Improved plasma uniformity through the use of a higher frequency signal to power the inner coil and a mixed signal of higher and lower frequencies to power the outer coil.

Abstract

A method for generating plasma. The method includes providing a plasma chamber configured to generate plasma by inductive coupling, comprising an electrostatic chuck (ESC) for supporting a substrate and a dielectric window provided opposite the ESC. The method includes supplying an inner coil provided above the dielectric window with a first radio frequency (RE) power signal operating at a first frequency. The method includes supplying an outer coil provided above the dielectric window with a mixed RE power signal comprising a first component that transmits a second RE power signal operating at a first frequency and a second component that transmits a third RE power signal operating at a second frequency, wherein the first frequency is greater than the second frequency.

Description

Technical Field

[0001] The present embodiment relates to semiconductor manufacturing, and more specifically, to a system and method for reducing ion tilt at the edge of a substrate by improving plasma uniformity through supplying power to one coil set using a high-frequency signal, and supplying power to the other coil set using a mixed radio frequency power signal that includes a higher-frequency signal and a lower-frequency signal of opposite phase.

Background Art

[0002] Many recent semiconductor chip manufacturing processes, such as plasma etching processes, are performed in a plasma processing chamber in which a substrate such as a wafer is supported on an electrostatic chuck (ESC). In a plasma etching process, the wafer is exposed to plasma generated within a plasma processing volume. The plasma contains various types of radicals, electrons, as well as cations and anions. Chemical reactions of various radicals, electrons, cations, and anions are used to etch features, surfaces, and materials of the wafer.

[0003] For example, when a process gas is supplied into the plasma processing chamber, one or more radio frequency (RF) signals provide power applied to one or more coils and electrodes of the plasma processing chamber, forming an electric field. The process gas is ionized into plasma by the RF signal, and plasma etching is performed on a predetermined layer provided on the wafer. Unfortunately, during wafer processing, non-uniformity of plasma originating from the plasma generation zone causes ions to strike the wafer in a non-vertical direction (e.g., ion tilt angle) across the entire wafer and along the extreme edge of the wafer, which may result in sloped etched features on the wafer.

[0004] It is against this background that embodiments of the present disclosure were developed.

Summary of the Invention

[0005] This embodiment relates to a method and apparatus for improving plasma uniformity, which achieves the minimum ion gradient across a wafer when generating an inductively coupled plasma by supplying an inner coil with a higher frequency signal and an outer coil with a mixed signal including a higher frequency signal and a lower frequency signal with opposite phases. Several advanced embodiments of this disclosure are described below.

[0006] Embodiments of the present disclosure providing a method for generating plasma are described. The method includes providing a plasma chamber configured to generate plasma by inductive coupling and comprising an electrostatic chuck (ESC) for supporting a substrate and a dielectric window provided opposite the ESC. The method includes supplying a first radio frequency (RF) power signal to an inner coil provided on the dielectric window, wherein the first RF signal operates at a first frequency. The method includes supplying a mixed RF power signal to an outer coil provided on the dielectric window, comprising a first component that transmits a second RF power signal operating at a first frequency and a second component that transmits 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 a system for generating plasma. The system comprises a plasma chamber configured to generate plasma by inductive coupling and having an electrostatic chuck (ESC) for supporting a substrate and a dielectric window provided opposite the ESC. The system comprises an inner coil provided above the dielectric window. The system comprises an outer coil provided above the dielectric window. The system comprises 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 operates at a first frequency. The system comprises a second RF power generator electrically coupled to the outer coil and configured to supply a second RF power signal operating at a first frequency. The system comprises 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. The mixed RF power signal is supplied to the outer coil and includes a first component containing a second RF power signal and a second component containing a third RF power signal, where the frequency of the first component is greater than the frequency of the second component.

[0008] Those skilled in the art will understand these and other advantages by reading the entire specification and claims. [Brief explanation of the drawing]

[0009] Each embodiment can be best understood by referring to the following description, which is to be interpreted in conjunction with the accompanying drawings.

[0010] [Figure 1] Figure 1 shows an embodiment of an inductively coupled plasma (ICP) processing system used for etching operations, including a radio frequency (RF) power source, according to one embodiment of the present disclosure.

[0011] [Figure 2A] Figure 2A is a top view illustrating an exemplary configuration of the inner and outer coils of an ICP processing system according to one embodiment of the present disclosure.

[0012] [Figure 2B] Figure 2B is a table showing exemplary power levels for different embodiments of the inner and outer coils of an ICP processing system according to one embodiment of the present disclosure.

[0013] [Figure 3] Figure 3 is a flowchart illustrating a method for reducing ion gradient at the edges of a substrate, according to one embodiment of the present disclosure, by supplying power to an inner coil with a higher frequency RF power signal and supplying power to an outer coil with a mixed RF power signal including higher and lower frequencies in opposite phase.

[0014] [Figure 4] Figure 4 shows the RF power signal supplied to the coil of an inductively coupled plasma generation system according to one embodiment of the present disclosure.

[0015] [Figure 5A] Figure 5A shows the non-uniform plasma density and edge sheath that result in an ion gradient at the edges of the substrate.

[0016] [Figure 5B] Figure 5B shows an end sheath resulting from a uniform plasma density and feeding of the inner coil with a higher frequency RF power signal and the outer coil with a mixed RF power signal including higher and lower frequencies in opposite phase, according to one embodiment of the present disclosure.

[0017] [Figure 6A] Figures 6A-6C show plasma generation zones related to plasma uniformity and non-uniformity in an inner coil and an outer coil powered using different signal configurations, according to one embodiment of the present disclosure. [Figure 6B]Figures 6A-6C show plasma generation zones related to plasma uniformity and non-uniformity in an inner coil and an outer coil powered using different signal configurations, according to one embodiment of the present disclosure. [Figure 6C] Figures 6A-6C show plasma generation zones related to plasma uniformity and non-uniformity in an inner coil and an outer coil powered using different signal configurations, according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0018] The following detailed description includes many specific details for illustrative purposes, but anyone skilled in the art will understand that many of the variations and modifications to the following details fall within the scope of this disclosure. Accordingly, the aspects of this disclosure described below are described without loss of generality to the claims that follow this specification, and without imposing limitations on the claims that follow this specification.

[0019] Broadly speaking, various embodiments of this disclosure describe methods and apparatus for reducing ion gradient across a wafer. In detail, the inner coil is fed with a higher frequency RF power signal, and the outer coil is fed with a mixed RF power signal containing higher and lower frequencies in opposite phase. Typically, the inner and outer coils of a plasma chamber can operate at high frequencies or above (e.g., 10 MHz or higher), but by having one coil 180 degrees out of phase with the other, the plasma generation zones of the two coils can be kept separated, thereby promoting plasma uniformity. By mixing higher and lower frequency signals and sending them to the outer coil, power isolation and plasma uniformity can be enhanced at lower power levels compared to using only the higher frequency signal. Also, because the outer coil is accompanied by a lower frequency signal, sputtering to the dielectric window may be reduced. As a result, the plasma generation zones of the two coils can remain separated, thus promoting plasma uniformity. Furthermore, by using a mixture of higher-frequency and lower-frequency signals, plasma uniformity is improved, thereby reducing the overall global tilt across the entire substrate.

[0020] Disclosed are a method and apparatus for mixing a low frequency or lower frequency signal with a high frequency or higher frequency of different phase in an outer coil. Advantages of various embodiments include enhanced power separation between the inner coil and the outer coil and improved separation of plasma generation zones. Furthermore, by mixing power signals in the outer coil to achieve power separation and plasma generation zone separation, ion tilt across the wafer is reduced, thereby resulting in better uniformity of plasma diffusion across the entire surface of the wafer, particularly at the edge, and / or better feature uniformity across the entire surface of the wafer. In addition, because a low frequency or lower frequency signal is involved, less sputtering to the dielectric window contributes to longer maintenance intervals. Furthermore, mixing a low frequency or lower frequency signal with a high frequency or higher frequency of different phase in the outer coil also reduces the applied power, and plasma is generated more efficiently particularly when using reduced power compared to the power level used when there is no frequency mixing in the outer coil.

[0021] Having broadly understood various embodiments as described above, exemplary details of the embodiments will now be described with reference to various drawings. Elements and / or components that are similarly numbered in one or more figures are generally intended to have the same structure and / or function. Furthermore, the figures are not necessarily drawn to scale, but are intended to exemplify and emphasize the 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 so as not to unnecessarily obscure the embodiments.

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

[0023] Figure 1 illustrates an embodiment of an inductively coupled plasma (ICP) processing system 100 configured to generate plasma 150 within a chamber 101. For example, the ICP processing system 100 may be used for etching operations. According to an embodiment of the present disclosure, the plasma chamber 101 comprises a chuck 110, a dielectric window 120 disposed opposite the chuck, and one or more radio frequency (RF) power sources. The chuck 110 may be an electrostatic chuck (ESC) for supporting a substrate 105 (e.g., a wafer) when the substrate 105 is present. For example, the ESC also comprises an electrostatic electrode to enable chucking and dechucking of the wafer, and the electrostatic electrode is powered by a filter and a DC clamping power source, or another control system, to lift the substrate 105 from the ESC 110. Although not shown, a pump is connected to the plasma chamber 101 to enable vacuum control and removal of gaseous byproducts from the plasma chamber during plasma processing operations.

[0024] In some embodiments, the ICP processing system 100 may include a controller 150 used to control various components of the ICP processing system 100. In one example, the controller 150 may be connected to a plasma generator (e.g., RF power source 147, RF power source 125A, RF power source 125B, bias RF power source 115), a gas source(s) 114 coupled to the plasma process chamber 101, and other components. In some embodiments, the controller 150 includes one or more recipes that include multiple setpoints and various operating parameters (e.g., voltage, current, frequency, pressure, flow rate, power level, temperature, timing parameters, process gas, mechanical operation of the substrate 120, etc.) for operating the ICP processing system 100. For example, depending on the process being performed, the controller 150 controls the delivery of process gas from the gas source(s) 114 to the process chamber 101 to achieve designed processing conditions, such as etching features and / or depositing or forming a film on the substrate 105. The selected gas is then distributed to the defined spatial volume portion on the substrate 120 placed on the ESC118.

[0025] The ICP processing system 100 is configured to generate plasma 150 by inductive coupling. Specifically, by supplying corresponding radio frequency (RF) power to inner coils 130 and outer coils 135 located near (e.g., above) the dielectric window, supplying inductively coupled power into the plasma processing chamber 101, and injecting process gas(s) into the plasma processing chamber, plasma 150 is formed between the dielectric window 120 and the ESC 110. In one embodiment, the inner coil is positioned in the space inside the outer coil along a planar and / or horizontal plane. The inner and outer coils enable the generation of a uniform plasma by inductive coupling by applying RF power to each coil independently. 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, as long as they can withstand the conditions of the 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 produce a corresponding toroidal power distribution within the plasma 150. Therefore, 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 the plasma chamber may operate at high or higher frequencies (e.g., 10 MHz or higher), but by having one coil 180 degrees out of phase with respect to the other, the plasma generation zones of the two coils can be kept separate, and in one embodiment, plasma uniformity can be promoted. However, because the two coils operate in different phases, plasma generation may be inefficient, and therefore, the power applied to the coils must be increased to obtain the desired result (e.g., to produce a constant plasma density and / or uniformity of plasma density). Furthermore, if both coils operate at the same high or higher frequency (but 180 degrees out of phase with respect to each other), the increased power may result in a higher dielectric window sheath voltage and increased ion sputtering onto the dielectric window.

[0028] In another embodiment, the inner coil 130 operates at a first frequency, while the other coil 135 operates at a mixed frequency that includes the same frequency (but with a different phase) used for the inner coil, along with a different lower frequency. By using a mixed frequency for the outer coil, the plasma generation zones from the two coils can be sufficiently separated, resulting in improved uniformity of plasma density across the entire wafer surface. Furthermore, the mixed frequency can lead to more efficient plasma generation because it requires less power to achieve similar results compared to using only high frequencies with different phases in the outer coil.

[0029] In detail, the RF power source 147, tuned by the matching network 145, supplies RF power to the inner coil 130. The RF power source 147 supplies a high-frequency or higher-frequency RF power signal. That is, the first RF power generator is configured to be electrically coupled to the inner coil 130 and to supply a first RF power signal to the inner coil, the first RF power signal operating at a first frequency. For example, the first frequency is a high frequency or higher frequency, in the range of 5 megahertz (MHz) to over 100 MHz. Furthermore, the first frequency may be a baseline frequency of 10 MHz, or 13.56 MHz, or 27 MHz, or 40 MHz, or 60 MHz, or 100 MHz. In one embodiment, the first operating frequency of the RF power source 147 is 13.56 MHz.

[0030] Furthermore, a mixed RF power signal is supplied to the outer coil 135, which includes a higher frequency but out-of-phase RF power signal supplied to the inner coil 130, a lower frequency RF power signal, and a lower frequency signal. Typically, the inner coil 130 and the outer coil 135 may operate at nearly the same high or higher frequencies, as previously described, but the RF power signal to one coil may be 180 degrees out of phase with respect to the RF power signal to the other coil.

[0031] The mixed RF power signal supplied to the outer coil 135 includes a first component containing a second RF power signal and a second component containing a third RF power signal. More specifically, for the first component, a second RF power generator is electrically coupled to the outer coil 135 and configured to apply a second RF power signal operating at a first frequency of the first RF power signal applied to the inner coil 130. For example, an RF power source 125A, tuned by a matching network 127A, supplies high-frequency RF power to the outer coil 135, and the frequency of the RF power supplied to the outer coil (i.e., high frequency) is approximately the same as the frequency of the RF power supplied to the inner coil 130 (i.e., from the RF power source 147), but in opposite phase (i.e., out of phase or 180 degrees out of phase, etc.). As previously mentioned, the first frequency of the RF power signal to the outer coil 135 is a high frequency or higher frequency, in the range of 5 MHz to over 100 MHz. Furthermore, the first frequency may be a baseline frequency of 10 MHz, 13.56 MHz, 27 MHz, 40 MHz, 60 MHz, or 100 MHz. In one embodiment, the first operating frequency of the RF power source 125A 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 configured to supply a third RF power signal operating at a second frequency, where the first frequency is greater than the second frequency. For example, an RF power source 125B, tuned by a matching network 127B, supplies an RF power signal of a lower frequency or lower frequency to the outer coil 135. The second frequency of the RF power signal output by RF power source 125B is lower than the first frequency of the RF power signal output by RF power source 125A, but may be considered a high-frequency signal. For example, the second frequency may be in the range of 10 kilohertz (kHz) to 5 MHz. In one embodiment, the second operating frequency of RF power source 125B is 2 MHz.

[0033] A dependent and / or synchronous controller 155 may be configured to synchronize the frequency of a second RF power signal to a first frequency of a first RF power signal. More specifically, the dependent and / or synchronous controller 155 is configured to provide a pulse synchronous output used to control one or more parameters of the high-frequency RF power signal generated by the RF power source 125A. That is, the dependent and / or synchronous controller 155 is configured to substantially align the high-frequency RF power signal sent from the RF power source 147 to the inner coil 130 and the high-frequency RF power signal sent from the RF power source 125A to the outer coil 135, for example, by aligning the frequencies of the two RF power signals. In some embodiments, the dependent and / or synchronous controller 155 works in conjunction with the controller 150 to substantially align the frequencies of the two RF power signals.

[0034] Furthermore, a fourth RF power signal, adjusted via a matching circuit, provides a bias voltage to the ESC110. Specifically, a matching circuit 117 is electrically coupled to a lower electrode (not shown) located within the ESC, and a bias RF power source 115 is electrically coupled to the matching circuit, with the bias RF power source configured to supply a bias voltage to the ESC110.

[0035] Figure 2A is a top view of an exemplary configuration of the inner coil 130 and outer coil 135 introduced first in the ICP processing system 100 of Figure 1, according to one embodiment of the present disclosure. As shown, the inner coil 130 is positioned in the space inside the outer coil 135 along a planar and / or horizontal plane.

[0036] In detail, an RF power source 147, tuned by a matching network 145, supplies RF power to the inner coil 130. For example, the RF power signal is sent to the input node 210 of the inner coil 130. To complete the circuit, the output node 215 of the inner coil 130 is connected to ground. The first frequency of the RF power signal to the inner coil is a high frequency or higher frequency.

[0037] Furthermore, a mixed RF power signal is supplied to the outer coil 135. For example, the mixed RF power signal is sent to the input node 220 of the outer coil 135. To complete the circuit, the output node 225 is coupled to ground. In detail, the mixed RF power signal includes a first component containing a higher frequency RF power signal in opposite phase (also supplied to the inner coil 130) and a second component containing a lower frequency RF power signal. For example, an RF power source 125A, tuned by a matching network 127A, supplies the outer coil 135 with a high-frequency RF power signal for the first component, where the frequency of the RF power signal (i.e., high frequency) is approximately the same as the frequency of the RF power signal supplied to the inner coil 130 (i.e., from the RF power source 147), but in opposite phase (i.e., out of phase, or 180 degrees out of phase, etc.). Furthermore, an RF power source 125B, tuned by a matching network 127B, supplies the outer coil 135 with a low-frequency or even lower-frequency RF power signal for the second component. As shown in the figure, a single matching circuit 127 may include the functions of matching circuits 127A and 127B.

[0038] One key means of reducing the overall ion gradient across the wafer is to prevent the plasma from interacting with the inner coil 130 and outer coil 135 as if they were one, regardless of the frequency of the RF power signal to the coils. Ideally, the plasma generation zones generated by each of the inner coil 130 and outer coil 135 should remain separate and non-overlapping. One hardware approach to achieving plasma generation zone separation is to increase the coil spacing. Specifically, by increasing the spacing between the coil sets (i.e., the inner coil 130 and the outer coil 135), the plasma generation zones from each coil are separated, thereby enhancing the uniformity of plasma density across the wafer surface. In one embodiment, the spacing is configured to be maximized based on the configuration of the ICP processing system (e.g., chamber size, coil housing size, and other constraints) in an attempt to separate the plasma generation zones of the two coils. However, at some point, the separation of the coils may lose its effectiveness, the uniformity of the plasma density may saturate, and / or the improvement in the overall ion gradient may reverse. To achieve increased uniformity of plasma density across the entire surface of the wafer, additional techniques, including providing mixed RF power to the outer coils, may be required.

[0039] An additional technique implemented through hardware would be winding the inner coil 130 and the outer coil 135 in opposite directions, particularly when supplying a mixed RF power signal to the outer coil 135 (i.e., when both low and high frequencies are passed through the outer coil). For example, as shown in Figure 2, the inner coil 130 is wound clockwise while the outer coil 135 is wound counterclockwise. As a result, the RF waves propagating from the inner and outer coils have a 180-degree phase difference and interfere destructively with each other when they meet, such as in the chamber of an ICP processing system. This destructive interference makes it difficult for the plasma to act as if both coils were a single coil (i.e., the plasma generation zones from the coils are separated). However, this occurs when the same frequency is used for both the inner coil 130 and the outer coil 135 (i.e., a high frequency or higher frequency). If the RF power signals are of different frequencies, the phases between different frequencies are always different relative to each other, so there is no or limited destructive interference between the RF waves.

[0040] Instead of winding the inner and outer coils in opposite directions, the high-frequency RF power signals supplied to the inner coil 130 and the outer coil 135 can be phased 180 degrees apart from each other, so as to be controlled by timing. For example, a controller (e.g., the dependent / synchronous controller 155 and / or controller 150 in Figure 1) may be configured to control the timing of the second RF power signal supplied to the outer coil 135 so that it is in a different phase from the first RF power signal supplied to the inner coil 130.

[0041] Figure 2B is Table 200B, showing exemplary power levels for different embodiments of the inner and outer coils of an ICP processing system according to one embodiment of the present disclosure. The values ​​shown in Table 200B are for illustrative purposes only. Table 200 shows four different exemplary configurations for applying RF power to the inner coil 130 and the outer coil, including row 251, applying high-frequency or higher-frequency RF power to the inner coil alone; row 252, applying low-frequency or lower-frequency RF power to the outer coil alone; row 253, applying a mixed RF power signal to the outer coil alone; row 254, performing current division using only high-frequency or higher-frequency RF power supplied to both the inner and outer coils; and row 255, applying high-frequency or higher-frequency RF power to the inner coil and a mixed RF power signal to the outer coil. Further configurations are also conceivable and applicable. Furthermore, for illustrative purposes, the high frequency or higher frequency of the RF power signal to the inner and / or outer coil is 13.56 MHz, but it is understood that it can be any value. Also, for illustrative purposes, the low frequency or lower frequency of the RF power signal to the outer coil is 2 MHz, but it is understood that it can be any value. In other embodiments, the configuration may be reversed so that a mixed RF power signal is applied to the inner coil and a high-frequency RF power signal is applied to the outer coil.

[0042] In one embodiment, an appropriate power level of the RF power signal can be provided by manipulating the current ratio between the inner and outer coils of the high-frequency or higher-frequency RF power signal applied for current division. For example, the current ratio of the high-frequency or higher-frequency RF power signal (e.g., 13.56 MHz) to the inner and outer coils can be defined using the following formula: (current ratio = high-frequency inner coil current / high-frequency outer coil current). In one embodiment, the current ratio can be in the range of "0.6 to 2.1".

[0043] Depending on the operation of the inner coil 130 and outer coil 135 in various configurations, the power range for each coil can be any value depending on the hardware tolerance and required plasma conditions. Furthermore, the power ratio of the power supplied to the outer and inner coils, where the power to the outer coil is typically greater than the power supplied to the inner coil, may range from zero (0) to infinity when either coil is operating alone, or from 2 (when the high-frequency RF power to the outer coil is minimal and no low-frequency RF power is present) to 60 (when the high-frequency RF power applied to the outer coil is maximum and the low-frequency RF power is maximum). Additionally, the power ratio of the RF power supplied to the outer coil between low-frequency RF power and high-frequency 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 the power ratio may range from 1.4 to 2 when the low-frequency RF power signal to the outer coil is maximum power and the high-frequency RF power signal to the outer coil varies according to the current ratio described above.

[0044] As illustrated in Table 200 and shown in row 251, in an operating setup where only the inner coil 130 is operating independently, there is no power supplied to the outer coil 135 (e.g., 0 watts (W)), and the power supplied to the independently operating inner coil will be in the range of up to 3 kilowatts (kW).

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

[0046] As shown in line 253, in an operating setup where only the outer coil is operating independently with a mixed RF power signal applied, no power is supplied to the inner coil (e.g., 0 watts), and the outer coil 135 may be supplied with up to 6.8 kW of power, which is divided between the low frequency (2 MHz) and high frequency (13.56 MHz) RF power signals. In one embodiment, the second component of the mixed RF power signal (e.g., the 13.56 MHz RF power signal) is supplied with more power than the first component. In another embodiment, the first component of the mixed RF power signal is supplied with more power than the second component.

[0047] In a current-division-only operation setup, as shown in line 254, where high-frequency or higher-frequency power signals are sent to each of the inner coil 130 and the outer coil 135, the power to the inner coil may be in the range of 100 watts to 1 kilowatt, and the power to the outer coil may be in the range of 2 kilowatts to 2.8 kilowatts. In one embodiment, when current-division of high-frequency RF power, more power is supplied to the outer coil than to the inner coil.

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

[0049] Figure 3 is a flowchart illustrating a method, according to one embodiment of the present disclosure, for improving plasma density uniformity and reducing ion gradients across a wafer by supplying one coil set with a higher frequency while supplying the other coil set with higher and lower frequencies in opposite phases. Specifically, the method for reducing ion gradients at the edges of the substrate, according to one embodiment of the present disclosure, includes supplying the inner coil with a higher frequency RF power signal and supplying the outer coil with a mixed RF power signal including higher and lower frequencies in opposite phases. The method of flowchart 300 may be implemented to control processes in the plasma processing systems of Figures 1 and 2A, as well as processes for other plasma processing systems.

[0050] In 310, the method includes providing a plasma chamber configured to generate plasma by inductive coupling, comprising an electrostatic chuck (ESC) for supporting a substrate and a dielectric window provided opposite the ESC. Depending on the process being performed to achieve desired processing conditions, such as etching features and / or depositing or forming a film on the substrate, a gas may be introduced into the plasma chamber.

[0051] In 320, the method includes supplying a first radio frequency (RF) power signal to an internal coil provided on a dielectric window, wherein the first RF signal operates at a first frequency. The frequency of the power signal may be high frequency or higher frequency. For example, the first frequency is high frequency or higher frequency, in the range of 5 megahertz (MHz) to over 100 MHz. As an example, the operating frequency of the first frequency is 13.56 MHz.

[0052] In 330, the method includes supplying a mixed RF power signal to an outer coil provided on a dielectric window. The mixed RF power signal includes a first component and a second component. The first component emits a second RF power signal operating at a 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 emitted to the inner coil.

[0053] The second component of the mixed RF power signal to the outer coil emits a third RF power signal operating at a second frequency, which is lower. For example, the second frequency of the second component of the mixed RF power signal may be in the range of 10 kilohertz (kHz) to 5 MHz. In one embodiment, the second operating frequency is 2 MHz. By applying a mixed RF power signal to the outer coil (e.g., mixing a low frequency with a high-frequency RF power signal with a different phase), power isolation from the plasma generation zones of each coil can be enhanced, improving the uniformity of plasma density across the entire surface of the substrate. When using a mixed RF power signal, plasma generation can be more efficient because a plasma with improved plasma density uniformity is generated with less power. Also, because the outer coil involves a lower frequency, sputtering to the dielectric window may be reduced. As a result, the plasma generation zones of the two coils can remain isolated due to the enhanced power isolation, thereby promoting uniformity of plasma density across the entire surface of the substrate. Furthermore, by using a mixture of higher-frequency and lower-frequency signals with different phases, plasma uniformity is improved, thus reducing the overall gradient across the entire wafer.

[0054] Figure 4 shows the RF power signals supplied to the coils of an inductively coupled plasma generation system according to one embodiment of the present disclosure. Specifically, by supplying one set of coils with a higher frequency while supplying the other set of coils with higher and lower frequencies in opposite phase, the uniformity of plasma density across the entire surface of the substrate is improved, and the ion gradient, particularly at the edges of the substrate, is reduced. The graph shown in Figure 4 includes aligning time axes 415A and 415B and an amplitude axis 410 containing two zero (0) points on each of the time axes 415A and 415B.

[0055] In detail, the RF power signal 420a is applied to the inner coil and operates at a first frequency which may be a high frequency or higher frequency. For illustrative purposes, the high first frequency may be 10 MHz. The period 425a of one cycle of the RF power signal 420a is shown in relation to the time axis 415A, and also shows the phase of the RF power signal 420a. The amplitude of the RF power signal 420a is shown purely for illustrative purposes.

[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 the RF power signal 420b operating at a first frequency. Of the mixed RF power signal to the outer coil, RF power signal 420b 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, the period 425b of one cycle of RF power signal 420b is shown in relation to the time axis 415B, and the period 425b of RF power signal 420b is equal to the period 425a of RF power signal 420a. However, the phase of RF power signal 420b is 180 degrees out of phase with RF power signal 420a, as shown by the time difference 430. Furthermore, the amplitude of RF power signal 420b is shown purely for illustrative purposes.

[0057] The second component is the RF power signal 440, which operates at a second frequency lower than the first frequency. For example, the operating frequency of the RF power signal 440 may be 2 MHz. The period 445 of one cycle of the RF power signal 440 is shown in relation to the time axis 415B. Furthermore, the amplitude of the RF power signal 440 is shown purely for illustrative purposes.

[0058] Figure 5A shows the plasma density and sheath across the wafer, which result in the gradient of ions colliding with the substrate being processed in a plasma processing system such as an ICP processing system. In detail, Figure 5A focuses on the substrate 105 supported by an electrostatic chuck (ESC) 110 during processing. An edge ring 530 may surround the ESC 110 and is configured to perform several functions. These functions include, but are not limited to, positioning the substrate 105 on the ESC 110, restricting the plasma to an area above the substrate 105, protecting the ESC 110 from erosion by plasma ions, shielding components below the plasma chamber from damage by plasma ions, and improving performance at the edges of the substrate.

[0059] Typically, a plasma processing system generates plasma. The plasma density profile 520A of the plasma is generated in partial response to a bias RF power signal on the ESC 110. As shown in the figure, the plasma density profile initially traverses horizontally along the inside of the substrate 105, but then rolls downward along the remaining length of the substrate. That is, non-uniformity of the plasma density profile may appear in the middle of the wafer (i.e., about half from the center to the edges), and possibly earlier (i.e., towards the center).

[0060] Furthermore, the sheath thickness 510A is typically inversely proportional to the plasma density profile 250. The sheath defines the region where electrons become depleted and is located on the substrate or wafer. As shown in the figure, the sheath thickness is initially horizontal on the substrate 105 (i.e., near the center of the substrate), but deforms as the substrate length progresses, rising upward at the edges. That is, the sheath may bend at the beginning of the middle part of the wafer (i.e., about half from the center to the edges), and in some cases earlier (i.e., towards the center).

[0061] Ions that escape the plasma and are partially pulled toward the substrate 105 by the bias RF power signal propagate perpendicular to the sheath thickness 510A. That is, ions 515A in zones on the substrate 105 where the plasma is uniform escape the plasma and propagate perpendicularly toward the substrate 105. On the other hand, ions 515B located where plasma non-uniformity begins on the substrate 105 exit the plasma at an angle such as perpendicular to the surface of the sheath, as determined by the sheath thickness 510A which increases as the plasma non-uniformity begins to appear. That is, ions 515B have a tilt offset from the vertical plane (i.e., the angle from the vertical plane through which the ions propagate). The ion tilt introduced onto the substrate results in unexpected etching features due to this ion tilt. For example, when etching the substrate, etching features on the substrate where non-uniformity or this sheath bending occurs will be angled (i.e., etched at an angle) and not vertical (i.e., etched vertically), whereas in a uniform plasma, etching features will be oriented vertically.

[0062] Figure 5B shows the plasma density and sheath on a substrate being processed in an ICP processing system such as system 100 in Figure 1, according to one embodiment of the present disclosure. Plasma density uniformity on substrate 105 is achieved, according to one embodiment of the present disclosure, by feeding the inner coil with a higher frequency RF power signal and feeding the outer coil with a mixed RF power signal including higher and lower frequencies in opposite phase. In detail, Figure 5B focuses on a region on substrate 105 where plasma uniformity is achieved by the above technique.

[0063] Typically, an ICP processing system generates plasma. The plasma density profile 520B of the plasma is generated in partial response to a bias RF power signal on the ESC 110. As shown in the figure, the plasma density profile initially crosses horizontally across the inside of the substrate 105. The plasma density profile is also uniformly horizontal across the rest of the substrate 105, so that the plasma density profile is uniform across the entire surface of the substrate, as partially shown in the highlighted range 550.

[0064] Furthermore, the sheath thickness 510B is typically inversely proportional to the plasma density profile 520B. The sheath defines the area where electrons become depleted and is located on the substrate or wafer. As shown in the figure, the sheath thickness is also uniformly horizontal across the rest of the substrate, so that the sheath thickness is uniform across the entire surface of the substrate, as shown partially in the highlighted area 550.

[0065] Ions that escape the plasma and are partially pulled toward the substrate 105 by the bias RF power signal propagate perpendicular to the sheath thickness 510B. That is, ions 515A' inside the substrate 105 escape the plasma and propagate vertically toward the substrate 105. Since the sheath thickness 510B is uniform across the entire surface of the substrate, including the edges of the substrate, ions 515C at the edges of the substrate also escape the plasma vertically (i.e., perpendicular to the horizontal sheath thickness 510B). That is, ions 515C have no gradient, or the ion gradient from the vertical plane is significantly reduced. Thus, features are uniform across the entire substrate so that features formed at the edges of the substrate and features formed inside the substrate are substantially similar. For example, when etching the substrate, etching features throughout the inside of the substrate and at the edges will be oriented vertically (i.e., etched vertically).

[0066] Figures 6A to 6C show plasma generation zones related to plasma uniformity and non-uniformity of the plasma in the inner and outer coils of an ICP plasma processing system powered using different signal configurations according to one embodiment of the present disclosure. Typically, the ICP processing system is configured to generate plasma by inductive coupling and partially includes an electrostatic chuck (ESC) 110 for supporting a substrate 105, and an inner coil 130 and an outer coil provided on a dielectric window. An edge ring 530 may surround the ESC 110.

[0067] Figure 6A shows the plasma generation zones of an ICP processing system in which RF power signals having the same frequency and being in phase with each other are applied to both the inner coil 130 and the outer coil 135, according to one embodiment of the present disclosure. For purely illustrative purposes, the RF power signals to the inner and outer coils may operate at frequencies of 10 MHz or 13.56 MHz, respectively. Applying the same frequency in phase to both coils can produce a continuous power deposition profile, as shown by the plasma generation zone 610a of the inner coil 130 and the plasma generation zone 620a of the outer coil 135, but this may not be sufficient to produce good uniformity of the plasma density profile across the entire substrate. In detail, region 650a shows the overlap between plasma generation zones 610a and 620a. Typically, separating the plasma generation zones of the inner and outer coils (i.e., ensuring the zones do not interact with or influence each other) is used to achieve a desirable uniform plasma density profile across the entire substrate.

[0068] Figure 6B shows the plasma generation zone of an ICP processing system in which a high-frequency RF power signal is applied to an inner coil 130 and a lower-frequency RF power signal is applied to an outer coil 135, according to one embodiment of the present disclosure. Purely as an 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 in the figure, feeding the inner and outer coils with RF power signals of different frequencies creates a kind of plasma separation, which enhances uniformity. In detail, the plasma generation zone 610b of the inner coil 130 and the plasma generation zone 620b of the outer coil 135 are shown separately, and the overlap between the plasma generation zones 610b and 620b is not shown in region 650b. While separation of the plasma generation zones of the inner and outer coils (i.e., the zones not interacting with or influencing each other) is desirable, a lower frequency RF power signal to the outer coil 135 alone can result in a thicker skin depth (i.e., a deeper plasma generation zone) and can ionize more by-product gases, which can further reduce plasma uniformity and make the plasma density profile non-uniform across the entire substrate.

[0069] Figure 6C shows the plasma generation zone of an ICP processing system in which a high-frequency RF power signal is applied to the inner coil 130 and a mixed RF power signal is applied to the outer coil. The mixed RF power signal includes a first component, which is a high-frequency RF power signal having the same frequency as the one applied to the inner coil but with a 180-degree phase difference, and a second component, which is a lower frequency or lower frequency RF power signal. Purely as an example, the high-frequency RF power signal to the inner and / or outer coil (i.e., the first component) may operate at a frequency of 10 MHz or 13.56 MHz, and the lower frequency RF power signal to the outer coil (i.e., the second component) may operate at a frequency of 2 MHz. As shown in the figure, both feeding the inner coil with a higher frequency RF power signal and feeding the outer coil with a mixed RF power signal containing a higher frequency RF power signal and a lower frequency RF power signal with opposite phases can separate and improve the uniformity of the plasma generation, as well as reduce the voltage across the window caused by sputtering. In detail, the plasma generation zone 610c of the inner coil 130 and the plasma generation zone 620c of the outer coil 135 are shown separately, and there is no overlap between the plasma generation zones 610c and 620c in region 650c. By mixing higher frequency and lower frequency signals and sending them to the outer coil 135, power isolation and plasma uniformity can be enhanced at a lower power level compared to using only higher frequency signals. Also, because the outer coil is accompanied by a lower frequency signal, sputtering to the dielectric window may be reduced. As a result, the plasma generation zones of the two coils can remain separated, thus promoting plasma uniformity. Furthermore, because plasma uniformity is improved by using a mixture of higher frequency and lower frequency signals, the overall gradient across the entire substrate is reduced.

[0070] In embodiments, the substrate positioning program may include chamber component control program code used to mount the substrate onto a pedestal or chuck and to control the spacing between the substrate and other components of the chamber, such as the gas inlet and / or object, which may be implemented by a control system or the controller 150 in Figure 1. In some embodiments, the controller is part of a system which may be part of the examples described above. Such a system may include semiconductor processing equipment such as one or more processing tools, one or more chambers, one or more processing platforms, and / or specific processing components (such as a substrate pedestal and a gas flow system). These systems may be integrated with electronic equipment for controlling the operation of the system before, during, and after processing of semiconductor wafers or substrates. Depending on the processing requirements and / or the type of system, the controller may be programmed to control any of the processes disclosed herein and processes performed to operate the plasma chamber. Program instructions may be instructions transmitted to the controller in the form of various individual settings (or program files) that define operating parameters for performing a specific process on or for a semiconductor substrate or for the system. In some embodiments, the operating parameters may be part of a recipe determined by a process engineer to achieve one or more processing steps in the manufacture of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and / or wafer molds.

[0071] In some embodiments, the controller may be part of a computer integrated with the system, coupled to the system, or otherwise networked to the system, or coupled to such a computer, or a combination thereof. For example, the controller may be all or part of a host computer system in a manufacturing plant that is in the “cloud” or enables remote access to board processing. This computer may, by enabling remote access to the system, monitor the current progress of manufacturing operations, verify the history of past manufacturing operations, and verify trends or performance criteria from multiple manufacturing operations, thereby modifying parameters of the current process, setting processing steps following the current process, or starting a new process. In some embodiments, a remote computer (e.g., a server) may provide process recipes to the system via a network that may include a local network or the internet.

[0072] Exemplary systems, though not limited to them, may include plasma etching chambers or modules, deposition chambers or modules, spin rinse chambers or modules, metal plating chambers or modules, clean chambers or modules, bevel edge etching chambers or modules, physical vapor deposition (PVD) chambers or modules, chemical vapor deposition (CVD) chambers or modules, plasma-excited chemical vapor deposition (PECVD) chambers or modules, atomic layer deposition (ALD) chambers or modules, atomic layer etching (ALE) chambers or modules, ion implantation chambers or modules, track chambers or modules, and any other semiconductor processing systems that may be associated with or used in the manufacturing and / or production of semiconductor wafers.

[0073] The above-mentioned embodiments are provided for illustrative and explanatory purposes only. They are not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are not typically limited to that particular embodiment, but where applicable, they are interchangeable and can be used in selected embodiments, even if not specifically illustrated or described. The above-described embodiments may also be modified in various ways. Such modifications should not be considered departures from the disclosure, and all such modifications are intended to be within the scope of the disclosure.

[0074] While the embodiments described above have been explained in some detail for clarity, it will be apparent that certain changes and modifications may be made within the scope of the claims in the appendix. Therefore, these embodiments are considered illustrative and not restrictive, and the embodiments are not limited to the details shown herein and may be modified within the scope of the embodiments and equivalents of the claims.

Claims

1. It is a method, To provide a plasma chamber configured to generate plasma by inductive coupling, comprising an electrostatic chuck (ESC) for supporting a substrate, and a dielectric window provided opposite the ESC, The method involves supplying a first radio frequency (RF) power signal to an inner coil provided on the dielectric window, wherein the first RF signal operates at a first frequency. The method includes supplying a mixed RF power signal to an outer coil provided on the dielectric window, which includes a first component that transmits a second RF power signal operating at the first frequency and a second component that transmits a third RF power signal operating at the second frequency. A method wherein the first frequency is greater than the second frequency.

2. The method according to claim 1, A method wherein the second RF power signal supplied to the outer coil has a different phase from the first RF power signal supplied to the inner coil.

3. The method according to claim 2, A method in which the inner coil is wound in the opposite direction to the outer coil.

4. The method according to claim 2, A method further comprising controlling the timing of the second RF power signal supplied to the outer coil so that it is in a different phase from the first RF power signal supplied to the inner coil.

5. The method according to claim 1, A method further comprising synchronizing the frequency of the second RF power signal with the first frequency of the first RF power signal.

6. The method according to claim 1, A method for supplying a fourth RF power signal, adjusted via a matching circuit, to a lower electrode located within the ESC in order to provide a bias voltage.

7. The method according to claim 1, A method further comprising supplying greater power to the outer coil than to the inner coil.

8. The method according to claim 1, The first frequency is 13.56 MHz, The method wherein the second frequency is 2 MHz.

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

10. The method according to claim 1, A method in which the inner coil is positioned in the space inside the outer coil along a horizontal plane.

11. It is a system, A plasma chamber configured to generate plasma by inductive coupling, comprising an electrostatic chuck (ESC) for supporting a substrate, and a dielectric window provided opposite the ESC, An inner coil provided on the dielectric window, An outer coil provided on the dielectric window, A first radio frequency (RF) power generator is 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 is electrically coupled to the outer coil and configured to supply a second RF power signal operating at the first frequency, The system comprises 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, The mixed RF power signal is supplied to the outer coil and comprises a first component including the second RF power signal and a second component including the third RF power signal. A system in which the first frequency is greater than the second frequency.

12. The system according to claim 10, A system in which the second RF power signal supplied to the outer coil has a different phase from the first RF power signal supplied to the inner coil.

13. The system according to claim 12, A system in which the inner coil is wound in the opposite direction to the outer coil.

14. The system according to claim 12, The system further comprises a controller configured to control the timing of the second RF power signal supplied to the outer coil so that it is in a different phase from the first RF power signal supplied to the inner coil.

15. The system according to claim 11, A system further comprising a synchronizer configured to synchronize the frequency of the second RF power signal with the first frequency of the first RF power signal.

16. The system according to claim 11, A matching circuit electrically coupled to the lower electrode located within the ESC, A system further comprising a bias RF generator electrically coupled to the matching circuit and configured to supply the lower electrode with a fourth RF power signal adjusted via the matching circuit to provide a bias voltage.

17. The system according to claim 11, A system that supplies more power to the outer coil than to the inner coil.

18. The system according to claim 11, The first frequency is 13.56 MHz, A system in which the second frequency is 2 MHz.

19. The system according to claim 11, A system that supplies more power to the second component of the mixed RF power signal than to the first component.

20. The system according to claim 11, A system in which the inner coil is positioned in the space inside the outer coil along a horizontal plane.

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