In this blog post, we delve into performance enhancements of SiC and GaN devices through the optimization of doping profiles using ion implantation. Our focus revolves around the pivotal role played by Dynamic SIMS (D-SIMS) and more specifically the IMS 7f-Auto in this optimization process.
The Strategic Significance of SiC and GaN Studies
Widely acknowledged as instrumental in reducing energy consumption, power electronic components for wide-bandgap semiconductors, namely SiC and GaN, assume a strategic position in the realms of electric mobility and power conversion. Despite the rapid evolution of SiC and GaN technologies, the fabrication processes encounter persistent challenges that impose limitations on device performance. The optimization of ion implantation doping profiles is one of the mostcritical factors in enhancing SiC and GaN device performance. The variation in implantation angles, known as tilt and twist angles, becomes paramount in avoiding or promoting channeling effects. Equally crucial is understanding the impact of implantation temperature which is widely used to the moderate implant defects on these substrates.
Strength in Collaboration: IBS and Project Initiatives
Collaboration emerges as a powerful force in addressing these challenges. Ion Beam Services (IBS), a vital partner in the YESvGaN1 and PIONEER2 projects, aims at developing dedicated ion implanters (Flexion and Flexion-P) for SiC and GaN susbtrates and at optimizing the associated doping processes, a prerequisite for manufacturing these crucial components and advancing this strategic industrial sector in France and Europe. As part of their efforts, IBS scrutinizes the effects of various implantation conditions, including energy, angle, dose, and temperature, on SiC and GaN samples. The IMS 7f-Auto (CAMECA factory, France) provides a robust platform for comparing different implantation conditions.
We were looking to validate the processes of our pilot line, but above all to optimize the processes and capabilities of our new Flexion and Flexion-P implanters for SiC and GaN. The collaboration with CAMECA and the analyses carried out on the IMS 7f-Auto enabled us to identify the optimum channeling for deep implanting in SiC, while for GaN, it showed us the influence of factors such as tilt and Dose and Temperature Influence in GaN temperature during implantation.
R&D Team, F. TORREGROSA & S. MORATA, at Ion Beam Services (IBS), France
Optimizing Processes with CAMECA IMS 7f-Auto
Turning our attention to the tool of choice, the CAMECA IMS 7f-Auto, we explore its role in optimizing implementation processes for SiC and GaN samples.
Twist Angle Variations in SiC
In the case of 4H-SiC samples implanted with 27Al, varying twist angles around different theoretical channeling directions becomes a focal point. D-SIMS data reveals notably two well-established channeling directions (T9, T10, T11 and T12, T13, 14 respectively) with the second channeling direction (1,1,-2,3) (corresponding to T12, T13, T14 samples) enabling deeper implantation at a same implantation energy. The two directions prove less sensitive to twist angle variations within the range of [-2°, +2°], as validated by simulations. SIMS data reveal that channeling directions have a strong influence on the 27Al implanted profiles in SiC (fig. 1) and allow implantation of deep layers without the need of an expensive high energy implanter. The profiles' insensitivity to twist angles renders this method suitable for production use.
Fig. 1. Al depth profiles of the six 4H-SiC, 27Al implanted samples.
Understanding Tilt Angle in GaN with 24Mg Implantation
Shifting focus to GaN, specifically during 24Mg implantation (45 keV, dose of 5E14 at/cm²), the effect of tilt angle variation is scrutinized. The data (fig. 2) reveal that a minimum tilt angle of 9° is crucial to avoid channeling in GaN, where only 7° is required in Silicon.
Fig. 2. Effect of tilt angle on Mg implantation profiles in GaN. T for tilt angle (e.g., T8 correspond to 8° tilt angle).
Dose and Temperature Influence in GaN
In the subsequent step, maintaining a tilt angle of 9°, the study explores the effect of implantation temperature (room temperature [RT] vs. 500°C) for different doses (2E15 and 5E14 at/cm²). Notably, the Mg D-SIMS profiles (fig. 3) obtained with doses up to 2E15/cm² do not exhibit abnormal shifts or significant dose losses when implanted at 500°C. This reinforces that no excessive etching occurred under these specific conditions, contrasting with the reported issues in GaN hot implantation at higher temperature.
Fig. 3. Mg depth profiles of the four GaN, 24Mg implanted samples with different doses and temperatures.
IMS 7f-Auto: Your Tool of Choice for Innovation
In SiC, the IMS 7f-Auto excels at identifying optimal channeling for deep implantation, while in GaN, it sheds light on the influential factors of tilt and temperature during implantation. Undoubtedly, it stands as the tool of choice for determining and validating the best implantation conditions, fostering innovation in power electronic components for wide-bandgap semiconductors.
Analytical conditions on the IMS 7f-Auto
4H-SiC samples: O2+ primary ion bombardment at 10 keV impact energy was used to measure 27Al, a mass resolution of ~2000 and electron gun ON. Analysis duration: ~20 and ~33 minutes / run. 2 runs / sample were performed.
GaN samples: Cs+ primary ion bombardment, collection of positive secondary ions MCs+ at 5 keV impact energy with low mass resolution was used to measure 24Mg. Analysis duration: ~11 minutes / run. 2 runs / sample were performed.
1YESvGaN project: European project for the development of a new class of vertical GaN power transistors, combining the performance benefits of vertical Wide Band Gap (WBG) transistors with the cost advantages of established silicon technology.
2PIONEER project: French project focused on developing innovative ion implantation equipment needed to produce SiC and GaN materials.
Authors: Laura CREON, Jinlei REN, Seoyoun CHOI, Marie ADIER