Patent Application
20210091245
In recent years, the semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation.
Photo sensing devices are used to sense radiation such as light. These devices often use arrays of pixels or photodiodes to absorb radiation projected thereto and convert the sensed radiation into electrical signals. As a part of evolution, the size of photo sensing device can be reduced. However, issues related to dark current are more and more difficult to deal with, and furthermore, as the pixel sizes decrease, the amount of photons received by the photo sensing device decreases. As a result, the effect of dark current becomes more pronounced. Therefore, minimizing dark current is a critical issue for advanced technology. Furthermore, photo sensing device often suffers dopant diffusion issues, wherein the speed of detection of the photo sensing device may be reduced due to undesired diffusion.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in the respective testing measurements. Also, as used herein, the terms “substantially,” “approximately,” or “about” generally means within a value or range which can be contemplated by people having ordinary skill in the art. Alternatively, the terms “substantially,” “approximately,” or “about” means within an acceptable standard error of the mean when considered by one of ordinary skill in the art. People having ordinary skill in the art can understand that the acceptable standard error may vary according to different technologies. Other than in the operating/working examples, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for quantities of materials, durations of times, temperatures, operating conditions, ratios of amounts, and the likes thereof disclosed herein should be understood as modified in all instances by the terms “substantially,” “approximately,” or “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the present disclosure and attached claims are approximations that can vary as desired. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Ranges can be expressed herein as from one endpoint to another endpoint or between two endpoints. All ranges disclosed herein are inclusive of the endpoints, unless specified otherwise.
Photosensitive materials can be utilized in photo sensing devices to absorb radiation, such as light, and convert the sensed radiation into electrical signal. In some embodiments, germanium (Ge) can be a material of a photosensitive layer. Particularly in the case of having a substrate including silicon at a top surface, it is beneficial to utilize germanium as the photosensitive materials for absorbing light with wavelength less than an infrared wavelength of less than 1,560 nm-1,600 nm since it is easier and cheaper to integrate germanium with silicon photonics. In the application of communication, devices integrated with germanium sensing layer can be utilized for data-communication (signal having wavelength about 1,310 nm) and longer distance tele-communication (signal having wavelength about 1,550 nm).
However, dislocation defects often arise in the cases of epitaxially growing a material on a substrate having different kinds of materials—often referred to as “heterostructure”—due to different crystalline lattice sizes. During the deposition operation, this lattice mismatch between the substrate and the deposited material causes stress during thermal cycles and may lead to dislocation defects. As a result, this may introduce undesired and abrupt changes in electrical and/or optical properties, which result in deteriorated device performance and/or negative effects (e.g. larger dark current). It is discovered that dark current may cause degraded performance, issues or failures, such as degrading signal-to-noise-ratio (SNR). In addition, in some cases threading dislocation may degrade physical properties of the dislocation and may lead to device failure.
In the example of growing germanium on a silicon substrate, there is a difference between a lattice constant of silicon and a lattice constant of germanium (about 4.2% under certain circumstances). It should be noted that when a thickness of germanium deposited thereon is less than a certain value (for example, 20 Å), the lattice mismatch may not cause obvious misfit dislocation since thinner germanium can be compressed (conformed to silicon lattice) and the lattice mismatch can be alleviated. However, in order to effectively absorbing signals within a certain range (for example, up to about 1,650 nm so that the device can be applied in the field of data-communication and tele-communication), it is more desired for such photo sensing layer to have a thickness greater than a value (for example, greater than 4,000 Å, or can be varied based on the need of certain application. In the example, when the thickness is significantly less than 4,000 Å, the collection of radiation may not be effective). In such case, on the contrary, lattice mismatch may cause detectable misfit dislocation or even threading dislocation, which may lead to degraded device performance, as the lattice mismatch may not be effectively alleviated by material conformation herein due to greater thickness.
In addition, a portion of the substrate may be removed before forming another material thereon. However, the exposed surface after such removal operation may be rough, and such rough surface serving as the starting surface may aggravate the issue of misfit dislocation and/or threading dislocation, which may lead to undesired effect such as dark current.
Furthermore, during fabrication of a photo sensing device, dopant (such as phosphorus, arsenic, n-type dopant, or other types of dopant) may diffuse quickly in photo sensing material (such as germanium or other semiconductor material) through an interface, which may result in undesired dopant diffusion into an intended intrinsic region, reduced photodetector bandwidth, and/or lowered detection speed.
The present disclosure provides a photo sensing device and method(s)for forming the photo sensing device in order to improve the device performance (which may be reflected on device detection speed) and mitigate the aforesaid issues (such as dark current and diffusion at interface). It should be noted that in the present disclosure, a germanium photosensitive layer forming on a silicon surface is used as an example. However, other suitable materials or compositions may also be used as a photosensitive layer or a substrate. For example, III-V group material (such as InGaAs, InP, etc.), other IV group material, or other combination/composition thereof may be other types of material that can be utilized as a photosensitive material in the application of photodetector.
The term “starting surface” for epitaxial growth refers to a surface provided as an underlying surface for growing an epitaxial layer thereon, wherein the starting surface may be in direct contact with the epitaxial layer after growth operation. The term “intrinsic” refers to a semiconductor material without intentionally adding dopants.
In some embodiments, the photosensitive member 3 includes a second semiconductor material different from the first semiconductor material. In some embodiments, the second semiconductor material is an epitaxial layer. In some embodiments, the second semiconductor material is germanium. In some embodiments, the photosensitive member 3 is made from intrinsic germanium. Alternatively in some other embodiments, the photosensitive member 3 includes other materials that can be utilized to absorb radiation, such as light, and further convert the radiation into electrical signal. It should be noted that a lattice constant of the first semiconductor material is different from a lattice constant of the second semiconductor material. For example, in the case of the first semiconductor material is silicon and the second semiconductor material is germanium, the difference thereof may be around 4.2% under certain circumstances.
A portion of the photosensitive member 3 is formed over a first region RA in the substrate 1. In some embodiments, the photosensitive member 3 extends into and is at least partially surrounded by the substrate 1. In some embodiments, a lower portion of the photosensitive member 3 is laterally surrounded by the surface layer 1c of the substrate 1, and an upper portion of the photosensitive member 3 protrudes from the first side FS of the substrate 1. The photosensitive member 3 may have a top surface 3TS, wherein the top surface 3TS of the upper portion of the photosensitive member 3 has a facet tapering toward the top surface 3TS.
Furthermore, a first portion 1z of the surface layer 1c directly under the photosensitive member 3 has a first thickness t1 less than a second thickness t2 of a second portion 1z* of the surface layer 1c surrounding the first portion 1z. The second portion 1z* of the surface layer 1c is over a second region RB and a third region RC, wherein the second region RB and the third region RC may be adjacent to the first region RA, the second region RB is at a first side of the first region RA and the third region RC is at a second side of the first region RA opposite to the first side. Alternatively stated, the surface layer 1c has an inner sidewall over a boundary between the first portion 1z and the second portion 1z*.
The photo sensing device 100 further includes a superlattice stack 6 spacing between the photosensitive member 3 and the substrate 1. The superlattice stack 6 is interposed between a bottom surface of the photosensitive member 3 and a top surface of the first portion 1z of the surface layer 1c. The superlattice stack 6 includes a structure of multiple ultra-thin layers. The superlattice stack 6 at least includes a first material and a second material different from the first material. For example (shown in
In some embodiments, the first material is identical or similar to the material of the substrate 1 or surface layer 1c (for example, intrinsic silicon or silicon), and the second material identical or similar to the material of the photosensitive member 3 (for example, intrinsic germanium or germanium). In the case of the substrate 1/surface layer 1c include intrinsic silicon and photosensitive member 3 includes intrinsic germanium, the superlattice stack 6 may include intrinsic silicon (or silicon) and silicon germanium, wherein the term “silicon germanium” is referred to as GexSi1-31 x, wherein 0<x<1. In some embodiments, intrinsic silicon (or silicon) and silicon germanium are alternately disposed in the superlattice stack 6. For the discussed example (shown in
Generally speaking, since it is easier for a thinner layer to be compressed than a thicker layer, wherein the lattice constant of a layer can be mildly altered based on a lattice constant of the underlying layer below. Thus, the alternating ultra-thin layers having different lattice constant may alleviate the lattice mismatch of different materials due to relatively prominent compression effect, wherein the lattice constant of each layer can be transitionally adjusted based on the underlying layer and the starting surface configured to have the photosensitive member 3 grew thereon thereby have an effective lattice constant closer to the second semiconductor material of the photosensitive member 3 (such as germanium), comparing to a lattice constant difference between the photosensitive member 3 and the first portion 1z of the surface layer 1c, which is relatively distal from the photosensitive member 3.
Furthermore, in order to further improve the transitional adjustment of lattice constant of each ultra-thin layers, the distribution of molar concentration of some of the layers can be adjusted. It is discovered that the lattice constant is related to the composition of a material. For example, in the case of the material of the second-type layers can be represented as GexSi1-x (0<x<1), the lattice constant of the second-type layers is related to the molar ratio of germanium. The lattice constant of a second-type layer may be closer to the lattice constant of the photosensitive member 3 (which may include germanium or intrinsic germanium) when x is closer to 1. Therefore, by having a first concentration of the second material (such as germanium or intrinsic germanium) at a first portion of the superlattice stack 6 proximal to the photosensitive member 3 greater than a second concentration of the second material at a second portion of the superlattice stack 6 distal to the photosensitive member 3 and below the first portion, the configuration of the superlattice stack 6 may further improve the transitional adjustment of the lattice constant. Such transitional adjustment of the lattice constant may allow the superlattice stack 6 to provide an improved starting surface (i.e. a top surface) for epitaxially growing the photosensitive member 3 thereon. Since the starting surface of the superlattice stack 6 may have a lattice constant closer to the photosensitive member 3, the dislocation issue caused by lattice mismatch (such as misfit dislocation and threading dislocation) may be alleviated.
For the aforesaid example shown in
Comparing to a comparative embodiment of having a photosensitive member directly disposed on a substrate, with the configuration of the superlattice stack 6 between the photosensitive member 3 and the substrate 1 in the present disclosure, the lattice mismatch between the photosensitive member 3 and the semiconductor layer of the superlattice stack 6 in direct contact with the photosensitive member 3 may be effectively reduced. For example, a top surface of the superlattice stack 6 for epitaxially growing the photosensitive member 3 has a lattice constant closer to the material of the photosensitive member 3, for example, intrinsic germanium.
In some embodiments, doped regions can be formed in the substrate 1 in order to create electrical properties. For example, a first doped region DR1 having a first conductivity type (for example, p-type) is formed over the second region RB and adjacent to the photosensitive member 3. A second doped region DR2 having a second conductivity type different from the first conductivity type (for example, n-type, such as phosphorous or arsenic) is formed over the third region RC opposite to the second region RB with regard to the photosensitive member 3, and adjacent to the photosensitive member 3. In some embodiments, the first doped region DR1 includes a lightly doped region DR1-L (wherein the concentration of the dopant can be referred as p+ in some examples) proximal to the photosensitive member 3 and a heavily doped region DR1-H (wherein the concentration of the dopant can be referred as p++ in some examples) adjacent to the lightly doped region DR1-L. In some embodiments, the second doped region DR2 includes a lightly doped region DR2-L (wherein the concentration of the dopant can be referred as n+ in some examples) proximal to the photosensitive member 3 and a heavily doped region DR2-H (wherein the concentration of the dopant can be referred as n++ in some examples) adjacent to the lightly doped region DR2-L.
Optionally, a third doped region DR1* having the first conductivity type can be formed in the photosensitive member 3 at a side adjacent to the lightly doped region DR1-L. In some embodiments, the third doped region DR1* may further include a portion of the first portion 1z of the surface layer 1c and a portion of the superlattice stack 6 adjacent to the lightly doped region DR1-L. Optionally, a fourth doped region DR2* having the second conductivity type can be formed in the photosensitive member 3 at a side adjacent to the lightly doped region DR2-L. In some embodiments, the fourth doped region DR2* may further include a portion of the first portion 1z of the surface layer 1c and a portion of the superlattice stack 6 adjacent to the lightly doped region DR2-L.
A diffusion barrier structure DBS is formed at the first side FS of the substrate 1 and spaced away from the photosensitive member 3. In some embodiments, the diffusion barrier structure DBS extends into the surface layer 1c and is at least partially surrounded by the surface layer 1c. At least a portion of the surface layer 1c is between the photosensitive member 3 and the diffusion barrier structure DBS. The diffusion barrier structure DBS includes a dielectric layer 10 and a diffusion barrier layer 69 surrounding a lower portion 10L of the dielectric layer 10. The term “diffusion barrier structure” may mean a structure that seeks to prevent spreading of dopant in a region via diffusion, especially under annealing operation, to another region where properties thereof may be affected by the dopant. For example, the diffusion barrier structure DBS is formed in the second doped region DR2 having a second conductivity type (such as n-type), or in some cases, in the lightly doped region DR2-L. As previously discussed, during the fabrication operations that require elevated temperature, the photosensitive member 3 may suffer from the diffusion from the adjacent doped region. Diffusion of n-type dopant (such as phosphorous or arsenic) may occur during or after high-thermal budget operation. Therefore, the diffusion barrier structure DBS is configured to laterally separate a portion of the second doped region DR2 from the photosensitive member 3. It should be noted that another diffusion barrier structure DBS may optionally be disposed in the first doped region DR1, but the present disclosure is not limited thereto.
In some embodiments, the diffusion barrier layer 69 may include silicon nitride, nitrided oxide, or other material that can be utilized as buffer layer for alleviating dopant diffusion. In some embodiments, the nitrided oxide further provides a smoother surface for forming the dielectric layer 10. In some embodiments, the dielectric layer 10 may include silicon oxide (siO2) or silicon nitride (SiN). In some embodiments, the dielectric layer 10 further include an upper portion 10E covering the first side FS of the substrate 1. The photosensitive member 3 protrudes from and is partially surrounded by the upper portion 10E of the dielectric layer 10. In some alternative embodiments, the insulation layer 10 may also cover the top surface 3TS of the photosensitive member 3. Optionally, in some of the embodiments, the photosensitive member 3 may be in direct contact with the upper portion 10E of the dielectric layer 10.
In some embodiments, a lateral distance X* between a sidewall of the photosensitive member 3 (or a sidewall of the superlattice stack 6) and the diffusion barrier structure DBS is in a range from about 20 nm to about 100 nm. In some embodiments, since the diffusion barrier structure DBS may include electrical insulation or high resistance material, placing the diffusion barrier structure DBS less than 20 nm from the photosensitive member 3 may deteriorate detection speed or device performance since the electrical property may be affected. When the lateral distance X* is greater than 100 nm, the performance of confining the dopant from diffusing into the photosensitive member 3 may not be desirable since the portion of the substrate 1 doped with dopant between the diffusion barrier structure DBS and the photosensitive member 3 may possess too much dopant that may not be obstructed from diffusing into the photosensitive member 3. In order to alleviate dopant diffusion, especially from the second doped region DR2, the lateral distance X* between the sidewall of the photosensitive member 3 and the diffusion barrier structure DBS is less than 100 nm and greater than 20 nm to reduce the quantity of dopant between the photosensitive member 3 and the diffusion barrier structure DBS without causing undesirably high resistance of the photo sensing device 100.
A silicide layer 11 may be formed above the heavily doped regions DR1-H and DR2-H and surrounded by the upper portion 10E of the dielectric layer 10. A capping layer 20 may be formed above the dielectric layer 10 and the top surface 3TS of the photosensitive member 3. In some alternative embodiments, the insulation layer 10 may also cover the top surface 3TS of the photosensitive member 3. The capping layer 20 may include insulation materials, such as silicon nitride (SiN) or oxide. A plurality of conductive contacts 21 may be formed in the capping layer 20 and respectively electrically connected to the silicide layer 11. In some embodiments, the conductive contacts 21 include metal. In some embodiments, the conductive contacts 21 may be directly above the heavily doped regions DR1-H and DR2-H. In some embodiments, the conductive contacts 21 may have a top surface coplanar with a top surface of the capping layer 20.
Furthermore, in order to further improve the transitional adjustment of lattice constant of each ultra-thin layers, each of the second-type layer, which may include GexSi1-x, may have different molar concentration of germanium (x). A molar concentration of germanium (x) of a second-type layer is greater than a molar concentration of germanium (x) of another underlying second-type layer. For example, the composition of each layers can be: the first first-type layer 6X includes intrinsic silicon, the first second-type layer 6X* includes Ge0.1Si0.9 (where x=0.1), the second first-type layer 6Y includes intrinsic silicon, the second second-type layer 6Y* includes Ge0.75Si0.25 (where x=0.75), the third first-type layer 6Z includes intrinsic silicon, and the third second-type layer 6Z* includes Ge0.9Si0.1 (where x=0.9). In some embodiments, in order to form the aforesaid configuration, each of the layers can be sequentially formed by selective epitaxial growth. It should be noted that the total number of layers herein is not limited to 6, which may also be less than 6 or greater than 6.
In some embodiments, during forming the photosensitive member 3 and/or the superlattice stack 6, the substrate 1 may be annealed. In some embodiments, during the aforesaid selective epitaxial growth (SEG) operations, a temperature of the substrate 1 may be elevated to be in a range from about 400° C. to about 700° C. Under an elevated temperature, the issue of dopant diffusion may be aggravated. As previously discussed in
The operations discussed in
By performing the doping operations discussed in
The present disclosure provides a photo sensing device 100 and a method of fabricating the photo sensing device 100. In order to alleviate the issues caused by lattice mismatch between the photosensitive member 3 (which may be intrinsic germanium) and the substrate 1 (which may have a surface layer 1c made by intrinsic silicon), a superlattice stack 6 can be formed in a recess formed in the substrate 1 prior to forming the photosensitive member 3. The superlattice stack 6 provides an underlying starting surface that has an effective lattice constant closer to the photosensitive member 3 for epitaxially growing the photosensitive member 3. Specifically, the superlattice stack 6 includes a multiple ultrathin layer structure that includes a first material (substantially identical with the substrate 1, such as intrinsic silicon) and a second material (substantially identical with the photosensitive member 3, such as intrinsic germanium). In some embodiments, the superlattice stack 6 is a silicon-silicon germanium superlattice stack or intrinsic silicon-silicon germanium superlattice stack. Each of the ultrathin layers has a thinner thickness (such as less than about 20 nm, 10 nm or even less than 1 nm), thus the effect of lattice conformation is more effective, and a lattice constant each of the ultrathin layers in the superlattice stack 6 may be relatively closer to the lattice constant of the underlying layer. As a result, the starting surface for growing the photosensitive member 3 has a lattice constant closer to the photosensitive member 3, thus, the issue of dislocation defects may be alleviated.
Furthermore, in order to further improve the transitional adjustment of lattice constant of each ultra-thin layers, the distribution of concentration of the first material and the second material can be adjusted. Therefore, by having a first concentration of the second material (such as germanium or intrinsic germanium) at a first portion of the superlattice stack 6 proximal to the photosensitive member 3 greater than a second concentration of the second material at a second portion of the superlattice stack 6 distal to the photosensitive member 3 and below the first portion, the configuration of the superlattice stack 6 may further improve the transitional adjustment of the lattice constant. Such transitional adjustment of the lattice constant may allow the superlattice stack 6 to provide an improved starting surface (i.e. a top surface) for epitaxially growing the photosensitive member 3 thereon. Since the starting surface of the superlattice stack 6 may have an effective lattice constant closer to the photosensitive member 3, the dislocation issue caused by lattice mismatch (such as misfit dislocation and threading dislocation) may be alleviated.
In addition, in order to alleviate the issue of dopant diffusion, a diffusion barrier structure is disposed in the doped region. For example, the diffusion barrier structure DBS is formed in the second doped region DR2 having a second conductivity type (such as n-type), or in some cases, in the lightly doped region DR2-L. As previously discussed, during the fabrication operations that require elevated temperature, the photosensitive member 3 may suffer from the diffusion from the adjacent doped region. The diffusion barrier structure DBS is configured to laterally separate a portion of the second doped region DR2 from the photosensitive member 3. In order to alleviate dopant diffusion, especially from the second doped region DR2, the lateral distance X* between the sidewall of the photosensitive member 3 and the diffusion barrier structure DBS is in a range from about 20 nm to about 100 nm to reduce the quantity of dopant between the photosensitive member 3 and the diffusion barrier structure DBS without causing undesirably high resistance of the photo sensing device 100.
Furthermore, in order to improve the carrier injection efficiency and reduce the issue of carrier trapping due to band-offset between the semiconductor layer 1c and the photosensitive member 3, a portion of the photosensitive member 3 and a portion of the superlattice stack 6 adjacent/proximal to the first doped region DR1 (having a first conductivity type) can be further doped with the first conductivity type dopant. Similarly, a portion of the photosensitive member 3 and a portion of the superlattice stack 6 adjacent/proximal to the second doped region DR2 (having a second conductivity type) can be further doped with the second conductivity type dopant.
Some embodiments of the present disclosure provide a photo sensing device, including a substrate, including a substrate, including a silicon layer at a front surface, a photosensitive member extending into and at least partially surrounded by the silicon layer, and a superlattice layer disposed between the photosensitive member and the silicon layer, wherein the superlattice layer includes a first material and a second material different from the first material, a first concentration of the second material at a portion of the superlattice layer proximal to the photosensitive member is greater than a second concentration of the second material at a portion of the superlattice layer distal to the photosensitive member.
Some embodiments of the present disclosure provide a photo sensing device, including a substrate, including a substrate, includes a silicon layer at a front surface, a photosensitive member extending into and at least partially surrounded by the silicon layer, a diffusion barrier structure extending into and at least partially surrounded by the silicon layer, and a superlattice layer disposed between the photosensitive member and the silicon layer, wherein the diffusion barrier structure is spaced away from a sidewall of the superlattice layer.
Some embodiments of the present disclosure provide a method for forming a photo sensing device, including providing a substrate, forming a recess in the substrate, forming a superlattice layer in the recess, wherein the superlattice layer includes a first material same as material in the silicon layer and a second material different from the first material, a first concentration of the second material of a first portion of the superlattice layer is less than a second concentration of the second material at a second portion of the superlattice layer above the first portion, and forming a photosensitive member over the superlattice layer, wherein the photosensitive member includes the second material.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other operations and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
This application claims the benefit of prior-filed provisional application No. 62/903,242, filed Sep. 20, 2019, which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62903242 | Sep 2019 | US |
