Method for removing copper ions in regenerated wafer

Abstract

The invention discloses a method for removing copper ions in a regenerated wafer, and the method comprises the following steps: S1, removing all metal films on the surface of the wafer, and guaranteeing that the surface is free of metal elements; s2, the wafer after film removal is placed in a heat treatment device to be subjected to heat treatment, and a gradient temperature rise mode is adopted in the heat treatment process; and S3, then, the wafer subjected to heat treatment is subjected to liquid medicine cleaning and ultrasonic-assisted cleaning, and Cu separated out to the surface is cleaned. Cu ions in the wafer are dried to the surface, the copper ions on the surface of the wafer are removed through liquid medicine and ultrasonic-assisted cleaning, damage to a silicon wafer is avoided, the internal structure of the wafer is not affected, a gradient heating mode is adopted in the heat treatment process, the gradient heating mode is beneficial for the copper ions to gradually adapt to temperature changes, and the heat treatment efficiency is improved. And the stress concentration in the wafer caused by sudden temperature change is avoided, so that the wafer damage risk is reduced, meanwhile, the copper ions are uniformly separated out in a proper temperature range, and the separation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of regenerated wafers, and in particular to a method for removing copper ions inside a regenerated wafer. Background Art

[0002] In semiconductor integrated circuits, individual components are connected via metal interconnects to form a complete circuit. Metal interconnect layers can be made of copper, tungsten, aluminum, cobalt, and other materials. Aluminum was commonly used in the early days, but copper is now being used more and more frequently. This is partly because copper is cheaper. Furthermore, producing dense metal interconnects requires electroplating and chemical mechanical polishing, processes that copper readily handles, with a controlled yield. Furthermore, copper exhibits strong resistance to electromigration, preventing voids in the interconnects caused by electromigration. This significantly improves the efficiency and reliability of integrated circuits, making it an ideal alternative material for large-scale deployment.

[0003] However, with the development of integrated circuits, semiconductor factories have an increasing demand for test wafers. In order to save costs, test wafer regeneration projects have emerged.

[0004] Despite the electrical conductivity and cost advantages of copper, copper interconnect structures present fundamental manufacturing issues and challenges. The strong migration of copper ions affects the resistivity of the doped regions, making them uncontrollable. This can easily lead to device failure, compromising product reliability, and contaminating or even endangering processing line facilities, including cross-contamination to Al processing lines that are not physically isolated from Cu processing lines.

[0005] Currently, treatment for Cu-containing silicon wafers is in the R&D stage. Surface film stripping is similar to that for N-Cu wafers. The mainstream polishing method after film stripping is to develop polishing slurries containing special chelating agents and Cu ion scavengers. These can remove residual polysilicon and silicon nitride films after etching, while also preventing cross-contamination between polished copper-containing silicon wafers and Al wafers. The report states that by properly selecting abrasives, copper scavengers, chelating agents, and pH adjusters, when the copper ion content in the polishing slurry is kept below 2 ppm, the copper concentration in both copper-containing and non-copper-containing wafers can be suppressed to 5E10 atoms / cm² after polishing. However, this still falls short of customer requirements.

[0006] Our company currently uses the process described in the patent document with publication number CN116575128A. During actual use, some copper ions inside the wafer are still not removed (which cannot meet customer needs), and during actual heat treatment, the wafer is easily damaged due to sudden temperature changes, and the yield rate is reduced. Therefore, this application provides a method for removing copper ions inside regenerated wafers to meet the needs. Summary of the Invention

[0007] The purpose of this application is to provide a method for removing copper ions inside a regenerated wafer, so as to solve the technical problems of incomplete removal of copper ions inside the existing wafer and low yield.

[0008] To achieve the above objectives, the present application provides the following technical solution: a method for removing copper ions from a regenerated wafer, characterized in that it comprises the following steps: S1: Remove all metal films on the wafer surface to ensure that there are no metal elements on the surface; S2: The wafer after film removal is placed in a heat treatment device for heat treatment. The heat treatment process adopts a gradient temperature increase method. The initial temperature is 150 degrees Celsius to 160 degrees Celsius, and the temperature is increased to 300 degrees Celsius at a rate of 10 degrees Celsius per minute and maintained for 10 minutes. S3: The heat-treated wafer is then cleaned with a chemical solution and ultrasonic-assisted cleaning with an ultrasonic frequency of 40kHz and a power density of 0.5W / cm² to clean the Cu precipitated on the surface.

[0009] As a preferred implementation in this embodiment, in step S3, the liquid cleaning adopts a multi-stage cleaning method, first using 5% dilute sulfuric acid for preliminary cleaning, then using deionized water for rinsing, and finally using 1% ammonia water for final cleaning.

[0010] As a preferred embodiment of this embodiment, in step S2, heat treatment is performed in a vacuum environment, and the vacuum degree is controlled at 1×10 -3 Pa to 1×10 -2 Between Pa.

[0011] As a preferred implementation in this embodiment, in step S2, a magnetic field generating device is provided in the heat treatment device to generate a uniform magnetic field perpendicular to the surface of the wafer.

[0012] As a preferred implementation in this embodiment, in step S2, the magnetic field generated by the magnetic field generating device is an alternating magnetic field, and the magnetic field intensity changes periodically between 0.3 Tesla and 0.7 Tesla, with a frequency of 10 times per second.

[0013] As a preferred implementation in this embodiment, in step S2, a pulse heater is provided in the heat treatment device, and the pulse heater performs short-time pulse heating at a rate of 100 degrees Celsius per second, with a duration of 1 second and an interval of 30 seconds.

[0014] As a preferred implementation in this embodiment, the pulse waveform of the pulse heater is a square wave.

[0015] As a preferred implementation method in this embodiment, the square wave pulse adopts a bipolar square wave design, that is, the pulse voltage alternates between positive and negative amplitudes, the positive amplitude is +12V, the negative amplitude is -8V, the pulse frequency is 100Hz, and the duty cycle is 50%.

[0016] In summary, the technical effects and advantages of the present invention are as follows: The present invention has a reasonable structure, performs heat treatment on the wafer, bakes the Cu ions inside the wafer to the surface, and removes the copper ions on the wafer surface through liquid medicine and ultrasonic-assisted cleaning. During the treatment process, no damage is caused to the silicon wafer, and the internal structure of the wafer is not affected. The heat treatment process adopts a gradient heating method, which helps the copper ions gradually adapt to temperature changes, avoids stress concentration inside the wafer caused by sudden temperature changes, thereby reducing the risk of wafer damage, and ensures that the copper ions are uniformly precipitated within a suitable temperature range, thereby improving precipitation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a process flow chart of the present invention; Figure 2 This is a comparison table of copper atom density on the surface of recycled wafers after being processed by traditional process and existing process. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] Example: Reference Figure 1 A method for removing copper ions from a regenerated wafer includes the following steps: S1: Remove all metal films on the wafer surface to ensure that there are no metal elements on the surface; S2: The wafer after film removal is placed in a heat treatment device for heat treatment. The heat treatment process adopts a gradient temperature increase method. The initial temperature is 150 degrees Celsius to 160 degrees Celsius, and the temperature is increased to 300 degrees Celsius at a rate of 10 degrees Celsius per minute and maintained for 10 minutes. S3: The heat-treated wafer is then cleaned with a chemical solution and ultrasonic-assisted cleaning with an ultrasonic frequency of 40kHz and a power density of 0.5W / cm² to clean the Cu precipitated on the surface.

[0021] During the regenerated wafer processing process, the wafer is heat-treated to bake out the Cu ions inside the wafer to the surface. The copper ions on the wafer surface are removed by chemical solution and ultrasonic-assisted cleaning. During the process, the silicon wafer is not damaged and the internal structure of the wafer is not affected. The heat treatment process uses a gradient heating method, which helps copper ions gradually adapt to temperature changes, avoiding stress concentration inside the wafer caused by sudden temperature changes, thereby reducing the risk of wafer damage. At the same time, it ensures that copper ions are uniformly precipitated within the appropriate temperature range, improving precipitation efficiency. The initial temperature is set to 150 to 160 degrees Celsius: Within this temperature range, it provides a mild starting environment for copper ions, helping them gradually adapt to temperature changes and avoid stress concentration inside the wafer caused by sudden temperature changes, thereby reducing the risk of wafer damage. At the same time, 150 to 160 degrees Celsius as the starting temperature also provides a stable starting point for the subsequent heating process, helping copper ions to precipitate evenly within the appropriate temperature range; The temperature is raised at a rate of 10 degrees Celsius per minute. This rate of heating is neither too fast to cause excessive temperature gradients inside the wafer, nor too slow to affect production efficiency. The appropriate heating rate ensures that copper ions gradually migrate to the wafer surface during the temperature change process, improving precipitation efficiency. At the same time, 300 degrees Celsius as the final temperature can ensure sufficient precipitation of copper ions without causing thermal damage to the wafer. Compared with the traditional process, the copper content of the wafer surface after treatment is less than 3.5E8atoms / cm² (such as Figure 2 As shown, Examples 1-5 are wafers processed by this method, and the comparative example is a wafer processed by the traditional process), and the yield rate is also improved from the original 78% to 95%.

[0022] As a preferred implementation in this embodiment, in step S3, the liquid cleaning adopts a multi-stage cleaning method, first using 5% dilute sulfuric acid for preliminary cleaning, then using deionized water for rinsing, and finally using 1% ammonia water for final cleaning.

[0023] The multi-stage cleaning method can gradually remove copper ions from the wafer surface. Dilute sulfuric acid can effectively dissolve copper ions, deionized water can rinse away residual sulfuric acid and dissolved copper ions, and ammonia can neutralize the acidic environment on the wafer surface to prevent copper ions from re-depositing, ensuring the cleaning effect and improving the efficiency of copper ion removal.

[0024] As a preferred embodiment of this embodiment, in step S2, heat treatment is performed in a vacuum environment, and the vacuum degree is controlled at 1×10 -3 Pa to 1×10 -2 Between Pa.

[0025] The vacuum environment can effectively reduce the interference of gases such as oxygen during the heat treatment process, prevent copper ions from being oxidized at high temperatures, thereby maintaining the activity of copper ions, promoting their migration from the inside of the wafer to the surface, and further improving the precipitation efficiency.

[0026] As a preferred implementation in this embodiment, in step S2, a magnetic field generating device is provided in the heat treatment device to generate a uniform magnetic field perpendicular to the surface of the wafer.

[0027] The uniform magnetic field generated by the magnetic field generator can produce a Lorentz force on copper ions, promoting their migration from the inside of the wafer to the surface. This magnetic field-assisted heat treatment method can significantly improve the precipitation efficiency of copper ions while maintaining the integrity of the wafer.

[0028] As a preferred implementation in this embodiment, in step S2, the magnetic field generated by the magnetic field generating device is an alternating magnetic field, and the magnetic field intensity changes periodically between 0.3 Tesla and 0.7 Tesla, with a frequency of 10 times per second.

[0029] The alternating magnetic field can generate a dynamically changing Lorentz force during the heat treatment process. This dynamic force field can more effectively break the equilibrium state of copper ions in the lattice and promote their migration from the inside of the wafer to the surface. The periodic variation of the magnetic field strength between 0.3 Tesla and 0.7 Tesla ensures sufficient Lorentz force while avoiding the adverse magnetic stress effects on the wafer due to excessive magnetic field strength. The frequency of change is 10 times per second, which can ensure sufficient migration of copper ions while avoiding energy loss and increased equipment complexity caused by excessive frequency. This alternating magnetic field assisted heat treatment method can significantly improve the precipitation efficiency of copper ions while maintaining the integrity of the wafer and the stability of the process.

[0030] As a preferred implementation in this embodiment, in step S2, a pulse heater is provided in the heat treatment device, and the pulse heater performs short-time pulse heating at a rate of 100 degrees Celsius per second, with a duration of 1 second and an interval of 30 seconds.

[0031] Pulse heating technology provides a high temperature environment for a short period of time, accelerating the copper ion precipitation process. Short pulse heating rapidly raises the wafer surface temperature, promoting the migration of copper ions to the surface. The intervals allow the internal temperature of the wafer to gradually rise, maintaining continuous copper ion precipitation. This heating method not only improves copper ion precipitation efficiency but also reduces the risk of thermal damage to the wafer caused by prolonged high temperature exposure.

[0032] As a preferred implementation in this embodiment, the pulse waveform of the pulse heater is a square wave.

[0033] The rapid heating characteristics of square wave pulses enable copper ions to reach the precipitation temperature in a short time. At the same time, its rapid change characteristics help to break the equilibrium state of copper ions in the crystal lattice, promoting the migration and precipitation of copper ions; the uniformity and stability of square wave pulse heating help to reduce the thermal stress caused by temperature fluctuations on the wafer.

[0034] As a preferred implementation method in this embodiment, the square wave pulse adopts a bipolar square wave design, that is, the pulse voltage alternates between positive and negative amplitudes, the positive amplitude is +12V, the negative amplitude is -8V, the pulse frequency is 100Hz, and the duty cycle is 50%.

[0035] By introducing negative amplitude pulses, a stronger electric field perturbation can be generated inside the wafer, which helps to break the equilibrium state of copper ions in the lattice and promote copper ion migration. At the same time, the alternating changes in positive and negative amplitudes can produce a more uniform heating effect, reduce the temperature gradient inside the wafer, and further improve the efficiency of copper ion precipitation. The positive amplitude of +12V generates a strong electric field inside the wafer, which helps to break the equilibrium state of copper ions in the crystal lattice and promote the migration of copper ions to the surface; The negative amplitude of -8V helps to generate a reverse electric field inside the wafer, balancing the electric field generated by the positive amplitude and reducing the charge accumulation on the wafer surface. At the same time, it also helps further precipitation of copper ions under the action of the electric field; The 100Hz pulse frequency can provide sufficient temperature control accuracy while ensuring heating efficiency. It ensures that the wafer temperature rises evenly during the heating process and reduces the impact of temperature fluctuations on copper ion precipitation. A 50% duty cycle means equal heating and cooling times, helping maintain wafer temperature stability during the heating process. It prevents the wafer from overheating due to prolonged continuous heating while ensuring that copper ions have sufficient time to migrate during the precipitation process.

[0036] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for removing copper ions from a regenerated wafer, characterized in that: The steps include: S1: Remove all metal films on the wafer surface to ensure that there are no metal elements on the surface; S2: The wafer after film removal is placed in a heat treatment device for heat treatment. The heat treatment process adopts a gradient temperature increase method. The initial temperature is 150 degrees Celsius to 160 degrees Celsius, and the temperature is increased to 300 degrees Celsius at a rate of 10 degrees Celsius per minute and maintained for 10 minutes. S3: The heat-treated wafer is then cleaned with a chemical solution and ultrasonic-assisted cleaning with an ultrasonic frequency of 40kHz and a power density of 0.5W / cm² to clean the Cu precipitated on the surface.

2. The method for removing copper ions from a regenerated wafer according to claim 1, wherein: In step S3, the liquid cleaning adopts a multi-stage cleaning method, first using 5% dilute sulfuric acid for preliminary cleaning, then using deionized water for rinsing, and finally using 1% ammonia water for final cleaning.

3. The method for removing copper ions from a regenerated wafer according to claim 1, wherein: In step S2, heat treatment is performed in a vacuum environment, and the vacuum degree is controlled at 1×10 -3 Pa to 1×10 -2 Between Pa.

4. The method for removing copper ions from a regenerated wafer according to claim 1, wherein: In step S2, a magnetic field generating device is provided in the heat treatment device to generate a uniform magnetic field perpendicular to the surface of the wafer.

5. The method for removing copper ions from a regenerated wafer according to claim 4, wherein: In step S2, the magnetic field generated by the magnetic field generating device is an alternating magnetic field, and the magnetic field intensity changes periodically between 0.3 Tesla and 0.7 Tesla, with a frequency of 10 times per second.

6. The method for removing copper ions from a regenerated wafer according to claim 1, wherein: In step S2, a pulse heater is provided in the heat treatment device, and the pulse heater performs short-time pulse heating at a rate of 100 degrees Celsius per second, with a duration of 1 second and an interval of 30 seconds.

7. The method for removing copper ions from a regenerated wafer according to claim 6, wherein: The pulse waveform of the pulse heater is a square wave.

8. The method for removing copper ions from a regenerated wafer according to claim 7, wherein: The square wave pulse adopts a bipolar square wave design, that is, the pulse voltage alternates between positive and negative amplitudes, the positive amplitude is +12V, the negative amplitude is -8V, the pulse frequency is 100Hz, and the duty cycle is 50%.

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