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Infineon Technologies Ag

Ola Knut Tylstedt

Anders Lindgren

Hans Norstr&ouml;m

Hans Erik Norstrom

Hans Norström

Stefan Nygren

In order to produce an electrical connection to an inner layer such as a bottom diffusion ( ), which has a good electrical conductivity and is located inside a bipolar semiconductor device isolated by trenches ( ) and which for example forms a subcollector of a NPN-transistor, a hole ( ) in a trench is used. The hole is filled with electrically conducting material and extends from the surface of the device to the bottom diffusion ( ), so that the electrically conducting material in the hole is in contact therewith. The hole ( ) is made aligned with a sidewall of the trench ( ) by using selective etching. The hole can be made at the same time as contact holes for metallization are made and then also be filled in the metallization step, to contact the bottom diffusion. For a lateral PNP-transistor the hole can be made as a closed groove constituting the outer confinement of the base area, passing all around the transistor. The outer sidewall of such a closed trench can, as seen from above, be bevelled by 45&deg;, so that no inner corners having too small angles are found in the trench, what facilitates the filling with oxide.

Trench-isolated bipolar devices

A bipolar transistor of type NPN has an active region at the surface of the component, which is surrounded, as seen along the surface of the component, in the conventional way by thick field oxide areas. The active region is partly covered by an electrically isolating surface layer, preferably comprising a nitride layer. A base region in the active region is defined by a well-defined opening, which is lithographically produced, in the electrically isolating surface layer. For a bipolar lateral transistor of type PNP, which instead has emitter and collector regions surrounded by such thick field oxide areas, the emitter and collector regions can in the corresponding way be defined by a lithographically defined opening in an electrically isolating surface layer. Owing to the well defined openings the base-collector capacitance and the emitter-collector capacitance respectively can be reduced in these cases, what results in better high frequency characteristics of the transistors. A region of the silicon nitride layer is at the same time used as an efficient dielectric in a simultaneously manufactured capacitor. The NPN-transistor can be provided with a thin side string made of nitride for isolation between an emitter connection and a base connection. In the same semiconductor plate special, deep and shallow substrate connecting terminals can be provided for electrically isolating component areas. Trenches can be used for electrical isolation of component areas and they can at their sidewalls have a laminate of at the bottom oxide and thereon nitride in order to facilitate planarizing etching and in order to act as a diffusion barrier.

Methods of manufacturing bipolar transistors for use at radio frequencies

In order to produce an electrical connection to an inner layer such as a bottom diffusion (103), which has a good electrical conductivity and is located inside a bipolar semiconductor device isolated by trenches (119) and which for example forms a subcollector of a NPN-transistor, a hole (157) in a trench is used. The hole is filled with electrically conducting material and extends from the surface of the device to the bottom diffusion (103), so that the electrically conducting material in the hole is in contact therewith. The hole (157) is made aligned with a sidewall of the trench (119) by using selective etching. The hole can be made at the same time as contact holes for metallization are made and then also be filled in the metallization step, to contact the bottom diffusion. For a lateral PNP-transistor the hole can be made as a closed groove constituting the outer confinement of the base area, passing all around the transistor. The outer sidewall of such a closed trench can, as seen from above, be bevelled by 45.degree., so that no inner corners having too small angles are found in the trench, what facilitates the filling with oxide.

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Vällingby, Sweden

Ola Knut Tylstedt