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Berlin, Germany
Apr 22-25

San Jose, CA, USA
Jun 26 - 28
SEMICON Europa 2011 - Advanced Packaging Conference


Messe Dresden
Dresden, Germany
Oct 11 - 13, 2011

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Low Temperature Glass-Thin-Films for use in Power and Sensor Applications

Abstract - Power generation and storage, electro mobility and mobile applications are driving the increasing demand for power electronics and foster the use of cost-effective packaging without compromising on reliability and performance of advanced power semiconductors. In this paper we describe a novel technology to manufacture robust and reliable borosilicate thin-films with CMOS back-end compatible processes. This allows bringing the benefit of glass-passivation to volume production and enables the use of wafer-level packaging and redistribution for applications in harsh environment.
Due to its excellent physical properties borosilicate glass is a very suitable material for electronic packaging. Its chemical inertness, its good electrical performance as well as its hermetic protection allow for a wide range of applications.
Using a plasma-enhanced deposition process (Lithoglas process) it is now possible to form dense, pin-hole free and hermetic borosilicate thin-films, which can be structured by standard lift-off lithography. The glass haze generated by evaporation condensates on the substrate materials at temperatures below 100 °C and is simultaneously compacted by a plasma ion source. Layers with all the beneficial properties of the bulk material may be deposited at rates of about 0,3 µm/min on a wide variety of substrate materials. Typical layer thicknesses range from about 100 nm to a few 10 µm with an uniformity as good as 1 % on a 6” wafer.
The microstructuring of these layers is done by lift-off with lateral dimensions of a few microns to several centimeters with maximum aspect ratios of approx. 2:1.
The borosilicate thin-films yield breakdown voltages as high as 250 V/µm and a typical specific resistance of 1E17 Ohm/cm at room temperature, a value which is very close to the specific resistance of bulk borosilicate glass.
The coefficient of thermal expansion of the borosilicate thin-film (3.2 ppm/°K) is match to silicon and enables systems to be reliable at high temperatures or in temperature cycling. Microstructured glass films were tested under extreme conditions e.g. up to temperatures as high as 650 °C as well as long-term temperature-humidity storage (85°C, 85% for 8000h).
We demonstrate the use of borosilicate thin-films as inter-dielectric layer in wafer-level redistribution, replacing standard polymers such as BCB or PI as a drop-in solution. Process parameters and reliability results are discussed.