Abstract:
A deposition system for alkali and alkaline earth metals may include a metal sputter target including cooling channels, a substrate holder configured to hold a substrate facing and parallel to the metal sputter target, and multiple power sources configured to apply energy to a plasma ignited between the substrate and the metal sputter target. The target may have a cover configured to fit over the target material, the cover may include a handle for automated removal and replacement of the cover within the deposition system, and a valve for providing access to the volume between the target material and the cover for pumping, purging or pressurizing the gas within the volume. Sputter gas may include noble gas with an atomic weight less than that of the metal target.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/417,108 filed Nov. 24, 2010, incorporated by reference in its entirety herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to deposition systems for alkali and alkaline earth metals, and more particularly to high throughput deposition systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Prior art alkali and alkaline earth metal deposition systems are known to have low throughput and lack ease of scalability for high throughput and large substrates. There is a need for alkali and alkaline earth metal deposition sources and systems that (1) can be adopted to different substrate formats, including circular, rectangular, etc., (2) may be scaled to accommodate any size of substrate and (3) allow for high throughput deposition—allowing for cost competitive manufacturing of devices such as thin film batteries and electrochromic windows. 
       SUMMARY OF THE INVENTION 
       [0004]    In general, embodiments of this invention provide high deposition rate sources and systems for deposition of alkali metals and alkaline earth metals which can be adapted to any chamber form factor and are scalable for any size of substrate. These systems may be configured with sputter targets with efficient cooling channels and an air tight, purgeable cover to protect the ambient sensitive targets prior to installation into a deposition chamber under an inert atmosphere. Furthermore, these systems may be configured to make use of: (1) lighter noble gases and/or a mixture of noble gases; and (2) single and multiple power sources, e.g., DC, pulsed DC, RF, RF-DC, pulsed DC-RF, pulsed DC-HF and/or other dual frequency power sources. Yet furthermore, these systems may be configured with a planar substrate parallel to a planar sputter target, the sputter target having a larger surface area (for cluster tool configurations) or larger width (for in-line configurations) than the substrate, thus providing a system which is capable of uniform deposition and scalable to accommodate any shape and size of planar substrate. The targets can also be a cylindrical or annular shape that rotates for high materials utilization applications. 
         [0005]    According to aspects of the invention, a deposition system for alkali/alkaline earth metals may comprise: a vacuum chamber; a metal sputter target within the vacuum chamber, the target comprising target material attached to a backing plate including cooling channels; a substrate holder within the vacuum chamber, the holder being configured to hold a substrate facing and parallel to the metal sputter target; and multiple power sources configured to apply energy to a plasma ignited between the substrate and the target material. The cooling channels may be round, rectangular or pyramidal in cross-section. Furthermore, lower temperature capable coolants may be used in the cooling channels to maximize the cooling efficiency, allowing the system to handle high power, high deposition rate and high throughput processing. The single and multiple power sources may include DC, pulsed DC, RF, RF-DC, pulsed DC-RF, pulsed DC-HF and/or other dual frequency power sources. The multiple frequency sources can allow de-convolution of the control of plasma characteristics (self bias, plasma density, ion and electron energies, etc.), so that the higher yielding conditions are reached at a lower power than is otherwise possible with a single power source. For example, a lower frequency power supply can be used to control self bias at the same time a higher frequency supply is used to control ion density. Furthermore, a cover may be used to protect the target material from ambient gases, the cover being removable in the vacuum chamber, the removal being either manual or automated. 
         [0006]    According to further aspects of the invention, a method of sputter depositing alkali and alkaline earth metals on a substrate may comprise: igniting a plasma between the substrate and a sputter target within a vacuum chamber, wherein the plasma includes noble gas species and the sputter target comprises target material attached to a backing plate including cooling channels; adding energy to the plasma by multiple power sources, wherein the multiple power sources include a first power source for controlling target material self bias, and a second power source for controlling ion density in the plasma; sputtering target material from the sputter target and depositing the sputtered target material on the substrate, wherein the sputtering is by noble gas species from the plasma and wherein the noble gas species include ions with an atomic weight less than the atomic weight of the target material; and during the sputtering, cooling the sputter target by pumping coolant through the cooling channels in the backing plate. Furthermore, the sputter target may be provided with a cover over the target material, the cover being sealed to the sputter target for protection of the target material from ambient gases, the method including installing the sputter target with the cover in the vacuum chamber and removing the cover from the sputter target in the vacuum chamber. The removal of the cover may be either manual or automated, and when automated may be done under vacuum. The adding energy may include one or more of adding RF-DC, pulsed DC-RF, pulsed DC-HF and/or other dual frequency power sources. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    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: 
           [0008]      FIG. 1  is a representation of a wafer based processing tool with an alkali/alkaline earth metal deposition chamber, according to some embodiments of the present invention; 
           [0009]      FIGS. 2A and 2B  show perspective and cross-sectional views, respectively, of an alkali/alkaline earth metal sputter target with a sealed cover for a wafer-based processing tool, according to some embodiments of the present invention; 
           [0010]      FIG. 3  is a representation of an in-line alkali/alkaline earth metal deposition tool, according to some embodiments of the present invention; 
           [0011]      FIG. 4  is a representation of a fabrication system with multiple in-line tools, including an alkali/alkaline earth deposition tool, according to some embodiments of the present invention; 
           [0012]      FIG. 5  is a schematic block diagram of an example combinatorial plasma deposition chamber, according to some embodiments of the present invention; 
           [0013]      FIG. 6  is a first cut-away perspective view of an alkali/alkaline earth metal sputter target with a sealed cover for an in-line processing tool, according to some embodiments of the present invention; 
           [0014]      FIG. 7  is a second cut-away perspective view of the alkali/alkaline earth metal sputter target of  FIG. 6 ; 
           [0015]      FIG. 8  is a cross-section through the metal target and backing plate of the alkali (alkaline earth) metal sputter target of  FIGS. 6 and 7  showing a backing plate with rectangular cooling channels, according to some embodiments of the present invention; and 
           [0016]      FIG. 9  is a cross-section through the metal target and backing plate of the alkali metal sputter target of  FIGS. 6 and 7  showing a backing plate with pyramidal cooling channels, according to some embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Embodiments of 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. 
         [0018]    Sputtering of alkali metals (such as Li, Na, K and Rb), and alkaline earth metals (such as Mg, Ca and Sr) are quite challenging because of their sensitivity to air ambient and due to their low melting temperatures, particularly those metals with lower atomic weight, such as Li, Na and Mg. The challenges come from (1) fabrication and shipment of the sputtering targets where the integrity of the materials must be maintained, (2) installation of the sputtering sources where the reaction with ambient air must be kept to a minimum, and (3) control of the sputtering process, which must keep the metal below its melting temperature to ensure a stable process. All of these factors can limit the sputtering characteristics especially when high deposition rates are required to attain a high throughput manufacturing process. 
         [0019]    In addition, the lower atomic weight elements such as Li and Na can suffer from irregular sputtering behaviors when typical noble gases of higher atomic weight, like Ar, are used as the sputtering agent. This irregular sputtering behavior may be “splattering” where the sputtering is not atom-by-atom, but “clusters of atoms” by “clusters of atoms.” Such a situation will adversely affect the deposition uniformity and surface microstructure. To minimize the splattering effect, a lower deposition rate process may be used; however, this leads to adverse manufacturing conditions for throughput. 
         [0020]    Some of the concepts of the present invention which address these issues are: (1) use of lighter noble gases such as He and Ne and/or mixture of noble gases such as: He/Ne, He/Ar and Ne/Ar and (2) single and multiple power sources, which may include DC (direct current), pulsed DC, RF (radio frequency), RF-DC, pulsed DC-RF, pulsed DC-HF and/or other dual frequency power sources. The lighter noble gases will lead to more balanced momentum transfer to produce atom-by-atom sputtering while the mixtures may lead to improved sputtering rate. For example, consider the He/Ar mixture for which: (1) the low atomic weight of He reduces the probability of “cluster sputtering” compared with heavier noble gases, (2) He undergoes Penning ionization, providing a high density of sputtering cations, (3) He is relatively inexpensive, particularly when compared with Ne, and (4) Ar increases the sputtering rate. The multiple power sources can lead to better control of sputtering environment (plasma density, sheet voltages, energetics of the plasma species, etc.) to enhance the sputtering behavior and deposition rates. The multiple frequency sources can allow de-convolution of the control of plasma characteristics (self bias, plasma density, ion and electron energies, etc.), so that the higher yielding conditions are reached at lower power than otherwise possible with single power source. For example, a lower frequency power supply can be used to control self bias at the same time a higher frequency supply is used to control ion density. Note that these multiple frequency power sources may both be coupled to the sputter target or the first to the sputter target and the second to the substrate, for example, as described in more detail below. Furthermore, sputtering targets protected from degradation due to exposure to the air and with improved cooling permit high deposition rates of alkali and alkaline earth metals. 
         [0021]      FIG. 1  is a representation of a cluster tool  400  for high throughput sputter deposition of alkali metals and alkaline earth metals on large area substrates, according to some embodiments of the present invention. An example of a suitable cluster tool is Applied Material&#39;s Endura™. The example shown in  FIG. 1  has a standard mechanical interface (SMIF)  410  to a cluster tool equipped with a reactive plasma clean (RPC) and/or sputter pre-clean (PC) chamber  420  and process chambers C 1 -C 4  ( 431 ,  432 ,  433 , and  434 , respectively), which may be utilized in the process steps described in more detail below. A glovebox  440  is also attached to the cluster tool. The glovebox can store substrates in an inert environment (for example, under a noble gas such as He, Ne or Ar), which is useful after alkali metal/alkaline earth metal deposition. The ante chamber  445  to the glovebox is a gas exchange chamber (inert gas to air and vice versa) which allows substrates to be transferred in and out of the glovebox without contaminating the inert environment in the glovebox. 
         [0022]      FIGS. 2A and 2B  show a cluster tool sputter target design for wafer processing, suitable for high throughput processing of 200 mm wafers, for example—the cluster tool sputter target design is suitable for a wide range of wafer sizes.  FIG. 2B  is a cross-sectional representation along a diameter of the target, through the valve  340 . The design consists of a cover  310  that can be placed on top of the sputtering target  330 , with an o-ring seal in between. In addition, the cover consists of valve(s)  340  through which the covered area can be pumped, purged and or pressurized with inert gas for transportation to and from fabrication and manufacturing sites under inert ambient. The covered target can also be placed under additional leak tight packaging, again under inert gas, for further protection of the reactive target material  330 . The cover  310  is to be removed during the installation steps. A handle  315  is used for placement and removal of the cover. The design of the cover is such that the target can be installed without removing the cover, so that the exposure of the actual target material  330  to the air ambient is minimized during the installation. The removal of the cover can be automated where the chamber is closed with the cover in place, then under vacuum, the cover is removed to a non sputtering zone adjacent to the target area. Note that, if necessary, the process chamber may be enlarged/elongated to allow cover removal within the chamber. In a manual removal of the cover, standard precautionary steps can be taken to minimize exposure of the target to the ambient. However, experience on an R&amp;D inline system indicates that these standard precautionary measures may not be necessary as the cover allows very minimal exposure to the ambient. Furthermore, a sputter clean may be sufficient to clean away any surface reacted layers. The sputter target backing plate  320  may be in contact with a reservoir of coolant for enabling efficient removal of heat from the target material  330 . 
         [0023]    The chambers C 1 -C 4  can be configured for process steps for manufacturing thin film battery devices which may include: deposition of a cathode layer (e.g. LiCoO 2  by RF sputtering); deposition of an electrolyte layer (e.g. Li 3 PO 4  by RF sputtering in N 2 ); and deposition of an alkali metal or alkaline earth metal. See U.S. Patent Application Publication No. 2009/0148764 for examples of fabrication process flows for thin film batteries. Furthermore, the chambers C 1 -C 4  can be configured for process steps for manufacturing electrochromic windows. See U.S. Patent Application Publication No. 2009/0304912 for examples of fabrication process flows for electrochromic windows. 
         [0024]      FIG. 3  is a representation of an in-line tool for high throughput sputter deposition of alkali and alkaline earth metals on large area substrates, according to some embodiments of the present invention. A substrate holder  1  containing a large area substrate  2  (the substrate holder is shown partially cut-away so that the substrate can be seen) is mounted on a track  3 , or equivalent device, for moving the holder and substrate through a sputter deposition tool  4 , as indicated. The in-line tool may be configured for substrates oriented either horizontally or vertically. For ease of illustration, only one processing tool is shown; however, multiple processing tools may be used on the same in-line processing system. See  FIG. 4 . Suitable in-line platforms for processing tool  4  are Applied Material&#39;s Aton™ and New Aristo™. 
         [0025]      FIG. 4  shows a representation of a fabrication system  10  with multiple in-line tools  4 ,  20 ,  30 ,  40 , etc., including an alkali deposition tool  4 , according to some embodiments of the present invention. The in-line tools may include pre- and post-conditioning chambers. For example, tool  20  may be a pump down chamber for establishing a vacuum prior to the substrate moving through a vacuum airlock  15  into alkali metal deposition tool  4 . Furthermore, the in-line tools may include process tools, such as deposition tools and patterning tools, for manufacturing devices such as thin film batteries and electrochromic windows. Some or all of these tools may be vacuum tools separated by vacuum airlocks  15 . Note that the order of process tools and specific process tools in the process line will be determined by the particular fabrication method being used. 
         [0026]      FIG. 5  shows an example of a combinatorial plasma deposition chamber for deposition of an alkali metal or alkaline earth metal according to some embodiments of the invention. The system includes a chamber  100  housing a sputter target  104  and the substrate holder  102  for holding a substrate. Pumping system  106  is connected to chamber  100  for controlling a pressure therein, and process gases  108  represents sources of gases supplied to chamber  100  used in the deposition process. According to aspects of the invention, combinatorial plasma is achieved by coupling appropriate plasma power sources  110  and  112  to both the substrate (in the substrate holder  102 ) and target  104 . An additional power source  114  may also be applied to the target  104 , or the substrate or be used for transferring energy directly to the plasma, depending on the type of plasma deposition technique. Furthermore, a microwave generator  116  may provide microwave energy to a plasma within the chamber through the antenna  118 . Microwave energy may be provided to the plasma in many other ways, as is known to those skilled in the art. The schematic is not meant to define orientation of the chamber with respect to gravity, i.e., the chamber may be oriented such that sputtering may be down, up or sideways, for example. 
         [0027]    Depending on the type of plasma deposition technique used, substrate power source  110  can be a DC source, a pulsed DC (pDC) source, a RF source, etc. Target power source  112  can be DC, pDC, RF, etc., and any combination thereof. Additional power source  114  can be pDC, RF, microwave, a remote plasma source, etc. 
         [0028]    Although the above provides the range of possible power sources, some specific examples of combinations of power source to target  104  plus power source to substrate for alkali metal/alkaline earth metal deposition are: (1) DC, pDC or RF at the target  104  plus HF or microwave plasma enhancement; (2) DC, pDC or RF at the target plus HF/RF substrate bias; and (3) DC, pDC or RF at the target  104  plus HF or microwave plasma plus HF/RF substrate bias. The nomenclature HF/RF is used to indicate the potential need for power sources of two different frequencies, where the frequencies are sufficiently different to avoid any interference. Although, the frequencies of the RF at the target  104  and at the substrate may be the same providing they are locked in phase. Furthermore, the substrate itself can be biased to modulate the plasma-substrate interactions. In particular, multiple frequency sources can allow deconvolution of the control of plasma characteristics (self bias, plasma density, ion and electron energies, etc.), so that the high yielding conditions are reached at lower power than otherwise possible with single power source. 
         [0029]    Furthermore, some specific examples of combinations of power sources to target  104  are: (1) RF 1  at the target plus RF 2  at the target, where the frequencies of RF 1  and RF 2  are sufficiently different to avoid interference; (2) DC at the target plus RF at the target; and (3) pDC at the target plus RF at the target. As described above, multiple frequency sources can allow deconvolution of the control of plasma characteristics (self bias, plasma density, ion and electron energies, etc.), so that the high yielding conditions are reached at lower power than otherwise possible with a single power source. Furthermore, increased ion density in the plasma, due to a higher frequency power supply, may enhance atom-by-atom deposition. 
         [0030]    Furthermore, the planar substrate and target in  FIG. 5  are configured parallel to each other. This parallel configuration allows the deposition system to be scaled for any size of planar substrate while maintaining the same deposition characteristics. Note, as discussed above, that the size of the substrate and the target are roughly matched, with the target area (cluster tool) or width (in-line tool) being larger than that of the substrate so as to avoid target edge effects in the deposition uniformity on the substrates. 
         [0031]      FIGS. 6 and 7  show the linear sputtering target design for an inline system. As can be seen, the design consists of a cover  210  that can be placed on top of the sputtering target, making an o-ring seal. In addition, the cover consists of valve(s)  240  through which the covered area can be pumped, purged and or pressurized with inert gas for transportation to and from fabrication and manufacturing sites under inert ambient. The covered target can also be placed under additional leak tight packaging, again under inert gas, for further protection of the reactive target material  230 . The cover  210  is to be removed during the installation steps. A handle  215  is used for placement and removal of the cover. 
         [0032]    The design of the cover is such that the target can be installed without removing the cover, so that the exposure of the actual target material  230  to the air ambient is minimized during the installation. The removal of the cover can be automated where the chamber is closed with the cover in place, then under vacuum, the cover is removed to a non sputtering zone adjacent to the target area. In a manual removal of the cover, standard precautionary steps can be taken to minimize exposure of the target to the ambient. However, experience on an R&amp;D inline system indicates that these standard precautionary measures may not be necessary as the cover allows very minimal exposure to the ambient. Furthermore, a sputter clean may be sufficient to clean away any surface reacted layers. 
         [0033]    The sputter target backing plate  220  includes cooling channels  225  for enabling efficient removal of heat from the target material  230 , as described in more detail with reference to  FIGS. 8 &amp; 9 . A coolant is pumped into the target backing plate  220  through cooling conduits  227 , which connect to the cooling channels  225 . The cooling channels  225  and conduits  227 , along with a pump and cooling system (not shown in figure), are configured to form a cooling circuit through which coolant may be pumped. 
         [0034]      FIGS. 8 and 9  show enlarged views of the backing plate, onto which the target material is bonded. An important aspect of the design is in the cooling channel of the backing plate, where the surface area of the backing plate is increased to increase thermal conduction between the backing plate and the cooling medium. This increased thermal conduction should help lower the temperature of the target which will allow using higher sputtering power densities for higher sputtering and deposition rates. Additionally, the cooling medium can be maintained at a temperature below zero degrees Celsius by using, for example, glycol based compounds, and thereby further enhancing the thermal conductivity of the whole system and the robustness of the system against thermal constraints of deposition rate processes. 
         [0035]      FIG. 8  shows a cross-section through the metal target and backing plate of the alkali metal/alkaline earth metal sputter target of  FIGS. 6 and 7  showing a backing plate with rectangular cooling channels.  FIG. 9  shows a cross-section through the metal target and backing plate of the alkali metal/alkaline earth metal sputter target of  FIGS. 6 and 7  showing a backing plate with pyramidal cooling channels. These particular shapes for cooling channels are provided as examples; other cooling channel shapes may also be used to effect. Furthermore, these cooling channel configurations may also be utilized with the backing plate of  FIGS. 2A and 2B . 
         [0036]    A method of sputter depositing alkali and alkaline earth metals on a substrate may comprise: igniting a plasma between the substrate and a sputter target within a vacuum chamber, wherein the plasma includes noble gas species and the sputter target comprises target material attached to a backing plate including cooling channels; adding energy to the plasma by multiple power sources, wherein the multiple power sources include a first power source for controlling target material self bias, and a second power source for controlling ion density in the plasma; sputtering target material from the sputter target and depositing the sputtered target material on the substrate, wherein the sputtering is by noble gas species from the plasma and wherein the noble gas species include ions with an atomic weight less than the atomic weight of the target material; and during the sputtering, cooling the sputter target by pumping coolant through the cooling channels in the backing plate. Furthermore, the sputter target may be provided with a cover over the target material, the cover being sealed to the sputter target for protection of the target material from ambient gases, the method including installing the sputter target with the cover in the vacuum chamber and removing the cover from the sputter target in the vacuum chamber. The removal of the cover may be either manual or automated, and when automated may be done under vacuum. The adding energy may include one or more of adding RF-DC, pulsed DC-RF, pulsed DC-HF and/or other dual frequency power sources. 
         [0037]    Although the targets are described herein as planar targets, the targets can also be cylindrical or annular shaped targets that are rotated for high materials utilization—in either cluster tool or in-line configurations. 
         [0038]    Although the present invention has been particularly described with reference to certain 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.