KR20050044799A - Wafer-level seal for non-silicon-based devices - Google Patents

Abstract

One embodiment disclosed relates to a method (100) for sealing an active area of a non-silicon-based device on a wafer. The method includes providing (104) a sacrificial material over at least the active area of the non-silicon-based device, depositing (108) a seal coating over the wafer so that the seal coating covers the sacrificial material, and replacing (112, 114) the sacrificial material with a target atmosphere. Another embodiment disclosed relates to an SAW device sealed at the wafer level (i.e. prior to separation of the die from the wafer). The device includes an active area to be protected, an electrical contact area (4), and a lithographically-formed structure (24) sealing at least the active area and leaving at least a portion of the electrical contact area (4) exposed.

Description

Wafer-level seals for non-silicon-based devices {WAFER-LEVEL SEAL FOR NON-SILICON-BASED DEVICES}

Related literature

This application is filed on August 28, 2002, entitled "Wafer-Level Seals for Non-Silicon-Based Devices," and US Patent Application No. 10 / 231,357, filed on August 28, 2002, and entitled "Seal for Surface Acoustic Wave Devices." Priority is claimed in US Patent Application No. 10 / 231,356, filed on 28 May.

FIELD OF THE INVENTION The present invention generally relates to integrated circuits, and more particularly, to integrated circuit fabrication methods and structures.

Various non-silicon based devices are being manufactured for use in communications and other fields. Such devices are often sensitive to pollution and the atmosphere in which they operate, and therefore need to be operated in a controlled atmosphere. Examples of these atmosphere-sensitive non-silicon-based devices include surface acoustic wave (SAW) devices, electro-optic modulators, acoustic-optic devices, and the like.

For example, consider SAW devices in more detail. SAW devices are used in communication devices such as, for example, mobile telephone receivers and high frequency (RF) filters in communication networks. SAW devices utilize waves that propagate along (or near) the surface of the substrate. As used herein, SAW devices include devices that use piezoelectrically-coupled Rayleigh waves and may include devices that use non-Raleigh (skimming or "leaky" waves). It may be. Typical SAW filters include input and output transducers formed on non-silicon based piezoelectric substrates such as, for example, lithium tantalate, lithium niobate, or single crystal quartz. The transducer may be a metal electrode, for example an interleaved aluminum finger. As an example of the size of a typical SAW device, a device operating at 2.5 GHz may have a minimum wiring width of about 0.4 microns for the aluminum finger of the converter.

The problem with SAW devices is that the area of the device where acoustic waves are present can be very sensitive to the presence of surface contaminants that change the speed of the wave and ultimately degrade device performance. Even a single layer of contaminants on the surface of the crystal can significantly alter the device's performance. In addition, the SAW element is preferably operated in a low pressure (near vacuum) atmosphere rather than in the atmosphere. Operating in this low pressure atmosphere can reduce the viscous damping of acoustic waves. Another problem associated with SAW devices is that the change in acoustic wave speed is temperature dependent. That is, the speed of the acoustic wave may change due to the change in temperature. This temperature dependency effectively limits the operational temperature range of the SAW device.

FIG. 1A is a cross-sectional view showing an unsealed non-silicon based device (SAW device in this case) fabricated on the surface of a wafer,

1B-1I are cross-sectional views illustrating various stages of the process of sealing non-silicon based devices in accordance with an embodiment of the invention,

FIG. 2 is a flowchart illustrating a method of sealing an active region of a non-silicon based element on a wafer (in this case, a wave propagation region of a SAW element) in accordance with an embodiment of the invention.

Like reference symbols in the various drawings indicate the same or similar members. The drawings are not isometric unless otherwise indicated.

One embodiment of the present invention is directed to a method of sealing an active region of a non-silicon based device on a wafer. The method includes providing a sacrificial material on at least an active region of a non-silicon based device, depositing a seal coating on the wafer such that the seal coating covers the sacrificial material, and replacing the sacrificial material with a target atmosphere. .

Yet another embodiment of the present invention is directed to non-silicon based devices that are sealed at the wafer level (ie, prior to separation from the wafer to the die). The device comprises an active region to be protected, and a lithographically formed structure that seals at least the active region and leaves at least a portion of the contact region exposed.

Yet another embodiment of the present invention is directed to a method of sealing an active region of a SAW device on a wafer. The method includes providing a sacrificial material over at least an active region of a SAW device, depositing a seal coating over the wafer such that the seal coating covers the sacrificial material, and replacing the sacrificial material with a target atmosphere.

Yet another embodiment of the present invention is directed to SAW devices that are sealed at the wafer level (ie, before separation from the wafer to the die). The device includes an active region to be protected, an electrical contact region, and a lithographically formed structure that seals at least the active region and leaves at least a portion of the electrical contact region exposed.

Features of the invention will be apparent to those skilled in the art upon reading the entirety of the specification, including the accompanying drawings and claims.

The foregoing problems and difficulties with non-silicon based devices may be overcome by controlling the atmosphere in which the devices operate.

One way to achieve this is to seal the device at the packaging level during packaging of the individual die. The seal may be formed, for example, in a metal or ceramic package. For example, the metal package may be welded or soldered to seal the device, and the individual leads may be sealed using separate glass seals to separate the leads from the metal. As another example, in a ceramic package, a metal seal band attached to the glassy material may be used to facilitate sealing by welding or solder, and the leads may be embedded in the ceramic itself. Other types of packages and other sealing techniques may also be used at the packaging level.

As described in detail herein, various and advantageous methods of controlling the atmosphere in which non-silicon-based devices operate operate fabrication of the seal at the wafer level (ie, before separation from the wafer to the die) using integrated circuit fabrication techniques. Fabricating the seal at the wafer level has various advantages over that performed at the packaging step.

One advantage is that the sealed non-silicon based devices on the die can be tested on the wafer prior to dicing. For example, current die sizes for SAW devices generally range from 1 to 1.5 mm such that about 6000 to 7000 die are fabricated on a single 4-inch wafer. Sealing at the wafer level of SAW devices enables the selection and verification of devices that pass permit testing before the die is separated from the wafer, avoiding some cumbersome testing of individual die after dicing and subsequent packaging currently in place can do.

In addition, a potential advantage is that dies produced by sealing at the wafer level may be mounted on a printed circuit board (PCB) without further packaging. This direct mounting onto the PCB is possible because non-silicon based devices are sealed at the wafer level during the manufacturing process. This direct mounting will avoid the processing time and additional costs associated with mounting to the lead frame, wire bonding, and encapsulation. This advantageously makes it possible to manufacture devices with high quality, high throughput, high yield, and low cost.

Another potential advantage relates to the compensation of thermal expansion of non-silicon crystals. The seal structure can be used to compensate for thermal expansion by causing strain in the crystal. The material and structural design used for the wafer level seals may be used to cause this deformation. The seal material will be chosen to have a crystal and coefficient of thermal expansion (TCE) mismatch. The structure will be designed such that the TCE mismatch effectively creates deformation as a counter force to the normal thermal expansion of the crystal.

In this specification, numerous details are provided, such as examples of devices, process variables, materials, process steps, and structures, to provide a thorough understanding of embodiments of the present invention. However, one skilled in the art will recognize that the invention may be practiced without one or more specific details. In other instances, well known details are not shown or described in order to avoid unclear aspects of the present invention.

FIG. 1A is a cross sectional view showing an unsealed non-silicon based device (SAW device in this case) fabricated on the surface of the wafer. The unsealed SAW device includes the substrate 2 and the converter structure 4 and may be manufactured using conventional techniques. The substrate 2 is generally a wafer of lithium tantalate, lithium niobate, or single crystal quartz. Such materials may allow acoustic waves to move substantially resiliently across the surface of the substrate. The transducer structure 4 is generally composed of aluminum which is patterned with electrodes “fingers” intertwined with contacts which conduct current to and from the structure 4. In general, one of the transducer structures is for input and the other for output. The wave propagation of interest occurs on the surface of the substrate 2 in the transducer structure 4 itself and in the region between the transducer structures 4. The SAW element may for example be used as a high frequency (RF) filter. Many different device configurations may be used.

1B-1I are cross-sectional views illustrating various steps of a method for sealing a non-silicon based device according to an embodiment of the invention.

FIG. 1B is a cross-sectional view illustrating the structure after depositing the sacrificial material 6. In one embodiment, the sacrificial material may be deposited as a (nearly) uniform polysilicon coating. The use of polysilicon as the sacrificial material 6 has the advantage that deposition can be used to increase the bulk or surface conductivity of SAW materials such as lithium niobate or lithium tantalate. This is due to chemical reduction processes known to occur when these substrates are heated in a vacuum. This chemical reduction process also occurs at the interface between easily oxidized materials such as silicon, creating a thin skin of chemically reduced material with increased conductivity. Such increased conductivity can be important in suppressing the accumulation of charge on these substantially insulating substrates resulting from the piezoelectric effect. Conventional lithium tantalates can accumulate thousands of volts of piezoelectric induced charge during temperature changes, and these accumulate charges improve SAW performance through formation of microscopic domains of inverted crystal orientations or damage to the transducer structure within the SAW active region. It can potentially degrade, potentially damage sensitive electronic components or wafers, and even break (because the piezoelectric induced voltage may exceed the breakdown voltage of the wafer material). As a result, by using a polysilicon sacrificial layer when manufacturing SAW devices, the devices may have excellent resistance to these harmful piezoelectric effects.

In another embodiment, the sacrificial material may include amorphous silicon. Advantageously, amorphous silicon may be deposited at lower temperatures than polysilicon.

In another embodiment, the sacrificial material 6 may be a polymeric material such as polyimide, photoresist, or polymethyl methacrylate (PMMA). These polymer sacrificial materials may be advantageous when low temperature processing is required through the sealing process. However, they have the following disadvantages: (a) the difficulty of removing material from within pockets with significant lateral dimensions due to the directionality of plasma etching; (b) impurities that do not react and remain as a residue (may not be a problem with PMMA); And (c) the formation of water molecules that may be absorbed by the surface inside the pocket and thus prevent hermeticity due to moisture.

Polysilicon may be deposited at a temperature near 550 ° C., which is below the Curie temperature of lithium tantalate, and is therefore a candidate material that can be used as a sacrificial material. Materials having a deposition temperature above the Curie temperature of the substrate (about 600 ° C. for congruent lithium tantalate or about 695 ° C. for stoichiometric lithium tantalate) are sacrificed because their high temperature adversely affects the substrate material. It is not a preferred material as a material. Amorphous silicon may be deposited at a low temperature of 150 ° C. and may be dry etched in a high selective manner using xenon difluoride gas.

1C is a cross-sectional view showing the structure after lithographic patterning of the sacrificial material 6. Patterning removes the unwanted portion 8 of the sacrificial material and leaves the remaining portion 10 of the sacrificial material. The remaining sacrificial material 10 covers a portion of the SAW device to be sealed. In particular, the remaining sacrificial portion 10 must cover at least the wave propagation area of the SAW element since the area must remain free of contamination. The wave propagation region is generally not only between two transducer structures 4 (shown in FIG. 1A) but also inside a substantial part of these structures 4, FIG. 1C shows the region between the transducer structures 4 and these structures 4. ) Shows the remaining sacrificial material 10 covering the wave propagation region therein.

1D is a cross-sectional view illustrating the structure after deposition of the seal coating 12. Seal coating 12 may be deposited on the entire wafer and may comprise, for example, a fairly thick layer of glassy material. The glassy material may be, for example, spin-on-glass or sputtered glass. The material may comprise silicon dioxide. Alternatively, the material may comprise silicon nitride or metal. Seal coating 12 should be of a material and thickness that is impermeable to unwanted contaminants. The availability and electrical properties of these coatings should be considered in the design of SAW devices.

1E is a cross-sectional view illustrating the structure after lithographic patterning of the seal coating 12. Patterning removes the portion 14 of the seal coating to expose the electrical contact pad portion of the transducer 4. In addition, the patterning removes portions 16 of the seal coating to create vias under the sacrificial material through the seal coating. In a preferred embodiment, the via is positioned to prevent the wave propagation area of the SAW device.

FIG. 1F is a cross-sectional view illustrating the structure after etching the remaining sacrificial material 10 with a via to create a pocket 18 surrounded by the structure 20 of the seal coating. Etching may be performed by a dry etch process that leaves no unwanted residue.

For example, in one embodiment etching of a polysilicon (or amorphous silicon) sacrificial material on a lithium tantalate (or lithium niobate, etc.) wafer with a sealing layer of silicon dioxide (or silicon nitride or metal) may cause the wafer to be xenon. It may also be carried out by positioning in a difluoride atmosphere. Xenon difluoride enters the vias to strike the sacrificial material at a high selectivity (ie, leaving the substrate and sealing coating substantially unetched). Xenon difluoride also removes sacrificial material without leaving substantial residue on the surface of the wafer. Not leaving an acoustically active portion of the surface residue prevents a reverse change in the wave propagation characteristics of the device. The pocket is thereby formed between the seal coating surface 20 and the surface of the wafer in the region previously occupied by the remaining sacrificial material 10. Alternatively, different gases having properties similar to xenon difluoride may be used to dry etch the sacrificial material.

1G is a cross-sectional view illustrating the structure after the wafer is mounted in the target atmosphere. This may be done by mounting the wafer in a sputtered, deposited or other vacuum chamber pumped into the target atmosphere. The target atmosphere may comprise a partial pressure of one or more target gases. The gas pressure in the chamber is equilibrated across the via to achieve the gas pressure in the same pocket 22 as in the chamber.

FIG. 1H is a cross-sectional view illustrating the structure after filling the via 16 to seal the target atmosphere 22 in the pocket. Vias (holes) 16 penetrating through the coating structure 20 may be filled at 24 by, for example, sputtering or deposition of silicon dioxide or metal.

When sputtering is configured to be isotropic, it will fill the via 16 by coating the rim of the hole and accumulating material from the rim until the via 16 is sealed. The isotropy of sputtering will introduce some of the silicon dioxide or metal into the pocket. If the sputtered material is placed in the area occupied by the surface acoustic waves, the propagation properties of the acoustic waves will change in a detrimental manner. To prevent this detrimental effect, the coating structure 20 may be designed such that the via 16 is not above or near the wave propagation region. This is to ensure that the amount of sputtered material lying on the wave propagation region is minimized or reduced in small amounts that do not affect the propagation of surface acoustic waves.

Alternatively, deposition may be used in which the silicon dioxide or metal beam is positioned at a predetermined angle on the wafer. Deposition tends to be highly directional. By positioning the beam at a significant angle to the wafer, a highly directional beam can fill via 16 at 24 without introducing significant amounts of deposited material into the pocket. An additional advantage of the deposition is that a high degree of vacuum may be achieved in the deposition chamber as compared to the sputtering chamber.

As shown in FIG. 1H, the selected gas and pressure are now contained within the sealed pocket at 24. This advantageously provides a controlled atmosphere for the acoustically active part of the device and protects the part from undesirable contamination. Sealed structures formed as described above should provide a hermetic seal. The hermetic seal is substantially enclosed in that it substantially prevents air or gas from entering / outflowing into or out of it. However, even in hermetic seals, small amounts of gas molecules will pass slowly over time through diffusion and penetration. Sealability of the seal can be significantly improved by coating with a silicon nitride film deposited using plasma enhanced chemical vapor deposition (PECVD).

FIG. 1I is a cross-sectional view showing the structure after the electrode 26 (bump) is formed on the contact portion of the transducer structure 4. Electrode 26 may be formed using conventional lithographic techniques. As shown in FIG. 1I, the electrode 26 is formed at a height greater than the height of the sealing structure. This makes the sealed surface suitable for surface-mount solder.

Prior to mounting the sealed device on the PCB board, the device may be individually tested on the wafer and selected for approval or rejection. The wafer is then diced to create an individual die with the device thereon. The licensed die is then mounted in a surface-mount device tape and reel for subsequent surface-mount solder on the printed circuit board. It may be.

2 is a flow chart illustrating a method of sealing an active region of a non-silicon based device (in this case, a wave propagation area of a SAW device) on a wafer in accordance with an embodiment of the present invention. As shown 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 device is fabricated on the wafer. The cross section of the SAW device fabricated before sealing is shown in FIG. 1A. As described in connection with FIG. 1A, an unsealed device may be fabricated on a substrate such as lithium tantalate, lithium niobate, or quartz using conventional techniques.

In a second step 104, sacrificial material is deposited on the wafer. The cross section after deposition of the sacrificial layer is shown in FIG. 1B. As described in connection with FIG. 1B, the sacrificial layer may comprise polysilicon, amorphous silicon, or a possible polymeric material.

In a third step 106, the sacrificial layer is patterned using lithography. The cross section after patterning of the sacrificial layer is shown in FIG. 1C. As described in connection with FIG. 1C, the remaining sacrificial material must cover at least the wave propagation area of the SAW element since it is the area to be sealed.

In a fourth step 108, a seal coating is deposited on the wafer. The cross section after seal coating deposition is shown in FIG. 1D. As described in connection with FIG. 1D, the seal coating may include a glassy material deposited by spin-on or sputtering. The material may comprise silicon dioxide. Alternatively, the material may comprise silicon nitride or metal.

In a fifth step 110, the seal layer is patterned using lithography. The cross section after patterning of the seal layer is shown in FIG. 1E. As described in connection with FIG. 1E, the patterning exposes the electrical contact pad portion of the transducer 4. In addition, the patterning creates vias that penetrate under the sacrificial material through the seal coating.

In a sixth step 112, the sacrificial material is etched by the vias to create pockets on the device. The cross section after etching of the sacrificial material is shown in FIG. 1F. As described in connection with FIG. 1F, the etching may be performed by a dry etch process that leaves no unwanted residue.

In a seventh step 114, the substrate is mounted in a target atmosphere and is in equilibrium. The cross section after mounting in the target atmosphere is shown in FIG. 1G. As described in connection with FIG. 1G, the gas pressure in the chamber is equilibrated across the via to achieve gas pressure inside the same pocket as the chamber interior.

In an eighth step 116, the vias are filled to seal the pockets. The step is performed while the wafer is still in the target atmosphere. The cross section after the via is filled is shown in FIG. 1H. As described in connection with FIG. 1H, the via may be filled, for example, by sputtering or deposition of silicon dioxide or metal.

Finally, in a ninth step 118, an electrode 26 is formed on the contact. The cross section after the via is filled is shown in FIG. 1I. As described with respect to FIG. 1I, the electrode 26 is formed at a height greater than the height of the sealing structure in order to make the sealed element suitable for surface mount solder.

Subsequent to ninth step 118, other steps may be performed to mount the device on a printed circuit board (PCB). For example, the devices are individually tested on the wafer, the wafer is diced to create individual dies, and the licensed die is then surface-mounted device tape and reel for subsequent surface-mounted solder on the PCB. It may be mounted in the).

While the foregoing description revolves around wafer-level seals in SAW devices, techniques for wafer level protection of other devices using non-silicon based materials having active regions to be protected may be applied. Such applications include high dielectric strength vacuum isolation, electro-optic modulators (eg, based on lithium tantalate or lithium niobate), and integration for domain patterning in ferroelectrics (such as lithium tantalate or lithium niobate). It includes a light structure. In each of these applications, non-silicon-based devices include means for receiving signals in electrical form, means for applying signals to active regions of the substrate, and means for hermetically sealing the active regions without disturbing the reception of electrical signals. It may be lithographically configured to include. For SAW devices, the active area to be protected will of course coincide with the wave propagation area. The technique may be applicable to other near surface devices. Elements near the surface include, for example, acoustic, optical, nonlinear optical, electro-optical, aco-optic, and other devices.

While specific embodiments of the invention have been provided, it is to be understood that these embodiments are for illustrative purposes only and are not intended to limit the invention. Many additional embodiments will be apparent to those of skill in the art upon reading this application. Therefore, the present invention is limited by the following claims.

Claims (40)

A method of sealing an active region of a non-silicon based device on a wafer, Providing a sacrificial material on at least the active region of the non-silicon based device; Depositing the seal coating on the wafer such that the seal coating covers the sacrificial material; And Replacing the sacrificial material with a target atmosphere, A method of sealing an active region of a non-silicon based device. The method of claim 1, The seal coating is sufficiently impermeable to hermetically seal the target atmosphere in a pocket, A method of sealing an active region of a non-silicon based device. The method of claim 1, Providing the sacrificial material; Depositing the sacrificial material onto the wafer; And Lithographically patterning the sacrificial material such that the sacrificial material is on at least an active region of the non-silicon-based device; A method of sealing an active region of a non-silicon based device. The method of claim 1, The sacrificial material comprises a material selected from the group of materials consisting of polysilicon, amorphous silicon, and polymeric material, A method of sealing an active region of a non-silicon based device. The method of claim 1, Wherein the seal coating comprises a material selected from the group consisting of silicon dioxide, silicon nitride, or metals, A method of sealing an active region of a non-silicon based device. The method of claim 1, Wherein the seal coating comprises a glassy material, A method of sealing an active region of a non-silicon based device. The method of claim 6, Wherein the glassy material is selected from the group of glassy materials consisting of spin-on-glass and sputtered glass, A method of sealing an active region of a non-silicon based device. The method of claim 1, Replacing the sacrificial material; Lithographically patterning the seal coating to create a via through the seal coating and to expose an electrical contact pad for the non-silicon based device; Etching the sacrificial material through the via to create a pocket surrounded by the seal coating; Mounting the wafer in the target atmosphere; And Filling the via to seal the target atmosphere within the pocket, A method of sealing an active region of a non-silicon based device. The method of claim 8, Etching the sacrificial material includes an etching process that leaves no significant residue A method of sealing an active region of a non-silicon based device. The method of claim 9, The sacrificial material comprises a silicon-based material, and the etching process includes placing the wafer in a xenon-difluoride atmosphere to dry etch the silicon-based material. A method of sealing an active region of a non-silicon based device. The method of claim 8, Allowing the atmosphere in the pocket to be in equilibrium with the target atmosphere prior to filling the via, A method of sealing an active region of a non-silicon based device. The method of claim 8, Filling the via includes sputtering a fill material until the via is filled, wherein the via is positioned to avoid the active region of the non-silicon based device. A method of sealing an active region of a non-silicon based device. The method of claim 8, Filling the via includes depositing a fill material until the via is filled, wherein the angle between the deposition beam and the wafer surface is small enough to prevent a significant amount of fill material from entering the pocket, A method of sealing an active region of a non-silicon based device. The method of claim 1, The method may further include forming an electrode connected to the contact pad of the non-silicon based device. A method of sealing an active region of a non-silicon based device. The method of claim 14, The wafer is subsequently diced to create a separate die and the licensed die is mounted in the surface-mount device tape and rail for subsequent printed circuit board mounting, A method of sealing an active region of a non-silicon based device. The method of claim 1, The active region includes a wave propagation region of the non-silicon based device, A method of sealing an active region of a non-silicon based device. A non-silicon based device sealed at the wafer level, Active area to be protected; Contact area; And A lithographically formed structure sealing at least the active region and leaving at least a portion of the contact region exposed; Non-silicon based device. The method of claim 17, Wherein the lithographically formed structure comprises a glassy material, Non-silicon based device. The method of claim 17, The non-silicon based device is fabricated on a substrate selected from the group of substrates consisting of lithium tantalate, lithium niobate, and quartz, Non-silicon based device. As a non-silicon-based device manufactured lithographically, An active region of the non-silicon based element sensitive to the atmosphere; And Wafer level means for sealing said active region of said non-silicon based device, Non-silicon based device. A method of sealing an active region of a surface acoustic wave (SAW) device on a wafer, Providing a sacrificial material on at least the active region of the SAW device; Depositing the seal coating on the wafer such that the seal coating covers the sacrificial material; And Replacing the sacrificial material with a target atmosphere, A method of sealing an active region of a surface acoustic wave element. The method of claim 21, The seal coating is sufficiently impermeable to hermetically seal the target atmosphere in a pocket, A method of sealing an active region of a surface acoustic wave element. The method of claim 21, Providing the sacrificial material; Depositing the sacrificial material onto the wafer; And Lithographically patterning the sacrificial material such that the sacrificial material is on at least an active region of the SAW device; A method of sealing an active region of a surface acoustic wave element. The method of claim 21, The sacrificial material comprises a material selected from the group of materials consisting of polysilicon, amorphous silicon, and polymeric material, A method of sealing an active region of a surface acoustic wave element. The method of claim 21, Wherein the seal coating comprises a material selected from the group consisting of silicon dioxide, silicon nitride, or metals, A method of sealing an active region of a surface acoustic wave element. The method of claim 21, Wherein the seal coating comprises a glassy material, A method of sealing an active region of a surface acoustic wave element. The method of claim 26, Wherein the glassy material is selected from the group of glassy materials consisting of spin-on-glass and sputtered glass, A method of sealing an active region of a surface acoustic wave element. The method of claim 21, Replacing the sacrificial material; Lithographically patterning the seal coating to create a via through the seal coating and to expose an electrical contact pad for the SAW device; Etching the sacrificial material through the via to create a pocket surrounded by the seal coating; Mounting the wafer in the target atmosphere; And Filling the via to seal the target atmosphere within the pocket, A method of sealing an active region of a surface acoustic wave element. The method of claim 28, Etching the sacrificial material includes an etching process that leaves no significant residue A method of sealing an active region of a surface acoustic wave element. The method of claim 29, The sacrificial material comprises a silicon-based material, and the etching process includes placing the wafer in a xenon-difluoride atmosphere to dry etch the silicon-based material. A method of sealing an active region of a surface acoustic wave element. The method of claim 28, Allowing the atmosphere in the pocket to be in equilibrium with the target atmosphere prior to filling the via, A method of sealing an active region of a surface acoustic wave element. The method of claim 28, Filling the via includes sputtering a fill material until the via is filled, wherein the via is positioned to avoid the active area of the SAW device, A method of sealing an active region of a surface acoustic wave element. The method of claim 28, Filling the via includes depositing a fill material until the via is filled, wherein the angle between the deposition beam and the wafer surface is small enough to prevent a significant amount of fill material from entering the pocket, A method of sealing an active region of a surface acoustic wave element. The method of claim 21, Forming an electrode connected to the contact pad of the SAW element; A method of sealing an active region of a surface acoustic wave element. The method of claim 34, wherein The wafer is subsequently diced to create a separate die and the licensed die is mounted in the surface-mount device tape and rail for subsequent printed circuit board mounting, A method of sealing an active region of a surface acoustic wave element. The method of claim 21, The active region comprises a wave propagation region of the SAW element, A method of sealing an active region of a surface acoustic wave element. A surface acoustic wave (SAW) device that is sealed at the wafer level, Active area to be protected; Electrical contact area; And A lithographically formed structure sealing at least the active region and leaving at least a portion of the electrical contact region exposed; Surface acoustic wave elements. The method of claim 37, Wherein the lithographically formed structure comprises a glassy material, Surface acoustic wave elements. The method of claim 37, The SAW device is fabricated on a substrate selected from the group of substrates consisting of lithium tantalate, lithium niobate, and quartz, Surface acoustic wave elements. A lithographically manufactured surface acoustic wave (SAW) device, Means for conveying surface acoustic waves; And A wafer level means for sealing said means for conveying said surface acoustic wave, Lithographically manufactured surface acoustic wave device.