MEMS device with reduced contact resistance

Abstract

The present invention discloses a method of fabricating a MEMS device, wherein the MEMS device has a cavity and a beam will move in the cavity to change the capacitance of the device. After most of the device stack has occurred, sacrificial material is removed to release the beam within the MEMS device cavity. Thereafter, the exposed ruthenium contacts are etched back with an etchant comprising chlorine to remove the top surfaces of both the top contact and the bottom contact. Due to this etch-back process, a low contact resistance can be achieved with less susceptibility to adhesion events. The adhesion performance can be further improved by conditioning the ruthenium contacts in a fluorine-based plasma. The fluorine-based plasma process or fluorine treatment can be performed before or after the etch-back process of the ruthenium contacts.

Description

[0001] This application claims priority to U.S. Provisional Patent Application No. 62 / 854,826, filed May 30, 2019, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] Embodiments of the present disclosure generally relate to a method for reducing contact resistance while preventing adhesion in a microelectromechanical system (MEMS) device including one or more ruthenium contacts. Background Art

[0003] Contact bonding or adhesion is one of the primary failure mechanisms in MEMS devices. Adhesion is one of the key challenges in fabricating viable MEMS devices. Ruthenium contacts provide low-resistance, durable contacts, but ruthenium contacts are vulnerable to potential adhesion events during the operating lifetime.

[0004] Accordingly, there is a need for low-resistance, durable contacts that are less vulnerable to adhesion events. Summary of the Invention

[0005] The present disclosure generally relates to a method of fabricating a MEMS device. The MEMS device has a cavity, and a beam will move within the cavity to change the capacitance of the device. After most of the device stack-up has occurred, sacrificial material is removed to release the beam within the MEMS device cavity. Thereafter, the exposed ruthenium contacts are etched back with an etchant including chlorine to remove the top surfaces of both the top contact and the bottom contact. Due to this etch-back process, low contact resistance can be achieved with less vulnerability to adhesion events. The adhesion performance can be further improved by conditioning the ruthenium contacts in a fluorine-based plasma. The fluorine-based plasma process or fluorine treatment can be performed before or after the etch-back process of the ruthenium contacts.

[0006] In one embodiment, a method of fabricating a MEMS device includes: forming one or more electrical contact stacks including ruthenium contact surfaces within a cavity; forming a beam structure above the one or more electrical contact stacks within the cavity, wherein the cavity contains sacrificial material; removing the sacrificial material from the cavity to release the beam to move within the cavity; etching a portion of the ruthenium contact surfaces with an etchant including chlorine; and sealing the cavity.

[0007] Those skilled in the art will appreciate the scope of the present disclosure and will recognize additional aspects thereof after reading the following detailed description of the preferred embodiments in conjunction with the accompanying drawings. Brief Description of the Drawings

[0008] The drawings incorporated in and forming a part of this specification illustrate several aspects of the present disclosure and, together with the detailed description, are used to explain the principles of the present disclosure.

[0009] Figure 1 Schematic illustration of a MEMS device before removal of sacrificial material and release of the beam.

[0010] Figure 2 After the sacrificial material has been removed and the beam has been released Figure 1 Schematic illustration of the MEMS device.

[0011] Figure 3A After the sacrificial material has been removed Figure 2 Enlarged schematic illustration of a portion of the MEMS device.

[0012] Figure 3B After the exposed ruthenium of the elements including the device has been etched back Figure 2 Enlarged schematic illustration of the MEMS device.

[0013] Figure 4 After the MEMS device has been sealed Figure 3B Schematic illustration of the MEMS device.

[0014] For the sake of facilitating understanding, the same reference numerals have been used to denote the same elements common to the figures whenever possible. It is envisioned that elements disclosed in one embodiment may be advantageously utilized in other embodiments without specific recitation. Detailed Description

[0015] In the following, reference is made to embodiments of the present disclosure. However, it should be understood that the present disclosure is not limited to the specific described embodiments. In fact, any combination of the following features and elements is covered to implement and practice the present disclosure, regardless of whether they are related to different embodiments. Additionally, although embodiments of the present disclosure may achieve advantages over other possible solutions and / or over the prior art, whether a particular advantage is achieved by a given embodiment does not limit the present disclosure. Thus, the following aspects, features, embodiments, and advantages are illustrative only and are not to be considered elements or limitations of the appended claims, unless explicitly recited in the claims. Similarly, references to "the present disclosure" should not be construed as a generalization of any inventive subject matter disclosed herein and should not be considered an element or limitation of the appended claims, unless explicitly recited in the claims.

[0016] The embodiments set forth below represent the necessary information for those skilled in the art to practice the embodiments and show the best mode of practicing the embodiments. When reading the following description in light of the drawings, those skilled in the art will understand the concepts of the present disclosure and will recognize applications of these concepts that are not specifically set forth herein. It should be understood that these concepts and applications fall within the scope of the present disclosure and the appended claims.

[0017] It should be understood that although terms such as first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" encompasses any combination and all combinations of one or more of the associated listed items.

[0018] It should be understood that when an element such as a layer, region, or substrate is referred to as "on another element" or extends "onto another element", it can be directly on the other element or directly extend onto the other element, or there may also be intermediate elements. In contrast, when an element is referred to as "directly on another element" or "directly extends onto another element", there are no intermediate elements. Similarly, it should be understood that when an element such as a layer, region, or substrate is referred to as "above another element" or extends "above another element", it can be directly above the other element or directly extend above the other element, or there may also be intermediate elements. In contrast, when an element is referred to as "directly above another element" or "directly extends above another element", there are no intermediate elements. It should also be understood that when an element is referred to as "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. In contrast, when an element is referred to as "directly connected" or "directly coupled" to another element, there are no intermediate elements.

[0019] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe the relationship of one element, layer, or region shown in the figures to another element, layer, or region. It should be understood that these terms, as well as those discussed above, are intended to cover different orientations of the device in addition to the orientation depicted in the figures.

[0020] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present disclosure. As used herein, the singular forms "a / an" and "the" are also intended to include the plural forms unless the context clearly dictates otherwise. It should be further understood that when used herein, the terms "comprises / comprising" and / or "includes / including" specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0021] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It should be further understood that the terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0022] The present disclosure generally relates to a method of manufacturing a MEMS device. The MEMS device has a cavity in which a beam will move to change the capacitance of the device. After most of the device stack-up has occurred, sacrificial material is removed to release the beam within the MEMS device cavity. Thereafter, the exposed ruthenium contacts are etched back with an etchant including chlorine to remove the top surfaces of both the top contact and the bottom contact. Due to this etch process, a low contact resistance can be achieved with less susceptibility to adhesion events. The adhesion performance can be further improved by conditioning the ruthenium contacts in a fluorine-based plasma. The fluorine-based plasma process or fluorine treatment can be performed before or after the etch process of the ruthenium contacts.

[0023] Figure 1 FIG. 100 is a schematic illustration of a MEMS device 100 prior to removal of sacrificial material and release of the beam. The MEMS device 100 includes a substrate 102, such as a CMOS substrate, that includes a plurality of layers for semiconductor devices. It is also contemplated that the substrate 102 can be only a semiconductor substrate containing silicon, germanium, or other suitable semiconductor materials.

[0024] Within the substrate, there are one or more contact electrodes 104A, 104B. The contact electrodes 104A, 104B can be RF conductors or RF electrodes. It should be understood that although two contact electrodes 104A, 104B are shown, a single contact electrode or even more than two contact electrodes are contemplated. The contact electrodes 104A, 104B can be composed of any conductive material suitable for use in semiconductor devices such as copper, aluminum, titanium nitride, tungsten, and combinations thereof.

[0025] Additional conductive material can be present on or above the substrate 102 and the contact electrodes 104A, 104B. For example, the anchor electrodes 106A, 106B are shown as a plurality of additional electrical contacts 108 in Figure 1 FIG. 100. The anchor electrodes 106A, 106B are electrodes for the beam structure 114, and the electrical contacts 108 can be used for pull-in electrodes. The anchor electrodes 106A, 106B and the electrical contacts 108 can be composed of any conductive material suitable for use in semiconductor devices such as copper, aluminum, titanium nitride, tungsten, and combinations thereof.

[0026] A dielectric layer 110 is present above the substrate 102 and includes being present above the electrical contact 108. It is foreseeable that the dielectric layer 110 encompasses an electrically insulating material such as silicon oxide, silicon dioxide, silicon nitride, silicon oxynitride, or a combination thereof.

[0027] A first sacrificial layer 112 is present above the dielectric layer 110. The first sacrificial layer 112 will ultimately be removed to release the beam structure 114. The first sacrificial layer 112 comprises a material different from the dielectric layer 110. Suitable materials for the first sacrificial layer 112 include spin-on materials such as carbon-based materials. The first sacrificial layer 112 may include carbon, hydrogen, nitrogen, and oxygen.

[0028] A second dielectric layer 110 is present above the first sacrificial layer 112, and a bottom portion of the beam structure 114 is present above the second dielectric layer 110. The second dielectric layer 110 may include the same material as the first dielectric layer 110. The beam structure 114 may include any conductive material suitable for use in semiconductor devices such as copper, aluminum, titanium nitride (TiN), tungsten, titanium aluminum nitride (TiAlN), tantalum nitride (TaN), and combinations thereof. The beam structure 114 further includes an intermediate portion, a top portion, and a post portion. Dielectric layers 110 are present on the top and bottom surfaces of the beam portion.

[0029] Additionally, in regions where the beam structure 114 is not located, additional sacrificial material 112 is present. The sacrificial material 112 may include the same material in all locations within the MEMS device 100. In fact, the sacrificial material 112 is present above the top portion of the beam structure 114. In contact with and on top of the topmost sacrificial material 112, an additional dielectric layer 110 is present. A pull-up electrode 116 is present above and on the additional dielectric layer 110. A dielectric top plate 118 is also present above the pull-up electrode 116. Release holes 120 are present through the dielectric top plate 118 and the topmost dielectric layer 110. The release holes 120 extend through the top plate 118 to expose the sacrificial material 112.

[0030] The bottom of the beam structure 114 includes two beam contact portions 122 that include ruthenium. Two electrical contact stacks with ruthenium contact surfaces 124 are present on each of the contact electrodes 104A, 104B and are aligned with the two beam contact portions 122. The inclusion of the ruthenium contact surface 124 is the platform location of the beam structure 114, as will be discussed later. The beam contact portions 122 contact the contact surfaces 124 and are in the pulled-down state when the beam structure 114 has been released, which is the maximum capacitance state. One or more additional electrical contact stacks with ruthenium contact surfaces 126 are disposed above portions of the electrical contact 108.

[0031] To release the beam structure 114 to move the device 100, the sacrificial material needs to be removed. Figure 2Schematic illustration of MEMS device 100 after sacrificial material 112 has been removed and beam 114 has been released. The sacrificial material 112 is removed by an etching process in which an etchant, which can be a wet etchant or a dry etchant, is introduced through release holes 120. Once the sacrificial material 112 is removed, the location that once used the sacrificial material is considered a cavity 202. Figure 1 Once the sacrificial material 112 is removed, the beam structure 114 is free to move within the cavity 202. The beam structure 114 can move back and forth from a first position spaced apart as needed from both the pull-up electrode 116 and the electrical contact stack containing the ruthenium contact surface 124 (

[0032] as shown in Figure 2 ), to a second position in contact with the contact surface 124, and to a third position disposed adjacent to the pull-up electrode 116 and spaced from the contact surface 124 by a greater distance than the first position. The terms "first position", "second position", and "third position" are not intended to be restrictive, and the beam structure 114 can move to and from any one of the three positions in any order.

[0033] As noted above, the sacrificial material 112 is removed, but everything else in the device 100 remains. Thus, the contact surfaces 124, 126 are now exposed as ruthenium-containing contact portions 122. As also noted above, ruthenium has a low resistance and is a durable contact, but ruthenium contacts are susceptible to potential adhesion events during the operating life. Thus, it has been unexpectedly found that additional treatment of ruthenium will result in less adhesion and further reduce the contact resistance of the device.

[0034] A fluorine-based treatment can be used to treat the ruthenium (i.e., the beam contact portion 122 and the contact surfaces 124, 126) of the components including the device 100. For example, a plasma containing fluorine and oxygen can optionally be introduced into the cavity 202 through the release holes 120. In one embodiment, the plasma is formed from O2 and CF4. It is contemplated that other fluorine-based gases, such as NF3, SF6, and CHF3, can be used. In one embodiment, a fluorocarbon-based self-assembled monolayer (SAM) can be utilized. Thus, the present disclosure is not limited to CF4. Excessive C x F y polymer formations can increase the contact resistance to an unacceptable level. Over-fluorination doping of ruthenium can increase the contact resistance to an unacceptable level. Thus, as little polymer formation as possible is needed to maintain a low contact resistance.

[0035] Figure 3A Schematic enlarged illustration of a portion of MEMS device 100 after sacrificial material 112 has been removed and / or after an optional fluorine-based treatment. As Figure 2 shown in Figure 3AAs shown, the spacer layer 330 or the residue layer may be disposed on the top surface 332 of the contact surface 124. During various formation operations of the MEMS device 100, such as during fabrication or construction, during the removal of the sacrificial material 112, or during an optional fluorine-based treatment, the spacer layer 330 or the residue layer may be formed on the contact surfaces 124, 126.

[0036] After the optional fluorine-based treatment, a chlorine (Cl) etching process is performed. In one embodiment, the chlorine etching process is performed before the optional fluorine-based treatment. Thus, the optional fluorine-based treatment may occur before or after the chlorine etching process. The chlorine etching process may occur after the removal of the sacrificial material 112. An etchant including chlorine, such as hydrochloric acid (HCl), boron trichloride (BCl3), or chlorine gas (Cl2), is introduced into the cavity 202 through the release holes 120. The chlorine etch-back process may be a "wet" or "dry" process. In addition to chlorine, the dry etch-back process may also include oxygen and / or a combination of oxygen and fluorine. The chlorine-containing etchant has a high etch selectivity such that the etchant etches only the ruthenium including the elements of the device 100 and residues such as the spacer layer 330. Thus, the chlorine-containing etchant etches portions of the contact electrode surfaces 124, 126 and / or the bottom portion of the crossbeam contact surface 122 without etching the crossbeam structure 114 or the dielectric layer 110. The chlorine etch-back process has an extremely high selectivity (20:1) for dielectrics, titanium, titanium nitride, and titanium aluminum nitride, which enables the etch-back process to selectively etch the contact electrode surfaces 124, 126 without adversely affecting other components inside the cavity.

[0037] Figure 3B For after etching the exposed ruthenium including the elements of the device 100 (i.e., the crossbeam contact portion 122 and the contact surfaces 124, 126) Figure 2 of the MEMS device 100 in an enlarged schematic illustration. In Figure 3B it, the top portions or surfaces 332 of the contact surfaces 124, 126 and the bottom portions or surfaces 334 of the crossbeam contact portion 122 have been partially removed by the chlorine etching process. Although Figure 3B shows the removal of ruthenium from both the contact surfaces 124, 126 and the crossbeam contact portion 122, the removal may occur only to the contact surfaces 124, 126, only to the crossbeam contact portion 122, or to both the contact surfaces 124, 126 and the crossbeam contact portion 122.

[0038] Etching the bottom portion or surface 334 of the crossbeam contact portion 122 causes the crossbeam contact portion 122 to recess into the crossbeam structure 114, and etching the top portions or surfaces 332 of the contact surfaces 124, 126 reduces the total height of the contact electrodes. As Figure 3BAs shown, the exposed ruthenium including the elements etched during the chlorine etch process (i.e., the top surface 332 of the contact surfaces 124, 126 and / or the bottom surface 334 of the crossbeam contact portion 122) can have a surface with increased roughness. In other words, the top surface 332 of the contact surfaces 124, 126 and / or the bottom surface 334 of the crossbeam contact portion 122 has a surface roughness to prevent etching by a chlorine-containing etchant. In one embodiment, the top surface 332 and the bottom surface 334 each have a root mean square roughness of about 1 nm to about 10 nm, such as about 2 nm to about 5 nm. The surface roughness can increase as the surfaces 332, 334 are more exposed to the chlorine-containing etchant. Additionally, after the chlorine etch process, any residues or interstitial layers 330 that may have been formed during the formation of the device 100 are removed from the exposed ruthenium including the elements by pumping an inert gas such as argon into the cavity.

[0039] The ruthenium etch rate of the chlorine-containing etchant is about 2 nm / min to about 10 nm / min, such as about 4 nm / min, and the selectivity ratio of the chlorine-containing etchant for etching ruthenium to the surrounding exposed materials such as oxides, TiAlN, and TiN is about 20:1 to about 25:1 (i.e., the chlorine-containing etchant etches ruthenium 20 to 25 times faster than it etches oxides, TiAlN, and TiN). The chlorine-containing etchant can be present in the cavity 202 for about 1 minute to 5 minutes, such as about 2.5 minutes to 3 minutes. The chlorine etch process can remove about 5 nm to 15 nm of ruthenium from each of the contact surfaces 124, 126 and the crossbeam contact portion 122. By etching ruthenium from the contact surfaces 124, 126 and the crossbeam contact portion 122, the contact resistance of the MEMS device 100 is effectively reduced. In one embodiment, compared to a conventional MEMS device, the chlorine etch process reduces the contact resistance of the device 100 by about 2 times.

[0040] Etching portions of the contact surfaces 124, 126 from each electrical contact stack and / or portions of each crossbeam contact portion 122 cleans the ruthenium surface in contact with the sacrificial material 112. The chlorine etch process further removes any residues, interstitial layers, or interstitial impurities that may have formed on the surface while forming the MEMS device 100, such as during manufacturing or construction, during the removal of the sacrificial material 112, or during an optional fluorine-containing plasma treatment. For example, the chlorine etch process can remove any C x F y polymer formations.

[0041] Once the sacrificial material 112 has been removed and the exposed ruthenium has been processed, the device 100 is ready to be sealed. Figure 4 For after the MEMS device has been sealed Figure 3BSchematic illustration of the MEMS device 100. As Figure 4 shown, a seal 402 is formed to seal the release hole 120. The seal 402 extends downward to contact the topmost dielectric layer 110 disposed on the beam structure 114. The seal 402 may include a dielectric material such as silicon oxide, silica, silicon nitride, silicon oxynitride, or a combination thereof.

[0042] By treating the exposed ruthenium surface after removing the sacrificial material, the resulting MEMS device will have a contact surface that has low resistance, is durable, and is less susceptible to adhesion events.

[0043] In one embodiment, a method of manufacturing a MEMS device includes: forming one or more electrical contact stacks including ruthenium contact surfaces within a cavity; forming a beam structure above the one or more electrical contact stacks within the cavity, wherein the cavity contains a sacrificial material; removing the sacrificial material from the cavity to release the beam to move within the cavity; etching a portion of the ruthenium contact surface using an etchant including chlorine; and sealing the cavity.

[0044] The etchant may further include an oxygen or fluorine-based gas. The etchant may be present in the cavity for a period between about 2.5 minutes and 3 minutes. About 5 nm to about 15 nm of the ruthenium contact surface may be removed by etching. The beam structure may include at least one contact portion including ruthenium. Etching a portion of the ruthenium contact surface using an etchant including chlorine may further include etching a bottom portion of at least one contact portion including ruthenium. Etching a portion of at least one contact portion including ruthenium may recess at least one contact portion including ruthenium into the beam structure. The MEMS device may include at least one contact electrode. At least one of the one or more electrical contact stacks including ruthenium contact surfaces may be formed above the at least one contact electrode.

[0045] The method may further include introducing a plasma containing fluorine and oxygen into the cavity before etching a portion of the ruthenium contact surface using an etchant including chlorine. The etchant including chlorine may include hydrochloric acid, boron trichloride, or chlorine gas. Etching a portion of the ruthenium contact surface using an etchant including chlorine may further remove any residues or interlayer fillings from the ruthenium contact surface. The etchant including chlorine may have an etching rate of about 4 nm / minute to about 6 nm / minute. The etchant including chlorine may have a selectivity ratio of about 20:1 for etching ruthenium versus oxide or titanium aluminum nitride.

[0046] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered to be within the scope of the concepts disclosed herein and the appended claims.

Claims

1. A method of fabricating a MEMS device, comprising: Forming one or more electrical contact stacks including ruthenium contact surfaces, with at least one of the one or more electrical contact stacks formed over at least one contact electrode; Disposing sacrificial material over the one or more electrical contact stacks; Forming a beam structure over the one or more electrical contact stacks such that the one or more electrical contact stacks are formed within a cavity filled with the sacrificial material; Removing the sacrificial material to release the beam structure to move within the cavity, wherein at least one contact portion of the beam structure is capable of contacting a contact surface of the at least one contact electrode; Etching a portion of the ruthenium contact surface within the cavity using an etchant including chlorine; And Sealing the cavity.

2. The method according to claim 1, wherein the etchant further comprises an oxygen or fluorine-based gas.

3. The method according to claim 1, wherein the etchant is present within the cavity for a period between 2.5 minutes and 3 minutes.

4. The method according to claim 1, wherein 5 nm to 15 nm of the ruthenium contact surface is removed by the etching.

5. The method according to claim 1, wherein the beam structure comprises at least one contact portion including ruthenium.

6. The method according to claim 5, wherein etching the portion of the ruthenium contact surface using the etchant including chlorine further comprises etching a bottom portion of the at least one contact portion including ruthenium.

7. The method according to claim 6, wherein etching the bottom portion of the at least one contact portion including ruthenium causes the at least one contact portion to be recessed into the beam structure.

8. The method according to claim 1, further comprising introducing a plasma containing fluorine and oxygen into the cavity prior to etching the portion of the ruthenium contact surface using the etchant including chlorine.

9. The method according to claim 1, wherein the etchant including chlorine comprises hydrochloric acid, boron trichloride, or chlorine gas.

10. The method according to claim 1, wherein etching the portion of the ruthenium contact surface using the etchant including chlorine further removes any residue or interlayer from the ruthenium contact surface.

11. The method according to claim 1, wherein the etchant including chlorine has an etching rate of 4 nm / minute to 6 nm / minute.

12. The method according to claim 1, wherein the etchant including chlorine has a selectivity ratio of 20:1 for etching ruthenium over etching oxide or titanium aluminum nitride.

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