Infrared control coating of thin film devices

Systems and methods for creating an infrared-control coated thin film device with certain visible light transmittance and infrared reflectance properties are disclosed. The device may be made using various techniques including physical vapor deposition, chemical vapor deposition, thermal evaporation, pulsed laser deposition, sputter deposition, and sol-gel processes. In particular, a pulsed energy microwave plasma enhanced chemical vapor deposition process may be used. Production of the device may occur at speeds greater than 50 Angstroms/second and temperatures lower than 200° C.

INTRODUCTION

Thin films are used in a variety of applications. For example, thins films are used in window assemblies. The window assembly has a window pane, and thin films can be deposited onto the window pane. Additionally, a thin film may be deposited on a thin substrate that can then be adhered to the window surface or applied to an insert that is then inserted into a window assembly.

Depending on the type of film used and the material of the window pane, depositing or inserting thin films on window panes can alter certain properties of the window pane. For example, thin films alter the transmittance of light through the window pane. A thin film may reduce the amount of visible light that passes through the window pane. Additionally, certain thin films reduce the amount of infrared light that passes through the window pane.

For certain applications, it is desirous to control the transmittance of specific wavelengths of electromagnetic radiation through a window pane. For example, a window assembly may be used as part of a structure that forms an internal space. As such, it may be desirous to control the temperature of the internal space. Additionally, it may also be desirous to allow people to see through the window. Using a thin film that reduces the amount of infrared light that passes through the window would reduce the total energy entering or exiting the internal space. Consequently, less energy would be required to keep the space at the desired temperature than if all infrared light were allowed to pass through the window. Furthermore, it may also be desirous to allow more transmittance of visible light through the window pane because doing so would allow people to see through the window easier than if the transmittance was low.

Thus, a thin film that could decrease the amount of infrared light that passed through the window pane while still allowing a significant amount of visible light is useful for certain applications.

It is with respect to these and other considerations that embodiments have been disclosed. Also, although relatively specific problems have been discussed, it should be understood that the embodiments should not be limited to solving the specific problems identified in the introduction.

Various embodiments are described more fully below with reference to the accompanying drawings, which form a part hereof, and which show specific exemplary embodiments. However, embodiments may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. Embodiments may be practiced as methods, systems or devices. The following detailed description is, therefore, not to be taken in a limiting sense.

Infrared Control Coating of Thin Film Devices

Systems and methods for creating an infrared-control coated thin film device with certain visible light transmittance and infrared reflectance properties are disclosed. The device may be made using various techniques including physical vapor deposition, chemical vapor deposition, thermal evaporation, pulsed laser deposition, sputter deposition, and sol-gel processes. In particular, a pulsed energy microwave plasma enhanced chemical vapor deposition process may be used. Production of the device may occur at static deposition rates greater than 50 Angstroms/second and substrate temperatures lower than 200° C.

{Claim Summary Section. Completed after Approval of Final Version Claims}

These and various other features as well as advantages which characterize the systems and methods described herein will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features are set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the technology. The benefits and features of the technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

DETAILED DESCRIPTION

Various embodiments are described more fully below with reference to the accompanying drawings, which form a part hereof, and which show specific exemplary embodiments. However, embodiments may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. Embodiments may be practiced as methods, systems or devices. The following detailed description is, therefore, not to be taken in a limiting sense.

Systems and method for producing infrared control coating on thin film devices are disclosed herein. Production of such devices may occur at a relatively low temperature and a relatively high speed. Though the materials are discussed with specificity, it will be appreciated that that various materials may be used in conjunction with the technology disclosed herein is not so limited. The systems and methods described herein may be used to create thin films that are amorphous, polycrystalline, nanocrystalline, nanocrystalline in an amorphous matrix, or ultra-nanocrystalline in an amorphous matrix. Such a matrix may provide a balance between infrared modulation and high visible transmission that may complement the response of the infrared reflection.

The technology described herein may be used in a variety of applications. For example, the technology may be deposited directly onto a window glass pane before integration into a window, deposited onto a stand-alone film that can be adhered directly to a window surface, or deposited onto a stand alone film that can be adhered to a thin plastic or glass substrate and later inserted into a window. The infrared control film may also be used in conjunction with an electrochromic device or other dynamic window system to provide a combination of active and passive control of heat flow through the window system.

Any actively controlled dynamic window glazing, such as an electrochromic device or motorized shading system, may be used in conjunction with a multilayered infrared-control coated thin film device, such as a dielectric stack, that is designed to control the infrared transmittance and reflectance. Further, the infrared-control coatings may be deposited on the same substrate as an electrochromic device, a window pane, an insert, or another substrate. Both the infrared control coating and the electrochromic device may adhere to an insert that fits between two panes of a window assembly or fits into the window well of an existing window. Alternatively, one or both panes may be coated with the thin film. The use of such coating may reduce infrared transmission while still maintaining high transparency with respect to the visible range of light. For example, the average transmittance of the visible light range (i.e., 400-730 nm) may be greater than 90% transparency while maintaining an average reflectance of solar infrared spectrum (i.e., 750-2500 nm) of greater than 70%. It should be noted that achieving other average transmittance and reflectance percentage rates at particular range of wavelengths may be desirous, e.g., any percentage between 0 and 100%.

Unless otherwise specified, the term visible light spectrum refers to the spectrum of light that is detectable by the human eye. For the purposes of this document, the visible spectrum is from about 400 to 730 nanometers (nm) in wavelength. Additionally, unless otherwise specified, the term infrared spectrum refers to the spectrum of light that is longer than those of visible light. Unless otherwise stated, the infrared region will refer to two discrete regions. First, the solar infrared from ˜750-2500 nm and the thermal infrared at wavelengths 2500-50,000 nm. The infrared control coating described herein may control one or both of these regions by varying the materials choices, thickness, and deposition technique.

FIG. 1illustrates an example of an infrared-control coated thin film device100. As illustrated, the infrared-control coated thin film device100includes a substrate102, a first layer104, a second layer106, and a third layer108, and a fourth layer110. In other embodiments, more or less layers may be present.

The substrate102is a transparent thin foil upon which other layers are deposited. In an embodiment, these layers are inorganic dielectric layers. The substrate102may be flexible or rigid. For example, the substrate102may be a material with a relatively low melting point compared to glass. In an embodiment, the substrate102is one of polyethylene terephthalate (“PET”), polyethylene napthalate (PEN), polycarbonate, transparent polymides, etc. In other embodiments, the substrate102may be a transparent organic polymer or a transparent inorganic polymer. Still in other embodiments, the substrate102is a ceramic or glass.

One or more layers of materials may be deposited onto the substrate102. Deposition of infrared-control layers will alter the transmittance and reflectance properties of the resulting infrared-control coated thin film device. Transmittance and reflectance properties are controlled through controlling layer material type, layer thickness, and layer quality.

Materials that may be deposited on a substrate include any transparent conductive oxide. Example transparent conductive oxides include gallium doped zinc oxide (“GZO”), indium tin oxide (“ITO”), Other materials include dielectric layers. Example dielectric materials are silicon dioxide (“SiO2”), titanium dioxide (“TiO2”), Alumina (“Al2O3”), and zinc oxide (“ZnO”). Other materials such as metals, may be used including silver (Ag) and gold (Au).

Each layer may be of a different material. Additionally, the same material may be used for multiple layers. For example, in one embodiment, the first layer104is GZO, the second layer106is SiO2, the third layer108is TiO2, and the fourth layer110is SiO2. In another embodiment, there are more than four layers deposited onto a substrate102. For example, a device may include layers of material in the following order: GZO, SiO2, TiO2, SiO2, TiO2, and SiO2. Layers may also include alloys of materials. Mixing materials together may help achieve a refractive index that is not easily achieved with a pure material.

Layer thickness may vary. Additionally, each layer may be of varying thickness relative to other layers. As illustrated, first layer104is thinner than third layer108, which is thinner than second layer106, which is thinner than forth layer110. It will be appreciated that theFIG. 1is not intended to be a to-scale illustration. In other embodiments, each layer is roughly the same size. In an embodiment, the first layer104, the second layer106, the third layer108, and the fourth layer110may have a thickness that ranges from 40 nm to 400 nano-meters.

Layer quality may be controlled by controlling process parameters during deposition of the material. Process parameters include temperature and pressure of a process chamber, and ion energy of plasma. For example, ion energy may be controlled during deposition processes such as sputtering deposition or microwave-enhanced chemical vapor deposition. Controlling the energy of the ions allows a layer, such as first layer104, to be deposited without or with very few interstitial voids while allowing proper film growth. This occurs because the energy of the ions affects the energy of deposition material as it strikes the substrate102. Material striking a substrate102with too high energy may disrupt the structure of material previously deposited onto the substrate102, thereby creating void spaces in the layer. Material having too low of energy may fail to form proper lattice structures. This will affect the properties of the deposited layer and ultimately the transmittance and reflectance properties of the device itself. One way to control ion material is through pulsed-chemical vapor deposition, which is discussed in more detail with reference toFIG. 7, below.

The device100will have certain reflectance and transmittance properties that are affected by the quality and materials of layers, such as first layer104, second layer106, third layer108, and fourth layer110. Using the technology described herein, embodiments of infrared-control coated thin film devices have been created having particularly advantageous transmittance and reflectance properties.

For the purpose of this discussion, and particularly with reference toFIGS. 2 through 5, the percent reflectance is defined as the percentage of light at a particular wavelength that is reflected from the thin film device.

Certain layers in the infrared control coating may be deposited using pulsed-energy controlled microwave plasma enhanced chemical vapor deposition. In an embodiment, the film is grown from liquid precursors with substantial vapor pressure such as hexamethyldisiloxane (HMDSO), diethyl zinc (DEZ), trimethyl aluminum (TMA), etc. and gases such as argon or oxygen. The liquid precursors and oxygen are fed into a deposition zone to achieve a total pressure from 10-400 mTorr. A plasma is generated with a linear microwave source which can partially dissociate the precursors enhancing their chemical reactivity and facilitating film growth on the substrate. The film growth may be further aided by increasing the temperature of the substrate.

Average transmittance and reflectance are described with reference to particular ranges of the electromagnetic spectrum.

In an embodiment of the infrared-control coated thin film device, the average transmittance of light in the range of about 400 to 730 nm is greater than 90% while maintaining an average reflectance of light from 700 nm to 2500 nm of greater than 48%. In another embodiment, the average transmittance is greater 90% while the reflectance is greater than 50%. In another embodiment, the average transmittance is greater than 95% while the reflectance is greater than 55%.

FIGS. 2 through 5are graphical representations of the modeled reflectance and transmittance properties of dielectric thin film devices that may be created using the methods described herein.FIG. 2is a graph200of the modeled reflectance and transmittance for a dielectric thin film device with PET as the substrate, GZO as a first layer, SiO2 as a second layer, TiO2 as a third layer, and SiO2 as a fourth layer. The graph200includes a reflectance line202and a transmittance line204. The visible spectrum206is from about 400 nm to about 730 nm. The infrared spectrum208illustrated on graph200is from about 750 to about 2500 nm. As illustrated, the average transmittance in the visible light range is about 92.12%. Further, the average reflectance in the infrared spectrum is about 50.52%.

Table 1 is a table of the reflectance and transmittance used to generate graph200.

FIG. 3is a graph300of the reflectance and transmittance for a dielectric thin film device with PET as the substrate, SiO2 as a first layer at a thickness of 360.45 nm, TiO2 as a second layer at 106.14 nm, SiO2 as a third layer at a thickness of 168.89 nm, TiO2 as a fourth layer at a thickness of 91.85 nm, and SiO2 as a fifth layer at a thickness of 72.12 nm. The graph300includes a reflectance line302and a transmittance line304. The visible spectrum306is from about 400 nm to about 730 nm. The infrared spectrum308is illustrated on graph300from about 750 to about 2500 nm. As illustrated, the average transmittance in the visible light range is about 95.46%. Further, the average reflectance in the infrared spectrum is about 52.31%.

Table 2 is a table of the reflectance and transmittance used to generate graph300.

FIG. 4is a graph400of the reflectance and transmittance for a dielectric thin film device with PET as the substrate, ZnO as a first layer at a thickness of 48.86 nm, Ag as a second layer at a thickness of 9 nm, and ZnO as a third layer at a thickness of 44.08 nm. The graph300includes a reflectance line402and a transmittance line404. The visible spectrum406is from about 400 nm to about 730 nm. The infrared spectrum408is illustrated on graph400from about 750 to about 2500 nm. As illustrated, the average transmittance in the visible light range is about 95.62%. Further, the average reflectance in the infrared spectrum is about 61.75%.

Table 3 is a table of the reflectance and transmittance used to generate graph400.

FIG. 5is a graph500of the reflectance and transmittance for a dielectric thin film device with PET as the substrate, ITO as a first layer at a thickness of 130 nm, Al2O3 as a second layer at a thickness of 142.63 nm, TiO2 as a third layer at a thickness of 99.37 nm, Al2O3 as a fourth layer at a thickness of 144.67 nm, TiO2 as a fifth layer at a thickness of 97.42 nm, Al2O3 as a sixth layer at a thickness of 146.48 nm, TiO2 as a seventh layer at a thickness of 90.39, and Al2O3 as an eight layer at a thickness of 34.13. The graph500includes a reflectance line502and a transmittance line504. The visible spectrum506is from about 380 nm to about 700 nm. The infrared spectrum508is illustrated on graph400from about 700 to about 2500 nm. As illustrated, the average transmittance in the visible light range is about 86.26%. Further, the average reflectance in the infrared spectrum is about 27.12%.

Table 4 is a table of the reflectance and transmittance used to generate graph500.

Furthermore, using the technology described herein, it is anticipated that embodiments of infrared-control coated thin film devices can be created that will have even more advantageous transmittance and reflectance properties. For example, in an embodiment, an infrared-control coated thin film device will have greater than 70% visible light transmittance while maintaining greater than 70% reflectance. In another embodiment, an infrared-control coated thin film device may have greater than 75% visible light transmittance while maintaining greater than 75% reflectance. In another embodiment, an infrared-control coated thin film device may have greater than 80% visible light transmittance while maintaining greater than 80% reflectance. In another embodiment, an infrared-control coated thin film device may have greater than 85% visible light transmittance while maintaining greater than 85% reflectance. In another embodiment, an infrared-control coated thin film device may have greater than 90% visible light transmittance while maintaining greater than 90% reflectance. In another embodiment, an infrared-control coated thin film device may have greater than 95% visible light transmittance while maintaining greater than 95% reflectance. In other embodiments, transparency and reflectance need not be equal. For example, an infrared-control coated thin film device may have greater than 85% visible light transmittance while maintaining greater than 55% reflectance.

FIG. 6illustrates a roll-to-roll system600for depositing one or more infrared controlling layers on a substrate. A roll-to-roll system allows the manufacture of multiple devices in a continuous or semi-continuous process. A roll-to-roll system is so named for having a web (e.g., a PET substrate) translate (i.e., move) from a starting roll, through a system, to another starting roll. During translation, one or more processes are performed on the web. At the end of the system, the web is wound or cut into individual devices. This allows for, in certain processes, a faster manufacturing time.

The system600causes translation of the web602housed on a unwind spool604. Process chamber606deposits one or more infrared-controlling layers on to the web602to form a post-process web608. The post-process web608is wound onto a wind spool610.

Translation of the web through the system600may be accomplished in various ways. A guide track or other means may be used to mechanically support the translation of the web602through system600. As illustrated spools604and606have mandrels612on which a web may be spooled. For example, a fully spooled mandrel may have 20″ outside diameter and a 6″ core, and be 1.2 meters wide. Various idler rollers614may guide the web602and the post process web608. Idler rollers may be designed for removal for periodic cleaning. In embodiments, the idler roller surface roughness may be 8 micro-inch rms. Idler rollers may spin freely, and they may have low rotational inertia. Idler rollers may have active sensors to indicate positive motion.

The web602may translate through the system600at specified rate. In an embodiment, for example, the system600at a rate of 1 to 48 inches per minute. This speed may be set to be constant during processing or may vary as needed. Acceleration and deceleration of spools604and610may be controlled, which may help prevent slack in the spool. Tension of the web602, may be set at 10-50 lbf for a 1 meter wide device or substrate.

Process chamber606is a chamber where one or more manufacturing techniques are used to deposit an infrared-control thin film layers. Processes in include physical vapor deposition, chemical vapor deposition, ion beam assisted evaporation, pulsed laser deposition, sputter deposition, and sol-gel processes.

In an embodiment, process chamber606includes a pulsed-energy microwave chemical vapor deposition process to form at least one layer, such as one or more infrared-controlling layers. In a pulsed-energy microwave chemical vapor deposition process, microwave energy is pulsed to ignite and maintain a plasma. It is believed that pulsing the microwave allows for the control of the rate of production of ions, the energy of ions, and the rate the ions strike a substrate or web. For certain pulse frequencies, this increases the deposition rate of material on a substrate at a given temperature while maintaining the quality of the deposited layer. Accordingly, lower temperatures may be used to achieve the same deposition rate. For example, the temperature of substrate may be kept at or below 250° C., 240° C., 230° C., 220° C., 210° C., or 200° C. during deposition, which allows for the use of substrates with lower melting points. Additionally, the rate of deposition may occur at a rate of greater than 50 angstroms per second, 60 angstroms per second, 70 angstroms per second, 80 angstroms per second, 90 angstroms per second, and 100 angstroms per second.

Though system600depicts only one process chamber, other embodiments may have more than one process chamber to deposit one or more infrared-control coated devices onto a web. Still, other embodiments include other process systems to further treat a web. For example, a first process chamber may use pulsed energy microwave plasma enhanced chemical vapor deposition. A second process chamber may use sputtering deposition. The sputtering chamber may deposit materials such as ITO.

Finished infrared-control coated devices may then be cut from the web by any suitable means. In alternative embodiments, a mechanical, hydraulic, or pneumatic press is employed. In such embodiments, formation of the post-process web608may occur in a semi-batch manner. A wind module610receives the post-process web608. Wind module has a mandrel612designed to receive the post-process web608.

FIG. 7is an embodiment of a microwave plasma enhanced chemical vapor deposition chamber700. As illustrated,FIG. 7includes a process chamber702defined by process chamber walls704, an inlet gas line706, an outlet gas line708, a plasma sheath710, a substrate712, a microwave wave guide714, and a microwave generator716. Temperature is controlled by a temperature control element718.

The process chamber702is a chamber defined by chamber walls704. The process chamber is generally configured to maintain an internal pressure. This pressure is determined in part by the inflow of gases from inlet gas line706and outlet gas line708. The pressure and temperature in the process chamber702affects the material deposited on the substrate712.

In an embodiment, non-reactive gases such as helium or argon flow in through inlet gas line706. Additionally, a source gas, such as hexamethyldisiloxane (HMDSO), diethyl zinc (DEZ), trimethyl aluminum (TMA), etc., are pumped into the chamber through the inlet gas line706. Gas exits the system from outlet gas line708. Process conditions in process chamber702vary. In an embodiment, the process pressure ranges from 100-220 mTorr. In an embodiment, HMDSO and O2 are pumped into the chamber708at a ratio of HMDSO to O2 ranging from 10-80.

Ions produced in the plasma sheath710have an energy distribution. The energy distribution of the produced ions is dependent on, inter alia, the microwave frequency and pulse produced by microwave generator716. Some of the source gas and/or its reactants will be deposited onto a substrate712. In an embodiment, the source gas reacts with one or more other process gases and the resulting compound deposits onto the substrate712. This reaction may occur at the surface of the substrate712, above the substrate712, and/or after material has been deposited on the substrate712.

Deposited material will form structures, and those structures depend on the kinetic energy of ions created in the plasma sheath710. For example, a layer of deposited material may be present on the substrate712. The deposited material, given certain process conditions, will form a lattice or crystal structure. A lattice structure occurs when the deposited material is arranged in a substantially ordered manner. In other process conditions, however, a lattice structure will not form. Process conditions include the presences of impurities, the kinetic energy of the source gas at the time of colliding with substrate712, and any other mechanisms that may control the transfer of kinetic energy of the deposited material. In embodiments, one such mechanism is to control the energy of ions through the use of the microwave generator712.

A plasma710is ignited using microwave energy. The microwave wave generator716may have a power controller. The microwaves may be directed at plasma sheath710through use of a microwave guide714. In an embodiment, the microwave generate will generate microwaves at a frequency of 2.54 GHz. In other embodiments, different microwave frequencies are used. The controller controls the power supplied to the microwave generator. In an embodiment, the microwave controller may pulse power to the microwave generator to form a pulsed waveform. In an embodiment, pulsing occurs at a rate of 100 Hz. In another embodiment, pulsing occurs at 10 Hz. Still in others, pulsing may occur at various cycles per second, including: 20 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz, 70 Hz, 80 Hz, 90 Hz, 110 Hz, 120 Hz, 130 Hz, 140 Hz, and 150 Hz. Indeed, the cycle speed of the microwave may vary over the course of a given deposition.

A heating element718may be used to heat the process chamber. The heating element718may generate heat through any means now known or later developed. Accordingly, may be one of conductive, convective, or radiative means.

FIG. 8is an embodiment of a method800for depositing infrared controlling layers on a substrate. Method800begins with select a substrate operation802. The substrate may be flexible or rigid. For example, the substrate may be a material with a relatively low melting point compared to glass. In an embodiment, the substrate is one of polyethylene terephthalate (“PET”), polyethylene napthalate (PEN), polycarbonate, or transparent polymides, etc. In other embodiments, the substrate may be a transparent organic polymer or a transparent inorganic polymer. Still in other embodiments, the substrate is a ceramic or glass.

The method800continues to select deposition material operation804. Selection of deposition material will determine the reflectance and transmittance properties of the infrared-control coated thin film device. In an embodiment, selection of deposition materials will determine the types of source gases that may be used.

The method the800continues to deposit material operation806. In an embodiment, pulsed microwave-energy chemical vapor deposition is used. In other embodiments, deposit material operation804occurs using at least one of physical vapor deposition, chemical vapor deposition, thermal evaporation, pulsed laser deposition, sputter deposition, and sol-gel processes. In an embodiment, one or more of these processes occurs in series.

For example, deposit in deposit material operation806, one or more layers may be deposited. For example, a first layer of SiO2 may be deposited using pulsed energy microwave plasma enhanced chemical vapor deposition. After the deposition of the SiO2, a layer of TiO2 may be deposited on the SiO2 layer. The TiO2 may be deposited using a variety of techniques listed above. In an embodiment, the TiO2 layer is deposited using microwave plasma enhanced chemical vapor deposition. The rate of pulsing of the microwave may be the same or different from the rate at which the microwave was pulsed during the deposition of the SiO2 layer.

FIGS. 9 through 16represents technology related to sputtering deposition that may be used to create one or more layers of an infrared-control coated thin film device.

FIG. 9represents prior art of a planar sputtering cathode system900. Planar sputtering cathode system900includes a target902, a cathode904, a plasma sheath906, a substrate908, deposited material910, a sputtered species912, ions914, and process gas particles916.

In a planar sputtering cathode system900, a target902may have a magnetic field applied to it. This magnetic field helps contain a plasma sheath906to the surface of a target902or near the surface of target902. The magnetic field may confine electrons and secondary electrons to on and/or near the surface of a target. In an embodiment, the characteristics of the magnetic field affect the path of the electrons that travel around the surface of a target902. The target902may be any material suitable for sputtering.

A cathode904has a voltage applied to it. In embodiments, a DC current is applied to a cathode904. This DC current, which may create a 300V energy potential between the cathode904and the substrate908, may be applied in order to ignite the plasma and generate ions914. Some electrons918produced within the plasma sheath906have sufficient energy to meet the first ionization potential of the process gas particle916. Consequently, some process gas particles916become positive ions914.

Ions914produced in the plasma sheath906have an energy distribution. The energy distribution of the produced ions914is dependent on, inter alia, the current applied to the cathode904, the waveform of that current, and the process gas used in the system.

Positive ions914accelerate toward a negatively charged cathode904. The positive ions may collide with a target902and cause a sputtered species912to be ejected. Some of the sputtered species912will then be deposited onto a substrate908. As such, sputtered species912may be the same material as both the target902and the deposited material910. In other embodiments, the target material reacts with one or more process gases and the resulting compound deposits onto the substrate908. This reaction may occur at the surface of the target902, during the travel of sputtered species912, and/or after material has been deposited on the substrate to form deposited material910.

Deposited material910will form structures, and those structures depend on the kinetic energy of incoming sputtered species912. For example, a layer of deposited material910may be present on the substrate908. The deposited material910, given certain process conditions, will form a lattice or crystal structure. A lattice structure occurs when the deposited material910is arranged in a substantially ordered manner. In other process conditions, however, a lattice structure will fail to form. Process conditions include the presences of impurities, the kinetic energy of the sputtered species912at the time of colliding with deposited material910, and any other mechanisms that may control the transfer of kinetic energy to the deposited material910. In embodiments, one such mechanism is to control the energy of ions914. The relationship between kinetic energy and lattice structure is described more fully with reference toFIG. 10.

In general, the energy of sputtered species912is directly proportional to the kinetic energy of the ions914. For example, some ions914collide with the target902and transfer energy to the target902. As a result of this collision, some material of the target902is ejected and becomes a sputtered species912. Thus, high-energy ions914striking a target902will cause sputtered species912to have a greater kinetic than low-energy ions914. Additionally, upon striking the substrate908, the sputtered species912transfers kinetic energy to the previously deposited material910.

Another way ions914may affect the kinetic energy transferred to deposited material910is through ion914bombardment of the deposited material910. For example, in instances where the polarity of the cathode is reversed, the positive ions914may accelerate toward a negatively charged substrate908. In another embodiment, the substrate908does not hold a charge and the positive ions914accelerate toward a negatively charged area near a substrate908. Ions914with a high kinetic energy that collide with deposited material910will transfer more kinetic energy than ions914with a lower kinetic energy. Furthermore, the more ions914that bombard deposited material910, the more kinetic energy will transfer to the deposited material910. Thus, the rate of ion914bombardment affects the kinetic energy transferred to deposited material910.

With respect toFIG. 10,FIG. 10illustrates a thin film1000. In the embodiment shown, a substrate1002is illustrated with a thin film of deposited material1004. Thin films with interstitial voids are known in the art. The deposited thin film1000is illustrated as having a substrate1002, a deposited material1004, interstitial voids1006, and a sputtered species1008.

For certain thin films, it may be desirous to remove or limit the number of interstitial voids1006that may form during deposition. For example, interstitial voids increase the electrical resistivity of thin films for certain materials. Controlling the transfer of kinetic energy to deposited material1004may limit the number of interstitial voids1006that form during deposition, and thus reduce the electrical resistivity of the thin film.

For certain deposited materials1004, interstitial voids1006occur when a target material fails to have sufficient kinetic energy to meet or overcome the Schwoebel-Ehrlich barrier. Failure to meet the Schwoebel-Ehrlich barrier causes deposited material1004to form sloping regions1010. Sloping regions1010tend to cause interstitial voids1006. On the other hand, deposited material1004that has sufficient energy to overcome the Schwoebel-Ehrlich barrier may form a surface with a high surface symmetry. That is, the deposited material1004will form less sloping regions and arrange more evenly across the surface of the substrate1002. As such, transfer of kinetic energy to a deposited material1004may allow the deposited material1004to have a sufficient energy to overcome the Schwoebel-Ehrlich barrier.

Additionally, it may also be desirous to limit the amount of kinetic energy transferred because too much kinetic energy transfer may damage the fidelity of the deposited material's1004lattice structure. Damaging the lattice structure may also increase the electrical resistivity of a thin film.

Controlling the transfer of kinetic energy may occur by controlling the kinetic energy of incoming sputtered species1008. Controlling the transfer of energy may also occur through controlling ion kinetic energy and the rate of ion bombardment. Energy transfer to a deposited material is discussed further with reference toFIG. 9.

As such, it may be desirable to have an energy waveform applied to a cathode that can create ions at an appropriate rate and an appropriate energy for generating thin films with a targeted electrical resistance. This waveform will be referred to as a finely tuned waveform.

With reference toFIGS. 11 and 12,FIG. 11illustrates the prior art of an RF waveform super positioned on a pulsed DC waveform1100.FIG. 12, which is not prior art, illustrates a composite waveform1200that combines RF super positioned on pulsed-DC with a reverse voltage limiting threshold. Waveform1100and composite waveform1200have a pulsed-DC waveform1102and an RF waveform1104. Composite waveform1200may be applied to a cathode of a sputtering deposition process in order to adjust the energy of the plasma.

Additionally the pulsed-DC waveform1102includes a plasma ignition portion1106, a steady-state portion1108, a reverse DC voltage portion1110, and a pulsed-DC termination point1114.

In an embodiment, the application of waveform1100or composite waveform1200to a cathode ignites a plasma in a sputtering deposition chamber. The plasma ignition occurs contemporaneous with a plasma ignition portion1106. In another embodiment, the application of an RF waveform1104causes a plasma to ignite.

In the waveform1100and composite waveform1200shown, a reverse DC voltage portion1110occurs after steady-state portion1108. When applied to a cathode, the reverse DC voltage portion1110changes the polarity of the cathode from negative to positive.

As shown, waveform1100and composite waveform1200have an RF waveform1104superimposed on the pulsed-DC waveform1102. An RF waveform has an RF initiation point1116, an amplitude1118, a frequency1120, and an RF application duration1122. As illustrated, the waveforms1100and1200have an RF power termination point1124.

In embodiments, an RF initiation point1116may occur at or near the same time as the plasma ignition portion1106. When the waveform1100or waveform1200is applied to a cathode, RF initiation point1116marks the initiation of the application of the RF waveform1104to a cathode of a sputtering deposition chamber. When applying RF waveform1104to a cathode, varying the frequency1120and the amplitude1118of the RF waveform1104will generate ions with certain energy distributions. Furthermore, the density of ions created in a plasma sheath is directly proportional to the frequency1120. For example, at 13.56 mhz an RF waveform1104may create ions at a faster rate than a lower frequency. Ion generation occurs during RF application duration1122until an RF power termination point1124. RF power termination point1124may occur sometime before a reverse DC voltage portion1110. Ensuring that the RF power termination point1124occurs before a reverse DC voltage portion1110may be accomplished by various analog and digital control techniques, or some combination of the two techniques.

Alternatively, RF is applied continuously until the final waveform cycle. In this embodiment, the RF is applied continuously through all stages of the pulsed-DC waveform1102.

A reverse DC voltage portion1110may occur by design or may be caused intrinsically by shutting off a DC power supply. When applied to a cathode, the reverse DC voltage portion1110reverses the polarity of the cathode from negative to positive. When this reversal occurs in a sputtering deposition chamber, the positive ions will accelerate toward the now negatively charged substrate (or a negatively charged area near the substrate). This depletes the ion density of the plasma sheath and substantially halts the deposition of sputtered species. In the prior art waveform1100, the kinetic energy of the ions striking the substrate is directly proportional to the magnitude of the reverse DC voltage portion1110.

In embodiments, it may be desirous to limit the magnitude of the reverse voltage. Composite waveform1200includes a reverse voltage threshold1212. This limits the magnitude of the reverse voltage limiting portion. Limiting the magnitude of the reverse voltage limits the kinetic energy of the ions accelerating toward the substrate during a reverse DC voltage portion1110.

Limiting the reverse voltage may be accomplished through electronic devices along with analog and digital controllers. In some embodiments where the target is non-metallic, a reverse voltage limiting may interfere with the RF waveform. As described in greater detail below, the systems and methods disclosed herein account for this and prevent interference with the RF waveform while still allowing the reverse DC voltage to be limited.

Application of the reverse voltage threshold1212may be depend on the specific sputtering environment. For example, in an embodiment where the process gas is Ar, and the deposition material is transparent conductive oxide (“TCO”), a reverse DC voltage portion1110may last for between 0.5 and 10 mircoseconds. In embodiments, the reverse DC voltage portion lasts for a microsecond. Additionally, a reverse voltage threshold1112may be set between 100 and 300 volts.

As shown, rest period1126is present in waveform1100and composite waveform1200. If applied to a cathode, rest period1126represents the time in which no pulsed-DC power is supplied to the cathode. The rest period1126is defined as the time between the termination of the application of a DC pulse and the next application of a DC pulse. A rest period may not be present or may be of a short or long duration relative to the DC pulse duration.

A cycle of a waveform1100or waveform1200is calculated by summing the time from the first application of power to the cathode until the end of a rest period1126.

FIG. 13illustrates the expected resistivity properties of thin films created when a waveform1100is applied to a cathode. The y-axis of the graph illustrates the minimum resistivity μOhm*cm. The x-axis represents the frequency at which the DC pulse would be applied to a cathode of a sputtering deposition chamber. Line1302illustrates the resistivity of a thin-film that may be produced by applying an embodiment waveform1100, i.e., an RF waveform superimposed on pulsed-DC waveform to a cathode of a sputtering deposition chamber.

Line1302may be understood as having three frequency ranges. In the first range, the minimum resistivity of the thin film decreases in a decreasing resistivity range1308. As illustrated, line1302illustrates the resistivity decreasing from ˜185 to ˜148 μOhm*cm over the decreasing resistivity range1308. This corresponds to a frequency of 0 to ˜100 kHz DC-pulsed. At a steady-state point1310the resistivity of the thin film no longer decreases. As illustrated, the steady-state point is ˜100 kHz. The steady-state point1310marks the start of a steady-state range1312. In a steady-state range1312, the resistivity of the produced thin-film does not vary substantially with varying pulsed-DC frequencies. As illustrated, line1302has a steady-state1312that corresponds to a frequency range from 100 kHz to ˜200 kHz. In some embodiments, at an inflection point1314the resistivity of the thin film begins to increase. As illustrated, the inflection point1314for line1302corresponds to a frequency of ˜200 kHz. After the inflection point1314, an increasing resistivity range1316may be present. In increasing resistivity range1316, the resistivity of the produced thin film increases as frequency of the pulsed-DC increases. As illustrated, line1302has an increasing resistivity range1316that corresponds to a frequency of ˜200 kHz to at least 300 kHz.

FIG. 14illustrates the expected resistivity properties of thin films created when a composite waveform1200is applied to a cathode. The y-axis of the graph illustrates the minimum resistivity μOhm*cm. The x-axis represents the frequency at which the DC pulse would be applied to a cathode of a sputtering deposition chamber. Line1404illustrates the resistivity of a thin-film that may be produced by applying an embodiment of a composite waveform1200, i.e., an RF waveform superimposed on pulsed-DC waveform combined with reverse voltage limiting. Additionally, line1406illustrates the resistivity of a thin-film produced that may be produced by applying an alternative embodiment of a composite waveform1200.

Line604may be understood as having two areas, a decreasing resistivity range1408and steady-state range1412. Additionally, line1406may be understood as having two areas, a decreasing resistivity range1414and a steady-state range1416. As illustrated, line1404has a decreasing resistivity range1412that is greater than the decreasing resistivity range1414of line1406. In embodiments, this may be because the composite waveform1200that produced the results illustrated by line1406has a lower reverse voltage threshold than the composite waveform1200that produced the results illustrated by line1404.

As illustrated, lines1404and lines1406have no increasing resistivity range. This may occur because the composite waveforms1200used to produce lines1404and1408have a reverse limiting voltage threshold. This reverse threshold may ensure that ions that strike the previously deposited material have a sufficiently low kinetic energy.

FIG. 15illustrates a method1500of applying an RF waveform super positioned on a pulsed DC waveform combined with reverse voltage threshold to a cathode of a sputtering deposition process. The method1500includes an apply a pulsed DC waveform to a cathode operation1502. The method1500also includes an apply an RF waveform to a cathode operation1504.

As illustrated, method1500begins with apply a pulsed DC waveform to a cathode operation1502. In other embodiments, the method1500begins with an apply an RF waveform to a cathode operation1504. Still in other embodiments, the operations1502and1504may occur at the same time.

FIG. 15Aillustrates the apply a pulsed DC waveform to a cathode operation1502. The applying a pulsed DC waveform operation1502includes an initiate plasma operation1502A, apply a controlled voltage operation1502B, a reverse the DC voltage operation1502C, a limit the reverse voltage operation1502D, and a terminate pulsed-DC operation1502E.

The apply a DC waveform to a cathode operation1502begins with an initiate plasma operation1502A. Initiate plasma operation1502A may result in a negative voltage spike for some period of time. For example, the spike lasts for between 0.5 to 10 microseconds in embodiments. In other embodiments, there is no spike, and an initiate plasma operation1502A merely marks the point at which a pulse DC waveform is first applied to a cathode.

The apply a DC waveform to a cathode operation next proceeds to an apply a controlled voltage operation1502B to a cathode operation. This operation results in a DC being applied for some time period at a substantially fixed voltage. For example, a DC waveform may have a controlled voltage operation1502B between −100V and −300V.

Next, operation1502proceeds to a reverse the DC voltage operation1502C. In an embodiment, reverse the DC voltage operation1502C causes the voltage to be reversed from negative to positive. As mentioned above, the reverse the DC voltage operation1502C may be an active operation as shown or may be a natural result of the termination of the operation1502B. In an embodiment where the original voltage was positive, the reverse the DC voltage operation1502C causes the voltage to be reversed from positive to negative. In an embodiment, the reverse DC voltage operation1502C causes the DC voltage to go to between +50 and +400V absent a limit the reverse voltage operation1502D described below.

A limit the reverse voltage operation1502D limits the degree to which the reverse the DC voltage operation1502C can reverse the voltage applied to the cathode. In embodiments, the limit the reverse voltage operation1502D causes the reverse voltage to be limited to one of the following voltages +50V, +60V, +70V, +80V, +90V, +100V, +110V, +120V, +130V, +140V, +150V, +160V, +170V, +180V, +190V, +200V, +210V, +220V, +230V, +240V, +250V, +260V, +270V, +280V, +290V, +300V, +310V, +320V, +330V, +340V, +350V, +360V, +370V, +380V, +390V, and +400V. A terminate pulsed-DC operation1502E ends the application of the reverse voltage to a cathode. This may occur naturally as a final result of terminating operation1502B.

The reverse voltage limiting operation1502D is presented here as a separate step, although the reader will recognize that the reverse voltage operation1502C, the limiting operation1502D and the DC pulse termination operation1502E may all occur at the same or substantially the same time and may be, in effect, a single operation. In an embodiment in which the reverse voltage is a transient effect caused by the termination of the DC pulse, the limiting operation1502D is achieved by the simultaneous activation of reverse voltage limiting electronics that prevent the reverse voltage from exceeding the set threshold.

In embodiments where the target is non-metallic, the timed activation of the electronics prevents interference with the applied RF waveform or other desired transient elements of the waveform, which would be detrimentally affected if the limiting electronics were active at all times. In an alternative embodiment, although difficult in practice using currently available technology, the entire waveform may be controlled by software so that the exact desired waveform is delivered at the chamber without the need to rely on inherent properties of the hardware to intrinsically create some or all of the waveform (e.g., the reverse voltage).

FIG. 15Billustrates an apply an RF waveform operation1504. In an embodiment, the apply an RF waveform operation1504includes a determine an RF frequency and amplitude operation1504A, an initiate an RF application1504B, an apply an RF operation1504C, and a terminate an RF application1504D.

Apply an RF waveform operation1504begins with a determine an RF frequency and amplitude operation1504A.

Next an initiate an RF application operation1504B initiates the application of an RF waveform to a cathode. The application of the RF waveform to a cathode continues through apply an RF waveform operation1504C. Apply an RF waveform operation1504C may last for a duration of the apply a controlled voltage operation1502B. Alternatively the apply the RF waveform operation1504C may last for the entire duration of all cycles of pulsed-DC waveform.

A terminate an RF application operation1504D stops the application of an RF waveform to a cathode. In embodiments, the terminate an RF application operation occurs before the limit the reverse voltage operation1502D.

FIG. 16illustrates a system to apply an RF and pulsed DC waveform combined with reverse voltage threshold to a cathode of a sputtering deposition process1600. As illustrated,FIG. 16includes a DC power supply1602, an RF power supply1604, a reverse voltage limiting device1606, and a control circuit1608. The DC power supply1602applies a pulsed-DC waveform1602to a cathode of a sputtering deposition chamber. The RF power supply1604applies an RF waveform1104to a cathode. A reverse voltage limiting device1606limits the reverse voltage of a pulsed-DC waveform1102. The reverse voltage limiting device1606may include any suitable signal modification circuits such as capacitors, inductors, selected low-pass or band-pass filters or other electronics as needed to achieve the desired responsiveness and voltage limiting for the particular application. Additionally, a control circuit1608controls the interaction and timing of the DC power supply1602, the RF power supply1604, and the activation of the reverse voltage limiting device1606. For example, the control circuit1608may ensure that the RF power supply1604turns off prior to the DC power supply1602applying a reverse DC voltage portion1110to a cathode of a sputtering process.

It will be clear that the systems and methods described herein are well adapted to attain the ends and advantages mentioned as well as those inherent therein. Those skilled in the art will recognize that the methods and systems within this specification may be implemented in many manners and as such is not to be limited by the foregoing exemplified embodiments and examples. In other words, functional elements being performed by a single or multiple components and individual functions can be distributed among different components. In this regard, any number of the features of the different embodiments described herein may be combined into one single embodiment and alternate embodiments having fewer than or more than all of the features herein described as possible.

While various embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the disclosed methods. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure.