JP2003302586A - Optical device and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device which can realize low insertion loss, a larger number of ports, low-voltage driving, and higher-precision mirror driving by securing sufficient flatness and smoothness of a mirror and making spring rigidity small and a manufacturing method of the optical device. <P>SOLUTION: On an electrode substrate 3, a plurality of electrode pads 2 are formed and above the electrode substrate 3, a movable mirror 1 is arranged, leaving a gap between the mirror and the electrode pads 2. On the electrode substrate 3, a column 5 and an anchor 7 are provided and a frame 9 is supported by the anchor 7 across a spring 8a. The center part of the frame 9 is hollowed and the movable mirror 1 arranged at the center part of the frame 9 is supported on the frame 9 across a spring 8b. Here, tm>ts, where tm is the thickness of the movable mirror 1 and ts is the thickness of the springs 8a and 8b. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device used in an optical communication system or the like and a method of manufacturing the same, and more particularly, to an optical device used in an optical switch or the like and spatially reflecting an optical signal using a mirror. And a manufacturing method thereof.

[0002]

2. Description of the Related Art With the increase in communication traffic, the spread of optical communication systems using an optical fiber as a transmission line is accelerating. Along with this, the added value of node systems such as OXC (Optical Cross Connect) for backbone systems and OADM (Optical Add / Drop Module) for mesh type networks has increased, leading to the optical devices that are the core of these systems. Expectations are increasing.

In particular, the optical switch has a merit that it can significantly reduce the system cost because it can perform high-speed switching as it is without converting an optical signal into an electric signal, and the node technology It is positioned as the core device of the.

As such an optical device, conventionally, US.P has been used.
There is one disclosed in atent 6,300,619. FIG. 17 shows this conventional optical device. The disk-shaped mirror 17, the frame 91 around the mirror 17, and the mirror fixing portion 20 are formed by depositing polysilicon, and the mirror 17, the frame 91, and the mirror fixing portion 20 are
They are connected via springs 30 and 32, respectively. The mirror fixing portion 20 is connected to the silicon substrate 13 serving as a base via the beams 19 and 26.

As a result, the beams 19, 26 are warped by thermal deformation, so that the mirror 17, the frame 91, and the spring 3 are formed.
The mirror structure composed of 0, 32, and the mirror fixing portion 20 can be projected from the silicon substrate 13 in the Z-axis direction (direction perpendicular to the paper surface).

Electrode pads (not shown) are formed on the silicon substrate 13 below the mirror 17,
A voltage is applied between the mirror 17 and the electrode pad, and the generated electrostatic force drives the mirror 17 to rotate. The mirror 17 is driven around the two axes (X axis and Y axis) of the springs 30 and 32, and the optical signal applied to the mirror 17 is reflected in an arbitrary direction to spatially perform optical path switching.

In the optical switch configured as described above, since the mirror 17 is formed by depositing polysilicon, it is difficult to improve the smoothness (roughness) of the mirror surface. Also, since the polysilicon itself has internal stress,
The mirror 17 is likely to be warped, and it is difficult to secure flatness. For this reason, the reflected optical signal is scattered, which causes a so-called insertion loss in the optical signal of the optical switch (hereinafter referred to as insertion loss).

Further, in order to reduce such warpage, it is difficult to increase the diameter of the mirror. As the mirror area gets smaller,
The inserted optical signal does not fully enter the mirror surface, causing so-called "eclipse", which also causes a large insertion loss.

In optical communication, when the intensity of an optical signal deteriorates,
It is necessary to add equipment for amplification. Therefore, the higher the insertion loss when passing through the optical switch and other devices, the more the system cost increases. That is, in the device for optical communication, reduction of insertion loss is a very important performance index.

Therefore, the conventional optical switch shown in FIG. 17 is considered to have a fatal problem from the viewpoint of reduction of insertion loss.

As a conventional technique for overcoming the problems in the mirror forming method by depositing polysilicon as described above, there is the International Conferrence of Optical MEMS.
"Single Crystalline Mirror A" announced in 2001
ctuated Electrostaticallyby Terraced Electrodes Wi
th High-Aspect Ratio Torsion Spring "by RenshiSaw
ada @NTT Telecommunications Energy Laboratories.

In this optical switch, similarly to the above-mentioned optical switch, the electrode and the mirror are arranged with a predetermined clearance, and the mirror is rotationally driven by electrostatic force. However, this optical switch does not use polysilicon for the mirror but uses single crystal silicon. Single crystal silicon can easily form a thick mirror and can form an extremely smooth mirror surface by polishing. Therefore, it is possible to form a smooth and flat mirror having a large diameter, and it is possible to realize low loss of an optical signal.

FIG. 18A is a sectional view showing a device structure of the conventional optical switch in the process of manufacturing, FIG. 18B is a plan view of the same, and FIG. 19 is a sectional view showing the obtained optical switch. . In this conventional technology, SOI (Silico
n On Insulator) Mirror 10 on device layer 101 of the substrate
2 is formed. That is, by patterning the shapes of the disk-shaped mirror 102 and the zigzag-shaped spring 103 on the device layer 101, and etching the backing material 106 to remove the portions aligned with the mirror 102 and the spring 103, thereby forming a mirror structure. 107 is formed. Next, the mirror structure 107 is bonded to the electrode substrate 104 on which the electrode 108 is formed via the pillars 105 provided on both sides of the electrode 108 to complete the optical switch.

In this case, in this type of optical switch, how to form the spring 103 softly becomes a major issue. Because the spring 103 is soft, the mirror 102 can be rotationally driven at a large angle, that is, the flying range of the reflected light can be widened. As a result, the scale of the switch can be increased (the number of input ports and the number of output ports can be increased).

Further, at that time, the voltage required for the electrostatic force can be suppressed to a low level, so that the system voltage can be reduced.

Further, in order to position and fix the mirror 102 at a certain angle, an attitude control technique is required. In this control as well, the spring is soft and can be driven by a weak electrostatic force. It is extremely advantageous in terms of accuracy and stability.

[0017]

However, in the optical switch disclosed above, the mirror 102 and the spring 103 are common depending on the thickness of the device layer 101. As mentioned above, it is desirable that the mirror is flat and has no warp. For this purpose, it is advantageous that the device layer 101 is as thick as possible. However, since the thickness of the spring 103 also increases accordingly, there is a limit to the other problem of softening the spring 103, and the structure is insufficient.

As described above, in the prior art, there is a limit to the flattening of the mirror, which makes it difficult to reduce the insertion loss of the mirror. This is because the mirror is formed by depositing polysilicon, and it is difficult to improve the smoothness (roughness) on the mirror surface formed of polysilicon. Further, since the polysilicon itself has internal stress, the mirror is apt to warp, and it is difficult to secure flatness. Therefore, the reflected optical signal is scattered and the insertion loss is increased.

Further, in order to reduce such warpage,
It is difficult to increase the diameter of the mirror. If the mirror diameter becomes smaller, the inserted optical signal will not fit on the mirror surface,
So-called "shaking" occurs, which also causes a large insertion loss.

The second problem in the conventional optical device is that it is difficult to increase the number of ports, drive at a low voltage, and further improve the precision of mirror drive. This is because the rigidity of the spring that supports the drive mirror cannot be reduced. In the conventional optical device, in order to reduce the loss on the mirror surface, even when single crystal silicon is used as the mirror, the mirror and the spring are determined by the thickness of the device layer of the SOI substrate and are therefore the same. As described above, it is preferable that the mirror is flat and has no warp. Therefore, although it is desired to make the device layer as thick as possible, the spring becomes thicker accordingly and the spring cannot be made soft. For this reason,
The mirror cannot be rotationally driven at a large angle, and the switch cannot be enlarged. Further, at that time, it is necessary to increase the voltage required for the electrostatic force, which makes it difficult to reduce the voltage of the system. Furthermore, in order to position and fix the mirror at a certain angle, attitude control technology is required. However, even in this control, the rigidity of the spring is high, which is disadvantageous from the viewpoint of accuracy and stability. Become.

As described above, in the conventional optical device, it was not possible to achieve both low insertion loss and increase in the number of ports.

The present invention has been made in view of the above problems, and sufficiently secures the flatness and smoothness of the mirror,
Further, by reducing the spring rigidity, it is possible to provide an optical device and a manufacturing method thereof, which can realize a low insertion loss, a large number of ports, low voltage driving, and high precision mirror driving. To aim.

[0023]

An optical device according to the present invention has a gap between an electrode substrate, an electrode pad formed on the electrode substrate, and the electrode pad above the electrode substrate. And a plurality of springs that connect the movable mirror and the supporting portion to support the movable mirror. Thickness tm and the spring thickness ts
Is tm> ts.

In this optical device, the movable mirror has a thickness tm of 8 μm or more and the support portion has a thickness ts of 5 μm.
It is preferably m or less.

The mounting position of the spring with respect to the movable mirror is, for example, an intermediate position in the thickness direction of the movable mirror.

Further, for example, a frame surrounding the movable mirror is provided, and some of the springs are arranged so as to connect between the supporting portion and the frame, and the remaining springs are provided for the frame and the mirror. It is arranged to connect between and.

Furthermore, the electrode pads are arranged at, for example, four equidistant positions in a region on the electrode substrate which overlaps the movable mirror in plan view.

In the method of manufacturing an optical device according to the present invention, a step of forming a plurality of electrode pads and electrode wirings connected to the electrode pads on the electrode substrate and providing pillars, and an etching stopper layer as an intermediate layer. A step of forming an impurity region on the surface of the formed mirror substrate by ion-implanting a portion to be a contour of the mirror and a region to be an anchor to reach the etching stopper layer, and ion-implanting the entire surface to reach the etching stopper layer. Not forming a thin impurity layer, patterning the plurality of springs and anchors connected to the mirror by etching the impurity layer deeper than the impurity layer, the mirror substrate and the electrode substrate And affixing the pillar and the anchor by joining the pillar and the mirror base. Is wet-etched using the etching stopper layer, the impurity layer, and the impurity region as a mask to selectively remove the mirror substrate, and then the etching stopper layer is removed to support the movable mirror in the air by the spring. Obtaining a floating structure,
And tm> ts, where tm is the thickness of the movable mirror and ts is the thickness of the spring.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. 1 is a plan view showing an optical switch according to an embodiment of the present invention, and FIG. 2 is a sectional view of the same. The optical device of the present invention has a structure in which the mirror 1 and the electrode pad 2 face each other across a space, and the mirror is driven by an electrostatic force generated between them.

The electrode substrate 3 is covered with an insulating film 5, and a plurality of electrode pads 2 and a plurality of electrode wirings 4 connected to the electrode pads 2 are formed on the electrode substrate 3. There is. The electrode wiring 4 is connected to a driving circuit (not shown), and a driving current is supplied to the electrode pad 3 via the electrode wiring 4 by this driving circuit. Electrode pad 2
Are fan-shaped and are arranged at equal intervals on the circumference of the circle with a proper interval between them. The number of electrode pads 2 is not limited to four.

Two pillars 6 are provided on the electrode substrate 3, and anchors 7 are laminated on the pillars 6, respectively. A spring 8a is attached to the two anchors 7.
The frame 9 is connected to the frame 9 via the springs 8a, so that the frame 9 is supported by the anchor 7 via the spring 8a. Further, the central portion of the frame 9 has a hollow shape, and the disk-shaped mirror 1 is arranged in the central portion of the frame 9. This mirror 1 has a frame 9 and a spring 8b.
Is supported through.

In the present embodiment, the spring 8a and the spring 8
The thickness ts of b is smaller than the thickness tm of the mirror 1 (t
m> ts). Therefore, the springs 8a and 8b have lower rigidity and are softer than those when the thickness is tm.
The mirror 1 has higher rigidity and better flatness than the case where the thickness is ts. As a result, the mirror 1 having high rigidity without warpage and the springs 8a and 8b having low rigidity that can be easily driven by a small electrostatic force are compatible with each other.

Next, with reference to FIGS. 3 to 11, a method of manufacturing the optical switch of this embodiment will be described, and the structure thereof will be described in more detail. In each figure, (a) is a plan view and (b) is a sectional view. First, as shown in FIG. 3, the insulating film 5 is formed on the surface layer of the electrode substrate 3 made of a silicon substrate.
To form. Examples of the insulating film 5 include an oxide film and a nitride film.

Next, as shown in FIG. 4, the electrode pad 2 having a predetermined shape and the electrode wiring 4 connected to the electrode pad 2 are formed on the insulating film 5. The electrode pad 2 can be formed by patterning a metal layer such as gold and tantalum or a polysilicon layer. However, as a constituent material of the electrode pad 2, it is necessary to select a material that is not damaged in a later step. The electrode wiring 4 is connected to a drive circuit (not shown).

Next, as shown in FIG. 5, a pair of columns 6 are formed on the electrode substrate 3 at positions sandwiching the electrode pads 2.
As a method of forming the pillar 6, for example, there is a method shown in FIGS. First, as shown in FIG. 11A, a pedestal 301 having a height of about several μm is provided on the electrode substrate 3, and a glass substrate 601 is attached onto the pedestal 301 as shown in FIG. 11B. At the same time, as shown in FIG. 11C, only the glass substrate 601 is cut at the boundary of the pedestal 301 by dicing, and the glass substrate 601 in the portion not bonded to the pedestal 301 is removed. Thereby, the column 6 can be provided.

As the column 6, besides the glass substrate,
For example, a resin such as polyimide can be used. It is also possible to form the support 6 by directly etching the electrode substrate 3 deeply by the height of the support, and the electrode substrate 3 and the support 6 can be formed from the same silicon substrate. Through the above steps, the layer structure on the electrode substrate 3 side is completed.

On the other hand, the mirror substrate side can be formed by using a multilayer substrate having an etching stopper layer in the middle. In this embodiment, as shown in FIG. 6, an insulator layer 12 made of a silicon oxide film is formed on a backing layer 13 made of a silicon layer, and a device layer 10 made of a silicon layer is formed on the insulator layer 12. An SOI (silicon on insulator) substrate is used. As the specifications of this SOI substrate, for example, the thickness of the silicon device layer 10 is 20 μm, the thickness of the insulator layer 12 made of a silicon oxide film is 0.5 μm, and the thickness of the silicon backing layer 13 is 525 μm.

In addition to the SOI substrate, a laminated body of a silicon layer and a silicon layer, or a silicon layer / glass substrate /
Any multi-layer substrate having an intermediate layer that can serve as an etching stopper layer in the etching step described later can be used, such as a multilayer silicon layer formed by electrostatic bonding.

Next, a method of forming the mirror substrate will be described. First, as shown in FIG. 6, boron is injected into a device layer 10 of an SOI substrate in a predetermined pattern and diffused to form a boron layer 11a and a boron layer 11b. The boron layer 11a is arranged in a ring shape so as to frame the region forming the mirror 1. Further, the boron layer 11b is arranged in a rectangular area forming the anchor 7.

In this case, as shown in FIG. 6A, both of the boron layers 11a and 11b are implanted so as to penetrate the device layer 10 over the entire thickness of the device layer 10. That is, the implanted boron is the device layer 10
Of the SOI substrate and reaches the insulator layer 12 which is the intermediate layer of the SOI substrate. By doing so, the thickness tm of the mirror 1 can be made the same as the thickness of the device layer 10 in the sacrifice layer etching step which is a later step. That is, by using the SOI substrate of the type in which the device layer 10 is sufficiently thick, the thickness of the mirror 1 can be increased, and as a result, the mirror 1 having no warp and high rigidity can be obtained. In the present embodiment, as described above, the thickness of the device layer 10 is 20 μm, so the thickness tm of the mirror layer 1 is also 20 μm.

Next, as shown in FIG. 7, a boron layer 11c is newly formed on the entire surface. The boron layer 11c will be a layer for forming the springs 8a and 8b and the frame 9 later. Since the thickness of the boron layer 11c corresponds to the thickness ts of the spring, it is sufficiently smaller than the thickness of the device layer 10. As described above, since it is necessary to keep the rigidity of the springs 8a and 8b low, it is possible to reduce the spring thickness and keep the rigidity low by thinning the boron layer 11c. The thickness of the boron layer 11c is, for example, 2 μm.
Is.

In order to obtain the effect of the present invention,
The desirable relationship between tm and ts is that tm is 8 μm or more, ts
Is 5 μm or less. In this relationship, the flatness of the mirror 1 can be ensured and the springs 8a and 8b can be secured.
It is possible to achieve both low rigidity.

The boron layer 11c is also implanted in the area of the mirror 1. The purpose of this is to use the boron layer 11c that has been implanted on the surface of the mirror 1 as an etch stopper surface when the mirror 1 is raised by the sacrifice layer etching in a later step.

Further, the reason why the boron layer 11c is made sufficiently thin with respect to the device layer 10 is to secure the mirror surface of the mirror surface. The surface layer of the region where boron has been implanted loses its specularity when foreign matter is injected into silicon. For this reason, the region in which boron is implanted cannot be the mirror surface. However, the boron layer 11
Since c will be the back surface of the mirror 1 later, it does not pose a problem in ensuring the specularity of the mirror 1. However, the boron layer 1
If 1c is formed over the entire thickness of the device layer 10, boron will reach the surface of the mirror 1 that will be the mirror surface, and the mirror surface specularity of the mirror surface will be impaired. Therefore, the boron layer 11c needs to be sufficiently thinner than the device layer 10. This is also the case in the present invention, for the shape of the mirror 1 that is desired to be retained, only at the edge thereof is the boron layer 11 over the entire thickness of the device layer 10.
This is also the reason why a and 11b were formed.

Subsequently, as shown in FIG. 8, the springs 8a, 8a
The periphery of b and the frame 9 is removed by etching by dry etching, and the shapes of the mirror 1, the springs 8a and 8b, and the frame 9 are determined. Here, by setting the depth of dry etching deeper than the depth of the boron layer 11c, the springs 8a and 8b and the frame 9 can be completely separated. In this way, the mirror substrate is completed.

Next, as shown in FIG. 9, the electrode substrate and the mirror substrate are bonded to each other by joining the pillar 6 and the boron layer 11c. As a joining method, various methods such as electrostatic joining, joining with an adhesive, and solder joining can be applied.

For example, when the electrode substrate and the mirror substrate are attached to each other by electrostatic bonding, and when glass is used as the support 6, the gap between the electrode substrate and the mirror substrate is 800.
By applying a voltage of about V and heating the whole to a temperature of about 400 ° C., SiO ₂ (oxide film) is formed at the interface between the glass column 6 and the boron layer 11c of the mirror substrate,
Joining is completed.

Finally, as shown in FIG. 10, the silicon backing layer 13 is wet-etched with EPW (ethylenediamine / pyrocatechol / water solution), and subsequently,
The insulator layer 12, which is an oxide film, is removed by hydrofluoric acid, and the mirror 1, the springs 8a and 8b, and the frame 9 are exposed in the space. In FIG. 10, reference numeral 100 indicates a mirror surface used as an optical device.

EPW etches silicon, but does not etch the boron-diffused region, so that this region remains unetched selectively. Further, even in the region where the oxide film is present, the film serves as a mask and is not etched.
Therefore, by etching with EPW, the backing layer 13 of the SOI substrate becomes an insulator layer 12 that is an oxide film.
This insulator layer 1 is used as an etching stopper layer.
All its parts up to 2 are etched. With respect to the device layer 10 as well, a region where boron is not diffused is etched. However, the area inside the mirror 1 is
Since the boron layer 11c formed on the surface layer, the boron layer 11a formed as a sidewall, and the insulator layer 12 are isolated from the EPW in all directions, they remain without being etched.

Here, as will be repeatedly described, by performing such a process, it is possible to form a thick mirror having high rigidity, that is, a mirror having no warp while maintaining the mirror surface property of the mirror surface 100. At the same time, the spring 8a,
It is also possible to obtain a spring with low rigidity by reducing the thickness of 8b.

As a method of forming the mirror 1, as in the boron layer 11a, boron is deeply diffused over the entire thickness of the mirror only along the contour of the mirror 1, and the thick mirror 1 is formed without roughening the mirror surface 100. Because it is.

Further, the springs 8a and 8b are also thick because they are determined by another shallow boron diffusion process called the boron layer 11c, in addition to the deep boron diffusion for determining the contour of the mirror 1. Mirror 1 and thin springs 8a, 8
b can be compatible.

In this way, the optical device of this embodiment shown in FIGS. 1 and 2 can be manufactured. Next, FIG.
The operation of this optical device will be described with reference to FIG. Specific electrode pad 2 among the plurality of electrode pads 2
By selectively applying a voltage to the electrode pad 2
And an electrostatic force are generated between the mirror 1 and the mirror 1. Due to this electrostatic force, a region of the mirror 1 close to the electrode pad 2 to which the voltage is applied is attracted to the electrode substrate 3 side, and the mirror 1 tilts as shown in FIG. At this time, the spring 8b is twisted.

In the embodiment of the present invention, the spring 8 is used as an example.
The thicknesses of a and 8b are 2 μm, and the clearance between the mirror 1 and the electrode pad 2 (height of the column 6) is 100 μm. Further, as an example, the diameter of the mirror is 600 μm. At this time, 100 between the mirror 1 and one electrode pad 2.
When a voltage of V is applied, a slope of θ = about 10 ° can be obtained. FIG. 12B shows the case where a voltage is applied to the electrode pad 2 on the right side of FIG.

Similarly, when a voltage is applied to the lower electrode pad 2 of FIG. 12A, the mirror 1 shown in FIG.
The mirror 1 can be tilted in a direction orthogonal to the tilt of. Further, by simultaneously applying a voltage to a pair of adjacent electrode pads 2, the mirror 1 is biaxially driven, and the value of the voltage applied to the electrode pad 2 is individually set, so that the mirror 1 can be set to an arbitrary value. Can be tilted in any direction.

In this way, by controlling the voltage applied to the electrode pad 2, the incident light L on the mirror 1 can be reflected in any direction.

FIG. 13 shows the configuration of the entire module when the optical device having the movable mirror 1 is used as an optical switch as described above. An optical signal is emitted from the emission end of the fiber array 21, which is a bundle of optical fibers. This optical signal is applied to the mirror array 22 arranged so as to face the fiber array 21. This mirror array 2
2 is configured by arranging a large number of movable mirrors 1 shown in FIGS. 1 and 2 described above in an array. Then, the light incident on the mirror array 22 is reflected in a predetermined direction, is incident on the next-stage mirror array 23, and is further reflected by the mirror array 2
The light is reflected in a predetermined direction at 3 and is collected in the fiber array 24. The plurality of movable mirrors arranged in the mirror arrays 22 and 23 can individually control the reflection direction as described above, and thus the light emitted from the fiber array 21 can be controlled by the fiber array 24. Can be incident on the optical fiber. As a result, the signal light entering the fiber array 21 is sent out to the target fiber array 24, and the switching is completed.

Next, another embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In the first embodiment described above, the SOI
A substrate having a device layer thickness of 20 μm was adopted as the substrate, and the mirror thickness was 20 μm. However, in order to further increase the flatness of the mirror, there is a demand for making the mirror thicker. Therefore, the device layer is 20μ
It is also conceivable to use an SOI substrate of m or more. However, for that purpose, it is necessary to implant boron in a portion which becomes the contour of the mirror by the thickness thereof. However, the diffusion depth of boron is generally proportional to the square root of the boron diffusion time. Therefore, the thicker the device layer, that is, the deeper the region where boron must be implanted, the longer the diffusion time becomes. Further, in reality, diffusing boron to a depth of 20 μm or more is not realistic in consideration of process stability and the like.

Therefore, in the second embodiment of the present invention,
As shown in FIG. 14A, first, a groove 15 (a groove extending in a ring shape) is formed in a portion which becomes the contour of the mirror 1a.
For example, if the thickness of the device layer 10a is 30 μm,
A groove 15 having a depth of about 20 μm is formed. Then, FIG.
As shown in FIG. 4B, boron is implanted into the groove 15 to form the boron layer 11d. In this case, the groove 1
Since the depth of 5 is 20 μm, the distance between the bottom of the groove 15 and the insulator layer 12a is 10 μm, and the depth of the boron layer 11d to be driven into the contour of the mirror 1a is 10 μm. .

By forming the groove 15, the thickness of the mirror 1a can be further increased.
The flatness can be further improved.

Further, in the embodiment shown in FIGS. 1 and 2, the mounting positions of the springs 8a and 8b deviate toward the rear surface side of the mirror 1 with respect to the center of the mirror 1 in the thickness direction, and the spring is attached to the mirror 1. 8a and 8b are so-called offset in the thickness direction of the mirror 1. That is, in the embodiment shown in FIGS. 1 and 2, the back surfaces (electrode side) of the springs 8a and 8b coincide with the back surface (electrode side) of the mirror 1.

However, when the mirror is driven as shown in FIG. 12 and its attitude is controlled, it is necessary to optimize this offset. Therefore, in the third embodiment,
As a pre-process of the ion implantation process shown in FIG. 7 of the first embodiment, as shown in FIG. 15, a region 71 forming a spring is dug by a depth Os. By adjusting this Os amount, the offset can be adjusted to an arbitrary amount.

As a result, as shown in FIG. 16, the mirror 1c having a thickness of tm is compared with the mirror 8c (t having a thickness of ts).
m> ts) can be connected to the middle of the mirror 1c in the thickness direction. That is, the spring 8 that supports the mirror 1c
The position of c can be set to any position in the thickness direction of the mirror 1c.

In the ion implantation step shown in FIG. 7, the spring is ion-implanted to a depth not less than the desired thickness, and then the region 71 for forming the spring is dug to a predetermined depth to form the spring. The thickness of the spring can be reduced to a desired thickness and the position of the spring can be adjusted.

[0065]

As described in detail above, according to the present invention, it is possible to form a mirror having a large thickness and a high rigidity, that is, a mirror having no warp while maintaining the mirror surface property of the mirror surface. The thickness of the spring that supports the mirror can be made thin with low rigidity. Therefore, an optical device with extremely low insertion loss can be obtained without scattering of the reflected optical signal.

Since the thickness of the mirror can be increased, it is easy to increase the diameter without causing warpage. For this reason, an optical device with a low insertion loss can be realized without causing so-called "eclipse" in which the inserted optical signal does not fully enter the mirror surface.

At the same time as the rigidity of the mirror is increased as described above, the spring thickness can be reduced to secure a spring with low rigidity. Therefore, the mirror can be rotationally driven at a large angle, and a large-scale optical device can be realized.
At that time, the voltage required for the electrostatic force can be reduced, and the system voltage can be reduced.
Furthermore, in order to position and fix the mirror at a certain fixed angle, attitude control technology is required. In this control as well, the rigidity of the spring is low, so accuracy and stability can be improved. it can.

As described above, the optical device of the present invention can satisfy the contradictory requirements of low insertion loss and large scale. In the optical device of the present invention, the flatness and smoothness of the mirror can be improved. An optical device that realizes low insertion loss, large scale, low voltage driving, and high accuracy can be obtained by sufficiently securing the spring rigidity and reducing the spring rigidity.

[Brief description of drawings]

FIG. 1 is a plan view showing an optical switch according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the same.

FIG. 3 is a diagram showing a method of manufacturing the optical switch according to the first embodiment of the present invention, in which (a) and (b) are a plan view and a sectional view, respectively.

FIG. 4 is also a diagram (step next to FIG. 3) showing the method of manufacturing the optical switch according to the first embodiment of the present invention,
(A), (b) is a top view and a sectional view, respectively.

FIG. 5 is also a diagram (step next to FIG. 4) showing the method of manufacturing the optical switch according to the first embodiment of the present invention,
(A), (b) is a top view and a sectional view, respectively.

FIG. 6 is a diagram (step next to FIG. 5) showing the method of manufacturing the optical switch according to the first embodiment of the present invention,
(A), (b) is a top view and a sectional view, respectively.

FIG. 7 is also a diagram (step next to FIG. 6) showing the method of manufacturing the optical switch according to the first embodiment of the present invention,
(A), (b) is a top view and a sectional view, respectively.

FIG. 8 is a diagram (step next to FIG. 7) showing the method of manufacturing the optical switch according to the first embodiment of the present invention,
(A), (b) is a top view and a sectional view, respectively.

FIG. 9 is also a diagram (step next to FIG. 8) showing the method of manufacturing the optical switch according to the first embodiment of the present invention,
(A), (b) is a top view and a sectional view, respectively.

FIG. 10 is also a diagram (step next to FIG. 9) showing the method of manufacturing the optical switch according to the first embodiment of the present invention,
(A), (b) is a top view and a sectional view, respectively.

11A to 11C are cross-sectional views showing a method of forming a pillar of this embodiment in the order of steps.

12A and 12B are respectively a plan view and a cross-sectional view showing the operation of this embodiment.

FIG. 13 is a diagram showing an application example of the optical switch of the present embodiment.

14A and 14B are cross-sectional views showing a method of manufacturing an optical switch according to a second embodiment of the present invention in the order of steps.

15A and 15B are respectively a plan view and a cross-sectional view showing a method of manufacturing an optical switch according to a third embodiment of the present invention.

FIG. 16 is a sectional view showing an optical switch according to a third embodiment of the present invention.

FIG. 17 is a plan view showing a conventional optical switch.

18 (a) and 18 (b) are a sectional view and a plan view showing another conventional optical switch.

FIG. 19 is a sectional view of the same.

[Explanation of symbols]

1, 1a, 1c: Mirror 2: Electrode pad 3: Electrode substrate 4: Electrode wiring 6: Support 7: Anchor 8a, 8b, 8c: spring 9: Frame

Claims (18)

[Claims] 1. An electrode substrate, an electrode pad formed on the electrode substrate, a movable mirror disposed above the electrode substrate with a gap between the electrode pad and the electrode substrate. And a plurality of springs that connect the movable mirror and the supporting portion to each other to support the movable mirror. The thickness tm of the movable mirror and the thickness ts of the spring are included. Is an tm> ts optical device. 2. The optical device according to claim 1, wherein the thickness tm of the movable mirror is 8 μm or more and the thickness ts of the support portion is 5 μm or less. 3. The optical device according to claim 1, wherein the mounting position of the spring with respect to the movable mirror is an intermediate position in the thickness direction of the movable mirror. 4. The optical device according to claim 1, wherein an insulating film is formed on the electrode substrate, and the electrode pad is formed on the insulating film. 5. A frame surrounding the movable mirror, wherein a part of the spring is arranged so as to connect between the supporting portion and the frame, and the remaining springs are formed between the frame and the mirror. The optical device according to claim 1, wherein the optical device is arranged so as to connect between them. 6. The optical device according to claim 1, wherein the electrode pads are arranged at four equal positions in a region on the electrode substrate which overlaps the movable mirror in a plan view. 7. A step of forming a plurality of electrode pads and electrode wirings connected to the electrode pads and providing columns on the electrode substrate, and a mirror on the surface of the mirror substrate on which an etching stopper layer is formed as an intermediate layer. And a step of forming an impurity region that reaches the etching stopper layer by ion-implanting into a region that becomes the contour and a region of the anchor, and a step of forming a thin impurity layer that does not reach the etching stopper layer by ion-implanting the entire surface. A step of patterning the plurality of springs connected to the mirror and the anchor by etching the impurity layer deeper than the impurity layer; and the mirror substrate and the electrode substrate, the pillar and the anchor. The step of adhering the mirror substrate by bonding, Wet etching using the pure material layer and the impurity region as a mask to selectively remove the mirror substrate and then remove the etching stopper layer to obtain a structure in which the movable mirror is supported by the spring and floats in the air. And, and the thickness of the movable mirror is t
m, where tm> ts, where m is the thickness of the spring and ts is the thickness of the spring. 8. The method of manufacturing an optical device according to claim 7, wherein in the step of forming the impurity region, ion implantation is performed after forming a groove in a portion which becomes a contour of the mirror. 9. The optical device according to claim 7, wherein in the step of forming the impurity layer, a region where the spring is to be formed is dug to thin the region, and then ion implantation is performed. Production method. 10. The method of manufacturing an optical device according to claim 7, wherein the electrode substrate is a silicon substrate on which an insulating film is formed. 11. The method of manufacturing an optical device according to claim 7, wherein the mirror substrate is an SOI (silicon on insulator) substrate, and the etching stopper layer is a silicon oxide film. 12. The impurity layer and the impurity region are
The method for manufacturing an optical device according to claim 11, which is formed by ion-implanting boron and then diffusing it. 13. The step of patterning the spring and the anchor, the anchor, a frame disposed around the movable mirror, a spring connecting the anchor and the frame, the frame and the movable. The method for manufacturing an optical device according to claim 7, wherein a spring connecting to the mirror is patterned. 14. The electrode substrate has a high step formed in a region where the pillar is to be formed, and after the pillar forming material is attached to the electrode substrate, the pillar forming material is cut along the contour of the step. The method of manufacturing an optical device according to claim 7, wherein the pillar is provided by the method. 15. The method of manufacturing an optical device according to claim 7, wherein the thickness ts of the spring is defined by the depth of the impurity layer. 16. The method of manufacturing an optical device according to claim 7, wherein the thickness tm of the movable mirror is defined by the depth of the impurity region. 17. The method of manufacturing an optical device according to claim 8, wherein the thickness tm of the movable mirror is defined by the sum of the depth of the impurity region and the depth of the groove. 18. The method of manufacturing an optical device according to claim 7, wherein the impurity layer and the impurity region are formed by ion implantation and diffusion of boron.