KR100404195B1 - micro mirror and method for fabricating micro mirror - Google Patents

Abstract

The present invention relates to an electrostatically-driven micromirror for use in an optical communication switch and a method of manufacturing the same. Electrodes, a plurality of pads formed on the first substrate and electrically connected to the electrodes, respectively, a second substrate formed on the first substrate and having a cavity in a central region; And a mirror positioned in the cavity area of the second substrate and rotating in a predetermined direction according to the applied voltage of the electrode. As described above, the present invention is manufactured by aligning two substrates to secure a sufficient distance between the mirror and the lower electrode to increase the degree of integration of the mirror, and the manufacturing process is simple, thereby improving process reliability.

Description

Micro mirror and its manufacturing method {micro mirror and method for fabricating micro mirror}

The present invention relates to an electrostatically driven micromirror used in an optical communication switch and a method of manufacturing the same.

Recently, various optical devices adopting MEMS (Micro-Electro Mechanical System) technology and optical communication systems using the same have been reported.

For example, an optical switch using a micro rotating mirror implemented by MEMS technology has advantages such as low optical interference and low dependence on wavelength and polarization.

Driving methods of the micromirrors include piezoelectric force, electro-thermal strain, electromagnetic force, electrostatic force, and the like.

Looking at each driving method, the mirror driven by the piezoelectric mechanism has the advantage that it can be driven at low voltage of less than several tens of volts, while the piezoelectric structure must be large in size to obtain a sufficient rotation angle of the mirror. There are disadvantages.

In the case of thermal driving, increasing the thermal response speed increases the power consumption.

In the case of the electromagnetic force, the driving current or power consumption is large, and compatibility with the existing integrated circuit process is difficult.

Lastly, in the case of constant power driving, it is difficult to process because a large area and a gap between two objects must be narrow in order to obtain a sufficient rotation angle, but there is little power consumption and it can be easily manufactured by the existing integrated circuit process. There is this.

1 is a view showing a two-axis rotatable micromirror of the constant power driving method according to the prior art.

The conventional micromirror is manufactured using a surface microfabrication technique as shown in FIG. 1, and is a structure for driving the micromirror after lifting the mirror upward by using a scratch drive actuator (SDA) and a support frame.

However, the micromirrors of such a structure have a limitation in increasing the density of mirrors in an n × n mirror array because the space for making the SDA and the supporting frame portion must be secured.

In addition, another method of fabricating a biaxial rotatable micromirror with a constant power drive method is to use a bimorph driver in which two metals having different coefficients of thermal expansion are bonded together.

However, in this case, since the space for making the bimorph driver must be secured, the fill factor of the mirror cannot be increased, the structure is very complicated, heat is generated, and power consumption is increased. there was.

An object of the present invention is to provide a micro-mirror and a method of manufacturing the same that can easily increase the degree of integration of the mirror by easily securing the distance between the mirror and the lower electrode.

Another object of the present invention is to provide a micromirror and a method of manufacturing the same which improves process reliability by a simple process.

1 shows a micromirror according to the prior art

Figure 2 shows a micro mirror in the present invention

3A and 3B show a manufacturing process of the micromirror according to the present invention.

4A-4F illustrate a process of manufacturing the second substrate of FIG. 3A.

5A through 5E illustrate a process of manufacturing the first substrate of FIG. 3A.

6 is a view showing a cross-connect optical switch using a micro mirror according to the present invention.

Explanation of symbols for main parts of the drawings

1,20: first substrate 2,24: lower electrode

3: pad 4,10: second substrate

5: mirror 6: ring frame

7: hinge 10a, 21: insulating layer

10b silicon 11 electrode layer

11a: Al layer 11b: Cr layer

12 photoresist 22 metal seed layer

23: plating frame 25: protective film

The micro-mirror according to the present invention is formed on the first substrate, a plurality of electrodes formed in the form of four rods are formed in the central region of the first substrate, arranged at a constant height and spacing, the first substrate A plurality of pads electrically connected to the electrodes, the second substrate being formed on the first substrate, the second substrate having a cavity in a center region, and positioned in a cavity region of the second substrate; It includes a mirror that rotates in a predetermined direction in accordance with the applied voltage of the electrode.

Here, the cavity of the second substrate is formed at a position corresponding to the electrode formed in the central region of the first substrate.

And, the height from the bottom surface to the top surface of the second substrate is higher than the height of the electrode.

At this time, the mirror is formed at a predetermined distance from the electrode.

In addition, the present invention, in addition to the above configuration, the ring frame located in the cavity area of the second substrate and surrounding the side of the mirror at a predetermined distance from the side of the mirror, the hinge connecting the mirror and the ring frame and connecting the ring frame and the second substrate It further comprises a (hinge).

Here, a silicon support for supporting them is formed below the mirror, the ring frame, and the hinge. In the method of manufacturing a micromirror, a first substrate having electrodes in a central region and a second substrate having a mirror in a cavity region are combined. Preparing a first substrate, forming an insulating layer on the upper and lower portions of the first substrate, and forming and patterning a metal seed layer on the insulating layer on the first substrate to form an electrical connection with the outside. Exposing an insulating layer of a region for forming the metal layer; and forming a plating mold so that the metal seed layer of the region for electrical connection is exposed, performing plating on the exposed metal seed layer and removing the plating mold. Preparing a first substrate and a second substrate to form a first substrate having the electrodes by forming electrodes and forming a protective film on the entire surface Forming an electrode layer on the second substrate, etching the central region of the electrode layer to form the mirror, etching the central region below the second substrate to form a membrane, and forming the membrane. A second step of manufacturing a second substrate having the mirror by etching a predetermined region on the substrate to release the mirror, and removing a portion of the metal layer; And a third step of aligning and bonding the second substrate having the mirror onto the first substrate having the electrode.

Here, the first substrate is a silicon substrate or a glass substrate, the second substrate is a silicon on insulator (SOI) substrate having an insulating layer therein, the plating frame is a photoresist, the metal seed layer is any one of Al, Cr, Au One.

In forming the membrane, the lower portion of the second substrate is etched using a deep reactive ion etching method.

As described above, the present invention manufactured can secure a sufficient distance between the mirror and the lower electrode by aligning the two substrates, thereby increasing the degree of integration of the mirror.

In addition, the present invention is simple in the manufacturing process, the process reliability is improved.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Referring to the accompanying drawings, preferred embodiments of the present invention having the features as described above are as follows.

The present invention implements a biaxial rotatable electrostatically driven micromirror for highly integrated optical cross connect using silicon micromachining technology and plating.

In the present invention, when the mirror is made of an array structure of n × n, in order to increase the degree of integration of the mirror, first, a mirror, which is an upper electrode, is formed on an independent substrate, and the lower electrode is independently manufactured on a separate substrate to assemble two substrates. Was introduced.

In addition, the present invention introduces a plating method when making the lower electrode to increase the degree of integration of the mirror, the membrane structure of the upper electrode is used to etch the silicon substrate vertically using a deep reactive ion etching (deep RIE) method Method was used.

FIG. 2 is a view illustrating a micromirror according to the present invention, and as shown in FIG. 2, lower electrodes 2 are formed in a central region of the first substrate 1.

Here, the lower electrodes 2 are arranged at regular intervals with four rod-shaped electrodes to rotate the mirror in two axes.

Four pads 3 are electrically connected to the lower electrodes 2 arranged in the center area on the first substrate 1. On the other hand, the second substrate 4 is disposed on the first substrate 1. ) Is formed, and a cavity is formed in the central region of the second substrate 4.

Here, the cavity of the second substrate 4 is formed at a position corresponding to the lower electrodes 2 of the first substrate 1.

In the cavity region of the second substrate 4, a mirror 5 (which serves as an upper electrode) 5 which rotates in a predetermined direction according to an applied voltage of the lower electrode 2, and a predetermined distance from the side surface of the mirror 5. A ring frame 6 is formed to cover the side of the mirror 5 apart from each other, and the mirror 5 and the ring frame 6 are connected to each other, and the ring frame 6 and the second substrate 4 are connected to each other. A hinge 7 is formed to connect.

Here, a silicon support (not shown) is formed under the mirror 5, the ring frame 6, and the hinge 7 to support them.

The support may be made of Si ₃ N ₄ , polysilicon, silicon, or the like, or a metal having a low stress such as Al, Ni, or the like.

In addition, the height of the second substrate 4, that is, the height from the bottom surface to the top surface of the second substrate 4 is made higher than the height of the lower electrodes 2 formed on the first substrate 1.

The reason for this is to secure a constant space between the lower electrode 3 and the mirror 6 as the upper electrode.

As described above, the present invention includes a second substrate having a mirror (upper electrode) formed in a cavity area and a first substrate having a lower electrode formed thereon, and using a deep reactive ion etching (deep RIE) process. If the membrane structure is formed by dry etching, the substrate can be etched vertically, so that the degree of integration of the mirror can be increased when compared to the membrane structure when wet etching with KOH.

Referring to FIG. 7 again, when wet etching in KOH to make a membrane structure using a silicon substrate on the (100) plane, the integration degree of the mirror is lowered because it is etched at an angle of 54.74 degrees with respect to the (111) plane.

In order to increase the degree of integration of the mirror by forming a membrane structure by vertically etching the substrate, a pole must be erected as a lower electrode to make an electrode.

This is to prevent a short problem between silicon used as a substrate of the lower electrode and the upper electrode when connecting the lower electrode and the bonding pad.

Therefore, since the lower electrode must be manufactured with a high pillar, four pillars are fabricated by placing LIGA (Lithographi, Galvanoformung, Abformung) process and plating technology as shown in FIG.

Referring to the operating principle of the present invention, as shown in Figure 2, by applying a voltage to the lower electrodes A and B at the same time to rotate the mirror in one direction with the X axis as the center axis, and simultaneously applying voltage to the electrodes C and D To rotate in the other direction.

In addition, by applying the same voltage to the electrodes A and D, the mirror can be rotated in one direction with the Y-axis as the center axis, and the same voltage can be applied to the electrodes B and C in the other direction.

3A and 3B illustrate a manufacturing process of a micromirror according to the present invention. First, as shown in FIG. 3A, a first substrate on which electrodes are formed and a second substrate on which a mirror is formed in a cavity are respectively etched in silicon. Produced by the process.

Subsequently, the first substrate and the second substrate are respectively bonded to each other so that the electrodes of the first substrate and the cavity of the second substrate correspond to each other.

In this case, the mirror and the lower electrode are spaced apart from each other by a predetermined distance.

The manufacturing process of the first substrate and the second substrate of the present invention will be described in more detail as follows.

4A to 4F are views illustrating a process of manufacturing the second substrate of FIG. 3A.

First, as shown in FIG. 4A, a second substrate 10 is prepared. In the present invention, a silicon on insulator (SOI) substrate is used to simplify the process.

The SOI substrate is a substrate having an insulating layer 10a in the silicon substrate 10b. In the present invention, the SOI substrate is used so as not to separately form an insulating layer for forming a membrane.

Subsequently, as shown in FIG. 4B, the Al layer 11a and the Cr layer 11b are stacked on the second substrate 10 to form the electrode layer 11, and then patterned to form the second substrate 10 in a predetermined region. Expose the surface.

Here, the Al layer 11a is a metal for forming a mirror surface having high reflectivity, and the Cr layer 11b is a metal for protecting the mirror surface in an etching process.

Next, as shown in FIG. 4C, a photoresist 12 is formed and patterned on the rear surface of the second substrate 10 to expose the second substrate 10 in the region where the membrane is formed, and to form a membrane. The second substrate 10 is etched using the resist 12 as a mask to expose the insulating layer 10a in the second substrate 10.

Here, the etching of the second substrate 10 is dry etching using a mixed gas of SF ₆ and O ₂ and a deep reactive ion etching (deep RIE) device.

As illustrated in FIGS. 4D and 4E, the silicon substrate 10a and the insulating layer 10b of the second substrate 10 exposed thereon are etched to release a mirror, a ring frame, a hinge, and the like. .

Subsequently, as illustrated in FIG. 4F, the Cr layer 11b used as the protective layer is removed to fabricate a second substrate having a mirror as an upper electrode.

5A to 5E are views illustrating a process of manufacturing the first substrate of FIG. 3A.

First, as shown in FIGS. 5A and 5B, after preparing the first substrate 20 made of silicon or glass, an insulating layer 21 is formed on the upper and lower portions of the prepared first substrate 20, respectively. The metal seed layer 22 is formed on the insulating layer 21 on the first substrate 20 by using metals such as Al, Cr, and Au.

Then, the metal seed layer 22 is patterned to form a bonding pad (not shown) for electrical connection with the lower electrode and the outside to be formed in the next process.

Subsequently, as shown in FIG. 5C, a photoresist is formed on the front surface including the metal seed layer 22 and patterned to expose the metal seed layer 22 of the bonding pad for electrical connection with the lower electrode 24 and the outside. The plating mold 23 is formed as much as possible.

Next, as shown in FIG. 5D, plating is performed on the exposed metal seed layer 22 and the plating mold 23 is removed to form lower electrodes 24 having a rod shape.

Subsequently, as shown in FIG. 5E, all portions except the bonding pad portion are passivated with the passivation layer 25 to fabricate the first substrate.

In the present invention, regardless of whether the first substrate or the second substrate is manufactured first, the manufacturing order is not relevant.

In this way, when the second substrate is aligned and bonded to the produced first substrate, the micromirror of the present invention is completed.

6 is a view showing a cross-connect optical switch using a micro mirror according to the present invention.

As shown in FIG. 6, a plurality of micromirrors of the present invention may be integrated and arranged on a substrate to switch optical paths of multiple optical signals.

The present invention will be used as a core device in applications such as two-dimensional optical scanners, large capacity cross-connect optical switching systems for DWDM, and the like.

As described above, the present invention manufactured by aligning the two substrates can easily secure a sufficient distance between the mirror and the lower electrode to increase the degree of integration of the mirror.

In addition, the present invention is simple in the manufacturing process, the process reliability is improved.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (13)

A first substrate; A plurality of electrodes formed in a central region of the first substrate and formed in four rod shapes arranged at regular heights and intervals; A plurality of pads formed on the first substrate and electrically connected to the electrodes, respectively; A second substrate formed on the first substrate and having a cavity in a central region; And, And a mirror positioned in the cavity area of the second substrate and rotating in a predetermined direction according to the applied voltage of the electrode. The micromirror of claim 1, wherein the cavity of the second substrate is formed at a position corresponding to an electrode formed in a central region of the first substrate. The micromirror of claim 1, wherein the height from the bottom surface to the top surface of the second substrate is higher than the height of the electrode. delete The micro mirror of claim 1, wherein the mirror is formed at a predetermined distance from the electrode. The method of claim 1, A ring frame positioned in a cavity area of the second substrate and surrounding a side of the mirror at a predetermined distance from the side of the mirror; And a hinge connecting the mirror and the ring frame and connecting the ring frame and the second substrate to each other. 7. The micromirror according to claim 6, wherein a silicon support for supporting the mirror, the ring frame, and the hinge is formed below the mirror, the ring frame, and the hinge. A method of manufacturing a micromirror in which a first substrate having electrodes in a central region and a second substrate having a mirror in a cavity region are combined, Preparing a first substrate, forming an insulating layer on the upper and lower portions of the first substrate, and forming and patterning a metal seed layer on the insulating layer on the first substrate to electrically connect to the outside. Exposing the insulating layer of the region, forming a plating mold such that the metal seed layer of the region for the electrical connection is exposed, performing plating on the exposed metal seed layer and removing the plating mold; Forming a first substrate having the electrodes by forming a thin film and forming a protective film on the entire surface thereof; Preparing a second substrate, forming an electrode layer on the second substrate, etching the central region of the electrode layer to form the mirror, and etching the central region below the second substrate to form a membrane. A second step of forming a second substrate having the mirror by forming and etching the predetermined region on the second substrate to release the mirror, and removing a portion of the metal layer; And, And a third step of aligning and bonding the second substrate having the mirror onto the first substrate having the electrode. The method of claim 8, wherein the first substrate is a silicon substrate or a glass substrate, and the second substrate is a silicon on insulator (SOI) substrate having an insulating layer therein. The method of claim 8, wherein the plating mold is a photoresist, and the metal seed layer is any one of Al, Cr, and Au. The method of claim 8, wherein in the second step, The metal layer formed on the second substrate is Cr / Al, a part of the metal layer to be removed is a micro mirror manufacturing method, characterized in that. The method of claim 8, wherein the second step is performed before the first step. The method of claim 8, wherein in the second step, a deep reactive ion etching (deep RIE) method is used in forming the membrane.