WO2001058804A2

WO2001058804A2 - Micromechanical component and corresponding production method

Info

Publication number: WO2001058804A2
Application number: PCT/DE2000/004554
Authority: WO
Inventors: Frank Fischer
Original assignee: Robert Bosch Gmbh
Priority date: 2000-02-09
Filing date: 2000-12-20
Publication date: 2001-08-16
Also published as: WO2001058804A3; DE10005555A1

Abstract

The invention relates to a micromechanical component comprising a substrate (1), a functional region (5) on the substrate (1) and a cap-like cover (10, 14, 18; 10`, 14`, 20, 25; 10``, 14``, 30) for covering the functional region (5). The cap-like cover (10, 14, 18; 10`, 14`, 20, 25; 10``, 14``, 30) comprises at least one upper and one lower protective layer (10, 14; 10`, 14`; 10``, 14``). The protective layers (10, 14; 10`, 14`; 10``, 14``) each comprise a hole arrangement (11, 15), displaced relative to each other, of which at least one is sealed by a sealing layer (17; 20, 25; 14``, 30).

Description

Micromechanical component and corresponding manufacturing method

STATE OF THE ART

The present invention relates to a micromechanical component with a subsrate, a functional area provided on the substrate and a cap-shaped cover for covering the functional area, and a corresponding manufacturing method, as known from DE 195 37 814 AI.

Although applicable to any micromechanical components and structures, in particular sensors and actuators, the present invention and the problem on which it is based will relate to a micro-mechanical component that can be produced in the technology of silicon surface micromechanics, e.g. an acceleration sensor explained.

DE 195 37 814 AI describes the structure of a functional layer system and a method for the hermetic capping of sensors in surface micromechanics. Here, the manufacture of the sensor structure is explained using known technological processes. The said hermetic capping takes place with a separate cap Wafer made of silicon, which is structured using complex structuring processes such as KHO etching. The cap wafer is applied with a glass solder (seal glass) on the Suostrat with the sensor (sensor wafer). For this, a wide bond frame is required around each sensor chip in order to ensure sufficient adhesion and tightness of the cap. This limits the number of sensor chips per sensor wafer. Due to the large amount of space required and the complex production of the cap wafer, the sensor capping incurs considerable costs.

ADVANTAGES OF THE INVENTION

The micromechanical component according to the invention with the features of claim 1 or the production method according to Claim 8 provides an at least two-layer structure with which micromechanical sensors or functon structures can be hermetically sealed. A defined gas and / or pressure connection can be guaranteed.

The core of the invention is therefore a human structure that is deposited by means of micromechanical sensors or functional structures and protects them from environmental influences. The sensor cap is not, as usual, structured separately by etching processes and connected to the sensor wafer or functon wafer using a seal glass soldering process, but the cap is directly attached to the sensor. sorfer is produced in such a way that a multi-layer scaffold is built up over the, for example, movable functional structures, the multi-layer scaffold being hermetically sealed by at least one sealing layer after a sacrificial layer etching.

This allows a much smaller cap-shaped cover than in the prior art. The multi-layer cap framework can be created using simple semiconductor processes. There is no need for PbO-containing seal glass, which causes massive corrosion on Al-Bond pads under the influence of moisture.

Advantageous further developments and improvements of the micromechanical component specified in claim 1 can be found in the subordinate claims.

According to a preferred development, a first sealing layer is arranged over the upper covering layer, and the hole arrangement of the upper covering layer is grafted through the first sealing layer.

According to a further preferred development, a second sealing layer is arranged between the upper and the lower cover layer, and the hole arrangement of the upper one

The top layer is sealed by fusing the second sealing layer. According to a further preferred development, the upper cover layer does not function as a closure layer for the hole arrangement of the lower cover layer. This can be achieved by choosing the material of the upper cover layer such that it has a lower melting point than the material of the lower cover layer and the upper cover layer is melted so that it closes the hole arrangement of the lower cover layer.

According to a further preferred development, the upper cover layer has connecting webs z-ir connection to the lower cover layer.

According to a further preferred development, the lower cover layer and / or the upper cover layer does not have polysilicon or aluminum.

According to a further preferred development, the sealing layer has aluminum, silicon, silicon metride, silicon dioxide, a glass or a lacquer.

DRAWINGS

Exemplary embodiments of the invention are shown in the above drawings and are explained in more detail in the following description.

It shows: Fig. La-g is a schematic cross-sectional view of the

Manufacturing steps of a micromechanical component according to a first embodiment of the present invention;

FIG. 1h shows a plan view of the micromechanical component according to the first embodiment to illustrate the different hole arrangements;

2a-e is a schematic cross-sectional view of the

Manufacturing steps of a micromechanical component according to a second embodiment of the present invention; and

3a-c is a schematic cross-sectional view of the

Manufacturing steps of a micromechanical component according to a third embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

In the figures, identical reference symbols designate identical or functionally identical components.

1a-g show a schematic cross-sectional view of the manufacturing steps of a micromechanical component according to a first embodiment of the present invention and FIG. 1h shows a corresponding top view to illustrate the different hole arrangements. According to FIG. 1 a, as described in the prior art, a sacrificial layer 2 made of SiO ₂ , a structured interconnect level 3 and a further sacrificial layer 4 made of SiO _{2 are} applied to a silicon substrate 1. A functional layer with the functional region 5 is applied to the sacrificial layer 4 and is structured by likewise known methods for the etching of trenches 6. For example, the method described in DE 42 41 045 AI can be used. The functional structural elements 7, which are shown here by way of example as three electrode fingers, are either made freely movable for the proposed component by a known method for sacrificial layer etching (see, for example, DE 43 17 274 A1), or they remain after deep etching still firmly on the

Tied up sacrificial layer 4, as shown in Figure la.

As shown in FIG. 1b, a thick sacrificial layer 8 is deposited on the functional structural elements 7 of the micromechanical component in a next step such that the structural trenches 6 are partially filled with the sacrificial material in the upper trench region 9. The sacrificial layer 8 covers the part of the structure which is to be capped in the final state. The sacrificial layer 8 preferably has a thickness of 1 μm to 20 μm and can consist, for example, of silicon dioxide, boron-phosphorus-silicate glass or amorphous silicon. However, any other material that is isotropic with an sufficient selectivity towards the functional structural elements 7 and the later cover layers can be etched.

1c, the lower cover layer 10 is deposited onto the sacrificial layer 8 and structured with a hole arrangement with small holes 11. The holes 11 can be angular or round. The diameter of the holes 11 is preferably between 0.5 μm and 20 μm. The perforation is designed so that it lies uniformly over the surface of the functional structural elements 7. The lower cover layer 10 is preferably between 0.5 μm and 10 μm thick and made of polysilicon or aluminum. However, it can also consist of any other material that is resistant to the sacrificial etching of the sacrificial layer 8 and further sacrificial layers. The lower cover layer 10 is pulled beyond the edge of the sacrificial layer 8 and is bonded to the layer with the functional structural elements 7. The lower cover 10 is ideally under mechanical tensile stress, which can be adjusted by suitable temperature treatment.

As illustrated in FIG. 1d, a second sacrificial layer 12 is applied to the first cover layer 10. This second sacrificial layer 12 ideally consists of the same material as the first sacrificial layer 8, that is to say of silicon dioxide, and is also selectively etchable with respect to the lower cover layer 10. The thickness of the second sacrificial layer 12 is preferably between 0.3 μm and 5 μm. The second victim 12 is then structured in such a way that it lies on the through hole arrangement 11 of the lower cover layer 10. The second sacrificial layer 12 also has a hole arrangement with holes 13, which are offset with respect to the holes 11 of the hole arrangement of the lower cover layer 10.

According to FIG. 1e, the upper cover layer 14 is deposited on the second sacrificial layer 12. This upper cover layer 14 is connected locally to the lower cover layer 10 via the holes 13 of the second sacrificial layer 12. In the top

Cover layer 14 is a hole arrangement with holes 15, the holes 15 being offset from the holes 11 of the lower cover layer 10, so that the holes 11 are all covered by the upper cover layer 14 and the lower cover layer 10 is located under the holes 15 everywhere , The perforation preferably has a diameter of 0.5 μm to 20 μm. The upper cover layer 14 is pulled beyond the edge of the second sacrificial layer 12 and is bonded to the lower cover layer 10 and preferably also to the periphery of the functional area 5. In other words, the upper cover layer 14 preferably also completely covers the lower cover layer 10. The upper cover layer 14 is between 0.5 μm and 30 μm thick and, like the lower cover layer 10, can consist, for example, of silicon or aluminum or other materials with the required etching properties.

As depicted in FIG. 1f, the first sacrificial layer 8 and the are then in a selective etching step second sacrificial layer 12 etched. Here, a wet chemical process such. B. BOE (BOE = buffered oxide etch = buffered oxide etching) or a dry etching process, such as the hydrofluoric acid vapor etching process known from DE 43 172 74 AI. The sacrificial layers 2 and 4 below the functional structural elements 7 can also be etched in this step, if this has not already happened before the first sacrificial layer 8 is deposited. After this selective etching step, a cap or dome, which is perforated with perforations, is stretched over the functional structural elements (here movable capacitor electrodes). This cap consists of the interconnected cover layers 10, 14, there being no straight path for gases or atoms or molecules through the cap, since the hole arrangements in the cover layers 10, 14 are arranged offset from one another.

In a further step, according to FIG. 1g, a closure layer 17 is provided on the upper cover layer 14, which closes the holes 15 of the outer cover layer 14 tightly by means of plugs 18. The sealing layer 17 preferably completely covers the upper covering layer 14. The closing process takes place under defined gas and pressure conditions. The sealing layer 17 can be made of aluminum, silicon, silicon nitride, silicon dioxide, a glass, a lacquer or another suitable material and is preferably by means of a CVD (Chemical Vapor Deposition) method, sputtering, vapor deposition, Process, flash evaporation process, spin-on process or spray process applied.

The sensor structure shown is thus hermetically capped, and under the capping in the functional area 5 with the functional structural elements there is a predetermined atmosphere and a predetermined pressure.

Figure lh illustrates the mutual orientation of the different perforations. The top view of FIG. 1h shows the offset of the holes 15 in the upper cover layer 14 with respect to the holes 11 in the lower cover layer 10. The connection points 13 between the lower cover layer 10 and the upper cover layer 14 are offset with respect to the two hole arrangements with the holes 11 and 15, so that gases (e.g. reaction products and educts in the case of sacrificial layer etching) can flow into the open through both hole arrangements.

2a-e illustrate a schematic cross-sectional view of the manufacturing steps of a micromechanical component according to a second embodiment of the present invention.

In the second embodiment of the micromechanical component according to the invention, as illustrated in FIG. 2a, a layer 20 is applied and structured to the lower cover layer 10 ', which preferably consists of aluminum or another fusible material with sufficient Surface tension u-id suitable adhesion or wetting exists on the material of the lower cover layer 10 ^Λ . The layer thickness of the second sealing layer 20 should be smaller than the thickness of the second sacrificial layer 12 ". Furthermore, the second sealing layer 20 is structured in such a way that it leaves the holes 11 in the lower covering layer 10 free and is arranged below the holes 15 in the upper covering layer 14 ^' is.

As shown in FIG. 2b, the upper sacrificial layer 12 is deposited and structured analogously to the first embodiment. However, the second sacrificial layer 12 - in this second embodiment does not necessarily contain holes for attaching the outer cover layer 14 'to the lower cover layer 10.

According to FIG. 2c, the sacrificial layer etching for etching the layers 2, 4, 8 and 12 'takes place in the next process step. After the sacrificial etching, a temperature step for the thermal cleaning of the sensor surfaces is expedient, which, however, must not exceed the melting temperature of the material of the second closure. After cleaning, the entire structure is introduced into a heating device, with which defined gas and pressure conditions can be established. Here, for example, a vacuum can be generated, or an inert gas or. another gas to increase the damping of the vibrations of the functional structural elements 7 are included. As shown in FIG. 2d, after regulating the gas and pressure ratios, the temperature in the heating device is increased above the melting point of the material of the second sealing layer 20, so that the material 20 contracts due to the surface tension and melts out. The position of these fusible beads on the lower cover layer 10 is controlled via the structural position and thickness of the second sealing layer 20 in such a way that the fusing beads form exactly under the holes 15 of the second covering layer 14 ^" . The material of the second sealing layer 20 is selected such that there is sufficient wetting with the material of the lower cover layer 10 * and the upper cover layer 14 ", and therefore the openings 15 of the upper cover layer 14 ^' are sealed from below. As a result, a predetermined atmosphere and a predetermined pressure can be set under the capping. When opening the heating device, however, one must wait until the temperature has dropped below the melting temperature of the material of the second sealing layer 20.

For permanent hermetic sealing, a further sealing layer 25 can optionally be deposited over the resulting structure as in the first embodiment, as shown in FIG. 2e.

3a-c are a schematic cross-sectional view of the manufacturing steps of a micromechanical component. measured a third embodiment of the present invention.

In the third embodiment, the material of the upper cover layer 14 "" is selected such that it has a lower melting point than the material of the lower cover layer 10 "". For example, the material of the upper cover layer 14 "" can be aluminum, which melts at 660 ° C., while the material of the lower cover layer 10 "" is a high-melting material, e.g. B. CVD silicon.

Figure 3a shows the state after the sacrificial layer etching corresponding to the state of Figure 2c or the state of Figure 1f.

As illustrated in FIG. 3b, after the sacrificial layer etching and a possible thermal cleaning of the surfaces, the material of the upper cover layer 14 "^{" is} melted in a heating device under defined gas and pressure conditions. If there is sufficient wetting between the lower and upper cover layer 10 "", 14 ^" ", the openings 11 in the lower cover layer 10 "" are then hermetically sealed by the upper cover layer 14 "".

As in the second embodiment, in this third embodiment as well, a further sealing layer 30 can be applied for the hermetic sealing, which is made of silicon dioxide, aluminum, niu, silicon nitride, silicon or another suitable material. This is shown in Fig. 3c.

Although the present invention has been described above on the basis of a preferred exemplary embodiment, it is not restricted to this but can be modified in a variety of ways.

In particular, any desired micromechanical basic materials can be used, and not just the exemplary silicon substrate.

The hole arrangements and the number and design of the cover layers and sacrificial layers can also be chosen as desired.

Furthermore, the structural elements of the different embodiments can be combined with one another.

Claims

1. Micromechanical component with:

a substrate (1);

a functional area (5) provided on the substrate (1); and

a cap-shaped cover (10, 14, 18; 10 ^λ , 14 20, 25; 10, 14 ^Λ \ 30) for covering the functional area (5);

by means of that

at least an upper and a lower outer layer ^(10, 14 30 10, 14, 18; 10 \ 14 \ 20, 25) the kappenformige cover (10, 14; 10 \ 14 \ - ^10, 14 ^{X Λ)} comprises; and

the cover layers (10, 14; 10 \ 14 \ - 10 \ 14 ^) each have a mutually offset hole arrangement (11, 15), at least one of which is closed by at least one closure layer (17; 20, 25; 14 ^x \ 30) is.

2. Micromechanical component according to claim 1, characterized in that a first sealing layer (17; 25; 30) is arranged over the upper cover layer (14; 14 ^λ ; 14 ') and the hole arrangement (15) of the upper cover layer (14; 1 X 14 ^, ) is grafted through the first sealing layer (17; 25; 30).

3. Micromechanical component according to claim 1 or 2, characterized in that a second sealing layer (20) between the upper and lower cover layer (14, 10 ^Λ ) is arranged and the hole arrangement (15) of the upper cover layer (14 ^λ ) by melting beads the second sealing layer (20) is sealed.

4. Micromechanical component according to one of the preceding claims, characterized in that the upper cover layer (14 ^Λ ') acts as a closure layer for the hole arrangement (11) of the lower cover layer (10'.

5. Micromechanical component according to one of the preceding claims 1 to 3, characterized in that the upper cover layer (14) has connecting webs for connection to the lower cover layer (10).

6. Micromechanical component according to one of the preceding claims, characterized in that the lower cover layer (10) and / or the upper cover layer (14) comprises polysilicon or aluminum.

7. Micromechanical component according to one of the preceding claims, characterized in that the closure layer (17) has aluminum, silicon, silicon nitride, silicon dioxide, a glass or a lacquer.

8. The method for producing a micromechanical component according to claim 1, comprising the steps:

Providing a first sacrificial layer (8) on the functional area (5);

Provide the lower cover layer (10; 10 10 ^Λ> ) with the hole arrangement (11) on the first sacrificial layer (8) in such a way that it extends beyond the edge of the first sacrificial layer (8) and on the periphery of the functional area (5th ) is connected;

Providing a second sacrificial layer (12; 12 ^Λ ) on the lower cover layer (10; 10 10);

Providing the upper cover layer (14; 14 14 ^λ> ) with the hole arrangement (15) on the second sacrificial layer (12; 12 ^λ ) such that it is pulled over the edge of the second sacrificial layer (12; 12 ^λ ) and on the lower ^Top layer (10; 10 ^λ , 10 ^λλ ) and optionally connected to the periphery of the functional area (5);

selectively removing the first sacrificial layer (8) and the second sacrificial layer (12; 12 '); and Closing at least one of the hole arrangements (11, 15) by at least one sealing layer (17; 20, 25; 14 ^{, λ} , 30).

9. The method according to claim 8, characterized in that a first closure layer (17; 25; 30) is provided over the upper cover layer (14; 14 '; 14 ^λ ) and the hole arrangement (15) of the upper cover layer (14; 14 ^λ ; 14 ^Λλ ) is ^grafted through the first sealing ^layer (17; 25; 30).

10. The method according to claim 8 or 9, characterized in that a second sealing layer (20) is provided on the lower cover layer (14 10 ') and the hole arrangement (15) of the upper cover layer (14 ^x ) by fusing the second sealing layer (20) is closed.

11. The method according to claim 8, wherein the material of the upper cover layer (14 ^{Λ Λ} ) is selected such that it has a lower melting point than the material of the lower cover layer (10 ^{, Λ} ), characterized in that the upper cover layer (14 ^{, , (} ) is melted so that it closes the hole arrangement (11) of the lower cover layer (10 ^{, λ} ).