The Commercial Availability of Larger-Diameter Sic Substrates and Improved Crystalline Quality Has Fostered an Ever-Increasing I
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THINK TANK Silicon carbide proving its value as a semiconductor substrate The commercial availability of larger-diameter SiC substrates and improved crystalline quality has fostered an ever-increasing interest in the development and manufacture of power electronic devices, exploiting the unique electrical and thermophysical properties of this wide-bandgap semiconductor material. Silicon carbide (SiC) isn’t a new material, but its use as a semiconductor substrate is helping to advance power electronics and high-frequency electronics applications. Silicon carbide is a compound semiconductor and wind energy; and industrial/commercial cost parity with silicon power devices in the material, synthesized by combining silicon applications such as server power supplies, years to come. and carbon, both from group IV of the UPS for data centers, motor drives and periodic table. It has superior properties medical imaging systems, all benefit from State-of-the-art bulk growth of SiC crystals relative to silicon, in terms of handling higher high-voltage and high-efficiency devices is carried out by the seeded sublimation voltages and temperatures. These increased made from SiC. The high-frequency devices process, often referred as the physical vapor capabilities give SiC-based chips the ability used in 5G telecommunication systems, such transport (PVT) growth method. to do tremendous work in small chip sizes. In as repeater stations, digital TV, radars and Conventional melt growth process adapted addition, SiC can switch efficiently at optoelectronic devices, also drive the for growing single crystal silicon can’t be incredible speeds. adoption of SiC material. adapted for SiC because of the lack of a stoichiometric liquid phase at reasonable Today, as markets and applications push Even though the SiC substrate cost is higher pressures. This makes the SiC crystal growth toward the ‘electrification of everything,’ the today when compared to silicon, at a fully technically challenging and time-consuming, need for devices made from SiC is integrated system level it already pays for which constrains the availability of SiC accelerating. The electric vehicle (EV) itself. SiC’s cost advantage will continue to devices, despite demand that is already high industry is literally driving the transition from grow as the cost of SiC substrates and and growing fast. While elemental traditionally used silicon-based power devices falls over time. Apart from cost semiconductor such as silicon can be grown electronic devices to SiC, but other savings, SiC power devices enable as a totally defect-free crystal, to date SiC industries also benefit from the material. miniaturization and system weight reduction, cannot be grown defect-free due to due primarily to their high power densities. fundamental challenges. Power conversion systems used in other With all eyes set on the new electrified era, at transport applications including electrified GT Advanced Technologies we are working SiC substrate development started in the rail, shipping and aircraft; renewable energy on further decreasing the cost of the SiC 1990s at the 2-inch level (i.e. the grown applications including solar photovoltaics substrate and this effort will help in achieving crystal had a diameter of 2 inches) and today 1 PES SOLAR THINK TANK Many applications exist across the power electronics industry for silicon carbide. Most prominently is the EV market which includes electrified vehicles and charging systems. it has reached 6-inch (150 mm) diameter. The availability of larger-diameter wafers is key to lowering the cost of the devices, as device yields increase dramatically as wafer sizes grow. Development work on 200mm (8-inch) SiC boules is well underway at leading SiC producers such as GT Advanced Technologies (GTAT). Our extensive thermal modeling skills, combined with equipment design innovations, has enabled our unique production process, resulting in high-quality boules with low micropipes and other crystalline defects and with the industry’s highest run-to-run reproducibility. With its established supply-chain resources, equipment design and process expertise growing SiC by the PVT method, GTAT is positioned to improve these drivers to offer low-cost, high-volume supply of SiC materials. Types of silicon carbide SiC can be crystallized in hexagonal (H), rhombohedral (R) and cubic (C) crystalline structures. Among the numerous SiC CrystX™ silicon carbide boule measuring 150mm in diameter with a target usable height (UH) of 25mm or polytypes, 4H, 6H and 3C are the materials greater and fewer than 0.5 micropipes per cm2 WWW.PESSOLAR.COM 2 THINK TANK SOLAR POWER WAFER DICING DEVICE FABRICATION DEVICE PACKAGING EPITAXY CHARGING ELECTRIC STATIONS VEHICLES FLAAT WAFER SLICING SIC READY FOR WAFER TOP & BOTTOM OF BOULE REMOVED & PRIMARY FLAT ADDED SILICON CARBIDE CRYSTAL BOULE EMERGES FURNACE HEATS TO tion 2,000+ DEGREES CELSIUS, PROMOTING CRYSTAL oduc GROWTH SILICON & CARBIDE SiC Pr POWDERS PLACED INTO THE FURNACE Production diagram showing the steps involved in making silicon carbide. GTAT focuses strictly on the SiC crystal, supplying it to downstream wafer manufacturers. widely studied and used today. N-type to provide crystals to customers worldwide material to craft, allows many companies to semiconducting 4H substrates with who will wafer them with a 325-micron-thick, both produce the crystal and then the wafers resistivity in the range 0.015 to 0.028 ohm cm atomically smooth surface on the silicon face made from those boules. Because SiC is are used for making power electronic devices by chemical-mechanical planarization. altogether different, many integrated device such as Schottky barrier diodes (SBD), PiN manufacturers (IDMs) need to externally All high-growth-rate epitaxial processes are diodes, metal oxide semiconductor source the crystal material because they based on single-wafer epi reactors. Batch field-effect transistors (MOSFETs), junction cannot produce it themselves. reactors are moving from silane to field-effect transistors (JFETs), thyristors trichlorosilane to achieve high growth rates. The illustration above shows the various and insulated gate bipolar transistors New developments in device fabrication production steps, starting at crystal growth (IGBTs). Semi-insulating (higher-resistivity) steps such as gate oxide and thermal and ending up as devices and circuits inside material is used for ultra-high-frequency oxidation processes further improve an electric vehicle. GTAT has made a devices such as high-electron-mobility reliability, yield and cost. The SiC device strategic decision to focus solely on crystal transistors (HEMTs). GTAT can further tailor value chain includes: growing the crystal growth, using its expertise to seed the the resistivity to a very narrow regime (GTAT’s core business), wafer processing, world’s wafer producers with a large supply depending on the device design and epitaxial layer growth (epi layer thickness of silicon carbide. Companies that specialize customer specifications. depends on breakdown voltage), device in offering silicon wafers can immediately SiC challenges processing, and packaging. The substrate include a SiC offering thanks to GTAT. This cost is currently about 50% of the device broadens and deepens the global supply of While the crystal growth of SiC is challenging, cost and GTAT has an aggressive roadmap to SiC wafers, which helps to push costs lower. the processing of this material into wafers is reduce it. These are market developments the EV also equally challenging because of its high industry welcomes. material hardness (second only to diamond), Enabling a deeper and broader supply of and to the in-built thermal stresses in the silicon carbide Illustrating this, in August 2019 GTAT signed a long-term agreement with GlobalWafers material arising from the growth process. The number of companies able to make (GWC) to supply its CrystX™ silicon carbide GTAT’s silicon and sapphire customers silicon carbide in production-run volumes is crystal. Already one of the world’s top-three possess years of experience in wafering, small, especially when compared to the producers of silicon wafers, GWC can now grinding and polishing of hard materials. larger number of downstream companies add SiC to its capabilities thanks to a Their relationships with integrated device that can turn these crystal boules into wafers long-term supply of SiC from GTAT. manufacturers (IDMs) help to further reduce that are ready for epitaxy and device cost and increase volume. GTAT is thus able manufacturing. Silicon, being a simpler www.gtat.com 3 PES SOLAR.