Photoresist patterning method

Abstract

The application discloses a photoresist patterning method, and belongs to the field of photoetching technology. The photoresist patterning method comprises the following steps: forming an inducing structure with a plurality of grooves on a substrate, depositing a block copolymer on the inducing structure to form a block copolymer layer; inducing the block copolymer layer to directionally self-assemble to generate a first polymer region and a second polymer region; forming a second photoresist layer on the first polymer region and the second polymer region; and exposing the second photoresist layer through a mask to form a patterned photoresist layer, wherein the patterned photoresist layer is formed on the top of the second polymer region, and a bonding layer is formed between the patterned photoresist layer and the second polymer region through reaction. By introducing a BCP material with a special structure, the adaptability to a photoetching pattern is good, the adhesion between the photoresist and the substrate can be improved, and the phenomenon of photoresist inversion in a high-aspect-ratio film layer can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of photolithography, and in particular to a method for patterning photoresist. Background Technology

[0002] Photoresist coating and development are crucial steps in semiconductor photolithography. The adhesion of the photoresist to the silicon substrate surface significantly impacts the photolithography and development process. Poor adhesion can lead to pattern cracks or even serious defects such as photoresist peeling and bleed-off. Because silicon contains silicon dioxide (SiO2) in oxide form, when exposed to air under certain humidity conditions, polar -OH bonds form on its surface, making the silicon substrate hydrophilic and exhibiting poor affinity for the non-polar or low-polarity resin molecules of the photoresist. Therefore, to modify the surface properties of the silicon wafer to make it hydrophobic, an adhesion-enhancing process is needed to improve the surface properties before photoresist coating.

[0003] Currently, the common method used in photolithography is to spin-coat a layer of hexamethyldisilane (HMDS) onto the silicon wafer surface. Research shows that optimal adhesion is achieved when HMDS, existing in vapor form, acts as a monolayer and chemically bonds to the silicon substrate surface in a heated matrix (75°C to 120°C). However, HMDS is usually spin-coated directly onto the silicon substrate as a liquid, primarily acting as a physical adhesion layer, and the improvement effect is not significant. Especially for products with high aspect ratio films, such as the thick resist layers in CIS (CMOS image sensor) platforms, the adhesion between HMDS and photoresist is insufficient, and resist peeling still occurs, affecting product safety and stability. Summary of the Invention

[0004] The purpose of this invention is to provide a photoresist patterning method to solve the problem of insufficient adhesion between existing photoresists and substrates.

[0005] To solve the above technical problems, the present invention provides a photoresist patterning method, comprising the following steps:

[0006] An induced structure with several trenches is formed on a substrate, and a block copolymer is deposited on the induced structure to form a block copolymer layer;

[0007] Inducing the directional self-assembly of the block copolymer layer to generate a first polymer region and a second polymer region;

[0008] A second photoresist layer is formed on the first polymer region and the second polymer region;

[0009] A patterned photoresist layer is formed by exposing the second photoresist layer using a photomask, wherein the patterned photoresist layer is formed corresponding to the top of the second polymer region, and a bonding layer is formed between the patterned photoresist layer and the second polymer region by reaction.

[0010] Develop the material, then remove the residue and the first polymer region.

[0011] Preferably, the second photoresist layer contains phenolic hydroxyl functional groups, and the block copolymer includes a first block and a second block. After inducing the block copolymer layer to self-assemble in a directional manner, the first block forms a first polymer region, and the second block forms a second polymer region, wherein the second block contains functional groups that react with the phenolic hydroxyl groups.

[0012] Preferably, the second block contains a chloromethyl functional group to undergo a bonding reaction with the patterned photoresist layer in contact with it.

[0013] Preferably, the block copolymer is a copolymer of polymethyl methacrylate and polychloromethyl styrene, wherein the first block is polychloromethyl styrene and the second block is polymethyl methacrylate.

[0014] Preferably, the second block contains a chloromethyl functional group, the second photoresist layer contains a phenolic hydroxyl group, and under heating conditions, the patterned photoresist layer reacts with the second polymer region to form the bonding layer.

[0015] Preferably, the step of forming the induced structure includes: forming a cross-linked resin layer on the substrate and performing an annealing treatment, then forming a first photoresist layer on the cross-linked resin layer, performing photolithography and development to obtain a cross-linked resin layer with several trenches, and then removing the remaining first photoresist layer.

[0016] Preferably, after removing the residual first photoresist layer, a polymer brush is coated on top of the crosslinked resin layer and in the trenches, and the portion of the polymer brush that is not grafted onto the substrate is removed, so that the height of the polymer brush is not higher than the crosslinked resin layer.

[0017] Preferably, after the patterned photoresist layer is formed by exposing the second photoresist layer through a photomask, the patterned photoresist layer is subjected to soft baking and development.

[0018] Preferably, after removing the residue and the first polymer region, at least a portion of the crosslinked resin layer is also removed.

[0019] Preferably, the substrate and the block copolymer layer thereon are annealed at a temperature of 180°C-200°C to induce directional self-assembly of the block copolymer layer.

[0020] In the photomask manufacturing method provided by the present invention, by introducing a BCP material with a special structure, not only is the cost lower, but it also has good compatibility with the photolithography pattern, improves the adhesion between the photoresist and the substrate, and can effectively improve the photoresist spillage phenomenon in high aspect ratio films. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the substrate and the cross-linked resin layer thereon;

[0022] Figure 2 This is a schematic diagram of the cross-linked resin layer subjected to photolithography.

[0023] Figure 3 This is a schematic diagram of the structure after removing the first photoresist layer on the crosslinked resin layer;

[0024] Figure 4 This is a schematic diagram of a polymer brush formed on a cross-linked resin layer;

[0025] Figure 5 This is a schematic diagram of the structure after removing the ungrafted portion from the polymer brush;

[0026] Figure 6 This is a schematic diagram of a block copolymer layer formed on an induced structure;

[0027] Figure 7 This is a schematic diagram of the structure after the block copolymer layer self-assembles to form periodic stripes;

[0028] Figure 8 This is a schematic diagram of the structure in which a second photoresist layer is formed on the first polymer region;

[0029] Figure 9 This is a schematic diagram of the structure for exposing the second photoresist layer;

[0030] Figure 10 This is a schematic diagram of the structure for soft baking of the second photoresist layer;

[0031] Figure 11 This is a schematic diagram of the structure after removing the residue from the exposed area.

[0032] In the picture,

[0033] 1. Substrate; 2. Crosslinked resin layer; 3. First photoresist layer; 4. Polymer brush; 5. Block copolymer layer; 51. First polymer region; 52. Second polymer region; 53. Bonding layer; 6. Second photoresist layer; 61. Patterned photoresist layer; 62. Residue; 7. Mask. Detailed Implementation

[0034] The method for manufacturing the photomask proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0035] The inventors discovered that the mechanism of HMDS involves the Si end of Si(CH3)3 bonding with the substrate, converting the hydrophilic -OH bonds into Si-O bonds (due to the decomposition of hydroxyl groups, releasing NH3), while the nonpolar -CH3 bonds move away from the substrate, forming a hydrophobic surface. If liquid HMDS is directly spin-coated onto the substrate, the HMDS layer only acts as a physical adhesion layer and does not improve adhesion. Secondly, during the pre-baking process, the HMDS layer releases NH3, which enters the cross-linked photoresist layer from near the substrate, thus inhibiting the development process. Furthermore, as a reference, HMDS is also a toxic substance, requiring careful handling. Therefore, how to enhance the adhesion between the photoresist and the substrate and avoid pattern defects is a pressing problem to be solved.

[0036] Based on this, the core idea of ​​the present invention is to introduce a block copolymer (BCP) material, and after inducing the block copolymer to self-assemble into the desired pattern, form the desired patterned photoresist on it. The patterned photoresist and one of the stripe blocks undergo a bonding reaction, which enhances the adhesion between the patterned photoresist layer and the substrate, thereby improving the wettability and adhesion of the photoresist to the substrate surface.

[0037] For details, please refer to Figures 1-11 This is a schematic diagram of an embodiment of the present invention. Figure 1 As shown, a photoresist patterning method includes the following steps:

[0038] First, an induction structure with several trenches is formed on a substrate 1, and a block copolymer is deposited on the induction structure to form a block copolymer layer 5. The block copolymer layer 5 is induced to oriented self-assemble to generate a first polymer region 51 and a second polymer region 52 to form the desired pattern. Second, a second photoresist layer 6 is formed on the first polymer region 51 and the second polymer region 52. The second photoresist layer 6 is exposed through a mask 7 to form a patterned photoresist layer 61, wherein the patterned photoresist layer 61 is formed corresponding to the top of the second polymer region 52, and a bonding layer 53 is formed between the patterned photoresist layer 61 and the second polymer region 52. Finally, development is performed, and then the residue 62 and the first polymer region 51 are removed.

[0039] Since the second block contains functional groups that can bond with the photoresist, after the second block forms the patterned second polymer region 52, it can react with the photoresist to form strong covalent bonds. This not only significantly improves the adhesion strength between the substrate 1 and the patterned photoresist layer 61, preventing photoresist delamination after development, but also, due to the directional self-assembly property of the block copolymer layer 5 itself, it can further improve the pattern height and product device performance that can be obtained by pixel film lithography to a certain extent.

[0040] Specifically, the second photoresist layer 6 contains phenolic hydroxyl functional groups (-OH), and the block copolymer includes a first block and a second block. After inducing the directional self-assembly of the block copolymer layer 5, the first block forms a first polymer region 51, and the second block forms a second polymer region 52, wherein the second block contains functional groups that react with the phenolic hydroxyl group.

[0041] Specifically, the second block contains chloromethyl functional groups to undergo a bonding reaction with the patterned photoresist layer 61 in contact with it.

[0042] In one embodiment, the block copolymer is a copolymer of polymethyl methacrylate and polychloromethyl styrene, wherein the first block is polychloromethyl styrene and the second block is polymethyl methacrylate.

[0043] This application introduces a block copolymer material: polymethyl methacrylate and polychloromethyl styrene copolymer (PSCl-b-PMMA), whose unit structure is as follows:

[0044]

[0045] PSCl-b-PMMA is a linear copolymer composed of two alternating segments with different chemical structures. Under certain induced structural and annealing conditions, it can form periodic nanoscale stripes through directional self-assembly (DSA). Based on the characteristic of BCP to form periodic stripes, this study utilizes the mechanism of two different blocks formed by BCP, namely PSCl blocks and PMMA blocks, to design a bonding reaction between the PSCl blocks and the photoresist. This increases the adhesion between the required patterned photoresist layer 61 and the substrate 1, thereby avoiding phenomena such as cracking, peeling, and drift in the photolithographic pattern. Compared with HMDS, the PSCl blocks form strong covalent bonds with the photoresist through a chemical reaction, which significantly improves the adhesion strength between the two, preventing peeling after development, and to a certain extent, further improving the pattern height and device performance achievable by pixel film lithography.

[0046] Specifically, the second block contains a chloromethyl functional group, and the second photoresist layer 6 contains phenolic hydroxyl groups. Under predetermined heating conditions, the patterned photoresist layer 61 reacts with the second polymer region 52 to form the bonding layer 53. The following reaction occurs:

[0047]

[0048]

[0049] The steps for forming the induced structure include: forming a cross-linked resin layer 2 on the substrate 1 and annealing it; then forming a first photoresist layer 3 on the cross-linked resin layer 2; performing photolithography and development to obtain a cross-linked resin layer 2 with several trenches; and then removing the remaining first photoresist layer 3. After removing the remaining first photoresist layer 3, a polymer brush 4 is coated on the top of the cross-linked resin layer 2 and in the trenches, and the portion of the polymer brush 4 that is not grafted onto the substrate 1 is removed, so that the height of the polymer brush 4 is not higher than the cross-linked resin layer 2.

[0050] like Figures 1-7 The process involves forming an induced structure on the surface of substrate 1. Before forming periodic stripes using BCP material, the surface of substrate 1 needs to be pretreated: the surface of substrate 1 is neutralized to obtain a layered structure, and the surface tension of substrate 1 is changed by using crosslinkable resin and transplantable polymer brush to keep it neutral for the two blocks formed by BCP.

[0051] like Figure 1 A cross-linked resin layer 2 is formed by coating a cross-linked resin layer on the surface of substrate 1 and then annealing it. Next, as shown... Figure 2 By coating a first photoresist layer 3 and sequentially performing photolithography, development, and etching steps, a cross-linked resin layer 2 with a trench structure is obtained. Excess first photoresist layer 3 is then removed to form... Figure 3 The structure.

[0052] like Figures 4-5 Through spin coating and annealing steps, polymer brush 4 is laid flat on cross-linked resin layer 2 and substrate 1. Polymer brush 4 can change the surface properties of substrate 1 exposed after etching. Some polymer brush 4 is not attached to substrate 1. The remaining unattached portions of polymer brush 4 are cleaned away with organic solution, thereby forming Figure 5 Induced structure.

[0053] The substrate 1 can be a silicon substrate, a semiconductor substrate including an epitaxial layer, or a silicon-on-insulator (SOI) substrate. The semiconductor substrate can also include one or more of the following: silicon carbide, gallium arsenide, indium arsenide, indium phosphide, germanium silicon, silicon germanium carbide, gallium arsenide phosphide, and indium gallium phosphide, in any combination thereof.

[0054] Then, a block copolymer layer 5 is formed on the induced structure, that is, BCP material PSCl-b-PMMA is spin-coated onto the surface of the induced structure and annealed. The block copolymer layer 5 is then placed in an annealing environment at 190°C to induce self-assembly of the block copolymer layer 5 to form periodic stripes.

[0055] Specifically, after the second photoresist layer 6 is exposed by the mask 7 to form a patterned photoresist layer 61, the patterned photoresist layer 61 is soft baked and then developed.

[0056] Specifically, after removing the residue 62 and the first polymer region 51, at least a portion of the crosslinked resin layer 2 is also removed.

[0057] Specifically, the substrate 1 and the block copolymer layer 5 thereon are annealed at a temperature of 180°C-200°C to induce the directional self-assembly of the block copolymer layer 5.

[0058] like Figures 8-9 A thick layer of photoresist, namely the second photoresist layer 6, is applied to the first polymer region 51 and the second polymer region 52. Here, only positive photoresist is used as an example. The photoresist is exposed using a pre-made mask 7, where the non-exposed area corresponds to the stripe area of ​​the PSCl block.

[0059] Because the surface of the second polymer region 52 contains a large number of chloromethyl functional groups, a bonding reaction will occur between the phenolic hydroxyl functional groups on the patterned photoresist layer 61 and the chloromethyl functional groups on the surface of the PSCl block under heating conditions.

[0060] In this process, a soft bake (PEB) is performed after exposure. Under PEB conditions, a bonding reaction can continue between the second polymer region 52 and the patterned photoresist layer 61. Finally, development is performed, and deionized water is used to rinse away the PR (photoresist) residue in the exposed area. An etching process removes the BCP stripe PMMA blocks and their underlying cross-linked resin portions, resulting in a high aspect ratio pattern. The thickness of the polymer brush 4 is negligible compared to the thickness of the patterned photoresist. It is understood that the phenolic hydroxyl functional groups on the patterned photoresist layer 61 and the chloromethyl functional groups on the PSCl block surface react under heating conditions, and the soft bake process can be directly performed to promote the bonding reaction.

[0061] In summary, the photomask manufacturing method provided in this invention utilizes BCP material to enhance the adhesion between the photoresist and the substrate. Compared to HMDS, the strong covalent bonds formed by the chemical reaction between the PSCl blocks and the photoresist significantly improve the adhesion strength, preventing photoresist delamination after development and further enhancing the pattern height and device performance achievable through pixel layer lithography. BCP material is readily available and has a low cost.

[0062] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for patterning photoresist, characterized in that, Includes the following steps: An induced structure with several trenches is formed on a substrate, and a block copolymer is deposited on the induced structure to form a block copolymer layer; Inducing the directional self-assembly of the block copolymer layer to generate a first polymer region and a second polymer region; A second photoresist layer is formed on the first polymer region and the second polymer region; A patterned photoresist layer is formed by exposing the second photoresist layer using a photomask, wherein the patterned photoresist layer is formed corresponding to the top of the second polymer region, and a bonding layer is formed between the patterned photoresist layer and the second polymer region by reaction. Develop the material, then remove the residue and the first polymer region; The second photoresist layer contains phenolic hydroxyl functional groups, and the block copolymer includes a first block and a second block. After inducing the block copolymer layer to self-assemble in a directional manner, the first block forms a first polymer region, and the second block forms a second polymer region, wherein the second block contains functional groups that react with the phenolic hydroxyl groups. The second block contains chloromethyl functional groups to form a bonding reaction with the patterned photoresist layer in contact with it; The block copolymer is a copolymer of polymethyl methacrylate and polychloromethyl styrene, wherein the first block is polychloromethyl styrene and the second block is polymethyl methacrylate.

2. The photoresist patterning method as described in claim 1, characterized in that, The second block contains a chloromethyl functional group, and the second photoresist layer contains phenolic hydroxyl groups. Under heating conditions, the patterned photoresist layer reacts with the second polymer region to form the bonding layer.

3. The photoresist patterning method as described in claim 1, characterized in that, The steps for forming the induced structure include: forming a cross-linked resin layer on the substrate and annealing it, then forming a first photoresist layer on the cross-linked resin layer, performing photolithography and development to obtain a cross-linked resin layer with several trenches, and then removing the remaining first photoresist layer.

4. The photoresist patterning method as described in claim 3, characterized in that, After removing the residual first photoresist layer, a polymer brush is coated on top of the cross-linked resin layer and in the trenches, and the portion of the polymer brush that is not grafted onto the substrate is removed, so that the height of the polymer brush is not higher than the cross-linked resin layer.

5. The photoresist patterning method as described in claim 1, characterized in that, After the second photoresist layer is exposed using a photomask to form a patterned photoresist layer, the patterned photoresist layer is then subjected to soft baking followed by development.

6. The photoresist patterning method as described in claim 3, characterized in that, After removing the residue and the first polymer region, at least a portion of the crosslinked resin layer is also removed.

7. The photoresist patterning method as described in claim 1, characterized in that, The substrate and the block copolymer layer thereon are annealed at a temperature of 180°C-200°C to induce directional self-assembly of the block copolymer layer.

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