Methods for reducing micro and macro scalloping on semiconductor devices

Abstract

Embodiments of the present disclosure relate to methods for patterning a material layer on a substrate. The method comprises the step of forming a hard mask layer on a material layer disposed on a substrate. The material layer comprises a plurality of first layers and a plurality of second layers alternately formed on the substrate. The method further comprises the step of performing a first etching process to form features in the material layer through the hard mask layer by supplying a first etching gas; the step of performing an oxidation process to oxidize the sidewalls of the features by supplying an oxidation gas; and the step of performing a second etching process to etch the sidewalls of the features formed in the material layer by supplying a second etching gas.

Description

Technology Field

[0001] The embodiments of the present disclosure generally relate to etching processes for structures in semiconductor applications. In particular, the embodiments of the present disclosure provide methods for etching multi-material layers to form features having sidewalls with reduced sidewall thickness variation. Background Technology

[0002] In smaller and lighter electronic devices with higher performance and increased features, three-dimensional (3D) integrated circuits (ICs) designed with through-vias and trenches have been adopted. Through-vias and trenches are used for electrical connections passing through multi-material layers formed on semiconductor substrates. The adoption of through-vias and trenches has faced challenges associated with high costs and mass manufacturing. One such challenge involves creating through-vias and trenches with sidewalls that have reduced sidewall thickness variation. Through-vias and trenches with reduced sidewall thickness variation are generally more robust and can be effectively filled with materials such as dielectrics and metals. In contrast, through-vias and trenches with large sidewall thickness variation (e.g., having scalloped sidewalls) can result in ineffective filling, leading to reduced yield and long-term device reliability issues. Unfortunately, conventional etching methods generate through-vias and trenches with large variations in sidewall thickness, or are impractical for mass manufacturing. Other factors influencing the adoption of through-vias and trenches include the cost of performing plasma etching, which is influenced, for example, by the overall etching rate.

[0003] Therefore, there is a need for a method to perform an etching process to form features with reduced sidewall thickness variation in multi-material layers at a fast etching rate.

[0004] Embodiments of the present disclosure provide a method for patterning a material layer on a substrate. The method comprises the step of forming a hard mask layer on a material layer disposed on a substrate. The material layer comprises a plurality of first layers and a plurality of second layers alternately formed on the substrate. The method further comprises the step of performing a first etching process to form features on the material layer through the hard mask layer by supplying a first etching gas; the step of performing an oxidation process to oxidize the sidewalls of the features by supplying an oxidation gas; and the step of performing a second etching process to etch the sidewalls of the features formed on the material layer by supplying a second etching gas.

[0005] Embodiments of the present disclosure also provide a method for etching a material layer on a substrate through a hard mask in a processing chamber. The method comprises the step of supplying a first etching gas to a material layer in a processing chamber to form features on the material layer—where a hard mask is formed on the material layer. The material layer comprises a plurality of first layers and a plurality of second layers alternately formed on a substrate. The method further comprises the step of supplying an oxidizing gas to oxidize the sidewalls of the features following the supplying of the first etching gas; and the step of exposing the features to a second etching gas following the supplying of the oxidizing gas.

[0006] Embodiments of the present disclosure also provide a method for reducing sidewall thickness variation of features etched in a material layer. The method comprises the steps of: flowing an oxidizing gas into a material layer in a processing chamber—the material layer comprises a plurality of first layers and a plurality of second layers alternately formed on a substrate—; and forming an oxide layer on the sidewalls of the features—the oxide layer has a first side and a second side, the first side of the oxide layer is positioned on the contour of the feature and is shape-following with respect to the contour, and the second side of the oxide layer has a second side variation of about 1 nm to about 2 nm, the second side variation is the difference between a maximum point of the second side and a minimum point of the second side. Brief explanation of the drawing

[0007] In a manner that the above-mentioned features of the present disclosure can be achieved and understood in detail, a more specific description of the present disclosure briefly summarized above may be made with reference to embodiments, which are illustrated in the accompanying drawings. FIG. 1 is a flowchart of a method for patterning a material layer on a substrate according to one or more embodiments of the present disclosure. FIG. 2a is a schematic cross-sectional view of a structure prior to a main etching process according to one or more embodiments of the present disclosure. FIG. 2b is a schematic cross-sectional view of a structure prior to a main etching process, in which a hard mask layer and an adhesive layer are disposed on the structure according to one or more embodiments of the present disclosure. FIG. 2c is a schematic cross-sectional view of features formed in multi-material layers prior to an oxidation process according to one or more embodiments of the present disclosure. FIG. 2d is a schematic cross-sectional view of features formed on multi-material layers (204) after a post-etch process in operation according to one or more embodiments of the present disclosure. FIG. 3a is a schematic cross-sectional view of a portion of a structure prior to oxidation according to one or more embodiments of the present disclosure. FIG. 3b is a schematic cross-sectional view of a portion of a structure after oxidation according to one or more embodiments of the present disclosure. For ease of understanding, the same reference numbers have been used where possible to designate identical elements common to the drawings. The elements and features of one embodiment are considered to be beneficially incorporated into other embodiments without further mention. However, it should be noted that the attached drawings are merely illustrative of exemplary embodiments of the present disclosure and should not be construed as limiting the scope of the present disclosure, as the present disclosure may allow for other equally valid embodiments. Specific details for implementing the invention

[0008] Methods for patterning features with reduced sidewall thickness variation in multiple material layers are provided. The methods utilize a first etching process to form features in a material layer through a hard mask layer by supplying a first etching gas, perform an oxidation process to oxidize the sidewalls of the features by supplying an oxidation gas, and perform a second etching process to etch the sidewalls of the features formed in the material layer by supplying a second etching gas. By doing so, features with reduced sidewall thickness variation can be formed with a high overall etching rate.

[0009] A processing chamber that can be adapted to benefit from the present disclosure is the CENTRIS® Sym3™ processing chamber available from Applied Materials, Inc., located in Santa Clara, California. Other process chambers, including those from other manufacturers, are considered to be adaptable to carry out the embodiments of the present disclosure.

[0010] FIG. 1 is a flowchart of a method (100) for patterning a material layer placed on a substrate. FIG. 2a through 2d are cross-sectional views of a structure (200) formed on a substrate (202) corresponding to various stages of the method (100). The method (100) can be utilized to etch high aspect ratio features, for example, ratios greater than 10:1, on a material layer.

[0011] The substrate (202) may be a silicon-based material, a suitable insulating material, or a conductive material, depending on the desired implementation. The substrate (202) is crystalline silicon (e.g., Si <100> or Si <111> It may include materials such as silicon oxide, strained silicon, silicon germanium, doped or undoped polysilicon, doped or undoped silicon wafers and patterned or unpatterned wafers, silicon on insulator (SOI), carbon-doped silicon oxides, silicon nitride, doped silicon, germanium, gallium arsenide, glass, or sapphire. The substrate (202) may have various diameters such as 200 mm, 300 mm, 450 mm, or other diameters, as well as be rectangular or square substrates. Unless otherwise noted, the embodiments and examples described herein are performed on substrates that are 200 mm diameter, 300 mm diameter, or 450 mm diameter substrates. In embodiments where an SOI structure is utilized for a substrate (202), the substrate (202) may comprise an embedded dielectric layer disposed on a silicon crystalline substrate. In the example described herein, the substrate (202) is a crystalline silicon substrate.

[0012] As illustrated in FIG. 2a, the structure (200) may include a multi-material layer (204) formed of a conductive material and utilized to form part of an integrated circuit, such as gate electrodes, interconnect lines, and contact plugs. In some embodiments, the multi-material layer (204) includes a plurality of stacked layers formed on a substrate (202). The multi-material layer (204) may include first layers (206) and second layers (208) formed alternately on the substrate (202). Although FIG. 2a illustrates six repeating layers of first layers (206) and second layers (208) formed alternately on the substrate (202), any desired number of repeating pairs of first layers (206) and second layers (208) may be utilized.

[0013] In some examples, the multi-material layer (204) may be formed of refractory metals, such as tungsten (W), molybdenum (Mo), tantalum (Ta), titanium (Ti), hafnium (Hf), vanadium (V), chromium (Cr), manganese (Mn), ruthenium (Ru), alloys thereof, silicide compounds thereof, nitride compounds thereof, or combinations thereof. In other examples, the first layer (206) and the second layer (208) may be other metals, such as copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), aluminum (Al), palladium (Pd), gold (Au), silver (Au), platinum (Pt), alloys thereof, nitride compounds thereof, or combinations thereof. In one embodiment, the first layers (206) are formed of silicon-germanium (SiGe), and the second layers (208) are formed of silicon (Si). The multi-material layer (204) may have a total thickness of about 0.2 μm to about 25 μm. Each of the first layers (206) may have a thickness of about 10 nm to about 100 nm. Each of the second layers (208) may have a thickness of about 10 nm to about 100 nm.

[0014] In operation (101), prior to the etching process, an etching resist hard mask layer (210) is formed on a multi-material layer (204) placed on a substrate in a processing chamber. As illustrated in FIG. 2b, the structure (200) comprises a hard mask layer (210) formed in a desired pattern on the multi-material layer (204). The pattern on the hard mask layer (210) may have openings (214) having dimensions of about 1.0 μm to about 1.3 μm to form features having a high aspect ratio (e.g., greater than about 5:1) and a pitch between adjacent openings (214) of about 50 nm to about 180 nm. The structure (200) may comprise an adhesive layer (212) formed between the multi-material layer (204) and the hard mask layer (210). The adhesive layer (212) can function as a barrier layer between the multi-material layer (204) and the hard mask layer (210). The adhesive layer (212) can also function as a polishing stop for subsequent chemical mechanical polishing (CMP) operations.

[0015] The hard mask layer (210) may be formed of tetraethyl-orthosilicate (TEOS) or silicon oxynitride (SiON) and may have a thickness of about 0.5 μm and about 2 μm, respectively. The adhesive layer (212) may be formed of any dielectric material, such as silicon nitride (Si3N4), and may have a thickness of less than about 100 nm. The hard mask layer (210) and the adhesive layer (212) may be deposited by any suitable deposition process, such as a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process, or a spin-on process. The hard mask layer (210) and / or the adhesive layer (212) are subsequently patterned by a photolithography process using a patterned photoresist layer (not shown) covering the hard mask layer (210).

[0016] In some embodiments, additional layers, such as an advanced patterning film (APF), a dielectric anti-reflection coating (DARC), a bottom anti-reflection coating (BARC), a top anti-reflection coating (TARC), a photoresist (PR) layer, a carbon layer, or other suitable layers, may be disposed on the hard mask layer (210). The APF may include a carbon film, an amorphous carbon film, or other suitable APF. The APF layer has a thickness of about 250 nm to about 750 nm, for example, about 500 nm. The DARC has a thickness of about 25 nm to about 100 nm, for example, about 80 nm. The BARC has a thickness of about 10 nm to about 50 nm, for example, about 25 nm. The TARC has a thickness of about 10 nm to about 50 nm, for example, about 25 nm. The PR layer may include a photosensitive material, such as a polymer, a sensitizer, or a baked solvent. The PR layer has a thickness of about 50 nm to about 500 nm, such as about 150 nm.

[0017] In operation (102), as illustrated in FIG. 2c, a first etching process (also referred to as the “main etching” process) is performed to form features (218) (e.g., trenches or vias) on the multi-material layer (204) through a hard mask layer (210). The features (218) may be formed using plasma-excited species or radicals in a plasma process chamber. In the main etching process in operation (104), the multi-material layer (204) is etched to a predetermined depth using an etching gas. In some embodiments, a process gas may be flowed along with the etching gas. In one embodiment, an HBr process gas / Cl2 etching gas mixture may be used because the chlorine-containing etching gas provides a fast etching rate for the multi-material layer (204). In some embodiments, the fast etching rate is about 100 nm / min to about 200 nm / min. In other embodiments, the fast etching rate is greater than about 200 nm / min. The main etching process may continue until the depth of the features (218) in the multi-material layer (204) reaches a predetermined depth. In some embodiments, the determined depth of the features (218) in the multi-material layer (204) is about 0.2 μm to about 4.5 μm. In other embodiments, the depth of the main etching process may be the depth of one first layer (206) and one second layer (208), e.g., about 20 nm to about 60 nm, and may be repeated until the depth of the features (218) reaches a predetermined depth.

[0018] In the main etching process in operation (102), due to the difference between the etching rate of the first layers (206) and the etching rate of the second layer (208), the etched features (218) (e.g., trenches or vias) in the multi-material layer (204) may have a contour consisting of rough sidewalls or other rough features having protrusions and depressions in scallop-shaped features (referred to as "scallops"). In the example illustrated in FIG. 2c, the first layers (206) have a slower etching rate than the second layers (208) during the main etching process in operation (104) using an etching gas mixture.

[0019] FIG. 3a is a schematic cross-sectional view of a portion of the structure (200) prior to the oxidation process. As a result of variations in the etching rate, as shown in FIG. 3a, the first layers (206) include depressions (340) that are recessed relative to the second layer (208), and the second layers (208) include protrusions (350) that are protruded relative to the first layer (206). The combination of the depressions (340) and the protrusions (350) is collectively referred to as "scalloping." In some embodiments, the protrusions (350) and the depressions (340) may not be directly aligned with the first layer (206) and the second layer (208), respectively. For example, depressions (340) may occur on a portion of the first layer (206) and a portion of the second layer (208), or protrusions (350) may occur on a portion of the first layer (206) and a portion of the second layer (208). The protrusions (350) and depressions (340) have an increased surface area compared to the desired flat surface of the trench or via.

[0020] Suitable examples of process gases include, but are not limited to, hydrocarbon-containing gases, such as methane (CH4), sulfur hexafluoride (SF6), silicon chloride (SiCl4), carbon tetrafluoride (CF4), hydrogen bromide (HBr), argon gas (Ar), chlorine (Cl2), nitrogen (N2), helium (He), and oxygen gas (O2). Additionally, process gases may include nitrogen, chlorine, fluorine, oxygen, and hydrogen-containing gases, such as, among others, BCl3, C2F4, C4F8, C4F6, CHF3, CH2F2, CH3F, NF3, NH3, CO2, SO2, CO, N2, NO2, N2O, and H2. Suitable examples of etching gases include SF6 or chlorine-containing gases, such as Cl2, SiCl4, BCl3, SiHCl3, SiH2Cl2, SiH3Cl, Si2Cl6, or combinations thereof. In one embodiment, the chlorine-containing etching gas includes SiCl4, Cl2, and BCl3.

[0021] During the main etching process in operation (104), some process parameters may also be adjusted. In one embodiment, etching gases, such as chlorine, are supplied at flow rates of about 10 sccm to about 1000 sccm, such as about 30 sccm to about 800 sccm, such as about 100 sccm to about 500 sccm. Process gases, such as HBr, may be supplied at flow rates of about 50 sccm to about 1000 sccm, such as about 300 sccm. In one embodiment, the ratio of process gas to etching gas (P:E ratio), such as the ratio of HBr to Cl2, may be about 1:10 to about 10:1, such as about 3:2 (e.g., about 300 sccm HBr to about 200 sccm Cl2). By increasing the processing gas in the P:E ratio, scalloping can be pushed deeper into trenches or vias. Too little processing gas may result in less warping in scalloping, but it can also lead to higher lateral loss due to the large amount of etching gas. Too much processing gas reduces the etching rate due to a lack of etching gas and exhibits more warping.

[0022] In one embodiment, the process pressure in the plasma processing chamber is controlled to about 3 mTorr to about 100 mTorr, for example, about 10 mTorr to about 50 mTorr, for example, about 15 mTorr. Lowering the chamber pressure can achieve greater directional etching and minimize lateral etching, thereby causing less warping.

[0023] In one embodiment, a second etching gas may be flowed into the chamber along with the process gas and the etching gas. The second etching gases may include silicon-containing etching gases. Suitable examples of silicon-containing etching gases include SiCl4, SiHCl3, SiH2Cl2, SiH3Cl, and Si2Cl6. The silicon-containing etching gas may contribute to silicon oxide passivation on the sidewalls and, accordingly, reduce scalloping. The silicon-containing etching gas may be flowed into the chamber at a flow rate of about 0 sccm to about 100 sccm, e.g., about 5 sccm to about 50 sccm, e.g., about 20 sccm. However, a larger amount of silicon-containing etching gas may contribute to a slower etching rate.

[0024] RF source and / or bias power may be utilized while performing the main etching process in operation (104). RF bias power applied when supplying the etching gas helps to form reactive etchants having a desired orientation so that they move down to the surfaces of the multi-material layer (204) exposed from the hard mask layer (210) to predominantly etch the multi-material layer (204). In contrast, the removal of RF bias power can help reactive species in the plasma to be distributed more uniformly across the hard mask layer (210). For example, RF source power of about 500 watts to about 2000 watts may be applied to maintain the plasma inside the processing chamber. RF bias power of about 500 watts to about 6000 watts, e.g. about 1500 watts, may be applied.

[0025] A substrate support pedestal for supporting a substrate (202) is maintained at a temperature of about 50°C to about 290°C, e.g., about 110°C, during the main etching process in operation (104).

[0026] In operation (103), an oxidation process is performed to reduce the sidewall thickness variation of the features (218) etched in the main etching process in operation (104). The oxidation process includes flowing an oxidizing gas into a chamber to form an oxide layer (360), as illustrated in FIG. 3B. In one embodiment, an oxidizing gas of about 50 sccm to about 250 sccm, e.g., about 180 sccm, is delivered into the chamber. The oxidizing gas may include O2, H2O, O3 (ozone), or a combination thereof. In some embodiments, the chamber pressure during the oxidation process is about 10 mTorr to about 50 mTorr, e.g., about 20 mTorr. RF bias power may be applied to maintain a plasma inside the processing chamber. The RF bias power may be applied at about 500 to about 600 watts, e.g., about 2500 watts. In an embodiment using O2, a dry oxidation process is performed. In an embodiment using H2O, a wet oxidation process is performed. In one embodiment, the first layers (206) are formed of silicon-germanium (SiGe), and the second layers (208) are formed of silicon (Si). The oxidation process forms a silicon oxide material (e.g., SiO2) on the surfaces of the first layer (206) and the second layer (208).

[0027] FIG. 3b is a schematic cross-sectional view of a portion of the structure (200) after the oxidation process. The increased surface area of ​​the scalloping depressions (340) and protrusions (350) promotes the growth of the oxide layer (360). The oxide layer (360) further comprises a first side (362) and a second side (364). The first side (362) of the oxide layer (360) is positioned over the sidewall of the features (218). In some embodiments, the oxide layer (360) is positioned over the contours of the sidewall of the features (218) and is shape-following with respect to those contours. The second side (364) of the oxide layer (360) is substantially linear, for example, the second side (364) has a second side variation of about 0 nm to about 5 nm, such as about 1 nm to about 2 nm. The second side variation is defined as the difference between the maximum point of the second side (364) and the minimum point of the second side (362). The growth of the oxide layer (360) on the sidewalls of the features (218) results in reduced sidewall variation within the trench or via. The sidewall variation is defined as the difference between the maximum point on the protrusion (350) and the minimum point on the depression (340). The sidewall variation due to the oxidation process is about 0 nm to about 5 nm, e.g., about 1 nm to about 2 nm.

[0028] In operation (104), a second etching process (also referred to as the “post-etching” process) is performed to further reduce the sidewall thickness variation of the features (218) etched in the main etching process in operation (104). FIG. 2d is a schematic cross-sectional view of the features (218) formed on the multi-material layers (204) after the post-etching process in operation (104). By using a fluorine-containing etching gas to remove byproducts of the oxidation process, the remaining sidewall variation from the oxidation process can be removed. Consequently, the protrusions (350) and depressions (340) formed on the sidewalls of the features (218) are reduced or removed into scallops having a size of less than about 1.5 nm. Suitable examples of fluorine-containing etching gases include SF6, CH2F4, C4F8, CF4, CHF3, C2F6, C3F8, NF3, HF, or combinations thereof.

[0029] In some embodiments, the post-etching process is performed by simultaneously supplying a fluorine-containing etching gas, a passivation gas, and an inert gas such as argon (Ar) into a plasma processing chamber.

[0030] The passivation gas selectively passivates the sidewalls of the features (218) to reduce the bending profiles of the sidewalls of the features (218). Suitable examples of the passivation gas include HBr, BCl3, SF6, or H2S. In one embodiment, the fluorine-containing etching gas includes SF6, and the passivation gas includes HBr.

[0031] An inert gas such as argon (Ar) is delivered at a high flow rate to create low pressure at or near the bottom of the features (218) in the multi-material layer (204), thereby allowing the second etching gas to reach the bottom of the features (218) in the multi-material layer (204). Accordingly, the variation in the sidewall thickness of the features (218) can be reduced.

[0032] During the post-etching process in operation (104), some process parameters may also be adjusted. In one example, SF6 and HBr gases may be supplied at flow rates of about 25 sccm to about 150 sccm, e.g., about 50 sccm, and about 10 sccm to about 1000 sccm, e.g., about 50 sccm, respectively. An inert gas such as argon (Ar) may be supplied at a flow rate of 100 sccm to about 1000 sccm, e.g., about 900 sccm. The fluorine-containing etching gas is supplied by pulsed with a pulse duration of about 1 second to about 10 seconds, e.g., about 5 seconds. The duty cycle (i.e., the ratio of the "on" period during which the fluorine-containing etching gas is supplied to the "off" period during which the fluorine-containing etching gas is not supplied) may be about 1:3 to about 3:1, e.g., about 1:1. The post-etching process in operation (104) may be repeated for about 6 seconds to about 1800 seconds, e.g., about 40 seconds, corresponding to about 4 pulse cycles, depending on the total thickness of the multi-material layer (304). In one embodiment, the process pressure in the plasma processing chamber is controlled to about 10 mTorr to about 5000 mTorr, e.g., about 20 mTorr to about 500 mTorr.

[0033] RF source and / or bias power may be utilized during the etching process. For example, less than about 2000 watts of RF source power may be applied to maintain plasma inside the processing chamber. Less than about 6000 watts of RF bias power may be applied when the fluorine-containing etching gas is supplied, and between about 1000 watts and about 6000 watts of RF bias power may be applied.

[0034] The plasma treatment chamber is maintained at a temperature of about 75°C to about 150°C, e.g., about 110°C, during the post-etching process in operation (104).

[0035] In some embodiments, to control the thickness variation of the sidewalls of the features (118) (e.g., the size of the scallops), the flow rate of SF6, the number of SF6 pulse periods, and the temperature in the plasma processing chamber are adjusted.

[0036] In some embodiments, trenches or vias are formed by performing a main etch on a multi-material layer (204), oxidizing the multi-material layer (204), and post-etching the multi-material layer (204). In other embodiments, trenches or vias are formed by performing a main etch on a single first layer (206) and a single second layer (208), oxidizing the first layer (206) and the second layer (208), post-etching the first layer (206) and the second layer (208), and repeating the main etch, oxidation, and post-etching on each subsequent first layer (206) and second layer (208). In other embodiments, trenches or vias are formed by performing a main etching on one or more first layers (206) and one or more second layers (208), oxidizing one or more first layers (206) and one or more second layers (208), post-etching one or more first layers (206) and one or more second layers (208), and repeating the main etching, oxidation, and post-etching on each of the subsequent one or more first layers (206) and one or more second layers (208).

[0037] The advantages of the present disclosure include improvements in patterning features having accurate and uniform profiles for three-dimensional (3D) semiconductor device structures. Methods according to the embodiments disclosed herein utilize a three-operation etching process, which comprises a main etching process for forming features through a multi-material layer by continuously supplying an etching gas, an oxidation process for oxidizing the sidewalls of the features to reduce thickness variation of the sidewalls, and a post-etching process for reducing sidewall thickness variation of the features through the multi-material layer by pulsed the etching gas. The main etching process provides a fast etching rate through the multi-material layer, while the oxidation process and the post-etching process are adjusted to reduce the sidewall thickness variation of the features to a desired sidewall thickness variation. By doing so, features with reduced sidewall thickness variation can be formed at a high overall etching rate.

[0038] Although the foregoing relates to embodiments of the present disclosure, other and additional embodiments of the present disclosure may be devised without departing from the basic scope of the present disclosure, and the scope of the present disclosure is determined by the following claims.

Claims

Claim 1 A method for patterning a material layer on a substrate, comprising the steps of: forming a hard mask layer on a material layer disposed on a substrate — said material layer comprises a plurality of first layers and a plurality of second layers alternately formed on said substrate —; performing a first etching process to form features on said material layer through the hard mask layer by supplying a first etching gas — said first etching process etches the plurality of first layers at a first etch rate and the plurality of second layers at a second etch rate to form a plurality of protrusions and a plurality of depressions on the sidewalls of said features —; performing an oxidation process to oxidize the sidewalls of said features by supplying an oxidation gas and forming an oxide layer — said first side of said oxide layer adjacent to the plurality of protrusions and the plurality of depressions is conformal to the plurality of protrusions and the plurality of depressions —; A method comprising the step of performing a second etching process on the oxide layer to etch a second side of the oxide layer by supplying a second etching gas ― wherein the second side is planar and opposite to the first side, and the difference between the maximum thickness and the minimum thickness of the oxide layer is 1 nm to 2 nm after performing the second etching process ―. Claim 2 The method according to claim 1, wherein the plurality of first layers and the plurality of second layers comprise tungsten (W), molybdenum (Mo), tantalum (Ta), titanium (Ti), hafnium (Hf), vanadium (V), chromium (Cr), manganese (Mn), ruthenium (Ru), alloys thereof, silicide compounds thereof, nitride compounds thereof, copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), aluminum (Al), palladium (Pd), gold (Au), silver (Au), platinum (Pt), alloys thereof, nitride compounds thereof, silicon-germanium (SiGe), silicon (Si), or combinations thereof. Claim 3 A method according to claim 1, wherein the material layer has a thickness of 0.2 μm to 25 μm, and each of the plurality of first layers and the plurality of second layers has a thickness of 10 nm to 30 nm. Claim 4 A method according to claim 1, wherein the second etching process further comprises supplying an inert gas to generate pressure at the bottom of the features so that the second etching gas reaches the bottom of the features. Claim 5 A method according to claim 1, wherein the first etching gas comprises Cl2, SiCl4, BCl3, SiHCl3, SiH2Cl2, SiH3Cl, Si2Cl6, or a combination thereof, and the second etching gas comprises SF6, CH2F4, C4F8, CF4, CHF3, C2F6, C3F8, NF3, HF, or a combination thereof. Claim 6 A method according to claim 1, wherein the oxidizing gas comprises O2, H2O, O3, or a combination thereof. Claim 7 A method according to claim 1, wherein during the oxidation process, the oxidation gas is flowed at a flow rate of 50 sccm to 250 sccm. Claim 8 A method according to claim 1, wherein the chamber pressure during the oxidation process is 10 mTorr to 50 mTorr and an RF power bias of 500 watts to 600 watts is applied. Claim 9 A method for etching a material layer on a substrate through a hard mask in a processing chamber to form features on the material layer, comprising the steps of: supplying a first etching gas to the material layer in the processing chamber, wherein a hard mask is formed on the material layer, and the material layer comprises a plurality of first layers and a plurality of second layers alternately formed on a substrate, and wherein the first etching gas etches the plurality of first layers at a first etching rate and the plurality of second layers at a second etching rate to form a plurality of protrusions and a plurality of depressions on the sidewalls of the features; subsequently, supplying the first etching gas, supplying an oxidizing gas to oxidize the sidewalls of the features and forming an oxide layer, wherein a first side of the oxide layer adjacent to the plurality of protrusions and the plurality of depressions is shape-following with respect to the plurality of protrusions and the plurality of depressions; and subsequently, exposing the features to a second etching gas. A method comprising the step of etching a second side of the oxide layer with the second etching gas, wherein the second side is flat and opposite to the first side, and the difference between the maximum thickness and the minimum thickness of the oxide layer is 1 nm to 2 nm. Claim 10 In claim 9, the plurality of first layers and the plurality of second layers comprise tungsten (W), molybdenum (Mo), tantalum (Ta), titanium (Ti), hafnium (Hf), vanadium (V), chromium (Cr), manganese (Mn), ruthenium (Ru), alloys thereof, silicide compounds thereof, nitride compounds thereof, copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), aluminum (Al), palladium (Pd), gold (Au), silver (Au), platinum (Pt), alloys thereof, nitride compounds thereof, silicon-germanium (SiGe), silicon (Si), or combinations thereof. Claim 11 In claim 9, the material layer has a thickness of 0.2 μm to 25 μm, and each of the plurality of first layers and the plurality of second layers has a thickness of 10 nm to 30 nm. Claim 12 A method according to claim 9, further comprising the step of supplying an inert gas following the supply of the second etching gas. Claim 13 A method according to claim 9, wherein the first etching gas comprises Cl2, SiCl4, BCl3, SiHCl3, SiH2Cl2, SiH3Cl, Si2Cl6, or a combination thereof, and the second etching gas comprises SF6, CH2F4, C4F8, CF4, CHF3, C2F6, C3F8, NF3, HF, or a combination thereof. Claim 14 In claim 9, the method wherein the oxidizing gas comprises O2, H2O, O3, or a combination thereof. Claim 15 In claim 9, the method wherein the oxidation gas is supplied at a flow rate of 50 sccm to 250 sccm. Claim 16 A method for reducing sidewall thickness variation of a feature etched in a material layer, comprising the step of flowing an oxidizing gas into a material layer in a processing chamber ― said material layer comprises a plurality of first layers and a plurality of second layers alternately formed on a substrate to form a feature, said plurality of first layers and said plurality of second layers form a plurality of protrusions and a plurality of depressions on the sidewall of said feature ―; and the step of forming an oxide layer on the sidewall of said feature ― said oxide layer has a first side and a second side, said oxide layer having a first side and a second side, said oxide layer having a shape-following side with respect to the plurality of protrusions and the plurality of depressions on the sidewall of said feature, said second side being flat and opposite to said first side, said oxide layer having a second side variation of 1 nm to 2 nm, said second side variation being the difference between the maximum thickness and the minimum thickness of said oxide layer ―. Claim 17 In claim 16, the plurality of first layers and the plurality of second layers comprise tungsten (W), molybdenum (Mo), tantalum (Ta), titanium (Ti), hafnium (Hf), vanadium (V), chromium (Cr), manganese (Mn), ruthenium (Ru), alloys thereof, silicide compounds thereof, nitride compounds thereof, copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), aluminum (Al), palladium (Pd), gold (Au), silver (Au), platinum (Pt), alloys thereof, nitride compounds thereof, silicon-germanium (SiGe), silicon (Si), or combinations thereof. Claim 18 In paragraph 16, the method wherein the oxidizing gas comprises O2, H2O, O3, or a combination thereof. Claim 19 In paragraph 16, the method wherein the oxidizing gas is flowed at a flow rate of 50 sccm to 250 sccm. Claim 20 In claim 16, the material layer has a thickness of 0.2 μm to 25 μm, and each of the plurality of first layers and the plurality of second layers has a thickness of 10 nm to 30 nm.

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