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WO2005119756A1 - Semiconductor package with transparent lid - Google Patents

Semiconductor package with transparent lid Download PDF

Info

Publication number
WO2005119756A1
WO2005119756A1 PCT/IB2005/001590 IB2005001590W WO2005119756A1 WO 2005119756 A1 WO2005119756 A1 WO 2005119756A1 IB 2005001590 W IB2005001590 W IB 2005001590W WO 2005119756 A1 WO2005119756 A1 WO 2005119756A1
Authority
WO
WIPO (PCT)
Prior art keywords
wafer
glass frit
optically active
integrated circuit
elements
Prior art date
Application number
PCT/IB2005/001590
Other languages
French (fr)
Inventor
Siegfried Buttner
Roy Knechtel
Original Assignee
Melexis Nv
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Melexis Nv filed Critical Melexis Nv
Priority to EP05748145A priority Critical patent/EP1751792A1/en
Publication of WO2005119756A1 publication Critical patent/WO2005119756A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14618—Containers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/481—Disposition
    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/48245—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
    • H01L2224/48247—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a bond pad of the item
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
    • H01L2924/102—Material of the semiconductor or solid state bodies
    • H01L2924/1025—Semiconducting materials
    • H01L2924/10251—Elemental semiconductors, i.e. Group IV
    • H01L2924/10253—Silicon [Si]

Definitions

  • the present invention relates to a method of manufacturing packaged integrated circuit devices and more particularly to a method of manufacturing packaged optical integrated circuit devices for use in radiation sensors, imaging systems, DVD systems, such as blue laser DVD systems and the like.
  • DVD readers operate by reflecting a narrow beam of light from the surface of a spinning DVD and detecting variations in the reflected light.
  • the narrow beam of light is typically generated by or from an LED, VCSEL, or laser diode.
  • the reflected light is detected by a light sensing means, typically a photodiode.
  • the light sensing means and associated amplification means are typically implemented as a single integrated circuit.
  • the integrated circuit is conventionally encapsulated in a protective package, said package having a passageway through which radiation may pass to the light sensing means, a glass lid being mounted in or over the passageway and retained in position by an epoxy adhesive.
  • the glass lid provides protection for the light sensing means from the ingress of contaminants or from physical impacts.
  • the additional step of fitting a glass lid to the package can be expensive and may cause further problems for instance: the atmosphere trapped between the light sensing means and the lid may contain moisture or contaminants that may affect the performance or reliability of the assembled device; the glass lid may not be aligned parallel to the sensitive surface of the light sensing means which may affect the focussing of incident light reflected from the DVD surface; or in blue light DVD systems, conventional polymer adhesives can be affected by the blue light such that they turn opaque with time thus affecting transmission of light to the light sensing means.
  • a method of manufacturing optical integrated circuit devices comprising the steps of: providing a first wafer, said first wafer incorporating an integrated circuit, said integrated circuit having at least one optically active element; providing a second wafer, said second wafer being transparent; and placing said second wafer over said first wafer, wherein a pattern of glass frit material is provided on either wafer, said pattern being arranged so as to surround said optically active element or elements when the second wafer is placed over the first wafer, said glass frit subsequently being reflowed to form a permanent seal between said first and second wafers.
  • a transparent substrate provides protection for the optically active elements
  • the transparent substrate may additionally be readily mounted parallel to the surface of the optically active elements to minimise effects on the focussing of incident or emitted light.
  • the method includes the further step of packaging said optical integrated circuit device.
  • This may be achieved by mounting and electrically connecting the device to a suitable lead frame; inserting the device and lead frame into the cavity of a moulding tool; and encapsulating said device and lead frame in a suitable moulding compound, the moulding tool being adapted such that the second wafer is not completely encapsulated in the moulding compound thereby allowing radiation to pass between the optically active element and the exterior of the package.
  • bond pads are provided on said first wafer by means of which electrical connections may be made between said integrated circuit and said lead frame.
  • peripheral portions of the lead frame project from the package facilitating connection of the device to external circuitry.
  • the steps of placing the second wafer over the first wafer and reflowing the glass frit take place either in a vacuum or in a controlled atmosphere such as a dry Nitrogen atmosphere.
  • the said first wafer is a standard CMOS wafer.
  • said second wafer is a glass wafer.
  • said second wafer has substantially the same coefficient of thermal expansion as said first wafer.
  • the method may further incorporate the step of backlapping the first wafer to reduce the thickness of the device.
  • said glass frit material is applied to either of said wafers by screen printing.
  • the glass frit pattem is aligned with the optically active element or elements in the integrated circuit.
  • the second wafer is aligned with the first wafer when it is placed over the first wafer such that the glass frit pattern is aligned with the optically active element or elements in the integrated circuit.
  • the glass frit material is reflowed by raising the temperature of the two wafers above the melting point of the glass frit material for a time interval such that the glass frit material is able to form a seal between the two wafers and around said optically active element or elements.
  • said glass frit material is processed before being applied to remove any organic compounds.
  • An example of one such suitable process is Organic Burn Out (OBO).
  • said glass frit material may be applied such that it surrounds each optically active element individually or may be applied such that it surrounds two or more elements collectively.
  • Said optically active elements may comprise light emitting means or light sensing means.
  • Light emitting means may be operable to emit light at visible, infra red or ultraviolet wavelengths as desired.
  • said light sensing means may be operative to sense light of visible, infra red or ultra violet wavelengths as desired.
  • said light sensing means may comprise an array of individual light sensing elements.
  • the areas of said second wafer not forming said cover may be removed.
  • this method incorporates the additional steps of introducing melted wax between said first and said second wafers so as to fill substantially the entire space between said first and second wafers except for the area occupied by said optically active elements, and allowing said wax to set before cutting said second wafer.
  • the wax when set provides protection for said integrated circuit during the cutting process.
  • said wax is removed after the cutting process is complete.
  • Said second wafer may be adapted by pre-etching, pre-cutting, use of a specially adapted cutting tool or by any other suitable means such that the edges of said cover are profiled.
  • the integrated circuit additionally comprises bond pads, said bond pads being provided towards the periphery of said integrated circuit such that when portions of the second wafer are removed said bond pads are exposed, facilitating testing and connection to external circuitry.
  • said second wafer comprises filtering means to limit the incoming radiation to a desired wavelength band.
  • said filtering means is in the form of a layer of filtering material deposited on one or both surfaces of said second wafer.
  • one or both surfaces of said second wafer are pre-etched to define a lens pattern to improve the effectiveness of the optical sensing elements.
  • one or more surfaces of the said glass wafer are pre-etched to reduce the reflection of optical radiation and/or improve the transmission efficiency of the said second wafer for radiation.
  • the integrated circuit is one of an array of like integrated circuits formed on said first wafer.
  • Said integrated circuit array may be manufactured using conventional semiconductor processing techniques.
  • the integrated circuit array can be an array of any type but is preferably a regular square or rectangular array.
  • individual devices are formed by applying glass frit to said first wafer so as to surround the optically active elements of each integrated circuit in the array, placing said second wafer over said first wafer, reflowing said glass frit and separating individual devices by cutting along cutting channels provided between the integrated circuits in the array.
  • an optical integrated circuit device manufactured in accordance with the method of the first aspect of the present invention.
  • optical integrated circuit device may incorporate any of the features of the first aspect of the present invention as desired or appropriate.
  • Figure 1 is a cross section of an integrated circuit device according to the present invention.
  • Figure 2 is a cross section of a packaged integrated circuit device according to the present invention.
  • an optical integrated circuit device comprises an integrated circuit formed on a silicon wafer 201 incorporating at least one optically active element or elements and a glass cap covering said optically active element or elements.
  • the glass cap is sealed in position over the optically active element or elements by means of glass frit.
  • the device is mounted on a lead frame 206 and connections are made between bond pads provided on the integrated circuit to peripheral portions of the lead frame.
  • the device is encapsulated in a suitable mould compound in such a manner that the upper surface of the transparent cap is not encapsulated, thus allowing light to pass between the optically active element or elements and the exterior of the package.
  • optical integrated circuit devices are formed from an array of like integrated circuits provided on a silicon wafer 100.
  • the array is typically a square or rectangular array.
  • Each integrated circuit incorporates one or more optically active elements 106, which may be optical emitting elements or optical sensing elements.
  • optically active elements 106 are adapted to emit and/or sense light of visible wavelengths however, in some applications such elements may be adapted to additionally and/or alternatively emit and/or sense infra red and/or ultra violet wavelengths.
  • a transparent wafer 101 is placed over the silicon wafer 100.
  • the transparent wafer 101 is securely sealed to the silicon wafer 100 by a pattern of glass frit material 104 applied to either or to both wafers 100, 101.
  • the glass frit pattern 104 is screen printed on to the appropriate wafer 100, 101 and is arranged so as to surround the or each optically active element or elements 106 of each integrated circuit if provided on said silicon wafer 100 or so that it may be aligned to surround the or each optically active element or elements 106 of each integrated circuit if it is provided on said transparent wafer 101.
  • each optically active element 106 may be individually surrounded by glass frit material 104 or two or more optically active elements 106 may be surrounded collectively by glass frit material 104. Either before or after application to the wafers, the glass frit material may be raised in temperature to remove organic compounds contained therein.
  • the two wafers 100, 101 are aligned and brought together in a dry Nitrogen atmosphere.
  • the wafers 100, 101 are then raised in temperature to cause the glass frit material 105 to reflow and seal the wafers together.
  • the glass frit 105 seals the gap between the two wafers 100, 101 such that the optically active elements 106 of each integrated circuit are sealed in a dry Nitrogen atmosphere.
  • these steps could be carried out in a vacuum.
  • a series of cuts are made through said transparent wafer 101, to provide individual covers 102 for the optically active elements of each integrated circuit. If the integrated circuits are formed in a square or rectangular array, this can be achieved by making a first series of parallel cuts through the transparent wafer 101, then making a second series of parallel cuts through the transparent wafer, the second series of cuts being perpendicular to the first series of cuts. After making the cuts the unwanted parts of the transparent wafer 101 are removed.
  • the transparent wafer 101 may be provided with pre-etched or pre-sawn grooves or channels extending part way through the substrate 101, to assist in the sawing process.
  • the edges 103 of the individual covers 102 may be profiled. This can be achieved by use of a specially adapted saw in the cutting process or by suitable pre-etching or pre-formation of the transparent substrate 101.
  • the covers may be formed either before or after the cutting process so as to reduce the reflection of radiation from the cover 102, improve the transmission efficiency of radiation through the cover 102 or to enable the cover 102 to act as a lens.
  • wax 105 is introduced into the space between the two wafers 100, 101 so as to fill this space with the exception of those areas surrounding the optically active elements.
  • the wax 105 sets and then acts as protection for the integrated circuit array during the cutting process.
  • the wax 105 may be removed by any suitable method, thus facilitating testing of the integrated circuit using any suitable technique, including industry standard probe techniques, and connection of the integrated circuit to external circuitry via bond pads.
  • the individual integrated circuits may then be separated by making cuts along scribe lines 107 provided between the integrated circuits in the array. If the array is a square array this can be achieved by making a first series of parallel cuts through the silicon wafer 100, then making a second series of parallel cuts through the silicon wafer 100, the second series of cuts being perpendicular to the first series of cuts. If a thinner device is desired, the silicon wafer 100 may be back lapped to reduce its thickness as is illustrated by line 108 in figure 1.
  • the individual integrated circuit devices may then be packaged in a protective housing. This is achieved by mounting the integrated circuit 104 on a lead frame (not shown), making connections between the bond pads of the integrated circuit 104 and peripheral portions of the lead frame; inserting the covered integrated circuit 104 and lead frame into the cavity of a moulding tool and encapsulating the covered integrated circuit and lead frame in a suitable moulding compound in such a manner that the peripheral portions of the lead frame and the upper surface of the cover are exposed.
  • the moulding tool may be adapted to have a projection or pin in contact with the upper surface of the cover or with a gel blob applied to the upper surface of the cover. Additionally or alternatively, the Boschmann film in mould process may be used to ensure the surface of the cover remains free from encapsulant.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Solid State Image Pick-Up Elements (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)

Abstract

A transparent wafer (101), typically a glass wafer, is placed over a silicon wafer (100) having an integrated circuit with one or more optically active elements (106) provided thereon. The transparent wafer (101) is securely sealed to the silicon wafer (100) by a pattern of glass frit material (104) applied to one or both wafers (100, 101). The glass frit pattern (104) is screen printed on to the appropriate wafer (100, 101) and is arranged so as to surround the or each optically active element or elements (106) of each integrated circuit. The two wafers (100, 101) are aligned and brought together. The wafers (100, 101) are then raised in temperature to cause the glass frit material (105) to reflow and seal the wafers together. In this manner, the glass frit (105) seals the gap between the two wafers (100, 101).

Description

SEMICONDUCTOR PACKAGE WITH TRANSPARENT LID
The present invention relates to a method of manufacturing packaged integrated circuit devices and more particularly to a method of manufacturing packaged optical integrated circuit devices for use in radiation sensors, imaging systems, DVD systems, such as blue laser DVD systems and the like.
DVD readers operate by reflecting a narrow beam of light from the surface of a spinning DVD and detecting variations in the reflected light. The narrow beam of light is typically generated by or from an LED, VCSEL, or laser diode. The reflected light is detected by a light sensing means, typically a photodiode. The light sensing means and associated amplification means are typically implemented as a single integrated circuit. The integrated circuit is conventionally encapsulated in a protective package, said package having a passageway through which radiation may pass to the light sensing means, a glass lid being mounted in or over the passageway and retained in position by an epoxy adhesive. The glass lid provides protection for the light sensing means from the ingress of contaminants or from physical impacts.
The additional step of fitting a glass lid to the package can be expensive and may cause further problems for instance: the atmosphere trapped between the light sensing means and the lid may contain moisture or contaminants that may affect the performance or reliability of the assembled device; the glass lid may not be aligned parallel to the sensitive surface of the light sensing means which may affect the focussing of incident light reflected from the DVD surface; or in blue light DVD systems, conventional polymer adhesives can be affected by the blue light such that they turn opaque with time thus affecting transmission of light to the light sensing means.
It is therefore an object of the present invention to provide a method of packaging a integrated circuit sensor which overcomes or alleviates at least some of the above problems.
According to a first aspect of the present invention there is provided a method of manufacturing optical integrated circuit devices comprising the steps of: providing a first wafer, said first wafer incorporating an integrated circuit, said integrated circuit having at least one optically active element; providing a second wafer, said second wafer being transparent; and placing said second wafer over said first wafer, wherein a pattern of glass frit material is provided on either wafer, said pattern being arranged so as to surround said optically active element or elements when the second wafer is placed over the first wafer, said glass frit subsequently being reflowed to form a permanent seal between said first and second wafers. This thus provides an optical integrated circuit device wherein a transparent substrate provides protection for the optically active elements, the transparent substrate may additionally be readily mounted parallel to the surface of the optically active elements to minimise effects on the focussing of incident or emitted light.
Preferably, the method includes the further step of packaging said optical integrated circuit device. This may be achieved by mounting and electrically connecting the device to a suitable lead frame; inserting the device and lead frame into the cavity of a moulding tool; and encapsulating said device and lead frame in a suitable moulding compound, the moulding tool being adapted such that the second wafer is not completely encapsulated in the moulding compound thereby allowing radiation to pass between the optically active element and the exterior of the package.
Preferably, bond pads are provided on said first wafer by means of which electrical connections may be made between said integrated circuit and said lead frame. Most preferably, peripheral portions of the lead frame project from the package facilitating connection of the device to external circuitry.
Preferably, the steps of placing the second wafer over the first wafer and reflowing the glass frit take place either in a vacuum or in a controlled atmosphere such as a dry Nitrogen atmosphere. Preferably, the said first wafer is a standard CMOS wafer. Preferably, said second wafer is a glass wafer. Most preferably, said second wafer has substantially the same coefficient of thermal expansion as said first wafer. The method may further incorporate the step of backlapping the first wafer to reduce the thickness of the device. Preferably said glass frit material is applied to either of said wafers by screen printing. Preferably, if the glass frit is applied to the first wafer, the glass frit pattem is aligned with the optically active element or elements in the integrated circuit. Preferably, if the glass frit is applied to the second wafer, the second wafer is aligned with the first wafer when it is placed over the first wafer such that the glass frit pattern is aligned with the optically active element or elements in the integrated circuit. Preferably the glass frit material is reflowed by raising the temperature of the two wafers above the melting point of the glass frit material for a time interval such that the glass frit material is able to form a seal between the two wafers and around said optically active element or elements.
Preferably, said glass frit material is processed before being applied to remove any organic compounds. An example of one such suitable process is Organic Burn Out (OBO).
In embodiments wherein there is more than one optically active element said glass frit material may be applied such that it surrounds each optically active element individually or may be applied such that it surrounds two or more elements collectively. Said optically active elements may comprise light emitting means or light sensing means. Light emitting means may be operable to emit light at visible, infra red or ultraviolet wavelengths as desired. Similarly, said light sensing means may be operative to sense light of visible, infra red or ultra violet wavelengths as desired. In some preferred embodiments said light sensing means may comprise an array of individual light sensing elements.
Preferably cuts are made in said second wafer so as to separate an area from the rest of the wafer thereby forming a cover over the optically active elements. The areas of said second wafer not forming said cover may be removed. Preferably, this method incorporates the additional steps of introducing melted wax between said first and said second wafers so as to fill substantially the entire space between said first and second wafers except for the area occupied by said optically active elements, and allowing said wax to set before cutting said second wafer. The wax when set provides protection for said integrated circuit during the cutting process. Most preferably, said wax is removed after the cutting process is complete. Said second wafer may be adapted by pre-etching, pre-cutting, use of a specially adapted cutting tool or by any other suitable means such that the edges of said cover are profiled.
Preferably the integrated circuit additionally comprises bond pads, said bond pads being provided towards the periphery of said integrated circuit such that when portions of the second wafer are removed said bond pads are exposed, facilitating testing and connection to external circuitry.
Preferably said second wafer comprises filtering means to limit the incoming radiation to a desired wavelength band. Preferably said filtering means is in the form of a layer of filtering material deposited on one or both surfaces of said second wafer.
Preferably one or both surfaces of said second wafer are pre-etched to define a lens pattern to improve the effectiveness of the optical sensing elements. Preferably one or more surfaces of the said glass wafer are pre-etched to reduce the reflection of optical radiation and/or improve the transmission efficiency of the said second wafer for radiation.
Preferably, the integrated circuit is one of an array of like integrated circuits formed on said first wafer. Said integrated circuit array may be manufactured using conventional semiconductor processing techniques. The integrated circuit array can be an array of any type but is preferably a regular square or rectangular array. Preferably, individual devices are formed by applying glass frit to said first wafer so as to surround the optically active elements of each integrated circuit in the array, placing said second wafer over said first wafer, reflowing said glass frit and separating individual devices by cutting along cutting channels provided between the integrated circuits in the array.
According to a second aspect of the present invention there is provided an optical integrated circuit device manufactured in accordance with the method of the first aspect of the present invention.
The optical integrated circuit device according to the second aspect of the present invention may incorporate any of the features of the first aspect of the present invention as desired or appropriate.
In order that the invention is more clearly understood, it will now be described further herein, by way of example only and with reference to the following drawings in which:
Figure 1 is a cross section of an integrated circuit device according to the present invention; and
Figure 2 is a cross section of a packaged integrated circuit device according to the present invention.
Referring first to figure 2, an optical integrated circuit device comprises an integrated circuit formed on a silicon wafer 201 incorporating at least one optically active element or elements and a glass cap covering said optically active element or elements. The glass cap is sealed in position over the optically active element or elements by means of glass frit. The device is mounted on a lead frame 206 and connections are made between bond pads provided on the integrated circuit to peripheral portions of the lead frame. The device is encapsulated in a suitable mould compound in such a manner that the upper surface of the transparent cap is not encapsulated, thus allowing light to pass between the optically active element or elements and the exterior of the package.
Referring now to Figure 1 , optical integrated circuit devices are formed from an array of like integrated circuits provided on a silicon wafer 100. The array is typically a square or rectangular array. Each integrated circuit incorporates one or more optically active elements 106, which may be optical emitting elements or optical sensing elements. Typically such elements 106 are adapted to emit and/or sense light of visible wavelengths however, in some applications such elements may be adapted to additionally and/or alternatively emit and/or sense infra red and/or ultra violet wavelengths.
A transparent wafer 101, typically a glass wafer, is placed over the silicon wafer 100. The transparent wafer 101 is securely sealed to the silicon wafer 100 by a pattern of glass frit material 104 applied to either or to both wafers 100, 101. The glass frit pattern 104 is screen printed on to the appropriate wafer 100, 101 and is arranged so as to surround the or each optically active element or elements 106 of each integrated circuit if provided on said silicon wafer 100 or so that it may be aligned to surround the or each optically active element or elements 106 of each integrated circuit if it is provided on said transparent wafer 101. If the integrated circuits have more than one optically active element 106, each optically active element 106 may be individually surrounded by glass frit material 104 or two or more optically active elements 106 may be surrounded collectively by glass frit material 104. Either before or after application to the wafers, the glass frit material may be raised in temperature to remove organic compounds contained therein.
The two wafers 100, 101 are aligned and brought together in a dry Nitrogen atmosphere. The wafers 100, 101 are then raised in temperature to cause the glass frit material 105 to reflow and seal the wafers together. In this manner, the glass frit 105 seals the gap between the two wafers 100, 101 such that the optically active elements 106 of each integrated circuit are sealed in a dry Nitrogen atmosphere. Alternatively, these steps could be carried out in a vacuum.
Once said wafers are joined, a series of cuts are made through said transparent wafer 101, to provide individual covers 102 for the optically active elements of each integrated circuit. If the integrated circuits are formed in a square or rectangular array, this can be achieved by making a first series of parallel cuts through the transparent wafer 101, then making a second series of parallel cuts through the transparent wafer, the second series of cuts being perpendicular to the first series of cuts. After making the cuts the unwanted parts of the transparent wafer 101 are removed.
In some embodiments of the invention, the transparent wafer 101 may be provided with pre-etched or pre-sawn grooves or channels extending part way through the substrate 101, to assist in the sawing process. The edges 103 of the individual covers 102 may be profiled. This can be achieved by use of a specially adapted saw in the cutting process or by suitable pre-etching or pre-formation of the transparent substrate 101. In further embodiments, the covers may be formed either before or after the cutting process so as to reduce the reflection of radiation from the cover 102, improve the transmission efficiency of radiation through the cover 102 or to enable the cover 102 to act as a lens.
In order to protect the integrated circuits whilst the cuts are made, melted wax 105 is introduced into the space between the two wafers 100, 101 so as to fill this space with the exception of those areas surrounding the optically active elements. The wax 105 sets and then acts as protection for the integrated circuit array during the cutting process. After the cutting process the wax 105 may be removed by any suitable method, thus facilitating testing of the integrated circuit using any suitable technique, including industry standard probe techniques, and connection of the integrated circuit to external circuitry via bond pads.
The individual integrated circuits may then be separated by making cuts along scribe lines 107 provided between the integrated circuits in the array. If the array is a square array this can be achieved by making a first series of parallel cuts through the silicon wafer 100, then making a second series of parallel cuts through the silicon wafer 100, the second series of cuts being perpendicular to the first series of cuts. If a thinner device is desired, the silicon wafer 100 may be back lapped to reduce its thickness as is illustrated by line 108 in figure 1.
The individual integrated circuit devices may then be packaged in a protective housing. This is achieved by mounting the integrated circuit 104 on a lead frame (not shown), making connections between the bond pads of the integrated circuit 104 and peripheral portions of the lead frame; inserting the covered integrated circuit 104 and lead frame into the cavity of a moulding tool and encapsulating the covered integrated circuit and lead frame in a suitable moulding compound in such a manner that the peripheral portions of the lead frame and the upper surface of the cover are exposed. The moulding tool may be adapted to have a projection or pin in contact with the upper surface of the cover or with a gel blob applied to the upper surface of the cover. Additionally or alternatively, the Boschmann film in mould process may be used to ensure the surface of the cover remains free from encapsulant.
It is of course to be understood that the invention is not to be limited to the details of the above embodiment which is described by way of example only.

Claims

1. A method of manufacturing optical integrated circuit devices comprising the steps of: providing a first wafer, said first wafer incorporating an integrated circuit, said integrated circuit having at least one optically active element; providing a second wafer, said second wafer being transparent; and placing said second wafer over said first wafer, wherein a pattern of glass frit material is provided on either wafer, said pattern being arranged so as to surround said optically active element or elements when the second wafer is placed over the first wafer, said glass frit subsequently being reflowed to form a permanent seal between said first and second wafers.
2. A method as claimed in claim 1 wherein the steps of placing the second wafer over the first wafer and reflowing the glass frit take place in a vacuum.
3. A method as claimed in claim 1 wherein the steps of placing the second wafer over the first wafer and reflowing the glass frit take place in a dry Nitrogen atmosphere.
4. A method as claimed in any preceding claim wherein the said first wafer is a standard CMOS wafer.
5. A method as claimed in any preceding claim wherein said second wafer is a glass wafer.
6. A method as claimed in any preceding claim wherein said second wafer has substantially the same coefficient of thermal expansion as said first wafer.
7. A method as claimed in any preceding claim wherein the method further incorporates the step of backlapping the first wafer to reduce the thickness of the device.
8. A method as claimed in any preceding claim wherein said glass frit material is applied to either of said wafers by screen printing.
9. A method as claimed in claim 8 wherein the glass frit is applied to the first wafer.
10. A method as claimed in claim 9 wherein the glass frit pattern is aligned with the optically active element or elements in the integrated circuit.
11. A method as claimed in claim 8 wherein the glass frit is applied to the second wafer.
12. A method as claimed in claim 11 wherein the second wafer is aligned with the first wafer when it is placed over the first wafer such that the glass frit pattern is aligned with the optically active element or elements in the integrated circuit.
13. A method as claimed in any preceding claim wherein the glass frit material is reflowed by raising the temperature of the two wafers above the melting point of the glass frit material for a time interval such that the glass frit material is able to form a seal between the two wafers and around said optically active element or elements.
14. A method as claimed in any preceding claim wherein said glass frit material is processed before application to remove any organic compounds.
15. A method as claimed in claim 14 wherein the process used is Organic Bum Out (OBO).
16. A method as claimed in any preceding claim wherein there is more than one optically active element and said glass frit material is applied such that it surrounds each optically active element individually.
17. A method as claimed in any preceding claim wherein there is more than one optically active element and said glass frit material is applied such that it surrounds two or more elements collectively.
18. A method as claimed in any preceding claim wherein said optically active elements comprise light emitting means.
19. A method as claimed in any preceding claim wherein said optically active elements comprise light sensing means.
20. A method as claimed in claims 18 or claim 19 wherein said light emitting means are operable to emit light at visible, infra red or ultraviolet wavelengths
21. A method as claimed in claim 19 or claim 20 wherein said light sensing means are operative to sense light of visible, infra red or ultraviolet wavelengths.
22. A method as claimed in any one of claims 19 to 21 wherein said light sensing means may comprise an array of individual light sensing elements.
23. A method as claimed in any preceding claim wherein cuts are made in said second wafer so as to separate an area from the rest of the wafer thereby forming a cover over the optically active elements.
24. A method as claimed in claim 23 wherein the areas of said second wafer not forming said cover are removed.
25. A method as claimed in claim 23 or 24 wherein this method incorporates the additional steps of introducing melted wax between said first and said second wafers so as to fill substantially the entire space between said first and second wafers except for the area occupied by said optically active elements, and allowing said wax to set before cutting said second wafer.
26. A method as claimed in claim 25 wherein said wax is removed after the cutting process is complete.
27. A method as claimed in any one of claims 23 to 26 wherein said second wafer is adapted such that the edges of said cover are profiled.
28. A method as claimed in claim 27 wherein said second wafer is adapted by pre- etching, pre-cutting, use of a specially adapted cutting tool.
29. A method as claimed in any preceding claim wherein said second wafer comprises filtering means to limit the incoming radiation to a desired wavelength band.
30. A method as claimed in claim 29 wherein said filtering means is in the form of a layer of filtering material deposited on one or both surfaces of said second wafer.
31. A method as claimed in any preceding claim wherein one or both surfaces of said second wafer are pre-etched to define a lens pattern to improve the effectiveness of the optical sensing elements.
32. A method as claimed in any preceding claim wherein one or more surfaces of the said glass wafer are pre-etched to reduce the reflection of optical radiation and/or improve the transmission efficiency of the said second wafer for radiation.
33. A method as claimed in any preceding claim wherein the method further comprises packaging the optical integrated circuit device.
34. A method as claimed in claim 33 wherein this is achieved by mounting and electrically connecting the device to a suitable lead frame; inserting the device and lead frame into the cavity of a moulding tool; and encapsulating said device and lead frame in a suitable moulding compound, the moulding tool being adapted such that the second wafer is not completely encapsulated in the moulding compound allowing radiation to pass between the optically active element and the exterior of the package.
35. A method as claimed in claim 34 wherein peripheral portions of the lead frame project from the package.
36. A method as claimed in any preceding claim wherein bond pads are provided on said first wafer.
37. A method as claimed in claim 36 wherein said bond pads are provided towards the periphery of said integrated circuit.
38. A method as claimed in any preceding claim wherein the integrated circuit is one of an array of like integrated circuits formed on said first wafer.
39. A method as claimed in claim 38 wherein individual devices are formed by applying glass frit to said first wafer so as to surround the optically active elements of each integrated circuit in the array, placing said second wafer over said first wafer, reflowing said glass frit and separating individual devices by cutting along cutting channels provided between the integrated circuits in the array.
40. An optical integrated circuit device manufactured in accordance with the method of any preceding claim.
PCT/IB2005/001590 2004-06-04 2005-06-06 Semiconductor package with transparent lid WO2005119756A1 (en)

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