(12) United States Patent
`Fiordalice et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,218,733 B1
`Apr. 17, 2001
`
`US006218733B1
`
`(54) SEMICONDUCTOR DEVICE HAVINGA
`TITANIUM-ALUMINUM COMPOUND
`
`(75) Inventors: Robert W. Fiordalice, Austin; Stanley
`M. Filipiak, P?ugerville; Johnson
`
`Olufemi Olowolafe; Hisao Kawasaki, both of Austin, all of TX (US)
`
`(73) Assignee: Motorola Inc., Schaumburg, IL (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`USC‘ 154(k)) by 0 days‘
`(21) A 1 N 08/254 854
`pp .
`0.:
`,
`
`5,306,952 * 4/1994 Matsuura etal. .................. .. 257/763
`5,312,775 * 5/1994 Fujii et al. ......................... .. 437/192
`5,313,101 * 5/1994 Harada et al.
`257/763
`5,360,995
`11/1994 Graas ................................. .. 257/751
`
`03256362 * 11/1991 (JP) .................................... .. 257/764
`
`*
`
`.
`
`cued by exammer
`
`.
`
`Primary Examiner—Roy Potter
`(74) Attorney, Agent, or Firm—George R. Meyer
`
`(22) Filed:
`
`Jun. 6, 1994
`
`(57)
`
`ABSTRACT
`
`,
`,
`Related U'S' Apphcatlon Data
`
`The present invention includes a process for forming an
`intermetallic layer and a device formed by the process. The
`
`(62) Division of application No. 08/024,042, ?led on Mar. 1,
`1993, now Pat. No. 5,358,901.
`(51) Int Cl 7
`H01L 23/48
`.
`.
`........................................
`........ ..
`~
`'
`(52) US. Cl. ........................ .. 257/751, 257/758, 225577776741,
`,
`(58) Fleld of Search """""
`
`'
`’
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`’
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`’
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`(56)
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`’
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`process Includes a reacnon stépwhere a metal'contalmng
`layer reacts With a metal-contammg gas, wherein the metals
`of the layer and gas are different. In one embodiment of the
`present invention, titanium aluminide may be formed on the
`Sides of an interconnect‘ The process may be performed in
`a variety of equipment, such as a furnace, a rapid thermal
`processor, a plasma etcher, and a sputter deposition machine.
`The reaction to form the intermetallic layer is typically
`performed While the substrate is at a temperature no more
`than 700 degrees Celsius.
`
`4,884,123
`
`11/1989 DiXit et al. ........................... .. 357/71
`
`6 Claims, 3 Drawing Sheets
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`US 6,218,733 B1
`
`1
`SEMICONDUCTOR DEVICE HAVING A
`TITANIUM-ALUMINUM COMPOUND
`
`This is a continuation divisional of application Ser. No.
`08/024,042, ?led Mar. 1, 1993 now US. Pat. No. 5,358,901
`?led on Oct. 25, 1994.
`
`FIELD OF THE INVENTION
`
`The present invention relates to the ?eld of semiconductor
`devices, and in particular, to processes for forming an
`intermetallic by reacting a metal With a gas and devices
`formed by the process.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`An intermetallic material is a material that comprises a
`plurality of metallic elements. Intermetallic materials, in
`Which one of the metallic elements is a refractory metal, are
`used in the aviation and aerospace industries. Refractory
`metal intermetallics are sometimes used in aircraft parts
`because of their light Weight and durability compared to
`other metals. In the aviation and aerospace industry,
`refractory-metal intermetallics are usually formed at tem
`peratures of at least 800 degrees Celsius. Such a high
`temperature of formation is unacceptable for the semicon
`ductor industry. The intermetallics are usually part of a
`contact, interconnect, or via and are formed relatively late in
`a semiconductor process How (after a silicide layer or doped
`regions, such as emitter or source/drain regions, have been
`formed). Heating a substrate to a temperature higher than
`about 700 degrees Celsius is generally undesired.
`Within the semiconductor industry, intermetallic materi
`als are being investigated to examine their ability to reduce
`electromigration and oxidation of metals Within contacts or
`interconnects. An example of an intermetallic used in the
`semiconductor industry is titanium aluminide (TiAl3). Tita
`nium aluminide may be formed by sputtering or evaporating
`a layer of aluminum, sputtering or evaporating a layer of
`titanium, and reacting the layers to form titanium aluminide.
`This method of forming titanium aluminide is actually a type
`of solid-solid reaction because one solid reacts With another
`solid.
`Although the solid-solid reaction that forms titanium
`aluminide is typically performed at a temperature less than
`700 degrees Celsius, the process suffers from several detri
`ments. As used in this speci?cation, intermetallic step cov
`erage is de?ned as the thickness of the intermetallic layer at
`its thinnest point along the side of a patterned metal layer
`divided by the thickness of the intermetallic layer formed on
`the top of the patterned metal layer. The intermetallic step
`coverage is expressed as a percentage. Using the solid-solid
`reaction that forms titanium aluminide, the intermetallic step
`coverage is typically no more than 10 percent and may even
`reach 0 percent in Which case, the titanium aluminide is not
`formed along all of the sides of the aluminum layer.
`Electromigration, oxidation, and hillock formation may not
`be suf?ciently reduced in a lateral direction because of the
`loWer intermetallic step coverage. The unreacted titanium
`may: 1) form undesired electrical connections because of
`etch complications, 2) have undesired reactions before form
`ing or With subsequently formed layers that contact the
`unreacted titanium, or 3) complicated a subsequent pattern
`ing step during the formation of interconnects.
`
`SUMMARY OF THE INVENTION
`
`The present invention includes a process for forming an
`intermetallic layer by reacting a metal layer over a substrate
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`With a metal-containing gas, Wherein the metals in the layer
`and the gas are different. The present invention also includes
`a device formed using the process. In one embodiment, a
`titanium aluminide layer is formed by reacting an
`aluminum-containing layer With titanium tetrachloride,
`Which is a gas during the reaction. The gas alloWs the
`titanium aluminide layer to be formed on exposed sideWalls
`of a patterned aluminum-containing layer. Different embodi
`ments of the invention may use a furnace, a rapid thermal
`processor, a plasma etcher, or a sputter deposition machine
`for a reactor. An embodiment of the present invention forms
`an intermetallic layer formed While the substrate is at a
`temperature no higher than 700 degrees Celsius during the
`reaction.
`Other features and advantages of the present invention
`Will be apparent from the accompanying draWings and from
`the detailed description that folloWs.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The present invention is illustrated by Way of example
`and not limitation in the ?gures of the accompanying
`draWings, in Which like references indicate similar elements,
`and in Which:
`FIGS. 1—3 each include cross-sectional vieWs of a portion
`of a substrate at various process steps in forming a titanium
`aluminide layer in accordance With one embodiment of the
`present invention.
`FIGS. 4—8 each include cross-sectional vieWs of a portion
`of a substrate at various process steps in forming a titanium
`aluminide layer in accordance With another embodiment of
`the present invention.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS
`
`The present invention includes a process for forming an
`intermetallic layer by reacting a metal layer over a substrate
`With a metal-containing gas, Wherein the metals in the layer
`and the gas are different. The present invention also includes
`a device formed using the process. Embodiments of the
`invention describe the use of the invention in a furnace, a
`rapid thermal processor, a plasma etcher, or a sputter depo
`sition machine. The intermetallic layer is typically formed
`While the substrate is at a temperature no higher than 700
`degrees Celsius. TWo examples are described immediately
`beloW. Bene?ts, fabricating options, and general reactions
`are described later in the speci?cation.
`
`EXAMPLE 1
`
`FIG. 1 includes a cross-sectional vieW of a semiconductor
`substrate prior to forming an interconnect. Adoped region 11
`lies Within a silicon substrate 10. Apatterned insulating layer
`12 lies over the substrate and includes a contact plug 13 to
`the doped region 11. The contact plug 13 includes a titanium
`silicide layer 131, a titanium nitride layer 132, and a
`tungsten layer 133. A metal layer is deposited on the
`insulating layer 12 and the contact plug 13 by a sputter
`deposition process. The metal layer is about 98 Weight
`percent aluminum With about 1 Weight percent silicon and
`about 1 Weight percent copper. The metal layer is patterned
`to form interconnects 21 and 22 as shoWn in FIG. 2.
`The substrate including the interconnects 21 and 22 are
`placed into a rapid thermal processor
`The RTP is
`pumped doWn to evacuate the reaction chamber of the RTP.
`After being pumped doWn, the temperature of the reaction
`chamber is adjusted to about 375 degrees Celsius. The
`
`

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`US 6,218,733 B1
`
`3
`substrate becomes about the same temperature as the reac
`tion chamber prior to performing the reaction. Gases includ
`ing titanium tetrachloride (TiCl4) at about 10 standard cubic
`centimeters per minute (SCCM), hydrogen (H2)at about 100
`SCCM, and argon
`at about 20 SCCM are introduced
`into the reaction chamber, and the reaction chamber pressure
`is adjusted to about 150 millitorr. The substrate is allowed to
`react With the gas at the pressure for about 45 seconds. The
`reaction forms titanium aluminide (TiAl3) layers 31 and 32
`that are each about 225 angstroms thick and are shoWn in
`FIG. 3. Aluminum chloride (AlCl3) is also a product of the
`reaction and is a gas during the reaction. After the substrate
`is removed from the RTP, only the titanium aluminide layers
`31 and 32 that are formed along the sides of the intercon
`nects 31 and 32 contact the insulating layer 12. Virtually no
`unreacted titanium is formed on the insulating layer 12. The
`reactor is purged With a relatively inert gas, such as nitrogen,
`argon, and the like, the reactor temperature is loWered, and
`the pressure is alloWed to reach about atmospheric pressure.
`The substrate is then removed from the RTP.
`
`EXAMPLE 2
`
`In another embodiment, the titanium aluminide layer may
`be formed from a portion of an aluminum layer that lies at
`the bottom of a via opening. As shoWn in FIG. 4, a doped
`region 11 lies Within a substrate 10. A patterned insulating
`layer 12 includes an opening With a contact plug, Which
`includes a titanium silide layer 131, a titanium nitride layer
`132, and a tungsten layer 133. After forming the contact
`plug, a ?rst metal layer 41, Which includes about 98 Weight
`percent aluminum, about 1 Weight percent silicon, and about
`1 Weight percent copper, is deposited over the patterned
`insulating layer 12 and the contact plug. A titanium nitride
`layer 42 is deposited on the ?rst metal layer 41. The ?rst
`metal and titanium nitride layers 41 and 42 are patterned to
`form a ?rst-level interconnect 40 as shoWn in FIG. 4.
`Apatterned interlevel dielectric (ILD) layer 51 is formed
`by depositing and etching a dielectric layer. The patterned
`ILD layer 51 includes a via opening 52. Although the
`titanium nitride layer 42 should act as an etch stop during the
`formation of the via opening 52, some or all of the titanium
`nitride layer 42 is etched. FIG. 5 includes an illustration in
`Which all of the titanium nitride layer 42 along the bottom
`the via opening 52 has been removed by the etch that forms
`the via opening 52. The metal layer 41 that lies at the bottom
`of the via opening 52 is exposed and may be attacked by
`chemicals. The ?rst-level interconnect 40 is more suscep
`tible to electromigration if a capping layer is not formed on
`the ?rst metal layer 41.
`Referring to FIG. 6, the substrate including the exposed
`?rst metal layer 41 at the bottom of the via opening 52 is
`placed into an RTP to form a titanium aluminide layer 61
`from a portion of the aluminum Within the ?rst metal layer
`41 that lies at the bottom of the via opening 52. The titanium
`aluminide is formed at about the same conditions as listed in
`the embodiment of Example 1. After the substrate is
`removed from the RTP, the titanium aluminide layer 61 is
`formed only along the bottom of the via opening 52 and does
`not contact the ILD layer 51 except near the bottom of the
`via opening 52. Virtually no unreacted titanium is formed on
`the ILD layer 51.
`FIG. 7 includes a cross-sectional vieW of the semicon
`ductor substrate after forming a second-level interconnect.
`The via opening 52 is ?lled to form a via plug. The via plug
`includes the previously described titanium aluminide layer
`61. The ia plug further includes a titanium nitride layer 72
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`and a tungsten layer 73. The formation of the titanium nitride
`and tungsten layers 72 and 73 Within the via opening 52 is
`performed using a conventional process. A second metal
`layer, Which includes 98 Weight percent aluminum, about 1
`Weight percent silicon, and about 1 Weight percent copper,
`is deposited on the ILD layer 51 and the via plug. The
`second metal layer is patterned to form the second-level
`interconnect 74 as shoWn in FIG. 7. Referring to FIG. 8, the
`substrate is placed in an RTP and exposed to an ambient
`including titanium tetrachloride to form a titanium alur
`ninide layer 84 on the second-level interconnect 74. The
`reaction conditions are the same as those used in the
`embodiment of Example 1. Apassivation layer 81 is formed
`over the titanium aluminide layer 84 and the ILD layer 51 to
`form a substantially completed device.
`Bene?ts and Fabrication Options of the Examples
`The embodiments described above includes many ben
`e?ts. Titanium aluminide helps to reduce electromigration
`and is more oxidation resistant compared to aluminum,
`titanium, and other titanium-containing compounds. The
`titanium aluminide is formed by reacting gaseous titanium
`tetrachloride With aluminum in the interconnect Without
`sputtering or evaporating titanium. Therefore, titanium alu
`minide is formed on all exposed surfaces of the interconnect,
`Which includes the sides. The intermetallic step coverage
`may be about 100 percent With the embodiments. As Will be
`described later, the titanium aluminide may be formed using
`a plasma method. Although the plasma method may have
`loWer intermetallic step coverage compared to the embodi
`ments of the examples, the intermetallic step coverage is
`typically at least 50 percent. Hillocks may be formed in a
`vertical or a lateral direction. The ability to form titanium
`aluminide With at least 50 percent intermetallic step cover
`age reduces the likelihood of forming lateral hillocks com
`pared to the solid-solid reaction that forms titanium alu
`minide.
`The embodiments of the Examples do not form an unre
`acted titanium layer. The solid-solid reaction that forms
`titanium aluminide may have unreacted titanium remaining
`after the reaction. Any unreacted titanium from the solid
`solid reaction that forms titanium aluminide typically needs
`to be removed after the reaction to form titanium aluminide.
`Removal of the unreacted titanium must be selected to both
`aluminum and titanium aluminide. Many etchants that etch
`titanium also etch aluminum. There is also a risk that the
`etchants that etch titanium also may etch titanium aluminiZe.
`If unreacted titanium Were not removed, the unreacted
`titanium may cause problems. The volume of aluminum and
`titanium before reaction is more than the volume of titanium
`aluminide formed by the reaction. Consider the folloWing
`situation. Layers of aluminum and titanium are deposited
`and patterned to form an interconnect. In this example, the
`solid-solid reaction betWeen the layers occurs, but not all of
`the aluminum and titanium layers are consumed by the
`solid-solid reaction. An insulating layer is placed over the
`interconnect. Subsequent thermal cycles may cause the
`unreacted titanium to further react With the aluminum layer.
`Because the volume of the titanium aluminide formed by the
`reaction is less than the volume of titanium and aluminum
`used in forming the titanium aluminide, the interconnect
`effectively shrinks in siZe thereby forming a void betWeen
`the interconnect and the insulating layer. Aluminum layers
`typically have tensile stress. The presence of a void may
`alloW the aluminum layer to peel aWay from the substrate,
`Which is undesirable.
`The unreacted titanium may cause other problems. If the
`titanium-sputter method Was used to form titanium alu
`
`

`
`US 6,218,733 B1
`
`5
`minide Within the via opening 52 of FIG. 5, unreacted
`titanium probably Would lie on the ILD layer 51 and on the
`titanium aluminide that is formed at the bottom of the via
`opening 52. If the unreacted titanium that lies on the
`titanium aluminide Within the via opening 52 is not
`removed, the unreacted titanium may react With oxygen or
`air to form a titanium-oxide material, Which is generally
`undesired. The resistance Within the via plug may be too
`high. In addition, the unreacted titanium may react With
`subsequently formed layers. Therefore, the unreacted tita
`nium may: 1) form undesired electrical connections because
`of etch complications, 2) have undesired reactions before
`forming or With subsequently formed layers that contact the
`unreacted titanium, or 3) complicated a subsequent pattern
`ing step during the formation of interconnects. The method
`of the present invention does not have the detriments of the
`solid-solid reaction that forms titanium aluminide. The tita
`nium of the titanium chloride reacts With the aluminum of
`the interconnect, and does not form unreacted titanium over
`the substrate. Therefore, complications that arise due to
`unreacted titanium do not exist With the present invention.
`Another bene?t of the present invention is the variety of
`equipment and processing conditions that may be used to
`form the titanium aluminide. The reaction to form titanium
`aluminide may be performed in a furnace, an RTP, sputter
`deposition machine, or etching equipment. Speci?c appli
`cations using these tvpcs of equipment are described later.
`The aluminum source is typically a metal layer that usually
`has at least 95 percent aluminum and/or small amounts of
`silicon or copper. The metal layer may include an amount of
`aluminum, Which is less than 95 percent. The titanium
`source should be a gas during the reaction With aluminum,
`and a compound Within the gas includes titanium and
`typically chlorine atoms. Titanium sources may include
`titanium tetrachloride, titanium-chloride-halide compounds,
`or organotitanium compounds that have chlorine radicals. If
`the titanium source does not have any chlorine atoms, a
`chlorine-containing gas, such as molecular chlorine (C12)
`may be added. The gas may consist of the titanium source or
`further include a non-oxidiZing diluent. The non-oxidiZing
`diluent may be hydrogen, argon, helium, nitrogen, or chlo
`rine. When the gas includes a diluent, the titanium source
`usually comprises no more than about 25 volume percent of
`the total gas composition.
`The pressure of the reaction chamber during the reaction
`is no higher than about atmospheric pressure. The highest
`pressure that may be used may depend on the titanium
`source. Titanium tetrachloride is a liquid at atmospheric
`pressure. Therefore, the reaction chamber must be under a
`vacuum When using titanium tetrachloride. For most
`applications, the pressure during reaction is no higher than
`about 500 millitorr. The actual ?oW rates of the titanium
`source and/or diluent depends on the reactor chamber pres
`sure and volume. The How rates typically are larger for
`higher pressures or larger volumes. The actual gas ?oWs
`listed in the embodiment of Example 1 are illustrative and
`not limiting.
`The substrate temperature during the reaction to form
`titanium aluminide is usually no higher than about 550
`degrees Celsius. For most applications, the substrate tem
`perature is no higher than 450 degrees Celsius. The reaction
`time depends on the temperature, pressure, and gas compo
`sition. Reaction times are addressed beloW With regards to
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`speci?c applications. The thickness of the titanium alu
`minide formed in the embodiment of Example 1 is about 225
`angstroms. The thickness of titanium aluminide using the
`method of the present invention has no knoWn limits, and a
`titanium aluminide layer betWeen about 2600—3000 ang
`stroms has been formed. For most applications, the thickness
`of the titanium aluminide is enough to achieve a desired
`resistance to electromigration or oxidation and is usually no
`thicker than 1000 angstroms.
`
`Applications With Various Pieces of Equipment
`The embodiments of the Examples Were performed using
`an RTP. In general, the reaction chamber When using the
`RTP is usually 300—450 degrees Celsius, and the reaction
`time is betWeen 10—300 seconds. The substrate has about the
`same temperature as the reaction chamber of the RTP during
`the reaction. Afurnace may be used for the reaction, but the
`furnace must be able to be evacuated to remove oxidiZing
`species. An example of such a furnace is a chemical vapor
`deposition furnace that is used to deposit ?lms, such as
`silicon dioxide, polysilicon, or silicon nitride. The furnace
`may be a single-Wafer processor or a batch processor. For a
`single-Wafer processor, the reaction conditions for the RTP
`may be used. Most batch processor types of furnaces are not
`able to perform a controlled reaction for a time in a range of
`10—300 second. The batch processor types of furnace may
`have reaction times up to 30 minutes. For example, a batch
`processor type of furnace may operate With a reaction
`chamber temperature of about 200 degrees Celsius. The
`substrates are at about the same temperature as the reaction
`chamber. The reaction time can be adjusted to about 10
`minutes at about 200 degrees Celsius by adjusting the
`reaction chamber pressure and the gas composition of the
`reaction chamber. LoWer pressures and less titanium source
`concentration Within the gas usually causes the reaction time
`to increase for a constant temperature.
`Titanium aluminide may be formed using a plasma, Which
`is an ioniZed gas. A plasma reaction may be used to form
`titanium aluminide. The temperature of the substrate should
`be about the same as it is for the RTP or furnace reaction. In
`an RTP or furnace, the temperature of the substrate is about
`the same as the reaction chamber itself. In a plasma reactor,
`the substrate may be placed on a susceptor that is maintained
`at a different temperature compared to the plasma. The
`substrate temperature should be adjusted to be at about the
`same temperature as listed above With respect to an RTP or
`furnace. The plasma reaction should occur at a faster rate
`compared to an RTP or furnace reaction performed at the
`same temperature. The parameters of the plasma may need
`to be adjusted, so that the titanium aluminide forms on both
`top and side surfaces of an exposed interconnect. Higher
`reactor pressure and loWer poWer may be used to form
`titanium aluminide along the sides of an interconnect. If the
`titanium aluminide is not to be formed on the sides of an
`interconnect, the plasma does not need this type of adjusting.
`Equipment capable of forming a plasma include furnaces,
`plasma etchers, and sputter deposition machines. A plasma
`enhanced deposition furnace is an example of one type of
`furnace that may be used.
`Complications may occur With a plasma etcher, but the
`complications are not insurmountable. In the embodiments
`
`

`
`US 6,218,733 B1
`
`7
`of the examples, patterning steps may be performed using
`photoresist masks. A hard mask may be used to allow the
`titanium aluminide reaction to occur Without exposing an
`aluminum-containing interconnect to oxygen or air. For
`example, consider forming titanium aluminide on an inter
`connect that lies at the bottom of a via opening. After an
`interconnect is formed, a relatively thick silicon dioxide
`layer and a relatively thin silicon nitride layer are sequen
`tially deposited over the interconnect. Aphotoresist mask is
`formed on the silicon nitride layer and includes a photoresist
`opening Within the photoresist mask that lies over the
`interconnect. A silicon nitride layer opening is etched
`through the silicon nitride layer and the photoresist mask is
`removed. The silicon dioxide layer opening is etched using
`the silicon nitride layer as a hard mask. The silicon dioxide
`layer is etched in a plasma etcher to form a silicon dioxide
`layer opening that extends through the silicon dioxide layer
`to the interconnect. The combination of the silicon dioxide
`layer opening and the silicon nitride layer opening form a via
`opening. A titanium aluminide layer is formed from a
`portion of the aluminum in the interconnect at the bottom of
`the via opening after the via opening is formed and before
`the interconnect at the bottom of the via opening is exposed
`to oxygen, air, or atmospheric pressure.
`A sputter deposition machine may also be used for the
`formation of titanium aluminide. Many types of sputter
`deposition machines have a plurality of chambers, Which
`can be heated to temperatures of at least 450 degrees
`Celsius. A substrate is placed into the machine, and the
`substrate is placed under a vacuum. A metal layer including
`aluminum is deposited over a substrate in a ?rst chamber
`using a conventional sputter deposition method. After
`depositing the metal layer, the substrate is moved to a second
`chamber Without exposing the metal layer to oxygen, air, or
`atmospheric pressure. The reaction to form titanium alu
`minide is performed in the second chamber. The reaction
`may occur at conditions similar to those used for an RTP if
`the chamber can be heated, or the reaction may be a plasma
`reaction, Wherein the plasma is directed at the substrate
`instead of a sputtering target.
`
`General Reactions
`
`Although much of the speci?cation has focused on tita
`nium aluminide, the present invention is not limited to
`titanium aluminide. The general reaction equation for the
`formation of the intermetallics in accordance With an
`embodiment of the present invention and the titanium alu
`minide reaction of the embodiment of Example 1 are as
`folloWs:
`
`Metal 1(s)+Other Reactant including Metal 2(g)—>Metal 1—Metal
`2 Intermetallic(s)+Other Product (g)
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`The phases (solids and gases) listed are the phases of the
`reactants and products during the reaction itself. As can be
`seen, the reaction to form the Metal 1-Metal 2 Intermetallic
`(titanium aluminide) is a type of solid-gas reaction, as
`opposed to a solid-solid reaction that may occur With
`deposition methods that include sputtering, evaporating, or
`chemical vapor depositing (CVD). The reaction does not
`form an unreacted Metal 2 solid on the Metal 1 or the Metal
`
`65
`
`8
`1-Metal 2 Intermetallic. In the case of the embodiments
`described above, unreacted titanium is not formed on the
`aluminum layer or the titanium aluminide layer. In the
`reaction, the Metal 1 (aluminum) and the Metal 1-Metal 2
`Intermetallic (titanium aluminide) are the only solids. The
`other reactant (titanium tetrachloride) and product
`(aluminum chloride) are gases during the reaction. Although
`the singular form of other reactant or other product is used,
`a plurality of other reactants may be used, or a plurality of
`other products may be formed. Because the other reactants
`and other product are gases, the unreacted portion of the
`other reactant and the other product may be easily removed.
`If diluents are used, they should also be gases during the
`reaction. A separate process step to remove unreacted
`reactants, Which typically occurs With a sputter deposition
`process, is not needed. In addition, because the other reac
`tant and product are not liquids or solids, particle and
`contamination problems are typically reduced compared to
`a sputter deposition process. The reaction typically occurs at
`the surface of a metal and not on insulating or dielectric
`layers. Therefore, the intermetallic may be formed in a
`self-aligned manner Without the need for a separate pattern
`ing step.
`Metal 1 can be any metal. In many semiconductor
`applications, metal 1 is copper or aluminum. The layer of
`Metal 1 may include small amounts of impurities. The other
`reactant includes Metal 2. Usually, the other reactant
`includes a metal halide or an organometallic compound.
`Because many metals etch With chlorine, the other reactant
`typically includes a metal chloride, a metal-chlorine halide
`or an organometallic compound With a chlorine radical that
`is attached to a metal atom. If the Metal 2 gas does not
`include any chlorine atoms, a chlorine-containing gas may
`be added, such as molecular chlorine. In semiconductor
`applications, the other reactant normally includes a transi
`tion element, and more speci?cally, a refractory metal, such
`at titanium, tungsten, tantalum, molybdenum, cobalt, and the
`like. In the embodiments of the Example 1, Metal 1 is
`aluminum and the other reactant is titanium tetrachloride.
`The selection of the other reactant may in part be determined
`by the Metal 1 and the fact that the other product needs to
`be a gas. In the embodiment of Example 1, the other reactant
`is titanium tetrachloride Which reacts With the aluminum to
`form for aluminum trichloride (AlCl3), Which is a gas during
`the reaction (at the reacting conditions). Although speci?c
`materials are listed above With respect to Metal 1 and the
`other reactant, the speci?c materials listed are to be illus
`trative and not limiting.
`The substrate should be at a temperature no higher than
`700 degrees Celsius during the reaction. Above 700 degrees
`Celsius, undesired complications may arise. Above 550
`degrees Celsius, a barrier layer typically degrades in per
`formance (as a barrier layer) and is generally not desired. In
`the embodiment of Example 1, the substrate Will normally
`be at a temperature no higher than 450 degrees Celsius
`during the reaction. Therefore, the reaction in the embodi
`ment of Example 1 should not have the problems discussed
`Within this paragraph.
`In the foregoing speci?cation, the invention has been
`described With reference to speci?c embodiments thereof. It
`Will, hoWever, be evident that various modi?cations and
`changes can be made thereto Without departing from the
`broader spirit or scope of the invention as set forth in the
`appended claims. The speci?cation and draWings are,
`
`

`
`US 6,218,733 B1
`
`9
`accordingly, to be regarded in an illustrative rather than a
`restrictive sense.
`What is claimed is:
`1. A semiconductor device comprising:
`
`a substrate;
`a patterned ?rst metal layer overlying the substrate,
`Wherein the patterned ?rst metal layer includes alumi
`num;
`an insulating layer including an opening that overlies the
`patterned ?rst metal layer;
`a via structure that lies adjacent to the patterned ?rst metal
`layer and lies at least partially Within the opening,
`Wherein:
`the via structure includes a titanium-aluminum com
`pound; and
`the via structure does not include a layer of elemental
`titanium; and
`a patterned second metal layer overlying the via structure.
`2. The device of claim 1, Wherein the via structure further
`comprises a barrier layer overlying the titanium-aluminum
`compound.
`3. The device of claim 1, Wherein:
`the titanium-aluminum compound lies on the patterned
`?rst metal layer;
`
`10
`a titanium nitride layer lies on the titanium-aluminum
`compound and Within the opening but does not overlie
`a top surface of the insulating layer;
`a tungsten layer lies on the titanium nitride layer and
`Within the opening; and
`the patterned second metal layer lies on the tungsten layer.
`4. The device of claim 1, Wherein:
`each of the patter