Patent Publication Number: US-2018051369-A1

Title: Apparatus for Evaporating a Material

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 62/136,831, filed Mar. 23, 2015, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field of the Invention 
     The disclosure relates to apparatus for evaporating materials, such as for use in the manufacture of solar cells. 
     Description of Related Art 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     Solar cells typically include a material that generates charge carriers in response to absorption of light. One such light-absorbing material is Cu(In,Ga)Se2 (CIGS). Introducing a controlled amount of sodium into CIGS (or a similar light-absorbing material) may passivate grain boundaries within the material. This reduces the amount of carrier recombination centers within the material, leading to increased solar cell efficiency as more generated charge carriers are collected before recombination. 
     One such process for introducing sodium into CIGS is to deposit CIGS (and perhaps other material layers) upon soda-lime glass to form a substrate, and during the process, heating the substrate to cause the sodium present in the soda-lime glass to diffuse into the CIGS layer. For material uniformity and repeatability, this method may be undesirable since it can be difficult to control material diffusion through metal layers. For this reason, this process does not scale up well for manufacturing large-area substrates. 
     Another process for introducing sodium into CIGS is to place a sodium-containing material (e.g., NaF, Na2Se, or Na2O) into a container, and then to heat the container so that the material evaporates or sublimates, resulting in the sodium-containing material being deposited upon a substrate that includes a CIGS layer above the container. This process also has not scaled up well for processing of large-area substrates due to the difficulty of evaporating and depositing a uniform amount of a sodium-containing material across a large-area substrate. Other processes for introducing sodium into CIGS films also suffer from difficulty in introducing uniform amounts of sodium into a large-area substrate. 
     SUMMARY 
     Example embodiments provide apparatuses and processes for depositing a predetermined amount of a material onto a substrate. Further, the embodiments allow for depositing a substantially uniform thickness of the material over a large-area substrate. The embodiments involve a substantially enclosed container having a cavity configured to contain the material. The substantially enclosed container, when heated under vacuum conditions, facilitates formation of a pressure differential between the cavity and a region external to the container. In accordance with the pressure differential, vacuum conditions exist in the region external to the container while a pressure sufficient for the material to form a liquid phase is present within the cavity. The elevated pressure within the cavity enable the material to be evaporated, instead of sublimated, onto the substrate above the container. 
     In one example, a process for depositing a predetermined amount of a material onto a substrate includes providing a container having a cavity. The container and the cavity are elongated along a first axis of the container and the container is located within a vacuum chamber. The container includes one or more openings distributed along the first axis, where the one or more openings provide fluid communication between the cavity and a region within the vacuum chamber that is external to the container. The process further includes inserting the material into the cavity of the container and heating the container, whereby the predetermined amount of the material evaporates and exits the container via the one or more openings. The process further includes moving the substrate above the one or more openings along a second axis of the container that is substantially perpendicular to the first axis, thereby depositing the predetermined amount of the material onto the substrate. 
     In another aspect, an example apparatus for depositing a predetermined amount of a material onto a substrate includes a container having a cavity configured to contain the material. The container and the cavity are elongated along a first axis of the container. The apparatus further includes one or more heaters that are (i) elongated along the first axis and (ii) configured to heat and evaporate the material by heating the container. The apparatus further includes a conveyor for moving the substrate in a direction substantially perpendicular to the first axis of the container. The apparatus further includes one or more openings in the container distributed along the first axis, where the one or more openings provide fluid communication between a region external to the container and the cavity. 
     These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section view of an example substrate. 
         FIG. 2  is a simplified cross-section view of an example apparatus for depositing a material onto a substrate. 
         FIG. 3  is a simplified cross-section view of another example apparatus for depositing a material onto a substrate. 
         FIG. 4  is an end perspective view of an example container and example heaters for depositing a material onto a substrate. 
         FIG. 5  is an end perspective view of an example container and example heaters for depositing a material onto a substrate. 
         FIG. 6  is an end perspective view of an example container and example heaters for depositing a material onto a substrate. 
         FIG. 7  is an end perspective view of an example container and example heaters for depositing a material onto a substrate. 
         FIG. 8  is a flow chart depicting an example process. 
     
    
    
     DETAILED DESCRIPTION 
     Example processes and apparatuses are described herein. Any example embodiment or feature described herein is not necessarily to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed apparatuses and processes can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. 
     Furthermore, the particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an example embodiment may include elements that are not illustrated in the Figures. 
     By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide. 
     As noted above, it may be useful to introduce a dopant material such as sodium into a light-absorbing material such as CIGS so that solar cells with increased efficiency can be fabricated using the doped light-absorbing material. Processing of solar cell substrates typically takes place under vacuum conditions to prevent contaminants in the atmosphere from being introduced into the substrate. Vacuum conditions cause many materials such as NaF, Na 2 Se, and Na 2 O to sublimate when sufficiently heated, as opposed to melting and evaporating. However, depositing a uniform thickness of a material over the area of a substrate is easier to achieve by evaporating the material from its source instead of sublimating it. The substantially enclosed container disclosed herein alleviates this problem by maintaining an elevated pressure within the container when the material inside the container is sufficiently heated. The pressure is elevated with respect to the pressure of a vacuum chamber that houses the container during processing. The pressure differential enables evaporation of the material and equilibration of the vapor inside the container or cavity and causes the evaporated material to diffuse toward the substrate above. 
       FIG. 1  illustrates an example substrate  100 . The substrate  100  includes a stainless steel layer  102 , a molybdenum (Mo) layer  104 , a CIGS layer  106 , and an iron(Fe)-blocking layer  108 . In some examples, the Mo layer  104  with thickness of approximately 50-1500 nm is deposited upon the Fe-blocking layer  108  having a thickness of approximately 50-500 nm. The Fe-blocking layer  108  may be deposited upon the stainless steel layer  102  having a thickness of approximately 20-250 μm. Further, the CIGS layer  106  having a thickness of approximately 0.8-2.0 μm may be deposited upon the Mo layer  104 . The Fe-blocking layer  108  may be made up of chromium and/or titanium (or other suitable metals) that help prevent Fe from the stainless steel layer  102  from diffusing into the Mo layer  104  and/or the CIGS layer  106  during high-temperature processing. The substrate  100  may undergo further processing and/or deposition of additional material layers, such as deposition of a buffer layer of cadmium sulfide, a transparent conductive oxide layer such as aluminum doped zinc oxide, or a metal contact grid layer such as nickel, aluminum, silver, or copper. One example of an additional process includes evaporating sodium or a sodium-containing material onto the CIGS layer  106  of the substrate  100 . Variants of this process are described below in detail. 
     The substrate  100  is described above for illustrative purposes only. The apparatuses or processes described herein may involve depositing any type of material onto any type of substrate. 
     In one example (not shown), the CIGS layer  106  might not be initially present on the substrate. An evaporated sodium-containing material may be deposited directly upon the Mo layer  104  using the process and apparatus described herein. The CIGS layer  106  may then be deposited onto the sodium-containing material while the sodium-containing material is heated, causing diffusion of the sodium-containing material into the CIGS layer  106 . 
     In another example (not shown), a CuInGa precursor layer is deposited on top of the Mo layer  104 . This precursor layer may or may not contain some amount of selenium (Se). Then, the sodium-containing material is evaporated and deposited upon the CuInGa precursor layer. Finally, a CIGS layer is formed by heated selenization of the CuInGa precursor layer. The heated selenization causes the sodium-containing material to diffuse throughout the CIGS layer as it is being formed. 
       FIG. 2  illustrates an apparatus  200  for depositing a material  218  onto a substrate  203 . The apparatus  200  may include a container  214  that includes a cavity  216  and one or more openings  220 . The apparatus may further include heaters  222  and  224 , and a conveyor comprising a feeding reel  204  and a collection reel  206 .  FIG. 2  also illustrates a pump  202 , and a vacuum chamber  201  that includes an external region  205 , an insertion point  208 , and a removal point  210 . 
     In some examples, the material  218  includes mixtures or compounds that include sodium or potassium, such as sodium fluoride (NaF), potassium fluoride (KF), sodium selenide (Na 2 Se), or sodium oxide (Na 2 O). In one particular example, the material  218  is in powder form. 
     The vacuum chamber  201  may include any chamber or container suitable for maintaining vacuum conditions inside the vacuum chamber  201  while ambient atmospheric conditions prevail outside of the vacuum chamber  201 . For example, the vacuum chamber  201  may be configured to maintain a pressure of less than 10 −2  Torr within the vacuum chamber  201  while the pressure outside of the vacuum chamber  201  is approximately 760 Torr. As an example, the vacuum chamber  201  is a steel chamber or a glass chamber. 
     The pump  202  may be fluidly coupled to the vacuum chamber  201  to evacuate the vacuum chamber  201  so that vacuum conditions exist within the vacuum chamber  201 . The pump  202  may include one or more mechanical pumps, turbo-molecular pumps, diffusion pumps, ion pumps, or cryopumps, among other possibilities. 
     The insertion point  208  of the vacuum chamber  201  may include a feedthrough suitable for inserting the substrate  203  into the vacuum chamber  201  while maintaining vacuum conditions inside the vacuum chamber  201 . Similarly, the removal point  210  of the vacuum chamber  201  may include a feedthrough suitable for removing the substrate  203  from the vacuum chamber  201  while maintaining vacuum conditions inside the vacuum chamber  201 . (In some examples, the vacuum chamber  201  may contain the entirety of the apparatus  200 , and such sealed feedthroughs may not be necessary. In other examples, the feeding reel  204  and/or the collection reel  206  may be located within respective load-lock chambers that are evacuated to vacuum conditions. In this case, the insertion point  208  and the removal point  210  may each include an interface for transferring the substrate  203  from one evacuated chamber to another.) The external region  205  of the vacuum chamber  201  may include any region within the vacuum chamber  201  that is not within the container  214 , as noted below. 
     In one example, the substrate  203  is similar to the substrate  100  illustrated in  FIG. 1  (or similar to other example substrates discussed with reference to  FIG. 1 ). Initially, at least a portion of the substrate  203  may be rolled up on the feeding reel  204 . The substrate  203  may be unfurled by the feeding reel  204  and advanced by the collection reel  206  such that the substrate  203  may be fed through the insertion point  208  and into the vacuum chamber  201 . The feeding reel  204  and the collection reel  206  may function to move the substrate  203  over the container  214  with a CIGS surface of the substrate  203  facing down toward the container  214  so that the material  218  may be evaporated onto the substrate  203  as the substrate  203  moves above the container  214 . As shown in  FIG. 2 , the substrate  203  may be moved by the collection reel  206  and the feeding reel  204  along the ‘z’ axis of the container  214 . Throughout this disclosure, the ‘z’ axis may be referred to as a second axis of the container  214 , but this is an arbitrary convention. 
     While moving through the vacuum chamber  201 , the substrate  203  may be heated by a substrate heater (not shown). The collection reel  206  and the feeding reel  204  may be configured to move the substrate  203  through the vacuum chamber  201  at a rate that allows a predetermined amount of the material  218  to be evaporated onto the substrate  203 . The substrate  203  may be removed from the vacuum chamber  201  at the removal point  210 , which may include a feedthrough similar to that of the insertion point  208 . 
     The container  214  may be a graphite block machined to include the cavity  216  and the one or more openings  220 . In  FIG. 2  the cavity  216  is depicted as cylindrical, but the cavity  216  may have other shapes as well. Both the container  214  and the cavity  216  are elongated along a first axis of the container  214 . The first axis may be referred to herein as a ‘y’ axis, but this is an arbitrary convention. The cavity  216  may be configured to contain the material  218 , such that when the container  214  is heated by the heaters  222  and  224 , the material  218  is also heated. The one or more openings  220  may be distributed along the ‘y’ axis of the container and provide fluid communication between the external region  205  and the cavity  216 . As used in this disclosure, “fluid communication” may encompass liquid communication and/or vapor communication. 
     The heaters  222  and  224  are also elongated along the ‘y’ axis and are configured to heat and evaporate the material  218  by heating the container  214 . The heaters  222  and  224  may each comprise a pair of graphite blocks machined to dimensions desired. Electric current may be passed through the graphite blocks to generate heat, which may then be radiated toward the container  214 . As shown in  FIG. 2 , the heaters  222  and  224  are located external to the container  214 ; however, in other examples, the heaters  222  and  224  are electrically isolated from the container and then embedded within the container  214  to heat the container  214  via heat conduction or radiation. 
     If the heated material were in the external region  205 , the vapor pressure of the heated material might quickly reach equilibrium with the ambient pressure of the external region  205 . In such a situation, the heated material may transition (i.e., sublimate) directly from a solid phase to a gaseous phase to be deposited upon the substrate  203 . However, sublimation of the heated material may result in non-uniform thickness of the material upon the substrate  203 . For this reason, evaporation of the material is preferable to sublimation. Evaporation of the material may result from proper temperature and pressure control within the container  214 , and having the total cross-sectional area of the one or more openings  220  sized appropriately. 
     For this reason, the container  214  may be substantially enclosed so as to maintain a pressure differential between the cavity  216  and the external region  205  when the material  218  is heated. For example, the one or more openings  220  may be sized such that when the material  218  is sufficiently heated by the heaters  222  and  224 , at least a portion of the material  218  melts from a solid phase into a liquid phase. By fluidly coupling the external region  205  and the cavity  216  with the one or more openings  220 , a vapor pressure of the material  218  that is sufficient for evaporation of the material  218  may be maintained. That is, the one or more openings  220  may be sized to restrict flow of vapor of the material  218  such that pressure within the cavity  216  does not reach equilibrium with the evacuated external region  205 . 
       FIG. 3  illustrates another example apparatus  300  for depositing a material  318  onto a substrate  303 . Also illustrated in  FIG. 3  is a container  314  that includes one or more openings  320 . The container  314  may be similar to the container  214  of  FIG. 2 , except that the one or more openings  320  have different shapes and locations when compared to the one or more openings  220  of  FIG. 2 . For example, the one or more openings  320  may include elbows or bends that provide fluid communication between the cavity  316  and the external region  305 . The one or more openings  320  may also be offset along the ‘z’ axis with respect to the cavity  316 . These differences are further explained below with reference to  FIGS. 6 and 7 . 
       FIG. 4  illustrates an example container  414  and example heaters  422  and  424  for depositing a material  418  onto a substrate (not shown) above the container  414 . Also shown in  FIG. 4  are openings  420 A,  420 B,  420 C, and  420 D that provide fluid communication between the cavity  416  and an external region  405  that is within a vacuum chamber (not shown) yet external to the container  414 . 
     As shown, the container  414  is elongated along the ‘y’ axis of the container  414  to facilitate uniform deposition of the material  418  onto the substrate. The substrate may span the ‘y’ axis and be conveyed along the ‘z’ axis. (See  FIGS. 2 and 3  for example substrates.) 
     As the material  418  is heated by the heaters  422  and  424 , at least a portion of the material  418  evaporates and diffuses through the openings  420 A-D, into the external region  405 , and onto the substrate. The openings  420 A-D may be distributed along the ‘y’ axis such that the openings  420 A-D have overlapping respective deposition profiles. That is, material  418  that evaporates and passes through the opening  420 A may sometimes deposit upon the substrate in the same place where material that evaporated and passed through the opening  420 B had also deposited upon the substrate. As shown in  FIG. 4 , the openings  420 A-D may include respective ports at a top exterior surface of the container  414 . In some examples, the respective ports may have a conical shape, but other shapes are possible. 
       FIG. 5  illustrates an example container  514  and example heaters  522  and  524  for depositing a material  518  onto a substrate (not shown) above the container  514 . Also shown in  FIG. 5  is an opening  520  that provides fluid communication between the cavity  516  and an external region  505  that is within a vacuum chamber (not shown) yet external to the container  514 . 
     The container  514  may differ from the container  414  in that the container  514  includes a single opening  520  that is aligned with the ‘y’ axis. The opening  520  may resemble a rectangular trench that provides fluid communication between the cavity  516  and the external region  505 ; however other shapes are possible. The vacuum chamber may be evacuated such that vacuum conditions exist in the external region  505 . In this context, maintaining a vapor pressure within the cavity  516  that is sufficient for a liquid phase of the material  518  to exist may require that the opening  520  is sized similarly to the openings  420  of  FIG. 4 . This could mean, for example, that for containers  514  and  414  of similar size, the total cross sectional area of the openings  420  may be substantially equal to the total cross sectional area of the opening  520 . As the material  518  is heated by the heaters  522  and  524 , at least a portion of the material  518  evaporates and diffuses through the opening  520  and onto the substrate. 
     Also depicted in  FIG. 5  is a plug  517 . The plug  517  may be sized appropriately to seal the cavity  516  at a front end of the container  514 , and a similar plug may seal the cavity  516  at a back end of the container  514 . The plug  517  may be comprised of graphite machined to have a cylindrical shape that fits snugly or threads into the cavity  516  or is configured to seal through any number of other methods. Having the cavity  516  sealed at front and back ends by respective plugs, caps, or other sealing means may result in the opening  520  providing the only fluid communication between the cavity  516  and the external region  505 . Similar plugs may also be used to seal front and back ends of the cavities  416  of  FIG. 4 , as well as cavity  616  of  FIG. 6  and cavity  716  of  FIG. 7 . 
       FIG. 6  illustrates an example container  614  and example heaters  622  and  624  for depositing a material  618  onto a substrate (not shown) above the container  614 . Also shown in  FIG. 6  are openings  620 A,  620 B,  620 C, and  620 D that provide fluid communication between the cavity  616  and an external region  605  that is within a vacuum chamber (not shown) yet external to the container  614 . 
     As shown in  FIG. 6 , both heater  622  and heater  624  are adjacent to the container  614  on opposite sides of the container  614 . The openings  620 A-D may be offset along the ‘z’ axis when compared to the cavity  616 . The openings  620 A-D may include ports at a top exterior surface of the container  614 . As shown, the heater  622  may be closer to the respective ports than to the cavity  616  and the heater  624  may be closer to the cavity  616  than to the respective ports. In some examples, the heater  622  may radiate more heat than the heater  624 , causing the evaporated material  618  to experience an increasing temperature gradient as the evaporated material  618  diffuses from the cavity  616  toward the substrate above the container  614 . This increasing temperature gradient help prevent the evaporated material  618  from condensing on the walls of the openings  620 A-D, which may otherwise disrupt the flow of the evaporated material  618  into the external region  605  and toward the substrate. 
       FIG. 7  illustrates an example container  714  and example heaters  722  and  724  for depositing a material  718  onto a substrate (not shown) above the container  714 . Also shown in  FIG. 7  is an opening  720  that provides fluid communication between the cavity  716  and an external region  705  that is within a vacuum chamber (not shown) yet external to the container  714 . 
     As shown in  FIG. 7 , both heater  722  and heater  724  are adjacent to the container  714  on opposite sides of the container  714 . The opening  720  may be offset along the ‘z’ axis when compared to the cavity  716 . The opening  720  may include a single port at a top exterior surface of the container  714 . As shown, the heater  722  may be closer to the port than to the cavity  716  and the heater  724  may be closer to the cavity  716  than to the port. In some examples, the heater  722  may radiate more heat than the heater  724 , causing the evaporated material  718  to experience an increasing temperature gradient as the evaporated material  718  diffuses from the cavity  716 , into the external region  705 , and toward the substrate above the container  714 . This increasing temperature gradient may help prevent the evaporated material  718  from condensing on the walls of the opening  720 , which may otherwise disrupt the flow of the evaporated material  718  toward the substrate. 
       FIG. 8  is a block diagram of an example process  800  for depositing a predetermined amount of a material onto a substrate. In some examples, the material includes mixtures or compounds that include sodium or potassium, such as sodium fluoride (NaF), potassium fluoride (KF), sodium selenide (Na 2 Se), or sodium oxide (Na 2 O). The container may be formed in whole or in part from graphite. For example, the container may be a graphite block machined to have features such as those of the containers described above with reference to  FIGS. 2-7 . 
     At block  802 , the process  800  involves providing a container having a cavity. The container and the cavity are elongated along a first axis of the container and the container is located within a vacuum chamber. The container comprises one or more openings distributed along the first axis, where the one or more openings provide fluid communication between the cavity and a region within the vacuum chamber that is external to the container. 
     Referring to  FIG. 2  for example, the container  214  is located within the vacuum chamber  201  and is elongated along the ‘y’ axis. The container includes one or more openings  220  that are distributed along the ‘y’ axis. The one or more openings  220  provide fluid communication between the cavity  216  and the external region  205 . 
     At block  804 , the process  800  involves inserting the material into the cavity of the container. In some examples, this includes spooning a powdered material into the cavity of the container, and then placing the container into the vacuum chamber so that the vacuum chamber may be evacuated. In other examples, the container is affixed to the vacuum chamber and the material is inserted into the cavity while the container sits within the vacuum chamber. 
     At block  806 , the process  800  involves heating the container, whereby the predetermined amount of the material evaporates and exits the container via the one or more openings. For example, the container  214  may be heated by the heaters  222  and  224 , resulting in a predetermined amount of the material  218  evaporating and exiting the container  214  via the one or more openings  220 . 
     If the one or more openings are sized appropriately and the container is placed within an evacuated vacuum chamber, heating the container causes at least some of the material to form a liquid phase inside of the cavity. That is, the one or more openings may be sized to restrict the flow of vapor of the material such that an elevated vapor pressure of the material is maintained within the cavity. 
     In some examples, heating the container may involve heating the container with one or more heaters that are elongated along the first axis of the container, as described above with reference to  FIGS. 2-7 . Such heaters are located external to the container. In other embodiments, the heaters are embedded within the container. 
     In other examples, heating the container may involve heating the container with a heater that is adjacent to the container, where the one or more openings comprise respective ports at an exterior surface of the container, and where the heater is closer to the respective ports than to the cavity. Referring to  FIG. 6  for example, the heaters  622  and  624 , which are adjacent to the container  614 , may heat the container  614 . The heater  622  may be closer to the ports respectively corresponding to the openings  620 A-D than to the cavity  616 . 
     In this context, heating the container may involve heating a portion of the container proximate to the respective ports to a first temperature, and heating a portion of the container proximate to the cavity to a second temperature that is less than the first temperature. 
     The container  614  may include one or more openings  620 A-D and respective ports that are located on the top exterior surface of the container  614 . The heater  622  may be set to radiate more heat than the heater  624 , and as a result, regions of the container  614  that are near the respective ports may be heated to a higher temperature than regions of the container near the cavity  616 . This may result in the evaporated material  618  experiencing an increasing temperature gradient as the evaporated material  618  diffuses from the cavity  616  to the external region  605 , through the one or more openings  620 A-D. 
     In another example, the heaters  622  and  624  may be set to radiate roughly equal amounts of power, but the distance separating the heater  622  and the respective ports may be less than the distance separating the heater  624  and the cavity  616 . This may also result in the evaporated material  618  experiencing an increasing temperature gradient as the evaporated material  618  diffuses from the cavity  616  to the external region  605 , through the one or more openings  620 A-D. 
     At block  808 , the process  800  involves moving the substrate above the one or more openings along a second axis of the container that is substantially perpendicular to the first axis, thereby depositing the predetermined amount of the material onto the substrate. For example, the substrate  203  may be moved above the one or more openings  220  along the ‘z’ axis, which is perpendicular to the ‘y’ axis along which the cavity  216  and the container  214  are elongated. 
     The above detailed description describes various features and functions of the disclosed systems and processes with reference to the accompanying figures. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. All embodiments within and between different aspects of the invention can be combined unless the context clearly dictates otherwise. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.