| 摘要 |
A method of fabricating bipolar transistors with low collector resistances uses the high density implantation of higher diffusivity dopants into the buried collector layer (20). A more lightly doped epitaxial layer (22) is then grown which will form the active collector region. During the heat cycle of the epitaxial growth, the higher diffusivity dopants up-diffuse into the overlying epitaxial active collector layer, thus decreasing the effective thickness of the active collector region. If the buried layer (20) and the high diffusivity sinker-up regions (28, 30) are implanted with separate masks, the sinker-up region can be restricted to the area beneath the area where the base (41) and emitter (42) will subsequently be formed, thus minimizing any increase in collector capacitance. After the base (41) and emitter (42) are implanted into the epitaxial layer, the thickness of the lightly doped epitaxial layer between the base and the up-diffused highly doped sinker-up region (30) is less than the thickness from the base (41) to the buried layer in the absence of a sinker-up region. Less distance translates into lower resistance and lower breakdown voltage. Since a separate mask is used to implant the sinker-up, the sinker-up can be excluded in any of the transistors; thus, both high and low resistance devices can be simultaneously fabricated on the same chip. If the same mask is used to implant the up-diffusion and the buried layer, a two-step active collector doping profile can be realized without using two separate epitaxial growths, and without adding any additional masks. |
