# Patent

## Title
Gas-phase tungsten etch

## Abstract

Methods of evenly etching tungsten liners from high aspect ratio trenches are described. The methods include a remote plasma etch using plasma effluents formed from a fluorine-containing precursor and a high flow of helium. Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents react with tungsten coating a patterned substrate having high aspect ratio trenches. The plasmas effluents react with exposed surfaces and evenly remove tungsten from outside the trenches and on the sidewalls of the trenches. The plasma effluents pass through an ion suppression element positioned between the remote plasma and the substrate processing region. Optionally, the methods may include concurrent ion bombardment of the patterned substrate to help remove potentially thicker horizontal tungsten regions, e.g., at the bottom of the trenches or between trenches.

## Background
FIELD
Embodiments of the invention relate to evenly etching tungsten from trench sidewalls.
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, fewer dry-etch processes have been developed to remove refractory metals like tungsten.
Methods are needed to etch tungsten selectively and evenly from patterned substrates using dry etch processes.
SUMMARY
Methods of evenly etching tungsten liners from high aspect ratio trenches are described. The methods include a remote plasma etch using plasma effluents formed from a fluorine-containing precursor and a high flow of helium. Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents react with tungsten coating a patterned substrate having high aspect ratio trenches. The plasmas effluents react with exposed surfaces and evenly remove tungsten from outside the trenches and on the sidewalls of the trenches. The plasma effluents pass through an ion suppression element positioned between the remote plasma and the substrate processing region. Optionally, the methods may include concurrent ion bombardment of the patterned substrate to help remove potentially thicker horizontal tungsten regions, e.g., at the bottom of the trenches or between trenches.
Embodiments include methods of etching tungsten. The methods include transferring a patterned substrate into a substrate processing region. The patterned substrate has a tungsten lining layer coating a high aspect ratio trench having a depth more than twenty times a width of the high aspect ratio trench. The methods further include flowing a fluorine-containing precursor with a fluorine flow rate into a remote plasma region fluidly coupled to a substrate processing region via perforations in a perforated plate. The methods further include flowing helium with a helium flow rate into the remote plasma region. The methods further include forming a remote plasma in the remote plasma region to produce plasma effluents from the fluorine-containing precursor and the helium, and flowing the plasma effluents into the substrate processing region through the perforations. The methods further include etching the tungsten lining layer. After etching the tungsten lining layer, a top sidewall thickness of the tungsten lining layer measured on a sidewall of the high aspect ratio trench near the opening of the high aspect ratio trench is within 20% of a bottom sidewall thickness of the tungsten lining layer measured on the sidewall of the high aspect ratio trench near the bottom of the high aspect ratio trench.
Embodiments include methods of etching tungsten. The methods include transferring a patterned substrate into a substrate processing region. The patterned substrate has a tungsten lining layer coating a high aspect ratio trench having a depth more than twenty times a width of the high aspect ratio trench. The methods further include flowing a fluorine-containing precursor into the substrate processing region. The methods further include flowing nitrogen trifluoride into a remote plasma region fluidly coupled to a substrate processing region via perforations in the perforated plate. The methods further include forming a remote plasma in the remote plasma region to produce plasma effluents from the nitrogen trifluoride and flowing the plasma effluents into the substrate processing region through the perforations. The methods further include applying local plasma power capacitively between the perforated plate and a substrate susceptor supporting the patterned substrate to create and accelerate re-ionized plasma effluents toward the patterned substrate. The methods further include etching the tungsten lining layer. Etching the tungsten lining layer reduces a thickness of the tungsten lining layer on a sidewall of the high aspect ratio trench at a top rate near the outermost portion of the sidewall of the high aspect ratio trench which is within 20% of a bottom rate near the innermost portion the sidewall of the high aspect ratio trench.
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 a tungsten liner etch process according to embodiments.
FIGS. 2A-2B are cross-sectional schematics of tungsten on high aspect ratio trenches before and after tungsten etch processes according to embodiments.
FIG. 3A shows a substrate processing chamber according to embodiments.
FIG. 3B shows a showerhead of a substrate processing chamber according to embodiments.
FIG. 4 shows a 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 evenly etching tungsten liners from high aspect ratio trenches are described. The methods include a remote plasma etch using plasma effluents formed from a fluorine-containing precursor and a high flow of helium. Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents react with tungsten coating a patterned substrate having high aspect ratio trenches. The plasmas effluents react with exposed surfaces and evenly remove tungsten from outside the trenches and on the sidewalls of the trenches. The plasma effluents pass through an ion suppression element positioned between the remote plasma and the substrate processing region. Optionally, the methods may include concurrent ion bombardment of the patterned substrate to help remove potentially thicker horizontal tungsten regions, e.g., at the bottom of the trenches or between trenches.
In order to better understand and appreciate the invention, reference is now made to FIG. 1 which is a flow chart of a tungsten liner (a.k.a. tungsten lining layer) etch process 100 according to embodiments. Prior to the first operation, the tungsten liner is formed on a substrate. A titanium nitride nucleation layer may be deposited before the tungsten liner in order to improve the tungsten growth process. The tungsten liner (and the titanium nitride nucleation layer) may be conformal over features present on a patterned substrate surface. The features include a high aspect ratio trench whose depth exceeds its width by a multiplicative factor of twenty, twenty five or thirty according to embodiments. The patterned substrate is then delivered into a substrate processing region (operation 110). In another embodiment, the tungsten liner may be formed after delivering the substrate to the substrate processing region.
Flows of helium and nitrogen trifluoride are introduced into a plasma region separate from the substrate processing region (operation 120). Other sources of fluorine may be used to augment or replace the nitrogen trifluoride. In general, a fluorine-containing precursor may be flowed into the plasma region and the fluorine-containing precursor comprises at least one precursor selected from the group consisting of atomic fluorine, diatomic fluorine, bromine trifluoride, chlorine trifluoride, nitrogen trifluoride, hydrogen fluoride, sulfur hexafluoride and xenon difluoride. Remote plasma power is applied to the remote plasma region to excite the fluorine-containing precursor (e.g. the nitrogen trifluoride) and form plasma effluents in operation 120 as well.
The separate plasma region may be referred to as a remote plasma region for all etch processes described herein and may be within a distinct module from the processing chamber or a compartment within the processing chamber. The separate plasma region is fluidly coupled to the substrate processing region by through-holes in a showerhead disposed between the remote plasma region and the substrate processing region. The hardware just described may also be used in all processes discussed herein. The remote plasma region may be a capacitively-coupled plasma region, in embodiments, and may be disposed remote from the substrate processing region of the processing chamber. For example, the capacitively-coupled plasma region (and the remote plasma region in general) may be separated from the substrate processing region by the showerhead.
The plasma effluents formed in the remote plasma region are then flowed into the substrate processing region. In embodiments, no local plasma power is applied to excite the plasma effluents in the substrate processing region (not shown). During such a process, the substrate processing region may be referred to as a “plasma-free” substrate processing region to indicate an exceedingly small concentration of ions or, equivalently, a very low electron temperature as described herein.
Alternatively, a local plasma power may also be applied (directly to the substrate processing region) to bombard the patterned substrate directionally with re-ionized plasma effluents (operation 130). The local plasma is optional and may be helpful to remove thicker portions of tungsten, if present, on horizontal surfaces of the patterned substrate. The tungsten may be slicker despite referring to the tungsten layer as a conformal tungsten layer herein. The optional directional bombardment may, for example, help to remove tungsten at the bottom of trenches faster than tungsten on sidewalls of a trench so tungsten on sidewalls and bottom are removed at roughly the same time. The tungsten is evenly removed from high aspect ratio trenches in operation 140. The tungsten liner on the substrate is etched such that tungsten liner on the sidewalls of the high aspect ratio trench is substantially uniformly removed or that a relatively uniform amount of tungsten remains near the conclusion of operation 140. 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 150).
The following flow rates apply to operation 120. The fluorine-containing precursor (e.g. NF3) may be flowed into the remote plasma region at a flow rate between about 5 sccm (standard cubic centimeters per minute) 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. Helium may be flowed into the remote plasma region at flow rates above about 125 sccm, above about 250 sccm, above about 1000 sccm, above about 1500 sccm or above about 2500 sccm in embodiments. The flow rate ratio of helium to fluorine-containing precursor into the remote plasma region may be greater than 15:1, greater than 20:1, greater than 25:1, greater than 40:1 or greater than 60:1 according to embodiments. The net atomic flow rate ratio of helium to fluorine into (or out of) the remote plasma region may be greater than 5:1, greater than 7:1, greater than 10:1 or greater than 20:1 in embodiments. A flow rate out of the remote plasma region is equivalent to a flow rate into the substrate processing region in embodiments. These high helium flow rate ratios have been found to result in high diffusivity and an even tungsten etch rate within high aspect ratio trenches.
The operation of forming the remote plasma involves applying a remote plasma power to the remote plasma region. The remote plasma power may be applied capacitively or inductively, in embodiments, and may be between about 10 watts and about 2500 watts, between about 30 watts and about 2000 watts, between about 70 watts and about 1500 watts, between about 100 watts and about 1000 watts or between about 200 watts and 600 watts. The remote plasma power may be greater than 50 watts in embodiments. The remote plasma power may be applied using radio frequencies (e.g. 13.56 MHz) or lower frequencies such as 350 kHz or 70 kHz, for example. The relatively low remote plasma powers correlate with greater uniformity of tungsten etch rate along the sides of high aspect ratio trenches. Higher powers sacrifice some of this uniformity in exchange for a higher etch rate.
The pressure in the substrate processing region is about the same as the pressure in the substrate processing region, according to embodiments, in all tungsten liner etch processes described herein. The pressure in the substrate processing region during application of the local plasma power (i.e. the bias plasma power) may be between about 0.01 Torr and about 2 Torr, between about 0.05 Torr and about 1 Torr or preferably between about 0.4 Torr and about 0.6 Torr in embodiments. Lower pressures improve uniformity between the tungsten etch rates near the top and bottom of the trenches. However, maintaining a process pressure about or above 0.4 Torr has been found to provide sufficient uniformity and allows for the use of less expensive pumping solutions. The temperature of the substrate may be between about −30° C. and about 300° C., between about −20° C. and about 200° C., between about −10° C. and about 100° C., between about 0° C. and about 50° C. or preferably between about 10° C. and about 30° C. in embodiments, during application of local and optional bias plasma power. Lower substrate temperatures have been found to improve uniformity of etch rate at the top and bottom of the high aspect ratio trenches. Lower substrate temperatures have also been found to increase the etch rate of titanium nitride relative to tungsten which may be desirable to remove a thin layer of titanium nitride underlying the tungsten layer. Titanium nitride may be used as a nucleation layer to grow the tungsten layer in the first place. No local plasma power (or no bias plasma power) is applied during the operation of forming the remote plasma according to embodiments. In other embodiments, a bias power is applied as outlined below.
The optional local plasma power (also referred to as the bias plasma power) may be concurrently applied with the remote plasma power in embodiments. The optional local plasma power may be applied capacitively and may be between about 10 watts and about 900 watts, between about 10 watts and about 700 watts, between about 20 watts and about 500 watts or preferably between about 20 watts and 300 watts according to embodiments. The local plasma power may be applied using radio frequencies (e.g. 13.56 MHz) or lower frequencies such as 350 kHz or 70 kHz, for example. The optional bias power may be applied to accelerate fluorine-containing ions formed from the nitrogen trifluoride toward the patterned substrate. A separate power source may be used to bias the inductively coupled plasma relative to the patterned substrate. In the case of a capacitively coupled plasma, the preferred embodiment, the capacitive plasma power already biases the fluorine-containing ions relative to the substrate.
In embodiments and operations employing a remote plasma, 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 fluorine plasma effluents to selectively etch tungsten. The ion suppressor may be included in each exemplary process described herein. Using the plasma effluents, an etch rate selectivity of tungsten 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 preferably 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 nearly all 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 order to further appreciate the invention, reference is now made to FIGS. 2A-2B, which are cross-sectional schematics of tungsten on high aspect ratio trenches before and after tungsten etch processes according to embodiments. A patterned substrate 200-1 begins with high aspect ratio structures as shown in FIG. 2A. A conformal tungsten liner 210-1 is present on the high aspect ratio structures prior to the etch processes described herein. FIG. 2D shows the tungsten liner 210-1 profile after tungsten liner etch process 100. The effect of the bombardment (operation 130) is to increase the removal rate of operation 140, for example, on the tops of the pylons so the amount of tungsten which remains is roughly the same on the top and sides. The bombardment also ensures that, if desired, the tungsten on the top and sides are removed at nearly the same time in the process. Over-etching the sides to fully remove tungsten on the top becomes unnecessary when tungsten from each region is “broken through” at the same time. Despite removing tungsten more rapidly on top with bombardment, the overall process may be referred to as a uniform tungsten etch due to the uniformity of the remaining tungsten near the conclusion of tungsten liner etch process 100.
FIGS. 2A-2B show patterned substrate 200 as one homogeneous material. Generally speaking, the high aspect ratio trench may be formed between pylons of a material which differs from the rest of the substrate. The pylons themselves may actually be stacks of multiple materials arranged in layers according to embodiments. Even more generally, the high aspect ratio trench may be formed into a substrate so the sidewalls are not formed on pylons at all, but on walls of a trench burrowed into the bulk substrate itself. “Substrate” will be used to refer to anything below the tungsten liner and so will include deposited and patterned layers, when present, on the surface of the bulk substrate (e.g. a silicon wafer). The high aspect ratio trench is formed between two pylons according to embodiments. One or both of the two adjacent stacks may include at least ten alternating layers of dielectric (e.g. silicon oxide) and tungsten in embodiments.
The high aspect ratio trench may have a variety of dimensions. The high aspect ratio trench may have a depth which exceeds its width by a multiplicative factor of twenty, twenty five or thirty according to embodiments. The depth of the high aspect ratio trench may be greater than one micron, greater than one and a half microns, or greater than two microns according to embodiments. The width of the high aspect ratio trench may be less than one hundred nanometers, less than seventy five nanometers, less than fifty nanometers or less than thirty nanometers in embodiments. Including a preponderance of helium, as described herein, assists the process by increasing the diffusivity of the other plasma effluents. The helium serves to deliver reactive plasma effluents deep within high aspect ratio trenches prior to chemical reaction. The helium helps make the etch rate near the top more similar to the etch rate near the bottom. Helium was selected due to a relatively high availability and a low atomic weight. Hydrogen reacts with the exposed tungsten making it a poor choice for this application. Neon would show some improvement in diffusivity, but would be less desirable than helium and is not nearly as plentiful.
The effect of etch during or after tungsten liner etch process 100 will now be described. Following the etch, a top sidewall thickness of the tungsten lining layer measured on a sidewall of the high aspect ratio trench near the opening of the trench may be within 20% of a bottom sidewall thickness of the tungsten lining layer measured on the sidewall of the high aspect ratio trench near the bottom of the trench. Once again, bottom and top are defined as deeper within the trench and closer to the opening of the trench respectively. The bottom sidewall thickness may be measured within the bottom 10% of the depth of the trench measured linearly and not by volume. Similarly, the top sidewall thickness may be measured within the top 10% of the depth of the trench. Etching the tungsten lining layer may reduce a thickness of the tungsten lining layer at a top rate near the outermost portion of the sidewall of the high aspect ratio trench which is within 20% of a bottom rate near the innermost portion of the sidewall of the high aspect ratio trench. Outermost portion and innermost portion are again defined as the top 10% and bottom 10% of the depth of the trench, respectively.
Additional process parameters are disclosed in the course of describing an exemplary processing chamber and system.
Exemplary Processing System
Processing chambers that may implement embodiments of the present invention may be included within processing platforms such as the CENTURA® and PRODUCER® systems, available from Applied Materials, Inc. of Santa Clara, Calif.
FIG. 3A is a substrate processing chamber 1001 according to embodiments. A remote plasma system 1010 may process a fluorine-containing precursor which then travels through a gas inlet assembly 1011. Two distinct gas supply channels are visible within the gas inlet assembly 1011. A first channel 1012 carries a gas that passes through the remote plasma system 1010 (RPS), while a second channel 1013 bypasses the remote plasma system 1010. Either channel may be used for the fluorine-containing precursor, in embodiments. On the other hand, the first channel 1012 may be used for the process gas and the second channel 1013 may be used for a treatment gas. The lid (or conductive top portion) 1021 and a perforated partition 1053 are shown with an insulating ring 1024 in between, which allows an AC potential to be applied to the lid 1021 relative to perforated partition 1053. The AC potential strikes a plasma in chamber plasma region 1020. The process gas may travel through first channel 1012 into chamber plasma region 1020 and may be excited by a plasma in chamber plasma region 1020 alone or in combination with remote plasma system 1010. If the process gas (the fluorine-containing precursor) flows through second channel 1013, then only the chamber plasma region 1020 is used for excitation. The combination of chamber plasma region 1020 and/or remote plasma system 1010 may be referred to as a remote plasma system herein. The perforated partition (also referred to as a showerhead) 1053 separates chamber plasma region 1020 from a substrate processing region 1070 beneath showerhead 1053. Showerhead 1053 allows a plasma present in chamber plasma region 1020 to avoid directly exciting gases in substrate processing region 1070, while still allowing excited species to travel from chamber plasma region 1020 into substrate processing region 1070.
Showerhead 1053 is positioned between chamber plasma region 1020 and substrate processing region 1070 and allows plasma effluents (excited derivatives of precursors or other gases) created within remote plasma system 1010 and/or chamber plasma region 1020 to pass through a plurality of through-holes 1056 that traverse the thickness of the plate. The showerhead 1053 also has one or more hollow volumes 1051 which can be filled with a precursor in the form of a vapor or gas (such as a fluorine-containing precursor) and pass through small holes 1055 into substrate processing region 1070 but not directly into chamber plasma region 1020. Showerhead 1053 is thicker than the length of the smallest diameter 1050 of the through-holes 1056 in this embodiment. The length 1026 of the smallest diameter 1050 of the through-holes may be restricted by forming larger diameter portions of through-holes 1056 part way through the showerhead 1053 to maintain a significant concentration of excited species penetrating from chamber plasma region 1020 to substrate processing region 1070. The length of the smallest diameter 1050 of the through-holes 1056 may be the same order of magnitude as the smallest diameter of the through-holes 1056 or less in embodiments.
Showerhead 1053 may be configured to serve the purpose of an ion suppressor as shown in FIG. 3A. Alternatively, a separate processing chamber element may be included (not shown) which suppresses the ion concentration traveling into substrate processing region 1070. Whether a showerhead or an ion suppressor is being described, the item may be referred to as a perforated plate having perforations which pass and neutralize some or substantially all of the plasma effluents. Lid 1021 and showerhead 1053 may function as a first electrode and second electrode, respectively, so that lid 1021 and showerhead 1053 may receive different electric voltages. In these configurations, electrical power (e.g., RF power) may be applied to lid 1021, showerhead 1053, or both. For example, electrical power may be applied to lid 1021 while showerhead 1053 (serving as ion suppressor) is grounded. The substrate processing system may include a RF generator that provides electrical power to the lid and/or showerhead 1053. The voltage applied to lid 1021 may facilitate a uniform distribution of plasma (i.e., reduce localized plasma) within chamber plasma region 1020. To enable the formation of a plasma in chamber plasma region 1020, insulating ring 1024 may electrically insulate lid 1021 from showerhead 1053. Insulating ring 1024 may be made from a ceramic and may have a high breakdown voltage to avoid sparking. Portions of substrate processing chamber 1001 near the capacitively-coupled plasma components just described may further include a cooling unit (not shown) that includes one or more cooling fluid channels to cool surfaces exposed to the plasma with a circulating coolant (e.g., water).
In the embodiment shown, showerhead 1053 may distribute (via through-holes 1056) process gases which contain fluorine, helium and/or plasma effluents of such process gases upon excitation by a plasma in chamber plasma region 1020. In embodiments, the process gas introduced into the remote plasma system 1010 and/or chamber plasma region 1020 may contain fluorine (e.g. F2, NF3 or XeF2). The process gas may also include a carrier gas such as argon, nitrogen (N2), etc. Plasma effluents may include ionized or neutral derivatives of the process gas and may also be referred to herein as radical-fluorine referring to the atomic constituent of the process gas introduced.
Through-holes 1056 are configured to suppress the migration of ionically-charged species out of the chamber plasma region 1020 while allowing uncharged neutral or radical species to pass through showerhead 1053 into substrate processing region 1070. These uncharged species may include highly reactive species that are transported with less-reactive carrier gas by through-holes 1056. As noted above, the migration of ionic species by through-holes 1056 may be reduced, and in some instances completely suppressed. Controlling the amount of ionic species passing through showerhead 1053 provides increased control over the gas mixture brought into contact with the underlying wafer substrate, which in turn increases control of the deposition and/or etch characteristics of the gas mixture. For example, adjustments in the ion concentration of the gas mixture can alter the etch selectivity.
In embodiments, the number of through-holes 1056 may be between about 60 and about 2000. Through-holes 1056 may have a variety of shapes but are most easily made round. The smallest diameter 1050 of through-holes 1056 may be between about 0.5 mm and about 20 mm or between about 1 mm and about 6 mm in embodiments. There is also latitude in choosing the cross-sectional shape of through-holes, which may be made conical, cylindrical or combinations of the two shapes. The number of small holes 1055 used to introduce unexcited precursors into substrate processing region 1070 may be between about 100 and about 5000 or between about 500 and about 2000 in different embodiments. The diameter of the small holes 1055 may be between about 0.1 mm and about 2 mm. Helium is delivered into chamber plasma region 1020 and then travels through through-holes 1056 into substrate processing region 1070. The process may optionally be improved by adding helium through small-holes 1055 such that a portion of the total helium in substrate processing region 1070 has not been excited in a plasma within chamber plasma region 1020.
Through-holes 1056 may be configured to control the passage of the plasma-activated gas (i.e., the ionic, radical, and/or neutral species) through showerhead 1053. For example, the aspect ratio of the holes (i.e., 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 showerhead 1053 is reduced. Through-holes 1056 in showerhead 1053 may include a tapered portion that faces chamber plasma region 1020, and a cylindrical portion that faces substrate processing region 1070. The cylindrical portion may be proportioned and dimensioned to control the flow of ionic species passing into substrate processing region 1070. An adjustable electrical bias may also be applied to showerhead 1053 as an additional means to control the flow of ionic species through showerhead 1053.
Alternatively, through-holes 1056 may have a smaller inner diameter (ID) toward the top surface of showerhead 1053 and a larger ID toward the bottom surface. In addition, the bottom edge of through-holes 1056 may be chamfered to help evenly distribute the plasma effluents in substrate processing region 1070 as the plasma effluents exit the showerhead and promote even distribution of the plasma effluents and precursor gases. The smaller ID may be placed at a variety of locations along through-holes 1056 and still allow showerhead 1053 to reduce the ion density within substrate processing region 1070. The reduction in ion density results from an increase in the number of collisions with walls prior to entry into substrate processing region 1070. Each collision increases the probability that an ion is neutralized by the acquisition or loss of an electron from the wall. Generally speaking, the smaller ID of through-holes 1056 may be between about 0.2 mm and about 20 mm. In other embodiments, the smaller ID may be between about 1 mm and 6 mm or between about 0.2 mm and about 5 mm. Further, aspect ratios of the through-holes 1056 (i.e., the smaller ID to hole length) may be approximately 1 to 20. The smaller ID of the through-holes may be the minimum ID found along the length of the through-holes. The cross sectional shape of through-holes 1056 may be generally cylindrical, conical, or any combination thereof.
FIG. 3B is a bottom view of a showerhead 1053 for use with a processing chamber according to embodiments. Showerhead 1053 corresponds with the showerhead shown in FIG. 3A. Through-holes 1056 are depicted with a larger inner-diameter (ID) on the bottom of showerhead 1053 and a smaller ID at the top. Small holes 1055 are distributed substantially evenly over the surface of the showerhead, even amongst the through-holes 1056 which helps to provide more even mixing than other embodiments described herein.
An exemplary patterned substrate may be supported by a pedestal (not shown) within substrate processing region 1070 when fluorine-containing plasma effluents arrive through through-holes 1056 in showerhead 1053. Though substrate processing region 1070 may be equipped to support a plasma for other processes such as curing, no plasma is present during the etching of patterned substrate according to embodiments.
A plasma may be ignited either in chamber plasma region 1020 above showerhead 1053 or substrate processing region 1070 below showerhead 1053. A plasma is present in chamber plasma region 1020 to produce the radical-fluorine from an inflow of the fluorine-containing precursor. An AC voltage typically in the radio frequency (RF) range is applied between the conductive top portion (lid 1021) of the processing chamber and showerhead 1053 to ignite a plasma in chamber plasma region 1020 during deposition. An RF power supply generates a high RF frequency of 13.56 MHz but may also generate other frequencies alone or in combination with the 13.56 MHz frequency.
The top plasma may be left at low or no power when the bottom plasma in the substrate processing region 1070 is turned on to either cure a film or clean the interior surfaces bordering substrate processing region 1070. A plasma in substrate processing region 1070 is ignited by applying an AC voltage between showerhead 1053 and the pedestal or bottom of the chamber. A cleaning gas may be introduced into substrate processing region 1070 while the plasma is present.
The pedestal may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate. This configuration allows the substrate temperature to be cooled or heated to maintain relatively low temperatures (from room temperature through about 120° C.). The heat exchange fluid may comprise ethylene glycol and water. The wafer support platter of the pedestal (preferably aluminum, ceramic, or a combination thereof) may also be resistively heated to achieve relatively high temperatures (from about 120° C. through about 1100° C.) using an embedded single-loop embedded heater element configured to make two full turns in the form of parallel concentric circles. An outer portion of the heater element may run adjacent to a perimeter of the support platter, while an inner portion runs on the path of a concentric circle having a smaller radius. The wiring to the heater element passes through the stem of the pedestal.
The chamber plasma region or a region in a remote plasma system may be referred to as a remote plasma region. In embodiments, the radical-fluorine is formed in the remote plasma region and travels into the substrate processing region to preferentially etch the tungsten. Plasma power may essentially be applied only to the remote plasma region, in embodiments, to ensure that the radical-fluorine (which may be referred to as plasma effluents) is not further excited in the substrate processing region unless the local bias power is applied.
In embodiments employing a chamber plasma region, the excited plasma effluents are generated in a section of the substrate processing chamber partitioned from the substrate processing region. The substrate processing region, is where the plasma effluents mix and react to etch the patterned substrate (e.g., a semiconductor wafer). The excited plasma effluents may also be accompanied by inert gases (in the exemplary case, argon). The substrate processing region may be described herein as “plasma-free” during etching of the substrate. “Plasma-free” does not necessarily mean the region is devoid of plasma. A relatively low concentration of ionized species and free electrons created within the plasma region do travel through pores (apertures) in the partition (showerhead/ion suppressor) due to the shapes and sizes of through-holes 1056. In some embodiments, there is essentially no concentration of ionized species and free electrons within the substrate processing region. The borders of the plasma in the chamber plasma region are hard to define and may encroach upon the substrate processing region through the apertures in the showerhead. In the case of an inductively-coupled plasma, a small amount of ionization may be effected within the substrate processing region directly. Furthermore, a low intensity plasma may be created in the substrate processing region without eliminating desirable features of the forming film. All causes for a plasma having much lower intensity ion density than the chamber plasma region (or a remote plasma region, for that matter) during the creation of the excited plasma effluents do not deviate from the scope of “plasma-free” as used herein.
Nitrogen trifluoride (or another fluorine-containing precursor) may be flowed into chamber plasma region 1020 at rates 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. Helium may be flowed into chamber plasma region 1020 at flow rates above about 125 sccm, above about 250 sccm, above about 1000 sccm, above about 1500 sccm or above about 2500 sccm in embodiments. The flow rate ratio of helium to fluorine-containing precursor may be greater than 15:1, greater than 20:1, greater than 25:1, greater than 40:1 or greater than 60:1 according to embodiments. The atomic flow rate ratio of helium to fluorine may be greater than 5:1, greater than 7:1, greater than 10:1 or greater than 20:1 in embodiments. These high helium flow rate ratios have been found to result in high diffusivity and an even tungsten etch rate within high aspect ratio trenches.
Combined flow rates of fluorine-containing precursor into the chamber may account for 0.05% to about 20% by volume of the overall gas mixture; the remainder being carrier gases. The fluorine-containing precursor is flowed into the remote plasma region but the plasma effluents have the same volumetric flow ratio, in embodiments. In the case of the fluorine-containing precursor, a purge or carrier gas may be first initiated into the remote plasma region before those of the fluorine-containing gas to stabilize the pressure within the remote plasma region.
Plasma power applied to the remote plasma region can be a variety of frequencies or a combination of multiple frequencies. In the exemplary processing system the plasma is provided by RF power delivered between lid 1021 and showerhead 1053. In an embodiment, the energy is applied using a capacitively-coupled plasma unit. When using a FrontierTM or similar system, the remote plasma source power may be between about 10 watts and about 3000 watts, between about 20 watts and about 2500 watts, between about 30 watts and about 2000 watts, or between about 50 watts and about 1500 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 according to embodiments.
Substrate processing region 1070 can be maintained at a variety of pressures during the flow of carrier gases and plasma effluents into substrate processing region 1070. 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 in embodiments. The pressure may be above or about 0.1 Torr, above or about 0.2 Torr, or above or about 0.5 Torr according to embodiments. Lower limits on the pressure may be combined with upper limits on the pressure in embodiments.
In one or more embodiments, the substrate processing chamber 1001 can be integrated into a variety of multi-processing platforms, including the ProducerTM GT, CenturaTM AP and EnduraTM platforms available from Applied Materials, Inc. located in Santa Clara, Calif. Such a processing platform is capable of performing several processing operations without breaking vacuum. Processing chambers that may implement embodiments of the present invention may include dielectric etch chambers or a variety of chemical vapor deposition chambers, among other types of chambers.
Embodiments of the deposition systems may be incorporated into larger fabrication systems for producing integrated circuit chips. FIG. 4 shows one such system 1101 of deposition, baking and curing chambers according to embodiments. In the figure, a pair of FOUPs (front opening unified pods) 1102 supply substrate substrates (e.g., 300 mm diameter wafers) that are received by robotic arms 1104 and placed into a low pressure holding areas 1106 before being placed into one of the wafer processing chambers 1108a-f. A second robotic arm 1110 may be used to transport the substrate wafers from the low pressure holding areas 1106 to the wafer processing chambers 1108a-f and back. Each wafer 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 wafer processing chambers 1108a-f may include one or more system components for depositing, annealing, curing and/or etching a flowable dielectric film on the substrate wafer. In one configuration, two pairs of the processing chamber (e.g., 1108c-d and 1108e-f) may be used to deposit dielectric material on the substrate, and the third pair of processing chambers (e.g., 1108a-b) may be used to etch the deposited dielectric. In another configuration, all three pairs of chambers (e.g., 1108a-f) may be configured to etch a dielectric film on the substrate. Any one or more of the processes described may be carried out on chamber(s) separated from the fabrication system shown in embodiments.
The substrate processing system is controlled by a system controller. In an exemplary embodiment, the system controller includes a hard disk drive, a floppy disk drive and a processor. The processor contains a single-board computer (SBC), analog and digital input/output boards, interface boards and stepper motor controller boards. Various parts of CVD system conform to the Versa Modular European (VME) standard which defines board, card cage, and connector dimensions and types. The VME standard also defines the bus structure as having a 16-bit data bus and a 24-bit address bus.
System controller 1157 is used to control motors, valves, flow controllers, power supplies and other functions required to carry out process recipes described herein. A gas handling system 1155 may also be controlled by system controller 1157 to introduce gases to one or all of the wafer processing chambers 1108a-f. System controller 1157 may rely on feedback from optical sensors to determine and adjust the position of movable mechanical assemblies in gas handling system 1155 and/or in wafer processing chambers 1108a-f. Mechanical assemblies may include the robot, throttle valves and susceptors which are moved by motors under the control of system controller 1157.
In an exemplary embodiment, system controller 1157 includes a hard disk drive (memory), USB ports, a floppy disk drive and a processor. System controller 1157 includes analog and digital input/output boards, interface boards and stepper motor controller boards. Various parts of multi-chamber processing system 1101 which contains substrate processing chamber 1001 are controlled by system controller 1157. The system controller executes system control software in the form of a computer program stored on computer-readable medium such as a hard disk, a floppy disk or a flash memory thumb drive. Other types of memory can also be used. The computer program includes sets of instructions that dictate the timing, mixture of gases, chamber pressure, chamber temperature, RF power levels, susceptor position, and other parameters of a particular process.
A process for etching, depositing or otherwise processing a film on a substrate or a process for cleaning chamber can be implemented using a computer program product that is executed by the controller. The computer program code can be written in any conventional computer readable programming language: for example, 68000 assembly language, C, C++, Pascal, Fortran or others. Suitable program code is entered into a single file, or multiple files, using a conventional text editor, and stored or embodied in a computer usable medium, such as a memory system of the computer. If the entered code text is in a high level language, the code is compiled, and the resultant compiler code is then linked with an object code of precompiled Microsoft Windows® library routines. To execute the linked, compiled object code the system user invokes the object code, causing the computer system to load the code in memory. The CPU then reads and executes the code to perform the tasks identified in the program.
The interface between a user and the controller may be via a touch-sensitive monitor and may also include a mouse and keyboard. In one embodiment two monitors are used, one mounted in the clean room wall for the operators and the other behind the wall for the service technicians. The two monitors may simultaneously display the same information, in which case only one is configured to accept input at a time. To select a particular screen or function, the operator touches a designated area on the display screen with a finger or the mouse. The touched area changes its highlighted color, or a new menu or screen is displayed, confirming the operator's selection.
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 nitride” of the patterned substrate is predominantly Si3N4 but may include minority concentrations of other elemental constituents (e.g. oxygen, hydrogen, carbon). 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 described herein consist essentially of silicon and oxygen. “Titanium nitride” is predominantly titanium and nitrogen but may include minority concentrations of other elemental constituents (e.g. nitrogen, hydrogen, carbon). Titanium nitride may consist of titanium and nitrogen.
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-fluorine” is a radical precursor which contains fluorine 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 tungsten, the method comprising:
transferring a patterned substrate into a substrate processing region, wherein the patterned substrate has a tungsten lining layer coating a high aspect ratio trench having a depth more than twenty times a width of the high aspect ratio trench;
flowing a fluorine-containing precursor with a fluorine flow rate into a remote plasma region fluidly coupled to a substrate processing region via perforations in a perforated plate;
flowing helium with a helium flow rate into the remote plasma region;
forming a remote plasma in the remote plasma region to produce plasma effluents from the fluorine-containing precursor and the helium, and flowing the plasma effluents into the substrate processing region through the perforations; and
etching the tungsten lining layer, wherein, after etching the tungsten lining layer, a top sidewall thickness of the tungsten lining layer measured on a sidewall of the high aspect ratio trench near the opening of the high aspect ratio trench is within 20% of a bottom sidewall thickness of the tungsten lining layer measured on the sidewall of the high aspect ratio trench near the bottom of the high aspect ratio trench.

2. The method of claim 1 wherein the fluorine-containing precursor comprises at least one precursor selected from the group consisting of atomic fluorine, diatomic fluorine, bromine trifluoride, chlorine trifluoride, nitrogen trifluoride, hydrogen fluoride, sulfur hexafluoride and xenon difluoride.

3. The method of claim 1 wherein the depth of the high aspect ratio trench is greater than one micron.

4. The method of claim 1 wherein the width of the high aspect ratio trench is less than one hundred nanometers.

5. The method of claim 1 wherein a ratio of the helium flow rate to the fluorine flow rate is greater than or about fifteen.

6. The method of claim 1 wherein the helium flow rate and the fluorine flow rate are selected such that a net atomic flow rate ratio of helium to fluorine into the substrate processing region is greater than or about five.

7. The method of claim 1 wherein the remote plasma is formed by applying a remote plasma power greater than 10 watts capacitively to the remote plasma region.

8. The method of claim 1 wherein no bias plasma power is applied during the operation of forming the remote plasma.

9. The method of claim 1 further comprising applying a bias plasma power in the substrate processing region to re-ionize plasma effluents and bombard the patterned substrate with fluorine-containing ions.

10. The method of claim 9 wherein the bias plasma power is between 10 watts and 900 watts.

11. The method of claim 1 wherein a temperature of the patterned substrate is between −30° C. and 300° C. during the operation of etching the tungsten lining layer.

12. The method of claim 1 wherein one or both of the two adjacent stacks comprises at least ten alternating layers of dielectric and tungsten.

13. The method of claim 1 wherein etching the tungsten lining layer reduces a thickness of the tungsten lining layer at a top rate near the outermost portion of the sidewall of the high aspect ratio trench which is within 20% of a bottom rate near the innermost portion of the sidewall of the high aspect ratio trench.

14. The method of claim 1 wherein the fluorine-containing precursor is nitrogen trifluoride.

15. A method of etching tungsten, the method comprising:
transferring a patterned substrate into a substrate processing region, wherein the patterned substrate has a tungsten lining layer coating a high aspect ratio trench having a depth more than twenty times a width of the high aspect ratio trench;
flowing a fluorine-containing precursor into the substrate processing region
flowing nitrogen trifluoride into a remote plasma region fluidly coupled to a substrate processing region via perforations in the perforated plate;
forming a remote plasma in the remote plasma region to produce plasma effluents from the nitrogen trifluoride and flowing the plasma effluents into the substrate processing region through the perforations;
applying local plasma power capacitively between the perforated plate and a substrate susceptor supporting the patterned substrate to create and accelerate re-ionized plasma effluents toward the patterned substrate; and
etching the tungsten lining layer, wherein etching the tungsten lining layer reduces a thickness of the tungsten lining layer on a sidewall of the high aspect ratio trench at a top rate near the outermost portion of the sidewall of the high aspect ratio trench which is within 20% of a bottom rate near the innermost portion the sidewall of the high aspect ratio trench.