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`USOOSZ81485A
`.
`[11] Patent Number:
`5,281,485
`[19]
`Unlt-ed States Patent
`
`Colgan et al. Jan. 25, 1994 [45] Date of Patent:
`
`
`4
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`Peter M. Fryer, Mamaroneck, both
`of NY
`
`[73] Assignee:
`
`International Business Machines
`Corporation, Armonk, N-Y-
`
`1211‘ Appl- No“ 31959.
`,
`
`[63]
`
`Related 113 Application Data
`.
`V
`Contmuanon of Ser. No. 604,556, Oct. 26, 1990, aban-
`donm'
`Int. Cl.5 ............................................ ..1332315/04
`[51]
`[52] U.S. c1. .................................. ..428/457; 428/469;
`428/472; 428/698; 428/704; 428/938;
`204/192 15- 204/192 17 204/192 21- 36/305-
`'
`1
`'
`1
`'
`1501/13;
`[58] Field of Search ............. .. 427/250, 252, 253, 294;
`501/134; 428/469, 472, 215, 216, 457, 938, 698,
`704; 204/19215, 192.17, 192.21; 361/305
`
`-
`FOREIGN PATENTDOCUMENTS
`1015143
`9/1962 United Kingdom ......... ..204/192.21
`OTHER PUBLICATIONS
`R. Petrovic et 211., “Electrical and Structural Properties
`of Tantalum Nitride Films Deposited by Sputtering,"
`Thin Solid FilmS, vol. 57, pp. 333—336 (1979).
`L. I. Maissel, et al., “Handbook. of Thin Film Technol-
`ogy,” McGraw—Hill, Inc., pp. 18—12 to 18—13 (1970).
`L. G. Feinstein, et 11]., “Factors Controlling the Struc-
`ture of Sputtered Ta Films,” Thin Solid Films, vol. 16,
`
`N. Schwartz, et al., “Impurity Effects in the Nucleation
`of Alpha (bcc)—Tantalum or Beta-Tantalum Films,” J.
`Electrochem. Soc: Solid-State Science and Technol-
`ogyy VOL 124! NO, 1’ pp. 12343] (Jan 1977)‘
`Pearson’s Handbook of Crystallographic Data for In-
`termetallic Phases vol. 3, American Society for Metals,
`pp. 3218, 2791 and 2792.
`Binary Alloy Phase Diagrams, Second Edition, Ameri-
`ca” society for Memls' “1'” Phase Diagram PP‘
`2703—2704.
`Primary Examiner—Ellis P. Robinson
`Assistam Examiner—Timmhy M. Speer
`Attorney, Agent, or Firm—Aziz M. Ahsan
`
`[561
`
`I
`
`ABSTRACT
`[57]
`to a structure
`resent invention relates
`enerall
`The
`y
`P
`.
`g
`-
`-
`and a method of making Alpha-Ta films, and more
`U s PATENT DO
`particularly, to a structure and a method of making
`3,406.043 11/1964 Balde ................................. .. 428/216
`3,558,461 - 1/1971 Parisi ............
`1?? Alpha-Ta in thin films. A seed layer of Ta reactiver
`3.663,408
`5/1972 Kumagai et 211.
`2
`/ 9"
`sputtered in a nitrogen containing environment
`is
`3,847,658 11/1974 Kumagai
`.... ..
`grown on the substrate, and using this seed layer of
`..
`3,878,079
`4/1975 Schauer
`. 204/192 SP
`4.058445 11/1977 Anders ........... ..
`Tam) layers 0f Alpha'Ta are the“ “med-
`204/15
`4.251.326
`2/1981 Arcidiacono et a1.
`_
`4,364,099 12/1982 Koyama at a].
`.................. .. 361/305
`26 Claims, 3 Drawing Sheets
`
`References Cited
`CUMENTS
`
`
`
`ALP HA—To
`
`SUBSTRATE
`
`To N
`
`Page 1 0f 9
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`TSMC Exhibit 1035
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`TSMC V. IP Bridge
`IPR2016—01249 & IPR2016-01264
`
`Page 1 of 9
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`

`

`US. Patent
`
`Jan. 25, 1994
`
`Sheet 1 of 3
`
`5,281,485
`
`BETA—Ta
`
`SUBSTRATE
`
`
`
`
`
`
`
`,
`
`
`
`
`
`1A
`FIG.
`(PRIOR ART)
`
`TG(N) 16—5_OOA FIG; EB
`
`N2 VARIED FIG. 38
`
`250A TO(N)
`
`Page 2 0f 9
`
`Page 2 of 9
`
`

`

`
`
`TOTAL
`
`RESISTIVITY
`(MICRO OHM—CM)
`
`500A To ON T0(N) SEED LAYER
`
`
`
`210
`
`190
`
`170
`
`150
`
`130
`
`110
`
`90
`
`7O
`
`50
`
`30
`
`200
`
`400.
`
`FIG. 2A
`
`T0(N) SEED LAYER THICKNESS (A)
`
`mm'S'n‘
`
`
`
`17661‘SZ"WI'
`
`9JOZlam-IS
`
`ssv‘Isz‘s
`
`Page 3 of 9
`
`

`

`c:
`jm
`
`wa
`
`:
`a,
`:3H.
`
`3
`
`1.
`"'5
`
`6%,
`
`2°
`3
`
`'
`“3
`f3
`
`.l)
`00
`(II
`
`230
`
`250A To/ZSOA To(N)
`
`
`TOTAL
`RESISTIVlTY
`(MICRO OHM—CM)
`
`210
`
`190
`
`170
`
`150
`
`130
`
`110
`
`90
`
`70
`
`50
`
`30
`
`o
`FIG 3A
`
`u
`
`.
`
`‘
`
`20
`1o
`%N2 IN Ar SPUTTER GAS FOR T0(N) LAYER
`
`30
`
`.
`
`Page 4 of 9
`
`

`

`1
`
`5,281,485,
`
`
`
`STRUCTURE AND METHOD OF MAKING
`ALPHA-TA IN THIN FILMS
`
`This patent application is a continuation of U5. pa-
`tent application Ser. No. 07/604,556, filed on Oct. 26,.
`1990, now abandoned.
`FIELD OF THE INVENTION
`
`The present invention relates generally to.a structure
`and a method of making alpha-Ta films, and more par—
`ticularly, to a structure and a method of making alpha-
`Ta in thin films. A seed layer of Ta reactively sputtered
`in a nitrogen containing environment is grown on the
`substrate, and using this seed layer of Ta(N) layers of
`alpha-Ta are then formed.
`BACKGROUND OF THE INVENTION
`
`Tantalum metal has two crystalline phases: the low
`resistivity (12—20 micro-ohm-cm) alpha (bcc) (body
`centered cubic) phase and a higher resistivity (160—170
`micro-ohm-cm) beta (tetragonal) phase. Due to the
`lower resistivity of the alpha phase, it is preferred for
`electronic applications over the beta phase.
`Tantalum films are generally deposited by magnetron
`sputtering; however, the beta phase is usually formed
`for films of typical thickness (less than 3000 angstroms)
`which are deposited by conventional sputtering meth—
`ods. This is illustrated in FIG. 1A, where beta-tantalum
`has been formed on a substrate.
`Most of the literature is inconsistent regarding meth-
`ods for reproducibly depositing a particular phase of
`tantalum in a' predictable fashion. Some researchers
`have produced results which suggest that there are tWo
`main variables which determine what phase of tantalum
`is grown: the first variable is the substrate temperature
`during deposition and the second variable is the amount
`of gaseous contamination in the vacuum system. This
`has been discussed by L. Maissel and R. Glang,
`in
`“Handbook of Thin Film Technology,” McGraw-Hill,
`page 18—12 (1970). They reported that if the substrate
`temperature exceeds 600° C., the alpha'phase is formed;
`, also, if the base pressure of the vacuum system is high,
`indicating high water vapor, nitrogen; and oxygen con-
`tent, the alpha phase may result.
`'
`These findings are not very useful for electronics
`applications because processing temperatures above
`400° C are typically not compatible With device fabrica-
`tion. It isalso difficult to maintain and control such a
`high substrate temperature during sputtered metal de-
`position. Furthermore, it is difficult to keep a controlla-
`ble amount of impurities in the system.
`In addition, other studies,
`including one by N.
`Schwartz and E. D. Feit, have found that they could
`not use these results to consistently predict Which phase
`of tantalum would grow. See, N. Schwartz and E. D.
`Feit, “Impurity Effects in the Nucleation of Alpha
`(bcc)-Tantalum or Beta-Tantalum Films”, Journal of
`the Electrochemical Society, Vol. 124, No. 1, pages
`123—131 (January 1977). Schwartz and-Feit proposed
`instead the existence of an “X” impurity which results
`in the formation of alpha. tantalum. The difference be—
`tween their work and that discussed by L. Maissel and
`R. Glang, was their hypothesis that the “X” impurity
`could simply be something on the substrate instead of
`something in the gas phase in the vacuum chamber.
`Finally, G. Feinstein and R. D. Huttemann studied
`substrate effects on the formation of alpha tantalum. G.
`
`10
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`15
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`20
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`25
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`Page 5 0f 9
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`2
`Feinstein and R. D. Huttemann, “Factors Controlling -
`the Structure of Sputtered Tantalum Films”,Thin Solid
`Films, Vol. 16, pages 129—145 (1973). They divided
`substrates into three groups: Group 1 contained sub-
`strates onto which only beta tantalum could be formed
`and included such substrates as 7059 glass, quartz, sap-
`phire, and metals such as copper and nickel. Group 11
`contained substrates onto which only alpha (bcc) tanta-
`lum could be grown. This group included substrates
`that had been coated with 5000 angstroms thick metal
`films 'such as gold, platinum, or tungsten. Finally,
`Group III consisted of substrates which normally pro-
`duced alpha tantalum, but could be induced to yield
`beta tantalum or mixtures of alpha and beta by suitable
`treatment of the surface. These included substrates
`coated with 5000Vangstrorns of molybdenum, silicon
`nitride, or stochiometric tantalum nitride (TazN). The
`use of such thick underlayers, as described by G. Fein-
`stein and R. D. Huttemann makes it impractical to use
`this concept to produce alpha tantalum for electronics
`use. Since it is generally preferred to not introduce extra
`materials into a device structure, the use of different
`materials (such as tungsten or molybdenum) is impracti-
`cal for electronics use.
`’ Parisi in US. Pat. No.3,558,461, discloses a method
`for fabricating thin film tantalum based resistors by
`reactive sputtering of tantalum in the presence of oxy-
`gen and nitrogen, followed by anodization and thermal
`pre-aging of the resultant deposited film. The films were
`reactiver sputtered in N2 and 02 containing ambient to
`control the TCR (Thermal Coefficient of Resistance).
`The resistivity ranged from 300 to 1500 micro-ohm-cm.
`The resulting film is referred to as “tantalum oxyni-
`tride,” which is different than the alphatantalum films
`that-are produced by the process of this invention.
`Kumagai, U. 5‘. Pat. No. 3,847,658, discloses deposit-
`ing nitrogen-doped beta-tantalum. A thin-film electrode
`comprising nitrogen-doped beta-tantalum is deposited
`upon a suitable electrically non-conductive substrate.
`The process produces N2 doped beta tantalum for ca-
`pacitor formation, as opposed to the alpha tantalum
`disclosed in this invention. The films have 0.1 percent to
`10 percent N2, and resistivities 10 atomic percent to 50
`percent higher than that of pure beta Ta films. Further-
`more, beta tantalum was grown on a Ta205 underlayer,
`whereas, the inventors of this invention disclose the use
`of Ta(N) as the seed or underlayer for the formation of
`alpha—Ta.
`Schauer in US. Pat. No. 3,878,079, discloses a
`method for producing thin films of tantalum in the alpha
`phase bcc (body centered cubic) lattice by heating a
`substrate to a temperature-above 300° C. and applying a
`high frequency discharge to a tantalum target member.
`The growth of alpha or beta tantalum depends on the
`N2 partial pressure in the sputtering gas. A nitrogen
`partial pressure is provided in the sputtering atmo-
`sphere, and by decreasing the nitrogen partial pressure,
`TaN, TazN, and finally alpha tantalum were succes-
`sively formed. This alpha tantalum was highly doped
`with foreign gases, in contrast with the invention de-
`scribed in this patent application which is pure alpha
`Ta. With‘further reduction in N2 partial pressnre, beta
`Ta is formed, and with still further reduction, alpha Ta
`can again be formed if the SubStrates are heated to over
`300° C. The resulting film resistivity of that alpha-tan-
`talum produced at above 300” C. was 25 micro-ohm-cm.
`In contrast, only modest substrate heating is required in
`the process of this invention, and the reactive gas is only
`
`Page 5 of 9
`
`

`

`3
`required for deposition of the seed layer, and not for the
`rest of the film as disclosed by Schauer. A Ta205 under-
`layer was used by Schauer to allow for easier substrate
`cleaning; his underlayer is not responsible for the pro-
`duction of the alpha tantalum film.
`Anders, US. Pat. No. 4,058,445, discloses a method
`for producing thin film tantalum capacitors having a‘
`tantalum thin film electrode mounted on a nonconduct-
`ing support member. The tantalum electrode is doped
`10
`with nitrogen to produce a nitrogen content in a range
`from the nitrogen content of beta~tantalum to that for .
`tantalum nitride. The process of Anders’ invention pro.-
`duces “alpha” tantalum deposited on a Ta205 coated
`substrate by introducing N2 into the argon sputtering
`gas at a partial pressure of 10—5 torr. These “alpha”_
`tantalum films have high resistivity (100 micro-ohm
`cm) with presumably high N2 content.
`*
`Arcidiacono et al. in US. Pat. No. 4,251,326, disclose
`a method for fabricating thin film RC networks by
`forming alpha tantalum capacitor'base electrodes on a
`substrate while simultaneously forming alpha tantalum
`anodizatio'n bus bars on the subStrate. The alpha-tan-
`talum film was obtained bysputtering a tantalum film
`on the substrate, thermally oxidizing the tantalum film
`to form an underlayer, and then sputtering'an alpha
`tantalum film over the deposited Ta205 underlayer. The
`purpose of the underlayer is. to protect the substrate
`from attack by corrosive etchants during subsequent
`proceSsing, and apparently has nothing to do with the
`formation of alpha Ta.’This is different than' the inven-
`tion of the applicants where the Ta(N) seed layer or
`underlayer is required to'produce the alpha tantalum.
`Alpha tantalum was deposited by Arcidiacono in' a
`Ar-Nz atmosphere at 3—6 mT pressure. The resulting
`film has BCC structure and contained 10-20 percent N2.
`The invention of this disclosure has Ta films' that have
`nitrogen in the seed layer only, and‘not throughout the
`bulk of the structure. Koyarna et a1. (U.S. Pat. No.
`4,364,099) discloses tantalum thin film capacitors,
`which are formed on a substrate which is reactEVely
`sputtered with tantalum in a nitrogen containing atmo-
`sphere (argon gas with nitrogen gas incorporated in an
`amount of from 10 to 30 percent) to deposit a highly
`nitrogen-doped tantalum film having a nitrogen concen-
`tration of from 14 to 30 atomic percent. Subsequently a
`layer of an alpha-tantalum thin film to form the lower
`electrode is sputtered on the highly nitrogen-doped
`tantalum film, this second thin film has a nitrogen con-
`centration of from 6 to 15 atomic percent. This interme-
`diate product is then further processed to obtain a tanta-
`lum thin film capacitor. During sputtering the tempera-
`ture of the substrate was maintained at 250° C. The
`thickness of the highly nitrogen-doped tantalum film
`was from 100 to 200 nm (1,000 to 2,000 angstroms), and
`the thickness of the nitrogen doped alpha-tantalum thin
`layer was at least 100 mm (1,000 angstroms).
`OBJECTS AND SUMMARY OF THE
`INVENTION
`
`15
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`30
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`35
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`40
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`45
`
`50
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`5,281,485
`
`'
`
`4
`Another object of this invention is the usage of Ta
`reactively sputtered in nitrogen as a seed layer to form
`alpha Ta during subsequent Sputtering.
`Yet another object of this invention is the process
`-window for the-formation of the Ta(N) seed layer.
`In one aspect, this invention discloses a method of
`making an alpha-Ta layer on a Substrate comprising the
`steps of:
`.'
`'
`(a) forming a seed layer of Ta(N), reactively sput-
`tered in a nitrogen containing ambient, on the sub-
`strate, and
`-
`I
`'
`‘
`(b) depositing a layer of alpha-Ta on the Ta(N) seed
`. layer.
`’
`-
`In another aspect this invention discloses a structure
`comprising a seed layer of Ta(N) on a' substrate, and an
`additional layer of alpha-Ta on the seed layer.
`In yet another aspect this invention discl'oSesa struc-
`ture comprising a seed layer of Ta(N) on'a‘ substrate,
`and having an additional layer of alpha-Ta on the Ta(N)
`seed layer, and’wherein the seed layer of Ta(N) is at
`least 20 angstroms thick.
`'
`..
`The thickness of the seed layer of Ta(N) could be
`between 20'and 500 angstroms, or it could be between
`20 and 40 angstroms.
`'
`The seed layer of Ta(N) preferably contains between
`0.1 and 50.0 atomic percent nitrogen, and more prefera—
`bly'betweend and 35 atomic percent nitrogen. Hence-'
`forth, all references to percent nitrogen are meant to be
`atomic percent nitrogen. Precise control of the nitrogen
`content
`(as needed for stdchiometric TazN) is not
`needed.
`'
`
`The alpha-Ta layer could be deposited at tempera-
`tures of preferably between l00°'C. and 600° C., and
`more preferably between 200° C. and 300‘ C., or the
`alpha-Ta layer-could be deposited atltemperatures of
`equal to or less than 200° C.
`The resistivity'of the alpha-Ta layer‘is equal to or less
`than 40 micro-ohm-cm.
`
`The total thickness of the Ta(N) seed layer and the
`alpha~Ta layer is preferably between 100 angstroms and
`4,000 angstroms, and more preferably between 500 ang—
`stroms and 2,000 angstroms.
`_
`.
`The layer of alpha-Ta can be at least 100 angstroms
`thick.
`A product can also be made by the method of this
`invention.
`v
`Similarly, an article of manufacture can also be made
`by the methodof this invention.
`'
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features of the invention believed to be novel and
`the elements characteristic of the invention are set forth
`with particularity in the appended claims. The figures
`are for illustration purposes only and are not drawn to
`scale. The invention itself, however, both as to organi-
`zation and methOd of operation, may best be understood
`by reference to the detailed description which follows
`taken in conjunction-with the accompanying drawings
`in which:
`.
`.
`FIG. 1A is a ’cross~sectional schematic view of a
`typical sputtered Ta film deposited by the prior art
`methods.
`‘
`,
`FIG. 1B is a cross-sectional schematic view of an
`embodiment ofthis invention showing the use of Ta(N)
`seed layer to form alpha-Ta.
`'
`FIG. 2A is a plot showing the effect of the Ta(N)
`seed layer thickness on the resistivity of the total struc-
`ture.
`
`An object of this invention is to provide a method for
`making Alpha—Ta in thin films.
`Another object of this invention is to provide a simple
`and highly reproducible method of producing thin Al’-
`pha-Ta films.
`.
`-
`_
`v
`Still another object of this-invention is to keep the
`resistivity (less than or equal to 40 micro-ohm-cm) of
`the final structure low enough to make the film a candi-
`date for use in electronics applications.
`
`65
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`Page 6 of 9
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`Page 6 of 9
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`

`

`5,281,485
`
`5
`FIG. 2B shows a cross-sectional schematic view of a
`typical sample prepared to generate the plot for FIG.
`2A.
`.
`.
`.
`FIG. 3A is a plot showing. the effect of the nitrogen
`concentration in argon, during seed layer deposition, on 5
`the resistivity of the total structure.
`FIG. 3B illustrates, a cross-sectional schematic view
`of a typical sample preparedto generate the plot for
`FIG. 3A.
`.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`10
`
`This invention discloses a simple process to reproduc-
`ibly deposit alpha (bcc) tantalum on a substrate. The
`process comprises first depositing a thin seed layer or 15
`underlayer of tantalum doped with a small amount of.
`nitrogen, and hereinafter referred to as Ta(N). This is-
`followed by depositing the required tantalum film-thick-
`ness in the conventional. way. A typical structure
`formed by the method of this invention is shown in
`FIG. 13.
`
`20
`
`6
`ambient 'varied from 0.5 percent to 35.0 percent. Alpha
`tantalum was also produced with 0.3 percent nitrogen in
`argOn, but the nitrogen in the tantalum was below the
`lower detectable limit 'of RBS.
`As shown in FIGS. 2A and 3A, the-thickness of the
`seed layer is not critical for the formation of alpha—Ta,
`- and neither high substrate temperature or controlled
`system impurities are required.
`The process disclosed in this invention is easily done
`in-situ by introducing N2 during the initial Ta deposi-
`tion. As we have seen in FIG. 3A, that the amount of
`nitrogen in the seed layer is not critical; therefore, no
`sophisticated reactive sputtering processes are required;
`If the alpha-tantalum layer is deposited in a batch
`tool, no intentional substrate heating is required. With a
`single wafer tool, the alpha-Ta layer could be deposited
`at temperatures of between l00° C. and 600° C., or
`preferably the alpha-Ta layer could be deposited at
`temperatures of equal to 0r less than 200° C.
`EXAMPLES
`
`25
`
`30
`
`It should be noted that the doped tantalum seed layer
`is not the same as depositing Ta2N, which requires
`precise control of the, gas composition during the depo-
`sition process. In contrast to the work of Feinstein and
`Huttemann where the various metal seed layers were
`5000 angstroms, the seed layer 'of this invention can be
`extremely thin (demonstrated to be as little as 32 ang-
`stroms or 3.2 nm) as shown in FIG. 2A, which plots
`total film resistivity (of the composite structure com-
`prising the Ta(N) seed layer and the alpha-Ta layer)
`versus Ta(N) seed layer thickness. With a seed layer
`thickness of 16 angstroms (nominal thickness) or less,
`the resistivity was greater than 50_micro-ohm-cm, indi-
`cating the formation of beta-tantalum or a mixture of 35
`alpha and beta-tantalum. With thicker seed layers, 32 to
`500 angstroms (nominal thickness), the total resistivity
`indicated the formation of alpha-tantalum. Therefore, it
`is assumed that seed layers as thin as 20 angstroms will
`result
`in alpha-Ta formation. The total resistivity in-
`creased with increased seed layer thickness due to the
`parallel resistance of the seed layer with the 500 ang-
`strom alpha—tantalum overlayer.
`The use of the seed layer results in tantalum films that
`are alpha (bcc) tantalum, as confirmed by X-ray diffrac-
`tion analysis and the previously mentioned resistivity
`measurements. The resistivity of tantalum films doped
`with nitrogen is typically greater than 180 micro-ohm-
`cms, but the resistivity of the stack of the alpha-tan-
`talum film deposited onto the seed layer can be as low_
`as 20 to 40 micro-ohm-cms depending on the thick-
`nesses as discussed elsewhere, for example asdiscussed
`in Example 2.
`FIG. 3A shows the effect of the amount of nitrogen
`in the argon sputtering gas during the seed layer deposi-
`tion on the total resistivity of the composite structure or
`film. With a constant Ta(N) seed layer thickness of 250
`angstroms and Ta overlayer thickness of 250 angstroms,
`the percent of nitrogen in argon sputtering gas was
`varied from 0 to atomic percent. The total resistivity
`indicated that alpha-Ta was formed with between 0.3
`percent to 35 atomic percent nitrogen in the argon dur—
`ing Ta(N) seed layer deposition. With no nitrogen pres-
`ent during the “seed layer” deposition, the high resistiv-
`ity indicates the formation of beta-tantalum. Rutherford
`Backseattering Spectroscopy (RBS) detected between 5
`percent and 50 percent nitrogen in the tantalum seed
`layer as the amount of nitrogen in the argon sputtering
`
`The following examples are intended to further illus-
`trate the invention and are not intended to limit the
`scope of the invention in any manner.
`EXAMPLE 1
`
`Typically, thin sputtered films are beta—Ta. A process
`has been developed in a batch tool. To deposit thin films
`of alpha-Ta, a Ta(N) seed. layer is used. This process
`consists of depositing a seed layer of nitrided Ta (for
`example, 5 atomic percent N2 in Ar during sputtering),
`which could be as thin as 32 Angstroms, and then'sput-
`tering Ta in argon with no nitrogen. The alpha-phase
`was produced, usingbetween 0.3 atomic percent and
`33.0 atomic percent N2 in the Ar sputtering ambient
`during seed layer deposition with seed layer thickness
`above 32 Angstroms. The pressure was varied between
`10 and 100 mT (milli-Torr) and alpha-Ta films as thin as
`125 Angstroms were produced. No intentional substrate
`heating was used, although the literature has reported
`the need for substrate heating. Due to the large change
`in resistivity between the Alpha and Beta phases, the
`main measurement technique used was sheet resistivity.
`Additionally, X-ray diffraction was performed to verify
`the phase formed and RBS was used to determine the
`nitrogen content of the seed layer. The X-ray diffrac-
`tion confirmed the formation of alpha (bcc) Ta in the
`samples having low resistivity.
`
`EXAMPLE 2
`A process has also been developed to produce thin,
`low resistivity (20 micro-ohm-cm) films of alpha-Ta on
`a Ta(N) seed layer using a single wafer tool. There is a
`wide process window in terms of N2 flow during seed
`layer deposition, seed layer thickness, and substrate
`temperature.
`The Ta deposition conditions were as follows: 1000
`watts RF, 5.2 mT, 100 sccm Ar, 0—10 sccm N2, and a
`substrate temperature between room temperature,
`which is approximately 20° C., and 300° C. Three sepa-
`rate sets of runs were performed. the N2 flow during the
`seed layer deposition was varied (O—lO seem), the seed
`layer thickness was varied (50—200 Angstroms), and the
`substrate temperature was varied (room temperature of
`20° C.—300° C.)
`The first runs varied the N2 flow during seed layer
`deposition. The seed layer was 200 Angstroms thick,
`and a subsequent 750 Angstroms of Ta was sputtered
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`7
`onto the seed layer. The substrate temperature was 200"
`C. for all of these runs. With no seed layer, the resistiv-
`ity was 115 micro-ohm-cm. For the runs with a seed
`layer, the resistivities were between 23.1 and 24.5 mi-
`cro-‘ohm-cm. ‘X-ray diffraction was performedon these
`films and verified that the films with a seed layer were
`in fact Alpha-Ta.
`‘
`The second set of runs varied the seed layer thickness
`between 50 and 200 Angstroms, while keeping the total
`thickness constant (1000 Angstroms nominal). The sub-
`. strate temperature was 200° C. The total resistivity
`(alpha-Ta and seed layer) increased from 18.7 to‘ 23.0
`micro-ohm-cm as the seed' layer thickness increased,
`due to the increased seed layer contribution. The seed
`layer was sputtered in a 5 percent Nz'in Ar mixture,
`resulting in a resistivity of approximately 200 micro-
`iohm-cm for the Ta(N).
`The final series of runs examined the effect of sub-
`strate heating. The total film thickness was approxi-
`mately lOOOAngstroms, with a 200 Angstrom Ta(N) (5
`atomic percent nitrogen in Ar) seed layer, and 750 Ang-
`stroms of Ta. No intentional heating'or cooling was
`used on the 22° C. sample; for this sample the tempera-
`ture was not controlled or monitored and the tempera-
`ture is assumed to have been at 22° C. The resistivities of
`the 22° CL, 150" C., 200° C., and 300' C. samples or runs
`indicate that the 22° C. run was Beta (104 micro-ohm-
`cm) and the remainder were Alpha Ta (22.4 to 21.0
`micro-ohm-cm). Samples prepared at 100° C. had inter-
`mediate resistivities (42 and 39 micro-ohm-cm), which
`perhaps indicates a mixture of Alpha and Beta-Ta
`phase.
`‘
`There is a wide process window for producing Al-.
`pha-Ta films in a single wafer sputtering tool. The resis-
`tivity is low, about 20 micro-ohm-cm. Unlike previous
`work on a batch tool (Example 1), substrate tempera-
`ture is importantia temperature of 150° C. or above is
`needed. This may be explained by the fact that with the
`batch tool, most processes heat the substrates to temper-
`atures equal to or greater than 200° C. without inten—
`tional heating.
`‘
`‘
`While the present
`invention has been particularly
`described, in conjunction with a‘specific preferred em-
`bodiment, it is evident that many alternatives, modifica-
`tions and variations will be apparent to those skilled in
`the art in light of the foregoing description. It is there;
`fore contemplated that the appended claims will em-
`brace any such alternatives, modifications‘and varia-
`tions as falling within the true scope and spirit of' the
`present invention.
`What is claimed is:
`1. A product made by forming an alpha-Ta layer that
`does not contain any detectable amount of nitrogen on
`a substrate comprising the steps of:
`(a) forming a seed layer of tantalum doped with nitro-
`gen (Ta(N)), reactively Sputtered in a nitrogen
`containing ambient, on said substrate, wherein said
`seed layer has a thickness of at least 20 angstroms,
`and
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`(b) depositing a layer of alpha-Ta on said Ta(N) seed
`layer in a nitrogen free ambient, wherein said layer
`or alpha-Ta does not contain any detectable
`amount of nitrogen and has a resistiVity of less than
`50 micro-ohm-cm.
`
`2. An article of manufacture made by forming an
`alpha-Ta layer that does not contain any detectable
`amount of nitrogen on a substrate comprising the steps
`of:
`*
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`5,281,485
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`8
`(a) forming a seed layer of tantalum doped with nitro-
`gen (Ta(N)), reactively sputtered in a nitrogen
`containing ambient, on said substrate, wherein said
`seed'layerhas a thickness of at least 20 angstroms,
`and
`-
`'
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`lo
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`(b) depositing a layer of alpha-Ta on said (Ta(N) seed
`layer in a nitrogen free ambient, wherein said layer
`of alpha-Ta does not contain any detectable
`amount of nitroge‘n'and has a resistivityof less than -
`50 micro-ohm-cm.
`.
`3. A structure comprisinga seed' layer of tantalum
`doped with nitrogen (Ta(N)) on a substrate, wherein
`said seed layer has a thickness of at least 20angstroms,
`and having a layer of alpha-Ta on said Ta(N) seed layer, .
`wherein said layer of alpha-Ta does not contain any
`detectable amount'of nitrogen and has a resistivity of
`less than 50 micro-ohm-cm.
`‘
`‘
`4. The structure of claim 3, wherein said layer of
`alpha-Ta is at least 100 angstroms thick.
`5. The structure of claim 3, wherein the total thick-
`ness of said Ta(N) seed layer and said alpha-Ta layer is»
`between 100 angstroms and 4,000'angstroms.
`6. The structure of claim 3, wherein the total thick-
`ness of said Ta(N) seed layer and said alpha-Ta layer is
`between 500 angstroms and.2,000'angstroms.
`7. A structure comprising a seed layer of tantalum
`doped with nitrogen (Ta(N)) on a substrate, and having
`a layer of alpha-Ta on said Ta(N)'seed layer, wherein
`said seed layer of Ta(N) is at least’20 angstroms thick,
`and wherein said layer of alpha-Ta has a resistivity of
`less than 50 micro-ohm-cm.
`'
`g
`’
`8. The structure of 'claim 7, wherein said layer of
`alpha-Ta is at least 100 angstroms thitk.
`9. The structure of claim 7, wherein the total thick-
`ness of aid Ta(N) seed layer and said alpha-Ta layer is
`between 100 angstroms and 4,000 angstroms.
`10,‘The structure of claim 7, wherein the total thick-
`ness of said Ta(N) seed-layer and said alpha-Ta layer is
`between 500 angstroms and 2,000 angstroms.
`. 11. The structure of claim 3, wherein the-resistivity of
`said alpha-Ta layer is equal to or less than'40 micro-
`ohm-cm.
`'
`.
`-
`12. The product of claimll, wherein the resistivity of
`said alpha-Ta layer is equal to or less than 40 micro-
`ohm-cm.
`'
`v
`'
`
`13. The article of manufacture of claim 2, wherein the
`resistivity of said alpha-Ta layer is equal to or less than
`40 micro-ohm-cm.
`,
`'
`’
`14. The structure of claim 7, wherein the resistivity of
`said alpha-Ta layer is equal to or less'than 40 micro-
`ohm-cm.
`*
`'
`'
`
`15. The product of claim 1, wherein saidseed layer of
`Ta(N) preferablycontains between 0.1 and 50.0 atomic
`percent nitrogen.
`.
`p
`v
`16. The article of manufacture of claim 2, wherein
`said seed layer of Ta(N) preferably contains betwee
`0.1 and 50.0 atomic percent nitrogen.
`'
`17. The structure of claim 3, wherein said seed layer
`of Ta(N) preferably contains between. 0.1 and 50.0
`atomic percent nitrogen.
`-
`'
`.
`18. The structure of claim 7, wherein said seed layer
`of Ta(N) preferably contains between 0.1 and 50.0
`atomic percent nitrogen.
`.
`19. The structure of claim 3, wherein said seed layer
`of Ta(N) preferably contains between 0.1 and 35.0
`atomic percent nitrogen.
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`5,281,485
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`10
`23. The structure of claim 3, wherein said seed layer
`of Ta(N) contains between 1 and 35 atomic percent
`nitrogen.
`_
`24. The structure of claim 7, wherein said seed layer
`of Ta(N) contains between 1 and 35 atomic percent
`nitrogen.
`,
`25. The structure of claim 3, wherein said seed layer
`of Ta(N) contains between 0.] and 1.0 atomic percent
`nitrogen.
`26. The structure of claim 7, wherein said seed layer
`of Ta(N) contains between 0.1 and 1.0 atomic percent
`nitrogenu
`t
`t
`It
`1:
`1r
`
`20. The structure of claim 7, wherein Said seed layer
`of Ta(N) preferably contains between 0.1 and 35.0
`
`atomic percent nitrogen.
`
`21. The product of claim 1, wherein said seed layer of
`
`Ta(N) contains between 1 and 35 atomic percent nitro-
`gen.
`
`22. The article of manufacture of claim 2, wherein
`said seed layer of Ta(N) containsrbetween 1 and 35
`atomic percent nitrogen.
`
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