Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of...
Reexamination Certificate
2000-06-28
2002-10-01
Sherry, Michael (Department: 2829)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Reexamination Certificate
active
06458713
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-182057, filed Jun. 28, 1999; and No. 11-186996, filed Jun. 30, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a method for manufacturing a semiconductor device, and in particular to a method of forming an insulating film of low dielectric constant, which is useful in a semiconductor device.
Due to the increasing integration and speed of semiconductor device through the miniaturization of semiconductor elements in recent years, the parasitic capacity of wiring now becomes a factor giving a great influence on the operation speed and power consumption of the device. Under the circumstances, there is now intensively studied for finding an insulating film having a dielectric constant which is lower than that of the conventional SiO
2
film.
As one of candidates for such a material, an insulating film of low dielectric constant represented by an organosilicon oxide film has been studied. This organosilicon oxide film is formed by a coating method. Namely, a precursor of the organosilicon oxide is dissolved in a solvent to obtain a liquid raw material or so-called varnish, which is then coated on a substrate and heated so as to volatilize the solvent and to perform the crosslinking (polymerization) of the precursor, thereby obtaining the organosilicon oxide film.
The insulating film formed through a coating method of this kind is featured in that the properties thereof such as dielectric constant and hygroscopicity are greatly influenced by the atmosphere of the heating step. Therefore, once it is desired to obtain an insulating film of stable properties, the atmosphere of the heating step is required to be precisely controlled.
An electric furnace of batch type which is now generally employed is defective in that it is difficult to make uniform the atmosphere inside the furnace, resulting in that the uniformity of temperature throughout the surface of the substrate as well as the reproducibility of heating condition for each of substrates would be deteriorated.
With a view to overcome these problems, there has been proposed a method of forming an insulating film by means of a coating method where a single wafer type hot plate is employed.
FIG. 1
illustrates a schematic view of a conventional insulating film-forming device for executing the aforementioned coating method.
In the formation of an insulating film by means of coating method, a heat treatment is required to be performed after the coating of a varnish on the surface of substrate in order to volatilize the solvent and to achieve the crosslinking of the precursor of the organosilicon oxide contained in the varnish.
The conventional insulating film-forming device shown in
FIG. 1
is designed to execute this heat treatment by making use of a plurality of hot plates.
Specifically, first of all, a varnish comprising polymethyl siloxane dissolved in a solvent is coated on the surface of an Si substrate (not shown) by making use of a coater
81
, and then, the Si substrate is transferred by means of a transferring arm
82
onto a hot plate
83
maintained at a temperature of 80° C. After being heat-treated for one minute on the hot plate
83
, the Si substrate is transferred onto another hot plate
84
maintained at a temperature of 200° C. so as to be heat-treated for one minute thereon. Thereafter, the Si substrate is again transferred onto still another hot plate
85
maintained at a temperature of 450° C. so as to be heat-treated for thirty minutes thereon, thereby obtaining an aimed insulating film.
According to this method where a plurality of hot plates are employed, it is possible to enhance the uniformity of temperature throughout the surface of the substrate and also to enhance the reproducibility of sintering condition for every one of substrate. This insulating film formed by making use of a plurality of hot plates however is accompanied with problems that the crack-resistant film thickness and mechanical strength thereof are relatively low as compared with an insulating film formed by making use of an electric furnace. By the way, this phrase of “crack-resistant film thickness” means a minimum film thickness which may allow the generation of cracking in the film due to an stress of the film per se. An insulating film formed by means of coating method is required to be large in crack-resistant film thickness.
FIG. 2
shows a result investigated of a relationship between the relative dielectric constant and the crack-resistant film thickness in an insulating film formed according to the aforementioned conventional method. The relative dielectric constant of the insulating film was adjusted in this case by decreasing the concentration of methyl group in the liquid raw material. It will be seen from
FIG. 2
that where the relative dielectric constant is 3.2 or less, the crack-resistant film thickness decreases in proportion to a decrease of the relative dielectric constant.
The reasons for the deterioration of the crack-resistant film thickness and mechanical strength of the insulating film can be attributed to as follows. Namely, according to the aforementioned conventional method, since a thermal history is applied as shown in
FIG. 3
to the film as the film is being formed, the temperature of substrate is lowered on the occasion of transferring the substrate from one hot plate to the next hot plate, but the temperature of substrate is caused to sharply increase immediately after the film is mounted on the next hot plate.
Therefore, in the case of the aforementioned conventional method, a thermal stress due to the lowering of substrate temperature as mentioned above is imposed on the film being formed and incomplete in crosslinking, which phenomenon is assumed to be one of the reasons for deteriorating the crack-resistant film thickness and mechanical strength of the film.
Further, in the case of the aforementioned conventional method, the generation of crosslinking defect as well as porosity is caused to increase in the film due to a sharp increase in temperature of the substrate as mentioned above, which phenomenon is also assumed to be one of the reasons for deteriorating the crack-resistant film thickness and mechanical strength of the film. This phenomenon is also a cause for the generation of surface ruggedness of the film.
On the other hand, when an insulating film is to be formed by means of coating method, the volatilization of solvent is generally performed at a temperature of not more than 200° C. and the crosslinking reaction is performed at a temperature of not less than 400° C.
By the way, according to the conventional heat treatment of the film, an unreacted portion is caused to remain in the film, thereby making the film unstable, thus raising problems such as degassing, moisture absorption, an increase in relative dielectric constant, the generation of cracks, etc.
As mentioned above, according to the conventional method of forming an insulating film by means of a coating method using hot plates, it is certainly possible to enhance the uniformity of temperature throughout the surface of the substrate and also to enhance the reproducibility of sintering condition for every one of substrate. However, the resultant insulating film is accompanied with problems that the crack-resistant film thickness and mechanical strength thereof are lowered.
Further, the conventional heat treatment is defective in that since an unreacted portion is caused to remain in the film, the resultant film becomes unstable, thereby raising problems such as degassing, moisture absorption, an increase in relative dielectric constant, the generation of cracks, etc.
BRIEF SUMMARY OF THE INVENTION
Therefore, an object of this invention is to provide a method of forming a film, which is capable of preventing the crack-resistant film thickness and mechanical strength of the film from being deteriorate
Kawai Motonobu
Miyajima Hideshi
Nakata Rempei
Yamada Nobuhide
Finnegan, Henderson, Garrett & Dunner, L.L.P.
Kilday Lisa
Sherry Michael
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