Influence of a New Defect Doubling Mechanism on High Power 4H-SiC Devices –

PAM-XIAMEN can supply conductive and semi-insulating SiC wafers, please consult: [email protected].

1. Abstract

The demand for high-power devices made of silicon carbide (SiC) is increasing in fields such as electric vehicles, rail transportation, renewable energy, and large-scale applications in the power grid. Their performance and reliability are greatly affected by crystal defects such as basal dislocations and stacking faults. This article reveals the microscopic mechanisms of three novel interactions between basal plane dislocations(BPDs) and threading mixed dislocations(TMDs), which lead to a significant increase in Shockley stacking faults (SSF) in SiC epitaxial layers. Firstly, a dual interaction model is proposed, in which two SSFs react with the same TMD, causing the SSFs to slip along multiple basal planes and forming locked partial dislocation dipoles (PDDs) due to the attraction between dislocations with opposite signs. Secondly, the interaction between SSF and tilted TMD was described, which can induce the generation of another SSF. The third mechanism involves the unlocking of locked PDDs when they intersect with other SSFs, releasing freely sliding dislocations and forming new SSFs, achieving further proliferation of stacking faults. The proliferation of SSF significantly increases the reverse leakage current and on resistance of the device, seriously damaging the reliability and performance of SiC high-power devices, ultimately leading to device failure.

2. Sample Preparation

This study used commercially prepared 180μm thick n-type doped SiC epitaxial layer as samples, with a doping concentration of 2 × 10 ¹⁴ cm ⁻ ³, grown on a 100 mm 4H-SiC substrate. The customized microscopy system equipped with 4W, 355nm ultraviolet lasers and high-precision automatic XYZ stage was used to perform ultraviolet photoluminescence (UVPL) imaging on the chip. The UVPL image acquisition of the entire chip takes about 5s, and a 665nm long pass filter and liquid nitrogen cooled CCD detector are used during the imaging process, with a spatial resolution of 2μm.

A complex fault structure was observed in the entire wafer image, whose formation and propagation mechanisms have been explored in previous studies, as shown in Fig. 1. This defect originates from the deflection of TMD towards the basal plane, forming the Frank fault, and undergoes multiple layer fault type transformations during epitaxial growth, including the generation of several SSFs.

Fig. 1 UVPL image of a complex fault containing two SSFs

Researchers focused on analyzing two SSFs and revealed their proliferation mechanism from two to five under UV excited carrier injection conditions. The expansion and proliferation phenomenon of such SSFs may occur in the bipolar operating mode of the device, ultimately leading to device failure. The researchers further utilized the same UVPL system to continuously image the selected SSF region with a spatial resolution of 1 μ m, with a single frame exposure time of approximately 1s. The carrier injection induced by ultraviolet excitation triggers the expansion and proliferation of SSF, allowing for clear observation of the interaction between SSF and TMD, as well as the novel proliferation behavior of SSF. A sequence of UVPL images demonstrating the dynamic process of SSF proliferation was generated using self-made image processing software.

3. Conclusion

This study reveals several new mechanisms of the interaction between SSF and TMD in silicon carbide. Firstly, a model is proposed for the dual interaction between two SSFs located on adjacent basal planes and an approximately perpendicular TMD, which results in the generation of a partial dislocation dipole separated by the two basal planes and triggers the sliding of the two SSFs between the three basal planes. The PDD formed by the mutual attraction between Si(g) and C(g) dislocations is usually locked and mostly distributed at positions separated by one to two basal planes.

Fig. 2 Dual action mechanism of SSF and TMD

Secondly, another interaction mechanism was described, namely the reaction between SSF and tilted TMD. Due to the large lateral spacing between Si(g) and C(g) in this situation, the generated PDD is not locked, allowing the Si (g) portion to slide freely, thereby generating a new SSF.

Fig. 3 Interaction between BPD and tilted TMD

In addition, it involves unlocking locked PDDs to achieve further proliferation of SSF. When the newly formed sliding SSF intersects with a locked PDD and combines with a portion of the dislocations to form a mixed dislocation structure, which contains both Si and C components, this process is triggered. Subsequently, the Si component continued to slip, while the C component relaxed to the equilibrium position. At this point, the Si component acts as a freely sliding dislocation, guiding the formation of another movable SSF. This type of interaction can continue to occur until all existing PDDs are fully unlocked, continuously generating additional SSFs.

Fig. 4 Unlocking mechanism of partial dislocation dipoles

The study also shows that in the initial state, there is no local area of SSF. After the multiple interactions mentioned above, up to five SSFs can be generated on the substrate, significantly increasing the leakage current and on resistance of high-power SiC devices, severely restricting their reliability and lifespan.

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

 

Reference:

Mahadik, N. A., Dudley, M., Raghothamachar, B., Chen, Z., Stahlbush, R. E., Hinojosa, M., … & Sung, W. (2024). Mechanism of novel defect multiplication impacting high power 4H-SiC devices. Materials & Design, 248, 113435.