Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-02-25
2001-04-10
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S474000
Reexamination Certificate
active
06214730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to semiconductor devices and manufacturing and, more particularly, to methods and structures which prevent degradation in semiconductor device wiring.
2. Background Description
Degradation occurs in metal lines in contact with insulator materials containing fluorine. This degradation is a serious concern because it represents a potential failure mechanism for an IC (integrated circuit). The degradation problem is costly to the industry by virtue of the process monitoring, inspections, and equipment maintenance requirements that it entails. No understanding of, much less a solution to, the degradation problem associated with metal lines in contact with insulators containing fluorine has been developed prior to the present invention.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide degradation resistance for metals in contact with fluorine-containing insulator materials.
It is another object of the present invention to provide corrosion resistance for aluminum lines in contact with oxide insulator lines containing fluorine.
It is yet another objective of this invention to prevent fluorine poisoning of metals used in IC metallization schemes to prevent undesired via resistance growth and to enhance the contact between a metallization layer and the metal in a via plug.
These and other objectives are achieved in the present invention by providing a fluorine-free barrier layer between an insulator material containing fluorine and a metal to effectively restrict diffusion of fluorine from the insulator material into the metal; thereby preventing metal degradation.
For purposes of the present invention, the terminology “degradation”, as used in connection with metal contact and metal-based conductors of electricity, encompasses “corrosion” or “poisoning” of a metal. “Corrosion” of a metal line or metal contact by exposure to fluorine means formation of a metal fluoride compound from fluorine and the metal via chemical reaction. “Poisoning” of a metal by exposure to fluorine means physical infiltration of the metal by fluorine as a contaminant in an amount adequate to increase the contact resistance of the contaminated metal interfaces.
While not desiring to be bound to any particular theory, it is thought that fluorine-containing insulating materials tend to release fluorine constituents during patterning of metal lines and metal conductors, particularly in the form of fluorine (F) or fluorine gas (F
2
), which initiates and/or promotes the corrosion and/or poisoning of metals, such as aluminum or titanium, that become exposed to and infiltrated by the released fluorine. This phenomenon has been observed to occur whether the fluorine is an intentional component of the insulator material or even an inadvertent contaminant thereof. For instance, fluorine has been found by the present investigators to be a contaminant in commonly-used TEOS (i.e., tetraethylorthosilicate) based insulator films which are commonly-used as insulating films between metal conductor lines. The presence of fluorine as a contaminant in the insulator layer nonetheless poses a potential degradation threat, once released, to adjacent metal conductor lines if not prevented by use of the intervening barrier layer employed in this invention.
It has been observed by the investigators of this invention that the rate of corrosion experienced in metal exposed to fluorine is positively related to the concentration of fluorine in the adjoining insulator film; that is, a lower-concentration of fluorine in the insulator film causes less metal corrosion than the case where higher concentrations of fluorine are present in the insulator film.
In this invention, a fluorine-free barrier layer is formed at the surface of an insulator film, such as a silicon oxide, silicon nitride, silicon, or carbon film, before a metal conductor layer is formed on the barrier layer and patterned to form circuitry wiring. In the present invention, it is imperative that the fluorine-free barrier layer material itself is free of fluorine and it should not emit fluorine or allow migration of fluorine therethrough during metal etching, resist stripping, cleaning, annealing, and other procedures associated with metallization operations. The term “fluorine-free” means no amount of fluorine present, although it is conceivable that a trace amount of contaminant fluorine could be present in an amount so minuscule that it would pose no bona fide degradation threat to impair the function(s) of metal conductor lines and via metals formed on or in the insulator film. Accordingly, the terminology “fluorine-free” should be construed in this light. The fluorine-free barrier material also should have dielectric properties compatible with BEOL (back end of the line) processing requirements and should be compatible with standard via processes.
The fluorine-free barrier layer can be formed in two different ways: one being basically an additive process while the other is subtractive in nature. As an additive technique, the barrier layer can be formed as an extraneous layer that is deposited upon the exposed surface of the fluorine-containing insulator material. Fluorine-free barrier materials which may be deposited to form a film include fluorine-free silane or TEOS-based films prepared in such a way as to minimize the fluorine contaminants. Other fluorine-free barrier materials which can be deposited as films in the practice of this invention include sputter-deposited oxides, plasma enhanced chemical vapor deposited silicon nitride, intrinsic physical vapor deposited silicon, undoped silicon oxide, vapor deposited amorphous carbon, and other like materials, that are free of fluorine.
As a subtractive technique for forming the fluorine-free barrier layer, it can be formed by modifying the composition of the surface regions of fluorine-containing material by denuding its fluorine content to effectively form an insulator material having a fluorine-rich interior and a fluorine-free exterior barrier layer. To form the fluorine-free barrier layer in this manner, the fluorine-containing insulator material can be annealed in hydrogen gas with or without plasma, or alternatively, can be exposed to a plasma of oxygen or ozone, to deplete and cause elimination of fluorine from the surface regions of a fluorine-containing insulator material to create a fluorine-free layer in the surface regions of the insulator material. With such hydrogen annealing, it is thought that HF gas is formed which evolves from the surface of the insulator material to provide the fluorine-free region. On the other hand, and although the exact mechanism is not completely understood at this time, it is theorized that the oxygen or ozone plasma brings about the formation of SiF or F gas, which evolves from the surface region of the insulator material to be replaced by fluorine-free SiO.
Whether formed by the additive or subtractive modes of this invention, the fluorine-free barrier layer must have a thickness adequate to preclude migration of fluorine therethrough. In general, the thickness of the fluorine-free barrier layer will depend on the barrier material and its particular morphology. The thickness of the fluorine-free barrier layer generally ranges from 1 nm to 300 nm.
In further embodiment of this invention, the fluorine-free barrier layer is especially useful in a situation where insulator films are intentionally doped with fluorine for the purpose of reducing the dielectric constant of the insulator films in order to reduce capacitive coupling between adjacent metal lines. This situation is contemplated in BEOL (back end of the line) technologies. In this embodiment of the invention, the fluorine-free barrier layer is formed between the fluorine-rich insulator film and the metal conductor lines to thwart the heightened corrosion dangers otherwise posed to metal lines.
In another further embodiment of the invention, the fluorine-barrier layer is used to decrease via r
Cooney, III Edward C.
Lee Hyun K.
McDevitt Thomas L.
Stamper Anthony K.
Chadurjian, Esq. Mark F.
International Business Machines - Corporation
Luu Chuong
McGuireWoods LLP
Smith Matthew
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