The present invention relates to an electrical component, in particular a high-frequency microelectronic or microelectromechanical component, as well as a method for manufacturing the same.
German Published Patent Application No. 100 37 385 discloses a micromechanically fabricated high-frequency short-circuit switch that has a thin metal bridge which is extended between two ground leads of a coplanar waveguide. This high-frequency short-circuit switch is usable, for example, for adaptive cruise control (ACC) or short-range radar (SRR) applications in motor vehicles, and is operated at operating frequencies of typically 24 or 77 gigahertz.
Many other microstructured or microsystem-engineering components are known besides, for example for applications in silicon-based high-frequency technology. These are also referred to as MEMS (microelectromechanical structures or systems) or HF-MEMS (high-frequency microelectromechanical structures or systems) components.
With microstructured components and in particular high-frequency microstructured components, it is generally necessary to protect them from environmental influences such as moisture, air, dirt particles, or other external media or gases. A capsule is often used for this purpose. To ensure that the functionality of the microstructured component enclosed by the capsule is not (or not too greatly) impaired, it is necessary to introduce a conductive structure into the capsule. The first problem that arises in this context is that of ensuring the requisite gas-tightness or moisture-tightness. In the context of passage of the conductor structure from the external space of the capsule into its interior space, it is also necessary to ensure, especially in the case of a high-frequency component, that the conductor structure remains transparent or permeable to high-frequency electromagnetic waves, i.e. there must be no appreciable damping of or interference with the propagation of the electromagnetic waves on the conductor structure.
U.S. Pat. No. 6,207,903 describes a microstructured silicon substrate in the form of a membrane having a high electrical conductivity that has feedthroughs between coplanar waveguides that are guided on different sides of the silicon substrate. These feedthroughs are embodied in the form of truncated circular cones and have been etched into the substrate from different sides thereof and filled with a metal, resulting in a high-frequency feedthrough between the coplanar waveguides guided on the upper side and lower side. The document moreover describes the fact that pyramidal feedthroughs penetrating through the substrate are also known. The etching method used in U.S. Pat. No. 6,207,903 for producing the feedthroughs is a wet-chemical etching method that utilizes the anisotropy of the etching rate in silicon single crystals along different crystal directions, so that (111) crystal planes always form as the side walls of the pyramidal feedthroughs. The side walls are thus not vertical, but always form an angle of 54.75° with the substrate plane. This method is explained in further detail in U.S. Pat. No. 5,913,134 in connection with the construction of high-frequency components having coplanar waveguides.
U.S. Pat. No. 6,365,513 discloses an electrical component, in particular a microelectronic or microelectromechanical component, having a base element that is provided with at least one feedthrough that connects, continuously at least for high-frequency electromagnetic waves, a first conductive structure extending on or in a vicinity of an upper side of the base element to a second conductive structure extending on or in a vicinity of a lower side of the base element, the feedthrough being embodied in the form of a right prism or a right cylinder.
U.S. Pat. No. 4,348,253 discloses an electrical component, in particular a high-frequency microelectronic or microelectromechanical component, having a base element that is provided with at least one feedthrough. The feedthrough connects a first conductive structure extending on or in a vicinity of an upper side of the base element and a second conductive structure extending on or in a vicinity of a lower side of the base element, the feedthrough being embodied in the form of a right prism or a right cylinder.
U.S. Pat. No. 5,618,752 describes a wafer having a via, extending from one surface to the other, that is etched into the base element using a plasma etching process.
U.S. Pat. No. 6,225,651 discloses a method for producing an electrical component having a feedthrough for high-frequency electromagnetic waves through a base element, an electrically conductive layer being applied at least locally on an upper side of the base element and an etching mask being applied on a lower side of the base element; at least one connection, penetrating through the base element and having at least almost perpendicular sidewalls, being etched into the base element by the etching mask in a plasma etching step; an electrically conductive layer being applied at least locally on the lower side after etching and after a removal of the etching mask; and the connection being at least largely filled or lined with an electrically conductive material.
The analysis of conductive vias that are insulated by silicon dioxide from a silicon wafer and serve to connect strip-shaped transmission channels is described in J. P. Quine, “Characterization of Via Connections in Silicon Circuit Boards,” IEEE Transactions in Microwave Theory and Techniques, Vol. 36, No. 1, pp. 21-27, January 1988.
Lastly, PCT Published Patent Application No. 02/33782 discloses an apparatus for guiding electromagnetic waves from a waveguide to a transmission channel. The apparatus encompasses coupling means containing at least one dielectric layer that has an opening which is embodied as an electrically conductive via.
The feedthroughs for high-frequency microelectronic or microelectromechanical components known from the aforesaid publications have the disadvantage that they require a great deal of space because of the anisotropic wet etching of silicon using the (111) plane as the etching stop, and that the coplanar waveguides for high-frequency electromagnetic waves in the gigahertz region guided on the silicon substrates described therein must be provided with special electrical adaptation structures to allow them to be integrated into a corresponding high-frequency component. These adaptation structures additionally result in a degradation of the high-frequency properties of the electrical components due to undesirable losses, a decrease in bandwidth, and the need for special impedance adaptation.
The object of the present invention was to make available an electrical component, in particular a high-frequency microelectronic or microelectromechanical component, that on the one hand can be hermetically encapsulated and on the other hand does not entail the aforesaid disadvantages of feedthroughs known from the existing art in terms of their high-frequency properties.
The electrical component according to the present invention and the method according to the present invention for manufacturing it have the advantage, as compared with the existing art, that the feedthroughs can be manufactured to be very much smaller than in the existing art; and that additional special adaptation structures for integration of those feedthroughs into a circuit having conductive structures for high-frequency electromagnetic waves, in particular in the range from 1 GHz to 80 GHz, can usually be dispensed with.
It is further advantageous that established technologies, such as those known e.g. from German Patent No. 42 41 045, can be used for the individual method steps when carrying out the method according to the present invention. In particular, feedthroughs or so-called “vias” having almost perpendicular and smooth sidewalls can be implemented by dry plasma etching, and are characterized by low electrical losses in particular for high-frequency electromagnetic waves, as well as very good capability for integration into a high-frequency circuit environment. Feedthroughs of this kind are furthermore usable in all lead types or conductive structures from the family of planar waveguides, i.e., for example, coplanar waveguides, microstrip conductors, or so-called “slot lines” such as those already described in Meinke and Gundlach, “Taschenbuch der Hochfrequenztechnik” [Handbook of high-frequency engineering], Vol. 2, Verlag Springer, 1992.
A farther advantage of the plasma etching technique used to produce the feedthrough is the fact that the feedthroughs can now be fabricated with a high aspect ratio, i.e. a high ratio of diameter to height, of typically 1:10 or more, and at the same time with almost any desired cross section when viewed in plan, i.e. for example round, square, rectangular, or oval.
Advantageous refinements of the invention are evident from the features recited in the dependent claims.
For example, it is advantageous in terms of the desired high-frequency properties if the feedthrough is filled or lined with a metal, for example gold, as an electrically conductive material.
The dimensions of the feedthrough, when viewed in plan, are preferably in the range of an area of 400 μm2 to 40,000 μm2, in particular 1,600 μm2 to 10,000 μm2, or a diameter of 20 μm to 200 μm, in particular 40 μm to 100 μm.
The base element, i.e. usually a high-resistance silicon wafer having a specific resistance of more than 100 Ω/cm, advantageously has, at least in the region of the feedthrough, a typical thickness of 100 μm to 650 μm, for example 200 μm.
Lastly, a central problem in terms of protecting packaged or encapsulated high-frequency components or micromechanical components or sensor elements from external influences or the irradiation of electromagnetic fields is that of leading conductive structures that are connected to the packaged electrical high-frequency component out from an interior space enclosed by a capsule, since such leadthroughs must be configured to be on the one hand hermetically sealed and on the other hand compatible with high frequencies. An electrical component encapsulated according to a refinement of the invention advantageously avoids the problem of leading the conductive structures through the capsule by way of a backside contact through the base element, so that there is available around the encapsulated component an open area that can be used as a bonding surface for the capsule.
The higher-capacitance lining inside feedthroughs 13 is taken into account by capacitances Cp.
The offset feedthroughs 13, 13′ (so-called “staggered vias”) according to
If feedthrough 13 has a size of, for example, 50 μm×50 μm, dielectric 15 preferably has a thickness of 45 nm to 1800 nm, in particular 90 nm to 900 nm, which are values readily attainable in the context of ordinary technologies; this means that it constitutes, with conductive structures 11, 12 and feedthrough 13, a capacitor having a capacitance of 0.05 pF to 4 pF, in particular 0.1 pF to 2 pF. It is furthermore preferably dimensioned (in plan view) to correspond with the area of feedthrough 13 or to be slightly larger, and can additionally also be provided on lower side 20 or alternatively only on lower side 20 of base element 10. The variant shown in
The overall result of using a dielectric layer 15 as shown in
Lastly, there is provided according to
The material of capsule 16 is preferably a material that has a coefficient of thermal expansion similar to that of the material of base element 10, i.e. silicon, and that can also be manufactured using microsystems engineering. Silicon and a float glass such as borosilicate float glass are preferably used as the material for capsule 16.
For the manufacture of capsule 16, suitably dimensioned cavities, in which electrical component 17 embodied, for example, as a high-frequency microelectromechanical component (“HF MEMS structure”) is later located, are etched in the usual fashion into a silicon disk or glass disk.
A glass frit is preferably used to mount capsule 16 on base element 10, in particular using a “bonding frame.” In the case of borosilicate float glass, anodic bonding can also be utilized. The encapsulated components are then diced by sawing 17, and integrated into a circuit environment. In addition, if necessary, the encapsulated electrical components 17 can also be provided on the integration side, after metallization of feedthroughs 13, with usual connection contacts (“bumps”) for a soldering or adhesive bonding process.
Capsule 16 thus creates a hermetically sealed interior space 18 in which electrical component 17—which is connected, continuously for high-frequency electromagnetic waves, via upper conductive structure 11 and feedthroughs 13 to lower conductive structures 12 and can be electrically activated thereby—is located on base element 10 or in the region of the surface of base element 10.
In all the aforementioned exemplified embodiments, feedthroughs 13 are constituted by trenches 14, etched into substrate 10 using a plasma etching method, that have been filled or lined with, for example, a metal. Feedthroughs 13 are thus embodied as filled or lined right prisms, i.e. solids having congruent polygons as their base outlines, the edges being perpendicular to the base outline; or as filled or lined right cylinders, i.e. solids delimited by a cylindrical surface having a closed directrix and two parallel planes (the base outlines of the cylinder). Feedthroughs 13 are, in particular, relatively small as compared with the existing art, and they have a relatively high aspect ratio with a largely arbitrary cross section. It should furthermore be emphasized that what primarily governs the high-frequency properties of feedthroughs 13 is not the thickness of base element 10 but rather their lateral dimensions and their shape.
The high-frequency feedthroughs (HF vias) according to the present invention can be utilized, for example, at crossover points, thereby allowing the construction of low-loss high-frequency crossovers.
In a crossover, one signal path is continued and the other is interrupted.
The method for manufacturing a feedthrough 13 as shown in
An alternative variant of this method provides that after the purified high-resistance silicon is made available as the starting material, firstly a dielectric layer is applied on one side onto upper side 21 and optionally patterned; then the conductive, electroplating-compatible metal layer is sputtered onto one side and optionally patterned; then a photoresist is again applied onto lower side 20 and photolithographically patterned in the region of feedthroughs 13 that are to be produced, resulting in a resist mask constituting an etching mask; and the silicon is then etched through in a plasma etching step, in the region of feedthroughs 13 that are to be produced, to the dielectric layer present on the opposite side, forming trenches 14 that penetrate perpendicularly through base element 10. After removal of the resist mask constituting the etching mask, the dielectric layer (which preferably is an oxide layer) is then firstly removed again at least in the region of feedthroughs 13 that are to be produced, and the side of base element that was initially not metallized is metallized, for example by sputtering, before conductive structures 11 and 12 are once again produced by the application of photoresist masks onto both sides of base element 10 and subsequent electroplating reinforcement, and feedthrough 13 is reinforced with metal or lined with a metal. Lastly, electroplating supply leads produced on either side of base element 10 are removed again in an etching step, so that only conductive structures 11, 12 and feedthrough 13 remain.
It should additionally be emphasized-that the methods explained above are suitable for the realization of all known types of conductive structures, in particular planar waveguides such as coplanar waveguides, microstrip leads, and so-called “slot lines.”
The method for producing an electrical component 5 according to
Alternatively or in addition to the use of a dielectric layer 15 for capacitative coupling, further series capacitances can also be used in the region of upper conductive structure 11 and/or in the region of lower conductive structure 12 for HF compensation, these being implemented e.g. by way of capacitative lead segments, for example interdigital capacitances, upstream from conductive structures 11, 12.
Number | Date | Country | Kind |
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10229578.6 | Jul 2002 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE03/02087 | 6/24/2003 | WO | 8/16/2005 |