Background of the invention

[0001] This invention relates to a method which uses directed electron beam to selectively produce two and three dimensional objects from solid substances.

State of the art

[0002] Application of electron beam for shaping of objects is often alternative of lithography for patterning metallic and semiconducting materials, or electron beam is applied for producing a three-dimensional object layer by layer using powdery materials (metals) as feedstock.

[0003] These two groups of methods are different in the intensity and dimensions of the applied electron beams. Electron beam lithography (EBL) and related methods have generally higher pattern resolution than photolithography (below 100 nm), therefore size of the electron beam is small. Contrary, electron beam melting and related methods which produce three-dimensional objects from powdery materials have low resolution (over 10 pm) and high density radiation of the electron beam is required.

[0004] Limited number of small (below 100 nm) two and three dimensional objects is being prepared by direct fabrication, or direct writing. Direct writing refers to the ability of producing arbitrary patterns of material in a single step (or as few as possible). While direct writing can be also used to fabricate a lithographic mask for subsequent pattern transfer, here this term will further describe the mask-less patterning. Recently, direct writing methods using electron beam reached the resolutions competitive with lithography, such methods are:

• electron beam induced deposition (EBID),

• scanning tunneling microscopy-chemical vapor deposition (STM-CVD), • scanning electrochemical microscopy (SCEM),

• direct write electron beam lithography (Direct-write EBL).

[0005] This class of direct-write strategies is involving electron-driven reaction at surfaces, when electrons initiate chemical reactions, dissociate vapor- or liquid- phase precursors or are involved in charge transfer (i.e. electrochemistry). By which reactions, the desired part or shape is formed.

[0006] Electron beams are now an important tool for materials fabrication. Method based on electron beam lithography involves a film (usually polymer), which is exposed to a focused electron beam to create a nanoscale pattern, and consequently several processing steps are implemented to transfer the pattern to a film (chemical treatment, pattern transfer, mask removal etc.). Methods based on electron beam induced deposition involve a vapor precursor at the substrate, which is dissociated by electron beam, resulting in localized deposition of material. The size of the deposited material depends on both the focus of the electron beam and dwell time (time spent by the beam at a particular position), than the resolution of the EBID is better than EBL. However, a critical drawback of the EBID is usually contamination by carbon coming from metal-organic precursor or the microscope. High resolution of EBID can be only superseded by scanning tunneling microscopy (STM), which enables manipulation of single atoms, but the process is much slower. Enhancement of STM by chemical vapor deposition (CVD) increases production speed significantly, STM is able to directly dissociate metal-organic vapors and the reactions are localized to the tip- substrate region. Than nanometer particles or lines (by scanning) were deposited in a single step, however problems with impurities are similar to EBID.

[0007] Electron beam melting and related methods produce three-dimensional objects from powdery materials layer by layer by melting and solidification caused by irradiation by electron beam. The powder sinters or melts and solidifies as the beam moves or sweeps over the working area. General desire in this technical field is to increase the production rate and to improve the product quality. Large efforts in this regard has been made by trying to optimize the electron beam irradiation procedure, by varying e.g. beam power, scanning velocity and scanning pattern, and in trying to improve the powder (varying of chemical composition, particle size distribution, etc.). Main limitations of this group of methods are tradeoff between productivity and obtained resolution, and necessity of using powdery materials.

[0008] Preparation of two and three dimensional object by direct application of electron beam is multi-step procedure, its require identification of a suitable precursor for the final object material. Therefore, many competing factors requiring some compromises are involved during preparation of 2D and 3D structures.

[0009] Patent WO 2004/067445 A1 describes growth of nanostructures on solid silicon substrate after heating by electron beam. The electron beam has impact on area with diameter of approximately 1 mm and whole area is effected by induced heat. Therefore, objects named in literature "nano dots" are formed, which are considered such as 1 D phenomena. Nano objects are separated due to different reaction of material on induced heat, and obviously it is not possible to fully control of nano dots positions, because they are formed on random defects in crystalline lattice. It is possible to create the defects by ion beam, but resolution does not enable control of nano dots positions. Silicon substrate with defined crystalline plane was used for growth of nano dots and the described procedure does not allow to prepare continual 3D object. The size of applied electron beam is approximately 10 OOOx bigger than prepared nano structures, contrary with the presented invention.

[0010] Aim of the presented invention is to present solid two and three dimensional objects by electron beam without disadvantages of current methods.

Features of the invention

[0011] The disadvantages of the current methods mentioned above are extensively eliminated by using of electron beam for preparation of two and three dimensional objects, when solid substrate is prepared, electron beam exposure area is defined, size of the electron beam is defined, acceleration voltage and electric current are defined. Consequently, at least on electron beam is applied for substrate exposure, and in principle time of the exposure is related to desired building of two and three dimensional objects.

[0012] In an advantageous embodiment the electron beam accelerating voltage is in range 0.1 to 10 kV.

[0013] In an advantageous embodiment the electron optics is used for modulation of electron beam.

[0014] In an advantageous embodiment the substrate exposure time is for each electron beam diverse.

[0015] In an advantageous embodiment the substrate is solid inorganic substances or porous materials or amorphous substances or crystalline substances.

Description of the drawings

[0016] The invention will be further explained by use of the drawings, where Fig. 1a presents a definition of the area scanned by electron beam, Fig. 1 b presents a build structure after the exposure; Fig. 2 presents a flow chart of basic steps in the proposed method to obtain defined 3D or 2D structures from solid substrate by electron beam; Fig. 3a presents an image gained by SEM showing changes after exposure of selected area by electron beam, Fig. 3b presents back scattered electrons (BSE) image showing different constitution (chemical or phase type) of E15 glass after exposure of defined area by electron beam; Fig. 4 shows grains exposed to electron beam, with constant parameters in various exposure time; Fig. 5a presents a structure of three crystalline grains before their joining by electron beam, Fig. 5b presents structure of three crystalline grains after their joining by electron beam.

Preferred embodiments of the invention

[0017] The presented method does not require any particulate precursors for formation of defined 2D or 3D structure and source of the material of the newly build structure is the solid substrate for example glass or ceramics. If the height of newly build structures is comparable with thickness of the substrate than newly build structure can be separated from substrate.

[0018] The term 2D structure is related to the objects with negligible height.

[0019] The process is step wise, where each electron beam exposure creates certain addition of mass on the irradiated spot. Several parameters can be changed to tune final shape and dimensions, the main principle is that the structure is grown only in places exposed by electron beam and in the immediate proximity. This can be repeated until the complete part is formed. Example of the structure grown after exposure by the electron beam is demonstrated on Fig. 1a and Fig. 1 b, when the area defined before scanning is on Fig. 1 a and final product on Fig. 1 b.

[0020] Electron beam is modulated by focusing and movement with various voltage and current values. Important parameter for building of the structure is time, if the electron beam parameters are constant, generally longer exposure time means bigger structure in one or all X, Y, Z directions. Generally, increase of the target area or volume requires increase of the scanning time and time of the scanning is adjusted based on the total exposed area.

[0021] More than one electron beam can be used and exposure time necessary to achieve same object development may be different for differently accelerated electron beams as well as for electron beams with same acceleration but with different intensity.

[0022] The final dimensions and size can be refined by electron beam parameters (modulation).

[0023] Resolution of the smallest build feature is determined mainly by ability of directing electron beam in the targeted area and ability to modulate the electron beam. The possible scale ranges from nanometers up to hundreds of micrometers.

[0024] In a preferred embodiment, solid inorganic substrate was scanned using electron beam with electron optics similar to Scanning Electron Microscope (SEM) apparatus, electron gun is source of electrons accelerated by voltage in range 0.1 to 30 kV, electron beam is tailored and focused by solenoid lens. Direct use of SEM is possible in special cases, if electron beam has intensity and accelerating voltage necessary for initiation of the described process.

[0025] Accelerating voltage of electron beam is chosen so that impact electron energy is in range from 100 to 10 000 eV.

[0026] Selected substrate can be solid inorganic substances or porous materials or amorphous substances or crystalline substances.

[0027] The exposed area was defined by a software directing mechanism which moves the electron beam in a repeating pattern of the exposed area.

[0028] Flow chart on Fig. 2 demonstrates sequence of steps the presented method of described invention. These steps are:

- preparation of solid substrate

- definition of area for electron beam exposure

- definition of electron beam x-y dimensions, voltage, current, and exposure over the area

- exposure of the area by the defined electron beam for chosen time

- inspection of dimensions of the created object, and

- formation of the final object

[0029] Some steps can be repeated up to final result is achieved, while sequence of steps "definition of area for electron beam exposure" and "definition of electron beam x-y dimensions, voltage, current, and exposure over the area" can be reversed.

[0030] Building of the 2D and 3D structures by modulated electron beam can cause also changes in chemical and phase compositions of the solid substrate, when also negative volume changes are possible. Changes in chemical and phase compositions or amorphous phase crystallization can be controlled during exposure by modulation of electron beam and exposure time. One type of possible changes is demonstrated on Fig. 3a, Fig. 3b , where the Fig. 3a is SEM image demonstrating volume changes in the exposed area (marked by dashed area) after exposure by electron beam; result is intrusion of flat surface, i.e. area outside the dashed area, and depression caused by chemical and phase change of material, in this example the material is glass type E15, and Fig. 3b is back scattered electron (BSE) image demonstrating the chemical and phase changes in constitution of the sample. Note from the figures that before the exposure by modulated electron beam chemical and phase composition was homogeneous in the same manner as it is outside the dashed area. As an example, glass type E15 can be shaped by the modulated electron beam, when changes in chemical and phase composition are formed.

[0031] The described method is suitable mainly for preparation of 2D and 3D structures with fine details directly from solid substrate. Source of material for building of 3D structures and support for building of 2D structures is inorganic solid substrate.

[0032] The presented method can use modulated electron beam applied on crystalline material initiating grain growth during densification, when grain growth and densification are related to time of the exposure. One example of such behavior is shown on Fig. 4, where grain size and density in part (a) correspond to few seconds of irradiation, in part (b) grain size and density correspond to longer time of tens of seconds, and in part (c) grain size and density correspond to long time exposure in order of minutes. Speed of the grain growth and densification typically depends on both modulation of the electron beam and the exposed material.

[0033] New connection between two and more amorphous or crystalline structures can be achieved by modulated electron beam when transfer of material to the place of new joint is carried out. SEM environment is one possible to be used to join the structures, when the material from joined parts or surrounded material is forming the solid conjunction. The created connection is done by movement of the material in by scanned electron beam and moved material has the ability to form solid connection with surface of the joined parts. No external material or material transformation is needed during the joining process. Example of the joining of crystalline grains is demonstrated on Fig. 5, where Fig. 5a shows structure of three crystalline grains before their joining, and Fig. 5b shows structure of three crystalline grains after their joining. Modulated electron beam transfers material from the joined crystalline grains to form new solid connections. The new connections show not obvious boundary between old and new parts. More than one modulated electron beam is desired to be used independently to manage the shape of the build connections.

[0034] The presented invention is a new direct writing method, which unlike the conventional direct writing methods does not require any further step after the final electron beam exposure.

[0035] The presented method for preparation of two and three dimension objects from solid substrate by using electron beam does not require any precursors, source of the material is the solid substrate on which the structure is built. The procedure is gradual and each exposure of material by electron beam form additional mass on the exposed area. This can be repeated until final structure is built, source of material for each layer is originally solid substrate.

[0036] The invention is not limited by the embodiments described above but can be modified in various ways within the scope of the claims.