Patent Publication Number: US-11651967-B2

Title: Non-atomic layer deposition (ALD) method of forming sidewall passivation layer during high aspect ratio carbon layer etch

Description:
RELATED APPLICATIONS 
     This continuation application claims the benefit of priority from U.S. Nonprovisional patent application Ser. No. 17/119,019, filed Dec. 11, 2020, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to the processing of substrates. In particular, it provides a novel method and process flow for forming a passivation layer on sidewall surfaces of an amorphous carbon layer (ACL) to avoid bowing during an ACL etch process. 
     As geometries in substrate processing continue to shrink, the technical challenges to forming structures on substrates via photolithography and etch techniques increase. As requirements for smaller geometry structures arose, a variety of techniques have been utilized for achieving suitable structures. Although reduced feature sizes are achieved, pattern performance problems have occurred in some conventional small geometry patterning and etch methods. 
     For example, photolithography techniques have been used to transfer patterns from a patterned layer to an organic mask layer, such as an amorphous carbon layer (ACL) film, underlying the patterned layer. ACL films are often used as a hard mask for patterning underlying layers using a variety of small geometry patterning methods. However, as feature sizes decrease, critical dimensions (“CDs”) become smaller and aspect ratios increase, leading to increasingly greater etch depths. Accordingly, high ion energy is often required to etch high-aspect ratio features (such as vias, contact holes and lines) in ACL films and underlying layers. When etching high-aspect ratio features, the thickness of the ACL film may be increased to withstand etching of the underlying layers. Increasing the thickness of the ACL, however, can create defects in the etched features. 
     For example, “bowing” may occur when conventional pattern transfer techniques are used to etch high-aspect ratio features in ACL films. Bowing occurs when plasma ions bombard sidewall surfaces of the ACL film to laterally etch the sidewall surfaces. The “bow CD” is measurement of bowing, which is generally defined as the cross-section or width of an opening formed in a layer in a direction perpendicular to the thickness of the layer. When bowing occurs, the bow CD is typically larger near the top of the layer than the bottom of the layer. 
       FIG.  1    (PRIOR ART) illustrates how bowing may occur when conventional pattern transfer processes are used to etch high-aspect features in an ACL film. As shown in  FIG.  1   , patterned substrate  100  may generally include a patterned layer  108  formed over a hard mask layer  106 , which in turn, is formed over one or more underlying layers, such as an oxide layer  104  and base substrate layer  102 . The patterned layer  108 , oxide layer  104  and base substrate layer  102  may be formed from any of a wide variety of materials, as is known in the art. The hard mask layer  106  is an amorphous carbon layer (ACL) film, which is used as a hard mask for transferring a pattern from the patterned layer  108  to the underlying oxide layer  104 . 
     In conventional pattern transfer processes, the patterned substrate  100  is exposed to light during a lithography step, and a wet or dry etch process is performed after the lithography step to remove the exposed portions of the hard mask layer  106  to create openings  110 . When a dry process is used, a process gas is converted by high-energy power into plasma and ions, which bombard exposed portions of the hard mask layer  106 . Although ion bombard is primarily anisotropic, ion scattering caused by collision of molecules in the plasma may lead to lateral etching of the opening  110  sidewalls and bowing. As shown in  FIG.  1   , the bow CD is generally larger near the top of the hard mask layer  106  underlying the patterned layer  108 . When significant bowing occurs, the hard mask layer  106  may collapse, closing the openings  110 . 
       FIGS.  2 A- 2 D  illustrate a conventional solution used to prevent bowing during an ACL etch process. In  FIG.  2 A , a patterned substrate  200  is formed including a patterned layer  208 , a hard mask layer  206 , an oxide layer  204  and a base substrate layer  202 , as described above in reference to  FIG.  1   . In  FIG.  2 B , the patterned substrate  200  is exposed to light during a lithography step, and a dry etch process  212  is performed to remove exposed portions of the hard mask layer  206  to create openings  210 . In some embodiments, the dry etch process  212  shown in  FIG.  2 B  may remove some, but not all, of the exposed portions of the hard mask layer  206 . For example, the dry etch process  212  may be configured to etch the exposed portions of the hard mask layer  206  to a first etch depth (d1). 
     In  FIG.  2 C , a passivation layer  216  is deposited onto the bottom and sidewall surfaces of the openings  210  formed in the hard mask layer  206  to prevent the sidewall surfaces of the hard mask layer  206  from bowing when the dry etch process  212  is resumed in  FIG.  2 D . In conventional ACL etch processes, an atomic layer deposition (ALD) process  214  or other plasma process is commonly used to deposit a silicon layer onto the bottom and sidewall surfaces of the hard mask layer  206 . Once the silicon layer is deposited, the ALD process  214  may expose the patterned substrate  200  to a nitrogen- or oxygen-containing gas and/or plasma to convert the silicon layer into a silicon oxide or silicon nitride passivation layer  216 . Then the dry etch process  212  may be resumed. When the dry etch process  212  is subsequently resumed (in  FIG.  2 D ), the passivation layer  216  protects the sidewall surfaces of the hard mask layer  206  from ion bombardment and lateral etching. While such processes reduce bowing and result in substantially vertical openings  210 , ALD processes are relatively time consuming, and thus, reduce throughput. 
     As known in the art, atomic layer deposition (ALD) is a process wherein conventional chemical vapor deposition (CVD) processes are divided into separate deposition steps to construct a thin film by sequentially depositing single atomic monolayers in each deposition step. The ALD technique is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. A typical ALD process consists of injecting a first precursor for a period of time until a saturated monolayer is formed on the substrate. Then, the first precursor is purged from the chamber using an inert gas to prevent the first precursor from mixing with a subsequent precursor gas species. After the chamber is purged, a second precursor is injected into the chamber, also for a period of time, thus forming a layer on the substrate from the reaction of the second precursor with the monolayer formed on the substrate. Then, the second precursor is purged from the chamber and the process of introducing the first precursor, purging the process chamber, introducing the second precursor, and purging the process chamber is often repeated a number of times to achieve a desired film thickness. 
     A wide range of ALD processes have been used to form ALD passivation layers on sidewall surfaces of hard mask layers. For example, ALD processes have been used to form silicon dioxide (SiO 2 ) passivation layers on the sidewall surfaces of hard mask layers by utilizing a cyclical process of exposing the substrate to a silicon precursor gas (e.g., silanes) followed by exposure to an oxygen-containing gas (e.g., oxygen, O 2 , ozone, O 3 , etc.). Other ALD processes have been used to form silicon nitride (SiN) passivation layers on the sidewall surfaces of hard mask layers by exposing the substrate to a silicon precursor gas (e.g., silanes) followed by exposure to an nitrogen-containing gas (e.g., nitrogen, N 2 , ammonia, NH 3 , etc.) in a cyclical process. In either case, the cyclical process of introducing a silicon precursor gas, purging the chamber, introducing the oxygen- or nitrogen-containing gas and purging the chamber is time consuming. Thus, throughput is reduced when ALD processes are used to form passivation layers on the sidewall surfaces of hard mask layers. Further, the ALD processes may contribute to sidewall roughness which may negatively impact the performance of the formed structures such as vias or contact holes. 
     As such, a need exists for an improved process and method for forming a passivation layer on sidewall surfaces of an amorphous carbon layer (ACL) to avoid bowing during an ACL etch process. 
     SUMMARY 
     Improved process flows and methods are provided herein for forming a passivation layer on sidewall surfaces of openings formed in an amorphous carbon layer (ACL) to avoid bowing during an ACL etch process. More specifically, improved process flows and methods are provided to form a silicon-containing passivation layer on sidewall surfaces of the openings created within the ACL without utilizing atomic layer deposition (ALD) techniques or converting the silicon-containing passivation layer to an oxide or a nitride. As such, the improved process flows and methods disclosed herein may be used to protect the sidewall surfaces of the ACL and prevent bowing during the ACL etch process, while also reducing processing time and improving throughput. 
     In one embodiment, a method for patterning a substrate is provided. The method may comprise forming an amorphous carbon layer (ACL) on one or more underlying layers formed on the substrate, wherein a thickness of the ACL is greater than 1 micrometer (μm) and forming a patterned layer over the ACL. The method further comprises etching exposed portions of the ACL not covered by the patterned layer to create openings in the ACL, wherein the exposed portions of the ACL are partially etched to a first depth, which is less than the thickness of the ACL. The method further comprises forming a silicon-containing passivation layer on sidewall surfaces of the openings created in the ACL by exposing the substrate to a silicon-containing precursor. The method then comprises continuing etching the exposed portions of the ACL to a second depth, which is greater than the first depth, without converting the silicon-containing passivation layer to an oxide or a nitride. 
     Variations of the method described above may be performed wherein said forming the silicon-containing passivation layer comprises exposing the substrate to the silicon-containing precursor in an absence of plasma to deposit a silicon monolayer on the sidewall surfaces of the openings created in the ACL. In another variation, said forming the silicon-containing passivation layer further comprises: (1) subsequently exposing the substrate to a hydrogen plasma to change a surface property of the silicon monolayer; and (2) repeating said exposing the substrate to the silicon-containing precursor in the absence of plasma and said subsequently exposing the substrate to the hydrogen plasma a number of times to form a plurality of silicon monolayers on the sidewall surfaces of the openings. In another variation, an atomic layer deposition (ALD) process is not used to deposit the silicon monolayer. 
     In yet another variation, said exposing the substrate to the silicon-containing precursor in the absence of plasma comprises: (1) providing the substrate within a plasma chamber coupled to a first radio frequency (RF) source and a second RF source; and (2) supplying the silicon-containing precursor to the plasma chamber without supplying power from the first RF source or the second RF to the plasma chamber. In still another embodiment, said providing the substrate within the plasma chamber comprises providing the substrate within a capacitively coupled plasma (CCP) chamber or an inductively coupled plasma (ICP) chamber. 
     In another embodiment, the silicon-containing precursor comprises an aminosilane. In yet another embodiment, the silicon-containing precursor comprises di-isopropylaminosilane. In some embodiments, the method further comprises repeating said forming the silicon-containing passivation layer on sidewall surfaces of the openings and said continuing etching the exposed portions of the ACL a number of cycles and/or until the exposed portions of the ACL are completely removed. In some embodiments, the number of cycles is 5 or more. 
     In a second embodiment, a method for patterning a substrate is provided. The method comprises: forming an amorphous carbon layer (ACL) on one or more underlying layers formed on the substrate, wherein a thickness of the ACL is greater than 1 micrometer (μm); forming a patterned mask layer over the ACL; and etching exposed portions of the ACL not covered by the patterned mask layer to create openings in the ACL, wherein the exposed portions of the ACL are partially etched to a first depth, which is less than the thickness of the ACL. The method further comprises exposing the substrate to a silicon-containing precursor in an absence of plasma to form a silicon monolayer on sidewall surfaces of the openings created in the ACL, and subsequently exposing the substrate to a hydrogen plasma to change a surface property of the silicon monolayer. The method also comprises forming a plurality of silicon monolayers on the sidewall surfaces of the openings by repeating said exposing the substrate to the silicon-containing precursor in the absence of plasma and said subsequently exposing the substrate to the hydrogen plasma a number of times. The method also comprise continuing etching the exposed portions of the ACL to a second depth, which is greater than the first depth. 
     The second embodiment may further comprise repeating said forming the plurality of silicon monolayers on the sidewall surfaces of the openings and said continuing etching the exposed portions of the ACL a number of cycles and/or until the exposed portions of the ACL are completely removed. In alternative, an atomic layer deposition (ALD) process is not used to form the silicon monolayer or the plurality of silicon monolayers. The second embodiment may further include said exposing the substrate to the silicon-containing precursor in the absence of plasma comprising: (1): providing the substrate within a plasma chamber coupled to a first radio frequency (RF) source and a second RF source; and (2) supplying the silicon-containing precursor to the plasma chamber without supplying power from the first RF source or the second RF to the plasma chamber. In another variation, said providing the substrate within the plasma chamber comprises providing the substrate within a capacitively coupled plasma (CCP) chamber or an inductively coupled plasma (ICP) chamber. In some variations, the silicon-containing precursor comprises an aminosilane. In some variations the silicon-containing precursor comprises di-isopropylaminosilane. In some variations, the plurality of silicon monolayers are not converted to an oxide or a nitride. In some variations, the number of times is three or more. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present inventions and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features. It is to be noted, however, that the accompanying drawings illustrate only exemplary embodiments of the disclosed concepts and are therefore not to be considered limiting of the scope, for the disclosed concepts may admit to other equally effective embodiments. 
         FIG.  1    (PRIOR ART) is a cross-sectional view of a patterned substrate illustrating the bowing that occurs when conventional pattern transfer processes are used to etch high-aspect features in an amorphous carbon layer (ACL) film. 
         FIGS.  2 A- 2 D  (PRIOR ART) illustrate a conventional pattern transfer process that prevents bowing during an ACL etch process by depositing a passivation layer onto sidewall surfaces of the ACL film using an atomic layer deposition (ALD) process. 
         FIGS.  3 A- 3 E  illustrate an improved pattern transfer process that prevents bowing during an ACL etch process by depositing a passivation layer onto sidewall surfaces of the ACL film without utilizing atomic layer deposition (ALD) techniques. 
         FIG.  4    is a flowchart diagram illustrating one embodiment of a method to pattern a substrate in accordance with the techniques described herein. 
         FIG.  5    is a flowchart diagram illustrating another embodiment of a method to pattern a substrate in accordance with the techniques described herein. 
         FIGS.  6 A- 6 C  are cross-sectional views of a patterned substrate after an ACL etch process is performed comparing the bow CD produced with and without the techniques described herein. 
         FIG.  7    is a block diagram illustrating one embodiment of a plasma processing system that may be used to pattern a substrate using the techniques described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Improved process flows and methods are provided herein for forming a passivation layer on sidewall surfaces of openings formed in an amorphous carbon layer (ACL) to avoid bowing during an ACL etch process. More specifically, improved process flows and methods are provided to form a silicon-containing passivation layer on sidewall surfaces of the openings created within the ACL without utilizing atomic layer deposition (ALD) techniques or converting the silicon-containing passivation layer to an oxide or a nitride. As such, the improved process flows and methods disclosed herein may be used to protect the sidewall surfaces of the ACL and prevent bowing during the ACL etch process, while also reducing processing time and improving throughput. 
     In the present disclosure, a patterned substrate is provided with an amorphous carbon layer (ACL), which is formed on one or more underlying layers, and a patterned layer formed over the ACL. In some embodiments, a thickness of the ACL may be greater than 1 micrometer (μm). After partially etching exposed portions of the ACL to a first depth to create openings within the ACL, the improved process flows and methods disclosed herein form a silicon-containing passivation layer on sidewall surfaces of the openings by exposing the patterned substrate to a silicon-containing precursor gas. In some embodiments, the silicon-containing precursor gas may comprise an aminosilane precursor, such as but not limited to, di-isopropylaminosilane (SiH 3 N(C 3 H 7 ) 2 , otherwise referred to as LTO520). Other aminosilane and silicon-containing precursor gases may also be used. For example, other precursors may include, but are not limited to, tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), dichlorosilane (DCS), tetrachlorosilane (SiCl 4 ), etc. 
     In a first embodiment, the silicon-containing passivation layer may be formed by exposing the patterned substrate to the silicon-containing precursor gas in the absence of plasma to deposit a silicon monolayer on the sidewall surfaces of the openings created in the ACL. This may be achieved, in some embodiments, by providing the patterned substrate within a plasma chamber coupled to a first radio frequency (RF) source and a second RF source, and supplying the silicon-containing precursor to the plasma chamber without supplying power from the first RF source or the second RF to the plasma chamber. In some embodiments, the plasma chamber may be a capacitively coupled plasma (CCP) chamber or an inductively coupled plasma (ICP) chamber. However, such chambers are exemplary and other deposition chambers and techniques, including non-plasma chambers may be utilized. 
     In a second embodiment, the silicon-containing passivation layer may be formed by: (a) exposing the patterned substrate to the silicon-containing precursor gas in the absence of plasma to form a silicon monolayer on the sidewall surfaces of the openings created in the ACL, (b) subsequently exposing the substrate to a hydrogen plasma to change a surface property of the silicon monolayer, and (c) repeating the steps of exposing the substrate to the silicon-containing precursor in the absence of plasma and subsequently exposing the substrate to a hydrogen plasma a number of times to form a plurality of silicon monolayers on the sidewall surfaces of the openings. 
     After the silicon-containing passivation layer is formed, the improved process flows and methods disclosed herein continue etching the exposed portions of the ACL to a second depth, which is greater than the first depth. If the second depth is less than the thickness of the ACL, the improved process flows and methods disclosed herein may repeat the process of forming silicon-containing passivation layer(s) on the sidewall surfaces of the openings and continue etching the exposed portions of the ACL for a number of cycles and/or until the exposed portions of the ACL are completely removed. 
     Unlike conventional processes, the silicon-containing passivation layer described herein is formed without utilizing atomic layer deposition (ALD) techniques or converting the silicon-containing passivation layer to an oxide or a nitride. Thus, the disclosed process flows and methods protect the sidewall surfaces of the ACL and prevent bowing during the ACL etch process, while reducing processing time and improving throughput. In the first embodiment, better clogging margin may be achieved by using a thinner passivation layer (i.e., a silicon monolayer). However, better sidewall protection may be achieved in the second embodiment by alternating between non-plasma and plasma processes to build the silicon monolayers up to provide a substantially thicker passivation layer. 
       FIGS.  3 A- 3 E  illustrate one embodiment of an improved process flow that utilizes the techniques disclosed herein. It will be recognized that the embodiment shown in  FIGS.  3 A- 3 E  is merely exemplary and the techniques described herein may be applied to other process flows. 
     As shown in  FIG.  3 A , patterned substrate  300  includes a patterned layer  308  formed over an amorphous carbon layer (ACL)  306 , which in turn, is formed over one or more underlying layers. In some embodiments, the one or more underlying layers may include an oxide layer  304  and a base substrate  302 , as shown in  FIG.  3 A . As shown and described, the base substrate  302  may be composed of a variety of patterned and unpatterned layers that were formed in prior non-shown processing steps, as is well known in the substrate processing art. It is recognized, however, that the underlying layers shown in the figures and described herein are merely exemplary, and more, less or other underlying layers may be utilized. Further, it will be recognized that for illustrative purposes to aid showing the various layers, the thicknesses of the underlying layers in the figures may be shown to be much thinner than thicknesses actually used. 
     Base substrate  302  may be any substrate for which the use of patterned features is desirable. For example, base substrate  302  may be a semiconductor substrate having one or more semiconductor processing layers formed thereon. In one embodiment, base substrate  302  may be a substrate that has been subject to multiple semiconductor processing steps which yield a wide variety of structures and layers, all of which are known in the substrate processing art. 
     Oxide layer  304  may be formed from any of a wide variety of materials, as is known in the art. In one embodiment, the oxide layer  304  may be any of a variety of oxide containing layers, such as but not limited to, a silicon dioxide (SiO 2 ) layer, a multi-layered oxide-nitride-oxide-nitride (ONON), a multi-layered oxide-polysilicon-oxide-polysilicon (OPOP), or layers containing an oxide. Oxide layer  304  may be formed using any of a wide variety of deposition processes as is well known in the art, such as but not limited to, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), capacitively coupled plasma (CCP) deposition, inductively coupled plasma (ICP) deposition, spin-on processes, atomic layer deposition (ALD), etc. In one embodiment, a silicon containing oxide layer is formed using TEOS chemical vapor deposition techniques. In some embodiments, one or more layers may be formed above and/or below the oxide layer  304  shown in  FIG.  3 A . 
     ACL  306  may also be formed from any of a wide variety of materials using any of a wide variety of deposition processes, as is known in the art. Examples of deposition processes that may be used to form ACL  306  include, but are not limited to, chemical vapor deposition (e.g., CVD, PECVD), physical vapor deposition (PVD), plasma deposition (e.g., CCP, ICP), spin-on processes, etc. In one or more of the deposition processes described above, ACL  306  may be deposited by exposing the patterned substrate  100  to a gas mixture comprising a hydrocarbon gas (e.g., C x H y ) and an inert gas (e.g., N 2 , Ar, He, Ne, Kr, Xe, etc.), possibly in combination with other gas sources, such as for example, a hydrogen-containing gas (e.g., H 2 ), a nitrogen-containing gas (e.g., N 2 , NH 3 ), etc. 
     In some embodiments, ACL  306  is used as a hard mask layer for etching high-aspect ratio features (such as vias, contact holes and lines) in one or more of the underlying layers. When etching high-aspect ratio features, the thickness of the ACL  306  may be increased to withstand etching of the ACL  306  and the one or more underlying layers. In some embodiments, the thickness (T) of the ACL  306  may be greater than 1 μm (micrometer). For example, the thickness of the ACL  306  may range between 1 μm and 4 μm. Further, feature widths and spaces of 300 nm or smaller and even 70 nm or smaller may be necessary to be formed in the ACL  306 . Thus, high aspect ratio features may need to be formed in the ACL  306 . Thus, aspect ratios of 10, 50 or even higher may be formed. 
     After ACL  306  is formed, a patterned layer  308  may be formed on the ACL  306  by depositing one or more material layers onto the ACL  306  and then patterning the material layer(s) using a lithography technique. A variety of deposition processes and a variety of lithography techniques may be used to form the patterned layer  308 , as is well known in the art. In addition, the patterned layer  308  may generally be formed from any of a wide variety of mask materials commonly used in lithography. For example, the patterned layer  308  may comprise a photoresist layer or other mask layers (for instance a mask layer that was patterned from a photoresist lithography and etch process as is known in the art), etc. 
     After the patterned layer  308  is formed, an ACL etch process  312  may be performed to remove exposed portions of the ACL  306  (i.e., portions of the ACL  306  not protected by the patterned layer  308 ) to create openings  310  in the ACL  306 . As shown in  FIG.  3 B , the ACL etch process  312  may be configured to partially etch the exposed portions of the ACL  306  to a first depth (d1), which is less than the thickness (T) of the ACL  306 . 
     Various etch chemistries may be used in the ACL etch process  312  shown in  FIG.  3 B . In some embodiments, for example, an etch chemistry comprising sulfur and oxygen may be used to etch the exposed portions of the ACL  306 . Examples of sulfur and oxygen containing etch chemistries include, but are not limited to, chemistries comprising sulfur dioxide (SO 2 ), carbonyl sulfide (COS), carbon monoxide (CO), carbon dioxide (CO 2 ), nitrogen (N 2 ), and/or hydrogen (H 2 ) In some embodiments, an oxygen-containing gas (e.g., O 2 , O 3 ) and/or an inert gas (e.g., N 2 , Ar, He, Ne, Kr, Xe, etc.) may be added to the etch chemistry used in the ACL etch process  312 . Further, any of a wide variety of chemistries utilized for ACL etching may be utilized, as the techniques disclosed herein are not limited to a particular chemistry. The techniques described herein are not limited, however, to any particular ACL etch chemistries. 
     In one example embodiment, the ACL etch process  312  shown in  FIG.  3 B  may be configured to supply a gas mixture comprising approximately 200 to 300 standard cubic centimeters (sccm) of sulfur dioxide (SO 2 ), approximately 80 to 150 sccm of oxygen (O 2 ) and approximately 20 to 80 sccm of argon (Ar) to a plasma chamber (e.g., a CCP or ICP chamber) in which the patterned substrate  100  is disposed. As known in the art, a plasma may be generated within the plasma chamber by supplying source power from a first radio frequency (RF) source and/or bias power from a second RF source to the plasma chamber, while the gas mixture is supplied to the plasma chamber. In some embodiments, relatively high source power (e.g., 1000 to 1400 W), relatively low bias power (e.g., 100 to 600 W), relatively low chamber pressure (e.g., 10 to 30 mT) and relatively low temperature (e.g., 0 to 60° C.) may be used to generate the plasma within the plasma chamber. During the ACL etch process  312 , ions generated within the plasma bombard the exposed portions of the ACL  306  to etch or remove the exposed portions of the ACL  306  to create openings  310 . 
     As noted above, the ACL etch process  312  shown in  FIG.  3 B  may be configured to partially etch the exposed portions of the ACL  306  to a first depth (d1), which is less than the thickness (T) of the ACL  306 . In some embodiments, the ACL etch process  312  may be timed to etch the exposed portions of the ACL  306  to the first depth (d1). The etch time and the etch depth may be dependent on several factors, such as the thickness (T) of the ACL  306 , the material composition of the ACL  306 , the etch chemistry, etc. In some embodiments, the etch time may range between 1 to 4 minutes to achieve a first etch depth (d1) of 500 to 2000 nm. Other etch times and etch depths may also be used. 
     After partially etching the exposed portions of the ACL  306  to create openings  310  in  FIG.  3 B , a silicon-containing passivation layer  316  may be formed on sidewall surfaces of the openings  310  by exposing the patterned substrate  100  to a silicon-containing precursor  314 . In some embodiments, the silicon-containing precursor  314  may comprise an aminosilane precursor, such as but not limited to, di-isopropylaminosilane (SiH 3 N(C 3 H 7 ) 2 , otherwise referred to as LTO520). Other aminosilane and silicon-containing precursor gases may also be used. For example, other precursors may include, but are not limited to, TEOS, TMOS, DCS, SiCl 4 , etc. However, other aminosilane and silicon-containing precursors may also be used. 
     Silicon-containing passivation layer  316  may be formed using any of a wide variety of deposition processes, such as but not limited to, chemical vapor deposition (e.g., CVD, PECVD), physical vapor deposition (PVD), and plasma deposition (e.g., CCP, ICP) processes. The silicon-containing passivation layer  316 , however, does not need to be formed as part of an atomic layer deposition (ALD) process. As noted above, ALD processes build up monolayers on a substrate surface by alternately exposing the substrate to a first precursor and a second precursor, while purging the processing chamber in between precursor gas exposure to prevent the first and second precursors from mixing. For example, conventional ALD processes have been used to form silicon dioxide (SiO 2 ) or silicon nitride (SiN) passivation layers on sidewall surfaces of hard mask layers by alternately exposing the substrate to a silicon precursor gas (e.g., silanes) followed by exposure to an oxygen-containing gas (e.g., O 2 , O 3 , etc.) or a nitrogen-containing gas (e.g., N 2 , NH 3 , etc.). These ALD processes are time consuming and limit throughput. 
     In one embodiment, the silicon-containing passivation layer  316  shown in  FIG.  3 C  may be formed on sidewall surfaces of the openings  310  using a plasma deposition (e.g., CCP, ICP) process. However, the silicon-containing passivation layer  316  is preferably formed by exposing the patterned substrate  100  to the silicon-containing precursor  314  in the absence of plasma to deposit a silicon monolayer on the sidewall surfaces of the openings  310 , as shown schematically in  FIG.  3 C . This may be achieved, in some embodiments, by supplying the silicon-containing precursor  314  to a plasma chamber (e.g., a CCP or ICP chamber) in which the patterned substrate  100  is disposed without supplying source or bias power to the plasma chamber. Non-plasma based chambers may also be utilized if desired for the passivation formation. Advantageously for throughput issues, it is desirable, however, to utilize the same chamber for the sidewall passivation formation and the etching of ACL  306 . Thus, in one exemplary embodiment described herein all the processes (etch and passivation formation) are performed in-situ in a single process chamber. 
     In one example embodiment, the silicon-containing passivation layer  316  may be formed on sidewall surfaces of the openings  310  by supplying a gas mixture comprising approximately 50 to 150 sccm of LTO520 and approximately 50 to 150 sccm of argon (Ar) to a plasma chamber (e.g., a CCP or ICP chamber) in which the patterned substrate  100  is disposed. Other gas mixtures may also be used. The gas mixture may be supplied to the plasma chamber at zero source power (0 W), zero bias power (0 W), relatively high chamber pressure (e.g., 200 to 400 mT) and relatively high temperature (e.g., 30 to 100° C.). Other process conditions may also be used. 
     In some embodiments, the ACL etch process  312  may continue after the silicon monolayer is formed in  FIG.  3 C . For example, the ACL etch process  312  may continue etching the exposed portions of ACL  306  until the exposed portions are completely removed, as shown in  FIG.  3 E . 
     In other embodiments, the processing steps shown in  FIGS.  3 C and  3 E  may be repeated a number of cycles and/or until the exposed portions of the ACL  306  are completely removed. For example, after partially etching the exposed portions of ACL  306  to the first depth (d1) in  FIG.  3 B  and forming a silicon monolayer on the sidewall surfaces of the openings  310  in  FIG.  3 C , the ACL etch process  312  may continue etching the exposed portions of the ACL  306  to a second depth (not shown), which is greater than the first depth (d1). If the second depth is less than the thickness (T) of the ACL  306 , the processing steps shown in  FIGS.  3 C and  3 E  may be repeated to form another silicon monolayer on the sidewall surfaces of the openings  310  and continue etching of the exposed portions of the ACL  306 . This process may be repeated for a number of cycles (e.g., 5 to 15) and/or until the exposed portions of the ACL  306  are completely removed, as shown in  FIG.  3 E . 
     In other embodiments, the silicon-containing passivation layer  316  may be formed by: (a) exposing the patterned substrate  100  to the silicon-containing precursor  314  in the absence of plasma to deposit a silicon monolayer on the sidewall surfaces of the openings  310 , as shown in  FIG.  3 C , (b) subsequently exposing the patterned substrate  100  to a hydrogen plasma  315 , as shown in  FIG.  3 D , and (c) repeating the steps of exposing the patterned substrate  100  to the silicon-containing precursor  314  in the absence of plasma ( FIG.  3 C ) and subsequently exposing the patterned substrate  100  to a hydrogen plasma  315  ( FIG.  3 D ) a number of times (e.g., 2 to 6) to build up or form a plurality of silicon monolayers on the sidewall surfaces of the openings  310 . 
     In one example embodiment, the hydrogen plasma  315  may be generated by supplying approximately 100 to 300 sccm of hydrogen (H 2 ) to a plasma chamber (e.g., a CCP or ICP chamber) in which the patterned substrate  100  is disposed. Other hydrogen containing gases may also be used. The hydrogen containing gas may be supplied to the plasma chamber at relatively high source power (e.g., 300 to 700 W), little to no bias power (e.g., 0 W), relatively low chamber pressure (e.g., 30 to 70 mT) and relatively high temperature (e.g., 50 to 100° C.). High chamber pressures (e.g. 100 to 500 mT) may also be utilized. Other process conditions may also be used. Other hydrogen-containing gases, such as for example, ammonia (NH 3 ) may be utilized and inert gases (such as Ar, N2, He, Ne, Kr, Xe) may alternatively be used or added to the gas flow. N 2  plasma processes may also be utilized. 
     Exposing the patterned substrate  100  to the hydrogen plasma  315  allows the thickness of passivation layer  316  to increase. The increase may result from various mechanisms, such as for example, but not limited to, surface property changes that allow the buildup of additional silicon monolayers, more complete silicon coverage due to making unabsorbed sites more active, etc. This results in the formation of a substantially thicker passivation layer  316 , which provides better sidewall protection when the ACL etch process  312  resumes than can be provided with a single silicon monolayer. However, exposure to the hydrogen plasma  315  does not convert the silicon monolayer to another material, such as an oxide or nitride. This enables improved throughput as opposed to ALD techniques. 
     In some embodiments, the ACL etch process  312  may continue in  FIG.  3 E  after the plurality of silicon monolayers are formed in  FIG.  3 D . For example, the ACL etch process  312  may continue etching the exposed portions of the ACL  306  until the exposed portions are completely removed, as shown in  FIG.  3 E . 
     In other embodiments, the processing steps shown in  FIGS.  3 C,  3 D and  3 E  may be repeated a number of cycles and/or until the exposed portions of the ACL  306  are completely removed. For example, after partially etching the exposed portions of ACL  306  to the first depth (d1) in  FIG.  3 B  and forming a plurality of silicon monolayers on the sidewall surfaces of the openings  310  in  FIGS.  3 C and  3 D , the ACL etch process  312  may continue etching the exposed portions of ACL  306  to a second depth (not shown), which is greater than the first depth (d1). If the second depth is less than the thickness (T) of ACL  306 , the processing steps shown in  FIGS.  3 C,  3 D and  3 E  may be repeated to form another plurality of silicon monolayers on the sidewall surfaces of the openings  310  and continue etching the exposed portions of the ACL  306 . This process may be repeated for a number of cycles and/or until the exposed portions of the ACL  306  are completely removed, as shown in  FIG.  3 E . 
       FIGS.  4 - 5    illustrate exemplary methods for use of the processing techniques described herein. It will be recognized that the embodiments of  FIGS.  4 - 5    are merely exemplary and additional methods may utilize the techniques described herein. Further, additional processing steps may be added to the methods shown in the  FIGS.  4 - 5    as the steps described are not intended to be exclusive. Moreover, the order of the steps is not limited to the order shown in the figures as different orders may occur and/or various steps may be performed in combination or at the same time. 
       FIG.  4    illustrates one embodiment of a method  400  that may be used to pattern a substrate using the techniques disclosed herein. In some embodiments, the method  400  may generally include forming an amorphous carbon layer (ACL) on one or more underlying layers formed on the substrate (in step  410 ), forming a patterned layer over the ACL (in step  420 ), and etching exposed portions of the ACL not covered by the patterned layer to create openings in the ACL, wherein the exposed portions of the ACL are partially etched to a first depth, which is less than a thickness of the ACL (in step  430 ). In some embodiments of the method  400 , the thickness of the ACL may be greater than 1 micrometer (μm). For example, the thickness of the ACL may range between 1 μm and 4 μm. 
     Further, the method  400  may include forming a silicon-containing passivation layer on sidewall surfaces of the openings created in the ACL by exposing the substrate to a silicon-containing precursor (in step  440 ). For example, the silicon-containing passivation layer may be formed (in step  440 ) by exposing the substrate to the silicon-containing precursor in the absence of plasma to deposit a silicon monolayer on the sidewall surfaces of the openings created in the ACL. After the silicon monolayer is deposited on the sidewall surfaces of the openings, the method  400  may continue etching the exposed portions of the ACL to a second depth, which is greater than the first depth, without converting the silicon-containing passivation layer to an oxide or a nitride (in step  450 ). In some embodiments, method  400  may repeat said forming a silicon-containing passivation layer on sidewall surfaces of the openings (in step  440 ) and said continuing etching the exposed portions of the ACL (in step  450 ) for a number of cycles and/or until the exposed portions of the ACL are completely removed. 
       FIG.  5    illustrates another embodiment of a method  500  that may be used to pattern a substrate using the techniques disclosed herein. In some embodiments, the method  500  may generally include forming an amorphous carbon layer (ACL) on one or more underlying layers formed on the substrate, wherein a thickness of the ACL is greater than 1 micrometer (μm) (in step  510 ), forming a patterned mask layer over the ACL (in step  520 ), and etching exposed portions of the ACL not covered by the patterned mask layer to create openings in the ACL, wherein the exposed portions of the ACL are partially etched to a first depth, which is less than the thickness of the ACL (in step  530 ). 
     The method  500  may further include exposing the substrate to a silicon-containing precursor in the absence of plasma to form a silicon monolayer on sidewall surfaces of the openings created in the ACL (in step  540 ), subsequently exposing the substrate to a hydrogen plasma to change a surface property of the silicon monolayer (in step  550 ), and forming a plurality of silicon monolayers on the sidewall surfaces of the openings by repeating said exposing the substrate to the silicon-containing precursor in the absence of plasma and said subsequently exposing the substrate to a hydrogen plasma a number of times (in step  560 ). After the plurality of silicon monolayers are formed on the sidewall surfaces of the openings, the method  500  may continue etching the exposed portions of the ACL to a second depth, which is greater than the first depth (in step  570 ). In some embodiments, method  500  may repeat said forming a plurality of silicon monolayers on the sidewall surfaces of the openings (in step  560 ) and said continuing etching the exposed portions of the ACL (in step  570 ) for a number of cycles and/or until the exposed portions of the ACL are completely removed. 
     The process flow shown in  FIGS.  3 A- 3 E  and the methods shown in  FIGS.  4 - 5    prevent bowing during ACL etch processes by providing improved methods for forming a silicon-containing passivation layer on sidewall surfaces of openings formed in the ACL. Unlike conventional process flows and methods, the silicon-containing passivation layer disclosed herein is formed without utilizing atomic layer deposition (ALD) techniques or converting the silicon-containing passivation layer to an oxide or nitride. As such, the process flows and methods described herein can be used to protect the sidewall surfaces of the ACL and prevent bowing during ACL etch processes, while also reducing processing time and improving throughput. 
       FIGS.  6 A- 6 C  are cross-sectional views of various amorphous carbon layers (ACLs) after an ACL etch process has performed to create openings in the ACL, illustrating the bow CD produced with and without the techniques described herein. In  FIG.  6 A , openings are created within ACL  600  without utilizing the techniques described herein. For example, ACL  600  having a thickness of approximately 3800 nanometers (nm) is etched using a conventional SO 2 /O 2  etch chemistry without sidewall passivation in  FIG.  6 A . When such conventional processes are used, lateral etching of the sidewall surfaces of the ACL  600  causes significant bowing. For example, and as shown in  FIG.  6 A , a bow CD of approximately 107 to 109 nm is produced near the top of the ACL  600  and a bow CD of approximately 119 to 121 nm is produced at approximately a third of the way down the structure when using a conventional SO 2 /O 2  etch chemistry without sidewall passivation. 
       FIGS.  6 B and  6 C  compare the openings created within an amorphous carbon layer when the techniques described herein are used. More specifically,  FIG.  6 B  illustrates the bow CD produced when an ACL  600  having a thickness of approximately 3800 nm is etched using the process flow shown in  FIGS.  3 B,  3 C and  3 E . In  FIG.  6 B , the etch/deposition/etch process flow of  FIGS.  3 B,  3 C and  3 E  was repeated ten times.  FIG.  6 C  illustrates the bow CD produced when an ACL  600  having a thickness of approximately 3800 nm is etched using the process flow shown in  FIGS.  3 B,  3 C,  3 D and  3 E . In  FIG.  6 C , for each step of forming the passivation layer, the passivation layer was formed by repeating the LTO/hydrogen plasma steps three cycles and the overall process of etch/deposition/etch was performed ten times. As shown in  FIGS.  6 B and  6 C , the improved process flow and methods disclosed herein produce much less bowing, and thus, a smaller bow CD (e.g., approximately 89 to 95 nm) than that produced using conventional techniques. As shown in  FIG.  6 B , a bow CD of approximately 95 to 91 nm is produced near the top of the ACL  600  and a bow CD of approximately 87 to 85 nm is produced at approximately a third of the way down the structure. As shown in  FIG.  6 C , a bow CD of approximately 89 to 93 nm is produced near the top of the ACL  600  and a bow CD of approximately 87 nm is produced at approximately a third of the way down the structure. Typical CDs at the bottom of the structure may be 60 to 70 nm, though such CDs are merely exemplary 
       FIG.  7    provides one example embodiment for a plasma processing system  700  that can be used with respect to the disclosed techniques and is provided only for illustrative purposes. Although the plasma processing system  700  shown in  FIG.  7    is a capacitively coupled plasma (CCP) processing system, one skilled in the art would recognize the techniques described herein could be performed in an inductively coupled plasma (ICP) processing system, microwave plasma processing system, Radial Line Slot Antenna (RLSATM) microwave plasma processing system, electron cyclotron resonance (ECR) plasma processing system, or other type of processing system or combination of systems. Thus, it will be recognized by those skilled in the art that the techniques described herein may be utilized with any of a wide variety of plasma processing systems. 
     The plasma processing system  700  can be used for a wide variety of operations including, but not limited to, etching, deposition, cleaning, plasma polymerization, plasma-enhanced chemical vapor deposition (PECVD), and so forth. The structure of a plasma processing system  700  is well known, and the particular structure provided herein is merely of illustrative purposes. It will be recognized that different and/or additional plasma process systems may be implemented while still taking advantage of the techniques described herein. 
     Looking in more detail to  FIG.  7   , the plasma processing system  700  may include a process chamber  705 . As is known in the art, process chamber  705  may be a pressure controlled chamber. A substrate  710  (in one example a semiconductor wafer) may be held on a stage or chuck  715 . An upper electrode  720  and a lower electrode  725  may be provided as shown. The upper electrode  720  may be electrically coupled to a first radio frequency (RF) source  730  through a first matching network  755 . The first RF source  730  may provide a source voltage  735  at an upper frequency (f U ) to the first matching network  755 . The lower electrode  725  may be electrically coupled to a second RF source  740  through a second matching network  757 . The second RF source  740  may provide a bias voltage  645  at a lower frequency (f L ) to the second matching network  757 . Though not shown, it will be known by those skilled in the art that a voltage may also be applied to the chuck  715 . 
     Components of the plasma processing system  700  can be connected to, and controlled by, a control unit  770  that in turn can be connected to a corresponding memory storage unit and user interface (all not shown). Various plasma processing operations can be executed via the user interface, and various plasma processing recipes and operations can be stored in a storage unit. Accordingly, a given substrate can be processed within the plasma processing chamber  705  with various microfabrication techniques. It will be recognized that control unit  770  may be coupled to various components of the plasma processing system  700  to receive inputs from and provide outputs to the components. 
     The control unit  770  can be implemented in a wide variety of manners. For example, the control unit  770  may be a computer. In another example, the control unit  770  may include one or more programmable integrated circuits that are programmed to provide the functionality described herein. For example, one or more processors (e.g., microprocessor, microcontroller, central processing unit, etc.), programmable logic devices (e.g., complex programmable logic device (CPLD)), field programmable gate array (FPGA), etc.), and/or other programmable integrated circuits can be programmed with software or other programming instructions to implement the functionality of a proscribed process recipe. It is further noted that the software or other programming instructions can be stored in one or more non-transitory computer-readable mediums (e.g., memory storage devices, FLASH memory, dynamic random access (DRAM) memory, reprogrammable storage devices, hard drives, floppy disks, DVDs, CD-ROMs, etc.), and the software or other programming instructions when executed by the programmable integrated circuits cause the programmable integrated circuits to perform the processes, functions, and/or capabilities described herein. Other variations could also be implemented. 
     During some processing steps, the plasma processing system  700  may apply power from the first RF source  730  and the second RF source  740  to the upper and lower electrodes to generate a plasma  760  in the process chamber  705 . When a plasma  760  is generated within the process chamber  705 , ions within the plasma  760  are attracted to the substrate  710 . The generated plasma  760  can be used for processing a target substrate (such as substrate  710  or any material to be processed) in various types of treatments such as, but not limited to, plasma etching, deposition and/or sputtering. For example, plasma  760  may be generated within the process chamber  705  to perform one or more of the process steps shown in  FIGS.  3 B,  3 D and  3 E . As noted above, however, other processing steps described herein may process the target substrate without generating a plasma. For example, the silicon-containing passivation layer  316  may be formed on the sidewall surfaces of the openings  310  in the absence of plasma. 
     In the CCP processing system shown in  FIG.  7   , application of power results in a high-frequency electric field being generated between the upper electrode  720  and the lower electrode  725 . Processing gas delivered to process chamber  705  can then be dissociated and converted into the plasma  760 . As shown in  FIG.  7   , the exemplary plasma processing system  700  described herein utilizes two RF sources. In an exemplary embodiment, the first RF source  730  provides source power at relatively high frequencies to convert the processing gas(es) delivered into the process chamber  705  into the plasma  760  and to control the plasma density. The second RF source  740  provides a bias power at lower frequencies to control ion bombardment energy. 
     In one example plasma processing system, for example, the first RF source  730  may provide about 0 to 1400 W of source power in a high-frequency (HF) range from about 3 MHz to 150 MHz (or above) to the upper electrode  720 , and the second RF source  740  may provide about 0 to 1400 W of bias power in a low-frequency (LF) range from about 0.2 MHz to 60 MHz to the lower electrode  725 . Different operational ranges can also be used depending on type of plasma processing system and the type of treatments (e.g., etching, deposition, sputtering, etc.) performed therein. 
     In one exemplary embodiment, the ACL etch process  312  shown in  FIGS.  3 B and  3 E  may be performed with process conditions of 1000 W to 1400 W source power, 200 W to 600 W bias power, 10 mT to 30 mT pressure, 0° C. to 40° C. electrostatic chuck temperature, and a gas flow mixture of 150 sccm SO 2 , 300 sccm O 2  and 50 sccm Ar. 
     In one exemplary embodiment, the deposition step shown in  FIG.  3 C  may be performed with process conditions of 0 W source power, 0 W bias power, 200 mT to 400 mT pressure, 50° C. to 100° C. electrostatic chuck temperature, and a gas flow mixture of 100 sccm LTO520 and 100 sccm Ar. 
     In one exemplary embodiment, the plasma step shown in  FIG.  3 D  may be performed with process conditions of 300 W to 700 W source power, 0 W bias power, 30 mT to 70 mT pressure (higher pressures may alternatively be utilized), 50° C. to 100° C. electrostatic chuck temperature, and 200 sccm H 2  gas flow. 
     It is noted that the techniques described herein may be utilized within a wide range of plasma processing systems. Although a particular plasma processing system  700  is shown in  FIG.  7   , it will be recognized that the techniques described herein may be utilized within other plasma processing systems. In one example system, the RF sources shown in  FIG.  7    may be switched (e.g., higher frequencies may be supplied to the lower electrode  725  and lower frequencies may be supplied to the upper electrode  720 ). Further, a dual source system is shown in  FIG.  7    merely as an example system. It will be recognized that the techniques described herein may be utilized with other plasma processing systems in which a modulated RF power source is provided to one or more electrodes, direct current (DC) bias sources are utilized, or other system components are utilized. It is further recognized that other plasma processing systems, such as an ICP processing system may also be used to perform one or more of the various deposition and etch processes described herein. 
     It is noted that various deposition and etch processes can be used to form one or more of the material layers shown and described herein. For example, one or more depositions can be implemented using chemical vapor deposition (e.g., CVD, PECVD), physical vapor deposition (PVD), plasma deposition (e.g., CCP, ICP), spin-on processes, atomic layer deposition (ALD), and/or other deposition processes. In one example deposition process, a gas mixture including but not limited to LTO520, is utilized. However, other aminosilanes and/or silicon-containing precursor gases may also be used. The process may optionally include a combination with one or more dilution gases (e.g., argon, nitrogen, etc.). The process may occur at a variety of pressure, power, flow, and temperature conditions to form a silicon-containing passivation layer on sidewall surfaces of openings formed in an amorphous carbon layer. 
     It is further noted that various etch processes can be used to etch one or more of the material layers shown and described herein. For example, one or more etch processes can be implemented using plasma etch processes, discharge etch processes, and/or other desired etch processes. In one example plasma etch process, a gas mixture including but not limited to SO 2  and O 2  optionally in combination with one or more dilution gases (e.g., argon, nitrogen, etc.) can be used at a variety of pressure, power, flow and temperature conditions to etch the exposed portions of the amorphous carbon layer. 
     Other operating variables for process steps can also be adjusted to control the various deposition and/or etch processes described herein. The operating variables may include, for example, the chamber temperature, chamber pressure, flowrates of gases, types of gases, and/or other operating variables for the processing steps. Variations can also be implemented while still taking advantage of the techniques described herein. 
     It is noted that reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not denote that they are present in every embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. Various additional layers and/or structures may be included and/or described features may be omitted in other embodiments. 
     The term “substrate” as used herein means and includes a base material or construction upon which materials are formed. It will be appreciated that the substrate may include a single material, a plurality of layers of different materials, a layer or layers having regions of different materials or different structures in them, etc. These materials may include semiconductors, insulators, conductors, or combinations thereof. For example, the substrate may be a semiconductor substrate, a base semiconductor layer on a supporting structure, a metal electrode or a semiconductor substrate having one or more layers, structures or regions formed thereon. The substrate may be a conventional silicon substrate or other bulk substrate comprising a layer of semi-conductive material. As used herein, the term “bulk substrate” means and includes not only silicon wafers, but also silicon-on-insulator (“SOI”) substrates, such as silicon-on-sapphire (“SOS”) substrates and silicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on a base semiconductor foundation, and other semiconductor or optoelectronic materials, such as silicon-germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. The substrate may be doped or undoped. 
     Systems and methods for processing a substrate are described in various embodiments. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronics device, and may, for example, be a base substrate structure, such as a semiconductor substrate or a layer on or overlying a base substrate structure such as a thin film. Thus, the term “substrate” is not intended to be limited to any particular base structure, underlying layer or overlying layer, patterned or unpatterned, but rather, is contemplated to include any such layer or base structure, and any combination of layers and/or base structures. 
     One skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale. 
     Further modifications and alternative embodiments of the described systems and methods will be apparent to those skilled in the art in view of this description. It will be recognized, therefore, that the described systems and methods are not limited by these example arrangements. It is to be understood that the forms of the systems and methods herein shown and described are to be taken as example embodiments. Various changes may be made in the implementations. Thus, although the inventions are described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present inventions. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and such modifications are intended to be included within the scope of the present inventions. Further, any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.