# US 6,877,209 B1 · Method for sealing an active area of a surface acoustic wave device on a wafer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,877,209 B1 - Document ID: US6877209B1 - Status: Granted - Kind: B1 - Application number: 10/231,356 - Filed: 2002-08-28 - Granted: 2005-04-12 - Earliest claimed: 2002-08-28 - Assignees: Silicon Light Machines Corporation - Inventors: Gregory D. Miller; Mike Bruner; Lawrence Henry Ragan; Gary Green - Web page: https://patentgrep.com/patent/US6877209B1 ## CPC - B81C 1/00293: {maintaining a controlled atmosphere with processes not provided for in B81C1/00285} - H03H 3/08: for the manufacture of resonators or networks using surface acoustic waves - H03H 9/02921: {Measures for preventing electric discharge due to pyroelectricity} - H03H 9/02984: {Protection measures against damaging} - H03H 9/1092: {the enclosure being defined by a cover cap mounted on an element forming part of the surface acoustic wave [SAW] device on the side of the IDT's} - B81C 2203/0136: Growing or depositing of a covering layer - Y10T 29/42: Piezoelectric device making - Y10T 29/49005: Acoustic transducer - Y10T 29/49007: Indicating transducer - Y10T 29/49011: Commutator or slip ring assembly - Y10T 29/4902: Electromagnet, transformer or inductor - Y10T 29/4908: Acoustic transducer - Y10T 428/12521: Both components Fe-based with more than 10% Ni - B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01) - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract One embodiment disclosed relates to a method for sealing an active area of a surface acoustic wave (SAW) device on a wafer. The method includes providing a sacrificial material over at least the active area of the SAW device, depositing a seal coating over the wafer so that the seal coating covers the sacrificial material, and replacing 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, and a lithographically-formed structure sealing at least the active area and leaving at least a portion of the electrical contact area exposed. ## Claims ### Claim 1 A method for sealing an active area of a surface acoustic wave (SAW) device on a wafer, the method comprising: providing a sacrificial material over at least the active area of the SAW device; depositing a seal coating over the wafer so that the seal coating covers the sacrificial material; and replacing the sacrificial material with a target atmosphere, wherein replacing the sacrificial material comprises: lithographically patterning the seal coating to create a via through the seal coating and to expose electrical contact pads coupled to transducer structures of the SAW device for conducting electrical current to and from the transducer structures; etching the sacrificial material by way of the via to create a pocket surrounded by the seal coating; placing the wafer in the target atmosphere; and filling the via to seal the target atmosphere in the pocket. ### Claim 2 (depends on 1) The method of claim 1, wherein etching the sacrificial material comprises an etching process that does not leave substantial residue. ### Claim 3 (depends on 2) The method of claim 2, wherein the sacrificial material comprises a silicon-based material, and wherein the etching process comprises placing the wafer in a xenon-difluoride atmosphere to dry etch the silicon-based material. ### Claim 4 (depends on 1) The method of claim 1, further comprising: allowing an atmosphere in the pocket to equilibriate with the target atmosphere prior to filling the via. ### Claim 5 (depends on 1) The method of claim 1, wherein filling the via comprises sputtering of a fill material until the via is filled, and wherein the via is placed to avoid the active area of the SAW device. ### Claim 6 (depends on 1) The method of claim 1, wherein filling the via comprises evaporating a fill material until the via is filled, and wherein an angle between evaporating beam and wafer surface is sufficiently low to avoid introducing a substantial amount of the fill material into the pocket. ### Claim 7 (depends on 1) The method of claim 1, further comprising: building up electrodes on top of and in direct contact with the contact pads of the SAW device. ### Claim 8 (depends on 7) The method of claim 7, wherein the wafer is subsequently diced to produce individual die and acceptable dies are placed into a surface-mount-device tape-and-reel for subsequent printed circuit board mounting. ### Claim 9 A method for sealing an active area of a surface acoustic wave (SAW) device on a wafer, the method comprising: providing a sacrificial material over at least the active area of the SAW device; depositing a seal coating over the wafer so that the seal coating covers the sacrificial material; and replacing the sacrificial material with a target atmosphere, wherein the active area comprises a wave propagation area of the SAW device. ### Claim 10 (depends on 9) The method of claim 9, wherein the seal coating has a sufficient impermeability so as to hermetically seal the target atmosphere within a pocket. ### Claim 11 (depends on 9) The method of claim 9, wherein providing the sacrificial material comprises: depositing the sacrificial material over the wafer; and lithographically patterning the sacrificial material so that the sacrificial material is over at least the active area of the SAW device. ### Claim 12 (depends on 9) The method of claim 9, wherein the sacrificial material comprises a material from a group of materials consisting of polysilicon and amorphous silicon. ### Claim 13 (depends on 9) The method of claim 9, wherein the seal coating comprises a material from a group of materials consisting of silicon dioxide, silicon nitride, or metal. ### Claim 14 (depends on 9) The method of claim 9, wherein the seal coating comprises a glassy material. ### Claim 15 (depends on 14) The method of claim 14, wherein the glassy material is from a group of glassy materials consisting of spin-on-glass and sputtered glass. ### Claim 16 (depends on 9) The method of claim 9, wherein the seal coating is of a sufficient thickness so as to be impermeable to undesired contaminants. ### Claim 17 (depends on 9) The method of claim 9, wherein the seal coating comprises a material selected to have a thermal coefficient-of-expansion (TCE) mismatch with the wafer so as to produce a countervailing force against normal thermal expansion of the wafer.