

In the apparatus shown in Fig. 2, abnormal discharge is detected by detecting that the current value has increased more than the reference value, but when abnormal discharge occurs, the terminal voltage of the charged particle beam generator 4 Therefore, the abnormal discharge detector may be used as a circuit that detects that this terminal voltage has fallen below the reference value, or it may be used as a circuit that differentiates the current supplied from the high-voltage power supply 1 to the charged particle beam generator 4. A similar effect can be obtained by using a circuit that uses a differentiating circuit to detect a sudden increase in current due to discharge, or a circuit that uses a circuit that differentiates the terminal voltage of the charged particle beam generator 4 to detect a sudden decrease in terminal voltage due to discharge.

In the apparatus shown in FIG. 2, the output voltage of the high-voltage power supply 1 is set by the beam control device 7, but the voltage limiter is an analog element, and the output voltage from the beam control device 7 is set as shown by the broken line in FIG. The amount of conduction of the voltage limiter may be controlled by the signal .In this case, the high voltage power supply 1 is one that outputs a constant voltage and has an appropriate internal impedance.

FIG. 3 is a connection diagram showing a specific embodiment of the voltage limiter of the device of the present invention. In the figure, one side of line a is connected to a negative potential output terminal of a high voltage power supply, and the other side is connected to a charged particle beam generator.
Line b is a ground potential line connected to the positive potential output terminal of the high voltage power supply and the charged particle beam generator. The voltage limiter consists of a plurality of transistors Q ₁₁ to Q ₁ n and their drive circuits connected in parallel with the charged particle beam generator between the lines a and b. The drive circuit consists of resistors R ₁₁ to R ₁ n,
It consists of resistors R ₂₁ to R ₂ n, phototransistors Q ₂₁ to Q ₂ n connected in parallel to the resistors R ₁₁ to R ₁ n, respectively, light emitting diodes D ₁ to Dn, and a current limiting resistor r. Also a phototransistor Q ₂₁ or Q ₂ n and a light emitting diode D ₁
or Dn, and are photoelectrically coupled directly or by optical fibers, etc., and the drive circuits of each transistor are insulated from each other. In the figure, B ₁ to Bn are balance circuits for equalizing the burden voltages of the series transistors Q ₁₁ to Q ₁ n, and generally resistors or resistors and capacitors are used.

When using the circuit shown in Fig. 3, during normal machining, the abnormal discharge detector indicated by A does not generate an output, and at this time, the light emitting diode _D1 or
Assuming that Dn is normally emitting light, phototransistors Q ₂₁ to Q ₂ n are conductive and transistors Q ₁₁ to Q ₁ n are in a cut-off state with their emitters and bases short-circuited. When abnormal discharge occurs, abnormal discharge detector A detects it and lights up the light emitting diode.
D ₁ to Dn stop emitting light, phototransistors Q ₂₁ to Q ₂ n are cut off, and transistor Q ₁₁
Q ₁ n conducts and short-circuits lines a and b.
As a result, as explained in Figure 2, the high-voltage power supply to the charged particle beam generator is limited to the sum of the voltage drops of transistors _Q11 to _Q1n , and the abnormal discharge that was occurring inside is stopped. become. When the abnormal discharge stops, the light emitting diodes D ₁ to Dn emit light again and cut off the transistors Q ₁₁ to Q ₁ n.

FIG. 4 is a connection diagram showing another embodiment of the voltage limiter. In the figure, transistors _Q1 to
In Q _o-1 , the bases of adjacent transistors are connected by resistors R ₃₁ to R ₃ n, and the output of the abnormal discharge detector A is supplied only to the n-th transistor Qn through the resistor R ₃ n. has been done. The abnormal discharge detector detects abnormal discharge when it occurs in the charged particle beam generator and connects line b and transistor.
A positive voltage signal is generated between the base of Qn to make transistor Qn conductive. When transistor Qn becomes conductive, transistors Q _o-1 to Q ₁ become conductive in sequence, resulting in a short circuit between lines a and b. When the abnormal discharge stops, transistor Qn is immediately cut off,
This allows all other transistors Q ₁ to Q _o-1
is also turned off and returns to its original state. If the transistor is configured as shown in Figure 4, its drive circuit will be 1
If this is done by driving the transistor closest to the ground potential, there is no need to insulate the drive circuit, unlike the case shown in FIG.

In addition to the example shown in Fig. 4, the circuit for driving the series transistors may be
Any circuit may be used as long as one transistor is made conductive when an abnormal discharge occurs and other transistors are made conductive or cut off in accordance with the conduction state of this particular transistor. Further, instead of these transistors, a thyristor (generally called a GTO) that can be turned off or a combination of a transistor and a thyristor may be used.

By the way, in the device shown in Fig. 2, if the high voltage power supply 1 is a feedback control type power supply that feeds back the output voltage, compares it with a reference signal, and keeps the output voltage constant using a difference signal, an abnormality may occur. When the discharge is detected and the voltage limiter 8 conducts and the terminals of the charged particle beam generator are shorted, the signal that the output voltage has decreased is fed back and the high voltage power supply outputs a large output to maintain the original output voltage. Works to get. As a result, the short-circuit current increases, which not only places a large load on the voltage limiter 8 but also overloads the high-voltage power supply, which has an overall adverse effect.

FIG. 5 is a block diagram showing an embodiment of the present invention that eliminates such drawbacks, and is obtained by adding an output voltage detector 9, a comparator 10, and a switching circuit 11 to the device shown in FIG. In the circuit shown in Figure 5, high voltage power supply 1
In normal operation, the power source performs feedback control in which the signal from the beam control device 7 and the output signal from the voltage detector 9 are compared by a comparator 10 and the output voltage is controlled based on the difference signal. As schematically shown in the figure, the switching circuit 11 is normally connected to the N side and supplies the output signal of the output voltage detector 9 to the comparator 10. When an abnormal discharge occurs in the charged particle beam generator 4, the output of the current detector 5 increases and becomes larger than the reference signal e _r1 , and the comparator 6 outputs an abnormal discharge occurrence signal. This output signal is supplied to the voltage limiter 8 to make it conductive, and is also supplied to the switching circuit 11 to switch it from N to E.
The feedback signal of the comparator 10 is switched from the output voltage signal to a reference signal e _r2 predetermined corresponding to the output voltage. When using the device shown in Fig. 5, even when an abnormal discharge occurs and the voltage limiter is activated and the output voltage is forcibly reduced, the output state corresponding to the reference signal e _r2 , which is a pseudo feedback signal, must be maintained. This prevents the high-voltage power supply from operating in the direction of obtaining an unnecessary large output as would be the case when performing simple feedback control, so a transient high voltage will occur when the voltage limiter shuts off again after discharging has stopped. No danger and better responsiveness.

As described above, when using the device of the present invention, when abnormal discharge occurs in the charged particle beam generator, the supply of high voltage power is immediately restricted, so the discharge can be stopped in an extremely short time, and furthermore, the discharge can be stopped in an extremely short time. As soon as the supply of high-voltage power for acceleration is restored, the time during which the charged particle beam is stopped in the event of abnormal discharge is shortened, and even if discharge occurs during machining, there will be no defects in the workpiece. Machining can be continued stably without any occurrence of this problem.

In addition, the voltage limiter that activates when an abnormal discharge occurs is connected in parallel to the charged particle beam generator, so even if it activates and shuts off the high-voltage power supply, a large transient voltage will be generated unlike conventional devices connected in series. Moreover, since no current flows through the voltage limiter during normal operation, a voltage limiter having a small withstand voltage and a small current capacity can be used, which is economical. Furthermore, since the voltage limiter is connected in parallel with the charged particle beam generator on the output side of the high-voltage power supply, even if the voltage limiter becomes permanently conductive due to a failure, the operation will be the same as when an abnormal discharge occurs.
The device will operate in a safer direction.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a conventional device, Fig. 2 is a block diagram showing an embodiment of the device of the present invention, and Figs. 3 and 4 are concrete diagrams of the voltage limiter in the embodiment of Fig. 2. The connection diagram, FIG. 5, is a configuration diagram showing another embodiment of the present invention. 1...High voltage power supply, 4...Charged particle beam, 5...
...Current detector, 6, 10...Comparator, 7...Beam control device, 8...Voltage limiter, 9...Voltage detector, 11...Switching circuit, _Q11 to _Qn1 ...Transistor.

Claims (1)

[Scope of Claims] 1. A charged particle beam generator that obtains accelerated power from a high voltage power source, an abnormal discharge detector that detects sudden changes in the output current or output voltage of the high voltage power source, and an output circuit of the high voltage power source. and a voltage limiter connected in parallel to the abnormal discharge detector to bypass the output of the high voltage power supply according to the output signal of the abnormal discharge detector. 2. The abnormal discharge detector outputs an abnormal discharge occurrence signal when the output current detector of the high voltage power supply, the reference current setter, and the output of the output current detector become larger than the output of the reference current setter. A charged particle beam processing apparatus according to claim 1, comprising a comparator that outputs an output. 3. The charged particle beam processing apparatus according to claim 1, wherein the abnormal discharge detector is a differentiating circuit that differentiates an output current of a high voltage power supply. 4. The abnormal discharge detector includes a voltage detector that detects the terminal voltage of the charged particle beam generator, a reference voltage setter, and when the output voltage of the voltage detector becomes lower than the output voltage of the reference voltage setter. 2. A charged particle beam processing apparatus according to claim 1, further comprising a comparator that outputs an abnormal discharge occurrence signal. 5. The charged particle beam processing apparatus according to claim 1, wherein the abnormal discharge detector is a differentiating circuit that differentiates a terminal voltage of a charged particle beam generator. 6. The voltage limiter is composed of a plurality of semiconductor switching devices or semiconductor analog control devices connected in series, and a drive circuit provided for each semiconductor device and an output of the abnormal discharge detector are guided to the drive circuit. A charged particle beam processing apparatus according to any one of claims 1 to 5, comprising an insulated coupling circuit for. 7. The voltage limiter is composed of a plurality of semiconductor switching devices or semiconductor analog control devices connected in series, and a specific one of the semiconductor devices is operated by the output signal of the abnormal discharge detector, and the other semiconductor devices are operated by the output signal of the abnormal discharge detector. The charged particle beam processing apparatus according to any one of claims 1 to 5, wherein the amount of conduction is controlled in accordance with the conduction state of the specific semiconductor element. 8. The charged particle beam processing apparatus according to any one of claims 1 to 5, wherein the voltage limiting element also serves as a controller for the amount of charged particle beam during processing. 9 A feedback-controlled high-voltage power supply that feeds back the output voltage to the input side to obtain a constant voltage output, a charged particle beam generator that obtains accelerating power from the high-voltage power supply, and a An abnormal discharge detector that detects sudden changes,
a voltage limiter connected in parallel to the output circuit of the high voltage power supply and bypassing the output of the high voltage power supply based on the output signal of the abnormal discharge detector; and a feedback signal of the high voltage power supply based on the output of the abnormal discharge detector. and a switching circuit that switches the output voltage signal of the high voltage power supply to a constant voltage predetermined corresponding to the output voltage.