Patent ID: 12187607

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent element, and redundant description is omitted.

[Configuration of Mirror Device]

FIG.1is a plan view of a mirror device1(actuator device) including a damascene wiring structure100(seeFIG.2) according to an embodiment. As shown inFIG.1, the mirror device1includes a support2, a first movable portion3, a second movable portion4, a pair of first connection portions5and6, a pair of second connection portions7and8, and a magnetic field generation unit9. The support2, the first movable portion3, the second movable portion4, the first connection portions5and6, and the second connection portions7and8are integrally formed by a semiconductor substrate (substrate30). That is, the mirror device1is configured as a micro electro mechanical systems (MEMS) device.

In the mirror device1, a first movable portion3including a mirror surface10is swung around a first axis X1and a second axis X2orthogonal to each other. The mirror device1can be used in, for example, an optical switch for optical communication, an optical scanner, or the like. The magnetic field generation unit9is configured by, for example, a permanent magnet arranged in a Halbach array or the like. The magnetic field generation unit9generates a magnetic field that acts on coils21and22described later.

The support2has, for example, a rectangular outer shape in plan view, and is formed in a frame shape. The support2is disposed on one side of the magnetic field generation unit9in a direction perpendicular to the mirror surface10. The first movable portion3is disposed inside the support2in a state of being separated from the magnetic field generation unit9. The “plan view” means a view from a direction perpendicular to the mirror surface10, in other words, a view from a direction perpendicular to a main surface31of the substrate30described later.

The first movable portion3includes an arrangement portion3a, a frame portion3bsurrounding the arrangement portion3a, and a plurality of (four in this example) connection portions3cconnecting the arrangement portion3aand the frame portion3bto each other. The arrangement portion3ais formed in, for example, a circular shape in plan view. For example, the mirror surface10of a circular shape is provided on the surface of the arrangement portion3aopposite to the magnetic field generation unit9. The mirror surface10is formed of a reflective film made of, for example, aluminum, an aluminum-based alloy, silver, a silver-based alloy, gold, or a dielectric multilayer film or the like.

The frame portion3bhas, for example, a rectangular outer shape in plan view and is formed in a frame shape. The plurality of connection portions3care arranged on both sides of the arrangement portion3aon the first axis X1and on both sides of the arrangement portion3aon the second axis X2, and connect the arrangement portion3aand the frame portion3bto each other on the first axis X1or the second axis X2.

The second movable portion4has, for example, a quadrangular outer shape in plan view and is formed in a frame shape. The second movable portion4is disposed inside the support2so as to surround the first movable portion3in a state of being separated from the magnetic field generation unit9.

The first connection portions5and6are disposed on both sides of the first movable portion3on the first axis X1. Each of the first connection portions5and6connects the first movable portion3and the second movable portion4to each other on the first axis X1so that the first movable portion3is swingable around the first axis X1. Each first connection portion5and6extends linearly along the first axis X1, for example.

The second connection portions7and8are disposed on both sides of the second movable portion4on the first axis X1. Each of the second connection portions7and8connects the second movable portion4and the support2to each other on the second axis line X2so that the second movable portion4is swingable around the second axis line X2. Each of the second connection portions7and8extends linearly along the second axis X2, for example.

The mirror device1further includes coils21and22, a plurality of wires12,13,14, and15, and a plurality of electrode pads25,26,27, and28. For example, the coil21is embedded in the frame portion3bof the first movable portion3and extends in a spiral shape in plan view. For example, the coil22is embedded in the second movable portion4and extends in a spiral shape in plan view. Each coil21and22is made of a metal material such as copper.

The plurality of electrode pads25,26,27, and28are provided on the support2. The wiring12electrically connects one end of the coil21and the electrode pad25. The wiring12extends from one end of the coil21to the electrode pad25via the first connection portion5, the second movable portion4, and the second connection portion7. The wiring13electrically connects the other end of the coil21and the electrode pad26. The wiring13extends from the other end of the coil21to the electrode pad26via the first connection portion6, the second movable portion4, and the second connection portion8.

The wiring14electrically connects one end of the coil22and the electrode pad27. The wiring14extends from one end of the coil22to the electrode pad27via the second connection portion8. The wiring15electrically connects the other end of the coil22and the electrode pad28. The wiring15extends from the other end of the coil22to the electrode pad28via the second connection portion7.

In the mirror device1configured as described above, when a drive signal for linear operation is input to the coil22via the electrode pads27and28and the wirings14and15, a Lorentz force acts on the coil22due to interaction with the magnetic field generated by the magnetic field generation unit9. By using the balance between the Lorentz force and the elastic force of the second connection portions7and8, the mirror surface10(the first movable portion3) can be linearly moved together with the second movable portion4around the second axis X2.

On the other hand, when the drive signal of the resonance motion is input to the coil21via the electrode pads25and26and the wirings12and13, the Lorentz force acts on the coil21by the interaction with the magnetic field generated by the magnetic field generation unit9. In addition to the Lorentz force, by using the resonance of the first movable portion3at the resonance frequency, the mirror surface10(first movable portion3) can be resonantly moved around the first axis X1.

[Damascene Wiring Structure]

The damascene wiring structure100of the coils21and22will be described with reference toFIGS.2to4. Since the coils21and22have the same configuration, the coil22will be described below, and the description of the coil21will be omitted.

As described above, the coil22is provided in the second movable portion4. The second movable portion4is constituted by, for example, the first silicon layer81of the substrate (base)30. The substrate30is a semiconductor substrate such as a silicon on insulator (SOI) substrate, for example. The substrate30includes, for example, a first silicon layer81, a second silicon layer82, and an insulating layer83disposed between the first silicon layer81and the second silicon layer82(FIGS.6and8to10). The support2is constituted by the first silicon layer81, the second silicon layer82, and the insulating layer83. The first movable portion3, the second movable portion4, the first connection portions5and6, and the second connection portions7and8are constituted by the first silicon layer81. The substrate30has a main surface31. In this example, the main surface31is a surface of the first silicon layer81opposite to the insulating layer83.

The main surface31is provided with a groove33(a recess). The groove33has a shape corresponding to the coil21, and extends in a spiral shape in plan view in this example. In a cross section perpendicular to the extending direction of the groove33, the groove33has, for example, a rectangular shape. The inner surface of the groove33is constituted by a bottom surface33a, a side surface33b, and an inclined surface33cconnected to the bottom surface33aand the side surface33b. The inclined surface33cis inclined with respect to the bottom surface33aand the side surface33bso as to form an obtuse angle (approximately 135 degrees in this embodiment) with the bottom surface33aand the side surface33bbetween the bottom surface33aand the side surface33b. Although only one cross section is shown inFIGS.2to4, for example, the damascene wiring structure100is uniformly configured in the extending direction of the groove33, and is similarly configured in any cross section perpendicular to the extending direction of the groove33. However, the damascene wiring structure100does not necessarily have to be configured uniformly with respect to the extending direction of the groove33.

The damascene wiring structure100includes an insulating layer40, a metal layer50, a wiring portion60, and a cap layer70in addition to a substrate30as a base. The insulating layer40is provided over the main surface31and the inner surface (i.e., the bottom surface33a, the side surface33b, and the inclined surface33c. The same shall apply hereinafter) of the groove33. More specifically, the insulating layer40includes a first portion41provided on the inner surface of the groove33and a second portion42formed integrally with the first portion41and provided on the main surface31. A boundary part43between the first portion41and the second portion42in the insulating layer40is located on a boundary part between the main surface31and the groove33in the substrate30.

The insulating layer40includes a first layer44and a second layer45. The first layer44is made of an oxide film and provided on the main surface31and the inner surface of the groove33. The oxide film constituting the first layer44is, for example, a silicon oxide film (SiO2) formed by thermally oxidizing silicon. The second layer45is made of a nitride film and provided on the first layer44. The nitride film constituting the second layer45is, for example, a silicon nitride film (SiN) or the like. The first portion41and the boundary part43are constituted by the first layer44and the second layer45, and the second portion42is constituted by the first layer44.

The metal layer50is provided over the first portion41of the insulating layer40. That is, the metal layer50is provided on the inner surface of the groove33via the first portion41. The metal layer50is made of a metal material such as titanium (Ti). The metal layer50can function as, for example, a seed layer for stably forming the wiring portion60on the semiconductor substrate, and a barrier layer for preventing diffusion of metallic elements contained in the wiring portion60into the first silicon layer81.

The wiring portion60is formed on the metal layer50embedded in the groove33. That is, the wiring portion60is provided in the groove33via the first portion41of the insulating layer40and the metal layer50. The wiring portion60is made of, for example, a metal material such as copper (Cu). The shape of the metal layer50in a cross section perpendicular to the extending direction of the wiring portion60(in other words, the extending direction of the groove33) corresponds to the cross-sectional shape of the groove33, and in this example, has a substantially rectangular shape. As in the present embodiment, when the wiring portion60extends spirally in plan view and the wiring portion60includes a first portion extending in a direction parallel to the first axis X1and a second portion extending in a direction parallel to the second axis X2, the extending direction of the wiring portion60is a direction parallel to the first axis X1in the first portion and a direction parallel to the second axis X2in the second portion. Alternatively, when the wiring portion60extends in a curved shape or having curves, the extending direction of a certain portion of the wiring portion60may be a tangential direction of the portion.

The cap layer70is provided so as to cover the second portion42of the insulating layer40, the end portion51of the metal layer50, and the wiring portion60. In this example, the cap layer70extends in a planar shape parallel to the main surface31. The thickness T1of the cap layer70is larger than the thickness T2of the insulating layer40. The cap layer70is made of, for example, a silicon nitride film and has an insulating property. That is, the cap layer70is made of the same material as the second layer45of the insulating layer40.

As shown inFIG.4, a surface41aof the first portion41of the insulating layer40opposite to the substrate30is, for example, a flat surface perpendicular to the main surface31. A surface42aof the second portion42of the insulating layer40opposite to the substrate30is, for example, a flat surface parallel to the main surface31. The surface42ais in contact with the cap layer70. In this embodiment, as an example, a surface43aof the boundary part43opposite to the substrate30includes an inclined surface43binclined with respect to the direction A1perpendicular to the main surface31when viewed from the extending direction of the wiring portion60. More specifically, the inclined surface43bis inclined outward with respect to the surface41aof the first portion41(so as to be away from the center of the groove33as the distance from the bottom surface34bof the groove33increases). In this example, the inclined surface43bis curved convexly toward the side opposite to the substrate30.

The end portion51of the metal layer50enters between the cap layer70and the inclined surface43b. More particularly, the end portion51has a portion disposed in a space formed between the cap layer70and the inclined surface43bin the direction A1perpendicular to the main surface31.

The end portion51has a first surface51a, a second surface51bcontinuous with the first surface51a, and a third surface51ccontinuous with the first surface51aon a side opposite to the second surface51b. The first surface51aextends along the cap layer70and is joined to the cap layer70. In this example, the first surface51ais a flat surface and is positioned on the same plane as the surface42aof the second portion42of the insulating layer40and the surface60aof the wiring portion60described later.

The second surface51bextends along the inclined surface43band is joined to the inclined surface43b. Similarly to the inclined surface43b, the second surface51bis inclined outward with respect to the direction A1perpendicular to the main surface31. The second surface51bis concavely curved toward the side opposite to the substrate30. The second surface51bis in contact with the second layer45constituting the boundary part43of the insulating layer40. That is, a portion of the insulating layer40in contact with the second surface51b(in this example, the second layer45constituting the boundary part43) is made of the same material (silicon nitride film) as a portion of the cap layer70in contact with the first surface51a. As described above, in this example, the entire cap layer70is formed of a silicon nitride film. This can increase the joining strength between the insulating layer40and the cap layer70.

The third surface51cis a surface opposite to the second surface51bin the end portion51. The third surface51cis inclined outward with respect to the direction A1when viewed from the extending direction of the wiring portion60. The degree of inclination of the third surface51cwith respect to the direction A1is gentler than the degree of inclination of the second surface51bwith respect to the direction A1. Accordingly, the thickness of the end portion51in the direction A2parallel to the main surface31gradually increases toward the tip of the end portion51. Apart61of the wiring portion60located at a boundary part between the metal layer50and the cap layer70enters between the cap layer70and the third surface51c. To be more specific, the part61of the wiring portion60is disposed in a space formed between the cap layer70and the first surface51cin the direction A1.

In the end portion51, the first surface51aand the second surface51bform an acute angle. In other words, the angle θ formed by the first surface51aand the second surface51bis smaller than 90 degrees. That is, the thickness of the end portion51in the direction A1perpendicular to the main surface31gradually decreases toward the tip of the end portion51(for example, the vertex formed by the first surface51aand the second surface51b). The angle θ may be, for example, 15 degrees to 88 degrees. The end portion51of the metal layer50is not provided on the second portion42of the insulating layer40.

The thickness (minimum thickness) of the end portion51in the direction A2parallel to the main surface31is larger than the thickness of a portion of the metal layer50other than the end portion51(for example, a portion of the metal layer50located in the middle in the direction A1perpendicular to the main surface31or a portion of the metal layer50located on the first portion41of the insulating layer40). The thickness (maximum thickness) of the tip portion of the metal layer50in the direction A1is smaller than the thickness T2of the insulating layer40. Here, the “tip portion of the metal layer50” means a portion of the metal layer50in which the thickness in the direction A2parallel to the main surface31is larger than the thickness in the direction A1perpendicular to the main surface31.

In this example, a surface60aof the wiring portion60that is in contact with the cap layer70is located on the same plane as the surface42aof the second portion42of the insulating layer40. The surface42ais a surface of the insulating layer40in contact with the cap layer70. A surface70aof the cap layer70on the substrate30side is a flat surface.

As described above, the groove33extends in a spiral shape in plan view. Thus, as shown inFIG.2, the groove33has a plurality of portions34adjacent to each other. The distance B between the portions34is smaller than the width W of the groove33. The width W of the groove33is smaller than the depth D of the groove33. The depth D of the groove33is, for example, a distance between the main surface31and the bottom surface33ain the direction A1perpendicular to the main surface31. The distance L between the bottom surface33aof the groove33in the direction A1perpendicular to the main surface31and the opposite surface of the substrate30opposite to the main surface31is larger than the depth D of the groove34. In this example, the opposite surface is the surface81aof the first silicon layer81on the insulating layer83side (opposite to the main surface31).

[Method of Manufacturing Damascene Wiring Structure]

Next, a method for producing the damascene wiring structure100(first step to eighth step) will be described with reference toFIGS.5to10. The process of manufacturing the damascene wiring structure100includes a process of manufacturing a semiconductor substrate (substrate30) having a groove33(first step to third step). InFIG.6andFIGS.8to10, each part is schematically illustrated. In particular, inFIG.8(b),FIG.9(a),FIG.9(b),FIG.10(a), andFIG.10(b), the inclined surface33cis not shown, and the groove33is simplified.

In the present embodiment, as an example, a substrate30having a groove33is manufactured from an SOI wafer SW as shown inFIG.5. That is, the plurality of substrate30are obtained by cutting the SOI wafer SW into an appropriate shape. As shown inFIG.6(a), the substrate30included in the SOI wafer SW includes a first silicon layer81, a second silicon layer82, and an insulating layer83. The thickness of the first silicon layer81is, for example, about 30 to 150 μm, and the thickness of the second silicon layer82is, for example, about 625 μm.

The SOI wafer SW has an orientation flat OF which is a (110) plane and a main surface31which is a (100) plane. InFIG.5, the Z-axis direction is a direction perpendicular to the main surface31, the X-axis direction is a direction along the orientation flat OF when viewed from the Z-axis direction, and the Y-axis direction is a direction perpendicular to both the Z-axis direction and the X-axis direction. Here, the silicon crystal included in the SOI wafer SW is cubic. Therefore, in the example ofFIG.5, a plane parallel to a plane orthogonal to the Y-axis direction (XZ plane) and a plane orthogonal to the X-axis direction (YZ plane) constitute equivalent crystal planes (that is, (110) planes). In addition, any plane inclined by 45 degrees with respect to the (100) plane when viewed from the Z-axis direction constitutes an equivalent crystal plane (that is, the (100) plane). The X-axis direction corresponds to a direction parallel to one of the first axis X1and the second axis X2shown inFIG.1, and the Y-axis direction corresponds to a direction parallel to the other of the first axis X1and the second axis X2. Depending on the processing accuracy in manufacturing the SOI wafer SW, the crystal orientation of the orientation flat OF may not strictly coincide with (110). That is, the crystal orientations of the respective surfaces described above do not necessarily have to perfectly coincide with each other, and may include some deviation.

(First Step)

First, a process including isotropic etching is performed on the main surface31of the substrate30. The “process including isotropic etching” is, for example, the Bosch process. In the Bosch process, a groove is formed by isotropic dry etching, and a protective film is formed on an inner wall of the groove. After only the protective film at the bottom of the groove is removed by anisotropic dry etching, the groove is formed again by isotropic dry etching. In the Bosch process, the groove is dug by repeating such processes. As a result, as shown inFIGS.6(b) and7(a), a groove32having a bottom surface32aand a side surface32bon which scallops are formed is formed.FIG.6(b)shows a cross section perpendicular to the extending direction of the groove32.FIG.7(a)is an SEM image of the bottom of the groove32(a portion including the bottom surface32a). The groove32is formed to extend in a direction parallel to the X-axis direction or the Y-axis direction. The scallops are a minute uneven structure formed on the side surface32b.

As shown inFIG.7(b), the bottom surface33a, the side surface33b, and the inclined surface33care integrally (continuously) formed. In the cross section perpendicular to the extending direction of groove33, the length of the bottom surface33ais longer than the length of the inclined surface33c. Between the side surface33band the inclined surface33c, there is formed a boundary line separating the side surface33band the inclined surface33c. That is, the boundary between the side surface33band the inclined surface33cis clear, and the corner portion between the side surface33band the inclined surface33cis not a gentle curve (curved surface). The difference between the first angle formed by the bottom surface33aand the inclined surface33cand the second angle formed by the side surface33band the inclined surface33cis 30 degrees or less. In the present embodiment, the first angle is an angle formed by the (100) plane and the (111) plane, and is approximately 125.3 degrees. The second angle is an angle formed by the (110) plane and the (111) plane, and is approximately 144.7 degrees. Therefore, the angle formed by the first angle and the second angle is approximately 19.4 degrees. The inclined surface33cis a flat surface. Accordingly, at a predetermined height position, the thickness t1of the substrate33increased by the formation of the inclined surface33cis larger than the thickness t2of the substrate30increased by the formation of the inclined surface if the inclined surface is the curved surface C (the curved surface recessed with respect to the space in the groove). Therefore, according to the inclined surface33cwhich is a flat surface, since the thickness of the substrate30in the vicinity of the bottom surface33aof the groove33can be suitably increased, the groove33can be structurally stabilized. The bottom surface33ais curved at least more than the inclined surface33cso as to be convex toward the side opposite to the opening side of the groove33. Since the bottom surface33ahas such a curved shape, the bottom surface33aand the inclined surface33care gently connected. As a result, concentration of stress on the corner portion between the bottom surface33aand the inclined surface33ccan be suitably suppressed.

The scallops S inevitably occur because the grooves are formed by alternately repeating the isotropic dry etching, the formation of the protective film, and the anisotropic dry etching. When the fourth step and the subsequent steps are performed in a state in which the scallops S remain, there is a concern that a void may occur between the insulating layer40(second layer45) and the metal layer50or a crack (rupture portion) may occur in the insulating layer40. The void can be structural weak point in the damascene wiring structure100. In addition, the crack may cause current flowing through the wiring portion60to leak into the substrate30. That is, the metals (the metal layer50and the wiring portion60) formed on the insulating layer40may come into contact with a part of the substrate30through the crack.

(Second Step and Third Step)

The second step and the third step are performed in order to avoid the above-described problems (i.e., occurrence of void, crack, or the like) caused by scallops S. First, hydrophilic treatment is performed on the side surface32bof the groove32(second step). The hydrophilic treatment is, for example, a treatment of performing O2ashing on the side surface32bor a treatment of immersing the side surface32bin a surfactant, alcohol, or the like. Instead of (or in combination with) the hydrophilic treatment, the groove32may be subjected to degassing treatment. For example, a degassing treatment for degassing the solution present in the groove32may be performed. The degassing treatment is a treatment for facilitating the filling of the groove32with the etching solution, and is also a kind of hydrophilic treatment.

Subsequently, anisotropic wet etching is performed on the groove32containing scallops S in a state where the bottom surface32aof the groove32is present (third step). As the etchant, for example, TMAH (tetramethylammonium hydroxide), KOH (potassium hydroxide), or the like is used. Here, “a state where the bottom surface32aof the groove32is present” means a state where the groove32is a non-through hole (groove). That is, the “state where the bottom surface32aof the groove32is present” is a state other than the state in which the bottom of the groove32is removed (that is, the state in which the groove32is a through hole penetrating from the main surface31to the surface of the second silicon layer82opposite to the insulating layer83).

By performing the wet etching, the scallops S formed on the side surface32bof the groove32are removed, and the side surface32bis planarized. As a result, as shown inFIGS.6(c) and7(b), a groove33having a flat side surface33bfrom which scallops S have been removed is obtained.FIG.6(c)shows a cross section perpendicular to the extending direction of the groove33.FIG.7(b)is an SEM image of the bottom of the groove33(the portion including the bottom surface33a). In the present embodiment, as shown inFIG.5, a first groove133extending along the Y-axis direction (first direction) and a second groove233extending along the X-axis direction (second direction) are obtained as the groove33. Further, from the relationship of the plane orientation shown inFIG.5, in both of the first groove133and the second groove233, the bottom surface33ais formed by a surface along the (100) surface (that is, a surface substantially parallel to the (100) surface), and the side surface33bis formed by a surface along the (110) surface (that is, a surface substantially parallel to the (110) surface). Further, the inclined surface33cis formed by a surface along the (111) plane inclined by 54.7 degrees with respect to each of the (100) plane and the (110) plane (that is, a surface substantially parallel to the (111) plane). That is, the plane orientation of the bottom surface33a, the plane orientation of the side surface33b, and the plane orientation of the inclined surface33care different from each other. As described above, the groove33is different from the groove32not only in that the scallops S are removed but also in the shape of the corner portion of the bottom portion (i.e., the region where the bottom surface and the side surface are connected).

The shape of the inner surface of the groove33as described above is formed by the difference in etching rate depending on the plane orientation. Specifically, at the corner of the bottom of the groove33, the etching rate in the direction perpendicular to the (111) plane is lower than the etching rate in the direction perpendicular to the (100) plane (i.e., the depth direction of the groove33) and the etching rate in the direction perpendicular to the (110) plane (i.e., the width direction of the groove33). As a result, the inclined surface33calong the (111) plane is formed.

Although the above-described hydrophilic treatment or degassing treatment (second step) is performed before the third step of performing anisotropic wet etching, the degassing treatment (second step) for the groove32may be performed simultaneously with the wet etching in the third step, instead of (or in combination with) the hydrophilic treatment or the degassing treatment. The degassing treatment for the groove32is, for example, a treatment for removing a reactive gas (e.g., H2) generated in the groove32by a reaction between the substrate30and the etching solution during wet etching or a gas (e.g., CO2, O2, N2, etc.) dissolved in the etching solution in the groove32by using ultrasonic waves.

In addition, in order to appropriately adjust the difference in the etching rate between the plane orientations described above, a chemical liquid (for example, a surfactant NCW, IPA (isopropyl alcohol), or the like) that affects the anisotropy of the etching rate may be added to the etching liquid in the second step. Accordingly, the shape of the groove33(inclined surface33c) can be appropriately adjusted.

As shown inFIG.8(a), the substrate30having the groove33formed in the main surface31is obtained by the above-described processes of manufacturing a semiconductor device (the processes up to the third step). The depth of the groove33is, for example, about 5 to 30 μm.

(Fourth Step)

Subsequently, as shown inFIG.8(b), an insulating layer40having a first portion41provided on the inner surface of the groove33and a second portion42formed integrally with the first portion41and provided on the main surface31is formed on the main surface31of the substrate30. More specifically, after a first layer44made of a silicon oxide film (thermal oxide film) is formed on the main surface31and the inner surface of the groove33, a second layer45made of a silicon nitride film (LP-SiN) is formed on the first layer44. The thickness of the first layer44and the second layer45is, for example, about 100 to 1000 nm.

More specifically, in the first step, the insulating layer40is formed such that a surface43a(a surface opposite to the substrate30) of the boundary portion43between the first portion41and the second portion42in the insulating layer40includes an inclined surface43binclined with respect to a direction A1perpendicular to the main surface31when viewed from the extending direction of the wiring portion60(seeFIG.4). For example, by forming the first layer44made of a silicon oxide film and the second layer45made of a silicon nitride film on the main surface31and the inner surface of the groove33, the inclined surface43bis formed on the surface43aof the boundary portion43. This is because the inclined shape is easily formed in the first layer44made of the silicon oxide film.

(Fifth Step)

Subsequently, as shown inFIG.9(a), a metal layer50is formed on the first portion41and the second portion42of the insulating layer40. In the fifth step, a metal layer55is formed on the metal layer50. The metal layer55is made of a metal material such as copper, for example. The metal layer55functions as a seed layer together with the metal layer50. The metal layer50and the metal layer55are formed by, for example, sputtering, but may be formed by atom layer deposition (ALD), chemical vapor deposition (CVD), ion-plating, or electroless plating. The total thickness of the metal layer50and the metal layer55is, for example, about 10 nm to 3000 nm.

(Sixth Step)

Subsequently, as shown inFIG.9(b), a wiring portion60is formed on the metal layer50embedded in the groove33. The wiring portion60is formed by plating, for example. The wiring portion60is formed, for example, such that the average thickness of the wiring portion60on the main surface31is 1 μm or more. In this example, since the metal layer55is made of the same material as the wiring portion60, the wiring portion60and the metal layer55are integrated when the wiring portion60is formed, and the interface between the wiring portion60and the metal layer55may be eliminated. In this case, the metal layer55may be regarded as constituting the wiring portion60.

(Seventh Step)

Subsequently, as shown inFIG.10(a), the metal layer50, the metal layer55, and the wiring portion60on the second portion42are removed by, for example, chemical mechanical polishing (CMP) so that the second portion42of the insulating layer40is exposed. In the seventh step, the insulating layer40, the metal layer50, the metal layer55, and the wiring portion60are subjected to chemical mechanical polishing from the side opposite to the substrate30. A portion of each of the insulating layer40, the metal layer50, the metal layer55, and the wiring portion60opposite to the main surface31or the bottom surface31ain the direction A1perpendicular to the main surface33is removed to planarize the insulating layer40, the metal layer50, the metal layer55, and the wiring portion60. At this time, in this example, a portion constituting the second portion42of the second layer45of the insulating layer40is removed.

(Eighth Step)

Subsequently, as shown inFIG.10(b), a cap layer70is formed to cover the second portion42of the insulating layer40, the end portion51of the metal layer50, and the wiring portion60. The cap layer70is made of, for example, a silicon nitride film (PE-SiN) and is formed to a thickness of about 200 to 3000 nm. Subsequently, the second silicon layer82and the insulating layer83are removed by etching or the like. Through the above steps, the above-described damascene wiring structure100is obtained.

[Effects]

In the above-described method of manufacturing a semiconductor substrate (first step to third step), after forming groove33having the bottom surface33aand the side surface32bon which scallops S are formed in the first step, the side surface32bof the groove32is subjected to the hydrophilic treatment or the degassing treatment, thereby improving wettability of the side surface32bof the groove32with the etchant. In addition, by performing anisotropic wet etching in a state where the bottom surface32aof the groove32exists, the groove32can be effectively filled with the etching solution. Thus, the entire side surface32bof the groove32can be wetted with the etching solution, and the scallops S formed on the side surface32bcan be effectively removed. That is, the groove33from which scallops S are removed is obtained. By removing the scallops S, structural weak points in the groove can be eliminated.

Furthermore, since anisotropic etching is performed in the third step, the etching rate of the side surface32bcan be made substantially uniform between the opening side and the bottom surface side of the groove32. As a result, it is possible to suppress the occurrence of a problem that the width of the groove32on the opening side is widened in a tapered shape. Therefore, according to the above described method of manufacturing a semiconductor substrate, the substrate30having the groove33with high reliability can be manufactured. That is, the groove33in which an appropriate shape is maintained and the scallops S are appropriately removed can be formed in the main surface31of the substrate30.

According to the above-described method of manufacturing a damascene wiring structure (the first step to the eighth step), the insulating layer40and the metal layer50are formed on the inner surface of the groove33from which the scallops S have been appropriately removed. As a result, it is possible to suppress the occurrence of voids, cracks, or the like described above, and thus it is possible to obtain the highly reliable damascene wiring structure100. That is, as a result of forming the groove33with high reliability, the reliability of the damascene wiring structure100formed in the groove33can be improved.

As shown inFIG.5, the main surface31of the substrate30extends along the (100) plane, and the groove33(the first groove133or the second groove233) extending in the direction along the (110) plane (the X-axis direction or the Y-axis direction in this embodiment) is formed in the first step. According to the above configuration, the bottom surface33aalong the (100) plane and the side surface33balong the (110) plane are formed. Further, by utilizing the difference in etching rate depending on the plane orientation, it is possible to form the inclined surface33calong the (111) plane and inclined with respect to the bottom surface33aand the side surface33bbetween the bottom surface33aand the side surface33b. The angle of the corner between the bottom surface33aand the side surface33bwhen the inclined surface33cis formed (i.e., the angle between the bottom surface33aand the inclined surface33cor the angle between the side surface33band the inclined surface33c) is larger than the angle of the corner when the inclined surface33cis not formed (i.e., the angle between the bottom surface33aand the side surface33b). In the present embodiment, the angle between the bottom surface33aand the inclined surface33cis approximately 125.3 degrees, and the angle between the side surface33band the inclined surface33cis approximately 144.7 degrees. On the other hand, when the inclined surface33cis not formed, the angle of the corner portion (that is, the angle formed by the bottom surface and the side surface) is approximately 90 degrees. That is, by forming the inclined surface33c, a more rounded corner portion (i.e., a corner portion gently bent in a stepwise manner) is formed than in the case where the inclined surface33cis not formed. According to such a corner portion, it is possible to make it difficult for the insulating layer40to crack at the corner portion. Therefore, according to the above configuration, a more reliable damascene wiring structure100can be obtained. That is, as a result of forming the groove33with higher reliability, the reliability of the damascene wiring structure100formed in the groove33can be further improved.

In the above-described substrate30(that is, the semiconductor substrate manufactured by the first to third steps), as described above, the angle of the corner portion between the bottom surface33aand the side surface33bis larger than the angle of the corner portion when the inclined surface33cis not provided. That is, the inclined surface33cforms a rounded corner portion (that is, a corner portion gently bent in a stepwise manner) as compared with the case where the inclined surface33cis not formed. According to the groove33having such a corner portion, for example, in a case where a predetermined material layer (in the present embodiment, the insulating layer40) is provided on the inner surface of the groove33, the occurrence of cracks in the material layer at the corner portion is suppressed. As described above, the reliability of the substrate30is enhanced by the groove33described above. The substrate30can be obtained relatively easily by utilizing the difference in etching rate depending on the plane orientation.

The above-described damascene wiring structure100is formed by embedding the wiring portion60or the like in the groove33having the bottom surface33a, the side surface33b, and the inclined surface33cas described above. Therefore, cracks in the insulating layer40are suppressed at the corners of the groove33. Therefore, in the damascene wiring structure100, reliability is enhanced by the groove33.

In the damascene wiring structure100, the bottom surface33ais a surface along the (100) plane, the side surface33bis a surface along the (110) plane, and the inclined surface33cis a surface along the (111) plane. According to the above-described configuration, the damascene wiring structure100having the above-described effects can be easily obtained by utilizing the difference in etching rate depending on the plane orientation.

FIG.11is a perspective view schematically showing a corner portion (that is, an outer corner portion where the first groove133and the second groove233intersect) of the damascene wiring structure100.FIG.11illustrates a state before the damascene wiring structure100is formed (i.e., a state before the wiring portion60and the like are embedded in the first groove133and the second groove233). As shown inFIG.11, at the corner where the first groove133and the second groove233meet, the first groove133and the second groove233share the bottom surface33a. That is, the bottom surface33aof the first groove133and the bottom surface33aof the second groove233are continuous at the corner portion.

The first groove133has a first side surface133band a first inclined surface133c. The first inclined surface133cis connected to the bottom surface33aand the first side surface133bbetween the bottom surface33aand the first side surface133b, and is inclined with respect to the bottom surface33aand the first side surface133b. As described above, in the present embodiment, the bottom surface33ais along the (100) plane, the first side surface133bis along the (110) plane, and the first inclined surface133cis along the (111) plane. Therefore, an angle between the bottom surface33aand the first inclined surface133cis about 125.3 degrees, and an angle between the first side surface133band the first inclined surface133cis about 144.7 degrees.

The second groove233has a second side surface233band a second inclined surface233c. The second inclined surface233cis connected to the bottom surface33aand the second side surface233bbetween the bottom surface33aand the second side surface233b, and is inclined with respect to the bottom surface33aand the second side surface233b. As described above, in the present embodiment, the bottom surface33ais along the (100) plane, the second side surface233bis along the (110) plane, and the second inclined surface233cis along the (111) plane. Therefore, an angle between the bottom surface33aand the second inclined surface233cis about 125.3 degrees, and an angle between the second side surface233band the second inclined surface233cis about 144.7 degrees.

An intermediate surface35is formed between the first side surface133band the second side surface233band between the first inclined surface133cand the second inclined surface233c. The intermediate surface35is connected to the first side surface133b, the second side surface233b, the first inclined surface133c, the second inclined surface233c, and the bottom surface33a. The intermediate surface35extends along a (100) plane parallel to a direction (X-axis direction) perpendicular to the main surface31(seeFIG.5). The intermediate surface35is formed by the difference in etching rate depending on the plane orientation. Specifically, since the etching rate of the (100) plane is lower than that of the (110) plane, the intermediate surface35as the (100) plane is exposed. The angle between the intermediate surface35and the first side surface133band the angle between the intermediate surface35and the second side surface233bare both obtuse angles. Specifically, each of the angles is substantially 135 degrees. The intermediate surface35may be a flat surface as shown inFIG.11, or a portion of intermediate surface35between the first side surface133band the second side surface233bmay be inclined with respect to a portion of intermediate surface35between the first inclined surface133cand the second inclined surface233c. Further, the intermediate surface35does not necessarily have to be formed perpendicular to the bottom surface33a, and the intermediate surface35may be inclined with respect to the bottom surface33a.

According to the above configuration, the angle of the corner at which the first groove133and the second groove233intersect (i.e., the angle between the intermediate surface35and the first side surface133bor the angle between the intermediate surface35and the second side surface233b) is larger than the angle of the corner when intermediate surface35is not formed (i.e., the angle between the first side surface133band the second side surface233b). In the present embodiment, the angle of the corner when the intermediate surface35is formed (i.e., the angle between the intermediate surface35and the first side surface133bor the angle between the intermediate surface35and the second side surface233b) is approximately 135 degrees, and the angle of the corner when the intermediate surface35is not formed is approximately 90 degrees. That is, by forming the intermediate surface35, a corner portion that is more rounded (that is, a corner portion that is bent in a stepwise manner) than in the case where the intermediate surface35is not formed is formed. Such a corner portion can effectively reduce stresses acting on the wiring portion60at the corner portion when vibration is applied to the substrate or the like. Therefore, according to the above-described configuration, it is possible to obtain the damascene wiring structure100with further improved reliability. In particular, in a case where the damascene wiring structure100is applied to the mirror device1as in the present embodiment, since vibrations are frequently applied to the substrate30as the first movable portion3or the second movable portion4swings, the above-described configuration of the corner portion (that is, the configuration in which the intermediate surface35is formed) is particularly effective.

In the damascene wiring structure100, the insulating layer40includes the first portion41provided on the inner surface of the groove33and the second portion42formed integrally with the first portion41and provided on the main surface31, and the cap layer70is provided so as to cover the second portion42of the insulating layer40, the end portion51of the metal layer50, and the wiring portion60. Accordingly, for example, compared to a case where the insulating layer40includes only the first portion41, it is possible to reduce the number of portions on which stress is likely to concentrate. That is, when the insulating layer40includes only the first portion41, the end portion of the insulating layer40is located in the vicinity of the boundary part between the main surface31and the groove33, and the main surface31and the cap layer70are in contact with each other. In this case, the substrate30, the end portion of the insulating layer40, the end portion51of the metal layer50, the wiring portion60, and the cap layer70are in contact with each other at positions close to each other. Stress tends to concentrate on such a portion. On the other hand, in the damascene wiring structure100, since the end portion of the insulating layer40is not present in the vicinity of the boundary part between the main surface31and the groove33, it is possible to reduce the number of places where stress is concentrated. Further, the end portion51of the metal layer50extends so as to contact the cap layer70. If the end portion51does not reach the cap layer70and remains at a position lower than the surface60aof the wiring portion60, a void may occur in a portion of the wiring portion60exposed from the metal layer50. On the other hand, in the damascene wiring structure100, the occurrence of such voids can be suppressed, and the peeling of the cap layer70or the like caused by the voids can be suppressed. Further, the surface40aof the boundary part43between the first portion41and the second portion42opposite to the substrate30in the insulating layer43includes an inclined surface43b, and the end portion51of the metal layer50enters between the cap layer70and the inclined surface43b. In the end portion51, the first surface51aalong the cap layer70and the second surface51balong the inclined surface43bform an acute angle. Accordingly, it is possible to suppress the stress from intensively acting on the cap layer70. As described above, the reliability of the damascene wiring structure100is improved.

In the damascene wiring structure100, the thickness T1of the cap layer70is larger than the thickness T2of the insulating layer40. Accordingly, the strength of the cap layer70can be increased, and the reliability can be further increased.

In the damascene wiring structure100, a portion of the cap layer70in contact with the first surface51aof the end portion51and a portion of the insulating layer40in contact with the second surface51bof the end portion51(the second layer45constituting the boundary part43) are made of the same material. Accordingly, the joining strength between the cap layer70and the insulating layer40can be increased in the vicinity of the contact portion between the cap layer70and the end portion51of the metal layer50, and the reliability can be further increased.

In the damascene wiring structure100, the insulating layer40includes the first layer44made of an oxide film and the second layer45made of a nitride film and provided on the first layer44. Accordingly, since the inclined shape can be easily formed in the first layer44made of the oxide film, the inclined surface43bcan be easily formed.

In the damascene wiring structure100, the inclined surface43bis convexly curved. Accordingly, it is possible to more reliably suppress the stress from intensively acting on the cap layer70.

In the damascene wiring structure100, the third surface50copposite to the second surface51bin the end portion51of the metal layer51is inclined, and the part61of the wiring portion60enters between the cap layer70and the third surface51c. Accordingly, the end portion51of the metal layer50can be pressed by the wiring portion60, and the stress acting on the cap layer70from the metal layer50can be reduced. Further, since the thickness of the part61of the wiring portion60in the direction A1perpendicular to the main surface31is reduced, the stress acting on the cap layer70from the wiring portion60can be reduced.

In the damascene wiring structure100, the thickness of the end portion51of the metal layer50in the direction A2parallel to the main surface31is larger than the thickness of the portion of the metal layer50other than the end portion51. Accordingly, the contact area between the end portion51of the metal layer50and the cap layer70can be increased, and the stress acting on the cap layer70from the metal layer50can be more suitably dispersed.

In the damascene wiring structure100, the thickness of the end portion51of the metal layer50in the direction A2parallel to the main surface31gradually increases toward the tip of the end portion51. Accordingly, the contact area between the end portion51of the metal layer50and the cap layer70can be further increased, and the stress acting on the cap layer70from the metal layer50can be further suitably dispersed.

In the damascene wiring structure100, the groove33extends in a spiral shape. Even when the groove33extends in a spiral shape as described above, high reliability can be obtained.

In the damascene wiring structure100, the interval B between the portions34adjacent to each other in the groove33may be smaller than the width W of the groove33. As a result, the pitch (interval) of the wirings can be narrowed, and space saving can be achieved.

In the damascene wiring structure100, the width W of the groove33is smaller than the depth D of the groove33. This makes it possible to save space and reduce the resistance of wiring.

In the damascene wiring structure100, the distance L between the bottom surface33aof the groove33in the direction A1perpendicular to the main surface31and the opposite surface (the surface81aof the first silicon layer81) of the substrate30opposite to the main surface31is larger than the depth D of the groove34. Accordingly, the strength of the substrate30can be increased, and the reliability can be further increased.

Modification

Although the preferred embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the above embodiments. The material and shape of each component are not limited to the examples described above. In the above embodiment, the damascene wiring structure100applied to the mirror device1has been described, but the damascene wiring structure100may be applied to a device other than the mirror device1. In addition, in the above-described embodiment, the two axis type mirror device1that is rotatable about two axes (the first axis X1and the second axis X2) is exemplified, but the damascene wiring structure100may be applied to a one axis type mirror device that is rotatable about one axis.

In the method of manufacturing a semiconductor substrate (first step to third step), trench-shaped grooves32,33extending in the direction along main surface31are formed for the purpose of manufacturing damascene wiring structure100, but in the first step to third step, for example, a via-shaped recess having a circular cross section or the like may be formed. Also in this case, the scallops formed on the side surface of the recess in the first step can be appropriately removed by wet etching in the third step. After the third step is performed, the bottom surface of the recess may be removed. For example, the bottom surface of the recess may be removed by performing polishing or the like from the surface of the second silicon layer82on the side opposite to the insulating layer83to form the through hole. Such a through hole can be used to embed a through electrode (metal), for example. When such a through-hole is formed, the inclined surface formed in the third step can be removed by polishing, and a through-hole that extends straight with an equal width and has no scallops can be obtained.

In the above embodiment, the SOI wafer SW having the orientation flat OF of the (110) plane is used. Therefore, the groove33is formed along the X-axis direction along the orientation flat OF or the Y-axis direction perpendicular to the orientation flat OF so that the side surface33bof the groove33is along the (110) plane. However, the SOI wafer used for manufacturing the substrate30is not limited to the SOI wafer SW. For example, when an SOI wafer having an orientation flat OF of the (100) plane is used, the plane orientation of the SOI wafer is opposite to the plane orientation shown inFIG.5. That is, the (100) plane shown inFIG.5becomes the (110) plane, and the (110) plane shown inFIG.5becomes the (100) plane. In this case, a groove having a side surface along the (110) plane can be formed by forming the groove along a direction inclined by 45 degrees with respect to the X-axis direction and the Y-axis direction. That is, even when an SOI wafer having a plane orientation different from that of the SOI wafer SW is used, a groove having a structure similar to that of the groove33can be formed by adjusting the design (extending direction) of the groove. In addition, in the SOI wafer SW, the crystal orientation of the first silicon layer81and the crystal orientation of the second silicon layer82may not necessarily coincide with each other.

The damascene wiring structure100may be configured as in a first modification shown inFIG.12. In the first modification, a boundary surface36inclined outward with respect to the direction A1perpendicular to the main surface31when viewed from the extending direction of the wiring portion60is provided at a boundary part between the main surface31and the groove33in the substrate30. The boundary surface36is, for example, a flat surface. Since the boundary part43of the insulating layer40is provided on the boundary surface36, it extends along the boundary surface36and is inclined outward with respect to the direction A1perpendicular to the main surface31. The inclined surface43bof the boundary part43and the second surface51bof the end portion51of the metal layer50are flat surfaces parallel to the boundary surface36. The third surface51cof the end portion51is also a flat surface inclined outward with respect to the direction A1. The inclination angle of the third surface51cwith respect to the direction A1is gentler than the inclination angle of the second surface51bwith respect to the direction A1. Accordingly, the thickness of the end portion51in the direction A2parallel to the main surface31gradually increases toward the tip of the end portion51.

In manufacturing the damascene wiring structure100of the first modification, for example, the groove33is formed by reactive ion etching using a non-Bosch process and a Bosch process. Accordingly, when the groove33is formed, the boundary surface36is formed at the boundary part between the main surface31and the groove33in the substrate30. The reliability can be improved by combining the non-Bosch process and the Bosch process.

According to the first modification, the reliability can be improved as in the above-described embodiment. Further, since the boundary surface36is provided at the boundary part between the main surface31and the groove33in the substrate30, the inclined surface43bcan be easily formed. Also in the first modification, the interval B between the portions34of the groove33may be smaller than the width W of the groove33. In the case of the first modification, the interval B is a distance between the inner surfaces other than the boundary surface36in the plurality of portions34(in other words, a distance between portions of the inner surfaces of the groove33extending along the direction A1perpendicular to the main surface31).

The damascene wiring structure100may be configured as in a second modification shown inFIG.13. In the second modification, the surface60aof the wiring portion60is located on the bottom surface33aside of the groove33with respect to the surface42aof the second portion42of the insulating layer40. The third surface51cof the end portion51of the metal layer50is covered by a boundary part71between a portion on the surface60aand a portion on the surface42ain the cap layer70. The boundary part71extends along the third surface51cand is inclined outward with respect to the direction A1perpendicular to the main surface31. In manufacturing the damascene wiring structure100of the second modification, for example, the amount of dishing of the wiring portion60(the amount of removal of the wiring portion60) is increased by adjusting the slurry in the chemical mechanical polishing of the seventh step. Thus, the wiring portion60including the shape shown inFIG.13can be formed.

According to the second modification, the reliability can be improved as in the above embodiment. Further, the surface60ais positioned on the bottom surface33aside of the groove33with respect to the surface42a. As a result, it is possible to further reduce the number of places where stress is likely to concentrate. Further, since the third surface51cof the end portion51is covered by the boundary part71, the contact area between the end portion51of the metal layer50and the cap layer70can be further increased, and the stress acting on the cap layer70from the metal layer50can be further suitably dispersed.

The damascene wiring structure100may be configured as in a third modification shown inFIG.14(a). In the third modification, as in the second modification, the surface60aof the wiring portion60is located on the bottom surface33aside of the groove33with respect to the surface42aof the second portion42of the insulating layer40. The third surface51cof the end portion51of the metal layer50is covered by the boundary part71of the cap layer70. In the third modification, the thickness T1of the cap layer70is larger than the distance H between the surface60aand the surface42ain the direction A1perpendicular to the main surface31. According to the third modification, the reliability can be improved as in the above embodiment. Further, since the thickness T1of the cap layer70is larger than the distance H between the surface60aand the surface42ain the direction A1perpendicular to the main surface31, the strength of the cap layer70can be further increased.

The damascene wiring structure100may be configured as in a fourth modification shown inFIG.14(b). In the fourth modification, as in the second modification, the surface60aof the wiring portion60is located on the bottom surface33aside of the groove33with respect to the surface42aof the second portion42of the insulating layer40. The third surface51cof the end portion51of the metal layer50is covered by the boundary part71of the cap layer70. In the fourth modification, the thickness T1of the cap layer70is smaller than the distance H between the surface60aand the surface42ain the direction A1perpendicular to the main surface31. According to the fourth modification, the reliability can be improved as in the above embodiment. Further, since the thickness T1of the cap layer70is smaller than the distance H between the surface60aand the surface42ain the direction A1perpendicular to the main surface31, the thickness of the wiring portion60in the direction A1can be reduced, and as a result, the stress acting on the cap layer from the wiring portion60can be further reduced.

The third surface51cof the end portion51of the metal layer50may extend along the second surface51b. For example, the degree of inclination (inclination angle) of the third surface51cmay be the same as the degree of inclination (inclination angle) of the second surface51b. The third surface51cand the second surface51bmay extend parallel to each other. The second portion42may be constituted by the first layer44and the second layer45. In this case, it is possible to further reduce the number of portions on which stress is likely to concentrate. When the cap layer70is formed of the same material as that of the second layer45of the insulating layer40, the area of a portion where the same materials are bonded to each other is increased, and thus the adhesion can be increased. The insulating layer40may be constituted by a single layer. The insulating layer40may be formed of a single layer made of an oxide film, for example. In this case, the cap layer70may be formed of an oxide film. When viewed from the extending direction of the wiring portion60, the first surface51aand the second surface51bmay be connected to each other such that the curvatures thereof are continuous. The damascene wiring structure100may be applied to configurations other than actuator devices.

REFERENCE SIGNS LIST

30: substrate (semiconductor substrate),31: main surface,32,33: groove,32a,33a: bottom surface,32b,33b: side surface,33: groove (recess),33c: inclined surface,35: intermediate surface,40: insulating layer,41: first portion,42: second portion,50: metal layer,51: end portion,60: wiring portion,70: cap layer,100: damascene wiring structure,133: first groove,133b: first side surface,133c: first inclined surface,233: second groove,233b: second side surface,233c: second inclined surface, S: scallops.