JPS6340013B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for ionizing liquid metal by electric field evaporation and extracting it as an ion beam.

In ion beam exposure using metal ions such as gallium, the diffusion of ions within the resist is smaller than in exposure using an electron beam.
Metal ion sources are attracting attention as an exposure means for producing sub-micron patterns, and research into metal ion sources is being carried out in various fields. FIG. 1 shows an example of a liquid metal ion source, in which numeral 1 is a reservoir made of metal such as tantalum or tungsten with pores 2 provided at the bottom. 3 is included. One end of a tungsten needle member 4 disposed through the pore 2 at the bottom of the reservoir is fixed to the side surface of the reservoir using, for example, a spotting solution, and the other end is made into a needle shape by electropolishing. is arranged opposite to the extraction electrode 5 which is kept at a negative potential with respect to the potential at the other end. A tungsten heater 6 is spot-welded to the reservoir 1, and a heating current is supplied to the heater 6 from a heating power source 7. Further, a positive high voltage is applied to the reservoir 1 and the needle member 4 from an acceleration power source 8. 9
is the support rod.

In the above-described ion source, a strong electric field is applied to the tip of the needle member 4, and as a result, the gallium inside the reservoir is drawn out through the pore 2 at the bottom to the tip of the needle member 4 by the strong electric field. . The gallium at the tip forms a conical protrusion T called a Taylor Cone by a strong electric field. The electric field is concentrated at the tip of this conical protrusion T,
The gallium at the tip is evaporated by the electric field and extracted as gallium ions. The relationship between the voltage applied between the tip of the needle member 4 and the extraction electrode 5 and the extracted ion beam current is as shown by the solid line A in FIG.

In a conventional field emission type ion beam generator that extracts ions from such an ion source as an ion beam, a voltage is applied between the tip of the needle member 4 and the extraction electrode 5 to stop generation of the ion beam. The power for applying was turned off. Therefore, since the extraction electric field disappears, the liquid metal moves (diffuses) toward the root of the needle-like member 4, and after a certain amount of time, a Taylor cone is formed at the tip of the needle-like member 4. There is no longer sufficient metal retention. Therefore, even if an extraction voltage is applied to generate an ion beam again, the ion beam cannot be generated immediately, and a waiting time of several to several tens of minutes may be required.
Even if it occurred immediately, the beam remained unstable until enough liquid metal was supplied to the tip.

The present invention solves these conventional problems and provides a field emission type ion beam generator that can generate a stable ion beam without waiting time even after a long period of time has passed since generation of the ion beam was stopped. The liquid metal stored in the reservoir is drawn out to the needle tip by an electric field formed between the needle tip and the extraction electrode, and the drawn liquid metal is ionized by electric field evaporation. In a device that extracts an ion beam as an ion beam, an ion beam detection means arranged in the ion beam path and a differential differential that compares the signal from the detection means with a reference signal and generates a signal according to the difference. an amplifier, an adder circuit for adding an output signal of the differential amplifier and a bias signal, and a voltage corresponding to the output signal of the adder circuit is configured to be applied between the needle tip and the extraction electrode; , is characterized by providing a means for zeroing the signal from the differential amplifier to the adder circuit.An embodiment of the present invention will be described below in detail based on FIG. 3, but the configuration is the same as that in FIG. Elements are given the same numbers and their explanations are omitted.

In FIG. 3, 10 is an insulator made of, for example, an insulator for fixing the support rod 9, and 11 is an installed accelerating electrode. Reference numeral 12 denotes an aperture plate for monitoring the generated ion beam, and the ion current signal detected by this aperture plate 12 is converted into a voltage signal by a current-voltage converter 13.
It is supplied to one input terminal of the differential amplifier 14. A reference signal from a reference signal source 15 is supplied to the other input terminal of the differential amplifier 14 via a switch 16. The output signal of the differential amplifier 14 is supplied to one input terminal of an adder circuit 17, and the output signal is supplied by a bias signal source 18 to the other input terminal of the adder circuit 17. This addition circuit 1
The output signal 7 is connected to the base of a gate transistor 19 whose collector terminal is connected to the power supply 20. The emitter output of the gate transistor 19 is supplied to a high frequency oscillator 21. The output from the high-frequency oscillator 21 is supplied to a step-up rectifier circuit 22 consisting of a step-up transformer 22a, a bridge rectifier 22b, etc., and this circuit 22 generates a voltage corresponding to the amplitude of the output of the high-frequency oscillator 21. A voltage is applied between the shaped member 4 and the extraction electrode 5. Further, the output signal of the bias signal source 18 is such that when a voltage is generated from the boost rectifier circuit 22 based only on this output signal, this voltage is slightly lower than the critical voltage at which a Taylor cone is formed, as shown in FIG.
It is set to the voltage indicated by V ₀ .

In such a configuration, if the output signal of the reference signal source 15 is set to a value corresponding to the amount of ion current shown as ₁ in FIG. When the signal is supplied to the dynamic amplifier 14, the output signal of the differential amplifier 14 and the output signal of the bias signal source 18 are added together in the adder circuit 17, and a signal is supplied to the base of the gate transistor 19. Therefore, an output based on this base input is supplied from the collector of the transistor 19 to the high frequency oscillator 21 to determine the oscillation amplitude of the high frequency oscillator ₂₁ . The ion beam is placed between the needle member 4 and the extraction electrode 5, and an ion beam is generated from the tip of the needle member 4. The amount of current of this ion beam is determined by the signal detected by the aperture plate 12 and the reference signal source 15.
Since the negative feedback loop that matches the reference signal with the reference signal is configured using the differential amplifier 14, the value matches the value ₁ mentioned above. Therefore, if the switch 16 is turned off to stop the generation of the ion beam, the output signal of the differential amplifier 14 will be 0.
However, since the output signal of the bias signal source 18 is continuously supplied to the adder circuit 17, the high frequency oscillator 21 generates a high frequency output with an amplitude corresponding to the emitter output corresponding to the output from the bias signal source 18. . Therefore, the voltage _V0 , which is slightly lower than the critical voltage at which a Taylor cone is formed (approximately 5 KV in this embodiment), is generated by the step-up rectifier circuit 22, and even after the switch 16 is turned off, the needle-shaped member 4
and the extraction electrode 5. Therefore, even after the switch 16 is turned off and generation of the ion beam is stopped, the liquid metal 3 is always attracted to the tip of the needle-like member 4, and a sufficient amount of liquid metal continues to stop at this tip. It will accumulate. Therefore, when the switch 16 is turned on again to generate an ion beam, a stable beam can be generated immediately.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of a liquid metal ion source, Figure 2 is a diagram showing the relationship between the extraction voltage applied during ion beam generation and the voltage applied when ion beam generation is stopped, and Figure 3. The figure is a diagram for showing one embodiment of the present invention. 1: Reservoir, 3: Liquid metal, 4: Needle member,
5: extraction electrode, 6: heater, 7: heating power supply, 8: acceleration power supply, 11: acceleration electrode, 12: aperture plate, 14: differential amplifier, 15: reference signal source, 16: switch, 17: addition circuit, 18: bias signal source, 19: gate transistor, 2
1: High frequency oscillator, 22: Boost rectifier circuit.

Claims (1)

[Claims] 1. The liquid metal stored in the reservoir is drawn out to the needle tip by an electric field formed between the needle tip and the extraction electrode, and the drawn liquid metal is ionized by electric field evaporation to form an ion beam. In the apparatus for extracting the ion beam, the ion beam detection means arranged in the ion beam path, a differential amplifier that compares the signal from the detection means with a reference signal and generates a signal according to the difference, and an adding circuit that adds the output signal of the dynamic amplifier and the bias signal;
A voltage corresponding to the output signal of the adder circuit is applied between the needle tip and the extraction electrode, and a means is provided for zeroing the signal from the differential amplifier to the adder circuit. Features: Field emission type ion beam generator.