WO2020210260A1

WO2020210260A1 - High step coverage tungsten deposition

Info

Publication number: WO2020210260A1
Application number: PCT/US2020/027107
Authority: WO
Inventors: Michael BOWES; Tsung-Han Yang; Anand Chandrashekar; Xing Zhang
Original assignee: Lam Research Corp
Current assignee: Lam Research Corp
Priority date: 2019-04-11
Filing date: 2020-04-07
Publication date: 2020-10-15
Anticipated expiration: 2021-10-11
Also published as: JP2022522226A; SG11202111277UA; TW202104638A; CN113710830A; US20220181158A1; US12002679B2; KR20210141762A

Abstract

Methods of depositing a tungsten nucleation layers that achieve very good step coverage are provided. The methods involve a sequence of alternating pulses of a tungsten-containing precursor and a boron-containing reducing agent, while co-flowing hydrogen (H2) with the boron-containing reducing agent. The H2 flow is stopped prior to the tungsten-containing precursor flow. By co-flowing H2 with the boron-containing reducing agent but not with the tungsten-containing precursor flow, a parasitic CVD component is reduced, resulting in a more self-limiting process. This in turn improves step coverage and conformality of the nucleation layer. Related apparatuses are also provided.

Description

HIGH STEP COVERAGE TUNGSTEN DEPOSITION

INCORPORATION BY REFERENCE

[0001] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or 5 priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in its entirety and for all purposes.

BACKGROUND

[0002] Tungsten (W) film deposition using chemical vapor deposition (CVD) techniques is an integral part of semiconductor fabrication processes. For example, tungsten films

10 may be used as low resistivity electrical connections in the form of horizontal interconnects, vias between adjacent metal layers, and contacts between a first metal layer and the devices on a silicon substrate. Tungsten films may also be used in various memory applications, including in formation of buried wordline (bWL) architectures for dynamic random access memory (DRAM), word lines for 3D NAND, and logic applications.

15 However, the continued decrease in feature size and film thickness brings various challenges including deposition of films having good step coverage.

[0003] The background description provided herein is for the purposes of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that

20 may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY

[0004] One aspect of the disclosure relates to a method including providing a substrate including a feature having an opening in a top surface, a sidewall and a bottom in a 25 chamber; and depositing a tungsten nucleation layer in the feature by performing multiple cycles of: flowing a boron-containing reducing agent pulse in the chamber, wherein the boron-containing reducing agent is adsorbed to the feature sidewall and feature bottom, purging the chamber, flowing a tungsten-containing precursor pulse in the chamber to react with the adsorbed boron-containing reducing agent, and purging the chamber, 30 wherein hydrogen (H₂) is flowed during the boron-containing reducing agent pulse and no H₂ is flowed during the tungsten-containing precursor pulse and wherein H₂ suppresses thermal decomposition of the boron-containing reducing agent.

[0005] In some embodiments, the tungsten nucleation layer is at least 10 Angstroms thick and step coverage throughout the feature is at least 90%, step coverage being the 5 ratio of the thickness of the tungsten nucleation layer at any point in the feature to the thickness of the tungsten nucleation layer at the top surface.

[0006] In some embodiments, depositing the nucleation layer further includes at least one cycle of flowing a silane pulse in the chamber; purging the chamber; flowing a tungsten-containing precursor pulse in the chamber; and purging the chamber, wherein 10 no hydrogen is flowed during the tungsten-containing precursor pulse.

[0007] In some embodiments, no hydrogen is flowed during the silane pulse. In some embodiments, hydrogen is flowed during the silane pulse. In some embodiments, the tungsten nucleation layer is between 10 Angstroms and 50 Angstroms thick. In some embodiments, the substrate temperature is below 350°C. In some embodiments, the

15 substrate temperature is between about 250°C and 300°C. In some embodiments, hydrogen reacts with decomposition byproducts of the boron-containing reducing agent.

[0008] In some embodiments, the boron-containing reducing agent pulse in the chamber is flowed into the chamber with an inert carrier gas.

[0009] In some embodiments, wherein the volumetric flow ratio of the H₂ to the boron- 20 containing reducing agent is between 20:1 and 400:1. In some embodiments, the boron- containing reducing agent is diborane.

[0010] Another aspect of the disclosure relates to a method including providing a substrate including a feature having an opening in a top surface, a sidewall and a bottom in a chamber; depositing a tungsten nucleation layer in the feature by performing multiple 25 cycles of: flowing a boron-containing reducing agent pulse in the chamber; purging the chamber; flowing a tungsten-containing precursor pulse in the chamber; and purging the chamber, wherein hydrogen is flowed during the boron-containing reducing agent pulse and no hydrogen is flowed during the tungsten-containing precursor pulse.

[0011] In some embodiments, the tungsten nucleation layer is at least 10 Angstroms 30 thick and step coverage throughout the feature is at least 90%, step coverage being the ratio of the thickness of the tungsten nucleation layer at any point in the feature to the thickness of the tungsten nucleation layer at the top surface.

[0012] In some embodiments, depositing the nucleation layer further includes at least one cycle of flowing a silane pulse in the chamber; purging the chamber; flowing a 5 tungsten-containing precursor pulse in the chamber; and purging the chamber, wherein no hydrogen is flowed during the tungsten-containing precursor pulse.

[0013] In some embodiments, no hydrogen is flowed during the silane pulse. In some embodiments, hydrogen is flowed during the silane pulse. In some embodiments, the tungsten nucleation layer is between 10 Angstroms and 50 Angstroms thick. In some 10 embodiments, the substrate temperature is below 350°C. In some embodiments, the substrate temperature is between about 250°C and 300°C. In some embodiments, hydrogen reacts with decomposition byproducts of the boron-containing reducing agent.

[0014] In some embodiments, the boron-containing reducing agent pulse in the chamber is flowed into the chamber with an inert carrier gas.

15 [0015] In some embodiments, the volumetric flow ratio of the H2 to the boron- containing reducing agent is between 20:1 and 400:1. In some embodiments, the boron- containing reducing agent is diborane.

[0016] Another aspect of the disclosure relates to an apparatus including: (a) a process chamber including at least one station having a pedestal configured to hold a substrate;

20 (b) at least one outlet for coupling to a vacuum; (c) one or more process gas inlets coupled to one or more process gas sources; and (d) a controller for controlling operations in the apparatus, including machine-readable instructions for: flowing a boron-containing reducing agent pulse in the chamber, purging the chamber, flowing a tungsten-containing precursor pulse in the chamber, and purging the chamber, wherein hydrogen is flowed

25 during the boron-containing reducing agent pulse and no hydrogen is flowed during the tungsten-containing precursor pulse.

[0017] In some embodiments, the controller includes instructions for maintaining a pedestal temperature less than 350°C. In some embodiments, the controller includes instructions for maintaining a pedestal temperature between 175°C to 300°C. In some

30 embodiments, the controller includes instructions for flowing a silane pulse in the chamber; purging the chamber; flowing a tungsten-containing precursor pulse in the chamber; and purging the chamber, wherein no hydrogen is flowed during the tungsten- containing precursor pulse.

[0018] These and other aspects are described below with reference to the drawings.

5 BRIEF DESCRIPTION OF DRAWINGS

[0019] Figures 1A-1H show examples of a features that may be filled with tungsten in accordance with embodiments disclosed herein.

[0020] Figure 2 shows a timing sequence diagram showing example cycles of a method for depositing a tungsten nucleation layer using diborane.

10 [0021] Figure 3 illustrates a schematic representation of an example of a feature provided in a partially manufactured semiconductor substrate with a tungsten nucleation layer formed with the feature.

[0022] Figure 4 is a schematic of an example of a process system suitable for conducting deposition processes in accordance with embodiments.

15 [0023] Figure 5 is a schematic of an example of a deposition station depicted suitable for conducting deposition processes in accordance with embodiments.

[0024] Figure 6 is a schematic of an example of a manifold system that may be used in accordance with various embodiments.

DETAILED DESCRIPTION

20 [0025] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail to not unnecessarily obscure the present invention. While the invention will be described in conjunction with the specific 25 embodiments, it will be understood that it is not intended to limit the invention to the embodiments.

[0026] Described herein are methods of filling features with tungsten and related systems and apparatus. Examples of application include logic and memory contact fill, DRAM buried wordline fill, vertically integrated memory gate/wordline fill, and 3-D integration with through-silicon vias (TSVs). The methods described herein can be used to fill vertical features, such as in tungsten vias, and horizontal features, such as vertical NAND (VNAND) wordlines, and The methods may be used for conformal and bottom-up or 5 inside-out fill.

[0027] According to various embodiments, the features can be characterized by one or more of narrow and/or re-entrant openings, constrictions within the feature, and high aspect ratios. Examples of features that can be filled are depicted in Figures 1A-1C. Figure 1A shows an example of a cross-sectional depiction of a vertical feature 101 to be filled 10 with tungsten. The feature can include a feature hole 105 in a substrate 103. The substrate may be a silicon wafer, e.g., 200-mm wafer, 300-mm wafer, 450-mm wafer, including wafers having one or more layers of material such as dielectric, conducting, or semi- conducting material deposited thereon. In some embodiments, the feature hole 105 may have an aspect ratio of at least about 2:1, at least about 4:1, at least about 6:1 or higher. 15 The feature hole 105 may also have a dimension near the opening, e.g., an opening diameter or line width, of between about 10 nm to 500 nm, for example between about 25 nm to 300 nm. The feature hole 105 can be referred to as an unfilled feature or simply a feature. The feature, and any feature, may be characterized in part by an axis 118 that extends through the length of the feature, with vertically-oriented features having vertical 20 axes and horizontally-oriented features having horizontal axes.

[0028] Figure IB shows an example of a feature 101 that has a re-entrant profile. A re- entrant profile is a profile that narrows from a bottom, closed end, or interior of the feature to the feature opening. According to various embodiments, the profile may narrow gradually and/or include an overhang at the feature opening. Figure IB shows an 25 example of the latter, with an under-layer 113 lining the sidewall or interior surfaces of the feature hole 105. The under-layer 113 can be for example, a diffusion barrier layer, an adhesion layer, a nucleation layer, a combination of thereof, or any other applicable material. The under-layer 113 forms an overhang 115 such that the under-layer 113 is thicker near the opening of the feature 101 than inside the feature 101.

30 [0029] In some embodiments, features having one or more constrictions within the feature may be filled. Figure 1C shows examples of views of various filled features having constrictions. Each of the examples (a), (b) and (c) in Figure 1C includes a constriction 109 at a midpoint within the feature. The constriction 109 can be, for example, between about 15 nm-20 nm wide. Constrictions can cause pinch off during deposition of tungsten in the feature using conventional techniques, with deposited tungsten blocking further 5 deposition past the constriction before that portion of the feature is filled, resulting in voids in the feature. Example (b) further includes a liner/barrier overhang 115 at the feature opening. Such an overhang could also be a potential pinch-off point. Example (c) includes a constriction 112 further away from the field region than the overhang 115 in example (b). As described further below, methods described herein allow void-free fill as 10 depicted in Figure 1C.

[0030] Horizontal features, such as in 3-D memory structures, can also be filled. Figure ID shows an example of a word line 150 in a VNAND structure 148 that includes a constriction 151. In some embodiments, the constrictions can be due to the presence of pillars in a VNAND or other structure. Figure IE, for example, shows a plan view of pillars

15 125 in a VNAND structure, with Figure IF showing a simplified schematic of a cross- sectional depiction of the pillars 125. Arrows in Figure IE represent deposition material; as pillars 125 are disposed between an area 127 and a gas inlet or other deposition source, adjacent pillars can result in constrictions that present challenges in void free fill of an area 127.

20 [0031] Figure 1G provides another example of a view horizontal feature, for example, of a VNAND or other structure including pillar constrictions 151. The example in Figure 1G is open-ended, with material to be deposited able to enter laterally from two sides as indicated by the arrows. (It should be noted that example in Figure 1G can be seen as a 2- D rendering 3-D features of the structure, with the Figure 1G being a cross-sectional 25 depiction of an area to be filled and pillar constrictions shown in the figure representing constrictions that would be seen in a plan rather than cross-sectional view.) In some embodiments, 3-D structures can be characterized with the area to be filled extending along three dimensions (e.g., in the X, Y and Z-directions in the example of Figure IF), and can present more challenges for fill than filling holes or trenches that extend along one or 30 two dimensions. For example, controlling fill of a 3-D structure can be challenging as deposition gasses may enter a feature from multiple dimensions. The methods may also be used to fill interconnects to tungsten wordlines as shown in Figure 1H, where interconnect features 170 may be filled with tungsten to connect to the tungsten wordlines 172. Examples of feature fill for horizontally-oriented and vertically-oriented features are described below. It should be noted that in most cases, the examples 5 applicable to both horizontally-oriented or vertically-oriented features.

[0032] Distribution of a material within a feature may be characterized by its step coverage. For the purposes of this description, "step coverage" is defined as a ratio of two thicknesses, e.g., the thickness of the material inside the feature divided by the thickness of the material near the opening. For purposes of this description, the term "inside the 10 feature" represents a middle portion of the feature located about the middle point of the feature along the feature's axis, e.g., an area between about 25% and 75% of the distance or, in certain embodiments, between about 40% and 60% of the distance along the feature's depth measured from the feature's opening, or an end portion of the feature located between about 75% and 95% of the distance along the feature's axis as measured 15 from the opening. The term "near the opening of the feature" or "near the feature's opening" represents a top portion of the feature located within 25% or, more specifically, within 10% of the opening's edge or other element representative of the opening's edge. Step coverage of over 100% can be achieved, for example, by filling a feature wider in the middle or near the bottom of the feature than at the feature opening or where a thicker 20 film is deposited within the feature than on or near the opening.

[0033] The methods described herein involve deposition of a tungsten nucleation layer prior to deposition of a bulk layer. A nucleation layer is typically a thin conformal layer that facilitates subsequent deposition of bulk tungsten-containing material thereon. According to various embodiments, a nucleation layer may be deposited prior to any fill of 25 the feature and/or at subsequent points during fill of the feature with tungsten or a tungsten-containing material.

[0034] In certain implementations, the nucleation layer is deposited sequentially injecting pulses of a reducing agent, optional purge gases, and tungsten-containing precursor from the reaction chamber. The process is repeated in a cyclical fashion until 30 the desired thickness is achieved. Nucleation layer thickness can depend on the nucleation layer deposition method as well as the desired quality of bulk deposition. In general, nucleation layer thickness is sufficient to support high quality, uniform bulk deposition. Examples may range from 5Å-100Å,or 12Å-50Å.

[0035] ALD techniques differ from chemical vapor deposition (CVD) techniques in which reactants are introduced together. In certain embodiments, the nucleation layer is 5 deposited using a pulsed nucleation layer (PNL) technique. In a PNL technique, pulses of a reducing agent, optional purge gases, and tungsten-containing precursor are sequentially injected into and purged from the reaction chamber. The process is repeated in a cyclical fashion until the desired thickness is achieved. PNL broadly embodies any cyclical process of sequentially adding reactants for reaction on a semiconductor substrate, including ALD 10 techniques.

[0036] Described herein are methods of depositing a tungsten nucleation layer that achieve very good step coverage. The methods involve a sequence of alternating pulses of a tungsten-containing precursor and a boron-containing reducing agent, while co- flowing hydrogen (H₂) with the boron-containing reducing agent. The H₂ flow is stopped

15 prior to the tungsten-containing precursor flow. By co-flowing H₂ with the boron- containing reducing agent but not with the tungsten-containing precursor flow, a parasitic CVD component is reduced, resulting in a more self-limiting process. This in turn improves step coverage and conformality of the nucleation layer.

[0037] ALD tungsten processes may use two half-reactions enabled by the sequential 20 delivery of two or more co-reactants. One co-reactant acts to functionalize the surface and permit the adsorption of tungsten-containing species to the substrate. Subsequent cycles result in the deposition of a conformal thin film. Flowing hydrogen in the background or as a carrier gas during the tungsten-containing precursor dose results in a higher deposition rate, thicker nucleation layer, and reduced conformality. This is due to part of 25 the tungsten-containing precursor being consumed by a parasitic CVD reaction with the hydrogen. However, it has been found that co-flowing H₂ with B₂H₆ improves conformality. This is because B₂H₆ can decompose during the ALD cycle (e.g., B₂H₆ 2/3 B₃ + 3H₂) which in turn results in parasitic reactions that contribute to the CVD reaction. The parasitic CVD contribution degrades the step coverage of the process. By co-flowing B₂H₆ and H₂, the 30 decomposition of B₂H₆ is suppressed. While some B₂H₆ may decompose, the presence of H₂ can significantly reduce the amount. Further, the H₂ may react with B₂H₆ decomposition products or other reaction byproducts to form diborane (e.g., 2B₃ + 9H₂ -> 3B₂H₆). The parasitic CVD contribution to the deposition is thus reduced or minimized. This shifts the thin film deposition process closer to a pure ALD process and improves the step coverage and conformality.

5 [0038] By flowing hydrogen with the diborane, chemisorption and physisorption of the diborane, rather than decomposition of diborane to boron, is promoted. This is distinct from other deposition processes that use a boron sacrificial layer.

[0039] Substrate temperatures may be below about 350°C, for example between about 175°C and 300°C, or between about 250°C and 300°C. Lower temperatures result in less

10 decomposition and more control over the deposition. Even at these relatively low temperatures, diborane is susceptible to decomposition. Examples of chamber pressure are between 10 torr and 60 torr, or 10 torr and 40 torr. In some embodiments, it is above 10 torr. It may also be below 10 torr to reduce fluorine incorporation, for example.

[0040] Example growth rates may be 2A-20A per cycle, or 4A-12A per cycle, with the 15 growth rates lower as more hydrogen is used to suppress the parasitic CVD reaction and increase step coverage.

[0041] The hydrogemdiborane volumetric flow ratio may be tuned to provide the desired effect for a particular structure. Too high, and the physisorption or chemisorption of the diborane may be unnecessarily slow. Too low, and the diborane may decompose, 20 causing the parasitic CVD effect described above. Examples of ranges of H₂:B₂H₆ are 20:1- 400:1.

[0042] In some embodiments, the diborane (or other reducing agent) is delivered with an inert gas. For example, B₂H₆ may be mixed with nitrogen (N₂) in a 20:1 N₂:B₂H₆ ratio. The H₂ to diborane/inert gas mixture may be 1:1-20:1 to obtain 20:1-400:1 H₂:B₂H₆ in that 25 example. Nitrogen is an example of gas that may be mixed with diborane or other reducing agent; any inert gas that is chemically compatible with the reducing agent and does not react with it may be used, with helium (He) another example.

[0043] Figure 2 shows an example of a timing sequence diagram showing example cycles of a method for depositing a tungsten nucleation layer using diborane. As shown in Figure 30 2, hydrogen is flowed only during the diborane pulse. [0044] The tungsten nucleation layers may be deposited using a silicon-based precursor (e.g., silane, SiH4) in addition to diborane. In some embodiments, silane pulses are added as part of the sequence: e.g., B/W/B/W/S/W, where B represents a diborane pulse, W a tungsten-containing precursor pulses, and S a silicon-containing precursors pulse;

5 intervening purges are not explicitly shown. In such embodiments, silane or other silicon- containing precursor may be pulsed without hydrogen.

[0045] The tungsten-containing precursor may be a tungsten halide that can be reduced by a boron-containing reducing agent including tungsten fluorides (e.g., WF6) and tungsten chlorides (e.g., WCI5 and WCI6). While the diborane is described above, the method may 10 be implemented with any reducing agent that is susceptible to decomposition at ALD processing temperatures. Examples include hexaborane and triborane.

[0046] In some embodiments, methods result in step coverages of at least 90%. Figure 3 illustrates a schematic representation of a feature 301 provided in a partially manufactured semiconductor substrate 303 with a tungsten nucleation layer 305 formed 15 with the feature 301. The figure also specifies different points of measurements of the layer thickness, including at the top of the feature, the bottom of the feature, and at various sidewall depths, as measured as % of feature depth. Step coverage is measured as the ratio of the thickness at a bottom or sidewall position to the top position, unless otherwise indicated.

20 [0047] Although the description herein refers to tungsten nucleation layer deposition using diborane, pulsing hydrogen with a co-reactant may be performed to improve conformality during ALD deposition of other materials and other co-reactants, when the co-reactants are susceptible to decomposition and are hydrides. Examples of other metals that may be deposited include molybdenum (Mo) and ruthenium (Ru).

25 Experimental

[0048] ALD of tungsten nucleation layers was performed in features using Processes A and B on structures of the same dimensions:

[0049] Process A: multiple cycles of (B₂H₆ - Ar purge - WF₆ - Ar purge) with H2 flow constant

30 [0050] Process B: multiple cycles of (B₂H₆ - Ar purge - WF₆ - Ar purge) with H2 flow constant only during B₂H₆ pulses.

[0051] Step coverage was measured at the top sidewall, middle sidewall and bottom sidewall with respect to the film deposited on the top horizontal surface. The top sidewall refers to a point about 5% of feature depth, middle about 50%, and bottom about 95% of 5 feature depth.

[0052] As can be seen from the above table, co-flowing H2 only during the B2H6 pulses results in significantly improved step coverage. A third process was used on a different structure:

Process C: multiple cycles of (B₂H₆ - Ar purge - WF₆ - Ar purge) with no H₂ at all:

10 [0053] After nucleation layer deposition, the feature may be filled with a bulk tungsten layer. In some implementations, tungsten bulk deposition can occur by a CVD process in which a reducing agent and a tungsten-containing precursor are flowed into a deposition chamber to deposit a bulk fill layer in the feature. In some implementations, tungsten bulk deposition can occur by an ALD process in which a reducing agent and a tungsten- 15 containing precursor are sequentially introduced into a deposition chamber to deposit a bulk fill layer in the feature. If CVD is used, this operation can involve flowing the reactants continuously until the desired amount is deposited. In certain implementations, the CVD operation may take place in multiple stages, with multiple periods of continuous and simultaneous flow of reactants separated by periods of one or more reactant flows 20 diverted. Still further, inhibition of tungsten growth and/or etching may be performed during feature fill.

[0054] Various tungsten containing gases including, but not limited to, WF6, WCI6, and W(CO)6 can be used as the tungsten-containing precursor. In certain implementations, the tungsten-containing precursor is a halogen-containing compound, such as WF6. In 5 certain implementations, the reducing agent is hydrogen gas, though other reducing agents may be used including silane (Sim), disilane (Si₂H₆) hydrazine (N₂H₄), diborane (B₂H₆) and germane (GeH₄). In many implementations, hydrogen gas is used as the reducing agent in the CVD process. In some other implementations, a tungsten precursor that can decompose to form a bulk tungsten layer can be used. Bulk deposition may also 10 occur using other types of processes including ALD processes.

[0055] Deposition may proceed according to various implementations until a certain feature profile is achieved and/or a certain amount of tungsten is deposited. In some implementations, the deposition time and other relevant parameters may be determined by modeling and/or trial and error. For example, for an initial deposition for an inside out

15 fill process in which tungsten can be conformally deposited in a feature until pinch-off, it may be straightforward to determine based on the feature dimensions the tungsten thickness and corresponding deposition time that will achieve pinch-off. In some implementations, a process chamber may be equipped with various sensors to perform in- situ metrology measurements for end-point detection of a deposition operation.

20 Examples of in-situ metrology include optical microscopy and X-Ray Fluorescence (XRF) for determining thickness of deposited films.

[0056] It should be understood that the tungsten films described herein may include some amount of other compounds, dopants and/or impurities such as nitrogen, carbon, oxygen, boron, phosphorous, sulfur, silicon, germanium and the like, depending on the 25 particular precursors and processes used. The tungsten content in the film may range from

20% to 100% (atomic) tungsten. In many implementations, the films are tungsten-rich, having at least 50% (atomic) tungsten, or even at least about 60%, 75%, 90%, or 99% (atomic) tungsten. In some implementations, the films may be a mixture of metallic or elemental tungsten (W) and other tungsten-containing compounds such as tungsten 30 carbide (WC), tungsten nitride (WN), etc.

[0057] CVD and ALD deposition of these materials can include using any appropriate precursors. For example, CVD and ALD deposition of tungsten nitride can include using halogen-containing and halogen-free tungsten-containing and nitrogen-containing compounds.

Apparatus

5 [0058] Any suitable chamber may be used to implement the disclosed embodiments.

Example deposition apparatuses include various systems, e.g., ALTUS^® and ALTUS^® Max, available from Lam Research Corp., of Fremont, California, or any of a variety of other commercially available processing systems. In some embodiments, atomic layer deposition (ALD) may be performed at a first station that is one of two, five, or even more 10 deposition stations positioned within a single deposition chamber. Thus, for example, a diborane (B₂H₆)/hydrogen (H2) co-flow and tungsten hexafluoride (WF6) may be introduced in alternating pulses to the surface of the semiconductor substrate, at the first station, using an individual gas supply system that creates a localized atmosphere at the substrate surface. Another station may be used for tungsten bulk layer deposition. Two 15 or more stations may be used to deposit tungsten in parallel processing. Alternatively a wafer may be indexed to have operations performed over two or more stations sequentially.

[0059] Figure 4 is a schematic of a process system suitable for conducting deposition processes in accordance with embodiments. The system 400 includes a transfer module 20 403. The transfer module 403 provides a clean, pressurized environment to minimize risk of contamination of substrates being processed as they are moved between various reactor modules. Mounted on the transfer module 403 is a multi-station reactor 409 capable of performing ALD and CVD according to various embodiments. Multi-station reactor 409 may include multiple stations 411, 413, 415, and 417 that may sequentially 25 perform operations in accordance with disclosed embodiments. For example, multi- station reactor 409 may be configured such that station 411 performs a tungsten nucleation layer deposition using a chlorine-containing tungsten precursor or a fluorine- containing precursor, and station 413 performs an ALD tungsten deposition operation according to various embodiments. In some embodiments, station 415 may also form an 30 ALD tungsten deposition operation, and station 417 may perform a CVD operation.

[0060] Stations may include a heated pedestal or substrate support, one or more gas inlets or showerhead or dispersion plate. An example of a deposition station 500 is depicted in Figure 5, including substrate support 502 and showerhead 503. A heater may be provided in pedestal portion 501.

[0061] Returning to Figure 4, also mounted on the transfer module 403 may be one or 5 more single or multi-station modules 407 capable of performing plasma or chemical (nonplasma) pre-cleans, other deposition operations, or etch operations. The module may also be used for various treatments to, for example, prepare a substrate for a deposition process. The system 400 also includes one or more wafer source modules 401, where wafers are stored before and after processing. An atmospheric robot (not shown) in the 10 atmospheric transfer chamber 419 may first remove wafers from the source modules 401 to loadlocks 421. A wafer transfer device (generally a robot arm unit) in the transfer module 403 moves the wafers from loadlocks 421 to and among the modules mounted on the transfer module 403.

[0062] In various embodiments, a system controller 429 is employed to control process 15 conditions during deposition. The controller 429 will typically include one or more memory devices and one or more processors. A processor may include a CPU or computer, analog and/or digital input/output connections, stepper motor controller boards, etc.

[0063] The controller 429 may control all of the activities of the deposition apparatus. The system controller 429 executes system control software, including sets of instructions 20 for controlling the timing, mixture of gases, chamber pressure, chamber temperature, wafer temperature, radio frequency (RF) power levels, wafer chuck or pedestal position, and other parameters of a particular process. Other computer programs stored on memory devices associated with the controller 429 may be employed in some embodiments.

25 [0064] Typically there will be a user interface associated with the controller 429. The user interface may include a display screen, graphical software displays of the apparatus and/or process conditions, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc.

[0065] System control logic may be configured in any suitable way. In general, the logic

30 can be designed or configured in hardware and/or software. The instructions for controlling the drive circuitry may be hard coded or provided as software. The instructions may be provided by "programming." Such programming is understood to include logic of any form, including hard coded logic in digital signal processors, application-specific integrated circuits, and other devices which have specific algorithms implemented as 5 hardware. Programming is also understood to include software or firmware instructions that may be executed on a general purpose processor. System control software may be coded in any suitable computer readable programming language.

[0066] The computer program code for controlling the germanium-containing reducing agent pulses, hydrogen flow, and tungsten-containing precursor pulses, and other 10 processes in a process sequence can be written in any conventional computer readable programming language: for example, assembly language, C, C++, Pascal, Fortran, or others. Compiled object code or script is executed by the processor to perform the tasks identified in the program. Also as indicated, the program code may be hard coded.

[0067] The controller parameters relate to process conditions, such as, for example,

15 process gas composition and flow rates, temperature, pressure, cooling gas pressure, substrate temperature, and chamber wall temperature. These parameters are provided to the user in the form of a recipe, and may be entered utilizing the user interface.

[0068] Signals for monitoring the process may be provided by analog and/or digital input connections of the system controller 429. The signals for controlling the process are 20 output on the analog and digital output connections of the deposition apparatus 400.

[0069] The system software may be designed or configured in many different ways. For example, various chamber component subroutines or control objects may be written to control operation of the chamber components necessary to carry out the deposition processes in accordance with the disclosed embodiments. Examples of programs or 25 sections of programs for this purpose include substrate positioning code, process gas control code, pressure control code, and heater control code.

[0070] In some implementations, a controller 429 is part of a system, which may be part of the above-described examples. Such systems can include semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or 30 platforms for processing, and/or specific processing components (a wafer pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the "controller," which may control various components or subparts of the system or systems. The controller 429, depending on the processing 5 requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of processing gases, temperature settings (e.g., heating and/or cooling), pressure settings, vacuum settings, power settings, radio frequency (RF) generator settings in some systems, RF matching circuit settings, frequency settings, flow rate settings, fluid delivery settings, positional and operation 10 settings, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system.

[0071] Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint 15 measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual 20 settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer.

25 [0072] The controller 429, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller 429 may be in the "cloud" or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor 30 current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that 5 enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type 10 of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by including one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication 15 with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber.

[0073] Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a

20 physical vapor deposition (PVD) chamber or module, a CVD chamber or module, an ALD chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers.

25 [0074] As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or 30 load ports in a semiconductor manufacturing factory.

[0075] The controller 429 may include various programs. A substrate positioning program may include program code for controlling chamber components that are used to load the substrate onto a pedestal or chuck and to control the spacing between the substrate and other parts of the chamber such as a gas inlet and/or target. A process gas control program may include code for controlling gas composition, flow rates, pulse times, 5 and optionally for flowing gas into the chamber prior to deposition in order to stabilize the pressure in the chamber. A pressure control program may include code for controlling the pressure in the chamber by regulating, e.g., a throttle valve in the exhaust system of the chamber. A heater control program may include code for controlling the current to a heating unit that is used to heat the substrate. Alternatively, the heater control program 10 may control delivery of a heat transfer gas such as helium to the wafer chuck.

[0076] Examples of chamber sensors that may be monitored during deposition include mass flow controllers, pressure sensors such as manometers, and thermocouples located in the pedestal or chuck. Appropriately programmed feedback and control algorithms may be used with data from these sensors to maintain desired process conditions.

15 [0077] The apparatus may include a gas manifold system, which provides line charges to the various gas distribution lines as shown schematically in Figure 6. Manifold 604 has inputs from a source 601 of a tungsten-containing precursor gas, which may include an accumulator (not shown),, which can also be referred to as a charge volume. Manifold 611 has an input from a source 609 of hydrogen (H2) and a source 610 of diborane-containing 20 mixture or other reducing gas (not shown). Both of these sources may include an accumulator (not shown). Manifold 621 has an input from a source 619 of purge gas, which also may include an accumulator. The manifolds 604, 611 and 6521 provide tungsten- containing precursor gas, co-reactant gas, and purge gas to the deposition chamber through valved distribution lines, 605, 613 and 625 respectively. The various valves may 25 be opened or closed to provide a line charge, i.e., to pressurize the distribution lines. For example, to pressurize distribution line 605, valve 606 is closed to vacuum and valve 608 is closed. After a suitable increment of time, valve 608 is opened and the co-flow gas is delivered to the chamber. After a suitable time for delivery of the gas, valve 608 is closed. The chamber can then be purged to a vacuum by opening of valve 606 to vacuum.

30 [0078] Similar processes can be used to deliver the reducing gas. To introduce the reducing gas, for example, distribution line 613 is charged by closing valve 615 and closing valve 617 to vacuum. Opening of valve 615 allows for delivery of the reducing gas to the chamber.

[0079] Similarly, to introduce the purge gas, distribution line 625 is charged by closing valve 627 and closing valve 623 to vacuum. Opening of valve 627 allows for delivery of the 5 argon or other inert purge gas to the chamber.

[0080] The diborane or other reducing gas can be mixed with hydrogen at any point in the process and is not limited to the arrangement of Figure 6. For example, a hydrogen/diborane mixture as stored may be used. Alternatively, it may be obtained from separate sources but mixed during the process at some point before delivery to the 10 chamber or may be delivered separately to the chamber with mixing occurring in the chamber.

[0081] Figure 6 also shows vacuum pumps in which valves 606, 617 and 623, respectively, can be opened to purge the system. The supply of gas through the various distribution lines is controlled by a controller, such as a mass flow controller which is 15 controlled by a microprocessor, a digital signal processor or the like, that is programmed with the flow rates, duration of the flow, and the sequencing of the processes.

[0082] Note that the processes described above may require precise timing of valves and mass flow controllers (MFCs) supplying pulses of reagent to the semiconductor substrate during deposition. In one way to make this possible, valve and MFC commands are 20 delivered to embedded digital input-output controllers (IOC) in discrete packets of information containing instructions for all time-critical commands for all or a part of a deposition sequence. The ALTUS systems of Lam Research provide at least one IOC sequence. The lOCs can be physically located at various points in the apparatus; e.g., within the process module or on a stand-alone power rack standing some distance away from the 25 process module. There may be multiple lOCs in each module (e.g., 3 per module). With respect to the actual instructions included in a sequence, all commands for controlling valves and setting flow for MFCs (for all carrier and reactant gases) may be included in a single IOC sequence. This assures that the timing of all the devices is tightly controlled from an absolute standpoint and also relative to each other. There are typically multiple IOC 30 sequences running at any given time. This allows for, say, ALD to run at station 1-2 with all timing controlled for all the hardware components needed to deposit a ALD nucleation layer at those stations. A second sequence might be running concurrently to deposit a bulk metal at other deposition stations in the same module. The relative timing of the devices controlling the delivery of reagents to stations 3-4 is important within that group of devices, but the relative timing of the ALD process at stations 1-2 can be offset from the 5 relative timing of stations 3-4. An IOC translates the information in a packetized sequence and delivers digital or analog command signals directly to MFC or pneumatic solenoid banks controlling the valves.

[0083] A pulse of tungsten-containing precursor gas may be generated as follows. Initially, the system diverts WF6 to a vacuum pump for a period of time while the MFC or

10 other flow-controlling device stabilizes. This may be done for a period of between about 0.5 to 5 seconds in one example. Next, the system pressurizes the tungsten gas delivery manifold by closing both the valve 606 to vacuum and the valve 608 to the deposition chamber. This may be done for a period of between about 0.1 and 5 seconds, for example, to create an initial burst of reagent when the valve to the deposition chamber is opened.

15 This is accomplished by opening valve 508 for between about 0.1 and 10 seconds in one example.

[0084] Thereafter, the tungsten-containing gas is purged from the deposition chamber using a suitable purge gas. Similar to above, the system may pressurize the purge gas delivery manifold by closing valve 623 and valve 627. Valves to an accumulator (not shown)

20 are also closed to permit the accumulator to pressurize. This may be done for a period of between about .1 and 5 seconds, for example, to rapidly flush reagent from the deposition chamber when the valve to the deposition chamber is opened. When valve 527 is opened to the deposition chamber, an accumulator outlet valve is opened simultaneously or shortly thereafter to increase the mass flow of purge gas into the deposition chamber.

25 Multiple accumulators may be used sequentially flow pressurized the same reactant or purge gas into the chamber during a single pulse operation. This can increases the overall mass flow rate.

[0085] The foregoing describes implementation of disclosed embodiments in a single or multi-chamber semiconductor processing tool. The apparatus and process described 30 herein may be used in conjunction with lithographic patterning tools or processes, for example, for the fabrication or manufacture of semiconductor devices, displays, LEDs, photovoltaic panels, and the like. Typically, though not necessarily, such tools/processes will be used or conducted together in a common fabrication facility. Lithographic patterning of a film typically includes some or all of the following steps, each step provided with a number of possible tools: (1) application of photoresist on a workpiece, i.e., 5 substrate, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or UV curing tool; (3) exposing the photoresist to visible or UV or x-ray light with a tool such as a wafer stepper; (4) developing the resist so as to selectively remove resist and thereby pattern it using a tool such as a wet bench; (5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) 10 removing the resist using a tool such as an RF or microwave plasma resist stripper

[0086] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and 15 apparatus of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.

20

Claims

1. A method comprising: providing a substrate including a feature having an opening in a top surface, a sidewall and a bottom in a chamber; and

5 depositing a tungsten nucleation layer in the feature by performing multiple cycles of: flowing a boron-containing reducing agent pulse in the chamber, wherein the boron-containing reducing agent is adsorbed to the feature sidewall and feature bottom, purging the chamber,

10 flowing a tungsten-containing precursor pulse in the chamber to react with the adsorbed boron-containing reducing agent, and purging the chamber, wherein hydrogen (H₂) is flowed during the boron-containing reducing agent pulse and no H₂ is flowed during the tungsten-containing precursor pulse, wherein H₂

15 suppresses thermal decomposition of the boron-containing reducing agent.

2. The method of claim 1, wherein the tungsten nucleation layer is at least 10 Angstroms thick and step coverage throughout the feature is at least 90%, step coverage being the ratio of the thickness of the tungsten nucleation layer at any point in the feature to the thickness of the tungsten nucleation layer at the top surface.

20 3. The method of claim 1, wherein depositing the nucleation layer further comprises at least one cycle of flowing a silane pulse in the chamber; purging the chamber; flowing a tungsten-containing precursor pulse in the chamber; and purging the chamber, wherein no hydrogen is flowed during the tungsten-containing precursor pulse.

4. The method of claim 3, wherein no hydrogen is flowed during the silane pulse.

25 5. The method of claim 3, wherein hydrogen is flowed during the silane pulse.

6. The method of claim 1, wherein the tungsten nucleation layer is between 10 Angstroms and 50 Angstroms thick.

7. The method of any of the above claims, wherein the substrate temperature is below

350°C.

5 8. The method of any of the above claims, wherein the substrate temperature is between about 250°C and 300°C.

9. The method of any of the above claims, wherein hydrogen reacts with decomposition byproducts of the boron-containing reducing agent.

10. The method of any of the above claims, wherein the boron-containing reducing agent

10 pulse in the chamber is flowed into the chamber with an inert carrier gas.

11. The method of any of the above claims, wherein the volumetric flow ratio of the H₂ to the boron-containing reducing agent is between 20:1 and 400:1.

12. The method of any of the above claims, wherein the boron-containing reducing agent is diborane.

15 13. A method comprising: providing a substrate including a feature having an opening in a top surface, a sidewall and a bottom in a chamber; depositing a tungsten nucleation layer in the feature by performing multiple cycles of: flowing a boron-containing reducing agent pulse in the chamber;

20 purging the chamber; flowing a tungsten-containing precursor pulse in the chamber; and purging the chamber, wherein hydrogen is flowed during the boron-containing reducing agent pulse and no hydrogen is flowed during the tungsten-containing precursor pulse.

25 14. An apparatus comprising: (a) a process chamber comprising at least one station having a pedestal configured to hold a substrate;

(b) at least one outlet for coupling to a vacuum;

(c) one or more process gas inlets coupled to one or more process gas sources; and

5 (d) a controller for controlling operations in the apparatus, comprising machine- readable instructions for: flowing a boron-containing reducing agent pulse in the chamber; purging the chamber; flowing a tungsten-containing precursor pulse in the chamber; and

10 purging the chamber, wherein hydrogen is flowed during the boron-containing reducing agent pulse and no hydrogen is flowed during the tungsten-containing precursor pulse.

15. The apparatus of claim 14, wherein the controller comprises instructions for maintaining a pedestal temperature less than 350°C.

15 16. The apparatus of claim 14, wherein the controller comprises instructions for maintaining a pedestal temperature between 175°C to 300°C.

17. The apparatus of claim 14, wherein the controller comprises instructions for flowing a silane pulse in the chamber; purging the chamber; flowing a tungsten-containing precursor pulse in the chamber; and purging the chamber, wherein no hydrogen is

20 flowed during the tungsten-containing precursor pulse.