JPS5889763A - Spot-like gas ion source - Google Patents

Abstract

PURPOSE:To obtain an ion beam with high intensity by setting the tip radius of curvature of a needle-like chip for ionizing the gas using the electric field ionization phenomenon within a specific range. CONSTITUTION:A spot-like gas ion source used for an ion beam microanalyzer or the like is formed by feeding decompressed gas to the tip of a needle-like chip applied with the positive high voltage to opposing electrodes so as to ionize the gas by the action of a high electric field, and in addition the tip radius of curvature R of the needle-like chip is set within a range of 0.2mum<=R<=2mum. Accordingly, the total radiated ion current varies depending on the electric field, temperature, gas pressure, and tip radius of curvature R of the needle- like chip, thereby an ion beam with high intensity can be generated by reducing the temperature of the needle-like chip and the gas to an optimum temperature, by setting the gas pressure at an optimum value, and by optimizing the tip radius of curvature R of the needle-like chip.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion beam micro-analyzer (IMA).
This article relates to a point gas ion source useful for ion beam application equipment such as.

The performance of ion beam application equipment depends largely on the capability of the ion source. A necessary condition for an ion source is to stably emit a high-intensity point-shaped ion beam for a long period of time. One means of achieving this goal is a point gas ion source that applies the electric field ionization phenomenon. This is done by applying a high positive voltage to the counter electrode and applying a 10-"foil to the tip of the nine-needle tip.
Gas is supplied at a reduced pressure to rr, and this gas is ionized by the action of a high electric field. This type of ion source.

It has begun to attract attention both domestically and internationally as a high-brightness point ion source that can be easily concealed compared to conventional duoplasmatron ion sources or liquid Kaede ion sources.

In order to emit a high-intensity gas ion beam from this ion source, it is safe to set various operating conditions in the IIk groove. Ion current (I) of this type of gas ion source
) are the electric field (F), the needle tip and the gas density (Tt
, T1) - gas pressure (P).

It depends on the radius of curvature (R) of the tip of the needle tip.

However, research into the practical use of this type of gas ion source began only after the n, m commuting operating conditions, which were extremely close to Rk, were determined. For example, when working with hydrogen gas ions, Tt
And if T5 is kept at an extremely low temperature of 4 to 20, a high-intensity Ht ion beam can be obtained < J, vac, S
ci,'l'echno1. l 6 (1979>18
75) High-intensity ion beams can be stably emitted by using iridium with (110> orientation) as a material for 6- or needle-shaped tips (J, Appl, PhYm 50(1)
979) 6026) has been reported to some extent.

In these cases, a sharp needle tip with a tip radius of curvature of 1000 Å or less is used.

The present invention specifies practical operating conditions for a single-point gas ion source, and in particular, defines the radius of curvature (R) of the needle tip, which is necessary as an ion source for ion beam application equipment such as IMA. It is something to give.

Hereinafter, the present invention will be explained in detail based on experimental results.

The total emitted ion current (I) of a point gas ion source is determined by the electric field (F), the needle tip and the gas mf (T
g, Tg) - varies depending on the gas pressure (P), the tip radius of curvature (R) of the needle tip. In order to obtain a high-intensity ion beam, these parameters (F, Tg
, T-, P, R).1 The inventors investigated the effects of these parameters through experiments.

11) Electric field (F), needle tip and gas temperature (Ti
, Tt) Figure 1 shows 10-! This figure shows the effect on F and T when ionizing Torr NC gas. In general, Tt is T−, and Tt = T.

Since the maximum ion current is obtained when T
t and T are made to be the same temperature. ion 111t
The flow (I) varies depending on T, but F = 1.8 ~ &2
It increases linearly rapidly in the V/person range and then increases slowly with increasing F. For W chip, F>6.5V/
Since electric field evaporation of the chip occurs above λ, it is necessary to operate below this electric field. As is clear from Fig. 1, it can be seen that the lower the T, the more the force tends to increase.

Figure 2 shows T and I/I for gas in each building. This shows the relationship between Engineering here. is determined by the ionic current at T=300K. The ion current tends to increase as T becomes lower, but if T is too low, the ion current decreases rapidly. This is because the gas condenses on the chip surface and becomes difficult to be supplied to the tip of the chip. This weir temperature transfer (T) is somewhat lower than the liquefaction temperature of the gas, and the difference (ΔT) is the aI of the gas.
Although it often changes, it is about ΔT=5 to 40.

In order to obtain a large ion current, it is effective to keep T just above the transition @ degree (T town. #g2 The relationship between T and I/IO shown in the figure is almost independent of the chip material and is
Similar results can be obtained using any of the materials, such as W+l*Pt and Re+Ta+Mo+C1.

(2) Gas pressure (P) FIG. 3 shows the relationship between He gas pressure (P) and ion current (I). <110. >W needle tip is used and T=20. P<P*(~2 x 104T
orr ) or below, the force increases in proportion to P, but the force reaches a maximum value at P*, and if P increases beyond this level, the force decreases and then enters the glow discharge region. Although the value varies slightly depending on the type of gas, i Hl + HCmNeIA'
1Nl l O! ＋に'eXe mCH4*BHI
5BC4+PH@ *h P” for PC4
It is approximately 10'' porr degree in the range of 8 X 10-'' to 5 X I Q-'' Torr. For the above gases.

In both cases, characteristics similar to those shown in FIG. 3 were obtained. As is clear from this figure, in order to obtain a large ion current, pt-p
It can be seen that keeping it near I is effective.

(3) Radius of curvature (R) of the needle-like tip Figure 4 shows the results of investigating the relationship between the radius of curvature (R) and the temperature under the conditions of Tt-T", and P=P". Here, l is the ion current emitted per unit solid angle instead of the total emitted ion current. It can be seen that (2) increases in proportion to the 25th or 3rd power. Figure 4 shows the maximum ion current that can be obtained in a gas ion source that utilizes the field ionization phenomenon.
or Tt-control.

In an ion source in an ion beam application device such as an IMA or an ion beam lithography device, an ion beam of 10 −IA/Sr or more is required to improve the performance of the device. As is clear from Figure 4, in order to obtain an ion current of more than 10"A/8r when I T IP is set to the optimum condition, it is necessary to achieve R>10"A or more. In actual ion beam application equipment, it is common practice to keep T and P at optimum values for a long time.
l1R for 2X10' I rarely needed to be in front of other people. The upper limit is determined by the practical insulation and edge breakdown voltage. K, which ionizes gas by electric field ionization, requires the application of a high voltage between the needle tip and the counter electrode, but due to the structure of the ion source and limitations on the materials that can be used, shear discharge and dielectric breakdown occur. To avoid this, the practical upper limit for high voltage is 100 ν. On the other hand, in order to ionize the gas, it is necessary that the electric field near the needle tip be a certain electric field (F-m) or higher.This F* changes depending on the amount of gas and the amount of gas. ,,He.

Ne, IA'#K' * Xem Ox mN2
+ CH4* BHs tBC4, PHs, PCta
For, F ~ 1 ~ 5V / AV: mark u voltage, to: constant (~5) relationship is approximately established, V < 1
00kV, F”>I V/person!!DR×2X10'
A person falls within the practical range.

In order to stably obtain an ion current of 10"" A/S r or more, it was found that it is effective to bend the tip of the 2X10"<R and 2X10'A. The range differs slightly depending on the gas type II') *
4 x 10” for Ht, A’ + N@
<R<2)G O' person, 2X10"<R for He
<4X10"A, Ne to d3X10"R x 10" people, 5X10"R x 2X10' people for Kr, Xe, Ot-CH, BHs.

For BO2-PHs and PO2, a range of 5xlo"<R and 1x104 is preferable.

As described above, in order to obtain a large ion current in a gas ion source that utilizes field ionization, the -m' of the needle tip and the gas must be lowered to an optimal 1 degree, and the gas pressure'! It is extremely effective to use a large needle-shaped tip while setting the appropriate pressure to
It was found that it was in the range of 0'A.

The needle tip material is F,? Any material may be used as long as it is electrically conductive and can withstand an electric field of IV/Å or more. Also,
The type of gas to be ionized is not limited to the gases mentioned in this specification, but in principle, there are six kinds of gases that can be ionized. This will be extremely useful in practical application of a point gas ion source using a gas ion source.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between electric field strength of a point gas ion source, gas and needle tip, and ion current, Figure 2 is a diagram showing the relationship between gas and needle tip, and ion current. Figure 3 shows the relationship between gas pressure and ion current, and Figure 4 shows the relationship between gas pressure and ion current.
The figure shows the relationship between the radius of curvature of the needle tip and the ion current. Agent Patent Attorney Toshiyuki Usuda Z Figure 0 56 100 150
300 SI, NOIE, (K) Fig. 3 Gas dead force (Tear)

Claims (1)

[Claims] In a point gas ion source that ionizes gas using the m-field ionization phenomenon, the radius of curvature R of the tip of the needle tip for ionization is in the range of 0.2 μm<R<2 μm. A point gas ion source characterized by: