Patent Application
20190362983
Embodiments of the present invention relate, in general, to etching of substrates and other materials. In particular, embodiments of the present invention relate to etching silicon oxide and silicon nitride and related materials.
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density. The demands for faster circuits with greater circuit densities impose corresponding demands on the materials used to fabricate such integrated circuits.
The production of silicon integrated circuits (IC) has placed difficult demands on fabrication steps to increase the number of devices while decreasing the minimum feature sizes on a chip. These demands have extended to fabrication steps including depositing layers of different materials onto difficult topologies and etching further features within those layers. Such a design that includes high aspect ratio features forms those features in a stack of alternating oxide layers and nitride layers to produce a desired structure. Etching a stack of alternating oxide layers and nitride layers (“ONON film stack”) effectively and efficiently with the appropriate critical dimensions and aspect ratios is a challenging task. Etching alternating oxide layers and nitride layers with high aspect ratios has presented difficult challenges, and is inefficient and costly using conventional gas mixtures, especially during batch processing.
Conventional processes to etch oxide-nitride (ONON) stacks involve numerous complex etching operations with various (7+) gases used in each step, these gases may or may not overlap among and between etching processes and the processing time for etching a batch can be over 1100 seconds. These multiple etching operations are employed to avoid undesirable results of etching during high-volume processes (HVP) e.g., batch processing of substrates. These undesirable results include mask (hole) entrance clogging, bowing and/or bending of the hole profile, striation, or other challenges that negatively impact the critical dimensions (CD) that are to be formed during etching. In an embodiment, the etching process is intended to produce a plurality of features such as holes and trenches through a layer or layers to expose a substrate. T
The plurality of features are of varying geometries and types and are each associated with a plurality of CD that include an average width throughout, feature top width, feature bottom width, sidewall profile, bottom profile, as well as other dimensions such as hole spacing. Trenches are narrow in one direction (depth measured perpendicular to the substrate) but wide in another direction (width measured parallel to the substrate). This is in contrast to holes which have a depth that exceeds a width by 20:1 or more for high aspect ratio features. Since trenches have a wide opening along one dimension, radicals that will etch nitrides and/or oxides will naturally propagate to the etch front. Accordingly, even for trenches having a high aspect ratio of above 20:1, the trenches are formed by both ions and radicals. The ions have directionality, while the radicals do not have directionality. In one embodiment, a majority of the etch species that etch trenches are ions, and a minority of the etch species are radicals. However, in some examples, the addition of the radicals changes the etch rate of the trenches as compared to the etch rate of holes.
The next generation in memory technology offers greater data storage in a smaller physical space (footprint). Creating next generation technology in memory applications enables greater data storage in a smaller physical structure, these smaller structures presents some fabrication issues. One of these challenges presented is etching alternating oxide layers and nitride layers (“ONON film stack”) in an efficient and cost effective process to produce high aspect ratio (HAR) features with a depth:width ratio of 20:1 or greater. In some embodiments, a target HAR is a depth:width from about 40:1 to about 100:1. Alternating oxide layers and nitride layers are included in the design of devices ultimately used in creating a device's memory gates. The current fabrication processes for etching multiple alternating oxide layers and nitride layers to produce high aspect ratio features typically use complex recipes, multiple process operations, and a multitude of conventional etch gases. This processing leads to high processing costs, decreases process efficiency, and further makes it difficult to create specialized high aspect ratio features with intricate geometries.
Thus, there remains a need for improved systems and methods for etching ONON film stacks.
The present disclosure generally relates to etching target materials including oxide-nitride layer stacks. In one example, a method of etching a substrate includes: providing an ionizable gas mixture to a processing chamber of an etch reactor, wherein the ionizable gas mixture includes C3H2F4 and C3F6; forming a plasma from the ionizable gas mixture. In some examples, forming the plasma includes producing a plurality of ions from ionizable gas mixture. The method further includes etching a stack of alternating oxide and nitride layers formed on a substrate using the plurality of ions to form a plurality of features through the stack. Further in this example, an aspect ratio of each feature of the plurality of features is from 20:1 to 100:1.
In another example, a method of etching an oxide-nitride stack includes: disposing, in a processing chamber, a gas mixture comprising: C3H2F4, a companion gas, and O2. The C3H2F4 includes a volume % of the gas mixture from 15 vol. % to 45 vol. %, the companion gas includes a volume % of the gas mixture from 15 vol. % to 50 vol. %, and the O2 includes a volume % of the gas mixture from 10 vol. % to 40 vol. %. Subsequently, a substrate is positioned in the processing chamber, the substrate includes a plurality of alternating oxide and nitride layers. The example method further includes etching, in response to exposure to the gas mixture, a plurality of features in the plurality of alternating oxide and nitride layers.
In another example, a method includes: providing an ionizable gas mixture to a processing chamber of an etch reactor, wherein the ionizable gas mixture includes C3H2F4 and a companion gas; forming a plasma from the ionizable gas mixture; and etching, via the plasma, a stack. The stack includes a plurality of alternating oxide and nitride layers to form a plurality of holes through the stack to selectively expose portions of the substrate.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
The present disclosure is about etching oxide-nitride stacks (ONON), in particular SixNy and SixOy stacks. Reactive ion etching (RIE) of ONON stacks can be done with various gas combinations, including CH2F2 in combination with C4F6 and/or C4F8. However, this combination can present challenges with etch selectivity control. For example, etching methods are provided for etching high aspect ratio features into a film stack of alternating oxide layers and nitride layers. The etching of a film stack having alternating layers of oxides and nitrides is performed in a single etch operation. This is in contrast to conventional etching methods that use seven or more gases across a plurality of operations that takes more than 1100 seconds to complete. In an embodiment of the present disclosure, an ionizable gas mixture containing C3H2F4 and a companion gas, is ionized using the application of RF power to a processing chamber to form a plasma suitable for etching high aspect ratio (an average of depth:width of 20:1-100:1 or more) features into a stack of alternating oxide layers and nitride layers. The companion gas is according to a formula CxFy. In one example, each of x and y in the formula CxFy are at least 1. Other gases, for example hydrogen-free fluorocarbons are added to the gas mixture to improve or control oxide etch rates and/or nitride etch rates. Additionally, in various embodiments, gases are introduced for polymer generation control or as a carrier gas. In an embodiment, a thickness of an ONON film stack etched according to methods of the present disclosure is from about 90 to about 130 pairs (180-260 oxide and nitride layers total), and having a total thickness of 4000 to 8500 nm.
Embodiments of the present invention provide methods to create a plurality of features in a stack of alternating oxide layers and nitride layers using C3H2F4 and a companion gas. The companion gas is a fluorinated gas such as CxFy. Thus, in one example of an etchant gas mixture, the mixture includes C3F6. In another example, O2 is used along with the C3H2F4and the companion gas, so the etchant gas mixture includes C3H2F4 and C3F6 and O2 In an embodiment, the C3H2F4 gas is ionized along with the companion gas in the presence of O2, producing plasma with desirable pluralities of ions, radicals, and various molecules. The plasma can be formed by applying power to the processing chamber, the power applied can be from 400 kHz to 121 MHz and, in some examples, the power applied to the processing chamber is 2 MHz. These pluralities of ions and various molecules selectively etch the oxide and nitride layers on a substrate, creating consistently-sized, “clean” (e.g., meeting the critical dimensions (CD)) features some of which include high aspect ratio features. In an embodiment, when the oxide layers are etched at the same rate as the nitride layers, a plurality of desired features are formed with CDs such that a sidewall profile is perpendicular to a substrate on which the ONON film stack is disposed. As discussed herein, “etch selectivity” is a ratio of etch rates between two materials, and an “etch rate” of a material, which can differ depending upon the feature being formed by the etching, is the rate at which material is removed during etching and is measured as depth/time, such as Angstroms/second or nm/minute. Thus, in one example, if a first material has an etch rate of 10 nm/min and a second material has an etch rate of 20 nm/min, the etch selectivity would be 10:20 or 1:2 under those conditions. Due to the alternating oxide and nitride layers on the substrate, both ions that etch nitride layers and ions that etch oxide layers should be propelled to the etch front. By managing the ratio of the etch gas species that are provided, as discussed herein, the ratio of ions that will etch oxides (e.g., ions containing F) to the ratio of ions that will etch nitride (e.g., ions containing H) is controlled.
In an embodiment, the processing chamber 100 includes a chamber body 102 and a lid 104 which enclose an interior volume 106. The chamber body 102 is typically fabricated from aluminum, stainless steel, quartz, or other suitable material. The chamber body 102 generally includes sidewalls 108 and a bottom 110. A substrate support pedestal access port (not shown) is generally defined in a sidewall 108 and selectively sealed by a slit valve to facilitate entry and egress of a substrate 101 from the processing chamber 100. In various embodiments discussed herein, a substrate 101 has an ONON film stack (not shown) formed thereon. An exhaust port 126 is defined in the chamber body 102 and couples the interior volume 106 to a pump system 128. The pump system 128 generally includes one or more pumps and a throttle valve utilized to evacuate and regulate the pressure of the interior volume 106 of the processing chamber 100. In one embodiment, the pump system 128 maintains the pressure inside the interior volume 106 at operating pressures typically between about 10 mT to about 500 mT.
In an embodiment, the lid 104 is sealingly supported on the sidewall 108 of the chamber body 102. The lid 104 may be opened to allow access to the interior volume 106 of the processing chamber 100 for maintenance. The lid 104 includes a window 142 that facilitates optical process monitoring. In one embodiment, the window 142 is comprised of quartz or other suitable material that is transmissive to a signal utilized by an optical monitoring system 140 mounted outside the processing chamber 100. The optical monitoring system 140 is positioned to view at least one of the interior volume 106 of the chamber body 102 and/or the substrate 101 positioned on a substrate support pedestal assembly 148 through the window 142. The optical monitoring system 140 is coupled to the lid 104 and facilitates an integrated deposition process that uses optical metrology to provide information that enables process adjustment to compensate for incoming substrate pattern feature inconsistencies (such as critical dimension (CD) variation and the like), provide process state monitoring (such as plasma monitoring, temperature monitoring, and the like) as needed.
A gas panel 158 is coupled to the processing chamber 100 to provide process and/or cleaning gases to the interior volume 106, including the mixture of etchant gases discussed herein, as well as carrier gases, inert gases, and other process gases employed in substrate of substrate batch processing. In the embodiment depicted in
Further in an embodiment of
A remote plasma source 177 is optionally coupled to the inlet ports 132′ and 132″ to facilitate providing a dissociated cleaning gas into the interior volume 106. A RF source power 143 is coupled through a matching network 141 to the showerhead assembly 130. The RF source power 143 typically is capable of producing up to about 4000 Watt tunable frequency in a range from about 50 kHz to about 200 MHz. During an etch process in the processing chamber, an RF source power from 2500 W to 4500 W and an RF bias power from 10000 W to 20000 W may be applied to the processing chamber 100 to form and maintain a plasma. The showerhead assembly 130 additionally includes a region 138 that is transmissive to an optical metrology signal. The optically transmissive region 138 is suitable for allowing the optical monitoring system 140 to view the interior volume 106 and/or the substrate 101 positioned on the substrate support pedestal assembly 148. In one embodiment, the optically transmissive region 138 includes a window 142 to prevent gas leakage through the optically transmissive region 138. The window 142 is a sapphire plate, quartz plate or other suitable material. In an embodiment, the window 142 is formed in the lid 104.
In one embodiment, the showerhead assembly 130 is configured with a plurality of zones. Each zone of the plurality of zones can be controlled separately to allow for separate control of gas flowing into the interior volume 106 of the processing chamber 100. In the embodiment
The substrate support pedestal assembly 148 holds the substrate 101 during processing. The substrate support pedestal assembly 148 generally includes a plurality of lift pins (not shown) positioned therethrough. The plurality of lift pins are configured to lift the substrate 101 from the substrate support pedestal assembly 148 and facilitate exchange of the substrate 101 with a robot (not shown). The robot is used to transfer the substrate 101 into and out of the processing chamber 100. An inner liner 118 closely circumscribes the periphery of the substrate support pedestal assembly 148. A second fluid source 124 may be employed in cooling the liner 118. In one embodiment, the substrate support pedestal assembly 148 includes a mounting plate 162, a base 164 and an electrostatic chuck 166. The mounting plate 162 is coupled to the bottom 110 of the chamber body 102 includes passages for routing utilities, such as fluids, power lines and sensor leads, among others, to the base 164 and the electrostatic chuck 166. The electrostatic chuck 166 includes at least one clamping electrode 180 for retaining the substrate 101 below showerhead assembly 130. In an embodiment, the electrostatic chuck 166 is driven by a chucking power source 182 to develop an electrostatic force that holds the substrate 101 to the chuck surface, as is conventionally known. Alternatively, the substrate 101 is retained to the substrate support pedestal assembly 148 by clamping, vacuum, or gravity.
At least one of the base 164 or electrostatic chuck 166 includes at least one optional embedded heater 176, at least one optional embedded isolator 174 and a plurality of conduits 168, 170 to control the lateral temperature profile of the substrate support pedestal assembly 148. The conduits 168, 170 are fluidly coupled to a fluid source 172 that circulates a temperature regulating fluid therethrough. The heater 176 is regulated by a power source 178. The conduits 168, 170 and the heater 176 are utilized to control the temperature of the base 164. The temperature control enables the heating and/or cooling of the electrostatic chuck 166 and ultimately, the temperature profile of the substrate 101 positioned thereon. The temperature of the electrostatic chuck 166 and the base 164 is monitored using a plurality of temperature sensors 190, 192. In an embodiment, the electrostatic chuck 166 further includes a plurality of gas passages (not shown), such as grooves, that are formed in a substrate support pedestal supporting surface of the chuck 166 and fluidly coupled to a source of a heat transfer (or backside) gas, such as He. In operation, the backside gas is provided at controlled pressure into the gas passages to enhance the heat transfer between the electrostatic chuck 166 and the substrate 101. In alternate embodiments, the plurality of heaters 176 are positioned not only in the base 164 or electrostatic chuck 166 but are also positioned in the showerhead assembly 130 and the chamber body 102. The substrate 101 may be held at a predetermined temperature during etching from 0° C.-80° C. via the heaters 176 in the base 164 or electrostatic chuck 166.
In one embodiment, the substrate support pedestal assembly 148 is configured as a cathode and includes an electrode 180 that is coupled to a plurality of RF power bias sources 184, 186. The RF bias power sources 184, 186 are coupled between two electrodes, the electrode 180 that is disposed in the substrate support pedestal assembly 148 and another electrode, such as the showerhead assembly 130 or ceiling (lid 104) of the chamber body 102. The RF bias power excites and sustains a plasma discharge formed from the gases introduced to the processing region of the chamber body 102.
In the embodiment depicted in
In one example mode of operation, the substrate 101 is positioned on the substrate support pedestal assembly 148 in the processing chamber 100. A process gas mixture is introduced into the chamber body 102 through the showerhead assembly 130 from the gas panel 158. The vacuum pump system 128 maintains the pressure inside the chamber body 102 while removing by-products of etching. A controller 150 is coupled to the processing chamber 100 to control operation of the processing chamber 100. The controller 150 is configured to control the processing chamber 100 operations including loading and executing gas recipes to be used in pre-processing, feature formation (etching), and post-processing. The controller 150 includes a central processing unit (CPU) 152, a memory 154, and a support circuit 156 utilized to control the process sequence and regulate the gas flows from the gas panel 158. The CPU 152 is configured for use to include a processor sufficient for use in an industrial setting. The software routines can be stored in the memory 154, such as random access memory (RAM), read only memory, floppy, or hard disk drive, or other form of digital storage. The support circuit 156 is conventionally coupled to the CPU 152 and includes cache, clock circuits, input/output systems, power supplies, and the like. Bi-directional communications between the controller 150 and the various components of the processing chamber 100 are handled through numerous signal cables such that the etching programs and other processing programs in the methods discussed herein are executed. The etching and other processing programs discussed herein can be stored on the memory 154 which can also be described as a non-transitory computer-readable medium.
At operation 206, a plurality of gases including ionizable gases and one of O2 are introduced into the processing chamber. One or more inert gases may also be employed at operation 206. In one example, a H-containing gas and a F-containing gas are introduced at operation 206 in order to etch both the oxide and nitride layers of the ONON film stack. Embodiments of the method 200 simplify and improve control of CDs as compared to conventional etch processes by introducing new gas mixtures and/or etch chemistries that use C3H2F4 a companion gas CxFy, in one example C3F6, and a carrier gas O2. The inert gases discussed herein may be employed in processing in various quantities depending upon the embodiment. The gases discussed herein may be employed at a flow rate of 200 sccm to 1000 sccm. In one example, which can be combined with examples herein, the C3H2F4 may be introduced at a flow rate of 100 sccm. In another example, which can be combined with other examples herein, the C3F6 is introduced at a rate of 150 sccm. In still another example, which can be combined with other examples herein the carrier gas is introduced at a rate of 100 sccm. One or more inert gases such as Ar, Kr or others may be introduced at a rate of 200 sccm depending upon the embodiment.
In an embodiment, the gases introduced at operation 206 are introduced via a gas panel such as the gas panel 158 in
At operation 208, the gases introduced at operation 206 are ionized in order to etch a pattern (a plurality of features) in at least one target layer of the film stack at operation 210. The ionization of the gases at operation 208 is enabled by using the RF source and bias power, such as 3500 W source power and 20000 W bias power. The substrate temperature during operation 208 may be from about 50˜100° C. This target layer is the ONON film stack which may have a thickness within a range from about 4000 nm thick to about 8500 nm thick or greater. In some examples, an etch rate (as exhibited during operation 210) of oxide layers in a target layer is within 10% of an etch rate of nitride layers in the target layer. In other examples, the relative etch rates may be within 5%, 2%, 1%, or less than 1%. The ionization at operation 206 may be performed in the processing chamber 100 discussed in
As discussed herein, a volume percentage of two or more components in a solution or a mixture is a measurement of a concentration of each of the two or more components in the solution or mixture. Accordingly, a volume percentage ratio is a ratio of the respective concentrations of each of the two or more components in the overall mixture. The gases ionized at operation 208 may be present in the etching chamber at a volume percentage ratio of the (C3H2F4+the companion gas) to carrier gas from 80:20 to 30:70. The volume percentage ratio of the carrier gas to the C3H2F4 in the etching chamber is from 0:100 to 90:10. In other examples, the volume percentage ratio of the carrier gas to the C3H2F4 in the etching chamber is from 15:85 to 25:75. In one example at operation 206, the gases introduced are C3H2F4, a companion gas, and O2. The C3H2F4 includes a volume percentage of the etchant gas mixture from 15 vol. % to 45 vol. %, the companion gas includes a volume % of the etchant gas mixture from 15 vol. % to 50 vol. %, and the O2 includes a volume % of the etchant gas mixture from 10 vol. % to 40 vol. %. Thus, a ratio of the ionizable gas mixture: O2 is from 90:10 to 60:40.
Further in
In an embodiment, the film stack 300 can be etched through the pattern mask 380 to create features having approximately the shape (width and/or geometry) of the openings in the pattern mask 380, as discussed in detail in
As discussed above, the etchants used may be employed in various volume ratios. In one example, volume percentage ratio of the carrier gas to the C3H2F4 in the etching chamber is from 0:100 to 90:10 or, in other examples, is from 15:85 to 25:75. In some examples, the volume percentage ratio of the carrier gas to the C3H2F4 in the etching chamber is from 10:90 to 40:60, or, in other examples, is from 15:85 to 25:75. The etchant mixture may be further defined by ranges of volume percentages of each gaseous component. In one example at operation 206, the gases introduced are C3H2F4, a companion gas, and O2. The C3H2F4 includes a volume percentage of the etchant from 15 vol. % to 45 vol. %, the companion gas includes a volume % of the etchant from 15 vol. % to 50 vol. %, and the O2 includes a volume % of the etchant from 10 vol. % to 40 vol. %.
In one embodiment, an oxide to nitride etch selectivity is approximately 1:1, meaning that the etch rate of the oxide layers is approximately equal to the etch rate of the nitride layers. Alternatively, the oxide to nitride etch selectivity is adjusted to cause a greater oxide etch rate or a greater nitride etch rate. The oxide to nitride etch selectivity is adjusted based on conditions of the oxide layers and/or nitride layers to be etched. For example, if a stack of alternating oxide layers and nitride layers has thicker nitride layers than oxide layers, then the nitride etch rate is increased in relation to the oxide etch rate. Similarly, if the oxide layer thickness is greater than the nitride layer thickness, then the oxide etch rate is increased relative to the nitride etch rate. In some embodiments the oxide-to-nitride etch selectivity is adjusted between approximately 1:2 and 2:1.
The etch rate for a feature (holes or trenches) may depend on factors such as the type of feature to be etched and a thickness of the stack. In particular, etched features are divided into the categories of trenches and holes. Holes have a horizontal diameter that is much less than a vertical depth of the holes. This creates a very high aspect ratio that is on the order of 20:1 to 100:1 or greater in some embodiments. To etch a hole in oxide and nitride layers on a substrate, a molecule first travels to the etch front at the bottom of the hole. Since radicals are neutral and thus have no charge, radicals are not propelled to the etch front by the electromagnetic field. The primary molecules that travel to the etch front are ions that are accelerated by the electromagnetic field produced by the etch reactor. The provided etch gases are decomposed into additional species, some of which are ions having charge. These ions are accelerated by the field and propelled to the etch front.
Each etched feature 908 has a depth along the same direction as the first axis 918, a bottom width 910 and a top width 912. As shown herein, the depth of each etched feature 908 is such that a portion of the substrate 904 is exposed when the etched feature 908 is formed. In an embodiment, the CDs discussed herein include a sidewall 906 profile, defined herein as an angle of the sidewall 906 of each etched feature 908 relative to the axis 916, as well as a bottom 908A profile of the features 908 which may include a bottom width 910 discussed below and/or a flatness of the bottom 908A. While each of the top 912 and bottom 910 widths are shown in
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims priority to U.S. Provisional Patent Application 62/675,666, titled “Systems and Methods for Etching Oxide Nitride Stacks,” filed May 23, 2018, and incorporated by reference in its entirety herein.
| Number | Date | Country | |
|---|---|---|---|
| 62675666 | May 2018 | US |
