A method for preparing an etch-resistant composite hard mask and its application

Abstract

This invention relates to a method for preparing an etch-resistant composite hard mask and its application, comprising the following steps: S1, spin-coating a negative photoresist onto the surface of a substrate to be etched, followed by soft baking and curing to obtain a bottom photoresist layer; S2, spin-coating a positive photoresist onto the bottom photoresist layer, followed by soft baking and curing to obtain a top photoresist layer; S3, covering the top photoresist layer with a photomask having a preset pattern, followed by exposure, exposure baking, and development to form a patterned photoresist layer; S4, subjecting the patterned photoresist layer to general exposure, exposing the top photoresist layer while leaving the covered bottom photoresist layer unexposed, then preparing a metal film layer on the patterned photoresist layer by chemical vapor deposition, followed by development to obtain the etch-resistant composite hard mask. The above-mentioned composite hard mask preparation method is simple, has good etching blocking effect, meets the requirements of deep etching processes, and allows for rapid and non-destructive removal of the hard mask from the substrate surface after etching, improving product yield.

Description

Technical Field

[0001] This invention relates to the field of semiconductor etching technology, and more specifically to a method for preparing an etch-resistant composite hard mask and its application. Background Technology

[0002] With the rapid development of microelectronics, microelectromechanical systems (MEMS), 3D integration, and advanced packaging, the functional integration and performance requirements of devices are increasing daily, and their microstructures are gradually moving from traditional two-dimensional planar designs to three-dimensional architectures. Under this trend, deep etching technology, capable of forming high aspect ratio (i.e., etching depth much greater than feature size) structures on substrate materials, has become a key process step in realizing these advanced devices. In existing deep etching lithography processes, the choice of mask is crucial for achieving high-precision, high aspect ratio pattern transfer. Currently, the mask schemes commonly used in the industry are mainly divided into two categories:

[0003] One method uses photoresist as a mask. The significant advantage of this method is its simple and rapid fabrication process, allowing patterning to be directly achieved using conventional photolithography techniques. However, photoresist materials themselves have poor etching resistance, especially under prolonged or high-intensity ion bombardment (such as during deep etching of silicon). The mask layer will be rapidly consumed, rendering it unable to effectively protect the underlying non-etched areas. This limitation severely restricts its application in processes requiring deep etching, making it difficult to further improve the aspect ratio of the final structure.

[0004] Another approach is to use a hard mask as an etching barrier layer. Commonly used hard mask materials include dielectric materials such as silicon dioxide (SiO2) and zinc sulfide (ZnS). These materials possess excellent etching resistance and remain stable in long-term plasma or reactive ion etching environments, thus ensuring pattern fidelity during deep etching. However, the fabrication process of hard masks is relatively complex and cumbersome. Typically, a complete dielectric film needs to be deposited on the substrate surface first, then a photoresist layer with a pre-defined pattern is formed on it through an additional photolithography process, and finally, the pattern is transferred from the photoresist layer to the underlying hard mask layer through an etching process. This two-step patterning process of "photolithography-etching" not only increases the complexity of the process and the production cycle, but also significantly increases the difficulty and cost of the patterning process when a thicker hard mask is required to cope with extreme etching conditions, and may even introduce additional pattern distortion or defects.

[0005] In summary, both existing masking methods have significant shortcomings: photoresist masks, while easy to fabricate, are not resistant to etching; hard masks, while resistant to etching, have complex fabrication processes, high costs, and difficulties in patterning thick films. This contradiction has become one of the bottlenecks restricting the further development of high aspect ratio micro / nano structure fabrication technology. Therefore, there is an urgent need in this field for a mask with a simple fabrication process and good etching resistance, capable of meeting the requirements of long-duration, deep etching processes, thereby achieving precise fabrication of high aspect ratio patterns. Summary of the Invention

[0006] To address the problems of existing photoresist masks, which are easy to fabricate but not resistant to etching, and hard masks, which are resistant to etching but suffer from complex fabrication processes, high costs, and difficulties in thick-film patterning, this invention provides a method for fabricating an etch-resistant composite hard mask and its application. This composite hard mask is fabricated through a one-step molding process, effectively avoiding the two-step photolithography-etching process required by traditional hard masks. More importantly, the fabricated composite hard mask not only possesses excellent resistance to ion bombardment, meeting the requirements of long-duration deep etching processes and thus enabling precise fabrication of high aspect ratio patterns, but also allows for rapid, thorough, and non-destructive removal from the material surface after the etching process, avoiding damage to the formed structure or substrate surface caused by subsequent cleaning processes.

[0007] Specifically, the following technical solutions are provided:

[0008] The first aspect of this invention provides a method for preparing an etch-resistant composite hard mask, comprising the following steps:

[0009] S1. Spin-coat a negative photoresist onto the substrate surface to be etched, and cure it after soft baking to obtain the bottom photoresist layer;

[0010] S2. A positive photoresist is spin-coated onto the bottom photoresist layer, and then cured after soft baking to obtain the top photoresist layer;

[0011] S3. A photomask with a preset pattern is covered on the top photoresist layer. After exposure, post-exposure baking and development, the exposed area of ​​the top photoresist layer is removed, the exposed area of ​​the bottom photoresist layer is cured, and the unexposed area of ​​the bottom photoresist layer covered by the unexposed area of ​​the top photoresist layer is retained to form a patterned photoresist layer.

[0012] S4. Perform a generalized exposure process on the patterned photoresist layer, controlling the exposure dose so that the remaining top photoresist layer is exposed, while the area of ​​the bottom photoresist layer covered by the remaining top photoresist layer is not exposed. Then, a metal film layer is prepared on the patterned photoresist layer by physical and / or chemical vapor deposition. After development, the remaining top photoresist layer and the metal deposited on its surface are removed, and the unexposed area of ​​the bottom photoresist layer is also removed. The exposed bottom photoresist layer and the metal film layer on its surface are retained, thus obtaining the etch-resistant composite hard mask.

[0013] Furthermore, the thickness of the bottom photoresist layer is greater than the thickness of the top photoresist layer.

[0014] Furthermore, the thickness of the top photoresist layer is greater than twice the thickness of the metal film layer, which facilitates the removal of the top photoresist layer and the peeling off of the metal film layer on its surface after development in step S4.

[0015] Furthermore, the thickness of the metal film can be 10 nm to 500 nm, such as 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., including but not limited to the thickness values ​​listed above. The thickness of the metal film can be selected according to the etching requirements.

[0016] Furthermore, in step S1, the substrate material can be a compound semiconductor epitaxial wafer, a silicon wafer, or sapphire, such as an infrared detector chip, a laser chip, a micro-led chip, and a MEMS chip.

[0017] Further, in step S1, the negative photoresist can be selected from one of SUN-1306, ROL-7133, HTIN160, NR series, and AZ series, wherein the NR series includes but is not limited to NR7-1000P, and the AZ series includes but is not limited to AZ125nXT, AZ 15nXT (115CPS), and AZ nLof 202.

[0018] Further, in step S2, the positive photoresist is selected from one of the AZ series, SPR955 series, S18XX series, SPR220 series, and HTI751 series, wherein the AZ series includes, but is not limited to, AZ6130 and AZ1500.

[0019] Furthermore, the area blocked by the photomask corresponds to the location on the substrate that ultimately needs to be etched.

[0020] Further, in step S3, the exposure metering is 150-200 mJ / cm.2 The exposure dose is light intensity (unit: mW / cm²). 2 The optimal exposure dose is the product of the exposure time (in seconds). The optimal exposure dose varies depending on the process requirements for different photoresists, but a common range is: approximately 100 mJ / cm² for positive photoresists. 2 The optimal exposure dose for negative photoresist is approximately 150 mJ / cm². 2 Since step S3 involves exposing the double-layer photoresist, the bottom negative photoresist needs to be exposed. Extensive experiments have shown that the optimal exposure dose here is 150-200 mJ / cm². 2 .

[0021] Furthermore, in step S3, the baking temperature after exposure is preferably 110-130 ℃, and the baking time is preferably 100-200 s, for example, baking at 130 ℃ for 150 s.

[0022] In this invention, a post-exposure baking process is performed after exposure. During this process, photoacid acts as a catalyst to promote the cross-linking reaction of resin molecules (such as phenolic resin) in the negative photoresist, forming a three-dimensional network structure. This cross-linking structure causes the negative photoresist in the exposed area to change from a soluble state to an insoluble state, thereby achieving complete curing of the negative photoresist in the underlying exposed area and avoiding its impact on subsequent development processes.

[0023] Furthermore, in step S3, the developing solution used is the developing solution of the positive photoresist or tetramethylammonium hydroxide, or other alkaline developing solutions.

[0024] Further, in step S4, the exposure dose for the generalized exposure is 50-90 mJ / cm². 2 For example, 50 mJ / cm 2 60mJ / cm 2 70 mJ / cm 2 80 mJ / cm 2 90 mJ / cm 2 In this invention, generalized exposure refers to non-selective exposure without a mask. The exposure dose here needs to be less than the typical value of the exposure dose for the top positive photoresist, so that the top positive photoresist is fully exposed while the bottom negative photoresist is unaffected by the exposure. Preferably, the exposure dose for generalized exposure is controlled at 50-90 mJ / cm². 2 Within this range, it does not affect subsequent development to remove the top photoresist layer and the unexposed areas of the bottom photoresist layer.

[0025] Furthermore, in step S4, the material of the metal film is selected from one or more of titanium, chromium, nickel, and titanium nitride.

[0026] In this invention, a metal film layer covers the entire surface of the patterned photoresist layer of the substrate. Since the patterned photoresist layer has a staggered structure, the metal film layer also creates a barrier as it adheres to the surface of the bottom photoresist layer and the surface of the top photoresist layer.

[0027] Furthermore, in step S4, the developing solution used is the developing solution of the positive photoresist or tetramethylammonium hydroxide, and the developing time is preferably 5-10 min, during which the metal film on the surface of the top photoresist layer can be observed to peel off.

[0028] The second aspect of the present invention provides an etch-resistant composite hard mask, which is prepared by the preparation method described in the first aspect.

[0029] Furthermore, the etch-resistant composite hard mask is composed of a photoresist layer and a metal film layer. The photoresist layer of the etch-resistant composite hard mask is in contact with the substrate material, which not only prevents metal ions in the metal film layer from diffusing into the substrate material and affecting product performance, but also makes it easier to remove after etching, avoiding damage to the substrate.

[0030] The third aspect of this invention provides an application of the etching-resistant composite hard mask described in the second aspect in photolithography processes.

[0031] Further, the etching-resistant composite hard mask is prepared on the surface of the substrate to be etched; the substrate with the etching-resistant composite hard mask on its surface is etched using an etching device, and the area on the substrate surface without mask coverage is etched; the etched substrate is immersed in a polar solvent to remove the etching-resistant composite hard mask, thus completing the patterning process of the substrate.

[0032] Furthermore, before etching, a substrate is treated with a glue applicator to remove residual glue from the pre-etched area.

[0033] Furthermore, the polar solvent includes acetone and / or N-methylpyrrolidone; preferably, the immersion time is not less than 20 min, so that the underlying photoresist is fully dissolved and the metal film layer on the surface of the photoresist is peeled off.

[0034] Furthermore, the aspect ratio of the graphical processing is greater than 4:1.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] This invention provides a method for fabricating an etch-resistant composite hard mask. By combining photolithography lift-off with chemical vapor deposition, a composite hard mask with a high etch selectivity can be fabricated simply and efficiently. This effectively avoids the two-step photolithography-etching process required by traditional hard masks, simplifying the fabrication process. More importantly, the fabricated composite hard mask not only possesses excellent resistance to ion bombardment, meeting the requirements of long-duration deep etching processes and enabling precise fabrication of patterns with aspect ratios greater than 4:1, but also allows for rapid, thorough, and non-destructive removal from the material surface after the etching process, avoiding damage to the formed structure or substrate surface during subsequent cleaning processes.

[0037] The etch-resistant composite hard mask provided by this invention offers an innovative solution for achieving high-quality deep etching efficiently and at low cost, and has promising application prospects in the fields of compound semiconductor processing such as infrared detector chips, Micro-LED chips, and solar cells, as well as in the field of semiconductor micro-nano processing. Attached Figure Description

[0038] Figure 1 A schematic diagram illustrating the fabrication process of the etching-resistant composite hard mask provided by this invention;

[0039] Figure 2 This is a SEM image of the micro / nano structure prepared using an etch-resistant composite hard mask in Example 1;

[0040] Figure 3 This is a SEM image of the micro / nano structure prepared using an etch-resistant composite hard mask in Example 2;

[0041] Figure 4 A schematic diagram of the mask fabrication process for Comparative Example 2, in which a positive photoresist is coated on the bottom layer and a negative photoresist is coated on the top layer;

[0042] In the figure, the numbers are as follows: 1 is the substrate, 2 is the bottom photoresist layer, 3 is the top photoresist layer, 4 is the photomask with a preset pattern, 5 is the top photoresist layer after exposure, 6 is the bottom photoresist layer after exposure, and 7 is the metal film layer. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms “comprising” or “including” used in this invention may also be replaced with the closed form “is” or “consisting of”.

[0045] Example 1: This example relates to the fabrication of an etch-resistant composite hard mask and micro / nano structure. The fabrication process is as follows: Figure 1 As shown, the details are as follows:

[0046] (1) Wet cleaning of the substrate material (2-inch InAs / GaSb type II superlattice epitaxial wafer) to be etched; spin coating of negative photoresist SUN-1306 onto the substrate surface using a spin coater at a spin coater speed of 4000 rpm and a thickness of 2 μm; then soft baking curing treatment at a temperature of 120 ℃ and a time of 180 s to form the bottom photoresist layer.

[0047] (2) Spin coat positive photoresist AZ1500 on the bottom photoresist surface at a spin speed of 3000 rpm and a thickness of 1.5 μm. Then perform soft baking curing at a temperature of 120 ℃ and a time of 100 s to form the top photoresist layer.

[0048] (3) Use a photomask to cover the preset etching area (the location to be etched) and expose it (exposure dose is 150mJ / cm). 2 The exposure time is 15s, followed by baking at 120℃ for 100s, and then developing in developer (RZX-3038) for 90s to remove the exposed portion of the top photoresist layer.

[0049] (4) Expose the developed substrate material to a wide range of light (exposure dose of 90 mJ / cm²). 2 Exposure time 9 s; then electron beam evaporation coating (vacuum degree 6×10) was used. -5 A titanium metal film is deposited on the wafer surface, and a titanium metal film with a thickness of 200 nm is formed on the photoresist on the substrate surface. Then, the wafer is immersed in the developer at room temperature for 10 min, the top photoresist is dissolved, and the metal film on the surface of the top photoresist is peeled off to form an etch-resistant composite hard mask on the substrate surface.

[0050] (5) The substrate material covering the metal hard mask is dry etched using an etching device (etching gas is Cl2 / H2 / Ar, volume ratio is 1:2:1) to etch out the trench structure of the preset pattern; after etching, the underlying photoresist and the metal film layer on its surface are removed by high pressure (0.3 MPa) flushing with acetone, isopropanol and deionized water in sequence to complete the preparation of a mesa isolation trench with a depth of 5 μm and a width of 1 μm on the surface of the substrate material.

[0051] The SEM image of the mesa isolation groove fabricated on the surface of the substrate material in this embodiment is shown below. Figure 2 As shown in the figure, the epitaxial material is etched with trenches having a depth-to-width ratio of 5:1 and steep sidewalls, which effectively ensures the duty cycle of the deep etching platform and improves the optoelectronic performance of the device.

[0052] Example 2: This example relates to the fabrication of an etch-resistant composite hard mask and micro / nano structure. The only difference from Example 1 is that the substrate material is a 2-inch GaSb wafer and the metal film is made of chromium. All other operations are the same. The corresponding etch-resistant composite hard mask is prepared on the substrate surface, and a mesa isolation trench with a depth of 9.7 μm and a width of 2.1 μm is prepared on the substrate surface through further etching.

[0053] The SEM image of the mesa isolation groove fabricated on the surface of the substrate material in this embodiment is shown below. Figure 3 As shown in the figure, the epitaxial material is etched with a depth-to-width ratio of 4.6:1, and the sidewalls are steep and smooth, which effectively ensures the duty cycle of the deep etching platform.

[0054] Example 3: This example relates to the fabrication of an etch-resistant composite hard mask and micro / nano structure. The only difference from Example 1 is that the negative photoresist is NR7-1000P and the positive photoresist is AZ6130. All other operations are the same. An etch-resistant composite hard mask is prepared on the substrate surface. Through further etching, a mesa isolation trench with a depth of 5 μm and a width of 1 μm is successfully prepared on the substrate material surface. The sidewalls are steep, which effectively ensures the duty cycle of the deeply etched mesa and improves the optoelectronic performance of the device.

[0055] Example 4: This example relates to the fabrication of an etch-resistant composite hard mask and micro / nano structure. The only difference from Example 1 is that the metal film is made of nickel. All other operations are the same. An etch-resistant composite hard mask is fabricated on the substrate surface. A mesa isolation trench with a depth of 5 μm and a width of 1 μm is successfully fabricated on the substrate material surface. The sidewalls are steep, which effectively ensures the duty cycle of the deeply etched mesa and improves the optoelectronic performance of the device.

[0056] Comparative Example 1: This comparative example relates to the fabrication of a metal mask and micro / nano structure. A metal mask layer is directly fabricated on the surface of a 2-inch InAs / GaSb type II superlattice epitaxial wafer using a metal lift-off process, as detailed below:

[0057] (1) Wet cleaning of the substrate material (2-inch InAs / GaSb type II superlattice epitaxial wafer) to be etched; spin coating of negative photoresist SUN-1306 onto the substrate surface using a spin coater at a spin coater speed of 4000 rpm and a photoresist thickness of 2 μm, and then soft baking curing treatment at a temperature of 120 ℃ and a time of 180 s to form a photoresist layer.

[0058] (2) Use a photomask to cover the preset etching area (the location to be etched) and expose it (exposure dose is 150mJ / cm). 2 The exposure time was 10 s, followed by baking at 120 ℃ for 100 s, and then developing in developer (RZX-3038) for 90 s to remove the unexposed parts of the photoresist layer.

[0059] (3) Then, electron beam evaporation coating is used (vacuum degree is 6×10). -5 A titanium metal film is deposited on the wafer surface, and a titanium metal film with a thickness of 200 nm is formed on the photoresist on the substrate surface. The photoresist and the metal film on the surface are removed by high pressure (0.3 MPa) sequentially rinsing with acetone, isopropanol and deionized water to expose the area to be etched.

[0060] (4) The substrate material covered with the metal hard mask is dry etched by an etching device (the etching gas is Cl2 / H2 / Ar, and the volume ratio is 1:2:1) to etch out the trench structure of the preset pattern; after etching, the metal mask layer is removed by concentrated hydrochloric acid to prepare a mesa isolation trench with a depth of 5 μm and a width of 1 μm on the surface of the substrate material.

[0061] This comparative example demonstrates the direct fabrication of a metal mask on the surface of an epitaxial wafer using a single-layer photoresist photolithography-lift process. Furthermore, the metal mask is used to fabricate mesa isolation trenches on the substrate material surface via dry etching. Results show that metal ions in the metal mask easily diffuse into the epitaxial wafer material, causing abnormal compound semiconductor performance. Moreover, removing the metal mask layer with an acidic etchant after etching damages the material. Additionally, removing the metal mask directly formed on the substrate material is difficult, and residual metal debris can create leakage channels, leading to increased dark current in the device.

[0062] Comparative Example 2: This comparative example relates to the fabrication of an etch-resistant composite hard mask and micro / nano structure. The only difference from Example 1 is that the bottom layer is coated with positive photoresist and the top layer is coated with negative photoresist. The specific operation is as follows:

[0063] (1) Wet cleaning of the substrate material (2-inch InAs / GaSb type II superlattice epitaxial wafer) to be etched; spin coating of positive photoresist AZ1500 on the substrate surface using a spin coater at a spin coater speed of 2000 rpm and a coating thickness of 2 μm, and then soft baking curing treatment at a temperature of 120 ℃ and a time of 180 s to form the bottom photoresist layer.

[0064] (2) Spin coat the negative photoresist SUN-1306 onto the bottom photoresist surface at a spin speed of 4000 rpm and a thickness of 2 μm. Then perform soft baking curing at a temperature of 120 ℃ for 100 s to form the top photoresist layer.

[0065] (3) Use a photomask to cover the preset etching area (the location to be etched) and expose it (exposure dose is 150mJ / cm). 2 The exposure time is 15s, followed by baking at 120℃ for 100s, and then development in developer (RZX-3038) for 90s to remove the unexposed portion of the top photoresist layer. The bottom photoresist layer in the exposed area is protected by the top photoresist and is not removed.

[0066] (4) Expose the developed substrate material to a wide range of light (exposure dose of 90 mJ / cm²). 2 Exposure time 9 s; then electron beam evaporation coating (vacuum degree 6×10) was used. -5 A titanium metal film is deposited on the wafer surface, and a titanium metal film with a thickness of 200 nm is formed on the photoresist on the substrate surface. Then the wafer is immersed in the developer at room temperature for 10 min. The bottom photoresist layer is dissolved, and the top photoresist layer and metal layer above the bottom photoresist layer are peeled off, making it impossible to form an etch-resistant composite hard mask on the substrate surface.

[0067] Furthermore, based on the preparation process of Comparative Example 2, the inventors further controlled the exposure dose in steps (3) and (4) simultaneously to ensure that the underlying photoresist in the exposed area was not affected after the first exposure, and that the exposure dose of the second generalized exposure was appropriate to fully expose the uncovered underlying photoresist, while the underlying photoresist covered by the top photoresist was not affected. Specifically, as shown below... Figure 4As shown. However, controlling the exposure dose in the two exposures greatly increases the difficulty of the process. In addition, in step (4), when preparing the titanium metal mask, it is necessary to dissolve the photoresist with the developer to peel off the metal film layer in the preset trench area. However, the metal in the preset trench area is deposited on the surface of the bottom photoresist. In order to peel off the metal film layer, the bottom photoresist must be dissolved. Since the bottom photoresist surface is covered by the metal film layer and the side is blocked by the top photoresist, it is difficult to dissolve the photoresist that needs to be peeled off, thus making it difficult to remove the metal film layer on its surface, which will eventually lead to the failure of mask preparation.

[0068] The embodiments described above are merely preferred embodiments for fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing an etch-resistant composite hard mask, characterized in that, Includes the following steps: S1. Spin-coat a negative photoresist onto the substrate surface to be etched, and cure it after soft baking to obtain the bottom photoresist layer; S2. A positive photoresist is spin-coated onto the bottom photoresist layer, and then cured after soft baking to obtain the top photoresist layer; S3. A photomask with a preset pattern is covered on the top photoresist layer. After exposure, post-exposure baking and development, the exposed area of ​​the top photoresist layer is removed, the exposed area of ​​the bottom photoresist layer is cured, and the unexposed area of ​​the bottom photoresist layer covered by the unexposed area of ​​the top photoresist layer is retained to form a patterned photoresist layer. S4. Perform a generalized exposure process on the patterned photoresist layer, controlling the exposure dose so that the remaining top photoresist layer is exposed, while the area of ​​the bottom photoresist layer covered by the remaining top photoresist layer remains unexposed. Then, a metal film layer is prepared on the patterned photoresist layer by physical and / or chemical vapor deposition. After development, the remaining top photoresist layer and the metal deposited on its surface are removed, and the unexposed area of ​​the bottom photoresist layer is also removed, while the exposed bottom photoresist layer and the metal film layer on its surface are retained, resulting in the etch-resistant composite hard mask; the exposure dose of the generalized exposure is 50-90 mJ / cm. 2 .

2. The preparation method according to claim 1, characterized in that, It must contain at least one of the following characteristics: (1) The thickness of the bottom photoresist layer is greater than the thickness of the top photoresist layer; (2) The thickness of the top photoresist layer is greater than twice the thickness of the metal film layer; (3) The thickness of the metal film is 10 nm-500 nm.

3. The preparation method according to claim 1, characterized in that, In step S1, the substrate is made of a compound semiconductor epitaxial wafer, a silicon wafer, or sapphire. The negative photoresist is selected from one of SUN-1306, ROL-7133, HTIN160, NR series, and AZ series.

4. The preparation method according to claim 1, characterized in that, In step S2, the positive photoresist is selected from one of the AZ series, SPR955 series, S18XX series, SPR220 series, and HTI751 series.

5. The preparation method according to claim 1, characterized in that, In step S3, the exposure metering is 150-200 mJ / cm. 2 ; The baking temperature after exposure is 110-130 ℃, and the time is 100-200 s; The developing solution used is the developing solution for the positive photoresist.

6. The preparation method according to claim 1, characterized in that, In step S4, The metal film is made of one or more of titanium, chromium, nickel, and titanium nitride. The developing solution used for developing is the developing solution for the positive photoresist; The development time is 5-10 minutes.

7. An etch-resistant composite hard mask, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. The application of the etch-resistant composite hard mask as described in claim 7 in photolithography.

9. The application according to claim 8, characterized in that, The etch-resistant composite hard mask is prepared on the surface of the substrate to be etched; the substrate with the etch-resistant composite hard mask on its surface is etched using an etching device, and the area on the substrate surface without mask coverage is etched. The etched substrate is immersed or rinsed with a polar solvent to remove the etching-resistant composite hard mask, thus completing the patterning process of the substrate.

10. The application according to claim 9, characterized in that, The polar solvents include acetone and / or N-methylpyrrolidone.

Images