CN101475135A - Method for preparing high depth-to-width ratio carbon micro electro-mechanical device - Google Patents
Method for preparing high depth-to-width ratio carbon micro electro-mechanical device Download PDFInfo
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- CN101475135A CN101475135A CNA2009100605554A CN200910060555A CN101475135A CN 101475135 A CN101475135 A CN 101475135A CN A2009100605554 A CNA2009100605554 A CN A2009100605554A CN 200910060555 A CN200910060555 A CN 200910060555A CN 101475135 A CN101475135 A CN 101475135A
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Abstract
The invention relates to a method for preparing a carbon micro electromechanical device with high depth-to-width ratio, belongs to a method for preparing a carbon micro structural device, and solves the problems that the micro electromechanical device with high depth-to-width ratio prepared by the prior method has complex process and high cost and is easy to separate from a substrate. The method comprises: (1) a preparation step; (2) a substrate etching step; (3) a pretreatment step; (4) a glue evening step, (5) an exposure step; (6) a development step; and (7) a pyrolysis step. The method combines photoetching and pyrolysis of thick glue to obtain the carbon micro electromechanical device with the high depth-to-width ratio applied to a micro electromechanical system, and has the characteristics of simple process, fine patterns, firm structure, no special requirement on equipment, and low cost; and the prepared device has high combination strength with the substrate and long service life, and can be used as an microelectrode applied to the MEMS fields such as micro battery, biological chip, micro electrochemical sensor, and the like.
Description
Technical field
The invention belongs to the preparation method of carbon micro structural component, be specifically related to a kind of preparation method of high depth-to-width ratio carbon micro electro-mechanical device.
Background technology
Material with carbon element is applied to MEMS (microelectromechanical system MEMS) has caused lot of domestic and foreign scholar's concern in recent years.Carbon is a kind of very common element that acquires a special sense again of occurring in nature, diamond, graphite, coke, vitreous carbon, and bucky-ball (C60) and the CNT that receives much attention recently, carbon nano-fiber etc. with special construction all are existence forms of carbon.Just because of this, just make material with carbon element be widely used in physics, chemistry, mechanics, calorifics and person in electronics.Selecting material with carbon element for use is innovation on MEMS development material again for decades.The advantage of material with carbon element is significant, and it has than the electrochemical stability window of the more perfect lattice structure of silicon, broad, chemical inertness, good bio-compatibility and electrical and thermal conductivity, and its preparation method is easy simultaneously, cost is low.There are some researches show, with the carbon film that obtains behind the photoresist high temperature pyrolysis, its character is similar to vitreous carbon (glassy carbon), have bio-compatibility, comprising that very application prospects is arranged on the microdevice that micro cell, biological MEMS, little electrochemical sensor etc. play a decisive role with electrode.
The preparation of material with carbon element micro-structural originates from the petrochemistry field, is to generate material with carbon element by organic gas is carried out high-temperature heat treatment; Also the someone uses advanced technologies such as FIB, reactive ion etching technology to prepare carbon structure, but this method is not only time-consuming but also expensive.Recently, little manufacture method of some unconventional carbon structures is in the news.People such as G.M.Whitesides are at " Fabricationand Characterization of Glassy Carbon MEMS " literary composition (Chemistry of Materials, 1997, Vol.9:1399-1406) reported with the method for soft lithographic and prepared vitreous carbon, they carry out moulding with resin material (as: furfuryl alcohol) in the rubber microscopic model, then put it into heating (500～1100 ℃) in the inert atmosphere, can make it to change into vitreous carbon.But this method still exists flow process complexity, shortcoming that cost is high, has limited its development prospect.
The preparation high aspect ratio microstructures is the research focus and the challenge in MEMS field always.For microelectrode, electrochemical reaction will be carried out in its surface, so the high-aspect-ratio electrode can bring the lifting of device performance.Yet present most microelectrode is the planar electrode structure of low depth-to-width ratio, and thickness of electrode is no more than the hundreds of nanometer, so the problem of plane electrode ubiquity small throughput., the past nearly all needs to apply high voltage and complicated technology though also having the trial of many raising plane electrode flux.Three-diemsnional electrode with high-aspect-ratio then can easily address this problem.
In the MEMS manufacture method, photoetching, electroforming and Shooting Technique (LIGA) are to make high-aspect-ratio three-dimensional structure successful method the most at present.By precipitous, the surfacing of the prepared three-dimensional structure device side wall of this technology, thickness can reach hundreds of to thousands of microns.But its needed synchrotron radiation light source and special mask version are very expensive, a series of LIGA alternative techniques has appearred at present, for example use full-bodied SU-8 photoresist to make the micro-structural of high-aspect-ratio, see people's such as LORENZ H paper " High-aspect-ratio; ultrathick, negative-tone near-UV photoresist anditsapplication for MEMS ", (Sensors and Actuators, 1998, Vol.64:33-39).The SU-8 photoresist can make depth-to-width ratio and reaches micro-structural more than 20 in theory.In addition, the SU-8 photoresist also has superior performance, and it not only has good mechanical mechanical performance and light plasticity, also has corrosion resistance, heat endurance preferably.
The micro-structural of using the SU-8 photoresist to make the superelevation depth-to-width ratio is a challenging problem always.The method of utilization mainly contains at present: embedded metal mask plate (3) modelling is used in (1) multiexposure, multiple exposure/development (2).But these three kinds of methods all can not obtain gratifying effect.First method causes top layer overexposure and bottom to cross the aliasing that heating causes easily, second kind then needs to carry out photoresist and metal alternating deposition loaded down with trivial detailsly, uses deep reaction ion etching (DRIE) and inductively coupled plasma (ICP) to carve deep hole on silicon chip and the situation that photoresist is difficult to flow into deep hole then often occurs as the method for photoresist microscopic model.
At the micro-electro-mechanical systems microelectronic of unifying, interface delamination (Delamination) phenomenon between the different materials often occurs, and causes the inefficacy of device and system.For using the SU-8 photoresist, if will make the micro-structural for preparing will be applied to reality, a very big problem that faces is the delamination (desorption) between micro-structural and substrate.If directly make SU-8 glue micro-structural on smooth substrate, along with the increase of micro-structural depth-to-width ratio, micro-structural is very easily collapsed in subsequent operation.The processing step that causes micro-structural to collapse easily mainly is a development operation.Because the SU-8 photoresist layer thickness that applies can reach hundreds of microns, the exposure dose that the bottom photoresist is accepted during with common ultraviolet source photo-etching machine exposal is often not enough, the intensity that " crossing erosion " phenomenon and photoresist take place the root that links to each other with substrate in micro-structural when causing development is also not enough, and this will cause the attachment surface of micro-structural and substrate and adhesive force to reduce.Add the vibration (also being aided with sonic oscillation sometimes) of developer solution when developing, very easily cause micro-structural and substrate to break away to cause and collapse to help development thoroughly.In addition, because the thermal coefficient of expansion of substrate and photoresist has very big difference, variations in temperature can make SU-8 photoresist generation thermal stress, also causes micro-structural generation buckling deformation easily and breaks away from substrate.As can be seen from the above analysis, in order to reduce peeling off of micro-structural, the adhesive force that improves between micro-structural and substrate is crucial.Conventional solution is that substrate is carried out surface treatment, and applying chemical adhesion promoter increases adhesion.But chemical adhesion promoter can only guarantee that device can effectively adhere to substrate at short notice and can not guarantee that device also has enough adhesions at long-term back and the substrate of using.
Summary of the invention
The invention provides a kind of preparation method of high depth-to-width ratio carbon micro electro-mechanical device, solve the problem of high-aspect-ratio micro electro mechanical device complex process, cost height and easy and the substrate desorption of existing method preparation.
The preparation method of a kind of high depth-to-width ratio carbon micro electro-mechanical device of the present invention, its step comprises:
(1) preparation process: at silicon chip superficial growth one deck SiO
2Layer perhaps directly selects for use the surface to have SiO
2The silicon chip of layer;
(2) substrate etch step: utilize photoetching process, the SiO of etch silicon substrate surface
2Layer is produced little hole figure SiO
2Mask; Use SiO again
2Mask etches little hole on silicon chip;
(3) pre-treatment step: the silicon chip to the good little hole of etching carries out the hydrophobization preliminary treatment;
(4) even glue step: on sol evenning machine,,, the silicon chip behind the even glue is carried out preceding baking handle until reaching the desired thickness glue-line to the even glue of pretreated silicon chip;
(5) step of exposure: the silicon chip after preceding baking handled is aimed at exposure, and the exposure area is overlapped with micro-pit array on the silicon chip, dries by the fire processing at once silicon chip being carried out after the exposure;
(6) development step: the silicon chip after the centering baking is handled develops, and whether the developer solution that constantly vibrates during development is removed fully with the unexposed glue-line in isopropyl alcohol check silicon chip surface; Carrying out the back baking after development is finished handles;
(7) pyrolysis step: will put into vacuum tube furnace through the silicon chip that baking is later handled and divide three temperature that progressively raise to carry out pyrolysis, and obtain high depth-to-width ratio carbon micro electro-mechanical device.
Described preparation method is characterized in that:
In the even glue step, used glue is the SU-8 negative photoresist; When preceding baking was handled, 65 ℃～95 ℃ of temperature heated 40～60 minutes;
In the described step of exposure, when middle baking was handled, 65 ℃～95 ℃ of temperature heated 20～25 minutes;
In the described development step, used developer solution is the special-purpose developer solution of SU-8 negative photoresist; When the back baking was handled, 110 ℃～130 ℃ of temperature heated 1～3 minute.
Described preparation method is characterized in that:
In the described pyrolysis step, the described branch process that temperature carries out pyrolysis that progressively raises for three times is: at first be raised to 250 ℃～300 ℃ from room temperature, be incubated 20～30 minutes; Be warmed up to 500 ℃～600 ℃ then, be incubated 20～30 minutes; Then be warmed up to 900 ℃～1000 ℃, be incubated 60～80 minutes; Naturally cool to room temperature at last; Whole process is at anaerobic and N
2Carry out in the atmosphere.
Among the present invention, the applicant selects for use the negative glue of SU-8 to obtain the cylindric carbon micro electro-mechanical device of high-aspect-ratio by thick resist lithography technology and three step pyrolytic processes.Because the micro-structural contraction is less after the pyrolysis, mainly is exactly to improve microstructure height so improve depth-to-width ratio.In order to improve carbon post height, the applicant has changed the technological parameter of even glue and has attempted reducing the method for sparing glue rotating speed and twice even glue.For SU-8 2100, the even glue-line maximum ga(u)ge that the reduction rotating speed can reach is about 280um, and twice even glue can greatly improve depth-to-width ratio to 20:1.Thick resist lithography is very responsive to technological parameter.Time for exposure also should increase when bondline thickness increases, and T shape top occurs but the glue column top then easily overexposure takes place.And this very high glue post pole easily collapses and cause the top to link to each other.The reason that produces this phenomenon is because the glue post is too high, and light is not easy to arrive the glue column bottom during exposure, causes the under-exposed easy deliquescing when developing in bottom.At last, rocking developer solution during development tempestuously causes the hypodynamic glue post of bottom support to collapse and the top links to each other.Therefore wanting success prepares high aspect ratio structure, and technological parameters such as exposure dose, developing time and baking condition are extremely important.
The present invention adheres to for SU-8 photoresist micro-structural by the little hole that etches a certain size and shape on substrate, make and produce chimeric mechanism between substrate and the micro-structural, the adhesion interface is played the effect of physical restriction desorption, thereby improved the bond strength between micro-structural and the substrate greatly, improved the service life of micro-structural.Prepared the little carbon electromechanical device that depth-to-width ratio reaches 10:1.
Specifically, the present invention adopts three step pyrolytic processes that sample is carried out pyrolysis, can reduce pyrolysis effectively and finishes the residual stress in the carbon structure of back and the quantity of microcrack, thereby reduce the phenomenon that the generation micro-structural is peeled off from substrate, increases the service life.In order to avoid oxygen in the boiler tube as far as possible, before heating up, three step pyrolysis utilize vavuum pump boiler tube to be vacuumized and feeds the N2 air-flow to the influence of pyrolysis.According to three step pyrolytic process temperature-rise periods sample is heat-treated then, to reach the purpose of pyrolysis.Last annealing naturally keeps feeding N
2Air-flow is cooled to room temperature fully until sample.
In sum, the present invention combines thick resist lithography with pyrolysis, make the carbon micro electro-mechanical device of high-aspect-ratio, apply in the MEMS, have that technology is easy, figure is meticulous, sound construction, equipment had special requirement, the characteristics that cost is low, device that makes and substrate bond strength height, long service life can be used as microelectrode and is applied in the MEMS fields such as minicell, biochip, miniature electrochemical.
Description of drawings
Fig. 1 (a) is the silicon chip vertical view after the etching;
Fig. 1 (b) is the silicon chip schematic cross-section after the etching;
Fig. 2 (a) is the SEM photo of SU-8 glue post array before embodiment 1 pyrolysis;
Fig. 2 (b) is the SEM photo of corresponding carbon post array after embodiment 1 pyrolysis;
Fig. 3 is the SEM photo of the carbon post array that obtains after embodiment 2 pyrolysis.
The specific embodiment
The present invention is further described below in conjunction with embodiment.
Embodiment 1:
(1) preparation process: use thermal oxidation method at 2 cun silicon chip surfaces growth one deck SiO
2Layer, thickness 20nm with acetone and deionized water thoroughly after the cleaning, is placed on that baking 10min makes its bone dry on 200 ℃ of hot plates;
(2) substrate etch step: use KW-4A type sol evenning machine (microelectronics center research department of the Chinese Academy of Sciences) at SiO
2Apply one deck BP218 eurymeric photoresist (Beijing Inst. of Chemical Reagent) on the layer, carry out photoetching (used litho machine model is Karl Suss MA6), just on photoresist, produced the figure of micro-pit array again through developing with 1# mask version; Then with remaining photoresist layer as mask, with the dilution HF solution (HF:H
2O=1:7) erode the SiO that exposes
2, remaining SiO
2Layer is just as the mask layer that corrodes silicon chip; Etching Si adopts TMAH (tetramethyl aqua ammonia) corrosive liquid, just after finishing, etching obtained little hole of required form, shown in Fig. 1 (a), Fig. 1 (b);
(3) pre-treatment step: with putting it into dense H behind the deionized water rinsing silicon chip
2SO
4With H
2O
2Mixed liquor (2:1) boils 15min at 80 ℃, rinses well with deionized water, uses HF solution (HF:H then
2O=1:20) silicon chip surface is carried out hydrophobization and handle, use a large amount of deionized water rinsings afterwards; Substrate is placed on 200 ℃ of hot plates at last and toasts 15min, the dring silicon substrate;
(4) even glue step: applying SU-8 2100 negative photoresists on to pretreated silicon chip on the KW-4A type sol evenning machine, sol evenning machine is earlier with low speed 500r/min rotation 15s, again with high speed 1350r/min rotation 30s, the thick 250um that is about of gained glue; Behind the even glue silicon chip is carried out preceding baking and handle, 65 ℃ of temperature heated 60 minutes; Preceding baking process makes solvent evaporates, makes glue-line be fixed up, glue-line and mask plate adhesion when then easily causing exposing as if preceding baking deficiency, the excessive photoresist molding effect that easily influences again of preceding baking; Preceding baking processing finishes the back cooling and carried out next step operation in 10 minutes again.
(5) step of exposure: the silicon chip after preceding baking handled uses 2# mask version to aim at exposure (used litho machine model is Karl Suss MA6), and the exposure area is overlapped with micro-pit array on the silicon chip, and exposure dose is 325mJ/cm
2, baking is handled in time silicon chip being carried out after the exposure; When middle baking was handled, 65 ℃ of temperature heated 25 minutes; Glue-line easily fold occurs because of being heated suddenly when silicon chip is put hot plate, silicon chip can be taken off cooling this moment and heat a moment again; Exposure and two steps of middle baking combine just can make SU-8 illumination part full cross-linked, if not obvious these two steps that then illustrate of figure are carried out insufficient; Middle baking finishes the back cooling and carried out next step operation in 10 minutes again.
(6) development step: the silicon chip after the centering baking is handled develops, developer solution is the supporting special-purpose developer solution of SU-8 photoresist, because glue-line is thicker, developer solution will constantly vibrate during development, to assist with sonic oscillation in case of necessity, fully wash away the photoresist of unexposed portion; Use isopropyl alcohol flushing print after having developed,, should put into the developer solution continuation and develop, whether remove fully with the unexposed photoresist of this repeated examinations if it is underdevelop the white film explanation to occur; Use deionized water lavage specimens sheet at last, and carry out the back baking and handle, 110 ℃ of temperature heated 3 minutes; The whole operation time is unsuitable long in case photoresist oxidation in air.More than each the step technological parameter as shown in table 1:
The thick resist lithography technological parameter of table 1 embodiment 1 (SU-8 2100 type photoresists)
(7) pyrolysis step: will put into GSL-1400X type vacuum tube furnace (high temperature Instr Ltd. of Luoyang Weida) through the silicon chip that baking is later handled, and divide three temperature that progressively raise to carry out pyrolysis, and obtain high depth-to-width ratio carbon micro electro-mechanical device.Detailed process is:
(7-1) vacuumizes, and vacuum reaches 10
-3Tor, purpose is to discharge oxygen in case photoresist structure is burnt;
(7-2) feed nitrogen with 2000 mark condition milliliter per minutes (sccm), and purpose is further to discharge unnecessary oxygen;
(7-3) are raised to 250 ℃ from normal temperature with 3 ℃/min of heating rate, and insulation 30min continues to feed nitrogen with 2000sccm; This process reaches the post bake effect in order that further removing steam strengthens adhering to, and with lower heating rate and 250 ℃ of maintenance 30min, is for post bake is fully carried out;
(7-4) then are raised to 500 ℃ with 5 ℃/min of heating rate from 250 ℃, and insulation 30min continues to feed nitrogen with 2000sccm; Thermal decomposition mainly occurs in this temperature range, and the quality of photoresist is shunk also maximum; Adopt lower heating rate to help abundant pyrolysis of photoresist and emission gases accessory substance; Insulation 30min is in order to make the violent glue-line of exhaust reaction be stablized a period of time, thereby makes nitrogen fully take away gaseous by-product, in order to avoid glue-line generation deformation;
(7-5) are warmed up to 900 ℃ with 10 ℃/min of heating rate from 500 ℃ at last, and feed nitrogen (95%)/hydrogen (5%) and be incubated 80min this moment, makes the glue-line carbonization more thorough, and resistivity is lower; The effect of hydrogen is further to reduce oxygen content in the mist;
Make silicon chip naturally cool to room temperature after (7-6) pyrolysis is intact,, continue simultaneously to feed nitrogen, not only can quicken cooling, and can take away the oxygen on pyrolytic carbon layer surface with 2000sccm to reduce the internal stress of film.
Set temperature-rise period and be, keep environment temperature to be lower than the vitrification point that glue-line progressively rises all the time, prevent glue-line generation flow distortion for the reason that progressively rises rather than settle at one go.Three step pyrolysis main technologic parameters are listed in the table 2 in the present embodiment.
The three-step approach pyrolytic process parameter of table 2 embodiment 1
Prepare the carbon micro electro-mechanical device that depth-to-width ratio is about 10:1 by above-mentioned technological process, shown in Fig. 2 (b), the glue post before the pyrolysis is shown in Fig. 2 (a).As can be seen from the figure, the carbon structure edge is comparatively neat, and sidewall is steep, does not have adhesion phenomenon between the electrode.Generate phenol, cresols, C in the pyrolytic reaction
2H
5, multiple organic matter such as isopropyl-phenol, isopropenyl phenol, bisphenol-A and discharged with gaseous form, so carbon structure shrinks to some extent, and shrink and mainly occur in vertically, cross-direction shrinkage is then less relatively, so the depth-to-width ratio of carbon post reduces to some extent after the pyrolysis.This material with carbon element process SEM micro-area composition analysis that is obtained by pyrolysis draws its carbon content rate and is about 93.6%.Utilize the four point probe instrument to record square resistance and be about 2.5 Ω/, resistivity is about 1.56 * 10
-5Ω m illustrates that electric conductivity is good.
For the firm degree that test component combines with silicon chip, the applicant puts into 40% KOH solution with silicon chip and soaks, and keeping solution temperature is 80 ℃, judges adhering power by the time of test glue-line and substrate generation desorption.Doing like this is to consider that the carbon microelectrode need be immersed in the various solution usually in the practical application, as electrolyte, biological solution etc., and this liquid environment that KOH solution immersion test is simulated just.In the KOH solution of heating, the Si substrate of print can be corroded and produce H
2, the print immersion wherein and at 80 ℃ was kept about 5 hours.Si can be corroded in KOH solution and produce hydrogen.Along with bubble overflows, can produce pull-out force to micro-structural, if adhesive force inadequately greatly then be difficult to resist desorption.Experimental result shows, it is chimeric to have added micromechanics, and the ability that micro-structural opposing KOH solution soaks is more intense, up to SiO
2Layer and following Si layer are caused the micromechanics telescoping part to lose efficacy by the KOH solution corrosion, and the carbon micro-structural just comes off from substrate, proves that chimeric can the assurance effectively of micromechanics has very high bond strength between micro-structural and the substrate.
Embodiment 2:
(1) preparation process: use thermal oxidation method at 2 cun silicon chip surfaces growth one deck SiO
2Layer, thickness 20nm with acetone and deionized water thoroughly after the cleaning, is placed on that baking 10min makes its bone dry on 200 ℃ of hot plates;
(2) substrate etch step: use KW-4A type sol evenning machine (microelectronics center research department of the Chinese Academy of Sciences) at SiO
2Apply one deck BP218 eurymeric photoresist (Beijing Inst. of Chemical Reagent) on the layer, carry out photoetching (used litho machine model is Karl Suss MA6), just on photoresist, produced the figure of micro-pit array again through developing with 1# mask version; Then with remaining photoresist layer as mask, with the dilution HF solution (HF:H
2O=1:7) erode the SiO that exposes
2, remaining SiO
2Layer is just as the mask layer that corrodes silicon chip; Etching Si adopts TMAH (tetramethyl aqua ammonia) corrosive liquid, just after finishing, etching obtained little hole of required form, shown in Fig. 1 (a), Fig. 1 (b);
(3) pre-treatment step: with putting it into dense H behind the deionized water rinsing silicon chip
2SO
4With H
2O
2Mixed liquor (2:1) boils 15min at 80 ℃, rinses well with deionized water, uses HF solution (HF:H then
2O=1:20) silicon chip surface is carried out hydrophobization and handle, use a large amount of deionized water rinsings afterwards; Substrate is placed on 200 ℃ of hot plates at last and toasts 15min, the dring silicon substrate;
(4) even glue step: applying the SU-82100 negative photoresist on to pretreated silicon chip on the KW-4A type sol evenning machine.Set the low speed 500r/min of sol evenning machine elder generation rotation 15s high speed 1350r/min rotation 30s again, the thick 250um that is about of gained glue.Behind the even glue silicon chip is carried out preceding baking and handle, 95 ℃ of temperature heated 40 minutes; Preceding baking process makes solvent evaporates, makes glue-line be fixed up, glue-line and mask plate adhesion when then easily causing exposing as if preceding baking deficiency, the excessive photoresist molding effect that easily influences again of preceding baking; Preceding baking finishes the back cooling and carried out next step operation in 10 minutes again.
(5) step of exposure: the silicon chip after preceding baking handled uses 2# mask version to aim at exposure (used litho machine model is Karl Suss MA6), and the exposure area is overlapped with micro-pit array on the silicon chip, and exposure dose is 325mJ/cm
2, baking is handled in time silicon chip being carried out after the exposure; When middle baking was handled, 95 ℃ of temperature heated 20 minutes; Glue-line easily fold occurs because of being heated suddenly when silicon chip is put hot plate, silicon chip can be taken off cooling this moment and heat a moment again; Exposure and two steps of middle baking combine just can make SU-8 illumination part full cross-linked, if not obvious these two steps that then illustrate of figure are carried out insufficient; Middle baking finishes the back cooling and carried out next step operation in 10 minutes again.
(6) development step: the silicon chip after the centering baking is handled develops, and developer solution is the supporting special-purpose developer solution of SU-8 photoresist; Because glue-line is thicker, the developer solution that will constantly vibrate during development will be assisted with sonic oscillation in case of necessity, fully washes away the photoresist of unexposed portion; Use isopropyl alcohol flushing print after having developed,, should put into the developer solution continuation and develop, whether remove fully with the unexposed photoresist of this repeated examinations if it is underdevelop the white film explanation to occur.Use deionized water lavage specimens sheet at last, and carry out the back baking and handle, 130 ℃ of temperature heated 1 minute, and the whole operation time is unsuitable long in case photoresist oxidation in air.More than each the step technological parameter as shown in table 3:
The thick resist lithography technological parameter of table 3 embodiment 2 (SU-8 2100 type photoresists)
(7) pyrolysis step: will put into GSL-1400X type vacuum tube furnace (high temperature Instr Ltd. of Luoyang Weida) through the silicon chip that baking is later handled, and divide three temperature that progressively raise to carry out pyrolysis, and obtain high depth-to-width ratio carbon micro electro-mechanical device.Detailed process is with embodiment 1.
Comparing that the carbon micro electro-mechanical device of preparing by above-mentioned technological process and example 1 are made is very alike, and just top device wants big, form "T"-shaped top, as shown in Figure 3.This is because the increase of preceding baking, middle baking temperature makes the top layer hardening of SU-8 photoresist to be not easy to remove during development, has just produced "T"-shaped top phenomenon.
Embodiment 3:
(1) the even glue step of preparation process, (2) substrate etch step, (3) pre-treatment step, (4), (5) step of exposure and (6) development step are complete identical with embodiment 1;
(7) pyrolysis step: will put into GSL-1400X type vacuum tube furnace (high temperature Instr Ltd. of Luoyang Weida) through the silicon chip that baking is later handled, and divide three temperature that progressively raise to carry out pyrolysis, and obtain high depth-to-width ratio carbon micro electro-mechanical device.Detailed process is:
(7-1) vacuumize, vacuum reaches 10
-3Tor, purpose is to discharge oxygen in case photoresist structure is burnt;
(7-2) feed nitrogen with 2000 mark condition milliliter per minutes (sccm), purpose is further to discharge unnecessary oxygen;
(7-3) be raised to 300 ℃ from normal temperature with 3 ℃/min of heating rate, insulation 20min continues to feed nitrogen with 2000sccm; This process reaches the post bake effect in order that further removing steam strengthens adhering to, and with lower heating rate and 300 ℃ of maintenance 20min, is for post bake is fully carried out;
(7-4) then be raised to 600 ℃ from 300 ℃ with 5 ℃/min of heating rate, insulation 20min, continue to feed nitrogen with 2000sccm, thermal decomposition mainly occurs in this temperature range, the quality of photoresist is shunk also maximum, adopts lower heating rate to help abundant pyrolysis of photoresist and emission gases accessory substance, and insulation 20min is in order to make the violent glue-line of exhaust reaction be stablized a period of time, thereby make nitrogen fully take away gaseous by-product, in order to avoid glue-line generation deformation;
(7-5) be warmed up to 1000 ℃ with 10 ℃/min of heating rate from 600 ℃ at last, feed nitrogen (95%)/hydrogen (5%) and be incubated 60min this moment, makes the glue-line carbonization more thorough, and resistivity is lower.The effect of hydrogen is further to reduce oxygen content in the mist;
(7-6) pyrolysis is intact makes silicon chip naturally cool to room temperature afterwards, to reduce the internal stress of film, continues simultaneously to feed nitrogen with 2000sccm, not only can quicken cooling, and can take away the oxygen on pyrolytic carbon layer surface.
Three step pyrolysis main technologic parameters are listed in the table 4 in the present embodiment.
The three-step approach pyrolytic process parameter of table 4 embodiment 3
The difference of embodiment 3 and embodiment 1 is pyrolysis temperature and asynchronism(-nization), the device made from preceding two embodiment on the appearance of device that embodiment 3 makes is about the same, this is because the reaction of SU-8 photoresist thermal decomposition mainly occurs in below 600 ℃, the quality of photoresist no longer includes big variation under the higher temperature, so the pattern of device is almost consistent.But higher temperature can make the glue-line carbonization more thorough.The analysis of process SEM micro-area composition draws its carbon content rate and is about 94.5%, has confirmed this point.Utilize the four point probe instrument to record resistivity and be about 1.44 * 10
-5Ω m shows the raising along with carbonizing degree, and the electric conductivity of the micro electro mechanical device that makes is better.
Claims (3)
1. the preparation method of a high depth-to-width ratio carbon micro electro-mechanical device comprises:
(1) preparation process: at silicon chip superficial growth one deck SiO
2Layer perhaps directly selects for use the surface to have SiO
2The silicon chip of layer;
(2) substrate etch step: utilize photoetching process, the SiO of etch silicon substrate surface
2Layer is produced little hole figure SiO
2Mask; Use SiO again
2Mask etches little hole on silicon chip;
(3) pre-treatment step: the silicon chip to the good little hole of etching carries out the hydrophobization preliminary treatment;
(4) even glue step: on sol evenning machine,,, the silicon chip behind the even glue is carried out preceding baking handle until reaching the desired thickness glue-line to the even glue of pretreated silicon chip;
(5) step of exposure: the silicon chip after preceding baking handled is aimed at exposure, and the exposure area is overlapped with micro-pit array on the silicon chip, dries by the fire processing at once silicon chip being carried out after the exposure;
(6) development step: the silicon chip after the centering baking is handled develops, and whether the developer solution that constantly vibrates during development is removed fully with the unexposed glue-line in isopropyl alcohol check silicon chip surface; Carrying out the back baking after development is finished handles;
(7) pyrolysis step: will put into vacuum tube furnace through the silicon chip that baking is later handled and divide three temperature that progressively raise to carry out pyrolysis, and obtain high depth-to-width ratio carbon micro electro-mechanical device.
2. preparation method as claimed in claim 1 is characterized in that:
In the even glue step, used glue is the SU-8 negative photoresist; When preceding baking was handled, 65 ℃～95 ℃ of temperature heated 40～60 minutes;
In the described step of exposure, when middle baking was handled, 65 ℃～95 ℃ of temperature heated 20～25 minutes;
In the described development step, used developer solution is the special-purpose developer solution of SU-8 negative photoresist; When the back baking was handled, 110 ℃～130 ℃ of temperature heated 1～3 minute.
3. preparation method as claimed in claim 1 or 2 is characterized in that:
In the described pyrolysis step, the described branch process that temperature carries out pyrolysis that progressively raises for three times is: at first be raised to 250 ℃～300 ℃ from room temperature, be incubated 20～30 minutes; Be warmed up to 500 ℃～600 ℃ then, be incubated 20～30 minutes; Then be warmed up to 900 ℃～1000 ℃, be incubated 60～80 minutes; Naturally cool to room temperature at last; Whole process is at anaerobic and N
2Carry out in the atmosphere.
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