High Thermally Conductive, High-Speed Deposition of AlN by Bipolar High Power Impulse Magnetron Sputtering

In advanced 3D monolithic packaging practices, the gap filling between dielectric chips is typically performed by PECVD <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SiO2</tex> , which has a thermal conductivity of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">~ 1</tex> W/m-K, hindering effective thermal management. Substituting <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SiO2</tex> with polycrystalline AlN could result in more than a 100-fold enhancement in thermal conductivity while maintaining a relatively low leakage current. However, achieving this substitution requires a low-defect density, high-speed deposition of AlN at low temperatures <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(< 400 ∘ C)</tex> . High-power impulse magnetron sputtering (HIPIMS) plus a reverse positive kick is a form of high-energy physical vapor deposition involving bipolar pulsing. In this study, single-texture 1-micron AIN film with a thermal conductivity of 121 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W/m· K</tex> was successfully deposited with a growth rate of 25 nm/min using an advanced bipolar HIPIMS plus Kick pulse generator on a native oxide-free Si (111) substrate. The substantial plasma current (50 A at peak) and a slight reverse positive target bias <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(+25V)</tex> are applied to ensure that 90% of the Al and Ar atoms are ionized with the precise controlled energy, leading to the maximization of the material's capacity for heat dissipation as measured by frequency domain thermoreflectance (FDTR).