A new test structure for the evaluation of graft-base lateral diffusion depth in high-performance bipolar transistors

A new test structure allows the first electrical measurement of lateral diffusion depth of the graft base in high-performance bipolar transistors. It is indispensable for realizing high cutoff frequency to control the graft-base depth. The test structure has two independent base electrodes and no emitter region. It can evaluate the effective intrinsic-base length by measuring resistance between two electrodes. Graft-base depth can be derived from the active-base length and the effective intrinsic-base width. The feasibility of this structure Is confirmed by evaluating 50-GHz and 30-GHz transistors, with graft-base depths of 0.05 /spl mu/m and 0.13 /spl mu/m, respectively. The new method is compared with conventional ones.<
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