US20100075060A1

US20100075060A1 - process tool including plasma spray for carbon nanotube growth

Info

Publication number: US20100075060A1
Application number: US12/236,739
Authority: US
Inventors: Pravin Narwankar; Victor Pushparaj; Omkaram Nalamasu
Original assignee: Individual
Current assignee: Applied Materials Inc
Priority date: 2008-09-24
Filing date: 2008-09-24
Publication date: 2010-03-25

Abstract

This invention provides a high volume manufacturing compatible process tool and method for integrating deposition of carbon nanotubes into device fabrication. A linear process tool for growing carbon nanotubes comprises a linear conveyor for moving a substrate through the linear process tool and a micro-plasma process unit including a plurality of micro-plasma spray guns arranged in an array, the micro-plasma process unit being positioned above the linear conveyor and configured to deposit material on the surface of the substrate as the substrate passes under the micro-plasma process unit on the linear conveyor. The micro-plasma process unit may include a first array of micro-plasma spray guns for depositing a catalyst material and a second array of micro-plasma spray guns for depositing the carbon nanotubes. A method of depositing carbon nanotubes on a substrate comprises: supplying a first precursor for a catalyst material to a first array of micro-plasma spray guns; creating a first plasma using the first array of micro-plasma spray guns and the first precursor; moving the substrate through the first plasma; activating the catalyst material; supplying a second precursor for the carbon nanotubes to a second array of micro-plasma spray guns; creating a second plasma using the second array of micro-plasma spray guns and the second precursor; moving the substrate through the second plasma.

Description

FIELD OF THE INVENTION

The present invention relates generally to manufacturing tools and methods, and more particularly to in-line processing tools for integrating carbon nanotubes into electrical devices and semiconductor devices.

BACKGROUND OF THE INVENTION

Carbon nanotubes (CNTs) have electrical and mechanical properties that make them attractive for integration into a wide range of electronic devices, including semiconductor devices. However, there is a need for cost effective and high-volume manufacturing (HVM) compatible fabrication technologies to enable broad market applicability of such devices.
Carbon nanotubes are nanometer-scale cylinders with walls formed of graphene—single atom thick sheets of graphite. Nanotubes may be either single-walled (cylinder wall composed of a single sheet of graphene, referred to as SWNTs) or multi-walled (cylinder wall composed of multiple sheets of graphene, referred to as MWNTs). Nanotubes have diameters as small as one nanometer, for a SWNT, and length to diameter ratios of the order of 10⁶. Carbon nanotubes can have either metallic or semiconducting electrical properties which make them suitable for integration into a variety of devices, such as solar cells, for example.
Carbon nanotubes can be grown using a variety of techniques including arc discharge, laser ablation and chemical vapor deposition. Most of the development of deposition processes for carbon nanotubes to date has been in research laboratories and there is a paucity of work on HVM compatible CNT deposition. Therefore, there is a need for HVM compatible CNT deposition equipment and methods.
Furthermore, due to the unique properties of CNTs, it is desirable to integrate CNTs into devices such as solar cells and semiconductor devices. The process conditions of the prevalent CNT growth processes, which may involve high temperatures and exposure to plasma, are not readily compatible with many substrates and devices. Consequently, there is a need for integration compatible processes for CNT growth.
Therefore, there remains a need for process equipment and methods that can significantly reduce the cost of integrating carbon nanotubes into electronic devices by enabling simplified, more HVM-compatible deposition equipment and methods.

SUMMARY OF THE INVENTION

This invention provides a high volume manufacturing compatible process tool and method for integrating deposition of carbon nanotubes into device fabrication. Carbon nanotubes have attractive electrical and mechanical properties that make integration of carbon nanotubes into a wide variety of electrical and semiconductor devices desirable. The concepts and methods of this invention allow for integration of carbon nanotube deposition into devices such as solar cells, batteries, capacitors, electrochromic devices, etc.
According to aspects of the invention a linear process tool for growing carbon nanotubes comprises a linear conveyor for moving a substrate through the linear process tool and a micro-plasma process unit including a plurality of micro-plasma spray guns arranged in an array, the micro-plasma process unit being positioned above the linear conveyor and configured to deposit material on the surface of the substrate as the substrate passes under the micro-plasma process unit on the linear conveyor. The micro-plasma process unit may include a first array of micro-plasma spray guns for depositing a catalyst material and a second array of micro-plasma spray guns for depositing the carbon nanotubes. An advantage for process integration of the micro-plasma spray guns is that the plasma is a low temperature plasma which allows for carbon nanotube deposition on temperature sensitive substrates.
According to further aspects of the invention a method of depositing carbon nanotubes on a substrate comprises: supplying a precursor for the carbon nanotubes to an array of micro-plasma spray guns; creating a plasma using the array of micro-plasma spray guns and the precursor; and moving the substrate through the plasma.
According to yet further aspects of the invention a method of depositing carbon nanotubes on a substrate comprises: supplying a first precursor for a catalyst material to a first array of micro-plasma spray guns; creating a first plasma using the first array of micro-plasma spray guns and the first precursor; moving the substrate through the first plasma; activating the catalyst material; supplying a second precursor for the carbon nanotubes to a second array of micro-plasma spray guns; creating a second plasma using the second array of micro-plasma spray guns and the second precursor; and moving the substrate through the second plasma.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein:

FIG. 1 shows a schematic side view of a linear deposition tool of the invention;

FIG. 2 shows a schematic top view of a linear deposition tool of the invention;

FIG. 3 shows a schematic side view of the linear deposition tool of FIG. 2, showing two alternative process gas supply configurations;

FIG. 4 shows a configuration of micro-plasma guns in a single process unit of a linear deposition tool of the invention;

FIG. 5 shows a vertical cross-sectional representation of a solar cell device fabricated using the linear deposition tool of the invention; and

FIG. 6 shows a vertical cross-sectional representation of a structure with vertically oriented carbon nanotubes fabricated using the linear deposition tool of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.
In general, the present invention contemplates a linear process tool comprising micro-plasma process units. The linear process tool of the invention may be used for growing carbon nanotubes as part of integrated device structures. Although the examples provided herein all include carbon nanotubes, there is no intention to limit the invention to devices and methods for carbon nanotube growth. For example, the linear process tool of the invention may be used for integrating silicon nanoparticles into solar cell devices.
FIG. 1 shows a schematic representation of a linear process tool 100 of the invention. A substrate 110 is carried on a linear conveyor 112 in the direction indicated. The substrate 110 may be glass, ceramic, plastic, polymer, semiconductor or any other suitable material on which deposition can be carried out. The substrate 110 may be a large format substrate, with an area of up to two square meters and more, or a collection of smaller substrates, with areas of several square centimeters and less, for example, held in a suitable frame, as is well known in the industry. The substrate 110 may be rigid, for example a sheet of glass, or flexible, for example a polymer film. The substrate 110 may be an insulator, a semiconductor or a metal. Furthermore, the substrate 110 may be a continuous flexible substrate, in which case the linear conveyor 112 is replaced by a reel-to-reel system for transporting the continuous substrate through the tool 100. In preferred embodiments the substrate is moved continuously through the process system during processing. The process system is designed for high throughput, with an expected linear speed of several meters per hour. Clearly, an equivalent tool configuration is a tool in which the substrate is stationary and the process unit/units are continuously moved over the substrate during processing. Yet further, the coordinated control of processing units and movement of the substrate may be used to provide a large-area patterning of structures grown on the substrate.
The linear process tool 100 comprises serial process units. In the particular embodiment shown in FIG. 1, the following process units are shown: a pre-heat unit 120; a micro-plasma process unit 130, comprising an array of micro-plasma spray guns 131; thermal anneal units 140; and a shower-head plasma unit 150. This particular arrangement of process units has been chosen for purposes of illustration. Many other arrangements of process units are envisaged. For example, FIGS. 2 and 3 show alternate micro-plasma process units 130 and annealing units 140.
The preheat unit 120 and the anneal units 140 may comprise halogen lamps, tungsten filaments, lasers, or other suitable sources of heat. The choice of heat source will be dependent on the substrate material, materials deposited and whether it is necessary to heat just the surface of the device being formed on the substrate, or to heat the entire substrate. Alternatively, the preheat and anneal units may be configured to heat the substrate from below (not shown).
The micro-plasma process unit 130 comprises an array of micro-plasma spray guns 131 which are fed from a common gas manifold 132 with either process gas or liquid. In the example shown in FIG. 1, process gas is supplied from a bubbler 134. Although, a liquid delivery system (not shown) may also be used to supply precursor to the micro-plasma guns 131. Each micro-plasma gun 131 may consume approximately 5 to 50 Watts; each micro-plasma process unit, comprising typically 100 micro-plasma spray guns 131, consumes approximately 500 to 5,000 Watts. Note that due to micro-plasmas being low temperature plasmas, this may enable deposition upon substrates comprising paper, plastics or polymers. The details of micro-plasma spray guns are well known to those skilled in the art of plasma deposition. Some examples of micro-plasma spray guns are provided in U.S. Pat. No. 7,115,832 to Blankenship et al. and U.S. Patent Application Publication No. 2005/0008550 to Duan.
The shower-head plasma unit 150 may be configured to generate a plasma. The shower head 150 is preferably fabricated from ceramic material, to withstand the reactive free radicals that are generated in the plasma. The plasma can be generated by parallel plates, or an alternative antennae, within the shower head 150. Alternatively, a plasma generator can be incorporated into the gas manifold 152. The shower head plasma unit 150 is fed from a gas manifold 152 with a process gas. In the example shown in FIG. 1, process gas is generated by pushing liquid from supply tank 154 through a liquid flow meter 156 and then through an injector valve 158, which vaporizes the liquid into the manifold 152. A push gas, such as nitrogen, helium, or other inert gas is used to push the liquid from the supply tank 154, as indicated by the arrows 155. A carry gas, such as nitrogen may be used in the manifold 152—it flows into the manifold 152 as shown by the arrow 151. Generally the lines of the manifold 152 must be heated in order to avoid condensation of process gas. Consequently, it is preferred that the length of the heated manifold lines is kept as short as can be accommodated. A second gas manifold 153 can be used to supply further process gases. The shower head plasma unit 150 may be used for plasma-enhanced chemical vapor deposition (PECVD) processes.
FIG. 2 is a schematic top view of a second embodiment of the linear process tool of the invention. A substrate 110 is carried on a linear conveyor 112 in the direction indicated under a plurality of process units. In the linear process tool 200 the following alternating process units are shown: micro-plasma process units 130, and thermal anneal units 140. This particular arrangement of process units is suitable for growing carbon nanotubes, as described with reference to FIG. 5 below. However, other process units may be used. For example, instead of micro-plasma process units 130, shower-head plasma units 150 may be used instead. The order and choice of process units is completely variable to fit the process requirements.
FIG. 3 shows a schematic side view of the linear process tool 200. A substrate 110 is carried on a linear conveyor 112 in the direction indicated under a plurality of alternating process units 130 and 140. Gas sources 336 and 338 provide process gases to the process units 130, through gas manifolds 331 and 333 respectively. The two gas supply systems are shown as alternatives in FIG. 3; although, both may be used in parallel to supply different process gases. An important consideration for the linear process tool of the invention is reducing the cost of the tool by efficient design of aspects such as process gas supply. The two alternatives shown in FIG. 3 illustrate the use of one gas supply system for either two or four process units. The limit in a linear process tool as to how many process units can be supplied from a single manifold and source is generally going to be the path length between the process gas source and the process unit. This is particularly the case for process gases which readily condense on the interior surfaces of the manifold. (Heated manifolds may be used to overcome this problem; however, heated manifolds are expensive to fabricate and operate).
FIG. 4 is a top view of the micro-plasma process unit 130 showing an example of a configuration of micro-plasma spray guns 131. The micro-plasma process unit 130 may contain approximately 100 micro-plasma spray guns 131 in order to achieve the desired uniformity of deposition. However, for ease of illustration only 28 micro-plasma spray guns 131 are shown in FIG. 4. The guns 131 are arranged to provide uniform deposition on a substrate, as the substrate is carried under the process unit. See FIGS. 1-3. Other configurations may be used to achieve uniform deposition, dependent on the specific properties of the micro-plasma guns. Furthermore, the micro-plasma process unit 130 may be separated into two, or more, banks of plasma guns 131; for example, the guns 131 to the right of dashed line 132 may be used for catalyst deposition and the guns 131 to the left of the dashed line 132 may be used for carbon nanotube deposition, where the substrate 110 is moving under the process unit 130 from right to left. In this case, where several banks of guns exist within a single micro-plasma process unit, each bank of guns will have its own precursor supply and operating control system.
FIG. 6 shows a cross-sectional representation of a substrate 110 with catalyst particles 602 and nanotubes 604. The catalyst particles and nanotubes can be deposited using the linear process tool of the invention. Methods for deposition of the carbon nanotubes are as follows, with reference to FIG. 1.
A first method for growing carbon nanotubes comprises the following steps. Providing a substrate 110 with catalyst material 602 on the surface. The catalyst material 602 may be a transition metal such as Co, Ni, and Fe, or a transition metal alloy such as Fe—Ni, Co—Ni and Mo—Ni. Heating the catalyst material 602 using a preheat unit 120 prior to the deposition of nanotubes—generally the catalyst must be activated by heating in order to grow nanotubes. (There is also the option of heating the substrate from below in order to activate the catalyst). Growing carbon nanotubes on the catalyst material using a micro-plasma unit 130. The micro-plasma unit 130 is supplied with precursor compounds such as xylene and ethanol. Mixtures of precursor compounds may also be used.
A second method for growing carbon nanotubes comprises the following steps. Providing a substrate 110 with catalyst material 602 on the surface. Heating the catalyst material 602 while growing carbon nanotubes on the catalyst material using a micro-plasma unit 130.
A third method for growing carbon nanotubes comprises the following steps. Providing a substrate 110 with catalyst material 602 on the surface. Growing carbon nanotubes on the catalyst material using a micro-plasma process unit 130, where the micro-plasma activates the catalyst allowing the growth of nanotubes. In some cases, activation of the catalyst material by the micro-plasma unit may be at room temperature. Furthermore, the micro-plasma may be effective in chemically reducing the catalyst material and providing a desirable surface of carbon nanotube growth.
A fourth method for growing carbon nanotubes comprises the following steps. Growing catalyst material 602 on the surface of substrate 110 using a first micro-plasma unit 130. A suitable precursor material delivered to the micro-plasma spray guns 131 is ferocene, for deposition of an iron catalyst. Activating the catalyst material using a pre-heat unit 120. Growing carbon nanotubes on the catalyst material using a micro-plasma process unit 130, where the micro-plasma activates the catalyst allowing the growth of nanotubes.
A fifth method for growing carbon nanotubes comprises the following steps. Depositing catalyst material while growing carbon nanotubes, using a micro-plasma process unit 130 configured, as described above, to deposit both catalyst and carbon nanotube precursor materials from separate banks of micro-plasma spray guns 131 within a single micro-plasma process unit 130. The substrate is moved under the separate banks so as to be coated in catalyst material prior to carbon nanotube growth. As above, a pre-heating step may be used, heating during growth may be used, or in some cases heating may not be needed—the micro-plasma itself may be effective in activating the catalyst.
A sixth method for growing carbon nanotubes comprises the following steps. Depositing catalyst material and growing carbon nanotubes simultaneously using a micro-plasma process unit 130 supplied with a mixture of precursors for both catalyst material and carbon nanotubes. Again, a pre-heating step may be used, heating during growth may be used, or in some cases heating may not be needed—the micro-plasma itself may be effective in activating the catalyst.
The carbon nanotubes may be grown with a vertical orientation, as shown in FIG. 6, by controlling the micro-plasma deposition conditions. Biasing the substrate relative to the micro-plasma process unit 130 during carbon nanotube growth may enhance the vertical orientation of the carbon nanotubes.
FIG. 5 shows a cross-sectional representation of a solar cell device 500 which may be manufactured using the process tool of the invention. The device 500 is comprised of a plurality of layers formed on a p-type doped silicon substrate 502. The substrate 502 may be a silicon wafer, or a polycrystalline substrate. There is a layer of p⁺-type doped silicon 501 on the bottom surface of the substrate 502. On the top surface of the substrate are: an n-type doped layer 503; a p-type doped layer 504; a stack of layers 505-508 which are comprised of silicon nanocrystals 520 and carbon nanotubes 530 in a matrix of Si0₂, SiC_x, SiN_xand similar insulators; and a layer of n-type doped silicon 509. The silicon nanocrystals 520 may be polydisperse or monodisperse and may have random or specific orientations. Preferably the silicon nanocrystals are quantum dots. (A quantum dot is a semiconductor of sufficiently small dimensions to confine excitons in three dimensions, where an exciton is a bound electron-hole pair in the semiconductor). Furthermore, in place of silicon nanoparticles, copper indium gallium selenide (CIGS) nanoparticles may be deposited.
Layers 505-508 of solar cell device 500 may be fabricated using the linear process tool of the invention as described herein. A method for growing a layer 505 of the device 500 comprises the following steps. Preheating the substrate using a pre-heat unit 120. Depositing a silicon rich insulating film using a PECVD shower-head plasma unit 150 or a micro-plasma process unit 130. The film is in the range of 2 to 15 nanometers thick. (For example, the CVD process may utilize a combination of the following process gases: SiH4, Si2H6, NH3 and H2. This results in a silicon-rich silicon nitride film.) Annealing the silicon-rich silicon nitride film using an annealing unit 140. The annealing process is tailored to grow silicon nanocrystals within the nitride thin film, where the diameter of the nanocrystals is preferably less than 5 nanometers and the nanocrystals are quantum dots. Growing catalyst material on the surface of the annealed film using a micro-plasma unit 130, followed by growing carbon nanotubes 530 on the catalyst material using either the same or a different micro-plasma unit 130. Note that the carbon nanotubes 530 may form a continuous layer, or discontinuous layer, depending on the coverage of the catalyst material. The carbon nanotubes 530, in FIG. 5, are shown connecting the silicon nanocrystals 520. This representation is used in order to emphasize the role of the carbon nanotubes 530 in enabling charge transfer to and from the silicon nanocrystals 520, and is not meant to indicate that the carbon nanotubes 530 are limited to being grown only where silicon nanocrystals 520 exist. The process described above is repeated for each layer of the stack 505-508.
Further to the solar cell shown in FIG. 5, other solar cell configurations may be manufactured using the linear process tool of the invention. For example, silicon nanocrystals may be deposited on a transparent conductive oxide (TCO) or other substrate. CIGS nanoparticles may be deposited.
The linear process tool of the invention and the methods described above may be used to grow nanoparticles and nanotubes as an integrated deposition process in the formation of solar cells, Li ion batteries, supercapacitors, displays, electrochromic devices, etc. Various processes may readily be integrated into the linear process tool of the invention, such as plasma-enhanced chemical vapor deposition (PECVD).
The methods described above for growing nanotubes and nanoparticles may also be implemented on process equipment such as the Applied Materials' Producer™ platform which has a platform architecture with Twin Chamber™ modules to achieve high throughput. The Twin Chamber™ unit can be configured for growth of carbon nanotubes, and up to three Twin Chamber™ units can be accommodated on one Producer™ platform.
Although the present invention has been particularly described with reference to the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims encompass such changes and modifications.

Claims

1. A linear process tool for growing carbon nanotubes comprising:

a linear conveyor for moving a substrate through said linear process tool;

a micro-plasma process unit including a plurality of micro-plasma spray guns arranged in an array, said process unit being positioned above said linear conveyor and configured to deposit material on the surface of said substrate as said substrate passes under said micro-plasma process unit on said linear conveyor; and

a heating unit configured to heat the surface of said substrate as said substrate passes under said heating unit on said linear conveyor.

2. A linear process tool as in claim 1 wherein said substrate is a large area substrate.

3. A linear process tool as in claim 2 wherein said substrate has an area greater than one square meter.

4. A linear process tool as in claim 1 wherein said substrate is a sheet of flexible material and said linear conveyor moves said sheet from a first reel at a first end of said linear process tool to a second reel at a second end of said linear process tool.

5. A linear process tool as in claim 1 wherein said micro-plasma process unit includes:

a first array of micro-plasma spray guns for depositing a catalyst material; and

a second array of micro-plasma spray guns for depositing said carbon nanotubes;

wherein said first array and said second array are configured so that said substrate moves on said linear conveyor under said first array and then under said second array.

6. A linear process tool as in claim 1 wherein said substrate is electrically biased with respect to said micro-plasma process unit.

7. A linear process tool as in claim 1 further comprising a shower-head plasma deposition unit, said shower-head plasma deposition unit being positioned above said linear conveyor and configured to deposit material on the surface of said substrate as said substrate passes under said shower-head plasma deposition unit on said linear conveyor.

8. A linear process tool as in claim 7 wherein said shower-head plasma deposition unit is made of ceramic material.

9. A method of depositing carbon nanotubes on a substrate comprising:

supplying a precursor for said carbon nanotubes to an array of micro-plasma spray guns;

creating a plasma using said array of micro-plasma spray guns and said precursor; and

moving said substrate through said plasma.

10. A method of depositing carbon nanotubes as in claim 9 wherein said precursor includes a mixture of xylene and ferocene.

11. A method of depositing carbon nanotubes as in claim 9 further comprising applying an electrical bias between said substrate and said array of micro-plasma spray guns.

12. A method of depositing carbon nanotubes as in claim 9 further comprising, before said creating step, applying a catalyst material to said substrate.

13. A method of depositing carbon nanotubes as in claim 12 further comprising activating said catalyst material.

14. A method of depositing carbon nanotubes as in claim 13 wherein said activating includes heating said catalyst material.

15. A method of depositing carbon nanotubes on a substrate comprising:

supplying a first precursor for a catalyst material to a first array of micro-plasma spray guns;

creating a first plasma using said first array of micro-plasma spray guns and said first precursor;

moving said substrate through said first plasma;

activating said catalyst material;

supplying a second precursor for said carbon nanotubes to a second array of micro-plasma spray guns;

creating a second plasma using said second array of micro-plasma spray guns and said second precursor; and

moving said substrate through said second plasma.

16. A method of depositing carbon nanotubes on a substrate as in claim 15 wherein said activating includes heating said catalyst material.

17. A method of depositing carbon nanotubes on a substrate as in claim 15 wherein said activating includes exposing said catalyst material to said second plasma.

18. A method of depositing carbon nanotubes on a substrate as in claim 15 wherein said first array of micro-plasma spray guns and said second array of micro-plasma spray guns are in the same micro-plasma deposition unit.