JP3048907B2 - High intensity point ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to focused ion beam (FIB) technology, and more particularly to molten salt,
The present invention relates to a novel high-brightness point ion source using a liquid ionic compound containing a mixture of an acid or a base. This new high-brightness point ion source is a conventional liquid metal ion source (LMI).
The desirable high brightness, ionic strength and energy distribution characteristics of S) relate to the possibility of significantly expanding the spectrum of ionic species. In particular, chemically reactive ions, including cations and anions, molecular ions, and even protons that were not possible with the conventional LMIS sources described above, can now be generated. According to the present invention, any conventional focused ion beam system can be easily adapted to use this novel high intensity point ion source.

[0002]

BACKGROUND OF THE INVENTION To date, almost all industrial point ion source applications are based on liquid metal ion sources (LMIS), which are focused ion beams (FIBs) during the period 1970-1980. Brought remarkable development of technology. The LMIS source exhibits very good optical quality (brightness and low energy dispersion) as compared to all other types of ion sources, and thus is well suited for industrial applications incorporating this LMIS source in a FIB system It has become possible to focus a submicron-sized ionic spot at a high current density of about several A / cm ² . In particular, FIB systems are a field of microelectronics, an advanced semiconductor product, typically an integrated circuit (IC).
It is widely used for modification, reconstitution, damage analysis and production, and its surface analysis. However, if the LMIS source is F
If it were to be the historical origin of IB technology development, it would have its own physical constraints, which would significantly limit the potential applications of the FIB system and the scientific instruments derived therefrom. When using an LMIS source, the ionizable source materials that can be used to generate ions are limited to some pure metals and some metal alloys. The most commonly used metal is gallium in terms of reliability and optical quality. Despite several benefits, the use of LMIS sources in standard FIB systems has some significant limitations and disadvantages, as described below.

First of all, unlike the conventional reactive ion etching process, for example, there is no chemical reaction effect accompanying the collision process of sputtering (ion bombardment). For this reason, the removal rate of the most commonly used target materials is limited to 1-4 sputter atoms per incident ion at an energy of about 30 kV. Because no by-product gas is formed, the sputter atoms do not evaporate during this process, and the sputter material re-adheres near the attacked area. This undesirable redeposition complicates many FIB-based etching processes. In particular,
If the redepositing material is conductive, it may form a parasitic connection on the semiconductor product. Moreover, the re-deposition of the sputtered material reduces the achievable sidewall angle,
As a result, the aspect ratio of the etch hole is at most about 6: 1.
Will be inadequate. Therefore, etching deep trenches requires a lengthy process, which can cause undesirable damage to the area near the hole.

[0004] Another effect of this lack of chemical reactivity is found in an analytical technique now called SIMS (SIMS is an acronym for Secondary Ion Mass Spectrometry). This technique is based on the use of gallium probes and has been recognized for high local resolution (a key requirement for focused ion beam applications). That is, the SIMS system can achieve a local resolution of tens of nanometers. However, one of the conditions for quantitative SIMS analysis is that secondary ion emission efficiency is high. Since gallium does not have a large secondary ion yield stimulating effect and has a high local resolution, the advantage of the small size of the gallium probe is offset by a low emission rate of the secondary ions to be analyzed. Conversely, commercially available SIMS systems using other ions that combine the chemistry with the impact of sputtering to increase secondary ion yield, unfortunately, have poor local resolution. Specifically, cesium (Cs), one of the most chemically reactive metals, significantly increases secondary ion yield. Industrial SIMS systems use conventional Cs sources (generally of the surface ionization type), but these ion sources have low brightness and are incomparable to Ga LMIS sources. Moreover, cesium reacts violently and is very difficult to handle. Many attempts have been made in the laboratory to produce Cs LMIS sources, but due to the high chemical reactivity of cesium, Cs LMIS sources have been found to have the acceptable reliability required for SIMS systems used in industry. Have not achieved the level.

[0005] Finally, in applications such as the fabrication of quantum devices, it is difficult to reduce the creation of ion beam induced defects simply by reducing the ion beam energy. This is because this operation involves a very large loss of current density, significantly increases the machining time and ultimately increases costs.

One attempt to solve the problem of the high chemical reactivity of alkali metals is disclosed in E. FIG. Bell et al., "Lithium ion emission from a liqu
id metal source of LiNO ₃ '', the International Jour
nal of Mass Spectrometry and Ion Processes, 88 (198
9), pp. 59-68. The authors are LMIS
The experiment was performed using an ion source similar to the source, and a compound containing an alkali metal was used instead of the alkali metal. Specifically, a pure molten binary salt, in this case lithium nitrate (L
Li ⁺ ions were generated at the source using iNO ₃ ). In this experiment, using a needle coated with the heated molten salt as the standard, called the ion source and "LiNO ₃ liquid metal ion source." That is, this is a modification of the LMIS source.
The authors observed the formation of bubbles and a very rapid evaporation of this molten salt. The energy distribution of the emitted ions is measured by a reverse voltage analyzer, and the FW of 110 eV consisting of two peaks is obtained.
HM (half width) energy dispersion was observed. The authors concluded that this was due to gas-phase field ionization in addition to the field desorption at the tip of the needle. Ion sources with such a large distribution of energy distribution are not suitable for use in industrial FIB systems. This is because the focusing of the ion beam is approximately limited by chromatic aberration.

On the other hand, proton microscopy techniques, ion beam lithography (no proximity effect on small structures, very high resist sensitivity to ions), localized Rutherford backscattering analysis (RBS), very high spatial resolution In some advanced microanalytical fields, such as high particle beam excitation X-ray spectroscopy (PIXE), conventional LM
The generation of protons (the lightest ions known) is not possible with the FIB system using an IS source. In fact, no matter how many attempts have been made to achieve a focused proton beam column, that effort has never led to successful industrial applications. Often the field ionization source was used in the gas phase. In this particular example, the ion source generally comprises a tungsten needle, which is cooled with liquid helium to a temperature of a few Kelvin. Field ionization generates a flux of hydrogen atoms at the tip of the needle. These sources have high theoretical brightness, but may require sophisticated and expensive equipment. Moreover, the reliability is very low and the total ion current is small.

Therefore, if a new high-brightness point ion source of the improved FIB system can be realized, in particular, an integrated circuit (I
It will be very interesting for C) SIMS analysis and also for many other applications. Such an ion source maintains the quality of a conventional LMIS source in terms of pinpoint emission characteristics and current density (brightness), and provides a wider range of ion species, including but not limited to alkali metals and halogens. Must be provided.
Finally, working in conjunction with ionizable source material selected from among the liquid ionic compounds, their existing can utilize the presence of ions in, Cs ⁺ ions and Cl ^- ions and chemical reactivity It would also be worthwhile to realize such a novel high intensity point ion source that could avoid the use of very high and dangerous ion species. The present invention satisfies all these requirements, and thus the conventional L
SUMMARY OF THE INVENTION An object is to provide a high intensity point ion source adapted to work with a liquid ionic compound which offers significant improvements and benefits compared to a MIS source.

[0009]

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide a novel high-brightness point ion source using a liquid ionic compound comprising a mixture, for example, a mixture of a molten salt, acid or base. .

Another primary object of the present invention is to provide a novel high intensity point ion source using a liquid ionic compound, wherein the discharge needle is made of a refractory ceramic material and can be heated directly or indirectly. Is to do.

Another object of the present invention is to provide a novel high-brightness point ion source using a liquid ionic compound comprising a mixture of a molten salt, acid or base having a low vapor pressure and a low melting point.

It is another object of the present invention to provide a novel high intensity point ion source adapted to use liquid ionic compounds while retaining the desired high intensity, pinpoint emission and low energy dispersion of a standard LMIS source. Is to provide.

Another object of the present invention is to provide a novel high-brightness point ion source using a liquid ionic compound, which is adapted to generate a wide range of highly reactive ionic species including alkali metals and halogens. It is in.

Another object of the present invention is to provide a novel high-brightness point ion source using a liquid ionic compound having ions already present in order to obtain a strong emission of cations and anions.

Another object of the present invention is to provide a novel high brightness point ion source using a liquid ionic compound adapted to generate protons.

Another object of the present invention is to provide such a novel high-brightness point ion source using a liquid ionic compound.
An object of the present invention is to provide a method for generating ions in a FIB column.

Another object of the present invention is to provide such a new high-brightness point ion source using a liquid ionic compound for generating a beam of a new ion species having a high local resolution and a spot size on the order of submicrons. Tailored, improved FI
B system.

[0018]

SUMMARY OF THE INVENTION In accordance with the present invention, a novel high brightness adapted to operate with a wide range of ionizable source materials, ie, liquid ionic compounds (hereinafter liquid ionic compounds). The point ion source is described for the first time. Usually, the liquid ionic compound is a molten salt,
Includes (eutectic or non-eutectic) mixtures of bases or acids. Generally, unlike a base or an acid that is liquid at room temperature, a salt mixture needs to be heated to its melting point in order to be liquid. A wide range of cations and anions of highly chemically reactive ionic species (eg, halogens, alkali metal radicals, etc.) and even protons become available. Since these ions are already present in the liquid ionic compound, a low extraction voltage (2.5-3.5) is required to initiate the ion release function.
kV).

The typical novel high intensity point ion source of the present invention basically consists of two parts, a needle assembly and an extraction assembly. The needle assembly consists of a pointed needle made of refractory ceramic material, the pointed tip of which is referred to as a tip. The needle is heated by a stainless steel coil tightly wound on the portion of the needle close to this tip. The other end of the needle is housed in a recess in an insulating support into which two pins are cast. Both ends of the coil are welded to the pins, respectively, and the pins are connected to a heating current source. The extraction assembly consists of a circular extraction electrode, which has a central opening, which is screwed into a cylindrical body so that the distance between the tip apex and the center of the opening can be adjusted. The extraction electrode and the cylindrical body are both made of metal. The needle assembly is mounted inside the cylindrical body and is precisely secured with a centering screw. An extraction voltage source applies a potential difference between the extraction assembly and the coil. Needle assembly, before use
For example, it is immersed in a crucible containing a liquid ionic compound and coated with the liquid ionic compound. The entire surface of the needle is wetted with the liquid ionic compound and a reservoir is formed at the coil location. The needle assembly is then inserted into the extraction assembly and secured properly. The high-brightness point ion source is now F
Ready to use in IB column.

The present invention further includes a focused ion beam column that has been modified to accommodate the new high intensity point ion source. In particular, the improved focused ion beam column of the present invention operates on some or all of the electrical components (supply voltage, electron lens, deflection electrodes, etc.) of the FIB system to work with both positive and negative ion beams. Such)
With a system adapted to give reversible polarity to the

Thus, the novel high-brightness point ion source of the present invention not only maintains most of the advantages of the conventional LMIS source, especially not only maintaining the same brightness, but also significantly improving it, and is therefore now known. It can be used advantageously in almost all industrial FIB applications.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of a novel high-brightness point ion source by direct heating of a liquid ionic compound according to the present invention.
It is a schematic diagram showing an embodiment. Referring to FIG. 1, an ion source 10 is basically comprised of two basic parts, a needle assembly 11 and an extraction assembly 12, which is necessary for ion emission and preferably comprises a housing for the needle assembly 11. Forming, including extraction means. In this embodiment, the needle assembly 11 is
And heating coil 14 and base 1 in plate or cup shape
5 and both ends of the coil 14 are referred to by 14a and 14b, respectively. Usually, the heating coil 14 is made of stainless steel or platinum. As is clear from FIG.
One end of 3 is pointed and forms a needle tip 13a. The needles 13 are preferably made of a refractory inert material such as alumina (Al ₂ O ₃ ) or ceramic containing zirconium oxide (ZrO ₂ ). The main reason for choosing a ceramic material instead of a metal is to avoid bubble formation, chemical / electrolytic corrosion or electroadhesion of electrolytic by-products formed on the needle 13 during normal operation of the ion source 10. . As a result, the undesirable instability of the emission region position (near the tip apex 13a 'where critical ionization phenomena occur) that occurs in that case is eliminated. Further in this preferred embodiment, the support base 15 is made of an insulating material (eg, alumina) and has a central aperture adapted to receive a hollow member 16 having a recess as shown in FIG. The needle 13 is housed in this cavity. The support base 15 further comprises two conductive pins 17a and 17b partially cast therein.
Is provided. Each end of the heating coil 14 (14a, 14b)
Are welded to the top of the respective pins (17a, 17b) to provide good electrical contact therebetween. on the other hand,
The proximal ends of the pins 17a, 17b are each connected to a corresponding terminal of a (DC or AC) heating current source 18. Current source 18 generates an appropriate current in heating coil 14 to raise needle 13 to a sufficient temperature if necessary. To avoid thermal shock, the current source 18 is adapted to generate a variable current and thus gradually raise the needle 13 to said sufficient temperature. Instead of using a heating coil as described above, other techniques for heating the needle, such as electronic bombardment, photon heating, in-tip heating, etc., are also conceivable. Finally, again in this embodiment, the extraction assembly 12 includes a cylindrical body 19 made of stainless steel and a cup-shaped extraction electrode 20 made of tantalum and having a central aperture 20a. The extraction electrode 20 is generally circular and is tightly fixed on the cylindrical body by, for example, screws to provide its cover. For this purpose, as shown in FIG.
The outer surface of the top of the rim and the inner surface of the rim of the extraction electrode 20 are threaded at location 21. Therefore, tip vertex 13a '
The gap between the electrode and the center of the opening 20a of the extraction electrode can be accurately adjusted. The diameter of this opening is about 1 mm, and the distance from the tip apex to the edge of the opening 20a is about 0.5 mm. Extraction assembly 12 includes a set of screws 22a and 22b.
Alternatively, it is secured to the support base 15 by any other suitable means and provides a housing for the needle assembly 11. Screws 22a and 22b
The needle assembly 11, especially the tip apex 13
Perfect centering of the extraction electrode 20 of a ′ with respect to the center of the opening 20a is enabled. In operation, the cylindrical body 19
Is connected to a first terminal of the extraction voltage source 23, and its second terminal is connected to the base of any of the aforementioned conductive pins, for example, the pin 17a. The voltage source 23 is adapted to apply a variable extraction voltage V, so that the ion emission can be varied. Optionally, an anti-adhesion shield 24 is mounted inside the housing to extend the life of the ion source 10 and to enable the extraction electrode 20
Can be prevented from being contaminated near the opening 20a.

The manufacture of the novel high-intensity ion source 10 will be described one after another. First, the needle 13 is manufactured. In a preferred embodiment, the starting material is 0.5 mm in diameter
(Al23) rod, for example, supplied by DEGUSSA of France. A piece of about 1 cm is cut out with a diamond saw and one end thereof is pointed to a length of about 1 mm using a diamond polishing plate, for example. In order to avoid instability of the emission point, it is preferable that the half angle of the tip apex is about 60 ° or less. The radius of curvature of the tip 13a is preferably 100 μm or less, and a typical value is 10 μm. This value of the radius of curvature is not considered to be a critical parameter in the present invention. Experiments conducted by the inventors have shown that half angles of 20 ° and 49.3 ° (exact values of Taylor's cone) are appropriate. Next, a standard diameter of 0.
The heating coil 14 is made from a 3 mm stainless steel wire. For example, commercially available stainless steel with part number 304L from WEBER metaux, France is suitable. Wrap this wire tightly around needle 13 or
Into the coil 14 to form the needle assembly 11 shown in FIG. Next, the needle assembly 11 is connected to the hollow member 16.
And fix it firmly there. Each end (14a, 14b) of the heating coil 14 is connected to the insulating support 15
To the corresponding pins (17a, 17b). The pins 17a and 17b are then electrically connected to the heating current source 18 to enable the ion source 10. The needle assembly 11 is now ready to coat the needle, especially its tip, with a thin film of a suitable ionizable source material.

According to the invention, such an ionizable source material comprises a liquid ionic compound, more particularly a salt,
It consists of a mixture, such as a mixture of bases or acids. For salts, (eutectic or non-eutectic) mixtures of salts have lower melting points and vapor pressures than pure binary salts. Pure binary ionic compounds generally have a high vapor pressure, and thus certainly have some serious problems, such as rapid evaporation of the source material, instability of ion emission, A.I. E. FIG. As Bell reports in the aforementioned reference, it will cause a large dispersion of the energy distribution caused by field ionization in the vapor phase.

First, as an example, a mixture of salts such as C
Consider the case of a mixture of sNO ₃ and CsCl. Pure binary salts are generally obtained in powder or particulate form. First, both salts are mixed in a crucible at an optimum ratio, that is, a ratio close to the eutectic composition. The eutectic composition can be obtained from the table, if not, is determined by experiment. In the example above, this optimal ratio is about 82% and 18%, respectively, as determined by the inventors by some experiments.
Raise the temperature of the crucible to the melting point of the mixture. Note that although acids and bases are often liquid at room temperature, salts generally need to be heated to their melting point to be liquid. A homogeneous mixture of the molten salt forms spontaneously in the crucible, so that stirring of the bath is not required. In a preferred embodiment, the needle 13 is filled with the ionic compound before placing the ion source 10 in a FIB column. Thus, the needle assembly 11 is connected to a heating current source 18 and the needle is gradually heated until the melting point of the mixture is reached to avoid thermal shock. It is desirable that a thermodynamic equilibrium be established between the needle and the molten salt mixture. The needle assembly is then immersed in a crucible to bring the entire exposed needle surface into contact with the molten salt mixture. As soon as the needles come into contact with the molten salt mixture, the adherent area force creates a coating layer 25 of the mixture, which flows along the needles, covers its entire surface and remains on the surface even if the needle assembly 11 is turned upside down. As is evident from FIG. 1, the coating 25 of the molten salt mixture which wets the needles consists of two parts. The first part forms a reservoir 25a at the location of the heating coil 14, and the second part consists of a thin film 25b covering the remaining surface of the needle, especially the tip 13a. Ceramic materials, especially those cited above, have excellent wettability. Alternatively, in another embodiment, the unheated needle is immersed in a crucible and covered with said thin layer 25,
As soon as the needle is removed, it solidifies. When using an acid or a base, the same means is usually applied except that heating is unnecessary. Heating coil 14 forming storage tank 25a
Is about several mm ³ . Next, the needle assembly 11 is removed from the crucible and cooled. If the liquid ionic compound is a mixture of salts as described above, after solidification of the salt, the coating layer 25 remains in place in a crystalline state. All of the above immersion, removal, and cooling steps can be performed at normal pressure, unlike LMIS sources that require high vacuum filling operations. Next, the extraction assembly 12 is prepared. The cylindrical body 19 is made of a stainless steel cylinder and has, for example, on a side wall thereof, an appropriate pump hole for sufficiently evacuating the internal space of the point ion source 10. The extraction electrode 20 is preferably made of tantalum, and when secured on the cylindrical body 19 so as to be screwed together as described above, forms a protective housing for the needle assembly 11. Finally, the needle assembly 11 is removed from the extraction assembly 12
And then secured therein with screws 22a, 22b. These screws make the tip apex 13a '
It is also used to perfectly center with the center of the Finally, the gap between the extraction electrode 20 and the tip 13a 'is precisely adjusted. The ion source 10 is now ready to be used in a vacuum column, such as a FIB column, once the source material has been filled (probably heated if the ionic compound is solid at room temperature).

FIG. 2 shows another embodiment of the ion source 10. This is preferred in the case of highly ionizable source materials that are highly reactive, as they prevent harmful effects between the metal forming the heating coil 14 and the liquid ionic compound. For this purpose, an intermediate mandrel is used which is made of a material which is electrically and thermally conductive, but which does not wet the liquid ionic compound very well. Graphite is satisfactory in all these respects. This mandrel is shown in FIG. The fabrication of the embodiment of FIG. 2 follows directly from the structure described above with reference to FIG.

Since the high intensity point ion source 10 of the present invention uses a liquid ionic compound, preferably a mixture of molten salts, bases or acids, the acronym LICI will be used below.
It will be referred to by S. This is Liquid Me
tal Ion Sources (liquid metal ion source)
Like the term LMIS, which stands for Liquid Io
nic Compound Ion Sources
(Liquid ionic compound ion source). For example, for an alkali metal ion source, the following two mixtures of ionic compounds have been used successfully. CsNO ₃ (82%)
And a mixture of CsCl (18%) and NaNO ₃ (70
%) And NaCl (30%) were converted to Cs ⁺
It has been found to be suitable for the production of / Cl ^- ions and Na ⁺ / Cl ^- ions, i.e., highly chemically reactive alkali metal ions and halogens. H ₃ PO ₄ (80%) and H
A mixture of ₂ SO ₄ (20%) is an excellent source of proton H ⁺ . The nature and polarity of the extracted ions depends on the polarity of the extraction voltage V applied from the voltage source 23, as described in more detail below.

The thermionic emission mechanism of the LICIS source is relatively simple. This is because an ionic compound that already contains existing ions is used, so that a separate ionization process is not required. As a result, a low extraction voltage (2.5 to 3.5 kV) and emission of cations and anions became possible. In addition, alkali metals and halogens,
Further, a wide range of highly reactive ion sources including protons can be obtained. Further, a LICIS source using these mixtures is easy to handle under vacuum or normal pressure. Moreover, its lifetime is of acceptable length. All of these advantages of this novel high intensity point ion source of the present invention are very important in many industrial FIB applications.

Now, consider a LICIS source 10 in a normal operating state, placed in a vacuum column of a normal FIB system and properly fixed therein. The LICIS source 10
The FIB column can be designed to be directly included in the FIB column, or may be slightly modified to fit snugly. The FIB column is composed of a plurality of electrostatic lenses, a mass filter (for example, a Wien filter) and the like as standard. Further, it is assumed that the liquid ionic compound is a mixture of salts as described above for the sake of consistency. First, after fabrication of the LICIS source 10 using the embodiment of FIG.
1 is connected to a heating current source 18 and the needle 13 is heated to the melting point of the salt mixture until the solidified salt coating 25 remaining on the needle 13 becomes liquid. Unlike mixtures of bases and acids, which are generally liquid at room temperature, salt mixtures generally take a crystalline phase on the surface of the needle 13 after cooling, as described above. An extraction voltage V is applied by a voltage source 23 between the extraction assembly 12 and the molten salt mixture. Since the cylindrical body 19 and the extraction electrode 20 constituting the extraction assembly 12 are made of metal, the first
Potential (V1). On the other hand, recall that the salt or salt mixture is conductive in the molten state. Therefore,
Coating layer 25 and coil 14 form a counter electrode (relative to extraction electrode 20), which is at the second electrode (V2). The value of the extraction voltage V (V = V1-V2) is gradually increased as usual. As soon as the threshold voltage value Vt is reached, ion beam emission appears and the ion beam is extracted as shown by the solid angle 27 in FIGS. The extraction voltage V is several k
V, about 2.5 to 3.5 kV, and LM under the same operating conditions.
Much lower than for the IS source (5-8 kV). When the salt mixture is brought to a positive potential with respect to the extraction electrode 20, the tip apex 13 covered with said thin film of liquid ionic compound
Under the influence of the strong electrostatic field created by the extraction voltage at a ', a beam of positive ions is extracted. The liquid cone that forms (similar to Taylor's cone in every respect) produces a pinpoint emission. This point emission, combined with the very high delivery function inside the liquid ionic compound, results in the best Ga L
It directly provides a high-brightness pinpoint source of the present invention, comparable to a MIS source (up to about 10 ⁶ A / cm ² / sr, energy dispersion less than 5 eV). In addition, the use of the needle 13 made of ceramic material avoids the electrochemical reactions that normally occur between the tip and the ionizable source material. On the other hand, release instability due to the formation of undesirable electrochemical by-products is also eliminated. Finally, LICIS sources are stable, extremely reliable and have a long life.

[0030] More generally, the ion compound in the mixture formula A ⁺ -B ^- and those represented by. In the case of salts such as NaCl, A represents an alkali metal and B represents a halogen, but it has been found that a large portion of the cation beam is composed of metallic Na ⁺ ions. On the other hand, in the case of an acid such as H ₂ SO ₄ , a beam of protons H ⁺ can be formed. Here, when the polarity of the extraction current source 23 is inverted,
Instead, anions are generated. For example, NaCl or C
When salts such as sNO ₃ are used, the respective cations Cl ⁻
Or molecular ions NO ₃ ^- is capable of generating.

As a result, even if there are any similarities between the structure of the novel LICIS source of the present invention and the conventional LMIS source, substantial differences remain. In either case, in operation, the needle is again covered with a thin film of liquid ionizable source material, which is subjected to a high electrostatic field at the tip apex immediately in front of the extraction electrode. But normal LMI
Unlike the S source, the LICIS source uses a liquid ionic compound instead of a liquid metal as the ionizable source material. Therefore, the mechanism of ion emission is very different, as will be explained.

Ion emission occurs in a thin film region covering the tip apex 13a '. Under the influence of the electrostatic field, the formation of small conical protrusions or tips, previously observed and reported by Taylor, resembling well-known cones in conventional LMIS sources was observed. This protrusion is the result of a balance between electrostatic force and surface tension. The presence of this protrusion guarantees pinpoint ion emission, thus providing a LICIS source with very desirable brightness. CsN
Still referring to the above example using an O ₃ / CsCl mixture, brightness as high as 10 ⁶ A / cm ² / sr was obtained, quite comparable to the best value obtained with a conventional Ga LMIS source. This is due to the high supply function of the liquid ionic compound.

This interpretation, made according to Taylor's model, is confirmed by the presence of the threshold electric field associated with the threshold voltage Vt described above. Ion emission starts at a current of about 1 μA or less. The threshold of the extraction voltage is determined by the LICIS source 10 of the present invention.
Is about 2.5 to 3.5 kV, and the same value can be obtained for both the positive ion beam and the negative ion beam. This confirms the assumption of a conical structure comparable to Taylor's cone. This is because the electrostatic energy proportional to the square of the electrostatic field generated between the extraction electrode 20 and the thin film 25b at the tip apex 13a 'does not depend on its polarity.

The ability to release anions is another important feature of the LICIS source 10 that uses liquid ionic compounds, a result that has not been achieved with an LMIS source. Reversing the polarity of the LMIS source initiates an uncontrollable strong field emission immediately after the formation of the Taylor cone. This is because the electrostatic field required to cause electron emission is an order of magnitude lower than the critical electrolysis required to extract anions from the liquid metal. As a result, the undesirable "explosive"
Electron emission starts, masking anion emission. In contrast, in the LICIS source, only ion emission occurs due to the reaction of the liquid ionic compound with the electrostatic field. This is because there is no electron gas and therefore no possibility of electron field emission. Above the threshold voltage, LICIS responds to its bias resistance with positive ion
Generates a beam or negative ion beam emission.

The mechanism of cation or anion extraction in the LICIS source is probably that the existing ion species evaporate at the top of the protrusion in a strong electrostatic field.
Despite some similarities to LMIS release, LICI
The emission mechanism of the S source is very different from the metal field emission that occurs with LMIS emission. This is because ions already exist in the liquid ionic compound before the influence of external static electricity.

Next, various characteristics of the LICIS source and the conventional L
An example of its advantages over a MIS source will be illustrated.

First, an anion, in this case, LI of the present invention
A secondary electron image of a 6 μm-wide copper lattice sample formed on an aluminum substrate was observed when scanning with a focused beam of Cl ⁻ ions generated by a CIS source. Submicron details were clearly observed. Since the LMIS source cannot generate anions, especially such Cl ^- ions,
It should be noted that similar images have never been obtained with an LMIS source.

Next, a second order of the same sample obtained with a low energy beam of 5 kV, which is significantly lower than the lower limit of energy normally required to obtain the same resolution with a conventional LMIS source with Cs ⁺ ions, The electronic image was observed. These images observed showed spatial resolution comparable to that obtained with a GaLMIS source.

In summary, the brightness of the LICIS source is at least equal to or better (at low energies) than the best Ga LMIS source, and interestingly, a wide range of new ion species such as alkali metals, halogens, protons, etc. Could be supplied.

The new LICIS source of the present invention is ion-
It can be further adapted to fit most of all the uses of a conventional LMIS source in a focused ion beam with physical interaction between the probe and the sample. For example, local ion beam micro-milling of a solid target that may be of value in applications such as IC repair, IC failure analysis, micro-fuse blowout reconstruction, etc. may be cited. Auger analysis, high resolution SEM and T
Samples for EM can be prepared by beveling, cross-section or by milling thin foils. Another use is
The field of scanning ion microscopy technology that visualizes a sample by detecting secondary electrons or secondary ions emitted by the bombardment of a scanned focused ion beam. Another application is for sputtered species (eg, S
Local target analysis by identification (in IMS technology); local modification of semiconductor electrical properties by ion implantation;
Found in local modifications of chemical bonds (ion beam lithography, polymer and semiconductor doping).
Thus, the LICIS source of the present invention is opening up a new field of possible applications for FIB systems.

First, consider the case of a liquid ion source that produces chemically reactive ions. Regarding halogen ions,
User of FIB systems with Ga LMIS sources often reactive halogen-based gas (Cl ₂ or X
eF _2, etc.) to obtain the chemical effect associated with the collision process of sputtering (gas enhanced etching).
The LICIS source uses these reactive elements directly as incident ions, thereby avoiding the use of highly reactive gases, which are known to be dangerous and corrosive. The use of highly reactive species, such as halogen ions, has several benefits. First of all, the removal rate of most target materials is significantly increased, reducing machining time and increasing throughput. Second, the halogen ions react chemically with the sputtered material, often forming gaseous by-products, which are removed by the pump system. Thus, the use of a LICIS source reduces sputter material redeposition near the attacked area. Finally, some halogens have high selectivity (eg, fluorine compounds etch insulators at a faster rate than metals such as aluminum), and
The operation window can be opened on the buried structure of C without damaging a part thereof. Considering the case of alkali metal ions, cesium, one of the most chemically reactive metals, significantly increases the yield of secondary ions. This is because LICI in SIMS analysis
Very important for various uses of the S source. To obtain a good quantized SIMS analysis result, it is necessary to obtain a primary ion species that gives a high ion beam current and a high secondary ion yield. On the other hand, especially in microelectronics, achieving a high spatial resolution on the sample to be analyzed is very important. This requires a well focused primary ion beam. The use of a LICIS source in a FIB column gives all of these qualities, i.e., cesium ions and high ion beam currents in submicron probes (up to 25 nm).

Turning now to the specific case of protons, it should be noted that the LICIS source of the present invention provides a high intensity proton source that opens up a wide range of possible applications. For example, proton microscopy ion beam lithography (no proximity effect on small structures, very high sensitivity of the resist to ions), localized Rutherford back, previously not possible with conventional techniques There is the field of scattering analysis (RBS), very high spatial resolution particle beam excited x-ray spectroscopy (PIXE).

Finally, for many applications, it is desirable to work with a low energy beam, for example, to reduce ion beam induced defect creation during TEM sample preparation. The LICIS source is about 1/1 of the conventional LMIS source.
It operates with an extraction voltage of 2. This makes it possible to work with beam energies from 2.5 to 3.5 kV without delaying the beam (the beam delay is a very large loss of current density and the subsequent machining time Will increase).

In summary, the following matters are disclosed regarding the configuration of the present invention.

(1) A high intensity point ion source (10) adapted to operate with a liquid ionic compound, comprising: a) a pointed end called a tip (13a);
An ion emitting means (11) including a needle (13) made of a refractory ceramic material adapted to be wetted by said liquid ionic compound, and means (15) for supporting the needle; and b) a conductive material comprising holes (20a). Extraction electrode (2
0), and the apex of the extraction electrode and the tip (13
a high intensity point ion source comprising ion extraction means (12), including means for maintaining the exact relationship of a '). (2) said ion emitting means is further coupled to a needle;
The high-brightness point ion source according to the above (1), further comprising heating means (14) for heating the needle to a temperature at or just above the melting point of the ionic compound. (3) The high-intensity point ion source according to (2), wherein the heating means comprises a heating coil tightly wound around the needle at a position adjacent to the tip of the needle. (4) The heating means collects a small amount of the liquid ionic compound to form a storage tank (25a) for the ionic compound, from which the ionic compound flows to form a thin film (2).
The high-brightness point ion source according to the above (3), characterized in that it can be wetted in 5b). (5) In order to prevent a chemical reaction between the material forming the coil and the liquid ionic compound, a mandrel (26) made of a heat conductive and electrically conductive material that is not easily wetted by the liquid ionic compound is used to form the coil and the needle. The high-brightness point ion source according to the above (3) or (4), which is arranged in the middle. (6) The high-brightness point ion source according to (5), wherein the mandrel is made of graphite. (7) said needle support means substantially comprising: (i) a hollow member (16) having a recess for securing a needle therein;
(3) The above (3), characterized in that it comprises an insulating support cast therein and having two pins (17a, 17b) at both ends adjacent to respective ends of the heating coil. A high-brightness point ion source according to any one of (6) to (6). (8) The above (1) to (7), wherein the extraction electrode has a generally circular shape and is fixed to a cylindrical metal body (19) to form a housing of the ion emitting means. The high brightness point ion source according to any one of the above. (9) The height according to (8), wherein the ion emitting means is mounted inside the cylindrical metal body and is tightly fixed therein by adjustable centering means (22). Bright point ion source. (10) The extraction electrode and the cylindrical body are provided with adjustable means (21) so that the distance between the center of the hole of the extraction electrode and the tip apex of the ion emitting means can be accurately adjusted. The high-intensity point ion source according to the above (8) or (9), characterized in that: (11) The refractory ceramic material is alumina (Al ₂
(1) to (10), which are selected from the group consisting of O ₃ ) and zirconium oxide (ZrO ₂ ).
The high brightness point ion source according to any one of the above. (12) The high-brightness point ion source according to any one of (1) to (11), further including an adhesion prevention shield (24). (13) The high-brightness point ion source according to any one of (1) to (12), wherein the ionic compound is a mixture of salts. (14) The salt mixture is 82% CsNO ₃ and 18%
The high-brightness point ion source according to the above (13), comprising a mixture of CsCl. (15) The salt mixture is 70% CsNO ₃ and 30%
The high-brightness point ion source according to the above (13), comprising a mixture of NaCl. (16) The high-brightness point ion source according to any one of (1) to (15), wherein the ionic compound is a mixture of acids. (17) The above (1), wherein the acid mixture comprises a mixture of 80% H ₃ PO ₄ and 20% H ₂ SO _4.
The high-brightness point ion source according to 6). (18) The high-brightness point ion source according to any one of the above (1) to (17), wherein the ionic compound comprises a mixture of an acid or a base. (19) A method of ion release in a vacuum column of a FIB system, comprising: a) preparing a mixture of liquid ionic compounds; b) coated with a coating of the mixture in liquid or solid form;
Fabricating an ion emitting element (11) consisting essentially of a needle (13) made of a refractory ceramic material having a pointed tip called a tip (13a); A metal extraction electrode (2) having a center hole (20a) fixed to the body (19)
Ion extraction element (12) consisting essentially of 0)
D) mounting the ion-emitting element in the ion-extracting element, firmly fixing and firmly centering therein;
Then precisely adjusting the spacing between the center of the extraction electrode hole and the tip apex to obtain a high intensity point ion source; e) placing the ion source at the emission point of the FIB column; f) Heating the needle if the coating is solid; and g) applying a suitable extraction voltage between the coating at the tip apex and the ion extraction element to generate an ion beam. Generating an electrostatic field.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the novel high-brightness point ion source of the present invention in which a liquid ionic compound is directly heated by a heating coil.

FIG. 2 is a schematic diagram illustrating a second embodiment of the novel high brightness point ion source of the present invention in which an indirect heating technique has been performed using a graphite mandrel, and thus no liquid ionic compound has contacted the heating coil. .

──────────────────────────────────────────────────続 き Continuing on the front page (73) Patent holder 594113931 Orsay-Physic France 91893, Orsay-Cedue, Club-Orsay-Humbersite, 29 Rue Jean-Rostan Park (72) Inventor Antoine Corvin France 75016 Paris Lieux de Pasie 80 (72) Inventor Pierre Sudrow France 91410 Saint-Cyr-sur-Drudon Lieux de Fwanard 2 (72) Inventor Rene Serre France Shan Lanier Batimon B (No address) (56) References JP-A-59-54156 (JP, A) JP-A-62-133643 (JP, A) JP-A-62-232838 (JP, A) Sho 61-279038 (JP, A) 3-245447 (JP, A) JP-A-60-138831 (JP, A) JP-A-63-221541 (JP, A) JP-A-5-205680 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 27/00-27/26 H01J 37/08

Claims (10)

(57) [Claims] 1. A high intensity point ion source adapted to operate with a liquid ionic compound, comprising a refractory ceramic material adapted to be wetted by said liquid ionic compound, having a pointed end called a tip. Ion extraction means comprising: a needle; and means for supporting the needle; an extraction electrode made of a conductive material having holes; and means for maintaining an accurate relationship between the extraction electrode and the apex of the tip. Wherein the ion emitting means further comprises heating means coupled to the needle for heating the needle to a temperature at or above the melting point of the ionic compound, wherein the heating means comprises a needle tip. It consists of a heating coil tightly wound around the needle at an adjacent position, and prevents liquid reaction between the material forming the coil and the liquid ionic compound. Mandrel made of an easily heat-conductive and electrically conductive material not wet, characterized in that it is disposed intermediate of said coil needle, high brightness point ion source. 2. The high intensity point ion source according to claim 1, wherein said mandrel is made of graphite. 3. A high intensity point ion source adapted to operate with a liquid ionic compound, comprising a refractory ceramic material adapted to be wetted by said liquid ionic compound, having a pointed tip called a tip. Ion extraction means comprising: a needle; and means for supporting the needle; an extraction electrode made of a conductive material having holes; and means for maintaining an accurate relationship between the extraction electrode and the apex of the tip. And wherein the ionic compound is a mixture of salts. 4. The high-brightness point ion source according to claim 1, wherein the ionic compound is a mixture of salts. 5. The mixture of salts comprises CsNO ₃ and CsC.
5. The high-brightness point ion source according to claim 3, wherein the high-brightness point ion source is selected from the group consisting of a mixture of C. 1 and a mixture of CsNO ₃ and NaCl. 6. The salt mixture comprises 82% CsNO ₃ and 1%.
The high intensity point ion source according to claim 5, characterized in that it comprises a mixture of 8% CsCl. 7. The method according to claim 1, wherein said salt mixture comprises 70% CsNO ₃ and 3%.
The high-brightness point ion source according to claim 5, comprising a mixture of 0% NaCl. 8. A high intensity point ion source adapted to operate with a liquid ionic compound, comprising a refractory ceramic material adapted to be wetted by said liquid ionic compound, having a pointed end called a tip. Ion extraction means comprising: a needle; and means for supporting the needle; an extraction electrode made of a conductive material having holes; and means for maintaining an accurate relationship between the extraction electrode and the apex of the tip. And wherein the ionic compound is a mixture of acids. 9. The high-brightness point ion source according to claim 1, wherein the ionic compound is a mixture of acids. 10. An acid mixture comprising 80% H ₃ PO ₄ and 2%.
Characterized by comprising 0% of a mixture of H ₂ SO _4, high-intensity point ion source of claim 9.