Activation and surface protection method for ion implantation SiC

Abstract

The invention discloses an activation and surface protection method for ion implantation SiC, and relates to the technical field of semiconductor manufacturing. Comprising the following steps: performing high-temperature ion implantation on a SiC wafer; pVD carbon film plating is carried out on the SiC wafer after high-temperature ion implantation; performing laser activation annealing on the SiC wafer plated with the carbon film; performing plasma physical etching on the annealed SiC wafer; carrying out sacrificial oxide layer treatment on the SiC wafer subjected to plasma physical etching; and carrying out BOE solution wet etching on the SiC wafer after sacrificial oxide layer treatment to obtain the SiC device. According to the method, through high-temperature ion implantation and laser annealing treatment and by adopting a multi-step carbon film removal process, the ion implantation impurity activation efficiency is remarkably improved, meanwhile, the morphology of the device is guaranteed, and the performance of the device is improved. The method has the advantages of simple process, high activation efficiency, good repeatability and the like, and is suitable for manufacturing SiC-based power semiconductor devices.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically, to a method for activating and protecting the surface of ion-implanted SiC. Background Technology

[0002] Silicon carbide (SiC), as a wide bandgap semiconductor material, has shown great application potential in power devices and high-frequency devices due to its excellent properties such as high thermal conductivity, high breakdown electric field and high electron saturation drift velocity.

[0003] Ion implantation is a key technology for doping SiC devices. During the ion implantation process, the bombardment of ions inevitably damages the SiC lattice structure and may even induce local amorphization, resulting in numerous defects. To restore lattice integrity and activate the dopant elements, high-temperature annealing is usually required.

[0004] Due to the high hardness and high melting point of SiC materials, the activation of impurities after ion implantation is extremely difficult, and usually requires extremely high temperatures (>1600℃) to achieve effective impurity activation.

[0005] In existing technologies, furnace tube high-temperature annealing is widely used due to the availability of equipment and the simplicity of the process. However, this global and long-term heating method (usually requiring more than 30 minutes) is not only inefficient, but also prone to prominent problems such as wafer warping, re-diffusion of doped impurities, and thermal activation defects due to its huge thermal budget, which has become a bottleneck in the fabrication of high-performance, micro-nano SiC devices.

[0006] Furthermore, during high-temperature annealing, severe thermal decomposition occurs on the SiC wafer surface, generating byproducts such as Si, Si2C, and SiC2. These byproducts redeposit on the wafer surface, leading to increased surface roughness and severely impacting device performance and reliability. Therefore, current technologies typically coat the SiC surface with a carbon film as a protective layer before annealing. Common carbon film coating methods include chemical vapor deposition (CVD), physical vapor deposition (PVD), and photoresist coating. However, CVD processes involve high temperatures, which can easily cause additional thermal damage to the wafer; photoresist coating struggles to achieve a uniform and dense film. While PVD offers advantages such as low temperature and good uniformity, completely removing the carbon film after annealing remains a significant challenge.

[0007] In summary, existing technologies for SiC ion implantation suffer from problems such as low impurity activation efficiency, easy surface damage, and residual carbon film after removal. Therefore, providing a method that achieves efficient impurity activation while effectively protecting the SiC surface and removing carbon film without residue has become a pressing technical problem to be solved in this field. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a method for activating and protecting the surface of ion-implanted SiC, so as to solve the problems of poor surface morphology, low activation efficiency and residual carbon film risk in the prior art after SiC wafer ion implantation activation.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: A method for activating and protecting the surface of ion-implanted SiC includes the following steps: S1. High-temperature ion implantation is performed on the SiC wafer; S2. Perform PVD carbon film deposition on SiC wafers after high-temperature ion implantation; S3. Perform laser-activated annealing on the SiC wafer after carbon film deposition; the energy used in laser-activated annealing is 6~8 J / cm. 2 ; S4. Perform plasma physical etching on the annealed SiC wafer; S5. Perform sacrificial oxide layer treatment on the SiC wafer after plasma physical etching; S6. Perform BOE (Buffered Oxide Etch, BOE) solution wet etching on the SiC wafer after sacrificial oxide layer treatment to obtain SiC devices.

[0010] In this invention, high-temperature ion implantation refers to a process technology in which the substrate (SiC wafer) is heated to 400-600°C (or even higher) before implantation. Heating the SiC wafer is achieved by heating the target disk. After high-temperature ion implantation, an implantation layer is formed on the surface of the SiC wafer.

[0011] In this invention, high-energy-density instantaneous irradiation with a laser beam is used to instantly raise the temperature of the micro-regions on the surface of the implanted layer to 1600°C or even exceed 1600°C within a timescale of milliseconds to microseconds, thus satisfying the thermodynamic conditions required for impurity activation. However, due to the extremely short duration of the process, the heat is strictly confined within the submicron-level implanted layer, with virtually no temperature rise in the deeper parts of the wafer, resulting in a very small heat-affected zone. This non-equilibrium thermal process of "instantaneous high temperature and rapid cooling" achieves an impurity activation rate comparable to or even higher than that of high-temperature furnace tubes, while fundamentally avoiding problems such as dopant re-diffusion and surface morphology degradation caused by prolonged high temperatures in traditional high-temperature furnace tube processes.

[0012] Furthermore, in step S1, the element implanted is one of aluminum, boron, nitrogen, and phosphorus; the temperature of the target disk during implantation is 480~520℃. In this invention, it is preferred to perform hot implantation on the SiC wafer at 500℃, and repair the reduced part of the lattice through dynamic annealing effect, thereby effectively maintaining the continuity of the lattice and creating favorable conditions for subsequent high-temperature activation annealing.

[0013] Furthermore, in step S1, the element implanted is aluminum, the implantation energy is 600~800 keV, and the implantation dose is 5×10⁻⁶. 13 atom / cm 2 The injection angle is 7° and the target plate rotation angle is 22°.

[0014] Furthermore, in step S2, the thickness of the PVD carbon-coated film is 80~120 nm; the equipment vacuum degree is less than 5×10⁻⁶. - 7 mbar, sputtering gas is Ar, gas flow rate is 50-70 sccm, sputtering power is 180-220 W, and substrate temperature is room temperature.

[0015] In this invention, PVD carbon-plated film is preferably used, which has the advantages of low process temperature, good film thickness uniformity, and strong adhesion, and can provide a high-quality protective layer without damaging the wafer.

[0016] Furthermore, in step S3, during laser-activated annealing, the wavelength is 305-310nm, the spot size is 0.5-10mm, and the frequency is 40-80Hz.

[0017] In this invention, laser-activated annealing is used, which uses a focused laser beam to perform scanning instantaneous annealing on the wafer, precisely limiting the energy to the surface injection area, thereby minimizing the thermal impact and improving the annealing efficiency by several orders of magnitude while achieving an ultra-high activation rate.

[0018] Furthermore, in step S4, during the plasma physical etching, O2 or Ar2 plasma is used for physical etching, with a gas flow rate of 900-1100 sccm, a chamber temperature of 150-200℃, and a power of 900-1100W.

[0019] Furthermore, in step S5, the temperature of the sacrificial oxide layer treatment is 1200~1300℃, the time is 20~40min, and the oxygen flow rate is 15-25slm.

[0020] Furthermore, in step S6, the BOE solution wet etching uses a mixture of 45-55% hydrofluoric acid aqueous solution and 35-45% ammonium fluoride aqueous solution, with a volume ratio of 6-8:1, and an etching time of approximately 8-12 minutes.

[0021] This invention overcomes the problems of low activation efficiency, easy surface damage, carbon film residue, and difficulty in large-scale production in existing technologies by employing hot injection to reduce lattice damage, PVD carbon film deposition to suppress surface decomposition, laser annealing for efficient activation, and a multi-step carbon film removal process. It improves activation efficiency while ensuring wafer surface quality; it ensures complete removal of the carbon film, avoids the risk of carbon film residue, and guarantees the electrical performance of subsequent devices. In other words, this invention achieves efficient and low-damage impurity activation of wafers. Compared with existing technologies, this invention not only effectively suppresses thermal decomposition of the SiC surface but also significantly improves impurity activation efficiency while reducing process complexity, thus possessing significant practical application value.

[0022] The present invention also provides the application of SiC devices obtained according to any of the above methods in power MOSFETs and Schottky diodes.

[0023] Compared with the prior art, the present invention has the following advantages: This invention solves the problems of low activation efficiency, easy surface damage, and difficult removal of carbon film residue in existing technologies by employing a combined and synergistic process of high-temperature ion implantation to reduce initial damage, PVD carbon film deposition for high-temperature protection, laser instantaneous and precise annealing, and multi-step progressive carbon film removal. In this invention, 6~8 J / cm 2 Laser instantaneous scanning annealing with high energy density concentrates energy in the injection layer, resulting in a very small heat-affected zone. This avoids problems such as excessive heat budget, doping re-diffusion, and defect reactivation in traditional high-temperature furnace tubes, achieving higher impurity activation rate under milder conditions, with lower sheet resistance and better conduction characteristics. Through a multi-step carbon film removal process involving plasma physical etching, sacrificial oxide layer treatment, and BOE wet etching, the carbon film is completely removed, resulting in a C / Si atomic ratio close to 1:1 and a surface roughness Ra as low as 0.08 nm. This process can be directly used for the large-scale manufacturing of SiC power MOSFETs, Schottky diodes, and other devices. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the method of the present invention.

[0025] Figure 2 These are SEM and EDS elemental content diagrams of the SiC surface after activation and film removal.

[0026] Figure 3 This is an AFM image of the SiC surface after activation and film removal.

[0027] Figure 4 This is the concentration SIMS spectrum of the left, middle and right regions after Al-implanted SiC wafer activation.

[0028] Figure 5This is a map of SiC RS after Al implantation into a SiC wafer for activation. Detailed Implementation

[0029] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0031] Unless otherwise specified, all materials and reagents used in this invention are available from commercially available products in the field.

[0032] Example 1 This embodiment provides an ion implantation method for SiC that achieves laser activation and surface protection through a multi-step carbon film removal process, such as... Figure 1 As shown, the specific steps are as follows: S1. High-temperature ion implantation is performed on the surface of a SiC wafer. The implanted ion species is Al, the energy is 700 keV, and the dose is 5 × 10⁻⁶. 13 atom / cm 2 The injection angle is 7°, the target plate rotation angle is 22°, and the target plate temperature is 500℃.

[0033] S2. A carbon film with a thickness of 100 nm is deposited on the surface of the SiC wafer after high-temperature ion implantation as described in S1 using a PVD method. The vacuum level of the equipment is less than 5 × 10⁻⁶. -7 mbar, sputtering gas is Ar, gas flow rate is 60 sccm, sputtering power is 210 W, and substrate temperature is room temperature.

[0034] S3. The SiC carbon-coated film obtained in S2 is placed in a laser annealing apparatus for laser-activated annealing with an energy of 7 J / cm². 2 The wavelength is 305-310nm, the spot size is 0.5-10mm, and the frequency is 40-80Hz.

[0035] S4. The surface carbon film of the laser-activated SiC wafer obtained in S3 is removed by physical etching with O2 and Ar2 plasma. The gas flow rate is 1000 sccm, the temperature in the chamber is 180℃, and the power is 1000W.

[0036] S5. Perform sacrificial oxide layer treatment on the SiC wafer obtained in S4. The treatment temperature is 1250℃, the treatment time is 30min, and the oxygen flow rate is 20slm.

[0037] S6. The wafer obtained in S5 is subjected to wet etching with BOE solution to remove the oxide layer on the wafer surface, so as to completely remove the residual carbon film. The BOE solution is a mixture of hydrofluoric acid aqueous solution with a mass concentration of about 49% and ammonium fluoride aqueous solution with a mass concentration of about 40%; the volume ratio of the two is 7:1, and the etching time is about 10 minutes.

[0038] The SiC wafer obtained in this embodiment was analyzed as follows: Elemental content results obtained by field emission scanning electron microscopy combined with energy dispersive spectroscopy show that, for example Figure 2 As shown, after activation and film removal, the C and Si element contents on the SiC wafer surface are 51.08 at.% and 48.92 at.%, respectively, with an atomic ratio close to 1:1, indicating that the carbon film has been completely removed during the high-temperature annealing process.

[0039] Atomic force microscopy (AFM) analysis showed that, for example Figure 3 As shown, the surface step undulation is only about ±0.27 nm (from... Figure 3 The highest and lowest values ​​in the third subplot indicate the smoothness of the wafer surface steps. After activation and film removal, the SiC surface is smooth and crack-free, with a roughness parameter Ra of 0.08 nm, lower than the initial roughness of the untreated wafer (Ra = 0.5 nm), indicating that the activation process did not introduce additional surface damage. Here, Ra is based on the scanned area (…). Figure 3 The statistical calculation results of the absolute values ​​of the height deviation of all pixels relative to the reference plane fitted by the least squares method (the second small figure) reflect the flatness level of the surface microtexture.

[0040] Secondary ion mass spectrometry depth profile curves show, as Figure 4 As shown, after activation and film removal, the Al concentration distribution in the left, middle and right regions of the SiC wafer is consistent, and the maximum deviation of the doped layer depth Rp is only 14 nm.

[0041] RS measurement results show that, Figure 5 As shown, after the activation and film removal process, the average RS value of the SiC wafer is 0.46 Ω / cm. 2 Compared to the average RS of 0.55 Ω / cm for unimplanted wafers. 2 The processed wafers achieved good carrier activation efficiency.

[0042] Comparative Example 1 Compared with Example 1, the difference in this embodiment is that the wafer obtained after processing in step S2 in step S3 is placed in a furnace tube for high-temperature activation annealing. The annealing temperature is 1750°C and the annealing time is 30 min, while the rest remains unchanged.

[0043] After high-temperature activation annealing of the furnace tubes, the average RS value was 0.51 Ω / cm. 2 The average RS value of laser annealing is only 0.46 Ω / cm. 2 Laser annealing reduced sheet resistance by approximately 9.8%, which confirms that Example 1 is significantly superior to the traditional furnace tube annealing process in improving the activation efficiency of doped ions.

[0044] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that, in step S3, the energy used during laser-activated annealing is 5 J / cm². 2 or 9J / cm 2 The rest remains unchanged; wafers B1 and B2 are obtained respectively.

[0045] The surface of the wafer obtained in this comparative example was observed. The carbon film on the surface of wafer B1 treated with 5 J / cm² energy remained smooth, and its macroscopic morphology was similar to that of the unactivated state after coating, indicating that the energy density failed to bring the film to the optimal threshold required for full activation and morphology transformation.

[0046] The surface carbon film of wafer B2, treated with 9 J / cm² energy, showed a significant darkening in color and identifiable surface undulations. Although the morphological change was noticeable, the overall transformation was minimal compared to the ideal morphology obtained with 7 J / cm² energy (Example 1), and the surface morphology undulations suggested a tendency for over-processing.

[0047] Comparative Example 3 The difference between this embodiment and embodiment 1 is that step S5 is omitted, while the rest remains the same.

[0048] The wafer obtained in this comparative example was tested, and the results showed that the C and Si element contents on the SiC wafer surface were 91.01 at.% and 8.99 at.%, respectively. This indicates that the carbon film after omitting step S5 cannot be completely removed, which will affect the subsequent detection of device performance.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for activating and protecting the surface of ion-implanted SiC, characterized in that, Includes the following steps: S1. High-temperature ion implantation is performed on the SiC wafer; S2. Perform PVD carbon film deposition on SiC wafers after high-temperature ion implantation; S3. Perform laser-activated annealing on the SiC wafer after carbon film deposition. The energy used in laser-activated annealing is 6~8 J / cm. 2 ; S4. Perform plasma physical etching on the annealed SiC wafer; S5. Perform sacrificial oxide layer treatment on the SiC wafer after plasma physical etching; S6. Perform BOE solution wet etching on the SiC wafer after sacrificial oxide layer treatment to obtain SiC device.

2. The method according to claim 1, characterized in that, In step S1, the element implanted is one of aluminum, boron, nitrogen, and phosphorus; the temperature of the target disk during implantation is 480~520℃.

3. The method according to claim 2, characterized in that, In step S1, the element implanted is aluminum, the implantation energy is 600~800 keV, and the implantation dose is 5×10⁻⁶. 13 atom / cm 2 The injection angle is 7° and the target plate rotation angle is 22°.

4. The method according to claim 1, characterized in that, In step S2, the thickness of the PVD carbon-coated film is 80~120 nm; the equipment vacuum level is less than 5×10⁻⁶. -7 mbar, sputtering gas is Ar, gas flow rate is 50-70 sccm, sputtering power is 180-220 W, and substrate temperature is room temperature.

5. The method according to claim 1, characterized in that, In step S3, during laser-activated annealing, the wavelength is 305-310nm, the spot size is 0.5-10mm, and the frequency is 40-80Hz.

6. The method according to claim 1, characterized in that, In step S4, during the plasma physical etching, O2 plasma is used for physical etching, with a gas flow rate of 900-1100 sccm, a chamber temperature of 150-200℃, and a power of 900-1100W.

7. The method according to claim 1, characterized in that, In step S5, the temperature of the sacrificial oxide layer treatment is 1200~1300℃, the time is 20~40min, and the oxygen flow rate is 15-25slm.

8. The method according to claim 1, characterized in that, In step S6, the BOE solution wet etching uses a mixture of 45-55% hydrofluoric acid aqueous solution and 35-45% ammonium fluoride aqueous solution, with a volume ratio of 6-8:1, and an etching time of 8-12 min.

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