Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-11-27
2003-09-23
Quach, T. N. (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S627000, C438S648000
Reexamination Certificate
active
06624062
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a wiring structure in a semiconductor device and a method for forming the wiring structure, and more specifically, it relates to a wiring structure in a semiconductor device, which wiring structure includes contacting holes such as a contact hole, a via hole and a through hole or a trench wiring, and a method for forming the wiring structure.
A semiconductor device has a number of contact holes, through holes or via holes (these will be also generically referred to as “contacting holes” hereinafter). Generally, a contacting hole is formed by forming an insulating layer on an impurity-including region, various electrodes or a lower wiring layer (these will be also generically referred to as “lower conductive layer” hereinafter) formed in or on a semiconductor substrate, or forming an insulating layer on various electrodes or the lower wiring layer formed on a lower insulating layer; forming an opening portion in the insulating layer; and then filling the opening portion with a metal material. With an increase in the integration degree of a semiconductor device, a fine design rule of a semiconductor production process is being employed, and it is an essential object to accomplish a technique of filling an opening portion having a high aspect ratio with a metal material. Further, as a kind of wiring, a trench wiring is practically used which is a technique for forming an insulating layer on a lower insulating layer, forming a trench portion in the insulating layer and then filling the trench portion with a metal material.
With an increase in the integration degree of a semiconductor device, the design rule of a wiring of a semiconductor device keeps on becoming finer, and a signal delay caused by an increase in a capacitance between wirings is a serious problem which inhibits the higher performance of a semiconductor device. As one means for overcoming the above problem, there is known a method in which an insulating layer is composed of a low dielectric constant material, and developments of low dielectric constant materials having a lower relative dielectric constant than a conventional silicon-oxide-film-based material (relative dielectric constant: 4.2) are under way.
The low dielectric constant materials are largely classified into an organic low dielectric constant material and an inorganic low dielectric constant material. Of these, it is said that an organic low dielectric constant material will be a main stream as a low dielectric constant material for materializing a relative dielectric constant of 3 or less required of a semiconductor device to which a design rule of 0.18 &mgr;m to 0.13 &mgr;m or smaller is applied. The low dielectric constant material is composed of, for example, carbon (C), fluorine (F), oxygen (O) and silicon (Si) as main components, and it is said that due to the contents of carbon (C) and fluorine (F) in particular, the density of the low dielectric constant material can be decreased, and further that the polarizability of molecules per se of the low dielectric constant material can be decreased, so that a low dielectric constant can be materialized.
There is being developed a method for forming a contacting hole and a trench wiring by providing a low dielectric constant material as an insulating layer, which method comprises the steps of forming the insulating layer, forming an opening portion and/or a trench portion in the insulating layer, then, forming a copper (Cu) layer on the entire surface of the insulating layer including insides of the opening portion and/or the trench portion, and then removing the copper layer on the insulating layer. Meanwhile, in the above method, it is required to form a barrier metal layer between the insulating layer and the copper layer for preventing the diffusion of copper atoms into the insulating layer. Tantalum nitride (TaN) is said to be useful as a material for forming the barrier metal layer. However, the barrier metal layer composed of tantalum nitride has problems that it has a high stress and that it shows a low polishing rate during its chemical/mechanical polishing.
There is therefore aggressively developed a method for forming a contacting hole and/or a trench wiring, in which an organic low dielectric constant material is provided for an insulating layer, the insulating layer is formed therefrom, an opening portion and/or a trench portion are formed in the insulating layer, a tungsten layer is formed on the entire surface of the insulating layer including the insides of the opening portion and/or the trench portion according to a chemical vapor deposition method (CVD method), and then, the tungsten layer on the insulating layer is etched back. The above method will be referred to as a blanket tungsten CVD method.
When the tungsten layer is formed on the insulating layer or on the insides of the opening portion and/or the trench portion by the blanket tungsten CVD method, it is required to form a barrier metal layer as an underlayer for the tungsten layer in advance. The reason therefor is that the tungsten layer formed by the blanket tungsten CVD method has poor adhesion to the insulating layer although it is excellent in step coverage. There is another reason that it is also required to prevent the corrosion of the lower conductive layer with a metal fluoride gas such as WF
6
which is a process gas for forming the tungsten layer. Further, there is still another reason that since the temperature for forming the tungsten layer by the blanket tungsten CVD method is a relatively high temperature, it is also required to improve the barrier properties for the lower conductive layer.
For the above reasons, the barrier metal layer is formed from, for example, titanium nitride (TiN). In this case, it is preferred to form a titanium (Ti) layer between the barrier metal layer and the lower conductive layer for forming an ohmic contact with the lower conductive layer.
In the formation of the tungsten layer according to a CVD method, conventionally, the insulating layer is heated up to 420 to 470° C. The temperature at which the insulating layer is heated for forming the tungsten layer according to the CVD method will be referred to as “forming temperature” hereinafter. However, when poly(aryl ether) of the following formula is used as a low dielectric constant material, and when the forming temperature is set at 420 to 470° C., there occurs a phenomenon that the inside of the opening portion can no longer reliably filled with a tungsten layer.
wherein R is an alkyl group C
n
H
2n+1
.
That is, a failure in filling a tungsten layer in the opening portion takes place. The above phenomenon is caused by the thermal decomposition or the pyrolysis of poly(aryl ether). A tungsten layer was formed at a forming temperature of 450° C. by a CVD method and analyzed by a secondary ion mass spectroscopy, and
FIG. 7A
shows the result. For reference purpose, a tungsten layer was also formed at a forming temperature of 375° C. by a CVD method and analyzed in the same manner, and
FIG. 7B
shows the result. When the results in
FIGS. 7A and 7B
are compared, it is seen that when the forming temperature is set at 450° C., the pyrolysis of poly(aryl ether) starts, and as a result, a tungsten layer includes larger contents of carbon atoms and oxygen atoms.
When poly(aryl ether) is measured by a Fourier-transform infrared spectroscopy, an infrared absorption spectrum caused by an ether bond is found around 1200 cm
−1
.
FIG. 8
shows the relationship between the heating temperature of poly(aryl ether) and a ratio of reduction in infrared absorption at 1200 cm
−1
. The heating was carried out at each temperature for 1 hour or two hours.
FIG. 8
also shows that the infrared absorption at 1200 cm
−1
based on an ether bond sharply decreases when the heating temperature is set at approximately 400° C. or higher, and this data means that the ether bond of poly(aryl ether) is broken at a heating temperature of approximately
Kananen, Esq. Ronald P.
Quach T. N.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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