United States Patent [19J
`Goetz et al.
`
`[75]
`
`[54] LOW TEMPERATURE REACTION
`BONDING
`Inventors: George G. Goetz, Ellicott City;
`Warren M. Dawson, Baltimore, both
`ofMd.
`[73] Assignee: AlliedSignal Inc., Morris Township,
`N.J.
`[21] Appl. No.: 161,039
`[22] Filed:
`Dec. 3, 1993
`
`[56]
`
`Related U.S. Application Data
`[63] Continuation-in-part of Ser. No. 894,142, Jun. 4, 1992,
`abandoned.
`Int. Cl.6 .............................................. B32B 31/00
`[51]
`[52] U.S. CI •.................................... 156/153; 156/281;
`156/273.9; 148/DIG. 22; 427/539; 427/573
`[58] Field of Search ..................... 156/153, 272.2, 281,
`156/273.9; 148/DIG. 12, DIG. 22, DIG. 83,
`DIG. 135; 437/974; 427/527, 539, 573
`References Cited
`U.S. PATENT DOCUMENTS
`H1,164 4/1993 Wade, Jr. eta! ................ 156/272.2
`3,679,985 7/1972 Fang eta!. ........................... 330/4.6
`4,170,662 10/1979 Weiss et al ............................ 427/38
`4,274,483 6/1981 Cottone et al. ..................... 165/153
`4,345,985 8/1982 Tohda et al. ........................ 204/192
`4,457,972 7/1984 Griffith et a!. ................... 156/272.2
`4,458,346 7/1984 Mitsuyu et al. ..................... 369/126
`4,547,432 10/1985 Pitts eta! ............................ 428/448
`4,638,552 1/1987 Shimbo et al .................... 156/273.9
`4,765,860 8/1988 Ueno et a! ........................ 156/272.6
`4,824,008 4/1989 Luszcz eta! ........................ 228/121
`4,849,247 7/1989 Scanlon et al. .................. 156/272.2
`4,884,737 12/1989 Newkirk eta! ..................... 228/121
`4,886,681 12/1989 Clabes eta! ........................... 427/38
`4,917,843 4/1990 Gyarmati eta! ...................... 264/60
`4,957,771 9/1990 Enloe .................................... 427/38
`4,960,736 10/1990 Luxzcz eta! ....................... 501/127
`4,983,251 1/1991 Haisma et a! ....................... 156/630
`5,008,723 4/1991 van der Have .................... 357/23.7
`5,010,036 4/1991 Calviello eta! ..................... 437/173
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US005427638A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,427,638
`Jun.27, 1995
`
`5,232,870 8/1993 Ito et a! ...................... 148/DIG. 12
`
`FOREIGN PATENT DOCUMENTS
`3091227 4/1991 Japan .......................... 148/DIG. 12
`
`OTHER PUBLICATIONS
`Lasky et al., Silicon-On-Insulator (SOl) by Bonding
`and Etch-Back, Proceedings of 1985 IEDM 684.
`J. B. Lasky, Wafer Bonding for Silicon-on-Insulator
`Technologies, Jan. 1986, Applied Physics Letters 48, pp.
`78-80.
`W. P. Maszara, et al, "Bonding of Silicon Wafers for
`Silicon-on-Insulator", Nov. 1988, J. Applied Physics,
`pp. 4943-4950.
`Rossnagle, S. M. ed Handbook of Plasma Processing
`Technology Noyes Publications, Park Ridge, N.J. (1990)
`pp. 206-215.
`G. G. Goetz "Generalized Reaction Bonding" The
`First International Symposium on Semiconductor
`Wafer Bonding Science, Technology and Application(cid:173)
`s-Oral Presentation Nov. 14, 1991.
`Primary Examiner-Chester T. Barry
`Attorney, Agent, or Firm-Howard G. Massung
`ABSTRACT
`[57]
`A method for reaction bonding surfaces at low tempera(cid:173)
`tures in which polished and cleaned surfaces are bom(cid:173)
`barded with a mixture of oxygen and fluorine ions to
`produce activated surfaces. The activated surfaces are
`then cleaned to remove particulates, then contacted at
`room temperature to affect a reaction bond therebe(cid:173)
`tween. The bond energy of the reaction bonded sur(cid:173)
`faces increase with time at room temperature. The rate
`at which the bond energy of the reaction bonded sur(cid:173)
`faces increases may be enhanced by moderate heating at
`a low temperature below a temperature which would be
`detrimental to any part of the reaction bonded struc(cid:173)
`ture. A satisfactory bond energy for silicon wafers can
`be achieved in four hours at room temperature and in
`less than 10 minutes at 50° C.
`
`19 Claims, 3 Drawing Sheets
`
`1.5
`
`FLUSH SURFACE WITH
`DEIONIZED WATER TO
`REMOVE PARTICULATES
`AND DRY
`
`1.2
`
`BOMBARD WITH:
`OXYGEN IONS,
`FLUORINE ION~ OR
`A MIXTURE OF
`OXYGEN AND FLUORINE IONS
`TO ACTIVATE SURFACE
`
`1.4
`
`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
`
`

`

`U.S. Patent
`
`June 27, 1995
`
`Sheet 1 of 3
`
`5,427,638
`
`12
`
`CLEAN SURFACE
`AND REMOVE ALL
`PARTICULATES
`
`BOMBARD WITH:
`OXYGEN IONS,
`FLUORINE IONS, OR
`A MIXTURE OF
`OXYGEN AND FLUORINE IONS
`TO ACTIVATE SURFACE
`
`15
`
`FLUSH SURFACE WITH
`DEIONIZED WATER TO
`REMOVE PARTICULATES
`AND DRY
`
`CONTACT SURFACES
`TO BE BONDED
`
`16
`
`18
`
`Fig-1
`
`Fig-2
`
`14
`
`1600
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`@1200
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`
`•
`
`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
`
`

`

`U.S. Patent
`
`June 27, 1995
`
`Sheet 2 of 3
`
`5,427,638
`
`1000
`
`BOO
`
`-C\J
`"' C) 600
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`u
`
`c...
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`Fig-3
`
`Fig-4
`
`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
`
`

`

`U.S. Patent
`
`J nne 27, 1995
`
`Sheet 3 of 3
`
`5,427,638
`
`1400~-------------------------------.
`0--26
`()---"'
`
`-. .1200
`(\J
`~ u
`ci .1000
`ffi
`....__
`>-
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`LLJ
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`
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`
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`OJ
`
`0
`2:
`~ 400
`
`200
`
`Fig-5
`
`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
`
`

`

`1
`
`5,427,638
`
`LOW TEMPERATURE REACTION BONDING
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`This patent application is a continuation-in-part of
`patent application Ser. No. 894,142, entitled "Improved
`Reaction Bonding Through Activation By Ion Bom(cid:173)
`bardment" filed Jun. 4 1992, now abandoned.
`
`2
`with silicon and quartz structures. However, utilization
`of the full potential of solid-to-solid bonding to create
`structures with unique combinations of mechanical,
`electrical, optical and thermal properties has been slow
`5 to develop, and in many practical applications, suffi(cid:173)
`cient bond energy was not obtainable at bonding tem(cid:173)
`peratures that were not detrimental to some part of the
`total structure.
`The invention is an improvement to solid-to-solid
`10 reaction bonding by achieving much higher bond
`strengths at low temperatures which can increase with
`time to an acceptable value.
`
`TECHNICAL FIELD
`The invention is related to the field of bonding semi(cid:173)
`conductor materials, oxides, nitrides and glasses to each
`other and, in particular, to a low temperature reaction
`bonding method which is obtained through surface 15
`activation by oxygen and fluorine ion bombardment.
`
`SUMMARY OF THE INVENTION
`In the method for enhancing the bond energy of
`solid-to-solid reaction bonding, the surfaces to be
`bonded are polished to a roughness in the order of
`BACKGROUND ART
`atomic dimensions then cleaned to remove contami-
`nants and particulates. The cleaned surfaces are then ion
`The ability to create direct bonds between solid ob-
`jects has been useful and valuable. There are two basic 20 bombarded in a gas plasma to activate the surface. For
`many gases (H2, N2, 0 2, CF4, SF6, CF4+02, SF6+02,
`requirements for achieving useful bonds. First, a size-
`able percentage ~f th~ a!oms on the tou~hing surfaces
`etc.), there are conditions which yield some enhance-
`must be brought mto mtunate contac:t wtth each other
`ment of bond energy, but sizeable increases have only
`and sec~md, the atoms of ~e touc~g surfac.es . must
`been demonstrated for gas plasmas containing either
`react wtth ea?h other. U~til rece~t tunes,. the mtun~te
`oxygen, fluorine, or a mixture of oxygen and fluorine.
`contact reqwred ~or solid-to-solid reaction bondmg
`The highest bond energies for low temperatures have
`co~d only be achieved when a glass was one of the
`been obtained with oxygen and fluorine mixtures. After
`solids.
`f
`ion bombardment, the activated surfaces are given a
`In these types ~ bon~s, heat and pressu~e were used
`final high pressure water jet flush to remove any partie-
`to pr_octuce s~cient VIScous flow to satisfy the first 30 ulates spun dried and then contact bonded. The bond
`bondmg reqwrement and undoubtedly the heat energy
`'
`'
`.
`also promoted the reaction of the atoms of the two
`energy between the contacted surfaces can mcrease
`thereafter, at temperatures as low as room temperature,
`urf:
`6
`s
`aces.
`t
`ff:t
`al
`·
`littl
`h
`Th
`·
`0 ~ sa Is ac ory v ue m as
`The use of an intermediate adhesive layer to bond
`e as our ou:s.
`er~ IS
`solid objects together has been a long standing altema- 35 a tune-temperature trade?ff s~ch that at 200 C:· a high
`bond energy can be obtained. m ~ess than 10 mmutes.
`tive to direct solid-to-solid bonding. The advantage of
`intermediate adhesives is that these adhesives can have
`Further advantages of activating the surfaces to be
`reaction bonded ~Y oxygen and .fluorine ion. bon:bar~-
`a low viscosity which reduces the requirements on the
`morphology of the surfaces being bonded or the viscos-
`me~t ma~ be o_btained from readmg the specificatiOn m
`ity of the solid being bonded. Also, the temperature 40 conJunction with the appended figures.
`required for the desired surface reaction usually is rela-
`BRIEF DESCRIPTION OF THE ORA WINGS
`tively low. However, adhesives often have a large nega(cid:173)
`tive impact on the characteristics of the bonded struc(cid:173)
`ture.
`In the semiconductor and allied fields where it is 45
`desirable and often necessary to maintain the physical
`and electrical properties of the respective solids at their
`bonded interface, the use of intermediate adhesives are
`generally froth with problems and are avoided when(cid:173)
`ever and wherever possible.
`The development of modem semiconductor process(cid:173)
`ing technology has made it possible to produce surfaces
`smooth enough and clean enough to satisfy the first
`requirement for solid-to-solid bonding with only elastic
`deformation of the contacting surfaces. This was first 55
`reported by J. B. Lasky et al., 1985 Proceedings IEDM,
`DETAILED DESCRIPTION OF THE
`page 684, for oxidized silicon wafers. This technique
`PREFERRED EMBODIMENT
`permitted the solid-to-solid bonding of semiconductor
`The invention is directed to enhancing the reaction
`materials without any of the problems encountered
`through the use of an adhesive. A key ingredient of this 60 bonding between Si02 or Si3N4 coated semiconductor
`approach is an initial solid-to-solid bonding at room
`materials such as silicon (Si), indium phosphide (InP),
`temperatllre generally called "contacting." This con-
`gallium arsenide (GaAs), etc. Bonding enhancement has
`tacting holds the surfaces in intimate contact with each
`also been demonstrated for all glasses tested, and it is
`other in a clean high temperature furnace without the
`expected that the general procedures involved will
`complications and potential contamination encountered 65 apply to any two surfaces that contain atoms which
`when externally applied forces are used to hold the
`react with each other. The details of the process will be
`surfaces together. It was quickly recognized that this
`discussed relative to the flow diagram illustrated in
`FIG. 1. As indicated in block 10, the substrates are frrst
`technology also had potential for manufacturing sensors
`
`25
`
`FIG. 1 is a flow diagram of the process for enhancing
`the bond energy of the surfaces to be bonded;
`FIG. 2 is a graph showing the bond energy as a func(cid:173)
`tion of the energy of the oxygen ions bombarding the
`surface;
`FIG. 3 is a graph showing the variation of bond en(cid:173)
`ergy as a function of bombardment time;
`FIG. 4 shows an example of the difference in the
`bond energy of surfaces activated by oxygen plus fluo(cid:173)
`rine ion bombardment and surfaces activated by water
`after 10 minutes as a function of bonding temperature;
`FIG. 5 is a graph showing the increase in bond en(cid:173)
`ergy, at room temperature, as a function of time.
`
`50
`
`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
`
`

`

`5,427,638
`
`3
`polished so that their surface roughness is in the order
`of atomic dimensions. A surface roughness of the order
`of atomic dimensions is less than 1 nanometer and pref(cid:173)
`erably less than one-half nanometer. The polished sur(cid:173)
`face is then cleaned, as indicated by block 12, using 5
`standard cleaning methods established for cleaning
`semiconductor parts to remove contaminants and par(cid:173)
`ticulates from the surfaces to be reaction bonded. The
`use of hydrofluoric acid dips normally used in standard
`cleaning methods should be avoided for surfaces which 10
`may be etched by the hydrofluoric acid.
`In the instances where the surface to be bonded is a
`thin oxide layer grown on the polished surface, it has
`been found that the thin oxide layer assumes the mor(cid:173)
`phology of the polished substrate and does not have to 15
`be polished. Thin deposited films of reactive metals or
`insulators also follow the substrate morphology and can
`be bonded without further polishing.
`The substrate is then placed in a vacuum chamber on
`a RF powered electrode. Normally, a pressure of ap- 20
`proximately 50 millitorr within the vacuum chamber
`has been used, but it is expected that any pressure that
`can support an RF plasma is a possibility. An RF in(cid:173)
`duced DC bias on the substrate accelerates the positive
`ions in the plasma toward the surfaces to be bonded 25
`with an energy determined by the magnitude of the bias.
`As can be seen in FIG. 2, the maximum bond energies
`for the conditions examined with an oxygen plasma,
`yielded maximum bond energies with 200 V bias. The
`bond energies dropped markedly for biases below 100 30
`V. Plasmas with fluorine containing gases have yielded
`much higher bond energies with low DC bias. For
`example, a SF6 plasma activation with a 14 V substrate
`bias yielded bond energies almost as large as a 200 V
`bias with a pure oxygen plasma activation. This differ- 35
`ence can be critical when it is important to either mini(cid:173)
`mize radiation damage in an insulator or minimize con(cid:173)
`tamination due to sputtering in the chamber.
`There is little evidence that a total ion dose much
`greater than several times the number of surface atoms 40
`is of benefit. This is evident from the graph shown in
`FIG. 3, there is only a small difference in the resultant
`bond energies for an oxide exposed to a 400 e V oxygen
`ion flux as the ion bombardment time varied from 13
`seconds to 1,800 seconds. The 13 second minimum bom- 45
`bardment time of FIG. 3 does not represent a lower
`limit but simply represents the minimum time limit of
`the ionization equipment used. Calculations indicate
`that an oxygen ion dose equivalent to the surface atom
`density of the substrate would be received by the sur- 50
`face in a time period in the order of one (1) second.
`The method of producing the oxygen and fluorine
`ions may be a DC or RF voltage, or any other type of
`ionization mechanism known in the art, provided they
`are accelerated to the indicated bombarding energies. 55
`After the surfaces to be bonded have been activated
`by .oxygen ion bombardment, fluorine ion bombard(cid:173)
`ment or a mixture of oxygen and fluorine ion bombard(cid:173)
`ment, the surfaces are given a high pressure deionized
`water flush to remove any particulates, spun dried, as 60
`indicated by block 15, then contacted to each other, as
`indicated by block 16. Heating to a predetermined tem(cid:173)
`perature, as indicated by block 18, increases the bond
`energy. FIG. 4 shows the bond energies of the reaction
`bonded surfaces as a function of the temperature to 65
`which the bonded surfaces were heated for 10 minutes
`after contacting at room temperature. The bond ener(cid:173)
`gies of the surfaces which have been activated by bom-
`
`4
`bardment with a mixture of oxygen and fluorine ion are
`indicated by the blocks 20, while the range of bond
`energies of surfaces activated by a standard water acti(cid:173)
`vation process are indicated by the circles 22. As is
`evident from the data shown in FIG. 4, the bond energy
`for the surfaces activated by oxygen and fluorine ion
`bombardment are over 3 times greater than the bond
`energies of surfaces activated by the standard water
`activation over most of the bonding temperature range
`examined. Effectively, reaction bonded components in
`which the surfaces were activated by bombardment
`with oxygen ions, fluorine ions or a mixture of oxygen
`and fluorine ions, may be bonded at significantly lower
`temperatures down to room temperature.
`In general, the lower the bonding temperature, the
`greater the relative enhancement by the addition of
`fluorine ions. This trend holds down to room tempera(cid:173)
`ture with the results that some surfaces that are a little
`too rough or non-flat to be contacted with standard
`activation may be contacted after fluorine ion activa(cid:173)
`tion. Carbon tetra-fluorine (CF4), trifluoromethane
`(CHF3) and sulfur hexafluoride (SF6) have been used as
`a source of fluorine ions in the ion bombardment activa(cid:173)
`tion. When oxygen is mixed with the above gases, the
`oxygen not only supplies oxygen ions to bombard and
`react with the substrate surface along with fluorine ions,
`but it also reacts with the carbon in the CF4 and CHF3
`gases or the sulfur in the SF6 gas and frees more fluo(cid:173)
`rine.
`The procedure for activating the surface to enhance
`the bond energy using a mixture of oxygen and fluorine
`ions is the same as the procedure set forth in FIG. ].,
`with the limitation that the surfaces are bombarded with
`both oxygen and fluorine ions. The optimum ratio of
`oxygen ions to fluorine ions depends upon several fac(cid:173)
`tors such as the composition of the surfaces, their
`roughness, the bonding temperature, etc. No effort has
`been made to determine what the optimum ratio of
`oxygen to fluorine ions may be. However, we have
`found clear bond enhancements with Si02, Si3N4 and
`aluminosilicate glass surfaces for bonding temperatures
`from room temperature to 400° C. with estimated oxy(cid:173)
`gen ion to fluorine ion ratios of 4 to 1.
`Surfaces activated by oxygen and fluorine ion bom(cid:173)
`bardment may also be reaction bonded at room temper(cid:173)
`ature. It has been experimentally verified that the bond
`energy of the surfaces activated by oxygen and fluorine
`ion bombardment will progressively increase at room
`temperature (22° C.) as a function of time. Curve 24
`shown on the graph of FIG. 5 shows the increase in
`bond energy of reaction bonded silicon dioxide (Si02)
`surfaces activated by oxygen and fluorine ion bombard(cid:173)
`ment. In less than four hours (240 minutes), the bond
`energy had increased to a value (::::400 erg/cm2) re(cid:173)
`quired for satisfactory silicon wafer bonding. As is obvi(cid:173)
`ous from curve 24, the bond energy will increase to 600
`erg!cm2 in 24 hours (1440 minutes) and will double to
`800 erg!cm2in approximately 120 hours (::::7X 103 min(cid:173)
`utes). Because the bond energy eventually increases to
`values over half that for bulk SiO, it is clear that the
`room temperature bond is very reliable.
`As indicated by the circles 26, the rate at which the
`bond energy of the reaction bonded surfaces activated
`by oxygen and fluorine ion bombardment increases may
`be enhanced by a low temperature bonding at approxi(cid:173)
`mately 50° C. As illustrated by the points shown in FIG.
`4, higher bonding energies may be obtained at higher
`bonding temperatures, but relative improvement ob-
`
`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
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`

`

`5,427,638
`
`5
`6
`said method further comprising the step of heating said
`served above 200• C. is not significant. However, if
`higher bond energies or shorter times are required,
`reaction bonded surfaces to a temperature which is hot
`detrimental to any part of said structure.
`bonding at a low temperature above room temperature
`4. The method of claim 1 wherein said step of polish-
`may be used such as bonding at a temperatilre of ap-
`proximately so• C. as illustrated by the circle 26 in FIG. 5 ing produces surfaces having a roughness of less than 1
`nanometer.
`5.
`5. The method of claim 1 wherein said step of ion
`The bond energy between the activated surfaces in-
`bombarding includes the step of bombarding said
`creases with an increase in the total flux of oxygen and
`cleaned surfaces using oxygen and fluorine ions having
`fluorine ions impinged on the surfaces up to a value
`approximately equivalent to a coverage of several mon- 10 energies preferably in the range from 10 to 400 eV.
`olayers. As shown in FIG. 3, a further increase of the
`6. The method of claim 1 wherein said step of ion
`numbers of the ions impinging on the surfaces do not
`bombardment includes the step of oxygen and fluorine
`further enhance the bond energy. Similar to the increase
`ion bombardment with ions having energies of approxi-
`in bond energy with an increase in bombardment en-
`mately 20 eV to inhibit sputtering, reactive ion etching
`ergy for oxygen ions as shown on FIG. 2, there also is 15 and radiation damage.
`an increase in bond energy with the bombardment en-
`7. The method of claim 1 wherein said step of ion
`ergy of the mixture of oxygen and fluorine ions. How-
`bombarding includes the steps of:
`ever, the bombardment energy for producing a maxi-
`placing said cleaned surfaces in an ion bombardment
`mum bond energy when using a mixture of oxygen and
`chamber having a reduced pressure oxygen atmo-
`fluorine ions is lower and varies as a function of the 20
`sphere;
`material of the surface and the percentage of fluorine in
`adding a predetermined quantity of a gas containing
`the oxygen fluorine ion mixture. Preferably, the born-
`fluorine to said oxygen atmosphere;
`bardment energy of the oxygen and fluorine ions is in
`ionizing said oxygen and said gas containing fluorine
`the range from 10 to 400 eV. However, higher born-
`to produce oxygen ions and fluorine ions; and
`bardment energy may be used. Because of the potential 25
`bombarding said cleaned surfaces with said oxygen
`for contamination from materials sputtered by high
`and fluorine ions having preselected energies to
`energy ions, for certain applications, it is preferred that
`produce said activated surfaces.
`the ion energies be approximately 20 eV.
`8. A method for reaction bonding two surfaces at a
`The advantage of being able to reaction bond at tem-
`low temperature comprising the steps of:
`peratures between room temperature and 200• C. is that 30
`polishing each of the two surfaces to be reaction
`it permits the bonding of two materials whose differ-
`bonded to have a roughness less: than a predeter-
`ence in thermal expansion is sufficiently large so as to
`mined roughness;
`cleaning said surfaces to remove contaminants and
`produce mechanical stresses when reaction bonded at
`elevated
`temperatures. These mechanical stresses
`particulates which would interfere with reaction
`weaken the resultant bond. It also permits the use of 35
`bonding;
`materials which in some way may deteriorate at the
`placing said cleaned surfaces in an ion bombardment
`higher bonding temperatures. This invention, because
`chamber having a reduced pressure oxygen atmo-
`the reaction bond can take place at a low temperature,
`sphere containing a predetermined quantity of a
`removes, these limitations and permits the reaction
`gas containing fluorine;
`bonding of materials not previously compatible with 40
`ionizing said oxygen and said gas containing fluorine
`reaction bonding.
`to produce oxygen and fluorine ions;
`While the best mode for carrying out the invention
`accelerating said oxygen ions and said fluorine ions
`has been described in detail, those familiar with the art
`toward said surfaces with a predetermined energy;
`bombarding said surfaces with said oxygen and flue-
`to which this invention relates will recognize various
`alternative designs and embodiments for practicing the 45
`rine ions having energies selected to produce acti-
`invention as defmed by the following claims.
`vated surfaces; and
`What is claimed is:
`contacting said activated surfaces at room tempera-
`1. A method for reaction bonding solid surfaces at a
`ture to produce a reaction bond therebetween.
`9. The method of claim 8 wherein said step of placing
`low temperature comprising the steps of:
`polishing each solid surface to be reaction bonded to 50 includes the step of placing said two surfaces in said ion
`bombardment chamber having a reduced pressure oxy-
`have a maximum roughness of the order of atomic
`dimensions to produce polished surfaces;
`gen atmosphere containing a gas selected from the
`cleaning each of said polished surfaces to remove
`group of gases consisting of CF4, CHF3, CF6 and SF6.
`10. The method of claim 8 wherein said step of polish-
`contaminants and particulates to produce cleaned
`surfaces;
`55 ing includes the step of polishing each surface to a
`ion bombarding said cleaned surfaces with a mixture
`roughness of the order of magnitude equal to atomic
`of oxygen and fluorine ions having an energies
`dimensions.
`preselected to produce activated surfaces; and
`11. The method of claim 8 wherein said step of accel-
`placing said activated surfaces in physical contact
`erating said oxygen and fluorine ions includes the step
`with each other at room temperature to reaction 60 of accelerating said oxygen and fluorine ions to prefera-
`bond said activated surfaces.
`bly have an energy less than 400 eV.
`2. The method of claim 1 further including the step of
`12. The method of claim 11 wherein said step of ac-
`storing said reaction bonded surfaces at room tempera-
`celerating said oxygen and fluorine ions includes the
`ture to increase a bond energy between said activated
`step of accelerating said oxygen and fluorine ions to
`surfaces.
`65 have an energy of approximately 20 eV to inhibit sput-
`3. The method of claim 1 wherein said reaction
`tering, reactive ion etching, and radiation damage.
`bonded surfaces are part of a structure having different
`13. The method of claim 8 wherein said reaction
`parts which may deteriorate at elevated temperatures,
`bonded surfaces are part of a structure having compo-
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`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
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`

`7
`nents which may deteriorate at temperatures above a
`predetermined temperature, said method further com(cid:173)
`prising the step of heating said structure at a tempera(cid:173)
`ture less than said predetermined temperature to en(cid:173)
`hance the bonding energy of said reaction bonded sur- 5
`faces.
`14. A method for increasing the reaction bond energy
`between two surfaces at a low temperature comprising
`the steps of:
`polishing each of the two surfaces to be reaction 10
`bonded to have a roughness less than a predeter(cid:173)
`mined roughness;
`cleaning said two surfaces to remove contaminants
`and particulates which would interfere with reac- 15
`tion bonding;
`placing said cleaned surfaces in an ion bombardment
`chamber having a reduced pressure atmosphere of
`oxygen and a gas containing fluorine;
`ionizing said oxygen and gas containing fluorine to 20
`generate oxygen and fluorine ions;
`accelerating said oxygen and fluorine ions toward
`said cleaned surfaces with a predetermined energy;
`bombarding said cleaned surfaces with said oxygen
`and fluorine ions to produce activated surfaces;
`reaction bonding said activated surfaces; and
`
`25
`
`5,427,638
`
`8
`storing said reaction bonded surfaces for a prese(cid:173)
`lected time at said low temperature to increase the
`bond energy of said reaction bonded activated
`surfaces to a desired minimum value.
`15. The method of claim 14 wherein said bonded
`surfaces are part of a structure having at least one com(cid:173)
`ponent which may deteriorate at temperatures above a
`limiting temperature, said step of storing further in(cid:173)
`cludes the step of heating said structure to a tempera(cid:173)
`ture below said limiting temperature to enhance said
`reaction bond.
`16. The method of claim 15 wherein said step of ac(cid:173)
`celerating includes the step of accelerating said oxygen
`and fluorine ions towards said cleaned surfaces with an
`energy preferably between 10 and 400 eV.
`17. The method of claim 15 wherein said step of ac(cid:173)
`celerating includes the step of accelerating said oxygen
`and fluorine ions toward said cleaned surfaces with an
`energy of approximately 20 eV.
`18. The method of claim 15 wherein said step of stor(cid:173)
`ing includes the step of storing said reaction bonded
`surfaces at room temperature for at least 4 hours to
`increase the bond energy to a desired minimum value.
`19. The method of claim 14 wherein said low temper(cid:173)
`ature is room temperature.
`* * * * *
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`35
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`40
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`45
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`60
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`65
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`TSMC1010
`IPR of U.S. Pat. No. 7,335,996
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