TW580734B - Method to fabricate vertical comb actuator by surface micromachining technology - Google Patents

Abstract

The method to fabricate vertical comb actuator of the present invention is to form a first sacrificial layer on the substrate by electroplating, and form the lower comb electrode on the first sacrificial layer by electroplating. Form the second sacrificial layer on the lower comb electrode by electroplating. Form the third sacrificial layer and the upper comb electrode on the second sacrificial layer by deposition. Finally, etch each sacrificial layer to obtain the vertical comb actuator. Thus, the problems of well-known technology such as bad actuating effect, limited actuating path and limited substrate material, or bad control resulted from the lateral pitch of the upper/lower electrodes due to the limitation of the alignment precision are resolved, and the effect of reducing the actuating voltage, increased path and using various substrate materials can be achieved.

Description

580734 V. Description of the invention (1) < Technical field to which the invention belongs > The present invention relates to a method for manufacturing a comb-shaped actuator, in particular to a vertical comb-shaped product manufactured by applying surface micormachining technology Actuator. < Previous technology > According to the press, a vertical comb actuator (Vertical Comb Drive, VCD) is used to fix one comb electrode to a substrate, and to suspend the other comb electrode by a twisted arm, and use static electricity. The principle drives these two interdigitated comb electrodes. Because the vertical comb actuator always maintains a fixed electrode gap during the actuation process, it can maintain an equal amount of electrostatic force. Compared with the traditional parallel electrode plate actuator, the vertical comb actuator can have a larger Of displacement. Conventional vertical comb-shaped actuators often use Deep Reactive Ion Etching (DRIE) and / or body engraving to produce two comb-shaped electrode structures with different upper and lower positions or different vertical thicknesses to achieve vertical Action effect. Or use deep reactive ion etching to make two upper and lower comb electrodes, and then use bonding techniques such as wafer bonding, voltage application, coating of glass or oxide films with adhesives, solder, or soldering methods to combine the upper and lower comb electrode structures. Join. Generally speaking, the conventional vertical comb-type actuators have an upper comb electrode supported by an elastomer and a lower comb electrode fixed. When a voltage is applied, an electrostatic force is generated. When the gap is shortened and the elastomer is extended, it will recover. When the restoring force is balanced with the electrostatic force, the movement is at rest (the equilibrium point is reached). Therefore, the gap between the moments is shortened and the restoring force is proportionally enlarged.

580734 V. Description of the invention (2) The electrode gap outside the stable range is controlled to ensure its operation. Among them, the related technology of the vertical comb actuator can refer to US Patent No. 2002/0 0 5 9 7 1 A1, or the paper of Lee et al. "Design and fabrication of scanning mirror for laser display M, Sensors and Actuators A, Vo 1. 96, 2002, pp. 233-230, or paper by Xie et al. N Vertical comb-finger capacitive actuation and sensing for CMOS-MEMS ", Sensors and Actuators A, Vo 1. 95, 2 0 0 2,

pp. 212-221, Paper by Selvakumar et al. ', Vertical Comb Array Microactuators 丨 丨, MEMS '95, Proceedings, 1 9 9 5, pp. 4 3-4 8, or Paper by Jeong et al. Milli-scale mirror actuator with bulk mi cromach i ned vertical combs ", Transducers '99, Sendai, 1999, pp. 1006-1009, or Hsieh et al. paper Using Extended BELST process in fabricating vertical comb actuator for optical application '', IEEE / LEOS International Conference on Optical MEMS, 2002, pp. 1 3 3- 1 3 4 °

However, the previously disclosed conventional vertical comb actuators are often limited by the structure type, and it is necessary to apply a higher voltage to achieve sufficient actuation displacement. Or the production is limited by the choice of base material {such as (1 1 1) wafer). Or a bonding technique such as wafer bonding is required, and the gap size between two comb electrodes must be controlled. Because the alignment must be precise during bonding, the lateral distance between the two comb-shaped electrodes is limited, so the range of motion is limited, and

Page 6 580734 V. Description of the invention (3) Excessive pitch will reduce the capacitance or electrostatic force generated between two comb electrodes. In addition, the gap between the two comb electrodes of the conventional vertical comb actuator must be very precise, usually must be controlled between 1 and 2 // m, if it exceeds the initial set gap, it will make the performance Great discount. The following description is given in conjunction with the drawings:… Please refer to the first and second drawings, which propose a multilayer structure having first and second conductive layers separated by an insulating film layer, and deep reactive ion etching in the multilayer structure Technically, the upper pattern and the insulating film layer are etched to define the second and first comb-shaped electrodes, and as shown in the second figure, comb-shaped φ structures 1 a and 1 b with different upper and lower positions are obtained. When a voltage difference V is applied, The comb-like structures 1 a and 1 b can be vertically actuated. However, the starting positions of the comb-like structures 1 a and 1 b are staggered with each other and fail to overlap with each other (0ver 1 ap), so the advantages of linear actuation of the comb-like actuators will be lost, and a higher Moving voltage. Please refer to the third figure, which uses the difference in vertical thickness of the planar comb structures 2 a and 2 b to achieve vertical actuation. However, its disadvantage is that the driving force is not good, and its actuation stroke is limited by the rear stage of the semiconductor. Number and thickness of film layers in the manufacturing process. Please refer to the fourth figure, which uses reactive ion etching and bulk etching to produce two sets of comb-like structures 3 a and 3 b with mutually different upper and lower positions. However, the disadvantage is that the thickness of the comb-like structures 3 a and 3 b is restricted by ions. The depth of doping, and _ causes a limit on the stroke that it can actuate. Or, for example, (111) wafers are used as the base material for manufacturing. The disadvantage is that the choice of the base material is limited. Please refer to the fifth, sixth and seventh images, which use deep reaction ionization.

Page 7 580734 V. Description of the invention (4) Sub-etching technology, two upper and lower comb electrodes 4 a and 4 b are respectively produced, and then joined. Because the precise alignment is required to control the lateral distance between the upper and lower comb electrodes, the limitation of the joining accuracy will cause an excessively large distance, which will reduce the capacitance or electrostatic force generated by the upper and lower electrodes, and make the process difficult. < Content of the Invention > The present invention is designed in view of the shortcomings of the above-mentioned conventional technology, and its main purpose is to provide a method for manufacturing a vertical comb actuator without wafer bonding, thereby providing an assembly process without any need. Vertical comb actuator. A secondary object of the present invention is to provide a method for manufacturing vertical comb actuators with the same pitch of upper and lower electrodes, so as to accurately control the electrode gap size of the vertical comb actuators. Another object of the present invention is to provide a method for manufacturing a vertical comb actuator capable of reducing driving voltage and increasing stroke. Another object of the present invention is to provide a method for manufacturing a vertical comb actuator that can be applied to a variety of different substrates, without sacrificing the substrate material due to the use of deep reactive ion engraving technology, providing more and more integration. Circuit integration space. Another object of the present invention is to provide a method for manufacturing a vertical comb actuator with a low temperature (less than 150 ° C), which can be easily integrated with an integrated circuit. To achieve the above object, the present invention is implemented as follows:

580734 V. Description of the invention (5) Processing technology The method of manufacturing a vertical comb actuator includes the following steps to form a first sacrificial layer by electroforming on a substrate to provide the height space required for the actuation stroke; The lower comb electrode structure is formed by electroforming on the material; the second sacrificial layer is formed by electroforming on the lower comb electrode structure to provide the height space required for the braking stroke; the third sacrificial layer is formed on the substrate by the deposition method, A lateral gap is provided between the upper and lower comb electrode structures, and an upper comb electrode structure is formed on the third sacrificial layer by a deposition method; and the foregoing sacrificial layers are removed to obtain a vertical comb actuator. Wherein, an electroforming starting layer may be formed on the substrate, and an electroforming mold (m ο 1 d) may be formed at the same time by exposure and development. In addition, the sacrificial layers and the comb-shaped electrode structures are formed of different materials, so a good etching selection ratio can be provided during etching, and the sacrificial layers are removed with an etching solution to obtain a desired electrode structure, and The method used for the deposition method can be electroforming, chemical vapor deposition, physical vapor deposition, or other common processes for semiconductor integrated circuits. At the same time, as the manufacturing method of the vertical comb-shaped actuator of the present invention is to combine lithography, precision electroforming, and deposition techniques to produce sacrificial layers and upper and lower comb-like electrode structures, and the sacrificial layers and the comb-like The materials of the electrodes are different. Adjusting the thickness of each sacrificial layer can control the lateral gap of the electrodes and the allowable movement stroke of the vertical comb actuator. With the above configuration, the method for manufacturing the vertical comb actuator of the present invention can be

580734 V. Description of the invention (6) Provide vertical comb-type actuators that do not require any assembly procedures, and at the same time maintain a good gap between the upper and lower comb-shaped electrodes to achieve the effect of reducing the driving voltage and increasing the stroke. < Implementation method > In order to make your reviewing committee understand the purpose, features, and effects of the present invention, the present invention will be described in detail through the following specific examples and the accompanying drawings, which will be described later.

Please refer to the eighth to thirteenth diagrams, which sequentially show schematic flowcharts of a preferred embodiment of a method for manufacturing a vertical comb actuator according to the present invention. Referring to FIG. 8, first, a silicon dioxide layer (or a nitride nitride layer) is deposited on the substrate 5 to provide electrical isolation, and an electrical ballast starting layer 5 1 is deposited, and a photoresist is used in combination with exposure, The lithography method forms a first electroformed mold 5 2 1, and electroforms a first sacriiical 1 ayer 5 3 1. The first sacrificial layer 5 3 1 is used to provide the space required for the actuation stroke. The first electroforming mold 5 2 1 is then removed.

In detail, the material of the substrate 5 is not limited, and the thickness of the silicon dioxide may be, for example, 1 // m. A photoresist is coated and patterned on the silicon dioxide layer, and then exposed and developed after baking, and two metal layers are deposited on the silicon dioxide layer by electron beam evaporation. The two metal layers may be, for example, gold and Titanium, a titanium clock starting layer 5 1 is formed from titanium metal, and is evaporated between the substrate 5 and gold to increase adhesion. Substrate 5 is then immersed in acetone and sonicated to remove the metal on the photoresist. The remaining metal can be used as conductive lines and pads. {Titanium metal layer and gold deposited by electron beam evaporation method Stepped overlay

Page 10 580734 V. Description of the invention (7) The cover (stepc 〇verage) is not good, so this method is adopted here. In the stripping and manufacturing process, it is more helpful to remove than the process of removing on the oxide layer. In addition to the titanium metal layer and the gold metal layer evaporated on the photoresist}. Subsequently, two metal layers are deposited on the substrate 5 as seed layers. The two metal layers may be, for example, nickel and chromium, and the chromium metal layer is also evaporated between the substrate 5 and the nickel metal layer. To increase adhesion. The photoresist layer is patterned selectively on the seed layer-openings to define the electroformed area. Before the electroforming, no hard baking is performed to avoid deformation of the photoresist pattern, and then the first sacrificial layer 5 3 1 is electroformed with copper metal, and then the photoresist pattern is removed with acetone. Please refer to the ninth figure, using a photoresist with exposure and lithography to form a second electroformed mold 5 2 2 with selective opening to define the electroformed area, and define the electroformed area differently from the first sacrifice. The metal material f of the layer 5 3 1 forms a fixed lower comb-shaped electrode structure 5 4. The photoresist is patterned using a photomask to form the second electroformed mold 5 2 2, and then the substrate 5 (wafer) is fixed to the cathode, and a pure nickel sheet is used as the anode. Nickel electroforming was performed at a temperature of 50 ° C. When a current of 100 mA was applied, a nickel layer was grown in the mold to fill the gap, so a fixed lower comb-like electrode structure 5 4 was formed. Referring to the tenth figure, the same second electroforming mold 5 2 2 is used to electroform a second sacrificial layer 5 3 2 on the comb electrode structure 5 4 below its defined electroforming area to provide the actuation stroke. Space, and then the second reference electroforming mold 5 2 2 is removed. Among them, the second sacrificial layer 5 3 2 is electroformed with copper metal on the lower comb-shaped electrode structure 54 and serves as a movable electrode structure between the comb-shaped electrode structure and the movable plate.

Page 11 580734 V. Description of the invention (8) Space between plates). After the electroforming is completed, remove the photoresist layer with acetone. Please refer to the eleventh figure, and use a photoresist to pattern a third electroforming mold to cover all areas except the anchor area on the surface of the substrate 5 (including First, the sacrificial layer 5 3 1, the second sacrificial layer 5 3 2 and the lower comb electrode structure 5 4 ′) are deposited with a third sacrificial layer 5 3 3 to provide an upper comb electrode structure (… not shown) and A lateral gap of the lower comb-shaped electrode structure 54. The third sacrificial layer 5 3 3 is a thin copper layer, which serves as a sacrificial space to separate the upper comb electrode (not shown) from the lower comb electrode 54. Please refer to the twelfth figure, using a photoresist to pattern a fourth electroformed mold, to deposit a comb electrode structure 5 5 and a movable plate 5 5 1 on a defined area on the third sacrificial layer 5 3 3 (movable plate ). Among them, the comb-shaped electrode structure 55 and the movable plate 5 51 are formed of a nickel metal structure. Before the final nickel structure is electroformed, it is patterned with a photoresist, and the electroformed path of nickel is still controlled at a temperature of 50 ° C. When DC power is supplied, the nickel layer grows on the uncovered sacrificial layer and the seed layer to form a comb electrode structure 5 5 and a movable plate 5 5 1 on a vertical comb actuator. This nickel is electroformed Growing on the surface and all sidewalls of the third sacrificial layer 5 3 3. When the grown nickel layers are in contact with each other, electroforming is completed. Referring to the thirteenth figure, the first, second, and third sacrificial layers 531, 532, and 533 are removed with an etching solution to obtain a comb-shaped actuator capable of vertical braking. Among them, the substrate 5 (wafer) is released in the etchant π ΝΗ40Η + Η2 02 π to release all the sacrificial copper layers within 1 to 1.5 hours.

Page 12 580734 V. Description of the invention (9) Controlled etching releases the upper comb electrode structure 5 5 and the movable plate 5 5 1. The nickel structure can withstand π ΝΗ40Η + Η2 02 π etching without any structural or chemical damage. Next, the substrate 5 (wafer) is immersed in the diluted H2S04 (the dilution ratio of H2S04 is 3 to 1) and the chrome mask etchant (CR-7T) for 40 to 60 seconds to remove the nickel seeds, respectively. Layer and chrome adhesion layer, and provide isolation between pads and individual devices. The aforementioned deposition method may be a method commonly used in semiconductor integrated circuit manufacturing processes such as electroforming, chemical vapor deposition, physical vapor deposition, etc., but is not limited thereto.

From the description of the previous embodiment, it can be known that due to the method for manufacturing the vertical comb-shaped actuator of the present invention, the vertical comb-shaped actuation of a metal structure is made by using micro-electroforming technology, optical lithography technology and surface micro-processing technology Device. Because the sacrificial layer and the upper and lower electrodes are different metals with a good etching selection ratio, they can be sequentially deposited by electroforming, without the need for wafer bonding technology to combine the upper and lower electrode structures, and the gap between the comb electrodes can be accurately controlled size. Therefore, it not only solves the problems of poor structure of the conventional technology, but also causes problems such as #cuts on the substrate and restricted substrate materials. At the same time, it also solves the alignment problem caused by the conventional technology when the upper and lower electrode structures are used to join. Relatively, the effect of reducing the actuation voltage and increasing the stroke can be achieved, and the advantages of the original comb-shaped actuator are maintained. And, by adjusting the thickness of each sacrificial layer, the lateral gap of the electrodes and the allowable movement stroke of the vertical comb actuator can be controlled separately. In summary, it can be seen that the manufacturing method of the vertical comb actuator of the present invention has indeed improved the conventional technology. The actuation voltage is too high, the actuation stroke is limited, the substrate material is limited, additional bonding and spacing are required. Too large to reduce the amount of electricity that can be generated

Page 13 580734 V. Description of the invention (ίο) Capacitive or electrostatic forces are a major breakthrough design, and the use of this method has never been seen before, so the invention should meet the novelty and progress of the invention patent Requirements and high industrial use value, but pray for the detailed review and grant the patent for prayer.

Page 580734 Brief description of the diagram The first diagram is a schematic diagram of the structure of a conventional vertical comb actuator. The second diagram is a conventional vertical comb actuator along the line A-A of the first diagram (a ) Schematic diagram of section 0 The second picture is a conventional vertical comb actuator (two) is not intended to be cut away. The fourth picture is a conventional vertical comb actuator (three) is not intended to be cut. Fifth picture It is a schematic diagram of the structure of a conventional vertical comb-shaped actuator (IV). The sixth Λ-7 is a conventional vertical comb-shaped actuator along the line B-B of the fifth figure (IV). Cross-sectional schematic diagrams of electrode joining steps. Eighth to tenth. First. The diagram is a schematic flow chart of a preferred embodiment of a method for manufacturing a vertical comb actuator in accordance with the present invention. Brief description of drawing number • 1 a, 1 b • • comb structure 2 a, 2 b · • comb structure 3 a 3 b reference comb structure 4 a, 4 b · • comb electrode 5 substrate 5 1 · plating Starting layer 5 2 1 • • First plating die 5 2 2 • • • Second plating die 5 3 1 • • First sacrificial layer 5 3 2 • • • Second sacrificial layer 5 3 3 • • Third sacrificial layer 5 4 · • lower comb electrode structure 5 5 • • upper comb electrode structure 5 5 1 • movable plate

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Claims (1)

580734 VI. Scope of patent application1. A method for manufacturing a vertical comb-shaped actuator by surface micromachining technology. It includes the following steps: The first sacrificial layer is formed by electroforming on the substrate to provide the actuation required Height space;. Electroforming on the substrate to form the lower comb electrode structure; · electroforming on the lower comb electrode structure to form a second sacrificial layer to provide the height space required for actuation; * travel; on the substrate A third sacrificial layer is formed on top by a deposition method to provide a lateral gap between the upper and lower comb-shaped electrode structures; an upper comb-shaped electrode structure is formed on the third sacrificial layer by a deposition method; φ and the aforementioned sacrificial layers are removed To obtain a vertical comb-shaped actuator. 2. The method according to item 1 of the scope of patent application, wherein the material of each sacrificial layer is different from the comb electrode structure. 3. The method according to item 1 of the scope of patent application, wherein each sacrificial layer is made of copper metal. 4. The method according to item 1 of the scope of patent application, wherein the comb-shaped electrode structure is selected from conductive materials. 5. The method as described in item 4 of the scope of patent application, wherein the conductive material is nickel metal. 6. The method according to item 1 of the scope of patent application, wherein before the first sacrificial layer is formed on the substrate, an insulating layer and an electroforming starting layer are formed on the substrate in advance. 7 · The method as described in item 6 of the scope of patent application, wherein the insulation layer is selected Page 16 580734 Sixth, the scope of application for patents is from one of the stone dioxide layer or the nitride stone layer. 8. The method according to item 6 of the scope of patent application, wherein an electroforming mold (mo 1 d) is formed on the electroforming starting layer by exposure and development. 9. The method according to item 1 of the scope of patent application, wherein the third sacrificial layer is deposited on the substrate including the first sacrificial layer, the second sacrificial layer, and the surface of the lower comb electrode structure. Page 17