Defects in 4H-SiC epilayers affecting device yield and reliability

Stahlbush, Robert E.; Mahadik, Nadeemullah A.; Bonanno, P. L.; Soto, Jake; Odekirk, B.; Sung, Woongje; Agarwal, Anant

doi:10.1109/irps48227.2022.9764473

Cited by 6 publications

(1 citation statement)

References 11 publications

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“…The primary sources of BPDs include (1) BPDs originating from the substrate that propagate into the drift region; (2) BPDs formed in the epitaxial layer (i.e., the drift region) during epitaxial growth; (3) BPD clusters formed due to inclusions (SiC down-fall); (4) small and tight BPD clusters formed around micropipes; (5) BPDs formed near the implanted region after P-type implantation and activation annealing [34]. A series of process improvements have been made, such as introducing a recombination-enhanced buffer layer between the substrate and the drift region, a KOH etching process before the conventional epitaxial growth to create BPD etch pits for enhancing the conversion of BPDs to threading edge dislocations (TEDs), and using ultraviolet photoluminescence (UVPL) on wafers to screen out dies with BPDs [37][38][39][40]. Stahlbush et al have demonstrated the high quality of commercial SiC wafers with an epi-layer thickness of 10 µm suitable for the 1.2 kV rating, and some vendors have achieved a near-equivalent quality of SiC wafers for the 3.3 kV rating with a 30 µm epi-layer thickness [34].…”

Section: Discussionmentioning

confidence: 99%

An Investigation of Body Diode Reliability in Commercial 1.2 kV SiC Power MOSFETs with Planar and Trench Structures

Qian,

Shi,

Jin

et al. 2024

Micromachines

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The body diode degradation in SiC power MOSFETs has been demonstrated to be caused by basal plane dislocation (BPD)-induced stacking faults (SFs) in the drift region. To enhance the reliability of the body diode, many process and structural improvements have been proposed to eliminate BPDs in the drift region, ensuring that commercial SiC wafers for 1.2 kV devices are of high quality. Thus, investigating the body diode reliability in commercial planar and trench SiC power MOSFETs made from SiC wafers with similar quality has attracted attention in the industry. In this work, current stress is applied on the body diodes of 1.2 kV commercial planar and trench SiC power MOSFETs under the off-state. The results show that the body diodes of planar and trench devices with a shallow P+ depth are highly reliable, while those of the trench devices with the deep P+ implantation exhibit significant degradation. In conclusion, the body diode degradation in trench devices is mainly influenced by P+ implantation-induced BPDs. Therefore, a trade-off design by controlling the implantation depth/dose and maximizing the device performance is crucial. Moreover, the deep JFET design is confirmed to further improve the body diode reliability in planar devices.

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Section: Discussionmentioning

confidence: 99%

An Investigation of Body Diode Reliability in Commercial 1.2 kV SiC Power MOSFETs with Planar and Trench Structures

Qian,

Shi,

Jin

et al. 2024

Micromachines

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Formation mechanism of horizontal-half-loop arrays and stacking fault expansion behavior in thick SiC epitaxial layers

Mahadik

Stahlbush

Sung

2022

Journal of Applied Physics

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The formation mechanism of half-loop arrays (HLAs) that form parallel (horizontal) to the step-flow direction in 120 μm thick 4H-silicon carbide (SiC) epitaxial layers was investigated using ultraviolet photoluminescence (UVPL) imaging and x-ray topography (XRT). The horizontal-HLAs are generated by the multiplication and glide of basal plane dislocation (BPD) loops that are created within the epitaxial layer. The BPD loops were initiated after ∼40–50 μm of growth from a small BPD segment, which glides toward the surface as well as the substrate interface. BPD multiplication occurs and several loops are generated. Some of these loops are terminated by the growth front and create HLAs due to the 4° offcut of the wafer. XRT images show that successive BPD loops interact with previously generated HLA segments. Successive loops also interact with the moving growth front and create new HLAs that are spatially displaced from the previous HLA segments. These appear as a string of horizontal-HLAs in the UVPL images. The expansion of stacking faults (SFs) from these horizontal-HLAs was investigated, and we show that they all lie on the same basal plane. The complex defect structure is created in the epitaxial layer from a single BPD loop but extends over a large (∼5 × 0.5 cm2) region of the SiC wafer during epitaxial growth. The high density of HLAs and BPDs would generate several SFs upon device operation leading to severe device degradation.

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Optoelectronic and structural characterization of trapezoidal defects in 4H-SiC epilayers and the effect on MOSFET reliability

El Hageali,

Guthrey,

Johnston

et al. 2023

Journal of Applied Physics

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To this day, trapezoidal defects are found in clusters and high counts in wafers representing the industry standard in terms of material quality being produced. This study sheds light on the nature, origin, behavior, and impact of this defect on device yield and reliability. Trapezoidal defects in 4H-SiC epitaxial layers were investigated by photoluminescence (PL) imaging, scanning electron microscopy (SEM), cathodoluminescence spectrum imaging (CLSI), SEM electron beam induced current (EBIC) imaging, and by transmission electron microscopy (TEM) observation. The bar-shaped stacking faults were identified by the PL and CL measurements with a peak emission wavelength of 420 and 450 nm. An optoelectronic behavioral study based on the recombination enhanced dislocation glide mechanism revealed how expanding dislocations and stacking faults interact with each other. Combining the luminescence and microscopy results, the nature of the stacking faults was identified as being a combination of Shockley-type and Frank-type stacking faults. The TEM analysis showed that these defects originate from the substrate and the stacking sequences of some of the faults were determined as (…2, 4, 2…) and (…2, 3, 2…) in the Zhdanov's notation by high-resolution TEM. The origin of this defect is speculated based on our results and previous reports. The EBIC imaging showed that the high density of SFs in these towers is a strong site of carrier recombination, which presumably has an impact on the transfer characteristics of SiC devices. Furthermore, these defects have shown to impact metal oxide semiconductor field effect transistors electrical performance via an increase in the on-state resistance depending on the coverage percentage of the tower of defects in the active area of the device.

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Defects in 4H-SiC epilayers affecting device yield and reliability

Cited by 6 publications

References 11 publications

An Investigation of Body Diode Reliability in Commercial 1.2 kV SiC Power MOSFETs with Planar and Trench Structures

An Investigation of Body Diode Reliability in Commercial 1.2 kV SiC Power MOSFETs with Planar and Trench Structures

Formation mechanism of horizontal-half-loop arrays and stacking fault expansion behavior in thick SiC epitaxial layers

Optoelectronic and structural characterization of trapezoidal defects in 4H-SiC epilayers and the effect on MOSFET reliability

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