Improved plasma uniformity using a higher frequency signal to power an inner coil and a mixed signal of higher and lower frequency signals to power an outer coil

Abstract

A method for generating plasma. The method including providing a plasma chamber configured for generating a plasma through inductive coupling, wherein the plasma chamber includes an electrostatic chuck (ESC) for supporting a substrate and a dielectric window disposed opposite the ESC. The method including supplying a first radio frequency (RE) power signal to an inner coil disposed over the dielectric window, wherein the first RE signal is operating at a first frequency. The method including supplying a mixed RE power signal to an outer coil disposed over the dielectric window, wherein the mixed RE power signal includes a first component delivering a second RE power signal operating at the first frequency and a second component delivering a third RE power signal operating at a second frequency, wherein the first frequency is greater than the second frequency.

Description

IMPROVED PLASMA UNIFORMITY USING A HIGHER FREQUENCY SIGNAL TO POWER AN INNER COIL AND A MIXED SIGNAL OF HIGHER AND LOWER FREQUENCY SIGNALS TO POWER AN OUTER COILTECHNICAL FIELD

[0001] The present embodiments relate to semiconductor fabrication, and more specifically to systems and methods for reducing tilting of ions at an edge of a substrate with improved plasma uniformity by powering one coil-set with a higher frequency signal while powering another coil-set with a mixed RF power signal including a reverse phase higher frequency signal and a lower frequency signal.BACKGROUND OF THE DISCLOSURE

[0002] Many modern semiconductor chip fabrication processes such as plasma etching processes are performed within a plasma processing chamber in which a substrate, e.g., wafer, is supported on an electrostatic chuck (ESC). In plasma etching processes, the wafer is exposed to a plasma generated within a plasma processing volume. Plasma contains various types of radicals, electrons, as well as positive and negative ions. The chemical reactions of the various radicals, electrons, positive ions, and negative ions are used to etch features, surfaces and materials of a wafer.

[0003] For example, when a process gas is supplied into the plasma processing chamber, one or more radio frequency (RF) signals provide power that are applied to one or more coils and electrodes of the plasma processing chamber to form an electric field. The process gas is turned into plasma by the RF signals, thereby performing plasma etching on a predetermined layer disposed on the wafer. Unfortunately, during wafer processing, the plasma non-uniformity arising from plasma generation zones may result in ions striking the wafer with a non-vertical direction (e.g., ion tilt angles) occurring all across the wafer and along the extreme edge of the wafer which may cause tilted etch features in the wafer.

[0004] It is in this context that embodiments of the disclosure arise.SUMMARY

[0005] The present embodiments relate to methods and apparatus for improving plasma uniformity to achieve a minimal ion tilt across the wafer when generating inductively coupled plasma by powering an inner coil with a higher frequency signal and by power an outer coil with a mixed signal including the higher frequency signal with a reverse phase and a lower frequency signal. Several inventive embodiments of the present disclosure are described below.

[0006] Embodiments of the present disclosure provide for a method for generating plasma is described. The method including providing a plasma chamber configured for generating aplasma through inductive coupling, wherein the plasma chamber includes an electrostatic chuck (ESC) for supporting a substrate and a dielectric window disposed opposite the ESC. The method including supplying a first radio frequency (RF) power signal to an inner coil disposed over the dielectric window, wherein the first RF signal is operating at a first frequency. The method including supplying a mixed RF power signal to an outer coil disposed over the dielectric window, wherein the mixed RF power signal includes a first component delivering a second RF power signal operating at the first frequency and a second component delivering a third RF power signal operating at a second frequency, wherein the first frequency is greater than the second frequency.

[0007] Other embodiments of the present disclosure provide for a system for generating plasma. The system includes a plasma chamber configured for generating a plasma through inductive coupling, wherein the plasma chamber includes an electrostatic chuck (ESC) for supporting a substrate, and a dielectric window disposed opposite the ESC. The system includes an inner coil disposed over the dielectric window. The system includes an outer coil disposed over the dielectric window. The system includes a first radio frequency (RF) power generator electrically coupled to the inner coil and configured to supply a first radio frequency (RF) power signal to the inner coil, wherein the first RF signal is operating at a first frequency. The system includes a second RF power generator electrically coupled to the outer coil and configured to supply a second RF power signal operating at the first frequency. The system includes a third RF power generator electrically coupled to the outer coil and configured to supply a third RF power signal operating at a second frequency. A mixed RF power signal is supplied to the outer coil and includes a first component including the second RF power signal and a second component including the third RF power signal, wherein the first frequency is greater than the second frequency.

[0008] These and other advantages will be appreciated by those skilled in the art upon reading the entire specification and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The embodiments may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

[0010] FIG. 1 illustrates an embodiment of a inductively coupled plasma (ICP) processing system utilized for etching operations including radio frequency (RF) power sources, in accordance with an implementation of the disclosure.

[0011] FIG. 2A illustrates a top view of an exemplary configuration of an inner coil and an outer coil of an ICP processing system, in accordance with one embodiment of the present disclosure.

[0012] FIG. 2B is a table illustrating exemplary power levels for different implementations of the inner and outer coils of an ICP processing system, in accordance with one embodiment of the present disclosure.

[0013] FIG. 3 is a flow diagram illustrating a method for reducing ion tilt at an edge of a substrate by powering an inner coil with a higher frequency RF power signal and by powering an outer coil with a mixed RF power signal including the higher frequency with reverse phase and a lower frequency, in accordance with one embodiment of the present disclosure.

[0014] FIG. 4 illustrates the RF power signals supplied to coils of an inductively coupled plasma generation system, in accordance with one embodiment of the present disclosure.

[0015] FIG. 5A illustrates non-uniform plasma density and an edge sheath contributing to tilting of ions at an edge of a substrate.

[0016] FIG. 5B illustrates a uniform plasma density and an edge sheath that is generated by powering an inner coil with a higher frequency RF power signal and by powering an outer coil with a mixed RF power signal including the higher frequency with reverse phase and a lower frequency, in accordance with one embodiment of the present disclosure.

[0017] FIGS. 6A-6C illustrate plasma generation zones of an inner coil and an outer coil that are powered using different signal configurations with reference to plasma uniformity and nonuniformity, in accordance with one embodiment of the present disclosure.DETAILED DESCRIPTION

[0018] Although the following detailed description contains many specific details for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the present disclosure. Accordingly, the aspects of the present disclosure described below are set forth without any loss of generality to, and without imposing limitations upon, the claims that follow this description.

[0019] Generally speaking, the various embodiments of the present disclosure describe methods and apparatus for reducing ion tilt in the entirety of the wafer. In particular, an inner coil is powered with a higher frequency RF power signal, and an outer coil is powered with a mixed RF power signal that includes the higher frequency with reverse phase and a lower frequency. Generally, inner coil and outer coil of a plasma chamber may operate at a high or higher frequency (e.g., 10 MHz or higher) but one coil may be 180 degree out of phase relative to other coil to keep plasma generation zones of the two coils separated and promote plasma uniformity. Mixing a higher frequency signal and a lower frequency signal for delivery to the outer coil can enhance power separation and plasma uniformity using lower power levels when compared to using only higher frequency signals. Also, because a lower frequency signal isinvolved at the outer coil there may be less sputtering on a dielectric window. As a result, plasma generation zones of the two coils may remain separated, which promotes plasma uniformity. Further, with improved plasma uniformity by using a mixture of a higher frequency signal and a lower frequency signal, there is reduced global tilt in the entirety of the substrate.

[0020] Advantages of the various embodiments, disclosing methods and apparatus for mixing a low or lower frequency signal and out-of-phase high or higher frequency at the outer coil include enhancement of power separation between inner and outer coils for improved separation of plasma generation zones. In addition, the mixing of power signals at the outer coil to achieve improved power separation and separation of plasma generation zones reduces ion tilt across the wafer, thereby providing for better uniformity of plasma spread across a surface of the wafer and especially at the edge and / or better uniformity of features across the surface of the wafer. Further, because of the involvement of the low or lower frequency signal, there is less sputtering on the dielectric window, which in part allows for increased duration of time between servicing. Also, the mix of low or lower frequency signal and out-of-phase high or higher frequency at the outer coil also provides for less power being applied, which makes for more efficient plasma generation when using reduced power, especially when compared to the power levels used when there is no mix of frequencies at the outer coil.

[0021] With the above general understanding of the various embodiments, example details of the embodiments will now be described with reference to the various drawings. Similarly numbered elements and / or components in one or more figures are intended to generally have the same configuration and / or functionality. Further, figures may not be drawn to scale but are intended to illustrate and emphasize novel concepts. It will be apparent, that the present embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail in order not to unnecessarily obscure the present embodiments.

[0022] Throughout the specification the terms substrate and wafer may be used interchangeably. Generally, plasma processing may be performed on a substrate and / or wafer to etch features on a surface, or to deposit layers on the surface of the substrate and / or wafer.

[0023] FIG. 1 illustrates an embodiment of a inductively coupled plasma (ICP) processing system 100 configured for generating plasma 150 in chamber 101. For example, IC processing system 100 may be utilized for etching operations. Plasma chamber 101 includes a chuck 110, a dielectric window 120 disposed opposite the chuck, and one or more radio frequency (RF) power sources, in accordance with an implementation of the disclosure. The chuck 110 can be an electrostatic chuck (ESC) for supporting the substrate 105 (e.g., wafer) when present. For example, the ESC also includes electrostatic electrodes to enable the chucking and dechuckingof the wafer that are powered by a filter and DC clamp power supply, or other control system, to lift the substrate 105 off of the ESC 110. Although not shown, pumps are connected to the plasma chamber 101 to enable vacuum control and removal of gaseous byproducts from the plasma chamber during operational plasma processing.

[0024] In some embodiments, the ICP processing system 100 may include a controller 150 that is used for controlling various components of the ICP processing system 100. In one example, the controller 150 can be connected to the plasma generators (e.g., RF power source 147, RF power source 125 A, RF power source 125B, Bias RF power source 115), to the gas source(s) 114 that are coupled to the plasma process chamber 101, and to other components. In some embodiments, the controller 150 includes one or more recipes including multiple set points and various operating parameters (e.g., voltage, current, frequency, pressure, flow rate, power levels, temperature, timing parameters, process gases, mechanical movement of the substrate 120, etc.) for operating the ICP processing system 100. For example, depending on the processing being performed, the controller 150 controls the delivery of process gases delivered from the gas source(s) 114 to the process chamber 101 in order to achieve a designed processing condition, such as to etch features and / or deposit or form films over the substrate 105. The chosen gases are then distributed in a space volume defined over the substrate 120 resting over the ESC 118.

[0025] ICP processing system 100 is configured for generating plasma 150 through inductive coupling. In particular, after supplying corresponding radio frequency (RF) power to each of an inner coil 130 and an outer coil 135 located near (e.g., disposed over) a dielectric window to provide inductively coupled power into the plasma processing chamber 101 and injecting process gas(es) into the plasma process chamber, plasma 150 is then formed between the dielectric window 120 and the ESC 110. In one embodiment, the inner coil is arranged within an inner space of the outer coil along a plane and / or a horizontal plane. The inner and outer coils enable generation of uniform plasma through inductive coupling by independently applying RF power to each coil. For example, the plasma 150 can be used to etch the surface of the substrate 105.

[0026] The dielectric window 120 can be defined from a ceramic type material. Other dielectric materials are also possible, so long as they are capable of withstanding the conditions of a semiconductor etching chamber. The dielectric window 120 is provided to separate the inner coil 130 and the outer coil 135 from the plasma processing chamber 101. For example, each of the inner and outer coils may be configured to generate corresponding toroidal power distributions in the plasma 150. As such, the dielectric window 120 is configured to allow energy to pass from the inner and outer coils to the plasma processing chamber 101.

[0027] The inner coil 130 and outer coil of a plasma chamber may operate at a high or higher frequency (e.g., 10 MHz or higher) but one coil may be 180 degree out of phase relative to other coil to keep plasma generation zones of the two coils separated and promote plasma uniformity, in one embodiment. However, since the two coils are operating out-of-phase, plasma generation may be inefficient, thereby requiring increased power being applied to the coils to achieve desired results (e.g., to generate a certain plasma density and / or plasma density uniformity). In addition, if both coils are operating at the same high or higher frequency (but 180 degrees out-of-phase with each other), the increased power may contribute to a higher sheath voltage on the dielectric window and increased ion sputtering on the dielectric window.

[0028] In another embodiment, the inner coil 130 operates at a first frequency, and the other coil 135 operates with mixed frequencies, including the same frequency used for the inner coil (but out-of-phase) and a different lower frequency. The use of mixed frequencies on the outer coil achieves sufficient separation of the plasma generation zones from the two coils, which results in improved plasma density uniformity across the surface of the wafer. Also, because the mixed frequencies use less power to achieve similar results when compared to using only an out of phase high frequency at the outer coil, plasma generation may be more efficient.

[0029] In particular, an RF power source 147, tuned by a match network 145, supplies RF power to the inner coil 130. The RF power source 147 supplies a high or higher frequency RF power signal. That is, a first RF power generator is electrically coupled to the inner coil 130 and is configured to supply a first RF power signal to the inner coil, wherein the first RF power signal is operating at a first frequency. For example, the first frequency is a high or higher frequency, and ranges between 5 megahertz (MHz) to over 100 MHz. Further, the first frequency may be a baseline frequency of 10 MHz or 13.56 MHz or 27 MHz or 40MHz or 60 MHz or 100 MHz. In one implementation, the first frequency of operation of the RF power source 147 is 13.56 MHz.

[0030] In addition, a mixed RF power signal is provided to the outer coil 135, wherein the mixed RF power signal includes the higher frequency RF power signal provided to the inner coil 130, but with reverse phase and a lower frequency RF power signal, and a lower frequency signal. In general, the inner coil 130 and the outer coil 135 may operate at an approximately similar high or higher frequency, as previously introduced, but the RF power signal on one coil may be 180 degrees out-of-phase relative to the RF power signal on the other coil.

[0031] The mixed RF power signal supplied to the outer coil 135 includes a first component including a second RF power signal and a second component including a third RF power signal. In particular, for the first component a second RF power generator is electrically coupled to the outer coil 135, and is configured to apply the second RF power signal that is operating at the firstfrequency of the first RF power signal being applied to the inner coil 130. For example, an RF power source 125A, tuned by a match network 127 A, supplies the high frequency RF power to the outer coil 135, wherein the frequency (i.e., high frequency) of the RF power supplied to the outer coil is approximately similar with the frequency of the RF power supplied to the inner coil 130 (i.e., from RF power source 147), but with reverse phase (i.e., out-of-phase or 180 degrees out-of-phase, etc.). As previously introduced, the first frequency of the RF power signal to the outer coil 135 is a high or higher frequency, and ranges between 5 MHz to over 100 MHz. Further, the first frequency may be a baseline frequency of 10 MHz or 13.56 MHz or 27 MHz or 40MHz or 60 MHz or 100 MHz. In one implementation, the first frequency of operation of the RF power source 125 A is 13.56 MHz.

[0032] For the second component of the mixed RF power signal, a third RF power generator is electrically coupled to the outer coil 135, and is configured to supply the third RF power signal that is operating at a second frequency, wherein the first frequency is greater than the second frequency. For example, RF power source 125B, tuned by match network 127B, supplies a low or lower frequency RF power signal to the outer coil 135. The second frequency of the RF power signal output by the RF power source 125B is lower than the first frequency of the RF power signal output by the RF power source 125 A, though it may be considered a high frequency signal. For example, the second frequency may range between 10 kilohertz (kHz) to 5 MHz. In one implementation, the second frequency of operation of the RF power source 125B is 2 MHz.

[0033] A slave and / or synchronization controller 155 may be configured to synchronize a frequency of the second RF power signal to the first frequency of the first RF power signal. In particular, the slave and / or synchronization controller 155 is configured to provide a pulse sync output used for controlling one or more parameters of the high frequency RF power signal generated by the RF power source 125A. That is, the slave and / or synchronization controller 155 is configured to substantially align the high frequency RF power signal delivered by the RF power source 147 to the inner coil 130 to the high frequency RF power signal delivered by the RF power source 125 A to the outer coil 135, including aligning the frequency of the two RF power signals. In some embodiments, the slave and / or synchronization controller 155 works in combination with the controller 150 to substantially align the frequencies of the two RF power signals.

[0034] Further, a fourth RF power signal that is tuned via a match circuit provides a bias voltage to the ESC 110. In particular, a match circuit 117 is electrically coupled to a lower electrode (not shown) located within the ESC; and a bias RF power source 115 is electricallycoupled to the match circuit, wherein the bias RF power source is configured to supply a bias voltage to the ESC 110.

[0035] FIG. 2A illustrates a top view of an exemplary configuration of an inner coil 130 and an outer coil 135 first introduced in the ICP processing system 100 of FIG. 1, in accordance with one embodiment of the present disclosure. As shown, the inner coil 130 is arranged within an inner space of the outer coil 135 along a plane and / or a horizontal plane.

[0036] In particular, RF power source 147, tuned by a match network 145, supplies RF power to the inner coil 130. For example, the RF power signal is delivered to input node 210 of the inner coil 130. To complete the circuit, output node 215 of the inner coil 130 is coupled to ground. A first frequency of the RF power signal to the inner coil is of a high or higher frequency.

[0037] Also, a mixed RF power signal is provided to the outer coil 135. For example, the mixed RF power signal is delivered to input node 220 of the outer coil 135. To complete the circuit, output node 225 is coupled to ground. In particular, the mixed RF power signal includes a first component including the higher frequency RF power signal (also provided to the inner coil 130), but with reverse phase, and a second component including a lower frequency RF power signal. For example, RF power source 125A, tuned by a match network 127 A, supplies the high frequency RF power signal to the outer coil 135 for the first component, wherein the frequency (i.e., high frequency) of the RF power signal is approximately similar with the frequency of the RF power signal supplied to the inner coil 130 (i.e., from RF power source 147), but with reverse phase (i.e., out-of-phase or 180 degrees out-of-phase, etc.). In addition, RF power source 125B, tuned by match network 127B, supplies a low or lower frequency RF power signal to the outer coil 135 for the second component. As shown, a single match circuit 127 may include the functionality of match circuits 127A and 127B.

[0038] One of the keys to reducing global tilt of ions across the wafer, is to keep the plasma from interacting with the inner coil 130 and the outer coil 135 as if the two coils were one regardless of the frequencies on the RF power signals to the coils. Ideally, plasma generation zones generated by each of the inner coil 130 and outer coil 135 should remain separated without overlap. One hardware approach to achieve separation of plasma generation zones is to increase coil spacing. Specifically, the spacing between the coil sets (i.e., the inner coil 130 and the outer coil 135) is increased to separate the plasma generation zones from each coil, resulting in enhance plasma density uniformity across a surface of a wafer. In one embodiment, the spacing is configured to be at a maximum based on the configuration of the ICP processing system (e.g., chamber size, coil enclosure size, other constraints, etc.) in an effort to separate plasma generation zones of the two coils. However, at some point separation of the coils loses itseffectiveness, such that the plasma density uniformity may become saturated and / or the improvement on global tilt of ions reverses, and to achieve increased plasma density uniformity across a surface of the wafer, additional techniques need to be performed to include providing a mixed RF power to the outer coil.

[0039] An additional technique implemented through hardware would be to have the inner coil 130 and the outer coil 135 wound in opposite directions, specifically when supplying a mixed RF power signal to the outer coil 135 (i.e., when running both low and high frequencies on the outer coil). For example, as is shown in FIG. 2 the inner coil 130 is wound in a clockwise direction, while the outer coil 135 is wound in a counter-clockwise direction. As a result, the RF waves propagating from each of the inner and outer coils are 180 degrees out-of-phase, and destructively interfere with each other when they meet, such as within the chamber of the ICP processing system. This destructive interference makes it harder for the plasma to act like both coils are a single coil (i.e., plasma generation zones from the coils are separated). However, this works when the same frequency is being used on both the inner coil 130 and the outer coil 135 (i.e., the high or higher frequency). There is no or limited destructive interference between RF waves when the RF power signals are of different frequencies, as the phase between the different frequencies will always be changing with respect to each other.

[0040] Instead of opposite winding of the inner and outer coils, the high frequency RF power signals supplied on the inner coil 130 and the outer coil 135 can be 180 degrees out-of-phase with each other as controlled through timing. For example, a controller (e.g., slave / sync controller 155 and / or controller 150 of FIG. 1) may be configured to control timing of the second RF power signal supplied to the outer coil 135 to be out-of-phase with the first RF power signal supplied to the inner coil 130.

[0041] FIG. 2B is a table 200B illustrating exemplary power levels for different implementations of the inner and outer coils of an ICP processing system, in accordance with one embodiment of the present disclosure. The values shown in table 200B are shown for purposes of illustration. Table 200 illustrates four different and exemplary configurations of applying RF power to the inner coil 130 and the outer coil, including applying high or higher frequency RF power to the inner coil in isolation in row 251; applying low or lower frequency RF power to the outer coil in isolation in row 252; applying a mixed RF power signal to the outer coil in isolation in row 253; performing current splitting only with high or higher frequency RF power supplied to both the inner and outer coils in row 254; and applying high or higher frequency RF power to the inner coil, and a mixed RF power signal to the outer coil in row 255. Still other configurations are contemplated and supported. Also for purposes of illustration, the high or higher frequency of the RF power signal to the inner coil and / or the outercoil is 13.56 MHz, but is understood that it can be any value. Also for purposes of illustration, the low or lower frequency of the RF power signal to the outer coil is 2 MHz, but is understood that it can be of any value. Also, the configurations may be reversed, such that the mixed RF power signal is applied to the inner coil, and the high frequency RF power signal is applied to the outer coil, in other embodiments.

[0042] In one embodiment, a current ratio on the inner and the outer coils for the high or higher frequency RF power signals being applied for current splitting can be manipulated to provide appropriate power levels of the RF power signals. For example, the current ratio for the high or higher frequency RF power signals (e.g., 13.56 MHz) to the inner and outer coils can be defined as being defined using the following equation: (Current Ratio = high frequency inner coil current / high frequency outer coil current). In one embodiment, the current ratio can range from — 0.6 to 2.1 — .

[0043] Depending on the operation of the inner coil 130 and the outer coil 135 in the various configurations, the power ranges to each of the coils could be of any value depending on what the hardware can tolerate and what plasma conditions are required. Also, a power ratio for power supplied to the outer coil and the inner coil, wherein power to the outer coil is generally greater than the power supplied to the inner coil, may range between zero (0) to infinity when either coil is running in isolation, or may range between 2 (when there is minimum high frequency RF power and no low frequency RF power to the outer coil) and 60 (when there is maximum high frequency RF power and maximum low frequency RF power applied to the outer coil). Further, a power ratio for RF power supplied to the outer coil between the low frequency RF power and the high RF power may range from zero (0) (i.e., when no low frequency RF power is applied) to infinity (i.e., when no high frequency RF power is applied), or when the low frequency RF power signal to the outer coil is at maximum power, and the high frequency RF power signal to the outer coil is varied according to the aforementioned current ratio, then the power ratio may range between — 1.4 to 2 — .

[0044] As is shown in table 200, for an operational setup where only the inner coil 130 is operating in isolation as shown in row 251, there would be no power (e.g., 0 watts - W) supplied to the outer coil 135, and the power supplied to the inner coil running in isolation could range up to 3 kilowatts (kW).

[0045] For an operational setup where only the outer coil 135 is operating using the low frequency RF power as shown in row 252, there would be no power (e.g., 0 watts) supplied to the inner coil 130, and the power supplied to the outer coil from the low or lower frequency RF power signal (e.g., 2 MHz) could range up to 4 kW.

[0046] For an operational setup with only the outer coil is operating in isolation with a mixed RF power signal being applied as shown in row 253, there would be no power (e.g., 0 watts) supplied to the inner coil, and up to 6.8 kW of power split between the low frequency (2 MHz) and the high frequency (13.56 MHz) RF power signals may be supplied to the outer coil 135. In one embodiment, more power is supplied to the second component (e.g., the 13.56 MHz RF power signal) of the mixed RF power signal than to the first component. In other embodiment, more power is supplied to the first component of the mixed RF power signal than to the second component.

[0047] For an operational setup with just current splitting as shown in row 254, wherein a high or higher frequency power signal delivered to each of the inner coil 130 and the outer coil 135, the power to the inner coil may range between 100 watts to 1 kilowatt, and the power to the outer coil may range between 2 to 2.8 kilowatts. In one embodiment, more power is supplied to the outer coil than to the inner coil when current splitting high frequency RF power.

[0048] For an operational setup with both low and high frequency RF power being supplied to the inner and outer coils as shown in row 255, the power of the high frequency RF power signal to the inner coil may range between 100 watts to 1 kilowatt, and up to 6.8 kW of power may be split between the low frequency (2 MHz) and the high frequency (13.56 MHz) RF power signals supplied to the outer coil 135. In one embodiment, more power is supplied to the second component (e g., the 13.56 MHz RF power signal) of the mixed RF power signal than to the first component. In other embodiment, more power is supplied to the first component of the mixed RF power signal than to the second component.

[0049] FIG. 3 is a flow diagram illustrating a method to reduce tilting of ions across the wafer with improved plasma density uniformity by powering one coil set with a higher frequency while powering the other coil set with a reverse phase of the higher frequency and a lower frequency, in accordance with one embodiment of the present disclosure. Specifically, the method for reducing ion tilt at an edge of a substrate includes powering an inner coil with a higher frequency RF power signal and by powering an outer coil with a mixed RF power signal including the higher frequency with reverse phase and a lower frequency, in accordance with one embodiment of the present disclosure. The method of flow diagram 300 may be implemented to control processes in the plasma processing systems of FIGS. 1 and 2A, as well as for other plasma processing systems.

[0050] At 310, the method includes providing a plasma chamber configured for generating a plasma through inductive coupling, wherein the plasma chamber includes an electrostatic chuck (ESC) for supporting a substrate and a dielectric window disposed opposite the ESC. Gases may be delivered to the plasma chamber depending on the processing being performed to achieve adesired processing condition, such as to etch features and / or to deposit or form films over a substrate.

[0051] At 320, the method includes supplying a first radio frequency (RF) power signal to an inner coil disposed over the dielectric window, wherein the first RF signal is operating at a first frequency. The frequency of the power signal may be of a high or higher frequency. For example, the first frequency is a high or higher frequency, and ranges between 5 megahertz (MHz) to over 100 MHz. As an example, a frequency of operation for the first frequency is 13.56 MHz.

[0052] At 330, the method includes supplying a mixed RF power signal to an outer coil disposed over the dielectric window. The mixed RF power signal includes a first component and a second component. The first component delivers a second RF power signal that is operating at the first frequency (i.e., the same or similar frequency as the RF power signal applied to the inner coil). The second RF power signal of the mixed RF power signal to the outer coil is 180 degrees out-of-phase with the first RF power signal delivered to the inner coil.

[0053] The second component of the mixed RF power signal to the outer coil delivers a third RF power signal that is operating at a second frequency, with the second frequency being lower. For example, the second frequency of the second component of the mixed RF power signal may range between 10 kilohertz (kHz) to 5 MHz. In one implementation, the second frequency of operation 2 MHz. Applying the mixed RF power signal to the outer coil (e.g., mixing the low frequency and the out-of-phase high frequency RF power signals) can enhance power separation from the plasma generation zones from each coil, and improve plasma density uniformity across a surface of a substrate. The plasma generation may be more efficient when using the mixed RF power signal as plasma is generated with improved plasma density uniformity using less power. Also, since a lower frequency is involved at the outer coil, this may produce less sputtering on the dielectric window. As a result, plasma generation zones of the two coils may remain separated because of the enhanced power separation, which promotes plasma density uniformity across the surface of the substrate. Further, with improved plasma uniformity achieved using a mixture of a higher frequency signal that is out-of-phase and a lower frequency signal, there is reduced global tilt across the entirety of wafer.

[0054] FIG. 4 illustrates the RF power signals supplied to coils of an inductively coupled plasma generation system, in accordance with one embodiment of the present disclosure. In particular, by powering one coil set with a higher frequency while powering the other coil set with a reverse phase of the higher frequency and a lower frequency improved plasma density uniformity is achieved across a surface of a substrate, which reduces tilting of ions especially at an edge of a substrate. The graph shown in FIG. 4 includes time axis 415A and 415B, which arealigned, and an amplitude axis 410 that includes two zero (0) points on each of the time axis 415A and 415B.

[0055] In particular, RF power signal 420a is applied to the inner coil, and is operating at a first frequency, which may be of a high or higher frequency. For purposes of illustration, the first frequency that is high may be 10 MHz. Period 425a of one cycle of the RF power signal 420a is shown with reference to the time axis 415A, and also illustrates the phase of the RF power signal 420a. The amplitude of the RF power signal 420a is shown purely for illustration.

[0056] A mixed RF power signal is applied to the outer coil, and includes a first component and a second component. The first component is RF power signal 420b, which operates at the first frequency. The RF power signal 420b of the mixed RF power signal to the outer coil has the same frequency as the RF power signal 420a to the inner coil, but the two RF power signals are 180 degrees out-of-phase with each other. For example, period 425b of one cycle of the RF power signal 420b is shown with reference to the time axis 415B, wherein period 425b of the RF power signal 420b is equal to period 425a of the RF power signal 420a. However, the phase of the RF power signal 420b is 180 degrees out-of-phase from the RF power signal 420a, as is shown by time different 430. Further, the amplitude of the RF power signal 420b is shown purely for illustration.

[0057] The second component is RF power signal 440, which operates at a second frequency that is lower than the first frequency. For example, the frequency of operation for the RF power signal 440 may be 2 MHz. period 445 of one cycle of the RF power signal 440 is shown with reference to time axis 415B. Further, the amplitude of the RF power signal 440 is shown purely for illustration.

[0058] FIG. 5A illustrates plasma density and sheath across the wafer contributing to tilting of ions striking a substrate undergoing processing within a plasma processing system, such as an ICP processing system. In particular, FIG. 5A focuses on a substrate 105 that is supported by an electrostatic chuck (ESC) 110 during processing. Edge ring 530 may surround the ESC 110, and is configured to perform many functions including, but not limited to, positioning the substrate 105 on the ESC 110, confining plasma to an area above the substrate 105, protecting the ESC 110 from erosion by ions of the plasma, and shielding underlying components of the plasma chamber from being damaged by ions of the plasma, improve performance at the edge of the substrate, etc.

[0059] In general, the plasma processing system generates a plasma. A plasma density profile 520A of the plasma is generated in part responsive to a bias RF power signal placed on the ESC 110. As shown, the plasma density profile is horizontal initially across the interior of the substrate 105, but rolls off downwards along the remaining substrate length. That is, non-uniformity of the plasma density profile may show up mid-wafer (i.e., approximately half way from the center to the edge), and sometimes even earlier (i.e., towards the center).

[0060] Also, a sheath thickness 510A is generally inversely proportional to the plasma density profile 250. The sheath defines an area where there is a depletion of electrons, and is located on the substrate or wafer. As shown, the sheath thickness is also horizontal initially on the substrate 105 (i.e., near the center of the substrate), but is deformed as the substrate length progresses, and rises upwards at the edge. That is, sheath may bend beginning at mid-wafer (i.e., approximately half way from the center to the edge), and sometimes even earlier (i.e., towards the center).

[0061] Ions escaping the plasma and pulled towards the substrate 105 in part by the bias RF power signal travel perpendicular to the sheath thickness 510A. That is, ions 515 A within the zone on the substrate 105 where plasma is uniform escape the plasma and travel in a vertical direction towards the substrate 105. On the other hand, ions 515B located where plasma nonuniformity starts on the substrate 105 exit the plasma at an angle, such as perpendicular to the surface of the sheath, as defined by the sheath thickness 510A, which is rising as the plasma nonuniformity starts to appear. That is, ions 515B have a tilt that is offset from vertical (i.e., the angle from vertical that the ions are traveling). The ion tilt introduced on the substrate contributes to unexpected etch features resulting from this ion tilt. For example, when etching the substrate, the etching features of the substrate where nonuniformity or this sheath bending takes place will be angled (i.e., etched at an angle) and not vertical (i.e., etched vertically), whereas in uniform plasma, the etching features will be vertically oriented.

[0062] FIG. 5B illustrates plasma density and sheath on a substrate undergoing processing within an ICP processing system, such as system 100 of FIG. 1, in accordance with one embodiment of the present disclosure. Uniformity of the plasma density on a substrate 105 is achieved by powering an inner coil with a higher frequency RF power signal and by powering an outer coil with a mixed RF power signal including the higher frequency with reverse phase and a lower frequency, in accordance with one embodiment of the present disclosure. In particular, FIG. 5B focuses on a region on a substrate 105 where this plasma uniformity is achieved with above technology.

[0063] In general, the ICP processing system generates a plasma. A plasma density profile 520B of the plasma is generated in part responsive to a bias RF power signal placed on the ESC 110. As shown, the plasma density profile is horizontal initially across the interior of the substrate 105. Also, the plasma density profile is uniformly horizontal across the rest of the substrate 105, such that the plasma density profile is uniform across the entirety of the surface of the substrate, as is shown partly in the highlighted area 550.

[0064] Also, a sheath thickness 51 OB is generally inversely proportional to the plasma density profile 520B. The sheath defines an area where there is a depletion of electrons, and is located on the substrate or wafer. As shown, the sheath thickness is also horizontal initially on the substrate 105, and uniformly horizontal across the rest of the substrate, such that the sheath thickness is uniform across the entirety of the surface of the substrate, as is shown partly in the highlighted area 550.

[0065] Ions escaping the plasma and pulled towards the substrate 105 in part by the bias RF power signal travel perpendicular to the sheath thickness 510B. That is, ions 515A’ within the interior of the substrate 105 escape the plasma and travel in a vertical direction towards the substrate 105. Because the sheath thickness 510B is uniform across the surface of the substrate, to include the edge of the substrate, ions 515C at the edge of the substrate also exit the plasma in the vertical direction (i.e., perpendicularly from the horizontal sheath thickness 510B. That is, ions 515C do not have a tilt, or the ion tilt from vertical is significantly reduced. In that manner, features across the entirety of the substrate are uniform, such that features formed at the edge of the substrate are substantially similar to features formed in the interior of the substrate. For example, when etching the substrate, the etching features throughout the interior and at the edge of a substrate will be vertically oriented (i.e., etched vertically).

[0066] FIGS. 6A-6C illustrate plasma generation zones of an inner coil and an outer coil of an ICP plasma processing system that are powered using different signal configurations with reference to plasma uniformity and non-uniformity, in accordance with embodiments of the present disclosure. Generally, the ICP processing system is configured for generating a plasma through inductive coupling and includes, in part, an electrostatic chuck (ESC) 110 for supporting a substrate 105, an inner coil 130 and an outer coil disposed over a dielectric window. And edge ring 530 may surround the ESC 110.

[0067] FIG. 6A illustrates plasma generation zones of an ICP processing system that applies the RF power signals having the same frequency to both the inner coil 130 and the outer coil 135, wherein the RF power signals are in phase with each other, in accordance with one embodiment of the present disclosure. Purely for example, the RF power signals to each of the inner and outer coils may operate at a frequency of 10 MHz or 13.56 MHz. Applying the same frequency in both coils and in phase may produce a continuous power deposition profile as is shown by the plasma generation zones 610a of the inner coil 130 and 620a of the outer coil 135, which may not be sufficient to produce good uniformity of the plasma density profile across a substrate. In particular, region 650a shows the overlap between the plasma generation zones 610a and 620a. In general, separation of the plasma generation zones of the inner and outer coils(i.e., the zones are not talking or influencing each other) achieves a desirable and uniform plasma density profde across the entirety of the substrate.

[0068] FIG. 6B illustrates plasma generation zones of an ICP processing system that applies a high frequency RF power signal to the inner coil 130 and a lower frequency RF power signal to the outer coil 135, in accordance with one embodiment of the present disclosure. Purely for example, the RF power signal to the inner coil may operate at a frequency of 10 MHz or 13.56 MHz, and the RF power signal to the outer coil may operate at a frequency of 2 MHz. As shown, powering the inner and outer coils with RF power signals of different frequencies produces some sort of plasma separation that enhances uniformity. In particular, plasma generation zones 610b of the inner coil 130 and 620b of the outer coil 135 are shown to be separated, such that region 650b shows no overlapping between the plasma generation zones 610b and 620b. While separation of the plasma generation zones of the inner and outer coils (i.e., the zones are not talking or influencing each other) is desirable, the lower frequency RF power signal to the outer coil alone to the outer coil 135 can produce a thicker skin depth (i.e., a deeper plasma generation zone) and ionize byproduct gases more that may further degrade plasma uniformity, such that the plasma density profde is non-uniform across the entirety of the substrate

[0069] FIG. 6C illustrates plasma generation zones of an ICP processing system that applies a high frequency RF power signal to the inner coil 130 and a mixed RF power signal to the outer coil. The mixed RF power signal includes a first component that is a high frequency RF power signal with the same frequency applied to the inner coil but 180 degrees out-of-phase, and a second component that is a low or lower frequency RF power signal. Purely for example, the high frequency RF power signal to the inner coil and / or to the outer coil (i.e., the first component) may operate at a frequency of 10 MHz or 13.56 MHz, and the low frequency RF power signal (i.e., the second component) to the outer coil may operate at a frequency of 2 MHz. As shown, powering the inner coil with a higher frequency RF power signal and powering the outer coil with a mixed RF power signal including a reverse phase of the higher frequency RF power signal and a lower frequency RF power signal, can both separate plasma generation enhancing uniformity and also may produce less voltage on the window for sputtering. In particular, plasma generation zones 610c of the inner coil 130 and 620c of the outer coil 135 are shown to be separated, such that region 650c shows no overlapping between the plasma generation zones 610c and 620c. Mixing a higher frequency signal and a lower frequency signal for delivery to the outer coil 135 can enhance power separation and plasma density uniformity using lower power levels when compared to using only higher frequency signals. Also, because a lower frequency signal is involved at the outer coil there may be less sputtering on a dielectricwindow. As a result, plasma generation zones of the two coils may remain separated, which promotes plasma uniformity. Further, with improved plasma uniformity by using a mixture of a higher frequency signal and a lower frequency signal, there is reduced global tilt across the entirety of substrate

[0070] In embodiments, a substrate positioning program may include program code for controlling chamber components that are used to load the substrate onto a pedestal or chuck and to control the spacing between the substrate and other parts of the chamber such as a gas inlet and / or target, which may be implemented by control system or controller 150 of FIG. 1. In some implementations, a controller is part of a system, which may be part of the abovedescribed examples. Such systems can comprise semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and / or specific processing components (a substrate pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The controller, depending on the processing requirements and / or the type of system, may be programmed to control any of the processes disclosed herein, and process implemented for operating a plasma chamber. Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor substrate or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and / or dies of a wafer.

[0071] The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” of all or a part of a fab host computer system, which can allow for remote access of the substrate processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g., a server) can provide process recipes to a system over a network, which may include a local network or the Internet.

[0072] Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapordeposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, a plasma enhanced chemical vapor deposition (PECVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and / or manufacturing of semiconductor wafers.

[0073] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

[0074] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein, but may be modified within their scope and equivalents of the claims.

Claims

CLAIMS1. A method, comprising: providing a plasma chamber configured for generating a plasma through inductive coupling, wherein the plasma chamber includes an electrostatic chuck (ESC) for supporting a substrate and a dielectric window disposed opposite the ESC; supplying a first radio frequency (RF) power signal to an inner coil disposed over the dielectric window, wherein the first RF signal is operating at a first frequency; and supplying a mixed RF power signal to an outer coil disposed over the dielectric window, wherein the mixed RF power signal includes a first component delivering a second power signal operating at the first frequency and a second component delivering a third power signal operating at a second frequency, wherein the first frequency is greater than the second frequency.

2. The method of claim 1, wherein second RF power signal supplied to the outer coil is out-of-phase with the first RF power signal supplied to the inner coil.

3. The method of claim 2, wherein the inner coil is wound opposite to the outer coil.

4. The method of claim 2, further comprising: controlling timing of the second RF power signal supplied to the outer coil to be out- of-phase with the first RF power signal supplied to the inner coil.

5. The method of claim 1, further comprising: synchronizing a frequency of the second RF power signal to the first frequency of the first RF power signal.

6. The method of claim 1, supplying a fourth RF power signal that is tuned via a match circuit to a lower electrode located within the ESC in order to provide a bias voltage.

7. The method of claim 1, further comprising: supplying more power to the outer coil than to the inner coil8. The method of claim 1, wherein the first frequency is 13.56 MHz, and wherein the second frequency is 2 MHz.

9. The method of claim 1, further comprising:supplying more power to the second component of the mixed RF power signal than to the first component.

10. The method of claim 1, wherein the inner coil is arranged within an inner space of the outer coil along a horizontal plane.

11. A system, comprising: a plasma chamber configured for generating a plasma through inductive coupling, wherein the plasma chamber includes an electrostatic chuck (ESC) for supporting a substrate, and a dielectric window disposed opposite the ESC; an inner coil disposed over the dielectric window; an outer coil disposed over the dielectric window; a first radio frequency (RF) power generator electrically coupled to the inner coil and configured to supply a first radio frequency (RF) power signal to the inner coil, wherein the first RF signal is operating at a first frequency; a second RF power generator electrically coupled to the outer coil and configured to supply a second RF power signal operating at the first frequency; a third RF power generator electrically coupled to the outer coil and configured to supply a third RF power signal operating at a second frequency, wherein a mixed RF power signal is supplied to the outer coil and includes a first component including the second RF power signal and a second component including the third RF power signal, wherein the first frequency is greater than the second frequency.

12. The system of claim 10, wherein second RF power signal supplied to the outer coil is out-of-phase with the first RF power signal supplied to the inner coil.

13. The system of claim 12, wherein the inner coil is wound opposite to the outer coil.

14. The system of claim 12, further comprising: a controller configured to control timing of the second RF power signal supplied to the outer coil to be out-of-phase with the first RF power signal supplied to the inner coil.

15. The system of claim 11, further comprising: a synchronizer configured to synchronizing a frequency of the second RF power signal to the first frequency of the first RF power signal.

16. The system of claim 11, further comprising: a match circuit electrically coupled to a lower electrode located within the ESC; and a bias RF generator electrically coupled to the match circuit and configured to supply a fourth RF power signal that is tuned via the match circuit to the lower electrode in order to provide a bias voltage.

17. The system of claim 11, further comprising: wherein more power is supplied to the outer coil than to the inner coil.

18. The system of claim 11, wherein the first frequency is 13.56 MHz, and wherein the second frequency is 2 MHz.

19. The system of claim 11, wherein more power is supplied to the second component of the mixed RF power signal than to the first component.

20. The system of claim 11, wherein the inner coil is arranged within an inner space of the outer coil along a horizontal plane.

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