JPH0618109B2 - Liquid metal ion source cleaning method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a liquid metal ion source used in an ion implantation apparatus using a focused ion beam.

(Prior Art) Focused ion beam (FIB) technology has been attracting attention as semiconductor elements are integrated and miniaturized. This technology is maskless and micron (μ
m) Milling, etching,
It is extremely important as a microfabrication technology because it can perform resist exposure and implantation. Liquid metal ion source (Liquid Metal Ion Source;
(Hereinafter referred to as LMIS) is indispensable and is mounted on the FIB device to form a microbeam.

Conventionally, as LMIS materials, literature, microelectronics-photonics, materials, sensors and technology (Microelectronics-Photonics, Materials, Sen
sors and Technology) Vol.10.p21, it can supply a relatively stable operating ion current, Ga
(Gallium), Au (gold) -Si (silicon), Au (gold)-
Si (silicon) -Be (beryllium) has been widely used.

(Problems to be solved by the invention) However, even in the above LMIS of Ga, Au-Si, and Au-Si-Be, the LM caused by the sputtering atoms is generated during the operation of the ion source.
Contamination of IS or LMIS due to residual gas during operation caused a decrease in ion current. In particular, during LMIS operation of the FIB device, carbon adhering to the emitter surface aggravates the flow of alloy at the emitter surface, and
It had the drawback of causing a decrease in the ionic current of B.

An object of the present invention is to provide a method for cleaning a liquid metal ion source capable of obtaining a stable FIB ion current.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention purifies a liquid metal ion source having a reservoir for melting and storing a metal to be ionized, an emitter, and an extraction electrode. In the method, after supplying one or both of hydrogen gas and argon gas to the liquid metal ion source, a voltage is applied between the emitter and the extraction electrode to cause a discharge, and the discharge causes the surface of the emitter to be discharged. It is characterized in that the carbon attached to the above is converted into a hydrocarbon to be volatilized, or the carbon attached to the emitter is removed by sputtering.

(Operation) As described above, according to the present invention, the H ₂ gas and / or the Ar gas is introduced into the LMIS portion by the gas supply means provided in the ion source portion of the FIB device, and is exhausted by the gas exhaust means, and Since the LMIS portion is discharged by the discharge means provided in the portion, as a result, the carbon attached to the emitter surface becomes hydrocarbon (C _m H _n (m, n = integer)) and volatilizes from the emitter surface. Therefore, the flow of the alloy on the emitter surface can be improved and a stable ion current can be obtained.

(Embodiment) FIGS. 1 to 3 are views for explaining an embodiment of the present invention, which will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a FIB device. 1 is a lens barrel, 2 is an emitter, 3 is a heater also serving as a reservoir for melting and holding a metal to be ionized, 4 is an extraction electrode, 5 is a lens system, 6 is a deflection electrode,
Reference numeral 7 is a sample, 8 is a valve, 9 is a gas introduction pipe for supplying a gas to the LMIS portion composed of the emitter 2, the heater 3 and the extraction electrode 4, 10 is a heating power supply, 11 is an ion extraction power supply, and 12 is Ion acceleration power source, 13 is a lens power source, 14 and 15 are beam deflection power sources, 16 and 17 are insulating terminals, and 18 is a vacuum gauge.

During the ion implantation by FIB, carbon attached to the surface of the emitter 2 is removed by the method described below. 1x lens barrel 1
After evacuating to a vacuum of about 10 ⁻⁶ Torr, the valve 8 is opened and hydrogen (H ₂ ) gas is introduced through the gas introducing pipe 9.

The H ₂ gas is introduced until the lens barrel 1 becomes a vacuum of about 1 × 10 ⁻³ Torr. After that, a current voltage of 5 to 10 kV is applied between the emitter 2 and the extraction electrode 4 by using the ion extraction power supply 11. In this state, a discharge occurs between the emitter 2 and the extraction electrode 4, and an ion current of about 1 to 10 mA usually flows. As a result, the carbon attached to the surface of the emitter 2 becomes a hydrocarbon (C _m H _n (m, n = integer)), volatilizes from the surface of the emitter 2, and is therefore cleaned. This surface treatment is usually performed before or after the operation of LMIS.

Figure 2 shows the extraction voltage (V _EX ) -ion current (I _i ) of LMIS using a eutectic alloy of Pd-Ni-As-B [Pd: Ni: As: B = 3: 3: 2: 2]. It is a release characteristic. The extraction voltage V _EX was operated by the ion extraction current 11, and the ion current I _i was measured at the position of the sample 7. In FIG. 2, (a) shows the emission characteristics after 20 hours of operation of the ion source, and in this state, the emitter 2 is contaminated with carbon. In Figure 2
(b) shows the emission characteristics of the ion source when hydrogen discharge is applied for about 10 minutes in the state of FIG. 2 (a). Compared to (a), (b) is the ion current I _{i with} respect to the extraction voltage V _EX. It can be seen that is large and stable. FIG. 3 shows the result of composition analysis (Auger spectrum) of the tip of the emitter 2 of LMIS.
In FIG. 3, (a) shows the composition after the ion source operation for 20 hours and before the hydrogen discharge, and (b) in FIG. 3 shows the composition after the ion source operation for 20 hours and the hydrogen discharge for about 10 minutes. It is an analysis result.

As shown in FIG. 3, it is understood that the carbon adhering to the emitter surface is removed after the hydrogen discharge. By this hydrogen discharge treatment, the contamination that suppresses the flow of the liquid metal on the surface of the emitter 2 is removed, and the clean surface of the LMIS is exposed again.

The results shown in FIG. 2 and FIG. 3 are obtained in the method of removing surface contamination by physical sputtering by introducing Ar gas through the gas introducing tube 9 and discharging the LMIS portion in addition to the hydrogen discharge described above. Also has the same effect.

(Effect of the Invention) As described in detail above, by performing hydrogen discharge according to the present invention, carbon on the emitter surface becomes a carbon atom-containing compound (C _m H _n (m, n1, integer)) and volatilizes. The LMIS is cleaned, the flow of the alloy to be ionized is stable, and good ion emission characteristics can be obtained.

Also, when performing discharge using Ar gas, carbon can be removed by sputtering, and the same effect as described above can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an FIB device for explaining an embodiment of the present invention, FIG. 2 is a diagram showing extraction voltage-ion current emission characteristics of LMIS, and FIG. 3 is a composition of an emitter tip of LMIS. It is an analysis chart.

Claims (1)

[Claims] 1. A method for cleaning a liquid metal ion source having a reservoir for melting and holding a metal to be ionized, an emitter, and an extraction electrode, wherein one or both of hydrogen gas and argon gas are used for the liquid metal. After supplying to the ion source, a voltage is applied between the emitter and the extraction electrode to cause discharge, and the discharge causes carbon adhering to the surface of the emitter to be converted into hydrocarbon and volatilized, or adhered to the emitter. A method for cleaning a liquid metal ion source, which comprises removing carbon by sputtering.