Copper electrodeposition sequence for cobalt-lined features

Abstract

In one example, an electroplating system includes a first bath, a second bath, a jig, a first anode in the first bath, a second anode in the second bath, and a direct current power source. The first bath contains a first electrolyte solution including an alkaline copper complex solution. The second bath contains a second electrolyte solution including an acidic copper plating solution. The DC power source generates a first DC current between the jig and the first anode to electroplate a first copper layer on a cobalt layer of the wafer immersed in the first electrolyte solution. The DC power source then generates a second DC current between the jig and the second anode to electroplate a second copper layer on the first copper layer of the wafer immersed in the second electrolyte solution.

Description

This application is a divisional application of the application with application number 201980024329.2, application date March 29, 2019, and invention name “Featured copper electrodeposition sequence for cobalt lining”. Priority claim

[0001] This application is a continuation of U.S. patent application Ser. No. 15 / 941,267, filed on Mar. 30, 2018, and claims the benefit of priority under 35 U.S.C. §120, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates generally to electroplating systems and methods, and more particularly to systems and methods for electroplating copper directly onto a cobalt liner. Background Art

[0003] In conventional electroplating methods, copper electrodeposition in the presence of additives can produce void-free plating of submicron features (such as vias and trenches) in dual damascene metallization. This method is often used to manufacture interconnects in advanced microprocessors below the 50nm technology node. However, as the size of interconnects decreases, it becomes increasingly difficult to scale the interconnect metallization process to narrower geometries. For example, physical vapor deposition (PVD) of copper on a cobalt liner can cause undesirable defects such as bumps or "protrusions" at the feature openings, resulting in pinch-off. In addition, the sidewall step coverage of these small features can also result in voids in the sidewalls after plating. Such defects can lead to electrical shorts and reliability issues.

[0004] The present disclosure attempts to address these shortcomings.It should be noted that the information described in this section is provided to provide those skilled in the art with some background to the following disclosed subject matter and should not be considered as admitted prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Some embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings:

[0006] Figure 1A is a block diagram of an electroplating system using a first electroplating bath according to an exemplary embodiment.

[0007] Figure 1B is a block diagram of an electroplating system using a second electroplating bath according to an exemplary embodiment.

[0008] Figure 2 is a flow chart of a method for processing a wafer according to an exemplary embodiment.

[0009] Figure 3 is a flow chart of a method for electroplating according to an exemplary embodiment.

[0010] Figure 4 is a flow chart of a method for electroplating according to another exemplary embodiment.

[0011] Figure 5 is a cross-sectional view of a wafer showing an example of depositing a copper layer on a cobalt layer.

[0012] Figure 6 is a block diagram illustrating an example of a machine on which one or more exemplary embodiments may be implemented or by which one or more exemplary embodiments may be controlled. DETAILED DESCRIPTION

[0013] The following description includes systems, methods, techniques, instruction sequences, and computing machine program products that implement exemplary embodiments of the subject matter of the present invention. In the following description, for the purpose of explanation, many specific details are provided to provide a thorough understanding of the exemplary embodiments. However, it is apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details.

[0014] A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by any person of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to any data as described below and in the accompanying drawings that form a part of this document: Copyright LAM Research Corporation, 2018, All rights reserved.

[0015] In this disclosure, various terms are used to describe semiconductor processing surfaces: "wafer" and "substrate" may be used interchangeably. The process of depositing or plating metal onto the conductive surface of a wafer via an electrochemical reaction is generally referred to as "electrodeposition" or "electroplating."

[0016] The wafer includes features such as trenches and vias that form interconnects. As the size of the interconnects decreases (e.g., to sizes less than 50 nm), metallization of features in narrower geometries becomes increasingly difficult. Advanced interconnect technologies (less than 50 nm) are migrating from copper plating onto PVD copper seeds to direct copper plating onto cobalt liners. Traditionally, filling of interconnect structures with PVD copper seeds is accomplished in a simple single-bath sequence. Applying the same single-bath strategy to fill cobalt-lined structures presents some challenges: conventional acid baths cause cobalt dissolution, leading to nucleation issues and sidewall voids. Dissolution of cobalt can be mitigated by using an alkaline copper composite plating bath. However, the use of an alkaline copper composite plating bath is generally insufficient because the alkaline copper composite plating bath still results in seam or center void defects in the features.

[0017] To address the above challenges, a two-bath sequence is being described. A first electrodeposition of a copper nucleation layer is performed in a first bath consisting of an alkaline copper composite bath. This first electroplating process uses an electrodeposition chemistry that enables copper to nucleate and deposit uniformly on a wafer (e.g., a 300 mm resistor wafer). An alkaline composite copper electrolyte bath can achieve high copper nucleation density and plating uniformity. Alkaline composite copper electrolytes are less sensitive to dissolution of the seed layer than acidic media. Therefore, one benefit of direct plating on cobalt from an alkaline composite copper bath is to minimize or eliminate sidewall voids.

[0018] The features are then subjected to a second electrodeposition of copper filling in a second bath consisting of an acid copper plating bath following the first bath. This "superfilling" of copper prevents the formation of seams or center voids in the wafer features.

[0019] In some exemplary embodiments of the present disclosure, an electroplating process is provided that uses a sequence comprising the following steps: cobalt pretreatment of the wafer, followed by a first electroplating bath consisting of an alkaline copper complex bath, and then a second electroplating bath consisting of an acid copper plating bath. This electroplating sequence enables the deposition of a copper layer directly on a cobalt liner on a wafer feature without creating seams or voids in the vias and trenches of the wafer.

[0020] In some exemplary embodiments of the present disclosure, the electroplating system includes a first bath, a second bath, a fixture, a first anode in the first bath, a second anode in the second bath, and a DC power supply. The first bath contains a first electrolyte solution, which includes an alkaline copper composite solution. The second bath contains a second electrolyte solution, which includes an acidic copper plating solution. The DC power supply generates a first direct current between the fixture and the first anode to electroplate a first copper layer on the cobalt layer of a wafer immersed in the first electrolyte solution. Then, the DC power supply generates a second direct current between the fixture and the second anode to electroplate a second copper layer on the first copper layer of the wafer immersed in the second electrolyte solution.

[0021] Figure 1A 1 is a block diagram of an electroplating system 100 using a first electroplating bath according to an exemplary embodiment. The electroplating system 100 includes a bath 112, a fixture 108, an anode 106, a direct current (DC) power source 104, and a controller 102.

[0022] Bath 112 contains an alkaline complex copper electrolyte solution 114. In one example, alkaline complex copper electrolyte solution 114 contains low copper (e.g., about 0.5 g / L to about 2.0 g / L), a complexing ligand (e.g., ethylenediaminetetraacetic acid or EDTA), and additives (e.g., promoters and inhibitors). Alkaline complex copper electrolyte solution 114 is continuously provided to bath 112 by a pump (not shown). Alkaline complex copper electrolyte solution 114 is circulated in and out of bath 112 by the pump.

[0023] The fixture 108 holds a wafer 110 immersed in an alkaline complex copper electrolyte solution 114. In one example, the fixture 108 includes a holding device, such as a chuck, mounted to a spindle that enables the fixture 108 and wafer 110 to rotate.

[0024] Wafer 110 includes features (vias and trenches) deposited with a cobalt layer using, for example, an atomic layer deposition (ALD) process or a chemical vapor deposition (CVD) process.

[0025] The DC power supply 104 generates a direct current that flows between the fixture 108 and the anode 106. The DC power supply 104 includes a negative output electrode 116 and a positive output electrode 118. The negative output electrode 116 is electrically connected to the fixture 108 and the wafer 110. The positive output electrode 118 is electrically connected to the anode 106 located in the alkaline composite copper electrolyte solution 114. The anode 106 is located in the alkaline composite copper electrolyte solution 114 at a position opposite to the wafer 110.

[0026] The controller 102 is connected to the DC power supply 104 and is programmed to control the DC power supply 104. For example, the controller 102 includes program instructions that specify the current and voltage levels to be applied to the wafer 110 along with the duration and number of times at which the current and voltage levels are varied. In an exemplary embodiment, the controller 102 controls the DC power supply 104 to generate a positive pulse between the clamp 108 / wafer 110 and the anode 106. During the positive pulse, the DC power supply 104 biases the wafer 110 to have a negative potential relative to the anode 106. This causes current to flow from the anode 106 to the wafer 110, and electrochemical reduction (e.g., Cu 2+ +2e - →Cu 0 ) is performed on the wafer surface (cathode), which causes copper to be deposited on the surface of wafer 110.

[0027] In another exemplary embodiment, the controller 102 controls the DC power supply 104 to generate a combination of a forward pulse and a reverse pulse between the chuck 108 / wafer 110 and the anode 106. The forward pulse includes a direct current that lasts for a predetermined duration (e.g., 100 ms), thereby causing copper to be deposited on the wafer 110 from the alkaline complex copper electrolyte solution 114. The reverse pulse includes a direct current of reverse polarity that lasts for a predetermined duration (e.g., 10 ms), thereby causing copper to be removed from the wafer 110. During the reverse pulse, the opposite occurs: the reaction on the wafer surface is oxidation (e.g., Cu 0 →Cu 2+ +2e - ), thereby resulting in the removal of copper from the surface of the wafer 110.

[0028] Figure 1B 1 is a block diagram of an electroplating system 101 using a second electroplating bath according to an exemplary embodiment. Bath 112 contains an acidic copper plating electrolyte solution 115. In one example, the acidic copper plating electrolyte solution 115 contains copper (e.g., about 2 g / L to about 40 g / L), an acid (e.g., about 10 g / L to about 20 g / L), and a chloride (e.g., 30 ppm to about 100 ppm). The acidic copper plating electrolyte solution 115 is continuously provided to the bath 112 with a pump (not shown). The acidic copper plating electrolyte solution 115 is circulated in and out of the bath 112 by the pump.

[0029] In an exemplary embodiment, Figure 1A and Figure 1B The same bath 112 for the alkaline composite copper electrolyte solution 114 and the acidic copper plating electrolyte solution 115 is shown. The alkaline composite copper electrolyte solution 114 is discharged from the bath 112 and replaced by the acidic copper plating electrolyte solution 115. In another exemplary embodiment, a different electroplating system can be used for each electroplating solution. For example, a separate bath and anode can be used for each electroplating solution. It should be appreciated by those of ordinary skill in the art that other variations of the electroplating system can be used to first electroplate with the alkaline composite copper electrolyte solution 114 and then electroplate with the acidic copper plating electrolyte solution 115.

[0030] Figure 2 2 is a flow chart of a method 200 for processing a wafer according to an exemplary embodiment. The method 200 includes: at operation 202, performing CVD (or ALD) of cobalt on the wafer 110. The ALD process deposits a very thin layer of cobalt using alternating doses of precursor materials that first saturate the surface and then form a thin cobalt layer deposit. The CVD process involves providing one or more gaseous reactants to a chamber that react to deposit a cobalt film on the wafer surface. Although ALD and CVD processes are typically used to deposit cobalt (or other semi-precious metal) layers, other deposition processes may also be used. At operation 204, the wafer 110 is pretreated with hydrogen-helium plasma at a temperature between about 75° C. and about 250° C.; at operation 206, the electroplating system deposits a copper nucleation layer on the wafer in an alkaline copper composite bath containing low copper (e.g., about 0.5 g / L to about 2.0 g / L), a coordination ligand (e.g., EDTA), and additives (e.g., accelerators and inhibitors); at operation 208, after the alkaline copper composite bath treatment, copper filling is performed in a separate acid copper plating bath containing copper (e.g., about 2 g / L to about 4.0 g / L), an acid (e.g., about 10 g / L to about 20 g / L), and a chloride (about 30 ppm to about 100 ppm); at operation 210, chemical mechanical planarization (CMP) is performed to planarize the wafer 110 and remove excess copper.

[0031] The present disclosure also includes another example method. In one example, reference Figure 3 , the electroplating method 300 includes, at operation 302, immersing a wafer in a first bath containing a first electrolyte solution (e.g., an alkali-based solution); at operation 304, generating an electric pulse (e.g., a direct current from a direct current power supply); at operation 306, depositing a copper nucleation layer on the cobalt layer of the wafer by applying the electric pulse to the wafer in the first electrolyte solution and to an anode disposed opposite to the wafer.

[0032] In some examples, the combination of the forward pulse and the reverse pulse includes a high convection forward pulse, followed by a high convection reverse pulse, followed by a low convection reverse pulse. The high convection forward pulse and the high convection reverse pulse each include a convection of at least about 150 rpm. The high convection forward pulse includes an intensity of at least about 0.85 mA / cm 2 The high convection reverse pulse comprises a forward direct current of at least about 100 ms and a no direct current of at least about 200 ms after the forward direct current. The high convection reverse pulse comprises an intensity of at least about 0.85 mA / cm 2 A forward direct current of at least about 100 ms, an intensity of at least about -0.85 mA / cm after the forward direct current 2 The low convection reverse pulse comprises a reverse direct current of at least about 10 ms and a direct current free state of at least about 200 ms after the reverse direct current. The low convection reverse pulse comprises a convection of up to about 20 rpm, wherein the low convection reverse pulse comprises a convection of at least about 0.85 mA / cm 2 A forward direct current of at least about 100 ms, an intensity of at least about 0.85 mA / cm after the forward direct current 2 The reverse direct current lasts for at least 10 ms and there is no direct current for at least about 200 ms after the reverse direct current. The electrolyte solution includes an alkaline complex copper electrolyte solution.

[0033] Figure 4 4 is a flow chart of a method 400 for electroplating a wafer according to another exemplary embodiment. The method 400 includes, at operation 402, immersing the wafer in a second bath containing a second electrolyte solution (e.g., an acid-based solution) after the first electrolyte solution; at operation 404, a DC power supply generates an electrical pulse; and at operation 306, filling the features (vias, trenches) of the wafer with a copper layer on the copper nucleation layer of the wafer by applying an electrical pulse to the wafer and an anode disposed opposite the wafer in the second electrolyte solution.

[0034] Figure 55 are cross-sectional views of wafers using different plating baths and plasma pretreatments. Cross section 502 of a wafer feature shows seams 510 when the wafer is plated using a single alkali-based plating bath with a plasma pretreatment at about 75°C. Cross section 504 of a wafer feature shows seams 512 when the wafer is plated using a single alkali-based plating bath with a plasma pretreatment at about 250°C. Cross section 506 of a wafer feature shows voids 514 when the wafer is plated using an alkali-based plating bath followed by an acid-based plating bath with a plasma pretreatment at about 75°C. Cross section 508 of a wafer feature is free of voids and seams when the wafer is plated using an alkali-based plating bath followed by an acid-based plating bath with a plasma pretreatment at about 250°C.

[0035] In some other examples, a combination of a forward pulse and a reverse pulse can be applied to the wafer (in the first plating solution or the second plating solution, or in the first plating solution and the second plating solution). In some examples, the combination includes a high convection forward pulse, a high convection reverse pulse, and a low convection reverse pulse. The high convection forward pulse and the high convection reverse pulse each include a convection of at least 150 rpm. The high convection forward pulse includes an intensity of at least about 0.85 mA / cm 2 The high convection reverse pulse comprises a forward direct current lasting at least about 100 ms, a reverse direct current lasting at least about 10 ms after the forward direct current, and no direct current lasting at least about 200 ms after the reverse direct current. The low convection reverse pulse comprises a convection of up to about 20 rpm, wherein the low convection reverse pulse comprises an intensity of at least about 0.85 mA / cm 2 A forward direct current of at least about 100 ms, an intensity of at least about -0.85 mA / cm 2 The reverse direct current lasts for at least about 10 ms and there is no direct current for at least 200 ms after the reverse current. The electrolyte solution includes an alkaline complex copper electrolyte solution.

[0036] In some examples, a non-transitory machine-readable medium includes instructions that, when read by a machine, cause the machine to control operations in the method, including at least the non-limiting example operations outlined above.

[0037] Figure 6600. In an alternative embodiment, the machine 600 may be operated as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine 600 may operate in the capacity of a server machine, a client machine, or both a server machine and a client machine in a server-client network environment. In an example, the machine 600 may act as a peer machine in a peer-to-peer (P2P) (or other distributed) network environment. In addition, although only a single machine 600 is described, the term "machine" should also be construed to include any collection of machines that individually or collectively execute a set (or multiple sets) of instructions to perform any one or more of the methods discussed herein, such as via cloud computing, software as a service (SaaS), or other computer cluster configurations.

[0038] Examples as described herein may include logic, multiple components or mechanisms, or may be operated by logic, multiple components or mechanisms. A circuit system is a collection of circuits implemented in a tangible entity, including hardware (e.g., simple circuits, gates, logic, etc.). Circuit system qualifications may be flexible over time and with potential hardware variability. A circuit system includes components that can perform specified operations individually or in combination when operating. In one example, the hardware of the circuit system may be designed to perform specific operations (e.g., hardwired) invariably. In one example, the hardware of the circuit system may include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.), which include computer-readable media modified by physical properties (e.g., magnetism, electrical properties, movable placement of unchanged cluster particles, etc.) to encode instructions for specific operations. In terms of connecting physical components, the potential electrical properties of hardware components are changed (e.g., from insulators to conductors, or vice versa). Instructions enable embedded hardware (e.g., execution units or loading mechanisms) to establish components of the circuit system in hardware via variable connections to perform partial specific operations when operating. Thus, when the device is operating, the computer readable medium is communicatively coupled to other components of the circuit system. In one example, any of the physical components can be used in more than one component of more than one circuit system. For example, in an operational state, an execution unit can be used in a first circuit of a first circuit system at one point in time and reused by a second circuit in the first circuit system, or by a third circuit in the second circuit system at a different time.

[0039] The machine (e.g., computer system) 600 may include a hardware processor 602 (e.g., a central processing unit (CPU), a hardware processor core, or any combination thereof), a graphics processing unit (GPU) 603, a main memory 604, and a static memory 606, some or all of which may communicate with each other via an interconnection link (e.g., a bus) 608. The machine 600 may also include a display device 610, an alphanumeric input device 612 (e.g., a keyboard), and a user interface (UI) navigation device 614 (e.g., a mouse). In one example, the display device 610, the alphanumeric input device 612, and the UI navigation device 614 may be a touch screen display. The machine 600 may additionally include a mass storage device (e.g., a drive unit) 616, a signal generating device 618 (e.g., a speaker), a network interface device 620, and one or more sensors 621 (such as a global positioning system (GPS) sensor, a compass, an accelerometer, or another sensor). The machine 600 may include an output controller 628, such as a serial (e.g., universal serial bus (USB)), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection, to communicate with or control one or more peripheral devices (e.g., a printer, a card reader, etc.).

[0040] The mass storage device 616 may include a machine-readable medium 622 on which is stored one or more sets of data structures or instructions 624 (e.g., software) embodied or utilized by any one or more of the techniques or functions described herein. The instructions 624 may also reside, completely or at least partially, within the main memory 604, within the static memory 606, within the hardware processor 602, or within the GPU 603 during execution thereof by the machine 600. In an example, one or any combination of the hardware processor 602, the GPU 603, the main memory 604, the static memory 606, or the mass storage device 616 may constitute the machine-readable medium 622.

[0041] Although the machine-readable medium 622 is illustrated as a single medium, the term “machine-readable medium” may include a single medium or multiple media (e.g., a centralized or distributed database, and / or associated caches and servers) configured to store one or more instructions 624.

[0042] The term "machine-readable medium" may include any medium that can store, encode, or carry instructions 624 for execution by the machine 600 and cause the machine 600 to perform any one or more of the techniques of the present disclosure, or that can store, encode, or carry data structures used by or associated with the instructions 624. Non-limiting examples of machine-readable media may include solid-state memory, and optical and magnetic media. In one example, the clustered machine-readable medium includes a machine-readable medium 622 having a plurality of particles, the particles having a constant (e.g., stationary) mass. Therefore, the clustered machine-readable medium is not a transient propagating signal. Specific examples of the clustered machine-readable medium may include non-volatile memory, such as semiconductor memory devices (e.g., electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The instructions 624 may also be transmitted or received over a communication network 626 using a transmission medium via the network interface device 620. .

[0043] Although the embodiments have been described with reference to specific exemplary embodiments, it is obvious that various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the present invention. Therefore, the description and the drawings should be regarded as illustrative rather than restrictive. The drawings forming a part of this article show specific embodiments by way of illustration and not limitation, in which the subject matter can be implemented. The illustrated embodiments are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments can be used and derived therefrom, so that structural and logical substitutions and changes can be made without departing from the scope of the present disclosure. Therefore, the specific implementation should not be regarded as having a limiting meaning, and the scope of the various embodiments is limited only by the attached claims and the complete scope of the equivalent schemes given with these claims.

[0044] Such embodiments of the subject matter of the present invention may be referred to herein individually and / or collectively by the term "invention" for convenience only, and if more than one invention or inventive concept is in fact disclosed, it is not intended to automatically limit the scope of the present application to any single invention or inventive concept. Therefore, although specific embodiments have been illustrated and described herein, it should be understood that any configuration calculated to achieve the same purpose may replace the specific embodiments shown. The present disclosure is intended to cover all adaptations or variations of the various embodiments. Upon reviewing the above description, the combination of the above embodiments with other embodiments not specifically described herein will be apparent to those skilled in the art.

Claims

1. An electroplating system, comprising: a bath configured to hold a first electrolyte solution, the first electrolyte solution comprising an alkaline copper complex solution, the bath configured to be drained and replaced with a second electrolyte solution and to hold the second electrolyte solution, the second electrolyte solution comprising an acidic copper plating solution; Clamps for: holding a substrate and immersing the substrate in the first electrolyte solution including the alkaline copper composite solution; as well as the fixture further immersing the substrate in the second electrolyte solution after the bath is drained of the first electrolyte solution and replaced with a second electrolyte solution including the acid copper plating solution and containing the second electrolyte solution, the substrate including at least some features having a cobalt layer deposited thereon; and an anode immersed in the first electrolyte solution, the anode subsequently immersed in the second electrolyte solution; and A DC power supply for generating a first DC current between the fixture and the anode and configured to electroplate a first copper layer on the cobalt layer of the substrate in the first electrolyte solution, and the DC power supply for generating a second DC current between the fixture and the anode and configured to electroplate a second copper layer on the first copper layer of the substrate in the second electrolyte solution.

2. The electroplating system according to claim 1, wherein: The first copper layer includes a copper nucleation layer formed on top of the cobalt layer of the wafer.

3. The electroplating system according to claim 2, wherein: The second copper layer includes a copper fill layer formed on top of the copper nucleation layer, the copper fill layer being configured to fill the features of the wafer.

4. The electroplating system according to claim 1, wherein: Prior to immersing the substrate in the first electrolyte solution, the substrate is pre-treated using a hydrogen-helium plasma treatment.

5. The electroplating system according to claim 4, wherein: The temperature of the hydrogen-helium plasma is between about 75 degrees Celsius and about 250 degrees Celsius.

6. The electroplating system according to claim 4, wherein: Prior to the hydrogen-helium plasma treatment, the cobalt layer is deposited on the substrate by chemical vapor deposition.

7. The electroplating system according to claim 1, wherein: The pH of the alkaline copper composite solution is greater than about 9, wherein the pH of the acidic copper plating solution is less than about 2.

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