A patterning method suitable for semiconductor processing

Abstract

A target layer to be patterned is formed on a support substrate. An etch stop layer and a first mask layer are prepared in sequence on the target layer. According to an embodiment of the invention, the first mask layer is patterned as a regular two-dimensional array of openings. In a first directional etching step, the openings in the first mask layer are enlarged, thereby forming a pattern of first parallel trenches in the first mask layer. A second mask layer can be prepared after thinning the patterned first mask layer. The second mask layer is patterned as the same regular array of openings, and then subjected to a second directional etching step which enlarges the openings in the second mask layer, thereby forming second parallel trenches extending in a direction crossing the first trench direction. The second directional etching also removes exposed portions of the first mask layer, so that the latter is finally patterned as a column pattern. After peeling off the second mask layer with respect to the columns, the column pattern is transferred to the target layer.

Description

Technical Field

[0001] This invention relates to semiconductor manufacturing processes, and more particularly to patterning methods applicable to said processes. Background Technology

[0002] Semiconductor manufacturing relies on advanced lithography and etching techniques that enable nanoscale patterns to be created at the deepest levels of both front-end and back-end processes. However, even the most advanced EUV lithography tools are limited in terms of achievable resolution, requiring expensive multiple-exposure methods to etch features smaller than these resolution limitations.

[0003] Producing columnar feature arrays with sub-resolution pitch using traditional single or multiple exposure lithography tools is particularly challenging. Summary of the Invention

[0004] This invention relates to a method according to the appended claims. A target layer to be patterned is formed on a support substrate. An etch stop layer and a first mask layer are sequentially fabricated on the target layer. According to an embodiment of the invention, the first mask layer is patterned as a regular two-dimensional array of openings. A regular array is an array in which the openings have the same in-plane dimensions and are ordered according to a repeating pattern. The array can be a square or rectangular pattern, in which the openings are arranged in vertical rows and columns. The openings can also be arranged in rows and columns at angles other than 90°. This is typically achieved by patterning a resist layer and transferring the resist pattern to the first mask layer, wherein the transfer may involve thinning the first mask and / or removing one or more upper sublayers of the first mask if the first mask is a multilayer stack. In a first directional etching step, the openings in the first mask layer are enlarged to form a pattern of first parallel trenches in the first mask layer. This trench pattern can then be transferred to the etch stop layer, or the transfer can be performed later in the process. A second mask layer can be fabricated after thinning the patterned first mask layer. The second mask layer is patterned into the same regular array of openings, and then a second directional etching step is performed on the second mask layer, which enlarges the openings in the second mask layer to form second parallel trenches extending in a direction intersecting the direction of the first trench. The second directional etching also removes portions of the first mask layer exposed to the etchant applied in the second directional etching step (which may be thinned), such that the latter (the first mask layer) is ultimately patterned into a pillar pattern. After the second mask layer is stripped relative to the pillars, the pillar pattern is transferred to the target layer.

[0005] When performing the above-described process by patterning the first and second mask layers using an identical rectangular array of openings, it is advantageous to perform a directional etching step in a direction that intersects the orthogonal directions of the rows and columns of the rectangular pattern. By applying such a directional etching direction, for example at 45° and 135° relative to the column and row directions, the resulting column array has a smaller spacing than the spacing of the openings in the array. Therefore, column arrays can be fabricated at sub-resolution spacing using only a single photomask.

[0006] Another useful application is achieved by applying a rectangular array of openings, but with the selected openings omitted; that is, the openings are etched in the individual mask layers before each directional etching step, except at selected locations. By applying directional etching directions along the row and column directions of the array, a pattern of lines and pillars is obtained that would otherwise be difficult to obtain without applying multiple masks.

[0007] This invention specifically relates to a patterning method suitable for semiconductor manufacturing processes, the method comprising the following steps: - Prepare the target layer to be patterned on the support substrate. - An etch stop layer is prepared on the target layer, and then a first mask layer is prepared on the etch stop layer. - The first mask layer is patterned to represent a pattern of either a regular two-dimensional array of openings or an array obtained by omitting one or more openings from a regular two-dimensional array. - A first directional etching step selectively applied relative to the etch stop layer is performed, wherein the first directional etching step widens the opening in a first direction, such that the first mask layer is patterned into an array of parallel linear trenches oriented along the first direction. - Then, a second mask layer is prepared. - The second mask layer is patterned according to the same pattern representing the array of openings. - A second directional etching step, selectively applied relative to the etch stop layer, is performed, wherein the second directional etching step expands the openings in the second mask layer in a second direction intersecting the first direction, such that the second mask layer is patterned into an array of parallel linear trenches oriented along the second direction, and wherein the second directional etching step further removes portions of the patterned first mask layer exposed to the etchant applied in the second directional etching step, such that the first mask layer is patterned into a final pattern comprising an array of pillars and / or lines. - Peel off the second mask layer relative to the pillars and / or lines. - Transfer the pattern defined by the pillars and / or lines to the target layer.

[0008] In the methods described in the preceding paragraph, the term 'directional etching' refers to any method in which an etching beam sweeps across a substrate to etch a layer on the substrate at a much higher etching rate in the scanning direction than in a direction orthogonal to the scanning direction. This capability allows the layer to be patterned by sweeping a plasma beam through an existing opening in the layer to 'stretch' that opening. The term 'stretch' can mean that the beam moves relative to the patterned layer and vice versa, but in this context it also refers to a type of directional etching in which the beam is stationary but oriented according to a given direction to thereby obtain the same elongation effect as a beam that is actually moving.

[0009] According to one embodiment, after the first directional etching step and before the step of preparing the second mask layer, the patterned first mask layer is thinned.

[0010] According to one embodiment, prior to the step of preparing the second mask layer, the pattern of the patterned first mask layer is transferred to the etch stop layer, and prior to the step of transferring the pattern defined by the pillars and / or lines to the target layer, the pattern of the patterned second mask layer is transferred to the etch stop layer.

[0011] According to one embodiment, prior to the step of preparing the second mask layer, the pattern of the patterned first mask layer is not transferred to the etch stop layer, and the pattern defined by the pillars and / or lines is transferred to the etch stop layer before the pattern defined by the pillars and / or lines is transferred to the target layer.

[0012] According to one embodiment: - A regular array of openings is a rectangular array extending in two perpendicular directions, with one or more openings omitted from this rectangular array. - The first direction of the first directional etching step is oriented according to one of the directions of the vertical direction of the array of openings, and - The second direction of the second directional etching step is oriented according to another direction in the vertical direction of the array of openings.

[0013] According to one embodiment: - The regular array with openings is a rectangular array extending in two vertical directions. - The first direction of the first directional etching step is oriented between the two orthogonal directions. - The second direction of the second directional etching step is perpendicular to the first direction.

[0014] According to one embodiment, the first direction is oriented at 45° relative to the two orthogonal directions.

[0015] According to one embodiment, the opening is a hole having a circular cross-sectional shape.

[0016] According to one embodiment, the first mask layer includes a stack of sublayers, the stack comprising, from bottom to top, the following layers: - A first hard mask layer with a thickness of t1 - A second hard mask layer with a thickness greater than t1. - A third hard mask layer with a thickness approximately equal to t1.

[0017] Furthermore, during the transfer of the opening pattern from the patterned resist layer formed on the first mask layer to the first mask layer, the third hard mask layer is consumed, such that a first directional etching step is performed on the stack formed by the first and second hard mask layers.

[0018] According to one embodiment, the second hard mask layer is peeled off relative to the first hard mask layer before the step of preparing the second mask layer.

[0019] According to one embodiment, the second mask layer includes a stack of sublayers, which, from bottom to top, include the following layers: - A first hard mask layer with a thickness of t1 - A second hard mask layer with a thickness less than t1. Furthermore, the second hard mask layer is consumed during the process of transferring the opening pattern from the patterned resist layer formed on the second mask layer to the second mask layer. Attached Figure Description

[0020] Figure 1 The main components of a tool suitable for directional etching are shown.

[0021] Figure 2a and 2b The process of directional etching is shown.

[0022] Figures 3 to 10 The method steps according to a first embodiment of the present invention, starting from an open rectangular array, are shown.

[0023] Figures 11a to 11c The diagram illustrates a pattern that can be obtained by starting with an array of openings (where several openings have been omitted from the complete array), which includes columnar and linear features.

[0024] Figures 12 to 18 A second embodiment of the invention is shown, wherein a column array is obtained with a smaller spacing than the array of openings that the method begins with. Detailed Implementation

[0025] For example, patent publication US10790155 describes the basic principles and construction for achieving directional patterning. According to the technique described in the cited document, a plasma beam is scanned relative to a substrate including the layer to be patterned. By adjusting several parameters and conditions, the plasma beam containing the etchant material can be guided such that the beam etches the layer on the wafer at a much higher etch rate in the scanning direction than in a direction orthogonal to the scanning direction. This capability allows an opening in the layer to be 'stretched' by scanning the plasma beam across it. The term 'stretch' can mean that the beam moves relative to the patterned layer and vice versa, but in this context it also refers to a type of directional etching in which the beam is stationary but oriented according to a given direction to thereby obtain the same elongation effect as a beam that is actually moving (see More for a more detailed reference to different types of directional etching).

[0026] Figure 1 A process tool 1 is shown for applying a specific directional etching technique currently known in the prior art. However, the invention is not limited to this technique. The tool includes a plasma chamber 2, which is surrounded by an RF coil 3 and used to generate plasma within the chamber. A gas inlet 4 is capable of supplying gaseous material, while the total pressure in the plasma chamber is maintained at a very low to vacuum level by a suitable vacuum pump device (not shown). The plasma chamber 2 is separated from the process chamber 5 by a separating wall 6 including a slit 7, from which a ribbon plasma beam 8 is emitted. The process chamber is also at a low to vacuum pressure. A meniscus 9 may be mounted at a distance from the slit 7, which may be set to control the propagation direction of the emitted beam 8. A wafer stage 15 is mounted in the process chamber 5. The wafer stage 15 is linearly movable as indicated by the arrow, such that a wafer 16 held by the wafer stage can be moved relative to one of the beams 8, thereby creating an equivalent scanning of the beam 8 on the wafer 16.

[0027] As described above, other directional etching techniques are known and can be applied to the method according to the invention. Ion beam-based techniques include a method in which a collimated beam of charged particles (e.g., Ar+) is accelerated across the entire wafer at a given incident angle. In the latter method, the wafer stage does not move relative to the beam as it irradiates the entire wafer. According to another known ion beam-based technique, a collimated beam of ionized gas clusters is accelerated to a point and scanned across the wafer surface at a given incident angle. In both of these latter techniques, the incident angle of the beam is adjusted by tilting the wafer.

[0028] Figure 2a and 2b It shows the use of Figure 1The tool shown illustrates the directional etching effect on layer 17 formed on wafer 16. This layer 17 is fabricated on an etch stop layer 18. Before applying the directional etching process, openings 19 are formed in layer 17 by standard photolithography and etching (e.g., by direct ion etching (DIE)). A plasma beam 8 is generated and oriented at an incident angle α, defined as the angle between the beam 8 and a direction perpendicular to the surface of layer 17. By along... Figure 1 The wafer stage 15 is moved in the direction shown, scanning the plasma beam 8 relative to layer 17 along the scanning direction X. The angle β between the beam 8 and the scanning direction X is an oblique angle equal to 90° + α. By applying a suitable combination of etching parameters (such as RF power, DC bias connected to the separator 6 and / or wafer stage 15, applied etchant, incident angle α, and scanning speed), scanning the beam across the opening 19 has the effect of stretching the opening in the scanning direction, as... Figure 2b As shown. The directional etching process is selective relative to the etch stop layer 18, ensuring that this layer remains substantially intact and preventing etching of the underlying support substrate 16. The etching rate in the X direction is significantly higher than the etching rates in the Y and Z directions. As a result, the opening 19 elongates in the X direction to form a linear trench 20. Due to the non-zero etching rate in the Y direction, the line is slightly larger than the original aperture of the opening in the Y direction. Etching in the Z direction results in a thinning of layer 17, with a reduction in layer thickness of a.

[0029] The method according to the first embodiment of the present invention is in Figures 3 to 13 As shown in the figure. The objective is to pattern a target layer 25 formed on a support substrate 26. The target layer 25 can be any layer that needs to be patterned during a semiconductor manufacturing process, such as a dielectric layer formed during the back-end manufacturing process of an integrated circuit fabricated on a silicon wafer, where the dielectric layer needs to be patterned by creating columnar and / or linear features. However, the invention is not limited to any type of layer to be patterned, nor is it limited to any specific stage of the semiconductor manufacturing process.

[0030] Reference Figure 3 An etch stop layer 27 is formed on top of the target layer 25, followed by a mask layer 28 comprising three sublayers: a bottom hard mask layer 28a, a middle hard mask layer 28b, and a top hard mask layer 28c. In this context, a mask layer is defined as any layer configured to be patterned into a given pattern and subsequently transferred to a layer below that mask layer. In this context, transferring a pattern from a patterned mask layer to a lower layer is defined as etching that lower layer by an etch process that reproduces the mask pattern in that lower layer.

[0031] The stacking of hard mask layers 28a-28c is one possible embodiment of the 'mask layer' mentioned in the appended claims. Within a broader scope of the invention, the mask layer can have other physical appearances. It can be a single layer, such as a photoresist layer. The three-sublayer stack 28a-28c can be used to fabricate very small features with dimensions on the nanometer scale. However, the invention is not limited to any specific size of the patterned features fabricated by the method of the invention.

[0032] The material of the etch stop layer 27 can depend on the combination of hard mask stack materials, but can be a metal-based material (e.g., Ti, TiN, TiO2, TiON, Ta, TaN…), an aluminum-based dielectric material, or a silicon-based material, such as amorphous silicon. The material of the bottom hard mask layer 28a depends on the combination of hard mask stack materials, but can be a dielectric material used in semiconductor manufacturing, such as spin-coated glass, SiOC, SiO2, SiN, SiON, SiCN, SiOCN, SiC, or a metal-based material (e.g., Ti, TiN, TiO2, TiON, Ta, TaN…) or an aluminum-based dielectric material. The middle hard mask layer 28b can be, for example, a layer containing organic carbon, such as amorphous carbon, diamond-like carbon (DLC), or spin-coated carbon (SOC). The top hard mask layer 28c can be made of the same material as the bottom layer 28a, or one of the possible materials for the bottom layer. The thicknesses of the top layer 28a and the bottom layer 28c are preferably the same and less than the thickness of the middle layer 28b. In a particular non-limiting embodiment shown in the accompanying drawings, the thicknesses of the top hard mask layer 28a and the bottom hard mask layer 28c can be on the order of 10-15 nm, while the thickness of the middle layer 28b can be on the order of 50-100 nm.

[0033] A resist layer 29 is formed on top of the mask layer 28 and patterned into a pattern of openings 30 using standard photolithography. This pattern is a regular array of circular openings 30 of uniform diameter, but other shapes of the opening cross-sections are also possible. In the case shown, the pattern is square, meaning the openings are arranged in orthogonal rows and columns, with the spacing between the openings constant in both directions. The diameter of the openings 30 can be on the order of 20 nm. Other array configurations are also possible, such as a hexagonal array of openings.

[0034] Reference Figure 4 The pattern of opening 30 is transferred to mask layer 28. This can be achieved by first etching the top mask layer 28c relative to resist 29 using a first etching formulation. Then, the intermediate hard mask layer 28b is etched using a second etching formulation that also etches resist 29. Thus, the resist is consumed when the opening is etched in the intermediate hard mask layer 28b. Then, the bottom hard mask layer 28a is etched using a third etching formulation, while the top hard mask layer 28c is consumed. This result in... Figure 4As shown, the pattern of the opening 30 has been transferred to the bottom hard mask layer 28a and the middle hard mask layer 28b, i.e., the opening 30 with upright sidewalls is formed through layers 28a+28b. The term 'upright sidewall' refers to a sidewall that is perpendicular to or nearly perpendicular to the plane of the supporting substrate 26, i.e., the term 'upright' includes a small deviation from the geometrically perpendicular orientation.

[0035] At this point, hard mask layers 28a and 28b undergo the directional etching steps described above, such as... Figure 5 As shown, a directional etching beam sweeps across the pattern of the opening in a direction parallel to the X-axis of the orthogonal coordinate system XYZ, thereby selectively etching layers 28a and 28b relative to the etch stop layer 27.

[0036] The directional etching process elongates the opening 30 by removing material from layers 28a and 28b, causing the openings to merge into a continuous trench 31 oriented along the X direction, such as... Figure 5 As shown. This may require the beam to be scanned multiple times in the +X and / or -X directions. As mentioned above, the hard mask layer 28b is thinned due to the given vertical etch rate. Due to the small etch rate in the Y direction, the width of the trench may be slightly larger than the original diameter of the opening.

[0037] Reference Figure 6 The pattern of trench 31 is transferred to the underlying etch stop layer 27, and then the intermediate hard mask layer 28b is selectively stripped relative to the bottom hard mask layer 28a. The target layer 25 is now exposed at the bottom of the transferred trench 31.

[0038] Then, refer to Figure 7 A second mask layer 32 is prepared, comprising a first hard mask layer 32a and a second hard mask layer 32b.

[0039] Layer 32a may be made of the same material and have the same thickness as the medium-hard mask layer 28b of the first mask layer 28, while layer 32b may be made of the same material and have the same thickness as the top-hard mask layer 28c of the first mask layer 28. The resist layer 29 is again formed on the second mask layer 32 and patterned into the same square pattern of openings 30, which are placed in the same positions and have the same diameter as the openings in the first array.

[0040] Reference Figure 8 The second square pattern is transferred to the second mask layer 32 in the same manner as described relative to the first mask layer 28, such that the bottom of the first trench 31 is exposed through the hard mask layer 32a to the bottom of the transferred opening 30.

[0041] Reference Figure 9Now, a second directional etching process is applied by scanning the etching beam in the +Y or -Y direction, or by repeating the scanning in the +Y and / or -Y directions. The second directional etching step enlarges the opening 30 by removing material from the hard mask layer 32a. However, at the bottom end of the sidewalls of the opening 30, the parallel stripes of the bottom hard mask layer 28a remain after the first directional etching step, so in the second directional etching step, regularly spaced portions of these stripes are also exposed to the etching beam (i.e., exposed to the etch material contained in the etching beam), and the material of these portions relative to the etching stop layer 27 is removed by the beam. The second directional etching process is applied until the opening 30 merges into a second trench 33 oriented perpendicularly to the first trench 31. At the bottom of the second trench 33, regularly spaced portions of the etching stop layer 27 are retained.

[0042] Then, the pattern of the second trench 33 is transferred to the etch stop layer 27, and the hard mask layer 32a is selectively peeled off relative to the hard mask layer 28a, thereby leaving a grid of pillars 34 on the target layer 25, as shown. Figure 10 As shown. Subsequently, the pillar mesh can be transferred to the target layer 25 via a suitable etching process that selectively etches the target layer relative to pillars 34. The materials of mask layers 28 and 32 are selected to enable the aforementioned steps. This requires, for example, that layer 32a can be selectively removed relative to the hard mask layer 28a and relative to the target layer 25.

[0043] According to an alternative embodiment, the pattern of the first trench 31 is not transferred to the etch stop layer 27 before the second directional etching process is applied; that is, the bottom of the transferred trench 31 is formed by the etch stop layer 27. Then, the etch stop layer 27 remains at the bottom of the opening 30 formed through the hard mask layer 32a, and the resulting grid of pillars 34 is transferred to the etch stop layer 27 and the target layer 25 in subsequent etching steps.

[0044] When the array of openings 30 is a square or rectangular array as described above, the resulting array of columns 34 is also a square or rectangular array with the same center spacing as the original array.

[0045] According to other embodiments, the same method is applied to a square or rectangular array of openings, wherein one or more openings are omitted from the array. Examples are shown in... Figures 11a to 11c As shown in the image. Figure 11a The original array with opening 30 is shown. Figure 11b The resulting array is shown, which now includes columns 34 and linear features 35. Figure 11cThe original opening 30 and the resulting array of pillars and lines are shown superimposed. Various arrays of pillar and line features can be fabricated by selecting the locations of omitted openings from the array. Therefore, this invention provides an alternative to existing patterning methods suitable for fabricating such patterns and involving the application of multiple photomasks, whereas this invention enables the fabrication of an array of given openings 30 to obtain such a pattern using a single photomask.

[0046] Another embodiment is in Figures 12 to 18 As shown in the figure. As described with respect to the first embodiment, the same mask layer and method steps are applied, but the scan directions of the two directional etching steps are different. See also... Figure 3 and 4 The described steps are therefore equally applicable to this embodiment. However, now, as Figure 12 As shown, a first directional etching step is performed in a scanning direction oriented at 45° relative to the X direction. The scanning can be repeated multiple times in the same or opposite directions. The first trench 31 is now formed by merging the openings 30 in the diagonal direction of the square pattern. This means that the trenches 31 are closer together than in the first embodiment. After the first directional etching step, the hard mask layer 28b is peeled off. Figure 13 ), and prepare the second mask layer 32 in the same manner as in the first embodiment, such as Figure 14 As seen in the image. The square pattern of opening 30 is also formed in the resist layer 29 and transferred to the second mask layer, as shown. Figure 15 As shown.

[0047] Reference Figure 16 Then, a second directional etching step is applied along a scanning direction perpendicular to the scanning direction of the first directional etching step (i.e., at 135° relative to the X direction). The scanning can also be repeated multiple times in the same or opposite directions. The second directional etching step is applied until a second trench 33 oriented perpendicular to the first trench 31 is formed.

[0048] After stripping the hard mask layer 32a, as Figure 17 As shown, the mesh of column 34' is obtained, which can be transferred to target layer 25.

[0049] like Figure 18 As shown in the overlay image, the center-to-center spacing of the pillar grid is smaller than the spacing of the original pattern of openings 30. Therefore, this embodiment is advantageous because the array can be fabricated at a smaller spacing than the initial array of openings 30. By starting with an array of openings 30 with a spacing close to the minimum spacing achievable through standard photolithography and etching, the present invention is thus able to fabricate feature arrays at sub-resolution spacing.

[0050] The orientation of the scanning directions for the two directional etching steps is not limited to the cases described above. For example, in the case of a rectangular array of openings 30 shown in the figures (with or without the selected openings), the scanning direction of the first step can be any direction between the two orthogonal directions defined by the rows and columns of the array of openings 30. The scanning direction of the second directional etching step is preferably perpendicular to the first scanning direction, but other orientations are not excluded.

[0051] The array of openings 30 (with or without omission) can be arranged according to an alternative pattern to the rectangular pattern shown in the figures, such as a hexagonal pattern, which allows for additional variations of the resulting column and / or line patterns. All practically applicable combinations of the array of openings 30 and the scanning directions of the first and second directional etching steps are included within the scope of this invention.

[0052] The step of transferring the pattern of pillars 34, 34' and / or lines 35 includes an embodiment in which a tone reversal is performed before the actual transfer of the pattern, i.e., positive features (pillars and / or lines) are converted into negative features (holes and / or trenches). This can be accomplished by depositing a layer to fill the space between the pillars and / or lines, planarizing the layer, and selectively removing the pillars and / or lines relative to the layer to obtain holes and / or trenches. These holes and / or trenches are then transferred to the target layer 25.

[0053] The array of openings 30 used in this method is a regular array of openings, i.e., an array of openings having the same in-plane dimensions (e.g., circular holes in the embodiment shown) and arranged according to a repeating pattern (such as the square array shown in the figures). Other regular arrays can be used, such as hexagonal arrays, where each opening is surrounded by six other openings at 60° angular spacing. Such arrays include rows and columns that are not perpendicular but at angles other than 90°. The etching direction of the directional etching step applied in this method can be adapted to these directions to obtain similar results as described above for the embodiment based on vertical rows and columns.

Claims

1. A patterning method suitable for semiconductor manufacturing processes, the method comprising the following steps: - The target layer (25) to be patterned is prepared on the support substrate (26). - An etch stop layer (27) is prepared on the target layer and then a first mask layer (28) is prepared on the etch stop layer. - The first mask layer (28) is patterned to represent a regular two-dimensional array of openings (30), or an array obtained by omitting one or more openings from a regular two-dimensional array. - Apply a first directional etching step selectively relative to the etch stop layer (27), wherein the first directional etching step expands the opening (30) in a first direction, such that the first mask layer is patterned as an array of parallel linear trenches (31) oriented along the first direction. -Then, a second mask layer (32) is prepared. - Pattern the second mask layer according to the same pattern representing the array of openings (30). - A second directional etching step selectively applied relative to the etch stop layer (27) is applied, wherein the second directional etching step expands the opening (30) in the second mask layer (32) in a second direction intersecting the first direction, such that the second mask layer (32) is patterned as an array of parallel linear trenches (33) oriented along the second direction, and wherein the second directional etching step also removes portions of the patterned first mask layer (28) exposed to the etchant applied in the second directional etching step, such that the first mask layer (28) is patterned as a final pattern comprising an array of pillars (34) and / or lines (35). -Remove the second mask layer (32) relative to the pillars and / or lines. - Transfer the pattern defined by the pillars and / or lines to the target layer (25).

2. The method according to claim 1, characterized in that, After the first directional etching step and before the step of preparing the second mask layer (32), the patterned first mask layer (28) is thinned.

3. The method according to claim 1 or 2, characterized in that, Prior to the step of preparing the second mask layer (32), the pattern of the patterned first mask layer (28) is transferred to the etch stop layer (27), and wherein the pattern of the patterned second mask layer (32) is transferred to the etch stop layer (27) prior to the step of transferring the pattern defined by the pillars and / or lines to the target layer (25).

4. The method according to claim 1 or 2, characterized in that, Prior to the step of preparing the second mask layer (32), the pattern of the patterned first mask layer (28) is not transferred to the etch stop layer (27), and the pattern defined by the pillars and / or lines is transferred to the etch stop layer (27) before the pattern defined by the pillars and / or lines is transferred to the target layer (25).

5. The method as described in claim 1, characterized in that: - The regular array of openings (30) is a rectangular array extending in two vertical directions, and one or more openings are omitted from the rectangular array. - The first direction of the first directional etching step is oriented according to one of the vertical directions of the array of openings, and - The second direction of the second directional etching step is oriented according to another direction in the vertical direction of the array of openings.

6. The method as described in claim 1, characterized in that: - The regular array of the opening (30) is a rectangular array extending in two vertical directions. - The first direction of the first directional etching step is oriented between the two orthogonal directions. - The second direction of the second directional etching step is perpendicular to the first direction.

7. The method according to claim 6, characterized in that, The first direction is oriented at 45° relative to the two orthogonal directions.

8. The method according to claim 1, characterized in that, The opening (30) is a hole with a circular cross-sectional shape.

9. The method according to claim 1, characterized in that, The first mask layer (28) comprises a stack of sublayers, the stack comprising the following layers from bottom to top: - First hard mask layer (28a) with a thickness of t1. - A second hard mask layer (28b) with a thickness greater than t1. - A third hard mask layer (28c) with a thickness approximately equal to t1. And during the transfer of the pattern of the opening (30) from the patterned resist layer (29) formed on the first mask layer to the first mask layer, the third hard mask layer (28c) is consumed, such that the first directional etching step is performed on the stack formed by the first hard mask layer (28a) and the second hard mask layer (28b).

10. The method according to claim 9, characterized in that, The second hard mask layer (28b) is peeled off relative to the first hard mask layer (28a) prior to the step of preparing the second mask layer (32).

11. The method according to claim 11, characterized in that, The second mask layer (32) comprises a stack of sublayers, which, from bottom to top, include the following layers: - First hard mask layer (32a) with a thickness of t1. - A second hard mask layer (32b) with a thickness less than t1. And the second hard mask layer (32b) is consumed during the transfer of the pattern of the opening (30) from the patterned resist layer (29) formed on the second mask layer to the second mask layer.

Images