Photoresist stripping method

Abstract

The invention discloses a photoresist stripping method, and relates to the technical field of semiconductors. The photoresist stripping method comprises the following steps: annealing a wafer to alloy a metal coating; soaking the wafer in a first organic solvent to soften the photoresist on the wafer; a second organic solvent and a third organic solvent are sequentially used for spraying the wafer, the second organic solvent comprises N-methyl pyrrolidone, and the volatility of the third organic solvent is higher than that of the second organic solvent; and drying the wafer. According to the photoresist stripping method provided by the invention, the photoresist on the wafer can be effectively removed, and meanwhile, the corrosion of NMP to the metal coating can be relieved, so that the yield of products can be improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a photoresist stripping method. Background Art

[0002] Semiconductor production relies on the use of photolithography, a process that uses photoresists to pattern integrated circuits with line widths of tens of nanometers or even less in specialized manufacturing tools. Photolithography accounts for more than one-third of the total production cost of microelectronics manufacturing because this stage is prone to defects. The photoresist stripping step must completely remove the unexposed photoresist without adversely affecting the material surface of the underlying wafer. One method of removing photoresist is to use organic solvents to dissolve the unexposed photoresist, thereby achieving the purpose of complete stripping.

[0003] In the related art, the method for stripping the photoresist on the wafer is to soak and rinse the wafer in an organic solution in sequence. However, the organic solvent used in the existing process includes N-methylpyrrolidone (NMP). Analysis shows that NMP will react with transition metals to cause metal feature corrosion. Therefore, the photoresist stripping method in the related art will lead to the problem of low product yield.

[0004] In view of this, this application is hereby filed. Summary of the invention

[0005] The purpose of the present application is to provide a photoresist stripping method, which can reduce the corrosion of the metal coating and improve the product yield.

[0006] This application is implemented as follows: The present application provides a photoresist stripping method for stripping photoresist on a wafer, wherein the wafer has a metal coating and photoresist, wherein the material of the metal coating includes at least two metals, wherein the at least two metals include a transition metal, and the photoresist stripping method includes: annealing the wafer to alloy the metal coating; soaking the wafer in a first organic solvent to soften the photoresist on the wafer; sequentially spraying the wafer with a second organic solvent and a third organic solvent, wherein the second organic solvent comprises N-methylpyrrolidone and the third organic solvent is more volatile than the second organic solvent; Dry the wafer.

[0007] In an optional embodiment, the annealing holding temperature is 160-200° C., and the holding time is 3-8 hours.

[0008] In an optional embodiment, the heating rate of annealing is 8-12°C / min, and the cooling rate is 3-6°C / min.

[0009] In an optional embodiment, the first organic solvent is selected from at least one of dimethyl sulfoxide and dimethylformamide.

[0010] In an optional embodiment, the third organic solvent is selected from at least one of isopropanol, ethanol and acetone.

[0011] In an optional implementation, during the process of spraying and drying the wafer, the wafer is controlled to rotate at a speed of 800-1000 r / min.

[0012] In an optional embodiment, the process of spraying the wafer with the second organic solvent lasts for 300 to 350 seconds, and the spraying pressure is 5 to 10 MPa.

[0013] In an optional embodiment, the process of spraying the wafer with the third organic solvent lasts for 5 to 20 seconds, and the spraying pressure is 0.1 to 0.2 MPa.

[0014] In an optional embodiment, the step of drying the wafer includes: Drying gas is continuously introduced into the chamber where the wafer is located, and the temperature of the drying gas is 50~75℃.

[0015] In an alternative embodiment, the drying gas is nitrogen.

[0016] This application has the following beneficial effects: The photoresist stripping method of the present application includes: annealing the wafer to alloy the metal coating; soaking the wafer in a first organic solvent to soften the photoresist on the wafer; spraying the wafer with a second organic solvent and a third organic solvent in sequence, wherein the second organic solvent contains N-methylpyrrolidone, and the volatility of the third organic solvent is stronger than that of the second organic solvent; and drying the wafer. In the photoresist stripping method provided by the present application, the metal coating is first alloyed by an annealing process, so that two different metals (such as copper and aluminum) in the metal coating can form an intermetallic compound (such as CuAl2 and CuAl3, etc.), which can effectively resist the corrosion of the organic solvent and reduce the corrosion damage of the metal coating. Further, after annealing, the wafer is first soaked in the first organic solvent to soften the photoresist, and at the same time, the photoresist can be made rough due to partial dissolution, and has a larger surface area, so the soaked photoresist is easier to be dissolved and removed during the spraying process, which is conducive to shortening the spraying time and reducing the corrosion of the metal coating by N-methylpyrrolidone (NMP) during the spraying process. The spraying process includes spraying with a second organic solvent, wherein the second organic solvent includes NMP, which is characterized in that the photoresist can be effectively dissolved and removed, and the cost is low. The spraying process also includes spraying the wafer with a third organic solvent, which has higher volatility than the second organic solvent, so the third organic solvent can not only effectively remove the second organic solvent remaining in the wafer, but also avoid corrosion of the metal coating, and its high volatility is also conducive to subsequent drying. It can be seen that, by the photoresist stripping method of the present application, the photoresist on the wafer can be effectively removed, and the corrosion of the metal coating by NMP can be alleviated, so the yield of the product can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is a flow chart of a photoresist stripping method in one embodiment of the present application; Figure 2 This is a scanning electron microscopic image of the metal coating of the wafer obtained in Example 1 of the present application; Figure 3 This is a surface microscopic image of the wafer obtained in Example 1 of the present application; Figure 4 This is a surface microscopic image of the wafer obtained in Comparative Example 1 of the present application; Figure 5This is a probe test curve diagram of the wafer obtained in Example 1 of the present application; Figure 6 This is a probe test curve diagram of the wafer obtained in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0019] As described in the background technology, in the process of removing photoresist (specifically, the photoresist to be removed, such as unexposed photoresist) in the related technology, although NMP has a good effect of dissolving and removing photoresist, it will corrode the metal coating, resulting in a decrease in product yield. In some prior arts, when deionized water is used to rinse the wafer to remove residual NMP, the deionized water and the residual NMP will form a new solvent system, which will have a solvation effect on the transition metal in the metal coating, thereby further aggravating the corrosion problem of the metal coating. Taking the metal coating containing copper as an example, the solvent system formed by deionized water and residual NMP will have a solvation effect on the copper ion complex, thereby aggravating copper corrosion. After the metal coating is corroded, it will have a performance impact on the final manufactured device (such as a surface acoustic wave filter), and even cause the device to fail.

[0020] In order to improve the problem in the related art that the metal coating is easily corroded and damaged during photoresist stripping, an embodiment of the present application provides a photoresist stripping method, which alleviates the corrosion damage of NMP to the metal coating by annealing, immersing and flushing the wafer with different solvents in sequence, thereby improving the product yield.

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0022] Figure 1 The flowchart of the photoresist stripping method in one embodiment of the present application. The photoresist stripping method provided in the embodiment of the present application is used to strip the photoresist on the wafer, wherein the wafer has a metal coating and a photoresist (specifically, the photoresist to be removed, such as the unexposed photoresist), and the material of the metal coating includes at least two metals, and at least two of the metals include a transition metal. For example, the metal coating includes copper and aluminum. Figure 1 As shown, the photoresist stripping method includes the following steps.

[0023] Step S100 , annealing the wafer to alloy the metal coating.

[0024] Through annealing, the transition metal in the metal coating can form an intermetallic compound, and the intermetallic compound has better corrosion resistance and can effectively reduce the corrosion of the metal coating when N-methylpyrrolidone (NMP) is used to clean the photoresist.

[0025] In an optional embodiment, the material of the metal plating layer includes copper and aluminum. Copper and aluminum can form intermetallic compounds such as CuAl2, Cu9Al4, Cu3Al and CuAl3 during annealing. These intermetallic compounds have better corrosion resistance than copper, so they can effectively improve the problem of copper corrosion.

[0026] Optionally, the annealing temperature is 160-200°C, and the insulation time is 3-8h. For example, the annealing temperature is any point value among 160°C, 170°C, 180°C, 190°C, 200°C, or a value between any two points; the insulation time is any point value among 3h, 4h, 5h, 6h, 7h, 8h, or a value between any two points.

[0027] Optionally, in the annealing process, the heating rate is 8-12°C / min, and the cooling rate is 3-6°C / min. The heating process in the annealing process refers to the process of increasing the temperature from room temperature to the insulation temperature, and the cooling process in the annealing process refers to the process of decreasing the temperature from the insulation temperature to room temperature.

[0028] It can be understood that parameters such as the holding temperature, holding time, heating rate and cooling rate will affect the alloying effect, that is, the amount and type of intermetallic compounds generated. The above parameters can be set according to specific needs. For example, in a specific embodiment, the holding temperature is 180°C, the holding time is 6h, the heating rate is 10°C / min, and the cooling rate is 5°C / min.

[0029] Step S200 , soaking the wafer in a first organic solvent to soften the photoresist on the wafer.

[0030] Optionally, the first organic solvent is selected from at least one of dimethyl sulfoxide (DMSO) and dimethylformamide. The first organic solvent itself is not easy to corrode the metal coating, and can effectively soften the photoresist. At the same time, it can also make the photoresist rough due to partial dissolution, and have a larger surface area. Therefore, the soaked photoresist is more easily dissolved and removed in the subsequent spraying process, which is conducive to shortening the spraying time and reducing the corrosion of the metal coating by N-methylpyrrolidone (NMP) during the spraying process.

[0031] The wafer may be immersed in an immersion tank filled with a first organic solvent for a immersion time of 10 to 60 minutes.

[0032] Step S300 , spraying the wafer with a second organic solvent and a third organic solvent in sequence, wherein the second organic solvent includes N-methylpyrrolidone, and the volatility of the third organic solvent is stronger than that of the second organic solvent.

[0033] In an embodiment of the present application, after the wafer is soaked, the wafer can be placed on a stage in a rinse tank and sprayed. During the spraying process, the wafer is controlled to rotate at a speed of 800-1000 r / min so that the sprayed organic solvent can be in uniform contact with the wafer to ensure that the photoresist can be completely cleaned. Optionally, the wafer is fixed by vacuum adsorption, and the front and back sides of the wafer are sprayed simultaneously using a nozzle. When the second organic solvent is used for spraying, the stepping track of the nozzle covers the entire wafer.

[0034] It can be understood that since the wafer is soaked in advance, the photoresist is easy to dissolve and remove when the second organic solvent is used for spraying, and the spraying time can be shortened. Optionally, the process of spraying the wafer with the second organic solvent lasts for 300 to 350 seconds, and the spraying pressure is 5 to 10 MPa. A shorter spraying time is conducive to preventing the metal coating from being corroded, and the spraying pressure is controlled at 5 to 10 MPa to ensure sufficient cleaning force to clean the photoresist.

[0035] After the wafer is sprayed with the second organic solvent, the wafer can be kept in a centrifugal rotating state, and the sprayed organic solvent can be changed to a third organic solvent. Optionally, the third organic solvent is selected from at least one of isopropyl alcohol (IPA), ethanol and acetone. The function of the third organic solvent is to dissolve and remove the residual second organic solvent and the residual photoresist. It can be understood that since the second organic solvent itself dissolves the photoresist, if the second organic solvent in which the photoresist is dissolved is not removed, the photoresist on the wafer cannot be cleaned up, and the NMP in the residual second organic solvent will still corrode the metal coating. The third organic solvent can dissolve the second organic solvent and the photoresist, and the volatility of the third organic solvent is stronger than that of the second organic solvent. Therefore, the third organic solvent can not only effectively remove the second organic solvent remaining in the wafer and avoid its corrosion to the metal coating, but also its high volatility is conducive to subsequent drying. Compared with using deionized water to rinse the second organic solvent, the third organic solvent will not form a solvent system with NMP that is highly corrosive to the metal coating, so it is beneficial to protect the metal coating from damage.

[0036] Optionally, the process of spraying the wafer with the third organic solvent lasts for 5 to 20 seconds, and the spraying pressure is 0.1 to 0.2 MPa. Since the third organic solvent is used to remove the residual second organic solvent (dissolved with a small amount of photoresist), it only takes a short time and a lower pressure to complete.

[0037] Step S400, drying the wafer.

[0038] In an embodiment of the present application, after the spraying is stopped, the drying gas can be continuously introduced into the chamber where the wafer is located (such as the spraying chamber), and the temperature of the drying gas is 50-75°C. Optionally, the drying gas is nitrogen. In other embodiments, inert gases such as argon and helium can also be used. During the drying process, the third organic solvent is completely volatilized to obtain a dry wafer.

[0039] Optionally, during the drying process, the wafer is still rotated, for example, at a speed of 800-1000 r / min. The drying time should be based on the principle that the wafer is completely dried. Optionally, the pressure of the drying gas during drying is 0.1-0.2 MPa.

[0040] The features and performance of the present application are further described in detail below in conjunction with the embodiments. The plating layer on the wafer in each embodiment includes a copper layer and an aluminum layer.

[0041] Example 1 The coated wafer is placed in an oven for annealing. The annealing temperature is 180°C, the insulation time is 6h, the heating rate is 10°C / min, and the cooling rate is 5°C / min. The annealed wafer is placed in DMSO (as the first organic solvent) and soaked for 30 minutes to soften the photoresist. The wafer is placed in a rinse tank and rotated at a speed of 1000r / min. NMP (as the second organic solvent) is used to spray the front and back of the wafer. The NMP spray time is 300s and the spray pressure is 8MPa. After that, the wafer keeps rotating and IPA (as the third organic solvent) is used to spray the front and back of the wafer. The IPA spray time is 15s and the spray pressure is 0.15MPa. After stopping the spraying, 70°C nitrogen is continuously introduced into the spray chamber at a pressure of 0.15MPa until the wafer is dried.

[0042] Example 2 The coated wafer is placed in an oven for annealing. The annealing temperature is 160°C, the insulation time is 8h, the heating rate is 12°C / min, and the cooling rate is 6°C / min. The annealed wafer is placed in dimethylformamide (as the first organic solvent) and soaked for 10 minutes to soften the photoresist. The wafer is placed in a rinse tank and rotated at 800r / min. NMP (as the second organic solvent) is used to spray the front and back of the wafer. The NMP spray time is 350s and the spray pressure is 10MPa. After that, the wafer keeps rotating and IPA (as the third organic solvent) is used to spray the front and back of the wafer. The IPA spray time is 20s and the spray pressure is 0.2MPa. After stopping the spraying, 75°C nitrogen is continuously introduced into the spray chamber at a pressure of 0.2MPa until the wafer is dried.

[0043] Example 3 The coated wafer is placed in an oven for annealing. The annealing temperature is 200°C, the insulation time is 3h, the heating rate is 8°C / min, and the cooling rate is 3°C / min. The annealed wafer is placed in DMSO (as the first organic solvent) and soaked for 20 minutes to soften the photoresist. The wafer is placed in a rinse tank and rotated at 900r / min. NMP (as the second organic solvent) is used to spray the front and back of the wafer. The NMP spray time is 330s and the spray pressure is 6MPa. After that, the wafer keeps rotating and ethanol (as the third organic solvent) is used to spray the front and back of the wafer. The ethanol spray time is 5s and the spray pressure is 0.1MPa. After stopping the spraying, 60°C nitrogen is continuously introduced into the spray chamber at a pressure of 0.1MPa until the wafer is dried.

[0044] Example 4 The coated wafer is placed in an oven for annealing. The annealing temperature is 170°C, the insulation time is 4h, the heating rate is 9°C / min, and the cooling rate is 4°C / min. The annealed wafer is placed in DMSO (as the first organic solvent) and soaked for 60min to soften the photoresist. The wafer is placed in a rinse tank and rotated at 800r / min. NMP (as the second organic solvent) is used to spray the front and back of the wafer. The NMP spray time is 300s and the spray pressure is 5MPa. After that, the wafer keeps rotating and acetone (as the third organic solvent) is used to spray the front and back of the wafer. The acetone spray time is 10s and the spray pressure is 0.15MPa. After stopping the spraying, 50°C nitrogen is continuously introduced into the spray chamber at a pressure of 0.2MPa until the wafer is dried.

[0045] Comparative Example 1 The only difference compared with Example 1 is that the wafer is not annealed.

[0046] Figure 2 This is a scanning electron microscopic image of the metal coating of the wafer obtained in Example 1 of the present application. Figure 2 As shown, the cross-section of the metal coating was observed using a scanning electron microscope. It can be seen that after annealing, strong alloying occurred between the copper layer and the aluminum layer, and the copper atoms migrated to the aluminum layer to produce intermetallic compounds, which can effectively resist corrosion. Figure 3 This is a microscopic image of the surface of the wafer obtained in Example 1 of the present application, in which the dark color is the metal coating. It can be seen that the surface of the metal coating is highly smooth, with no obvious corrosion and photoresist residue. Figure 4 This is a microscopic image of the surface of the wafer obtained in Comparative Example 1 of the present application. Figure 4 It can be seen that some areas (such as Figure 4 There is copper corrosion in the circled area.

[0047] The embodiment of the present application provides a photoresist stripping method, which can be applied in the process of manufacturing a surface acoustic wave filter, wherein the metal plating layer is used to form an interdigital electrode (IDT) of the surface acoustic wave filter. When the surface acoustic wave filter is working, the piezoelectric effect causes the IDT to vibrate at a certain frequency, and the IDT with copper corrosion has its quality and continuity destroyed, causing its vibration mode to change, thereby affecting the performance of the surface wave filter.

[0048] Figure 5 This is a probe test curve diagram of the wafer obtained in Example 1 of the present application; Figure 6 This is a probe test curve of the wafer obtained in Comparative Example 1 of this application. Figure 5 and Figure 6 As shown in the test results of the wafer obtained by the process method of the embodiment, the passband did not collapse and the insertion loss was normal. However, due to the presence of copper corrosion, the wafer in comparative example 1 affected the vibration of the IDT, resulting in the failure of the piezoelectric effect, the passband of RX and TX collapsed, and the frequency in the passband could not be effectively filtered, and the entire device failed.

[0049] In summary, the present application provides a photoresist stripping method, including annealing a wafer to alloy a metal coating; soaking the wafer in a first organic solvent to soften the photoresist on the wafer; spraying the wafer with a second organic solvent and a third organic solvent in sequence, wherein the second organic solvent contains N-methylpyrrolidone, and the volatility of the third organic solvent is stronger than that of the second organic solvent; and drying the wafer. In the photoresist stripping method provided by the present application, the metal coating is first alloyed by an annealing process, so that two different metals (such as copper and aluminum) in the metal coating can form an intermetallic compound, which can effectively resist the corrosion of the organic solvent and reduce the corrosion damage of the metal coating. Further, after annealing, the wafer is first soaked in the first organic solvent to soften the photoresist, and at the same time, the photoresist can be made rough due to partial dissolution, and has a larger surface area, so the soaked photoresist is easier to be dissolved and removed during the spraying process, which is conducive to shortening the spraying time and reducing the corrosion of the metal coating by N-methylpyrrolidone (NMP) during the spraying process. The spraying process includes spraying with a second organic solvent, wherein the second organic solvent includes NMP, which is characterized in that the photoresist can be effectively dissolved and removed, and the cost is low. The spraying process also includes spraying the wafer with a third organic solvent, which has higher volatility than the second organic solvent, so the third organic solvent can not only effectively remove the second organic solvent remaining in the wafer, but also avoid corrosion of the metal coating, and its high volatility is also conducive to subsequent drying. It can be seen that, by the photoresist stripping method of the present application, the photoresist on the wafer can be effectively removed, and the corrosion of the metal coating by NMP can be alleviated, so the yield of the product can be improved.

[0050] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A photoresist stripping method for stripping photoresist on a wafer, wherein the wafer has a metal coating and the photoresist, wherein the material of the metal coating comprises at least two metals, wherein the at least two metals include a transition metal, wherein: The photoresist stripping method comprises: annealing the wafer to alloy the metal coating; Soaking the wafer in a first organic solvent to soften the photoresist on the wafer; sequentially spraying the wafer with a second organic solvent and a third organic solvent, wherein the second organic solvent comprises N-methylpyrrolidone and the third organic solvent is more volatile than the second organic solvent; The wafer is dried.

2. The photoresist stripping method according to claim 1, characterized in that: The annealing is carried out at a holding temperature of 160-200° C. and a holding time of 3-8 hours.

3. The photoresist stripping method according to claim 1, characterized in that: The annealing temperature rise rate is 8-12°C / min, and the cooling rate is 3-6°C / min.

4. The photoresist stripping method according to claim 1, characterized in that: The first organic solvent is selected from at least one of dimethyl sulfoxide and dimethylformamide.

5. The photoresist stripping method according to claim 1, characterized in that: The third organic solvent is selected from at least one of isopropanol, ethanol and acetone.

6. The photoresist stripping method according to any one of claims 1 to 5, characterized in that: During the process of spraying and drying the wafer, the wafer is controlled to rotate at a speed of 800-1000 r / min.

7. The photoresist stripping method according to any one of claims 1 to 5, characterized in that: The process of spraying the wafer with the second organic solvent lasts for 300 to 350 seconds, and the spraying pressure is 5 to 10 MPa.

8. The photoresist stripping method according to any one of claims 1 to 5, characterized in that: The process of spraying the wafer with the third organic solvent lasts for 5 to 20 seconds, and the spraying pressure is 0.1 to 0.2 MPa.

9. The photoresist stripping method according to any one of claims 1 to 5, characterized in that: The step of drying the wafer comprises: The drying gas is continuously introduced into the chamber where the wafer is located, and the temperature of the drying gas is 50-75°C.

10. The photoresist stripping method according to claim 9, characterized in that: The drying gas is nitrogen.

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