Production method for a micromechanical component, and a micromechanical component

A production method for a micromechanical component and a micromechanical component apparatus are provided encompassing the steps of: forming a housing having an incident light window, forming a multitude of optically active surfaces on a wafer, subdividing the wafer into a multitude of chips having at least one optically active surface in each case, which surface is designed in such a way that, at least in a deactivated operating mode of the chip, the optically active surface is situated in an initial position with respect to the chip, and affixing at least one of the chips inside the housing, the optically active surface of the chip in its initial position being aligned at an angle of inclination that is not equal to 0° and not equal to 180° with respect to the incident light window.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German Application No. 10 2008 040 528.0, filed in the Federal Republic of Germany on Jul. 18, 2008, which is expressly incorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a production method for a micromechanical component and to a micromechanical component.

BACKGROUND INFORMATION

The mounting and use of an optical element, e.g., an optically active surface, in a micromechanical component poses special challenges to the packaging of the micromechanical component, which do not present themselves when a microelectrical and/or a purely micromechanical element is used in the micromechanical component. Microelectrical and/or purely micromechanical elements such as sensors or mechanical actuators, for example, usually have only electrical interfaces. This simplifies a complete encapsulation of the microelectrical and/or purely micromechanical elements at the wafer level. The encapsulation can take place in a clean or super-clean environment. In addition, the complete encapsulation of a microelectronic and/or purely micromechanical element at the wafer level is able to be implemented in a relatively cost-effective manner because processes run in parallel. Following the encapsulation, the microelectronic and/or purely micromechanical elements can be separated, cleaned and/or processed further in a normal, clean environment. For instance, an installation inside a chip housing, the development of an electrical contacting and/or an insertion into a system take(s) place.

The use of an optical element in a micromechanical component inside a protective housing usually requires optical radiation to be coupled in and/or out. The incoupling and/or decoupling of optical radiation frequently takes place via an incident light window made of a light-transmitting material having a refractive index not equal to 1. For example, such an incident light window is formed in the encapsulation of an active surface from at least one glass wafer, since glass wafers have suitable optical properties such as transparency, roughness and planarity. An encapsulation of the optical element with the aid of a glass wafer is possible at a wafer level as well.

FIG. 1shows a schematic illustration of a first conventional micromechanical component having an optically active surface. Conventional micromechanical component10has a reflective surface of a reflective plate12as optically active area. To protect against environmental effects, reflective plate12is situated inside a housing formed by a frame part14, an upper cover16, and a lower cover18. Upper cover16is at least partially made of a light-transmitting material. The housing formed by components14through18may have an airtight design, for instance.

Reflective plate12is joined to the housing formed by components14through18via at least one spring element20. Via an electrostatic and/or magnetic drive, reflective plate12is able to be rotated about an axis of rotation running along the longitudinal axis of spring element20. Dashed lines12ashow possible positions of reflective plate12with respect to covers16and18.

A beam of light22incident on the boundary surfaces of upper cover16is partially reflected. The transmitted component of incident beam of light22strikes reflective plate12, which directs it as a deflected beam of light24to an image plane26. Depending on the position of reflective plate12, deflected beam of light24strikes various points of image plane26. Beam of light28reflected at the boundary surfaces of upper cover16may at least partially also strike image plane26and thus lead to an interference reflex on image plane26. If upper cover16has a large reflection coefficient for the angle of incidence of incident beam of light22, then the interference reflex may have a relatively high light intensity. The interference reflex, unlike beam of light24deflected by reflective plate12, is not variable in its location.

One may—for preventing interference reflexes—dispense with the use of a housing which completely surrounds reflective plate12. In this case, however, a reflective plate12is no longer protected from environmental influences. In addition, a reflective plate12not protected by a housing is often more difficult to separate and/or able to be installed in a device only with more difficulty. More specifically, in such a case it is frequently impossible to utilize standard processes for the separation or the installation.

FIG. 2shows a schematic illustration of a second conventional micromechanical component having an optically active surface.

Illustrated micromechanical component30includes the already described components12,14,18, and20. In addition, micromechanical component30has an upper glass cover32made up of a glass cover plate34and a side plate36. Glass cover plate34on which an incident beam of light22impinges is aligned at an angle with respect to a center position of reflective plate12. Beam of light28reflected at the boundary surfaces of cover plate34is therefore not deflected to image plane26of reflective plate12. This prevents interference reflexes at image plane26.

However, upper glass cover32is difficult to realize at the wafer level. Producing a glass wafer having sloped surfaces is relatively work-intensive and thus relatively expensive. Especially the polishing of the sloped surfaces is frequently not able to be accomplished in satisfactory manner, so that the sloped surfaces have high transparency and very low roughness.

SUMMARY

Embodiments of the present invention provide a production method for a micromechanical component, including: forming a housing (100,108,116) having an incident light window (108); forming a multitude of optically active surfaces (50) on a wafer (52); subdividing the wafer (52) into a multitude of chips (80) having at least one optically active surface (50) in each case, which is designed in such a way that at least in a deactivated operating mode of the chip (80), the optically active surface (50) is disposed in an initial position with respect to the chip (80); and mounting at least one of the chips (80) in the housing (100,108,116), the optically active surface (50) of the chip (80) in its initial position being aligned with respect to the incident light window (108) at an angle of inclination that is not equal to 0° and not equal to 180°.

Embodiments of the present invention provide a micromechanical component including: a chip (80) including an optically active surface (50), which at least in a deactivated operating mode of the chip (80) is situated in an initial position with respect to the chip (80); and a housing (100,108,116), which completely surrounds the chip (80) and has an incident light window (108); the chip (80) being affixed inside the housing (100,108,116) in such a way that the optically active surface (50) in its initial position has an inclined alignment with respect to the incident light window (108), the angle of inclination being not equal to 0° and not equal to 180°.

Embodiments of the present invention provide for a realization that the conventional requirement of an encapsulation at the wafer level, which is difficult to accomplish, is unnecessary when the incident light window for coupling a beam of light in and/or out is formed at the level of the chip housing. Thus, for example, subsequently or prior to developing the incident light window, the chip is affixed inside the chip housing in such a way that the incident light window is tiled with respect to the optically active surface of the chip by an angle of inclination not equal to 0° and not equal to 180°. The occurrence of an interference reflex is thus able to be prevented in an uncomplicated manner.

In embodiments of the present invention, the production of components of the housing may be implemented by injection molding (premold). This enables a cost-effective production of housing components in high piece numbers. The mounting of the incident light window may be implemented by a separate step.

Embodiments of the present invention provide a cost-effective production of a housing by packaging technology using standardized machinery. Although a wafer-level encapsulation, which requires expensive and complicated production steps, is dispensed with, sawing and packaging is possible nevertheless, the active surfaces being protected.

In embodiments of the present invention, the optically active surface is formed in recessed manner with respect to an equidirectional front side of the wafer. This ensures additional protection for the optically active surface during the production process.

In embodiments of the present invention, prior to subdividing the wafer, a cover wafer is fixed in place on a rear side of the wafer oriented counter to the optically active surface, the cover wafer being subdivided into a multitude of protective covers, so that each chip is provided with a protective cover. For example, the chips furnished with the protective cover and having at least one active surface may be held under normal, clean environmental conditions using standard systems (handling), transported, and/or installed in the housing.

In addition, for example, prior to subdividing the wafers the front side of the wafer, which has the same orientation as the optically active surface, may be covered by a sawing foil. Temporary capping of the optically active surface by the sawing foil facilitates the separation of the optically active surfaces formed on the wafer in high numbers.

In embodiments of the present invention, a first adjustment element may be developed on an outer side of the housing, and a precisely fitting second adjustment element may be developed on a mounting board, the first adjustment element and the second adjustment element being brought into contact with each other in such a way that they establish a mechanical connection between the housing and the mounting board. This facilitates the placement of the housing in a preferred position on the mounting board. In addition, for example, using the self-adjusting structures and/or self-adjusting cut-outs, it is possible to minimize the tolerances that occur in the alignment of the housing on the mounting board.

The advantages described in the paragraphs above are also ensured for a corresponding micromechanical component.

In embodiments of the present invention, the housing includes a wall having a continuous opening, and the incident light window is situated on a first contact surface of the wall in such a way that the incident light window covers the opening at least partially, the chip being disposed on a second contact surface of the wall, and the second contact surface being aligned with respect to the first contact surface at an angle of inclination that is not equal to 0° and not equal to 180°. This can enable a cost-effective implementation of the present invention.

In embodiments of the present invention, the housing has a first adjustment element, and the chip has a precisely fitting second adjustment element, and the chip is affixed inside the housing in such a way that the two adjustment elements form a mechanical connection between the chip and the housing. For example, the first adjustment element and/or the second adjustment element may include a conical, semispherical and/or pyramid-shaped projection, the first adjustment element and/or the second adjustment element including a cut-out that is a precise fit with the conical, semispherical and/or pyramid-shaped projection. This ensures a minimum of deviations in the adjustment of the chip inside the housing.

The advantages described in the above paragraphs are also achieved in a corresponding production method.

Additional features and advantages of the present invention are elucidated in greater detail below, with reference to the drawings.

DETAILED DESCRIPTION

FIGS. 3A and 3Bshow schematic representations of a wafer to illustrate an embodiment of the production method according to the present invention.

In a first step of the method, a multitude of optically active surfaces50is formed on a wafer52. For more clarity, only one optically active surface50, which is developed as reflective surface, is shown inFIG. 3A.

Wafer52may at least partially consist of conductive material, such as (doped) silicon, and/or at least one metal, for example. In the illustrated example, wafer52includes a lower silicon layer54, a center insulating layer56, and an upper silicon layer58. Center insulating layer56may be an oxide layer. For example, wafer52may be an SOI wafer (silicon-on-insulator).

The method described below is not restricted to an SOI wafer as starting material. Other known wafers may also be used to implement the production method.

If wafer52is an SOI wafer, then a multitude of cut-outs may be etched through upper silicon layer58so as to form the multitude of optically active surfaces50. The regions of center insulating layer56exposed in this manner are subsequently removed. Then, separation trenches60are etched through lower silicon layer54, so that each optically active surface50is connected to wafer52only via at least one spring element62.

In an embodiment, each optically active surface50is able to be adjusted during a subsequent operation via a drive, for instance an electrostatic and/or magnetic drive. When structuring optically active surface50and the at least one spring element62, it is also possible to form at least one subunit of the electrostatic and/or magnetic drive. Since the present invention is not restricted to a particular type of drive, the development of a drive will not be addressed here.

The present invention is not restricted to the production of an adjustable optically active surface50. Consequently, the method described here may also be used to produce optically active surfaces50that are non-adjustable during the subsequent operation of the micromechanical component.

Once the structuring has been accomplished, a reflective coating may be applied to form optically active surface50.

Because method steps for applying reflective coatings are known from the related art, they will not be discussed here. However, optically active surface50may also be formed by smoothing, planar etching and/or polishing.

In a second step of the production method, a cover wafer68is affixed on a rear side of wafer52. The rear side of wafer52points in the opposite direction of optically active surface50. Cover wafer68advantageously is a glass wafer. In this case cover wafer68is able to be mounted on lower silicon layer54of wafer52via anodic bonding. The material of cover wafer68need not necessarily be a light-transmitting material. For example, the material of cover wafer68is embossed glass and/or etched silicon.

In an embodiment, the second step of the production method may be implemented prior to the afore-described first step of the production method. The enumeration of the steps here does not stipulate a particular sequence for implementing the production method.

In an embodiment, regardless of the method sequence, cavities66lie under optically active surfaces50. This ensures sufficient free space for adjusting optically active surface50with the aid of a drive. The size of each cavity66may be selected such that, in a later operation of the chip produced in the further course, a swing-out of optically active surface50from an initial position with the aid of a drive will not be hampered.

In an embodiment, cover wafer68may include separation trenches70. They are either structured by etching or embossed. For example, separation trenches70subdivide cover wafer68into a multitude of protective caps72, each of which covers a rear side of an optically active surface50. This protects the rear side of each active surface50from decontamination.

In an embodiment, it is possible to apply further function-bearing layers, e.g., bond pads74for the electrical contacting of the drive for adjusting optically active surface50, on the regions of lower silicon layer54exposed by separation trenches70. For example, the possibility of applying function-bearing layers onto rear side of wafer52therefore remains, even after the rear side of optically active surface50has been covered.

The example result of the method steps described in the above paragraphs is shown inFIG. 3A. Optically active surface50is in a recessed position with respect to the front side and the rear side of wafer52. As a result, for example, optically active surface50lies at a distance from the height of the outer surface of upper silicon layer58. Wafer52is therefore easy to hold and process, optically active surface50being securely protected from direct contact.

In a further method step of an example embodiment, the front side of wafer52is covered by a sawing foil76. Since optically active surface50is not disposed on an outer surface of one of the two silicon layers54and58in the exemplary embodiment shown, but instead is applied on the inner surface of lower silicon layer54, sufficient clearance is ensured between sawing foil76and optically active surface50. Optically active surface50is thus not contaminated or damaged by the application of sawing foil76.

In an embodiment, sawing foil76and the multitude of protective caps72seal a multitude of interior spaces with optically active surfaces50in a dustproof manner. This avoids contamination of and/or damage to optically active surfaces50during the subsequently executed sawing operation.

The sawing operation is schematically illustrated inFIG. 3B. During the sawing operation, wafer52is subdivided into a multitude of individual chips80with the aid of a saw blade78. Frame parts82, which frame at least one optically active surface50in two dimensions, are formed from the material of wafer52. If any linked regions still exist between individual protective caps72, then they, too, may be separated during the sawing. The sawing through both wafers52and68is able to be implemented without intermediate relamination of wafers52and68.

The regions having bond pads74are freely accessible during the sawing operation. During the subsequently or simultaneously implemented cleaning this offers the decisive advantage that occurring contamination from sawing is able to be removed without a trace. It is pointed out here once again that optically active surfaces50are unable to be contaminated or damaged by the particle dust produced during the sawing because of their shielding by sawing foil76and protective caps72.

The subdivision of wafers52and/or68into individual chips80is carried out in such a way that each chip80has at least one optically active surface50and a protective cap72. After separation and possibly undertaken cleaning of the outer sides of chips80, each chip80may be held individually on its rear side, that is to say, at its protective cap72, and be removed from sawing foil76. For example, this can make it possible to insert each chip80into a housing. The production of a suitable housing and the insertion of chip80is discussed herein.

FIGS. 4A through 4Eshow schematic representations of a housing in order to illustrate an embodiment of the production method and apparatus.

Housing100schematically shown inFIG. 4Ais able to be at least partially made of plastic. For example, housing100may be produced by an injection molding process. During the injection molding process connections101may be integrally cast in housing100, which saves work.

Housing100has one side that includes a continuous opening102. Outer contact surfaces104and inner contact surfaces106are formed on housing100adjacent to opening102. Outer contact surfaces104frame continuous opening102on an outer side of housing100. Inner contact surfaces106correspondingly frame continuous opening102on an inner side of housing100.

Each region of outer contact surfaces104is separated from a region of inner contact surfaces106by a wall of housing100. The wall of housing100situated between contact surfaces104and106is formed in such a way that outer contact surfaces104are aligned with respect to inner contact surfaces106at an angle of inclination not equal to 0° and not equal to 180°. In an embodiment, it is therefore possible to refer to outer contact surfaces104with their sloped design and inner contact surfaces106as drafts.

A frame is definable for continuous opening102, which lies on the boundary surface of housing100adjacent to continuous opening102. The frame has a maximum height h1and a minimum height h2not equal to maximum height h1. Contact surfaces104and106abut the frame.

An incident light window108, which is at least partially made of a light-transmitting material, is able to be affixed on outer contact surfaces104. For example, incident light window108is adhesion-bonded to outer contact surfaces104using an adhesive110.FIG. 4Bshows housing100following the installation of incident light window108. Incident light window108is tiltingly aligned with respect to inner contact surfaces106at the previously already mentioned angle of inclination which is not equal to 0° and not equal to 180°. An inclined orientation of incident light window108may be understood to denote that a center plane of incident light window108is oriented at an incline with respect to inner contact surfaces106.

In an example embodiment, incident light window108covers opening102completely. The light-transmitting material of incident light window108may have a refractive index not equal to 1. For example, the refractive index lies between 1.4 and 2.4. For example, incident light window108is made of glass. An incident light window108made of glass may be sawed out of a glass wafer with the aid of a standard process. Prior to the sawing of the glass wafer, for example, a sawing foil is applied on the glass wafer. Using screen printing, adhesive110is able to be applied on the glass wafer. This may take place prior to or following the sawing. Sawed incident light windows108are then able to be removed from the sawing foil and mounted on housing100. Of course, a mounting process for affixing incident light window108on housing100, in which the separation of incident light windows108takes place only after fixing incident light window108in place on outer contact surfaces104, is provided.

In an example embodiment, the adhesive110seals opening102in a dustproof manner. This ensures reliable protection of the interior of housing100against contamination. For example, adhesive110is able to seal opening102in an airtight manner. In this case, the interior of housing100is reliably protected also from penetrating steam. If adhesive110is a reflow adhesive, then housing100and window108may be tempered jointly.

As an alternative to the installation, incident light window108may also be injection cast in opening102. For example, because of different heights h1and h2of the framing of opening102, an incident light window108having a minimum thickness and a maximum thickness not equal to the minimal thickness may be formed in such a case. The two boundary surfaces of incident light window108are then formed at an incline with respect to each other. Given a sufficiently large angle of inclination of the two boundary surfaces with respect to each other, it is possible to dispense with a slanted design of contact surfaces104and106.

Subsequently, in an embodiment, a chip80is installed in housing100, as shown inFIG. 4C. Chip80is affixed on inner contact surfaces106. For example, an adhesive112is used to bond chip80to inner contact surfaces106.

In an embodiment, chip80is able to be produced with the aid of the afore-described production method. Chip80includes at least one optically active surface50. In an embodiment, chip80has a protective cap72, which protects the interior of chip80against contamination and/or damage from a rear side facing away from optically active surface50. Frame part82of chip80is fixed in place on inner contact surfaces106in such a way that optically active surface50is pointing toward incident light window108and protective cap72is pointing in the opposite direction of incident light window108.

In an embodiment, at least in a deactivated operating mode of chip80, optically active surface50of chip80is in an initial position with respect to frame part82and protective cap72.

In an embodiment, in an active operating mode of chip80, optically active surface50is able to be adjusted from the initial position into at least one other position via a drive, for instance an electrostatic and/or magnetic drive. The initial position is therefore understood as the position of optically active surface50from which it is adjustable only via an operation of the drive. If the current flow to the drive is switched off, for example, then optically active surface50is in its initial position.

For example, chip80is fixed in place on inner contact surfaces50in such a way that the initial position of optically active surface50, for example, in the case of a deactivated chip80, is aligned at an incline with respect to incident light window108, the angle of inclination being not equal to 0° and not equal to 180°. Consequently, the angle of inclination is not equal to 0° and not equal to 180° between optically active surface50and a center plane of incident light window108. A corresponding angle of inclination not equal to 0° and not equal to 180° may also exist with respect to at least one boundary surface of incident light window108.

Because of the angle of inclination not equal to 0° and not equal to 180° between optically active surface50and incident light window108, a beam of light impinging on incident light window108will be reflected away from an image plane of optically active surface50at the boundary surfaces of incident light window108. This prevents the occurrence of an interference reflex on an image produced by an operation of optically active surface50.

FIG. 4Dshows an example housing100including chip80after an electrical contacting with wire bonds114has been established. Wire bonds114connect the bond pads (not shown) of chip80with connections101.

In an embodiment, in a further method step, shown inFIG. 4E, a housing lid116is mounted on housing100. Housing lid116preferably seals housing100in a dustproof manner. In an embodiment, because of the aforementioned advantages, an airtight sealing of housing100is provided. Housing lid116may be produced by an injection molding process, for example. Housing lid116is also able to be produced as embossed metal element. Connections101may then be bent into a desired form.

FIG. 5shows a schematic illustration of a first specific development of the micromechanical component.

Illustrated micromechanical component120includes chip80, described earlier, and housing100having components101through116. Micromechanical component120is able to be produced in a cost-effective manner using the production method described above with the aid ofFIGS. 3A and 3Band4A through4E. For example, a production of micromechanical component120by standardized method steps is possible. It is then ensured that optically active surface50is reliably protected against contamination and/or damage during the separation of chip80.

In an embodiment, in a deactivated state of chip80, optically active surface50in micromechanical component120is in an initial position, in which it is situated at an incline with respect to incident light window108, the angle of inclination being not equal to 0° and not equal to 180°. This prevents that a beam of light impinging on incident light window108is reflected into an image plane of optically active surface50and leads to interference reflexes there. This helps to improve the quality of the image produced with the aid of micromechanical component120.

In micromechanical component120, incident light window108is aligned at an incline with respect to housing lid116. In an embodiment, as an alternative, the inner contact surfaces106can be formed in such a way that they are aligned at an incline with respect to housing lid116, which is inserted subsequently. In this case, for example, incident light window108may be disposed parallel to housing lid116. The occurrence of interference reflexes in the image plane of optically active surface50is prevented in such a micromechanical component120.

FIG. 6shows a schematic illustration of a part of a second development of the micromechanical component.

Schematically reproduced micromechanical component130includes already described chip80and housing100having components101through116. Chip80is situated inside housing100in such a way that optically active surface50of chip80in its initial position is inclined at an angle of inclination with respect to incident light window108. The definition of the initial position reference is described herein.

As addition to the afore-described component ofFIG. 5, micromechanical component130has adjustment elements132,133and134, which facilitate the adjustment of chip80inside housing100and the adjustment of micromechanical component130on a mounting board136via an adjustment element137of the mounting board. For example, adjustment elements132,133and134ensure that the positions of chip80and micromechanical component130relative to mounting board136are observed. Since an imprecise adjustment of chip80inside housing100and/or micromechanical component130on mounting board136normally has a significant detrimental effect on the operability of the system, adjustment elements132,133,134and137also improve the operability of the system.

For example, a first adjustment element132is a conical projection on inner contact surface104. A cut-out which corresponds to first adjustment element132is developed as second adjustment element133at a suitable location on frame part82of chip80. Adjustment elements132and133ensure that chip80is easily adjustable in a preferred position in the interior of housing100. For example, adjustment elements132and133enable a self-adjustment of chip80inside housing100.

A pyramid-shaped projection is developed as third adjustment element134on an outer wall of housing100. A cut-out137corresponding to pyramid-shaped projection used as adjustment element134is present on mounting board136. Mounting board136may be, for instance, a printed circuit board (PCB). Conical adjustment element134and associated cut-out137facilitate the placement of micromechanical component130in a desired position relative to mounting board136.

FIG. 7shows a schematic illustration of a part of an embodiment of the development of the micromechanical component.

Components80and100through116of micromechanical component140have already been described earlier. It has likewise already been discussed in greater detail that optically active surface50of chip80in its initial position is inclined at an angle of inclination with respect to incident light window108.

In an embodiment, micromechanical component140, as well, includes adjustment elements142,143and144. First adjustment element142is a pyramid-shaped projection for which a corresponding cut-out is formed as second adjustment element143in frame part82of chip80. This ensures a simple adjustment of chip80in a position within housing100.

In an embodiment, third adjustment element144of micromechanical component140is a semispherical cut-out. A corresponding semispherical projection is formed on mounting board136. Second adjustment element144and precisely fitting semispherical projection146of mounting board136ensure that micromechanical component140is easily adjustable in the desired position with respect to mounting board136.

Conical, semispherical and/or pyramid-shaped projections on housing100, frame part82and/or on mounting board136may be formed as adjustment elements132,133,134,142,143and144. In the same way, in an embodiment, corresponding cut-outs can be formed, into which the conical, semispherical and/or pyramid-shaped projections may be placed, on housing100, frame part82of chip80, and/or mounting board136. In an embodiment, the corresponding cut-outs are formed so as to have a precise fit with the conical, semispherical and/or pyramid-shaped projections.

In an embodiment, the projections and cut-outs are designed such that a self-adjustment of chip80within housing100and/or a self-adjustment of micromechanical component130or140on mounting board136is possible. The self-adjustment may take place in all three spatial directions. This in particular facilitates the direct adjustment of chip80relative to mounting board136.

Micromechanical components120,130or140described in the above paragraphs are able to be used, for instance, in a head-up display, in the motor vehicle field or in a mini-projector in the consumer field. Use of micromechanical components120,130or140as switches in optical networks (optical cross connect) or in a surface scanner is also conceivable.