Patent Publication Number: US-10332730-B2

Title: Method for balancing consumption of targets in pulsed dual magnetron sputtering (DMS) processes

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. § 120 
     The present application for patent is a Divisional application of patent application Ser. No. 14/333,407 entitled “S YSTEM AND  M ETHOD FOR  B ALANCING  C ONSUMPTION OF  T ARGETS IN  P ULSED  D UAL  M AGNETRON  S PUTTERING  (DMS) P ROCESSES ” filed Jul. 16, 2014, pending, and assigned to the assignee hereof and hereby expressly incorporated by reference herein, which claims priority to U.S. Provisional Application No. 61/847,498, filed on Jul. 17, 2013, entitled System and Method for Balancing Consumption of Targets in Pulsed Dual Magnetron Sputtering (DMS) Processes. 
    
    
     COPYRIGHT 
     A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. 
     FIELD OF THE INVENTION 
     The present invention relates generally to plasma-based sputtering, and more specifically to reactive sputtering. 
     BACKGROUND OF THE INVENTION 
     Reactive sputtering is performed in a magnetron sputtering system. The material sputtered from the magnetron is combined with a reactive gas at the substrate (item being coated) to form a compound at its surface. The reactive gas also reacts with the target surface, forming a compound there. These systems can operate open loop in either the metallic mode, where a small fraction of the target is covered with the compound, or the poisoned mode, where a large fraction of the target is covered with compound. In some cases, the compound has a sputtering yield much lower than the native target material. In fact, the sputtering yield for a target completely covered with reactive compound (poisoned) can be 10% or less that of the native target material. Because of this, it is desirable to run these processes in the transition mode, to achieve a higher deposition rate. The transition mode is typically inherently unstable, so feedback control is usually required to stabilize the process there. Feedback can be, for example, process voltage, reactive gas partial pressure, and optical emission from the target. 
     A common implementation of reactive sputtering is dual magnetron sputtering (DMS) shown in  FIG. 1 . A key advantage is the absence of explicit anodes, and the challenges that come with them. The two magnetrons alternate roles as cathode and anode. When a purpose built bipolar pulsed supply is used to drive the process, the power to each magnetron can be regulated individually. Fast read backs of power, voltage, and current for each magnetron can be provided to the user for use in monitoring and controlling the process. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims. 
     According to one aspect, a sputtering system includes at least one dual magnetron pair comprising a first magnetron and a second magnetron, each magnetron of the dual magnetron pair configured to support target material. The system may also include a DMS component having a DC power source in connection with a plurality of switching components and a plurality of voltage sensors, the DMS component configured to independently control an application of power to each of the magnetrons, and to provide measurements of voltages at each of the magnetrons. The system may also include one or more actuators configured to control the voltages at each of the magnetrons using the measurements provided by the DMS component. The DMS component and the one or more actuators balance the consumption of the target material by controlling the power and the voltage applied to each of the magnetrons in response to the measurements of voltages at each of the magnetrons. 
     According to another aspect, a method for sputtering is disclosed. The method may include arranging at least two magnetrons to form at least one dual magnetron pair and affixing target material to each of the at least two magnetrons. The target material is sputtered on to a substrate and consumption of the target material is balanced by balancing power and voltage that is applied to each of the at least two magnetrons. 
     According to another aspect, a DMS supply having switching components configured to receive DC power and apply pulsed-DC power to each of at least two magnetrons is disclosed. A control portion controls the switching components to balance an application of power to each of the at least two magnetrons, and voltage measurement components provide measurements of voltages at each of the magnetrons to enable actuators to control the application of voltages to the magnetrons. 
     As previously stated, the above-described embodiments and implementations are for illustration purposes only. Numerous other embodiments, implementations, and details of the invention are easily recognized by those of skill in the art from the following descriptions and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following detailed description and to the appended claims when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  illustrates a general arrangement of a sputtering system according to an embodiment; 
         FIG. 2  graphically illustrates a relationship between voltage and reactive gas flow for two magnetrons; 
         FIG. 3  illustrates a relationship between voltage and current over a period of time; 
         FIG. 4  illustrates a schematic of an embodiment of a DMS system; 
         FIG. 5  illustrates a schematic of one embodiment of a DMS component and system interface; 
         FIG. 6  is a block diagram depicting physical components of an exemplary computing device; and 
         FIG. 7  is a flow diagram depicting an exemplary method. 
     
    
    
     DETAILED DESCRIPTION 
     In DMS systems, targets can end up with uneven consumption due to differences in reactive sputtering working point and differences in power delivered to each magnetron of the pair. To overcome this problem, and referring now to  FIG. 1 , the DMS disclosed herein includes a target A  101  having a first metal and target B  102  having a second metal exposed to a first reactive gas  103  and/or a second reactive gas  104 , to cause a reaction leading to a material deposition on a substrate  105 . A power supply  106 , which may be a bipolar pulsed supply, applies alternating power to each of the targets  101 ,  102 . In order to achieve fully balanced target consumption, it has been found that it is beneficial for both targets  101 ,  102  to be at substantially the same working point, and to deliver equal power to each target. As a consequence, in many embodiments, both the working point of the two targets and the power delivered to each of the targets  101 ,  102  is balanced. 
     In a pulsed dual magnetron system, it is possible to control the power delivered to each of the targets  101 ,  102  independently. For many practical reactively sputtered compounds, voltage is an excellent indicator of the fraction of the target surface covered with the reactive compound, and can be used as a feedback signal to control the process. 
     Referring next to  FIG. 2 . It shows the voltage versus reactive gas flow control space of a dual magnetron system. A key point is that each magnetron has its own control curve, and they are different due to inevitable asymmetries in the hardware. As seen in  FIG. 2 , curve  201  relates to a control curve for, for example, a magnetron associated with target A  101 , while control curve  202  relates to a control curve for, for example, another magnetron associated with target B  102 . For a given reactive gas flow, and with identical power delivered to each magnetron, the voltage is different. This indicates a different fraction of the target covered with compound, and a different target material removal rate for each target. 
     The highest performance strategy to match the target material removal rate for each magnetron would match the burning voltage of each magnetron as well as the power to each magnetron. In this case, there are two things to be controlled, so two actuators are required. Power balance can be achieved explicitly by the pulsed power supply. Voltage balance can be achieved by modifying the flow of reactive gas to one magnetron relative to the other by using, for example, a secondary gas manifold and/or means of controlling gas flow (e.g., means for controlling mass flow rate). When rotatable magnetrons are used, it is also possible to move the transition curve to the left by increasing the rotation speed, as shown in  FIG. 2  (see for example,  Reactive Sputter Deposition , Section 5.5.3 on rotating magnetrons, edited by Depla and Mahieu, Springer, 2008). 
     In cases where a second actuator is not available, there are two clear possibilities. The first is to simply balance the power delivered to each magnetron. The second is to match the voltage of the two magnetrons, and accept the power imbalance. This may actually result in the minimum difference in target material removal rate, since it can be such a strong function of voltage. With a fast read back of the power delivered to each magnetron, it is possible to monitor the power imbalance, and predict the mismatch in target consumption. 
     A waveform for driving pulsed DMS arrangements is shown in  FIG. 3 . Here, the waveform interval to be averaged for fast voltage feedback is defined. More specifically, the voltage  301  in the encircled flat line interval  301   a  reflects a quasi-DC burning voltage of the magnetron, and as such is a good indicator of the fraction of the target surface of, for example, target  101 ,  102  covered with the reactive compound, and therefore, the sputtering yield of the target surface. 
     It should also be noted that, as seen in  FIG. 3 , the changes in current are also tracked and controlled. First, a fast current slew rate and higher start up threshold at the beginning of the cycle are desired. This provides an approximation of a current source, which is beneficial for driving magnetron sputtering processes in a quasi-DC mode. 
     Referring next to  FIG. 4 , is a schematic block diagram that illustrates a sputtering system  400  having a plasma sputtering chamber  410  configured to receive DC pulses applied by a DMS component  430  for causing a substrate  420  to receive a compound  422  formed at the surface of the substrate  420 , according to an embodiment. In many implementations, the DMS component  430  is configured to modify DC power pulses (e.g., consistent with  FIG. 3 ) delivered to the magnetrons  452 ,  454  independently to balance an application of power to the magnetrons  452 ,  454 . In addition, the DMS component  430  measures a voltage at each of the magnetrons  452 ,  454  to enable a voltage that is applied to the each of the magnetrons  452 ,  454  to be controlled using one or more actuators (e.g., mass flow controllers  456   a ,  456   b  and rotation controllers  458   a ,  458   b ). By independently controlling the application of power (using the switched power of the DMS component  430 ) and the voltage at each of the magnetrons  452 ,  454  (using one or more of the actuators  456   a ,  456   b ,  458   a ,  458   b ) the consumption of target material on each magnetron may be balanced. Although rotation controllers  458   a ,  458   b  are depicted in this embodiment, this is certainly not required. As discussed above, not all magnetrons are enabled with rotational capability, and the operating voltage of each of the magnetrons  452 ,  454  may be varied by control of reactive gas flow. 
     The DMS component  430  may be realized by a DC power source in connection with switching components to apply power to each of the magnetrons  452 ,  454  as discussed above, and voltage sensors known to those of ordinary skill in the art may be utilized to provide feedback in the control of the actuators. U.S. Pat. No. 5,917,286 entitled Pulsed Direct Current Power Supply Configurations for Generating Plasmas and U.S. patent application No. 20110248633 entitled Methods and Apparatus for Applying Periodic Voltage Using Direct Current, both of which are incorporated herein by reference, disclose exemplary components that may be used, in part, to realize the DMS component  430 . In addition, control logic, which may be realized by hardware, or software in connection with hardware, may be utilized to control the switching components and generate control signals based upon the feedback from voltage sensors. 
     In some variations of the embodiment depicted in  FIG. 4 , the DMS component  430  may provide control signals  460   a - d  to control the actuators  456   a ,  456   b ,  458   a ,  458   b . But in other embodiments the DMS component  430  provides one or more outputs  462  that include voltage measurement information that may be used by an external controller to generate the control signals  460   a - d.    
     As discussed above, voltage balance can be achieved by modifying the flow of reactive gas  456   a ,  456   b  to one magnetron relative to the other, by using secondary gas manifolds and gas flow control means (known to those of ordinary skill in the art) of controlling gas flow. And when rotatable magnetrons are used, it is also possible to move the transition curve to the left by increasing the rotation speed, as shown in  FIG. 2 . 
     Turning now to  FIG. 5 , shown are components that may be utilized to realize the DMS component  430 . As shown, a controller  501  is operatively coupled to a power source  502  with a control signal  506  and a plurality of switching components  503  with switching control signals  504 . The controller  501  in this embodiment generates the switching control signals  504  to operate the switching components  503  (which may be implemented in an H-bridge configuration). The controller also provides mass flow control signals  460   a ,  460   b  (to control the mass flow controllers  456   a ,  456   b ) and rotation control signals  460   c ,  460   d  (to control the rotation controllers  458   a ,  458   b ). As shown, the controller  501  receives feedback from at least one current transducer  507  and voltage pickups  508  to receive an indication of the current and voltage at the electrodes or magnetrons  452 ,  454 . The signals  504 ,  460   a ,  460   b ,  460   c ,  460   d ,  506  are generated in response to the feedback from the sensed current and sensed voltage. In some embodiments, the switching components  503  may be configured and controlled as disclosed in U.S. patent application Ser. No. 13/104,942 or U.S. Pat. No. 8,391,025, the disclosures of which are incorporated herein by reference. 
     Referring now to  FIG. 3  alongside  FIG. 5 , the controller  501  generates signals  504 ,  506  that, taken together, control the voltage  301  and current  302  applied, and the average voltage read back over the interval  301   a  between an end boost and a turn-off represents a quasi-DC burning voltage. As discussed, the interval  301   a , as well as the voltage  301  and current  302  may be controlled to balance the consumption of target material. 
     The controller  501  may be implemented or performed in part with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in processor executable instructions encoded in non-transitory processor readable medium, or in a combination of the two. A software module (including non-transitory processor executable instructions) may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
     Referring next to  FIG. 6 , shown is a block diagram depicting physical components that may be utilized to realize the controller  501  according to an exemplary embodiment. As shown, in this embodiment a display portion  612  and nonvolatile memory  620  are coupled to a bus  622  that is also coupled to random access memory (“RAM”)  624 , a processing portion (which includes N processing components)  626 , and a transceiver component  628  that includes N transceivers. Although the components depicted in  FIG. 6  represent physical components,  FIG. 6  is not intended to be a detailed hardware diagram; thus many of the components depicted in  FIG. 6  may be realized by common constructs or distributed among additional physical components. Moreover, it is contemplated that other existing and yet-to-be developed physical components and architectures may be utilized to implement the functional components described with reference to  FIG. 6 . 
     This display portion  612  generally operates to provide a user interface for a user, and in several implementations, the display is realized by a touchscreen display. In general, the nonvolatile memory  620  is non-transitory memory that functions to store (e.g., persistently store) data and processor executable code (including executable code that is associated with effectuating the methods described herein). In some embodiments for example, the nonvolatile memory  620  includes bootloader code, operating system code, file system code, and non-transitory processor-executable code to facilitate the execution of a method described with reference to  FIG. 7  described further herein. 
     In many implementations, the nonvolatile memory  620  is realized by flash memory (e.g., NAND or ONENAND memory), but it is contemplated that other memory types may be utilized as well. Although it may be possible to execute the code from the nonvolatile memory  620 , the executable code in the nonvolatile memory  620  is typically loaded into RAM  624  and executed by one or more of the N processing components in the processing portion  626 . 
     The N processing components in connection with RAM  624  generally operate to execute the instructions stored in nonvolatile memory  620  to effectuate a balanced consumption of target material. For example, non-transitory processor-executable instructions to effectuate the methods described with reference to  FIGS. 1 through 4 and 6  may be persistently stored in nonvolatile memory  620  and executed by the N processing components in connection with RAM  624 . As one of ordinarily skill in the art will appreciate, the processing portion  626  may include a video processor, digital signal processor (DSP), graphics processing unit (GPU), and other processing components. 
     The input component operates to receive signals that are indicative of the consumption of a first target material and a second target material, which may include measurements of voltages at each magnetron in a dual magnetron system. The input component may also receive signals (e.g., from the current transducers  107 ) that are indicative of the current provided to the magnetrons  452 ,  454 . And the output component may operate to provide the signals  460   a ,  460   b ,  460   c ,  460   d ,  504 ,  506  as discussed above. 
     The depicted transceiver component  628  includes N transceiver chains, which may be used for communicating with external devices via wireless networks. Each of the N transceiver chains may represent a transceiver associated with a particular communication scheme. 
     Turning now to  FIG. 7 , a method  700  according to one embodiment is described. The method  700  includes arranging  702  at least two magnetrons to form at least one dual magnetron pair, affixing  704  target material to each of the at least two magnetrons, sputtering  706  the target material on to a substrate, and balancing  708  consumption of the target material by balancing both the power and voltage that are applied to each of the at least two magnetrons. The method  700  may be achieved using the embodiments described herein with reference to  FIGS. 1-6 . The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.