Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
  • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
  • B81C1/00261—Processes for packaging MEMS devices
  • B81C1/00277—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS
  • B81C1/00293—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS maintaining a controlled atmosphere with processes not provided for in B81C1/00285
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P72/00—Handling or holding of wafers, substrates or devices during manufacture or treatment thereof
  • H10P72/04—Apparatus for manufacture or treatment
  • H10P72/0444—Apparatus for wiring semiconductor or solid-state device
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W72/00—Interconnections or connectors in packages
  • H10W72/071—Connecting or disconnecting
  • H10W72/075—Connecting or disconnecting of bond wires
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C2203/00—Forming microstructural systems
  • B81C2203/01—Packaging MEMS
  • B81C2203/0145—Hermetically sealing an opening in the lid

Definitions

• the invention relates to a method for closing a vent formed in a wall of a microstructure under a controlled atmosphere.
• the invention also relates to the use of a machine for the implementation of this method.
• microdetectors infrared microbolometer
• MEMS type components RF microswitch
• MEMS-type devices produced collectively on silicon wafers generally contain mobile elements making up electrical, mechanical or optical assemblies. These devices are in all cases fragile and their manufacture therefore includes an encapsulation step, the function of which is at least to provide mechanical protection of the sensitive parts. Sometimes this encapsulation is an integral part of the device by supporting electrodes, contact recovery pads, or mechanical stops in the direction perpendicular to the plane of the plate.
• the encapsulation of devices under a controlled atmosphere that is to say under vacuum or under a gaseous atmosphere, conventionally consists in forming a microstructure delimiting a cavity around the device, piercing a vent in a wall of the microstructure and closing the vent by a stopper, after placing under a controlled atmosphere. As shown in FIG.
• a microcomponent according to the prior art comprises at least one elementary device 1, previously produced on a substrate 2.
• a microstructure 3 is then produced around the device 1, for example by means of a mold in resin, with a wall 4 delimiting a cavity 5 around the device 1 to be encapsulated.
• a small orifice 6, called a vent is then formed in the wall 4 of the microstructure 3, in order to remove the resin which served as a mold and create a vacuum inside the cavity 5.
• the vent 6 is then closed by depositing a sealing material, while maintaining the vacuum in the cavity 5.
• the major difficulty of this type of process lies in obtaining a hermetic closure of the microstructure 3, while controlling the atmosphere inside the latter.
• microstructure only represents very small volumes, the thickness and the surface of the microstructure being very limited. This succession of steps therefore has the drawback of using sensitive and delicate processes.
• a plurality of microstructures to be closed are generally arranged on the same plate, also called a wafer. It is then necessary to plan to separate the microstructures in order to encapsulate them in individual boxes.
• the microstructures are placed under a controlled atmosphere, through the vent which then remains open.
• the object of the invention is to remedy these drawbacks and its object is to provide a simple and effective vent obturation method, which can be applied equally to a single microstructure or to an entire wafer provided with 'a plurality of microstructures. According to the invention, this object is achieved by the appended claims and, more particularly, by the fact that the method comprises at least the following steps:
• the invention also relates to an ultrasonic welding machine for implementing the sealing process.
• FIG. 1 schematically shows a microstructure with a vent according to the prior art.
• FIG. 2 represents a vent closed by a method of metallic deposition by evaporation according to the prior art.
• Figures 3 and 4 schematically represent two steps of a method of closing a vent according to a first embodiment of the invention.
• FIGS. 5 to 10 schematically represent different stages of the sealing of a vent by means of an ultrasonic welding machine according to the invention.
• a vent 9 is formed in a wall 10 of a microstructure 3 under a controlled atmosphere.
• the vent 9 is of frustoconical shape, but it can take any other shape, in particular cylindrical.
• a first step consists in depositing an attachment stud 1 1 on the wall 10 at the periphery of the vent 9, more particularly, at the periphery of its end opening out opposite the cavity formed in the microstructure 3.
• the attachment stud 11 is produced by depositing a layer of metal chosen from gold, silver, aluminum or copper.
• the attachment stud is preferably produced by depositing a layer of gold via a mask (not shown), so as to form a patch, preferably annular, around the orifice formed. through the vent 9.
• the vent 9 can be produced after the deposition of the metal layer intended to form the attachment stud 11, for example by laser etching.
• a ball 12 is formed by fusion at one end of a metal wire 13.
• the metal wire 13 and the ball 12 can be of ductile metal chosen from gold, silver, aluminum or copper.
• the ball 12 and the attachment stud 11 are made of the same material, in order to facilitate their subsequent work hardening.
• the ball 12 is then deposited on the end of the vent 9 and on the attachment stud 11 (FIG. 3) and the closure of the vent 9 is then effected by deformation of the ball 12 and welding of the ball 12 on the attachment stud 11.
• a compression force F or crushing force, is applied to the ball 12 by means of a welding electrode 14 (FIG. 8), so that the ball 12 deforms and plugs the vent 9 by resting on the attachment stud 11, as shown in FIG. 4.
• vibrations preferably, ultrasonic of low amplitude, are generated by the welding electrode 14 , to ultrasonically weld the deformed ball 12 and the attachment stud 11, at the contact zones between the attachment stud
• the process described above is carried out at a temperature, preferably of the order of 150 ° C., which is much lower than the melting temperature of gold, silver, aluminum and copper , in order to facilitate the deformation and the welding of the ball 12.
• a temperature preferably of the order of 150 ° C., which is much lower than the melting temperature of gold, silver, aluminum and copper , in order to facilitate the deformation and the welding of the ball 12.
• the crushing of the ball 12 makes it possible to obtain perfect contact of the ball 12 on the attachment stud 11, with in addition a final mechanical junction.
• the shutter is therefore perfectly airtight.
• gold is best suited to meet this sealing function, because it is very ductile.
• the bond thus obtained is not only mechanical but also electrical, because gold also has good conductivity.
• oxidizing the wall 10 of the microstructure 3 it is possible to include an additional step of oxidizing the wall 10 of the microstructure 3.
• An oxidized layer (not shown) is then formed between the wall 10 and the bonding pad 11.
• the oxidized layer has for function of electrically isolating the attachment stud 11 from the wall 10.
• An ultrasonic welding machine conventionally comprises a welding electrode 14, crossed by the metal wire 13, and a work table 15.
• the machine conventionally comprises means 16, intended for the formation of the ball 12 by melting the metal wire 13.
• a high tension can, for example, be applied between the metal wire 13 and a terminal 16, causing the fusion of the wire 13 and the appearance of the ball 12 which will then be hardened.
• the microstructure 3, provided with at least one vent 9 to be closed is placed on the work table 15 (FIGS. 7 to 10).
• the ends of the electrode 14 and of the metal wire 13 are introduced into an enclosure 17, the atmosphere of which can be controlled.
• the enclosure 17 can be placed under vacuum or under a partial pressure of inert gas, after formation of the ball 12 in the enclosure 17.
• the machine conventionally comprises means for moving the electrode 14 perpendicular to the work table 15.
• the ball 12 can thus be deposited on the end of the vent 9 and on the attachment stud 11 of the supported microstructure 3 by the work table 15.
• the machine also conventionally comprises means for generating ultrasound, intended to cause the vibration of the welding electrode 14.
• the means for moving the electrode 14 and the means for generating d 'ultrasound is formed by any suitable means used in conventional ultrasonic welding machines.
• the electrode 14 is moved to be brought into contact with the ball 12 and to apply, perpendicular to the work table 15, a crushing force F on the ball 12. This causes compression and deformation of the ball 12 on the attachment stud 11 of the microstructure 3 and the closure of the vent 9.
• the application of an ultrasonic vibration force F us preferably parallel to the work table 15, at the the electrode 14 in contact with the ball 12 causes the ball 12 to be welded to the attachment stud 11.
• FIGS. 9 and 10 the welding has been carried out and the sealing of the vent 9 is finished.
• the welding electrode 14 then returns to its initial position, away from the microstructure 3, going up perpendicularly to the work table 15 (figure 9).
• the metal wire 13 is then, for example, broken at the level of the deformed ball 12, for example, by a tensile force exerted on the wire 13.
• a small piece of residual wire 13 may possibly remain on the upper surface of the ball distorted 12.
• solder wire 13 can be used to make an electrical connection, by connecting the free end of the residual wire 13 to a connection pad of an encapsulation box, or alternatively d another component.
• the metal wire 13 can be cut simultaneously with the production of the next ball 12, in order to allow automation of the sealing process.
• the machine may include means for relative displacement of the microstructure 3 and of the welding electrode 14, both perpendicularly to the work table 15 and parallel to it.
• the microstructure 3 can be integral with the work table 15, which can be in motion relative to the welding electrode 14.
• the lateral movement of the work table 15 makes it possible to scroll the microstructures 3 one after the other under the welding electrode 14, in the enclosure 17.
• the work table 15 supports, outside the enclosure 17, a microstructure 3 whose vent 9 has already been closed, and in the enclosure 17 of the machine, a microstructure 3 ready to be closed.
• the method according to the invention can thus be implemented by any known ultrasonic welding machine, the additional means necessary for the implementation of the vent sealing method, namely the enclosure 17 with a controlled atmosphere and the means for moving the microstructure 3 inside the enclosure 17, being easy to install and use.
• the additional means necessary for the implementation of the vent sealing method namely the enclosure 17 with a controlled atmosphere and the means for moving the microstructure 3 inside the enclosure 17, being easy to install and use.
• vent sealing process and the ultrasonic welding machine described above provide the following advantages, namely good sealing of the microstructure 3, an efficient sealing process, carried out at low temperature and easy to put on. and a welding machine for applying the sealing process for a unitary microstructure or for a plurality of microstructures produced on an entire wafer before cutting.
• the invention is more particularly advantageous during the manufacture of microstructures constituting accelerometers, bolometers, RF or power microswitches.

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing & Machinery (AREA)
• Micromachines (AREA)
• Pressure Welding/Diffusion-Bonding (AREA)
• Wire Bonding (AREA)
• Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (4)

Families Citing this family (4)

Family Cites Families (10)

• 2004
  • 2004-05-12 FR FR0405128A patent/FR2870227B1/fr not_active Expired - Fee Related
• 2005
  • 2005-05-03 EP EP05769285A patent/EP1747169A1/de not_active Withdrawn
  • 2005-05-03 US US11/587,241 patent/US20080000948A1/en not_active Abandoned
  • 2005-05-03 WO PCT/FR2005/001125 patent/WO2005121018A1/fr not_active Ceased

Non-Patent Citations (1)

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