MANUFACTURING METHOD OF BIPOLAR TRANSISTOR

PURPOSE:To obtain a bipolar transistor capable of reducing base area and accelerating the operational velocity by a method wherein a base region and a field oxide film as well as an intrinsic base region and an emitter region are to be formed simultaneously and self-matchingly. CONSTITUTION:The first nitride film 5 and an oxide film 6 are formed on a semiconductor substrate 1 whereon a buried layer 2 and an epitaxial layer 3 are grown and element-separated 4 and then the films 6 and 5 excluding the emitter electrode formation region are removed. Next, the second nitride film 7 is formed and anisotropically etched away to leave the nitride films 8 on both sidewall parts of the nitride film 5 and the oxide film 6 and then the exposed substrate surface is oxidized to form field oxide films 9. Next, the nitride films 8 are removed to form base regions on the exposed substrate further forming a polycrystalline silicon film, a photoresist and then flattened and etched away to expose the oxide film surface 6. Finally, the oxide film 6 is removed and after forming an intrinsic base region on the substrate beneath the nitride film 5, the polycrystalline silicon film surface is oxidized to remove the nitride film 5 further forming an emitter region on the exposed substrate 1.