Abstract:
A method of sealing an optical fiber in a microchip includes providing a device microchip, a top microchip and an optical fiber; forming a groove in at least one of the device microchip and the top microchip; coating metal on the optical fiber; depositing metal on the groove and top surfaces of the device microchip and the top microchip; depositing solder on the top surface of at least one of the device microchip and the top microchip; placing the optical fiber in the groove; placing the top microchip on the device microchip; and reflowing the solder to form a hermetic seal.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to optical connections to microchips, and more particularly to optical connections to microchips having an effective environmental seal. 
     Micro-optical electromechanical systems (MOEMS) is a relatively new technology. Traditional optical packages are hermetic at the carrier level. These packages are very expensive from a materials and fabrication standpoint. In addition, the critical optical components are not protected until the final packaging step, which typically lowers yield. Greater losses are incurred when yield losses are experienced in this final packaging step. Also, because a greater variety of materials exist inside the larger carrier level package, reliability concerns are amplified due to out gassing and corrosion, often limiting material selection. 
     U.S. Patent Application Publication 20020090761 discloses a hermetic sealing method for an electronic circuit module, however, it does not disclose a method of sealing a fiber optic into the circuit module. 
     U.S. Pat. No. 6,300,151 discloses a method of aligning an optical fiber to an optical module. However, the fiber interconnect and hermetic sealing is not discussed. 
     U.S. Pat. No. 6,019,523 discloses a method of aligning an optical fiber. A noise reducing seal is made from the external environment. The seal is not hermetic. It is possible that moisture may enter through the entire package. 
     U.S. Pat. No. 5,852,696 relates to a coupling structure of an optical fiber and an optical semiconductor element. A V groove is formed using known masking and anisotropic etching techniques. An optical fiber is bonded into the V groove using an index matching UV curable adhesive or other suitable known adhesive. A chip and optical fiber hermetic seal is not disclosed. 
     U.S. Pat. No. 5,717,803 discloses optical fibers arranged in a V groove formed at the surface of a silicon substrate and a cover provided thereon. This is an optical coupling device without an environmental seal. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to hermetically seal a top chip and an optical fiber interconnect to a micromachined device, thereby eliminating the need for a hermetic carrier level package. 
     The invention will be better understood, and further objects, features, and advantages thereof will become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
     FIG. 1 is a perspective view of a device microchip and a top microchip. 
     FIGS. 2A,  2 B,  2 C and  2 D are cross-sectional views of some exemplary groove shapes. 
     FIGS. 3A and 3B show an optical fiber. 
     FIG. 4 is a plan view of the device microchip showing patterned metal. 
     FIG. 5 is a plan view of the device microchip showing patterned solder. 
     FIG. 6 is a cross-section of the assembled microchips and optical fiber. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A chip level hermetic package provides protection of critical devices much earlier in the packaging process, increasing yields and reducing the expense of each yield loss. The inventive package is preferable formed from batch fabrication of silicon, thereby dramatically reducing material and fabrication costs. The chip level seal provides protection from later packaging process steps and materials and has the potential to increase device reliability and longevity. The invention provides hermetic optical fiber interconnects and a cap seal to a micromachined device at the chip level. 
     Important features of the invention include an optical fiber interconnect sandwiched between two chips. Grooves in the one or both of the chips are micromachined, for example, using KOH or DRIE etching techniques. The round optical fiber is sealed in the faceted groove. A seal ring is provided around the perimeter of each chip. The sealing of the optical fiber and the chips is hermetic. An important application of the invention is to seal optical switches. 
     FIG. 1 is a perspective view of a device microchip  10  and a top microchip  12 . Microchips  10 ,  12  may be made of, for example, silicon, silicon on insulator, or quartz. Microchips  10 ,  12  have top surfaces  22 , 24  that mate when assembled. At least one groove  14 , 18  is formed in the top surface of one or both microchips  10 ,  12 . More than one groove may be formed in the microchips, depending on the intended use. An optical fiber will be placed in groove  14 , 18 . 
     FIGS. 2A-2D are cross-sectional views of some exemplary groove shapes. FIG. 2A shows a rectangular groove  14 , 18  as shown in FIG.  1 . In FIG. 2A, as in FIG. 1, a portion of the complete groove is located in each of the microchips  10 , 12 . FIG. 2B shows a rectangular groove  26  that is formed only in the device microchip  10 . FIG. 2C shows a V groove  28  that is formed only in the device microchip  10 . In FIGS. 2B and 2C, none of the groove is formed in the top microchip  12 . In FIG. 2D, a portion  30  of the faceted groove is formed in the device microchip  10  and a portion  32  of the faceted groove is formed in the top microchip  12 . The grooves may be formed by known methods, for example, KOH or DRIE etching. In the remaining discussion of the inventive method, the embodiment of FIG. 2A will be used, although it should be understood that the invention is applicable to grooves having varying geometries. 
     FIGS. 3A and 3B show a round optical fiber  34 . As shown in FIG. 3A, at least a portion  36  of the optical fiber  34  that is to be disposed in the groove  14 ,  18  is coated with metal, for example, by patterning with gold. Optionally, although not necessary, the portion  36  of the optical fiber  34  that is coated with metal may additionally be coated with solder, for example by patterning. FIG. 3B shows optical fiber  34  patterned with solder  42  on the metallized area  36 . 
     Metal is deposited on the top surfaces  22 ,  24  of the device and top microchips  10 , 12  around their perimeters and in their grooves  14 , 18 . An exemplary way to deposit the metal is by patterning with gold. FIG. 4 is a plan view of the device microchip  10  showing patterned metal  38  around the perimeter of the top surface  22  and in groove  14 . In FIG. 4, all of groove  14  is shown patterned with metal  38 . However, it should be understood that only a portion of groove  14  need be patterned with metal  38 , preferably that portion of groove  14  adjacent the perimeter of microchip  10 . Metal is similarly deposited or patterned on the top surface  24  and groove  18  of top microchip  12 . 
     Solder may be applied to the microchips  10 , 12  and or optical fiber  34  in a variety of ways. At a minimum, solder is deposited on the metallized area of at least one of the top surfaces  22 ,  24  of the device and top microchips  10 , 12  to facilitate formation of the perimeter seal ring. For example, the solder may be patterned on the metallized area around the perimeter prior to assembly of the two microchips, or the solder may be dispensed on the metallized area to form the perimeter seal ring as part of an assembly step of the two microchips. Alternatively, solder may be deposited on the metallized area around the perimeter of both microchips  10 , 12 . 
     In one embodiment, the solder covers only the metallized areas of the perimeters (whether applying solder to one or both microchips), for example the metallized areas of the perimeter shown in FIG.  4 . In another embodiment, the solder may cover areas of the perimeter in addition to the metallized areas (whether applying solder to one or both microchips). FIG. 5 is a plan view of the device microchip  10  showing patterned solder  40  that covers areas of the perimeter in addition to the metallized areas of the perimeter shown in FIG.  4 . Solder may be similarly deposited on the top microchip  12 . 
     With regard to the groove  14  of FIG. 4 (and likewise for groove  18  in microchip  12 ), several variations of applying solder are possible. First, solder may not be deposited on groove  14  prior to assembling the two microchips. In such a case, solder may be coated on the optical fiber  34 , or solder may be dispensed in the groove  14  as part of an assembly step, or both. Second, solder may be deposited on a portion of groove  14  that is metallized, for example, as shown in FIG.  4 . Third, solder may be deposited on a portion of groove  14  that is metallized and, in addition, solder may be deposited on nonmetallized areas in and around the groove  14 , as shown in FIG.  5 . 
     Optical fiber  34  is placed in groove  14  with the metallized portion of the fiber disposed in the groove. If solder was coated on the metallized portion of the optical fiber, then the soldered and metallized portion is disposed in the groove. The microchips  10 , 12  are assembled with the top surfaces  22 , 24  facing each other. The groove  18  in top chip  12  is aligned over optical fiber  34  and groove  14  in device chip  10 . The solder is then reflowed to seal the optical fiber and the two microchips. If solder was not deposited on the groove  14  or coated on the fiber  34 , then solder is dispensed, for example, manually, into groove  14 ,  18  around optical fiber  34  to seal fiber  34 . 
     FIG. 6 is a cross-section of the assembled microchips  10 , 12  and optical fiber  34  showing the seal  44  around the optical fiber  34  and between the microchips  10 , 12 . 
     While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.