# Formation of Highly Doped and Defect-Free P-Type Junctions in SiC by Using High Temperature Implants and UV-Laser Annealing

Louis Thuries, Zeinab Chehadi, Fulvio Mazzamuto, Mathieu Opprecht, Sébastien Kerdilès, Mihai Lazar

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Louis Thuries, Zeinab Chehadi, Fulvio Mazzamuto, Mathieu Opprecht, Sébastien Kerdilès, et al. Formation of Highly Doped and Defect-Free P-Type Junctions in SiC by Using High Temperature Implants and UV-Laser Annealing. International Conference on Silicon Carbide and Related Materials (ICSCRM 2024), Sep 2024, Raleigh (North Carolina), United States. pp.712-713. hal-04796873

HAL Id: hal-04796873

https://cnrs.hal.science/hal-04796873v1

Submitted on 21 Nov 2024

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Distributed under a Creative Commons Attribution 4.0 International License
Formation of highly doped and defect-free p-type junctions in SiC by using
high temperature implants and UV-Laser Annealing

L. Thuries¹), Z. Chehadi¹), F. Mazzamuto²), M. Opprecht³), S. Kerdilès³, M. Lazar⁴)

1) Laser Systems & Solutions of Europe (LASSE), Gennevilliers, France

2) Axcelis Technologies, Inc., Beverly, MA USA

³) Université Grenoble Alpes, CEA LETI, Grenoble, France

4) L2n, UMR CNRS 7076, UTT, 12 rue Marie Curie CS 42060, 10004 Troyes

E-mail: louis.thuries@screen-lasse.com

Formation of highly doped and defect-free p-type junctions at reduced cost remains one of the important limitations for the manufacturing of high performance SiC devices. Today process of record presents some limitations in terms of defectivity, maximal implanted doses (~1E15 at/cm²) and cost (carbon cap required during furnace annealing to avoid SiC dissociation) [1]. Indeed, if the implanted dose becomes too important (>4E15 at/cm²), basal stacking faults (BSF) are formed during the furnace annealing step [2].

To overcome these limitations, an alternative solution based on high-temperature (>500°C) ion implantation and microsecond ultraviolet laser annealing (later referred as UV-LA) is proposed. This solution presents the advantages to enable implantation and activation of high doses of aluminum (1E16 at/cm²) while remaining defect-free. Moreover, the manufacturing costs with this solution are reduced since there is no need of any carbon cap during the laser annealing step.

UV-LA is an attractive solution for the activation of high-doses in SiC thanks to its short irradiation time (<100 µs) and the extremely high temperatures (>2500°C) enabled by the use of UV wavelength in the range of 300 to 400 nm which provides a surface-localized anneal. Moreover, the common optimization of laser fluence (E<sub>x</sub>) and irradiation time (τ<sub>x</sub>) permits to have an accurate control of the temperature profile during the laser annealing as described in Fig. 1.

4H-SiC substrates with 4 µm of low doping epitaxy were implanted with a dose of 1E16 at/cm² by using a multistep approach to form an Al box profile over 250 nm as shown in Fig. 2. Increasing temperature is expected to reduce crystal defectivity during the implantation step which later will help to boost dopants activation [3]. In this scope, two implant temperatures have been studied: 500°C and 800°C.

Then the two samples (500 and 800°C) have been cleaved. For each implant temperatures, one half has been directly laser annealed whereas the other half has been carbon capped and furnace annealed under standard conditions (1700°C during 30 min) [1]. Laser annealing conditions have been optimized to reach temperatures below the SiC melting point to avoid SiC dissociation as shown in Fig. 3.

To assess crystal quality before and after annealing, samples were measured by Raman spectroscopy (476 nm). Spectra were normalized to the E2T peak (776 cm⁻¹) [4]. Fig. 4 demonstrates that crystal recovers proportionally with laser irradiation times (dwell) until reaching the level of pristine SiC for the sample at 800°C. Same trend is observed for the 500°C implanted sample. This trend is later confirmed in Fig. 5 since the levels of ThermalWave (thermal emissions responses are directly proportional to implant induced damage density [5]) are almost similar between the laser annealed, furnace annealed and a pristine SiC samples which confirmed again that UV-LA can recover high-doses implanted SiC. TEM images are not shown here; however, we do not observe the presence of BSF on the laser annealed samples. Dopant activation has been later assessed by Sheet Resistance (4PP Rs) and SCM-SMM (not shown here). As shown in Fig. 6, the Rs of the laser annealed samples are up to 3 times lower than the reference one [1] annealed in furnace. Moreover, the Rs of the 800°C sample is 25% lower than the sample implanted at 500°C. This difference may be attributed to the better crystal quality during the implantation as shown in Fig. 5.

In summary, we have demonstrated that UV-LA is able to fully cure high-doses implanted SiC but also leads to higher activation ratio than the standard furnace anneal. This improvement can be attributed to the absence of BSF that can act as deep level traps [6]. This solution is also cost-effective since it does not
require the use of any carbon cap. Moreover, increasing the implantation temperature helps to boost the
dopant activation by reducing the crystal damage during the implantation.

[1] Y. Negoro et al. Journal of Applied Physics, 96(9), 4916-4922 (2004).

[2] R. Nipoti et al. Materials Science in Semiconductor Processing, 78, 13-21 (2017).

[3] N. S. Saks et al. Appl. Phys. Lett. 84, 5195 (2004)

[4] Q. Jia et al. Appl. Phys. Lett. 112(19), 192102 (2018)

[5] S. Wurn et al. Appl. Phys. A 47(2):147-155 (1988)

[6] G. Pensl et al. Microelectronic Engineering, 83(1), 146-149 (2006)

<figure><img src="image_3.png" /><figcaption>Fig. 1: Thermal Simulations of UV-LA</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Fig. 2: SIMS profiles of as-implanted samples at 500°C and 800°C (1E16 at/cm²)</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 3: Thermal Simulations with optimized UV-LA conditions for SiC Activation</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 4: Normalized (ET2) Raman spectrums before and after UV-LA for the 800°C implanted sample</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 5: ThermalWave levels for pristine, as-implanted, furnace and laser annealed samples</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 6: Sheet Resistances for furnace (500°C implanted, and laser annealed samples (respectively 500 and 800°C implanted)</figcaption></figure>