METHOD AND WAFER FOR FABRICATING TRANSDUCER DEVICES

Abstract

A wafer for use in fabricating a plurality of individual transducer devices comprises a bracing structure for partitioning the wafer into a plurality of regions, and a plurality of transducer devices fabricated in one or more of the plurality of regions.

Claims

1. A wafer for use in fabricating a plurality of individual transducer devices, the wafer comprising: a bracing structure for partitioning the wafer into a plurality of regions; and a plurality of transducer devices fabricated in each of at least one or more of the plurality of regions, wherein a transducer device fabricated in the water comprises a micro-electrical-mechanical system (MEMS) transducer, comprising: a substrate; a back-volume formed in the substrate; and a membrane formed over the back-volume and on the substrate; wherein the back-volume comprises a first back-volume portion and a second back-volume portion, the first back-volume portion being separated from the second back-volume portion by a step in a sidewall of the back-volume; wherein the bracing structure is formed from areas of the wafer where no transducer devices are fabricated within the wafer.

2. A wafer as claimed in claim 1, wherein the bracing structure comprises one or more bracing rings (101.sub.1-101.sub.N).

3. A wafer as claimed in claim 2 comprising a plurality of concentric bracing rings (101.sub.1-101.sub.N), and wherein the plurality of concentric bracing rings (101.sub.1-101.sub.N) are of substantially the same radial thickness.

4. A wafer as claimed in claim 2, wherein one of the concentric bracing rings (101.sub.1) abuts a perimeter of the wafer, or is positioned adjacent to the perimeter of the wafer and within a predetermined distance of the perimeter.

5. A wafer as claimed in claim 2, wherein the one or more concentric bracing rings (101.sub.1-101.sub.N) are configured to be: evenly spaced between the center and the perimeter of the wafer; or more closely spaced to each other the closer the concentric bracing rings are to the perimeter of the wafer.

6. A wafer as claimed in claim 2, wherein the one or more concentric bracing rings (101.sub.1-101.sub.N) form concentric bands between each pair of concentric bracing rings where transducer devices are fabricated.

7. A wafer as claimed in claim 1, wherein the bracing structure comprises at least one radial bracing component (103.sub.1 to 103.sub.M) configured to extend in a radial direction from the center of the wafer towards the perimeter of the wafer.

8. A wafer as claimed in claim 7, wherein the at least one radial bracing component (103.sub.1 to 103.sub.M) extends from the center of the wafer to the perimeter of the wafer, through at least one of the one or more concentric bracing rings (101.sub.1-101.sub.N).

9. A wafer as claimed in claim 7, wherein the at least one radial bracing component (103.sub.1 to 103.sub.M) extends from the center of the wafer to the perimeter of the wafer, through each of the one or more concentric bracing rings (101.sub.1-101.sub.N).

10. A wafer as claimed in claim 7, to comprising two or more radial bracing components, wherein the two or more radial bracing components are equally spaced in a circumferential direction around the wafer.

11. A wafer as claimed in claim 7, wherein the at least one radial bracing component comprises four radial bracing components (103.sub.1 to 103.sub.4), and wherein: the four radial bracing components are equally spaced in a circumferential direction around the wafer; and each radial bracing component (103.sub.1 to 103.sub.4) extends from the center of the wafer to the perimeter of the wafer, interconnecting each of the one or more concentric bracing rings (101.sub.1-101.sub.N).

12. A wafer as claimed in claim 7, wherein the at least one radial bracing component comprises a plurality of radial bracing components (103.sub.1 to 103.sub.M), and wherein: the plurality of radial bracing components are equally spaced in a circumferential direction around the wafer; and a first of the plurality of radial bracing components (103.sub.1 to 103.sub.M) extends in a direction from the center of the wafer to the perimeter of the wafer, interconnecting a first set of concentric bracing rings (101.sub.1-101.sub.N); and a second of the plurality of radial bracing components (103.sub.1 to 103.sub.M) extends in a direction from the center of the wafer to the perimeter of the wafer, interconnecting a second set of concentric bracing rings (101.sub.1-101.sub.N).

13. A wafer as claimed in claim 12, wherein the first and second radial bracing components are adjacent bracing components.

14. A wafer as claimed in claim 12, wherein interconnections between a first set of concentric bracing rings are interleaved in a circumferential direction with interconnections between a second set of concentric bracing rings.

15. A wafer as claimed in claim 1, wherein the bracing structure comprises: a plurality of rectangular bracing elements distributed within the perimeter of the wafer, each rectangular bracing element defining a region; or a plurality of square bracing elements distributed within the perimeter of the wafer, each square bracing element defining a region; or a plurality of hexagonal bracing elements distributed within the perimeter of the wafer, each hexagonal bracing element defining a region.

16. A wafer as claimed in claim 1, whereby within a particular region defined by the bracing structure, a mechanical stress within a transducer device fabricated in that particular region is substantially uniform with the mechanical stress of another transducer device fabricated in that particular region.

17.-19. (canceled)

20. A method of fabricating a plurality of transducer devices on a semiconductor wafer, the method comprising: forming a bracing structure in the semiconductor wafer; wherein the bracing structure partitions the semiconductor wafer into a plurality of processing regions where transducer devices are fabricated in each of the plurality of regions; forming the plurality of transducer devices in the form of micro-electrical-mechanical system (MEMS) transducers comprising: a substrate; a back-volume formed in the substrate; and a membrane formed over the back-volume and on the substrate; wherein the back-volume comprises a first back-volume portion and a second back-volume portion, the first back-volume portion being separated from the second back-volume portion by a step in a sidewall of the back-volume; and wherein the bracing structure is formed from areas of the wafer where no transducer devices are fabricated within the wafer.

21.-56. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

[0035] FIG. 1a is a schematic view of a MEMS device;

[0036] FIG. 1b is a schematic view of the MEMS device of FIG. 1a from underneath;

[0037] FIG. 2a is a schematic view of another MEMS device;

[0038] FIG. 2b is a schematic view of the MEMS device of FIG. 2a from underneath;

[0039] FIG. 3a is a plan view of a wafer;

[0040] FIG. 3b is a side view of a wafer;

[0041] FIG. 3c is a side view through a portion of a wafer, illustrating an example of a transducer device fabricated therein;

[0042] FIG. 3d is a side view through a portion of a wafer, illustrating another example of a transducer device fabricated therein;

[0043] FIG. 4a illustrates an example of a wafer comprising a bracing structure according to an embodiment;

[0044] FIG. 4b illustrates another example of a wafer comprising a bracing structure according to an embodiment;

[0045] FIG. 5 illustrates another example of a wafer comprising a wafer bracing structure according to an embodiment;

[0046] FIG. 6 illustrates another example of a wafer comprising a wafer bracing structure according to an embodiment;

[0047] FIG. 7 illustrates another example of a wafer comprising a wafer bracing structure according to an embodiment;

[0048] FIG. 8 illustrates another example of a wafer comprising a wafer bracing structure according to an embodiment;

[0049] FIG. 9 illustrates another example of a wafer comprising a wafer bracing structure according to an embodiment;

[0050] FIG. 10 illustrates another example of a wafer comprising a wafer bracing structure according to an embodiment; and

[0051] FIG. 11 shows an example of a method according to an embodiment.

DETAILED DESCRIPTION

[0052] The embodiments below are described in relation to a wafer, for example a semiconductor wafer such as a silicon wafer, used in the fabrication of transducer devices, for example MEMS transducer devices comprising a substrate and a membrane. It will be appreciated, however, that the invention is equally applicable to fabrication of other forms of transducer or electronic devices, including MEMS transducer devices having different structures, or indeed any other form of device.

[0053] The embodiments described herein are related to a wafer and method of fabrication that reduce wafer process and/or stress variation due to its sag or flexibility. The embodiments herein have an advantage of, on the one hand reducing wafer sag, while on the other not affecting wafer yield significantly i.e. by sacrificing too many MEMS die as a result of allowing space on the wafer for a bracing structure(s).

[0054] As will be described in further detail below, the embodiments herein involve partitioning a wafer into regions, such that areas of the wafer act as a bracing structure to help provide more rigidity to the overall wafer and/or within a specific region(s) of the wafer, thereby reducing deformation, flexing or sagging during processing, handling, storage and transportation scenarios.

[0055] The partitioning of the wafer into regions provides a localised stiffening within the wafer, such that individual regions of the wafer have a higher rigidity (relative to the wafer as a whole) hence helping to stabilise the processing and intrinsic stress in the transducer devices being fabricated on the wafer, for example stabilising an intrinsic stress within a MEMS layer of a MEMS device.

[0056] Referring to FIG. 4a, according to an embodiment, there is provided a wafer for use in fabricating a plurality of individual transducer devices (not shown). The wafer comprises a bracing structure 101, 103 for partitioning the wafer into a plurality of regions 105. The wafer comprises a plurality of transducer devices (not shown) fabricated in one or more of the plurality of regions 105.

[0057] In one embodiment, since a plurality of transducer devices are fabricated only in one or more of the plurality of regions 105 that have been partitioned using the bracing structure, the bracing structure acts to provide support and rigidity to the wafer as a whole, and/or within each region on the wafer. In some embodiments, the bracing structure 101, 103 comprises regions of the wafer where no transducer devices are fabricated within the wafer. In some embodiments, the bracing structure 101, 103 comprises regions of the wafer where no bulk micromachining is performed within the wafer.

[0058] In other embodiments, the bracing structure 101, 103 comprises regions of the wafer where one or more transducer devices, or portions of one or more transducer devices, formed within, do not themselves have inherent thickness reducing structures (such as back volume portions 7a and 7b of FIG. 2a formed therein, for example using bulk micromachining or back etching techniques). In this manner, the rigidity of the wafer is improved by avoiding the placement of thickness reducing devices or regions within the areas forming the bracing structure, e.g. the non-bulk micromachined bracting structure.

[0059] The bracing structure may comprise one or more bracing rings 101.sub.1-101.sub.N.

[0060] For example, in the embodiment of FIG. 4a, the bracing structure comprises a bracing ring 101.sub.1 that abuts or is positioned adjacent to the perimeter of the wafer. In some embodiments the bracing ring 101.sub.1 is positioned adjacent to the perimeter of the wafer and within a predetermined distance of the perimeter. The radial thickness of the bracing ring 101.sub.1 can be selected according to a particular application. For example the radial thickness can be increased to provide more rigidity in the wafer if the transducer devices being fabricated on the wafer are ones with large etched areas themselves. In the embodiment of FIG. 4a the bracing structure further comprises radial bracing components 103.sub.1 to 103.sub.4, which may also be referred to as cross-beams. The radial bracing components 103.sub.1 to 103.sub.4 extend from a center portion 102 of the wafer to the perimeter of the wafer, and couple or interconnect with the bracing ring 101.sub.1. In this example the radial bracing components 103.sub.1 to 103.sub.4 are equally spaced in a circumferential direction around the wafer. Since there are four radial bracing components 103.sub.1 to 103.sub.4 in this example, they are therefore spaced at 90 degrees apart. In other non-illustrated examples, three radial bracing components could be employed and could be spaced 120 degrees apart or five radial bracing components could be employed and could be spaced 72 degrees apart, and so on and so forth.

[0061] It is noted that the bracing structure may comprise any number of bracing rings 101.sub.1 to 101.sub.N and any number of radial bracing components 103.sub.1 to 103.sub.M. In addition, although the example of FIG. 4a has the radial bracing components equally spaced, they can be arranged differently depending on a particular application, for example what type of fabrication process or handling is involved, or what type of transducer devices are being fabricated.

[0062] Therefore, according to some embodiments, in their broadest sense the bracing structure comprises one or more bracing rings 101.sub.1-101.sub.N and/or at least one radial bracing component 103.sub.1 to 103.sub.M configured to extend in a radial direction from a center portion of the wafer towards the perimeter of the wafer.

[0063] The center portion 102 may interconnect with the at least one radial bracing component 103.sub.1 to 103.sub.M.

[0064] The bracing structure of FIG. 4a partitions the wafer into a plurality of regions 105.sub.1 to 105.sub.4 where transducer devices are fabricated. Put another way, the layout of where the transducer devices are fabricated in a plurality of regions 105.sub.1 to 105.sub.4 define the shape of the bracing structure 101, 103.

[0065] FIG. 4b shows an example of a similar embodiment, illustrating how the plurality of transducer devices may be fabricated within the at least one region 105.sub.1 to 105.sub.4. It is noted that each region 105.sub.1 to 105.sub.4 may comprise thousands of such transducer devices, whereas only a limited number are shown in enlarged format for clarity and illustrative purposes.

[0066] In some embodiment, dummy transducer devices may be fabricated in areas corresponding to where the bracing structure exists, and/or within a predetermined threshold distance within the border of a particular partitioned region. The dummy transducer devices may comprise transducer devices which are fabricated in a similar manner to other transducer devices on the wafer, but whereby the dummy transducer devices do not have any through hole etch, for example no bulk micromachining. As such, the areas corresponding to the bracing structure, and/or within a predetermined threshold distance within the border of a particular partitioned region, are areas of solid unperforated wafer.

[0067] FIG. 5 shows an example of another embodiment. The embodiment of FIG. 5 comprises a plurality of concentric bracing rings 101.sub.1-101.sub.N, and in particular three concentric bracing rings 101.sub.1-101.sub.3 in this example. The plurality of concentric bracing rings 101.sub.1-101.sub.N may be of substantially the same radial thickness. In other examples, one or more of the plurality of concentric bracing rings 101.sub.1-101.sub.N may have a different radial thickness to the other concentric bracing rings. In the example of FIG. 5 the concentric bracing ring 101.sub.1 that abuts the perimeter of the wafer has a thicker radial thickness that the inner concentric bracing rings 101.sub.2 and 101.sub.3.

[0068] In some examples the one or more concentric bracing rings 101.sub.1-101.sub.N are evenly spaced between the center and the perimeter of the wafer. In other examples, the spacing of the concentric bracing rings can be distributed non-evenly, for example whereby the concentric bracing rings are configured to be more closely spaced to each other the closer the concentric bracing rings are to the perimeter of the wafer.

[0069] The one or more concentric bracing rings 101.sub.1-101.sub.N form concentric bands (105.sub.X1, 105.sub.X2 and 105.sub.X3 in this example) between each pair of concentric bracing rings, where transducer devices are fabricated.

[0070] The bracing structure of the embodiment of FIG. 5 further comprises radial bracing components 103.sub.1 to 103.sub.4 configured to extend in a radial direction from the center portion 102 of the wafer towards the perimeter of the wafer. In this embodiment the radial bracing components 103.sub.1 to 103.sub.4 extend from the center portion 102 of the wafer to the perimeter of the wafer, through each of the concentric bracing rings 101.sub.1 to 101.sub.3, thereby interconnecting the bracing rings 101.sub.1 to 101.sub.3.

[0071] In the embodiment of FIG. 5 the four radial bracing components 103.sub.1 to 103.sub.4 are equally spaced in a circumferential direction around the wafer. Furthermore, each radial bracing component 103.sub.1 to 103.sub.4 extends from the center of the wafer to the perimeter of the wafer, interconnecting each of the concentric bracing rings 101.sub.1 to 101.sub.3.

[0072] The bracing structure therefore partitions the wafer into a plurality of regions 105 where transducer devices are fabricated. For example, in the bottom right quadrant of FIG. 5, the wafer is partitioned into regions 105.sub.11, 105.sub.12, 105.sub.13. As noted earlier, the bracing structure may comprise any number of concentric bracing rings 101, and/or any number of radial bracing components 103.

[0073] FIG. 6 shows an example of another embodiment. In a similar manner to FIG. 5, the embodiment of FIG. 6 comprises a plurality of concentric bracing rings 101.sub.1 to 101.sub.3. As with FIG. 5, in this example the concentric bracing ring 101.sub.1 that abuts the perimeter of the wafer has a thicker radial thickness than the inner concentric bracing rings 101.sub.2 and 101.sub.3. It is noted, however, that the plurality of concentric bracing rings 101.sub.1-101.sub.3 may be of substantially the same radial thickness, or have other combinations of thicknesses. As with FIG. 5, the one or more concentric bracing rings 101.sub.1-101.sub.3 may be evenly spaced between the center and the perimeter of the wafer, or distributed in a non-even manner.

[0074] The bracing structure of the embodiment of FIG. 6 further comprises a plurality of radial bracing components 103 configured to extend in a radial direction from the center of the wafer towards the perimeter of the wafer. However, in this embodiment the radial bracing components 103 extend from the center portion 102 of the wafer to the perimeter of the wafer, such that a first of the plurality of radial bracing components, e.g. 103.sub.1, extends in a direction from the center portion 102 of the wafer to the perimeter of the wafer, interconnecting a first set of concentric bracing rings, e.g. interconnecting concentric bracing rings 101.sub.1 and 101.sub.2 in this example, while a second of the plurality of radial bracing components, e.g. 103.sub.2, extends in a direction from the center portion 102 of the wafer to the perimeter of the wafer, interconnecting a second set of concentric bracing rings, e.g. interconnecting concentric bracing rings 101.sub.2 and 101.sub.3 in this example.

[0075] In one example, the first and second radial bracing components referred to above are adjacent bracing components. The embodiment of FIG. 6 provides such radial bracing components in an alternating manner around the wafer. For example, the first and second radial bracing components may be interleaved in a circumferential direction.

[0076] In some examples, interconnections between the first set of concentric bracing rings are interleaved in a circumferential direction with interconnections between the second set of concentric bracing rings.

[0077] In the embodiment of FIG. 6 each of the radial bracing components 103 also connects the center portion 102 of the wafer to the inner concentric bracing ring 101.sub.3. It is noted that other variations may be provided.

[0078] Therefore, as with FIG. 5, the bracing structure partitions the wafer into a plurality of regions 105 where transducer devices are fabricated (only one region 105 labelled for clarity in FIG. 6).

[0079] In the embodiments of FIGS. 5 and 6, it is noted that the bracing structure comprises a central portion 102, for example a circular portion.

[0080] It should be appreciated that the number of radial bracing components between concentric bracing rings may differ.

[0081] For example, referring to the embodiment of FIG. 7, between the central portion 102 of the wafer and the innermost concentric bracing ring 101.sub.3 there are three radial bracing components, between the innermost bracing ring 101.sub.3 and the next outer concentric bracing ring 101.sub.2 there are four radial bracing components, and between the outermost bracing ring 101.sub.1 of the wafer and the next inner concentric bracing ring 101.sub.2 there are five radial bracing components. This embodiment illustrates that the inner regions of the wafer are inherently more rigid than the outer regions, and as such the number of radial bracing components and their respective thicknesses can be reduced towards the center of the wafer compared to the outer part of the wafer. An outer band of the wafer may comprise more radial bracing components compared to an inner band of the wafer, in order to reduce the respective areas of each region within the outer band, for example such that they correspond to the areas of each region within an inner band.

[0082] FIG. 8 shows an example of an embodiment comprising only bracing rings 101.sub.1 to 101.sub.3 and a central portion 102.

[0083] FIG. 9 shows an arrangement according to another embodiment. In this embodiment the bracing structure comprises a plurality of rectangular bracing elements 107 distributed within the perimeter of the wafer, wherein each rectangular bracing element 107 defines a region where transducer devices are fabricated. The example of FIG. 9 also comprises a bracing ring 101.sub.1 around the periphery of the wafer. Other shapes may be used, for example a plurality of square bracing elements distributed within the perimeter of the wafer, each square bracing element defining a region within which transducer devices are fabricated.

[0084] FIG. 10 shows an example in which the bracing structure comprises a honeycomb structure, for example a plurality of hexagonal bracing elements 108 distributed within the perimeter of the wafer, each hexagonal bracing element 108 defining a region within which a plurality of transducer devices may be fabricated.

[0085] In the embodiments described herein, within a particular region defined by the bracing structure a mechanical stress within a transducer device fabricated in that particular region may be substantially uniform with the mechanical stress of another transducer device fabricated in that particular region.

[0086] In another embodiment there is provided a wafer for fabricating a plurality of individual transducer devices. The wafer comprises a plurality of processing regions where a plurality of transducer devices are fabricated. The plurality of processing regions are separated by a bracing structure for providing rigidity to the wafer subsequent to fabrication of the plurality of transducer devices.

[0087] In the embodiments described herein, it is noted that a wafer may comprise, for example, a silicon wafer.

[0088] Referring to FIG. 11, according to another aspect there is provided a method of fabricating a plurality of transducer devices on a semiconductor wafer, for example a silicon wafer.

[0089] The method comprises forming a bracing structure in the semiconductor wafer, step 901, wherein the bracing structure partitions the wafer into a plurality of processing regions where transducer devices are fabricated. The method may comprise fabricating a plurality of transducer devices within one or more of the regions defined by the bracing structure.

[0090] The step of forming the bracing structure may comprises forming one or more concentric bracing rings 101.sub.1-101.sub.N.

[0091] The step of forming one or more concentric bracing rings may comprise forming one or more concentric bracing rings 101.sub.1-101.sub.N that are of substantially the same radial thickness.

[0092] In some examples, the step of forming the one or more concentric bracing rings comprises forming one of the concentric bracing rings 101.sub.1 to abut a perimeter of the wafer, or be formed within a predetermined distance of the perimeter of the wafer.

[0093] In some examples, the step of forming the one or more concentric bracing rings comprises forming the one or more concentric bracing rings 101.sub.1 to 101.sub.N such that they are evenly spaced between the center and the perimeter of the wafer, or more closely spaced to each other the closer the concentric bracing rings are to the perimeter of the wafer.

[0094] Forming the one or more concentric bracing rings may comprise forming transducer devices within concentric bands, wherein the concentric bands define the one or more concentric bracing rings 101.sub.1 to 101.sub.N.

[0095] The step of forming the bracing structure may comprise forming at least one radial bracing component 103.sub.1 to 103.sub.M to extend in a radial direction from the center of the wafer towards the perimeter of the wafer. For example, the step of forming the at least one radial bracing component may comprise forming at least one radial bracing component 103.sub.1 to 103.sub.M to extend from a center portion of the wafer to the perimeter of the wafer, through at least one of the one or more concentric bracing rings 101.sub.1-101.sub.N. In such a method the at least one bracing component 103 acts to interconnect at least a first and second concentric bracing ring.

[0096] In another example, the step of forming the at least one radial bracing component comprises forming at least one radial bracing component 103.sub.1 to 103.sub.M to extend from a center portion of the wafer to the perimeter of the wafer, through each of the one or more concentric bracing rings 101.sub.1-101.sub.N. In such a method the at least one bracing component 103 acts to interconnect all of the concentric bracing rings.

[0097] In some examples the method comprises forming two or more radial bracing components, wherein the two or more radial bracing components are equally spaced in a circumferential direction around the wafer.

[0098] In one example, forming the at least one radial bracing component comprises forming four radial bracing components 103.sub.1 to 103.sub.4 such that the four radial bracing components are equally spaced in a circumferential direction around the wafer, and such that each radial bracing ring component 103.sub.1 to 103.sub.4 extends from the center of the wafer to the perimeter of the wafer, through each of the one or more concentric bracing rings 101.sub.1-101.sub.N.

[0099] In another example, forming the at least one radial bracing component comprises forming a plurality of radial bracing components 103.sub.1 to 103.sub.M such that the plurality of radial bracing components are equally spaced in a circumferential direction around the wafer, and a first of the plurality of radial bracing components (103.sub.1 to 103.sub.M) extends in a direction from the center of the wafer to the perimeter of the wafer, interconnecting a first set of concentric bracing rings 101.sub.1-101.sub.N, and a second of the plurality of radial bracing components 103.sub.1 to 103.sub.M extends in a direction from the center of the wafer to the perimeter of the wafer, interconnecting a second set of concentric bracing rings 101.sub.1-101.sub.N.

[0100] The first and second radial bracing components may be formed as adjacent bracing components.

[0101] The method may comprise forming the bracing structure such that interconnections between a first set of concentric bracing rings are interleaved in a radial direction with interconnections between a second set of concentric bracing rings.

[0102] In another embodiment, the step of forming the bracing structure comprises forming a plurality of rectangular bracing elements distributed within the perimeter of the wafer such that each rectangular bracing element defines a region, or forming a plurality of square bracing elements distributed within the perimeter of the wafer such that each square bracing element defines a region, or forming a plurality of hexagonal bracing elements distributed within the perimeter of the wafer such that each hexagonal bracing element defines a region.

[0103] In the embodiments of the method described herein, within a particular region defined by the bracing structure, a mechanical stress within a transducer device fabricated in that particular region is substantially uniform to the mechanical stress of another transducer device fabricated in that particular region.

[0104] In some examples the step of forming a bracing structure may comprise fabricating transducer devices in certain areas of the wafer, such that the bracing structure becomes defined in areas of the wafer where no transducer devices are fabricated. In other examples, the bracing structure comprises regions of the wafer where one or more transducer devices, or portions of one or more transducer devices, formed within, do not themselves have inherent thickness reducing structures.

[0105] In some embodiments the step of forming the bracing structure may comprise using an etching mask to protect the regions where the bracing structure is to be formed. For example, the etching mask may comprise an etching mask used to etch through holes in the plurality of transducer devices.

[0106] According to another embodiment, there is a method of fabricating a plurality of transducer devices on a semiconductor wafer, for example a silicon wafer. The method comprises fabricating the transducer devices within the wafer such that they form a plurality of regions where no transducer devices are fabricated, wherein the plurality of regions form a bracing structure for providing rigidity to the wafer subsequent to fabrication of the transducer devices.

[0107] According to another embodiment, there is provided a method of fabricating a plurality of transducer devices on a wafer. The method comprises partitioning the wafer into a plurality of processing regions where the transducer devices are to be fabricated, wherein the plurality of processing regions are separated by a bracing structure for providing rigidity to the wafer subsequent to fabrication of the transducer devices.

[0108] The wafer and method described above may be used to fabricate any form of transducer device. In some embodiments, the transducer devices fabricated in the wafer are MEMS transducers, for example MEMS microphones, whereby part of the MEMS microphone is etched away to provide a back volume.

[0109] For example, a transducer device fabricated in a wafer according to the embodiments described herein may comprise a micro-electrical-mechanical system (MEMS) transducer comprising: a substrate; a back-volume formed in the substrate; and a membrane formed over the back-volume and on the substrate; wherein the back-volume comprises a first back-volume portion and a second back-volume portion, the first back-volume portion being separated from the second back-volume portion by a step in a sidewall of the back-volume.

[0110] In one example the step in the sidewall may comprise substantially a right angle. In another example the step in the sidewall may comprise a discontinuity in the cross-sectional area of the back volume in a plane parallel to the substrate. In another example the step in the sidewall may comprise a discontinuity in a rate of change of cross-sectional area of the back volume in a plane parallel to the substrate with distance from the membrane. In some examples the step in the sidewall is curved. In some examples the step in the sidewall comprises a change in the gradient of the sidewall. In some examples, the step in the sidewall comprises two or more changes in the gradient of the sidewall.

[0111] The first back-volume portion may have a cross-sectional area that is smaller than the cross-sectional area of the membrane in a plane where the first back-volume portion and the membrane meet. The cross-sectional area of the second back-volume portion may be greater than the cross-sectional area of the membrane.

[0112] In some embodiments the first back-volume portion comprises substantially vertical walls or, alternatively, sloped walls. In some embodiments the second back-volume portion comprises substantially vertical walls or, alternatively, sloped walls.

[0113] In some embodiments the back-volume further comprises a third back-volume portion.

[0114] According to another embodiment, there is provided a semiconductor wafer comprising a bracing structure for partitioning the wafer into a plurality of regions, and a plurality of MEMS microphones fabricated in one or more of the plurality of regions. At least some of the plurality of MEMS microphones comprise a back-volume that comprises a first back-volume portion and a second back-volume portion, the first back-volume portion being separated from the second back-volume portion by a discontinuity in a sidewall of the back-volume.

[0115] The bracing structure may comprise a plurality of MEMS microphones that comprise no back-volume portion.

[0116] According to another embodiment there is provided a semiconductor wafer comprising a bracing structure for partitioning the wafer into a plurality of regions, and a plurality of MEMS microphones fabricated in one or more of the plurality of regions. At least some of the plurality of MEMS microphones comprise a back-volume that comprises a single back-volume portion.

[0117] The bracing structure may comprise a plurality of MEMS microphones that comprise no back-volume portion.

[0118] The bracing structures described herein are particularly advantageous for providing rigidity in a wafer when manufacturing transducer devices such as the MEMS transducers described above, for example rigidity within each particular region of the wafer.

[0119] Controlling the wafer stiffness via the bracing structures described herein has the advantage of allowing for higher and more stable production yield.

[0120] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word comprising does not exclude the presence of elements or steps other than those listed in a claim, a or an does not exclude a plurality, and a single feature or other unit may fulfil the functions of several units recited in the claims. Any reference signs in the claims shall not be construed so as to limit their scope.