Ion-implanted depletion-mode IGFET

P-channel IGFET's have been ion-implanted with boron to produce a Gaussian dopant profile which is almost entirely in the silicon. These IGFET's exhibit depletion mode device behavior due to a subsurface built-in channel, and they have more reproducible conductance characteristics than those fabricated by leading edge implants for which only simple shifts of threshold voltage occur. The built-in subsurface channel structure results in a device which is characterized by both a flatband (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FB</inf> ) and a drain saturation voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DSAT</inf> ) rather than a threshold voltage. The fabrication process users 120 keV boron ions implanted through an Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (500Å)-Sio <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (1000Å) gate dielectric into Si at an angle of 7° from the axis. Typical device parameters for an ion dosage of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5.5 × 10¹¹</tex> /cm 2 are <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VFB = -0.9</tex> volt, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VDSAT = -2.45</tex> volt at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VGS = 0</tex> . For W/L = 1, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gₘ = 17</tex> µmhos at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VGS = 0</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VD = -5</tex> volt.