METHOD FOR SEALING ENTRIES IN A MEMS ELEMENT

Abstract

A method for sealing entries in a MEMS element. The method includes: providing a functional layer having a functional region; producing a cavity underneath the functional region of the functional layer with the aid of a first entry outside of the functional region of the functional layer; sealing the first entry; producing a second entry to the cavity outside of the functional region of the functional layer; melting sealing material in the region of the second entry; and cooling off the melted sealing material to seal the second entry.

Claims

1-15. (canceled)

16. A method for sealing entries in a MEMS element, comprising the following steps: providing a functional layer having a functional region; producing a cavity underneath the functional region of the functional layer using a first entry outside of the functional region of the functional layer; sealing the first entry; producing a second entry to the cavity, outside of the functional region of the functional layer; melting sealing material in a region of the second entry; and cooling off the melted sealing material to seal the second entry.

17. The method as recited in claim 16, wherein the sealing material situated in the region of the second entry is melted using a laser beam, and/or the sealing material to be melted is moved into the region of the second entry using a laser beam.

18. The method as recited in claim 16, wherein additional sealing material is deliberately deposited as the sealing material in the region of the second entry.

19. The method as recited in claim 16, wherein the sealing material for melting is provided exclusively in the form of surrounding material of a surrounding area of the second entry.

20. The method as recited in claim 16, wherein the sealing material is provided in the form of insulating material.

21. The method as recited in claim 16, wherein the sealing material is provided in the form of silicon oxide, and/or silicon nitride and/or silicon oxinitride.

22. The method as recited in claim 16, wherein a layer system for forming a eutectic upon melting is positioned as the sealing material in the region of the second entry.

23. The method as recited in claim 16, wherein starting from the cavity, the second entry is produced in a lateral direction, outside of the first entry, or starting from the cavity, the second entry is produced in the lateral direction, between the cavity and the first entry.

24. The method as recited in claim 16, wherein the first entry is produced to have a trench running around at least part of the functional region.

25. The method as recited in claim 16, wherein in a sealing region of the first entry, the second entry is produced in such a manner, that the second entry is connected to the cavity via the first entry.

26. The method as recited in claim 16, wherein the second entry is formed to have an opening, whose lateral cross-sectional area is less than that of an opening of the first entry.

27. The method as recited in claim 16, wherein the second entry is formed by an unsealed portion of an opening of the first entry, and/or by partially opening the sealed, first entry.

28. The method as recited in claim 16, wherein the second entry is connected to the cavity by a lateral channel and via the first entry.

29. The method as recited in claim 16, wherein the second entry is sealed in the same manner as the first entry.

30. The method as recited in claim 16, wherein the second entry is produced after the sealing of the first entry using a plasma etching method, in which the functional layer is etched through.

31. A MEMS element, comprising: a functional layer; and a cavity situated under a functional region of the functional layer, the cavity having at least two sealed entries, which are situated outside of the functional region of the functional layer, at least one of the two entries being sealed by melting sealing material in a region of the at least one entry and subsequently cooling off the melted material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows a top view and cross-sectional view of a MEMS element according to a specific embodiment of the present invention.

[0043] FIG. 2 shows a top view and cross-sectional view of a MEMS element according to a specific embodiment of the present invention.

[0044] FIG. 3 shows a top view and cross-sectional view of a MEMS element according to a specific embodiment of the present invention.

[0045] FIG. 4 shows MEMS elements according to top views and cross-sectional views of specific embodiments according to the present invention.

[0046] FIG. 5 show steps of a method according to a specific embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0047] In each of FIGS. 1 and 2, on the left side, a top view and a cross-sectional view of a MEMS element having two entries are shown, at the top and at the bottom, respectively, after the sealing of the first, and prior to the sealing of the second entry; and on the right side, a top view and a cross-sectional view of a MEMS element are shown, at the top and at the bottom, respectively, after the sealing of the first and second entries.

[0048] FIG. 1 shows a top view and cross-sectional view of a MEMS element according to a specific embodiment of the present invention.

[0049] In detail, a MEMS element 1, which includes a functional layer 16, is shown in schematic form in FIG. 1. Functional layer 16 has a functional region 2, which takes the form of a measuring diaphragm. Underneath functional layer 16, further layers 12, 13, 15 are situated one on top of the other, so that on the whole, MEMS element 1 has a layer construction. A cavity 4, which interrupts layers 13, 15 and is occluded at the bottom by layer 12, is situated underneath functional region 2. In this case, layer 12 may be understood as a layer on a substrate or as a substrate itself, and may be made up of a silicon wafer, for example. In this context, cavity 4 is connected via a, in particular, slot-shaped, peripheral trench 5, which is situated outside of the diaphragm surface, that is, outside of functional region 2, and has an opening 11, and via laterally positioned etching channels 9, which are used together as etching access for cavity 4. Thus, in this connection, the trench 5 with its opening 11 forms, together with etching channels 9, a first entry to cavity 4. For example, with the aid of a gas-phase etching method, sacrificial material may be removed from cavity 4 via opening 11 of trench 5, trench 5, and etching channels 9. Alternatively, sacrificial material may also be removed from cavity 4, using a wet-chemical etching method.

[0050] In addition, MEMS element 1 includes at least one further channel 6, which runs laterally and is situated underneath functional layer 16 and inside of the layer construction. In this context, lateral channel 6 is connected to cavity 4. In FIG. 1, the channel 6 running laterally is situated inside of layer 13. After the opening 11 of circumferential trench 5 has been sealed by sealing material 3, for example, with the aid of silicon oxide, a vertical entry 7 to lateral channel 6, including opening 8, is subsequently laid out in a region outside of functional region 2, so that cavity 4 may be ventilated or evacuated via lateral channel 6, vertical entry 7, and its opening 8. Therefore, lateral channel 6 and vertical entry 7 having opening 8 form a second entry to cavity 4. The vertical entry 7 having opening 8 may be laid out, for example, with the aid of a plasma etching method, in which functional layer 16 is suitably etched through, outside of functional region 2, in order to produce a connection to buried, lateral channel 6 in the vertical direction. In FIG. 1, starting from cavity 4, opening 8 is situated beyond opening 11 of trench 5 in the lateral direction. As an alternative, opening 8 may also be situated between cavity 4 and opening 11 of trench 5 in the lateral direction. Here, opening 8 takes the form of an access hole. For example, if functional region 2 takes the form of a flexible diaphragm, a stiffening element or the like (not shown in FIG. 1), which is used to locally reinforce the flexible diaphragm, may also be provided underneath functional region 2, on functional layer 16. In addition, further semiconductor circuit components and/or MEMS components (not shown in FIG. 1), which are used for the functionality and the operation of MEMS element 1, may be situated below functional region 2. Furthermore, opening 8 of second entry 6, 7, 8 to cavity 4 may be sealed, alternatively or additionally, using silicon nitride or a multilayer layer system made up of silicon oxide, silicon nitride and/or silicon oxinitride. In order to seal opening 11 of trench 5 and/or of the upper region and/or opening 8 of vertical entry 7, a silicon oxide seal, a silicon nitride seal, a silicon oxinitride seal, a seal made up of a combination of oxide, nitride, and oxinitride layers, or also a laser resealing method utilizing a laser source having, for example, a wavelength between 500 nm and 700 nm and/or between 900 nm and 1200 nm, may be used: Vertical entry 7 and/or trench 5 are sealed by locally melting and subsequently cooling sealing material in the region of opening 8 of vertical entry 7 and/or of opening 11 of trench 5. In this context, the entire functional region 2, thus, here in FIG. 1, the entire diaphragm surface, may be covered by an additional silicon nitride layer.

[0051] FIG. 2 shows a top view and cross-sectional view of a MEMS element according to a specific embodiment of the present invention.

[0052] A MEMS element 1 according to FIG. 1 is essentially shown in FIG. 2. In contrast to MEMS element 1 according to FIG. 1, in MEMS element 1 shown in FIG. 2, additional sealing material 10 is now situated on functional layer 16, in the region of opening 8 of vertical entry 7; the sealing material allowing a gas-tight seal of vertical entry 7, for example, through melting with the aid of a laser and subsequent cooling. It is also possible for sealing material 10 to be applied in the region of opening 11 of trench 5, and for this to be melted, for example, with the aid of a laser. Thus, after subsequent cooling, a gas-tight seal of trench 5 may also be provided.

[0053] Functional layer 16, which is situated on layer 15, may have a thickness between 10 nm and 500 μm and be made of polycrystalline or monocrystalline silicon. The thickness of functional layer 16 may preferably be between 100 nm and 2500 nm.

[0054] FIG. 3 shows a top view and cross-sectional view of a MEMS element according to a specific embodiment of the present invention.

[0055] A MEMS element 1 according to FIG. 1 is essentially shown in FIG. 3. In contrast to MEMS element 1 according to FIG. 1, in MEMS element 1 shown in FIG. 3, no vertical entry 7 is positioned with lateral channel 6, but vertical entry 7 is laid out in functional layer 16, which is situated above trench 5, in order to ventilate/evacuate cavity 4. The upper region, that is, access hole 8, of vertical entry 7 is then sealed again in an appropriate manner.

[0056] In this case, trench 5 is situated below functional layer 16, in the, or in one of the, layers 13, 15 situated under it. Thus, as described above, if, in functional layer 16, within the region of trench 5, at least one vertical entry 7 is laid out, for example, with the aid of a plasma etching method, which extends from the upper surface of functional layer 16 into trench 5, then this vertical entry 7 may be used, first of all, to remove material from cavity region 4 and, secondly, to ventilate or evacuate cavity 4 in a specific manner. As already described above, the at least one vertical entry 7 may be sealed, for example, using a silicon oxide seal, a silicon nitride seal, a silicon oxinitride seal, a seal made of a combination of oxide and nitride layers, or also using a laser resealing method, in which vertical entry 7 may be sealed by locally melting and subsequently cooling material in the upper region, that is, at, on, and/or in opening 8 of vertical entry 7. In this case, as well, it is possible, in turn, to deposit additional sealing material 10 on functional layer 16, in the upper region, that is, at, on, and/or in and around opening 8 of vertical entry 7, in order to seal vertical entry 7 with it.

[0057] FIG. 4 shows cross-sections of MEMS elements according to specific embodiments of the present invention.

[0058] In each instance, a MEMS element 1 according to FIG. 1 is shown at the top of FIG. 4 and at the bottom of FIG. 4. In contrast to MEMS element 1 according to FIG. 1, in the MEMS elements 1 shown in FIG. 4, the specific lateral channel 6 for connecting vertical entry 7 and cavity 4 is situated at different elevations, starting out from bottom layer 12, in such a manner, that subregions of trench 5 and etching channels 9, which are connected to cavity 4, are used in order to be able to obtain etching access and/or ventilation/evacuation of cavity 4. In other words, cavity 4 is produced and/or ventilated/evacuated via etching channels 9, trench 5, the lateral channel 6 connected to it, and vertical entry 7 and its opening 8. The trench 5 itself is sealed in the region of functional layer 16.

[0059] FIG. 5 shows steps of a method according to a specific embodiment of the present invention.

[0060] Steps of a method for sealing entries in a MEMS element are shown in FIG. 5. In this context, the method includes the following steps.

[0061] In a first step S1, a functional layer having a functional region is provided.

[0062] Then, in a further step S2, a cavity is produced underneath the functional region of the functional layer with the aid of a first entry outside of the functional region of the functional layer.

[0063] Subsequently, in a further step S3, the first entry is sealed.

[0064] Then, in a further step S4, a second entry to the cavity is produced outside of the functional region of the functional layer.

[0065] Subsequently, in a further step S5, sealing material in the region of the second entry is melted.

[0066] Then, in a further step S6, the melted sealing material is cooled, in order to seal the second entry.

[0067] In summary, at least one of the specific embodiments of the present invention has at least one of the following advantages: [0068] Simple and reliable sealing of thin layers, in particular, in the range of 10 nm to 500 μm, in particular, approximately 2 μm. [0069] Simple implementation. [0070] Cost-effective implementation. [0071] Higher flexibility with regard to the positioning of the entries. [0072] Characteristics of the functional region are not changed by the sealing. [0073] No entries in the area of the functional region, therefore, no adverse influence on the same. [0074] No additional and/or other materials in the functional region of the functional layer, therefore, uniform thermal expansion and uniform mechanical characteristics. [0075] Prevention of fluctuations in thickness in the functional region caused by the sealing method. [0076] Adjustment of the internal pressure is independent of the first sealing method.

[0077] Although the present invention was described in light of preferred exemplary embodiments, it is not limited to them, but is modifiable in numerous ways. Thus, for example, a plurality of second entries may be produced. These may be sealed with the aid of the same or different methods.