Method for fabricating an NPN transistor in a BICMOS technology
AssigneeSGS-Thomson Microelectronics S.A.
InventorYvon Gris
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Abstract
The present invention relates to a bipolar transistor of NPN type implemented in an epitaxial layer within a window defined in a thick oxide layer, including an opening formed substantially at the center of the window, this opening penetrating into the epitaxial layer down to a depth of at least the order of magnitude of the thick oxide layer, an N-type doped region at the bottom of the opening, a first P-type doped region at the bottom of the opening, a second lightly-doped P-type region on the sides of the opening, and a third highly-doped P-type region in the vicinity of the upper part of the opening, the three P-type regions being contiguous and forming the base of the transistor.
Claims9
A bipolar transistor of NPN type implemented in an epitaxial layer within a window defined in a thick oxide layer, including:
- an opening formed substantially at the center of the window, the opening penetrating into the epitaxial layer down to a depth of at least the order of magnitude of the thick oxide layer, the walls of the opening being coated with a layer of silicon oxide and with a layer of silicon nitride,
- a polysilicon spacer formed on the lateral walls and a portion of the bottom wall of the opening,
- an N-type highly-doped polysilicon layer formed in the opening and in contact with the epitaxial layer at the bottom of the opening within the space defined by the spacer,
- an N-type doped region at the bottom of the opening,
- a first P-type doped base region at the bottom of the opening,
- a second lightly-doped P-type region on the sides of the opening, and
- a third highly-doped P-type region formed in the vicinity of the upper part of the opening, this third region being in contact with an N-type doped polysilicon layer, the three P-type regions being contiguous and forming the base of the transistor.
A method for fabricating an NPN transistor in an epitaxial layer of type N, including the steps of:
- defining a window in a thick oxide region,
- depositing a polysilicon layer and a silicon oxide layer,
- substantially opening at the center of the window the silicon oxide and polysilicon layers,
- performing a thermal oxidation,
- forming in the opening an insulating layer of a first material which is selectively etchable with respect to the silicon oxide,
- forming spacers in a second material which are selectively etchable with respect to the silicon oxide and to the first material,
- opening the bottom of the opening within the area defined by the spacers,
- depositing an N-type doped polysilicon layer,
- including, after the step of opening of the polysilicon and silicon oxide layers, the step of further opening to a determined depth the epitaxial layer and of implanting a P-type doping in the epitaxial layer at the bottom of the opening and on the walls thereof.
Dependencies are inferred from the claim text.