BIPOLAR JUNCTION TRANSISTORS (BJTS) WITH SECOND SHALLOW TRENCH ISOLATION (STI) REGIONS, AND METHODS FOR FORMING SAME

摘要

The present invention relates to bipolar junction transistors (BJTS). The collector region of each BJT is located in a semiconductor substrate surface and adjacent to a first shallow trench isolation (STI) region. A second STI region is provided, which extends between the first STI region and the collection region and undercuts a portion of the active base region with an undercut angle of not more than about 90°. For example, the second STI region may a substantially triangular cross-section with an undercut angle of less than about 90°, or a substantially rectangular cross-section with an undercut angle of about 90°. Such a second STI region can be fabricated using a porous surface section formed in an upper surface of the collector region.