EP1256126A1 - Etching solution and method - Google Patents

Etching solution and method

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Publication number
EP1256126A1
EP1256126A1 EP01905084A EP01905084A EP1256126A1 EP 1256126 A1 EP1256126 A1 EP 1256126A1 EP 01905084 A EP01905084 A EP 01905084A EP 01905084 A EP01905084 A EP 01905084A EP 1256126 A1 EP1256126 A1 EP 1256126A1
Authority
EP
European Patent Office
Prior art keywords
etching solution
water
carboxylic acid
etching
solution
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01905084A
Other languages
German (de)
French (fr)
Inventor
George Matamis
Heidi L. Denton
Michael J. Davison
Jeffrey A. Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NXP USA Inc
Original Assignee
Motorola Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc filed Critical Motorola Inc
Publication of EP1256126A1 publication Critical patent/EP1256126A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3105—After-treatment
    • H01L21/311—Etching the insulating layers by chemical or physical means
    • H01L21/31105—Etching inorganic layers
    • H01L21/31111—Etching inorganic layers by chemical means
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K13/00—Etching, surface-brightening or pickling compositions
    • C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
    • C09K13/08—Etching, surface-brightening or pickling compositions containing an inorganic acid containing a fluorine compound

Definitions

  • the present invention relates, in general, to an etching solution and, more particularly, to an etching solution for etching semiconductor and Micro Electro-Mechanical System (MEMS) devices .
  • MEMS Micro Electro-Mechanical System
  • MENS devices such as micro-sensors, micro-actuators and micro-switches
  • micro-machining Etching of a sacrificial dielectric layer, such as silicon dioxide, is an important micro- machining method employed in the fabrication of MEMS devices as well as in the formation of semiconductor devices.
  • the sacrificial oxide is typically provided in a polysilicon structure that may also include silicon nitride and metallization, e.g. aluminum or copper.
  • silicon nitride and metallization e.g. aluminum or copper.
  • etching solution For MENS and other semiconductor devices, a high etch selectivity for oxide relative to metal, for example, is desirable.
  • One prior etching solution is a so-called Buffered Oxide Etch (BOE) solution that contains HF buffered by ammonium fluoride.
  • BOE Buffered Oxide Etch
  • the BOE solution exhibits poor etch selectivity in that this solution severely etches exposed metal, polysilicon, and/or nitride surfaces during the etching of the sacrificial oxide.
  • aluminum metallization is often completely etched before the sacrificial oxide is removed in its entirety.
  • a common use for micro-machining as described above is the formation of a MEMS sensor. Furthermore, it is becoming desirable to form integrated electronics on the same device used to form the MEMS sensor. Thus, when forming a combination MEMS sensor, which requires the etching of a sacrificial oxide, and an integrated circuit, it is critical that the metallization and passivation features of the chip not be detrimentally etched by the sacrificial oxide etching solution.
  • the present invention generally provides an etching solution that is a mixture of anhydrous HF, a carboxylic acid and water.
  • the solution is useful for the etching of oxides used in the fabrication of MEMS devices such as, for example, micro-sensors and micro- machines.
  • An important advantage of the etching solution of the present invention is that it has a high etch selectivity for silicon oxide relative to other materials including metals, nitrides and polysilicon that form the structural components of MEMS and electronic devices.
  • the etching solution of the present invention can remove sacrificial oxides with only relatively minor etching of these other non-oxide materials.
  • the etching solution of the present invention improves the fabrication process of MEMS and electronic devices.
  • the etching solution is described further below in one embodiment of the present invention with an example of its use PhosphoSilicate Glass (PSG) created by chemical vapor deposition.
  • PSG PhosphoSilicate Glass
  • Thermally grown Si0 2 and PSG are two examples of oxide films used as a sacrificial oxide layer in the formation of a micro-machined structure.
  • the sacrificial oxide layer is in contact with portions of the micro-structure prior to sacrificial oxide etching.
  • the etching solution is also generally applicable to the removal of other types of oxides that may be used in MEMS and electronic devices where metals, nitrides and/or polysilicon materials that form the micro- structure or electronic components could be exposed to the etching solution during oxide removal.
  • CMOS Complementary Metal Oxide Semiconductor
  • the carboxylic acid used can be selected generally as any acid having one or more carboxyl groups and more specifically including, for example, oxalic acid, formic acid, lactic acid, tartaric acid, malic acid, succinic acid, citric acid and acetic acid. It has been found that acetic acid, combined with the above identified ingredients, is particularly useful for selectively etching thermally grown Si0 2 and PSG.
  • the mixing ratio of anhydrous HF to carboxylic acid is not considered to be critical, but it has been found that a preferred range is approximately 0.1% anhydrous HF, up to the solubility limit of the particular carboxylic acid.
  • One preferred mixture, which has shown superior experimental results is approximately 10% anhydrous HF relative to the carboxylic acid. Dilution of the solution with respect to the amount of HF, will result in slower etch rates. It should be understood that the mixing ratio of anhydrous HF to carboxylic acid is not a limitation of the present invention.
  • the preferred range of water introduced to one embodiment of the present etching solution is in the range of approximately 0.5% to 5.0% by weight.
  • use of an anhydrous carboxylic acid, e.g., glacial acetic acid, is preferred in order to more precisely control the amount of water in the etching solution.
  • the etching solution is created by injecting anhydrous HF into an aqueous solution of a carboxylic acid, such as glacial acetic acid, having a precisely controlled minimal amount of water.
  • a carboxylic acid such as glacial acetic acid
  • the temperature required for use of the etching solution according to the present invention is not considered to be critical. In general, during etching it is preferred to use a cooler temperature of below approximately 30 degrees Celsius (°C), e.g., in the range of approximately 15°C-30°C. An advantage of such a cooler temperature is a reduction in the evaporative loss of the etching solution. Also, it is preferable that the etching solution is in the liquid phase during etching.
  • the etching solution and device having a sacrificial oxide to be etched be placed in a sealed environment substantially free of non-solution water.
  • a sealed container or etching bath with a closed lid having been purged with an inert gas such as nitrogen can be used. It has been discovered that water absorption from the atmosphere above the controlled minimal water levels of the etching solution undesirably increases the metal etching rate.
  • the etching was performed at 18 °C. and the sample etch rates measured as follows:
  • Etch selectivities of sacrificial oxides relative to metals, polysilicons, and nitrides are derived from the associated etch rates.
  • an etching solution of HF, carboxylic acid, and a minimal controlled amount of water approximately in the ratio of 10:89:1
  • the etch selectivity for thermally grown SiO? relative to aluminum or copper is in the range of approximately 9 to 80; whereas, the etch selectivity for thermally grown Si0 2 relative to polysilicon is in the range of approximately 65 to 320.
  • the etch selectivity for thermally grown Si0 2 relative to silicon nitride is in the range of approximately 9-40.
  • the etch selectivity for PSG relative to aluminum or copper is in the range of approximately 666 to 50,000.
  • the etch selectivity for PSG relative to polysilicon is in the range of approximately 5,000 to 200,000.
  • the etch selectivity for PSG relative to silicon nitride is in the range of approximately 714 to 25,000.
  • the wide range of etch selectivities for PSG is dependent on certain process parameters which include, but are not limited to whether the PSG film is annealed, the phosphorous doping level and the deposition temperature .

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • General Chemical & Material Sciences (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Computer Hardware Design (AREA)
  • Physics & Mathematics (AREA)
  • Power Engineering (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Weting (AREA)
  • ing And Chemical Polishing (AREA)
  • Micromachines (AREA)
  • Pressure Sensors (AREA)

Abstract

An etching solution of Hydrogen Fluoride (HF), carboxylic acid and water having a high etch selectivity for silicon oxide relative to metal, polysilicon and nitride. The etching solution is created by injecting anhydrous HF into a carboxylic acid having a precisely controlled minimal amount of water. The etching solution is useful in the fabrication of Micro Electro-Mechanical System (MEMS) devices, as well as the fabrication of MEMS devices in combination with integrated electronics on the same chip.

Description

ETCHING SOLUTION AND METHOD
Field of the Invention
The present invention relates, in general, to an etching solution and, more particularly, to an etching solution for etching semiconductor and Micro Electro-Mechanical System (MEMS) devices .
Background of the Invention
The deposition and etching of dielectric and metal layers to form MENS devices such as micro-sensors, micro-actuators and micro-switches is generally known as micro-machining. Etching of a sacrificial dielectric layer, such as silicon dioxide, is an important micro- machining method employed in the fabrication of MEMS devices as well as in the formation of semiconductor devices.
The sacrificial oxide is typically provided in a polysilicon structure that may also include silicon nitride and metallization, e.g. aluminum or copper. When etching the sacrificial oxide, it is desirable to minimize the extent to which the polysilicon, metal and nitride materials that form portions of the final structure are etched by the sacrificial oxide etching solution.
The extent to which a particular etching solution etches non-oxide materials is characterized by the etch selectivity of the solution. For MENS and other semiconductor devices, a high etch selectivity for oxide relative to metal, for example, is desirable. One prior etching solution is a so-called Buffered Oxide Etch (BOE) solution that contains HF buffered by ammonium fluoride. However, the BOE solution exhibits poor etch selectivity in that this solution severely etches exposed metal, polysilicon, and/or nitride surfaces during the etching of the sacrificial oxide. In particular, aluminum metallization is often completely etched before the sacrificial oxide is removed in its entirety.
A common use for micro-machining as described above is the formation of a MEMS sensor. Furthermore, it is becoming desirable to form integrated electronics on the same device used to form the MEMS sensor. Thus, when forming a combination MEMS sensor, which requires the etching of a sacrificial oxide, and an integrated circuit, it is critical that the metallization and passivation features of the chip not be detrimentally etched by the sacrificial oxide etching solution.
Accordingly, it is desirable to provide a chemical solution for etching a sacrificial oxide having a high etch selectivity for silicon oxide relative to metal, polysilicon, and nitride and which is suitable for the fabrication of MENS devices and electronic devices on the same chip.
Detailed Description
The present invention generally provides an etching solution that is a mixture of anhydrous HF, a carboxylic acid and water. The solution is useful for the etching of oxides used in the fabrication of MEMS devices such as, for example, micro-sensors and micro- machines. An important advantage of the etching solution of the present invention is that it has a high etch selectivity for silicon oxide relative to other materials including metals, nitrides and polysilicon that form the structural components of MEMS and electronic devices. As a result of this etch selectivity, the etching solution of the present invention can remove sacrificial oxides with only relatively minor etching of these other non-oxide materials. Thus, the etching solution of the present invention improves the fabrication process of MEMS and electronic devices.
The etching solution is described further below in one embodiment of the present invention with an example of its use PhosphoSilicate Glass (PSG) created by chemical vapor deposition. Thermally grown Si02 and PSG are two examples of oxide films used as a sacrificial oxide layer in the formation of a micro-machined structure. Typically, the sacrificial oxide layer is in contact with portions of the micro-structure prior to sacrificial oxide etching. However, one of ordinary skill in the art will recognize that the etching solution is also generally applicable to the removal of other types of oxides that may be used in MEMS and electronic devices where metals, nitrides and/or polysilicon materials that form the micro- structure or electronic components could be exposed to the etching solution during oxide removal.
The high etch selectivity of the present etching solution permits the removal of the sacrificial oxide without significant degradation of the exposed metal, nitride or polysilicon surfaces. One important result is that electronic devices, e.g., Complementary Metal Oxide Semiconductor (CMOS) devices, can be integrated in a practical process flow onto the same chip used to form the MEMS device .
Prior art etching solutions used to remove the sacrificial oxide layer, such as buffered HF, had the deleterious effect of etching the exposed metal surfaces such as aluminum and copper. However, the use of a carboxylic acid combined with a controlled amount of water, as a solvent or dilutent for HF has been found to overcome the problem of undesirable metal etching. It is believed that the carboxylic acid, combined with a controlled amount of water, in the etching solution slows the dissolution rate of aluminum. Experimental results have confirmed that an etching solution of anhydrous HF, a carboxylic acid, and a controlled amount of water exhibits significantly reduced etching of metals such as aluminum and copper, as well as exhibiting a relatively minimal etch rate of polysilicon and silicon nitride.
The carboxylic acid used can be selected generally as any acid having one or more carboxyl groups and more specifically including, for example, oxalic acid, formic acid, lactic acid, tartaric acid, malic acid, succinic acid, citric acid and acetic acid. It has been found that acetic acid, combined with the above identified ingredients, is particularly useful for selectively etching thermally grown Si02 and PSG.
The mixing ratio of anhydrous HF to carboxylic acid is not considered to be critical, but it has been found that a preferred range is approximately 0.1% anhydrous HF, up to the solubility limit of the particular carboxylic acid. One preferred mixture, which has shown superior experimental results is approximately 10% anhydrous HF relative to the carboxylic acid. Dilution of the solution with respect to the amount of HF, will result in slower etch rates. It should be understood that the mixing ratio of anhydrous HF to carboxylic acid is not a limitation of the present invention.
More important is the need to control the amount of water in the etching solution. The preferred range of water introduced to one embodiment of the present etching solution is in the range of approximately 0.5% to 5.0% by weight. Furthermore, use of an anhydrous carboxylic acid, e.g., glacial acetic acid, is preferred in order to more precisely control the amount of water in the etching solution.
The etching solution is created by injecting anhydrous HF into an aqueous solution of a carboxylic acid, such as glacial acetic acid, having a precisely controlled minimal amount of water. The proportions of the chemicals used for mixing are as described above.
The temperature required for use of the etching solution according to the present invention is not considered to be critical. In general, during etching it is preferred to use a cooler temperature of below approximately 30 degrees Celsius (°C), e.g., in the range of approximately 15°C-30°C. An advantage of such a cooler temperature is a reduction in the evaporative loss of the etching solution. Also, it is preferable that the etching solution is in the liquid phase during etching.
Furthermore, it is preferred that the etching solution and device having a sacrificial oxide to be etched be placed in a sealed environment substantially free of non-solution water. For example, a sealed container or etching bath with a closed lid having been purged with an inert gas such as nitrogen can be used. It has been discovered that water absorption from the atmosphere above the controlled minimal water levels of the etching solution undesirably increases the metal etching rate.
A working example of the use of anhydrous HF, glacial acetic acid, and water is provided below, only for the purpose of further illustration and is not intended to limit the scope of applicability of the present invention. As discussed hereinbefore, the preferred embodiment of the present invention is applicable to and useful for a wide variety of oxide sacrificial layers, micro-structures, and electronic components.
Example
A mixture of anhydrous HF (10%), glacial acetic acid (89%) and water (1%) , by weight, was prepared and used to etch a sample device having aluminum silicon alloy, doped polysilicon, silicon nitride, thermally grown Si02, and PSG surfaces. The etching was performed at 18 °C. and the sample etch rates measured as follows:
Material Etch Rate (angstroms/minute)
Al:Si 2-15
Polysilicon (doped) 0.5-2.0
Silicon nitride 4-14
Thermally grown Si02 130-160
PSG 10,000-100,000
Etch selectivities of sacrificial oxides relative to metals, polysilicons, and nitrides are derived from the associated etch rates. When using an etching solution of HF, carboxylic acid, and a minimal controlled amount of water, approximately in the ratio of 10:89:1, the etch selectivity for thermally grown SiO? relative to aluminum or copper is in the range of approximately 9 to 80; whereas, the etch selectivity for thermally grown Si02 relative to polysilicon is in the range of approximately 65 to 320. The etch selectivity for thermally grown Si02 relative to silicon nitride is in the range of approximately 9-40.
When using the same etching solution for a PSG sacrificial layer, the etch selectivity for PSG relative to aluminum or copper is in the range of approximately 666 to 50,000. The etch selectivity for PSG relative to polysilicon is in the range of approximately 5,000 to 200,000. The etch selectivity for PSG relative to silicon nitride is in the range of approximately 714 to 25,000. The wide range of etch selectivities for PSG is dependent on certain process parameters which include, but are not limited to whether the PSG film is annealed, the phosphorous doping level and the deposition temperature .
It has been discovered that controlling the amount of water in the etching solution to relatively small levels by the use of anhydrous HF and carboxylic acid, results in even more dramatic improvement in etch selectivity, especially with respect to aluminum and copper. The etch selectivity generally increases as the free water content of the etching solution decreases. The etch selectivities with respect to polysilicon and nitride are also high in the controlled minimal water embodiment.
By now it should be appreciated that there has been provided a novel etching solution of anhydrous HF, carboxylic acid, and water that is useful for etching sacrificial oxides during fabrication of MEMS devices. The etch selectivity of the present etching solution for sacrificial oxide layers relative to polysilicon, nitride, and metal is significantly higher than for prior sacrificial oxide etching solutions and now permits the practical integration of MEMS devices on the same chip as integrated circuit electronics.
Although the invention has been particularly shown and described with reference to an exemplary and preferred embodiment, it will be understood by those skilled in the art that changes in form and detail may be made therein without departing from the spirit and scope of the invention. For example, other suitable metals besides copper and aluminum can include alloys of aluminum and alloys of copper.

Claims

Claims
1. An etching solution, comprising: anhydrous hydrogen fluoride; a carboxylic acid; and water.
2. The etching solution of claim 1, wherein the carboxylic acid comprises at least one member selected from the group consisting of oxalic acid, lactic acid, tartaric acid, malic acid, succinic acid, citric acid and acetic acid.
3. The etching solution of claim 1, wherein the etching solution is characterized by an etching rate of a metal in the range of approximately 2 to 15 angstroms/minute, wherein the metal is selected from the group of metals consisting of aluminum, an alloy of aluminum, copper, and an alloy of copper.
4. The etching solution of claim 1, wherein the etching solution is made by injecting the hydrogen fluoride in a gaseous phase into a solution of the carboxylic acid and the water in a ratio of approximately 10:89:1 parts by weight hydrogen fluoride to carboxylic acid to water.
5. The etching solution of claim 1, wherein the etching solution is comprised of an amount of the water in the range of approximately 0.5% to 5% by weight.
6. A method for manufacturing a component having a dielectric material, comprising: providing an etch solution comprising: an aqueous mixture of water and a carboxylic acid; and hydrogen fluoride; and using the etch solution to etch the dielectric material.
7. The method of claim 6, wherein providing the etch solution comprises : forming an aqueous mixture of water and a carboxylic acid; 35 and injecting an anhydrous hydrogen fluoride into the aqueous mixture of water and the carboxylic acid.
8. A method of producing an etching solution, comprising: forming an aqueous mixture of water and a carboxylic acid; 15 and injecting an anhydrous hydrogen fluoride into the aqueous mixture of the water and the carboxylic acid, such that an amount of water in the etching solution is in the range of approximately 0.5% by weight to approximately 5% by weight.
9. A method for manufacturing a semiconductor component, comprising : providing a substrate having a dielectric material disposed thereon; and etching a portion of the dielectric material using an etching solution comprising: hydrogen fluoride; a carboxylic acid; and water.
10. A method for manufacturing a Micro Electro-Mechanical System (MEMS) component, comprising: providing a substrate having a dielectric material disposed thereon; and etching a portion of the dielectric material using an etching solution comprising: hydrogen fluoride; a carboxylic acid; and water .
EP01905084A 2000-02-04 2001-01-26 Etching solution and method Withdrawn EP1256126A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US49786400A 2000-02-04 2000-02-04
US497864 2000-02-04
PCT/US2001/002569 WO2001057921A1 (en) 2000-02-04 2001-01-26 Etching solution and method

Publications (1)

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EP1256126A1 true EP1256126A1 (en) 2002-11-13

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EP (1) EP1256126A1 (en)
JP (1) JP2003536242A (en)
KR (1) KR20020075907A (en)
AU (1) AU2001233002A1 (en)
WO (1) WO2001057921A1 (en)

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Publication number Priority date Publication date Assignee Title
TWI282814B (en) * 2002-09-13 2007-06-21 Daikin Ind Ltd Etchant and etching method
KR100626382B1 (en) 2004-08-03 2006-09-20 삼성전자주식회사 Etchant solutions and methods of forming a magnetic memory device using the same
JP4828451B2 (en) * 2006-03-27 2011-11-30 東京エレクトロン株式会社 Substrate processing method, semiconductor device manufacturing method, and substrate processing apparatus
WO2007140193A1 (en) * 2006-05-25 2007-12-06 Honeywell International Inc. Selective tantalum carbide etchant, methods of production and uses thereof

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4395304A (en) * 1982-05-11 1983-07-26 Rca Corporation Selective etching of phosphosilicate glass
US5824601A (en) * 1997-06-30 1998-10-20 Motorola, Inc. Carboxylic acid etching solution and method

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0157921A1 *

Also Published As

Publication number Publication date
KR20020075907A (en) 2002-10-07
JP2003536242A (en) 2003-12-02
WO2001057921A1 (en) 2001-08-09
AU2001233002A1 (en) 2001-08-14

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