Channel Implantation and Crystal Plane Effect of High Energy Al Ions in 4H-SiC +

4H-SiC has become an ideal wide bandgap semiconductor material for high-voltage and low loss power devices due to its high breakdown electric field, high electron saturation drift rate, and excellent thermal conductivity. In the voltage range of 1.2-3.3 kV, SiC MOSFETs are gradually replacing Si IGBTs, significantly reducing switching losses, and are widely used in electric vehicles and high-speed railway drive systems. To further reduce the on resistance, a super junction (SJ) structure is introduced into SiC devices, with the core being the preparation of alternating p-type and n-type doped pillars. However, the extremely low impurity diffusion coefficient in SiC makes it difficult for traditional thermal diffusion processes to achieve deep doping regions, making ion implantation a key technology. High energy ion implantation, especially the use of channeling technology, provides a potential low-cost alternative for achieving deep doping. PAM-XIAMEN is able to provide ion implantation services for 4H-SiC wafer, please consult: [email protected]

1. Aluminum Ion Implantation

1.1 Limitations of Ultra-High Energy Non-Channel Injection

In the study of high-energy and ultra-high energy aluminum ion implantation, Belanche et al. revealed the characteristics and limitations of different implantation methods through experiments. In the ultra-high energy non channel injection experiment, aluminum ions with 30MeV and 48MeV were implanted into 4H-SiC. Although the implantation depths reached 7.9μm and 11.9μm, respectively, which were consistent with SRIM simulation, significant charge dispersion occurred in the beam, especially at 48MeV where multiple charge state peaks (such as Al ⁵⁺, Al ⁶⁺, Al ⁸⁺) appeared, resulting in multiple peaks in the doping profile and a decrease in uniformity. In addition, high-energy injection is accompanied by a decrease in beam intensity and potential activation of heavy impurity nuclei, which limits its practical applications.

1.2 Technical Challenges and Breakthroughs in High-Energy Channel Injection

To achieve deeper and more uniform doping at lower energies, high-energy channel injection technology has been proposed. This technology utilizes crystal channels to reduce ion lattice collisions and significantly increase implantation depth. Belanche et al. conducted channel injection experiments along the [0001] and [1123] directions at 12, 15, and 20 MeV. The main challenge they faced was the extremely small critical angle (θ _crit) (such as only 0.08 ° at 20 MeV), which was much larger than the crystallographic tolerance of commercial SiC chips (0.5 °~5 °). Therefore, high-precision crystallographic pre characterization and sample alignment were required.

The research team compared two alignment methods: one is to pre characterize through X-ray diffraction and combine it with customized aluminum sample racks; The second is to use Rutherford backscattering spectroscopy (RBS) channel map and a six axis angle measuring instrument to achieve in-situ high-precision alignment. The latter successfully achieved channel injection of 1-20MeV on the 3MV accelerator of HZDR, becoming the highest energy aluminum channel injection case in the literature to date.

SIMS measurements show that the channel depths along the [0001] direction at 12 and 15MeV are 7.22μm and 7.97μm, respectively, with a depth ratio (R_ch/Rp) of 1.69; The depths along the [1123] direction are 9.96μm and 11.02μm, respectively, with a depth ratio of 2.34, indicating that 17° oblique injection can significantly improve penetration depth, but the concentration uniformity is poor. In addition, the injection dose has a significant impact on the channel effect: as the dose increases, crystal damage accumulates, leading to a decrease in channel rate and an increase in random scattering. At low doses, the direction can approach a “box shaped” profile, while at high doses, a clear trailing edge appears; The [1123] direction is less sensitive to dose changes due to its larger channel cross-section, making it more suitable for deep injection applications.

Fig. 1 Experimental results of high-energy aluminum channel injection using RBS channel map at the optimal alignment position: (a) diversion along the [0001] direction, (b) diversion along the [1123 ̄] direction

2. Influence of Crystal Plane on Channel Injection

Kato studied the effects of Si face (0001) and C face (000-1) on aluminum channel implantation. Due to the non centrosymmetric structure of 4H-SiC, the atomic arrangement on the Si and C surfaces is different: the concentration of Si atoms per unit area on the C surface is twice that of the Si surface, while the mass of Al and Si atoms is similar, making them more prone to collisions and reducing channel effects.

The experimental results show that whether injected on the C surface treated by mechanical polishing or chemical mechanical polishing (CMP), the channeling component is lower than that on the Si surface (Fig. 2). The comparison between the random injection profile simulated by SRIM and the experiment further confirms this point. Therefore, in the manufacturing of 4H-SiC devices, selecting Si surface for aluminum channel implantation is more beneficial for obtaining deeper doping profiles and higher channel efficiency.

Fig. 2 SIMS distribution of Al concentration in 4H-SiC: (a) Samples before and after annealing of CMP treated Si surface and mirror polished C surface; (b) Samples with CMP treated Si and C surfaces without annealing

The high-energy channel Al ion implantation technology has shown significant advantages in the preparation of 4H-SiC deeply doped regions, especially in overcoming the charge dispersion and beam current limitations of ultra-high energy implantation. By combining RBS channel maps with high-precision angle measuring instruments, alignment accuracy better than 0.01° can be achieved, successfully promoting channel effects. In addition, the selection of crystal planes has a significant impact on channel efficiency, with the Si-face being superior to the C-face because its atomic arrangement is more conducive to the channel movement of aluminum ions.

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References:

1. Belanche, M., Yonezawa, Y., Heller, R., Müller, A., Vockenhuber, C., Martinella, C., … & Grossner, U. (2024). Aluminum channeling in 4H-SiC by high-energy implantation above 10 MeV. Materials Science in Semiconductor Processing, 179, 108461.
2. Kato, M. (2025). Difference between the Si-and C-faces in channeling Al ion implantation along the direction in 4H-SiC. Japanese Journal of Applied Physics, 64(8), 088002.