# Patent

## Title
Microelectromechanical devices and fabrication methods

## Abstract

There are many inventions described and illustrated herein. In one aspect, the present invention is directed to a MEMS device, and technique of fabricating or manufacturing a MEMS device, having mechanical structures encapsulated in a chamber prior to final packaging. An embodiment further includes a buried polysilicon layer and a “protective layer” deposited over the buried polysilicon layer to prevent possible erosion of, or damage to the buried polysilicon layer during processing steps. The material that encapsulates the mechanical structures, when deposited, includes one or more of the following attributes: low tensile stress, good step coverage, maintains its integrity when subjected to subsequent processing, does not significantly and/or adversely impact the performance characteristics of the mechanical structures in the chamber (if coated with the material during deposition), and/or facilitates integration with high-performance integrated circuits. In one embodiment, the material that encapsulates the mechanical structures is, for example, silicon (polycrystalline, amorphous or porous, whether doped or undoped), silicon carbide, silicon-germanium, germanium, or gallium-arsenide.

## Background
RELATED APPLICATIONS
This application is related to U.S. patent application Ser. No. 10/454,867, filed Jun. 4, 2003, which is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
The disclosed embodiments relate to semiconductor devices and methods for fabricating the same.
BACKGROUND
This invention relates to electromechanical systems and techniques for fabricating microelectromechanical and nanoelectromechanical systems; and more particularly, in one aspect, to fabricating or manufacturing microelectromechanical and nanoelectromechanical systems with high performance integrated circuits on a common substrate.
Microelectromechanical systems (“MEMS”), for example, gyroscopes, resonators and accelerometers, utilize micromachining techniques (i.e., lithographic and other precision fabrication techniques) to reduce mechanical components to a scale that is generally comparable to microelectronics. MEMS typically include a mechanical structure fabricated from or on, for example, a silicon substrate using micromachining techniques.
The mechanical structures are typically sealed in a chamber. The delicate mechanical structure may be sealed in, for example, a hermetically sealed metal container (for example, a TO-8 “can”, see, for example, U.S. Pat. No. 6,307,815) or bonded to a semiconductor or glass-like substrate having a chamber to house, accommodate or cover the mechanical structure (see, for example, U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and 6,507,082). In the context of the hermetically sealed metal container, the substrate on, or in which, the mechanical structure resides may be disposed in and affixed to the metal container. The hermetically sealed metal container also serves as a primary package as well.
In the context of the semiconductor or glass-like substrate packaging technique, the substrate of the mechanical structure may be bonded to another substrate whereby the bonded substrates form a chamber within which the mechanical structure resides. In this way, the operating environment of the mechanical structure may be controlled and the structure itself protected from, for example, inadvertent contact. The two bonded substrates may or may not be the primary package for the MEMS as well.
MEMS that employ a hermetically sealed metal container or a bonded semiconductor or glass-like substrate to protect the mechanical structures tend to be difficult to cost effectively integrate with high performance integrated circuitry on the same substrate. In this regard, the additional processing required to integrate the high performance integrated circuitry, tends to either damage or destroy the mechanical structures.
Another technique for forming the chamber that protects the delicate mechanical structure employs micromachining techniques. (See, for example, International Published Patent Applications Nos. WO 01/77008 A1 and WO 01/77009 A1). In this regard, the mechanical structure is encapsulated in a chamber using a conventional oxide (SiO2) deposited or formed using conventional techniques (i.e., oxidation using low temperature techniques (LTO), tetraethoxysilane (TEOS) or the like). (See, for example, WO 01/77008 A1, FIGS. 2-4). When implementing this technique, the mechanical structure is encapsulated prior to packaging and/or integration with integrated circuitry.
While employing a conventional oxide to encapsulate the mechanical structures of the MEMS may provide advantages relative to hermetically sealed metal container or a bonded semiconductor or glass-like substrate, a conventional oxide, deposited using conventional techniques, often exhibits high tensile stress at, for example, corners or steps (i.e., significant spatial transitions in the underlying surface(s)). Further, such an oxide is often formed or deposited in a manner that provides poor coverage of those areas where the underlying surface(s) exhibit significant spatial transitions. In addition, a conventional oxide (deposited using conventional techniques) often provides an insufficient vacuum where a vacuum is desired as the environment in which the mechanical structures are encapsulated and designed to operate. These shortcomings may impact the integrity and/or performance of the MEMS.
Moreover, a conventional oxide, deposited using conventional techniques, may produce a film on the mechanical structures during the encapsulation process. This film may impact the integrity of the mechanical structures and, as such, the performance or operating characteristics of the MEMS (for example, the operating characteristics of a resonator).
There is a need for, among other things, MEMS (for example, gyroscopes, resonators, temperature sensors and/or accelerometers) that (1) overcome one, some or all of the shortcomings of the conventional materials and techniques and/or (2) may be efficiently integrated on a common substrate with high performance integrated circuits and/or additional MEMS.
There are many inventions described and illustrated herein. In a first principal aspect, the present invention is a method of sealing a chamber of an electromechanical device having a mechanical structure disposed within the chamber. The method includes depositing a sacrificial layer over at least a portion of the mechanical structure and depositing a first encapsulation layer (for example, a polycrystalline silicon, amorphous silicon, germanium, silicon/germanium or gallium arsenide) over the sacrificial layer. At least one vent is formed through the first encapsulation layer, and at least a portion of the sacrificial layer is removed to form the chamber. Thereafter, a second encapsulation layer is deposited over or in the vent to seal the chamber wherein the second encapsulation layer is a semiconductor material (for example, polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide).
In one embodiment of this aspect of the invention, the first encapsulation layer is a semiconductor material that is doped with a first impurity to provide a first region of a first conductivity type, and the second encapsulation layer is doped with a second impurity to provide a second region with a second conductivity type. The first conductivity type is opposite the second conductivity type. In one embodiment, the first and second encapsulation layers are deposited using an epitaxial or a CVD reactor.
The method may also include planarizing an exposed surface of the second encapsulation layer and removing a sufficient amount of the second encapsulation layer to thereby expose the first encapsulation layer and provide junction isolation.
In one embodiment, a first portion of the first encapsulation layer is comprised of a monocrystalline silicon and a second portion is comprised of a polycrystalline silicon. In this embodiment, a surface of the second encapsulation layer may be planarized to expose the first portion of the first encapsulation. Thereafter, a monocrystalline silicon may be grown on the first portion of the first encapsulation.
In another principal aspect, the present invention is a method of manufacturing an electromechanical device having a mechanical structure that resides in a chamber. The chamber may include a fluid having a pressure that provides mechanical damping for the mechanical structure. The method comprises depositing a first encapsulation layer (comprised of a semiconductor material, for example, polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide) over the mechanical structure. At least one vent is then formed in the first encapsulation layer and the chamber is formed. Thereafter, a second encapsulation layer (comprised of a semiconductor material, for example, polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide) is deposited over or in the vent to seal the chamber.
In one embodiment of this aspect of the invention, the first encapsulation layer is doped with a first impurity to provide a first region of a first conductivity type, and the second encapsulation layer is doped with a second impurity to provide a second region with a second conductivity type. The first conductivity type is opposite the second conductivity type. The first and second encapsulation layers may be deposited using an epitaxial or a CVD reactor.
In one embodiment, a first portion of the first encapsulation layer is comprised of a monocrystalline silicon and a second portion is comprised of a polycrystalline silicon. In this embodiment, a surface of the second encapsulation layer may be planarized to expose the first portion of the first encapsulation. Thereafter, a monocrystalline silicon may be grown on the first portion of the first encapsulation.
In another principal aspect, the present invention is an electromechanical device comprising a chamber including a first encapsulation layer (for example, polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, germanium, silicon/germanium, gallium arsenide, silicon nitride or silicon carbide), having at least one vent, and a mechanical structure having at least a portion disposed in the chamber. The electromechanical device also includes a second encapsulation layer comprised of a semiconductor material (for example, polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide), deposited over or in the vent, to thereby seal the chamber.
In one embodiment, the first encapsulation layer is a semiconductor material that is doped with a first impurity to provide a first region of a first conductivity type. The second encapsulation layer is doped with a second impurity to provide a second region with a second conductivity type. The first conductivity type is opposite the second conductivity type.
The device may also include a contact (i.e., a conductive region, such as the contact area and/or contact via, that is partially or wholly disposed outside of the chamber) disposed outside the chamber. The contact may be a semiconductor that is doped with impurities to increase the conductivity of the area. The contact may be surrounded by the semiconductor of the first conductivity type and the semiconductor of the second conductivity type, which, in combination, forms a junction isolation.
The device of this aspect of the present invention may include a first portion of the first encapsulation layer that is comprised of a monocrystalline silicon and a second portion is comprised of a polycrystalline silicon. In addition, the present invention may include a field region disposed outside and above the chamber wherein the field region is comprised of a monocrystalline silicon.
In one embodiment, the first portion of the first encapsulation layer may be comprised of a monocrystalline silicon and a second portion comprised of a porous or amorphous silicon. In this embodiment, the second encapsulation layer overlying the second portion of the first encapsulation layer is a polycrystalline silicon.



BRIEF DESCRIPTION OF THE DRAWINGS
In the course of the detailed description to follow, reference will be made to the attached drawings. These drawings show different aspects of the present invention and, where appropriate, reference numerals illustrating like structures, components, materials and/or elements in different figures are labeled similarly. It is understood that various combinations of the structures, components, materials and/or elements, other than those specifically shown, are contemplated and are within the scope of the present invention.
FIG. 1 is a block diagram of microelectromechanical system disposed on a substrate, in conjunction with interface circuitry and data processing electronics;
FIG. 2 illustrates a top view of a portion of micromechanical structure, for example, or portion of the interdigitated or comb-like finger electrode arrays of an accelerometer, in conjunction with a contact area and field regions;
FIG. 3 illustrates a cross-sectional view (sectioned along dotted line a-a of FIG. 2) of the portion of the interdigitated or comb-like finger electrode array and contact area and field regions of FIG. 2, in accordance with certain aspects of the present invention;
FIGS. 4A-4G illustrate cross-sectional views of the fabrication of the microstructure of FIG. 3 at various stages of the process, according to certain aspects of the present invention;
FIGS. 5A-5C illustrate cross-sectional views of additional fabrication processes of the microstructure of FIG. 3, according to certain aspects of the present invention;
FIGS. 6A-6F illustrate cross-sectional views of the fabrication of the microstructure, according to certain aspects of the present invention, at various stages of the process;
FIGS. 7A-7C illustrate, among other things, cross-sectional views of more representative illustrations of the growth of single crystal structures using non-conformal and conformal deposition, growth and/or formation techniques;
FIGS. 8A-8E illustrate cross-sectional views of the fabrication of the microstructure at various stages of an encapsulation process where the first encapsulation layer is a permeable material, according to certain aspects of the present invention;
FIGS. 9A-9C illustrate a portion of the fabrication of the interdigitated or comb-like finger electrode array microstructure of FIG. 2, sectioned along dotted line a-a, in accordance with another aspect of the present invention including implementation of three or more encapsulation layers (FIG. 9A) and contact interconnect (FIG. 9C);
FIGS. 10A-10F illustrate cross-sectional views of the fabrication of the microstructure, according to certain aspects of the present invention, at various stages of the process;
FIG. 11A illustrates a cross-sectional view of a portion of a plurality of micromechanical structures, each having one or more electromechanical systems, which are monolithically integrated on or within the substrate of a MEMS, in accordance with certain aspects of the present invention;
FIG. 11B-11D illustrate cross-sectional views of a portion of a micromechanical structure, having a plurality of microstructures, which are monolithically integrated on or within the substrate of a MEMS, in accordance with certain aspects of the present invention
FIG. 12A-12C illustrate cross-sectional views of MEMS, according to certain aspects of the present inventions, including a micromachined mechanical structure portion and an integrated circuit portion, both portions of which are disposed or integrated on a common substrate;
FIG. 13 illustrates a cross-sectional view of a portion of a micromachined micromechanical structure, having a microstructure, which includes a layer of the second encapsulation layer deposited thereon;
FIGS. 14-17 illustrate a buried polysilicon process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 18 illustrates a gasket layer process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 19 illustrates an alignment mark process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 20 illustrates a functional epipoly process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 21 illustrates a contact gasket process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 22 illustrates a vent process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 23 illustrates a sealing process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 24 illustrates a insulation trench process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof;
FIG. 25 illustrates a contact Aluminum process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof; and
FIG. 26 illustrates an Aluminum process step for fabricating a semiconductor device having a micromechanical structure, and the elements thereof.



DETAILED DESCRIPTION
There are many inventions described and illustrated herein. In one aspect, the present invention is directed to a MEMS device, and technique of fabricating or manufacturing a MEMS device, having mechanical structures encapsulated in a chamber prior to final packaging and/or completion of the device. The material that encapsulates the mechanical structures may include one or more of the following attributes: low tensile stress, good step coverage, maintains integrity when subjected to subsequent processing, does not significantly and/or adversely affect the performance characteristics of the mechanical structures (if coated with the material during its deposition, formation and/or growth) within the chamber, maintains designed, appropriate and/or suitable encapsulation attributes over operating conditions and/or time, and/or facilitates integration with high-performance integrated circuits. In one embodiment, the mechanical structures are encapsulated by a semiconductor material, for example, silicon (for example, monocrystalline silicon, polycrystalline silicon, amorphous silicon or porous polycrystalline silicon, whether doped or undoped), germanium, silicon-germanium, silicon carbide or gallium arsenide, or combinations thereof. Such materials may maintain one or more of the following attributes over typical operating conditions and the lifetime of the MEMS.
With reference to FIG. 1, in one exemplary embodiment, a MEMS 10 includes a micromachined mechanical structure 12 that is disposed on substrate 14, for example, an undoped semiconductor-like material, a glass-like material, or an insulator-like material. The MEMS 10 may also include data processing electronics 16, to process and analyze information generated by, and/or control or monitor the micromachined mechanical structure 12. In addition, MEMS 10 may also include interface circuitry 18 to provide the information from micromachined mechanical structure 12 and/or data processing electronics 16 to an external device (not illustrated), for example, a computer, indicator/display and/or sensor.
The data processing electronics 16 and/or interface circuitry 18 may be integrated in or on substrate 14. In this regard, MEMS 10 may be a monolithic structure including mechanical structure 12, data processing electronics 16 and interface circuitry 18. The data processing electronics 16 and/or interface circuitry 18 may also reside on a separate, discrete substrate that, after fabrication, is bonded to or on substrate 14.
With reference to FIG. 2, in one embodiment, micromachined mechanical structure 12 includes mechanical structures 20a-d disposed on, above and/or in substrate 14. The mechanical structures 20a-20d may be comprised of, for example, materials in column IV of the periodic table, for example silicon, germanium, carbon; also combinations of these, for example silicon germanium, or silicon carbide; also of III-V compounds for example gallium phosphide, aluminum gallium phosphide, or other III-V combinations; also combinations of III, IV, V, or VI materials, for example silicon nitride, silicon oxide, aluminum carbide, or aluminum oxide; also metallic silicides, germanides, and carbides, for example nickel silicide, cobalt silicide, tungsten carbide, or platinum germanium silicide; also doped variations including phosphorus, arsenic, antimony, boron, or aluminum doped silicon or germanium, carbon, or combinations like silicon germanium; also these materials with various crystal structures, including single crystalline, polycrystalline, nanocrystalline, or amorphous; also with combinations of crystal structures, for instance with regions of single crystalline and polycrystalline structure (whether doped or undoped).
Moreover, the micromachined mechanical structure 12 may be an accelerometer, gyroscope or other transducer (for example, pressure sensor, strain sensor, tactile sensor, magnetic sensor and/or temperature sensor), or resonator. The micromachined mechanical structure 12 may also include mechanical structures of a plurality of transducers or sensors including one or more accelerometers, gyroscopes, pressure sensors, tactile sensors and temperature sensors. Where micromachined mechanical structure 12 is an accelerometer, mechanical structures 20a-d may be a portion of the interdigitated or comb-like finger electrode arrays that comprise the sensing features of the accelerometer (See, for example, U.S. Pat. No. 6,122,964).
With continued reference to FIG. 2, field regions 22a and 22b and contact area 24 are also disposed on or in substrate 14. The field regions 22 may provide a substrate material for the electronic or electrical components or integrated circuits (for example, transistors, resistors, capacitors, inductors and other passive or active elements) of data processing electronics 16 and/or interface circuitry 18. The contact area 24 may provide an electrical path between micromachined mechanical structure 12 and data processing electronics 16, interface circuitry 18 and/or an external device (not illustrated). The field regions 22 and contact area 24 may be comprised of, for example, silicon (whether doped or undoped), germanium, silicon/germanium, silicon carbide, and gallium arsenide.
FIG. 3 illustrates a cross-sectional view of micromachined mechanical structure 12, including mechanical structures 20a-d, along dotted line a-a′, in accordance with one embodiment of the present invention. The mechanical structures 20a-d are disposed within chamber 26. In one embodiment, chamber 26 is sealed or encapsulated via encapsulating layers 28a and 28b. 
The encapsulating layers 28a and 28b may be comprised of, for example, a semiconductor. In one embodiment, encapsulating layers 28a and 28b may contain silicon (for example, monocrystalline silicon, polycrystalline silicon, amorphous silicon or porous polycrystalline silicon, whether doped or undoped), germanium, silicon/germanium, silicon carbide, and gallium arsenide (and combinations thereof). The encapsulating layers 28a and 28b may be the same materials or different materials.
The encapsulating layers 28a and 28b may be deposited, formed and/or grown using the same or different techniques. For example, encapsulating layer 28a may be a polycrystalline silicon deposited using a low pressure (“LP”) chemically vapor deposited (“CVD”) process (in a tube or EPI reactor) or plasma enhanced (“PE”) CVD process and encapsulating layer 28b may be a doped polycrystalline silicon deposited using an atmospheric pressure (“AP”) CVD process. Alternatively, for example, encapsulating layer 28a may be a silicon germanium deposited using a LPCVD process and encapsulating layer 28b may be doped polycrystalline silicon deposited using a PECVD process. Indeed, all semiconductor materials and deposition techniques, and permutations thereof, for encapsulating chamber 26, whether now known or later developed, are intended to be within the scope of the present invention.
It should be noted that the mechanical structures of one or more transducers or sensors (for example, accelerometers, gyroscopes, pressure sensors, tactile sensors and/or temperature sensors) may be contained or reside in a single chamber and exposed to an environment within that chamber. Under this circumstance, the environment contained in chamber 26 provides a mechanical damping for the mechanical structures of one or more micromachined mechanical structures (for example, an accelerometer, a pressure sensor, a tactile sensor and/or temperature sensor).
Moreover, the mechanical structures of the one or more transducers or sensors may themselves include multiple layers that are vertically and/or laterally stacked or interconnected. (See, for example, micromachined mechanical structure 12b of FIG. 11A; mechanical structure 12 of FIGS. 11B and 11C; and mechanical structures 20a and 20b, contact areas 24a and 24b, and buried contacts 24′ and 24′′ of FIG. 11D). Thus, under this circumstance, the mechanical structures are fabricated using one or more processing steps to provide the vertically and/or laterally stacked and/or interconnected multiple layers.
With reference to FIGS. 4A and 4B, an exemplary method of fabricating or manufacturing a micromachined mechanical structure 12 may begin with a partially formed device including mechanical structures 20a-d and contact area 24 disposed on first sacrificial layer 30, for example, silicon dioxide or silicon nitride. Mechanical structures 20a-d and contact area 24 may be formed using well-known deposition, lithographic, etching and/or doping techniques as well as from well-known materials (for example, semiconductors such as silicon, germanium, silicon-germanium or gallium-arsenide). Moreover, field regions 22a and 22b and first sacrificial layer 30 may be formed using well-known silicon-on-insulator fabrication techniques (FIG. 4A) or well-known formation, lithographic, etching and/or deposition techniques using a standard or over-sized (“thick”) wafer (FIG. 4B). Notably, field regions 22a and 22b, mechanical structures 20 and contact area 24 may be comprised of single or monocrystalline structures (for example, monocrystalline silicon) as illustrated in FIG. 4A, polycrystalline structures, or both monocrystalline and polycrystalline structures as illustrated in FIG. 4B (i.e., field regions 22a and 22b are comprised of single or monocrystalline structures, for example, monocrystalline silicon, and mechanical structures 20 and contact area 24 may be comprised of polycrystalline structures, for example, polycrystalline silicon. Indeed, all techniques, materials and crystal structures for creating a partially formed device including mechanical structures 20a-d and contact area 24 disposed on first sacrificial layer 30, whether now known or later developed, are intended to be within the scope of the present invention.
With reference to FIG. 4C, following formation of mechanical structures 20a-d and contact area 24, a second sacrificial layer 32, for example, silicon dioxide or silicon nitride, may be deposited and/or formed to secure, space and/or protect mechanical structures 20a-d during subsequent processing, including the encapsulation process. In addition, an opening 34 may be etched or formed into second sacrificial layer 32 to provide for subsequent formation of an electrical contact. The opening 34 may be provided using, for example, well known masking techniques (such as a nitride mask) prior to and during deposition and/or formation of second sacrificial layer 32, and/or well known lithographic and etching techniques after deposition and/or formation of second sacrificial layer 32.
With reference to FIGS. 4D, 4E and 4F, thereafter, first encapsulation layer 28a may be deposited, formed and/or grown on second sacrificial layer 32 (see, FIG. 4D). In one embodiment, the thickness of first encapsulation layer 28a in the region overlying second sacrificial layer 32 may be between 1 μm and 25 μm. The external environmental stress on, and internal stress of first encapsulation layer 28a after etching second sacrificial layer 32 may impact the thickness of first encapsulation layer 28a. Slightly tensile films may self-support better than compressive films which may buckle.
The first encapsulation layer 28a may be etched to form passages or vents 36 (see, FIG. 4E). In one exemplary embodiment, the vents have a diameter or aperture size of between 0.1 μm to 2 μm.
The vents 36 are intended to permit etching and/or removal of at least selected portions of first and second sacrificial layers 30 and 32, respectively (see, FIG. 4F). For example, in one embodiment, where first and second sacrificial layers 30 and 32 are comprised of silicon dioxide, selected portions of layers 32 and 32 may be removed/etched using well known wet etching techniques and buffered HF mixtures (i.e., a buffered oxide etch) or well known vapor etching techniques using vapor HF. Proper design of mechanical structures 20a-d and sacrificial layers 30 and 32, and control of the HF etching process parameters may permit the sacrificial layer 30 to be sufficiently etched to remove all or substantially all of layer 30 around mechanical elements 20a-d and thereby release elements 20a-d to permit proper operation of MEMS 10.
In another embodiment, where first and second sacrificial layers 30 and 32 are comprised of silicon nitride, selected portions of layers 30 and 32 may be removed/etched using phosphoric acid. Again, proper design of mechanical structures 20a-d and sacrificial layers 30 and 32, and control of the wet etching process parameters may permit the sacrificial layer 30 to be sufficiently etched to remove all or substantially all of sacrificial layer 30 around mechanical elements 20a-d which will release mechanical elements 20a-d. 
It should be noted that there are: (1) many suitable materials for layers 30 and/or 32 (for example, silicon dioxide, silicon nitride, and doped and undoped glass-like materials, e.g., phosphosilicate (“PSG”) or borophosphosilicate (“BPSG”)) and spin on glass (“SOG”)), (2) many suitable/associated etchants (for example, a buffered oxide etch, phosphoric acid, and alkali hydroxides such as, for example, NaOH and KOH), and (3) many suitable etching or removal techniques (for example, wet, plasma, vapor or dry etching), to eliminate, remove and/or etch sacrificial layers 30 and/or 32.
Indeed, layers 30 and/or 32 may be a doped or undoped semiconductor (for example, polycrystalline silicon, silicon/germanium or germanium) in those instances where mechanical structures 20a-d and contact area 24 are the same or similar semiconductors (i.e., processed, etched or removed similarly). However, in such an instance, mechanical structures 20a-d and contact area 24 may require protection during the etching or removal processes. For example, structures 20a-d and area 24 may be “protected” during the etch or removal process with an oxide layer protecting a silicon based structures 20a-d).
Accordingly, all materials, etchants and etch techniques, and permutations thereof, for eliminating, removing and/or etching, whether now known or later developed, are intended to be within the scope of the present invention.
It should be further noted that, in certain embodiments, in addition to forming vents 36, the etching process of first encapsulation layer 28a also forms contact via 38 (see, FIG. 4F) to facilitate electrical continuity from electrical contact area 24 to a level to or above first encapsulation layer 28a. In this way, additional processing may be avoided, eliminated and/or minimized, for example, processing related to removal of the portion of first encapsulation layer 28a overlying electrical contact area 24 and deposition, formation and/or growth of a suitable material (to provide adequate electrical contact between the various layers of MEMS 10, for example, monocrystalline silicon). Indeed, the resistivity or conductivity of contact via 38 may be adjusted (for example, resistivity reduced and/or conductivity enhanced) using well-known impurity implantation techniques.
Moreover, contact 24 may remain partially, substantially or entirely surrounded by first and second sacrificial layers 30 and/or 32. For example, with reference to FIG. 4F, while mechanical structures 20a-d are released from their respective underlying oxide columns, a column 40 of sacrificial layer 30 beneath or underlying electrical contact area 24 may provide additional physical support as well as electrical isolation for electrical contact area 24.
With reference to FIG. 4G, after releasing mechanical elements 20a-d, a second encapsulation layer 28b may be deposited, formed and/or grown. The second encapsulation layer 28b may be, for example, a silicon-based material (for example, a polycrystalline silicon or silicon-germanium), which is deposited using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD). The deposition, formation and/or growth may be by a conformal process or non-conformal process. The material may be the same as or different from first encapsulation layer 28a. However, it may be advantageous to employ the same material to form first and second encapsulation layers 28a and 28b. In this way, for example, the thermal expansion rates are the same and the boundaries between layers 28a and 28b may enhance the “seal” of chamber 26.
In one embodiment, second encapsulation layer 28b may be epitaxially deposited using an epitaxy reactor and conditions similar to conventional selective epitaxial silicon growth. This may be in a silane, dichlorosilane, or trichlorosilane process with H2, and/or HCl gases. These processes may typically be run from 600° C. to 1400° C.
In one embodiment, the thickness of second encapsulation layer 28b in the region overlying second first encapsulation layer and elements 20a-d may be between 1 μm and 10 μm. Indeed, as MEMS 10, including mechanical structure 12, scale over time and various and/or different materials are implemented, the suitable or necessary thicknesses of first encapsulation layer 28a, second encapsulation layer 28b and combination thereof are likely to change. As such, a ratio of about 1:1 to 1:10 between thicknesses of first encapsulation layer 28a and second encapsulation layer 28b may be advantageous. It is noted, however, that other ratios and thicknesses are clearly suitable (see, for example, FIGS. 7A, 7B, and 8A-E).
The second encapsulation layer 28b may doped with impurities having an opposite conductivity relative to the impurities in first encapsulation layer 28a. For example, first encapsulation layer 28a may be doped with boron and second encapsulation layer 28b may be doped with phosphorous. In this way, upon completion of the sealing or encapsulation process, junctions surrounding electrical contact area 24 are formed which electrically “isolate” contact area 24 from, for example, field region 22b. 
It should be noted that portions of second encapsulation layer 28b are disposed near, next to and/or around contact area 24 may also be subjected to ion implantation after deposition, formation and/or growth. In that way, the electrical “isolation” may be increased or enhanced. In those instances where second encapsulation layer 28b is deposited and/or formed without impurity dopants, the ion implantation may provide primary, all or substantially all of the electrical isolation between contact area 24 and, for example, field region 22b. Indeed, in those instances where second encapsulation layer 28b extends over or between field regions (thereby providing electrical connection there between), the ion implantation of portions of second encapsulation layer 28b (whether doping or counter-doping of a doped second encapsulation layer 28b) that are disposed near, next to and/or around contact area 24 may provide all or substantially all of the electrical isolation between contact area 24 and, for example, field region 22b. 
With reference to FIG. 5A, in another set of embodiments, micromachined mechanical structure 12 may be substantially planarized using, for example, polishing techniques (for example, chemical mechanical polishing (“CMP”)). In this regard, where second encapsulation layer 28b is deposited, formed and/or grown to a level that exceeds first encapsulation layer 28a (see, for example, FIG. 4G), the planarization process removes a portion of second encapsulation layer 28b to provide a “smooth” surface layer and/or (substantially) planar surface. It may be advantageous to remove a sufficient amount of second encapsulation layer 28b so that contact via 38 is electrically isolated by oppositely doped semiconductor layer 28b (See, FIG. 5A) relative to the first encapsulation layer 28a. This exposed planar surface may further provide a well-prepared base (in, for example, field regions 22) upon which integrated circuits (for example, CMOS transistors) and/or micromachined mechanical structure 12 may be fabricated on or in using well known fabrication techniques and equipment.
To facilitate integration of high performance integrated circuits in MEMS 10, it may be advantageous to include field regions 22a and/or 22b that are comprised of monocrystalline silicon in or on which such circuits may be fabricated. In this regard, with reference to FIG. 5B, in one embodiment, a portion of first encapsulation layer (i.e., 22a2 and 22b2) overlying field regions 22a1 and/or 22b1 may be recrystalized thereby “converting” or re-arranging the crystal structure of the polycrystalline material to that of a monocrystalline or substantially monocrystalline material. In this way, transistors or other components of, for example, data processing electronics 16, that are integrated in MEMS 10 may be fabricated in monocrystalline field regions.
In another embodiment, the portion of first encapsulation layer 28a overlying field regions 22a1 and/or 22b1 may be removed, using conventional etching techniques, to expose field regions 22a1 and/or 22b1. Thereafter, monocrystalline silicon may be grown on field regions 22a1 and/or 22b1 to thereby provide field regions 22a2 and/or 22b2.
In yet another embodiment, the portion of first encapsulation layer 28a overlying field regions 22a1 and/or 22b1 may be etched to expose field regions 22a1 and/or 22b1, which are comprised of monocrystalline silicon. Thereafter, transistors or other active components may be integrated in or on field regions 22a and/or 22b using well-known fabrication techniques.
With reference to FIGS. 6A-F, in another set of embodiments, the monocrystalline field regions 22a2 and 22b2 may be grown before, concurrently (simultaneously) or shortly after deposition, formation and/or growth of first encapsulation layer 28a. For example, with reference to FIG. 6A, before or after deposition or formation of second sacrificial layer 32, an epitaxially deposited encapsulation layer of monocrystalline silicon field regions 22a2 and 22b2 may be grown to a level that is above or exceeds second sacrificial layer 32. Alternatively, monocrystalline silicon field regions 22a2 and 22b2 are not grown to a level that is above or exceeds second sacrificial layer 32 (not illustrated).
With reference to FIG. 6B, in one embodiment, after growing monocrystalline silicon field regions 22a2 and 22b2 (and contact area 24), first encapsulation layer 28a may be deposited, formed and/or grown. The first encapsulation layer 28a may be, for example, a silicon-based material (for example, silicon/germanium, silicon carbide, monocrystalline silicon, polycrystalline silicon or amorphous silicon, whether doped or undoped), germanium, and gallium arsenide (and combinations thereof), which is deposited and/or formed using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD). The deposition, formation and/or growth may be by a conformal process or non-conformal process. The material may be the same as or different from first monocrystalline silicon field regions 22a2 and 22b2. In the illustrated embodiment, first encapsulation layer 28a is comprised of a polycrystalline silicon material.
The subsequent processing of micromachined mechanical structure 12 is substantially similar to that described above with respect to FIGS. 4E-4G. As such, the discussion above with respect to micromachined mechanical structure 12, in conjunction with FIGS. 4E-4G, is entirely, fully and completely applicable to this set of embodiments. For the sake of brevity, that description will not be repeated but rather will be summarized.
Briefly, first encapsulation layer 28a may be etched (see, FIG. 6C) to form passages or vents 36 that are intended to permit etching and/or removal of at least selected portions of first and second sacrificial layers 30 and 32, respectively (see, FIG. 6D). Again, proper design of mechanical structures 20a-d and sacrificial layers 30 and 32, and control of the etch process parameters may permit the sacrificial layer 30 to be sufficiently etched to remove all or substantially all of layer 30 around mechanical elements 20a-d and thereby release mechanical elements 20a-d to permit proper operation of MEMS 10 (see, FIG. 6D).
After releasing mechanical elements 20a-d, second encapsulation layer 28b may be deposited, formed and/or grown (see, FIG. 6E). The second encapsulation layer 28b may be, for example, a silicon-based material (for example, a monocrystalline silicon, polycrystalline silicon and/or silicon-germanium), which is deposited using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD). The deposition, formation and/or growth may be by a conformal process or non-conformal process. The material may be the same as or different from first encapsulation layer 28a. As mentioned above, however, it may be advantageous to employ the same material to form first and second encapsulation layers 28a and 28b in order to enhance the “seal” of chamber 26.
It should be noted that the materials and/or surfaces underlying second encapsulation layer 28b, as well as the techniques employed to deposit, form and/or grow first and second encapsulation layer 28b, may initially determine the crystalline structure of the underlying material. For example, in an epitaxial environment having a predetermined set of parameters, the single/mono crystalline structure of encapsulation layers 28a and/or 28b may deposit, form and/or grow in a “retreating” manner (see, FIG. 7A). In contrast, with another predetermined set of parameters, the single/mono crystalline structure of encapsulation layers 28a and/or 28b may deposit, form and/or grow in an “advancing” manner (see, FIG. 7B). The structures and elements herein may be deposited, formed and/or grown in these or other manners. Accordingly, the single/mono crystalline structure (for example, field region 22a2) that is deposited, formed and/or grown on a material having single/mono crystalline structure (for example, field region 22a1) is illustrated schematically as depositing, forming and/or growing in the perpendicular direction (see, for example, FIG. 7C) regardless of the manner or processes of employed.
It should be further noted that the material comprising second encapsulation layer 28b may deposit, form or grow over surfaces in chamber 26 (for example, the surfaces of mechanical structures 20a-d) as the chamber is sealed or encapsulated. When depositing, forming and/or growing second encapsulation layer 28b, care may need to be taken to preserve the desired integrity of the structures and/or surfaces within chamber 26 (see, for example, FIG. 13).
As mentioned above, in certain embodiments, second encapsulation layer 28b is doped with impurities having an opposite conductivity relative to the impurities in first encapsulation layer 28a. In this way, upon completion of the sealing or encapsulation process, junctions surrounding electrical contact area 24 are formed which electrically “isolate” contact area 24 from, for example, field region 22b. 
Further, as mentioned above, in another set of embodiments, where second encapsulation layer 28b is deposited, formed and/or grown to a level that exceeds first encapsulation layer 28a, it may be advantageous to substantially planarize the exposed surface using, for example, polishing techniques (for example, CMP). The planarization process removes a portion of second encapsulation layer 28b to provide a “smooth” surface layer and/or (substantially) planar surface. Indeed, the planarization process may remove a sufficient portion of second encapsulation layer 28b so that contact via 38 is electrically isolated by a ring of oppositely doped semiconductor layer 28b (See, FIG. 6F). Again, as mentioned above, this exposed planar surface may further provide a well-prepared base upon which integrated circuits (for example, CMOS transistors) and/or micromachined mechanical structure 12 may be fabricated on or in using well known fabrication techniques and equipment.
As illustrated, monocrystalline silicon field region 22b2 grows on and above contact area 24. In another embodiment, field region 22b2 does not grow on or over contact area 24. In this embodiment, contact via 38 is comprised primarily of polycrystalline silicon rather than monocrystalline silicon. Moreover, as described above, contact via 38 may be doped with impurities to enhance the conductivity of the material comprising contact via 38.
With reference to FIGS. 8A-E, in another set of embodiments, first encapsulation layer 28a may be a permeable or semi-permeable material (for example, an amorphous sputtered silicon or porous CVD and/or epitaxial deposited polycrystalline silicon). In this set of embodiments, the process of etching or removing layers 30 and 32 may be performed through the permeable or semi-permeable material comprising layer 28a. Thereafter, when depositing, forming and/or growing second encapsulation layer 28b (for example, polycrystalline silicon) on first encapsulation layer 28a, the material may migrate to, fill and/or occupy the pores of first encapsulation layer 28a. Under this circumstance, relatively little material may deposit on the surfaces of the structures within chamber 26 during deposition, formation and/or growth of second encapsulation layer 28b. As such, chamber 26 may be “sealed” or encapsulated towards the upper surfaces of first encapsulation layer 28a (i.e., the surface that are first exposed to the deposition, formation and/or growth process—see, for example, FIG. 8D).
For example, in one embodiment, where the permeable or semi-permeable material is an amorphous sputtered silicon or porous CVD deposited polycrystalline silicon, having a thickness of between 0.1 μm and 2 μm. After etching and/or removal of layers 30 and 32, second encapsulation layer 28b may be a thickness of between 5 μm and 25 μm.
With reference to FIG. 8C, the material comprised of first encapsulation layer 28a may also be densified and thereby “closed” and chamber 26 “sealed” using an annealing process. That is, in this embodiment, heat treating micromachined mechanical structure 12, after etching first and second sacrificial layers 30 and 32, may cause the material of layer 28a to densify thereby sealing or encapsulating chamber 26. As such, a second encapsulation layer 28b may not be necessary to initially seal chamber 26.
With reference to FIG. 8E, in one embodiment, the encapsulation process of chamber 26 may include three or more encapsulation layers. The second encapsulation layer 28b and third encapsulation layer 28C (or subsequent/additional layers) may be deposited, formed and/or grown to “seal” chamber 26. In particular, second encapsulation layer 28b may be, for example, a semiconductor material (for example, silicon, silicon carbide, silicon-germanium or germanium) or metal bearing material (for example, silicides or TiW), which is deposited using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD or PECVD). The deposition, formation and/or growth may be by a conformal process or non-conformal process. The material comprising encapsulation layer 28b may be the same as or different from first encapsulation layer 28a. 
Thereafter, third encapsulation layer 28c may be deposited, formed and/or grown (see, FIG. 8E). The third encapsulation layer 28c may “seal” or close, or more fully “seal” or close chamber 26. The deposition, formation and/or growth of third encapsulation layer 28c may be the same as, substantially similar to, or different from that of encapsulation layers 28a and/or 28b. In this regard, third encapsulation layer 28c may be comprised of, for example, a semiconductor material, an insulator material (for example, silicon nitride or silicon oxide), plastic (for example, photo resist or low-K dielectric) or metal bearing material. The third encapsulation layer 28c may be deposited and/or formed using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD or PECVD). The deposition, formation and/or growth process may be conformal or non-conformal.
It should be noted that the techniques described above to facilitate integration of high performance integrated circuits in MEMS 10, may be implemented with the embodiment illustrated in FIGS. 8A-8E. In this regard, it may be advantageous to include field region 22a that is comprised of monocrystalline silicon in or on which such circuits may be fabricated. In one embodiment, a portion of first encapsulation layer overlying field region 22a may be recrystalized thereby “converting” or re-arranging the crystal structure of the amorphous sputtered silicon or porous CVD and/or epitaxial deposited polycrystalline silicon to that of a monocrystalline or substantially monocrystalline material. In this way, transistors or other components of, for example, data processing electronics 16, that are integrated in MEMS 10 may be fabricated in monocrystalline field regions 22a and/or 22b. 
In another embodiment, the portion of first encapsulation layer 28a (and/or second encapsulation layer 28b) overlying field region 22a may be removed, using conventional etching techniques, to expose field region 22a. Thereafter, monocrystalline silicon may be grown on field region 22a. Alternatively, the portion of first encapsulation layer 28a (and second encapsulation layer 28b) overlying field region 22a may be etched to expose the single crystal material and, thereafter transistors or other active components may be integrated in or on field region 22a using well-known fabrication techniques.
It should be further noted that encapsulation layer 28c (see, for example, FIG. 8E and FIG. 9A) may be deposited, formed and/or grown to, for example, provide a more planar surface, an etch stop layer for subsequent processing, an insulation layer, a ground plane, a power plane, and/or enhance the “seal” of chamber 26 and thereby enhance the barrier to diffusion of fluid 42. For example, with reference to FIGS. 9A-C, layer 28c may be an insulation layer which, in addition (or in lieu thereof) facilitates suitable interconnection with contact area 24 and contact via or plug 38 (for example, using a highly doped polysilicon or metal layer). Thereafter (or currently therewith), layer 28c is patterned to provide contact opening 44 (FIG. 9B). A highly conductive (low electrical resistance) material (for example, a heavily doped semiconductor and/or a metal such as aluminum, chromium, gold, silver, molybdenum, platinum, palladium, tungsten, titanium, and/or copper) may then be deposited to facilitate interconnection (FIG. 9C).
It should be noted that deposition, formation and/or growth of insulation layer 28c and layer 46 may be two of the final process step in the “back-end” of the integrated circuit fabrication of MEMS 10. In this regard, such processing is “combined” with the insulating and contact formation step of the “back-end” of the integrated circuit fabrication of MEMS 10. In this way, fabrication costs may be reduced.
Depending upon the purpose or function of encapsulation layer 28c, it may be, for example, a semiconductor material (for example, a polycrystalline silicon, silicon carbide, silicon/germanium or germanium), an insulator material (for example, silicon dioxide, silicon nitride, BPSG, PSG, or SOG) or metal bearing material (for example, silicides). The encapsulation layer 28c may be, for example, deposited, formed or grown using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD or PECVD). The deposition, formation and/or growth may be by a conformal process or non-conformal process. The material comprising encapsulation layer 28c may be the same as or different from the other encapsulation layers.
In another set of embodiments, second encapsulation layer 28b may be comprised of metal (for example, aluminum, chromium, gold, silver, molybdenum, platinum, palladium, tungsten, titanium, and/or copper), metal oxide (for example, aluminum oxide, tantalum oxide, and/or indium oxide), metal alloy (for example, titanium-nitride, titanium-tungsten and/or Al—Si—Cu) and/or metal-silicon compound (for example, silicides such as tungsten silicide, titanium silicide, and/or nickel silicide) (hereinafter, collectively called “metal bearing material(s)”) deposited and/or formed using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD). In this set of embodiments, first encapsulation layer 28a may be comprised of metal bearing material, semiconductor material or insulator material deposited and/or formed using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD).
For example, with reference to FIG. 10A, after formation of the integrated circuit portion of MEMS 10 (if any), first encapsulation layer 28a is deposited, grown and/or formed on second sacrificial layer 32 (see, FIG. 10A) while selected portions of field region 22 and contact area 24 are protected via a mask or re-exposed by etching. The first encapsulation layer 28a may be, for example, an insulator material (for example, a silicon nitride, silicon dioxide, PSG or BPSG), which is deposited using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD). The deposition, formation and/or growth may be by a conformal process or non-conformal process. Indeed, deposition, formation and/or growth of first encapsulation layer 28a may be a process step in the “back-end” of the integrated circuit fabrication of MEMS 10.
Thereafter, first encapsulation layer 28a may be etched to form passages or vents 36 (see, FIG. 10B). At least selected portions of first and second sacrificial layers 30 and 32, respectively, (see, FIG. 10C) which releases mechanical elements 20a-d to permit proper operation of MEMS 10.
After releasing mechanical elements 20a-d, second encapsulation layer 28b may be deposited, formed and/or grown (see, FIG. 10D). In this embodiment, second encapsulation layer 28b is metal bearing material that is deposited using, for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD). The deposition and/or formation may be by a conformal process or non-conformal process. The deposition, formation and/or growth of second encapsulation layer 28b may also be “combined” with the contact formation step of the “back-end” of the integrated circuit fabrication of MEMS 10. In this way, fabrication costs may be reduced.
Thereafter, it may be advantageous to electrically “isolate” contact area 24 from, for example, field region 22. In one embodiment, this is accomplished using a planarization technique. In this regard, the exposed surface of second encapsulation layer 28b is substantially planarized using, for example, polishing techniques (for example, CMP). The planarization process removes a sufficient portion of second encapsulation layer 28b to electrically isolated contact area 24 (see, FIG. 10E). In another embodiment, selected portions of second encapsulation layer 28b may be etched (see, FIG. 10F).
It should be noted that the portion of second encapsulation layer 28a overlying field region 22 may be removed, using conventional etching techniques, to expose field region 22. In this way, monocrystalline silicon may be grown and/or formed on field region 22. Thereafter, transistors or other active components may be integrated in or on MEMS 10 using well-known fabrication techniques.
Indeed, in those situations where first encapsulation layer 28a is deposited, formed and/or grown over field region 22 and/or contact area 24 without the use of a mask, selected portions of first encapsulation layer 28a that are overlying field area 22 and/or contact area 24 may be etched to expose portions of the monocrystalline silicon. Thereafter, monocrystalline silicon may be grown permitting integration of transistors or other active components as described above.
It should be further noted that the environment (for example, the gas or gas vapor pressure) within chamber 26 determines to some extent the mechanical damping for mechanical structures 20a-d. In this regard, chamber 26 includes fluid 42 that is “trapped”, “sealed” and/or contained within chamber 26. The state of fluid 42 within chamber 26 (for example, the pressure) may be determined using conventional techniques and/or using those techniques described and illustrated in non-provisional patent application entitled “Electromechanical System having a Controlled Atmosphere, and Method of Fabricating Same”, which was filed on Mar. 20, 2003 and assigned Ser. No. 10/392,528 (hereinafter “the Electromechanical System having a Controlled Atmosphere Patent Application”).
The inventions described and illustrated in the Electromechanical System having a Controlled Atmosphere Patent Application may be implemented with any and all of the inventions described and illustrated in this application. For example, the encapsulation techniques described above may be implemented with techniques described in the Electromechanical System having a Controlled Atmosphere Patent Application to trap and/or seal a fluid having a selected, desired and/or predetermined state within the chamber. In this way, the fluid provides a desired, predetermined, appropriate and/or selected mechanical damping for mechanical structures within the chamber.
As another example, the Electromechanical System having a Controlled Atmosphere Patent Application describes a MEMS that includes a plurality of monolithically integrated micromachined mechanical structures having one or more electromechanical systems (for example, gyroscopes, resonators, temperature sensors and/or accelerometers). With reference to FIG. 11A, in one embodiment, MEMS 10 includes a plurality of micromachined mechanical structures 12a-c that are monolithically integrated on or disposed within substrate 14. Each micromachined mechanical structure 12a-c includes one or more mechanical structures 20a-p (for the sake of clarity only a portion of which are numbered) that are disposed in chambers 26a-d. 
In certain embodiments, chambers 26a-d are sealed or encapsulated using the techniques described above. The chambers 26a-d may be sealed or encapsulated in the same or substantially the same manner or using differing techniques. In this way, the plurality of structures 12a-d may be fabricated in ways that provide the same, substantially the same, different or substantially different desired, predetermined, appropriate and/or selected mechanical damping for mechanical structures 20a-p. 
Indeed, in at least one embodiment, structure 12c includes a plurality of chambers, namely chambers 26c and 26d, each containing fluid 42c and 42d, respectively. The chambers 22c and 22d may be sealed or encapsulated in a manner that fluids 42c and 42d, respectively, are maintained at the same or substantially the same selected, desired and/or predetermined states. As such, in this embodiment, fluids 42c and 42d may provide the same or substantially the same desired, predetermined, appropriate and/or selected mechanical damping for mechanical structures 20h-k and 20l-p, respectively.
Alternatively, in at least another embodiment, chambers 26c and 26d may be sealed or encapsulated using different or differing techniques such that fluids 24c and 24d may be “trapped”, “sealed”, maintained and/or contained in chambers 26c and 26d, respectively, at different or substantially different selected, desired and/or predetermined states. In this embodiment, chambers 26c and 26d may be “sealed” using different processing techniques, different processing conditions and/or different materials (for example, gases or gas vapors). As such, after encapsulation, fluids 42c and 42d provide different or substantially different mechanical damping characteristics for mechanical structures 20h-k and 20l-p, respectively. In this way, micromachined mechanical structure 12c may include different electromechanical systems (for example, gyroscopes, resonators, temperature sensors and accelerometers) that require different or substantially different mechanical damping characteristics for optimum, predetermined, desired operation.
For the sake of brevity, all of the inventions described and illustrated in the Electromechanical System having a Controlled Atmosphere Patent Application will not be repeated here. It is expressly noted, however, that the entire contents of the Electromechanical System having a Controlled Atmosphere Patent Application, including for example, the features, attributes, alternatives, materials, techniques and advantages of all of the inventions, are incorporated by reference herein.
As mentioned above, in one set of embodiments, a monolithic structure may include mechanical structure 12 and data processing electronics 16 and/or interface circuitry 18 that are integrated on or in a common substrate. With reference to FIGS. 12A-12C, MEMS 10 includes micromachined mechanical structure 12, having structures 20a-20d and contact area 24, as well as data processing electronics 16, including integrated circuits 50 disposed in field region 22b (and/or region 22a—not illustrated). As mentioned above, mechanical structures 20a-20d (and contact 24) may be formed from, for example, a single crystalline material (FIGS. 12A and 12B) or a polycrystalline material (FIG. 12C). Moreover, contact via or plug 38 may also be formed from, for example, primarily a single crystalline material (FIG. 12B) or a polycrystalline material (FIGS. 12A and 12C).
It should be noted that mechanical structure 12 may be electrically connected to integrated circuits 50 via low resistance layer 46. The integrated circuits 50 may be fabricated using conventional techniques.
In particular, in those instances where contact 24 is accessed directly by integrated circuitry 50, it may be advantageous to provide a low resistance electrical path. The insulation layer 48 may be deposited, formed and/or grown and patterned to provide or facilitate interconnection with contact area 24. Thereafter, a low resistance layer 46 (for example, a heavily doped polysilicon or metal such as aluminum, chromium, gold, silver, molybdenum, platinum, palladium, tungsten, titanium, and/or copper) is formed.
There are many inventions described and illustrated herein. While certain embodiments, features, materials, configurations, attributes and advantages of the inventions have been described and illustrated, it should be understood that many other, as well as different and/or similar embodiments, features, materials, configurations, attributes, structures and advantages of the present inventions that are apparent from the description, illustration and claims. As such, the embodiments, features, materials, configurations, attributes, structures and advantages of the inventions described and illustrated herein are not exhaustive and it should be understood that such other, similar, as well as different, embodiments, features, materials, configurations, attributes, structures and advantages of the present inventions are within the scope of the present invention.
For example, any and all of the embodiments illustrated and described herein may include multiple layers of mechanical structures, contacts areas and buried contacts that are vertically and/or laterally stacked or interconnected (see, for example, micromachined mechanical structure 12 of FIGS. 11B, 11C and 11D). Moreover, single layer and multiple layers of mechanical structures may be themselves be vertically and/or laterally stacked or interconnected (see, for example, micromachined mechanical structure 12b of FIG. 11A). Further, the resulting micromachined mechanical structure 12 may be integrated with integrated circuitry 50 on a common substrate 14. Any vertical and/or lateral location of micromachined mechanical structure 12, relative to integrated circuitry 50, may be suitable.
Moreover, with reference to FIG. 13, in those instances where the material comprising a second or subsequent encapsulation layer (for example, second encapsulation layer 28b) deposits, forms or grows over selected surfaces of the structures in chamber 26 (for example, the surfaces of mechanical structures 20a-d and field areas 22a and 22b) as chamber 26 is sealed or encapsulated, it may be advantageous to design and fabricate mechanical structures 20a-d to account for the deposition, formation or growth of the additional material. The thickness of the additional material 28b′ on the surfaces of mechanical structures 20a-d may be approximately equal to the width or diameter of vent 36. Accordingly, in one set of embodiments, the design (for example, thickness, height, width and/or lateral and/or vertical relation to other structures in chamber 36) of mechanical structures 20a-d incorporates therein such additional material 28b′ and the fabrication of mechanical structures 20a-d to provide a final structure includes at least two steps. A first step which fabricates mechanical structures 20a-d according to initial dimensions (for example, as described above with respect to FIGS. 4A and 4B) and a second step that includes the deposition, formation or growth of material 28b′ as a result of deposition, formation or growth of at least one encapsulation layer, for example, second encapsulation layer 28b and/or subsequent encapsulation layer.
With reference to FIGS. 14-26, an embodiment is described that includes a buried interconnect polysilicon layer. The buried polysilicon layer includes conductive paths and one or more electrodes. The embodiment includes a semiconductor device including a microelectromechanical device and a method of fabricating the same, including the buried polysilicon layer. The embodiment further includes a “protective layer” deposited over the buried polysilicon layer to prevent possible erosion of, or damage to the buried polysilicon layer during processing steps. Such damage may result in shorting between the buried polysilicon, the substrate and the functional layer. In one embodiment, a silicon nitride layer is deposited to encapsulate the buried polysilicon layer. The silicon nitride protects the buried polysilicon layer from exposure during a subsequent HF vapor etch step. The buried polysilicon is encapsulated and protected from melting or reflowing during subsequent high temperature processing steps. Such an embodiment will be described with reference to FIGS. 14-26, which illustrate a device that includes a microelectromechanical structure and process steps for making the device.
FIG. 14 is a diagram of a buried polysilicon (“BP”) process step according to an embodiment, including a substrate 14, a buried polysilicon layer (“buried poly”) 1402, thermal oxide 1404, and IR alignment marks 1406 on thermal oxide 1404. Functions of the BP step include patterning buried poly conductive paths and electrode(s), forming IR alignment marks for aligning Epitaxy and CMP processing, and placing UT marks (not shown) at every reticle for following steps.
FIGS. 15-17 are diagrams that further illustrate the BP step. Referring to FIG. 15, thermal oxide 1404 is etched as shown in field areas, leaving oxide 1404 under the buried poly 1402. A layer of silicon nitride (“nitride”) 1502 is deposited over the top of the entire assembly, including the buried poly 1402, as shown. Referring to FIG. 16, an oxide layer 1602 (above the buried poly 1402) is deposited to fill the etched oxide area. In one embodiment, first oxide layer 1602 is silicon dioxide layer, such as TEOS. Referring to FIG. 17, the surface of TEOS 1602 is planarized. In one embodiment, TEOS 1602 is planarized using a CMP process.
FIG. 18 is a diagram of a gasket process step. A function of the gasket process step is to perform etching to provide a contact to buried poly 1402. Etching includes two separate etch processes. One etch process is an oxide etch to cut contact areas 1804 and areas 1802 in TEOS 1602. The other etch process is a nitride etch to remove nitride 1502 in areas 1802 and contact areas 1804.
FIG. 19 is a diagram of an alignment mark process step. Functions of the alignment mark step include growing monocrystalline areas 1902, and growing a polysilicon layer of functional epitaxy polysilicon (“epipoly”) 1904 over the planarized TEOS 1602. Functions of the alignment mark step further include planarizing functional epipoly 1904, and generating alignment marks 1406 after the planarization of functional epipoly 1904.
FIG. 20 is a diagram of a functional epipoly (“EP”) process step of one embodiment. Functions of the EP step include forming or patterning a micromechanical structure 2012 in functional epipoly 1904. In one embodiment, micromechanical structure 2012 is a movable sensor structure. Functions of the EP step further include patterning posts 2002 in functional epipoly 1904 for a subsequent cap layer, and patterning insulation gaps 2004 in functional epipoly 1904.
FIG. 21 is a diagram of a contact gasket (“CG”) process step of one embodiment. Functions of the CG step include depositing a sacrificial oxide layer 2106 that fills the vertical gaps defining movable sensor structure 2012 and posts 2002 in functional epipoly 1904 as shown. In one embodiment, sacrificial oxide layer 2106 is TEOS. Sacrificial oxide layer 2106 is etched to provide a post contact 2102 and an electrode contact 2104 between functional epipoly 1904 and buried poly 1402. Functions of the CG step further include providing areas for monocyrstalline growth.
FIG. 22 is a diagram of a vent process step of one embodiment. A thin seed layer (for example 2 microns) of epipoly 2202 is grown over TEOS 2106. Layer 2202 is a first encapsulation layer that encapsulates the structure 2102. Epipoly 2202 is etched to provide vents 2204 so that the structure 2012 can be released with HF-vapor etch. Vents 2204 are located over movable structure 2012 and, if possible, cross trenches in functional epipoly 1904, to facilitate a homogenous release. In one embodiment, a wet etch, such as a hydrofluoric acid etch, is not practical. This is because the gaps surrounding structure 2012 are small (e.g., a few microns) and the structure 2012 is flexible. During a wet etch, parts of structure 2012 may stick to one side of the gap.
FIG. 23 is a diagram of a sealing process step. FIG. 23 shows the device after HF-vapor release has evacuated areas 2306. Areas 2306 form a chamber in which structure 2012 is enclosed. A thick epipoly cap layer 2304 is deposited over the previous epipoly layer 2202. Layer 2304 is a second encapsulation layer that encapsulates the structure 2102. Some epipoly 2302 is deposited on areas of the functional epipoly 1904, as shown, so as to “line” evacuated areas 2306. In one embodiment, the deposition process for epipoly 2304 is selective such that deposition does not occur on oxide, but some deposition occurs on silicon. Vents 2204 are sealed during this process. “New” alignment marks 1406 are made after CMP planarization of layer 2304. Optionally, a CMOS device or devices may be fabricated in the monocrystalline area 1902 to the right of the diagram.
FIG. 24 is a diagram of an insulation trench process step. Functions of the insulation trench step include creating insulation trenches 2402 in layer 2304. Trenches 2402 stop at layer 2106.
FIG. 25 is a diagram of a contact Aluminum (“Al”) process step of an embodiment. Layer 2502, which in one embodiment is TEOS, is deposited over layer 2304 and refills insulation trenches 2402. Layer 2502 lies on a conductive layer (epipoly 2304), so posts and contacts are insulated. Functions of the contact Al step include providing contact between cap layer 2304 and conductive Al paths (shown in FIG. 26).
FIG. 26 is a diagram of an Aluminum (“Al”) processing step of an embodiment. Al contacts 2602 are attached to contact areas 2504. Bonding pad 2604 is attached to layer 2502.
The microelectromechanical systems and, and the methods for encapsulating and fabricating same, as described herein, include a method of sealing a chamber of an electromechanical device having a mechanical structure overlying a substrate, wherein the mechanical structure is in the chamber. In an embodiment, the method comprises: depositing a sacrificial layer over at least a portion of the mechanical structure; depositing a first encapsulation layer over the sacrificial layer; forming at least one vent through the first encapsulation layer to allow removal of at least a portion of the sacrificial layer; removing at least a portion of the sacrificial layer to form the chamber; and depositing a second encapsulation layer over or in the vent to seal the chamber wherein the second encapsulation layer is a semiconductor material.
In an embodiment, the semiconductor material is comprised of polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide.
In an embodiment, the first encapsulation layer is comprised of a polycrystalline silicon, amorphous silicon, germanium, silicon/germanium or gallium arsenide.
In an embodiment, the first encapsulation layer is a semiconductor material that is doped with a first impurity to provide a first region of a first conductivity type, and the second encapsulation layer is doped with a second impurity to provide a second region with a second conductivity type and wherein the first conductivity type is opposite the second conductivity type.
In an embodiment, the method further includes planarizing an exposed surface of the second encapsulation layer.
In an embodiment, the method further includes planarizing an exposed surface of the second encapsulation layer and removing a sufficient amount of the second encapsulation layer to thereby expose the first encapsulation layer.
In an embodiment, depositing the first and second encapsulation layers includes using an epitaxial or a CVD reactor.
In an embodiment, the first encapsulation layer is comprised of a porous polycrystalline silicon or amorphous silicon and wherein the second encapsulation layer is comprised of polycrystalline silicon.
In an embodiment, a first portion of the first encapsulation layer is comprised of a monocrystalline silicon and a second portion is comprised of a polycrystalline silicon.
In an embodiment, the method further includes planarizing a surface of the second encapsulation layer to expose the first portion of the first encapsulation.
In an embodiment, the method further includes growing a monocrystalline silicon on the first portion of the first encapsulation.
Embodiments described herein further include a method of manufacturing an electromechanical device having a mechanical structure that resides in a chamber and wherein the chamber includes a fluid having a pressure that provides mechanical damping for the mechanical structure, the method comprising: depositing a first encapsulation layer over the mechanical structure wherein the first encapsulation layer is a semiconductor material; forming at least one vent in the first encapsulation layer; forming the chamber; and depositing a second encapsulation layer over or in the vent to seal the chamber wherein the second encapsulation layer is a semiconductor material.
In an embodiment, the first encapsulation layer is comprised of polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide.
In an embodiment, the second encapsulation layer is comprised of polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide.
In an embodiment, the semiconductor material of the first encapsulation layer is doped with a first impurity to provide a first region of a first conductivity type, and the semiconductor material of the second encapsulation layer is doped with a second impurity to provide a second region with a second conductivity type and wherein the first conductivity type is opposite the second conductivity type.
In an embodiment, the method further includes planarizing an exposed surface of the second encapsulation layer to expose the first encapsulation layer.
In an embodiment, a first portion of the first encapsulation layer is a monocrystalline silicon and a second portion is a polycrystalline silicon.
In an embodiment, the method further includes planarizing a surface of the second encapsulation layer to expose the first portion of the first encapsulation.
In an embodiment, the method further includes growing a monocrystalline silicon on the first portion of the first encapsulation.
Embodiments described herein further comprise an electromechanical device comprising: a chamber including a first encapsulation layer having at least one vent; a mechanical structure, wherein at least a portion of the mechanical structure is disposed in the chamber; a second encapsulation layer comprised of a semiconductor material, deposited over or in the vent, to thereby seal the chamber.
In an embodiment, the second encapsulation layer is comprised of polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide.
In an embodiment, the first encapsulation layer is comprised of polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, germanium, silicon/germanium, gallium arsenide, silicon nitride or silicon carbide.
In an embodiment, the first encapsulation layer is a semiconductor material that is doped with a first impurity to provide a first region of a first conductivity type, and the semiconductor material of the second encapsulation layer is doped with a second impurity to provide a second region with a second conductivity type and wherein the first conductivity type is opposite the second conductivity type.
In an embodiment, the electromechanical device further includes a contact disposed outside the chamber.
In an embodiment, the contact is a semiconductor that is doped with impurities to increase the conductivity of the area.
In an embodiment, a first portion of the first encapsulation layer is comprised of a monocrystalline silicon and a second portion is comprised of a polycrystalline silicon.
In an embodiment, a first portion of the first encapsulation layer is comprised of a monocrystalline silicon and a second portion is comprised of a porous or amorphous silicon.
In an embodiment, the second encapsulation layer overlying the second portion of the first encapsulation layer is a polycrystalline silicon.
In an embodiment, the electromechanical device of claim 28 includes a field region disposed outside and above the chamber wherein the field region is comprised of a monocrystalline silicon.
The term “depositing” and other forms (i.e., deposit, deposition and deposited) in the claims, means, among other things, depositing, creating, forming and/or growing a layer of material using, for example, a reactor (for example, an epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD, or PECVD)).
Further, in the claims, the term “contact” means a conductive region, partially or wholly disposed outside the chamber, for example, the contact area and/or contact via.
Finally, it should be further noted that while the present inventions have been described in the context of microelectromechanical systems including micromechanical structures or elements, the present inventions are not limited in this regard. Rather, the inventions described herein are applicable to other electromechanical systems including, for example, nanoelectromechanical systems. Thus, the present inventions are pertinent to electromechanical systems, for example, gyroscopes, resonators, temperatures sensors and/or accelerometers, made in accordance with fabrication techniques, such as lithographic and other precision fabrication techniques, which reduce mechanical components to a scale that is generally comparable to microelectronics.

## Claims

1. An electromechanical device comprising:
a substrate layer;
a first insulation layer over the substrate layer;
a buried polysilicon layer over the first substrate layer;
a first plurality of alignment marks placed adjacent the buried polysilicon layer over the first substrate layer and for aligning equipment for epitaxy and polish processing;
a chamber including a first encapsulation layer having at least one vent;
a mechanical structure, wherein at least a portion of the mechanical structure is disposed in the chamber and the at least one vent is disposed over the mechanical structure;
a protective layer over the buried polysilicon layer, wherein the buried polysilicon layer includes conductive paths and at least one electrode, wherein the protective layer forms at least part of a separating layer between the chamber and the buried polysilicon layer, wherein the protective layer comprises a nitride;
a second insulation layer over the protective layer;
the first encapsulation layer encapsulating the mechanical structure, wherein the first encapsulation layer is etched to provide the at least one vent so that the mechanical structure can be released;
a second plurality of alignment marks aligned to the first plurality of alignment marks and formed within the first encapsulation layer by growing monocrystalline areas defining the second plurality of alignment marks and growing a first epitaxy polysilicon layer over the protective nitride layer; and
a second encapsulation layer comprised of a semiconductor material formed by a second and relatively thick epitaxy polysilicon layer deposited over the first epitaxy polysilicon layer to line an inner surface of an evacuated area surrounding the mechanical structure, and to encapsulate the released mechanical structure and seal the at least one vent, and wherein final alignment marks corresponding to the second plurality of alignment marks are formed in the second encapsulation layer.

2. The electromechanical device of claim 1 wherein the second encapsulation layer is comprised of polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, silicon carbide, silicon/germanium, germanium, or gallium arsenide.

3. The electromechanical device of claim 2 wherein the first encapsulation layer is comprised of polycrystalline silicon, porous polycrystalline silicon, amorphous silicon, germanium, silicon/germanium, gallium arsenide, silicon nitride or silicon carbide.

4. The electromechanical device of claim 1 wherein:
the first encapsulation layer is a semiconductor material that is doped with a first impurity to provide a first region of a first conductivity type, and
the semiconductor material of the second encapsulation layer is doped with a second impurity to provide a second region with a second conductivity type and wherein the first conductivity type is opposite the second conductivity type.

5. The electromechanical device of claim 1 further including a contact disposed outside the chamber.

6. The electromechanical device of claim 5 wherein the contact is a semiconductor that is doped with impurities to increase the conductivity of the area.

7. The electromechanical device of claim 6 includes a field region disposed outside and above the chamber wherein the field region is comprised of a monocrystalline silicon.

8. The electromechanical device of claim 5 wherein the second encapsulation layer overlying the second portion of the first encapsulation layer is a polycrystalline silicon.

9. The electromechanical device of claim 1 wherein the first encapsulation layer comprises;
a first portion comprised of a monocrystalline silicon; and
a second portion comprised of a polycrystalline silicon.

10. The electromechanical device of claim 1 wherein the first encapsulation layer comprises;
a first portion comprised of a monocrystalline silicon; and
a second portion comprised of a porous or amorphous silicon.

11. An electromechanical device comprising:
a substrate;
an insulation layer over the substrate;
a buried polysilicon layer over the insulation layer;
a first plurality of alignment marks placed adjacent the buried polysilicon layer over the first substrate layer and for aligning equipment for epitaxy and polish processing;
a chamber including a first encapsulation layer having a plurality of vents disposed over the chamber;
a mechanical structure, wherein at least a portion of the mechanical structure is disposed in the chamber;
a protective nitride layer over the buried polysilicon layer and the insulation layer, wherein the protective layer forms at least part of a separating layer between the chamber and the buried polysilicon layer;
the first encapsulation layer encapsulating the mechanical structure, wherein the first encapsulation layer is etched to provide the plurality of vents so that the mechanical structure can be released
a second plurality of alignment marks aligned to the first plurality of alignment marks and formed within the first encapsulation layer by growing monocrystalline areas defining the second plurality of alignment marks and growing a first epitaxy polysilicon layer over the protective nitride layer; and
a second encapsulation layer comprised of a semiconductor material formed by depositing a second and relatively thick epitaxy polysilicon layer over the first epitaxy polysilicon layer to line an inner surface of an evacuated area surrounding the mechanical structure, and disposed to seal the plurality of vents and encapsulate the mechanical structure, and wherein final alignment marks corresponding to the second plurality of alignment marks are formed in the second encapsulation layer.