Abstract:
MEMS devices ( 40 ) using etched cavities ( 42 ) are desirably formed using multiple etching steps. Preliminary cavities ( 20 ) formed by locally anisotropic etching to nearly the final depth have irregular ( 46 ) sidewalls ( 44 ) and steep and/or inconsistent sidewall ( 44 ) to bottom ( 54 ) intersection angles ( 48 ). This leads to less than desired cavity diaphragm ( 26 ) burst strengths. Final cavities ( 42 ) with smooth sidewalls ( 50 ), smaller and consistent sidewall ( 50 ) to bottom ( 54 ) intersection angles ( 58 ), and having more than doubled cavity diaphragm ( 26 ) burst strengths are obtained by treating the preliminary cavities ( 20 ) with TMAH etchant, preferably relatively dilute TMAH etchant. In a preferred embodiment, a cleaning step is performed between the etching step and the TMAH treatment step to remove any anisotropic etching by-products present on the preliminary cavities&#39; ( 20 ) initial sidewalls ( 44 ). The multi-step cavity etching procedure is especially useful for forming robust MEMS pressure sensors, but is applicable to any type of MEMS device.

Description:
FIELD OF THE INVENTION 
     Embodiments of this invention relate generally to arrangements and methods for etching cavities in substrates, especially semiconductor substrates, and devices embodying etched cavities. 
     BACKGROUND OF THE INVENTION 
     There is a need in the electronic arts, especially semiconductor arts, to etch cavities of various depths into substrates. Etched cavities are often used to provide thin diaphragms in connection with micro-electro-mechanical system (“MEMS”) elements. For example and not intended to be limiting, by placing a deflection sensor on such a thin diaphragm, a pressure sensor MEMS element can be created. It is common to have other electronic and/or optical devices, integrated circuits (ICs), and various other sensors or actuators associated with MEMS elements. As used herein, the terms “MEMS”, “MEMS element” and “MEMS device” are intended to include such other devices, ICs, sensors and actuators. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying figures in the drawings in which like numerals denote like or analogous elements, and wherein: 
         FIG. 1  is a simplified cross-sectional conceptual view of a pressure sensor MEMS device employing an etched cavity; 
         FIGS. 2-4  are simplified cross-sectional views of an etched cavity MEMS device analogous to that of  FIG. 1 , during various stages of manufacture, illustrating various difficulties than can arise and how they can be minimized or avoided according to an embodiment of the invention; and 
         FIGS. 5-6  are simplified block diagrams of methods of producing MEMS devices employing etched cavities, according to further embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description. 
     For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawings figures are not necessarily drawn to scale. For example, the dimensions of some of the elements or regions in the figures may be exaggerated relative to other elements or regions to help improve understanding of embodiments of the invention. 
     The terms “first,” “second,” “third,” “fourth” and the like in the description and the claims, if any, may be used for distinguishing between somewhat similar elements and not necessarily for describing a particular spatial arrangement or sequence or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation or construction in sequences, orientations and arrangements other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have” and any variations thereof, are intended to cover non-exclusive inclusions, such that a process, method, article, or apparatus that comprises a list of elements or steps is not necessarily limited to those elements or steps, but may include other elements or steps not expressly listed or inherent to such process, method, article, or apparatus. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. As used herein the terms “substantial” and “substantially” mean sufficient to accomplish the stated purpose in a practical manner and that minor imperfections, if any, are not significant for the stated purpose. 
     As used herein, the terms “semiconductor” and the abbreviation “SC” are intended to include any semiconductor whether single crystal, poly-crystalline or amorphous and to include type IV semiconductors, non-type IV semiconductors, compound semiconductors as well as organic and inorganic semiconductors. Further, the terms “substrate” and “substrate wafer” are intended to include single crystal structures, polycrystalline structures, amorphous structures, thin film structures, layered structures as for example and not intended to be limiting, combinations of dielectric and SC layers or materials including but not limited to semiconductor-on-insulator (SOI) structures, and combinations thereof. For convenience of explanation and not intended to be limiting, electronic structures and methods of fabrication are described herein for substrates employing silicon, but persons of skill in the art will understand that other semiconductors and composite materials may also be used. 
     In the electronic arts, cavities are etched into substrates for a variety of purposes. For example and not intended to be limiting, various MEMS devices can be formed by etching cavities in substrates, often semiconductor wafers. The cavity is typically etched from a first surface part way through the substrate, leaving a comparatively thin diaphragm of the substrate material proximate an opposed second surface. By placing sensors or actuators on or near such diaphragm a wide variety of MEMS devices can be created. For example, if such diaphragm is exposed to pressure or other force, it can deflect and such deflection measured, thereby providing a force or pressure sensing MEMS element. If such diaphragm is exposed to fluid, it is more sensitive to heat transfer and can be used to form a fluid flow sensor or temperature sensor. If such diaphragm is coupled to an actuator, it can be used to form a variety of useful devices such as flexible mirrors, etc. These are non-limiting examples of the wide variety of useful MEMS devices that can be formed using etched cavities. For convenience of explanation, the etching of cavities associated with the manufacture of MEMS devices is described herein, by way of example, for the case of a simple pressure sensor. However, persons of skill in the art will understand that the various embodiments illustrated herein apply generally to all types of MEMS elements and other structures employing etched cavities and are not limited merely to pressure sensors. 
       FIG. 1  is a simplified cross-sectional conceptual view of pressure sensor MEMS device  19  employing etched cavity  20 . MEMS device  19  is formed in substrate  21 . Substrate  21  comprises in this example, semiconductor (e.g., silicon) body  22  having lower surface  23  and upper surface  27 . Dielectric layer  28  (e.g., silicon oxide) of thickness  281  is formed on upper surface  27 . Overlying dielectric layer  28  is layer  30  (e.g., silicon or silicon-germanium or other semiconductor or resistive or piezo-resistive material) of thickness  301  having upper surface  31 . Layers  28 ,  30  form composite layer  33  having thickness  331  of which central portion  26  above cavity  20  acts as the diaphragm of MEMS device  19 . For convenience of description, central portion  26  of composite layer  33  is also referred to as diaphragm  26 . Overlying layer  30  is dielectric layer  32  (e.g., silicon oxide). Also overlying layer  30  of diaphragm  26  are, in this example, metal contacts  34  and dielectric passivation layer  36 . 
     As pressure or force  37  is applied to diaphragm  26 , the deflection of diaphragm  26  causes, for example, resistance  41  of the central portion of layer  30  of diaphragm  26  to change. This change can be detected via metal contacts  34 . This is intended merely as an example of device  39  located within, on, over, or a combination thereof of central part  43  of diaphragm  26  proximate surface  31 , that can be used to detect deflection of diaphragm  26 . In various other embodiments, other types of device  39  may be used. Thus, device  39  may be more generally referred to as micro-electro-mechanical system (MEMS) element  39 , where MEMS element  39  may be any type of electronic or electro-mechanical or electro-optical device proximate location  43  that interacts with diaphragm  26 . Non-limiting examples are mass, force, pressure, flow, temperature, optical, electrical and magnetic sensors and actuators, and references to MEMS element  39  is intended to include these and other physical phenomena and functions. References to MEMS device  19  and references to later described MEMS device  40  are intended to include such other functions as well as the pressure sensor function illustrated herein. 
     It has been found that the robustness of MEMS device  19  and the manufacturing yield associated with MEMS device  19  depend significantly on the properties of cavity  20  and the process used in its formation.  FIGS. 2-3  are simplified cross-sectional views of etched cavity MEMS device  19 ,  40  analogous to MEMS device  19  of  FIG. 1 , during stages  202 - 203  of manufacture, illustrating various cavity etching related difficulties than can arise and how they can be minimized or avoided, according to embodiments of the invention.  FIG. 4  showing further manufacturing stage  204  beyond stage  203  of  FIG. 3  and applies to improved MEMS device  40 , according to an embodiment of the present invention. Where appropriate, the same reference numbers are used in  FIGS. 2-4  as in  FIG. 1  to identify analogous elements, and the descriptions of such analogous elements in connection with  FIG. 1  are incorporated herein by reference. 
     Referring now to manufacturing stage  202  of  FIG. 2 , substrate  21  is provided, comprising body  22  and layers  28  and  30 . Overlying substrate  21  are layers or contacts  32 ,  34 ,  36 , preferably with MEMS sensor element  39  already included. Dielectric layer  28  is desirable but not essential. For convenience of description, it is assumed hereafter that sensor element  39  (including layers, contacts and/or regions  32 ,  34 ,  36 ) has already been formed, but this is not essential and sensor element  39  and the various layers and contacts associated therewith may be provided later in the manufacturing process, even after formation of cavity  42  of  FIG. 4 . In manufacturing stage  202 , sacrificial protection layer  38  is desirably provided over MEMS element  39 , and mask layer  25  is provided on lower surface  23  of body  22 . The purpose of layer  38  is to protect MEMS element  39  (and preferably also surrounding areas) during etching of cavity  20 ,  42  of  FIGS. 3-4  analogous to cavity  20  of  FIG. 1 . Phosphorous doped silicate glass (PSG), boron doped silicate glass (BSG), and other dielectric materials having etch rates larger than thermal silicon oxide are examples of suitable materials for sacrificial protection layer  38  and mask layer  25 , but other materials of equivalent etch resistance can also be used. Mask layer  25  has opening  29  formed therein defining the desired location of cavity  20 ,  42  of  FIGS. 3-4 . Because of the nature of etchants used to form cavity  20 ,  42  of  FIGS. 3-4 , mask layer  25  is preferably a hard mask. Structure  302  results from manufacturing stage  202 . 
     Referring now to manufacturing stage  203  of  FIG. 3 , structure  302  is preferably subjected to localized anisotropic etching to form preliminary cavity  20  having preliminary sidewalls  44  extending substantially through body  22 , desirably but not essentially, to dielectric layer  28  when present. Any type of anisotropic etching may be used, varying according to the material of body  22  and the arrangement used for laterally localizing the etching. Reactive ion etching (RIE), particularly relatively high rate deep reactive ion etching (DRIE), is preferred, but other etching means may also be used. The Pegasus Chamber manufactured by SPP Process Technology Systems, Ltd of San Jose, Calif., USA and Newport NP182TA, UK is a non-limiting example of a suitable RIE chamber and reagents for anisotropic etching of semiconductors such as silicon (as well as other materials) are well known in the art. Structure  303  results from manufacturing stage  203 . One of the consequences of such etching is that preliminary sidewalls  44  of preliminary cavity  20  often exhibit significant irregularities  46  and intersect bottom  54  of cavity  20  at comparatively steep and sometimes uncertain angle  48 . A problem encountered with MEMS devices  19  formed in this fashion, is that the burst or fracture strength of diaphragm  26  of such MEMS devices when used, for example, as pressure or force sensors or in actuators is often less than desired, as is explained more fully later. 
     Referring now to manufacturing stage  204  of  FIG. 4 , structure  303  containing preliminary cavity  20  with preliminary sidewalls  44  is subjected to further etching using tetra-methyl-ammonium hydroxide (TMAH). TMAH concentrations in the range of about 1 to 40 weight percent TMAH in water are useful, concentrations in the range of about 2 to 10 weight percent TMAH in water are convenient, and concentrations in the range of about 2 to 3 weight percent TMAH in water are preferred. TMAH is available from Air Products and Chemicals, Inc., Allentown, Pa., USA and other suppliers. While it is known to etch semiconductors (e.g., silicon) using TMAH, it has typically been used as an anisotropic (e.g., substantially vertical) etch. Its usefulness to smooth out the irregularities caused by RIE and other anisotropic etching, and to provide improved cavity sidewall to bottom intersection angles, has not previously been recognized. 
     It has been found that TMAH etching of anisotropically etched preliminary cavity  20  substantially mitigates or removes irregularities  46  on preliminary sidewalls  44  of cavity  20  of  FIG. 3 , thereby providing substantially smoother final sidewalls  50  of final cavity  42  of  FIG. 4 . It has been further found that TMAH etching also provides more gradual and consistent sidewall transition portion  52  between near vertical final sidewalls  50  and approximately horizontal bottom  54  of cavity  42 , e.g. at dielectric layer  28 . Somewhat similar sidewall transition  56  is also found at the top of cavity  42  where it meets surface  23  of body  22 . Angle  58  is usefully in the range of about 20 to less than 90 degrees, more conveniently in the range of about 40 to 70 degrees and preferably in the range of about 50 to 60 degrees. Where body  22  is [100] oriented single crystal silicon, angle  58  is typically 54.74 degrees, but other values for angle  58  generally in the ranges noted above are also useful. Such angles and the manufacturing consistency of such angles are favorable for reducing stress concentration in diaphragm  26  of MEMS device  40  around perimeter  59  of final cavity  42 . Perimeter  59  is where sidewall portion  52  of body  22  at the periphery of cavity  42  meets cavity bottom or floor  54 . This further capability of TMAH cavity etching has not previously been recognized. Structure  304  results from manufacturing stage  204 . Layers  38  and  25  may be removed or left in place for subsequent manufacturing operations as needed. 
     As a consequence of the changes in the properties of cavity  42  obtained by using the TMAH etch following the anisotropic etch, the burst strength of MEMS device  40  is much improved compared to the burst strength of MEMS device  19  that has not received the TMAH etch. Experimental comparisons are provided in Table I below. In these tests, the higher pressure was applied to the cavity side of diaphragm  26 . 
                                                           TABLE I                   BURST PRESSURE FOR DIFFERENT       CAVITY ETCH PROCEDURES                ETCH PROCESS USED                RIE ETCH   RIE + TMAH           ONLY   ETCH                        MINIMUM DIFFERENTIAL BURST   ~180   ~650       PRESSURE (kPa)       MAXIMUM DIFFERENTIAL   ~315   ~900       BURST PRESSURE (kPa)                    
It will be apparent that the combination of anisotropic cavity etch followed by TMAH cavity etch improves the minimum burst pressure differential by ˜260 percent and improves the maximum burst pressure differential by ˜186 percent. This is a significant advance in the art.
 
     In order to obtain maximum benefit from the TMAH etch, it is desirable to insert between the anisotropic etch and the TMAH etch a surface cleaning step to remove any residual contamination, e.g., surface oxides that may be present on preliminary sidewalls  44  of preliminary cavity  20  after RIE etching. Hydrofluoric acid (HF) is a useful cleaning agent. Concentration ratios of water to hydrofluoric acid (H 2 O:HF) by volume in the range of about H 2 O:HF=500:1 to H 2 O:HF=25:1 are useful, concentration ratios of about H 2 O:HF=200:1 to H 2 O:HF=50:1 are convenient and concentration ratios of about H 2 O:HF=125:1 to H 2 O:HF=75:1 are preferred. Room temperature cleaning times in the range of about 10 to 100 seconds are useful, cleaning times in the range of about 20 to 50 seconds are convenient and cleaning times in the range of about 30 to 40 seconds are preferred. In general, for such cavity surface cleaning step, the combination of etchant concentration and etch or cleaning time should be chosen so that, if present, dielectric layer  28  exposed on cavity bottom  54  is not significantly affected. 
       FIGS. 5 and 6  are simplified block diagrams of methods  500  and  600 , respectively, of producing a MEMS device  40  comprising cavity  42  by etching substrate  21 , according to further embodiments of the invention. Referring now to  FIG. 5 , method  500  begins with START  501  and initial step  502  wherein there is provided a substrate ( 21 ) having first ( 31 ) and second ( 23 ) principal surfaces with a desired MEMS element ( 39 ) location ( 43 ) proximate the first surface ( 31 ). The MEMS element ( 39 ) may have been provided prior to of during manufacturing stage  502  or may be provided after manufacturing stage  502 . Either arrangement is useful. In step  504 , a preliminary cavity ( 20 ) is locally anisotropically etched in the substrate ( 21 ) extending toward the first surface ( 31 ) and underlying the desired MEMS element ( 39 ) location ( 43 ). In one embodiment according to path  505 - 1 , method  500  proceeds to step  508  wherein the preliminary cavity ( 20 ) is exposed to TMAH etchant (e.g., as described above), and then to END  510 . In another embodiment according to path  505 - 2 , method  500  proceeds from step  504  to step  506  wherein the preliminary cavity ( 20 ) is cleaned of anisotropic cavity etching byproducts and then along path  507  to step  508  and then to END  510 . Either arrangement is useful. As has been previously explained, the exposure of preliminary cavity  20  to TMAH in step  508  reduces irregularities  46  on preliminary sidewalls  44  thereby providing smoother final sidewalls  50 . This TMAH exposure also decrease intersection angle  58  between bottom  54  of final cavity  42  and final sidewalls  50 ,  52 , e.g. compared to angle  48  between preliminary sidewalls  44  and cavity bottom  54 . This is very useful. 
     Referring now to  FIG. 6 , method  600  begins with START  601  and initial step  602  wherein there is provided a substrate ( 21 ) having first ( 31 ) and second ( 23 ) principal surfaces with a desired MEMS element ( 39 ) location ( 43 ) proximate the first surface ( 31 ). The MEMS element ( 39 ) may have been provided prior to manufacturing stage  602  or may be provided after manufacturing stage  602 . Either arrangement is useful. If the MEMS element ( 39 ) is already present, then according to a further embodiment via path  603 - 1 , method  600  proceeds to step  604  wherein such MEMS element ( 39 ) is protected from etching, and then via path  605  to step  606  described hereafter. If the MEMS element ( 39 ) is not already present, then according to a still further embodiment, method  600  proceeds via path  603 - 2  to step  606  wherein there is provided a mask layer ( 25 ) on the second surface ( 23 ) having therein an etch window ( 29 ) opposite the desired MEMS element location ( 43 ). Method  600  then proceeds from step  606  to step  608  wherein a preliminary cavity ( 20 ) extending toward the first surface ( 31 ) is anisotropically etched through the mask window ( 29 ). According to a yet further embodiment, method  600  proceeds via path  609 - 1  from step  608  to step  612  wherein the preliminary cavity ( 20 ) is exposed to TMAH etchant (e.g., as has already been described). According to a still yet further embodiment, method  600  proceeds via path  609 - 2  from step  608  to step  610  wherein the preliminary cavity ( 20 ) is cleaned of anisotropic etching byproducts, and then via path  611  to step  612  already described. If the MEMS element ( 39 ) is already present, then according to path  613 - 1  method  600  proceeds from step  612  to END  616 . If the MEMS element ( 39 ) is not already present, then in step  614  the MEMS element ( 39 ) can be provided and method  600  then proceeds to END  616 . Either arrangement is useful. Step  614  may be carried out at any time during method  600  between START  601  and END  616 . As has been previously explained, the exposure of preliminary cavity  20  to TMAH in step  612  reduces irregularities  46  on preliminary sidewalls  44  thereby providing smoother final sidewalls  50 . This TMAH exposure also decreases intersection angle  58  between bottom  54  of final cavity  42  and final sidewalls  50 ,  52 , e.g. compared to angle  48  between preliminary sidewalls  44  and cavity bottom  54 . This is very useful. 
     According to a first embodiment, there is provided a method ( 500 ,  600 ) for producing a MEMS device ( 40 ) comprising, for a substrate ( 21 ) having first ( 31 ) and second ( 23 ) principal surfaces with a desired MEMS element ( 39 ) location ( 43 ) proximate the first ( 31 ) surface, locally anisotropically etching in the substrate ( 21 ) a preliminary cavity ( 20 ) extending toward the first surface ( 31 ) and underlying the desired MEMS element ( 39 ) location ( 43 ), and exposing the preliminary cavity ( 20 ) to tetra-methyl-ammonium hydroxide (TMAH) etchant. According to a further embodiment, the method further comprises prior to the etching step, providing a protective layer ( 38 ) over at least the MEMS element ( 39 ) location ( 43 ). According to a still further embodiment, the method further comprises prior to the etching step, providing a mask layer ( 25 ) having an etch window ( 29 ) therein on the second surface ( 23 ) opposite the desired MEMS element ( 39 ) location ( 43 ), and thereafter performing the etching step through the etch window ( 29 ). According to a yet further embodiment, the etching step comprises reactive ion etching. According to a still yet further embodiment, the method further comprises prior to the exposing step, cleaning the preliminary cavity ( 20 ) of anisotropic cavity etching byproducts. According to a yet still further embodiment, following the exposing step, a subsequent cavity ( 42 ) is formed having a sidewall portion ( 52 ) making an angle ( 58 ) with a bottom ( 54 ) of the subsequent cavity ( 42 ) in the range of about 20 to less than 90 degrees. According to another embodiment, the TMAH etchant comprises TMAH concentrations in the range of about 1 to 40 weight percent TMAH in water. According to a still another embodiment, the TMAH etchant comprises TMAH concentrations in the range of about 2 to 10 weight percent TMAH in water. 
     According to a second embodiment, there is provide a method ( 500 ,  600 ) for etching a cavity ( 42 ) in a substrate ( 21 ), comprising, for a semiconductor substrate ( 21 ) having a first principal surface ( 31 ) and an opposed second principal surface ( 23 ), anisotropically locally etching a preliminary cavity ( 20 ) in the substrate ( 21 ) extending from the second principal surface ( 23 ) toward the first principal surface ( 31 ), and exposing the preliminary cavity ( 20 ) to a tetra-methyl-ammonium hydroxide (TMAH) etchant thereby forming a final cavity ( 42 ) having a smoother final sidewall ( 50 ). According to a further embodiment, the smoother final sidewall ( 50 ) has a portion ( 52 ) making an angle ( 58 ) with a bottom ( 54 ) of the final cavity ( 42 ) in the range of about 20 to less than 90 degrees. According to a still further embodiment, the TMAH etchant comprises TMAH concentrations in the range of about 1 to 40 weight percent TMAH in water. According to a yet further embodiment, the TMAH etchant comprises TMAH concentrations in the range of about 2 to 10 weight percent TMAH in water. According to a still yet further embodiment, the etching step comprises reactive ion etching. According to a yet still further embodiment, the method further comprises, prior to the exposing step, cleaning preliminary sidewalls ( 44 ) of the preliminary cavity ( 20 ) of anisotropic cavity etching byproducts. According to another embodiment, the cleaning step comprises using a water-hydrofluoric acid mixture having a concentration ratio in the range of about H 2 O:HF=500:1 to H 2 O:HF=25:1. 
     According to a third embodiment, there is provided a method ( 500 ,  600 ) for producing a pressure sensor device ( 40 ) comprising, for a substrate ( 21 ) having a substantially silicon body ( 22 ) abutting a first principal surface ( 23 ) of the substrate ( 21 ) and having a second principal surface ( 31 ) spaced from the first principal surface ( 23 ) and having a pressure sensor element ( 39 ) location ( 43 ) proximate the second principal surface ( 31 ), locally anisotropically etching a preliminary cavity ( 20 ) extending partly through the silicon body ( 22 ) toward the second principal surface ( 31 ), wherein the preliminary cavity underlies the pressure sensor element ( 39 ) location ( 43 ) and has a preliminary sidewall ( 44 ), and exposing the preliminary sidewall ( 44 ) of the preliminary cavity ( 20 ) to tetra-methyl-ammonium hydroxide (TMAH) etchant to provide a final cavity ( 42 ) underlying the pressure element ( 39 ) location ( 43 ). According to a further embodiment, the final cavity ( 42 ) has a final sidewall ( 50 ) having a portion ( 52 ) making an angle ( 58 ) with a bottom ( 54 ) of the final cavity ( 42 ) in the range of about 20 to less than 90 degrees. According to a still further embodiment, the method further comprises to the etching step, providing a mask layer ( 25 ) on the first principal surface ( 23 ) having an etch window ( 29 ) therein opposite the pressure sensor element ( 39 ) location ( 43 ), and thereafter etching the preliminary cavity ( 20 ) through the etch window ( 29 ). According to a yet further embodiment, the substrate ( 21 ) further comprises a dielectric layer ( 28 ) between the body ( 22 ) and the pressure sensor element ( 39 ) location ( 43 ), and wherein the dielectric layer ( 28 ) forms a bottom ( 54 ) of the final cavity ( 42 ). According to a still yet further embodiment, the substrate  21  further comprises a further semiconductor region ( 30 ) overlying the dielectric layer ( 28 ) and wherein the pressure sensor element ( 39 ) location ( 43 ) includes a portion of the further semiconductor region ( 30 ). 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described and methods of preparation in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.