US 20070221326A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2007/0221326 A1 ROW an et al. (43) Pub. Date: Sep. 27, 2007 (54) SILICON CARBIDE BONDING (30) Foreign Application Priority Data (76) Inventors: Sheila Rowan, Glasgow (GB); James Apr. 8, 2004 (GB)......................................... O4O7953.9 Hough, Glasgow (GB); Eoin John Elife, Kildare (IE) Publication Classification Correspondence Address: (51) Int. Cl. NIXON & VANDERHYE, PC C04B 3.5/565 (2006.01) 901 NORTH GLEBE ROAD, 11TH FLOOR (52) U.S. Cl. .............................................................. 156/325 ARLINGTON, VA 22203 (US) (57) ABSTRACT (21) Appl. No.: 111578,119 A method for bonding at least two parts, at least one part (22) PCT Filed: Apr. 6, 2005 comprising silicon carbide, the method comprising forming a layer of silica on the silicon carbide Surface,and applying (86). PCT No.: PCT/GBOS/O1362 to it a bonding Solution that includes hydroxide ions. Once this is done, the part that is to be bonded to the silicon S 371(c)(1), carbide is moved into contact with the solution coated silica (2), (4) Date: Oct. 10, 2006 Surface. Clean the surface of the silicon carbide Oxidise the surface of the silicon carbide Place a hydroxide bonding solution on the oxidised stirface Place another appropriate surface in contact with the solution-coated surface Hold the two parts together to enable the bond to settle Teave bonded assembly to ce Patent Application Publication Sep. 27, 2007 Sheet 1 of 2 US 2007/0221326 A1 Clean the surface of the silicon carbide Oxidise the surface of the silicon carbide Place a hydroxide bonding solution on the oxidised surface Place another appropriate surface in contact with the solution-coated surface Hold the two parts together to enable the bond to settle Leave bonded assembly to ce Figure 1. US 2007/0221326 A1 Sep. 27, 2007 SILICON CARBIDE BONDING 0011. In a third preferred aspect, the present invention provides a device or assembly comprising silicon carbide FIELD OF THE INVENTION bonded to another part, for example another silicon carbide 0001. The present invention relates to silicon carbide part, by an interface material that comprises silica treated bonding. In one aspect, a method is set out for bonding with a solution, preferably an aqueous solution, which silicon carbide components to themselves or to components includes hydroxide ions. of other selected materials. 0012. In a fourth preferred aspect, the present invention provides a device or assembly comprising silicon carbide BACKGROUND bonded to another part, for example another silicon carbide 0002 Silicon carbide is a material that is finding part, by an interface material that comprises a siloxane increased use for space-borne applications, for example in network. telescope structures and optical benches. This is because of 0013 Preferred and/or optional features will now be set its high strength to weight ratio. Other new applications are out. These are applicable singly or in any combination with now emerging in the semiconductor industry. Most Such any of the aspects of the invention, unless the context applications require that pieces of silicon carbide be joined demands otherwise. together or mounted on other Substrates such as silica or Sapphire. A number of ways of joining silicon carbide are 0014 Preferably, the step of forming a layer of silica described in the article “Silicon Carbide Technology for involves oxidising the silicon carbide Surface. submillimeter space based telescopes” by F. Safa et al., 48th 0.015 Preferably, the method further includes the step of International Astronautical Congress, Turin, October 1997. curing the bond. These joining methods include bolting; brazing; epoxying, and molecular bonding/optical contacting. 0016. The method may further comprise the step of cleaning the bonding Surfaces of contaminants. Preferably, 0003. Unfortunately, each of the known techniques for the step of cleaning uses at least one of the following: bonding to silicon carbide has disadvantages for precision methanol, acetone, opticlear and an ultrasonic bath. A clean construction. For example, if bolting is used there is the ing Solution to be used in this step may consist of at least one possibility of dimensional drift and lack of stability. Brazing of the following: piranha Solution, Sodium hydroxide solu has to be carried out at high temperature, resulting in the tion, micro-D-90, cerium oxide, bi-carbonated soda. possibility of induced thermal stress and distortion of the system on cooling. Furthermore, precise adjustment during 0017 Preferably, the bonding solution is an aqueous jointing is very difficult. Epoxying results in a system whose Solution. The bonding Solution may comprises a source of dimensions are liable to drift with time and as a result of the hydroxide ions selected from the group: lithium hydroxide, vapour pressure of the epoxy may cause pollution of other Sodium hydroxide, potassium hydroxide, rubidium hydrox nearby components particularly if in a high vacuum envi ide, caesium hydroxide. The bonding Solution may com ronment. Molecular bonding tends to be unreliable in terms prises an aqueous solution including a silicate material Such of bond strength and repeatability and allows no fine adjust as Sodium silicate. ment of position before jointing actually occurs. Thus to 0018 Preferably, the bonding solution is alkaline. manufacture, for example, a silicon carbide-based precision optical bench for flight in a satellite environment, no suitable 0019. In the case where the two parts are both silicon joining method is currently available. carbide, a silica layer is preferably formed on the surface of each of these parts, before the bond is formed. SUMMARY OF THE INVENTION 0020. Utilising the invention, pieces of figured, polished 0004. A preferred object of the present invention is to silicon carbide may be joined in a very precise way to each provide an improved method for bonding to silicon carbide. other. To achieve this joining, the pieces should first be oxidised. Subsequently, when cool, the pieces are preferably 0005 Accordingly, in a general aspect, the present inven pushed together with a very Small quantity of hydroxide tion provides bonding for silicon carbide via interaction solution between them, creating the join or bond. This between a silica layer and hydroxide ions. joining can also be achieved between the oxidised silicon 0006. In a first preferred aspect, the present invention carbide and a variety of other materials, provided that they provides a method for bonding at least two parts, at least one too are suitably figured and polished. These materials part comprising silicon carbide, the method comprising: include silica, Sapphire, alumina-based materials, ULE and Zerodur. Joining is also possible with aluminium, Silicon and 0007 forming a layer of silica on the silicon carbide zinc, however the process occurs more reliably if these Surface, the silica layer forming a bonding Surface; materials are oxidised first in the same manner as silicon carbide. Using this technique, the pieces being bonded may 0008 applying a bonding solution including hydroxide be adjusted in relative position for a short period of time ions to the bonding Surface of at least one of the parts, (approximately 30 secs) before bonding takes place. This is and advantageous for applications where precision positioning is 0009 positioning the parts or the bonding surfaces so needed, as minor adjustments can be made. The resulting that a bond can be formed between them. bond is very strong, very stable, and non-polluting. There is no mechanical or thermal distortion associated with this 0010. In a second preferred aspect, the present invention method as the bonding takes place at room temperature. If provides an assembly of bonded parts obtained or obtainable desired, curing can be enhanced by gently heating but only by the method of the first aspect. to a level where thermal distortion effects are negligible. US 2007/0221326 A1 Sep. 27, 2007 BRIEF DESCRIPTION OF THE DRAWINGS chemical compounds whose nature it is to ionise in water and render the Solution alkaline, giving a pH value above 7. 0021 Preferred embodiments of the invention are Alternatively, the bonding Solution may comprise an alka described by way of example and with reference to the line aqueous solution including a material comprising silica accompanying drawings, in which: (SiO) and a source of hydroxide ions. The source of the 0022 FIG. 1 shows a flow diagram of a method for hydroxide ions may be selected from the group consisting bonding to silicon carbide, and of lithium hydroxide, Sodium hydroxide, potassium hydrox 0023 FIG. 2 shows a schematic cross-section through an ide, rubidium hydroxide, caesium hydroxide. assembly that comprises two pieces of silicon carbide that 0027. Once the bonding solution is applied to the first are bonded together. silica coated piece of silicon carbide the other piece is then gently placed on top of it, with the silica Surfaces facing each DETAILED DESCRIPTION OF PREFERRED other, as shown in FIG. 2(a). The two pieces are then slightly EMBODIMENTS compressed. This causes the applied hydroxide solution to 0024. The present invention relates to the use of hydrox spread over both of the silica coated surfaces, primarily due ide-catalysis bonding for joining pieces of silicon carbide. to capillary action, and results in the formation of a siloxane Hydroxide-catalysis bonding typically involves introducing network between the surfaces due to the interaction of the small volumes of a hydroxide solution with/without colloi silica based surface layers and the hydroxide solution. The dal SiO, between pieces of a chemically reactive substrate pieces are then carefully aligned and held in position until Such that the pieces are bonded together due to the produc dehydration commences. This is the initial setting of the tion of chemical chains such as siloxane. The pieces to be bond and occurs in times ranging from tens of seconds to as jointed should be figured such that the relative figures of the long as 10 minutes.