JPH0588503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ion beam apparatus that generates an ion beam and irradiates a material to be imaged.

[Prior Art] In an ion beam apparatus equipped with a gas phase ion source, an extraction voltage is applied between an emitter and an extraction electrode to extract an ion beam. Second
The figure shows a conventional example of such an ion beam device. In the figure, 1 is an emitter of a gas phase ion source, 2 is an extraction electrode, and 3 is an ion beam current detector for detecting the current of emitted ions. 4 is a focusing lens, 5 is an objective lens, 6 is a material to be drawn, 7 is an acceleration power source, 8a is an extraction power source, 8b is a control circuit for controlling the output voltage of the extraction power source 8a, 9 is an amplifier, and 10 is a 11 is a limit circuit; 12 is a summing amplifier; 13 is an ion beam current designation signal generating circuit for setting a target value of the amount of ion beam current emitted from emitter 1; 14; is an extraction voltage designation signal generation circuit for setting the target value of the extraction voltage. The limit circuit 11 has input/output characteristics as shown by characteristic line A in FIG. In other words, if the input signal
It outputs a signal Y up to ΔY, and when the input signal is smaller than -ΔX, it outputs a signal of -ΔY, and when the input signal is larger than +ΔX, it outputs a signal with a signal value of +ΔY.

Now, in the case of a gas phase ion source, the emitted ion beam current I has a maximum point with respect to the extraction voltage V, as shown by characteristic line A in FIG. Since it is desirable to extract a large amount of ion beam, when attempting to extract an ion beam current amount close to the maximum value from the ion source, the designation signal is set as follows. That is, for example, the ion beam designation signal generation circuit 1 generates a signal designating the ion beam current Io corresponding to the point Po in FIG.
At the same time, a signal corresponding to the extraction voltage Vo is generated from the extraction voltage designation signal generation circuit 14. Then, a signal is outputted from the differential amplifier 10 by amplifying the deviation between the output of the amplifier 9 which amplified the output signal from the ion beam current detector 3 and the ion beam current designation signal from the ion beam current designation signal generation circuit 13. Ru. This signal is converted by a limit circuit 11 according to the conversion characteristic and then sent to a summing amplifier 12. Limit circuit 1
1 and the output signal from the output voltage designation signal generation circuit 14 are added in the summing amplifier 12, and the output signal of the output of the summing amplifier 12 is sent to the control circuit 8b. It is controlled to generate the extraction voltage corresponding to Po.

If the limit circuit 11 is not present, the extraction voltage may shift to the right side of the voltage Vp corresponding to the peak value Ip for some reason during negative feedback control. In such a case, the negative feedback control system determines that the extraction voltage is insufficient, and the extraction power source 8a applies the maximum value of the extraction voltage to the extraction electrode 2. Therefore, the ion beam current is further reduced, and the negative feedback loop is broken. The limit circuit 11 is provided to solve this problem, and since the limit circuit 11 limits the range of the input signal to the summing amplifier 12, the negative feedback loop will not be disconnected.

[Problems to be solved by the invention] By the way, the ion beam current I shown in FIG.
The relationship between and the extraction voltage V is a characteristic after the ion beam has been sufficiently generated, and in the initial state when generating the ion beam, an extraction voltage considerably higher than the extraction power source must be applied between the emitter and the extraction electrode. No ion beam is generated. However, in the conventional device, the limit circuit 1
1, the magnitude of the control signal fed back to the control circuit 8b is limited, making it necessary to perform the following complicated operations.

That is, first, the operator removes the feedback loop, manually sets the output voltage of the extraction power source 8a to a high value, starts generating a beam from the emitter 1, checks the amount of beam current with an ammeter, and determines the beam current. When the voltage has increased enough to form a feedback loop, manually lower the extraction voltage to the voltage corresponding to the set beam current.
Therefore, a negative feedback loop is activated.

The present invention solves these conventional drawbacks, and makes it possible to generate an ion beam from an emitter without complicated operations by an operator, and to perform negative feedback control to maintain a predetermined ion beam current value. The purpose is to provide an ion beam device.

[Means for Solving the Problems] Therefore, the present invention provides an extraction power source for applying an extraction voltage between an emitter and an extraction electrode of a gas phase ion source, and detects the amount of ion beam current generated from the emitter. an ion beam current designation signal generation circuit for setting a target value of the ion beam current amount; and a deviation between an output signal from the detection means and an output signal of the ion beam current designation signal generation circuit. an amplifier for amplification, a limit circuit for limiting the range of the output signal value of the amplifier to within a predetermined width, and an extraction voltage designation signal for generating a signal for specifying the output voltage of the extraction power supply. In an ion beam apparatus comprising a generation circuit and means for controlling the output voltage of the extraction power source based on the output signal of the limit circuit and the output signal of the extraction voltage designation signal generation circuit, the operation of the ion beam apparatus is performed. a reference signal source that generates a reference signal corresponding to an ion beam current that is greater than the ion beam current generated by the emitter at the start and smaller than the ion beam current designated by the ion beam current designation signal generation circuit; and means for comparing the output signal from the detection means with the reference signal, and when the output signal from the detection means is smaller than the reference signal, the limit circuit is brought into a non-operating state, and when the output signal is larger than the reference signal, the limit circuit is switched to an operating state. It is characterized by

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing one embodiment of the present invention, and in FIG. 1, the same components as in FIG. 2 are denoted by the same reference numerals.

In FIG. 1, 11 is a limit circuit;
The limit circuit 11 includes a Zener diode 11a,
11b and a resistor 11c. 15 is a comparison circuit, to which a signal obtained by amplifying the output signal of the ion beam detector 3 is sent as well as an output signal from the reference signal source 16. The reference signal source is a reference signal corresponding to an ion beam current larger than the ion beam current generated by the emitter 1 at the start of operation of the ion beam apparatus and smaller than the ion beam current specified by the ion beam current specification signal generation circuit 13. It generates a signal. The output signal of the comparison circuit 15 is sent to the timer circuit 17.
The output signal of 7 is sent to an on/off switch circuit 18. The switch circuit 18 is the timer circuit 17
The conduction and non-conduction are controlled based on the set time end signal.

In an apparatus having such a configuration, the reference signal source 1
6, the output signal of the reference signal source 16 is set so as to generate a signal corresponding to the current Ic shown in FIG.
Further, the output signal of the ion beam current designation signal generation circuit 13 is set to a value corresponding to the current value Io in FIG. 4, and the output signal of the extraction voltage designation signal generation circuit 14 is set to a value corresponding to the voltage value Vo in FIG. Set it to the value you want. When the apparatus is operated, the detection signal of the ion beam detector 3 does not exceed the reference signal from the reference signal source 16 in the initial state, so the output signal of the comparison circuit 15 and the output signal of the timer circuit 17 based on it are The signal becomes low level, and the switch circuit 18 becomes non-conductive. Therefore, the limit circuit 11 becomes inactive. Therefore, the signal sent from the differential amplifier 10 to the summing amplifier 12 increases, and since an extremely large signal from the summing amplifier 12 is sent to the control circuit 8b, the output power source 8a
The resulting extraction voltage is close to the maximum value.

When such a large voltage is applied between the emitter 1 and the extraction electrode 2, the emitter 1 starts generating an ion beam. Further, since the ion beam current generated by the emitter 1 gradually increases, the detection signal from the ion beam detector 3 exceeds the output signal from the reference signal source 16. the result,
The output signal of the comparison circuit 15 becomes high level, and the timer circuit 17 starts counting the passage of time. When the time preset in the timer circuit 17 has elapsed, the signal sent from the timer circuit 17 to the switch circuit 18 becomes high level. Therefore, the switch circuit 18 becomes conductive, and the limit circuit 11 is switched to a movable state and has the characteristics shown in FIG. As a result, the output signal range of the amplifier 10 is converted into a signal ranging from Vo-ΔV to Vo+ΔV in FIG. 4, and is sent to the summing amplifier 12. At this point, the characteristics of the gas phase ion source are as shown in Figure 4 A, so the negative feedback loop automatically starts working, and the amount of ion beam current generated from emitter 1 is set to the set value Io. will be maintained. Therefore, it is possible to generate an ion beam from the emitter and to control the ion beam current to a predetermined value by negative feedback without the above-mentioned complicated operations.

The embodiment described above is only one embodiment of the present invention,
The present invention can be implemented in variations.

For example, in the above-described embodiment, the width of the range on the negative side of X may be set to be N times as wide as the range on the positive side, as shown in FIG. 5 for the characteristics of the limit circuit 11.

Further, in the above-described embodiment, the current generated from the emitter 1 is detected using a diaphragm-shaped detector placed in the ion beam optical path, but a resistor is installed between the accelerating power source 8a and the emitter 1. The ion beam current may be detected by arranging an element and extracting the current flowing through this resistance element.

Further, in the above-described embodiment, the switch circuit 18 is not operated until the set time elapses by the timer circuit 17 after the ion beam detection signal exceeds the output signal of the reference signal source 16. The timer circuit 17 can also be omitted if the negative feedback loop can be operated immediately after the output signal of the source 16 is exceeded.

Furthermore, the extraction power supply is divided into two power supplies, and the output voltage of one power supply is controlled based on the output signal of the extraction voltage designation signal generation circuit, and the output voltage of the other power supply is controlled by the ion beam current designation signal generation circuit. The summing amplifier can also be omitted by controlling based on the output signal of the circuit and using the sum of the output voltages of both power supplies as the extraction voltage.

[Effects of the Invention] As is clear from the above description, in the apparatus based on the present invention, the limit circuit for limiting and outputting the output signal of the differential amplifier is used to compare the ion beam detection signal with the reference value. Since it is equipped with a control means for switching between a movable state and a non-movable state based on the Negative feedback control can be performed.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing a conventional device, Fig. 3 is a diagram showing characteristics of a limit circuit, and Fig. 4 is an ion beam generation source. FIG. 5 is a diagram showing the relationship between the ion beam current and the extraction voltage, and FIG. 5 is a diagram showing another example of the characteristics of the limit circuit. 1... Emitter, 2... Extraction electrode, 3... Ion beam current detector, 4... Focusing lens, 5...
Objective lens, 6... Material to be drawn, 7... Acceleration power source, 8a... Output power source, 8b... Control circuit, 9...
... Amplifier, 10 ... Differential amplifier, 11 ... Limit circuit, 12 ... Summing amplifier, 13 ... Beam current designation signal generation circuit, 14 ... Extraction voltage designation signal generation circuit, 15 ... Comparison circuit, 16 ... ...Reference signal source, 17...Timer circuit, 18...Switch circuit.

Claims (1)

[Claims] 1. An extraction power supply for applying an extraction voltage between the emitter and extraction electrode of the gas phase ion source, a detection means for detecting the amount of ion beam current generated from the emitter, and a target value of the amount of ion beam current. an ion beam current designation signal generation circuit for setting, an amplifier for amplifying the deviation between the output signal from the detection means and the output signal of the ion beam current designation signal generation circuit, and an output signal value of the amplifier. a limit circuit for outputting a signal with a limited range within a predetermined width; a draw voltage designation signal generation circuit that generates a signal for specifying the output voltage of the draw power source; and an output signal of the limit circuit and the draw voltage. In an ion beam device comprising means for controlling the output voltage of the extraction power source based on an output signal of a specified signal generation circuit, the ion beam current generated by the emitter is larger than the ion beam current generated by the emitter at the start of operation of the ion beam device. a reference signal source that generates a reference signal corresponding to an ion beam current smaller than the ion beam current specified by the beam current specification signal generation circuit, and a reference signal source that compares the output signal from the detection means with the reference signal, An ion beam apparatus characterized by comprising means for setting the limit circuit in a non-operating state when the output signal from the means is smaller than the reference signal, and switching it to an operating state when the output signal is larger than the reference signal.