Patent Application
20130017315
Embodiments of the present invention generally relate to substrate processing systems, and methods of controlling power distribution therein.
Toroidal source plasma reactors may be utilized to generate high density plasmas for etching or doping applications. In some conventional designs, two independent toroidal plasma sources may be used, for example, for plasma doping processes. Such designs utilize two frequency tuning radio frequency (RF) generators, one for each toroidal path of the reactor. Each RF generator is used without any impedance matching network. However, although such designs do provide certain benefits, for example, offering a large grounded surface area for high bias to develop on a substrate being processed, the inventors have discovered certain drawbacks of these designs.
Thus, the inventors have provided improved methods and apparatus for controlling power distribution in toroidal source plasma reactors.
Methods and apparatus for controlling power distribution in a substrate processing system are provided herein. In some embodiments, an apparatus includes a substrate processing system including a process chamber having a substrate support disposed in the process chamber and a processing region disposed above the substrate support; a first conduit disposed above the processing region to provide a portion of a first toroidal path that extends through the first conduit and across the processing region; a second conduit disposed above the processing region to provide a portion of a second toroidal path that extends through the second conduit and across the processing region; an RF generator coupled to the first and second conduits to provide RF energy having a first frequency to each of the first and second conduits; an impedance matching network disposed between the RF generator and the first and second conduits; and a power divider to control the amount of RF energy provided to the first and second conduits from the RF generator.
In some embodiments, a method of controlling power distribution in a substrate processing system having an RF energy source coupled to a pair of electrodes via a power divider that controls the amount of RF current respectively provided to each electrode includes adjusting a position of a variable element of the power divider based on a pre-determined relationship between the position of the variable element and a current ratio to divide the magnitude of a current provided by an RF energy source between a first and a second toroidal path; measuring a first magnitude of a first current provided to the first toroidal path and a first magnitude of a second current provided to the second toroidal path; and adjusting the position of the variable element from a first position to a second position if the difference between a first value of the current ratio and a desired value of the current ratio is not within a desired tolerance level, wherein the first value of the current ratio is determined from the measured first magnitudes of the first and second currents.
In some embodiments, a computer readable medium is provided having instruction stored thereon that, when executed by a processor, cause a process chamber to perform a method of controlling power distribution in a substrate processing system having an RF energy source coupled to a pair of electrodes via a power divider that controls the amount of RF current respectively provided to each electrode. In some embodiments, the method may be any of the methods described herein.
Other and further embodiments of the present invention are described below.
Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
Methods and apparatus for controlling power distribution in a substrate processing system are disclosed herein. The inventive methods and apparatus may advantageously reduce particle and/or metal contamination from plasma sources by improving power delivery to a plurality of conduits in a toroidal source plasma reactor. For example, embodiments of the inventive apparatus may reduce instabilities a plasma generated in the reactor by better matching power delivery to each of the plurality of conduits. Embodiments of the present inventive methods may advantageously allow an operator to input a desired value for a current ratio used to distribute power between each of the plurality of conduits based on a pre-determined relationship between a position of a variable element in the power divider and the current ratio.
Referring to
A pair of external reentrant conduits, a first conduit 126 and a second conduit 128, establish reentrant toroidal paths for plasma currents passing through the processing region, the toroidal paths intersecting in the processing region 124. For example, the first conduit 126 may be disposed above the processing region 124 to provide a portion of a first toroidal path 127 that extends through the first conduit 126 and across the processing region 124. Similarly, the second conduit 126 (shown in cross sectional view in
In some embodiments, as illustrated in a top down view in
Returning to
Each of the one or more conductive coils 136 is coupled to an RF energy source 138. The RF energy source 138 provides RF energy to each of the first and second conduits 126, 128 and further controls a power distribution of the RF energy provided to each of the first and second conduits 126, 128. For example, the RF energy source 138 may include an RF generator 140, an impedance matching network 141 disposed between the RF generator 140 and the first and second conduits 126, 128, and a power divider 143 disposed between the impedance matching network 141 and the first and second conduits 126, 128 to control the amount of power provided to the first and second conduits 126, 128.
In some embodiments, the RF generator 140 may provide between about 100 to about 3000 watts of RF energy at a frequency of about 400 kHz to about 14 MHz to the first and second conduits 126, 128. The RF energy coupled from the RF energy source 138 produces plasma ion currents in the first and second toroidal paths 127, 129 extending through the respective first and second conduits 126, 128 and through the processing region 124. These ion currents oscillate at the frequency provided by the RF generator 140. In some embodiments, bias power may be applied to the substrate support 108 by a bias power generator 142 through an impedance matching network 144.
The impedance matching network 141 facilitates a large tuning space that covers the special impedance of the toroidal plasmas. The large tuning range ensures maximum power coupling with minimum reflected power, thereby advantageously providing a stable plasma that may reduce particle and metal contamination from the plasma sources as compared to conventional toroidal reactors. Moreover, the improved power coupling provided by embodiments of the present invention may also facilitate widening the process window or operating range of the apparatus as compared to conventional toroidal reactors.
The power divider 143 may be coupled between the impedance matching network 141 and the first and second conduits 126, 128. Alternatively, the power divider 143 may be a part of the impedance matching network 141, in which case the impedance matching network 141 will have two outputs—one corresponding to each conduit 126, 128. The power divider 143 may include a variable element 145 to divide a magnitude of current provided by the RF energy source 138 between the first and second conduits 126, 128. For example, in some embodiments, the variable element 145 may be an adjustable capacitor.
The power divider 143 (or the impedance matching network 141, when the power divider 143 is a part of the impedance matching network) is designed to provide a configurable current ratio between two outputs to the respective toroidal plasma. In some embodiments, the power divider 143 (or the impedance matching network 141, when the power divider 143 is a part of the impedance matching network) is designed to tune to the configurable current ratio. For example, a current sensor (not shown) may be provided for each output that measures the current. The values sensed by the sensors are provided to a controller, such as a controller in the impedance matching network 141, the controller 154 discussed below, or some other similar controller. The controller calculates the actual current ratio and compares the actual ratio to the desired ratio (for example, a setpoint from the recipe on the tool). The controller may then adjust the power divider 143 to match the measurement (the actual current ratio) to the setpoint (the desired current ratio). In some embodiments, the tuning may be continuously performed to make sure that both the impedance tuning requirement (minimum reflected power) and the current ratio tuning requirement are met at the same time. The current ratio may be predetermined, for example, by a tool operator while developing a particular process recipe. The range of the current ratio may be sufficiently large to allow tuning of the uniformity of the plasma above a substrate disposed on the substrate support (e.g., downstream of the two toroidal plasmas in the respective first and second conduits). In some embodiments, a power meter (not shown), such as Z'Scan®, commercially available from Advanced Energy, can be incorporated to measure other RF parameters, such as voltage, phase angle, and the like, thereby facilitating calculation of the net power applied.
Plasma formation and subsequent processes, such as etching, doping, or layer formation may be performed by introducing the process gases into the chamber 124 through the gas distribution plate 112 and applying sufficient source power from the RF energy source 138 to the first and second conduits 126, 128 to create toroidal plasma currents in the conduits and in the processing region 124. The plasma flux proximate the substrate surface is determined by the substrate bias voltage applied by the RF bias power generator 142. The plasma rate or flux (number of ions sampling the substrate surface per square cm per second) is determined by the plasma density, which is controlled by the level of RF energy applied by the RF energy source 138. The cumulative ion dose (ions/square cm) at the substrate 110 is determined by both the flux and the total time over which the flux is maintained. For example, by adjusting the variable element 145, the plasma density along each of the first and second toroidal paths 127, 129 may be changed.
If the substrate support 108 is an electrostatic chuck, then a buried electrode 146 is provided within an insulating plate 148 of the substrate support, and the buried electrode 146 is coupled to the bias power generator 142 through the impedance match circuit 144. A DC chucking supply 150 may also be coupled to the buried electrode 146, or to another electrode disposed in the substrate support 108 to provide a DC chucking voltage for retaining a substrate on the substrate support 108.
In operation, a process, such as etching, doping, or layer formation on the substrate 110 can be achieved by placing the substrate 110 on the substrate support 108, introducing one or more process gases into the chamber 102 and striking a plasma from the process gases. The substrate bias voltage delivered by the RF bias power generator 142 can be adjusted to control the flux of ions to the substrate surface.
A controller 154 comprises a central processing unit (CPU) 156, a memory 158, and support circuits 160 for the CPU 156 and facilitates control of the components of the chamber 102 and, as such, of the etch process, as discussed below in further detail. To facilitate control of the process chamber 102, for example as described below, the controller 154 may be one of any form of general-purpose computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory 158, or computer-readable medium, of the CPU 156 may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits 160 are coupled to the CPU 156 for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. The inventive methods described herein may be stored in the memory 158 as a software routine. The software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU 156.
The method begins at 302 by adjusting a position of the variable element 145 of the power divider 143 based on a pre-determined relationship between the position of the variable element 145 and a current ratio to divide the magnitude of a current provided by the RF energy source 138 between the first and the second toroidal path 127, 129. For example, an operator may provide a desired value of the current ratio as an input and the position of the variable element 145 may be automatically adjusted to provide the desired value of the current ratio based on the pre-determined relationship. For example, the pre-determined relationship may be determined from a calibration procedure or the like, preformed at startup of the reactor 100 or at any desired time, such as when the reactor 100 is serviced or the like. In some embodiments, use of predetermined tuning element values may facilitate speeding up the tuning process. The number of different presets can be predetermined for various applications which may have different operational parameters, such as chamber pressure, gas flow, gas compositions, power levels, and the like.
At 304, a first magnitude of a first current provided to the first toroidal path 127 and a first magnitude of a second current provided to the second toroidal path 129 is measured. The magnitudes of the first and second currents may be obtained as discussed above. If the difference between a first value of the current ratio and the desired value of the current ratio is within a desired tolerance level, then the reactor 100 may be suitable for operation at the desired value of the current ratio. The first value of the current ratio may be determined from the measured first magnitudes of the first and second currents. However, if the difference between the first value and the desired value is not with the desired tolerance level, the method may proceed to 306.
At 306, the position of the variable element 145 may be adjusted from a first position to a second position if the difference between the first value of the current ratio and the desired value of the current ratio is not within the desired tolerance level. For example, a control method for adjusting the variable element may be any suitable control method, such as proportional-integral-derivative (PID) control or the like. For example, after an adjustment is made to the second position, a second magnitude of the first current and a second magnitude of the second current may be measured when the variable element 145 is set in the second position. If the difference between a second value of the current ratio—determined from the measured second magnitudes of the first and second currents—and the desired current ratio is not within the desired tolerance level, the position of the variable element may be adjusted from the second position to a third position, and further to as many successive positions as necessary to reach the desired value within the desired tolerance level. In some embodiments, the desired value of the current ratio is about 1 (e.g., the apparatus may be controlled to provide the same RF current to each conduit).
Thus, methods and apparatus for controlling power distribution in a substrate processing system are disclosed herein. Embodiments of the inventive methods and apparatus may advantageously reduce particle and/or metal contamination from plasma sources by improving power delivery to a plurality of conduits in a toroidal source plasma reactor. For example, embodiments of the inventive apparatus may reduce instabilities a plasma generated in the reactor by better matching power delivery to each of the plurality of conduits. Embodiments of the inventive methods may advantageously allow an operator to input a desired value for a current ratio used to distribute power between each of the plurality of conduits based on a pre-determined relationship between a position of a variable element in the power divider and the current ratio.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. For example, although discussed above as used in connection with a toroidal plasma chamber, any RF delivery for two separate inductively coupled plasma sources can potentially benefit from embodiments of the methods and apparatus described above.
