Method for manufacturing an integrated MEMS transducer device and integrated MEMS transducer device

Abstract

In an embodiment, a method for manufacturing a micro-electro-mechanical systems (MEMS) transducer device includes providing a substrate body with a surface, depositing an etch-stop layer (ESL) on the surface, depositing a sacrificial layer on the ESL, depositing a diaphragm layer on the sacrificial layer and removing the sacrificial layer, wherein depositing the sacrificial layer includes depositing a first sub-layer of a first material and depositing a second sub-layer of a second material, and wherein the first material and the second material are different materials.

Claims

1. A method for manufacturing a micro-electro-mechanical systems (MEMS) transducer device, the method comprising: providing a substrate body with a surface; depositing an etch-stop layer (ESL) on the surface; depositing a sacrificial layer on the ESL; depositing a diaphragm layer on the sacrificial layer; and removing the sacrificial layer, wherein depositing the sacrificial layer comprises depositing a first sub-layer of a first material and depositing a second sub-layer of a second material, wherein the first material and the second material are different materials, wherein the first sub-layer is deposited on the ESL and the second sub-layer is deposited on the first sub-layer, wherein the first material has a lower moisture content and/or a higher density compared to the second material, and wherein the first material has a lower etch rate compared to the second material.

2. The method according to claim 1, wherein the first and second materials are dielectrics.

3. The method according to claim 1, wherein the second material is an undoped silica glass (USG) deposited by a low density CVD technique.

4. The method according to claim 1, wherein the first material is a fluorinated silica glass (FSG) or a silica glass deposited via high-density plasma chemical vapor deposition (HDP-CVD).

5. The method according to claim 1, wherein the sacrificial layer is deposited with a thickness of the sacrificial layer in a vertical direction, which is perpendicular to a main plane of extension of the substrate body, of equal to or less than 3 μm, inclusive.

6. The method according to claim 1, wherein depositing the sacrificial layer further comprises depositing a third sub-layer of a third material, and wherein the third material is different from the first and second materials or corresponds to the first material.

7. The method according to claim 1, wherein the substrate body comprises a cover layer and/or an electrode layer, and wherein the surface is a surface of the cover layer and/or the electrode layer.

8. The method according to claim 1, further comprising patterning and structuring the diaphragm layer prior to removing the sacrificial layer.

9. The method according to claim 1, wherein depositing the diaphragm layer comprises depositing an adhesion layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following description of figures of exemplary embodiments may further illustrate and explain aspects of the improved method. Components and parts of the integrated transducer device with the same structure and the same effect, respectively, appear with equivalent reference symbols. In so far as components and parts of the transducer device correspond to one another in terms of the function in different figures, the description thereof is not repeated for each of the following figures.

(2) FIGS. 1A to 1E show cross sections of intermediate steps of an exemplary embodiment of the improved manufacturing method of an integrated transducer device;

(3) FIGS. 2A to 2F show cross sections of intermediate steps of a further exemplary embodiment of the manufacturing method of an integrated transducer device;

(4) FIG. 3 shows a cross section of a finalized integrated transducer device manufactured with the improved method; and

(5) FIGS. 4A to 4E show cross sections of intermediate steps of a conventional manufacturing method of an integrated transducer device.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(6) FIGS. 1A to 1E show cross sections of intermediate steps of an exemplary manufacturing method of an integrated transducer device. In this embodiment, depositing the sacrificial layer 3 comprises depositing a first sub-layer 4 and a second sub-layer 5.

(7) FIG. 1A shows a cross section of an intermediate product of a transducer device before the release etch. The integrated transducer device comprises a substrate body 1 of a substrate material, which may be silicon. The substrate body 1 may also comprise an integrated circuit, which may in particular be a CMOS circuit with active and passive circuitry. Such integrated circuits are known per se, and are not shown in the figures. The integrated circuit may especially be provided for an evaluation of signals from the transducer, such as a capacitance of the transducer.

(8) A cover layer 2, which may include a wiring embedded in an inter-metal dielectric layer and/or a passivation, for instance, is applied on a surface of the substrate body 1. The inter-metal dielectric layer may comprise silicon dioxide, and the passivation may comprise a combination of silicon dioxide and silicon nitride, for instance. The part of the transducer device that includes the substrate body 1 and the cover layer 2 may be similar to a conventional semiconductor device with an integrated circuit. The transducer device differs from such a semiconductor device by an arrangement of transducer elements on a surface of the cover layer 2 facing away from the semiconductor body 1. A thickness of the cover layer 2 may be in the order of 100 nm-5 μm, or even 100-200 nm.

(9) An electrode layer 7 may be arranged on the surface of the cover layer 2 facing away from the substrate body 1 and patterned and structured, for example via lithography and etching, in order to form a first electrode of a transducer, especially a capacitive transducer, for instance. The first electrode of such a transducer may be referred to as the bottom electrode. An etch-stop layer, ESL, 8 is arranged on a surface of the electrode layer 7 facing away from the substrate body 1. Thicknesses of the electrode layer 7 and the ESL 8 may be in the order of 20-500 nm, or even 50-300 nm.

(10) A sacrificial layer 3 is arranged on a surface of the ESL 8 facing away from the substrate body 1. The ESL 8 is made of a material with a significantly lower etch rate regarding a fluorine-based etchant compared to a material of the sacrificial layer 3. For example, the ESL 8 comprises silicon nitride, such as silicon-rich silicon nitride, while the sacrificial layer 3 comprises silicon or silicon dioxide. The sacrificial layer 3 comprises a first and a second sub-layer 4, 5, wherein the first sub-layer is of a first material and arranged on the surface of the ESL 8 and the second sub-layer 5 is of a second material and arranged on the first sub-layer 4. The first material may be fluorinated silica glass, FSG, which is characterized by a low moisture content compared to the second material, which may be an undoped silica glass, USG, for instance. A total thickness of the sacrificial layer may be in the order of 200 nm-5 μm, or even 500 nm to 3 μm.

(11) A diaphragm layer 6 is deposited on a surface of the sacrificial layer 3 facing away from the substrate body 1 and patterned and structured in a subsequent step for forming openings 10. The diaphragm layer 6 may comprise a sequence of layers and may particularly include a main layer and an adhesion layer. The latter is configured to facilitate the arrangement of the diaphragm layer 6 on the sacrificial layer 3. A material of the adhesion layer may be characterized by a larger adhesion to the sacrificial layer 3 compared to a material of the main layer. The adhesion layer may for example comprise titanium, titanium nitride, TiN, or a combination of titanium and TiN. The main layer may be a metal such as tungsten. The thickness of the diaphragm layer 6 may be in the order of 50 nm-2 μm, or even 50-300 nm. Parameters, such as size and spacing, of the openings 10 have to be considered when choosing both thicknesses of the first and the second sub-layer 4, 5 of the sacrificial layer 3, as this may influence the etching process.

(12) In the following FIGS. 1B to 1E, the labelling is omitted for illustration purposes. The shading of the respective layers is kept consistent throughout all figures.

(13) FIG. 1B shows a cross section of the intermediate product according to FIG. 1A after initiating the release by introducing the vHF etchant through the openings 10 of the diaphragm layer 6. As the second sub-layer 5 possesses significantly higher moisture content compared to the first sub-layer 4, the etch rate for the former is significantly higher.

(14) FIG. 1C shows a cross section of the intermediate product according to FIG. 1B after the second sub-layer 5 has been completely removed. Due to the low moisture content, the first sub-layer 4 shows, if at all, only minor decrease in thickness due to the etch. Since the diaphragm layer 6 is fully released already at this point, the vHF etchant is able to attack the entire surface of the first sub-layer 4 facing away from the substrate body 1 enabling an isotropic etch, as illustrated in FIG. 1E, which shows a first sub-layer 4 with reduced thickness.

(15) FIG. 1E shows a cross section of the intermediate product according to FIG. 1D after also the first sub-layer 4, and therefore the entire sacrificial layer 3, has been completely removed. The ESL 8 remains on the finalized transducer and serves as protective layer for the otherwise exposed electrode layer 7.

(16) In contrast to the embodiment shown in FIGS. 1A to 1E, a reverse order of the sub-layers 4, 5 is likely possible. This case, in which the first sub-layer 4 is characterized by a faster etch rate compared to the second sub-layer 5 regarding a specific etchant, may be employed if protection of the diaphragm layer has to be considered, while the ESL 8 may have a high enough selectivity such that a well-controlled etch is not crucial at this point. For example, the first sub-layer 4 may in this embodiment comprise USG and the second sub-layer 5 may comprise FSG. The thicknesses of the sub-layers 4, 5 in this embodiment may be tailored to the specific design and/or manufacturing process.

(17) FIGS. 2A to 2F show cross sections of intermediate steps of a further exemplary manufacturing method of an integrated transducer device. Compared to FIGS. 1A to 1E, in this embodiment, depositing the sacrificial layer 3 further comprises depositing a third sub-layer 9 on the second sub-layer 5.

(18) FIG. 2A, analogous to FIG. 1A, shows a cross section of an intermediate product of a transducer device before initiating the release etch. This embodiment is particularly relevant if the diaphragm layer comprises an adhesion layer of Ti and or TiN, for example. The adhesion layer not only promotes adhesion of the main layer to the sacrificial layer 3, but Titanium also acts as a getter material that reduces the partial pressure of hydrogen in the cavity, i.e. the void between the ESL 8 and the diaphragm layer 6. For this reason, etching of the adhesion layer and consequent formation of TiF.sub.4 residues should be avoided. To this end, the third material of the third sub-layer 9 like the first sub-layer 4 is characterized by a low moisture content resulting in a low etch rate. For example, the first and the third material is HDP-CVD silica glass.

(19) In the following FIGS. 2B to 2F, the labelling is omitted for illustration purposes. The shading of the respective layers is kept consistent throughout all figures.

(20) FIG. 2B shows a cross section of the intermediate product according to FIG. 2A after initiating the release by introducing the vHF etchant through the openings 10 of the diaphragm layer 6. After etching through the third sub-layer 9, the second sub-layer 5, comprising USG, is preferentially etched, as also illustrated in FIGS. 2C and 2D. Due to this preferential etching, the third sub-layer 9 substantially covers the diaphragm layer 6 after the second sub-layer 5 has been completely removed.

(21) FIG. 2E shows a cross section of the intermediate product according to FIG. 2D after the second and the third sub-layer 5, 9 have been completely removed and the thickness of the first sub-layer 4 is significantly decreased.

(22) FIG. 2F shows a cross section of the intermediate product according to FIG. 2E after also the first sub-layer 4, and therefore the entire sacrificial layer 3, has been completely removed. Like in the embodiment of FIG. 1E, the ESL 8 remains on the finalized transducer.

(23) FIG. 3 shows a cross section of a finalized integrated transducer device manufactured after an embodiment of the improved method. The transducer device comprises a structured electrode layer 7 arranged on a cover layer 2, with the electrode layer 7 forming a bottom electrode of the transducer and contacts for the diaphragm layer 6. The electrode layer is completely covered with an ESL 8 facing away from the substrate body 1 owing to the improved manufacturing method described in the previous figures. The diaphragm layer 6 constitutes a perforated MEMS membrane, for example, having a main layer 6B arranged in between an adhesive layer 6A and a protective layer 6C, protecting the main layer 6B during the release etch on both surfaces of the main layer 6B. The diaphragm layer 6 is interconnected with contact pads of the electrode layer and/or contacts of circuitry of the substrate body, for instance belonging to an integrated circuit, via anchors ii of an anchor structure.

(24) As the sacrificial layer 3 in between individual anchors is sealed from the cavity that is delimited by the ESL 8, the diaphragm layer 6 and the anchor structure, the release etch does not remove said portion of the sacrificial layer 3, which therefore remains in between said anchors in the finalized transducer. The FIG. 3 further shows a cap layer 12 deposited after the release etch serving as a protective layer of the transducer.

(25) FIGS. 4A to 4E FIGS. 2A to 2F show cross sections of intermediate steps of a conventional manufacturing method of an integrated transducer device. The conventional method employs a sacrificial layer 3 consisting of a single unilayer, for example of USG. The procedure of the release etch is analogous to that shown in FIGS. 1A to 1E and 2A to 2F. The unilayer results in an anisotropic etch, i.e. faster etching in a vertical direction towards the substrate body 1 compared to the etch rate in lateral direction parallel to a main plane of extension of the substrate body 1. This anisotropic etch results in an uneven removal of the sacrificial layer and may cause uneven removal of the ESL 8, which may in turn influence the capacitance between the top and bottom electrode and hence decrease the sensitivity.

(26) The embodiments shown in the FIGS. 1A to 3 as stated represent exemplary embodiments of the improved manufacturing method and the integrated transducer device, therefore they do not constitute a complete list of all embodiments according to the improved method. Actual transducer device configurations may vary from the embodiments shown in terms of shape, size and materials, for example.

(27) Although the invention has been illustrated and described in detail by means of the preferred embodiment examples, the present invention is not restricted by the disclosed examples and other variations may be derived by the skilled person without exceeding the scope of protection of the invention.