`
`
`
`
`Hongetal.
`
`
`
`
`[54]
`
`
`
`[75]
`
`
`
`
`
`[73]
`
`
`
`DIFFUSION BARRIER TRILAYER FOR
`
`
`
`
`MINIMIZING REACTION BETWEEN
`METALLIZATION LAYERS OF
`INTEGRATED CIRCUITS
`
`
`
`
`
`
`
`
`
`
`
`
`Inventors: Qi-Zhong Hong, Dalias; Shin-Puu
`
`
`
`
`
`
`
`Jeng, Plano; Robert H. Havemann,
`
`
`
`
`
`Garland,all of Tex.
`
`
`
`
`
`
`
`Assignee: Texas Instruments Incorporated,
`
`
`
`
`Dallas, Tex.
`
`
`
`(21)
`
`
`
`[22]
`
`
`
`Appl. No.: 685,159
`
`
`
`
`Filed:
`Jul. 23, 1996
`
`
`
`
`
`
`
`
`
`
`Related U.S. Application Data
`
`
`
`[60]
`
`
`
`[54]
`[52]
`[58]
`
`
`
`
`
`Continuation of Ser. No. 474,286, Jun. 7, 1995, abandoned,
`
`
`
`
`
`
`
`which is a division of Ser. No. 412,473, Mar. 28, 1995,
`
`
`
`
`
`
`
`
`
`abandoned.
`
`Tint. CLS occ HOLL 21/44; HOIL 29/43
`
`
`
`
`
`
`
`
`US. Ce es eecsestsssesseesaeseee 257/751; 257/915; 438/653
`
`
`
`
`
`Field of Search ......ccccccsccesscscceeseene 257/751, 915;
`
`
`
`
`
`437/190, 195
`
`
`
`[56]
`
`
`
`OEYATR
`
`US005668411A
`
`
`
`{11) Patent Number:
`[45] Date of Patent:
`
`
`
`
`
`
`
`5,668,411
`
`
`Sep. 16, 1997
`
`
`
`
`
`
`0525 637 Al
`
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`
`.
`2/1993 European Pat. Off.
`
`
`
`
`OTHER PUBLICATIONS
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Kaizuka T. et al. “AL(111/CVD-TiN(111) Stacked Film
`
`
`
`
`
`
`
`
`
`
`Formation Technique with High Aspect-Ratio Contact Hole
`Filling for Highly Reliable Interconnects”, International
`
`
`
`
`
`
`
`
`
`
`
`
`Conference on Solid State Devices and Materials, Aug. 29,
`1993, pp. 555-557.
`
`
`
`Hideki Shibata, et al. “The Effects of AL(111) Crystal
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Orientation on Electromigration in Half-Micron Layered
`
`
`
`
`
`
`
`AL Interconnects”, Japanese Journal of Applied Physics,
`
`
`
`
`
`
`
`
`
`Oct. 1, 1993, vol. 32, No. 10, Part 1, pp. 4479-4484.
`B. Lee, E.C. Douglas, K. Pourrezaei, and N. Kumar, “Effect
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`of Oxygen on the Diffusion Barrier Properties of TIN”, VLSI
`Multilevel Interconnect Conference (VMIC) Proceedings,
`
`
`
`
`
`
`
`
`pp. 344-350, (1987).
`M. Inoue, K. Hashizume, K. Watanabe, and H. Ysuchikawa,
`
`
`
`
`
`
`“The Properties of Reactive Sputtered TiN Films For VLSI
`
`
`
`
`
`
`
`
`Metallization”, VMIC Proceedings, pp. 205—211, (1988).
`
`
`
`
`
`
`H. P. Kattelus, J. Tandon, C. Sala, and M. —A. Nicolet,
`
`
`
`
`
`
`“Bias—induced Stress Transisitions in Sputtered TiN Films”,
`
`
`
`
`
`
`
`
`
`
`
`
`J. Vac. Sci. Technol. A 4, pp. 1850-1854, (1986).
`
`
`
`
`
`
`H. Joswig and W. Palmer, “Improved Performance of
`TiN—Diffusion Barriers After a Post—Treatment”, VMIC
`
`
`
`
`
`
`
`
`Proceedings, p. 477, (1990).
`W. Sinke, G. Frinjlink, and F. Saris, “Oxygen in Titanium
`
`
`
`
`
`
`
`Nitride Diffusion Barriers”, Appl. Phys. Lett. 47, pp.
`
`
`
`
`
`
`
`
`
`
`471473, (1985).
`T. Kikkawa, H. Aoki, J. Drynan, “A Quarter—-Micrometer
`
`
`
`
`
`
`
`
`
`Interconnection Technology Using a TiN/Al-Si-Cu/TiN/
`ALSi-Cu/TiN/Ti Multilayer Structure”, IEEE Transactions
`
`
`
`
`
`on Electron Devices, vol. 40, No.2, Feb. 1993, pp. 296—302.
`
`
`
`
`
`
`
`
`
`
`Primary Examiner—Tom Thomas
`
`
`Assistant Examiner—David B. Hardy
`
`
`Attorney, Agent, or Firm—Kay Houston; W. James Brady,
`
`
`
`
`
`IM; Richard L. Donaldson
`
`
`ABSTRACT
`
`[57]
`
`
`
`
`
`
`
`
`
`
`A diffusion barrier trilayer 42 is comprised of a bottom layer
`44, a seed layer 46 and a top layer 48. The diffusion barrier
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`trilayer 42 prevents reaction of metallization layer 26 with
`the top layer 48 upon heat treatment, resulting in improved
`
`
`
`
`
`
`
`sheet resistance and device speed.
`
`
`
`
`
`
`
`
`
`
`
`15 Claims, 3 Drawing Sheets
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`SSSawVIIILELAEDEATA
`
`
`
`
`SSSSSSSSSS
`
`
`Bates
`
`
`
`
`
`34 eye
`
`
`
`
`SN
`
`
`
`
`
`
`
`42
`
`
`
`oe
`
`
`
`Page 1 of 9
`
`TSMC Exhibit 1009
`
`References Cited
`
`
`
`U.S. PATENT DOCUMENTS
`
`
`
`.
`5,008,216
`4/1991 Huang et al.
`
`
`
`
`3/1992 Higuchi .........
`5,093,710
`
`
`
`
`6/1992 Kumar et al.
`.
`5,118,385
`
`
`
`
`4/1993 Fujii et al.
`....
`5,202,579
`
`
`
`
`7/1993 Bost etal.
`....
`5,231,053
`
`
`
`
`.
`8/1993 Hindman et al.
`5,240,880
`
`
`
`9/1993 Nulman et al.
`...
`5,242,860
`
`
`
`
`5,270,254 12/1993 Chen et al.
`...
`
`
`
`
`1/1994 Gelatos ........
`5,275,973
`
`
`
`
`5,312,772
`5/1994 Yokoyama etal....
`
`
`
`
`
`5,312,775
`5/1994 Fujii et al.
`........
`
`
`
`
`
`5,313,100
`5/1994 Ishii et al.
`.
`9/1994 Kikkawa.......
`5,345,108
`5/1995 Fiordalice etal.
`5,420,072
`
`
`
`
`- 437/192
`7/1995 Nulman etal. ....
`5,434,044
`
`
`
`
`
`« ABT/LIS
`9/1995 Maeda...............
`5,449,641
`
`
`
`
`
`6/1996 Merchant ef al. o..cssseseceesees 437/190
`5,523,259
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`TSMC Exhibit 1009
`
`Page 1 of 9
`
`
`
`U.S. Patent
`
`
`
`Sep. 16, 1997
`
`
`
`
`Sheet 1 of 3
`
`
`
`5,668,411
`
`
`
`IN
`
`
`
`
`
`
`
`FIG. VALLLLLLLLLLLLLLLO1
`
`(PRIOR ART)
`
`
`
`
`2
`
`20
`
`
`
`
`
`
`
`
`RMA
`RRRRRRAKERREREASEN 6
`
`
`
` Fig. 2 *
`
`LLLLLLLLLLLLL LL
`ZZ
`(PRIOR ART)
`
`
`
`22
`
`
`20
`
`
`1.0
`
`1.2
`
`
`
`
`Energy (Mev)
`
`
`1.4
`
`
`
`1.6
`
`
`
`1.8
`
`
`
`WP
`
`
`
`
`
`— Si02/TiN/Al-Cu, As—deposited
`1 cycle at 450°C
`eee Si0>/TiN/Al-Cu,
`
`
`
`
`
`
`Normalized
`
`Yield
`
`
`10
`
`
`
`
`
`
`
`(PRIOR ART)
`
`
`FIG. 8
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 2 of 9
`
`Page 2 of 9
`
`
`
`US. Patent
`
`
`
`
`Sep. 16, 1997
`
`
`
`Sheet 2 of 3
`
`
`5,668,411
`
`
`20~ SSXQQ
`FIG. 4 Baie
`LdSAYVi2tS
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`20
`
`‘
`
`(PRIOR ART) 34 NSSENG
`34-ESXCN=—_ FIG. §
`
`SN
`
`
`MAN
`
`28 SSSSSSHAHN .ENLeza
`
`
`
`
`
`
`
`
`
`
`
`
`(PRIOR ART)
`
`
`
`
`
`
`
`
`
`*
`
`
`
`ss
`
`
`
`
`
`
`
`
`
`
`mI. 6
`(PRIOR ART)
`
`2
`%
`
`f
`38
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 3 of 9
`
`Page 3 of 9
`
`
`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 3 of 3
`
`5,668,411
`
`40
`t
`
`40
`f
`
`40
`f
`
`FIC. 8 SESS “"
`
`38
`
`38
`
`0.6
`
`0.8
`
`Energy (Mev)
`1.0
`1.2
`
`1.4
`
`1.6
`
`—Al-Cu/TiN/Al-Cu, As—deposited
`oo Al~Cu/TiN/Al-Cu,
`1 cycle at 450°C
`
`seed) 0
`
`
`Normalized
`ield
`
`Bottom Al
`
`100
`
`450
`
`200
`
`300
`250
`Channel
`FIG. 9
`
`350
`
`400
`
`450
`
`Page 4 of 9
`
`Page 4 of 9
`
`
`
`5,668,411
`
`
`
`
`2
`
`
`
`
`
`
`
`
`FIG. 2 is a prior art drawing showing the wafer of FIG. 1
`
`
`
`
`
`
`
`
`after heat
`treatment, where the metallization layer has
`reacted with the diffusion barrier;
`
`
`
`
`
`
`
`1
`DIFFUSION BARRIER TRILAYER FOR
`
`
`
`
`MINIMIZING REACTION BETWEEN
`
`
`
`METALLIZATION LAYERS OF
`
`
`INTEGRATED CIRCUITS
`
`
`
`This is a continuation of application Ser. No. 08/474,286
`
`
`
`
`
`filed Jun. 2, 1995, now abandoned, which is a division of
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`application Ser. No. 08/412,473, filed Mar, 28, 1995, now
`abandoned.
`
`
`FIELD OF THE INVENTION
`
`
`
`
`
`
`
`
`
`
`
`This invention relates generally to the fabrication of
`
`
`
`
`
`
`semiconductor devices, and more specifically to metalliza-
`
`
`
`
`tion layers of integrated circuits.
`BACKGROUND OF THE INVENTION
`
`
`
`
`
`
`
`
`
`
`Semiconductors are widely used in integrated circuits for
`
`
`
`
`
`electronic applications,
`including radios, computers,
`
`
`
`
`
`
`
`televisions, and high definition televisions. Such integrated
`
`
`
`
`
`
`
`circuits typically use multiple transistors fabricated in single
`
`
`
`
`
`
`
`
`crystal silicon. Many integrated circuits now contain mul-
`
`
`
`
`
`
`tiple levels of metallization for interconnections.
`
`
`
`
`
`
`Aluminum-copper (AlCu) alloys are typically used in
`
`
`
`
`
`
`
`VLSI (very large scale integration) metallization. To
`
`
`
`
`
`
`
`
`
`enhance the speed of devices, a low and stable sheet
`
`
`
`
`
`
`
`
`resistance is required for AlCu. However, AlCu can react
`
`
`
`
`
`
`
`
`
`with other metals (e.g. W) thereby increasing its sheet
`resistance. Sheet resistance is a measurement of a conduc-
`
`
`
`
`
`
`
`
`
`
`
`
`tive material with a magnitude proportional to resistivity and
`inverse of thickness. TIN has been applied as a diffusion
`
`
`
`
`
`
`
`
`barrier between AlCu and the other metals to suppress their
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`reactions. However, heat treatment of AlCu/TiN layered
`
`
`
`
`
`
`
`
`structures at 450° C. induces reactions between the AlCu and
`TiN, leading to an increase in the sheet resistance of the
`
`
`
`
`
`
`
`
`
`AlCu.
`
`
`
`
`
`
`
`
`
`Several attempts have been made to improve the barrier
`
`
`
`
`
`
`properties of TiN in AI/TiN/Si, Al/TiN/silicide/Si and
`
`
`
`
`
`
`
`
`AIV/TIiN/W structures. In the past, the improvement of TiN
`
`
`
`
`
`
`
`
`barriers have mostly been achieved by optimizing the
`
`
`
`
`
`
`
`parameters during TiN deposition, such as introducing oxy-
`
`
`
`
`
`
`
`gen flow during deposition, changing the substrate
`
`
`
`
`
`
`
`temperature, or adding a substrate voltage bias. Other
`attempts have included post-deposition treatments such as
`
`
`
`
`
`
`
`
`
`
`
`thermal annealing and exposureto air.
`SUMMARY OF THE INVENTION
`
`
`
`The present invention is a method and structure for a
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`diffusion barrier trilayer comprising a bottom layer depos-
`ited on a substrate, a seed layer deposited on the bottom
`
`
`
`
`
`
`
`
`
`layer, a top layer deposited on the seed layer, and a metal-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`lization layer deposited on the top layer. Reaction of the
`
`
`
`
`
`
`
`
`
`
`metallization layer with the top layer, which may occur upon
`
`
`
`
`
`
`
`heattreatment, is minimized due to the improved properties
`
`
`
`
`
`
`
`
`
`
`of the top layer of the diffusion barrier trilayer. This results
`in no degradation of sheet resistance of the metallization
`
`
`
`
`
`
`
`
`layer upon heat treatment, and no loss of integrated circuit
`
`
`
`
`
`
`
`
`
`
`
`device speed.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`In the drawings, which form an integral part of the
`specification and are to be read in conjunction therewith, and
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`in which like numerals and symbols are employed to des-
`
`
`
`
`
`
`
`ignate similar components in various views unless otherwise
`indicated:
`
`FIG. 1 is a prior art drawing of a cross-sectional view of
`
`
`
`
`
`
`a semiconductor wafer having a TiN diffusion barrier
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`between the metallization layer and the substrate;
`
`Page 5 of 9
`
`
`
`
`
`FIG. 3 is a Rutherford Backscattering Spectroscopy
`(RBS) of a prior art wafer before and after heat treatment;
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`FIG,4 is a prior art drawing showing a typical via plug
`
`
`
`
`
`structure used to connect a metallization layer to underlying
`
`
`
`
`circuitry or metal layers;
`
`
`
`
`
`
`
`
`
`
`
`
`FIG. 5 shows the wafer of FIG. 4 after heat treatment,
`
`
`
`
`
`
`
`
`
`with a portion of the metallization layer reacted with the
`diffusion barrier;
`
`
`
`
`
`
`
`
`
`FIG. 6 demonstrates the crystal structure of the diffusion
`
`
`
`
`
`
`barrier of prior art, having a polycrystalline structure with
`
`
`
`high-angle grain boundaries;
`
`
`
`
`
`FIG. 7 is a cross-sectional view of the present invention,
`
`
`
`
`a diffusion barrier trilayer;
`
`
`
`
`
`
`
`
`
`
`
`
`
`FIG. 8 demonstrates the crystal structure of the top layer
`
`
`
`
`
`
`of the diffusion barrier trilayer, having a single-crystal-like
`appearance;
`,
`
`
`
`
`
`
`
`
`
`
`
`FIG. 9 is a Rutherford Backscattering Spectroscopy
`
`
`
`
`
`(RBS) of an experimental wafer having a diffusion barrier
`
`
`
`
`
`
`
`bilayer, before and after heat treatment; and
`
`
`
`
`10
`
`
`
`15
`
`
`
`20
`
`
`
`25
`
`
`
`30
`
`
`
`
`
`
`
`
`
`FIG. 10 shows the present invention implemented on the
`structure shown in FIG.4.
`
`
`
`
`
`
`35
`
`
`
`40
`
`
`
`45
`
`
`
`50
`
`
`
`55
`
`
`
`DETAILED DESCRIPTION OF PREFERRED
`
`
`EMBODIMENTS
`
`
`
`
`It has been found that the methods used in the past to
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`improvethe barrier properties ofTiN are inadequate. Chang-
`
`
`
`
`
`
`
`ing deposition temperature may induce change in other
`
`
`
`
`
`
`
`
`
`properties of TiN, such as stress and grain size, making it
`difficult to optimize these parameters at the same time.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Adding substrate bias induces ion bombardment of the TIN
`
`
`
`
`
`
`
`layer, which may result radiation damage to existing
`
`
`
`
`
`
`devices. Post-deposition treatments involve additional pro-
`
`
`
`
`
`
`
`cessing steps, increasing process cycle time. Moreover,
`
`
`
`
`
`
`thermal annealing (densification) of TiN is possible only at
`
`
`
`
`
`
`
`
`the contact level on the integrated circuitry where AlCu is
`
`
`
`
`
`
`
`not present. Dosing with oxygen during deposition is
`
`
`
`
`
`
`
`undesirable, since oxygen may contaminate the Ti sputtering
`
`
`
`
`
`
`
`
`
`target, form oxide particles and increase the sheet resistance
`
`
`
`
`
`
`
`
`
`
`of TiN. Exposure of TiN to air for 24 hours has not been
`
`
`
`
`
`
`
`found to improve the barrier properties of TiN.
`
`
`
`
`
`
`
`
`The making and use of the presently preferred embodi-
`ments are discussed below in detail. However, it should be
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`appreciated that the present invention provides many appli-
`cable inventive concepts which can be embodied in a wide
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`variety of specific contexts. The specific embodiments dis-
`
`
`
`
`
`
`
`
`cussed are merely illustrative of specific ways to make and
`use the invention, and do not delimit the scope of the
`
`
`
`
`
`
`
`
`
`
`
`invention.
`
`
`
`
`
`
`
`The following is a description of a preferred embodiment
`
`
`
`
`
`
`
`of the present invention, including manufacturing methods.
`
`
`
`
`
`
`
`Corresponding numerals and symbols in the differentfigures
`
`
`
`
`
`
`
`refer to corresponding parts unless otherwise indicated.
`Table 1 below provides an overview of the elements of the
`
`
`
`
`
`
`
`
`
`
`
`embodiments and the drawings.
`
`65
`
`
`
`Page 5 of 9
`
`
`
`
`3
`
`5,668,411
`
`
`
`TABLE 1
`
`
`Draw- Preferred
`
`
`Generic
`Other Alternate Examples or
`ing
`or Specific
`
`
`
`
`
`
`
`Descriptions
`Element Examples
`Term
`
`
`
`
`
`Semiconductor
`20
`
`wafer
`
`Substrate
`
`
`
`
`22
`
`
`
`«SiO,
`
`
`
`4
`
`
`
`
`
`
`
`
`diffusion barrier 24, where the metallization layer 26 usually
`comprised 6000 A of AlCu, having a sheet resistance of
`
`
`
`
`
`
`
`
`
`
`approximately 50-60 m{2/square.
`
`
`
`
`
`
`In semiconductor manufacturing, heat treatments of sub-
`
`
`
`
`
`
`
`
`sequently deposited layers (not shown) are often required.
`
`
`
`
`
`
`
`
`For example, some dielectric layers are cured at 400°-450°
`
`
`
`
`
`
`
`
`C. Also, the final stage of some semiconductor manufactur-
`
`
`
`
`
`
`
`
`ing methods is a sintering step to repair the damage in
`transistors, in which the wafer is also heated to around 450°
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`C. Reflow of aluminum conductive layers may be required
`
`
`
`
`
`
`
`
`
`for some integrated circuits. Heating the wafer 20 causes the
`
`
`
`
`
`
`
`atoms in the metallization layer 26 and diffusion barrier 24
`to become more mobile, causing a reaction between the two.
`
`
`
`
`
`
`
`
`Diffusion
`
`
`
`
`
`
`
`
`This chemical reaction creates a reacted portion 28 of the
`barrier
`15
`
`
`
`
`
`
`
`
`
`
`metallization layer 26, shown in FIG. 2. The reacted portion
`
`26==6AlCu Metallization Aluminum alloy comprising
`
`
`
`
`
`
`
`
`
`
`
`
`28 is comprised of an aluminum-titanium and/or aluminum-
`0.5-4% copper by weight.
`layer
`
`
`
`
`28 Aluminum-=Reacted portion Aluminum nitride; other com-
`
`
`
`
`
`
`
`
`nitrite compound having a high sheet resistance, which may
`
`
`
`
`
`
`
`
`of metallization pounds having a higher sheet
`titanium
`extend into the metallization layer as much as 500-800 A.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`compound
`layer 26
`resistance than the metallization
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`The reacted portion 28 of the metallization layer 26
`layer 26.
`20
`
`
`
`
`
`
`
`
`
`
`increases the sheet resistance (for example, up to 15%, or 70
`
`30=SiO», Dielectric layer Other dielectric materials.
`
`
`
`
`
`
`
`Other conductors.
`First via ner
`32
`«C«Ti
`
`
`
`
`
`
`
`
`mYsquare) of the metallization layer 26, which has a
`
`
`
`
`
`
`
`Second via
`Other conductors.
`«TiN
`34
`
`
`
`
`
`
`
`
`
`
`
`
`
`deleterious effect on device speed, a critical feature of VLSI
`liner
`circuits.
`
`
`Via plug
`
`
`Grain
`
`
`
`
`FIG. 3 is a Rutherford Backscattering Spectroscopy
`
`boundaries
`
`
`
`
`
`
`
`(RBS) of the conventional AiCu/TiN layered structure
`Crystal plane
`
`
`shown in FIGS. 1 and 2 before and after heat treatments at
`directions
`
`
`
`
`
`
`
`
`
`Diffusion
`TiN/AICWTiN; Other metal
`
`
`
`
`
`
`
`
`
`
`450° C. The tail of the Ti signals indicates reaction has
`
`
`
`
`barrier trilayer
`layers with a top layer having a
`
`
`
`
`
`
`
`occurred between AlCu and the underlying TiN.
`
`
`
`
`
`
`
`single-crystal-like structure.
`
`
`
`
`
`
`
`
`FIG.4 shows another application of a diffusion barrier 24
`Bottom layer of 100-2000AofTiN,other metals
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`diffusion
`such as TiW, TiWN, TiAIN,
`found in priorart, where a dielectric layer 30 comprising, for
`
`
`
`
`
`barrier trilayer TiSiN, Ta, TaN TaSiN or other
`
`
`
`
`
`
`
`
`
`example, SiO, has been deposited and etched so that elec-
`
`
`
`
`
`
`crystalline or amorphous
`
`
`
`
`
`
`
`
`
`
`trical contact may be made to underlying substrate 22.A first
`diffusion barriers.
`
`
`
`
`
`
`
`
`
`via liner 32, typically comprised of titanium is deposited,
` 200-1000Aof Ti; 100-6000A
`Seed layer of
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`and next a second via liner 34, comprised of TiN, for
`of AlCu alloy with 0.5-4% by
`diffusion
`
`
`
`
`
`
`barrier trilayer weight copper solutes; a material
`
`
`
`
`
`
`
`example, is deposited. The via plug 36 is usually formed.
`
`
`
`
`
`with a similar crystal structure
`
`
`
`
`
`
`
`
`
`
`
`
`
`from a metal such as tungsten, but may also comprise other
`to that of the top layer 48 of the
`
`
`
`
`
`
`
`
`
`
`
`
`metals or alloys. The diffusion barrier 24 of TiN is deposited
`diffusion barrier trilayer.
`
`
`
`
`
`
`
`
`
`
`next, followed by metallization layer 26, again comprised of
`
`48 Top layer of—100-2000Aof TIN, other metals100A of
`
`
`
`
`
`
`
`
`AlCu.
`diffusion
`such as TiW, TiWN or other
`TiN
`
`
`
`
`
`
`
`
`barrier trilayer crystalline diffusion barriers.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`As with the other prior art example, when the structure is
`
`
`
`
`
`
`
`
`exposed to heat, the metallization layer 26 reacts with the
`
`
`
`
`
`
`
`
`diffusion barrier 24 to leave a reacted portion 28 of the
`
`
`
`
`
`
`metallization layer 26 as shown in FIG. 5, increasing the
`
`
`
`
`
`
`sheet resistance of the metallization layer 26.
`
`
`
`
`
`
`
`
`
`A problem recognized herein with the prior art examples
`discussed is the microstructure of the diffusion barrier 24.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`TiN deposited on amorphous SiO, has a randomly oriented
`
`
`
`
`
`
`
`polycrystalline structure, as shown in FIG. 6. The crystal
`
`
`
`
`
`
`
`structure has many high-angle grain boundaries 38 where
`
`
`
`
`
`
`
`
`atoms can migrate easily when the structure is heated. The
`
`
`
`
`
`
`
`
`crystal plane directions 40 of each crystal are highly irregu-
`lar and resemble those of a polycrystalline material where
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`the directions of the crystal planes are not all aligned, e.g.
`
`
`
`
`
`
`
`
`
`parallel. Therefore, the crystal structure of the TiN allows
`
`
`
`
`
`
`
`
`atoms to easily migrate when a wafer is heated. The present
`
`
`
`
`
`
`
`
`invention solves this problem by forming a layer of TiN
`
`
`
`
`
`
`adjacent the metallization layer 26 having single-crystal-like
`
`
`
`
`
`
`
`qualities. The terms “‘single-crystal-like” and “textured” are
`defined as having a molecular crystalline structure similar to
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`that of a single crystal, where the direction of the crystal
`
`
`
`
`
`
`
`planes are aligned substantially in the same direction.
`
`
`
`
`
`
`The present invention is shown in cross-section in FIG. 7.
`
`
`
`
`
`
`
`A diffusion barrier trilayer 42 is deposited on the substrate
`
`
`
`
`
`
`
`
`22, upon which metallization layer 26 is deposited. The
`
`
`
`
`
`
`diffusion barrier trilayer 42 is comprised of a bottom layer
`
`
`
`
`
`
`
`
`
`
`
`44, a seed layer 46 anda top layer 48. The layers 44, 46, 48
`
`
`
`
`
`
`
`
`The present invention is a diffusion barrier trilayer that
`
`
`
`
`
`
`
`minimizes the reaction of a metallization layer with under-
`
`
`
`
`
`
`
`
`lying barrier layers of integrated circuits. The trilayer com-
`
`
`
`
`
`
`
`
`
`prises a bottom layer similar to the single TiN layer used in
`the past, a seed layer comprising a material with a similar
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`crystal structure as the top layer, and preferably with a
`
`
`
`
`
`
`single-crystal-like microstructure, and a top layer grown
`
`
`
`
`
`
`
`upon the seed layer, also having a single-crystalline-like
`
`
`
`
`
`
`
`microstructure. The top layer of the diffusion barrier trilayer
`
`
`
`
`
`
`
`
`
`is adjacent the metallization layer. Reaction between the top
`
`
`
`
`
`
`
`
`layer of the diffusion barrier trilayer and the metallization
`
`
`
`
`
`
`
`layer is eliminated or minimized, maintaining the sheet
`
`
`
`
`
`
`
`
`resistance of the metallization layer and enhancing the speed
`
`
`
`
`
`
`
`
`
`of the integrated circuit. As device size shrinks to quarter
`micron range, maintaining a low sheet resistance of metal-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`lization layers used to form conductors becomes increas-
`
`
`ingly important.
`
`
`
`
`
`
`
`
`
`First, problems recognized herein with the prior art will be
`discussed with FIGS. 1-6 used for reference. FIG. 1 shows
`
`
`
`
`
`
`
`
`
`a cross-sectional view of a semiconductor wafer 20, with a
`
`
`
`
`
`
`
`diffusion barrier 24 deposited on a substrate 22. The sub-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`strate 22 may comprise SiO,, but may also comprise tung-
`65
`sten vias, other metal layers or semiconductor elements. The
`
`
`
`
`
`
`
`
`diffusion barrier 24 of the past typically comprised a 500 A
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`layer of TiN. A metallization layer 26 was deposited over the
`
`Tungsten vias, other metal layers
`
`
`
`
`
`or other semiconductor
`
`
`
`elements, (e.g. transistors,
`
`
`
`diodes); compound semi-
`
`
`
`conductors (e.g. GaAs, InP,
`
`
`
`
`Si/Ge, SiC) may be used in
`
`
`
`
`place of Si.
`
`500A
`
`
`10
`
`24
`
`
`
`TiN
`
`
`
`
`36
`
`38
`
`
`40
`
`
`
`42
`
`
`
`44
`
`
`
`OW
`
`
`
`Other conductors; stud.
`
`
`
`
`
`TiN/TVTIN
`
`
`400A of
`
`TiN
`
`
`46
`
`
`
`SOOAofTi
`
`
`
`
`25
`
`
`
`30
`
`
`
`
`
`
`
`
`
`
`
`45
`
`50
`
`
`
`355
`
`60
`
`
`
`Page6 of 9
`
`Page 6 of 9
`
`
`
`
`5
`
`
`
`
`
`
`
`
`are typically deposited by sputtering but also may be depos-
`
`
`
`
`
`
`
`
`ited by chemical vapor deposition, or electron beam
`
`
`
`
`
`
`
`
`
`deposition, for example. The TiN of bottom layer 44 and top
`
`
`
`
`
`layer 48 is preferably sputtered on at approximately 400° C.
`
`
`
`
`
`
`The seed layer 46 is preferably 500 A of Ti sputtered on at
`
`
`
`
`
`
`
`300° C. The bottom layer 44 preferably comprises 100-6000
`
`
`
`
`
`
`
`
`A of TiN (morepreferably 400 A of TiN), and is used to
`
`
`
`
`
`
`
`
`
`
`isolate the seed layer 46, top layer 48 and metallization layer
`
`
`
`
`
`
`
`
`26 from underlying metals (e.g. W via plugs or studs). The
`
`
`
`
`
`
`
`seed layer 46 mayalso be 100-6000 A of AlCu comprising
`
`
`
`
`
`
`
`
`0.54% by weight of copper, or other metals. The seed layer
`
`
`
`
`
`
`
`
`
`46 acts as a seed, to alter the crystal structure and properties
`
`
`
`
`
`
`
`
`
`
`
`of the top layer 48. The seed layer 46 is also used as a
`
`
`
`
`
`
`
`
`sacrificial layer to isolate the bottom layer 44 from the top
`
`
`
`
`
`
`
`layer 48 so that very little interdiffusion occurs between
`
`
`
`
`
`
`
`
`
`these two TiN layers. The top layer 48 is preferably
`
`
`
`
`
`
`
`100-1000 A ofTiN (more preferably, 100 A ofTiN), grown
`
`
`
`
`
`
`
`
`on top of the seed layer 46 in an epitaxial manner. The top
`
`
`
`
`
`
`
`
`layer 48 isolates the metallization layer 26 from the seed
`
`
`
`
`
`
`
`
`layer 46. Due to the improved properties of the crystalline
`
`
`
`
`
`
`
`
`structure of the top layer (caused by the existence of the seed
`
`
`
`
`
`
`
`
`
`
`layer 46), the TiN does not react significantly with the
`
`
`
`
`
`
`
`
`
`metallization layer 26 and the sheet resistance of the met-
`
`
`
`
`
`
`
`allization layer 26 remains unchanged uponheattreatment.
`
`
`
`
`
`
`
`
`
`
`
`Moreover, the top layer 48 does not react with the seed layer
`46.
`
`
`
`
`
`
`
`In semiconductor technology, when silicon is grown, a
`
`
`
`
`
`
`
`
`
`seed is used to orient the crystal structure in the desired
`
`
`
`
`
`
`
`configuration. Similarly, the seed layer 46 of the trilayer 42
`
`
`
`
`
`
`
`
`orients the crystal structure of the subsequently deposited
`
`
`
`
`
`
`
`
`
`
`top layer 48. The seed layer 46 of the diffusion barrier
`trilayer 42 is a material such as Ti or AlCu that is chosen for
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`its crystal structure, lattice parameters and crystal alignment.
`
`
`
`
`
`
`
`
`
`
`Accrystal structure and lattice parameters are desired that are
`
`
`
`
`
`
`
`
`
`
`similar to those of the top layer 48. As a result, the top layer
`48 has a single-crystal-like structure, as shown in FIG.8.
`
`
`
`
`
`
`
`
`
`
`
`
`
`Experiments have been performed to demonstrate the
`
`
`
`
`
`
`
`advantages of the present invention. FIG. 9 shows an RBS
`of a structure comprising a metallization layer 26 of AlCu,
`
`
`
`
`
`
`a top layer 48 of TiN, and a seed layer 46 of AlCu, subjected
`
`
`
`
`
`
`
`
`
`to the same heat treatment of 450° C. as described in FIG.
`
`
`
`
`
`
`
`
`3. In contrast to FIG. 3, no reaction takes place betweenthe
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`AlCu and TiN. In the experiment, the seed layer 46 is
`
`
`
`
`
`
`
`
`
`comprised of AlCu and the bottom layer 44 is not used. The
`RBS results of the experiment were confirmed by cross-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`section transmission electron microscopy. X-ray diffraction
`
`
`
`
`
`
`
`
`
`
`show by using the seed layer 42, the top layer 48 of TiN
`becomes more strongly textured or more single-crystalline-
`
`
`
`
`
`
`like compared with polycrystalline TiN deposited on amor-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`phous SiO,. The (111) X-ray peak intensity of the TiN on
`SiO,is less than one tenth of that of the TIN on AlCu. The
`
`
`
`
`
`
`
`
`
`
`enhanced texture of the TiN top layer 48 on the AlCu seed
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`layer 46 is due to the fact that the sputtered AlCu seedlayer
`46 has a strong (111) texture and the crystallographic
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`structure and lattice parameters of TiN top layer 48 are
`similar to those of AL
`
`
`
`
`
`
`
`
`
`
`
`
`Preferably, the top layer 48 is thinner than the bottom
`layer 44, which causes less reaction between the metalliza-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`tion layer 26 of AlCu. The use of the seed layer 46 allows
`
`
`
`
`
`
`
`
`the top layer 48 of TiN to be thin enough to minimize the
`
`
`
`
`
`
`
`
`
`reactions with the metallization layer 26, while the bottom
`
`
`
`
`
`
`layer 44 of TiN may be of sufficient thickness to provide
`
`
`
`
`
`
`electromigration resistance and suppression of possible
`
`
`
`
`
`
`
`interdiffusion between the metal stack (metallization layer
`
`
`
`
`
`
`
`
`
`26/top layer 48/seed layer 46) and underlying metals, for
`
`
`
`
`
`
`
`
`
`example,
`the tungsten via plug 36 shown in FIG. 10.
`
`
`
`
`
`
`
`
`Because of the thinness and improved properties (due to the
`
`10
`
`15
`
`
`
`20
`
`25
`
`
`
`30
`
`35
`
`
`
`45
`
`
`
`50
`
`
`
`55
`
`65
`
`
`
`
`
`Page 7 of 9
`
`5,668,411
`
`
`
`
`6
`
`
`
`
`
`
`
`
`
`
`
`existence of the seed layer) of the top layer 48,the top layer
`
`
`
`
`
`
`
`
`
`48 does not react significantly with the metallization layer
`
`
`
`
`
`
`
`
`
`26 and the sheet resistance of the metallization layer remains
`
`
`
`
`
`
`
`
`unchanged upon heat treatment. Moreover, the top layer 48
`
`
`
`
`
`
`
`
`
`
`
`does not react with the seed layer 46, either, which can be
`seen in the RBS of FIG. 9.
`
`
`
`
`
`
`
`
`
`
`
`
`Alternates for processes and element materials are appro-
`
`
`
`
`
`
`
`
`
`priate and will be obvious to those skilled in the art. For
`
`
`
`
`
`
`
`
`example, the top layer 48 may comprise other crystalline
`
`
`
`
`
`
`
`
`diffusion barrier materials such as TiW, TiWN, TiAIN,
`
`
`
`
`
`
`
`
`TiSiN, Ta or TaN. The bottom layer 44 may comprise other
`
`
`
`
`
`
`erystalline or amorphous diffusion barrier materials such as
`
`
`
`
`
`
`
`
`
`TiW, TIWN,TiAIN, TiSiN, Ta, TaN, or TaSiN. The substrate
`
`
`
`
`
`
`
`may be a dielectric (e.g. SiO., PETEOS, BPSG), a metal
`
`
`
`
`
`
`
`
`
`(e.g. W, Au) or a semiconductor (e.g. Si, GaAs). The seed
`
`
`
`
`
`
`
`
`layer 46 may comprise other materials having a crystal
`
`
`
`
`
`
`
`
`
`structure suitable for aligning the crystal structure of the top
`
`
`
`
`
`
`
`
`layer 48. The metallization layer 26 may comprise
`
`
`
`
`
`
`
`
`aluminum, copper, alloys thereof, or other metals. The
`
`
`
`
`
`
`diffusion barrier trilayer 42 may be configured as continuous
`
`
`
`
`
`
`
`
`
`films over the entire substrate 22, or patterned after
`
`
`
`
`
`
`
`deposition, possibly into features with submicron dimen-
`sions.
`
`
`
`
`
`
`
`
`The present invention disclosed herein of a diffusion
`
`
`
`
`
`
`
`barrier trilayer offers an advantage over conventional diffu-
`
`
`
`
`
`
`
`
`
`sion barriers in that reaction of metallization layers upon
`
`
`
`
`
`
`
`
`treatment with the underlying diffusion barriers is
`heat
`minimized or eliminated, resulting in no increase in sheet
`
`
`
`
`
`
`
`
`
`
`
`
`
`resistance of the metallization layer, and thus no detrimental
`
`
`
`effect on device speed.
`While the invention has been described with reference to
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`illustrative embodiments, this description is not intended to
`be construed in a limiting sense. Various modifications and
`
`
`
`
`
`
`
`combinations of the illustrative embodiments, as well as
`
`
`
`
`
`
`
`
`
`
`
`
`other embodiments of the invention, will be apparent to
`persons skilled in the an upon reference to the description.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`It is therefore intended that the appended claims encompass
`any such modifications or embodiments.
`
`
`
`
`Whatis claimedis:
`
`
`
`
`
`
`
`
`1. A diffusion barrier trilayer for semiconductor wafers,
`
`comprising:
`
`
`
`
`a bottom metal layer;
`
`
`
`
`
`
`
`
`
`a seed metal layer adjacent said bottom layer and having
`/
`a crystalline structure; and
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`a top metal layer adjacent said seed metal layer and
`
`
`
`having a crystalline structure;
`
`
`
`
`
`
`
`
`wherein said crystalline structures of said top metal layer
`
`
`
`
`
`
`
`
`and said seed metal layer are single-crystal-like, and
`
`
`
`
`
`
`
`
`wherein said crystalline structure of said top metal
`
`
`
`
`
`
`
`layer is aligned to said crystalline structure of said seed
`
`
`metal layer,
`
`
`
`
`
`
`
`
`wherein said bottom layer comprises TiN, said seed metal
`
`
`
`
`
`
`
`
`layer comprises Ti, and said top metal layer comprises
`TiN.
`
`
`
`
`
`
`
`2. A diffusion barrier trilayer for semiconductor wafers,
`
`comprising:
`a bottom metal layer;
`
`
`
`
`
`
`
`
`
`
`
`
`
`a seed metal layer adjacent said bottom layer and having
`a crystalline structure; and
`
`
`
`
`
`
`
`
`
`
`
`
`
`a top metal layer adjacent said seed metal layer and
`
`
`
`having a crystalline structure;
`
`
`
`
`
`
`
`
`wherein said crystalline structures of said top metal layer
`
`
`
`
`
`
`
`
`and said seed metal layer are single-crystal-like, and
`
`
`
`
`
`
`
`
`wherein said crystalline structure of said top metal
`
`
`
`
`
`
`
`layer is aligned to said crystalline structure of said seed
`
`
`metal layer,
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 7 of 9
`
`
`
`5,668,411
`
`
`
`
`
`
`7
`
`
`
`
`
`
`
`
`
`wherein said bottom layer comprises TiN, said seed metal
`
`
`
`
`
`
`
`layer comprises an aluminum-copper alloy, and said
`
`
`
`
`
`top metal layer comprises TiN.
`3. A semiconductor wafer metallization structure, com-
`
`
`
`
`
`
`
`prising:
`a substrate;
`
`
`
`
`
`
`
`
`a bottom layer adjacent said substrate;
`
`
`
`
`
`
`
`
`
`a seed metal layer adjacent said bottom layer and having
`
`
`
`a crystalline structure;
`
`
`
`
`
`
`
`
`
`
`a top metal layer adjacent said seed metal layer and
`
`
`
`
`having a crystalline structure; and
`
`
`
`
`
`
`
`
`a metallization layer adjacent said top metal layer;
`
`
`
`
`
`
`
`
`wherein said crystalline structures of said top metal layer
`
`
`
`
`
`
`
`
`and said seed metal layer are