Pseudo-fractal showerhead for substrate processing tool

Abstract

A pseudo-fractal showerhead for a substrate processing tool includes a gas inlet to receive processing gas and a gas distribution structure. The gas distribution structure includes a plurality of flow channels arranged in a plurality of hierarchical layers. The gas distribution structure includes a first hierarchical layer of flow channels, a second hierarchical layer of flow channels branching from the first hierarchical layer according to a pseudo-fractal pattern, and a plurality of inter-layer connection channels connecting the first hierarchical layer to the second hierarchical layer.

Description

Docket No. LRC24310PPCTPSEUDO-FRACTAL SHOWERHEAD FOR SUBSTRATE PROCESSING TOOLBACKGROUND

[0001] Semiconductor processing tools can include components designed to emit processing gases through an arrangement of outlet holes distributed over an area to expose a substrate to the processing gases. Such components are commonly referred to in the industry as “showerheads.”SUMMARY

[0002] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

[0003] One example provides a pseudo-fractal showerhead for a substrate processing tool. The pseudo-fractal showerhead comprises a gas inlet to receive processing gas; and a gas distribution structure. The gas distribution structure includes a plurality of flow channels arranged in a plurality of hierarchical layers including a first hierarchical layer of flow channels, a second hierarchical layer of flow channels branching from the first hierarchical layer according to a pseudo-fractal pattern, and a plurality of inter-layer connection channels connecting the first hierarchical layer to the second hierarchical layer.

[0004] In some examples, the pseudo-fractal showerhead further comprises a plurality of gas outlets, and wherein each gas outlet of the plurality of gas outlets is connected to the gas inlet through a different gas flow path that passes through a different subset of the plurality of flow channels.

[0005] In some examples, alternatively or additionally each different gas flow path has a substantially equal path length.

[0006] In some examples, alternatively or additionally one or more of the plurality of inter-layer connection channels receives processing gas from a differentDocket No. LRC24310PPCT quantity of immediately preceding flow channels from others of the plurality of interlayer connection channels.

[0007] In some such examples, alternatively or additionally the plurality of hierarchical layers includes three or more hierarchical layers, and wherein an outletterminating hierarchical layer of the three or more hierarchical layers is interleaved between its two preceding hierarchical layers.

[0008] In some such examples, alternatively or additionally the first hierarchical layer is an uppermost layer relative to the gas inlet, the second hierarchical layer is a lowermost layer relative to the gas inlet, and wherein each additional hierarchical layer of the three or more hierarchical layers is interleaved between its two preceding hierarchical layers.

[0009] In some such examples, alternatively or additionally the inter-layer connection channels each extend in a direction substantially parallel to a central axis of the gas inlet.

[0010] In some such examples, alternatively or additionally a plurality of gas outlets are formed in a faceplate of the pseudo-fractal showerhead, such that the processing gas exiting the plurality of gas outlets is exiting the pseudo-fractal showerhead through the faceplate.

[0011] In some such examples, alternatively or additionally the pseudo-fractal showerhead further comprises a faceplate, and wherein a plenum is disposed between the gas distribution structure and the faceplate, such that the processing gas exiting a plurality of gas outlets of the gas distribution structure enters the plenum.

[0012] In some such examples, alternatively or additionally the pseudo-fractal showerhead further comprises a plurality of support posts extending through the plenum and connecting the gas distribution structure to the faceplate.

[0013] In some such examples, alternatively or additionally the plurality of support posts are arranged on the faceplate in a grid.

[0014] In some such examples, alternatively or additionally a support post of the plurality of support posts has a cylindrical shape.

[0015] In some such examples, alternatively or additionally a support post of the plurality of support posts has a substantially rectangular shape, and wherein a subset of the plurality of support posts collectively define a segmented hexagon on the faceplate.Docket No. LRC24310PPCT

[0016] In some such examples, alternatively or additionally the plurality of flow channels is a first plurality of flow channels, and wherein the pseudo-fractal showerhead further comprises a second plurality of flow channels within the gas distribution structure hierarchically branching from a second gas inlet, wherein the first plurality of flow channels and the second plurality of flow channels are separate.

[0017] In some such examples, alternatively or additionally the second plurality of flow channels are arranged in a second plurality of hierarchical layers, and wherein the plurality of hierarchical layers of the first plurality of flow channels is interleaved with the second plurality of hierarchical layers of the second plurality of flow channels.

[0018] In some such examples, alternatively or additionally the second plurality of flow channels is rotated and scaled relative to the first plurality of flow channels.

[0019] In some such examples, alternatively or additionally at a hierarchical layer of the plurality of hierarchical layers, an intra-layer subset of the plurality of flow channels form an edge extension to the pseudo-fractal pattern of the hierarchical layer.

[0020] In some such examples, alternatively or additionally the pseudo-fractal pattern is a hexagonal pseudo-fractal pattern.

[0021] Another example provides a substrate processing tool. The substrate processing tool comprises a processing chamber; and a pseudo-fractal showerhead to emit processing gas into the processing chamber. The pseudo-fractal showerhead comprises a gas inlet to receive processing gas, and a plurality of flow channels arranged in a plurality of hierarchical layers of a gas distribution structure. The gas distribution structure includes a first hierarchical layer of flow channels, a second hierarchical layer of flow channels branching from the first hierarchical layer according to a pseudo-fractal pattern, and a plurality of inter-layer connection channels connecting the first hierarchical layer to the second hierarchical layer.

[0022] Another example provides a pseudo-fractal showerhead for a substrate processing tool. The pseudo-fractal showerhead comprises a gas inlet to receive processing gas, and a gas distribution structure. The gas distribution structure includes a plurality of flow channels hierarchically branching from the gas inlet and connected to a plurality of gas outlets. The plurality of flow channels includes three or more hierarchical layers, such that each gas outlet of the plurality of gas outlets is connected to the gas inlet through a different gas flow path that passes through a different subset of the plurality of flow channels, wherein an outlet-terminating hierarchical layer of theDocket No. LRC24310PPCT three or more hierarchical layers is interleaved between two preceding hierarchical layers.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 shows a schematic depiction of an example substrate processing tool including a showerhead.

[0024] FIG. 2 schematically shows a cross-sectional view of an example showerhead to distribute processing gases across a substrate.

[0025] FIG. 3 schematically represents a plurality of flow channels within an example gas distribution structure of a showerhead.

[0026] FIG. 4 schematically shows a perspective view of an example arrangement of flow channels of a pseudo-fractal showerhead.

[0027] FIG. 5 schematically shows a perspective view of example flow channels including an edge extension to a pseudo-fractal pattern.

[0028] FIG. 6 schematically illustrates example interleaving of hierarchical layers within a gas distribution structure.

[0029] FIG. 7 schematically shows a perspective view of an example of a first plurality of flow channels and a second, separate plurality of flow channels each using a same pseudo-fractal pattern.

[0030] FIG. 8 schematically depicts an example showerhead in cross section, the showerhead including a plenum disposed between a gas distribution structure and a faceplate.

[0031] FIG. 9 schematically represents an example arrangement of support posts on a showerhead faceplate.

[0032] FIG. 10 schematically represents another example arrangement of support posts on a showerhead faceplate.DETAILED DESCRIPTION

[0033] The term “atomic layer deposition” (ALD) generally represents a process in which a film is formed on a substrate in one or more individual layers by sequentially adsorbing a precursor to a substrate and then chemically transforming the adsorbed precursor to form a film layer.

[0034] The term “backplate” generally represents a component of a showerhead. The backplate faces away from a substrate holder of a processing tool.Docket No. LRC24310PPCT

[0035] The term “chemical vapor deposition” (CVD) generally represents a process in which a film is formed on a substrate by exposing the substrate to a flow of reactive gas phase precursors.

[0036] The term “etch” generally represents removal of a material from a substrate. A dry etch uses gas phase chemicals and / or plasmas to remove material from a substrate.

[0037] The term “faceplate” generally represents a part of a showerhead that faces toward a substrate holder of a processing tool. A faceplate includes openings to emit processing gases from the showerhead.

[0038] The terms “film” or “film layer” generally refer to a layer of material deposited on the substrate (e.g., semiconductor wafer).

[0039] The term “flow channel” refers to a space within a showerhead gas distribution structure through which processing gases flow between a gas inlet and a gas outlet. The showerhead may include a network of interconnected flow channels.

[0040] The term “gas distribution structure” refers to a component of a showerhead that receives processing gases through a gas inlet, and includes a plurality of flow channels within the gas distribution structure to carry the processing gases to a plurality of gas outlets.

[0041] The term “gas inlet” generally refers to an opening through which a showerhead receives processing gases.

[0042] The term “gas outlet” generally refers to an opening in a showerhead through which processing gases exit the showerhead. As examples, gas outlets may be formed in a gas distribution structure and / or a faceplate, and include, for example, the outlet holes formed in the faceplate.

[0043] The term “plenum” generally represents a volume of space between a faceplate and a backplate of a showerhead. Processing gases flow into the plenum from a gas distribution structure, and flow out of the plenum toward a substrate through a plurality of gas outlets. The gas outlets extend through a faceplate to fluidly connect the plenum with an environment external to the plenum.

[0044] The term “pseudo-fractal” generally refers to an arrangement of flow channels of a gas distribution structure in which, at each of a number of hierarchical layers connected by inter-layer connection channels, the flow channels hierarchically branch into increasingly small iterations of a same pseudo-fractal pattern. At each hierarchical layer, the lengths of the flow channels are shorter as compared to theDocket No. LRC24310PPCT preceding hierarchical layer. The length of each path through the gas distribution structure (i.e., each path from the gas inlet to the gas outlet) is substantially equal, although due to the pseudo-fractal nature of the branching, not all inter-layer connection channels are connected to the same number of preceding flow channels.

[0045] The term “processing chamber” generally represents an enclosure in which chemical and / or physical processes are performed on substrates. Processing tool components such as a showerhead and a pedestal are located within the processing chamber.

[0046] The term “showerhead” generally represents a structure for distributing processing gases across a surface of a substrate. A showerhead can comprise a plenum between a faceplate and a backplate, and plurality of openings formed in the faceplate.

[0047] The term “substrate” generally represents any structure that can be processed using a processing tool.

[0048] The term “support post” generally represents a structural support that extends between a faceplate and a backplate of a showerhead across a plenum of the showerhead, and is attached to the faceplate and backplate, to resist deformation of the showerhead when exposed to thermal and mechanical stresses.

[0049] As mentioned above, showerheads are used in many semiconductor processing tools to distribute processing gases across a substrate. It is generally desirable to distribute the processing gases uniformly - e.g., such that any position on the surface of the substrate is exposed to a similar flow rate of processing gas as other positions on the surface of the substrate. Depending on the design of the showerhead, uniform flow rates across all outlet holes of a showerhead faceplate can be difficult to achieve. For instance, during substrate processing, portions of the substrate (such as the center) may be exposed to a higher flow rate of processing gas as compared to other portions on the substrate (such as the periphery). This can have an effect on the processing operation, such as by affecting the thickness of a film deposited on the substrate — i.e., thicker film formed near the center of the substrate than the periphery of the substrate. Similarly, it is generally desirable for different positions on the surface of the substrate to receive processing gases at substantially the same time, rather than some portions of the substrate receiving processing gas significantly before or after other portions of the substrate. For example, if the center of the substrate is exposed to processing gases earlier than is the periphery of the substrate, a thicker film will beDocket No. LRC24310PPCT formed near the center, even if the flow rates of processing gas at the center and at the periphery are the same.

[0050] Accordingly, examples are disclosed that relate to showerhead designs for a substrate processing tool. The disclosed showerhead designs use a pseudo-fractal arrangement of flow channels to improve the uniformity with which processing gases are distributed across the surface of a substrate relative to other showerhead flow channel structures. As used herein, “uniformity” may include spatial uniformity, referring to the amount of processing gas received at any given position on the substrate surface throughout substrate processing operations, and / or temporal uniformity, referring to the difference in arrival time of processing gas at each different outlet of the showerhead.

[0051] The example showerheads described herein include a gas distribution structure, in which a plurality of flow channels carry processing gases from a gas inlet to a plurality of gas outlets. The flow channels within the gas distribution structure hierarchically branch at a plurality of different hierarchical layers according to a pseudo-fractal pattern. In other words, each flow channel in a first hierarchical layer is connected to two or more flow channels in a second hierarchical layer, where the arrangement of channels in the first layer serves as a fractal subunit that is repeated two or more times on a smaller scale in the second layer. This may be continued for any suitable number of layers - e.g., at each successive layer, the fractal subunit is repeated a greater number of times and at a smaller scale, as compared to its preceding layer. In one example, the first hierarchical layer receives processing gas from an inlet, and splits or branches into six different flow channels. Each of these six flow channels in the first hierarchical layer connect to the second hierarchical layer through inter-layer connection channels, where each of the flow channels branch another six times to form six sets of flow channels in the second hierarchical layer, thereby repeating the fractal subunit six times. In this example, the first layer includes six flow channels, the second layer includes thirty-six flow channels, and so on. This example arrangement will be illustrated and described in more detail below.

[0052] Using a pseudo-fractal branching pattern in this manner beneficially creates an arrangement where each gas outlet of the gas distribution structure is connected to the gas inlet through a different flow path that passes through a different subset of flow channels, and the length of each flow path is substantially the same. In other words, the gas exiting the showerhead from each gas outlet has traveled aDocket No. LRC24310PPCT substantially similar total distance from the gas inlet through the network of flow channels of the gas distribution structure. This can improve the spatial and temporal uniformity of processing gas distributed across the surface of the substrate during substrate processing operations compared to other showerhead designs. Because the processing gas is emitted from each of the plurality of gas outlets at substantially the same time and with substantially the same flow rate, each position on the surface of the substrate receives processing gas at substantially the same time and substantially the same rate, which improves the uniformity of the film deposited on the substrate compared to a showerhead that exposes a substrate to processing gas at different times and / or flow rates with different gas outlets.

[0053] The flow channels of the disclosed examples branch according to a “pseudo-fractal” pattern, rather than a purely fractal pattern. This means that, for a plurality of inter-layer connection channels carrying processing gas between each hierarchical layer, some inter-layer connection channels may receive processing gas from a different quantity of preceding flow channels from other inter-layer connection channels, which would not be the case in pure fractal arrangements. This will be described in more detail below with respect to FIG. 4. While effectively pure fractal branching patterns can be used to distribute processing gases over the surface of the substrate, it has been observed that such patterns often require the showerhead to be oversized relative to the size of the substrate to achieve suitable coverage, and / or such patterns may produce sizeable voids bereft of gas outlets. The term “effectively” indicates that the branching pattern over the substrate is pure fractal, but that the fractal pattern may be broken at a radial location beyond an edge of a substrate. Both of these scenarios provide disadvantages relative to the disclosed pseudo-fractal patterns.

[0054] Referring now to FIG. 1, an example processing tool 100 for processing a substrate is shown. The processing tool 100 can be configured for thermal or plasma- enhanced chemical vapor deposition (CVD), including metal organic chemical vapor deposition (MOCVD), thermal or plasma-enhanced atomic layer deposition (ALD), and / or other substrate processes. It will be understood that, in other examples, a showerhead as described herein may alternatively or additionally be used for suitable substrate etching processes, and is not limited to deposition processes. The processing tool 100 comprises a processing chamber 102 including a showerhead 104. The showerhead 104 comprises a stem 106 connected to the processing chamber. TheDocket No. LRC24310PPCT showerhead 104 also includes a lower portion 110 that extends radially outwardly from a bottom of the stem 106.

[0055] It will be understood that the specific configuration shown in FIG. 1 is illustrative, and that the arrangements described herein can be applied to a wide variety of different suitable showerheads and substrate processing scenarios. In particular, in some examples, a showerhead as described herein need not include a stem but may be attached directly to the processing chamber wall and / or lid.

[0056] The processing tool 100 further includes a pedestal 114. The depicted pedestal 114 is configured as an electrostatic chuck (ESC) pedestal. During operation, a substrate 116 is arranged on the pedestal 114. Electrodes 118 may be biased to electrostatically attract the substrate 116 during processing to hold the substrate securely. In other examples, other types of pedestals can be used.

[0057] The processing tool 100 is configured to perform plasma-enhanced substrate treatments, such as plasma-enhanced atomic layer deposition (PEALD) and / or plasma-enhanced chemical vapor deposition (PECVD). Thus, the processing tool 100 includes an RF generating system 120 to generate and output RF power. In this example, the pedestal 114 is configured as a powered electrode, and the showerhead 104 is grounded. In other examples, the showerhead 104 can receive power from the RF generating system 120, and the pedestal 114 can be grounded. The RF generating system 120 includes an RF generator 122 that generates the RF power. The RF generating system 120 further includes a matching and distribution network 124. The substate processing tool further includes an actuator 126 and a lift pin assembly 128. The lift pin assembly includes P lift pins 128, where P is an Integer greater than 2. The actuator 126 and the lift pin assembly 128 are used during loading and unloading of the substrate 116 from the chamber.

[0058] The processing tool 100 further comprises a gas delivery system 130. The gas delivery system 130 includes one or more gas sources 132-1, 132-2, ... , and 132-N (collectively gas sources 132), where N is an integer greater than zero. The gas sources 132 supply one or more processing gases such as deposition precursors, purge gas, etch gas, etc. In some examples, vaporized precursors may also be used (not shown). The gas sources 132 are connected by valves 134-1, 134-2, ... , and 134-N (collectively valves 134), mass flow controllers 136-1, 136-2, ... , and 136-N (collectively mass flow controllers 136), and valves 138-1, 138-2, ... , and 138-N (collectively valves 138) to a manifold 140. An output of the manifold 140 is fed by theDocket No. LRC24310PPCT gas delivery system 130 to the processing chamber 102. For example, the output of the manifold 140 is fed to the showerhead 104.

[0059] A heater controller 142 (“HC”) is connected to resistive heaters arranged in the pedestal 114. The heater controller 142 can be used to control a temperature of the pedestal 114. In addition, the pedestal 114 can include internal channels (not shown) to flow a fluid from a fluid source (not shown) to provide further control of the pedestal and substrate temperatures.

[0060] A valve 150 and pumping system 152 can be used to evacuate reactants and products from the processing chamber 102 and / or to control pressure in the processing chamber. A controller 160 can be used to control the various components of the processing tool 100 described herein. For example, the controller 160 can cause a robot arm 170 to load the substrate 116 onto the pedestal 114, and unload the substrate 116 from the pedestal 114. The controller 160 communicates with the gas delivery system 130 to control supply of process, purge and / or inert gases. The controller communicates with the valve 150 and pump 152 to control pressure within the processing chamber and / or evacuation of reactants. The controller 160 also causes a voltage source 172 to output voltage to the electrodes 118 to clamp and unclamp the substrate.

[0061] FIG. 2 shows a simplified representation of an example showerhead 200. Showerhead 200 includes a gas inlet that receives processing gas 204. The processing gas flows through a gas distribution structure 206. In this simplified example, details of the gas distribution structure are omitted. Processing gas flows through flow channels within the gas distribution structure, and thus is distributed throughout the volume of the showerhead. The processing gas exits the showerhead through a plurality of gas outlets formed in a faceplate 207 of the showerhead. Three of these gas outlets are labeled as outlets 208A, 208B, and 208C. Processing gas exits the gas outlets toward a substrate 210 for substrate processing.

[0062] For the sake of visual clarity, in FIG. 2, processing gas is only shown (by arrows) as exiting six of the gas outlets of the showerhead. However, it will be understood that the processing gas may exit all of the gas outlets in faceplate 207 toward the substrate. Furthermore, as discussed above, the arrangement of flow channels within the gas distribution structure may improve the spatial and temporal uniformity of processing gas distribution across the surface of the substrate. For instance, each gas outlet in faceplate 207 may emit substantially the same volume of processing gasDocket No. LRC24310PPCT toward the substrate at substantially the same flow rate, and processing gas may begin flowing out of each gas outlet at substantially the same time. For the purposes of the present disclosure, “substantially the same” may refer to a difference of less than 2%.

[0063] In this example, processing gas exiting the gas distribution structure passes directly through a plurality of gas outlets formed in the faceplate of the showerhead, such that the processing gas exiting the plurality of gas outlets is exiting the showerhead through the faceplate. In other examples, the showerhead may include a plenum disposed between the gas distribution structure and the faceplate, such that the processing gas exiting the gas distribution structure enters the plenum, rather than directly exiting the showerhead. Use of a plenum can in some circumstances improve the uniformity of processing gas exiting the gas outlets. For instance, inclusion of a plenum may enable the number of hierarchical layers in the gas distribution structure to be reduced. Depending on the intended processing operations, and depending on any applicable constraints affecting the size, complexity, and cost of the showerhead, a plenum may or may not be included. An example showerhead that includes a plenum will be described below with respect to FIG. 8.

[0064] FIG. 3 schematically represents a plurality of flow channels 302 in a gas distribution structure 300 of a showerhead. The showerhead is an example of a pseudofractal showerhead, although is shown in cross section, so the pseudo-fractal branching pattern is not observed in FIG. 3. It will be understood that the arrangement depicted in FIG. 3 is highly simplified and provided to illustrate flow channels that branch hierarchically at different layers. It will be understood that the concepts described with respect to FIG. 3 may be applied to other, more complex arrangements of flow channels, such as will be described below with respect to FIG. 4.

[0065] As shown, in FIG. 3, the plurality of flow channels is connected to a gas inlet 301, through which the plurality of flow channels receive processing gas. The gas inlet 301 splits into (or branches out to) two flow channels 302A and 302B at a first hierarchical layer 303A. As shown, the flow channels 302A and 302B of the first hierarchical layer are connected to inter-layer connection channels 304A and 304B, which connect the first hierarchical layer 303A to a second hierarchical layer 303B. Connection channel 304 A splits into two flow channels 302C and 302D of the second hierarchical layer, while connection channel 304B splits into another two flow channels 302E and 302F. In this manner, the arrangement of the first hierarchical layer (e.g., one inlet splitting into two flow channels) is fractally repeated two times in the secondDocket No. LRC24310PPCT hierarchical layer. The flow channels of the second layer each connect to additional inter-layer connection channels 304C, 304D, 304E, and 304F, which in turn connect to a third hierarchical layer 303C. The inter-layer connection channels split into additional flow channels 302G-302N of the third hierarchical layer 303C. In this manner, the arrangement of the first hierarchical layer is fractally repeated four times in the third hierarchical layer.

[0066] In this example, only three hierarchical layers are used, meaning that the flow channels of the third hierarchical layer are connected to corresponding gas outlets 306A-306H, though which processing gas exits the gas distribution structure. In other examples, any suitable number of two or more hierarchical layers may be used.

[0067] As shown, in this example, the plurality of flow channels hierarchically branch from the gas inlet and are connected to the plurality of gas outlets, such that each gas outlet of the plurality of gas outlets is connected to the gas inlet through a different gas flow path that passes through a different subset of the plurality of flow channels. Two of these paths are shown as flow paths 308A and 308B. As discussed above, in this example, each different gas flow path has a substantially equal path length. In other words, processing gas flowing from inlet 301 to gas outlet 306 A along path 308A travels substantially the same distance as processing gas flowing from gas inlet 301 to gas outlet 306F along path 308B. This is beneficial to the spatial and temporal uniformity of processing gas distributed across the surface of the substrate, as discussed above.

[0068] Furthermore, as is shown in FIG. 3, the different hierarchical layers are connected through a plurality of inter-layer connection channels. The inter-layer connection channels each extend in a direction that is substantially perpendicular to the hierarchical layers, and substantially parallel to a central axis of the gas inlet. In FIG. 3, this is labeled as central axis 310 of gas inlet 301, and each of the inter-layer connection channels 304A-304F are substantially parallel to axis 310. It will be understood that “substantially parallel” does not require that the inter-layer connection channels are exactly parallel to the gas inlet. Rather the inter-layer connection channels may extend in a direction that differs from the gas inlet on the order of single degrees, for example. It is preferred that the inter-layer connection channels connecting the same neighboring hierarchical layers are substantially symmetric around the central axis 310 — i.e., they have the substantially same length, and, when they are not parallel to the central axis, they form the substantially same slope or angle with respect to the centralDocket No. LRC24310PPCT axis 310. Furthermore, it will be understood that the interface between a flow channel and an inter-layer connection channel need not be separated by an edge having a right angle, as is shown in FIG. 3. Rather, in some examples, the interface between flow channels and inter-layer connection channels may have curved, sloping, chamfered, and / or other edge configurations.

[0069] This arrangement can beneficially serve to reduce lateral momentum of processing gas between different hierarchical layers. In other words, lateral momentum accumulated by the processing gas while flowing through the flow channels in one hierarchical layer is lost as the processing gas flows through the inter-layer connection channels. This can promote a more even distribution of the processing gas in the next hierarchical layer of the gas distribution structure relative to other gas distribution structure arrangements where hierarchical layers are not used, or where inter-layer connection channels do not reduce the lateral momentum of the processing gas (e.g., due to the shape and / or slope of the inter-layer connection channels). By reducing the lateral momentum of the processing gas entering a hierarchical layer, the processing gas is more likely to evenly flow through each of the flow channels in the hierarchical layer, rather than favoring flow channels that preserve the earlier lateral momentum of the processing gas - e.g., flow channels that allow the processing gas to continue flowing in the same lateral direction as it did in the previous hierarchical layer.

[0070] FIG. 4 schematically shows a perspective view of another example arrangement of flow channels of a gas distribution structure. In this example, the flow channels hierarchically branch in a pseudo-fractal pattern. The flow channels are distributed in three hierarchical layers 400A, 400B, and 400C. The different hierarchical layers are shown as being separated in FIG. 4 for visual clarity. However, it will be understood that the different hierarchical layers are connected by inter-layer connection channels having a vertical component as discussed above.

[0071] Beginning with the first hierarchical layer 400A, processing gas is received through a gas inlet 402, which is connected to six flow channels. Two of the flow channels are labeled as channels 404A and 404B. As discussed above, the arrangement of flow channels in the first hierarchical layer serves as a fractal subunit that is repeated in each successive hierarchical layer of the gas distribution structure. In other words, in this example, the plurality of flow channels hierarchically branch in a hexagonal pseudo-fractal pattern, as the ends of each flow channel define different corners of a hexagon. In other examples, other pseudo-fractal geometries may be used.Docket No. LRC24310PPCTFor instance, as one example, an octagonal pseudo-fractal pattern may be used, where the fractal subunit includes a gas inlet branching into eight flow channels.

[0072] In FIG. 4, each of the flow channels in the first hierarchical layer 400A connect to inter-layer connection channels, two of which are labeled as channels 406A and 406B. These connect the first hierarchical layer to the second hierarchical layer 400B. As shown, within the second hierarchical layer, the inter-layer connection channel 406A branches into another six flow channels, two of which are labeled as flow channels 408 A and 408B. Similarly, inter-layer connection channel 406B branches into its own set of six flow channels, two of which are labeled as flow channels 408C and 408D. Each of the other inter-layer flow channels extending from the first hierarchical layer also branches into its own corresponding set of six flow channels in the second hierarchical layer, thereby recreating the fractal subunit six times.

[0073] Similarly, the flow channels of the second hierarchical layer 400B are each connected to a plurality of inter-layer connection channels that connect the second hierarchical layer to the third hierarchical layer 400C. For instance, flow channel 408A connects to inter-layer connection channel 410A, while flow channel 408C is connected to inter-layer connection channel 410B. Within the third hierarchical layer, each of the inter-layer connection channels again branch into six different flow channels, thereby repeating the fractal subunit in the third hierarchical layer. For instance, inter-layer connection channel 410A branches into six different flow channels, one of which is labeled as flow channel 412A. This in turn connects to another inter-layer connection channel 414A, which may connect to the next hierarchical layer of flow channels (e.g., in the case where the showerhead includes four or more layers), or may terminate as a gas outlet in the gas distribution structure.

[0074] Notably, as discussed above, the flow channels of FIG. 4 branch according to a pseudo-fractal pattern, as opposed to a pure fractal pattern. This is because, for the plurality of inter-layer connection channels connecting the plurality of flow channels, one or more inter-layer channels receives processing gas from a different quantity of preceding flow channels from others of the plurality of inter-layer connection channels. For instance, with respect to the second hierarchical layer 400B, inter-layer connection channel 410A is immediately preceded by a single flow channel 408 A. By contrast, inter-layer connection channel 410B is shared between, and immediately preceded by, two different flow channels - 408B and 408C. In other words, inter-layer connection channel 410A (and other inter-layer connection channelsDocket No. LRC24310PPCT around the edge of the hierarchical layer) only receives processing gas from a single immediately preceding flow channel, while other inter-layer connection channels are shared between two different flow channels, and thus receive processing gas from two preceding flow channels. This would not be the case in pure fractal designs, where each inter-layer connection channel receives processing gas from the same number of preceding flow channels (e.g., only one flow channel), regardless of the radial position of the inter-layer connection channel in the gas distribution structure. As discussed above, use of a pseudo-fractal flow pattern can enable use of a showerhead that has a smaller size and better distribution of outlet holes as compared to pure fractal patterns.

[0075] In this example, some inter-layer connection channels are preceded by two flow channels, while others are preceded only by one flow channel. However, it will be understood that this configuration is non-limiting. For instance, in some scenarios, one or more inter-layer connection channels may be preceded by more than two flow channels, depending on the fractal geometry of the gas distribution structure.

[0076] In some examples, flow of processing gas through flow channels positioned at the edge of the gas distribution structure can be facilitated through edge tuning, i.e., changing the flow characteristics of the processing gas near the edge of the gas distribution structure, relative to the central axis of the gas distribution structure. This may be done by adding an edge extension to one or more of the hierarchical layers, serving as a partial extension to the pseudo-fractal pattern of the hierarchical layer. This is schematically illustrated with respect to FIG. 5, showing a single hierarchical layer 500 of two or more hierarchical layers of a gas distribution structure. As shown, layer 500 has structural similarities to hierarchical layer 400B of FIG. 4. Layer 500 in FIG. 5 receives processing gas through a plurality of inter-layer connection channels, one of which is labeled as inter-layer connection channel 502A. This divides into six flow channels, two of which are labeled as flow channels 504A and 504B, which in turn connect to subsequent inter-layer connection channels 506A and 506B, respectively.

[0077] However, in this example, a subset of the flow channels within the hierarchical layer (e.g., an “intra-layer subset” of flow channels) form an edge extension 508, shown in dashed lines to more easily distinguish it from the configuration shown in FIG. 4. The edge extension constitutes a partial extension of the pseudo-fractal pattern - e.g., including four flow channels that partially recreate the six-channel hexagonal pattern used elsewhere in the hierarchical layer. It will be understood that this edge extension concept may be extended to any suitable degree depending on theDocket No. LRC24310PPCT implementation - e.g., any suitable number of additional flow channels may be added to the edge of a hierarchical layer. For instance, another two flow channels may be added to edge extension 508 to fully recreate the six-channel hexagonal pattern. Use of such an edge extension can beneficially improve flow of processing gas through the gas distribution structure by improving the volume of processing gas that is able to flow through the edge flow channels of the gas distribution structure, and thereby improve the flow rate uniformity of processing gas exiting edge gas outlets of the showerhead, as compared to more central gas outlets. Furthermore, use of an edge extension can bias flow of processing gas, such that the flow rate is higher at the edge of the hierarchical layer. This can, for instance, offset the effect of a high reaction rate at the edge due to a temperature difference between the edge and the center of the showerhead.

[0078] Thus far, the present disclosure has focused on examples where the hierarchical layers of the gas distribution structure become increasingly branched and divided as their distance from the gas inlet increases. For instance, in FIG. 4, hierarchical layer 400A is the closest to the gas inlet of the showerhead, and has the smallest number of flow channels. Layer 400B is further from the gas inlet and has a greater number of flow channels, while layer 400C - the furthest from the gas inlet and closest to the gas outlets - has the most flow channels of the three layers. However, it will be understood that this need not always be the case. Rather, in some examples where three or more hierarchical layers are used, an outlet-terminating hierarchical layer may be interleaved between its two preceding hierarchical layers. The “outletterminating” hierarchical layer refers to the final hierarchical layer - i.e., the layer that connects to the gas outlets of the gas distribution structure.

[0079] FIG. 6 schematically represents a gas distribution structure where such an interleaving configuration is used. It will be understood that FIG. 6 is highly simplified and represents only a small number of individual flow channels in the gas distribution structure. It will be understood that the interleaving concepts described with respect to FIG. 6 may be applied to more complicated arrangements of flow channels, such as the configuration described with respect to FIG. 4.

[0080] As shown, in FIG. 6, the gas distribution structure includes a first hierarchical layer 602A, which is the uppermost layer relative to the gas inlet. This is connected to a second hierarchical layer 602B. Unlike the configuration shown in FIG. 4, in this example, the second hierarchical layer is the lowermost layer relative to the gas inlet. The second hierarchical layer 602B is connected to a third layer 602C, whichDocket No. LRC24310PPCT is interleaved between its two preceding hierarchical layers - e.g., interleaved between layers 602A and 602B. This is the case for each additional hierarchical layer in the gas distribution structure - e.g., the fourth hierarchical layer 602D is interleaved between its preceding layers 602C and 602B, while the fifth hierarchical layer 602E is interleaved between its preceding layers 602D and 602C. In the example of FIG. 6, layer 602E is the outlet-terminating hierarchical layer, and thus connects to a gas outlet 604. It will be understood that, in other examples, interleaving may be applied to any suitable number of three or more hierarchical layers.

[0081] Interleaving in this manner can enable an improvement to processing gas uniformity without increasing showerhead thickness, or may enable a reduction in the overall thickness of the showerhead while still achieving suitable uniformity. As discussed above, these channels may serve to arrest the lateral momentum of the processing gas between hierarchical layers. In scenarios where no interleaving is used, it may be necessary for the sum of the lengths of the inter-layer connection channels to be relatively higher in order to achieve suitable uniformity, increasing the thickness of the showerhead as compared to scenarios where interleaving is used. However, it may not be possible to increase showerhead thickness (e.g., as constrained by the geometry of the processing chamber), thus requiring shorter inter-layer connection channels that can potentially reduce the uniformity of the processing gas. By contrast, use of layer interleaving can enable the lengths of the inter-layer connection channels to be relatively longer without increasing showerhead thickness, resulting in higher momentum reduction and therefore higher uniformity. Having a relatively thinner showerhead provides a technical benefit by reducing the materials required to construct the showerhead. Furthermore, a relatively thinner showerhead may provide a more uniform temperature gradient relative to a vertical axis of the showerhead. For instance, when the showerhead is thinner, there may be a smaller difference in temperature between the side of the showerhead facing toward the substrate and the side of the showerhead facing away from the substrate, and this can reduce thermal strain.

[0082] Thus far, the present disclosure has focused on scenarios where the gas distribution structure includes a single interconnected network of flow channels. In some examples, the gas distribution structure may include two or more different sets of flow channels that are separate and independent, such that two or more different types of processing gases can flow through the showerhead at once without mixing within the gas distribution structure.Docket No. LRC24310PPCT

[0083] This is schematically illustrated with respect to FIG. 7, showing aspects of an example gas distribution structure 700. This includes a first plurality of flow channels 702A, shown in white, along with a second plurality of flow channels, shown with a fill pattern, which is separate from the first plurality of flow channels. The first plurality of flow channels branches from a first gas inlet 704A, which splits into six flow channels in a first hierarchical layer as discussed above, one of which is labeled as flow channel 706A. This is connected to a second hierarchical layer, which also includes a plurality of flow channels, one of which is labeled as flow channel 708A. Separately, the gas distribution structure includes a second gas inlet 704B, and a second plurality of flow channels that hierarchically branch from the second gas inlet. Specifically, in a first hierarchical layer, the second gas inlet splits into six flow channels, one of which is labeled as flow channel 706B. This is connected to a second hierarchical layer of flow channels, one of which is labeled as 708B. Each of these different networks of flow channels may ultimately terminate at different sets of gas outlets, enabling two different types of processing gases to separately flow through the gas distribution structure at the same time. This provides a technical benefit of preventing unwanted or premature chemical reactions from occurring within the showerhead from different processing gases.

[0084] In this example, the two different networks of flow channels each respectively include two hierarchical layers. In other examples, each network of flow channels may include any other suitable number of two or more hierarchical layers between its respective gas inlet and its respective set of gas outlets.

[0085] In this example, the second plurality of flow channels is arranged in a second plurality of hierarchical layers. The hierarchical layers of the first plurality of flow channels 702A are interleaved with the hierarchical layers of the second plurality of flow channels 702B. For instance, the first hierarchical layer of the second plurality of flow channels (e.g., including flow channel 706B) is interleaved between the two hierarchical layers of the first plurality of flow channels. In other words, the hierarchical layer including flow channel 706B is interleaved between the hierarchical layers including flow channels 706A and 708A. Similarly, the hierarchical layer including flow channel 708A is interleaved between the layers including channels 706B and 708B. Such interleaving may beneficially reduce the thickness of the gas distribution structure, and therefore reduce the thickness of the showerhead, while still enabling two separate networks of flow channels to be used.Docket No. LRC24310PPCT

[0086] In the example of FIG. 7, the two different networks of flow channels each use the same pseudo-fractal pattern - e.g., each hierarchical layer is defined by the same fractal subunit of an inlet channel that branches into six flow channels. However, in this example, the second plurality of flow channels is rotated and scaled relative to the first plurality of flow channels. For instance, in this example, the second network of flow channels is rotated by approximately 30 degrees and has a smaller size as compared to the first network of flow channels. This may beneficially enable the two different networks of flow channels to fit together within the confines of the gas distribution structure. In other examples, where other pseudo-fractal geometries are used, other suitable rotations and / or scaling factors may be applied. Furthermore, different pseudo-fractal patterns may in some cases be used for different flow channel networks within the same gas distribution structure.

[0087] As discussed above with respect to FIG. 2, in some examples, the outlet holes of the gas distribution structure terminate as outlets in the faceplate of the showerhead. Thus, processing gas exiting the gas distribution structure is also exiting the showerhead toward the substrate. In other examples, however, the showerhead may include a plenum disposed between the gas distribution structure and the faceplate, such that the processing gas exiting the plurality of gas outlets enters the plenum. This is schematically illustrated with respect to FIG. 8, showing another example showerhead 800. The showerhead includes a gas inlet 802 to receive processing gas. The processing gas is distributed through a gas distribution structure 804. Details of the gas distribution structure are omitted in FIG. 8 for the sake of visual clarity, although it includes a plurality of flow channels that branch hierarchically as discussed above. The gas distribution structure includes a plurality of gas outlets, two of which are labeled as gas outlets 806A and 806B. In this example, a plenum 808 is disposed between the gas distribution structure 804 and a faceplate 810, such that the processing gas exiting the gas outlets enters the plenum. The processing gas then exits the showerhead through outlet holes in the faceplate, two of which are labeled as outlet holes 812A and 812B.

[0088] Additionally, in this example, the showerhead further comprises a plurality of support posts extending through the plenum and connecting the gas distribution structure to the faceplate. The support posts may be used to provide mechanical support to the showerhead - e.g., resisting deformation of the showerhead due to thermal and mechanical stresses. The manner in which support posts are distributed may furthermore be used to guide the gas flow within the plenum.Docket No. LRC24310PPCTAdditionally, support posts may in some cases be used to provide a conduction path for heat flow from the showerhead faceplate (facing toward the high-temperature pedestal) to the showerhead backplate, which may include an embedded cooling loop. This can beneficially help to maintain the showerhead faceplate at a relatively uniform temperature. Two of the support posts are labeled as posts 814A and 814B. The support posts may take any suitable form, having any suitable size, shape, and distribution. Furthermore, the showerhead may include any suitable number of support posts.

[0089] In some examples, a support post of the plurality of support posts has a cylindrical shape. This is shown in FIG. 8, where each support post takes the form of a cylinder. This is also schematically illustrated with respect to FIG. 9, showing an example faceplate 900 of a showerhead. As shown, the faceplate includes a plurality of support posts represented as black circles, two of which are labeled as support posts 902A and 902B. In this example, the support posts each have a cylindrical shape. Furthermore, in this example, the plurality of support posts are arranged on the faceplate in a hexagonal grid, with an outlet hole disposed between each set of six support posts. One of the outlet holes is labeled as outlet hole 904. It will be understood that, in other examples, the support posts may have other suitable shapes, and other suitable distributions across the showerhead faceplate.

[0090] For instance, in some examples, a support post of the plurality of support posts has a substantially rectangular shape, rather than a cylindrical shape. Furthermore, in some examples, a subset of the support posts collectively define a segmented hexagon on the faceplate. This is schematically illustrated with respect to FIG. 10, showing another example showerhead faceplate 1000. Faceplate 1000 includes a plurality of support posts, two of which are labeled as support posts 1002 A and 1002B. In this example, the support posts take the form of segments with squared corners - e.g., some of which have substantially rectangular profiles in FIG. 10. Furthermore, the support posts form multiple concentric segmented hexagons on the faceplate. Use of such an arrangement can beneficially serve to guide the flow of processing gas within the plenum of the showerhead. For instance, the hexagonal arrangement may divide the space into multiple zones. By controlling the space between the support posts, flow of processing gas out of each zone can be controlled to improve uniformity. The gas outlets may have any suitable distribution with respect to the faceplate and the support posts. For instance, in some examples, the gas outlets may be formed in the gaps between different support posts of the concentric segmented hexagons.Docket No. LRC24310PPCT

[0091] Showerheads as described herein may be manufactured in any suitable way. For instance, the gas distribution structure including the flow channels described herein may take any suitable pseudo-fractal form. In some examples, the gas distribution structure takes the form of a block of material that includes internal voids defining the flow channels. For instance, the gas distribution structure may be constructed as a series of metal plates, with flow channels of each hierarchical layer machined into the metal plates. The metal plates may then be welded or otherwise attached together to form the gas distribution structure. In other examples, the gas distribution structure may take another suitable form. For instance, the flow channels may take the form of tubes, where the side walls of each tube separate the inside of the tubes from the external environment, rather than being formed as voids within a solid block. In further examples, the gas distribution structure can take the form of an additively manufactured structure, such as formed by three-dimensional printing methods.

[0092] To summarize, the present disclosure describes example designs for showerheads for substrate processing, in which a plurality of hierarchically branching flow channels arranged in a pseudo-fractal pattern are used to improve the spatial and temporal uniformity of processing gas distributed across the surface of a substrate. As one example, the pseudo-fractal pattern may be a hexagonal pattern, in which a fractal subunit of the pseudo-fractal pattern is defined by an inlet channel that branches into six flow channels. This subunit may be repeated an increasing number of times, and at an increasingly small scale, at each successive hierarchical layer of the showerhead. This beneficially creates a scenario where each potential flow path in the showerhead, between the gas inlet and each different gas outlet, has substantially the same path length.

[0093] It will be understood that the configurations and / or approaches described herein are exemplary in nature, and that these specific examples or examples are not to be considered in a limiting sense, because numerous variations are possible.

[0094] The subject matter of the present disclosure includes all novel and non- obvious combinations and sub-combinations of the various processes, systems and configurations, and other features, functions, acts, and / or properties disclosed herein, as well as any and all equivalents thereof.

Claims

Docket No. LRC24310PPCTCLAIMS:

1. A pseudo-fractal showerhead for a substrate processing tool, the pseudo-fractal showerhead comprising: a gas inlet to receive processing gas; and a plurality of flow channels arranged in a plurality of hierarchical layers of a gas distribution structure, the gas distribution structure including: a first hierarchical layer of flow channels; a second hierarchical layer of flow channels branching from the first hierarchical layer according to a pseudo-fractal pattern; and a plurality of inter-layer connection channels connecting the first hierarchical layer to the second hierarchical layer.

2. The pseudo-fractal showerhead of claim 1, further comprising a plurality of gas outlets, and wherein each gas outlet of the plurality of gas outlets is connected to the gas inlet through a different gas flow path that passes through a different subset of the plurality of flow channels.

3. The pseudo-fractal showerhead of claim 2, wherein each different gas flow path has a substantially equal path length.

4. The pseudo-fractal showerhead of claim 1, wherein one or more of the plurality of inter-layer connection channels receives processing gas from a different quantity of immediately preceding flow channels from others of the plurality of inter-layer connection channels.

5. The pseudo-fractal showerhead of claim 1, wherein the plurality of hierarchical layers include three or more hierarchical layers, and wherein an outlet-terminating hierarchical layer of the three or more hierarchical layers is interleaved between its two preceding hierarchical layers.

6. The pseudo-fractal showerhead of claim 5, wherein the first hierarchical layer is an uppermost layer relative to the gas inlet, the second hierarchical layer is a lowermost layer relative to the gas inlet, and wherein each additional hierarchical layerDocket No. LRC24310PPCT of the three or more hierarchical layers is interleaved between its two preceding hierarchical layers.

7. The pseudo-fractal showerhead of claim 1, wherein the inter-layer connection channels each extend in a direction substantially parallel to a central axis of the gas inlet.

8. The pseudo-fractal showerhead of claim 1, wherein a plurality of gas outlets are formed in a faceplate of the pseudo-fractal showerhead, such that the processing gas exiting the plurality of gas outlets is exiting the pseudo-fractal showerhead through the faceplate.

9. The pseudo-fractal showerhead of claim 1, wherein the pseudo-fractal showerhead further comprises a faceplate, and wherein a plenum is disposed between the gas distribution structure and the faceplate, such that the processing gas exiting a plurality of gas outlets of the gas distribution structure enters the plenum.

10. The pseudo-fractal showerhead of claim 9, further comprising a plurality of support posts extending through the plenum and connecting the gas distribution structure to the faceplate.

11. The pseudo-fractal showerhead of claim 10, wherein the plurality of support posts are arranged on the faceplate in a grid.

12. The pseudo-fractal showerhead of claim 10, wherein a support post of the plurality of support posts has a cylindrical shape.

13. The pseudo-fractal showerhead of claim 10, wherein a support post of the plurality of support posts has a substantially rectangular shape, and wherein a subset of the plurality of support posts collectively define a segmented hexagon on the faceplate.

14. The pseudo-fractal showerhead of claim 1, wherein the plurality of flow channels is a first plurality of flow channels, and wherein the pseudo-fractal showerhead further comprises a second plurality of flow channels within the gasDocket No. LRC24310PPCT distribution structure hierarchically branching from a second gas inlet, wherein the first plurality of flow channels and the second plurality of flow channels are separate.

15. The pseudo-fractal showerhead of claim 14, wherein the second plurality of flow channels are arranged in a second plurality of hierarchical layers, and wherein the plurality of hierarchical layers of the first plurality of flow channels is interleaved with the second plurality of hierarchical layers of the second plurality of flow channels.

16. The pseudo-fractal showerhead of claim 15, wherein the second plurality of flow channels is rotated and scaled relative to the first plurality of flow channels.

17. The pseudo-fractal showerhead of claim 1, wherein, at a hierarchical layer of the plurality of hierarchical layers, an intra-layer subset of the plurality of flow channels form an edge extension to the pseudo-fractal pattern of the hierarchical layer.

18. The pseudo-fractal showerhead of claim 1, wherein the pseudo-fractal pattern is a hexagonal pseudo-fractal pattern.

19. A substrate processing tool, comprising: a processing chamber; and a pseudo-fractal showerhead to emit processing gas into the processing chamber, the pseudo-fractal showerhead comprising: a gas inlet to receive processing gas; and a plurality of flow channels arranged in a plurality of hierarchical layers of a gas distribution structure, the gas distribution structure including: a first hierarchical layer of flow channels; a second hierarchical layer of flow channels branching from the first hierarchical layer according to a pseudo-fractal pattern; and a plurality of inter-layer connection channels connecting the first hierarchical layer to the second hierarchical layer.

20. A pseudo-fractal showerhead for a substrate processing tool, the pseudo-fractal showerhead comprising: a gas inlet to receive processing gas; andDocket No. LRC24310PPCT a gas distribution structure including: a plurality of flow channels hierarchically branching from the gas inlet and connected to a plurality of gas outlets, the plurality of flow channels including three or more hierarchical layers, such that each gas outlet of the plurality of gas outlets is connected to the gas inlet through a different gas flow path that passes through a different subset of the plurality of flow channels, wherein an outlet-terminating hierarchical layer of the three or more hierarchical layers is interleaved between its two preceding hierarchical layers.

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