Patent ID: 12191114

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited by embodiments of the present disclosure. On the contrary, these embodiments are provided to make the present disclosure thorough and complete and to fully convey the scope of the disclosure to those skilled in the art.

As shown inFIG.1, an existing inductive coupled plasma (ICP) etching apparatus mainly includes a chamber body1, an upper radio frequency system2, a dielectric window3, a liner4, and an electrostatic chuck5, a focus ring6, an electrostatic chuck base7, a lower radio frequency system8, a pressure control valve9, a vacuum system10, a process gas nozzle11, and a wafer transfer gap12.

The dielectric window3is arranged on a top of the chamber body1. The electrostatic chuck5is arranged in the chamber body1and placed on the electrostatic chuck base7to carry the wafer. An area between the dielectric window3and the electrostatic chucks5is a plasma generation area. The process gas nozzle11is arranged on the dielectric window3and configured to transfer the process gas to the above-mentioned plasma generation area. The upper radio frequency system2is arranged above the dielectric window3and configured to excite the process gas to form the plasma. The lower radio frequency system8is electrically connected to the electrostatic chuck5and configured to apply a bias power to the electrostatic chuck5. In addition, the focus ring6is arranged around the electrostatic chuck5. The liner4is arranged around the above-mentioned plasma area of the chamber body1. The vacuum system10is evacuated through an outlet from the lower part of the chamber body1.

However, the existing plasma etching apparatus is configured to mix the plasma generation gas (such as argon) and the process reaction gas (such as chlorine) into a same channel, which makes it difficult to precisely and quickly control the gas injection, and the formed plasma energy density is high, which is easy to form an overreaction, affects the fine etching of the wafer pattern. For processing a tiny structure with little or no space, when the plasma bombards the wafer, the tiny structure may be damaged on the wafer.

FIG.2is a schematic structural diagram of a plasma etching apparatus. With reference toFIG.2, the apparatus includes a reaction chamber94. A quartz cover92is arranged above the reaction chamber94. A gas inlet nozzle mounting hole91is arranged at an approximate center of the quartz cover92. A gas inlet nozzle mounted here may be configured to inject the process gas outside the reaction chamber94into the gas distribution chamber90located at a lower part of the reaction chamber94. In addition, an electrostatic chuck97is arranged in the reaction chamber94and configured to adsorb and fix the wafer99. A focus ring98is arranged around the electrostatic chuck97and configured to protect the lower electrode part from being bombarded by the plasma. A liner93is arranged around an inner wall of the reaction chamber94and configured to prevent the inner wall of the reaction chamber94from being contaminated by the etching reaction product. In addition, a plurality of small holes are arranged at a bottom of the liner93and configured to transfer the reaction product in the reaction chamber94to the gas extraction chamber95and discharge the reaction product from the gas outlet96of the gas extraction chamber95.

FIG.3is a schematic structural exploded view of a gas distribution device. With reference toFIG.3, the gas distribution device26includes a support plate20located at an upper position and a spray head electrode22located at a lower position, which are assembled together to form a gas distribution chamber. In order to make the gas flow distribution more uniform, a choked flow assembly is arranged in the above-mentioned gas distribution chamber, which includes one or more choked flow plates (30A,30B,30C, . . . ). The gas distribution device may be particularly suitable for a dual-zone (dual-path) gas inlet system. A first path gas (i.e., a central zone gas) may enter the device through the central gas inlet pipeline40arranged on a support plate20. A second-path gas (i.e., gas in an edge area) may enter the device from an edge gas inlet channel44arranged on the support plate20. In the choked flow plate30A closest to the support plate20, a central area42and an edge area46are separated by a seal ring38. Thus, the first path gas may enter the central area42of the gas distribution chamber, and the second path gas may enter the edge area46of the gas distribution chamber. A uniform gas distribution may be obtained ultimately at a backside28of the spray head electrode22. Then, the gas uniformly distributed here may enter the reaction chamber through the spray head electrode22(an upper electrode of the semiconductor etching apparatus) and form a uniform gas distribution above the processed wafer in the reaction chamber. In addition, gas hole channels52A,52B,52C,54, etc., which are substantially perpendicular to the upper and lower surfaces, are evenly distributed on the above-mentioned choked flow assembly and the spray head electrode22.

The gas distribution chamber90shown inFIG.2is configured to cause the process gas to uniformly enter the reaction chamber94. The gas distribution device shown inFIG.3can achieve the purpose of uniform gas diffusion by distributing the gas through four layers of sieve plates with holes. It can be seen that the gas distribution chamber90shown inFIG.2and the gas distribution device shown inFIG.3are mainly configured to distribute the process gas uniformly, but neither can reduce the energy density of the plasma.

First Embodiment

With reference toFIG.4, the present embodiment provides a semiconductor reaction chamber, including a dielectric window108, a reaction chamber body100, a spray head107, and a process reaction gas inlet member106. The material of the dielectric window108may be a ceramic material or a quartz material. The dielectric window108is arranged above the reaction chamber body100. The plasma generation area is below the dielectric window108. In addition, a central nozzle system109is arranged on the dielectric window108and configured to introduce a plasma generation gas (such as argon) into the above-mentioned plasma generation area. In addition, a chamber body100includes a base103configured to carry a wafer117. The base103may be, for example, an electrostatic chuck. The electrostatic chuck is arranged in the reaction chamber body100through the electrostatic chuck base102.

With reference toFIG.5AandFIG.5Btogether, the spray head107, for example, is made of a metal material. The spray head107is arranged between the dielectric window108and a top wall of the reaction chamber body100and divides the above-mentioned plasma generation area into an strong plasma area128at an upper part and a weak plasma area129at a lower part. The strong plasma area128may facilitate plasma ignition. In addition, a plurality of through-holes120are distributed in the central area of the spray head107and configured to allow the plasma in the strong plasma area128to pass through. The through-holes120can reduce the energy of the plasma, which enters the through-holes120from the strong plasma area128. Thus, the plasma entering the weak plasma area129may be a plasma with low energy density, which can provide a plasma source with the low energy for etching processes, such as plasma etching or atomic layer etching. The plasma damage may be reduced. Especially when microstructures with little or no space are processed, the microstructures on the wafer may be prevented from being damaged. In addition, with the aid of the first gas channel in the edge area of the spray head and the second gas channel in the process reaction gas inlet member, an input channel configured to introduce the process reaction gas into the weak plasma area alone may be formed. Thus, the gas can be controlled and input fast and precisely to satisfy gas fast control requirement of the atomic layer etching process.

As shown inFIG.4, the first gas channel is arranged in the edge area of the spray head107. A gas outlet end of the first air channel is communicated with the weak plasma area129. The process reaction gas inlet member106is located on a side where the inlet end of the first channel of the spray head107is located. The second gas channel is arranged in the process reaction gas inlet member106. The second gas channel may be configured to introduce the process reaction gas (such as chlorine) into the first gas channel. With the aid of the first gas channel in the edge area of the spray head107and the second gas channel in the process reaction gas inlet member106, an input channel configured to introduce the process reaction gas into the weak plasma area128alone can be formed, which can realize rapid and precise control and input of the gas to satisfy the gas rapid control requirements of the atomic layer etching process.

In some embodiments, as shown inFIG.5AandFIG.5B, the above-mentioned first gas channel includes a plurality of gas holes119distributed at intervals along a circumferential direction of the spray head107, which are configured to uniformly distribute the process reaction gas. Further, in some embodiments, in order to facilitate the communication between the gas inlet end of the gas hole119and the gas outlet end of the above-mentioned second gas channel, the gas outlet end of the gas hole119is communicated with the weak plasma area128. Each gas hole119is arranged obliquely, that is, an axis of each gas hole119forms an included angle with an axis of the reaction chamber body100. The gas outlet end of the gas hole119may be closer to the axis of the reaction chamber body100than the gas inlet end.

The above-mentioned spray head107may have various structures. For example, as shown inFIG.5AandFIG.5B, the spray head107includes a circular plane member107aand an annular member107bconnected to the spray head107and surrounding the circular plane member107a. The circular plane member107ais in a circular disk shape. The plurality of through-holes120are evenly distributed on the circular plane member107a, for example, uniformly distributed on the circular plane member107ain a concentric circle manner. In some embodiments, the axis of the through-hole120is perpendicular to the plane where the circular plane member107ais located. The plurality of gas holes119are distributed at intervals along the circumferential direction of the annular member107b.

In some embodiments, optionally, a thickness of the annular member107bmay be greater than the thickness of the circular plane member107a. A lower surface of the annular member107bmay be flush with a lower surface of the circular plane member107a. The annular member107bmay be located on an inner side of the reaction chamber body100. An annular flange may be arranged surrounding an outer peripheral wall of the annular member107b. The annular flange may be stacked at the top of the reaction chamber body100to realize the fixed connection between the annular member107band the reaction chamber body100. The gas inlet end of each gas hole119may be located on the upper surface of the above-mentioned annular flange. The gas outlet end of each gas hole119is located on the lower surface of the annular member107b, which facilitates the communication between the gas inlet end of the gas hole119and the gas outlet end of the second gas channel. The gas outlet end of the gas hole119may be communicated with the weak plasma area128.

It should be noted that, in the present embodiment, one circular plane member107amay be included. However, embodiments of the present disclosure are not limited to this. In practical applications, a plurality of circular plane members107amay be provided and be stacked with each other.

In some embodiments, a diameter of a through-hole120may range from φ1 mm to φ10 mm, preferably φ4 mm. A porosity of the circular plane member107amay range from 10% to 80%, preferably 60%. By setting the diameter of the through-hole120and the porosity of the circular plane member107awithin the above two ranges, the plasma entering the weak plasma area129may be guaranteed to be the low energy density plasma. Of course, in practical applications, the diameter of the through-hole120and the porosity of the circular plane member107acan be freely set according to parameters such as a gas flow rate of the spray head107and a plasma ignition pressure.

In some embodiments, the diameter of the gas hole119can be set to range from φ1 mm to φ8 mm. In some embodiments, a nozzle can be arranged at the gas hole119. The diameter of the nozzle may range, for example, from φ1 mm to φ5 mm. In some embodiments, a number of the gas holes119may be 8, and the diameter of the gas hole119may be set to φ4 mm.

In some embodiments, optionally, a vertical distance between the upper surface of the circular plane member107aof the spray head107and the lower surface of the dielectric window108may range from 20 mm to 200 mm, preferably from 40 mm to 100 mm. A vertical distance between the lower surface of the circular flat member107aof the spray head and the upper surface of the wafer placed on the base103may range from 20 mm to 100 mm, preferably from 30 mm to 80 mm. For example, the vertical distance between the upper surface of the circular plane member107aof the spray head107and the lower surface of the dielectric window108may be 60 mm. The lower surface of the circular plane member107aof the spray head and the upper surface of the wafer on the base103may be 40 mm.

In some embodiments, optionally, the above-mentioned process reaction gas inlet member106may be a gas distribution and support ring. The gas distribution and support ring may mainly include two functions, first, being used as a support member for the dielectric window108and forming a chamber inside, and second, being used as a gas distribution mechanism to cause the process reaction gas to enter the above-mentioned first gas channel through the second gas channel. In some embodiments, at least a part of the gas distribution and support ring may be stacked on the upper surface of the spray head107and correspond to the plurality of gas holes119. A plurality of gas outlet ends of the above-mentioned second gas channel may be provided and located on a surface of the gas distribution and support ring that contacts the upper surface of the spray head107and communicated with the gas inlet ends of the plurality of gas holes119in a one-to-one correspondence to communicate the second gas channel with the first gas channel.

In some embodiments, optionally, with reference toFIG.6B, one gas inlet end118aof the second gas channel has one gas inlet end118a, which is located on the upper surface of the gas distribution and support ring and configured to be communicated with the gas inlet pipeline118. As shown inFIG.6A, the second gas channel includes a plurality of arc-shaped sub-gas channel groups that are concentric with the above-mentioned gas distribution and support ring and have different radii and a plurality of lower outlets123. A plurality of arc-shaped sub-gas channel groups may be communicated in sequence. In two communicated arc-shaped sub-gas channel groups, a number of arc-shaped sub-gas channels in a downstream arc-shaped sub-gas channel group may be two times a number of arc-shaped sub-gas channels in an upstream arch-shaped sub-gas channel group. Thus, a path process reaction gas entering arc-shaped sub-gas channels of a most upstream arc-shaped sub-gas channel group from the gas inlet ends118aof the second gas channel may be divided into a plurality of sub-paths on average by a corresponding number of arc-shaped sub-gas channels in the plurality of downstream arc-shaped sub-gas channel groups in sequence. That is, a path process reaction gas may be first divided into two sub-paths, and the two paths may be then divided into four sub-paths, and so on. A number of the gas outlet ends of the arc-shaped sub-gas channels of the most downstream arc-shaped sub-gas channel group may have a same number of the gas holes119. The gas outlet ends may be communicated with the gas holes119through the plurality of lower outlets123in a one-to-one correspondence.

For example, as shown inFIG.6AandFIG.7, three arc-shaped sub-gas channel groups are included and include a first arc-shaped sub-gas channel group131, a second arc-shaped sub-gas channel group132, and a third arc-shaped sub-gas channel group133in a gas inlet direction. The radius of the third arc-shaped sub-gas channel group133may be greater than the radius of the second arc-shaped sub-gas channel group132and smaller than the radius of the first arc-shaped sub-gas channel group131. In addition, the first arc-shaped sub-gas channel group131may include an arc-shaped sub-gas channel. The second arc-shaped sub-gas channel group132may include two centrally symmetric arc-shaped sub-gas channels. The third arc-shaped sub-gas channel group133may include four centrally symmetric arc-shaped sub-gas channels. Each arc-shaped sub-gas channel may include one gas inlet end and is located in the middle position. Each arc-shaped sub-gas channel may include two gas outlet ends and located at two ends. Specifically, the inlet end of the arc-shaped sub-gas channel of the first arc-shaped sub-gas channel group131at the middle position may be used as the gas inlet end118aof the second gas channel and may be communicated with the gas inlet pipeline118. The two gas outlet ends of the arc-shaped sub-gas channel at both ends may be communicated with the gas inlet ends of the two arc-shaped sub-gas channels in the second arc-shaped sub-gas channel group132at the middle position, respectively. The two gas outlet ends of the two arc-shaped sub-gas channels at both ends may be communicated with the gas inlet ends of the four arc-shaped sub-gas channels in the third arc-shaped sub-gas channel group133at the middle position. As shown inFIG.6A, the two gas outlet ends located at the two ends of the four arc-shaped sub-gas channels are all communicated with the lower outlets123. Thus, the one path process reaction gas can be evenly divided into the plurality of sub-paths, and the gas flow paths of the sub-paths can be guaranteed to be the same. Thus, the process reaction gas in the sub-paths can reach the lower outlets123simultaneously. In some embodiments, a number of the lower outlets123may be 4 to 12. Thus, the one path process reaction gas may be divided into 4 to 12 portions correspondingly.

In some embodiments, optionally, surface processing such as anti-plasma spray may be performed on a surface of the part in contact with the plasma. For example, for an aluminum material, surface oxidation processing and yttrium oxide spray processing may be required.

Second Embodiment

With reference toFIG.8, the semiconductor reaction chamber of the present embodiment, compared with the above-mentioned first embodiment, also includes a dielectric window108, a reaction chamber body100, a spray head107, and a process reaction gas inlet member106. Since the structures and functions of these components have been described in detail in the above-mentioned first embodiment, the structures and functions of these components are not repeated here. Only the differences between the semiconductor reaction chambers provided in the present embodiment and the above-mentioned first embodiment are described in detail below.

Specifically, the semiconductor reaction chamber further includes a gas distribution ring110. The gas distribution ring110is arranged around below the spray head107. As shown inFIG.9AtoFIG.9C, a plurality of third gas channels are arranged at intervals along a circumferential direction in the gas distribution ring110. The gas inlet ends of the third gas channels are communicated with the gas outlet ends of the gas holes119in a one-to-one correspondence. The gas outlet ends of the gas holes119may be communicated with the weak plasma area129through the above-mentioned third gas channels. The third gas channel may include a plurality of structures. For example, as shown inFIG.9C, a third gas channel includes a first through-hole122arranged along an axial direction of the gas distribution ring110and a second through-hole121arranged along a radial direction of the gas distribution ring110. The gas inlet end of the first through-hole122may be used as the gas inlet end of the third gas channel and located on an upper surface of the gas distribution ring110. The gas outlet end of the first through-hole122may be communicated with the gas inlet end of the second through-hole121. The gas outlet end of the second through-hole121may be used as the gas outlet end of the third gas channel and located on an inner sidewall of the gas distribution ring110.

In some embodiments, a spray head may be arranged at the third gas channel. A diameter of the spray head may be, for example, φ2 mm.

On one hand, the gas distribution ring110may be configured to uniformly and controllably transfer the process reaction gas to the weak plasma area129. On another hand, the gas distribution ring110may fill the inner chamber of the reaction chamber body100. The weak plasma area129may be formed and enclosed by the spray head107, the gas distribution ring110, and the base103. Compared with the conventional reaction chamber body100, the volume of the weak plasma area129may be greatly reduced, which is beneficial to reduce gas flow retention time, improve switching efficiency of etching processing and auxiliary time, and provide a hardware basis for atomic layer plasma etching.

For example, the gas distribution ring110may be located inside the above-mentioned reaction chamber body100and be stacked on the lower surface of the annular member107bof the spray head107.

It should be noted that, in the present embodiment, the second through-hole121may be arranged along the radial direction of the gas distribution ring110. However, embodiments of the present disclosure are not limited to this. In practical applications, the second through-hole121may also have a predetermined included angle with the axial direction of the reaction chamber body100to obtain a desired gas inlet direction.

It should also be noted that, in the present embodiment, the third gas channel may include the first through-hole122and the second through-hole121. However, embodiments of the present disclosure are not limited to this. In practical applications, the third gas channel may also be a through-hole that is inclined and has a predetermined angle with the axial direction of the reaction chamber body100or any other structure.

Structures and functions of other components of the present embodiment may be same as those of the above-mentioned first embodiment. Since the structures and functions of the other components are described in detail the above-mentioned first embodiment, the structures and functions of the other components will not be repeated here.

In the above-mentioned first and second embodiments, optionally, the semiconductor reaction chamber may further include a focus ring105and a liner101. The focus ring105may be arranged outside the base103(e.g., an electrostatic chuck) and configured to protect the lower components. The liner101may be arranged between the gas distribution ring110and the base103and around the inner wall of the reaction chamber body100to prevent the etching reaction product from contaminating the reaction chamber. The lower part and the side part of the liner101may be provided with grid holes to facilitate the gas flow.

In some embodiments, the semiconductor reaction chamber may further include a base ring104. The base ring104may be arranged around the base103. The focus ring105may be arranged on the base ring104.

In addition, a opening111may be arranged on the liner101and the reaction chamber body100and configured to transfer the wafer117. The opening111may be provided with an inner door (the gap is closed after the transfer is completed). When the wafer117is transferred, the inner door may be opened. After the wafer117is loaded on the electrostatic chuck, the inner door is closed to form a plasma area in a sealed area. The transfer of the wafer117between the transfer platform and the semiconductor reaction chamber can be achieved by a vacuum manipulator116.

In summary, in the semiconductor reaction chambers of embodiments of the present disclosure, the plasma generation area may be divided into the strong plasma area at the upper part and the weak plasma area at the lower part through the spray head. The plurality of through-holes distributed at the middle area in the spray head may be configured to reduce the energy of the plasma that enters the through-holes from the strong plasma area. Thus, the plasma that enters the weak plasma area may be the plasma with low energy density to provide the low energy plasma source for the etching processes of the plasma etching or atomic layer etching and reduce the plasma damage. Especially, when the microstructure with little or no space is processed, the microstructures on the wafer may be prevented from being damaged. In addition, with the aid of the first gas channel in the edge area of the spray head and the second gas channel in the process reaction gas inlet member, an input channel is configured to introduce the process reaction gas into the weak plasma area alone. Thus, the rapid and precise control and input of the gas may be achieved, which satisfies the gas rapid control requirement of the atomic layer etching process.

Third Embodiment

The present embodiment provides an atomic layer plasma etching apparatus. The plasma etching apparatus can be configured to complete conventional low-density plasma etching processing and perform atomic layer etching processing in combination with the principle of atomic layer etching.

With reference toFIG.10, the plasma etching apparatus includes a semiconductor reaction chamber, an upper radio frequency system112, and a lower radio frequency system113. The above-mentioned semiconductor reaction chamber is the semiconductor reaction chamber of embodiments of the present disclosure. A base103configured to carry a wafer is arranged in the semiconductor reaction chamber. The semiconductor reaction chamber includes a reaction chamber body100, and a process reaction gas inlet member106and a dielectric window108that are sequentially stacked on the top of the reaction chamber body100along the direction away from the reaction chamber body100. In addition, the spray head107is arranged between the dielectric window108and the top wall of the reaction chamber body100and located on an inner side of the above-mentioned process reaction gas inlet member106. In some embodiments, the gas distribution ring110is arranged around below the spray head107.

In addition, a central nozzle system109may be arranged on the dielectric window108and configured to introduce the plasma generation gas into the plasma generation area. The upper radio frequency system112may be arranged above the dielectric window108and configured to excite the plasma generation gas to form the plasma. The lower radio frequency system113may be electrically connected to the base103and configured to load bias power. For example, the upper radio frequency system112may be configured to provide a high-frequency power supply and ionize the gas to generate the plasma. The lower radio frequency system113may apply the bias power to the base103, which can accelerate the plasma to move toward the surface of the wafer117to realize the plasma etching processing of the wafer117. A pressure control valve114and a vacuum pump system115may be arranged at the lower portion of the reaction chamber body100and configured to control the pressure and evacuation in the reaction chamber body100. The vacuum pump system115may include a gas exhaust opening130configured to exhaust the gas.

In addition, a opening111may be arranged on the liner101and the reaction chamber body100and configured to transfer the wafer117. The opening111may be provided with an inner door (the opening111is closed after the transfer is completed). When the wafer117is transferred, the inner door may be opened. After the wafer117is loaded on the base103, the inner door may be closed to form a plasma area in a sealed area. The transfer of the wafer117between the transfer platform and the reaction chamber may be achieved by a vacuum manipulator116.

The main process of performing the atomic layer etching using the above-mentioned plasma etching apparatus includes as follows.

1) The process reaction gas provided by the gas inlet pipeline118enters the second channel of the process reaction gas inlet member106. After being evenly distributed in the second channel, the process gas flows into the third channel of the gas distribution ring110through the gas holes119of the spray head107and flows into the weak plasma area129through the third channels. A layer of gas that can react with the to-be-etched material (remove) chemically may be absorbed in the to-be-etched surface (without mask) of the wafer117. The reaction occurs to form the reaction product. The includes but is not limited to chlorine gas, tetrafluorocyclobutane, etc.

2) The remaining excessive process reaction gas is pumped out by the vacuum pump system115.

3) The plasma generation gas (e.g., argon) is transferred into the strong plasma area128through the central nozzle system109arranged on the dielectric window108. The pressure control valve114controls the pressure in the reaction chamber body100, the upper radio frequency system112feeds the high-frequency radio frequency power, and the ionized gas is ignited to generate a high-density strong plasma. Through a high vacuum function of the vacuum pump system115, a part of the plasma is driven to move from the strong plasma area128to the weak plasma area129. The plasma bombards the unmasked surface of the wafer117. The wafer reacts with the etching process gas to generate the reaction product. The reaction product is stripped off.

4) The vacuum pump system115is configured to pump all the gases and reaction products in the reaction chamber body100out of the reaction chamber body100. By making the above four steps as one cycle, the material of the atomic layer thickness of the etched material may be removed by one cycle. The predetermined target material etching is realized through a plurality of cycles.

It should be noted that, in the atomic layer plasma etching apparatus provided in the present embodiment, the semiconductor reaction chamber may be the semiconductor reaction chamber of the first embodiment or the second embodiment of the present disclosure.

The atomic layer plasma etching apparatus of embodiments of the present disclosure can provide the low-energy plasma source, reduce plasma damage, and realize rapid and precise control and input of the gas through the semiconductor reaction chamber of various embodiments of the present disclosure. Thus, the gas rapid control requirement of the atomic layer etching process may be satisfied.

Various embodiments of the present disclosure have been described above, and the above descriptions are exemplary, not exhaustive, and not limited the disclosed embodiments. Modifications and variations may be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles of the embodiments, the practical applications, or technical improvements in the marketplace or to enable those of ordinary skill in the art to understand the various embodiments disclosed herein.