Since aluminum nitride (AlN) is an insulating material with the property of high thermal conductivity, it can be used as a heat dissipation substrate for semiconductor devices.
A wafer heating susceptor made of AlN for semiconductor production equipment has been commercialized by NGK as a result of the research into halogen gas-corrosion resistant materials.
Based on research into the microstructure control of AlN ceramics, NGK has developed two types of electrically conductive AlN ceramics.
One type has a volume resistivity that corresponds to the boundary region of the insulator and the semiconductor. This volume resistivity can be controlled from 1E9 to 1E12 Ohm-cm (Medium Resistivity type). The other type has volume resistivity in the semiconductor region. This volume resitivity can be controlled from 1E1 to 1E3 Ohm-cm (Low Resistivity type).
To provide electrical conductivity to insulating materials, generally more than 20% conductive particles must be included; but for these new materials, only several percent of sintering aids are used.
Consequently, these materials can be produced by the conventional sintering process, and are still able to keep the original properties of AlN, such as a coefficient of thermal expansion, mechanical strength, a coefficient of thermal conductivity at a minimum of 100 W/mK, and so on.
Usually, with insulating ceramics the volume resistivity decreases with increasing temperature, but the change of the electrical resistivity for temperature variation of the Medium Resistivity type is about half of that of conventional AlN ceramics. For the Low Resistivity type, the change of resistivity with change of temperature is almost zero.
The Medium Resistivity type has already been used as a material for electrostatic chucks in semiconductor production equipment.
These new electrically conductive aluminum nitride ceramics have other possible applications in components used under high temperatures or in corrosive environments where metallic materials cannot be used, and for components in which electric field control and/or an electric discharge function are required, such as in electric or electronic equipment.
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