CN101905857A - Method for preventing structural layer materials of MEMS (Micro-Electromechanical System) devices from being electrochemically corroded on large scale - Google Patents
Method for preventing structural layer materials of MEMS (Micro-Electromechanical System) devices from being electrochemically corroded on large scale Download PDFInfo
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- CN101905857A CN101905857A CN 201010235859 CN201010235859A CN101905857A CN 101905857 A CN101905857 A CN 101905857A CN 201010235859 CN201010235859 CN 201010235859 CN 201010235859 A CN201010235859 A CN 201010235859A CN 101905857 A CN101905857 A CN 101905857A
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Abstract
The invention discloses a method for preventing structural layer materials of MEMS (Micro-Electromechanical System) devices from being electrochemically corroded on a large scale, which utilizes photoresist as a high polymer material for prevent the structural layer materials of the devices and noble metal from forming an electric passage of the original battery in HF (Hydrogen Fluoride)-based corrosive liquid. The method comprises the following step of spinning a layer of photoresist on the surfaces of the devices before the wet corrosion of an SiO2 layer to fully cover the photoresist on the surface of a noble metal layer. By utilizing the method, the photoresist forms a compact type high polymer structure with lower hole density to prevent the noble metal and the structural layer materials from forming the original battery circuit in the HF-based corrosive liquid, thereby effectively preventing the structural layer materials from being oxidized and corroded. By only increasing one standard photoetching step in the standard MEMD process, the method can effectively avoid device performance reduction caused by the electrochemical corrosion of the structural layer materials and has simple process enforcement; and due to the compatibility with an IC (Integrated Circuit) process, the method is beneficial to the batch production of the devices.
Description
Technical field
The present invention relates to MEMS device manufacturing technology field, relate in particular to a kind of method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically, with the MEMS device architecture layer material of boundary belt noble metal at SiO
2Be not etched electrochemically in the wet etching course of layer.
Background technology
From the eighties in last century MEMS (Micro Electromechanical System, MEMS) technology flourish since, increasing MEMS device is widely applied in the middle of the daily life.Micro-acceleration gauge from safe automobile air bag, the micropressure sensor in the tire, the gyroscope in the navigator, the micro-switch array in micro-resonator, wave filter and the radar in the wireless telecommunication system again.These MEMS devices have promoted the development of technology, have improved people's quality of the life.
The processing of MEMS device is the micromachined technology of utilizing same microelectronic integrated circuit (IC) manufacturing technology compatible mutually.Common MEMS device is a kind of sandwich construction, mainly comprises structure sheaf, sacrifice layer and metal level.The MEMS device is generally by semi-conducting material, as the polysilicon of low pressure gas phase deposition (LPCVD) or single crystal silicon material etc., as the device architecture layer, and selects for use silica material as device isolation layer and sacrifice layer.Select for use silica as insulating barrier and sacrificial layer material, be because silica is widely used in IC technology, can stand high temperature processes such as thin-film deposition and annealing, and in HF base corrosive liquid corrosion rate faster be arranged, some materials such as silicon, silicon nitride have higher selectivity relatively.Sacrifice layer SiO
2The course of reaction that takes place in HF base corrosive liquid is: SiO
2+ 6HF → H
2SiF
6+ 2H
2O.
Based on to the MEMS device demand of high-performance and function more, precious metal material more and more is incorporated in the middle of the MEMS device architecture.For example, noble metal be used to strengthen optical surface reflectivity, reduce transmission line resistance, and as welded disc, electrode and long-life structural material etc.Yet, this MEMS device that has noble metal is being carried out SiO with HF base corrosive liquid
2Wet etching the time, tend to the semiconductor structure layer material is produced heavy corrosion, the electric property and the mechanical performance of device are obviously worsened, as, the resistivity of structural material enlarges markedly, Young's modulus reduces, and mechanical strength descends and material internal stress gradient rising etc., thereby has reduced the yield rate and the reliability of MEMS device.
This electrochemical corrosion is because the standard electric chemical potential of precious metal material is higher than the electrochemical potential of semiconductor structure layer material, in HF base corrosive liquid, the noble metal that links to each other constitutes galvanic cell with semi-conducting material, as the structural material of galvanic cell positive pole generation oxidation reaction and being corroded in HF base corrosive liquid.With the polysilicon structure layer is example, and the electrochemical corrosion reaction of its generation is:
Si+2HF+λh
+→SiF
2+2H
++(2-λ)e
-
SiF
2+2HF→SiF
4+H
2
SiF
4+2HF→H
2SiF
6
Wherein, h
+Be the valence band hole that noble metal provides, λ is the hole number of required participation reaction.Its product H
2SiF
6Water-soluble, the polysilicon structure laminar surface of most MEMS devices can generate porous silicon.If release solution is dense hydrofluoric acid or the pure hydrofluoric acid of gaseous state more than 40%, also following reaction can take place:
Si+2H
2O+4h
+→SiO
2+4H
+
SiO
2+6HF→SiF
6 2-+2H
2O+2H
+
In addition, because structural material is corroded, layering also can take place in metal layer material attached to it, even peels off.Therefore, for yield rate and the reliability that improves device, explore at SiO
2The method of avoiding structural material to be corroded in the wet corrosion technique is very important.
At present, avoid MEMS device architecture layer material at SiO
2Wet etching course in the method that is etched electrochemically roughly be divided into following a few class.One class is by changing device architecture, for example punching on the device architecture layer and shorten SiO
2The etching time of layer perhaps in HF base corrosive liquid, increases the area ratio of structural material to the layer of precious metal material, weakens the electrochemical corrosion ability, reduces the corrosion of corrosive liquid to structural material with this.These class methods can alleviate the corrosion of HF base corrosive liquid to the semiconductor structure layer material, but effect is limited, and therefore finally cause device performance to change to the change that device architecture is done, so the scope of application of these class methods is very limited.
Another kind of is not change device architecture, but it is poor to change the electrochemical potential of structural material and precious metal material by additional circuit.Second class methods also have significant effect for the electrochemical corrosion that weakens structural material, but complex process often, the cost height is unfavorable for the batch process of MEMS device.
Also having class methods is by adding redox buffer in corrosive liquid, slowing down the electrochemical corrosion to structural material.For example at layer of precious metal many deposits of surface layer of metal Ti, in HF base corrosive liquid electrochemical reaction takes place with Ti alternative structure layer material, thereby effectively avoided structural material to be etched electrochemically.But the complicated part of this method is for need carry out quantitatively Ti at different structure, and need prevent the too fast diffusion of Ti in HF base corrosive liquid.
Summary of the invention
(1) technical problem that will solve
In view of this, protecting MEMS device architecture layer material not to be etched electrochemically is the difficult point problem of being badly in need of solution in the MEMS technology.In order to overcome deficiency of the prior art, what main purpose of the present invention was to provide a kind of improvement utilizes HF base corrosive liquid wet etching SiO
2The method of layer is not etched electrochemically with protection MEMS device architecture layer material, avoids the device performance decline that is corroded and causes because of structural material.
(2) technical scheme
For achieving the above object, the invention provides a kind of method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically, this method is to utilize this macromolecular material of photoresist to come the structural material of block device and noble metal forms galvanic cell in HF base corrosive liquid electric path, specifically comprises:
At SiO
2Before the wet etching of layer,, make it cover the layer of precious metal surface fully at device surface spin coating one deck photoresist.
In the such scheme, described photoresist is insoluble to HF base corrosive liquid, and can be attached to device surface in HF base corrosive liquid and do not come off at least 60 minutes.
In the such scheme, this method further comprises when the spin coating photoresist: control the post bake condition of photoresist, adopt the drying glue process that slowly heats up and cool off naturally, improve the compactness of photoresist.
In the such scheme, this method further comprises behind the spin coating photoresist: define etch pit by photoetching on photoresist, make the corrosive liquid inflow of HF base and directly contact SiO by this etch pit
2Layer.
In the such scheme, at SiO
2After wet etching finished, this method further comprised: remove photoresist, obtain protected MEMS device architecture.
(3) beneficial effect
From technique scheme as can be seen, the present invention has following beneficial effect:
1, utilizes the present invention, at SiO
2Before the layer wet etching, by the lithographic definition etch pit, cover precious metal surface with photoresist, regulate the back baking condition of photoresist, promptly adopt the drying glue process that slowly heats up and cool off naturally, make photoresist form fine and close build macromolecular structure with low hole density, blocking-up noble metal and the structural material galvanic cell circuit in HF base corrosive liquid, thus effectively avoided the oxidized corrosion of structural material.
2, utilize the present invention, only in the standard MEMS device manufacturing process, increase by a step standard lithography step, just can effectively avoid because of the structural material device performance that causes that is etched electrochemically descends, and process implementing is simple, compatible mutually with IC technology, be beneficial to the mass production of device.
Description of drawings
Fig. 1 does not have MEMS device SiO under the situation that layer of precious metal exists
2Layer wet etching schematic diagram;
Fig. 2 has under the situation of layer of precious metal existence, and structure sheaf (as polysilicon) is at SiO
2Corrosion mechanism schematic diagram in the wet corrosion technique;
Fig. 3 covers the schematic diagram of layer of precious metal to avoid structure sheaf to be corroded with photoresist;
Fig. 4 is with the structure sheaf polysilicon of layer of precious metal MEMS device at SiO
2Resistivity is with the change curve of etching time in the wet corrosion technique.
Among the figure: 1. structure sheaf (as polysilicon), 2.SiO
2Layer, 3. layer of precious metal (as Au, Pt), 4. photoresist cover layer, 5. etch pit, 6. separation layer is (as SiN
x), 7. substrate (as silicon chip, quartz glass plate etc.).
The specific embodiment
For making the purpose, technical solutions and advantages of the present invention clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, the present invention is described in more detail.
This method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically provided by the invention can effectively protect MEMS device architecture layer material not to be etched electrochemically in HF base corrosive liquid.At SiO
2Before the layer wet etching, by the lithographic definition etch pit, cover precious metal surface with photoresist, regulate the back baking condition of photoresist, promptly adopt the drying glue process that slowly heats up and cool off naturally, make photoresist form fine and close build macromolecular structure with low hole density, blocking-up noble metal and the structural material galvanic cell circuit in HF base corrosive liquid, thus effectively avoided the oxidized corrosion of structural material.
In utilizing standard technology making MEMS device process, SiO
2Before the wet etching of layer, add a step standard lithography step (gluing, preceding baking, exposure, development, back baking).By this insulating materials of photoresist, come the structural material of block device and noble metal forms galvanic cell in HF base corrosive liquid electric path.
At first, make it cover the layer of precious metal surface fully at device surface spin coating one deck photoresist.Selected photoresist should be insoluble to HF base corrosive liquid, and can be attached to device surface in HF base corrosive liquid and do not come off for a long time.This photoresist is carried out drying by the fire, expose, developing before the isothermal, define etch pit, can make HF base corrosive liquid flow into and directly contact SiO by this hole
2Layer makes SiO
2Corrosion unaffected.
Carefully control the back baking condition of photoresist then, adopt and slowly to heat up and the drying glue process of cooling naturally, but not dry by the fire behind the direct isothermal of being taked during common photoetching.This step is very crucial, because slowly the back baking process that heats up can make photoresist form fine and close build macromolecular structure, has low hole density.This dense form macromolecular structure can effectively stop HF base corrosive liquid to penetrate glue contact with noble metal, thereby has suppressed cation in the basic corrosive liquid of HF at the precious metal surface electron gain, the generation reduction reaction; Also cut off simultaneously the electricity loop of galvanic cell in HF base corrosive liquid that links to each other with the structure sheaf semi-conducting material and constitute by noble metal; therefore avoided MEMS device architecture layer material in HF base corrosive liquid because of the oxidized corrosion of betatopic, reach the purpose that effective protection MEMS device architecture layer material is not etched electrochemically.
In addition; adopt the back baking process that slowly heats up and cool off naturally; can also avoid photoresist when post bake, to form micro-crack, and the formation of micro-crack will cause photoresist that layering even peeling phenomenon take place in wet corrosion technique subsequently, thereby can't play a protective role.
Be MEMS device wet etching SiO in HF base corrosive liquid of structure sheaf below with the low stress polysilicon
2Be example, the present invention is prevented that on a large scale the method that MEMS device architecture layer material is etched electrochemically is elaborated.
Fig. 1 is not for the MEMS device of metal level wet etching SiO in HF base corrosive liquid
2Schematic diagram.Wherein, SiO
2 Layer 2 has corrosion rate faster in HF base corrosive liquid, its course of reaction is similar: SiO
2+ 6HF → H
2SiF
6+ 2H
2O, its product H
2SiF
6Water-soluble, so SiO
2Layer 2 is corroded and removes.And be compared to SiO
2Layer 2, polysilicon structure layer 1 is extremely slow with the HF reaction, can not cause excessive influence to device performance usually.
In Fig. 2, the MEMS device surface has layer of precious metal 3, and it links to each other with polysilicon structure layer 1.Because the standard electric chemical potential of precious metal material 3 is higher than the electrochemical potential of polysilicon structure layer 1 in HF base corrosive liquid, therefore in HF base corrosive liquid, the noble metal 3 that links to each other constitutes galvanic cell with polysilicon structure layer 1, in HF base corrosive liquid oxidation reaction takes place and is corroded as the polysilicon structure layer 1 of galvanic cell positive pole.Its reaction equation is:
Si+2HF+λh
+→SiF
2+2H
++(2-λ)e
-
SiF
2+2HF→SiF
4+H
2
SiF
4+2HF→H
2SiF
6
Its product H
2SiF
6Water-soluble, polysilicon structure layer 1 is corroded, and generates porous silicon, causes device performance to reduce even inefficacy.
By Fig. 3, at SiO
2Before the wet etching of layer 2, add a step standard lithography step (gluing, preceding baking, exposure, development, back baking).By photoresist 4 this insulating materials, come the electricity loop of polysilicon structure layer 1 with noble metal 3 formation galvanic cell in HF base corrosive liquid of block device.Selected photoresist 4 should be insoluble to HF base corrosive liquid, and can be attached to device surface in HF base corrosive liquid and do not come off for a long time, as AZ 6130, S 9912.
At first, at device surface spin coating one deck photoresist 4, make it cover the layer of precious metal surface fully.This photoresist is carried out drying by the fire, expose, developing before the isothermal, define etch pit 5.Can make the corrosive liquid inflow of HF base and directly contact SiO by this hole
2Layer 2 makes SiO
2The corrosion of layer 2 is not subjected to the influence of photoresist cover layer 4.
Adopt the back baking process that slowly heats up and cool off naturally then, make photoresist 4 form fine and close build macromolecular structure with low hole density.The macromolecular structure of this densification has effectively stoped HF base corrosive liquid to penetrate photoresist cover layer 4 to contact with noble metal 3, at noble metal 3 surperficial electron gains reduction reaction takes place thereby suppressed the cation in the solution; So also just cut off the electricity loop of galvanic cell in HF base corrosive liquid that links to each other with polysilicon structure layer 1 and constitute by noble metal 3; therefore avoided MEMS device polysilicon structure sheaf 1 in HF base corrosive liquid because of the oxidized corrosion of betatopic, reached the purpose that protection MEMS device polysilicon structure sheaf 1 is not etched electrochemically.
Fig. 4 is with the MEMS device of layer of precious metal 3 at SiO
2In the wet corrosion technique of layer 2, the resistivity of its polysilicon structure layer 1 is with the change curve of etching time.As can be seen from the figure, for not with the MEMS device of photoresist protective layer 4, the resistivity of its polysilicon structure layer 1 is along with SiO
2The prolongation of layer 2 etching time and enlarging markedly, in the resistivity of corrosion polysilicon structure layer 1 after 30 minutes greater than 10
3Ω cm.And for the MEMS device of band photoresist protective layer, the resistivity of its polysilicon structure layer 1 was at 60 minutes SiO
2Substantially remain unchanged in layer 2 wet etching course.
SiO
2After the wet etching of layer 2 finishes, need to remove photoresist, obtain protected device architecture.
Above-described specific embodiment; purpose of the present invention, technical scheme and beneficial effect are further described; institute is understood that; the above only is specific embodiments of the invention; be not limited to the present invention; within the spirit and principles in the present invention all, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (5)
1. method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically, it is characterized in that, this method is to utilize this macromolecular material of photoresist to come the structural material of block device and noble metal forms galvanic cell in HF base corrosive liquid electric path, specifically comprises:
At SiO
2Before the wet etching of layer,, make it cover the layer of precious metal surface fully at device surface spin coating one deck photoresist.
2. the method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically according to claim 1 is characterized in that, described photoresist is insoluble to HF base corrosive liquid, and can be attached to device surface in HF base corrosive liquid and do not come off at least 60 minutes.
3. the method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically according to claim 1 is characterized in that, this method further comprises when the spin coating photoresist:
Control the post bake condition of photoresist, adopt the drying glue process that slowly heats up and cool off naturally, improve the compactness of photoresist.
4. the method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically according to claim 1 is characterized in that this method further comprises behind the spin coating photoresist:
On photoresist, define etch pit by photoetching, make the corrosive liquid inflow of HF base and directly contact SiO by this etch pit
2Layer.
5. the method that prevents that on a large scale MEMS device architecture layer material is etched electrochemically according to claim 1 is characterized in that, at SiO
2After wet etching finished, this method further comprised:
Remove photoresist, obtain protected MEMS device architecture.
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|---|---|---|---|
| CN2010102358592A CN101905857B (en) | 2010-07-21 | 2010-07-21 | Method for preventing structural layer materials of MEMS (Micro-Electromechanical System) devices from being electrochemically corroded on large scale |
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|---|---|---|---|
| CN2010102358592A CN101905857B (en) | 2010-07-21 | 2010-07-21 | Method for preventing structural layer materials of MEMS (Micro-Electromechanical System) devices from being electrochemically corroded on large scale |
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| CN101905857B CN101905857B (en) | 2012-07-25 |
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5726480A (en) * | 1995-01-27 | 1998-03-10 | The Regents Of The University Of California | Etchants for use in micromachining of CMOS Microaccelerometers and microelectromechanical devices and method of making the same |
| CN1327086A (en) * | 2001-05-18 | 2001-12-19 | 北京大学 | Silicon etching liquid and its preparing method |
| CN1581448A (en) * | 2004-05-17 | 2005-02-16 | 西安交通大学 | Sealing method for protecting metal connecting line of micro mechanical device in corrosion process |
| US7094696B2 (en) * | 2002-02-21 | 2006-08-22 | Optical Etc Inc. | Method for TMAH etching of CMOS integrated circuits |
| CN100509611C (en) * | 2007-05-15 | 2009-07-08 | 东南大学 | Microelectron mechanical system obverse structure releasing protecting method |
-
2010
- 2010-07-21 CN CN2010102358592A patent/CN101905857B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5726480A (en) * | 1995-01-27 | 1998-03-10 | The Regents Of The University Of California | Etchants for use in micromachining of CMOS Microaccelerometers and microelectromechanical devices and method of making the same |
| CN1327086A (en) * | 2001-05-18 | 2001-12-19 | 北京大学 | Silicon etching liquid and its preparing method |
| US7094696B2 (en) * | 2002-02-21 | 2006-08-22 | Optical Etc Inc. | Method for TMAH etching of CMOS integrated circuits |
| CN1581448A (en) * | 2004-05-17 | 2005-02-16 | 西安交通大学 | Sealing method for protecting metal connecting line of micro mechanical device in corrosion process |
| CN100509611C (en) * | 2007-05-15 | 2009-07-08 | 东南大学 | Microelectron mechanical system obverse structure releasing protecting method |
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|---|---|
| CN101905857B (en) | 2012-07-25 |
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