JP2005537661A - Sealing of non-silicon-based devices at the wafer stage - Google Patents

Abstract

One embodiment of a method (100) for sealing active regions of non-silicon based devices on a wafer is disclosed. The method includes mounting a sacrificial material on at least an active region of a non-silicon-based device (104), depositing a seal coating on the wafer (108) so that the seal coating covers the sacrificial material, and Replacing the sacrificial material with a specific gas (112, 114). In another embodiment, a surface acoustic wave (SAW) device is disclosed that is sealed at the wafer stage (ie, before separating the die from the wafer). The element includes an active region to be protected, an electrical contact region (4), and a lithographic structure (24) that seals at least the active region and exposes at least the contact region.

Description

  The present invention relates generally to integrated circuits, and more particularly to the manufacture and structure of integrated circuits.

RELATED APPLICATIONS The present invention relates to US patent application Ser. No. 10 / 231,357, filed Aug. 28, 2002, entitled “Sealing of Non-Silicon Devices at the Wafer Stage” and U.S. Application, filed Aug. 28, 2002. Claims priority based on patent application number 10 / 231,356, name “Seal of surface acoustic wave device”.

2. Description of Technical Background Various non-silicon based devices have been manufactured for use in communications and others. Since such devices are often sensitive to the environment of use or contamination, it is preferable to operate in a controlled environment. Examples of such non-silicon-based elements that are sensitive to the use environment include surface acoustic wave (SAW) elements, photoelectric modules, optical wave elements, and the like.

  For example, the SAW element will be described in more detail. SAW elements are often used in communication elements such as radio frequency (RF) filters in mobile phone handsets and communication networks, for example. The SAW element uses a wave transmitted along the surface (or near the surface) of the substrate. Here, SAW elements include elements that use piezoelectrically coupled Rayleigh waves and elements that use piezoelectrically coupled non-Rayleigh waves (surface waves or “leaky” waves). In general, a SAW filter has an input converter and an output converter formed on a non-silicon-based substrate such as lithium tantalate, lithium niobate, or quartz single crystal. The transducer may be, for example, a metal electrode in which aluminum fingers are arranged with each other. As an example of a typical SAW device, one operating at 2.5 GHz can have a transducer aluminum finger with a minimum size of about 0.4 microns.

  One problem faced by SAW devices is that the region in which the sound waves of the device are generated is very sensitive to surface contamination that changes the speed of sound and consequently degrades the performance of the device. Even single crystal contaminants on the crystal surface can greatly change the performance of the device. The SAW element is preferably operated in a low-pressure gas (close to vacuum) rather than in the atmosphere. By operating in such a low-pressure gas, the viscous attenuation of sound waves can be reduced. Another problem with SAW devices is that the speed of sound waves varies with temperature. In other words, when the temperature changes, the speed of the sound wave changes. This temperature dependence effectively limits the operating temperature range of SAW devices.

  One embodiment of the present invention relates to a method for sealing active regions in non-silicon based devices on a wafer. The method includes attaching a sacrificial material to at least an active region of a non-silicon-based device, depositing a seal coating over the sacrificial material with a seal coating, and replacing the sacrificial material with a gas of interest. And steps.

  Other embodiments of the invention relate to non-silicon-based devices that are sealed at the wafer stage (ie, before separating the die from the wafer). The device includes an active region to be protected, a contact region, and a lithographic structure that seals at least the active region and exposes at least the contact region.

  Another embodiment of the invention relates to a method for sealing an active area on a wafer. The method includes attaching a sacrificial material to at least the active region of the SAW element, applying a seal coating over the sacrificial material with a seal coating, and replacing the sacrificial material with a gas of interest. Is included.

  Another embodiment of the invention relates to a SAW device that is sealed at the wafer stage (ie, prior to separating the die from the wafer). The element includes an active region to be protected, an electrical contact region, and a lithographic structure that seals at least the active region and exposes at least the electrical contact region.

  These and other features of the present invention will be readily apparent to those of ordinary skill in the art upon reading this specification, including the accompanying drawings and claims.

  The problems and difficulties associated with non-silicon based devices described above may be overcome by controlling the ambient gas in which the device operates.

  One way to do this is to seal each die at the packaging stage where it is incorporated into the package. The seal may be applied, for example, in a metal or ceramic package. For example, a metal package may be sealed with welding or solder, and each lead may be sealed using a separate glass seal to separate each lead from the material. In another example, a ceramic seal band with a vitreous material attached may be used in a ceramic package to facilitate sealing by welding or soldering, and leads may be embedded in the ceramic itself. Other types of packages and other sealing techniques may be used during the packaging stage.

  As disclosed in detail in this application, a different and advantageous method of controlling the environment in which non-silicon-based devices are operated is an integrated circuit manufacturing technique at the wafer stage (ie, before separating the die from the wafer). It is to give a seal using. Applying a seal at the wafer stage has various advantages over applying a seal at the package stage.

  Non-silicon-based devices sealed on the die have the advantage that they can be tested on the wafer before dicing. For example, modern die sizes for SAW devices are typically in the range of 1 mm to 1.5 mm so that 6000 to 7000 dies can be made on a single 4 inch wafer. By sealing the SAW device at the wafer stage, it is possible to identify and select devices that pass acceptance inspection before separating the die from the wafer, thereby eliminating the more cumbersome testing after dicing. In addition, it is possible to omit the work to be incorporated into a package which is often performed recently.

  In addition, the die produced by sealing at the wafer stage has the potential advantage that it can be mounted on a printed circuit board (PCB) without further incorporation into a package. Since non-silicon-based devices are sealed at the wafer stage in the manufacturing process, it may be possible to mount them directly on the PCB in this way. Such direct mounting eliminates the cost and processing time associated with lead wires, wire bonding, and container encapsulation. This leads to the advantages of manufacturing the device with high quality, high throughput, high productivity and low expenditure.

  Another potential advantage relates to the ability to compensate for the temperature expansion of non-silicon crystals. By using the seal structure, tension can be generated in the crystal to compensate for temperature expansion. Depending on the structural design and materials used for the wafer stage seal, such tensions can be generated. As the seal material, a material whose crystal and thermal expansion coefficient (TCE) do not match is selected. The structure is designed to effectively create tension that counteracts normal thermal expansion in the crystal due to TCE mismatch.

  Numerous specific details of example devices, process parameters, materials, process steps, and structures are disclosed to provide a thorough understanding of embodiments of the present invention. Those of ordinary skill in the art will understand, however, that the invention may be practiced without one or more of the specific details. In other instances, well-known matters are not shown or described in order not to obscure the features of the invention.

  FIG. 1A is a cross-sectional view depicting an unsealed non-silicon-based device (SAW device in this example) made on the surface of a wafer. Unsealed SAW elements have a substrate and transducer structure and are manufactured using conventional techniques. The substrate 2 is usually a single crystal wafer of lithium tantalate, lithium niobate, or quartz. Such materials can transmit acoustic waves substantially elastically through the surface of the substrate. The transducer structure 4 typically consists of “finger” electrodes formed by interdigitated aluminum patterns and contacts for allowing current to flow in and out of the structure 4. Usually, one of the transducer structures is for input and the other is for output. Waves are transmitted on the surface of the region between the transducer structures 4 and between the transducer structures 4. The SAW element may be used as a radio frequency (RF) filter, for example.

  1B, 1C, 1D, 1E, 1F, 1G, 1H, and 1I are cross-sectional views depicting various steps of a non-silicon-based device sealing process according to an embodiment of the present invention. It is.

  FIG. 1B is a cross-sectional view depicting the structure after the sacrificial material has been deposited. In one embodiment, the sacrificial material can be deposited as a (substantially) uniformly coated polysilicon. The use of polysilicon as the sacrificial material 6 has the advantage that vapor deposition can be used to increase the mass productivity and surface conductivity of SAW devices such as lithium niobate and lithium tantalate. This is due to a chemical reduction action known to occur when these substrates are heated in vacuum. Such a chemical reduction action also occurs between materials that are susceptible to oxidation, such as silicon, thereby producing a thin film of chemically reduced material with increased conductivity. Increasing the conductivity is useful in reducing charge buildup on the substantially insulated substrate due to the pyroelectric effect. Conventional lithium tantalate accumulates charges of up to several thousand volts due to the pyroelectric effect when the temperature changes. Due to the accumulation of this charge, it is possible to damage the transducer region or to reverse the crystal direction in the active region of the SAW. This may potentially degrade the SAW characteristics due to the formation of the region, damage sensitive electronic elements and damage the wafer (voltage induced by the pyroelectric effect above the breakdown voltage of the wafer material). The wafer may be destroyed). Thus, the use of a polysilicon layer in the manufacture of SAW elements necessitates that the SAW element is an element that can withstand the adverse effects of these pyroelectric effects.

  In other embodiments, the sacrificial material may be amorphous silicon. Amorphous silicon has the advantage that it can be deposited at a lower temperature than polysilicon.

  In still other embodiments, the sacrificial material 6 may be a polyimide, a photoresist, or a polymer material such as polymethyl methacrylate (PMMA). These polymer sacrificial materials are attractive when low temperature processing is required in the sealing process. However, these have the following drawbacks. That is, (a) it is difficult to remove material from the pocket having a remarkable lateral dimension due to the directional characteristics of plasma etching, and (b) impurities that do not react and leave a residue (may not be a problem of PMMA) (C) formation of water molecules that may be absorbed by the surface layer in the pocket and impair the sealing property due to moisture.

  The polysilicon may be deposited at a temperature of 550 degrees Celsius, which is below the Curie temperature of lithium tantalate, thereby making the polysilicon a candidate for a sacrificial material. A material having a deposition temperature higher than the Curie temperature of the substrate (about 600 ° C. for congruent lithium tantalate and about 695 ° C. for stoichiometric lithium tantalate) adversely affects the substrate material due to the high temperature. It is not a good candidate for use. Amorphous silicon can be deposited at a temperature of 150 ° C., and can be dry-etched with high selectivity using xenon difluoride gas.

  FIG. 1C is a cross-sectional view depicting the structure after the sacrificial material 6 has been patterned by lithography. The unwanted portion 8 of the sacrificial material is removed by patterning, while the remaining portion 10 of the sacrificial material is left. The remaining sacrificial material 10 covers and seals the SAW element portion. Since the SAW element wave transmission area must be kept clean from contamination, the remaining sacrificial material 10 should cover at least the SAW element wave transmission area, in particular. In FIG. 1C, the wave-transmitting region is generally between the two transducer structures 4 (as shown in FIG. 1A) and at the same time within a substantial portion of these structures, so that in FIG. The sacrificial material is drawn so as to cover the region between the transducer structures 4 and the region transmitting the waves inside these transducer structures 4.

  FIG. 1D is a cross-sectional view depicting the structure after the seal coating 12 has been deposited. The seal coating 12 is deposited over the entire wafer and is composed of a relatively thick layer, such as a glassy material. The vitreous material may be, for example, spin-on glass or sputtered glass. Alternatively, the material may include silicon nitride or metal. The seal coating 12 should be of a material and thickness that will not allow unwanted contaminants to pass through. The proximity effects and electrical properties of these coatings must be considered in the design of SAW devices.

  FIG. 1E is a cross-sectional view depicting the structure after the seal coating 12 has been patterned by lithography. Part 14 of the seal coating is removed to expose the electrical contact pad portion of the transducer 4 by patterning. In addition, a portion 16 of the seal coating is removed by patterning to form a via through the seal coating to the underlying sacrificial material. In the preferred embodiment, the via is formed avoiding the area where the wave of the SAW element is transmitted.

  FIG. 1F is a cross-sectional view depicting the structure after the remaining sacrificial material has been etched away using vias to form 18 surrounded by seal coating structure 20. The etching may be performed by a dry etching process that does not leave an unnecessary residue.

  For example, in one embodiment, etching of a polysilicon (or amorphous silicon) sacrificial material on, for example, lithium tantalate (or lithium niobate) with a silicon dioxide (or silicon nitride or metal) seal layer is performed on a wafer. Is placed in a gas of xenon difluoride. Xenon difluoride enters the via and acts on the sacrificial material with high selectivity (ie, substantially without etching the substrate and seal coating). Xenon difluoride removes the sacrificial material without leaving any substantial residue on the wafer. By eliminating the residue in the acoustically active portion of the surface, it is possible to prevent alteration that is not good for the sound transmission characteristics of the device. In this way, it is formed in the area between the seal coating structure 20 and the wafer previously occupied by the rest of the sacrificial material. Alternatively, a gas having characteristics similar to xenon difluoride may be used for dry etching of the sacrificial material.

  FIG. 1G is a cross-sectional view depicting the configuration after placing the wafer in a particular gas. This is done by placing the wafer in a sputtering chamber, evaporation chamber, or other vacuum chamber that is pumped to a particular gaseous state. A particular environment includes a partial pressure of one or more particular gases. The gas partial pressure in the chamber is balanced through the vias, and the same gas partial pressure in the pocket 22 as the gas partial pressure in the chamber is achieved.

  FIG. 1H is a cross-sectional view depicting the configuration after the via 16 is plugged to seal the specific gas 22 in the pocket. Vias (holes) 16 through the coating structure 20 are closed 24 by, for example, sputtering or deposition of silicon dioxide or metal.

  Sputtering is isotropic in nature and plugs the via 16 by coating the periphery of the hole and bulging material from the periphery until the via 16 is plugged. Due to the isotropic nature of sputtering, silicon dioxide or metal is induced in the pocket. If material sputtered by sputtering landed in an area occupied by surface acoustic waves, the transmission characteristics of the acoustic waves may change in a detrimental direction. In order to avoid such harmful effects, the coating structure 20 may be designed so that vias do not come on or in the vicinity of the wave transmitting region. This minimizes the amount of material bounced off by sputtering that lands on the wave-transmitting region, or reduces it to a substantially negligible amount that has little effect on surface acoustic wave transmission. .

  Alternatively, vapor deposition can be used when the silicon dioxide or metal beam is positioned at an angle with the wafer. Vapor deposition tends to have a strong direction in nature. By placing the beam at a sufficient angle with respect to the wafer, the via 16 can be plugged 24 without substantially introducing the deposit into the pocket by the strongly directional beam. Another advantage of vapor deposition is that the vapor deposition chamber can achieve a higher vacuum than the sputtering chamber.

  As depicted in FIG. 1H, the selected gas and pressure are confined in a sealed 24 pocket. This advantageously provides a controlled gas of the acoustically active portion of the device, which can be protected from unwanted contamination. The sealing structure formed as described above provides a hermetic seal. The hermetic seal is a substantially airtight state in which air and gas do not substantially enter and exit. However, even with a hermetic seal, a small amount of gas molecules pass through little by little due to diffusion and penetration over time. The hermeticity of the seal can be substantially enhanced by coating with a thin film of silicon nitride using plasma enhanced chemical vapor deposition (PECVD).

  FIG. 1I is a cross-sectional view depicting the structure after electrodes (bumps) 26 are formed at the contact portion of the transducer structure. Electrode 26 can be formed using conventional lithographic techniques. As depicted in FIG. 1I, the electrode 26 is formed at a height higher than the height of the seal structure. Thus, the sealed element has a structure suitable for surface mounting.

  Prior to mounting the sealed device on the PCB board, the device is individually tested on the wafer and selected to accept or reject. The wafer can then be diced to produce individual dies with the elements attached. Then, the die satisfying the standard is mounted on a surface mount element tape and a reel for surface mounting on a printed circuit board.

  FIG. 2 is a flowchart depicting a method of sealing an active region of a non-silicon-based device (a transmission region of a SAW device in this example) on a wafer according to an embodiment of the present invention. As depicted in FIG. 2, the method 100 includes nine steps (102, 104, 106, 108, 110, 112, 114, 116, and 118).

  In a first step 102, an unsealed element is made on the wafer. A cross-sectional view before sealing the formed SAW element is shown in FIG. 1A. As described in connection with FIG. 1A, an unsealed device is fabricated on a substrate such as lithium tantalate, lithium niobate, or quartz using conventional techniques.

  In a second step 104, a sacrificial material is deposited on the wafer. A cross section after depositing the sacrificial material layer is shown in FIG. 1B. As described in connection with FIG. 1B, the sacrificial material layer can be composed of polysilicon, amorphous silicon, or possibly a polymeric material.

  In a third step 106, the sacrificial material is patterned using a lithograph. A cross section after the sacrificial material has been patterned is shown in FIG. 1C. As described in connection with FIG. 1C, the remaining sacrificial material should cover at least the region of the SAW element that transmits the waves, since that region is to be sealed.

  In a fourth step 108, a seal coating is deposited on the wafer. A cross section after depositing the seal coating is shown in FIG. 1D. As described in connection with FIG. 1D, the seal coating consists of a vitreous material deposited by spin-on or sputtering. This material may be made of silicon dioxide. Alternatively, this material may be made of silicon nitride or metal.

  In a fifth step 110, the seal layer is patterned using a lithograph. The transmission surface after patterning of the seal layer is shown in FIG. 1E. As described in connection with FIG. 1E, patterning exposes the electrical contact pad portion of the transducer 4. Further, patterning forms vias (holes) through the seal coating to the underlying sacrificial material.

  In a sixth step 112, the sacrificial material is removed by etching through the vias to form pockets on the device. A cross section after the sacrificial material is removed by etching is shown in FIG. 1F. As described in connection with FIG. 1F, the etching may be performed by a dry etching process that leaves no unnecessary residue.

  In a seventh step 114, the substrate is placed in a particular gas and allowed to equilibrate. A cross-section after placement in a particular gas is shown in FIG. 1G. As described in connection with FIG. 1G, the gas partial pressure in the chamber is balanced through the vias and the same gas partial pressure in the pocket 22 as the gas partial pressure in the chamber is achieved.

  In the eighth step 116, the via is closed to seal the pocket. This step is performed when the wafer is still in a particular gas. A cross section after closing the via 1 is shown in FIG. 1H. As described in connection with FIG. 1H, the via is plugged 24 by, for example, sputtering or deposition of silicon dioxide or metal.

  Finally, in a ninth step 118, the electrode 26 is formed at the contact portion. A cross section after closing the via 1 is shown in FIG. As described in connection with FIG. 1I, the electrode 26 is formed at a height that is higher than the height of the sealing structure so that the sealed element has a structure suitable for surface mounting.

  Subsequent to the ninth step 118, other steps for placing the device on a printed circuit board (PCB) are performed. For example, devices are individually tested on a wafer, wafers are diced to make individual dies, and dies that meet the criteria are mounted on surface mount device tapes and reels for surface mounting on PCBs. The

  While the above discussion has focused on sealing the SAW device at the wafer level, this technique protects other devices at the wafer level that employ non-silicon-based materials with active areas to be protected. It can be applied to. Examples of such applications include ferroelectrics (such as lithium tantalate or lithium niobate), photoelectric converters (eg, based on lithium tantalate or lithium niobate), and embedded optical structures. Includes patterning of regions for vacuum insulation with high dielectric strength. In each of these applications, the non-silicon-based device includes a means for receiving a signal in electrical form, a means for sending this signal to the active area in the substrate, and an active area without interfering with reception of the electrical signal. And a means for hermetic sealing. For SAW devices, the active area to be protected will, of course, be the area corresponding to the wave transmitting area. This technique can also be applied to elements near the surface. The elements in the vicinity of the surface include, for example, an acoustic element, an optical element, a nonlinear optical element, a photoelectric element, a photosonic element, and other elements.

  While specific embodiments of the invention have been presented individually, it is to be understood that these embodiments are for illustrative purposes and are not intended to limit the invention. It will be apparent to those skilled in the art to which the present disclosure pertains that many other embodiments are possible. Accordingly, the invention is limited only as described in the claims.

FIG. 3 is a cross-sectional view depicting an unsealed non-silicon-based device (SAW device in this example) formed on the surface of a wafer. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. It is sectional drawing on which the various steps of the sealing process of the non-silicon system element by one embodiment of the present invention were drawn. 6 is a flowchart depicting a method for sealing an active region of a non-silicon-based device (a transmission region of a SAW device in this example) on a wafer according to an embodiment of the present invention.

  The same markings in different figures indicate the same or similar elements. Unless noted, the drawings are not to scale.

Claims (40)

A method for sealing an active region of a non-silicon-based device on a wafer,
Mounting a sacrificial material on at least an active region of the non-silicon-based element;
Depositing a seal coating on the wafer such that the seal coating covers the sacrificial material;
Replacing the sacrificial material with a specific gas;
A method comprising:   The method of claim 1, wherein the seal coating is sufficiently impermeable to hermetically seal the particular gas in a pocket. The step of attaching the sacrificial material includes:
Depositing the sacrificial material on the wafer;
Patterning the sacrificial material with a lithography so that the sacrificial material covers at least the active region of the non-silicon-based device;
The method of claim 1 comprising:   The method of claim 1, wherein the sacrificial material comprises one material of a material group consisting of polysilicon, amorphous silicon, and a polymer material.   The method of claim 1, wherein the seal coating comprises one material from a group of materials consisting of silicon dioxide, silicon nitride, or metal.   The method of claim 1, wherein the seal coating comprises a vitreous material.   The method of claim 6, wherein the vitreous material is selected from the vitreous material group consisting of spin-on glass and sputtered glass. Replacing the sacrificial material comprises:
Lithographically patterning the seal coating to form vias through the seal coating and to expose electrical contact pads of the non-silicon based device;
Etching away sacrificial material through vias to form a pocket surrounded by the seal coating;
Placing the wafer in a specific gas;
Plugging the via to seal a particular gas in the pocket;
The method of claim 1 comprising:   9. The method of claim 8, wherein the step of etching away the sacrificial material includes an etching process that substantially leaves no residue.   The method of claim 9, wherein the sacrificial material comprises a silicon-based material, and the etching process comprises placing in a xenon difluoride gas to dry-etch the silicon-based material.   The method of claim 8, comprising equilibrating a gas in the pocket with a particular gas before plugging the via.   The method according to claim 8, wherein the step of closing the via includes a step of sputtering until the via is plugged with a plugging material, and the via is disposed to avoid an active region of a non-silicon-based element.   9. The step of plugging the via includes depositing until the via is plugged with a plugging material, wherein an angle between the deposition beam and the wafer is sufficiently small so as not to introduce a deposit into the pocket. The method described. Furthermore, forming an electrode connected to the contact pad of the non-silicon-based element,
The method of claim 1 comprising:   15. The method of claim 14, wherein the wafer is diced to produce a die, and a die that meets the criteria is mounted on a surface mount device tape and reel for surface mounting on a printed circuit board.   The method of claim 1, wherein the active region comprises a region that transmits a wave of the non-silicon-based device. A non-silicon-based device sealed at the wafer stage,
An active area to be protected;
A contact area;
A structure formed by lithograph sealing at least the active region and exposing at least the contact region;
A non-silicon element comprising:   18. A device according to claim 17, wherein the structure formed by the lithograph is made of a vitreous material.   The device of claim 17, wherein the non-silicon-based device is produced on one substrate of a group of substrates consisting of lithium tantalate, lithium niobate, or quartz. A non-silicon-based element formed by lithography, wherein the non-silicon-based element is
An active region sensitive to the surrounding gas of the non-silicon-based device;
Means for sealing the active region of the non-silicon based device at a wafer stage;
A device comprising: A method for sealing an active area of a surface acoustic wave (SAW) of an element on a wafer comprising:
Depositing a sacrificial material on at least the active region of the SAW element;
Depositing a seal coating on the wafer such that the seal coating covers the sacrificial material;
Replacing the sacrificial material with a specific gas;
A method comprising:   The method of claim 21, wherein the seal coating is sufficiently impermeable to hermetically seal the particular gas in a pocket. The step of attaching the sacrificial material includes:
Depositing the sacrificial material on the wafer;
Patterning the sacrificial material with a lithography so that the sacrificial material covers at least the active region of the non-silicon-based device;
The method of claim 21, comprising:   The method of claim 21, wherein the sacrificial material comprises one material of a material group consisting of polysilicon, amorphous silicon, and a polymeric material.   The method of claim 21, wherein the seal coating comprises one material from a group of materials consisting of silicon dioxide, silicon nitride, or metal.   The method of claim 21, wherein the seal coating comprises a vitreous material.   27. The method of claim 26, wherein the vitreous material is selected from the vitreous material group consisting of spin-on glass and sputtered glass. Replacing the sacrificial material comprises:
Lithographically patterning the seal coating to form vias through the seal coating to expose the electrical contact pads of the SAW element;
Etching away sacrificial material through vias to form a pocket surrounded by the seal coating;
Placing the wafer in a specific gas;
Plugging the via to seal a particular gas in the pocket;
The method of claim 21, comprising:   29. The method of claim 28, wherein etching away the sacrificial material comprises an etching process that substantially leaves no residue.   30. The method of claim 29, wherein the sacrificial material comprises a silicon-based material and the etching process comprises placing in a xenon difluoride gas to dry etch the silicon-based material.   29. The method of claim 28, comprising equilibrating a gas in the pocket with a particular gas prior to plugging the via.   29. The method of claim 28, wherein plugging the via includes sputtering until the via is plugged with a plugging material, the via being located away from the active area of the non-silicon based device.   The step of plugging the via includes depositing until the via is plugged with a plugging material, and the angle between the deposition beam and the wafer is sufficiently small so that the deposition is not substantially introduced into the pocket. The method described. Forming an electrode connected to the contact pad of the SAW element;
The method of claim 21 comprising:   35. The method of claim 34, wherein the wafer is diced to produce a die, and a die that meets the criteria is mounted on a surface mount device tape and reel for surface mounting on a printed circuit board.   The method of claim 21, wherein the active region comprises a region transmitting waves of the SAW element. A surface acoustic wave (SAW) device sealed at the wafer stage,
An active area to be protected;
An electrical contact area;
A structure formed by lithograph sealing at least the active region and exposing at least the electrical contact region;
A surface acoustic wave (SAW) device comprising:   38. The device of claim 37, wherein the structure formed by the lithograph is made of a vitreous material.   38. The device of claim 37, wherein the SAW device is produced on one substrate of a group of substrates consisting of lithium tantalate, lithium niobate, or quartz. A surface acoustic wave (SAW) element formed by a lithograph,
Means for transmitting surface acoustic waves;
Means for sealing the means for transmitting the surface acoustic wave at the wafer stage;
A surface acoustic wave (SAW) device comprising:

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