A Review on Die Attach Materials for SiC-Based High-Temperature Power Devices
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INTRODUCTION
MICROELECTRONIC packaging provides interconnection, physical protection. and mechanical support for semiconductor devices for them to function in a specific condition.[1] Therefore, die attach materials, which connect the die and device to the rest of the system, play an important role to ensure the entire system works consistently. It is commonly accepted that both tin-based solder alloys (leaded [SnPb] and lead-free solder alloys [SnAgCu]) and conductive adhesives are used widely as die attach materials because of their ease of processing at temperatures below 573 K (300 C).[2] However, with higher temperature applications (>623 K (350 C)) in automotive, down-hole oil and gas industries for well logging, aircraft, space exploration, nuclear environment, and radars,[3] these solder alloys and conductive adhesives cannot meet their stringent requirements, and one of the obvious drawbacks is their low melting and operating temperatures. To operate at a higher temperature, silicon carbide (SiC) has been identified as one of the potential semiconductor wafers for the future generation of power devices. This is because SiC intrinsically is a wide band gap semiconductor with superb electronic, physical, chemical, and mechanical properties that enable it to withstand high temperature, power, and voltage.[4] In fact, when using this semiconductor, a dramatic reduction in volume and weight of a power module can be achieved, as the SiC die can be shrunk, and the cooling system can be simplified.[5] Research also indicates that SiC-based power devices possess an excellent switching HUI SHUN CHIN, Associate Researcher, KUAN YEW CHEONG, Associate Professor, and AHMAD BADRI ISMAIL, Senior Lecturer, are with the Energy Efficient & Sustainable Semiconductor Research Group, School of Materials & Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia. Contact e-mail: [email protected]. Manuscript submitted January 22, 2010. Article published online April 6, 2010. 824—VOLUME 41B, AUGUST 2010
characteristic and stable functionality even at temperatures greater than 623 K (350 C).[6–8] However, less attention has been paid to the development of technology and material that is related to microelectronic packaging, particularly die attach material, operating at the aforementioned temperature. A few alternative die attach materials that can withstand high temperatures have been reported.[2,9–16] Silver is a promising material, as it possesses a high melting temperature (1233 K (960 C)), high electrical and thermal conductivity, and good reliability, but it is less preferable as a die attach material in industry because of its extremely high sintering temperature. There are two strategies to lower the sintering temperature, namely inducing pseudo-hydrostatic pressure[9] and reducing silver particle size into the nanometer range and sintering without applying any pressure.[2] Other potential die attach materials being reported are off-eutectic gold-based alloy,[10–13] bismuth-based,[14]
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