JP4349548B2 - Manufacturing method of light modulation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a light modulation device that modulates (switches) light by changing the reflection direction of an incident light beam, and more specifically, a light modulation device having a basic structure that deforms a beam having a light reflection region by electrostatic force. About. The light modulation device of the present invention can be widely applied to image devices such as an optical writing device in an electrophotographic process and video devices such as a projector.
[0002]
[Prior art]
  KEPetersen announced in 1977 a device that switches a cantilever beam by electrostatic force to change the direction of light reflection and switches it (Applied Physics Letters, Vol. 31, No.8, pp521-pp523). In addition, DMBloom et al. Have announced an element for optical switching by driving a diffraction grating with an electrostatic force (Optics Letters, Vol. 7, No. 9, pp 688 to pp 690, Japanese Patent No. 2941952 and Japanese Patent Publication No. No. 3016871, JP 10-510374).
[0003]
  Further, as an image apparatus using a light modulation system, CHIBO et al. Disclosed in JP-A-6-138403 a digital micromirror device (generally called DMD) arranged one-dimensionally or two-dimensionally. Yes.
[0004]
  Furthermore, as an element structure of a digital micromirror device, L.J. Hornbeck discloses a torsion beam type or cantilever beam type digital micromirror device (Proc. SPIE Vol.1150, pp.86-102 (1989)). In this torsion beam type or cantilever type digital micromirror device, the mirror part is used in an inclined state.
[0005]
  Furthermore, Japanese Patent Laid-Open No. 2000-2842 discloses an element that performs light modulation at high speed by bending and deforming a both-end fixed beam into a cylindrical shape by Gelbert.
[0006]
[Problems to be solved by the invention]
  The optical switch using the cantilever beam announced by KEPetersen and the digital micromirror device of torsion beam type and cantilever beam type released by LJHornbeck are difficult to ensure the stability of the beam and the response speed is not fast. HaveTheYes. In addition, the optical switch elements disclosed in Japanese Patent Nos. 2941952 and 3016871 by D.M.Bloom have a drawback that the wavelength of incident light is limited.
[0007]
  On the other hand, the element disclosed in Japanese Patent Application Laid-Open No. 2000-2842 by Gelbert, that is, the element that has parallel gaps between the electrodes and deflects both ends of the fixed beam into a cylindrical shape by the electrostatic attraction can be deformed at high speed. Since it is possible, it has an advantage that the response speed can be increased, but there are also the following disadvantages.
[0008]
  That is, in the element disclosed in Japanese Patent Application Laid-Open No. 2000-2842, as shown in FIG. 1A (schematic cross-sectional view) and FIG. Opposite the electrode 103 through the film 106, on the plane of the substrate 102, one opposite both ends (left and right both ends in the figure) of the beam 101 are fixed ends, and the other opposite both ends (near in the figure front).WhenThe back end is the free end. The beam 101 in the upper part of the gap is in contact with the substrate plane and has a flat plate shape. Therefore, in order to easily deform the beam 101 by an electrostatic force, that is, to enable driving with a low voltage, it is necessary to reduce the thickness of the beam 101.ButThere is a disadvantage that the driving voltage must be increased if the beam film thickness cannot be reduced in terms of manufacturing yield.
[0009]
  Furthermore, since the beam 101 is fixed at both ends, it is required that the beam 101 expands when deformed. In particular, when the amount of deformation is larger than the beam film thickness, a relatively large amount of beam needs to be expanded. Become. As a result, compared to the torsion beam type such as a digital micromirror device, it has a drawback that the driving voltage for deformation becomes relatively high. This defect becomes significant when the amount of flexure deformation is larger than that of.
[0010]
  Furthermore, the air gap 105In general, the beam 101 formed through the structure has a residual internal stress. When the residual internal stress is a compressive stress, the beam 101 is bent or buckled, and cannot maintain flatness. Therefore, it is necessary to design the process (manufacturing process) so that the residual internal stress of the beam 101 becomes a tensile stress. In this case, that is, when the residual internal stress of the beam 101 is a tensile stress, in order to deform the beam 101 using electrostatic attraction, there is a drawback that an increase in driving voltage is required to compensate for the tensile internal stress. is there.
[0011]
  Further, in order to form the beam 101 through the gap 105 as shown in FIG. 1A, the etching is performed by etching a hollow portion (corresponding to the gap 105) in the substrate 102, sacrificial layer deposition, and CMP (Chemical Mechanical). In general, flattening by a polishing technique is required, but the CMP process is an expensive process compared to a normal photoengraving technique, and has a drawback of increasing costs. Further, the variation in the distance between the beam 101 and the electrode 103 includes both the variation in the etching due to the etching and the variation in the flattening due to the CMP technique. There is a disadvantage in that the variation in the interval becomes large, thereby increasing the variation in the driving voltage.
[0012]
  The present invention has been made mainly in view of the drawbacks of the prior art as described with reference to FIG. 1, and one object thereof is light modulation capable of beam deformation, that is, light modulation with a lower drive voltage. To provide an apparatus. Another object is to provide an optical modulation device that can reduce the manufacturing cost without performing the planarization of the sacrificial layer by a general CPMP technique in the manufacturing process. Another object is to provide an optical modulation device with little variation in drive voltage and good manufacturing yield. Another object is to provide a light modulation device that can easily return to a flat surface when no drive voltage is applied, can suppress variations in light modulation properties (that is, variations in directionality of reflected light), and has a high response speed. is there. Another object is to provide a light modulation device capable of improving the design flexibility of the manufacturing process. Another object of the present invention is to provide a manufacturing method for realizing an optical modulation device having the advantages as described above.
[0013]
  The object and other objects of the present invention described above will be specifically described in the following description of embodiments.
[0014]
[Means for Solving the Problems]
In order to achieve the object, according to the invention, as claimed in claim 1,
A light modulation device that performs light modulation by deforming a beam for reflecting light by electrostatic force,
An electrode for applying an electrostatic force to the beam is provided inside a recess of the substrate opened on the upper surface of the substrate, and the beam protrudes from the upper surface of the substrate to a position facing the electrode. Held on the substrate,
In a state where no electrostatic force acts on the beam, a gap is formed between the beam and the depression,
A method of manufacturing a light modulation device having a support close to a fixed end of the beam for assisting restoration of the beam when an electrostatic force acting on the beam is released,
Forming the recess in the substrate;
Forming the electrode inside the depression;
Forming a protective layer covering the electrode;
Depositing a sacrificial layer over the entire surface of the substrate;
Patterning the sacrificial layer corresponding to the beam by photolithography,
Depositing a layer for constituting the support over the entire surface;
Etching back the layer by anisotropic dry etching to form the support and leaving it at the end of the patterned sacrificial layer;
Forming the beam; and
Removing the sacrificial layer
A method for manufacturing a light modulation device is provided.
[0015]
  According to another aspect of the present invention, in the method for manufacturing an optical modulation device according to claim 1, the support is made of the same material as the beam.
[0016]
  According to another aspect of the present invention, in the method for manufacturing an optical modulation device according to claim 1, the beam is made of a film having a tensile residual stress.
[0017]
  The features of the present invention described above and other features will be described in detail below in relation to the embodiments.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
  A first embodiment of the present invention will be described with reference to FIGS.
[0019]
  2A and 2B are diagrams for explaining the configuration of the light modulation device according to the present embodiment. FIG. 2A is a schematic cross-sectional view, and FIG. 2B is a schematic plan view. However, Figure 2 (a) Is shown in FIG.b) Represents a cross section taken along line AB of FIG.
[0020]
  In FIG. 2, 201 is a substrate made of silicon, optical glass or the like. In this embodiment, a silicon substrate having a (100) surface on the surface is used as the substrate 201, but is not limited to this. An insulating film 202 such as a silicon oxide film is formed on the substrate 201. An electrode 203 is formed in a recessed portion formed in the insulating film 202. This electrode 203 is one electrode for driving the beam 205 with electrostatic force. Specifically, a metal such as Al, Au, Ti, TiN, and Cr, a conductive thin film such as ITO, an impurity, etc. Is formed by substrate silicon having a low resistance. Reference numeral 204 denotes a protective film made of an insulating film such as a silicon nitride film, and serves to prevent the electrode 203 from coming into contact with the beam 205 and short-circuiting. Although not shown in the drawing, a pad opening may be formed in the protective film 204 as a portion connecting the electrode 203 and an external signal.
[0021]
  The beam 205 is a both-ends fixed beam having a light reflecting layer 206 on the surface, and is formed so as to protrude from the upper surface of the substrate by an L-shaped fixed end 210 thereof. The light reflecting layer 206 is not limited to a separately deposited film, including the examples described later, and it is only necessary that a light reflecting region contributing to the performance of the device is formed on the beam 205. Reference numeral 207 denotes a pad provided for applying a voltage to the beam 205 and plays a role of taking out another electrode for driving the beam 205. The pad 207 is formed on the beam 205 when a conductive film is used as the beam 205, and is formed on the light reflecting layer 206 when a conductive film is used for the light reflecting layer 206. The electrostatic force that deflects the beam 205 is generated by applying a voltage between the electrode 203 facing the beam 205 and the beam 205 or the light reflection layer 206 via the air gap 208.
[0022]
  The beam 205 is formed of a metal film or a thin film such as single crystal silicon, polycrystalline silicon, or silicon nitride film. Beams made of single crystal silicon have few defects and long life. In addition, since a beam formed of polycrystalline silicon can use a technique such as CVD, the cost can be reduced and the residual stress of the film can be easily controlled from compressive stress to tensile stress. In addition, a beam formed of a thin silicon nitride film can increase the switching response speed due to the strong tensile stress of the film. Further, when the beam is formed of single crystal and polycrystalline silicon, it is possible to reduce the resistance of the single crystal silicon or polycrystalline silicon with impurities to make it conductive.
[0023]
  In this embodiment, after forming the insulating film 202 on the substrate 201, the insulating film 202 is patterned by photolithography and dry etching to form the void 208. However, the substrate 201 can be similarly patterned, and then the insulating film 202 can be deposited.
[0024]
  FIG. 3 shows an enlarged cross section of a characteristic part of the light modulation device of this embodiment. In FIG. 3, the beam 205 includes a fixed end portion 210 (“L-shaped fixed end portion of the beam”), and an inner portion thereof functions as a substantial beam. As described below,The L-shaped fixed end 210 can be arbitrarily set in height t and angle θ by patterning the sacrificial layer. Also, the length d can be arbitrarily set by patterning the beam 205. 303 is"Almost rectangular gap ",Reference numeral 302 denotes a non-parallel gap below the substrate plane. The non-parallel gap 208 shown in FIG. 2 is a total of the non-parallel gap 302 and the substantially rectangular gap 303. Claim3In the invention described in the above, the beam 205 (beam member) is formed of a film having a tensile residual stress. In practice, however, a silicon nitride film formed by a CVD method or the like at around 800 ° C., or 500 A polycrystalline silicon film obtained by heat-treating an amorphous silicon film formed by a CVD method at 600 ° C. to about 900 ° C. in a nitrogen atmosphere is used. These films can have a strong tensile residual stress of about 0.5 GPa to about 2.0 GPa depending on the formation conditions.
[0025]
  The manufacturing method of the light modulation device of the present invention described above will be described with reference to FIGS. 4 to 9 show typical steps in order, in which (a) is a schematic cross-sectional view (cross-section taken along line AB), and (b) is a schematic plan view.
[0026]
  FIG. 4 A substrate 201 is a silicon substrate on which a silicon oxide film 202 is formed. A resist pattern having an arbitrary film thickness at a position corresponding to the depression by a photoengraving method using a photomask in which a pattern having an area gradation is formed on the substrate 201 or a photoengraving method in which a resist pattern is thermally deformed after forming a resist pattern. After that, a hollow portion is formed by a dry etching method. The non-parallel gap 302 is formed by the recessed portion.
[0027]
  FIG. 5 An electrode 203 is formed inside a hollow portion corresponding to the gap 302, and a protective film 204 is formed thereon. For example, a titanium nitride (TiN) thin film having a thickness of 0.01 μm is formed by sputtering using Ti as a target, and an electrode 203 is formed by photolithography and dry etching, and then a silicon nitride film is formed. A protective film 204 is formed with a thickness of 0.2 μm by atmospheric CVD.
[0028]
  <FIG. 6> A silicon oxide film is formed with an arbitrary film thickness by plasma CVD, and then patterned by photolithography using a resist to form a sacrificial layer 209. When the sacrificial layer 209 is removed as shown in FIG. 9, the thickness of the silicon oxide film as the sacrificial layer 209 is such that the beam shrinks due to its own tensile residual stress and can be flattened parallel to the substrate plane. To decide. Furthermore, it is desirable that the sacrificial layer 209 be patterned so as to completely cover the recessed portion with respect to the cross-sectional direction of FIG. The effect is that even if a slight misalignment occurs during photoengraving for patterning of the sacrificial layer 209, the beam on the gap 208 is always flat, thereby suppressing variations in light modulation properties and variations in drive voltage. It can be done.
[0029]
  << FIG. 7 >> A silicon nitride film is formed on the entire surface of the substrate by a thermal CVD method to a thickness of, for example, 0.1 μm, and this film is patterned by a photoengraving method and a dry etching method to form a beam 205.
[0030]
  <FIG. 8> A Cr thin film serving as a reflective layer for incident light flux is formed on the entire surface of the substrate by sputtering, for example, with a thickness of 0.05 .mu.m. The surface reflection layer 206 is formed by patterning. At this time, since the residual internal stress of the surface reflection layer 206 also affects the planarization of the beam when the sacrificial layer is removed as shown in FIG. 9, the process is designed so as to obtain an appropriate residual stress. The Cr film formed by the DC sputtering method has a residual internal stress of about 1.0 GPa, contributing to the planarization of the beam when removing the sacrificial layer. In FIG. 8, the surface reflection layer 206 is shown so as not to overlap the L-shaped fixed end of the beam.ThisHowever, the fixed end portion may be covered with the surface reflection layer 206 in order to increase the strength at the fixed end portion.
[0031]
  <FIG. 9> The sacrificial layer 209 formed so as to cover the hollow portion is removed by a wet etching method using a diluted solution of hydrofluoric acid. Based on the etching selectivity between the sacrificial layer 209 and the electrode protective film 204 and the beam 205, the beam 205 and the protective film 204 maintain the required thickness even after the sacrificial layer etching is completed. The initial film thicknesses of the beam 205 and the protective film 204 are determined. By removing the sacrificial layer, the beam 205 shrinks so as to relieve the inherent tensile residual stress and is flattened parallel to the substrate plane. Thus, a non-parallel gap 208 composed of a non-parallel gap 302 in the lower part of the substrate plane and a substantially rectangular gap 303 in the upper part of the substrate plane is formed.
[0032]
  Although the illustration and description of the etching opening of the protective film 204 in the pad portion on the electrode 203 are omitted, the electrode 203 is extended from the recessed portion to the substrate surface and can be performed in the process between FIG. 7 and FIG. Is possible.
[0033]
  Next, a second embodiment of the present invention will be described with reference to FIGS..
[0034]
  10A and 10B are diagrams for explaining the configuration of the light modulation device according to the present embodiment. FIG. 10A is a schematic cross-sectional view, and FIG. 10B is a schematic plan view. However, Fig.10 (a) represents the AB sectional view of FIG.10 (b).
[0035]
  The components of the light modulation device of this embodiment are the same as those of the first embodiment, but there are significant differences from the first embodiment.,A support 211 is provided near the fixed end of the beam 205;,The support 211 and the beam 205 are made of the same material. The material of the support 211 needs to have at least good etching selectivity with respect to the sacrificial layer 209. In this embodiment, a silicon nitride film or a polycrystalline silicon film is used. In particular, the claims2In the described invention, the support 211 is formed using the same silicon nitride film as the beam 205.
[0036]
  FIG. 18 shows an enlarged cross-sectional view of a portion that is a feature of the light modulation device of this embodiment. In FIG. 18, reference numeral 701 denotes a fixed end portion of the beam 205 and a support 211 adjacent to the fixed end portion. The length 211 of the support 211 formed by the manufacturing method described later can be arbitrarily set by the film thickness of the support forming layer (601), and the height h of the support 211 can be set. It can be set arbitrarily depending on the amount of overetching during etch back and the film thickness of the sacrificial layer.
[0037]
  A specific method for manufacturing the light modulation device of this embodiment will be described with reference to FIGS..FIG. 11 to FIG. 17 show typical steps in order, in which (a) is a schematic sectional view (cross section taken along line AB), and (b) is a schematic plan view.
[0038]
  << FIG. 11 >> The substrate 201 is a silicon substrate on which a silicon oxide film 202 is formed. A resist pattern having an arbitrary film thickness at a position corresponding to the depression by a photoengraving method using a photomask in which a pattern having an area gradation is formed on the substrate 201 or a photoengraving method in which a resist pattern is thermally deformed after forming a resist pattern. After that, a hollow portion is formed by a dry etching method. The non-parallel gap 302 is formed by the recessed portion.
[0039]
  << FIG. 12 >> The electrode 203 is formed with a thin film of TiN in the hollow portion corresponding to the gap 302. For example, a TiN thin film having a thickness of 0.01 μm is formed by sputtering using Ti as a target, and the electrode 203 is formed by photolithography and dry etching. Thereafter, a silicon nitride film having a thickness of 0.2 μm, for example, was formed as a protective film 204 for the electrode 203 by atmospheric pressure CVD.
[0040]
  <FIG. 13> A silicon oxide film is formed in an arbitrary thickness by plasma CVD, and then patterned by a photoengraving method using a resist to form a sacrificial layer 209. Next, a silicon nitride film is deposited on the entire surface as a support formation film 601 with an arbitrary film thickness. At this time, the length L of the support 211 can be set arbitrarily wide by increasing the thickness of the support forming film 601.
[0041]
  <FIG. 14> The support formation film 601 is etched back by an etch-back method, which is a general semiconductor technology technique, to leave a film portion that becomes the support 211 on the end face of the sacrificial layer 209. By increasing the amount of over-etching at the time of etch back, the height h of the support 211 can be set arbitrarily low.
[0042]
  <FIG. 15> A silicon nitride film is formed on the entire surface of the substrate by a thermal CVD method, for example, to a thickness of 0.1 μm, and then patterned to form a beam 205 by a photoengraving method and a dry etching method. At this time, unnecessary portions of the support 211 are also etched away.
[0043]
  <FIG. 16> A Cr thin film serving as a reflective layer for incident light flux is formed on the entire surface of the substrate by sputtering, for example, to a thickness of 0.05 μm. Thereafter, the Cr film is patterned by a photoengraving method and a dry etching method to form the surface reflection layer 206. Since the residual internal stress of the surface reflection layer 206 also affects the planarization of the beam 205 when the sacrificial layer 209 is removed as shown in FIG. 17, the process is designed so as to have an appropriate residual stress. The Cr film formed by the DC sputtering method has a residual internal stress of about 1.0 GPa, contributing to the planarization of the beam 205 when removing the sacrificial layer. In FIG. 15, the surface reflection layer 206 is illustrated so as not to overlap the L-shaped fixed end portion of the beam 205, but in order to increase the strength at the fixed end portion, the surface reflection layer 206 is fixed to the fixed end portion. May be covered.
[0044]
  <FIG. 17> The sacrificial layer 209 formed so as to cover the hollow portion is removed by a wet etching method using a diluted solution of hydrofluoric acid. Note that, based on the etching selectivity between the sacrificial layer 209 and the protective film 204 of the electrode and the beam 205, the beam 205 and the protective film 204 are maintained to have a desired thickness even after the etching of the sacrificial layer 209 is completed. The initial film thickness of the beam 205 and the protective film 204 is determined. In addition, in this embodiment, the etching selectivity with the support 211 needs to be considered.,Since a silicon nitride film that is the same material as the beam 205 is used, this is not necessary. By removing the sacrificial layer 209, the beam 205 is shrunk so as to relax the inherent tensile residual stress, and is flattened parallel to the substrate plane. As a result, a non-parallel gap 208 composed of a non-parallel gap 302 in the lower part of the substrate plane and a substantially rectangular gap 303 in the upper part of the substrate plane is formed. Since the support 211 is provided, the resistance against breakage of the beam fixed end during the relaxation of the residual stress is improved (the mechanical strength is increased).
[0045]
  Although the illustration and description of the etching opening of the protective film 204 in the pad portion on the electrode 203 are omitted, the electrode 203 is extended from the recessed portion to the substrate surface and is performed in the process between FIGS. 16 and 17. Good.
[0046]
  Next, the method for manufacturing the light modulation device of the present invention described with reference to FIGS.InThe effect of lowering the drive voltage will be described with reference to FIGS. FIG. 20 is a cross-sectional view of the light modulation device before and after the sacrificial layer removal by the manufacturing method of the present invention. FIG. 19 shows a cross-sectional view of the light modulation device before and after removing the sacrificial layer by the conventional manufacturing method, which is plotted in association with FIG.
[0047]
  According to the conventional method, before removing the sacrificial layer, as shown in FIG. 19A, the beam formed on the substrate plane flattened by the CMP technique causes the force F1 caused by the inherent tensile residual stress. Are pulled on each other. Even after the sacrificial layer is removed, the force F1 of the same magnitude remains as shown in FIG. Therefore, in order to bend the beam by electrostatic attraction, it is necessary to increase the drive voltage in order to compensate for the remaining force F1.
[0048]
  On the other hand, according to the method of the present invention, before removal of the sacrificial layer, as shown in FIG. The force resulting from the tensile residual stress in this state is defined as F1. After the sacrificial layer is removed, as shown in FIG. 20B, the beams are pulled and contracted due to the tensile residual stress, and the flattening of the beam is achieved and the tensile residual stress is relaxed to reduce the beam. The remaining force F2 is smaller than F1. Therefore, the drive voltage can be lowered by an amount corresponding to the decrease in the drive voltage for compensating the remaining force F2.
[0049]
  Furthermore, in the conventional method, as is apparent from FIG. 19B, the length W1 of the beam is defined by the length of the recessed portion in the substrate. On the other hand, according to the method of the present invention, as is apparent from FIG. 20B, the length W2 of the beam is defined by the length of the sacrificial layer. Compared with the prior art, W2 can be made longer than W1. Further, the substantial length of the beam is further increased by adding the height of the beam defined by the height of the sacrificial layer (the amount of protrusion from the substrate plane) t to W2. The drive voltage required to deform the beam is approximately inversely proportional to the square of the beam length, so that the drive voltage can be further reduced by the increase in the beam length (W2 + t). .
[0050]
  Next, a modification of the light modulation device according to the first embodiment will be described with reference to FIG. FIG. 21A shows a modification in which the apex of the non-parallel gap is moved to a position of about W2 / 4 from one fixed end of the beam when the length of the beam is W2. FIG. 21B shows a modification in which the apex of the non-parallel gap is moved to the vicinity of one fixed end of the beam. By moving the position of the apex of the non-parallel gap in this way, the shape of the beam displaced by the electrostatic force can be changed to a shape that provides the desired light modulation property.
[0051]
  Finally, the light modulation operation by the light modulation device of the present invention will be described using the configuration of the first embodiment as an example. FIG. 22 is an explanatory diagram thereof.
[0052]
  FIG. 22A shows a state in which no driving voltage is applied, and since the electrostatic force does not act on the beam (205), the L-shaped fixed end portion stands perpendicular to the plane of the substrate (201). It is in the state. The incident light beam is regularly reflected on the beam surface, and the reflected light beam travels in a target direction as indicated by an arrow. FIG. 22B shows a state in which a low drive voltage is applied, and the beam bends so that the gap (208) is attracted to the electrode (203) side from a narrow region by the action of electrostatic force. The direction of the reflected light changes because the surface of the beam bends. FIG. 22 (c) shows a state in which a higher driving voltage is applied. A strong electrostatic force acts on the beam, and the beam is greatly attracted to the electrode (203) and bent greatly. Thereby, the reflected light travels in a direction different from the target direction. When viewed from the reflection direction shown in FIG. 22A, in the state of FIG.TheAppearance (ON operation state), and in the state of FIG. 22C, the reflection direction completely changes, so it looks dark (OFF operation state). In this way, light modulation is performed.
[0053]
  In the configuration of the first embodiment, the gap (208) under the beam (205) is formed non-parallel to the beam. Such a void shape is effective in reducing the voltage required for the deformation of the beam. The electrostatic force acting on the beam is inversely proportional to the square of the distance between the electrode (203) and the beam. That is, the smaller the distance, the larger the electrostatic force that acts. Therefore, when a driving voltage is applied, the beam starts to deform from a narrow gap. Further, the deformation of the beam gradually narrows due to the deformation of the beam, and the deformation of the beam proceeds at a lower voltage than in the case of the parallel air gap. Figure22(D) shows the behavior of the L-shaped fixed end portion 210 of the beam in the transient state shown in FIG. 22 (b). In FIG. 22D, when a portion of the light reflecting layer of the beam starts to bend due to the electrostatic attractive force 1001 acting between the electrodes, a rotation operation 1002 using the L-shaped fixed end 210 as a fulcrum occurs. Due to such a rotation operation of the fixed end portion 210, the deformation of a certain region of the light reflecting layer of the beam easily occurs at a low voltage as compared with the conventional technique.
[0054]
【The invention's effect】
  According to the present inventionThe light modulator is
(1) Since the beam protrudes from the substrate surface so that a substantially rectangular gap is formed in the upper part of the substrate plane, deformation of the beam easily occurs due to rotation about the fixed end of the beam, The substantial length of the beam makes it easier for the beam to bend due to electrostatic attraction, allowing the beam to be deformed or light modulated at a lower drive voltage.WhenIs possible. further,In the manufacturing processSince the residual internal stress of the beam is relieved when the sacrificial layer is removed, the beam is easily bent due to electrostatic attraction, and the drive voltage can be further reduced..Therefore, it is possible to reduce the voltage of an image device such as an optical writing device or a video device such as a projector in an electrophotographic process using this light modulation device.
(2)SoIn this manufacturing process, it is not necessary to planarize the sacrificial layer by a general CMP technique, and the cost of the manufacturing process can be reduced.
(3)In the manufacturing process,The variation in the distance between the beam and the electrode is determined by both the variation in the digging due to the etching of the hollow portion formed in the substrate and the variation due to the formation of the sacrificial layer film, and it is not necessary to use a CMP technique having a large pattern dependency. Therefore, it is easy to suppress variations in drive voltage, and the manufacturing yield can be improved.
(4)Since the beam protrudes from the substrate surface and has a support in the vicinity of the fixed end of the beam, the beam can be easily restored to the original plane after being deflected by electrostatic attraction. Variation (that is, directional variation in reflected light) can be suppressed, and the response speed can be increased. In addition, the mechanical strength of the fixed end of the beam can be improved, the production yield can be improved, and so on.
(5)By using the same material for the support and the beam, the adhesion between the two members can be improved. further,In the manufacturing process,Since the etching solution between the beam and the sacrificial layer when removing the sacrificial layer can be set without considering the support (that is, without considering the etching damage of the support), the degree of freedom in process design is improved. .
(6)In order to form a beam using a film having a tensile residual stress,In the manufacturing process,When removing the sacrificial layer, the beams are pulled by the fixed end portion as a fulcrum due to the tensile residual internal stress, and have an effect of planarizing parallel to the substrate surface.
[0055]
  A method for manufacturing a light modulation device according to the present invention includes:As aboveA light modulation device can be realized, and in particular, by patterning the sacrificial layer and flattening the beam when removing the sacrificial layer, the drive voltage can be reduced, the manufacturing cost can be reduced, and the yield can be improved. Has the effect ofAnd alsoThe support layer can be provided in the vicinity of the fixed end of the beam by having a step of depositing the support component layer over the entire surface and etching back the support component layer by anisotropic dry etching.RuIt has effects such as.
[Brief description of the drawings]
1A and 1B are a schematic cross-sectional view and a schematic plan view for explaining a light modulation device according to a conventional technique.
FIG. 2 is a schematic cross-sectional view and a schematic plan view for explaining a first embodiment of the light modulation device according to the present invention.
FIG. 3 is an enlarged schematic cross-sectional view for explaining a characteristic part of the light modulation device according to the first embodiment;
4A and 4B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the first embodiment.
5A and 5B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the first embodiment.
FIGS. 6A and 6B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the first embodiment. FIGS.
7A and 7B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the first embodiment.
FIGS. 8A and 8B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the first embodiment. FIGS.
FIGS. 9A and 9B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the first embodiment. FIGS.
FIG. 10 is a schematic cross-sectional view and a schematic plan view for explaining a second embodiment of the light modulation device according to the present invention.
FIGS. 11A and 11B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the second embodiment. FIGS.
12A and 12B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the second embodiment.
13A and 13B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the second embodiment.
14A and 14B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the second embodiment.
FIGS. 15A and 15B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the second embodiment. FIGS.
FIGS. 16A and 16B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the second embodiment. FIGS.
FIGS. 17A and 17B are a schematic cross-sectional view and a schematic plan view for explaining a manufacturing process of the light modulation device according to the second embodiment. FIGS.
FIG. 18 is an enlarged schematic cross-sectional view for explaining a fixed end portion and a support of a beam.
FIG. 19 is a schematic cross-sectional view for explaining the beam before and after sacrificial layer removal in the prior art.
FIG. 20 is a schematic cross-sectional view for explaining the beam before and after removing the sacrificial layer in the present invention.
FIG. 21 is a schematic cross-sectional view for explaining a modification of the first embodiment.
FIG. 22 is a schematic cross-sectional view for explaining the operation of the light modulation device according to the present invention.
[Explanation of symbols]
  201 substrate
  202 Insulating film
  203 electrodes
  204 Protective film
  205 Beam
  206 Light reflection layer
  208 gap
  209 Sacrificial layer
  210 Fixed end of beam
  211 Support
  302 Almost rectangular gap
  303 Non-parallel air gap

Claims (3)

A light modulation device that performs light modulation by deforming a beam for reflecting light by electrostatic force,
  An electrode for applying an electrostatic force to the beam is provided in a recess of the substrate opened on the upper surface of the substrate, and the beam protrudes from the upper surface of the substrate to a position facing the electrode. Held on the substrate,
  In a state where no electrostatic force acts on the beam, a gap is formed between the beam and the depression,
  A method of manufacturing a light modulation device having a support close to a fixed end of the beam for assisting restoration of the beam when an electrostatic force acting on the beam is released,
  Forming the recess in the substrate;
  Forming the electrode inside the depression;
  Forming a protective layer covering the electrode;
  Depositing a sacrificial layer over the entire surface of the substrate;
  Patterning the sacrificial layer in correspondence with the beam by photolithography,
  Depositing a layer for constituting the support over the entire surface;
  Etching back the layer by anisotropic dry etching to form the support and leaving it at the end of the patterned sacrificial layer;
  Forming the beam; and
  Removing the sacrificial layer
A method of manufacturing a light modulation device, comprising: The method for manufacturing an optical modulation device according to claim 1, wherein the support is made of the same material as the beam. 2. The method of manufacturing an optical modulation device according to claim 1, wherein the beam is made of a film having a tensile residual stress.

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