# Patent

## Title
Vertical gate separation

## Abstract

Methods of selectively etching tungsten from the surface of a patterned substrate are described. The methods electrically separate vertically arranged tungsten slabs from one another as needed. The vertically arranged tungsten slabs may form the walls of a trench during manufacture of a vertical flash memory cell. The tungsten etch may selectively remove tungsten relative to films such as silicon, polysilicon, silicon oxide, aluminum oxide, titanium nitride and silicon nitride. The methods include exposing electrically-shorted tungsten slabs to remotely-excited fluorine formed in a remote plasma region. Process parameters are provided which result in uniform tungsten recess within the trench. A low electron temperature is maintained in the substrate processing region to achieve high etch selectivity and uniform removal throughout the trench.

## Background
FIELD
The subject matter herein relates to electrical separation of gates in a vertical memory structure.
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 increasingly 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 generation of nitrogen trifluoride in combination with ion suppression techniques enables silicon to be and selectively removed from a patterned substrate when the plasma effluents are flowed into the substrate processing region.
Methods are needed to broaden the utility of selective dry etch processes.
SUMMARY
Methods of selectively etching tungsten from the surface of a patterned substrate are described. The methods electrically separate vertically arranged tungsten slabs from one another as needed. The vertically arranged tungsten slabs may form the walls of a trench during manufacture of a vertical flash memory cell. The tungsten etch may selectively remove tungsten relative to films such as silicon, polysilicon, silicon oxide, aluminum oxide, titanium nitride and silicon nitride. The methods include exposing electrically-shorted tungsten slabs to remotely-excited fluorine formed in a remote plasma region. Process parameters are provided which result in uniform tungsten recess within the trench. A low electron temperature is maintained in the substrate processing region to achieve high etch selectivity and uniform removal throughout the trench.
Embodiments include methods of etching a patterned substrate. The methods include placing the patterned substrate in a substrate processing region of a substrate processing chamber. The patterned substrate includes electrically-shorted tungsten slabs arranged in at least one of two adjacent vertical columns. A trench is formed between the two adjacent vertical columns. The methods further include flowing a fluorine-containing precursor into a remote plasma region within the substrate processing chamber and exciting the fluorine-containing precursor in a remote plasma in the remote plasma region to produce plasma effluents. The remote plasma region is fluidly coupled with the substrate processing region through a showerhead and the remote plasma is capacitively-coupled. The methods further include flowing the plasma effluents into the substrate processing region through the showerhead and etching the electrically-shorted tungsten slabs.
The remote plasma may be capacitively-coupled with a remote plasma power of between 100 watts and 500 watts. An electron temperature in the substrate processing region while selectively etching the electrically-shorted tungsten slabs may be below 0.5 eV. Etching the electrically-shorted tungsten slabs electrically may isolate the electrically-shorted tungsten slabs from one another to form electrically-isolated tungsten slabs. The fluorine-containing precursor may include at least one of atomic fluorine, diatomic fluorine, bromine trifluoride, chlorine trifluoride, nitrogen trifluoride, hydrogen fluoride, fluorinated hydrocarbons, sulfur hexafluoride and xenon difluoride. A depth-to-width aspect ratio of the trench may be at least ten. At least one of the two adjacent vertical columns include at least thirty tungsten slabs. A depth of the trench may be greater than one micron. A temperature of the patterned substrate may be maintained at between 50° C. and about 80° C. during etching the electrically-shorted tungsten slabs. The electrically-shorted tungsten slabs may consist of tungsten and a barrier layer. A pressure within the remote plasma region may be between 5 Torr and 12 Torr during etching the electrically-shorted tungsten slabs.
Embodiments include methods of etching a patterned substrate. The methods include placing the patterned substrate in a substrate processing region of a substrate processing chamber. The patterned substrate includes electrically-shorted conducting slabs arranged in a vertical column. A trench is disposed between the vertical column and an adjacent vertical column. The methods further include gas-phase etching the electrically-shorted conducting slabs. The operation of gas-phase etching electrically separates the electrically-shorted conducting slabs to form electrically-isolated conducting slabs. The methods further include recessing the electrically-isolated conducting slabs beyond an extent of insulating material between each adjacent pair of the electrically-isolated conducting slabs by a recessed amount.
A standard deviation of a statistical distribution of the recessed amounts of all the electrically-isolated conducting slabs may be less than 0.5 nm prior to the operation of gas-phase etching the electrically-shorted conducting slabs and/or may be less than 0.5 nm after the operation of gas-phase etching the electrically-shorted conducting slabs.
Embodiments include methods of etching a patterned substrate. The methods include placing the patterned substrate in a substrate processing region of a substrate processing chamber. The patterned substrate comprises electrically-shorted tungsten slabs arranged in at least one of two adjacent vertical columns. A trench is disposed between the two adjacent vertical columns. The methods further include flowing a radical-fluorine precursor into the substrate processing region. The methods further include selectively etching the electrically-shorted tungsten slabs. Selectively etching the electrically-shorted tungsten slabs electrically isolates each of the electrically-shorted tungsten slabs from one another to form electrically-isolated tungsten slabs.
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 embodiments may be realized by reference to the remaining portions of the specification and the drawings.
FIGS. 1A and 1B are cross-sectional views of a patterned substrate during an tungsten etch process according to embodiments.
FIG. 2 is a flow chart of a tungsten 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 tungsten from the surface of a patterned substrate are described. The methods electrically separate vertically arranged tungsten slabs from one another as needed. The vertically arranged tungsten slabs may form the walls of a trench during manufacture of a vertical flash memory cell. The tungsten etch may selectively remove tungsten relative to films such as silicon, polysilicon, silicon oxide, aluminum oxide, titanium nitride and silicon nitride. The methods include exposing electrically-shorted tungsten slabs to remotely-excited fluorine formed in a remote plasma region. Process parameters are provided which result in uniform tungsten recess within the trench. A low electron temperature is maintained in the substrate processing region to achieve high etch selectivity and uniform removal throughout the trench.
Vertical flash memory may be referred to as 3-D flash memory and includes a plurality of electrically-isolated conducting slabs arranged in at least one of two adjacent vertical columns. Tungsten is currently in widespread use for the conducting slab material. The number of slabs is increasing to increase the amount of storage per integrated circuit (IC). As the number of slabs is increased, the depth of a trench between two adjacent vertical columns is also increased. Maintaining a uniform removal from the top of the trench down to the bottom of the trench is desirable for a tungsten etch operation to recess and separate the tungsten slabs. The methods described herein provide benefit which arises from a more uniform reduction of tungsten film thickness up and down the sides of the trench using a single operation rather than a sequence of operations which possess offsetting inhomogeneous etch rates. The benefit includes a larger average amount of tungsten remaining after electrical separation which improves the electrical performance of the memory. The methods provide benefit from decreased process complexity in that no non-uniform compensating operations are necessary in embodiments. The methods may also avoid reliance on the use of a local plasma or a bias plasma power. No local plasma (e.g. no bias power) is applied to the substrate processing region during all etching operations described herein. The etch selectivity is desirably increased by avoiding local plasma excitation (applying plasma power directly to the substrate processing region).
To better understand and appreciate the embodiments described herein, reference is now made to FIGS. 1A and 1B which are cross-sectional views of a 3-D flash memory cell during a method 201 (see FIG. 2) of forming the 3-D flash memory cells according to embodiments. In one example, a flash memory cell on patterned substrate 101 comprises alternatively stacked silicon oxide 105 and tungsten 110-1 in two adjacent columns. Tungsten 110-1 has recently been deposited into the stack, replacing sacrificial silicon nitride at the levels shown in FIG. 1A. FIG. 1A shows only five levels of tungsten to allow a more detailed discussion of the tungsten etch process 201. There may be more than thirty, more than fifty, more than seventy or more than ninety tungsten levels according to embodiments.
Tungsten deposited outside the stack shorts the tungsten levels together as shown in FIG. 1A. Tungsten 110 may consist essentially of or consist of tungsten in embodiments. Tungsten 110 may consist of tungsten and a barrier layer in embodiments. The trench in which tungsten has been deposited may be called a “slit trench” between the two adjacent columns to indicate that this trench has a much larger length-to-width aspect ratio (longer into the page) than the memory hole also shown in FIG. 1A. The depth-to-width aspect ratio (depth divided by width) of the slit trench may be greater than ten, fifteen or twenty according to embodiments. The depth is measured vertically and the width is measured horizontally in the plane of FIG. 1A. The sides of the memory hole are lined with a conformal ONO layer. The ONO layer includes a silicon oxide layer 115 (often referred to as IPD or interpoly dielectric), a silicon nitride layer 120 (which serves as the charge trap layer) and a silicon oxide layer 125 (the gate dielectric). “Top” and “Up” will be used herein to describe portions/directions perpendicularly distal from the substrate plane and further away from the center of mass of the substrate in the perpendicular direction. “Vertical” will be used to describe items aligned in the “Up” direction towards the “Top”. Other similar terms may be used whose meanings will now be clear. The vertical memory hole may be circular as viewed from above.
The conformal ONO layer may be used as an etch stop for the selective gas-phase tungsten etch and the structure of the conformal ONO layer will now be described. The tungsten barrier layer may also be used as an etch stop in embodiments. Silicon oxide layer 115 may be in contact with silicon nitride layer 120, which may be in contact with silicon oxide layer 125 in embodiments. Silicon oxide layer 115 may contact stacked silicon oxide layers 105 and stacked tungsten layers 110 whereas silicon oxide layer 125 may contact silicon 101 (epitaxially grown) or a polysilicon layer in embodiments. Silicon oxide layer 115 may have a thickness less than or about 8 nm or less than 6 nm in embodiments. Silicon oxide layer 115 may comprise or consist of silicon and oxygen in embodiments. Silicon nitride 120 may have a thickness less than or about 8 nm or less than 6 nm in embodiments. Silicon nitride layer 120 may comprise or consist of silicon and nitrogen in embodiments. Silicon oxide layer 125 may have a thickness less than or about 8 nm or less than 6 nm in embodiments. Silicon oxide layer 125 may comprise or consist of silicon and oxygen in embodiments. The constrained geometries and thinness of the layers result in damage to the memory cell when liquid etchants are used, further motivating the gas-phase etching methods presented herein. Liquid etchants cannot be as completely removed and continue to etch after etchants are supposedly removed in embodiments. Liquid etchants may ultimately form and/or penetrate through pinholes and damage devices after manufacturing is complete.
Patterned substrate 101 as shown in FIG. 1A is delivered into a substrate processing chamber. Patterned substrate 101 is transferred into a substrate processing region within a substrate processing chamber (operation 210) to initiate method 201 of forming a flash memory cell. A flow of nitrogen trifluoride is then introduced into a remote plasma region where the nitrogen trifluoride is excited in a remote plasma struck within the remote plasma region in operation 220. The remote plasma region may be a remote plasma system (RPS) located outside the substrate processing chamber and/or a chamber plasma region located inside the substrate processing region. The remote plasma region is separated from the substrate processing region by an aperture or a showerhead. In general, a fluorine-containing precursor may be flowed into the chamber 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, fluorinated hydrocarbons, sulfur hexafluoride and xenon difluoride. Also in operation 220, plasma effluents formed in the remote plasma region are flowed through the aperture or showerhead into the substrate processing region housing patterned substrate 101.
According to embodiments, the plasma effluents may pass through a showerhead and/or ion suppressor to reduce the electron temperature (to reduce the ion concentration) in the substrate processing region. Reduced electron temperatures as described subsequently herein have been found to increase the etch selectivity of tungsten compared to other exposed materials (e.g. silicon oxide or silicon nitride). Reduced electron temperatures apply to all tungsten etch operations described herein using either chamber plasma regions or remote plasma systems or the combination of the two in the integrated process described below. The low electron temperatures are described later in the specification (e.g. <0.5 eV). Operation 230 (and all etches described herein) may be referred to as a gas-phase etch to distinguish from liquid etch processes. In operation 230, tungsten is selectively etched back to electrically separate tungsten layers 110-1 from one another to form separate tungsten layers 110-2. The reactive chemical species are removed from the substrate processing region and the substrate is removed from the substrate processing region in operation 240.
For the purposes of dimensions and other characterizations described herein, tungsten and tungsten slabs will be understood to include their barrier layers or other conformal layers useful for forming or using the tungsten or tungsten slabs. Exemplary tungsten barrier layers may include titanium, titanium nitride, tantalum or tantalum nitride in embodiments. The barrier layer may also provide etch stop functionality in the etch processes described herein.
In addition to the fluorine-containing precursor flowing into the remote plasma region, some additional precursors may be helpful to make the etch operation 230 selective of the tungsten slabs 110-1. An oxygen-containing precursor, e.g. molecular oxygen, may be flowed into the remote plasma region in combination or to combine with the fluorine-containing precursor in embodiments. Alternatively, or in combination, a hydrogen-containing precursor, e.g. molecular hydrogen, may be flowed into the remote plasma region in combination or to combine with the fluorine-containing precursor in embodiments. According to embodiments, the plasma effluents may pass through a showerhead and/or ion suppressor to reduce the electron temperature (to reduce the ion concentration) in the substrate processing region. Reduced electron temperatures as described subsequently herein have been found to increase the etch selectivity of tungsten in tungsten slabs 110 compared to other exposed materials.
Operation 220 may include applying energy to the fluorine-containing precursor while in the chamber plasma region to generate the plasma effluents. As would be appreciated by one of ordinary skill in the art, the plasma may include a number of charged and neutral species including radicals and ions. The plasma may be generated using known techniques (e.g., radio frequency excitations, capacitively-coupled power or inductively coupled power). In an embodiment, the energy is applied using a capacitively-coupled plasma unit. The remote plasma power may be between 25 watts and 2000 watts, between 50 watts and 1000 watts or between 100 watts and 500 watts according to embodiments. The capacitively-coupled plasma unit may be disposed remote from a substrate processing region of the processing chamber. For example, the capacitively-coupled plasma unit and the plasma generation region may be separated from the substrate processing region by a showerhead. All process parameters (e.g. power above, temperature and pressure below) apply to all remote plasma embodiments herein unless otherwise indicated.
In operations described herein, the fluorine-containing precursor (e.g. NF3) is supplied at a flow rate of between 5 sccm and 500 sccm, between 10 sccm and 300 sccm, between 25 sccm and 200 sccm, between 50 sccm and 150 sccm or between 75 sccm and 125 sccm. The temperature of the patterned substrate may be between −20° C. and 200° C. during tungsten selective etches described herein. The patterned substrate temperature may also be maintained at between 30° C. and 110° C., between 50° C. and 80° C. or between 55° C. and 75° C. during all the gas-phase etching processes according to embodiments. These process parameters apply to all the embodiments described herein. The pressure within the substrate processing region is below 50 Torr, below 30 Torr, below 20 Torr, below 15. The pressure may be above 0.5 Torr, above 1.0 Torr, above 1.5 Torr or above 3 Torr in embodiments. In a preferred embodiment, the pressure while etching may be between 5 Torr and 12 Torr. However, any of the upper limits on temperature or pressure may be combined with lower limits to form additional embodiments.
An advantage of the processes described herein lies in the conformal rate of removal of material from the substrate. The methods do not rely on a high bias power (or any bias power in embodiments) 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.
The tungsten slabs 110-2 of the 3-D flash memory device formed using etch process 201 may each end up recessed within 1 nm of the average recess of the electrically-isolated tungsten slabs in embodiments. The standard deviation of the lengths of each tungsten slab 110-2 (measured left-right in FIG. 1B) may be under 0.5 nm before and/or after operation 230 according to embodiments. Operation 230 electrically isolates the electrically-shorted tungsten slabs 110-1 from one another to form electrically-isolated tungsten slabs 110-2 having more homogeneous recesses compared to previously-developed processes. Electrically-isolated tungsten slabs 110-2 may each be electrically-isolated from every other of the electrically-isolated tungsten slabs 110-2 according to embodiments.
In each remote 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 (which may be the showerhead) may be used to provide radical and/or neutral species for gas-phase etching. The ion suppressor may also be referred to as an ion suppression element. In embodiments, for example, the ion suppressor is used to filter etching plasma effluents en route from the remote plasma region to the substrate processing region. The ion suppressor may be used to provide a reactive gas having a higher concentration of radicals than ions. Plasma effluents pass through the ion suppressor disposed between the remote plasma region and the substrate processing region. The ion suppressor functions to dramatically reduce or substantially eliminate ionic species traveling from the plasma generation region to the substrate. The ion suppressors described herein are simply one way to achieve a low electron temperature in the substrate processing region during the gas-phase etch processes described herein.
In embodiments, an electron beam is passed through the substrate processing region in a plane parallel to the substrate to reduce the electron temperature of the plasma effluents. A simpler showerhead may be used if an electron beam is applied in this manner. The electron beam may be passed as a laminar sheet disposed above the substrate in embodiments. The electron beam provides a source of neutralizing negative charge and provides a more active means for reducing the flow of positively charged ions towards the substrate and increasing the etch selectivity in embodiments. The flow of plasma effluents and various parameters governing the operation of the electron beam may be adjusted to lower the electron temperature measured in the substrate processing region.
The electron temperature may be measured using a Langmuir probe in the substrate processing region during excitation of a plasma in the remote plasma. 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 electron beam, showerhead and/or the ion suppressor. Uncharged neutral and radical species may pass through the electron beam and/or the openings in the ion suppressor to react at the substrate. Such a process using radicals and other neutral species can reduce plasma damage compared to conventional plasma etch processes that include sputtering and bombardment. Embodiments are also advantageous over conventional wet etch processes where surface tension of liquids can cause bending and peeling of small features.
The substrate processing region may be described herein as “plasma-free” during the etch processes described herein. “Plasma-free” does not necessarily mean the region is devoid of plasma. Ionized species and free electrons created within the plasma region may travel through pores (apertures) in the partition (showerhead) at exceedingly small concentrations. 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. Furthermore, a low intensity plasma may be created in the substrate processing region without eliminating desirable features of the etch processes described herein. All causes for a plasma having much lower intensity ion density than the chamber plasma region during the creation of the excited plasma effluents do not deviate from the scope of “plasma-free” as used herein.
The etch selectivities during the tungsten etches described herein (tungsten:silicon oxide or tungsten:silicon nitride or tungsten:polysilicon and tungsten:titanium nitride (or another barrier material listed herein)) may be greater than or about 50:1, greater than or about 100:1, greater than or about 150:1 or greater than or about 250:1 according to embodiments.
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 fluorine-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 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 fluorine-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 fluorine, e.g., NF3. 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-fluorine 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-fluorine 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-fluorine precursor. Plasma power may essentially be applied only to the remote plasma region in embodiments to ensure that the radical-fluorine precursor provides the dominant excitation.
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 fluorine-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 fluorine-containing precursor, a purge or carrier gas may be flowed initially into the remote plasma region before the fluorine-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.
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 the preceding description, for the purposes of explanation, numerous details have been set forth to provide an understanding of embodiments of the subject matter described herein. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.
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 such as nitrogen, hydrogen and carbon. In embodiments, silicon oxide films etched using the methods taught herein consist essentially of or consist of silicon and oxygen. Analogous definitions will be understood for “tungsten”, “titanium”, “titanium nitride”, “tantalum” and “tantalum nitride”.
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 term “gap” is used with no implication that the etched geometry has a large length-to-width aspect ratio. Viewed from above the surface, gaps may appear circular, oval, polygonal, rectangular, or a variety of other shapes. The term “gap” refers to a “trench” or a “via”. A length-to-width aspect ratio of the via may be about 1:1, as viewed from above, whereas a length-to-width aspect ratio of the trench may be greater than 10:1. A trench may be in the shape of a moat around an island of material in which case the length-to-width aspect ratio would be the circumference divided by the width of the gap averaged around the circumference. The term “via” is used to refer to a low length-to-width aspect ratio trench 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 embodiments described herein. Accordingly, the above description should not be taken as limiting the scope of the claims.
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 embodiments described, 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 a patterned substrate, the method comprising:
placing the patterned substrate in a substrate processing region of a substrate processing chamber, wherein the patterned substrate comprises electrically-shorted tungsten slabs arranged in at least one of two adjacent vertical columns, wherein a trench is disposed between the two adjacent vertical columns;
flowing a fluorine-containing precursor into a remote plasma region within the substrate processing chamber and exciting the fluorine-containing precursor in a remote plasma in the remote plasma region to produce plasma effluents, wherein the remote plasma region is fluidly coupled with the substrate processing region through a showerhead and the remote plasma is capacitively-coupled; and
flowing the plasma effluents into the substrate processing region through the showerhead and etching the electrically-shorted tungsten slabs, wherein an electron temperature in the substrate processing region while selectively etching the electrically-shorted tungsten slabs is below 0.5 eV, and wherein a pressure within the remote plasma region is between 5 Torr and 12 Torr during etching the electrically-shorted tungsten slabs.

2. The method of claim 1 wherein the remote plasma is capacitively-coupled with a remote plasma power of between 100 watts and 500 watts.

3. The method of claim 1 wherein etching the electrically-shorted tungsten slabs electrically isolates the electrically-shorted tungsten slabs from one another to form electrically-isolated tungsten slabs.

4. The method of claim 1 wherein the fluorine-containing precursor comprises at least one of atomic fluorine, diatomic fluorine, bromine trifluoride, chlorine trifluoride, nitrogen trifluoride, hydrogen fluoride, fluorinated hydrocarbons, sulfur hexafluoride and xenon difluoride.

5. The method of claim 1 wherein a depth-to-width aspect ratio of the trench is at least ten.

6. The method of claim 1 wherein the at least one of the two adjacent vertical columns comprise at least thirty tungsten slabs.

7. The method of claim 1 wherein a depth of the trench is greater than one micron.

8. The method of claim 1 wherein a temperature of the patterned substrate is maintained at between 50° C. and about 80° C. during etching the electrically-shorted tungsten slabs.

9. The method of claim 1 wherein the electrically-shorted tungsten slabs consist of tungsten and a barrier layer.

10. A method of etching a patterned substrate, the method comprising:
placing the patterned substrate in a substrate processing region of a substrate processing chamber, wherein the patterned substrate comprises electrically-shorted conducting slabs arranged in a vertical column, wherein a trench is disposed between the vertical column and an adjacent vertical column;
generating a plasma in a remote plasma region of the substrate processing chamber, wherein the remote plasma region is physically separated from the substrate processing region by at least one chamber component, and wherein the plasma produces plasma effluents;
reducing the electron temperature of the plasma effluents by passing the plasma effluents through an electron beam generated in the substrate processing region of the chamber, wherein the substrate processing region is maintained plasma free;
gas-phase etching the electrically-shorted conducting slabs, wherein the operation of gas-phase etching electrically separates the electrically-shorted conducting slabs to form electrically-isolated conducting slabs; and
recessing the electrically-isolated conducting slabs beyond an extent of insulating material between each adjacent pair of the electrically-isolated conducting slabs by a recessed amount.

11. The method of claim 10 wherein each conducting slab is characterized by a length parallel to the substrate, and wherein the length of each slab is within 0.5 nm of an average length for all conducting slabs prior to the operation of gas-phase etching the electrically-shorted conducting slabs.

12. The method of claim 10 wherein each conducting slab is characterized by a length parallel to the substrate, and wherein the length of each slab is within 0.5 nm of an average length for all conducting slabs after the operation of gas-phase etching the electrically-shorted conducting slabs.

13. A method of etching a patterned substrate, the method comprising:
placing the patterned substrate in a substrate processing region of a substrate processing chamber, wherein the patterned substrate comprises electrically-shorted tungsten slabs arranged in at least one of two adjacent vertical columns, wherein a trench is disposed between the two adjacent vertical columns, wherein the tungsten slabs are disposed vertically from one another within the vertical columns, and wherein each tungsten slab is vertically separated from at least one other tungsten slab by a region of silicon oxide;
flowing a radical-fluorine precursor into the substrate processing region; and
selectively etching the electrically-shorted tungsten slabs, wherein selectively etching the electrically-shorted tungsten slabs electrically isolates each of the electrically-shorted tungsten slabs from one another to form electrically-isolated tungsten slabs.

14. The method of claim 13, wherein the tungsten slabs are electrically shorted by a region of tungsten extending perpendicular to the substrate and contacting each vertically separated tungsten slab.

15. The method of claim 14, wherein the selective etching removes the region of tungsten extending perpendicular to the substrate.