Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-08-25
2001-04-17
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S004000
Reexamination Certificate
active
06218304
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to a method of fabricating a semiconductor device and, more specifically, to a method of determining an endpoint of a reduction reaction in the fabrication of a semiconductor device.
BACKGROUND OF THE INVENTION
In semiconductor integrated circuits, the formation of metal interconnect layers is important to the proper operation of such devices. These metal interconnect signal lines connect to lower conductive layers and “active” device regions of the integrated circuit through vias or through contact windows. Metal interconnect lines also serve as lines or runners on surface layers of integrated circuits to connect to other device areas. For best operation of the device, the metal must have sufficient conductivity to carry the electric signal and at the same time possess the ability to adhere to adjacent layers.
As the semiconductor industry attempts to reduce line widths to create smaller, faster devices, new materials will be used to overcome many of the physical limitations required by these reduced line widths. To overcome the interconnect resistance and improve electromigration resistance, many semiconductor manufacturers are turning to copper for the metal layers. However, in the past the use of copper in semiconductor devices has been limited. Copper atoms will readily diffuse through silicon causing contamination problems that cause leakage currents at p-n junctions, failure of dielectric layers, and deterioration of carrier lifetime. Therefore, unsuccessful containment of copper can have fatal effects on a semiconductor device. Copper is also subject to reaction with atmospheric oxygen or moisture during the formation of metal layers and interconnect lines. Such adverse reactions form undesirable compounds having lower conductivity and poor adhesion to other materials used in semiconductor fabrication. Accordingly, copper processing technology is an extremely important and new problem for the semiconductor industry.
To form suitable interconnects, copper metal surface layers formed on the semiconductor device must be free of any oxidized regions. Once the copper metal layer is formed and subject to an oxidizing environment, such as air, the resulting oxidized areas must be reduced back to unoxidized copper or subsequent layers will not adhere. Therefore, the subsequent process must first have an oxide reduction step where the copper layers and interconnects are subjected to a copper reduction reaction to convert any oxidized portion back to copper metal. Such reduction processes must be carefully controlled. Incomplete reduction results in a metal surface containing residual oxidized portions. Yet, if the reaction is allowed to proceed too long, the surface of the metal layers or interconnects become pitted. In either case, the performance of the device is adversely affected. Therefore, conditions that result in removal of the oxide regions without related pitting must be determined.
To solve the problems associated with reduction of oxidized copper on layers and interconnects, several approaches can be used. Currently, conditions for producing suitable copper metal surfaces and interconnects are determined manually. After a time the device is inspected to determine if the reduction is complete. The process is repeated until all oxide is removed. However, determining the endpoint of the reduction reaction in this way is both time consuming and expensive.
Accordingly, what is needed in the art is an automated method for detecting the endpoint of a reduction reaction in the fabrication of a semiconductor device. The method of the present invention addresses these needs.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a method of determining an endpoint of a reduction reaction of a metal deposited on a semiconductor wafer. In a preferred embodiment, the method comprises reducing an oxidized portion of the metal by subjecting the oxidized portion to a reducing agent that forms a reduction by-product and detecting the endpoint of the reduction reaction by monitoring a physical characteristic of either the reducing agent or the reduction by-product. This method is, therefore, particularly applicable in the fabrication of an integrated circuit device, such as a CMOS transistor, an NMOS transistor, a PMOS transistor, or a bi-polar transistor.
Thus, in a broad scope, the present invention provides a method of easily and quickly detecting when an oxidized portion of a metal has been removed from the surface of the semiconductor wafer, which reduces both the time required to monitor such processes and the cost associated with integrated circuit fabrication. Moreover, the present invention provides more accurate control over the oxidation process, which produces an integrated circuit device having fewer defects.
In one embodiment, the step of reducing an oxidized portion of the metal includes reducing a copper oxide, which in certain applications may be copper (II) oxide, Cu
2
O. Thus, with the increased use of copper, the present invention has substantial application in present integrated circuit fabrication processes.
In yet other aspects of the present invention, the metal may be reduced with ammonia. The reduction reaction reduces the oxidized portions of the metal to form by-products. In one example, the by-product comprises a gaseous species, such as water. However, other gaseous species produced by the reduction reaction may be monitored as well.
One way in which the endpoint can be detected is with a spectrophotometer. The range of frequency may vary, but one particular range is the ultraviolet light frequency. In such instances, the spectrophotometer is preferably an infrared spectrophotometer, and more specifically is an UV-visible spectrophotometer. As previously stated, a physical characteristic of either the reducing agent or the reduction reaction by-products may be monitored. As such, in one embodiment detecting an endpoint includes monitoring a physical characteristic of the reducing agent, and another embodiment provides that detecting an endpoint includes monitoring a physical characteristic of the reaction by-product.
In another aspect, the present invention provides a method of fabricating a semiconductor device, such as an integrated circuit device. This particular method includes forming active device regions on a semiconductor wafer, forming a metal within the semiconductor device wherein an oxidized surface forms on the metal surface during an intermediate phase of the fabrication of the semiconductor device reducing the oxidized portion by subjecting the oxidized portion to a reducing agent that forms a reduction by-product, detecting an endpoint of the reduction reaction by monitoring a physical characteristic of either the reducing agent or the reduction by-product, and completing the fabrication of the semiconductor device. Accordingly, this particular embodiment is particularly useful in fabricating a semiconductor device, which preferably includes an integrated circuit, such as a CMOS transistor, an NMOS transistor, a PMOS transistor, or a bi-polar transistor.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 4842891 (1989-06-01), Miyazaki et al.
patent: 6010749 (2000-01-01), Goldman
Yasushi Sawada, Hiroshi Tamaru,
Bowers Charles
Lucent Technologies - Inc.
Pert Evan
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