HK1110061B - Packaging for micro electro-mechanical systems and methods of fabricating thereof - Google Patents

Description

MEMS package and method of manufacturing the same

Cross Reference to Related Applications

This application claims priority from U.S. provisional patent application Serial No. 60/553,178, "Hermetic Packaging for MEMS," filed 3/15/2004, the entirety of which is hereby incorporated by reference.

Technical Field

The present invention relates generally to microelectromechanical devices, and more particularly to packages for microelectromechanical devices.

Background

Adapting microelectronic packages to microelectromechanical systems (MEMS) devices involves some challenging packaging requirements. The typical three-dimensional and moving elements of many MEMS devices often require the use of some type of cavity package (cavity package) to provide free space above the active surface of the MEMS device. The interior of the cavity must generally be free of contamination, including without excessive outgassing of the material. MEMS devices may also require thermal insulation in the package and require mounting methods that minimize mechanical stress on the device. The cavity may be evacuated or filled with an atmosphere control agent such as a getter.

In addition to these requirements, MEMS devices are susceptible to damage during conventional micropackaging processes. The presence of the movable three-dimensional mechanical structure makes the unpackaged MEMS devices more fragile. By way of example, if handled roughly, the movable MEMS structures may contact and permanently adhere together (stiction).

In addition, the cost of MEMS packages is also a critical factor for many applications. For example, 50-90% of the manufacturing cost of a MEMS device is consumed in packaging the MEMS device. For example, surface structures and cavity requirements for MEMS devices typically require the use of low cost transfer molded plastic packages used in most integrated circuits to be prohibitive. In addition, common sealing techniques, such as injection molding, typically require high pressures, which can easily damage the microstructures.

Thus, the aforementioned inefficiencies and inadequacies have heretofore not been addressed in the industry.

Disclosure of Invention

Embodiments of the present invention provide systems and methods for fabricating microelectromechanical device packages. Broadly speaking, one embodiment of the system includes a micro-electromechanical device formed on a substrate layer; and a thermally decomposable sacrificial structure that protects at least a portion of the microelectromechanical device, wherein the sacrificial structure is formed on the base layer and surrounds a gas cavity that surrounds an active surface of the microelectromechanical device; and an overcoat layer disposed on a portion of the substrate layer, the overcoat layer being a different structure from the substrate layer and protecting at least a portion of the microelectromechanical device, wherein the overcoat layer surrounds a portion of the gas cavity surrounding the active surface of the microelectromechanical device; and the outer coating is made of a molded polymer that is permeable to decomposition gases generated by decomposition of the sacrificial polymer within the gas cavity.

Embodiments of the invention may also provide a packaged microelectromechanical device system, comprising: a micro-electromechanical device formed on the base layer; and an overcoat layer disposed on a portion of the substrate layer, the overcoat layer being a different structure from the substrate layer and protecting at least a portion of the microelectromechanical device, wherein the overcoat layer surrounds a portion of a gas cavity surrounding an active surface of the microelectromechanical device; and the outer coating is made of a molded polymer having the property of being permeated by a decomposition gas generated by decomposition of the sacrificial polymer while forming a gas cavity.

Embodiments of the invention may also provide methods for fabricating microelectromechanical device packages. In this regard, one of the embodiments of the method may be broadly summarized as including the steps of: forming a pyrolytic sacrificial layer on a substrate of a micro-electromechanical device, wherein the sacrificial layer surrounds a gas cavity, the gas cavity surrounding a portion of the micro-electromechanical device; forming an overcoat layer around the sacrificial layer; and a thermally decomposable sacrificial layer, wherein decomposed molecules of the sacrificial layer permeate through the overcoat layer, and a gas cavity is formed at a formation position of the thermally decomposable sacrificial layer; wherein the overcoat is disposed on a portion of the substrate layer, the overcoat being a different structure from the substrate and protecting at least a portion of the microelectromechanical device, wherein the overcoat surrounds a portion of the gas cavity surrounding the active surface of the microelectromechanical device.

Other systems, methods, features and advantages that are within the scope of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.

Drawings

The invention may be better understood with reference to the following drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the figures, like referenced numerals designate corresponding elements throughout the different views.

Figure 1 is a view of a MEMS package according to one embodiment of the invention.

Fig. 2 is a flow diagram of a representative process for manufacturing the MEMS package shown in fig. 1.

Fig. 3 is a view of a manufacturing step of the process shown in fig. 2.

FIG. 4 is a diagram of an embodiment of a process for performing the step of applying a sacrificial layer described in FIG. 2.

FIG. 5 is a diagram of an embodiment of a MEMS device suitable for implementing the process shown in FIG. 4.

FIG. 6 is a diagram of an embodiment of a process for performing the step of applying a sacrificial layer described in FIG. 2.

FIG. 7 is a diagram of an embodiment of a MEMS device suitable for implementing the process shown in FIG. 6.

FIG. 8 is a diagram of one embodiment of a MEMS device suitable for performing one of the etching processes of the step of applying the sacrificial layer depicted in FIG. 2.

Fig. 9A-9D are views of the packaging process shown in fig. 4 for an SOI beam resonator.

Fig. 10A-10F are views of the packaging process shown in fig. 6 for a HARPSS polysilicon ring gyroscope.

Fig. 11A-11B are graphs of the frequency response of the SOI beam resonator shown in fig. 9A-9D before and after packaging.

Fig. 12-15 are views of different embodiments of a MEMS package that may be implemented using portions of the process shown in fig. 2.

Fig. 16 is a view of a manufacturing process for attaching a MEMS device to a leadframe package according to the present invention.

Fig. 17 is a diagram of various packaging techniques that may be employed with the MEMS package of the present invention.

Detailed Description

Fig. 1 illustrates a MEMS device package 100 according to one embodiment of the present invention. In this regard, the MEMS device package 100 is for packaging a free standing MEMS structure 110 and generally includes: a base layer 105; one or more MEMS structures 110 formed on the base layer 105; a cavity or air gap or gas cavity 108 surrounding the free-standing MEMS structure 110; a shielding layer 120 surrounding the cavity 108 for providing mechanical, electrical, chemical and/or environmental protection to the MEMS device; a plurality of electrical connections extending from the inside to the outside of the cavity (through or under the shield 120 to conduct electrical signals from the outside to the inside); and contacts 130 formed on substrate 105 for connecting package 100 to external points or terminals. After packaging the free-standing or released MEMS structure 110 into the MEMS package 100, the package 100 may be attached to a circuit board or system by a wide variety of unique and different means, as described in detail below.

The base layer 105 may be made of a material suitable for use in a particular MEMS system or device. Exemplary materials include, but are not limited to, glass, diamond, quartz, sapphire, silicon compounds, germanium compounds, gallium compounds, indium compounds, or other semiconductors and/or compounds. In addition, base layer 105 may comprise, for example, a non-semiconductor base material, including any dielectric material, metal (e.g., copper and aluminum), or ceramic or organic material used in printed circuit boards. The contact 130 may be formed of a conductor, such as a metal and/or metal alloy, in consideration of suitable conditions such as adhesion and thermal properties.

As previously described, the shielding layer 120 surrounding the cavity 108 provides mechanical, electrical, chemical, and/or environmental protection to the MEMS device. Different levels of protection are required based on the particular MEMS device or the particular application. Generally, an air gap or cavity is an enclosed area that contains a gas that does not need to be gas permeable, and in some embodiments, the air gap is under vacuum. The air gap or cavity is typically covered by an overlying structure.

In general, the MEMS structure 110 is encapsulated to ensure that the device is protected from the operating environment and the environment is protected from materials and operation. As an example, one level of protection provides protection from interference with other mechanical structures or objects to ensure the structural integrity of the MEMS structure 110. In this type of enclosure structure, the shield layer 120 should be made of a material that is capable of withstanding the typically harsh conditions of the particular MEMS device operating environment. Another additional level of protection may further provide protection from exposure to oxygen or water (e.g., a sealed enclosure). Thus, for this type of protection, the shield 120 is typically made of a metallic material that provides a hermetic seal around the air cavity 108. In addition, some levels of shielding 120 may also provide additional levels of protection to further provide protection from exposure to any outside gases. For the final level of protection, a vacuum is created within the air cavity 108, and the shield 120 is typically made of a metallic material that maintains the vacuum within the air cavity 108.

A process (method) 200 for manufacturing a MEMS device package 100 according to one embodiment of the invention will be described with reference to fig. 2 and 3. The process 200 is based on the thermal decomposition of a sacrificial material, as described herein. It should be noted that certain parts of the manufacturing process are not included in fig. 2 for clarity. Likewise, the fabrication processes described below are not meant to exhaustively list all of the steps required for fabricating the MEMS device package 100. Furthermore, the manufacturing process is flexible in that the processing steps may be performed in a different order than that shown in FIG. 2, or some steps may be performed simultaneously.

Referring now to fig. 2 and 3, a pyrolytic sacrificial polymer (e.g., Unity 200 of LLC, Brecksville, ohio, usa) is applied 210 onto the surface of a released MEMS device 310 to produce a MEMS device package 320 having a sacrificial layer 325. The sacrificial polymer material is patterned to encapsulate a surface or portion of a surface of the MEMS device 310 to create a sacrificial layer 325. By way of example, a photosensitive or photosetting sacrificial polymer material may be used to make the sacrificial layer 325. Thus, the photocurable polymer may be deposited on the substrate 328 using techniques such as spin coating, doctor blade coating, sputtering, lamination, screen or stencil printing, melt dispensing, Chemical Vapor Deposition (CVD), and plasma-based deposition systems.

Next, after patterning with the sacrificial material 325, the MEMS device is overcoated with a dielectric material (e.g., Avatrel, Polyamide, SU8)335 on top of the sacrificial layer 325 and any other desired areas on the MEMS structure. At this point, an overcoat is applied (220) onto the MEMS structure 320 to produce a MEMS device package 330 having a sacrificial layer 325 and an overcoat 335. Overcoat 335 can be deposited on substrate 328 using techniques such as spin coating, photo-setting methods, doctor blade coating, sputtering, lamination, screen or stencil printing, melt dispensing, Chemical Vapor Deposition (CVD), and plasma-based deposition systems. The overcoat material may also be patterned to expose various features, such as bond pads (pads) or contacts.

After overcoat 335 is prepared, sacrificial layer 325 is decomposed by heating the sacrificial polymer material of sacrificial layer 325 to a temperature sufficient to decompose the polymer (e.g., 200 ℃ F. and 250 ℃ C.). As an example, the sacrificial layer 325 may be decomposed (230) above the thermal decomposition temperature of the sacrificial layer 325 in a furnace to produce a MEMS device package 340 having a substantially residue-free low residual air gap or residue-free cavity 348 covered by the overcoat layer 335. If the residue is below a "substantial" value, little or no effect on the final product may be considered "residue free". By way of example, in MEMS devices, residues of less than 10nm generally have no effect on the final product and are considered residue-free.

During this process, decomposition products of the sacrificial layer 325 diffuse or permeate through the overcoat layer 335. In an additional step, additional metallic material 355 is added 240 to the MEMS structure to cover the overcoat 335 (e.g., by sputtering and patterning the metallic material) to create a MEMS device package 350 with a metallic cap or shield 355 to protect the active surface 358 of the MEMS device. The metal shield 355 provides one type of protection for the MEMS device 310 from external forces or elements. In particular, metals are known to provide a gas-tight barrier. Thus, the metal hermetic shield 355 allows the MEMS device to be exposed to ambient conditions.

In some embodiments, it is desirable to vacuum encapsulate the MEMS device. One of the embodiments for implementing a vacuum package for a MEMS device employs the process 200 described above. However, to add additional metal material at step 335, the MEMS device 340 is placed in a vacuum chamber, such as an evaporator, and the air within the air cavity region 348 is evacuated. Metal is then deposited onto the overcoat material under vacuum, as previously described in step 255. The metal shield 355 prevents air from entering the area of the metal enclosure, thus providing a vacuum package for the MEMS device. Note that in some embodiments, the step for removing the sacrificial layer may also be performed in a vacuum chamber, so that multiple steps may be performed simultaneously.

It is also noted that in some embodiments, the fabrication of the MEMS package need not go through each of the foregoing steps in fig. 2, but can also accommodate further processing to provide electrical connections to external points or terminals, as discussed below.

The sacrificial polymer used to create the sacrificial layer 325 may be a polymer that slowly decomposes and does not create excessive pressure build-up when the air pocket region 348 is formed within the peripheral material. . In addition, the gas molecules produced by the decomposition of the sacrificial polymer are small enough to permeate through the overcoat layer 335. In addition, the sacrificial polymer has a decomposition temperature that is lower than the decomposition or degradation temperature of the MEMS structure and the overcoat material. In addition, the decomposition temperature of the sacrificial material should be above the deposition or curing temperature of the overcoat material, but below the degradation temperature of the components in the structure in which the sacrificial polymer is used.

The sacrificial polymer may include compounds such as, but not limited to, polynorbornenes, polycarbonates, polyethers, polyesters, functionalized compounds of each, and combinations thereof. Polynorbornenes can include, but are not limited to, alkenyl substituted norbornenes (e.g., norbornene cyclopropenes). Polycarbonates may include, but are not limited to, norbornene carbonate, polypropylene carbonate, polyethylene carbonate, polycyclohexene carbonate, and combinations thereof.

In addition, the sacrificial polymer may include additional components that can alter the processability of the sacrificial polymer (e.g., increase or decrease the stability of the sacrificial polymer to heat and/or light radiation). In this regard, the initiator may include, but is not limited to, a photoinitiator and a photoacid initiator.

Examples of disclosed sacrificial compositions include, but are not limited to, a sacrificial polymer and one or more positive color (positive tone) or negative color (negative tone) compositions. The orthochromatic component may include a photoacid generator.

As an example, the sacrificial member may include any one of a negative color component and/or a positive color component. The negative-coloring component may include a compound that produces a reactant that can cause crosslinking in the sacrificial polymer. The negative color-developing component may include a compound such as, but not limited to, a photosensitive radical generator. Other negative color components, such as photoacid generators (e.g., in epoxy-functionalized systems), can also be used.

A negative-acting photosensitive free radical generator is a compound that, upon exposure to light, will break into two or more compounds, at least one of which is a free radical. In particular, the negative color photoinitiator may include, but is not limited to, bis (2, 4, 6-trimethylbenzoyl) -phenylphosphine oxide (Irgacure 819, available from gasoline and refining corporation); 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (Irgacure 369 from Ciba specialty Chemicals); 2, 2-dimethoxy-1, 2-diphenylethan-1-one (Irgacure 651 from Ciba specialty Chemicals); 2-methyl-1 [4- (methylthio) -phenyl ] -2-morpholinopropan-1-one (Irgacure 907, product of gasoline and Seiko); benzoin ethyl ether (BEE, Aldrich Co.); 2-methyl-4' (methylthio) -2-morpholinyl-propiophenone; 2, 2' -dimethoxy-2-phenyl-acetophenone (Irgacure 1300 from baba corporation); 2, 6-bis (4-azidobenzylidene) -4-ethylcyclohexanone (BAC-E); and combinations thereof.

The orthochromatic component may include, but is not limited to, a photoacid generator. In particular, the orthochromatic photoacid generator can include, but is not limited to, nucleophilic halides (e.g., diphenyliodonium salts, diphenylfluoro salts) and complex and metal halide anions (e.g., trithionium salts). In particular, the photoacid generator may be 4-methylphenyl [4- (1-methylethyl) phenyl ] tetrakis (pentafluorophenyl) borate]Onium (DPI-TPFPB); tris (4-tert-butylphenyl) sulfonium tetrakis- (pentafluorophenyl) borate (TTBPS-TPFBP); tris (4-tert-butylphenyl) sulfonium hexafluorophosphate (TTBPS-HFP); trithiophenyl triflate (TPS-Tf); bis (4-tert-butylphenyl) onium trifluoromethanesulfonate (DTBPI-Tf); triazine (TAZ-101); trithio hexafluorophosphate (TPS-103); rhodosil-^TMPhotonititor 2074 (FABA); bis (perfluoromethanesulfonyl) imide trithionate (TPS-N1); bis (perfluoromethanesulfonyl) imide di- (p-tert-butyl) phenylium (DTBPI-N1); triphenylsulfur; tris (perfluoromethanesulfonyl) methide (TPS-C1); tris (perfluoromethanesulfonyl) methyldi- (p-tert-butylphenyl) onium (DTBPI-C1); and combinations thereof.

The photoacid generator can be about 0.5% to 5% by weight of the sacrificial component. In particular, the photoacid generator can be about 1% to 3% by weight of the sacrificial component.

In addition to the photoacid generator and the sacrificial polymer (e.g., about 50% to about 99%), the remaining proportion of the sacrificial component can include solvents such as, but not limited to, trimethylbenzene, N-methyl-2-pyrrolidone, propylene carbonate, anisole, cyclohexanone, propylene glycol, -methyl ether acetate, N-butyl acetate, diglyme, ethyl ethoxypropionate, and combinations thereof.

Pyrolysis of the sacrificial material may be accomplished by heating the MEMS device to the pyrolysis temperature of the sacrificial polymer and holding at that temperature for a period of time (e.g., 1-2 hours). The pyrolysis products then diffuse or permeate through the outer coating polymer layer, leaving a hollow structure (air cavity) with little residue.

Overcoat 335 can be any mode of polymer or deposited film (e.g., silicon dioxide, silicon nitride, etc.) that has the property of being permeable or semi-permeable to the decomposition gases produced by the decomposition of the sacrificial polymer while forming air gaps or cavities. In addition, the outer coating polymer layer is resilient so as not to break or fracture during manufacture and use. In addition, the overcoat layer 335 is stable at temperatures at which the sacrificial polymer decomposes. Examples of overcoat layer 335 include compounds such as polyimide, polynorbornene, epoxy, polyarylether, and parylene. In particular, the overcoat 335 includes a compound such as Amoco Ultrael^TM 7501，BF Goodrich Avatrel^TMDieelecric Polymer, DuPont 2611, DuPont 2734, DuPont 2771, and DuPont 2555. Overcoat layer 335 can be deposited on the substrate using techniques such as spin coating, doctor blade coating, sputtering, lamination, screen or stencil printing, melt dispensing, Chemical Vapor Deposition (CVD), and plasma-based deposition systems.

Various measures may be used to apply the pyrolytic sacrificial layer and the overcoat layer to the MEMS device. In this regard, FIG. 4 depicts one such method suitable for packaging a micromachined MEMS device, such as a silicon-on-insulator (SOI) resonator or other MEMS device with small holes (e.g., H > g and t < 50 μm, where H is the height of the air cavity, g is the width of the hole, and t is the thickness of the sacrificial layer), as shown in FIG. 5.

In this packaging implemented by the patterned (PVP) approach, a photo-settable sacrificial polymer Unity 200 (promeus, LLC, Brecksville, ohio) is first spin coated on the surface of the MEMS device 410 to create a thin sacrificial layer 412, and the MEMS device is soft baked (420). Then, deep ultraviolet exposure (λ 248nm) is performed (420) to pattern the thin sacrificial layer 412. Sacrificial layer 412 is baked and developed (430) at about 110 deg.C to decompose the exposed areas, and then sacrificial material (440) is sealed (encapsulated) with a photo-settable polymeric overcoat Avatrel (Promeris, LLC) 414.

After sealing 440, bond pads 416 are revealed by a photolithographic patterning process of overcoat material 414. The sacrificial material covering the MEMS structure underneath the overcoat layer is then thermally decomposed (460) at about 200-300 deg.C to create the air cavity 418. This is the highest temperature step in the overall process. Byproducts of thermal decomposition may readily diffuse out through overcoat 414. An aluminum layer 417 may be sputtered to hermetically seal the packaged MEMS device.

After the sacrificial material is decomposed, the interior of cavity 418 is cleaned of the sacrificial material, and device structure 419 is intact and free to move, leaving no residue on the device. For example, in one experiment, a 25 μm thick SOI beam resonator (frequency of 2.6 MHz) with a 1 μm air gap was encapsulated by Unity sacrificial material by the PVP method. The Unity sacrificial material is a photo-settable polycarbonate that has good adhesion on silicon, oxides and metals and can be thermally decomposed at low temperatures. In addition, Unity sacrificial materials are characterized by complete decomposition over a narrow temperature range. In this experiment, the Q factor of the device (Q8000) was unchanged after encapsulation and after removal of the sacrificial material.

Alternatively, fig. 6 shows a packaging method in which a layer of pyrolytically sacrificial material is applied by a dispensing technique (PVD). The method is more suitable for packaging a bulk micromachined structure (e.g., a HARPSS gyroscope/accelerometer) using a fragile element and a wide and deep cavity (e.g., L > g, where L represents the length of air cavity 710 and g represents the width of hole 720), as shown in fig. 7.

In this method, a sacrificial thermolabile material 610 (not necessarily photosetting) is applied 620 with an adjustable drop size (e.g., 1mm to 1cm) by a syringe-type dispensing tool (e.g., manually or automatically) to cover the air cavity 612. The sacrificial material 610 is then overcoated 630 with an Avatrel overcoat material, followed by a continuing processing sequence similar to the PVP process, including a heat release step 640 for decomposing the sacrificial layer 610 and a metallization step 650 for adding a metallic shield 617 to the air cavity 612. A final metallization step (650) may result in a hermetically sealed package 618.

The methods described above are examples of methods for applying the sacrificial material 325 and/or the shielding material 120 (e.g., overcoat material, metal layers, other protective shields, etc.) onto the MEMS device. However, the present invention is not limited to the methods described above with reference to FIGS. 4-7. For example, other lithographic or etching techniques used in semiconductor manufacturing processes may be employed. In this regard, the MEMS device may also be packaged by a mask etch process on a thick sacrificial material, which is suitable for packaging small MEMS structures (e.g., HARPSS resonators, RF switches) with fragile elements or wide and deep cavities (e.g., t > L > 50 μm, where t represents the thickness of sacrificial layer 810 and L represents the length of air cavity 820), as shown in FIG. 8. In this regard, an oxygen mask may be used to remove the sacrificial material from the undesired regions by means of an oxygen plasma.

The feasibility of implementing the foregoing method to package MEMS devices has been successfully demonstrated. By way of example, a 15 μm thick, 2.6MHz SOI beam resonator (released) with 1 μm gap spacing is shown in FIG. 9A (where the SCS beam and isolation trench are labeled), which is packaged with PVP. Narrow trenches are etched down to the buried oxide to define the shape of the resonator and sensor/drive pad, and then the buried oxide is removed in an HF solution. Fig. 9B shows the resonator after being subjected to PVP. As shown, the resonator exhibits a 15 μm high cavity with a 20 μm thick overcoat.

Figure 9C shows the unpackaged resonator after DC sputtering of gold to hermetically seal the device. In this device, the Avatrel overcoat extends on top of the isolation trenches. Fig. 9D shows a broken-away cross-section of a packaged resonator (with SCS beams labeled) showing a 15 μm high, 80 μm wide cavity with a 20 μm thick Avatrel cap.

To evaluate the PVD method, a 50 μm thick polysilicon HARPSS ring gyroscope was fabricated with a 1 μm gap and a 200 μm deep cavity, as shown in FIG. 10A. The HARPSS processing sequence begins with patterning the nitrogen ties and defines trenches. A thin layer of sacrificial oxide is deposited to uniformly cover the trench sidewalls and define the capacitive gap between the SCS and polysilicon electrodes. The trench is refilled with doped polysilicon to form a ring, a spring and an electrode. Finally, the sensor is released in a DRAIE tool, and then the sacrificial oxide is removed in an HF solution. Fig. 10B shows the device after manual removal of the sacrificial material. Fig. 10C is the device after forming a thick (120 μm) overcoat cap and decomposing the sacrificial material from inside the cavity. Fig. 10D shows the device after breaking the 2mm wide Avatrel enclosure, confirming a clean cavity and an intact device structure (the device is free to vibrate).

FIGS. 10E and 10F are close-up views of the electrodes showing a 1 μm capacitive gap, and a 4 μm wide polysilicon ring and support spring. The figure clearly shows that the sacrificial material can be decomposed by a very thick outer coating to create a hard cap. At room temperature, it takes several hours for air molecules to escape through the Avatrel cap in the vacuum chamber, and the structure can start resonating with a high Q factor.

The unpackaged resonators shown in figures 9A-9D were tested at the wafer level in a vacuum probe station. A DC polarization voltage in the range of 70-80V was applied while the electrodes were directly connected to the network analyzer. Fig. 11A shows the frequency response of the resonator in vacuum before packaging, and fig. 11B shows the frequency response of the resonator in vacuum after packaging. The high Q factor of the device, about 5000, did not change, demonstrating that thermal decomposition of the Unity sacrificial material after encapsulation had no effect on device performance.

As previously mentioned, various MEMS device packages may be manufactured with various levels of protection against environmental elements. Accordingly, various embodiments of MEMS packages include, but are not limited to, the following.

In fig. 12, one embodiment of a MEMS device package 1200 is shown. In this embodiment, MEMS device package 1200 includes a substrate layer 1210, a MEMS device active area 1220, a vacuum sealed air cavity area 1225, contacts 1230, an overcoat layer 1240, and a shield layer 1250. Package 1200 is fabricated in a process similar to that described above with reference to fig. 2, wherein sacrificial layer 325 is removed to form overcoat layer 1240 and barrier layer 1250, which can provide varying degrees of hermetic protection to the MEMS device. During this process, air within cavity 1225 is evacuated to create a vacuum within cavity 1225, wherein metal barrier 1250 prevents air from entering air cavity region 1225.

By converting sacrificial material 325 into a gaseous material that permeates through overcoat 1240, cavity 1225 is free of residue, including any residual sacrificial material. Accordingly, outer coating 1240 is also free of residues and can maintain structural integrity because any sacrificial material can be removed without perforating the outer coating.

The MEMS package 1200 may be connected to an external point or subjected to additional packaging by various methods including wire bonding techniques, flip chip technology, packaging with a lead frame, surface mount packaging, ceramic packaging, or other high performance technologies, as described below. The particular processing techniques that can be used for MEMS devices may depend on the level of protection provided by the overcoat and the shield, as different techniques can apply varying degrees of pressure and precision to the microelectronic device.

Referring now to fig. 13, another embodiment of a MEMS package 1300 is shown. In fig. 13, a MEMS device package 1300 includes a base layer 1310, an active surface 1320 of the MEMS device, an air cavity 1325 surrounding the active surface of the MEMS device, a contact 1330, an overcoat layer 1340, and a shield layer 1350. Package 1300 is fabricated in a process similar to that described above with reference to fig. 2, wherein sacrificial layer 325 is removed to form overcoat layer 1340 and shield layer 1350. However, in this embodiment, the process of forming a vacuum within air cavity 1325 is not performed, as there are many MEMS devices that do not require a vacuum seal. At this point, the shield 1350 still prevents air and moisture from entering the air cavity area 1325 enclosed by the shield 1350 (e.g., a metal layer). Furthermore, by transforming the sacrificial material 325 into a gaseous material that permeates through the overcoat 1340, there is no residue in the air cavity 1325, including any residual sacrificial material. Accordingly, the overcoat 1340 is also free of residue and can maintain structural integrity, as no perforation of the overcoat is required to remove any sacrificial material. The MEMS device package 1300 may be connected to an external point by various methods including wire bonding techniques, flip chip technology, packaging with a lead frame, surface mount packaging, ceramic packaging, or other high performance techniques, as described below. The particular processing techniques that can be used for MEMS devices may depend on the level of protection provided by the overcoat and the shield, as different techniques can apply varying degrees of pressure and precision to the microelectronic device.

In another embodiment, FIG. 14 shows a MEMS device package 1400 having a substrate layer 1410, an active surface 1420 of the MEMS device, an air cavity region 1425 surrounding the active surface of the MEMS device, contacts 1430, and an overcoat 1440 that also serves as a protective layer. The package 1400 is fabricated in a partial process similar to that described above with reference to FIG. 2, wherein sacrificial layer 325 is removed to form an overcoat layer 1440. However, in this example, package 1400 is completed after sacrificial layer 325 is removed (230), and overcoat 1440 remains.

Thus, as part of the step of adding the overcoat (220), the overcoat material is typically baked to harden and cure the overcoat, which can serve as suitable protection against external forces for many applications and types of MEMS devices. In addition, by transforming sacrificial material 325 into a gaseous material that permeates through overcoat 1440, air cavity 1425 is free of residue, including any residual sacrificial material. Accordingly, overcoat 1440 is also free of residue and can maintain structural integrity because any sacrificial material can be removed without perforating the overcoat. The MEMS device package 1400 may be connected to an external point by various methods including wire bonding techniques, flip chip techniques, packaging with a lead frame, surface mount packaging, ceramic packaging, or other high performance techniques, depending on the particular quality of the packaging process and the protection requirements of the particular MEMS device.

Referring now to fig. 15, another embodiment of a MEMS device package 1500 is shown. In this embodiment, the MEMS device package 1500 includes a base layer 1510, an active surface 1520 of the MEMS device, an air cavity 1525 surrounding the active surface of the MEMS device, contacts 1530, and a sacrificial layer 1540. Package 1500 is fabricated in a partial process similar to that described above with reference to fig. 2, wherein a sacrificial material is applied to form sacrificial layer 325. However, in this particular example, the process is complete after the step of adding the sacrificial layer (210) is performed. Thus, as part of the step of adding the sacrificial layer, the sacrificial material is encapsulated around the active surface 1520 of the MEMS device, which may serve as suitable protection against external forces, after which the MEMS device may be attached to external points or terminals by current wire bonding techniques and/or surface mounting methods.

After the MEMS device is packaged, the MEMS device may not only assemble an integrated circuit (e.g., with wire bond pads, coated surfaces, etc.), but may also be processed and packaged like many integrated circuits. For example, the following process for mounting a MEMS device onto a support structure, which may be a metal frame (e.g., a leadframe) conventionally used for attaching integrated circuits, may be considered.

As shown in fig. 16, a method for attaching a MEMS device 1500 having a sacrificial layer 1540 surrounding the MEMS device is described. At this point, a lead frame 1600 is provided. In this example, a thin metal plate (e.g., copper) is processed into a lead frame 1600 having formed pads 1610 for mounting a microelectronic device package and lead fingers 1620 for connecting leads to bond pads or contacts of the microelectronic device. Accordingly, MEMS device package 1630 with sacrificial layer 1540 is attached 1625 to leadframe 1600 (by mounting or bonding package 1630 to leadframe 1600 molding pad 1610). In addition, metal leads 1640 are connected 1625 to lead fingers 1620 or terminals of leadframe 1600 and bond pads or contacts 130 of MEMS device package 1630. Then, as part of the molding process, a coating material 1650 (e.g., a plastic molding compound, a thermosetting polymer, an epoxy, etc.) is applied 1645 to the MEMS device package and a portion of the surface of the leadframe 1600.

The curing temperature of the coating material 1650 used during this process is lower than the thermal decomposition temperature of the sacrificial material 1540 in the MEMS device package 1500. Thus, the coating material 1650 is cured at a lower temperature (i.e., below the thermal decomposition temperature of the sacrificial material) to harden the coating material. Coating material 1650 has the property of being permeable or semi-permeable to decomposition gases generated by decomposition of the sacrificial polymer of sacrificial layer 1540.

The coating material 1650 is used to provide a moisture resistant material to the surface of the assembly of the MEMS device and leadframe assembly, i.e., the "chip", to minimize packaging stress on the surface of the chip and to provide additional protection against corrosion. This is a standard step in low cost microelectronic packaging of integrated circuits. However, for MEMS devices, for example, such steps often negatively interfere with and compromise the operation of the MEMS structure without the protective coating. Thus, coating material 1650 does not contact the active surface of the MEMS device through sacrificial layer 1540.

After the coating material 1650 is cured and hardened, the MEMS chip is baked at a temperature above the thermal decomposition temperature of the sacrificial material. Thereafter, the sacrificial material is converted to a gaseous state and permeates or diffuses through the coating material 1650. After the sacrificial layer is decomposed, an air cavity is formed around the active surface of the MEMS device, and the coating material 1650 is used as a protective layer as a whole to prevent various elements from entering the air cavity and to protect the MEMS device. Then, as part of a standard chip packaging process, MEMS chip 1660 is removed from the leadframe by a dicing separation process (1655), and the leads of the chip are bent into the desired shape.

The process described immediately above works well for thin epoxy packages such as TSOP (thin and small outline packages) and TQFP (thin square flat packages).

By way of example, for one embodiment (as shown in FIG. 14) the MEMS device package includes an overcoat 1440 that provides additional support to the MEMS device without affecting the thermal decomposition of the sacrificial material 1425. Accordingly, such a MEMS device package may also be attached to a leadframe using the process described in fig. 16.

Additionally, in other embodiments (as shown in fig. 12 and 13), the MEMS device package may not include a sacrificial layer and instead include additional support structures, such as shielding layers 1250, 1350. In this regard, these MEMS device packages do not require baking at a temperature above the curing temperature of the coating material, since no sacrificial material is present. Otherwise, the process depicted in fig. 16 may additionally package such MEMS device packages by employing common integrated circuit packaging processes (e.g., leadframe packaging).

According to the present disclosure, some embodiments of a microelectromechanical device package generally include one or more MEMS devices; an interconnection from the device to the package; surrounding or containing structures for providing mechanical as well as electrical, chemical and environmental protection simultaneously; and a bonding structure for attaching the package to a circuit board or system. Such embodiments provide a wafer-level universal packaging process for MEMS devices that is generally applicable to packaging devices made by processes for various purposes. Thus, embodiments of the present invention can be adapted to well developed integrated circuit packaging technologies, as shown in FIG. 17.

Referring now to fig. 17, the MEMS device package 1710 of the present invention can be fabricated to meet a wide variety of packaging requirements and desires. By way of example, MEMS device package 1710 may be packaged to provide various levels or degrees of hermetic protection for the MEMS device. As shown in fig. 17, hermetic protection levels include, but are not limited to, mechanical protection 1720 (e.g., to prevent accidental access, to provide additional packaging, etc.), protection 1730 to prevent contact with oxygen and water in addition to mechanical protection, and protection 1740 to prevent exposure to any gas in any form in addition to mechanical protection (e.g., with a pure vacuum).

In addition to different degrees of hermetic protection, MEMS device package 1710 may also utilize various bonding techniques to provide electrical connection to external points or terminals. Such bonding techniques include, but are not limited to, wire bonding techniques 1750 and flip chip bonding techniques 1760.

In addition, the MEMS device package 1710 of the present invention can also be adapted to various microelectronic device packaging technologies that are already in common use. By way of example, the MEMS device package may use conventional integrated circuit technology, including, but not limited to, low cost plastic packaging technology 1770, and ceramic or other high performance packaging technology 1780. For any of these approaches, other packaging techniques are also available, including, but not limited to, surface mount processes 1790 and through-hole plug-in mounting processes 1795.

Advantageously, embodiments of the present invention provide various improved ways to protect MEMS devices. By way of example, in accordance with the present invention, the sacrificial layer on the MEMS device can be removed without the need to perforate the sacrificial layer and the overcoat layer of the active structure surrounding the MEMS device. In addition, the thickness of the overcoat and/or shield layers may be adjusted or tailored (e.g., in the range of 50nm to 500 μm) to withstand the ambient pressure and pressures encountered during packaging and to provide suitable protection for the MEMS device. By way of example, the overcoat layer may be spin coated at different speeds, or the viscosity of the overcoat material may be varied to adjust the thickness of the overcoat layer formed on the MEMS device. Thus, the thickness of the overcoat material can be made as thick as reasonably needed (e.g., 5 cm).

Advantageously, because the sacrificial material and the overcoat material are polymeric substances and have good thermal mismatch properties with common substrate materials, embodiments of the present invention may also provide a protective layer on any substrate material that does not cause deformation of the MEMS structure. In addition, there is a wide range of sacrificial materials that can be employed with the present invention over a wide range of thermal decomposition temperatures. Thus, a desired thermal decomposition temperature (e.g., 80 ℃ to 400 ℃) may be selected, and based on the selected temperature, the sacrificial material may be selected. Thus, the decomposition time and temperature can be optimized for each application based on the thickness of the overcoat. Further, the sacrificial material may be selected based on whether it is desired to use a photosensitive sacrificial material.

It should be emphasized that the above-described embodiments of the present invention are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing from the spirit and principles of the invention. All such variations and modifications are intended to be included within the scope of the present invention.

Claims (8)

1. A packaged microelectromechanical device system, comprising:

a micro-electromechanical device formed on the base layer; and

an overcoat layer disposed on a portion of the substrate layer, the overcoat layer being a different structure from the substrate layer and protecting at least a portion of the microelectromechanical device, wherein the overcoat layer surrounds a portion of a gas cavity surrounding an active surface of the microelectromechanical device; and is

The outer coating is made of a molded polymer having the property of being permeated by a decomposition gas generated by decomposition of the sacrificial polymer while forming a gas cavity.

2. The system of claim 1, wherein the gas cavity is vacuum sealed.

3. The system of claim 1, further comprising:

a metal encapsulation frame to which the micro-electromechanical device is attached, wherein a portion of the base layer is disposed on the metal encapsulation frame;

the overcoat layer encloses a portion of the assembly of the microelectromechanical device and the metal encapsulation frame, wherein the overcoat layer is not pre-processed prior to application to the base layer.

4. A packaged microelectromechanical device system, comprising:

a micro-electromechanical device formed on the base layer;

a thermally decomposable sacrificial structure that protects at least a portion of the microelectromechanical device, wherein the sacrificial structure is formed in a gas cavity that surrounds an active surface of the microelectromechanical device; and

an overcoat layer disposed on a portion of the substrate layer, the overcoat layer being a different structure from the substrate layer and protecting at least a portion of the microelectromechanical device, wherein the overcoat layer surrounds a portion of a gas cavity surrounding an active surface of the microelectromechanical device; and is

The outer coating is made of a molded polymer that is permeable to decomposition gases generated by the decomposition of the sacrificial polymer within the gas cavity.

5. The system of claim 4, further comprising:

a metal encapsulation frame to which the micro-electromechanical device is attached, wherein a portion of the base layer is disposed on the metal encapsulation frame;

wherein the outer coating encapsulates a portion of an assembly of the micro-electromechanical device and the metal encapsulation frame;

the pyrolytic sacrificial structure comprises a sacrificial polymer;

the overcoat layer has a property of being permeable to a decomposition gas generated by decomposition of the sacrificial polymer at a temperature higher than a curing temperature of the coating material, has elasticity, and is stable in a temperature range in which the sacrificial polymer is decomposed.

6. A method for fabricating a micro-electromechanical device package, comprising:

forming a pyrolytic sacrificial layer on a substrate of a microelectromechanical device, the sacrificial layer enclosing a portion of the microelectromechanical device;

forming an overcoat layer around the sacrificial layer; and

thermally decomposing the sacrificial layer, wherein decomposed molecules of the sacrificial layer permeate through the overcoat layer, and a gas cavity is formed at a formation location of the thermally decomposable sacrificial layer;

wherein the overcoat is disposed on a portion of the substrate layer, the overcoat being a different structure from the substrate and protecting at least a portion of the microelectromechanical device, wherein the overcoat surrounds a portion of the gas cavity surrounding the active surface of the microelectromechanical device.

7. The method of claim 6, further comprising the steps of:

attaching the micro-electromechanical device to the metal encapsulation frame prior to formation of the overcoat layer, wherein the overcoat layer comprises an epoxy resin encapsulating the assembly of the micro-electromechanical device and the metal encapsulation frame;

heating the microcomponent at a temperature suitable for curing the overcoat; and

heating the micro-component at a temperature suitable for decomposing the sacrificial layer, wherein the temperature suitable for decomposing the sacrificial layer is above the decomposition temperature of the sacrificial layer but below the decomposition or degradation temperature of the micro-electromechanical device or the degradation temperature of the overcoat layer.

8. The method of claim 6, further comprising the steps of:

generating a vacuum in the gas cavity by heating the micro-electromechanical device in a chamber;

after vacuum generation, forming a barrier layer within the chamber around the outer coating to provide a vacuum-tight enclosure around the gas cavity, the barrier layer comprising a metallic material and providing greater protection against mechanical forces than the outer coating;

attaching a micro-electromechanical device to an integrated circuit package structure; and

an electromechanical device and an integrated circuit package structure are enclosed in an enclosure structure.