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`Case 6:20-cv-01216-ADA Document 41-16 Filed 10/06/21 Page 1of8
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`EXHIBIT 16
`EXHIBIT 16
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`case 620-ev-01216-ADA DocumeMMPIIANAMATEEURE
`Case 6:20-cv-01216-ADA Document 41-16 Filed 10/06/21 Page 2 of 8
`US006156480A
`
`United States Patent 55
`6,156,480
`[11] Patent Number:
`
`[45] Date of Patent: Dec. 5, 2000
`Lyons
`
`[54] LOW DEFECT THIN RESIST PROCESSING
`FOR DEEP SUBMICRON LITHOGRAPHY
`
`[75]
`
`Inventor: Christopher F. Lyons, Fremont, Calif.
`
`[73] Assignee: Advanced Micro Devices, Inc.,
`Sunnyvale, Calif.
`
`[21] Appl. No.: 09/336,455
`
`[22]
`
`Filed:
`
`Jun. 18, 1999
`
`PSL]
`Tent, C0 eee eccceeeeeccesnneeeceennensecnnnees GO3F 7/004
`
`[52]
`.. 430/270.1; 430/312
`[58] Field of Search 0. eee 430/270.1, 312;
`216/47
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,273,856
`5,723,258
`5,892,096
`6,020,269
`
`12/1993 Lyonset al. woes 430/191
`.. 430/270.1
`3/1998 Kimetal. ov...
`
`eeeeee 558/393
`4/1999 Meadoret al.
`occ
`1/2000 Wang et al. oo. eeee 438/717
`OTHER PUBLICATIONS
`
`“Ultrathin Photoresists for EUV lithography”, Rao,V. et al,
`SPIE, vol. 3676, pt.2, 1999, 615-626.
`Moreau et al., “Speed Ehancement of PMMAResist”, J.
`Vac. Sci. Technol., Vol. No. 16, No. 6 (Nov./Dec. 1979) pp.
`1989-1991.
`
`Havard et al., “Design of a Positive Tone Water-Soluble
`Resist”, Department of Chemistry and Chemical Engineer-
`ing, University of Texas, SPIE vol. 3049, pp. 437-447.
`
`Miles et al., “New Thermally Crosslikable Electron—Beam
`Resists:
`1.
`Itaconic Anhydride—Methyl Methacrylate
`Copolymers”, Polymer, 91, vol. 32, No. 3, (1991) pp.
`484-488.
`
`Primary Examiner—Janet Baxter
`Assistant Examiner—Rosemary Ashton
`Attorney, Agent, or Firm—Renner, Otto, Boisselle, & Sklar,
`LLP
`
`[57]
`
`ABSTRACT
`
`invention relates to a
`the present
`In one embodiment,
`method of forming a short wavelength thin photoresist
`coating having a low defect density by depositing sequen-
`tially at least two discrete ultra-thin photoresist layers to
`form the short wavelength thin photoresist coating, each
`ultra-thin photoresist layer independently having a thickness
`from about from about 200 A to about 2,500 A, the short
`wavelength thin photoresist coating, having a thickness of
`about 5,000 A orless.
`
`20 Claims, 1 Drawing Sheet
`
`

`

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`Case 6:20-cv-01216-ADA Document 41-16 Filed 10/06/21 Page 3 of 8
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`U.S. Patent
`
`Dec. 5, 2000
`
`6,156,480
`
`14
`
`FIG. 1
`
`22c
`
`22a
`
`22b
`
`22
`
`FIG. 2
`
`

`

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`6,156,480
`
`1
`LOW DEFECT THIN RESIST PROCESSING
`FOR DEEP SUBMICRON LITHOGRAPHY
`
`TECHNICAL FIELD
`
`invention generally relates to improved
`The present
`lithography methods. In particular,
`the present invention
`relates to using multiple layers of ultra-thin photoresists to
`form a thin photoresist coating having a low defect density.
`
`BACKGROUND ART
`
`In the semiconductor industry, there is a continuing trend
`toward higher device densities. To achieve these high den-
`sities there has been and continues to be efforts toward
`scaling down the device dimensions on semiconductor
`wafers. In order to accomplish such high device packing
`density, smaller and smaller features sizes are required. This
`includes the width and spacing of interconnecting lines, gate
`conductors, trenches, vias and various other devices and
`features that are formed with the aid of lithography. Since
`numerous devices, interconnecting lines and other features
`are typically present on a semiconductor wafer, the trend
`toward higher device densities is a notable concern.
`The requirement of small features (and close spacing
`between adjacent features) requires high resolution photo-
`lithographic processes.
`In general,
`lithography refers to
`processes for pattern transfer between various media. It is a
`technique used for integrated circuit fabrication in which a
`siliconslice, the wafer, 1s coated uniformly with a radiation-
`sensitive film, the resist, and an exposing source (such as
`optical
`light, X-rays, or an electron beam)
`illuminates
`selected areas of the surface through an intervening master
`template, the photomask,for a particular pattern. The litho-
`graphic coating is generally a radiation-sensitized coating
`suitable for receiving a projected image of the subject
`pattern. Once the image is projected,it is indelibly formed
`in the coating. The projected image maybeeither a negative
`or a positive of the subject pattern. Exposure of the coating
`through the photomask causes a chemical transformation in
`the exposed areas of the coating thereby making the image
`area either more or less soluble (depending on the coating)
`in a particular solvent developer. The more soluble areas are
`removed in the developing process to leave the pattern
`image in the coating as less soluble polymer.
`Projection lithography is a powerful and essential tool for
`microelectronics processing. Using light having smaller
`wavelengths to selectively expose photoresists prior to
`development
`increases the resultant resolution. This is
`because precise control over the exposure area is increased
`as the wavelength of light decreases. As a result, there is
`trend toward the use of photoresists that are patterned using
`light having a relatively short wavelength. However, there
`are several concerns associated with using shorter wave-
`lengths of light. As the wavelength of light decreases, the
`penetration depth of that
`light
`into a given photoresist
`generally decreases. This is a problem when most photore-
`sists are coated on a semiconductor substrate at a thickness
`between 10,000 A and 20,000 A.
`Simply applying a thinner coating of a photoresist does
`not enable adequate and/or reliable use of the photoresist.
`This is because coated photoresists typically contain pinhole
`defects. Pinhole defects inhibit crisp pattern formation and
`critical dimensional control in developedphotoresists. When
`a photoresist has a thickness of 10,000 Aor higher, pinhole
`defects are not a concern since the pinholes are relatively
`small in relation to the photoresist thickness. As the thick-
`ness of a photoresist decreases, the deleterious effects, of
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`pinhole defects increases. This is shown in FIG. 1. FIG. 1
`illustrates a substrate 10 with a thin photoresist 12 having a
`thickness of about 5,000 A. The thin photoresist 12 has a
`numberof relatively large pinholes 14; that is, relatively
`large compared to the photoresist thickness. Minimizing the
`deleterious effects of pinhole defects or the occurrence of
`pinhole defects in relatively thin photoresists is therefore
`desired.
`
`SUMMARYOF THE INVENTION
`
`The present invention provides methods of forming small
`features, in some instances on the sub-micron scale. The
`present invention specifically provides methods of making
`thin photoresist coatings with very low defect densities by
`depositing multiple layers of ultra-thin photoresists. As a
`result, the present invention effectively addresses the con-
`cerns raised by the trend towards the mimiaturization of
`semiconductor devices.
`
`the present invention relates to a
`In one embodiment,
`method of forming a short wavelength thin photoresist
`coating having a low defect density by depositing sequen-
`tially at least two discrete ultra-thin photoresist layers to
`form the short wavelength thin photoresist coating, each
`ultra-thin photoresist layer independently havinga thickness
`from about from about 200 A to about 2,500 A, the short
`wavelength thin photoresist coating having a thickness of
`about 5,000 A orless.
`In another embodiment, the present invention relates to a
`method of forming a short wavelength thin photoresist
`coating having a low defect density by depositing sequen-
`tially at least three discrete ultra-thin photoresist layers to
`form the short wavelength thin photoresist coating, each
`ultra-thin photoresist layer independently having a thickness
`from about 250 A to about 2,000 A and comprising a
`pre-crosslinked photoresist material, the short wavelength
`thin photoresist coating having a thickness of about 5,000 A
`or less.
`
`In yet another embodiment, the present invention relates
`to a method of decreasing pinhole size in a thin photoresist
`coating by forming the thin photoresist coating by sequen-
`tially depositing at least two discrete layers of an ultra-thin
`photoresist, each ultra-thin photoresist layer independently
`havinga thickness from about from about 300 A to about
`1,500 A,the thin photoresist coating having a thickness from
`about from about 600 A to about 4,500 A, the thin photo-
`resist coating having smaller pinholes than a photoresist of
`the same thickness formed by depositing one layer of a
`photoresist material.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`FIG. 1 illustrates, in a cross-sectional view, pinholes in a
`conventional thin photoresist.
`FIG. 2 illustrates, in a cross-sectional view, a thin pho-
`toresist made according to several aspects of the present
`invention.
`
`DISCLOSURE OF INVENTION
`
`The present invention involves making thin photoresists
`with low defect density. The present invention more spe-
`cifically involves using multiple layers of ultra-thin photo-
`resists to form a thin photoresist coating having a low defect
`density. The size of any pinholes is limited by the thickness
`of a given photoresist layer. By depositing multiple, discrete
`layers ofultra-thin photoresist layers, the size of pinholes, if
`any,
`is thus limited by the thickness of the individual
`
`

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`6,156,480
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`3
`ultra-thin photoresist layers. And pinholes in the individual
`ultra-thin photoresist layers have an extremely low prob-
`ability of being positioned directly over one another. Form-
`ing thin photoresists with low defect densities facilitates the
`use of short wavelength photolithography. Expanding the
`use of short wavelength photolithography, in turn, increases
`the resolution of photoresist patterns further enabling mini-
`turization and device scaling.
`The thin photoresist, comprised of multiple layers of
`ultra-thin photoresist layers, is formed over a substrate. The
`substrate is typically a silicon substrate with or without
`various devices, elements and/or layers thereover; including
`metal
`layers, barrier layers, dielectric layers, device
`structures, active elements and passive elements including
`polysilicon gates, wordlines, source regions, drain regions,
`bit lines, bases, emitters, collectors, conductive lines, con-
`ductive plugs, etc. The thin photoresist is provided over a
`portion of the substrate or over the entire substrate.
`The thin photoresist has a thickness of about 5,000 Aor
`less. In another embodiment,
`the thin photoresist has a
`thickness of about 3,500 A or
`less.
`In yet another
`embodiment, the thin photoresist has a thickness of about
`2,000 A orless. In still yet another embodiment, the thin
`photoresist has a thickness of about 1,500 A orless.
`The thin photoresist is deposited by multiple depositions
`of ultra-thin photoresist
`layers using conventional spin-
`coating or spin casting techniques. The thin photoresist
`contains at least two layers of an ultra-thin photoresist. In
`another embodiment, the thin photoresist contains at least
`three layers of an ultra-thin photoresist.
`In yet another
`embodiment, the thin photoresist contains atleast four layers
`of an ultra-thin photoresist. In still yet another embodiment,
`the thin photoresist contains at
`least five layers of an
`ultra-thin photoresist. Although there is no upperlimitto the
`number of ultra-thin photoresist layers, typically the thin
`photoresist contains from 2 to about 20, and more typically
`from 3 to about 10 layers of an ultra-thin photoresist.
`The multiple ultra-thin photoresist layers that comprise
`the thin photoresist coating may have the same thickness,
`substantially the same thickness, or different thicknesses. In
`a preferred embodiment, the multiple ultra-thin photoresist
`layers of the thin photoresist coating have the same thick-
`ness or substantially the same thickness. Each ultra-thin
`photoresist layer has a thickness from about 200 Ato about
`2,500 A. In another embodiment, eachultra-thin photoresist
`layer has a thickness from about 250 Ato about 2,000 A. In
`yet another embodiment, each ultra-thin photoresist layer
`has a thickness from about 300 A to about 1,500 A.In still
`yet another embodiment, each ultra-thin photoresist layer
`has a thickness from about 400 A to about 1,000 A.
`The multiple ultra-thin photoresist layers are deposited in
`such a manner that
`intermixing or redissolving between
`layers is minimized or preferably prevented. In other words,
`intermixing or redissolving is minimized or prevented when
`an ultra-thin photoresist layer is deposited on an underlying,
`previously deposited ultra-thin photoresist layer. The solu-
`bility of adjacent ultra-thin photoresist layers is extremely
`low. Depositing photoresist layers in this manneris termed
`depositing “discrete” ultra-thin photoresist layers. This can
`be accomplished in at least two ways.
`In one embodiment, a pre-crosslinked or partially cured
`photoresist is deposited to form each ultra-thin photoresist
`layer. Pre-crosslinking in the photoresists is typically
`accomplished via acetal linkages, condensation reactions,
`such as anhydride and amide formation, and similar reac-
`tions. Acetal
`linkages are,
`in turn, accomplished by
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`crosslinking at least a portion of the acetal groups of a
`polymer. See, for example, U.S. Pat. No. 5,723,258 which
`describes incorporating acetal groups into photoresist poly-
`mer systems and is incorporated by reference for its teach-
`ings in this regard. Incorporation of anhydride groups into
`photoresist polymer systemsis described in Moreauetal., J.
`Vac. Sci. Technol., Vol. 16, No. 6, November/December
`1979, which is hereby incorporated by reference for its
`teachings in this regard.
`Pre-crosslinking or partial curing may be induced by heat
`and/or irradiation. The temperature to which the ultra-thin
`photoresist material is heated and/or the particular wave-
`length employed to induce partial curing depends upon the
`chemical constitution of the photoresist material, and suit-
`able temperatures and wavelengths can be determined by
`those skilled in the art. Partial curing, however, does not
`prevent or degrade subsequent development of the thin
`photoresist.
`In this embodiment, the photoresist material is contained
`in a solvent, which is deposited on the substrate or on
`another ultra-thin photoresist layer. Prior to depositing a
`subsequent ultra-thin photoresist layer, the solvent is per-
`mitted and/or induced to evaporate. The time required for
`the solvent to evaporate primarily depends uponthe identity
`of the solvent and the amount of solvent employed. In one
`embodiment, the time between depositions of the individual
`ultra-thin photoresist layers is at least about 5 seconds, and
`typically from about 5 seconds to about 5 minutes.
`In
`another embodiment, the time between depositions of the
`individual ultra-thin photoresist layers is at least about 10
`seconds, and from about 10 seconds to about 2 minutes.
`In another embodiment, partial curing is effected after
`each ultra-thin photoresist layer is deposited. Again, partial
`curing may be induced by heat and/or irradiation. Also in
`this embodiment, the temperature to which the ultra-thin
`photoresist layer is heated and/or the particular wavelength
`employedto induce partial curing depends upon the chemi-
`cal constitution of the photoresist material, and suitable
`temperatures and wavelengths can be determined by one
`skilled in the art. Partial curing, however, does not prevent
`or degrade subsequent developmentof the thin photoresist.
`One example of partial curing is so-called B-staging.
`In this embodiment, the time between depositions of the
`individual ultra-thin photoresist layers is longer than the
`embodiment where a pre-crosslinked photoresist material is
`employed. In one embodiment, the time between depositions
`of the individualultra-thin photoresist layers is at least about
`15 seconds, and typically from about 30 secondsto about 10
`minutes. In another embodiment, the time between deposi-
`tions of the individual ultrathin photoresist layers is at least
`about 30 seconds, and from about 30 seconds to about 5
`minutes.
`
`Thin resists may be processed using small wavelength
`radiation, such as deep UV and extreme UV radiation. As
`used herein, small wavelength radiation means electromag-
`netic radiation having a wavelength of about 250 nm orless.
`In one embodiment, small wavelength radiation includes
`electromagnetic radiation having a wavelength of about 200
`mm or less.
`In another embodiment, small wavelength
`radiation includes extreme UV electromagnetic radiation
`having a wavelength of about 25 nm orless. In yet another
`embodiment, small wavelength radiation includes extreme
`UVelectromagnetic radiation having a wavelength of about
`15 nm orless.
`
`Small wavelength radiation increases precision and thus
`the ability to improvecritical dimension control and reso-
`
`

`

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`6,156,480
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`5
`lution. Specific examples of wavelengths to which the thin
`photoresists are sensitive (undergo chemical transformation
`enabling subsequent development) include about 248 nm,
`about 193 nm, about 157 nm, about 13 nm, about 11 nm and
`about 1 nm. Specific sources of radiation include KrF
`excimer lasers having a wavelength of about 248 nm, a
`XeHg vapor lamp having a wavelength from about 200 nm
`to about 250 nm, mercury-xenon arc lamps having a wave-
`length of about 248 nm, an ArF excimer laser having a
`wavelength of about 193 nm, an F, excimer laser having a
`wavelength of about 157 nm, extreme UV light having
`wavelengths of about 13.4 nm and about 11.5 nm, and
`X-rays having a wavelength of about 1 nm.
`The thin photoresist coating is suitable for functioning as
`a mask for etching underlying layers and/or selectively
`depositing films wherein the patterns or openings formed in
`the subsequently developed thin photoresist layer are less
`than about 0.25 um, about 0.18 ym orless, about 0.15 um or
`less, about 0.13 um orless, about 0.1 um or less, about 0.075
`um or less, and even 0.05 um or less. Since the thin
`photoresist layers are relatively thin compared with I-line
`and other photoresists, improved critical dimension control
`is realized.
`
`In embodiments where the patterns or openings formed in
`the developed thin photoresist layer are from about 0.15 wm
`to about less than 0.25 um, a 248 yum sensitive photoresist or
`a 193 nm sensitive photoresist is preferably employed. In
`embodiments where the patterns or openings formed in the
`developed thin photoresist layer are from about 0.1 um to
`about 0.15 wm, a 157 nm sensitive photoresist or a 193 nm
`sensitive photoresist 1s preferably employed. In embodi-
`ments where the patterns or openings formed in the devel-
`oped thin photoresist layer are about 0.1 um or less, a 13 nm
`sensitive photoresist or an 11 nm sensitive photoresist
`(extreme UV photoresist) is preferably employed.
`Positive or negative thin photoresists may be employed in
`the methods of the present invention. An example of a deep
`UV chemically amplified photoresist
`is a partially
`t-butoxycarbonyloxy substituted poly-p-hydroxystyrene.
`Photoresists are commercially available from a number of
`sources,
`including Shipley Company, Kodak, Hoechst
`Celanese Corporation, and Brewer.
`Referring to FIG. 2, the present invention is illustrated. A
`substrate 20 is provided, which may or may not have any
`number of layers, devices and/or elements (not shown)
`thereon. A thin photoresist 22 having a thickness of about
`5,000 A or less (about 5,000 A in this embodiment) is
`formed on the substrate 20 by depositing multiple, discrete
`layers of an ultra-thin photoresist 22a, 22b, and 22c.
`Although not always present, pinholes 24 havea relatively
`small size comparedto the pinholes 14 in the thin photoresist
`12 of the prior art, as shown in FIG. 1.
`After all of the ultra-thin photoresist layers are deposited
`to form the thin photoresist coating, thin photoresist coating
`is exposed to radiation and developed to provide a patterned
`photoresist. Either the exposed or unexposed portionsof the
`thin photoresist layer are removed or developed to provide
`the patterned photoresist. The patterned photoresist is then
`used as a mask to either selectively etch portions of the
`underlying substrate or selectively deposit a material on the
`exposed portions of the underlying substrate. The patterned
`photoresist is then stripped using a suitable stripper.
`Although the invention has been shown and described
`with respect
`te a certain preferred embodiment or
`embodiments, it is obvious that equivalent alterations and
`modifications will occur to others skilled in the art upon the
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`reading and understanding of this specification and the
`annexed drawings. In particular regard to the various func-
`tions performed by the above described components
`(assemblies, devices, circuits, etc.), the terms (including any
`reference to a “means”) used to describe such components
`are intended to correspond, unless otherwise indicated, to
`any component which performsthe specified function of the
`described component(i.e., that is functionally equivalent),
`even though not structurally equivalent to the disclosed
`structure which performs the function in the herein illus-
`trated exemplary embodimentsof the invention. In addition,
`while a particular feature of the invention may have been
`disclosed with respect to only one of several embodiments,
`such feature may be combined with one or more other
`features of the other embodiments as may be desired and
`advantageous for any given or particular application.
`Whatis claimedis:
`1. A method of forming a short wavelength thin photo-
`resist coating having a low defect density, comprising:
`depositing sequentially at least
`two discrete ultra-thin
`photoresist layers to form the short wavelength thin
`photoresist coating, each ultra-thin photoresist layer
`independently having a thickness from about from
`about 200 A to about 2,500 A, the short wavelength
`thin photoresist coating having a thickness of about
`5,000 A orless.
`2. The method of claim 1, wherein at least three discrete
`ultra-thin photoresist layers are deposited to form the short
`wavelength thin photoresist coating.
`3. The method of claim 1, wherein at least five discrete
`ultra-thin photoresist layers are deposited to form the short
`wavelength thin photoresist coating.
`4. The method of claim 1, wherein the ultra-thin photo-
`resist layers comprise a pre-crosslinked material.
`5. The method of claim 4, wherein the pre-crosslinked
`material of the ultra-thin photoresist
`layers comprises a
`polymer with at least one of acetal groups and anhydride
`groups.
`6. The method of claim 1, wherein each ultra-thin pho-
`toresist
`layer is partially cured prior to deposition of a
`subsequent ultra-thin photoresist layer.
`7. The method of claim 1, wherein the short wavelength
`thin photoresist coating comprises a photoresist material
`sensitive to a wavelength of about 250 nm orless.
`8. A method of forming a short wavelength thin photo-
`resist coating having a low density, comprising:
`depositing sequentially at least three discrete ultra-thin
`photoresist layers to form the short wavelength thin
`photoresist coating, each ultra-thin photoresist layer
`independently having a thickness from about 250 Ato
`about 2,000 A and comprising a pre-crosslinked pho-
`toresist material, the short wavelength thin photoresist
`coating having a thickness of about 5,000 A orless.
`9. The method of claim 8, wherein the pre-crosslinked
`photoresist material of the ultra-thin photoresist layers com-
`prises a polymer with at least one of acetal groups and
`anhydride groups.
`10. The method of claim 8, wherein the pre-crosslinked
`photoresist material of the ultra-thin photoresist layers is
`pre-crosslinked by at least one of thermal crosslinking and
`photo crosslinking.
`11. The method of claim 8, wherein the short wavelength
`thin photoresist coating comprises a photoresist material
`sensitive to a wavelength of about 200 nm orless.
`12. The method of claim 8, wherein the short wavelength
`thin photoresist coating comprises a photoresist material
`sensitive to a wavelength of about 25 nm orless.
`
`

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`6,156,480
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`7
`13. The method of claim 8, wherein the time between
`depositions of the discrete ultra-thin photoresist layers is
`from about 5 seconds to about 5 minutes.
`
`14. The method of claim 8, wherein the short wavelength
`thin photoresist coating has a thickness of about 3,500 Aor
`less.
`15. A method of decreasing pinhole size in a thin photo-
`resist coating, comprising:
`forming the thin photoresist coating by sequentially
`depositing at least two discrete layers of an ultra-thin
`photoresist, each ultra-thin photoresist layer indepen-
`dently having a thickness from about from about 300 A
`to about 1,500 A,the thin photoresist coating having a
`thickness from about from about 600 A to about 4,500
`A,the thin photoresist coating having smaller pinholes
`than a photoresist of the same thickness formed by
`depositing one layer of a photoresist material.
`
`8
`16. The method of claim 15, wherein the thin photoresist
`coating comprises a photoresist material sensitive to a
`wavelength of about 200 nm orless.
`17. The method of claim 15, wherein each ultra-thin
`photoresist layer comprises a pre-crosslinked material.
`18. The method of claim 15, wherein each ultra-thin
`photoresist layer is partially cured prior to deposition of a
`subsequent ultra-thin photoresist layer.
`19. The method of claim 18, wherein each ultra-thin
`photoresist layer is partially cured by at least one of thermal
`crosslinking and photo crosslinking.
`20. The method of claim 15, wherein from 2 to about 20
`discrete layers of an ultra-thin photoresist are deposited to
`form the thin photoresist coating.
`*
`*
`*
`*
`
`*
`
`10
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`15
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`

`

`PATENT NO.©: 6,156,480 Page 1 of 1
`
`
`DATED
`: December 5, 2000
`INVENTOR(S): Christopher F. Lyons
`
`It is certified that error appears in the above-identified patent and that said Letters Patentis
`hereby corrected as shown below:
`
`Column 5
`Line 65, replace “tc” with -- to --.
`
`Column 6
`Line 46, replace “low density” with -- low defect density --.
`
`Case 6:20-cv-01216-ADA Document 41-16 Filed 10/06/21 Page 8 of 8
`UNITED STATES PATENT AND TRADEMARK OFFICE
`CERTIFICATE OF CORRECTION
`
`Acting Director of the United States Patent and Trademark Office
`
`Signed and Sealed this
`
`Second Day of October, 2001
`
`Wiholos P Lbdbiss
`
`NICHOLASP. GODICI
`
`Attest:
`
`Attesting Officer
`
`