Multiple patterning structures and methods of making the same

Abstract

This application provides a multi-patterned structure and its fabrication method, comprising: forming an epitaxial layer on a substrate; etching a Sigma trench within the epitaxial layer; the Sigma trench having a first inclined sidewall and a second inclined sidewall disposed opposite to each other; conformally depositing a metal hard mask layer on the surface of the Sigma trench; performing anisotropic etching back on the metal hard mask layer; retaining the metal hard mask layer on the first inclined sidewall and the second inclined sidewall respectively; using the metal hard mask layers of the first inclined sidewall and the second inclined sidewall as pattern transfer masks, etching downwards onto the substrate to form a multi-patterned structure. This method utilizes a single photolithography step to form multiple patterns, avoiding the challenge of controlling the overlay accuracy between two photolithography steps in traditional processes; simultaneously, the metal hard mask and the substrate have an ultra-high etch selectivity, maintaining good contour conformability and low line roughness.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a multi-patterned structure and its fabrication method. Background Technology

[0002] In the semiconductor manufacturing field, as the feature size of integrated circuits continues to shrink, a single photolithography exposure can no longer directly form the required dense patterns. Therefore, multiple patterning technology has become a key process for achieving smaller pitch patterns.

[0003] Currently, the mainstream dual patterning processes mainly include two technical routes: LELE and SADP. The LELE process requires two complete photolithography flows, involving two coating, exposure, development, and etching operations. Because of the alignment requirements between the two photolithography steps, the overlay accuracy between the upper and lower patterns directly determines the dimensional uniformity and positional accuracy of the final pattern. As feature sizes decrease, the tolerance for overlay accuracy becomes increasingly stringent, placing extremely high demands on the alignment performance and stability of the photolithography machine, significantly increasing equipment costs and process control difficulty.

[0004] SADP technology is mainly used in the front-end fabrication of fins for fin field-effect transistors. However, SADP typically uses silicon nitride as the spacer hard mask material. Due to limitations in the etching resistance and film quality of silicon nitride, the roughness of the hard mask edges is difficult to control, thus affecting the final pattern formation quality. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to form multiple patterns with controllable line edge roughness and reduced pitch with relatively low process difficulty.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for fabricating a multi-patterned structure, comprising: An epitaxial layer is formed on the substrate; A Sigma trench is etched within the epitaxial layer; the Sigma trench has a first inclined sidewall and a second inclined sidewall disposed opposite to each other. A metal hard mask layer is conformally deposited on the surface of the Sigma trench, and the metal hard mask layer is anisotropically etched back, with the metal hard mask layer retained on the first inclined sidewall and the second inclined sidewall respectively. Using the metal hard mask layers of the first and second inclined sidewalls as pattern transfer masks, the substrate is etched downwards to form a multi-patterned structure.

[0007] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is as follows: A multi-patterned structure is prepared by the above-described method for preparing a multi-patterned structure.

[0008] As described above, the present invention provides a multi-patterned structure and its fabrication method. By forming a metal hard mask layer on the inclined sidewalls of a Sigma trench and using the metal hard mask layers on the two inclined sidewalls as pattern transfer masks for etching, an unexpected effect is that a pair of mutually separated metal hard mask patterns can be obtained on the two inclined sidewalls using a single opening defined by a single photolithography step. This can convert a single photolithographic opening pattern into a multi-pattern with a smaller pitch, avoiding the problem of controlling the overlay accuracy between two photolithography steps in the traditional LELE process. At the same time, the metal hard mask and the substrate have an ultra-high etch selectivity, and the metal hard mask is almost undamaged during the downward etching process, so that the pattern transferred to the substrate can maintain good contour conformation and low line edge roughness. Attached Figure Description

[0009] Figure 1 This is a flowchart illustrating a method for preparing a multi-patterned structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the formation of an epitaxial layer in a method for preparing a multi-patterned structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the coating and exposure process in a method for preparing a multi-patterned structure according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the formation of Sigma grooves in a method for preparing a multi-patterned structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the deposited metal layer in a method for preparing a multi-patterned structure according to an embodiment of the present invention; Figure 6 This is a schematic diagram of hard mask etch-back in a method for fabricating a multi-patterned structure according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the deposition and filling material in a method for preparing a multi-patterned structure according to an embodiment of the present invention; Figure 8 This is a schematic diagram of grinding in a method for preparing a multi-patterned structure according to an embodiment of the present invention; Figure 9 This is a schematic diagram of the multiple pattern in a method for preparing a multiple patterned structure according to an embodiment of the present invention; Label Explanation: 101. Epitaxial layer; 102. Second silicon oxide layer; 103. Titanium nitride layer; 104. First silicon oxide layer; 105. First amorphous carbon layer; 106. Silicon carbide layer; 107. Second amorphous carbon layer; 108. Silicon oxide antireflective layer; 109. Photoresist layer; 110. Antireflective coating; 1. First inclined sidewall; 2. Second inclined sidewall; 3. Metal hard mask layer. Detailed Implementation

[0010] Definitions of terms are shown in Table 1: Table 1. Glossary of Terms

[0011] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0012] In existing dual patterning processes, the LELE process requires two complete photolithography steps, which presents challenges such as difficulty in controlling the overlay and high requirements for equipment. The SADP process, primarily used for fin formation in front-end processes for fin-type field-effect transistors, also suffers from difficulties in controlling the roughness of the silicon nitride hard mask line edges.

[0013] To at least address the aforementioned issues, Sigma-deposited metal is used as a hard mask for etching, enabling the creation of multiple patterns in a single photomask etching process. This method can be used to form multiple patterns with pitches of 14nm and smaller. Furthermore, the metal as a hard mask offers extremely high selectivity, resulting in better shape retention and improved control over edge roughness during pattern transfer.

[0014] The following describes in detail a method for preparing a multi-patterned structure according to the present invention. Please refer to [link / reference]. Figure 1 The method 100 includes S1 to S4: S1. An epitaxial layer 101 is formed on the substrate; S2. A Sigma trench is formed by etching within the epitaxial layer 101; the Sigma trench has a first inclined sidewall 1 and a second inclined sidewall 2 disposed opposite to each other. The cross-section of the Sigma trench is hexagonal, and the opposite left and right sides of the hexagon serve as the first inclined sidewall 1 and the second inclined sidewall 2, respectively.

[0015] S3. A metal hard mask layer 3 is conformally deposited on the surface of the Sigma trench. The metal hard mask layer 3 is then anisotropically etched back, leaving the metal hard mask layer 3 on the first inclined sidewall 1 and the second inclined sidewall 2, respectively. That is, after the metal hard mask layer 3 is deposited on the surface of the structure in S2, the deposited metal hard mask layer 3 is etched away to remove the metal hard mask layer 3 on the first inclined sidewall 1 and the second inclined sidewall 2.

[0016] S4. Using the metal hard mask layer 3 of the first inclined sidewall 1 and the second inclined sidewall 2 as a pattern transfer mask, the substrate is etched downward to form a multi-patterned structure.

[0017] As described above, the present invention provides a multi-patterned structure and its fabrication method. By forming a metal hard mask layer 3 on the inclined sidewalls of the Sigma trench, and using the metal hard mask layer 3 on the two inclined sidewalls as pattern transfer masks for etching, a pair of mutually separated metal hard mask patterns can be obtained on the two inclined sidewalls using a single opening defined by a single photolithography. This can convert a single photolithographic opening pattern into a multi-pattern with a smaller pitch, avoiding the problem of controlling the overlay accuracy between two photolithography processes in the traditional LELE process. At the same time, the metal hard mask and the substrate have an ultra-high etch selectivity, and the metal hard mask is almost undamaged during the downward etching process, so that the pattern transferred to the substrate can maintain good contour conformation and low line edge roughness.

[0018] In one embodiment of the present invention, the epitaxial layer 101 includes a silicon epitaxial layer, namely Si(111), having a (111) crystal orientation.

[0019] As can be seen from the above description, when using a silicon epitaxial layer with a (111) crystal orientation, the (111) crystal orientation silicon has a slower etching rate in the tetramethylammonium hydroxide etching solution, which can automatically form Sigma trench sidewalls with precise tilt angles in the silicon epitaxial layer, thus ensuring the uniformity of the sidewall angles.

[0020] In one embodiment of the present invention, step S2, forming a Sigma trench by etching the epitaxial layer 101, specifically comprises: S201. Dry etching is used to open the second silicon oxide layer 102 covering the epitaxial layer 101, exposing the epitaxial layer 101.

[0021] S202, Anisotropic wet etching is performed on the exposed epitaxial layer 101 along the (111) crystal orientation to form a Sigma trench with two inclined sidewalls.

[0022] As described above, the second silicon oxide layer 102 is first opened by dry etching to expose the silicon surface, and then anisotropic etching is performed along the (111) crystal direction by wet etching. The hard second silicon oxide layer 102 is opened quickly by dry etching to ensure the accurate transfer of pattern size. The selective etching characteristics of different crystal directions of silicon by wet etching are then utilized. The etching rate of the {100} crystal direction is much faster than that of the (111) crystal direction, so that a Sigma groove with two symmetrical tilted sidewalls can be automatically formed. The combination of dry and wet etching takes into account both pattern conformability and controllability of sidewall morphology.

[0023] In one embodiment of the present invention, the anisotropic wet etching of the exposed epitaxial layer 101 along the (111) crystal orientation in S2 includes: Anisotropic wet etching was performed using an etching solution containing tetramethylammonium hydroxide.

[0024] As described above, anisotropic wet etching is performed using an etchant containing tetramethylammonium hydroxide (TMAH). Since TMAH is an etchant with significant anisotropic etching characteristics for silicon, its etching rate for the silicon (111) crystal plane is much lower than that for the {100} and {110} crystal planes. This huge difference in etching rate causes the (111) crystal plane to be naturally exposed and become the etching termination surface during the TMAH etching process, thereby automatically forming a Sigma groove with two inclined sidewalls in the silicon epitaxial layer.

[0025] In one embodiment of the present invention, the mass percentage concentration of tetramethylammonium hydroxide in the etching solution in S2 is 22wt% to 24wt%.

[0026] As described above, the concentration of tetramethylammonium hydroxide in the TMAH etching solution is controlled within the range of 22wt% to 24wt%. Within this concentration range, the etching selectivity of the TMAH etching solution for the Si{100} and Si(111) crystal orientations reaches an optimal balance. This ensures a sufficiently fast etching rate for the {100} crystal orientation to meet process capacity requirements, while also ensuring a sufficiently slow etching rate for the (111) crystal orientation sidewalls, resulting in a flat and smooth inclined sidewall surface. If the concentration is below 22wt%, the etching rate for the {100} crystal orientation decreases, leading to longer process time and reduced capacity. If the concentration is above 24wt%, the etching rate for the (111) crystal orientation increases, resulting in impaired sidewall flatness and deteriorated edge roughness. Therefore, limiting the concentration to the narrower preferred range of 22wt% to 24wt% balances both the requirements for etching rate and sidewall quality.

[0027] In one embodiment of the present invention, the temperature of the anisotropic wet etching in S2 is 75°C to 85°C. The etching time is determined based on the specific morphology of the Sigma groove to be formed.

[0028] As described above, the temperature of TMAH anisotropic wet etching should be controlled within the range of 75°C to 85°C. Too low a temperature (below 75°C) results in insufficient anisotropic etching reactivity in the TMAH etchant, leading to a low etching rate for the {100} crystal orientation, significantly extending the process time required to form a complete Sigma trench and reducing production capacity. Conversely, too high a temperature (above 85°C) weakens the selective inhibition effect of the TMAH etchant on the (111) crystal orientation, causing significant etching of the (111) crystal orientation sidewalls, reducing sidewall smoothness, causing the tilt angle to deviate from the expected value, and potentially even deforming the bottom contour of the Sigma trench. Limiting the etching temperature to the preferred range of 75°C to 85°C ensures a sufficient etching rate while maximizing the etching inhibition effect of TMAH on the (111) crystal orientation, resulting in a Sigma trench morphology with smooth sidewalls and a clear contour.

[0029] In one embodiment of the present invention, S2, prior to performing anisotropic wet etching of the exposed epitaxial layer 101 along the (111) crystal orientation, includes cleaning the surface of the exposed epitaxial layer 101. That is, after dry etching is completed, the structure is cleaned; subsequently, an anisotropic etching is performed in the Si(111) crystal orientation using an etching solution containing tetramethylammonium hydroxide (TMAH), thereby automatically forming Sigma trenches along the crystal orientation.

[0030] As described above, by opening the second silicon oxide layer 102 and exposing the surface of the epitaxial layer 101 through dry etching and before performing TMAH anisotropic wet etching, a cleaning step is added to the exposed surface of the epitaxial layer 101. The CFx-containing gas used in the dry etching process may leave fluoropolymer byproducts and oxide thin layers on the surface of the epitaxial layer 101 after plasma etching. If these residues are not removed, they will hinder the effective contact between the TMAH etching solution and the silicon surface, resulting in uneven wet etching rate, deviation of the sidewall morphology of the Sigma tank from the expected angle, and even local defects that cannot be etched. By performing a pre-cleaning step before TMAH etching, the residues from dry etching and the natural oxide layer can be effectively removed, so that the silicon surface of the epitaxial layer 101 exposes a clean lattice structure, ensuring that the TMAH etching solution can uniformly contact the silicon surface and perform anisotropic etching along the (111) crystal direction, thereby improving the smoothness and morphological uniformity of the sidewall of the Sigma tank.

[0031] In one embodiment of the present invention, the material of the metal hard mask layer 3 is selected from materials with high coverage and filling properties and etch resistance, such as TaN / Ta2O3 / HfO.

[0032] As described above, a material with high coverage and etch resistance is selected as the metal hard mask layer 3. The high coverage ensures that a continuous, pinhole-free conformal cover layer can be formed on the inclined sidewall of the Sigma trench, avoiding pattern defects caused by discontinuous coverage. The etch resistance allows the metal hard mask layer 3 to withstand the long-term etching environment during subsequent downward etching, maintaining the integrity of the pattern outline and ensuring high-fidelity transfer of multiple patterns.

[0033] In one embodiment of the present invention, the step of conformally depositing the metal hard mask layer 3 in S3 specifically includes: The metal hard mask layer 3 is deposited using atomic layer deposition (ALD). The ALD temperature is 220°C to 260°C, and the pressure is 0.1 Torr to 0.5 Torr. Taking Ta₂O₃ as an example: tert-butyliminotantalum is chemically deposited with water vapor at 220-260°C and a low pressure of 0.1-0.5 Torr.

[0034] As described above, the metal hard mask layer 3 is deposited using atomic layer deposition (ALD), with the deposition temperature controlled between 220°C and 260°C and the pressure controlled between 0.1 Torr and 0.5 Torr. By utilizing the layer-by-layer growth characteristics of ALD technology, atomic-level conformal coverage can be achieved on the Sigma trench surface, ensuring that the film thickness is consistent across the top, middle, and bottom of the sidewalls, thus providing a uniform etching reference surface for subsequent anisotropic etching back.

[0035] In one embodiment of the present invention, the thickness of the metal hard mask layer 3 after conformal deposition in S3 is greater than 5 nanometers.

[0036] As described above, by controlling the thickness of the conformally deposited metal hard mask layer 3 to be greater than 5 nanometers, this thickness can ensure that sufficient mask thickness is retained on the inclined sidewalls to withstand the consumption of downward etching during the subsequent anisotropic etch-back process.

[0037] In one embodiment of the present invention, after anisotropic etching back of the metal hard mask layer 3 and before downward etching of the substrate using the retained metal hard mask layer 3 as a mask, the method further includes: A filler material, such as silicon, is deposited in the region between and outside the metal hard mask layer 3 located on the two inclined sidewalls in the Sigma trench; the filler material is then chemically and mechanically polished until the top surface of the filler material is flush with the top surface of the epitaxial layer 101.

[0038] The anisotropic etching of the metal hard mask layer 3 includes etching the metal hard mask layer 3 outside the Sigma trench and the oxide layer opening sidewalls using a combination of physical bombardment and chemical reaction. Specifically, etching gas containing CHF3 and Ar is introduced into the reaction chamber, and the metal hard mask material layer is decomposed by physical bombardment (Source / bias 1000 / 250-500). At the same time, the fluoride generated by the reaction of the decomposition products with the etching gas is extracted from the reaction chamber.

[0039] The specific steps of chemical mechanical polishing include: firstly, rough polishing is used to initially remove the filler material on the epitaxial layer 101 and the second silicon oxide layer 102; then, fine polishing is performed on the remaining filler material on the epitaxial layer 101, and the polishing torque is detected in real time during the polishing process. When the change value of the polishing torque reaches the preset threshold, it is determined that the polishing has reached the interface of the epitaxial layer 101, and the polishing is stopped.

[0040] As described above, after anisotropic etching and before downward etching, a filler material is deposited in the Sigma trench and chemically mechanically ground until the top surface of the filler material is flush with the top surface of the epitaxial layer 101. The filler material provides mechanical support to the area between the metal hard mask layers 3 on both sides of the Sigma trench, preventing collapse or displacement caused by the metal hard mask layers 3 being suspended or under uneven stress during subsequent downward etching. At the same time, grinding flattens the surface of the structure, eliminating the surface height difference caused by the Sigma trench, providing a uniform etching starting plane for subsequent downward etching, and ensuring the uniformity of the etching depth.

[0041] In one embodiment of the present invention, the filling material is polycrystalline silicon.

[0042] As described above, polycrystalline silicon is used as the filler material. Polycrystalline silicon and silicon epitaxial layer belong to the same material system. During chemical mechanical polishing, it has a polishing rate that matches that of silicon epitaxial layer, which makes it easy to accurately control the polishing endpoint by changing the polishing torque. At the same time, polycrystalline silicon and metal hard mask layer 3 have a high polishing selectivity, which can automatically stop at the top surface of metal hard mask layer 3 during polishing, avoiding over-polishing damage to the top of metal hard mask layer 3 and ensuring the high consistency of metal hard mask layer 3.

[0043] In one embodiment of the present invention, the substrate comprises, from bottom to top, a titanium nitride layer 103, a first silicon oxide layer 104, a first amorphous carbon layer 105, and a silicon carbide layer 106; subsequently, an epitaxial layer 101 is formed on the silicon carbide layer 106. During etching, the epitaxial layer 101, the silicon carbide layer 106, the first amorphous carbon layer 105, and the first silicon oxide layer 104 are etched to form a multi-patterned structure.

[0044] As described above, the substrate structure is specifically defined as a multilayer stacked structure comprising, from bottom to top, a titanium nitride layer 103, a first silicon oxide layer 104, a first amorphous carbon layer 105, and a silicon carbide layer 106. The titanium nitride layer 103 serves as the bottom conductive and adhesion layer, providing good electrical contact and interlayer adhesion in subsequent processes. The first silicon oxide layer 104 serves as an isolation layer, acting as a grinding stop layer and etching barrier layer during subsequent chemical mechanical polishing and downward etching. The first amorphous carbon layer 105 serves as a sacrificial filler material in the hard mask stack, protecting the underlying structure during dry etching and polishing. The silicon carbide layer 106, as a top layer material with high hardness and high etch resistance, provides a high-quality lattice-matched substrate for the subsequent growth of the epitaxial layer 101. Furthermore, during the formation of the Sigma trench above the epitaxial layer 101 and the downward etching of the metal hard mask, the silicon carbide layer 106 can withstand the etching environment and maintain structural stability, ensuring the integrity of the pattern transfer.

[0045] In one embodiment of the present invention, forming the epitaxial layer 101 on the substrate includes: The epitaxial layer 101 is epitaxially grown on the silicon carbide layer 106; A second silicon oxide layer 102, a second amorphous carbon layer 107, and a silicon oxynitride antireflective layer 108 are sequentially deposited on the epitaxial layer 101. A patterned photoresist layer 109 is formed on the silicon oxynitride antireflective layer 108, and the pattern of the photoresist layer 109 defines the opening position of the Sigma trench. During etching, the patterned photoresist layer 109 is formed on the silicon oxynitride antireflective layer 108. Then, using the photoresist layer 109 as a mask, the silicon oxynitride antireflective layer 108, the second amorphous carbon layer 107, and the second silicon oxide layer 102 are sequentially etched using fluorocarbon gas (CFx) until the epitaxial layer 101 is exposed.

[0046] As described above, by epitaxially growing a (111) oriented silicon epitaxial layer on the silicon carbide layer 106, the silicon carbide and silicon have a good lattice matching degree, which can obtain a high-quality, low-defect-density single-crystal silicon epitaxial layer, providing a structural basis for the subsequent TMAH anisotropic wet etching to form precise (111) oriented Sigma trench sidewalls. Furthermore, a second silicon oxide layer 102, a second amorphous carbon layer 107, and a silicon oxynitride antireflective layer 108 are sequentially deposited on the epitaxial layer 101. This three-layer stacked structure performs specific functions in both photolithography and dry etching processes. The pattern of the photoresist layer 109 defines the opening position of the Sigma trench, allowing the basic position for subsequent formation of multiple patterns to be determined in a single photolithography step, avoiding the overlay accuracy problem between two photolithography steps.

[0047] Please refer to Figures 2 to 9 This embodiment provides a specific preparation process to illustrate the preparation method of the above-mentioned multiple patterned structures: Step 1, forming epitaxial layer 101: An epitaxial layer 101 (111) is grown on the silicon carbide layer 106; please refer to Figure 2 The substrate, from bottom to top, comprises a titanium nitride layer 103, a first silicon oxide layer 104, a first amorphous carbon layer 105, and a silicon carbide layer 106; an epitaxial layer 101 (111), a second silicon oxide layer 102, a second amorphous carbon layer 107, and a silicon oxynitride antireflective layer 108 are sequentially formed on the silicon carbide layer 106. That is, S1 is executed.

[0048] Step 2, Applying Adhesive and Exposure: Please refer to... Figure 3 A bottom anti-reflective coating 110 and a photoresist layer 109 are sequentially disposed on the silicon oxynitride anti-reflective layer 108.

[0049] Step 3: Etching to form Sigma grooves: Please refer to... Figure 4 The structure is etched using a combination of dry and wet etching to form Sigma trenches in epitaxial layer 101. This is equivalent to executing S2.

[0050] Step 4, Deposit the metal layer: Please refer to... Figure 5 A metallic hard mask layer 3 is formed on the surface of the structure using the ALD method. That is, the step of conformally depositing the metallic hard mask layer 3 on the surface of the Sigma trench in S3 is performed.

[0051] Step 5, Hard Mask Etching Back: Please refer to... Figure 6 The metal hard mask layer 3, outside the oxide layer opening sidewalls and on both sides of the Sigma tank, is removed through physical bombardment and chemical reaction. Execution S3 is complete.

[0052] Step 6, Deposition of filling material: Please refer to... Figure 7 Silicon is deposited in a Sigma tank, ensuring that silicon is deposited both inside the Sigma tank and on the surface of the structure. In this step, polycrystalline silicon can be deposited.

[0053] Step 7, Grinding: Please refer to... Figure 8 The structure is polished by CMP to the interface between the second silicon oxide layer 102 and the epitaxial layer 101 (including filled polysilicon and Si(111)).

[0054] Step 8: Create a multiplicity graph: Please refer to... Figure 9 The metal hard mask layer 3 deposited in step 4 is used as a hard mask for downward etching to form a multi-layered pattern.

[0055] The present invention also provides a multi-patterned structure, comprising: a substrate and an epitaxial layer disposed on the substrate; a Sigma trench formed in the epitaxial layer; the cross-section of the Sigma trench is hexagonal, including a first inclined sidewall 1 and a second inclined sidewall 2 disposed opposite to each other; and a metal hard mask layer 3 located on the first inclined sidewall 1 and the second inclined sidewall 2.

[0056] In summary, this invention provides a multi-patterned structure and its fabrication method. By forming a metal hard mask layer on the inclined sidewalls of a Sigma trench and using the metal hard mask layers on the two inclined sidewalls as pattern transfer masks for etching, an unexpected effect is achieved: Based on a single aperture pattern defined by a single lithography step, a pair of separate metal hard mask patterns can be obtained simultaneously on the two inclined sidewalls of the Sigma groove. Without performing a second lithography step, a single pattern can be converted into a double pattern with a pitch reduced by half. This fundamentally eliminates the impact of overlay accuracy deviation between multiple lithography steps on the final pattern quality and breaks through the bottleneck of existing LELE processes that are limited by the alignment accuracy of the lithography machine.

[0057] Building upon this, the metal hard mask exhibits a significantly higher etch selectivity for the underlying silicon / silicon oxide material than the silicon nitride mask. This ensures that the two metal hard mask patterns maintain their contour integrity throughout the etching process, avoiding the edge roughness degradation caused by the etching of the silicon nitride hard mask in the SADP process. This achieves superior pattern conformal preservation and critical dimension uniformity compared to existing solutions without introducing complex sidewall process steps.

[0058] As can be seen, this invention breaks away from the existing technical paths of "frequency doubling by two lithography steps" (LELE) and "frequency doubling by sidewalls" (SADP). Instead, it utilizes the geometric features of the Sigma groove itself as the structural basis for pattern frequency doubling. Under single lithography conditions, it simultaneously achieves the triple goals of pitch reduction, overlay elimination, and line edge roughness improvement. This represents a fundamental shift in technical thinking. Moreover, it does not require high-precision overlay equipment or complex sidewall process control. Those skilled in the art would find it difficult to readily conceive of using the self-aligned Sigma groove as the structural basis for pattern frequency doubling based on existing technologies.

[0059] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a multi-patterned structure, characterized in that, include: An epitaxial layer is formed on the substrate; Sigma trenches are etched within the epitaxial layer; The Sigma groove has a first inclined sidewall and a second inclined sidewall that are arranged opposite to each other; A metal hard mask layer is conformally deposited on the surface of the Sigma trench, and the metal hard mask layer is anisotropically etched back, with the metal hard mask layer retained on the first inclined sidewall and the second inclined sidewall respectively. Using the metal hard mask layers of the first and second inclined sidewalls as pattern transfer masks, the substrate is etched downwards to form a multi-patterned structure.

2. The method for preparing a multiple patterned structure according to claim 1, characterized in that, The epitaxial layer includes a silicon epitaxial layer having a (111) crystal orientation.

3. The method for preparing a multiple patterned structure according to claim 2, characterized in that, The step of etching to form Sigma trenches in the epitaxial layer specifically includes: Dry etching is used to open the second silicon oxide layer covering the epitaxial layer, exposing the epitaxial layer. The exposed epitaxial layer is anisotropically wet-etched along the (111) crystal orientation to form a Sigma trench with two inclined sidewalls.

4. The method for preparing a multiple patterned structure according to claim 3, characterized in that, Prior to performing anisotropic wet etching of the exposed epitaxial layer along the (111) crystal orientation, the process includes: The exposed surface of the epitaxial layer is cleaned.

5. The method for preparing a multiple patterned structure according to claim 1, characterized in that, After anisotropic etching back of the metal hard mask layer, and before downward etching of the substrate using the retained metal hard mask layer as a mask, the method further includes: A filler material is deposited in the region between and outside the metal hard mask layer located on the two inclined sidewalls in the Sigma trench; and the filler material is chemically and mechanically ground until the top surface of the filler material is flush with the top surface of the epitaxial layer.

6. The method for preparing a multiple patterned structure according to claim 5, characterized in that, The filler material is polycrystalline silicon.

7. The method for preparing a multiple patterned structure according to claim 1, characterized in that, The substrate comprises, from bottom to top, a titanium nitride layer, a first silicon oxide layer, a first amorphous carbon layer, and a silicon carbide layer.

8. The method for preparing a multiple patterned structure according to claim 7, characterized in that, The formation of the epitaxial layer on the substrate includes: The epitaxial layer is epitaxially grown on the silicon carbide layer; A second silicon oxide layer, a second amorphous carbon layer, and a silicon oxynitride antireflective layer are sequentially deposited on the epitaxial layer, and a patterned photoresist layer is formed on the silicon oxynitride antireflective layer, wherein the pattern of the photoresist layer defines the opening position of the Sigma trench.

9. A multi-graphical structure, characterized in that, It is prepared by the method for preparing a multi-patterned structure according to any one of claims 1-8.

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