Method of making microstructure device, and microstructure device made by the same

A microstructure device is made by processing a material substrate consisting of e.g. a first process layer, a second process layer and a middle layer arranged between the first and the second process layers. The microstructure device includes a first structural part and a second structural part that has a portion facing the first structural part via a gap. The first and the second structural parts are connected to each other by a connecting part extending across the gap. This connecting part is formed in the first process layer to be in contact with the middle layer. The microstructure device also includes a protective part extending from the first structural part toward the second structural part or vice versa. The protective part is formed in the first or second process layer to be in contact with the middle layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to microstructure devices such as micromirror elements, acceleration sensors, angular-speed sensors and vibration elements made by micromachining technology.

2. Description of the Related Art

In recent years, microstructure devices manufactured by means of micromachining technology are gathering attention, and efforts are being made for making practical application of element devices which have a micro-structure. Microstructure devices include micromirror elements, acceleration sensors, angular-speed sensors and other micro moving devices which have tiny moving parts or vibrating parts therein. Micromirror elements are used in the field of optical disc technology and optical communications technology for example, as a light reflection device. Acceleration sensors and angular-speed sensors find areas of application in the field of attitude control of robots, correction of camera shake, and so on. These micro moving devices generally include a fixed structural part, a moving part relatively displaceable with respect to the fixed structural part, and a connecting part which connects the fixed structural part and the moving part each other. Microstructures as described are disclosed in the following Patent Documents 1 through 3 for example:Patent Document 1: JP-A-2003-19700Patent Document 2: JP-A-2004-341364Patent Document 3: JP-A-2006-72252

FIG. 35andFIG. 36show a conventional microstructure device80as an example.FIG. 35is a plan view of the microstructure device80whereasFIG. 36is a sectional view taken in lines XXXVI-XXXVI inFIG. 35.

The microstructure device80includes a first structural part81, a second structural part82and a connecting part83which connects the first structural part81and the second structural part82with each other. When the microstructure device80of such a principal structure serves as a micro moving device, the first structural part81represents the moving part, the second structural part82represents the fixed structural part, and the moving part and the fixed structural part are connected with each other by the connecting part83.

FIG. 37andFIG. 38show a process of forming the microstructure device80.FIG. 37andFIG. 38show a section in a series to illustrate how the first structural part81, the second structural part82and the connecting part83are formed. The section featured in the figures is a conceptual composite collected from a plurality of fragmentary sections of a row material substrate (wafer) to which a series of manufacturing operations are made.

In the manufacture of the microstructure device80, first, a material substrate90as shown inFIG. 37(a) is prepared. The material substrate90is an SOI (Silicon on Insulator) wafer, and has a laminated structure including a silicon layer91, a silicon layer92and an insulation layer93between the silicon layers. The insulation layer93has a thickness of about 1 μm.

Next, as shown inFIG. 37(b), anisotropic dry etching is performed to the silicon layer91via a predetermined mask, to form structures to be built on the silicon layer91(i.e. the first structural part81, part of the second structural part82, and the connecting part83). In this step, a predetermined etching apparatus equipped with a vacuum chamber is used to perform the dry etching in the vacuum chamber under predetermined vacuum conditions.

Next, as shown inFIG. 37(c) andFIG. 37(d), a sub-carrier94is bonded onto the silicon layer91side of the material substrate90via the bonding member95. The bonding member95is provided by resist, grease or sealant for example. In this step, the material substrate90and the sub-carrier94are bonded together under heat and pressure. A purpose of bonding the sub-carrier94in such a way is to prevent damage to the material substrate90and to the etching apparatus in the next manufacturing step. In the next manufacturing step, etching is performed to the silicon layer92in the vacuum chamber of the etching apparatus. In this process, mechanical strength of the material substrate90decreases substantially because of the etching performed to the silicon layer92, with the silicon layer91having already been etched. The sub-carrier94serves as a reinforcing member for the material substrate90, and prevents the material substrate90from breaking. If the material substrate90breaks in the vacuum chamber, broken pieces can damage the etching apparatus. Therefore, damage prevention of the material substrate90by the sub-carrier94also contributes to damage prevention of the apparatus.

In the manufacture of the microstructure device80, next, as shown inFIG. 38(a), anisotropic dry etching is performed to the silicon layer92via a predetermined mask, to form a structure to be built on the silicon layer92(i.e. part of the second structural part82). Like the step described above with reference toFIG. 37(b), this step also employs a predetermined etching apparatus equipped with a vacuum chamber to perform the dry etching in the vacuum chamber under predetermined vacuum conditions.

Next, as shown inFIG. 38(b), the material substrate90is separated from the sub-carrier94. This step is performed outside of the vacuum chamber of the etching apparatus. Thereafter, as shown inFIG. 38(c), the insulation layer93is subjected to isotropic etching in order to remove exposed portions of the insulation layer93. Through the above-described process, the microstructure device80is completed.

However, in the process of making the microstructure device80, the connecting part83is likely to be broken after the step described with reference toFIG. 38(a).

In the step described with reference toFIG. 37(b), the silicon layer91is partially etched off, exposing part of the insulation layer93in the silicon layer91. Then, as the step inFIG. 38(a) proceeds or finishes, the insulation layer93is also exposed in the silicon layer92, with portions S (double-side exposed portions) of the insulation layer93which are bonded neither to the silicon layer91nor to the silicon layer92. The insulation layer93is substantially thin and the portions S are brittle enough to fracture easily.

During the step inFIG. 38(a) which is performed in the vacuum chamber, and until the separation thereafter of the material substrate90from the sub-carrier94as shown inFIG. 38(b) outside the vacuum chamber, a constant pressure (e.g. a predetermined level of vacuum) is maintained on the surface of the insulation layer93exposed in the silicon layer91. On the contrary, the surface of the insulation layer93exposed in the silicon layer92is subject to pressure changes: During the step inFIG. 38(a), the surface is under a constant level of vacuum which is set for and maintained in the vacuum chamber, but the surface comes under a normal atmospheric pressure after the vacuum in the vacuum chamber is broken. As a result, the two surfaces of the portions S in the insulation layer93are pressed by substantially different pressures at least in one of the two occasions i.e. during the step inFIG. 38(a) and for a certain period of time thereafter. The substantial pressure difference can be a cause of the fracture in the portions S.

There is another cause if the bonding member95is formed of a volatile material. Under the bond between the material substrate90and the sub-carrier94inFIG. 38(a), spaces in the silicon layer91backed by the insulation layer93is filled with gas as the bonding member95evaporates, and as the pressure increases in the spaces, risk of fracture increases for the insulation layer93, i.e. the portions S.

The fracture occurs anywhere in the portions S (double-side exposed portion) of the insulation layer93. For example, once a fracture Z occurs as shown inFIG. 39(a), the fracture Z often extends as shown inFIG. 39(b) for example, within the portion S, and then further in the insulation layer93, crossing the area of connection with the connecting part83. When the fracture Z crosses the area of the insulation layer93connected with the connecting part83, an impact acts upon the connecting part83, destroying the connecting part83.

As described, the conventional technique is faced by challenges in manufacturing microstructure devices which include the first structural part, the second structural part and the connecting part connecting the first and the second structural part.

SUMMARY OF THE INVENTION

The present invention has been proposed under the above-described circumstances, and it is therefore an object of the present invention to provide a method suitable for manufacturing a microstructure device which includes the first structural part, the second structural part and the connecting part connecting the first and the second structural parts, as well as to provide the microstructure device made thereby.

A first aspect of the present invention provides a method of making a microstructure device including a first structural part, a second structural part having a portion opposed to the first structural part, and a connecting part connecting the first and the second structural parts, from a material substrate having a laminated structure including a first process layer, a second process layer and a middle layer between the first process layer and the second process layer. The method includes a first processing step and a second processing step. In the first processing step, etching is performed to the first process layer whereby formation is made for: a first-structural-part component and a second-structural-part component opposed to each other via a separation gap where the middle layer makes partial exposure; a connecting part connecting the first and the second-structural-part components with each other across the separation gap while being in contact with the middle layer; and a protective part extending from the first-structural-part component or the second-structural-part component into the separation gap while being in contact with the middle layer. In the second processing step, etching is performed to the second process layer whereby at least a portion of the middle layer exposed to the separation gap on the first process layer side, and a portion of the middle layer contacted by the connecting part are exposed to the second process layer side. In the present invention, the first-structural-part component is a portion constituting at least part of the first structural part whereas the second-structural-part component is a portion constituting at least part of the second structural part.

According to the first processing step in the present method, as described above, a protective part which extends from the first-structural-part component or the second-structural-part component into the separation gap while being in contact with the middle layer is formed in the first process layer, along with the connecting part which connects the first and the second-structural-part components across the separation gap while being in contact with the middle layer. As a result, breakage of the connecting part which is in contact with the middle layer is reduced under a circumstance resulted from the second processing step where the middle layer is formed with a portion (double-side exposed portion) which is exposed both to the separation gap on the first process layer side and to the second process layer side. If a fracture occurs locally anywhere in the double-side exposed portion of the middle layer, presence of the protective part which is in contact with the middle layer may successfully prevent the fracture from spreading. As a growing fracture runs across an area of the middle layer contacted by the protective part extended into the separation, an impact reaches the protective part, and the protective part absorbs at least part of the energy necessary for the fracture to grow further. With the presence of the protective part which can provide the above-described function, breakage probability of the connecting part which crosses the separation gap while being in contact with the middle layer is decreased. The breakage probability of the connecting part tends to decrease if the protective part is closer to the connecting part. Also, the breakage probability of the connecting part tends to decrease with increase in the number of protective parts provided. As described, the present method decreases breakage probability of the connecting part. Therefore, the present method is suitable for manufacturing microstructure devices which include a connecting part that connects the first structural part and the second structural part.

A second aspect of the present invention provides a method of making a microstructure device including a first structural part, a second structural part having a portion opposed to the first structural part, and a connecting part connecting the first and the second structural parts, from a material substrate having a laminated structure including a first process layer, a second process layer and a middle layer between the first process layer and the second process layer. The method includes a first processing step and a second processing step. In the first processing step, etching is performed to the first process layer whereby formation is made for: a first-structural-part component and a second-structural-part component opposed to each other via a separation gap where the middle layer makes partial exposure; a connecting part connecting the first and the second-structural-part components with each other across the separation gap while being in contact with the middle layer; a first protective part extending from the first-structural-part component into the separation gap while being in contact with the middle layer; and a second protective part extending from the second-structural-part component into the separation gap while being in contact with the middle layer. In the second processing step, etching is performed to the second process layer whereby at least a portion of the middle layer exposed to the separation gap on the first process layer side, and a portion of the middle layer contacted by the connecting part are exposed to the second process layer side.

According to the first processing step in the present method, as described above, formation is made in the first process layer for: a first protective part which extends from the first-structural-part component into the separation gap while being in contact with the middle layer; and a second protective part which extends from the second-structural-part component into the separation gap while being in contact with the middle layer; along with the connecting part which connects the first and the second-structural-part components across the separation gap while being in contact with the middle layer. As a result, breakage of the connecting part which is in contact with the middle layer is reduced under a circumstance resulted from the second processing step where the middle layer is formed with a portion (double-side exposed portion) which is exposed both to the separation gap on the first process layer side and to the second process layer side. Like in the method according to the first aspect of the present invention described earlier, here again, presence of the protective parts decreases breakage probability of the connecting part in the present method according to the second aspect of the present invention. Therefore, the present method is also suitable for manufacturing microstructure devices which include a connecting part that connects the first structural part and the second structural part.

According to the first and the second aspects of the present invention, the second processing step may also expose a portion of the middle layer contacted by the protective part in the first process layer, to the second process layer side.

According to a preferred embodiment of the first and the second aspects of the present invention, the second processing step includes further formation in the second process layer of: an additional first-structural-part component and/or an additional second-structural-part component; and a protective part extending from the additional first-structural-part component or the additional second-structural-part component while being in contact with the middle layer. These protective parts which are in contact with the middle layer and are formed in the second processing step also contribute to reduced breakage of the connecting part which is in contact with the middle layer.

According to another preferred embodiment of the first and the second aspects of the present invention, the second processing step includes further formation in the second process layer of: an additional first-structural-part component and an additional second-structural-part component; a first protective part extending from the additional first-structural-part component while being in contact with the middle layer; and a second protective part extending from the additional second-structural-part component while being in contact with the middle layer. These protective parts which are in contact with the middle layer and are formed in the second processing step also contribute to reduced breakage of the connecting part which is in contact with the middle layer.

A third aspect of the present invention provides a method of making a microstructure device including a first structural part, a second structural part having a portion opposed to the first structural part, and a connecting part connecting the first and the second structural parts, from a material substrate having a laminated structure including a first process layer, a second process layer and a middle layer between the first process layer and the second process layer. The method includes a first processing step and a second processing step. In the first processing step, etching is performed to the first process layer whereby formation is made for: a first-structural-part component and a second-structural-part component opposed to each other via a separation gap where the middle layer makes partial exposure; and a connecting part connecting the first and the second-structural-part components with each other across the separation gap while being in contact with the middle layer. In the second processing step, etching is performed to the second process layer: for formation of an additional first-structural-part component and/or an additional second-structural-part component, and a protective part extending from the additional first-structural-part component or the additional second-structural-part component while being in contact with the middle layer; and for exposure of a portion of the middle layer exposed to the separation gap on the first process layer side, and a portion of the middle layer contacted by the connecting part, to the second process layer side.

According to the second processing step in the present method, as described above, formation is made in the second process layer, for a protective part which extends from the additional first-structural-part component or the additional second-structural-part component while being in contact with the middle layer. This protective part is formed in contact with the second process layer side of the middle layer, at a portion that is exposed to the separation gap on the first process layer side. As a result, breakage of the connecting part which is in contact with the middle layer is reduced under a circumstance where the middle layer is formed with a portion (double-side exposed portion) which is exposed both to the separation gap on the first process layer side and to the second process layer side. Like in the method according to the first aspect of the present invention described earlier, here again, presence of the protective part decreases breakage probability of the connecting part in the present method according to the third aspect of the present invention. Therefore, the present method is also suitable for manufacturing microstructure devices which include a connecting part that connects the first structural part and the second structural part.

A fourth aspect of the present invention provides a method of making a microstructure device including a first structural part, a second structural part having a portion opposed to the first structural part, and a connecting part connecting the first and the second structural parts, from a material substrate having a laminated structure including a first process layer, a second process layer and a middle layer between the first process layer and the second process layer. The method includes a first processing step and a second processing step. In the first processing step, etching is performed to the first process layer whereby formation is made for: a first-structural-part component and a second-structural-part component opposed to each other via a separation gap where the middle layer makes partial exposure; and a connecting part connecting the first and the second-structural-part components with each other across the separation gap while being in contact with the middle layer. In the second processing step, etching is performed to the second process layer: for formation of an additional first-structural-part component and an additional second-structural-part component, a first protective part extending from the additional first-structural-part component while being in contact with the middle layer, and a second protective part extending from the additional second-structural-part component while being in contact with the middle layer; and for exposure of a portion of the middle layer exposed to the separation gap on the first process layer side, and a portion of the middle layer contacted by the connecting part, to the second process layer side.

According to the second processing step in the present method, as described above, formation is made in the second process layer, for a first protective part which extends from the additional first-structural-part component while being in contact with the middle layer, and a second protective part which extends from the additional second-structural-part component while being in contact with the middle layer. These protective parts are formed in contact with the second process layer side of the middle layer, at portions that are exposed to the separation gap on the first process layer side. As a result, breakage of the connecting part which is in contact with the middle layer is reduced under a circumstance where the middle layer is formed with a portion (double-side exposed portion) which is exposed both to the separation gap on the first process layer side and to the second process layer side. Like in the method according to the first aspect of the present invention described earlier, here again, presence of the protective part decreases breakage probability of the connecting part in the present method according to the fourth aspect of the present invention. Therefore, the present method is also suitable for manufacturing microstructure devices which include a connecting part that connects the first structural part and the second structural part.

Each of the manufacturing methods according to the first through the fourth aspects of the present invention preferably includes: a step after the first processing step and before the second processing step, of bonding a support substrate to the first process layer side of the material substrate; and a step of separating the material substrate from the support substrate after the second processing step. There are cases where performing the bonding step helps perform the second processing step that follows, appropriately.

In the bonding step according to the first through the fourth aspects of the present invention, preferably, the support substrate is bonded to the first process layer side of the material substrate via a bonding material such as resin composition. Such an arrangement is suitable to perform the bonding step appropriately.

A fifth aspect of the present invention provides a microstructure device made from a material substrate having a laminated structure including a first process layer, a second process layer and a middle layer between the first process layer and the second process layer. The microstructure device includes a first structural part, a second structural part, a connecting part and a protective part. The second structural part has a portion opposed to the first structural part via a gap. The connecting part is formed in the first process layer, at a place contacted by the middle layer, and connects the first structural part and the second structural part across the gap. The protective part is formed in the first process layer or the second process layer, at a place contacted by the middle layer, and extends from the first structural part toward the second structural part or from the second structural part toward the first structural part.

The present microstructure device is made by a method according to the first or the third aspect of the present invention. According to such a microstructure device, the same technical advantages are enjoyed as described earlier in relation to the first or the third aspect during the manufacturing process.

A sixth aspect of the present invention provides a microstructure device made from a material substrate having a laminated structure including a first process layer, a second process layer and a middle layer between the first process layer and the second process layer. The microstructure device includes a first structural part, a second structural part, a connecting part, a first protective part and a second protective part. The second structural part has a portion opposed to the first structural part via a gap. The connecting part is formed in the first process layer, at a place contacted by the middle layer, and connects the first structural part and the second structural part across the gap. The first protective part is formed in the first process layer or the second process layer, at a place contacted by the middle layer, and extends from the first structural part toward the second structural. The second protective part is formed in the first process layer or the second process layer, at a place contacted by the middle layer, and extends from the second structural part toward the first structural part.

The present microstructure device is made by a method according to the second or the fourth aspect of the present invention. According to such a microstructure device, the same technical advantages are enjoyed as described earlier in relation to the second or the fourth aspect, during the manufacturing process.

In the fifth and the six aspect of the present invention, the connecting part may be thinner than the first structural part and the second structural part. A thinner connecting part has a lower torsional stiffness and bending stiffness. The protective part may also be thinner than the first structural part and the second structural part.

Preferably, the protective part is thicker than the connecting part. A thicker protective part is more preferable in the reduction of connecting part breakage probability. Preferably, the protective part is wider than the connecting part. A wider protective part is more preferable in the reduction of connecting part breakage probability.

Preferably, the first structural part is a moving part, and the second structural part is a fixed structural part. Such an arrangement as this allows a microstructure device according to the present invention to be configured as a micro moving device. Preferably, the microstructure device according to the fifth and the sixth aspect of the present invention further includes a first comb-teeth electrode fixed to the moving part, and a second comb-teeth electrode fixed to the fixed structural part. The second comb-teeth electrode is brought into facing relation to the first comb-teeth electrode.

According to a preferred embodiment, the first comb-teeth electrode and the second comb-teeth electrode constitute driving force generation means capable of generating electrostatic attraction between the first and the second comb-teeth electrodes. Such an arrangement as this enables to utilize the electrostatic attraction as a driving force to displace the moving part relatively to the fixed structural part.

According to another preferred embodiment, the first comb-teeth electrode and the second comb-teeth electrode constitute detection means for detecting electrostatic capacity change between the first and the second comb-teeth electrodes. Such an arrangement as this enables to know a relative amount of displacement of the second comb-teeth electrode with respect to the first comb-teeth electrode, i.e. a relative amount of displacement of the moving part with respect to the fixed structural part, based on the electrostatic capacity change.

In the fifth and the sixth aspects of the present invention, the connecting part may serve as a supporting part for temporarily fixing the moving part to the fixed structural part. This supporting part provides connection or reinforces connection between the moving part and the fixed structural part until it is cut. It is cut before the micro moving device is utilized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1throughFIG. 6show a micromirror element X1according to a first embodiment of the present invention.FIG. 1is a plan view of the micromirror element X1,FIG. 2is another plan view of the micromirror element X1.FIG. 3throughFIG. 6are sectional views taken in lines III-III, IV-IV, V-V, and VI-VI respectively.

The micromirror element X1includes a moving part1, a frame2, a pair of connecting parts3, a plurality of protective parts4, and comb-teeth electrodes5,6,7,8, and is manufactured by micromachining technology such as MEMS technology, from a material substrate provided by an SOI (silicon on insulator) substrate. The material substrate has a laminated structure provided by a first and a second silicon layers and an insulation layer between the silicon layers. Each silicon layer has a predetermined electrical conductivity due to doping with an impurity. The above mentioned parts in the micromirror element X1are primarily formed out of the first silicon layer and/or the second silicon layer. For the sake of illustrative clarity, however, hatching is made inFIG. 1on those portions which are derived from the first silicon layer and are higher than the insulation layer toward the viewer of the figure. Likewise, inFIG. 2, hatching is made on those portions which are derived from the second silicon layer and are higher than the insulation layer toward the viewer of the figure.

The moving part1is derived from the first silicon layer, and has a surface provided with a mirror surface1′ capable of reflecting light.

As shown inFIG. 1, the frame2surrounds the moving part1, and as shown inFIG. 3throughFIG. 6, has a laminated structure which includes a first layer2a, a second layer2band an insulation layer2cbetween them. The first layer2ais a portion derived from the first silicon layer whereas the second layer2bis a portion derived from the second silicon layer.

Each of the connecting parts3is a portion derived from the first silicon layer, and as shown inFIG. 1,FIG. 2andFIG. 7, it connects the moving part1and the frame2across a gap G between the moving part1and the frame2. Each connecting part3connects with the moving part1, and with the first layer2aof the frame2. The connecting part3provides electrical connection between the moving part1and the first layer2a. Also, as shown inFIG. 8, each connecting part3in the present embodiment is thinner than the moving part1and the first layer2aof the frame2in a thickness direction H of the element. The pair of connecting parts3provides a pivotal axis A for pivotal displacement or pivotal movement of the moving part1with respect to the frame2.

Each of the protective parts4is a portion derived from the first silicon layer, and as shown inFIG. 1andFIG. 7, extends from the first layer2ain the moving part1or in the frame2, into the gap G. In the present embodiment, each connecting part3is provided closely thereto, with two protective parts4extending from the moving part1and two protective parts4extending from the first layer2a.FIG. 1shows that the protective parts4are disposed on both sides of and parallel to the connecting part3. As shown inFIG. 8, each protective part4in the present embodiment has the same thickness as the moving part1and the first layer2aof the frame2in the thickness direction H of the element. Further, each protective part4is wider than the connecting part3.

The comb-teeth electrode5has a plurality of electrode teeth5aderived from the first silicon layer, and is fixed to the moving part1. As shown inFIG. 1,FIG. 2andFIG. 6, each of the electrode teeth5aextends from the moving part1. As shown inFIG. 1,FIG. 2andFIG. 4, the electrode teeth5aare parallel to each other.

The comb-teeth electrode6has a plurality of electrode teeth6aderived from the first silicon layer, and is fixed to the moving part1to face away from the comb-teeth electrode5. As shown inFIG. 1,FIG. 2andFIG. 6, each of the electrode teeth6aextends from the moving part1. As shown inFIG. 1,FIG. 2andFIG. 5, the electrode teeth6aare parallel to each other. The comb-teeth electrode6is electrically connected with the comb-teeth electrode5via the moving part1.

The comb-teeth electrode7has a plurality of electrode teeth7aderived from the second silicon layer, and as shown inFIG. 2, fixed to the second layer2bof the frame2. Each of the electrode teeth7aextends from the second layer2b. As shown inFIG. 1,FIG. 2andFIG. 4, the electrode teeth7aare parallel to each other. The comb-teeth electrode7works with the comb-teeth electrode5to generate electrostatic attraction (driving force). A pair of comb-teeth electrodes5,7constitutes an actuator for the micromirror element X1.

The comb-teeth electrode8has a plurality of electrode teeth8aderived from the second silicon layer, and fixed to the second layer2bof the frame2as shown inFIG. 2. Each of the electrode teeth8aextends from the second layer2b. As shown inFIG. 1,FIG. 2andFIG. 5, the electrode teeth8aare parallel to each other. The comb-teeth electrode8works with the comb-teeth electrode6to generate electrostatic attraction (driving force). A pair of comb-teeth electrodes6,8constitutes an actuator for the micromirror element X1. The portion in the second layer2bof the frame2where the comb-teeth electrode8is fixed to is electrically separated from the portion of the second layer2bwhere the comb-teeth electrode7is fixed to. Therefore, the comb-teeth electrodes7,8are electrically separated from each other.

According to the micromirror element X1it is possible to pivot the moving part1about the pivotal axis A by applying a predetermined electric potential as necessary, to the comb-teeth electrodes5through8. Electric potential application to the comb-teeth electrodes5,6can be achieved through the first layer2aof the frame2, each connecting part3and the moving part1. The comb-teeth electrodes5,6are grounded for example. On the other hand, electric potential application to the comb-teeth electrode7can be achieved through part of the second layer2bin the frame2whereas electric potential application to the comb-teeth electrode8can be achieved through a different part of the second layer2b. Since the comb-teeth electrodes7,8are electrically separated from each other, electric potential application to the comb-teeth electrodes7,8can be made independently from each other.

When a predetermined electric potential is given to each of the comb-teeth electrodes5,7, thereby generating a desirable electrostatic attraction between the comb-teeth electrodes5,7, the comb-teeth electrode5is drawn to the comb-teeth electrode7. As a result, the moving part1pivots about the pivotal axis A to a displacement angle where the electrostatic attraction is balanced by a total of torsional resistances of the twisted connecting parts3. The amount of pivotal displacement in such a pivotal movement can be controlled by varying the amount of electric potential applied to the comb-teeth electrodes5,7. When the electrostatic attraction between the comb-teeth electrodes5,7is turned off, each connecting part3releases its torsional stress and returns to its natural state.

Likewise, when a predetermined electric potential is given to each of the comb-teeth electrodes6,8, thereby generating a desirable electrostatic attraction between the comb-teeth electrodes6,8, the comb-teeth electrode6is drawn to the comb-teeth electrode8. As a result, the moving part1pivots about the pivotal axis A in the reverse direction from the pivotal movement described in the previous paragraph, to a displacement angle where the electrostatic attraction is balanced by a total of torsional resistances of the twisted connecting parts3. The amount of pivotal displacement in such a pivotal movement can be controlled by varying the amount of electric potential applied to the comb-teeth electrodes6,8. When the electrostatic attraction between the comb-teeth electrodes6,8is turned off, each connecting part3releases its torsional stress and returns to its natural state.

According to the micromirror element X1, it is possible to change light reflection directions of the mirror surface1′ formed on the moving part1, by pivotally driving the moving part1as outlined above.

FIG. 9throughFIG. 11show a method of making the micromirror element X1. The method is an example of how the micromirror element X1can be manufactured through micromachining technology.FIG. 9throughFIG. 11show a section in a series, illustrating a formation process of various parts shown inFIG. 11(c), i.e. a moving part M, frames F1, F2, F3, connecting parts C1, C2, protective parts P1, P2, and a set of comb-teeth electrodes E1, E2. The section featured in the figures is a conceptual composite collected from a plurality of fragmentary sections of a material wafer to which a series of manufacturing operations are made to form a single micromirror element. The moving part M represents a portion of the moving part1. The frames F1, F2, F3, each representing the frame2, are cross-sections of selected portions in the frame2. The connecting parts C1, representing the connecting part3, is a section taken in the direction in which the connecting part3extends. The connecting parts C2, representing the connecting part3, is a cross-section of the connecting part3. The protective parts P1, P2, each representing the protective part4, are cross-sections of the protective part4. The comb-teeth electrode E1, representing the comb-teeth electrodes5,6, is a partial cross-section of the comb-teeth electrodes5,6. The comb-teeth electrodes E2, representing the comb-teeth electrodes7,8, is a partial cross-section of the comb-teeth electrodes7,8.

In the manufacture of the micromirror element X1, first, a material substrate10as shown inFIG. 9(a) is prepared. The material substrate10is an SOI (Silicon on Insulator) wafer which has a laminated structure including silicon layers11,12, and an insulation layer13between the silicon layers11,12. The insulation layers11,12are made of an electrically conductive silicon material doped with impurity. The impurity may be a p-type impurity such as boron, or an n-type impurity such as phosphorus and antimony. The insulation layer13is made of oxide silicon for example. The silicon layer11has a thickness of e.g. 5 through 100 μm, the silicon layer12has a thickness of e.g. 100 through 500 μm, and the insulation layer13has a thickness of e.g. 0.2 through 2 μm. The silicon layers11,12and the insulation layer13are the first and the second process layers and the middle layer according to the present invention.

Next, as shown inFIG. 9(b), a mirror surface1′ is formed on the silicon layer11. Specifically, first, a film of Cr (50 nm) for example, and then a film of Au (200 nm) for example are formed by spattering on the silicon layer11. Next, these metal films are etched sequentially via a predetermined mask. Through the procedure, the mirror surface1′ is patterned on the silicon layer11. The etchant for Au may be aqueous potassium iodide-iodine solution. The etchant for Cr may be aqueous cerium ammonium nitrate solution.

Next, as shown inFIG. 9(c), an oxide film pattern21and a resist pattern22are formed on the silicon layer11, and an oxide film pattern23is formed on the silicon layer12. The oxide film pattern21has a pattern for forming the moving part M, the frames F1, F2, F3, the protective parts P1, P2and the comb-teeth electrode E1. The resist pattern22has a pattern for forming the connecting parts C1, C2. The oxide film pattern23has a pattern for forming the frames F1, F2, F3and the comb-teeth electrode E2.

The oxide film pattern21may be formed as follows: First, a film of silicon dioxide is formed by e.g. CVD method on the silicon layer11, to a thickness of e.g. 1 μm. Next, the oxide film on the silicon layer11is patterned by etching via a mask of a predetermined resist pattern. It should be noted here that the oxide film pattern23and other oxide film patterns to be described later may also be formed in the same procedure including film formation of resist pattern formation on the oxide film using an oxide material, and etching thereafter. On the other hand, the resist pattern22is formed by first forming a film of photoresist on the silicon layer11through spin coating of a liquid photoresist, and then exposing, developing and patterning the photoresist film. Examples of the photoresist include AZP4210 (manufactured by AZ Electronic Materials) and AZ1500 (manufactured by AZ Electronic Materials). Other resist patterns to be described later can also be formed through essentially the same processes of photoresist film formation followed by exposure and development.

As shown inFIG. 9(d), the next step in the manufacture of the micromirror element X1is anisotropic dry etching by DRIE (Deep Reactive Ion Etching) to the silicon layer11to a predetermined depth, with masks provided by the oxide film pattern21and the resist pattern22. The predetermined depth is a depth equal to the thickness of the connecting parts C1, C2, being 5 μm for example. This step uses a predetermined etching apparatus equipped with a vacuum chamber to perform the DRIE in the vacuum chamber under predetermined vacuum conditions. Good anisotropic etching can be performed in the DRIE if a Bosch process is employed in which etching and side-wall protection are alternated with each other. The DRIE in this step and those described later may be performed by using the Bosch process.

Next, as shown inFIG. 10(a), the resist pattern22is removed with a remover such as AZ Remover 700 (manufactured by AZ Electronic Materials). This remover may also be used to remove resist patterns to be described later.

Next, as shown inFIG. 10(b), using the oxide film pattern21as a mask, anisotropic etching by DRIE is performed to the silicon layer11until the insulation layer13is reached while leaving the thin connecting parts C1, C2which contact the insulation layer13. In this step again, a predetermined etching apparatus equipped with a vacuum chamber is used as in the previous step described with reference toFIG. 9(d), and the dry etching operation is performed in the vacuum chamber under predetermined vacuum conditions. This step yields the connecting parts C1, C2, as well as the moving part M, part of the frames F1, F2, F3(the first layer2a), the protective parts P1, P2, and the comb-teeth electrode E1.

The moving part1and the first layer2aof the frame2formed in the present step oppose to each other, across a separation gap G′ to which the insulation layer13exposes partially. Each of the connecting parts3is in contact with the insulation layer13, and connects the moving part1and the first layer2aacross the separation gap G′. Each of the protective parts4is in contact with the insulation layer13, and extends from the moving part1or from the first layer2ainto the separation gap G′.

Next, as shown inFIG. 10(c) andFIG. 11(a), a sub-carrier24is bonded to the silicon layer1side of the material substrate10via a bonding member25. The sub-carrier24is provided by a silicon substrate, a quartz substrate or a metal substrate for example. The bonding member25is provided by resist, thermoconductive grease, sealant or a tape. An example of the resist is Resist AZP4210 (manufactured by AZ Electronic Materials). In this step, the material substrate10and the sub-carrier24are bonded to each other under heat and pressure. A purpose of bonding the sub-carrier24in such a way is to prevent damage to the material substrate10and to the etching apparatus in the next manufacturing step. In the next manufacturing step, etching is performed to the silicon layer12in the vacuum chamber of the etching apparatus. In this process, mechanical strength of the material substrate10decreases substantially because of the etching performed to the silicon layer12, with the silicon layer11having already been etched. The sub-carrier24serves as a reinforcing member for the material substrate10, and prevents the material substrate10from breaking. If the material substrate10breaks in the vacuum chamber, broken pieces can damage the etching apparatus. Therefore, damage prevention of the material substrate10by the sub-carrier24also contributes to damage prevention of the apparatus.

Next, as shown inFIG. 11(b), using the oxide film pattern22as a mask, anisotropic etching by DRIE is performed to the silicon layer12until the insulation layer13is reached. In this step again, a predetermined etching apparatus equipped with a vacuum chamber is used as in the previous step described with reference toFIG. 9(d), and the dry etching operation is performed in the vacuum chamber under predetermined vacuum conditions. This step yields part of the frames F1, F2, F3(the second layer2b) and the comb-teeth electrode E2. Also, the present step exposes the insulation layer13partially in the silicon layer12. The exposed portion includes the portions S (double-side exposed portion) which expose also to the separation gap G′ on the silicon layer11side, portions contacted by the connecting parts C1, C2(each of the connecting parts3), and portions contacted by the protective parts P1, P2(each of the protective parts4).

After this step, the material substrate10and the sub-carrier24are separated from each other. If the bonding member25is provided by resist, a predetermined remover may be applied to the bonding member25to separate the material substrate10from the sub-carrier24.

Next, as shown inFIG. 11(c), exposed areas of the insulation layer13and the oxide film patterns21,23are etched off. The etching may be dry etching or wet etching. If dry etching is used, examples of usable etching gas include CF4 and CHF3. If wet etching is used; the etchant used in this process may be buffered hydrofluoric acid (BHF) which contains hydrofluoric acid and ammonium fluoride.

By performing the above-described sequence of steps, it is possible to form a moving part M, frames F1, F2, F3, connecting parts C1, C2, protective parts P1, P2, and a set of comb-teeth electrodes E1, E2, and thereby to manufacture a micromirror element X1. The process described with reference toFIG. 9(c) throughFIG. 10(b), i.e. a series of micromachining operations performed to the silicon layer11represent the first processing step according to the present invention. The process described with reference toFIG. 9(c) andFIG. 11(b), i.e. micromachining operations performed to the silicon layer12represent the second processing step according to the present invention.

In the first processing step according to the present method, protective parts4which make contact with the insulation layer13and extend from the moving part1or from the first layer2ainto the separation gap G1are formed out of the silicon layer11, along with the connecting parts3which are in contact with the insulation layer13and provide connection between the moving part1and the first layer2aof the frame2across the separation gap G′. As a result, breakage of the connecting parts3which contact the insulation layer13is reduced under circumstances resulted from the second processing step performed to the portions S (double-side exposed portion) in the insulation layer13. If a local fracture Z occurs as shown inFIG. 12(a), in the portion S of the insulation layer13, the protective parts4which is in contact with the insulation layer13prevents the fracture Z from reaching the connecting part3as shown inFIG. 12(b).

As a fracture Z runs across an area of the insulation layer13contacted by a protective part4extended into the separation gap G′, an impact from the fracture reaches the protective part4, and the protective part4absorbs at least part of the energy necessary for the fracture Z to grow further. With the presence of these protective parts4which can provide the above-described function, breakage probability of the connecting part3which is in contact with the insulation layer13and bridges across the separation gap G′ is decreased. The breakage probability of the connecting part tends to decrease if the protective part4is closer to the connecting part. Also, the breakage probability of the connecting part tends to decrease with increase in the number of protective parts4provided.

As described, the present method decreases breakage probability of the connecting part3, and therefore, the present method is suitable for manufacturing micromirror elements (microstructure devices) which include connecting parts3that connect a moving part (the first structural part) and the frame (the second structural part).

As shown inFIG. 13(a), in the micromirror element X1, the connecting parts3may have the same thickness as the moving part1, the first layer2aof the frame2and the protective parts4, in the thickness direction H of the element. Thick connecting parts3such as these can be formed in the same way as the thick protective parts4.

As shown inFIG. 13(b), the protective parts4may have the same thickness as the thin connecting parts3, in the thickness direction H of the element. Thin protective parts4such as these can be formed in the same way as the thin connecting parts3.

The micromirror element X1may have protective parts4shaped as shown inFIG. 14(a). In this variation, each of the protective part4extending from the moving part1as well as each of the protective parts4extending from the frame2is narrower toward its tip.

The protective parts4may also have a shape shown inFIG. 14(b). In this variation, each of the protective part4extending from the moving part1as well as each of the protective parts4extending from the frame2is wider toward its tip.

The protective parts4may also have a shape shown inFIG. 14(c). In this variation, each of the protective parts4extending from the moving part1has a round side4a.

In the micromirror element X1, four protective parts4are provided for each connecting part3as shown inFIG. 7: Alternatively, six protective parts4may be provided for each connecting part3as shown inFIG. 14(d). Similarly, six protective parts as shown inFIG. 14(e) may be4provided for each connecting part3.

In the micromirror element X1some of the protective parts4may be replaced by protective parts4′ as shown inFIG. 15andFIG. 16. The protective parts4′ are thinner than the first layer2aof the frame2, and extend from the first layer2ainto the gap G, along the frame2.

As has been exemplified with the variations described above, the shape, number, layout, etc. of the protective parts4may be varied as necessary.

In the micromirror element X1, the connecting parts3have a shape as shown inFIG. 7: Alternatively, the shape may be as shown inFIG. 17(a). The connecting part3inFIG. 17(a) includes two bars spaced from each other with increasing distance from the frame2toward the moving part1. Similarly, the connecting parts3may have a shape shown inFIG. 17(b) or inFIG. 17(c). As has been exemplified with these variations, the shape of the connecting parts3may be varied as needed.

As shown inFIG. 18andFIG. 19, the micromirror element X1may further include a supporting part3′ and a set of protective parts4formed closely to the supporting part3′. The supporting part3′, which reinforces the connection provided by the connecting part3between the moving part1and the frame2, is cut or removed before the micromirror element X1is utilized. The supporting part3′ can be cut or removed by a beam of Nd:YAG laser.

The comb-teeth electrodes5through8constitute an actuator (drive means): In the present invention, at least one of the comb-teeth electrode pair5,7and the comb-teeth electrode pair6,8may be constituted to serve as detection means for detection of electrostatic capacity change between the comb-teeth electrodes. Such an arrangement enables to obtain information on a relative amount of displacement of the moving part1with respect to the frame2, based on the electrostatic capacity change.

In the present invention, a material substrate may be formed therein, with a row of micromirror elements X1. These micromirror elements X1arranged in a one-dimensional array as described have all of their pivotal axes A for the moving parts1being parallel to each other for example.

In the present invention, a material substrate may be formed therein, with rows of micromirror elements X1. These micromirror elements X1arranged in a two-dimensional array as described have all of their pivotal axes A for the moving parts1being parallel to each other for example.

In the present invention, the micromirror element X1may further include an outer frame which surrounds the frame2, and a pair of connecting parts which connect the outer frame and the frame2. This additional pair of connecting parts preferably provides a pivotal axis for pivotal displacement or pivotal movement of the frame2with respect to the outer frame as well as of associated movement of the moving part1. Preferably, this pivotal axis is perpendicular to the pivotal axis A.

A microstructure device according to the present invention may be the micromirror element X1which does not include one of the connecting parts3. In such a microstructure device, the moving part1which is connected with the frame2by only one connecting part3can swing in any directions across the direction along which the connecting part3extends.

FIG. 20is a plan view of a micromirror element X2according to a second embodiment of the present invention.FIG. 21is an enlarged partial view of the micromirror element X2.FIG. 22is a sectional view taken in lines XXII-XXII inFIG. 21.

The micromirror element X2includes a moving part1, a frame2, a pair of connecting parts3, a plurality of protective parts4A, and comb-teeth electrodes5,6,7,8. The micromirror element X2differs from the micromirror element X1only in that it has protective parts4A instead of the protective parts4, and thus can be driven in the same way as the micromirror element X1.

Each of the protective parts4A is a portion derived from the first silicon layer, and extends from the moving part1or the first layer2aof the frame2, into the gap G. Closely to each connecting part3, two protective parts4A extend from the moving part1, and two protective parts4A extend from the first layer2a. As shown inFIG. 22, all of the protective parts4A are thinner than the moving part1and the first layer2aof the frame2in the thickness direction H of the element.

FIG. 23throughFIG. 25show a method of making the micromirror element X2. The method is an example of how the micromirror element X2can be manufactured through micromachining technology.FIG. 23throughFIG. 25show a section in a series, illustrating a formation process of various parts shown inFIG. 25(c), i.e. a moving part M, frames F1, F2, F3, connecting parts C1, C2, protective parts P1, P2, and a set of comb-teeth electrodes E1, E2. The section featured in the figures is a conceptual composite collected from a plurality of fragmentary sections of a material wafer to which a series of manufacturing operations are made to form a single micromirror element. The protective parts P1, P2, each representing the protective part4A, are cross-sections of the protective part4A. The moving part M, the frames F1, F2, F3, the connecting parts C1, C2and the comb-teeth electrodes E1, E2are formed in the same way as described for the micromirror element X1.

In the manufacture of the micromirror element X2, first, a mirror surface1′ is formed on a material substrate10as shown inFIG. 23(a). The material substrate10is the same as in the first embodiment, having a laminated structure provided by silicon layers11,12and an insulation layer13.

Next, as shown inFIG. 23(b), an oxide film pattern31, a resist pattern22and a nitride film pattern32are formed on the silicon layer11, and an oxide film pattern23is formed on the silicon layer12. The oxide film pattern31has a pattern for forming the moving part M, the frames F1, F2, F3, and the comb-teeth electrode E1. The resist pattern22has a pattern for forming the connecting parts C1, C2as described earlier in relation to the method of manufacturing the micromirror element X1. The nitride film pattern32has a pattern for forming the protective parts P1, P2. The oxide film pattern23has a pattern for forming the frames F1, F2, F3and the comb-teeth electrode E2as described earlier in relation to the method of manufacturing the micromirror element X1. When forming the nitride film pattern32, first, a film of silicon nitride is formed by CVD for example, on the silicon layer11to a thickness of e.g. 500 nm. Next, the nitride film on the silicon layer11is patterned by etching with a mask of predetermined resist pattern. The patterning may be made by dry etching, using CF4as etching gas.

Next, as shown inFIG. 23(c), anisotropic dry etching by DRIE is performed to the silicon layer11to a predetermined depth, with masks provided by the oxide film pattern31, the resist pattern22and the nitride film pattern32. The predetermined depth is a depth equal to the thickness of the connecting parts C1, C2, being 5 μm for example. Thereafter, as shown inFIG. 21(d), the resist pattern22is removed by remover.

Next, as shown inFIG. 24(a), anisotropic dry etching by DRIE is performed to the silicon layer11to a predetermined depth, with masks provided by the oxide film pattern31and the nitride film pattern32. The predetermined depth is a depth equal to a difference between the thickness of protective parts P1, P2and the thickness of connecting parts C1, C2, being 5 through 50 μm for example. Thereafter, as shown inFIG. 24(b), the nitride film pattern32is removed. The nitride film pattern32can be removed by etching with hot phosphoric acid.

Next, as shown inFIG. 24(c), using the oxide film pattern31as a mask, anisotropic etching by DRIE is performed to the silicon layer11until the insulation layer13is reached while leaving the connecting parts C1, C2which contact the insulation layer13as well as leaving the protective parts P1, P2. In this step, a predetermined etching apparatus equipped with a vacuum chamber is used, and the dry etching operation is performed in the vacuum chamber under predetermined vacuum conditions. This step yields the connecting parts C1, C2, the protective parts P1, P2, as well as the moving part M, part of the frames F1, F2, F3(the first layer2a) and the comb-teeth electrode E1.

The moving part1and the first layer2aof the frame2formed in the present step oppose to each other across a separation gap G′ to which the insulation layer13exposes partially. Each of the connecting parts3is in contact with the insulation layer13, and connects the moving part1and the first layer2aacross the separation gap G′. Each of the protective part4is in contact with the insulation layer13, and extends from the moving part1or from the first layer2ainto the separation gap G′.

Next, as shown inFIG. 25(a), a sub-carrier24is bonded to the silicon layer11side of the material substrate10via a bonding member25. Thereafter, as shown inFIG. 25(b), anisotropic etching by DRIE is performed to the silicon layer12until the insulation layer13is reached, using the oxide film pattern23as a mask. In this step, a predetermined etching apparatus equipped with a vacuum chamber is used, and the dry etching operation is performed in the vacuum chamber under predetermined vacuum conditions. This step yields part of the frames F1, F2, F3(the second layer2b) and the comb-teeth electrode E2. Also, the present step exposes the insulation layer13partially in the silicon layer12. The exposed portion includes the portions S (double-side exposed portions) which expose also to the separation gap G′ on the silicon layer11side, portions contacted by the connecting parts C1, C2(each of the connecting parts3), and portions contacted by the protective parts P1, P2(each protective part4). After this step, the material substrate10is separated from the sub-carrier24.

Next, as shown inFIG. 25(c), exposed areas of the insulation layer13and the oxide film patterns23,31are etched off. The etching may be dry etching or wet etching.

By performing the above-described sequence of steps, it is possible to form a moving part M, frames F1, F2, F3, connecting parts C1, C2, protective parts P1, P2, and a set of comb-teeth electrodes E1, E2, and thereby to manufacture a micromirror element X2. The process described with reference toFIG. 23(b) throughFIG. 24(c), i.e. a series of micromachining operations performed to the silicon layer11represent the first processing step according to the present invention. The process described with reference toFIG. 23(b) andFIG. 25(b), i.e. micromachining operations performed to the silicon layer12represent the second processing step according to the present invention.

In the first processing step according to the present method, protective parts4A which are in contact with the insulation layer13and extend from the moving part1or from the first layer2ainto the separation gap G′ are formed out of the silicon layer11, along with the connecting parts3which are in contact with the insulation layer13and provide connection between the moving part1and the first layer2aof the frame2across the separation gap G′. As a result, breakage of the connecting parts3which are in contact with the insulation layer13is reduced under circumstances resulted from the second processing step performed to the portions S (double-side exposed portions) in the insulation layer13. With the presence of the protective parts, breakage probability of the connecting parts3is decreased in the method of manufacturing the micromirror element X2just as in the method of manufacturing the micromirror element X1, for reasons described with reference toFIG. 12. Therefore, the present method is also suitable for manufacturing micromirror elements (microstructure devices) which include connecting parts3that connect a moving part (the first structural part) and the frame (the second structural part).

FIG. 26throughFIG. 28show a micromirror element X3according to a third embodiment of the present invention.FIG. 26is a plan view of the micromirror element X3whereasFIG. 27is another plan view of the micromirror element X3.FIG. 28is a sectional view taken in lines XXVIII-XXVIII inFIG. 26.

The micromirror element X3includes a moving part1A, a frame2, a pair of connecting parts3, a plurality of protective parts4B and comb-teeth electrodes5,6,7,8. The micromirror element X3differs from the micromirror element X1only in that it has a moving part1A instead of a moving part1and protective parts4B instead of protective parts4, and thus can be driven in the same way as the micromirror element X1.

The moving part1A has a first layer1aand a second layer1b. The first layer1ais provided with a mirror surface1′ capable of reflecting light. The first layer1ais a portion derived from the first silicon layer whereas the second layer1bis a portion derived from the second silicon layer. As shown inFIG. 28, the first layer1aand the second layer1bare bonded to each other via an insulation layer1c. The comb-teeth electrodes5,6of the micromirror element X3are fixed to the first layer1aof the moving part1A.

Each of the protective parts4B is a portion derived from the second silicon layer1b, and as shown inFIG. 27andFIG. 28, extends from the second layer in the moving part1A toward the frame2, or from the second layer2bof the frame2toward the moving part1A. Closely to each of the connecting parts3, two protective parts4extend from the second layer1band two protective parts4extending from the second layer2b. As shown inFIG. 30for example, each of the protective parts4is thinner than the second layer1bof the moving part1A and the second layer2bof the frame2in the thickness direction H of the element.

FIG. 31throughFIG. 33show a method of making the micromirror element X3. The method is an example of how the micromirror element X3can be manufactured through micromachining technology.FIG. 31throughFIG. 33show a section in a series, illustrating a formation process of various parts shown inFIG. 33(c), i.e. a moving part M, frames F1, F2, F3, connecting parts C1, C2, protective parts P1, P2, and a set of comb-teeth electrodes E1, E2. The section featured in the figures is a conceptual composite collected from a plurality of fragmentary sections of a material wafer to which a series of manufacturing operations are made to form a single micromirror element. The protective parts P1, P2, each representing the protective part4B, are cross-sections of the protective part4B. The moving part M, the frames F1, F2, F3, the connecting parts C1, C2and the comb-teeth electrodes E1, E2are formed in the same way as described for the micromirror element X1.

In the manufacture of the micromirror element X3, first, a mirror surface1′ is formed on a material substrate10as shown inFIG. 31(a). The material substrate10is the same as in the first embodiment, having a laminated structure provided by silicon layers11,12and an insulation layer13.

Next, as shown inFIG. 31(b), an oxide film pattern31and a resist pattern22are formed on the silicon layer11, and an oxide film pattern23and a resist pattern33are formed on the silicon layer12. The oxide film pattern31has a pattern for forming the moving part M, the frames F1, F2, F3, and the comb-teeth electrode E1as in the method of manufacturing the micromirror element X2described earlier. The resist pattern22has a pattern for forming the connecting parts C1, C2as described earlier in relation to the method of manufacturing the micromirror element X1. The oxide film pattern23has a pattern for forming the frames F1, F2, F3and the comb-teeth electrode E2as described earlier in relation to the method of manufacturing the micromirror element X1.

Next, as shown inFIG. 31(c), anisotropic dry etching by DRIE is performed to the silicon layer11to a predetermined depth, with masks provided by the oxide film pattern31and the resist pattern22. The predetermined depth is a depth equal to the thickness of the connecting parts C1, C2, being 5 μm for example. Thereafter, as shown inFIG. 31(d), the resist pattern22is removed by remover.

Next, as shown inFIG. 32(a), using the oxide film pattern31as a mask, anisotropic etching by DRIE is performed to the silicon layer11until the insulation layer13is reached while leaving the thin connecting parts C1, C2which contact the insulation layer13. In this step, a predetermined etching apparatus equipped with a vacuum chamber is used, and the dry etching operation is performed in the vacuum chamber under predetermined vacuum conditions. This step yields the connecting parts C1, C2, as well as part of the moving part M (the first layer1a), part of the frames F1, F2, F3(the first layer2a), and the comb-teeth electrode E1.

The first layer1aof the moving part1A and the first layer2aof the frame2formed in the present step oppose to each other across a separation gap G′ to which the insulation layer13exposes partially. Each of the connecting parts3is in contact with the insulation layer13, and connects the moving part1and the first layer2aacross the separation gap G′.

Next, as shown inFIG. 32(b), a sub-carrier24is bonded to the silicon layer11side of the material substrate10via a bonding member25. Thereafter, as shown inFIG. 32(c), using the oxide film pattern23and the resist pattern33as masks, anisotropic dry etching by DRIE is performed to the silicon layer12to a predetermined depth. The predetermined depth is a depth equal to the thickness of the protective part P1, P2, being 5 through 55 μm for example. This step uses a predetermined etching apparatus equipped with a vacuum chamber to perform the dry etching in the vacuum chamber under predetermined vacuum conditions. Thereafter, the resist pattern33is removed with remover as shown inFIG. 33(a).

Next, as shown inFIG. 33(b), using the oxide film pattern23as a mask, anisotropic dry etching by DRIE is performed to the silicon layer12until the insulation layer13is reached while leaving the protective part P1, P2which contact the insulation layer13. In this step, a predetermined etching apparatus equipped with a vacuum chamber is used, and the dry etching operation is performed in the vacuum chamber under predetermined vacuum conditions. This step yields the protective parts P1, P2as well as part of the moving part M (second layer1b), part of the frames F1, F2, F3(second layer2b), and the comb-teeth electrode E2. Also, the present step exposes the insulation layer13partially in the silicon layer12. The exposed portion includes portions S (double-side exposed portions) which are exposed also to the separation gap G′ on the silicon layer11, and portions contacted by the connecting parts C1, C2(each of the connecting parts3). After this step, the material substrate10is separated from the sub-carrier24.

Next, as shown inFIG. 33(c), exposed areas of the insulation layer13and the oxide film patterns23,31are etched off. The etching may be dry etching or wet etching.

By performing the above-described sequence of steps, it is possible to form a moving part M, frames F1, F2, F3, connecting parts C1, C2, protective parts P1, P2, and a set of comb-teeth electrodes E1, E2, and thereby to manufacture a micromirror element X3. The process described with reference toFIG. 31(b) throughFIG. 32(a), i.e. a series of micromachining operations performed to the silicon layer11represent the first processing step according to the present invention. The process described with reference toFIG. 31(b) andFIG. 32(b) throughFIG. 33(b), i.e. micromachining operations performed to the silicon layer12represent the second processing step according to the present invention.

In the second processing step according to the present method, protective parts4B which are in contact with the insulation layer13and extend from the first layer1bof the moving part1A or from the second layer2bof the frame2are formed out of the silicon layer12. These protective parts4B are in contact with the silicon layer12side of the insulation layer13, at places where the insulation layer exposes itself to the separation gap G′ on the silicon layer11side. As a result, breakage of the connecting parts3which contact the insulation layer13is reduced under circumstances resulted from the second processing step performed to the portions S (double-side exposed portions) in the insulation layer13. With the presence of the protective parts, breakage probability of the connecting parts3is decreased in the method of manufacturing the micromirror element X3just as in the method of manufacturing the micromirror element X1, for reasons described with reference toFIG. 12. Therefore, the present method is also suitable for manufacturing micromirror elements (microstructure devices) which include connecting parts3that connect a moving part (the first structural part) and the frame (the second structural part).

As shown inFIG. 34(a), in the micromirror element X3, each of the protective parts4B may have the same thickness as the second layer1bof the moving part1A and the second layer2bof the frame2. Thick protective parts4B such as these can be formed in the same way as the thick second layers1b,2b.

As shown inFIG. 34(b) andFIG. 34(c), the micromirror element X3may also include protective parts4C in addition to the protective parts4B. Each of the protective parts4C extends from the first layer1aof the moving part1A or the first layer2aof the frame2. The protective parts4B which extend from the second layer1bof the moving part1A are connected with the protective parts4C which extend from the first layer1aof the moving part1A, via an insulation layer. The protective parts4B which extend from the second layer2bof the frame2are connected with the protective parts4C which extend from the first layer2aof the frame2, via an insulation layer. The protective parts4C inFIG. 34(b) have the same thickness as the first layers1a,2ain the thickness direction H of the element. The protective parts4C inFIG. 34(c) have a thickness which is thinner than the first layers1a,2aand thicker than the connecting parts3.