Patent ID: 7144789

Claim:
A method of fabricating complementary bipolar transistors with SiGe base regions, comprising the steps forming on a wafer a first collector region and a second collector region, each comprising an epitaxial layer of silicon; and depositing a layer of silicon enhanced with germanium over each collector region in steps each separate from the other so that crystalline SiGe layers of differing germanium profiles materialize over said collector regions, wherein: prior to a first step of the deposition of the layer of silicon enhanced with germanium over said collector regions, a continuous layer of silicon dioxide is deposited and over said layer of silicon dioxide a polycrystalline layer of silicon is deposited, after which said polycrystalline layer of silicon and said layer of silicon dioxide over said first collector region are removed; the first step of the deposition of the layer of silicon enhanced with germanium is implemented so that a continuous layer of silicon enhanced with germanium is deposited that comprises a crystalline layer of SiGe formed over the epitaxial layer of silicon in said first collector region and a polycrystalline layer of SiGe formed over said polycrystalline layer of silicon; after which a continuous etch stop is deposited over said crystalline layer of SiGe and said polycrystalline layer of SiGe; prior to a second step of the deposition of the layer of silicon enhanced with germanium over said second collector region, portions of said etch stop, said polycrystalline layer of SiGe and said polycrystalline layer of silicon as well as said layer of silicon dioxide are removed from over said second collector region; the second step of deposition of said layer of silicon enhanced with germanium is implemented so that a continuous further layer of silicon is crystalline deposited, enhanced with germanium so that over said epitaxial layer of silicon in said second collector region said further layer of crystalline SiGe is formed and over said polycrystalline layer of SiGe a further layer of polycrystalline SiGe is formed; after which a continuous resist is deposited; and then said resist ( 38 ) and said further layer of polycrystalline SiGe are totally removed, said further layer of crystalline SiGe remaining over said second collector region.