Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Removal of imaged layers
Reexamination Certificate
2000-07-12
2003-02-11
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Removal of imaged layers
C430S311000, C134S001300
Reexamination Certificate
active
06517998
ABSTRACT:
TITLE OF THE INVENTION
The present invention relates to a method of removing a film containing an organic composition, particularly to a method of removing a photoresist film containing an organic polymer composition used in a photolithographic process for producing a semiconductor device and the like, and to an apparatus used in the method.
DESCRIPTION OF THE RELATED ART
A photoresist material is generally used in a photolithographic process for forming a fine pattern and/or in a subsequent etching step for forming an electrode pattern in course of manufacturing a semiconductor device, such as an integrated circuit, a transistor, a liquid crystal device, a diode and the like.
For example, when a silicon oxide layer is formed in a desired pattern on a semiconductor substrate such as a silicon substrate (referred to as a silicon wafer), a silicon oxide layer is first deposited on the surface of the substrate and cleaned before a photoresist material suited for forming the desired pattern is applied to the silicon oxide layer to form a photoresist film. Then, a photo mask having a pattern corresponding to the desired pattern is placed on the photoresist film, exposed to light and then developed. Thereby, a photoresist film having the desired pattern, referred to a photoresist pattern, is obtained. In the subsequent etching step, the silicon oxide layer is removed according to the resulting photoresist pattern. Finally, after the removal of the remaining photoresist film and the cleaning of the surface of the substrate, the silicon oxide layer is remained on the substrate in the desired pattern.
In the etching step, an art-known method of removing a part of the photoresist film unnecessary for the formation of the desired pattern includes, for example, [1] a method using an oxygen gas plasma and [2] a method using various oxidizing agents.
In the method using an oxygen gas plasma [1], an oxygen is introduced in the photoresist film under vacuum and a high voltage to generate an oxygen gas plasma. Then, the photoresist film is decomposed and removed by reacting with the oxygen gas plasma. However, there had been some problems in this method [1], including the requirement of an expensive apparatus for generating the oxygen gas plasma, a potential of damaging the substrate containing an electrical element due to the presence of charge carriers in the plasma, and the like.
Alternatively, as an example of the method [2] using various oxidizing agents to decompose and remove the photoresist film, for example, a method using hot concentrated sulfuric acid or a mixture of hot concentrated sulfuric acid and hydrogen peroxide as the oxidizing agent is known.
When using hot concentrated sulfuric acid, however, there is a disadvantage, such as an extremely high risk of heating strong sulfuric acid up to 150° C.
On the other hand, when using the mixture of hot concentrated sulfuric acid and hydrogen peroxide, a substance having an oxidizing and decomposing action is released according to the following scheme. In the scheme, on adding hydrogen peroxide to hot concentrated sulfuric acid heated to about 140° C., peroxosulfuric acid (H
2
SO
5
; generally referred to as Caro's acid) and an oxygen atom (O) are generated as follows:
H
2
SO
4
+H
2
O
2
⇄H
2
SO
5
+H
2
O (1)
H
2
O
2
→O+H
2
O (2)
The organic photoresist film may be oxidized by the strong acidity of both peroxosulfuric acid and oxygen atom to be converted to an inorganic substance. The inorganic substance is decomposed by reacting with hot concentrated sulfuric acid and then removed from the surface of the substrate.
However, as shown in the above schemes (1) and (2), this method [2] has a problem that, since a sulfuric medium is diluted with water produced upon every addition of hydrogen peroxide to hot concentrated sulfuric acid, the concentration of hot concentrated sulfuric acid after mixing is decreased with time. The method [2] also has disadvantages, including the extremely high risk as described for the method [1], i.e. the use of strong sulfuric acid at an elevated temperature, and the heat generated when mixing hot concentrated sulfuric acid with hydrogen peroxide, and the necessity system generating strong ventilation in order to operate the method in a clean room, and the like.
As another oxidizing agent used to decompose the photoresist film other than hot concentrated sulfuric acid, there has been developed a water-immiscible solution for exclusively removing a photoresist film, such as, for example, a solution #
106
consisting of 30% by volume of dimethylsulfoxide and 70% by volume of monoethanolamine. However, such oxidizing agent has problems, including its lower oxidation power than hot concentrated sulfuric acid and a mixture of hot concentrated sulfuric acid and hydrogen peroxide, and the difficulty of treating the foul solution which is immiscible with water.
In order to overcome the problems of the above methods [1] and [2], a method of removing a photoresist film using a mixture of ozone with hot sulfuric acid as the oxidizing agent has been proposed (Japanese Patent Kokai Publication No. Sho 57 (1982)-180132). This publication discloses decomposing and removing the organic substance (i.e. the photoresist film) or the inorganic substance deposited on the substrate or the insulating layer by bubbling an ozonized gas in hot sulfuric acid. It also describes a washing apparatus used in the method cross sectional view of the apparatus is illustrated in FIG.
8
).
The washing apparatus shown in
FIG. 8
includes a quartz container
6
″ filled with hot concentrated sulfuric acid 5′ heated at approximately 110° C., which is laid on a heater
11
, and a quartz tube
120
having plural of outlet
3
′. A raw gas (generally, oxygen) supplied through a gas-introducing tube
111
provided outside the quartz container
6
″ is converted to an ozonized gas in on an ozone generator
1
. The ozonized gas is then injected through the quartz tube
120
into hot concentrated sulfuric acid
5
′ in the quartz container
6
to react with sulfuric acid, and thereby, peroxosulfric acid and an oxygen atom are produced. Oxidizing the photoresist film with the strong acidity of both peroxosulfric acid and oxygen causes the removal of the photoresist film from the surface of the substrate
8
(held with a substrate cassette
9
) immersed in hot concentrated sulfuric acid.
In the method described in the above publication, the concentration of the sulfuric acid does not change since water is not generated during the decomposition of the photoresist film, and therefore, the frequency of changing the sulfuric acid may be decreased. The method, however, had a problem that the cost for raw materials is too high because a large amount of the sulfuric acid is needed to operate. Additionally, the method and apparatus disclosed in the above publication also have a high risk on working because of the use of strong sulfuric acid at an increased temperature in the same way as the conventional method, and also needs an extremely strong ventilation since the oxidizing agent is volatilized by bubbling the ozonized gas.
Accordingly, an object of the present invention is to provide a method of removing a photoresist film at an increased rate, which decreases both usage of the raw materials and the cost for any exhaust system and is also environment-friendly, and to further provide an apparatus used in the method, in order to overcome the above problems with the art-known method of removing the photoresist film and with the conventional apparatus used therefore.
Definition of the Technical Terms
As using herein, an “ozonized gas” means a gas mixture containing oxygen and a given amount of ozone. Hereinafter, a “sealed system” is thermodynamically classified into an open system, but it means one in which any of a gas and a solution are introduced therein and a gas or a vapour gene
Kuzumoto Masaki
Miyamoto Makoto
Noda Seiji
Oya Izumi
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