A modified $I^2L$ structure having self-aligned collectors and heavy doping in the extrinsic base region has been fabricated by a new process requiring only five masks.
The new fabrication process, which uses the spin-on sources as the diffusion sources, utilizes the hardened spin-on source as a diffusion mask. The sheet resistance in the intrinsic base region can be controlled independently by this new process.
$I^2L$ test devices including 13-stage ring oscillator have been fabricated with silicon wafers of 6.5㎛ epi-layer by the new process. An upward npn current gain of 8 for a three-collector $I^2L$, a speed power product of 3.5 pJ and a minimum propagation delay time of 50 ns with standard device breakdown (BV$_{CEO}$) of 22 volts have been obtained. And the test results show that the current gain control of the npn transistor can be easily achieved by varying the sheet resistance in the intrinsic base region during boron predeposition step.
