DE102016217817A1 - Method for producing a protective wafer with oblique optical windows - Google Patents

Abstract

The invention relates to a method for producing a protective wafer with oblique optical windows. The invention also relates to a protective wafer having oblique optical windows, comprising a front side wafer (100) having a main extension plane (110), with a first surface structure (150) comprising a first window frame surface (155) arranged obliquely to the main extension plane (110) a backside wafer (200) having a second surface structure (250) which is at least partially complementary to the first surface structure (150), wherein the first surface structure (150) and the second surface structure (250) are arranged at least in regions, wherein between the first Surface structure (150) and the second surface structure (250) an optically transparent elastic membrane (300) is arranged, wherein the protective wafer has a recess which is bounded by the first window frame surface (155), wherein the membrane (300) in the recess oblique optical window (350) forms. The invention also relates to a wafer stack with oblique optical windows, the wafer stack having such a protective wafer with oblique optical windows and a MEMS wafer.

Description

State of the art

The invention relates to a method for producing a protective wafer with oblique optical windows. The invention also relates to a protective wafer with oblique optical windows and a wafer stack with oblique optical windows, wherein the wafer stack has a protective wafer with oblique optical windows and a MEMS wafer.

MEMS devices must be protected to protect against harmful external environmental factors, such as the ingress of particles, etc. Protection against mechanical contact or destruction as well as enabling separation from a wafer composite into individual chips by sawing is also required. In many cases can be dispensed with a hermetic encapsulation and it is sufficient to dust and contact protection.

The encapsulation of MEMS devices with a cap wafer, which has cavities and through holes in the wafer composite is established. For this purpose, a cap wafer is adjusted to the wafer with the MEMS structures and joined with it. Joining can be carried out both by anodic bonding and direct bonding (bonding agent-free connection between glass and silicon), via eutectic joining layers and via glass solders or adhesives. Under the cavities of the cap wafer is usually the MEMS device, the electrical bond pads for connecting the component with thin wires are accessible via the through hole in the cap wafer.

For optical MEMS (MOEMS), such as. B. for micromirror is the protection described above and also a transparent window with high optical quality and if necessary. Also required with special optical coatings. For cost-sensitive applications and in those applications in which an outer outer packaging ensures sufficient moisture and media protection, a hermetic encapsulation of the MEMS elements can be dispensed with. In these cases, organic materials can also be used for the encapsulation. It is important to ensure that these are suitable for the manufacturing process and for operation, eg. B. cause no harmful outgassing. The use of organic materials brings significant cost advantages, since these compared to inorganic materials, such. As glass and silicon in the procurement and processing are much cheaper. Suitable materials that can be used are available in the market, for example, polyetheretherketone (PEEK) or liquid crystal polymer (FKP). As organic material for optically transparent windows with high optical quality z. As nitrocellulose can be used.

As optical rays pass through the transparent window, reflections occur at the interfaces. If the fixed reflections lie in the scanning range of the μ-mirror, their intensity exceeds that of the projected image and therefore has a disturbing effect. These disturbing reflections can only be reduced in their intensity by an anti-reflex coating of the optical window. Since the mirror is usually oscillated or deflected symmetrically about its rest position, the reflex is always in the scanning range, if the optical window is parallel to the rest position of the mirror surface and the distance between the mirror plane and the optical window is small (in MEMS this is always the case). The only way to avoid the interference from the reflections is to direct them out of the scan area, since the optical window and the mirror surface (in the rest position, ie in the undeflected state) are not parallel to one another. There are two possibilities for this: inclination of the optical window or the rest position of the mirror. Both possibilities are already known from publications and patents in multiple embodiments. Inclined windows for individual chips are z. B. off EP1688776A1 known.

Inclined windows or other forms of windows with which the reflections can be avoided are for wafer-level packaging in US2007 / 0024549 described. The three-dimensional surface structures (eg, inclined windows) embodied in the latter patent are to be made of a transparent material (glass or plastic) in a wafer composite. The methods by which the three-dimensional structures can be made are either very expensive or do not provide the required optical quality. Wafers with corresponding three-dimensional structures are also problematic during processing (eg during wafer bake), since the structures can be damaged in the process.

Other methods for producing protective cap with inclined optical windows are for example in the publications DE 10 2010 062 118 A1 and DE 10 2012 206 858 A1 described. However, these methods are still relatively expensive for high volume applications or the optical windows have only a limited optical quality.

The company MARADIN (Israel) has developed an optically transparent protective chip for plastic micromirrors. In this case, individual protection chips are produced and then laked individually on the wafer and glued to it. For relatively large and unevenly thick optical However, windows can result in significant optical distortions of the projected image and transmission losses.

Object of the invention

The object of the invention is to provide a very cost-effective production method for a non-hermetic plastic protective wafer with cavities and inclined transparent windows with high optical quality for the protection of a micromechanical wafer.

Advantages of the invention

• a) Bereitstellen eines Vorderseitenwafers mit einer Haupterstreckungsebene, mit einer ersten Oberflächenstruktur umfassend eine erste Fensterrahmenfläche, welche schräg zur Haupterstreckungsebene angeordnet ist, Bereitstellen eines Rückseitenwafers mit einer zweiten Oberflächenstruktur, welche zur ersten Oberflächenstruktur wenigstens bereichsweise komplementär ausgestaltet ist, Bereitstellen einer optisch transparenten elastischen Membran,
• b) wenigstens bereichsweise Aufbringen von Kleber auf die erste Oberflächenstruktur oder auch die zweite Oberflächenstruktur oder auch die Membran,
• c) Zusammendrücken des Vorderseitenwafers und des Rückseitenwafers, derart, dass die erste Oberflächenstruktur und die zweite Oberflächenstruktur wenigstens bereichsweise komplementär aneinander anliegen, wobei die Membran dazwischen angeordnet ist.

Vorteilhaft ist ein Herstellungsverfahren für geneigte optische Fenster zur Vermeidung störender Reflexe geschaffen. Vorteilhaft ist dies ein sehr kostengünstiges, großserientaugliches Herstellungsverfahren. Vorteilhaft begünstigt das erfindungsgemäße Verfahren die Vermeidung von Kratzern, Partikeln und Beschädigungen auf den geneigten optischen Fenstern während der weiteren Verarbeitung des Schutzwafers.The invention relates to a method for producing a protective wafer with oblique optical windows, comprising the steps:

• a) providing a front side wafer having a main extension plane, with a first surface structure comprising a first window frame surface which is arranged obliquely to the main extension plane, providing a back side wafer having a second surface structure which is at least partially complementary to the first surface structure, providing an optically transparent elastic membrane,
• b) at least partially applying adhesive to the first surface structure or the second surface structure or else the membrane,
• c) compressing the front-side wafer and the backside wafer, such that the first surface structure and the second surface structure at least partially abut each other in a complementary manner, wherein the membrane is arranged therebetween.

Advantageously, a manufacturing process for inclined optical windows to avoid disturbing reflections created. This is advantageously a very cost-effective, large-scale production process. Advantageously, the method according to the invention promotes the avoidance of scratches, particles and damage on the inclined optical windows during the further processing of the protective wafer.

An advantageous embodiment of the method according to the invention provides that prior to step a) the front side wafer and the back side wafer are produced by injection molding from a plastic, in particular polyetheretherketone (PEEK) or liquid crystal polymer (FKP), or from metal. Advantageously, the two wafers can be produced so quickly and inexpensively.

An advantageous embodiment of the method according to the invention provides that in step d) an antireflection coating is applied on a front side and / or on a back side of the membrane at least in the region of an optical window. Advantageously, this disturbing light reflections can be further reduced.

The invention also relates to a protective wafer with oblique optical windows, with a front wafer having a main extension plane, with a first surface structure comprising a first window frame surface, which is arranged obliquely to the main extension plane, with a back side wafer having a second surface structure, which is designed to be complementary to the first surface structure, wherein the first surface structure and the second surface structure are arranged adjacent to one another, wherein an optically transparent elastic membrane is arranged between the first surface structure and the second surface structure, wherein the protective wafer has a recess which is bounded by the first window frame surface, wherein the membrane in the recess forms a slanted optical window.

An advantageous embodiment of the protective wafer according to the invention provides that the front-side wafer or else the back-side wafer consist at least of a plastic, in particular of polyetheretherketone (PEEK) or liquid-crystal polymer (FKP), or of metal.

An advantageous embodiment of the protective wafer according to the invention provides that the membrane consists of nitrocellulose or an optically transparent elastomer. Advantageously, this membrane is flexible, easy to form and very thin, which improves the optical properties, in particular reduces the phenomenon of optical distortions.

The invention also relates to a wafer stack with oblique optical windows, wherein the wafer stack has a protective wafer according to the invention with oblique optical windows and a MEMS wafer.

drawing

The 1a to 1c show schematically an embodiment of a method according to the invention for producing a protective wafer with oblique optical windows.

2 schematically shows a plan view of a section of a protective wafer according to the invention with oblique optical windows.

3 schematically shows an inventive method for producing a protective wafer with oblique optical windows.

4 schematically shows a wafer stack with oblique optical windows.

description

Hereinafter, the manufacturing method of an organic material protective wafer having cavities and transparent inclined windows of optical quality will be described. The order of the manufacturing process is listed here only as an example and can also be done otherwise.

The 1a to 1c show schematically an embodiment of a method according to the invention for producing a protective wafer with oblique optical windows. The protective wafer according to the invention consists of three components, namely the front side wafer 100 , the backside wafer 200 and the optically transparent membrane 300 , For example, the front and back wafers are made of polyetheretherketone (PEEK) or liquid crystal polymer (FKP). Using injection molding technology, both parts can be produced in three dimensions. The optically transparent membrane is z. B. of very thin nitrocellulose and is elastically extensible. Such optically transparent membranes are used as dust protection for photolithography (pellicle). It can be realized membrane thicknesses below 1 micron, which can also be provided on both sides with anti-reflective layers. Due to the very small thickness, the optical distortions of such membranes are very small.

In the first step, the front and back side wafers are produced in a suitably three-dimensionally structured manner, for example by means of injection molding technology. The front side wafer 100 and the backside wafer 200 have a main extension plane 110 on. In the area of optical windows, window frame surfaces are inclined for each chip of a wafer 155 shaped, each having a through hole 350 enclose ( 1a and 2 ). The window frame surfaces 155 are opposite to a carrier plane parallel to the main extension plane 110 sublime. The front side wafer 100 thus has a first surface structure 150 on, and the backside wafer 200 has a second surface structure 250 on. The raised structures of the backside wafer (or front side wafer) fit into the corresponding recess in the front side wafer (or the back side wafer, respectively). They each form the negative form of the other wafer. The first surface structure 150 and the second surface structure 250 are thus configured at least partially complementary.

On the back of the front-side wafer 100 and on the front of the backside wafer 200 An adhesive is applied at suitable locations. Between front and back side wafers, the membrane 300 brought in. Front and back wafers are now compressed. The intermediate membrane is pressed onto the corresponding surfaces of the structures and thereby stretched ( 1b ). In the area of the through holes 350 creates a free membrane and thus an optical window 355 , whose inclination due to the inclination of the surrounding window frame surface 155 is defined ( 1c ). This condition is permanently preserved by the curing of the adhesive. The structures of the front and back wafers are designed so that the two wafers act self-centering upon compression. Optionally, separate structures can be applied to the wafer to ensure such self-centering.

After completion of the protective wafer as a wafer stack of front wafer, membrane and backside wafer, an anti-reflection layer can be applied in each case on the front or on the back of the inclined membrane. In order to reduce shadowing in the deposition of this layer near the wall, the walls of the through hole 350 be funnel-shaped on both sides. This is in 1c shown schematically with dashed lines.

In an alternative embodiment of the method according to the invention, the anti-reflection layer can be applied to the membrane before the membrane is introduced between the front-side wafer and the back-side wafer.

Since the membrane windows are located within the wafer stack, they are protected from mechanical contact during further processing.

2 schematically shows a plan view of a section of a protective wafer according to the invention with oblique optical windows. Shown is the protective wafer according to the invention with recesses 350 in the form of through-holes in which the membrane 300 optical windows 355 forms. Furthermore, corresponding to the 1A and B the positions of the section lines AA 'and BB' drawn.

3 schematically shows an inventive method for producing a protective wafer with oblique optical windows. In step a), a front-side wafer is provided 100 with a main extension plane 110 , with a first surface structure 150 comprising a first window frame surface 155 , which are inclined to the main extension plane 110 is arranged. Furthermore, a provision of a backside wafer takes place 200 with a second surface structure 250 leading to the first surface structure 150 at least partially complementary designed. Finally, providing an optically transparent elastic membrane 300 , In step b), adhesive is applied at least in regions to the first surface structure 150 or the second surface structure 250 or on the membrane 300 , In step c), the front-side wafer is compressed 100 and the backside wafer 200 , such that the first surface structure 150 and the second surface structure 250 at least partially abut complementary to each other, wherein the membrane 300 is arranged in between.

Optionally, prior to step a), the front side wafer 100 and the backside wafer 200 be made by injection molding of a plastic, in particular polyetheretherketone (PEEK) or liquid crystal polymer (FKP).

In one embodiment of the method according to the invention is in a step d) on a front side or on a back of the membrane 300 at least in the region of an optical window 355 an anti-reflection coating applied.

4 schematically shows a wafer stack with oblique optical windows. The wafer stack essentially consists of a MEMS wafer 400 and a protective wafer according to the invention arranged thereon. The MEMS wafer 400 has micromechanical structures, in particular MOEMS components, such as micromirrors. The MEMS wafer 400 can be along the dashed line in chips 500 to be isolated.

LIST OF REFERENCE NUMBERS

100

Front wafer

110

Main plane

150

first surface structure

155

Window frame surface

200

Backside wafer

250

second surface structure

300

optically transparent membrane

330

Anti-reflection coating

350

Through Hole

355

optical window

400

MEMS wafer

500

chip

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1688776 A1 [0005]
• US 2007/0024549 [0006]
• DE 102010062118 A1 [0007]
• DE 102012206858 A1 [0007]

Claims (7)

Method for producing a protective wafer having oblique optical windows, comprising the steps of: a) providing a front-side wafer ( 100 ) with a main extension plane ( 110 ), with a first surface structure ( 150 ) comprising a first window frame surface ( 155 ), which obliquely to the main extension plane ( 110 ), providing a backside wafer ( 200 ) having a second surface structure ( 250 ) leading to the first surface structure ( 150 ) is at least partially complementary configured, providing an optically transparent elastic membrane ( 300 b) at least partially applying adhesive to the first surface structure ( 150 ) and / or the second surface structure ( 250 ) and / or the membrane ( 300 ), c) compressing the front side wafer ( 100 ) and the backside wafer ( 200 ), such that the first surface structure ( 150 ) and the second surface structure ( 250 ) abut each other at least partially in complementary fashion, wherein the membrane ( 300 ) is arranged therebetween. Method for producing a protective wafer with oblique optical windows according to claim 1, characterized in that before step a) the front-side wafer ( 100 ) and the backside wafer ( 200 ) are made by injection molding from a plastic, in particular from polyetheretherketone (PEEK) or liquid crystal polymer (FKP), or from metal. Method for producing a protective wafer with oblique optical windows according to claim 1, characterized in that in a step d) on a front side and / or on a back side of the membrane ( 300 ) at least in the region of an optical window ( 350 ) An antireflection coating is applied. Protective wafers with oblique optical windows, - with a front wafer ( 100 ) with a main extension plane ( 110 ), with a first surface structure ( 150 ) comprising a first window frame surface ( 155 ), which obliquely to the main extension plane ( 110 ), - with a backside wafer ( 200 ) having a second surface structure ( 250 ) leading to the first surface structure ( 150 ) is at least partially complementary designed, - wherein the first surface structure ( 150 ) and the second surface structure ( 250 ) are arranged at least partially adjacent to each other, - wherein between the first surface structure ( 150 ) and the second surface structure ( 250 ) an optically transparent elastic membrane ( 300 ), - wherein the protective wafer has a recess ( 350 ), which through the first window frame surface ( 155 ), wherein the membrane ( 300 ) in the recess ( 350 ) an oblique optical window ( 355 ). Protective wafer according to claim 4, characterized in that the front side wafer ( 100 ) and / or the backside wafer ( 200 ) consist of at least one plastic, in particular polyetheretherketone (PEEK) or liquid crystal polymer (FKP), or of metal. Protective wafer according to claim 4 or 5, characterized in that the membrane ( 300 ) consists of nitrocellulose or an optically transparent elastomer. Wafer stack with oblique optical windows, wherein the wafer stack has a protective wafer with oblique optical windows according to one of claims 4 to 6 and a MEMS wafer ( 400 ) having.

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