JP5465634B2 - Dissolved wafer manufacturing process and associated microelectromechanical device with supporting substrate with spacing mesa - Google Patents

Description

(Field of Invention)
The present invention relates to a microelectromechanical device and a method for manufacturing the device. In particular, the invention comprises a microelectromechanical device having a support substrate including a mesa for supporting various mechanical members of the microelectromechanical device and / or a doped region of a partially sacrificial substrate that defines the electromechanical member, and The invention relates to a method for manufacturing a device.

(Background of the Invention)
Traditionally, miniaturization of mechanical systems and / or electromechanical systems has been hampered by manufacturing limitations of small and lightweight mechanical or electromechanical components. Due to the complexity of the parts, manufacturing on a small scale has been difficult and impossible. For example, until recently, heavy, large gimbal systems were used in navigation guidance systems in the aerospace industry. These systems included metal, typically large, heavy mechanical parts. However, since the mechanical parts are complex, it has been difficult to reduce the size of the navigation guidance system.

  However, in recent years, with the generalization and higher precision of semiconductor manufacturing procedures, the use of microelectromechanical structures (MEMS) manufactured by semiconductor manufacturing technology instead of many mechanical structures and electromechanical structures of mechanical systems. Can be done. For example, some use a gyroscope that includes one or more MEMS devices instead of a gimbal system. Examples of these gyroscopes are described in Greiff et al. US Pat. No. 5,650,568, the contents of which are incorporated herein by reference.

  The Greiff et al. '568 patent describes a gimbaled vibrating wheel gyroscope for detecting rotational speed in inertial space. Instead of the typical gimbal of a larger, heavy mechanical system, a lighter and smaller MEMS device is used. These MEMS devices that form the various mechanical and / or electromechanical parts of the gyroscope are manufactured by conventional semiconductor technology. The electrical characteristics of the gyroscope are then used to power these components and receive signals from these components.

  An important advantage of using MEMS devices for mechanical and electromechanical systems is that miniaturization and weight reduction can be achieved over conventional mechanical systems that use metal parts. However, many mechanical and electromechanical systems, such as the gimbal system described above, have many moving parts that must be accurately manufactured to operate properly with the required accuracy. Thus, the ability to use MEMS devices manufactured by semiconductor manufacturing technology instead of metal parts is limited by the accuracy achievable with semiconductor manufacturing technology. Although current semiconductor manufacturing techniques are used to manufacture MEMS devices, these manufacturing procedures result in some limitations described below with respect to the Greiff et al. '568 patent.

  In this regard, FIGS. 1A-1D illustrate a conventional method for manufacturing MEMS devices by conventional semiconductor manufacturing techniques. The process shown in these figures is commonly known as the dissolved wafer process (DWP) and is described in the Greiff et al. '568 patent.

  In particular, with reference to FIG. 1A, a silicon substrate 10 and a support substrate 12 are shown. In a typical MEMS device, the silicon substrate is etched to form the mechanical and / or electromechanical members of the device. The mechanical member and / or electromechanical member is generally supported above the support substrate so that the mechanical member and / or electromechanical member can move freely. The support substrate is typically manufactured from an insulating material such as PYREX® glass.

  As shown in FIG. 1A, the support member 14 is first etched from the inner surface of the silicon substrate. These support members are generally known as mesas and are exposed through an appropriately patterned layer of photoresist 16 to etch those portions of the silicon substrate inner surface using potassium hydroxide (KOH) or the like. It is formed by. Etching is preferably continued until a sufficiently high mesa 14 is formed.

  With reference to FIG. 1B, a predetermined depth of doping is then performed such that the etched inner surface 18 of the silicon substrate is doped, such as with boron, and the silicon substrate 10 has both a doped region 20 and an undoped sacrificial region 22. Region 20 is provided. With reference to FIG. 1C, a trench is then formed that extends through the doped region 20 of the silicon substrate 10, such as by reactive ion etching (RIE). These grooves form the mechanical and / or electromechanical members of the MEMS device.

  As shown in FIGS. 1A-1C, the support substrate 12 is also etched first to form metal electrodes 26 and conductive traces (not shown) on the inner surface of the support substrate. These electrodes and conductive traces are then electrically connected to various mechanical and / or electromechanical members of the MEMS device.

  Once the support substrate 12 is processed to form electrodes and conductive traces, the silicon substrate 10 and the support substrate 12 are combined. With reference to FIG. 1D, the silicon substrate and the support substrate are bonded at the contact surface 28 on the mesa 14 by anodic bonding or the like. As a final step, the undoped sacrificial region 22 of the silicon substrate is etched away so that only the doped regions containing the mechanical and / or electromechanical members of the resulting MEMS device remain. Therefore, the mesa extending outward from the silicon substrate supports the mechanical member and / or the electromechanical member so that the member can freely move above the supporting substrate. Further, the electrode formed by the support substrate is electrically connected to the mechanical member and / or the electromechanical member when the mesa contacts the electrode.

  As is known to those skilled in the art, the step of reactive ion etching a groove through the doped region 20 of the silicon substrate 10 is such that the resulting groove is accurately positioned on the inner surface of the partially sacrificial substrate, and the width of the groove and Controls must be made to ensure that the walls are formed very accurately. For example, grooves formed by RIE must generally be formed within a tolerance of 0.1 to 0.2 microns of a given width. Furthermore, it is important that the trench extends through the doped region. Therefore, the inner surface of the silicon substrate must be planar and the doped region must be a predetermined thickness. Although the silicon substrate 10 can be initially formed to have a planar inner surface, the inner surface of the silicon substrate is then etched to form a mesa 14. Unfortunately, due to the etching process, the surface is no longer planar and some surface irregularities occur. Thus, since the surface is no longer planar, the next RIE step cannot produce a precisely located groove on the inner doped region of the partially sacrificial substrate, and etches the groove walls very accurately. I can't. Furthermore, in the next RIE step, a trench that extends through the doped region cannot be created, or it extends too far into the undoped sacrificial region of the silicon substrate.

  Accordingly, the plane of the silicon substrate is such that the trench formed by RIE extends through the doped region of the sacrificial silicon substrate and is precisely located on the inner surface of the doped region of the silicon substrate and has a precisely defined wall. What is needed is a method for manufacturing MEMS devices using semiconductor manufacturing techniques that separates various mechanical and / or electromechanical members by performing RIE through the inner surface of the substrate. Furthermore, there is a need for a method for manufacturing a gimbal vibrating wheel gyroscope for detecting rotational speed in an inertial space where the gyroscope mechanical and / or electromechanical components are manufactured with high precision.

(Summary of Invention)
As described below, the method for forming a MEMS device of the present invention, and associated MEMS devices, overcomes deficiencies associated with conventional methods. In particular, the method of the present invention allows various types of MEMS devices to be etched by etching through the inner surface of a planar partially sacrificial substrate, such as by RIE, so that the resulting grooves are accurately defined with respect to size, location, and depth. Separate mechanical and / or electromechanical components. In particular, for MEMS devices that are primarily comprised of a doped region of a partially sacrificial substrate and a support substrate, the method of the present invention etches the support mesa from the support substrate rather than the partially sacrificial substrate. By etching the mesa from the support substrate rather than the inner surface of the partially sacrificial substrate, the inner surface of the partially sacrificial substrate remains planar for the etching procedure that separates the precise mechanical and / or electromechanical members. Therefore, a MEMS device having a mechanical member and / or an electromechanical member can be reliably manufactured.

  The present invention further provides a MEMS device that includes a support substrate having a mesa extending outwardly therefrom. The MEMS device of the present invention also includes a partially sacrificial substrate from which mechanical and / or electromechanical members supported by mesas are formed. Since the mesa is formed from the support substrate rather than the partially sacrificial substrate, the inner surface of the partially sacrificial substrate remains planar for subsequent etching, separating the mechanical and / or electromechanical members.

  In accordance with the present invention, these and other advantages are provided by a method for forming a MEMS device that initially provides a partially sacrificial substrate having a planar inner surface. The partially sacrificial substrate is doped such that the partially sacrificial substrate includes both doped and undoped sacrificial regions, and the doped region is adjacent to the inner surface of the partially sacrificial substrate. The method of the present invention also provides a support substrate, typically formed from a dielectric material, for supporting the partially sacrificial substrate. To suspend the partially sacrificial substrate above the support substrate, the method of the present invention includes forming at least one mesa on the support substrate such that the mesa extends outwardly from the remaining portion of the inner surface of the support substrate.

  The method of the present invention further couples the inner surface of the partially sacrificial substrate to the mesa so that the partially sacrificial substrate is suspended above the rest of the support substrate and the doped region of the partially sacrificial substrate faces the support substrate. Including the steps of: By forming the mesa on the support substrate, the inner surface of the partially sacrificial substrate remains flat, so that the mechanical member and / or the electromechanical member of the MEMS device can be easily formed.

  The method of the present invention further includes dissolving or removing the undoped sacrificial region of the partially sacrificial substrate after the partially sacrificial substrate is bonded to the mesa of the support substrate. By removing the undoped region of the partially sacrificial substrate, the mechanical member and / or the electromechanical member formed from the doped region of the partially sacrificial substrate can be freely moved. Further, removing the undoped sacrificial region of the partially sacrificial substrate reduces the heat retention by the resulting MEMS device.

  Another important aspect of the present invention is establishing appropriate electrical connections with the mechanical and / or electromechanical members of the MEMS device. To facilitate this connection, the method of the present invention places a conductive material over at least a portion of the mesa surface, and once the partially sacrificial substrate and support substrate are bonded, the doped region of the partially sacrificial substrate. Forming an electrode in electrical communication therewith. The electrode can then establish an electrical connection with the mechanical and / or electromechanical member of the MEMS device.

  According to one advantageous embodiment, the method of the present invention includes forming at least one mesa having a contact surface extending between a set of inclined sidewalls. Thus, the conductive material can be disposed on at least a portion of the contact surface and at least one inclined sidewall of the mesa. Since the side walls of the mesa are inclined, the metal material can be arranged more easily on the mesa.

  In a further embodiment of the method of the present invention, a mesa having inclined sidewalls is formed by applying a photoresist layer on the surface of the support substrate at a location corresponding to a predetermined location of the mesa. Preferably, the dimensions of the photoresist layer are close to the dimensions of each base of the mesa. The method of this embodiment further etches the exposed surface of the support substrate while simultaneously reducing the size of the photoresist layer so that the resulting mesa has a contact surface extending between a set of inclined sidewalls. Including the steps of: As the photoresist layer shrinks during the etching process, the contact surface of each mesa is smaller than the corresponding base.

  The present invention also provides a MEMS device having precisely defined mechanical and / or electromechanical members. The MEMS device of this embodiment includes a semiconductor substrate having an inner surface. The MEMS device of the present invention further includes a support substrate, typically formed from a dielectric material, having at least one outwardly extending mesa for supporting the semiconductor substrate. Each mesa includes a contact surface that supports the semiconductor substrate such that the semiconductor substrate is suspended above the rest of the support substrate. Since the mesa extends outwardly from the support substrate and is therefore not etched from on the semiconductor substrate, the MEMS device can include precisely defined mechanical and / or electromechanical members.

  The mesa of the MEMS device can include a contact surface that extends between two inclined sidewalls. Furthermore, because the inclined sidewalls allow the metal material forming the electrodes and traces to be more easily placed, the MEMS device of this embodiment has at least one inclined sidewall of the contact surface and the mesa. And an electrode formed on both.

  Thus, the manufacturing method and associated MEMS device of the present invention provide a mesa etched from a support substrate. By etching the mesa from the support substrate, the inner surface of the partial sacrificial substrate is planar so that the resulting MEMS device mechanical and / or electromechanical members can be more accurately and reliably formed from the partial sacrificial substrate. Remains as it is.

1 is a series of cross-sectional views of a conventional method for forming a MEMS device. 1 is a series of cross-sectional views of a conventional method for forming a MEMS device. 1 is a series of cross-sectional views of a conventional method for forming a MEMS device. 1 is a series of cross-sectional views of a conventional method for forming a MEMS device. FIG. 3 is a series of cross-sectional views illustrating operations performed to form a MEMS device, according to one embodiment of the invention. FIG. 3 is a series of cross-sectional views illustrating operations performed to form a MEMS device, according to one embodiment of the invention. FIG. 3 is a series of cross-sectional views illustrating operations performed to form a MEMS device, according to one embodiment of the invention. FIG. 3 is a series of cross-sectional views illustrating operations performed to form a MEMS device, according to one embodiment of the invention. FIG. 3 is a series of cross-sectional views illustrating operations performed to form a MEMS device, according to one embodiment of the invention. FIG. 3 is a series of cross-sectional views illustrating operations performed to form a MEMS device, according to one embodiment of the invention. FIG. 4 is a block diagram of operations performed to manufacture a MEMS device, according to one embodiment of the invention. FIG. 3 is a block diagram of operations performed to form a mesa on a support substrate, according to one embodiment of the invention. FIG. 6 is a block diagram of operations performed to form an electrode on a support substrate, according to one embodiment of the invention. FIG. 6 is a block diagram of operations performed to form a mechanical member and / or an electromechanical member of a MEMS device from a doped region of a partially sacrificial substrate, according to one embodiment of the invention. FIG. 4 is a block diagram of operations performed to form a mesa having inclined sidewalls on a support substrate, according to one embodiment of the invention. 1 is a plan view of a vibrating wheel gyroscope according to one embodiment of the present invention. FIG. FIG. 9 is a cross-sectional view of the gyroscope of FIG. 8 at various stages of manufacture, according to one embodiment of the invention. FIG. 9 is a cross-sectional view of the gyroscope of FIG. 8 at various stages of manufacture, according to one embodiment of the invention. FIG. 9 is a cross-sectional view of the gyroscope of FIG. 8 at various stages of manufacture, according to one embodiment of the invention. FIG. 9 is a cross-sectional view of the gyroscope of FIG. 8 at various stages of manufacture, according to one embodiment of the invention. FIG. 9 is a cross-sectional view of the gyroscope of FIG. 8 at various stages of manufacture, according to one embodiment of the invention. FIG. 9 is a cross-sectional view of the gyroscope of FIG. 8 at various stages of manufacture, according to one embodiment of the invention. FIG. 9 is a partial cross-sectional view of the gyroscope of FIG. 8.

Detailed Description of Preferred Embodiments
The present invention will now be described more clearly hereinafter with reference to the accompanying drawings, which illustrate one preferred embodiment of the invention. However, the present invention may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, this embodiment is provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Throughout the drawings, the same reference number represents the same element.

  The method of the present invention maintains the flatness of the inner surface of the partially sacrificial substrate so that mechanical and / or electromechanical components can be spaced apart or otherwise formed in a precise and reliable manner. Produce unique MEMS devices with precisely defined mechanical and / or electromechanical components. 2A-2F illustrate one advantageous embodiment of the method of operation and device performed to manufacture a MEMS device according to the present invention. 2A to 2F and the block diagram of FIG. 3, the manufacturing method of the present invention includes a step of providing a partial sacrificial substrate 30 having an inner surface 30a and an outer surface 30b (see step S100). In a preferred embodiment, the partially sacrificial substrate is silicon, but the partially sacrificial substrate may be made of any particular material that can be doped to form a doped region, such as gallium arsenide or germanium.

  The method of the present invention further comprises doping a portion of the partially sacrificial substrate such that the partially sacrificial substrate includes both a doped region 32 adjacent to the inner surface 30a and an undoped sacrificial region 34 adjacent to the outer surface 30b. Step S120). The partially sacrificial substrate is doped with a dopant to a predetermined depth, eg, 10 microns, with respect to the inner surface.

  In one preferred embodiment, the dopant is added into the partially sacrificial substrate by diffusion methods well known in the art. However, the method of the present invention is not limited to this technique, and therefore the doped region adjacent to the inner surface of the partially sacrificial substrate can be formed by any method known in the art. Further, although the partially sacrificial substrate is doped with a boron dopant in the exemplary embodiment, the dopant may comprise any type of dopant that forms a doped region within the partially sacrificial substrate.

  2A and 3, the method of the present invention also includes providing a support substrate 36 (see step S130). In a preferred embodiment, the support substrate is formed from a dielectric material such as PYREX® glass so that the support substrate also electrically insulates the MEMS device. However, it should be understood that the support substrate can be formed from any desired material, including semiconductor materials.

  Referring also to FIGS. 2A and 3, the method of the present invention includes etching several sections of the support substrate, thereby forming a mesa 38 extending outwardly from the inner surface 36a of the support substrate 36 (steps). (See S140). Referring to FIGS. 2A and 4, a mesa is first formed by placing a photosensitive layer or coating (not shown) on the inner surface of the support substrate. As is known to those skilled in the art, this photosensitive coating is usually called a photoresist (see step S142). Thereafter, the photosensitive coating is at least partially covered with a mask, and the exposed portion of the photosensitive coating is illuminated (see step S144). In this regard, the photosensitive coating is typically illuminated by a UV light source, but the photosensitive coating can be illuminated by any particular light source that can expose the photosensitive coating.

  After exposing a part of the photosensitive material, a part of the photosensitive film is removed by exposing the photosensitive film to a developer solution such as Shiply developer condensate (see step S145). As is known to those skilled in the art, depending on whether a positive or negative photosensitive coating is utilized, a portion of the exposed photosensitive coating or a portion of the unexposed photosensitive coating, respectively. Remove. Next, the portion of the support substrate that is not covered by the remaining photosensitive film is etched by reactive ion etching (RIE) or the like (see step S146). The etching process continues until a portion of the support substrate surrounding mesa 38 is removed so that the mesa has the desired height. Thereafter, the remaining part of the photosensitive layer is removed (see step S147).

  2B, 2C, and 3, after forming the mesa 38 on the support substrate, the method of the present invention further deposits a metal material on the inner surface 36a of the support substrate 36, particularly on the mesa 38, to form the electrode 42. (See step S150). However, to prevent the metal deposited on the mesa from extending too far above the surface of the mesa, the mesa is first selectively etched to define a recessed area where the metal can be deposited. Referring to FIGS. 2B, 2C, and 5, forming the electrodes on the mesa 38 places a photosensitive material (not shown) on the inner surface 36a of the support substrate 36, and a region of the inner surface 36a where no metal is deposited. Patterning the photosensitive material so that only the photosensitive material covers it. That is, the portion of the inner surface of the support substrate that is etched and then coated with metal is not covered by the patterned photosensitive material and is therefore exposed (see steps S152, S154, and S155). The method of the present invention further includes the step of etching the exposed portion of the inner surface of the support substrate, for example by BOE, to form the recessed regions 46 in a predefined pattern (see step 156).

  Referring to FIGS. 2C and 5, the method of the present invention further includes depositing a metal material in the etched recess 46 to form electrodes 42 and conductive traces (not shown) (see step S158). . As is known in the art, the electrodes and traces may be comprised of any conductive material such as a multi-layer deposition of titanium, platinum, and gold and may be deposited by any suitable technique such as sputtering. Thereafter, the remaining part of the photosensitive layer is removed (see step S159).

  Referring to FIGS. 2C and 3, the inner surface of the partially sacrificial substrate is also etched to separate or otherwise form the resulting MEMS device's mechanical and / or electromechanical members (see step S160). As previously mentioned, procedures for forming mechanical and / or electromechanical members require tight tolerances so that members having precise dimensions can be reliably formed. In particular, the mesa is formed on the support substrate rather than the inner surface of the partially sacrificial substrate, so that the portion of the inner surface of the partially sacrificial substrate that is later etched to form the mechanical and / or electromechanical members is at least flat, This facilitates precise formation of mechanical and / or electromechanical components.

  Specifically, referring to FIGS. 2C, 2D, and 6, the mechanical and / or electromechanical member is formed by first coating the inner surface of the partially sacrificial substrate with a photosensitive layer 48 (see step S161). After the photosensitive layer is covered with a mask that finally defines a region to be etched, the exposed portion of the photosensitive layer is illuminated (see step S162). After removing the mask, a part of the photosensitive layer 50 is removed so that the remaining part 51 of the photosensitive layer does not cover the region of the inner surface of the partially sacrificed substrate to be finally etched (see step S163).

  Referring to FIG. 2E, the exposed portion of the inner surface of the partial sacrificial substrate is then etched by RIE etching or the like to form a trench through the doped region of the partial sacrificial substrate (see step S164). As described below, the doped region of the partially sacrificial substrate that extends between the trenches forms the mechanical and / or electromechanical members of the resulting MEMS device. After the mechanical and / or electromechanical members of the MEMS device are defined by the etched trench, the method of the present invention removes the remaining photosensitive material 51 from the inner surface of the partially sacrificial substrate (see step 165).

  Referring to FIGS. 2F and 3, the method of the present invention also includes positioning the inner surface of the partially sacrificial substrate in contact with the mesa, including electrodes deposited on the surface of the mesa (see step S170). Next, a bond between the partially sacrificed substrate and the mesa is formed (see step S180). It should be understood that in one preferred embodiment the bond is an anodic bond, but the bond may be of any type that provides a fixed engagement.

  It is also often advantageous to remove the undoped sacrificial regions of the partially sacrificial substrate so that the mechanical and / or electromechanical members can rotate, move and curve. This technique is commonly referred to as a dissolved wafer process (DWP). Accordingly, in one embodiment, the method of the present invention further includes the step of removing the undoped sacrificial region of the partially sacrificial substrate (see step S190). Removal of the undoped sacrificial region is typically performed by etching away the undoped sacrificial region using, for example, an ethylenediamine pyrocatechin (EDP) etch process, but any doping / selective etch procedure can be used. .

  As mentioned above, removal of the undoped sacrificial region of the partially sacrificial substrate provides several advantages. For example, removal of this material allows the mechanical and / or electromechanical members etched from the doped region to have freedom of movement such that they move or curve with respect to the support substrate. Furthermore, removal of the undoped sacrificial region of the partially sacrificial substrate also decouples the mechanical and / or electromechanical member from the remaining portion of the doped region of the partially sacrificial substrate that is outside the trench etched through the doped region.

  Referring to FIG. 2A, it is often advantageous to provide a mesa 38 having a contact surface 56 that extends between a set of inclined sidewalls 58. These inclined sidewalls 58 allow metal to be deposited on the contact surface and at least one mesa sidewall by “stepping” the metal up the sidewall to the contact surface.

  It is important to note that the mesas can take any geometric shape. For example, in this embodiment, the mesa is formed in a pyramid shape, but the cross-sectional shape of the mesa may take other shapes such as an octagon or a cylinder as required in a specific application example. Furthermore, although the inclined sidewalls are referred to as a set of inclined sidewalls, it should be understood that in some applications, only one of the set of sidewalls may be inclined.

  Referring to FIG. 7, which illustrates the operations necessary to create a mesa with sloping sidewalls, the method of this embodiment of the present invention is patterned to cover only the location corresponding to the final location of the mesa. A step of applying the photosensitive layer to the inner surface of the support substrate (see steps S200, S202, and S204). Thus, the photosensitive layer is formed from a number of pads, each pad defining a mesa. Each pad is dimensioned to approximate the size of the base of the respective mesa. The method of the present invention further includes the step of etching the exposed inner surface of the support substrate (see step S206). When the etching step is performed, the etchant also etches the photosensitive layer, thereby gradually reducing the dimensional size of various portions of the photoresist (see step S208). As shown in FIG. 2A, the pad size is thus gradually reduced to create a mesa 38, each mesa having a set of inclined sidewalls 58 and a contact surface 40 extending therebetween. Have. As shown, the contact surface 40 is smaller in size than the mesa base 54.

  In addition to the method of making a MEMS device, the present invention is also directed to the resulting MEMS device, for example, as shown in FIG. 2F. As described above in connection with the method, the resulting MEMS device of the present invention includes a semiconductor substrate 30 that includes a first inner surface 30a. As described above, the semiconductor substrate may be made of silicon, gallium arsenide, germanium, or the like, and has a doped region 32 adjacent to the first inner surface 30a. The doped region of the semiconductor substrate forms the mechanical member of the MEMS device. In addition, the doped region is typically doped with boron, but this region can be doped with other dopants such as indium, thallium, and aluminum.

  Furthermore, the MEMS device of this embodiment of the invention includes a support substrate 36. The support substrate serves to suspend the semiconductor substrate, whereby the mechanical and / or electromechanical parts defined by the semiconductor substrate have a higher degree of freedom of movement or bending. However, the support substrate can also perform other functions, for example by acting as an electrical insulator or heat sink for the mechanical and / or electromechanical portions of the MEMS device. Therefore, the support substrate is usually formed from a dielectric material such as PYREX® glass.

  The MEMS device of the present invention, more specifically the support substrate, further includes at least one mesa 38. The mesa extends outward from the remaining portion of the support substrate 36 and functions to support the semiconductor substrate 36. As described above, since the mesa 38 is formed on the support substrate as opposed to the semiconductor substrate, the inner surface of the semiconductor substrate maintains high flatness, and the trench is precisely and controlled through the doped region of the semiconductor substrate. Easy etching. As described above, the mesa includes the contact surface 56 that supports the inner surface 30 a of the semiconductor substrate, whereby the semiconductor substrate is suspended to cover the remaining portion of the support substrate 38.

  In one embodiment of the MEMS device of the present invention, an electrode 42 is formed on the mesa 38 to provide an electrical connection to the mechanical and / or electromechanical members of the MEMS device. In one preferred embodiment of the present invention, the mesa includes a contact surface 56 that extends between a set of inclined sidewalls 58. In this embodiment, electrodes are deposited on the mesa contact surface 56 and at least one inclined sidewall 58. Thus, the resulting electrode is exposed on the side wall of the mesa to facilitate electrical contact.

  As described above, the contact surface 56 of the mesa supports the inner surface 30a of the semiconductor substrate. In some embodiments, the contact surface of the mesa and the inner surface of the semiconductor substrate are bonded or otherwise bonded. For example, the contact surface of the mesa and the inner surface of the semiconductor substrate can be bonded by anodic bonding or the like.

  As previously mentioned, MEMS devices are used in a variety of applications. In particular, one application is a gimbaled vibrating wheel gyroscope, such as that described in Greiff et al. US Pat. No. 5,650,568. As described in the Greiff et al. Patent and illustrated in FIG. 8, a gyroscope includes a plurality of mechanical and / or electromechanical members etched from a semiconductor substrate. These members typically include a wheel assembly or rotor 62, a stator 64, and a plurality of drive electrodes 66 a-h that terminate in a plurality of finger-like members 68. According to the present invention, unlike Greiff et al., These members are supported to cover a support substrate (not shown) by a plurality of mesas 70a-h extending outwardly from the support substrate. .

  As shown in FIG. 8, the rotor 62 includes a central hub 72 suspended by a pair of post assemblies 74a and 74b so as to cover the support substrate, a plurality of spokes 76a to 76d, and a plurality of finger-like members. 80 includes an outer wheel or rim 78 extending therefrom. The rotor finger-like members 80 are interleaved with the finger-like members 68 of the stator 64 for electrostatic actuation by the stator 64. Each spoke 74a-b includes a box-shaped strain relief portion 82a-d, respectively.

  Each post assembly 74a and 74b includes a support post 84a and 84b and a post curve 86a and 86b, also referred to as output curve 86a and 86b, respectively. A drive circuit (not shown) is also coupled to the stator drive electrodes 66a-h.

  When the drive electrodes 66a-h are energized, the rim 78 of the wheel assembly 62 vibrates in the plane of the assembly around the drive shaft 88 or rotationally vibrates. The gyroscope can be operated in a self-vibrating manner or can be operated in an open loop. When the wheel rim 78 is in rotational vibration, the rotational variability with respect to the input shaft 90 of the vehicle to which the gyroscope is attached causes the wheel assembly rim to move around the output shaft 92 out of the plane of the gyroscope. Distort.

  A plurality of sensing areas 94 a, 94 b extend from the rim 78 of the wheel assembly 62 along the input shaft 90. The sensing electrodes 94a and 94b are disposed on the support substrate and below the respective sensing regions 94a and 94b, and sense distortion of the assembly 62 out of the plane.

  As described in the Greiff patent, these gyroscopes are typically constructed using the dissolved wafer process (DWP) described below. However, it should be understood that any microelectromechanical manufacturing process may be used to manufacture the improved gyroscope of the present invention.

  Referring initially to FIG. 9, a support substrate 200 is provided with a thickness of about 750 microns. In one embodiment, the support substrate 200 is made of glass, such as PYREX® glass. As described above, the support substrate has an inner surface or upper surface 202 that is patterned and etched according to a conventional lithographic process to provide a mesa 204 that supports other parts of the gyroscope.

  Referring now to FIG. 10, a semiconductor substrate 206 having a thickness on the order of 500 microns is first doped to a predetermined depth, eg, about 10 microns, to provide a doped region 208 and an undoped sacrificial region 210. In the exemplary embodiment, region 208 is doped with boron. This boron doped region 208 ultimately forms the gyroscopic wheel assembly 62.

  Referring to FIG. 11, the semiconductor substrate is then patterned and etched, eg, by RIE etching, to define a wheel assembly 62 according to the requirements of a particular application. In the exemplary embodiment, etching the semiconductor substrate of FIG. 10 forms regions 212 and 214 that provide a portion of the outer rim 78 along axis C (see FIG. 8), and are spaced apart as shown. A central portion is spaced from the disposed regions 212 and 214. The portion 216 of the doped region 208 between the regions 212 and 214 forms the gyroscope central hub 72 (see FIG. 8) and output curves 86a and 86b.

  Referring now to FIGS. 11 and 12, a cross section of the gyroscope taken along the input axis A (FIG. 8) is shown following the manufacturing steps described above. More specifically, in FIG. 11, the semiconductor substrate 206 is also shown having a boron doped region 208. Note that this cross section of the gyroscope along axis A is not cut through a region similar to regions 212 and 214 of FIG.

  The RIE etch in which the structure of FIG. 10 is formed further forms three regions 218, 220, and 222 along axis A, as shown in FIG. The central region 220 forms a central hub 72 (see FIG. 8), and the spaced regions 218 and 222 form part of the outer rim 78 of the wheel assembly 62.

  Referring also to FIG. 13, a cross section of the gyroscope along axis B (FIG. 8) is shown. The RIE etch that forms the structure shown in FIGS. 10 and 12 produces the structure of FIG. More specifically, the etching step cuts through the boron doped region 206 as shown. The remaining portion of the boron doped region 206 forms spoke curves 74b and 74d, a central hub 72, and finger members 80 of the wheel assemblies 62 and finger members 68 of the stator 64 that are interleaved.

  Referring to FIG. 15, a cross-sectional view of the complete gyroscope of FIG. 8 is shown taken along axis C. The sensing electrodes 94 a and 94 b are formed so as to cover the upper surface 202 of the support substrate 200. The sensing electrodes 94a and 94b may be made of any suitable conductive material, such as a multilayer deposition of titanium, platinum, and gold, and can be deposited by any suitable technique, such as sputtering. Conductive traces 224 are also provided on the top surface 202 of the support substrate 200 and extend from the contact surface 226 on the mesa down the at least one sidewall 228 of the mesa to the edge portion of the support substrate 202. Further, trace 224 provides an electrical connection to drive electrodes 66a-h (not shown) for applying drive signals to the drive electrodes.

  After processing the support substrate 200 to form the sensing electrodes 94a and 94b and the conductive traces 224, the wheel assembly structure shown along various axes in the cross-sections of FIGS. To the contact surface 226. More specifically, the semiconductor substrate is inverted and bonded to the support substrate 200 by anodic bonding. Although not shown, it should be understood that any undoped region 210 of the semiconductor substrate can be removed, for example, by DWP. Accordingly, the wheel assembly 62 and the stator 64 are suspended by the mesa extending outward from the upper surface of the support substrate so as to cover the support substrate 200 as shown in FIG. The mechanism of the wheel assembly 62 shown in the view of FIG. 17 includes a central hub 72, output bends 86 a and 86 b, an output rim 78, and a rotor finger-like electrode 80.

  As described above and illustrated in FIGS. 9 and 17, the gyroscope of the present invention includes a mesa formed in the support substrate 200 as opposed to the semiconductor substrate 206. As the mesa is etched from the support substrate, the inner surface of the semiconductor substrate remains flat prior to forming the trenches that define the resulting gyroscopic mechanical and / or electromechanical members.

  Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing description and the accompanying drawings. Accordingly, it is to be understood that the invention is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein, they are used in a general and descriptive sense only and are not limiting.

Claims (8)

A method for forming a microelectromechanical structure comprising:
Providing a partially sacrificial substrate having a first surface;
Doping a portion of the partially sacrificial substrate with a dopant such that the partially sacrificial substrate includes a doped region and an undoped region, the doped region being adjacent to the first surface of the partially sacrificial substrate;
Providing a support substrate for supporting the partially sacrificial substrate;
Forming the at least one mesa on the surface of the support substrate such that the at least one mesa extends outwardly from the surface of the support substrate, the at least one mesa being a set of inclined surfaces Having a contact surface extending between the sidewalls;
Forming a recessed region in a predefined pattern on the contact surface of the mesa;
Disposing a conductive material on the recessed area and at least one of the inclined sidewalls of the mesa of the support substrate to form an electrode;
The partial sacrificial substrate has a first surface suspended above a portion other than the at least one mesa of the support substrate, and the doped region of the partial sacrificial substrate faces the support substrate. Bonding a first surface of a sacrificial substrate to the at least one mesa.   The method of claim 1, further comprising removing the undoped region of the partially sacrificial substrate after the combining step.   The method of claim 1, wherein the bonding step comprises anodically bonding the doped first surface of the partially sacrificial substrate to the mesa of the support substrate. The method of claim 1, wherein the step of forming the at least one mesa comprises
Applying a photoresist layer to the surface of the support substrate at a position corresponding to a predetermined position of the mesa, and bringing the dimensions of the photoresist layer close to the dimensions of the base of the mesa;
Etching the exposed surface of the support substrate;
Gradually reducing the size of the photoresist layer during the etching such that the resulting mesa includes a contact surface that is smaller in size than the base of the mesa that extends between the set of inclined sidewalls. .   2. The method of claim 1, wherein the doping step comprises doping the substrate with a dopant selected from the group consisting of boron, indium, thallium, and aluminum.   The method of claim 1, wherein the providing step comprises providing a partially sacrificial substrate selected from the group of substrates formed from silicon, germanium, and gallium arsenide.   The method of claim 1, further comprising providing a support substrate formed from a dielectric material. A method for use in a molten wafer process to form a microelectromechanical device comprising:
Providing a partially sacrificial substrate having a first surface;
Doping a portion of the partially sacrificial substrate with a dopant such that the partially sacrificial substrate includes both a doped region and an undoped region, the doped region being adjacent to the first surface of the partially sacrificial substrate; When,
Etching selected regions of the doped region and undoped region of the partially sacrificial substrate, and the remaining doped regions of the partially sacrificial substrate forming members of the resulting microelectromechanical device;
Providing a support substrate comprising a dielectric material to support the partially sacrificial substrate;
Forming the at least one mesa on the surface of the support substrate such that the at least one mesa having a contact surface extends outwardly from the surface of the support substrate;
Forming a recessed region in a predefined pattern on the contact surface of the mesa;
Disposing a conductive material in the recessed area of the mesa surface to form an electrode;
A first surface of the partial sacrificial substrate is suspended above a portion of the surface of the support substrate other than the at least one mesa so that the doped region of the partial sacrificial substrate faces the support substrate. Coupling the first surface of the partial sacrificial substrate to the at least one mesa such that the electrode is in electrical communication with the doped region of the partial sacrificial substrate;
After the bonding step, from the partially sacrificial substrate, the at least one of the members of the resulting microelectromechanical device defined by the doped region of the partially sacrificial substrate is movable with respect to the support substrate. Dissolving the undoped region.

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