Metal film stripping method based on metal hard mask
By using a metal hard mask in the metal film stripping process, the problem of the photoresist mask being affected by stress at high temperatures is solved, and high-precision metal film graphic transfer is achieved, especially for applications on pyroelectric effect substrates.
Patent Information
- Application Number
- CN202510929018.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-07
- Publication Date
- 2025-10-17
AI Technical Summary
In traditional metal film stripping methods, the photoresist mask is susceptible to mechanical and thermal stress at high temperatures, resulting in edge wrinkling and local detachment, affecting the accuracy of pattern transfer, especially on substrates with pyroelectric effects.
The use of a metal hard mask includes forming a metal seed layer on a substrate, forming a patterned photoresist mask through a photolithography process, and thickening the area not covered by the photoresist to form a metal hard mask. The photoresist is then removed, and a metal film is formed by wet etching and physical vapor deposition. Finally, the covering metal film is peeled off, and the mechanical strength and high temperature resistance of the metal hard mask are used to shield the charge interference caused by the pyroelectric effect.
It achieves high-precision patterned transfer of metal films at high temperatures, avoids the mechanical and thermal stress effects of the photoresist mask, and improves the accuracy and reliability of patterned transfer, especially in applications on pyroelectric effect substrates.
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Figure CN120809573A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the field of semiconductor and optoelectronic process manufacturing, and particularly relates to a metal thin film stripping method based on a metal hard mask. BACKGROUND
[0002] Traditional metal thin film stripping methods usually use photoresist as a mask material. However, in the deposition process of the metal thin film, the high-speed bombardment of metal atoms will generate mechanical stress on the mask, and a high temperature (≥ 150℃) is required in the deposition of metal thin films such as Au or Ti, so the photoresist mask is difficult to withstand the double action of thermal stress and mechanical stress, and is prone to edge wrinkling, local separation, and even carbonization, resulting in failure of pattern transfer. SUMMARY
[0003] In view of the above problems of the prior art, the technical problem to be solved by the present application is to provide a metal thin film stripping method based on a metal hard mask.
[0004] To solve the above technical problems, the present application provides the following technical solutions.
[0005] A metal thin film stripping method based on a metal hard mask, comprising the following steps:
[0006] S100, forming a metal seed layer on a substrate by physical vapor deposition;
[0007] S200, forming a patterned photoresist mask on the metal seed layer by a photolithography process;
[0008] S300, selectively thickening the region of the metal seed layer not covered by the photoresist mask to form a mask thickening layer; the mask thickening layer and the underlying metal seed layer form a metal hard mask;
[0009] S400, removing the photoresist mask to expose the region of the metal seed layer that has not been thickened by electroplating, forming an opening window region;
[0010] S500, removing the metal seed layer in the opening window region by wet etching;
[0011] S600, depositing a metal thin film by physical vapor deposition;
[0012] S700, removing the metal hard mask on the substrate and stripping the metal thin film thereon, leaving the metal thin film in the opening window region.
[0013] Further, the metal seed layer comprises a metal adhesion layer and an electroplating seed layer; in the S100 step, the metal adhesion layer is first formed on the substrate by physical vapor deposition, and then the electroplating seed layer is formed on the metal adhesion layer by physical vapor deposition.
[0014] Further, the metal adhesion layer is a Ti layer, and the thickness of the Ti layer is 45nm±22.5nm; the electroplating seed layer is a first Au layer, and the thickness of the first Au layer is 80nm±40nm.
[0015] Further, in the S500 step, first, wet etching is performed using an Au etching solution until the first Au layer outside the electroplating thickening region is completely removed; then wet etching is performed using a Ti etching solution until the Ti layer outside the electroplating thickening region is completely removed.
[0016] In the S700 step, first, the first Au layer of the electroplating thickening region is removed using an Au etching solution, and the metal thin film Cr covering thereon is peeled off; then the Ti layer below the electroplating thickening region is removed using a Ti etching solution, and the substrate surface is exposed.
[0017] Further, the Au etching solution is a solution of iodine: potassium iodide: water = 50g-60g: 190g-200g: 2700mL-2800mL;
[0018] The Ti etching solution is a solution of ammonia: hydrogen peroxide: water = 1mL-2mL: 1mL-2mL: 90mL-100mL.
[0019] Further, in the S200 step, the photoresist used is a positive photoresist, and the thickness of the photoresist is 2μm±1μm.
[0020] Further, in the S200 step, the cross section of the photoresist mask is a right trapezoid; in the S300 step, the cross section of the mask thickening layer is an inverted trapezoid.
[0021] Further, in the S300 step, the thickness of the mask thickening layer formed is less than the thickness of the photoresist mask.
[0022] Further, in the S300 step, the mask thickening layer is a homogeneous mask thickening layer formed by electroplating using the same metal as the metal seed layer.
[0023] Further, in the S300 step, the mask thickening layer is a heterogeneous mask thickening layer formed by electroplating using a heterogeneous metal which has good adhesion with the metal of the metal seed layer.
[0024] In the present application, the stripping mask adopts a metal hard mask, which has strong mechanical strength and high-temperature resistance, and solves the problem that the photoresist mask will wrinkle and partially fall off due to stress during deposition of the metal thin film, resulting in failure of pattern transfer. Meanwhile, for the substrate with pyroelectric effect, the metal hard mask can form opposite shielding charges through electrostatic induction, thereby neutralizing the net electric field generated on the substrate surface due to the pyroelectric effect, inhibiting the interference of the charges on the photoresist, and eliminating the influence of the surface charge accumulation due to the pyroelectric effect on the photoetching pattern. BRIEF DESCRIPTION OF DRAWINGS
[0025] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and serve to explain the principles of the application, and do not limit the application. In the drawings:
[0026] Figure 1 A structure schematic diagram after the photoresist mask is made on the substrate in the conventional scheme.
[0027] Figure 2 A structure schematic diagram after the metal thin film is deposited in the conventional scheme.
[0028] Figure 3 A structure schematic diagram after the photoresist mask is removed in the conventional scheme.
[0029] Figure 4 A flowchart of one embodiment of the metal thin film stripping method based on the metal hard mask of the present application.
[0030] Figure 5 A structure schematic diagram after the metal seed layer is formed on the substrate.
[0031] Figure 6 A structure schematic diagram after the photoresist mask is formed on the metal seed layer.
[0032] Figure 7 A structure schematic diagram after the mask thickening layer is formed.
[0033] Figure 8 A structure schematic diagram after the photoresist mask is removed to form the windowed area.
[0034] Figure 9 A structure schematic diagram after the metal seed layer in the windowed area is removed.
[0035] Figure 10 A structure schematic diagram after the metal thin film is deposited.
[0036] Figure 11 A structure schematic diagram after the metal hard mask and the metal thin film covering the same are removed.
[0037] The reference signs in the specification drawings are as follows:
[0038] Base-1, 11; Metal seed layer-2; Photoresist mask-3, 13; Mask thickening layer-4; Windowed area-5; Metal film-6, 16; First metal film-6a; Second metal film-6b; Gap-7. DETAILED DESCRIPTION
[0039] The embodiments of the present application will be described in detail below with specific reference to specific examples. The drawings provided in the following examples only schematically illustrate the basic concept of the present application, and the following examples and features in the examples can be combined with each other without conflict.
[0040] Referring to Figure 1 , when using the conventional metal film stripping method, a photoresist mask 13 is first made on the base 11 by a photolithography process as a mask for stripping the metal film 16. Referring to Figure 2 , then the metal film 16 is deposited by physical vapor deposition. Referring to Figure 3 , finally, the photoresist mask 13 is removed by an organic solvent and the metal film 16 covering the photoresist mask 13 is stripped, thereby leaving the metal film 16 directly covering the base 11, and thus realizing pattern transfer.
[0041] For a base 11 with pyroelectric effect (such as lithium niobate base, lithium tantalate base, etc.), surface charge accumulation is easily caused by temperature fluctuation during the photolithography process, which leads to problems such as distortion of the pattern edge of the photoresist mask 13, line width deviation, etc., and seriously affects the precision of the subsequent patterning of the metal film 16 in the stripping process.
[0042] At present, the improvement scheme is mostly focused on optimizing the photoresist mask 13, but this method cannot fundamentally eliminate the influence of pyroelectric effect and stress on the photoresist mask 13. Therefore, there is an urgent need for a mask material capable of eliminating surface charge interference and resisting thermal stress and mechanical stress, and a corresponding stripping process, to meet the manufacturing requirements of high-precision metal film patterning on a base with pyroelectric effect.
[0043] Referring to Figure 4 , Figure 4 is a flowchart of an embodiment of the metal film stripping method based on metal hard mask of the present application. The metal film stripping method based on metal hard mask of the present application includes the following steps:
[0044] S100, referring to Figure 5A metal seed layer 2 is formed on a substrate 1 by physical vapor deposition. In this embodiment, the substrate 1 can be a substrate exhibiting a pyroelectric effect, for example, a Z-cut lithium niobate wafer. Alternatively, the substrate 1 can be another lithium niobate substrate or a substrate made of other materials such as lithium tantalate. The metal seed layer 2 includes a metal adhesion layer and an electroplating seed layer. In this embodiment, the metal adhesion layer is preferably a Ti layer, and the electroplating seed layer is preferably a first Au layer.
[0045] In this step, a Ti layer with a thickness of 45 nm ± 22.5 nm is first deposited on substrate 1 by physical vapor deposition as a metal adhesion layer to improve the adhesion of the subsequent electroplating seed layer. A first Au layer with a thickness of 80 nm ± 40 nm is then deposited on the Ti layer (i.e., the metal adhesion layer) by physical vapor deposition as an electroplating seed layer. The physical vapor deposition in this step can be electron beam evaporation.
[0046] S200, please refer to Figure 6 A patterned photoresist mask 3 is formed on the metal seed layer 2 using a photolithography process. The photoresist used in the photolithography process is a positive photoresist. In this embodiment, AZ1500 positive photoresist with a thickness of 2±1 μm is first spin-coated on the metal seed layer 2. Of course, other positive photoresists can also be used. Pre-baking, exposure, and development are then performed to obtain the patterned photoresist mask 3. The cross-section of the photoresist mask 3 formed by photolithography is preferably a positive trapezoid (i.e., a trapezoid with a small top and a large bottom).
[0047] S300, please refer to Figure 7 The metal seed layer regions not covered by the photoresist mask 3 are selectively thickened to form a mask thickening layer 4. The mask thickening layer 4 and the underlying metal seed layer 2 form a metal hard mask. The mask thickening layer 4 can be a homogeneous mask thickening layer 4 formed by electroplating the same metal as the metal seed layer 2. The mask thickening layer 4 can also be a heterogeneous mask thickening layer 4 formed by electroplating a heterogeneous metal that has good adhesion to the metal of the metal seed layer 2.
[0048] The thickness of the mask thickening layer 4 is generally less than that of the photoresist mask 3, but the thickness of the mask thickening layer 4 is generally much greater than the thickness of the metal seed layer 2. In this embodiment, since the cross-section of the photoresist mask 3 is a regular trapezoid, the cross-section of the formed mask thickening layer 4 is an inverted trapezoid (i.e., a trapezoid with a larger top and a smaller bottom).
[0049] In this embodiment, a second Au layer with a thickness of 1 μm ± 0.5 μm is electroplated in the area of the metal seed layer 2 not covered by the photoresist mask 3 through an electroplating process to form a homogeneous mask thickening layer 4. Since the metal seed layer 2 below the photoresist mask 3 is covered, the second Au layer will not be formed in this area during the electroplating process, thereby achieving selective thickening of the metal seed layer 2 through the photoresist mask 3.
[0050] S400, please refer to Figure 8 , the photoresist mask 3 is removed, thereby exposing the area of the metal seed layer 2 below the photoresist mask 3 that has not been electroplated and thickened, forming the window area 5. The photoresist mask 3 can be removed by heating in an acetone water bath. Of course, other organic solvents can also be used to dissolve and remove the photoresist mask 3. Since the cross-section of the photoresist mask 3 is a regular trapezoid, the cross-section of the window area 5 formed after removing the photoresist mask 3 is also a regular trapezoid.
[0051] S500, please refer to Figure 9 , wet etching is used to remove the metal seed layer 2 in the window area 5 that has not been thickened by electroplating. Since the metal thickness in the mask thickening layer 4 area is increased (the thickness of the metal seed layer 2 plus the mask thickening layer 4), and the thickness of the mask thickening layer 4 is much greater than the thickness of the metal seed layer 2, when the metal seed layer 2 in the window area 5 is removed by wet etching, only a small part of the mask thickening layer 4 is removed, and the overall thickness of the metal hard mask still meets the requirements of subsequent processes.
[0052] In this embodiment, since the metal seed layer 2 includes two metal layers (i.e., a Ti layer and a first Au layer), the metal seed layer 2 is removed in two steps in this step. First, wet etching is performed using an Au etching solution until the first Au layer outside the electroplating thickening area is completely removed. The Au etching solution can be a solution of iodine: potassium iodide: water = 50g-60g: 190g-200g: 2700mL-2800mL. Then, wet etching is performed using a Ti etching solution until the Ti layer outside the electroplating thickening area is completely removed. The Ti etching solution can be a solution of ammonia water: hydrogen peroxide: water = 1mL-2mL: 1mL-2mL: 90mL-100mL.
[0053] S600, please refer to Figure 10The physical vapor deposition metal film 6 includes a first metal film 6a formed on the surface of the substrate 1 in the windowed area 5 and a second metal film 6b formed on the upper end surface of the mask thickening layer 4. In this embodiment, since the cross section of the windowed area 5 is a right trapezoid, the first metal film 6a does not completely cover the surface of the substrate 1 in the windowed area 5, so that a gap 7 is left between the first metal film 6a and the metal hard mask, so as to facilitate the etching of the metal seed layer 2 at the lower part of the metal hard mask through the gap 7. In this embodiment, Cr is deposited as the metal film 6 by electron beam evaporation, and the thickness is 300 nm ± 150 nm.
[0054] S700, please refer to Figure 11 The metal mask etching liquid is used to remove the metal hard mask on the substrate 1 and strip the second metal film 6b covering it, and the first metal film 6a in the windowed area 5 is retained, so as to realize the patterned transfer of the metal film 6. The specific method is as follows: first, the Au etching liquid is used to remove the first Au layer in the electroplating thickening area, and the Cr layer (i.e. the second metal film 6b) covering it is stripped. Then, the Ti etching liquid is used to remove the Ti layer below the electroplating thickening area, so as to expose the surface of the substrate 1. Since the Au etching liquid does not directly etch the Cr layer, the Cr layer (i.e. the first metal film 6a) covering the substrate 1 is retained, so as to realize the selective stripping of the metal film 6.
[0055] In this embodiment, the metal hard mask is used as the mask when stripping the metal film 6. Since the metal hard mask has strong mechanical strength and high temperature resistance, the problem of wrinkling and partial peeling of the photoresist mask 3 caused by stress during the deposition of the metal film 6, which leads to the failure of patterned transfer, is solved. At the same time, for the substrate 1 with pyroelectric effect, the metal hard mask can form opposite shielding charges through electrostatic induction. These shielding charges form a reverse electric field at the metal-substrate 1 interface, which can neutralize the net electric field generated on the surface of the substrate 1 due to the pyroelectric effect, and inhibit the interference of the charges on the photoresist, so as to eliminate the influence of the surface charge accumulation caused by the pyroelectric effect on the photoetching pattern.
[0056] The above embodiments only express the preferred embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, some modifications and improvements can be made without departing from the concept of the present application, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.
Claims
1. A metal film stripping method based on a metal hard mask, characterized in that: The following steps are involved: S100, forming a metal seed layer on the substrate by physical vapor deposition; S200, forming a patterned photoresist mask on the metal seed layer using a photolithography process; S300, selectively thickening the metal seed layer region not covered by the photoresist mask to form a mask thickening layer; The mask thickening layer and the metal seed layer thereunder form a metal hard mask; S400, removing the photoresist mask to expose the metal seed layer area that has not been electroplated and thickened, thereby forming a window area; S500, removing the metal seed layer in the window area by wet etching; S600, using physical vapor deposition metal film; S700 , removing the metal hard mask on the substrate and peeling off the metal film covering it, leaving the metal film in the window area.
2. The metal thin film stripping method based on a metal hard mask according to claim 1, wherein: The metal seed layer includes a metal adhesion layer and an electroplating seed layer; in the step S100, the metal adhesion layer is first formed on the substrate by physical vapor deposition, and then the electroplating seed layer is formed on the metal adhesion layer by physical vapor deposition.
3. The metal thin film stripping method based on a metal hard mask according to claim 2, wherein: The metal adhesion layer is a Ti layer, and the thickness of the Ti layer is 45nm±22.5nm; the electroplating seed layer is a first Au layer, and the thickness of the first Au layer is 80nm±40nm.
4. The metal thin film stripping method based on a metal hard mask according to claim 3, wherein: In the step S500, wet etching is first performed using an Au etching solution until the first Au layer outside the electroplating thickened area is completely removed; then wet etching is performed using a Ti etching solution until the Ti layer outside the electroplating thickened area is completely removed; In the step S700, the first Au layer in the electroplated thickened area is removed using an Au etching solution, and the metal film Cr covering it is peeled off; then the Ti layer below the electroplated thickened area is removed using a Ti etching solution to expose the substrate surface.
5. The metal thin film stripping method based on a metal hard mask according to claim 4, wherein: The Au etching solution is a solution of iodine: potassium iodide: water = 50g-60g: 190g-200g: 2700mL-2800mL; The Ti etching solution is a solution of ammonia water: hydrogen peroxide: water = 1 mL to 2 mL: 1 mL to 2 mL: 90 mL to 100 mL.
6. The metal thin film stripping method based on a metal hard mask according to any one of claims 1 to 5, wherein: In the step S200 , the photoresist used is a positive photoresist with a thickness of 2 μm±1 μm.
7. The metal thin film stripping method based on a metal hard mask according to any one of claims 1 to 5, characterized in that: In the step S200, the cross section of the photoresist mask is a regular trapezoid; in the step S300, the cross section of the mask thickening layer is an inverted trapezoid.
8. The metal thin film stripping method based on a metal hard mask according to any one of claims 1 to 5, characterized in that: In the step S300 , the thickness of the mask thickening layer formed is smaller than the thickness of the photoresist mask.
9. The metal thin film stripping method based on a metal hard mask according to any one of claims 1 to 5, characterized in that: In the step S300 , the mask thickening layer is a homogeneous mask thickening layer formed by an electroplating process using the same metal as the metal seed layer.
10. The metal thin film stripping method based on a metal hard mask according to any one of claims 1 to 5, characterized in that: In the step S300 , the mask thickening layer is a heterogeneous mask thickening layer formed by an electroplating process using a heterogeneous metal having good metal adhesion to the metal seed layer.