Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2000-01-27
2002-05-14
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S625000, C427S245000
Reexamination Certificate
active
06387824
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of forming a porous film used as, e.g., an inter-layer dielectric in a semiconductor integrated circuit device.
As the integration density of a semiconductor integrated circuit has increased, an increased wiring delay time resulting from an increase in wire-to-wire capacitance, which is aparasitic capacitance between metal wires, has presented an obstacle to the implementation of a semiconductor integrated circuit with higher performance. The wiring delay time is a so-called RC delay which is proportional to the product of the resistance of the metal wire and the wire-to-wire capacitance.
To reduce the wiring delay time, therefore, it is necessary to reduce the resistance of the metal wire or the wire-to-wire capacitance.
As a method of reducing the wire-to-wire capacitance, the reduction of the dielectric constant of an inter-layer dielectric formed between the metal wires has been considered. As an inter-layer dielectric having a low dielectric constant, a porous film has been under study as a replacement for a conventional silicon oxide film. It can be said that the porous film is only the film capable of providing a dielectric constant of 2.0 or lower.
In view of the foregoing, there have been proposed various methods of forming porous films.
As a first conventional method of forming a porous film, there has been known one wherein a solution of a siloxane polymer precursor containing a thermally unstable organic component is prepared and coated on a substrate to form a coated film, which is then subjected to a thermal process for decomposing and eliminating the organic component such that numerous fine holes are formed in hollow portions from which the organic component has eliminated.
As a second conventional method of forming a porous film, there has been known one wherein a wet gel is formed on a substrate by coating a silica sol solution on the substrate or by performing CVO and then the condensation reaction of the silica sol is caused in the wet gel, while the volume reduction of the wet gel is suppressed by controlling the speed at which the solvent eliminates from the wet gel, thus forming the porous film.
As a third conventional method of forming a porous film, there has been known a method wherein a solution of silica fine particles is coated on a substrate to form a coated film, which is then sintered such that numerous fine holes are formed between the adjacent silica fine particles.
However, the first conventional method has the problem of higher cost since it is necessary to prepare the solution of the siloxane polymer precursor. Moreover, since the coated film is formed by coating the precursor solution on the substrate, the amount of silanol remaining: in the coated film is increased to cause such problems as a degassing phenomenon which is the elimination of moisture or the like in a thermal process step performed subsequently and the degradation of the porous film resulting from the absorption of moisture by the film.
On the other hand, the second conventional method has the problem of higher cost since it requires a special coating apparatus for controlling the speed at which the solvent eliminates from the wet gel. Moreover, since a large number of silanol groups remain on the surfaces of the fine holes, they may cause serious degradation of the film because of high moisture absorption, unless they are removed. It is therefore necessary to silylate the surfaces of silanol groups, resulting in a complicated process. In the case of forming the wet gel by CVD, a special CVD apparatus different from a plasam CVD apparatus used normally in a semiconductor process is also required, which also increases cost.
In accordance with the third conventional method, the diameters of the fine holes formed between the adjacent silica fine particles are determined by a geometric configuration in which the silica fine particles are deposited so that the diameters of the fine particles are increased significantly. Accordingly, it is difficult to adjust the dielectric constant of the porous film to 2 or less.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the forgoing problems at once and allow the formation of a porous film having a dielectric constant of 2 or less in a simple process at low cost.
To attain the above object, a first method of forming a porous film according to the present invention comprises the steps of: depositing an organic-inorganic hybrid film on a substrate by plasma enhanced CVD using a gas mixture of a silicon alkoxide and an organic compound as a reactive gas; and forming a porous film composed of the organic-inorganic hybrid film by performing a plasma process using a plasma derived from a gas containing a reducing gas with respect to the organic-inorganic hybrid film.
In accordance with the first method of forming a porous film, the organic-inorganic hybrid film is deposited by plasma enhanced CVD using the gas mixture of the silicon alkoxide and the organic compound. Accordingly, a low-cost material can be used to deposit the organic-inorganic hybrid film. Since the plasma process is performed by using the reducing gas with respect to the organic-inorganic hybrid film deposited by plasma enhanced CVD, the decomposed organic component eliminates and the numerous fine holes are formed in the hollow portions from which the organic compound has eliminated. This ensures the formation of the porous film composed of the organic-inorganic hybrid film and allows molecular-level control of the diameters of the fine holes in the porous film.
A second method of forming a porous film according to the present invention comprises the steps of: depositing an organic-inorganic hybrid film on a substrate by plasma enhanced CVD using a gas mixture of a silicon alkoxide and an organic compound as a reactive gas; and forming a porous film composed of the organic-inorganic hybrid film by performing a thermal process with respect to the organic-inorganic hybrid film in an atmosphere containing a reducing gas.
In accordance with the second method of forming a porous film, the organic-inorganic hybrid film is deposited by plasma enhanced CVD using the gas mixture of the silicon alkoxide and the organic compound. Accordingly, a low-cost material can be used to deposit the organic-inorganic hybrid film. Since the thermal process is performed with respect to the organic-inorganic hybrid film in the atmosphere containing the reducing gas, the decomposed organic component eliminates and the numerous fine holes are formed in the hollow portions from which the organic component has eliminated. This ensures the formation of the porous film of the organic-inorganic hybrid film and allows molecular-level control of the diameters of the fine holes in the porous film.
In accordance with the first or second method of forming a porous film, there is formed the porous film composed of the organic-inorganic hybrid film deposited by plasma enhanced CVD using the gas mixture of the silicon alkoxide and the organic compound. This obviates the necessity for a precursor solution, which is indispensable to the deposition of an organic-inorganic hybrid film by coating, and allows the deposition of the organic-inorganic hybrid film using a low-cost material. Consequently, the cost of the porous film is reduced.
Moreover, since the organic component in the organic-inorganic hybrid film is eliminated by the plasma process using the plasma derived from the gas containing a reducing gas or by the thermal process performed in the gas atmosphere containing the reducing gas and the fine holes are formed in the hollow portions from which the organic component has eliminated, the fine holes having molecular-size diameters can be formed and the dielectric constant of the porous film is reduced reliably.
Furthermore, since the organic-inorganic hybrid film is deposited by plasma enhanced CVD, the amount of remaining silanol is reduced significantly compared with an organic-inorganic hybrid film d
Le Dung Anh
Nelms David
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