MEMS device and fabrication method thereof

A method for fabricating a MEMS device having a fixing part fixed to a substrate, a connecting part, a driving part, a driving electrode, and contact parts, includes patterning the driving electrode on the substrate; forming an insulation layer on the substrate; patterning the insulation layer and etching a fixing region and a contact region of the insulation layer; forming a metal layer over the substrate; planarizing the metal layer until the insulation layer is exposed; forming a sacrificial layer on the substrate; patterning the sacrificial layer to form an opening exposing a portion of the insulation layer and the metal layer in the fixing region; forming a MEMS structure layer on the sacrificial layer to partially fill the opening, thereby forming sidewalls therein; and selectively removing a portion of the sacrificial layer by etching so that a portion of the sacrificial layer remains in the fixing region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Micro Electro Mechanical System (MEMS) device and a fabrication method thereof. More particularly, the present invention relates to an electrostatic driving MEMS device having a driving electrode in an embedded structure and a fabrication method thereof.

2. Description of the Related Art

Micro Electro Mechanical System is a technology that implements mechanical and electrical parts, using semiconductor processing techniques. A conventional MEMS device generally includes floating driving parts that are movable over a substrate in order for the device fabricated using MEMS technology to perform mechanical operations.

FIG. 1illustrates a cross-sectional view schematically showing a conventional MEMS device. The conventional MEMS device ofFIG. 1includes a substrate10, a fixing part30attached to the substrate10, and a driving part40extending from the fixing part30. The fixing part30is generally referred to as an anchor or a support. The fixing part30connects the driving part40to the substrate10.

The driving part40is spaced to float over the substrate10. The driving part40is movable in an upward and downward direction, as shown by the broken lines inFIG. 1. The movement of the driving part40is controlled by a predetermined driving force from an electrode part20formed on the substrate10. The driving part40is typically fabricated in a shape such as a beam, a membrane, or the like depending on device requirements.

FIG. 2AtoFIG. 2Eillustrate views for sequentially illustrating stages in a process for fabricating a conventional electrostatic drive-type RF MEMS device.

As shown inFIG. 2A, a driving electrode layer220, for providing an electrostatic driving force, is formed on a substrate210through patterning. InFIG. 2B, a metal layer is formed on the substrate and then the metal layer is patterned so metal layer areas230having similar shapes remain. The metal layer areas230are an anchor part to acts as a fixing part fixed on the substrate210and an RF line to act as input and/or output terminals of an RF signal. The metal layer areas230are formed in a thick layer having a thickness of 2 to 3 μm in consideration of the skin depth effect.

Next, referring toFIG. 2C, an insulation layer240is formed to surround the driving electrode layer220formed on the substrate210.

Thereafter, as shown inFIG. 2D, a sacrificial layer250is formed on the resultant structure on the substrate210. The sacrificial layer250over the anchor part fixed on the substrate210is etched through predetermined patterning. Referring toFIG. 2E, a MEMS structure layer is then formed on the patterned sacrificial layer250. The MEMS structure layer includes a driving part260and a connection part261.

Subsequently, predetermined etching access holes (not shown) are formed in the driving part260of the MEMS structure layer, and an etchant is supplied through the etching access holes to selectively etch only the sacrificial layer250. Accordingly, as shown inFIG. 2E, a conventional MEMS device is fabricated such that the driving part260floats over the substrate210after the removal of the sacrificial layer250.

As stated above, a conventional fabrication process proceeds regardless of a step-height difference between the metal layer areas230and the driving electrode layer220. Consequently, a step-height difference between the metal layer areas230and the driving electrode layer220causes the driving part260, which is formed by a subsequent procedure, to be formed unevenly, as may be seen inFIG. 2E. Thus, the reliability of such a MEMS device decreases. Moreover, since unevenness of the driving part is not expected during the designing of the device, a significant error exists between the design of the device and the fabrication process. Further, unevenness in the driving part260causes a problem in that the driving of the driving part260may be incomplete when the MEMS device is driven.

Further, in the stages of the fabrication process shown inFIGS. 2D and 2E, the connection part261of the MEMS structure layer, which is formed on an anchor part and the substrate210, is formed in a bent shape that is relatively thinner than the anchor part and the MEMS structure layer.

Accordingly, the connection part261having a thin and bent shape causes a problem in the stability of the MEMS device, since the general operation of the MEMS device involves the movement of the MEMS structure, i.e., the driving part260.

SUMMARY OF THE INVENTION

In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a MEMS device having enhanced reliability and a stable driving capability and a fabrication method thereof.

The above feature of the present invention is provided by a first embodiment wherein a method for fabricating a MEMS device having a fixing part fixed to a substrate, a driving part connected to the fixing part by a connecting part, wherein the driving part is floating over the substrate, a driving electrode for driving the driving part by a predetermined driving force, and contact parts selectively switchable with the driving part, including patterning the driving electrode on the substrate; forming an insulation layer on the substrate on which the driving electrode is formed; patterning the insulation layer and etching a fixing region and a contact region of the insulation layer, in which the fixing part and the contact parts, respectively, are to be formed; forming a metal layer over the substrate including the fixing and contact regions; planarizing the metal layer until the insulation layer is exposed; forming a sacrificial layer on the substrate; patterning the sacrificial layer to form an opening exposing a portion of the insulation layer and the metal layer in the fixing region; forming a MEMS structure layer on the sacrificial layer to partially fill the opening, thereby forming sidewalls therein, wherein the MEMS structure layer forms the fixing part, the driving part and the connection part connecting the fixing part and the driving part on the sacrificial layer; and selectively removing a portion of the sacrificial layer by etching so that a portion of the sacrificial layer remains in the fixing region.

Preferably, the insulation layer is formed as a thick film having a thickness at least as thick as the thickness of the driving electrode so that the driving electrode is embedded in the insulation layer.

Preferably, in the step for forming the opening, the opening is substantially formed over the entire portion remaining except for the portion matched with a connection part connecting the fixing part and the driving part. A width of the connection part is preferably narrower than that of the fixing part.

Before the selective removal of the sacrificial layer, the method preferably further includes forming etching access holes in the MEMS structure layer. Preferably, the etching access holes are formed in the driving part of the MEMS structure layer.

Preferably, the insulation layer is a TetraEthyl OrthoSilicate (TEOS) oxide film. The metal layer is preferably gold. The planarization is preferably performed by polishing. The sacrificial layer is preferably a material selected from the group consisting of aluminum, copper, oxide, and nickel.

The above feature of the present invention may also be provided by a second embodiment wherein a method for fabricating a MEMS device having a fixing part fixed to a substrate, a driving part connected to the fixing part by a connecting part, wherein the driving part is floating over the substrate, a driving electrode for driving the driving part by a predetermined driving force, and contact parts selectively switchable with the driving part, including patterning the driving electrode on the substrate; forming a first insulation layer on the substrate on which the driving electrode is formed; patterning the insulation layer and etching a fixing region and a contact region of the insulation layer, in which the fixing part and the contact parts, respectively, are formed; forming a metal layer over the substrate including the fixing and contact regions; planarizing the metal layer until the driving electrode is exposed; forming a second insulation film covering the driving electrode to electrically isolate the driving electrode and the driving part; forming a sacrificial layer on the substrate; patterning the sacrificial layer to form an opening exposing a portion of the first insulation and the metal layer in the fixing region; forming a MEMS structure layer on the sacrificial layer to partially fill the opening, thereby forming sidewalls therein, wherein the MEMS structure layer forms the fixing part, the driving part, and the connection part connecting the fixing part and the driving part on the sacrificial layer; and selectively removing a portion of the sacrificial layer by etching so that a portion of the sacrificial layer remains in the fixing region.

The above feature of the present invention may also be provided by a MEMS device including a fixing part fixed to a substrate; a driving part connected to the fixing part by a connecting part and floating over the substrate; an electrode part for driving the driving part; and contact parts selectively switchable with the driving part, wherein the electrode part and the contact parts are planarized on the substrate.

Preferably, the electrode part includes an electrode and an insulation layer covering the electrode to electrically isolate the driving part and the electrode, the electrode being embedded in the insulation layer.

The MEMS device preferably also includes an anchor inserted between the fixing part and the substrate for fixing the fixing part on the substrate; and sidewalls on at least a portion of side surfaces of the anchor.

Preferably, the sidewalls are substantially formed over the entire portion remaining except for a portion corresponding to a connection part connecting the fixing part and the driving part. A width of the connection part is preferably narrower than that of the fixing part.

The sidewalls, fixing part, and driving part are preferably integrally formed in one body, and the sidewalls are in contact with the substrate.

Accordingly, the step difference between the RF lines and the driving electrode is removed, so the MEMS structure layer to be subsequently formed for the driving part driven by an electrostatic force can be prevented from being transformed.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application No. 2002-12985, filed on Mar. 11, 2002, and entitled: “MEMS Device and Fabrication Method Thereof,” is incorporated by reference herein in its entirety.

An electrostatic drive-type RF MEMS relay is described below as a MEMS device according to an embodiment of the present invention.

FIG. 3AtoFIG. 3Fillustrate views for sequentially showing stages in a process for fabricating an electrostatic drive-type MEMS relay according to an embodiment of the present invention.

First, as shown inFIG. 3A, a driving electrode layer320for providing an electrostatic driving force is formed on a substrate310through patterning. As shown inFIG. 3B, a flattening mold330is formed as an insulation layer on the substrate310on which the driving electrode layer320is formed. A TetraEthyl OrthoSilicate (TEOS) oxide film is preferably used for the insulation layer.

Thereafter, the flattening mold330of the insulation layer is patterned, and the regions for an anchor part A of the MEMS relay and a contact part A′ for input and output terminals of an RF signal are etched. That is, the insulation layer330formed in the flattening mold becomes an insulation layer of the driving electrode layer320. The electrode layer320is formed to prevent an electric short-circuit of the driving electrode layer320and a driving part to be described later.

Next, as shown inFIG. 3C, a metal layer340is formed to a predetermined thickness on the resultant structure and on the substrate where regions of the anchor part A and the contact part A′ are etched. For example, gold (Au), a metal substance having excellent conductivity, is preferably used for the metal layer340.

Subsequently, the substrate on which the metal layer340is formed to a predetermined thickness is planarized. This planarization is preferably performed by polishing. In a case where the planarization is performed by polishing, an amount of time until the insulation layer330, which is formed underneath the metal layer340, is exposed is monitored so that it may be determined for how long to perform the planarization. That is, as shown inFIG. 3D, the polishing progresses until the insulation layer330is exposed.

After the planarization, the metal layer340for the RF lines is formed in a thick film having a thickness of about 2 to 3 μm in consideration of the skin depth effect, for which the flattening mold330of the insulation layer is formed in the thick film having a thickness of at least about 2 to 3 μm.

Accordingly, the metal layer340is formed on the anchor part A and the RF line part A′ to a thickness matching the thickness of the insulation layer mold previously processed, so that the electrode part in which the driving electrode layer320and the insulation layer330are formed and the RF lines are evenly formed with respect to thickness, i.e., there is no difference of step heights.

Thus, an electrostatic drive-type MEMS relay is formed having a structure in which the driving electrode320thereof is embedded in the insulation layer330.

Next, as shown inFIG. 3E, a sacrificial layer350is formed on the resultant structure on the planarized substrate310, and the sacrificial layer350is etched to form a groove-shaped opening in one rim portion B of the anchor part A through a predetermined patterning. The sacrificial layer350may be formed of material such as aluminum (Al), copper (Cu), oxide, nickel (Ni), or the like.

As shown inFIG. 3F, a MEMS structure layer360is formed on the patterned sacrificial layer350. The MEMS structure layer360includes an anchor part and a driving part and is formed of a deposited metal layer of a substance such as gold (Au). Accordingly, the MEMS structure layer360is formed in the groove-shaped opening formed in the rim portion B of the anchor part, and the MEMS structure layer360is also formed on the resultant structure on the substrate310on which the sacrificial layer350is formed.

Subsequently, predetermined etching access holes (not shown) are formed in the driving part of the MEMS structure layer360, which is to be driven by the driving electrode320. Then, an etchant able to selectively etch only the sacrificial layer350is supplied through the etching access holes. Accordingly, the sacrificial layer350is removed, as shown inFIG. 3F, so that a MEMS relay having the driving part of the MEMS structure layer360floating over the substrate310is fabricated.

At this time, a sidewall C is formed in the connection part between the anchor part and the driving part of the MEMS structure layer360formed in the rim B of the anchor part, as shown inFIG. 3F, so that a portion of the sacrificial layer350adjacent to the connection part and the anchor part in the rim B is not removed by the etchant.

As stated above, a step-height difference, that is, a difference in thickness between the metal layers340for the RF lines of the contact parts and the driving electrode320formed in a structure embedded in the insulation layer330of the electrode part is eliminated through the planarizing process, so that a MEMS relay having enhanced reliability and a stable drive capability may be fabricated.

Further, a step for forming the insulation layer330on the driving electrode layer320compared to the prior art can be excluded, to thereby simplify a fabrication process.

Additionally, a portion of the sacrificial layer350near the anchor part remains by the sidewall C formed in the connection part between the anchor part A and the driving part of the MEMS structure layer360, so that a MEMS device having greater stability may be fabricated.

FIG. 4AtoFIG. 4Gillustrate views for sequentially showing stages in a planarizing process for an electrostatic drive-type MEMS relay according to another embodiment of the present invention, in which a driving electrode layer420formed on the substrate410is formed without a step-height difference with respect to metal layer areas440of RF lines.

First, as shown inFIG. 4A, a driving electrode layer420for providing an electrostatic driving force is patterned on a substrate410and is formed to a predetermined thickness. Next, as shown inFIG. 4B, a first insulation layer430is formed on the substrate410on which the driving electrode layer420is formed. Thereafter, the regions of the anchor part A of the MEMS relay and the contact parts A′ of the RF lines are patterned and etched.

Next, as shown inFIG. 4C, a metal layer440is deposited to a predetermined thickness on the resultant structure on the substrate and on the substrate410in the regions where the anchor part A and the contact part A′ have been etched.

A planarizing step is then performed through the polishing of the resultant structure on the substrate on which the metal layer440is formed to a predetermine thickness. As shown inFIG. 4D, the polishing progresses until the driving electrode layer420is exposed. Further, the metal layer areas440of the RF lines are polished so as to be formed in a thick film having a thickness of between about 2 to 3 μm in consideration of the skin depth effect.

Next, as shown inFIG. 4E, a second insulation layer450covering the driving electrode layer420is formed.

Accordingly, the metal layer areas440of the contact part and the driving electrode layer420are formed having a planarized surface as compared to the prior art.

Next, the fabrication stages shown inFIGS. 4F and 4Gare similar to the stages shown inFIGS. 3E and 3Fin connection with the first-described embodiment of the present invention and a further description thereof will be omitted.

As stated above, the step-height difference between the metal layer areas440of RF lines and the driving electrode420is eliminated so that the driving part of MEMS structure layer470fabricated in the subsequent steps is prevented from being transformed and a MEMS device having a greater stability may be fabricated.

Accordingly, a MEMS relay having enhanced reliability and a more stabilized drive capability may be fabricated.

According to the present invention, the step difference between the RF lines and the driving electrode is eliminated, so the MEMS structure layer to be subsequently formed for the driving part, which is driven by an electrostatic force, may be prevented from being transformed.

Further, a portion of the sacrificial layer near the anchor part remains by the sidewall formed in the connection part between the anchor part and the driving part, so that a more stable MEMS device may be fabricated.