CN101905858B - Method for preventing MEMS (Micro-Electromechanical System) device structural layer material from being electrochemically corroded - Google Patents
Method for preventing MEMS (Micro-Electromechanical System) device structural layer material from being electrochemically corroded Download PDFInfo
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- CN101905858B CN101905858B CN2010102358709A CN201010235870A CN101905858B CN 101905858 B CN101905858 B CN 101905858B CN 2010102358709 A CN2010102358709 A CN 2010102358709A CN 201010235870 A CN201010235870 A CN 201010235870A CN 101905858 B CN101905858 B CN 101905858B
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Abstract
The invention discloses a method for preventing an MEMS (Micro-Electromechanical System) device structural layer material from being electrochemically corroded. The method comprises the following steps of: further settling a metal Ti layer on the surface of a precious metal layer in a metallization process of an MEMS device; and then covering the metal Ti layer by photoresist. Because the electrochemical potential of metal Ti in HF base corrosive liquid is lower than that of a structural layer semiconductor material, Ti instead of the semiconductor material forms a primary battery with the precious metal layer and is used as an anode of the primary battery for carrying out oxidation reaction in the HF base corrosive liquid, thereby effectively preventing the semiconductor structural layer material from being electrochemically corroded and ensuring the firm combination of the metal layer and other structural layers.
Description
Technical field
The present invention relates to MEMS device manufacturing technology field, relate in particular to the method that a kind of MEMS of preventing device architecture layer material is etched electrochemically, prevent that promptly structural material with the MEMS device of noble metal is at SiO
2The method that is etched electrochemically in the wet etching course.
Background technology
From the eighties in last century MEMS (Micro Electromechanical System, MEMS) technology flourish since, the market value of various MEMS devices rises rapidly.Micro-acceleration gauge from safe automobile air bag, the micropressure sensor in the tire, the gyroscope in the navigator, the micro-resonator in the wireless telecommunication system again, the micro-switch array in filter and the radar.These MEMS devices have promoted 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; Like the polysilicon of low pressure gas phase deposition (LPCVD) or single crystal silicon material etc.,, and select for use silica as device isolation layer or sacrifice layer as the device architecture layer; Be widely used in IC technology mainly due to silica; Can stand pyroprocesses such as thin film deposition and annealing, and in HF base corrosive liquid, corrosion rate faster arranged, and some materials such as silicon, silicon nitride there is higher selectivity relatively.Sacrifice layer SiO
2The course of reaction that in HF base corrosive liquid, takes place is: SiO
2+ 6HF → H
2SiF
6+ 2H
2O.
Because MEMS device function demand often needs precious metal material as structure sheaf, electricity connecting line layer and bond pad 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 serious electrochemical corrosion, the electric property of device and mechanical performance 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 rate of finished products and the reliability of MEMS device.
This type 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 primary cell with semi-conducting material, as the anodal structural material of primary cell 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, cause the polysilicon structure laminar surface of MEMS device can form porous silicon.If releasing 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 rate of finished products and the reliability that improves device, explore at SiO
2The method of effectively 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 two types.One type is through changing device architecture, as on the device architecture layer, punching, shortening SiO
2The etching time of layer in HF base corrosive liquid perhaps reduces the area ratio that layer of precious metal is occupied in device architecture, weaken the attack of electrochemical corrosion to semiconductor structure layer.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 method is that to utilize additional circuit to change the electrochemical potential of structure sheaf semi-conducting material and layer of precious metal material poor, or through in corrosive liquid, adding redox buffer, slows down the electrochemical corrosion to structural material.These class methods can effectively be alleviated the influence of electrochemical corrosion, but complex process, cost are high, the extensive manufacturing that is not suitable for the MEMS device.
Summary of the invention
The technical problem that (one) will solve
A key technical problem that faces to many MEMS device making technics midium or long terms; Be of the electrochemical corrosion of HF base corrosive liquid to the semiconductor structure layer material; Main purpose of the present invention is the method that provides a kind of MEMS of preventing device architecture layer material to be etched electrochemically, to prevent that MEMS device architecture layer material with noble metal is at SiO
2In the wet etching course by the electrochemical corrosion of HF base corrosive liquid.
(2) technical scheme
For achieving the above object; The invention provides the method that a kind of MEMS of preventing device architecture layer material is etched electrochemically; This method is in the metallization process of MEMS device, and the further deposit layer of metal Ti layer on the layer of precious metal surface covers this metal Ti layer then with photoresist.
In the such scheme, said metal Ti layer is accomplished in same single metal metallization processes with said layer of precious metal, and is positioned at said layer of precious metal surface.
In the such scheme, the thickness of said metal Ti layer is by SiO
2The length of wet etching time and structure sheaf and the noble metal exposed area in corrosive liquid is than decision, SiO
2The wet etching time is long more, and perhaps noble metal is bigger than more with the structure sheaf area, and required metal Ti layer is just thick more.
In the such scheme, this method realizes the covering protection of photoresist to whole metal Ti layer through photoetching.
In the such scheme, this method adopts photoetching to define etch pit, makes HF base corrosive liquid through the direct contact corrosion SiO of etch pit
2Layer.
In the such scheme, this method is to SiO
2Wet etching further comprises after finishing: remove the metal Ti layer that photoresist and precious metal surface are not exhausted by HF base corrosive liquid, obtain protected device architecture.
(3) beneficial effect
Can find out that from technique scheme the present invention has following beneficial effect:
1, utilizes the present invention; Because the electrochemical potential of metal Ti in HF base corrosive liquid is lower than the electrochemical potential of structure sheaf semi-conducting material; Thereby Ti alternative semiconductors material, constitute primary cell with layer of precious metal, and in HF base corrosive liquid, oxidation reaction takes place as the primary cell positive pole; Thereby effectively avoided the semiconductor structure layer material to be etched electrochemically, and guaranteed the strong bonded of metal level and other structure sheaf.
2, utilize the present invention, need not increases complex process steps in the manufacturing process of MEMS device, just can effectively avoid at SiO
2Wet etching course in, the semiconductor structure layer material is etched electrochemically, and guarantees that device performance is not affected.This method can be used for SiO
2Long-time wet etching (1～2 hour), not only simple and reliable, and with the IC process compatible, can be extended to the step routine techniques of MEMS devices in batches in producing.This method need not original device architecture is carried out any change, and process implementing is simple, cost is low, is applicable to the batch making of device.
Description of drawings
Fig. 1 is the SiO that does not have MEMS device under the situation that layer of precious metal exists
2The sketch map of layer wet etching;
Fig. 2 has under the situation of layer of precious metal existence, and structure sheaf (like polysilicon) is at SiO
2Corrosion mechanism sketch map in the wet corrosion technique;
Fig. 3 is that the MEMS of avoiding device architecture layer provided by the invention is at SiO
2The method sketch map that is corroded in the wet corrosion technique;
Fig. 4 is at no metal level, layer of precious metal is arranged and has under the Ti protective layer condition, and the polysilicon structure layer is at SiO in the MEMS device
2The relation of resistivity and etching time in the wet corrosion technique;
Fig. 5 be in the MEMS device of band different-thickness Ti protective layer the polysilicon structure layer at SiO
2The variation relation of resistivity and etching time in the wet corrosion technique;
Among the figure: 1. structure sheaf (like polysilicon), 2.SiO
2Layer, 3. layer of precious metal (like Au, Pt), 4. metal Ti protective layer, 5. photoresist cover layer, 6. etch pit, 7. separator is (like SiN
x), 8. substrate (like silicon chip, quartz glass plate etc.).
Embodiment
For making the object of the invention, technical scheme and advantage clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, to further explain of the present invention.
This protection MEMS device architecture layer material provided by the invention is at SiO
2The method that is not etched electrochemically in the wet corrosion technique is in the metallization process of device, at layer of precious metal surface deposition layer of metal Ti layer, covers whole metal level then with photoresist.Because the electrochemical potential of metal Ti layer in HF base corrosive liquid is lower than the electrochemical potential of structure sheaf semi-conducting material; Thereby Ti alternative semiconductors material; Constitute primary cell with layer of precious metal; And in HF base corrosive liquid oxidation reaction takes place as the primary cell positive pole, thus effectively avoided the semiconductor structure layer material to be etched electrochemically, and guaranteed the strong bonded of metal level and other structure sheaf.
In the metallization process of MEMS device, at the layer of precious metal surface deposition layer of metal Ti of required deposit layer, the metal Ti layer is accomplished in same single metal metallization processes with other layer of precious metal.Through standard photolithography process (drying by the fire behind baking before gluing, the isothermal, exposure, development, the isothermal), realize the covering protection of photoresist then to whole metal level; And the etch pit through lithographic definition, make HF base corrosive liquid directly corrode SiO
2Layer.
According to SiO
2The length of wet etching time, and structure sheaf and the exposed area ratio of noble metal in corrosive liquid can be made the metal Ti layer of different-thickness.Crossing thin T i layer can exhausted in long-time wet etching course, can not prevent effectively that the semiconductor structure layer material from being attacked by electrochemistry; Blocked up Ti layer can increase the manufacturing cost of device.
The metal Ti layer is very easily oxidized generation 3 valency ion titanium Ti in HF base corrosive liquid
3+:
2Ti+6HF→2TiF
3+3H
2。
In the disclosed method of the present invention, HF base corrosive liquid penetrates photoresist and Ti reacts, the Ti of generation
3+Being free in photoresist and layer of precious metal surrounds in the zonule that forms.Because Ti
3+To Ti
4+Electrochemical potential be lower than the electrochemical potential of semiconductor structure layer material, Ti
3+Preferential and noble metal constitutes the primary cell circuit in HF base corrosive liquid.Ti
3+Contribute an electronics to give and be oxidized to Ti at the cation of primary cell negative pole generation reduction reaction
4+:
TiF
3+3HF+λh
+→H
2TiF
6+H
++(1-λ)e
-。
Because electrochemical reaction has taken place in metal Ti layer alternative structure layer material in HF base corrosive liquid, thereby has effectively avoided structural material to be etched electrochemically.
If there is not photoresist layer, following reaction can directly take place in Ti:
Ti+6HF→TiF
6 2-+2H
++2H
2
Ti+2H
2O→TiO
2+4H
++4e
-
TiO
2+6HF→TiF
6 2-+2H
++2H
2O
Its product TiF
6 2-Water-soluble, too fast the exhausting of metal Ti layer meeting can not be protected the semiconductor structure layer material.
Be example to contain polysilicon structure layer MEMS device architecture below, the present invention is further explained.
Fig. 1 is not for the MEMS device of metal level wet etching SiO in HF base corrosive liquid
2Sketch map.Wherein, SiO
2Layer has corrosion rate faster in HF base corrosive liquid, its course of reaction is:
SiO
2+6HF→H
2SiF
6+2H
2O
Its product H
2SiF
6Water-soluble, so SiO
2Layer is corroded.And 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 primary cell with polysilicon structure layer 1, in HF base corrosive liquid, oxidation reaction takes place and is corroded as the anodal polysilicon structure layer 1 of primary cell.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 making device performance to reduce even inefficacy.
Among Fig. 3, when implementing the metallization process of MEMS device, at the layer of precious metal 3 surface deposition layer of metal Ti layers 4 of required deposit, metal Ti layer 4 is accomplished in same single metal metallization processes with other layer of precious metal 3.Photoetching process through standard then: dry by the fire behind baking before gluing, the isothermal, exposure, development, the isothermal, with AZ6130 photoresist cover layer 5 covering metal Ti layers 4.On photoresist cover layer 5, define etch pit 6 through photoetching again.Can make HF base corrosive liquid directly contact SiO through this etch pit 6
2Layer 2 makes SiO
2Wet etching unaffected.Because metal Ti layer 4 is very easily penetrated the HF base corrosive liquid of photoresist cover layer 5 and is oxidized to 3 valency ion titanium Ti
3+, and be free in the Ti that photoresist cover layer 5 and layer of precious metal 3 surround the zonule that forms
3+, the electrochemical potential in HF base corrosive liquid is lower than the electrochemical potential of polysilicon structure layer 1, therefore substitutes polysilicon structure layer 1 and constitutes primary cell and oxidized corrosion with noble metal 3, thereby effectively avoided polysilicon structure layer 1 to be etched electrochemically.Because the protection of photoresist cover layer 5 is arranged, can not cause the too fast dissipation of metal Ti layer 4, can protect polysilicon structure layer 1 not to be etched electrochemically for a long time.
As can beappreciated from fig. 4, for the MEMS device of the band layer of precious metal 3 that does not carry out any safeguard measure, 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 1000 Ω cm; And for not with the MEMS device of noble metal and the MEMS device that the band layer of precious metal 3 of metal Ti layer 4 is arranged, the resistivity of its polysilicon structure layer 1 was at 60 minutes SiO
2Significant change does not take place in the wet etching course.
Can know that by Fig. 5 metal Ti layer 4 is consumed in the process of protection MEMS device polysilicon structure sheaf 1.SiO
2The wet etching time of layer 2 is long more, i.e. the time of polysilicon structure layer 1 required protection is long more, and the metal Ti layer 4 that needs is thick more.Therefore according to SiO
2The length of 2 wet etching time of layer, and polysilicon structure layer 1 and the exposed area ratio of noble metal 3 in corrosive liquid can be made the metal Ti layer 4 of different-thickness.Crossing thin metal Ti layer 4 can be exhausted in long-time wet etching course, can not prevent fully that polysilicon structure layer 1 is etched electrochemically; Blocked up metal Ti layer 4 can increase the manufacturing cost of device.
SiO
2After the wet etching of layer 2 finishes, need to remove photoresist, and remove the metal Ti layer 4 that noble metal 3 surfaces are not exhausted by HF base corrosive liquid, obtain protected device architecture.
Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; Be not limited to the present invention; All within spirit of the present invention and principle, 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 MEMS device architecture layer material is etched electrochemically is characterized in that this method comprises:
In the metallization process of MEMS device, the further deposit layer of metal Ti layer on the layer of precious metal surface covers this metal Ti layer then with photoresist; Wherein, utilize metal Ti to replace semi-conducting material preferentially to form the negative pole of primary cell, can reach the purpose of protecting semiconductor structure layer, metal Ti self is consumed in this process; And
To SiO
2After wet etching finishes, remove the metal Ti layer that photoresist and precious metal surface are not exhausted by HF base corrosive liquid, obtain protected device architecture.
2. the method that the MEMS of preventing device architecture layer material according to claim 1 is etched electrochemically is characterized in that said metal Ti layer is accomplished in same single metal metallization processes with said layer of precious metal, and is positioned at said layer of precious metal surface.
3. the method that the MEMS of preventing device architecture layer material according to claim 1 is etched electrochemically is characterized in that the thickness of said metal Ti layer is by SiO
2The length of wet etching time and structure sheaf and the noble metal exposed area in corrosive liquid is than decision, SiO
2The wet etching time is long more, and perhaps noble metal is bigger than more with the structure sheaf area, and required metal Ti layer is just thick more.
4. the method that the MEMS of preventing device architecture layer material according to claim 1 is etched electrochemically is characterized in that, this method realizes the covering protection of photoresist to whole metal Ti layer through photoetching.
5. the method that the MEMS of preventing device architecture layer material according to claim 1 is etched electrochemically is characterized in that, this method adopts photoetching to define etch pit, makes HF base corrosive liquid through the direct contact corrosion SiO of etch pit
2Layer.
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|---|---|---|---|
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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 CN2010102358709A patent/CN101905858B/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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