KR20060024470A - The methodology for nano scale material joint and welding using scanning electron microscope - Google Patents

Abstract

As the packing density of industrialization has increased rapidly, "nanotechnology" has emerged as researches showing new physical phenomena and improved material properties in the nano-micron domain have been activated. Among the nanotechnology fields, the most prominent fields are carbon nanotubes (CNTs). Since such ultrafine CNTs have a diameter of several tens to hundreds of nm, they cannot be observed by a conventional optical microscope, and can only be observed by an electron microscope or an atomic force microscope. Furthermore, no technology has been developed to bond ultra-fine nanomaterials that can only be observed with these special microscopes.

The task is to apply a technique specially designed to maximize the emission current by changing a part of the high pressure supply device such as CNTs to the scanning electron microscope. Realize the resolution of several nm focused electron beam through functions such as Aperture, and remove the alternative lens and variable aperture at the observation point mechanically or electrically at the observation point and apply only the objective lens at the time of coalescent welding. It includes the method of implementing the technical method and device that can directly weld and join the ultra-fine nanomaterials such as CNT by applying the probe current up to ~ 50uA by applying the self-developed technology. .

Electron beams, probe currents, scanning electron microscopy, nanojunction, welding of ultra-fine nanomaterials.

Description

The methodology and apparatus for nano scale material joint and welding using Scanning Electron Microscope             

Representative figure is a comparison of electron microscope mode and electron beam welding mode in the present invention.

1 is a schematic view of an electron microscope and an electron beam welding device (left) scanning electron microscope (right) an electron beam welding device.

2 is an electron gun specification comparison diagram of a scanning electron microscope and an electron welder.

3 is an electron diagram of the interior of a control system of an electron microscope;

4 is a revised circuit diagram of the reflector as an embodiment of the present invention.

5 is a dual slit schematic of Electron Optics.

6 is a nanotube image of an extremely fine material taken with the present apparatus (scanning electron microscope mode).

7 is a structure of a backscattered electron detector capable of observing a welding state as an embodiment of the present invention.

8 is a welding case applied to the Gold Ball as an embodiment of the present invention.

Figure 9 is an example of welding by welding a copper wire in one embodiment of the present invention.

10 is an electron beam path structure diagram in an electron microscope mode and an electron beam welding mode.

As the packing density of electronic devices is rapidly increased and miniaturized, the width between micro devices should be reduced, and it is reported that it is very useful to use CNT (Carbon Nano Tube), which is an extremely fine nano material, as wiring instead of the conventional metal film wiring method. have. CNTs are also receiving the most attention in the realization of new materials and industrial applications in the fields of information and communication and materials. In particular, research on next-generation technology for making circuits with CNTs in the semiconductor field is being actively conducted worldwide. The present invention includes such ultra-fine nanomaterial welding methods and implementation techniques as CNTs.

To make CNT circuits made of ultra-fine nanomaterials, the technique of electrically connecting the tubes is required. In the previous study, the method of electrically conducting CNTs was not simple, and the tunnel junction instead of ohmic contact was used. It shows how to create Tunnel Junction. That is, these implementation techniques are not designed in connection with the next productivity, but are focused on experimental purposes for research.

In recent research on the mechanical manipulation of nanotubes, Ruoff et al. [2] focused beams of scanning electron microscopes deposit hydrocarbon contaminants and attach nanotubes using tips from an atomic force microscope. . However, since this method inevitably requires dual operation of AFM and electron microscope and a combination thereof, a technical device design to integrate them is a challenge.

In addition, research on coalescence welding using a scanning electron microscope has also been conducted. In other words, applications have been reported to deposit nanotubes by depositing amorphous carbons while decomposing residual organic matters at the electron beam concentration using contaminants (including organic contaminants) on the sample surface. However, this technique is not a welding but a brazing concept, and the current value that can be realized by the conventional electron microscope cannot be implemented to the extent that it can be welded. In addition, there is a disadvantage that the applicability of the brazing is extremely limited.

Conventional scanning electron microscopes have to be designed with a small electron beam in order to achieve high resolution. That is, in principle, in order to realize high resolution in a scanning electron microscope, the probe current of the electron beam may be reduced to ~ pA. However, welding of the material is impossible at these current values. In order to overcome this limitation, a device designed with high power (high voltage / high current) is a dedicated electron beam welding device (EBW). The electron beam welding device is a device designed to allow welding of metal materials because it can generate a probe current of up to 1000 mA by applying a high voltage of 60 to 150 KeV or more. However, the dedicated electron beam welding device has a beam resolution of several tens of um, so that the application field as a macro welding device is effective, but the application of ultra-fine materials such as CNT (Varbon Nano Tube) to welding is impossible because the base metal cannot be observed.

In order to overcome these limitations and to overcome these limitations, the present invention employs the principle of using electron microscopy and the electron beam welding device that realizes high probe current when welding them together. In other words, the device is designed to increase the amount of radiation current by changing the circuit of the high-voltage power supply of the conventional electron microscope and to apply the observation mode using the scanning electron microscope and the electron beam welding mode. Therefore, it is possible to freely switch between scanning electron microscopy mode and electron beam welding mode without changing the focal position of the electron beam, thereby enabling a method and apparatus for enabling direct welding / bonding between these materials while enabling nanoscale ultra-fine material observation. Doing.

As the nanotechnology of the electronic industry is developed and the size of electronic devices is miniaturized, the wiring width between the microdevices is also reduced, so that nano-bonding technology such as nano wire or nanotube will be required. The development of such nanotechnology is delayed due to the deterioration of device technology for processing nanomaterials including nano welding and nano processing technology. The present invention includes a breakthrough implementation method and device technology for nano welding, which is a core technology among these nano technologies.

Scanning electron microscopy should increase the acceleration voltage and minimize the amount of current probed to the sample (nA ~ pA) in order to achieve a good resolution (a few nm) as shown in Fig. 1 and representative. That is, as shown in FIG. 2, the lower the probe current 105, the smaller the resolution. The strength of this amount of current has little effect on the surface of the material (10 to 20 ^o C surface temperature rise), so welding or joining is impossible. In addition, when applying the function of high current electron beam welding device (EBW) in order to process the coalescing welding of the junction, the beam diameter is up to several tens of um, there is a limit that is impossible to observe the ultra-fine image.

As shown in FIG. 3, the patented technology specifically remodels the high voltage tank 21 of FIG. 4 within the control system configuration based on the scanning electron microscope, thereby hardly affecting the resolution of the electron microscope. It has technical features designed to maximize welding current and welding and joining treatment. That is, a work-piece such as a carbon nanotube (CNT) 31 as shown in FIG. 6 cannot be observed except for a special device such as an electron microscope. Therefore, observation using an electron microscope is inevitable to confirm the position to be bonded. That is, the current value was increased by changing the circuit of the reflector 23 constituting the high pressure applying unit 22 in the HV tank 21 of the self-developed scanning electron microscope. That is, the radiation current 106 and the probe current (by changing the circuit of the back pressure 23, which is the high pressure applying unit 22 of the existing electron microscope, without fabricating a high pressure applying unit 22 for a separate electron beam welding apparatus) 105) designed to maximize. The main feature of the present invention is based on the work of lowering the value of the capacitor 24 in the cockroft-walton circuit of the reflector part at the rear of the transformer inside the device for generating high pressure. The amount of emission current 106 generated in the electron microscope cathode 102 of FIG. 2 under controlled conditions such that voltage drop and S / W frequency remain unchanged. Led to an increase. That is, during loading, the voltage drop in the Cockroft-walter circuit is expressed as follows.

V _DROP = Iload / (fC) * (2/3 n3 + 1/2 n2-1/6 n); Where Iload is the load current (Amps), C is the stage capacitance (Farads), f is the AC frequency (Hz), n is the number of stages.

For capacitors of all stages (C1 through C (2 * n), the ripple voltage can be derived from the equation: Eripple = Iload / (fC) * n * (n + 1) / 2

In the above formula, the ripple is greatly increased depending on the number of capacitor 24 steps. That is, in the experiment of the present invention, as shown in FIG. 4, the filament 101 is artificially maintained while constantly changing the ripple voltage in the high voltage tank 21 to which the voltage of the scanning electron microscope is applied. The capacitor 24 capacity was changed from 2200 (pF) to 1000 pF without changing the Wennel-Tt 103 and anode-104 voltages. In order to evaluate the degree of change of frequency at this time, the device manufactured under the same condition was examined. As a result, there was no difference from the S / W frequency value. Therefore, high current generation was induced as a result of artificially maintaining parameters such as voltage of other circuit parts artificially and lowering the capacitor 24. That is, according to the present invention, the radiation current 106 applied by the same acceleration voltage from the high voltage applying unit 22 was induced to 200uA or more higher than the radiation current value 100uA applied in the conventional scanning electron microscope. In order to minimize the decrease in resolution caused by the increase of the discharge current at this time, the tube part was additionally designed as follows for this experiment. That is, as shown in FIG. 5, the magnetic field of the condenser lens 12, 13 for focusing the electron beam radiated from the electron gun 11 in the scanning electron microscope is increased, and when converted to the electron welding mode, In order to minimize the spread of the beam, a dual slit 16 was applied to the objective lens 15 to process the dual field lens.

An electron microscope is a device that structurally focuses an electron beam to reduce the size of the beam to achieve high resolution. Therefore, the size of the electron beam is controlled to be small by a combination of focusing lenses (condenser lenses) 12 and 13 and aperture 14. Therefore, the size of the electron beam is reduced in the course of passing the upper-turecher 14 having a predetermined size of Hall, but a large amount of current is lost, so that the electron beam irradiated to the final sample surface is several nm in size. The amount of probe current 105 of nm to pA is realized. Therefore, as shown in the representative view, when the SEM image of the electron microscope is implemented, the junction is observed by scanning electron microscope, and during the welding process, the electron beam is fixed at the same point as the observation point to be bonded. The electron beam is fixed at the welding position observed at, and the electric condenser lens (12, 13) that focuses the strong electron beam radiated from the electron gun to minimize the current loss is electrically turned off. In order to pass the electron beam and adjust the size of the electron beam, the aperture 14, which allows the electron beam to pass through a hole of a certain size, is mechanically easily removed (mechanical in / out treatment) to substantially remove the aperture. By focusing the electron beam using only the objective lens 15 structured as a double slit (16), the current of the electron beam is several tens of uA (self test result). ~ It could be maximized by applying more than 50uA available).

The present invention maximizes the electron beam radiation current through the circuit change as mentioned above, and applies the conventional electron microscope structure to the size of the beam through the focusing lens (12, 13) and aperture-14, etc. By minimizing the resolution to implement a few nm resolution it can be observed the base material such as ultra-fine CNT (31). At this time, when switching to the welding mode as shown in the representative diagram, in order to observe the welding state by installing a backscattered electron detector (BSE; Backscattered Electron Detector) (BSE) as shown in Figure 7, the thin Al of the conventional secondary electron detector In order to minimize damage to the thin film and replace the existing patented technology such as seam tracking, it is designed to observe the welding state at the same time. As a result of applying the present invention, the electron beam position observed in the scanning electron microscope was able to proceed without changing the position.

In general, in this experiment, the size of the electron beam at a probe current of 30 to 50 uA exhibits a resolution of about several um. Therefore, it is difficult to observe welding of ultrafine materials such as CNT through backscattered electrons during the welding process. However, if the above procedure is reversed to observe the result of the coalescence welding and observed in the scanning electron microscope mode, the welding state can be easily observed. Experimental results using the proposed device, the probe current 105 was possible to implement more than 50uA, as shown in Figures 8 and 9 it is easy to weld to the copper wire and gold ball with a melting point of 1000 ^o C or more The breakthrough results can be obtained.

The present invention can be evaluated as a breakthrough technology for the bonding technology of CNT bonding and welding, which is an ultrafine nanomaterial that can be observed only in an electron microscope or an atomic microscope in nanotechnology. Conventionally, the device and implementation technology designed to observe the location of ultra-fine nanomaterials using an electron microscope and to weld and bond materials with a melting point of 1300 ^o C by maximizing probe current up to 50uA by switching to electron beam welding mode It is characterized by.

Until now, research on nano-bonding technology that has been implemented by incorporating various chemical and physical methods has been published, but there is no case in which technology capable of processing extremely fine shapes, such as the present invention, can be directly processed easily. Therefore, as a very unusual invention technology, it is estimated that commercialization can be applied immediately from the time of publication and application data. In other words, it is expected to play a pivotal role in activating R & D of various nanomaterial technologies such as semiconductor processing, semiconductor packaging technology, and CNT.

Another effect of the present technology is as shown in the results of welding copper with a melting temperature of 1000 ^o C or higher, as experimentally verified, and it is possible to weld small and medium-sized general metals in addition to nanotechnology. In the electron beam welding device market, it is possible to give great meaning in terms of import substitution effect as an electron beam welding device developed for the first time in Korea and supply of them at a low price.

Therefore, the expectation for the marketability of the next generation welding equipment is high in that it can be commercialized immediately.

Claims (4)

In order to achieve the technical problem to be achieved by the present invention, the present invention is characterized by increasing the amount of radiation current by modifying the reflector circuit terminal of the high-pressure application portion of the scanning electron microscope of the conventional probe current of about nA ~ pA as shown in FIG. do. That is, (1) in the conventional scanning electron microscope high pressure device section 21, the high pressure applying section 22 shortens the S / W frequency in the back pressure 23, and ② doubles the capacity of the capacitor 24 in the Cockroft-Walton circuit. 3) By changing the structure of the back pressure 23, the conditions of other voltage drop (filament 101, anode 104, Wennel 103, voltage drop, etc.) are artificially kept constant. ④ 50uA or more probe current to apply high current load to electron gun Cathode 102 and to maximize the radiated current 106 and probe current 105 under the same acceleration voltage condition for welding and bonding with electron beam High voltage device unit (HV Tank) 21 for implementing the circuit device. The method of claim 1, By applying the designed high pressure device, a condenser lens (Condenser1, condenser2) 12, 13 and a variable aperture with 200um hole as shown in the representative view (a) in the scanning electron microscope mode 14 ) And the size of the electron beam (current amount) is reduced to maintain the resolution without changing the conditions of the conventional scanning electron microscope and to observe the extremely fine shape. When switching to the welding mode, as shown in the representative view (b), the condenser lens 12 and 13 are electrically turned off at the same observation point, and the variable aperture 14 is mechanically operated (turned and processed). After switching to the welding mode, the electron beam is focused only at the objective lens 15 having its own designed double slit 16 to reduce the energy (current) loss. An implementation technique method of directly probing at an objective lens (15) stage to implement probe current (105) values up to ˜50 uA to process welding, brazing and joining of ultrafine base materials and general metal materials. The method of claim 2, Another feature of the present invention is equipped with a back-scattered Electron detector to observe the image during welding, the ultra-fine image is observed using a secondary electron detector used in conventional scanning electron microscope When switching to the welding mode, damage occurs with the secondary electron detector, so that the generated electrons of high kinetic energy and high current can be detected without damage to the detector itself through the backscattered electron detector, and the welding process is imaged by imaging. An implementation technology method that can replace Seam tracking, which is a conventional patented technology that can be observed. The method of claim 2, Another feature of the present invention is the method of implementing the technique including the expansion of the field emission scanning electron microscope and various electron microscopes in addition to the thermo-electron emission electron microscope applied in this paper, the principle of operation and the principle of application are similar.

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