Method for forming a target structure

Abstract

A method for forming a target structure includes: providing an etchable base layer for forming the target structure, the etchable base layer including multiple regions, the top surface of the target structure forming a curved surface profile on the multiple regions, and the etchable base layer being capable of being patterned using semiconductor etching processes; forming multiple etch stop structures protruding from the etchable base layer on the etchable base layer, and the etch stop structures located in the multiple regions having different pattern densities; etching a part of the thickness of the etchable base layer exposed by the etch stop structures to form protrusions protruding from the remaining etchable base layer; removing the protrusions to form the target structure, and the top surface of the target structure having a curved surface profile. By forming etch stop structures with different pattern densities on different regions of the etchable base layer, the present invention controls the etching depth of each region, so that the top surface of the target structure has a curved surface profile, and a target structure with a controllable top surface profile is obtained.

Description

Technical Field

[0001] Embodiments of the present invention relate to the field of semiconductor manufacturing, and particularly to a method for forming a target structure. Background Art

[0002] Traditional optical systems use optical lenses with a curved top surface, thereby increasing the design freedom of the optical system, reducing the number of lenses, decreasing the lens size, simplifying the system structure, and further improving the imaging quality, expanding the field of view, detection distance, and measurement accuracy.

[0003] Currently, there are many processing methods for obtaining a three-dimensional profile. For example, pattern transfer is achieved through a mask material with a curved profile, or a stepped top surface profile is obtained by multiple exposure and etching, or patterning is performed using a gray-tone mask with multiple transmittance rates. However, the current processing methods have large limitations and it is difficult to precisely control the top surface profile. Summary of the Invention

[0004] The problem solved by the embodiments of the present invention is to provide a method for forming a target structure to obtain a target structure with a controllable top surface profile.

[0005] To solve the above problem, embodiments of the present invention provide a method for forming a target structure, including: providing an etchable base layer for forming the target structure, the etchable base layer including a plurality of regions, the top surface of the target structure forming a curved profile on the plurality of regions, and the etchable base layer being capable of being patterned using semiconductor etching processes; forming a plurality of etch stop structures protruding from the etchable base layer on the etchable base layer, and the etch stop structures in the plurality of regions having different pattern densities; using the etch stop structures as masks to etch a part of the thickness of the etchable base layer exposed by the etch stop structures to form a protruding portion protruding from the remaining etchable base layer; removing the protruding portion to form a target structure, the top surface of the target structure having a curved profile.

[0006] Optionally, the plurality of regions of the etchable base layer include a central region and a plurality of annular regions arranged concentrically around the central region.

[0007] Optionally, in the step of forming the etch stop structures on the etchable base layer, in the direction from the center to the edge of the etchable base layer, the pattern density of the etch stop structures in each region decreases.

[0008] Optionally, in the step of forming the etch stop structures, the etch stop structures are pattern lines; or the etch stop structures are arranged in a dot matrix on the etchable base layer.

[0009] Optionally, the step of removing the protrusion includes: performing maskless etching on the protrusion and the remaining to-be-etched base layer exposed by the protrusion.

[0010] Optionally, the step of removing the protrusion includes: etching the protrusion using an etching process, and the etching process has a lateral etching rate.

[0011] Optionally, the etching process includes a wet etching process or a dry etching process.

[0012] Optionally, before removing the protrusion, it further includes: removing the etching stop structure.

[0013] Optionally, using an anisotropic etching process to etch a part of the thickness of the to-be-etched base layer exposed by the etching stop structure.

[0014] Optionally, before forming the etching stop structure on the to-be-etched base layer, it further includes: providing a plurality of base layers, and the plurality of base layers have the same material as the to-be-etched base layer; forming a plurality of etching stop structures on the plurality of base layers respectively, and the pattern densities on the plurality of base layers are different; etching the plurality of base layers exposed by the etching stop structures respectively under the same etching conditions, and measuring the etching depths corresponding to the different pattern densities respectively; performing fitting through the plurality of pattern densities and the etching depths corresponding to the pattern densities to obtain a fitting relationship, where the independent variable in the fitting relationship is the pattern density and the dependent variable is the etching depth; determining the etching depth of the to-be-etched base layer in each region according to the surface profile of the target structure; and obtaining the pattern density corresponding to each region according to the etching depth of the to-be-etched base layer in each region and the fitting relationship.

[0015] Optionally, in the step of forming the etching stop structure on the to-be-etched base layer, the pattern density in the plurality of regions is negatively correlated with the line width of the etching stop structure in the corresponding region.

[0016] Optionally, the material of the etching stop structure includes a hard mask material or a photoresist.

[0017] Optionally, in the step of etching a part of the thickness of the to-be-etched base layer exposed by the etching stop structure, the ratio of the bottom line width of the protrusion to the etching depth of the region where it is located is greater than 1 / 100.

[0018] Optionally, in the step of etching a part of the thickness of the to-be-etched base layer exposed by the etching stop structure, the top line width of the protrusion is less than or equal to 1 / 20 of the lateral dimension of the surface profile.

[0019] Optionally, along a direction parallel to the surface of the substrate layer to be etched, the shape of the substrate layer to be etched is circular, and the diameter of the substrate layer to be etched is greater than or equal to 100 micrometers.

[0020] Optionally, the height difference between the concave surface and the convex surface in the curved surface profile is greater than or equal to 3 micrometers.

[0021] Optionally, the target structure includes a curved mirror, and the curved mirror includes a lens.

[0022] Optionally, the material of the substrate layer to be etched includes semiconductor material, quartz or glass.

[0023] Compared with the prior art, the technical solutions of the embodiments of the present invention have the following advantages:

[0024] In the method for forming a target structure provided by the embodiment of the present invention, a plurality of etching barrier structures protruding from the substrate layer to be etched are formed on the substrate layer to be etched, and the etching barrier structures in the plurality of regions have different pattern densities. Subsequently, using the etching barrier structures as a mask, the part of the substrate layer to be etched with a certain thickness exposed by the etching barrier structures is etched. After forming a raised portion protruding from the remaining substrate layer to be etched, the raised portion is removed to form a target structure; since the etching barrier structures in the plurality of regions have different pattern densities, under the same etching conditions, the etching gas is more likely to contact the substrate layer to be etched in the region with a smaller pattern density, and the contact area is also larger, and the etching depth is correspondingly larger. That is to say, the etching depth is related to the pattern density of the region where it is located. The smaller the interval of the etching barrier structure and the larger the pattern density, the smaller the etching depth, corresponding to the part with a higher top surface height in the curved surface profile of the target structure, and vice versa, the larger the etching depth, corresponding to the part with a smaller top surface height in the curved surface profile of the target structure. Therefore, by forming etching barrier structures with different pattern densities on different regions of the substrate layer to be etched, the etching depth of each region can be controlled, so that the top surface of the formed target structure has a curved surface profile, and a target structure with a controllable top surface profile can be obtained. Description of the Drawings

[0025] Figures 1 to 2 is a schematic structural diagram corresponding to each step in a method for forming a target structure;

[0026] Figures 3 to 4 is a schematic structural diagram corresponding to each step in another method for forming a target structure;

[0027] Figures 5 to 8 is a schematic structural diagram corresponding to each step in yet another method for forming a target structure;

[0028] Figures 9 to 12It is a schematic structural diagram corresponding to each step in an embodiment of the method for forming the target structure of the present invention;

[0029] Figure 13 It is a schematic structural diagram of the target structure formed in another embodiment of the method for forming the target structure of the present invention. Detailed implementation manners

[0030] Currently, it is difficult to obtain a target structure with a controllable top surface profile. Now, in combination with some methods for forming the target structure, the reasons for the difficulty in precisely controlling the top surface profile of the target structure are analyzed.

[0031] Figures 1 to 2 It is a schematic structural diagram corresponding to each step in a method for forming a target structure.

[0032] Reference Figure 1 , a to-be-etched base layer 10 for forming a target structure is provided; a mask layer 11 is formed on a partial area of the to-be-etched base layer 10.

[0033] Reference Figure 2 , using the mask layer 11 as a mask, etching a partial thickness of the to-be-etched base layer 10 to form a target structure 12 having a raised portion (as shown by the dotted circle in Figure 2 ).

[0034] By transferring the pattern of the mask layer 11 into the to-be-etched base layer 10, a raised portion is formed, so that the top surface of the target structure 12 has a three-dimensional profile.

[0035] However, this method can usually only obtain four types of top surface profiles, specifically: the angle between the side wall of the raised portion and the surface of the target structure 12d is a positive angle, or the angle between the side wall of the raised portion and the surface of the target structure 12d is a negative angle, or the side wall of the raised portion is perpendicular to the surface of the target structure 12d, or the top angle of the raised portion is a rounded corner, resulting in a limited adjustment effect on the top surface profile.

[0036] Moreover, when the top line width of the raised portion is large (for example, much larger than the height of the raised portion), the top surface of the raised portion is usually still a plane, making it difficult to control the profile of the raised portion, that is, it is difficult to control the top surface profile of the target structure 12.

[0037] Figures 3 to 4 It is a schematic structural diagram corresponding to each step in another method for forming a target structure.

[0038] Reference Figure 3 , a to-be-etched base layer 20 for forming a target structure is provided; an initial photoresist layer 21 is formed on a partial area of the to-be-etched base layer 10.

[0039] Reference Figure 4, the initial photoresist layer 22 is subjected to a reflow process to form a photoresist layer 22 with a curved surface shape.

[0040] Subsequently, using the photoresist layer 22 as a mask, a part of the thickness of the substrate layer 20 to be etched is etched to form a target structure with a curved surface profile on the top surface.

[0041] In this method, by preparing a photoresist layer 22 with a curved surface profile, the profile of the photoresist layer 22 is transferred into the substrate layer 20 to be etched, thereby obtaining a target structure with a curved surface profile.

[0042] However, by the method of performing a reflow process on the initial photoresist layer 22, a more complex top surface profile (such as an aspherical shape) cannot be obtained, resulting in limited adjustment effect on the top surface profile.

[0043] Moreover, when using the above method to obtain a target structure with a curved surface profile, the overall morphology of the photoresist layer 22 after the reflow process, the etching selectivity between the photoresist layer 22 and the substrate layer 20 to be etched, and the etching depth are usually adjusted. Therefore, the top surface profile of a local area cannot be controlled.

[0044] Secondly, the thickness of the photoresist layer 22 is limited. When the etching depth is large, a high requirement is imposed on the etching selectivity of the etching process. For example, the maximum thickness of the photoresist layer 22 is 40 microns, and the maximum value of the difference between the maximum and minimum values of the etching depth is 400 microns. Correspondingly, the etching selectivity between the substrate layer 20 to be etched and the photoresist layer 22 needs to reach 10:1.

[0045] Thirdly, when the line width of the photoresist layer 22 is large (for example, much larger than the thickness of the photoresist layer 22), it is difficult for the photoresist layer 22 to form a curved surface profile in the middle area of the top surface (as shown by the dotted circle in Figure 4 ). The top surface of the middle area is usually flat. Correspondingly, after transferring the profile of the photoresist layer 22 into the substrate layer 20 to be etched, it is difficult to obtain a target structure with a curved surface profile.

[0046] Figures 5 to 8 It is a schematic diagram of the structures corresponding to the steps in another method for forming a target structure.

[0047] Reference Figure 5 , a substrate layer 30 to be etched for forming a target structure is provided.

[0048] Combined with reference Figure 5 and Figure 6 , a first patterning process is performed, including: forming a first mask layer 31 on a part of the area of the substrate layer 30 to be etched; using the first mask layer 31 as a mask, etching a part of the thickness of the substrate layer 20 to be etched to form a first stepped portion 32.

[0049] After forming the first stepped portion 32, the first patterning process further includes: removing the first mask layer 31.

[0050] Reference Figure 7 , perform a second patterning process, including: forming a second mask layer 33 covering the first stepped portion 32, and the second mask layer 33 further extends to cover a part of the substrate to be etched 30 around the first stepped portion 32; using the second mask layer 33 as a mask, etch a part of the thickness of the substrate to be etched 30 to form a second stepped portion 34 whose top surface is connected to the side wall of the first stepped portion 32.

[0051] After forming the second stepped portion 34, the second patterning process further includes: removing the second mask layer 33.

[0052] Reference Figure 8 , perform a third patterning process, including: forming a third mask layer 35 covering the first stepped portion 32 and the second stepped portion 34, and the third mask layer 35 further extends to cover a part of the substrate to be etched 30 around the second stepped portion 34; using the third mask layer 35 as a mask, etch a part of the thickness of the substrate to be etched 30 to form a third stepped portion 36 whose top surface is connected to the side wall of the second stepped portion 34.

[0053] After forming the third stepped portion 3, the third patterning process further includes: removing the third mask layer 35.

[0054] Subsequently, the patterning process can be repeated multiple times to obtain more stepped portions, thereby forming a target structure with a curved surface profile.

[0055] However, in order to obtain a sufficiently fine and smooth curved surface profile, multiple exposures are required, and the alignment accuracy requirements for the lithography process are relatively high. Therefore, the process cost of this method is high and the process is complex.

[0056] In addition, when the protrusion height of the curved surface profile is relatively large, the number of patterning processes is also relatively large. In the subsequent lithography process of the patterning process, the photoresist needs to cover each formed stepped portion, resulting in great process difficulty in photoresist coating.

[0057] Another method is to perform patterning using a gray-tone mask with multiple light transmittances.

[0058] In this method, by setting the gray values at different positions of the mask, when the light source passes through the mask to expose the photoresist, the gray-tone pattern on the gray-tone mask can modulate the intensity of the parallel light emitted by the exposure light source, so that the photoresist is irradiated by light with different light intensities, realizing uneven exposure of the photoresist, thereby obtaining a three-dimensional curved surface pattern on the surface of the photoresist, and then transferring the pattern to the substrate to be etched through the photoresist with the three-dimensional curved surface pattern.

[0059] This method can achieve single patterning, and can obtain top surface profiles of various shapes (such as aspherical shapes). Moreover, by precisely controlling the exposure dose gradient in different regions, a target structure with a larger size can be fabricated.

[0060] However, the technical source for photomask fabrication is relatively limited, and the cost of photomasks is high. Secondly, when the thickness of the photoresist is limited and the maximum etching depth of the substrate layer to be etched is large, a high requirement is imposed on the etching selectivity of the etching process. For example, when the maximum thickness of the photoresist layer is 40 μm and the maximum difference between the maximum and minimum etching depths is 400 μm, correspondingly, the etching selectivity between the substrate layer to be etched and the photoresist layer needs to reach 10:1.

[0061] Therefore, there is an urgent need to provide a method for forming a target structure with a controllable top surface profile.

[0062] To solve the above technical problems, an embodiment of the present invention provides a method for forming a target structure, including: providing a substrate layer to be etched for forming a target structure, the substrate layer to be etched includes multiple regions, the top surface of the target structure forms a curved surface profile on the multiple regions, and the substrate layer to be etched can be patterned by a semiconductor etching process; forming multiple etching barrier structures protruding from the substrate layer to be etched on the substrate layer to be etched, and the etching barrier structures located in the multiple regions have different pattern densities; using the etching barrier structures as a mask, etching a part of the thickness of the substrate layer to be etched exposed by the etching barrier structures to form a protruding portion protruding from the remaining substrate layer to be etched; removing the protruding portion to form a target structure, and the top surface of the target structure has a curved surface profile.

[0063] In the method for forming a target structure provided by the embodiment of the present invention, when forming multiple etching barrier structures protruding from the substrate layer to be etched on the substrate layer to be etched, under the same etching conditions, the etching gas is more likely to contact the substrate layer to be etched in the region with a smaller pattern density, and the contact area is also larger, and the etching depth is correspondingly larger. That is to say, the etching depth is related to the pattern density of the region where it is located. The smaller the interval of the etching barrier structure and the larger the pattern density, the smaller the etching depth, corresponding to the part with a higher top surface height in the curved surface profile of the target structure, and vice versa, the larger the etching depth, corresponding to the part with a smaller top surface height in the curved surface profile of the target structure. Therefore, by forming etching barrier structures with different pattern densities in different regions of the substrate layer to be etched, the etching depth of each region can be controlled, and thus the top surface of the formed target structure has a curved surface profile, and a target structure with a controllable top surface profile can be obtained.

[0064] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description of specific embodiments of the present invention with reference to the accompanying drawings.

[0065] Figures 9 to 12 It is a schematic structural diagram corresponding to each step in an embodiment of the method for forming the target structure of the present invention.

[0066] Referring to Figure 9 , a to-be-etched base layer 100 for forming a target structure is provided. The to-be-etched base layer 100 includes a plurality of regions 100d. The top surface of the target structure forms a curved surface profile on the plurality of regions 100d, and the to-be-etched base layer 100 can be patterned using semiconductor etching processes.

[0067] Wherein, Figure 9 shows a top view of the to-be-etched base layer.

[0068] Subsequently, by etching the to-be-etched base layer 100, a target structure with a curved surface profile on the top surface is formed, that is, the top surface profile of the target structure is a three-dimensional curved surface.

[0069] The to-be-etched base layer 100 can be patterned using semiconductor etching processes, so that subsequent semiconductor etching processes can be used to pattern the to-be-etched base layer 100.

[0070] In this embodiment, the target structure includes a curved mirror. Specifically, the curved mirror includes a lens, and the target structure can be applied in fields such as infrared remote sensing or imaging.

[0071] As an example, the curved mirror is a convex lens. Correspondingly, the top surface profile of the subsequent target structure is a spherical surface.

[0072] The to-be-etched base layer 100 can be patterned using semiconductor etching processes. In this embodiment, the material of the to-be-etched base layer 100 includes semiconductor materials, quartz, or glass. For example, the semiconductor material can include silicon.

[0073] As an example, the target structure is a silicon lens. Correspondingly, the material of the to-be-etched base layer 100 is silicon.

[0074] It should be noted that in other embodiments, according to the application scenario of the target structure, the to-be-etched base layer can also be other materials that can be patterned using semiconductor etching processes, and the material of the to-be-etched base layer is determined according to the use function of the target structure.

[0075] In this embodiment, along the direction parallel to the surface of the to-be-etched base layer 100, the shape of the to-be-etched base layer 100 is circular.

[0076] In other embodiments, according to the actual situation, the shape of the substrate layer to be etched may also be other types, such as rectangular.

[0077] In this embodiment, according to the application requirements, the forming method is used to prepare a large-sized target structure.

[0078] As an example, the diameter of the substrate layer 100 to be etched is greater than or equal to 100 micrometers.

[0079] In this embodiment, the substrate layer 100 to be etched includes a plurality of regions 100d. Subsequently, by controlling the etching depth of different regions 100d, the top surface topography of the remaining substrate layer 100 to be etched after etching is controlled, so that the top surface of the formed target structure forms a curved surface profile on the plurality of regions 100d.

[0080] Specifically, compared with the region 100d with a larger etching depth, in the region 100d with a smaller etching depth, the top surface of the remaining substrate layer 100 to be etched after etching is higher. On the contrary, compared with the region 100d with a smaller etching depth, in the region 100d with a larger etching depth, the top surface of the remaining substrate layer 100 to be etched after etching is lower, so that a top surface profile with concave and convex surfaces can be obtained.

[0081] Therefore, the distribution of the plurality of regions 100d on the substrate layer 100 to be etched is determined by the top surface profile of the target structure.

[0082] In this embodiment, the forming method is used to form a regularly shaped curved surface profile. Therefore, the plurality of regions 100d include a central region 100a and a plurality of annular regions 100e arranged in concentric circles around the central region 100a.

[0083] Specifically, taking the number of the annular regions 100e as two as an example, the annular regions 100e include a first annular region 100b surrounding the central region 100a and a second annular region 100c surrounding the first annular region 100b.

[0084] Reference Figure 10 , an etching stop structure 120 protruding from the substrate layer 100 to be etched is formed on the substrate layer 100 to be etched, and the etching stop structures 120 located in the plurality of regions 100d have different pattern densities.

[0085] In this embodiment, the etching stop structure 120 is a graphic line, and adjacent etching stop structures 120 enclose a mask opening 130. That is to say, the etching stop structures 120 are arranged in a line array on the substrate layer 100 to be etched.

[0086] For example, a mask layer 110 with a mask opening 130 is formed on the substrate layer 100 to be etched, and the remaining part in the mask layer 110 serves as the etching stop structure 120.

[0087] The etching stop structures 120 located in the multiple regions 100d have different pattern densities. Therefore, under the same etching conditions, the etching gas is more likely to come into contact with the substrate layer 100 to be etched in the region 100d with a smaller pattern density, and the contact area is also larger, so the etching depth is correspondingly greater. That is to say, the etching depth is related to the pattern density of the region 100d where it is located. The smaller the interval of the etching stop structure 120 (i.e., the smaller the line width s of the mask opening 130) and the larger the pattern density, the smaller the etching depth, corresponding to the part with a higher top surface height in the curved surface profile of the target structure; conversely, the larger the etching depth, corresponding to the part with a smaller top surface height in the curved surface profile of the target structure. Therefore, by forming etching stop structures 120 with different pattern densities on different regions 100d of the substrate layer 100 to be etched, the etching depth of each region 100d can be controlled, so that the top surface of the formed target structure has a curved surface profile, and a target structure with a controllable top surface profile can be obtained.

[0088] It should be noted that compared with the solution of forming a mask layer with a curved surface profile on the substrate layer to be etched and transferring the profile of the mask layer to the substrate layer to be etched, by forming etching stop structures 120 with different pattern densities on different regions 100d of the substrate layer 100 to be etched to control the etching depth of each region 100d, so that the top surface of the formed target structure has a curved surface profile, even if the size of the substrate layer 100 to be etched is large in the direction parallel to the surface of the substrate layer 100 to be etched, this embodiment can significantly reduce the probability that the top surface of the middle region of the target structure is flat. That is to say, this embodiment is more likely to obtain a curved surface profile, and the profile controllability is relatively high, and a target structure with a large size can be prepared.

[0089] It should also be noted that the size of the substrate layer 100 to be etched is large in the direction parallel to the surface of the substrate layer 100 to be etched, which also provides a sufficient process window for forming etching stop structures 120 with different pattern densities in different regions 100d (for example, less restricted by the lithography process). Correspondingly, in the process, the process difficulty of forming the mask layer 110 is reduced, and it is easier to form etching stop structures 120 with different pattern densities, and the process controllability is higher.

[0090] The material of the etching barrier structure 120 satisfies that the etching barrier structure 120 can achieve pattern transfer. Specifically, the material of the etching barrier structure 120 includes a hard mask (HM) material or a photoresist (PR).

[0091] As an example, the material of the etching barrier structure 120 is a hard mask material, that is, the mask layer 110 is a hard mask layer.

[0092] Hard mask materials are usually inorganic materials (for example, hard mask materials include silicon nitride, silicon oxide, or titanium nitride). Compared with organic materials, hard mask materials have higher hardness, and the etching selectivity between the substrate 100 to be etched and the hard mask layer is relatively high. During the etching of the substrate 100 to be etched, the etching rate of the hard mask layer is relatively low. Therefore, by first transferring the pattern into the hard mask layer and then transferring the final pattern into the substrate 100 to be etched through the hard mask layer, it is beneficial to improve the accuracy of pattern transfer.

[0093] In particular, when the maximum etching depth of the substrate 100 to be etched is relatively large, by selecting a hard mask material, the probability that the etching barrier structure 120 is completely consumed in advance can be significantly reduced.

[0094] In this embodiment, the hard mask material is silicon nitride.

[0095] As an example, first form a mask material layer covering the entire substrate 100 to be etched, and then pattern the mask material layer to form a mask layer 110 with mask openings 130. The mask layer 110 further includes an etching barrier structure 120 for blocking a part of the substrate 100 to be etched.

[0096] Specifically, the mask layer 110 is a hard mask layer, and the mask material layer is etched by an anisotropic etching process (for example, an anisotropic dry etching process).

[0097] It should be noted that compared with the solution of forming a curved surface profile composed of multiple stepped portions through multiple patterning processes, in this embodiment, by means of single patterning, the etching barrier structures 120 with different pattern densities are formed in multiple regions 100d, which is not only beneficial to improving the alignment accuracy of the lithography process and reducing the process difficulty of photoresist coating, but also has lower process costs. Moreover, compared with the solution using a gray-tone mask, the process cost of this embodiment is also lower.

[0098] In other embodiments, in the step of forming the etching barrier structure, the etching barrier structures are arranged in a dot matrix pattern on the substrate to be etched, which can also achieve different pattern densities of the etching barrier structures located in the multiple regions.

[0099] In this embodiment, the curved surface profile of the top surface of the subsequent target structure is a spherical surface. Therefore, in the direction from the center to the edge of the to-be-etched base layer 100, the pattern density of the etch stop structures 120 in each region 100d decreases.

[0100] That is to say, the closer to the edge of the to-be-etched base layer 100, the larger the line width s of the mask opening 130 (i.e., the size of the region exposed by adjacent etch stop structures 120), and the greater the etching depth of the to-be-etched base layer 100 exposed by the mask opening 130 with a larger line width s. Therefore, in the direction from the center to the edge of the to-be-etched base layer 100, the etching depth increases in sequence. The closer to the edge of the to-be-etched base layer 100, the smaller the top surface height of the target structure, so that the top surface of the target structure presents a spherical curved surface profile.

[0101] Specifically, the annular region 100e includes a first annular region 100b surrounding the central region 100a and a second annular region 100c surrounding the first annular region 100b. Therefore, the pattern densities in the central region 100a, the first annular region 100b, and the second annular region 100c decrease in sequence.

[0102] In this embodiment, the pattern density in the multiple regions 100d is negatively correlated with the line width w of the etch stop structures 120 in the corresponding regions. That is to say, in the region 100d with a smaller pattern density, the line width w of the etch stop structures 120 is larger. On the contrary, in the region 100d with a larger pattern density, the line width w of the etch stop structures 120 is smaller.

[0103] When subsequently etching a partial thickness of the to-be-etched base layer 100 along the mask opening 130, not only longitudinal etching will be performed in the direction perpendicular to the surface of the to-be-etched base layer 100, but also lateral etching of the etch stop structures 120 is likely to occur in the direction parallel to the surface of the to-be-etched base layer 100, resulting in a gradual decrease in the line width w of the etch stop structures 120. Moreover, in the region 100d with a greater etching depth, the amount of lateral etching of the etch stop structures 120 is larger. Therefore, by making the pattern density in the multiple regions 100d negatively correlated with the line width w of the etch stop structures 120 in the corresponding regions, while ensuring that the etching depth of each region 100d meets the process requirements, it is ensured that each etch stop structure 120 can function as an etch mask, so that the pattern of the etch stop structures 120 in each region 100d can be transferred to the to-be-etched base layer 100.

[0104] Specifically, on the premise of ensuring that the etching depth of each subsequent region 100d reaches a preset value and ensuring that the subsequently formed protrusions do not break or collapse, an etching stop structure 120 with the minimum line width w obtainable by the process is selected according to the process capabilities.

[0105] It should be noted that in this embodiment, before forming the etching stop structure 120 on the substrate 100 to be etched, the following steps are further included: providing a plurality of substrate layers, the plurality of substrate layers being made of the same material as the substrate 100 to be etched; forming a plurality of etching stop structures 120 on the plurality of substrate layers respectively, the pattern densities on the plurality of substrate layers being different; etching the plurality of substrate layers exposed by the etching stop structures 120 respectively under the same etching conditions, and measuring the etching depths corresponding to the different pattern densities respectively; performing fitting through the plurality of pattern densities and the etching depths corresponding to the pattern densities to obtain a fitting relationship, where the independent variable in the fitting relationship is the pattern density and the dependent variable is the etching depth; determining the etching depth of the substrate 100 to be etched in each region according to the surface profile of the target structure; and obtaining the pattern density corresponding to each region according to the etching depth of the substrate 100 to be etched in each region and the fitting relationship.

[0106] The plurality of substrate layers are used to collect data, and the plurality of substrate layers are made of the same material as the substrate 100 to be etched, so that the fitting relationship can be applied to the substrate 100 to be etched.

[0107] By first collecting data and obtaining a fitting relationship between the pattern density and the etching depth, the pattern density of each region 100d can be determined according to the surface profile of the target structure, thereby preparing for forming the mask layer 110.

[0108] Moreover, if the top surface profile of the target structure is determined, the etching depth of the substrate 100 to be etched in each region can be correspondingly determined, and thus the pattern density corresponding to each region can be obtained through the fitting relationship. This reduces the process complexity of the forming method, enables the method to be applicable to forming target structures with various types of top surface profiles, and is conducive to precisely controlling the top surface profile morphology of the subsequent target structure.

[0109] Reference Figure 11 , using the etching stop structure 120 as a mask, etch a part of the thickness of the substrate 100 to be etched exposed by the etching stop structure 120 to form a protrusion 40 protruding from the remaining substrate 100 to be etched.

[0110] The interface between the protruding portion 40 and the remaining substrate layer to be etched 100, and the top surface of the remaining substrate layer to be etched 100 exposed by the protruding portion 40 are used to form the top surface of the subsequent target structure. Subsequently, by removing the protruding portion 40, a target structure with a curved surface profile on the top surface is formed.

[0111] In this embodiment, using the mask layer 110 as a mask, etching is performed along the mask opening 130.

[0112] In this embodiment, an anisotropic etching process is adopted to etch a part of the thickness of the substrate layer to be etched 100 along the mask opening 130.

[0113] The longitudinal etching rate of the anisotropic etching process is much greater than its lateral etching rate. By selecting the anisotropic etching process, it is beneficial to accurately transfer the pattern of the mask opening 130 into the substrate layer to be etched 100, so that it is easy to adjust the top surface profile of the target structure by adjusting the etching depth of different regions 100d.

[0114] As an example, the anisotropic etching process can be a plasma dry etching process.

[0115] It should be noted that after forming the protruding portion 140, the top line width (not marked) of the protruding portion 140 should not be too large. If the top line width of the protruding portion 140 is too large, it is easy to form an obvious step on the top surface of the target structure after removing the protruding portion 140, making it difficult to form a smooth top surface profile. Therefore, in this embodiment, the top line width of the protruding portion 140 is less than or equal to 1 / 20 of the lateral dimension of the curved surface profile.

[0116] That is to say, the smaller the top line width of the protruding portion 140, the smoother the top surface profile of the subsequent target structure.

[0117] Wherein, the lateral direction refers to: the direction parallel to the surface of the substrate layer to be etched 100.

[0118] For example, in this embodiment, the curved mirror is a convex lens, the top surface profile of the target structure is a spherical surface, and correspondingly, the lateral dimension of the curved surface profile refers to the diameter of the spherical surface.

[0119] However, it is necessary to ensure that the bottom line width (not marked) of the protrusion 140 is not too small. If the bottom line width of the protrusion 140 is too small, it is easy to cause the protrusion 140 to break, thereby affecting the top surface profile of the subsequent target structure. For example, the protrusion 140 needs to be removed later. During the process of removing the protrusion 140, a certain amount of etching will also be caused to the remaining substrate layer 100 to be etched. At the position where the break occurs, the remaining substrate layer 100 to be etched loses the protection of the protrusion 140, resulting in the remaining substrate layer 100 at this position being etched erroneously, and further causing the profile at this position to not match the target profile. Therefore, in this embodiment, the ratio of the bottom line width of the protrusion 140 to the etching depth of the area where it is located is greater than 1 / 100.

[0120] Correspondingly, for the area with dense patterns, the etching depth is small, and the bottom line width of the protrusion 140 located in this area can be small, while for the area with sparse patterns, the etching depth is large, and the bottom line width of the protrusion 140 located in this area should be large.

[0121] In particular, after the protrusion 140 is formed, it is difficult to ensure that the side wall of the protrusion 140 is completely parallel to the surface normal direction of the substrate layer 100 to be etched. Usually, the top line width of the protrusion 140 is greater than its bottom line width. Therefore, by reasonably setting the line width of the protrusion 140, while obtaining a smooth top surface profile, the integrity of each protrusion 140 is ensured.

[0122] Correspondingly, in the actual process, according to the parameters of the etching process and the line width of the protrusion 140, the line width w of the etching stop structure 120 is reasonably set.

[0123] Reference Figure 12 , the protrusion 140 is removed (as Figure 11 shown), and the target structure 150 is formed. The top surface of the target structure 150 has a curved surface profile.

[0124] As can be seen from the foregoing description, the interface between the protrusion 40 and the remaining substrate layer 100 to be etched, and the top surface of the remaining substrate layer 100 exposed by the protrusion 40 are used to form the top surface of the target structure 150. And by controlling the etching depth of each area 100d, the top surface profile of the target structure 150 is obtained. Therefore, the controllability of the top surface profile of the target structure 150 is relatively high.

[0125] In this embodiment, the step of removing the protrusion 140 includes: performing a blanket etch on the protrusion 140 and the remaining substrate layer 100 exposed by the protrusion 140 (as Figure 11 shown).

[0126] By adopting a maskless etching method, the photomask is saved, which not only reduces the process complexity of removing the protrusion 140, but also reduces the process cost.

[0127] Wherein, the protrusion 140 protrudes from the remaining substrate layer to be etched 100. Therefore, during the maskless etching process, the etching rate of the protrusion 140 is greater than that of the remaining substrate layer to be etched 100, and the etching amount of the remaining substrate layer to be etched 100 exposed by the protrusion 140 will not be too large. As the etching amount increases, the protrusion 140 is finally removed, and the top surface of the target structure 150 is made smooth.

[0128] Moreover, during the maskless etching process, the difference in etching depth between the sparse area and the dense area is still maintained. As the etching amount increases, the protrusion 140 is finally removed, and the top surface of the target structure 150 has a curved surface profile, and the top surface profile of the target structure 150 meets the design requirements.

[0129] In this embodiment, an etching process is used for etching to remove the protrusion 140. Wherein, the etching process has a lateral etching rate.

[0130] Compared with the height of the protrusion 140, the line width of the protrusion 140 is smaller. Therefore, by adopting an etching process with a lateral etching rate, it is beneficial to increase the removal rate of the protrusion 140, thereby reducing the etching time. Furthermore, while completely removing the protrusion 140, the effect of reducing the etching amount of the remaining substrate layer to be etched 100 is more significant, that is, the top surface profile of the remaining substrate layer to be etched 100 between the protrusions 140 is maintained, so that the top surface of the target structure 150 has a curved surface profile, and the top surface profile of the target structure 150 meets the design requirements.

[0131] In this embodiment, the etching process includes a wet etching process or a dry etching process.

[0132] As an example, a wet etching process is adopted to perform maskless etching on the protrusion 140 and the remaining substrate layer to be etched 100 exposed by the protrusion 140. The wet etching process has a large removal rate and a simple process.

[0133] For example, the material of the substrate layer to be etched 100 is silicon. Therefore, the etching solution used in the wet etching process is a mixed solution of hydrofluoric acid (HF) and nitric acid (HNO3).

[0134] When a dry etching process is adopted, the process parameters and conditions of the dry etching process are adjusted accordingly. For example, the bias voltage is reduced, and an etching is performed using a reaction gas that can generate a lighter polymer to enhance the isotropic effect during the dry etching process, thereby achieving lateral etching. And when the lateral etching rate is large enough, the raised portion can be removed.

[0135] In this embodiment, the top surface of the target structure 150 has a curved surface profile. Therefore, the top surface of the target structure 150 is uneven.

[0136] Among them, the height difference H between the concave surface and the convex surface in the curved surface profile should not be too small. If the height difference H between the concave surface and the convex surface in the curved surface profile is too small, correspondingly, in the step of etching a part of the thickness of the base layer to be etched 100 along the mask opening 130, it is easy to cause a small difference in the etching depth of each region 100d. Affected by the process variation of the etching process, the difficulty of controlling the etching depth of each region 100d becomes larger, and it is easy to cause the top surface profile of the target structure 150 to not meet the design requirements. For this reason, in this embodiment, the height difference H between the concave surface and the convex surface in the curved surface profile is greater than or equal to 3 microns.

[0137] For example, in this embodiment, the curved surface profile of the top surface of the target structure 150 is a spherical surface. Therefore, the height difference H between the concave surface and the convex surface in the curved surface profile is: the distance from the highest point to the lowest point of the top surface of the target structure 150.

[0138] It should be noted that after the raised portion 140 is formed and before the raised portion 140 is removed, the forming method further includes: removing the etching blocking structure 120 (i.e., the mask layer 110).

[0139] By removing the etching blocking structure 120, the top surface of the raised portion 140 is exposed, so that during the process of removing the raised portion 140, the removal rate of the raised portion 140 can be increased.

[0140] As an example, the material of the etching blocking structure 120 is silicon nitride, then a wet etching process is used to remove the etching blocking structure 120, and the etching solution used in the wet etching process is a phosphoric acid solution.

[0141] In other embodiments, the step of the etching blocking structure can also be omitted, thereby saving process steps.

[0142] For example, during the process of removing the protrusion, the etch stop structure will also suffer a certain degree of loss, thereby achieving the effect of removing the etch stop structure; or, when using an etching process with a lateral etching rate to remove the protrusion, the etching process can remove the protrusion by laterally etching the sidewalls of the protrusion.

[0143] It should also be noted that in this embodiment, only two annular regions 100e are illustrated, namely the first annular region 100b and the second annular region 100c surrounding the first annular region 100b. However, according to the top surface contour morphology of the target structure, the number of the annular regions is not limited to two.

[0144] In addition, in this embodiment, the pattern density of the etch stop structures 120 in each region 100d decreases. In other embodiments, according to the top surface contour morphology of the target structure, the distribution of the pattern density of the etch stop structures can also be of other types.

[0145] For example, with reference to Figure 13 , Figure 13 is a schematic structural diagram of a target structure formed by another embodiment of the method for forming the target structure of the present invention.

[0146] In this embodiment, the top surface contour of the target structure 250 is aspherical.

[0147] Correspondingly, the number of the annular regions is greater than two (for example, five), and in the step of forming the mask layer, along the direction from the center to the edge of the substrate to be etched, the pattern density of the etch stop structures in each region first decreases, then increases, and finally decreases again.

[0148] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for forming a target structure, characterized in that, Comprising: Providing an etchable base layer for forming a target structure, the etchable base layer including a plurality of regions, the top surface of the target structure forming a curved surface profile over the plurality of regions, and the etchable base layer being capable of being patterned using a semiconductor etching process; Forming a plurality of etch stop structures protruding from the etchable base layer on the etchable base layer, the etch stop structures in the plurality of regions having different pattern densities, and the pattern density in the plurality of regions being negatively correlated with the line width of the etch stop structures in the corresponding regions; Using the etch stop structures as a mask to etch a part of the thickness of the etchable base layer exposed by the etch stop structures, forming a protruding portion protruding from the remaining etchable base layer; Removing the protruding portion to form a target structure, the top surface of the target structure having a curved surface profile.

2. The forming method according to claim 1, characterized in that The plurality of regions of the etchable base layer include a central region and a plurality of annular regions surrounding the central region and arranged in concentric circles in sequence.

3. The forming method according to claim 2, wherein In the step of forming the etch stop structures on the etchable base layer, along the direction from the center to the edge of the etchable base layer, the pattern density of the etch stop structures in each region decreases.

4. The forming method according to claim 1, characterized in that, In the step of forming the etch stop structures, the etch stop structures are graphic lines; or, the etch stop structures are arranged in a dot matrix pattern on the etchable base layer.

5. The forming method according to claim 1, wherein The step of removing the protruding portion includes: performing maskless etching on the protruding portion and the remaining etchable base layer exposed by the protruding portion.

6. The forming method according to claim 1, characterized in that, The step of removing the protruding portion includes: etching the protruding portion using an etching process, the etching process having a lateral etching rate.

7. The forming method according to claim 6, wherein The etching process includes a wet etching process or a dry etching process.

8. The forming method according to claim 1, wherein After forming the protruding portion and before removing the protruding portion, further including: removing the etch stop structures.

9. The forming method according to claim 1, characterized in that, Using an anisotropic etching process to etch a part of the thickness of the etchable base layer exposed by the etch stop structures.

10. The forming method according to claim 1, wherein, Before forming the etch stop structures on the etchable base layer, further including: Providing a plurality of base layers, the plurality of base layers being of the same material as the etchable base layer; Forming a plurality of etch stop structures on the plurality of base layers respectively, the pattern densities on the plurality of base layers being different; Using the same etching conditions to etch the plurality of base layers exposed by the etch stop structures respectively, and measuring the etching depths corresponding to different pattern densities respectively; Performing fitting through a plurality of pattern densities and the etching depths corresponding to the pattern densities to obtain a fitting relationship, the independent variable in the fitting relationship being the pattern density and the dependent variable being the etching depth; According to the curved surface profile of the target structure, determining the etching depth of the etchable base layer in each region; According to the etching depth of the etchable base layer in each region and the fitting relationship, obtaining the pattern density corresponding to each region.

11. The forming method according to claim 1, characterized in that, The material of the etch stop structures includes a hard mask material or a photoresist.

12. The forming method according to claim 1, wherein In the step of etching a part of the thickness of the etchable base layer exposed by the etch stop structures, the ratio of the bottom line width of the protruding portion to the etching depth of the region where it is located is greater than 1 / 100.

13. The forming method according to claim 1, characterized in that, In the step of etching the part of the to-be-etched base layer with the exposed thickness of the etching stop structure, the top line width of the convex portion is less than or equal to 1 / 20 of the lateral dimension of the curved surface profile.

14. The forming method according to claim 1, wherein Along the direction parallel to the surface of the to-be-etched base layer, the shape of the to-be-etched base layer is circular, and the diameter of the to-be-etched base layer is greater than or equal to 100 micrometers.

15. The forming method according to claim 1, characterized in that, The height difference between the concave surface and the convex surface in the curved surface profile is greater than or equal to 3 micrometers.

16. The forming method according to claim 1, wherein The target structure includes a curved mirror, and the curved mirror includes a lens.

17. The forming method according to claim 1, wherein The material of the to-be-etched base layer includes semiconductor material, quartz or glass.

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