Self-aligned mask formed utilizing differential oxidation rates of materials
First Claim
1. A method for forming a self-aligned oxide mask on a composite base of a bipolar transistor comprised of a collector, an emitter, and the composite base which includes a polycrystal Si on a field and a single crystal Si at an active area, wherein the method comprises:
- forming an oxide layer over both the poly Si and the single crystal Si of the composite base by using a thermal oxidation process to form a thick oxide layer over the poly Si and a thin oxide layer over the single crystal Si;
performing a controlled oxide etch to remove the thin oxide layer over the single crystal Si while leaving a self-aligned oxide mask layer over the poly Si.
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Abstract
A self-aligned oxide mask is formed utilizing differential oxidation rates of different materials. The self-aligned oxide mask is formed on a CVD grown base NPN base layer which compromises single crystal Si (or Si/SiGe) at active area and polycrystal Si (or Si/SiGe) on the field. The self-aligned mask is fabricated by taking advantage of the fact that poly Si (or Si/SiGe) oxidizes faster than single crystal Si (or Si/SiGe). An oxide film is formed over both the poly Si (or Si/siGe) and the single crystal Si (or Si/siGe) by using an thermal oxidation process to form a thick oxidation layer over the poly Si (or Si/siGe) and a thin oxidation layer over the single crystal Si (or Si/siGe), followed by a controlled oxide etch to remove the thin oxidation layer over the single crystal Si (or Si/siGe) while leaving the self-aligned oxide mask layer over the poly Si (or Si/siGe). A raised extrinsic base is then formed following the self-aligned mask formation. This self-aligned oxide mask blocks B diffusion from the raised extrinsic base to the corner of collector.
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Citations
11 Claims
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1. A method for forming a self-aligned oxide mask on a composite base of a bipolar transistor comprised of a collector, an emitter, and the composite base which includes a polycrystal Si on a field and a single crystal Si at an active area, wherein the method comprises:
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forming an oxide layer over both the poly Si and the single crystal Si of the composite base by using a thermal oxidation process to form a thick oxide layer over the poly Si and a thin oxide layer over the single crystal Si;
performing a controlled oxide etch to remove the thin oxide layer over the single crystal Si while leaving a self-aligned oxide mask layer over the poly Si. - View Dependent Claims (2, 3, 4, 5)
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6. A method for forming a self-aligned oxide mask on a composite base of a bipolar transistor comprised of a collector, an emitter, and the composite base includes a polycrystal Si/SiGe, which means a layer of polycrystal silicon on top of a layer of polycrystal silicon germanium on a field, and a single crystal Si/SiGe, which means a layer of single crystal silicon on top of a layer of single crystal silicon germanium, at an active area, wherein the method comprises:
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forming an oxide layer over both the poly Si/SiGe and the single crystal Si/SiGe of the composite base by using a thermal oxidation process to form a thick oxide layer over the poly Si/SiGe and a thin oxide layer over the single crystal Si/SiGe;
performing a controlled oxide etch to remove the thin oxide layer over the single crystal Si/SiGe while leaving a self-aligned oxide mask layer over the poly Si/SiGe. - View Dependent Claims (7, 8, 9, 10, 11)
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Specification