Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Including dielectric isolation means
Reexamination Certificate
2002-11-21
2003-11-11
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Including dielectric isolation means
C257S515000, C257S517000, C257S518000, C257S523000, C257S526000
Reexamination Certificate
active
06646320
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the manufacture of semiconductor integrated circuits and, in particular, to a method of forming a reliable ohmic contact to a polysilicon filled trench isolation region in a single poly bipolar or bi-CMOS process.
BACKGROUND OF THE INVENTION
Deep trench isolation is used in many bipolar and bi-CMOS process technologies. As shown in
FIG. 1
, this isolation technique utilizes a deep trench
10
etched into a silicon substrate
12
that is lined with thin silicon oxide
14
and then filled with undoped polysilicon
16
. The poly filled trench is then capped with field oxide
18
. For the typical application of isolation, the undoped polysilicon fill
16
is left electrically floating by interposing dielectric material
20
between the poly fill
16
and the overlying metal interconnect structure
22
of the integrated circuit.
There may be applications in which a contact to the undoped polysilicon fill region
16
of the isolation structure is desirable As shown in
FIG. 2
, the simplest way to form this contact is to cut a via in the dielectric material
20
and form a metal contact
22
down to the polysilicon fill
16
. Those skilled in the art will appreciate that, depending on the topology of the device structure, the contact
22
a may be formed as part of the formation of the metal layer
22
itself or as separate plug, e.g. tungsten, prior to formation of the metal layer
22
.
However, the formation of the contact
22
a
may present several problems. For example, the metal contact
22
a
may form a schottky diode with the undoped polysilicon fill region
16
, rather than the desired ohmic contact. Also, the contact could be made on an active (non-field) region and this would not be compatible with modern silicided processes in that the silicide from the active region could short across the oxide liner to the exposed trench fill.
SUMMARY OF THE INVENTION
In an embodiment of a method of fabricating an isolation structure in a semiconductor integrated circuit in accordance with the present invention, a trench is formed in a semiconductor substrate and lined with dielectric material. The lined trench is then filled with undoped polysilicon. A layer of dielectric material is then formed over an upper surface of the polysilicon filled lined trench and an opening is formed in the layer of second dielectric material to expose an upper surface of the undoped polysilicon. A layer of heavily doped polysilicon is then formed over the dielectric material and extending into the opening formed in the dielectric material such that the layer of doped polysilicon is in contact with an upper surface of the undoped polysilicon. A heat treatment step then causes dopant from the doped polysilicon to diffuse into the undoped polysilicon that fills the trench, thereby creating an ohmic contact between the doped polysilicon and the undoped polysilicon. A patterned layer of dielectric material is then formed over the doped polysilicon and an opening is formed in the dielectric material. A layer of conductive material is then formed over the dielectric material to extend into the opening to make electrical contact with the doped polysilicon.
In a preferred embodiment of the invention, these steps are carried out in the implementation of a bipolar process or a bi-CMOS process.
REFERENCES:
patent: 4745081 (1988-05-01), Beyer et al.
patent: 5569621 (1996-10-01), Yallup et al.
patent: 2002/0179976 (2002-12-01), Takahashi
patent: 2003/0102486 (2003-06-01), Inoue et al.
Greene Pershelle
National Semiconductor Corporation
Stallman & Pollock LLP
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