JPS647457B2 - - Google Patents

Description

Detailed Description of the Invention The present invention uses a high-brightness point ion source such as a liquid metal ion source or a gas field ion source, and focuses an ion beam minutely to perform ion implantation, etching, or resist exposure. Regarding a focused ion beam device intended for the purpose of Regarding.

Conventionally, in the production of devices that require minute dimensions such as semiconductor circuits represented by VLSI and Josephson devices, a pattern is formed on a resist film on a substrate using light exposure or electron beam exposure technology, and this is used as a mask. Processes such as ion implantation, etching, and thin film deposition are performed. However, recently, it has become possible to obtain micro-diameter ion beams of 1 μm or less for various elements by using high-intensity ion sources such as those mentioned above. injection and etching,
Alternatively, as an alternative to electron beams, a process of forming patterns on a resist using ion beams has been attracting attention.

However, it is also true that new problems have arisen due to focusing on the beam. Here, we will discuss this problem by pointing out the structural features of a focused ion beam device that uses a liquid metal ion source, which has a high degree of perfection as an ion source and can extract many elements as ions.

The configuration of the apparatus varies depending on the type of ion source used and the purity of the ion species composition to be incident on the substrate required for each target process. For example, Li, Al, Ga, In, Sn, Cs, Au, Pb, Bi, etc.
Elements with low vapor pressure at their melting point can be ionized singly, and monovalent and divalent atomic ions and molecular ions are extracted in different proportions depending on the element. If the intended process does not require selection of these ion species, the apparatus can be constructed by using a suitable electrostatic lens for beam focusing.

On the other hand, if it is necessary to select these ion species, use an ion source that uses samples such as B, Be, Ge, As, Sb, etc. that cannot be ionized unless alloyed with other elements. In some cases, it is essential to have a configuration that has a mass separation function.

However, these devices are currently required to obtain a beam diameter of approximately several hundred Å to 1 μm at as high an ion current as possible. Therefore, the existence of geomagnetism and residual magnetization of the materials that make up the device, which would not have been a problem in the past, or the passage through a mass separator itself have become essential factors that hinder efficient focusing. It was. In order to get a feel for the magnitude of this problem, let's consider a concrete numerical example of the Ga ion source, which is the most commonly used liquid metal ion source.

Ga contains 40% isotopes of ⁷¹ Ga and ⁶⁹ Ga.
It is known that the composition of emitted ions is approximately 99% monovalent atomic ions and the remaining 1% divalent atomic ions and molecular ions. Therefore, with normal application techniques, an ion beam of sufficiently high purity can be obtained without special mass separation. The configuration of a focused ion beam device in such a case is shown in FIG.

The generated ions are accelerated to a desired voltage by the ground electrode 3 by a negative voltage applied from the ion source 1 to the extraction electrode 2, and are focused onto the sample 5 by the ions 4. For example, if the earth's magnetism exists in a direction perpendicular to the plane of the paper, the orbit would shift as shown by symbols 6b and 6c in accordance with the mass-to-charge ratio of the ion, compared to the orbit 6a when there is no influence of any magnetic field. , which causes an expansion w in this direction in the beam diameter. As mentioned above, in the Ga ion source, ⁶⁹ Ga ⁺ and ⁷¹ Ga ⁺ ions are the main ions, so we assume that these two ions are on the orbits 6b and 6c, and evaluate the deviation of the two on the sample.

The cyclotron radius r ₀ (cm) is the uniform magnetic field B (Gauss), the mass-to-charge ratio k, and the accelerating voltage V
(volts), it is given by the following formula (1).

r ₀ = (144/B)・√ (kV) ………(1) Then, the distance from the ion source tip to the sample is L.
(cm), the deviation S from the orbit 6a when there is no magnetic field is given by the following equation (2).

S=L ² /2r ₀ ......(2) Here, if we substitute the following values as general and reasonable values: B = 0.5 Gauss V = 50000 volts L = 15 cm, we can see that it follows trajectory 6c.
S = 2.103 μm for ⁶⁹ Ga ⁺ , ⁷¹ Ga ⁺ along orbit 6b
Then, S=2.073 μm, so the beam diameter spread w is about 300 Å. Even with this value, it is several hundred Å.
This becomes a problem when a request is made to obtain a beam diameter of .

In the Ga ion source used as an example, the intensity of divalent ions and molecular ions is weak, but in ion sources such as Sn, Pb, and Au, monovalent and divalent ions are extracted in approximately equal proportions; Orbital deviation in ion species
From the above equations (1) and (2), it becomes several thousand Å, and when it reaches this order, it becomes a problem even when obtaining a beam with a diameter of 1 μm.

On the other hand, similar problems occur when using a focused ion source with a mass separator.

FIG. 2 shows an example of the configuration of such an apparatus, and components corresponding to those in FIG. 1 are given the same reference numerals. A so-called E×B mass separator 11 having a direct electric field and a magnetic field separates the ions according to mass/charge ratio, and after passing only desired ions through an aperture 7, a sample 5 is separated by a lens 8 as shown by a trajectory 9a. focused on.

In this way, when only the trajectory 9a of ions with a certain mass/charge ratio is selected and focused by the aperture 7, the beam diameter will not expand due to the effects of geomagnetism, etc., but the efficiency of the ion current will drop considerably. It turns out. This is because in applications such as ion implantation and etching, the chemical and physical properties of isotopes can be completely ignored, and it is therefore desirable from the viewpoint of beam efficiency to focus these isotopes together if possible. However, when a mass separator is used for the purpose of selecting different ion species, such as the device shown in the second figure, the isotopic Even the ions are affected by the mass separator, causing a shift D in the focusing position at the aperture 7, which results in a beam diameter broadening w on the sample 5. Displacement D at aperture 7
is the mass-to-charge ratio for the orbit 9a, _k is that for the isotopic ion element, Lm is the length of the mass separator, L ₀ is the distance between the exit of the separator and the aperture 7, and is the cyclotron radius. When r is ₀ , it is given by the following equation (3).

D (1/2)・(｜k−k ₀ |/k ₀ )・(Lm ² /r ₀ )・[(1/2
)
+(L ₀ /Lm) ] ………(3) For example, k ₀ is ⁶⁹ Ga ⁺ and k is ⁷¹ Ga ⁺
If we take L ₀ = 5 cm, Lm = 5 cm, and r ₀ = 1000 cm, then D 4 μm, and the beam diameter will expand to the same extent as these values on the sample.

However, if only ⁶⁹ Ga ⁺ is focused, approximately 40% of ^{the 71} Ga ⁺ current will be wasted. These points become even more serious when using a Sn ion source. Sn has many isotopes from ¹¹² Sn to ¹²⁴ Sn, and the one with the largest proportion is ¹²⁰ Sn, accounting for approximately 33%. However, no matter how large the ratio is, if only this ¹²⁰ Sn is taken out, approximately 70% of the current is essentially wasted.

The present invention has been made in view of these circumstances, and provides a focused ion beam device that can efficiently focus ions to a minute diameter by correcting the spread of the beam diameter due to the influence of external magnetic fields such as earth's magnetism and residual magnetization of the device. It was created with the aim of providing

Embodiments of the present invention will be described in detail below with reference to FIG. 3 and subsequent figures.

The embodiment shown in FIG. 3 has a function of canceling the influence of external magnetism such as terrestrial magnetism, and is an improvement on the conventional example shown in FIG. 1. Corresponding components will be described with the same reference numerals as in FIG. 1, and descriptions of parts that do not require modification may be omitted.

The feature of this device is that the magnetic field generator 1 generates a magnetic field in the opposite direction to undesirable magnetic fields such as earth's magnetism.
0 is provided around the beam traveling path, and in this embodiment, it is provided below the lens 4.

According to such a configuration, the trajectory 6c of ions with a smaller mass-to-charge ratio follows the magnetic field generating section 10.
The trajectory 6b can be largely bent toward the ions, and therefore, by appropriately selecting the strength of the magnetic field, the focusing position on the sample 5 can be made to coincide with that of the trajectory 6b.

The magnitude of the required magnetic field varies depending on the ion accelerating voltage, mass-to-charge ratio, area of the magnetic field generating part, positional relationship with respect to the sample 5, etc., but approximately several tens of Gauss is sufficient, and an air-core coil or A permanent magnet or the like can be used as the magnetic field generator. Of course,
The position of the magnetic field generating section is not limited to the illustrated position, and may be such that the magnetic field acts above the lens or over the entire orbit. In other words, the correction may be made after the deviation has occurred, or the correction may be made in advance by shifting in the opposite direction in anticipation of the deviation, or a combination of both may be used.

In addition, if the direction of the magnetic field is unknown, the fifth
As shown in the figure, a total of four air-core coils 12a, 12b, 13a, 13b, each pair, are arranged in a plane Y that is substantially orthogonal to the traveling direction X of the ion beam, so that they are generally orthogonal to each other. By appropriately selecting the magnetic force generated by each pair of coils by adjusting the applied current, it is possible to generate a magnetic field in any direction. Therefore, the current value applied to these coil pairs should be adjusted so that the spread of the beam diameter is minimized. It would be a good idea to adjust. Incidentally, this situation is schematically shown in Fig. 5, where the direction and magnitude of the magnetic force due to the first coil pair seem to be indicated by the first vector f12, and the magnetic force due to the second coil pair is indicated by the first vector f12. Assuming that the second vector f13 is as shown, the direction and magnitude of the composite magnetic force applied to the beam traveling direction will be as shown by the vector.

Conventionally, in the field of electron microscopy, the method to negate the effects of geomagnetism has been to surround the entire device with magnetic shielding material, but this method is very large-scale and expensive, and also requires the use of materials that make up the device. The residual magnetization cannot be canceled. In contrast, the present invention has the great advantage of being able to cancel out the effects of such undesirable magnetic fields with a very simple and inexpensive device.

Next, an embodiment of the apparatus of the present invention for solving the problems caused by the intervention of the mass separator having the apparatus shown in the second figure will be described with reference to FIG.

As in the first embodiment, corresponding components will be described with the same reference numerals, but here, the mass separator 1
Magnetic field generating unit 10 in the opposite direction to the direction of the magnetic field in 1
is added between the aperture 7 and the lens 8, and by controlling the strength of the magnetic field generated by this, the sample 5
At the top, it is designed to focus all isotopic elements to one point. Of course, in this embodiment as well, the position of the magnetic field generating section is not limited to the illustrated position as in the previous embodiment, and may be taken into consideration in the same manner as in the previous embodiment, or as shown in the fifth figure. Any configuration may be adopted. Moreover, the strength of the magnetic field is also sufficient if it is on the order of several tens of Gauss.

In any case, as detailed above, according to the present invention, beam blurring can be kept to a minimum even in devices that must focus the beam to 1 μm or less, which is particularly in demand these days. At the same time, it is possible to obtain the remarkable effect of increasing the efficiency of ion utilization.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional ion beam device, FIG. 2 is a schematic diagram of a conventional ion beam device with a mass separator, and FIGS. 3 and 4 are:
FIG. 5, which is a schematic configuration diagram of a focused ion beam device as an embodiment of the present invention, is a magnetic field generating device used to carry out the present invention. In the figure, 1 is an ion source, 4 is a lens, 5 is a sample,
7 is an aperture, 10 is a correction magnetic field generator, 11 is a mass separator, 12a, b, 13a, b are each a pair of magnetic field generating coils, X is an ion beam traveling direction perpendicular to the plane of the paper, and Y is perpendicular to this. f ₁₂ and f ₁₃ are vectors of magnetic force generated by the coils 12 and 13, and f _T is a vector of these combined magnetic forces.

Claims (1)

[Claims] 1. In a focused ion beam device that focuses an ion beam extracted from an ion source onto a sample, different ions due to differences in mass/charge ratio are arranged in a plane substantially orthogonal to the traveling direction of the ion beam. A focused ion beam device, comprising: a correction magnetic field generating unit that corrects the beam trajectory and focuses the ion beams on the different trajectories together at one point on the sample.