Method for removing photoresist after thick aluminum etching process

Abstract

The invention provides a method for removing photoresist after a thick aluminum etching process, which comprises the following steps of: S1, providing a wafer after thick aluminum etching, and forming the photoresist to be removed on the surface of the wafer; s2, introducing mixed gas of oxygen and nitrogen, carrying out plasma surface pretreatment on the wafer, and removing a carbonized hard shell on the surface of the photoresist; and S3, carrying out dry photoresist removing treatment on the wafer, wherein the dry photoresist removing treatment comprises a water vapor treatment process and an oxygen photoresist removing process which are circularly carried out. According to the method, the pretreatment step is added, oxygen and a small amount of nitrogen are introduced, high-activity oxygen free radicals are used for rapidly removing carbonized hard shells on the surface of the photoresist, and the content of carbon in a polymer is reduced. By means of the improvement, the efficiency of the follow-up degumming step is remarkably improved, the situation that the degumming capacity is insufficient due to the carbonized hard shell is effectively avoided, the phenomenon of residual gum is reduced, and the product quality is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and particularly to a method for removing photoresist after a thick aluminum etching process. Background Art

[0002] In the field of semiconductor manufacturing, the aluminum dry etching process is a key technology widely used. This process mainly uses chlorine-based gases as the etching medium. However, during the etching process, a large amount of chlorine-containing metal polymers (Al-C-Cl) will inevitably be generated, and these polymers often adhere to the surface of the photoresist. Once the etching is completed, the photoresist must be removed immediately. Otherwise, if the chlorine-containing metal polymers adhered to the photoresist come into contact with tiny water droplets in the environment, chloride ions will react with water to form hydrochloric acid, which will then cause corrosion of aluminum, seriously damaging the performance of semiconductor devices.

[0003] In the etching process of thick aluminum (thickness greater than 1 μm), due to the higher energy and longer time required for etching, the corresponding etching by-products also increase. On the one hand, the surface of the photoresist is more likely to be carbonized and gradually hardened under the long-term bombardment of high-energy plasma, forming a hard shell that is difficult to remove; on the other hand, a large amount of etching by-products (chlorine-containing metal polymers) will accumulate on the surface of the photoresist, thus forming a barrier layer between the photoresist and the external environment. This barrier layer will significantly hinder the direct contact between oxygen and the photoresist during the photoresist removal process. Therefore, in the photoresist removal step after thick aluminum etching, the phenomenon of photoresist residue is likely to occur. If the residual photoresist cannot be completely removed, it will ultimately have an extremely adverse impact on the performance of semiconductor devices, seriously affecting the reliability and stability of products. Summary of the Invention

[0004] To solve all or part of the above-mentioned problems in the prior art, the present invention provides a method for removing photoresist after a thick aluminum etching process. By adding a pretreatment step, introducing oxygen and a small amount of nitrogen, highly reactive oxygen free radicals are used to quickly remove the carbonized hard shell on the surface of the photoresist and reduce the carbon element content in the polymer. This improvement significantly improves the efficiency of the subsequent photoresist removal step, effectively avoids the insufficient photoresist removal ability caused by the carbonized hard shell, reduces the occurrence of residual photoresist phenomenon, and ensures product quality.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for removing photoresist after a thick aluminum etching process, comprising the following steps:

[0007] S1. Provide a wafer after thick aluminum etching, and a photoresist to be removed is formed on the surface of the wafer;

[0008] S2. Introduce a mixed gas of oxygen and nitrogen, and perform plasma surface pretreatment on the wafer to remove the carbonized hard shell on the surface of the photoresist.

[0009] S3. Perform dry photoresist stripping on the wafer, and the dry photoresist stripping process includes a water vapor treatment and an oxygen photoresist stripping process that are carried out cyclically.

[0010] The water vapor treatment process in step S3 includes: introducing water vapor to perform plasma surface treatment on the wafer to remove the chlorine-containing metal polymer on the surface of the photoresist.

[0011] The oxygen photoresist stripping process in step S3 includes: introducing oxygen, water vapor, and nitrogen to perform plasma surface treatment on the wafer to remove the photoresist.

[0012] The water vapor treatment and the oxygen photoresist stripping in step S3 constitute a photoresist stripping cycle, which is repeated 3 - 5 times.

[0013] In step S2, the volume ratio of oxygen to nitrogen in the mixed gas is 4:1 to 20:1.

[0014] The process parameters of the oxygen treatment in step S2 are: oxygen flow rate 2000 - 5000 sccm, nitrogen flow rate 200 - 800 sccm, radio frequency power 800 - 1200 W, pressure 2 - 4 torr, and treatment time 30 - 60 s.

[0015] The process parameters of the water vapor treatment in step S3 are: water vapor flow rate 200 - 800 sccm, radio frequency power 800 - 1400 W, pressure 1 - 4 torr, and treatment time 20 - 100 s.

[0016] The process parameters of the oxygen photoresist stripping in step S3 are: oxygen flow rate 2000 - 5000 sccm, water vapor flow rate 200 - 800 sccm, nitrogen flow rate 200 - 800 sccm, radio frequency power 800 - 1400 W, pressure 1 - 4 torr, and treatment time 60 - 300 s.

[0017] Both steps S2 and S3 are carried out under the condition of constant temperature, and the temperature is controlled within the range of 220 - 280 °C.

[0018] The wafer in step S1 is obtained after completing the aluminum layer etching process with a thickness ≥ 1 μm. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 This is a flowchart of a method for removing photoresist after a thick aluminum etching process according to an embodiment of the present invention. Detailed implementation manners

[0021] The technical solutions in the specific embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] In the embodiments of the present invention, with reference to Figure 1 as shown, a method for removing photoresist after a thick aluminum etching process is provided. For a wafer obtained after the aluminum layer etching process with a thickness ≥ 1 μm is completed, the following steps are performed:

[0023] S1. Provide a wafer after thick aluminum etching, and a photoresist to be removed is formed on the surface of the wafer;

[0024] S2. Introduce a mixed gas of oxygen and nitrogen, and perform plasma surface pretreatment on the wafer to remove the carbonized hard shell on the surface of the photoresist;

[0025] S3. Perform dry photoresist removal on the wafer, and the dry photoresist removal process includes a water vapor treatment and an oxygen photoresist removal process that are performed cyclically.

[0026] The present invention adds a pretreatment step before the water vapor treatment. This pretreatment step requires introducing oxygen and a small amount of nitrogen, and for other process parameters, such as the energy required for the reaction, the temperature during the treatment process, etc., they can be selected to be maintained at a level similar to that of the photoresist removal step.

[0027] In the pre-treatment stage, the oxygen free radicals in the generated plasma have high activity. By virtue of this high activity, the reaction rate between the oxygen free radicals and the carbides existing on the surface of the photoresist is significantly accelerated. Due to the characteristics of the thick aluminum etching process, a hardened carbon shell often forms on the surface of the photoresist, and the above-mentioned highly active oxygen free radicals can quickly remove these carbon shells. At the same time, a part of the carbon element contained in the metal polymer attached to the photoresist will also react with the oxygen free radicals. This reaction effectively avoids the aggregation of carbon elements on the surface of the photoresist. Because once carbon elements aggregate, it is easy to promote the mutual stacking of polymers and form a hardened barrier layer on the surface of the photoresist, and this pre-treatment step can prevent this situation from occurring, making the polymers maintain a relatively loose state, thereby greatly weakening the blocking effect of the polymers on the subsequent photoresist stripping process. In particular, the introduction of water vapor must be prevented in this pre-treatment step. Under normal chemical action, water vapor can react with the chlorine element in the metal polymer and generate gaseous substances, but in the process system involved in the present invention, the removal of chlorine element will cause the aggregation of carbon elements, and this aggregation of carbon elements is not conducive to the realization of the goal of efficient photoresist stripping in the present invention.

[0028] By adding this pre-treatment step, when the subsequent photoresist stripping step is carried out, the reaction efficiency between the oxygen free radicals and the photoresist is significantly improved. Without changing the photoresist stripping time, the photoresist stripping ability is enhanced. This enhancement effect can avoid the occurrence of residual photoresist during the photoresist removal process, because residual photoresist will have a negative impact on the quality of the product, such as affecting the electrical performance and reliability of the chip. In addition, since the photoresist can be effectively removed in one go, the problem of reduced machine utilization efficiency caused by multiple photoresist stripping operations is also avoided, thereby ensuring the high efficiency and stability of the entire semiconductor manufacturing process.

[0029] Specifically, the gas introduced in step S2 is mainly oxygen supplemented with a small amount of nitrogen, and the volume ratio of oxygen to nitrogen is controlled within the range of 4:1 to 20:1. In a radio frequency environment, nitrogen is ionized to generate nitrogen free radicals, which can react with the sidewalls of the aluminum wires to form a thin passivation protection layer, thus effectively avoiding damage to the aluminum wires in this step. At the same time, oxygen is ionized to generate a large number of oxygen free radicals (plasma), which have high reactivity and can quickly react with the carbon element in the polymer to generate gaseous substances, making the polymer become loose and facilitating the subsequent degluing step. Without the generation of a large amount of oxygen plasma, it will be difficult to break the carbonized hard shell on the surface of the photoresist and react quickly with the carbon element deep inside the polymer only by relying on pure oxygen. In addition, this step requires a certain radio frequency power, and a power similar to that of the degluing step can be selected to increase the stability of the degluing machine tool and prevent the frequent switching of power from affecting the stability and service life of the machine tool. At the same time, the nitrogen flow rate can also be set with reference to the degluing step to protect the sidewalls of the aluminum wires without affecting the activity of the oxygen free radicals. In this embodiment, the specific process parameters for pretreatment are as follows: oxygen flow rate 2000 - 5000 sccm, nitrogen flow rate 200 - 800 sccm, radio frequency power 800 - 1200 W, pressure 2 - 4 torr, and treatment time 30 - 60 s. The treatment time is set to 30 - 60 s because the metal polymers agglomerate together and have complex compositions, and it takes a certain amount of time for the oxygen free radicals to penetrate deep into the polymer and the carbonized shell. If the treatment time is short, it will be difficult to achieve the goal of removing a large amount of carbon elements; while if the time is too long, it is easy to cause a large accumulation of chlorine elements and bury them inside the photoresist, which will not only burden the subsequent water vapor treatment step and prevent the water vapor treatment step from efficiently removing chlorine elements, but also reduce the operating efficiency of the machine tool and affect the running efficiency of the machine tool for goods production.

[0030] In step S3, water vapor treatment introduces water vapor to perform plasma surface treatment on the wafer. The main purpose is to remove the chlorine-containing metal polymers on the photoresist surface. The water vapor is ionized into plasma at a certain energy, and through chemical reactions, the chlorine element in the chlorine-containing metal polymers is converted into hydrogen chloride and removed. Subsequently, in the oxygen ashing step, a mixed gas of oxygen, water vapor, and nitrogen is used, with the oxygen content exceeding 90%. Oxygen ashing removes the photoresist by performing plasma surface treatment on the wafer and using oxygen radicals to react with the photoresist. The water vapor treatment and oxygen ashing together constitute a complete ashing cycle, and the number of executions of this cycle can be adjusted according to the thickness of the photoresist. In this embodiment, this ashing cycle is repeated 3 to 5 times to ensure that the photoresist is completely removed. The specific process parameters of the water vapor treatment are: water vapor flow rate 200 - 800 sccm, radio frequency power 800 - 1400 W, pressure 1 - 4 torr, and treatment time 20 - 100 s. The specific process parameters of the oxygen ashing are: oxygen flow rate 2000 - 5000 sccm, water vapor flow rate 200 - 800 sccm, nitrogen flow rate 200 - 800 sccm, radio frequency power 800 - 1400 W, pressure 1 - 4 torr, and treatment time 60 - 300 s. By precisely controlling these parameters, an efficient and stable photoresist removal effect can be achieved, while ensuring the quality of the wafer surface and the compatibility of subsequent processes.

[0031] The above steps are all carried out under the condition of constant temperature, controlled within the range of 220 - 280 °C. In this embodiment, the temperature is controlled at 250 °C. Maintaining a high temperature state can significantly enhance the reaction activity of reaction radicals, thereby accelerating the progress of chemical reactions and improving the efficiency of the entire process. At the same time, keeping the temperature constant not only helps to reduce the control burden of the machine tool, lower the complex control requirements caused by temperature fluctuations, but also can effectively increase the service life of the machine tool and reduce equipment losses caused by temperature changes. In addition, avoiding frequent temperature rises and falls can significantly improve the goods running efficiency during the production process, ensure the continuity and stability of the process, and thus improve the overall production efficiency while ensuring product quality.

[0032] The key parameters of the present invention focus on the setting of oxygen flow rate and treatment time during the pretreatment process in step S2. Without adding the pretreatment step, using a typical photoresist stripping process, the residual amount of photoresist after 1μm aluminum etching can reach 20%. After adding oxygen pretreatment, experiments show that: under the conditions of an oxygen flow rate of 5000 sccm and a treatment time of 15 s, and an oxygen flow rate of 2000 sccm and a treatment time of 60 s, no photoresist residue is detected. The oxygen flow rate should not be too small, otherwise it cannot effectively remove the carbonized hard shell and polymers on the photoresist surface; but it also cannot reach the upper limit flow rate of the machine, so as not to exceed the processing capacity of the equipment or cause other process problems. If the treatment time is too short, it is difficult to achieve the expected photoresist stripping effect, and if it is too long, it will reduce the production efficiency of the machine. Under the conventional oxygen flow rate, a treatment time of about 60 s is sufficient to achieve a good photoresist stripping effect.

[0033]

[0034]

[0035] In the thick aluminum etching process, due to the long etching time and high required energy, the photoresist is exposed to a high-energy plasma environment for a long time, resulting in a higher degree of carbonization on the photoresist surface and more metal polymers accumulated on the surface. In the conventional water vapor treatment step, although the chlorine ions in the polymers can be reacted, the breaking of C-Cl bonds in this process will trigger the formation of more C-C bonds. These newly formed C-C bonds further increase the adhesion amount of high-carbon-containing polymers on the photoresist surface, and then make the carbonized hard shell on the photoresist surface become thicker. This situation is extremely unfavorable for the subsequent photoresist stripping process. During the photoresist stripping process, when oxygen reacts with the thick hard shell, due to the increase in the degree of carbonization and the thickness of the hard shell, the reaction rate will become slower. Eventually, this situation will lead to insufficient photoresist stripping ability and the problem of residual glue will follow.

[0036] The innovation of the present invention lies in adding a pretreatment step before the water vapor treatment step of the original process. This pretreatment step focuses on effectively removing the carbon element in the polymers on the sidewalls and surface of the photoresist, while the chlorine element that may cause corrosion problems is arranged to be removed in the subsequent water vapor treatment step. After being treated by the pretreatment step designed by the present invention, the carbon content in the photoresist-related polymers can be significantly reduced. And in terms of machine settings, when keeping the parameters of the original photoresist stripping process menu unchanged, only by adding a pretreatment step of 30 - 60 s, the photoresist stripping ability after thick aluminum etching can be significantly improved, effectively avoiding the situation of glue residue, thereby ensuring product quality. At the same time, this improvement has little impact on the utilization efficiency of the machine, and can achieve an efficient photoresist removal effect without significantly changing the existing process flow.

[0037] It should be noted that, for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for removing photoresist after thick aluminum etching process, characterized in that: The following steps are involved: S1. Providing a wafer after thick aluminum etching, a photoresist to be removed is formed on the surface of the wafer; S2. introducing a mixed gas of oxygen and nitrogen to perform plasma surface pretreatment on the wafer to remove the carbonized crust on the surface of the photoresist; S3. Performing a dry degumming process on the wafer, wherein the dry degumming process includes a cyclic water vapor treatment and an oxygen degumming process.

2. The method according to claim 1, characterized in that The water vapor treatment process in step S3 includes: introducing water vapor to perform plasma surface treatment on the wafer to remove the chlorine-containing metal polymer on the surface of the photoresist.

3. The method according to claim 1, characterized in that The oxygen stripping process in step S3 includes: introducing oxygen, water vapor and nitrogen to perform plasma surface treatment on the wafer to remove the photoresist.

4. The method according to claim 1, characterized in that The water vapor treatment and oxygen degumming in step S3 constitute a degumming cycle, which is repeated 3-5 times.

5. The method according to claim 1, characterized in that The volume ratio of oxygen to nitrogen in the mixed gas in step S2 is 4:1 to 20:

1.

6. The method according to claim 1, characterized in that The process parameters of the oxygen treatment in step S2 are: oxygen flow rate 2000-5000sccm, nitrogen flow rate 200-800sccm, RF power 800-1200W, pressure 2-4torr, and treatment time 30-60s.

7. The method according to claim 1, characterized in that The process parameters of the water vapor treatment in step S3 are: water vapor flow rate 200-800 sccm, RF power 800-1400 W, pressure 1-4 torr, and treatment time 20-100 s.

8. The method according to claim 1, characterized in that: The process parameters of oxygen stripping in step S3 are: oxygen flow rate 2000-5000sccm, water vapor flow rate 200-800sccm, nitrogen flow rate 200-800sccm, RF power 800-1400W, pressure 1-4torr, and processing time 60-300s.

9. The method according to claim 1, characterized in that: Steps S2 and S3 are both carried out under constant temperature conditions, and the temperature is controlled within the range of 220-280°C.

10. The method according to claim 1, characterized in that The wafer in step S1 is obtained after completing an aluminum layer etching process with a thickness of ≥1 μm.

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