Lattice Recovery Behavior of 4H-SiC by Ion Implantation: Laser Annealing and Thermal Annealing +

4H-SiC, as a wide bandgap semiconductor, has important applications in power electronic devices. Due to its high binding energy and low diffusion coefficient, ion implantation has become the main means of achieving selective doping. PAM-XIAMEN can provide ion implantation services for SiC wafers. For details, please consult: [email protected].

However, the injection process can introduce a large amount of lattice damage, such as point defects, dislocation loops, and stacking faults, which seriously affect the electrical performance of the device. Therefore, annealing treatment becomes a key step in restoring crystal structure and activating dopants. Although traditional high-temperature furnace annealing can partially restore the lattice, it may introduce secondary defects; Laser annealing, as a non-equilibrium process, has the advantages of fast, low-temperature, and localized processing, and has received widespread attention in recent years.

1. Lattice Recovery and Defect Suppression in 4H-SiC by Laser Annealing

Calabretta et al. systematically studied the lattice recovery effect of XeCl laser annealing assisted by graphite coating on P/Al double injected 4H-SiC epitaxial layer. Research has found that a 180nm graphite coating can effectively protect the surface from erosion and maintain good crystal quality at an energy density of 0.6 J/cm². Through μ – Raman analysis, it was found that the full width at half maximum of the E₂ (TO) mode decreased to (4.5 ± 0.1) cm⁻¹ at 0.6 J/cm², which is better than the traditional furnace annealing of 4.9 cm⁻¹, indicating that laser annealing has potential in crystal recovery.

Further MAADF-STEM and HAADF-STEM analysis showed that no extension defects, such as dislocation loops or stacking faults, were found in the laser annealed samples, while they were commonly present in traditional annealed samples. Instead, local point defect clusters appeared in the laser annealing area, manifested as bright spots in the image. These areas were considered to be carbon gap atom clusters, but due to the extremely short annealing time, they did not further evolve into extended defects. This discovery indicates that laser annealing can effectively suppress the formation of elongation defects, but the complete elimination of point defects remains a challenge.

Fig. 1 XTEM comparison between a) high-temperature annealing and b) laser annealing samples, showing fewer defects in the laser samples

Fig. 2 MAADF-STEM image shows point defect agglomeration area

2. 4H-SiC Lattice Strain Recovery and Defect Evolution during Thermal Annealing

Mello et al. investigated the lattice strain recovery of P/Al injected 4H-SiC after high-temperature annealing (1675-1825°C) using high-resolution X-ray diffraction and reciprocal space mapping system. Research has found that ion implantation introduces significant tensile strain along the c-axis direction, with an initial strain of up to 11.6 × 10⁻³, but after annealing at 1825°C, the strain decreases to about 1.6 × 10⁻³, a decrease of 7 times. It is worth noting that the in-plane strain can always be ignored, indicating that lattice deformation mainly occurs along the [0001] direction.

Despite a significant reduction in strain, HRDC and TEM analysis showed that the crystal structure had not fully recovered. During the annealing process, point defects (such as carbon vacancies V_c, carbon gaps C_i, and anti site defects) aggregate to form nanoclusters with sizes ranging from 5-20nm. These clusters exhibit diffusion scattering background in XRD and exhibit broad emission bands in the range of 420-570nm through PL spectroscopy, corresponding to the luminescence of D_I and D_II defect centers.

Fig. 3 HRDC spectrum of strain recovery and defect scattering: experimental (black solid line) and simulation curves (red solid line) of (a), (b) P injection (sample RS) and (c), (d) Al injection (sample RP)

Fig. 4 HRDC spectra of strain recovery and defect scattering under thermal annealing: experimental (black solid line) and simulation curves (red solid line) of (a), (b) P injection (sample RS) and (c), (d) Al injection (sample RP)

Fig. 5 Room temperature PL spectra of P injected samples before (sample RS) and after (sample R6) high-temperature annealing

Fig. 6 Room temperature PL spectra of a) P and b) Al injected samples after annealing

Fig. 7 HRTEM images after annealing show defect clusters and dislocation loops: (a), (b) P injected into sample R6; (c), (d) Al injected into sample R11

3. Lattice Recovery Mechanism and Limitations of Laser and Thermal Annealing

There are significant differences in the lattice recovery mechanism between the two annealing methods:

Laser annealing is carried out under non thermal equilibrium conditions, with an extremely short annealing time (nanosecond level), allowing the dopant to quickly enter the substitution site and ionize, but the diffusion and annihilation of point defects are insufficient. Therefore, although the extension defects are suppressed, the aggregation of point defects still exists.

High-temperature annealing is carried out under thermal equilibrium conditions, with a relatively long annealing time (in minutes), which is beneficial for the migration and aggregation of point defects, but also promotes the formation of dislocation loops and stacking faults. In addition, the migration energy of carbon interstitial atoms at high temperatures is relatively low (~1eV), making it easy to form stable composite defect structures, such as (C₂) Si and (C₂) C – (C₂) Si clusters.

4. Correlation between Electrical Properties and Lattice Recovery of 4H-SiC

Calabretta et al. found through CTLM measurement that laser annealing can achieve a thin layer resistance of (7.28 ± 1.15) × 10²Ω/sq at 0.9J/cm², which is better than the traditional furnace annealing of (9.16 ± 1.25) × 10²Ω/sq. However, under the condition of 0.6J/cm², although μ – Raman showed a high P activation concentration of 7 × 10¹⁹ cm⁻³ through FTA mode analysis, its thin layer resistance was still as high as 3.17 × 10⁴Ω/sq. This contradiction indicates that dopant activation is a rapid process, while lattice damage recovery is a slow process, and there are differences between the two on a time scale.

Mello et al. also pointed out that although high-temperature annealing significantly reduces lattice strain, residual point defect clusters still compensate for charge carriers and affect electrical activation efficiency.

During the lattice recovery process of 4H-SiC ion implantation layer, laser annealing and thermal annealing exhibit obvious complementary characteristics: laser annealing can quickly activate dopants and effectively suppress extension defects, especially suitable for devices with high requirements for surface morphology and local electrical control; Thermal annealing is more effective in reducing overall lattice strain, but it is prone to introducing secondary defects during the process, so it is necessary to optimize the trade-off between annealing temperature and time parameters. Future research should focus on composite annealing strategies, such as laser pretreatment+high-temperature short-term annealing, to achieve the optimal balance between lattice recovery and electrical properties.

Whether you need 4H-SiC for research or for industrial applications, please contact us email at [email protected] and [email protected].

 

References:

1. Calabretta, C., Pecora, A., Agati, M., Muoio, A., Scuderi, V., Privitera, S., … & La Via, F. (2024). Exploring crystal recovery and dopant activation in coated laser annealing on ion implanted 4H–SiC epitaxial layers. Materials Science in Semiconductor Processing, 174, 108175.
2. Mello, D., Severino, A., Burresi, E., Anastasi, G., Piluso, N., Arena, M., & Tapfer, L. (2025). Lattice recovery and microstructural defects in thermally annealed phosphorous and aluminum implanted (0001) 4H-SiC. Journal of Applied Physics, 137(17).