Optical device, method for manufacturing optical device, and optical scanner

An optical device includes a base made of silicon and including a movable portion provided with a light reflecting portion having light reflectivity and capable of oscillating around a oscillation axis, at least one connection portion that extends from the movable portion, and a support portion that supports the connection portion, and a stray light suppression layer provided on a surface of the base and having a function of suppressing light reflection. In a plan view in which the base is viewed in a thickness direction thereof, the stray light suppression layer is provided on portions other than an edge of the connection portion, an edge that connects an edge of the movable portion to the edge of the connection portion, and an edge that connects an edge of the support portion to the edge of the connection portion.

BACKGROUND

1. Technical Field

The present invention relates to an optical device, a method for manufacturing the optical device, and an optical scanner.

2. Related Art

There is a known optical device employing a structure including a torsional oscillator formed by processing a silicon substrate with the aid of MEMS (micro-electro-mechanical systems) technology (see JP-A-2005-107069, for example). The optical device is used as an optical scanner that deflects light in a printer, a display, or other apparatus.

For example, the optical scanner described in JP-A-2005-107069 includes a reflection mirror having a reflection surface that reflects light incident thereon and elastic beams connected to the reflection mirror. In the optical scanner, the reflection mirror oscillates when the beams deform.

In the optical scanner, when light is incident on the beams or portions other than the reflection surface of the reflection mirror, the light is reflected off the beams and the reflected light forms stray light, which degrades the quality of a resultant image.

To address the problem, for example, the optical scanner described in JP-A-2005-107069 has a non-reflection film made of nickel oxide provided on the entire surface of each of the beams on the side where the light reflection surface is present. The structure including the reflection mirror and the beams is formed by etching a silicon substrate.

When the structure is formed in a dry etching process, irregularities called scallops are disadvantageously formed on the side surfaces of the reflection mirror and the beams. On the other hand, when the structure is formed in a wet etching process, corners resulting from the silicon crystal plane are disadvantageously formed along the interface between the reflection mirror and the beams.

When such irregularities and corners are formed on the beams, stress concentration tends to occur when the reflection mirror oscillates, resulting in decrease in lifetime of the optical scanner. It is therefore necessary to planarize the irregular side surfaces and round the corners. To this end, it is effective to perform a thermal treatment using silicon surface diffusion motion.

This approach, however, involves the step of forming the non-reflection film and the step of planarizing the irregular side surfaces and rounding the corners to prevent stress concentration, disadvantageously resulting in increase in the number of steps and decrease in productivity.

SUMMARY

An advantage of some aspects of the invention is to provide an optical device, a method for manufacturing the optical device, an optical scanner, and an image formation apparatus that allow the lifetime of the optical device, the optical scanner, and the image formation apparatus to be prolonged relatively readily in a configuration in which a stray light prevention layer is provided over a base having an oscillatory system.

An optical device according to an aspect of the invention includes: a base made of silicon and including a movable portion provided with a light reflecting portion having light reflectivity and capable of oscillating around an oscillation axis, at least one connection portion that extends from the movable portion, and a support portion that supports the connection portion, and a stray light suppression layer provided on a surface of the base and having a function of suppressing light reflection, wherein in a plan view in which the base is viewed in a thickness direction thereof, the stray light suppression layer is provided on portions other than an edge of the connection portion, an edge that connects an edge of the movable portion to the edge of the connection portion, and an edge that connects an edge of the support portion to the edge of the connection portion.

According to the optical device described above, the side surface of the portion where the movable portion is connected to the connection portion, the side surface of the portion where the support portion is connected to the connection portion, and the side surface of the connection portion can be entirely planarized with the stray light suppression layer formed on the base. Further, the edge that connects the edge of the movable portion to the edge of the connection portion, the edge that connects the edge of the support portion to the edge of the connection portion, and the edge of the connection portion can be rounded at the same time in the planarization process. The planarization and the rounding prevent stress concentration from occurring at the connection portion and portions therearound when the movable portion oscillates or reduce the amount of the stress concentration. As a result, the lifetime of the optical device can be prolonged.

In the optical device according to the aspect of the invention, each of the edge of the connection portion, the edge that connects the edge of the movable portion to the edge of the connection portion, and the edge that connects the edge of the support portion to the edge of the connection portion preferably has an exposed surface made of the silicon.

The side surface of the portion where the movable portion is connected to the connection portion, the side surface of the portion where the support portion is connected to the connection portion, and the side surface of the connection portion can therefore be entirely planarized.

In the optical device described above according to the aspect of the invention, each of the edge of the connection portion, the edge that connects the edge of the movable portion to the edge of the connection portion, and the edge that connects the edge of the support portion to the edge of the connection portion is preferably planarized.

The planarization prevents stress concentration from occurring at the connection portion and portions therearound when the movable portion oscillates or reduces the amount of the stress concentration.

In the optical device according to the aspect of the invention, the stray light suppression layer preferably has a roughened surface.

The thus formed stray light suppression layer enhances its function of suppressing light reflection.

In the optical device described above according to the aspect of the invention, the stray light suppression layer is preferably provided on a surface of the base on the side where the light reflecting portion is provided.

The thus configured stray light suppression layer effectively prevents stray light from occurring.

In the optical device described above according to the aspect of the invention, in the plan view in which the base is viewed in the thickness direction thereof, the stray light suppression layer is preferably provided on the entire surface of the base other than the surface of the movable portion on which the light reflecting portion is provided, the edge of the connection portion, the edge that connects the edge of the movable portion to the edge of the connection portion, and the edge that connects the edge of the support portion to the edge of the connection portion.

The thus configured stray light suppression layer effectively prevents stray light from occurring.

In the optical device described above according to the aspect of the invention, the stray light suppression layer is preferably further provided on a surface of the base that faces away from the surface on which the light reflecting portion is provided.

The thus configured stray light suppression layer more effectively prevents stray light from occurring.

In the optical device according to the aspect of the invention, the stray light suppression layer is preferably formed of a silicon oxide film.

A silicon oxide film can be relatively readily formed by thermally oxidizing silicon. Further, when hydrogen annealing is performed as the planarization, minute irregularities can be formed on the surface of the stray light suppression layer. The irregular stray light suppression layer can suppress light reflection.

A method for manufacturing an optical device according to another aspect of the invention includes: forming an insulating layer on a surface of a silicon substrate, forming a base by etching the silicon substrate, the base including a movable portion capable of oscillating around an oscillation axis, at least one connection portion that extends from the movable portion, and a support portion that supports the connection portion, and performing planarization on the base to planarize a surface where the insulating layer is not formed and form irregularities on a surface of the insulating layer, wherein in the formation of the insulating layer, in a plan view in which the base is viewed in a thickness direction thereof, the insulating layer is formed on portions other than an edge of the connection portion, an edge that connects an edge of the movable portion to the edge of the connection portion, and an edge that connects an edge of the support portion to the edge of the connection portion.

According to the method for manufacturing an optical device described above, the side surface of the portion where the movable portion is connected to the connection portion, the side surface of the portion where the support portion is connected to the connection portion, and the side surface of the connection portion can be entirely planarized with the insulating layer formed on the base. Further, the edge that connects the edge of the movable portion to the edge of the connection portion, the edge that connects the edge of the support portion to the edge of the connection portion, and the edge of the connection portion can be rounded at the same time in the planarization process.

In the resultant optical device, the planarization and the rounding prevent stress concentration from occurring at the connection portion and portions therearound when the movable portion oscillates or reduce the amount of the stress concentration. As a result, the lifetime of the optical device can be prolonged.

In the method for manufacturing an optical device according to the aspect of the invention, the planarization is preferably hydrogen annealing or the hydrogen annealing followed by annealing in an Ar atmosphere.

In this way, the side surface of the portion where the movable portion is connected to the connection portion, the side surface of the portion where the support portion is connected to the connection portion, and the side surface of the connection portion can be planarized. Further, the edge that connects the edge of the movable portion to the edge of the connection portion, the edge that connects the edge of the support portion to the edge of the connection portion, and the edge of the connection portion can be rounded.

An optical scanner according to still another aspect of the invention includes: a base made of silicon and including a movable portion provided with a light reflecting portion having light reflectivity and capable of oscillating around an oscillation axis, at least one connection portion that extends from the movable portion, and a support portion that supports the connection portion, and a stray light suppression layer provided on a surface of the base and having a function of suppressing light reflection, wherein in a plan view in which the base is viewed in a thickness direction thereof, the stray light suppression layer is provided on portions other than an edge of the connection portion, an edge that connects an edge of the movable portion to the edge of the connection portion, and an edge that connects an edge of the support portion to the edge of the connection portion.

According to the optical scanner described above, the side surface of the portion where the movable portion is connected to the connection portion, the side surface of the portion where the support portion is connected to the connection portion, and the side surface of the connection portion can be entirely planarized with the stray light suppression layer formed on the base. Further, the edge that connects the edge of the movable portion to the edge of the connection portion, the edge that connects the edge of the support portion to the edge of the connection portion, and the edge of the connection portion can be rounded at the same time in the planarization process. The planarization and the rounding prevent stress concentration from occurring at the connection portion and portions therearound when the movable portion oscillates or reduce the amount of the stress concentration. As a result, the lifetime of the optical scanner can be prolonged.

An image formation apparatus according to yet another aspect of the invention includes: a light source that emits light, and an optical scanner that deflects the light from the light source, wherein the optical scanner includes a plate-shaped base made of silicon and including a light reflecting portion having light reflectivity, a movable portion provided with the light reflecting portion and capable of oscillating around an oscillation axis, at least one connection portion connected to the movable portion, and a support portion that supports the connection portion, and a stray light prevention layer provided on a surface of the base and having a function of suppressing light reflection, and in a plan view in which the base is viewed in a thickness direction thereof, the stray light suppression layer is provided on portions other than an edge of the connection portion, an edge that connects an edge of the movable portion to the edge of the connection portion, and an edge that connects an edge of the support portion to the edge of the connection portion.

According to the image formation apparatus described above, the planarization and the rounding prevent stress concentration from occurring at the connection portion and portions therearound when the movable portion oscillates or reduce the amount of the stress concentration. As a result, the lifetime of the optical scanner and hence the lifetime of the image formation apparatus can be prolonged.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

An optical device, a method for manufacturing the optical device, an optical scanner, and an image formation apparatus according to preferred embodiments of the invention will be described below with reference to the accompanying drawings. The following description will be made with reference to a case where the optical device according to the preferred embodiments of the invention is used as an optical scanner.

First Embodiment

An optical scanner according to a first embodiment of the invention will first be described.

FIG. 1is a plan view (top view) showing the optical scanner (optical device) according to the first embodiment of the invention.FIG. 2is a cross-sectional view taken along the line A-A shown inFIG. 1.FIG. 3is a plan view (bottom view) showing a base (a structure including a movable plate, a support portion, and a pair of elastic portions) provided in the optical scanner shown inFIG. 1.FIG. 4is a partial enlarged view of the base shown inFIG. 3.FIGS. 5A to 5Dand6A to6D are cross-sectional views describing a method for manufacturing the optical scanner shown inFIG. 1.FIG. 7shows a surface state after hydrogen annealing is performed on a silicon structure covered with a stray light prevention layer formed of a silicon oxide film. In the following sections, the upper side and the lower side inFIGS. 2,5A to5D, and6A to6D are referred to as “upper” and “lower,” respectively, for ease of description.

An optical scanner1includes a plate-shaped base2having an oscillatory system, a support3that supports the base2, and a driver4that oscillates the oscillatory system of the base2, as shown inFIG. 1.

The base2includes a movable plate (movable portion)21having a light reflecting portion211provided thereon, a pair of connection portions23and24connected to the movable plate21, and a support portion22that supports the pair of connection portions23and24. In other words, the support portion22supports the movable plate21via the connection portions23and24, and the pair of connection portions23and24connect the movable plate21and the support portion22to each other.

In the thus configured optical scanner1, the driver4produces a drive force that oscillates the movable plate21around a predetermined axis along the connection portions23and24while torsionally deforming the connection portions23and24. Light reflected off the light reflecting portion211is thus deflected along a predetermined direction.

The components that form the optical scanner1will be sequentially described below in detail.

The base2includes the movable plate21, on which the light reflecting portion211is provided, the support portion22, which supports the movable plate21, and the pair of connection portions23and24, which connect the movable plate21and the support portion22to each other, as described above.

The base2is made of silicon, and the movable plate21, the support portion22, and the connection portions23and24are formed integrally with each other. The base2is formed by etching a silicon substrate, as will be described later in detail, and a polygonal through hole25passing therethrough in the thickness direction is formed in the etching process. Since silicon is light and as rigid as SUS, the base2made of silicon has excellent oscillation characteristics. Further, since silicon can be etched with high dimensional precision, as will be described later, the base2formed of a silicon substrate can be processed into a desired shape (having desired oscillation characteristics). The silicon substrate is typically formed of a single crystal silicon substrate.

The base2will be further described below in detail.

The support portion22has a frame-like shape, as shown inFIG. 1. More specifically, the support portion22has an annular shape with an internal circumference along the outer circumference of the movable plate21and the side surfaces of each of the connection portions23and24. That is, the through hole25described above is so formed that the width thereof is minimized and uniform but large enough to permit the oscillating motion of the movable plate21and the torsional deformation of the connection portions23and24. The thus formed through hole25prevents unwanted light from passing therethrough from the upper side to the lower side of the base2or reduces the amount of the unwanted light. The thus formed support portion22supports the movable plate21via the pair of connection portions23and24. The shape of the support portion22is not limited to a specific one and may be any shape that can support the movable plate21via the pair of connection portions23and24. For example, the support portion22may be divided in correspondence with the connection portions23and24.

The movable plate21is disposed inside the support portion22.

The movable plate21has a plate-like shape. In the present embodiment, the movable plate21has a rectangular shape (square shape in the present embodiment) in the plan view. The shape of the movable plate21in the plan view is not limited to a rectangle and may, for example, be a pentagon, a hexagon, or any other polygonal shape, a circle, or an ellipse.

The light reflecting portion211having light reflectivity is provided on the upper surface of the movable plate21.

Each of the connection portions23and24has an elongated shape and is elastically deformable. The connection portion23and the connection portion24are disposed on opposite sides of the movable plate21. The connection portions23and24connect the movable plate21and the support portion22to each other in such a way that the movable plate21can oscillate relative to the support portion22. The pair of connection portions23and24are coaxially disposed along a oscillation axis X, and the movable plate21oscillates relative to the support portion22around the oscillation axis X.

Each of the connection portions23and24has a rectangular cross-sectional shape. In the present embodiment, each of the connection portions23and24has upper and lower surfaces parallel to each other along the surfaces of the base2and a pair of side surfaces parallel to each other and perpendicular to the upper and lower surfaces. The cross-sectional shape of each of the connection portions23and24is not limited to a rectangle and may alternatively be, for example, a trapezoid or a parallelogram. Each of the connection portions23and24may alternatively be formed of a plurality of beams parallel to each other.

In the thus configured base2, edges of the connection portions23and24and edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24(edges that connect the edges of the movable plate21and the support portion22to the edges of the connection portions23and24) are planarized. In the present embodiment, a wall surface251of the through hole25in the base2is entirely planarized.

Edges used herein refer to outer portions of a member in question and portions around the outer portions. In particular, in the present embodiment, the edges of the movable plate21, the support portion22, and the connection portions23and24correspond to the portions of the movable plate21, the support portion22, and the connection portions23and24that face the through hole25.

More specifically, the side surface212of the movable plate21is planarized, as shown inFIG. 2. Further, the corner213formed at each edge of the upper and lower surfaces of the movable plate21is rounded in the planarization process.

A pair of side surfaces231of the connection portion23and the side surface221of the support portion22are also planarized, as shown inFIG. 4.

Further, a pair of corners232formed in the vicinity of the boundaries between the side surface212of the movable plate21and the side surfaces231of the connection portion23and corners233formed in the vicinity of the boundaries between the side surfaces231of the connection portion23and the side surface221of the support portion22are rounded in the planarization process.

Although not shown, a pair of side surfaces of the connection portion24are planarized as well as the side surfaces231of the connection portion23. A pair of corners formed in the vicinity of the boundaries between the side surface212of the movable plate21and the side surfaces of the connection portion24and corners formed in the vicinity of the boundaries between the side surfaces of the connection portion24and the side surface221of the support portion22are also rounded in the planarization process, as in the case of the corners232and233.

The planarization prevents stress concentration from occurring at the pair of connection portions23and24when the torsional deformation of the connection portions23and24oscillates the movable plate21or reduces the amount of the stress concentration. As a result, the lifetime of the optical scanner1can be prolonged. The planarization will be described later in detail.

A stray light prevention layer (stray light suppression layer)61is provided on the upper surface (one surface) of the base2, and an insulating layer62is provided on the lower surface (the other surface) of the base2. A conductive pattern8formed of a coil41, wiring lines72and74, and electrodes73and75is provided on the surface of the insulating layer62that faces away from the base2. The coil41, the wiring lines72and74, and the electrodes73and75will be described in detail in association with the description of the driver4.

In particular, the stray light prevention layer61and the insulating layer62are provided on portions other than the following portions in a plan view in which the base2is viewed in a thickness direction thereof: the edges of the connection portions23and24, first connection edges214that connect the edge of the movable plate21to the edges of the connection portions23and24, and second connection edges222that connect the edge of the support portion22to the edges of the connection portions23and24. In other words, the stray light prevention layer61and the insulating layer62are provided on portions other than the edges of the connection portions23and24and edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24.

The configuration described above allows the side surfaces of the movable plate21, the support portion22, and the connection portions23and24to be entirely planarized relatively readily with the stray light prevention layer61and the insulating layer62formed on the base2, as will be described later. Further, the edges and corners of the movable plate21, the support portion22, and the connection portions23and24can be rounded at the same time in the planarization process.

The planarization prevents stress concentration from occurring at the connection portions23and24when the movable plate21oscillates or reduces the amount of the stress concentration. As a result, the lifetime of the optical scanner1can be prolonged.

More specifically, neither the stray light prevention layer61nor the insulating layer62is formed on the side surfaces of the movable plate21, the connection portions23and24, and the support portion22. As a result, each of the side surfaces of the movable plate21, the connection portions23and24, and the support portion22has substantially no insulating layer formed thereon but an exposed surface made of silicon.

Since the edges of the connection portions23and24and the edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24have exposed surfaces made of silicon, the side surfaces of the movable plate21, the support portion22, and the connection portions23and24can be entirely planarized.

The phrase “substantially no insulating layer formed” used herein conceptually means not only that no insulating layer is formed at all but also that a silicon oxide film formed in natural oxidation or any other similar insulating film is formed. More specifically, the average thickness of such an insulating film, if any, is smaller than 10 nm. On the other hand, each of the stray light prevention layer61, which is an insulating layer as will be described later, and the insulating layer62is not an ultra-thin insulating layer formed in natural oxidation but has a thickness of 10 nm or greater.

The stray light prevention layer61is so disposed that it covers the upper surface of the base2other than the upper surface of the movable plate21(that is, light reflecting portion211), the edges of the upper surfaces of the connection portions23and24, and the edge of the upper surface of the support portion22in the vicinity of the boundary between the support portion22and each of the connection portions23,24, as shown inFIG. 1. Each of the upper surface of the movable plate21(that is, light reflecting portion211), the edges of the upper surfaces of the connection portions23and24, and the edge of the upper surface of the support portion22in the vicinity of the boundary between the support portion22and each of the connection portions23,24therefore has substantially no insulating layer formed thereon but an exposed surface made of silicon.

That is, the stray light prevention layer61is so disposed that it covers substantially the entire area of the upper surface of the base2in the plan view of the base2except the upper surface of the movable plate21, the edges of the connection portions23and24, and the edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24. This configuration more effectively prevents stray light from occurring.

On the other hand, the insulating layer62is so disposed that it covers the lower surface of the base2other than the edge of the lower surface of the movable plate21, the edges of the lower surfaces of the connection portions23and24, and the edge of the lower surface of the support portion22in the vicinity of the boundary between the support portion22and each of the connection portions23,24, as shown inFIG. 3. Each of the edge of the lower surface of the movable plate21, the edges of the lower surfaces of the connection portions23and24, and the edge of the lower surface of the support portion22in the vicinity of the boundary between the support portion22and each of the connection portions23,24therefore has substantially no insulating layer formed thereon but has an exposed surface made of silicon.

That is, the insulating layer62is so disposed in the plan view of the base2that it covers substantially the entire area of the lower surface of the base2other than the edges of the connection portions23and24and the edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24. The components of the conductive pattern8can thus be reliably insulated from each other. Further, the insulating layer62has a stray light prevention capability, as will be described later, and the stray light prevention capability works well in this configuration.

Since neither the stray light prevention layer61nor the insulating layer62is formed on the side surfaces of the movable plate21, the connection portions23and24, the support portion22, as well as the upper and lower portions in the vicinity of the side surfaces, the side surfaces can be entirely planarized and the corners can be rounded by performing planarization with the stray light prevention layer61and the insulating layer62formed on the base2, as will be described later.

Each of the upper and lower portions in the vicinity of the side surfaces described above where no stray light prevention layer61or the insulating layer62is formed has a width (“a” shown inFIG. 3) that is not particularly limited to a specific value as long as the side surfaces can be planarized and the corners can be rounded but is approximately greater than or equal to 1 μm, preferably greater than or equal to 1 μm but smaller than or equal to 20 μm. When the width is too small, the side surfaces cannot be fully planarized or the corners cannot be fully rounded, whereas when the width is too large, the stray light prevention layer61and the insulating layer62tend to show a decrease in capability of preventing stray light depending on the configuration of the optical scanner1, conditions under which the optical scanner1is installed, and other factors.

The stray light prevention layer61has a function of preventing or suppressing light reflection. The stray light prevention layer61, which is provided on the surface of the base2on the side where the light reflecting portion211is provided, can effectively prevent stray light from occurring. In the present embodiment, the insulating layer62also has a function of preventing or suppressing light reflection. The insulating layer62, which also works as a stray light prevention layer and is provided on the surface of the base2that faces away from the light reflecting portion211, can further effectively prevent stray light from occurring. Each of the stray light prevention layer61and the insulating layer62forms an antireflection film that prevents light having entered the optical scanner from being reflected. The stray light prevention layer61and the insulating layer62also have a function of diffusing light. The stray light prevention layer61and the insulating layer62, which have the antireflection and light diffusion capabilities, prevent light other than the light reflected off the light reflecting portion211on the movable plate21from being reflected off portions other than the light reflecting portion211and forming stray light. That is, each of the stray light prevention layer61and the insulating layer62forms a stray light prevention layer that prevents stray light from occurring.

The surface of each of the stray light prevention layer61and the insulating layer62is roughened. That is, the surface of each of the stray light prevention layer61and the insulating layer62has minute irregularities formed of a plurality of recesses or protrusions arranged in an irregular pattern. The irregularities on the stray light prevention layer61and the insulating layer62prevent or suppress light reflection in an excellent manner.

Specific surface roughness Rz (JIS B 0601) of the stray light prevention layer61and the insulating layer62is not limited to a specific value but may be any value that roughly prevents stray light from occurring, for example, approximately greater than or equal to 20 nm but smaller than or equal to 50 nm.

Each of the stray light prevention layer61and the insulating layer62is formed, for example, of a silicon oxide film.

A silicon oxide film is insulative and can be relatively readily formed by thermally oxidizing silicon. When hydrogen annealing is performed as the planarization, minute irregularities can be formed on the surface of each of the stray light prevention layer61and the insulating layer62. The irregular stray light prevention layer61and insulating layer62prevent or suppress light reflection.

The insulating layer62, when not required to prevent stray light, may be formed of a silicon nitride film. A method for forming the stray light prevention layer61and the insulating layer62will be described in detail later in association with the description of a method for manufacturing the base2.

Each of the stray light prevention layer61and the insulating layer62is insulative, which prevents the coil41, the wiring lines72and74, and the electrodes73and75provided on the insulating layer62and forming the conductive pattern from being short-circuited.

The thickness of each of the stray light prevention layer61and the insulating layer62is not limited to a specific value and is approximately, for example, greater than or equal to 10 nm but smaller than or equal to 1500 nm.

The support3supports the base2described above. The support3also supports permanent magnets42and43, which form the driver4, which will be described later.

The support3has a box-like shape having a recess31open upward. In other words, the support3is formed of a plate-shaped portion32having a plate-like shape and a frame-shaped portion33having a frame-like shape and provided along the outer periphery of the upper surface of the plate-shaped portion32. The lower surface of the support portion22of the base2described above is bonded to the upper surface of the support3, which is the portion outside the recess31, that is, the upper surface of the frame-shaped portion33. A space that allows the movable plate21to oscillate is thus formed between the movable plate21/the pair of connection portions23,24of the base2and the support3.

The material of which the support3is made is not limited to a specific one and may, for example, be quartz glass, PYREX glass (“PYREX” is a registered trade mark), TEMPAX glass, or any other glass material; single crystal silicon, polysilicon, or any other silicon material; or LTCC (low-temperature cofire ceramic).

A method for bonding the base2to the support3, which is determined as appropriate in accordance with the material, the shape, and other factors of the support3, is not limited to a specific method and may be an adhesive-based method, anodic bonding, direct bonding, or any other suitable method.

Driver

The driver4, which includes the coil41and the pair of permanent magnets42and43, oscillates the movable plate21of the base2described above by electromagnetically driving the movable plate21(more specifically, based on a moving coil method). Electromagnetic driving can produce a large drive force. The driver4based on electromagnetic driving can therefore produce a large oscillating angle of the movable plate21while using a reduced drive voltage.

The coil41is disposed along the lower surface of the movable plate21via the insulating layer62, as shown inFIG. 2. Since the coil41is disposed on the insulating layer62disposed on the surface of the movable plate21that faces away from the light reflecting portion211, the conductive pattern8can be formed by making effective use of the surface of the base2that faces away from the light reflecting portion211. The light reflecting portion211can be designed with a full degree of freedom at the same time.

In the present embodiment, the coil41has a spiral shape along the surface of the movable plate21, as shown inFIG. 3. The spiral coil41produces a larger magnetic force than a simple annular coil and is more simply configured and more readily manufactured than a coil formed by stacking wires in the thickness direction of the movable plate21. That is, the coil41produces a large magnetic force while being configured relatively simply and driven with a reduced voltage.

An end of an elemental wire that forms the coil41(the end of the outermost line of the spiral) is electrically connected to the electrode73via the wiring line72. The other end of the elemental wire that forms the coil41(the end close to the center of the spiral) is electrically connected to the electrode75via the wiring line74. The coil41can be energized by applying voltage between the electrode73and the electrode75thus connected thereto.

The wiring line72is disposed on the lower surface of the connection portion23along the longitudinal direction thereof, and the wiring line74is disposed on the lower surface of the connection portion24along the longitudinal direction thereof.

The electrodes73and74are disposed on the lower surface of the support portion22.

The wiring line74extends to the vicinity of the center of the movable plate21, and an insulating layer63formed, for example, of a silicon oxide film or a silicon nitride film is provided between the wiring line74and the coil41.

The other end of the elemental wire that forms the coil41(the end close to the center of the spiral) may alternatively be connected to the wiring line74via a bonding wire.

The material of which the coil41, the wiring lines72and74, and the electrodes73and75, which form the conductive pattern8, are made is not limited to a specific one and may be any material that is conductive and resistant to heat generated in the planarization process in a method for manufacturing the base2, which will be described later, for example, Pt, Ir, Os, Re, W, Ta, Ru, Tc, Mo, and Nb, preferably Ta among others. Ta has relatively excellent conductivity and an extremely high melting point. These properties make Ta suitable for a conductor and resistant to heat generated in hydrogen annealing or any other heat treatment used in the planarization process. On the other hand, the pair of permanent magnets42and43are bonded and fixed to the support3.

The permanent magnet42is disposed on one side (left side inFIGS. 1 and 2) of the oscillation axis X of the movable plate21, and the permanent magnet43is disposed on the other side (right side inFIGS. 1 and 2) of the oscillation axis X of the movable plate21. The pair of permanent magnets42and43are disposed on opposite sides of the movable plate21.

The permanent magnet42is so disposed that the north pole thereof faces the movable plate21and the south pole thereof faces away from the movable plate21. On the other hand, the permanent magnet43is so disposed that the south pole thereof faces the movable plate21and the north pole thereof faces away from the movable plate21. The pair of permanent magnets42and43produces a magnetic field in the vicinity of the movable plate21, and the magnetic field is parallel to the surfaces of the movable plate21that is not in oscillating motion and perpendicular to the oscillation axis X of the movable plate21.

Each of the permanent magnets42and43is not limited to a specific one and can, for example, preferably be a neodymium magnet, a ferrite magnet, a samarium-cobalt magnet, an alnico magnet, a bonded magnet, and any other magnet magnetized with a hard magnetic material.

The number, layout, polarity, and other properties of the permanent magnets are not limited to those shown in the drawings and may, of course, be any number, layout, and polarity that allow the movable plate21to oscillate based on the interaction with the magnetic field produced by the coil41.

The thus configured optical scanner1operates as follows. Periodically changing voltage (such as AC voltage, intermittent current) is applied between the electrode73and the electrode75. The applied voltage alternately and periodically switches the magnetic field between a first magnetic field produced when the upper side of the coil41is the north pole and the lower side of the coil41is the south pole and a second magnetic field produced when the upper side of the coil41is the south pole and the lower side of the coil41is the north pole.

When the first magnetic field is produced, the upper side of the coil41is attracted to the permanent magnet42, whereas the lower side of the coil41is attracted to the permanent magnet43, whereby the movable plate21oscillates around the oscillation axis X clockwise inFIG. 2(first state). Conversely, when the second magnetic field is produced, the upper side of the coil41is attracted to the permanent magnet43, whereas the lower side of the coil41is attracted to the permanent magnet42, whereby the movable plate21oscillates around the oscillation axis X counterclockwise inFIG. 2(second state). The first and second states are alternately repeated, and the movable plate21oscillates around the oscillation axis X.

As described above, the movable plate21, which is disposed in the magnetic field produced by the pair of permanent magnets42and43, pivots (oscillates) relative to the support portion22while torsionally deforming the connection portions23and24.

According to the thus configured optical scanner1, since the stray light prevention layer61and the insulating layer62are provided on portions other than the edges of the connection portions23and24, the edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24, the side surfaces of the movable plate21, the support portion22, and the connection portions23and24can be entirely planarized relatively readily with the stray light prevention layer61and the insulating layer62formed on the base2. Further, the edges and corners of the movable plate21, the support portion22, and the connection portions23and24can be rounded at the same time in the planarization process. The planarization and the rounding prevent stress concentration from occurring at the connection portions23and24when the movable plate21oscillates or reduce the amount of the stress concentration. As a result, the lifetime of the optical scanner1can be prolonged.

Method for Manufacturing Optical Device

The optical scanner1described above can be manufactured, for example, as follows: As an example of a method for manufacturing an optical device according to an embodiment of the invention, a method for manufacturing the optical scanner1will be described with reference toFIGS. 5A to 5Dand6A to6D.FIGS. 5A to 5Dand6A to6D are cross-sectional views corresponding toFIG. 2.

The method for manufacturing the optical scanner1includes the step of forming the base2.

The step of forming the base2includes [A] the step of forming the stray light prevention layer61and the insulating layer62, [B] the step of forming the conductive pattern8, and [C] the step of forming the base2.

Each of the steps will be sequentially described below in detail.

[A] Step of Forming Stray Light Prevention Layer61and Insulating Layer62

A silicon substrate102is first provided, as shown inFIG. 5A.

The silicon substrate102will form the base2after undergoing etching and planarization, which will be described later.

An insulating layer161is then uniformly formed on the upper surface of the silicon substrate102, and an insulating layer162is uniformly formed on the lower surface of the silicon substrate102, as shown inFIG. 5B.

Each of the insulating layers161and162is formed of a silicon oxide film.

A method for forming the insulating layers161and162is not limited to a specific one, and thermal oxidation can, for example, be used.

The stray light prevention layer61and the insulating layer62are then formed by removing part of the insulating layers161and162, as shown inFIG. 5C.

More specifically, a resist film (not shown) is first formed on each of the insulating layers161and162. The resist film can be made of a positive or negative resist material.

One of the resist films is then exposed to light and developed to form a mask having the shape corresponding to the stray light prevention layer61in the plan view, and the other resist film is similarly processed to form a mask having the shape corresponding to the insulating layer62in the plan view. The masks are used to etch away part of the insulating layers161and162, and then the masks (resist films) are removed.

The etching described above is not limited to a specific one and may, for example, be reactive ion etching (RIE) or dry etching using CF4.

A method for removing the masks (resist films) is not limited to a specific one and may, for example, be sulfuric-acid washing or O2ashing.

[B] Step of Forming Conductive Pattern8

The conductive pattern8including the coil41is then formed on the insulating layer62, as shown inFIG. 5D. The insulating layer63is also formed.

More specifically, for example, the coil41and the wiring line72, and the electrode73are formed together. After the insulating layer63is formed, the wiring line74and the electrode75are formed together.

A method for forming the conductive pattern8(coil41, wiring lines72and74, and electrodes73and75) is not limited to a specific one and may, for example, be vacuum evaporation, sputtering (low-temperature sputtering), ion plating or any other dry plating; electrolysis plating, electroless plating, or any other wet plating; flame spraying; or metal foil bonding. A method for forming the insulating layer63is not limited to a specific one and may, for example, be plasma CVD, LPCVD, or any other vapor deposition.

[C] Step of Forming Base2

A mask200having the shape corresponding to the base2in the plan view is then formed on the insulating layer62, as shown inFIG. 6A.

More specifically, a resist film (not shown) is formed on the insulating layer62. The resist film can be made of a positive or negative resist material.

The resist film is then exposed to light and developed to form a mask200having the shape corresponding to the base2in the plan view.

The mask200may alternatively be formed on the stray light prevention layer61or on each of the stray light prevention layer61and the insulating layer62.

The silicon substrate102with the mask200formed thereon then undergoes dry etching to form a base102A having the shape corresponding to the base2, as shown inFIG. 6B.

A through hole125passing through the base102A in the thickness direction thereof is formed in the dry etching process. Minute irregularities are also formed in the dry etching process on the wall surface of the through hole125. The through hole125undergoes planarization, which will be described later, to form the through hole25.

The dry etching used to form the through hole125is not limited to a specific one and may, for example, be plasma etching, reactive ion etching, beam etching, or light-assisted etching. The method for forming the through hole125may alternatively be wet etching using, for example, a KOH aqueous solution. In this case, the mask200may be formed also on the upper surface of the base102.

The mask200is then removed. The stray light prevention layer61and the insulating layer62are thus exposed, as shown inFIG. 6C.

A method for removing the mask200(resist film) is not limited to a specific one and may, for example, be sulfuric-acid washing or O2ashing.

The base102A then undergoes planarization, by which the base2is provided, as shown inFIG. 6D.

At this point, the wall surface of the through hole125and the portions of the upper and lower surfaces of the base102A that are in the vicinity of the open ends of the through hole125and are not covered with the stray light prevention layer61or the insulating layer62are exposed.

The wall surface of the through hole125is therefore planarized, and corners present on the wall surface of the through hole125, that is, a portion in the vicinity of the boundary between the side surface of the movable plate21and the side surface of each of the connection portions23and24and a portion in the vicinity of the boundary between the side surface of the support portion22and the side surface of each of the connection portions23and24, are rounded.

Further, the upper and lower surfaces of the base102A that are in the vicinity of the open ends of the through hole125and are not covered with the stray light prevention layer61or the insulating layer62are also rounded.

The planarization method is not limited to a specific one and can, for example, preferably be a heat treatment (more specifically, hydrogen annealing performed in an H2-introduced Ar atmosphere (the proportion of H2is 2% or higher) at a temperature ranging from about 900 to 1300° C. under the atmospheric pressure or a lower pressure by a few torrs or the hydrogen annealing continuously followed by annealing performed at a temperature ranging from about 900 to 1300° C. under about the atmospheric pressure after the atmosphere is switched to an Ar atmosphere). In this way, the side surfaces of the movable plate21, the support portion22, and the connection portions23and24can be planarized, and the edges and corners of the movable plate21, the support portion22, and the connection portions23and24can be rounded.

When hydrogen annealing is performed as the planarization, minute irregularities are formed at the same time on the surfaces of the stray light prevention layer61and the insulating layer62, each of which is formed of a silicon oxide film, as shown inFIG. 7.

Although not shown, the support3is then bonded to the base2, and the pair of permanent magnets42and43are placed. The optical scanner1is thus produced by carrying out the steps described above.

According to the method for manufacturing the optical scanner1described above, in the step of forming the stray light prevention layer61and the insulating layer62, the stray light prevention layer61and the insulating layer62are formed on portions other than the edges of the connection portions23and24and the edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24in the plan view of the base2, which will be formed. As a result, the side surfaces of the movable plate21, the support portion22, and the connection portions23and24can be entirely planarized relatively readily with the stray light prevention layer61and the insulating layer62formed on the base102A. Further, the edges and corners of the movable plate21, the support portion22, and the connection portions23and24can be rounded at the same time in the planarization process. In the resultant optical scanner1, stress concentration will not occur at the connection portions23and24when the movable plate21oscillates, or the amount of the stress concentration can be reduced. As a result, the lifetime of the optical scanner1can be prolonged.

Second Embodiment

A second embodiment of the invention will next be described.FIG. 8is a cross-sectional view showing an optical scanner according to the second embodiment of the invention, andFIG. 9is a plan view (bottom view) of a base (a structure including a movable plate, a support portion, and a pair of elastic portions) provided in the optical scanner shown inFIG. 8. The optical scanner according to the second embodiment will be described below, primarily about what differs from the optical scanner according to the embodiment described above, and no description of similar items will be made.

The optical scanner according to the second embodiment is substantially the same as the optical scanner1according to the first embodiment but differs therefrom in terms of the shape of the insulating layer provided on the lower surface of the base2. The same components as those in the embodiment described above have the same reference characters.

An optical scanner1A according to the present embodiment includes an insulating layer62A provided on the lower surface of the base2, as shown inFIGS. 8 and 9. The coil41, the wiring lines72and74, and the electrodes73and75are provided along the base2with the insulating layer62A therebetween. The insulating layer62A has the same shape as that of the conductive pattern8formed of the coil41, the wiring lines72and74, and the electrodes73and75. That is, the insulating layer62A is formed only immediately below the conductive pattern8.

The planarization can be performed in the same manner as in the first embodiment described above with the thus shaped insulating layer62A formed on the lower surface of the base2.

When the insulating layer62A has the same shape as that of the conductive pattern8, the insulating layer62A can be patterned in an etching process using the conductive pattern8as a mask.

In the present embodiment, the insulating layer62A, which is covered with the conductive pattern8, does not have a function of preventing stray light from occurring, but the through hole25described above is so formed that the width thereof is minimized and uniform but large enough to permit the oscillating motion of the movable plate21and the torsional deformation of the connection portions23and24, whereby unwanted light will not pass through the through hole25from the upper side to the lower side of the base2, or the amount of the unwanted light is reduced.

In the optical scanner1A according to the second embodiment described above, in which the stray light prevention layer61and the insulating layer62A are provided on portions other than the edges of the connection portions23and24and the edges of the movable plate21and the support portion22in the vicinity of the connection portions23and24, the side surfaces of the movable plate21, the support portion22, and the connection portions23and24can be entirely planarized relatively readily with the stray light prevention layer61and the insulating layer62A formed on the base2. Further, the edges and corners of the movable plate21, the support portion22, and the connection portions23and24can be rounded at the same time in the planarization process.

The planarization and the rounding prevent stress concentration from occurring at the connection portions23and24when the movable plate21oscillates or reduce the amount of the stress concentration. As a result, the lifetime of the optical scanner1A can be prolonged.

The optical scanners described above can suitably be used with a projector, a laser printer, an imaging display, a barcode reader, a scanning confocal microscope, and other image formation apparatus. Such an image formation apparatus therefore has excellent image drawing characteristics.

Since such an image formation apparatus includes the optical scanner1or1A described above, the lifetime of the image formation apparatus can be prolonged.

Image Formation Apparatus

Image formation apparatus according to embodiments of the invention will be described.

Projector

FIG. 10is a schematic view showing an image formation apparatus (projector) according to an embodiment of the invention. In the following description, the longitudinal direction of a screen Sc is called a “horizontal direction,” and the direction perpendicular to the longitudinal direction is called a “vertical direction,” for ease of description.

A projector9shown inFIG. 10includes a light source91that emits light, such as laser light, a cross-dichroic prism92, a pair of optical scanners93and94according to any of the embodiments of the invention (optical scanner configured in the same manner as the optical scanner1, for example), and a fixed mirror95.

The light source91includes a red light source911that emits red light, a blue light source912that emits blue light, and a green light source913that emits green light.

The cross-dichroic prism92is an optical element formed by bonding four right-angle prisms and combines light fluxes emitted from the red light source911, the blue light source912, and the green light source913.

In the thus configured projector9, the cross-dichroic prism92combines the light fluxes emitted from the red light source911, the blue light source912, and the green light source913based on image information from a host computer (not shown), and the combined light is deflected by the optical scanners93and94, reflected off the fixed mirror95, and forms a color image on the screen Sc.

How the optical scanners93and94deflect light will be specifically described.

The light combined in the cross-dichroic prism92is first deflected by the optical scanner93in the horizontal direction (primary scan). The light deflected in the horizontal direction is then further deflected by the optical scanner94in the vertical direction (secondary scan). A two-dimensional color image can thus be formed on the screen Sc. Using the optical scanner according to any of the embodiments of the invention as each of the optical scanners93and94provides an extremely excellent image drawing characteristic.

It is noted that the projector9is not necessarily configured as described above but can be configured differently as long as the optical scanners deflect light to form an image on an intended surface. For example, the fixed mirror95can be omitted.

According to the thus configured projector9, which includes the optical scanners93and94, each of which has the same configuration as that of the optical scanner1described above, a high-quality image can be produced at low cost.

FIG. 11is a schematic view showing an image formation apparatus (head-up display) according to another embodiment of the invention. In the following description, the same components as those in the projector9described above will not be described.

A head-up display9A shown inFIG. 11is an apparatus that projects a variety of pieces of information on a windshield SC1in a mobile vehicle, such as an automobile and an airplane.

The head-up display9A includes the red light source911, the blue light source912, the green light source913, the cross-dichroic prism92, the pair of optical scanners93and94according to any of the embodiments of the invention, and a fixed mirror95A.

The fixed mirror95A is a concave mirror and projects the light from the optical scanner94onto the windshield SC1. An operator of the mobile vehicle can view a displayed image that is a virtual image in an imaginary plane SC2positioned in front of the windshield SC1.

An optical device, a method for manufacturing the optical device, an optical scanner, and an image formation apparatus according to embodiments of the invention have been described with reference to the drawings, but the invention is not limited to the embodiments. For example, in each of the optical device, the optical scanner, and the image formation apparatus according to the embodiments of the invention, the configuration of each component can be replaced with an arbitrary configuration that provides the same function as that provided in the component described above and an arbitrary configuration can be added thereto. In the method for manufacturing the optical device according to the any of the embodiments of the invention, an arbitrary step can be added. The above embodiments have been described with reference to the case where the movable plate has a symmetrical shape with respect to at least one of the oscillation axis and a line perpendicular thereto in the plan view, but the movable plate is not necessarily shaped this way. The movable plate may have an asymmetrical shape with respect to the oscillation axis and a line perpendicular thereto in the plan view.

Further, the above embodiments have been described with reference to the case where a pair of connection portions that pivotally connect the movable plate to the support portion are provided. The number of connection portions may alternatively be one or three or more as long as the connection portions pivotally connect the movable plate to the support portion. The above embodiments have been described with reference to the case where the optical device according to any of the embodiments of the invention is used as an optical scanner, but the optical device according to any of the embodiments of the invention is not necessarily used as an optical scanner. For example, the optical device according to any of the embodiments of the invention can be used as an optical switch, an optical attenuator, or other optical devices.

The above embodiments have been described with reference to the case where the driver that oscillates the movable plate is a moving coil driver that electromagnetically drives the movable plate. The driver may alternatively be a moving magnet driver that also electromagnetically drives the movable plate, or an electrostatic driver, a piezoelectric driver, or any other driver based on a non-electromagnetic driving method. The above embodiments have been described with reference to the case where the conductive pattern provided along the base via an insulating layer includes a coil. The conductive pattern is not necessarily configured this way but may be configured differently as long as electric conduction is achieved. For example, the conductive pattern may include wiring lines for conducting current to a variety of drive sources or wiring lines connected to a variety of sensors. The position and the area where the stray light prevention layer is formed and the size, the shape, and other factors thereof are determined in accordance with the shape, the size, the installation conditions, and other factors of the optical device and hence are not limited to those described in the embodiments described above as long as the stray light prevention layer is provided on portions other than the edges of the connection portions and the edges of the movable plate and the support portion in the vicinity of the connection portions in the plan view of the base. For example, the stray light prevention layer may not be provided on the support portion or over the connection portions entirely in the longitudinal direction thereof. Further, the stray light prevention layer may be formed on part of the movable plate on the side where the light reflecting portion is provided. The entire disclosure of Japanese Patent Application No. 2011-058557, filed Mar. 16, 2011 is expressly incorporated by reference herein.