Patent Publication Number: US-2021193456-A1

Title: Systems and methods for preventing stiction of high aspect ratio structures and/or repairing high aspect ratio structures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/575,705, filed on Oct. 23, 2017. The entire disclosures of the applications referenced above are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to processing of substrates, and more particularly to methods for preventing stiction of high aspect ratio (HAR) structures and/or repairing HAR structures. 
     BACKGROUND 
     The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Substrate processing systems may be used to deposit film on a substrate such as semiconductor wafer or to etch, clean and/or otherwise treat the surface of the substrate. In some processes, the substrates may be subjected to wet processing. In these processes, the substrate may be mounted on a rotary chuck. As the rotary chuck is rotated, fluid nozzles may be used to dispense fluid such as a liquid or gas and/or heat may be applied to treat the substrate. 
     Some of the substrates include high aspect ratio (HAR) structures. For example, the HAR structures may include nanopillars, trenches or vias. The HAR structures have a width (parallel to a surface of the substrate) that is significantly less than a depth (perpendicular to a surface of the substrate) of the feature. HAR structures having an aspect ratio greater than 5:1 are fairly common. More advanced processes include HAR structures having even higher aspect ratios. Pattern collapse occurs when one or more of the HAR structures collapse, move laterally relative to a surface of the substrate and/or directly contact adjacent HAR structures. Pattern collapse is often encountered during drying after a wet clean process 
     Several processes have been used to reduce pattern collapse when drying substrates. For example, the substrate can be dried using supercritical CO 2 . However, supercritical CO 2  is relatively expensive and has implementation issues. The surface of the substrate can be modified with a layer to prevent stiction. However, surface modification is often expensive since it requires extra chemistries to be used. Surface modification also leads to material loss since the modified layer needs to be removed. The substrate can also be dried using isopropyl alcohol (IPA) that is delivered to the surface of the substrate at a temperature close to the boiling point of IPA. However, some aspect ratios cannot be dried using boiling IPA without pattern collapse. 
     The substrate can also be treated using hydrofluoric (HF) vapor etching in vacuum equipment operated at vacuum pressures. However, the vacuum equipment is typically expensive and cannot be used to perform wet cleaning. The preceding wet clean step is often necessary to remove organic or metal contaminants from the surface of the substrate. 
     Repairing collapsed structures can be performed using plasma etching in vacuum equipment. However, the plasma etching hardware that is required is expensive. 
     SUMMARY 
     A method for treating high aspect ratio (HAR) structures arranged on a surface of a substrate includes a) spin rinsing the surface of the substrate using a first rinsing liquid; b) spinning off the first rinsing liquid from the surface of the substrate; and c) directing a gas mixture containing hydrogen fluoride onto the surface of the substrate after the first rinsing liquid is dispensed. 
     In other features, the hydrogen fluoride is a first reactive component and the gas mixture further contains a second reactive component. At least one of the second reactive component is a proton acceptor, and/or the second reactive component includes an OH-group. 
     The second reactive component is selected from a group consisting of water vapor, alcohol vapor, ammonia and amine. 
     In other features, c) is performed after b) or c) is performed within 60 seconds after a). The gas mixture further contains an inert carrier gas and alcohol vapor. The inert carrier gas includes molecular nitrogen and the alcohol vapor includes isopropyl alcohol. The gas mixture is delivered by a nozzle located in a range from 1 mm to 40 mm from the surface of the substrate. The gas mixture is delivered from the nozzle at a dispense velocity in a range from 1 to 50 m/s. The gas mixture is delivered from the nozzle at a flow rate of 1 to 20 slm. 
     In other features, a cross-sectional area of an orifice of the nozzle is in a range from 3 to 30 mm 2 . a), b) and c) are performed at a temperature in a range from 20° C. to 400° C. a), b) and c) are performed at a temperature in a range from 50° C. to 150° C. a), b) and c) are performed when the substrate is maintained at a predetermined pressure in a range from 900 hPa to 1100 hPa. a), b) and c) are performed with the substrate arranged on a rotary chuck of a device. 
     In other features, the device further comprises a first liquid dispenser connected to a first rinsing liquid source, a vapor supply to supply solvent vapor, and a gas dispenser connected to a gas source and the vapor supply to dispense the gas mixture onto a surface of the substrate. The gas dispenser comprises a showerhead. 
     In other features, the gas dispenser comprises an arm, a nozzle, and a motor to scan the arm across the substrate while the gas mixture is supplied. 
     In other features, a), b) and c) are performed at a temperature greater than 100° C. The gas mixture further comprises ammonia. 
     In other features, the first rinsing liquid comprises an organic, water miscible solvent. 
     In other features, the gas mixture includes hydrogen fluoride in a range from 0.05% to 10% volume, alcohol in a range from 0.05% to 10% volume, and an inert gas in a range from 80% to 99.9% volume. The gas mixture includes hydrogen fluoride in a range from 0.5% to 5% volume, alcohol in a range from 0.5% to 2.5% volume, and an inert gas in a range from 92.5% to 99% volume. The gas mixture includes hydrogen fluoride in a range from 0.1% to 5% volume, alcohol in a range from 0.1% to 5% volume, and an inert gas in a range from 90% to 99.8% volume. 
     A device for treating high aspect ratio (HAR) structures arranged on a surface of a substrate includes a rotary chuck to rotate the substrate. A first nozzle rinses the surface of the substrate using a first rinsing liquid as the rotary chuck rotates the substrate. A second nozzle directs a gas mixture containing hydrogen fluoride onto the surface of the substrate after the first rinsing liquid is dispensed. 
     In other features, a first liquid dispenser is connected to a first rinsing liquid source. A vapor supply supplies a second reactive component. A gas dispenser is connected to a gas source and the vapor supply dispenses the gas mixture onto a surface of the substrate. 
     In other features, a mixing manifold mixes the hydrogen fluoride and second reactive component. An open chamber surrounds the rotary chuck. A closed chamber surrounds the rotary chuck. A vapor supply supplies solvent vapor. The gas mixture further contains the solvent vapor. 
     In other features, the solvent vapor is selected from a group consisting of water vapor and alcohol vapor. The second nozzle directs the gas mixture containing hydrogen fluoride onto the surface of the substrate after the first rinsing liquid is spun off the substrate. The second nozzle directs the gas mixture containing hydrogen fluoride onto the surface of the substrate within 60 seconds after the first rinsing liquid is dispensed. 
     In other features, a heater heats the substrate to a temperature in a range from 20° C. to 400° C. The heater heats the substrate to a temperature in a range from 50° C. to 150° C. The substrate is maintained at a predetermined pressure in a range from 900 hPa to 1100 hPa. A heater to heat the substrate to a temperature greater than 100° C. and the gas mixture further contains ammonia. 
     In other features, a controller controls rotation of the rotary chuck, dispensing of the first rinsing liquid from the first nozzle and dispensing of the gas mixture from the second nozzle. 
     In other features, the second nozzle is located in a range from 1 mm to 40 mm from the surface of the substrate. The gas mixture is delivered from the second nozzle at a dispense velocity in a range from 1 to 50 m/s. The gas mixture is delivered from the second nozzle at a flow rate of 1 to 20 slm. A cross-sectional area of an orifice of the second nozzle is in a range from 3 to 30 mm 2 . 
     In other features, the gas mixture includes hydrogen fluoride in a range from 0.5% to 5% volume, alcohol in a range from 0.5% to 2.5% volume, and inert gas in a range from 92.5% to 99% volume. 
     In other features, the gas mixture includes an inert gas in a range from 80% to 99.9% volume, hydrogen fluoride in a range from 0.05% to 10% volume, and alcohol in a range from 0.05% to 10% volume. The gas mixture includes an inert gas in a range from 90% to 99.8% volume, hydrogen fluoride in a range from 0.1% to 5% volume, and alcohol in a range from 0.1% to 5% volume. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIGS. 1A-1C  are side cross-sectional views illustrating a substrate before and after wet cleaning and drying and after repair according to the present disclosure; 
         FIG. 2A  is a functional block diagram of an example of a rotary chuck arranged in a closed chamber for processing a substrate according to the present disclosure; 
         FIG. 2B  is a plan view of the rotary chuck of  FIG. 2A ; 
         FIG. 2C  is a functional block diagram of an example of a rotary chuck arranged in an open chamber for processing a substrate according to the present disclosure; 
         FIG. 3  is a functional block diagram of another example of a rotary chuck for processing a substrate according to the present disclosure; 
         FIG. 4  is a flowchart illustrating an example of a method for processing a substrate according to the present disclosure; 
         FIG. 5  is a flowchart illustrating another example of a method for processing a substrate according to the present disclosure; 
         FIG. 6  is a functional block diagram illustrating a wet processing device and a separate collapse repair device according to the present disclosure; 
         FIG. 7  is a functional block diagram of a collapse repair device utilizing an arm and a nozzle according to the present disclosure; and 
         FIG. 8  is a functional block diagram of a collapse repair device utilizing a showerhead according to the present disclosure. 
     
    
    
     In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
     DETAILED DESCRIPTION 
     Systems and methods according to the present disclosure relate to wet processing and dry etching of a substrate including high aspect ratio (HAR) structures. The wet processing and dry etching can be performed at or near atmospheric pressure in a wet clean tool after the substrate is processed. The combination of wet processing and dry etching in a single hardware device provides a less expensive alternative to the other drying processes and adds little or no processing time. Alternately, the wet processing can be completed in the wet processing tool and the repair process can be performed in a separate repair tool. 
     In some examples, after exposure to a rinsing liquid such as isopropyl alcohol (IPA), a gas mixture is dispensed onto the surface of the substrate. The gas mixture includes hydrofluoric (HF) gas. In some examples, the gas mixture may further include a second reactive component (such as a solvent vapor or a proton acceptor or component having an OH-group) and/or a carrier gas. 
     In some examples, the carrier gas includes an inert gas such as molecular nitrogen (N 2 ). However, other inert gases can be used. In some examples, the second reactive component includes water or alcohol (methanol, IPA, or other alcohol). Other alcohols can be used. For example, an alcohol with 1 to 4 carbon (C) atoms can be used. For example, 2-propanol (IPA) can be used. In some examples, the mixing method for the gases includes mixing N 2  with IPA and then dding pure HF gas to the IPA/N 2  mixture. 
     For example, an adsorbed layer of the solvent is formed and HF 2  is generated. SiO 2  reacts with HF 2  and SiF 4  is formed, which leads to evaporation (etching) of the SiO 2  layer. In some examples, the gas mixture includes HF in a range from 0.5% to 5% volume, alcohol in a range from 0.5% to 2.5% volume, and an inert gas in a range from 92.5% to 99% volume. 
     In some examples, the gas mixture is generated by flowing N 2  gas as a carrier gas through concentrated aqueous HF (with HF concentration in a range from 45% to 55% volume (e.g. 49% volume)). In other examples, the gas mixture is prepared by mixing the inert gas (such as molecular nitrogen) with the alcohol and then adding pure HF to the inert gas and alcohol mixture. 
     In other examples, the gas mixture includes an inert gas in a range from 80% to 99.9% volume, HF in a range from 0.05% to 10% volume, and alcohol in a range from 0.05% to 10% volume. In other examples, the gas mixture includes an inert gas in a range from 90% to 99.8% volume, HF in a range from 0.1% to 5% volume, and alcohol in a range from 0.1% to 5% volume. 
     In other examples, ammonia (NH 3 ), or any amine (e.g. ethyl amine, ethylene diamine, pyrrolidine) is optionally added to the gas mixture when the processing temperature is greater than 100° C. Addition of NH 3  works in particular at temperatures above 100° C. where formation of NH 4 F is inhibited (as it is above the sublimation temperature) and volatile (NH 4 ) 2 SiF 4  is formed. 
     As an alternative, the process can also be applied to the substrate after the rinsing liquid has been spun off the substrate and the substrate is relatively dry. In some examples, the process can include exposure while the rinsing liquid is present and again after the rinsing liquid has been spun off and is dry. The process can be repeated one or more times. 
     In some examples, the process is performed at or near atmospheric pressures. For example, the substrate surface may be maintained at a pressure in a range from 900 to 1100 hectopascals (hPa) during processing. In some examples, the gas mixture is delivered to the substrate using a nozzle that is scanned across the surface of the substrate. Alternatively, the gas mixture can also be delivered to the substrate using a showerhead arranged above the surface of the substrate. In addition, vapors that can potentially enhance the process such as water or ammonia NH 3  vapors (gases) or amines can be supplied. 
     In some examples, the process is performed at a predetermined temperature in a range from 20° C. to 400° C. In other examples, the process is performed at a predetermined temperature in a range from 50° C. to 150° C. Partial pressures of HF and solvent vapor can be varied between 1 mTorr and up to their respective saturated vapor pressures at the specific process temperature. 
     Adding a reactive vapor (e.g. HF/solvent vapor combination) to a drying process provides improved results relative to other IPA drying processes. In some examples, controllability of the vapor etching is performed using a substrate heater with radial heating and/or a nozzle that can be scanned over the substrate. In addition to reducing hardware and chemistry costs, the method described herein increases the yield of the process. 
     Referring now to  FIGS. 1A-1C , processing of a substrate is shown. In  FIG. 1A , a substrate  10  is shown prior to wet processing and drying. Substrate  10  includes high aspect ratio (HAR) structures  12 - 1 ,  12 - 2 ,  12 - 3  and  12 - 4  (collectively HAR structures  12 ) defined on one or more underlying layers  14 . For example, the HAR structures  12  include pillars, vias, trenches, and/or other features. The substrate  10  in  FIG. 1A  is subjected to wet processing and drying. 
     In  FIG. 1B , the substrate  10  is shown after the wet processing and drying. The HAR structures  12 - 2  and  12 - 3  partially collapse and lean towards one another. In some examples, a bridging oxide  20  is formed between the HAR structures  12 - 2  and  12 - 3 . Examples of bridging oxides that may be formed include silicon oxide (SiO x ), silicon oxynitride (SiO x N y ), titanium oxide (TiO x ), etc. In  FIG. 1C , the substrate  10  is shown after treatment using the methods described herein such that the bridging oxide  20  is removed and the collapsed HAR structures  12 - 2  and  12 - 3  are repaired. 
     Referring now to  FIG. 2A , an example of a rotary chuck  50  for wet processing and repairing a substrate is shown. The rotary chuck  50  includes a chamber  52  housing a rotary chuck  56 . A substrate  58  is arranged on a surface of the rotary chuck  50 . The rotary chuck  50  rotates the substrate  58  while liquid is dispensed onto the substrate  58  and/or to spin off the liquid. The substrate  58  may be attached to the rotary chuck  50  using any suitable mechanism. For example, the substrate  58  can be attached to the rotary chuck  50  using gripping pins  59 . Suitable examples of gripping pins are shown and described in commonly-assigned “Method and Apparatus for Processing Wafer-Shaped Articles”, U.S. patent application Ser. No. 15/232,594 (Attorney Docket Number 3877-1US), which is hereby Incorporated by reference in its entirety. 
     In some examples, the surface  60  of the rotary chuck  56  is transparent and a heater  61  is arranged under the surface  60 . In some examples, the heater  61  includes a plurality of light emitting diodes (LEDs) that are arranged in one or more radial zones to allow radial heating of the substrate  60 . In some examples, the heater  61  can be operated to provide a moving heat wave that moves from a central location of the substrate outwardly to a radially outer edge thereof. In some examples, the rotary chuck  56  rotates and the heater  61  is stationary. Suitable examples of a rotary chuck performing radial heating of the substrate are shown and described in U.S. patent application Ser. No. 15/232,594. 
     In some examples, the rotary chuck  56  is rotated by a motor  62  via a drive shaft  63  as shown. In other examples, the motor  62  includes a rotor and stator and the rotor is driven magnetically without physical contact. Suitable examples are shown in commonly-assigned U.S. Pat. No. 6,485,531, which is hereby incorporated by reference in its entirety. Rinsing liquid is delivered by an arm  64  and a nozzle  66  that are scanned across the substrate  58  by a motor  70 . A valve  72  selectively supplies the rinsing liquid from a liquid supply  74  to the arm  64 . 
     Another arm  84  (shown in an inactive position in  FIG. 2A ) and a gas nozzle  86  may be used to deliver a gas mixture including one or more of hydrofluoric (HF) gas, carrier gas, and second reactive component (e.g. solvent vapor and/or ammonia (NH 3 )) as will be described further below. In some examples, an outlet of the gas nozzle  86  is arranged within a predetermined distance of a surface of the substrate  58 . In some examples, the predetermined distance is in a range from 1 mm to 40 mm. In some examples, the predetermined distance is in a range from 2 mm to 2 cm. In some examples, the gas mixture is delivered at a predetermined velocity in a range from 1 to 50 m/s. In some examples, the gas mixture is delivered at a predetermined flow in a range from 1 to 20 standard liters per minute (slm). In some examples, a cross-sectional area of an orifice of the nozzle  86  is in a range from 3 to 30 mm 2 . 
     A motor  90  may be used to scan the nozzle  86  across the substrate  58  and a valve  92  may be used to selectively supply the gas mixture. A gas delivery system  100  includes a vapor supply  102  and a valve  104 . In some examples, the vapor supply  102  includes a heated liquid ampoule, bubbler or other vaporizer. The gas delivery system  100  further includes one or more gas supplies  112 - 1 ,  112 - 2 , . . . , and  112 -N (collectively gas supplies  112 ) and valves  114 - 1 ,  114 - 2 , . . . , and  114 -N (collectively valves  114 ). An optional manifold  110  may be used to allow the gases and vapors to mix prior to delivery via the optional valve  92 . In some examples, mass flow controllers (not shown) are provided to more precisely control the gases and/or solvent vapor. A controller  130  controls the valves, the motors and the gas delivery system  100 . 
     In  FIG. 2B , the arms  64  and  84  are shown in plan view. The arm  64  is shown in a dispensing position over the substrate  58  while the arm  84  is shown in an inactive position. The arm  64  dispenses the rinsing liquid onto the substrate and the rinsing liquid is spun off. After dispensing the rinsing liquid, the arm  64  is moved to the inactive position and the arm  84  dispenses the gas mixture as will be described further below 
     Referring now to  FIG. 2C , a rotary chuck with an open chamber can also be used. Additional details of an open chamber rotary chuck are shown in commonly-assigned U.S. Pat. No. 9,484,229, which is hereby incorporated by reference in its entirety. A rotary chuck  150  is arranged in a chamber  151  that is open at a top portion thereof. A bottom portion of the chamber  151  can be opened or closed. The chamber  151  defines one or more exhaust channels  152 . In some examples, the one or more exhaust channels  152  are located in a plane including the substrate  58 , are directed in a radially outward direction and are connected to a vacuum source. In some examples, the vacuum source includes a valve  153  and a pump  154  that are in fluid communication with the one or more exhaust channels  152 . 
     In some examples, the rotary chuck  150  includes a plurality of gripping pins  155  arranged thereon and a transparent plate  156  arranged below the substrate  58 . A heater  157  such as a printed circuit board including light emitting diodes (LEDs) may be arranged below the transparent plate  156  to heat the substrate  58 . In some examples, the heater  157  produces a moving heat wave that is used during cleaning and/or repair. The moving heat wave moves from a central location of the substrate outwardly to a radially outer edge thereof. In some examples, the heater  157  is stationary and the rotary chuck  150  rotates. Suitable examples of a rotary chuck performing radial heating of the substrate are shown and described in U.S. patent application Ser. No. 15/232,594. In some examples, a fan  158  supplies airflow  159  to the top surface of the chamber  151  during processing. 
     Referring now to  FIG. 3 , another example of a rotary chuck for processing a substrate is shown. Instead of using the arm  84  and the nozzle  86 , the gas mixture is dispensed using a showerhead  136  arranged above a surface of the substrate  58 . Other suitable examples of a delivering gas through a showerhead onto a rotary chuck are shown and described in commonly-assigned U.S. Pat. No. 8,926,788 and commonly-assigned U.S. Patent Publication Nos. US2012/0131815 and US2014/0026926, which are hereby incorporated by reference in their entirety. 
     In some examples, the showerhead  136  includes a plate including a plurality of through holes. The gas mixture is delivered by the gas delivery system  100  and the valve  92  to a gas plenum  134 . The gas mixture flows into the gas plenum  134 , through the showerhead  136 , and into the chamber  52  to expose the substrate  58 . In some examples, a vertical position of the showerhead  136  and the gas plenum  134  is adjusted by one or more motors  170  to a location closer to the substrate prior to delivery of the gas mixture when repairing or preventing collapse. 
     Referring now to  FIGS. 4-5 , examples of methods for processing a substrate is shown. In  FIG. 4 , a method  180  for processing a substrate is shown. At  184  in  FIG. 5 , the substrate is arranged on the rotary chuck. At  188 , the rotary chuck is rotated. At  192 , rinsing liquid is dispensed onto the substrate. At  194 , the rinsing liquid is spun off. 
     After a predetermined period (at  198 ), a gas mixture is supplied at  202 . In other examples, the gas mixture can be applied in an overlapping manner during  194 . The substrate can be either rotating or not rotating when applying the gas mixture. 
     In some examples, the predetermined period is in a range from 0 to 60 seconds. In some examples the gas mixture starts to be supplied before the rinsing step  192  has ended. In some examples, the gas mixture includes hydrofluoric (HF) gas and a carrier gas. The gas mixture is delivered for a predetermined period to prevent collapse and/or to repair HAR structures by removing bridging oxides. 
     In  FIG. 5 , a method  210  for processing a substrate is shown. Steps  184  to  198  are similar to those described above. After a predetermined period ( 198 ), a gas mixture is supplied at  214 . The gas mixture includes hydrofluoric (HF) gas, a carrier gas and at least one of solvent vapor and ammonia gas. The gas mixture is delivered for a predetermined period to prevent collapse and/or to repair HAR structures. Without being limited to a particular theory, the collapse and/or to repair of the HAR structures occurs by directing HF gas onto the substrate to remove stiction forces such as Van der Waals forces, hydrogen bonds and covalent oxide bridges. 
     In one example, the repair process according to the present disclosure was tested on a substrate with HAR structures including nanopillars (silicon (Si) cylinders having a diameter of 30 nm, a pitch of 90 nm and a height of 600 nm). The repair process reduced the collapse percentage from almost 90% with the repair process according to the present disclosure to less than 10%. 
     Referring now to  FIGS. 6-8 , wet processing and collapse repair can be performed in separate devices. In  FIG. 6 , a system  288  includes a wet processing device  290  that performs a wet processing step. After wet processing in the wet processing device  290 , the substrate is moved to a collapse repair device  300 . In some examples, the wet processing step includes wet cleaning. In some examples, the wet processing step is performed by a rotary chuck. 
     In  FIG. 7 , the collapse repair device  300  is shown. The collapse repair device  300  includes a chamber  310  and a substrate support  312  for supporting a substrate  314 . The substrate support  312  includes a heater  320  such as a resistive heater and/or cooling channels to control a temperature of the substrate  314  during processing. The controller  130  controls the motor  90 , the valve  92  and the gas delivery system  100  to perform collapse repair. Since the collapse repair device  300  does not perform wet cleaning, the nozzles and rotary chuck associated with wet processing device are omitted and the collapse repair device  300  can be simplified. 
     In  FIG. 8 , another example of a collapse repair device  350  is shown. The nozzle  86 , the arm  84  and the motor  90  of the collapse repair device in  FIG. 7  are replaced by a showerhead  360  arranged above a surface of the substrate  314 . In some examples, the showerhead  360  includes a plate including a plurality of through holes. The gas mixture is delivered by the gas delivery system  100  and/or a valve  92  to a gas plenum  362 . The gas mixture flows into the gas plenum  362  and through the showerhead  360  to expose the substrate  314 . 
     The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure. 
     Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”