FI122010B - Ion beam etching method and plant - Google Patents

Description

ION ION BREAKING METHOD AND APPARATUS

FIELD OF THE INVENTION

The present invention relates to the manufacture of three-dimensional (3D) nanostructures, in particular 5 nanostructures having dimensions less than 100 nm.

BACKGROUND OF THE INVENTION

There are many different techniques for manufacturing three-dimensional (3D) nanostructures of 10 different materials. For example, UV lithography has traditionally been widely used, particularly in the micro-electronics industry. However, there is a fundamental threshold below which structural dimensions cannot be reduced. When using deep UV light, this limit is somewhere near 100 nm.

More sophisticated methods based on electron beam lithography (EBL) can provide even smaller dimensions and have been used, for example, to produce etched lines of 5-7 nm wide on 20 silicon substrates. However, when vaporizing metal structures through masks made with EBL, the limit is higher, about 20-50 nm. The disadvantage of EBL is that it is a relatively slow method.

Focused ion beam (FIB) is a method which is conceptually similar to EBL, except that electrons are replaced by focused heavy ions. The FIB method has been successfully used for very local etching and cutting, however, even within the micrometer rather than the nanometer range.

To the best of the inventors' knowledge, there are no reports

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imported 3D structures made using the FIB method,

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with dimensions significantly below 100o to nm. In addition, the FIB is very expensive. On the other hand, for industrial manufacturing purposes, FIB is extremely slow and not at all compatible with the idea of mass production.

In the past, the inventors have published the basic concept of a completely new approach in reducing the dimensions of pre-fabricated nanostructures by ion-jet sputtering (Applied Physics A 79, 1769-1773, 2004). The principle is to expose the processable nanostructure to a jet of low-energy, medium-mass ions at an oblique angle of attack. The energy of the ions colliding with the surface layer of the object 10 causes the surface atoms to release. This physical process is controlled by careful selection of process variables such as ion energy and mass, ion jet inlet angle, and ion jet current. A sample is swirled around the azimuth angle to ensure isotropic etching. The process can be accomplished with commercially available ion-jets and vacuum systems with the addition of a sample processing device for tilting and rotating. The inventors have found that a process of this kind can produce structures up to 10 nm with high accuracy and producing extreme surface smoothness (Nano Letters, Vol. 5, No. 6, 1029-1033, 2005). Despite promising preliminary results, it is difficult to apply this method to a variety of materials, as well as structure shapes and dimensions in finding the optimal set of process variables. Even the theory of ion-sputtering of conventional macroscopic 2D structures is not fully understood and is naturally very much more complex in predicting the results of the nanostructuring process of 3D structures smaller than 100 nm.

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PURPOSE OF THE INVENTION o

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It is an object of the present invention to provide o 0X1 a novel, well-controllable method and apparatus for processing high-precision 3-dimensional nanostructured nanostructures at nano-meter surface roughness.

SUMMARY OF THE INVENTION

The method of the present invention is characterized in that is set forth in claim 1. The apparatus of the present invention is characterized in that set forth in claim 10.

Firstly, the present invention relates to an ion-beam etching process for processing three-dimensional (3D) nanostructures of less than 100 nm, wherein a prefabricated nanostructure formed on a substrate and preferably having the desired final shape of the nanostructure is etched in a three-dimensional by an ion beam at an angle of inclination, possibly while rotating the nanostructure about an axis 20 perpendicular to the substrate. The etching of the present invention may have two uses. First, the aim may be to reduce the pre-fabricated sample to a three-dimensional size and shape of the nanostructure by means of a well-controlled ion-beam etching process, which allows production of dimensions well below conventional manufacturing methods. On the other hand, the etching process of the invention can only be used to smooth the surface of a sample prepared by any conventional processing method, such as electron beam printing, LIGA, or nanoimprint. Etching is based on a physical sputtering process, whereby the surface atoms of the object c are released by collisions with the energetic ions that hit the sample.

In contrast to two-dimensional (2D) or planar structures such as planar films or strips having a thickness substantially less than the length and width of the tape, three-dimensional here refers to nano-structures which also have substantially the same height dimensions. as a horizontal measure (s). Examples of such 3D structures include various threads, beams, islands, and combinations thereof. Inlet angle here means the angle between the surface normal and the longitudinal axis of the shower. The inclined angle of the ion beam as well as the rotation of the sample is required for isotropic etching, i.e. the same etching rate for both horizontal and vertical surfaces 10. Also, the roughness of the etched surface is very low because each point of the sample is bombarded from different directions due to rotation about an axis perpendicular to the substrate. "Perpendicular to the substrate" herein means a direction substantially perpendicular to the main plane of the substrate. On typical planar substrates, such as round discs, this is an unambiguous definition. For non-planar substrates, this direction is the direction of the nanostructure from the substrate. The phrase "possibly 20 rotating" means that, of course, it is also possible to hold the nanostructure in place and bombard it from only one direction. This kind of directional castle etching allows for the controlled deformation of the nanostructure.

According to the invention, the ion energy per mass is in the range of 0.0025 to 0.0225 keV / amu, where amu represents the atomic mass unit (1.66 * 10 ~ 27kg), and the angle of arrival of the ion beam relative to the substrate is in the range of 30-50 degrees. , preferably about 40 degrees. This combination of secondary 30 variables was surprisingly found to provide an effective yet g subtle and well-controlled etching system.

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process resulting in isotropic etching and 05 producing extremely low surface roughness. This set of? 35 variables is also very common, with a wide variety of materials to apply. Both of these 5 variables are discussed in more detail below.

Bombing an object with an ion beam perpendicular to the surface of the target will usually cause the io-5 nit to penetrate the target quite deep from the point of view of nano-machining. In addition, the surface roughness resulting from perpendicular bombardment is typically at least several nanometers. If there is a defect in the material of the object, the surface roughness becomes even worse 10 due to the faster etching around the defects.

Thus, at one and the same time, a tilt angle is required for the opposite directions. Contrary to previously published results, the optimal angle, together with the above-mentioned variable definitions, was avoided at about 40 degrees.

Traditionally, 2D sputtering processes use high energy ions with multiple keV energies. Referring to what has been said above about penetration depth and controllability, and as you also realize that the higher the energy, the higher the probability of damage, subtle processing of the sample requires lower energy. This also contributes to achieving surface roughness in the nanometer class. On the other hand, 25 too low energy will not cause any etching. In addition to the kinetic energy, which depends on the acceleration voltage and ion charge, the ion mass also influences the process of removing the surface atoms of the sample, since the probability of removing the atom of the target depends on the amount of motion of the ion. Therefore, the mass must also be taken into account when selecting the ion type and energy. This is the reason for determining the energy relative to io-

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n mass. As a compromise, reasonable sputtering

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medium speed ions are preferably used between speed, surface damage prevention and availability of various types of ions. The range of 0.0025 to 0.0225 keV / amu, along with other variables defined in the claims, was found to be experimentally optimal for most etched materials.

It is important to note that there is currently no comprehensive theory regarding the mechanism of etching of ion-jet auxiliary nanostructures. Therefore, despite some indicative theoretical assumptions, optimization of interrelated process variables is largely based on experimental research. As usual with the nanotek-10 ankle, in this case too, the final conclusions led to a set of variables that are fundamentally different from what one would have expected.

The aspect ratio of the prefabricated sample preferably fulfills the condition -> 1, where h and w are the height and width of structure w 15, respectively. This condition relates to the need to preserve the original shape of the pre-fabricated sample during the etching process. Shape retention greatly simplifies the entire manufacturing process, since an already fabricated structure may have the desired desired geometry of the nanostructure. Contrary to previously published test structures based on assumptions of a suitable cross section, the inventors found that keeping the parts at least as high as they are wide, with the angle of incidence and energy per mass as defined above, is most effective in ensuring the original shape of the sample with slight changes. Of course, if no preservation of the original shape of the processed nanostructure is required, the ratio between height and width of 30 can be any value.

In one preferred embodiment of the present invention, the ion energy per mass is in the range of 0.01 to 0.015 keV / amu, preferably about 0.0125 keV / amu, which has been found to be optimal for most of the o 35 sample materials and ion types.

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The ion beam current is preferably in the range of 10 to 20 μΑ / cm 2. Contrary to expectations, the lower bound of the observed area comes from the need for sufficient dynamic surface cleaning. Dynamic cleaning refers to the process of inhibiting growth of the treated material on the treated surface. For example, since there is always some residual oxygen in the vacuum chamber, an oxide layer could easily be formed, for example, on a metal surface without sufficient ion beam current density. On the other hand, excessive current density could lead to unwanted surface damage and / or overheating, resulting in poor control of the etching process.

In order to provide a sufficiently large processing area, or region 15, in the plane of the substrate surface at which etching can take place, and thus allowing simultaneous processing of several nanostructures on the same substrate, the ion beam bombarded with the nanostructure preferably has a diameter of at least about 10 mm. A large shower also helps to even out the ion flux through the shower. The width of the shower depends on the characteristics of the installation. It can be adjusted to some extent by selecting the acceleration voltage: the higher the voltage, the narrower the shower. Depending on the substrate 25, it is thus possible that the cross-section of the jet is even comparable to the substrate size. However, the intensity usually has a Gaussian or other uneven distribution. Therefore,

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The area can be further increased as well as the homogeneity of the ionic stream 30 can be improved by deflecting the ion beam relative to the substrate in the direction perpendicular to the longitudinal axis of the jet during processing.

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wide area. The diversion can be accomplished either by 05 diverting the jet or the nanostructure profitable § 35 platform,

Preferably, the nanostructure is grounded to prevent accumulation of charge in the sample. The accumulation of charge caused by ionic charges could destroy the sample as a result of electric discharge during subsequent processing of the sample. Grounding can be done, for example, with bonded metal wires connecting the sample to a metallic, grounded sample holder.

Charge accumulation can also be prevented on the semiconductor or metallic substrate on which the sample is made. A non-insulating substrate effectively reduces the charge of 10 samples.

Particularly in the case where the sample is made on an insulating substrate, it is preferable to introduce additional electrons in the vicinity of the nanostructure to counteract the irradiation of the sample due to the charged ions of the jet. The excess electrons, for example in the form of an electron cloud, may be provided by a conventional charge neutralizer (e.g., heated tungsten wire) connected to the apparatus. The present invention has been found by the inventors 20 to be applicable to various metals such as bismuth, aluminum and tin, inorganic insulators such as alumina, mica and silica, as examples of semiconductors as well as organic PMMA resistors. Et dry rates are different for different materials making 25 etching very selective. The smallest nanometer scale structures are within the 5 nm range. The achievable surface roughness has been shown to be about 1 nm. Due to the delicate process, also very fragile nano-cp 30 structures, such as single electron electron transistors, can be etched by the process of the present invention.

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The present invention also relates to an ion-jet etching apparatus for etching pre-fabricated nanostructures on a planar o g 35 substrate less than 100 nm. The apparatus comprises a vacuum chamber, a sample processing device attached to the vacuum chamber, and comprising a sample holder for attaching the sample thereto, and an ion jet source arranged to emit low energy medium-mass ions at an inclined inlet angle 5 to the substrate attached thereto. The sample processing device may rotate the sample holder and thus the substrate thereon about an axis perpendicular to the substrate.

According to the invention, the ion jet source can emit ions having energy per mass in the range of 0.0025 to 0.0225 keV / amu and the angle of inlet of the ion jet relative to the substrate on the sample holder is in the range of 30 to 50 degrees, preferably about 40 degrees. These hardware features, combined with the geometry of properly selected samples, allow for a highly controllable and subtle isotropic etching process that produces a high quality etched surface.

Preferably, the ion beam etching apparatus 20 can produce an ion beam current density in the range of 10 to 20 μΑ / cm 2. This has been found to be a suitable area for efficient dynamic cleaning of the processed surface.

Preferably, the ion jet source can produce an Io-25 wheat jet having a diameter of at least 10 mm to ensure a sufficiently large processing area and thus to simultaneously etch several nanostructures on the same substrate.

Preferably, the apparatus also comprises means for deflecting the ion beam cp 30 relative to the substrate in a direction perpendicular to the longitudinal axis 1 of the jet to expand the processing area and improve the homogeneity of the ion flux Q_ in the processing region. This feature allows simultaneous etching and uniform etching of a large number of nanostructures on a single substrate.

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Preferably, the apparatus also comprises means for introducing additional electrons in the vicinity of the sample holder to counteract the charge of the nanostructure due to the charged ions of the ion beam to be bombarded.

In summary, the present invention enables the fabrication of nanostructures up to 10 nm in a controlled manner using low-cost equipment wetted from a commercial ion source and 10 vacuum systems added to a sample processing device.

In addition to the dimensional accuracy, the processed surface also has excellent flatness. In contrast to, for example, the FIB process, a large number of nanostructures formed on a single substrate can be processed simultaneously at a uniform etching rate throughout the substrate, enabling industrial mass production. The method and apparatus of the present invention are also highly flexible. Sample preparation can be performed by any known manufacturing method and can be applied to most materials used in micro and nanoelectronics. Also, the ion type can be freely selected as long as the definitions in the claims are followed.

BRIEF DESCRIPTION OF THE DRAWINGS

o The following pictures are included

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In order to provide a further understanding of the invention, which form part of this specification, together with the description, explain the principles of the invention.

κ Figure 1 shows a schematic diagram of the subject

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o of the ion-jet etching apparatus according to the invention.

Figure 2 represents an example of nanostructures processed by the method of the present invention.

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Figures 3a and 3b are AFM (Atomic Force Microscope) images of a nanostructure before and after the etching process of the present invention.

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DETAILED DESCRIPTION OF THE INVENTION

Reference will be made in detail to the embodiments and examples of the present invention which are set forth in the accompanying drawings.

The ion-jet etching apparatus 1 of FIG. at an inclined angle α1 to the normal N. of the substrate. Preferably, the apparatus also includes means for adjusting this angle. The sample processing device 20 also has means for rotating the sample holder about an axis N perpendicular to the surface of the substrate and, consequently, for rotating the sample about an aze angle. The jet deflection system 9 is connected to an ion gun to deflect the jet in a direction perpendicular to the jet axis to expand the etching area. The apparatus also comprises a charge neutralizer 10 attached to the vacuum chamber o in the vicinity of the sample holder to send electrons 11 towards the sample to neutralize the charge accumulated in the sample due to the charged ions.

Of course, the apparatus also includes conventional x £ control means, which are not specific to this invention and are thus not shown in the figure. For example, the sample processing device may have a combined

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35 a current meter for measuring ion current, which can be recalculated (integrated) into 12 doses of ion. The entire hardware is preferably controlled by a computer.

Figure 2 shows a piece of substrate 8 formed on a series of nanowires 12. The wire cross-section has a height h greater than or equal to the width w. This, together with properly selected process variables, ensures that the shape of the cross-section remains substantially unchanged during the etching process. As far as scale is concerned, it is important to note that for illustration purposes the length of the yarns is much smaller than they actually are. The substrate 8 is preferably made of at least partially conductive material for electrically connecting the nanowires through the substrate to the sample holder. Grounding prevents the charge from accumulating in the nanostructures, which could otherwise occur due to the charge of the bombs ions.

The AFM figures 3a and 3b show an ethanol filament made of aluminum before and after the process of the present invention. It can be seen from the pictures that not only the dimensions but also the surface uniformity of the nano wire is greatly improved. In fact, experiments have shown that the present invention can achieve roughness up to about 1 nm.

It will be obvious to one skilled in the art that as technology advances, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; its

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instead, they may vary within the scope of the claims.

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Claims (14)

1. Ion beam etching process for processing three-dimensional nanostructures below 100 nm, 5. which a pre-fabricated nanostructure (12), imaged on a substrate (8), is etched three-dimensionally by bombarding the nanostructure under vacuum conditions with a jet (5) of ions with an intermediate angle energy mass at an angle of incidence (ai) relative to the substrate and, if possible, simultaneously rotate the nanostructure relative to the substrate around the vertical axis (N), characterized in that the ionic energy per mass is in the range 0 0025 - 0.0225 keV / amu; and 15. The angle of incidence (ai) of the ion beam (5) relative to the substrate (8) is in the range of 30 - 50 degrees, preferably about 40 degrees. 2. Ion wood etching method according to claim 1, characterized in that the shape ratio of each part of the manufactured nanostructure satisfies the requirement -> 1, in which h and w w are the height and width of the structure respectively. Process according to Claim 1 or 2, characterized in that the energy of the ions per mass is in the range 0.0100 - 0.0150 keV / amu, preferably about 0.0125 keV / amu. O Method according to any of Claims 1 to 3, characterized in that the current strength of the ion beam (5) is in the range 10 - 20 µΑ / cm. The beam (5) which collides with the nanostructure (12) and supports up to about 10 mm or more to ensure a sufficiently wide processing area. 17 Method according to any of claims 1 CL -4, characterized in that the diameter of Method according to any one of claims 1-5, characterized in that the ion beam (5) is deflected in relation to the substrate (8) in a direction which is vertical in relation to the axis (5) of the beam for expanding the processing area. and to improve the homogeneity of the ion flow strength in the processing area. Method according to any one of claims 16, characterized in that the nanostructure 10 (12) is electrically grounded at a metallic, grounded sample holder for a test with compound, bonded metal trees to prevent accumulation of the charge at the nanostructure due to charged ions. in the bombarding beam (5). 15 Method according to any of claims 1 to 7, characterized in that the substrate (8) is a semiconductor or metal material for preventing the accumulation of the charge due to charged ions in the bombarding beam (5). 20 Method according to any one of claims 1-8, characterized in that in the vicinity of the nanostructure (12), a cloud of extra electrons (11) is provided with a charge neutralizer to neutralize the charge of the nanostructure (12) due to charged 25 ions in the bombardment. the beam (5). An ion beam etching plant (1) for three-dimensional etching of a substrate (8) formed, manufactured nanostructures (12) having a size of less than 100 nm with an ion beam, comprising a vacuum chamber (2). , a sample processing device o (6) attached to the vacuum chamber, a sample holder (7) associated with the sample processing device for attaching CL of the nanostructure to it, and an ion beam source (4) CD arranged to transmit a jet (5) of ions 35 generic mean mass against the sample holder at oblique infancy angle (ai) relative to the substrate disposed on the sample holder, in which plant the sample processing device (6) can rotate the sample holder (7) relative to the substrate disposed on the sample holder the shaft (N), characterized in that the 5. ion beam source (4) can transmit ions having an energy per mass in the range of 0.0025 - 0.0225 keV / amu; and the angle of incidence (oh) of the ion beam relative to the substrate (8) disposed on the sample holder (7) is in the range of 30 to 50 degrees, preferably about 40 degrees. Plant (1) according to claim 10, characterized in that the ion beam source (4) can produce a current of the ion beam (5) which is in the range 10 - 20 μΑ / cm 2. Plant (1) according to claim 11 or 10, characterized in that the ion beam source (4) can produce an ion beam (5) whose diameter is at least 10 mm at the sample holder to ensure a sufficiently wide processing area. System (1) according to any of claims 10 - 12, characterized in that the system (1) comprises means (9) for deflecting the ion beam 25 (5) relative to the sample holder at an angle which is vertical to the axis (5) of the beam for expanding the processing area and for improving the homogeneity of the ionic flow strength in the processing area. if System (1) according to any of claims 10 - 13, characterized in that system (1) comprises a charge neutralizer (10) for x providing a cloud of extra electrons (11) for neutralization of charge of the nanostructure (12), which is due to 2 of charged ions in the ion beam (5), which is bombarded in § 35 in the vicinity of the sample holder (7). o o CVJ