# Patent

## Title
Selective etch for metal-containing materials

## Abstract

Methods of selectively etching metal-containing materials from the surface of a substrate are described. The etch selectively removes metal-containing materials relative to silicon-containing films such as silicon, polysilicon, silicon oxide, silicon germanium and/or silicon nitride. The methods include exposing metal-containing materials to halogen containing species in a substrate processing region. A remote plasma is used to excite the halogen-containing precursor and a local plasma may be used in embodiments. Metal-containing materials on the substrate may be pretreated using moisture or another OH-containing precursor before exposing the resulting surface to remote plasma excited halogen effluents in embodiments.

## Background
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the benefit of U.S. Prov. Pat. App. No. 61/903,240 filed Nov. 12, 2013, and titled “SELECTIVE ETCH FOR METAL-CONTAINING MATERIALS” by Ingle et al., which is hereby incorporated herein in its entirety by reference for all purposes.


FIELD
This invention relates to selectively removing metal-containing material.
BACKGROUND
Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective of the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed that selectively remove one or more of a broad range of materials.
Dry etch processes are often desirable for selectively removing material from semiconductor substrates. The desirability stems from the ability to gently remove material from miniature structures with minimal physical disturbance. Dry etch processes also allow the etch rate to be abruptly stopped by removing the gas phase reagents. Some dry-etch processes involve the exposure of a substrate to remote plasma by-products formed from one or more precursors. For example, remote plasma excitation of ammonia and nitrogen trifluoride enables silicon oxide to be selectively removed from a patterned substrate when the plasma effluents are flowed into the substrate processing region. Remote plasma etch processes have recently been developed to selectively remove a variety of dielectrics relative to one another. However, relatively few dry-etch processes have been developed to selectively remove metal-containing materials.
SUMMARY
Methods of selectively etching metal-containing materials from the surface of a substrate are described. The etch selectively removes metal-containing materials relative to silicon-containing films such as silicon, polysilicon, silicon oxide, silicon germanium and/or silicon nitride. The methods include exposing metal-containing materials to halogen containing species in a substrate processing region. A remote plasma is used to excite the halogen-containing precursor and a local plasma may be used in embodiments. Metal-containing materials on the substrate may be pretreated using moisture or another OH-containing precursor before exposing the resulting surface to remote plasma excited halogen effluents in embodiments.
Embodiments of the invention include methods of etching metal-containing material. The methods include transferring a substrate into a substrate processing region of a substrate processing chamber. The substrate includes the metal-containing material. The methods further include flowing a halogen-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents. The methods further include etching the metal-containing material from the substrate by flowing the plasma effluents into the substrate processing region through through-holes in a showerhead. The showerhead is disposed between the remote plasma region and the substrate processing chamber.
Embodiments of the invention include methods of etching aluminum oxide. The methods include transferring a substrate into a substrate processing region of a substrate processing chamber. The substrate includes the aluminum oxide. The methods further include flowing a gas-phase oxygen-and-hydrogen-containing precursor into the substrate processing region. The gas-phase oxygen-and-hydrogen-containing precursor includes an OH group. The methods further include flowing a chlorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents. The methods further include etching the aluminum oxide from the substrate by flowing the plasma effluents into the substrate processing region through through-holes in a showerhead.
Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed embodiments. The features and advantages of the disclosed embodiments may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification.



DESCRIPTION OF THE DRAWINGS
A further understanding of the nature and advantages of the disclosed embodiments may be realized by reference to the remaining portions of the specification and the drawings.
FIG. 1 is a flow chart of an aluminum oxide selective etch process according to embodiments.
FIG. 2 is a flow chart of an aluminum oxide selective etch process according to embodiments.
FIG. 3A shows a schematic cross-sectional view of a substrate processing chamber according to embodiments.
FIG. 3B shows a schematic cross-sectional view of a portion of a substrate processing chamber according to embodiments.
FIG. 3C shows a bottom view of a showerhead according to embodiments.
FIG. 4 shows a top view of an exemplary substrate processing system according to embodiments.



In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.
DETAILED DESCRIPTION
Methods of selectively etching metal-containing materials from the surface of a substrate are described. The etch selectively removes metal-containing materials relative to silicon-containing films such as silicon, polysilicon, silicon oxide, silicon germanium and/or silicon nitride. The methods include exposing metal-containing materials to halogen containing species in a substrate processing region. A remote plasma is used to excite the halogen-containing precursor and a local plasma may be used in embodiments. Metal-containing materials on the substrate may be pretreated using moisture or another OH-containing precursor before exposing the resulting surface to remote plasma excited halogen effluents in embodiments.
In order to better understand and appreciate the invention, reference is now made to FIG. 1 which is a flow chart of an aluminum oxide selective etch process 100 according to embodiments. The aluminum oxide may have a variety of stoichiometries which may be determined by the method of forming the aluminum oxide. Prior to the first etch operation, aluminum oxide is formed on a substrate. The aluminum oxide may be in the form of a blanket layer on the substrate or it may reside in discrete portions of a patterned substrate surface. In either case, the aluminum oxide forms exposed surfaces of the surface of the substrate. The substrate is then delivered into a substrate processing region (operation 110). In another embodiment, the aluminum oxide may be formed after delivering the substrate to the processing region, for example, by treating exposed portions of aluminum to a reactive oxygen source.
A flow of boron trichloride is introduced into a remote plasma region separate from the processing region (operation 120). Other sources of halogen may be used to augment or replace the boron trichloride. In general, a halogen-containing precursor, a bromine-containing precursor or a chlorine-containing precursor may be flowed into the remote plasma region in embodiments. The halogen-containing precursor may include one or more of atomic chlorine, atomic bromine, molecular bromine (Br2), molecular chlorine (Cl2), hydrogen chloride (HCl), hydrogen bromide (HBr), or boron trichloride (BCl3) in embodiments. The halogen-containing precursor may be a boron-and-bromine-containing precursor according to embodiments, such as boron tribromide (BBr3), BBr(CH3)2 or BBr2(CH3). The halogen-containing precursor may be a carbon-and-halogen-containing precursor according to embodiments, such as CBr4 or CCl4. The halogen-containing precursor may comprise boron, in embodiments, to further increase the etch selectivity relative to one or more of silicon, silicon germanium, silicon oxide or silicon nitride.
The separate plasma region may be referred to as a remote plasma region herein and may be within a distinct module from the processing chamber or a compartment within the processing chamber. The separate plasma region may is fluidly coupled to the substrate processing region by through-holes in a showerhead disposed between the two regions. The hardware just described may also be used in all processes discussed herein.
The plasma effluents formed in the remote plasma region are then flowed into the substrate processing region (operation 125) through the through-holes the showerhead separating the remote plasma region and the substrate processing region. Aluminum oxide on the substrate is selectively etched (operation 135) such that aluminum oxide may be removed more rapidly than a variety of other materials. Without binding the claim coverage to the accuracy of hypothetical mechanisms, the selective removal of aluminum oxide (e.g. Al2O3) may proceed by (1) forming BCl2* in the plasma effluents, (2) reacting BCl2* with exposed surfaces of Al2O3 to form AlxOyClz+Al+Cl* and (3) reacting Al and Cl* to form AlCl3. AlxOyClz and AlCl3 desorb from the surface once they are formed and are therefore characterized as volatile. The formation of B2O3 and B—Si complexes may enhance the aluminum oxide etch selectivity to silicon (e.g. poly), silicon nitride and silicon oxide. The reactive chemical species and any process effluents are removed from the substrate processing region and then the substrate is removed from the substrate processing region (operation 145).
All etch processes disclosed herein may be used to remove a broad range of metal-containing materials and aluminum oxide is simply one example. Generally speaking, all disclosed etch processes may be used to selectively remove metal-containing materials such as metal, a metal oxide or a metal nitride according to embodiments. The metal-containing materials may be aluminum oxide, titanium oxide, titanium nitride, tantalum nitride, tungsten, tungsten oxide or cobalt in embodiments. The metal-containing materials may comprise one or more of aluminum, titanium, tantalum, tungsten or cobalt. In these examples, aluminum, titanium, tantalum, tungsten and cobalt are the “metal” in the metal-containing materials because, in relatively pure form, each conducts electricity.
The processes disclosed herein (FIG. 1 as well as FIGS. 2-3 to be discussed shortly) display etch selectivities of metal-containing materials relative to a variety of other materials. The metal-containing material may be selectively etched relative to a silicon-containing film which may also be present as exposed regions on the substrate. The etch selectivity of a metal-containing material relative to silicon (including single crystal, polysilicon or amorphous silicon) may be greater than or about 10:1, greater than or about 15:1, greater than or about 20:1 or greater than or about 25:1 in embodiments. The etch selectivity of a metal-containing material relative to silicon nitride may be greater than or about 15:1, greater than or about 20:1, greater than or about 25:1 or greater than or about 30:1 in embodiments. The etch selectivity of a metal-containing material relative to silicon oxide may be greater than or about 20:1, greater than or about 25:1, greater than or about 30:1 or greater than or about 50:1 in embodiments. The etch selectivity of a metal-containing material relative to silicon germanium may be greater than or about 20:1, greater than or about 25:1, greater than or about 30:1 or greater than or about 50:1 in embodiments. High etch selectivities of metal-containing materials relative to these materials are helpful in creating a variety of devices by, for example, allowing aluminum oxide to be removed more conformally from sidewalls of trench structures.
In embodiments, the halogen-containing precursor (e.g. BCl3) is supplied at a flow rate of between about 5 sccm and about 500 sccm, between about 10 sccm and about 300 sccm, between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm.
The method also includes applying energy to the halogen-containing precursor in the remote plasma region to generate the plasma effluents. The plasma may be generated using known techniques (e.g., radio frequency excitations, capacitively-coupled power, inductively coupled power). In an embodiment, the energy is applied using a capacitively-coupled plasma unit. The remote plasma source power may be between about 100 watts and about 3000 watts, between about 200 watts and about 2000 watts, between about 300 watts and about 1000 watts in embodiments.
A low-intensity plasma may be applied (concurrently with the remote plasma) in the substrate processing region to create a low ion density and direct the low ion-density towards the substrate to accelerate the removal rate of the aluminum oxide. A plasma in the substrate processing region may also be referred to as a local plasma or a direct plasma. The low-intensity plasma in the substrate processing region may be applied capacitively, in embodiments, and will be referred to herein as a bias plasma because ions are being directed towards the substrate. The bias plasma may be applied with a bias power which is less than about 20% of the remote plasma power, less than about 10% of the remote plasma power or less than about 5% of the remote plasma power in embodiments. In embodiments, the bias power may be less than or about 100 watts, less than or about 75 watts, less than or about 50 watts, less than or about 25 watts or essentially no bias power. The term “plasma-free” will be used herein to describe the substrate processing region during application of essentially no bias power. The high neutral radical density enables such a low bias power to be used productively to etch metal-containing materials.
Reference is now made to FIG. 2 which is a flow chart of an aluminum oxide selective etch process 200 according to embodiments. The various traits and process parameters discussed with reference to FIG. 1 may not be repeated here except when they deviate from those traits and process parameters.
A substrate is delivered into a substrate processing region (operation 210) and aluminum oxide is formed on the surface or already present before delivery. Moisture (H2O in the form of water vapor) is introduced into the substrate processing region (operation 220) and reacts with exposed surfaces of aluminum oxide on the surface of the substrate. Exposing aluminum oxide to moisture may result in the formation of Al(OH)3 absorbed on the surface of the substrate. Ammonia (NH3) may be concurrently added to or present in the substrate processing region as well to increase the rate of reaction between the aluminum oxide and the moisture. Maintaining a pressure greater than 0.5 Torr or 1.0 Torr may avoid dehydration of the Al(OH)3 absorbates.
A flow of chlorine (Cl2) is then introduced into a remote plasma region separate from the substrate processing region (operation 225). The chlorine (Cl2) is excited in a remote plasma ignited within the remote plasma region. Other sources of chlorine may be used to augment or replace the molecular chlorine. In general, a chlorine-containing precursor may be flowed into the remote plasma region in embodiments. The chlorine-containing precursor comprises one or more of atomic chlorine, molecular chlorine (Cl2), hydrogen chloride (HCl), or boron trichloride (BCl3) in embodiments.
The plasma effluents formed in the remote plasma region are then flowed into the substrate processing region (operation 230). The plasma effluents may be flowed into the substrate processing region after operation 220 in embodiments. Aluminum oxide on the substrate is selectively etched (operation 235) such that aluminum oxide may be removed more rapidly than a variety of other materials. The plasma effluents may be converting Al(OH)3 to AlCl3, a volatile chemical species that readily desorbs from the surface. Following removal of aluminum oxide, the reactive chemical species and any process effluents are removed from the substrate processing region and then the substrate is removed from the substrate processing region (operation 245).
Generally speaking, a gas-phase oxygen-and-hydrogen-containing precursor may be used in place of the moisture, so long as the gas-phase oxygen-and-hydrogen-containing precursor includes an OH group. The gas-phase oxygen-and-hydrogen-containing precursor may be moisture in the form of water vapor or an alcohol in embodiments. The substrate processing region may be purged of gas-phase oxygen-and-hydrogen-containing precursor between operation 220 and operation 230 in embodiments. In the general case, ammonia (NH3) may also be concurrently added to or present in the substrate processing region as well to increase the rate of reaction between the aluminum oxide and the gas-phase oxygen-and-hydrogen-containing precursor.
A low-intensity plasma may be applied to the oxygen-containing precursor in the substrate processing region to create a low ion density plasma to assist with the reaction which forms adsorbed Al(OH)3 on the surface of the aluminum oxide. The low-intensity plasma in the substrate processing region may be applied capacitively in embodiments. The low-intensity plasma power may be less than or about 100 watts, less than or about 75 watts, less than or about 50 watts, less than or about 25 watts or essentially zero in embodiments. The term “plasma-free” used to describe the substrate processing region herein corresponds to applying no plasma power to the gas-phase oxygen-and-hydrogen-containing precursor. Alternatively or in combination, the gas-phase oxygen-and-hydrogen-containing precursor may be flowed through the remote plasma region and excited with a remote plasma. The remote plasma power used to excite the gas-phase oxygen-and-hydrogen-containing precursor may be less than or about 100 watts, less than or about 75 watts, less than or about 50 watts, less than or about 25 watts or essentially zero in embodiments. In embodiments, the gas-phase oxygen-and-hydrogen-containing precursor is not excited in any plasma before encountering the aluminum oxide of the substrate.
In embodiments, the gas-phase oxygen-and-hydrogen-containing precursor is supplied at a flow rate of between about 100 sccm and about 2 slm (standard liters per minute), between about 200 sccm and about 1 slm, or between 500 sccm and about 1 slm in embodiments. The chlorine-containing precursor (e.g. Cl2) may be supplied at a flow rate of between about 5 sccm and about 500 sccm, between about 10 sccm and about 300 sccm, between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm in embodiments.
The method also includes applying energy to the chlorine-containing precursor in the remote plasma region to generate the plasma effluents. The plasma may be generated using known techniques (e.g., radio frequency excitations, capacitively-coupled power, and inductively coupled power). The remote plasma source power may be between about 100 watts and about 3000 watts, between about 200 watts and about 2000 watts, or between about 300 watts and about 1000 watts in embodiments.
Reference is now made to FIG. 3 which is a flow chart of an aluminum oxide selective etch process 300 according to embodiments. The aluminum oxide may have a variety of stoichiometries which may be determined by the method of forming the aluminum oxide. Prior to the first etch operation, aluminum oxide is formed on a substrate. The aluminum oxide may be in the form of a blanket layer on the substrate or it may reside in discrete portions of a patterned substrate surface. In either case, the aluminum oxide forms exposed surfaces of the surface of the substrate. The substrate is then delivered into a substrate processing region (operation 310). In another embodiment, the aluminum oxide may be formed after delivering the substrate to the processing region, for example, by treating exposed portions of aluminum to a reactive oxygen source.
A flow of boron tribromide (BBr3) is introduced into the substrate processing region (operation 320). Other sources of halogen may be used to augment or replace the boron tribromide. In general, a halogen-containing precursor, a bromine-containing precursor or a chlorine-containing precursor may be flowed into the remote plasma region in embodiments. The halogen-containing precursor may include one or more of atomic chlorine, atomic bromine, molecular bromine (Br2), molecular chlorine (Cl2), hydrogen chloride (HCl), hydrogen bromide (HBr), or boron trichloride (BCl3) in embodiments. The halogen-containing precursor may be a boron-and-bromine-containing precursor according to embodiments, such as boron tribromide (BBr3), BBr(CH3)2 or BBr2(CH3). The halogen-containing precursor may be a carbon-and-halogen-containing precursor according to embodiments, such as CBr4 or CCl4. The halogen-containing precursor may comprise boron, in embodiments, to further increase the etch selectivity relative to one or more of silicon, silicon germanium, silicon oxide or silicon nitride.
Aluminum oxide on the substrate is selectively etched (operation 330) such that aluminum oxide may be removed more rapidly than a variety of other materials. The selective removal of aluminum oxide (e.g. Al2O3) may proceed by thermal means (without the assistance of a local or remote plasma exciting the boron tribromide) in embodiments. The reaction and removal of aluminum oxide with BBr3 is exothermic. In contrast, the reaction of BBr3 with silicon is endothermic which enables a high Al2O3:Si etch selectivity for aluminum oxide selective etch process 300. Unused BBr3 and any process effluents are removed from the substrate processing region and then the substrate is removed from the substrate processing region (operation 340).
Again, all etch processes disclosed herein may be used to remove a broad range of metal-containing materials and aluminum oxide is simply one example. Generally speaking, all disclosed etch processes may be used to selectively remove metal-containing materials such as metal, a metal oxide or a metal nitride according to embodiments. The metal-containing materials may be aluminum oxide, titanium oxide, titanium nitride, tantalum nitride, tungsten, tungsten oxide or cobalt in embodiments. The metal-containing materials may comprise one or more of aluminum, titanium, tantalum, tungsten or cobalt. In these examples, aluminum, titanium, tantalum, tungsten and cobalt are the “metal” in the metal-containing materials because, in relatively pure form, each conducts electricity. Etch selectivites were discussed previously and are not repeated here for the sake of brevity.
In embodiments, the halogen-containing precursor (e.g. BBr3) is supplied at a flow rate of between about 5 sccm and about 500 sccm, between about 10 sccm and about 300 sccm, between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm.
The reactions may proceed thermally, excited only by the temperature of the substrate itself, according to embodiments. Alternatively, the method may include applying energy to the halogen-containing precursor in a remote plasma region to generate plasma effluents, which are then introduced into the substrate processing region in embodiments. FIG. 1 and associated discussion described details of just such an embodiment. Also alternatively, a local plasma may be used to excite the halogen-containing precursor. In the embodiments which include a plasma, the plasma may be generated using known techniques (e.g., radio frequency excitations, capacitively-coupled power, inductively coupled power). In an embodiment, the energy is applied using a capacitively-coupled plasma unit for either the remote plasma or the local plasma. The remote plasma source power or the local plasma source power may be between about 100 watts and about 3000 watts, between about 200 watts and about 2000 watts, between about 300 watts and about 1000 watts in embodiments. In embodiments which rely on the temperature of the substrate to effect the etching reaction, the term “plasma-free” may be used herein to describe the substrate processing region during application using no or essentially no plasma power.
The substrate temperatures described next apply to all the embodiments herein. The substrate temperature may be between about 30° C. and about 400° C. in embodiments. In embodiments, the temperature of the substrate during the etches described herein is greater than or about 30° C., greater than or about 50° C., greater than or about 100° C., greater than or about 150° C. or greater than or about 200° C. The substrate temperatures may be less than or about 400° C., less than or about 350° C., less than or about 325° C., less than or about 300° C., and may be between about 200° C. and about 300° C. in embodiments. These relatively low temperatures may be used, in embodiments, for remote or local plasma processes or etch processes that use carbon-containing precursors (e.g. CBr4, CCl4, BrB(CH3)2 or BrB2(CH3)) as etch precursors. Higher substrate temperatures may be used in embodiments which use select precursors (e.g. BBr3) low-intensity plasma or no plasma to excite the halogen-containing precursor. Therefore, generally speaking, the substrate temperature may be between about 30° C. and about 800° C. in embodiments. In embodiments, the temperature of the substrate during the etches described herein may be between about 30° C. and about 800° C., between about 300° C. and about 800° C., preferably between about 400° C. and about 800° C., more preferably between about 500° C. and about 800° C.
The process pressures described next apply to all the embodiments herein. The pressure within the substrate processing region is below or about 50 Torr, below or about 30 Torr, below or about 20 Torr, below or about 10 Torr or below or about 5 Torr. The pressure may be above or about 0.1 Torr, above or about 0.2 Torr, above or about 0.5 Torr or above or about 1 Torr in embodiments. In a preferred embodiment, the pressure while etching may be between about 0.3 Torr and about 10 Torr. However, any of the upper limits on temperature or pressure may be combined with lower limits to form additional embodiments. Pressures greater than 0.5 Torr or 1.0 Torr may reduce dehydration of the chemical intermediate, Al(OH)3, in the embodiments described in connection with FIG. 2.
For some materials and precursor combinations, the etch rate may drop in time and benefit from etch-purge-etch and etch-purge-etch cycles. This may be the case for boron-containing precursors used to etch at least aluminum oxide, but other materials may also display this effect. Therefore, the etching operations of all processes may have a pause in the flow of precursors to either the remote plasma or into the substrate processing region during the processes disclosed and claimed herein. The remote plasma region and/or the substrate processing region may be actively purged using a gas which displays essentially no chemical reactivity to the exposed materials on the patterned substrate. After purging the flows of precursors may be resumed to restart the removal of metal-containing material from the patterned substrate at a rejuvenated or renewed etch rate (which may be the same or similar to the initial etch rate of the etch process).
Generally speaking, the processes described herein may be used to etch metal-containing materials. In the case of aluminum oxide, the films contain aluminum and oxygen (and not just any specific example of stoichiometric aluminum oxide). The remote plasma etch processes may remove aluminum oxide which includes an atomic concentration of about 20% or more aluminum and about 60% or more oxygen in embodiments. The aluminum oxide may consist essentially of aluminum and oxygen, allowing for small dopant concentrations and other undesirable or desirable minority additives, in embodiments. Aluminum oxide may have roughly an atomic ratio 2:3 (Al:O). The aluminum oxide may contain between 30% and 50% aluminum and may contain between 50% and 70% oxygen in embodiments.
An advantage of the processes described herein lies in the conformal rate of removal of metal-containing material from the substrate. The methods do not rely on a high bias power to accelerate etchants towards the substrate, which reduces the tendency of the etch processes to remove material on the tops and bottom of trenches before material on the sidewalls can be removed. As used herein, a conformal etch process refers to a generally uniform removal rate of material from a patterned surface regardless of the shape of the surface. The surface of the layer before and after the etch process are generally parallel. A person having ordinary skill in the art will recognize that the etch process likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances.
In each remote plasma or local plasma described herein, the flows of the precursors into the remote plasma region may further include one or more relatively inert gases such as He, N2, Ar. The inert gas can be used to improve plasma stability, ease plasma initiation, and improve process uniformity. Argon is helpful, as an additive, to promote the formation of a stable plasma. Process uniformity is generally increased when helium is included. These additives are present in embodiments throughout this specification. Flow rates and ratios of the different gases may be used to control etch rates and etch selectivity.
In embodiments, an ion suppressor as described in the exemplary equipment section may be used to provide radical and/or neutral species for selectively etching substrates. The ion suppressor may also be referred to as an ion suppression element. In embodiments, for example, the ion suppressor is used to filter halogen-containing plasma effluents to selectively etch aluminum oxide. The ion suppressor may be included in each exemplary process described herein. Using the plasma effluents, an etch rate selectivity of metal-containing material to a wide variety of materials may be achieved.
The ion suppressor may be used to provide a reactive gas having a higher concentration of radicals than ions. The ion suppressor functions to dramatically reduce or substantially eliminate ionically charged species traveling from the plasma generation region to the substrate. The electron temperature may be measured using a Langmuir probe in the substrate processing region during excitation of a plasma in the remote plasma region on the other side of the ion suppressor. In embodiments, the electron temperature may be less than 0.5 eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35 eV. These extremely low values for the electron temperature are enabled by the presence of the showerhead and/or the ion suppressor positioned between the substrate processing region and the remote plasma region. Uncharged neutral and radical species may pass through the openings in the ion suppressor to react at the substrate. Because most of the charged particles of a plasma are filtered or removed by the ion suppressor, the substrate is not necessarily biased during the etch process. Such a process using radicals and other neutral species can reduce plasma damage compared to conventional plasma etch processes that include sputtering and bombardment. The ion suppressor helps control the concentration of ionic species in the reaction region at a level that assists the process. Embodiments of the present invention are also advantageous over conventional wet etch processes where surface tension of liquids can cause bending and peeling of small features.
In all the examples described herein, a hydrocarbon may be added to the halogen-containing precursor in the remote plasma region. The hydrocarbon may be an alkane of the form CxHy such as methane, ethane, ethane, propane and propene. Inclusion of a hydrocarbon in the process may make silicon surfaces more inert to the plasma effluents, further increasing the etch selectivity of the aluminum oxide etch processes described herein.
FIG. 3A shows a cross-sectional view of an exemplary substrate processing chamber 1001 with a partitioned plasma generation region within the processing chamber. During film etching, a process gas may be flowed into chamber plasma region 1015 through a gas inlet assembly 1005. A remote plasma system (RPS) 1002 may optionally be included in the system, and may process a first gas which then travels through gas inlet assembly 1005. The process gas may be excited within RPS 1002 prior to entering chamber plasma region 1015. Accordingly, the chlorine-containing precursor as discussed above, for example, may pass through RPS 1002 or bypass the RPS unit in embodiments.
A cooling plate 1003, faceplate 1017, ion suppressor 1023, showerhead 1025, and a substrate support 1065 (also known as a pedestal), having a substrate 1055 disposed thereon, are shown and may each be included according to embodiments. Pedestal 1065 may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate. This configuration may allow the substrate 1055 temperature to be cooled or heated to maintain relatively low temperatures, such as between −20° C. to 200° C. Pedestal 1065 may also be resistively heated to relatively high temperatures, such as between 100° C. and 1100° C., using an embedded heater element.
Exemplary configurations may include having the gas inlet assembly 1005 open into a gas supply region 1058 partitioned from the chamber plasma region 1015 by faceplate 1017 so that the gases/species flow through the holes in the faceplate 1017 into the chamber plasma region 1015. Structural and operational features may be selected to prevent significant backflow of plasma from the chamber plasma region 1015 back into the supply region 1058, gas inlet assembly 1005, and fluid supply system 1010. The structural features may include the selection of dimensions and cross-sectional geometries of the apertures in faceplate 1017 to deactivate back-streaming plasma. The operational features may include maintaining a pressure difference between the gas supply region 1058 and chamber plasma region 1015 that maintains a unidirectional flow of plasma through the showerhead 1025. The faceplate 1017, or a conductive top portion of the chamber, and showerhead 1025 are shown with an insulating ring 1020 located between the features, which allows an AC potential to be applied to the faceplate 1017 relative to showerhead 1025 and/or ion suppressor 1023. The insulating ring 1020 may be positioned between the faceplate 1017 and the showerhead 1025 and/or ion suppressor 1023 enabling a capacitively coupled plasma (CCP) to be formed in the first plasma region.
The plurality of holes in the ion suppressor 1023 may be configured to control the passage of the activated gas, i.e., the ionic, radical, and/or neutral species, through the ion suppressor 1023. For example, the aspect ratio of the holes, or the hole diameter to length, and/or the geometry of the holes may be controlled so that the flow of ionically-charged species in the activated gas passing through the ion suppressor 1023 is reduced. The holes in the ion suppressor 1023 may include a tapered portion that faces chamber plasma region 1015, and a cylindrical portion that faces the showerhead 1025. The cylindrical portion may be shaped and dimensioned to control the flow of ionic species passing to the showerhead 1025. An adjustable electrical bias may also be applied to the ion suppressor 1023 as an additional means to control the flow of ionic species through the suppressor. The ion suppression element 1023 may function to reduce or eliminate the amount of ionically charged species traveling from the plasma generation region to the substrate. Uncharged neutral and radical species may still pass through the openings in the ion suppressor to react with the substrate.
Plasma power can be of a variety of frequencies or a combination of multiple frequencies. In the exemplary processing system the plasma may be provided by RF power delivered to faceplate 1017 relative to ion suppressor 1023 and/or showerhead 1025. The RF power may be between about 10 watts and about 5000 watts, between about 100 watts and about 2000 watts, between about 200 watts and about 1500 watts, or between about 200 watts and about 1000 watts in embodiments. The RF frequency applied in the exemplary processing system may be low RF frequencies less than about 200 kHz, high RF frequencies between about 10 MHz and about 15 MHz, or microwave frequencies greater than or about 1 GHz in embodiments. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the remote plasma region.
A precursor, for example a chlorine-containing precursor, may be flowed into substrate processing region 1033 by embodiments of the showerhead described herein. Excited species derived from the process gas in chamber plasma region 1015 may travel through apertures in the ion suppressor 1023, and/or showerhead 1025 and react with an additional precursor flowing into substrate processing region 1033 from a separate portion of the showerhead. Alternatively, if all precursor species are being excited in chamber plasma region 1015, no additional precursors may be flowed through the separate portion of the showerhead. Little or no plasma may be present in substrate processing region 1033 during the remote plasma etch process. Excited derivatives of the precursors may combine in the region above the substrate and/or on the substrate to etch structures or remove species from the substrate.
The processing gases may be excited in chamber plasma region 1015 and may be passed through the showerhead 1025 to substrate processing region 1033 in the excited state. While a plasma may be generated in substrate processing region 1033, a plasma may alternatively not be generated in the processing region. In one example, the only excitation of the processing gas or precursors may be from exciting the processing gases in chamber plasma region 1015 to react with one another in substrate processing region 1033. As previously discussed, this may be to protect the structures patterned on substrate 1055.
FIG. 3B shows a detailed view of the features affecting the processing gas distribution through faceplate 1017. The gas distribution assemblies such as showerhead 1025 for use in the processing chamber section 1001 may be referred to as dual channel showerheads (DCSH) and are additionally detailed in the embodiments described in FIG. 3A as well as FIG. 3C herein. The dual channel showerhead may provide for etching processes that allow for separation of etchants outside of the processing region 1033 to provide limited interaction with chamber components and each other prior to being delivered into the processing region.
The showerhead 1025 may comprise an upper plate 1014 and a lower plate 1016. The plates may be coupled with one another to define a volume 1018 between the plates. The coupling of the plates may be so as to provide first fluid channels 1019 through the upper and lower plates, and second fluid channels 1021 through the lower plate 1016. The formed channels may be configured to provide fluid access from the volume 1018 through the lower plate 1016 via second fluid channels 1021 alone, and the first fluid channels 1019 may be fluidly isolated from the volume 1018 between the plates and the second fluid channels 1021. The volume 1018 may be fluidly accessible through a side of the gas distribution assembly 1025. Although the exemplary system of FIGS. 3A-3C includes a dual-channel showerhead, it is understood that alternative distribution assemblies may be utilized that maintain first and second precursors fluidly isolated prior to substrate processing region 1033. For example, a perforated plate and tubes underneath the plate may be utilized, although other configurations may operate with reduced efficiency or not provide as uniform processing as the dual-channel showerhead as described.
In the embodiment shown, showerhead 1025 may distribute via first fluid channels 1019 process gases which contain plasma effluents upon excitation by a plasma in chamber plasma region 1015. In embodiments, the process gas introduced into RPS 1002 and/or chamber plasma region 1015 may contain chlorine, e.g., Cl2 or BCl3. The process gas may also include a carrier gas such as helium, argon, nitrogen (N2), etc. Plasma effluents may include ionized or neutral derivatives of the process gas and may also be referred to herein as a radical-chlorine precursor referring to the atomic constituent of the process gas introduced.
FIG. 3C is a bottom view of a showerhead 1025 for use with a processing chamber in embodiments. Showerhead 1025 corresponds with the showerhead shown in FIG. 3A. Through-holes 1031, which show a view of first fluid channels 1019, may have a plurality of shapes and configurations to control and affect the flow of precursors through the showerhead 1025. Small holes 1027, which show a view of second fluid channels 1021, may be distributed substantially evenly over the surface of the showerhead, even amongst the through-holes 1031, which may help to provide more even mixing of the precursors as they exit the showerhead than other configurations.
The chamber plasma region 1015 or a region in an RPS may be referred to as a remote plasma region. In embodiments, the radical precursor, e.g., a radical-chlorine precursor, is created in the remote plasma region and travels into the substrate processing region where it may or may not combine with additional precursors. In embodiments, the additional precursors are excited only by the radical-chlorine precursor. Plasma power may essentially be applied only to the remote plasma region in embodiments to ensure that the radical-chlorine precursor provides the dominant excitation. Chlorine or another chlorine-containing precursor may be flowed into chamber plasma region 1015 at rates between about 5 sccm and about 500 sccm, between about 10 sccm and about 150 sccm, or between about 25 sccm and about 125 sccm in embodiments.
Combined flow rates of precursors into the chamber may account for 0.05% to about 20% by volume of the overall gas mixture; the remainder being carrier gases. The chlorine-containing precursor may be flowed into the remote plasma region, but the plasma effluents may have the same volumetric flow ratio in embodiments. In the case of the chlorine-containing precursor, a purge or carrier gas may be first initiated into the remote plasma region before the chlorine-containing gas to stabilize the pressure within the remote plasma region. Substrate processing region 1033 can be maintained at a variety of pressures during the flow of precursors, any carrier gases, and plasma effluents into substrate processing region 1033. The pressure may be maintained between 0.1 mTorr and 100 Torr, between 1 Torr and 20 Torr or between 1 Torr and 5 Torr in embodiments.
Embodiments of the dry etch systems may be incorporated into larger fabrication systems for producing integrated circuit chips. FIG. 4 shows one such processing system (mainframe) 1101 of deposition, etching, baking, and curing chambers in embodiments. In the figure, a pair of front opening unified pods (load lock chambers 1102) supply substrates of a variety of sizes that are received by robotic arms 1104 and placed into a low pressure holding area 1106 before being placed into one of the substrate processing chambers 1108a-f. A second robotic arm 1110 may be used to transport the substrate wafers from the holding area 1106 to the substrate processing chambers 1108a-f and back. Each substrate processing chamber 1108a-f, can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation, and other substrate processes.
The substrate processing chambers 1108a-f may be configured for depositing, annealing, curing and/or etching a film on the substrate wafer. In one configuration, all three pairs of chambers, e.g., 1108a-f, may be configured to etch a film on the substrate, for example, chambers 1108a-d may be used to etch the gapfill silicon oxide to create space for the airgap while chambers 1108e-f may be used to etch the polysilicon.
As used herein “substrate” may be a support substrate with or without layers formed thereon. The patterned substrate may be an insulator or a semiconductor of a variety of doping concentrations and profiles and may, for example, be a semiconductor substrate of the type used in the manufacture of integrated circuits. Exposed “silicon” or “polysilicon” of the patterned substrate is predominantly Si but may include minority concentrations of other elemental constituents such as nitrogen, oxygen, hydrogen and carbon. Exposed “silicon” or “polysilicon” may consist of or consist essentially of silicon. Exposed “silicon nitride” of the patterned substrate is predominantly silicon and nitrogen but may include minority concentrations of other elemental constituents such as oxygen, hydrogen and carbon. “Exposed silicon nitride” may consist essentially of or consist of silicon and nitrogen. Exposed “silicon oxide” of the patterned substrate is predominantly SiO2 but may include minority concentrations of other elemental constituents (e.g. nitrogen, hydrogen, carbon). In some embodiments, silicon oxide films etched using the methods disclosed herein consist essentially of silicon and oxygen. “Aluminum oxide” is predominantly aluminum and oxygen but may include minority concentrations of other elemental constituents (e.g. nitrogen, hydrogen, carbon). Aluminum oxide may consist essentially of aluminum and oxygen. “Aluminum” is predominantly aluminum but may include minority concentrations of other elemental constituents (e.g. nitrogen, hydrogen, oxygen, carbon). Aluminum oxide may consist essentially of aluminum. Analogous definitions will be understood for other metal-containing materials.
The term “precursor” is used to refer to any process gas which takes part in a reaction to either remove material from or deposit material onto a surface. “Plasma effluents” describe gas exiting from the chamber plasma region and entering the substrate processing region. Plasma effluents are in an “excited state” wherein at least some of the gas molecules are in vibrationally-excited, dissociated and/or ionized states. A “radical precursor” is used to describe plasma effluents (a gas in an excited state which is exiting a plasma) which participate in a reaction to either remove material from or deposit material on a surface. “Radical-halogen” (or “radical-hydrogen”) are radical precursors which contain halogen (or hydrogen) but may contain other elemental constituents. The phrase “inert gas” refers to any gas which does not form chemical bonds when etching or being incorporated into a film. Exemplary inert gases include noble gases but may include other gases so long as no chemical bonds are formed when (typically) trace amounts are trapped in a film.
The terms “gap” and “trench” are used throughout with no implication that the etched geometry has a large horizontal aspect ratio. Viewed from above the surface, trenches may appear circular, oval, polygonal, rectangular, or a variety of other shapes. A trench may be in the shape of a moat around an island of material. The term “via” is used to refer to a low aspect ratio trench (as viewed from above) which may or may not be filled with metal to form a vertical electrical connection. As used herein, a conformal etch process refers to a generally uniform removal of material on a surface in the same shape as the surface, i.e., the surface of the etched layer and the pre-etch surface are generally parallel. A person having ordinary skill in the art will recognize that the etched interface likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances.
Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosed embodiments. Additionally, a number of well-known processes and elements have not been described to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the dielectric material” includes reference to one or more dielectric materials and equivalents thereof known to those skilled in the art, and so forth.
Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.

## Claims

1. A method of etching aluminum oxide, the method comprising:
flowing a gas-phase oxygen-hydrogen-containing precursor into the substrate processing region, wherein the gas-phase oxygen-and-hydrogen-containing precursor comprises an OH group;
flowing a halogen-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents, wherein the halogen-containing precursor comprises one or more precursors selected from the group consisting of atomic chlorine, atomic bromine, molecular bromine (Br2), molecular chlorine (Cl2), hydrogen chloride (HCl), hydrogen bromide (HBr), boron tribromide (BBr3), and boron trichloride (BCl3); and
etching the aluminum oxide from a substrate by flowing the plasma effluents into the substrate processing region through through-holes in a showerhead, wherein the showerhead is disposed between the remote plasma region and the substrate processing chamber.

2. The method of claim 1 wherein the halogen-containing precursor contains one of boron or carbon.

3. The method of claim 1 further comprising forming a local plasma in the substrate processing region.

4. A method of etching aluminum oxide, the method comprising:
transferring a substrate into a substrate processing region of a substrate processing chamber, wherein the substrate comprises the aluminum oxide;
flowing a gas-phase oxygen-and-hydrogen-containing precursor into the substrate processing region, wherein the gas-phase oxygen-and-hydrogen-containing precursor comprises an OH group;
flowing a chlorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents; and
etching the aluminum oxide from the substrate by flowing the plasma effluents into the substrate processing region through through-holes in a showerhead.

5. The method of claim 4 wherein the gas-phase oxygen-and-hydrogen-containing precursor reacts with the aluminum oxide to form Al(OH)3 on the surface of the substrate.

6. The method of claim 4 wherein the gas-phase oxygen-and-hydrogen-containing precursor is purged from the substrate processing region before the operation of flowing the plasma effluents into the substrate processing region.

7. The method of claim 4 wherein the chlorine-containing precursor comprises one or more of atomic chlorine, molecular chlorine (Cl2), hydrogen chloride (HCl), or boron trichloride (BCl3).

8. The method of claim 4 wherein a pressure in the substrate processing region is greater than 0.3 Torr during the operation of flowing the gas-phase oxygen-and-hydrogen-containing precursor into the substrate processing region.