Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-10-29
2001-01-30
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S622000, C438S637000, C438S700000, C438S738000, C438S623000
Reexamination Certificate
active
06180518
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of semiconductor processing, and, more particularly, to a method for forming a via through a low dielectric constant material in a semiconductor device.
BACKGROUND OF THE INVENTION
Semiconductor devices continue to shrink in size and increase in complexity. As a result, a semiconductor device requires very close spacing of interconnect lines, and often requires a plurality of conductive layers for interconnecting the circuits formed therein. Dielectric layers separate the conductive layers and vias. Capacitance and cross talk between adjacent interconnect lines becomes more of a problem as the device geometries shrink and densities increase.
Typically, a dielectric layer includes silicon dioxide. Attempts have been made to replace silicon dioxide with a low dielectric constant material, i.e., with a material having a dielectric constant less than 4. The lower the dielectric constant, the better the insulator, thus lowering the capacitance between closely spaced interconnect lines. A dielectric material having a dielectric constant less than about 3.5 sufficiently reduces the capacitance between interconnect lines in typical sub-micron circuits.
Unfortunately, a low dielectric constant material may have low mechanical strength and poor dimensional stability. These characteristics require extra processing steps when forming a via through a low dielectric constant material. Porous sidewalls of the via may cause stability and adhesion problems during barrier and seed layer deposition. One approach to these problems is to perform a coating deposition step after via etch and clean, but prior to deposition of the barrier and seed layers.
The coating deposition forms a layer on the porous sidewalls of the via making them conformal. This layer fills in the porous openings in the sidewalls thus allowing the barrier and seed layers to be conformal when deposited. Unfortunately, deposition of the coating layer adds extra processing steps when making a semiconductor device. As discussed above, this added step is performed after the coating on the sidewalls of the via has been etched and cleaned. During the coating deposition step, the bottom of the via is also coated. Consequently, another processing step is required to etch and clean the bottom of the via.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the present invention to reduce the number of processing steps when making a semiconductor device having a via, such as formed through a low dielectric constant material.
This and other objects, advantages and features in accordance with the present invention are provided by a method for making a semiconductor device comprising the steps of forming a first conductive layer adjacent a substrate, forming an etch stop layer on the first conductive layer, and forming a dielectric layer on the etch stop layer. The dielectric layer preferably comprises a material having a low dielectric constant, and a via is formed through the dielectric layer to expose the etch stop layer at the bottom, with porous sidewalls of the via being produced. The method preferably further includes etching the exposed etch stop layer using an etchant, and while the etchant cooperates with etched material from the etch stop layer to form a polymeric layer to coat the porous sidewalls of the via.
The polymeric layer is advantageously formed in-situ with formation of the via, thus reducing the number of processing steps by at least one when making a semiconductor device having a via formed through a low dielectric constant material. Since the etchant cooperates with the etched material from the etch stop layer to form the polymeric layer coating the porous sidewalls of the via, a separate coating layer deposition step is not required after the via is etched and cleaned.
The method preferably further comprises the step of etching polymeric material from the bottom of the via, thus cleaning the via. The etchant preferably comprises at least one of monofluoromethane, difluoromethane and trifluoromethane. To control formation of the polymeric layer, the etchant preferably further includes predetermined amounts of argon and oxygen.
The dielectric layer preferably comprises a material having a dielectric constant less than about 4. The lower the dielectric constant, the lower the capacitance between closely spaced interconnect lines. The method preferably further includes the step of etching polymeric material from the bottom of the via.
After the sidewalls have been coated and polymeric material has been removed from the bottom of the via, the method further includes the steps of forming a barrier metal layer on the polymeric layer, and forming a seed layer on the barrier metal layer. A second conductive layer is formed on the seed layer contacting the first conductive layer.
Another aspect of the invention relates to a method for forming a polymeric layer on porous sidewalls of a via in a semiconductor device comprising an etch stop layer on a first conductive layer and a dielectric layer on the first conductive layer. The method preferably comprises the steps of forming the via through the dielectric layer to expose the etch stop layer at the bottom and producing porous sidewalls, and etching the exposed etch stop layer using an etchant that cooperates with etched material from the etch stop layer to form a polymeric layer to coat the porous sidewalls of the via.
REFERENCES:
patent: 5209817 (1993-05-01), Ahmad et al.
patent: 5472913 (1995-12-01), Havemann et al.
patent: 5510294 (1996-04-01), Dixit et al.
patent: 6071806 (2000-06-01), Wu et al.
Layadi Nace
Merchant Sailesh Mansinh
Molloy Simon John
Roy Pradip Kumar
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Bowers Charles
Lucent Technologies - Inc.
Pham Thanhha
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