A glass of boron oxide used to chemically bond silicon-containing surfaces and articles thereof

Abstract

Described herein is a method of joining two silicon-containing surfaces together using a glass of boron oxide. The method comprises (i) providing a first part having a first attachment surface, wherein the first attachment surface comprises silicon and a second part having a second attachment surface, wherein the second attachment surface comprises silicon; (ii) disposing a glass of boron oxide between the first and second attachment surfaces to form an assembly; and (iii) heating the assembly to convert at least a portion of the glass of boron oxide to a borosilicate glass. Such articles can find use in photonic integrated chips.

Description

PA101901W002A GLASS OF BORON OXIDE USED TO CHEMICALLY BOND SILICON-CONTAINING SURFACES AND ARTICLES THEREOF TECHNICAL FIELD

[0001] The use of a glass comprising primarily boron oxide to adhere silicon-containing surfaces is discussed. Methods of joining at least two silicon-containing surfaces and articles thereof are also discussed. Such methods can be used, for example, to precisely adhere optical interconnects in a printed circuit board.SUMMARY

[0002] A photonic integrated chip (PIC) is a component of an optical electronic device (e.g., silicon photonic packaging), which performs optical operations on the device. The limits of PICs are being pushed to achieve faster, smaller, more efficient devices similar to the Moore’s law trend in electronic microchips.

[0003] In PICs, optical components such as waveguides, are incorporated into a silicon wafer. A plurality of optical fiber cables are registered into an optical interconnect, which is aligned with an optical component on the silicon wafer. There is a need to identify an adherent to connect the optical interconnect to the silicon wafer, which enables precise placement of the optical interconnect without seepage of the adherent which could interfere with optical performance. Desirably, the adherent should have a similar coefficient of thermal expansion as the attachment surfaces and have good thermal stability.

[0004] In one aspect, a glass comprising at least 90% by weight boron oxide used to chemically adhere two silicon-containing surfaces is described, wherein each silicon-containing surface is selected from the group consisting of silicon dioxide, silicon nitride, silicon, doped silica, or combinations thereof.

[0005] In another aspect, an article is described. The article comprises a first part having a first attachment surface, wherein the first attachment surface comprises silicon and second part having a second attachment surface, wherein the second attachment surface comprises silicon; and a layer derived from a glass of boron oxide, wherein a first surface of the layer is attached to the first attachment surface via borosilicate bonds, and wherein a second surface of the layer is attached to the second attachment surface via borosilicate bonds.

[0006] In yet another aspect, a method of joining two silicon-containing surfaces is described. The method comprising: providing a first part having a first attachment surface, wherein the first attachment surface comprises silicon and a second part having a second attachment surface, wherein the second attachment surface comprises silicon; disposing a glass of boron oxide between the first and second attachment surfaces to form an assembly; and heating the assembly to convert at least a portion of the glass of boron oxide to a borosilicate glass.

[0007] In some embodiments, the first part is an optical interconnect and the second part is a silicon wafer.

[0008] In some embodiments, both the first part and the second part are optical interconnects.

[0009] In yet another aspect, a kit is described. The kit comprising (i) an optical receiver comprising a silicon-containing surface for adhering to a piece of glass; and (ii) the piece of glass comprising at least 90% by weight boron oxide.

[0010] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which:

[0012] Fig. 1 is a cross-sectional view of an exemplary article, according to various embodiments disclosed herein;

[0013] Fig. 2 is a perspective view of an exemplary PIC substrate comprising waveguides and a two-part separable optical interconnect;

[0014] Fig. 3 is an optical microscopy image of a cross-section of Comparative Example 3; and

[0015] Fig. 4 is an optical microscopy image of a cross-section of Example 5.

[0016] In the figures, like reference numerals indicate like elements. While the above-identified figures, which may not be drawn to scale, set forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed disclosure by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure.DETAILED DESCRIPTION

[0017] As used herein, the term“a”, “an”, and “the” are used interchangeably and mean one or more; and“and / or” is used to indicate one or both stated cases may occur, for example A and / or B includes, (A and B) and (A or B).

[0018] Also herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0019] Also herein, recitation of “at least one” includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0020] As used herein, “comprises at least one of’ A, B, and C refers to element A by itself, element B by itself, element C by itself, A and B, A and C, B and C, and a combination of all three.

[0021] Herein, the term “comprises” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. Such terms will be understood to imply the inclusion of astated step or element or group of steps or elements, but not the exclusion of any other step or element or group of steps or elements. By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of.” Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present. By “consisting essentially of’ is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase “consisting essentially of’ indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present depending upon whether or not they materially affect the activity or action of the listed elements. Any of the elements or combinations of elements that are recited in this specification in open-ended language (e.g., comprise and derivatives thereof), are considered to additionally be recited in closed-ended language (e.g., consist and derivatives thereof) and in partially closed-ended language (e.g., consist essentially, and derivatives thereof).

[0022] The terms used to indicate the direction, such as “■top” and “bottom”, are relative terms, and may change based on a relative position of a viewer.

[0023] The present disclosure is directed toward using a glass of boron oxide to chemically adhere silicon-containing surfaces together. In some embodiments, these silicon-containing surfaces are photonic components of an optical electronic device.

[0024] The present disclosure can be understood by reference to Fig. 1, which shows one embodiment of the present disclosure. Article 10 includes parts 12 and 14, which are adhered together by layer 16. Part 12 comprises first attachment surface 13 and part 14 comprises second attachment surface 15. Layer 16 is derived from a glass of boron oxide, which chemically reacts with the first and second attachment surfaces to form borosilicate bonds, adhering parts 12 and 14 together.

[0025] A glass of boron oxide as used herein comprises at least 90, 92, 94, 95, 96, 97, 98, 99, 99.5, or even 100 %by weight of boron oxide (B2O3). In some embodiments, the glass of boron oxide comprises small amounts of other metals such as Na, K, Mg, Mn, Ca, Fe, Si, Al, or combinations thereof and metal oxides thereof; or compounds such as OH, H2O, and the like. Boron oxide is a hygroscopic solid and is not considered a durable material nor one that maintains a hermetic seal. However, in the present disclosure it has been discovered that using a glass of boron oxide with silicon-containing surfaces enables the formation of borosilicate bonds, which overcome the above disadvantages and have surprising benefits as will be discussed below.

[0026] The glass of boron oxide is a material made from boron oxide heated to form solid glass units. The glass of boron oxide is a fully dense material. In some embodiments, the glass unit has a density that is at least 95, 96, 97, 98, 99, 99.5, or even 100% of the theoretical density of an annealed boron oxide glass (i.e., 1.83 g / cm3) as measured under ambient conditions. In some embodiments, the glass unit has a low porosity, for example a porosity less than 10, 8, 6, 5, 4, 3, 2, 1, 0.5, or even 0.1% by volume as determined by microscopy (optical or scanning electron microscopy) or pycnometry.

[0027] Boron oxide (B2O3) may be made by treatment of borax with sulfuric acid, or heat treatment of boric acid to drive off the water as known in the art. Boron oxide, as disclosed herein, is commercially available in granular, sheet, flakes, frits, or other shaped forms.The commercially available boron oxide can be processed to form shapes of precise volumes by melting and casting, laser melting and quenching, slurry processing and casting and melting or flame processing of boron oxide (B2O3) as known in the art.

[0028] The first and second attachment areas of the present disclosure comprise a silicon-containing surface. In some embodiments, the surface to be attached comprises at least 45, 50, 60, 70, 80, 90, 95, or even 100 % wt of Si. Such silicon containing surfaces include silicon dioxide (SiCh), doped silicon dioxide, silicon nitride (SisN^, silicon (Si), or combinations thereof. A doped silicon dioxide may comprise less than 0.5, or even 0.1 wt% of other elements. Exemplary elements include germanium; phosphorous; boron; barium; aluminum; titanium; and rare earth metals such as Er, Yb, Tm, and Nd.

[0029] In some embodiments of the present disclosure, the first and second attachment areas have an area of less than 25, 20, 10, 5, 1, or even 0.5 mm2.

[0030] In some embodiments of the present disclosure, the first and second attachment areas are parts of a silicon photonic package. A glass of boron oxide adherent may find use in adhering optical interconnects to a PIC substrate. Shown in Fig. 2 is portion of a optical electronic device comprising a two-part optical interconnect which is used to couple optical fiber cables to a waveguide in a silicon wafer. PIC substrate comprises waveguides 29 fabricated into silicon wafer 24. The two-part interconnect comprises (1) receiver 22 which comprises optical component 27, which is used to shape and direct the light beam from optical fiber cable 21 to waveguides 29; and (2) optical ferrule 28, which collates optical fiber cables 21. Receiver 22 is attached to silicon wafer 24 and is designed to fit optical ferrule 28. The receivers are typically only 5 mm in width or less. Thus, it is important that receiver 22 is precisely positioned on silicon wafer 24. Shown in Fig. 2 is a two-part optical interconnect comprising receiver 22 and optical ferrule 28. In some embodiments, the optical interconnect is one piece, wherein the optical fiber cables are connected directly to the receiver.

[0031] In current commercial manufacture, an organic adhesive, such as an epoxy resin, is used to adhere optical interconnects to the silicon wafer. However, epoxy resins and other organic adhesives tend to have disadvantages. In some instances, the optical electronic device comprising a PIC is exposed to high temperatures (e.g., 200-300°C used for solder reflow), whether deliberately done to manufacture components onto the circuit board or temperature excursions during operation of the PICs. The organic adhesives can off-gas or degrade when heated, causing shifting of the interconnect components such as the receiver, leading to misalignment. Further, due to the differences in the coefficient of thermal expansion between the organic adhesive and the silicon-containing attachment surface, the optical interconnect on the silicon wafer can become misaligned. For example, a ceramic receiver has a coefficient of thermal expansion (cte) of about at least 0.5xl0'6 / °C to at most 3.3xl0'6 / °C, while an organic adhesive has a cte of about at least 9xlO'6 / °C to at most 20xl0'6 / °C. Coefficient of thermalexpansion of materials is determined using techniques known in the art, measured over a linear portion of a thermal expansion curve, e.g., dilatometry.

[0032] In the present disclosure, a glass of boron oxide, which reacts with silicon wafer 24 and receiver 22 is used to adhere the two parts together. In some embodiments, the receiver is one part of a two-part interconnect as shown in Fig. 2. In other embodiments, the receiver is a single interconnect including the optical fibers. Also contemplated in the present disclosure is using a glass of boron oxide to adhere two optical interconnects together, forming a stacked configuration, wherein one interconnect is disposed atop another interconnect.

[0033] In the present disclosure, a glass of boron oxide is positioned between two silicon-containing surfaces and then heated. The glass of boron oxide is heated such that the boron oxide reacts with silicon to form a borosilicate bond, thereby chemically bonding the components together. Exemplary heating includes placing the assembly (i.e., the glass of boron oxide disposed on the first attachment surface and / or the second attachment surface) in a furnace or targeting a heating source, such as a laser, to the glass of boron to cause localized heating. Generally, the temperature (in the furnace or localized) should be at least 450, 475, 500, 525, or even 550 °C at ambient pressure to generate the reaction of the boron oxide with the silicon-containing surface.

[0034] Because glass of boron oxide is hygroscopic and is not chemically durable, it generally is not considered a viable adherent. However, in the present disclosure, because the glass of boron oxide reacts with the silicon-containing attachment surface, it forms borosilicate bonds, which do have good chemical durability. Advantageously, certain types of low expansion borosilicate glasses have ctes similar to silicon-containing surfaces. For example, borosilicate glass Type 1, Class A has a cte of 3.3 xlO-6 / °C. With a cte of 2.5 xlO-6 / °C for silicon and 0.5 xlO-6 / °C for silicon dioxide, the low cte for the borosilicate glass results in minimal stress in the bond area from cte mismatching. Further, borosilicate glass has a higher melting point than organic adhesives and does not off-gas or degrade, minimizing misalignment of the adhered components during subsequent heating events.

[0035] In some embodiments, a precise amount of the glass of boron oxide is used, which is just enough to cover the attachment areas, and not so much that there is excessive seepage of the adherent around the part (e.g., the receiver or optical interconnect) or potentially interfering with the function of the article (e.g., filling the optical components on the PIC or optical interconnect). For example, in some embodiments, the volume of the glass of boron oxide used is at least 1.6 x 10'9cm3to at most 4 x 10'3cm3. In some embodiments the precise volume of the boron oxide used is the same for all the boron oxide glass adherent particles used to attach the silicon containing surfaces. Generally, the glass of boron oxide should be such that it forms a chemical bond of borosilicate glass between the two attachment areas. In preferred embodiments, the surface area of the glass of boron oxide in contact with the first attachment area is smaller than the surface area of the first attachment area.

[0036] The glass of boron oxide may have any shape depending on the application. Such shapes include spheres, spheroid, gumdrop, cylindrical shapes, polygonal prisms, polygonal pyramids, conical shapes, frustums of cones, frustums of pyramids, and combinations thereof.

[0037] In some embodiments, the first attachment area is located in a recessed portion of the part. For example, a receptacle is fabricated into the receiver, which enables ready placement and holding of the glass of boron oxide and can act to contain the material once reacted.

[0038] In some embodiments, at least a portion of the surface of at least one of the glass of boron oxide, the first attachment area, the second attachment area, or combinations thereof comprise a fugitive coating. The fugitive enables the part to be held accurately in place during the handling of the assembly. Such fugitives include epoxies, acrylates, urethanes, or combinations thereof.

[0039] In some embodiments, the first attachment part is an optical interconnect. Such optical interconnects are described in U.S. Publ. Pat. No. 20240418940 (Haase) as cradles. In some embodiments, the ceramic optical interconnect is a ceramic housing which is used to connect terminal waveguides. The ceramic housing can be made of silica, silicate, silicon nitride, or combinations thereof.

[0040] In some embodiments, the second attachment part is a silicon wafer. Such parts may optionally have superficial surface layers of silicon dioxide and / or silicon nitride.

[0041] In some embodiments, the second attachment part is a second optical interconnect, wherein two optical interconnects are stacked upon one another.EXAMPLES

[0042] Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods.

[0043] The following abbreviations are used in the Example Section: g = gram, mg = milligram, min = minute, and °C= degrees Celsius.Table 1. Materials ListDESIGNATION DESCRIPTIONBorosilicate glass Lithium potash borosilicate glass powder, product 7070 from Coming Inc., Coming, NY.Sealing glass 1 A bismuth, zinc and boron low temperature, lead-free glass powder,product EG-2992 SRRG from Ferro Corp., Mayfield Heights, OHSealing glass 2 Powder obtained under the trade designation 8422 from Schott AG,Mainz, Germany.Vitreous bond Powder bonding for abrasives obtained under the trade designation“VO 82075M” from Reimbold & Strick Handels, Cologne, Germany.Glass of boron 1 Granular diboron trioxide obtained from U.S. Borax, Chicago, IL,reported melting point 450-465 °C.Glass of boron 2 Boron anhydride, glass chucks and shards, obtained from Matheson Coleman & Bell, Norwood, OH.Si substrate Silicon wafer, available from Silicon Valley Microelectronics, Inc.,Santa Clara, CACeramic part Silica article prepared similarly to method described in U.S. Pat.No.11,884,550 (Humpal et al.)

[0044] The various boron-containing materials were analyzed for the amount of boron oxide present as follows: Samples were prepared for XRF (X-ray fluorescence) analysis in the following manner:

[0045] Powders (25-30 g) of Borosilicate glass, Sealing glass 2, Vitreous bond, Glass of boron 1 and Glass of boron 2were placed in platinum crucibles and heated to a viscous state (for Glass of boron 1 and 2 were heated at 20°C / min from room temperature to 950°C and for the others they were heated at 20°C / min from room temperature to 1600°C). The samples were held at the final temperature for 2 hours and then poured into a heated graphite mold to form a glass disk.

[0046] Powder of Sealing glass 1 (10 g) was placed in a graphite mold, heated at 10°C / min to 460°C, held for 5 min at 460°C, and then hot-pressed to full density using a dental firing / pressing furnace (Ivoclar Vivadent Programat EP 5000, Schaan, Liechtenstein).

[0047] All samples were ground using SiC abrasive on an 8 inch (20 centimeter) grinding wheel to create a flat surface on one side and then polished with diamond lapping film to a 3 micrometer finish. Cooling water was used with all samples except Glass of boron 1, which was ground and polished dry because of its hygroscopicity. Prior to data collection, each polished sample was placed directly into a stainless steel XRF sample holder and analyzed for most of the elements in the periodic table (from boron to uranium inclusive) using a Rigaku Primus II wavelength dispersive X-ray fluorescence spectrometer (Tokyo, Japan) equipped with a rhodium X-ray source, a vacuum atmosphere, and a 20 millimeter diameter measurement area. Each sample was analyzed three times and an average and standard deviation calculated and reported for each element detected and converted to oxide. The results for the amount of boron oxide (B2O3) in each material are reported in Table 2.Table 2Material Weight % of B2O3Borosilicate glass 25.2 ± 0.1Sealing glass 1 67.5 ± 0.4Sealing glass 2 9.1 ± 0.3Vitreous bond 14.6 ± 0.1Glass of boron 1 99.6 ± 0.2Glass of boron 2 99.87 ± 0.01

[0048] For each sample, a designated amount of bond material was placed in the center of the Si substrate. The ceramic part was then placed on top of the bond material, and the assembly was placed inthe furnace and heat treated. The heat treatment schedule used for each sample was the following: fast ramp (about 55°C / min) to 700°C, then 20°C / min to 800°C, hold for 30 min, slow cool (about 8.5°C / min) to 300°C. When 300°C was reached, the furnace was opened and the bonded stack was allowed to cool to room temperature. The optical quality of the assembly after heat treatment was noted.

[0049] The strength of the resulting bond was tested using a slow-speed diamond wafering saw (Techcut 4 from Allied High Tech Products, Inc., Cerritos, CA) using water as a coolant. Each bonded stack was mounted on the edge of a glass slide using Crystalbond 509 mounting adhesive from SPI Supplies (West Chester, PA). The bonded stack was then sawn in half. If the bond remained intact, the bond material was designated ‘Pass. ’ If the Ceramic part separated from the Si substrate, the bond material was designated ‘Fail.’ For the samples where the bond remained intact, the quality of the bond was also noted. Shown in Figs. 3-4 are optical images (taken by optical microscopy) of the cut part for Comparative Example 3 and Example 5, respectively. Fig. 3, depicts the nonuniform bonding / interface between ceramic part 32 and Si substrate 34. Fig. 4, depicts the uniform bonding / interface between ceramic part 42 and Si substrate 44, wherein the two materials appear to be seamlessly touching.

[0050] Shown in Table 3 is the bond material and amount used for each sample. The assembly was weighed before and after heat treatment and the difference (initial weight -final weight) is reported in Table 3 along with the Cut Test result. Also reported in Table 3 is the optical quality of the assembly after heat treatment as well as the quality of the interface.Table 3Sample Bond Bond Difference Visual Cut Visual material mass in total quality of Test quality of shape (mg) mass (mg) the the bond assemblyComparative 1 Borosilicate 0.8 0.2 Clear Failglass portions Notand white Applicable or hazyportionsComparative 2 Sealing glass 0.9 0.5 Hazy Fail Not1 Applicable Comparative 3 Sealing glass 1.0 -0.1 Clear Pass rough2 with large interface bubblesComparative 4 Vitreous 1.7 0.5 Hazy Pass Very rough bond interface Example 5 Glass of 1.1 0.9 Clear Passboron 1 Noobservableinterface material Example 6 Glass of 1.3 1.0 Clear Pass Noboron 2, Flat observable slab interface material Example 7 Glass of 0.5 0.2 Clear Pass Noboron 2, Thin observable rectangle interface material Example 8 Glass of 0.4 0.2 Clear pass Noboron 2, Thin observable rectangle interfacematerial

[0051] Example 5 was exposed to boiling water for 15min., and the assembly remained intact, suggesting that the glass of boron oxide either entirely reacted with the Si-containing surfaces or became hermetically sealed, preventing any reaction of the boron oxide with the water.

[0052] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned or incorporated by reference herein, this specification as written will prevail.

Claims

What is claimed is:

1. Using a glass comprising at least 90% by weight boron oxide to chemically adhere two silicon- containing surfaces, wherein each silicon-containing surface is selected from the group consisting of silicon dioxide, silicon nitride, silicon, doped silica, or combinations thereof.

2. An article comprising a first part having a first attachment surface, wherein the first attachment surface comprises silicon and second part having a second attachment surface, wherein the second attachment surface comprises silicon; and a layer derived from a glass of boron oxide, wherein a first surface of the layer is attached to the first attachment surface via borosilicate bonds, and wherein a second surface of the layer is attached to the second attachment surface via borosilicate bonds.

3. The article of claim 2, wherein the first attachment area comprises silica, silicate, or combinations thereof.

4. The article of any one of claims 2-3, wherein the second attachment area comprises silica, silicate, or combinations thereof.

5. The article of any one of claims 2-3, wherein the second attachment area comprises silicon.

6. The article of any one of claims 2-5, wherein the glass of boron oxide comprises at least 90% by weight of boron oxide.

7. The article of any one of claims 2-6, wherein the glass of boron oxide has a porosity of at most 10%.

8. The article of any one of claims 2-7, wherein the first part is an optical interconnect of a photonic integrated chip.

9. The article of any one of claims 2-8, wherein the second part is an optical interconnect.

10. The article of any one of claims 2-8, wherein the second part is a silicon wafer for a photonic integrated chip.

11. The article of any one of claims 2-10, wherein the first part comprises a receptacle for receiving the layer.

12. A method of joining two silicon-containing surfaces, the method comprising:providing a first part having a first attachment surface, wherein the first attachment surface comprises silicon and a second part having a second attachment surface, wherein the second attachment surface comprises silicon;disposing a glass of boron oxide between the first and second attachment surfaces to form an assembly; andheating the assembly to convert at least a portion of the glass of boron oxide to a borosilicate glass.

13. The method of claim 12, wherein the second attachment surface is an optical interconnect.

14. The method of any one of claims 12 to 13, wherein the glass of boron oxide is a single piece.

15. The method of any one of claims 12 to 13, wherein the glass of boron oxide has a shape selected from spheres, spheroid, gumdrop, cylindrical shapes, polygonal prisms, polygonal pyramids, conical shapes, frustums of cones, frustums of pyramids, or combinations thereof.

16. The method of any one of claims 12 to 15, wherein surface area of the glass of boron oxide in contact with the first attachment area is smaller than the surface area of the first attachment area.

17. The method of any one of claims 12 to 16, wherein the glass of boron oxide fits within a receptacle in the first part.

18. The method of any one of claims 12 to 17, wherein at least one of the glass of boron oxide, the first attachment area, the second attachment area, or combinations thereof comprise a fugitive coating.

19. The method of claim 18, wherein the fugitive coating is an adhesive comprised of epoxies, acrylates, urethanes, or combinations thereof.

20. The method of any one of claims 12 to 19, wherein an oven is used for heating the assembly.

21. The method of any one of claims 12 to 20, wherein electromagnetic energy is used for heating the assembly.

22. The method of any one of claims 12 to 21, wherein the first part is an optical interconnect of a photonic integrated chip.

23. The method of any one of claims 12 to 22, wherein the second part is an optical interconnect of a photonic integrated chip.

24. The method of any one of claims 12 to 23, wherein the second part is a silicon wafer.

25. A kit comprising (i) an optical receiver comprising a silicon-containing surface for adhering to a piece of glass; and (ii) the piece of glass comprising at least 90% by weight boron oxide.

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