The role of fluorine in npn and pnp polysilicon emitter bipolar transistors
The role of fluorine in npn and pnp polysilicon emitter bipolar transistors
This thesis investigates the role of fluorine in both npn and pnp polysilicon emitter bipolar transistors. Fluorine is often introduced into pnp polysilicon emitters as part of a BF2 implant. In this thesis fluorine is introduced separately into the polysilicon layer in order to study it's effect independently from the boron with which it is normally associated. The effects resulting from the presence of fluorine can be split into three areas; passivation, enhanced interfacial break up and enhanced epitaxial realignment of the polysilicon layer.
Passivation is seen in two different ways. First for very low thermal budget emitter drive-ins, passivation results in a drop in base current. For example, fluorine implanted pnp devices, given an emitter drive-in of 15 minutes at 850°C have a base current 5.5 times lower than that of devices which had not. Second, the presence of fluorine improves the base current ideality particularly in devices where the emitter/base junction is very shallow. For example, fluorine implanted pnp devices given an RTA emitter drive-in of 10 seconds at 1025°C have a base current ideality factor of 1.21 compared to 1.43 for unimplanted devices. This passivation effect is attributed to the fluorine attaching itself to the dangling bonds at the polysilicon/silicon interface thereby decreasing the interface trapping state density.
Enhanced break up of the interfacial oxide at the polysilicon/silicon interface is observed for higher thermal budget emitter drive-ins, and this results in a rise in base current. For example, fluorine implanted pnp devices when given an emitter drive-in of 120 minutes at 850°C show a rise in base current by a factor of 2.5 when compared to unimplanted devices.
University of Southampton
1994
Moiseiwitsch, Nicholas E
(1994)
The role of fluorine in npn and pnp polysilicon emitter bipolar transistors.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis investigates the role of fluorine in both npn and pnp polysilicon emitter bipolar transistors. Fluorine is often introduced into pnp polysilicon emitters as part of a BF2 implant. In this thesis fluorine is introduced separately into the polysilicon layer in order to study it's effect independently from the boron with which it is normally associated. The effects resulting from the presence of fluorine can be split into three areas; passivation, enhanced interfacial break up and enhanced epitaxial realignment of the polysilicon layer.
Passivation is seen in two different ways. First for very low thermal budget emitter drive-ins, passivation results in a drop in base current. For example, fluorine implanted pnp devices, given an emitter drive-in of 15 minutes at 850°C have a base current 5.5 times lower than that of devices which had not. Second, the presence of fluorine improves the base current ideality particularly in devices where the emitter/base junction is very shallow. For example, fluorine implanted pnp devices given an RTA emitter drive-in of 10 seconds at 1025°C have a base current ideality factor of 1.21 compared to 1.43 for unimplanted devices. This passivation effect is attributed to the fluorine attaching itself to the dangling bonds at the polysilicon/silicon interface thereby decreasing the interface trapping state density.
Enhanced break up of the interfacial oxide at the polysilicon/silicon interface is observed for higher thermal budget emitter drive-ins, and this results in a rise in base current. For example, fluorine implanted pnp devices when given an emitter drive-in of 120 minutes at 850°C show a rise in base current by a factor of 2.5 when compared to unimplanted devices.
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Published date: 1994
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Local EPrints ID: 458577
URI: http://eprints.soton.ac.uk/id/eprint/458577
PURE UUID: 1cd11c18-872e-4835-b971-f8f6648b517a
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Date deposited: 04 Jul 2022 16:51
Last modified: 04 Jul 2022 16:51
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Author:
Nicholas E Moiseiwitsch
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