WO2008081987A1 - Joining method and joining members - Google Patents

Joining method and joining members Download PDF

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Publication number
WO2008081987A1
WO2008081987A1 PCT/JP2007/075401 JP2007075401W WO2008081987A1 WO 2008081987 A1 WO2008081987 A1 WO 2008081987A1 JP 2007075401 W JP2007075401 W JP 2007075401W WO 2008081987 A1 WO2008081987 A1 WO 2008081987A1
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WO
WIPO (PCT)
Prior art keywords
sheet member
joining
optical functional
functional film
film
Prior art date
Application number
PCT/JP2007/075401
Other languages
French (fr)
Inventor
Shouji Nishida
Takayuki Fujiwara
Norihito Nosaka
Original Assignee
Fujifilm Corporation
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
Priority claimed from JP2006355829A external-priority patent/JP2008162861A/en
Application filed by Fujifilm Corporation filed Critical Fujifilm Corporation
Publication of WO2008081987A1 publication Critical patent/WO2008081987A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C27/00—Joining pieces of glass to pieces of other inorganic material; Joining glass to glass other than by fusing
    • C03C27/02—Joining pieces of glass to pieces of other inorganic material; Joining glass to glass other than by fusing by fusing glass directly to metal
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/20—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy
    • H01L21/2003—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy characterised by the substrate
    • H01L21/2007—Bonding of semiconductor wafers to insulating substrates or to semiconducting substrates using an intermediate insulating layer

Definitions

  • the present invention relates to a method of joining sheet members formed of different materials in the production process of imaging devices and members to be joined.
  • a junction step is carried out for joining a sheet member formed of, for example, silicon (Si) to a sheet member formed of, for example, glass.
  • a solid-state imaging apparatus including a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) used in a digital camera or a cellular phone is produced such that a solid-state imaging element wafer being a sheet member on which the light receiving portions of a large number of solid-state imaging elements are formed is joined to a light transmissive substrate (glass wafer) being a sheet member with spacers inbetween which are formed correspondingly with the position surrounding each light receiving portion to downsize and mass produce the solid-state imaging apparatus, thereafter both wafers pass through processes such as the formation of through wirings, dicing and others (refer to, for example, Patent Documents 1 or 2).
  • CMOS complementary metal oxide semiconductor
  • the anodic bonding is carried out using a junction apparatus 1 with components such as a first sheet member 10 as a first member, a second sheet member 11 as a second member, a table 12 on which the first sheet member 10 is placed and a high voltage power supply 13 connected to the table 12 and the second sheet member 11.
  • the first and the second sheet member 10 and 11 brought into contact with each other are heated by a heating apparatus (not shown) at a high temperature of 400 0 C to 500 0 C and subjected to a direct-current voltage of about 500 V to 1000 V by the high voltage power supply 13 with the second sheet member 11 as a cathode.
  • Patent Document 1 Japanese Patent Laid-Open No. 2001 -351997
  • Patent Document 2 Japanese Patent Laid-Open No. 2004-88082
  • Patent Document 3 Japanese Patent Laid-Open No. 2001-64041
  • Patent Document 4 Japanese Patent Laid-Open No. 2005-187321
  • Patent Document 5 Japanese Patent Laid-Open No. 2006-73780
  • Patent Document 6 Japanese Patent Laid-Open No. 2006-248895
  • an optical functional film such as a MgF 2 , SiO, SiO 2 film for preventing reflection (referred to as “reflection preventing film” or “AR film”) is formed on the surface of the glass wafer.
  • a transparent glass wafer such as, for example, "Pyrex (registered trademark) glass" which is comparable in thermal expansion coefficient to Si is used as the glass wafer.
  • the glass wafer is different in material from the optical functional film and also different in thermal expansion coefficient from the film, so that the glass wafer is warped by heating in the junction process. This results in a defect in junction between the solid-state imaging element wafer and the glass wafer and poses a problem in the junction process for the solid-state imaging apparatus.
  • the surfaces of the members to be joined are desirably mirror-finished to the extent that surface roughness is 1 nm or less.
  • the optical functional film is occasionally or often 10 nm or more in surface roughness.
  • the optical functional film occasionally contains water-repellent fluoride compound and has fine defects because it significantly changes in film density depending upon conditions for forming the film, and therefore the optical functional film is occasionally not suited for a joining method such as the anodic bonding.
  • warp is reduced by, for example, providing a temperature gradient in the thickness direction of the joining member or sandwiching one member between two members which have the same thermal expansion coefficient.
  • the present invention has been made in view of the above problems, and has for its object to provide a joining method and a joining member which reduce warp produced at the time of joining sheet members different in thermal expansion coefficient by heating, prevents the deterioration of the joining member resulting from the warp, maintains the performances of the optical functional film and satisfactorily joins the sheet members with high air tightness.
  • the joining method in a joining method by which a process involving heating is carried out when a first and a second sheet member formed of Si, SiO 2 or glass and of a different material from each other are joined together, is characterized by comprising joining the first and the second sheet member together by adjusting any one or more of conditions of a ratio of thickness between the first and the second sheet member, a temperature-rise rate at the time of junction and a difference in thermal expansion coefficient between the first and the second sheet member.
  • any one or more of the conditions is adjusted of a ratio of thickness between the first and the second sheet member, a temperature-rise rate at the time of junction and a difference in thermal expansion coefficient between the first and the second sheet member.
  • Glass which is lower in thermal expansion coefficient such as "Pyrex (registered trademark) glass," for example, is more preferably used as the glass for forming any of the first and the second sheet member, but not limited to that, it is preferable to use a glass which is about twice or less as small as the other sheet material in thermal expansion coefficient.
  • a wafer on which a semiconductor element for an imaging device such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) is formed may be used as the first and the second sheet member.
  • each sheet member is adjusted by a value determined by a ratio of thickness between the first and the second sheet member and a ratio of the moduli of longitudinal elasticity between the first and the second sheet member so as to minimize the radius of curvature at the time of cooling the heated joining members.
  • a third aspect of the present invention is characterized in that, in the invention according to the first aspect, the temperature-rise rate is 10 0 C or less per minute. According to the third aspect, heating the joining members at a temperature-rise rate slower than a normal temperature-rise rate starts junction in incremental steps at a temperature lower than a temperature at which junction is carried out, which does not cause each sheet member to expand beyond necessity to reduce warp and junction defects when the joining members return to normal temperature.
  • a fourth aspect of the present invention is characterized in that, in the invention according to the first aspect, the difference in thermal expansion coefficient is adjusted by forming a film having a thermal expansion coefficient between the thermal expansion coefficients of the first and the second sheet member on a junction surface where the first and the second sheet member are joined together between the first and the second sheet member.
  • the film having a thermal expansion coefficient between the thermal expansion coefficients of the first and the second sheet member is formed on the junction surface where the first and the second sheet member are joined to each other.
  • a fifth aspect of the present invention is characterized in that, in the invention according to the first aspect, the difference in thermal expansion coefficient is adjusted by containing a component of any one of the first and the second sheet member into the other sheet member in the vicinity of the junction surface.
  • any one of the first and the second sheet member forms a layer containing a component of the other sheet member in the thickness direction with respect to the junction surface.
  • the component in the layer containing the component of the other sheet member gradually lessens as it gets far from the junction surface.
  • a sixth aspect of the present invention is characterized in that, in a joining method by which a first sheet member on which solid-state imaging elements are formed is joined to a second sheet member all over or up to the vicinity of the outer periphery of one side of which, or all over or up to the vicinity of the outer periphery of both sides of which an optical functional film being an antireflection film made of oxide film, nitride film, or fluoride film for preventing reflection is formed with a gap provided between the first and the second sheet member through a spacer, the joining method is characterized by comprising subjecting the optical functional film on the junction surface where the first sheet member is joined to the second sheet member to any one or more of processing: change of surface properties including surface roughness, constituent element and density value; removal; activation by plasma; smoothing by
  • a solid-state imaging element wafer as the first sheet member on which solid-state imaging elements are formed is joined to a glass wafer as the second sheet member all over or up to the vicinity of the outer periphery of one side of which, or all over or up to the vicinity of the outer periphery of both sides of which an optical functional film being an antireflection film made of oxide film, nitride film, or fluoride film for preventing reflection is formed, with a gap provided between the first and the second sheet member through a spacer.
  • the members are joined by a direct joining method such as an anodic bonding or a surface active joining method. At the time of junction, the optical functional film is processed to be adapted for junction.
  • Any one or more of processing: change of surface properties including surface roughness, constituent element and density value; removal; activation by plasma; smoothing by plasma; or division by forming a plurality of grooves are provided only for the optical functional film formed on the junction surface where the solid-state imaging element wafer is joined to the glass wafer.
  • the optical functional film for part of which the processing is not provided is masked to be left on the glass wafer.
  • the surface properties including surface roughness, constituent element and density value of the optical functional film are changed to conditions adapted for junction by changing conditions for polish and film-formation.
  • removing the optical functional film formed on the junction surface where the solid-state imaging element wafer is joined to the glass wafer by a method such as etching joins the solid-state imaging element wafer to the glass wafer without sandwiching the optical functional film.
  • the optical functional film is activated by plasma, thereby the solid-state imaging element wafer is satisfactorily joined to the glass wafer with high air tightness by surface activation junction.
  • the optical functional film is activated and smoothened by plasma, which does not leave polishing residues unlike smoothing by polishing to satisfactorily join the solid-state imaging element wafer to the glass wafer with high air tightness.
  • a plurality of grooves are formed in the optical functional film in the lengthwise and crosswise directions by a method such as dicing or etching to divide the optical functional film, reducing warp caused by the difference in thermal expansion coefficient between the optical functional film and the glass wafer at the time of heating at the junction process.
  • a seventh aspect of the present invention is characterized in that, the optical functional film is formed on the second sheet member with a thickness which is greater than a desired thickness of the optical functional film required after joining the first sheet member to the second sheet member, and after that, the first sheet member is joined to the second sheet member. According to the seventh aspect, smoothing enables optical characteristics to be maintained even if the thickness is changed when surface properties of the optical functional film such as roughness or contained elements are controlled to change the optical characteristic.
  • An eighth aspect of the present invention is characterized in that, in a joining method by which a first sheet member on which solid-state imaging elements are formed is joined to a second sheet member on one or both sides of which an optical functional film for preventing reflection is formed with a gap provided between the first and the second sheet member through a spacer, the joining method is characterized by comprising joining the first sheet member to the second sheet member on which the spacer is formed and then the optical functional film is formed.
  • the solid-state imaging element wafer as the first sheet member is joined to the glass wafer as the second sheet member on which the optical functional film is formed, between which a gap is provided through a spacer.
  • a member for the spacer is first joined to the glass wafer to form the spacer by a method such as a dry etching method and then the optical functional film is formed on the glass wafer, thereafter, the solid-state imaging element wafer is joined to the glass wafer. This satisfactorily joins the solid-state imaging element wafer to the glass wafer with high air tightness without impairing the performance of the optical functional film.
  • the joining method and the joining member of the present invention when the sheet members different in thermal temperature coefficient from each other are joined by heating, influence due to the difference in thermal temperature coefficient is reduced to reduce warp produced, preventing the deterioration of the joining members resulted from the warp.
  • the optical functional film is processed to be suited for junction without the degradation of the performance thereof, which satisfactorily joins the solid-state imaging element wafer to the glass wafer with high air tightness.
  • Figure 1 is a schematic diagram of junction process in a junction apparatus according to the present invention.
  • Figure 2 is a perspective view of a solid-state imaging apparatus according to the present invention.
  • Figure 3 is a cross section illustrating warped joining members
  • Figures 4A, 4A' to 4D, 4D' are cross sections illustrating difference in the junction at the time of changing a temperature-rise rate
  • Figures 5A, 5A' to 5C, 5C are cross sections illustrating joining members having a film inbetween and normal joining members;
  • Figures 6A, 6A' to 6C, 6C are cross sections illustrating joining members one of which contains the component of the other member and a normal joining member
  • Figures 7A, 7A' to 1C, 1C are cross sections of the joining members in which the surface properties of the optical functional film are changed;
  • Figures 8A, 8A' to 8C, 8C are cross sections of joining members to which the optical functional film activated by plasma is joined;
  • Figures 9A, 9A' to 9D, 9D' are cross sections of joining members joined together with the optical functional film removed;
  • Figures 1OA, 1OA' to 1OC, 1OC' are cross sections illustrating a joining method by which the optical functional films are formed on both sides of the member 11;
  • Figure 11 is a schematic diagram illustrating a junction apparatus for anodic bonding.
  • Figure 1 is a schematic diagram illustrating the outline of the joining method according to the present invention and of a junction process in a junction apparatus for producing the joining members according to the present invention.
  • a first and a second member 10 and 11 made of Si, SiO 2 or glass and of a different material from each other are placed in a low pressure chamber, subjected to oxygen plasma processing and then to nitrogen plasma processing.
  • the first and the second sheet member 10 and 11 are returned to the atmosphere.
  • the entire junction surfaces of both members are brought into close contact with each other to temporarily join them.
  • the first and the second sheet member 10 and 11 are pressurized and heated by a heating apparatus (not shown) to a junction temperature (400°C to 500 0 C, for example).
  • a high direct- current (DC) voltage of, for example, 500 V to 1000 V is applied between the first and the second sheet member 10 and 11 with the second sheet member 11 as a cathode by a high voltage power supply 13.
  • first and the second sheet member 10 and 11 are mirror-finished and are 100 ⁇ m in flatness and 1 nm or less in roughness.
  • the joining method according to the present invention and the junction apparatus for producing the joining members according to the present invention can be applied to any known junction process involving a heating process as well as the above junction process.
  • FIG. 2 is a perspective view illustrating the external shape of a solid-state imaging apparatus according to the embodiment of the present invention.
  • a solid-state imaging apparatus 1 includes a solid-state imaging element chip 2 on which solid-state imaging elements 3 are provided, a spacer 5 which is fixed to the solid-state imaging element chip 2 and surrounds the solid-state imaging elements 3 and a cover glass 4 which is fixed over the spacer 5 and seals the solid-state imaging elements 3.
  • the solid-state imaging element chip 2 includes a rectangular chip substrate formed by cutting the sheet member on which the solid-state imaging elements 3 are formed by a dicing device, the solid-state imaging elements 3 formed on the chip substrate and a plurality of pads (electrodes) 6 which is arranged outside the solid-state imaging elements 3 and used for external wiring.
  • the chip substrate uses, for example, silicon single crystal and is approximately 300 ⁇ m in thickness.
  • the cover glass 4 is formed by cutting the sheet member formed of glass by dicing.
  • the cover glass 4 uses a transparent glass, for example, Pyrex (registered trademark) glass which is comparable in thermal expansion coefficient to silicon and is approximately 500 ⁇ m in thickness, for example.
  • An optical functional film made of the AR film such as oxide film, nitride film, MgF 2 being magnesium fluoride film, SiO or SiO 2 film for preventing reflection is formed on the surface of the cover glass 4.
  • the spacer 5 uses, for example, polycrystalline silicon because the spacer 5 is desirably an inorganic material and comparable in properties such as thermal expansion coefficient to the chip substrate and the cover glass 4.
  • the frame-shaped spacer 5 is approximately 200 ⁇ m wide and 100 ⁇ m thick in cross section, for example.
  • the spacer 5 is joined to the solid-state imaging element chip 2 and the cover glass 4 by a direct joining method such as an anodic bonding or a surface active joining method.
  • Figure 3 is a cross section illustrating warped joining members.
  • the first and the second sheet member 10 and 11 are heated to a junction temperature at the time of junction and warped at radius of curvature R shown in Figure 3 due to a difference in thermal expansion coefficient between the first and the second sheet member 10 and 11 when they are cooled, after joined, to a temperature before they are joined.
  • the thickness ratio "n" is preferably n ⁇ 0.8 or 2.5 ⁇ n, and more preferably n ⁇ 0.48 or 5 ⁇ n. It is still more preferable that n ⁇ 0.2 or 15 ⁇ n at which the amount of warp ⁇ is 300 ⁇ m or less.
  • the value "r" is preferably larger than 5.3, more preferably larger than 30 at which the amount of warp ⁇ is 300 ⁇ m or less and still more preferably larger than 100 at which the amount of warp ⁇ is 100 ⁇ m.
  • Figures 4A, 4A' to 4D, 4D' are cross sections illustrating difference in the junction at the time of changing a temperature-rise rate.
  • the first and the second sheet member 10 and 11 are pressurized by pressing means (not shown) with their junction surfaces brought into contact with each other.
  • the first and the second sheet member 10 and 11 ( Figures 4 A, 4C, and 4D) illustrated on the left side are rapidly heated in an environment set at normal temperature to, for example, 100°C to 50O 0 C, and the first and the second sheet member 10 and 11 ( Figures 4A', 4B ⁇ 4C, and 4D') illustrated on the right side are heated slower than the former members.
  • first and the second sheet member 10 and 11 expand as the temperature rises.
  • a partial junction starts between the first and the second sheet member 10 and 11 which are heated at a slower temperature-rise rate, at a temperature lower than an apparent junction temperature (for example, 400 0 C to 500°C) which the first and the second sheet member 10 and 11 are caused to ultimately reach, starting forming bonds 14 which are portions where the first sheet member 10 is joined to the second sheet member 11 therein.
  • an apparent junction temperature for example, 400 0 C to 500°C
  • the first and the second sheet member 10 and 11 which are heated at a normal temperature-rise rate will form the bonds 14 at a temperature higher than the members heated at a slower temperature-rise rate because the temperature rise is sharp.
  • the first and the second sheet member 10 heated at a faster and a slower temperature-rise rate are continued to be heated in this condition to the apparent junction temperature which the first and the second sheet member 10 and 11 are caused to ultimately reach, as illustrated in Figure 4C ⁇ the bonds 14 formed in the members heated at a slower temperature-rise rate tilt toward the direction to which the members are extended by expansion.
  • first and the second sheet member 10 and 11 heated at a faster temperature-rise rate form the bonds 14 perpendicularly with respect to the first and the second sheet member 10 and 11 because the bonds 14 are formed with the first and the second sheet member 10 and 11 sufficiently expanded.
  • the temperature-rise rate is preferably 10 0 C or less per minute and more preferably 5°C or less per minute.
  • Figures 5 A, 5A' to 5C, 5C are cross sections illustrating joining members having a film inbetween and normal joining members.
  • first and the second sheet member 10 and 11 are made of glass material such as, for example, Si and SiO 2 respectively, a layer made of, for example, SiO 2 , B 2 O 3 , Al 2 O 3 and Na 2 O of which thermal expansion coefficient is controlled by the component ratio is formed, as the intermediate layer, on any one of the junction surfaces of the first and the second sheet member 10 and 11.
  • the first and the second sheet member 10 and 11 between which the intermediate film 15 is formed are heated to the junction temperature suppress the difference in the amount of expansion caused by the difference in thermal expansion coefficient between the first and the second sheet member 10 and 11 when the joining members are heated.
  • Figures 6A, 6A' to 6C, 6C are cross sections illustrating joining members one of which contains the component of the other member and a normal junction portion.
  • the component of the other member is formed on any one ( Figure 6A') of the first and the second sheet member 10 and 11 which are brought into close contact with each other and pressed by a pressing means (not shown).
  • a pressing means not shown.
  • the containing layer 16 there exist components with a gradient such that the containing amount of the component of the other member reduces as it gets far from the junction surface.
  • the component of the second sheet member 11 shall be contained in the first sheet member 10.
  • the component of the second sheet member 11 is contained in the containing layer 16, so that the containing layer 16 is comparable to the second sheet member 11 in thermal expansion coefficient, which suppresses the difference in the amount of expansion caused by the difference in thermal expansion coefficient between the first and the second sheet member 10 and 11. This makes the members unsusceptible to influences from the difference in thermal expansion coefficient between the joining members to reduce warp at the time of heating.
  • Figures 7A, 7A' to 7C, 1C are cross sections of the joining members in which the surface properties of the optical functional film are changed.
  • an optical functional film 17 made of the AR film such as MgF 2 , SiO or SiO 2 film is formed on one surface of the second sheet member 11 as a glass wafer which becomes a cover glass 4 by cutting the glass wafer by a dicing device.
  • the optical functional film 12 is desirably formed all over the surface of the second sheet member 11 or up to the vicinity of the outer periphery thereof (for example, up to a position of 0.2 mm, more desirably, 0.1 mm inward from the outer periphery).
  • a spacer 5 is joined to the second sheet member 11 on which the optical functional film 17 is formed, as illustrated in Figures 7B and 7B' .
  • the spacer 5 is so formed beforehand as to surround a plurality of solid-state imaging elements 3 formed on the first sheet member 10 as a solid-state imaging element wafer which becomes a solid-state imaging element chip 2 by cutting the solid-state imaging element wafer into pieces by dicing.
  • the spacer 5 is joined to the second sheet member 11 by a direct joining method such as an anodic bonding. Smoothing the optical functional film 17 by plasma etching changes a surface roughness Rrms from 10 nm or more in normal state to Rrms ⁇ 2 nm.
  • the surface properties of the optical functional film 17 may be changed not only by plasma etching but, for example, polishing, reflow, ion injection, wet etching or annealing method, whereby the surface roughness, constituent element and density value of the optical functional film 17 may be changed.
  • the surface properties may be changed while or after the optical functional film 17 is formed.
  • the spacers 5 are joined to the processed portions 18, which does not affect light incident on the solid-state imaging elements 3 not to impair the function of the optical functional film 17 at the portion on which light is incident, thereby the first sheet member 10 is satisfactorily joined to the second sheet member 11 with high air tightness.
  • the first and the second sheet member 10 and 11 joined together are cut by the dicing device to be divided into individual solid-state imaging apparatuses.
  • Figures 8A, 8A' to 8C, 8C are cross sections of joining members to which the optical functional film activated by plasma is joined.
  • the optical functional film 17 made of an AR film such as a MgF 2 , SiO, SiO 2 film is formed on one face of the second sheet member 11.
  • the optical functional film 12 is desirably formed all over the surface of the second sheet member 11 or up to the vicinity of the outer periphery thereof (for example, up to a position of 0.2 mm, more desirably, 0.1 mm inward from the outer periphery of the second sheet member 11).
  • the spacer 5 is formed on the second sheet member 11 on which the optical functional film 17 is formed. The spacer 5 is so formed in advance as to enclose a plurality of the solid-state imaging elements 3 formed on the first sheet member 10.
  • the spacer 5 is joined to the second sheet member 11 by a surface activation joining method by which the surface of the optical functional film 17 is activated and smoothed by a method such as plasma radiation.
  • a surface activation joining method by which the surface of the optical functional film 17 is activated and smoothed by a method such as plasma radiation.
  • the surface of the optical functional film 17 is masked except the surface where the first and the second sheet member 10 and 11 are joined together through the spacer 5.
  • the optical functional film 17 only on the junction surface is activated and smoothed.
  • the optical functional film 17 such as the prevention of reflection
  • the surface activation such as plasma radiation
  • only the portion to which the spacer 5 is joined is activated and smoothed, and only an activated portion 19 is deteriorated in characteristics.
  • the spacer 5 is joined to the activated portion 19, which does not affect light incident on the solid-state imaging element 3 not to impair the function of the optical functional film 17 at the portion on which light is incident, thereby the first sheet member 10 is satisfactorily joined to the second sheet member 11 with high air tightness.
  • the first and the second sheet member 10 and 11 joined together are cut by the dicing device to be divided into individual solid-state imaging apparatuses.
  • Figure 9A, 9A' to 9C, 9C are cross sections of joining members joined together with the optical functional film removed.
  • the optical functional film 17 made of the AR film such as MgF 2 , SiO or SiO 2 film is formed on one face of the second sheet member 11.
  • the optical functional film 12 is desirably formed all over the surface of the second sheet member 11 or up to the vicinity of the outer periphery thereof (for example, up to a position of 0.2 mm, more desirably, 0.1 mm inward from the outer periphery of the second sheet member 11).
  • the spacer 5 is formed on the second sheet member 11 on which the optical functional film 17 is formed.
  • the spacer 5 is so formed in advance as to enclose a plurality of the solid-state imaging elements 3 formed on the first sheet member 10.
  • the optical functional film 17 on the surface where the first and the second joined sheet member 10 and 11 are joined together through the spacer 5 is removed by etching or dicing to directly join the sheet member 11 to the spacer 5 as illustrated in Figure 9C.
  • the spacer 5 is joined to the sheet member 11 by a direct joining method such as an anodic joining method or a surface activation joining method.
  • the spacer 5 is joined to the second sheet member 11 not through the optical functional film 17, so that they are satisfactorily joined together with high air tightness.
  • the spacer 5 is joined to the second sheet member 11 by a direct joining method
  • a member used for the spacer 5 joined in advance to the second sheet member 11 is processed by a method such as dry etching to form the spacer 5 on the second sheet member 11 on the surface of which the optical functional film 17 is not formed.
  • the optical functional film 17 may be formed on the second sheet member 11 on which the spacer 5 is not formed.
  • first sheet member 10 is satisfactorily joined to the second joined sheet member 11 with high air tightness without deteriorating the performance of the optical functional film 17.
  • the optical functional film 17 when the optical functional film 17 is removed by a method such as etching or dicing, a plurality of grooves are formed in the lengthwise and crosswise directions in the optical functional film 17 which are not removed to be divided into plural pieces. This reduces warp caused by difference in thermal expansion coefficient between the optical functional film 17 and the second sheet member 11 at the time of heating for junction, enabling the first and the second joined sheet member 10 and 11 to be satisfactorily joined to each other with high air tightness.
  • optical functional film 17 is formed only on the one side of the second sheet member 11, the present invention is not limited to that, but is also suitably embodied if the optical functional film 17 is formed on both sides of the second sheet member 11 as illustrated in Figure 1OA' .
  • the thickness of the optical functional film 17 formed on the second sheet member 11 in the present embodiment is 100 nm or more and 500 nm or less, for example, which is a normally required thickness, the present invention is not limited to this thickness, but the thickness may be greater than the thickness of the optical functional film 17 which is required after the first sheet member 10 has been joined to the second sheet member 11
  • the thickness may be greater than the normally required thickness by 50 nm, desirably greater than that by 100 nm).
  • the table lists results of junction tests on the joining methods according to the present invention. It was examined how thickness ratio, temperature gradient, junction property and amount of warp change with the thermal expansion coefficient ratio fixed (Test Nos. 1 to 5).
  • the joining method and the joining member of the present invention when the sheet members different in thermal temperature coefficient are heated to be joined together and any one or more of thickness ratio, temperature-rise rate at the time of junction and difference in thermal temperature coefficient is adjusted, influence due to the difference in thermal temperature coefficient is reduced to reduce warp, preventing the joining member from being deteriorated by warp.
  • the optical functional film is processed to be suited for junction without degrading the performance thereof, thereby the solid-state imaging element wafer is satisfactorily joined to the glass wafer with high air tightness.

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Abstract

An aspect of the present invention provides a joining method by which a process involving heating is carried out when a first and a second sheet member formed of Si, SiO2 or glass and of a different material from each other are joined together, the joining method characterized by comprising: joining the first and the second sheet member together by adjusting any one or more of the conditions of a ratio of thickness between the first and the second sheet member, a temperature-rise rate at the time of junction and a difference in thermal expansion coefficient between the first and the second sheet member.

Description

DESCRIPTION
JOINING METHOD AND JOINING MEMBERS
Technical Field
The present invention relates to a method of joining sheet members formed of different materials in the production process of imaging devices and members to be joined.
Background Art In the production process of imaging devices, a junction step is carried out for joining a sheet member formed of, for example, silicon (Si) to a sheet member formed of, for example, glass.
A solid-state imaging apparatus including a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) used in a digital camera or a cellular phone is produced such that a solid-state imaging element wafer being a sheet member on which the light receiving portions of a large number of solid-state imaging elements are formed is joined to a light transmissive substrate (glass wafer) being a sheet member with spacers inbetween which are formed correspondingly with the position surrounding each light receiving portion to downsize and mass produce the solid-state imaging apparatus, thereafter both wafers pass through processes such as the formation of through wirings, dicing and others (refer to, for example, Patent Documents 1 or 2).
A method based on an anodic bonding has been proposed so far in which such two different kinds of sheet members brought into contact with each other are subjected to voltage and heated at a high temperature to be joined (refer to, for example, Patent Documents 3 or 4).
As illustrated in Figure 11, for example, the anodic bonding is carried out using a junction apparatus 1 with components such as a first sheet member 10 as a first member, a second sheet member 11 as a second member, a table 12 on which the first sheet member 10 is placed and a high voltage power supply 13 connected to the table 12 and the second sheet member 11.
In the junction apparatus 1, the first and the second sheet member 10 and 11 brought into contact with each other are heated by a heating apparatus (not shown) at a high temperature of 4000C to 5000C and subjected to a direct-current voltage of about 500 V to 1000 V by the high voltage power supply 13 with the second sheet member 11 as a cathode.
This generates a large electrostatic attraction between the first and the second sheet member 10 and 11, and the first and the second sheet member 10 and 11 are firmly joined with a chemical bond at their interfaces.
In addition to the above, a method of joining two different kinds of sheet members has been proposed in which the junction surfaces of sheet members are activated by energy waves such as plasma or ion beams (refer to, for example, Patent Documents 5 or 6). Patent Document 1 : Japanese Patent Laid-Open No. 2001 -351997
Patent Document 2: Japanese Patent Laid-Open No. 2004-88082 Patent Document 3: Japanese Patent Laid-Open No. 2001-64041 Patent Document 4: Japanese Patent Laid-Open No. 2005-187321 Patent Document 5: Japanese Patent Laid-Open No. 2006-73780 Patent Document 6: Japanese Patent Laid-Open No. 2006-248895
Since the glass wafer used in the solid-state imaging apparatus described in Patent Documents 1 and 2 is required to have such a high optical transmissivity as to efficiently introduce light into a solid-state imaging element, an optical functional film such as a MgF2, SiO, SiO2 film for preventing reflection (referred to as "reflection preventing film" or "AR film") is formed on the surface of the glass wafer.
On the other hand, a transparent glass wafer such as, for example, "Pyrex (registered trademark) glass" which is comparable in thermal expansion coefficient to Si is used as the glass wafer. However, the glass wafer is different in material from the optical functional film and also different in thermal expansion coefficient from the film, so that the glass wafer is warped by heating in the junction process. This results in a defect in junction between the solid-state imaging element wafer and the glass wafer and poses a problem in the junction process for the solid-state imaging apparatus.
The surfaces of the members to be joined are desirably mirror-finished to the extent that surface roughness is 1 nm or less. However, the optical functional film is occasionally or often 10 nm or more in surface roughness. In addition, the optical functional film occasionally contains water-repellent fluoride compound and has fine defects because it significantly changes in film density depending upon conditions for forming the film, and therefore the optical functional film is occasionally not suited for a joining method such as the anodic bonding.
Disclosure of the Invention Since the joining methods described in Patent Documents 3 to 6 include steps in which heat is applied at the time of junction, a difference in thermal expansion coefficient between the two sheet members causes warp in the joining members while the sheet members are cooled, which poses a significant problem at a post process in the production of imaging devices using semiconductors. To cope with the above problem, in the joining methods described in Patent
Documents 3 to 6, warp is reduced by, for example, providing a temperature gradient in the thickness direction of the joining member or sandwiching one member between two members which have the same thermal expansion coefficient.
However, it is difficult for these methods to precisely control cooling temperature above and below the junction surface. Particularly when thin members are joined, they are small in heat capacity, so that temperature instantaneously becomes uniform throughout the member, which does not enable a temperature gradient to be provided. In addition, when one member is sandwiched between two members which have the same thermal expansion coefficient, another member which would not otherwise be required needs to be joined, which adds a new problem in that a process or cost is increased.
The present invention has been made in view of the above problems, and has for its object to provide a joining method and a joining member which reduce warp produced at the time of joining sheet members different in thermal expansion coefficient by heating, prevents the deterioration of the joining member resulting from the warp, maintains the performances of the optical functional film and satisfactorily joins the sheet members with high air tightness.
To achieve the object, according to a first aspect of the present invention, in a joining method by which a process involving heating is carried out when a first and a second sheet member formed of Si, SiO2 or glass and of a different material from each other are joined together, the joining method is characterized by comprising joining the first and the second sheet member together by adjusting any one or more of conditions of a ratio of thickness between the first and the second sheet member, a temperature-rise rate at the time of junction and a difference in thermal expansion coefficient between the first and the second sheet member.
According to the invention of the first aspect, in a method of joining two sheet members by carrying out a heating process in which a first and a second sheet member which are formed of Si, SiO2 or glass and of a different material from each other brought into contact with each other are heated, any one or more of the conditions is adjusted of a ratio of thickness between the first and the second sheet member, a temperature-rise rate at the time of junction and a difference in thermal expansion coefficient between the first and the second sheet member. Glass which is lower in thermal expansion coefficient such as "Pyrex (registered trademark) glass," for example, is more preferably used as the glass for forming any of the first and the second sheet member, but not limited to that, it is preferable to use a glass which is about twice or less as small as the other sheet material in thermal expansion coefficient. A wafer on which a semiconductor element for an imaging device such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) is formed may be used as the first and the second sheet member.
This makes the first and the second sheet member unsusceptible to influence by the difference in thermal expansion coefficient, reducing warp caused after heating process. A second aspect of the present invention is characterized in that, in the invention according to the first aspect, when the ratio of thickness is taken to be "n" and the ratio of moduli of longitudinal elasticity is taken to be "m," n < 0.8 or n>2.5, and "r" represented by the equation of r = (mn3 + 1) x (mn + l)/mn (n + I)2 + 3 is greater than 5.3.
According to the invention of the second aspect, thickness of each sheet member is adjusted by a value determined by a ratio of thickness between the first and the second sheet member and a ratio of the moduli of longitudinal elasticity between the first and the second sheet member so as to minimize the radius of curvature at the time of cooling the heated joining members.
This reduces influence due to stress generated in the first and the second sheet member to decrease warp of the joining members.
A third aspect of the present invention is characterized in that, in the invention according to the first aspect, the temperature-rise rate is 100C or less per minute. According to the third aspect, heating the joining members at a temperature-rise rate slower than a normal temperature-rise rate starts junction in incremental steps at a temperature lower than a temperature at which junction is carried out, which does not cause each sheet member to expand beyond necessity to reduce warp and junction defects when the joining members return to normal temperature.
A fourth aspect of the present invention is characterized in that, in the invention according to the first aspect, the difference in thermal expansion coefficient is adjusted by forming a film having a thermal expansion coefficient between the thermal expansion coefficients of the first and the second sheet member on a junction surface where the first and the second sheet member are joined together between the first and the second sheet member.
According to the fourth aspect, the film having a thermal expansion coefficient between the thermal expansion coefficients of the first and the second sheet member is formed on the junction surface where the first and the second sheet member are joined to each other.
Thereby, the difference in thermal expansion coefficient between the first and the second sheet member is reduced by the film formed on the junction surface to reduce the warp of the joining members.
A fifth aspect of the present invention is characterized in that, in the invention according to the first aspect, the difference in thermal expansion coefficient is adjusted by containing a component of any one of the first and the second sheet member into the other sheet member in the vicinity of the junction surface.
According to the fifth aspect, any one of the first and the second sheet member forms a layer containing a component of the other sheet member in the thickness direction with respect to the junction surface. The component in the layer containing the component of the other sheet member gradually lessens as it gets far from the junction surface.
Thereby, the layer comparable in thermal expansion coefficient to the other sheet member is formed in the one sheet member in the vicinity of the junction surface, reducing the difference in thermal expansion coefficient between the first and the second sheet member to reduce the warp of the joining members. A sixth aspect of the present invention is characterized in that, in a joining method by which a first sheet member on which solid-state imaging elements are formed is joined to a second sheet member all over or up to the vicinity of the outer periphery of one side of which, or all over or up to the vicinity of the outer periphery of both sides of which an optical functional film being an antireflection film made of oxide film, nitride film, or fluoride film for preventing reflection is formed with a gap provided between the first and the second sheet member through a spacer, the joining method is characterized by comprising subjecting the optical functional film on the junction surface where the first sheet member is joined to the second sheet member to any one or more of processing: change of surface properties including surface roughness, constituent element and density value; removal; activation by plasma; smoothing by plasma or division by forming a plurality of grooves.
According to the sixth aspect, a solid-state imaging element wafer as the first sheet member on which solid-state imaging elements are formed is joined to a glass wafer as the second sheet member all over or up to the vicinity of the outer periphery of one side of which, or all over or up to the vicinity of the outer periphery of both sides of which an optical functional film being an antireflection film made of oxide film, nitride film, or fluoride film for preventing reflection is formed, with a gap provided between the first and the second sheet member through a spacer. The members are joined by a direct joining method such as an anodic bonding or a surface active joining method. At the time of junction, the optical functional film is processed to be adapted for junction.
Any one or more of processing: change of surface properties including surface roughness, constituent element and density value; removal; activation by plasma; smoothing by plasma; or division by forming a plurality of grooves are provided only for the optical functional film formed on the junction surface where the solid-state imaging element wafer is joined to the glass wafer. The optical functional film for part of which the processing is not provided is masked to be left on the glass wafer.
For the change of surface properties, the surface properties including surface roughness, constituent element and density value of the optical functional film are changed to conditions adapted for junction by changing conditions for polish and film-formation.
For the removal of the optical functional film, removing the optical functional film formed on the junction surface where the solid-state imaging element wafer is joined to the glass wafer by a method such as etching joins the solid-state imaging element wafer to the glass wafer without sandwiching the optical functional film.
For activation by plasma, the optical functional film is activated by plasma, thereby the solid-state imaging element wafer is satisfactorily joined to the glass wafer with high air tightness by surface activation junction.
For smoothing by plasma, the optical functional film is activated and smoothened by plasma, which does not leave polishing residues unlike smoothing by polishing to satisfactorily join the solid-state imaging element wafer to the glass wafer with high air tightness. For division by forming a plurality of grooves, a plurality of grooves are formed in the optical functional film in the lengthwise and crosswise directions by a method such as dicing or etching to divide the optical functional film, reducing warp caused by the difference in thermal expansion coefficient between the optical functional film and the glass wafer at the time of heating at the junction process. This reduces the difference in expansion caused by the difference in thermal expansion coefficient between the optical functional film and the glass wafer to reduce the warp of the glass wafer to satisfactorily join the solid-state imaging element wafer to the glass wafer with high air tightness without impairing the performance of the optical functional film. A seventh aspect of the present invention is characterized in that, the optical functional film is formed on the second sheet member with a thickness which is greater than a desired thickness of the optical functional film required after joining the first sheet member to the second sheet member, and after that, the first sheet member is joined to the second sheet member. According to the seventh aspect, smoothing enables optical characteristics to be maintained even if the thickness is changed when surface properties of the optical functional film such as roughness or contained elements are controlled to change the optical characteristic.
An eighth aspect of the present invention is characterized in that, in a joining method by which a first sheet member on which solid-state imaging elements are formed is joined to a second sheet member on one or both sides of which an optical functional film for preventing reflection is formed with a gap provided between the first and the second sheet member through a spacer, the joining method is characterized by comprising joining the first sheet member to the second sheet member on which the spacer is formed and then the optical functional film is formed.
According to the eighth aspect, the solid-state imaging element wafer as the first sheet member is joined to the glass wafer as the second sheet member on which the optical functional film is formed, between which a gap is provided through a spacer. A member for the spacer is first joined to the glass wafer to form the spacer by a method such as a dry etching method and then the optical functional film is formed on the glass wafer, thereafter, the solid-state imaging element wafer is joined to the glass wafer. This satisfactorily joins the solid-state imaging element wafer to the glass wafer with high air tightness without impairing the performance of the optical functional film.
As described above, according to the joining method and the joining member of the present invention, when the sheet members different in thermal temperature coefficient from each other are joined by heating, influence due to the difference in thermal temperature coefficient is reduced to reduce warp produced, preventing the deterioration of the joining members resulted from the warp. The optical functional film is processed to be suited for junction without the degradation of the performance thereof, which satisfactorily joins the solid-state imaging element wafer to the glass wafer with high air tightness.
Brief Description of the Drawings
Figure 1 is a schematic diagram of junction process in a junction apparatus according to the present invention;
Figure 2 is a perspective view of a solid-state imaging apparatus according to the present invention;
Figure 3 is a cross section illustrating warped joining members; Figures 4A, 4A' to 4D, 4D' are cross sections illustrating difference in the junction at the time of changing a temperature-rise rate;
Figures 5A, 5A' to 5C, 5C are cross sections illustrating joining members having a film inbetween and normal joining members;
Figures 6A, 6A' to 6C, 6C are cross sections illustrating joining members one of which contains the component of the other member and a normal joining member, Figures 7A, 7A' to 1C, 1C are cross sections of the joining members in which the surface properties of the optical functional film are changed;
Figures 8A, 8A' to 8C, 8C are cross sections of joining members to which the optical functional film activated by plasma is joined; Figures 9A, 9A' to 9D, 9D' are cross sections of joining members joined together with the optical functional film removed;
Figures 1OA, 1OA' to 1OC, 1OC' are cross sections illustrating a joining method by which the optical functional films are formed on both sides of the member 11; and
Figure 11 is a schematic diagram illustrating a junction apparatus for anodic bonding.
Description of Symbols
1 Junction apparatus
2 Solid-state imaging element chip
3 Solid-state imaging element
4 Cover glass
5 Spacer
6 Pad
10 First sheet member
11 Second sheet member
13 High voltage power supply
14 Bond
15 Intermediate film
16 Containing layer
17 Optical functional film
18 Processed portion
19 Activated portion
Best Mode for Carrying Out the Invention A preferable embodiment of a joining method and a joining member according to the present invention is described below with reference to the accompanied drawings. Figure 1 is a schematic diagram illustrating the outline of the joining method according to the present invention and of a junction process in a junction apparatus for producing the joining members according to the present invention.
In the junction apparatus, a first and a second member 10 and 11 made of Si, SiO2 or glass and of a different material from each other are placed in a low pressure chamber, subjected to oxygen plasma processing and then to nitrogen plasma processing.
This activates and smoothes the surfaces of the first and the second sheet member 10 and 11 and makes them hydrophilic.
The first and the second sheet member 10 and 11 are returned to the atmosphere. The entire junction surfaces of both members are brought into close contact with each other to temporarily join them. Following the temporary junction, the first and the second sheet member 10 and 11 are pressurized and heated by a heating apparatus (not shown) to a junction temperature (400°C to 5000C, for example). In this condition, a high direct- current (DC) voltage of, for example, 500 V to 1000 V is applied between the first and the second sheet member 10 and 11 with the second sheet member 11 as a cathode by a high voltage power supply 13.
This generates a large electrostatic attraction between the first and the second sheet member 10 and 11 and chemically bonds the interface portion between them to firmly join the first sheet member 10 to the second sheet member 11. In the above joining method, it is desirable that the first and the second sheet member 10 and 11 are mirror-finished and are 100 μm in flatness and 1 nm or less in roughness.
The joining method according to the present invention and the junction apparatus for producing the joining members according to the present invention can be applied to any known junction process involving a heating process as well as the above junction process.
Figure 2 is a perspective view illustrating the external shape of a solid-state imaging apparatus according to the embodiment of the present invention. A solid-state imaging apparatus 1 includes a solid-state imaging element chip 2 on which solid-state imaging elements 3 are provided, a spacer 5 which is fixed to the solid-state imaging element chip 2 and surrounds the solid-state imaging elements 3 and a cover glass 4 which is fixed over the spacer 5 and seals the solid-state imaging elements 3. The solid-state imaging element chip 2 includes a rectangular chip substrate formed by cutting the sheet member on which the solid-state imaging elements 3 are formed by a dicing device, the solid-state imaging elements 3 formed on the chip substrate and a plurality of pads (electrodes) 6 which is arranged outside the solid-state imaging elements 3 and used for external wiring. The chip substrate uses, for example, silicon single crystal and is approximately 300 μm in thickness.
The cover glass 4 is formed by cutting the sheet member formed of glass by dicing. The cover glass 4 uses a transparent glass, for example, Pyrex (registered trademark) glass which is comparable in thermal expansion coefficient to silicon and is approximately 500 μm in thickness, for example. An optical functional film made of the AR film such as oxide film, nitride film, MgF2 being magnesium fluoride film, SiO or SiO2 film for preventing reflection is formed on the surface of the cover glass 4.
The spacer 5 uses, for example, polycrystalline silicon because the spacer 5 is desirably an inorganic material and comparable in properties such as thermal expansion coefficient to the chip substrate and the cover glass 4. The frame-shaped spacer 5 is approximately 200 μm wide and 100 μm thick in cross section, for example.
The spacer 5 is joined to the solid-state imaging element chip 2 and the cover glass 4 by a direct joining method such as an anodic bonding or a surface active joining method.
A first embodiment of the joining method according to the present invention is described below. Figure 3 is a cross section illustrating warped joining members.
The first and the second sheet member 10 and 11 are heated to a junction temperature at the time of junction and warped at radius of curvature R shown in Figure 3 due to a difference in thermal expansion coefficient between the first and the second sheet member 10 and 11 when they are cooled, after joined, to a temperature before they are joined.
When the length of the member is taken to be L and the amount of warp as δ, the amount of warp δ can be expressed by the equation: δ = R ± SQRT (R2 - L2/4).
The radius of curvature R can be expressed by R = (hi + h2)/{6(α2 - αl) x ΔT} x {(mn3 + 1) x (mn + l)/mn (n + I)2 + 3}, where, hi and h2 are thickness of the first and the second sheet member 10 and 11 respectively, αl and α2 are the thermal expansion coefficients of the first and the second sheet member 10 and 11 respectively, ΔT is a temperature raised by heating, "m" is a ratio between the moduli of longitudinal elasticity of the first and the second sheet member 10 and 11 and "n" is a ratio between the thicknesses of the first and the second sheet member 10 and 11.
Where, since the thermal expansion coefficients and the moduli of longitudinal elasticity of the first and the second sheet member 10 and 11 depend on materials thereof, if "r" is taken to be (mn3 + 1) x (mn + l)/mn (n + I)2 + 3, changing the respective thicknesses of the first and the second sheet member 10 and 11 changes "n" being the thickness ratio to change the value "r." This also changes the radius of curvature R.
When the radius of curvature R is changed to a smaller optimal value, if the first sheet member 10 is made of Si or SiO2 and the second sheet member 11 is made of a transparent glass material such as Pyrex (registered trademark) glass, and if the modulus of longitudinal elasticity of the first sheet member 10 is taken as 180 GPa, the modulus of longitudinal elasticity of the second sheet member 11 is taken as 90 GPa and ΔT is taken as 100 K, the thickness ratio "n" is preferably n < 0.8 or 2.5 < n, and more preferably n < 0.48 or 5 < n. It is still more preferable that n < 0.2 or 15 < n at which the amount of warp δ is 300 μm or less.
In addition, the value "r" is preferably larger than 5.3, more preferably larger than 30 at which the amount of warp δ is 300 μm or less and still more preferably larger than 100 at which the amount of warp δ is 100 μm.
A second embodiment of the joining method according to the present invention is described below. Figures 4A, 4A' to 4D, 4D' are cross sections illustrating difference in the junction at the time of changing a temperature-rise rate.
As illustrated in Figures 4A and 4A', the first and the second sheet member 10 and 11 are pressurized by pressing means (not shown) with their junction surfaces brought into contact with each other. The first and the second sheet member 10 and 11 (Figures 4 A, 4C, and 4D) illustrated on the left side are rapidly heated in an environment set at normal temperature to, for example, 100°C to 50O0C, and the first and the second sheet member 10 and 11 (Figures 4A', 4B\ 4C, and 4D') illustrated on the right side are heated slower than the former members.
At this point, the first and the second sheet member 10 and 11 expand as the temperature rises. As illustrated in Figure 4B, a partial junction starts between the first and the second sheet member 10 and 11 which are heated at a slower temperature-rise rate, at a temperature lower than an apparent junction temperature (for example, 4000C to 500°C) which the first and the second sheet member 10 and 11 are caused to ultimately reach, starting forming bonds 14 which are portions where the first sheet member 10 is joined to the second sheet member 11 therein.
At this point, the first and the second sheet member 10 and 11 which are heated at a normal temperature-rise rate will form the bonds 14 at a temperature higher than the members heated at a slower temperature-rise rate because the temperature rise is sharp. When the first and the second sheet member 10 heated at a faster and a slower temperature-rise rate are continued to be heated in this condition to the apparent junction temperature which the first and the second sheet member 10 and 11 are caused to ultimately reach, as illustrated in Figure 4C\ the bonds 14 formed in the members heated at a slower temperature-rise rate tilt toward the direction to which the members are extended by expansion. Conversely, the first and the second sheet member 10 and 11 heated at a faster temperature-rise rate form the bonds 14 perpendicularly with respect to the first and the second sheet member 10 and 11 because the bonds 14 are formed with the first and the second sheet member 10 and 11 sufficiently expanded.
When the joining members in which the first and the second sheet member 10 and 11 are joined to each other are cooled in this condition to a normal temperature, the first and the second sheet member 10 and 11 shrink to their original size. The bonds 14 tilting toward the direction to which the members are extended, in the first and the second sheet member 10 and 11 heated both at a slower temperature-rise rate, become perpendicular to the first and the second sheet member 10 and 11.
On the other hand, the bonds 14 perpendicular to the first and the second sheet member 10 and 11, in the joining members in which the first and the second sheet member 10 and 11 are joined to each other, heated at a faster temperature-rise rate, tilt toward the direction to which the members shrink by the influence of difference in thermal expansion coefficient between the first and the second sheet member 10 and 11, which produces a significant warp. Furthermore, the bonds are cut in order to reduce warp, which occasionally produces a partial junction defect.
Accordingly, slowing a temperature-rise rate makes the joining members unsusceptible to difference in thermal expansion coefficient between the joining members to reduce warp produced after the heating process. In the present embodiment, the temperature-rise rate is preferably 100C or less per minute and more preferably 5°C or less per minute.
A third embodiment of the joining method according to the present invention is described below. Figures 5 A, 5A' to 5C, 5C are cross sections illustrating joining members having a film inbetween and normal joining members.
In the third embodiment, as illustrated in Figure 5 A and 5A', an intermediate film
15 having a thermal expansion coefficient between the first and the second sheet member 10 and 11 is formed on any one (Figure 5A') of the first and the second sheet member 10 and 11 which are brought into close contact with each other and pressed by a pressing means (not shown).
If the first and the second sheet member 10 and 11 are made of glass material such as, for example, Si and SiO2 respectively, a layer made of, for example, SiO2, B2O3, Al2O3 and Na2O of which thermal expansion coefficient is controlled by the component ratio is formed, as the intermediate layer, on any one of the junction surfaces of the first and the second sheet member 10 and 11.
Thus, the first and the second sheet member 10 and 11 between which the intermediate film 15 is formed are heated to the junction temperature suppress the difference in the amount of expansion caused by the difference in thermal expansion coefficient between the first and the second sheet member 10 and 11 when the joining members are heated.
This makes the members unsusceptible to influences from the difference in thermal expansion coefficient between the joining members to reduce warp at the time of heating.
A fourth embodiment of the joining method according to the present invention is described below. Figures 6A, 6A' to 6C, 6C are cross sections illustrating joining members one of which contains the component of the other member and a normal junction portion.
In the fourth embodiment, as illustrated in Figures 6 A and 6A', a containing layer
16 containing the component of the other member is formed on any one (Figure 6A') of the first and the second sheet member 10 and 11 which are brought into close contact with each other and pressed by a pressing means (not shown). In the containing layer 16, there exist components with a gradient such that the containing amount of the component of the other member reduces as it gets far from the junction surface. In the present embodiment, the component of the second sheet member 11 shall be contained in the first sheet member 10.
As described above, when the first and the second sheet member 10 and 11 in the vicinity of the junction surface of which the containing layer 16 is formed are heated to the junction temperature, the component of the second sheet member 11 is contained in the containing layer 16, so that the containing layer 16 is comparable to the second sheet member 11 in thermal expansion coefficient, which suppresses the difference in the amount of expansion caused by the difference in thermal expansion coefficient between the first and the second sheet member 10 and 11. This makes the members unsusceptible to influences from the difference in thermal expansion coefficient between the joining members to reduce warp at the time of heating.
A fifth embodiment of the joining method according to the present invention is described below. Figures 7A, 7A' to 7C, 1C are cross sections of the joining members in which the surface properties of the optical functional film are changed. As illustrated in Figures 7 A and 7A', an optical functional film 17 made of the AR film such as MgF2, SiO or SiO2 film is formed on one surface of the second sheet member 11 as a glass wafer which becomes a cover glass 4 by cutting the glass wafer by a dicing device.
The optical functional film 12 is desirably formed all over the surface of the second sheet member 11 or up to the vicinity of the outer periphery thereof (for example, up to a position of 0.2 mm, more desirably, 0.1 mm inward from the outer periphery).
This prevents stress from locally concentrating on the periphery due to the gap caused by the optical functional film 17 not being formed in the vicinity of the outer periphery of the second sheet member 11 after the first sheet member 10 as the solid-state imaging element wafer has been joined to the second sheet member 11, preventing the first and the second sheet member 10 and 11 from being damaged.
A spacer 5 is joined to the second sheet member 11 on which the optical functional film 17 is formed, as illustrated in Figures 7B and 7B' . The spacer 5 is so formed beforehand as to surround a plurality of solid-state imaging elements 3 formed on the first sheet member 10 as a solid-state imaging element wafer which becomes a solid-state imaging element chip 2 by cutting the solid-state imaging element wafer into pieces by dicing. The spacer 5 is joined to the second sheet member 11 by a direct joining method such as an anodic bonding. Smoothing the optical functional film 17 by plasma etching changes a surface roughness Rrms from 10 nm or more in normal state to Rrms < 2 nm. It is preferable to change the surface roughness Rrms < 0.5 nm. Thus, changing the surface properties of the optical functional film 17 makes the surface of the optical functional film 17 mirror-shaped suited for junction, which satisfactorily joins the optical functional film 17 with high air tightness.
The surface properties of the optical functional film 17 may be changed not only by plasma etching but, for example, polishing, reflow, ion injection, wet etching or annealing method, whereby the surface roughness, constituent element and density value of the optical functional film 17 may be changed. The surface properties may be changed while or after the optical functional film 17 is formed.
As illustrated in Figure 7B', as for the processing of the optical functional film 17, it is desirable to process only the optical functional film 17 on the junction surface where the first and the second sheet member 10 and 11 are joined to each other through the spacer 5. This occasionally deteriorates characteristics such as the prevention of reflection due to the processing such as polishing, however, unlike the case where the entire surface is processed as illustrated in Figure 7B, only the portion to which the spacer 5 is joined is processed, so that only the processed portions 18 are deteriorated. As illustrated in Figure 1C, the spacers 5 are joined to the processed portions 18, which does not affect light incident on the solid-state imaging elements 3 not to impair the function of the optical functional film 17 at the portion on which light is incident, thereby the first sheet member 10 is satisfactorily joined to the second sheet member 11 with high air tightness. The first and the second sheet member 10 and 11 joined together are cut by the dicing device to be divided into individual solid-state imaging apparatuses.
A sixth embodiment of the joining method for the solid-state imaging apparatus according to the present invention is described below. Figures 8A, 8A' to 8C, 8C are cross sections of joining members to which the optical functional film activated by plasma is joined.
As illustrated in Figures 8 A and 8A', the optical functional film 17 made of an AR film such as a MgF2, SiO, SiO2 film is formed on one face of the second sheet member 11. The optical functional film 12 is desirably formed all over the surface of the second sheet member 11 or up to the vicinity of the outer periphery thereof (for example, up to a position of 0.2 mm, more desirably, 0.1 mm inward from the outer periphery of the second sheet member 11). As illustrated in Figures 8B and 8B', the spacer 5 is formed on the second sheet member 11 on which the optical functional film 17 is formed. The spacer 5 is so formed in advance as to enclose a plurality of the solid-state imaging elements 3 formed on the first sheet member 10.
The spacer 5 is joined to the second sheet member 11 by a surface activation joining method by which the surface of the optical functional film 17 is activated and smoothed by a method such as plasma radiation. At this point, as illustrated in Figure 8B', the surface of the optical functional film 17 is masked except the surface where the first and the second sheet member 10 and 11 are joined together through the spacer 5. Unlike the case where the entire surface is activated and smoothed as illustrated in Figure 8B, the optical functional film 17 only on the junction surface is activated and smoothed.
Thus, although characteristics of the optical functional film 17 such as the prevention of reflection are occasionally deteriorated by the surface activation such as plasma radiation, only the portion to which the spacer 5 is joined is activated and smoothed, and only an activated portion 19 is deteriorated in characteristics. The spacer 5 is joined to the activated portion 19, which does not affect light incident on the solid-state imaging element 3 not to impair the function of the optical functional film 17 at the portion on which light is incident, thereby the first sheet member 10 is satisfactorily joined to the second sheet member 11 with high air tightness.
The first and the second sheet member 10 and 11 joined together are cut by the dicing device to be divided into individual solid-state imaging apparatuses.
A seventh embodiment of the joining method for the solid-state imaging apparatus according to the present invention is described below. Figure 9A, 9A' to 9C, 9C are cross sections of joining members joined together with the optical functional film removed.
In the seventh embodiment, as illustrated in Figure 9A, the optical functional film 17 made of the AR film such as MgF2, SiO or SiO2 film is formed on one face of the second sheet member 11. The optical functional film 12 is desirably formed all over the surface of the second sheet member 11 or up to the vicinity of the outer periphery thereof (for example, up to a position of 0.2 mm, more desirably, 0.1 mm inward from the outer periphery of the second sheet member 11). As illustrated in Figures 9B, the spacer 5 is formed on the second sheet member 11 on which the optical functional film 17 is formed. The spacer 5 is so formed in advance as to enclose a plurality of the solid-state imaging elements 3 formed on the first sheet member 10.
When the spacer 5 is joined to the second sheet member 11, the optical functional film 17 on the surface where the first and the second joined sheet member 10 and 11 are joined together through the spacer 5 is removed by etching or dicing to directly join the sheet member 11 to the spacer 5 as illustrated in Figure 9C. The spacer 5 is joined to the sheet member 11 by a direct joining method such as an anodic joining method or a surface activation joining method. The spacer 5 is joined to the second sheet member 11 not through the optical functional film 17, so that they are satisfactorily joined together with high air tightness.
In addition, in the seventh embodiment, as illustrated in Figure 9 A', the spacer 5 is joined to the second sheet member 11 by a direct joining method, alternatively, a member used for the spacer 5 joined in advance to the second sheet member 11 is processed by a method such as dry etching to form the spacer 5 on the second sheet member 11 on the surface of which the optical functional film 17 is not formed. After that, as illustrated in Figure 9C\ the optical functional film 17 may be formed on the second sheet member 11 on which the spacer 5 is not formed.
Thereby the first sheet member 10 is satisfactorily joined to the second joined sheet member 11 with high air tightness without deteriorating the performance of the optical functional film 17.
Incidentally, when the optical functional film 17 is removed by a method such as etching or dicing, a plurality of grooves are formed in the lengthwise and crosswise directions in the optical functional film 17 which are not removed to be divided into plural pieces. This reduces warp caused by difference in thermal expansion coefficient between the optical functional film 17 and the second sheet member 11 at the time of heating for junction, enabling the first and the second joined sheet member 10 and 11 to be satisfactorily joined to each other with high air tightness.
Although the optical functional film 17 is formed only on the one side of the second sheet member 11, the present invention is not limited to that, but is also suitably embodied if the optical functional film 17 is formed on both sides of the second sheet member 11 as illustrated in Figure 1OA' .
As illustrated in Figures 1OB and 1OB', when the first sheet member 10 is joined to the second sheet member 11 by a healing method, forming the optical functional films 17 on both sides of the second sheet member 11 joins the first sheet member 10, the second sheet member 11 and the optical functional film 17 to one another while each of them is differently expanded in length due to the difference in thermal expansion coefficient among them. The second sheet member 11 and the optical functional film 17 which are cooled after they have been joined shrink differently in length, causing warp on the second sheet member 11 only on one side of which the optical functional film 17 is formed, as illustrated in Figure 1OC. The second sheet member 11 on both sides of which the optical functional films 17 are formed shrinks equally in length on the upper and the lower portion thereof, as illustrated in Figure 1OC', reducing the difference in expansion caused by the difference in thermal expansion coefficient to reduce warp of the glass wafer.
This allows the first and the second sheet member 10 and 11 to be satisfactorily joined to each other with high air tightness.
Although the thickness of the optical functional film 17 formed on the second sheet member 11 in the present embodiment is 100 nm or more and 500 nm or less, for example, which is a normally required thickness, the present invention is not limited to this thickness, but the thickness may be greater than the thickness of the optical functional film 17 which is required after the first sheet member 10 has been joined to the second sheet member 11
(for example, the thickness may be greater than the normally required thickness by 50 nm, desirably greater than that by 100 nm).
This enables the optical characteristic to be maintained by smoothening the optical functional film 17 to reduce its thickness to a required value even if the thickness is changed when surface properties of the optical functional film 17 such as roughness or contained elements are controlled to change the optical characteristics. Polishing as well as plasma etching may be used for reducing the thickness. [Example]
Figure imgf000021_0001
The table lists results of junction tests on the joining methods according to the present invention. It was examined how thickness ratio, temperature gradient, junction property and amount of warp change with the thermal expansion coefficient ratio fixed (Test Nos. 1 to 5).
Difference appeared, when thickness ratios were changed, injunction property under conditions of Nos.1 and 2 and of Nos. 3 to 5. The members smaller in thickness ratio failed to be joined together, but increasing the thickness ratio improved junction property. The reason the members Nos. 1 and 2 failed to be joined together seems to be attributed to the amount of warp.
Difference appeared, when temperature gradients were changed, injunction property and the amount of warp (Nos. 3 to 5). The gentler the temperature gradient, the smaller the amount of warp becomes. Incidentally, although warp was smaller in rapid heating, a large number of junction defects were found. This seems that insufficient junctions reduced warp as a whole. The junctions in Nos. 6 and 7 which are comparable in thermal expansion coefficient were satisfactory injunction property and the amount of warp irrespective of thickness ratio and temperature gradient.
As described above, according to the joining method and the joining member of the present invention, when the sheet members different in thermal temperature coefficient are heated to be joined together and any one or more of thickness ratio, temperature-rise rate at the time of junction and difference in thermal temperature coefficient is adjusted, influence due to the difference in thermal temperature coefficient is reduced to reduce warp, preventing the joining member from being deteriorated by warp. The optical functional film is processed to be suited for junction without degrading the performance thereof, thereby the solid-state imaging element wafer is satisfactorily joined to the glass wafer with high air tightness.

Claims

1. A joining method by which a process involving heating is carried out when a first and a second sheet member formed of Si, SiO2 or glass and of a different material from each other are joined together, the joining method characterized by comprising: joining the first and the second sheet member together by adjusting any one or more of conditions of a ratio of thickness between the first and the second sheet member, a temperature-rise rate at the time of junction and a difference in thermal expansion coefficient between the first and the second sheet member.
2. The joining method according to claim 1, characterized in that when a ratio of thickness is taken to be "n" and a ratio of moduli of longitudinal elasticity is taken to be "m," n < 0.8 or n>2.5, and "r" represented by the equation of r = (mn3 + 1) x (mn + l)/mn (n + I)2 + 3 is greater than 5.3.
3. The joining method according to claim 1, characterized in that the temperature-rise rate is 100C or less per minute.
4. The joining method according to claim 1 , characterized in that the difference in thermal expansion coefficient is adjusted by forming a film having a thermal expansion coefficient between the thermal expansion coefficients of the first and the second sheet member on a junction surface where the first and the second sheet member are joined together between the first and the second sheet member.
5. The joining method according to claim 1 , characterized in that the difference in thermal expansion coefficient is adjusted by containing a component of any one of the first and the second sheet member into the other sheet member in the vicinity of the junction surface.
6. A joining method by which a first sheet member on which solid-state imaging elements are formed is joined to a second sheet member all over or up to the vicinity of the outer periphery of one side of which, or all over or up to the vicinity of the outer periphery of both sides of which an optical functional film being an antireflection film made of oxide film, nitride film, or fluoride film for preventing reflection is formed, with a gap provided between the first and the second sheet member through a spacer, the joining method characterized by comprising: subjecting the optical functional film on the junction surface where the first sheet member is joined to the second sheet member to any one or more of processing: change of surface properties including surface roughness, constituent element and density value; removal; activation by plasma; smoothing by plasma or division by forming a plurality of grooves.
7. The joining method according to claim 6, characterized in that the optical functional film is formed on the second sheet member with a thickness which is greater than a desired thickness of the optical functional film required after joining the first sheet member to the second sheet member, and after that, the first sheet member is joined to the second sheet member.
8. A joining method by which a first sheet member on which solid-state imaging elements are formed is joined to a second sheet member on one or both sides of which an optical functional film for preventing reflection is formed with a gap provided between the first and the second sheet member through a spacer, the joining method characterized by comprising: joining the first sheet member to the second sheet member on which the spacer is formed and then the optical functional film is formed.
9. A joining member produced by a joining method in which a process involving heating is carried out when a first and a second sheet member formed of Si, SiO2 or glass and of a different material from each other are joined together, characterized in that the joining method comprises: joining the first and the second sheet member together by adjusting any one or more of the conditions of a ratio of thickness between the first and the second sheet member, a temperature-rise rate at the time of junction and a difference in thermal expansion coefficient between the first and the second sheet member.
10. The joining member according to claim 9, characterized in that when the ratio of thickness is taken to be "n" and the ratio of moduli of longitudinal elasticity is taken to be "m," n < 0.8 or n>2.5, and "r" represented by the equation of r = (mn3 + 1) x (mn + l)/mn (n + I)2 + 3 is greater than 5.3.
11. The joining member according to claim 9, characterized in that the temperature-rise rate is 100C or less per minute.
12. The joining member according to claim 9, characterized in that the difference in thermal expansion coefficient is adjusted by forming a film having a thermal expansion coefficient between the thermal expansion coefficients of the first and the second sheet member on a junction surface where the first and the second sheet member are joined together between the first and the second sheet member.
13. The joining member according to claim 9, characterized in that me difference in thermal expansion coefficient is adjusted by containing a component of any one of the first and the second sheet member into the other sheet member in the vicinity of the junction surface.
14. A joining member produced by joining a first sheet member on which solid-state imaging elements are formed to a second sheet member all over or up to the vicinity of the outer periphery of one side of which, or all over or up to the vicinity of the outer periphery of both sides of which an optical functional film being an antireflection film made of oxide film, nitride film, or fluoride film for preventing reflection is formed, with a gap provided between the first and the second sheet member through a spacer, the joining member produced by following process (i) or (ii):
(i) subjecting the optical functional film on the junction surface where the first sheet member is joined to the second sheet member to any one or more of processing: change of surface properties including surface roughness, constituent element and density value; removal; activation by plasma; smoothing by plasma or division by forming a plurality of grooves; (ii) joining the first sheet member to the second sheet member on which the spacer is formed and then the optical functional film is formed.
15. The joining member according to claim 14, characterized in that the optical functional film is formed on the second sheet member with a thickness which is greater than a desired thickness of the optical functional film required after joining the first sheet member to the second sheet member, and after that, the first sheet member is joined to the second sheet member.
PCT/JP2007/075401 2006-12-28 2007-12-27 Joining method and joining members WO2008081987A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07130590A (en) * 1992-08-07 1995-05-19 Shin Etsu Handotai Co Ltd Manufacture of semiconductor substrate
WO1998020543A2 (en) * 1996-11-05 1998-05-14 Commissariat A L'energie Atomique Method for making a thin film on a support and resulting structure
JP2000068491A (en) * 1998-08-24 2000-03-03 Nikon Corp Image pickup element, manufacture of the same and aligner

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07130590A (en) * 1992-08-07 1995-05-19 Shin Etsu Handotai Co Ltd Manufacture of semiconductor substrate
WO1998020543A2 (en) * 1996-11-05 1998-05-14 Commissariat A L'energie Atomique Method for making a thin film on a support and resulting structure
JP2000068491A (en) * 1998-08-24 2000-03-03 Nikon Corp Image pickup element, manufacture of the same and aligner

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