CN100406618C - Method and device for processing complex three-dimensional microstructure on metal surface - Google Patents

Abstract

It involves the processing of complex three-dimensional microstructures on metal surfaces using the technology of constrained etchant layers. The steps are to fix the processing tool with the microstructure on the fixed frame; inject the etching solution into the container; enter the processing tool into the solution; start the electrochemical system to generate etchant on the surface of the processing tool; use the scavenger to compress the etchant layer To nano-level or micron-level thickness; start the driving device, etch the workpiece, so that the surface of the workpiece is depressed and separated from the etchant layer, until the etching is completed. The processing device includes a processing tool, a fixed frame, a driving device, a computer, and an electrochemical system. It can carry out batch replication processing of various complex three-dimensional microstructures; complete the etching of batch microstructures in one step, eliminating the need for gluing, exposure, development and degumming in photolithography, reducing costs, and improving processing accuracy and surface smoothness; The machining process is distance-sensitive, and the machining volume can be precisely controlled by precisely controlling the feeding distance of the template.

Description

Method and device for processing complex three-dimensional microstructure on metal surface

(1) Technical field

The invention relates to a microprocessing method using an electrochemical method, in particular to a processing method and a device for performing complex three-dimensional microstructures on a metal surface by using a constrained etchant layer technology.

(2) Background technology

Micromachining technology is the key to MEMS and MEMS technology. There are two types of existing micro-processing technology, one is point-by-point processing technology, such as high-energy beam processing such as laser beam, electron beam and ion beam, micro-EDM and scanning probe microscope (SPM) processing (including STM, SECM) , AFM, etc.). In this type of processing method, the range of each processing is only one point, so the processing efficiency is very low, which is not conducive to batch processing. The other is the batch processing technology of microstructure, such as IC technology, LIGA technology, constrained etchant layer technology, microcontact printing technology, EFAB technology, plasma etching technology and reactive ion etching technology. In this type of technical method, a batch (or an array) of microstructures can be processed at a time. If the microfabrication technology is classified according to the processing environment and medium, one is wet processing and the other is dry processing, and the types of methods are the same as above.

Etching metal materials with IC technology is only suitable for making three-dimensional structures with basically vertical sides (this simple three-dimensional three-dimensional structure should be called 2.5-dimensional to distinguish it from the real complex three-dimensional structure), and it is difficult to achieve absolute vertical , this is because the corrosion of most metal materials in the corrosive solution is isotropic, resulting in lateral undercutting, which causes the lateral expansion of micropores or microchannels. It is precisely because of this that conventional photolithography processes cannot process microstructures with large aspect ratios on metal surfaces. To process complex three-dimensional structures, such as spheres and cones, it is necessary to use multi-step etching, the so-called overlay process, and its resolution is very limited. The photolithography process is inherently quite complicated, and the overlay process composed of multi-step etching is even more complicated. And for ultrafine structures, fine alignment at each step is more difficult.

Microcontact printing (microcontact printing, referred to as μCP) is a research group of Professor Whitesides of Harvard University (Kumar A, Whitesides G M, Appl. , 10:1498.) A micromachining method mainly introduced. This method takes advantage of the high resolution of silicone rubber plastic casting, uses the silicon chip with microstructure as a template, and molds the surface pattern of the microstructure on the surface of silicone rubber, which becomes an elastic "stamp" for subsequent microcontact printing processing. ". Taking the micromachining of gold film as an example, the "seal" is dipped in alkanethiol "ink", and then "stamped" on the surface of the gold film, and the micrographics are printed on the gold surface by this "ink". Alkylthiol "ink" forms a self-assembled molecular monolayer on the gold surface, and this self-assembled molecular monolayer acts as a photoresist in some chemical etching solutions (such as KCN+KOH+O ₂ ), namely It has a barrier effect on chemical etchant. After chemical etching, the same fine structure as the original microstructure is obtained on the gold surface. This technology, like conventional photolithography, is only suitable for making three-dimensional structures with vertical sides, and cannot process complex three-dimensional structures, and it is difficult to manufacture microstructures with large aspect ratios.

Metallic materials can also be processed by combining photolithography with electrochemical anodic dissolution. The advantage of this method (Datta M, J.Elctrochem.Soc.1995, 142:3801-805.) is that it can use less corrosive neutral salt electrolytes, such as Na ₂ SO ₄ , NaCl, NaNO _{3 ,} etc., which are harmful to the environment Small pollution, wide range of applicable materials, fast etching speed. However, there are the following disadvantages: 1) complex three-dimensional structures (such as various curved surfaces) cannot be processed, and the material can only be etched directly up and down (2.5 dimensions); 2) the microstructure of the metal determines its anodic dissolution. Uniformity, generally speaking, the anodic dissolution surface is quite rough, so it is difficult to obtain a microscopically smooth etching surface; 3) The anodic dissolution of metals is generally isotropic, although the etching current distribution can be changed by changing some external Conditions can be controlled to a certain extent, but undercutting under the mask will inevitably occur, which will affect the processing accuracy; 4) It is limited to processing conductive materials.

LIGA --- a method of combining synchrotron radiation X-ray lithography and electrodeposition to manufacture microstructures (Romankiw L T, Electrochimica Acta, 1997, 42: 2985.), known as LIGA technology (abbreviation of Lithografie Galvanoformung Abformung, for Combination process of photolithography, electroforming and casting). It was invented in the late 1980s by researchers at the Karlsruhe Institute for Nuclear Research in Germany. This method can obtain a microstructure with a very high aspect ratio, and the sidewall alignment of the photoetched microstructure is very good. However, the LIGA process has the following disadvantages: 1) it requires an expensive synchrotron radiation X-ray source, which limits its popularization and application; 2) like the conventional photolithography process, it is also difficult to process complex three-dimensional structures, such as Spheres, cones, etc.

EFAB (abbreviation for Electrochemical Fabrication) is the research group of Professor Adam Cohen, Institute of Information Science, University of Southern California (Cohen A, et al, 12th IEEE International Microelectro-mechanical Systems Conference, 1999, Technical Digest, IEEE. Cohen A et al, Solid Freeform Fabrication Symposium1998, Proceedings, The University of Texas at Austin.) Researched in 1999. It is a technology that uses electrochemical methods to fabricate three-dimensional multilayer microstructures. The basic principle of EFAB is: first use 3D CAD software to decompose the graphics to be processed into a series of two-dimensional graphics suitable for making lithography templates, and then a series of masks can be made from them, and then the required metals and The sacrificial layer metal is electrodeposited layer by layer according to the pattern of the mask, and finally the pattern of the desired material is obtained after the sacrificial layer metal is dissolved. Using EFAB technology, if you want to process complex three-dimensional structures, such as hemispheres and cones, you need to make a lot of templates, which is similar to the principle of processing complex three-dimensional structures with conventional photolithography (overlay), and the process is complicated.

People such as Schuster of the Fritz-Haber Institute in Germany reported the application of ultra-short potential pulses for metal microparticles in the 2000 "Science" magazine (Schuster R, Kircher V, Allongue P, Ert G, Science.2000, 289:98.) Processing method. Its basic principle is: in the electrolyte solution, the charging time constant of the electric double layer on the processed workpiece (as the anode) increases with the increase of the solution resistance between the tool electrode (as the cathode) and the processed workpiece, due to The closer the workpiece surface is to the tool electrode, the smaller the solution resistance between the two, and the faster the electric double layer charges. When an ultra-short potential pulse is applied between the workpiece electrode and the tool electrode, within the pulse range, only the electric double layer of the workpiece (anode) directly below the tool electrode is charged to a potential sufficient for anodic dissolution, while the other In other places, due to the long distance, large resistance, and slow charging, no anode dissolution or a very small amount of dissolution occurs, which results in selective dissolution (etching) of the workpiece surface directly below the tool electrode. Through the movement of the tool electrode, it can be processed A simple three-dimensional structure. The disadvantages of this method are: 1) It is quite difficult to generate picosecond-level ultrashort strong pulses; 2) When batch processing complex three-dimensional microstructures on a large plane, the resolution is very low because the current distribution is difficult to control . So far, there is no complex three-dimensional ultrafine metal structure processing method with low cost, simple process, and high batch processing resolution.

(3) Contents of the invention

The present invention aims to provide a processing method and its device which can overcome the above-mentioned shortcomings and are mainly used for processing complex three-dimensional microstructures on metal surfaces.

Processing method of the present invention is:

1). Fix the processing tool with microstructure on the fixed frame;

2). Pour the etching solution into the container;

3) Move the fixed frame to make the processing tool enter the etching solution;

4). Start the electrochemical system to generate etchant on the surface of the processing tool;

5) compressing the etchant layer to a nanoscale or micron-scale thickness using a scavenger in the etching solution;

6). Start the driving device that controls the relative distance between the processing tool and the processed workpiece, and gradually move the processing tool with a micron- or nanometer-thick etchant layer to the processed workpiece. When the etchant on the processing tool When the most protruding point of the enveloping surface of the layer touches the workpiece to be processed, it starts to etch the workpiece to be processed, and the etching makes the surface of the workpiece to be recessed to separate from the etchant layer, and the etching stops;

7) The driving device continuously moves the processing tool to the workpiece to keep the etchant layer in contact with the workpiece, so that the etching continues. When the etching is completed, the processing tool leaves the surface of the workpiece.

The metal surface complex three-dimensional microstructure processing device of the present invention is provided with processing tool, fixed frame, driving device, information processing computer, electrochemical system, and processing tool is fixed on the bottom of fixed frame, and the top of fixed frame is connected to the vertical of driving device. An axis micro-drive controller, and a vertical-axis micro-drive controller connected to an information processing computer. The electrochemical system is equipped with a potentiostat, an auxiliary electrode, a reference electrode, and a container. The etching solution is placed in the container, and the processing tool and the fixing frame are connected to the potentiostat as the working electrode of the potentiostat. The connection between the auxiliary electrode and the reference electrode One end is connected to a potentiostat, the other end is inserted into the etching solution in the container, and the container is set on the horizontal axis micro-drive controller of the driving device.

Among them, the processing tool can adopt a template with high-resolution complex three-dimensional graphics.

The workpiece to be processed is a metal material, and the driving device is used to control the relative distance between the template and the workpiece. The etching solution contained in the container (the container can use an electrolytic cell, etc.) immerses the above-mentioned template and workpiece, and can generate etchant under specific conditions, and the relevant electrochemical system is used to cause the etching solution on the surface of the template to generate related The electrochemical reaction generates an etchant that can etch the workpiece. The etching solution contains a scavenger (or capture agent), which can react rapidly with the etchant on the surface of the template in the etching solution to make the etching The life of the agent is shortened. Due to the shortened lifetime of the etchant, it can only diffuse for a short distance, so the etchant layer formed on the surface of the template is extremely thin, which is called a constrained etchant layer. The enveloping surface of this constrained etchant layer preserves the complex three-dimensional pattern of the template at extremely high resolution.

Said template has a microstructure that is complementary to the microstructure that needs to be processed on its surface; it can also be an extremely smooth plane (a limit of the microstructure) (roughness Ra＜5nm), and its complementary microstructure is also extremely smooth. smooth surface.

The template can be made of an inert conductive material or a non-conductive material covered with a conductive film, and the inert conductive material will not be chemically or electrochemically corroded in the etching solution and under the electrode potential of the etchant. Said inert conductive material is one of platinum or gold.

The material of the workpiece to be processed can be metals such as copper, nickel, aluminum, titanium and cadmium.

Said fixing frame can be made of stainless steel, and the part immersed in etching solution is insulated and protected by corrosion-resistant coating.

The processing tool with the microstructure (eg template) is fixed on the holder mechanically or with conductive glue. The fixture (together with the processing tool, such as the template) is mounted on a computer-controlled drive.

The drive device is equipped with a feed system or a drive controller that can perform nanoscale steps in the three directions of X, Y, and Z, so as to control the relative distance and position between the processing tool and the workpiece.

Said electrolytic cell is installed on the horizontal workbench where the XY of the driving device is the driving controller, and its position is below the fixed frame.

The etching solution contains one of Fe ⁺² , Cl ^-1 , NO ₃ ^-1 , NO ₂ ^-1 , SO ₃ ^-2 , SO ₄ ^-2 , PO ₃ ^-3 , OH ^- or F ^-1 One or more species, the concentration range is 0.01-1M. An etching solution is contained in an electrolytic cell.

The workpiece to be processed is placed horizontally on the bottom of the electrolytic cell.

The electrochemical system includes a potentiostat, a working electrode, an auxiliary electrode and a reference electrode, which play the role of controlling the potential or controlling the current. When the template or processing tool is used as the working electrode in the system, it can cause the relevant electrochemical reaction of the etching solution on the surface of the template to generate an etchant that can etch the workpiece.

The template is connected to the electrochemical system as a working electrode through a conductive stainless steel holder.

The production mode of said etchant can be expressed as:

R→O+ne (1)

Here, the template or machining tool acts as the anode. R is one or more of the components listed in the etching solution, O is an etchant, n is the number of electrons, and e is an electron.

Said etchant can also be generated photoelectrochemically:

R(+hv)→O+ne (2)

The scavenger (or capture agent) may be one or a combination of SnCl ₂ , hydroquinone, KHB and NaOH. The removal reaction of the scavenger (or capture agent) to the etchant O can be expressed as:

O+S→R+Y (3)

Here, S is a scavenger, also known as a capture agent, Y is a reaction product, and S, R and Y have no etching effect.

The scavenging reaction of etchant O can also be completed by the decomposition and deactivation reaction of O itself:

O→Y (4)

Here, Y is the reaction product.

The so-called constrained etchant layer is due to the removal of the etchant by the scavenger (or capture agent), the life of the etchant is shortened and it can only diffuse for a short distance, so it can only form an extremely thin layer on the surface of the template. The etchant layer, called the constrained etchant layer, generally has a thickness of nanometer or micrometer, and the specific thickness depends on the rate constant of the removal reaction. The enveloping surface of this constrained etchant layer preserves the complex three-dimensional pattern of the template at extremely high resolution.

The innovations and advantages of the present invention are: 1) batch replication processing of various complex three-dimensional microstructures (such as hemispherical surfaces, conical surfaces, etc.); The complex process of gluing, exposure, development and final degumming in the process does not require a multi-step overlay process to process complex three-dimensional microstructures, which greatly reduces costs and improves processing accuracy and surface smoothness; 3) Processing process With distance sensitivity, the processing amount can be precisely controlled by precisely controlling the feeding distance of the template, instead of relying on the estimated etching time and etching speed to control the processing amount. If the amount of processing is controlled by controlling the etching time and etching speed, all factors affecting the etching reaction speed must be controlled. But to control the processing amount by controlling the distance, you only need to control the feed distance of the template, which belongs to single-parameter control. The current piezoelectric ceramics can precisely control the single-step displacement to the nanometer level, so we can obtain the processing size and precision we need; 4) The original surface flatness of the processed material is not high, and the final processing surface depends on the template or The surface accuracy of the processing tool, but the template does not need to be in contact with the material to be processed; 5) Different "etching-constraint" systems can be selected to process different materials, including metal and non-metal materials, conductors and non-conductor materials; 6) No High energy beam machining can cause damage or modification to the adjacent area of the machined surface.

Comparing the characteristics of the above-mentioned constrained etchant layer technology, it can be seen that the constrained etchant layer technology has unique advantages in processing complex three-dimensional structures.

(4) Description of drawings

Fig. 1 is a schematic diagram of the composition of an embodiment of the processing device of the present invention.

Fig. 2 is a structural schematic diagram of the driving device of the processing device of the present invention.

Fig. 3 is a schematic diagram of the processing process of the present invention.

(5) specific implementation

The following embodiments will further illustrate the present invention in conjunction with FIGS. 1 and 2 .

Fig. 1 shows the composition schematic diagram of the processing device embodiment of the present invention. The processing tool adopts a template 5 with high-resolution complex three-dimensional graphics, and the template 5 is fixed on the lower part of the metal fixing frame 4. The metal frame 4 can adopt two sections of cylinders with different diameters, and its upper part is connected to the Z-axis (vertical Axis) micro-drive controller 2, Z-axis micro-drive controller 2 is connected with information processing computer 3. The electrochemical system is equipped with a potentiostat 1, an auxiliary electrode 8, a reference electrode 9, an etching solution 10, an electrolytic cell 11, etc. In fact, the template 5 can also be regarded as a component of the electrochemical system, and the template 5 passes through the metal fixing frame 4 is connected to the potentiostat 1 and becomes the working electrode. The auxiliary electrode 8 and the reference electrode 9 are inserted into the etching solution 10 , and the etching solution 10 is filled into the electrolytic cell 11 . The electrolytic cell 11 is arranged on the XY axis (horizontal axis) micro-drive controller 7 of the driving device. The processed material 6 is placed in the electrolytic cell 11 . Referring to Fig. 2, the driving device includes a Z-axis micro-drive controller and an XY-axis micro-drive controller. The micro-positioning workbench 22 is connected, and the two ends of the cantilever beam 23 are respectively connected with the micro-positioning workbench 22 and the template holder 4, and the template 5 is fixed on the lower end of the holder 4. The XY plane motion table 71 of the XY axis micro-drive controller is arranged on the base 72 .

The basic principle of the present invention is: in the electrolyte, etchant O is produced on the surface of the template (or microprocessing tool) with complex three-dimensional microstructure by electrochemical reaction or photochemical reaction, for example:

1. Electrochemical method (template or processing tool is anode): see formula (1).

2. Photoelectrochemical method: see formula (2), where R is the reduced state of the etchant O.

Due to the addition of a chemical reagent (called a capture agent) that can reduce the etchant O to the electrolyte and make it lose its etching activity, the lifetime of the etchant O is greatly shortened through such a homogeneous capture reaction, so that it cannot The template diffuses farther away, so the thickness of the etchant layer is constrained (or compressed) within a small range (micron or nanometer) close to the template or processing tool. It is also possible to constrain the thickness of the etchant O diffusion layer by decomposing deactivation reactions, such as:

1. Homogeneous capture reaction: see formula (3).

2. Decomposition or deactivation reaction: see formula (4). In the formula, S is a binding agent, also known as a capture agent. Y is the reaction product. For the above two types of reactions, the thickness μ of the constrained etchant layer is approximately:

μ=(D/K _s ) ^1/2 (5)

where D is the diffusion coefficient of the etchant in the liquid phase, and _KS is the pseudo-first-order reaction rate constant of the bound reaction.

We can use the above-mentioned template or processing tool 5 with a micron or nanoscale thickness etchant layer to etch the substrate M (as shown in FIG. 3 ). Let the template or processing tool gradually approach the surface of the substrate material, and when the etchant layer on the template or processing tool touches the substrate material, the substrate will be etched, as shown in Figure 3b (as shown in Figure 3a before etching) :

O+M→R+P (6)

Here, M is the matrix material, R is the reduced state of the etchant O, and P is other reaction products.

As the substrate is continuously etched, in order to ensure that the constrained etchant layer can continue to contact the substrate and etch the substrate, the precision driving device needs to continuously move the template towards the substrate. (as shown in Figure 3c).

Finally, when the microstructure is completely etched (as shown in FIG. 3d ), the template leaves the substrate surface (as shown in FIG. 3e ).

When processing with processing tools, this method can process complex three-dimensional microstructures of arbitrary shapes. When processing with templates, this method can process complex three-dimensional microstructures complementary to templates, and the processing accuracy is at the nanometer level.

Claims (3)

1. the working method of metallic surface complicate three dimension microstructure is characterized in that the complete processing step is:

1). the machining tool that will have microstructure is fixed on the anchor;

2). according to the difference of institute's processing metallic, different etching solutions is injected container; The metal of being processed is nickel, aluminium and titanium;

3). mobile anchor makes machining tool enter this etching solution;

4). start electro-chemical systems, according to different etching solutions, produce different etching agents on the machining tool surface, the producing method of said etching agent is expressed as: R → O ten ne; R is the ortho states of going back of O, and O is an etching agent, and n is an electronic number, and e is an electronics;

Said etching solution contains Fe ^{+ 2}, Cl ^-1, NO ₃ ^-1, NO ₂ ^-1, SO ₃ ^-2, SO ₄ ^-2, PO ₃ ^-3, OH ^-Or F ^-1Among one or more, its concentration range is 0.01～1M;

5) add different scavenging agents in the different etching solution, utilize the scavenging agent in the solution that the etching agent lamination is reduced to nano level or micron order thickness; Scavenging agent is expressed as the cleaning reaction of etching agent O: O+S → R+Y, and wherein, S is scavenging agent or trapping agent, and Y is a reaction product, and S, R and Y all do not have corrasion; Said scavenging agent or trapping agent are at least a among Resorcinol, KHB and the NaOH;

6). the drive unit of relative distance between start-up control machining tool and the workpiece to be machined, the machining tool that will have the etching agent layer of micron or nanometer grade thickness progressively moves to workpiece to be machined, when the protruding point of the etching agent layer enveloping surface on the machining tool touches workpiece to be machined, promptly begin workpiece to be machined is carried out etching, make workpiece surface break away from the etching agent layer thereby etching is removed the part material on workpiece to be machined surface, etching promptly stops;

7) drive unit constantly moves machining tool keeping the etching agent layer to contact with workpiece to be machined all the time to workpiece to be machined, thereby etching is constantly carried out, and finishes to etching, and machining tool leaves the workpiece to be machined surface.

2. metallic surface as claimed in claim 1 complicate three dimension microstructure processing unit (plant), it is characterized in that being provided with machining tool, anchor, drive unit, information processing computer, electro-chemical systems, machining tool is fixed in the bottom of anchor, the top of anchor connects the little driving governor of Z-axis of drive unit, and the little driving governor of Z-axis connects the information processing computer; Electro-chemical systems is provided with potentiostat, supporting electrode, reference electrode, container, the etching solution of packing in the container, machining tool and anchor are connected to potentiostat as the working electrode of potentiostat, one termination potentiostat of supporting electrode and reference electrode, the other end inserts in the interior etching solution of container, and container is located on the little driving governor of transverse axis of drive unit; Said machining tool adopts the template that has high resolving power complex three-dimensional solid figure; Said template surface has the microstructure complementary microstructure with required processing; Or be the plane of dead smooth, its roughness Ra＜5nm, its complementary microstructure also is the plane of dead smooth, its roughness Ra＜5nm;

Said template adopts inactive, conductive material or for non-conducting material covers with the inactive, conductive material film, and in etching solution and under the electropotential that produces etching agent, this inactive, conductive material does not take place chemical or galvanic corrosion; Said inactive, conductive material is platinum or gold.

3. metallic surface as claimed in claim 2 complicate three dimension microstructure processing unit (plant), it is characterized in that said drive unit is provided with feed system or the driving governor that carries out the nano level stepping in X, Y, three directions of Z, with relative distance and position between control machining tool and the workpiece.

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