United States Patent [191
`Bhattacharyya et al.
`
`[11] Patent Number:
`[45] Date of Patent!
`
`4,776,922
`Oct. 11, 1988
`
`[54] FORMATION OF VARIABLE-WIDTH
`SIDEWALL STRUCTURES
`
`[56]
`
`References Cited ,
`U.S. PATENT DOCUMENTS
`
`.
`[751 lnvem°rs= A11"? Bhamcharyya, ESS¢X_J“"°"°";
`Mlehael L- Kerbaush, Burllngfon;
`Robert M. Quinn, South Burlmgton;
`:lelfg:
`Robinson’ Essex Junction’
`'
`
`'
`
`,
`
`4,424,621 1/1984 Abbas et al. .................. .. 156/657 X
`4,502,914 3/1985 Trumpp et al.
`156/655 x
`4,577,391 3/1986 Hsia et a1, ................... .. 437/56 x
`4,648,937 3/1987 Ogura et a]. ...................... .. 156/643
`Primary Examiner-William A. Powell
`Attorney, Agent, or Firm—-Mark F. Chadurjian
`
`[73] Assignee: International Business Machines
`Corporation, Armonk, N-Y-
`
`21 A 1’ N _, 114 59
`[
`1
`pp
`0
`,9
`_
`122] Flled:
`
`oct- 30’ 1987
`
`[51] Int. Cl.‘ ...................... .. B44C 1/22; C03C 15/00;
`-
`C23F 1/02; B29C 37/00
`[52] US. Cl. .................................. .. 156/643; 156/646;
`156/648; 156/653; 156/656; 156/657;
`156/659.1; 156/668; 204/ 192.37; 437/228;
`437 /235; 437/245
`'
`'
`[58] Field of Search ............. .. 156/643, 646, 648, 652,
`156/653, 656, 657, 659.1, 668; 430/313, 314,
`317, 318; 204/192.32, 192.35, 192.36, 192.37;
`437/40, 41, 56-59, 61,63, 80, 203, 228, 235, 245
`
`.
`ABSTRACT
`[57]
`Spacers are formed having widths that vary as a func
`tion of the spacing between the mandrels upon which
`the conformal material that de?nes the spacers is depos
`ited and etched. As the spacing between adjacent man
`drels decreases, the width of the resulting spacers de
`creases. The correlation between mandrel spacing and
`sidewall structure width is independent of the thickness
`of the conformal material as-deposited. As the spacing
`between'the mandrels decreases, the decrease in width
`becomes more pronounced, particularly, at mandrel
`spacings of ?ve microns or less. Thus, by making adja
`cent mandrels closer together or further apart and ad
`justing mandrel height, active/ passive components hav
`ing differing widths/lengths may be formed from the
`same conformal layer.
`
`6 Claims, 5 Drawing Sheets
`
`Page 1 of 9
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`IP Bridge Exhibit 2027
`TSMC v. IP Bridge
`IPR2016-01246
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`

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`US. Patent 0a. 11, 1988
`U.S. Patent
`Oct. 11, 1988
`
`Sheet 1 of5
`Sheet 1 015
`
`4,776,922
`4,776,922
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`FIG.2
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`Page 2 of 9
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`Page 2 of 9
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`

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`US. Patent Oct.11,1988
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`Sheet 2 of5
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`4,776,922
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`F|G.3
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`FIG.4
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`Page 3 of 9
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`

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`US. Patent
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`Oct. 11, 1988
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`Sheet 3 of 5
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`Page 4 of 9
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`U.S. Patent
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`Oct. 11, 1988
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`Sheet 4 of 5
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`U.S. Patent
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`Oct. 11,1988
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`Sheet 5 of 5
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`4,776,922
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`Page 6 of 9
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`

`

`1
`
`FORMATION OF VARIABLE-WIDTHTSIDEWALL
`STRUCTURES
`
`4,776,922
`2
`Several workers have explored the relationship be
`tween the characteristics of the conformal layer as
`deposited and the characteristics of the resulting spac
`ers. See e.g. an article by Dhong et al, entitled “Side.
`wall Spacer Technology For MOS and Bipolar De
`vices,” J. Electrochem. Soc, Vol. 133, No. 2, Feb. 1986,
`pp. 389-396. Dhong found that the spacer width in
`creases as the angle of the mandrel sidewalls increases
`toward 90°, and that as the thickness of the conformal
`layer as-deposited increases, both the slope and height
`of the resulting spacers decrease.
`The above studies established that the resulting spac
`ers are sensitive to processing variations. This led the
`inventors to consider controllably varying the process
`to produce controllable variations in the widths of the
`spacers. However, neither of the above-noted process
`ing sensitivities would provide good results. That is, it
`would be extremely dif?cult to controllably vary either
`the mandrel height or the thickness of the conformal
`material across a given wafer without using additional
`masking/etching steps.
`Thus, a need exists in the art for a method of control
`lably varying the widths of the spacers formed on a
`workpiece without introducing extra process complex
`ity.
`
`5
`
`25
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`Reference is made to US. patent application Ser. No.
`924,233, entitled “Lithographic Image Size Reduction,”
`?led Oct. 28, 1986, by Beyer, now US. Pat. No.
`4,707,218 and assigned to the assignee of the invention.
`The application relates to the general idea of using
`inorganic conformal layers to de?ne sidewall spacers on
`vertically-imaged photoresist. The spacers de?ne im
`ages having an area less than the images normally
`printed by the photolithographic exposure system.
`BACKGROUND ART
`Over the past several years, many different methods
`of forming sub-micron images have been proposed in
`the integrated circuit processing art. Many of these
`methods rely on state-of-the-art photolithographic tool
`ing. Other methods rely on more exotic exposure sys
`tems (e.g., X-ray, E-beam, etc.). Whichever of the
`above exposure systems are used, its source intensity,
`beam focus, and other properties combine to establish a
`minimum feature size that can be reliably printed.
`One method of supplementing this minimum image is
`by the use of sidewall structures.
`In “sidewall spacer” or “spacer” technology, a con
`formal layer is coated on a “mandre ,” which is a block
`of material typically having substantially vertical side
`walls. The conformal layer is then etched in an aniso
`tropic mode, so that portions thereof overlaying hori
`zontal surfaces (e.g., the upper surface of the mandrel)
`are removed, while portions thereof overlaying vertical
`surfaces (i.e., the sidewalls of they mandrels remain to
`form the spacers. The substrate is then treated in an
`etchant that selectively attacks the mandrels without
`substantially attacking the spacers.
`An example of forming sub-micron images by utiliz
`ing sidewall technology is shown in US. Pat. No.
`4,358,340, entitled “Submicron Patterning Without
`Using Submicron Lithographic Technique,” issued
`Nov. 9, 1982, to Fu and assigned to Texas Instruments.
`A layer of polysilicon is deposited on an oxide mandrel
`and is etched to de?ne polysilicon spacers. The mandrel
`is then removed without removing the polysilicon spac—
`ers.-The patent teaches that since the width of the side
`wall structures is a function of the thickness of the layer
`as-deposited (rather than the image size of the exposure
`system), polysilicon gate electrodes may be formed
`having widths on the order of % micron.
`~
`Attendant with the drive towards forming smalle
`structures is the need to simultaneously provide larger
`structures. For example, a chip that requires 5 micron
`gate widths for the transfer FET devices in a dynamic
`random access memory array may also require one
`micron gate widths for the FETs in the support cir
`cuitry that sink large currents or drive large loads. If
`one has the luxury of utilizing a 1: micron exposure
`system, it would be a simple matter to print one micron
`images. However, if one were utilizing the above
`described spacer technology, one would need a method
`for controllably varying the width of the sidewall struc
`tures so that both 5 micron and one micron spacers
`could be produced on the same wafer from the same
`conformal layer deposit.
`
`30
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`45
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`55
`
`60
`
`SUMMARY'OF THE INVENTION
`It is thus an object of the present invention to provide
`a process for controllably varying the widths of spacers
`formed on a workpiece.
`It is another object of the invention to provide a
`process that varies spacer widths without introducing
`additional process steps.
`The above and other objects of the invention are
`realized by varying the spacing between the mandrels
`upon which the conformal material is deposited and
`etched. As the spacing between adjacent mandrels de
`creases, the width of the resulting sidewall structures
`decreases. The amount of this decrease can be con
`trolled by adjusting the mandrel height and the thick
`ness of the conformal material as-deposited. As the
`spacing between the mandrels decreases below three
`microns, the decrease in width becomes more pro
`nounced. Thus, by making adjacent mandrels closer
`together or further apart, structures having differing
`widths may be formed from the same conformal layer.
`
`BRIEF DESCRIPTION OF THE DRAWING
`The above and other structures and teachings of the
`invention will become more apparent upon a review of
`the detailed description thereof as rendered below. In
`the description to follow, reference will be made to the
`accompanying Drawing, in which:
`FIG. 1 is a top view SEM of a test wafer showing the
`proximity effect;
`FIG. 2 is a cross-sectional SEM of a test wafer having
`a mandrel spacing of one microns;
`FIG. 3 is a cross-sectional SEM of a test wafer having
`a mandrel spacing of two microns;
`FIG. 4 is a cross-sectional SEM of a test ,wafer having
`a mandrel spacing of three microns;
`FIG. 5 is a graph showing the variation in spacer
`width as a function of mandrel spacing for two different
`mandrel heights/conformal layer thicknesses;
`FIG. 6 is a graph showing the variation in the prox
`imity effect as a function of mandrel height, for three
`different conformal layer thicknesses; and
`
`Page 7 of 9
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`

`

`4,776,922
`3
`4
`FIG. 7 is a graph showing the variation in the prox
`mandrel height increases. Since the resulting spacers are
`imity effect as a function of conformal layer thickness,
`used as a mask to anisotropically etch the underlaying
`for two different mandrel heights.
`polysilicon layer, the width of the spacer bottoms will
`determine the width of the resulting polysilicon lines.
`The curves show that spacer width decreases as man
`drel spacing decreases. The decrease appears to become
`signi?cant (i.e., on the order of 0.2 microns or more) at
`mandrel spacings below approximately ?ve microns.
`Moreover, note that the total effect (in terms of the
`spacer width difference between points at either end of
`the curve) is approximately 0.15 microns for the lower
`curve and 0.40 microns for the upper curve. In other
`words, the proximity effect is enhanced by increasing
`the mandrel height and/or the conformal layer thick
`ness. In particular, note the 0.12 difference in the upper
`curve at a mandrel spacing of 2.0 microns versus 1.5
`microns.
`FIG. 6 is a graph showing the proximity effect versus
`mandrel height for different conformal layer thick
`nesses. The proximity effect value is given by the differ
`ence between the spacer width at a mandrel spacing of
`15 microns and a mandrel spacing of 2.5 microns. Thus,
`for example, for a mandrel height of 1.00 microns and a
`conformal layer thickness of 0.50 microns, the differ
`ence between the spacer widths at 15 micron versus 2.5
`micron mandrel spacings is approximately 0.085 mi
`crons. FIG. 6 shows that increased mandrel height will
`increase the proximity effect. For the 0.4 micron thick
`conformal layer, the effect increases from 0.065 pm to
`0.105 as the mandrel height is raised from 1.0 microns to
`1.5 microns. This enhancement of the proximity effect is
`greater as the thickness of the conformal layer is in
`creased. FIG. 7 is a graph showing the change in prox
`imity effect versus conformal material thickness, as a
`function of different mandrel heights. Again, note that
`the 1.5g mandrels produce a greater proximity effect
`for a given nitride thickness. In general, the curves of
`FIGS. 6 and 7 con?rm that the proximity effect in
`creases with increasing mandrel height and increasing
`conformal layer thickness. Moreover, because the
`slopes of the curves shown in FIGS. 6 and 7 are rela
`tively similar, mandrel height and conformal layer
`thickness are equivalent factors in determining the
`change in spacer width. However, since neither of these
`parameters can be varied across a given wafer without
`adding process steps, in the present invention it is pre
`ferred to use them to enhance the proximity effect by
`providing a greater swing in spacer widths (as shown
`e.g., in the upper curve versus the lower curve in FIG.
`5). More particularly, since the invention is intended to
`be used to provide minimum spacer widths (e.g., such
`that 0.l—l.0 micron conformal layers would be used), it
`is preferred to enhance the proximity effect by simply
`raising the mandrel heights above 1.5 microns. It should
`be noted that while the proximity effect shown in FIG.
`6 and 7 is referenced from a mandrel spacing of 2.5
`micron, the observed effect would be signi?cantly en
`hanced when referenced from a mandrel spacing of 1.5
`microns (as demonstrated in FIG. 5).
`Thus, by controlling the spacing between mandrels
`formed on a wafer, spacers having varying, well-de
`?ned linewidths can be formed from the same confor
`mal layer deposition. This technique can be used to
`form FET gate electrodes (and other active and passive
`components) having varying lengths/widths on the
`same wafer. While the invention has been practiced by
`the use of CVD silicon nitride, the source depletion
`mechanism will be present for any conformal material
`
`DETAILED DESCRIPTION OF THE BEST
`MODE FOR CARRYING OUT THE INVENTION
`It has been observed that when the spacing between
`mandrels decreases, the width of the resulting spacers
`decreases. This is shown by the scanning electron mi
`croscope (SEM) photograph in FIG. 1. The dark lines
`are the spacers. The grey spaces to the left of the spacer
`on the left, and inside the box defined by the spacer on
`the right, are portions of the substrate that were previ
`ously covered by mandrel structures. Note that the
`portions of the sidewall structures that diverge from
`one another are much thicker than the portions that are
`in close proximity to one another.
`This “proximity effect” is shown in cross-section in
`FIGS. 2-4 by the SEM’s shown. In these Figures,
`plasma enhanced chemical vapor deposited (PECVD)
`20
`silicon nitride was conformally deposited on polyimide
`mandrels of approximately 1.6 microns in height. While
`the SEM’s appear to show mandrels having an “under
`cut" or overhang pro?le, in practice the mandrels had
`vertical sidewalls. In taking a cross section of the wafer,
`25
`the polyimide material adjacent to the nitride was
`pulled away due to sample preparation techniques. The
`silicon nitride deposition was carried out for a time
`sufficient to form a layer of 0.65 microns on a ?at sur
`face. The spacing between mandrels is approximately
`one micron in FIG. 2, two microns in FIG. 3, and three
`microns in FIG. 4. Note that the amount of silicon
`nitride deposited on the sidewalls of the mandrels is
`much less in FIG. 2 as it is in FIG. 3; note also that the
`difference in sidewall deposition thickness is much less
`between FIGS. 3 and 4 as compared to FIGS. 2 and 3.
`The proximity effect appears to be caused by the
`mechanisms of vapor deposition. Source materials are
`supplied to the reaction chamber in gaseous form. The
`amount of material deposited is a function of the amount
`40
`of source gas available. As the spacing between man
`drels decreases, the amount of source gas decreases (or
`is depleted) relative to the surfaces to be covered. Thus,
`since less source gas is available, a smaller amount of
`material is deposited.
`45
`Subsequent studies con?rmed the proposed proxim
`ity effect mechanism. Test sites were prepared in accor
`dance with the method described in US. Pat. No.
`4,648,937 (issued 3/10/87 to Ogura et al and assigned to
`the assignee of the present invention), the teachings of
`50
`which are completely incorporated herein by reference.
`That is, the resulting silicon nitride spacers were used as
`masks to pattern an underlaying polysilicon layer. The
`resistivity of the resulting polysilicon lines indicates the
`width of spacers as formed.
`FIG. 5 is a graph of spacer width versus mandrel
`spacing for mandrels having a height of 1.3 microns
`(lower curve) and 1.6 microns (upper curve), and for a
`conformal layer of 0.45 microns in thickness (lower
`curve) and 0.57 microns in thickness (upper curve).
`First of all, note that the width of the spacers at the
`maximum mandrel spacings of 15 microns is shown on
`the graph as 0.72 microns (upper curve) and 0.55 mi—
`crons (lower curve). As discussed in the Dhong et al
`article, the width of the spacer bottom will be greater
`than the thickness of the conformal material as-depos
`ited. This effect is enhanced as the thickness of the
`conformal material as-deposited increases and/or as the
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`4,776,922
`5
`6
`41 The method as recited in claim 1, wherein said
`that is vapor deposited. Thus, the invention can be used
`conformal layer comprises a insulative material selected
`to form insulative (e.g., silicon oxide, silicon nitride,
`from the group consisting of silicon oxide, silicon ni- '
`silicon oxynitride, etc.) or conductive e.g. a, CVD
`tride, silicon oxynitride, and alumina.
`metal such as tungsten, molybdenum, hafnium, etc.)
`5. A method of forming a ?rst set ‘of spacers having
`spacers on organic mandrels (e.g., photosensitive poly
`?rst widths and a second set of spacers having second
`mers, polyimide, etc.) or inorganic mandrels (e.g. sili
`widths greater than said ?rst widths on a substrate,
`con oxide, silicon nitride, alumina, etc.).
`.comprising the steps of:
`It is to be understood that while the invention has
`forming a plurality of mandrels having substantially
`been shown and described with reference to a, particular
`vertical sidewalls and a height greater than approx
`embodiment, the scope of the invention is not to be
`imately one micron on the substrate, a ?rst set of
`limited thereby. That is, modi?cations may be made to
`said mandrels being spaced from one another by a
`the embodiments shown without departing from the
`distance less than approximately two microns and a
`ambit of the invention as re?ected by the several claims.
`second set of said mandrels being spaced from one
`another by a distance greater than approximately
`What is claimed is:
`?ve microns;
`1. A method of forming spacers having respective
`depositing a conformal layer on the substrate and said
`widths that vary from one another on a substrate, com
`mandrels; and
`prising the steps of forming mandrels on the substrate at
`anisotropically etching said conformal layer to re
`respective varying distances from one another, at least
`move portions of said conformal layer other than
`some of said respective varying distances being less than
`portions thereof disposed on said sidewalls of said
`approximately ?ve microns, depositing a conformal
`mandrels, the ?rst set of spacers being formed on
`layer on said mandrels, and anisotropically etching said
`said sidewalls of said mandrels in said ?rst set of
`conformal layer to provide said spacers.
`mandrels and the second set of spacers being
`2. The method as recited in claim 1, wherein said
`formed on said sidewalls of said mandrels in said
`mandrels comprise an organic resin selected from the
`second set of mandrels.
`group consisting of photosensitive polymers and polyi~
`6. The method as recited in claim 5, wherein said
`mides.
`conformal layer has a thickness of 0.1 to 1.0 microns
`as-deposited.
`3. The method as recited in claim 1, wherein said
`conformal layer comprises a CVD metal.
`
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