Microstructure and patterning method thereof and micro-electromechanical system device

Abstract

A microstructure can be provided by forming a metal layer, such as a molybdenum layer, over a substrate. An aluminum nitride layer is formed on a top surface of the metal layer. A surface portion of the aluminum nitride layer is converted into a continuous aluminum oxide-containing layer by oxidation. A dielectric spacer layer can be formed over the continuous aluminum oxide-containing layer. A contact via cavity extending through the dielectric spacer layer, the continuous aluminum oxide-containing layer, and the aluminum nitride layer and extending downward to a corresponding portion of at least one metal layer can be formed using an etching process, the etching process containing a wet etching step while suppressing the formation of an undercut in the aluminum nitride layer. A contact via structure can be formed in the contact via cavity. The microstructure can include a microelectromechanical system (MEMS) device including a piezoelectric transducer.

Description

Technical Field

[0001] The embodiments of the present invention relate to a microstructure and a patterning method thereof and a micro-electromechanical system device. Background Art

[0002] The present disclosure relates to semiconductor devices, and in particular, to patterned structures including aluminum nitride structures such as piezoelectric micro-electromechanical systems (MEMS) and methods of forming the same.

[0003] Aluminum nitride is commonly used in MEMS devices. However, integrating aluminum nitride components and conductive structures into MEMS devices is a challenge due to the significant difference in material properties between aluminum nitride and conductive materials. Summary of the invention

[0004] A microstructure includes at least one metal layer and at least one contact via structure. The at least one metal layer is formed in an interlayer dielectric material layer overlying a substrate. The interlayer dielectric material layer includes an aluminum nitride layer overlying a topmost metal layer in the at least one metal layer. The at least one contact via structure contacts a corresponding one of the at least one metal layer and includes a corresponding top portion. The top portion is spaced apart from the interlayer dielectric material layer in a vertical direction by an aluminum oxide-containing layer and a corresponding dielectric spacer structure. The dielectric spacer structure includes a dielectric material substantially free of metal elements. The aluminum oxide-containing layer contacts a corresponding portion of a top surface of the aluminum nitride layer.

[0005] A microelectromechanical system (MEMS) element includes: at least one metal layer and at least two contact through-hole structures. The at least one metal layer is formed in an interlayer dielectric material layer overlying a substrate. The interlayer dielectric material layer includes an aluminum nitride layer overlying a topmost metal layer in the at least one metal layer. The at least two contact through-hole structures contact corresponding portions of the at least one metal layer and include corresponding top portions. The top portions are spaced apart from the interlayer dielectric material layer in a vertical direction by an aluminum oxide-containing layer and corresponding dielectric spacer structures. The MEMS element includes a piezoelectric transducer, which uses the at least two contact through-hole structures as electrical nodes and the aluminum nitride layer as a piezoelectric conversion element.

[0006] A method of patterning a microstructure includes the following operations. At least one metal layer is formed above a substrate. An aluminum nitride layer is formed on a top surface of the at least one metal layer. The surface portion of the aluminum nitride layer is converted into a continuous aluminum oxide-containing layer by oxidizing the surface portion of the aluminum nitride layer. A dielectric spacer layer is formed above the continuous aluminum oxide-containing layer. A plurality of contact via cavities extending through the dielectric spacer layer, the continuous aluminum oxide-containing layer, and the aluminum nitride layer and extending downward to corresponding portions of the at least one metal layer are formed using an etching process. The etching process includes a wet etching step that etches the actual exposed portion of the aluminum nitride layer while suppressing the formation of undercuts in the aluminum nitride layer. A plurality of contact via structures are formed in the plurality of contact via cavities. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] When read in conjunction with the accompanying drawings, the various aspects of the present disclosure are best understood from the following detailed description. It should be noted that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the size of the various features may be arbitrarily increased or reduced for clarity of discussion.

[0008] Figure 1 is a vertical cross-sectional view of an exemplary structure after forming at least one dielectric buffer layer and a proximal aluminum nitride layer over a substrate according to an embodiment of the present disclosure.

[0009] Figure 2A is a vertical cross-sectional view of an exemplary structure after forming a metal layer and an aluminum nitride layer according to an embodiment of the present disclosure.

[0010] Figure 2B for Figure 2A Horizontal cross-sectional view of a first exemplary pattern of a metal layer in an exemplary structure of FIG.

[0011] Figure 2C for Figure 2A Horizontal cross-sectional view of a second exemplary pattern of a metal layer in an exemplary structure of FIG.

[0012] Figure 3A is a vertical cross-sectional view of a first exemplary configuration of an exemplary structure after converting a surface portion of an aluminum nitride layer into a continuous aluminum oxide-containing layer according to an embodiment of the present disclosure.

[0013] Figure 3B is a vertical cross-sectional view of a second exemplary configuration of an exemplary structure after converting a surface portion of an aluminum nitride layer into a continuous aluminum oxide-containing layer according to an embodiment of the present disclosure.

[0014] Figure 4 is a vertical cross-sectional view of an exemplary structure after forming a dielectric spacer layer according to an embodiment of the present disclosure.

[0015] Figure 5is a vertical cross-sectional view of an exemplary structure after forming a contact via cavity through a dielectric spacer layer and a continuous aluminum oxide-containing layer according to an embodiment of the present disclosure.

[0016] Figure 6 is a vertical cross-sectional view of an exemplary structure after extending the second contact via cavity and the third contact via cavity in the vertical direction according to an embodiment of the present disclosure.

[0017] Figure 7 is a vertical cross-sectional view of an exemplary structure after extending the third contact via cavity in the vertical direction according to an embodiment of the present disclosure.

[0018] Figure 8 is a vertical cross-sectional view of an exemplary structure after removal of a patterned photoresist layer according to an embodiment of the present disclosure.

[0019] Fig. 9 is a vertical cross-sectional view of an exemplary structure after depositing a conductive material layer according to an embodiment of the present disclosure.

[0020] Fig.10 is a vertical cross-sectional view of an exemplary structure after patterning a conductive material layer, a dielectric spacer layer, and optionally penetrating an aluminum oxide-containing layer according to an embodiment of the present disclosure.

[0021] Fig.11 is a vertical cross-sectional view of an exemplary structure after removal of a patterned photoresist layer according to an embodiment of the present disclosure.

[0022] Fig.12 is a vertical cross-sectional view of an exemplary structure after forming at least one front-side passivation layer according to an embodiment of the present disclosure.

[0023] Fig.13 is a vertical cross-sectional view of an exemplary structure after backside patterning according to an embodiment of the present disclosure.

[0024] Fig.14 is a vertical cross-sectional view of an exemplary structure after removing at least one front-side passivation layer according to an embodiment of the present disclosure.

[0025] Fig.15 Schematic diagram showing the general processing steps of the method of the present disclosure.

[0026] Description of Figure Numbers

[0027] 10: substrate;

[0028] 12: Semiconductor devices;

[0029] 14: Metal interconnect structure;

[0030] 20: dielectric buffer layer;

[0031] 30: aluminum nitride layer;

[0032] 32: proximal aluminum nitride layer;

[0033] 34: first intermediate aluminum nitride layer;

[0034] 36: second intermediate aluminum nitride layer;

[0035] 38: distal aluminum nitride layer;

[0036] 39, 39L: containing aluminum oxide layer;

[0037] 39A: aluminum oxynitride layer;

[0038] 39B: aluminum oxide layer;

[0039] 40: metal layer;

[0040] 42: proximal metal layer;

[0041] 44: middle metal layer;

[0042] 46: distal metal layer;

[0043] 50: dielectric spacer structure;

[0044] 50L: dielectric spacer layer;

[0045] 51: first photoresist layer;

[0046] 53: second photoresist layer;

[0047] 55: third photoresist layer;

[0048] 59A: first contact through-hole cavity;

[0049] 59B: second contact through-hole cavity;

[0050] 59C: third contact via cavity;

[0051] 60: contact through-hole structure;

[0052] 60A: first contact through-hole structure;

[0053] 60B: second contact through hole structure;

[0054] 60C: third contact through-hole structure;

[0055] 60L: conductive material layer;

[0056] 67: Photoresist material part;

[0057] 70: first front side passivation layer;

[0058] 72: second front side passivation layer;

[0059] 1510, 1520, 1530, 1540, 1550, 1560: steps. DETAILED DESCRIPTION

[0060] The following disclosure provides many different embodiments or examples for implementing the different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these components and arrangements are only examples and are not intended to be restrictive. For example, in the following description, the formation of a first feature above or on a second feature may include an embodiment in which the first feature is formed in direct contact with the second feature, and may also include an embodiment in which an additional feature may be formed between the first feature and the second feature so that the first feature and the second feature may not be in direct contact. In addition, the present disclosure may repeat figure numerals and / or letters in various examples. This repetition is for the purpose of simplicity and clarity, and does not itself specify the relationship between the various embodiments and / or configurations discussed.

[0061] Additionally, for ease of description, spatially relative terms such as "beneath," "below," "lower," "above," "upper," etc. may be used herein to describe the relationship of one element or feature to another element or feature as shown in the drawings. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the drawings. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0062] According to one aspect of the present disclosure, an aluminum nitride layer that can be used to form a microstructure is protected from undercutting at an interface with a dielectric material layer by converting a surface portion of the aluminum nitride layer that can be used to form a microstructure into an aluminum oxide-containing layer, the dielectric material layer comprising an oxide, oxynitride, or nitride of a semiconductor material. The aluminum oxide-containing layer may comprise stoichiometric aluminum oxide (Al2O3) or may comprise a compound of aluminum, oxygen, and nitrogen. The oxygen content in the distal portion of the aluminum oxide-containing layer located on the opposite side of the interface with the rest of the aluminum nitride layer may be sufficiently high that no aluminum nitride crystalline structure is present at the distal surface of the aluminum oxide-containing layer (i.e., on the opposite side of the interface). A dielectric spacer layer comprising a dielectric material (e.g., silicon oxide, silicon nitride, or silicon oxynitride) may be formed on the distal surface of the aluminum oxide-containing layer. The absence of an aluminum nitride crystalline structure at the distal surface of the aluminum oxide-containing layer allows a gapless interface to be formed between the aluminum oxide-containing layer and the dielectric spacer layer, which renders the layer stack of the aluminum nitride layer, the aluminum oxide-containing layer, and the dielectric spacer layer resistant to any undercut formation during a subsequent isotropic etch process using an isotropic etchant. Specifically, the formation of an undercut at the interface between the dielectric spacer layer and the aluminum oxide-containing layer can be suppressed during the subsequent isotropic etch process.

[0063] Aluminum nitride is a piezoelectric material and is used in many MEMS devices. For reasons that are not yet fully understood, the interface between the aluminum nitride layer and the silicon oxide layer is susceptible to undercutting during a wet etching process, such as a wet etching process using phosphoric acid (which is a typical aluminum nitride etchant). This may be due to the roughness of the aluminum nitride layer and / or the poor wetting ability of the silicon oxide layer with aluminum nitride, or a combination of both. Capillary action may allow the wet etchant (e.g., phosphoric acid) to penetrate the interface of silicon oxide with aluminum nitride. The lateral extension length of the undercut in the upper portion of the aluminum nitride layer and the overlying silicon oxide layer may typically be 3 to 8 times the thickness of the etched aluminum nitride layer. Apparently, the interface etching mechanism that accelerates the aluminum nitride material operates at the interface. Such undercutting in the patterned stack of aluminum nitride and silicon oxide layers is not conducive to the proper functionality of the aluminum nitride layer, such as as a piezoelectric component of a MEMS device.

[0064] refer to Figure 1, showing an exemplary structure according to an embodiment of the present disclosure. The exemplary structure may include a substrate 10, which may be a semiconductor substrate, such as a commercially available silicon substrate. A semiconductor device 12 may optionally be formed on the top surface of the substrate 10. For example, the semiconductor device 12 may include a transistor, such as a complementary metal-oxide-semiconductor (CMOS) field effect transistor and / or a bipolar transistor. The semiconductor device 12 may include passive devices, such as capacitors, resistors, and / or inductors (varactors), and may include radio frequency (RF) devices, diodes, varactors, and / or other semiconductor devices known in the art.

[0065] At least one dielectric buffer layer 20 may be formed over the top surface of the substrate 10. The at least one dielectric buffer layer 20 includes at least one dielectric material that may provide electrical isolation of overlying structures that will be subsequently formed from the substrate 10. In one embodiment, the at least one dielectric buffer layer 20 may include an interconnect-level dielectric material layer that may have been formed within a metal interconnect structure 14. The metal interconnect structure 14 may provide electrical connections to and from the semiconductor device 12, and may provide electrical connections between the semiconductor device 12 and corresponding pairs of corresponding portions of a microelectromechanical system (MEMS) device that will be subsequently formed over the at least one dielectric buffer layer 20 and / or between the semiconductor device 12 and corresponding pairs of contact via structures that will be subsequently formed over the at least one dielectric buffer layer 20.

[0066] In one embodiment, each of the at least one dielectric buffer layer 20 may include a dielectric material such as undoped silicate glass, doped silicate glass, organosilicate glass, amorphous fluorinated carbon, porous variants thereof, or combinations thereof. Each of the metal interconnect structures 14 may include at least one conductive material, which may be a combination of a metal liner layer (e.g., a metal nitride or a metal carbide) and a metal filler material. Each metal liner layer may include TiN, TaN, WN, TiC, TaC, and WC, and each metal filler material portion may include W, Cu, Al, Co, Ru, Mo, Ta, Ti, alloys thereof, and / or combinations thereof. Other suitable materials within the scope of the present disclosure may be used.

[0067] An aluminum nitride layer 30 may be formed on the topmost surface of at least one dielectric buffer layer 20. In general, at least one aluminum nitride layer 30 (which may be a single aluminum nitride layer or multiple aluminum nitride layers located at different layers) may be formed over at least one dielectric buffer layer 20. In embodiments where more than one aluminum nitride layer 30 is formed over at least one dielectric buffer layer 20, the aluminum nitride layer 30 formed in this processing step is referred to herein as a proximal aluminum nitride layer 32 or as a bottommost aluminum nitride layer 32. The proximal aluminum nitride layer 32 is the one aluminum nitride layer that is closest to the substrate 10 among all the aluminum nitride layers 30 that may be formed over at least one dielectric buffer layer 20.

[0068] The proximal aluminum nitride layer 32 may be deposited by atomic layer deposition (ALD) using an aluminum-containing precursor gas and a nitrogen-containing precursor gas. For example, the proximal aluminum nitride layer 32 may be deposited using a combination of tris(diacetamido)aluminum(III) (TDEAA) and hydrazine (N2H4) or ammonia (NH3) at a deposition temperature in the range of 150 degrees Celsius (°C) to 300 degrees Celsius. Alternatively, the aluminum nitride may be deposited using plasma-enhanced atomic layer deposition at a lower temperature, such as in the range of 0 degrees Celsius to 150 degrees Celsius. Furthermore, the aluminum nitride may be deposited by physical vapor deposition (PVD) (i.e., sputtering). The proximal aluminum nitride layer 32 may have a thickness in the range of 3 nanometers to 100 nanometers, such as 6 nanometers to 50 nanometers, although lesser and greater thicknesses may also be used.

[0069] refer to Figure 2A , the metal layer 40 and the other aluminum nitride layers 30 may be alternately formed over the proximal aluminum nitride layer 32. Each metal layer 40 may be patterned once deposited before depositing the next aluminum nitride layer 30. For example, a photoresist layer (not shown) may be applied over the metal layer 40, and the photoresist layer may be patterned photolithographically to cover one area of ​​the metal layer 40 and not cover another area of ​​the metal layer 40. An anisotropic etch process may be performed to transfer the pattern in the photoresist layer through the metal layer 40, thereby patterning the metal layer 40.

[0070] The pattern of each metal layer 40 may be selected to provide a suitable microstructure (a structure having at least one dimension less than 10 microns), which may be a microelectromechanical system (MEMS) device. Figure 2B and 2CNon-limiting exemplary shapes of metal layers 40 that may be used for the exemplary structure are shown in a horizontal view. In general, each metal layer 40 may be patterned into any suitable shape that is conducive to optimal performance of the MEMS device to be formed within the exemplary structure. In one embodiment, the microstructure includes a microelectromechanical system (MEMS) device containing a piezoelectric transducer that uses at least one and / or all of the aluminum nitride layer 30 as a piezoelectric conversion element and uses a subset of the contact via structures to be formed later as electrical nodes for the piezoelectric transducer.

[0071] Return to reference Figure 2A , a plurality of other aluminum nitride layers 30 and a plurality of metal layers 40 may be formed over the proximal aluminum nitride layer 32. In one embodiment, the plurality of other aluminum nitride layers 30 may include a first intermediate aluminum nitride layer 34, a second intermediate aluminum nitride layer 36, and a distal aluminum nitride layer 38. In one embodiment, the plurality of metal layers 40 may include a proximal metal layer 42 (also referred to as a bottom metal layer), an intermediate metal layer 44, and a distal metal layer 46 (also referred to as a top metal layer). An alternating sequence of metal layers 40 and aluminum nitride layers 30 may be formed.

[0072] Although the present disclosure is described with an embodiment using three metal layers 40, embodiments using one metal layer 40, two metal layers 40, four metal layers 40, or five or more metal layers 40 are expressly contemplated herein. Furthermore, although the present disclosure is described with an embodiment using four aluminum nitride layers 30, embodiments using two aluminum nitride layers 30, three aluminum nitride layers 30, five aluminum nitride layers 30, or six or more aluminum nitride layers are expressly contemplated herein. Although the present disclosure is described with an embodiment in which each metal layer 40 is patterned before the next aluminum nitride layer 30 is deposited, embodiments in which a combination of metal layers 40 and aluminum nitride layers 30 are patterned simultaneously are expressly contemplated herein.

[0073] The metal layer 40 may be formed in the aluminum nitride layer 30, which may collectively serve as a dielectric matrix with the metal layer 40 formed therein. In such embodiments, the aluminum nitride layer 30 may serve as an interlayer dielectric material layer that provides vertical isolation between adjacent pairs of metal layers 40 in a vertical direction. The interlayer dielectric material layer overlies the substrate 10 and has the aluminum nitride layer 30 (i.e., aluminum nitride layer 32, aluminum nitride layer 34, aluminum nitride layer 36, aluminum nitride layer 38) formed therein. The interlayer dielectric material layer (including the set of aluminum nitride layers 30) includes a distal aluminum nitride layer 38 (i.e., a topmost aluminum nitride layer) overlying a distal metal layer 46 (which is the topmost metal layer in the metal layer 40).

[0074] Each of the metal layers 40 may be deposited by a corresponding deposition method, which may be selected from chemical vapor deposition, physical vapor deposition, atomic layer deposition, vacuum evaporation or other thin film deposition methods. Each of the metal layers 40 may include a suitable metal material having a lattice constant that matches the lattice constant of aluminum nitride and / or may be substantially composed of the metal material. In one embodiment, at least one or each of the metal layers 40 may include molybdenum and / or may be substantially composed of molybdenum. In one embodiment, each of the metal layers 40 may have a thickness in the range of 5 nanometers to 100 nanometers, for example 10 nanometers to 50 nanometers, but smaller and larger thicknesses may also be used. In one embodiment, a plurality of metal layers 40 may include a plurality of molybdenum layers having a corresponding thickness in the range of 5 nanometers to 100 nanometers and / or may be substantially composed of the plurality of molybdenum layers.

[0075] Each of the other aluminum nitride layers (aluminum nitride layer 34, aluminum nitride layer 36, aluminum nitride layer 38) can be deposited using any of the deposition methods that can be used to deposit the proximal aluminum nitride layer 32. The atomic percentage of aluminum atoms in each aluminum nitride layer 30 can be 50%, or can be greater than 50% and less than 52% if the corresponding aluminum nitride layer 30 is aluminum-rich (i.e., nitrogen-deficient). Each of the other aluminum nitride layers 30, except the distal aluminum nitride layer 38, can have a thickness in the range of 3 nanometers to 100 nanometers, such as 6 nanometers to 50 nanometers, although lesser and greater thicknesses can also be used. The distal aluminum nitride layer 38 can have a thickness in the range of 4 nanometers to 120 nanometers, such as 8 nanometers to 70 nanometers, although lesser and greater thicknesses can also be used.

[0076] refer to Figure 3A and 3B , the surface portion of the distal aluminum nitride layer 38 (i.e., the topmost aluminum nitride layer) can be converted into a continuous aluminum oxide-containing layer 39L by performing an oxidation process. The unconverted portion of the distal aluminum nitride layer 38 continues as the distal aluminum nitride layer 38, and can include stoichiometric or non-stoichiometric aluminum nitride consisting essentially of aluminum atoms and nitrogen atoms. After the oxidation process (i.e., after converting the surface portion into the continuous aluminum oxide-containing layer 39L), the distal aluminum nitride layer 38 can have a thickness in the range of 3 nanometers to 100 nanometers, for example, 6 nanometers to 50 nanometers, although smaller and larger thicknesses can also be used.

[0077] Will be like Figure 2A The oxidation process for converting the surface portion of the distal aluminum nitride layer 38 into the continuous aluminum oxide-containing layer 39L provided at the processing step of may include a plasma oxidation process and / or may include a thermal oxidation process. For example, a plasma oxidation process using a radio frequency plasma of O2 at a temperature of 400 degrees Celsius may be used to convert the aluminum nitride layer 38 into the continuous aluminum oxide-containing layer 39L. Figure 2AThe surface portion of the distal aluminum nitride layer 38 provided at the processing step is converted into a continuous aluminum oxide-containing layer 39L. The thickness of the continuous aluminum oxide-containing layer 39L can be in the range of 1 nm to 20 nm, such as 2 nm to 15 nm, although smaller and larger thicknesses can also be used.

[0078] In general, the concentration of oxygen atoms in the continuous aluminum oxide containing layer 39L tends to increase with vertical distance from the interface with the distal aluminum nitride layer 38. The distal aluminum nitride layer 38 may consist essentially of aluminum atoms and nitrogen atoms, and the continuous aluminum oxide containing layer 39L includes a region containing aluminum atoms, nitrogen atoms, and above trace levels (i.e., above one part in ten thousand). In general, the continuous aluminum oxide containing layer 39L includes a graded aluminum oxide nitride layer 39A having a compositional gradient, wherein the concentration of oxygen atoms increases from 0 at the interface with the distal aluminum nitride layer 38 to a percentage in the range of 50% to 60% at the distal surface spaced apart from the interface with the distal aluminum nitride layer 38. Depending on the thickness of the continuous aluminum oxide containing layer 39L and depending on the process parameters used to form the continuous aluminum oxide containing layer 39L, the topmost portion of the continuous aluminum oxide containing layer 39L may or may not contain nitrogen atoms.

[0079] Figure 3A A first exemplary configuration of an exemplary structure is shown, wherein the topmost portion of the continuous aluminum oxide-containing layer 39L comprises an aluminum oxide material that does not contain nitrogen atoms, which may be a stoichiometric aluminum oxide material having an Al2O3 material composition. In this case, the continuous aluminum oxide-containing layer 39L includes an aluminum oxide layer 39B that contacts the graded aluminum oxynitride layer 39A at the distal surface. The oxygen atomic concentration at the distal surface may be 60%. Thus, the atomic concentration of oxygen atoms in the continuous aluminum oxide-containing layer 39L may gradually increase from 0% at the interface of the graded aluminum oxynitride layer 39A with the distal aluminum nitride layer 38 to 60% at the interface with the aluminum oxide layer 39B, and the atomic concentration of oxygen atoms may be at 60% within the aluminum oxide layer 39B. The aluminum oxide layer 39B may be composed of aluminum oxide. In one embodiment, the thickness of graded aluminum oxynitride layer 39A may range from 1 nm to 15 nm, such as 3 nm to 6 nm, and the thickness of aluminum oxide layer 39B may range from 0.3 nm to 14 nm, although lesser and greater thicknesses for each may be used.

[0080] Figure 3BA second exemplary configuration of an exemplary structure is shown, wherein the topmost portion of the continuous aluminum oxide-containing layer 39L comprises an aluminum oxynitride material including nitrogen atoms. In this case, the continuous aluminum oxide-containing layer 39L may be composed of a graded aluminum oxynitride layer 39A having a composition gradient, wherein the oxygen atomic concentration increases from 0 at the interface with the distal aluminum nitride layer 38 (i.e., the topmost aluminum nitride layer) to a percentage equal to or greater than 50% and less than 60% at the actual exposed distal surface, which is spaced apart from the interface with the distal aluminum nitride layer 38. In this case, a dielectric spacer layer may then be deposited directly on the distal surface of the graded aluminum oxynitride layer 39A. In one embodiment, the thickness of the graded aluminum oxynitride layer 39A (in this case, the same as the thickness of the continuous aluminum oxide-containing layer 39L) may be in the range of 1 nanometer to 15 nanometers, such as 3 nanometers to 6 nanometers, although smaller and larger thicknesses may also be used.

[0081] refer to Figure 4 , the dielectric spacer layer 50L may be formed directly above and above the actual exposed distal surface (i.e., the top surface) of the continuous aluminum oxide-containing layer 39L. In one embodiment, the dielectric spacer layer 50L may be free of metal elements. In one embodiment, the dielectric spacer layer 50L may be free of dielectric metal oxide, dielectric metal nitride, or dielectric metal oxynitride. In one embodiment, the dielectric spacer layer 50L may include a dielectric material free of metal elements, such as silicon oxide, silicon nitride, silicon oxynitride, organic silicate glass, polyimide, or silicon-based inorganic polymer. In one embodiment, the dielectric spacer layer 50L may include a silicon oxide material and / or may be substantially composed of a silicon oxide material, such as an undoped silicate glass or a doped silicate glass. The dielectric spacer layer 50L may be deposited by plasma enhanced chemical vapor deposition or high density plasma chemical vapor deposition, and may have a thickness ranging from 100 nanometers to 2,000 nanometers, such as 200 nanometers to 1,000 nanometers, but smaller and larger thicknesses may also be used.

[0082] In general, the distal aluminum nitride layer 38, the continuous aluminum oxide-containing layer 39L, and the dielectric spacer layer 50L may be formed over the at least one metal layer 40. At least two contact via structures contacting respective portions of the at least one metal layer 40 may be formed in subsequent processing steps. During the formation of the at least one contact via structure, the dielectric spacer layer 50L may be patterned to form the at least two dielectric spacer structures. Figures 5 to 11 An exemplary sequence of processing steps that may be used to form at least two contact via structures is shown. However, it should be understood that Figures 5 to 11 The processing steps shown in FIG. 1 are merely exemplary, and other processing steps may be used to form at least two contact via structures on the at least one metal layer 40 and / or on the metal interconnect structure 14 formed within the at least one dielectric buffer layer 20 .

[0083] refer to Figure 5 , a first photoresist layer 51 may be applied over the dielectric spacer layer 50L, and the first photoresist layer 51 may be patterned photolithographically to form openings therethrough. Each of the openings in the first photoresist layer 51 may be formed in a corresponding region, wherein a contact via structure extends to one of the at least one metal layer 40 (including the distal metal layer 46) and / or to one of the metal interconnect structures 14 (e.g., metal lines) formed within the at least one dielectric buffer layer 20.

[0084] An etching process may be performed to transfer the pattern in the first photoresist layer 51 through the dielectric spacer layer 50L and the continuous aluminum oxide-containing layer 39L, and optionally into the upper portion of the distal aluminum nitride layer 38. The etching process may include an anisotropic etching process and / or an isotropic etching process. The etching process may include multiple etching steps that may sequentially etch through the unmasked portion of the dielectric spacer layer 50L and the continuous aluminum oxide-containing layer 39L. In one embodiment, the etching process may include an anisotropic etching process such as a reactive ion etching process that etches through the actual exposed portion of the dielectric spacer layer 50L. For example, if the dielectric spacer layer 50L includes a silicon oxide material, a reactive ion etching process may be performed that may use a series of etching gases such as CF4 / O2, CF4 / CHF3 / Ar, C2F6, C3F8, C4F8 / CO, C5F8, and / or CH2F2.

[0085] Each contact via cavity (contact via cavity 59A, contact via cavity 59B, contact via cavity 59C) may be formed through the dielectric spacer layer 50L and the continuous aluminum oxide-containing layer 39L and through the distal aluminum nitride layer 38 or partially into the distal aluminum nitride layer 38. Each contact via cavity (contact via cavity 59A, contact via cavity 59B, contact via cavity 59C) may include at least one first contact via cavity 59A, at least one second contact via cavity 59B, and optionally at least one third contact via cavity 59C, and optionally any other contact via cavity (not shown) overlying a corresponding one of the metal interconnect structures 14. The first photoresist layer 51 may then be removed, for example, by ashing.

[0086] refer to Figure 6, a second photoresist layer 53 may be applied over the dielectric spacer layer 50L, and the second photoresist layer 53 may be patterned photolithographically to form openings therethrough. Each of the openings in the second photoresist layer 53 may be formed within the region of the second contact via cavity 59B, the third contact via cavity 59C, and any other contact via cavity. An etching process may be performed to transfer the pattern in the second photoresist layer 53 through any underlying portion of the distal aluminum nitride layer 38, through the distal metal layer 46, and completely or partially through the second intermediate aluminum nitride layer 36. The etching process may include an anisotropic etching process, such as a reactive ion etching process. The etching process may include multiple etching steps, which may sequentially etch through the unshielded portion of the distal aluminum nitride layer 38 and the distal metal layer 46, and completely or partially through the second intermediate aluminum nitride layer 36.

[0087] The second contact via cavity 59B, the third contact via cavity 59C, and any other contact via cavities may extend in a vertical direction through the distal aluminum nitride layer 38, through the distal metal layer 46, and completely or partially through the second intermediate aluminum nitride layer 36, while at least one first contact via cavity 59A is covered by the second photoresist layer 53. The second photoresist layer 53 may then be removed, for example, by ashing.

[0088] refer to Figure 7 , a third photoresist layer 55 may be applied over the dielectric spacer layer 50L, and the third photoresist layer 55 may be patterned photolithographically to form openings therethrough. Each of the openings in the third photoresist layer 55 may be formed within the region of at least one third contact via cavity 59C and any other contact via cavity (if present). An etching process may be performed to transfer the pattern in the third photoresist layer 55 through any underlying portion of the second intermediate aluminum nitride layer 36, through the intermediate metal layer 44, and completely or partially through the first intermediate aluminum nitride layer 34. The etching process may include an anisotropic etching process, such as a reactive ion etching process. The etching process may include multiple etching steps, which may sequentially etch through the unshielded portion of the second intermediate aluminum nitride layer 36, through the intermediate metal layer 44, and completely or partially through the first intermediate aluminum nitride layer 34.

[0089] At least one third contact via cavity 59C and any other contact via cavities (if present) may extend in a vertical direction through the second intermediate aluminum nitride layer 36, through the intermediate metal layer 44, and completely or partially through the first intermediate aluminum nitride layer 34, while the first contact via cavity 59A and the second contact via cavity 59B are covered by the third photoresist layer 55. The third photoresist layer 55 may then be removed, for example, by ashing.

[0090] refer to Figure 8, an isotropic etching process may be performed to remove substantially exposed portions of aluminum nitride layer 30 underlying each of the contact via cavities (contact via cavity 59A, contact via cavity 59B, contact via cavity 59C). The isotropic etching process substantially exposes portions of the top surface of metal layer 40, and removes any interfacial compounds or impurities from the substantially exposed top surface of metal layer 40 underlying the contact via cavities (contact via cavity 59A, contact via cavity 59B, contact via cavity 59C). For example, wet etching using phosphoric acid may be performed to recess the substantially exposed surface of aluminum nitride layer 30, and then clean the substantially exposed surface of metal layer 40.

[0091] In some processes, a silicon oxide material (e.g., dielectric spacer layer 50L) may be deposited directly on the top surface of the topmost aluminum nitride layer (e.g., aluminum nitride layer 38). When a contact via cavity is formed through such a layer stack and an isotropic wet etching process (e.g., phosphoric acid wet etching process) is performed, an undercut is formed around each contact via cavity at the interface between the silicon oxide material and the topmost aluminum nitride layer. Depending on the process parameters of the phosphoric acid wet etching process, the lateral extension length of the undercut in one direction may range from 3 to 8 times the thickness of the topmost aluminum nitride layer. Adhesion testing shows that the interface between the topmost aluminum nitride layer (e.g., aluminum nitride layer 38) and the silicon oxide material (e.g., dielectric spacer layer 50L) exhibits an adhesion strength of level 5B. Therefore, the weak adhesion between the topmost nitride layer (e.g., nitride layer 38) and the silicon oxide material (e.g., dielectric spacer layer 50L) is not the cause of the formation of the undercut.

[0092] Without wishing to be bound by any particular theory, it is believed that the silicon oxide material (e.g., dielectric spacer layer 50L) or other deposited dielectric material layer is unable to wet the top surface of the topmost aluminum nitride layer (e.g., aluminum nitride layer 38). It is possible that the polycrystalline structure of the aluminum nitride layer (e.g., aluminum nitride layer 38) provides a surface topography that is not conducive to wetting by the subsequently deposited dielectric material (e.g., dielectric spacer layer 50L). Therefore, nano- or sub-nanometer-scale cavities may exist at the interface between the topmost aluminum nitride layer (e.g., aluminum nitride layer 38) and the deposited silicon oxide material (e.g., dielectric spacer layer 50L). It is also possible that during the isotropic wet etching process, capillary forces play a role in causing lateral penetration of molecules of the isotropic etchant. Regardless of the validity of the assumptions made above and regardless of the actual mechanism of undercut formation, it is a well-known fact that undercuts are formed at the interface between an aluminum nitride layer (e.g., aluminum nitride layer 38) and a silicon oxide material (e.g., dielectric spacer layer 50L) and other similar materials during a wet etching process such as a phosphoric acid wet etching process.

[0093] In embodiments where the dielectric spacer layer 50L comprises a silicon oxide material, the undercut at the interface between the topmost aluminum nitride layer 38 and the dielectric spacer layer 50L is significantly reduced or eliminated. In theory, converting the surface portion of the aluminum nitride layer into an aluminum oxide-containing layer provides an impermeable interface between the remainder of the aluminum nitride layer and the aluminum oxide-containing layer. In addition, in theory, the actual exposed surface of the aluminum oxide-containing layer is beneficial for forming another impermeable interface when the dielectric material is subsequently deposited. Without wishing to be bound by a particular theory, the amorphous nature of the actual exposed surface of the aluminum oxide-containing layer may be the reason for the formation of an impermeable interface when the dielectric spacer layer is deposited. It is believed that most dielectric materials, and particularly dielectric materials that do not contain metals (e.g., dielectric metal oxides or dielectric metal nitrides), are likely to form such an impermeable interface.

[0094] In general, the contact via cavities (contact via cavities 59A, 59B, 59C) may extend in a vertical direction through the dielectric spacer layer 50L, the continuous aluminum oxide-containing layer 39L, and the distal aluminum nitride layer 38, and optionally through one or more metal layers 40 and optionally through one or more other aluminum nitride layers 30. The contact via cavities (contact via cavities 59A, 59B, 59C) may extend in a vertical direction downward to a corresponding portion of at least one metal layer 40. The formation of the contact via cavities (contact via cavities 59A, 59B, 59C) may be achieved by combining at least one anisotropic etching process with a terminal etch process, which may be a wet etching process that etches the actual exposed portion of the aluminum nitride layer 30 (including the distal aluminum nitride layer 38) while suppressing the formation of undercuts in the aluminum nitride layer 30.

[0095] refer to Fig. 9, at least one conductive material may be deposited to form a conductive material layer 60L in the form of a continuous extended thin film, the conductive material layer 60L extending into each of the contact via cavities (contact via cavity 59A, contact via cavity 59B, contact via cavity 59C) and extending over the dielectric spacer layer 50L. The at least one conductive material may include a metal liner and a metal filler material. For example, the metal liner may include a conductive metal nitride material such as TiN, TaN and / or WN, and may have a thickness ranging from 3 nanometers to 100 nanometers, but smaller and larger thicknesses may also be used. Other suitable materials for the metal liner are within the scope of the present disclosure. The metal liner may be deposited by physical vapor deposition or chemical vapor deposition. The metal filler material may include a metal, a metal alloy, or a heavily doped semiconductor material. For example, the metal filler material may include Cu, Al, Ag, Au, W, Mo, Ru, Co, another elemental metal, an alloy thereof (e.g., an Al-Cu alloy), and / or a layer stack thereof. Other suitable materials for the metal fill material are within the scope of the present disclosure. The thickness of the metal fill material can range from 100 nanometers to 5,000 nanometers as measured above the dielectric spacer layer 50L, but smaller and larger thicknesses can also be used. The metal fill material can be deposited by physical vapor deposition, chemical vapor deposition, electroplating, vacuum evaporation, or other deposition methods.

[0096] refer to Fig.10 , a photoresist layer may be applied over the conductive material layer, and the photoresist layer may be patterned photolithographically to form discrete photoresist material portions 67. An anisotropic etching process may be performed to transfer the pattern of discrete photoresist material portions 67 through the conductive material layer 60L and the dielectric spacer layer 50L and optionally through the continuous aluminum oxide-containing layer 39L. Each patterned portion of the conductive material layer 60L includes a contact via structure 60, which may include: at least one first contact via structure 60A formed in a corresponding first contact via cavity 59A; at least one second contact via structure 60B formed in a corresponding second contact via cavity 59B; at least one third contact via structure 60C formed in a corresponding third contact via cavity 59C; and optionally at least one other contact via structure (if present) formed in a corresponding other contact via cavity extending to a corresponding metal interconnect structure 14.

[0097] The dielectric spacer layer 50L may be patterned into dielectric spacer structures 50 that laterally surround the vertically extending portion of the corresponding contact via structure 60. Each dielectric spacer structure 50 may have a vertical or tapered inner sidewall and a vertical or tapered outer sidewall. In one embodiment, each dielectric spacer structure 50 may include a cylindrical opening therethrough and may thus be topologically homeomorphic to a torus, i.e., may be continuously deformed into the shape of a torus without forming new holes or removing existing holes. The outer sidewall of each dielectric spacer structure 50 may coincide with the sidewall of the overlying portion of the contact via structure 60 in the vertical direction, i.e., be located in the same vertical plane as the sidewall.

[0098] The continuous aluminum oxide-containing layer 39L may be patterned into a plurality of aluminum oxide-containing layers 39. Each aluminum oxide-containing layer 39 may include a graded aluminum oxynitride layer 39A. Each aluminum oxide-containing layer 39 may include Figure 3A The aluminum oxide layer 39B shown in FIG. 1 may be formed by Figure 3B Each dielectric spacer structure 50 may be in contact with the top surface of the corresponding aluminum oxide layer 39. In one embodiment, each dielectric spacer structure 50 may include a dielectric material substantially free of metal elements (e.g., a silicon oxide material), and / or may be substantially composed of the dielectric material.

[0099] refer to Fig.11 , the discrete photoresist material portions 67 may be removed, for example, by ashing.

[0100] In general, at least two contact via structures 60 may contact respective portions of at least one metal layer 40. Each of the at least two contact via structures 60 may include a respective top portion that is vertically spaced apart from the interlayer dielectric material layer (e.g., aluminum nitride layer 30) by the aluminum oxide-containing layer 39 and the respective dielectric spacer structure 50.

[0101] In one embodiment, at least one metal layer 40 may be formed in an interlayer dielectric material layer (which may include aluminum nitride layer 30) overlying substrate 10. The interlayer dielectric material layer may include a distal aluminum nitride layer 38 overlying a distal metal layer 46 (i.e., the topmost metal layer) in the at least one metal layer 40. In one embodiment, the interlayer dielectric material layer may include at least one other aluminum nitride layer (e.g., proximal aluminum nitride layer 32, first intermediate aluminum nitride layer 34, and second aluminum nitride layer 36) located between distal metal layer 46 and substrate 10.

[0102] In one embodiment, at least one metal layer 40 may include a plurality of metal layers 40, and one of the at least two contact via structures (e.g., the first contact via structure 60A) may contact the distal metal layer 46 (i.e., the topmost metal layer), and another of the at least two contact via structures (e.g., the second contact via structure 60B or the third contact via structure 60C) may contact a metal layer (e.g., the proximal metal layer 42 or the intermediate metal layer 44) other than the distal metal layer 46 in the plurality of metal layers 40. In one embodiment, the plurality of metal layers 40 include a plurality of molybdenum layers having respective thicknesses ranging from 5 nanometers to 100 nanometers.

[0103] In one embodiment, the exemplary structure may include a MEMS device including a piezoelectric transducer using at least two contact via structures 60 as electrical nodes and using at least one and / or each of the aluminum nitride layers 30 as a piezoelectric conversion element. In one embodiment, the piezoelectric transducer may include a microphone or a speaker.

[0104] refer to Fig.12 , at least one front side passivation layer (front side passivation layer 70, front side passivation layer 72) can be deposited over the exemplary structure by a conformal or non-conformal deposition process. For example, the first front side passivation layer 70 can deposit a first dielectric material, such as undoped silicate glass, doped silicate glass, organosilicate glass, or a dielectric polymer material. Optionally, at least one opening through the aluminum nitride layer 30 and the metal layer 40 can be formed by forming a patterned photoresist layer (not shown) over the first front side passivation layer 70 and by anisotropically etching the unmasked portion of the aluminum nitride layer 30 and the metal layer 40. The second front side passivation layer 72 can be deposited in the at least one opening and over the first front side passivation layer 70. The total thickness of the planar area of ​​the at least one front side passivation layer (front side passivation layer 70, front side passivation layer 72) can be in the range of 1 micron to 30 microns, although lesser and greater thicknesses can also be used.

[0105] refer to Fig.13 , the substrate 10 may be thinned, for example, by grinding, polishing, an anisotropic etching process, or an isotropic etching process. The thickness of the thinned substrate 10 may be in the range of 1 micron to 60 microns, but lesser and greater thicknesses may also be used. A patterned etch mask layer (not shown) may be formed over the polished backside surface of the substrate 10, and an etching process may be performed to etch through at least one dielectric buffer layer 20. The aluminum nitride layer 30 and the metal layer 40 may be used as an etch stop structure for the etching process. The etching process may be an isotropic etching process or an anisotropic etching process. The patterned etch mask layer may then be removed, for example, by ashing.

[0106] refer to Fig.14, at least one front side passivation layer (front side passivation layer 70, front side passivation layer 72) can be selectively removed with respect to the aluminum nitride layer 30, the metal layer 40, and the contact via structure 60. For example, a wet etching process using dilute hydrofluoric acid can be used to etch at least one front side passivation layer (front side passivation layer 70, front side passivation layer 72). A solder ball (not shown) can be attached to the contact via structure 60, and the example structure can be attached to a semiconductor die or a package substrate using C4 bonding or wire bonding.

[0107] refer to Fig.15 , the flow chart shows a general processing sequence that can be used to form various embodiments of the present disclosure. Referring to step 1510, a metal layer 40 (e.g., distal metal layer 46) can be formed over a substrate 10. Referring to step 1520, an aluminum nitride layer 30 (e.g., distal aluminum nitride layer 38) can be formed on a top surface of the metal layer 40. Referring to step 1530, a surface portion of the aluminum nitride layer 30 can be converted into a continuous aluminum oxide-containing layer 39L by oxidizing the surface portion. Referring to step 1540, a dielectric spacer layer 50L can be formed over the continuous aluminum oxide-containing layer 39L. Referring to step 1550, contact via cavities (contact via cavity 59A, contact via cavity 59B, contact via cavity 59C) extending through dielectric spacer layer 50L, continuous aluminum oxide-containing layer 39L, and aluminum nitride layer 30 and extending down to corresponding portions of at least one metal layer 40 may be formed using an etching process that includes a wet etching step for etching substantially exposed portions of aluminum nitride layer 30 while suppressing the formation of undercuts in aluminum nitride layer 30. Referring to step 1560, contact via structures 60 are formed in the contact via cavities (contact via cavity 59A, contact via cavity 59B, contact via cavity 59C).

[0108] By oxidizing the topmost aluminum nitride layer 38 to form the aluminum nitride oxide layer 39, the aluminum nitride layer 38 can be protected from undercutting that may occur when phosphoric acid is introduced in a wet etching process. The presence of the aluminum nitride oxide layer 39L eliminates the need for a sacrificial molybdenum layer that can be used in conventional processes. By eliminating the need for a sacrificial molybdenum layer, the operations of depositing additional sacrificial layers and removing the remaining portions of the sacrificial layers can be avoided. This avoidance simplifies the overall fabrication of the microstructure and shortens the cycle time for fabricating the microstructure.

[0109] With reference to all the drawings and according to various embodiments of the present disclosure, a microstructure (which may include a microelectromechanical system (MEMS) device) is provided. The microstructure includes at least one metal layer 40, the at least one metal layer 40 being formed in an interlayer dielectric material layer (including an aluminum nitride layer 30) overlying a substrate 10. The interlayer dielectric material layer includes an aluminum nitride layer (e.g., a distal aluminum nitride layer 38) overlying a topmost metal layer (e.g., a distal metal layer 46) in the at least one metal layer 40. The microstructure includes at least one contact via structure 60, the at least one contact via structure 60 being in contact with a corresponding one of the at least one metal layer 40 and including a corresponding top portion, the top portion being spaced apart from the interlayer dielectric material layer (e.g., the aluminum nitride layer 30) in a vertical direction by an aluminum oxide-containing layer 39 and a corresponding dielectric spacer structure 50, the dielectric spacer structure 50 including a dielectric material substantially free of metal elements. The aluminum oxide containing layer 39 contacts corresponding portions of the top surface of the aluminum nitride layer (eg, the distal aluminum nitride layer 38 ).

[0110] According to another aspect of the present disclosure, a microelectromechanical system (MEMS) device is provided, comprising: at least one metal layer 40, the at least one metal layer 40 being formed in an interlayer dielectric material layer (including an aluminum nitride layer 30) overlying a substrate 10. The interlayer dielectric material layer comprises an aluminum nitride layer (e.g., a distal aluminum nitride layer 38) overlying a topmost metal layer (e.g., a distal metal layer 46) in the at least one metal layer 40. The MEMS device comprises: at least two contact via structures 60, the at least two contact via structures 60 being in contact with respective portions of the at least one metal layer 40 and comprising respective top portions, the top portions being spaced apart from the interlayer dielectric material layer in a vertical direction by an aluminum oxide-containing layer 39 and respective dielectric spacer structures 50. The MEMS device comprises a piezoelectric transducer, the piezoelectric transducer using the at least two contact via structures 60 as electrical nodes and the aluminum nitride layer (e.g., the distal aluminum nitride layer 38) as a piezoelectric conversion element.

[0111] According to another aspect of the present disclosure, a method of patterning a microstructure is provided. The method includes the following operations: forming a metal layer 40 over a substrate 10, and forming an aluminum nitride layer 38 on a top surface of the metal layer 40. The method further includes the following operations: converting a surface portion of the aluminum nitride layer 38 into a continuous aluminum oxide-containing layer 39 by oxidizing the surface portion thereof. The method also includes the following operations: forming a dielectric spacer layer 50 over the continuous aluminum oxide-containing layer 39. The method also includes the following operations: forming a contact via cavity 59 extending through the dielectric spacer layer 50, the continuous aluminum oxide-containing layer 39, and the aluminum nitride layer 38 and extending downward to a corresponding portion of the at least one metal layer 40 using an etching process, the etching process including a wet etching step of etching the actual exposed portion of the aluminum nitride layer 38 while suppressing the formation of undercuts in the aluminum nitride layer 38. The method also includes the following operations: forming a contact via structure 60 in the contact via cavity 59.

[0112] In some embodiments, the aluminum oxide-containing layer comprises a graded aluminum oxynitride layer having a composition gradient, wherein the concentration of oxygen atoms increases from 0 at an interface with a topmost aluminum nitride layer to a percentage in a range of 50% to 60% at a distal surface spaced apart from the interface with the topmost aluminum nitride layer.

[0113] In some embodiments, the aluminum oxide containing layer includes an aluminum oxide layer in contact with the graded aluminum oxynitride layer at the distal surface and an oxygen atomic concentration of 60% at the distal surface.

[0114] In some embodiments, the distal surface contacts a bottom surface of the dielectric spacer structure.

[0115] In some embodiments, the dielectric spacer structure includes a silicon oxide material.

[0116] In some embodiments, the aluminum oxide-containing layer has a thickness ranging from 3 nanometers to 60 nanometers.

[0117] In some embodiments, the at least one metal layer includes multiple metal layers, one of the at least two contact via structures contacts the topmost metal layer and another of the at least two contact via structures contacts a metal layer of the multiple metal layers other than the topmost metal layer.

[0118] In some embodiments, the interlayer dielectric material layer includes at least one other aluminum nitride layer between the topmost metal layer and the substrate.

[0119] In some embodiments, the plurality of metal layers includes a plurality of molybdenum layers having respective thicknesses ranging from 5 nanometers to 100 nanometers.

[0120] In some embodiments, the dielectric spacer structure contacts a top surface of the aluminum oxide containing layer and comprises a dielectric material that does not contain a metal element.

[0121] In some embodiments, the aluminum oxide-containing layer comprises a graded aluminum oxynitride layer having a composition gradient, wherein the concentration of oxygen atoms increases from 0 at an interface with a topmost aluminum nitride layer to a percentage in a range of 50% to 60% at a distal surface spaced apart from the interface with the topmost aluminum nitride layer.

[0122] In some embodiments, the aluminum oxide containing layer includes an aluminum oxide layer in contact with the graded aluminum oxynitride layer at the distal surface and an oxygen atomic concentration of 60% at the distal surface.

[0123] In some embodiments, the distal surface contacts a bottom surface of the dielectric spacer structure.

[0124] In some embodiments, the dielectric spacer structure includes a silicon oxide material and the aluminum oxide-containing layer has a thickness ranging from 3 nanometers to 60 nanometers.

[0125] In some embodiments, the above method further includes depositing a conductive material layer in the multiple contact through-hole cavities and above the dielectric spacer layer and patterning the conductive material layer and the dielectric spacer layer, wherein the patterned portion of the conductive material layer includes the multiple contact through-hole structures and the patterned portion of the dielectric spacer layer includes a dielectric spacer structure that laterally surrounds a vertically extending portion of a corresponding one of the multiple contact through-hole structures.

[0126] In some embodiments, the method further includes performing a plasma oxidation process to convert the surface portion of the aluminum nitride layer into the continuous aluminum oxide-containing layer, wherein the continuous aluminum oxide-containing layer includes a graded aluminum oxynitride layer having a composition gradient, wherein the concentration of oxygen atoms increases from 0 at the interface with the aluminum nitride layer to a percentage in the range of 50% to 60% at a distal surface, the distal surface being spaced apart from the interface with the aluminum nitride layer.

[0127] In some embodiments, the at least one metal layer comprises a molybdenum layer having a corresponding thickness in a range of 5 nm to 100 nm and the aluminum nitride layer has a thickness in a range of 3 nm to 60 nm after the surface portion is converted into the aluminum oxide-containing layer.

[0128] In some embodiments, the microstructure includes a microelectromechanical system (MEMS) element including a piezoelectric transducer that uses a subset of the contact via structures as electrical nodes and the aluminum nitride layer as a piezoelectric conversion element.

[0129] Various embodiments of the present disclosure may be used to provide a microstructure comprising an aluminum nitride layer, an aluminum oxide-containing layer, and a dielectric spacer structure 50, within any undercut at the interface between the aluminum oxide-containing layer and the dielectric spacer structure 50. A structurally robust contact via structure 60 may be formed on the underlying metal layer 40. The microstructure may include a MEMS device including a piezoelectric element. The enhanced structural integrity of the contact via structure 60 and the dielectric spacer structure 50 may increase the mechanical strength and reliability of the MEMS device.

[0130] The foregoing summarizes the features of several embodiments so that those skilled in the art can better understand the various aspects of the present disclosure. Those skilled in the art will appreciate that they can easily use the present disclosure as a basis for designing or modifying other processes and structures for achieving the same purposes and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art will also recognize that these equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and modifications herein without departing from the spirit and scope of the present disclosure.

Claims

1. A microstructure comprising: at least one metal layer formed in an interlayer dielectric material layer overlying the substrate, wherein the interlayer dielectric material layer comprises an aluminum nitride layer overlying a topmost metal layer in the at least one metal layer; as well as at least one contact via structure contacting a corresponding one of the at least one metal layer and comprising a corresponding top portion, the top portion being vertically spaced apart from the interlayer dielectric material layer by an aluminum oxide-containing layer and a corresponding dielectric spacer structure, the dielectric spacer structure comprising a dielectric material that does not contain a metal element, The aluminum oxide containing layer is in contact with corresponding portions of a top surface of the aluminum nitride layer.

2. The microstructure of claim 1 , wherein the aluminum oxide-containing layer comprises a graded aluminum oxynitride layer having a composition gradient wherein the concentration of oxygen atoms increases from 0 at an interface with a topmost aluminum nitride layer to a percentage in a range of 50% to 60% at a distal surface spaced apart from the interface with the topmost aluminum nitride layer.

3. The microstructure according to claim 2, wherein: the aluminum oxide containing layer comprises an aluminum oxide layer in contact with the graded aluminum oxynitride layer at the distal surface; and The oxygen atomic concentration at the distal surface is 60%. The microstructure of claim 2 , wherein the distal surface is in contact with a bottom surface of the dielectric spacer structure. The microstructure of claim 1 , wherein the dielectric spacer structure comprises a silicon oxide material.

6. The microstructure of claim 1, wherein the aluminum oxide-containing layer has a thickness ranging from 3 nanometers to 60 nanometers.

7. A micro-electromechanical system (MEMS) device, comprising: at least one metal layer formed in an interlayer dielectric material layer overlying the substrate, wherein the interlayer dielectric material layer comprises an aluminum nitride layer overlying a topmost metal layer in the at least one metal layer; as well as at least two contact via structures contacting respective portions of the at least one metal layer and comprising respective top portions vertically spaced apart from the interlayer dielectric material layer by respective dielectric spacer structures and the aluminum oxide-containing layer, The micro-electromechanical system device includes a piezoelectric transducer, which uses the at least two contact through-hole structures as electrical nodes and the aluminum nitride layer as a piezoelectric conversion element.

8. The MEMS device according to claim 7, wherein: The at least one metal layer comprises a plurality of metal layers; One of the at least two contact via structures is in contact with the topmost metal layer; Another one of the at least two contact via structures contacts a metal layer of the plurality of metal layers except the topmost metal layer.

9. The MEMS device of claim 8, wherein the interlayer dielectric material layer comprises at least one other aluminum nitride layer between the topmost metal layer and the substrate.

10. The MEMS device of claim 8, wherein the plurality of metal layers comprises a plurality of molybdenum layers having respective thicknesses ranging from 5 nanometers to 100 nanometers. 11 . The MEMS device of claim 7 , wherein the dielectric spacer structure contacts a top surface of the aluminum oxide-containing layer and comprises a dielectric material that does not contain a metal element.

12. The MEMS device of claim 11 , wherein the aluminum oxide-containing layer comprises a graded aluminum oxynitride layer having a composition gradient in which an oxygen atomic concentration increases from 0 at an interface with a topmost aluminum nitride layer to a percentage in a range of 50% to 60% at a distal surface spaced apart from the interface with the topmost aluminum nitride layer.

13. The MEMS device according to claim 12, wherein: the aluminum oxide containing layer comprises an aluminum oxide layer in contact with the graded aluminum oxynitride layer at the distal surface; and The oxygen atomic concentration at the distal surface is 60%. 14 . The MEMS device of claim 12 , wherein the distal surface contacts a bottom surface of the dielectric spacer structure.

15. The MEMS device according to claim 7, wherein: The dielectric spacer structure comprises a silicon oxide material; The aluminum oxide-containing layer has a thickness ranging from 3 nanometers to 60 nanometers.

16. A method of patterning a microstructure, comprising: forming at least one metal layer over the substrate; forming an aluminum nitride layer on a top surface of the at least one metal layer; converting a surface portion of the aluminum nitride layer into a continuous aluminum oxide-containing layer by oxidizing the surface portion of the aluminum nitride layer; forming a dielectric spacer layer over the continuous aluminum oxide-containing layer; forming a plurality of contact via cavities extending through the dielectric spacer layer, the continuous aluminum oxide-containing layer, and the aluminum nitride layer and down to respective portions of the at least one metal layer using an etching process, the etching process including a wet etching step for etching substantially exposed portions of the aluminum nitride layer while inhibiting formation of undercuts in the aluminum nitride layer; as well as A plurality of contact via structures are formed in the plurality of contact via cavities.

17. The method according to claim 16, further comprising: depositing a layer of conductive material in the plurality of contact via cavities and over the dielectric spacer layer; as well as patterning the conductive material layer and the dielectric spacer layer, wherein the patterned portion of the conductive material layer includes the plurality of contact via structures; and Wherein the patterned portion of the dielectric spacer layer includes a dielectric spacer structure that laterally surrounds a vertically extending portion of a corresponding one of the plurality of contact via structures.

18. The method of claim 16, further comprising performing a plasma oxidation process to convert the surface portion of the aluminum nitride layer into the continuous aluminum oxide-containing layer, wherein the continuous aluminum oxide-containing layer comprises a graded aluminum oxynitride layer having a composition gradient in which a concentration of oxygen atoms increases from 0 at an interface with the aluminum nitride layer to a percentage in a range of 50% to 60% at a distal surface spaced apart from the interface with the aluminum nitride layer.

19. The method of claim 16, wherein: The at least one metal layer comprises a molybdenum layer having a corresponding thickness in the range of 5 nanometers to 100 nanometers; and The aluminum nitride layer has a thickness ranging from 3 nanometers to 60 nanometers after the surface portion is converted into the aluminum oxide-containing layer.

20. The method of claim 16, wherein the microstructure comprises a microelectromechanical system (MEMS) element including a piezoelectric transducer using a subset of the contact via structures as electrical nodes and the aluminum nitride layer as a piezoelectric conversion element.

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