Anti-adhesion Enhancement of Ruthenium Contact

Abstract

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 contact is exposed to fluorine to do any of the following: dope the exposed ruthenium and reduce surface adhesion, form a fluorinated self-assembled monolayer on the exposed ruthenium surface, deposit a nano-passivation film on the exposed ruthenium, or change the surface roughness of the ruthenium. Due to the fluorine treatment, there are low-resistance, durable contacts, and the contacts are less susceptible to adhesion events.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to a method for enhancing the anti-sticking properties of ruthenium contacts in microelectromechanical systems (MEMS) devices. Background Art

[0002] Contact sticking is one of the main failure mechanisms in MEMS devices. Sticking is one of the key challenges in manufacturing viable MEMS devices. Ruthenium contacts provide low-resistance, durable contacts, but ruthenium contacts are vulnerable to potential sticking events during the operating life.

[0003] Therefore, there is a need for low-resistance, durable contacts that are less vulnerable to sticking events. Summary of the Invention

[0004] The present disclosure generally relates to a method of manufacturing a MEMS device. 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 stacking has occurred, sacrificial material is removed to release the beam within the MEMS device cavity. Thereafter, the exposed ruthenium contacts are exposed to fluorine to do any of the following: dope the exposed ruthenium and reduce surface adhesion, form a fluorinated self-assembled monolayer on the exposed ruthenium surface, deposit a nano-passivation film on the exposed ruthenium, or change the surface roughness of the ruthenium. Due to the fluorine treatment, there are low-resistance, durable contacts, and the contacts are less vulnerable to sticking events.

[0005] In one embodiment, a method of manufacturing a MEMS device includes: forming a beam structure within a cavity, wherein the cavity contains sacrificial material; removing the sacrificial material from the cavity to release the beam to move within the cavity; introducing fluorine into the cavity; and sealing the cavity.

[0006] Those skilled in the art will understand the scope of the present disclosure and recognize additional aspects of the present disclosure after reading the following detailed description of the preferred embodiments in conjunction with the accompanying drawings. Brief Description of the Drawings

[0007] The drawings incorporated in and forming a part of this specification illustrate several aspects of the present disclosure and, together with the description, are used to explain the principles of the present disclosure.

[0008] Figure 1 is a schematic illustration of a MEMS device before removing the sacrificial material and releasing the beam.

[0009] Figure 2 is after the sacrificial material has been removed and the beam has been released Figure 1 of the MEMS device.

[0010] Figure 3 It is a graph showing the resistance of various parameters versus the number of cycles.

[0011] Figure 4 It is after the MEMS device has been sealed Figure 2 A schematic illustration of the MEMS device.

[0012] For ease of understanding, the same reference numerals have been used, where possible, to denote the same elements common to the figures. Upon consideration, the elements disclosed in one embodiment can be advantageously used in other embodiments without specific recitation. Detailed Description

[0013] 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 accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and will recognize applications of these concepts 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.

[0014] It should be understood that although the terms 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" includes any combination and all combinations of one or more of the associated listed items.

[0015] 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 intervening elements. In contrast, when an element is referred to as "directly on another element" or "directly extends onto another element", there are no intervening 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 intervening elements. In contrast, when an element is referred to as "directly above another element" or "directly extends above another element", there are no intervening 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 intervening elements. In contrast, when an element is referred to as "directly connected" or "directly coupled" to another element, there are no intervening elements.

[0016] As used herein, relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used 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.

[0017] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the disclosure. As used herein, the singular forms "a / an" and "the" are intended to include the plural forms as well, unless the context clearly indicates 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 combinations thereof.

[0018] Unless otherwise defined, all terms used herein (including technical and scientific terms) 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.

[0019] The present disclosure generally relates to a method of fabricating a MEMS device. The MEMS device has a cavity in which a beam will move during operation. After most of the device stack-up has occurred, sacrificial material is removed to release the beam within the MEMS device cavity. Thereafter, an exposed ruthenium contact is exposed to fluorine to do any of the following: dope the exposed ruthenium and reduce surface adhesion, form a fluorinated self-assembled monolayer on the exposed ruthenium surface, deposit a nano-passivation film on the exposed ruthenium, or alter the surface roughness of the ruthenium. Due to the fluorine treatment, there are low-resistance, durable contacts, and the contacts are less susceptible to adhesion events.

[0020] Figure 1FIG. 0 is a schematic illustration of the MEMS device 100 before removal of the sacrificial material and release of the beams. The MEMS device includes a substrate 102, such as a CMOS substrate, which includes a number of layers for semiconductor devices. It is also contemplated that the substrate 102 can be just a semiconductor substrate containing silicon, germanium, or other suitable semiconductor materials. In some embodiments, the substrate 102 can include glass, quartz, fused silica, sapphire, titanium, titanium tungsten, cobalt, metal silicides, and the like. Any suitable material can be used for the substrate 102, and thus, the material of the substrate 102 is not intended to be limiting.

[0021] Within the substrate, there are one or more RF electrodes 104A, 104B. It should be understood that although two RF electrodes 104A, 104B are shown, a single RF electrode or even more than two RF electrodes are contemplated. The RF electrodes 104A, 104B can include any conductive material suitable for semiconductor devices, such as ruthenium, copper, aluminum, titanium nitride, tungsten, titanium aluminum, titanium aluminum nitride, and combinations thereof. Any suitable material can be used for the RF electrodes 104A, 104B, and thus, the material of the RF electrodes 104A, 104B is not intended to be limiting.

[0022] Additional conductive material can be present on or above the substrate 102 and the RF electrodes 104A, 104B. For example, Figure 1 the anchor electrodes 106A, 106B are shown as a number of additional electrical contacts 108. 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 include any conductive material suitable for use in semiconductor devices, such as copper, aluminum, titanium nitride, tungsten, and combinations thereof.

[0023] A dielectric layer 110 is present above the substrate 102 and the electrical contacts 108. It is contemplated that the dielectric layer 110 includes an electrically insulating material, such as silicon oxide, silicon dioxide, silicon nitride, silicon oxynitride, or combinations thereof.

[0024] 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 includes 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 can include carbon, hydrogen, nitrogen, and oxygen.

[0025] 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 a semiconductor device, such as copper, aluminum, titanium nitride, tungsten TiAlN, and combinations thereof. The beam structure 114 additionally includes a top portion and a column portion. The dielectric layer 110 is present on the top and bottom surfaces of the beam portion. 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 at all locations within the MEMS device 100. In fact, the sacrificial material 112 is present above the top portion of the beam structure 114. Above and in contact with the topmost sacrificial material 112, an additional dielectric layer 110 is present. A pull-up electrode 116 is present above and over the additional dielectric layer 110. A dielectric top plate 118 is also present above the pull-in electrode 116. Release holes 120 are also present. The release holes 120 extend through the top plate 118 to expose the sacrificial material 112.

[0026] The bottom of the beam structure 114 has a beam contact portion 122 that includes ruthenium. An electrical contact stack with a ruthenium-containing contact surface 124 is present above each of the RF electrodes 104A, 104B. The ruthenium contact surface 124 is a platform location for the beam structure 114, as will be discussed later. The beam contact portion 122 contacts the contact surface 124 and is in a pulled-down state when the beam structure 114 has been released, which is the maximum capacitance state.

[0027] To release the beam structure 114 to move within the device 100, the sacrificial material needs to be removed. Figure 2 is after the sacrificial material has been removed and the beam has been released Figure 1 A schematic illustration of the MEMS device 100. The sacrificial material 112 is removed by an etching process in which an etchant, which may be a wet etchant or a dry etchant, is introduced through the release holes 120. Once the sacrificial material 112 is removed, the location where the sacrificial material was located is considered a cavity 202. The beam structure 114 moves freely within the cavity 202.

[0028] As noted above, the sacrificial material 112 is removed, but everything else within the device 100 remains the same. Thus, the contact surface 124 is now exposed as is the contact portion 122. Both the contact surface 124 and the contact portion 122 contain ruthenium. As noted above, ruthenium has a low resistance and is a durable contact, but ruthenium contacts are vulnerable to potential adhesion events during the operating life. Thus, it has been unexpectedly found that additional treatment of ruthenium will result in less adhesion.

[0029] Fluorine or a fluorine-containing compound is introduced into the cavity 202 via the release hole 120 to treat the exposed ruthenium surface. In some embodiments, fluorine may be introduced into the cavity 202 before depositing the first sacrificial layer 112 to treat the exposed ruthenium surface. Fluorine or a fluorine-containing compound may be introduced into the cavity 202 using a plasma comprising fluorine. In one embodiment, the plasma is formed from CF4 and / or O2. In another embodiment, gaseous HF or F2 is introduced into the cavity 202. In yet another embodiment, the fluorine introduced into the cavity 202 forms a fluorinated self-assembled monolayer (F-SAM) on the exposed ruthenium surface. The F-SAM may include any suitable head group at the substrate level, any suitable tail as the molecular chain, and any suitable functional group as the end. In yet another embodiment, TiF4 or MoF6 may be introduced into the cavity.

[0030] Upon further consideration, other fluorine-based gases, such as NF3, may be used. Thus, the present disclosure is not limited to CF4. It has been unexpectedly found that an insufficient amount of fluorine will not provide sufficient surface modification to the ruthenium to provide reliable operation over the device lifetime. Additionally, excessive C x F y polymer formation will increase the contact resistance to an unacceptable level. Excessive fluorine doping of the ruthenium will increase the contact resistance to an unacceptable level. Thus, as little polymer formation as possible is needed to maintain a low contact resistance, while sufficient fluorine exposure is needed to obtain sufficient adhesion tolerance.

[0031] When using a fluorine-containing plasma, the plasma may be generated by a plasma reactor comprising a vacuum chamber, one or more gas sources for introducing reaction gases into the chamber, and one or more RF electrodes or antennas capable of generating a plasma in the vacuum chamber. The plasma may be generated in the reactor at a pressure of about 10 mT to about 2000 mT and at a power of about 100 W to about 2000 W. Two main types of sources may be used: capacitively coupled plasma (CCP) or inductively coupled plasma (ICP). Suitable sources that may be utilized include the plasma reactors of the following U.S. patents: US 4,948,458; US 4,576,918; and US 5,710,486.

[0032] Figure 3 is a graph showing the resistance versus the number of cycles for various parameters when using a fluorine-containing plasma according to one embodiment. Figure 3 The results may be obtained using an ICP reactor at a pressure of about 10 mT to about 50 mT and at a power of about 500 W to about 2000 W. As Figure 3As shown, there are optimal points for the fluorine content and for the exposure time. For example, it has been found that the plasma exposure should last for a period between about 20 seconds and about 60 seconds. Additionally, it has been found that the ratio of CF4 to O2 should be between about 1:4 and about 4:1. When the plasma exposure occurs outside of the period and ratio, the device resistance is unacceptable, as Figure 3 shown. More specifically, operating for a period of 60 seconds at a ratio of 1:4 produces acceptable results. Additionally, operating for a period of 20 seconds at a ratio of 4:1 produces acceptable results.

[0033] However, operating for a period of 60 seconds at a ratio of 4:1 does not produce acceptable results. Similarly, operating for a period of 20 seconds at a ratio of 1:4 does not produce acceptable results. Other ratios and times are possible. For example, a ratio of 1:6 within a period of about 100 seconds is also considered. Figure 3 The results and data shown in the graph of Figure 3 depend on the plasma reactor used and the plasma conditions used, such as plasma power, process pressure, excitation frequency, etc. Thus,

[0034] 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 is a schematic illustration of the MEMS device 100 Figure 2 after the MEMS device has been sealed. As Figure 4 shown, a seal 402 is formed to seal the release holes 120. The seal 402 may comprise a dielectric material, such as silicon oxide, silicon dioxide, silicon nitride, silicon oxynitride, or a combination thereof.

[0035] By processing the exposed ruthenium surface after the sacrificial material has been removed, the resulting MEMS device will have a contact surface that has a low resistance and is durable and less susceptible to adhesion events.

[0036] In one embodiment, a method of fabricating a MEMS device includes: forming a beam structure within a cavity, wherein the cavity contains a sacrificial material; removing the sacrificial material from the cavity to release the beam to move within the cavity; introducing fluorine into the cavity; and sealing the cavity. The fluorine can be introduced using a fluorine-containing plasma. The plasma can be formed from an oxygen-containing gas and a fluorine-containing gas. The oxygen-containing gas can be O2. The fluorine-containing gas can be CF4. The plasma can be present in the cavity for a period between about 20 seconds and about 60 seconds. The ratio of CF4 to O2 can be between about 1:4 and about 4:1. The ratio is about 1:4, and the plasma can be present for a period of about 60 seconds. The ratio can be about 4:1, and the plasma can be present for a period of about 20 seconds. The beam structure can include at least one contact portion including ruthenium. The fluorine introduced into the cavity can form a fluorinated self-assembled monolayer on one or more exposed surfaces within the cavity.

[0037] The MEMS device includes an RF electrode having a contact surface including ruthenium. The ruthenium surface of the beam structure can contact the ruthenium contact surface of the RF electrode. The contact surface including ruthenium contains C on the surface x F y polymer or a fluorinated self-assembled monolayer. The contact surface including ruthenium includes fluorine. The fluorine is introduced for a period between about 20 seconds and about 60 seconds.

[0038] 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 following claims.

Claims

1. A method of manufacturing a MEMS device, comprising: forming a substrate including a radio frequency (RF) electrode having a first contact surface including ruthenium, wherein a first anchor electrode is disposed above the substrate and a second anchor electrode is disposed above the substrate, wherein the RF electrode is disposed in the substrate between the first and second anchor electrodes, and wherein a pull-up electrode is disposed above a beam structure between the first and second anchor electrodes; forming the beam structure within a cavity, wherein the beam structure includes a contact portion having a second contact surface including ruthenium, the contact portion being disposed above the first contact surface of the RF electrode, and when the beam structure is in a pulled-down state, the second contact surface contacts the first contact surface; and the cavity contains a sacrificial material; removing the sacrificial material from the cavity to release the beam structure to move within the cavity, wherein the first and second contact surfaces are exposed within the cavity, and when the beam structure is in a pulled-down state, the second contact surface of the contact portion contacts the first contact surface of the RF electrode; introducing fluorine into the cavity such that the first contact surface including ruthenium is fluorine-modified and the second contact surface including ruthenium is fluorine-modified; and sealing the cavity.

2. The method according to claim 1, wherein the fluorine is introduced using a fluorine-containing plasma, and wherein the plasma is formed from an oxygen-containing gas and a fluorine-containing gas.

3. The method according to claim 2, wherein the oxygen-containing gas is O2.

4. The method according to claim 3, wherein the fluorine-containing gas is CF4.

5. The method according to claim 4, wherein the plasma is present in the cavity for a period between 20 seconds and 60 seconds.

6. The method according to claim 5, wherein the ratio of CF4 to O2 is between 1:4 and 4:

1.

7. The method according to claim 6, wherein the ratio is 1:4 and the plasma is present for a period of 60 seconds.

8. The method according to claim 6, wherein the ratio is 4:1 and the plasma is present for a period of 20 seconds.

9. The method according to claim 1, wherein the first contact surface comprising ruthenium is fluorine-modified and comprises C x F y polymer on the surface.

10. The method according to claim 1, wherein the fluorine introduced into the cavity forms a fluorinated self-assembled monolayer on the first and second contact surfaces.

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