BACKGROUND
Electronic components, such as microelectrical mechanical systems (MEMS), may be encapsulated within a package to protect the electronic component from environmental hazards such as humidity, electrical interference, dust, physical contact, and the like. Providing a hermetically sealed atmosphere for the electronic component within a package maybe reduce the effect of such environmental hazards. Some sealing materials used to seal electronic component packages may degrade the life or operation of the component or may result in a non-hermetic seal. Other sealing methods may require the package to undergo heating to a temperature that may damage the electronic components or may create a mis-match between the coefficient of thermal expansion of the package lid and the container. This may stress the electronic component or may result in a failure of the seal between the container and the lid. Still other sealing methods may require welding or high compression forces that are not suited for certain types of packaging materials such as glass or ceramics.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional side view of one embodiment of a container.
FIG. 2 is a schematic side view of one embodiment of a polishing device.
FIG. 3 is a schematic cross-sectional side view of one embodiment of an electronic component mounted on one embodiment of a container
FIG. 4 is a schematic cross-sectional side view of one embodiment of a process of plasma activating one embodiment of a container and a lid.
FIG. 5 is a schematic cross-sectional side view of one embodiment of a process of sealing one embodiment of a container and a lid.
FIG. 6 is a schematic cross-sectional side view of one embodiment of a sealed container and a lid.
FIG. 7 is a schematic perspective view of another embodiment of a sealed container and a lid.
FIG. 8 is a schematic cross-sectional side view of another embodiment of a sealed container and a lid.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional side view of one embodiment of a container 10. Container 10 may include a support surface 12 for receiving an electronic component, such as a microelectronic device 14 (see FIG. 3) thereon, and a sealing surface 16 that may extend around a perimeter 18 of container 10. Container 10 may further include connection pins 20 on an underside thereof for accessing microelectronic device 14 (see FIG. 3) when the microelectronic device is mounted on container 10. Container 10 may be manufactured of metal, a metal alloy, ceramic, plastic, silicon, glass, or any other suitable material.
FIG. 2 is a schematic side view of one embodiment of a polishing device 22. Polishing device 22 may include a sample holder 24 that may hold a plurality of containers 10 such that sealing surfaces 16 of the containers 10 may be positioned facing downwardly in a direction 25. Device 22 may further include a polishing structure, such as a polishing wheel 26, that may rotate about a drive shaft 28 in a direction 30. Polishing wheel 26 may include a polyurethane polishing pad attached to a rigid platen and may be powered by a motor (not shown) so as to rotate at speeds of approximately 100 rpm or more. A polishing solution, such as a slurry 32 of silica particles in a potassium hydroxide (KOH) solution may be placed on a polishing surface 34 of polishing wheel 26. Holder 24 may be positioned above polishing surface 34 such that when holder 24 is lowered, sealing surfaces 16 of containers 10 may be mechanically planarized, such as being polished, by polishing surface 34 of polishing wheel 26 with slurry 32 thereon. In one embodiment, sealing surfaces 16 are polished to a smoothness of at most a 20 Angstroms root mean square (rms) surface roughness over a 2 micrometer by 2 micrometer area. Of course, other polishing and/or planarizing structures or methods may be utilized to smooth or planarize sealing surfaces 16 of containers 10.
FIG. 3 is a schematic cross-sectional side view of one embodiment of a microelectronic device 14 mounted on container 10. Microelectronic device 14 in the exemplary embodiment may comprise a microelectrical mechanical system (MEMS) chip but in other embodiments may comprise any type of microelectronic structure. Microelectronic device 14 may be secured to container 10 on support surface 12 by any known method and may include electrical connection structure, such as wires 36, so that device 14 is in electrical communication with connection pins 20. Accordingly, after a lid 38 (see FIG. 4) is secured to container 10 so as to enclose device 14 therein, the device 14 may still be electronically accessed from an exterior of the device packaging 40 (see FIG. 6).
FIG. 4 is a schematic cross-sectional side view of one embodiment of a process of plasma activating one embodiment of container 10 and lid 38. Lid 38 may be manufactured of metal, a metal alloy, ceramic, plastic, silicon, glass, or any other suitable material. Lid 38 may include a sealing surface 46 that may extend around a perimeter 48 of the lid.
The process may include enclosing container 10 and lid 38 in an enclosure 42 and then filling or creating within enclosure 42 a plasma atmosphere 44 by the addition of energy at a radio frequency in the range of 10 kHz to 14 MHz. Plasma atmosphere 44 may be formed of nitrogen, oxygen, argon, a mixture thereof, or any other suitable component or components. As an alternative, the sealing surfaces can be activated under an ambient plasma with air, nitrogen, oxygen, or other suitable gas. Subjecting container 10 and lid 38 to plasma atmosphere 44 may activate sealing surface 46 of lid 38 and sealing surface 16 of container 10 so that the sealing surfaces will form a covalent bond therebetween when corresponding sealing surfaces 46 and 16 are positioned in contact with one another. Exposure of container 10 and lid 38 to plasma atmosphere 44 may be conducted at any temperature or pressure suitable to activate the sealing surfaces but in one exemplary embodiment, the pressure within enclosure 42 may be in a range of 50 mtorr to 1 atmosphere and the temperature within enclosure 42 may be in a range of 25 to 100 degrees Celsius, wherein container 10 and lid 38 may be exposed to plasma atmosphere 44 for a time period in a range of 10 to 100 seconds.
The process may include hydrating the sealing surface 46 of lid 38 or sealing surface 16 of container 10. The hydration process can be done with water plasma in a plasma chamber under vacuum, or in an open environment under an ambient water plasma. A trace of water vapor, such as vaporized deionized water, can be drawn into the process gas, such as nitrogen, oxygen, or argon, to form a water plasma. The hydration process results in a higher density of silanol groups on the sealing surface 46 of lid 38 and sealing surface 16 of container 10 so that the sealing surfaces will form a strong covalent bond therebetween when corresponding sealing surfaces 46 and 16 are positioned in contact with one another. Due to the plasma activation and hydration process of the sealing surfaces of container 10 and lid 38, the container and the lid may each be manufactured of a unique material. For example, due to the plasma activation and hydration process, a glass or a silicon lid 38 may be bonded to a ceramic container 10 at a temperature of at most 100 degrees Celsius at ambient pressure to form a hermetic seal therebetween.
FIG. 5 is a schematic cross-sectional side view of one embodiment of a process of sealing one embodiment of container 10 and lid 38. In this exemplary embodiment, after planarizing sealing surface 16 of container 10, a buffer layer, such as a bonding layer 50 may be positioned on sealing surface 16 of container 10 around perimeter 18 of the container. Bonding layer 50 may be manufactured of oxide, glass frit, amorphous silicon, or any other suitable material or mixtures thereof, and may be deposited by any suitable means such as chemical vapor deposition, sputtering or the like. Bonding layer 50 generally is manufactured of a non-epoxy, non-solder, and non-organic material because these excluded materials may not form a hermetic seal and may degrade the life or performance of microelectronic device 14.
Lid 38 and container 10 are then plasma activated and hydrated to prepare the sealing surfaces 50a and 46 for covalent bonding. Lid 38 is then contacted with container 10 such that sealing surface 46 of lid 38 contacts bonding layer 50 of container 10 so as to form a hermetic seal of covalent bonding around perimeter 18 of container 10 and around perimeter 48 of lid 38, wherein the perimeter of the base substantially mates in size and shape with the perimeter of the lid. In other words, an exposed mating surface of container 10, which may comprise an exposed surface 50a of bonding layer 50, is contacted with an exposed mating surface 46 of lid 38 to form a bond therebetween. The perimeter of each of container 10 and lid 38 may be round, square, rectangular, oval, or any shape as desired. A light compression force, such as a force of approximately 50 Newtons, may be applied to hold container 10 and lid 38 together for a sufficient time, such as a time period of approximately 10 seconds, for container 10 and lid 38 to seal to one another. The contacting may be conducted at a pressure in a range of approximately 100 mtorr to 1 atmosphere, and at a temperature in a range of approximately 25 to 200 degrees Celsius. Because the contacting pressure and temperature are relatively low, the package may be sealed with substantially no mis-match between the coefficient of thermal expansion of the lid and the container and with substantially no heating of the microelectronic device to a temperature that may damage the electronic component.
Still referring to FIG. 5, in the embodiment shown, bonding layer 50 may be positioned on sealing surface 16 of container 10 after polishing of sealing surface 16. However, in other embodiments, bonding layer 50 may be positioned on sealing surface 16 without polishing of the sealing surface. In the embodiment shown, bonding layer 50 is not polished prior to contact with lid 38. However, in another embodiment, after bonding layer 50 has been positioned on sealing surface 16, the exposed surface of bonding layer 50 may be planarized or polished on polishing wheel 26 (see FIG. 2) by placement of container 10 in holder 24 (see FIG. 2). In other embodiments, a bonding layer 50 may be positioned on both of container 10 and lid 38, or only on lid 38, wherein the sealing surfaces of the container and lid, and the exposed surface of the bonding layer or layers may or may not be polished prior to contact therewith.
FIG. 6 is a schematic cross-sectional side view of one embodiment of container 10 and lid 38 sealed together to form a package 52 having an airtight seal, such as a hermetic seal 54, of covalent bonding around a perimeter 56 thereof. In another embodiment, seal 54 may comprise other types or methods of bonding. Package 52 defines an enclosed interior atmosphere 58 in which microelectronic device 14 is positioned. Interior atmosphere 58 may include a desiccant 60, which may be secured to an underside of lid 38, wherein desiccant 60 may reduce the humidity within interior atmosphere 58. Hermetic seal 54 provides some protection of microelectronic device 14 from environmental conditions outside package 52 such as humidity, electrical interference, dust, physical contact, and the like. Lid 38 may include a coating 62 on an upper side thereof which may function as an aperture for an optical MEMS device.
FIG. 7 is a schematic perspective view of another embodiment of a sealed container 10 and a lid 38 that defines a cylindrical shaped package 52. In this embodiment, package 52 includes two connection pins 20 and a lid 38 having a height 64 greater than a height 66 of container 10. Of course, any dimensions may be utilized for the package of the present invention.
FIG. 8 is a schematic cross-sectional side view of another embodiment of a sealed container 10 and a lid 38 that define a package 52 having a hermetic seal 54. In this embodiment, wires 36 are connected horizontally to connection pins 20 that extend through container 10 to an exterior of package 52. This embodiment does not include a desiccant 60 or a bonding layer 50.
Other variations and modifications of the concepts described herein may be utilized and fall within the scope of the claims below.
Patent Application
20060033188
