MEMS SWITCH INCLUDING AN EMBEDDED METAL CONTACT

Abstract

A MEMS switch that includes a substrate with a first insulating layer and a silicon layer thereabove, a fixed portion and a movable switching portion being formed in the silicon layer.

A first metal layer is situated in recesses in the silicon layer at a side of the silicon layer facing away from the substrate, the first metal layer forming at least one switchable electrical contact between the fixed portion and the switching portion.

A method for manufacturing a MEMS switch including at least one embedded metal contact is also described.

Claims

1-12. (canceled)

13. A method for manufacturing a MEMS switch that includes at least one embedded metal contact, including the following steps: A) providing a substrate that includes a silicon layer thereabove; B) introducing narrow trenches into the silicon layer using anisotropic etching; C) filling the narrow trenches by deposition of a first metal layer; D) removing the first metal layer at a surface of the silicon layer, the first metal layer remaining in the narrow trenches and thus creating at least one embedded metal contact; H) structuring the silicon layer via a trenching process, a fixed portion and a switching element being formed, and a contact area of the embedded metal contact being exposed with respect to the silicon layer.

14. The method for manufacturing an electrically actuatable MEMS switch including metal contacts as recited in claim 13, wherein a substrate including a first insulating layer and the silicon layer thereabove is provided in step A, and after step H, the insulating layer is etched below a structured area of the silicon layer in a step I, the switching element being exposed and made movable.

15. The method for manufacturing an electrically actuatable MEMS switch including metal contacts as recited in claim 13, wherein prior to depositing the first metal layer, a thin adhesive layer or a nucleation layer which does not fill the trenches is deposited.

16. The method for manufacturing an electrically actuatable MEMS switch including metal contacts as recited in claim 15, wherein the thin adhesive layer or nucleation layer is deposited via a silicon reducing reaction that partially removes the silicon layer at a surface thus coated.

17. The method for manufacturing an electrically actuatable MEMS switch including metal contacts as recited in claim 16, wherein WF6 is utilized as a component of the reducing reaction.

18. The method for manufacturing an electrically actuatable MEMS switch including metal contacts as recited in claim 13, wherein after step D, narrow, continuous trenches extending to the first insulating layer are etched into the silicon layer in a step E, and a dielectric material is subsequently deposited and structured on the silicon layer in a step F, the continuous trenches being filled with the dielectric material.

19. The method for manufacturing an electrically actuatable MEMS switch including metal contacts as recited in claim 18, wherein further layer sequences of dielectric and/or metallic layers are applied and structured after step F and prior to step H, and a second metal layer is applied and structured in a step G.

20. The method for manufacturing an electrically actuatable MEMS switch including metal contacts as recited in claim 15, wherein the etching in step H is carried out in such a way that the metal contact protrudes beyond the silicon edge by at least 20 nm in a vertical direction.

21. A MEMS switch, comprising: a substrate with a first insulating layer and a silicon layer thereabove, a fixed portion and a movable switching portion being formed in the silicon layer, wherein a first metal layer is situated in recesses in the silicon layer at a side of the silicon layer facing away from the substrate, the first metal layer forming at least one switchable electrical contact between the fixed portion and the switching portion.

22. The MEMS switch as recited in claim 21, wherein the first metal layer is made of tungsten.

23. The MEMS switch as recited in claim 21, wherein the first metal layer is made of nickel or a nickel-containing material.

24. The MEMS switch as recited in claim 21, wherein the first metal layer is situated in recesses in the silicon layer and protrudes laterally from the silicon layer with an overhang, at least in a contact area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 schematically shows a capacitively actuatable MEMS switch including an out-of-plane switching element in the related art.

[0024] FIG. 2 schematically shows a capacitively actuatable MEMS switch including an in-plane switching element.

[0025] FIG. 3 schematically shows the capacitively actuatable MEMS switch including the in-plane switching element in a top view,

[0026] FIGS. 4A through 4I show a method according to the present invention for manufacturing a MEMS switch including embedded metal contacts, at various manufacturing stages.

[0027] FIG. 5 schematically shows the method according to an example embodiment of the present invention for manufacturing a MEMS switch including at least one embedded metal contact.

[0028] FIGS. 6A and 6B show in a first exemplary embodiment of the present invention a MEMS switch according to the present invention including embedded metal contacts in the unswitched state.

[0029] FIGS. 7A and 7B show the MEMS switch according to the present invention including embedded metal contacts from FIGS. 6A and 6B in the switched state.

[0030] FIG. 8 shows in a second exemplary embodiment of the present invention a MEMS switch according to the present invention including embedded metal contacts and a cap in a sectional illustration.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0031] FIG. 1 schematically shows a capacitively actuatable MEMS switch including an out-of-plane switching element in the related art, in a sectional illustration. A first electrode 2 and a first contact surface 3 are provided on a substrate 1. A lever structure 4 is situated above both structures, separated by a distance. If a voltage is applied between the lever and the first electrode, a movement out of the substrate plane (out-of-plane) results. The lever is deflected essentially perpendicularly toward the substrate, and a contact between the lever and the contact surface is established.

[0032] FIG. 2 schematically shows a capacitively actuatable MEMS switch including an in-plane switching element, in a sectional illustration. A first insulating layer 100, a silicon layer 110, a second insulating layer 9, and a metal layer 10 are situated one on top of the other on a substrate 1. The silicon layer, the second insulating layer, and the metal layer together form a micromechanical functional layer 120 in which a fixed portion 121, an electrically actuatable, deflectable switching element 122, and fixed electrodes 8 are formed.

[0033] A first contact area 1210 is formed in metal layer 10 of fixed portion 121, and a second contact area 1220 is formed in metal layer 10 of switching element 122. The switching element is deflectable in at least one first direction 7 in parallel to a main plane of extension (x, y) of the substrate. The first and the second contact area may thus come into mechanical contact with one another and thus close an electrical contact 11. The deflection of switching element 122 is effectuated by applying a voltage to oppositely situated electrode fingers 8 that are anchored to the substrate. First contact area 1210 and second contact area 1220 are each connected to their own strip conductor. An electrical connection between the strip conductors may thus be switched on and off by deflection of switching element 122.

[0034] FIG. 3 schematically shows the capacitively actuatable MEMS switch including an in-plane switching element, in a top view. Suspension springs 6 that are anchored to underlying substrate 1 carry movable switching element 122. In addition, fixed electrodes 8 and fixed portion 121 are shown. The fixed electrodes are situated opposite from corresponding formations of switching element 122, and together with same form the capacitor plates of a capacitive drive. The capacitive drive may effectuate a movement of the switching element in first direction 7. Fixed portion 121 and an oppositely situated area of switching element 122 are covered with metal layer 10 and form switchable electrical contact 11 there.

[0035] FIGS. 4A through 4I show a method according to the present invention for manufacturing a MEMS switch including embedded metal contacts, at various manufacturing stages. The device is illustrated in each case in a sectional view and in a 3D view.

[0036] A first sacrificial layer 100, preferably an oxide layer, is deposited on a substrate 1. A silicon layer 110 is applied to the oxide layer (FIG. 4A). A polysilicon layer is preferably deposited, or a silicon substrate is bonded on and back-thinned to the target thickness. A silicon layer having a thickness between 5 μm and 50 μm is preferably used.

[0037] Narrow trenches 12 are introduced into silicon layer 110 with the aid of anisotropic etching (FIG. 4B). Trenches are preferably predominantly etched that are at least as deep as they are wide. Trenches having a depth of 0.5 μm to 5 μm are preferably etched.

[0038] A first metal layer 13 is deposited (FIG. 4C). In particular, a tungsten layer is deposited. Enough tungsten is preferably deposited so that the narrow trenches are completely closed.

[0039] Alternatively, a nickel layer or a nickel-containing layer may be deposited. Nickel is somewhat poorer with regard to the electrical flashover resistance, but has a lower contact resistance.

[0040] Prior to depositing the first metal layer, a thin adhesive layer or a nucleation layer which does not fill the trenches may also optionally be deposited. A seed layer that is created in part by a reduction of the silicon surface is particularly advantageous.

[0041] First metal layer 13 is polished down at least to the height of silicon layer 110 (FIG. 4D).

[0042] Narrow, insulating, continuous trenches 19 up to oxide layer 100 are optionally etched into silicon layer 110 (FIG. 4E).

[0043] Continuous trenches 19 are subsequently filled with a dielectric material 20, resulting in filled insulation trenches 33, and a layer made of the dielectric material is also formed at the surface of silicon layer 110 (FIG. 4F). The trenches are preferably filled with a SiRiN layer. The dielectric layer is also structured at the surface of silicon layer 110.

[0044] A second metal layer 21 is optionally applied and structured (FIG. 4G). An aluminum layer is preferably applied.

[0045] Further layer sequences of dielectric and metallic layers are optionally applied and structured.

[0046] Silicon layer 110 is structured via a trenching process (FIG. 4H). The trenching process is carried out in such a way that a first contact area 1210 and a second contact area 1220 of first metal layer 13 are exposed. In particular, a trenching process is selected that produces a retraction of the silicon edge of at least 50 nm beneath the structuring mask. A horizontal protrusion of the metal edge relative to the silicon edge is thus produced around and underneath the exposed contact areas. An overhang 15 of the particular contact area beyond adjoining silicon layer 110 is preferably at least 25 nm.

[0047] Oxide layer 100 beneath a partial area of silicon layer 110 is removed in a sacrificial etching step (FIG. 4I). A gas phase etching process using HF is preferably used.

Further Embodiments of the Manufacturing Method

[0048] A cavity SOI wafer may also be utilized in an alternative manufacturing process. By using a fairly costly cavity SOI wafer, the exposure of the movable structure may already take place with the structuring of the silicon layer via a trenching process, and the etching of the first insulating layer may be dispensed with.

[0049] A polishing stop layer may optionally be applied to the silicon layer prior to the trenching step. An oxide layer or a nitride layer or an oxide nitride layer or a SiRiN layer may preferably be utilized. The structuring of the polishing stop layer may preferably take place together with the trenching step, using the same resist mask. The polishing of the tungsten layer then takes place up to the polishing stop layer. This layer may be completely or partially removed in one of the subsequent steps.

[0050] Second metal layer 21 may be used as a first component of a eutectic bonding material in order to arrange a cap 22 above the movable structures to protect these structures. The metal layer may thus be advantageously utilized not only as a strip conductor, but also as a bonding material.

[0051] FIG. 5 schematically shows the method according to the present invention for manufacturing a MEMS switch including embedded metal contacts.

[0052] A substrate including a silicon layer thereabove is provided in a step A.

[0053] Narrow trenches are introduced into the silicon layer in a step B.

[0054] A first metal layer is deposited and the narrow trenches are filled with same in a step C.

[0055] The first metal layer is removed at the surface up to the silicon layer in a step D, the first metal layer remaining in the narrow trenches and thus creating embedded metal contacts.

[0056] The silicon layer is structured using a trenching process in a step H, a fixed portion and a switching element being formed, and contact areas of the embedded metal contacts being exposed with respect to the silicon layer.

[0057] FIGS. 6A and 6B show in a first exemplary embodiment a MEMS switch according to the present invention including embedded metal contacts in the unswitched state. FIG. 6A, in a semitransparent top view, shows a relay according to the present invention together with a capacitive drive and a bonding frame in the basic state. A detail around a switchable contact is shown in enlarged scale in FIG. 6B.

[0058] The device includes a silicon layer 110 above a substrate 1 and an insulating layer (not visible in the top view). A fixed portion 121 and a movable switching portion 122 are formed in the silicon layer. A structured first metal layer is embedded in the silicon layer from above. The first metal layer is exposed in areas with respect to the adjoining silicon layer, and together with a first contact area 1210 and an oppositely situated second contact area 1220 forms a switchable electrical contact 11 between fixed portion 121 and switching portion 122. A second structured metal layer 21 is arranged thereabove. The second metal layer forms bond pads 30, the first component of an electrically insulated bonding frame 31, and forms strip conductors 32 that are electrically insulated from silicon layer 110 and that also traverse filled insulation trenches 33.

[0059] Silicon layer 110 is divided into individual mutually insulated areas with the aid of filled insulation trenches 33, for example to form stationary counter electrodes 8, and in the switching state to apply a potential to them that is electrically different from the movable mass. Fixed electrodes 8 together with movable electrodes of the switching element form a capacitive drive as described with reference to FIGS. 2 and 3, and are used to move switching element 122 in first direction 7. The embedded first metal layer is also structured to form strip conductors 36 which locally increase the conductivity. The conductivity may be increased even further by the second metal layer in partial areas 37 in which second metal layer 21 fulfills no other function (cf. also FIG. 8 in each case).

[0060] FIGS. 7A and 7B show the MEMS switch according to the present invention including embedded metal contacts from FIGS. 6A and 6B in the switched state. Switching portion 122 is deflected in first direction 7 and rests against fixed portion 121, the first and second contact areas of the embedded metal contacts resting against one another. Electrical contact 11 is thus closed.

[0061] FIG. 8 shows in a second exemplary embodiment a MEMS switch according to the present invention including embedded metal contacts and a cap, in a sectional illustration. The illustration shows a capacitively actuatable MEMS switch that includes a substrate 1 with a first insulating layer 100 and a silicon layer 110 thereabove, a fixed portion 121 and a movable switching portion 122 being formed in the silicon layer. A first metal layer 13 made of tungsten is situated in recesses in the silicon layer at a side of the silicon layer, the top side, facing away from the substrate, and is thus embedded. The first metal layer is exposed in areas with respect to the adjoining silicon layer, and together with a first contact area 1210 and an oppositely situated second contact area 1220 forms a switchable electrical contact 11 between fixed portion 121 and switching portion 122. A structured dielectric layer 20 is arranged on silicon layer 110 and in insulation trenches 19. Mechanically connected areas of the silicon layer are thus electrically insulated. A structured second metal layer 21 made of aluminum is arranged on dielectric layer 20. The second metal layer forms bond pads 30, the first component of an electrically insulated bonding frame 31, and forms strip conductors 32 that are electrically insulated from silicon layer 110 and that also traverse insulation trenches 19. A third metal layer 21a made of germanium is arranged on second metal layer 21 in the area of the bonding frame, and together with the second metal layer made of aluminum forms a eutectic bond via which a cap 22 is fastened above the micromechanical structures.

LIST OF REFERENCE NUMERALS

[0062] 1 substrate [0063] 2 first electrode [0064] 3 first contact surface [0065] 4 lever structure [0066] 6 suspension springs [0067] 7 first direction [0068] 8 fixed electrode [0069] 9 second insulating layer [0070] 10 metal layer [0071] 11 contact [0072] 12 narrow trenches [0073] 13 first metal layer [0074] 15 overhang [0075] 19 continuous trenches [0076] 20 dielectric layer [0077] 21 second metal layer [0078] 21a third metal layer [0079] 22 cap [0080] 30 bond pad [0081] 31 insulated bonding frame [0082] 32 metal layer [0083] 33 filled insulation trenches [0084] 36 strip conductor [0085] 37 partial area [0086] 100 first insulating layer [0087] 110 silicon layer [0088] 120 micromechanical functional layer [0089] 121 fixed portion [0090] 122 deflectable switching element [0091] 1210 first contact area [0092] 1220 second contact area