Characterization and Treatment of Time-dependent Haze Issues in Silicon Carbide Substrate

LIU Xiaoqin; CHEN Yanyu; OUYANG Penggen; WANG Siyue

doi:10.16490/j.cnki.issn.1001-3660.2026.19.013

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Surface Technology ›› 2026, Vol. 55 ›› Issue (19) : 148-155. DOI: 10.16490/j.cnki.issn.1001-3660.2026.19.013

Precision and Ultra-precision Machining

Characterization and Treatment of Time-dependent Haze Issues in Silicon Carbide Substrate

LIU Xiaoqin¹, CHEN Yanyu¹, OUYANG Penggen^1,*, WANG Siyue²

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Abstract

As 6-inch 4H conductive silicon carbide (SiC) substrates are increasingly applied in power-device manufacturing, the control of the Time-Dependent Haze (TDH) defect has become more important. However, the ultra-precision machining and surface cleaning of SiC materials face significant challenges, particularly the Time-Dependent Haze (TDH) defect. TDH manifests as the gradual appearance of haze or particulate contaminants on the surface of initially clean wafers after a period of storage under specific environmental conditions, which can severely impact the yield and reliability of subsequent epitaxial growth and device fabrication. Although TDH has been extensively studied in silicon-based materials, research on its formation mechanism and control on SiC substrates, especially the differences between the silicon face (Si-face) and the carbon face (C-face), remains limited. This study aims to systematically investigate the characteristics and formation mechanisms of TDH on 4H-SiC substrates and to propose an effective process control solution to eliminate this defect. In this study, the 6-inch 4H-SiC conductive substrates with a 4° off-axis angle were utilized. A series of comparative experiments were conducted by adjusting the cleaning and rinsing parameters in an automated RCA cleaning line. Specifically, the experiments focused on optimizing the number of ultra-pure water (UPW) replacement cycles in the Quick Dump Rinse (QDR) tank and varying the concentration of hydrofluoric acid (DHF) used for oxide removal. To characterize the defects, a combination of high-intensity light visual inspection (Sunlonge SL8900-W) and a Candela 8520 surface defect inspection system was employed. The chemical composition of surface residues was analyzed quantitatively by Inductively Coupled Plasma Mass Spectrometry (ICP-MS, Perkin Elmer NexION 1000G) for metal ions and Ion Chromatography (IC, Metrohm 940) for inorganic ions. The storage condition for inducing TDH was controlled at 23 ℃ with 50% humidity for 48 hours. Characterization results revealed significant anisotropy in TDH manifestation between crystal faces. The incidence rate of TDH on the C-face (approx. 50% in baseline conditions) was significantly higher than that on the Si-face (approx. 12%). Morphologically, the Si-face exhibited aggregated white particles recognizable by standard defect mapping, whereas the C-face presented a diffuse, mist-like blue haze, which was distinctively identified through anomalies in the Scatter Normal (SCN) channel of the Candela system. Mechanism analysis based on ICP-MS data showed no significant correlation between TDH and metal ion residues (such as Na, Ca). Conversely, IC analysis confirmed that the haze formation was primarily driven by the moisture absorption and recrystallization of residual inorganic ions, specifically chloride ions (Cl^-), ammonium ions (NH₄⁺), and sulfate ions (SO₄^2-), trapped within the surface oxide or damage layers. Notably, sulfate ions were more difficult to remove from the C-face because of stronger adsorption and spatial hindrance within the oxide layer, making standard rinsing less effective. Based on these findings, an optimized rinsing-and-etching cleaning strategy was proposed. The validation experiments demonstrated that simply increasing the terminal UPW rinsing cycles to 3 times effectively eliminated TDH on the Si-face. However, for the C-face, it was necessary to simultaneously increase the DHF ratio from the standard 1 : 50 to 1 : 30 to enhance the removal of the oxide layer containing trapped deep-level ions. The optimized process successfully reduced the TDH incidence rate to 0% for both Si- and C-faces, significantly improving the long-term surface quality stability of the substrates. This study reveals the differences in the formation mechanisms of time-dependent haze on different silicon carbide crystal faces, providing engineering guidance for the low-cost and high-efficiency improvement of related cleaning processes, which holds significant practical application value for enhancing the mass production yield.

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silicon carbide substrate / time-dependent haze / defect characterization / surface cleaning / ion residue / process optimization

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LIU Xiaoqin, CHEN Yanyu, OUYANG Penggen, WANG Siyue. Characterization and Treatment of Time-dependent Haze Issues in Silicon Carbide Substrate[J]. Surface Technology. 2026, 55(19): 148-155

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