Method for word line separation in 3D-NAND devices

Abstract

Methods of word line separation in semiconductor devices (e.g., 3D-NAND) are described. A metal film is deposited in the word lines and on the surface of a stack of spaced apart oxide layers. The metal film is removed by high temperature oxidation and etching of the oxide, or by low temperature atomic layer etching that oxidizes the surface in a single layer fashion and etches the oxide. After the metal cap layer is removed, the word lines are filled with the metal film.

Description

[0001] This application is a divisional application of application number 201880033951.5, filed on May 22, 2018, entitled "Method for word line separation in 3D-NAND device". Technical Field

[0002] The embodiments of this disclosure generally relate to methods for filling gaps or features in semiconductor devices. More specifically, the embodiments of this disclosure relate to methods for gap filling using tungsten in three-dimensional semiconductor devices. Background Technology

[0003] The semiconductor and electronics manufacturing industries continue to strive for greater productivity while improving the uniformity of layers deposited on substrates with larger surface areas. These same factors, combined with new materials, also provide higher circuit integration per substrate area. As circuit integration increases, the demand for greater uniformity in layer thickness and process control also rises. Consequently, various techniques have been developed to deposit layers on substrates cost-effectively while maintaining control over layer properties.

[0004] V-NAND, or 3D-NAND (three-dimensional NAND gate) structures are used in flash memory applications. V-NAND devices are vertically stacked NAND structures with a large number of cells arranged in blocks. Gate-last word line formation is currently the mainstream process flow in 3D-NAND manufacturing. Before word line formation, the substrate is a layered oxide stack supported by memory strings. Tungsten is used to fill the gap spaces using CVD or ALD. The top / sidewalls of the memory stack are also coated with tungsten. Tungsten is removed from the top / sidewalls of the stack by an etching process (e.g., reactive ion etching (RIE) or radical-based etching), so that the tungsten exists only in the gap spaces and each tungsten filler is completely separated from the others. However, due to the loading effect of the etching process, separation etching often results in different word line recesses at the top and bottom of the stack. This difference becomes more pronounced as the number of oxide stack layers increases.

[0005] Therefore, there is a need in the art for a method for word line separation in three-dimensional structured devices. Summary of the Invention

[0006] One or more embodiments of this disclosure relate to a method of processing a substrate. A substrate is provided having a stack of spaced oxide layers with gaps between them. The stack has a top and sides, and each gap can form a word line. Metal is deposited on the stack such that the metal fills the gaps and covers the top and sides of the stack with a metal overburden thickness. The metal is oxidized to a depth approximately the thickness of the overburden to form a metal oxide on the top and sides of the stack, leaving the metal in the gaps as word lines. The metal oxide is etched from the top and sides of the stack, leaving the metal in the word lines.

[0007] Further embodiments of this disclosure relate to a method of processing a substrate. A substrate is provided having a stack of spaced oxide layers with gaps between them. The stack has a top and sides, and each gap can form a word line. Metal is deposited on the stack such that the metal fills the gaps and covers the top and sides of the stack with a metal overlay thickness. The surface of the metal is repeatedly oxidized to form a metal oxide and etched from the stack until the metal overlay is removed, leaving the metal in the gaps as word lines.

[0008] Further embodiments of this disclosure relate to a method of processing a substrate. A substrate is provided having a stack of spaced oxide layers with gaps between them. The stack has a top and sides, and each gap can form a word line. Optionally, a barrier layer is formed on the spaced oxide layers. The barrier layer comprises TiN, and the thickness of the TiN is approximately... to approximately Within the range of [specific parameters]. Tungsten is deposited on the stack such that it fills the gaps and covers the top and sides of the stack with a tungsten capping layer of thickness. The surface of the tungsten is repeatedly oxidized to form tungsten oxide and the surface of the tungsten oxide is etched to remove the tungsten capping layer. The tungsten in the gaps is left substantially flush with the sides of the stack. The oxidation of the surface includes exposure to O2, and the etching of the tungsten oxide includes exposure to one or more of WCl5 or WCl6. Tungsten deposition, tungsten oxidation, and etching of the tungsten oxide occur at a temperature less than or equal to about 400°C. Attached Figure Description

[0009] To gain a more detailed understanding of the features described above, the present disclosure, as briefly summarized above, can be described in more detail by referring to the embodiments, some of which are illustrated in the accompanying drawings. The drawings show only typical embodiments of the present disclosure and should therefore not be considered limiting, as other equivalent embodiments are permissible.

[0010] Figure 1This illustration shows a stack of oxide layers that will form word lines, according to one or more embodiments of the present disclosure;

[0011] Figure 2 Shown in Figure 1 A metal film formed on a stack of oxide layers;

[0012] Figure 3A and Figure 3B This illustrates a high-temperature oxidation and etching process according to one or more embodiments of the present disclosure; and

[0013] Figures 4A to 4D A low-temperature oxidation and etching process according to one or more embodiments of the present disclosure is shown. Detailed Implementation

[0014] Before describing several exemplary embodiments of this disclosure, it should be understood that this disclosure is not limited to the details of the construction or process steps set forth in the following description. This disclosure can have other embodiments and can be practiced or performed in various ways.

[0015] As used herein, “substrate” refers to any substrate or material surface formed on a substrate, on which a film treatment is performed during a manufacturing process. For example, depending on the application, substrate surfaces on which treatments can be performed include materials such as silicon, silicon oxide, strained silicon, silicon-on-insulator (SOI), carbon-doped silicon oxide, amorphous silicon, doped silicon, germanium, gallium arsenide, glass, sapphire, and any other materials such as metals, metal nitrides, metal alloys, and other conductive materials. Substrates include, but are not limited to, semiconductor wafers. Substrates may be exposed to pretreatment processes such as polishing, etching, reduction, oxidation, hydroxylation, annealing, UV curing, electron beam curing, and / or baking of the substrate surface. In addition to performing film treatments directly on the surface of the substrate itself, any of the film treatment steps disclosed in this disclosure may also be performed on an underlayer formed on the substrate as disclosed in more detail below, and the term “substrate surface” is intended to include such an underlayer as indicated by the context. Thus, for example, where a film / layer or a portion thereof has been deposited onto a substrate surface, the exposed surface of the newly deposited film / layer becomes the substrate surface.

[0016] One or more embodiments of this disclosure advantageously provide a method for depositing a tungsten film in the gaps of a three-dimensional structure. Some embodiments of this disclosure advantageously provide a method for depositing a conformal tungsten oxide film and selectively removing the tungsten oxide. Some embodiments advantageously provide a method for filling the lateral features of a V-NAND with a high-quality tungsten film having a uniform thickness from the top to the bottom of an oxide stack.

[0017] One or more embodiments of this disclosure relate to word line separation methods based on highly conformal metal (e.g., tungsten) oxidation and highly selective metal oxide (e.g., tungsten oxide) removal. These methods may employ high-temperature or low-temperature processes.

[0018] Reference Figure 1 The substrate 10 has a stack 12 of multiple layers. The substrate 10 can be any suitable substrate material and is not limited to the same material as any of the individual layers. For example, in some embodiments, the substrate is an oxide, nitride, or metal layer. The stack 12 has a plurality of oxide layers 14 spaced apart from each other to form gaps 16 between the oxide layers 14, such that each gap forms a word line or a shell for a word line to be formed. The stack 12 has a top 13 and side surfaces 15.

[0019] The stack 12 may have any suitable number of oxide layers 14 or gaps 16. In some embodiments, the stack 12 has about 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 gaps 16 formed, which can be used to form the same number of word lines. The number of gaps 16 is measured on either side of the memory string 11 connecting all the individual oxide layers 14. In some embodiments, the number of gaps 16 is a multiple of 2. In some embodiments, the number of gaps is equal to 2. n , where n is any positive integer. In some embodiments, the number of gaps 16 is approximately 96.

[0020] like Figure 2 As shown, metal 20 is deposited on stack 12. Metal 20 fills gaps 16 to form letter lines 19. Metal 20 is formed around stack 12 such that it covers the top 13 and sides 15 of stack 12 with a metal capping layer 22 of thickness. Capping layer 22 is a material deposited outside gaps 16. Depending on the process used to deposit metal 20, the capping layer can have any suitable thickness. In some embodiments, the thickness of capping layer 22 is approximately... to approximately Within the range. In some embodiments, the thickness of the cover layer 22 is greater than or equal to approximately or

[0021] Metal 20 can be any suitable metal for word line applications. In some embodiments, the metal film includes tungsten. In some embodiments, the metal film does not contain tungsten. In some embodiments, the metal film is substantially composed of tungsten. As used herein, the term "substantially composed of tungsten" means that the bulk metal film comprises more than or equal to about 95%, 98%, or 99% tungsten on an atomic basis. The bulk metal film does not contain surface portions of metal 20 that may contact another surface (e.g., an oxide surface) or be open for further processing, because these areas may have some small amount of atomic diffusion with adjacent material or have some surface moiety such as hydride termination.

[0022] Metal 20 can be deposited using any suitable technique, including but not limited to chemical vapor deposition (CVD) or atomic layer deposition (ALD). Metal 20 is deposited within interstitial spaces and on the top / sidewalls of the memory stack.

[0023] Reference Figure 3A and Figure 3B This illustrates high-temperature oxidation with a low-temperature etching process. Figure 3A In this process, metal 20 is oxidized into metal oxide 25 to a depth approximately equal to the thickness of capping layer 22. Essentially all of capping layer 22 can be oxidized in a single oxidation process. The oxidation of the capping layer can be influenced by factors such as oxidizing gas flow, oxidizing gas partial pressure, wafer temperature, and process time to achieve highly conformal oxidation of the metal capping layer 22.

[0024] The oxidizing gas can be any suitable oxidizing gas that can react with the deposited metal 20. Suitable oxidizing gases include, but are not limited to, O2, O3, H2O, H2O2, NO, NO2, or combinations thereof. In some embodiments, the oxidizing gas includes one or more of O2 or O3. In some embodiments, the oxidizing gas consists essentially of one or more of O2 or O3. As used in this manner, the term "consistently of" means that the oxidizing component of the oxidizing gas is greater than or equal to about 95%, 98%, or 99% of the species. The oxidizing gas may contain an inert gas, a diluent gas, or a carrier gas. For example, the oxidizing gas may be co-flowed with one or more of Ar, He, or N2 or diluted with one or more of Ar, He, or N2.

[0025] Some embodiments of the metal oxide 25 include tungsten oxide (WO3). xIn some embodiments, metal oxide 25 is a derivative of metal 20, which may or may not contain oxygen. Suitable derivatives of the metal film include, but are not limited to, nitrides, borides, carbides, oxynitrides, oxyborides, oxycarbides, carbonitrides, boron carbide, boronitride, boron carbonitride, borooxycarbonitride, oxycarbonitride, borooxycarbide, and borooxynitride. Those skilled in the art will understand that the deposited metal film may have an atomic number not stoichiometric according to the metal film. For example, a film designated as WO may have varying amounts of tungsten and oxygen. A WO film may, for example, be 90 atomic percent tungsten. The use of WO to describe a tungsten oxide film means that the film comprises tungsten atoms and oxygen atoms, and should not be considered as limiting the film to a particular composition. In some embodiments, the membrane is essentially composed of specified atoms. For example, a membrane essentially composed of WO means that the membrane composition is greater than or equal to about 95%, 98%, or 99% tungsten atoms and oxygen atoms.

[0026] exist Figure 3A and Figure 3B In the illustrated process, the oxidation process occurs at a high temperature. As used herein, the term "high temperature" means a temperature greater than or equal to about 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or 850°C. In some embodiments, the oxidation process temperature is in the range of about 400°C to about 950°C, or in the range of about 450°C to about 900°C, or in the range of about 500°C to about 850°C.

[0027] The pressure during the oxidation process can range from about 0.1 Torr to about 760 Torr. The process time (exposure time) can range from about 0.1 seconds to 12 hours. The pressure and process time can be affected by the temperature during the oxidation process.

[0028] In some embodiments, the metal 20 of the overlay 22 is oxidized to form metal oxide 25 on the top 13 and sides 15 of the stack 12, while leaving the metal 20 in the gaps 16 to form word lines 19. In some embodiments, substantially all of the metal 20 in the gaps 16 is retained after oxidation. As used in this manner, the term "substantially all" means that the metal 20 is oxidized to the sides of the stack 12. Inside.

[0029] Reference Figure 3BThe metal oxide 25 formed by the capping layer 22 is etched from the top 13 and sides 15 of the stack 12 to leave metal 20 as word lines 19 in the gaps 14. Some embodiments use a selective etching process that removes the metal oxide 25 with substantially no impact on the metal 20.

[0030] In some embodiments, the etchant comprises a metal halide etchant. The etchant in some embodiments consists essentially of a metal halide etchant. As used herein, the term "consistently of a metal halide etchant" means that the specified metal halide etchant species constitute 95%, 98%, or 99% of the total metal halide etchant species (excluding inert gases, dilution gases, or carrier gases). The metal halide etchant may have the same metal species as or different from the metal oxide 25. In some embodiments, the metal halide etchant comprises the same metal species as the metal oxide 25.

[0031] In some embodiments, the metal halide etchant comprises halogen atoms that are essentially composed of chlorine. As used herein, the term "essentially composed of chlorine" means that chlorine constitutes more than or equal to about 95%, 98%, or 99% of the halogen atoms in the metal halide etchant on an atomic basis.

[0032] In some embodiments, the metal halide etchant comprises one or more of WCl5 or WCl6. In some embodiments, the metal halide etchant is substantially composed of one or more of WCl5 or WCl6. As used herein, the term "substantially composed of" means that the species constitutes more than or equal to about 95%, 98%, or 99% of the metal halide in molar terms.

[0033] In some embodiments, the etching temperature is lower than the temperature during oxidation. In some embodiments, the etching temperature is in the range of about 300°C to about 600°C, or in the range of about 400°C to about 500°C. In some embodiments, the etching temperature is less than or equal to about 600°C, 550°C, 500°C, 450°C, 400°C, or 350°C. In some embodiments, the temperature during etching is greater than or equal to about 50°C, 75°C, 100°C, 125°C, or 150°C lower than the temperature during oxidation. In some embodiments, both oxidation and etching occur at a temperature greater than or equal to about 400°C.

[0034] After etching the metal oxide 25, the metal overlay 22 is removed, and the metal 20 remaining in the gap 14 as word lines 19 is substantially flush with the side surface 15 of the stack 12. As used in this manner, the term "substantially flush" means that the word lines 19 within the gap 16 are flush with the side surface 15 of the stack 12. Inside.

[0035] Figure 3A and Figure 3B The embodiments shown illustrate a high-temperature oxidation-low-temperature etching process. Figures 4A to 4D The embodiments shown illustrate low-temperature oxidation and etching processes. Some differences between these processes include, but are not limited to, lower-temperature oxidation and slower removal of the overlay.

[0036] After stacking 12 to form a covering layer 22 on the metal 20 (as shown in the image) Figure 2 As shown in the diagram, the removal of the overlay can be performed using an atomic layer etching (ALE) process. An ALE process may consist of multiple repeated processes that modify the surface to be etched, and then evaporate or remove the modified surface to expose the new surface underneath.

[0037] Reference Figure 4A The capping layer 22 is oxidized to form a metal oxide 25 on its surface. The oxidation process can be used with... Figure 3A The embodiments shown use the same reagents and parameters, but with some modifications to allow atomic layer etching (ALE) processes to occur. In some embodiments, the oxidation process occurs at temperatures ranging from about 300°C to about 500°C. In some embodiments, oxidation occurs at temperatures less than or equal to about 500°C, 450°C, 400°C, or 350°C. The pressure during the low-temperature oxidation process can range from about 0.1 Torr to about 760 Torr. The process or exposure time can range from about 0.001 seconds to about 60 seconds. In the atomic layer etching process, each oxidation and etching process is self-limiting because the process stops once a reaction has been made with an active surface site. For example, once all active surface sites of metal 20 are exposed to the oxidant and react with it to form a metal oxide 25 film, further oxidation cannot easily occur. Similarly, once the etchant has removed the oxide film to expose the fresh metal 20 underneath, the etchant has no further oxide to remove.

[0038] Reference Figure 4B After forming metal oxide 25 on metal 20, stack 12 is exposed to the etchant. The etchant and etching conditions are detailed in the documentation. Figure 3B The etchant and etching conditions shown and described are the same. The metal oxide 25 layer on metal 20 is more... Figure 3A and Figure 3B The embodiments shown are thin, which makes the etching process take less time. In some embodiments, the etchant process time ranges from about 0.1 seconds to about 60 seconds.

[0039] In some embodiments, the temperature during the oxidation and etching processes occurs at a temperature less than or equal to about 400°C. Figure 4B The etching process temperature shown in the figure can be compared with... Figure 4A The oxidation process is the same, which allows the substrate containing the stack 12 to be quickly moved from one processing area of ​​the processing chamber to another processing area of ​​the processing chamber to sequentially expose the substrate to oxidation and etching conditions.

[0040] This type of ALE process can be called spatial ALE, in which various reactive gases (e.g., oxidants and etchants) flow into separated regions of the processing chamber, and the substrate moves between and within these regions. Different processing regions are separated by gas curtains comprising one or more purge gas flows and / or vacuum flows to prevent the oxidant and etchant from mixing in the gas phase. The ALE process can also be performed via time-domain processing, in which the processing chamber is filled with oxidant, purged to remove excess oxidant and reaction products or byproducts, filled with etchant, and then purged again to remove excess etchant and reaction products or byproducts. In time-domain processing, the substrate can remain stationary.

[0041] Figure 4C and Figure 4D The process is shown to involve repeated exposure to an oxidant to form a metal oxide 25 and exposure to an etchant to remove the metal oxide. Although the process is shown to use two cycles, those skilled in the art will understand that this is only one example and that more than two cycles can be used to remove the capping layer 22 and leave the metal 20 in the gap 16 as word lines 19.

[0042] In some embodiments, a barrier layer is formed on the oxide layer 14 prior to the deposition of metal 20. The barrier layer can be any suitable barrier material. In some embodiments, the barrier layer comprises titanium nitride. In some embodiments, the barrier layer is substantially composed of titanium nitride. As used in this manner, the term "substantially composed of titanium nitride" means that the composition of the barrier layer is greater than or equal to about 95%, 98%, or 99% titanium atoms and nitrogen atoms on an atomic basis. The thickness of the barrier layer can be any suitable thickness. In some embodiments, the thickness of the barrier layer is approximately... to approximately Within the range.

[0043] Throughout this specification, references to "one embodiment," "some embodiments," "one or more embodiments," or "embodiment" mean that a particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this disclosure. Therefore, the appearance of phrases such as "in one or more embodiments," "in some embodiments," "in one embodiment," or "in an embodiment" throughout this specification does not necessarily refer to the same embodiment of this disclosure. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0044] Although this disclosure has been described with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of this disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the methods and apparatus of this disclosure without departing from the spirit and scope of this disclosure. Therefore, it is contemplated that this disclosure includes modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. A method for processing a substrate, the method comprising the following steps: A substrate is provided having a stack of spaced-apart oxide layers with gaps between the oxide layers, the stack having a top and sides, and each gap forming a word line; Metal is deposited on the stack such that the metal fills the gaps and covers the top and sides of the stack with a metal overlay thickness; The metal is oxidized to a depth within ±1 Å of the side surface of the stack to form a metal oxide on the top and side surface of the stack, and the metal is left in the gap as a letter line; as well as The metal oxide is etched from the top and sides of the stack, leaving the metal in the letter lines.

2. The method as described in claim 1, characterized in that, The metal includes tungsten, and the metal oxide includes tungsten oxide.

3. The method as described in claim 1, characterized in that, The metal is primarily composed of tungsten.

4. The method of claim 1, further comprising the step of forming a barrier layer on the oxide layer, and the metal being deposited on the barrier layer.

5. The method as described in claim 4, characterized in that, The barrier layer comprises TiN, and the thickness of TiN is in the range of 20 Å to 50 Å.

6. The method as described in claim 1, characterized in that, There are more than 50 word lines.

7. The method as described in claim 1, characterized in that, After etching the metal oxide, the metal overlay is removed, and the metal used to form the letter lines in the gap is substantially flush with the sides of the stack.

8. The method as described in claim 1, characterized in that, The oxidation and etching occur at a temperature greater than or equal to 400°C.

9. The method as described in claim 1, characterized in that, The step of etching the metal oxide includes exposing the metal oxide to a metal halide etchant.

10. The method as described in claim 9, characterized in that, The metal halide etchant comprises the same metal species as the metal oxide.

11. The method as described in claim 9, characterized in that, The metal halide etchant includes metal species that are different from the metal species of the metal oxide.

12. The method as described in claim 1, characterized in that, The step of oxidizing the metal includes exposing the metal to O2.

13. The method as described in claim 1, characterized in that, The thickness of the metal overlay is greater than or equal to 5 Å.

Images