Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-01-27
2001-08-28
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S622000
Reexamination Certificate
active
06281113
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming an interlayer insulating film and, more particularly, to a method for forming an interlayer insulating film having a low dielectric constant, which is necessary for a highly-integrated semiconductor device.
2. Description of the Related Art
Progress in high integration of semiconductor devices in recent years has resulted in a narrower interval between wiring lines. As the narrowed interval between the wiring lines causes an increase in capacitance between the wiring lines, a need has been created for an interlayer insulating film which has a low dielectric constant.
More specifically, recent progress in high integration of an LSI device, has led to the wiring lines being micronized and multilayered which, in turn, has led to an increase in capacitance between the wiring lines. Such an increase in capacitance has caused a great reduction in operating speed. Thus, improvement in this regard has been strongly demanded. As one improvement measure, a method for reducing capacitance between the wiring lines has been studied. This method uses an interlayer insulating film which has a dielectric constant lower than that of SiO
2
currently used for an interlayer insulating film.
Typical interlayer insulating films of low dielectric constants currently under study are {circle around (1)} an SiOF film, and {circle around (2)} an organic insulating film of a low dielectric constant. Description will now be made of these films.
{circle around (1)} SiOF Film
An SiOF film is formed by using source gas containing F and substituting Si—F bonds for a portion of the Si—O bonds in SiO
2
. This SiOF film has a relative dielectric constant which is reduced as concentration of F in the film increases.
For forming such SiOF films, several methods have been reported (see p. 82 of monthly periodical “Semiconductor World”, February issue of 1996). Most promising among these methods is one for forming an SiOF film by using SiH
4
, O
2
, Ar and SiF
4
as source gases in a high-density plasma enhanced CVD method (HDPCVD method). The relative dielectric constant of an SiOF film formed by this method is in a range of 3.1 to 4.0 (varies depending on F concentration in the film). This value is lower than the relative dielectric constant 4.0 of SiO
2
, which has conventionally been used for the interlayer insulating film.
{circle around (2)} Organic Insulating Film of Low Dielectric Constant
As an insulating film which has a lower dielectric constant (3.0 or lower) compared with the SiOF film, an organic insulating film of a low dielectric constant is now a focus of attention. Table 1 shows a few organic insulating films of low dielectric constants, which have been reported, and respective relative dielectric constants and thermal decomposition temperatures thereof.
TABLE 1
Organic
Relative
Thermal
Insulating
Dielectric
Decomposition
Film
Constant
Temperature (° C.)
Note
Fluorine-contain-
2.4
420
P. 82 of monthly
ing resin
periodical “Semi-
conductor World”,
February issue of
1997
Cytop
2.1
400
P. 90 of monthly
periodical “Semi-
conductor World”,
February issue of
1996
Amorphous telon
1.0
400
P. 91 of monthly
periodical “Semi-
conductor World”,
February issue of
1996
However, the SiOF film is disadvantageous in that an increase in concentration of F in the film leads to a reduction in moisture absorption resistance. The reduced moisture absorption resistance poses a serious problem, because a transistor characteristic and adhesion of a superimposed barrier metal layer are affected.
The organic insulating film of a low dielectric constant is easily peeled off, because of poor adhesion to a silicon wafer or the SiO
2
film. Furthermore, the organic insulating film is disadvantageous in that heat resistivity is low since its thermal decomposition temperature is around 400° C. The disadvantage of low heat resistivity poses a problem for annealing a wafer at a high temperature.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for forming an interlayer insulating film of a low dielectric constant, which has good moisture absorption resistance and heat resistivity. It is another object of the invention to provide a semiconductor device made by the above method.
According to the method of the present invention for forming an interlayer insulating film, first, an SiO
2
film containing H
2
O, C or hydrocarbon is formed on a substrate. Then, this SiO
2
film is subjected to plasma or vacuum annealing. The vacuum annealing is performed by heating in a vacuum, i.e., at a pressure of 0.1 Torr or lower. If the pressure is 0.1 Torr or lower, a small quantity of N
2
or Ar may be contained in the atmosphere.
Then, by the annealing, gas contained in the SiO
2
film is discharged from the film, and the SiO
2
film becomes a porous SiO
2
film.
By experiment, the present inventor confirmed that the dielectric constant of the porous SiO
2
film lies in a range of 2.0 to 3.0. This value is smaller than the dielectric constant 4.0 of a conventional SiO
2
film having no porosity.
Since the porous SiO
2
film is formed by a conventional chemical vapor deposition method, better heat resistivity is provided.
After formation of the porous SiO
2
film, its surface can be made more stable by H (hydrogen) plasma treatment. In other words, by substituting Si—H bonds for dangling Si—O bonds in the surface, adsorption of water can be prevented.
Then, by forming a conventional SiO
2
film on the porous SiO
2
film, adsorption of water can be further prevented.
In a second embodiment of the method of the present invention for forming an interlayer insulating film, a first film is formed in concavities of a surface which has concavities and convexities. A first insulating film is then formed on the first film. The first insulating film has an etching rate lower than that of the first film. Then, holes are bored in the first insulating film, and selective etching of the first film is performed through the holes to eliminate corresponding areas of the first film. Then, a second insulating film is formed on the first insulating film to close the holes formed in the first insulating film.
Then, a cavity is formed within each concavity of the substrate and the first and second insulating films thereby become porous. Accordingly, an interlayer insulating film having cavities is formed on the substrate. The dielectric constant of this interlayer insulating film having cavities is apparently lower than that of a similar film without cavities. By experiment, the present inventor has confirmed that the dielectric constant of the interlayer insulating film having cavities was about 2.0. This value is lower than the dielectric constant 4.0 of a conventional SiO
2
film having no cavities. In addition, since the cavities are surrounded by the substrate and the conventional insulating film, no water adsorption occurs in the cavity. In other words, the above process results in formation, on the substrate, of an interlayer insulating film of a low dielectric constant, which has good moisture absorption resistance.
In a third embodiment of the method of the present invention for forming an interlayer insulating film, a first film is formed on a substrate. Then, a pattern is formed in the first film, i.e., a damascene trench which reaches the substrate. Then, a first insulating film is formed on the first film, on a side portion of the damascene trench and on a bottom portion of the same. Anisotropic etching is then performed for the first insulating film to eliminate the first insulating film formed on the bottom portion of the damascene trench while leaving the same formed on the side portion of the damascene trench. Subsequently, a Cu-plated film is buried in the damascene trench. In this case, by the first insulating film formed previously in the side portion of the damascene trench, a component in the first film can be prevented from dispersing into the Cu-plated film. Then, a barrier metal film is formed on the
Canon Sales Co., Inc.
Lorusso & Loud
Nelms David
Nhu David
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