Method for removing photoresist on mask substrate

Abstract

The invention relates to a method for removing photoresist on a mask substrate, which comprises the following steps: step S10: the mask substrate is horizontally placed in a washing solution to be soaked, the photoresist surface of the mask substrate is placed downwards, and the glass surface opposite to the photoresist surface is placed upwards; and S20, enabling the substrate after the photoresist layer is removed to rotate around the axis of the substrate in the horizontal direction, and washing the substrate with pure water. According to the method for removing the photoresist on the mask substrate, the photoresist layer is rapidly separated from the substrate of the mask substrate by utilizing gravity and centrifugal force, the photoresist and a washing agent can be effectively prevented from remaining on the surface of the mask substrate, and the method has the advantages of stable and good removal effect.

Description

Technical Field

[0001] The invention relates to a photoresist removal technology, in particular to a method for removing photoresist from a mask substrate. Background Art

[0002] In semiconductor chip manufacturing or integrated circuit manufacturing, the mask substrate is the pattern transfer master in the microelectronics manufacturing process, see Figure 1 The mask substrate includes a substrate 10 and a photoresist layer 20, wherein the substrate 10 includes a glass sheet 11 and a coating layer 12 disposed on the glass sheet, and the photoresist layer 20 is disposed on the coating layer 12. Among them, photoresist is a transitional material, and its removal is a key step in pattern manufacturing. After the pattern manufacturing is completed, the photoresist on the coating layer must be accurately removed for subsequent processes. In addition, the removal of photoresist is directly related to the accuracy of the circuit pattern. The thickness, uniformity and contamination of the photoresist layer 20 are key indicators to be examined. The coating of photoresist will produce different proportions of defective products, and at least more than 50% of the yield loss is caused by minor contamination; in addition, the photoresist may also have different types of defects such as glue spots, discoloration, and fish eyes, which make the mask substrate unusable. For a defective photoresist layer, it is necessary to remove the photoresist on the substrate and then re-coat it.

[0003] The existing method for removing the photoresist from the mask substrate is to place the mask substrate in a washing tank filled with sodium hydroxide or potassium hydroxide alkali solution for immersion (DIP), so that the alkali solution softens the photoresist and causes the photoresist to fall off the coating layer of the substrate.

[0004] However, in the prior art of photoresist softening, part of the photoresist does not react fully, forming flocs and agglomerated particles, which easily adhere to the coating layer of the substrate (on the front side of the substrate) and the back side of the substrate, resulting in the problem of unclean removal of the photoresist from the mask substrate. Summary of the invention

[0005] Based on this, the purpose of the present invention is to overcome the defects or shortcomings of the prior art and provide a method for removing photoresist from a mask substrate, comprising:

[0006] Step S10: placing the mask substrate horizontally in the washing liquid for immersion, wherein the photoresist surface of the mask substrate is placed downward, and the glass surface facing away from the photoresist surface is placed upward;

[0007] Step S20: rotating the substrate after removing the photoresist layer in a horizontal direction around its axis, and rinsing the substrate with pure water.

[0008] The method for removing photoresist from a mask substrate of the present invention utilizes gravity and centrifugal force to rapidly separate the photoresist layer from the substrate of the mask substrate, which can effectively prevent photoresist and lotion from remaining on the surface of the mask substrate and has the advantage of stable and good removal effect.

[0009] Furthermore, after step S20, the method further includes:

[0010] Step S30: rotating the substrate in a horizontal direction around its axis, and sequentially cleaning the coating surface of the substrate with sulfuric acid and rinsing with pure water.

[0011] Further, step S30 specifically includes: step S32: facing the coating surface of the substrate after being rinsed with pure water in step S20 upward, rotating the substrate around its axis in the horizontal direction, and dripping dilute sulfuric acid on the coating surface of the substrate to evenly coat the dilute sulfuric acid on the coating surface of the substrate.

[0012] Furthermore, after step S32, the method further includes: step S33: reducing the rotation speed of the substrate to allow the dilute sulfuric acid to infiltrate the coating layer of the substrate.

[0013] Furthermore, after step S32, the method further includes: step S34: rotating the substrate around its axis in the horizontal direction, and washing the coated surface of the substrate with 40-60° C. hot pure water; step S36: rotating the substrate around its axis in the horizontal direction, and washing the coated surface of the substrate with room temperature pure water.

[0014] Furthermore, in steps S32 to S36, while the substrate coating surface is cleaned with sulfuric acid and rinsed with pure water, the glass surface facing away from the coating surface is rinsed with room temperature pure water.

[0015] Furthermore, the substrate rotation speed in step S32 is 30-50 rpm, the concentration of the dilute sulfuric acid is 50%-80%, and the volume of the added dilute sulfuric acid is 5-10 mL; the substrate rotation speed in step S32 is 10-40 rpm and is less than the substrate rotation speed in step S32, and the rotation time is 60-120 s.

[0016] Furthermore, the substrate rotation speed in steps S34 to S36 is 30 to 50 rpm, and the rotation time is 30 to 60 s.

[0017] Further, step S40: the substrate is rotated around its axis in the horizontal direction, and the coated surface of the substrate is ultrasonically washed; step S50: the substrate is rotated around its axis in the horizontal direction, and the coated surface of the substrate and the glass surface facing away from the coated surface are simultaneously rinsed with pure water; step S60: the substrate is rotated around its axis in the horizontal direction so that there is no liquid attached to the surface of the substrate.

[0018] Further, in step S10, the developer is TMAH developer, the mask substrate is immersed in the washing solution for 80 to 120 seconds, and the glass surface of the substrate is flush with the surface of the washing solution; in step S20, the rotation speed of the substrate is 30 to 50 rpm; steps S32 to S36 are repeated 5 times or more; in step S40, the rotation speed of the substrate is 30 to 50 rpm; the processing time is 50 to 100 s, the ultrasonic frequency is 1 to 1.5 MHZ, and the power is 50 to 150 W; in step S50, the rotation speed of the substrate is 30 to 50 rpm, and the processing time is 30 to 60 s; in step S60, the rotation speed of the substrate is 300 to 500 rpm, and the processing time is 30 to 60 s.

[0019] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of the mask substrate.

[0021] Description of the drawings: substrate 10 , glass sheet 11 , coating layer 12 , photoresist layer 20 . DETAILED DESCRIPTION

[0022] Aiming at the problem that the existing mask substrate photoresist is not removed cleanly, the present invention provides a method for removing the mask substrate photoresist with good removal effect, comprising the following steps:

[0023] Step S10: Soaking and degumming: Place the mask substrate horizontally in the washing liquid and soak for 80 to 120 seconds, so that most of the photoresist is softened and separated from the coating layer of the substrate, and obtain a substrate after removing the photoresist layer. The photoresist surface of the mask substrate is placed downward, and the glass surface facing away from the photoresist surface is placed upward. Preferably, the glass surface is placed flush with the surface of the washing liquid.

[0024] Placing the photoresist surface of the mask substrate downward can allow the softened photoresist to automatically separate from the coating layer under the action of gravity, while reducing the adhesion of incompletely softened photoresist flocs and agglomerated particles on the glass sheet and the coating layer.

[0025] Step S20: pure water washing: the substrate after the photoresist layer is removed is rotated in the horizontal direction around its axis, and the coated surface of the substrate and the glass surface facing away from the coated surface are washed with pure water at the same time to remove the photoresist adhering to the substrate. Among them, washing the coated surface of the substrate with pure water can make the glue blocks remaining on the coated layer fall off; washing the glass surface facing away from the coated surface with pure water can prevent the photoresist blocks falling off from the coated layer from being washed onto the glass sheet by the water flow and adhering to the glass sheet. In addition, the washing liquid used for immersion can be removed during the pure water washing.

[0026] Preferably, the rotation speed of the substrate is 30 to 50 rpm; the coated surface of the substrate faces downward, and the glass surface facing away from the coated surface faces upward, so that the softened photoresist can be fully separated from the coating layer under the action of centrifugal force and gravity; in addition, when the substrate is rotated and rinsed, only one substrate is arranged in the same vertical direction to avoid cross-contamination caused by the residual glue between different substrates due to the cross-movement of water flow during the rinsing process.

[0027] The technicians of this application remove the photoresist on the mask substrate through the above steps S10 to S20, and the test results show that the photoresist removal effect of the mask substrate is good. When the mask substrate is applied to the subsequent process, the technicians further found that defects such as notches will appear near the pattern lines formed by photolithography. Further analysis shows that the reason may be that the coating layer is damaged during the photoresist cleaning process, resulting in pinhole-shaped depressions, light leakage or changes in the optical properties of the film surface, thereby affecting the accuracy of photolithography. In this regard, the technicians carefully analyzed and found that the problem lies in the washing liquid used in step S10. The washing liquid is sodium hydroxide or potassium hydroxide lye, which is highly corrosive. When soaking, the coating layer is damaged by the corrosive action of the washing liquid; in addition, although the pure water in step S20 can rinse the lye on the surface of the substrate, the metal ions such as potassium ions or sodium ions in the lye can directly contact the coating layer, and the metal ions are easily precipitated into the coating layer and destroy the coating layer, causing the problem of the coating layer being concave.

[0028] In view of the above problems, the technical personnel of the present application further improved the method of removing the photoresist from the mask substrate:

[0029] The washing solution in step S10 is a developer, and the developer is preferably a 2.38% TMAH (tetramethylammonium hydroxide) developer. The developer is non-corrosive to the coating layer and can cause the photoresist layer on the mask substrate to fall off in agglomerates.

[0030] After step S20, the method further includes:

[0031] Step S30: Sulfuric acid cleaning and pure water rinsing: the substrate is rotated in the horizontal direction around its axis, and the coating surface of the substrate is sequentially cleaned with sulfuric acid, rinsed with hot pure water at 40-60° C., and rinsed with pure water at room temperature.

[0032] Step S30 specifically includes:

[0033] Step S32: Sulfuric acid cleaning: facing the coated surface of the substrate after being rinsed with pure water in step S20 upward, and rotating the substrate in the horizontal direction around its axis, setting the rotation speed of the substrate to 30-50 rpm, preferably 40 rpm, dripping 50%-80% concentration of dilute sulfuric acid on the coated surface of the substrate, so that the dilute sulfuric acid can stay on the coated layer and fully react with the photoresist remaining on the coated surface of the substrate to soften the photoresist;

[0034] Step S34: Rinse with hot pure water: The substrate is rotated around its axis in the horizontal direction at a speed of 30 to 50 rpm, and the coated surface of the substrate is rinsed with hot pure water at 40 to 60°C for 30 to 60 seconds to fully dissolve the dilute sulfuric acid and remove the dilute sulfuric acid and softened photoresist; at the same time, it can prevent the glass sheet from breaking. Specifically, the glass sheet has been cut, polished, coated and other processes, and there are damages and hidden scratches on the glass surface, and there is heat generation when washing with sulfuric acid. If the dilute sulfuric acid is directly removed by washing with pure water at room temperature, the temperature of the glass sheet will change rapidly and the temperature difference will be large, further leading to the accident of the glass sheet breaking. Therefore, washing with hot pure water at 40 to 60°C can prevent the glass sheet from breaking, and at the same time can increase the solubility of dilute sulfuric acid and fully wash the dilute sulfuric acid;

[0035] Step S36: Rinse with room temperature pure water: the substrate is rotated horizontally around its axis at a speed of 30 to 50 rpm, and the coated surface of the substrate is rinsed with room temperature pure water for 30 to 60 seconds to further remove the residual dilute sulfuric acid and photoresist on the coated surface.

[0036] The technicians tested the effect of the mask substrates cleaned by the above method and found that some substrates had optical parameter deviation problems, such as changes in light transmittance, which affected the accuracy of subsequent photolithography. The technicians of the present invention further analyzed the problem of substrate optical parameter deviation and found that there were two specific phenomena. One phenomenon was that there was a small amount of photoresist residue on the corners of the coated surface of the substrate, which caused the optical parameter deviation; the other phenomenon was that there was a layer of foggy marks on the glass surface of the substrate, which caused the optical parameter deviation. And these two defects usually do not exist on the same substrate at the same time. The technicians tried to solve the above problem by adjusting the parameters such as the substrate rotation speed and the concentration of dilute sulfuric acid, but found that although adjusting the above parameters can reduce the number of substrates with the above defects to a certain extent, it still cannot completely solve the problem. The technicians further analyzed the above two phenomena and found that the key lies in the reaction time and dosage of dilute sulfuric acid. Specifically, a short reaction time or insufficient dosage of dilute sulfuric acid will easily lead to a small amount of photoresist residue on the corners of the coated surface of the substrate; excessive dosage of dilute sulfuric acid will cause the dilute sulfuric acid to escape onto the glass surface of the substrate, leaving a layer of foggy mark on the glass surface.

[0037] In view of the above problems, the technical personnel of the present application further improved the method of removing the photoresist from the mask substrate:

[0038] Step S30 also includes: while cleaning and rinsing the coating surface of the substrate, rinsing the glass surface facing away from the coating surface with pure water at room temperature.

[0039] Specifically, in step S32, the dilute sulfuric acid is dripped at the center of the substrate, and the dripping volume is set to 5-10 ml;

[0040] After step S32, the method further includes:

[0041] Step S33: Sulfuric acid soaking: adjust the substrate rotation speed to 10-40rpm and less than the substrate rotation speed in step S32, preferably 35rpm, and keep rotating for 60-120s, at which time the dilute sulfuric acid added in step S32 soaks the substrate coating layer. In the present invention, while rotating the substrate in the horizontal direction, dilute sulfuric acid soaks the substrate coating layer, forming a SPIN photoresist removal method that is completely different from the DIP method of the prior art, which can ensure that the corners of the substrate coating layer are coated with sufficient sulfuric acid to fully react with the photoresist; at the same time, it can avoid the dilute sulfuric acid flowing to the glass surface of the substrate to cause pollution, and reduce the waste of dilute sulfuric acid, saving production costs;

[0042] In steps S32 to S36, while cleaning with sulfuric acid, soaking in sulfuric acid, rinsing with hot pure water, and rinsing with pure water at room temperature, the glass surface facing away from the coated surface is rinsed with pure water at room temperature to prevent sulfuric acid from remaining on the glass surface and to prevent photoresist clumps that have fallen off the coating layer from being washed onto the glass sheet and adhering to the glass sheet.

[0043] As a further optimization of the above scheme, steps S32 to S36 are repeated for more than 5 times, thereby reducing the interference of pure water rinsing on the glass surface on the residence of dilute sulfuric acid on the coating surface in a "small amount and multiple times" manner, so that a sufficient amount of dilute sulfuric acid can stay on the coating surface for a sufficient time, thereby achieving the goal of fully removing the photoresist on the coating surface while avoiding the problem of deviation of the substrate optical parameters caused by residual dilute sulfuric acid.

[0044] As a further optimization of the above solution, step S30 further includes:

[0045] Step S40: Ultrasonic water washing: The substrate is rotated around its axis in the horizontal direction at a speed of 30 to 50 rpm, and the coated surface of the substrate is ultrasonically washed for 50 to 100 seconds. Preferably, the substrate is rotated at a speed of 45 rpm; the ultrasonic water washing time is 90 seconds, the ultrasonic frequency is set to 1.25 MHZ, and the power is set to 100 W. Among them, the 1.25 MHZ mega-ultrasound removes dense particles that adhere firmly and particles at the corners, especially particles of 0.2 microns and below. At the same time of ultrasonic water washing, the glass surface facing away from the coated surface is rinsed with pure water at room temperature to prevent the photoresist clumps that fall off the coating layer from being washed onto the glass sheet and adhering to the glass sheet.

[0046] Step S50: pure water rinsing: the substrate is rotated around its axis in the horizontal direction at a speed of 30-50 rpm, and the coated surface of the substrate and the glass surface facing away from the coated surface are rinsed with pure water for 30-60 seconds to remove the photoresist adhering to the substrate.

[0047] Step S60: Spin-drying: the substrate is rotated around its axis in the horizontal direction at a rotation speed of 300-500 rpm for 30-60 seconds to make sure that no liquid adheres to the surface of the substrate.

[0048] Example 1

[0049] Take 10 Q6025 mask substrates as samples, whose photoresist is I-line positive photoresist, the specific photoresist type is IP3500, and the thickness is 465nm. Fully expose under white light, and perform steps S10 to S60 on the exposed mask substrate. The specific process parameters and processing methods corresponding to each step are summarized in the following table:

[0050] Table 1 Process parameters and processing methods corresponding to each step of the method for removing photoresist from the mask substrate

[0051]

[0052] Effect detection

[0053] Table 2 Reflectivity and OD value (optical density value) of the coating layer before and after removing the photoresist by the method of the present invention

[0054] state Average reflectivity (at 436nm) OD mean (at 450nm) Before treatment 11.3％ 3.15 After treatment 11.2％ 3.14 The difference before and after processing 0.1％ 0.01

[0055] The test results show that the reflectivity and OD of the 10 samples before and after the photoresist is removed are almost unchanged, indicating that the coating layer is almost not damaged. It can be seen that the method for removing the photoresist from the mask substrate of the present invention can prevent the coating layer from being damaged.

[0056] Table 3 Average number of surface particles of the coating layer before and after the photoresist is removed by the method of the present invention

[0057]

[0058] The test results show that the number of particles on the surfaces of the 10 samples did not increase before and after the photoresist was removed, indicating that no photoresist particles were attached to the coating layer. The method of removing the photoresist from the mask substrate of the present invention has a good effect on clearing the photoresist.

[0059] The particles did not increase, indicating that the coating layer was almost not damaged. It can be seen that the method for removing the photoresist from the mask substrate of the present invention has the effect of cleaning without residue.

[0060] Compared with the prior art, the method for removing photoresist from a mask substrate of the present invention utilizes gravity and centrifugal force to quickly separate the photoresist layer from the substrate of the mask substrate, which can effectively prevent the photoresist and lotion from remaining on the surface of the mask substrate, and the removal effect is stable and good, thereby ensuring that the subsequent photolithography has a high precision. In addition, steps S32 to S33 form a SPIN photoresist removal method, and the dilute sulfuric acid cleaning method can reduce the damage to the coating layer during the photoresist removal process; and the centrifugal force and gravity are used to make the dilute sulfuric acid and the photoresist fully react to achieve the purpose of clean removal; and by setting reasonable parameters such as the volume of dilute sulfuric acid, dilute sulfuric acid is prevented from escaping and remaining, and waste is avoided; further, the cleanliness of the substrate is improved by repeating steps S32 to S36. In addition, the tiny and firmly adhered photoresist is removed from the substrate in combination with ultrasonic treatment.

[0061] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A method for removing photoresist from a mask substrate, characterized in that: include: Step S10: placing the mask substrate horizontally in a washing solution for immersion, wherein the photoresist surface of the mask substrate is placed downward, so that the photoresist is separated from the substrate of the mask substrate; Step S20: rotating the substrate around its axis in a horizontal direction, and rinsing the substrate with pure water.

2. The method for removing photoresist from a mask substrate according to claim 1, characterized in that: After step S20, the method further includes: Step S30: rotating the substrate in a horizontal direction around its axis, and sequentially cleaning the coating surface of the substrate with sulfuric acid and rinsing with pure water.

3. The method for removing photoresist from a mask substrate according to claim 2, characterized in that: Step S30 specifically includes: Step S32: The coated surface of the substrate after being rinsed with pure water in step S20 is facing upward, and the substrate is rotated around its axis in the horizontal direction, and dilute sulfuric acid is dripped on the coated surface of the substrate.

4. The method for removing photoresist from a mask substrate according to claim 3, characterized in that: After step S32, the method further includes: Step S33: reducing the rotation speed of the substrate to allow the dilute sulfuric acid to infiltrate the coating layer of the substrate.

5. The method for removing photoresist from a mask substrate according to claim 4, characterized in that: After step S32, the method further includes: Step S34: rotating the substrate in a horizontal direction around its axis, and washing the coating surface of the substrate with 40-60° C. hot pure water; Step S36: rotating the substrate in a horizontal direction around its axis, and washing the coating surface of the substrate with pure water at room temperature.

6. The method for removing photoresist from a mask substrate according to claim 5, characterized in that: In steps S32 to S36, while the coated surface of the substrate is cleaned with sulfuric acid and rinsed with pure water, the glass surface facing away from the coated surface is rinsed with pure water at room temperature.

7. The method for removing photoresist from a mask substrate according to claim 6, characterized in that: The substrate rotation speed in step S32 is 30-50 rpm, the concentration of the dilute sulfuric acid is 50%-80%, and the volume of the added dilute sulfuric acid is 5-10 mL; The substrate rotation speed in step S32 is 10-40 rpm and is less than the substrate rotation speed in step S32, and the rotation time is 60-120 s.

8. The method for removing photoresist from a mask substrate according to claim 7, characterized in that: The substrate rotation speed in steps S34 to S36 is 30 to 50 rpm, and the rotation time is 30 to 60 s.

9. The method for removing photoresist from a mask substrate according to claim 8, characterized in that: After step S30, the method further includes: Step S40: rotating the substrate in a horizontal direction around its axis, and performing ultrasonic water washing on the coating surface of the substrate; Step S50: rotating the substrate in a horizontal direction around its axis, and washing the coating surface of the substrate and the glass surface facing away from the coating surface with pure water at the same time; Step S60: rotating the substrate in a horizontal direction around its axis so that no liquid adheres to the surface of the substrate.

10. The method for removing photoresist from a mask substrate according to claim 9, characterized in that: In step S10, the developer is TMAH developer, the mask substrate is immersed in the developer for 80 to 120 seconds, and the glass surface of the substrate is flush with the surface of the developer; In step S20, the rotation speed of the substrate is 30-50 rpm; Steps S32 to S36 are repeated 5 times or more; In step S40, the rotation speed of the substrate is 30-50 rpm; the processing time is 50-100 s, the ultrasonic frequency is 1-1.5 MHZ, and the power is 50-150 W; In step S50, the rotation speed of the substrate is 30-50 rpm, and the processing time is 30-60 s; In step S60, the rotation speed of the substrate is 300-500 rpm, and the processing time is 30-60 s.

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