An electroplating process for preparing deeply etched thick metal masks

Abstract

This invention discloses an electroplating process for preparing a deeply etched, thick metal mask, belonging to the field of electroplating technology for microelectromechanical systems (MEMS). The process includes the following steps: First, a positive resist is used for photolithography and patterning on the wafer surface; next, a seed layer is sputtered onto the patterned wafer, and a peel-off process is used to form an area to be electroplated with a preset pattern; then, a negative resist is used for photolithography on the area to be electroplated to form a thick resist layer with a thickness greater than the preset metal plating thickness; finally, electroplating is performed on the area to be electroplated to obtain a metal plating layer of the preset thickness. This method, by employing a negative resist process, effectively suppresses the lateral growth of the metal plating layer, improves the verticality of the metal plating layer sidewalls, and avoids damage to the wafer surface caused when removing the seed layer from the non-electroplated area. It solves the problems of "mushroom-shaped" protrusions and grain coarsening at the edges of the plating layer in existing electroplating methods.

Description

Technical Field

[0001] This invention belongs to the field of electroplating technology for microelectromechanical systems (MEMS), specifically relating to an electroplating process for preparing a deeply etched thick metal mask. Background Technology

[0002] Sensors based on microelectromechanical systems (MEMS) technology have significant application value in the extreme operating conditions of aero-engines, including high temperature, high pressure, and strong vibration. For example, they can monitor turbine blade temperature, combustion chamber pressure, or vibration status in real time. However, traditional silicon-based sensors are limited by the intrinsic properties of the material, and are prone to problems such as a sharp increase in carrier concentration and PN junction failure in high-temperature environments above 600°C, leading to signal drift or even device damage. Third-generation semiconductor silicon carbide (SiC) has become an ideal choice for core materials of high-temperature sensors due to its wide bandgap, high thermal conductivity, and excellent chemical stability. However, its high bond energy and strong chemical inertness result in extremely low wet etching rates, requiring high-energy dry etching processes. This places stringent requirements on the mask's resistance to ion bombardment, thermal stability, and pattern fidelity. For example, in deep reactive ion etching (DRIE), the mask needs to withstand local temperature rises of over 200°C and plasma erosion. If the mask thickness is insufficient or the sidewall tilt angle deviation exceeds 3°, it will cause microgroove effect or pattern distortion on the etched sidewalls, which will seriously affect the quality factor Q and long-term reliability of the sensor resonant structure.

[0003] Electroplating, a key process in metal mask fabrication, is a technique that deposits a thin metal film on the surface of a seed layer using electrochemical methods. Electroplating enhances the conductivity and corrosion resistance of the substrate, and also provides a metal mask during substrate etching, protecting non-etched areas and improving etching selectivity. For example, the invention patent application CN202411263164.3 discloses a wafer electroplating method and its wafer electroplated products. This method significantly improves the bonding strength between the metal coating and the SiC substrate by optimizing wafer surface pretreatment and electroplating solution formulation. While this method addresses the adhesion problem of the metal coating, it fails to fully resolve issues such as "mushroom-shaped" protrusions at the coating edges and grain coarsening. These defects can easily trigger localized plasma focusing during etching, leading to abnormal etching at the mask edges or micromask residue, ultimately causing the critical dimension (CD) deviation of the device to exceed the design value.

[0004] Based on this, the present invention proposes an electroplating process for preparing a deeply etched thick metal mask, so as to obtain MEMS devices with better morphology and stable performance through etching, thereby solving the problems existing in the prior art. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an electroplating process for preparing deeply etched thick metal masks, which solves the problems of "mushroom-shaped" protrusions and grain coarsening at the edges of the plating layer during existing electroplating methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] An electroplating process for preparing a deeply etched, thick metal mask includes the following steps:

[0008] Step S1: After standard cleaning of the substrate to be plated, photolithography is performed on the substrate using positive resist.

[0009] Step S2: Sputter a seed layer onto the substrate surface with positive resist after photolithography;

[0010] Step S3: Perform wet stripping of the seed layer to achieve seed layer visualization;

[0011] Step S4: Photolithography is performed on the substrate with seed layer patterning using negative photoresist. Thick negative photoresist is prepared by photolithography in the area without seed layer. The negative photoresist and the positive photoresist in step S1 are photolithographically aligned.

[0012] Step S5: After negative photolithography, the substrate with negative photoresist is placed in an electroplating solution for electroplating, and a metal coating of a preset thickness is obtained through electroplating.

[0013] Step S6: After electroplating, the substrate is immersed in acetone and anhydrous ethanol in sequence to perform ultrasonic cleaning on the negative adhesive; after the substrate is dried, oxygen plasma is used to perform dry etching cleaning on the substrate to form a high verticality thick metal mask with a preset metal coating thickness on the substrate surface.

[0014] In one feasible embodiment of the present invention, when performing standard cleaning on the substrate to be plated, RCA cleaning technology is used for cleaning.

[0015] In one feasible embodiment of the present invention, in step S2, during the photolithography process of the substrate to be plated using positive resist, the positive resist is a photoresist, which is one of positive photoresist AZ4620 and ultraviolet photoresist thin film S1813, and the thickness of the positive resist is 2-5μm.

[0016] In one feasible embodiment of the present invention, the seed layer includes an adhesive layer and a pre-plating layer, the adhesive layer being located below the pre-plating layer, and the thickness ratio of the adhesive layer to the pre-plating layer being greater than 1:10.

[0017] In one feasible embodiment of the present invention, the seed layer is formed by magnetron sputtering and the thickness of the seed layer is 110-440 nm.

[0018] In one feasible embodiment of the present invention, in step S4, during the photolithographic preparation of thick negative resist in the seedless region, the negative resist is a photoresist, the photoresist is negative photoresist RDP-910, and the thickness of the negative resist is greater than the thickness of the preset metal coating.

[0019] In one feasible embodiment of the present invention, the angle of the mask for the pattern position of the negative photoresist layer in step S4 is 80°-90°.

[0020] In one feasible embodiment of the present invention, the electroplating solution in step S5 comprises: sodium sulfate with a concentration of 250 g / L, boric acid with a concentration of 40 g / L, saccharin with a concentration of 1 g / L, 2-ethylhexyl sulfate with a concentration of 0.5 mL / L, and nickel chloride with a concentration of 40 g / L.

[0021] In one feasible embodiment of the present invention, during the electroplating process in step S5, the electroplating solution temperature is 35-55°C, the pH value of the electroplating solution is 3.0-5.0, and the electroplating current density is 15-25 mA·cm⁻¹. -2 .

[0022] In one feasible embodiment of the present invention, when dry etching and cleaning the substrate using oxygen plasma in step S6, the dry etching parameters include: ICP power: 1500W; Table power: 300W; O2 flow rate: 80sccm; Chamber pressure: 20mTorr; Time: 600s.

[0023] Compared with the prior art, the present invention provides an electroplating process for preparing a deeply etched thick metal mask, which has the following beneficial effects:

[0024] 1. In the process of preparing a thick metal mask by electroplating, the present invention effectively suppresses the lateral growth of the metal coating by using a negative adhesive process; at the same time, by using negative adhesive as a buffer for the metal coating to support the metal coating, the sidewall morphology of the metal coating can be improved, the verticality of the sidewall of the metal coating can be improved, and damage to the substrate surface is avoided when removing the seed layer in the non-electroplated area.

[0025] 2. This invention, through a wet stripping method, achieves impurity-free and micromask-free etched areas, thereby ensuring the surface quality of the etched surface. It avoids problems such as metal residue and substrate damage caused by incomplete removal of the seed layer during full-surface substrate sputtering, thus guaranteeing the fabrication effect of thick metal masks. It also solves the problems of "mushroom-shaped" protrusions and grain coarsening at the edges of the plating layer in existing electroplating methods. Attached Figure Description

[0026] Figure 1 This is an electroplating flow chart illustrating the electroplating process for preparing a deeply etched thick metal mask according to the present invention.

[0027] Figure 2 This is a flowchart of the electroplating method in Comparative Example 1 of the present invention.

[0028] Figure 3 This is a flowchart of the electroplating method in Comparative Example 2 of the present invention.

[0029] Figure 4 The electroplating process for preparing a deeply etched metal mask is shown in the comparison diagram of the electroplating effects of the electroplating methods in Comparative Example 1 and Comparative Example 2.

[0030] Figure 5 This is a technical flow chart of the electroplating process for preparing a deeply etched thick metal mask according to the present invention.

[0031] The components are: 1. Base; 2. Positive adhesive; 3. Seed layer; 4. Negative adhesive; 5. Coating.

[0032] exist Figure 4 In the figure, Figure a shows the effect of mask preparation by the electroplating method in Comparative Example 2; Figure b shows the effect of mask preparation by the electroplating method in Comparative Example 1; and Figure c shows the effect of mask preparation by the electroplating method of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Please see Figures 1-5 The present invention provides a technical solution:

[0035] An electroplating process for preparing a deeply etched thick metal mask is disclosed. This method is used to prepare a thick metal mask with high verticality. All raw materials used in this embodiment and comparative examples are commercially available products. The specific steps include:

[0036] Step S1: After standard cleaning of the wafer substrate 1 to be plated, the substrate 1 is photolithographically patterned using positive resist 2.

[0037] Step S2: Sputter seed layer 3 onto the surface of substrate 1 with positive resist 2 after photolithography;

[0038] Step S3: Wet stripping of seed layer 3 is performed using solutions such as acetone and anhydrous ethanol to achieve patterning of seed layer 3;

[0039] Step S4: Photolithography is performed on the substrate 1 that has patterned the seed layer 3 using negative photoresist 4. Thick negative photoresist 4 is prepared by photolithography in the area without the seed layer. The negative photoresist 4 and the positive photoresist 2 in step S1 are photolithographically aligned.

[0040] Step S5: After negative photolithography, the substrate 1 with negative photoresist 4 is placed in the electroplating solution for electroplating, and a metal coating 5 of a preset thickness is obtained through one or more electroplating processes.

[0041] Among them, the thickness of the metal coating 5 is less than the thickness of the negative adhesive 4;

[0042] Step S6: After electroplating, the substrate 1 is immersed in acetone and anhydrous ethanol in sequence, and the negative adhesive 4 is ultrasonically cleaned to remove the negative adhesive 4 on the surface of the wafer substrate 1. After the substrate 1 dries, oxygen plasma is used to perform dry etching cleaning on the wafer substrate 1 to completely remove the residual negative adhesive 4 on the surface of the wafer substrate 1, and a high verticality thick metal mask with a preset metal plating thickness is formed on the surface of the substrate 1.

[0043] Specifically, the common sizes for substrate 1 are 4, 6, and 8 inches.

[0044] Specifically, step S1, the standard cleaning process for the wafer substrate 1 to be plated, utilizes RCA cleaning technology. This includes standard cleaning with acetone, anhydrous ethanol, a mixed solution of concentrated sulfuric acid and hydrogen peroxide (4:1 ratio), and hydrofluoric acid to remove organic matter, the original oxide layer, and other substances from the surface of substrate 1. The specific process includes:

[0045] 1) At room temperature, the surface of the wafer substrate 1 was initially removed by soaking in acetone for 5 minutes and then in anhydrous ethanol for 2 minutes. The substrate was then rinsed with ultrapure water (DI water) for 5 minutes at room temperature to remove the cleaning solution.

[0046] 2) At 120℃, soak the wafer substrate 1 in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a mixing ratio of 4:1 for 15 minutes to remove organic matter from the surface of the wafer substrate 1 again, and then rinse it with DI water at room temperature for 5 minutes to remove the cleaning solution.

[0047] 3) Immerse the wafer substrate 1 in a mixed solution of ammonia, hydrogen peroxide and water at 70-80℃ for 15 minutes to remove micro-dust, and then rinse it with DI water at room temperature for 5 minutes to remove the cleaning solution.

[0048] 4) Immerse the wafer substrate 1 in a mixed solution of hydrochloric acid, hydrogen peroxide and water at 70-80℃ for 15 minutes to remove metal ions from the surface of the wafer substrate 1, and then rinse it with DI water at room temperature for 5 minutes to remove the cleaning solution.

[0049] 5) At room temperature, soak the substrate 1 in a 1:50 mixture of hydrofluoric acid and water for 30 seconds to remove the original oxide layer on the surface, and then rinse it with DI water for 5 minutes at room temperature to remove the cleaning solution.

[0050] Specifically, in step S1, during the photolithography process of the wafer substrate 1 to be plated using positive photoresist 2, positive photoresist 2 is a photoresist, preferably one of positive photoresist AZ4620 and ultraviolet photoresist thin film S1813, and the thickness of positive photoresist 2 is preferably 2-5μm.

[0051] Specifically, step S1, which involves photolithography of the wafer substrate 1 to be coated with positive photoresist 2, includes the following steps:

[0052] 1) Pre-bake the substrate 1 to be plated (400℃) to remove most of the moisture adsorbed on the surface of the wafer substrate 1 and improve the adhesion of the photoresist.

[0053] 2) After pre-baking, the substrate 1 to be coated should be immediately coated with photoresist using a spin coater, also known as photoresist coating. Photoresist coating generally includes four parts: pre-coating (at a low speed, the purpose is to spread the photoresist evenly on the wafer), acceleration (usually accelerating to thousands of revolutions per minute within a fraction of a second, which is very important for the uniformity of the photoresist thickness), coating (at a constant speed under high speed, the speed determines the thickness of the photoresist), and edge removal (at a speed several times that of coating, to a certain extent eliminating edge beads).

[0054] 3) After coating, perform soft baking (usually at 100-110℃ for 3 minutes) (the specific parameters of the photoresist are closely related to the specific type of photoresist; here we only use positive photoresist AZ4620 as an example) to enhance the adhesion of the photoresist and remove the solvent from the photoresist.

[0055] 4) If the pattern requires the superposition of two processes, alignment is necessary, i.e., overlaying is performed using alignment marks; otherwise, proceed directly to step 5).

[0056] 5) Exposure was performed using deep ultraviolet light (projection exposure), with an exposure dose of 350 mJ / cm². 2 The exposure power is 150mW / cm 2 ;

[0057] 6) After exposure, perform intermediate baking to reduce the standing wave effect (usually at 90-120℃ for 60-90 seconds).

[0058] 7) Use chemical developer to dissolve the soluble areas of the photoresist caused by exposure. The main purpose is to accurately copy the mask pattern into the photoresist. (Positive photoresist development removes the parts irradiated by deep ultraviolet light.) Positive photoresist developer is generally an alkaline solution, such as TMAH tetramethylammonium hydroxide.

[0059] 8) Harden the film to eliminate moisture introduced into the adhesive during development and spraying, thereby increasing adhesion;

[0060] 9) Microscopic inspection to check the accuracy of photolithographic alignment and the distortion of key linewidths.

[0061] Specifically, in step S2, when preparing the seed layer 3, magnetron sputtering is preferably used. The thickness of the seed layer 3 is preferably 110-440 nm, more preferably 110-220 nm, and even more preferably 220 nm. Furthermore, the seed layer 3 may be made of materials such as chromium / gold or titanium / gold.

[0062] Specifically, the seed layer 3 includes an adhesive layer and a pre-plating layer. The adhesive layer is used to improve the bonding force between different materials and ensure that the pre-plating layer can be firmly attached to the surface of the substrate 1. The pre-plating layer is used to form a regular and dense film on the surface of the substrate 1, which enhances the adhesion between the electrolyte and the metal and promotes the surface uniformity of the deposit.

[0063] Common materials for the adhesive layer include titanium (Ti) and chromium (Cr); common materials for the seed layer include gold (Au), nickel (Ni), and copper (Cu); the thickness ratio of the adhesive layer to the pre-plated layer is greater than 1:10.

[0064] Specifically, in step S2, when sputtering the seed layer 3 on the surface of the substrate 1 with the positive resist 2 after photolithography, the specific process of sputtering the seed layer 3 using magnetron sputtering includes:

[0065] Magnetron sputtering: The cleaned substrate 1 is placed in a magnetron sputtering machine, and the target is replaced with a chromium or gold target. The reaction chamber pressure is maintained at 0.2 Torr. A voltage of 380V and a current of 150mA are applied to the chromium target and maintained for 1 min. A 20nm thick chromium film can be prepared on the surface of substrate 1. The target is rotated to the gold target, and a voltage of 380V and a current of 150mA are applied in the same way and maintained for 5 min. A 200nm thick gold film can be prepared on the surface of substrate 1.

[0066] Specifically, step S3, which involves wet stripping the seed layer 3 using acetone and anhydrous ethanol, includes the following steps:

[0067] After obtaining the seed layer 3 in step S2, the substrate 1 is immersed in acetone solution and cleaned with an ultrasonic vibration table at 40W power for 5 minutes. The acetone dissolves the positive glue 2, and the seed layer 3 on the surface of the positive glue 2 becomes free in the acetone solution due to the loss of the attached material. After the positive glue 2 is completely dissolved, the substrate 1 is taken out and immersed in anhydrous ethanol for cleaning to remove the acetone and the residual seed layer 3. Thus, the patterning of the seed layer 3 is achieved.

[0068] Specifically, in step S4, during the photolithography preparation of the thick negative resist 4 in the seedless area of ​​the substrate 1, the photoresist is preferably a negative photoresist RDP-910, and the sidewall angle of the photoresist is preferably 80°-90°.

[0069] Specifically: if the sidewall angle of the photoresist is poor, it will result in a poor mask angle for the coating. Since the coating is filled on the basis of the photoresist shape, in order to obtain a coating with high verticality, the sidewall angle of the photoresist is limited to 80°-90°.

[0070] Specifically, step S4, the process of photolithographically preparing the thick negative resist 4 in the seedless layer region, includes:

[0071] 1) Pre-bake the substrate 1 after step S3 (400℃) to remove most of the moisture adsorbed on the surface of the substrate 1 and improve the adhesion of the photoresist.

[0072] 2) After pre-baking, substrate 1 should be immediately coated with photoresist using a spin coater, also known as photoresist coating. Photoresist coating generally includes four parts: pre-coating (at a low spin speed, the purpose of which is to spread the photoresist evenly on the wafer), acceleration (usually accelerating to thousands of revolutions per minute within a fraction of a second, which is very important for the uniformity of the photoresist thickness), coating (at a constant speed under high spin speed, the spin speed determines the photoresist thickness), and edge removal (at a spin speed several times that of coating, to a certain extent eliminating edge beads).

[0073] 3) After coating, perform soft baking (usually at 100-110℃ for 3 minutes) (the specific parameters of the photoresist are closely related to the specific photoresist type; here we only use negative photoresist RDP-910 as an example) to enhance the adhesion of the photoresist and remove the solvent from the photoresist.

[0074] 4) If the pattern requires the superposition of two processes, alignment is necessary, i.e., overlaying is performed using alignment marks; otherwise, proceed directly to step 5).

[0075] 5) Exposure was performed using deep ultraviolet light (projection exposure), with an exposure dose of 350 mJ / cm². 2 The exposure power is 150mW / cm 2 ;

[0076] 6) After exposure, perform intermediate baking to reduce the standing wave effect (usually at 90-120℃ for 60-90 seconds).

[0077] 7) Use chemical developer to dissolve the soluble areas of the photoresist caused by exposure. The main purpose is to accurately copy the mask pattern into the photoresist. (Negative photoresist development removes the parts that have not been exposed to deep ultraviolet light.) Negative photoresist developer is generally an alkaline solution, such as TMAH tetramethylammonium hydroxide.

[0078] 8) Harden the film to eliminate moisture introduced into the adhesive during development and spraying, thereby increasing adhesion;

[0079] 9) Microscopic inspection to check the accuracy of photolithographic alignment and the distortion of key linewidths.

[0080] Specifically, DC electroplating is preferably used in step S5 of the electroplating process.

[0081] Specifically, in step S5, the electroplating solution used includes sodium sulfate (concentration of 250 g / L), boric acid (concentration of 40 g / L), saccharin (concentration of 1 g / L), 2-ethylhexyl sulfate (concentration of 0.5 mL / L), and nickel chloride (concentration of 40 g / L).

[0082] Specifically, in the electroplating process of step S5, the temperature of the electroplating solution is preferably 35-55℃, more preferably 45-55℃, and even more preferably 55℃; the pH value of the electroplating solution is preferably 3.0-5.0, more preferably 3.0-4.0, and even more preferably 3.5; the electroplating current density is preferably 15-25 mA·cm. -2 More preferably 15-20 mA·cm -2 The preferred value is 20 mA·cm. -2 .

[0083] Specifically, the electroplating process in step S5 includes:

[0084] The substrate 1 with negative adhesive 4 obtained in step S4 is clamped on an electric fixture and placed in an electroplating solution. The electroplating solution is placed in a water bath at a constant temperature of 55°C. A constant current source outputs current to provide current to the substrate 1, and the electroplating rate is 100 nm / min.

[0085] Specifically, in step S6, when dry etching and cleaning the wafer substrate 1 using oxygen plasma, the dry etching parameters include: ICP power: 1500W; Table power: 300W; O2 flow rate: 80sccm; chamber pressure: 20mTorr; time: 600s. This process removes the viscous and thick, difficult-to-remove negative adhesive 4 remaining on the surface of the wafer substrate 1.

[0086] Specifically, the electroplating method described in this embodiment does not limit the specific size of the substrate 1, the type of seed layer metal, the type of electroplated coating metal, or its thickness, and has a certain degree of universal applicability.

[0087] Specifically, in the two photolithography processes of step S1 and step S4, each type of photoresist plays a different role. Specifically, the positive photoresist 2 used in step S1 is relatively soft and easily dissolved by organic solvents such as acetone and anhydrous ethanol, making it suitable for wet stripping of the seed layer. The negative photoresist 4, on the other hand, is harder and more viscous, making it less easily compressed; therefore, it is suitable as a support layer for metal coatings, controlling the morphology of the metal coating and improving its perpendicularity.

[0088] Please see Figures 1-5 When using the electroplating process described above to prepare a high-verticality thick metal mask, the specific operation is as follows:

[0089] Example 1:

[0090] Step S1: After standard cleaning of the wafer substrate 1 to be plated, the substrate 1 is photolithographically patterned using positive resist 2.

[0091] Step S2: Sputter seed layer 3, 10nm chromium and 100nm gold onto the surface of substrate 1 with positive resist 2 after photolithography;

[0092] Step S3: Wet stripping of seed layer 3 is performed using solutions such as acetone and anhydrous ethanol to achieve patterning of seed layer 3;

[0093] Step S4: Photolithography is performed on the substrate 1 that has patterned the seed layer 3 using negative photoresist 4. Thick negative photoresist 4 is prepared by photolithography in the area without the seed layer. The negative photoresist 4 and the positive photoresist 2 in step S1 are photolithographically aligned.

[0094] Among them, the sidewall angle of negative adhesive 4 is 80°;

[0095] Step S5: After negative photolithography, the substrate 1 with negative photoresist 4 is placed in the electroplating solution for electroplating, and a metal coating 5 of a preset thickness is obtained through one or more electroplating processes.

[0096] Among them, the thickness of the metal coating 5 is less than the thickness of the negative adhesive 4;

[0097] The electroplating parameters were as follows: electroplating solution temperature 35℃, pH 3.0, and current density 15 mA·cm⁻¹. -2 ;

[0098] Step S6: After electroplating, the substrate 1 is immersed in acetone and anhydrous ethanol in sequence, and the negative adhesive 4 is ultrasonically cleaned to remove the negative adhesive 4 on the surface of the substrate 1. After the substrate 1 dries, oxygen plasma is used to perform dry etching cleaning on the wafer substrate 1 to completely remove the residual negative adhesive 4 on the surface of the wafer substrate 1, and a high verticality thick metal mask with a preset metal plating thickness is formed on the surface of the substrate 1.

[0099] Example 2:

[0100] Step S1: After standard cleaning of the wafer substrate 1 to be plated, the substrate 1 is photolithographically patterned using positive resist 2.

[0101] Step S2: Sputter seed layer 3, 40nm chromium and 400nm gold on the surface of substrate 1 with positive resist 2 after photolithography;

[0102] Step S3: Wet stripping of seed layer 3 is performed using solutions such as acetone and anhydrous ethanol to achieve patterning of seed layer 3;

[0103] Step S4: Photolithography is performed on the substrate 1 that has patterned the seed layer 3 using negative photoresist 4. Thick negative photoresist 4 is prepared by photolithography in the area without the seed layer. The negative photoresist 4 and the positive photoresist 2 in step S1 are photolithographically aligned.

[0104] Among them, the sidewall angle of negative adhesive 4 is 90°;

[0105] Step S5: After negative photolithography, the substrate 1 with negative photoresist 4 is placed in the electroplating solution for electroplating, and a metal coating 5 of a preset thickness is obtained through one or more electroplating processes.

[0106] Among them, the thickness of the metal coating 5 is less than the thickness of the negative adhesive 4;

[0107] The electroplating parameters were as follows: electroplating solution temperature 45℃, pH 5.0, and current density 25 mA·cm⁻¹. -2 ;

[0108] Step S6: After electroplating, the substrate 1 is immersed in acetone and anhydrous ethanol in sequence, and the negative adhesive 4 is ultrasonically cleaned to remove the negative adhesive 4 on the surface of the wafer substrate 1. After the substrate 1 dries, oxygen plasma is used to perform dry etching cleaning on the wafer substrate 1 to completely remove the residual negative adhesive 4 on the surface of the wafer substrate 1, and a high verticality thick metal mask with a preset metal plating thickness is formed on the surface of the substrate 1.

[0109] Example 3:

[0110] Step S1: After standard cleaning of the wafer substrate 1 to be plated, the substrate 1 is photolithographically patterned using positive resist 2.

[0111] Step S2: Sputter seed layer 3, 20nm chromium and 200nm gold on the surface of substrate 1 with positive resist 2 after photolithography;

[0112] Step S3: Wet stripping of seed layer 3 is performed using solutions such as acetone and anhydrous ethanol to achieve patterning of seed layer 3;

[0113] Step S4: Photolithography is performed on the substrate 1 that has patterned the seed layer 3 using negative photoresist 4. Thick negative photoresist 4 is prepared by photolithography in the area without the seed layer. The negative photoresist 4 and the positive photoresist 2 in step S1 are photolithographically aligned.

[0114] Among them, the sidewall angle of negative adhesive 4 is 80°-90°;

[0115] Step S5: After negative photolithography, the substrate 1 with negative photoresist 4 is placed in the electroplating solution for electroplating, and a metal coating 5 of a preset thickness is obtained through one or more electroplating processes.

[0116] Among them, the thickness of the metal coating 5 is less than the thickness of the negative adhesive 4;

[0117] The electroplating parameters were as follows: electroplating solution temperature 55℃, pH 3.5, and current density 20 mA·cm⁻¹. -2 ;

[0118] Step S6: After electroplating, the substrate 1 is sequentially immersed in acetone and anhydrous ethanol, and the negative adhesive 4 is ultrasonically cleaned to remove the negative adhesive 4 from the surface of the wafer substrate 1. After the substrate 1 dries, oxygen plasma is used to perform dry etching cleaning on the wafer substrate 1 to completely remove the residual negative adhesive 4 from the surface of the wafer substrate 1, forming a microstructure morphology of a high-verticality thick metal mask with a preset metal plating thickness on the surface of the substrate 1, as shown in the figure. Figure 4 As shown in Figure c, the sidewall angle of the prepared metal mask is 90°.

[0119] Please see Figures 1-5 By comparing the electroplating method of Example 3 of the present invention with two existing metal mask preparation methods, Comparative Examples 1 and 2, the advantages of the electroplating method of the thick metal mask described above in this embodiment in preparing a high verticality thick metal mask are illustrated.

[0120] Comparison Example 1:

[0121] Step 1: Sequentially form 20nm chromium and 200nm gold seed layers on a wafer substrate using magnetron sputtering technology;

[0122] Step 2: Spin-coat positive resist and perform photolithography and development to form a mask, with a mask angle of 80°-90°;

[0123] Step 3: Perform electroplating in the electroplating solution. The electroplating parameters are set as follows: current density is 20 mA·cm. -2 The electroplating solution temperature is 55℃, and the pH value of the electroplating solution is 3.5.

[0124] Step 4: Clean the photoresist with solutions such as acetone and anhydrous ethanol; and remove the seed layer by IBE etching.

[0125] Electroplating process as follows Figure 2 As shown, the mask fabrication effect is as follows: Figure 4 As shown in Figure b, the sidewall angle of the prepared metal mask is 97°.

[0126] Comparison Example 2:

[0127] Step 1: Spin-coat positive resist onto the wafer substrate and perform photolithography and development to form a mask with a mask angle of 80°-90°;

[0128] Step 2: Use magnetron sputtering to sequentially form 20nm chromium and 200nm gold seed layers on the mask surface;

[0129] Step 3: Clean the photoresist with solutions such as acetone and anhydrous ethanol, and peel off the metal seed layer on the surface of the photoresist;

[0130] Step 4: Perform electroplating in the electroplating solution. The electroplating parameters are set as follows: current density is 20 mA·cm⁻¹. -2 The electroplating solution temperature is 55℃, and the pH value of the electroplating solution is 3.5.

[0131] Electroplating process as follows Figure 3 As shown, the mask fabrication effect is as follows: Figure 4 As shown in Figure a, the sidewall angle of the prepared metal mask is 50°.

[0132] Through the comparative analysis of different metal mask preparation methods using the above comparative examples, it can be seen that, under the same electroplating parameters, the quality of the mask is closely related to the preparation of the seed layer and the treatment of the photoresist. Example 3 of this invention, through precise control of the electroplating process, obtained an ideal metal mask with good sidewall angles and metal layer thickness. In contrast, the sidewall angles and structures of the masks in Comparative Examples 1 and 2 differ, demonstrating the influence of process differences on the final mask performance, further highlighting the advantages of the electroplating process proposed in this invention for preparing deeply etched, thick metal masks in the preparation of highly vertical, thick metal masks.

[0133] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An electroplating process for preparing a deeply etched, thick metal mask, characterized in that, Includes the following steps: Step S1: After standard cleaning of the substrate to be plated, photolithography is performed on the substrate using positive resist. Step S2: Sputter a seed layer onto the substrate surface with positive resist after photolithography; Step S3: Perform wet stripping of the seed layer to achieve seed layer visualization; Step S4: Photolithography is performed on the substrate with seed layer patterning using negative photoresist. Thick negative photoresist is prepared by photolithography in the area without seed layer. The negative photoresist and the positive photoresist in step S1 are photolithographically aligned. The thickness of the negative photoresist is greater than the thickness of the preset metal plating layer, and the angle of the mask for the pattern position of the negative photoresist layer is 80°-90°. Step S5: After negative photolithography, the substrate with negative photoresist is placed in an electroplating solution for electroplating, and a metal coating of a preset thickness is obtained through electroplating. Step S6: After electroplating, the substrate is immersed in acetone and anhydrous ethanol in sequence, and the negative adhesive is ultrasonically cleaned. After the substrate dries, oxygen plasma is used to perform dry etching and cleaning on the substrate to form a high-verticality thick metal mask with a preset metal coating thickness on the substrate surface.

2. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, In step S1, when performing standard cleaning on the substrate to be plated, RCA cleaning technology is used.

3. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, In step S2, during the photolithography process of the substrate to be plated, the positive photoresist is a photoresist, which is one of the positive photoresist AZ4620 and the ultraviolet photoresist thin film S1813, and the thickness of the positive photoresist is 2-5μm.

4. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, The seed layer includes an adhesive layer and a pre-plating layer. The adhesive layer is located below the pre-plating layer, and the thickness ratio of the adhesive layer to the pre-plating layer is greater than 1:

10.

5. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, The seed layer is formed by magnetron sputtering and has a thickness of 110-440 nm.

6. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, In step S4, during the photolithography preparation of thick negative resist in the seedless region, the negative resist is photoresist, specifically negative photoresist RDP-910.

7. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, The electroplating solution in step S5 consists of: sodium sulfate at a concentration of 250 g / L, boric acid at a concentration of 40 g / L, saccharin at a concentration of 1 g / L, 2-ethylhexyl sulfate at a concentration of 0.5 mL / L, and nickel chloride at a concentration of 40 g / L.

8. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, In step S5, during the electroplating process, the electroplating solution temperature is 35-55℃, the pH value of the electroplating solution is 3.0-5.0, and the electroplating current density is 15-25 mA·cm⁻¹. -2 .

9. The electroplating process for preparing a deeply etched thick metal mask as described in claim 1, characterized in that, In step S6, when dry etching and cleaning the substrate using oxygen plasma, the dry etching parameters include: ICP power: 1500W; Table power: 300W; O2 flow rate: 80sccm; Chamber pressure: 20mTorr; Time: 600s.

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