US006512266B1
`(10) Patent No:
`a2) United States Patent
`US 6,512,266 B1
`Deshpandeet al.
`(45) Date of Patent:
`Jan. 28, 2003
`
`
`(54) METHOD OF FABRICATING SIO, SPACERS
`AND ANNEALING. CAPS
`
`(75)
`
`Inventors: SadanandV. Deshpande,Fishkill, NY
`(US); Bruce B. Doris, Brewster, NY
`(US); Rajarao Jammy, Wappingers
`Falls, NY (US); William H. Ma,
`Fishkill, NY (US(US)
`International Business Machines
`Corporation, Armonk, NY (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`US.C. 154(b) by 0 days.
`
`(73) Assignee:
`
`(*) Notice:
`
`6,034,388 A
`............... 257/296
`3/2000 Brownet al.
`6,087,706 A
`7/2000 Dawsonetal. .............. 257/520
`6,121,100 A
`9/2000 Andidehetal. ............ 438/305
`G.127,712 A * 102000 WAcern 257/410
`
`”
`29s
`CY CE AN veseseees
`6,160,299 A
`12/2000 Rodder............ccccece eee 257/408
`OTHER PUBLICATIONS
`“Preservation of Integrity of Protective Coatings During
`Anneal in Oxygen—Free Ambients,” IBM Technical Disclo-
`sure Bulletin, vol. 30, No. 5, pp. 328-329, Oct. 1987.
`eos
`.
`cited by examiner
`Primary Examiner—Nathan J. Flynn
`Assistant Examiner—Scott R. Wilson
`(74) Attorney, Agent, or Firm—Margaret A. Pepper
`
`Divotfill methods of incorporating thin SiO, spacer and/or
`Jul. 11, 2001
`Filed:
`(22)
`
`(SL) Lint. C0? oe cecccccccccccseesesseescesceseeeesense HO1L 29/76=annealing caps into a complementary metal oxide semicon-
`(52) US. Ch. ceccccsseesseees 257/333; 257/346; 257/387;
`ductor (CMOS)processing flow are provided. In accordance
`257/340; 257/412; 257/388; 438/585
`with the present invention, the divotfill processes provide a
`(58) Field of Search ......ccccccsssseeeeeee 257/333, 346,|meansfor protecting the exposed surfaces of the thin SiO,
`257/387, 388, 340, 900, 412: 438/585
`spacer and/or annealing cap such that those surfaces are not
`,
`°
`,
`,
`,
`capable of being attacked by a subsequentsilicide pre-
`References Cited
`cleaning step. CMOS devices including thin SiO, spacer
`and/or annealing caps whose surfaces are protected such that
`those surfaces are not capable of being attacked by a
`subsequentsilicide pre-cleaning or other process steps are
`also provided.
`
`(56)
`
`U.S. PATENT DOCUMENTS
`5,880,500 A
`3/1999 Iwataet ale scccccccsseseoses 257/336
`5,895,246 A *
`4/1999 Lee cveccceccccscssseseeseeees 438305
`
`5,936,279 A *
`8/1999 Chuang ove 257/346
`6,010,954 A
`1/2000 Ho et al. ns iseseeserecees 438/596
`
`24 Claims, 7 Drawing Sheets
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`aNSW 28
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`TSMC 1220
`TSMC 1220
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`

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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 1 of 7
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`US 6,512,266 B1
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 2 of 7
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`US 6,512,266 B1
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 3 of 7
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`US 6,512,266 B1
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 4 of 7
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`US 6,512,266 B1
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 5 of 7
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`US 6,512,266 B1
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`FIG. 2C
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 6 of 7
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 7 of 7
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`US 6,512,266 B1
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`US 6,512,266 Bl
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`1
`
`METHOD OF FABRICATING SIO, SPACERS
`AND ANNEALING CAPS
`
`DESCRIPTION
`
`Field of the Invention
`
`The present invention relates to complementary metal
`oxide semiconductor (CMOS) devices, and more particu-
`larly to metal oxide semiconductor field effect transistors
`(MOSFETs) that include an oxide spacer to reduce parasitic
`capacitance and an annealing cap that prevents dopantloss
`in the gate material during an activation-annealing step. The
`present invention also provides methods of manufacturing
`the CMOS devices of the present invention.
`
`BACKGROUNDOF THE INVENTION
`
`In the semiconductor industry thin, SiN spacers are typi-
`cally used to implant source/drain extensions (SDE) and
`halos for CMOS devices. The use of SiO, spacers is
`advantageous compared to SiN spacers because the lower
`dielectric constant of SiO., reduces the parasitic capacitance
`between the gate and S/D regions.
`Annealing caps are used to protect the patterned gate
`stack, source/drain (S/D) and SDE regions from dopant loss
`during activation annealing. The utilization of a deposited
`oxide material as the annealing cap is advantageous since
`low energy implantation can be performed through the bare
`Si substrate. After the implant, a low temperature SiO, film
`may be deposited over the entire wafer to prevent dopant
`loss during annealing. The SiO. cap also serves as an etch
`stop for the thicker SiN spacer formation used to implant the
`S/D regions. As in the case of the thin SiO, spacer, the SiO,
`annealing cap reduces the parasitic capacitance between the
`gate and S/D regions. Simulations have shown that switch-
`ing from a nitride annealing cap to an oxide annealing cap
`improves the ring oscillation delay by as much as 5%.
`A major problem of integrating thin SiO, spacers and/or
`SiO, annealing caps into prior art processes is that any SiO,
`that is exposed during the pre-silicide cleaning or other
`process steps may be excessively etched. In the case of the
`thin SiO. spacer, excessive etching may cause the entire
`SiO. spacer to be removed thus leaving Si substrate area
`exposed. This leads to gate to substrate shorting by silicide
`bridging. In the case of the SiO, annealing cap, if the etching
`is excessive then the thick SiN spacers are undercut and may
`become completely detached rendering the device inoper-
`able. This leads to silicide bridging since the spacers are
`present to prevent this from occurring.
`In view of the above,
`there is a continued need for
`developing a new and improved method wherein thin SiO,
`spacers and/or annealing caps can be integrated into a
`CMOSprocessing flow without exhibiting any of the prob-
`lems mentioned hereinabove.
`
`SUMMARY OF THE INVENTION
`
`One object of the present invention is to provide a method
`of forming a CMOS device in which a thin S10, spacer
`and/or annealing cap is employed.
`Another object of the present invention is to provide a
`method of forming a CMOSdevice in which the thin SiO,
`spacer and/or annealing cap is not aggressively attacked
`during the silicide pre-cleaning step or other process.
`These and other objects and advantages are achieved in
`the present invention by utilizing a divot fill process which
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`overcomes the above-mentioned drawbacks in the priorart.
`In accordance with the present
`invention,
`the divot fill
`process provides a means for protecting the exposed sur-
`faces of the thin SiO, spacer and/or annealing cap such that
`those surfaces are not capable of being attacked by a
`subsequent silicide pre-cleaning or other process steps.
`Specifically, a first method of the present invention, which
`forms an SiO. annealing cap, comprises the steps of:
`(a) forming an oxide film on vertical and horizontal
`surfaces of a semiconductor structure, said semicon-
`ductor structure comprises at least a semiconductor
`substrate having at least one patterned gate stack region
`formed thereon;
`(b) forming thick spacers on portions of said oxide film
`that are adjoining said at least one patterned gate stack
`region, said thick spacers being composedofa dielec-
`tric material other than an oxide;
`(c) recessing said oxide film so as to form at least a divot
`region between said thick spacers and a top surface of
`said patterned gate stack region; and
`(d) forming a divot fill material in said divot region, said
`divot fill material being composed ofa dielectric mate-
`rial other than an oxide. Note that in the first method of
`the present invention, the oxide film remaining in the
`structure after the recessing step is in the shape of the
`letter “L”. Hence,
`the oxide film remaining in the
`structure after recessing is present on portions of the
`vertical sidewalls of the patterned gate stack region as
`well as on a portion of the semiconductor substrate.
`The first method of the present invention provides a CMOS
`device which comprises:
`a semiconductor structure having at least one patterned
`gate stack region formed thereon, said patterned gate
`stack region having vertical sidewalls;
`an oxide film formed on portions of said vertical sidewalls
`of said at least one patterned gate stack region as well
`as portions of said semiconductor substrate;
`thick spacers formed on said oxide film, wherein said
`thick spacers extend beyond edges of said oxide film
`such that a divot region is present betweenatleast said
`thick spacers and a top surface of said patterned gate
`stack region; and
`a divot fill material present in said divot region.
`A second method of the present invention, which forms a
`thin SiO. spacer and/or annealing cap comprises the steps
`of:
`
`(a) forming an oxide film on vertical and horizontal
`surfaces of a semiconductor structure, said semicon-
`ductor structure comprises at least a semiconductor
`substrate having at least one patterned gate stack region
`formed thereon;
`(b) etching said oxide film so as to remove said oxidefill
`from said horizontal surfaces of said structure;
`(c) forming thick spacers on portions of said oxide film
`that are adjoining said at least one patterned gate stack
`region, said thick spacers being compesed of a dielec-
`tric material other than an oxide;
`(d) recessing, said oxide film so as to form at least a divot
`region between said thick spacers and a top surface of
`said patterned gate stack region; and
`(e) forming a divot fill material in said divot region, said
`divot fill material being composed of a dielectric mate-
`rial other than an oxide.
`The second method of the present invention provides a
`CMOSdevice which comprises:
`
`

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`US 6,512,266 Bl
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`3
`a semiconductor structure having at least one patterned
`gate stack region formed thereon, said patterned gate
`stack region having vertical sidewalls;
`an oxide film formed on portions ofsaid vertical sidewalls
`of said at least one patterned gate stack region;
`thick spacers formed on said oxide film and said semi-
`conductor substrate, wherein said thick spacers extend
`beyond edgesof said oxide film such that a divot region
`is present between at least said thick spacers and a top
`surface of said patterned gate stack region; and
`a divot fill material present in said divot region.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. 1A-IFare pictorial representations (through cross-
`sectional views) illustrating the inventive CMOS device
`through various processing steps employed in the first
`method of the present invention.
`FIGS. 2A-2Gare pictorial representations (through cross-
`sectional views) illustrating the inventive CMOS device
`through various processing steps employed in a second
`method of the present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The present invention, which relates to CMOS devices
`containing oxide spacers and/or annealing caps and methods
`of fabricating the same, will now be described in more detail
`by referring to the drawings that accompany the present
`application. It is noted that in the accompanying drawings,
`like and/or corresponding elements are referred to by like
`reference numerals.
`
`Reference is first made to the embodiment depicted in
`FIGS. 1A-1F whichillustrate a first method of the present
`invention wherein an SiO, annealing cap is formed.
`Specifically, FIG. 1A illustrates an initial structure that is
`employed in the present invention. The initial structure
`shown in FIG. 1A comprises semiconductor substrate 10,
`patterned gate dielectric 12 formed on a portion of semi-
`conductor substrate 10, and patterned gate stack 14 formed
`atop patterned gate dielectric 12. It is noted that although the
`drawings depict the presence of only one patterned gate
`region (.e., patterned gate dielectric and patterned gate
`stack) on the semiconductor substrate, the present invention
`worksin cases wherein a plurality of patterned gate regions
`are present on the semiconductor substrate.
`The structure shown in FIG. 1A is comprised of conven-
`tional materials well known in the art and the illustrated
`structure is fabricated utilizing processing steps that are also
`well knownin the art. For example, semiconductor substrate
`10 is comprised of a semiconductor material including, but
`not limited to: Si, Ge, SiGe, GaAs, InAs, InP andall other
`Il/V semiconductor compounds. Semiconductor substrate
`10 mayalso include a layered substrate comprising the same
`or different semiconductor material, e.g., Si/Si or Si/SiGe, as
`well as a silicon-on-insulator (SOD substrate. The substrate
`may be of the n- or p-type depending on the desired device
`to be fabricated.
`
`Additionally, semiconductor substrate 10 may contain
`active device regions, wiring regions, isolation regions or
`other lke regions that are typically present m CMOS-
`containing devices. Forclarity, these regions are not shown
`in the drawings, but are nevertheless meant to be included
`within region 10. In one highly preferred embodimentof the
`present invention, semiconductor substrate 10 is comprised
`of Si.
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`Next, a layer of gate dielectric material such as an oxide,
`nitride, oxynitride or any combination and multilayer
`thereof is then formed on a surface of semiconductor sub-
`
`strate 10 utilizing a conventional process well knownin the
`art. For example, the layer of gate dielectric material may be
`formed utilizing a conventional deposition process such as
`chemical vapor deposition (CVD), plasma-assisted CVD,
`evaporation or chemical solution deposition, or
`alternatively, the gate dielectric material may be formed by
`a thermal growing process such as oxidation, nitridation or
`oxynitridation. It is noted that the gate dielectric material
`will be subsequently patterned and etched into patterned
`gate dielectric 12 shown in FIG. 1A.
`The thicknessof the layer of gate dielectric material is not
`critical
`to the present
`invention, but
`typically,
`the gate
`dielectric material has a thickness of from about 1 to about
`20 nm after deposition, with a thickness of from about 1.5
`to about 10 nm being more highly preferred. It is noted that
`the gate dielectric material employed in the present inven-
`tion may be a conventional dielectric material such as SiO,
`or Si,N,, or alternatively, high-k dielectrics such as oxides
`of Ta, Zr, Al or combinations thereof may be employed. In
`one highly preferred embodiment of the present invention,
`gate dielectric 12 is comprised of an oxide such as Si0,,
`ZrO,, Ta,O; or ALO.
`After forming the gate dielectric material on the surface of
`semiconductor substrate 10, gate stack 14 which includesat
`least a gate material is formed on the gate dielectric material.
`The term “gate material” as used herein denotes a conduc-
`tive material, a material that can be made conductive via a
`subsequent process such as ion implantation, or any com-
`bination thereof. Illustrative examples of suitable gate mate-
`rials include, but are not limited to: polysilicon, amorphous
`silicon, elemental metals that are conductive such as W,Pt,
`Pd, Ru, Rh and Ir, alloys of these elemental metals,silicide
`or nitrides of these elemental metals and combinations
`
`thereof, e.g., a gate stack including a layer of polysilicon and
`a layer of conductive metal. Ahighly preferred gate material
`employed in the present invention is a gate material that is
`comprised of polysilicon or amorphoussilicon.
`The gate material is formed on the surface of the gate
`dielectric material utilizing a conventional deposition pro-
`cess including, but not limited to: CVD, plasma-assisted
`CVD, evaporation, plating or chemical solution deposition.
`When metal silicides are employed, a conventional silicide
`process may be used in forming the silicide layer. One such
`silicide process that can be used in the present invention
`includes the steps of: first forming an elemental metal on the
`gate dielectric material, annealing the layers so as to form a
`metal silicide layer therefrom, and removing any unreacted
`elemental metal utilizing a conventional wet etch process
`that has a high selectivity for removing elemental metal as
`compared io silicide.
`When polysilicon is employed as the gate material, the
`polysilicon layer may be formed utilizing an in-situ doping
`deposition process or by a conventional deposition process
`followed by ion implantation. Note that the ion implantation
`step may be formed immediately after deposition of the
`polysilicon layer, or in a later step of the present invention,
`ie., after patterning of the gate stack.
`It is noted that in embodiments wherein a gate stack
`including a layer of polysilicon and a layer of conductive
`elemental metal is employed, an optional diffusion barrier
`(not shown in the drawings) may be formed between each
`layer of the gate stack. The optional diffusion barrier, which
`is formed utilizing a conventional deposition process such as
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`CVD or plasma-assisted CVD, is comprised of a material
`such as SiN, TaN, TaSiN, WN, TiN, and other like materials
`which can prevent diffusion of a conductive material there-
`through.
`After forming the gate stack on the gate dielectric
`material,
`the gate stack and the gate dielectric are then
`patterned utilizing conventional processing steps weil
`known in the art which are capable of forming the patterned
`structure shown in FIG. 1A. Specifically,
`the structure
`shown in FIG. 1A is formed bylithography and etching.
`The lithography step includes the following: applying a
`photoresist (not shownin the drawings) to the top surface of
`the gate stack, exposing the photoresist to a pattern of
`radiation and developing the pattern utilizing a conventional
`resist developer solution.
`Etching is performed utilizing a conventional dry etching
`process such as reactive-ion etching, plasma etching, ion
`beam etching, laser ablation or a combination thereof. The
`etching step may remove portions of the gate stack and the
`underlying gate dielectric material that are not protected by
`the patterned photoresist in a single step, or alternatively,
`multiple etching steps may be performed wherein the
`exposed portions of the gate stack is first removed stopping
`on a surface of the gate dielectric material, and thereafter the
`exposed portions of the gate dielectric are removed stopping
`on the surface of semiconductor substrate 16. Following the
`etching process, the patterned photoresist is removed utiliz-
`ing a conventional stripping process well known in the art
`providing the structure shown, for example, in FIG. 1A.
`At this point of the present invention, source/drain exten-
`sion and halo implants may be performed. Note in FIG. 1A,
`region 18 denotes the source/drain extension regions and
`region 20 denotes the halo implant region. In other embodi-
`ment of the present invention, the source/drain extension
`and halo implant implants may be formed after the structure
`shown in FIG. 1B is formed.
`
`Note that the deep source/drain diffusion regions (labeled
`as 16 in FIG. 1C) are formed utilizing conventional pro-
`cesses (i.e., ion implantation and annealing) anytime after
`the structure shown in FIG. 1C is formed, 1e., after thick
`spacers 24 are formed in the structure.
`the
`invention,
`In another embodiment of the present
`structure illustrated in FIG. 1Ais subjected to a conventional
`reoxidation process prior to proceeding to the next step of
`the present invention.
`FIG. 1B illustrates the structure after oxide film 22 is
`
`formed over the patterned gate stack structure of FIG. 1A.
`The oxide film, which is the annealing cap or thin inner
`spacer of the inventive structure, is formed utilizing any
`conformal deposition processthat is capable of depositing a
`film that follows the contour of the structure shown in FIG.
`
`1A. Specifically, CVD, plasma-assisted CVD, evaporation
`or chemical solution deposition may be employed in form-
`ing oxide film 22 on the structure.
`In one embodiment of the present invention, fluorine or
`nitrogen-containing dopants may be incorporated (via ion
`implantation or another conventional process} into oxide
`film 22 se asto alter the dielectric constant of oxide film 22.
`
`A highly preferred oxide film employed in the present
`invention is a film that is comprised of SiO, which may or
`maynot be doped with fluorine or nitrogen.
`The thickness of oxide film 22 is not critical to the present
`invention, but typically oxide film 22 has a thickness of from
`about 2 A to about 40 nm, with a thickness of from about 5
`to about 10 nm being more highly preferred.
`At this point of the present invention, an annealing step
`may be performedto activate the dopants, if implanted, and
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`60
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`the implant damage. The activation-
`to possibly heal
`annealing step is conducted utilizing conditions well known
`in the art. Por example, activation annealing at a temperature
`of about 900° C. or greater for a time period of about 30
`seconds or less may be employedatthis point of the present
`invention. Additionally,
`the various implants steps men-
`tioned hereinabove may also be performed at this point of
`the present invention.
`Next, thick spacers 24, which may include a single spacer
`material or a combination of spacer materials, are formed on
`the oxide film that abuts the patterned gate stack so as to
`provide the structure shown in FIG. 1C. The thick spacers
`are formed of a dielectric material other than an oxide.
`Specifically, the thick spacers are comprised of a nitride, an
`oxynitride or combinations and multilayers thereof.
`The thick spacers are formed by a conventional deposition
`process such as CVD or plasma-assisted CVD, followed by
`etching. When the thick spacers are comprised of a combi-
`nation of spacer materials,
`the spacer materials may be
`deposited sequentially followed by a single etching step, or
`alternatively, one spacer material
`is first deposited and
`etched, and thereafter a second spacer material is deposited
`and etched. This combination of spacer material deposition
`and etching may be repeated any number of times. The
`etching step used in forming thick spacers 24 is a highly
`anisotropic etching process which is capable of removing
`the spacer material from atop the oxide layer that lays above
`the patterned gate stack.
`The term “thick spacers” is used herein to denote spacers
`that have a thickness of from about 2 to about 100 nm, with
`a thickness of from about 20 to about 80 nm being more
`highly preferred.
`As stated above, and at this point of the present invention,
`the deep source/drain diffusion regions, may be formed by
`utilizing conventional ion implantation and annealing pro-
`cesses well known in the art.
`
`After forming thick spacers 24, the structure shown in
`FIG. 1C is then subjected to an etching step wherein oxide
`film 22 is recessed below the uppermost horizontal edge of
`thick spacers 24 providing the structure shown, for example,
`in FIG. 1D. Specifically, an etching step is employed in the
`present invention so as to provide divot regions 26 which
`exist between the thick spacers 24 and patterned gate stack
`14. Optionally,
`the recessing process may be conducted
`laterally providing divot region 26 between the thick spacers
`and semiconductor substrate 10. Note this recessing step
`converts oxide film 22 into an L-shaped structures 23.
`The etching process used in forming divots 26 in the
`structure includes a wet chemical etch process or a dry
`chemical etch process. When wet etching is employedin the
`present invention in forming divots 26, a chemical etchant
`such as HFthat has a high selectivity for removing portions
`of the oxide film as compared with either the thick spacer
`material, the patterned gate stack and the semiconductor
`substrate is employed.
`Whendry etching is employed in forming the divots, the
`dry etching process includes any dry etch process which is
`also capable of selectively removing portions of the oxide
`film as compared with either the thick spacer material, the
`patterned gate stack and the semiconductor substrate is
`employed.
`After recessing the oxide film, divot fill material 28 is
`formed by a conformal deposition process such as CVD or
`plasma-assisted CVD so as to provide the structure shown,
`for example, in FIG. 1E. The divotfill material includes a
`dielectric material other than an oxide, e.g., nitride, or
`
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`

`US 6,512,266 Bl
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`7
`is not capable of being removed by a
`that
`oxynitride,
`subsequent silicide precleaning or other processes which
`follow the processing steps of the present invention.
`The thicknessofthe divotfill material is not critical to the
`present invention, but typically the thickness of the divotfill
`material is from about 4 to about 80 nm with a thickness of
`from about 10 to about 20 nm being more highly preferred.
`The divot fill material is next etched back by utilizing a
`spacer type etching process or a combination of isotropic
`and anisotropic etches that removes the divot fill material
`from horizontal surfaces and possibly removes some of the
`divot fill material from the vertical surfaces so that the divot
`
`is left completely or partially covering the
`fill material
`recessed oxide film (both on the vertical and lateral
`portions). The etch back step results in the formation of the
`structure shown in FIG. 1F.
`
`The silicidation process is performed after the structure
`illustrated in FIG. 1F is formed. Specifically, the silicidation
`process includesthe steps of forming a refractory metal such
`as Co, Ni or Ti on the surface of semiconductor substrate 10,
`annealing the refractory metal under conditions that are
`capable of converting the refractory metal layer into a metal
`silicide layer, and, if needed, removing any non-reactant
`refractory metal from the structure.
`invention also
`In addition to silicidation,
`the present
`contemplates other well known CMOSprocessing steps that
`are typically employed in the prior art. For example, the
`present invention also contemplates forming a metal contact
`to the metal silicide layer, and connecting the metal contact
`to an external contact.
`Reference will now be made to FIGS. 2A-2G which
`illustrate a second method of the present invention wherein
`an “I” shaped oxide film is employed as an extension and
`halo spacer. Specifically, FIG. 2A showsan initial structure
`that
`is employed in the second method of the present
`application. The initial structure includes semiconductor
`substrate 10, patterned gate dielectric 12 formed on a portion
`of semiconductor substrate 10, and patterned gate stack 14
`formed atop patterned gate dielectric 12.
`Note that the initial structure shown in FIG. 2A is iden-
`tical to the one shown in FIG. 1A therefore no further details
`concerning the initial structure is needed herein. Thatis, the
`detailed description concerning the various elements of the
`structure shown in FIG. 2A as well as the processing steps
`used in forming the same are identical to that previously
`described in connection with FIG. 1A; therefore the above
`description regarding FIG. 1A is incorporated herein by
`reference.
`
`After forming the initial structure shown in FIG. 2A,
`various ion implantation steps may be performed to implant
`source/drain extension regions and halo implant regions into
`the semiconductor substrate. Note that these implant regions
`are shown in FIG. 2A. Alternatively, the various implant
`steps may be postponed until after the structures shown in
`FIGS. 2B or 2C have been formed. The deep source/drain
`diffusion regions are again formed anytimeafter spacers 24
`are present on the structure, ie., after the formation of the
`structure shown in FIG. 2D.
`FIG. 2B showsthe structure that is obtained after oxide
`
`film 22 is formed over the patterned gate region as well as
`the exposed surface of semiconductor substrate 10. In some
`embodiments of the present invention, oxide film 22 may
`include dopantions such as nitrogen or fluorine incorporated
`therein via ion implantation so as to provide an oxide layer
`that has a modified dielectric constant. In a highly preferred
`embodiment of the present
`invention, oxide film 22 is
`
`wn
`
`10
`
`boCAL
`
`30
`
`40
`
`8
`comprised of SiO,, which may or may not include dopant
`ions incorporated therein.
`As mentioned previously herein, oxide film 22 is formed
`by a conventional deposition processes such as CVD and
`plasma-assisted CVD which are capable of forming a con-
`formal oxide film on the structure. The thickness of oxide
`film 22 is not critical to the present invention, but typically
`oxide film 22 has a thickness of from about 2 to about 30 nm,
`with a thickness of from about 5 to about 15 nm being more
`highly preferred.
`Following formation of the oxide film on the structure, a
`spacer etch step is performed so as to provide the structure
`shown in FIG. 2C. Note that
`the spacer etch forms “I”
`shaped oxide film 25 on the structure. Specifically, a spacer
`etching step is performed so as to convert oxide film 22 into
`“T” shaped spacers 25 which are present on at least a portion
`of the vertical sidewalls of the patterned gate stack. Note that
`in FIG. 2C, the I-shaped oxide spacers are not present on the
`upper portion of the patterned gate stack.
`the I-shaped
`In accordance with the present invention,
`oxide spacers are formed byutilizing an etching process that
`is highly anisotropic so that the dielectric film is removed
`from all horizontal surfaces, but still remains on substan-
`tially all the vertical surfaces. A conventional reactive ion
`etching process or any other like dry etching process may be
`utilized in etching oxide film 22 into I-shaped oxide spacers
`25.
`
`Next, thick spacers 24, which may be comprised of a
`single spacer material or a combination of spacer materials,
`are formed on the structure such that the structure shown in
`FIG. 2D is formed. The thick spacers are comprised of a
`dielectric material, such as a nitride, or an oxynitride, which
`is different from I-shaped oxide spacers 25. For example,
`when the thin spacers are comprised of Si0.,, then the thick
`spacers are formed of a nitride (e.g., Si,N,) or oxynitride
`(e.g., SION). Note that thick spacers 24 are formed utilizing
`the processing steps mentioned hereinabove,e.g., deposition
`and etching.
`At this point of the present invention, deep source/drain
`diffusion regions 16 may be formed in the substrate (for
`either NFET, PFET or both) utilizing conventional
`ion
`implantation and annealing processes well known to those
`skilled in the art.
`
`FIG. 2E shows the structure wherein I-shaped oxide
`spacers 25 are recessed to a level below that of the thick
`spacers so as to form divot region 26 in the structure. The
`oxide spacer recessing step may be carried out by a wet
`chemical etching process which includes the use of a chemi-
`cal etch such as HFthat has a high selectivity for recessing
`oxide spacer 25 as compared with thick spacer 24. Note that
`the I-shaped spacers are recessed below the top most edge of
`the thick spacers.
`The recess may also be achieved by utilizing a dry etching
`process that is capable of etching oxide spacer 25 but is
`selective to the gate stack material, the thick spacers and the
`semiconductor substrate.
`FIG. 2F showsthe structure that is obtained after divot fill
`
`material 28 is formed on all exposed surfaces of the struc-
`ture. The divot fill material includes the same material as
`
`60
`
`mentioned previously in respect to the first method of the
`present invention and it is formed utilizimg one of the above
`mentioned processing steps.
`FIG. 2G shows the structure that is obtained after the
`divotfill material has been subjected to the above-mentioned
`etch back process. Specifically, the etch back process may
`include a spacer type etching process or a combination of
`
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`US 6,512,266 Bl
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`9
`isotropic etching and anisotropic etching that removes some
`of the material from the vertical surfaces so that the divotfill
`material is left completely or partially covering oxide spac-
`ers 25.
`
`The silicidation process is performed after the structure
`illustrated in FIG. 2G is formed. Specifically, the silicidation
`process includesthe steps of forming a refractory metal such
`as Co, Ni or Ti on the surface of semiconductor substrate 10,
`annealing the refractory metal under conditions that are
`capable of converting the refractory metal layer into a metal
`silicide layer, and, if needed, removing any non-reactant
`refractory metal from the structure.
`invention also
`In addition to silicidation,
`the present
`contemplates other well known complementary oxide semi-
`conductor (CMOS) processing steps that are typically
`employed in the prior art. For example, the present invention
`also contemplates forming a metal contact
`to the metal
`silicide layer, and connecting the metal contact to an external
`contact.
`
`Whi