United States Patent
`King et al.
`
`[ 19]
`
`[ 11]
`
`[45]
`
`4,006,070
`Feb. 1, 1977
`
`{ 541 MET AL OXIDE FILMS
`[ 75]
`
`Inventors: Robert David King, Solihull; Robert
`Hiscutt, Birmingham, both of
`England
`
`Primary Examiner-Oscar R. Vertiz
`Assistant Examiner-Wayne A. Langel
`Attorney, Agent, or Firm-Sughrue, Rothwell, Mion,
`Zinn & Macpeak
`
`[73) Assignee: Triplex Safety Glass Company
`Limited, London, England
`Jan. 26, 1972
`[21] Appl. No.: 220,899
`
`[22] Filed:
`
`[ 301
`
`Foreign Application Priority Data
`
`Feb. 5, 1971
`
`United Kingdom ............... 4234/71
`
`[52] U.S. Cl . ............................... 204/192; 204/298;
`428/432
`[51 J Int. Cl.2
`......................................... C23C 15/00
`[58] Field of Search ........... 204/192, 298; 428/432,
`428/539
`
`[56]
`
`References Cited
`UNITED ST ATES PATENTS
`
`3,414,503 12/1968 Brichard ............................ 204/192
`3,619,402 11/1971 Wurm ct al. ...................... 204/192
`3,630,873 12/1971 Moore ct al. ...................... 204/192
`3.907.660
`9/1975 Gillery ............................... 204/298
`
`FOREIGN PATENTS OR APPLICATIONS
`
`1.938, I 3 I
`1,147,318
`1,201,743
`
`1/1971
`1969
`8/1970
`
`Germany
`United Kingdom ............... 204/192
`United Kingdom
`
`[57]
`ABSTRACT
`A substantially uniform, transparent, electrically con(cid:173)
`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
`and another gas or gases (preferably an inert gas) at
`reduced pressure, by providing access for the sputter(cid:173)
`ing atmosphere to penetrate into the whole of the
`working space between the cathode and the substrate
`so as to maintain a substantial degree of uniformity in
`the oxygen concentration in the working space. Access
`for the atmosphere may be provided by means of pas(cid:173)
`sages extending through the cathode assembly, by di(cid:173)
`viding the catho.de assembly into parallel strips sepa(cid:173)
`rated by gaps, and the atmosphere may be supplied
`direct to the working space through such gaps. Relative
`movement is effected between the cathode assembly
`and the substrate, e.g. by reciprocating the paratrel
`strips of the divided cathode in the direction perpendic(cid:173)
`ular to their length.
`
`48 Claims, 11 Drawing Figures
`
`62
`
`64
`
`Page 1 of 18
`
`APPLIED MATERIALS EXHIBIT 1073
`
`

`

`U.S. Patent Feb. 1, 1977
`
`Sheet 1 of 7
`
`4,006,070
`
`12
`
`11
`
`13
`
`14
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`AG.I.
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`32a
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`AG.5.
`
`Page 2 of 18
`
`

`

`U.S. Patent Feb. 1, 1977
`
`Sheet 2 of 7
`
`4,006,070
`
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`0
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`C
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`/
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`//x
`o
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`x FILM THICKNESS (A)
`o OHMS/ SQUARE
`o SPECIFIC·
`RESISTIVITY
`(OHMS/c.m.J
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`... X OXYGEN
`10
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`CLOSED
`HAZE IN
`END
`FILM
`45
`25
`40
`20
`35
`30
`DJSrANCE ALONG CATHODE (c.m.)
`
`AG.2.
`
`Page 3 of 18
`
`

`

`U.S. Patent
`
`Feb. 1, 1977
`
`Sheet 3 of 7
`
`4,006,070
`
`10-3 4 8000 --~
`
`80
`
`1000
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`DECREASING OXYGEN----,-4-
`
`HAZE
`
`10
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`15
`
`45
`40
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`25
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`DISTANCE ALONG CATHODE (c.m.)
`
`AG.3.
`
`Page 4 of 18
`
`

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`62
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`·44
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`Page 5 of 18
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`57
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`Page 6 of 18
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`

`

`U.S. Patent
`U.S. Patent
`
`Fen-1, 1977
`Feb. 1, 1977
`
`w
`
`H
`
`Sheet 6 of7
`·. Sheet 6 of 7
`
`4,006,070
`4,006,070
`
`271
`
`
`
`F1G.lA.
`
`Page 7 of 18
`
`Page 7 of 18
`
`

`

`U.S. Patent
`
`Feb. 1, 1977
`
`Sheet 7 of 7
`
`4,006,070
`
`271
`
`31
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`'la OXYGEN AT INLET
`
`Page 8 of 18
`
`

`

`1
`
`4,006;070
`
`2
`specific electrical resistivity and adequate transparency
`over the whole area of the substrate to be coated.
`The existence of the above-mentioned oxygen gradi(cid:173)
`ent has been found to be most detrimental to the depo-
`5 sitiori of a uniform film. The effect can generally be
`detected where each lateral dimension, i.e. length and
`width, of the substrate is substantially greater than the
`distance between the cathode and substrate, e.g. is
`greater than 10 cm., and particularly if they are greater
`IO than 30 crri.
`
`METAL OXIDE FILMS
`BACKGROUND OF THE INVENTION
`I. Cross-Reference to .Related Application
`The invention is related to that described in cospend(cid:173)
`ing Application Ser. No. 144,541 filed May 18, 1971.
`2. Field of the Invention
`·
`This invention relates to rriethods and apparatus for
`depositing transparent, electrically · conducting, metal
`oxide films on to s~bstrates, such as glass, and to arti(cid:173)
`OBJECT OF THE INVENTION .
`cles having such metal oxide films applied the.reto. By
`An object of this invention is to provide an improved
`way of example; the article may be a windscreen, e.g.
`method and apparatus for depositing films on larger
`an aircraft windscreen, on which the film can provide
`substrates than hitherto practicable, e.g. substrates
`electrical resistance heating means for de-icing or de- 15
`having both lateral dimensions greater than 30 cm., and
`misting.
`in particular on substrates such as windscreens for
`3. Description of Prior Art
`aircraft and land vehicles, whose dimension can reach
`Various proposals have been made for reactively
`100 cm. and more.
`sputtering a transparent, electrically conducting, metal .
`oxide film on.to the surface of a substrate supported in 20
`SUMMARY OF THE INVENTION
`a vacuum vessel having an atmosphere of oxygen and
`According to the invention, we provide a method of
`another gas or gases, from a metal cathode near the
`depositing a transparent, electrically conducting metal
`substrate surface to be coated. One exarnple of such a
`processis described in U.S. Patent application Ser. No.
`oxide film by reactive sputtering on to the surface of a
`144,541.
`· · ·
`25 substrate of extended lateral dimensions which is main-
`tained at a controlled elevated temperature in a vac-
`Such processes have been successful in producing
`uum chamber containing an atmosphere of oxygen and
`transparent, electrically conducting, films, of reason-
`another gas or gases at a controlled reduced pressure, a
`ably unfform characteristics on substrate.s of relatively
`small latf:lr!ll dimensions, e.g. 4 cm. in width, but diffi-
`high negative potential being applied to a cathode as-
`culties have been experienced with larger articles. Even 30 sembly of the metal which is arranged in the vicinity of
`though the cathod.e is enlarged commensurately with
`the substrate and presents a surface or surfaces extend-
`the article, so. as to cover the· whole substrate area and
`ing substantially parallel to the substrate surface so that
`to maintain the direct sputter:ingj,ath from cathode to
`sputtering takes place substantially perpendicularly on
`substrate at the optimum value (between 2 cm. and 10
`to all parts of the substrate, wherein access is provided
`cm. depending on the applied potential difference), it is 35 for ~e atmosphere to penetrate into the whole of the
`found that the film produced tends to be non-uniform.
`working space between the cathode assembly and the
`Variations. are found in the thickness and specific elec-
`subst!at~ so as to maintain a subs~ntia! degree of u.ni-
`trical resistivity of the film, which result in wide varia-
`form1ty. m the oxygen ·concentration m the workmg
`tions in .. its resistance and dimi.nish or destroy its utility 40 space.
`..
`.
`.
`,, .
`as a r:esistance heating means. In extreme cases, the
`The term extended _ lateral d1m~ns1o~s
`IS to be
`film is also found to be less transparent near the middle
`~nderstood to mean hav1?g lateral d1mens10ns substan-
`of the article, Any . such reduction in transparency is
`tially greater than. the distance _bet~een the cathode
`unacceptable in a windscreen, for example.
`~d su~strate, and generally havmg its smallest lateral
`The. present inventors have deduced. that the non- 45 d1me11:s1~n gr~ater than 30 cm.
`.
`Variation m the oxrgen con.centra~o~. has been
`uniformity of the film is due to a reduction in the oxy-
`gen concentration in the atmosphere in the working
`found .to affect the spec~c e_lectri~al res!stiv1ty (p) and
`the th1~kness <.t) deposited m a given time and hence
`space between the cathode and the substrate, which is
`~e res1sta_nce m ohrnjsqu~re of the sputt~red film, as
`believed to be caused· by the consumption of the oxy-
`gen originally present during the formation of the film, 50 d1scl?se? m the .Specification of ~o-pendmg U.S. Pat.
`and by the slow rate at which fresh oxygen can diffuse
`apphc~tion Se~. No. 144,541..It.wdl be understood t~at
`the resistance m ohm/sq~are 1s. mdepe°:dent of the size
`into this sp~c:e. As the process proceeds, a gradient of
`oxygen concentration is thus established in the atmo-
`of th.e squ~e .u?der cons~deration and 1s relat~d to the
`sphere in .the working space in a plane parallel to the
`specific re.s1stiV1ty and th~ckness by the equation
`cathode surface, the concentration falling towards the 55
`centre of the cathode ..
`For economy in production, it is desirable to have a
`high deposition rate and to achieve a minimum specific
`By providing access for the atmosphere into the whole
`resistivity (p). However, as the rate of deposition is
`increased,· the . rate of consumption of oxygen is also .. 60 of the working space so as to maintain the oxygen con(cid:173)
`increased ·.and the effect of the gradient in the oxygen
`centration substantially uniform, we have found it pos(cid:173)
`concentration will become more severe. Further, as the
`. sible to produce articles of considerable size coated
`area of the· substrate and cathode is increased ,so· the
`· with films having substantially uniform low resistance
`in ohm/square and substantially uniform high light
`gradient of oxygen concentration is establish,ed over
`greater distances, the oxygen starvation at the centre of 65 transmission.
`·
`In orie form of the invention, passages extend
`the substrate becomes more pronounced. Conse:
`quently it is no longer possible to maintain the desired
`through the cathode assembly to provide the access for
`oxygen concentration necessary to provide a minimum
`the atmosphere into the working space. Preferably
`
`R O=J!....
`
`l
`
`Page 9 of 18
`
`

`

`4,006,070
`
`55
`
`30
`
`4
`3
`FIG. 4 is a schematic perspective view ofa first form
`relative movement is provided between the cathode
`of modified cathode assembly for sputtering a large
`assembly and the substrate in a direction parallel to the
`area substrate surface in accordance with the method
`substrate surface. In a preferred embodiment of the
`of the present invention;
`invention, the cathode assembly is divided into spaced
`parallel strips so as to provide the passages for the 5
`FIG. 5 is a schematic section through the cathode
`assembly of FIG. 4;
`atmosphere between the strips, and the relative move-
`FIG. 6 is a perspective view of an apparatus accord-
`ment is provided between the strips and the substrate in
`ing to the invention incorporating a cathode assembly
`a direction transverse to the length of the strips so that
`as illustrated in FIGS. 4 and 5;
`the strips cover all parts of the substrate surface for
`FIG. 7 is a longitudinal axial section through the
`equal deposition periods during one part or another of 10
`apparatus of FIG. 6, modified to deposit a film on a
`the deposition process. Preferably the relative move-
`substrate which is curved from end to end;
`ment between the strips and the substrate is a recipro-
`FIG. 7 A is a detail sectional view to a larger scale, of
`eating movement. Advantageously the relative move-
`one of the cathode sections used in the apparatus of
`ment is substantially equal to the spacing between the
`centre lines of adjacent strips. The strips may move on 15 FIG. 6 and FIG. 7;
`FIG. 8 is a schematic section through a fourth form of
`guide rails relative to the substrate.
`The invention also provides an article of extended
`modified cathode assembly;
`lateral dimensions having a transparent electrically
`FIG. 9 is a similar view of a fifth form of modified
`conducting film deposited on a surface thereof by a
`cathode assembly; and
`method as described above, said film having a specific 20
`FIG. 10 is a graph of specific electrical resistivity
`electrical resistivity between 2 x I 0- 4 ohm. cm. and 20
`against percentage oxygen concentration in the atmo-
`x I 0-4 ohm. cm. and preferably between 2 x I 0-4 ohm.
`sphere of sputtering apparatus having one of the modi-
`cm. and 4 x 10-4 ohm. cm., a thickness of between 500
`tied cathode assemblies of FIGS. 4 to 9, for a series of
`A and I 0,000 A, and a light transmission figure of over
`examples in which the oxygen concentration is main-
`70%. Where the film thickness is below 5000 A, the 25 tained substantially uniform between the cathode or
`light transmission figure may be over 80%.
`cathodes and a large area of substrate surface.
`The invention further provides a glass article of ex-
`·
`tended lateral dimensions having a transparent electri-
`DETAILED DESCRIPTION
`cally conducting film of indium/tin oxide deposited on
`Referring to FIG. 1, there is shown a vacuum vessel
`10 for connection by conduit 11 to a vacuum pump
`a surface thereof, said film having a substantially uni-
`form resistance of between 2 and 40 ohm/square and a
`(not shown). A further conduit 12 passing through the
`light transmission figure of over 80%.
`wall of the vacuum vessel 10 is connected via gas flow
`The invention further provides apparatus for deposit-
`meters 13, 14 to separate sources of oxygen and argon
`ing a transparent, electrically conducting metal oxide 35 respectively. These gas flow meters 13, 14 are provided
`to ensure accurate control of the rate of flow ot the
`film by reactive sputtering on to the surface of a sub-
`strate of extended lateral dimensions, comprising a
`oxygen into the argon and thence into the atmosphere
`of the vacuum vessel 10.
`vacuum chamber, means for supporting the substrate in
`the vacuum chamber, means for maintaining the sub-
`Within the vacuum vessel 10 there is mounted a
`strate at a controlled elevated temperature in the vac- 40 substrate 17 which is to be coated with an electrically
`uum chamber, means for supplying an atmosphere of
`conductive film by sputtering from a water cooled cath-
`ode 18. The substrate 17 is supported on a heated
`oxygen and another gas or gases at reduced pressure
`into the vacuum chamber, a cathode assembly ar-
`block 19 which is heated by an internal electric heating
`element 20 connected by leads 21, 22 to an external
`ranged in the vacuum chamber in the vicinity of the
`substrate and presenting a surface or surfaces capable 45 source of low voltage electrical power. The cathode 18
`of extending over the whole of the substrate surface
`is connected by a lead 23 to the negative terminal of an
`external source of high voltage. An earthed electro-
`and substantially parallel thereto, and means for apply-
`static screen 24 is provided round the cathode 18, and
`ing a high negative potential to the cathode assembly,
`the heated block 19 and vacuum vessel 10 are also
`wherein means is provided for allowing access for the
`atmosphere to penetrate into the whole of the working s-0 earthed as indicated at 25. Instead of the heated block
`space between the cathode assembly and the substrate
`19 being heated internally, the heating element 20 may
`so as to maintain a substantial degree of uniformity in
`be disposed on insulated support pillars on the upper
`surface of the block 19 so that the substrate is heated
`the oxygen concentration in the working space.
`mainly by radiation.
`BRIEF DESCRIPTION OF THE DRAWINGS
`In order to determine and to control the temperature
`of the substrate 17 at the required value, a thermo-
`In the accompanying drawings:
`FIG. 1 is a diagrammatic layout of a known type of
`couple 26 is attached to the edge of the substrate 17 .so
`as to be in thermal contact with it. The thermocouple
`apparatus for reactively sputtering a film on a relatively
`provides a measure of the surface temperature of the
`small substrate surface;
`,
`FIG. 2 is a graph of the resistance in ohm/square, 60 substrate 17, as it is heated by the heated block 19. As
`thickness and specific electrical resistivity of a sput-
`the substrate 17 is exposed to the plasma induced by
`tered film as a function of the distance along the cath-
`the electric field existing between the cathode and the
`ode in an experiment in which an oxygen concentration
`substrate 17, the additional power injected by the
`gradient is deliberately established along the cathode,
`plasma heats the substrate, and it is consequently nee-
`starting with a known initial oxygen concentration;
`65 essary to gradually reduce the electric power supplied
`to the heating element 20 inside the block 19, in order
`FIG. 3 is a similar graph to FIG. 2 in respect of a
`similar experiment but starting with a higher initial
`to maintain the temperature of the substrate at the
`oxygen concentration;
`required value.
`
`Page 10 of 18
`
`

`

`4,006;070
`
`5
`6
`. Upon removal of the glass substrate from the vessel it
`The substrate 17, which may be of toughened soda-
`lime-silica glass, is placed on the lieated block 19 in the
`was immediately obvious that the characteristics of the
`vacuum vessel 10. The vacuum vessel 10 is theh evacu-
`film varied considerably from one end to the other. In
`ated to a pressure of say 5 X I 0- 4 mm Hg as measured
`particular, at the end where access of the sputtering
`on a Penning vacuum pressure gauge 101, and low 5 atmosphere had been allowed the film was substantially
`transparent although slightly hazy. At the other end
`voltage (say 10 volts) electric power applied to heating
`element 20 through leads 21, 22. The substrate surface
`where access of the sputtering atmosphere and been
`is thereby heated to a selected temperature between
`restricted the film was completely opaque and metallic
`240° C and 400° C. Oxygen gas is then admitted to the
`in appearance. Indeed the film showed characteristics
`vacuum vessel 10 through the gas flow meter 13 and Io over the 45 cm, length of the cathode which .would be
`argon gas through the gas flow meter 14 at desired flow
`consistent with a considerable drop in the percentage
`rates. This flow of gas results in the presence of a se-
`of oxygen concentration.
`lected percentage of oxygen between I% and JO% by
`The above experiment was repeated employing an
`volume of the total gas in the vacuum vessel and pro-
`atmosphere of 94% argon and 6% oxygen, with a cath-
`duces an increase in the pressure in the vessel to a 15 ode voltage of -2.75 KV. As expected, it was found
`that the reduction in cathode voltage and increase in
`selected value of the order of 5 X I 0-2 mm Hg as mea-
`sured on a Macleod vacuum pressure gauge 102.
`oxygen concentration reduced the degree of haze and
`The cathode 18 is supported at a selected distance of
`shifted the specific resistivity curve to the right. At the
`say 3 to 4 cm. from the glass substrate surface to be
`end of the film where access of the sputtering atmo-
`coated, and a selected negative voltage of between 20 sphere had been allowed, a highly transparent, haze-
`free film having a specific resistivity less than IO x I 0-4
`-1.0 KV and -5 KV is applied to the cathode. The
`power applied to the heating element 20 is gradually
`ohm. cm. was obtained. The film at the other end was
`reduced in order to maintain the glass substrate surface
`very hazy and had a much higher resistivity. The results
`of this experiment are shown in FIG. 2 which comprises
`at the desired temperature, this step being necessary
`owing to the heating effect produced by ionic and elec- 25 a graph of the resistance in ohm/square, the film thick-
`tronic bombardment from the glow discharge between
`ness in A and th~ specific resistivity (p) in ohm. cm. as
`the cathode and substrate.
`a function of the distance along the cathode. This graph
`The ionised argon ions bombard the surface of the
`clearly shows that there is a percentage of oxygen con-
`cathode 18 thus removing metal from the cathode and
`centration which results in a minimum specific resistiv-
`thereby reactively sputtering a film of oxide on to the 30 ity.
`upper surface of the glass substrate 17. At the comple-
`The experiment as again repeated using the same
`tion of this process, the power supplies to the cathode
`reduced cathode voltage of-2.75 KV but with an in-
`18 and the heating element 20 are disconnected, the
`creased oxygen concentration of 7% in the sputtering
`gas flows turned off and the glass substrate allowed to
`atmosphere. The results of this experiment are shown
`cool.
`35 in FIG. 3 which is again a graph of the resistance in
`The coated glass substrate is then removed from the
`ohms/square, the film thickness in A and the specific
`vessel and the physical characteristics· of the film may
`resistivity (p) in ohm. cm. as a function of the distance
`be determined by measurement and calculation.
`along the cathode. As before the graph shows that
`The above method is applicable to the coating of a
`there is a percentage of oxygen concentration which
`transparent and haze-free film on a glass substrate from 40 results in a minimum specific resistivity.
`a single, stationary cathode having a lateral dimension,
`These results indicated to the inventors that if the
`e.g. a width or length, of IO cm. or less. However, for
`oxygen concentration in the sputtering atmosphere in
`substrates and cathodes of greater lateral dimensions, it
`the working space between the cathode and substrate
`could be controlled, it should be possible to maintain
`has been found that the method results in the produc-
`tion of a non-uniform film which does· not have the 45 adequate uniformity of transparency, specific resistiv-
`ity, thickness, and thus resistance in ohm/square of the
`desired resistance in ohm/square and may not be haze-
`free, and the present inventors deduced that this effect
`sputtered film.
`is due to variation of the oxygen concentration in the
`According to the invention, access is provided for the
`atmosphere in the working space between the cathode
`atmosphere to penetrate into the whole of the working
`and the substrate surface. To investigate and measure 50 space so as to maintain a substantial degree of uniform-
`this effect, there was employed a cathode measuring 45
`ity of the oxygen concentration between the cathode
`cm. long by 15 cm. wide. A 60 cm. long by 30 cm. wide
`and the substrate. Such access may be provided by a
`by 4 mm thick soda-lime-silica glass substrate was
`particular construction of the cathode and/or by the
`placed at a distance 38 mm from the cathode surface.
`provision of relative motion between the cathode and
`The gaps formed between the edges of the cathode and 55 the substrate surface. Some examples will now be de-
`scribed of suitable methods of controlling the uniform-
`the surface of the substrate were blanked off along the
`two long sides and one end by three pieces of glass.
`ity of oxygen concentration over the area of the sub-
`There was thus access for the sputtering atmosphere at
`strate surface.
`one end only.
`FIGS. 4 and 5 illustrate diagrammatically a first type
`The vacuum vessel was evacuated to a pressure or 5 60 of modified cathode assembly 27 for carrying out the
`x Io-• mm Hg and a voltage of IO volts was applied to
`method of the present invention. The cathode assembly
`the heater 20 to raise the temperature of the substrate
`27 is divided into four parallel sections or strips 271,
`surface to 300° C. A gas mixture consisting of 96%
`each strip measuring 60 cm. in length and 8 cm. in
`argon and 4% oxygen by volume, was admitted to the
`width and being surrounded by a separate earthed elec-
`vacuum vessel thereby increasing the pressure in the 65 trostatic shield 28. The cathode sections or strips 271
`vessel to 6.5 x I 0-2 mm Hg. The cathode was then
`are spaced apart by gaps 29 of equal width. The indi-
`energised to a voltage of '--3.0 KV and sputtering was
`vidual gaps may be varied in width, for example be-
`allowed to take place for a period of IO minutes.
`tween 1.0 cm. and IO cm., and are provided to allow
`
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`type, the outer conductor being earthed. Similar cables
`access for diffusion of the atmosphere from the under
`side of the cathode assembly 27 to the side adjacent to
`44 connect the strips 271 to one another.
`the substrate 31, as indicated by the arrows 30 in FIG.
`Above the horizontal guide rails 42, a pair ofhorizon-
`ta! support rails 53 (only one of which is shown) are
`5.
`.
`Means (not shown in FIGS. 4 and 5) are provided s secured to opposite sides of the vessel 40 to support a
`substrate 31 which is to be provided with a transparent
`which effect relative motion between the substrate 31
`and the cathode assembly 27 in a direction parallel to
`conducting film.
`their facing surfaces. The preferred direction of rela-
`Above the position of the substrate 31, radiant heater
`tive motion is perpendicular to the length of the cath-
`54 is secured in the vessel 40, fed through low-tension
`ode strips 271. The motion is preferably an oscillatory 10 leads 55 and busbars 56 from a low voltage power unit
`motion of the cathode assembly 27 with a constant
`57. The heater 54 extends over the whole area of the
`speed of traverse between reversing points, as shown by
`substrate 31.
`the double headed arrow 32a in FIG. 4, the amplitude
`A thermocouple 58 is placed on the upper surface of
`of the oscillations being equal to the spacing between
`the substrate 31 and connected through leads 59 to a
`the centre lines of adjacent cathode strips 271. By this 15 calibrated dial instrument 60 to indicate the tempera-
`ture of the substrate.
`means, during sputtering the gradient of oxygen con-
`centration in the atmosphere in the working space 32
`A vacuum pump (not shown) is connected to the
`between the cathode and substrate, which would result
`interior of the vessel 40 through an exhaust connection
`61 and a gas supply 62 of the selected atmosphere is
`from the use of a single large area cathode, is reduced
`to an acceptable limit. As a consequence of the reduc- 20 connected through a flow meter 63 and needle valve 64
`tion in the oxygen gradient in the sputtering atmo-
`to an inlet 65 opening into the vessel. The inlet 65 is at
`sphere, a substantially uniform conductive film of
`the opposite end of the vessel 40 from the exhaust
`connection 61 so that gas flow from inlet to exhaust
`lower specific resistivity can be produced. The spacing
`between adjacent strips 271 is chosen to be the mini-
`tends to pass through the working space between the
`mum which will provide adequate diffusion of the sput- 25 cathode assembly and substrate and thereby assists in
`tering atmosphere into the working space 32, while
`maintaining uniformity of the oxygen concentration in
`maintaining a sufficient coating rate.
`the working space.
`FIG. 6 illustrates an apparatus incorporating a cath-
`In use, when the substrate 31 has been placed on the
`ode assembly of the kind described above with refer-
`support rails 53 and the end closures have been sealed,
`ence to FIGS. 4 · and 5. The apparatus comprises a 30 the vessel 40 is evacuated through the exhaust connec-
`tion 61 and the selected sputtering atmosphere is sup-
`cylindrical vacuum vessel 40 with removable vacuum-
`plied through the inlet 6S, while the substrate is heated
`tight end closures (not shown). The cathode assembly
`27 comprises a plurality of spaced, parallel sections of
`to the desired temperature by the heater S4. The cath-
`strips 271 having upper surfaces of indium/tin alloy.
`ode assembly 27 comprising the strips 271 is oscillated
`Each strip 271 has an earthed electrostatic shield 28. 35 back and forth along the guide rails 42 by the motor SO
`Only three sections or strips 271 are shown in FIG. 6,
`and the high negative voltage is applied to the strips
`for clarity. In practice, the number of strips used will
`271 by the source 4S. The vessel 40 and rails 42, S3, as
`depend on the length of the substrate to be coated,
`well as the electrostatic shields 28, are earthed. A film
`being generally chosen so that an oscillation having an
`of indium/tin oxides is thus sputtered on to the lower
`amplitude equal to the spacing between the centre lines 40 surface of the substrate 31. The heating effect on the
`of the strips will cause all parts of the substrate to be
`substrate of the plasma in the working space is such
`covered. The strips 271 are mounted on pairs of rollers
`that the heating current supply from the low voltage
`41 at each of their ends, and these rollers run on hori-
`power unit has to be reduced to maintain the substrate
`zontal guide rails 42 secured to opposite sides of the
`temperature constant within ± I 0° C of the desired
`vessel 40. The strips 271 are connected to one another 45 value. An automatic control circuit of known type (not
`by adjustable link rods 43 which maintain their spacing
`shown) can be used for this purpose.
`The amplitude of the oscillatory motion of the strips
`and parallel alignment with one another and ensure
`271 is adjusted to equal the spacing between the centre
`that all the strips can move together along the guide
`rails in the direction perpendicular to their length. A
`lines of the strips. This spacing can be adjusted by
`flexible high-tension lead 44 connects the strips 271 to 50 means of the link rods 43. All parts of the substrate 31
`the negative terminal of a high-voltage source 45.
`are effectively covered for equal deposition times by
`A pair of pulleys 46 is mounted on a transverse shaft
`the strips during one part or another of each oscillatory
`47 at each end of the vessel 40 and a pair of traction
`cycle.
`wires or cables 48 connected at each end to the electro-
`The spaces between the strips 271 allow free circula-
`static shields 28 of the end strips 271 are led over the 55 tion of the sputtering atmosphere so that no substantial
`pulleys 46 to form drive means. One of the shafts 47
`oxygen gradient can become established. With an oxy-
`passes through the wall of the vessel 40 and is con-
`gen content of 3 .0% by volume in the atmosphere sup-
`nected via a variable-amplitude oscillatory motion de-
`plied, it is believed that the reduction in the oxygen
`vice 49 to an electric motor SO.
`content in the working space is not more than 0.2%, i.e.
`Each of the strips 271 is hollow, as shown in FIG. 7A, 60 a reduction from 3.0% to 2.8%. A substantially uniform
`its interior being filled with cooling water which is
`highly transparent film of low specific resistivity can
`supplied through a flexible pipe 52 which enters near
`thus be deposited on the substrate. Variations in the
`one end of the strip. The water leaves through a second
`specific resistivity can readily be kept with± 10% of a
`flexible pipe 51 near the other end of the strip 271. The
`means value.
`pipes St, S2 connect the strips 271 in series, but the 65
`FIG. 7 illustrates a modification of the apparatus of
`FIG. 6 for use in depositing a film on to a substrate 311
`pipes extending between the adjacent strips have been
`omitted from FIGS. 6 and 7 for clarity. The high-ten-
`which is longer than the substrate 31 shown in FIG. 6
`sion lead 44 from source 4S is of the co-axial cable
`and is curved from end to end, e.g. a windscreen for a
`
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`motor vehicle. The support rails 531 and the guide rails
`· In each example, the cathode comprises 80% indium
`421 are similarly curved, as seen in elevation, and can
`and 20% tin, by weight,