EP3075003A1 - Etching process - Google Patents

Etching process

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Publication number
EP3075003A1
EP3075003A1 EP14825103.6A EP14825103A EP3075003A1 EP 3075003 A1 EP3075003 A1 EP 3075003A1 EP 14825103 A EP14825103 A EP 14825103A EP 3075003 A1 EP3075003 A1 EP 3075003A1
Authority
EP
European Patent Office
Prior art keywords
gas
gas mixture
etching
process according
oxygen
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Withdrawn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
EP14825103.6A
Other languages
German (de)
French (fr)
Inventor
Michael Pittroff
Thomas Schwarze
Christian Janssen
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.)
Solvay SA
Original Assignee
Solvay SA
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 Solvay SA filed Critical Solvay SA
Priority to EP14825103.6A priority Critical patent/EP3075003A1/en
Publication of EP3075003A1 publication Critical patent/EP3075003A1/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Withdrawn legal-status Critical Current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
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
    • H01L21/3065—Plasma etching; Reactive-ion etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F4/00—Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
    • 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
    • H01L21/31116—Etching inorganic layers by chemical means by dry-etching
    • 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
    • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
    • H01L21/321—After treatment
    • H01L21/3213—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer
    • H01L21/32133—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only
    • H01L21/32135—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only
    • H01L21/32136—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only using plasmas

Definitions

  • GWP Global Warming Potential
  • the invention makes available an improved process for the manufacture of the aforementioned and other devices. It is an objective of the present invention to provide a process which is more ecological, e.g. by using a gas mixture with an improved GWP. It is a further objective to provide a process which is more economical, e.g. by using a gas mixture comprising cheaper components and/or by enabling the use of less complex equipment. It is a further objective to provide a process with improved etching characteristics, e.g. by an improved anisotropy, an improved etching selectivity and/or by an improved etching rate.
  • the invention concerns a process for the manufacture of a device comprising at least one etching step wherein an inorganic material is etched using an etching agent which is generated in a transformation step starting from a gas mixture comprising, consisting of or essentially consisting of SF 4 .
  • the term "consists essentially of is intended to denote that the gas mixture consists of SF 4 as well as optionally trace amounts of further components, e.g. impurities, wherein the optional further components do not alter the essential characteristics of the gas mixture.
  • gas mixture also encompasses SF 4 as such without the presence of another component in the gas mixture.
  • SOF 2 is used instead of SF 4 or a mixture of SOF 2 and F 4 is used.
  • SOF 2 has a further advantage of being a fluorine-bearing as well as an oxygen-bearing gas.
  • SOF 4 is used instead of SF 4 , a mixture of SOF 4 and SF 4 or a mixture of SOF 4 , SOF 2 and SF 4 is used.
  • SOF 4 also has the further advantage of being a fluorine-bearing as well as an oxygen-bearing gas.
  • the device is selected from the list consisting of a
  • the device is a microelectromechanical system.
  • Microelectronic circuits process the information gathered by sensors from the environment through measuring mechanical, thermal, biological, chemical, optical or magnetic phenomena.
  • the dry etching hardware generally involves a vacuum chamber, a special gas delivery system, and an exhaust system and in case of a plasma generated by radio frequency discharge, a radio frequency generator.
  • Said radio frequency generator is preferably located outside of the vacuum chamber to allow for longer lifetime of the equipment involved.
  • the process is best performed using the Bosch process which may be carried out in plasma etchers available from Alcatel, Advanced Materials, Plasma-Therm or Surface Technology Systems.
  • the plasma is generated by a magnetron or microwave irradiation.
  • the SF 4 can be applied in the gas mixture as such, i.e. without diluent or additional compounds.
  • the concentration of the SF 4 in the gas mixture is >10 Vol %, preferably > 35 Vol %, more preferably > 50 Vol % and most preferably > 90 Vol %. It is also preferred to apply it diluted by an inert gas and/or in the presence of oxygen or an oxygen-bearing gas and/or in the presence of gases or vapors which have a passivating effect.
  • Preferred inert gases are selected from the group consisting of N 2 , Ar, Xe, He and Ne, more preferably N 2 .
  • additives like hydrogen or passivating gases can also be added.
  • the gas mixture comprises SF 4 and at least one further gas selected from the group consisting of an inert gas and an oxygen-bearing gas.
  • the gas mixture used in the process is a ternary gas mixture comprising SF 4 , an oxygen-bearing gas and an inert gas, preferably the gas mixture consists of or essentially consists of SF 4 , Ar and 0 2 .
  • the process for the manufacture of the MEMS may involve a step of anisotropic and isotropic etching.
  • anisotropic etching the etching gas forms a trench by etching the bottom of the trench without or nearly without affecting the side walls. If isotropic etching is desired, prevention of side wall etching is not necessary. In anisotropic etching, side wall etching is undesired.
  • a preferred method of anisotropic etching is performed by either including a passivating gas into the etching gas wherein the passivating gas protects the side walls, or by sequential etching with the etching agent and in a separate step, forming a passivating layer on the side walls using a passivating gas.
  • At least 50 % of the hydrogen atoms of the respective saturated or unsaturated compound are substituted by fluorine atoms.
  • Preferred gas mixtures for passivation only (with low or no anisotropic etching effect) in MEMS preparation include one or more of the above- mentioned aliphatic cyclic, linear or branched fluorocarbons or
  • hydrofluorocarbons with 1 to 6 carbon atoms (saturated) or 2 to 6 carbon atoms (unsaturated).
  • a hydrogen or a hydrogen-releasing gas a gas that releases hydrogen under thermal conditions, especially at temperatures at or higher than 200°C, or in a plasma, preferably difluoromethane or
  • trifluoromethane is also present, especially, if perf uorinated compounds are applied as passivating gas.
  • hydrogen or a hydrogen-releasing gas is present, it is preferably comprised in an amount of 1 to 5 Vol %. Also, it is possible to include argon for improving the plasma.
  • the process for MEMS etching can principally be performed in two alternatives : the structure is treated with the etching agent and the passivating gas simultaneously, or treatment with the etching agent is performed in one step, and treatment with the passivating gas is performed in another step; the second alternative wherein etching and passivation are consecutively performed is called “Bosch" process. The "Bosch"-type process is preferred.
  • an additional step can be performed to achieve underetching, as described in GB 2 290 413. In this step, it is preferred only to apply the etching agent.
  • the etching step is performed on a structure that later forms part of the device or the structure itself constitutes said device.
  • the temperature of the structure during plasma treatment will generally be kept in a range from 20°C to 100°C, but it may be higher.
  • the pressure during the plasma treatment is preferably from 1.5 ⁇ 10 ⁇ 2 mbar to 15 mbar. Preferably, the pressure is equal to or greater than 1 ⁇ 10 "1 mbar. It is preferably equal to or lower than 1.5 mbar.
  • the structure may have variable forms, it is preferably in the shape of a wafer.
  • the structure is generally made from an inorganic material.
  • the inorganic material is Si, SiO x N y , Si0 2 , TaN, TiN or W, more preferably it is amorphous Si.
  • the structure used in the etching step is a silicon wafer.
  • the etching can be performed according to the bulk micromachining technology wherein the whole thickness of the item to be etched, e.g. a silicon wafer, is used to build the micromechanical structure.
  • the etching can be performed according to the surface micromachining technology wherein layers are produced by applying coatings and selective etching of them.
  • the etching process can generally be used in the deep reactive ion etching
  • the process according to the present invention can be applied to produce semiconductors for microelectromechanical systems, for example, acceleration sensors, magnetic recording heads, ink jet printers, gyroscopes and other items as described above.
  • One advantage of the process according to the present invention is that NF 3 and/or SF 6 can be substituted by a gas mixture which is environmentally friendly in view of GWP. It has been found that the gas mixtures in the process according to the present invention are, for many applications, comparable and sometimes better than the conventional etching or cleaning processes using NF 3 and/or SF 6 .
  • a further advantage of the process is that the gas mixtures according to the present invention can be used as drop-in substitutes for the respective conventional mixtures. Accordingly, another embodiment of the present invention concerns a process wherein the gas mixtures comprising or consisting of SF 4 are used as a drop-in substitute for gas mixtures comprising NF 3 and/or SF 6 , preferably under substantially the same conditions.
  • Another aspect of the present invention concerns the use of a gas mixture comprising, consisting of or essentially consisting of SF 4 for the preparation of an etching agent used in the manufacture of a device, preferably the etching agent is prepared in a thermal transformation step or a radiofrequency discharge transformation step starting from the gas mixture.
  • the device is selected from the list consisting of a semiconductor material, a solar panel, a flat panel, or a microelectromechanical system, preferably the device is a microelectromechanical system.
  • Yet another aspect of the present invention concerns a gas mixture comprising, consisting of or essentially consisting of SF 4 , Ar and 0 2 .
  • inventive gas mixture can also be used to clean the vacuum chamber of such unwanted deposits. Accordingly, still another aspect of the present invention concerns the use of a gas mixture comprising, consisting of or essentially consisting of SF 4 for chamber cleaning.
  • temperature in the chamber is controlled and can be varied between room temperature (around 20°C) and 300°C.
  • the remote plasma source is usually ignited in the presence of pure argon.
  • the gas mixture comprising SF 4 is introduced.
  • the etch rates was determined in situ by reflectrometry using a 645 nm laser directed to the sample.
  • the etch rate is calculated by dividing the thickness of the film by the time when the removal endpoint was detected.
  • the size of the samples is 20 ⁇ 20 mm.
  • the investigated material is deposited on a 150 nm thermal Si0 2 layer to allow interferometric measurement.
  • the SiON and Si0 2 samples are deposited on bulk silicon since their optical properties allow interferometric measurements.
  • SiON 1000 nm SiO x N y (referred to as SiON) on bulk silicon, deposited by a conventional TEOS/ozone CVD process
  • Example 2 MEMS production
  • a silicon wafer for a MEMS device is coated with a photo resist lacquer. After partial exposure of the photo resist lacquer with light according to the desired structure including desired trenches, non-exposed parts of the lacquer are removed. The silicon wafer is then put into a plasma chamber. A gas mixture according to example 1.1 is introduced into the chamber at a pressure of about 0.2 mbar, and the microwave radiation is started to initiate plasma conditions. Silicon in regions not covered by the photo resist is etched away isotropically whereby a trench forms in the silicon. After a trench with a width of about 20 ⁇ is formed, the etching agent is removed from the reactor, and a passivation gas according to example 1.5 is introduced into the reactor, and the microwave radiation is started to initiate the plasma.
  • the hexafluorobutadiene introduced into the reactor essentially forms a fluoropolymer coating on the walls of the trenches formed in the silicon, while the argon stabilizes the plasma.
  • the passivating gas is removed, and fresh etching gas is re-introduced into the reactor.
  • the silicon layer is then again isotropically etched, thereby deepening the trench formed in the first etching step.
  • the passivating layer protects the wall of the trench.
  • passivating gas is introduced, and another passivating step is performed. Thereafter, the passivating gas is removed, and the anisotropic etching is continued. Etching and passivation are consecutively performed until a trench with desired depth has formed.
  • the etched wafer can be removed from the chamber.
  • a silicon wafer is coated with a dielectric layer of silicon dioxide which, in turn, is coated with a photo resist lacquer. After partial exposure of the photo resist lacquer with light according to the desired structure including desired trenches, non-exposed parts of the lacquer are removed.
  • the silicon wafer is then put into a plasma chamber.
  • a gas mixture according to example 2.1 is introduced into the chamber at a pressure of about 0.2 mbar, and the microwave radiation is started to initiate plasma conditions. Silicon dioxide in regions not covered by the photo resist is etched away. During etching, a trench forms. Simultaneously, a fluoropolymer passivation layer is formed on the walls of the trench. The treatment is continued until the trench has the desired depth.
  • the etching agent and passivating gas are removed from the reactor, and the etched silicon wafer can be removed from the chamber.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
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  • Condensed Matter Physics & Semiconductors (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
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Abstract

Processes for the manufacture of devices including microelectromechanical systems comprising a step in which a substrate is etched using an etching agent prepared from SF4 are disclosed.

Description

Etching Process
This application claims priority to European application No. EP
13194774.9 filed on 28 November 2013, the whole content of this application being incorporated herein by reference for all purposes. The present invention relates to a method for the manufacture of a device comprising a step in which a substrate is etched using an etching agent prepared from a SF4-containing mixture.
NF3 and SF6 are often used in dry etching steps in the production of devices like semiconductors, solar cells and/or microelectromechanical systems (MEMS). NF3 and SF6 can be used to etch inorganic coatings like SiON, amorphous Si, Si02, TiN, TaN or W. For example, WO 88/08930 discloses a process for etching deep trenches into silicon using NF3 and SF6.
However, both NF3 and SF6 show a relatively high Global Warming Potential (GWP).
Now therefore, the invention makes available an improved process for the manufacture of the aforementioned and other devices. It is an objective of the present invention to provide a process which is more ecological, e.g. by using a gas mixture with an improved GWP. It is a further objective to provide a process which is more economical, e.g. by using a gas mixture comprising cheaper components and/or by enabling the use of less complex equipment. It is a further objective to provide a process with improved etching characteristics, e.g. by an improved anisotropy, an improved etching selectivity and/or by an improved etching rate.
These and other objects of the present invention are achieved by the process according to the claims.
In a first embodiment the invention concerns a process for the manufacture of a device comprising at least one etching step wherein an inorganic material is etched using an etching agent which is generated in a transformation step starting from a gas mixture comprising, consisting of or essentially consisting of SF4.
The term "consists essentially of is intended to denote that the gas mixture consists of SF4 as well as optionally trace amounts of further components, e.g. impurities, wherein the optional further components do not alter the essential characteristics of the gas mixture. The term "gas mixture" also encompasses SF4 as such without the presence of another component in the gas mixture. In an alternative embodiment, SOF2 is used instead of SF4 or a mixture of SOF2 and F4 is used. SOF2 has a further advantage of being a fluorine-bearing as well as an oxygen-bearing gas. In another alternative embodiment, SOF4 is used instead of SF4, a mixture of SOF4 and SF4 or a mixture of SOF4, SOF2 and SF4 is used. SOF4 also has the further advantage of being a fluorine-bearing as well as an oxygen-bearing gas.
Preferably, the device is selected from the list consisting of a
semiconductor material, a solar panel, a flat panel, or a micro electromechanical system (MEMS). Preferably, the device is a microelectromechanical system.
MEMS are very small devices, generally ranging in the size from a micrometer to a millimeter. Common applications include inkjet printers operating with piezoelectrics or thermal bubble ejection, accelerometers in cars, e.g. for airbag deployment in collisions, gyroscopes, silicon pressure sensors e.g. for monitoring car tires or blood pressure, optical switching technology or bio-MEMS applications in medical and health-related technologies.
Microelectronic circuits process the information gathered by sensors from the environment through measuring mechanical, thermal, biological, chemical, optical or magnetic phenomena.
Devices like semiconductor materials, solar panels, flat panels, or microelectromechanical systems are usually manufactured using a dry etching step, i.e. a step involving the removal of material using an etching agent. The term "etching agent" is intended to denote the active agent which is involved in this etching step by chemically reacting with the inorganic material to be etched. This etching agent usually comprises ions, i.e. the etching agent is a plasma, and it can be prepared by transformation of a gas mixture for example by thermal transformation or by radio frequency discharge. If the etching agent is generated thermally, the temperature during the transformation step is equal to or higher than 200°C, and equal to or lower than 500°C.
The dry etching hardware generally involves a vacuum chamber, a special gas delivery system, and an exhaust system and in case of a plasma generated by radio frequency discharge, a radio frequency generator. Said radio frequency generator is preferably located outside of the vacuum chamber to allow for longer lifetime of the equipment involved. The process is best performed using the Bosch process which may be carried out in plasma etchers available from Alcatel, Advanced Materials, Plasma-Therm or Surface Technology Systems. The plasma is generated by a magnetron or microwave irradiation.
One advantage of SF4 over SF6 and NF3 is that a plasma can be generated under thermal conditions, i.e. without the use of a radiofrequency generator.
Accordingly, the transformation step is preferably a thermal transformation step or a radiofrequency discharge transformation step, more preferably a remote- source radiofrequency discharge step.
SF4 can be applied in the gas mixture as such, i.e. without diluent or additional compounds. Preferably, the concentration of the SF4 in the gas mixture is >10 Vol %, preferably > 35 Vol %, more preferably > 50 Vol % and most preferably > 90 Vol %. It is also preferred to apply it diluted by an inert gas and/or in the presence of oxygen or an oxygen-bearing gas and/or in the presence of gases or vapors which have a passivating effect. Preferred inert gases are selected from the group consisting of N2, Ar, Xe, He and Ne, more preferably N2. Further, additives like hydrogen or passivating gases can also be added. Also preferably, the gas mixture comprises SF4 and at least one further gas selected from the group consisting of an inert gas and an oxygen-bearing gas.
The term "oxygen-bearing gas" is intended to denote a gas the chemical structure of which contains an oxygen atom. Preferred oxygen-bearing gases are selected from the group consisting of 02, 03, N20, C02, CO and S02, more preferably the oxygen-bearing gas is 02. Amongst other roles, the oxygen- bearing gas can have the role to oxidize certain other compounds, e.g. the SF4 and/or other sulphur-containing compounds. Some of these other compounds might be converted into volatile components by this oxidation process.
Most preferably, the gas mixture used in the process is a ternary gas mixture comprising SF4, an oxygen-bearing gas and an inert gas, preferably the gas mixture consists of or essentially consists of SF4, Ar and 02.
The process for the manufacture of the MEMS may involve a step of anisotropic and isotropic etching. In anisotropic etching, the etching gas forms a trench by etching the bottom of the trench without or nearly without affecting the side walls. If isotropic etching is desired, prevention of side wall etching is not necessary. In anisotropic etching, side wall etching is undesired. A preferred method of anisotropic etching is performed by either including a passivating gas into the etching gas wherein the passivating gas protects the side walls, or by sequential etching with the etching agent and in a separate step, forming a passivating layer on the side walls using a passivating gas. The passivating gas is applied to form a protective layer on the trench walls to prevent them to react with the etching agent. The nature of the passivating gas depends on the kind of structure. For silicon as structure, bromine sources, for example elemental bromine or HBr can be applied as passivating gas. A layer of non- volatile SixBrY compounds is formed as a protective layer. Other sources forming a protective layer with silicon are CS2 or a combination of SiCl4 and N2. The passivating gas is preferably selected from cyclic, linear or branched saturated aliphatic compounds with 1 to 6 carbon atoms, substituted by at least one fluorine atom, or from cyclic, linear or branched unsaturated aliphatic compounds with 2 to 6 carbon atoms, substituted by at least one fluorine atom. These compounds consist of carbon and fluorine and optionally hydrogen.
Preferably, at least 50 % of the hydrogen atoms of the respective saturated or unsaturated compound are substituted by fluorine atoms. Saturated
hydrofluorocarbons and saturated f uorocarbons with 1 to 6 carbon atoms and unsaturated hydrofluorocarbons and unsaturated fluorocarbons with 2 to 6 carbon atoms are preferred. Highly preferred compounds which are applicable as passivating gas are C-C4F6, c-CsFs, CH2F2, CHF3, CF4, C2F6, C3F8, C2F4, C4F6, and C4F8. The compounds c-C6F6 and CF3I are also suitable. C4F6 is especially preferred as passivating gas. The expert knows that some of the suitable compounds have a boiling point which is higher than 20°C at normal pressure and is aware that for these compounds, the term "gas" should be understood to mean "vapor". These compounds are suitable even if not gaseous at 20°C because the process of the present invention is performed at a pressure low enough for these compounds to be no longer liquids but in the form of a vapor.
Preferred gas mixtures for passivation only (with low or no anisotropic etching effect) in MEMS preparation include one or more of the above- mentioned aliphatic cyclic, linear or branched fluorocarbons or
hydrofluorocarbons with 1 to 6 carbon atoms (saturated) or 2 to 6 carbon atoms (unsaturated). Optionally, a hydrogen or a hydrogen-releasing gas (a gas that releases hydrogen under thermal conditions, especially at temperatures at or higher than 200°C, or in a plasma), preferably difluoromethane or
trifluoromethane, is also present, especially, if perf uorinated compounds are applied as passivating gas. If hydrogen or a hydrogen-releasing gas is present, it is preferably comprised in an amount of 1 to 5 Vol %. Also, it is possible to include argon for improving the plasma. The process for MEMS etching can principally be performed in two alternatives : the structure is treated with the etching agent and the passivating gas simultaneously, or treatment with the etching agent is performed in one step, and treatment with the passivating gas is performed in another step; the second alternative wherein etching and passivation are consecutively performed is called "Bosch" process. The "Bosch"-type process is preferred.
If desired, after forming the trench by etching and passivation, an additional step (or multitude of steps) can be performed to achieve underetching, as described in GB 2 290 413. In this step, it is preferred only to apply the etching agent.
The etching step is performed on a structure that later forms part of the device or the structure itself constitutes said device.
The temperature of the structure during plasma treatment will generally be kept in a range from 20°C to 100°C, but it may be higher. The pressure during the plasma treatment is preferably from 1.5 · 10~2 mbar to 15 mbar. Preferably, the pressure is equal to or greater than 1 · 10"1 mbar. It is preferably equal to or lower than 1.5 mbar.
While the structure may have variable forms, it is preferably in the shape of a wafer. The structure is generally made from an inorganic material.
Preferably, the inorganic material is Si, SiOxNy, Si02, TaN, TiN or W, more preferably it is amorphous Si. Most preferably, the structure used in the etching step is a silicon wafer.
The etching can be performed according to the bulk micromachining technology wherein the whole thickness of the item to be etched, e.g. a silicon wafer, is used to build the micromechanical structure. Alternatively, the etching can be performed according to the surface micromachining technology wherein layers are produced by applying coatings and selective etching of them. The etching process can generally be used in the deep reactive ion etching
technology.
The process according to the present invention can be applied to produce semiconductors for microelectromechanical systems, for example, acceleration sensors, magnetic recording heads, ink jet printers, gyroscopes and other items as described above.
One advantage of the process according to the present invention is that NF3 and/or SF6 can be substituted by a gas mixture which is environmentally friendly in view of GWP. It has been found that the gas mixtures in the process according to the present invention are, for many applications, comparable and sometimes better than the conventional etching or cleaning processes using NF3 and/or SF6. A further advantage of the process is that the gas mixtures according to the present invention can be used as drop-in substitutes for the respective conventional mixtures. Accordingly, another embodiment of the present invention concerns a process wherein the gas mixtures comprising or consisting of SF4 are used as a drop-in substitute for gas mixtures comprising NF3 and/or SF6, preferably under substantially the same conditions.
Another aspect of the present invention concerns the use of a gas mixture comprising, consisting of or essentially consisting of SF4 for the preparation of an etching agent used in the manufacture of a device, preferably the etching agent is prepared in a thermal transformation step or a radiofrequency discharge transformation step starting from the gas mixture. Also preferably, the device is selected from the list consisting of a semiconductor material, a solar panel, a flat panel, or a microelectromechanical system, preferably the device is a microelectromechanical system.
Yet another aspect of the present invention concerns a gas mixture comprising, consisting of or essentially consisting of SF4, Ar and 02.
During operation of the vacuum chamber, depositions can occur on the inside walls of the vacuum chamber. Regular removal of such deposits is desirable to obtain stable and repeatable deposition results with uniform surfaces at acceptable particle levels. This process is known under the name "chamber cleaning". The inventive gas mixture can also be used to clean the vacuum chamber of such unwanted deposits. Accordingly, still another aspect of the present invention concerns the use of a gas mixture comprising, consisting of or essentially consisting of SF4 for chamber cleaning.
Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.
The following examples shall explain the invention in further detail, but they are not intended to limit the scope of the invention.
Examples :
Example 1 : Etching of structures of different materials :
Used apparatus : Experiments are performed in a custom-made stainless steel vacuum chamber (26 liters volume) with an attached remote Astron Astex plasma source, made by MKS Astron, operated at 13.56 MHz, located 32 cm above the sample. The chamber is evacuated with a turbo molecular pump and a BOC Edwards dry pump. The exhaust gases are analyzed by mass spectroscopy; a differentially pumped Leybold-Inficon Transpector 200 amu unit is used. The structure to be etched is placed on a chuck in the center of the reactor chamber. The
temperature in the chamber is controlled and can be varied between room temperature (around 20°C) and 300°C.
The remote plasma source is usually ignited in the presence of pure argon.
Directly after the plasma is in a stable condition, the gas mixture comprising SF4 is introduced.
Determination of etch rates :
The etch rates was determined in situ by reflectrometry using a 645 nm laser directed to the sample. The etch rate is calculated by dividing the thickness of the film by the time when the removal endpoint was detected.
Preparation of the mixtures :
The individual components are filled in their corresponding ratios into a pressure vessel, thereby forming a homogeneous mixture of the compounds. Structures to be etched :
The size of the samples is 20χ20 mm. The investigated material is deposited on a 150 nm thermal Si02 layer to allow interferometric measurement. The SiON and Si02 samples are deposited on bulk silicon since their optical properties allow interferometric measurements.
The following structures are used :
a) 1000 nm SiOxNy (referred to as SiON) on bulk silicon, deposited by a conventional TEOS/ozone CVD process
b) 1000 nm Si02, thermally grown on bulk silicon
c) 300 nm tungsten, deposited by a conventional PVD process
d) 300 nm TiN, deposited by a conventional PVD process
e) 200 nm TaN, deposited by a conventional PVD process
Example 2 : MEMS production
Mixtures suitable for etching silicon in MEMS production
General procedure : the different constituents are passed in gaseous form from respective storing bottles to a stainless steel container stored therein in gaseous form. By controlling the volume during storing the respective gases, gas mixtures comprising the appropriate amounts of gases given in table 1 are prepared.
Table 1 : Gas mixtures (amounts given in % by volume)
Table 2 : Passivating gas mixtures (amounts given in % by volume)
Table 3 : Gas mixtures suitable for simultaneous etching and passivating
(amounts given in % by volume)
) Hexafluorobutadiene, available as Sifren® from Solvay Fluor GmbH, Hannover, Germany
Preparation of a MEMS device by consecutive etching and passivating (bulk micromachining)
A silicon wafer for a MEMS device is coated with a photo resist lacquer. After partial exposure of the photo resist lacquer with light according to the desired structure including desired trenches, non-exposed parts of the lacquer are removed. The silicon wafer is then put into a plasma chamber. A gas mixture according to example 1.1 is introduced into the chamber at a pressure of about 0.2 mbar, and the microwave radiation is started to initiate plasma conditions. Silicon in regions not covered by the photo resist is etched away isotropically whereby a trench forms in the silicon. After a trench with a width of about 20 μιη is formed, the etching agent is removed from the reactor, and a passivation gas according to example 1.5 is introduced into the reactor, and the microwave radiation is started to initiate the plasma. The hexafluorobutadiene introduced into the reactor essentially forms a fluoropolymer coating on the walls of the trenches formed in the silicon, while the argon stabilizes the plasma. After a coating with desired thickness has formed on the walls, the passivating gas is removed, and fresh etching gas is re-introduced into the reactor. The silicon layer is then again isotropically etched, thereby deepening the trench formed in the first etching step. The passivating layer protects the wall of the trench. When the desired additional depth of the trench is achieved, etching is terminated and the etching agent is removed from the plasma reactor. Once again, passivating gas is introduced, and another passivating step is performed. Thereafter, the passivating gas is removed, and the anisotropic etching is continued. Etching and passivation are consecutively performed until a trench with desired depth has formed. The etched wafer can be removed from the chamber.
Preparation of a MEMS device by simultaneous etching and passivating (bulk micromachining)
A silicon wafer is coated with a dielectric layer of silicon dioxide which, in turn, is coated with a photo resist lacquer. After partial exposure of the photo resist lacquer with light according to the desired structure including desired trenches, non-exposed parts of the lacquer are removed. The silicon wafer is then put into a plasma chamber. A gas mixture according to example 2.1 is introduced into the chamber at a pressure of about 0.2 mbar, and the microwave radiation is started to initiate plasma conditions. Silicon dioxide in regions not covered by the photo resist is etched away. During etching, a trench forms. Simultaneously, a fluoropolymer passivation layer is formed on the walls of the trench. The treatment is continued until the trench has the desired depth. The etching agent and passivating gas are removed from the reactor, and the etched silicon wafer can be removed from the chamber.

Claims

C L A I M S
1. A process for the manufacture of a device comprising at least one step wherein an inorganic material is etched using an etching agent which is generated in a transformation step starting from a gas mixture comprising, consisting of or essentially consisting of SF4.
2. The process according to claim 1 wherein the device is selected from the list consisting of a semiconductor material, a solar panel, a flat panel, or a microelectromechanical system, preferably the device is a
microelectromechanical system.
3. The process according to claim 1 or 2 wherein the etching agent is generated in a thermal transformation step or a radio frequency discharge transformation step, preferably a remote-source radio frequency discharge transformation step.
4. The process according to any one of claims 1 to 3 wherein the concentration of the SF4 in the gas mixture is >10 Vol %, preferably > 35 Vol %, more preferably > 50 Vol % and most preferably > 90 Vol %.
5. The process according to any one of claims 1 to 4 wherein the gas mixture comprises SF4 and at least one further gas selected from the group consisting of an inert gas and an oxygen-bearing gas.
6. The process according to claim 5 wherein the inert gas is selected form the group consisting of N2, Ar, Xe, He and Ne.
7. The process according to claim 5 wherein the oxygen-bearing gas is selected from the group consisting of 02, 03, N20, C02, CO and S02, preferably the oxygen-bearing gas is 02.
8. The process according to any one of claims 1 to 7 wherein the gas mixture is a ternary gas mixture comprising SF4, an oxygen-bearing gas and an inert gas, preferably the gas mixture consists of or essentially consists of SF4, Ar and 02.
9. The process according to any one of claims 1 to 8 wherein the inorganic material is Si, SiOxNy, Si02, TaN, Ti or W.
10. The process according to any one of claims 1 to 9 wherein the gas mixture is used as a drop-in substitute for gas mixtures comprising NF3 and/or SF6, preferably under substantially the same conditions.
11. Use of a gas mixture comprising, consisting of or essentially consisting of SF4 for the preparation of an etching agent used in the manufacture of a device.
12. The use according to claim 11 wherein the etching agent is prepared in a thermal transformation step or a radio frequency discharge transformation step starting from the gas mixture.
13. The use according to claim 11 or 12 wherein the device is selected from the list consisting of a semiconductor material, a solar panel, a flat panel, or a microelectromechanical system, preferably the device is a
microelectromechanical system.
14. A gas mixture comprising, consisting of or essentially consisting of SF4, Ar and 02.
15. Use of a gas mixture comprising, consisting of or essentially consisting of SF4 for chamber cleaning.
EP14825103.6A 2013-11-28 2014-11-19 Etching process Withdrawn EP3075003A1 (en)

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JP2964605B2 (en) * 1990-10-04 1999-10-18 ソニー株式会社 Dry etching method
DE4420962C2 (en) 1994-06-16 1998-09-17 Bosch Gmbh Robert Process for processing silicon
US6127271A (en) * 1998-04-28 2000-10-03 Balzers Hochvakuum Ag Process for dry etching and vacuum treatment reactor
TWI291201B (en) * 2000-07-18 2007-12-11 Showa Denko Kk Cleaning gas for semiconductor production equipment
CN102866458B (en) * 2012-08-20 2015-05-13 东南大学 Preparation process for etching deep optical waveguide

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Title
PATEAU AMAND ET AL: "Modeling of inductively coupled plasma SF6/O2/Ar plasma discharge: Effect of O2on the plasma kinetic properties", JOURNAL OF VACUUM SCIENCE AND TECHNOLOGY: PART A, AVS /AIP, MELVILLE, NY., US, vol. 32, no. 2, 1 January 1901 (1901-01-01), XP012184288, ISSN: 0734-2101, [retrieved on 19010101], DOI: 10.1116/1.4853675 *
See also references of WO2015078749A1 *

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