The present invention relates generally to methods of processing a substrate, and, in particular embodiments, to low-temperature etching of materials and systems.
Generally, a semiconductor device, such as an integrated circuit (IC) is fabricated by sequentially depositing and patterning layers of dielectric, conductive, and semiconductor materials over a substrate to form a network of electronic components and interconnect elements (e.g., transistors, resistors, capacitors, metal lines, contacts, and vias) integrated in a monolithic structure. Many of the processing steps used to form the constituent structures of semiconductor devices are performed using plasma processes.
The semiconductor industry has repeatedly reduced the minimum feature sizes in semiconductor devices to a few nanometers to increase the packing density of components. Accordingly, the semiconductor industry increasingly demands plasma processing technology to provide processes for patterning features with accuracy, precision, and profile control, often at atomic scale dimensions. Meeting this challenge along with the uniformity and repeatability needed for high volume IC manufacturing requires further innovations of plasma processing technology.
In accordance with an embodiment of the present invention, a method of processing a substrate that includes: flowing dioxygen (02) and a hydrogen-containing gas into a plasma processing chamber that is configured to hold the substrate, the substrate including an organic layer and a patterned etch mask, the hydrogen-containing gas including dihydrogen (H2), a hydrocarbon, or hydrogen peroxide (H2O2); generating an oxygen-rich plasma while flowing the gases; maintaining a temperature of the substrate in the plasma processing chamber between −150° C. and −50° C.; and while maintaining the temperature, exposing the substrate to the oxygen-rich plasma to form a recess in the organic layer.
In accordance with an embodiment of the present invention, a method of processing a substrate that includes: cooling the substrate in a plasma processing chamber to a temperature of −50° C. or lower, the substrate including a dielectric layer, an amorphous carbon layer (ACL) and a patterned etch mask; flowing dioxygen (O2) and a hydrogen-containing gas into a plasma processing chamber; generating a plasma in the plasma processing chamber, where portions of dioxygen and the hydrogen-containing gas react under the plasma to form water (H2O) molecules; and exposing the substrate to the plasma to form a recess in the organic layer, the recess having an aspect ratio of at least 20:1, the substrate being kept at around the temperature.
In accordance with an embodiment of the present invention, a method of forming a high-aspect ratio (HAR) feature on a substrate in a plasma processing chamber that includes: depositing an amorphous carbon layer (ACL) hardmask over a dielectric layer including silicon oxide formed over the substrate; depositing and pattern an etch mask layer over the ACL hardmask; flowing dioxygen(O2), a hydrogen-containing gas, and a noble gas to a plasma processing chamber; generating a halogen-free and sulfur-free plasma in the plasma processing chamber while flowing O2, the hydrogen-containing gas, and the noble gas, where portions of O2 and the hydrogen-containing gas react under the plasma to form water (H2O) vapor; maintaining a temperature of the substrate between −150° C. and −50° C.; patterning the ACL hardmask by exposing the substrate to the halogen-free and sulfur-free plasma in the plasma processing chamber, while maintaining the temperature of the substrate, to the plasma; and forming a HAR feature in the a dielectric layer by etching the dielectric layer using the patterned ACL hardmask as an etch mask, the HAR feature having an aspect ratio of at least 20:1.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
This application relates to fabrication of semiconductor devices, for example, integrated circuits comprising semiconductor devices, and more particularly to high capacity three-dimensional (3D) memory devices, such as a 3D-NAND (or vertical-NAND), 3D-NOR, or dynamic random access memory (DRAM) device. The fabrication of such devices may generally require forming conformal, high aspect ratio (HAR) features (e.g., a contact hole) of a circuit element. Features with aspect ratio (ratio of height of the feature to the width of the feature) higher than 50:1 are generally considered to be high aspect ratio features, and in some cases fabricating a higher aspect ratio such as 100:1 may be desired for advanced 3D semiconductor devices. In such applications, HAR features may be formed in a dielectric layer (e.g., silicon oxide, silicon nitride, or oxide/nitride layer stack) by a highly anisotropic plasma etch process with high fidelity. To enable ideal etch performance for HAR features, an etch mask, for example, amorphous carbon layer (ACL), must with a HAR also be prepared prior to etching the dielectric layer. This etch process for the etch mask (e.g., ACL) may be based on O2-sulfur chemistry to achieve highly vertical etch profile, high etch rate with minimal irregularities (e.g., contact edge roughness, line edge roughness, and/or line width roughness). However, the use of sulfur in the etch process, although helpful in passivating sidewalls to minimize lateral etching, can cause acidic contamination during the process. Therefore, a new etch method that does not require sulfur may be desired for patterning an etch mask with high aspect ratio (HAR). Embodiments of the present application disclose methods of fabricating HAR features by a plasma etch process based on a combination of H2O-based sidewall passivation and low-temperature plasma etching conditions.
In the following, an exemplary plasma etch process to form a high aspect ratio (HAR) feature is described in accordance with various embodiments referring to
In one or more embodiments, the substrate 100 may be a silicon wafer, or a silicon-on-insulator (SOI) wafer. In certain embodiments, the substrate 100 may comprise a silicon germanium wafer, silicon carbide wafer, gallium arsenide wafer, gallium nitride wafer and other compound semiconductors. In other embodiments, the substrate comprises heterogeneous layers such as silicon germanium on silicon, gallium nitride on silicon, silicon carbon on silicon, as well layers of silicon on a silicon or SOI substrate.
In various embodiments, the substrate 100 is a part of, or include, a semiconductor device, and may have undergone a number of steps of processing following, for example, a conventional process. For example, the semiconductor structure may comprise a substrate 100 in which various device regions are formed. At this stage, the substrate 100 may include isolation regions such as shallow trench isolation (STI) regions as well as other regions formed therein. Accordingly, the substrate 100 is used to collectively refer to any structures formed therein.
The underlying layer 110 may be formed over the substrate 100. In various embodiments, the underlying layer 110 is a target layer that is to be patterned by a subsequent plasma etch process after patterning the material layer 120. In certain embodiments, the feature being etched into the underlying layer 110 may be a contact hole, slit, or other suitable structures comprising a recess. In various embodiments, the underlying layer 110 may comprise a dielectric material. In certain embodiments, the underlying layer 110 may be a silicon oxide layer. In alternate embodiments, the underlying layer 110 may comprise silicon nitride, silicon oxynitride, or an O/N/O/N layer stack (stacked layers of oxide and nitride). The underlying layer 110 may be deposited using an appropriate technique such as vapor deposition including chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), as well as other plasma processes such as plasma enhanced CVD (PECVD) and other processes. In one embodiment, the underlying layer 110 has a thickness between 1 μm and 10 μm.
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Fabricating the HAR feature in the material layer 120 may be performed by a plasma etch process based on O2 etch chemistry. In various embodiments, an oxygen-containing gas such as dioxygen (O2) may be used as a primary etch gas. In addition, a hydrogen-containing gas may be included in a process gas such that, under a plasma condition, water (H2O) vapor may be formed in a plasma processing chamber. The inventors of this application identified that the water molecules formed may be adsorbed on surface at a sufficiently low temperature and advantageously provide sidewall passivation during the plasma etch process to form the HAR feature. In various embodiments, to enable the sidewall passivation with H2O, low-temperature conditions (e.g., <−50° C.) may be used. In various embodiments, the hydrogen-containing gas may comprise dihydrogen (H2), a hydrocarbon (e.g., CH4), or hydrogen peroxide (H2O2). In certain embodiments, other gases such as a noble gas and/or a balancing agent may also be added.
The addition of the hydrogen-containing gas in the process gas may also benefit the etch rate, which may in turn enable a shorter process time compared to conventional HAR etch methods. Although not wishing to be limited by any theory, the addition of the hydrogen-containing gas may advantageously enhance the dissociation of O2 in the plasma and increase the number of reactive species such as oxygen radicals. In addition, the formation of the physisorbed H2O at the etch front may also serve as an etchant layer to assist in reactive ion etching, specifically by releasing atomic O and H upon ion bombardment, leading to etch by-product formation.
Conventional methods of etching carbon materials such as amorphous carbon layer (ACL) may use O2 and sulfur, where sulfur is added for sidewall passivation. Sulfur, however, may cause acidic contamination. With a cleaner alternative of H2O-based passivation, the methods described in this disclosure may advantageously eliminate the need of sulfur while maintaining or improving the etch rate. Accordingly, in various embodiments, the plasma used in the plasma etch process may be a sulfur-free plasma. Similarly, the plasma may be a halogen-free plasma in certain embodiments. Avoiding halogen for the methods of etching carbon materials such as ACL may be particularly advantageous for fabricating HAR structures, for example, for 3D-NAND devices. This is because such a fabrication process typically involves (1) ACL patterning, followed by (2) a dielectric etch using the patterned ACL as an etch mask, and halogen-free etch chemistry in the ACL patterning can provide better etch selectivity to the etch mask for ACL patterning (e.g., the patterned mask layer 130 in
In
In various embodiments, process parameters may be selected to optimize the characteristics of the high aspect ratio (HAR) feature considering various factors comprising etch rate, selectivity to the etch mask (e.g., the patterned mask layer 130), sidewall passivation in the HAR feature, and good critical dimension uniformity (CDU) among others. The process parameters may comprise gas selection, gas flow rates, pressure, temperature, process time, and plasma conditions such as source power, bias power, RF pulsing conditions.
In certain embodiments, a ratio of a flow rate of the oxygen-containing gas (e.g., O2) to a flow rate of the hydrogen-containing gas (e.g., H2) may be between 100:1 and 1:1. In one or more embodiments, the ratio of the flow rate may be between 20:1 and 10:1. In various embodiments, the gas composition and their flow rates may be selected to obtain an oxygen-rich plasma for the plasma etch process, which can be generally used for etching carbon materials such as ACL. In the oxygen-rich plasma, reactive species are predominantly oxygen-containing species, where the amount of oxygen-absent species are not greater than that of oxygen-containing species. In certain embodiments, the plasma may be an oxygen-rich, halogen-free plasma.
In various embodiments, the substrate temperature may be kept at a low temperature such that sufficient H2O adsorption may be enabled. Accordingly, a low temperature in this disclosure may refer to a temperature of −50° C. or lower. In certain embodiments, the substrate temperature may be kept between −150° C. and −50° C., or between −120° C. and −70° C. in another embodiment, during the plasma etch process. A total pressure in the plasma processing chamber may be kept between 0.1 mTorr and 500 mTorr. In one embodiment, the process conditions may comprise the following: an etch time of 60 seconds, a pressure of 15 mTorr, a source power of 2500 W, a bias power of 570 W, an O2 flow rate of 360 sccm, a H2 flow rate of 40 sccm, and a substrate temperature of −50° C.
The recesses 135 may be in any shapes and structures, including a contact hole, slit, or other suitable structures comprising a recess useful for semiconductor device fabrication. In various embodiments, the features defined by the recesses 135 has a critical dimension (CD) of 200 nm or less. In certain embodiments, the CD may be between 50 nm and 200 nm. For example, the feature may comprise a slit with a CD of about 150 nm. In alternate embodiments, the recesses 135 may comprise a hole that has a top opening with a diameter of 80 nm or less.
The HAR feature in the material layer 120 prepared in
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In certain embodiments, the subsequent plasma etch process may be advantageously performed as a continuous process with a process time of 60 min or less to form a high aspect ratio (HAR) feature in the underlying layer 110 with an aspect ratio of 50:1 or higher. Further processing may follow conventional processing, for example, by removing any remaining portion of the material layer 120.
In various embodiments, the plasma etch process for the material layer 120 (
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The inventors of this disclosure identified an effective temperature range for H2O adsorption on ACL (
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The plasma system 600 is by example only. In various alternative embodiments, the plasma system 600 may be configured to sustain inductively coupled plasma (ICP) with RF source power coupled to a planar coil over a top dielectric cover, or capacitively coupled plasma (CCP) sustained using a disc-shaped top electrode in the plasma processing chamber 650. Alternately, other suitable configurations such as electron cyclotron resonance (ECR) plasma sources and/or a helical resonator may be used. The RF-bias power source 634 may be used to supply continuous wave (CW) or pulsed RF power to sustain the plasma. Gas inlets and outlets may be coupled to sidewalls of the plasma processing chamber, and pulsed RF power sources and pulsed DC power sources may also be used in some embodiments. In various embodiments, the RF power, chamber pressure, substrate temperature, gas flow rates and other plasma process parameters may be selected in accordance with the respective process recipe.
As described above, various embodiments may use a combination of O2 and a hydrogen-containing gas (e.g., H2) for fabricating a high aspect ratio (HAR) feature in, for example, amorphous carbon layer (ACL). The addition of the hydrogen-containing gas may advantageously provide H2O-based sidewall passivation and also improve the etch rate. The inventors of this application experimentally demonstrated that the addition of H2 to the process gas increases the amount of dissociated oxygen atom species in the plasma, which may lead to the higher etch rate. The experiments were performed to characterize the plasma composition at −50° C. for six gas flow conditions: 400 sccm O2; 350 sccm O2 and 50 sccm H2; 300 sccm O2 and 100 sccm H2; 250 sccm O2 and 150 sccm H2; 200 sccm O2 and 200 sccm H2; 160 sccm O2 and 240 sccm H2. An optical emission spectroscopy (OES) analysis revealed that the emission intensity assigned to oxygen at 700.2 nm was highest with 350 sccm O2 and 50 sccm H2 (O2:H2 ratio=7:1), followed by 300 sccm O2 and 100 sccm H2 (O2:H2 ratio=3:1). These two gas flow conditions exhibited higher emission intensity than the baseline condition of 400 sccm O2 (without H2) despite the decreased O2 flow rate. These results suggest the dissociation of O2 was enhanced by the addition of H2 with a critical range of oxygen-hydrogen ratio greater than 3:1 in one example. It should be noted, however, that in other embodiments, a different oxygen-hydrogen ratio may be used depending on various process parameters. In further experiments, unexpectedly, about 40% enhancement in etch rate was observed at −50° C. with a gas flow condition of 360 sccm O2 and 40 sccm H2 compared to 400 sccm O2 alone. On the other hand, no substantial improvement in bowing was observed. A better sidewall passivation may be achieved by further lowering the substrate temperature even further to increase the surface coverage with condensed H2O. The inventors of this application identified that the particular combination of O2 and a hydrogen-containing gas (e.g., H2) without halogen-based etch chemistry as well as their particular flow rate ratio and process temperature can be critical in sufficiently providing the effect of H2O adsorption during etching carbon materials such as ACL.
Example embodiments of the invention are summarized here. Other embodiments can also be understood from the entirety of the specification as well as the claims filed herein.
Example 1. A method of processing a substrate that includes: flowing dioxygen (O2) and a hydrogen-containing gas into a plasma processing chamber that is configured to hold the substrate, the substrate including an organic layer and a patterned etch mask, the hydrogen-containing gas including dihydrogen (H2), a hydrocarbon, or hydrogen peroxide (H2O2); generating an oxygen-rich plasma while flowing the gases; maintaining a temperature of the substrate in the plasma processing chamber between −150° C. and −50° C.; and while maintaining the temperature, exposing the substrate to the oxygen-rich plasma to form a recess in the organic layer.
Example 2. The method of example 1, where the organic layer includes amorphous carbon layer (ACL).
Example 3. The method of examples 1 or 2, where the temperature of the substrate is between −120° C. and −70° C.
Example 4. The method of one of examples 1 to 3, where a ratio of a flow rate of O2 to a flow rate of the hydrogen-containing gas is between 100:1 and 1:1.
Example 5. The method of one of examples 1 to 4, further including flowing a noble gas into the plasma processing chamber.
Example 6. The method of one of examples 1 to 5, where the oxygen-rich plasma is a halogen-free plasma.
Example 7. The method of one of examples 1 to 6, where the oxygen-rich plasma is a sulfur-free plasma.
Example 8. The method of one of examples 1 to 7, where the oxygen-rich plasma is an inductively coupled plasma (ICP).
Example 9. The method of one of examples 1 to 8, where portions of O2 and the hydrogen-containing gas react in the plasma processing chamber to form water (H2O) vapor that condenses on the substrate while forming the recess.
Example 10. The method of one of examples 1 to 9, where the substrate further includes a dielectric layer below the organic layer, further including, performing an anisotropic etch process to extend the recess into the dielectric layer.
Example 11. A method of processing a substrate that includes: cooling the substrate in a plasma processing chamber to a temperature of −50° C. or lower, the substrate including a dielectric layer, an amorphous carbon layer (ACL) and a patterned etch mask; flowing dioxygen (O2) and a hydrogen-containing gas into a plasma processing chamber; generating a plasma in the plasma processing chamber, where portions of dioxygen and the hydrogen-containing gas react under the plasma to form water (H2O) molecules; and exposing the substrate to the plasma to form a recess in the organic layer, the recess having an aspect ratio of at least 20:1, the substrate being kept at around the temperature.
Example 12. The method of example 11, where a ratio of a flow rate of O2 to a flow rate of the hydrogen-containing gas is between 100:1 and 1:1.
Example 13. The method of one of examples 11 or 12, where the temperature is between −120° C. and −70° C.
Example 14. The method of one of examples 11 to 13, where a total pressure in the plasma processing chamber is kept between 0.1 mTorr and 500 mTorr.
Example 15. The method of one of examples 11 to 14, where the recess defines a feature having a critical dimension between 50 nm and 200 nm.
Example 16. The method of one of examples 11 to 15, where the dielectric layer includes silicon oxide or silicon nitride.
Example 17. A method of forming a high-aspect ratio (HAR) feature on a substrate in a plasma processing chamber that includes: depositing an amorphous carbon layer (ACL) hardmask over a dielectric layer including silicon oxide formed over the substrate; depositing and pattern an etch mask layer over the ACL hardmask; flowing dioxygen(O2), a hydrogen-containing gas, and a noble gas to a plasma processing chamber; generating a halogen-free and sulfur-free plasma in the plasma processing chamber while flowing O2, the hydrogen-containing gas, and the noble gas, where portions of O2 and the hydrogen-containing gas react under the plasma to form water (H2O) vapor; maintaining a temperature of the substrate between −150° C. and −50° C.; patterning the ACL hardmask by exposing the substrate to the halogen-free and sulfur-free plasma in the plasma processing chamber, while maintaining the temperature of the substrate, to the plasma; and forming a HAR feature in the a dielectric layer by etching the dielectric layer using the patterned ACL hardmask as an etch mask, the HAR feature having an aspect ratio of at least 20:1.
Example 18. The method of example 17, where a ratio of a flow rate of O2 to a flow rate of the hydrogen-containing gas is between 100:1 and 1:1.
Example 19. The method of one of examples 17 or 18, where a passivation layer is formed on sidewalls of the ACL hardmask while patterning the ACL hardmask, the passivation layer including condensed H2O.
Example 20. The method of one of examples 17 to 19, where the aspect ratio of the HAR feature is at least 20:1.
While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.