DE2203080A1 - Method for producing a layer with a certain thickness on a substrate - Google Patents

Description

Böblingen, January 5, 1972 bm / we

Applicant: International Business Machines Corporation, Armonk, N.Y. 10504 Official File number: New registration Applicant's file number: Docket YO 970 084

Method of making a layer
with a certain thickness on a pad

The invention relates to a method for producing a layer with a certain thickness on a substrate.

Thin layers, for example made of oxides, nitrides or sulfides, are produced in particular in connection with semiconductor components. For example, you need devices with Josephson junctions very thin layers of less than 50 8 thickness as tunnel barriers between two superconducting electrodes. Usually the base electrode is oxidized to form the barrier layer. Another component that the manufacture of a very requires a thin, insulating layer is the field effect transistor. Such layers are usually created by the reaction of the material of the base obtained with another, mostly gaseous material. A typical example is manufacturing an oxide layer through oxidation of the substrate on its surface.

In the repeated formation of such thin layers, it is important to that all layers have the same thickness. For example, the tunnel current changes exponentially in Josephson arrangements with the thickness of the tunnel barrier, so that already very small Changes in the barrier layer thickness between the individual

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Orders pose serious problems when several of these arrangements with the same electrical properties are required.

Another difficulty in producing thin layers is the appearance of impurities. Often the document on which the layer is to be formed, placed in the glow discharge between a cathode and an anode. Here finds However, a certain atomization of the cathode material takes place, which, in spite of a shield, is then often deposited on the substrate and thus contaminates the layer. It is still very much important that the layer is even. Fine pores and impurities, for example in insulating layers, can contribute cause short circuits during later use. It is therefore with the known method for the production of thin layers of It is very important that the equipment used is as clean as possible.

These methods also have no way of precisely controlling the thickness of the layer formed. Usually the The growth process ended after a certain period of time, it being assumed that the layer was about a certain time during this time Has reached thickness. Especially with very thin layers, e.g. B. with a thickness of less than 50 8, but can significant deviations from the intended thickness occur. In the case of oxidation, for example, due to the undesired presence additional oxygen ions are released by water vapor, so that the oxide layer is thicker than intended. In addition, the quality of this layer is reduced.

It is therefore the object of the present invention to provide a method for producing a layer in which the thickness of the finished layer is independent of the duration of the process. Repeated formation of layers should also always result in the same layer thickness. Furthermore, the layers should have a high

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Be of quality, regardless of the degree of pollution of the environment. These objects are achieved in the method according to the invention for producing a layer with a certain thickness on a base in that a removal process for the layer is carried out simultaneously with a growth process, a speed dependent on the thickness of the layer being selected for at least one of these two processes will. The growth is preferably carried out by converting the material of the base. For this purpose, a base made of a metal, an oxide or a semiconductor is advantageously used, the conversion taking place through the action of oxygen, nitrogen, hydrogen, sulfur, HS and / or CH ₄ . The growth process and the removal process are preferably dependent on the thickness of the layer. To reduce the thickness of a layer, the removal rate is selected to be greater than the growth rate at the beginning. The removal is advantageously carried out by cathode sputtering.

The base can consist of any material, for example a semiconductor or a metal. A responsive one Agent is brought into contact with the substrate so that the desired layer is formed. Such layers consist of Oxides, nitrides, sulphides, etc. While the layer is being grown, a process takes place at the same time that causes the layer to grow is partially removed again. After a certain period of time, a state of equilibrium develops in which the growth rate is equal to the removal rate. The thickness of the layer no longer changes. She is after reaching of the state of equilibrium independent of the process time.

In the special case of the formation of an oxide layer, a high-frequency discharge can occur can be used with low energy in oxygen for oxidation. The pad is attached to the cathode of the discharge path attached, so that at the same time as the oxidation there is also a certain amount of atomization on the surface of the base

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occurs. If the oxidation rate is higher than the atomization rate at the beginning, then an oxide layer forms. However, the rate of oxide formation decreases with increasing oxide thickness, as this is a process determined by diffusion is. The speed of atomization, on the other hand, is independent of the thickness of the bombarded oxide. So if at a certain Oxide thickness, the growth rate has fallen to the value of the removal rate, then the equilibrium is established one in which the thickness of the oxide is kept at a constant value.

Conversely, if an oxide layer with a certain thickness is already present and the initial rate of atomization is higher than that of growth, then the oxide thickness decreases to to a value at which equilibrium is reached. By specifying the two speeds, the oxide layer can can be removed to a predetermined thickness.

Another possibility is to apply an oxide layer by a suitable means, such as. B. hydrogen to reduce. the Glow discharge then takes place in hydrogen. The thickness of the reduced layer is also determined by the ratio of reduction and removal rate determined. For example, a base made of lead oxide can be reduced by bombarding it with hydrogen ions so that a layer of lead with a predetermined thickness is formed on the lead oxide.

Cathode sputtering with simultaneous growth is special suitable for the production of very thin layers with constant thickness. Layers less than 100 8 thick can can be readily produced, with the following parameters having to be set in a corresponding manner: (1) the temperature the substrate, (2) the radio frequency energy, (3) the pressure of the reactive gases, (4) the composition of the gases in the Atomization chamber. Some of these parameters influence the

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carrying process stronger, while the other have a greater effect to own the waxing process. Other factors, such as the level of contamination, have no effect on the formation of the Layer.

The substrates to be coated are preferably on the cathode attached. A glow discharge is then ignited between the anode and cathode. The gases that react with the substrate are introduced into the atomization chamber, the discharge being maintained by the applied high-frequency voltage will. The growth and the removal process now take place at the same time, with one being dependent on the individual parameters certain thickness of the newly formed layer of equilibrium adjusts. Since the pads are arranged directly on the cathode, no sputtered cathode material is deposited on them from what, however, would have been the case if the documents had been placed in the discharge space between anode and cathode. In addition, layers with a non-uniform thickness could then form, as there would also be a certain amount of atomization between the substrate and the cathode could occur. These difficulties are avoided if the pads are attached directly to the cathode are. The discharge between the anode and cathode is not disturbed either. This makes the process easier to control, and the For this reason, layers obtained in this way also have greater uniformity.

With the present method, layers can still be used changing composition are created by the fact that the gas composition is changed in the chamber during the manufacture of the layers.

Another advantage of the method is that special measures for cleaning the chamber are not required. at In the known methods, before the deposition on the substrate, a discharge of longer duration takes place through which the chamber is cleaned. Because the layer material is removed

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and is formed anew at the same time, all impurities originally contained therein are removed. One thus obtains Layers that have been freed of impurities to the greatest possible extent and therefore of high quality. Even if the layer becomes thicker than intended as a result of contamination, then it will open again due to the equilibrium leveling off brought back the desired thickness.

Although a DC voltage discharge is possible, a high frequency feed discharge is preferred. The discharge can sustained with high frequency at lower pressures. This makes it easier to adhere to the layer formed Remove particles before applying a subsequent layer. Is z. B. an oxide layer on a metallic base produced, and if another metal layer is to be applied as a counter electrode, then it is easier to apply the To remove oxygen atoms adhering to the oxide layer when the glow discharge is operated with high frequency instead of direct voltage will.

Although the procedure is carried out with the help of a sputtering chamber appears particularly advantageous, the growth and the removal process can also be carried out in other ways will. For example, these two operations can be carried out with separate apparatus. For example, an ion beam can be used to remove the growing layer. Another combination of waxing and erosion is the anodic Precipitation on a surface in a liquid, through which this precipitate is partially dissolved again. It is thus it is evident that the growth and removal are separate processes that can be set independently of one another and that do the same thing or old different equipment. The growth and removal speeds can be changed at any time during the formation of the layer or can be changed or adjusted beforehand in any way, so that the equilibrium

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- 7 level is set at a desired layer thickness.

The invention is illustrated below with reference to in the figures Embodiments explained in more detail.

Ee show:

Fig. 1 shows a high-frequency atomization system in which the

claimed processes can be carried out,

2A shows the thickness χ of a grown by oxidation Shift as a function of time,

2B shows the thickness χ of one subjected to a sputtering process Shift as a function of time,

Figure 2C shows the rate of oxidation and atomization depending on the time,

3A, 3B, 3C show the production of an oxide layer on a base and

4A, 4B, 4C, the production of a metal layer with a certain Thickness on an oxide pad.

The present method uses the simultaneous occurrence of a growth and a removal process in order to have layers reproducible thickness and good quality on different substrates. This method is advantageous based on the Describes the formation of an oxide layer of a given thickness on a base. It goes without saying that other layers such as nitrides, sulfides, etc. can be produced on an appropriate base. Since the wake-up process and the removal process can be controlled independently of one another, the state of equilibrium can be achieved at any desired thickness will.

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In the special case of the formation of an oxide layer, a discharge with low high-frequency energy takes place in the sputtering chamber in an oxygen atmosphere. The documents are at the Cathode attached and are simultaneously oxidized and atomized. Here the oxidation is responsible for the growth process and the atomization the erosion process. If the rate of oxidation at the beginning is greater than the atomization speed, then. an oxide layer can form on the substrates. The rate of oxidation decreases with increasing oxide thickness, since oxidation is a diffusion-limited process. However, the atomization speed is independent of the thickness of the shot Oxyds. Therefore, the oxide thickness increases until the rate of oxidation reaches the value of the rate of atomization has decreased. From this point on, the oxide thickness remains constant, regardless of the further duration of the process.

Conversely, if there is already an oxide layer on the base is and the atomization speed is higher than the oxidation speed at the beginning, then the oxide layer becomes so far removed until the two speeds have the same value. With applied high-frequency voltage, this means that these two speeds equalize over a full period of tension. This can be done during one half period one of the two speeds dominates, while the other speed is greater in the other half-period. With The process described here produced thin layers of oxide 20 to 50 pounds thick. The desired thickness of the Layers can be adjusted using the parameters of the sputtering system. These include oxygen pressure, high frequency energy, the composition of the atmosphere in the chamber and the temperature of the documents. With these parameters you can the speeds of atomization and oxidation can be controlled independently of one another. In this way each achieve desired thickness.

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doc, “YO 970 084 ₂₀ 9840/1 123 CS

FIG. 1 shows a system with which layers are formed by simultaneous oxidation and atomization can. This atomization system, known per se, has a chamber IO made of glass with an upper and a lower plate HA and HB made of metal. A high frequency cathode 12 is from a Collar 13 held, which isolates it from the plate HA. The cathode 12 is water-cooled and has an inlet line 14 and an outlet line 16. The cathode is connected to a high frequency voltage source connected by a discharge with a

2
Power density of 0.03 to 2 watts / cm is fed.

The cathode is surrounded by a grounded screen 18 which protects it from undesired bombardment. The documents 19 on which Layers are formed with the desired thickness, are arranged in a holding device 20, which is secured by screws 22 to the Cathode 12 is attached. In a typical case, the cathode is made of copper and the retainer is made of aluminum, it can however, other materials can also be used.

The plates HA and HB are grounded and serve as an anode. With the Chamber 10 is connected via a valve 24 to a vacuum system with a pump 25 which supplies the desired vacuum in the chamber 10. Furthermore, via a manually operated valve 26 is a source 27 for the gas that reacts with the documents and possibly other gases are connected to the chamber 10. If desired, the Cathode can also be surrounded by an aluminum ring, which is used to clean the chamber during a previous DC voltage discharge.

In the chamber 10 is also a source 28 for a material that is on the pads 19 or on those formed thereon Layers can be knocked down. Insulating material 30 provides electrical isolation from the lower plate HB. A shield 32, which can be moved by means of a rotary knob 34, is arranged above the source 28, with which a nebulization of the Material of the source 28 can be avoided.

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The documents 19 are preferably initially by means of an atomization process cleaned, for example during a performance

2 - ■?

density of 0.8 watt / cm at an argon pressure of 4 10 Torr. The flow of argon into the chamber 10 is balanced by the pump so that a constant pressure is maintained. The removal of oxide residues or photoresist particles and others Contamination from the surface of the substrates requires atomization times of about 1 to 5 minutes.

Immediately after this cleaning process, the argon is released from the chamber 10 removed and replaced by oxygen or an argon-oxygen mixture. An oxide layer forms on the substrates 19 from, with a high-frequency discharge with an energy density of about 0.03 to 0.1 watt / cm for a period of 10 to Is maintained for 20 minutes. In the example shown, an oxide layer with a thickness of less than 50 8 is produced.

The argon in the gas mixture is ionized during the formation of the layer and used to bombard the substrates. If not If argon is present, only the oxygen itself is used for atomization the oxide layer. In this case it is the atomization speed but less than with the additional presence of argon.

The atomization is the result of bombardment with positives Ions, while oxidation is dependent on the presence of negative oxygen ions. The discharge in oxygen is present in the present Example maintained at a frequency of 13.56 MHz. This causes the usual ion envelope, which is called the dark room is visible near the cathode surface. The potential of the cathode surface changes over time, being negative Has a peak value that almost approaches the highest amplitude of the applied voltage. Atomization occurs when positive Ions from the envelope are attracted to the cathode by the negative potential of the latter. It can be assumed that the negative ions required for oxidation from the plasma

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drawn out or generated at the oxide-gas interlayer by binding electrons. The one by binding the electrons negative bias voltage resulting at the oxide-gas intermediate layer can intensify the oxidation, as this gives an additional driving force for the diffusion of cations through the oxide is.

The rate of oxide formation can be expressed by the following relationship:

dx _β dx dx .. »

dt dt oxidation "dt atomization ^v '

In thermal oxidation the rate of oxidation usually decreases with increasing oxide thickness. For very thin oxide films, there is often a direct logarithmic relationship between the oxide formation and the time. If this logarithmic relationship is assumed for the present example, then the rate of oxidation can be expressed by the expression Ke ~ ^x ' ^x o, where K and χ represent oxidation parameters which depend on such factors as pressure and temperature. In addition, if the atomization speed is expressed by a constant R, then from the relation (1):

«Ke ° - R for χ> O (2)

For the balance between the rate of oxidation and atomization applies dx / dt = O, so that one for the occurring here Value x. receives the following relationship:

x _L = x _o In (K / R) (3)

From this relationship it can be seen that the value x_, which the

Il

Represents the final thickness of the oxide layer, through various process parameters, z. B. the oxygen pressure, the high frequency generator

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- 12 pour or the substrate temperature can be set.

This relationship is consistent with experimental results in which x_ was found to increase with oxygen pressure. This shows that the rate of oxidation increases faster than the rate of atomization with increasing oxygen pressure. The thickness of the oxide layer can be further influenced by the use of an oxygen-argon geroic, which in comparison to pure oxygen the atomization rate increases and the oxidation rate decreases. The speed of atomization continues to increase with high frequency energy due to higher ion density and ion energy. Tests have shown that the atomization rate is more dependent on the high frequency power than the rate of oxidation. Since the Energy of the impacting ions is large compared to the value k · T, where k is the Boltzmann constant and T is the temperature of the If the temperature of the documents increases, there is only a slight change in the atomization speed. However, the oxidation is a diffusion-dependent process and therefore also depends on the temperature of the substrates.

By integrating equation (2) one obtains the dependence of the oxide thickness on the time:

Γκ κ ^x i / ^x o ~ ^{Rt / x} r »~ l χ - x _o ln [J - <| - e * °) e ⁰ J for χ> O (4)

x ^ here means the original thickness of the oxide layer. the

Relationship (4) can be traced back to relationship (3),

—Rt / x
if the expression e 'ο goes against O. It should be noted that the final thickness x _{L is} greater than, equal to or less than the original thickness x. can be. This depends on the ratio of the initial speeds for the oxidation and the atomization.

An effective time constant t = χ / R be won. From the information for thermal oxidation and for oxidation in a direct voltage glow discharge in acidic

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substance, a value in the range from 1.5 to 3.5 8 is obtained for x _Q. The atomization rate is about 0.1 8 / sec for a

Energy density of 0.1 watt / cm for an oxygen pressure in the range of 10 ~ ² Torr. The effective time constant therefore results in a value of around one minute.

The process variables that can be changed to reduce the oxidation and the sputtering process are essentially the temperature of the substrates, the high-frequency power, the Type of gases that react with the documents and their composition the gases in the chamber.

If the temperature of the substrates is changed, then the rate of oxidation is essentially affected while the atomization speed hardly changes. Since the oxidation is limited by the diffusion, means an increase in the Temperature of the base also an increase in the rate of oxidation. Conversely, a lowering of this temperature causes also a reduction in the rate of oxidation.

The atomization speed is essentially dependent on the high-frequency energy. An increase in the voltage on the cathode influences the ionization of the oxygen to a great extent, whereby the atomization rate increases. A possible The influence of the high-frequency energy on the rate of oxidation cannot be ruled out, but this is common to everyone Trap negligible compared to influencing the atomization speed. Since the voltage at the cathode is the energy of the determined by the impacting ions, this is a simple way of doing this to adjust the atomization speed.

The pressure of the gas that reacts with the supports in the discharge space has a direct influence on the oxidation process. When the oxygen pressure is increased in the discharge space, there will be more oxygen ions released per unit of time, so that the rate of oxidation

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increases at constant high frequency energy. However, it is possible that the atomization is also increased, since there are more oxygen ions available. However, since it was found that the thickness of the Layers increases when the pressure of the reactive gas is increased, it is found that the influence on the rate of oxidation is greater than that on the atomization speed.

A change in the composition of the gases in the discharge space can act both on the rate of oxidation and on the rate of atomization and on both at the same time. If z. B. the oxygen content is increased, then also increases the rate of oxidation. If, on the other hand, the proportion of argon is increased, then the speed of atomization also increases.

Figures 2A to 2C show diagrams of the growth of Layer thickness during the oxidation process, the decrease in layer thickness during the atomization process and the rate of oxidation and atomization depending on the time. In FIG. 2A, the thickness of an oxide layer is dependent on the oxidation process represented by time. The thickness approaches a final value with increasing duration, since the oxidation is essentially is a diffusion limited process.

FIG. 2B shows the thickness of a layer as a function of time, which is removed by a sputtering process. The thickness χ here decreases linearly with time. Finally, in FIG. 2C, the rate of oxidation and atomization are for the processes shown in FIGS. 2A and 2B can be seen. The rate of oxidation decreases exponentially with time, however, after a certain time a constant value is established. The atomization speed is constant because the Removal takes place linearly with time. At the point in time T, the two curves intersect, i.e. that is, at this point is the rate of oxidation equal to the atomization speed. the

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The thickness of the layer produced has thus reached its final value. The point in time T is therefore dependent on the desired layer thickness.

FIGS. 3A to 3C show the formation of an oxide layer according to the present method. In Figure 3A, a base with the height h at time T. is shown. This base is placed in a chamber according to FIG. 1, in which the oxidation and atomization processes take place. An oxide layer with the final thickness x _L , which is reached after time T ₂ , is thus formed on the surface of the substrate. As a result of the expansion during the oxidation process, the arrangement now has a height h + L ·. The arrangement remains in the atomization chamber, the oxidation and atomization speeds being equal to one another. At a later point in time T ₃ , the oxide layer continues to have the thickness x _L , while the total thickness of the arrangement is now less than h.

The reduction of an oxide substrate according to the present method can be seen from FIGS. 4A to 4C. An oxide layer with the height h shown at time T. in FIG. 4A is assumed. Part of this oxide layer should be reduced. FIG. 4B shows the arrangement at time T ₂ after the reduction. A metal layer with the thickness x ~ has formed on the oxide. Lead oxide, for example, can be used as the oxide, so that the metal layer obtained by reduction consists of lead. To carry out the reduction, the oxide layer according to FIG. 4A is again brought into the sputtering system according to FIG. The gas that reacts with the oxide is hydrogen. Here, too, after some time, that is to say at time T _2, the reduction and sputtering speeds are in equilibrium, so that the metal layer maintains the thickness x _{T achieved} in the further course of the process.

Ju

This state is shown in FIG. 4C, which changes the arrangement to a later Time T represents. Due to the constant reduction and atomization process, the thickness is x. the metal layer remained the same, however, the height of the entire arrangement has fallen below the value h.

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The documents can be made from any material including Metals and semiconductors exist. The layers formed thereon can also be constructed from a variety of materials be, so z. B. from oxides, nitrides, sulfides or semiconductors. If z. B. the pad is made of lead and that reacts with it Gas is H ^ S, then there is a lead sulfide layer of certain thickness. Lead sulfide is a semiconductor material.

The claimed method can be advantageous in semiconductor technology and especially in the manufacture of Josephson arrays be performed. Josephson devices require very thin tunnel barriers of uniform and reproducible thickness. By appropriately setting the process parameters in the process described here, tunnel barriers can be removed from each any thickness can be generated. The same apparatus can also be used to place a counter electrode on the layer formed to raise. For this purpose, z. B. an evaporation source 28 made of lead can be introduced into the chamber 10 according to FIG. as Underlay can be used, for example, a niobium layer of 6000 8 thickness, which is achieved by high-frequency atomization in argon a pressure of 10 ~ Torr and a speed of 400 S / min on a glass substrate, which has a temperature of 670 ° K, is applied will. During this process, the substrate holder is earthed. The niobium layer is used to create the tunnel barrier en arranged on the high-frequency cathode, and the measures described for forming an oxide layer are carried out. A lead counter electrode is then vapor deposited on the tunnel barrier layer thus formed.

As stated earlier, the present process is not limited to metals and the oxidation process. If other gases that react with the pad are used, e.g. B. H ₂ , N, H ₂ S, CH. etc., then corresponding layers form.

Layers of different materials can also be made because the gas reacting with the substrate during

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of the growth and removal process is changed. Leave it Layers of different composition or structure are thus formed if the corresponding process parameters are used in a suitable manner be changed.

A method for producing thin layers has been described, in which a growth and a removal process take place at the same time. At least one of these operations is dependent on the thickness of the layer produced. Through a state of equilibrium that is established during the production of the layer The final thickness of the layer is determined by the rate of growth and removal. The speed of growth and removal can can be adjusted independently of each other so that any desired thickness can be achieved. In the preferred embodiment the growth was achieved by oxidation and the removal by atomization. However, the claimed method is not limited to these two special operations. The layer material can be applied to a base in any way, so z. By vapor deposition, sputtering, plating, etc. The removal can also be carried out by any known process be performed. Examples are treatment with ion or electron beams or cathode sputtering.

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Claims (9)

PATENT CLAIMS 1. Method for producing a layer with a specific color on a base, characterized in that at the same time a removal process for the layer is also carried out with a growth process, with at least one of these two processes, a speed dependent on the thickness of the layer is selected. 2. The method according to claim 1, characterized in that the growth is achieved by converting the material of the base he follows . 3. The method according to claim 2, characterized in that a substrate made of a metal, an oxide or a semiconductor is used, and that the conversion is carried out by the action of oxygen, nitrogen, hydrogen, sulfur, HS and / or CH ₄ . 4. The method according to any one of claims 1 to 3, characterized in that that the growth process is dependent and the removal process is independent of the thickness of the layer. 5. The method according to any one of claims 1 to 4, characterized in that that to reduce the thickness of a layer, the removal rate is selected to be greater than at the beginning the wake-up speed. 6. The method according to any one of claims 1 to 5, characterized in that that the removal takes place by cathode sputtering. 7. The method according to claim 6, characterized in that the substrate is brought to the potential of the cathode. Docket YO 970 084 ₂₀ 98A0 / 1123 8. The method according to claim 6 or 7, characterized in that that in addition to the gas which reacts with the substrate, an inert gas is also brought into the atomizing chamber. 9. The method according to any one of claims 6 to 8, characterized in that that the determination of the speed for the Growing and erosion through a corresponding adjustment of the pressure and the composition of the gases in the sputtering chamber, the temperature of the substrate and / or the applied voltage. Docket YO 970 084 2 0 9 8 A 0/1 1 2 3