Patent Application
20240312955
The present invention relates to bonding structures between a substrate and an electronic component, especially bonding structures between an optoelectronic component and a silicon photonic substrate.
Optoelectronic devices are primarily transducers. Therefore, they can convert one energy form to another. These devices produce light by expending electrical energy. They can also detect light and transform light signals to electrical signals. For example, semiconductor optical amplifiers (SOAs), photodiodes (PDs) and laser diodes (LDs) are optoelectronic devices.
An optoelectronic device can be interconnected to a silicon photonic substrate by for example, soldering or eutectic bonding. However, these methods can be sensitive to errors. For example, non-uniformity of bonding temperature and bonding force can cause non-uniformity of bonding quality. Further, non-uniform melting near eutectic temperature and non-uniform bonding force can cause squeezing of bonding material, which can result in electrical shortage and optical misalignment. Furthermore, a small stopper area and thick bonding materials combined with fragile optoelectronic components can cause crack formation in the optoelectronic components. Thus, there is need for improving the bonding structure between the optoelectronic device and the silicon photonic substrate.
The object of at least some embodiments is to provide a high quality bonding structure with squeezing control of molten metal and a large stopper area for preventing an optical device for breakage. Further, the object of at least some embodiments is to provide precise alignment between the optical device and a silicon photonic substrate.
According to a first aspect of the present invention, there is provided a bonding structure for forming at least one electrical connection between a photonic substrate and an optoelectronic component, the bonding structure comprising: an electroconductive pad between the photonic substrate and the optoelectronic component, which electroconductive pad comprises at least two separated portions, and a bond layer between the electroconductive pad and the optoelectronic component, and between the at least two portions of the electroconductive pad.
According to an embodiment, the bond layer comprises a eutectic alloy, a solder alloy or an intermetallic alloy.
According to an embodiment, the electroconductive pad (110) has a predetermined height of 0.2 to 1 μm.
According to an embodiment, the bonding structure comprises an optical connection between the photonic substrate and the optoelectronic component.
According to an embodiment, the bonding structure comprises a passivation layer on the photonic substrate.
According to an embodiment, the optoelectronic component comprises at least one groove and the photonic substrate comprises at least one protrusion configured to the at least one groove for aligning the optoelectronic component with the photonic substrate.
According to an embodiment, the bond layer extends on the at least one protrusion and/or on the at least one groove.
According to an embodiment, the at least one protrusion has a shape of a pillar, which pillar is tapering towards the optoelectronic component, and the at least one groove has substantially the same shape than the at least one protrusion and is widening towards the photonic substrate.
According to an embodiment, the photonic substrate is silicon photonic chip or wafer.
According to an embodiment, the optoelectronic component is a semiconductor optical amplifier, a photodiode or a laser diode.
According to a second aspect of the present invention, there is provided a method for forming at least one electrical connection between a photonic substrate and an optoelectronic component comprising: providing an electroconductive pad on a surface of the photonic substrate, providing a first bonding material layer directly and at least partially on a surface of the electroconductive pad, providing a second bonding material layer on a surface of the optoelectronic component, and bonding the first bonding material layer with the second bonding material layer for forming a bond layer, wherein the electroconductive pad for the at least one individual electrical connection comprises at least two separated portions for receiving extra bonding material of the bond layer between the portions.
According to an embodiment, the method comprises providing a first bonding material layer on the surface of the photonic substrate.
According to an embodiment, the method comprises providing a passivation layer on the photonic substrate.
According to an embodiment, a bonding temperature for bonding the first bonding material layer with the second bonding material layer is lower than a melting temperature of the electroconductive pad.
According to an embodiment, bonding of the first bonding material layer with the second bonding material layer is provided by eutectic bonding; solder bonding or solid-liquid interdiffusion.
According to an embodiment, the method comprises: providing at least one groove in the optoelectronic component, and providing at least one protrusion on the photonic substrate for aligning the optoelectronic component with the photonic substrate.
According to an embodiment, the method comprises providing the first bonding material layer on the at least one protrusion and/or the second bonding material layer on the at least one groove.
According to an embodiment, the photonic substrate is silicon photonic chip or wafer.
According to an embodiment, the optoelectronic component is a semiconductor optical amplifier, a photodiode or a laser diode.
According to a second aspect of the present invention, the bonding structure is used in a telecommunication, a datacommunication, an environmental sensing, an industrial sensing, a medial or a light detection and ranging application.
In the present context, “photonic substrate” refers to a wafer or a chip comprising photonic functionality. The wafer can be for example, silicon wafer. The chip can comprise a waveguide.
In the present context, “optoelectronic component” comprise for example, a semiconductor optical amplifier (SOA), a photodiode (PD) or a laser diode (LD).
In the present context, “gap” refers to a space between portions of an electroconductive pad.
Generally, bonding an optoelectronic component to photonic substrate is sensitive for errors. The present embodiments provide a high quality bonding structure with squeezing control of molten metal.
At least in some embodiments, at least part of the molten metal is contained within the pad. Extra metal flows in the at least one gap between the portions of the pad. So, the dimensions of the final connection structure are better controlled.
The photonic substrate can comprise silicon. Silicon is very reliable photonic substrate material as it suffers very little fatigue and can have long service lifetimes without breaking. In single crystal form, silicon has virtually no hysteresis and hence almost no energy dissipation.
The photonic substrate 101 can be silicon photonic chip or wafer.
The optoelectronic component 102 can be a semiconductor optical amplifier, a photodiode or a laser diode.
According to some embodiments, the bond layer 120 comprises a eutectic alloy, a solder alloy or an intermetallic alloy.
Suitable eutectic, solder and intermetallic alloys comprise, for example, gold-tin (AuSn), aluminium-germanium (AlGe), copper-tin (CuSn).
According to some embodiments, the electroconductive pad 110 has a predetermined height of 0.2 to 1 μm. Thus, the electroconductive pad controls a height of a gap between the photonic substrate and the optoelectronic component.
The electroconductive pad 110 can comprise for example, doped silicon.
Alternatively, the electroconductive pad 100 can comprise metal or metal alloy, such as platinum (Pt), molybdenum (Mo), titanium-tungsten (TiW), aluminum (Al) or tantalum nitride (TaN). These metals enable good and reliable electrical connection.
The passivation layer can comprise silicon dioxide (SiO2), aluminum oxide (Al2O3) or aluminum nitride (AlN), for instance.
According to some embodiments, the bond layer 120 extends on the at least one protrusion 150 and/or on the at least one groove 140. This provides better contact between the protrusion and the groove.
The protrusion 150 can have a shape of a pillar, which pillar is tapering towards the optoelectronic component 102. In addition, the groove 140 can have substantially the same shape than the protrusion and widen towards the photonic substrate 101. Then, the protrusion match the groove. Therefore, the protrusion and the groove is easy to set in contact, and the photonic substrate and the optoelectronic component can be aligned to each other with high precision.
The protrusion 150 can have a cross-sectional shape of a square, a circle, an oval or any other suitable shape.
The protrusion 150 can comprise electrical insulator material.
According to some embodiments, a method for forming at least one electrical connection between a photonic substrate 101 and an optoelectronic component 102 comprises providing an electroconductive pad 110 on a surface of the photonic substrate 101. The method comprises providing a first bonding material layer 121 directly and at least partially on a surface of the electroconductive pad 110. The method comprises providing a second bonding material layer 122 on a surface of the optoelectronic component 102. The method comprises bonding the first bonding material layer 121 with the second bonding material layer 122 for forming a bond layer 120. The electroconductive pad 110 for the at least one individual electrical connection comprises at least two separated portions for receiving extra bonding material of the bond layer 120 between the portions.
The first bonding material layer 121 is provided directly on a surface of the electroconductive pad 110. Then, there is no layer, such as a sealing layer, between the first bonding material layer and the electroconductive pad. This enables precise alignment between the photonic substrate and the optoelectronic component, and precise thickness control of a structure between the photonic substrate and the optoelectronic component.
According to some embodiments, the method comprises providing a first bonding material layer 121 on the surface of the photonic substrate 101.
According to some embodiment, the method comprises providing a passivation layer 130 on the photonic substrate 101. Then, the electroconductive pad 110 can be provided on the surface of the passivation layer 130.
According to some embodiments, a bonding temperature for bonding the first bonding material layer 121 with the second bonding material layer 122 is lower than a melting temperature of the electroconductive pad 110. The bonding temperature can be for example, at least 150° C., preferably 150 to 550° C., lower than the melting temperature of the electroconductive pad 110. For example, gold-tin (AuSn) bonding can be conducted at about 220° C. or gold-indium (AuIn) can be conducted at about 150° C., while the melting temperature of the electroconductive pad 110 comprising aluminum is about 660° C. Thus, the electroconductive pad 10 is not deformed or melted during the bonding. The electroconductive pad ensures that the photonic substrate 101 and the optoelectronic component 102 are separated by the gap between the photonic substrate 101 and the optoelectronic component 102 during the bonding. In addition, a height of the gap can be adjusted by the height of the electroconductive pad. Thus, the electroconductive pad provides good gap control between the photonic substrate and the optoelectronic component.
According to some embodiments, bonding of the first bonding material layer 121 with the second bonding material layer 122 is provided by eutectic bonding, solder bonding or solid-liquid interdiffusion.
Eutectic bonding does not require use of high contact force during the bonding. Eutectic bonding is less sensitive to surface flatness irregularities, scratches, as well as to particles compared to the direct wafer bonding methods, because the eutectic bonding process goes through a liquid phase.
In eutectic bonding, temperature can be raised to a value lower than the eutectic temperature of the eutectic alloy. Then, temperature can be maintained constant for short time to reach uniform heating of both the photonic substrate and the optoelectronic component. After that, temperature can be increased to a temperature exceeding the eutectic point. Finally, the structure can cool down to a temperature below the eutectic temperature.
Eutectic bonding can be conducted 10 to 20° C. above eutectic temperature of a eutectic alloy. For example, gold-tin (AuSn) bonding can be conducted at 220° C., aluminum-germanium (AlGe) bonding can be conducted at 420° C., gold-indium (AuIn) bonding can be conducted at 150° C., and copper-tin (CuSn) bonding can be conducted at 400° C.
Bonding can be conducted in a bonding chamber. A controlled vacuum pressure can be formed in the bonding chamber. The vacuum pressure can be for example, 0.8 10−5 mbar. One or more inert gases, such as argon and nitrogen, can be introduced to the bonding chamber.
The first bonding material layer 121 and the second bonding material layer 122 can comprise same or different materials. The first bonding material layer 121 and the second bonding material layer 122 can comprise metal or metal alloy.
Both the first bonding material layer 121 and/or the second bonding material layer 122 can comprise tin (Sn), gold (Au), aluminium (Al), germanium (Ge), copper (Cu), indium (In), gold-tin (AuSn), aluminium-germanium (AlGe), copper-tin (CuSn), gold-indium (AuIn) or tantalum nitride (TaN).
For example, the first bonding material layer 121 can comprise tin (Sn) and the second bonding material layer can comprise copper (Cu), or vice versa. For example, the first bonding material layer 121 can comprise tin (Sn) and the second bonding material layer can comprise copper-tin (CuSn), or vice versa. For example, the first bonding material layer 121 can comprise Cu (copper) and the second bonding material layer can comprise copper-tin (CuSn), or vice versa. For example, the first bonding material layer 121 and the second material layer 122 can comprise copper-tin (CuSn). Corresponding metal or metal alloy combinations may also be formed by the other metals and metal alloys listed above.
The first bonding material layer 121 can comprise two layers, a first layer 121a and a second layer 121b. The first layer 121a and the second layer 121b can be at least partially on top of each other. The first layer 121a and the second layer 121b can comprise different metals. For example, the first layer 121a can comprise gold (Au), aluminium (Al) or copper (Cu), and the second layer 121b can comprise tin (Sn), germanium (Ge) or tin (Sn), respectively.
Alternatively or in addition, the second bonding material layer 122 can comprise two layers, a first layer 122a and a second layer 122b. The first layer 122a and the second layer 122b can be at least partially on top of each other. The first layer 122a and the second layer 122b can comprise different metals. For example, the first layer 122a can comprise gold (Au), aluminium (Al) or copper (Cu), and the second layer 122b can comprise tin (Sn), germanium (Ge) or tin (Sn), respectively.
The electroconductive pad 110 comprising at least two portions can comprise at least one gap between the portions. The bond layer 120 can be located in the gap. The gap between the portions of the electroconductive pad can have a predetermined width of 3 to 100 μm, such as 5 to 20 μm.
According to some embodiments, the method comprises providing at least one groove 140 in the optoelectronic component 102 and at least one protrusion 150 on the photonic substrate 101 for aligning the optoelectronic component 102 with the photonic substrate 101. This provides better alignment accuracy between the photonic substrate and the optoelectronic component. Better alignment accuracy minimizes risk for fractures of the photonic substrate and the optoelectronic component.
A layer of protrusion material can be formed over the surface of the photonic substrate using deposition techniques, such as sputtering, evaporation, chemical vapor deposition or physical vapor deposition.
The protrusion 150 can be formed from a material of the passivation layer
The protrusion 150 can be formed from the protrusion material by for example, optical photolithography.
The groove can be formed in the optoelectronic component 102 by for example, optical photolithography.
According to some embodiments, the method comprises providing the first bonding material layer 121 on the at least one protrusion 150 and/or the second bonding material layer 122 on the at least one groove 140. The bonding material layer(s) 121, 122 provides smooth movement of the protrusion into the groove during the bonding the photonic substrate and the optoelectronic component, because liquid metal reduces friction between the surfaces of the protrusion and the groove by working as a lubricant.
The bonding structure 100 can be used in a telecommunication, a datacommunication, an environmental sensing, an industrial sensing, a medial or a light detection and ranging (LIDAR) application.
It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20215792 | Jul 2021 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2022/050482 | 6/30/2022 | WO |
