METHOD FOR PRODUCING A MICRO-ELECTROMECHANICAL OSCILLATORY SYSTEM AND PIEZOELECTRIC MICROMACHINED ULTRASONIC TRANSDUCER

Abstract

A method for producing a micro-electromechanical oscillatory system. A carrier substrate with a first surface is provided and a first passivation layer is applied onto the first surface. A first polysilicon layer grows on top of the first passivation layer and/or the first surface of the carrier substrate and a second passivation layer is applied onto a second surface of the first polysilicon layer. A second polysilicon layer grows on top of the first polysilicon layer and/or the second passivation layer. A transducer element is applied onto a third surface of the second polysilicon layer. A first trench is produced through the carrier substrate and the first polysilicon layer in the direction of the transducer element. The first trench extends as far as the second passivation layer, such that an oscillatable transducer plate of the micro-electromechanical oscillatory system is produced adjoining the first trench using the second polysilicon layer.

Claims

1-14. (canceled)

15. A method for producing a micro-electromechanical oscillatory system, the method comprising the following method steps: providing a carrier substrate with a first surface; applying a first passivation layer onto the first surface of the first carrier substrate; epitaxially growing a first polysilicon layer on top of the first passivation layer and/or the first surface of the carrier substrate; applying a second passivation layer onto a second surface of the first polysilicon layer, the second surface being oriented substantially parallel to the first surface of the first carrier substrate; epitaxially growing a second polysilicon layer on top of the second surface of the first polysilicon layer and/or the second passivation layer; arranging a transducer element of the micro-electromechanical oscillatory system on a third surface of the second polysilicon layer, the third surface being oriented substantially parallel to the first surface of the first carrier substrate; and producing a first trench through the carrier substrate and through the first polysilicon layer in a direction of the transducer element, the first trench extending as far as the second passivation layer such that an oscillatable transducer plate of the micro-electromechanical oscillatory system is produced adjoining the first trench using the second polysilicon layer.

16. The method as recited in claim 15, wherein the micro-electromechanical oscillatory system is a piezoelectric micromachined ultrasonic transducer.

17. The method as recited in claim 15, wherein, following the step of epitaxially growing the first polysilicon layer on top of the first passivation layer and/or the first surface of the carrier substrate, a circumferential second trench, produced by trenching, is produced through the first polysilicon layer, an area of the second surface enclosed by the circumferential second trench having, in plan view, a defined shape and size of the oscillatable transducer plate to be produced.

18. The method as recited in claim 17, wherein, during the step of applying the second passivation layer onto the second surface of the first polysilicon layer, the second circumferential trench becomes filled at least in part with the second passivation layer and is closed by the second passivation layer at an upper end of the second trench.

19. The method as recited in claim 18, wherein the second trench extends as far the first passivation layer.

20. The method as recited in claim 15, wherein, following application of the second passivation layer onto the second surface of the first polysilicon layer, the second passivation layer is removed in part using a first etching mask such that the second passivation layer remains only in a contiguous first sub-region of the second passivation layer, the first sub-region having, in plan view, a shape and size including length, which correspond to the oscillatable transducer plate to be produced.

21. The method as recited in claim 15, wherein, following application of the first passivation layer onto the first surface of the first carrier substrate, the first passivation layer is removed in a second sub-region of the first passivation layer using a second etching mask, the second sub-region of the first passivation layer having a shape and an area which correspond to the oscillatable transducer plate produced.

22. The method as recited in claim 15, wherein, in the step of producing the first trench, a trenching step is performed, in which a fourth opening of a fourth trench mask has a a diameter which is smaller than a size of an area of the transducer plate, the first trench being enlarged in a following isotropic silicon etching step, until the second passivation layer is reached.

23. The method as recited in claim 15, wherein the first and/or the second passivation layer serve as etch stop layers.

24. The method as recited in claim 15, wherein the first and/or the second passivation layers is a silicon oxide layer.

25. The method as recited in claim 15, wherein, following production of the first trench the first and second passivation layers are removed at least in part.

26. A piezoelectric micromachined ultrasonic transducer, comprising: a carrier substrate of silicon; a first polysilicon layer; a second polysilicon layer; a first passivation layer; a transducer element; and an oscillatable transducer plate; wherein the carrier substrate has a first surface, on which the first polysilicon layer is at least in part arranged, the first surface of the carrier substrate and the first polysilicon layer being separated from one another at least in part by the first passivation layer, the first polysilicon layer having a second surface, the second surface being oriented substantially parallel to the first surface of the first carrier substrate, the second polysilicon layer being arranged on the second surface, the transducer element including a piezo element, of the piezoelectric micromachined ultrasonic transducer being arranged on a third surface of the second polysilicon layer, the third surface being oriented substantially parallel to the first surface of the first carrier substrate, a first trench extending in a direction of the transducer element through the carrier substrate and the first polysilicon layer as far as the second polysilicon layer such that the oscillatable transducer plate is formed, directly adjoining the first trench.

27. The piezoelectric micromachined ultrasonic transducer as recited in claim 26, wherein the first trench has a main direction of extension which is oriented substantially perpendicular to the first surface of the first carrier substrate.

28. The piezoelectric micromachined ultrasonic transducer as recited in claim 26, wherein the first trench has a smaller diameter in a region of the first polysilicon layer than in a region of the carrier substrate.

29. The piezoelectric micromachined ultrasonic transducer as recited in claim 26, wherein the first polysilicon layer has a first thickness in a range from 10 ?m to 80 ?m, and the second polysilicon layer has a second thickness in a range from 2 ?m to 80 ?m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows a first embodiment of a method for producing a micro-electromechanical oscillatory system, according to the present invention.

[0017] FIG. 2 shows a second embodiment of a method for producing a micro-electromechanical oscillatory system, according to the present invention.

[0018] FIG. 3 shows a third embodiment of a method for producing a micro-electromechanical oscillatory system, according to the present invention.

[0019] FIG. 4 shows a fourth embodiment of a method for producing a micro-electromechanical oscillatory system, according to the present invention.

[0020] FIG. 5 shows a fifth embodiment of a method for producing a micro-electromechanical oscillatory system, according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0021] FIG. 1 is a schematic representation of a first embodiment of a method for producing a micro-electromechanical oscillatory system. In this case, the micro-mechanical-oscillatory system is a piezoelectric micromachined ultrasonic transducer. In a first method step 30, a carrier substrate 1 is provided and subsequently a first passivation layer 2 is applied onto the first surface 3 of the first carrier substrate 1. Thereafter, in this first exemplary embodiment, the first passivation layer 2 is removed in a second sub-region 18 of the first passivation layer 2 by means of a second etching mask, not shown here. The second sub-region 18 of the first passivation layer 2 here has a shape and an area which correspond to the subsequently to be produced oscillatable transducer plate 19. Thereafter, a first polysilicon layer 7 grows on top of the first passivation layer 2 and the first surface of the carrier substrate 1. Furthermore, following the step of growing the first polysilicon layer 7, a circumferential second trench 4a and 4b is produced through the first polysilicon layer 7. The circumferential second trench 4a and 4b is a trench produced by trenching. In plan view, an area of the second surface 6 enclosed by the circumferential second trench 4a and 4b here has the shape and size of the oscillatable transducer plate 19 to be produced. The second trench 4a extends as far as the first passivation layer 2. Furthermore a second passivation layer 5 is applied onto a second surface 6 of the first silicon layer 7. The second surface 6 is here oriented substantially parallel to the first surface 3 of the first carrier substrate 1. During the step of applying the second passivation layer 5 onto the second surface 6 of the first polysilicon layer 7, the second circumferential trench 4a and 4b becomes filled at least in part with the second passivation layer 5 and is closed by the second passivation layer 5 at an upper end, in particular an opening, of the second trench 4a and 4b. Thereafter, the second passivation layer 5 is removed in part by means of a first etching mask (not shown here) in such a way that the second passivation layer 5 only remains in a contiguous first sub-region 21 of the second passivation layer 5. The first sub-region here has a shape and a size, in particular length, which correspond to the subsequently to be produced oscillatable transducer plate 19.

[0022] In a following method step 31, a second polysilicon layer 11 grows on top of the second surface 6 of the first polysilicon layer 7 and the second passivation layer 5. In addition, a transducer element 10 of the piezoelectric micromachined ultrasonic transducer is applied onto a third surface 8 of the second polysilicon layer 11. The third surface 8 is here oriented substantially parallel to the first surface 3 of the first carrier substrate 1. The transducer element 10 in this case is a piezo element, which is additionally electrically connected by means of electrical contact elements 9.

[0023] In a following method step 32, a first trench 14 is produced right through the carrier substrate 1 and through the first polysilicon layer 7 in the direction of the transducer element 10 by means of trenching. A main direction of extension 16 of the first trench 14 here runs substantially perpendicular to the first surface 3 of the first carrier substrate 1. The first trench 14 extends here as far as the second passivation layer 5, such that an oscillatable transducer plate 19 of the micro-electromechanical oscillatory system is produced adjoining the first trench 14 by means of the second polysilicon layer 11. The first and second passivation layers 3 and 5 respectively serve as etch stop layers and take the form of silicon oxide layers.

[0024] In a following method step 33, the second passivation layer 5 is completely removed within the channel 14.

[0025] The first trench 14 of the piezoelectric micromachined ultrasonic transducer 20a produced widens out in the form of a funnel until the first polysilicon layer 7 is reached.

[0026] FIG. 2 is a schematic representation of a second embodiment of a method for producing a micro-electromechanical oscillatory system in the form of a piezoelectric micromachined ultrasonic transducer 20b. Unlike the embodiment in FIG. 1, in a method step 36 following method step 31 first of all a trenching step is performed with a fourth trench mask (not shown here) to produce the first trench 43. The trench mask has a fourth opening of a size, in particular a diameter, which is significantly smaller than the size of a length of the transducer plate 19 to be produced. The trenching step extends into the first polysilicon layer 7 but does not reach the second passivation layer 5. In a following method step 37, the first trench 43 is enlarged in an isotropic silicon etching step until the second passivation layer 5 is reached. The second passivation layer 5 is then removed.

[0027] FIG. 3 is a schematic representation of a third embodiment of a method for producing a micro-electromechanical oscillatory system in the form of a piezoelectric micromachined ultrasonic transducer 20c. Unlike in the embodiments described above, in a first method step 38, the second passivation layer is here allowed to remain over the entire surface. This embodiment is advantageous for electrical isolation between transducer plate 19 and carrier substrate 1.

[0028] FIG. 4 is a schematic representation of a fourth embodiment of a method for producing a micro-electromechanical oscillatory system in the form of a piezoelectric micromachined ultrasonic transducer 20d. Here, unlike in the above-described embodiments, the second circumferential trench is omitted in method step 42. This results in just the first passivation layer 2 on the first surface and the second passivation layer 5 on the second surface. In a method step 44 following method step 31, the first passivation layer 2 serves, on trenching of the first trench 61, as a type of aperture through which the trench then extends until the second passivation layer 5 is reached. Since the first channel 61 or the wall 60 of the first channel 61 is then widened more in the region of the first polysilicon layer 7 than in the above-described embodiments, in this case the first sub-region 23 of the second passivation layer 5 is also broader than in the above-described embodiments. In a method step 45 following method step 44, the second passivation layer 5 is completely removed within the channel 61. This method offers the advantage of simple and inexpensive implementation, wherein the accuracy of the dimensions of the transducer plate 29 to be produced is still high.

[0029] FIG. 5 is a schematic representation of a fifth embodiment of a method for producing a micro-electromechanical oscillatory system in the form of a piezoelectric micromachined ultrasonic transducer 20e. Unlike the above-described embodiments, in method step 46, the first passivation layer 3 is here formed in the region of the second sub-region 18 with perforations or a grating. In a method step 48 following method step 31, the trench for producing the first channel 72 initially extends almost completely through the carrier substrate 1 and through the perforations or grating of the first passivation layer 3, In the course of method step 48, when the perforated second sub-region 18 is reached is identifiable and is used to terminate trenching. Narrow webs 71 arise within the first polysilicon layer 2. In a following method step 49, the first channel with the wall 74 is then produced entirely by means of silicon sacrificial layer etching. This embodiment offers the advantage that the first passivation layer can be made very thin.