Selective oxidation of a substrate

Abstract

This document describes a method for selectively oxidizing a substrate. The method includes forming a non-conformal layer on at least one side surface of a trench or via of the substrate. After forming the non-conformal layer, the at least one trench or via may be selectively oxidized, wherein the non-conformal layer and exposed portions of at least one sidewall not covered by the non-conformal layer are oxidized to form an oxide layer. The oxide layer is thicker at the lower portion of at least one sidewall than at the upper portion of the at least one sidewall, such that the sidewall is tapered.

Description

Selective oxidation of substrates Embodiments of the present disclosure generally relate to a method for oxidizing a substrate, wherein the method for oxidizing uses a non-conformal layer to achieve selective oxidation between different regions of the substrate. In the semiconductor industry, devices are manufactured using a number of fabrication processes that produce structures of ever-decreasing size. Some of these devices include high aspect ratio structures that include a plurality of holes or trenches in the device. To fabricate some devices, an oxidation step is performed. However, it has been found that when oxidizing high aspect ratio structures, an oxide layer forms primarily on the upper portion of the structure, and the thickness of the oxide layer becomes thinner as it moves deeper into the structure. This is believed to occur because when an oxidant is applied to the structure, the oxidant first interacts with the upper portion of the high aspect ratio structure, depleting the chemical species that causes the oxidation. As the oxidant interacts with the upper region, the oxidant is consumed and an oxide layer begins to form in the upper region, which prevents or blocks the oxidant from migrating downward to the lower portion of the high aspect ratio structure. Consequently, this results in the formation of a non-conformal oxide layer, where the top or upper portion of the high aspect ratio feature has a thicker oxide layer than the bottom or lower portion of the high aspect ratio feature, which may have a thinner or even no oxide layer. In some embodiments of the present invention, a method for oxidizing a substrate is provided. The method may include forming a non-conformal layer on at least one sidewall of a trench formed in the substrate, wherein the non-conformal layer is formed on an upper portion of the at least one sidewall and decreases in thickness with increasing depth into the trench. The non-conformal layer may include nitrogen or carbon. In some embodiments, the method may include selectively oxidizing at least one trench including the non-conformal layer. The non-conformal layer and exposed portions of the at least one sidewall not covered by the non-conformal layer are oxidized to form an oxide layer. The oxide layer is thicker at a lower portion of the at least one sidewall than at an upper portion of the at least one sidewall. In another embodiment of the present invention, an article is provided that includes a substrate. The substrate may include at least one trench formed therein, the at least one trench having a top surface, a bottom surface, and at least one sidewall. The article may also include an oxide layer on at least one sidewall of the at least one trench, wherein the oxide layer is thicker at a lower portion of the at least one sidewall than at an upper portion of the at least one sidewall. In another embodiment of the present invention, another method is provided. The other method includes receiving a substrate including at least one trench formed therein. The at least one trench has at least one sidewall, wherein the at least one sidewall of the trench includes a non-conformal layer that coats an upper portion of the at least one sidewall and does not coat a lower portion of the at least one sidewall. The method may also include selectively oxidizing the substrate to form an oxide layer on the at least one sidewall, wherein the non-conformal layer is converted to a gas and removed from the at least one sidewall as the oxide layer forms. The oxide layer is thicker at a lower portion of the at least one sidewall of the at least one trench than at an upper portion of the at least one sidewall. During device fabrication, many devices (e.g., semiconductor devices) produced using nanofabrication and microfabrication processes are oxidized to form an oxide layer over the device structure. Depending on the nature of the device, the location where the oxide layer is formed, and / or other variables, the oxide layer can serve a variety of purposes. The thickness of the oxide layer can be controlled to minimize device performance variations and / or achieve sufficient yield. In embodiments of the present invention, the oxide layer formed on the substrate is tapered, such that the oxide layer is thicker at the bottom than at the top. Embodiments disclosed herein describe a method for selectively oxidizing a substrate. The method for selectively oxidizing a substrate may include forming a non-conformal layer on at least one sidewall of a trench or other high-aspect-ratio feature (e.g., such as a hole) formed on the substrate. The non-conformal layer is formed on an upper portion of the at least one sidewall and decreases in thickness with increasing depth into the trench or other high-aspect-ratio feature. In embodiments, the non-conformal layer may include nitrogen or carbon. The method may further include oxidizing the at least one trench or other high-aspect-ratio feature including the non-conformal layer. The non-conformal layer and exposed portions of the at least one sidewall not covered by the non-conformal layer are oxidized to form an oxide layer. Due to the presence of the non-conformal layer on the sidewall, the oxide layer may be thicker at a lower portion of the at least one sidewall than at an upper portion of the at least one sidewall. In some embodiments of the method, the oxidation may include an initial oxidation process having a first selectivity and at least one additional oxidation process having a second selectivity. In some embodiments, the initial oxidation process may be performed to achieve a target taper of the oxide layer, and the at least one additional oxidation process may be performed to achieve a target thickness of the oxide layer. In some embodiments, the initial oxidation process may be performed to achieve approximately 5% to approximately 50% of the thickness of the oxide layer, and the at least one additional oxidation process may be performed to achieve the remaining thickness of the oxide layer. Embodiments described herein relate to forming a non-conformal layer and ultimately an oxide layer on the sidewalls of a trench in a substrate. However, it should be understood that a trench is one example of a high aspect ratio (HAR) feature operable with the techniques described herein. It should be further understood that the techniques described herein with respect to trenches are equally applicable to any other type of high aspect ratio feature. Aspect ratio features may be features (e.g., such as trenches, holes, channels, etc.) having a length / depth to width / diameter ratio greater than a threshold length / depth to width / diameter ratio. The threshold length / depth to width / diameter ratio may be, for example, 5:1, 10:1, 20:1, 50:1, 100:1, 200:1, 300:1, or other thresholds. Additionally, it should be understood that the embodiments are also suitable for selective oxidation of features on a substrate that are not high aspect ratio features. In some embodiments, the non-conformal layer is formed via a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a radical plasma process (e.g., a radical plasma deposition or growth process), or a thermal process. In embodiments using a CVD or ALD process, the process can be tuned to deposit more on the upper portion of the substrate than on the lower portion. In some embodiments of CVD and / or ALD processes, deposition can be achieved by a combination or sequential cycling of ammonia and a precursor for non-conformal deposition, which can be performed at a temperature between approximately 250°C and approximately 750°C. The precursor can be dichlorosilane (DCS), hexachlorodisilane (HCDS), or a combination thereof. In embodiments using a radical plasma process, a remote plasma process can be used, including one using nitrogen, ammonia, hydrogen, argon (Ar), helium (He), or a combination thereof. In embodiments using a thermal process, ammonia can be used. In either the free radical plasma process or the thermal process, the process may be performed at a temperature of about 250° C. to about 1250° C. for about 5 seconds to about 4 hours. The pressure may be selected to ensure that the non-conformal layer is deposited or grown more on the upper portion of the substrate than on the lower portion of the substrate. In some embodiments, the oxidation may be performed via thermal oxidation. Thermal oxidation is known in the art. During thermal oxidation, an oxygen source is introduced into a chamber containing the substrate while the substrate is heated to a high temperature, and a layer of oxide grows on the substrate surface. In some embodiments, the thermal oxidation may be performed using an oxidizing plasma. In another embodiment, the thermal oxidation may be performed without an oxidizing plasma. In some embodiments of the method, the oxide layer formed on at least one sidewall can be silicon dioxide. For example, if the sidewall is formed of silicon or polysilicon, the oxide can react with the silicon or polysilicon to form silicon dioxide. In certain embodiments of the method, selectively oxidizing the at least one trench may include reacting the non-conformal layer with an oxidant to grow an oxide layer on the non-conformal layer, while the non-conformal layer may be simultaneously converted to a gas and removed from the at least one sidewall. Alternatively or additionally, the oxidant may react with the oxide layer to form a gas that consumes a portion of the non-conformal layer. In some embodiments of the method, the non-conformal layer can have a thickness of about 5 Å to about 50 Å, about 10 Å to about 45 Å, about 15 Å to about 40 Å, about 20 Å to about 35 Å, or about 25 Å to about 30 Å, or any subranges thereof. In some embodiments, the non-conformal layer can have a thickness of about 5 Å, about 10 Å, about 15 Å, about 20 Å, about 25 Å, about 30 Å, about 35 Å, about 40 Å, about 45 Å, or about 50 Å, or any value therein. In some embodiments of the method, the non-conformal layer is not formed on a lower portion of the at least one sidewall, resulting in the lower portion of the at least one sidewall being an exposed portion of the at least one sidewall. In some embodiments, the non-conformal layer is a tapered layer that is thickest at the top or entrance of the trench and gradually becomes thinner as the depth into the trench increases. In some embodiments, the non-conformal layer is formed on about 25% of at least one sidewall, about 50% of at least one sidewall, about 75% of at least one sidewall, or about 80% of at least one sidewall. In some embodiments of the method, selective oxidation may be performed using a process comprising peroxide, steam (H 2O) or H 2:O 2 oxidants, where H 2 and O 2 is from 5.5:1 to about 9:1. In some embodiments of the method, the substrate may be or include silicon, polysilicon, and / or silicon nitride. In another embodiment of the present invention, an article is provided. The article may include a substrate, wherein the substrate includes at least one trench formed therein, the at least one trench having a top surface, a bottom surface, and at least one sidewall. The article may further include an oxide layer on at least one sidewall of the at least one trench, wherein the oxide layer is thicker at a lower portion of the at least one sidewall than at an upper portion of the at least one sidewall. The oxide layer on the sidewall of the at least one trench of the article may be formed according to the methods described herein. In certain embodiments of the article, the oxide layer on the lower portion of at least one sidewall may have a thickness of about 50 Å to about 100 Å, about 55 Å to about 95 Å, about 60 Å to about 90 Å, about 65 Å to about 85 Å, or about 70 Å to about 80 Å, or any value or subrange therein. The oxide layer may be a tapered oxide layer that is thicker at or near the bottom of the trench and thinner at or near the top of the trench. In certain embodiments of the article, the oxide layer on the upper portion of at least one sidewall may have a thickness of about 25 Å to about 50 Å, or may be about 25 Å, about 30 Å, about 35 Å, about 40 Å, about 45 Å, or about 50 Å, or any subrange or value therein. To date, nanofabrication processes and micromanufacturing techniques have not been able to form a tapered layer on high-aspect ratio features, where the layer is thickest at the deepest region of the high-aspect ratio features (e.g., those features furthest from the uppermost region of the features). Embodiments described herein enable the formation of tapered oxide layers on high-aspect ratio features, which can be beneficial for certain types of devices, such as certain types and / or structures of semiconductor devices. In yet another embodiment, a method is provided. The method includes receiving a substrate including at least one trench formed therein, the at least one trench having at least one sidewall. The at least one sidewall of the trench includes a non-conformal layer that coats an upper portion of the at least one sidewall and does not coat a lower portion of the at least one sidewall. The method further includes selectively oxidizing the substrate to form an oxide layer on the at least one sidewall, wherein the non-conformal layer is converted to a gas and removed from the at least one sidewall as the oxide layer forms. The oxide layer is thicker at a lower portion of the at least one sidewall of the at least one trench than at an upper portion of the at least one sidewall. As used herein, the term "substrate" refers to a surface, or portion of a surface, upon which a process operates. Examples of substrates include semiconductor wafers (optionally having one or more features, layers, etc. formed thereon), displays (optionally having one or more features, layers, etc. formed thereon), and the like. It should also be understood by those skilled in the art that reference to a substrate may also refer to only a portion of a substrate, unless the context clearly indicates otherwise. Additionally, reference to deposition on a substrate may refer to both a bare substrate and a substrate having one or more films / layers or features deposited or formed thereon. As used herein, a substrate may also refer to any substrate or material surface formed on a substrate on which film processing is performed during a manufacturing process. For example, depending on the application, substrate surfaces on which processing may be performed include materials such as silicon, polysilicon, silicon oxide, strained silicon, silicon on insulator (SOI), carbon-doped silicon oxide, silicon nitride, doped silicon, silicon germanium, and any other materials such as metals, metal nitrides, metal alloys, and other conductive materials. Substrates include, but are not limited to, semiconductor wafers. The substrate may be exposed to a pre-treatment process to grind, etch, reduce, oxidize, hydroxylate (or otherwise create or graft target chemical moieties to impart chemical functionality), anneal and / or bake the substrate surface. In addition to film treatments directly on the surface of the substrate itself, in the present case, any of the disclosed film treatment steps may also be performed on an underlying layer formed on the substrate as disclosed in more detail below, and the term "substrate surface" is intended to include such underlying layer as the context indicates. Thus, for example, where a film / layer or portion of a film / layer has been deposited onto the substrate surface, the exposed surface of the most recently deposited film / layer becomes the substrate surface. What a given substrate surface comprises will depend on the film to be deposited, and the particular chemistry being used. In one or more embodiments, the first substrate surface may comprise a metal, a metal oxide, or an H-terminated Si x Gei 1-x , and the second substrate surface may include a Si-containing dielectric, and vice versa. In some embodiments, the substrate surface may include certain functional groups (such as -OH, -NH, etc.). Referring now to the drawings, FIG. 1 illustrates a substrate processing system 100 that can be used to perform the selective oxidation method described herein. Other deposition chambers may also benefit from the present disclosure, and the parameters disclosed herein may vary depending on the specific deposition chamber used to form the HAR structure described herein. For example, other deposition chambers may have larger or smaller volumes using gas flow rates greater than or less than those used herein. The substrate processing system 100 includes a thermal processing chamber 102 and a precursor activator 180 coupled to the thermal processing chamber 104 and configured to provide plasma radicals to a processing region 113 within the thermal processing chamber 102. The precursor activator 180 can also be configured to provide an activated gas mixture other than a plasma, for example by applying energy to a gas that does not significantly ionize the gas. The thermal processing chamber 102 has a processing region 113 enclosed by one or more sidewalls 114 (e.g., four sidewalls) and a base 115. The upper portion of the sidewalls 114 can be sealed to a window assembly 117 (e.g., using an O-ring). A radiant energy assembly 118 is positioned above and coupled to the window assembly 117. The radiant energy assembly 118 includes a plurality of lamps 119, which can be tungsten-halogen lamps. Each tungsten-halogen lamp is mounted in a socket 121 and positioned to emit electromagnetic radiation into the processing region 113. Window assembly 117 of FIG. 1 has a plurality of light pipes 141, but window assembly 117 may simply have a flat, solid window without light pipes. Window assembly 117 has an outer wall 116 (e.g., a cylindrical outer wall) that forms a rim surrounding the circumference of window assembly 117. Window assembly 117 also has a first window 120 covering a first end of the plurality of light pipes 141 and a second window 122 covering a second end of the plurality of light pipes 141, opposite the first end. First window 120 and second window 122 extend to and engage outer wall 116 of window assembly 117 to enclose and seal the interior of window assembly 117, including the plurality of light pipes 141. In such cases, when light pipes are used, a vacuum can be created within the plurality of light pipes 141 by applying a vacuum conduit 153 through outer wall 116 to one of the plurality of light pipes 141, which is then fluidically connected to the remaining pipes. The substrate 101 is supported in the thermal processing chamber 102 by a support ring 162 within the processing region 113. The support ring 162 is mounted on a rotatable drum 163. Rotation of the rotatable drum 163 causes the support ring 162 and the substrate 101 to rotate during processing. The pedestal 115 of the thermal processing chamber 102 has a reflective surface 111 for reflecting energy onto the backside of the substrate 101 during processing. Alternatively, a separate reflector (not shown) may be positioned between the pedestal 115 and the support ring 162 of the thermal processing chamber 102. The thermal processing chamber 102 may include a plurality of temperature probes 171 disposed through the pedestal 115 of the thermal processing chamber 102 to detect the temperature of the substrate 101. If a separate reflector is used, as described above, the temperature probes 171 are also disposed through the separate reflector for optically accessing electromagnetic radiation from the substrate 101. The rotatable drum 163 is supported by a magnetic rotor 164, a cylindrical member having lugs 165 on which the rotatable drum 163 rests when both members are installed in the thermal processing chamber 102. The magnetic rotor 164 has a plurality of magnets within a magnet region 166 below the lugs 165. The magnetic rotor 164 is positioned along the base 115 in an annular well 160 located in a peripheral region of the thermal processing chamber 102. A cover 173 rests on a peripheral portion of the base 115 and extends over the annular well 160 toward the rotatable drum 163 and support ring 162, leaving a tolerance gap between the cover 173 and the rotatable drum 163 and / or support ring 162. The cover 173 generally protects the magnetic rotor 164 from exposure to process conditions within the processing region 113. The magnetic rotor 164 is rotated by magnetic energy from a magnetic stator 167 disposed about the susceptor 115. The magnetic stator 167 has a plurality of electromagnets 168 that are powered according to a rotational pattern during processing of the substrate 101 to form a rotating magnetic field. This rotating magnetic field provides magnetic energy to rotate the magnetic rotor 164. The magnetic stator 167 is coupled to a linear actuator 169, which in this case is a screw drive, via a support 170. Operating the linear actuator 169 moves the magnetic stator 167 along an axis 172 of the thermal processing chamber 102, which in turn moves the magnetic rotor 164, the rotatable cylinder 163, the support ring 162, and the substrate 101 along the axis 172. Process gases are supplied to the thermal processing chamber 102 through a chamber inlet 175 and exhausted through a chamber outlet oriented out of the page and generally along the same plane as the chamber inlet 175 and the support ring 162 (not shown in FIG. 1 ). Substrates enter and exit the thermal processing chamber 102 through an access port 174 formed in the sidewall 114 and shown at the rear in FIG. 1 . Substrate transport processes are not described herein. The precursor activator 180 includes a body 182 surrounding an interior space 184 in which a plasma 183 of ions, radicals, and electrons can form. A liner 185 made of quartz or sapphire protects the body 182 from chemical attack by the plasma. The interior space 184 is preferably free of any potential gradient that could attract charged particles (e.g., ions). A gas inlet 186 is positioned at a first end 187 of the body 182 and is opposite a gas outlet 188 located at a second end 189 of the body 182. When the precursor activator 180 is coupled to the thermal processing chamber 102, the gas outlet 188 is in fluid communication with the thermal processing chamber 102 via a delivery line 190 to the chamber inlet 175, so that radicals in the plasma 183 generated within the interior space 184 are supplied to the processing region 113 of the thermal processing chamber 102. The gas outlet 188 can have a larger diameter than the gas inlet 186 to allow for efficient exhaust of excited radicals at a target flow rate and to minimize contact between the radicals and the liner 185. If desired, a separate orifice can be inserted into the liner 185 at the gas outlet 188 to reduce the internal dimensions of the interior space 184 at the gas outlet 188. The diameter of the gas outlet 188 (or orifice, if used) can be selected to provide a pressure differential between the processing region 113 and the precursor activator 180. The pressure differential can be selected to produce a composition of ions, radicals, and molecules flowing into the thermal processing chamber 102 that is suitable for the process being performed therein. To provide gas for plasma processing, a first gas source 192 is coupled to the gas inlet 186 via a first input of a four-way valve 194 and a valve 197 for controlling the flow rate of the gas released from the first gas source 192. A second input of the four-way valve 194 can be coupled to a second gas source 198. A third input of the four-way valve can be coupled to a third gas source 199. Each of the first gas source 192, the second gas source 198, and the third gas source 199 can be or include one or more of a nitrogen-containing gas, an oxygen-containing gas, a silicon-containing gas, a hydrogen-containing gas, or a plasma-forming gas such as argon or helium. A flow controller 196 is connected to the four-way valve 194 to switch the four-way valve 194 between different positions depending on the process to be performed. The flow controller 196 also controls the switching of the four-way valve 194. The precursor activator 180 may be coupled to an energy source (not shown) to provide excitation energy to the precursor activator 180, such as energy having a microwave or radio frequency (RF) frequency, to activate the process gas traveling from the first gas source 192 into the plasma 183. 2), the plasma activation in the precursor activator 180 generates N* radicals, positively charged ions (such as N+ and N 2+) and electrons. By positioning the precursor activator 180 away from the processing region 113 of the thermal processing chamber 102, the substrate's exposure to ions can be minimized. Ions can damage sensitive structures on the semiconductor substrate, while free radicals are reactive and can be used to initiate beneficial chemical reactions. Using an activated gas source such as the precursor activator 180 promotes exposure of the substrate 101 to free radicals and minimizes exposure of the substrate 101 to ions. In some embodiments, a second hydrogen source (not shown) is fluidly coupled to the thermal processing chamber 102. The second hydrogen source delivers hydrogen to the processing region 113, where the hydrogen can be activated by a remote plasma delivered from the precursor activator 180 to the processing region 113. In some embodiments where a high percentage of hydrogen is targeted, hydrogen can be supplied to the processing region 113 via the third gas source 199 and the second hydrogen source. FIG2 is a flow chart illustrating a method 200 for selectively oxidizing a substrate according to an embodiment of the present disclosure. In method 200, at block 205, a patterned substrate is received. The substrate may be patterned to have at least one trench and / or other feature. The substrate will be discussed with reference to a trench, but it should be understood that the trench may be replaced with any other type of feature, including a high aspect ratio feature. The at least one trench may have a top surface, at least one sidewall surface, and a bottom surface. For example, the substrate may have a trench as shown in FIG. 3A . FIG. 3A illustrates a trench 306 of a substrate 303 according to an embodiment of the present invention. In FIG. 3A , a substrate 303 is shown having a trench 306. The substrate 303 may comprise silicon or silicon nitride. The trench 306 has at least one sidewall 302. The trench may be etched into the substrate (e.g., into a silicon wafer) and / or may be etched or otherwise formed in one or more layers formed on the surface of the substrate. In one embodiment, the trench walls 302 are formed from the same material as the trench bottom. In other embodiments, the trench walls 302 are formed from a different material than the trench bottom (e.g., such as if a silicon nitride layer has been formed on a silicon wafer and the silicon nitride layer is etched to expose the silicon wafer at the trench bottom). In some embodiments, at least one sidewall 302 may have a layer (not shown) formed on the sidewall 302. In one embodiment, the layer may comprise silicon nitride (SiN). In other embodiments, the layer may be silicon, damaged silicon nitride, silicon oxide, or a low-κ material. As understood herein, the term "low-κ material" refers to a material having a relatively low relative dielectric constant (κ, kappa) relative to silicon dioxide. Due to the selective oxidation of at least one trench 306, method 200 of the present disclosure allows for the formation of a thicker oxide layer on a lower portion 302b of at least one sidewall than on an upper portion 302a of at least one sidewall 302. Referring back to FIG. 2 , after receiving the patterned substrate, a non-conformal layer may be formed on at least one sidewall of a trench formed in the substrate in block 210 . This can be seen in FIG. 3B , which illustrates trench 306 of FIG. 3A after a non-conformal layer 304 has been deposited on sidewalls 302 of trench 306, according to an embodiment of the present disclosure. In FIG. 3B , a non-conformal layer 304 is formed onto an upper portion 302a of at least one sidewall 302. In some embodiments, the non-conformal layer 304 may also be referred to as a "poison" layer or a "retard" layer. In some embodiments, the non-conformal layer 304 acts as a barrier layer to control the oxidation rate of the trench in the substrate. Non-conformal layer 304 is a tapered layer whose thickness decreases as the depth into trench 306 increases. The non-conformal layer has a thickness of about 5 Å to about 50 Å at the upper portion of at least one sidewall 302. In some embodiments, non-conformal layer 304 may have a thickness of about 5 Å, about 10 Å, about 15 Å, about 20 Å, about 25 Å, about 30 Å, about 35 Å, about 40 Å, about 45 Å, or about 50 Å at the upper portion 302a of at least one sidewall 302. As shown in FIG. 3B , non-conformal layer 304 may not be formed on lower portion 302b of at least one sidewall 302, resulting in lower portion 302b of at least one sidewall being an exposed portion of at least one sidewall 302. In some embodiments, non-conformal layer 304 is formed on approximately 50% of at least one sidewall 302, on approximately 55% of at least one sidewall 302, on approximately 60% of at least one sidewall 302, on approximately 65% ​​of at least one sidewall 302, on approximately 70% of at least one sidewall 302, on approximately 75% of at least one sidewall 302, on approximately 80% of at least one sidewall 302, on approximately 85% of at least one sidewall 302, or on approximately 90% of at least one sidewall 302. In some embodiments, non-conformal layer 304 is a layer comprising nitrogen. In some embodiments, non-conformal layer 304 is a nitride layer, such as silicon nitride. In some embodiments, non-conformal layer 304 comprises carbon. In some embodiments, non-conformal layer 304 is a carbide layer, such as silicon carbide. The formation of the non-conformal layer can be achieved by a chemical vapor deposition (CVD) process, or a radical plasma process (e.g., a radical plasma deposition or growth process). In the radical plasma process, a remote plasma containing radicals can be generated. The remote plasma can include nitrogen plasma (e.g., having nitrogen radicals), ammonia plasma (e.g., having ammonia radicals), or a combination of the two. The radical plasma process can be performed at a relatively high pressure (e.g., at 1 Torr or above) and generate excited states at the high pressure. For example, if nitrogen plasma is used, N 2 * In another example, if ammonia plasma is used, NH 2 or NH radical fragments. The pressure should be controlled to be low enough to induce reaction with the substrate. For example, the pressure can be controlled to produce a radical lifetime that concentrates the free radical plasma process near the upper portion of the substrate. In addition, the process time should also be set to a short period of time (e.g., about 5 seconds to about 4 hours) to allow selective reaction on the target area of ​​the substrate (e.g., the upper portion 302a). In some embodiments, the pressure used for performing the free radical plasma process can be from about 0.5 Torr (T) to about 5 T, or about 0.5 T, about 1 T, about 2 T, about 3 T, about 4 T, about 5 T, or any value or subrange therein. The time period for performing the free radical plasma process can be from about 5 seconds to about 1 hour. By performing a radical plasma process for forming the non-conformal layer 304, the energy of the radicals can be controlled such that the radicals do not react along the entire sidewall 302, but rather selectively react with the upper portion 302a of the sidewall 302 of the substrate (e.g., without reaching or reacting with the lower portion 302b of the sidewall 302). In another embodiment, the thermal process can be performed under similar conditions, except that the pressure can be between about 0.5°F and about 500°F. In some embodiments, the non-conformal layer 304 is formed via CVD or ALD. There are various types of chemical vapor deposition processes, and the specific type of process can be selected based on several factors, such as the surface to be coated, the coating material, the chemical interaction between the surface and the coating material, the target material thickness, the target coating characteristics, and the like. Some examples of CVD processes include atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), vapor phase epitaxy, and the like. In some embodiments, any of these CVD processes can be used. For various CVD processes, the substrate is exposed to one or more volatile precursors, which react and / or decompose on the surface of the article to produce the target coating. Byproducts may be produced, which are removed by exhausting the byproducts from the deposition chamber in which the CVD process is performed. FIG. 4 illustrates an exemplary chemical vapor deposition (CVD) system that may be used to coat an article according to an embodiment. The system includes a chemical vapor precursor supply system 405 and a CVD reactor 410. The vapor precursor supply system 405 generates a vapor precursor 420 (such as the vapor precursor for the non-conformal layer 304) from a starting material 415. The vapor precursor can be in solid, liquid, or gaseous form. The vapor is then delivered to the CVD reactor 410 and deposited as a thin film 445 on a substrate 430 (e.g., which can correspond to substrate 300A in FIG. 3A ). The substrate 430 can be positioned on a holder 435. The CVD reactor 410 uses a heater 440 to heat the substrate 430 to the deposition temperature. In some embodiments, the heater can heat the walls of the CVD reactor (also known as a "hot-wall reactor"), and the reactor walls can transfer heat to the substrate 430. In other embodiments, the substrate can be heated while the walls of the CVD reactor remain cool (also known as a "cold-wall reactor"). It should be understood that the CVD system configuration should not be construed as limiting. The CVD system can utilize a variety of equipment, and the equipment is selected to achieve optimal processing conditions that produce coatings with uniform thickness, surface morphology, structure, and composition. Various CVD processes include the following process steps: (1) generating a reactive gaseous reactant species (also referred to as a "precursor") from a starting material; (2) delivering the precursor into a reaction chamber (also referred to as a "reactor"); (3) absorbing the precursor onto a heated substrate (i.e., onto the upper portion 302a of the substrate 300A); (4) engaging in a chemical reaction between the precursor and the substrate at a gas-solid interface to form a deposit and gaseous by-products; and (5) removing the gaseous by-products and unreacted gaseous precursor from the reaction chamber. Suitable CVD precursors can be stable at room temperature, have a low evaporation temperature, produce a vapor that is stable at low temperatures, have a suitable deposition rate (low for thin film coatings and high for thick film coatings), be relatively low in toxicity, be cost-effective, and be relatively pure. For some CVD reactions, such as thermal decomposition (also known as "pyrolysis") or disproportionation reactions, a chemical precursor alone may be sufficient to achieve deposition. For other CVD reactions, in addition to chemical precursors, other reagents or reactants (such as oxygen- or fluorine-containing reactants) may be used to achieve deposition to form protective metal fluoride coatings such as those described herein. CVD has many advantages, including its ability to deposit highly dense and pure coatings with good reproducibility and adhesion at relatively high deposition rates. In embodiments, layers deposited using CVD can have porosity below 1% and below 0.1% (e.g., approximately 0%). Therefore, when sufficiently low amounts of precursor are used so that the precursor does not reach (or a relatively small amount of the precursor reaches) areas not targeted for deposition, this deposition can be used to coat complex-shaped components and deposit non-conformal films. Referring back to FIG. 3B , in some embodiments, the non-conformal layer 304 may include nitrogen. In some embodiments, the non-conformal layer 304 may also include silicon. For example, the non-conformal layer 304 may include silicon nitride. In some embodiments, the non-conformal layer 304 including nitrogen is formed by nitriding the substrate 303. Nitriding may be performed by applying nitrogen (N 2) Ammonia (NH 3) Hydrogen (H 2), argon (Ar), helium (He), or a combination of these gases. In some embodiments, nitridation can be achieved using plasma. The plasma may include nitrogen (N 2) Ammonia (NH 3) Hydrogen (H 2), argon (Ar), helium (He), or a combination thereof. In some embodiments, nitridation can be achieved by applying ammonia to the substrate with or without plasma. Nitridation can be performed at a pressure of about 0.5°C to about 5°C, about 0.5°C, about 1°C, about 2°C, about 3°C, about 4°C, or about 5°C, or any value or sub-range therein. Nitridation can be performed at a temperature of about 250°C to about 1250°C, about 350°C to about 1150°C, about 450°C to about 1050°C, about 550°C to about 950°C, about 650°C to about 850°C, or about 250°C, about 350°C, about 450°C, about 550°C, about 650°C, about 750°C, about 950°C, about 1050°C, about 1150°C, or about 1250°C, or any value or sub-range therein. In some embodiments, prior to forming the non-conformal layer 304, a native oxide may form on the surface of the substrate 303 (e.g., on the sidewalls 302 of the substrate 303). For example, the native oxide may form if the substrate 303 is exposed to oxygen and / or moisture. In some embodiments, the native oxide may hinder the formation of the non-conformal layer 304. Therefore, in some embodiments, a cleaning or etching process is performed to remove the native oxide before forming the non-conformal layer 304. Referring back to FIG. 2 , after the non-conformal layer is formed on a portion of at least one sidewall of the trench, at block 215 an oxidant is applied to the at least one sidewall having the non-conformal layer. The oxidant may include peroxide, steam (H 2O) or H 2:O 2, where H 2 and O 2 is from 5.5: 1 to about 9: 1. In an embodiment, the oxidizing agent is applied while the substrate is heated. The oxidant is chosen based on its ability to selectively oxidize the substrate. In some embodiments, preferred oxidants are highly selective, reacting quickly with the material in the substrate (i.e., silicon) while reacting more slowly with non-conformal layers (i.e., nitrogen- or carbon-containing layers). For example, a hydrogen (H)-rich oxidant may be more selective during this step. In another example, steam (H) 2O) and / or hydrogen peroxide (H 2O 2) can be a selective oxidant. On the contrary, oxygen free radicals (O * ) and / or hydroxide (OH) selectivity may be low. At block 220, an oxidant reacts with the non-conformal layer and the substrate to grow an oxide layer thereon for a period of time. As shown in FIG. 3C , an oxide layer 305 grows along at least one sidewall 302 of a trench 306, while the non-conformal layer 304 is reduced on at least one sidewall 306. FIG. 3C illustrates the trench of FIG. 3B after the oxidation process has begun and before the oxidation process is completed, according to an embodiment of the present disclosure. The time period for the oxidant reaction may depend on the selectivity of the oxidant. In some embodiments, the time period may be about 30 seconds, about 45 seconds, about 1 minute, about 5 minutes, about 10 minutes, about 15 minutes, about 20 minutes, about 30 minutes, about 45 minutes, about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, or about 6 hours, or any value therein. In some embodiments, a variety of different oxidation chemistries may be used. For example, a first oxidation step may be performed using a first oxidant having a first selectivity (e.g., a lower selectivity between exposed portions of sidewalls 302 and portions of sidewalls covered by a non-conformal layer), and a second oxidation step may be performed using a second oxidant having a second selectivity (e.g., a higher selectivity between exposed portions of sidewalls 302 and portions of sidewalls covered by a non-conformal layer). The first time period for the first oxidation step and the second time period for the second oxidation step may be selected to adjust the selectivity of the overall oxidation process to a target selectivity, which may be between the first selectivity of the first oxidation step and the second selectivity of the second oxidation step. Additional oxidation steps may be performed to control the selectivity of the oxidation. Referring back to FIG. 2 , at block 225 , while the oxide layer is being grown, the non-conformal layer is simultaneously removed from the trench. In some embodiments, when the oxidant reacts with the non-conformal layer, it may convert a portion of the non-conformal layer into a gas phase. The reacted gas phase of the non-conformal layer may then be removed from the process chamber where the oxidation is occurring (e.g., by pumping out reaction byproducts). For example, if the non-conformal layer includes nitrogen, the oxidant may react with both the substrate and the nitrogen to cause the oxide layer to begin growing on the exposed portion of at least one sidewall of the trench in the substrate while converting the nitrogen into a gas so that the oxide layer eventually replaces it. Thus, the oxide layer may grow only on the substrate itself because the non-conformal layer was removed during the selective oxidation process. At block 230, an oxide layer is formed that is thicker at the lower portion of at least one sidewall than at the upper portion of at least one sidewall. This is also shown in FIG. 3D. FIG. 3D illustrates the trench of FIG. 3B after the oxidation operation is completed, according to an embodiment of the present disclosure. As shown in FIG. 3D, the oxide layer 205 is thicker at the lower portion 302b of the trench and gradually thins near the upper portion 302a of the sidewall 302 of the trench 306. In some embodiments, the oxide layer grows to form a thicker layer on the lower exposed portion of at least one sidewall of the trench in the substrate because the oxidation of a non-conformal layer (e.g., nitride) is slower than the oxidation of the exposed portion of the sidewall (e.g., silicon). Therefore, the oxidation rate and taper are controlled to achieve a target thickness and a target taper amount (e.g., a target thickness profile on the surface of the trench sidewall, in embodiments). In some embodiments, the oxide layer on the lower portion of at least one sidewall may have a thickness of about 50 Å to about 100 Å, about 55 Å to about 95 Å, about 60 Å to about 90 Å, about 65 Å to about 85 Å, or about 70 Å to about 80 Å, or any value or sub-range therein. In some embodiments, the oxide layer on the lower portion of at least one sidewall may have a thickness of about 50 Å, about 55 Å, about 60 Å, about 65 Å, about 70 Å, about 75 Å, about 80 Å, about 85 Å, about 90 Å, about 95 Å, or about 100 Å. In some embodiments, the oxide layer on the upper portion of at least one sidewall may have a thickness of about 25 Å to about 50 Å, or may be about 25 Å, about 30 Å, about 35 Å, about 40 Å, about 45 Å, or about 50 Å, or any subrange or value therein. In some embodiments, the oxide layer on the upper portion of at least one sidewall may have a thickness of about 25 Å, about 30 Å, about 35 Å, about 40 Å, about 45 Å, or about 50 Å. In some embodiments, the oxide layer on at least one sidewall may gradually thicken (e.g., may be tapered) from an upper portion to a lower portion of the at least one sidewall. The thickness of the lower and upper portions, as well as the amount of tapering, may be controlled based on the non-conformal layer formed in an earlier step of the method, the selectivity of the oxidation process, and the time and / or temperature of the oxidation. In some embodiments, a selective oxidation method may be performed in a first oxidation step to grow a target profile on at least one sidewall of a trench in a substrate, followed by a second oxidation step (e.g., a free radical oxidation step) to complete the trench oxidation of the substrate. In some embodiments, the second oxidation step allows the substrate to be oxidized at a faster rate. In some embodiments, the first oxidation step has a higher selectivity but a lower oxide growth rate, and the second oxidation step has a lower selectivity but a higher growth rate. In some embodiments, complete oxidation of the trench of the substrate (selective oxidation followed by free radical oxidation) can be performed in less than about one hour. As described above, in some embodiments, a native oxide may be formed on the sidewalls of a trench in a substrate before forming a non-conformal layer on the sidewalls of the trench. In some embodiments, an electronic device manufacturing system including a cluster tool is used to process the substrate. After forming the trench in the substrate and before forming the non-conformal layer on the sidewalls of the trench, the substrate may be held in a vacuum. By moving the substrate between chambers without breaking the vacuum, the formation of native oxide may be prevented. FIG5 illustrates a schematic top view of an electronic device manufacturing system 500 according to an embodiment of the present disclosure. Electronic device manufacturing system 500 is configured to process substrates and may include a mainframe (also known as a transfer chamber) 504 having four facets 501A through 501D. Although the four facets 501A through 501D are shown in a rectangular configuration, mainframe 504 may alternatively have other numbers of facets (e.g., 5, 6, 7, 8, etc.) and / or other shapes. In embodiments, the facets may have the same size (e.g., the same width) or different sizes. In one embodiment, mainframe 504 has a rectangular shape, wherein facets 501A and 501C are substantially parallel to each other, facets 501B and 501D are substantially parallel to each other, and facets 501A and 501C are substantially perpendicular to facets 501B and 501D. In one embodiment, mainframe 504 has a pentagonal shape. In one embodiment, the main body includes a first facet having a first length, a second facet and a third facet on either side of the first facet, the second facet and the third facet each having a second length greater than the first length, and a fourth facet and a fifth facet connected to the second facet and the third facet, respectively, the fourth facet and the fifth facet each having a third length greater than or equal to the first length and less than the second length. Mainframe 504 may include an interior volume 534, wherein facets 501A-501D may define sidewalls of interior volume 534. Mainframe 504 may further include a base (not shown) and a lid (not shown). Facets 501A-501D, the base, and the lid may collectively define interior volume 534. A robotic arm (also referred to as a robotic assembly) 536 may be positioned within interior volume 534 of mainframe 504. Interior volume 534 may typically be under vacuum during operation of mainframe 504. Each facet 501A-501D may include one or more substrate access ports 532. Each substrate access port 532 may be configured to allow a horizontally oriented substrate 540 to pass therethrough. The substrate 540 may be a wafer (e.g., a semiconductor wafer or a non-semiconductor device substrate), a glass plate or panel, and / or other workpieces used in the manufacture of electronic devices or circuit components. Each substrate access port 532 may be, for example, an elongated slot or slit formed in a sidewall of the mainframe 504. Each substrate access port 532 may include, for example, a slit valve or other suitable device for opening and closing the substrate access port 534, and / or a local center finder (LCF) suitable for determining the position of a substrate 540 transferred through the substrate access port 530. The slit valve may be of any suitable conventional configuration, such as an L-motion slit valve. Other suitable devices may also be used to open and close the substrate access port 532. In some embodiments, the substrate access port 532 may include a single gate or dual gates (eg, a first gate on the interior of the replaceable interface board at the substrate access port and a second gate on the exterior of the replaceable interface board at the substrate access port). The process chambers 506, 508, 510, 512, 514, 516 are attached to respective facets 501A-501D of the mainframe 504. Each of the process chambers 506-516 has a chamber port that is aligned with the substrate access port 532. The load lock chambers 126 can each be a batch-type or single-substrate-type load lock chamber. In some embodiments, the load lock chambers 526 can be stacked load lock chambers. For example, the load lock chambers 126 can be a double-stacked load lock chamber, a triple-stacked load lock chamber, a load lock chamber with four or more stacked load locks (e.g., a quad-load lock chamber), and so on. Alternatively, the load lock chambers 126 can be single-volume load lock chambers. The load lock chambers 126 can each have one or more chamber ports that correspond to corresponding substrate access ports 532. For example, a stacked load lock chamber 126 that can have two separate substrate volumes can have two vertically aligned chamber ports that correspond to vertically aligned substrate access ports 532, respectively. A triple-stacked load lock chamber that can have three separate substrate volumes can have three vertically aligned chamber ports that correspond to vertically aligned substrate access ports. A single-volume load lock chamber may have a single chamber port corresponding to a single substrate access port 532. Any one or more of the load lock chambers 126 may be a stacked load lock chamber, a triple-stacked load lock chamber, and / or a single-volume load lock chamber. Furthermore, in some embodiments, any one or more of the load lock chambers 126 may be process-capable chambers. That is, any one or more of the load lock chambers 126, or any of the volumes herein, may be capable of performing a substrate preheat process, a letdown process, a cooldown process, and / or another treatment process. The mainframe 504, process chambers 506-516, and / or load lock chamber 526 can each operate under vacuum pressure. Each of the process chambers 506-516 can perform the same or different processes on the substrate 540, including, for example, deposition, oxidation, nitridation, etching, polishing, cleaning, lithography, inspection, etc. Other processes can also be performed in the process chambers. The mainframe 504 may also include a robotic assembly 536 within the interior volume 534. The robotic assembly 536 may be configured to transfer one or more substrates 540 to and from each of the process chambers 506-516 and the load lock chamber 526. The robotic assembly 536 may be configured to transfer substrates 540 directly from any chamber to any other chamber attached to the mainframe 504. In some embodiments, the substrates 540 may be transferred by the robotic assembly 536 in any order or direction. In some embodiments, the robotic assembly 536 may have dual transfer blades (or more transfer blades, also known as end effectors), each of which may be independently extended and retracted to and from any chamber attached to the mainframe 504, thereby increasing system throughput by enabling simultaneous substrate transfer. In some embodiments, the robotic assembly 536 may have a single transfer blade and / or may be a selective compliance articulated robot arm (SCARA) robot. Alternatively, the robotic assembly 536 may be any suitable mechanism for transferring substrates between chambers attached to the mainframe 504, such as a linear robot or a nonlinear robot. The load lock chamber 126 can be coupled to the factory interface 502, which can be coupled to one or more front opening unified pods (FOUPs) 518. The one or more load lock chambers 126 can provide a first vacuum interface between the factory interface 502 and the transfer chamber 126. In some embodiments, each of the load lock chambers 526 can be alternately connected to the mainframe (transfer chamber) 504 and the factory interface 502 to increase substrate throughput. That is, while one load lock chamber 526 or any volume of a stacked or tri-stacked load lock chamber is in communication with the transfer chamber 504, other load lock chambers 126 or other volumes of the stacked or tri-stacked load lock chambers can be in communication with the factory interface 502. Substrates can be transferred between the factory interface 502, the load lock chambers 126, and the transfer chamber 504 in any other suitable manner. Each of the FOUPs 518 can be a container having a fixed cassette therein for holding a plurality of substrates. Each of the FOUPs 518 can have a front-opening interface configured for use with the factory interface 502. The factory interface 502 can have a buffer chamber (not shown) and one or more robotic assemblies 538 configured to transfer substrates 540 via linear, rotational, and / or vertical movement between the FOUPs 518 and the load lock chamber 126. The substrates can be transferred between the FOUPs 518 and the load lock chamber 126 in any order or direction. The load lock chamber 126 can each be a batch-type or single-substrate-type load lock chamber. Controller 571 can control the operation of robotic assembly 538, robotic assembly 536, and / or the electronic device manufacturing system. Controller 571 can control the processing and movement of substrates 540 within and through the electronic device manufacturing system. Controller 571 can be, for example, a general-purpose computer and / or can include a microprocessor or other suitable CPU (central processing unit), memory for storing software routines for controlling the electronic device manufacturing system, input / output peripherals, and support circuitry (such as, for example, a power supply, clock circuitry, circuitry for driving robotic assemblies 538, 536, cache memory, etc.). Controller 571 can be programmed, for example, to sequentially process one or more substrates through each process chamber attached to host computer 504. In other embodiments, controller 571 can be programmed to process substrates in any order through the process chambers. In other embodiments, controller 571 can be programmed to skip and / or repeat processing of one or more substrates in one or more process chambers. Controller 571 may alternatively be programmed to process one or more substrates in an electronic device manufacturing system in any suitable manner. The electronic device manufacturing system may have any suitable number of FOUPs 518 and / or load lock chambers 526 other than the FOUPs 518 and / or load lock chambers 526 shown. In some embodiments, the number of load lock chambers coupled to facet 501A may be independent of the number of process chambers coupled to any of facets 501B through 501D. For example, the number of load lock chambers may be different from the highest number of process chambers coupled to a facet. Furthermore, in some embodiments, depending on the size of mainframe 504 relative to the size of the four process chambers, up to four process chambers may be coupled to a single facet, or more than four process chambers may be coupled to a single facet. In one embodiment, a substrate can be moved into the mainframe 504, and multiple processes can be performed in the various process chambers 506 to 516 without breaking vacuum. For example, process chamber 506 can form a trench in the substrate, process chamber 508 can form a non-conformal layer on the sidewalls of the trench, and process chamber 510 can perform oxidation to form an oxide layer on the sidewalls of the trench and remove the non-conformal layer. Substrate 540 can be transferred between process chambers 506 to 516 under vacuum by robot 532. Therefore, in some embodiments, no native oxide can grow on the substrate between forming the trench, forming the non-conformal layer on the trench, and forming the oxide layer on the trench. The present method can be used to form tapered oxide layers in or on features with high aspect ratios. For example, high aspect ratio processes can benefit from thicker oxide layers in the lower portion of trenches. This can be achieved using the method described above. The previous description sets forth many specific details, such as examples of specific systems, components, methods, etc., to provide a good understanding of several embodiments of the present invention. However, it will be apparent to those skilled in the art that at least some embodiments of the present invention can be practiced without these specific details. In other cases, well-known components or methods are not described in detail or are presented in a simple block diagram format to avoid unnecessarily obscuring the present invention. Therefore, the specific details set forth are merely exemplary. Specific implementations may differ from these exemplary details and still be contemplated as being within the scope of the present invention. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the term "or" is intended to mean an inclusive or rather than an exclusive or. When the terms "about" or "approximately" are used herein, they are intended to mean that the nominal value presented is accurate to within ±10%. Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be changed so that certain operations may be performed in a reverse order, or so that certain operations may be performed at least partially concurrently with other operations. In another embodiment, instructions or sub-operations of different operations may be performed in an intermittent and / or alternating manner. It should be understood that the above description is intended to be illustrative and not restrictive. Many other embodiments will become apparent to those skilled in the art upon reading and understanding the above description. Accordingly, the scope of the present invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 100: Substrate processing system 101: Substrate 102: Thermal processing chamber 111: Reflective surface 113: Processing area 114: Sidewall 115: Base 116: Outer wall 117: Window assembly 118: Radiant energy assembly 119: Lamp 120: First window 121: Socket 122: Second window 126: Load lock chamber 141: Light pipe 153: Pipe 160: Annular well 162: Support ring 163: Rotatable cylinder 164: Magnetic rotor 165: Convex Ear 166: Magnetic Region 167: Magnetic Stator 168: Electromagnet 169: Linear Actuator 170: Support 171: Temperature Probe 172: Axis 173: Cover 174: Access Port 175: Chamber Entrance 180: Precursor Activator 182: Body 183: Plasma 184: Internal Space 185: Liner 186: Gas Inlet 187: First End 188: Gas Outlet 189: Second End 190: Delivery Line 192: First Gas Source 194: Cross-Connect Valve 196: Flow controller 197: Valve 198: Second gas source 199: Third gas source 200: Method 205: Operation 210: Operation 215: Operation 220: Operation 225: Operation 230: Operation 302: Sidewall 302a: Upper portion 302b: Lower portion 303: Substrate 304: Non-conformal layer 305: Oxide layer 306: Groove 405: Chemical vapor precursor supply system 410: CVD reactor 415: Starting material 420: Vapor precursor 430: Substrate 435: Holder 440: Heater 500: Electronic Device Manufacturing System 501A: Facet 501B: Facet 501C: Facet 501D: Facet 504: Mainframe 506: Process Chamber 508: Process Chamber 510: Process Chamber 512: Process Chamber 514: Process Chamber 516: Process Chamber 518: Front-Opening FOUP 532: Robot 534: Internal Volume 536: Robot Arm 540: Substrate 571: Controller The present invention is illustrated by way of example and not limitation. Like reference numerals indicate like elements in the figures of the accompanying drawings. It should be noted that different references to "an" or "one" embodiment herein do not necessarily refer to the same embodiment; such references mean at least one embodiment. FIG1 shows a cross-sectional view of a remote plasma system; FIG2 is a flow chart illustrating a method for selectively oxidizing a substrate according to an embodiment of the present invention; FIG3A illustrates a trench of a substrate according to an embodiment of the present invention; FIG. 3B illustrates the trench of FIG. 3A after a non-conformal layer is deposited on the sidewalls of the trench, according to an embodiment of the present invention; FIG3C illustrates the trench of FIG3B before an oxidation operation is completed according to an embodiment of the present invention; FIG. 3D illustrates the trench of FIG. 3B after the oxidation operation is completed according to an embodiment of the present invention; FIG4 illustrates an exemplary chemical vapor deposition (CVD) system; FIG. 5 is a schematic top view of an electronic device manufacturing system. Domestic deposit information (please note in the order of deposit organization, date, and number) None Foreign deposit information (please note in the order of deposit country, organization, date, and number) None 200:Method 205: Operation 210: Operation 215: Operation 220: Operation 225: Operation 230: Operation

Claims

1. A method for oxidizing a substrate, comprising the steps of: forming a non-conformal layer on at least one sidewall of a trench or a hole formed on a substrate, wherein the non-conformal layer is formed on an upper portion of the at least one sidewall and its thickness decreases with increasing depth into the trench or the hole, and wherein the non-conformal layer comprises nitrogen; and oxidizing the at least one sidewall of the trench or the hole containing the non-conformal layer, wherein the non-conformal layer and an exposed portion of the at least one sidewall not covered by the non-conformal layer are oxidized to form an oxide layer, wherein the oxide layer is thicker at a lower portion of the at least one sidewall than at the upper portion of the at least one sidewall.

2. The method as claimed in claim 1, wherein the oxidation step comprises an initial oxidation process having a first selectivity and at least one additional oxidation process having a second selectivity.

3. The method as described in claim 2, wherein the initial oxidation process is performed to achieve a target taper of the oxide layer, and the at least one additional oxidation process is performed to achieve a target thickness of the oxide layer.

4. The method as described in claim 2, wherein the initial oxidation process is performed to achieve a thickness of about 5% to about 50% of the oxide layer.

5. The method as described in claim 1, wherein the step of forming the non-conformal layer is achieved via a chemical vapor deposition process, a thermal process, or a free radical plasma process.

6. The method as described in claim 1, wherein the formation of the non-conformal layer comprising nitrogen is performed by performing nitriding of the substrate.

7. The method as described in claim 6, wherein the nitriding is achieved by applying nitrogen (N2), ammonia (NH3), hydrogen (H2), argon (Ar), helium (He), or a combination of the above gases.

8. The method as described in claim 7, wherein the nitriding is carried out at a pressure of about 0.5 T to about 500 T.

9. The method as described in claim 7, wherein the nitriding is carried out at a temperature of about 250°C to about 1250°C.

10. The method as described in claim 1, wherein the oxidation step is performed via thermal oxidation.

11. The method as described in claim 1, wherein the oxide layer comprises silicon dioxide.

12. The method as described in claim 1, wherein the nonconformal layer has a thickness of about 5 Å to about 50 Å on the upper portion of the at least one sidewall.

13. The method as described in claim 1, wherein the non-conformal layer is not formed on the lower portion of the at least one sidewall, resulting in the lower portion of the at least one sidewall being the exposed portion of the at least one sidewall.

14. The method as described in claim 1, wherein the non-conformal layer is formed on about 25% of the at least one sidewall.

15. The method as claimed in claim 1, wherein the oxidation system is carried out using an oxidizing agent comprising a peroxide, vapor (H2O) or H2:O2, wherein the ratio of H2 to O2 is from 5.5:1 to about 9:

1.

16. The method as described in claim 1, wherein the substrate comprises silicon or silicon nitride.

17. An article comprising: a substrate, wherein the substrate includes at least one trench or at least one hole formed therein, the at least one trench or at least one hole having a top surface, a bottom surface and at least one sidewall; and an oxide layer on the at least one sidewall of the at least one trench or at least one hole, wherein the oxide layer is thicker at a lower portion of the at least one sidewall than at an upper portion of the at least one sidewall.

18. The article of claim 17, wherein the oxide layer on the lower portion of the at least one sidewall has a thickness of about 50 Å to about 100 Å.

19. The article of claim 17, wherein the oxide layer on the upper portion of the at least one sidewall has a thickness of about 25 Å to about 50 Å.

20. A method for oxidizing a substrate, comprising the steps of: receiving a substrate including at least one trench or at least one hole formed therein, the at least one trench or at least one hole having at least one sidewall, wherein the at least one sidewall of the trench or the hole includes a non-conformal layer coated on an upper portion of the at least one sidewall but not on a lower portion of the at least one sidewall; and selectively oxidizing the substrate to form an oxide layer on the at least one sidewall, wherein the step of selectively oxidizing the at least one trench or the at least one hole includes the steps of: reacting the non-conformal layer with an oxidizing agent to grow the oxide layer, while simultaneously removing the non-conformal layer from the at least one sidewall, wherein the growth rate of the oxide layer is slowed down by the nitrogen-containing non-conformal layer such that the oxide layer is thicker at the lower portion of the at least one sidewall of the at least one trench or the at least one hole than at the upper portion of the at least one sidewall.

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