Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 1 of 19
`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 1 of 19
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`EXHIBIT 8
`EXHIBIT 8
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`case 620-ev-01216-ADA DocumerMMBIMITHTRANEMERTAGHAAE
`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 2 of 19
`US006140023A
`6,140,023
`(114) Patent Number:
`United States Patent 55
`Levinson et al.
`[45] Date of Patent:
`Oct. 31, 2000
`
`
`6/1990 Thomaset al. oo. 257/742
`4,933,743
`[54] METHOD FOR TRANSFERRING PATTERNS
`CREATED BY LITHOGRAPHY 5,091,339—2/1992 Carey ccecseccsccsecsecreecseseeeeenes 216/18
`
`5,318,877
`6/1994 Oberet al. wu.
`... 430/270
`
`2338als
`yt008 runsvoldetal srtereteneneeenaeeenaesBons
`3399,
`achdev et al.
`.....
`we
`5,759,748
`ssecssssssssssssensreeen 430/323
`6/1998 Chum et al.
`
`Inventors: Harry J. Levinson, Saratoga; Scott A.
`.
`*
`Bell,San enBNewyen FLyons,
`
`[75]
`
`Mateo; Fei Wang; Chih Yuh Yang,
`both of San Jose, all of Calif.
`
`[73] Assignee: Advanced Micro Devices, Inc.,
`Sunnyvale, Calif.
`
`Primary Examiner—S. Rosasco
`Attorney, Agent, or Firm—Amin, Eschweiler & Turocy,
`LLP
`
`[57]
`
`ABSTRACT
`
`A lithographic process for fabricating sub-micron features is
`[21] Appl. No.: 09/203,447
`provided. A silicon containing ultra-thin photoresist
`is
`14.
`
`[22]|Filed: Dec. 1, 1998 formed on an underlayer surface to be etched. The ultra-thin
`
`[SL]
`Tint, C0 i ceecccccccsssseecsessseessssseeeessneees G03F 9/00
`photoresist layer is patterned with short wavelength radia-
`[52] US. Ch. eeccccccsteessceseees 430/313; 216/41; 216/51
`tion to define a pattern. The ultra-thin photoresist is oxidized
`[58] Field of Search oo...eceeeeees 430/313, 317,
`so as to convert the silicon therein to silicon dioxide. The
`430/318, 322, 323, 325, 966, 967; 216/41,
`oxidized ultra-thin photoresist layer is used as a hard mask
`51
`during an etch step to transfer the pattern to the underlayer.
`The etch step includes an etch chemistry that
`is highly
`selective to the underlayer over the oxidized ultra-thin
`photoresist layer.
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`4,808,511
`
`2/1989 Holmes ou... ceceeeeeeeeeeeeenee 430/325
`
`30 Claims, 11 Drawing Sheets
`
`Peed bedded ede tebetteaee
`we 1%
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 3 of 19
`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 3 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 1 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 4 of 19
`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 4 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 2 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 5 of 19
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`U.S. Patent
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`6,140,023
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`Oct. 31, 2000
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`Sheet 3 of 11
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 6 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 4 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 7 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 5 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 8 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 6 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 9 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 7 of 11
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`Fig. 15
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 10 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 11 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 9 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 12 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 10 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 13 of 19
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`U.S. Patent
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`Oct. 31, 2000
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`Sheet 11 of 11
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`6,140,023
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`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 14 of 19
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`6,140,023
`
`1
`METHOD FOR TRANSFERRING PATTERNS
`CREATED BY LITHOGRAPHY
`
`TECHNICAL FIELD
`
`invention generally relates to photo-
`The present
`lithography, and moreparticularly relates to a method of
`forming sub-micron devices and/or features via short wave-
`length radiation and ultra-thin photoresists.
`BACKGROUND OF THE INVENTION
`
`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
`may include the width and spacing of interconnecting lines
`and the surface geometry such as corners and edges of
`various features.
`
`The requirement of small features with 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 the image area to become
`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. As feature sizes are driven
`smaller and smaller, optical systems are approaching their
`limits caused by the wavelengths of the optical radiation. A
`recognized way of reducing the feature size of circuit
`elements is to lithographically image the features with
`radiation of a shorter wavelength. “Long” or “soft” x-rays
`(a.k.a, extreme ultraviolet (EUV)), wavelength range of
`lambda=50 to 700 Angstroms(A)are nowatthe forefront of
`research in an effort to achieve the smaller desired feature
`sizes.
`
`Although EUV lithography provides substantial advan-
`tages with respect to achieving high resolution patterning,
`the shorter wavelength radiation is highly absorbed by the
`photoresist material. Consequently, the penetration depth of
`the radiation into the photoresist is limited. The limited
`penetration depth of the shorter wavelength radiation
`requires the use of ultra-thin photoresists so that the radia-
`tion can penetrate the entire depth of the photoresist in order
`to effect patterning thereof. However, the thinness of such
`ultra-thin photoresists results in the etch resistance thereof to
`be relatively low.
`In other words,
`the etch protection
`afforded by ultra-thin photoresists is limited which in turn
`limits the EUV lithographic process.
`SUMMARYOF THE INVENTION
`
`The present invention relates to a method to facilitate
`lithographic processes employing extreme ultra-violet
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`2
`(EUV) radiation and/or deep UV radiation in fabricating
`sub-micron devices and/or features. As noted above, EUV
`and deep UV radiation are preferred radiation sources in
`lithographic processes wherefine resolution is desired. The
`short wavelengths of these types of radiation afford for fine
`patterning (e.g., <0.25 wm). However, these types of radia-
`tion are highly absorbed by photoresist material which
`consequently limits the depth of penetration by the radiation
`into the photoresist material.
`The present invention employs an ultra-thin photoresist
`material containing silicon. The ultra-thin photoresist
`is
`patterned with short wavelength radiation. Thereafter, the
`patterned photoresist is exposed to an oxygen plasma which
`transformsthe silicon in the photoresist to silicon dioxide
`thus transforming the photoresist into a hard mask compris-
`ing silicon dioxide. The silicon dioxide hard mask of the
`present invention affords for expanding available etch chem-
`istries useable in EUV and/or deep UV lithographic pro-
`cesses. In particular, these types of lithographic processes
`require the use of very thin photoresists as a result of the
`depth of penetration limitations of the short wavelength
`radiation. Such very thin photoresists are limited in their
`capacity as etch barriers due to the thickness thereof.
`is
`In the present
`invention,
`the ultra-thin photoresist
`employed in patterning devices and/or features of very fine
`resolution and after transformation of the photoresist to a
`silicon dioxide hard mask, the hard mask is employed in a
`subsequent underlayer etch process. The silicon dioxide
`hard mask hassubstantially better etch resistance character-
`istics than the original silicon containing ultra-thin photo-
`resist. The present invention expands available etch chem-
`istries associated with lithography utilizing ultra-thin
`photoresists and short wavelength radiation. Thus,
`the
`present invention affords for taking advantage of the fine
`resolution patterning available from EUV and deep UV
`lithographic processes and mitigates the limitations associ-
`ated therewith with respect to etch chemistry.
`In accordance with one aspect of the present invention, a
`lithographic process for fabricating sub-micron features is
`provided. A silicon containing ultra-thin photoresist
`is
`formed on an underlayer surface to be etched. The ultra-thin
`photoresist layer is patterned with short wavelength radia-
`tion to define a pattern. The ultra-thin photoresist is oxidized
`so as to convert the silicon therein to silicon dioxide. The
`
`oxidized ultra-thin photoresist layer is used as a hard mask
`during an etch step to transfer the pattern to the underlayer.
`The etch step includes an etch chemistry that
`is highly
`selective to the underlayer over the oxidized ultra-thin
`photoresist layer.
`invention relates to a
`Another aspect of the present
`lithographic process. An intermediate layer is formed on an
`underlayer surface. An ultra-thin photoresist is formed on
`the intermediate layer,
`the ultra-thin photoresist includes
`silicon. The ultra-thin photoresist layer is patterned with
`short wavelength radiation to define a pattern. The ultra-thin
`photoresist is oxidized so as to convert the silicon therein to
`silicon dioxide. The oxidized ultra-thin photoresist layer is
`used as a hard mask during an etch step to transfer the
`pattern to the intermediate layer and the underlayer. The etch
`step includes an etch chemistry that
`is selective to the
`intermediate layer and the underlayer over the oxidized
`ultra-thin photoresist layer.
`Still another aspect of the present invention relates to a
`lithographic process for fabricating conductive lines. A
`barrier layer is formed over a substrate. A conductive layer
`is formed over the barrier layer. An intermediate layer is
`
`

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`6,140,023
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`3
`formed over the conductive layer. An ultra-thin photoresist
`is formed over the intermediate layer, the ultra-thin photo-
`resist including at least 5% silicon, the ultra-thin photoresist
`layer having a thickness within the range of 50 Ato 2000 A.
`The ultra-thin photoresist
`layer is patterned with short
`wavelength radiation to define a pattern of conductive lines,
`the short wavelength radiation having a wavelength within
`the range of 4 nm to 200 nm. The ultra-thin photoresist is
`oxidized with an O, plasma so as to convert the silicon
`therein to silicon dioxide. The oxidized ultra-thin photoresist
`layer is used as a hard mask during an etch step to transfer
`the pattern to the intermediate layer and the conductive
`layer. The etch step includes an etch chemistrythat is highly
`selective to the intermediate layer and the conductive layer
`over the oxidized ultra-thin photoresist layer. The oxidized
`ultra-thin photoresist layer and the intermediate layer are
`then removed.
`
`To the accomplishmentof the foregoing and related ends,
`the invention, then, comprises the features hereinafter fully
`described and particularly pointed out in the claims. The
`following description and the annexed drawingsset forth in
`detail certain illustrative embodiments of the invention.
`These embodimentsare indicative, however, of but a few of
`the various ways in which the principles of the invention
`may be employed. Other objects, advantages and novel
`features of the invention will become apparent from the
`following detailed description of the invention when con-
`sidered in conjunction with the drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a prior art schematic cross-sectional illustration
`of a conventional patterned resist used in lithographic pro-
`cesses;
`
`FIG. 2 is a perspective illustration of conductive lines
`formed in accordance with one aspect of the present inven-
`tion;
`FIG. 3 is a schematic cross-sectional illustration of a
`silicon substrate having a barrier oxide layer formed thereon
`in accordance with one aspect of the present invention;
`FIG. 4 is a schematic cross-sectional illustration of a
`
`conductive layer formed overthe barrier oxide layer of FIG.
`3 in accordance with one aspect of the present invention;
`FIG. 5 is a schematic cross-sectional illustration of an
`organic intermediate layer formed over the conductive layer
`of FIG. 4 in accordance with one aspect of the present
`invention;
`FIG. 6 is a schematic cross-sectional illustration of an
`
`ultra-thin photoresist layer formed over the organic inter-
`mediate layer of FIG. 5 in accordance with one aspect ofthe
`present invention;
`FIG. 7 is a schematic cross-sectional illustration of the
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`ultra-thin photoresist layer of FIG. 6 undergoing a patterning
`step in accordance with one aspect of the present invention;
`FIG. 8 is a schematic cross-sectional illustration of the
`
`55
`
`ultra-thin photoresist layer of FIG. 7 after the patterning step
`is substantially complete in accordance with one aspect of
`the present invention;
`FIG. 9 is a schematic cross-sectional illustration of the
`
`ultra-thin photoresist layer of FIG. 8 undergoing an oxidiz-
`ing step in accordance with one aspect of the present
`invention;
`FIG. 10 is a schematic cross-sectional illustration of the
`
`ultra-thin photoresist layer of FIG. 9 after the oxidizing step
`is substantially complete to form a hard mask in accordance
`with one aspect of the present invention;
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`4
`FIG. 11 is a schematic cross-sectional illustration of the
`intermediate layer, and conductive layer of FIG. 10 under-
`going an etching step in accordance with one aspect of the
`present invention;
`FIG. 12 is a schematic cross-sectional illustration of the
`
`intermediate layer and conductive layer of FIG. 11 after the
`etching step is substantially complete in accordance with
`one aspect of the present invention;
`FIG. 13 is a schematic cross-sectional illustration of the
`hard mask and organic intermediate layer undergoing a
`removal step in accordance with one aspect of the present
`invention;
`FIG. 14 is a schematic cross-sectional illustration of the
`
`conductive lines substantially complete in accordance with
`one aspect of the present invention;
`FIG. 15 is a perspectiveillustration of the conductive lines
`of FIG. 14 in accordance with one aspect of the present
`invention;
`FIG. 16 illustrates an ultra-thin photoresist layer formed
`over an underlayer in accordance with one aspect of the
`present invention;
`FIG. 17 illustrates the ultra-thin photoresist layer under-
`going a patterning process in accordance with one aspect of
`the present invention;
`FIG. 18 illustrates the ultra-thin photoresist layer under-
`going an oxidizing step in accordance with one aspectof the
`present invention;
`FIG. 19 illustrates an oxidized ultra-thin photoresist layer
`which will serve as a hard mask during etching of the
`underlayer in accordance with one aspect of the present
`invention;
`FIG. 20 illustrates the underlayer undergoing an etching
`step wherein the hard maskis used to shield maskedportions
`of the underlayer from being etched in accordance with one
`aspect of the present invention;
`FIG. 21 illustrates the etched underlayer in accordance
`with one aspect of the present invention;
`FIG. 22 illustrates the hard mask being removed via a
`stripping step in accordance with one aspect of the present
`invention; and
`FIG. 23 illustrates the underlayer after the etching step
`and stripping step are substantially complete in accordance
`with one aspect of the present invention.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The present invention will now be described with refer-
`ence to the drawings, wherein like reference numerals are
`used to refer to like elements throughout. The method of the
`present invention will be described with reference to the
`formation of conductive lines via a photolithographic pro-
`cess employing radiation of short wavelength (e.g., EUV
`radiation and/or deep UVradiation) and an ultra-thin pho-
`toresist. Although the present invention is described prima-
`rily within the context of fabricating conductive lines, it is
`to be appreciated that the present invention may be applied
`in the fabrication of a wide variety of devices and/or features
`at the sub-micron level. All such applications of the present
`invention are intendedto fall within the scope of the hereto
`appended claims. The following detailed description is of
`the best modes presently contemplated by the inventors for
`practicing the invention. It should be understood that the
`description of these preferred embodiments are merely illus-
`trative and that they should not be taken in a limiting sense.
`FIG. 1 is a cross-sectional illustration of a conventional
`
`photoresist layer 20 being used in the formation of conduc-
`
`

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`6,140,023
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`5
`tive lines. As shown,the photoresist layer 20 is substantially
`thick (e.g., 5,000-10,000 A). The photoresist layer 20 is
`patterned so as to define conductive lines which will be
`etched from the underlying metal layer 26. However, the
`thickness of the photoresist 20 is not conducive for use with
`short wavelength radiation because these types of radiation
`would be highly absorbed by the photoresistlayer 20 and not
`penetrate the entire thickness “t” of the layer 20. As a result,
`such a conventional scheme for forming a device or feature
`(e.g., conductive lines) would not be able to take advantage
`of the improvedresolution of patterning offered by the short
`wavelength radiation.
`Turning now to the present invention in detail, FIG. 2
`illustrates conductive lines 30 formed in accordance with the
`
`6
`such as novolac, polyimide based resins and the like. More
`particularly, polyimide commercially available from Ciba-
`Geigy sold underthe trade name XU284 and Probimide 285
`sold by E. I. DuPont De Nemours Company underthe trade
`name PI2610 may be employed. The intermediate layer 70
`may also function as an etch stop layer to protect
`the
`underlying layer 66.
`The intermediate layer 70 may be deposited by any
`suitable process (e.g., spin-on coating, Low Pressure Chemi-
`cal Vapor Deposition (LPCVD), Plasma Enhanced Chemical
`Vapor Deposition (PECVD), or High Density Plasma
`Chemical Vapor Deposition (HDPCVD))to a desired thick-
`ness.
`
`10
`
`present invention. The conductive lines 30 are formed over
`a substrate 60. A barrier layer 62 is interposed between the
`conductive lines 30 and the substrate layer 60. The ever
`increasing demand for miniaturization in the integrated
`circuits industry has led to an ever constant demand for
`reduction in separation between conductivelines (e.g., metal
`lines)
`in order to reduce integrated circuit size and/or
`increase density. The conductive lines 30 are formed via
`photolithographic techniques utilizing short wavelength
`radiation and ultra-thin photoresists. Accordingly, substan-
`tially smaller dimensions of the conductive lines 30 and
`separation thereof are achieved as compared to conductive
`lines formed in accordance with the prior art
`technique
`discussed with respect to FIG. 1. For example, the conduc-
`tive lines 30 may be separated by a distance “d” less than
`about 0.25 wm, and such small dimension is not obtainable
`using conventional
`lithographic processes.
`In another
`embodiment, the conductive lines 30 may have a separation
`distance “d’” less than about 0.18 ym.
`Turning now to FIGS. 3-15, the fabrication of the con-
`ductive lines 30 is discussed in greater detail. It is to be
`appreciated that the thicknesses of the various layers in the
`figures are not necessarily drawn to scale so as to facilitate
`review of the specification and understanding of the present
`invention. FIG. 3 is a cross-sectional
`illustration of the
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`FIG. 6 illustrates an ultra-thin photoresist layer 80 formed
`over the intermediate layer 70. The ultra-thin photoresist
`layer 80 has a thickness of about 500 A-5000 A, however,
`it is to be appreciated that the thickness thereof may be of
`any dimension suitable for carrying out the present inven-
`tion. Accordingly, the thickness of the ultra-thin photoresist
`80 can vary in correspondence with the wavelength of
`radiation used to pattern the ultra-thin photoresist 80. One
`aspect of the present invention provides for forming the
`ultra-thin photoresist layer 80 to have a thickness within the
`range of 1000 A to 4000 A. Another aspect of the present
`invention provides for forming the ultra-thin photoresist
`layer 80 to have a thickness within the range of 2000 Ato
`3000 A. Yet another aspect of the present invention provides
`for forming the ultra-thin photoresist layer 80 to have a
`thickness within the range of 500 A to 2000 A. Theultra-thin
`photoresist 80 may be formed over the intermediate layer 70
`via conventional spin-coating or spin casting deposition
`techniques, for example.
`The ultra-thin photoresist layer 80 has a thickness suitable
`for functioning as a mask for etching the underlying inter-
`mediate layer 70 and layer 66 and for forming patterns or
`openings in the developed ultra-thin photoresist layer 80 that
`are 0.25 ym orless. Since the ultra-thin photoresist layer 80
`is relatively thin compared with I-line, regular deep UV, and
`other photoresists, improved critical dimension control is
`substrate 60 and the barrier layer 62 formed thereon. FIG. 4
`realized. It will be appreciated that for certain applications
`is a cross-sectionalillustration of a layer 66 formed over the
`the ultra-thin photoresist layer 80 may be used solely as a
`barrier layer 62—the conductive lines 30 will be etched
`mask for etching the underlying intermediate layer 70, and
`from the layer 66. The layer 66 may comprise any suitable
`the intermediate layer 70 will serve as a mask for etching the
`conductive material employable for forming conductive
`layer 66.
`patterns in the semiconductor industry. Preferably, the con-
`Ultra-thin resists are processed using short wavelength
`ductive material includes a memberselected from the group
`radiation. Short wavelength radiation increases precision
`consisting of refractory materials, such as titanium and
`and thus the ability to improvecritical dimension control.
`titanium alloys, tungsten and tungsten alloys, aluminum and
`Specific examples of wavelengths to which the ultra-thin
`aluminum alloys, copper and copper alloys. The layer 66
`photoresist 80 is sensitive (undergo chemical transformation
`may be deposited by any of a variety of suitable deposition
`enabling subsequent development) include about 248 nm,
`techniques, such as CVD processes including low pressure
`about 193 nm, about 157 nm, about 13 nm, about 11 nm, and
`chemical vapor deposition (LPCVD) and plasma enhanced
`as low as 4 nm. Specific sources of radiation include KrF
`chemical vapor deposition (PECVD), melting or sputtering.
`excimer lasers having a wavelength of about 248 nm, a
`Although the present invention is being described within the
`XeHg vapor lamp having a wavelength from about 200 nm
`context of forming conductive lines, it is to be appreciated
`to about 250 nm, mercury-xenon arc lamps having a wave-
`that the present invention may be applied to forming many
`length of about 248 nm, an ArF excimer laser having a
`different types of patterns in a material. Accordingly, the
`wavelength of about 193 nm, an F, excimer laser having a
`layer 66 may comprise other types of material(e.g., silicon
`wavelength of about 157 nm, and EUV having a wavelength
`nitride, titanium,titanium nitride) from whichapatternis to
`60
`be formed.
`of about 15 nm to about 10 nm,and as low as 4 nm. It will
`be appreciated that the radiation being employed may have
`a wavelength of, for example, less than about 200 nm,less
`than about 160 nm,less than about 100 nm,less than about
`13 nm, or less than about 11 nm.
`Positive or negative ultra-thin photoresists may be
`employed in the methods of the present invention. Photo-
`resists containing silicon are commercially available from a
`
`45
`
`50
`
`55
`
`65
`
`FIG. 5 illustrates an intermediate layer 70 deposited over
`the layer 66. Because the layer 66 typically does not have a
`planar surface (in part due to the uneven surface of the
`underlying substrate 60), the intermediate layer 70 is depos-
`ited with a thickness sufficient
`to present an essentially
`planar surface. The composition of the intermediate layer is
`not critical, and may be any suitable intermediate material
`
`

`

`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 17 of 19
`Case 6:20-cv-01216-ADA Document 41-8 Filed 10/06/21 Page 17 of 19
`
`6,140,023
`
`7
`number of sources, including Shipley Company, Hoechst
`Celanese Corporation, and Brewer. The scope of the present
`invention as defined by the hereto appended claims is
`intended to include any ultra-thin photoresist suitable for
`carrying out the present invention. It is to be appreciated that
`the ultra-thin photoresist 80 of the present invention includes
`silicon which will be transformed into silicon dioxide so as
`
`10
`
`15
`
`20
`
`8
`exposing the patterned photoresist to an oxygen (O,) plasma
`which will oxidize the patterned photoresist so as to form a
`hard mask containing silicon dioxide (SiO). Alternatively,
`provided the photoresist 100 is substantially thin, a thermal
`oxidation technique may be employed. For example, accord-
`ing to one specific aspect of the invention an entire wafer
`including the aforementioned layers formed thereon may be
`placed in a quartz tube in a vertical or horizontal type heat
`to transform the ultra-thin photoresist into a hard mask
`treatment furnace. An oxidizing source such as oxygen and
`comprising silicon dioxide.
`water vapor is fed into the quartz tube, and the wafer is
`In one embodimentofthe present invention, the ultra-thin
`heated up (ie., annealed) to approximately 900° C.
`to
`photoresist 80 includes at least 5% silicon by weight. In
`oxidize the patterned ultra-thin photoresist 100. Depending
`another embodiment of the present invention, the ultra-thin
`on the thermal budget for a particular device, the anneal may
`photoresist 80 includes at
`least 10% silicon by weight.
`be either a furnace anneal, a rapid thermal anneal (RTA) or
`Another embodiment of the present invention hasthe ultra-
`any other suitable anneal. As a result of the anneal, the
`thin photoresist 80 including at least 20% silicon by weight.
`silicon containing ultra-thin photoresist 100 is transformed
`In yet another embodiment of the present invention,
`the
`into a hard mask containing silicon dioxide.
`ultra-thin photoresist 80 includes at least 30% silicon by
`It is to be appreciated that any suitable oxidation tech-
`weight. Still yet another embodimentof the present inven-
`niques for oxidizing the silicon in the ultra-thin photoresist
`tion has the ultra-thin photoresist 80 including at least 40%
`100 in accordance with the present
`invention may be
`silicon by weight.
`employed and is intended to fall within the scope of the
`Referring to FIG. 7, the ultra-thin photoresist layer 80
`present invention.
`then undergoes an exposure/developmentstep 90 to provide
`FIG. 10 illustrates an oxidized ultra-thin photoresist layer
`a patterned photoresist 100 (FIG. 8). The patterned photo-
`120 after completion of the oxidizing step 110. The silicon
`resist 100 is formed using electromagnetic radiation having
`25
`in the ultra-thin photoresist layer 100 has been transformed
`a relatively small wavelength (for example, less than 200
`to silicon dioxide via the oxidation process 110. Asaresult,
`nom). In this embodiment, electromagnetic radiation having
`the patterned ultra-thin photoresist layer 100 has become
`a wavelength of about 13 nm is employed. Since relatively
`hardened in that the oxidized ultra-thin layer 120 comprises
`small wavelengths are used, reflectivity concerns are mini-
`silicon dioxide, which imparts substantially greater etch
`mized because larger wavelengths are more frequently asso-
`resistance characteristics to the oxidized ultra-thin layer 120
`ciated with reflectivity problems. The ultra-thin photoresist
`as compared to the unoxidized photoresist layer 100. The
`layer 80 is selectively exposed to radiation; that is, selected
`oxidized ultra-thin layer 120 will serve as a hard mask
`portions of the ultra-thin photoresist layer 80 are exposed to
`during a subsequent intermediate layer/layer 66 etch.
`radiation. Either the exposed or unexposed portions of the
`Referring now to FIG. 11, the oxidized photoresist layer
`ultra-thin photoresist layer 80 are removed or developed to
`120 is used as a mask for selectively etching the intermediate
`provide the patterned photoresist 100.
`layer 70 and the layer 66 to pattern the layer 66 from an etch
`Thecritical feature dimension “d” of the exposed portion
`step 130. Any suitable etch technique may be used to etch
`of the intermediate layer 70 (opening 102 in the patterned
`the intermediate layer 70 and the layer 66. Preferably, the
`photoresist 100 as shownin FIG. 8) is about 0.25 ym orless,
`intermediate layer 70 and the layer 66 are etched using an
`including about 0.18 umor less, about 0.09 um orless, about
`anisotropic etching process—dry or wet etching techniques
`0.075 xm orless and about 0.05 um or less, depending on the
`may be employed, although dry etching is preferred. An
`wavelength of the radiation used.
`intermediate layer/layer 66: photoresist etch technique may
`The selectively exposed ultra-thin photoresist layer 80 is
`be used to etch the intermediate layer 70 and the layer 66 to
`developed by contact with a suitable developer that removes
`provide the patterned conductive lines 30. Preferably, a
`either the exposed or unexposed portions of the ultra-thin
`selective etch technique may be used to etch the material of
`photoresist layer 80. The identity of the developer depends
`the intermediate layer 70 and the layer 66 at a relatively
`upon the specific chemical constitution of the ultra-thin
`greater rate as compared to the rate that the material of the
`photoresist
`layer 80. For example, an aqueous alkaline
`oxidized photoresist 120 is etched. For example, the etching
`solution may be employed to remove unexposedportions of
`process 130 mayinclude a reactive ion etch (RIE), that