Formation of arrays of nanostructures

Abstract

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

Description

[Technical Field]

[0001] The present invention relates to the formation of an array of nanostructures, which is part of or comprises a self-aligned multiple patterning process. [Background technology]

[0002] Integrated circuits have a limited supply, and there is a great need to continue miniaturizing electronic components such as transistors and memory chips. Developing and miniaturizing integrated circuits is extremely difficult. Production involves extremely high costs, a heavy environmental burden, and large investments. Direct patterning, such as with optical lithography, is not always possible due to the extremely tight scaling of critical dimensions in modern electronic components. This is because the critical dimensions are much smaller than the wavelength of light used in optical lithography. Therefore, diffraction of light limits the resolution of direct patterning.

[0003] Therefore, multiple patterning techniques have been introduced and are now used as complementary techniques to optical lithography. These patterning processes allow for further scaling of critical dimensions to smaller sizes. There are several different patterning techniques used in industry today to complement standard optical lithography. One example of an industrial multiple patterning method is called self-aligned multiple patterning, SAMP, or SAxP, and includes self-aligned double patterning, SADP, self-aligned quadruple patterning (SAQP), and self-aligned octuple patterning (SAOP). Self-aligned multiple patterning processes enable the fabrication of patterns below 100 nm.

[0004] The self-aligned multiple patterning process flow is an indirect patterning method that is typically used in combination with direct patterning, typically using optical lithography, in high-volume manufacturing. Self-aligned multiple patterning is used as an extension of traditional direct patterning to create smaller features that cannot be produced using available lithography. Self-aligned multiple patterning is used in applications such as the formation of fins in field-effect transistors (FETs), shallow trench isolation, lines and spaces for electrical interconnects, and bitline / wordline structures in memory devices. Very good process control is essential for self-aligned multiple patterning.

[0005] In self-aligned double patterning, spacer structures are formed on the sidewalls of an array of original structures disposed on a substrate or material layer. The spacer structures are typically formed by depositing a film over the existing pattern and then etching away all film material on the horizontal surfaces, leaving only the material on the sidewalls. Typically, the deposition on the existing pattern and the etching away of all film material on the horizontal surfaces are performed in different processing chambers, which leads to high costs and technical difficulties in controlling the process results. The array of original structures is then removed, leaving only the spacer structures. The structure density is doubled in this case, as there are now two spacer structures for every original structure.

[0006] A known problem with self-aligned double patterning is whether the spacer structures can remain in place after the original structure array material has been removed. Another problem is whether the profile of the spacer structures is acceptable. Yet another problem is whether the etching that removes the original structure array material will damage the underlying material. Furthermore, pattern transfer is complicated by situations where the removal of the original structure array material also removes some of the underlying material, or where the underlying material is insufficiently removed at corners. This can result in differences in the topography of the layer directly under the spacer structure or in the layer adjacent to the spacer structure.

[0007] When self-aligned double patterning is repeated, a further halving of the pitch is achieved. This is called self-aligned quadruple patterning. Repeating this process a second time results in a further halving of the pitch. This is called self-aligned octuple patterning. The number of iterations of this process is typically limited to eight patternings due to the accumulation of structural defects resulting from the above-mentioned problems of self-aligned double patterning.

[0008] In view of the above, there is room for improvement in the self-aligned multiple patterning process. Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above, it is an object of the present invention to provide an improved self-aligned multiple patterning process. [Means for solving the problem]

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

[0011] In this context, the phrase "nanostructures" should be interpreted as structures of intermediate size between structures on the scale of micrometers and structures made of single atoms.

[0012] This method can be applied multiple times, as with quadruple and octuple patterning, thus further increasing the resulting array density, and ultimately, by repeating the method a sufficient number of times, it can form arrays of structures made from a single atom. This allows for the formation of nanostructures of very small dimensions, preferably less than 20 nm, and even more preferably less than 10 nm, by using relatively large starting nanostructures, typically in the range between 1000 nm and 10 nm.

[0013] In this method, improved process control can be achieved due to the selective application of spacer structures onto the sidewalls of the first sacrificial nanostructure array. The selective application of spacer structures onto the sidewalls of the first sacrificial nanostructure array allows the self-aligned multiple patterning process to be performed multiple times within a single processing chamber, i.e., all process steps can be performed without repositioning the layer structure between different process steps. Furthermore, the selective application of spacer structures results in reduced distortion of the nanostructures, which in turn results in a more uniform array of "resulting" nanostructures formed from the self-aligned multiple patterning process. Nanostructures with fewer defects can also be provided. Therefore, effects of the self-aligned multiple patterning process, known as footing, shrinkage, bird's beak, tilting, kinking, and asymmetric gouging of the formed nanostructures, can be reduced or avoided.

[0014] Selectively applying spacer structures onto the sidewalls of the array of first sacrificial nanostructures comprises a cyclic modification process, each cycle of which comprises: i) isotropic modification of the exposed surface of the array of first sacrificial nanostructures and the exposed surface of the first material layer; and ii) anisotropic etching of the modified material from the top surface of the first material layer and the top surface of the first sacrificial nanostructures. The cyclic modification process is provided to form spacer structures on the sidewalls of the array of first sacrificial nanostructures.

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

[0016] The anisotropic etching may comprise dry etching.

[0017] In each cycle of the cyclic modification process, anisotropic etching may immediately follow isotropic surface modification.

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

[0019] The method may further comprise, between selectively applying spacer structures onto 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 structures on the sidewalls of the first material layer as an etch mask, and selectively applying additional spacer structures onto the sidewalls of the spacer structures and onto the sidewalls of the first material layer exposed by etching away the sublayer of the first material layer. Selectively applying additional spacer structures may be performed by the cyclic modification process discussed above.

[0020] The method further comprises subjecting the array of nanostructures formed from the first material layer to a cyclic etching process, each cycle comprising subjecting the array of nanostructures to surface modification by one or more of chemisorption, deposition, conversion, and extraction; and exposing 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, the particle beam having a direction that is parallel to a surface normal of the substrate within a deviation of ±20°, thereby achieving selective etching of the major surfaces of the array of nanostructures relative to the walls of the array of nanostructures, so that recesses are formed in each of the nanostructures in the array of nanostructures.

[0021] Additionally, the method may comprise a combination of isotropic surface modification and anisotropic selective material removal from horizontal surfaces in the same process step or in two consecutive, overlapping steps.

[0022] All steps of the method can be performed in the same processing chamber, thus reducing process time and costs, thus enabling sustainable and economical scaling of electronic and optical devices.

[0023] The spacer structures can be fabricated from hard masks such as carbon, TiN, silicon, silicon-germanium alloys, nitrides, oxides such as hafnium oxide, silicon oxide, aluminum oxide, and polymers such as fluorocarbon polymers.

[0024] The first sacrificial nanostructure can be fabricated from a mandrel material, such as an optical resist material, an extreme ultraviolet lithography (EUV) resist, an electron beam sensitive resist, a nanoimprint resist, or other polymers, carbon, amorphous carbon, crystalline silicon, amorphous silicon, polycrystalline silicon, nitrides, oxides, or other semiconductor materials, such as III-V or II-VI semiconductors, or alternatively, metals. These are just some examples of various materials that can be used to form the mandrels.

[0025] The substrate may be made of an insulating material, such as an oxide. Further areas of applicability will become apparent from the description provided hereinafter. However, it should be understood that the detailed description and specific examples are given by way of example only.

[0026] 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 should be noted that, as used in this specification and the appended claims, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of an element, unless the context clearly dictates otherwise. In this case, for example, reference to "a unit" or "the unit" may include several devices, etc. Furthermore, the words "comprising," "including," "containing," and similar terms do not exclude other elements or steps.

[0027] The above and other aspects are described in more detail below with reference to the accompanying figures, which should not be considered limiting, but rather are used for explanation and understanding.

[0028] As shown in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate general structures. Like reference numbers refer to like elements throughout. [Brief explanation of the drawings]

[0029] [Figure 1] 1A-1G comprise a schematic illustration of the formation of spacer structures on the sidewalls of an array of nanostructures using a cyclic modification process. [Figure 2] 2A-2D are diagrams illustrating the process steps of a self-aligned multiple patterning process. [Figure 3] 3A-3G illustrate schematically an alternative process for forming spacer structures on the sidewalls of an array of nanostructures using a cyclic modification process. [Figure 4] 4A to 4D are diagrams illustrating the process steps of a self-aligned multiple patterning process. [Figure 5] 5A-5G schematically illustrate a further alternative process for forming spacer structures on the sidewalls of an array of nanostructures using a cyclic modification process. [Figure 6] 6A and 6B comprise a schematic illustration of etching recesses in nanostructures formed using processes disclosed in the present disclosure. [Figure 7A] 1A-1D illustrate examples of nanostructured patterned surfaces that can be formed using the processes disclosed in the present disclosure. [Figure 7B] 1A-1D illustrate examples of nanostructured patterned surfaces that can be formed using the processes disclosed in the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown, although the invention can be embodied in many different forms.

[0031] The present disclosure is directed to improvements in self-aligned multiple patterning. Improvements in at least two different aspects of the self-aligned multiple patterning process are contemplated. Improvements are contemplated in both the formation of spacer structures on the sidewalls of the array of "starting" nanostructures and in the patterning of the "resulting" array of nanostructures formed from the self-aligned multiple patterning process.

[0032] The formation of spacer structures on the sidewalls of an array of "starting" nanostructures is discussed in connection with FIG. 1, which includes FIGS. 1A-1G. FIG. 1A shows a schematic representation of a starting layer structure comprising a starting pattern for a self-aligned multiple patterning process. The starting layer structure comprises a substrate 100 having an array of first sacrificial nanostructures 120 disposed thereon, and a first material layer 110 disposed between the substrate 100 and the array of first sacrificial nanostructures 120. It will be appreciated that the starting layer structure may comprise additional layers, so long as the top layer is an array of first sacrificial nanostructures 120. The array of first sacrificial nanostructures 120 represents the starting pattern. The array of first sacrificial nanostructures 120 may be formed, for example, by optical lithography. The width of the first sacrificial nanostructures 120 is typically in the range of 3-100 nm. The height of the first sacrificial nanostructures 120 is typically in the range of 3-200 nm. The pitch of the array of first sacrificial nanostructures 120 is typically in the range of 10 to 200 nm.

[0033] The substrate 100 may be formed from an oxide, a nitride, crystalline silicon, amorphous silicon, polycrystalline silicon, or other semiconductor material such as a III-V or II-VI semiconductor, or alternatively a metal or a polymer.

[0034] The first material layer 110 can be a hard mask, or a material such as crystalline silicon, amorphous silicon, polycrystalline silicon, an oxide, a nitride, or other semiconductor material such as a III-V or II-VI semiconductor, or alternatively a metal or a polymer.

[0035] The first sacrificial nanostructures 120 may be formed from a mandrel material, such as an optical resist, an extreme ultraviolet lithography resist, 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.

[0036] Selective application of spacer structures onto the sidewalls of the first sacrificial nanostructure array can be enabled, at least in part, by surface-controlled reactions such as adsorption, conversion, and extraction. Specifically, surface-limited adsorption reactions are important in atomic layer deposition, molecular layer deposition, atomic layer etching, and combinations thereof. Adsorption can be achieved by chemisorption, physisorption, diffusion, ion implantation, and combinations thereof. Conversion can be achieved by oxidation, nitridation, densification, crystallization, and combinations thereof. In the case of extraction, certain elements in the composite material of the top material layer are selectively removed, thus modifying the top surface. Extraction can also be achieved by oxidation. It is recognized that these surface-limited reactions need not be ideal, and several additional subsurface-limited processes may occur simultaneously. Therefore, effects known as process uniformity across multiple production wafers and pitch walking, known as pitch variation between different features resulting from process variations across multiple production wafers and causing mismatches in the critical dimensions of different features, can be reduced or even avoided in self-aligned multiple patterning processes.

[0037] Selective application of spacer structures onto the sidewalls of the first sacrificial nanostructure array can be made possible, at least in part, by anisotropically and selectively removing material generated on horizontal surfaces by an isotropic surface-controlled reaction. This can be achieved by gently activating the modified surface so as not to damage the material remaining on the surface. This anisotropic removal can be achieved, for example, by irradiating the nanostructure array with 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, with the particle beam oriented parallel to the surface normal of the substrate within ±20°, thereby achieving selective etching of the major surface of the nanostructure array relative to the nanostructure array walls. Thus, a final structure with reduced damage or completely damage-free at the final stage can be achieved, allowing the process to be repeated four or more times to create nanostructures that can be directly used as active structures in electronic and optical devices.

[0038] 1B-1G, formation of spacer structures 130 on sidewalls 122 of the array of first sacrificial nanostructures 120 is performed by selectively applying spacer structures 130 onto sidewalls 122 of the first sacrificial nanostructures 120. The process of selectively applying spacer structures 130 onto sidewalls 122 of the first sacrificial nanostructures 120 may comprise a cyclic modification process. FIGS. 1B and 1C schematically illustrate a first cycle of the cyclic modification process, FIGS. 1D and 1E schematically illustrate a second cycle of the cyclic modification process, and FIGS. 1F and 1G schematically illustrate a third cycle of the cyclic modification process. In this manner, the cyclic modification process comprises multiple cycles. It is understood that the cyclic modification process may comprise more than the three cycles illustrated in connection with FIG. 1.

[0039] The spacer structures 130 on the sidewalls 122 can be a hard mask, a semiconductor material, a metal, or a polymer such as a fluorocarbon polymer. The width of the spacer structures 130 is typically in the range of 3-100 nm. The height of the spacer structures is typically similar to the height of the first sacrificial nanostructures 120.

[0040] Each cycle in the cyclic modification process comprises: i) isotropic modification of the exposed surfaces of the array of first sacrificial nanostructures 120 and the exposed surface of first material layer 110; and ii) anisotropic etching of the modified material from the top surfaces of the first sacrificial nanostructures 120 and from the top surface of first material layer 110. The top surfaces may also be referred to as the horizontal surfaces of the first sacrificial nanostructures 120 and first material layer 110, respectively. In FIGS. 1B-1G, this is illustrated as first performing an isotropic modification of the exposed surfaces of the array of first sacrificial nanostructures 120 and the exposed surface of first material layer 110 (see FIGS. 1B, 1D, and 1F), followed by an anisotropic etching of the modified material from the top surfaces of the first sacrificial nanostructures 120 and from the top surface of first material layer 110 after each such isotropic modification (see FIGS. 1C, 1E, and 1G). As a result, with each cycle, spacer structures are progressively formed on the sidewalls 122 of the array of first sacrificial nanostructures 120. This is seen schematically in Figures 1C, 1E, and 1G by the progressively thicker structures on the sidewalls 122 of the array of first sacrificial nanostructures 120. After the final cycle of the cyclic modification process, spacer structures 130 are formed, see Figure 1G.

[0041] With reference to the schematic diagrams presented in FIGS. 1B-1G, the cyclic modification process is shown as having three cycles. It should be recognized that the schematic diagrams presented in FIGS. 1B-1G are merely schematic diagrams created to provide an understanding of the process. In practice, the number of cycles in the cyclic modification process can be in the range of 2 and 1000, preferably in the range of 3 to 50. The number of cycles can vary depending on the desired width of the spacer structures 130. The number of cycles can vary depending on which process is used to isotropically modify the exposed surfaces 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.

[0042] Isotropic modification can be viewed as a surface modification process. Therefore, all surfaces exposed to isotropic modification undergo surface modification. Isotropic modification includes one or more of deposition, adsorption, conversion, and extraction. Specifically, deposition can be by sputtering, epitaxy, evaporation, chemical vapor deposition, atomic layer deposition, molecular layer deposition, and combinations thereof. Adsorption can be by chemisorption, physisorption, diffusion, ion implantation, and combinations thereof. Conversion can be by oxidation, nitridation, densification, crystallization, and combinations thereof. In the case of extraction, certain elements are selectively removed in the composite material of the top material layer, thus modifying the top surface. Extraction can also be achieved by oxidation. Deposition can be performed by atomic layer deposition processes such as plasma-enhanced atomic layer deposition and thermal atomic layer deposition. Atomic layer deposition does not need to be ideal; quasi-atomic layer deposition processes can also be used.

[0043] Anisotropic etching includes dry etching. Suitable dry etching methods are continuous or cyclic etching methods. Examples of continuous etching methods include low-energy particle beam sputtering, e.g., using Ar ions, and low-energy particle beam sequential reactive ion etching, e.g., using 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 that has similar but slightly different process parameters from ideal atomic layer etching, e.g., process parameters outside the saturation region. The slightly different process parameters may indicate non-self-limiting process behavior. Quasi-atomic layer etching may offer a faster etching process at the expense of process stability, which may be preferable in some cases.

[0044] Preferably, in each cycle of the cyclic modification process, the anisotropic etching immediately follows the isotropic surface modification. This avoids the formation of a continuous film on the top surface of the first sacrificial nanostructures 120 and on the top surface of the first material layer 110, since the etching is carried out before any film nucleates on the top surface. This also avoids the formation of strain in the layer applied by the surface modification.

[0045] The cyclical reforming process may include additional steps, such as pumping, purging, and combinations, overlaps, and repetitions thereof. Pumping refers to pumping all process gases and reaction products and by-products out of the process chamber to a low pressure of at least 10E-3 Torr, preferably less than 10E-5 Torr. Purging refers to pumping an inert gas through the chamber at a high pressure, typically in the range of 1000 to 0.001 Torr, preferably in the range of 1 Torr to 10 mTorr.

[0046] After the formation of spacer structures 130 on the sidewalls 122 of the array of first sacrificial nanostructures 120, the self-aligned multiple patterning process can continue by selectively etching away, preferably dry etching, the array of first sacrificial nanostructures 120 so that the spacer structures 130 form an array of second sacrificial nanostructures 140. This is illustrated in connection with FIGS. 2A and 2B, where the selective etching away of the array of first sacrificial nanostructures 120 begins with the layer structure shown in FIG. 2A (the same layer structure as in FIG. 1F) and ends with the layer structure shown in FIG. 2B. In some applications, the self-aligned multiple patterning process can stop at this step. The array of second sacrificial nanostructures 140 may not be a sacrificial nanostructure in such applications, but may comprise an array of nanostructures for use in various applications, such as transistor channels, electrical interconnects, optical elements such as optical lattices, photonic crystals, and optical waveguides.

[0047] In some applications, the self-aligned multiple patterning process may continue by anisotropically etching the first material layer 110 using the array of second sacrificial nanostructures 140 as an etch mask. This is shown in connection with Figures 2B and 2C, i.e., etching of the first sacrificial nanostructures 110 begins with the layer structure shown in Figure 2B and ends with the layer structure shown in Figure 2C. Etching may be performed such that the first material layer is etched completely through, exposing the underlying layer, in this case, substrate 100.

[0048] The self-aligned multiple patterning process may continue by selectively removing, preferably using dry etching, the array of second sacrificial nanostructures 140. This is illustrated in connection with Figures 2C and 2D, i.e., removal of the array of second sacrificial nanostructures 140 begins with the layer structure shown in Figure 2C and ends with the layer structure shown in Figure 2D. This process exposes the array of nanostructures 150 formed from the first material layer.

[0049] As discussed in connection with FIG. 3 , including FIGS. 3A-3G , anisotropic etching of material from the top surface of the first material layer 110 can be performed during the cyclic modification process. This etching of material from the top surface of the first material layer 110 can form a slope 112 on the surface that forms the interface between the spacer structure 130 and the first material layer 110. This slope is a sloping surface of the material layer 110 that defines the flat surface of the material layer 110. The slope angle is typically within a range of 0 to 90 degrees, preferably 30 to 80 degrees, relative to the original surface. The width of the slope 112 is typically within a range of 3 to 100 nm, and the height of the slope 112 is typically within a range of 3 to 200 nm. Etching of material from the top surface of the first material layer 110 can be performed during one or more of the cycles of the cyclic modification process. Thus, etching of material from the top surface of the first material layer 110 can be performed during a portion of the cycles of the cyclic modification process. Alternatively, etching away 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. Anisotropic etching away material from the top surface of the first material layer 110 is shown schematically in Figures 3A-3G. In this schematic, anisotropic etching away material from the top surface of the first material layer 110 is performed in each cycle of the cyclic modification process, but as noted above, this is not always the case, and etching away material from the top surface of the first material layer 110 may be performed in only some of the cycles. Just as in the process described in connection with Figure 1, isotropic modification of the exposed surfaces of the array of first sacrificial nanostructures 120 and the exposed surface of the first material layer 110 (see Figures 3B, 3D, and 3F) occurs first in each cycle of the cyclic modification process.However, in addition to 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 layer of the exposed top surface of the first material layer 110 is also etched away in connection with the anisotropic etching (see FIGS. 3C, 3E, and 3G). Thus, a bevel at the surface forming the interface between the spacer structures 130 and the first material layer 110 is formed during the cyclic modification process by etching away material from the top surface of the first material layer 110 simultaneously with the gradual formation of the spacer structures 130 on the sidewalls 122 of the array of first sacrificial nanostructures 120. After the final cycle of the cyclic modification process, the spacer structures 130 are formed (see FIG. 3G), and these spacer structures 130 have a bevel 112 at the surface forming the interface between the spacer structures 130 and the first material layer 110.

[0050] As discussed in connection with FIG. 4, comprising FIGs. 4A-4D, after the formation of spacer structures 130 on the sidewalls 122 of the array of first sacrificial nanostructures 120, the self-aligned multiple patterning process can continue by selectively etching away the array of first sacrificial nanostructures 120 such that the spacer structures 130 form an array of second sacrificial nanostructures 140. The selective etching away of the array of first sacrificial nanostructures 120 is shown schematically in connection with FIGs. 4A and 4B, i.e., the selective etching away of the array of first sacrificial nanostructures 120 begins with the layer structure shown in FIG. 4A (the same layer structure as in FIG. 3F) and ends with the layer structure shown in FIG. 4B. 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 FIG. 2. To avoid undue repetition, reference is made to the above discussion. The self-aligned multiple patterning process may continue by etching the first material layer 110 using the array of second sacrificial nanostructures 140 as an etch mask. This is shown in conjunction with FIGS. 4B and 4C, i.e., etching of the first sacrificial nanostructures 110 begins with the layer structure shown in FIG. 4B and ends with the layer structure shown in FIG. 4C. Etching of the first material layer 110 is discussed in more detail above in conjunction with the discussion of FIG. 2 and will not be repeated here. Etching may be performed such that the first material layer is etched completely through to expose the underlying layer, in this case, the substrate 100. The self-aligned multiple patterning process may continue by removing the array of second sacrificial nanostructures 140. Removal of the array of second sacrificial nanostructures 140 is shown in conjunction with FIGS. 4C and 4D, i.e., removal of the array of second sacrificial nanostructures 140 begins with the layer structure shown in FIG. 4C and ends with the layer structure shown in FIG. 4D. The removal of the second array of sacrificial nanostructures 140 is discussed in more detail above in connection with the discussion of Figure 2 and will not be repeated here. This process exposes the array of nanostructures 150 formed from the first layer of material.The top surfaces of the nanostructures 150 thus formed are sloped due to the anisotropic etching removal of material from the top surface of the first material layer 110 as discussed in connection with Figure 3. This is one type of patterning of the "resulting" array of nanostructures formed from a self-aligned multiple patterning process, i.e., a sloped top surface of the "resulting" array of nanostructures may be formed.

[0051] With reference to FIG. 5, and particularly with reference to FIGS. 5A-5G of FIG. 5, an alternative patterning of the "resulting" array of nanostructures formed from the self-aligned multiple patterning process is described below. This alternative patterning of the "resulting" array of nanostructures formed from the self-aligned multiple patterning process aims to form a stepped top surface of the nanostructures in the array. A layer structure similar to that discussed with reference to FIG. 1A is used as a starting structure. The starting structure is shown in FIG. 5A. However, it is recognized that a different starting layer structure may be used, so long as the top layer in the layer structure is an array of first sacrificial nanostructures 120. Next, spacer structures 130 on the sidewalls of the array of first sacrificial nanostructures 120 are formed according to the process of selectively applying spacer structures 130 onto the sidewalls of the array of first sacrificial nanostructures 120 discussed above with reference to FIGS. 1B-1G. The resulting layer structure is shown in FIG. 5B. Note that the layer structure in FIG. 5B is similar to the layer structure in FIG. 1G. As the next step in the self-aligned multiple patterning process, portions of the first material layer 110 are etched away using the first sacrificial nanostructures 120 and the spacer structures 130 on the sidewalls 122 of the first material layer 110 as an etch mask. The result of such etching away of the portion of the first material layer 110 is shown schematically in FIG. 5C. Additional spacer structures 132 are then selectively applied onto the sidewalls of the spacer structures 130 and onto the sidewalls of the first material layer 110 exposed by etching away the portion of the first material layer 110. The additional spacer structures 132 are typically fabricated from the same material as the spacer structures 130. However, a different material from the material of the spacer structures 130 may also be used. The width of the additional spacer structures 132 is typically in the range of 3-100 nm. The height of the additional spacer structures 132 is typically in the range of 3-200 nm. The result of etching away the portion of the first material layer 110 is shown schematically in FIG. 5D. The selective application of the additional spacer structures 132 is preferably done by a cyclical modification process such as that discussed above in connection with FIG.To avoid excessive repetition, reference is made to the discussion above for providing a manner for selectively applying the additional spacer structures 132. The spacer structures 130 and the additional spacer structures 132 together form a stepped spacer structure 134. This process may continue by repeating the etching away of further portions of the layer of first material layer 110 and the selective application of further additional spacer structures to form one or more additional steps in the stepped spacer structure 134.

[0052] After the formation of the staircase-like spacer structures 134, the self-aligned multiple patterning process may continue by selectively etching away the first sacrificial nanostructures 120, such that the staircase-like spacer structures 134 form an array of second sacrificial nanostructures 140. The second sacrificial nanostructures 140 are composed of the same or modified material as the staircase-like spacer structures 134 and have the same or similar dimensions as the staircase-like spacer structures 134. The selective etching of the array of first sacrificial nanostructures 120 is illustrated schematically in connection with FIGS. 5D and 5E, i.e., the selective etching of the array of first sacrificial nanostructures 120 begins with the layer structure illustrated in FIG. 5D and ends with the layer structure illustrated in FIG. 5E. The selective etching of the array of first sacrificial nanostructures 120 is preferably performed in the same manner as discussed above in connection with FIG. 2. To avoid undue repetition, reference is made to the above discussion.

[0053] The self-aligned multiple patterning process may continue by etching the first material layer 110 using the array of second sacrificial nanostructures 140 as an etch mask. This is illustrated in connection with Figures 5E and 5F, i.e., etching of the first material layer 110 begins with the layer structure shown in Figure 5E and ends with the layer structure shown in Figure 5F. Etching of the first material layer 110 is discussed in more detail above in connection with the discussion of Figure 2 and will not be repeated here. Etching may be performed such that the first material layer is etched completely through to expose the underlying layer, in this case, the substrate 100.

[0054] The self-aligned multiple patterning process can continue by removing the array of second sacrificial nanostructures 140. Removal of the array of second sacrificial nanostructures 140 is illustrated in connection with FIGS. 5F and 5G, i.e., removal of the array of second sacrificial nanostructures 140 begins with the layer structure illustrated in FIG. 5F and ends with the layer structure illustrated in FIG. 5G. Removal of the array of second sacrificial nanostructures 140 was discussed in more detail above in connection with the discussion of FIG. 2 and will not be repeated here. This process exposes an array of nanostructures 150 formed from the first material layer 110. The array of nanostructures 150 is composed of the same material as the first material 110 or a modified material. The width of the nanostructures 150 is typically in the range of 3 to 100 nm. The height of the nanostructures 150 is typically in the range of 3 to 200 nm. The top surfaces of the nanostructures 150 thus formed are stepped due to the process of applying the stepped spacer structures 134. This is another type of patterning of the resulting nanostructure array formed from a self-aligned multiple patterning process, i.e., a stepped top surface of the resulting nanostructure array can be formed.

[0055] Arrays of nanostructures 150 formed according to any of the processes discussed above, i.e., arrays of nanostructures 150 formed according to the discussion of any one of Figures 2, 4, or 5, can be further divided into more finely stepped arrays of nanostructures. This is discussed in more detail in connection with Figures 6A and 6B, in which an array of nanostructures 150 formed as discussed in connection with Figure 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 comprises i) subjecting the array of nanostructures 150 to surface modification, and then ii) exposing the array of nanostructures to a particle beam, where the surface modification comprises one or more of chemisorption, deposition, conversion, and extraction. Here, the particle beam comprises 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. Here, the particle beam has a direction parallel to the surface normal of the layer structure within a deviation of ±20°, preferably ±10°. Particle beams with such low energy and direction relative to the major surfaces achieve a selective etching process that forms recesses in the exposed nanostructures starting from their major surfaces. Such cyclic etching processes for etching recesses in nanostructures are discussed in more detail in WO2017157902. Thus, the cyclic etching process achieves selective etching of the major surfaces of the array of nanostructures 150 relative to the walls of the array of nanostructures 150, such that one or more recesses 152, 154 are formed in each of the nanostructures 150 in the array. In the example of nanostructures 150 shown in connection with FIG. 6, two recesses are formed in each nanostructure 150. This is because each nanostructure 150 is stepped and has two distinct major surfaces.

[0056] All process steps of the self-aligned multiple patterning process discussed above can be performed in the same processing chamber. Furthermore, already established semiconductor foundries can be used to perform the processes discussed above.

[0057] Those skilled in the art will recognize that the present invention is by no means limited to what has been expressly described above, but rather many modifications and variations are possible within the scope of the appended claims.

[0058] For example, the top surfaces of the nanostructures formed by patterning the "resulting" nanostructure arrays discussed above can take on different shapes by combining the processes discussed in connection with Figures 3A-3G and 5A-5D. In this case, a mixture of slopes and steps can be formed. Some examples of such morphologies are shown schematically in Figures 7A and 7B.

[0059] Additionally, variations can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Claims

1. 1. A method for forming an array of nanostructures, comprising: providing a layer structure including an array of first sacrificial nanostructures (120) disposed on a support layer structure comprising at least a first material layer (110) and a substrate (100); selectively applying spacer structures (130) onto the sidewalls (122) of the array of first sacrificial nanostructures (120); Selectively etching away the array of first sacrificial nanostructures (120) such that the spacer structures (130) form an array of second sacrificial nanostructures (140); Etching the first layer of material (110) using the array of second sacrificial nanostructures (140) as an etch mask; removing the second array of sacrificial nanostructures (140), thereby exposing an array of nanostructures (150) formed from the first layer of material; Equipped with Selectively applying spacer structures (130) onto the sidewalls (122) of the array of first sacrificial nanostructures (120) comprises a cyclic modification process, each cycle comprising: an isotropic modification of the exposed surfaces of the array of first sacrificial nanostructures (120) and the exposed surface of the first material layer (110); 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); Equipped with whereby said spacer structures (130) are progressively formed on the sidewalls (122) of the array of said first sacrificial nanostructures (120).

2. The method of claim 1 , wherein the isotropic modification comprises one or more of deposition, adsorption, conversion, and extraction.

3. The method of claim 1 or 2, wherein the anisotropic etching comprises a dry etching.

4. 4. The method of claim 1, wherein in each cycle of the cyclic modification process, the anisotropic etching immediately follows the isotropic surface modification.

5. 5. The method of claim 1, wherein one or more of the cycles of the cyclic reforming process further comprises intermediate steps for removing residual gases and by-products, such as pumping steps, purging steps, or a combination thereof.

6. 6. The method of claim 1, further comprising anisotropically etching away material from a top surface of the first material layer (110) during the cyclical modification process, thereby forming a bevel (112) on a surface that forms an interface between the spacer structure (120) and the first material layer (110).

7. between selectively applying spacer structures (130) onto 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 nanostructures (120) and the spacer structures (130) on the sidewalls (122) of the first material layer (110) as an etching mask; 7. The method of claim 1, further comprising selectively applying additional spacer structures (132) onto sidewalls of the spacer structures (130) and onto sidewalls of the first material layer (110) exposed by the etching away of the portion of the first material layer.

8. The selective application of additional spacer structures (132) is accomplished by a cyclical modification process, each cycle comprising: isotropically modifying the exposed surfaces of the array of first sacrificial nanostructures (120) and the exposed surface of the first material layer (110); 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); Equipped with The method of claim 7, whereby the additional spacer structures (132) are formed incrementally on sidewalls of the spacer structures (130).

9. 9. The method of claim 1, further comprising: subjecting the array of nanostructures formed from the first material layer to a cyclic etching process, each cycle comprising subjecting the array of nanostructures to surface modification by one or more of chemisorption, deposition, conversion, and extraction; and exposing the array of nanostructures to a particle beam consisting of particles having an energy of less than 1000 eV, the particle beam having a direction that is parallel to a surface normal of the substrate within a deviation of ±20°, thereby achieving selective etching of a major surface of the array of nanostructures relative to a wall of the array of nanostructures, so as to form a recess in each of the nanostructures in the array of nanostructures.

10. 10. The method of claim 1, wherein all of the method steps are performed in the same processing chamber.

Images