JPH03241647A - Open filament detecting circuit - Google Patents

Abstract

PURPOSE:To surely detect an open circuit by using the voltage applied to a filament and the current fed to it. CONSTITUTION:The logical product of an AND circuit 60 is not satisfied and a relay 61 is not operated unless the filament voltage VF exceeds a preset value and the filament current IF becomes 0 or a value near 0. The detection action point of a voltage detecting circuit 40a can be reduced to the minimum possible. The above condition is satisfied only when a filament 20 is opened during lighting, the logical product of the circuit 60 is not satisfied when the current IF is increased by the control of a filament control circuit 30 and the voltage VF is increased or when the voltage VF is lowered by the decrease of the current IF. The open filament 20 can surely be detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to, for example, an ion processing apparatus that irradiates a wafer with an ion beam in a vacuum and performs a process such as ion implantation on the wafer. The present invention relates to a filament breakage detection circuit that detects breakage of a filament, etc. for supplying electrons (for sexualization).

[Conventional technology]

In the above-mentioned ion processing equipment, in order to prevent the wafer from being charged due to ion beam irradiation, a filament is installed near the wafer, and the primary electrons emitted from the filament are applied to a Faraday cup, etc., from which secondary electrons are generated. In some cases, the secondary electrons are emitted and supplied to the wafer in the ion beam irradiation area to neutralize the positive charge caused by the ion beam on the surface of the wafer.

An example of a power supply circuit for such a filament is shown in the second
As shown in the figure.

In this example, a trip circuit breaker 12 and a cyrisk circuit 1 are connected between the input power source 11 and the transformer 14.
Power is supplied from the filament power supply 10 formed by inserting the filament 3 into the filament 20 for neutralization as described above. The thyrisk circuit 13 receives a signal from the filament control circuit 30 and changes the voltage applied to the primary side of the transformer 14. As a result, the amount of primary electrons emitted from the filament 20 is controlled by adjusting the current (1) flowing through the filament 20.

The filament 20 breaks due to its lifespan, and if this is not detected, the process will continue without neutralizing the wafer, resulting in problems such as electrical discharge on the wafer surface. occurs.

Therefore, conventionally, a filament breakage detection circuit 40 having the following configuration is provided.

That is, another transformer 4I is connected to the secondary side of the transformer 14 of the filament power supply 10, and the output of the secondary side is rectified by the rectifier 42. This rectified voltage is divided by a volume 43 and a resistor 44, and is further divided by a resistor 44.
The voltage is divided by voltages 5 and 46 and applied to the base of transistor 47, and when this voltage exceeds the output voltage of transistor 47, transistor 47 is turned on. A relay 48 is connected to the collector side of this transistor 47, and when the transistor 47 is turned on, the relay 48 is also turned on.

The voltage VF applied to the filament 20 (that is, the secondary voltage of the transformer 14) is, for example, about 2 to 3 cm when the filament 20 is lit normally, but when the filament 20
When 0 is disconnected and there is no load, the voltage rises to about 8V.

Therefore, by adjusting the volume 43, the filament 20
A break in the filament 20 can be detected by setting the transistor 47 and the relay 48 to turn on only when the voltage .

In this example, for safety and the like, the trip circuit of the wiring breaker 12 of the filament power supply 10 is operated by the contact 48a of the relay 48, and the breaker 12 is activated.
I try to cut it.

[Problem to be solved by the invention]

The filament breakage detection circuit 40 includes a volume 43
The operating point of the relay 48 is adjusted by adjusting the voltage (2) applied to both ends of the filament 20, but the current IF flowing through the filament 20 changes variously under the control of the filament control circuit 30. If the current (2) increases, the voltage (2) across the filament 20 also increases accordingly, which may result in malfunction depending on the operating point adjustment.

However, if the operating point is raised in an attempt to prevent malfunctions, there is a possibility that the relay 48 will not operate even if the filament 20 is actually broken, that is, it may not be possible to detect the breakage of the filament 20.

SUMMARY OF THE INVENTION The main object of the present invention is to provide a filament breakage detection circuit that can reliably detect filament breakage by improving the above-mentioned problems.

[Means to solve the problem]

In order to achieve the above object, the filament breakage detection circuit of the present invention includes a voltage detection circuit that detects when the voltage applied to the filament exceeds a set value, and a voltage detection circuit that detects when the voltage applied to the filament exceeds a set value, and the voltage flowing through the filament becomes 0 or a value close to it. The present invention is characterized in that it includes a current detection circuit that detects this, and an AND circuit that calculates the logical product of outputs from both detection circuits.

[Operation] According to the above configuration, the logical product in the AND circuit does not hold unless the voltage applied to the filament exceeds the set value and the current flowing through the filament reaches zero or a value close to zero.

Both of these conditions are met only when the filament is disconnected while it is lit; otherwise, for example, when the voltage across the filament is increased by increasing the current flowing through the filament through control, or when the voltage across the filament is increased.
Conversely, even if the voltage across the filament decreases by reducing the current flowing through the filament, the AN
The logical product in the D circuit does not hold.

Therefore, according to the above configuration, it is possible to reliably detect filament breakage.

〔Example〕

FIG. 1 is a circuit diagram showing an example of a power supply circuit including a filament breakage detection circuit according to an embodiment of the present invention. The same reference numerals are given to the same or corresponding parts as in the conventional example shown in FIG. 2, and the differences from the conventional example will be mainly explained below.

In this embodiment, a voltage detection circuit 40a, a current detection circuit 50, and an AND circuit 60 constitute a filament breakage detection circuit.

The voltage detection circuit 40a has the same configuration as the conventional filament breakage detection circuit 40, and is designed to turn on the relay 48 when it detects that the voltage (filament voltage) VF applied to the filament 20 exceeds a set value. ing. The details of its configuration and operation are as described above, so the explanation thereof will be omitted here.

The current detection circuit 50 detects the current (
A current transformer 51 is provided in the path of the filament current IF, that is, in the line connecting the filament power supply 10 and the filament 20, so that the filament current 1. is converted into voltage. This voltage is rectified by a rectifier 52 and applied to the input of a photocoupler 54 via a resistor 53. This photocoupler 54
The output part of is connected between the collector and base of the transistor 55, and the collector of the transistor 55 is connected to the resistor 5.
6 and a relay 57 to a DC power source.

Therefore, when the filament current I is flowing, the photocoupler 54 is on, and accordingly the transistor 55 and the relay 57 are also on. However, when the filament current IP reaches 0 or a value close to it, the photocoupler 54 is on. turns off, and as a result, transistor 5 turns off.
5 and relay 57 are also turned off, thereby making it possible to detect that the filament current (2) has reached zero or a value close to it.

On the other hand, in the AND circuit 60, the voltage detection circuit 40a
The contact (a contact) 48a of the relay 48 and the current detection circuit 5
The contact (b contact) 57b of the relay 57 of 0 is connected in series, thereby calculating the AND of the outputs of both the detection circuits 40a and 50.

Further, in this example, the relay 61 is connected to the input power source 11 through both contacts 48a and 157b, so that the relay 48 of the voltage detection circuit 40a operates (that is, detects that the filament voltage ■ exceeds the set value), and , when the relay 57 of the current detection circuit 50 has returned to its original state (that is, it has detected that the filament current ■ has become O or a value close to it), the relay 61
is working.

Among the several contacts 61a of this relay 61, in this example, one is used for self-holding, one is used for tripping the wiring breaker 12 in the filament power supply 10, and one is used for detection output. There is. This detection output can be used in various ways; for example, it can be used to issue an alarm display or to stop ion beam irradiation on the wafer.

According to the above configuration, the filament voltage (1) exceeds the set value, and the filament current (1) exceeds the set value. Unless the value becomes 0 or a value close to 0, the logical product in the AND circuit 60 does not hold, and the relay 61 does not operate. Therefore, voltage detection circuit 4
The operating point of detection at 0a can be lowered to the bare minimum.

The above two conditions are met only when the filament 20 is disconnected while it is lit; otherwise,
For example, if the filament voltage VF is increased by increasing the filament current IF under the control of the filament control circuit 30, or if the filament voltage VF is decreased by decreasing the filament current IF, the AND circuit 60 is not established, and the relay 61 does not operate.

Therefore, according to the above configuration, disconnection of the filament 20 can be detected reliably.

In the above description, the case of detecting a break in the filament 20 for neutralization in an ion processing apparatus has been described as an example, but the present invention can also be applied to detecting a break in a filament other than that, such as detecting a break in a filament in an ion source. Of course, it can also be applied to

〔Effect of the invention〕

As described above, according to the present invention, filament breakage is detected using both the voltage applied to the filament and the current flowing through the filament, so that filament breakage can be reliably detected.

[Brief explanation of drawings]

0 FIG. 1 is a circuit diagram showing an example of a power supply circuit including a filament breakage detection circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing an example of a power supply circuit including a conventional filament breakage detection circuit. 10... filament power supply, 20. ,, filament, 40a... voltage detection circuit, 50... current detection circuit, 60... AND circuit.

Claims (1)

[Claims] (1) A voltage detection circuit that detects when the voltage applied to the filament exceeds a set value, and a current detection circuit that detects when the voltage flowing through the filament reaches 0 or a value close to it. AN to calculate the logical product of the outputs of
A filament breakage detection circuit comprising a D circuit.