Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2000-11-06
2001-09-25
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S223000, C438S296000, C438S424000, C438S427000, C438S433000
Reexamination Certificate
active
06294419
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an isolation method and structure used in semiconductor integrated circuits and more particularly to a dual depth shallow trench isolation (STI) structure with an impurity region formed under the trench.
BACKGROUND OF THE INVENTION
Semiconductor integrated circuits are becoming increasingly complex, yet there is a constant drive to decrease the size of the circuits. The drive to decrease the size and increase the density of these circuits can result in several problems which may cause circuit failures if they are not addressed. Latch-up is one problem which can occur frequently in densely packed devices if not properly addressed. Latch-up can be triggered by many mechanisms and can cause the circuit to fail. Latch-up is commonly caused by the close proximity of n-type and p-type devices in CMOS circuits, where the parasitic NPN bipolar transistors can be triggered into a low resistance holding state. This low resistance state can draw large currents which can be destructive.
STI is commonly used to isolate n-channel and p-channel devices in CMOS circuits. STI reduces the likelihood of latch-up, among other advantages. However, as semiconductor devices become smaller and more densely packed, certain features of the device also become smaller, while other features remain constant:. For example, the n+ and p+ space, as well as the STI trench depth has scaled smaller, while EPI thickness has remained constant.
The EPI thickness needs to remain constant in order to accommodate retrograde wells. A retrograde well is one in which the surface doping is lower than the doping of the well deeper into the substrate, that is, the further in the substrate, the higher the doping concentration. Hence, a retrograde well requires a fairly thick EPI to accommodate the deeper retrograde wells.
The STI depth is required to be deep enough to adequately isolate devices. As the STI width is scaled smaller, higher aspect ratio trenches are formed that are difficult to fill. When a trench with a high aspect ratio is filled, voids are often created in the fill which may cause a variety of problems. Additionally, as the size of the STI is reduced, latch-up immunity is decreased. Therefore, there is a need for an isolation structure which is easy to manufacture and which also improves the latch-up of densely packed semiconductor devices.
SUMMARY OF THE INVENTION
A structure and a method for improved latch-up using a dual depth STI with an impurity implant formed under the deep trench is provided. In one embodiment of the invention, a dual depth trench is formed in a substrate. The trench includes a first substantially horizontal surface at a first depth and a second substantially horizontal surface at a second depth which is deeper than the first depth. A first well having a first type dopant and a second well having a second type dopant are formed in the substrate so that both wells abut the trench. A doped region is formed in the substrate abutting both the first well and the second well. The doped region is formed below the second substantially horizontal surface of the trench in order to lower a beta product between the wells. The beta product is the product of the parasitic bipolar device gains (NPN and PNP betas).
In a further embodiment, well edge implants are formed in the first and second wells. The well edge implant formed in the first well is a highly doped area of the first conductivity type and the well edge implant in the second well is a highly doped area of the second conductivity type. The well edge implants are formed in their respective wells preferably adjacent to the deepest portion of the trench.
In one method for forming the dual depth trench, a substrate having at least one dielectric layer formed thereon and a resist layer deposited on the at least one dielectric layer is provided. The resist layer is patterned and a trench is formed through the dielectric into the substrate according to the patterned resist. A dopant is implanted into the substrate using the patterned resist layer as a mask to form a highly doped region in the substrate at a distance below the trench. The resist is stripped and another resist layer is deposited and patterned to provide a wider opening for the formation of a wide trench STI region. The newly exposed substrate and the existing trench are both etched until a bottom of the existing trench reaches the highly doped region, resulting in a dual depth trench. The dual depth trench is then filled with an oxide and wells of opposite conductivity types are implanted into the substrate on opposite sides of the trench.
In another method, a hybrid resist is used to form the trench and potentially the wells also. A hybrid resist may also be used to form the well edge implants adjacent to the trench.
REFERENCES:
patent: 6033949 (2000-03-01), Baker et al.
patent: 6069057 (2000-05-01), Wu
patent: 6150212 (2000-11-01), Divakaruni et al.
patent: 6165870 (2000-12-01), Shim et al.
patent: 6174785 (2001-01-01), Parekh et al.
patent: 6177333 (2001-01-01), Rhodes
patent: 6218704 (2001-04-01), Brown et al.
patent: 6235610 (2001-05-01), Nicotra et al.
Brown Jeffrey Scott
Gauthier Jr. Robert J.
Mann Randy William
Voldman Steven Howard
Chadurjian Mark F.
Connolly Bove Lodge & Hutz
International Business Machines - Corporation
Jones Josetta I
Niebling John F.
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