Fabrication of integrated circuit structures for bipolar transistors

A method of forming an integrated circuit (IC) structure, the method comprising:

• providing a substrate including:
• a first semiconductor region, a second semiconductor region, and a trench isolation (TI) laterally between the first and second semiconductor regions;
• forming a seed layer on the TI of the substrate, leaving the first and second semiconductor regions exposed;
• forming an epitaxial layer on the first and second semiconductor regions of the substrate, and on the seed layer, wherein the epitaxial layer includes:
• a first semiconductor base material positioned above the first semiconductor region of the substrate, a precursor base positioned above the second semiconductor region of the substrate, and an extrinsic base material positioned above the seed layer;
• forming an insulator on the first semiconductor base material, the precursor base, and the extrinsic base material;
• forming an opening within the insulator to expose the precursor base;
• and
• growing a semiconductor material on the precursor base to yield a second semiconductor base material, wherein a height of the second semiconductor base material above the substrate is greater than a height of the first semiconductor base material above the substrate.

A method of forming an integrated circuit (IC) structure, the method comprising:

• providing a substrate including:
• a first semiconductor region, a second semiconductor region, and a trench isolation (TI) laterally between the first and second semiconductor regions;
• forming a first mask on the TI and the second semiconductor region of the substrate, leaving the first semiconductor region exposed;
• forming a first semiconductor base material on the first semiconductor region of the substrate;
• forming a sacrificial insulator on the first semiconductor base material;
• after forming the sacrificial insulator, removing a portion of the first mask to expose the second semiconductor region of the substrate;
• forming a second semiconductor base material on the second semiconductor region of the substrate, wherein a height of the second semiconductor base material above the substrate is greater than a height of the first semiconductor base material above the substrate;
• and
• removing the sacrificial insulator after forming the second semiconductor base material.