JP4559273B2 - Actuator manufacturing method - Google Patents

Description

The present invention relates to a manufacturing method of the actuator.

  Conventionally, it is known that a silicon substrate is processed using a MEMS (Micro-Erectro-Mechanical-Systems) technique to form a micro structure such as an optical switch. FIG. 4 is a perspective view showing a conventional optical switch manufactured by MEMS technology. A comb-shaped comb-shaped electrode 1a and a beam portion 1b that supports the comb-shaped electrode 1a are integrally formed to constitute the movable portion 1, and the movable portion 1 is also integrally formed at the end of the beam portion 1b. The supported electrode 2 is used as a fulcrum and is held in a hollow state on the flat surface of the silicon support substrate 3c. (For example, see Patent Documents 1 and 2)

  A comb-shaped counter electrode 4a formed integrally with the frame portion 4 constituting the outer edge of the optical switch is provided at a position facing the comb-tooth electrode 1a, and a voltage is applied between the facing electrodes. When applied, an electrostatic attractive force is generated between the respective comb teeth (between the electrodes), and the beam portion 1b of the movable portion 1 bends so that the entire movable portion 1 follows the flat surface of the silicon support substrate 3c with the support electrode 2 as a fulcrum. Rocks. The tip of the movable part 1 is formed as a mirror base 5 that is widened, and a prismatic mirror part 6 is provided on the upper part. When the movable part 1 swings due to electrostatic attraction, the optical path of the light applied to the mirror part 6 is deflected and functions as an optical switch.

FIG. 5 is a diagram for explaining a manufacturing process of the conventional optical switch shown in FIG. Hereinafter, a manufacturing process of a conventional optical switch will be described with reference to FIG.
Step (a): Sputtering a masking resistant film 7 on the entire surface of the silicon active layer 3a of the silicon laminate (SOI substrate) 3 composed of the silicon active layer 3a, the intermediate layer 3b as a silicon oxide layer, and the silicon support substrate 3c. Etc. are formed. The resistant film 7 is made of, for example, chromium (Cr), and is a film that is resistant to deep anisotropic silicon reactive ion etching and hydrofluoric acid (HF).

  Step (b): The resistant film 7 is patterned into a desired pattern shape by etching to form a first masking pattern 7a. The first masking pattern 7a is for forming a main structure (movable part 1, support electrode 2, etc.) constituting an optical switch on the silicon support substrate 3c of the SOI substrate 3 by etching. The pattern shape is the same as the outer shape of these structures viewed from above. (First masking process)

  When patterning the resistant film 7, first, a positive photoresist is uniformly applied to the surface of the resistant film 7 by spin coating. After coating, the photoresist is covered with a photomask having a desired masking pattern shape, and the photoresist is exposed to ultraviolet rays. After the exposure, the exposed region of the photoresist is removed using a developer. Thereafter, the resistant film 7 in the exposed region is removed by wet etching using the photoresist pattern formed by the above steps as an etching mask.

  Step (c): Using the first masking pattern 7a formed in the previous step (b) as an etching mask, the silicon active layer 3a in the exposed region is an etching stop layer by deep anisotropic reactive ion etching. Etching is performed until the intermediate layer 3b is exposed. Thereby, the silicon active layer 3a is processed, and main structures (movable part 1, support electrode 2, etc.) constituting the optical switch are formed.

  Step (d): The first masking pattern 7a used as the etching mask in the previous step (c) is removed by wet etching.

  Step (e): A resistant film 7 made of chromium (Cr) is formed on the entire surface of the silicon active layer 3a including the surface of the intermediate layer 3b in the exposed region by sputtering or the like. The resistant film 7 is the same as that used in the step (a).

  Step (f): The resistant film 7 formed in the previous step (e) is patterned into a desired pattern shape by wet etching following the step (b) to form a second masking pattern 7b. The second masking pattern 7b is for forming the mirror portion 6 on the mirror base 5 by etching, and the pattern shape is the same as the outer shape of the mirror portion 6 viewed from above. (Second masking process)

  Step (g): Using the second masking pattern 7b formed in the previous step (f) as an etching mask, the silicon active layer 3a in the exposed region is etched by a certain amount by deep anisotropic reactive ion etching. The etching amount may be appropriately selected according to the height of the mirror part 6 to be formed, and is, for example, 50 μm in the depth direction. As a result, a prismatic mirror portion 6 is formed on the mirror base 5.

  Step (h): The second masking pattern 7b used as the etching mask in the previous step (g) is removed by wet etching.

  Step (i): The intermediate layer 3b is removed by isotropic wet etching except for a part (the lower part of the support electrode 2, the lower part of the frame part 4, etc.), and a part of the silicon active layer 3a (the movable part 1) is made of silicon. Separate from support substrate 3c. As an etchant used for wet etching, for example, hydrofluoric acid (HF) can be used, but other etchants may be used as long as only the intermediate layer 3b can be selectively etched.

  Through the above steps, each structure constituting the optical switch is formed on the silicon support substrate 3c, and the optical switch is completed. Then, the entire completed optical switch is cleaned by immersing it in a cleaning solution such as acetone, and then the cleaning solution is dried.

JP 2000-28935 A JP 2003-57569 A

  In the optical switch described above, the gap between the bottom surface of the movable part formed on the silicon support substrate and the surface of the silicon support substrate is very narrow, such as several μm. Therefore, the structure is cleaned with the cleaning liquid after the structure is formed. In addition, due to the surface tension of the cleaning liquid that has entered between the bottom surface of the movable part and the surface of the silicon support substrate, there has been a problem that “stiction” occurs in which the bottom surface of the movable part sticks to the silicon support substrate surface after the cleaning liquid is dried. Such a phenomenon is likely to occur on the bottom surface of the mirror base having a relatively large area among the bottom surfaces of the movable part.

  Specifically, immediately after the SOI substrate on which the structure is formed is released from the immersion of the cleaning liquid, a certain amount of cleaning liquid exists between the bottom surface of the movable part and the surface of the silicon support substrate. It is in a state where it can swing on the surface of the silicon support substrate depending on the flow, but when the cleaning liquid between the bottom surface of the movable part and the silicon support substrate surface evaporates and gradually decreases in the subsequent cleaning liquid drying process, Along with this, the bottom surface of the movable part is pulled toward the silicon support substrate surface due to the surface tension of the cleaning liquid, and if the surface tension of the cleaning liquid is strong, the bottom surface of the movable part is in the swing position at the moment when the cleaning liquid is completely evaporated. It sticks to the surface of the silicon support substrate. When stiction occurs in this way, it is a matter of course that a normal operation cannot be performed as an optical switch, resulting in a failure.

The present invention has been made in view of the above problems, and an object thereof is movable bottom face to provide a method of manufacturing an actuator which suppresses the occurrence of stiction sticking to the silicon support substrate surface.

While having a movable portion held in a hollow state via a flexible beam portion with a fixed portion fixed on the flat surface of the base portion having a flat surface as a fulcrum , a pedestal portion is provided in the movable portion, to the base portion bottom surface, a convex stepped portion protruding stepwise towards the said base portion is formed, the said base portion bottom surface facing the region of the base projecting stepwise towards the said base portion bottom surface A method of manufacturing an actuator in which convex stepped portions are formed and tip portions of the respective convex stepped portions are opposed to each other, and at least an intermediate layer is sandwiched between a silicon support substrate and a silicon active layer Engineering and as you form Ma scan King pattern on the silicon active layer surface of the laminate, the skilled 該Ma scan King pattern as an etching mask, the silicon active layer of the exposed region and the intermediate layer is exposed until Dee etching And The fixed portion on the base the serial silicon support substrate as the base, the beam portion, and forming a main structure constituting the movable portion, and an actuator including the pedestal portion, before Kemah scan King pattern removing the the steps of removed by Rijo by the intermediate layer e etching except for the portion including the fixing subordinate part and the base part lower, the surface of the silicon support substrate and the silicon active layer wherein the oxide film forming step of forming an oxide film by oxidizing, and a said oxide film and oxide film and intermediate layer removing step of removing the portion of the e etching of the intermediate layer, and the oxide film forming step oxidation the film and intermediate layer removing step, the intermediate layer remaining between the said pedestal base portion by repeating a plurality of times until all removed, to face the base portion bottom surface of said base and said base portion bottom surface Territory A method of manufacturing an actuator for forming said convex stepped portion.

  In the present invention, the convex step is formed on the bottom surface of the mirror pedestal, and the convex step portion is also formed in the region facing the mirror pedestal bottom surface of the substrate. The surface area of the cleaning liquid acting between the bottom surface of the mirror base and the surface of the silicon support substrate immediately below it is reduced, and the bottom surface of the movable part sticks to the surface of the silicon support substrate immediately after the cleaning liquid is dried. Is prevented.

  A convex step is formed on the bottom surface of the mirror pedestal at the tip of the movable portion, and a convex step portion is also formed in a region facing the mirror pedestal bottom surface of the substrate to face the surface area of the mirror pedestal bottom surface and the mirror pedestal bottom surface. The surface tension of the cleaning liquid acting between the bottom surface of the mirror base and the surface of the silicon support substrate is reduced by reducing the area of the silicon substrate surface.

  1A and 1B are views showing an embodiment of an optical switch according to the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line AA. The basic configuration is the same as that of a conventional optical switch, and a flexible beam portion formed integrally with a supporting electrode 2 fixed on a silicon supporting substrate 3c via an intermediate layer 3b as a fulcrum. 1b and the movable part 1 having the comb-shaped electrode 1a formed integrally are held in a hollow state on the silicon support substrate 3c with a certain gap. A mirror base 10 that is widened is provided at the tip of the movable portion 1, and a prismatic mirror portion 6 is integrally formed on the upper portion thereof. Further, a frame portion 4 made of a silicon active layer 3a is provided at the peripheral portion of the silicon support substrate 3c so as to surround the above structure, and the comb-tooth electrode 1a of the movable portion 1 on the inner periphery side thereof is provided. A counter electrode 4a having a comb-tooth electrode that meshes with the comb-tooth electrode 1a is formed integrally with the frame portion 4 at the facing position.

  Here, as a feature of the present invention, in this embodiment, in addition to the above-described conventional configuration, a convex step portion 10a projecting stepwise toward the silicon substrate 3c is formed on the bottom surface of the mirror base 10, and the silicon substrate 3c is formed. In the region facing the bottom surface of the pedestal portion, there is formed a convex step portion 3d that protrudes stepwise toward the bottom surface side of the pedestal portion, and the tip portions of the respective convex step portions are arranged to face each other. .

  The convex stepped portion 10a formed on the bottom surface of the mirror base 10 and the convex stepped portion 3d formed on the silicon substrate 3c opposite to the convex stepped portion 10a are opposed to each other with a very small surface at the tip of each convex stepped portion. Thus, the absolute amount of the cleaning liquid interposed between the bottom surface of the mirror base 10 and the surface of the silicon support substrate 3c can be reduced, and the effect of preventing stiction can be achieved.

  Next, a method for manufacturing the optical switch of the present invention will be described. FIG. 2 shows a manufacturing process of the optical switch according to the present invention, and is a cross-sectional view of an essential part for each process. Hereinafter, the manufacturing process will be described with reference to FIG. Since steps (a) to (h) shown in FIG. 2 are the same as the conventional manufacturing steps, detailed description thereof is omitted.

  Step (a): Sputtering a masking resistant film 7 on the entire surface of the silicon active layer 3a of the silicon laminate (SOI substrate) 3 composed of the silicon active layer 3a, the intermediate layer 3b as a silicon oxide layer, and the silicon support substrate 3c. Etc. are formed.

  Step (b): The resistant film 7 is patterned into a desired pattern shape by etching to form a first masking pattern 7a.

  Step (c): Using the first masking pattern 7a formed in the previous step (b) as an etching mask, the silicon active layer 3a in the exposed region is an etching stop layer by deep anisotropic reactive ion etching. Etching is performed until the intermediate layer 3b is exposed. Thereby, the silicon active layer 3a is processed, and main structures (movable part 1, support electrode 2, etc.) constituting the optical switch are formed.

Step (d): The first masking pattern 7a used as the etching mask in the previous step (c) is removed by wet etching.
Step (e): A resistant film 7 made of chromium (Cr) is formed on the entire surface of the silicon active layer 3a including the surface of the intermediate layer 3b in the exposed region by sputtering or the like. The resistant film 7 is the same as that used in the step (a).

  Step (f): The resistant film 7 formed in the previous step (e) is patterned into a desired pattern shape by wet etching following the step (b) to form a second masking pattern 7b. The second masking pattern 7b is for forming the mirror portion 6 on the mirror base 10 by etching. (Second masking process)

  Step (g): Using the second masking pattern 7b formed in the previous step (f) as an etching mask, the silicon active layer 3a in the exposed region is etched by a certain amount by deep anisotropic reactive ion etching. The etching amount may be appropriately selected according to the height of the mirror part 6 to be formed, and is, for example, 50 μm in the depth direction. Thereby, the prismatic mirror portion 6 is formed on the mirror base 10.

  Step (h): The second masking pattern 7b used as the etching mask in the previous step (g) is removed by wet etching. The manufacturing process so far is the same as in the prior art.

  Step (i): The intermediate layer 3b is removed by isotropic wet etching except for a part (lower part of the mirror base 10, lower part of the support electrode 2, lower part of the frame part 4), and a part of the silicon active layer 3a (comb teeth) The electrode 1a) is separated from the silicon support substrate 3c. Here, the mirror pedestal 10 is performed by managing the etching time so as not to be separated. As an etchant used for wet etching, for example, hydrofluoric acid (HF) can be used, but other etchants may be used as long as only the intermediate layer 3b can be selectively etched.

  Step (j): The optical switch having undergone the above steps is put into an oxidation furnace, and an oxide film 11 is formed on the silicon active layer 3a and the silicon support substrate 3c. The oxide film 11 is formed on the surface of the optical switch structure excluding the intermediate layer 3b which is a silicon oxide layer.

  Step (k): The oxide film 11 formed in the previous step (j) and a part of the intermediate layer 3b remaining under the mirror base 10 are removed by isotropic wet etching. Here, the oxide film forming step of step (j) and the oxide film / intermediate layer removing step of step (k) are repeated a plurality of times until all of the intermediate layer 3b under the mirror base 10 is removed. Thereby, the convex stepped portion 10a on the bottom surface of the mirror base 10 and the convex stepped portion 3d of the silicon support substrate 3c are formed in a stepped shape, respectively. The convex step portions 10a and 3d formed in this process have the same shape.

  The process of forming the convex step portion 10a of the mirror pedestal 10 and the convex step portion 3d of the silicon support substrate 3c facing this will be further described with reference to a partially enlarged view in the vicinity of the mirror pedestal in FIG.

  FIG. 3A shows a state in which the intermediate layer 3b has been removed, and a part of the intermediate layer 3c remains in the lower part of the mirror pedestal.

  FIG. 3B shows a state where the oxide film 11 is formed. In general, when silicon is oxidized, it is known that 45% of the grown oxide film thickness grows inside the silicon substrate and 55% grows outside, but the mirror 6, mirror base 10 shown in FIG. Also in the silicon support substrate 3c, about half of the formed oxide film thickness is grown inside.

  FIG. 3C shows a state in which the oxide film 11 is removed by isotropic wet etching. By removing the oxide film 11 grown to the inside of silicon, the bottom surface of the mirror base 10 is convex. A step 10a is formed, and a convex step 3d is formed on the silicon support substrate 3c. A part of the intermediate layer 3b remaining under the mirror pedestal is also removed.

  FIGS. 3D to 3G show a state in which the oxide film formation and the oxide film removal are further repeated, and the convex stepped portion is formed in a step shape by performing a plurality of times, and the tip end area is reduced. is decreasing. Further, the intermediate layer 3b remaining in the lower part of the mirror base 10 is gradually removed in the oxide film removing step, and finally removed completely. In this configuration, the oxide film formation and the oxide film removal are repeated three times to form three stepped convex steps, the intermediate layer 3b is completely removed, and the lower part of the mirror base 10 and the silicon support substrate 3c is cut off.

The optical switch which prevented the stiction of this invention is completed according to the above process.
In the present specification, the case where the technique according to the present invention is applied to an optical switch has been described. Needless to say, the present invention can also be applied to actuators for other purposes in which a mirror portion is not formed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one Embodiment of the optical switch by this invention, (a) is a top view, (b) is AA sectional drawing. Sectional drawing of the principal part for every process which shows the manufacturing method of the optical switch by this invention Partial enlarged view near the mirror base A perspective view showing a conventional optical switch Cross-sectional view of main parts for each process showing the manufacturing process of a conventional optical switch

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Movable part 1a Comb electrode 1b Beam part 2 Support electrode 3 Silicon laminated body (SOI substrate)
3a Silicon active layer 3b Intermediate layer 3c Silicon support substrate 3d Convex step part 4 Frame part 4a Counter electrode 5 Mirror base 6 Mirror part 7 Resistant film 7a First masking pattern 7b Second masking pattern 7c First masking pattern 7d First masking pattern 10 Mirror base 10a Convex step 11 Oxide film

Claims (1)

While having a movable portion held in a hollow state via a flexible beam portion with a fixed portion fixed on the flat surface of the base portion having a flat surface as a fulcrum, a pedestal portion is provided in the movable portion, A convex stepped portion is formed on the bottom surface of the pedestal portion so as to protrude in a stepped manner toward the base side, and a convex portion protruding in a stepped manner toward the bottom surface side of the pedestal portion is formed in a region facing the bottom surface of the pedestal portion. A method of manufacturing an actuator in which a mold step portion is formed and the tip portions of the respective convex step portions are arranged to face each other.
at least,
Forming a masking pattern on the surface of the silicon active layer of the silicon laminate formed by sandwiching the intermediate layer between the silicon support substrate and the silicon active layer;
Using the masking pattern as an etching mask, etching the silicon active layer in an exposed region until the intermediate layer is exposed, and using the silicon support substrate as the base, the fixed part, the beam part, the movable part, And forming a main structure constituting the actuator including the pedestal portion;
Removing the masking pattern;
Removing the intermediate layer excluding a part of the region including the lower portion of the fixed portion and the lower portion of the pedestal portion by etching;
An oxide film forming step of oxidizing the silicon active layer and the surface of the silicon support substrate to form an oxide film;
An oxide film / intermediate layer removal step of removing a part of the oxide film and the intermediate layer by etching;
The oxide film forming step and the oxide film / intermediate layer removing step are repeated a plurality of times until all of the intermediate layer remaining between the pedestal portion and the base portion is removed, whereby the bottom surface of the pedestal portion and the base portion The method for manufacturing an actuator, wherein the convex stepped portion is formed in a region facing the bottom surface of the pedestal portion.

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