`
`[19]
`United States Patent
`[11] Patent Number:
`6,156,647
`[45] Date of Patent: Dec. 5, 2000
`Hogan
`
`
`
`USOO6156647A
`
`[54] BARRIER LAYER STRUCTURE WHICH
`PREVENTS MIGRATION OF SILICON INTO
`AN ADJACENT METALLIC LAYER AND
`THE METHOD OF FABRICATION OF THE
`BARRIER LAYER
`
`US. Patent Application, Serial No. 08/511,825 of Xu et al.,
`filed Aug. 7, 1995.
`
`US. Patent Application Serial No. 08/824,911 of Ngan et al.,
`filed Mar. 27, 1997.
`
`[75]
`
`Inventor: Barry Hogan, Santa Clara, Calif.
`
`[73] Assignee: Applied Materials, Inc., Santa Clara,
`Calif.
`
`[21] Appl. No.: 08/958,472
`
`[22]
`
`Filed:
`
`Oct. 27, 1997
`
`Int. Cl.7 ................................................. .. H01L 21/461
`[51]
`[52] US. Cl.
`......................... .. 438/653; 438/685; 438/643
`[58] Field of Search ................................... .. 438/653, 685,
`438/643, 627
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`................................. .. 427/38
`
`7/1990 Lu et a1.
`4,944,961
`2/1991 Nishida .
`4,990,997
`........................... .. 257/751
`5,175,608 12/1992 Nihei et a1.
`5,320,728
`6/1994 Tepman ........ ..
`. 204/192.12
`
`.... .. 257/751
`5,514,908
`5/1996 Liao et a1.
`
`.... .. 437/192
`5,543,357
`8/1996 Yamada et a1.
`. . . . .
`5,663,088
`9/1997 Sandhu et a1.
`. . . . .. 438/396
`
`. . . . .
`5,723,382
`3/1998 Sandhu et a1.
`. . . . .. 438/653
`5,895,266
`4/1999 Fu et a1.
`................................ .. 438/648
`
`OTHER PUBLICATIONS
`
`B. Pécz et al., “Electron microscopy characterization of TiN
`films on Si, grown by dc. reactive magnetron sputtering”,
`Thin Solid Films, 268, pp. 57—63 (1995).
`S.M. Rossnagel and J. Hopwood, “Metal ion deposition
`from ionized magnetron sputtering discharge”, J. Vac. Sci.
`Technol. B, vol. 12, No. 1, pp. 449—453 (Jan/Feb. 1994).
`
`US. Patent Application Serial No. 08/825,216 of Ngan et
`al., filed Mar. 27, 1997.
`
`Primary Examiner—Caridad Everhart
`Attorney, Agent, or Firm—Kenyon & Kenyon; Shirley L.
`Church
`
`[57]
`
`ABSTRACT
`
`An improved barrier layer structure for the prevention of
`migration within a semiconductor device can be formed
`from a refractory metal compound such as a refractory metal
`nitride. The preferred barrier layer structure includes at least
`two adjacent layers of essentially the same chemical com-
`position having an essentially continuous interfacial region
`between them, wherein the interfacial region is at least 10 A
`thick. As an alternative to having a continuous interfacial
`region, a series of adjacent layers which provide sufficient
`interfacial regions can be used in combination to block the
`migration of mobile atoms such as silicon. When a series of
`layers is used, there should be at least 3 layers, and prefer-
`ably 5 or more layers, where each layer is at least about 50
`A thick. In addition,
`to break the continuity of channels
`passing through grain boundaries, alternating layers of sub-
`stantially grain oriented, columnar microstructure and
`amorphous, non-columnar structure are preferred. The pre-
`ferred embodiment used to demonstrate the invention is a
`
`titanium nitride-comprising barrier layer structure prepared
`using ion metal plasma or reactive ion metal plasma depo-
`sition techniques to create the interfacial regions.
`
`12 Claims, 4 Drawing Sheets
`
`348
`
`346
`
`
`
`aim]MIMI]llil'ilm'flilkiil"Miliiliflm’imlf/fllflWilling}iii/iiflflii'iw
`
`
`(v
`I
`4
`‘ -
`‘.
`“
`Wllm
`
`
`ammoniumimamr1mmmmlminimumimammm
`
`Mmmmmmmmmrwm
`.ll‘llli'fifl'i'lll Ifl HI'dmmiuii;itmmuw.mmnumm.va
`(mtwmnvmmmmmmw
`MIMWMIWNWMMMWMM/N
`
`
`334
`
`330
`
`
`
`342
`
`338
`
`
`
`
`
`Page 1 of 13
`
`TSMC V. IP Bridge
`
`IP Bridge Exhibit 2040
`
`|PR2016-01264
`
`
`
`Page 1 of 13
`
`IP Bridge Exhibit 2040
`TSMC v. IP Bridge
`IPR2016-01264
`
`

`

`US. Patent
`
`Dec. 5,2000
`
`Sheet 1 0f4
`
`6,156,647
`
`112
`
`106
`
`PRIOR ART
`
`FIG.
`
`1
`
`
`
`
`
`‘
`
`
`
`Page 2 of 13
`
`
` .
`
`
`
`k
`
`400.10001!szmm:wmmmmmmww:0w;mm'1:almanaxmm3m mnmsmmwm
`
`.12.
`mm! was 225
`
`
`
`224[8b3 223
`
`fliMWMIMMMMx-HWMMMMIBFMMMill“?
`215“
`
`MWWMWMMM
`
`Page 2 of 13
`
`

`

`US. Patent
`
`Dec. 5,2000
`
`Sheet 2 0f4
`
`6,156,647
`
`30
`
`/
`
`Page 3 of 13
`
`Page 3 of 13
`
`

`

`US. Patent
`
`Dec. 5,2000
`
`Sheet 3 0f4
`
`6,156,647
`
`348
`
`
`
`0m?” 4‘5/"(\(
`
`J
`
`mmamwI.0Hmmmmmmalrzmmmv/m'mmmwmmum
`
`3
`
`344
`34
`
`{lflnfll'lgtl'llfllfllflmum»mmmwnw.110500000000m01w
`mmmunwmmmmwwm
`Ell‘ll.’.'.l‘.‘_'l'.Wl'fl‘i{I'dMIMICWMIHMml!!!‘6MFILIIIIHJEIIILMMfl
`
`332 MMWMIWMMMMMWMM/fl'
`
`
`
`3 38
`
`334
`
`
`
`
`
`
`
` fl
`2438
`I
`0
`0000. :23:
`, 0 W
`WWW
`09""“Wm'WW w
`'0“$3”
`‘
`#31
`“I WW"
`t" W W
`WWII/MW 3/4364”
`“0.0w"j“ 030WW” Wm; M>0
`“»
`’v W":
`F" W W W! "h.
`:23:
`5l
`'
`A,
`1
`0
`1
`‘4‘
`3“ («W U
`0 ’
`V
`m WW 0 s m 0 0
`9
`W
`a...
`k*.—w—
`v"
`“J I
`6” 7“! [I "4’
`63”“.
`ii #422
`M
`m"HH
`‘$418
`“WNW? MM“
`
`
`
`I
`
`r
`
`
`
`
`
`
`
`Page 4 of 13
`
`

`

`
`
`US. Patent
`
`6,156,647
`
`AoomvAISAoomv22vAoomv22v
`
`5,vVCONm.o:Domon
`.NrficfigN£225m:8“..mvs:mvegmw2.Vm8cmom%so?2588v2588v95o_0vMNcm%£225£225ONSVCBE3%mm#8.“..mxowmof48a
`Ngmcfis
`
`__8.
`
`m
`
`Aoomv92vAoomv22vAoomvAZUV
`
`>878->0md:
`
`onom
`
`.v
`
`
`
`
`
`Nrucfig3:225owWémEzEm38;Wv.8;02if
`
`3%
`
`2:—
`
`Page 5 of 13
`
`
`
`
`
`
`
`5%e3258:22...xmiooméééx
`
`Page 5 of 13
`
`
`

`

`
`
`6,156,647
`
`1
`BARRIER LAYER STRUCTURE WHICH
`PREVENTS MIGRATION OF SILICON INTO
`AN ADJACENT METALLIC LAYER AND
`THE METHOD OF FABRICATION OF THE
`BARRIER LAYER
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention pertains to a barrier layer used in
`the formation of semiconductor devices. The barrier layer
`has a particular structure, and may be formed in a continuous
`process to reduce fabrication costs. In the most preferred
`embodiment, the barrier layer is titanium nitride which is
`used to line a contact via having a particularly high aspect
`ratio.
`
`2. Brief Description of the Background Art
`In the field of semiconductor device fabrication, particu-
`larly with the continuing trend toward smaller device feature
`sizes, the reliability of electrical contacts has become criti-
`cal. This reliability is particularly threatened for contacts
`between aluminum and diffused junctions into single-crystal
`silicon, where the aluminum and silicon tend to interdiffuse.
`As is well known in the art, conventional integrated circuit
`process steps can cause aluminum atoms to diffuse from a
`metal electrode of pure aluminum into single-crystal silicon
`to such a depth as to short out a shallow p-n junction in the
`silicon; this phenomenon is known as junction spiking.
`To prevent junction spiking, barrier layers have been
`introduced between the silicon and the overlying aluminum
`layer. Typically these barrier layers are formed of refractory
`metal compound such as titanium tungsten (TiW), or a
`refractory metal nitride such as titanium nitride (TiN).
`US. Pat. No. 5,543,357 to Yamada et al., issued Aug. 6,
`1996, describes a process for manufacturing a semiconduc-
`tor device wherein a titanium film is used as an under film
`
`for an aluminum alloy film to prevent the device character-
`istics of the aluminum alloy film from deteriorating. The
`thickness of the titanium film is set to 10% or less of the
`thickness of the aluminum alloy film and at most 25 nm. In
`the case of the aluminum alloy film containing no silicon,
`the titanium film is set to 5% of less of the thickness of the
`aluminum alloy film. The aluminum film is formed at a
`substrate temperature of 200° C. or less by a sputtering
`process, and when the aluminum film or an aluminum alloy
`film is to fill a via hole, the substrate is heated to fiuidize the
`aluminum. The pressure during the aluminum film forma-
`tion and during the fiuidization is lower than 10'7 Torr. A
`titanium nitride barrier layer may be applied on an interlay-
`ered insulating film (or over a titanium layer which has been
`applied to the insulating film), followed by formation of a
`titanium film over the titanium nitride film, and finally by
`formation of the aluminum film over the titanium film. After
`
`formation of the titanium nitride barrier layer, the barrier
`layer is heated to a temperature of about 600° C. to 700° C.
`in a nitrogen atmosphere using a halogen lamp so that any
`titanium which is not nitrided will become nitrided. The
`
`titanium nitride barrier layer is said to be a poor barrier layer
`if un-nitrided titanium is present within the layer.
`To further improve the performance of TiN barrier layer
`properties, an oxide has been incorporated at grain bound-
`aries within a titanium nitride film, to increase the ability of
`the film to prevent
`the mutual diffusion of silicon and
`aluminum through the barrier layer. Placement of the oxide
`at the grain boundaries is known as “oxygen stuffing”. US.
`Pat. No. 5,514,908 to Liao et al.,
`issued May 7, 1996,
`describes an even further improvement in an oxygen-stuffed
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`TiN film, where a titanium silicide layer is formed at the
`exposed silicon surface, followed by the formation of a
`titanium oxynitride layer, followed by the titanium nitride
`layer. In a preferred embodiment of the invention, a porous
`titanium nitride layer is formed over the titanium metal from
`which the silicide is to be formed. The wafer is then exposed
`to an oxygen-bearing atmosphere, to allow oxygen to enter
`the film. Subsequently, the wafer is rapid thermal annealed
`to cause silicidation at the silicon-titanium interface and to
`
`cause the titanium nitride to densify into a high density film
`with a titanium oxynitride layer at the silicide/nitride inter-
`face.
`
`The Liao patent referenced above describes a technique
`used to form a relatively low density titanium nitride where
`the reactive sputtering of titanium nitride is carried out at
`relatively cool substrate temperatures (on the order of 100°
`C.) and at relatively weak vacuum conditions (on the order
`of about 10 mT). This is contrasted with conventional high
`density titanium nitride which is reactive sputtered at sub-
`strate temperatures on the order of 300° C., and at vacuums
`of “at most” 4 mT to provide the large grain sizes and high
`density desired in the prior art
`to provide barrier layer
`performance.
`B. Pecz et al. in an article entitled “Electron microscopy
`characterization of TiN films on Si, grown by DC. reactive
`magnetron sputtering”, Thin Solid Films 268 (1995) 57—63,
`describe the structural characteristics of titanium nitride
`
`films deposited by DC. reactive magnetron sputtering on
`<001> silicon wafers. In particular, the shape and size of the
`titanium nitride crystallites were investigated as a function
`of deposition temperature, substrate bias voltage and nitro-
`gen fiow rate (nitrogen content of the process gases). The
`titanium nitride films are said to exhibit a columnar growth
`showing preferred orientation along <111> direction. The
`crystal orientation of the silicon substrate was not seen to
`affect the mode of crystallite growth. However, when the
`substrate bias was low, Vb of —40V, intercolumnar voids
`formed along the grain boundaries. No significant changes
`in the morphology of the grains were observed over depo-
`sition temperatures ranging from room temperature to 550°
`C. At high flow rates of nitrogen, stoichiometric TiN was the
`only compound formed, however, at sufficiently low nitro-
`gen fiow rates, a film consisting of a mixture of Ti2N with
`a small amount of Ti is formed, and the columnar morphol-
`ogy is said to be absent.
`A series of ten sequential layers deposited at different
`thicknesses, where the growth conditions for the TiN film
`were slightly varied. For example,
`the bias voltage was
`varied from —120V to —125V, and the nitrogen flow rate was
`varied from about 2.3 sccm to 2.5 sccm (within the nitrogen
`flow rates where stoichiometric TiN was the only compound
`formed). Distinct interfaces appeared between the sequential
`thin layers. However, when the deposition was interrupted
`(for periods up to 10 minutes) there was no change in the
`lattice of the TiN grains due to the interruption. The colum-
`nar morphology appeared at an early state of growth and was
`interrupted only at the interfaces where the growth condi-
`tions changed.
`US. Pat. No. 4,944,961 to Lu et al., issued Jul. 31, 1990,
`describes a process for partially ionized beam deposition of
`metals or metal alloys on substrates, such as semiconductor
`wafers. Metal vaporized from a crucible is partially ionized
`at the crucible exit, and the ionized vapor is drawn to the
`substrate by an imposed bias. Control of substrate tempera-
`ture is said to allow non-conformal coverage of stepped
`surfaces such as trenches or vias. When higher temperatures
`are used, stepped surfaces are planarized. The examples
`
`Page 6 of 13
`
`
`
`Page 6 of 13
`
`

`

`
`
`6,156,647
`
`3
`given are for aluminum deposition, where the non-
`conformal deposition is carried out with substrate tempera-
`tures ranging between about 150° C. and about 200° C., and
`the planarized deposition is carried out with substrate tem-
`peratures ranging between about 250° C. and about 350° C.
`S. M. Rossnagel and J. Hopwood describe a technique of
`combining conventional magnetron sputtering with a high
`density,
`inductively coupled RF plasma in the region
`between the sputtering cathode and the substrate in their
`1993 article titled “Metal ion deposition from ionized mag-
`netron sputtering discharge”, published in the J. Vac. Sci.
`Technol. B. Vol. 12, No. 1, January/February 1994. One of
`the examples given is for titanium nitride film deposition
`using reactive sputtering, where a titanium cathode is used
`in combination with a plasma formed from a combination of
`argon and nitrogen gases.
`US. patent application Ser. No. 08/511,825 of Xu et al.,
`filed Aug. 7, 1995, assigned to the assignee of the present
`application, and hereby incorporated by reference in its
`entirety, describes a method of forming a titanium nitride-
`comprising barrier layer which acts as a carrier layer. The
`carrier layer enables the filling of apertures such as vias,
`holes or trenches of high aspect ratio and the planarization
`of a conductive film deposited over the carrier layer at
`reduced temperatures compared to prior art methods.
`A “traditionally sputtered” titanium nitride-comprising
`film or layer is deposited on a substrate by contacting a
`titanium target with a plasma created from an inert gas such
`as argon in combination with nitrogen gas. A portion of the
`titanium sputtered from the target reacts with nitrogen gas
`which has been activated by the plasma to produce titanium
`nitride, and the gas phase mixture contacts the substrate to
`form a layer on the substrate. Although such a traditionally
`sputtered titanium nitride-comprising layer can act as a
`wetting layer for hot aluminum fill of contact vias, good fill
`of the via generally is not achieved at substrate surface
`temperature of less than about 500° C. To provide for
`aluminum fill at a lower temperature, Xu et al. (as described
`in US. patent application Ser. No. 08/511,825 now US. Pat.
`No. 5,962,923), developed a technique for creating a tita-
`nium nitride-comprising barrier layer which can act as a
`smooth carrier layer, enabling aluminum to flow over the
`barrier layer surface at lower temperatures (at temperatures
`as low as about 350° C., for example). A typical barrier layer
`described by Xu et al.,
`is a combination of three layers
`including a first layer of titanium (Ti) deposited over the
`surface of the via; a second layer of titanium nitride (TiN)
`is deposited over the surface of the first titanium layer;
`finally a layer of TiNx is deposited over the TiN second layer.
`The three layers are deposited using Ion Metal Plasma (IMP)
`techniques which are described subsequently herein. Typi-
`cally the first layer of titanium is approximately 100 A to
`200 A thick; the second layer of TiN is about 800 A thick,
`and the third layer of TiNx is about 60 A thick. A good fill
`of contact vias having 0.25y diameter through holes having
`an aspect ratio of about 5 was achieved.
`US. patent application Ser. No. 08/825,216 of Ngan et al.,
`filed Mar. 27, 1997 now US. Pat. No. 5,925,225, discloses
`various process techniques which can be used to control the
`crystal orientation of a titanium nitride barrier layer as it is
`deposited. By producing a titanium nitride barrier layer
`having a high <111> grain orientation content, the <111>
`grain orientation of an overlying aluminum layer is
`increased, whereby the electromigration properties of the
`aluminum are improved.
`US. patent application Ser. No. 08/824,911 of Ngan et al.,
`filed Mar. 27, 1997 discloses improved Ti/TiN/TiNx barrier/
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`wetting layer structures which enable the aluminum filling
`of high aspect vias while providing an aluminum fill exhib-
`iting a high degree of aluminum <111> grain orientation.
`Although deposition of a metallic interconnect
`layer
`which exhibits a reduced tendency for electromigration and
`for general diffusion of the metal from the metallic layer is
`helpful, there is still the problem of the migration of mobile
`silicon atoms during device fabrication. The use of oxygen
`stuffing reduces the silicon migration problem, but requires
`a thermal annealing which is time consuming and increases
`the cost of the fabrication equipment. It would, then, be
`highly desirable to have a barrier layer structure which
`prevents silicon migration without
`the need for oxygen
`stuffing and without the need for high temperature annealing
`of the barrier layer structure (as required for oxygen stuffing
`and for the formation of a silicide layer).
`SUMMARY OF THE INVENTION
`
`An improved barrier layer structure for the prevention of
`migration within a semiconductor device can be formed
`from a refractory metal compound such as a refractory metal
`nitride. The barrier layer structure includes at
`least two
`adjacent layers of essentially the same chemical composition
`having an essentially continuous interfacial region between
`them, wherein the interfacial region is at least 10 A thick. As
`an alternative to having a continuous interfacial region, a
`series of adjacent layers which provide sufficient interfacial
`regions can be used in combination to block the migration of
`mobile atoms such as silicon. When a series of layers is used,
`there should be at least 3 layers, and preferably 5 or more
`layers, where each layer is at least about 50 A thick. In
`addition, to break the continuity of channels passing through
`grain boundaries, alternating layers of substantially grain
`oriented, columnar microstructure and amorphous, non-
`columnar structure are preferred.
`The preferred embodiment used to demonstrate the inven-
`tion is a titanium nitride-comprising barrier layer structure
`prepared using reactive ion metal plasma deposition tech-
`niques.
`To create an interface between at least two layers, the
`process of layer deposition is altered to the extent during
`crystal formation that the majority of the grain orientation
`changes from one form to another form. An alternative
`interfacial structure is one in which one layer is deposited in
`a manner which provides a grain-oriented columnar or
`semi-columnar structure while an adjacent layer is deposited
`in a manner which disrupts crystal formation sufficiently that
`an amorphous, non-columnar structure is produced. Typi-
`cally an amorphous structure is produced when approxi-
`mately 50% or less of the structure exhibits a grain orien-
`tation.
`
`When the barrier layer material is titanium nitride, to form
`a continuous interfacial layer, it is preferable to go imme-
`diately from a <111> TiN grain orientation to an amorphous
`TiN structure.
`
`Changes from one grain orientation to another, or to no
`grain orientation are achieved by changes in the deposition
`process variables. In the physical vapor deposition process
`of ion metal plasma deposition (IMP) or reactive ion metal
`plasma deposition (RIMP), changes in grain orientation are
`achieved as follows. By increasing the DC power to the
`metal or metal-comprising target, a TiN <111> grain orien-
`tation can be obtained. When the substrate on which the
`
`barrier layer is to be deposited is not biased during deposi-
`tion of the barrier layer, an increase in the RF power to the
`IMP ionization source is used to change a TiN <111> grain
`
`Page 7 of 13
`
`
`
`Page 7 of 13
`
`

`

`
`
`6,156,647
`
`5
`orientation to a <200> grain orientation. When RIMP is used
`to create the TiN, and there is less than a stoichiometric
`amount of nitrogen in the ionization area, an increase in the
`nitrogen flow to the reaction chamber can be used to increase
`the amount of <200> grain orientation. When the substrate
`is biased to attract ions toward the substrate surface, an
`increase in the substrate bias is used to produce a structure
`having no grain orientation. By manipulating this combina-
`tion of variables, one can obtain the interfacial regions
`between layers of barrier material and improve the overall
`performance of the barrier structure.
`Apreferred embodiment method of forming the titanium
`nitride structure comprising at least two individual layers
`having a continuous interfacial region between them,
`wherein the interfacial region is at least 10 A thick com-
`prises the following steps:
`a) IMP or RIMP depositing a layer of barrier layer
`material using a substrate bias power which enables the
`formation of an amorphous structure; and
`b) depositing at least one adjacent layer of barrier layer
`material in a manner which enables the formation of a
`
`structure wherein the majority of the structure has the
`same grain orientation.
`Preferably the adjacent layer exhibiting grain orientation
`is also deposited using IMP or RIMP deposition techniques.
`For a TiN barrier layer structure, preferably the grain
`orientation is <111>.
`
`The most economical method of forming this barrier layer
`is to apply all of the layers in a continuous process without
`removing the semiconductor substrate from the process
`chamber. Since no high temperature annealing step is
`required to form the silicon-immobilizing barrier layer,
`fabrication in a single process chamber is easily carried out.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a schematic of the critical elements of an ion
`
`metal plasma deposition or reactive ion metal plasma depo-
`sition process chamber, including a sputtering target, an RF
`powered coil for creating and maintaining ionized species
`within a plasma over the surface of the semiconductor
`substrate, and a means for application of RF power to the
`support platen on which the substrate sets, enabling the
`creation of a bias on the substrate.
`FIG. 2 is a schematic of a cross-sectional view of the
`
`microstructure of a barrier layer, produced using high reso-
`lution transmission electron microscopy tunneling electron
`microscope (TEM), where a plurality of layers have been
`deposited, with each layer produced under a different set of
`process condition variables, for evaluation of the effect of
`the set of variables on the composition and microstructure of
`each individual layer.
`FIG. 3A illustrates a schematic of cross-sectional view of
`
`the microstructure (determined by TEM) of a conductive
`contact formed within a high aspect ratio via, and shows, in
`particular, a multilayered barrier structure of the kind
`described in this patent application.
`FIG. 3B is a schematic of an enlargement of the area
`marked 3B on FIG. 3A, for purposes of discussing tile
`microstructure of the individual layers within the multilay-
`ered structure.
`FIG. 4 is a schematic of a cross-sectional view of the
`
`microstructure (by TEM) of a second barrier layer structure
`where a plurality of layers have been deposited, with each
`layer produced under a different set of process condition
`variables, for evaluation of the effect of a set of variables on
`the composition and microstructure of each individual layer.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`FIG. 5 is a graph showing XRD data for various layers of
`TiN deposited using RIMP deposition techniques.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`An improved barrier layer for the prevention of the
`migration of silicon within a semiconductor device can be
`formed from a refractory metal compound or a refractory
`metal nitride by the creation of a structure comprising at
`least two individual layers having a continuous interfacial
`region between them, wherein the interfacial region is at
`least 10 A thick. As an alternative to having a continuous
`interfacial region, a series of individual layers can be used
`to block the migration of the silicon. When a series of layers
`is used, there should be at least 3 layers, where each layer is
`at least 50 A thick. In addition, to avoid the formation of
`channels which cross grain boundaries, alternating layers of
`highly grain oriented and amorphous structure are preferred.
`I. DEFINITIONS
`
`As a preface to the detailed description, it should be noted
`that, as used in this specification and the appended claims,
`the singular forms “a”, “an”, and “the” include plural
`referents, unless the context clearly dictates otherwise. Thus,
`for example, the term “a semiconductor” includes a variety
`of different materials which are known to have the behav-
`ioral characteristics of a semiconductor, reference to a
`“plasma” includes a gas or gas reactants activated by an RF
`glow discharge, reference to “the contact material” includes
`aluminum, aluminum alloys, and other conductive materials
`which have a melting point enabling them to be sputtered
`over the temperature range described herein.
`Specific terminology of particular importance to the
`description of the present invention is defined below.
`The term “aluminum” includes alloys of aluminum of the
`kind typically used in the semiconductor industry. Such
`alloys include aluminum-copper alloys, and aluminum-
`copper-silicon alloys, for example. The preferred embodi-
`ments described herein were for aluminum comprising about
`0.5% copper.
`The term “aspect ratio” refers to the ratio of the height
`dimension to the width dimension of particular openings
`into which an electrical contact is to be placed. For example,
`a via opening which typically extends in a tubular form
`through multiple layers has a height and a diameter, and the
`aspect ratio would be the height of the tubular divided by the
`diameter. The aspect ratio of a trench would be the height of
`the trench divided by the minimal travel width of the trench
`at its base.
`
`The term “feature” refers to contacts, vias, trenches, and
`other structures which make up the topography of the
`substrate surface.
`
`The term “ion-deposition sputtered” and the term “ion
`metal plasma” (IMP) refer to sputter deposition, preferably
`magnetron sputter deposition (where a magnet array is
`placed behind the target). A high density,
`inductively
`coupled RF source is positioned between the sputtering
`cathode and the substrate support electrode, whereby at least
`a portion of the sputtered emission is in the form of ions at
`the time it reaches the substrate surface.
`
`The term “reactive ion deposition” or “reactive ion metal
`plasma” (RIMP) refers to ion-deposition sputtering wherein
`a reactive gas is supplied during the sputtering to react with
`the ionized material being sputtered, producing an ion-
`deposition sputtered compound containing the reactive gas
`element.
`
`Page 8 of 13
`
`
`
`Page 8 of 13
`
`

`

`
`
`6,156,647
`
`7
`The term “Rutherford Backscattering Spectra” or “RBS”
`refers to a technique used to determine the composition and
`the atomic ratio of the components of a given barrier layer.
`RBS spectra are acquired by exposing a sample to an
`incident helium beam, with the sample perpendicular to the
`beam. Then data are collected using a normal angle detector
`and a glancing angle detector to measure backscattered
`helium ions at angles of 160°, and 100° or 95°, respectively.
`In the present instance the data are used to determine the
`composition of TiN layers.
`The term “traditional sputtering” refers to a method of
`forming a film layer on a substrate wherein a target is
`sputtered and the material sputtered from the target passes
`between the target and the substrate to form a film layer on
`the substrate, and no means is provided to ionize a substan-
`tial portion of the target material sputtered from the target
`before it reaches the substrate. One apparatus configured to
`provide traditional sputtering is disclosed in US. Pat. No.
`5,320,728, the disclosure of which is incorporated herein by
`reference. In such a traditional sputtering configuration, the
`percentage of target material which is ionized is less than
`10%, more typically less than 1%, of that sputtered from the
`target.
`
`The term “XRD” (X-ray Diffraction) refers to a technique
`commonly used to measure crystalline orientation, wherein
`radiation over particular wavelengths is passed through the
`material
`to be characterized, and the diffraction of the
`radiation, caused by the material through which it passes, is
`measured. A map is created which shows the diffraction
`pattern, and the crystal orientation is calculated based on this
`map.
`
`II. AN APPARATUS FOR PRACTICING THE
`INVENTION
`
`A process system in which the method of the present
`invention may be carried out is the Endura® Integrated
`Processing System available from Applied Materials, Inc. of
`Santa Clara, Calif. In particular, one of the process chambers
`in the Endura® System can be used to produce sputter
`deposited barrier layer structures, and in particular, reactive
`ion metal plasma sputter deposited barrier layer structures.
`The critical elements of a reactive ion metal plasma
`sputter deposition system are shown in a schematic format
`in FIG. 1. Process chamber 100 is used for the IMP depo-
`sition of a barrier layer such as a Ti/TiN/TiNx layer.
`Process chamber 100 is typically is a magnetron chamber
`which employs a standard sputter magnet (not shown) to
`confine the sputtering plasma, enabling an increased sput-
`tering rate. In addition,
`the process chamber includes an
`inductively coupled RF source 110, typically in the form of
`a coil 108, positioned between a sputtering cathode (target)
`102 and the substrate support electrode 104, whereby at least
`a portion of the sputtered emission is in the form of ions at
`the time it reaches the substrate surface. An RF power source
`106 is used to apply a bias to substrate support electrode 104,
`enabling formation of a DC bias on semiconductor substrate
`105. Typically a shield 113 surrounds the area in which
`plasma 105 is created from gases which enter through
`channels 103. Shield 113 is surrounded by a vacuum cham-
`ber 112 which enables the evacuation of gases from the
`substrate processing area 107 through evacuation channels
`(not shown). In the preferred embodiment of the present
`invention where the barrier layer to be formed is a refractory
`metal nitride, titanium nitride, the refractory metal nitride is
`formed by sputtering a titanium target using techniques
`known in the art, where argon is gas used to create sputtering
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`ions, and by adding nitrogen to the process chamber 100
`through channels 103. At least a portion of the nitrogen is
`ionized as it passes by ionization coil 108. The reactive
`nitrogen is free to react with reactive titanium to form
`titanium nitride which is then attracted toward the surface of
`
`semiconductor substrate 105 by the bias placed on that
`substrate.
`
`EXAMPLE ONE
`
`To form the titanium-nitride (TiNx) comprising barrier
`layer structures of the present invention,, a titanium target
`cathode of about 14 inches (35.5 cm) in diameter was used,
`and a DC power was applied to this cathode over a range
`from about 2.5 kW to about 5 kW. The substrate, comprising
`an 8 inch (20.3 cm) diameter silicon wafer, was placed a
`distance of about 5.5 inches (14 cm) from the target cathode.
`A high density, inductively coupled RF plasma was gener-
`ated in the region between the target cathode and the
`substrate. The inductively coupled plasma was generated by
`applying RF power to a coil having at least one turn and
`preferably from about 1 to 3 turns. The power was applied
`at a frequency of about 2 MHz and at a wattage of about 2.5
`kW. Typically the coil is fabricated from metal tubing which
`permits water cooling, and has a diameter of about 0.125
`inch (0.32 cm). However, the coil can be fabricated from a
`sheet or ribbon, or other form which provides the desired
`function.
`
`A substrate bias voltage ranging from 0 to about —300 V
`DC was applied to the substrate by application of RF power
`to the platen on which the substrate sets. The RF power at
`a frequency of about 400 kHz was applied at wattages
`ranging from zero W to about 450 W.
`Depending on the desired composition of the TiNx, where
`X ranged from about 0.8 to about 1.5, the amount of nitrogen
`gas fed to the chamber ranged from about 20 sccm of
`nitrogen to about 70 sccm of nitrogen, with a constant feed
`of argon at about 25 sccm, for plasma production and
`substrate heat transfer purposes.
`
`III. THE COMPOSITION AND
`
`MICROS