Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2001-07-24
2003-01-21
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S790000
Reexamination Certificate
active
06509279
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for processing a silica group coating film having a low dielectric constant used in a copper damascene method, and more specifically to a method for processing a silica group coating film having a dielectric constant equal to or less than 3.2 in the formation of a multi-layer wiring structure using a copper damascene method.
2. Description of Prior Art
The need for high integration of semiconductor devices is increasingly rising, and now we are entering into a generation of 0.13 &mgr;m gate lengths. It is already recognized that, by using Cu as a wiring material in such instances in place of the conventional Al, the characteristics of manufactured semiconductor elements can be improved in the following aspects.
Cu is superior to Al in tolerance for EM (i.e., electromigration). Also, Cu has low resistance, and thereby it is possible to reduce signal delay due to wiring resistance. The use under high current density can be achieved, that is, an allowable current density can be improved by three (3) times or more by the use of Cu as described herein, and thereby the width of wiring used can be fine.
However, since it is difficult to control the etching rate of Cu compared to Al, a copper damascene method attracts attention as a method for realizing multi-layer wiring of Cu without any etching process. Proposals have been made (for example, Japanese unexamined patent application publication No. 2000-174023 and Japanese unexamined patent application publication No. 2000-174121).
Explanation of the copper damascene method will be given with reference to FIG.
5
.
First, as shown in FIG.
5
(
a
), an intermediate insulating film, being comprised of SiO
2
deposited through a CVD method or of SOG and having a low dielectric constant, is formed on a substrate, and a resist mask having a pattern is provided thereon. By etching, as shown in FIG.
5
(
b
), wiring gutters are formed. Next, as shown in FIG.
5
(
c
), the wiring gutters are lined with barrier metal, and as shown in FIG.
5
(
d
), Cu is embedded into the gutters by means of electrolysis plating so as to form a lower layer wiring. After polishing the barrier metal and Cu by chemical polishing, another intermediate insulating film is formed thereon as shown in FIG.
5
(
e
). In the same manner, by selectively etching the intermediate insulating film through a resist mask having a pattern, as shown in FIG.
5
(
f
), via-holes (or contact holes) and trench holes (i.e., gutters for an upper layer wiring) are formed (dual damascene). As shown in FIG.
5
(
g
), the via-holes and the gutters for an upper layer wiring are lined with barrier metal and, as shown in FIG.
5
(
h
), Cu is embedded into the via-holes and the gutters for an upper layer wiring by means of electrolysis plating or the like, and thereby an upper layer wiring is formed.
In the above-mentioned explanation, copper is used for forming wiring in a damascene method. However, a damascene method forming can be conducted with aluminum. The present invention can be applied to a damascene method using various conductive metals as alternatives to copper.
When multi-layer wiring is formed by a damascene method, it is required that an aspect ratio (i.e., height/width) of via-holes should be increased for fine wiring. However, if SiO
2
formed through a CVD method is used for an intermediate insulating film, the aspect ratio will be at most 2. Also, the dielectric constant of SiO
2
is relatively high (∈=4.1), which is not satisfactory.
The use of organic or inorganic SOG having a lower dielectric constant has been examined as a means of overcoming this drawback. Further, it is desired to make organic or inorganic SOG having a lower dielectric constant.
It is recognized that the dielectric constant of an intermediate insulating film can be decreased by making the intermediate insulating film porous. However, the lower dielectric constant of such an intermediate insulating film corresponds to a decrease in the density of the film. As a result, damage or cracking occurs in the intermediate insulating film when a plasma ashing of a resist film is conducted as a subsequent process, and thus it is difficult to obtain a reliable semiconductor element thereby.
It is supposed that the reason for damage to the intermediate insulating film in this case is that Si—R group (R refers to lower alkyl group or hydrogen atom) is decomposed (R group is separated) by the ashing process and a Si—OH bond is produced.
For example, in the case of organic SOG, a Si—CH
3
bond (CH
3
is an example) is broken to be Si—OH. In the case of inorganic SOG, a Si—H bond is broken to be Si—OH.
SUMMARY OF THE INVENTION
According to the present invention, to solve the problems as mentioned above, there is provided a method for processing a coating film comprising the steps of forming a silica group coating film having a dielectric constant equal to or less than 3.2 (preferably equal to or less than 2.7) on a substrate, conducting an etching process to the silica group coating film through a resist pattern, processing the silica group coating film, to which an etching process has been conducted, with plasma induced from inactive gas such as helium gas or the like, and removing the resist pattern by an ashing process.
It is possible to prevent damage resulting from an ashing process by conducting a pre-ashing process with plasma induced from inactive gas such as helium gas or the like. It is supposed that the reason for this preventive effect is that plasma induced from inactive gas such as helium gas or the like attacks the coating film having a Si—H group and the Si—H bond in the surface layer is changed into a Si—O—Si bond.
The dielectric constant equal to or less than 3.2 is required for an intermediate insulating film used in a damascene method. A lower dielectric constant is preferred. The silica group coating film is not limited to a particular one as long as it has such a dielectric constant. The silica group coating film having such a dielectric constant can be achieved by forming with coating liquid as follows:
The coating liquid can include a condensation product which is obtained through hydrolysis of trialkoxysilane within an organic solvent under an acid catalysis. In particular, it is preferable to obtain the coating liquid by dissolving trialkoxysilane having a concentration of 1%-5% by weight in a case of conversion into SiO
2
using alkylene glycol dialkyl ether, adding water of 2.5-3.0 mols per 1 mol of the trialkoxysilane to this solution and adjusting the content of alcohol produced through a reaction in a reacting mixture to be less than or equal to 15% by weight after conducting a hydrolytic condensation under an acid catalyst.
An intermediate insulating film having a ladder structure can be obtained by using trialkoxysilane having a concentration of 1%-5% by weight in a case of conversion into SiO
2
. Independent of being organic or inorganic, by making a ladder structure, a film which is dense and has a low dielectric constant can preferably be formed.
As the above-mentioned trialkoxysilane, it is possible to list trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, diethoxy monomethoxysilane, monomethoxy dipropoxysilane, dibutoxy monomethoxysilane, ethoxy methoxy propoxysilane, monoethoxy dimethoxysilane, monoethoxy dipropoxysilane, butoxy ethoxy propoxysilane, dimethoxy monopropoxysilane, diethoxy monopropoxysilane, and monobutoxy dimethoxysilane. Among these, compounds preferable in practice are: trimethoxysilane, triethoxysilane, tripropoxysilane, and tributoxysilane. In particular, trimethoxysilane and triethoxysilane are preferable.
As the solvent, in order to increase the stability of preservation, it is necessary to use alkylene glycol dialkyl ether. By using this, it is possible to control a decomposition reaction of a H—Si group in trialkoxysilane or a substitution reaction of a hydroxy group for an alkoxy group in silanol produced as an intermediate produ
Fujii Yasushi
Matsushita Atsushi
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Dang Phuc T.
Nelms David
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