Ablation Free Dicing of 4H-SiC Wafers with Feed Rates up to 200 mm/s by Using Thermal Laser Separation
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Ablation Free Dicing of 4H-SiC Wafers with Feed Rates up to 200 mm/s by Using Thermal Laser Separation Dirk Lewke1, Matthias Koitzsch1, Martin Schellenberger1, Lothar Pfitzner1, Heiner Ryssel1, Hans-Ulrich Zühlke2 1 Fraunhofer Institute for Integrated Systems and Device Technology IISB, Erlangen 2 JENOPTIK Automatisierungstechnik GmbH, Jena
ABSTRACT This paper presents Thermal Laser Separation (TLS) as a novel dicing technology for silicon carbide (SiC) wafers. Results of this work will play an important role in improving the SiC dicing process regarding throughput and edge quality. TLS process parameters were developed for separating 4H-SiC wafers. Separated SiC dies were analyzed and compared with results produced with current state of the art blade dicing technology. For the first time, fully processed 100 mm 4H-SiC wafers with a thickness of 450 µm, including epi-layer and back side metal layers, could be separated with feed rates up to 200 mm/s. Besides the vastly improved dicing speed, the TLS separation process results in two important features of the separated SiC devices: First, edges are free of chipping and therefore of higher quality than the edges produced by blade dicing. Second, the TLS process is kerf free, which allows for reducing the necessary dicing street width and hence increasing the number of devices per wafer. INTRODUCTION AND MOTIVATION Current challenges in energy efficiency, electromobility, and green technologies drive the need for innovative novel power electronics. Since state of the art silicon (Si) based power electronics faces obstacles, e.g., in operation temperature, new materials have to be used for power electronics. The compound semiconductor SiC is a promising candidate for substituting Si as material for high voltage and high power applications [1], [2]. It has numerous advantages over Si, which include a wide band gap, high thermal conductivity allowing for higher junction temperatures and narrower drift regions due to a high critical electrical breakdown field value [3]-[5]. The polytype 4H-SiC is typically preferred for power switching devices because of the availability of the bulk material, its higher mobility, and reduced mobility anisotropy [6]. SiC is almost as hard as diamond [7] and that is why mechanical processing is a major hurdle. Mechanically cutting dies out of SiC wafers with a rotating diamond coated blade is current state of the art separation technology for SiC. The mechanical wafer saw is a well-established dicing technology for Si. However, the hardness of SiC leads to low feed rates, low edge quality and excessive wear of the dicing blade. The increasing demand for SiC based electron devices, like diodes, JFETs, and MOSFETs, drives the need for novel dicing technologies. A novel dicing technology has to fulfill requirements regarding high throughput, high edge quality and long tool life. To meet these requirements, the dicing technology has to be faster than the mechanical wafer saw to increase throughput; it should produce smooth edges free of chippin
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