Plasma processing system and method using radio frequency and microwave power

Abstract

A plasma processing system comprises a vacuum system, a plasma processing chamber including a chamber cavity coupled to the vacuum system, a substrate holder including a surface inside the chamber cavity, and a radio frequency (RF) source electrode coupled to an RF power source, wherein the RF source electrode is configured to ignite plasma in the chamber cavity. The system comprises a microwave source coupled to a microwave oscillator and an electromagnetic (EM) metasurface, wherein the EM metasurface has a main surface electromagnetically coupled to the microwave source, and the main surface is configured to couple microwave power to the plasma in the chamber cavity.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 145,048 (filed February 3, 2021), which is incorporated herein by reference.

[0003] Technology field

[0004] The present invention generally relates to a system and method for a plasma process, and in a specific embodiment, to a system and method for plasma treatment of a semiconductor wafer using radio frequency (RF) and microwave power. Background Technology

[0005] Generally, semiconductor devices, such as integrated circuits (ICs), are manufactured by sequentially depositing and patterning layers of dielectric, conductive, and semiconductor materials on a substrate to form a network of electronic components and interconnect elements (e.g., transistors, resistors, capacitors, metal lines, contacts, and vias) integrated into a monolithic structure. A number of processing steps used to form the structural components of semiconductor devices are performed using plasma processing techniques, including sputtering, reactive ion etching (RIE), plasma-enhanced chemical vapor deposition (PECVD), and plasma-enhanced atomic layer etching (PEALE) and atomic layer deposition (PEALD).

[0006] At each successive technology node, the minimum feature size has shrunk, reducing costs by nearly doubling component packing density. Innovations in patterning techniques, such as immersion photolithography, multi-patterning, and 13.5 nm wavelength extreme ultraviolet (EUV) optical systems, have reduced the critical feature size to approximately 10 nanometers. Simultaneously, unconventional materials, such as organics, ferroelectrics, and chalcogenides, are being increasingly used in products. This scenario presents challenges for plasma technology in providing a platform for patterning features at the atomic scale, through precise sizing, fine placement, and tight control. Further innovation is required to address this challenge, along with the uniformity and repeatability requirements for mass IC fabrication.

[0007] A plasma processing system comprises a vacuum system; a plasma processing chamber comprising a chamber cavity coupled to the vacuum system and a substrate holder having a surface inside the chamber cavity; and a radio frequency (RF) source electrode coupled to an RF power source, wherein the RF source electrode is configured to ignite plasma in the chamber cavity. The system comprises a microwave source coupled to a microwave oscillator and an electromagnetic (EM) metasurface, wherein the EM metasurface has a main surface electromagnetically coupled to the microwave source, and the main surface is configured to couple microwave power to plasma in the chamber cavity.

[0008] A plasma processing system comprises: a plasma processing chamber; an RF source electrode configured to ignite a plasma in the plasma processing chamber as a radio frequency (RF) source electrode coupled to an RF power source; an electromagnetic (EM) metasurface having a main surface configured to couple microwave power to the plasma in the plasma processing chamber as a microwave power system coupled to the plasma by microwave power; a microwave power system comprising a microwave source coupled to a microwave oscillator; and a controller configured to adjust a spatial uniformity metric of the EM power supplied to the plasma by executing commands.

[0009] A method for plasma processing of a semiconductor wafer comprises the steps of: loading a semiconductor wafer into a plasma processing chamber coupled to a radio frequency (RF) source electrode and a microwave power system including a microwave oscillator and a microwave source; igniting a plasma by coupling RF power from the RF source electrode to a gas in the plasma processing chamber; coupling microwave power from the microwave power system to the plasma ignited in the plasma processing chamber by coupling the microwave oscillator to the microwave source; and controlling a spatial uniformity metric of coupled electromagnetic (EM) power supplied to the plasma by adjusting the microwave power. Brief explanation of the drawing

[0010] For a more complete understanding of the present invention and the advantages of the present invention, we now refer to the following description together with the accompanying drawings. FIG. 1a is a cross-sectional view of an inductively coupled plasma (ICP) processing chamber having an electromagnetic (EM) metasurface in a substrate holder of an ICP chamber according to an embodiment; FIG. 1b is a perspective view of an EM metasurface according to an embodiment; FIG. 1c is a perspective view of an EM metasurface according to an embodiment; FIG. 2a is a cross-sectional view of an ICP processing chamber having an EM metasurface on the top cover of the ICP chamber according to an embodiment; FIG. 2b is a perspective view of an EM metasurface according to an embodiment; FIG. 2c is a perspective view of an EM metasurface according to an embodiment; FIG. 2d is a perspective view of an EM metasurface according to an embodiment; FIG. 3 is a cross-sectional view of a capacitively coupled plasma (CCP) processing chamber having an electromagnetic (EM) metasurface in a substrate holder of a capacitively coupled plasma (CCP) chamber according to an embodiment; FIG. 4 is a cross-sectional view of a CCP processing chamber having an EM metasurface at the top electrode of the CCP chamber according to an embodiment; FIG. 5 is a cross-sectional view of a CCP processing chamber having an EM metasurface below the upper electrode of the CCP chamber according to an embodiment; and FIG. 6 is a flowchart illustrating a method for plasma treatment of a semiconductor wafer using radio frequency (RF) power and microwave power according to an embodiment. Specific details for implementing the invention

[0011] The present disclosure describes embodiments of a plasma processing system and method for processing semiconductor wafers, wherein radio frequency (RF) power is supplemented by microwave power within the total electromagnetic (EM) power applied to ignite, sustain, and control the plasma in a plasma processing chamber. The spatial distribution of microwave power coupled to the plasma may differ from and be complementary to the spatial distribution of RF power coupled to the plasma. It is desirable to have a spatially uniform distribution of coupled EM power coupled to the plasma. In exemplary embodiments, while the plasma may be ignited and sustained using power from an RF power source, a microwave power system providing microwave power from a microwave source is used to adjust the spatial distribution of the total electromagnetic (EM) power supplied to the plasma. This adjustment may improve the spatial uniformity metric of the total EM power supplied to the plasma. By utilizing two independent sources of EM power, the system and method exemplified by the exemplary embodiments of the present disclosure provide the advantage of achieving a more uniform plasma, and thus the advantage of achieving spatially more uniform characteristics for the processed semiconductor wafer.

[0012] As described in more detail below, the adjustment of EM power distribution is performed outside the plasma processing chamber using a controller for the microwave power system to control the microwave power. Accordingly, the embodiment provides the advantage of having plasma control parameters that can be used to adjust the distribution of EM power. Specific control parameter values ​​may be selected for a specific plasma process recipe and / or a specific set of values ​​may be selected for a specific periodic or multi-stage plasma process recipe, for example, for multi-stage plasma etching. The control parameter values ​​may be selected by a process control system as part of feedback or feedforward control in a process flow for semiconductor device manufacturing.

[0013] In the embodiments described in this disclosure, fixed surface EM waves in the microwave frequency band are activated at an EM metasurface positioned in close proximity to the plasma inside a processing chamber to couple microwave power from a microwave source to the plasma. Generally, an EM metasurface represents a repetitive two-dimensional (2D) array of patterns of conductors and insulators with subwavelength characteristics. Incident EM radiation at the resonant frequency or near-resonant frequency of the repetitive unit of the 2D array can activate the surface EM waves. One example of an EM metasurface is a wavy metal surface, which is an array of trench-shaped openings etched into a metal layer. When the quarter wavelength of the impacting EM radiation is significantly close to the depth of the groove, EM activation is observed propagating along the metal to the dielectric interface in a direction perpendicular to the groove. Such surface EM activation is sometimes referred to as camouflage surface plasmon polaritons.

[0014] Surface plasmon polaritons (SPPs) are EM surface waves at the interface between a dielectric and a conductor activated through the coupling of an EM field to an electron plasma of a metal using a suitably designed coupler. Surface electromagnetic field oscillations on the dielectric side and plasma oscillations of free electrons on the metal side are localized and propagated at the interface with a minute electric field having a subwavelength decay length perpendicular to the direction of the wave. Typically, at lower frequencies (e.g., 10 13 At frequencies below Hz, most metals behave as ideal conductors, so the vibration frequency of the SPP is high (e.g., 10 14 Hz to 10 15 Hz), this means that the frequency-dependent composite dielectric constant has a real part equal to zero. Nevertheless, in the microwave range (e.g., 10 9 Hz to 10 11Artificial SPP modes at Hz have been demonstrated using EM metasurfaces that mimic the localization and dispersion characteristics of natural SPPs; thus, they are referred to as camouflage surface plasmon polaritons (SSPPs).

[0015] In the embodiments described in this disclosure, the microwave power system comprises a microwave source coupled to a microwave oscillator and an EM metasurface. The EM metasurface has a main surface configured to receive microwave power from the microwave source and couple the microwave power to the plasma. Surface EM activation similar to the SSPP activation described above is generated between two conductive regions: the EM metasurface and a charge-neutral region of the high electron density plasma. The dielectric between these two conductors comprises a plasma sheath, which is a peripheral space-charge region of the localized plasma where moving electrons are depleted. As described in more detail below, the EM metasurface may have various patterns and arrangements in various embodiments.

[0016] FIG. 1a illustrates an exemplary embodiment of a plasma processing system (100) comprising a plasma processing chamber (150) comprising a substrate holder (112). In FIG. 1a, the plasma processing chamber (150) is an inductively coupled plasma (ICP) processing chamber illustrated in a cross-sectional view. An RF source electrode (108) having the shape of a flat coil disposed on a top cover comprising a dielectric window (126) is an RF source that provides RF power to ignite and sustain the plasma (106). The dielectric window (126) may comprise, for example, ceramic, such as quartz.

[0017] The microwave source of the plasma processing system (100) is a microwave antenna (110) shown as being placed on the side wall (124) of the plasma processing chamber (150). In this exemplary embodiment, the side wall (124) may comprise a conductive material, for example, aluminum or stainless steel coated with yttria. The microwave antenna (110) has a center frequency ( f c ) around, bandwidth(Δ f It is configured to emit EM waves inside the plasma processing chamber (150) in ). The center frequency is selected to be in the microwave range, and the bandwidth (Δ f )silver ( f c It may be approximately ± 5% to approximately ± 15% of ). Radiation emitted from the antenna (110) will have the same frequency as the output signal of the microwave oscillator (190) coupled to the antenna (110). In an embodiment of the present disclosure, the microwave oscillator (190) may be an adjustable microwave oscillator (190), and the frequency may be a range ( f c ±Δ f It is adjusted in / 2). The microwave frequency suitable for plasma treatment may be about 1 GHz to about 100 GHz in various embodiments and 2.45 GHz in one embodiment.

[0018] As illustrated in FIG. 1a, a semiconductor wafer (120) exposed to the internal environment of a chamber cavity (102) is loaded onto a substrate holder (112). The substrate holder (112) is generally an electrostatic chuck comprising a conductive pedestal, e.g., a conductive pedestal (118). The upper portion of the pedestal (118) is an EM metasurface (134), and the main surface (130) of the EM metasurface (134) is the upper surface of the pedestal (118) (the surface facing the chamber cavity (102)). The main surface (130) is electromagnetically coupled to the antenna (110) so that a portion of the emitted microwave power is received by the main surface (130) to activate EM surface waves or SSPP. In some embodiments, the main surface (130) of the EM metasurface (134) and the pedestal (118) comprise the same conductor (e.g., copper, aluminum, tungsten, or brass), but in other embodiments, they may not comprise the same conductor. In FIG. 1a, the EM metasurface (134) and the pedestal (118) form a single monolithic structure. However, it is understood that separate structures assembled together are also possible.

[0019] In the exemplary embodiment illustrated in FIG. 1a, the main surface (130) of the EM metasurface (134) includes an opening formed in the pedestal (118) in a pattern described in more detail below with reference to FIG. 1b and FIG. 1c. The opening may be filled with an insulating gas (e.g., air or nitrogen) that can be sealed at the opening by a separator (122) comprising a solid dielectric layer covering the main surface (130) of the EM metasurface (134). This causes the insulating gas within the opening to be at a pressure (e.g., atmospheric pressure) much higher than the pressure in the chamber cavity (102), thereby helping to prevent the occurrence of incidental arcs, as in low-pressure gas exposed to a high electric field. Suitable materials for the separator (122) include quartz, alumina, and glass. The sides of the pedestal (118) are covered by any dielectric structure (116).

[0020] Note that the conductive pedestal (118) may be configured to additionally function as an RF bias electrode, a DC bias electrode, or a combination of a DC bias electrode and an RF bias electrode.

[0021] FIGS. 1B and FIGS. 1C illustrate perspective views of two exemplary EM metasurfaces (134A and 134B) that can be used in the plasma processing system (100) illustrated in FIG. 1A. The EM metasurfaces of FIGS. 1B and FIG. 1C may be the pedestal (118) of the substrate holder (112) described with reference to FIG. 1A. Either the main surface (130A) ( FIG. 1B) and the main surface (130B) ( FIG. 1C) may be the main surface (130) of the EM metasurface (134) illustrated in FIG. 1A. As mentioned above, the EM metasurface and the pedestal (118) form a monolithic structure, and the top surface of the monolithic structure is the main surface (130) of the EM metasurface (134). The pedestal (118) serves as a conductive base on the top surface where an array of openings is patterned.

[0022] In FIG. 1b, the main surface (130A) comprises an array of long, narrow, parallel trenches, each having a top opening shaped like a rectangle. Thus, the array is a line and space pattern formed by conductive lines spaced apart by a gas insulator. The conductive walls of each trench are nearly vertical sidewalls that terminate at a nearly flat bottom wall. All trenches in the array have nearly the same depth. The separator (122) covering the main surface (130) of FIG. 1a is shown above the main surface (130A) in the exploded view illustrated in FIG. 1b.

[0023] The main surface (130B) illustrated in FIG. 1c comprises a rectangular array of prism-shaped holes, each having a top opening with a square shape. The conductive sides of the prism-shaped holes are nearly vertical, and the bottom portions are flat conductive surfaces. In the embodiment illustrated in FIG. 1c, the openings are square-shaped prisms. However, it is understood that prisms with other shapes, such as cylinders and pyramids, may be used. In some embodiments, curved grooves may be used instead of prism-shaped grooves having flat sides with edges.

[0024] Although referred to as surface waves, the electromagnetic field of SSPP activation exists in the dielectric region of the main surface (130A / 130B) as well as in the dielectric region between the main surface (130A / 130B) and the plasma (106) (exemplified in FIG. 1a). Thus, the main surfaces (130A and 130B) include conductive sidewalls of hollow openings in addition to conductive surfaces covered by separators (122) on the sides facing the chamber cavity (102) (see FIG. 1a).

[0025] The feature size of the patterned main surfaces (130A and 130B) of the EM metasurface exemplified in FIG. 1b and 1c determines the resonance mode for the structure. As mentioned above, EM radiation incident at the resonance frequency can activate the respective SSPP modes on the main surface of the EM metasurface. As indicated by the wavy symbol with an arrow in FIG. 1b, microwave radiation can be coupled to the EM metasurface (134A) at the edge of the main surface (130A), and the SSPP mode activated thereby can propagate microwave power from the edge of the main surface (130A) toward the central region. One condition for resonance for the main surfaces (130A and 130B) is that the aperture is at a depth substantially close to λ / 4 ( d It means that it has ), and λ is the wavelength of the incident EM radiation. dThe condition = λ / 4 applies to the microwave frequency range mentioned above, 1 GHz < f c For < 100 GHz, the depth of the openings on the main surfaces (130A and 130B) is 7.5 cm < d It implies that it should be in the range of < 0.75 mm. Generally, the size of various features on the EM metasurface used in various embodiments of the plasma processing system described in this disclosure may be about 1 mm to about 10 cm.

[0026] FIG. 2a illustrates a cross-sectional view of another plasma processing system (200) that uses both RF power and microwave power to process a semiconductor wafer (120) in a plasma processing chamber (150) configured as an ICP chamber. Similar to the plasma processing system (100) described above with reference to FIG. 1a, the RF source electrode (108) is positioned over a dielectric window (126), and the microwave source is a microwave antenna (110) positioned on a sidewall (124). Similar to the pedestal (118) described above with reference to FIG. 1a, the substrate holder (112) of the plasma processing system (200) includes a conductive pedestal (119) in which the side of the pedestal (119) is covered by any dielectric structure (116). However, unlike the pedestal (118), the top surface of the pedestal (119) is not the main surface of the EM metasurface of each plasma processing system (200). In the plasma processing system (200), the EM metasurface (234) is embedded in the dielectric window (126), and the main surface (230) is a side facing downward toward the substrate holder (112). For stronger coupling with the plasma (106), it is preferable that the EM metasurface (234) be positioned close to the side of the dielectric window (126) facing the chamber cavity (102) to accommodate a relatively thin solid dielectric layer that functions as the separator (122) described above with reference to FIG. 1a. Surrounded by the solid dielectric of the dielectric window (126), the main surface (230) is sealed from gas in the chamber cavity (102).

[0027] FIGS. 2b through 2d illustrate perspective views of three exemplary main surfaces of EM metasurfaces (234A, 234B, and 234C) suitable for the plasma processing system (200) illustrated in FIG. 2a. FIG. 2b illustrates a main surface (230A) including an opening formed in a conductor, and FIGS. 2c and 2d illustrate two exemplary designs of main surfaces (230B and 230C) using microstrip metamaterials. Due to the location of the EM metasurface (234) of the plasma processing system (200) (as illustrated in FIG. 2a), the EM field generated by the RF source electrode (108) will be partially shielded by the conductive zones of the EM metasurface (234) structure. Therefore, the patterns selected for the main surfaces (230A, 230B, and 230C) do not include a conductive plate. If the main surface (230) of FIG. 2a includes a conductive plate, RF source power can be almost blocked from igniting plasma in the chamber cavity (102).

[0028] Similar to the main surfaces (130A and 130B) described above with reference to FIG. 1b and 1c, the main surface (230A) illustrated in FIG. 2b is another exemplary EM metasurface designed as an array of openings in a conductive matrix. As illustrated in FIG. 2b, the openings extend through a conductor to remove the flat bottom wall present in the trench-shaped openings of the main surface (130A). Removing the bottom wall allows the EM field originating from the RF source electrode (108) (illustrated in FIG. 2a) to be coupled to the plasma (106) in the chamber cavity (102). Likewise, another embodiment similar to the rectangular array of prismatic holes of the main surface (130B) in FIG. 1c can be used in a plasma processing system (200) (see FIG. 2a) after modifying the design by extending the holes through a conductive matrix to form perforations. As mentioned above, since the EM metasurface (234) of the plasma treatment system (200) will be embedded in the solid dielectric material of the dielectric window (126), there is no dielectric separator as shown in FIG. 2b; therefore, the separator is unnecessary for sealing the main surface (230A) from the chamber cavity (102).

[0029] FIGS. 2c and 2d illustrate examples of EM metasurfaces (234B and 234C) using microstrip metamaterials that may be suitable for a plasma processing system (200). This structure comprises a planar repeating array of patterns of metal in a dielectric matrix (226), similar to a microstrip antenna printed on a monolithic microwave integrated circuit (MMIC) or a printed circuit board (PCB) used for microwave frequency communication. The dielectric of the microstrip metamaterial may include quartz, glass, ceramic, silicon, etc., and the conductor may include a metal, e.g., copper, tungsten, brass, silver, gold, etc. The main surfaces (230B and 230C) of the EM metasurfaces (234B and 234C) comprise an array of microstrips, and the microstrips are 2D patterns of conductive material embedded within the dielectric matrix (226). For the plasma processing system (200), the dielectric matrix (226) may be, for example, a solid dielectric layer of the dielectric window (126). Note that while a microstrip antenna array used in microwave circuits generally has a flat conductive sheet under the plane of an array of patterned conductors that can be used as a ground plane, the EM metasurface (234) does not have such a conductive sheet because the EM metasurface (234) can be placed in the dielectric window (126) located in the area between the chamber cavity (102) and the RF source electrode (108) of the plasma processing system (200), as illustrated in FIG. 2a.

[0030] Referring to FIG. 2c, the main surface (230B) comprises a rectangular array of microstrips having a two-dimensional pattern referred to as a split ring resonator. The split ring resonator has a shape similar to an incomplete rectangular ring with a hole on one side of the ring, as exemplified in FIG. 2c. Now referring to FIG. 2d, the microstrip pattern used for the main surface (230C) has a comb-like shape, and each tooth of the comb has a rectangular shape. The microstrip patterns used on the main surfaces (230B and 230C) are by example. It is understood that various other microstrip patterns may be used in various embodiments.

[0031] FIGS. 3, 4, and 5 illustrate embodiments of plasma processing systems (300, 400, and 500) that use radio frequency (RF) power supplemented by microwave power coupled to plasma (106) in a plasma processing chamber (150), similar to the plasma processing systems (100 and 200) described above with reference to FIGS. 1a and 2a. However, the plasma processing systems (300, 400, and 500) differ from the plasma processing systems (100 and 200) in the configuration used for each plasma processing chamber (150). While the plasma processing chamber (150) of the plasma processing systems (300, 400, and 500) is configured as a capacitively coupled plasma (CCP) chamber, the plasma processing chamber (150) of the plasma processing systems (100 and 200) is configured as an inductively coupled plasma (ICP) chamber. Generally, in a CCP configuration, the RF source electrode has a substantially flat conductive surface and is placed in a plasma processing chamber (150). However, as described below, in some embodiments, the conductive surface of the RF source electrode comprises the main surface of the EM metasurface used in each plasma processing system. As mentioned above with reference to FIGS. 1b, 1c, and 2b, the main surface may be a perforated surface or a wavy surface that includes a pattern of openings in the conductor. Thus, in some embodiments, the surface of the RF source electrode may not be flat, for example, if the surface comprises the wavy main surface of the EM metasurface. In some other embodiments, the conductive surface of the RF source electrode may be a smooth surface similar to the plates of a parallel plate capacitor.

[0032] As illustrated in FIGS. 3 through 5, the plasma processing system (300, 400 and 500) includes a top electrode (302) having a shape such as a conductive plate. A central portion of the top electrode (302) may extend through an opening in the top cover (304) of the plasma processing chamber (150). The opening may be part of a showerhead assembly used to flow gas into the chamber cavity (102). Gas may also be introduced into the chamber cavity (102) through a gas inlet in the sidewall (124). In addition to the top electrode (302), a conductive portion of the substrate holder (112), for example, the conductive pedestal (118) in FIG. 3 and the conductive pedestal (119) in FIGS. 4 and 5, may be configured as a bottom electrode. In a CCP configuration, the top electrode (302) or the bottom electrode (for example, the pedestals (118 and 119)) may be configured as an RF source electrode. In contrast, in an ICP configuration, the RF source is located outside the plasma processing chamber (150) and is generally shaped like an RF coil, as illustrated in the cross-sectional view in FIGS. 1a and FIGS. 2a. In some embodiments, the top electrode (302) of the CCP chamber may be configured to function as an RF source electrode, and the pedestal (118) (or pedestal (119)) may be configured to function as an RF bias electrode, a DC bias electrode, or a ground connection, or a combination of a DC bias electrode and an RF bias electrode. In some other embodiments, the plasma processing chamber (150) of FIGS. 3 through 5 may have a CCP chamber configuration with two inverted electrodes.

[0033] As illustrated in FIGS. 3 to 5, the microwave source may be a microwave antenna (110) placed on the side wall (124) of the plasma processing chamber (150), similar to the microwave antenna (110) of the plasma processing system (100 and 200) described above with reference to FIGS. 1a and 2a. Microwave radiation emitted from the microwave antenna (110) may be coupled to the EM metasurfaces (134, 434 and 534), respectively, at the edges of the main surfaces (130, 430 and 530) of the plasma processing system (300, 400 and 500), as illustrated in FIGS. 3, 4 and 5. As described above, microwave radiation at the resonant frequency or near-resonant frequency of the EM metasurfaces (134, 434, and 534) can activate the respective SSPP mode, and through this mode, microwave power can be propagated from the edge toward the central region of the main surface (130, 430, and 530).

[0034] FIG. 3 illustrates a cross-sectional view of a plasma processing system (300) in which the EM metasurface (134) is a conductive pedestal (118). The pedestal (118) of the substrate holder (112) of the plasma processing system (300) is similar to the pedestal (118) of the plasma processing system (100) described above with reference to FIG. 1a through 1c. The upper conductive surface of the pedestal (118) is the main surface (130) of the EM metasurface (134).

[0035] FIG. 4 illustrates a cross-sectional view of a plasma processing system (400) in which an EM metasurface (434) is a lower region of an upper electrode (302), and the lower surface thereof comprises the main surface (430) of the EM metasurface (434). In the exemplary embodiment illustrated in FIG. 4, the EM metasurface (434) and the upper electrode (302) form a single monolithic structure. However, it is understood that separate structures assembled together are also possible. The main surface (430) (of the upper electrode (302) in FIG. 4) is similar to the main surface (130) of the lower electrode (pedestal (118)) of the plasma processing system (300) (described above with reference to FIG. 3). As illustrated in FIG. 4, the monolithic EM metasurface (434) and the upper electrode (302) are embedded in a solid dielectric upper layer (406). Accordingly, in this exemplary embodiment, the main surface (430) of the EM metasurface (434) is sealed from the chamber cavity (102) by a solid dielectric top layer (406) without providing a solid dielectric separator, e.g., the separator (122) of FIG. 3. Note that for the plasma processing system (300), the separator (122) is a part of the top surface of a substrate holder (112) on which a semiconductor wafer (120) can be placed, as illustrated in FIG. 3. In contrast, in the plasma processing system (400), the semiconductor wafer (120) can be placed on the top surface of a conductive pedestal (119). However, as is known to those skilled in the art, in some embodiments, the substrate holder (112) may be an electrostatic chuck comprising a dielectric top surface on the conductive pedestal (119).

[0036] The dielectric upper layer (406) of FIG. 4 is depicted as extending across the chamber like a second ceiling, leaving a small space between the dielectric upper layer and the top cover (304). However, it is understood that the dielectric upper layer may have various other shapes in various embodiments. For example, the transverse length of the dielectric upper layer may be smaller and leave a gap between the top electrode (302) and the side wall (124). In another embodiment, the upper portion of the dielectric upper layer may extend further upward and may even be adjacent to the bottom of the top cover (304).

[0037] FIG. 5 illustrates another embodiment of a plasma processing system (500), similar to the plasma processing system (400), in which an EM metasurface (534) is positioned to be embedded in a dielectric upper layer (406) above the plasma (106) in a plasma processing chamber (150) configured as a CCP chamber. Instead of using a monolithic structure comprising an EM metasurface and a top electrode (302), the EM metasurface (534) is positioned below the top electrode, where the main surface (530) of the EM metasurface (534) faces the substrate holder (112). As illustrated in FIG. 5, the main surface (530) of the EM metasurface (534) and the bottom surface of the top electrode (302) are embedded in the dielectric upper layer (406). The main surface (530) is similar to the main surface (230) of the plasma processing system (200) illustrated in FIG. 2a through 2d. In FIG. 5, the main surface (530) includes an opening extending through a conductive matrix, similar to the exemplary main surface (230A) described with reference to FIG. 2b. However, similar to the main surface (230), the main surface (530) of the EM metasurface (534) of the plasma processing system (500) may also include a 2D array of microstrips, such as the exemplary main surfaces (230B and 230C) described with reference to FIG. 2c and FIG. 2d.

[0038] The dielectric of the dielectric upper layer (406) fills the gap between the conductive top electrode (302) and the conductive pattern of the main surface (530) of the EM metasurface (534). However, it is understood that some variations of the exemplary structure illustrated in FIG. 5 are possible in various embodiments. For example, the dielectric between the conductive features of the EM metasurface may contain a gas (e.g., air) sealed from the chamber cavity (102) by the solid dielectric upper layer (406) and the conductive top electrode (302).

[0039] FIG. 6 is a flowchart illustrating a method (600) for processing a semiconductor wafer by performing a plasma process using a plasma processing system such as an exemplary embodiment of the plasma processing system (100, 200, 300, 400, and 500) described above with reference to FIG. 1a through 5. In this plasma processing system, microwave power supplements RF power to provide some of the advantages mentioned above, such as a more uniform plasma, and thus, spatially more uniform characteristics for the processed semiconductor wafer. A method (600) for plasma processing is described below with reference to FIG. 1a through 6.

[0040] As indicated by the box (610) in FIG. 6, a semiconductor wafer (120) can be loaded onto a substrate holder (112) in the chamber cavity (102) of a plasma processing chamber (150). An RF power source can be coupled to an RF source electrode to provide RF power to the plasma processing chamber (150) using a suitable configuration. For example, in an ICP configuration (Figs. 1a and 2a), an RF coil can be used as the RF source electrode (108), whereas in a CCP configuration (Figs. 3 to 5), an upper electrode (302) or a lower electrode (pedestal (118 and 119)) can be used as the RF source electrode. A gas mixture of process gas and carrier gas can flow through the chamber cavity (102) at a specific flow rate, and the gas mixture can be maintained at a low pressure, for example, controlled by a vacuum system coupled to the chamber cavity (102). As indicated by the box (620) in FIG. 6, RF power from the RF source electrode can be coupled to the gas mixture to ignite and maintain the plasma (106) in the chamber cavity (102). As indicated by the box (630) in FIG. 6, in addition to RF power, microwave power can be coupled to the plasma (106). A microwave antenna (110) placed on the side wall (124) of the plasma processing chamber (150) can be a microwave source when coupled to a microwave oscillator (190). Coupling the microwave oscillator (190) to the microwave antenna (110) can emit microwaves into the chamber cavity (102). The microwave power emitted from the microwave antenna (110) may be less than the RF power emitted by the RF source electrode. In various embodiments, the microwave power emitted by the microwave antenna (110) may be 10% to 50% of the combined EM power supplied to the RF source electrode and the microwave antenna.The frequency of the microwave oscillator (190) can be selected to be a repetitive pattern of resonant frequency or near-resonant frequency on the main surface of the EM metasurface of each plasma processing system (e.g., main surface (130, 230, 430, or 530)). As described above, microwave radiation of a repetitive pattern of resonant frequency or near-resonant frequency on the main surface of the EM metasurface can activate each SSPP mode at the edge of the main surface. This surface EM activation can propagate EM power from the edge to the central region of the main surface.

[0041] Surface microwave SSPP activation generates a minute electric field within the plasma sheath. Thus, activating surface EM waves involves coupling microwave power emitted from the antenna (110) to the plasma (106). The spatial distribution of RF power and microwave power can be complementary. A plasma powered by EM radiation at a higher microwave frequency (e.g., 2.45 GHz) can generate a high-density plasma having a different radial distribution than a plasma maintained at much lower RF frequencies (e.g., 13.56 Hz and 27.15 Hz). For example, without a microwave source, the plasma power density can be higher near the edge of the semiconductor wafer (120) compared to the center, indicating that there is stronger coupling of RF power to the plasma closer to the edge. Microwave power can be coupled more strongly closer to the center region; Therefore, a more uniform plasma power density can be achieved by supplemental microwave power. Furthermore, spatial distribution depends on various other plasma process parameters, such as chamber pressure and plasma species. For this reason, it is advantageous to improve process uniformity and process control by adjusting the spatial distribution of EM power.

[0042] As described below with reference to box (640), the spatial distribution of coupled EM power coupled to the plasma (106) can be controlled by using method (600). In the plasma processing system described in this disclosure, a command is transmitted from a controller (180) outside the chamber cavity (102) to a microwave power system to adjust the frequency of the microwave oscillator (190) coupled to the antenna (110), thereby adjusting the frequency of the microwave radiation emitted from the antenna (110). As described in more detail below, this adjustment can be utilized to adjust the spatial uniformity metric of the EM power supplied to the plasma, for example, the spatially localized magnitude of the EM power supplying the plasma.

[0043] The microwave power delivered to the plasma processing chamber (150) may be less than the RF power delivered by the RF source electrode. In various embodiments, the microwave power may be 10% to 50% of the combined EM power supplied to the RF source electrode and the microwave source. If the microwave power is too small, to the extent of a fraction of the total EM power, it may not be effective in adjusting the spatial distribution of the total EM power combined in the plasma (106). Meanwhile, regarding the fixed total EM power specified for plasma processing, if the microwave power is the primary source of EM power, each RF power may be insufficient to ignite and sustain the plasma (106), whereas in the embodiments described in this disclosure, this is the RF power used to ignite and sustain the plasma (106).

[0044] As indicated by the box (640) in FIG. 6, microwave power can be used to adjust the distribution of coupled EM power supplied to the plasma (106). The microwave power coupled to SSPP activation depends on the frequency of the EM radiation striking the main surface of the EM metasurface. Since the coupling is strongest at the resonant frequency of the pattern on the main surface, it will decrease rapidly at the frequency of the narrow band around the resonant frequency. Furthermore, the attenuation of activation with distance is dependent on frequency. Therefore, adjusting the spatial distribution of EM power may involve adjusting the frequency of the microwave oscillator (190), and the frequency of the microwave radiation is equal to the frequency of the signal from the microwave oscillator (190). Thus, using an adjustable microwave oscillator (190) when the frequency of the microwave vibration can be controlled by a command transmitted from outside the chamber cavity (102) to the microwave power system provides the advantage of controlling the spatial distribution to the plasma processing system; Therefore, by adjusting the spatial uniformity metric of the EM power, a more spatially uniform distribution of the EM power coupled to the plasma is achieved.

[0045] The microwave frequency can be selected using a regulator configured to adjust the frequency of the microwave oscillator (190) according to a command instruction received from the controller (180) in the plasma processing system (100, 200, 300, 400, and 500). The controller (180) can be configured to adjust the distribution of EM power supplied to the plasma by selecting the frequency targeted by the regulator by executing a command, for example, a command coded in a process recipe that commands the controller (180) to transmit a command instruction to the microwave power system.

[0046] The embodiments of the plasma processing system described in the present disclosure provide the advantage of achieving a more uniform plasma and having plasma control parameters that can be used to adjust the distribution of EM power.

[0047] Exemplary embodiments discussed in this application are summarized herein. Other embodiments may also be understood from the entire scope of the claims as well as the specification submitted herein.

[0048] Example 1. A plasma processing system comprising: a vacuum system; a chamber cavity (e.g., 102) coupled to the vacuum system; and a substrate holder (e.g., 112) having a surface inside the chamber cavity (e.g., 102), a plasma processing chamber (e.g., 150); a radio frequency RF source electrode (e.g., 108) coupled to an RF power source, configured to ignite a plasma (e.g., 106) in the chamber cavity (e.g., 102), an RF source electrode (e.g., 108); and a microwave source (e.g., 110) coupled to a microwave oscillator (e.g., 190); A system comprising an electromagnetic (EM) metasurface (e.g., 134, 234, 334, 434, 534), wherein the EM metasurface has a main surface (e.g., 130, 230, 430, or 530) electromagnetically coupled to a microwave source, and the main surface (e.g., 130, 230, 430, or 530) is configured to couple microwave power from a chamber cavity (e.g., 102) to a plasma (e.g., 106).

[0049] Example 2. The system of Example 1, further comprising a regulator configured to adjust the frequency of the microwave oscillator, wherein the microwave source comprises a microwave antenna (e.g., 110).

[0050] Example 3. A system in which, in either Example 1 or Example 2, the substrate holder comprises an electrically conductive pedestal (e.g., 118, 119), a portion of the pedestal comprises an EM metasurface, the main surface of the EM metasurface faces the chamber cavity, and the EM metasurface is insulated from the surrounding environment of the chamber cavity by a separator comprising a solid dielectric layer disposed between the main surface of the EM metasurface and the chamber cavity.

[0051] Example 4. A system in any one of Examples 1 to 3, wherein the EM metasurface comprises a conductor, the main surface of the EM metasurface comprises a two-dimensional (2D) pattern of openings, and the openings comprise an insulator.

[0052] Example 5. A system in any one of Examples 1 to 4, wherein the opening has a conductive bottom wall located at a specific depth, and the depth is the distance from the top of the opening to the conductive bottom wall.

[0053] Example 6. A system in any one of Examples 1 to 5, wherein the opening extends through a conductor.

[0054] Example 7. In any one of Examples 1 to 6, the 2D pattern of the openings is an array of openings, the openings have a line-like shape, and the lines have a length dimension greater than the width dimension, a system.

[0055] Example 8. A system in any one of Examples 1 to 7, wherein the 2D pattern of the openings is an array of openings, the openings have a shape similar to prisms, and the prisms have transverse dimensions of nearly the same size.

[0056] Example 9. A system in any one of Examples 1 to 8, wherein the EM metasurface comprises a microstrip metamaterial, the main surface of the EM metasurface comprises a 2D array of microstrips, and each microstrip is a 2D pattern of a conductive material embedded inside a solid dielectric layer.

[0057] Example 10. A system in any one of Examples 1 to 9, wherein the 2D pattern of the conductive material of the microstrip is in the shape of a comb, and each tooth of the comb is in the shape of a rectangle.

[0058] Example 11. A system in any one of Examples 1 to 10, wherein the 2D pattern of the conductive material of the microstrip has the shape of a split ring resonator, and the split ring resonator has the shape of an incomplete rectangular ring having a hole on one side of the ring.

[0059] Example 12. In any one of Examples 1 to 11, the plasma processing chamber is an inductively coupled plasma (ICP) chamber, and a portion of the ICP chamber includes a solid dielectric window disposed opposite the substrate holder; the RF source electrode is an RF coil disposed outside the plasma processing chamber adjacent to the solid dielectric window; and the EM metasurface is embedded in the solid dielectric window and the main surface of the EM metasurface is on the opposite side of the substrate holder.

[0060] Example 13. In any one of Examples 1 to 12, the plasma treatment chamber is a capacitively coupled plasma (CCP) chamber having an electrode shaped like a plate and positioned opposite a substrate holder; the EM metasurface is positioned below the electrode, the main surface of the EM metasurface is on the opposite side of the substrate holder, and the main surface of the EM metasurface and the bottom surface of the electrode are embedded in the dielectric upper layer.

[0061] Example 14. In any one of Examples 1 to 13, the plasma processing chamber is a capacitively coupled plasma (CCP) chamber having an electrode shaped like a plate, and the electrode includes a surface disposed inside the CCP chamber opposite the substrate holder; the region of the electrode includes an EM metasurface, the surface of the electrode includes a main surface of the EM metasurface, and the main surface of the EM metasurface is embedded in a solid dielectric upper layer, a system.

[0062] Example 15. A plasma processing system comprising: a plasma processing chamber; a radio frequency (RF) source electrode coupled to an RF power source, configured to ignite a plasma in the plasma processing chamber; an electromagnetic (EM) metasurface having a main surface configured to couple microwave power to the plasma in the plasma processing chamber, as a microwave power system coupled to the plasma by microwave power; a microwave power system comprising a microwave source coupled to a microwave oscillator; and a controller configured to execute commands to adjust a spatial uniformity metric of the EM power supplied to the plasma.

[0063] Example 16. The system of Example 15, further comprising a regulator configured to adjust the frequency of a microwave oscillator, wherein the regulator is configured to receive a command instruction and adjust the frequency from a controller, and the microwave source comprises a microwave antenna.

[0064] Example 17. A method for plasma processing of a semiconductor wafer, comprising: loading a semiconductor wafer into a plasma processing chamber coupled to a radio frequency (RF) source electrode and a microwave power system including a microwave oscillator and a microwave source; igniting a plasma by coupling RF power from the RF source electrode to a gas in the plasma processing chamber; coupling microwave power from the microwave power system to the plasma ignited in the plasma processing chamber by coupling the microwave oscillator to the microwave source; and controlling a spatial uniformity metric of coupled electromagnetic (EM) power supplied to the plasma by adjusting the microwave power.

[0065] Example 18. The method of Example 17, wherein coupling a microwave oscillator to a microwave source comprises providing 10% to 50% of the microwave power of the coupled EM power supplied to the microwave source and the RF source electrode.

[0066] Example 19. In either Example 17 or Example 18, adjusting the spatial uniformity metric of the EM power comprises transmitting a command from a controller to a microwave power system to adjust the frequency of a microwave oscillator, wherein the microwave source comprises a microwave antenna.

[0067] Example 20. A method in any one of Examples 17 to 19, further comprising the step of activating surface EM waves on the main surface of an EM metasurface by means of a microwave source, wherein the microwave power system further comprises an EM metasurface.

[0068] Although the present invention has been described with reference to exemplary embodiments, this description is not intended to be interpreted in a limiting sense. By referring to the description, various modifications and combinations of other embodiments as well as the exemplary embodiments of the present invention will become apparent to those skilled in the art. Accordingly, the appended claims are intended to include any such modifications or embodiments.

Claims

Claim 1 A plasma processing system comprising: a vacuum system; a plasma processing chamber comprising: a chamber cavity coupled to the vacuum system; and a substrate holder comprising a surface inside the chamber cavity; a radio frequency (RF) source electrode coupled to an RF power source configured to ignite a plasma in the chamber cavity; a microwave source coupled to a microwave oscillator; and an electromagnetic (EM) metasurface comprising: an EM metasurface comprising a main surface electromagnetically coupled to the microwave source, wherein the main surface is configured to couple microwave power to the plasma in the chamber cavity. Claim 2 A system according to claim 1, further comprising a regulator configured to adjust the frequency of the microwave oscillator, wherein the microwave source comprises a microwave antenna. Claim 3 A system according to claim 1, wherein the substrate holder comprises an electrically conductive pedestal, a portion of the pedestal comprises the EM metasurface, the main surface of the EM metasurface faces the chamber cavity, and the EM metasurface is insulated from the surrounding environment of the chamber cavity by a separator comprising a solid dielectric layer disposed between the main surface of the EM metasurface and the chamber cavity. Claim 4 A system according to claim 1, wherein the EM metasurface comprises a conductor, the main surface of the EM metasurface comprises a two-dimensional (2D) pattern of openings, and the openings comprise an insulator. Claim 5 A system according to paragraph 4, wherein the opening has a conductive bottom wall located at a specific depth, and the depth is the distance from the top of the opening to the conductive bottom wall. Claim 6 In paragraph 4, the system, wherein the opening extends through the conductor. Claim 7 In paragraph 4, the 2D pattern of the opening is an array of openings, the openings have a line-like shape, and the line has a length dimension greater than the width dimension, a system. Claim 8 In paragraph 4, the 2D pattern of the openings is an array of openings, the openings have a shape similar to prisms, and the prisms have transverse dimensions of nearly the same size, a system. Claim 9 A system according to claim 1, wherein the EM metasurface comprises a microstrip metamaterial, the main surface of the EM metasurface comprises a 2D array of microstrips, and each microstrip is a 2D pattern of a conductive material embedded within a solid dielectric layer. Claim 10 A system according to claim 9, wherein the 2D pattern of the conductive material of the microstrip is in the shape of a comb, and each tooth of the comb is in the shape of a rectangle. Claim 11 A system according to claim 9, wherein the 2D pattern of the conductive material of the microstrip is shaped like a split ring resonator, and the split ring resonator is shaped like an incomplete rectangular ring having a hole on one side of the ring. Claim 12 A system according to claim 1, wherein the plasma processing chamber is an inductively coupled plasma (ICP) chamber, and a portion of the ICP chamber comprises a solid dielectric window disposed opposite the substrate holder; the RF source electrode is an RF coil disposed outside the plasma processing chamber adjacent to the solid dielectric window; and the EM metasurface is embedded in the solid dielectric window and the main surface of the EM metasurface is on the opposite side of the substrate holder. Claim 13 A system according to claim 1, wherein the plasma processing chamber is a capacitively coupled plasma (CCP) chamber having the RF source electrode, the RF source electrode has a plate-like shape and is positioned opposite the substrate holder; the EM metasurface is positioned below the electrode, the main surface of the EM metasurface is on the opposite side of the substrate holder, and the main surface of the EM metasurface and the bottom surface of the electrode are embedded in the dielectric upper layer. Claim 14 In claim 1, the plasma processing chamber is a capacitive coupled plasma (CCP) chamber having an electrode having a plate-like shape, and the electrode includes a surface disposed inside the CCP chamber opposite the substrate holder; a region of the electrode includes the EM metasurface, and the surface of the electrode includes the main surface of the EM metasurface, and the main surface of the EM metasurface is embedded in a solid dielectric upper layer, a system. Claim 15 A plasma processing system comprising: a plasma processing chamber; a radio frequency (RF) source electrode coupled to an RF power source, configured to ignite a plasma in the plasma processing chamber; an electromagnetic (EM) metasurface having a main surface configured to couple microwave power to the plasma in the plasma processing chamber, as a microwave power system coupled to the plasma by microwave power; a microwave power system comprising a microwave source coupled to a microwave oscillator; and a controller configured to execute commands to adjust a spatial uniformity metric of the EM power supplied to the plasma. Claim 16 A system according to claim 15, further comprising a regulator configured to adjust the frequency of the microwave oscillator, wherein the regulator is configured to receive a command instruction and adjust the frequency from the controller, and the microwave source comprises a microwave antenna. Claim 17 A method for plasma treatment of a semiconductor wafer comprising: loading the semiconductor wafer into a plasma treatment chamber coupled to a radio frequency (RF) source electrode and a microwave power system including a microwave oscillator and a microwave source; igniting the plasma in the plasma treatment chamber by coupling RF power from the RF source electrode to a gas; activating surface EM waves on the main surface of an EM metasurface by the microwave source by coupling the microwave oscillator to the microwave source; coupling microwave power from the microwave power system to the plasma ignited in the plasma treatment chamber; and controlling the spatial uniformity metric of the coupled electromagnetic (EM) power supplied to the plasma by adjusting the microwave power, wherein the microwave power system further comprises the EM metasurface. Claim 18 A method according to claim 17, wherein coupling the microwave oscillator to the microwave source comprises providing 10% to 50% of the microwave power of the coupled EM power supplied to the microwave source and the RF source electrode. Claim 19 A method according to claim 17, wherein adjusting the spatial uniformity metric of the combined EM power comprises transmitting a command instruction from a controller to the microwave power system to adjust the frequency of the microwave oscillator, wherein the microwave source comprises a microwave antenna. Claim 20 delete

Images