WO2020152097A1

WO2020152097A1 - Method for compensating for process fluctuations in a plasma process and closed-loop controller for a power generator for supplying a plasma process

Info

Publication number: WO2020152097A1
Application number: PCT/EP2020/051267
Authority: WO
Inventors: Moritz Heintze; Jan Peter ENGELSTÄDTER; Krzysztof Ruda
Original assignee: TRUMPF Hüttinger GmbH + Co. KG
Priority date: 2019-01-22
Filing date: 2020-01-20
Publication date: 2020-07-30
Also published as: DE102019200761A1

Abstract

The invention relates to a method for compensating for process fluctuations in a plasma process, which process is supplied with power by a power generator (2), comprising the method steps: a. specifying a nominal power P_soll for the plasma process; b. detecting or specifying at least one process variable; c. generating a power P according to the at least one process variable, which power varies within specified limits about P_soll.

Description

Process for compensating process fluctuations of a plasma process and realer for a power generator

Versorauna of a plasma process

The invention relates to a method for compensating for process fluctuations in a plasma process which is supplied with power by a power generator. The invention also relates to a control arrangement for a power generator for supplying a plasma process.

Plasma processes are used, for example, for the treatment of substrates, in particular for the coating of large substrates in a continuous coating system, for example by means of sputtering, in particular magnetron sputtering. The problem of longitudinal inhomogeneities can arise here. The cause can be temporal fluctuations in the process conditions. They can arise, for example, from non-circular tube targets and gaps between the substrates. The continuous substrate movement can lead to local fluctuations in the thickness of the coating in the direction of flow. A power generator in the sense of this invention is an electrical power supply device or power converter device, that is to say a device which can provide direct or alternating voltage for the plasma process. The AC voltage can be at low frequencies up to a few kHz, at medium frequency (MF) from 10 kHz to 1 MHz, at high frequencies (HF) greater than or equal to 1 MHz, in particular also at VHF greater than 30 MHz or in the microwave range. The power generators for supplying a coating process are often equipped with a fast control to a constant output power. Basically, this ensures a constant sputtering rate and layer thickness in a continuous coater. Exceptions can occur if the process conditions, for example the plasma volume and thus the plasma density, the supply or the consumption of reactive gas, fluctuate because the tube magnetrons used are out of round and therefore the magnetic field strength on the target surface fluctuates over time due to the target rotation. Another reason can be the gaps of a few centimeters between the substrates, which affect the gas supply and thus the coverage of the target surface with oxygen or nitrogen.

The object of the following invention is therefore to provide a method with which fluctuations in the sputter rate are compensated for, i.e. can be compensated.

This object is achieved according to the invention by a method for compensating for process fluctuations in a plasma process which is supplied with power by a power generator, with the method steps: a. Specification of a target power P _S oii for the plasma process; b. Capturing or specifying at least one process variable; c. Generate a power P, in particular within predetermined limits, around P _SO II

depending on the at least one process variable. According to the invention it is accordingly provided that the usually constant output power is modulated or varied around a desired value in order to thereby keep the coating rate constant. This should compensate for fluctuations in layer thickness. In particular, in order to compensate for fluctuations in the sputter rate, the output power can be varied around the actual target value, in particular to a limited extent, by means of a suitable additional control loop.

Compensation can in particular mean keeping the coating rate on a substrate constant within predetermined limits. Compensation can also mean, in particular, that the ablation rate in the plasma process is kept constant over time within specified limits.

The step c. generated power P can be 0.9 x P _SO II <P <l, lx Psoii, in particular 0.95 x Psoii <P <1.05 x P _SO M, preferably 0.98 x P _SO M <P <1 , 02 x P _SO II.

The step c. can be carried out for a predetermined period of time and then the power P can be regulated to P _so n. The maximum deviation of the output power from the setpoint, ie from P _SO II, can be freely selected using suitable parameters.

A control gain and / or a control speed for step c. can be given or set before. In particular, the control speed can be lower than the control speed for P _SO II. This is particularly so because the disturbance variables change relatively slowly. Since the relationship between the output power, plasma impedance and sputter rate differs depending on whether the cause is the target rotation or gaps between the substrates, the invention can be carried out so that between these two and further causes of process fluctuations can be distinguished. The regulation can compensate for these different causes independently of one another. The different disturbance variables can therefore be included in the modulation of the output power.

The step c. can be carried out when a predetermined event occurs. For example, the modulation, ie the variation of the power P by P _SO II, can be carried out when a predetermined process variable exceeds or falls below a predetermined threshold value. Other typical predetermined events can be temporal fluctuations in the process conditions, for example caused by non-round tube targets and / or gaps between the substrates.

In one embodiment of the method, a target power difference APsoii can be determined depending on the process variable and / or the predetermined event.

In a further embodiment of the method, the target power difference APsoii can be added to or subtracted from the target power P _SO II and a changed target power P _SO II ± AP _SO II can be determined.

In a further embodiment of the method, the power for the power generator can be regulated with the changed target power P _S oii ± APsoii.

The plasma impedance, an output current of the power generator, an output voltage of the power generator, the rotational speed of a target, the rotational position of a target and / or the distance from adjacent substrates to be coated can be recorded as a process variable. It is particularly preferred if the rotational position of a target or the plasma impedance are recorded. A particularly reliable parameter for detecting changes in process conditions is the detection of the plasma impedance. Alternatively or additionally, it can be provided that the process speed is the rotation speed of the target, the rotation position of the target and / or the distance between adjacent substrates. There are particular advantages of the method if the plasma process is carried out in a continuous coating system, since changes in the sputtering rate occur particularly often in such systems.

In a learning phase, a performance profile can be created from recorded and / or predetermined process variables, which for step c. is taken into account. In particular, in a learning phase, a controller can recognize the target speed or the frequency (time sequence) of substrates and thus the distance between adjacent substrates from the time profile of the output current and output voltage and can drive an optimal performance profile in order to optimally influence the influence of these disturbance variables on the coating rate balance.

The scope of the invention also includes a control arrangement for a power generator for supplying a plasma process with an input for specifying a target power P _SO II, an input for a process variable and an output for outputting a manipulated variable, the control arrangement being set up is to generate the manipulated variable as a function of the process variable in such a way that the power generator generates a power which varies by the target power P _SO II. By means of such a control arrangement, the power can be varied, ie modulated, by a desired variable, so that fluctuations in the coating rate or the sputtering rate can be compensated for and this can in particular be kept constant. In particular, a modulation of the power of a control can be superimposed on the target power by the control arrangement. The power varying around the target power Psoii can be generated in particular within predetermined limits.

The control arrangement can be set up to generate the manipulated variable in a predetermined operating state such that the setpoint power is generated by the power generator. In one configuration, the control arrangement can have a compensation device. A compensation device can be an electronic circuit with one or more inputs for electrical signals and at least one output for an electrical signal. The electronic circuit can be set up to perform the functions described below. A compensation device can also be a software component stored on a program memory, which is set up to generate at least one output variable from one or more input variables during operation and to carry out the functions described below.

In one configuration, the compensation device can be set up to determine a target power difference APsoii during operation as a function of the detected process variable.

In one configuration, the compensation device can have an input for an event variable, and the compensation device can be set up to determine the desired power difference APsoii during operation as a function of the event variable. An event variable can be influenced if a specified process variable exceeds or falls below a specified threshold value. Other typical predefined events that lead to a change in the event variable can be temporal fluctuations in the process conditions, for example caused by non-circular tube targets and / or gaps between the substrates.

In one configuration, the control arrangement can have an adder which is set up to add or subtract the setpoint power difference APsoii from the setpoint power P _SO II during operation and thus to determine a changed setpoint power P _SO II ± APSoii. An adder can be an electronic circuit with multiple inputs of electrical signals and at least one output for an electronic signal. The electronic circuit can be set up to add or subtract the signals at its input using a calculation method, in particular and the result of the calculation as electrical Output signal at its output. An adder can also be a software component stored on a program memory, which is set up to generate at least one output variable during operation from one or more input variables. The output variable can be the result of a calculation, for example an addition or subtraction.

In a further embodiment, the control arrangement can have a comparator and a controller connected to the comparator, and the changed desired power P _SOM ± APSoii and a measured actual power P _is fed to the comparator, so that the controller operates during operation The changed setpoint power P _SO II ± APSoii generates controlled manipulated variable for controlling the power generator. A comparator can be an electronic circuit with multiple inputs for electrical signals and at least one output for an electrical signal. The electronic circuit can be set up to compare the signals at its input using a predetermined method, in particular addition or subtraction, and to output the result of the calculation as an electrical signal at its output. A comparator can also be a software component stored in a program memory. The software component can be set up to generate at least one output variable during operation from one or more input variables. The output variable can be the result of a calculation, for example an addition or subtraction. A controller can be an electronic circuit with at least one input for an electrical signal and at least one output for an electrical signal. The electronic circuit can be configured, depending on the signal at its input, to output an electrical signal at its output by means of a predetermined control method, which can serve as a manipulated variable for subsequent devices. A controller can also be a software component stored on a program memory. The software component can be set up to generate at least one output variable during operation from at least one input variable. The output variable can be the result of a control method and can be used to control a subsequent device with a manipulated variable. The output power of the power generator can be controlled by the control arrangement, especially if no compensation of the coating rate is necessary. A computer program product for compensating for process fluctuations in a plasma process also falls within the scope of the invention, the computer program product comprising at least one non-volatile computer-readable storage medium with program code stored thereon, the program code comprising:

a program code for receiving a target power P _SO II;

a program code for receiving at least one process variable; a program code for determining a power P which varies within predetermined limits by the target power P _SO II as a function of the at least one process variable.

In addition, the use of the method according to the invention, the control arrangement according to the invention or the computer program product according to the invention for coating substrates with a constant coating rate in the event of process fluctuations falls within the scope of the invention.

Further features and advantages of the invention result from the following detailed description of an embodiment of the invention, with reference to the figures of the drawing, which shows details essential to the invention, and from the claims. The features shown there are not necessarily to be understood to scale and are presented in such a way that the special features according to the invention can be made clearly visible. The various features can each be implemented individually or in groups in any combination in variants of the invention. In the schematic drawing, an embodiment of the invention is Darge and explained in more detail in the following description.

Show it :

Fig. 1 is a schematic representation of a controller according to the invention;

Fig. 2 is a flowchart to illustrate the method according to the invention;

3a shows a diagram with the exemplary course of the power and impedance according to the prior art;

3b shows a diagram with the exemplary course of the current and the voltage according to the prior art;

4a shows a diagram with the exemplary course of the power and impedance according to the invention; Fig. 4b is a diagram with the exemplary course of the current and the voltage according to the invention.

FIG. 1 shows a control arrangement 1 for a power generator 2, which in this case represents a controlled system.

The control arrangement 1 has an input 3 for specifying a target power Psoii, and an input 4 for a process variable. A control variable is output at output 5 and transferred to power generator 2. In a conventional control arrangement 1, the input power Psoii entered at the input 3 is compared in a comparator 6 with an actual variable and a control deviation is thereby generated. The control deviation is fed to a controller 7, for example a PID controller, which then determines a manipulated variable which is output at the output 5 and transferred to the power generator 2. At exit 10 of the Power generator 2 or the controlled system, an actual variable Pj _S t is detected. This is done, for example, by a measuring device 11. The measuring device 11 can be passed, for example, current I (t) and voltage U (t), which are present at the output 10 of the power generator 2 as actual values. The measuring device 11 can be used to determine an actual power P _is t from the actual variables I (t), U (t), which is supplied to the comparator 6.

According to the invention, it is now provided that the measuring device 11 determines a process variable. The process variable can be, for example, the impedance of the plasma. In particular, the current and voltage detected at the output of the power generator 2 can be taken into account to determine the impedance. It is also conceivable that the process device 11 determines another process variable of the plasma process. The process variable can first be fed to a filter 12, for example a bandpass filter. The filter 12 is followed by a compensation device 13, by means of which, depending on the detected process variable, a variable AP _SO II is determined, which is fed to an adder 14. APsoii can have a positive or negative sign. An event variable 15 can be fed to the compensation device 13. Accordingly, if there is no predetermined event, the output of the compensation device 13 can be zero, so that no power varying by the power Psoii is set. If, on the other hand, a predetermined event occurs and the event variable assumes a corresponding value, an APsoii can be generated, which is added to or subtracted from the power Psoii by the adder 14. The output of the adder 14 is then fed to the comparator 6, by means of which a power AP which is different from P _SO II, or, if AP _SO II is not equal to zero, a power AP which differs from the changed desired power P _SO M ± APsoii, and the controller 7 is supplied. The manipulated variable output at the output 5 is therefore generated in such a way that the generator 2 sets a power which varies by the value Psoii or, if APsoii is not equal to zero, a power which varies from the changed target power P _SO II ± APsoii. The method according to the invention is shown schematically in FIG. In step 101, a target power Psoii is specified for a plasma process. In step 101, a process variable is recorded or specified. In step 102, a power P varying by Psoii is generated as a function of the at least one process variable. It can be provided that step 102 is only carried out when a predetermined event has occurred, for example a variation in the layer thickness.

FIG. 3a shows, by way of example, the course of the power (solid line) and impedance (dashed line) in a plasma process, in particular in a coating process, according to the prior art. The power generator controls a constant output power of 10 kW.

In the present example, however, the impedance fluctuates between 9.9 W and 9.945 W. The cause could be non-circular tubular magnetrons. In the case of non-circular Rohrmag netrons, the magnetic field strength on the target surface fluctuates over time due to the target rotation. In the example, the fluctuation takes place with a period of approx. 6 s.

3b shows the curves of current (solid line) and voltage (dotted line) belonging to FIG. 3a. The voltage and current are so out of phase that the power remains constant even though the impedance changes.

4a shows, by way of example, the curve of the power and impedance (plasma impedance) in a plasma process, in particular in a coating process, according to the invention.

Here, too, the plasma impedance changes e.g. with the rotation of the target. The power is tracked here depending on the process variable: 'plasma impedance'. Since the power now changes with the (plasma) impedance, current and voltage now change in phase, as shown in FIG. 4b.

Claims

1. Method for compensating for process fluctuations in a plasma process which is supplied with power by a power generator (2), with the method steps:

a. Specification of a target power P _SO II for the plasma process;

b. Capturing or specifying at least one process variable;

c. Generating a power P which varies, in particular within predetermined limits, by P _SO II as a function of the at least one process variable.

2. The method according to claim 1, characterized in that the power generated in step lc P 0.9x P _SO II <P <l, lx P _SO II in particular 0.95 x P _SO II <P <1.05 x Psoii, preferably 0.98 x P _SO II <P <1.02 x P _SO II.

3. The method according to any one of the preceding claims, characterized in that step lc is carried out for a predetermined period of time and then the power P is regulated to P _SO II.

4. The method according to any one of the preceding claims, characterized in that a control gain and / or a control speed for step l.c. is specified or set.

5. The method according to any one of the preceding claims, characterized in that step l .c. is carried out when a predetermined event occurs.

6. The method according to any one of the preceding claims, characterized in that a target power difference APsoii is determined depending on the process variable and / or the predetermined event.

7. The method according to claim 6, wherein the target power difference APsoii is added to or subtracted from the target power P _SO II and thus a changed target power

± APsoii is determined.

8. The method according to claim 7, wherein the power for the power generator (2) is regulated with the changed target power P _SO II ± APsoii.

9. The method according to any one of the preceding claims, characterized in that the process impedance, the plasma impedance, an output current of the power generator, an output voltage of the power generator, the rotational position of a target, the rotational speed of a target and / or the distance between adjacent substrates to be coated is detected .

10. The method according to any one of the preceding claims, characterized in that the rotational speed of the target, the rotational position of the target and / or the distance between adjacent sub strates is specified as the process variable.

11. The method according to any one of the preceding claims, characterized in that the plasma process is carried out in a continuous coating system.

12. The method according to any one of the preceding claims, characterized in that in a learning phase from detected and / or predetermined

Process variables a performance profile is created, which is taken into account for step lc.

13. control arrangement (1) for a power generator (2) for supplying a plasma process with an input (3) for specifying a target power P _SO II, an input (4) for a process variable and an output (5) for outputting a manipulated variable, The control arrangement (1) is designed to generate the manipulated variable as a function of the process variable in such a way that the power generator (2) generates a power which varies by the target power P _SO II.

14. Control arrangement according to claim 13, characterized in that the power varying by target power P _SO II is generated within predetermined limits.

15. Control arrangement according to one of the preceding claims 13-14, characterized in that the control arrangement (1) is set up, in a predetermined operating state, to generate the manipulated variable in such a way that the setpoint power is generated by the power generator (2).

16. Control arrangement according to one of the preceding claims 13-15, characterized in that the control arrangement (1) has a compensation device (13).

17. Control arrangement according to claim 16, characterized in that the compensation device (13) is set up to determine a target power difference AP _SO II in operation as a function of the detected process variable.

18. Control arrangement according to one of the preceding claims 16-17, characterized in that the compensation device (13) has an input for an event variable (15), and the Kompensationsein direction (13) is set up in operation depending on the event variables ( 15) determine the target power difference AP _SO II.

19. Control arrangement according to one of the preceding claims 16-18, characterized in that the control arrangement (1) an adder (14) which is set up to add or subtract the target power difference APsoii to the target power P _SO II during operation and thus to determine a changed target power P _SO II ± APS ₀ n.

20. Control arrangement according to one of the preceding claims 16-19, characterized in that the control arrangement has a comparator (6) and a controller (7) connected to the comparator (6), and the changed target power P _SO II ± APS ₀ n and a measured actual power Pist is fed to the comparator (6) so that the controller generates a manipulated variable for controlling the power generator (2), which is regulated to the changed target power P _SO II ± APS ₀ n.

21. Power generator (2) with a control arrangement according to one of the preceding claims 13 - 20, wherein the output power of the power generator (2) is regulated by the control arrangement (1).

22. Computer program product for compensating for process fluctuations in a plasma process, the computer program product comprising at least one non-volatile computer-readable storage medium with program code stored thereon, the program code comprising:

a program code for receiving a target power P _SO II;

a program code for receiving at least one process variable;

a program code for determining a power P which varies within predetermined limits by the target power P _SO II as a function of the at least one process variable.

23. Use of the method, the control arrangement (1), the power generator (2) or computer program product according to one of the preceding claims for coating substrates with a constant coating rate in the event of process fluctuations.