Method of forming silicon-containing insulation film having...

Semiconductor device manufacturing: process – Controlling charging state at semiconductor-insulator interface

Reexamination Certificate

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C438S680000

Reexamination Certificate

active

06818570

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a semiconductor technique and more particularly to a method for forming on a semiconductor substrate a silicon-containing insulation film having high mechanical strength by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of the Related Art
As semiconductors have progressed to accommodate a demand for high speed and high density in recent years, a reduction of capacitance between lines is required to avoid signal delays in the multi-layer wiring technology field. Because a reduction in the dielectric constant of a multi-layer wiring insulation film is required in order to reduce the capacitance between lines, insulation films having low dielectric constants have been developed.
Conventionally, a silicon oxide (SiO
x
) film is formed by adding oxygen (O
2
), nitric oxide (NO) or nitrous oxide (N
2
O) as an oxidizing agent to a silicon source gas such as SiH
4
and Si(OC
2
H
5
)
4
and applying heat or plasma energy to the source gas. A dielectric constant (&egr;) of this film was approximately 4.0.
By contrast, by using a spin-coat method using inorganic silicon oxide glass (SOG) materials, a low dielectric constant insulation film having a dielectric constant (&egr;) of approximately 2.3 was formed.
By using a plasma CVD method with CxFyHz as a source gas, a low dielectric constant fluorinated amorphous carbon film having a dielectric constant (&egr;) of approximately 2.0 to 2.4 was formed. Further, by using a plasma CVD method using a silicon-containing hydrocarbon (for example, P-TMOS (phenyltrimethoxysilane) as a source gas, a low dielectric constant insulation film having a dielectric constant (&egr;) of approximately 3.1 was formed. Additionally, by using a plasma CVD method using a silicon-containing hydrocarbon having multiple alkoxy groups as a source gas, a low dielectric constant insulation film having a dielectric constant (&egr;) of approximately 2.5 was formed when optimizing film formation conditions.
However, the above-mentioned conventional approaches have the following problems:
In the case of the inorganic SOG insulation film formed by the spin-coat method, there are problems in that the materials properties are not distributed equally on a silicon substrate and that a device used for a curing process after coating the material is expensive.
In the case of the fluorinated amorphous carbon film formed by the plasma CVD method using CxFyHz as a source gas, there are problems such as low heat resistance (370° C. or lower), poor adhesion with silicon materials, and low mechanical strength of the film formed.
Furthermore, among silicon-containing hydrocarbons, when P-TMOS is used, a polymerized oligomer cannot form a linear structure such as a siloxane polymer because P-TMOS contains three alkoxy groups. Consequently, a porous structure is not formed on a silicon substrate, and hence a dielectric constant cannot be reduced to a desired degree.
When a silicon-containing hydrocarbon containing two alkoxy groups is used, a polymerized oligomer can form a linear structure such as a siloxane polymer by optimizing film formation conditions. Consequently, a porous structure can be formed on a silicon substrate and a dielectric constant can be reduced to a desired degree. However, there are problems in that oligomers having the linear structure have weak bonding power therebetween and thus the mechanical strength of a resultant film is low.
SUMMARY OF THE INVENTION
In view of the above problems, an object of the present invention is to provide a method of forming an insulation film having a low dielectric constant and high mechanical strength. Another object of the present invention is to provide a method of forming an insulation film having a low dielectric constant without increasing device costs.
To solve the above-mentioned problems, in an embodiment of the present invention, the method of forming an insulation film having a low-dielectric constant according to the present invention comprises the following processes: A process of bringing a reaction gas comprising a silicon-containing hydrocarbon having cross-linkable groups such as multiple alkoxy groups and/or vinyl groups, a cross-linking gas, and an inert gas into a reaction chamber, a process of applying radio-frequency power by overlaying first radio-frequency power and second radio-frequency power or applying the first radio-frequency power alone for generating a plasma reaction field inside the reaction chamber, and a process of optimizing the flow rates of respective source gases and the intensity of each radio-frequency power.
As the source gas, a silicon-containing hydrocarbon having multiple cross-linkable groups is used singly or in combination with one or more other silicon-containing hydrocarbons such as those having one or more cross-linkable groups. The cross-linkable groups include, but are not limited to, alkoxy groups and/or vinyl groups. For example, if a silicon-containing hydrocarbon having no or one alkoxy group is exclusively used, a linear siloxane oligomer can be formed when supplementing oxygen using an oxygen-supplying gas as necessary. However, in that case, it is difficult to cross-link oligomers by using a cross-linking gas in order to increase mechanical strength of a resultant film. A silicon-containing hydrocarbon having no or one alkoxy group can be used in an amount less than a silicon-containing hydrocarbon having two or more alkoxy groups. In an embodiment, 10% or more (including 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%) of the gas may be a silicon-containing hydrocarbon having two alkoxy groups in order to predominantly or significantly form linear oligomers. Preferably, as the source gas, the silicon-containing hydrocarbon having multiple alkoxy groups is a linear compound such as dimethyldimethoxysilane (DM-DMOS) or 1,3-dimethoxy-tetramethyldisiloxane (DMOTMDS). A silicon-containing hydrocarbon having a cyclic main structure may be used in an amount less than a linear silicon-containing hydrocarbon. In the above, alkoxy groups include —OC
n
H
2n+1
(n is an integer of 1-4). The source gas can be a compound containing vinyl groups such as 1,3-divinyltetramethyldisiloxane, and similarly to a compound having alkoxyl groups, the compound can form oligomers.
As a cross-linking gas (“cross-linker”), any suitable reactive gas such as CO
2
, ethylene glycol, 1,2-propanediol, isopropyl alcohol (IPA), ethylene, N
2
or diethyl ether can be used which can cross-link oligomers of silicon-containing hydrocarbon. For example, any suitable alcohol, ether, and/or unsaturated hydrocarbon can be used, which include an alcohol selected from the group consisting of C
1-6
alkanol and C
4-12
cycloalkanol, and the unsaturated hydrocarbon selected from the group consisting of C
1-6
unsaturated hydrocarbon, C
4-12
aromatic hydrocarbon unsaturated compounds, and C
4-12
alicyclic hydrocarbon unsaturated compounds. In the foregoing, compounds having a higher number of carbon atoms include, but are not limited to: 1,4-cyclohexane diol (b.p. 150° C./20 mm), 1,2,4-trivinylcyclohexane (b.p. 85-88° C./20 mm), 1,4-cyclohexane dimethanol (b.p. 283° C.), and 1,3-cyclopentane diol (80-85° C./0.1 Torr). Further, compounds having multiple reactive groups (‘mixed’ functionalities, i.e., unsaturated hydrocarbon and alcohol functionalities) can also be used as cross-linkers, which include, but are not limited to: C
3-20
ether such as ethylene glycol vinyl ether H
2
C═CHOCH
2
OH (b.p. 143° C.), ethylene glycol divinyl ether H
2
C═CHOCH
2
CH
2
OCH═CH
2
(b.p. 125-127° C.), and 1,4-cyclohexane dimethanol divinyl ether (b.p. 126° C./14 mm) (H
2
C═C(OH)—CH
2
)
2
—(CH
2
)
6
); and C
5-12
cycloalkanol compounds such as 1-vinylcyclohexanol (b.p. 74° C./19 mm). Usable reactive gases are not limited to the above and will be explained below. As an inert gas, Ar, Ne, and/or He may be used. Further, as an oxygen-supplying gas, O
2
, NO, O
3
, H
2
O or N
2
O can be incl

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