Skjerven, Morrill, MacPherson, Franklin & Friel LLP
Use of oblique implantation in forming emitter of bipolar transistor
 A bipolar transistor is fabricated by a process in which first and second dopants of the same conductivity type are introduced into a semiconductor body through at least partially overlapping sections, preferably the same section, of the body's upper surface to form an emitter. The first dopant is introduced at a greater dosage than the second dopant such that the emitter consists at least of a main emitter region constituted primarily with the first dopant. The introduction of the second dopant into the body entails ion implanting the second dopant at a tilt angle of at least 15.degree. relative to a direction generally perpendicular to the body's upper surface. Part of the second dopant is so implanted into an extension zone that extends laterally beyond the main emitter region. The extension zone may be of the same conductivity type as, or of opposite conductivity type to, the main emitter region. In either case, the extension zone is lightly doped and reduces transistor performance degradation by reducing the electric field along the emitter-base junction, especially along the upper semiconductor surface. 
National Semiconductor Corporation
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inventional inventional inventional
Hung-Sheng Chih Sieh
Chen Teng