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WO2008152666A1 - Process for the deposition of layers of hydrogenated silicon carbide - Google Patents

Process for the deposition of layers of hydrogenated silicon carbide Download PDF

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Publication number
WO2008152666A1
WO2008152666A1 PCT/IT2007/000431 IT2007000431W WO2008152666A1 WO 2008152666 A1 WO2008152666 A1 WO 2008152666A1 IT 2007000431 W IT2007000431 W IT 2007000431W WO 2008152666 A1 WO2008152666 A1 WO 2008152666A1
Authority
WO
WIPO (PCT)
Prior art keywords
deposition
silicon carbide
layers
hydrogenated silicon
substrate
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.)
Ceased
Application number
PCT/IT2007/000431
Other languages
French (fr)
Inventor
Giovanni Taglioni
Luca Novella
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.)
Selex Galileo SpA
Original Assignee
Galileo Avionica SpA
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 Galileo Avionica SpA filed Critical Galileo Avionica SpA
Priority to PCT/IT2007/000431 priority Critical patent/WO2008152666A1/en
Publication of WO2008152666A1 publication Critical patent/WO2008152666A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
    • 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
    • C23C16/32—Carbides
    • C23C16/325—Silicon carbide
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors

Definitions

  • the present invention relates to a process for the deposition of layers of hydrogenated silicon carbide.
  • SiC Silicon carbide
  • SiC is a ceramic material with physical properties that make it particularly suitable for the production of high-performance mirrors in a wide range of applications. ' In. particular, SiC has proved to . be very interesting i ' n applications with a wavelength interval ranging from infrared to X rays, and in which high thermal stability and low weight .are required. Due to these characteristics, SiC mirrors are very interesting for space applications.
  • SiC substrates can be produced in different ways, and in all cases the substrate obtained is not particularly dense or homogeneous. In fact, due to its residual porosity, the substrate requires a surface polishing operation to obtain a particularly polished reflecting surface.
  • the deposition takes place in a reactor at a temperature of between 1000 and 2000 0 C according to the process used.
  • a temperature of between 1000 and 2000 0 C constitutes a problem in relation to the thermal and mechanical stability of the mirror.
  • not all substrates can withstand such high temperatures, and furthermore said temperatures require careful assessment of the respective coefficients of thermal expansion of the coating and substrate.
  • the aim of the present invention is to provide a process for the deposition of layers of SiC, the technical characteristics of which are such as to overcome the drawbacks of the known art.
  • the object of the present invention is a process for the deposition of layers of hydrogenated silicon carbide by means of PECVD technique, characterised by
  • the organosilane compound is (CH 3 ) 3 -Si-NH-Si-(CH 3 ) 3
  • the system 1 comprises a deposition chamber 2, pumping means 3 for obtaining the vacuum inside the deposition chamber 2, an electrode 4 on which a substrate 5 is fixed, on which the deposit is made, and an inlet unit 6 for a gaseous mixture which will constitute the plasma.
  • the pressure inside the deposition chamber 2 must be between 0.1 and 0.5 mbar.
  • the electrode 4 can be fixed or rotating and is connected to a radio frequency generator 7 via a Match Box 8.
  • the radio frequency generator 7 operates at a frequency of 13.65 MHz while the power sent depends on the dimensions of the electrode and can vary from a few hundred to a few thousand Watts .
  • the inlet unit 6 comprises a heated tank 9, inside which the liquid organosilane compound is placed, a conduction system 10 comprising a plurality of heated pipes suitable for conveying the gaseous mixture which has formed between the organosilane compound and an inert gas, a flow control device 11, and a diffuser element 12 positioned at a certain distance from the electrode 4 and from which the gaseous mixture flows out in a uniform manner .
  • the organosilane compound will be present inside the tank 9 both in the liquid phase and in the vapour phase.
  • This vapour is appropriately mixed with an inert gas and conveyed by means of the conduction system 10 to the diffuser 12.
  • the flow of inert gases depends on the dimensions of the deposition chamber 2 .
  • the gaseous mixture flowing out of the diffuser 12 forms a plasma under the action of the electromagnetic field generated by the electrode 4. Inside the plasma, dissociation of the organosilane compound takes place and subsequent deposition of the hydrogenated silicon carbide on the substrate 5.
  • the organosilane compound used is hexamethyldisilazane or hexamethyldisiloxane. It has been found that by using the hexamethyldisilazane, a layer of hydrogenated silicon carbide more resistant to oxidisation is obtained.
  • the temperature of the electrode 4 and, therefore, of the ' substrate 5 fixed to it, is kept if necessary at a pre-set temperature by means of a known external cooling/heating circuit not illustrated for the sake of simplicity.
  • EXAMPLE Depositions • of hydrogenated silicon carbide were produced with a thickness of 200 ⁇ m on different substrates, for example aluminium alloys, sintered SiC etc., the ' surfaces of which were prepared with standard mechanical finishing techniques.
  • the deposition was performed by using a circular electrode with a diameter of 150 mm and connected to a radio frequency generator operating at 13.65 MHz, at a power of 400W obtaining an initial self-polarisation of approximately -200 Volt.
  • the electrode was kept at a temperature of 100 0 C.
  • the deposition chamber was depressurised to a base value of 10 "4 mbar and kept at a value of 10 "1 mbar during the deposition process.
  • the coating layer of hydrogenated silicon carbide obtained has characteristics of high adherence and compactness. These characteristics, in combination with a final surface polishing operation, provide micro-roughness values of below 10 A rms .
  • the process of the present invention due above all to the characteristic of compactness of the layer deposited, allows the production of hydrogenated silicon carbide mirrors, produced wholly by PECVD deposition and therefore without substrate produced by different techniques.
  • the process of the present invention by subjecting the substrate to be treated to temperatures approximately 10 times lower than those used in the techniques of the known art, offers the considerable advantage of being applicable " to a wide range of materials including ceramic materials, metals and also heat-sensitive materials such as polymeric materials (e.g. Teflon ® , Kapton ® ) .
  • the layer obtained by the process of the present invention with respect to the one obtained by the techniques of the known art can be adjusted in terms of hardness thus providing a more easily machinable surface and reducing surface machining times by up to 50-70%; it can also be deposited in high thicknesses from one millimetre upwards.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Vapour Deposition (AREA)

Abstract

A process for the deposition of layers of hydrogenated silicon carbide by means of the PECVD technique, comprising the steps of - placing in a deposition chamber (2) a gaseous mixture comprising an inert carrier gas and an organosilane compound with formula (CH3)3-Si-X-Si-(CH3)3 in which X is selected from the group consisting of O and NH; - generating a plasma from the mixture; and - depositing a layer of SiC on a substrate (5) positioned inside' the deposition chamber (2).

Description

PROCESS FOR THE DEPOSITION OF LAYERS OF HYDROGENATED SILICON CARBIDE
TECHNICAL FIELD
The present invention relates to a process for the deposition of layers of hydrogenated silicon carbide.
BACKGROUND ART
Silicon carbide (SiC) is a ceramic material with physical properties that make it particularly suitable for the production of high-performance mirrors in a wide range of applications. ' In. particular, SiC has proved to . be very interesting i'n applications with a wavelength interval ranging from infrared to X rays, and in which high thermal stability and low weight .are required. Due to these characteristics, SiC mirrors are very interesting for space applications.
SiC substrates can be produced in different ways, and in all cases the substrate obtained is not particularly dense or homogeneous. In fact, due to its residual porosity, the substrate requires a surface polishing operation to obtain a particularly polished reflecting surface.
One of the most commonly adopted solutions relates to the deposit of a layer of SiC coating produced by means of CVD
(Chemical Vapour Deposition) technique, on a SiC substrate.
The deposition takes place in a reactor at a temperature of between 1000 and 20000C according to the process used. Such a high temperature constitutes a problem in relation to the thermal and mechanical stability of the mirror. In fact, not all substrates can withstand such high temperatures, and furthermore said temperatures require careful assessment of the respective coefficients of thermal expansion of the coating and substrate. DISCLOSURE OF INVENTION
The aim of the present invention is to provide a process for the deposition of layers of SiC, the technical characteristics of which are such as to overcome the drawbacks of the known art.
The object of the present invention is a process for the deposition of layers of hydrogenated silicon carbide by means of PECVD technique, characterised by
- placing in a deposition chamber a gaseous mixture comprising an inert carrier gas and an organosilane compound with formula
(CH3) 3-Si-X-Si-(CH3)3 in which X is selected from the group consisting of O and NH;
- generating a plasma from said mixture; and
- depositing a layer of SiC on a substrate positioned inside said deposition chamber.
According to a preferred embodiment, the organosilane compound is (CH3) 3-Si-NH-Si-(CH3) 3
BRIEF DESCRIPTION OF THE DRAWING
The following example is intended as a non-limiting illustration, for a better understanding of the invention with the aid of the accompanying figure, which illustrates in schematic form a deposition system for the implementation of the process of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
In the figure the deposition system of the process of the present invention is indicated overall by reference number 1.
The system 1 comprises a deposition chamber 2, pumping means 3 for obtaining the vacuum inside the deposition chamber 2, an electrode 4 on which a substrate 5 is fixed, on which the deposit is made, and an inlet unit 6 for a gaseous mixture which will constitute the plasma.
In particular, the pressure inside the deposition chamber 2 must be between 0.1 and 0.5 mbar.
The electrode 4 can be fixed or rotating and is connected to a radio frequency generator 7 via a Match Box 8. The radio frequency generator 7 operates at a frequency of 13.65 MHz while the power sent depends on the dimensions of the electrode and can vary from a few hundred to a few thousand Watts .
By means of the self-polarisation induced on the electrode 4, it is possible to adjust the hardness of the film deposited. In particular, a self-polarisation is induced on the electrode 4 with Volt values between -200 for very hard compact films and -100 for less compact but functional films.
The inlet unit 6 comprises a heated tank 9, inside which the liquid organosilane compound is placed, a conduction system 10 comprising a plurality of heated pipes suitable for conveying the gaseous mixture which has formed between the organosilane compound and an inert gas, a flow control device 11, and a diffuser element 12 positioned at a certain distance from the electrode 4 and from which the gaseous mixture flows out in a uniform manner .
Once heated, the organosilane compound will be present inside the tank 9 both in the liquid phase and in the vapour phase. This vapour is appropriately mixed with an inert gas and conveyed by means of the conduction system 10 to the diffuser 12. As is known to a person skilled in the art, the flow of inert gases depends on the dimensions of the deposition chamber 2 .
The gaseous mixture flowing out of the diffuser 12 forms a plasma under the action of the electromagnetic field generated by the electrode 4. Inside the plasma, dissociation of the organosilane compound takes place and subsequent deposition of the hydrogenated silicon carbide on the substrate 5.
The organosilane compound used is hexamethyldisilazane or hexamethyldisiloxane. It has been found that by using the hexamethyldisilazane, a layer of hydrogenated silicon carbide more resistant to oxidisation is obtained.
The temperature of the electrode 4 and, therefore, of the ' substrate 5 fixed to it, is kept if necessary at a pre-set temperature by means of a known external cooling/heating circuit not illustrated for the sake of simplicity.
EXAMPLE : Depositions • of hydrogenated silicon carbide were produced with a thickness of 200 μm on different substrates, for example aluminium alloys, sintered SiC etc., the ' surfaces of which were prepared with standard mechanical finishing techniques.
The deposition was performed by using a circular electrode with a diameter of 150 mm and connected to a radio frequency generator operating at 13.65 MHz, at a power of 400W obtaining an initial self-polarisation of approximately -200 Volt. The electrode was kept at a temperature of 1000C.
The deposition chamber was depressurised to a base value of 10"4 mbar and kept at a value of 10"1 mbar during the deposition process.
The coating layer of hydrogenated silicon carbide obtained has characteristics of high adherence and compactness. These characteristics, in combination with a final surface polishing operation, provide micro-roughness values of below 10 A rms .
The process of the present invention, due above all to the characteristic of compactness of the layer deposited, allows the production of hydrogenated silicon carbide mirrors, produced wholly by PECVD deposition and therefore without substrate produced by different techniques.
As is obvious from the above description, the process of the present invention, by subjecting the substrate to be treated to temperatures approximately 10 times lower than those used in the techniques of the known art, offers the considerable advantage of being applicable " to a wide range of materials including ceramic materials, metals and also heat-sensitive materials such as polymeric materials (e.g. Teflon®, Kapton®) .
Furthermore, the layer obtained by the process of the present invention with respect to the one obtained by the techniques of the known art can be adjusted in terms of hardness thus providing a more easily machinable surface and reducing surface machining times by up to 50-70%; it can also be deposited in high thicknesses from one millimetre upwards.

Claims

1. Process for deposition of layers of hydrogenated silicon carbide by means of the PECVD technique, characterised by - placing in a deposition chamber (2) a gaseous mixture comprising an inert carrier gas and an organosilane compound with formula
(CH3 ) 3-Si-X-Si-(CH3) 3 in which X is selected from the group consisting of 0 and NH; - generating a plasma from said mixture; and
- depositing a layer of SiC on a substrate (5) positioned inside said deposition chamber (2.) .
' 2. Process for the deposition- of layers of hydrogenated silicon carbide as claimed in claim 1, characterised in that the organosilane compound is (CH3) 3-Si-NH-Si- (CH3) 3.
3. Process for the deposition of layers of hydrogenated silicon carbide as claimed in claim 1,_ or 2, characterised in that said substrate 5 is treated at a temperature below 2000C.
4. Process for the deposition of layers of hydrogenated silicon carbide as claimed in claim 3, characterised in that said deposition chamber (2) has an operating pressure of between 0.1 and 0.5 mbar .
5. Process for the deposition of layers of hydrogenated silicon carbide as claimed in claim 4, characterised in that said substrate (5) is fixed to an electrode (4) connected to a radio frequency generator (7) operating at a frequency of
13.65 MHz, and such as to produce on the electrode (4) an initial self-polarisation between -300 and -100 Volt.
PCT/IT2007/000431 2007-06-14 2007-06-14 Process for the deposition of layers of hydrogenated silicon carbide Ceased WO2008152666A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/IT2007/000431 WO2008152666A1 (en) 2007-06-14 2007-06-14 Process for the deposition of layers of hydrogenated silicon carbide

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IT2007/000431 WO2008152666A1 (en) 2007-06-14 2007-06-14 Process for the deposition of layers of hydrogenated silicon carbide

Publications (1)

Publication Number Publication Date
WO2008152666A1 true WO2008152666A1 (en) 2008-12-18

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ITRM20090675A1 (en) * 2009-12-21 2011-06-22 Galileo Avionica Spa PROTECTIVE TREATMENT FOR OPTICAL COMPONENTS TO TRANSMIT IN THE IR
WO2014074229A1 (en) * 2012-11-09 2014-05-15 Dow Corning Corporation Method for preparing an organo-functional silane

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1191123A2 (en) * 2000-09-12 2002-03-27 Applied Materials, Inc. Dual frequency plasma enhanced chemical vapor deposition of silicon carbide layers
EP1420439A2 (en) * 2002-11-14 2004-05-19 Air Products And Chemicals, Inc. Non-thermal process for forming porous low dielectric constant films
US20040126929A1 (en) * 2002-12-30 2004-07-01 Novellus Systems, Inc. Silicon carbide having low dielectric constant

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1191123A2 (en) * 2000-09-12 2002-03-27 Applied Materials, Inc. Dual frequency plasma enhanced chemical vapor deposition of silicon carbide layers
EP1420439A2 (en) * 2002-11-14 2004-05-19 Air Products And Chemicals, Inc. Non-thermal process for forming porous low dielectric constant films
US20040126929A1 (en) * 2002-12-30 2004-07-01 Novellus Systems, Inc. Silicon carbide having low dielectric constant

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
A. M. WRÓBEL ET AL: "Remote hydrogen plasma chemical vapor deposition of silicon-carbon thin-film materials from a hexamethyldisilane source: Characterization of the process and the deposits", JOURNAL OF APPLIED POLYMER SCIENCE, vol. 86, no. 6, 7 November 2002 (2002-11-07), Wilmington, DE, United States, pages 1445 - 1458, XP002499263 *
SEEKAMP J ET AL: "PECVD a-SiC:H thin films from liquid organosilanes dependence of photoluminescence on starting material", 1 May 2000, JOURNAL OF NON-CRYSTALLINE SOLIDS, NORTH-HOLLAND PHYSICS PUBLISHING. AMSTERDAM, NL, PAGE(S) 704 - 707, ISSN: 0022-3093, XP004198630 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ITRM20090675A1 (en) * 2009-12-21 2011-06-22 Galileo Avionica Spa PROTECTIVE TREATMENT FOR OPTICAL COMPONENTS TO TRANSMIT IN THE IR
WO2014074229A1 (en) * 2012-11-09 2014-05-15 Dow Corning Corporation Method for preparing an organo-functional silane

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