Patent ID: 12243749

DETAILED DESCRIPTION

The present disclosure provides various embodiments of processes and methods that provide uniform wet etching of material within high aspect ratio features. In the present disclosure, a wet etch process is used to etch material within high aspect ratio features, such as deep trenches and holes, provided on a patterned substrate. Uniform wet etching is provided in the present disclosure by ensuring that wall surfaces of the material being etched (or wall surfaces adjacent to the material being etched) exhibit a neutral surface charge when exposed to the etch solution used to etch the material.

When an etch solution is used to remove material within high aspect ratio features (such as, e.g., deep trenches and holes), the rate at which the material is removed (i.e., the etch rate) may differ depending on a variety of factors, such as the critical dimension (CD), depth and/or aspect ratio of the features, the etchant chemical(s) used within the etch solution, the solvent(s) used within the etch solution, the ratio of etchant chemical(s) to solvent(s) used within the etch solution, the pH of the etch solution and the material being etched. When a wet etch process is used to etch material within features having a high aspect ratio (AR=depth:CD) greater than or equal to 5, the etch rate within the features may vary significantly along the depth of the features. The difference in etch rate that occurs along the depth of high aspect ratio features is known in the art as AR-dependent etching.

FIGS.1A-1Billustrate AR-dependent etching of material within high aspect ratio features. In the illustrated embodiments, a patterned substrate100having at least one feature115formed within a material layer105is exposed to an aqueous-based etch solution130(inFIG.1A) and a non-aqueous organic-based etch solution140(inFIG.1B) to etch back the material layer105within the at least one feature115. As used herein, an aqueous-based etch solution130is a solution that includes one or more etchant chemicals mixed with an aqueous solvent (e.g., water (H2O) or deionized water). A non-aqueous organic-based etch solution140, on the other hand, is a solution that includes one or more etchant chemicals mixed with an organic solvent. In some embodiments, the non-aqueous organic-based etch solution140may include an etchant chemical that contains water (e.g., hydrofluoric acid (HF) containing for example 49% HF and 51% water, or ammonium hydroxide (NH4OH) containing for example 29% NH4OH and 71% water, in terms of weight %) and thus, may include a minimal amount of water.

The material layer105may include a wide variety of semiconductor materials. For example, the material layer105may include one or more silicon-containing materials (such as, e.g., amorphous silicon (a-Si), polysilicon (poly-Si), silicon dioxide (SiO2), silicon nitride (SiN), silicon carbon nitride (SiCN) or silicon oxynitride (SiON)). Other materials, such as conductive materials (such as copper (Cu), aluminum (Al), etc.), may also be utilized for the at least one material layer105. In some embodiments, the at least one material layer105may include a plurality of material layers, wherein one or more of the material layers includes a different material composition.

The at least one feature115may include a wide variety of features, such as but not limited to, a deep trench or hole. A critical dimension (CD) of the feature115may be relatively small (e.g., less than or equal to 100 nm) compared to the etch depth (D) of the at least feature115. In some embodiments, the at least one feature115may be a high aspect ratio feature that was previously formed within the material layer105using, e.g., a dry etch process. As used herein, a high aspect ratio feature may have an aspect ratio (AR=etch depth:CD) greater than or equal to 5.

A wide variety of etch solutions may be utilized to etch back the material105within at least one feature115. In the embodiment shown inFIG.1A, for example, the patterned substrate100is exposed to an aqueous-based etch solution130that includes one or more etchant chemicals and an aqueous solvent. As noted above, an aqueous-based etch solution130is a solution that includes an etchant chemical mixed with an aqueous solvent (e.g., water (H2O) or deionized water). The etchant chemical(s) included within the aqueous-based etch solution130may include anions (negatively charged ions) or cations (positively charged ions) as the main reactive species. Examples of etchant chemicals that include anions as the main reactive species include, but are not limited to, hydrofluoric acid (HF), ammonium hydroxide (NH4OH), hydrochloric acid (HCl), hydrogen peroxide (H2O2), nitric acid (HNO3), phosphoric acid (H3PO4), potassium hydroxide (KOH) and Tetramethylammonium hydroxide (TMAH). Other etchant chemicals containing anions as the main reactive species may also be utilized.

When the patterned substrate100is exposed to an aqueous-based etch solution130containing anions as the main reactive species, wall surfaces120of the material layer105exposed to the aqueous-based etch solution130may exhibit a negative surface charge, as shown inFIG.1A, depending on the pH of the etch solution and the material composition of the wall surfaces120. For example, the exposed wall surfaces120of the material layer105may exhibit a negative surface charge (as shown inFIG.1A) when the patterned substrate100is exposed to an aqueous-based etch solution130containing hydrofluoric acid (HF) mixed with water and the wall surfaces120include a silicon-containing material (such as a-Si, poly-Si, SiO2, SiCN or SiON) or a conductive material (such as Cu or Al). However, other silicon-containing materials, such as silicon nitride (SiN), may exhibit a positive surface charge (not shown inFIG.1A) when the patterned substrate100is exposed to an aqueous-based etch solution130containing hydrofluoric acid (HF) mixed with water. This is shown inFIG.5and described in more detail below.

When the patterned substrate100is exposed to an aqueous-based etch solution130, as shown inFIG.1Aand described above, the anions within the etchant chemical are repelled by the negatively charged wall surfaces120. This decreases the local concentration of anions within the feature115, which in turn, decreases the etch rate of the material layer105. As etching progresses to increase the CD and/or the etch depth (D) of the feature115, the repulsive force between the anions and the negatively charged wall surfaces120may further decrease the local concentration of anions within the feature115, causing fewer and fewer anions to reach the bottom of the feature115, which causes the etch rate to be lower near the bottom of the feature115than the etch rate achieved near the top of the feature. This may result in under etching, causing CD variations along the depth of the feature115.

In the embodiment shown inFIG.1B, the patterned substrate100is exposed to a non-aqueous organic-based etch solution140that includes one or more etchant chemicals mixed with an organic solvent. The etchant chemical(s) included within the non-aqueous organic-based etch solution140may include anions (negatively charged ions) or cations (positively charged ions) as the main reactive species. Examples of etchant chemicals that include anions as the main reactive species are provided above.

A wide variety of organic solvents may be used within the non-aqueous organic-based etch solution140. Examples of organic solvents that may be included within the non-aqueous organic-based etch solution140include, but are not limited to, various alcohols (e.g., methanol (CH4O), ethanol (C2H6O), isopropyl alcohol (C3H8O), benzyl alcohol (C7H8O), etc.), polyhydric alcohols (e.g., ethylene glycol (C2H6O2) etc.), acetic acid (CH3COOH), ketones (e.g., acetone (C3H6O), propylene carbonate (C4H6O3), etc.), alkanes (e.g., n-hexane (C6H14), cyclohexane (C6H12), etc.), ethers (e.g., diethyl ether (C4H10O), tetrahydrofuran (C4H8O), etc.), aromatic hydrocarbons (e.g., benzene (C6H6), toluene (C7H8), etc.), halogen compounds (e.g., dichloromethane (CH2Cl2), trichloroethylene (C2HCl3), 1,1,1-trichloroethane (C2H3Cl3), 1,2-dichloroethane (C2H4Cl2), etc.), nitrogen compounds (e.g., N-methyl-2-pyrrolidone (C5H9NO), etc.), sulfuric compounds (e.g., dimethyl sulfoxide (C2H6OS), etc.), and other volatile, carbon-based solvents such as ethyl lactate (C5H10O3), ethanolamine (C2H7NO) and propylene glycol methyl ether acetate (C6H12O3).

When the patterned substrate100is exposed to a non-aqueous organic-based etch solution140containing anions as the main reactive species, wall surfaces120of the material layer105exposed to the non-aqueous organic-based etch solution140may exhibit a positive surface charge, as shown inFIG.1B, depending on the pH of the etch solution and the material composition of the wall surfaces120. For example, the exposed wall surfaces120of the material layer105may exhibit a positive surface charge (as shown inFIG.1B) when the patterned substrate100is exposed to a non-aqueous organic-based etch solution140containing hydrofluoric acid (HF) mixed with an organic solvent (e.g., IPA, AA, EG or PC) and the wall surfaces120include a silicon-containing material (such as a-Si, poly-Si, SiO2, SiCN or SiON) or a conductive material (such as Cu or Al).

When the patterned substrate100is exposed to a non-aqueous organic-based etch solution140, as shown inFIG.1Band described above, the anions within the etchant chemical are attracted to the positively charged wall surfaces120. This increases the local concentration of anions within the feature115, which in turn, increases the etch rate of the material layer105. As etching progresses to increase the CD or the etch depth (D) of the feature115, the attractive force between the anions and the positively charged wall surfaces120may further increase the local concentration of anions within the feature115, causing more and more anions to reach the bottom of the feature115, which causes the etch rate to be higher near the bottom of the feature115than the etch rate achieved near the top of the feature. This may result in over etching, causing CD variations along the depth of the feature115.

When etching the material layer105within the feature115, the etch rate of the material layer105may depend on a variety of factors, including the CD, depth and/or aspect ratio of the feature115, the particular etchant chemical(s) and/or reactive species used within the etch solution, the particular solvent(s) used within the etch solution, the ratio of etchant chemical(s) to solvent(s) used within the etch solution and/or the pH of the etch solution. In addition to these factors, the electric potential (or surface charge) exhibited by the wall surfaces120when exposed to the etch solution may also affect the etch rate of the material layer105, depending on the particular etch solution used.

As shown inFIGS.1A-1B and2, aqueous-based etch solutions130and non-aqueous organic-based etch solutions140may have the opposite effect on etch rate when: (a) wall surfaces120of the material layer105being etched exhibit a negative surface charge when exposed to aqueous solutions of certain pH, and (b) anions are used as the main reactive species. When the aqueous-based etch solution130shown inFIG.1Ais used to etch the material layer105, for example, wall surfaces120exposed to the etch solution may attain a negative surface charge, which repels the anions within the etch solution and decreases the etch rate within the feature115. However, when the non-aqueous organic-based etch solution140shown inFIG.1Bis used to etch the material layer105, the wall surfaces120exposed to the etch solution may attain a positive surface charge, which attracts the anions within the etch solution and increases the etch rate within the feature115. This may be due, at least in part, to the Zeta potential and the electric double layer (EDL) that exists between the wall surfaces120and the etch solution.

FIG.3is a schematic diagram illustrating Zeta potential and the electric double layer that exists between the wall surfaces of a material being etched and the etch solution used to etch the material. As noted above and shown inFIG.3, the etch solution includes cations (positively charged ions) and anions (negatively charged ions). When the etch solution comes in contact with a wall surface having negative surface potential, as shown inFIG.3, cations within the etch solution are attracted to and adsorbed onto the wall surface by electrostatic and/or van der Walls forces. The opposite is true when the etch solution comes in contact with a wall surface having positive surface potential (i.e., anions within the etch solution are attracted to and adsorbed onto the wall surface). This attraction produces an electric double layer (i.e., a layer that does not satisfy electroneutrality) between the charged wall surface and the etch solution.

According to the Stern model, the electric double layer (EDL) is divided into two parts separated by a plane, referred to as the Stern plane. The centers of adsorbed ions are located in the Stern layer between the wall surface and the Stern plane. Ions with centers located beyond the Stern plane form the Diffuse layer of the EDL. As shown inFIG.3, the electric potential (Ψ) near the wall surface changes linearly between Ψ0and Ψδ(the potential at the Stern plane) and decays exponentially with distance from Ψδto zero in the Diffuse layer and beyond. The Zeta potential (ζ) is the electric potential that exists at the Surface of Shear between the charged wall surface and the etch solution. The Zeta potential (ζ) may be positive, zero or negative, depending on the wall material and the pH of the etch solution.

FIG.4depicts a graph400illustrating Zeta potential (expressed in mV) vs pH for various wall materials. As shown inFIG.4, the Zeta potential generally increases with decreasing pH and decreases with increasing pH. In some embodiments, the Zeta potential between a charged wall surface and an etch solution can be changed by changing the pH of the etch solution (e.g., by changing the etchant chemical(s) used within the etch solution, or by adding an acid or base to the etch solution), as shown inFIG.4. In other embodiments, the Zeta potential between a charged wall surface and an etch solution can be changed by adding a surfactant to the etch solution. In yet other embodiments, the Zeta potential between a charged wall surface and an etch solution can be changed by utilizing an etch solution that mixes an etchant chemical with an organic solvent and an aqueous solvent (depending on the pH of the etch solution). This is illustrated in the graph500shown inFIG.5.

The graph500shown inFIG.5illustrates the Zeta potential vs pH for various etch solutions and wall surface materials (e.g., SiN, a-Si and SiCN). When hydrofluoric acid (HF) is mixed with an aqueous solvent and used as an etch solution, the Zeta potential (denoted with a Δ) between the etch solution and the wall surface material is: (a) negative for a-Si and SiCN (resulting in a negatively charged wall surface), and (b) positive for SiN (resulting in a positively charged wall surface). When hydrofluoric acid (HF) is mixed with organic solvent, instead of an aqueous solvent, the Zeta potential (denoted with a ●) is positive for a-Si, SiCN and SiN (resulting in positively charged wall surfaces). When hydrofluoric acid (HF) is mixed with an organic solvent and an aqueous solvent, the Zeta potential (denoted with an X) is positive for SiN (resulting in positively charged wall surfaces), yet relatively neutral for a-Si and SiCN (resulting in wall surfaces without surface charge).

The graph500shown inFIG.5shows that, while organic solvents have little to no effect on the Zeta potential between an etch solution and an already positively charged wall surface, the Zeta potential between the etch solution and a negatively charged wall surface can (sometimes) be changed to a positive surface potential by using an organic solvent, instead of an aqueous solvent, within the etch solution. This difference in Zeta potential may explain, at least in part, the opposing effects that aqueous-based etch solutions and non-aqueous organic-based solutions may have on etch rate when: (a) the material being etched within the features is adjacent to a wall material having a negative surface charge in aqueous solutions of certain pH, and (b) the etchant chemical used within the etch solutions includes anions as the main reactive species.

The graph500shown inFIG.5further shows that when an etchant chemical is mixed with an organic solvent and an aqueous solvent, the Zeta potential between the etch solution and the wall surface may be neutral, or substantially equal to 0 mV. A neutral surface charge may reduce or eliminate the electrostatic forces, which would otherwise occur between the reactive ions in the etch solution and a positively or negatively charged wall surface. By preventing the wall surfaces of the material being etched from attaining a surface charge, a uniform concentration of reactive species can be maintained within the feature to provide a uniform etch rate along the depth of the feature.

The present disclosure provides various embodiments of processes and methods that provide uniform wet etching of material within high aspect ratio features (such as deep trenches and holes) by ensuring that wall surfaces of the material being etched (or wall surfaces adjacent to the material being etched) exhibit a neutral surface charge when exposed to the etch solution used to etch the material. In some embodiments, the etch solution used to etch the material may include one or more etchant chemicals mixed with an organic solvent and an aqueous solvent, and the particular etchant chemical(s) and organic solvent used in the etch solution, as well as the ratio between the etchant chemical(s), organic solvent and aqueous solvent used, may be selected to ensure that the wall surfaces of the material being etched (or wall surfaces adjacent to the material being etched) exhibit a neutral surface charge (or electroneutrality) at the pH of the etch solution.

Embodiments of the present disclosure may also utilize other techniques to ensure that wall surfaces of the material being etched (or wall surfaces adjacent to the material being etched) exhibit electroneutrality in the presence of the etch solution. In some embodiments, the pH of the etch solution may be adjusted and/or surfactant(s) may be added to adjust the surface potential of the wall surfaces to ensure that the wall surfaces exhibit a neutral surface charge in the presence of the etch solution.

FIGS.6A-6Cillustrate one embodiment of a wet etch process600that utilizes the techniques described herein to provide uniform wet etching of material within high aspect ratio features. As described in more detail below, the wet etch process600provides uniform wet etching of material within high aspect ratio features by ensuring that the wall surfaces of the material being etched exhibit a neutral surface charge when exposed to the etch solution used to etch the material. In some embodiments, the wet etch process600may be performed to etch back material within at least one high aspect ratio feature (e.g., a deep trench or hole), as shown inFIGS.6A-6C. As described herein, a high aspect ratio feature may have an aspect ratio greater than or equal to 5. It is noted, however, that the wet etch process600shown inFIGS.6A-6Cis not strictly limited to the example substrate shown therein and may be applied to a wide variety of substrates and material layers having a wide variety and number of high aspect ratio features formed therein.

As shown inFIG.6A, the wet etch process600may generally begin (in step610) by providing a patterned substrate100having at least one feature115formed within a material layer105formed on the patterned substrate100. The material layer105may include a wide variety of semiconductor materials. For example, the at least one material layer105may be a silicon-containing material (such as, e.g., amorphous silicon (a-Si), polysilicon (poly-Si), silicon dioxide (SiO2), silicon nitride (SiN), silicon carbon nitride (SiCN) or silicon oxynitride (SiON)). Other materials, such as a conductive material (e.g., copper (Cu), aluminum (Al), etc.), may also be utilized for the at least one material layer105. In some embodiments, the material layer105may include a plurality of material layers, wherein one or more of the material layers includes a different material composition.

The at least one feature115may include a wide variety of features, such as but not limited to, a deep trench or hole. In some embodiments, the at least one feature115may be formed within the material layer105using, for example, a dry etch process. The at least one feature115formed by the dry etch process may have an initial critical dimension (CD1) and etch depth (D1). As shown inFIG.6A, the CD1of the at least one feature115may be relatively small (e.g., less than or equal to 100 nm) compared to the etch depth (D1) of the at least one feature115. In some embodiments, the at least one feature115may be a high aspect ratio having an aspect ratio (AR=etch depth:CD) greater than or equal to 5.

After the patterned substrate100is provided as shown inFIG.6A, the wet etch process600may expose the patterned substrate100to an etch solution150to etch back the material layer105to increase the CD (e.g., from CD1to CD2) and/or the etch depth (e.g., from D1to D2) of the at least one feature115(in step620), as shown inFIG.6B. The etch solution150is selective to the material layer105. When the patterned substrate100is exposed to the etch solution150, the etch solution150reacts with the material layer105and promotes dissolution of the reaction products to selectively etch the material layer105. In some embodiments, the wet etch process600may continue etching the material105with the etch solution150until the at least one feature reaches a target CD (CDT) and/or a target etch depth (DT)(in step630), as shown inFIG.6C. In doing so, the wet etch process600may provide a uniform etch rate from a top of the at least one feature115to the target etch depth.

A wide variety of etch solutions may be utilized inFIG.6Bto etch back the material layer105within the at least one feature115. The etch solution150used to etch back the material105may generally contain one or more etchant chemicals mixed with an organic solvent and an aqueous solvent (e.g., water (H2O) or deionized water). In some embodiments, the etch solution150may contain one or more additional components, such as an acid or base (which may be used to adjust the pH of the etch solution) or a surfactant (which may be used to adjust the Zeta potential between exposed wall surfaces of the feature being etched and the etch solution). The pH value of the etch solution150may generally depend on the etchant chemical(s) and the additional components (if any) utilized therein.

The etchant chemical(s) used within the etch solution150may generally include anions (negatively charged ions) and cations (positively charged ions). In some embodiments, the etchant chemical(s) used within the etch solution150may include anions as the main reactive species. Examples of etchant chemicals containing anions as the main reactive species include, but are not limited to, hydrofluoric acid (HF), ammonium hydroxide (NH4OH), hydrochloric acid (HCl), hydrogen peroxide (H2O2), nitric acid (HNO3), phosphoric acid (H3PO4), potassium hydroxide (KOH) and Tetramethylammonium hydroxide (TMAH). In other embodiments, the etchant chemical(s) used within the etch solution150may include cations as the main reactive species. For example, when NH4OH is used as the etchant chemical, the cation NH4+may sometimes be used as the main reactive species, instead of the anion OH−.

A wide variety of organic solvents may also be utilized within the etch solution150. Examples of organic solvents include, but are not limited to, various alcohols (e.g., methanol (CH4O), ethanol (C2H6O), isopropyl alcohol (C3H8O), benzyl alcohol (C7H8O), etc.), polyhydric alcohols (e.g., ethylene glycol (C2H6O2) etc.), acetic acid (CH3COOH), ketones (e.g., acetone (C3H6O), propylene carbonate (C4H6O3), etc.), alkanes (e.g., n-hexane (C6H14), cyclohexane (C6H12), etc.), ethers (e.g., diethyl ether (C4H10O), tetrahydrofuran (C4H8O), etc.), aromatic hydrocarbons (e.g., benzene (C6H6), toluene (C7H8), etc.), halogen compounds (e.g., dichloromethane (CH2Cl2), trichloroethylene (C2HCl3), 1,1,1-trichloroethane (C2H3Cl3), 1,2-dichloroethane (C2H4Cl2), etc.), nitrogen compounds (e.g., N-methyl-2-pyrrolidone (C5H9NO), etc.), sulfuric compounds (e.g., dimethyl sulfoxide (C2H6OS), etc.), and other volatile, carbon-based solvents such as ethyl lactate (C6H10O3), ethanolamine (C2H7NO) and propylene glycol methyl ether acetate (C6H12O3).

In some embodiments, the etch solution150may include an etchant chemical containing anions as the main reactive species (e.g., hydrofluoric acid, ammonium hydroxide or hydrochloric acid) mixed with water and an organic solvent. In some embodiments, the organic solvent may be an alcohol (e.g., isopropyl alcohol, IPA), a polyhydric alcohol (e.g., ethylene glycol, EG), acetic acid (AA) or a ketone (e.g., propylene carbonate, PC). In at least one preferred embodiment, the etch solution150may include hydrofluoric acid (HF) mixed with water and either IPA, AA, EG or PC. Other organic solvents or other etchant chemicals (such as NH4OH or HCl) described herein may also be used within the etch solution150. Although the etchant chemicals can be mixed with many different organic solvents, the compatibility and solubility of the etchant chemical(s) and organic solvent must be carefully considered.

When the patterned substrate100is exposed to the etch solution150inFIG.6B, exposed portions of the material layer105are selectively removed by the etch solution150. During etching, wall surfaces120of the material layer105are exposed to the etch solution150. Unlike the embodiments shown inFIGS.1A and1B, however, the wall surfaces120exposed to the etch solution150do not attain a positive or negative surface charge. Instead, when exposed to the etch solution150, the wall surfaces120of the material105being etched exhibit a neutral surface charge at the pH value of the etch solution150.

As used herein, wall surfaces120that exhibit a neutral surface charge when exposed to the etch solution150have a Zeta potential that is minimal at the pH value of the etch solution150. In some cases, the Zeta potential of the wall surfaces120may be substantially equal to 0 mV when exposed to the etch solution150. As used herein, a Zeta potential “substantially equal to 0 mV” may fall within a first range comprising −20 mV to +20 mV, more preferably within a second range comprising −10 mV to +10 mV, and even more preferably within a third range comprising −5 mV to +5 mV. The graph400shown inFIG.4provides various examples of materials having a Zeta potential substantially equal to 0 mV at various pH. For example, silica (silicon dioxide, SiO2) and polyvinyl alcohol (PVA) are illustrated inFIG.4as having a Zeta potential substantially equal to 0 mV when exposed to an etch solution having a pH value of 4. Other materials not explicitly shown and described herein may also exhibit a Zeta potential substantially equal to 0 mV when exposed to etch solutions having similar or different pH.

The etch solution150used to selectively etch the at least one material layer105may be carefully selected to ensure that the wall surfaces120do not attain a surface charge when exposed to the etch solution150. For example, the constituents of the etch solution150(i.e., the etchant chemical(s), organic solvent and aqueous solvent), and the ratios thereof, may be selected (or modified) to ensure that the wall surfaces120exhibit electroneutrality (or a neutral surface charge) in the presence of the etch solution150. In some embodiments, the pH of the etch solution150may be adjusted and/or surfactant(s) may be added to the etch solution150to adjust the surface potential of the wall surfaces120and ensure that the wall surfaces120exhibit a neutral surface charge in the presence of the etch solution150.

Unlike the embodiments shown inFIGS.1A and1B, in which wall surfaces120of the material105being etched exhibit a positive surface charge (e.g., a surface charge substantially greater than 0 mV) or a negative surface charge (e.g., a surface charge substantially less than 0 mV) in the presence of the etch solutions130and140, the wall surfaces120of the material105being etched inFIG.6Bexhibit a neutral surface charge (e.g., a surface charge substantially equal to 0 mV) when exposed to the etch solution150. When the wall surfaces120of the material105being etched are exposed to the etch solution150, as shown in step620ofFIG.6B, the neutral surface charge of the wall surfaces120reduces or eliminates electrostatic forces between the wall surfaces120and the reactive ion species utilized in the etch solution150. This enables the wet etch process600shown inFIG.6Bto maintain a uniform concentration of reactive ion species within the at least one feature115and provide uniform etching of the material105along the etch depth (D) of the at least one feature115.

The wet etch process600shown inFIGS.6A-6Cprovides uniform wet etching of material105within high aspect ratio features (e.g., deep trenches and holes) formed on a patterned substrate100. In the wet etch process600, uniform etching is provided along the entire etch depth (D) of the at least one feature115by exposing the patterned substrate100to an etch solution150, which prevents the wall surfaces120of the material105being etched from attaining a surface charge. By ensuring that the wall surfaces120of the material105being etched exhibit electroneutrality (or a neutral surface charge) when exposed to the etch solution150, the wet etch process600described herein maintains a uniform concentration of reactive ion species within the at least one feature115and provides a uniform etch rate from the top of the at least one feature115to the target etch depth (DT). This improves etching of material within high aspect ratio features by preventing over/under-etching and reducing CD variations along the depth of the high aspect ratio features.

The wet etch process600shown inFIGS.6A-6Ccan be used in some applications to etch back the material105, so as to increase the CD and/or the etch depth of the high aspect ratio feature115formed on the patterned substrate100. It is noted, however, that the techniques described herein are not strictly limited to such applications and can also be used to provide uniform etching of material within a wide variety of features and semiconductor structures utilized in other applications.FIGS.7A-7CandFIGS.8A-8Cillustrate other embodiments of wet etch processes that utilize the techniques described herein to provide uniform wet etching of material within high aspect ratio features.

FIGS.7A-7Cillustrate one embodiment of a wet etch process700that utilizes the techniques described herein to provide uniform wet etching of material within high aspect ratio features. Like the previous embodiment, the wet etch process700provides uniform wet etching of material within high aspect ratio features by ensuring that the wall surfaces of the material being etched exhibit a neutral surface charge when exposed to the etch solution used to etch the material. In the embodiment shown inFIGS.7A-7C, the wet etch process700is used to etch back a material layer, which has been conformally deposited within a high aspect ratio feature (e.g., a deep trench or hole).

As shown inFIG.7A, the wet etch process700may generally begin (in step710) by providing a patterned substrate100having at least one feature115formed within a plurality of material layers formed on the patterned substrate100. In the embodiment shown inFIG.7A, the at least one feature115is initially formed within the material layer105using, e.g., a dry etch process. After the at least one feature115is formed, another material layer110may be conformally deposited on the patterned substrate100and within the at least one feature115using a wide variety of deposition processes such as, e.g., spin-on, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. The material layer105and the material layer110may each include a wide variety of semiconductor materials. For example, the material layer105may be silicon-containing layer such as, e.g., a-Si, poly-Si, SiO2, SiN, SiCN or SiON. The material110may be a silicon-containing layer (e.g., SiO2, SiN, SiCN or SiON) or a metal layer (e.g., Cu, Al, etc.).

Like the previous embodiment shown inFIG.6A, the at least one feature115formed in the embodiment shown inFIG.7Amay have an initial critical dimension (CD1) and etch depth (D1). As shown inFIG.7A, the CD1of the at least one feature115may be relatively small (e.g., less than or equal to 100 nm) compared to the etch depth (D1) of the at least one feature115. In some embodiments, the at least one feature115may be a high aspect ratio having an aspect ratio (AR=etch depth:CD) greater than or equal to 5.

After the patterned substrate100is provided as shown inFIG.7A, the wet etch process700may expose the patterned substrate100to an etch solution150to etch back the material layer110to increase the CD (e.g., from CD1to CD2) and/or the etch depth (e.g., from D1to D2) of the at least one feature115(in step720), as shown inFIG.7B. The etch solution150is selective to the material layer110. When the patterned substrate100is exposed to the etch solution150, the etch solution150reacts with the material layer110and promotes dissolution of the reaction products to selectively etch the material layer110. In some embodiments, the wet etch process700may continue etching the material110with the etch solution150until the at least one feature115reaches a target CD (CDT) and/or a target etch depth (DT) (in step730), as shown inFIG.7C. In doing so, the wet etch process700may provide a uniform etch rate from a top of the at least one feature115to the target etch depth.

Like the previous embodiment shown inFIGS.6A-6C, the wet etch process700shown inFIGS.7A-7Cprovides uniform wet etching of material110within high aspect ratio features (e.g., deep trenches and holes) formed on a patterned substrate100by ensuring that the wall surfaces120of the material110being etched exhibit a neutral surface charge when exposed to the etch solution150used to etch the material110. The etch solution150used to etch the material110may generally include one or more etchant chemicals mixed with an organic solvent and an aqueous solvent. As noted above, the constituents of the etch solution150(i.e., the etchant chemical(s), organic solvent and aqueous solvent), and the ratios thereof, may be selected (or modified) to ensure that the wall surfaces120exhibit electroneutrality (or a neutral surface charge) in the presence of the etch solution150. In some embodiments, the pH of the etch solution150may be adjusted and/or surfactant(s) may be added to the etch solution150to adjust the surface potential of the wall surfaces120and ensure that the wall surfaces120exhibit a neutral surface charge in the presence of the etch solution150.

In the wet etch process700, uniform etching is provided along the entire etch depth (D) of the at least one feature115by exposing the patterned substrate100to an etch solution150, which prevents the wall surfaces120of the material layer110being etched from attaining a surface charge. By ensuring that the wall surfaces120of the material layer110being etched exhibit electroneutrality (or a neutral surface charge) when exposed to the etch solution150, the wet etch process700described herein maintains a uniform concentration of reactive ion species within the at least one feature115and provides a uniform etch rate from the top of the at least one feature115to the target etch depth (DT). This improves etching of material within high aspect ratio features by preventing over/under-etching and reducing CD variations along the depth of the high aspect ratio features.

FIGS.8A-8Cillustrate yet another embodiment of a wet etch process800that utilizes the techniques described herein to provide uniform wet etching of material within high aspect ratio features. Unlike the previous embodiments shown inFIGS.6A-6C and7A-7C, the wet etch process800shown inFIGS.8A-8Cprovides uniform wet etching of material within high aspect ratio features by ensuring that the wall surfaces adjacent to the material being etched exhibit a neutral surface charge when exposed to the etch solution used to etch the material. In the embodiment shown inFIGS.8A-8C, a high aspect ratio feature (e.g., a deep trench or hole) is formed within a stack of material layers, including alternating layers of a first material layer and a second material layer, and the wet etch process800is used to etch back (or completely remove) the second material layer without etching the first material layer.

As shown inFIG.8A, the wet etch process800may generally begin (in step810) by providing a patterned substrate100having at least one feature115formed within a stack of material layers comprising alternating layers of a first material layer105and a second material layer110. In the embodiment shown inFIG.8A, the at least one feature115may be initially formed within the stack of material layers using, e.g., a dry etch process. The material layer105and the material layer110may each include a wide variety of semiconductor materials. For example, the material layer105may be a first silicon-containing layer such as, e.g., a-Si, poly-Si, or SiO2. The material110may be a second silicon-containing layer such as, e.g., SiN or silicon geranium (SiGe). The second silicon-containing layer may generally differ from the first silicon-containing layer.

The material composition of the material layer105and the material layer110may generally depend on the semiconductor device being formed. For example, the material layer105may be silicon dioxide (SiO2) and the material layer110may be silicon nitride (SiN) when forming a three-dimensional (3D) memory device, such as a 3D NAND memory device. On the other hand, the material layer105may be silicon (e.g., a-Si or poly-Si) and the material layer110may be silicon geranium (SiGe) when forming a transistor nanosheet. Other silicon-containing materials can also be used to form a stack of material layers, as is known in the art.

Like the previous embodiments shown inFIGS.6A and7A, the at least one feature115formed in the embodiment shown inFIG.8Amay have an initial critical dimension (CD1) and etch depth (D1). As shown inFIG.8A, the CD1of the at least one feature115may be relatively small (e.g., less than or equal to 100 nm) compared to the etch depth (D1) of the at least one feature115. In some embodiments, the at least one feature115may be a high aspect ratio having an aspect ratio (AR=etch depth:CD) greater than or equal to 5.

After the patterned substrate100is provided as shown inFIG.8A, the wet etch process800may expose the patterned substrate100to an etch solution150to etch the second material layer110without etching the first material layer105(in step820), as shown inFIG.8B. The etch solution150is selective to the second material layer110. When the patterned substrate100is exposed to the etch solution150, the etch solution150reacts with the second material layer110and promotes dissolution of the reaction products to selectively etch the second material layer110without etching the first material layer105. Because the etch solution150is highly selective to the second material layer110, the wet etch process800does not increase the critical dimension (CD1) or the etch depth (D1) of the at least one feature115. Instead, the wet etch process800may continue etching the second material layer110with the etch solution150to etch back or remove portions of the second material layer110(in step830), as shown inFIG.8C. In other embodiments (not shown), the wet etch process800may continue etching the second material layer110with the etch solution150until the second material layer110is completely removed.

In the wet etch process800, uniform etching is provided along the entire etch depth (D1) of the at least one feature115by exposing the patterned substrate100to an etch solution150, which prevents the wall surfaces120adjacent to the second material layer110being etched from attaining a surface charge. By ensuring that the wall surfaces120adjacent to the second material layer110being etched exhibit electroneutrality (or a neutral surface charge) when exposed to the etch solution150, the wet etch process800described herein maintains a uniform concentration of reactive ion species within the at least one feature115and provides uniform etching of the second material layer110along the depth (D1) of the at least one feature115. This improves etching of material within high aspect ratio features by preventing over/under-etching and reducing CD variations along the depth of the high aspect ratio features.

The wet etch processes600,700and800disclosed herein provide uniform etching of material within high aspect ratio features formed on a patterned substrate. It is recognized that the wet etch processes600,700and800disclosed herein may be utilized during the processing of a wide range of substrates. The substrate may be any substrate for which the patterning of the substrate is desirable. For example, in one embodiment, the substrate may be a semiconductor substrate having one or more semiconductor processing layers (all of which together may comprise the substrate) formed thereon. Thus, in one embodiment, the substrate may be a semiconductor substrate that has been subject to multiple semiconductor processing steps which yield a wide variety of structures, features and layers, all of which are known in the substrate processing art, and which may be considered to be part of the substrate. For example, in one embodiment, the substrate may be a semiconductor wafer having one or more semiconductor processing layers formed thereon. The concepts disclosed herein may be utilized at any stage of the substrate process flow.

The graph900shown inFIG.9illustrates normalized etch rate vs trench CD (expressed in nm) when an etch solution150having one or more etchant chemicals, an organic solvent (e.g., acetic acid) and an aqueous solvent is utilized to etch trenches of varying CD within a SiCN layer. In the graph900, the “normalized etch rate” is the ratio of the etch rate in trenches having smaller CD to the etch rate in trenches having larger CD. As shown in the graph900, the normalized etch rate increases with decreasing CD when using an etch solution having an organic solvent (e.g., H2O:AA:HF=0:200:20), and decreases with decreasing CD when using an etch solution having an aqueous solvent (e.g., H2O:AA:HF=200:0:20). However, when the substrate is exposed to an etch solution having both an aqueous solvent and an organic solvent, a uniform etch rate (e.g., a normalized etch rate close to “1”) is provided within the trenches of varying CD.

The graph900shown inFIG.9depicts the normalized etch rate vs trench CD for a variety of different etch solutions, which mix water (H2O) and acetic acid (AA) with hydrofluoric acid (HF). For example, the graph900depicts the normalized etch rate vs trench CD for: (a) a first etch solution (denoted with a □) that combines H2O, AA and HF at a ratio of 0:200:20, (b) a second etch solution (denoted with a ∘) that combines H2O, AA and HF at a ratio of 200:0:20, (c) a third etch solution (denoted with a ⋄) that combines H2O, AA and HF at a ratio of 70:130:20, (d) a fourth etch solution (denoted with a) that combines H2O, AA and HF at a ratio of 90:110:20, (e) a fifth etch solution (denoted with a blue-A) that combines H2O, AA and HF at a ratio of 110:90:20, (f) a sixth etch solution (denoted with a x) that combines H2O, AA and HF at a ratio of 150:50:20, (g) a seventh etch solution (denoted with a black) that combines H2O, AA and HF at a ratio of 170:30:20, and (h) an eighth etch solution (denoted with a +) that combines H2O, AA and HF at a ratio of 190:10:20. Of these etch solutions, the seventh etch solution (denoted with a) and the eighth etch solution (denoted with a +) meet the process window requirements for uniform etch rate within the trenches of varying CD.

The graph1000shown inFIG.10illustrates normalized etch rate vs trench CD (expressed in nm) when another etch solution150having one or more etchant chemicals, an organic solvent (e.g., ethylene glycol) and an aqueous solvent is utilized to etch trenches of varying CD within a SiCN layer. Similar to the graph900shown inFIG.9, the graph1000shown inFIG.10shows the normalized etch rate increases with decreasing CD when using an etch solution having an organic solvent (e.g., H2O:EG:HF=0:200:20), and decreases with decreasing CD when using an etch solution having an aqueous solvent (e.g., H2O:EG:HF=200:0:20). However, when the substrate is exposed to an etch solution having both an aqueous solvent and an organic solvent, a uniform etch rate (e.g., a normalized etch rate close to “1”) is provided within the trenches of varying CD.

The graph1000shown inFIG.10depicts the normalized etch rate vs trench CD for a variety of different etch solutions, which mix water (H2O) and ethylene glycol (EG) with hydrofluoric acid (HF). For example, the graph1000depicts the normalized etch rate vs trench CD for: (a) a first etch solution (denoted with a blue ⋄) that combines H2O, EG and HF at a ratio of 0:200:20, (b) a second etch solution (denoted with a ∘) that combines H2O, EG and HF at a ratio of 200:0:20, (c) a third etch solution (denoted with x) that combines H2O, EG and HF at a ratio of 170:30:20, and (d) a fourth etch solution (denoted with a □) that combines H2O, EG and HF at a ratio of 190:10:20. Of these etch solutions, the fourth etch solution (denoted with a □) meet the process window requirements for uniform etch rate within the trenches of varying CD.

Although the graphs900and1000provide example etch solutions that meet the process window requirements for uniform etch rate within the trenches of varying CD, the same or similar etch solutions may also be used in the wet etch processes described herein to provide a uniform etch rate of material within high aspect ratio features, such as deep trenches and holes having an aspect ratio greater than or equal to 5. This is because the same mechanism (e.g., the electric double layer, or EDL) may play a part in both CD-dependent etching within features of different CD and AR-dependent etching within features having high aspect ratio. By providing an etch solution that avoids generating an electric double layer (EDL) between wall surfaces of a material being etched (or wall surfaces adjacent to a material being etched) and the etch solution, a uniform etch rate is provided in both features of different CD and high aspect ratio features.

As described herein, one mechanism that may cause the variation in etch rates when using the various etch solutions, wall materials, CDs and aspect ratios is a mechanism related to surface potentials. However, the techniques described herein are not strictly limited to such techniques. Thus, the CD and AR independent etch rates described herein may be accomplished through other mechanisms and the etch rate advantages described and obtained with the techniques provided herein are not limited to the particular surface potential mechanisms described above. Rather, the advantages may be obtained utilizing other mechanisms also.

FIGS.11-12illustrate exemplary methods that utilize the techniques described herein to provide uniform etching of material within high aspect ratio features formed on a patterned substrate, such as but not limited to, the patterned substrate100shown inFIGS.6A-6C,FIGS.7A-7CandFIGS.8A-8C. It will be recognized that the embodiments shown inFIGS.11-12are merely exemplary and additional methods may utilize the techniques described herein. Further, additional processing steps may be added to the methods shown inFIGS.11-12as the steps described are not intended to be exclusive. Moreover, the order of the steps is not limited to the order shown in the figures as different orders may occur and/or various steps may be performed in combination or at the same time.

FIG.11illustrates a method1100of etching, in accordance with one embodiment of the present disclosure. The method1100shown inFIG.11may generally be used to provide uniform wet etching of material within high aspect ratio features (e.g., deep trenches and holes) formed on a patterned substrate by ensuring that the wall surfaces of the material being etched exhibit a neutral surface charge when exposed to the etch solution used to etch the material, as shown for example inFIGS.6A-6CandFIGS.7A-7C.

In some embodiments, the method1100shown inFIG.11may begin (in step1110) by providing a patterned substrate having at least one feature formed within a material layer formed on the patterned substrate. The at least one feature formed within a material layer may have a critical dimension (CD) and an etch depth. Next, the method1100may expose the patterned substrate to an etch solution to etch the material layer and increase the CD and the etch depth of the at least one feature (in step1120). The etch solution may include reactive ions and may have a pH value, as described above. When exposed to the etch solution (in step1120), wall surfaces of the material layer being etched may exhibit a neutral surface charge substantially equal to 0 mV at the pH value of the etch solution. As a result of the neutral surface charge, the method1100may maintain a uniform concentration of the reactive ions within the at least one feature and provide uniform etching along the etch depth of the at least one feature. In some embodiments, the method1100may continue etching the material layer until the at least one feature reaches a target etch depth. In such embodiments, the method1100may provide a uniform etch rate from a top of the at least one feature to the target etch depth.

The material layer being etched (in step1120) may include a wide variety of semiconductor materials. In some embodiments, for example, the material layer being etched (in step1120) may include a silicon-containing layer or a metal layer. Examples of silicon-containing layers include, but are not limited to, amorphous silicon (a-Si), polysilicon (poly-Si), silicon dioxide (SiO2), silicon nitride (SiN), silicon carbon nitride (SiCN) and silicon oxynitride (SiON).

FIG.12illustrates a method1200of etching, in accordance with another embodiment of the present disclosure. The method1200shown inFIG.12may generally be used to provide uniform wet etching of material within high aspect ratio features (e.g., deep trenches and holes) formed on a patterned substrate by ensuring that the wall surfaces adjacent to the material being etched exhibit a neutral surface charge when exposed to the etch solution used to etch the material, as shown for example inFIGS.8A-8C.

The method1200shown inFIG.12may begin (in step1210) by providing a patterned substrate having at least one feature formed within a stack of material layers comprising alternating layers of a first material layer and a second material layer. Next, the method1200may expose the patterned substrate to an etch solution to etch the second material layer without etching the first material layer (in step1220). The etch solution may include reactive ions and may have a pH value, as described above. When exposed to the etch solution (in step1220), wall surfaces of the first material layer adjacent to the second material layer being etched may exhibit a neutral surface charge substantially equal to 0 mV at the pH of the etch solution. This enables the method1000to maintain a uniform concentration of the reactive ions within the at least one feature and provide uniform etching along the depth of the at least one feature.

The first material layer and the second material layer may each include a wide variety of semiconductor materials. In some embodiments, the first material layer may include a first silicon-containing layer and the second material layer may include a second silicon-containing layer that differs from the first silicon-containing layer. As noted above, the material composition of the first material layer and the second material layer may generally depend on the semiconductor device being formed. For example, the first material layer may be silicon dioxide (SiO2) and the second material layer may be silicon nitride (SiN) when forming a three-dimensional (3D) memory device, such as a 3D NAND memory device. On the other hand, the first material layer may be silicon (e.g., a-Si or poly-Si) and the second material layer may be silicon geranium (SiGe) when forming a transistor nanosheet. Other silicon-containing materials can also be used to form a stack of material layers, as is known in the art.

In some embodiments, the etch solution used within the method1100and the method1200may include one or more etchant chemicals, an organic solvent and an aqueous solvent. For example, the one or more etchant chemicals may include one or more of hydrofluoric acid (HF), ammonium hydroxide (NH4OH), hydrochloric acid (HCl), hydrogen peroxide (H2O2), nitric acid (HNO3), phosphoric acid (H3PO4), potassium hydroxide (KOH) and Tetramethylammonium hydroxide (TMAH). The organic solvent may include one or more of methanol (CH4O), ethanol (C2H6O), isopropyl alcohol (C3H8O), benzyl alcohol (C7H8O), ethylene glycol (C2H6O2), acetic acid (CH3COOH), acetone (C3H6O), propylene carbonate (C4H6O3), n-hexane (C6H14), cyclohexane (C6H12), diethyl ether (C4H10O), tetrahydrofuran (C4H8O), benzene (C6H6), toluene (C7H8), dichloromethane (CH2Cl2), trichloroethylene (C2HCl3), 1,1,1-trichloroethane (C2H3Cl3), 1,2-dichloroethane (C2H4Cl2), N-methyl-2-pyrrolidone (C5H9NO), dimethyl sulfoxide (C2H6OS), ethyl lactate (C5H10O3), ethanolamine (C2H7NO) and propylene glycol methyl ether acetate (C6H12O3). The aqueous solvent may include water (H2O) or deionized water.

As noted above, the constituents of the etch solution (i.e., the etchant chemical(s), organic solvent and aqueous solvent), and the ratios thereof, may be selected to selectively etch the material layer (in step1120ofFIG.11) or the second material layer (in step1220ofFIG.12). The etch solution may also be selected (or modified) to ensure that the wall surfaces of the material layer being etched (in step1120ofFIG.11) or the wall surfaces of the first material layer adjacent to the second material layer being etched (in step1220ofFIG.12) exhibit electroneutrality (or a neutral surface charge) in the presence of the etch solution. In some embodiments, the method1100and/or the method1200may further include adjusting the pH value of the etch solution to ensure that the wall surfaces of the material layer being etched (in step1120ofFIG.11) or the wall surfaces of the first material layer adjacent to the second material layer being etched (in step1220ofFIG.12) exhibit the neutral surface charge at the pH value of the etch solution. In other embodiments, the method1100and/or the method1200may further include adding a surfactant to the etch solution to ensure that the wall surfaces of the material layer being etched (in step1120ofFIG.11) or the wall surfaces of the first material layer adjacent to the second material layer being etched (in step1220ofFIG.12) exhibit the neutral surface charge at the pH value of the etch solution.

It is noted that reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not denote that they are present in every embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. Various additional layers and/or structures may be included and/or described features may be omitted in other embodiments.

The term “substrate” as used herein means and includes a base material or construction upon which materials are formed. It will be appreciated that the substrate may include a single material, a plurality of layers of different materials, a layer or layers having regions of different materials or different structures in them, etc. These materials may include semiconductors, insulators, conductors, or combinations thereof. For example, the substrate may be a semiconductor substrate, a base semiconductor layer on a supporting structure, a metal electrode or a semiconductor substrate having one or more layers, structures, features or regions formed thereon. The substrate may be a conventional silicon substrate or other bulk substrate comprising a layer of semi-conductive material. As used herein, the term “bulk substrate” means and includes not only silicon wafers, but also silicon-on-insulator (“SOI”) substrates, such as silicon-on-sapphire (“SOS”) substrates and silicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on a base semiconductor foundation, and other semiconductor or optoelectronic materials, such as silicon-germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. The substrate may be doped or undoped.

Wet etch processes and methods for processing a substrate are described in various embodiments. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronics device, and may, for example, be a base substrate structure, such as a semiconductor substrate or a layer on or overlying a base substrate structure such as a thin film. Thus, the term “substrate” is not intended to be limited to any particular base structure, underlying layer or overlying layer, patterned or unpatterned, but rather, is contemplated to include any such layer or base structure, and any combination of layers and/or base structures.

One skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

Further modifications and alternative embodiments of the described wet etch processes and methods will be apparent to those skilled in the art in view of this description. It will be recognized, therefore, that the described wet etch processes and methods are not limited by the examples described herein. It is to be understood that the forms of the processes and methods herein shown and described are to be taken as example embodiments. Various changes may be made in the implementations. Thus, although the inventions are described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present inventions. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and such modifications are intended to be included within the scope of the present inventions. Further, any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.