Formation of arrays of nanostructures

Abstract

A method for forming an array of nanostructures is presented. The method comprises: providing a layer structure comprising an array of first sacrificial nanostructures arranged on a support layer structure, the support layer structure comprising at least a first material layer and a substrate; selectively applying spacer structures on sidewalls of the array of first sacrificial nanostructures; selectively etching away the array of first sacrificial nanostructures such that the spacer structure forms an array of second sacrificial nanostructures; etching the first material layer using the array of second sacrificial nanostructures as an etch mask; and removing the array of second sacrificial nanostructures, thereby exposing the array of nanostructures formed from the first material layer.

Description

Technical Field

[0001] The present invention relates to the formation of arrays of nanostructures as part of or constituting a self-aligned multiple patterning process. Background Art

[0002] The supply of integrated circuits is limited, and there is a great need to continue to reduce the size of electronic components such as transistors and memory chips. The development and scaling of integrated circuits is very challenging. Production involves extremely high costs, a heavy burden on the environment, and a large investment. Due to the extreme scaling of the critical dimensions of modern electronic components, direct patterning using methods such as optical lithography is not always possible. This is because the critical dimensions are much smaller than the wavelength of light used for optical lithography. Therefore, light diffraction limits the resolution of direct patterning.

[0003] Therefore, multiple patterning techniques have been introduced and are currently used as a complementary technology to optical lithography. These patterning processes enable further scaling of critical dimensions to smaller sizes. A variety of different patterning techniques are currently used in the industry to supplement standard optical lithography. Examples of industrial multiple patterning methods are called self-aligned multiple patterning (SAMP) or SAxP, and include self-aligned double patterning (SADP), self-aligned quadruple patterning (SAQP), and self-aligned octuplet patterning (SAOP). The self-aligned multiple patterning process enables pattern fabrication below 100 nm.

[0004] The self-aligned multi-patterning (SAMP) process flow is an indirect patterning method used in conjunction with direct patterning methods, typically in conjunction with optical lithography in high-volume manufacturing. SAMP is used as an extension of conventional direct patterning to produce increasingly smaller patterns that are impossible to create using available photolithography. SAMP is used, for example, in the formation of fin structures in field-effect transistors (FETs), shallow trench isolation, line and space for electrical interconnects, and bitline / wordline structures in memory devices. Very good process control is essential for SAMP.

[0005] In self-aligned double patterning, spacer structures are formed on the sidewalls of an array of original structures arranged on a substrate or material layer. The spacer structures are typically formed by depositing a film over the existing pattern and then etching to remove all film material on the horizontal surfaces, leaving only material on the sidewalls. Typically, film deposition over the existing pattern and etching to remove all film material on the horizontal surfaces are performed in separate process chambers, resulting in high costs and technical difficulties in controlling process results. Subsequently, the array of original structures is removed, leaving only the spacer structures. Two spacer structures exist for each original structure, thus doubling the structure density.

[0006] A known issue with self-aligned double patterning is whether the spacer structure can remain in place after removing the material of the array of original structures. Another issue is whether the profile of the spacer structure is acceptable. Yet another issue is whether the underlying material is eroded by the etching process that removes the material of the array of original structures. Furthermore, pattern transfer is complicated by the fact that the removal of the material of the array of original structures also removes a small amount of underlying material or insufficiently removes the underlying material in corners. This can result in differences in the topography of the layer directly below or adjacent to the spacer structure.

[0007] When self-aligned double patterning is repeated, an additional halving of the pitch is achieved. This is known as self-aligned quadruple patterning. Another repetition of this process results in an additional halving of the pitch. This is known as self-aligned octuplet patterning. Due to the aforementioned issues with self-aligned double patterning, which lead to accumulated structural defects, the number of repetitions of this process is typically limited to octuplet patterning.

[0008] In view of the foregoing, there is room for improvement in the self-aligned multi-patterning process. Summary of the Invention

[0009] In view of the above, an object of the present invention is to provide an improvement in the self-aligned multiple patterning process.

[0010] According to a first aspect, a method for forming an array of nanostructures is provided. The method comprises: providing a layer structure comprising an array of first sacrificial nanostructures disposed on a supporting layer structure comprising at least a first material layer and a substrate; selectively applying a spacer structure to sidewalls of the array of first sacrificial nanostructures; selectively etching away the array of first sacrificial nanostructures such that the spacer structure forms an array of second sacrificial nanostructures; etching the first material layer using the array of second sacrificial nanostructures as an etch mask; and thereby removing the array of second sacrificial nanostructures. The method forms part of or constitutes a self-aligned multi-patterning process.

[0011] In this context, the phrase "nanostructure" should be interpreted as a structure of an intermediate size between micrometer-sized structures and structures composed of single atoms.

[0012] This method can be applied multiple times, similar to quadruple and octuplet patterning, in order to further increase the density of the resulting array, and ultimately, an array of structures composed of single atoms can be formed by repeating this method a sufficient number of times. This allows the formation of nanostructures with very small dimensions, preferably below 20 nm, and even more preferably below 10 nm, by using relatively large starting nanostructures, typically in the range of 1000 nm to 10 nm.

[0013] By the present method, improved process control can be achieved due to the selective application of spacer structures on the sidewalls of the array of first sacrificial nanostructures. The selective application of spacer structures on the sidewalls of the array of first sacrificial nanostructures enables the self-aligned multi-patterning process to be performed multiple times in a single processing chamber, i.e., all process steps can be performed without the need to reposition the layer structure between different process steps. In addition, the selective application of spacer structures provides reduced strain on the nanostructures. This in turn provides a more uniform array of "resulting" nanostructures formed by the self-aligned multi-patterning process. Nanostructures with fewer defects can also be provided. Therefore, the effects of the nanostructures formed in the self-aligned multi-patterning process, such as footing, shrinkage, bird's beak, tilting, kinking, and asymmetric planing, can be reduced or even avoided.

[0014] Selectively applying a spacer structure to the sidewalls of the array of first sacrificial nanostructures comprises a cyclic modification process. Each cycle in the cyclic modification process comprises: i) isotropically modifying the exposed surfaces of the array of first sacrificial nanostructures and the first material layer, and ii) anisotropically etching the modified material from the first material layer and the top surfaces of the first sacrificial nanostructures. A cyclic modification method for forming a spacer structure on the sidewalls of the array of first sacrificial nanostructures is provided.

[0015] Isotropic modification may include one or more of deposition, adsorption, conversion, and extraction.

[0016] The anisotropic etching may include dry etching.

[0017] In each cycle of the cyclic modification process, anisotropic etching may be followed by isotropic surface modification.

[0018] The method may further include anisotropically etching away material from a top surface of the first material layer during the cyclic modification process, thereby forming a slope in a surface forming a boundary between the spacer structure and the first material layer.

[0019] The method may further include, between selectively applying the spacer structure on the sidewalls of the array of first sacrificial nanostructures and selectively etching away the array of first sacrificial nanostructures: etching away a sublayer of the first material layer using the first sacrificial nanostructures and the spacer structure on the sidewalls of the first material layer as an etching mask; and selectively applying an additional spacer structure on the sidewalls of the spacer structure and on the sidewalls of the first material layer exposed by etching away the sublayer of the first material layer. The selective application of the additional spacer structure may be performed through the cyclic modification process described above.

[0020] The method may further include subjecting the array of nanostructures formed from the first material layer to a cyclic etching process, wherein each cycle includes subjecting the array of nanostructures to surface modification by one or more of chemical adsorption, deposition, conversion, and extraction, and subjecting the array of nanostructures to a particle beam consisting of particles having an energy of less than 10,000 eV, preferably less than 1,000 eV, and more preferably less than 100 eV, wherein the direction of the particle beam is parallel to the surface perpendicular to the substrate within a deviation of ±20°, thereby achieving selective etching of the main surface of the array of nanostructures relative to the walls of the array of nanostructures, so that a recess is formed in each nanostructure in the array of nanostructures.

[0021] Furthermore, the method may comprise combining isotropic surface modification and anisotropic selective material removal from horizontal surfaces in the same process step or in two adjacent and overlapping steps.

[0022] All steps of the method can be performed in the same process chamber. Thus, reduced processing times and reduced processing costs can be achieved in this way, thereby enabling sustainable and economical scaling of electronic and optical devices.

[0023] The spacer structure may be made of a hard mask such as carbon, tin, silicon, silicon-germanium alloy, nitride, oxide such as hafnium oxide, silicon oxide, aluminum oxide, and polymer such as fluorocarbon polymer.

[0024] The first sacrificial nanostructure can be made of a template material such as an optical resist material, a resist for extreme ultraviolet lithography (EUV), an electron beam sensitive resist, a nanoimprint resist or other polymer, carbon, amorphous carbon, crystalline silicon, amorphous silicon, polycrystalline silicon, nitride, oxide or other semiconductor material (e.g., Group III-V or Group II-VI semiconductor), alternatively, or made of a metal. These are just examples of different materials that can be used to form the template.

[0025] The substrate may be made of an insulator material such as an oxide.

[0026] Further areas of applicability will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples are given by way of illustration only.

[0027] It should be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. It must be noted that, as used in the specification and the appended claims, the articles "a," "an," "the," and "said" are intended to indicate the presence of one or more elements, unless the context clearly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, etc. Furthermore, the words "comprising," "including," "containing," and similar expressions do not exclude other elements or steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other aspects will now be described in more detail with reference to the accompanying drawings, which should not be considered limiting; rather, they are for explanation and understanding.

[0029] As shown in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, therefore, are provided to illustrate the general structure. Like reference numerals refer to like elements throughout.

[0030] Figure 1 (including Figures 1A to 1G ) schematically illustrates the formation of spacer structures on the sidewalls of an array of nanostructures using a cyclic modification process.

[0031] Figure 2 (including Figures 2A to 2D ) schematically illustrates the process steps in the self-aligned multiple patterning process.

[0032] Figure 3 (including Figures 3A to 3G ) schematically illustrates an alternative process for forming spacer structures on the sidewalls of an array of nanostructures using a cyclic modification process.

[0033] Figure 4 (including Figures 4A to 4D ) schematically illustrates the process steps in the self-aligned multiple patterning process.

[0034] Figure 5 (including Figures 5A to 5G ) schematically illustrates yet another alternative process for forming spacer structures on the sidewalls of an array of nanostructures using a cyclic modification process.

[0035] Figure 6 (including Figure 6A and Figure 6B ) schematically illustrates etching of recesses in nanostructures formed using the process disclosed in this disclosure.

[0036] Figure 7A and Figure 7B Examples of patterned surfaces of nanostructures that can be formed using the processes disclosed in this disclosure are shown. DETAILED DESCRIPTION

[0037] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. However, the invention can be embodied in many different forms.

[0038] The present disclosure relates to improvements in self-aligned multiple patterning. Improvements in at least two different aspects of the self-aligned multiple patterning process are contemplated. Both improvements in forming spacer structures on the sidewalls of an array of "starting" nanostructures and improvements in patterning of an array of "resulting" nanostructures formed by the self-aligned multiple patterning process will be discussed.

[0039] Combined with Figure 1 (including Figures 1A to 1G ) discusses the formation of spacer structures on the sidewalls of an array of "starting" nanostructures. Figure 1A , a starting layer structure including a starting pattern for a self-aligned multiple patterning process is schematically shown. The starting layer structure includes a substrate 100, on which an array of first sacrificial nanostructures 120 is arranged, and a first material layer 110 arranged between the substrate 100 and the array of first sacrificial nanostructures 120. It should be appreciated that the starting layer structure may include additional layers as long as the topmost layer is the array of first sacrificial nanostructures 120. The array of first sacrificial nanostructures 120 represents the starting pattern. The array of first sacrificial nanostructures 120 can be formed, for example, by optical lithography. The width of the first sacrificial nanostructures 120 is typically in the range of 3 nm to 100 nm. The height of the first sacrificial nanostructures 120 is typically in the range of 3 nm to 200 nm. The pitch of the array of first sacrificial nanostructures 120 is typically in the range of 10 nm to 200 nm.

[0040] The substrate 100 may be formed of oxide, nitride, crystalline silicon, amorphous silicon, polysilicon, or other semiconductor materials (eg, Group III-V or Group II-VI semiconductors), alternatively, metal or polymer.

[0041] The first material layer 110 may be a hard mask or a material such as crystalline silicon, amorphous silicon, polysilicon, nitride, oxide, or other semiconductor materials (eg, Group III-V or Group II-VI semiconductors), alternatively a metal or a polymer.

[0042] The first sacrificial nanostructure 120 can be formed of a template material such as a photoresist, a resist for extreme ultraviolet lithography, an electron beam sensitive resist, a nanoimprint resist or other polymer, carbon, amorphous carbon, crystalline silicon, amorphous silicon, polycrystalline silicon, nitride, oxide or other semiconductor material (such as a III-V or II-VI semiconductor), or alternatively, a metal.

[0043] The selective application of the spacer structure on the sidewalls of the array of the first sacrificial nanostructure can be achieved at least in part by surface-controlled reactions (such as adsorption, conversion and extraction). Specifically, surface-limited adsorption reactions are important for atomic layer deposition, molecular layer deposition, atomic layer etching and combinations thereof. Adsorption can be carried out by chemical adsorption, physical adsorption, diffusion, ion implantation and combinations thereof. Conversion can be accomplished by oxidation, nitridation, densification, crystallization and combinations thereof. In the case of extraction, a specific element is selectively removed from the compound material of the top material layer so as to modify the topmost surface. Extraction can also be achieved by oxidation. It is recognized that these surface-limited reactions do not need to be ideal, and some additional and quasi-surface-limited processes can occur simultaneously. Therefore, the effects of process uniformity across production wafers and pitch walking, which is called pitch variation between different features, can be reduced or even avoided in the self-aligned multiple patterning process, which causes inconsistencies in the critical dimensions of different features resulting from process variations across production wafers.

[0044] The spacer structure is selectively applied to the sidewall of the array of the first sacrificial nanostructure and can be achieved at least in part by anisotropically and selectively removing the material produced by the isotropic surface control reaction on the horizontal surface. This can be achieved by using a surface modified by gentle activation so that the material remaining on the surface remains undamaged. This anisotropic removal can be achieved, for example, by a particle beam consisting of particles with an energy less than 10000eV, preferably less than 1000eV, more preferably less than 100eV, wherein the direction of the particle beam is parallel to the surface perpendicular to the substrate within a deviation of ± 20 °, thereby achieving the selective etching of the main surface of the array of nanostructures relative to the wall of the array of nanostructures. Therefore, a final structure with reduced damage or ultimately completely undamaged can be achieved in this way, so that the process can be repeated more than three times, and a nanostructure that can be directly used as an active structure in electronic and optical devices is created.

[0045] If now combined Figures 1B to 1G As discussed, the spacer structures 130 are formed on the sidewalls 122 of the array of first sacrificial nanostructures 120 by selectively applying the spacer structures 130 on the sidewalls 122 of the first sacrificial nanostructures 120. The process of selectively applying the spacer structures 130 on the sidewalls 122 may include a cyclic modification process. Figure 1B and Figure 1C The first cycle in the cyclic modification process is schematically shown. Figure 1D and Figure 1E The second cycle in the cyclic modification process is schematically shown, and Figure 1F and Figure 1GThe third cycle in the cyclic modification process is schematically shown. Therefore, the cyclic modification process includes multiple cycles. It should be understood that the cyclic modification process can include more than the three cycles shown in Figure 1.

[0046] The spacer structure 130 on the sidewall 122 can be a hard mask or a semiconductor material, a metal, a polymer, such as a fluorocarbon polymer. The width of the spacer structure 130 is typically in the range of 3 nm to 100 nm. The height of the spacer structure is typically similar to the height of the first sacrificial nanostructure 120.

[0047] Each cycle in the cyclic modification process includes i) isotropically modifying the exposed surfaces of the array of first sacrificial nanostructures 120 and the exposed surfaces of the first material layer 110, and ii) anisotropically etching the modified material from the top surfaces of the first sacrificial nanostructures 120 and from the top surface of the first material layer 110. The top surfaces may also be referred to as the horizontal surfaces of the first sacrificial nanostructures 120 and the first material layer 110, respectively. Figures 1B to 1G In this, this is shown as first performing an isotropic modification of the exposed surfaces of the array of first sacrificial nanostructures 120 and the exposed surfaces of the first material layer 110, see Figure 1B 、 Figure 1D and Figure 1F , and after each such isotropic modification, an anisotropic etching of the modified material is performed from the top surface of the first sacrificial nanostructure 120 and from the top surface of the first material layer 110, see Figure 1C 、 Figure 1E and Figure 1G Thus, in each cycle, a spacer structure is gradually formed on the sidewalls 122 of the array of first sacrificial nanostructures 120. Figure 1C 、 Figure 1E and Figure 1G As shown schematically in FIG, the structure on the sidewall 122 of the array of the first sacrificial nanostructure 120 gradually becomes thicker. After the last cycle in the cyclic modification process, the spacer structure 130 is formed, see Figure 1G .

[0048] Combine Figures 1B to 1G In the schematic diagram presented in FIG, the cyclic modification process is shown as having three cycles. It should be recognized that Figures 1B to 1GThe schematic diagrams presented in FIG are merely schematic diagrams for the purpose of providing an understanding of the process. In practice, the number of cycles in the cyclic modification process can be in the range of two to one thousand, preferably between three and fifty. The number of cycles can vary depending on the desired width of the spacer structure 130. The number of cycles can vary depending on which process is used for the isotropic modification of the exposed surface of the array of first sacrificial nanostructures 120 and the exposed surface of the first material layer 110. The number of cycles can also vary depending on the material used for the sacrificial nanostructures 120.

[0049] Isotropic modification can be considered as a surface modification process. Therefore, all surfaces exposed to isotropic modification are subjected to surface modification. Isotropic modification can include one or more of deposition, adsorption, conversion and extraction. Specifically, deposition can be carried out by sputtering, epitaxy, evaporation, chemical vapor deposition, atomic layer deposition, molecular layer deposition and combinations thereof. Adsorption can be carried out by chemical adsorption, physical adsorption, diffusion, ion implantation and combinations thereof. Conversion can be accomplished by oxidation, nitridation, densification, crystallization and combinations thereof. In the case of extraction, a specific element is selectively removed from the compound material in the top material layer to modify the topmost surface in this way. Extraction can also be achieved by oxidation. Deposition can be carried out by atomic layer deposition processes such as plasma enhanced atomic layer deposition and thermal atomic layer deposition. It should be appreciated that atomic layer deposition does not need to be ideal and a quasi-atomic layer deposition process can be used.

[0050] Anisotropic etching includes dry etching. Suitable dry etching methods are continuous etching methods or cyclic etching methods. Examples of continuous etching methods are low-energy particle beam sputtering (e.g., with Ar ions) and low-energy particle beam continuous reactive ion etching (e.g., with Ar gas and Cl2 gas). Examples of cyclic etching methods are atomic layer etching and quasi-atomic layer etching. Here, quasi-atomic layer etching refers to a different process in which process parameters are similar to but somewhat different from those of ideal atomic layer etching, for example, outside the saturation region, which may mean non-self-limiting process behavior. Quasi-atomic layer etching can provide a faster etching process at the expense of process stability, and may be preferred in some cases.

[0051] Preferably, in each cycle of the cyclic modification process, anisotropic etching is performed immediately after isotropic surface modification. This prevents the formation of a continuous film on the top surface of the first sacrificial nanostructure 120 and the top surface of the first material layer 110. This is because etching is performed before any film has even nucleated on the top surface. This also prevents the formation of strain in the layer applied by the surface modification.

[0052] The cyclic reforming process may include additional steps such as pumping steps, purge steps, and combinations, overlaps, and repetitions thereof. The pumping step means pumping all process gases and reaction products and by-products from the processing chamber in a manner that achieves a low pressure of at least 10E-3 Torr, preferably less than 10E-5 Torr. The purge step means pumping an inert gas through the chamber at high pressure (typically in the range of 1000 Torr to 0.001 Torr, preferably in the range of 1 Torr to 10 mTorr).

[0053] After forming the spacer structures 130 on the sidewalls 122 of the array of first sacrificial nanostructures 120, the self-aligned multiple patterning process can be continued by selectively etching away the array of first sacrificial nanostructures 120 (preferably dry etching) so that the spacer structures 130 form the array of second sacrificial nanostructures 140. Figure 2A and Figure 2B Schematically illustrating that the array of first sacrificial nanostructures 120 is selectively etched away. Figure 2A The layer structure shown in Figure 1F same layer structure in Figure 2B . For some applications, the self-aligned multi-patterning process may stop at this step. In such applications, the array of second sacrificial nanostructures 140 may not be sacrificial nanostructures, but may constitute an array of nanostructures used in various applications (e.g., transistor channels, electrical interconnects, optical elements such as gratings, photonic crystals, optical waveguides).

[0054] For some applications, the self-aligned multiple patterning process can continue by anisotropically etching the first material layer 110 using the array of second sacrificial nanostructures 140 as an etch mask. Figure 2B and Figure 2C As shown, that is, the etching of the first material layer 110 is Figure 2B The layer structure shown starts at Figure 2C The etching may be performed such that the first material layer is completely etched away by exposing the underlying layer (in this case the substrate 100).

[0055] The self-aligned multiple patterning process can continue by selectively removing the array of second sacrificial nanostructures 140, preferably using dry etching. Figure 2C and Figure 2D It is explained that the removal of the array of second sacrificial nanostructures 140 is Figure 2C The layer structure shown starts at Figure 2D The layer structure shown ends at .Through this process step, the array of nanostructures 150 formed by the first material layer is exposed.

[0056] As shown in Figure 3 (including Figures 3A to 3G ), during the cyclic modification process, anisotropic etching of material from the top surface of the first material layer 110 can be performed. By such etching of material from the top surface of the first material layer 110, a slope 112 can be formed in the surface forming the boundary between the spacer structure 130 and the first material layer 110. The slope is an inclined surface of the material layer 110 that defines the flat surface of the material layer 100. The angle of the slope is in the range of 0 degrees to 90 degrees relative to the original surface, preferably in the range of 30 degrees to 80 degrees. The width of the slope 112 is typically in the range of 3 nm to 100 nm, and the height of the slope 112 is typically in the range of 3 nm to 200 nm. Etching of material from the top surface of the first material layer 110 can be performed during one or more cycles of the cyclic modification process. Therefore, etching of material from the top surface of the first material layer 110 can be performed during a sub-portion of a cycle of the cyclic modification process. Alternatively, etching of material from the top surface of the first material layer 110 can be performed during each cycle of the cyclic modification process. Preferably, etching away material from the top surface of the first material layer 110 is performed during an isotropic etch in a cycle of the cyclic modification process. Figures 3A to 3G , anisotropic etching of material from the top surface of the first material layer 110 is schematically shown. In this schematic, anisotropic etching of material from the top surface of the first material layer 110 is performed in each cycle of the cyclic modification process. However, as described above, this is not always the case and etching of material from the top surface of the first material layer 110 may be performed only in some cycles. As in the process described in conjunction with FIG. 1 , isotropic modification of the exposed surface of the array of first sacrificial nanostructures 120 and the exposed surface of the first material layer 110 is first performed in each cycle of the cyclic modification process, see FIG. Figure 3B 、 Figure 3D and Figure 3F However, in addition to anisotropically etching the modified material from the top surface of the first sacrificial nanostructure 120 and from the top surface of the first material layer 110, an anisotropic etch is also incorporated to etch away the top layer of the exposed top surface of the first material layer 110, see Figure 3C 、 Figure 3E and Figure 3G Therefore, during the cyclic modification process, since material is etched away from the top surface of the first material layer 110 while the spacer structure 130 is gradually formed on the sidewalls 122 of the array of the first sacrificial nanostructures 120, a slope is formed in the surface forming the boundary between the spacer structure 130 and the first material layer 110. After the last cycle in the cyclic modification process, the spacer structure 130 is formed, see Figure 3G However, these spacer structures 130 have an inclination 112 in a surface forming a boundary between the spacer structure 130 and the first material layer 110 .

[0057] As shown in Figure 4 (including Figures 4A to 4D ), after forming the spacer structure 130 on the sidewalls 122 of the array of the first sacrificial nanostructures 120, the self-aligned multi-patterning process can be continued by selectively etching away the array of the first sacrificial nanostructures 120 so that the spacer structure 130 forms the array of the second sacrificial nanostructures 140. Figure 4A and Figure 4B The schematic diagram shows the selective etching of the array of the first sacrificial nanostructures 120, that is, the selective etching of the array of the first sacrificial nanostructures 120. Figure 4A The layer structure shown in Figure 3F same layer structure in Figure 4B The selective etching of the array of first sacrificial nanostructures 120 is preferably performed in the same manner as discussed above in conjunction with FIG. 2 . To avoid undue supplementation, reference is made to the discussion above. The self-aligned multiple patterning process can continue by etching the first material layer 110 using the array of second sacrificial nanostructures 140 as an etch mask. This is combined with Figure 4B and Figure 4C As shown, that is, the etching of the first material layer 110 is Figure 4B The layer structure shown starts at Figure 4C The etching of the first material layer 110 is discussed in more detail in conjunction with the discussion of FIG. 2 above and will not be repeated here. The etching can be performed so that the first material layer is completely etched by exposing the underlying layer (in this case, the substrate 100). The self-aligned multiple patterning process can continue by removing the array of second sacrificial nanostructures 140. Figure 4C and Figure 4D The removal of the array of second sacrificial nanostructures 140 is shown, that is, the removal of the array of second sacrificial nanostructures 140 is shown in FIG. Figure 4C Starting at the layer structure shown in Figure 4D 3 . The top surface of the nanostructures 150 formed in this manner is tilted due to the anisotropic etching of material from the top surface of the first material layer 110 as discussed in conjunction with FIG. 3 . This is a type of patterning of the array of “resulting” nanostructures formed by the self-aligned multiple patterning process. That is, the tilt of the top surface of the array of “resulting” nanostructures can be formed.

[0058] Combined with Figure 5, especially with Figure 5 Figures 5A to 5G, an alternative to patterning the array of "resultant" nanostructures formed by the self-aligned multiple patterning process will now be discussed. This alternative to patterning the array of "resultant" nanostructures formed by the self-aligned multiple patterning process is intended to form a stepped top surface of the nanostructures of the array. Figure 1A A similar layer structure as discussed was used as a starting structure. Figure 5A However, it should be appreciated that different starting layer structures may be used, as long as the topmost layer in the layer structure is an array of first sacrificial nanostructures 120. Next, according to the above combined Figures 1B to 1G The process of selectively applying the spacer structure 130 on the sidewalls of the array of the first sacrificial nanostructures 120 discussed above forms the spacer structure 130 on the sidewalls of the array of the first sacrificial nanostructures 120. The resulting layer structure is Figure 5B Note that Figure 5B The layer structure is similar to Figure 1G As a next step in the self-aligned multiple patterning process, a sub-layer of the first material layer 110 is etched away using the first sacrificial nanostructure 120 and the spacer structure 130 and on the sidewalls 122 of the first material layer 110 as an etch mask. Figure 5C The result of such etching away of the sub-layer of the first material layer 110 is schematically shown in FIG. Thereafter, an additional spacer structure 132 is selectively applied to the sidewalls of the spacer structure 130 and to the sidewalls of the first material layer 110 exposed by etching away the sub-layer of the first material layer 110. The additional spacer structure 132 is typically made of the same material as the spacer structure 130. However, a material different from that of the spacer structure 130 may be used. The width of the additional spacer structure 132 is typically in the range of 3 nm to 100 nm. The height of the additional spacer structure 132 is typically in the range of 3 nm to 200 nm. Figure 5D The result of such etching away a sublayer of the first material layer 110 is schematically shown in FIG. The selective application of the additional spacer structure 132 is preferably performed by a cyclic modification process as discussed above in conjunction with FIG. To avoid unnecessary repetition, reference is made to the above discussion to provide a manner of how to selectively apply the additional spacer structure 132. The spacer structure 130 and the additional spacer structure 132 together form a stepped spacer structure 134. The process can continue to form one or more additional steps in the stepped spacer structure 134 by repeating the etching away of another sublayer of the first material layer 110 and the selective application of the additional spacer structure.

[0059] After forming the stepped spacer structure 134, the self-aligned multiple patterning process can continue by selectively etching away the array of first sacrificial nanostructures 120 so that the stepped spacer structure 134 forms an array of second sacrificial nanostructures 140. The second sacrificial nanostructures 140 are composed of the same or modified material as the stepped spacer structure 134 and have the same or similar dimensions as the stepped spacer structure 134. Figure 5D and Figure 5E The selective etching of the array of the first sacrificial nanostructures 120 is schematically shown, that is, the selective etching of the array of the first sacrificial nanostructures 120 is Figure 5D Starting at the layer structure shown in Figure 5E The selective etching away of the array of first sacrificial nanostructures 120 is preferably performed in the same manner as discussed above in connection with Figure 2. To avoid undue elaboration, reference is made to the above discussion.

[0060] The self-aligned multiple patterning process can continue by etching the first material layer 110 using the array of second sacrificial nanostructures 140 as an etch mask. Figure 5E and Figure 5F As shown, that is, the etching of the first material layer 110 is Figure 5E The layer structure shown starts at Figure 5F The layer structure shown ends at .The etching of the first material layer 110 is discussed in more detail in conjunction with the discussion of FIG2 above and will not be repeated here.The etching can be performed so that the first material layer is completely etched by exposing the underlying layer (in this case, the substrate 100).

[0061] The self-aligned multi-patterning process can continue by removing the array of second sacrificial nanostructures 140. Figure 5F and Figure 5G The removal of the array of second sacrificial nanostructures 140 is shown, that is, the removal of the array of second sacrificial nanostructures 140 is shown in FIG. Figure 5F Starting at the layer structure shown in Figure 5G2 above, and will not be repeated here. Through this process, an array of nanostructures 150 formed by the first material layer 110 is exposed. The array of nanostructures 150 is composed of a material that is the same as or modified from the first material 110. The width of the nanostructures 150 is typically in the range of 3 nm to 100 nm. The height of the nanostructures 150 is typically in the range of 3 nm to 200 nm. The top surface of the nanostructures 150 formed in this way is stepped due to the process of applying the stepped spacer structure 134. This is another type of patterning of the array of "resulting" nanostructures formed by the self-aligned multiple patterning process. That is, a stepped top surface of the array of "resulting" nanostructures can be formed.

[0062] An array of nanostructures 150 formed according to any of the processes discussed above, i.e., an array of nanostructures 150 formed according to the discussion of any of Figures 2, 4, or 5, can be further divided into arrays of finer hierarchical nanostructures. Figure 6A and Figure 6B In more detail, an array of nanostructures 150 formed as discussed in conjunction with FIG. 5 will be used as an example. To further shape the nanostructures 150 in the array of nanostructures 150, they can be subjected to a cyclic etching process. Each cycle in such a cyclic etching process includes i) subjecting the array of nanostructures 150 to surface modification, and then ii) subjecting the array of nanostructures to a particle beam. The surface modification includes one or more of chemical adsorption, deposition, conversion, and extraction. The particle beam is composed of particles having an energy of less than 1000 eV, preferably less than 400 eV, more preferably less than 150 eV, and even more preferably less than 100 eV. The direction of the particle beam is parallel to the surface of the layer structure within a deviation of ±20°, preferably within a deviation of ±10°. The particle beam having such low energy and such a direction relative to the major surface provides a selective etching process that forms recesses in the exposed nanostructures starting from their major surface. Such a cyclic etching process for etching recesses in the etched nanostructures is discussed in more detail in WO2017157902. Thus, through the cyclic etching process, selective etching of the major surfaces of the array of nanostructures 150 relative to the walls of the array of nanostructures 150 is achieved, so that one or more recesses 152, 154 are formed in each nanostructure 150 in the array of nanostructures 150. In the example of the nanostructures 150 shown in FIG6, two recesses will be formed in each nanostructure 150. This is because each nanostructure 150 is stepped and includes two different major surfaces.

[0063] All process steps in the self-aligned multiple patterning process can be performed in the same process chamber. In addition, an established semiconductor manufacturing plant can be used to perform the process.

[0064] Those skilled in the art will realize that the present invention is by no means limited to what has been explicitly described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0065] For example, by combining Figures 3A to 3G and 5A to 5D The top surface of the nanostructures formed by patterning the array of "resulting" nanostructures discussed above can take different shapes. Thus, a mixture of slopes and steps can be formed. Figure 7A and Figure 7B Some examples of such forms are schematically shown in .

[0066] Additionally, variations can be understood and effected by the skilled artisan in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Claims

1. A method for forming an array of nanostructures, the method comprising the steps of: providing a layer structure comprising an array of first sacrificial nanostructures (120) arranged on a supporting layer structure comprising at least a first material layer (110) and a substrate (100); selectively applying a spacer structure (130) to the sidewalls (122) of the array of the first sacrificial nanostructures (120); selectively etching away the array of the first sacrificial nanostructures (120) such that the spacer structure (130) forms an array of second sacrificial nanostructures (140); etching the first material layer (110) using the array of the second sacrificial nanostructures (140) as an etching mask; as well as removing the array of second sacrificial nanostructures (140) to expose the array of nanostructures (150) formed from the first material layer, wherein selectively applying the spacer structure (130) to the sidewalls (122) of the array of the first sacrificial nanostructures (120) comprises a cyclic modification process, wherein each cycle comprises: isotropically modifying the exposed surface of the array of the first sacrificial nanostructures (120) and the exposed surface of the first material layer (110), and Anisotropically etching the modified material from the top surface of the first material layer (110) and the top surface of the first sacrificial nanostructure (120), The spacer structure (130) is thereby gradually formed on the sidewalls (122) of the array of the first sacrificial nanostructures (120).

2. The method according to claim 1, wherein The isotropic modification includes one or more of deposition, adsorption, conversion and extraction.

3. The method according to claim 1 or 2, wherein: The anisotropic etching includes dry etching.

4. The method according to any one of claims 1 to 3, wherein In each cycle of the cyclic modification process, the anisotropic etching is immediately followed by the isotropic surface modification.

5. The method according to any one of claims 1 to 4, wherein One or more of the cycles of the cyclic reforming process may further include an intermediate step for removing residual gas and by-products, such as a pumping step, a purge step, or a combination thereof.

6. The method according to any one of claims 1 to 5 further comprises anisotropically etching away material from the top surface of the first material layer (110) during the cyclic modification process, thereby forming a slope (112) in the surface forming the boundary between the spacer structure (120) and the first material layer (110).

7. The method of any one of claims 1 to 6, further comprising, between selectively applying a spacer structure (130) on the sidewalls (122) of the array of first sacrificial nanostructures (120) and selectively etching away the array of first sacrificial nanostructures (120): etching away a sublayer of the first material layer (110) using the first sacrificial nanostructure (120) and the spacer structure (130) on the sidewall (122) of the first material layer (110) as an etching mask; and Additional spacer structures (132) are selectively applied on the sidewalls of the spacer structures (130) and on the sidewalls of the first material layer (110) exposed by etching away sub-layers of the first material layer.

8. The method according to claim 7, wherein: Additional spacer structures (132) are selectively applied through a cyclic modification process, wherein each cycle comprises: isotropically modifying the exposed surface of the array of the first sacrificial nanostructures (120) and the exposed surface of the first material layer (110), and Anisotropically etching the modified material from the top surface of the first material layer (110) and the top surface of the first sacrificial nanostructure (120), Thereby, the additional spacer structure (132) is gradually formed on the side wall of the spacer structure (130).

9. The method of any one of claims 1 to 8, further comprising subjecting the array of nanostructures formed from the first material layer to a cyclic etching process, wherein each cycle comprises subjecting the array of nanostructures to surface modification by one or more of chemical adsorption, deposition, conversion, and extraction, and subjecting the array of nanostructures to a particle beam consisting of particles having an energy of less than 1000 eV, wherein The direction of the particle beam is parallel to the surface perpendicular to the substrate within a deviation of ±20°, thereby achieving selective etching of the main surface of the array of nanostructures relative to the wall of the array of nanostructures, so that a recess is formed in each nanostructure in the array of nanostructures.

10. The method according to any one of claims 1 to 9, wherein All steps of the method are performed in the same process chamber.

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