Alternatively, the upper side may be described as a first side, the bottom side as a second side opposite the first side, and the edge as the intermediate area between the first and second sides, with the edge typically extending substantially perpendicular to the first and/or second sides. However, in order to facilitate the comprehension of the present invention and to approximate the present invention to a typical description, terms such as upper side, lower side, and circumferential edge will be used below as explained above. Also, the edge may have a height of 0, so that in this case the upper side will directly bear on the lower or bottom side, for example in the case where the functional area merely includes a thin functional layer.

The upper side of the cavity can then be formed by a top layer such as a substrate, sheet (wafer) or platelet. Furthermore, for example, the circumferential edge of the cavity may be formed by the top layer projecting downward or by the lower layer projecting upward, for example by having the lower layer abrasively hollowed out. The bottom of the cavity can finally be formed by a lower layer, a substrate, sheet (wafer), or platelet and can be arranged below the upper layer.

The cavities are in particular provided in the form of accommodation cavities. This means that electronic circuits, sensors, MEMSs or MOEMSs can be integrated in the respective cavities, for example. These aforementioned devices such as in particular electronic circuits, sensors, or MEMSs will therefore be enclosed by the package all around, i.e. on all sides thereof, since they are arranged inside the accommodation cavity.

The at least two substrates or the base substrate and the cap are arranged or attached to one another such that they come to lie flat against one another without any other sheets, layers, or inclusions present between the at least two substrates or between the base substrate and the cap. For technical reasons, there might be unavoidable minor gas inclusions between the layers in the contact areas, which may be caused by some possible unevenness. The amount of gas trapped in the 2-dimensional contact area can be further reduced by increasing the pressure, for example, such as in particular by pressing the substrate layers, or by a surface treatment in particular of the contact surfaces, such as a grinding process. Prior evacuation is beneficial. Filling with a type of gas or else with a liquid may also be advantageous, depending on the process parameters and the materials to be employed.

In other words, the substrate layers or the base substrate and the cap are stacked directly and in direct contact to each other, i.e. arranged so as to adjoin each other. Foreign materials are excluded as far as possible between the substrate layers, so that the most cohesive surface contact possible is created between one substrate layer and the adjoining substrate layer. In the case of two substrates, for example, the base substrate is arranged in direct contact to the cover substrate, in particular without any other materials or any spacing between the base substrate and the cover substrate. In the example of more than two substrates, the base substrate is arranged directly adjoining the one or the first one of the intermediate substrate layer(s), the cover substrate in turn is arranged directly adjoining the one or the last one of the intermediate substrate layer(s). In the example of base substrate and cap, these are arranged so as to adjoin each other, with the cap having the contact surfaces on its end faces, where a direct, immediate and optionally full-surface contact is established between the end faces of the cap and the base substrate.

Then, the substrates are joined together using the novel laser welding process. In this case, a planar substrate layer is directly joined or bonded to the immediately adjoining planar substrate layer or planar end face without providing or requiring any foreign material or non-planar material or intermediate layers for this purpose. That is, the substrates are bonded directly to one another. The laser bonding line introduced into the two-dimensional contact area between two substrate layers bonds the directly adjoining substrate layers to one another, i.e. directly adjacent to one another, in a non-releasable manner. The fused zone of the laser bonding line is therefore present in both substrates and seamlessly extends from the first substrate into the immediately adjoining second substrate, that is, for example, from the base substrate into the cap.

Thus, a direct two-dimensional or even full-surface transition is formed from one substrate layer to the next substrate layer, i.e. a substrate-to-substrate transition or a glass-to-glass transition, for example. A locally limited volume in the form of a welding zone or laser bonding line is created, which includes material transferred or mixed between the adjoining substrate layers which in particular have a sheet-like shape. In other words, material of the first substrate, for example the cover substrate, penetrates into the adjoining substrate, for example the intermediate substrate or the base substrate, and vice versa, i.e. material from the adjoining substrate penetrates into the first substrate, so that the welding zone includes a complete mixture of material from the adjoining substrates. The welding zone can therefore also be referred to as a convection zone.

The novel laser welding technique for producing the non-releasable glass-to-glass transition or substrate-to-substrate transition is particularly advantageously free of intermediate layers, glass frits, foils, or adhesives that had to be introduced between the substrates in earlier prior art processes. Rather, the non-releasable bond can be produced without such interfering intermediate layers or additional materials. This saves the use of additional materials, increases the achievable strength of the end product, and enables reliable hermetic sealing of the functional area or of the cavity/cavities. The laser welding zone can be identified in the finished end product, for example by the specific local change in the refractive index of the materials in the small fusion area.

Optionally, a gap that might arise between the substrates or between the base substrate and the cap has a width of less than or equal to 5 μm, or less than or equal to 1 μm. Such a gap arises, for example, due to tolerances in the substrate manufacturing, by thermal impacts or by inclusions of particles such as dust. Even with such a tolerable spacing which is still considered to be immediately adjoining in the context of the present invention, it is possible to laser weld in such a manner that the welding zone is between 10 and 50 μm in thickness so that a hermetic seal is ensured. Again, in this case, the welding zone extends from the first substrate into the second substrate adjoining the first substrate. Thus, the welding zone is introduced in the contact area between the first and second substrates and directly fuses the substrates to one another to form an inseparable bond. In other words, when the adjoining substrates are bonded in the welding zone, material of both substrates is directly melted in the welding zone, and the material of the first substrate mixes with the material of the second substrate to form an inseparable integral bond. The package produced in this way therefore includes an integral, i.e. monolithic bond between the substrates in the welding zone.

A contact area does not have to be optically transparent. It is also advantageous if the transparent substrate or the transparent cap is opaque in the visible wavelength range. Only the substrate through which the laser passes to reach the contact area has at least one spectral “window” such that at least the wavelength of the employed laser can be transmitted through the substrate at least partially or at least in sections thereof. The contact area is adapted such that the laser is able to deposit energy there. For example, the surfaces of the two adjoining substrates may be joined by optical contact bonding and may furthermore optionally exhibit a roughness in the nanometer range. The laser radiation will at least partially be absorbed at this interface, so that energy can be introduced there. In the sense of the present application, contact area is generally understood to mean an interface at which the incident laser beam can deposit energy so that a bonding process can be performed along the contact area. A simple case of such an interface is the contact area between the cap and the base substrate. The substrates are bonded or joined to one another in order to form a joint package and to hermetically seal the cavities.

The step of hermetically sealing the package is achieved by bonding along the at least one contact area of each package by a laser welding process. In other words, a laser can be used to deposit energy in the contact area, in particular locally limited to such an extent that it can be referred to as a cold welding process. That is, the thermal energy provided for the bonding is focused to the extension of the laser bonding line and only comparatively slowly diffuses into the rest of the material of the package, so that in particular no significant temperature rise will occur inside the cavity. This protects the electronics disposed in the cavity from overheating.

The laser is used to locally melt material of the two substrates or the cap along the laser bonding line, so that the at least two substrates are bonded locally. For this purpose, a person skilled in the art may refer to Applicant's EP 3 012 059 B1, for example, which is hereby incorporated by reference.

A particular advantage of a transparent package made of glass or predominantly made of glass, in particular borosilicate glass, is its chemical inertness.

The one or more substrate(s) may also have a coating. For example, AR coatings, protective coatings, bioactive films, optical filters, conductive layers such as made of ITO or gold may be employed, as long as it is ensured that transparency or at least partial transparency for the employed laser wavelength is provided in the irradiation area of the laser.

The at least one transparent substrate is optionally made of glass, glass ceramics, silicon, or sapphire, or of a combination of the aforementioned materials, i.e., for example, glass/silicon, a glass/silicon/sapphire combination, or a silicon/sapphire combination. The one or more further substrate(s) may also include or consist of Al₂O₃, sapphire, Si₃N₄, or AlN. Combining a transparent substrate with a different type of substrate allows to obtain semiconductor properties, for example. Coatings may also be employed, for example piezo-resistive Si layers, in particular for pressure sensors, or thicker layers for micro-mechanical applications such as pulse measurement via an MEMS.

In this case, at least one of the lateral circumferential edge, the bottom, or the upper side are transparent for some range of wavelengths, at least in sections thereof. In other words, it is sufficient if at least one component of the package is transparent for optional wavelength range at least in a portion of the component, the wavelength range being known in advance so that the material can accordingly be adapted to the wavelength of the laser to be used, if desired.

The package is joined using a laser welding process to form the hermetically sealed package. In other words, the edge, bottom, and upper side initially include or consist of more than one piece, for example of two or three parts or even more, and the parts are laser-welded to one another to complete the package.

In a further embodiment, the package may be chemically toughened at least partially and/or in sections thereof. For example, one surface of the package is chemically toughened, i.e. for example the upper side. It is also possible that the upper side and the edge are chemically toughened. Optionally, the upper side and the edge and the lower side are chemically toughened, so that the respective surface of the upper side and the lower side as well as the respective edge, i.e. the rim, is chemically toughened.

Prior to the step of producing the laser bonding line for joining along the contact areas of each package, the substrates may be bonded to one another at least temporarily by optical contact bonding.

The present invention will now be explained in more detail by way of exemplary embodiments and with reference to the figures in which identical and similar elements are partially denoted by the same reference numerals, while the features of the different exemplary embodiments can be combined with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1a is a view of the opened accommodation cavity from above;

FIG. 1b is a perspective view of a sealed package;

FIG. 1c shows an alternative open package;

FIG. 1d is a sectional view through the welding zone;

FIG. 2 shows a plan view of a package on a base substrate;

FIG. 3 is a sectional view along line A-B of an embodiment of a package as shown in FIG. 2;

FIG. 4a is a sectional view along line C-D of another embodiment of the package as shown in FIG. 2;

FIG. 4b is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2 but with the package including an intermediate substrate and two laser welding zones;

FIG. 5 is a sectional view along line A-B of yet another embodiment of the package as shown in FIG. 2;

FIG. 6 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2;

FIG. 7 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2;

FIG. 8 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2;

FIG. 9 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2;

FIG. 10 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2;

FIG. 11 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2;

FIG. 12 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2;

FIG. 13 is a sectional view along line C-D of yet another embodiment of the package as shown in FIG. 2; and

FIG. 14 shows steps of a method for producing a package.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1a shows the accommodation item 2 to be protected, introduced in a base substrate 3 such as a wafer or a printed circuit board, in particular one made of aluminum nitride. Functional area 13 is in the form of a recess in the base substrate 3, as made by an abrasive process such as a sandblasting process, for example. In other words, the base substrate 3 has a recess 13 in which the accommodation item 2 is placed. So, base substrate 3 includes a portion 3a which defines the bottom 22 of package 1. In other words, the package 1 is formed with a portion of the substrate 3 as the bottom 22 (see FIG. 6), and the package 1 is firmly connected, in particular joined, to the substrate 3. A cap 5 is shown, which is intended for covering the accommodation item 2. Cap 5 may be a glass plate, for example, which is placed on the recess 13 in the base substrate 3. Thus, the components 3 and 5 jointly define the package 1 around accommodation item 2 which is arranged in the functional area 13, here a cavity 12 (see FIG. 1c), when the package 1 is closed. In other words, when the cap 5 is placed on the base substrate 3 in the example of FIG. 1a, a closed accommodation cavity 12 is formed, which will have to be hermetically sealed in a subsequent step.

FIG. 1b shows the created hermetically sealed package 1 which was joined by a laser welding process. The package includes the cap 5 stacked on top of the base substrate 3, thereby forming a contact area 25 between cap 5 and substrate 3, along which a laser bonding line 8 has been introduced.

FIG. 1c shows a further embodiment of the package 1, in which the cap 5 includes a top portion 5b and a circumferential skirt 5a. Cap 5 is placed on the substrate 3, with the contact area on the end face of circumferential skirt 5a, specifically in the area of the underside 3a of the package 1, which will then form the bottom 22 (see FIG. 6) of the cavity 12 when the package 1 is completed.

FIG. 1d shows a detail of the joining area, clearly illustrating the interface zone, i.e. the contact area 25 and the laser welding zone 8. Laser welding zone 8 is located in contact area 25.

FIG. 2 shows a plan view of a package 1 according to the invention, with the circumferential laser welding zone 8 surrounding the functional area 13. Functional area 13 may be implemented in different ways. Exemplary embodiments of functional area 13 as well as for other options of a package can be seen in FIGS. 3 through 13. The various designs of functional area 13 can all be schematically illustrated as in FIG. 2, as they will be similar in such a plan view. Lines A-B and C-D indicate section lines along which the sectional views of FIGS. 3 to 13 are reproduced.

The functional area may implement various tasks, for example it may include an optical receiver or a technical, electro-mechanical, and/or electronic component which is disposed in the functional area 13. It is also possible to implement a plurality of such tasks in the functional area 13. On the upper side, the package 1 is covered by upper substrate 5 or cap 5. The laser welding zone 8 extends into this upper substrate 5.

Referring to FIG. 3 which shows a first sectional view of a first embodiment of a package 1, which includes a base substrate 3 and a flat cap 5 in the form of a cover substrate 5. In other words, package 1 is made of or composed of two layers, namely base layer 3 and cover layer 5. FIG. 3 also shows the structure of laser welding line 8 in the form of a string of multiple laser pulse impact areas 16 which are placed so close to one another that the material of the base substrate 3 and of the cover substrate 5 seamlessly fuses to one another thereby hermetically sealing the functional area 13 or the cavity 12.

FIG. 4a shows a sectional view of an embodiment of a package 1 along line C-D as shown in FIG. 2. FIG. 4a furthermore shows a section through the functional area 13, 13a which extends inside the package 1, for example in the form of a continuous hollow space or cavity. In other words, the cavity extends from base substrate 3 into the cover substrate 5 and, for example, is in the form of a recess made in the base substrate 3 and/or in the cap 5. For example, the functional area 13a may also include an active layer such as an electrically conductive layer, and the functional area 13 includes the cavity. The laser welding zone 8 provided circumferentially around the functional area 13, 13a seals the functional area 13, 13a all around along the lateral sides thereof. It is conceivable to leave gaps in the laser welding zone 8 so that the functional area 13, 13a will not be sealed all around, for example in order to keep open a communication channel or space for an electrical connection, which may however also be used to establish fluid communication with the environment, for example. In other words, it might be contemplated to not seal predefined locations or points using the focused laser beam 9, but to rather achieve a hermetic seal by other means there, such as by an adhesive. Optionally, the functional area 13, 13a is sealed along all of its sides and without any gaps.

In FIG. 4b, a package 1 includes an intermediate substrate 4 which is arranged between the heat-dissipating base substrate 3 and the cap 5, and in this example the base substrate 3 is joined to the intermediate substrate 4 in a first bonding plane by at least one first laser bonding line 8, and the cap 5 is joined to the intermediate substrate 4 in a second bonding plane by at least one second laser bonding line 8. Further, the cap 5 may define the upper side of the functional area 13 or cavity, the intermediate substrate 4 may define the laterally circumferential edge, and the heat-dissipating base substrate 3 may define the bottom of the functional area 13 or cavity, which together completely enclose the accommodation cavity.

Referring to FIG. 5 which shows a further embodiment in which incident laser pulses 16 create the laser welding zone 8 where the cover substrate 5 is welded or joined to the base substrate 3 along contact area 25. This embodiment has the further special feature to have the surfaces of the first substrate 3 and of the second substrate 5 toughened all around, that is to have toughened layers 27, 28, and 29. For example, the cap 5 can be dipped into a toughening bath with its upper side before being bonded to the base substrate 3, or else after having been bonded to the base substrate 3, so that the finished package 1 will be chemically toughened, i.e. will have at least one toughened surface 27 and/or has at least one toughened layer. In other words, the finished package 1 is toughened at least in sections thereof or at least partially, in particular chemically toughened. With the chemical toughening, a compressive stress is established on the cover substrate 5.

In the embodiment shown in FIG. 5, the package 1 is toughened on all outer surfaces, i.e. both the two opposite major surfaces have toughened layers 27 and 29, and the circumferential edge 14 of the package has a toughened layer 28, the circumferential edge 14 extending circumferentially around the package 1. In other words, in the case of a cuboid package, all four narrow sides that are found on a cuboid jointly form the edge 14. The edge 14 can also be understood or referred to as an edge 21 of the package, which extends around the cavity. A package 1 as shown in FIG. 5 can be obtained, for example, by immersing the finally welded package including the cap 5 and the base substrate 3 in a toughening solution and in particular chemically toughening it there. The toughened layers 27, 28, 29 are thus disposed directly at the outer surfaces of the package 1. Thus, inwards of the toughened layers 27, 28, 29 there remains an area for the welding line 8 which is possibly introduced with a spacing to the toughened layers 27, 28, 29.

FIG. 6 shows an embodiment of the package 1 comprising a cap 5 having a skirt 5a placed on the base substrate 3. The view of FIG. 6 may correspond to a section along line C-D as shown in FIG. 2. In this embodiment, the functional area 12, 13, 13a is designed so as to be provided on the base substrate 3 and to extend into the cap 5. Welding line 8 is provided around the cavity 12 so that the cavity 12 is hermetically sealed on all sides thereof. Cap 5 may be round or square and may in principle be of any free shape.

The accommodation item 2, for example a sensor or actuator, is arranged on the bottom 22 of cavity 12, for example glued thereto. Metallic pads 32, 32a for making electrical contact with the accommodation item 2 are provided on either side of the accommodation item. Contacting wires 36, 36a such as bond wires, for example, electrically connect the accommodation item 2 with the contact points 32, 32a. The contact points 32, 32a may be metallic contact areas. Connectors 35, 35a establish an electrical connection to second contacts 34, 34a that are arranged outside cavity 12, so that the accommodation item on base substrate 3 such as a printed circuit board 3 can be contacted from outside. In the present example, the second contacts 34, 34a are arranged on the underside or lower surface of the base substrate 3, thereby allowing the size of the individual package 1 to be kept small. It has to be ensured that the contacting wires 36, 36a are hermetically sealed, for example by applying the second contacts 34, 34a directly on the connectors 35, 35a. The cap 5 is directly joined to the base substrate 3 by laser bonding lines 8. In the present case, two closed circumferential laser welding zones 8 were formed by directing the laser 9 twice around the cavity along contact area 25 or along the outer edges of cap 5, but not on an exactly identical path. Rather, with each revolution around the cavity 12 the laser 9 was directed along a laterally offset path so that two laser welding zones 8 are created next to one another. For example, the micro-welding zones 8 in the present example have dimensions of 5 μm×10 μm or 10 μm×50 μm.

For example, AF45 may be used as the material for the cap 5. The base substrate 3 may include an AlN ceramic of single-layer design. This is advantageous if cost-efficient fabrication is desired, for example for power semiconductors or for LEDs. The characteristic value of the coefficient of thermal expansion (CTE) of the two in particular different materials of the cap 5 and the base substrate 3 can be selected so as to be matched to one another between the layers. For example, the CTEs may be similar or even identical, in order to have little or no thermal stress at all in the package 1. The CTEs of AF45 and AlN match surprisingly well for the desired application; hardly any thermal stress was determined on the package 1. Si₃N₄may also be employed as the material for the base substrate. A special feature of the package 1 according to the invention is that the substrate 3 is a highly thermally conductive material, in the embodiments of FIGS. 6-9 and 13 in the form of a single-layer ceramic, in the embodiments of FIGS. 10-12 in the form of a multi-layer ceramic.

FIG. 7 shows a further embodiment of a package 1 along section line C-D, and in this example, again, the functional area 13 or cavity 12 is provided inside the cap 5. In this example, the accommodation item 2, such as a high power LED, has an upper side contact area and a lower side contact area. Thus, the accommodation item 2 is arranged on contact 32a and is directly electrically connected thereto. A second electrical connection is established between contact 32 and the upper side of accommodation item 2 via contacting wire 36. Cap 5 is fused and hermetically sealed to the base substrate 3 by bonding lines 8. In all embodiments, the same reference numerals denote the same features in the figures.

The joint along bonding line 8 was optionally introduced into relaxed, i.e. non-toughened material of the cap 5 and of the base substrate 3. The base substrate 3 is joined directly to the cap 5, so that no further layer or no further substrate is arranged between the base substrate 3 and the cap 5. The functional area 13 is in the form of a cavity 12. AF45 or 8337b can be used as the material for the cap 5, for example, and the base substrate 3 may be a single-layer or multi-layer AlN ceramic. The vias or contacting feedthroughs