United States Patent (19)
`Wirz, et al.
`
`Patent Number:
`11
`45) Date of Patent:
`
`4,895,631
`Jan. 23, 1990
`
`54 PROCESS AND APPARATUS FOR
`CONTROLLING THE REACTIVE DEPOST
`OF COATINGS ON SUBSTRATES BY MEANS
`OF MAGNETRON CATHODES
`75 Inventors:
`Peter Wirz, Waldernbach;
`Friedrich-Werner Thomas,
`Gelnhausen, both of Fed. Rep. of
`Germany
`Leybold Aktiengesellschaft, Hanau I,
`Fed. Rep. of Germany
`21 Appl. No.: 326,404
`22 Filed:
`Mar. 20, 1989
`
`73 Assignee:
`
`63
`
`Related U.S. Application Data
`Continuation of Ser. No. 59,559, Jun. 8, 1987, aban
`doned.
`Foreign Application Priority Data
`30
`Mar. 20, 1987 DE Fed. Rep. of Germany ....... 370977
`511 Int. Cl. .............................................. C23C 14/34
`52 U.S. Cl. .......................... 204/192.13; 204/192.12;
`204/298
`58) Field of Search ...................... 204/192.12, 192.13,
`204/192.33, 298 MT, 298 GF, 298 ME, 298
`SC, 298 ET
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,166,784 9/1979 Chapin et al................... 204/298 X
`4,362,936 12/1982 Hoffmann et al. .
`... 204/298 X
`4,407,709 10/1983 Enjouji et al......
`... 204/298 X
`4,428,811 1/1984 Sproul et al. ................... 2O4/298 X
`Primary Examiner-Nam X. Nguyen
`Attorney, Agent, or Firm-Felfe & Lynch
`57
`ABSTRACT
`A reaction gas is admitted in the immediate vicinity of
`a target on the cathode and a plasma is generated be
`tween the target and a substrate to be coated. The inten
`sity of the spectral line of a target material is measured,
`and is used to provide a first signal with a relatively
`short time constant to a controller via a first control
`circuit. A property of the finished coating is sensed after
`the substrate leaves the coating zone, and is used to
`provide a second signal with a relatively long time
`constant to the controller via a second control circuit.
`The controller uses the combined signals to regulate the
`admission of the reaction gas so that a pre-established
`property of the finished coating is kept substantially
`COnStant.
`
`10 Claims, 1 Drawing Sheet
`
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`
`NSN
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`9.
`sman
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`2SNNSZ
`SH
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`3
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`Page 1 of 7
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`APPLIED MATERIALS EXHIBIT 1044
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`

`

`U.S. Patent
`US. Patent
`
`Jan. 23, 1990
`Jan. 23, 1990
`
`4,895,631
`4,895,631
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`2—5: :_::::::3
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`Page 2 of 7
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`0
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`30
`
`1.
`
`PROCESSANDAPPARATUS FOR CONTROLLING
`THE REACTIVE DEPOST OF COATINGS ON
`SUBSTRATES BY MEANS OF MAGNETRON
`CATHODES
`This application is a continuation, of application Ser.
`No. 059,559, filed Jun. 8, 1987 abondoned.
`BACKGROUND OF THE INVENTION
`The invention relates to a process for controlling the
`reactive deposit of a coating on a substrate with a mag
`netron cathode operated at constant power and a target
`having an electrically conductive component of the
`coating material. The process includes measuring the
`15
`intensity of at least one spectral line of the target mate
`rial in the plasma of a sputtering process, and admitting
`reaction gas in the vicinity of the target according to
`this intensity. PROCESS AND APPARATUS FOR
`CONTROLLING THE REACTIVE DEPOSIT OF
`20
`COATINGS ON SUBSTRATES BY MEANS OF
`MAGNETRON CATHODES
`The invention relates to a controlling process accord
`ing to the general part of claim 1.
`In such coating processes, an electrically conductive
`25
`target, usually a metal target, is sputtered in a reactive
`atmosphere so that the magnetron cathode can be sup
`plied with direct current. A coating of the reaction
`product of the target material then deposits itself on the
`substrate, and the composition of the coating material
`depends very greatly on the atmosphere surrounding
`the magnetron cathode.
`In this kind of coating process, three different modes
`of operation of the magnetron cathode are distin
`guished, namely the "metallic mode,' 'reactive mode,”
`35
`and "transitional mode.' In the "metallic mode' the
`sputtering surface of the target is of a metallic, i.e.,
`conductive character. In the "reactive mode' a corre
`sponding reaction product is found on the sputtering
`surface of the target, and, as a rule, it is an electrical
`40
`insulator, and the sputtering rate, i.e., the amount of
`target material sputtered per unit time, is considerably
`reduced. The "transitional mode' is between these two
`operating modes and is considered to be unstable to a
`very great extent, because it threatens to tilt in the one
`45
`or in the other direction. This "transitional mode' is a
`peculiarity typical of magnetron cathodes, in which an
`erosion pit forms due to the locally restricted sputtering
`process, and becomes increasingly deeper. While the
`walls of the erosion pit can still be kept very largely free
`50
`of reaction products, the rest of the target surface be
`comes coated with the reaction products, and thus pro
`duces the unstable operating behavior previously de
`scribed.
`In order to prevent or suppress this unstable opera
`55
`tion insofar as possible, it is already known to feed the
`reaction gas in at a point that is remote from the target
`surface and shielded by a mask, and to feed into the
`vicinity of the target an inert gas which produces the
`sputtering (DE-OS3331707). If, when employing such
`a measure, the feeding of the reaction gas is performed
`according to the intensity of one or more spectral lines,
`the result would be time constants that are extraordi
`narily long for such a control method, and which are
`unacceptable in a production process, especially a con
`65
`tinuous production process. Moreover, in such a case a
`slow alternation takes place between the "metallic
`mode' and the "reactive mode” especially because the
`
`4,895,631
`2
`breakdown of the reaction product on the sputtering
`surface of the target takes, relatively, a very long time
`on account of the sputtering rate which in this case is
`very low.
`It has already been recognized that this alternation
`between the "metallic mode' and the "reactive mode'
`can be expressed by a hysteresis curve if the reaction
`gas flow exceeding the stoichiometric ratio is plotted
`over the reaction gas flow (EP-OS 0121 019), to which
`U.S. Pat. No. 4,428,811 corresponds. Even a control
`process founded on this relationship and using a mass
`spectrometer does not lead to the elimination of the
`instability problems, because the time constants of the
`individual components of the measuring and control
`circuit are too long.
`In reactive coating processes the object is, as a rule,
`to produce a chemical compound having the required
`coating properties. These coating properties are to be
`produced within close tolerances and with great long
`term stability. A whole series of proposals have been
`made for regulating a parameter of the process of mag
`netron sputtering by means of control circuits having a
`sensor for detecting a particular coating property. All
`proposals, however, have led to only very limited suc
`cess. This is because many coating properties cannot be
`measured in the coating zone, or they can be measured
`only very imprecisely due to the effect of the plasma on
`the measuring signals. In such control circuits, there
`fore, the measurement has always been performed out
`side of the coating zone. An obstacle to the achievement
`of close tolerances in this kind of procedure is the time
`difference between the end of the coating process and
`the measurement. Since the time constant has to be
`made substantially greater than this time difference, in
`the interest of the stability of the control circuit, the
`result is large substrate areas which fail to be coated
`within the tolerances. These substrate areas can extend
`over several of the substrates or, in the case of film
`coating, over great lengths of the film, which conse
`quently have to be considered as rejects.
`Still more important than the disadvantages cited
`above of using the measured value of a property of the
`coating for control purposes is the disadvantage that
`such control circuits do not guarantee the stability of
`the reactive coating process. Causes of such instabilities
`are, for example, undesired changes in the gas composi
`tion, and arc discharges at the target which express
`themselves in variations in the properties of the depos
`ited coatings. Such instabilities can tilt the process away
`from the "metallic mode' to the "reactive mode.” Such
`a tilt during the coating of the substrate signifies com
`plete rejection as far as the coating properties are con
`cerned.
`This so-called "tilting' occurs at a critical flow of the
`reaction gas, under otherwise constant electrical sput
`tering parameters. This rate is a measure of the basic
`stability of the reactive process. If the reaction gas flow
`is less than the critical flow, the magnetron cathode
`operates in the so-called "metallic range' in which the
`discharge can be stabilized by very simple means. In this
`range of operation the required coating processes are
`generally achieved by keeping such process parameters
`as power and reaction gas flow constant, and by timing.
`On the other hand, in the "metallic range' it is gener
`ally impossible to deposit coatings of reaction products
`with the required stoichiometry. By taking special mea
`sures to eliminate the influence of the reaction gas on
`the target or on the substrate, such coatings can be
`
`Page 3 of 7
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`

`

`10
`
`5
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`4,895,631
`3
`produced at correspondingly lower rates (see, for exam
`ple, the previously mentioned DE-OS 33 31 707).
`In the procedures described above for the attainment
`of the required coating properties, the reaction gas flow
`and/or an electrical working parameter have been ei
`ther kept constant or controlled.
`In controlling the process on the basis of a measured
`property of the coating, however, not only is the previ
`ously mentioned time interval between the end of the
`coating and the measurement disadvantageous, but also
`the time lag in the covering of the target is even more
`critical. Necessary changes in the covering of the tar
`get, which occur for example in the case of a change in
`the power, can bring about a time lag that is greater
`than the above-mentioned time interval resulting from
`the location of the point of measurement of the coating
`parameters. This time shift can amount to between sev
`eral seconds and several minutes, so that unacceptable
`changes in the coating process are the consequence.
`For economical reasons, coatings generally can be
`20
`achieved with a high reactivity of the compound and
`high rates of deposition only in the so-called "transi
`tional mode,' which is an unstable or metastable state of
`operation of the sputtering process, which has been
`referred to above. In the erosion pit in the target, coat
`25
`ing with reaction products is just barely prevented,
`while the reaction products are deposited on the sub
`strate with a high reactivity and at high rates. Working
`in the "transitional mode' requires the stabilization of
`the discharge by additional means.
`30
`U.S. Pat. No. 4,166,784 discloses a method of regula
`tion by detecting the intensity of a characteristic line of
`the target material in the plasma. The stabilization of a
`working point of the reactive discharge is performed by
`means of a control circuit by which an electrical param
`35
`eter of the power supply at constant reaction gas flow is
`regulated on the basis of the intensity signal as the found
`value, or the reaction gas flow is controlled at constant
`electrical operating parameters.
`Through DD-PS 239,810 it is known to tune light
`radiation out of a plasma discharge and use a spectral
`line or group of spectral lines to form a signal for the
`purpose of regulating the gas flow. DD-PS239,811 also
`discloses how a reference signal can be found for fixing
`the position of the working point.
`45
`control circuits for assuring the process stability of a
`given working point of the discharge in a reactive cath
`ode sputtering process utilizing an emission signal gen
`erally cannot prevent the properties of the coating from
`being out of tolerance and/or from shifting over a long
`50
`period of time. There are a number of reasons for this:
`When new substrate surfaces are brought into the coat
`ing area, surface coatings are released by the action of
`the plasma on the substrate. This causes the gas com
`position in the discharge, and consequently also the
`55
`emission signal, to vary in an uncontrollable manner.
`Desorption from parts of the apparatus after a target
`change likewise produces undesired changes in the
`emission signals. What is critical in this phenomenon
`is its uncontrollability and the fact that it is present
`over long periods of time, even for hours.
`Furthermore, all geometrical changes during the coat
`ing process, especially progressive target erosion,
`produce unwanted changes in the emission signal.
`The problem to which the invention is addressed is to
`devise a process of the kind described above, whereby it
`will be possible in a reactive coating process to regulate
`the coating properties and achieve close tolerances.
`
`4.
`SUMMARY OF THE INVENTION
`The intensity of the spectral line of the target material
`is measured in the plasma between the target and the
`substrate. At least one property of the finished coating
`is measured and a reference value is produced which is
`slidingly adjusted in relation to said property. Reaction
`gas admitted during the build-up of the coating is regul
`lated according to the intensity of the spectral line and
`the reference value so that a pre-established coating
`property is kept substantially constant.
`It is important that the measurement be performed at
`least of one spectral line in the plasma between target
`and substrate. This is an optical measurement, i.e., a
`measurement made with a spectral photometer aimed
`directly at the plasma. This means, when a magnetron
`cathode is used, that the optical sensor must be aimed at
`elements of volume very close to the target surface. The
`area in which the measurement is performed parallel to
`the target surface is preferably about 10 to 30 mm in
`front of the target surface.
`The accuracy of such a measurement also differs
`decidedly from a measurement performed with a mass
`spectrometer in which elements of volume of the gas
`atmosphere are aspirated out of the coating area and
`analyzed at a point remote therefrom. This method of
`measurement suffers from a considerable time lag, and
`furthermore has the disadvantage that the composition
`of the gas can change along the way.
`The regulation of the reaction gas inlet with the
`shortest possible time constant is to be seen in conjunc
`tion with the admission of the reaction gas close to the
`target. In this manner it is possible to adapt the flow of
`the reaction gas very quickly to any change in the
`working conditions.
`The measurement of at least one property of the fin
`ished coating is performed necessarily with a decidedly
`longer time constant, because first the substrate with the
`finished coating has to be transported from the coating
`zone to the measuring zone. So in this case the adapta
`tion of the reference value is performed at a slower
`speed. This, however, as experience has shown, is en
`tirely sufficient for the achievement of the object of the
`invention.
`What is involved in principle is the superimposition
`of two regulating circuits, one of which has an ex
`tremely short and the other a markedly longer time
`constant. By controlling the weighting of the influence
`of the measured signals on the plasma side, on the one
`hand, and on the substrate side on the other, the stability
`of the overall regulating process can be decidedly im
`proved. It is possible, for example, to set the percentage
`of the measured signal from the plasma at 60 to 90% and
`the percentage of the measured signal from the sub
`strate measurement at 10 to 40%.
`The procedure according to the invention, of achiev
`ing a necessary process stability on the one hand and at
`the same time achieving the necessary constancy of the
`coating properties on the other, by means based on
`different principles, has proven to be an extremely ef
`fective solution of the stated problem. It has been found
`that a qualitative improvement of the control of plasma
`emission for process stabilization is made possible when
`the time constant of the control circuit in question is
`kept as short as possible. Reducing the time constants of
`this control circuit can be achieved, however, only if
`the time lag in the feeding of the reaction gas is over
`COe.
`
`65
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`Page 4 of 7
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`

`

`15
`
`4,895,631
`5
`6
`Short paths for the diffusion of the reaction gas from
`period until a flow of the reaction gas is reached which
`the inlet to the area of the dense plasma in the magnetic
`approximately determines the level to be preset for at
`trap over the erosion profile are assured by admitting
`least one coating property.
`the reaction gas as closely as possible to the target. This
`It is then especially advantageous if the value of the at
`kind of admission, in which the target area and the
`least one intensity signal measured for the flow of the
`substrate are coupled very closely, would result in a
`reaction gas at the end of the conditioning period and
`drastic reduction of the basic stability of the discharge
`adjustment period is compared with the reference value
`for the coating properties. The reference value for the
`were it not for continuous variation of the reference
`value. The close coupling between the inlet of the reac
`first control circuit is formed on the basis of the compar
`tion gas and the target surface is contrary to the stan
`1SO,
`dard practice of providing for extensive decoupling
`The emission intensity measured at the end of the
`between the target and the substrate area in the interest
`conditioning characterizes a defined starting state. The
`of a high basic stability.
`working point in the reactive operation at which the
`required coating property is achieved is initially identi
`The short time constant, and with it the close feed
`back of the measurement signal from the plasma, in
`fied by a reference intensity value which is determined
`conjunction with the continuous variation of the preset
`on the basis of preliminary experiments.
`value, permit stable operation at arbitrarily selected
`The invention also relates to an apparatus for the
`working points in the "transition range.” This means in
`performance of the process described above. For the
`practice the gaining of degrees of liberty in the process,
`solution of the same problem, this apparatus is charac
`e.g., for the achievement of coatings with a wide range
`terized in that
`20
`of specifically controllable properties. For example, the
`(a) An optical sensor of a spectral photometer system is
`index of refraction of aluminum nitride coatings can be
`aimed at the space between the magnetron cathode
`varied in a range from 1.95 to 2.1. In the production of
`and the substrate, the sensor beam path being parallel
`indium-tin oxide coatings the specific resistance can be
`to the target surface and being disposed very close to
`varied by orders of magnitude.
`the latter,
`25
`If the coupling created by the plasma emission con
`(b) A gas distributing system is disposed close to the
`trol between the target area and the substrate area is still
`target surface and is connected through a control
`further strengthened, coating properties can be
`valve to a source of the reaction gas,
`(c) The output of the spectral photometer system is
`achieved which have never before been achieved with
`means of the prior art. For example, indium-tin oxide
`connected through an amplifier and a controller to an
`30
`coatings are produced on unheated substrates with sur
`actuator of the control valve, the optical sensor, spec
`face resistances under 1X 10 ohms/cm, as compared
`tral photometer system, amplifier, controller, actua
`with 8x10-4 ohms/cm with prior-art methods.
`tor and control valve forming a first control circuit
`An explanation as to why the discharge can neverthe
`with a short time constant, equal to or less than 150
`less be kept stable in the procedure according to the
`ms and preferably equal to or less than 50 ms,
`35
`invention can be seen in the fact that, on account of the
`(d) In the path of the substrate coated immediately
`close coupling, the percentage of the reaction gas that is
`before, a second sensor for sensing at least one prop
`reacted to the desired chemical compound relatively
`erty of the coated substrate is disposed, the output of
`increases because the excitation of the reaction gas in
`the second sensor being delivered to a second ampli
`the vicinity of the substrate also increases. On the other
`fier whose output is delivered to a reference value
`hand, the close coupling and the basic stability thereby
`generator for the controller, while the second sensor,
`produced has the consequence that changes in the gas
`the second amplifier, the reference value generator,
`composition as a result of desorption processes lead to
`the controller, the actuator and the control valve
`an intensified effect on the emission signal and hence on
`connected to the output form a second control circuit
`the coating properties.
`with a longer time constant than that of the first con
`45
`Due to the close coupling of the partial processes at
`trol circuit, and the first and second control circuits
`the target on the one hand, and at the substrate on the
`are connected together in the controller.
`other, the control process according to the invention
`BRIEF DESCRIPTION OF THE DRAWING
`makes the influence exercised by the state of erosion of
`the target (the change in which leads to a shift in the
`The sole figure is a partial section view of the vacuum
`50
`sputtering rate and in the excitation of the reaction gas)
`chamber, and also schematically shows the apparatus
`on the coating properties become relatively greater.
`and circuitry for controlling the reactive gas.
`The shift in the coating properties provoked by the two
`DETAILED DESCRIPTION OF THE
`effects, however, has a great time constant and can be
`PREFERRED EMBODIMENT
`effectively prevented by the coupling of the control
`process according to the invention via the continuous
`In the drawing is represented a section of a vacuum
`adjustment of the reference value.
`chamber 1 through which a substrate 2 is guided along
`Thus, it is especially advantageous that the regulation
`a path of movement which is indicated by broken lines.
`according to the invention is not performed until after
`In a floor plate 3 of the vacuum chamber, surrounded
`the conditioning of the target surface is completed. By
`on all sides by an insulating space that is smaller than the
`this is meant the cleaning of the surface of a new target
`dark space to be observed under operating conditions, is
`or of a target that has been exposed to the ambient air.
`a magnetron cathode 4 which consists of the following
`In this case it is especially advantageous to proceed,
`parts: a basic cathode body 5 with a face plate 6 is in
`after the conditioning of the target surface is completed,
`serted into the floor plate 3 with the interposition of a
`by setting process parameters close to the working
`ring 7 of insulating material.
`65
`point as required for the needed coating properties by
`On the upper side of the face plate 6, which is pro
`programming the timing of the influx of the reaction gas
`vided with cooling passages, is a target 8 of an electri
`and steadily increasing it within a given adjustment
`cally conductive material constituting the one compo
`
`O
`
`55
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`

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`15
`
`4,895,631
`7
`8
`nent of the coating material. On the bottom of the face
`of the substrate 2, the signal corresponding to the coat
`plate 6 is a magnet system 9 which consists of a ferro
`ing properties is produced with a time delay which is
`magnetic yoke plate and permanent magnets disposed
`great in comparison to the time constant of the first
`one inside the other thereon, the inner and outer mag
`control circuit. As a rule the lag will amount to at least
`nets having opposite polarity, which is indicated by the
`0.5 second. The elements from the sensor 21 through
`arrows. In the immediate marginal area of the target 8 is
`the reference value generator 25 to the control valve 11
`a gas distributing system 9, but, as seen in plan, it comes
`constitute a second control circuit with a large time
`just short of overlapping the target 8. The gas distribut
`constant, parts of the first and second control circuit
`ing system 9 consists of one or two tubes which follow
`after the controller 19 being identical.
`the periphery of the target, at least on a large portion of 10
`Furthermore, in the path of the substrate 2just ahead
`the circumference, and have perforations through
`of the coating station formed by the magnetron cathode
`which the reaction gas can flow toward the target. The
`4 with the reaction zone 14, a third sensor 28 is disposed
`gas distribution system 9 is connected through throttle
`for detecting the properties of the substrate entering the
`valves 10 and a common regulating valve 11 to a source
`coating station, which is connected through a third
`12 of a reaction gas or of a mixture of a reaction gas and
`amplifier 29 to the microprocessor 24. In the micro
`a working gas (argon). The voltage source for supply
`processor 24 the signals of the sensors 21 and 28 are
`ing the magnetron cathode 4 with a negative direct-cur
`compared, so that only changes in the properties of the
`rent voltage between 400 and 1000 volts has been omit
`substrate in the coating station occurring within the
`ted for the sake of simplicity.
`reaction zone 14 are determined. This measure is impor
`Between the magnetron cathode 4 and the substrate 2
`tant for the case, among others, that the coating station
`20
`a shield system 13 is disposed close to the substrate and
`with the reaction zone 14 is preceded by another coat
`can serve also as an anode and can either be at the same
`ing station, so that the substrate enters the reaction zone
`potential as the vacuum chamber or at a higher positive
`14 with one or more previous coatings.
`potential. The target 8, the substrate 2 and the shield
`We claim:
`system 13 substantially define a reaction zone 14 in
`1. Process for controlling the reactive deposit of a
`25
`which a reactive process takes place to coat the sub
`coating on a substrate using a magnetron cathode oper
`strate 2 with a compound of the target material and the
`ated at constant power and having a target with an
`reaction gas.
`electrically conductive component of the coating mate
`Anoptical sensor 15 is aimed at a narrow portion of
`rial, said method comprising the steps of
`the reaction zone 14 along a beam path running parallel
`introducing said substrate into a coating zone adja
`30
`to the target 8. This beam pathis situated within a range
`cent to said target,
`of 10 to 30 mm above the target 8. From the optical
`admitting a reaction gas in the immediate vicinity of
`sensor 15 a glass fiber cable 16 leads to a spectral pho
`the target,
`tometer system 17 which can consist, for example, of an
`generating a plasma between said target and said
`optoelectronic converter with interference filters or of
`substrate, said plasma containing material from said
`35
`a controllable monochromator. In this manner it is pos
`target, said material producing at least one spectral
`sible to select from the light signal from the sensor 15
`line,
`one or more spectral lines and analyze them for their
`measuring the intensity of said spectral line,
`intensity. At the output 17a of the spectral photometer
`automatically sensing a property of the finished coat
`system, therefore, an electrical signal appears which is
`ing after said substrate leaves said coating zone and
`proportional to the intensity of the spectral line or lines.
`producing a sliding reference value which is con
`To the output of the spectral photometer system is
`tinuously and automatically adjusted in relation to
`connected an amplifier 18 which is in turn followed by
`said property as sensed,
`a controller 19 which acts upon an actuator 20 that
`regulating the admission of said reaction gas during
`operates the control valve 11. This system forms a first
`the build-up of the coating according to the inten
`regulating circuit with an extremely short time constant
`sity of said spectral line and said sliding reference
`that is less than 150 ms. The composition of the gas
`value so that a pre-established property of the fin
`atmosphere and of the plasma in the reaction zone 14
`ished coating is kept substantially constant, the
`can therefore be adjusted very rapidly.
`time constant which represents the time lag be
`In the path of the substrate 2, after the exit from the
`tween the measurement of the intensity and the
`50
`reaction zone 14, there is a second sensor 21, which can
`admission of the reaction gas being kept to a mini
`be an optical and/or an electrical sensor depending on
`mum by the admission of the reaction gas in the
`the coating property that is to be measured. The output
`immediate vicinity of the target.
`signal from this sensor is fed through a line 22 to an
`2. Process according to claim 1, characterized in that
`additional amplifier 23 whose output is in turn con
`the measurement of said intensity produces a signal that
`55
`nected to a microprocessor 24. From this microproces
`is amplified and electronically processed in a first con
`sor another line leads to a reference level generator 25
`trol circuit and said time constant is equal to or less than
`which is preset by an adjusting means 26 (potentiome
`150 ms, and that the sliding reference value is deter
`ter). Since the sensor 21 registers certain changes in the
`mined by a second control circuit to which a signal
`coating properties on the substrate 2, the result is that, at
`obtained from said sensing of a coating property is fed.
`the output of the reference level generator 25, a so
`3. Process according to claim 2, characterized in that
`called sliding reference value is present which is fed
`said sensing of a coating property is performed outside
`through a line 27 to the controller 19. In the controller
`of the coating zone and is fed to the second control
`19, consequently, signals corresponding to the output
`circuit with a time constant equal to or greater than 0.5
`signals of the sensors 15 and 21 are combined for the
`65
`SCC
`exercise of control. Since the properties of the finished
`4. Process according to claim 2, characterized in that
`coating cannot be determined by the sensor 21 without
`an additional measurement signal is fed to the second
`a time lag corresponding to the velocity of movement
`control circuit, which signal is characteristic of the
`
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`4,895,631
`10
`substrate properties before the coating process, and that
`target, a source of reaction gas, and a control valve
`the measurement signal from said sensing a property of
`between said source and said admitting means,
`a first control circuit comprising a spectral photome
`the finished coating is compared with the additional
`measurement signal and the result of the comparison is
`ter system having an optical sensor aimed at said
`used as a correction value for adjusting the sliding refer
`reaction zone along a beam path parallel to said
`target, an amplifier connected to the output of said
`ence value.
`spectral photometer system, a controller, and an
`5. Process according to claim 2, characterized in that
`the target surface is conditioned in preparation for the
`actuator for said control valve, said first control
`reactive deposit and then said regulating the admission
`circuit having a relatively short time constant
`of said reaction gas is accomplished by time-scheduling
`which represents the time lag between the mea
`the flow of the reaction gas and steadily increasing it
`surement of the intensity and the admission of the
`during a given adjustment time until the flow of the
`gas,
`reaction gas is approximately the flow which will pro
`a second control circuit comprising a second sensor
`duce said pre-established property of the finished coat
`which automatically senses a property of the fin
`ished coating after the substrate leaves the coating
`1ng.
`6. Process according to claim 5, characterized in that
`zone, a second amplifier connected to said second
`an actual value of the intensity signal is obtained at the
`sens