Hardware for uniform dispensing of active substances for semiconductor film processing

Abstract

A substrate processing system is provided, the substrate processing system having a processing chamber. A processing chamber includes a cover plate, one or more chamber sidewalls, and a chamber base, the cover plate, the one or more chamber sidewalls, and the chamber base collectively defining a processing volume. The annular plate is coupled to the cap plate, and the edge manifold is fluidly coupled to the processing chamber through the annular plate and the cap plate. In one embodiment, a substrate processing system includes a central manifold coupled to a cover plate.

Description

[0001] field

[0002] Embodiments herein relate to systems for electronic device fabrication, and more particularly, embodiments herein relate to gas distribution systems for forming structures containing tungsten and molybdenum in semiconductor devices. Background Art

[0003] Related technical description

[0004] Tungsten (W) is widely used in integrated circuit (IC) device manufacturing to form conductive features where relatively low resistance and relatively high electromigration resistance are desired. For example, tungsten can be used as a metal fill material to form source contacts, drain contacts, metal gate fills, gate contacts, interconnect structures (e.g., horizontal features formed in the surface of a dielectric material layer), and vias (e.g., vertical features formed through a dielectric material layer to connect other interconnect features disposed above and below the dielectric material layer). Due to its relatively low resistivity and high melting point, tungsten is also commonly used to form bit lines and word lines, which are used to address individual memory cells in a memory cell array of a dynamic random access memory (DRAM) device.

[0005] As circuit density increases and device features continue to shrink to meet the needs of next generation semiconductor devices, reliably producing tungsten features becomes increasingly challenging. Advances in integrated circuit technology necessitate improved methods of depositing refractory metals, particularly tungsten, to enhance uniform deposition over a substrate. Conventional deposition methods using point source distribution of active material to a substrate do not allow for adjustability of the active material between the center and edge of the substrate. Layer thickness uniformity from the center to the edge of the substrate is affected by the inability to adjust the deposition gas.

[0006] Therefore, there is a need for a system for regulating gas distribution of radical species from the center to the edge of a substrate. Summary of the invention

[0007] In some embodiments, a substrate processing system is provided, the substrate processing system having a processing chamber. The processing chamber includes a cover plate, one or more chamber sidewalls and a chamber base, the cover plate, the one or more chamber sidewalls and the chamber base together defining a processing space. An annular plate is coupled to the cover plate, and an edge manifold is fluidically coupled to the processing chamber through the annular plate and the cover plate. The substrate processing system includes a central manifold, the central manifold being coupled to the cover plate.

[0008] In some embodiments, a gas delivery system is provided, the gas delivery system comprising a cover plate having a first major surface and a second major surface opposite the first major surface. An annular plate is coupled to the first major surface of the cover plate. The gas delivery system comprises a partition plate coupled to the second major surface of the cover plate. The gas delivery system comprises a central manifold, the central manifold being fluidly coupled to an opening of the cover plate. An edge manifold is fluidly coupled to the central manifold and the annular plate.

[0009] In some embodiments, a method of processing a substrate is provided, the method comprising depositing a nucleation layer by exposing the substrate to a refractory metal-containing gas using a gas delivery system. The method comprises exposing the substrate to a radical species supplied to an edge region of a blocker plate disposed above the substrate, the edge region being fluidly isolated from an interior region of the blocker plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to be able to understand in detail the manner of the above-mentioned features of the present disclosure, the present disclosure briefly summarized above may be described in more detail by reference to embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings illustrate only exemplary embodiments and therefore should not be regarded as limiting the scope of the present disclosure, and other equivalent embodiments may be admitted.

[0011] Figure 1 Depicted is a schematic side view of a processing system according to some embodiments.

[0012] Figure 2A Depicted is a top view of a gas delivery system according to some embodiments.

[0013] Figure 2B Depicted is a cross-sectional bottom view of an annular plate of a gas delivery system according to some embodiments.

[0014] Figure 2C A top view of a cover is depicted according to some embodiments.

[0015] Figure 3 A top view of a blocker plate according to some embodiments is shown.

[0016] Figure 4 A process flow diagram of a method of processing a substrate according to some embodiments is depicted.

[0017] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION

[0018] Figure 1A processing system 100 is schematically depicted that can be used to perform the processing methods described herein. Here, the processing system is configured to provide processing conditions for processing a substrate and for cleaning the interior of a processing chamber 102.

[0019] like Figure 1 As shown, the processing system 100 includes: a processing chamber 102; a gas delivery system 104, which is fluidly coupled to the processing chamber 102; and a system controller 108. The processing chamber 102 includes a chamber lid assembly 110, one or more sidewalls 112, and a chamber base 114, which together define a processing space 115. The processing space 115 is fluidly coupled to an exhaust device 117 (such as one or more vacuum pumps) for maintaining the processing space 115 at sub-atmospheric conditions and exhausting processing gases and processing byproducts therefrom.

[0020] The chamber lid assembly 110 includes a lid plate 116 and a showerhead 118 coupled to the lid plate 116 to define a gas distribution space 119 together with the lid plate. The showerhead 118 faces a substrate support assembly 120 disposed in the processing space 115. As described below, the substrate support assembly 120 is configured to move a substrate support 122 between an elevated substrate processing position (as shown) and a lowered substrate transfer position (not shown), and thus move a substrate 130 disposed on the substrate support 122. When the substrate support assembly 120 is in the elevated substrate processing position, the showerhead 118 and the substrate support 122 define a processing area 121.

[0021] The gas delivery system 104 is fluidly coupled to the processing chamber 102 through the central manifold 107 and the edge manifold 103. The central manifold 107 is coupled to the cover plate 116 and is fluidly coupled to the processing chamber 102 through the central gas inlet 123 disposed through the cover plate 116. The process gas or cleaning gas delivered by using the gas delivery system 104 flows through the central gas inlet 123 into the gas distribution space 119 and is distributed to the processing area 121 through the showerhead 118. In some embodiments, the process gas or cleaning gas flows through the edge manifold 103. The edge manifold 103 is coupled to the annular plate 129 disposed on the outer surface of the cover plate 116. The edge manifold 103 is fluidly coupled to the processing chamber 102 through the opening 210 of the annular plate 129 and the edge gas holes 204 through the cover plate 116. The isolation valve 105 is disposed on the edge manifold 103 and is configured to control the gas flow rate through the edge manifold 103. The opening 210 of the annular plate 129 is fluidly coupled to the edge manifold 103 and a channel 212 disposed in the annular plate 129. The channel 212 is fluidly coupled to the edge air holes 204 disposed in the cover plate 116.

[0022] The edge air holes 204 are channels extending from the outer surface to the inner surface of the cover plate 116. In some embodiments, the edge air holes 204 are arranged in a first shape that approximates the shape of an annular plate, such as a circle. In some embodiments, about 15 to about 25 (such as about 17 to about 20) edge air holes 204 are arranged around the cover plate 116. In some embodiments, the edge air holes 204 are angled radially inward from the outer surface to the inner surface of the cover plate 116. The outlet of the edge air holes 204 at the inner surface of the cover plate 116 forms a second shape, which has a different size from the first shape at the outer surface of the cover plate. It has been found that angling the edge air holes can leave space in the opening of the annular plate 129 (such as the central manifold 107) for components to be fixed to the cover plate 116. It has been further found that angling the edge air holes can provide gas to a specific space, such as near the edge of a substrate disposed in a processing chamber. In some embodiments, the diameter of the first shape is equal to or greater than the diameter of the second shape, such as about 1% larger, such as about 2% larger, such as about 5% larger, such as about 8% larger to about 10% larger.

[0023] In some embodiments, the chamber lid assembly 110 further includes a perforated blocker plate 125 disposed between the central gas inlet 123 and the showerhead 118. In these embodiments, the gas flowing into the gas distribution space 119 is first diffused by the blocker plate 125 to provide a more uniform or desired distribution of gas flow into the processing region 121 together with the showerhead 118.

[0024] Process gases and process byproducts are exhausted radially outward from the process region 121 through an annular channel 126 surrounding the process region 121. The annular channel 126 may be formed in a first annular liner 127 disposed radially inwardly of one or more sidewalls 112 (as shown) or may be formed in one or more sidewalls 112 for protecting the inner surface. In some embodiments, the process chamber 102 includes: one or more second liners 128 of one or more sidewalls 112; or a chamber base 114 that is protected from corrosive gases and / or undesirable material deposition.

[0025] In some embodiments, the purge gas source 137 includes a first connection in fluid communication with the processing volume 115, such that the purge gas source can be used to flow a chemically inert purge gas, such as argon (Ar), to a region disposed at the periphery of the substrate and / or below the substrate disposed on the substrate support 122, for example, through an opening in the chamber base 114 surrounding the support shaft 162 of the substrate support assembly 120. During substrate processing, the purge gas can be used to create a positive pressure region above the substrate 130 disposed on the substrate support 122 (compared to below the substrate). In some configurations, the purge gas is introduced through the chamber base 114, such that the purge gas flows upward from the chamber base and around the edge of the substrate support 122 to be exhausted from the processing volume 115 through the annular channel 126. In such a configuration, the purge gas reduces undesirable material deposition on the surface below the substrate support 122 by reducing and / or preventing material precursor gases from flowing into the substrate support.

[0026] The substrate support assembly 120 includes a movable support shaft 162 that extends sealingly through the chamber base 114, such as surrounded by a bellows 165 in an area below the chamber base 114, and a substrate support 122 that is disposed on the movable support shaft 162. To facilitate transfer of substrates to and from the substrate support 122, the substrate support assembly 120 includes a lift pin assembly 166 that includes a plurality of lift pins 167 that are coupled to or disposed in engagement with a lift pin ring 168. The plurality of lift pins 167 are movably disposed in an opening formed through the substrate support 122.

[0027] The substrate 130 is transferred to and from the substrate support 122 through a door 171 (e.g., a slit valve disposed in one of the one or more sidewalls 112). Here, one or more openings in an area surrounding the door 171 (e.g., an opening in a door housing) are fluidly coupled to a purge gas source 137 (e.g., an argon (Ar) gas source). The purge gas is used to prevent process gases and cleaning gases from contacting and / or decomposing seals surrounding the door, thereby extending the useful life of the door.

[0028] The substrate support 122 is configured for vacuum chucking, wherein the substrate 130 is secured to the substrate support 122 by applying a vacuum, such as a vacuum source 172 , to an interface between the substrate 130 and a substrate receiving surface.

[0029] In some embodiments, the processing chamber 102 is configured for direct plasma processing. In these embodiments, the showerhead 118 may be electrically coupled to a first power source 131 (such as an RF power source) that supplies power to form and maintain a capacitively coupled plasma using a process gas flowing through the showerhead 118 to the processing region 121. In some embodiments, the processing chamber 102 alternatively includes an inductively coupled plasma generator (not shown), and forms plasma by inductively coupling RF power through an antenna disposed on the processing chamber 102 with a process gas disposed in the processing space 115.

[0030] The processing system 100 is advantageously configured to perform each of the tungsten nucleation and bulk tungsten deposition processes without removing the substrate 130 from the processing chamber 102. Gases used to perform the various processes and clean residues from interior surfaces of the processing chamber are delivered to the processing chamber 102 using a gas delivery system 104 fluidly coupled to the processing chamber.

[0031] Typically, the gas delivery system 104 includes one or more remote plasma sources, here first and second radical generators 106A-106B; deposition gas sources 187A, 187B; and a conduit system 194 that fluidly couples the radical generators 106A-106B and the deposition gas source 140 to the lid assembly 110. The gas delivery system 104 further includes a plurality of isolation valves, here first and second valves 190A-190B, respectively disposed between the radical generators 106A-106B and the lid plate 116, which can be used to fluidly isolate each of the radical generators 106A-106B from the processing chamber 102 and from each other. The conduit system 194 is used to deliver deposition gases (e.g., tungsten-containing precursors, molybdenum-containing precursors, and reducing agents) from the deposition gas source 140 to the processing chamber 102.

[0032] Each of the radical generators 106A-106B is coupled to a corresponding power source 193A-193B (such as a radio frequency (RF) power source). The power sources 193A-193B are used to ignite and maintain a plasma delivered to the plasma chamber space using a gas provided from a corresponding first gas source or second gas source 187A-187B that is fluidly coupled to the power source. In some embodiments, the first radical generator 106A can be used to ignite and maintain a treatment plasma from a halogen-free gas mixture delivered to the first plasma chamber space from the first gas source 187A. The second radical generator 106B can be used to generate cleaning radicals used in a chamber cleaning process by igniting and maintaining a cleaning plasma of a halogen-containing gas mixture (e.g., HCl, Cl2, F2) delivered to the second plasma chamber space from the second gas source 187B.

[0033] The system controller 108 facilitates the operation of the processing system 100. The system controller 108 includes a programmable central processing unit, here a CPU 195, which is operable in conjunction with a memory 196 (e.g., non-volatile memory) and support circuits 197. The CPU 195 is one of any form of general purpose computer processor used in an industrial setting, such as a programmable logic controller (PLC), for controlling various chamber components and subprocessors. The memory 196 coupled to the CPU 195 facilitates the operation of the processing chamber. The support circuits 197 are typically coupled to the CPU 195 and include caches, clock circuits, input / output subsystems, power sources, etc., and combinations thereof coupled to various components of the processing system 100 to facilitate control of substrate processing operations in conjunction with the various components of the processing system.

[0034] The instructions in the memory 196 take the form of a program product, such as a program that implements the method of the present disclosure. In one example, the present disclosure can be implemented as a program product stored on a computer-readable storage medium for use by a computer system. The program(s) of the program product define the functions of the embodiments (including the methods described herein). Therefore, the computer-readable storage medium is an embodiment of the present disclosure when carrying computer-readable instructions that direct the functions of the methods described herein.

[0035] Figure 2A is a top view of the gas delivery system 104, and Figure 2B 1 is a cross-sectional bottom view of the gas delivery system 104. The gas delivery system 104 includes an edge manifold 103 extending from the central manifold 107 to the annular plate 129. The edge manifold 103 is in fluid communication with the annular plate 129 through an opening 210 disposed in the annular plate 129. Figure 2A and Figure 2B A single edge manifold 103 is depicted coupled to a single opening 210 in the annular plate 129, but additional edge manifolds extending from the center manifold 107 to additional openings in the annular plate 129 are also contemplated. The additional manifolds may be equally spaced relative to each other and provide enhanced gas distribution. Gas is provided through the edge manifold 103, which enters the opening 210 and passes through an outer channel 212 disposed in the edge manifold 103. The outer channel 212 distributes the gas at one or more points along the inner channel 206. In some embodiments, the outer channel 212 is coupled to a first intermediate channel 208a and a second intermediate channel 208b. The first intermediate channel 208a and the second intermediate channel 208b are each coupled to two or more of the points along the inner channel 206. Although Figure 2A and Figure 2BFour points along the inner channel 206 coupled to the outer channel 212 are depicted, although additional or fewer points, such as two to ten points, such as three or four points, spaced about the inner channel 206 are also contemplated.

[0036] Figure 2C A top view of the cover plate 116 is depicted. The cover plate 116 includes a plurality of edge air holes 204 arranged in a circle similar to the shape of the annular plate 129. The inner channel 206 of the annular plate 129 is fluidly coupled to the edge air holes 204 of the cover plate 116.

[0037] Figure 3 A top view of the blocker plate 125 is depicted. The blocker plate 125 includes an edge region 302 and an inner region 304. Each of the edge air holes 204 is fluidly coupled to the edge region 302 of the blocker plate 125. The central manifold 107 is fluidly coupled to the inner region 304 of the blocker plate 125. Each of the inner region 304 and the edge region 302 includes a plurality of slits 306. The slits 306 are in fluid communication with the gas distribution space 119 and diffuse into the processing region 121 through the showerhead 118. The gas delivery system described herein is capable of regulating the processing gas between the inner region and the edge region of the substrate disposed below the showerhead 118. The inner region and the edge region of the substrate correspond to the inner region 304 and the edge region 302 of the blocker plate 125. It has been found that the regulation between the inner region and the edge region can achieve uniform film deposition over the substrate. In contrast, conventional gas distribution assemblies (such as point source systems) use asymmetric free radical species delivery paths to deliver processing gases. Conventional point source systems include a single point, such as a central region, to direct gas to the center of a gas diffuser, such as a showerhead with or without a baffle. As a result, the film thickness decreases near the peripheral portion of the substrate relative to the portion disposed radially inward.

[0038] In some embodiments, adjusting the process gas includes switching the gas flow between the edge manifold 103 to the edge region 302 and the central manifold 107 to the inner region 304. In some embodiments, adjusting the process gas includes co-flowing gas between the edge manifold 103 to the edge region 302 and the central manifold 107 to the inner region 304. The ratio of the gas flow to the edge region 302 to the gas flow to the inner region 304 is about 1:4 to about 4:1, such as about 1:3 to about 1:2 or about 2:1 to about 3:1. In some embodiments, the total volumetric flow rate is about 100 sccm to about 500 sccm of process gas (such as a gas mixture of nitrogen and argon). In some embodiments, the process gas flows for about 5 seconds to about 20 seconds, such as about 10 seconds to about 15 seconds. In some embodiments, the gas flow to the edge region 302 is about 100 sccm to about 200 sccm, and the gas flow to the inner region 304 is about 300 sccm to about 400 sccm. In some embodiments, the gas flow to the inner region 304 is about 100 sccm to about 200 sccm, and the gas flow to the edge region 302 is about 300 sccm to about 400 sccm.

[0039] The edge region 302 is formed between an outer peripheral edge 312 and an inner peripheral partition 310 that separates the inner region 304 from the edge region 302. The annular width of the edge region 302 between the outer peripheral edge 312 and the inner peripheral partition 310 is about .25" to about 1.0". The inner region 304 includes a diameter ratio of about 5:2. The edge region 302 is divided into a plurality of segments, such as about 2 segments to about 8 segments, such as about 4 segments to about 6 segments, between the segment dividers 308. It has been found that the segment dividers 308 provide locations for mounting holes to secure the blocker plate 125 and can enhance the uniformity of flow through the edge region 302 of the blocker plate 125.

[0040] In some embodiments, two or more gases, such as an incubation process gas, a gas such as a nitrogen-containing radical, and an argon-containing gas, flow simultaneously to the edge manifold 103. The ratio of the nitrogen-containing gas to the argon-containing gas is adjusted based on predetermined process parameters for film deposition. Similarly, for the gas flowing through the central manifold 107, the ratio of the two or more components of the gas can be controlled. The central manifold 107 and the edge manifold 103 can be controlled independently of each other. Although the gas sources are depicted in the figure as being coupled to the edge manifold 103 through the central manifold 107, additional gas sources can also be coupled to the edge manifold 103 at other locations along the edge manifold 103.

[0041] Example

[0042] Figure 4A process flow diagram of a method 400 of processing a substrate in some embodiments is depicted. The method includes, at activity 402, depositing a nucleation layer by exposing a substrate to a gaseous precursor using a gas delivery system.

[0043] At activity 404, the nucleation layer on the substrate is exposed to free radical species. In some embodiments, exposing the substrate to the free radical species includes exposing a central portion of the substrate to the free radical species. The inner region may be exposed at a pressure of about 0.5 Torr to about 2 Torr for about 5 seconds to about 15 seconds, such as about 10 seconds. The free radical species may be generated and delivered from a remote plasma source. In some embodiments, a purge gas (such as argon) is provided to edge portions of the substrate, while the central portion is exposed to the free radical species.

[0044] In some embodiments, the remote plasma source may be turned off or diverted so that the substrate is not exposed to additional radical species for about 5 seconds or less, such as about 2 seconds to about 4 seconds.The radical species are delivered to the substrate using a central manifold to a central opening in the cover plate.

[0045] In some embodiments, after exposing the center portion of the substrate and after turning off the plasma source, the edge portion of the substrate is exposed to the gas for about 1 second to about 5 seconds, such as about 2 seconds to about 3 seconds. In some embodiments, the gas is a non-reactive gas, such as argon. In some embodiments, after exposing the edge portion to the gas, the edge portion of the substrate may be exposed to the free radical species at a pressure of about 0.5 torr to about 2 torr for about 5 seconds to about 15 seconds, such as about 10 seconds. The free radical species are delivered to the substrate using an edge manifold to a plurality of edge holes in the cover plate. In some embodiments, a purge gas (such as argon) is provided to the center portion of the substrate while the edge portion is exposed to the free radical species.

[0046] At activity 406, a bulk layer is deposited over the plasma treated nucleation layer. In some embodiments, the bulk layer is deposited by providing process gases through a central manifold of the assembly. In some embodiments, process gases are provided through edge manifolds in addition to the central manifold.

[0047] It has been found that flowing the plasma to the center of the substrate at a single point source, such as using conventional methods, enables bulk film thickness to be deposited at the center of the substrate but tapers at the edge of the substrate, such that the film thickness at the edge of the substrate is much smaller relative to the center of the substrate. For example, for a substrate having a 150 mm radius, the thickness of the outermost 50 mm of the substrate radius of the comparative sample is about 25% to about 45% less than the thickness measured at the center of the substrate. In contrast, substrates treated using the systems and methods provided herein exhibit a substantially uniform substrate thickness over the entire substrate. The stacked films described herein (a combination of the nucleation layer from 402, the plasma treatment from 404, and the deposited bulk layer from 406) exhibit a thickness difference of less than 25%, such as about 5% to about 20%, at the outermost 50 mm of the substrate radius relative to the substrate thickness at the center of the substrate.

[0048] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope of the disclosure, and the scope of the disclosure is determined by the claims that follow.

Claims

1. A substrate processing system, comprising: a processing chamber, the processing chamber comprising a cover plate, one or more chamber side walls and a chamber base, wherein the cover plate, the one or more chamber side walls and the chamber base together define a processing space; an annular plate coupled to the cover plate; an edge manifold fluidly coupled to the process chamber through the annular plate and the cover plate; as well as A central manifold is coupled to the cover plate. 2 . The substrate processing system of claim 1 , further comprising a blocker plate coupled to the cover plate on a side opposite to the annular plate.

3. The substrate processing system of claim 2, wherein the annular plate includes one or more channels in fluid communication with the edge manifold and edge air holes disposed through the cover plate.

4. The substrate processing system of claim 3, wherein the edge vents of the cover plate are fluidly coupled to an edge region of the blocker plate, the blocker plate further comprising a central region fluidly isolated from the edge region. 5 . The substrate processing system of claim 4 , further comprising a valve assembly capable of switching the gas flow provided to the edge region of the blocker plate and the gas flow provided to the center region of the blocker plate.

6. The substrate processing system of claim 1, wherein the annular plate includes a channel disposed about the annular plate, wherein the channel is fluidly coupled to edge vents in a cover interface surface of the annular plate.

7. A gas delivery system, comprising: a cover plate having a first major surface and a second major surface opposite to the first major surface; an annular plate coupled to the first major surface of the cover plate; a partition plate coupled to the second major surface of the cover plate; a central manifold fluidly coupled to the opening of the cover plate; as well as An edge manifold is fluidly coupled to the central manifold and the annular plate.

8. The gas delivery system of claim 7, wherein the gas delivery system further comprises a showerhead coupled to the blocker plate.

9. The gas delivery system of claim 7, wherein the cover plate includes a plurality of edge air holes extending from the first major surface to the second major surface of the cover plate.

10. The gas delivery system of claim 9, wherein the plurality of edge air holes are angled radially inward from the first major surface to the second major surface.

11. The gas delivery system of claim 9, wherein each inlet of each edge gas hole is in fluid communication with one or more channels of the annular plate.

12. The gas delivery system of claim 7, wherein the blocker plate includes an edge region defined between an outer peripheral edge of the blocker plate and an inner peripheral partition of the blocker plate.

13. The gas delivery system of claim 12, wherein the edge region comprises a plurality of segments separated by dividers.

14. A method for processing a substrate, the method comprising: depositing a nucleation layer by exposing the substrate to a refractory metal-containing gas using a gas delivery system; as well as The substrate is exposed to a free radical species supplied to an edge region of a blocker plate disposed above the substrate, the edge region being fluidly isolated from an interior region of the blocker plate.

15. The method of claim 14, wherein depositing the nucleation layer comprises supplying the refractory metal-containing gas to the interior region of the blocker plate.

16. The method of claim 15, wherein exposing the substrate to the radical species comprises exposing the substrate to a nitrogen-containing species and a non-reactive species.

17. The method of claim 14, further comprising opening a valve to allow the free radical species to flow from a central manifold to an edge manifold of the gas delivery system.

18. The method of claim 14, wherein exposing the substrate to the free radical species comprises supplying the free radical species to the interior region of the blocker plate before supplying the free radical species to the edge region of the blocker plate.

19. The method of claim 14, further comprising depositing a bulk layer over the nucleation layer.

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