`
`
`United States Patent
`
`
`King et al.
`I
`
`
`[19]
`‘
`
`'
`
`[54] METAL OXIDE FILMS
`
`
`
`
`[75]
`Inventors: Robert David King, Solihull; Robert
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`
`Hiscutt, Birmingham, both of
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`England
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`[73] Assignee: Triplex Safety Glass Company
`
`
`
`Limited, London, England
`.Ian. 26, 1972
`Filed:
`[22]
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`
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`
`
`[2]] Appl. No.: 220,899
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`
`[30]
`Foreign Application Priority Data
`Feb. 5, 1971
`United Kingdom ............... 4234/71
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`
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`[52] US. Cl. ............................... 204/192; 204/298;
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`
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`428/432
`
`[51]
`Int. Cl.2 ......................................... C23C 15/00
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`
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`[58] Field of Search ........... 204/192, 298; 428/432,
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`
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`
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`428/539
`
`
`[56]
`
`
`References Cited
`
`
`UNITED STATES PATENTS
`
`
`
`Brichard ............................ 204/192
`12/1968
`3,414,503
`
`
`
`
`
`11/1971 Wurm ct al.
`204/192
`3.619.402
`
`
`
`
`
`
`
`12/1971 Moore ct al.
`204/192
`3.630.873
`
`
`
`
`
`
`9/1975 Gillcry ............................... 204/298
`3,907,660
`
`
`
`
`
`FOREIGN PATENTS OR APPLICATIONS
`
`
`1/1971
`Germany
`
`
`1969 United Kingdom ............... 204/192
`
`
`
`
`8/1970 United Kingdom
`
`
`
`
`1.938.131
`
`1,147,318
`
`
`1,201,743
`
`
`
`
`
`
`
`[,1]
`
`[45]
`
`
`4,006,070
`
`
`Feb. 1, 1977
`
`
`
`
`Primary Examiner—Oscar R. Vertiz
`
`
`
`Assistant Examiner—Wayne A. Langel
`
`
`
`
`
`Attorney, Agent, or Firm—Sughrue, Rothwell, Mion,
`
`
`Zinn & Macpeak
`
`
`
`ABSTRACT
`[57]
`
`
`
`
`
`
`A substantially uniform, transparent. electrically con-
`
`
`
`
`
`
`
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`ducting, metal oxide film (e.g. of indium/tin oxide) can
`
`
`
`
`
`
`
`be deposited on to a substrate such as glass of large
`
`
`
`
`
`
`lateral dimensions, e.g. a windscreen for an aircraft or
`
`
`
`
`
`
`
`a land vehicle, by low-pressure reactive sputtering from
`
`
`
`
`
`
`
`a cathode of the metal, using an atmosphere of oxygen
`
`
`
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`
`
`and another gas or gases (preferably an inert gas) at
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`
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`
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`reduced pressure, by providing access for the sputter—
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`
`
`
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`
`
`
`ing atmosphere to penetrate into the whole of the
`
`
`
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`
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`
`
`working space between the cathode and the substrate
`
`
`
`
`
`so as to maintain a substantial degree of uniformity in
`
`
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`
`
`the oxygen concentration in the working space. Access
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`
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`for the atmosphere may be provided by means of pas-
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`
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`sages extending through the cathode assembly, by di—
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`viding the cathode assembly into parallel strips sepa-
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`rated by gaps, and the atmosphere may be supplied
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`direct to the working space through such gaps. Relative
`
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`movement is effected between the cathode assembly
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`and the substrate, e.g. by reciprocating the parallel
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`strips of the divided cathode in the direction perpendic-
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`ular to their length.
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`48 Claims, 11 Drawing Figures
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`Page 1 of 18
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`APPLIED MATERIALS EXHIBIT 1073
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`Page 1 of 18
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`APPLIED MATERIALS EXHIBIT 1073
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`US. Patent
`
`
`
`
`Feb. 1,1977
`
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`
`I.
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`Sheetlof7
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`4,006,070
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`Page 2 of 18
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`US. Patent
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`Feb..1, 1977
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`_ Sheet20f7
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`4,006,070
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`
`
`70
`E
`o
`Z
`g
`I
`.0
`S
`t
`0
`5%
`3‘
`E
`'5 2
`L3
`LL14>
`
`G
`m
`<:
`8
`
`
`
`
`x FILM THICKNESS c4)
`
`
`:1 OHMS/SQUARE
`o SPECIFIC
`
`
`
`RES/STIV/TY
`
`(OHMS/cm.)
`
`‘
`
`g
`V
`40 :3
`.3
`30 g '
`
`
`DECREAS/NG
`'.0XYGEN
`
`
`
`"
`
`
`
`
`
`
`
`0
`
`
`
`5
`
`70
`
`SLIGHT
`E IN
`HAZ
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`75
`
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`
`
`SEVERE
`HAZE IN
`FILM
`
`
`
`45
`40
`20
`25
`35
`30
`
`
`
`
`DISTANCE ALONG CATHODE (cm)
`
`
`
`
`
`FIG. 2.
`
`
`
`4 8000
`
`
`
`80
`
`E:
`‘0
`2
`a:
`E
`
`3 6000
`
`‘2
`:1
`LL
`
`400
`
`.3
`
`
`
`Lu
`3;
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`Page 3 of 18
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`Page 3 of 18
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`US. Patent
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`Feb. 1,1977
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`’
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`Sheet3of7
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`4,006,070
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`x FILM THICKNESS (Ii)
`
`
`= OHMS/SQUARE
`
`
`o SPECIFIC IESISTlV/TY
`
`
`
`
`g/n
`
`7 2000
`
`
`
`(4) 88FILMTHICKNESS(A)
`
`RESISTANCE(OHM/SQUARE)
`
`
`
`
`
`
`
`0
`5
`10
`75
`
`
`
`
`
`
`35
`30
`25
`20
`40
`
`
`
`DISTANCE ALONG CATHODE (cm)
`
`
`
`45
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`
`
`. FIGJ
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`Page 4 of 18
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`Page 4 of 18
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`

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`US. Patent
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`Feb. 1,1977
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`Sheet 4 of7
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`4,006,070
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`Page 5 of 18
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`Page 5 of 18
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`

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`U.S. Patent
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`Feb. 1, 1977
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`Sheet 5 of 7
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`4,006,070
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`Page 6 of 18
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`Page 6 of 18
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`

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`U.S. Patent
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`Feb..1, 1977
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`,,
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`Sheet 6 of 7
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`Page 7 of 18
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`US. Patent
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`Feb. 1, 1977
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`'_
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`Sheet 7 of7
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`4,006,070
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`277 277
`
`3—2
`
`/
`
`\
`
`
`
`
`—4 MQ
`
`
`
`20KV
`
`NO RES/S
`
`TlV/TYOHMcmx70Mto4:.01\1
`
`
`0
`
`
`
`1
`
`
`
`5
`3
`4
`2
`
`
`
`
`
`
`% OXYGEN AT/NLET 7
`
`
`
`'
`5
`
`no; /0,
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`Page 8 of 18
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`Page 8 of 18
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`

`

`1
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`4,006,070
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`10
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`‘
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`2
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`specific electriCal resistivity and adequate transparency
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`over the whole area of the substrate to be coated.
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`The existence of the above—mentioned oxygen gradi-
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`ent has been found to be most detrimental to the depo-
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`sition of a unifonn film. The effect can generally be
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`detected 'where each lateral dimension, i.e. length and
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`width, of the substrate is substantially greater than the
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`distance between the cathode and substrate, e.g.
`is
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`greater than ’10 cm., and particularly if they are greater
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`than 30cm.
`j
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`
`OBJECT OF THE INVENTION ,
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`‘ An object of this invention is to provide an improved
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`method and apparatus for depositing films on larger
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`Substrates than' hitherto practicable, e.g. substrates
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`having both lateral dimensions greater than 30 cm., and
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`in particular-On substrates such as windscreens for
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`aircraft and land vehicles, whose dimension can reach
`100 cm. and more.’
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`SUMMARY OF THE INVENTION
`
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`According to the invention, we provide a method of
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`depositing a transparent, electrically conducting metal
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`oxide film by reactive sputtering on to the surface of a
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`substrate of extended lateral dimensions which is main-
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`tained at a controlled elevated temperature in a vac-
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`uum‘ chamber containing an atmosphere of oxygen and
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`another gas or gases at a controlled reduced pressure, a
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`high negative potential being applied to a cathode as-
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`sembly of the metal which is arranged in the vicinity of
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`the substrate and presents a surface er surfaces extend-
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`ing substantially parallel to the substrate surface so that
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`sputtering takes place substantially perpendicularly on
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`to all parts of the substrate, wherein access is provided
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`for the atmosphere to penetrate into the whole ofthe
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`werking space between the cathode assembly and the
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`substrate so as to maintain a substantial degree of uni-
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`formity. in the oxygen concentration in the working
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`space.
`'
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`The term “extended lateral dimensions" is to be
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`understood to‘ mean having lateral dimensions substan-
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`tially greater thanthe distance between the cathode
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`and' substrate, and generally having its smallest lateral
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`dimension greater than 30 cm.
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`Variation in the oxygen concentration has been
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`found to affect the specific electrical resistivity (.p) and
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`the thickness (t) deposited in a given time and hence
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`the resistance in. ohm/square of the sputtered film, as
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`disclosed in theSpecification of co~pending U.S. Pat.
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`application Ser. No. 144,541. It will be understood that
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`the resistance in'ohm/square is independent of the size
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`of the square under consideration and is related to the
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`specific resistivity andth‘ickness by the equation
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`METAL OXIDE FILMS
`
`
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`BACKGROUND OF THE INVENTION 2
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`1. Cross~Reference to Related Application '
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`The inventionis related to that described in co-pe'nd-
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`ing Application Ser. No. 144,541 filed May 18, 1971.
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`2. Field of the ln'Vention
`'
`‘
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`This invention relates to methods and apparatus for .
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`depositing transparent, electrically conducting, metal
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`oxide films on to snbstrates, such as‘glass, and to arti-
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`cles having such metal oxide films applied thereto. By
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`way of example, the article may be a windscreen, e.g.
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`an aircraft windscreen, on which the film can provide .
`15
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`electrical resistance heating means for de-icing or de-
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`misting.
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`,
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`3. Description of Prior Art
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`Various proposals have been made for reactively
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`sputtering a transparent, electrically conducting, metal
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`oxide film onto the surface of‘a substrate supported in
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`a vacuum vessel having an atmosphere 'of oxygen and
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`another gas: or gases, frOm a metal, cathode near the
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`substrate surface to be coated. One example of such a
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`processis described in U.S. Patent application Ser. No.‘
`25
`
`. _
`144,541.
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`Such processes have been successful
`in preducing
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`transparent, electrically Conducting, films, of reason—
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`ably unifonn characteristics on substrates of relatively
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`small lateral dimensions, e.g. '4 cm. in ‘width, but difi'r-
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`culties have been experienced with larger articles. Even
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`though the. Cathode is enlarged commensurately with
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`the article", so, as to cover the "Whole substrate area and
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`to maintain the direct sputteringpath from cathode to
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`substrate at the optimum value (between 2 cm. and 10
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`cm. depending on the applied potential difference), it is
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`found that the film produced tends to be non-uniform.
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`Variationsare found in the thickness and specific elec-
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`trical resistivity of the film, which result in Wide varia-
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`tions in, its resistance and diminish or destroy its utility
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`as aresistance heating means. In extreme cases, the
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`film is also feund to be less transparent near the middle
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`of the article. Anysuch reduction in transparency is
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`unacceptable in a windscreen, for example.
`45
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`Thepresent inventors have deduced'that the non-
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`unifonnity of the film is due to a reduction in the oxy-
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`gen concentration in the atmOsphere in the working
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`space between the cathode and the substrate, which is
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`believed to be caused by the consumption of the oxy-
`50
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`gen originally present during the formation of the film,
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`and-by the slow rate at whichfresh oxygen can diffuse
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`into this space. As the process proceeds, a gradient of
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`oxygen concentration is thus established in the atmo—
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`sphere in the working space in a plane parallel to the
`55
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`cathode surface, the concentration falling towards the
`centre of the cathode,
`.
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`For economy in production, it is desirable to have a
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`high deposition rate and to achieve a 'minimum specific
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`resistivity (p).~ However, as the rate of deposition is
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`‘60
`increased, therate of consumption of oxygen is also
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`increasedxand the effect of the gradient in the oxygen
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`concentration will become more severe. Further, as the
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`area of the‘substrate and cathode is increased .sothe
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`gradient of oxygen concentration is established over
`65
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`greater distances, the oxygen starvation at the centre of
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`the substrate becomes more pronounced. ~-Conse‘-
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`quently it is no longer possible to maintain the desired
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`oxygen concentration necessary to provide a minimum
`
`2'0
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`30
`.
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`35
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`40
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`RD=f—.
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`”By providing access for the atmosphere into the whole
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`of the working space so as to maintain the oxygen con-
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`centration substantially unifOrm, we have found it pos—
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`l. sible to produce articles of considerable size coated
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`' with films having substantially uniform low resistance
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`in ohm/square and substantially uniform high light
`
`7
`transmission.
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`In one form of the invention, passages extend
`
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`through the cathode assembly to provide the access for
`
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`the atmosphere into the working space. Preferably
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`Page 9 of 18
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`Page 9 of 18
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`relative movement is provided between the cathode
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`assembly and the substrate in a direction parallel to the
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`substrate surface. In a preferred embodiment of the
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`invention. the cathode assembly is divided into spaced
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`parallel strips so as to provide the passages for the
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`atmosphere between the strips, and the relative move-
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`ment is provided between the strips and the substrate in
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`a direction transverse to the length of the strips so that
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`the strips cover all parts of the substrate surface for
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`equal deposition periods during one part or another of
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`the deposition process. Preferably the relative move-
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`ment between the strips and the substrate is a recipro—
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`cating movement. Advantageously the relative move-
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`ment is substantially equal to the spacing between the
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`centre lines of adjacent strips. The strips may move on
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`guide rails relative to the substrate.
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`The invention also provides an article of extended
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`lateral dimensions having a transparent electrically
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`conducting film deposited on a surface thereof by a
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`method as described above, said film having a specific
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`electrical resistivity between 2 X 10" ohm. cm. and 20
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`x 10“ ohm. cm. and preferably between 2 X 10“ ohm.
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`cm. and 4 X 10‘4 ohm. cm., a thickness of between 500
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`A and 10,000 A, and a light transmission figure of over
`70%. Where the film thickness is below 5000 A, the
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`light transmission figure may be over 80%.
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`The invention further provides a glass article of ex-
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`tended lateral dimensions having a transparent electri-
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`cally conducting film of indium/tin oxide deposited on
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`a surface thereof, said film having a substantially uni-
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`form resistance of between 2 and 40 ohm/square and a
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`light transmission figure of over 80%.
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`The invention further provides apparatus for deposit~
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`35
`ing a transparent, electrically conducting metal oxide
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`film by reactive sputtering on to the surface of a sub
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`strate of extended lateral dimensions, comprising a
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`vacuum chamber, means for supporting the substrate in
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`the vacuum chamber, means for maintaining the sub-
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`strate at a controlled elevated temperature in the vac-
`40
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`uum chamber, means for supplying an atmosphere of
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`oxygen and another gas or gases at reduced pressure
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`into the vacuum chamber, a cathode assembly ar-
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`ranged in the vacuum chamber in the vicinity of the
`45
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`substrate and presenting a surface or surfaces capable
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`of extending over the whole of the substrate surface
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`and substantially parallel thereto, and means for apply-
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`ing a high negative potential to the cathode assembly,
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`wherein means is provided for allowing access for the
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`atmosphere to penetrate into the whole of the working
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`space between the cathode assembly and the substrate
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`so as to maintain a substantial degree of uniformity in
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`the oxygen concentration in the working space.
`BRIEF DESCRIPTION OF THE DRAWINGS
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`In the accompanying drawings:
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`FIG. 1 is a diagrammatic layout of a known type of
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`apparatus for reactively sputtering a film on a relatively
`small substrate surface;
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`FIG 2 is a graph of the resistance in ohm/square,
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`thickness and specific electrical resistivity of a sput-
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`tered film as a function of the distance along the cath-
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`ode in an experiment in which an oxygen concentration
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`gradient is deliberately established along the cathode,
`65
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`starting with a known initial oxygen concentration;
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`FIG. 3 is a similar graph to FIG. 2 in respect of a
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`similar experiment but starting with a higher initial
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`oxygen concentration;
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`FIG. 4 is a schematic perspective view of a first form
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`of modified cathode assembly for sputtering a large
`area substrate surface in accordance with the method
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`of the present invention;
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`FIG. 5 is a schematic section through the, cathode
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`assembly of FlG. 4;
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`FIG. 6 is a perspective view of an apparatus accord-
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`ing to the invention incorporating a cathode assembly
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`as illustrated in FIGS. 4 and 5;
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`FIG. 7 is a longitudinal axial section through the
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`apparatus of FIG. 6, modified to deposit a film on a
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`substrate which is curved from end to end;
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`FIG. 7A is a detail sectional view to a larger scale, of
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`one of the cathode sections used in the apparatus of
`FIG 6 and FIG. 7,
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`FIG 8IS a schematic section through a fourth form of
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`modified cathode assembly;
`FIG. 9 is a similar view of a fifth form of modified
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`cathode assembly; and
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`FIG. 10 is a graph of specific electrical resistivity
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`against percentage oxygen concentration in the atmo-
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`sphere of sputtering apparatus having one of the modi-
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`fied cathode assemblies of FIGS. 4 to 9, for a series of
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`examples in which the oxygen concentration is main-
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`tained substantially uniform between the cathode 'o'r
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`cathodes and a large area of substrate surface.
`DETAILED DESCRIPTION
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`Referring to FIG. 1, there is shown a vacuum vessel
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`10 for connection by conduit 11 to a vacuum pump
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`(not shown). A further conduit 12 passing through the
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`wall of the vacuum vessel 10 is connected via gas flow
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`meters 13,14 to separate sources of oxygen and argon
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`respectively. These gas flow meters 13, 14 are provided
`to ensure accurate control of the rate of flow of the
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`oxygen into the argon and thence into the atmosphere
`of the vacuum vessel 10.
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`Within the vacuum vessel 10 there is mounted a
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`substrate 17 which is to be coated with an electrically
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`conductive film by sputtering from a water cooled cath-
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`ode 18. The substrate 17 is supported on a heated
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`block 19 which is heated by an internal electric heating
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`element 20 connected by leads 21, 22 to an external
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`source of low voltage electrical power. The cathode 18
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`is connected by a lead 23 to the negative terminal of an
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`extemal source of high voltage. An earthed electro-
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`static screen 24 is provided round the cathode 18, and
`the heated block 19 and vacuum vessel 10 are also
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`'earthed as indicated at 25. Instead of the heated block
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`19 being heated internally, the heating element 20 may
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`be disposed on insulated support pillars on the upper
`surface of the block 19 so that the substrate is heated
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`mainly by radiation.
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`In order to determine and to control the temperature
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`of the substrate 17 at the required value, a thermo-
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`couple 26 is attached to the edge of the substrate l7,so
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`as to be in thermal contact with it. The themocouple
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`provides a measure of the surface temperature of the
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`substrate 17, as it is heated by the heated block 19. "As
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`the substrate 17 is exposed to the plasma induced by
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`the electric field existing between the cathode and the
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`substrate 17,
`the additional power injected by the
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`plasma heats the substrate, and it is consequently nec-
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`essary to gradually reduce the electric power supplied
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`to the heating element 20 inside the block 19, in order
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`to maintain the temperature of the substrate at the
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`required value.
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`5.0
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`55
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`60
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`4,006,070
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`4
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`IO
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`15
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`20
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`25
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`30
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`3
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`Page 10 of 18
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`Page 10 of 18
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`25
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`35
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`4,006,070
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`6
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`5
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`- Upon removal of the glass substrate from the vessel it
`The substrate 17, which may be of toughened soda-
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`was immediately obvious that the characteristics of the
`lime-silica glass, is placed on the heated block 19 in the
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`film varied considerably from one end to the other. In
`vacuum vessel 10. The vacuum vessel 10 is then evacu-
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`particular, at the end where access of the sputtering
`ated to a pressure of say 5 X 10“ mm Hg as measured
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`atmosphere had been allowed the film was substantially
`on a Penning vacuum pressure gauge 101, and low
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`transparent although slightly hazy. At the other end
`voltage (say 10 volts) electric power applied to heating
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`where access of the sputtering atmosphere and been
`element 20 through leads 21, 22. The substrate surface
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`restricted the film was completely opaque and metallic
`is thereby heated to a selected temperature between
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`in appearance. Indeed the film showed characteristics
`240° C and 400° C. Oxygen gas is then admitted to the
`10
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`over the 45 cm. length of the cathode which would be
`vacuum Vessel 10 through the gas flow meter 13 and
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`consistent with a considerable drop in the percentage
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`argon gas through the gas flow meter 14 at desired flow
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`of oxygen concentration.
`rates. This flow of gas results in the presence of a se-
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`The above experiment was repeated employing an
`lected percentage of oxygen between 1% and 10% by
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`atmosphere of 94% argon and 6% oxygen, with a cath-
`volume of the total gas in the vacuum vessel and pro-
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`ode voltage of —2.75 KV. As expected, it was found
`(15
`duces an increase in the pressure in the vessel to a
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`that the reduction in cathode voltage and increase in
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`selected value of the order of 5 X 10”2 mm Hg as mea-
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`oxygen concentration reduced the degree of haze and
`sured on a Macleod vacuum pressure gauge 102.
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`shifted the specific resistivity curve to the right. At the
`The cathode 18 is supported at a selected distance of
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`end of the film where access of the sputtering atmo-
`say 3 to 4 cm. from the glass substrate surface to be
`20
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`sphere had been allowed, a highly transparent, haze-
`coated, and a selected negative voltage of between
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`free film having a specific resistivity less than ID x 10“
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`—l.0 KV and —5 KV is applied to the cathode. The
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`ohm. cm. was obtained. The film at the other end was
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`power applied to the heating element 20 is gradually
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`very hazy and had a much higher resistivity. The results
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`reduced in order to maintain the glass substrate surface
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`of this experiment are shown in FIG. 2 which comprises
`at the desired temperature, this step being necessary
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`a graph of the resistance in ohm/square, the film thick-
`owing to the heating effect produced by ionic and elec-
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`ness in A and the specific resistivity (p) in ohm. cm. as
`tronic bombardment from the glow discharge between
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`a function of the distance along the cathode. This graph
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`the cathode and substrate.
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`clearly shows that there is a percentage of oxygen con-
`The ionised argon ions bombard the surface of the
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`centration which results in a minimum specific resistiv-
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`cathode 18 thus removing metal from the cathode and
`30
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`ity.
`thereby reactively sputtering a film of oxide on to the
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`The experiment as again repeated using the same
`upper surface of the glass substrate 17. At the comple-
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`reduced cathode voltage of —2.75 KV but with an in-
`tion of this process, the power supplies to the cathode
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`creased oxygen concentration of 7% in the sputtering
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`18 and the heating element 20 are disconnected, the
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`atmosphere. The results of this experiment are shown
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`gas flows turned off and the glass substrate allowed to
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`cool. .
`in FIG. 3 which is again a graph of the resistance in
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`ohms/square, the film thickness in A and the specific
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`The coated glass substrate is then removed from the
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`resistivity (p) in ohm. cm. as a function of the distance
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`vessel and the physical characteristics'of the film may
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`along the cathode. As before the graph shows that
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`be determined by measurement and calculation.
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`there is a percentage of oxygen concentration which
`The above method is applicable to the coating of a
`40
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`results in a minimum specific resistivity.
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`transparent and haze-free film on a glass substrate from
`These results indicated to the inventors that if the
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`a single, stationary cathode having a lateral dimension,
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`oxygen concentration in the sputtering atmosphere in
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`e.g. a width or length, of 10 cm. or less. However, for
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`the working space between the cathode and substrate
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`substrates and cathodes of greater lateral dimensions, it
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`could be controlled, it’should be possible to maintain
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`has been found that the method results in the produc-
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`45
`adequate uniformity of transparency, specific resistiv-
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`tion of a non-uniform film which does not have the
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`ity, thickness, and thus resistance in ohm/square of the
`desired resistance in ohm/square and may not be haze-
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`sputtered film.
`free, and the present inventors deduced that this effect
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`According to the invention, access is provided for the
`is due to variation of the oxygen concentration in the
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`atmosphere to penetrate into the whole of the working
`atmosphere in the working space between the 'cathode
`
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`space so as to maintain a substantial degree of uniform~
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`and the substrate surface. To investigate and measure
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`ity of the oxygen concentration between the cathode
`this effect, there was employed a cathode measuring 45
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`and the substrate. Such access may be provided by a
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`cm. long by 15 cm. wide. A 60 cm. long by 30cm. wide
`
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`particular construction of the cathode and/or by the
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`by 4 mm thick soda—lime-silica glass substrate was
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`provision of relative motion between the cathode and
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`placed at a distance 38 mm from the cathode surface.
`55
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`the substrate surface. Some examples will now be de-
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`The gaps formed between the edges of the cathode and
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`scribed of suitable methods of controlling the uniform-
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`the surface of the substrate were blanked off along the
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`ity of oxygen concentration over the area of the sub-
`two long sides and one end by three pieces of glass.
`‘ strate surface.
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`There was thus access for the sputtering atmosphere at
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`FIGS. 4 and 5 illustrate diagrammatically a first type
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`one end only.
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`60
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`of modified cathode assembly 27 for carrying out the
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`The vacuum vessel was evacuated to a pressure or 5
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`method of the present invention. The cathode assembly
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`X 10“ mm Hg and a voltage of 10 velts was applied to
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`27 is divided into four parallel sections or strips 271,
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`the heater 20 to raise the temperature of the substrate
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`each strip measuring 60 cm. in length and 8 cm.
`in
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`surface to 300° C. A gas mixture consisting of 96% .
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`width and being surrounded by a separate earthed elec-
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`argon and 4% oxygen by vOIume, was admitted to the
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`trostatic shield 28. The cathode sections or strips 271
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`vacuum vessel thereby increasing the pressure in the
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`are spaced apart by gaps 29 of equal width. The indi-
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`vessel to 6.5 X 10‘2 mm Hg. The cathode was then
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`vidual gaps may be varied in width, for example be-
`energised to a voltage of ‘—-3.0 KV and sputtering was
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`tween 1.0 cm. and 10 cm., and are provided to allow
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`allowed to take place for a period of 10 minutes.
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`50
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`Page 110f18
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`Page 11 of 18
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`7
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`access for diffusion of the atmosphere from the under
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`side of the cathode assembly 27 to the side adjacent to
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`the substrate 31, as indicated by the arrows 30 in FIG.
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`5.
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`Means (not shown in FIGS. 4 and 5) are provided
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`which effect relative motion between the substrate 31
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`and the cathode assembly 27 in a direction parallel to
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`their facing surfaces. The preferred direction of rela-
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`tive motion is perpendicular to the length of the cath-
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`ode strips 271. The motion is preferably an oscillatory
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`motion of the cathode assembly 27 with a constant
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`speed of traverse between reversing points, as shown by
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`the double headed arrow 32a in FIG. 4, the amplitude
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`of the oscillations being equal to the spacing between
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`the centre lines of adjacent cathode strips 271. By this
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`means, during sputtering the gradient of oxygen con-
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`centration‘in the atmosphere in the working space 32
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`between the cathode and substrate, which would result
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`from the use of a single large area cathode, is reduced
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`to an acceptable limit. As a consequence of the reduc-
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`tion in the oxygen gradient in the sputtering atmo-
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`sphere, a stibstantially uniform conductive film of
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`lower specific resistivity can be produced. The spacing
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`between adjacent strips 271 is chosen to be the mini-
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`mum which will provide ade