Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
  • C01B15/055—Peroxyhydrates; Peroxyacids or salts thereof
  • C01B15/14—Peroxyhydrates; Peroxyacids or salts thereof containing silicon
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/082—Compounds containing nitrogen and non-metals and optionally metals
  • C01B21/0821—Oxynitrides of metals, boron or silicon
  • C01B21/0823—Silicon oxynitrides
• • 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
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
  • C23C16/308—Oxynitrides

Definitions

• the present invention relates to nitrogen doped silica, which may also be called silicon oxynitride or SiO x N y . More particularly, the present invention relates to nitrogen doped silica formed by using silazane or siloxazane starting materials.
• Silicon oxynitride is used in a variety of applications.
• the ability to vary the refractive index of silicon oxynitride over a wide range makes it an attractive material for optical applications.
• the refractive index of pure SiO 2 is 1.46
• the refractive index of Si 3 N 4 is 2.1. Therefore, the refractive index of silica doped with nitrogen can be varied between 1.46 and 2.1.
• doping silica optical waveguides with nitrogen helps to prevent UV radiation damage to the waveguide which causes undesirable losses.
• silicon oxynitride In optical waveguide applications, silicon oxynitride has been produced by plasma and nonplasma CVD processes, using silane and/or ammonia gases. For optical applications, however, use of ammonia is undesirable because ammonia contains hydrogen, and the resulting synthesized silicon oxynitride may contain a substantial proportion of hydrogen which significantly contributes to losses in the waveguide.
• silane raw materials must be handled very carefully due to the violent reaction caused when air is introduced into a closed container of silane.
• Silane is typically used in producing thin films on semiconductor substrates, which requires the deposition of a film having good characteristics for semiconductor applications. In the manufacture of semiconductor thin films the properties of the film are more important than deposition rate. In the production of optical devices, however, large quantities of material must be produced quickly, and the deposition rates for producing optical devices such as optical waveguides are much faster than deposition rates for semiconductor thin films.
• Silicon oxynitride may also be produced by the pyrolysis or hydrolysis of organometallic halides such as silicon tetrachloride.
• organometallic halides such as silicon tetrachloride.
• use of halides is not favored because the pyrolysis and hydrolysis of these materials produces chlorine or a very strong acid by-product, hydrochloric acid (HCl).
• Hydrochloric acid is detrimental not only to many deposition substrates and to reaction equipment but also is harmful to the environment.
• a carrier gas is bubbled through a liquid organic silicon containing compound.
• the resulting vaporous compound is transported to a burner via a carrier gas, wherein the vaporous gas streams are combusted in a burner flame fueled with natural gas and oxygen.
• the presence of oxygen in conventional OVD processes converts the vaporous reactants to their respective oxides, exiting the burner orifice to form a stream of volatile gases and fmely-divided spherical particles of soot that may be deposited onto a substrate forming a porous blank or preform of soot, for example, silica soot.
• OMCTSZ is a white solid at room temperature and has a boiling point of 225 °C.
• An OVD process described in U.S. Patent No. 5,152,819, which used OMCTSZ as a feedstock for the process produced a pure silica soot with less than 0.01% nitrogen contained in the soot.
• a method for manufacturing silicon oxynitride comprising the steps of providing a vaporous gas stream of a compound selected from the group consisting of siloxazanes and silazanes.
• a compound selected from the group consisting of siloxazanes and silazanes As one example of processing a compound in accordance with the method of the present invention, solid octamethylcyclotetrasilazane (OMCTSZ) is heated, preferably to a temperature of about 130 °C to about 225 °C, to provide OMCTSZ liquid, and a vaporous gas stream may be provided by bubbling an inert carrier gas through the OMCTSZ liquid to create a vaporous OMCTSZ gas stream.
• OMCTSZ solid octamethylcyclotetrasilazane
• the vaporous silazane gas stream is delivered to an enclosed reaction site which is heated to a temperature of at least about 500 °C, preferably between 700 °C and about 900 °C, where the gas stream is converted into particles of silicon oxynitride containing greater than 0.1% nitrogen by weight.
• the amount of oxygen present at the reaction site is strictly limited to prevent formation of pure silica at the reaction site and to promote the formation of silicon oxynitride.
• the level of oxygen at the reaction site is limited to very low levels by controlling the partial pressure of oxygen in the enclosed reaction site.
• the amount of oxygen present at the reaction site will depend on the desired composition of the silicon oxynitride end product produced by the method of the present invention.
• the stream of vaporous silazane forms silicon oxynitride at the heated reaction site.
• the stream of vaporous silazane gas can be combined with a vaporous gas stream of a silicon containing compound such as octamethylcyclotetrasiloxane.
• the present invention provides a method for manufacturing silicon oxynitride which does not contain a substantial proportion of hydrogen and provides a method which avoids the preferential bonding of oxygen atoms to silicon atoms encountered in OVD processes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
• the present invention provides a method of manufacturing silicon oxynitride using silazane or siloxazane starting materials.
• the present invention provides a method of manufacturing silicon oxynitride comprising the steps of providing a vaporous gas stream of a siloxazane or a silazane and delivering the vaporous gas stream to an enclosed reaction site, which is heated to a temperature of at least about 500 °C.
• siazane means an organosilicon nitrogen compound containing one or more silicon-nitrogen bonds, including amino silazanes, linear silazanes, and cyclosiloxanes, wherein a nitrogen atom and a single element or group of elements are bonded to the silicon atom.
• siloxazane as used in this application are compounds containing the unit [O-Si-N], including linear and cyclic siloxanes.
• a variety of silazanes and siloxazane may be used in the method of the present invention, including polysilazanes and polysiloxazanes.
• Delivery of the vaporous silazane or siloxazane gas stream to the reaction site may be accomplished by using an inert carrier gas such as nitrogen, argon, or helium.
• an inert carrier gas such as nitrogen, argon, or helium.
• the amount of oxygen present at the reaction site is strictly limited to prevent the formation of silica.
• the amount of oxygen at the reaction site is limited by controlling the partial pressure of the oxygen in the enclosed reaction site.
• a vaporous silazane gas stream is provided by heating solid octamethylcyclotetrasilazane (OMCTSZ) to provide OMCTSZ liquid.
• OMCTSZ solid octamethylcyclotetrasilazane
• the solid OMCTSZ should be heated to at least about 120 °C, preferably to about
• the solid OMCTSZ may be contained in a vessel and heated with any suitable heat source such as a hot plate, an oil bath, or heat tape.
• the method may further comprise bubbling an inert carrier gas through the OMCTSZ liquid to create a vaporous OMCTSZ gas stream.
• inert gas means a nonreactive gas, such as argon, nitrogen, or helium.
• the vaporous OMCTSZ is then delivered to an enclosed reaction site heated to about 700°C to about 800°C, where the amount of oxygen is strictly controlled to promote the formation of SiO x N y particles containing greater than 0.1% nitrogen by weight.
• the enclosed reaction site may be, for example, a fused silica tube.
• the tube may be placed in a furnace to heat the reaction site, or the tube may be surrounded by a heating element or a flame. By sealing the tube, the amount of oxygen inside the tube may be controlled.
• the vaporous OMCTSZ gas may be delivered by into the tube by a mass flow controller.
• the oxygen present at the reaction site may be controlled several ways. For example, delivering oxygen to the reaction site via a mass flow controller enables control of the amount of oxygen in the composition of the final SiON product. Limiting the amount of oxygen present at the reaction site promotes the formation silicon oxynitride and prevents the formation of pure silica.
• the composition of the silicon oxynitride produced by the process of the present invention can be varied according to the desired end use of the material.
• the material may, for example, be used for optical waveguide applications, and the amount of nitrogen in the silicon oxynitride composition would depend on the optical properties of the waveguide such as the desired refractive index profile of the waveguide.
• the optimum flow rate of the OMCTSZ gas stream and oxygen gas can be determined by experimentation.
• the amount of oxygen present at the reaction site may also be limited by simply enclosing the reaction site, for example in a sealed tube,, and allowing the reaction to occur with the oxygen present in the ambient air inside the tube.
• SiON it may not be necessary to supply any oxygen to the reactor tube.
• solid OMCTSZ was heated to 133 °C to form OMCTSZ liquid, and
• OMCTSZ gas stream 200 standard cubic centimeters per minute of nitrogen was bubbled through the liquid to form a vaporous OMCTSZ gas stream.
• the OMCTSZ gas stream was delivered to a reaction site, which was a silica tube heated to 750 °C. No oxygen was added to the reaction site, and the final SiON material produced contained 25.84% oxygen, as determined by electron spectroscopy for chemical analysis (ESCA).
• ESA electron spectroscopy for chemical analysis
• the silicon oxynitride made by the method of the present invention may be used for optical waveguides.
• the refractive index of Si 3 N 4 is higher than the refractive index of SiO 2 .
• a silica waveguide with nitrogen to form SiO x N y By doping a silica waveguide with nitrogen to form SiO x N y , a waveguide core may be formed, over which a silica cladding may be added to form an optical waveguide.
• the amount of nitrogen contained within the core material will depend on the desired refractive index profile of the waveguide.
• reaction stream of vaporous silazane or siloxazane can be combined with the with reaction stream of another silicon containing organic material such as octamethylcyclotetrasiloxane, which is delivered to the reaction site to provide an additional silica source material.
• An optical waveguide preform may be fabricated by using the method of the present invention wherein silicon oxynitride is deposited inside a fused silica tube.
• the silicon oxynitride deposited material forms a core region having a higher index of refraction than the cladding region which may comprise the wall of the silica tube.
• optical waveguide fabrication is a three-step process. Most of the processes currently used for the manufacture of optical waveguides involve a laydown process wherein a blank is manufactured by a CVD process such as OVD, MCVD, AVD, or PCVD.
• CVD process such as OVD, MCVD, AVD, or PCVD.
• the second stage of an optical fiber manufacturing process typically involves heat treating the blank in a helium/chlorine atmosphere to full consolidation.
• the third stage the blank is drawn into a waveguide, such as a waveguide fiber.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Chemical Vapour Deposition (AREA)
• Silicon Compounds (AREA)

Priority Applications (7)

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Cited By (1)

Citations (2)

• 1998
  • 1998-08-05 BR BR9811384-4A patent/BR9811384A/pt unknown
  • 1998-08-05 CA CA002297329A patent/CA2297329A1/en not_active Abandoned
  • 1998-08-05 ID IDW20000597A patent/ID24748A/id unknown
  • 1998-08-05 EP EP98938414A patent/EP1025041A1/en not_active Withdrawn
  • 1998-08-05 WO PCT/US1998/016358 patent/WO1999011573A1/en not_active Application Discontinuation
  • 1998-08-05 CN CN98808408A patent/CN1268099A/zh active Pending
  • 1998-08-05 JP JP2000508620A patent/JP2001514151A/ja not_active Withdrawn
  • 1998-08-05 KR KR1020007002095A patent/KR20010023452A/ko not_active Application Discontinuation
  • 1998-08-27 TW TW087114318A patent/TW509660B/zh active

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