Plasma processing system and method for chemically treating a substrate

Abstract

The plasma processing system includes a radical source chamber including a gas inlet, an electrode connected to a radio frequency (RF) power source and configured to generate radicals in the radical source chamber, and an outlet for the radicals generated in the radical source chamber, a plenum attached to the outlet of the radical source chamber, the plenum being made of a first thermal conductor and having a wall including an opening for gas flow, and a process chamber connected to the radical source chamber through the plenum, the process chamber including a substrate holder disposed below the plenum, a gas outlet below the substrate holder, and a process chamber wall including a second thermal conductor, the process chamber wall of the process chamber being thermally coupled to the plenum wall.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of priority and the filing date of U.S. Patent Application No. 17 / 003,734, filed on August 26, 2020, and the entire disclosure of the same is incorporated herein by reference.

[0002] The present invention generally relates to systems and methods for processing substrates, and in particular embodiments, to plasma processing systems and methods for chemically processing substrates.

Background Art

[0003] Generally, semiconductor devices such as integrated circuits (ICs) are fabricated by continuously depositing and patterning layers of dielectric, conductor, and semiconductor materials on a semiconductor substrate to form a network that integrates electronic components and interconnecting elements (e.g., transistors, resistors, capacitors, metal lines, contacts, vias) in a monolithic structure. Many of the deposition and etching processes used to form the constituent structures of semiconductor devices involve plasma - assisted processing. Plasma processing techniques include chemical dry etching (CDE) (e.g., plasma ashing), plasma or sputter etching, combinations of physical and chemical dry etching (e.g., reactive ion etching (RIE)), and plasma - enhanced CVD (PECVD), plasma - enhanced atomic layer etch (PEALE), and plasma - enhanced atomic layer deposition (PEALD).

[0004] Each time a technology node evolves, the minimum feature size is reduced by almost doubling the component packing density for cost reduction. Due to the demand for high-performance and low-cost electronic components, the feature size has been miniaturized to a few nanometers, and the challenges in semiconductor manufacturing technology have become even more severe. In particular, in plasma processing technology, in many cases, it is necessary to uniformly fabricate nanostructures with dimensions precisely controlled at the atomic level over a wide (e.g., 300 mm) wafer. To meet the stringent requirements for precision, uniformity, stability, and repeatability in the manufacture of smaller semiconductor devices, further innovation in plasma equipment and process design may be required.

Summary of the Invention

[0005] A plasma processing system includes a radical source chamber having a gas inlet, an electrode coupled to a radio frequency (RF) power source and configured to generate radicals within the radical source chamber, and an outlet for the radicals generated within the radical source chamber; a plenum attached to the outlet of the radical source chamber and fabricated from a first heat conductor, the walls of which include openings for a gas flow; and a process chamber connected to the radical source chamber through the plenum. The process chamber includes a substrate holder disposed below the plenum, a gas outlet below the substrate holder, and a process chamber wall including a second heat conductor, and the process chamber wall of the process chamber is thermally coupled to the wall of the plenum.

[0006] The plasma processing system includes a plenum, which includes a bottom wall, side walls along the edges of the bottom wall, a rim extending outward from the side walls, and a radical ballast region between the side walls and the bottom wall. The plenum is a heat conduction structure. The system includes a radical source chamber including a gas inlet, a radio frequency (RF) electrode, and a bottom outlet attached to the rim of the plenum, and a process chamber including a heat conduction wall physically attached to the plenum at the rim, wherein the plenum includes an opening connecting the process chamber to the radical source chamber through the radical ballast region, and further includes a substrate holder disposed under the bottom wall of the plenum.

[0007] The plasma processing method includes steps of placing a substrate on a substrate holder disposed near the bottom of the process chamber, introducing a process gas and a carrier gas into the radical source chamber through a gas inlet, wherein the radical source chamber includes an outlet attached to a plenum disposed under the radical source chamber, holding a plasma in the radical source chamber, wherein the plasma contains radicals, transporting the radicals to the substrate in a gas flow through an opening in the wall of the plenum, chemically treating the surface of the substrate with the radicals, and exhausting excess reactants and gas by-products from the process chamber through a gas outlet disposed under the substrate holder.

Brief Description of the Drawings

[0008] To more fully understand the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings.

[0009]

Figure 1A

Figure 1B

Figure 1C

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0010] In the present disclosure, embodiments of a plasma system and method for chemically treating the surface of a substrate at a relatively low substrate temperature by exposing the substrate to a gaseous reactant containing radicals extracted from a plasma radical source are described. In the plasma processing method in which the plasma system according to the present disclosure can be used for that purpose, the substrate is not directly exposed to the plasma. In these techniques, the substrate is processed by causing a chemical reaction using energy radicals extracted from a plasma located at a position away from the substrate and then transported to the surface of the substrate for chemical treatment in a gas flow. The embodiments described in the present disclosure provide several advantages such as efficient radical transport, less damage by plasma-induced radiation, and a stable processing environment, which are realized by equipment design for efficient heat dissipation as described in more detail below.

[0011] Surface chemical treatment at relatively low substrate temperatures is often done by exposing the surface to a gas containing high-energy radicals that are present at relatively high radical-to-ion ratios. In general, indirect plasma systems are preferred for chemical treatment to reduce physical damage to the substrate from ion bombardment and to reduce plasma-induced radiation damage from high-energy electromagnetic radiation (e.g., ultraviolet light) generated by the plasma discharge. Typically, an indirect plasma system has three sections: a first section containing a radical source physically separated from the substrate, a second section through which the radicals can be transported in a gas stream, and a third section in contact with the second section where the substrate can be placed on a substrate holder and its surface chemically treated with radicals, and excess reactants and gaseous by-products are removed through a gas outlet.

[0012] In the indirect plasma system described in the present disclosure, the first section is called a radical source chamber and can be configured to hold a plasma, the second section is called a plenum and includes a radical ballast region, and the third section is called a process chamber and can be connected to the radical source chamber through the plenum such that a substrate can reach radicals for chemical processing. Exemplary embodiments of the present disclosure can provide a higher ratio of radical flux to ion flux in a gas stream by using a radio frequency (RF) electrode configured to hold a purely inductively coupled plasma within the radical source chamber. The embodiments described with respect to FIGS. 1A - 3B use a helical resonator as the RF electrode of the radical source chamber, whereas in the exemplary embodiment shown in FIG. 4 a plasma coil is used. Radical losses during transport were reduced by using an adjacent plasma design instead of a remote plasma design. In the adjacent plasma design of the exemplary embodiment, the radical source chamber is separated from the process chamber by only a short radical ballast region. Plasma induced damage is reduced not only by physically separating the plasma from the substrate in the process chamber by interposing the plenum therebetween, but also by configuring the walls of the plenum to block ultraviolet light within the direct line of sight from the radical source chamber to the substrate holder using an ultraviolet light impermeable material. Instability of the processing environment is reduced by designing the material and shape of the plenum for efficient heat dissipation, which helps to maintain a stable low temperature during processing. Further, the expansion and contraction of the surface associated with temperature transients during processing can cause peeling of deposits, thereby generating unwanted particles in the process chamber.

[0013] The position of the opening for the gas flow through the plenum wall can be designed in a configuration that directs the gas entering the process chamber through the plenum wall to flow in a desired pattern over the surface of the substrate placed on the substrate holder within the process chamber. FIGS. 1A - 1C show an indirect plasma system 100 of an embodiment in which the gas flow is laterally guided from the periphery of the substrate. In the embodiment shown in FIGS. 2A - 2B, the gas flow within the plasma system 200 is vertically guided from above, and in another plasma system 300 of the embodiments shown in FIGS. 3A - 3B, the gas is guided from one side to generate an alternating current on the substrate.

[0014] Referring now to FIG. 1A, the plasma system 100 includes a radical source chamber 110, a plenum 120 attached to the outlet of the radical source chamber 110, and a process chamber 130 connected to the radical source chamber 110 through the plenum 120.

[0015] The radical source chamber 110 of the plasma system 100 can be in the shape of an inverted open cylinder having a gas inlet 102 within the upper cover 108 and a radio frequency (RF) electrode 104 disposed outside the side wall 106. The RF electrode 104 can be a conductive helix wound longitudinally around the side wall 106 including a dielectric (e.g., ceramic material). The upper cover includes a conductive material having a dielectric coating on the inner-facing surface of the radical source chamber 110, such as aluminum coated with alumina or yttria. Various gases (e.g., argon, oxygen, sulfur hexafluoride, and tetrafluoromethane, nitrogen trifluoride, etc.) can be introduced into the chamber, and a controlled gas discharge plasma is formed as a radical source.

[0016] The electrode 104 is coupled to an RF power source (not shown). The length of the conductor can be designed to be a quarter wavelength (λ / 4) or a half wavelength (λ / 2) of the RF electromagnetic vibration of the electrode powered by the RF power source. In various embodiments, the oscillation frequency f can be from about 15 MHz to about 500 MHz, and in one embodiment from about 15 MHz to about 200 MHz. The electrode 104 operates in a purely inductively coupled mode to maintain a plasma at an RF power density of about 0.01 W / cm 3 ~ about 1 W / cm 3 in the radical source chamber 110.

[0017] In this exemplary embodiment of the present disclosure, the radical source chamber 110 of width d has an open bottom such that, as shown in FIG. 1A, radicals are transported from the radical source chamber 110 into the radical ballast region 128 of a plenum 120 attached to the outlet in the gas flow exiting the radical source chamber 110. The plenum 120 includes a bottom wall 122, side walls 126 along the edges of the bottom wall 122, a rim 124 extending outwardly from the side walls, and a radical ballast region 128 between the side walls 126 and the bottom wall 122. The plenum 120 can be in the shape of an inverted hat with a ring-shaped rim 124 having a central opening that leads to the radical ballast region 128 delimited by the side walls 126 and the bottom wall 122, as can be seen in the perspective view of FIG. 1B. The width of the central opening of the rim 124 is designed to be less than or equal to the width d of the radical source chamber 110. (In FIG. 1A, the width of the opening of the rim 124 is shown equal to d by way of example only. This allows the bottom outlet of the radical source chamber 110 to be physically attached to the rim 124 of the plenum 120, as shown in FIG. 1A. Radicals can thus exit the radical source chamber 110 through the central opening of the rim 124 and enter the radical ballast region 128.)

[0018] Also, as shown in FIG. 1A, a process chamber 130 disposed below the rim 124 is also attached to the rim 124. In the embodiments described in the present application such as the plasma system 100 shown in FIG. 1A, the rim 124 extends outward from the sidewall 126 to cover the upper portion of the process chamber 130 and is attached to the vertical portion of the wall 134 of the process chamber 130. In various other embodiments, the rim 124 may extend partway toward the edge of the process chamber 130 and be attached to the upper cover of the process chamber 130, or the rim 124 and the wall 134 may be of a single monolithic structure.

[0019] The process chamber 130 shown in FIG. 1A includes an annular region adjacent to the sidewall 126 and further extends downward into a cylindrical region adjacent to the bottom wall 122. The substrate holder 132 can be disposed in an adjacent region below the bottom wall 122 of the plenum. The substrate 140 is shown as being placed on the substrate holder 132. The gas outlet 136 can be disposed below the substrate holder 132, through which excess reactants and gas by-products can be excluded from the process chamber 130. Although the process chamber design used is common to all embodiments of the present disclosure, the gas outlet 136 can be asymmetrically disposed in embodiments such as the plasma system 300 (see FIG. 3A) to facilitate creating a desired asymmetric gas flow pattern above the substrate holder 132. It should be understood that each of the exemplary plasma systems of the present disclosure shows one gas inlet and one gas outlet, but multiple gas inlets and multiple gas outlets can also be used.

[0020] One aspect of the design of the plasma system described in this disclosure is efficient heat dissipation. For that purpose, the walls of the plenum 120, such as the bottom wall 122, the rim 124, and the side wall 126, and the wall 134 of the process chamber 130 include a heat-conductive material such as aluminum, copper, or others, and are physically and thermally coupled to each other. As is known among those skilled in the art, the conductive walls of a plasma system such as the plasma system 100 can be electrically connected to the system ground (reference potential). In the plasma system 100, heat can be generated by the positively charged energetic ions in the gas flow that collide inelastically with the grounded wall of the plenum 120, and that energy is transferred to the wall as heat. Random collisions of the walls around the radical ballast region 128 by radicals having energy also contribute to heat generation. The rapid removal of the generated heat can be facilitated not only by using materials with high thermal conductivity, but also by reducing the number of connections between components in the mechanical design of the structure. The thermal contact of metal joints can be degraded over time by gaps that spread into the grooves due to the mechanical stress of the suspended components connected by joints such as lap joints, T-joints, or corner joints.

[0021] In addition to using heat-conductive materials, the structure with the plenum 120 hat shown in FIG. 1B upside down can be designed as a monolithic structure to reduce the thermal resistance in order to achieve efficient heat flow to the process chamber wall 134. In one embodiment, the plenum 120 and the process chamber wall 134 can be integrally formed as a monolithic structure, for example, by casting or any other metal forming process.

[0022] The process chamber wall 134 can have a heat capacity that operates as a heat sink, or can be thermally connected to an external heat sink. As described above, efficient heat removal provides the advantage of helping to maintain a stable processing environment. Conditioning of the wall 134 of the process chamber 130 and / or coating of the walls of the plenum 120 facing the adjacent process chamber with a thin layer of a material such as alumina or yttria on the surface also helps to stabilize the processing environment.

[0023] The coating layer 121 shown in FIG. 1A can be provided using various techniques, for example, anodized aluminum, coating with yttria, or conditioning of the process chamber 130 is used. The coating layer 121 can include one material for the wall of the plenum 120 and a different material for the wall 134 of the process chamber 130. Generally, the chemical state of a plasma process chamber changes during processing due to ion bombardment and chemical reactions with various radicals and gaseous by-products. The coating layer 121 provides the additional advantage of reducing such variability in the chemical state of the walls and thus further stabilizing the plasma processing environment.

[0024] The process chamber 130 is connected to the radical source chamber 110 through the radical ballast region 128 of the plenum 120. The width D of the radical ballast region 128 is greater than or equal to the width of the opening of the rim 124, which is also designed as an outlet for radicals, as described above. Thus, in the embodiments described in the present disclosure, radicals extracted from the plasma in the radical source chamber 110 can be transported to the substrate 140 in the gas flow only through the holes in the walls of the plenum. Therefore, the configuration of the openings in the design of the plenum 120 can be used to guide the gas flow through the plenum 120 and in the desired pattern within the process chamber 130. In the embodiments shown in FIGS. 1A - 4, the width D of the radical ballast regions 128 and 328 of the radical ballast regions is also greater than or equal to the width of the respective substrate holder 132.

[0025] In FIG. 1A, the width of the central opening of the rim 124 is shown to be equal to the width d of the radical source chamber 110. However, it should be understood that the width of the central opening within the rim 124 can be smaller, for example, in a design where the rim 124 extends further inward to constrict the opening connecting the radical source chamber 110 to the radical ballast region 128.

[0026] In FIG. 1A, the gas flow between the gas inlet 102 and the gas outlet 136 is shown to flow through a channel that includes the following three consecutive sections: the radical source chamber 110, the plenum 120, and the process chamber 130, as indicated by the block arrows in FIG. 1A. A gas flow system (not shown) including a vacuum pump connected to the gas outlet 136 can be used to create a controlled pressure gradient to maintain a stable gas flow. In the plasma system 100, the substrate holder 132 (and the substrate 140) is guided radially inward from the periphery of the process chamber. The configuration of the various openings in the design of the plasma system 100 is used to direct the flow, as will be understood with respect to FIGS. 1A - 1C.

[0027] A gas mixture, for example a mixture of oxygen and argon, can be introduced through the gas inlet 102 in the upper cover 108 of the radical source chamber 110. The gas can be ionized, and a plasma containing oxygen radicals can be maintained inside the radical source chamber 110 using electromagnetic energy from the electrode 104 coupled to an RF power source. In the plasma system 100, the electrode 104 is disposed outside the ceramic sidewall 106 and is a helical resonator inductively coupled to the plasma. The dimensions of the radical source chamber 110 are designed to initiate and confine a gas discharge plasma within the specified volume of the radical source chamber 110. For example, the height h and the width d of the radical source chamber are at least several times the skin depth. In various embodiments, h is from about 5 cm to about 20 cm, and d is from about 10 cm to about 20 cm.

[0028] Radicals (e.g., oxygen radicals) can be transported in the gas stream from the radical source chamber 110 through the bottom outlet to the radical ballast region 128 of the plenum 120. As shown in the perspective view of FIG. 1B, the radical ballast region 128 is a cavity of the plenum 120 with an inverted hat shape. The radical ballast region has a cylindrical shape with a width D and a depth L. In the plasma system 100, the solid bottom wall 122 (without an opening) blocks the vertical flow, thereby guiding the gas radially outward to the vertical side walls 126 of the cylindrical radical ballast region 128, as indicated by the blocked arrows in FIGS. 1A and 1B. The openings for allowing the gas to flow out of the plenum 120 and into the process chamber 130 are symmetrically positioned within the side walls 126 of the radical ballast region 128. Guiding the gas radially outward toward the wall 134 of the process chamber helps increase the ratio of radicals to ions in the gas. By increasing the surface area-to-volume ratio of the annular region surrounding the ballast region 128, the collisions with the wall 134 of the process chamber increase. In the collisions with the wall 134, the adhesion coefficient of ions is higher than that of radicals. Therefore, as the collision speed increases, the ratio of radicals to ions increases. The substrate holder 132 and the substrate 140 are disposed directly below the plenum 120, and the gas outlet 136 is positioned directly below the substrate holder 132. With this configuration, the structure is substantially axisymmetric around an axis perpendicular to the surface of the substrate 140, and an azimuthally symmetric flow of gas is generated over the substrate 140.

[0029] FIG. 1C shows a side view of the side wall 126 having a rectangular opening 127 with a length approximately equal to the width W and the depth L of the plenum 120. The side wall 126 is disposed along the edge of the circular bottom wall 122 and has a circumferential length of πD. In the design of the dimensions of the radical ballast region 128 and the opening 127 of the side wall 126, the requirements regarding both the gas flow and the heat flow out of the plenum are considered. When W and L are smaller, the gas flow is restricted, but the heat flow out of the plenum is improved.

[0030] The dimensions of the radical ballast region 128 can be designed such that a substantially stable and uniform density can be achieved before the gas enters the process chamber 130, and a sufficient pressure gradient can be provided to prevent backflow into the radical source chamber 110. Generally, the depth L is several times the diffusion length, and each width D is designed to achieve the desired pressure gradient and volumetric flow rate. The known relationships between the volumetric flow rate, pressure gradient, and geometric parameters of various-shaped conduits can be utilized in the design of the radical ballast region. The radical ballast region 128 of the embodiment shown in FIG. 1C has a cylindrical shape. In other embodiments, the radical ballast region can have different shapes. For example, the radical ballast regions 328 in FIGS. 3A and 3B have a rectangular shape. In various embodiments, the depth L is from about 5 cm to about 15 cm, and the ratio D / L is from about 3 to about 10. In various embodiments, the width W of the rectangular opening 127 can be from about 0.1 cm to about 5 cm. The pressure in the process chamber 130 can be constrained by the specifications of the process recipe and can be from about 0.01 Torr to about 0.25 Torr in various embodiments. To increase the radical-to-ion ratio, avoid unwanted sputtering, and help prevent backflow, the pressure in the radical source chamber 110 is relatively high and is typically twice that of the choked flow state in the plenum 120. In various embodiments, the pressure in the radical source chamber 110 can be from about 0.5 Torr to about 1 Torr.

[0031] The solid bottom wall 122 of the plenum 120 of the plasma system 100 can provide the additional advantage of blocking harmful electromagnetic waves, such as ultraviolet rays, from reaching the substrate. As previously described and as shown in FIG. 1A, the width D of the plenum 120 is also the width of the bottom wall 122, but is designed to be greater than the width of the substrate holder 132 (and the substrate 140) and also greater than the width of the radical source chamber 110 in which the plasma can be confined. Also as previously described, the walls of the plenum (including the bottom wall 122) can include a metal such as aluminum or copper. As is known among those skilled in the art, metals such as aluminum and copper do not transmit electromagnetic radiation for all practical purposes because the free electron density of these materials is very high. Thus, in the design of the plasma system 100, the dimensions can be adjusted such that the bottom wall 122 is within the line of sight between the plasma and the substrate, and thus the substrate 140 can be appropriately shielded from damage by plasma-induced radiation.

[0032] FIGS. 2A and 2B show a plasma system 200. One difference between the plasma system 100 and the plasma system 200 is that in the plasma system 200, as indicated by the block arrows in FIGS. 2A and 2B, the gas flow into the process chamber 130 through the plenum 220 is guided vertically through the opening 227 in the bottom wall 222 of the plenum 220. As shown in FIGS. 2A and 2B, the opening 227 for the gas flow is configured symmetrically around an axis perpendicular to the surface of the substrate holder 132 and the substrate 140 positioned directly below the plenum 220 within the process chamber 130. Similar to the plasma system 100, there is a gas outlet 136 directly below the substrate holder 132. Thus, the gas flows symmetrically outward around the substrate 140 over the substrate 140 and exits the process chamber 130 through the gas outlet 136.

[0033] Since the bottom wall 222 of the plenum 220 has an opening 227, the ability to block electromagnetic radiation emitted from the plasma within the plasma system 200 may be reduced compared to the plasma system 100. However, the opening 227 can be designed to maintain approximately the same blocking ability. For example, the width of the hole (opening 227) in the bottom wall 222 can be designed to be narrow to provide a high aspect ratio. When the aspect ratio is high, the total solid angle for keeping the substrate 140 exposed to ultraviolet light within the line of sight of the plasma is significantly reduced, whereby, for example, less than 1% of the ultraviolet energy emitted by the plasma in the radical source chamber reaches the substrate 140.

[0034] Figures 3A - 3B show a plasma system 300 in which an asymmetric gas flow is generated by the asymmetric configuration of the openings in the walls of the plasma system 300. One difference between the plasma system 100 and the plasma system 300 is that in the plasma system 300, as shown by the blocking arrows in Figures 3A - 3B, the gas flow into the process chamber 330 through the radical ballast region 328 is asymmetrically guided towards one side of the plenum 320 (e.g., the left side in Figures 3A - 3B), and when it exits the plenum 320, the gas flows as a direct alternating current in the process chamber 330 over the substrate holder 132 (and the substrate 140) towards the opposite side of the plenum 320 (e.g., the right side in Figures 3A - 3B).

[0035] In the example shown in FIGS. 3A - 3B, a one - direction linear flow is desired within the radical ballast region 328. To generate such a flow pattern, it is preferable to use a shape in which the rectangular cap for the plenum 320 is inverted. As shown in the perspective view of FIG. 3B, the radical ballast region 328 can be designed to extend laterally between four rectangular vertical faces of the sidewall 326 and to extend vertically from the rim 324 downward toward the rectangular bottom wall 322. The shape of the rim 324 can remain the same as the rim 124 of the plasma system 100. The one - direction linear flow pattern can be generated by configuring the plenum 320 to have an opening in one rectangular face of the sidewall 326, and the remaining three faces of the sidewall 326 of the plenum 320 and the rectangular bottom wall 322 are designed to block the solid (no - opening) gas flow. Since the opening of the sidewall 326 is positioned asymmetrically on one side, for example, on the left side in FIG. 3, the gas flow inside the radical ballast region 328 is guided to the left as shown in FIG. 3. The gas flow pattern on the substrate 140 can be guided by configuring the process chamber 330 to have a gas outlet 336 located on the right side of the plenum 320, which is the opposite side of the side where the opening of the sidewall 326 is positioned. The position of the substrate holder 132 within the process chamber 330 can remain directly below the plenum 320.

[0036] The radical source chambers of the plasma systems 100, 200, and 300 include an electrode 104, which can be configured as a helical resonator for coupling an RF power source to the plasma. FIG. 4 shows a plasma system 400, where the radical source chamber 410 is equipped with an electrode 404 in the shape of a planar coil. The electrode 404 can be coupled to an RF power source. As shown in FIG. 4, the electrode 404 can be disposed on top of a dielectric (e.g., ceramic) cover 408 and configured to supply the RF power to the plasma by inductive coupling. The sidewall 406 of the radical source chamber 410 can include a conductive material such as aluminum or copper, and the gas inlet 402 can be positioned to introduce a gas (e.g., argon, oxygen, sulfur hexafluoride, tetrafluoromethane, nitrogen trifluoride, and others).

[0037] A flowchart of the processing method is shown in FIG. 5. As shown in block 510 of FIG. 5, the substrate can be placed on a substrate holder positioned inside the process chamber, for example, near the bottom of the process chamber. In block 520, a gas mixture of a process gas and a carrier gas can be introduced into, for example, a radical source chamber disposed above the process chamber. The radical source chamber can have a bottom outlet attached to a plenum including a radical ballast region. As shown in block 530, a plasma can be ignited and maintained in the radical source chamber. The plasma can contain radicals and thus can be a reduction in the generation of radicals to be used downstream to chemically treat the surface of the substrate. As shown in block 540, the radicals exiting the radical source chamber and entering the plenum can be transported through an opening in the wall of the plenum to the substrate in the process chamber. The radicals can be moved in the gas flow over the substrate. In block 550, the exposed surface of the substrate can be chemically treated with radicals. As shown in block 560, the gas flow can expel excess reactants and gas by-products through the gas outlet of the process chamber. The gas outlet can be positioned under the substrate holder.

[0038] Exemplary embodiments of the present invention are summarized here. Other embodiments can also be understood from the entire specification and the claims filed herein.

Examples

[0039] Example 1. The plasma processing system includes: a radical source chamber having a gas inlet, an electrode coupled to a radio frequency (RF) power source and configured to generate radicals within the radical source chamber, and an outlet for the radicals generated within the radical source chamber; a plenum attached to the outlet of the radical source chamber, the plenum being fabricated from a first thermal conductor and having walls with openings for gas flow; a process chamber to which the radicals are connected from the source chamber through the plenum, the process chamber including a substrate holder disposed below the plenum, a gas outlet below the substrate holder, and a process chamber wall including a second thermal conductor, the process chamber wall being thermally coupled to the wall of the plenum. and,

[0040] Example 2. In the system according to Example 1, the first thermal conductor includes a material that does not transmit ultraviolet light.

[0041] Example 3. In the system according to one of Examples 1 or 2, the plenum is interposed between the radical source chamber and the substrate holder, and the plenum is configured to block ultraviolet light emitted from within the radical source chamber within a direct line of sight from the radical source chamber to the substrate holder.

[0042] Example 4. In the system according to one of Examples 1 to 3, the first thermal conductor includes aluminum coated on one side with alumina or yttria.

[0043] Example 5. In the system according to one of Examples 1 to 4, the first thermal conductor and the second thermal conductor include the same thermal conductor.

[0044] Example 6. In the system according to one of Examples 1 to 5, the electrode is a conductor in the shape of a planar coil disposed above an upper cover including a dielectric material outside the radical source chamber.

[0045] Example 7. In the system according to one of Examples 1 to 6, the electrode is a conductor in the shape of a helix disposed around a cylindrical side wall containing a dielectric material outside the radical source chamber, and the length of the conductor is a multiple of one-fourth of the wavelength of the RF electromagnetic vibration in the electrode powered by the RF power supply.

[0046] Example 8. The plasma processing system includes: a plenum including a bottom wall, side walls along the edges of the bottom wall, a rim extending outward from the side walls, and a radical ballast region between the side walls and the bottom wall, the plenum being a heat conduction structure; a radical source chamber including a gas inlet, a radio frequency (RF) electrode, and a bottom outlet attached to the rim of the plenum; a process chamber including a heat conduction wall physically attached to the plenum at the rim, the plenum having an opening connecting the process chamber to the radical source chamber through the radical ballast region; and a substrate holder disposed under the bottom wall of the plenum.

[0047] Example 9. In the system according to Example 8, the plenum is in the shape of an inverted hat having a rim in the shape of a ring.

[0048] Example 10. In the system according to one of Examples 8 or 9, the width of the opening of the rim is smaller than or equal to the width of the outlet of the radical source chamber, the width of the radical ballast region is larger than or equal to the width of the outlet of the radical source chamber, the width of the radical ballast region is larger than or equal to the width of the substrate holder, the depth of the radical ballast region is 5 cm to 15 cm, and the width-to-depth ratio of the radical ballast region is 3 to 10.

[0049] Example 11. In the system according to one of Examples 8 to 10, the opening is symmetrically positioned around the axis passing through the substrate holder on the side wall of the plenum.

[0050] Example 12. In the system according to one of Examples 8 to 11, the opening is asymmetrically positioned on one side of the mirror plane passing through the substrate holder on the side wall of the plenum.

[0051] Example 13. In the system according to one of Examples 8 to 12, the radical ballast region is in the shape of a rectangular cavity, and the opening is positioned on one of the four rectangular faces of the side wall of the plenum.

[0052] Example 14. In the system according to one of Examples 8 to 13, the opening is positioned on the bottom wall of the plenum.

[0053] Example 15. In the system according to one of Examples 8 to 14, the opening in the bottom wall of the plenum is configured to limit the ultraviolet energy passing through the opening to less than 1% of the ultraviolet energy incident on the upper surface of the bottom wall.

[0054] Example 16. The system according to one of Examples 8 to 15 further includes a gas outlet disposed on only one face of the process chamber, and the gas outlet is configured to guide the gas flow to a region adjacent to only one face of the plenum of the process chamber to generate an alternating current above the substrate holder.

[0055] Example 17. The plasma processing method includes: placing a substrate on a substrate holder disposed near the bottom of the process chamber; introducing a process gas and a carrier gas into a radical source chamber through a gas inlet, wherein the radical source chamber includes an outlet attached to a plenum disposed below the radical source chamber; maintaining a plasma in the radical source chamber, wherein the plasma contains radicals; transporting the radicals to the substrate in a gas flow through an opening in the wall of the plenum; chemically treating the surface of the substrate with the radicals; and exhausting excess reactants and gas by-products from the process chamber through a gas outlet disposed below the substrate holder.

[0056] Example 18. In the method according to Example 17, the transporting step includes guiding the gas flow symmetrically around the axis passing through the substrate holder through the side wall of the plenum.

[0057] Example 19. In the method according to one of Examples 17 or 18, the transporting step includes guiding the gas flow through the side wall of the plenum on only one side of the plenum.

[0058] Example 20. The method according to one of Examples 17 to 19 further includes generating an alternating current of radicals above the substrate.

[0059] As described above, various embodiments of the plasma system and method for chemically treating the surface of the substrate have been described. The described embodiments provide several advantages, including low radical loss and high radical-to-ion ratio, reduction or elimination of damage due to plasma-induced radiation, and efficient heat dissipation providing a stable temperature during processing. There can be many variations in the design of the plasma system, some of which have been described in this disclosure. However, it should be understood that those skilled in the art can devise many other variations from the exemplary embodiments described. For example, the RF power supply can also be provided from a capacitive coupling or a microwave source, the openings for the gas flow in the plenum can also have different shapes, such as circular holes or a two-dimensional array of rectangular holes, the geometric design of the heat conductor can be changed, and different dimensions and materials can be used in the design of the structure of the plasma system.

[0060] The present invention has been described with reference to exemplary embodiments, but this specification is not intended to be construed in a limiting sense. Those skilled in the art will, by referring to this specification, become aware of various modifications and combinations of those exemplary embodiments and other embodiments of the present invention. Therefore, the appended claims are intended to encompass any such modifications or embodiments.

Claims

1. A plasma processing system, comprising: A radical source chamber, comprising: A gas inlet; An electrode coupled to a radio frequency (RF) power source, the electrode being configured to generate radicals within the radical source chamber; An outlet for the radicals generated within the radical source chamber; A plenum attached to the outlet of the radical source chamber, the plenum being fabricated from a first heat conductor, the side walls of the plenum including openings for gas flow; A process chamber connected to the radical source chamber through the plenum, the process chamber including a substrate holder disposed beneath the plenum, a gas outlet beneath the substrate holder, and a process chamber wall including a second heat conductor thermally coupled to the wall of the plenum; The plenum is configured to block ultraviolet light emitted from within the radical source chamber within a direct line of sight from the radical source chamber to the substrate holder.

2. The system of claim 1, wherein the first heat conductor comprises a material that does not transmit ultraviolet light, and the plenum is interposed between the radical source chamber and the substrate holder.

3. The system of claim 1, wherein the first heat conductor comprises aluminum coated on one side with alumina or yttria.

4. The system of claim 1, wherein the first heat conductor and the second heat conductor comprise the same heat conductor.

5. The system of claim 1, wherein the electrode is a conductor in the shape of a planar coil disposed on top of an upper cover including a dielectric material outside the radical source chamber.

6. The system of claim 1, wherein the electrode is a conductor in the shape of a helix disposed around a cylindrical side wall including a dielectric material outside the radical source chamber, and the length of the conductor is a multiple of one quarter of the wavelength of the RF electromagnetic vibration within the electrode powered by the RF power source. ​ ​ ​ ​ ​ ​

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