Barrier Properties of Titanium Nitride Films Grown by Low
`Temperature Chemical Vapor Deposition from Titanium
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`Tetraiodide
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`Cheryl Faltermeier, Cindy Goldberg, Michael Jones, Allan Upham, Dirk Manger, Gregory Peterson,
`Janice Lau, and Alain E. Kaloyeros
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`New York State Center for Advanced Thin Film Technology and Department of Physics, The University at Albany,
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`State University of New York, Albany, New York 12222, USA
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`Barry Arkles
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`Gelest, Incorporated, Tullytown, Pennsylvania 19007, USA
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`Ajit Paranjpe®
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`Texas Instruments, Incorporated, Dallas, Texas 75265, USA
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`ABSTRACT
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`__ Results are presented from a systematic study of the composition, texture, and electrical properties of titanium nitride
`(TiN) films and their performanceas diffusion barrier in multilevel interconnect schemesof ultralarge scale integration
`(ULSI) computer chip device structures. The films were grown by low temperature (<450°C) inorganic chemical vapor
`deposition using titanium tetraiodide as source precursor and ammonia and hydrogen as co-reactants. The TiN films were
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`nitrogen-rich., with iodine concentrations below 2 atom percent, displayed resistivities in the range 100 to 150 pQ cm
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`depending on thickness, and exhibited excellent step coverage with better than 90% conformality in both nominal 0.45 wm,
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`3:1 aspect ratio and 0.25 wm, 4:1 aspect ratio contact structures. A comparison of the properties of chemical vapor
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`deposited (CVD) TiN with equivalent physical vapor deposited (PVD) TiN showedthat reactivity with Al-0.5 a/o Cu alloys
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`was equivalent in both cases. In particular, a 10% increase in the Al-Cu/TiN stack sheet resistance was observed for both
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`types of TiN after a 450°C, 30 minsinter. Similarly, the characteristics of CVD tungsten and reflow plug fills were iden-
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`tical on both types of TiN films. However, barrier performance for CVD TiN in aluminum and tungsten plug technologies
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`was superior to that of PVD TIN,as evidenced by lower contact diode leakage for CVD TiN in comparison with PVD TiN
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`films of equal thickness. This improved barrier performance could be attributed to a combination of factors, which
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`include the nitrogen-rich composition, higher density, and enhanced conformality of the CVD TiN phase in comparison
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`with the PVD TiN.In view of the superior step coverage and diffusion barrier characteristics, the low temperature inor-
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`ganic CVD route to TiN seems to provide an adequate replacementfor conventional PVD TiN in emerging ULSI metal-
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`lization interconnect schemes.
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`plicity, controllability, and ability to coat large area sub-
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`Introduction
`strates with excellent uniformity at industrially viable
`Titanium nitride (TIN) is a commonly used material in
`growth rates, CVD could potentially meet performance
`current integrated circuit (IC) technologies.’ Its applica-
`demands well into the 0.18 wm device technology and
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`tions range from diffusion barrier and glue layer at the
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`beyond.
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`contact/via level to diffusion barrier and antireflection
`Early attempts at preparing CVD TiN used mostly tita-
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`coating in the interconnect stack.” Such applications are
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`nium tetrachloride (TiCl,) and ammonia (NH,) to yield stoi-
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`madepossible by the desirable properties of TiN, includ-
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`chiometric TiN films having good step coverage.’ The
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`ing its refractory nature at elevated temperature, excellent
`impurities produced by this process, mainly chlorine, were
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`mechanical, chemical, and thermal inertness, and good
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`within 1 atomic percent (a/o). Unfortunately, the process-
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`resistance to corrosion. These properties allow TiN to
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`ing temperatures required to produce these films were in
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`withstand the repeated thermal cycles use in multilevel
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`excess of 650°C, and were thus prohibitive for use above
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`metallization of IC devices, and makeits continued use in
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`the contact level. Efforts to reduce deposition tempera-
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`emerging subquarter micron device technologies highly
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`tures included plasma-assisted CVD (PACVD)of TiCL, ina
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`desirable. However, the suitability of TiN for such appli-
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`mixture of nitrogen and hydrogen,electron cyclotron res-
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`cationsis only possible if it is deposited with good confor-
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`onance (ECR) plasma CVD of TiCl, in a nitrogen atmos-
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`mality in subquarter micron features, leading to void-free
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`phere,’ and atmospheric pressure CVD (APCVD) using
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`plug formation, reduced junction leakage, and low con-
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`TiCl, and isopropylamine or tert-butylamine as the co-
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`tact/via resistance. This requirement is further complicat-
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`reactant.? These efforts led to an appreciable reduction in
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`ed by a strong pushto reducebarrier thickness, as device size
`process temperatures to within the acceptable range of
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`shrinks, to provide thecross section of aluminum or copper
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`about 350 to 500°C. However, various reliability issues
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`conductor required for optimum device performance.
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`ranging from poor step coverage (30 to 70%) in somecases,
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`Conventional physical vapor deposition (PVD)routes to
`to high resistivities (> 200 ~ em) and chlorine contami-
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`TiN, with their inherent line of sight type deposition,
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`nation above several atomic percent, in other cases, pre-
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`appear to have reached their maximum useful lifetime,
`vented their incorporation in the IC process flow.
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`even with the addition of special features such as collima-
`There are several recent reports on metallorganic CVD
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`tors.2 Modified PVD processes,
`including high density
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`(MOCVD)of TiN from dialkylamino derivatives of titani-
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`plasma sputtering, appear to provide acceptable near term
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`um of the type Ti(NR,),, where R is a methyl or ethyl
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`solutions, at least for the 0.25 ~m device generation.**
`group.” Additional MOCVD studies involved the use of
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`Chemical vapor deposition (CVD), on the other hand,
`single-source
`titanium precursors
`of
`the
`type
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`offers a low temperature alternative which is inherently
`[TiCl,(NHR,)(NH,R)-»] and [TiCL(NR;).], and cyclopenta-
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`capable of conformal metal growth. By combining sim-
`dienyl-based titanium compoundsof the type biscyclopen-
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`tadieny} titanium diazide, Cp,Ti(N,), (where Cp = C,H,).”
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`2 Present address: CVC Products, Inc., Rochester, New York
`These activities led to the developmentof robust and ver-
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`14603, USA.
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`JU. Electrochem. Soc., Vol. 144, No.3, March 1997 © The Electrochemical Society, Inc.
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`Tianma Exhibit 1014
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`1002
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`Page | of 7
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`Page 1 of 7
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`Tianma Exhibit 1014
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`

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`J, Electrochem. Soc., Vol. 144, No.3, March 1997 © The Electrochemical Society, Inc.
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`1003
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`satile MOCVD TiN processes,” with MOCVD from
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`Ti(NEt,),, for example, yielding resistivity below 300 20
`cm, carbon contamination under 3 a/o, and step coverage
`as high as 70% in 0.35 ym device structures.
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`The strategy espoused herein has focused, instead, on
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`low temperature inorganic CVD of TiN from titanium
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`tetraiodide (Til,). Til, was selected because the dissocia-
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`tion energy of the Ti-I is relatively low, with a correspond-
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`ing heat of formation at 298 K of —92 kcal/mol. This
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`value is well below the heat of formation for TiCl,, name-
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`ly, ~192 keal/mol. Accordingly, and in view of the similar
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`chemical characteristics of the two halide chemistries, Til,
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`is expected to yield TiN films in an ammonia atmosphere
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`with properties and performance similar to those from
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`TiCl, but at significantly lower temperature.
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`Additionally, the activation energy for iodine diffusion
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`is expected to be significantly higher than chlorine, given
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`that I is a much heavier element than Cl. This expectation
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`is based on work on the interaction of fluorine and chlo-
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`rine with (111) Si,“ and which showed that the barrier for
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`chlorine penetration into the Si surface is much larger
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`than that for fluorine. This behavior was a consequence of
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`the larger size, and hence ionicity and resulting coulomb
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`interaction, of the chlorine atom in comparison with fluo-
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`rine. This property has important implications for the
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`effects of residual halide incorporation in the deposited
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`TiN, with 1 a/o iodine requiring appreciably higher ther-
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`mal energy to diffuse out of TiN lattice than its chlorine
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`counterpart. This observation is also supported by the
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`findings presented herein, including diode leakage meas-
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`urements, and which indicate that 2 a/o iodine did not
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`affect TIN performanceas diffusion barrier/adhesion pro-
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`moter.
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`Thepaperis the secondin a series of reports on the iden-
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`tification and optimization of a low temperature inorgan-
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`ic CVD process for TiN from Til,."* The first report has
`focused on the development of a low-temperature,in situ,
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`sequential CVD process for the deposition of ultrathin
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`Ti/TiN bilayers for applications in device ULSI technolo-
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`gies. In this article, results are presented from a systemat-
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`ic study of the microstructural, microchemical, and elec-
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`trical characteristics of TiN films, as well as their
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`performance in 0.45 ym, 3:1 aspect ratio contact/plug
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`device structures. The findings from this study are com-
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`pared and contrasted with those from PVD TiN grown by
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`conventional PVD techniques.
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`Experimental
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`The CVD reactor used for inorganic CVD of TiN from
`Til, was a custom-made,8 in. wafer, cold wall system, and
`wasdescribed in detail elsewhere.” Briefly, it consisted of
`a parallel plate plasma configuration with the wafer locat-
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`ed on the bottom electrode, which was resistively heated
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`using an externally positioned boron nitride-coated
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`graphite heater. The top active electrode was formed in the
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`shape of a circular meshto allow unrestricted flow of the
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`reactants through a cone-shaped shower head located
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`above the mesh. Pumping was achieved through eight
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`ports which were symmetrically distributed below the
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`heater chuck to permit uniform gas flow distribution. A
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`standard pressure based sublimator was used to store the
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`solid Til, precursor, which was delivered to the reaction
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`zone with the assistance of a hydrogen carrier gas.
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`Ammonia reactant flow was delivered through a sideline
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`directly to the reaction zone. A soft hydrogen plasma pre-
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`deposition clean was performed on all samples prior to
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`deposition. However, no plasma was used during actual
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`deposition. Several types of wafers were processed, as
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`shownin Table I, using the process conditions summarized
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`in Table II.
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`Methodsof Analysis
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`The TiN film microchemical, microstructural, and elec-
`trical properties were thoroughly analyzed at the New
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`York State Center for Advanced Thin Film Technology by
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`Page 2 of 7
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`Table |. Type and numberof wafers used in the study.
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` Wafer type Numberof wafers Thickness CVD TiN
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`1000 A PETEOS/Si
`900 + 50A
`2
`30 +2A
`2
`Si
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`230+5A_
`2
`Si
`0.45 2m contact
`620+ 12A
`3
`0.45 pm contact
`230 +5 A,
`2
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`0.45 4m contact
`300 + 10A
`1
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`0.45 zm contact
`400+ 10A
`1
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`0.45 pm contact/n*
`30 +2A
`3
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`salicide junction
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`0.45 ~m contact/n*
`230 +5A
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`salicide junction
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`0.45 4m contact/n*
`400 +10A
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`salicide junction
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`3
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`TableII. Summary of processing parameters.
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`Process parameter
`Value
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`Source precursor
`Wafer temperature
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`Source temperature
`Reactor pressure
`Ammoniareactant flow
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`Hydrogen carrier gas flow
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`In situ predeposition
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`Hydrogen Plasma clean
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`Til,
`430°C
`140°C
`0.3 torr
`600 sccm
`30 sccm
`13.56 Mhz@
`0.08 W/cm?
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`x-ray photoelectron spectroscopy (XPS), Rutherford
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`backscattering (RBS), x-ray diffraction (KRD), four-point
`resistivity probe, and cross-sectional scanning electron
`microscopy (CS-SEM). In these studies, the results were
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`standardized using a pure TiN standard deposited by col-
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`limated sputtering at SEMATECH. Additional composi-
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`tional and structural characterization was also carried out
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`independently at SEMATECH.
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`Film composition was determined using XPS and RBS.
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`XPS was carried out on a Perkin-Elmer PHI 5500 Multi-
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`Technique System. A magnesium x-ray source at 15 kV
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`and 300 W wasused. High resolution XPS scans employed
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`a 23.50 eV pass energy to resolve shifts from particular
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`photoelectron peaks.
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`In addition to performing compositional characteriza-
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`tion, RBS was also employed, in conjunction with CS-
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`SEM,
`for thickness and growth rate measurements.
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`Rutherford backscattering (RBS) spectra were taken using
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`a 2 MeV He* beam, and calibrated with bulk samples of
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`gold and carbon, while CS-SEM investigations employed
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`a Zeiss DSM 940 microscope using a 20 keV primary elec-
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`tron beam. Four-point probe resistivity measurements
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`used a Signatone four-point probe. Deposition rates were
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`defined as T/t, where T is film thickness andt is run time.
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`Run time was measuredstarting form the instant when the
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`precursor was actually being delivered to the reactor.
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`X-ray diffraction was done on a Scintag XDS 2000 x-ray
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`diffractometer. X-rays were generated with a Cu K, x-ray
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`source at typical tube operating power of 1.8 kW, which
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`corresponds to 40 mA and 45 kV. XRD spectra were col-
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`lected both in normal incidence and 5° grazing angle
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`geometries. The resulting TIN XRD patterns were com-
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`pared with the sputtered TiN standard provided by
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`SEMATECH anda TiN reference pattern from the stan-
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`dard JCPDS powderdiffraction file (PDF).
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`A complete evaluation of the physical properties and
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`barrier characteristics of the TiN films was carried out at
`
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`the Semiconductor Process and Device Center of Texas
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`Instruments. The microchemical and electrical measure-
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`ments performed above at the Albany Center were repeat-
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`ed as an independent checking mechanism of TiN film
`
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`properties. The parameters measured and corresponding
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`methods of analysis are summarized in Table III and dis-
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`cussed in more detail in the following sections. In these
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`studies, the results were standardized using a pure TiN
`
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`standard deposited by collimated sputtering at Texas
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`Instruments.
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`Page 2 of 7
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`

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`1004
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`J. Electrochem. Soc., Vol. 144, No.3, March 1997 © The Electrochemical Society, Inc.
`
`Table IV. Summary of results.
`TableIll. Methodsof analysis.
`
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`
`
`Method
`Parameter
`Parameter
`Value
`
`
`
`
`
`
`
`
`
`Four-pgint probe (900 A TiN on
`Deposition rate (A/min)
`200
`Sheet resistance
`.
`Nonuniformity (%, 1c)
`1000 A PETEOS/Si)
`5 to 8
`
`
`Step coverage (%)
`Profilometry (900 A TiN on 1000 A
`90
`PETEOS/Si) RBS
`.
`Resistivity (uM cm)
`100 to 150
`
`
`Density Weight gain (900ATiN on 1000 A Stoichiometry (Ti:N) 1:1.06
`
`
`
`
`
`
`
`
`
`5
`PETEOS/Si)
`<2 a/o iodine
`Impurities
`.
`
`
`
`
`
`
`RBS and XPS(900 A TiN on 1000 A
`<1 a/o oxygen
`
`
`
`
`
`
`
`
`PETEOS/Si)
`1.1 times that of PVD TiN
`Density
`
`
`
`
`CS-SEM (230, 400, 900 A TiN on
`Golden
`Color
`
`
`
`
`
`
`
`
`0.45 and 0.25 wm contact)
`Zero
`Stability (AR,/2 h, %)
`
`
`230, 400, 600 A TiN on
`Similar to PVD TiN
`CVD W plugfill
`
`
`
`
`
`
`
`
`
`
`0.45 2m contact
`Similar to PVD TiN
`Al reflow plugfill
`
`
`
`
`Used 30 to 230 A CVD TINonSi:
`Similar to PVD TiN
`Reactivity with Al-Cu
`
`
`
`
`
`
`(i) Deposited 600 A Al-0.5 a/o Cu
`Barrier property
`Superior to PVD TiN
`
`
`
`
`
`
`
`then sintered at 450 to 550°C for
`
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`
`
`
`
`
`
`30 to 60 min. (ii) Measured pre-
`
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`
`
`and post Al-Cu sheet resistance.
`
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`
`
`
`
`
`
`RBS analysis of TiN on Si also supported the XPS
`(ii) After sintering, metal was
`
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`
`
`
`
`
`
`
`
`results, and indicated the presence of about 2 a/o iodine
`stripped and optical microscopy
`
`
`
`
`
`
`used to quantify pit density in Si.
`
`
`
`
`
`incorporation, as displayed in Fig. 4.
`
`(iv) Samples on Si, plasma TEOS,
`
`
`
`
`The composition of the CVD produced TiN films was
`
`
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`
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`
`
`PVD TiN were similarly processed
`
`
`
`
`nitrogen-rich in comparison with the SEMATECHcolli-
`and used for comparison.
`
`
`
`
`
`
`
`
`
`
`
`
`mated PVD TiN. Levels of iodine in the films are not
`CS-SEM (230, 400, 900 A TiN on
`
`
`
`
`
`
`
`
`
`
`
`0.45 ym contact
`
`
`
`
`
`30 to 400 A TiN on 0.45 pm
`
`
`
`
`contact/n* salicide junction
`
`
`
`30 to 400 A TiN on 0.45 pm
`
`
`
`
`
`contact/n* salicide junction
`
`
`
`
`
`
`
`
`
`
`Thickness
`
`Composition
`
`Step coverage
`
`Barrier attack
`
`Barrier properties
`
`
`
`
`
`
`W plugfill
`Contact resistance
`
`Diode leakage
`
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`
`
`
`
`
`
`
`100
`
`
`
`
`
`
`
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`
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`Sputter Time (mins.}
`
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`
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`
`
`(%)
`AtomicConcentration
`
`
`
`
` NormalizedIntensity(arbitraryunits) a
`
`
`
`NormalizedIntensity(arbitraryunits)
`
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`
`The 900 A CVD TIN films on plasmatetraethylorthosil-
`icate (PETEOS) were analyzed for sheet resistance, sheet
`thickness, density and composi-
`resistance uniformity,
`tion/stoichiometry. Sheet resistance was measured using a
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`four-point probe, thickness was calculated using a pro-
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`filometer, density was determined from weight gain
`
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`measurements, and composition/stoichiometry was
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`
`
`determined from RBS analysis. For the RBS analysis, a
`
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`
`
`PVD (conventional sputtering) TiN film was used as
`indicates a stoichiometric TiN phase
`Fig. 1. XPS depth profiling
`
`
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`
`
`
`control for comparison.
`with iodine concentration below 2 a/o. No oxygen or other conta-
`
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`
`
`The 30 to 230 A CVD TINfilms on Si were used for bar-
`minants were found within the detection limitsofXPS.
`
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`
`
`
`rier studies. A 6000 A AI-0.5 a/o Cu film was sputter
`
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`deposited on the CVD TiN andthe stack was subjected to
`
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`sintering at 450 to 550°C for 30 to 60 min. Sheet resistance
`
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`
`measurements prior to and after sintering were used to
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`quantify the reaction between Al-Cu and CVD TIN. After
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`sintering was complete, the metal was stripped and the
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`density of pits in the silicon was measured on an optical
`
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`
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`microscope to quantify the quality of the CVD TiN barri-
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`er. 6000 A Al-0.5 a/o Cu films deposited directly on Si,
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`plasma TEOS, and PVD TiN were also subjected to simi-
`
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`lar sinter cycles for comparison. The patterned contact
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`wafers were used for step coverage measurements and to
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`evaluate nucleation, barrier attack, and plug-fill during
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`CVD tungsten deposition. Finally, the contacts on the n*
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`salicided junctions were used to measure contact resist-
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`ance and contact-induced diode leakage.
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`Results
`
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`
`
`The TiN films thus produced were metallic, mirror-like,
`
`
`
`
`and gold colored. Their physical properties are summa-
`rized in Table IV and discussed in more detail below. In
`particular, deposition nonuniformityis slightly high, but is
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`an equipment not a process issue, given that a custom-
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`made, nonoptimum,reactor was used in the study.
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`Film composition.—The composition of the films was
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`
`
`examined by XPS and RBS. XPS depth profiling, as
`
`
`
`
`
`
`
`shown in Fig. 1, indicated a nitrogen-rich TiN,; phase
`with iodine concentration below 2 a/o. No oxygen or other
`
`
`
`
`
`
`contaminants were found within the detection limits of XPS
`
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`
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`(~1a/o). Additionally, XPS high resolution spectra of ele-
`
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`
`
`mental core levels yielded a Ti 2p;,. core peak at 455.1 eV,
`
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`
`
`
`as displayed in Fig. 2, corresponding to a pure TiN phase.
`
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`
`
`Figure 3 shows the N 1s binding energy at 397.3 eV, also
`
`
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`
`
`
`indicating a pure TiN phase.
`
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`Page 3 of 7
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`De3
`
`402
`
`398
`Binding Energy (eV)
`
`394
`
`» S °
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`Fig. 3. The XPS N 1s binding energy at 397.3 eV indicates a pure
`
`
`TiN phase.
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`470
`
`466
`
`458
`462
`Binding Energy (eV)
`
`454
`
`450
`
`
`
`
`
`Fig. 2. XPS high resolution spectrum of Ti 2p,,. indicates a core
`
`
`
`
`
`peak at 455.1 eV corresponding to a pure TiN phase.
`
`
`
`
`
`
`
`—T
`390
`
`
`10
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`& a ~
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`Page 3 of 7
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`

`

`J. Electrochem. Soc., Vol. 144, No. 3, March 1997 © The Electrochemical Society,inc.
`
`1005
`
`Units)
`Intensity(Arbitrary
`
`
`10 oO
`
`
`
`NormalizedYield
`
`iS]So
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`
`100
`
`200
`
`300
`Channel
`
`500
`
`600
`
`Fig. 4. RBS analysis of TiN on Si sup
`indicates the incorporation of about 2 a
`
`
`
`
`rts the XPS results, and
`0 iodine.
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`
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`expected to pose any reliability problems, such as Si
`wormhole formation and metal corrosion. This assessment
`is attributed to the higher activation energy for iodinedif-
`fusion as compared with chlorine, given that I is much
`
`
`
`
`
`
`
`
`heavier than Cl. Accordingly, it is expected that 1 a/o
`
`
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`
`
`
`iodine might require appreciably higher thermal energy to
`
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`
`
`
`
`diffuse out of the TiN lattice than its chlorine counterpart,
`
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`
`thus posingless of a reliability problem. This assumption
`
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`
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`
`
`
`
`is supported by the findings presented herein and which
`
`
`
`
`
`
`
`demonstrate that TiN barrier integrity and device perfor-
`
`
`
`
`
`
`
`
`
`mance are not compromisedby2 a/o residualiodinelevels.
`
`
`
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`
`
`It is also in agreement with similar work reported by
`
`
`
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`
`
`
`
`Yokoyama et al. on the mobility of chlorine in CVD TiN
`
`
`
`
`
`
`
`produced from the reaction of TiCl, and NH.”
`
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`Film texture—Figure 5 shows a typical XRD spectrum
`
`
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`
`
`
`
`
`
`of a CVD TiNfilm. The spectrum exhibited reflections cor-
`
`
`
`
`
`
`responding to 20 = 42.34° (111) and 61.98 (220), with the
`(111) orientation exhibiting the highest diffraction inten-
`
`
`
`
`
`
`sity. Interestingly, the XRD spectrum displayed in Fig. 6
`
`
`
`
`
`
`
`
`from SEMATECH'’s sputter-deposited TiN film showed a
`
`
`
`
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`
`
`
`
`different XRD texture, with the (200) orientation showing
`
`
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`
`
`the strongest diffraction peak. Interestingly, Yokoyamaetal.
`
`
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`
`
`
`also observed textural variations between CVD and PVD
`
`
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`
`
`TiN.”
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`The textural variations observed might havesignificant
`
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`
`
`
`implications for the barrier characteristics and associated
`
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`
`
`
`
`differences in the peformance of CVD and PVD grown
`films. Additionally, it has been shown that the texture of
`
`
`
`
`
`
`the TiN film can significantly affect that of the overlaying
`
`
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`
`
`
`aluminum film. Primarily, predominantly (200) textures
`
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`
`TiN leads to the formation of similarly textured alu-
`
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`
`Intensity(ArbitraryUnits)
`
`30
`
`40
`
`0
`
`60
`
`70
`
`Angle 2@ (degrees)
`
`Fig. 5. Typical XRD spectrum of a CVD TiN film. The diffraction
`peak locations and intensities are in good agreement with those
`‘om a standard TiN powder sample,indicating that the TiN film is
`
`
`polycrystalline.
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`Page 4 of 7
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`30
`
`40
`
`60
`50
`Angle 26 (degrees)
`Fig. 6. XRD spectrum of a sputter-deposited TiN film.
`
`70
`
`
`
`
`
`
`
`
`
`
`
`
`minum, while (111) oriented TiN produces an identical
`aluminum orientation. This effect is important since pre-
`dominantly (111) oriented aluminum exhibits enhanced
`electromigration resistance and increased mean time to
`
`
`
`
`
`
`
`failure (MTTF) underelectromigration stress conditions in
`
`
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`
`
`
`
`comparison with its (200) counterpart.’ Additional stud-
`
`
`
`
`
`ies are underway to study these effects and will be report-
`
`
`
`
`
`
`ed in a subsequent publication.
`
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`
`
`Aggressive structure fill and resistivity—Figure 7 dis-
`
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`
`
`
`
`
`plays typical CS-SEM micrographs of TiN step coverage
`
`
`
`in aggressive device trench structures, with nominal fea-
`ture size of 0.45 xm, 3:1 aspect ratio. As can be seen, step
`
`
`
`
`
`coverage is excellent, with 90% conformality observed in
`
`
`
`
`
`
`
`the structures examined. Interestingly, highly conformal
`
`
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`
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`
`
`TiN coverage was achieved across a wide process window,
`
`
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`
`
`
`
`
`as demonstrated in Fig. 8 which shows 90% TiN step cov-
`
`
`
`
`
`
`
`erage in 0.25 wm, 4:1 aspect ratio structures. These sam-
`
`
`
`
`
`ples were processed at a substrate temperature of 425°C,
`
`
`
`
`
`
`
`
`source temperature of 140°C, reactor pressure of 0.5 Torr,
`
`
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`and hydrogen carrier gas and ammonia reactant flowsof,
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`respectively, 30 and 400 sccm. The values observed are sig-
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`nificantly higher than those that can be obtained using
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`collimated PVD TiN. Film resistivity ranged from 100 20
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`em for 1000 A films up to 150 u cm for 100 A films.
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`Barrier properties—The density of the film is high, 1.1
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`times that of the collimated PVD TiN as tested by Texas
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`Instruments, and the films have a strong golden color.
`Films are stable in air and showed noevidenceof oxida-
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`tion, even after prolonged exposureto air. Plug filling with
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`CVDtungsten and Ai reflow are similar for vias lined with
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`CVD TiN or PVD TIN.Reactivity with Al-0.5% Cu during
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`a 450°C, 30 min forminggas sinter wassimilar to the reac-
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`tivity of PVD TiN. The sheet resistance increase upon sin-
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`tering is marginally lower for CVD TiN compared to PVD
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`TiN, as observed in Fig. 9. The various splits indicate that
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`the sheet resistance increase is due to interaction between
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`the Al-Cu and TiN rather than between Al-Cu and Si.
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`After a 550°C, 60 minsinter, splits 1, 2, and 4 show pitting
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`of the Si surface indicative of barrier failure. However the
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`density of pits is maximum for the case of no barrier, and
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`is minimum for the CVD TIN barrier.
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`Superiority of the CVD TiN barrier can also be gauged
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`from the contact-induced diode leakage for a diode with
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`250,000 contacts (Fig. 10). The diode leakage characteris-
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`tics for a 230 A CVD TINfilm are equivalent to those for a
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`500 A PVDTIN film. Increasing the CVD TiN thickness to
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`400 A decreases the leakage further. There is no apprecia-
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`ble difference in diode leakage for block diodes with few
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`contacts except for the case of 30 A CVD TiN which
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`appearsto be too thin, or possibly not even continuous, to
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`yield a reliable measurement (Fig. 11). Additionally, the
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`wider dispersion in the diode leakage current for the 400 A
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`TiN film is attributed to a larger than typical thickness
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`Page 4 of 7
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`

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`1006
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`J. Electrochem. Soc., Vol. 144, No. 3, March 1997 © The Electrochemical Society, Inc.
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`Faeoe
`568 ne
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`Fig. 7. Typical CS-SEM micrograph of TiN step coverage in 0.45 um, 3:1 aspect ratio contacts.
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`variation across the specific wafer used in those measure-
`ments. Accordingly, the worst leakage value corresponded to
`a spot on the wafer where the TiN wasthinner than 400 A.
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`Discussion and Conclusions
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`The results discussed above demonstrate that the low
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`temperature inorganic CVD route is a viable approach for
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`the deposition of TiN for applications as barrier layer and
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`adhesion promoter in emerging subquarter micron device
`technologies. The TiN films thus produced weregold col-
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`ored, stoichiometric, and exhibited metallic conductivity,
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`withresistivities in the range of 100 to 150 pO cm, depend-
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`ing on film thickness. Microchemical analyses showed that
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`the films were free from oxygen or carbon contamination,
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`within the detection limits of XPS, with iodine concentra-
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`Fig. 8. Typical CS-SEM mi-
`crograph of TiN step coverage
`in 0.25 pm, 4:1 aspect ratio
`contacts.
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`Page 5 of 7
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`6o6e131
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`|e) ee on eee
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`tions below 2 a/o. Such levels of iodine concentrations are
`not expected to causereliability problems in device oper-
`ation. This expectation is based on the assumption that
`iodine is significantly heavier than chlorine and will thus
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`require higher activation energy for diffusion out of the
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`TiN matrix. The diode leakage data presented herein
`seems to also support this assessment.
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`A systematic evaluation wasalso carried out of the bar-
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`rier characteristics of CVD TiN using PVD TINas baseline
`material. The data showed that reactivity with Al-0.5 a/o
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`Cu alloys was equivalent in both cases, with the CVD TiN
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`film exhibiting a marginally better performance as com-
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`pared to its PVD counterpart. Similarly, the characteris-
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`tics of CVD tungst