Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-06-02
2003-07-01
Duda, Kathleen (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S313000, C430S327000, C430S330000, C216S041000
Reexamination Certificate
active
06586163
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a new method of forming a fine pattern through use of a nitride-silicon-based film. Particularly, the present invention relates to a method of forming a fine pattern, which can minimize the effectiveness of a standing wave in a photoresist film during a photolithography step at the time of formation of a fine pattern and can improve the stability of a nitride-silicon-based film during a device fabrication step. The present invention can be utilized as, for example, a method of forming a fine pattern in the course of fabrication of a semiconductor device.
2. Description of the Background Art
A technique of diminishing the amount of exposing radiation reflected by a substrate (i.e., an anti-reflection technique) has been known as a peripheral technique required for satisfying the dimensional precision and resolution needed in fabrication of an ULSI device. In the event that exposing radiation is reflected by a substrate, a thin-film interference phenomenon arises within a photosensitive thin film, such as a photoresist film. As a result of occurrence of the thin-film interference phenomenon, there arise variation in exposure light in the thicknesswise direction of the resist film, which inconsistencies are called standing waves, thereby resulting in deteriorated resolution of a resist pattern.
Further, in the event that exposing radiation is reflected by a substrate, there arise variations in the dimension of a pattern associated with variations in the thickness of a resist, the variations being called multiple interference. The variations in turn deteriorate the dimensional precision of the resist pattern. The exposing radiation reflected by the substrate randomly travels in an oblique direction, because of irregularities in the substrate. As a result, regions which are originally intended to be shielded may be exposed, thereby hindering formation of a desired pattern (i.e., resulting in occurrence of a halation phenomenon). The problem becomes more noticeable in proportion to the intensity of the light reflected from the substrate. Consequently, if the reflected light is diminished, the problem is prevented. For this reason the number of attempts to diminish the light reflected from the substrate becomes higher than ever.
Anti-reflection methods can be roughly divided into two categories. One of those is a method in which a so-called absorptive film or a film having the characteristic of strongly absorbing exposing radiation is employed as an anti-reflection film. The other is a method which prevent reflection utilizing light interference.
The former anti-reflection method is typified by an ARC (Anti-Reflective Coating) method under which an absorptive organic film is applied to a substrate in advance before coating of resist. The almost portion of light that has passed through a resist film and travels toward a substrate is absorbed by the absorptive organic film before the light reaches the surface of the substrate. Therefore, the intensity of the light which has returned from the substrate is diminished. The ARC method is described in “Proceeding of SPIE, Vol. 1463, pp. 16 to 29, 1991, as well as in Japanese Patent Application Laid-Open No. 93448/1984.
An example anti-reflection method using light interference is a method of depositing an anti-reflection film, such as SiO
X
N
Y
or SiN
X
, on a high-reflection substrate such as Al, W, Si, or WSi. According to this method, the thickness of the anti-reflection film is set such that the light reflected from a boundary surface between a photoresist film and an anti-reflection film is reverse in phase with the light reflected from a boundary surface between the anti-reflection film and the substrate. In this case, the reflected light rays cancel each reflected light which enters the photoresist film.
The latter anti-reflection method is described in Japanese Patent Application Laid-Open Nos. 6540/1984, 130481/1982, “Proceeding of SPIE” Vol. 2197, pp. 722 to 732, 1994, and “Technical Digests of International Electronic Device Meeting” pp. 399 to 402, 1982.
In a case where a substrate having a large step is subjected to the ARC method, as shown in
FIG. 1
, the portion of an anti-reflection film
102
located above the step becomes thinner than the portion of the same surrounding the step. For this reason, the thickness of the anti-reflection film
102
must be set to a sufficient value in consideration of the diminished thickness portion of the anti-reflection film located above the step. However, in a case where a thick anti-reflection film is used for forming a fine pattern, the ratio of the thickness of the anti-reflection film to the width of a pattern; that is, an aspect ratio, becomes very large. In this case, processing of an anti-reflection film becomes very difficult, wherewith a failure, such as a tilt, is likely to arise in the thus-formed pattern.
The anti-reflection film, which is made of SiO
X
N
Y
or SIN
X
and is used for preventing reflection through utilization of light interference, can be deposited by means of the CVD method. Even in a case where a step arises in the substrate, a uniform thickness can be attained. Therefore, the anti-reflection method utilizing light interference provides an anti-reflection effect better than that achieved by the ARC method.
The surface of an anti-reflection film, which is made of, e.g., SiO
X
N
Y
or SiN
X
and has conventionally been used for the anti-reflection method utilizing light interference, contains a large amount of basic nitrogen. In a case where the substrate is exposed while a positive chemically-amplified resist is applied to the anti-reflection film, acid contained in the resist bonds to the lone pair of electrons of each of nitrogen atoms contained in the surface of the anti-reflection film during the course of a baking step (PEB step) to which the resist is to be subjected after exposure. As a result, there arises a reduction in the acid content in the boundary surface between the resist and the substrate.
The photoresist has the property such that an area whose acid content is decreased is less soluble in a developer solution. Because of this property, in the event of a reduction arising in the acid content in the boundary surface between the photoresist and the substrate, rounded corners are likely to arise in the resist pattern. The rounded corners are not preferable, because control of a pattern width is deteriorated by the rounded corners arising in the resist pattern.
In order to solve the problem, there has been proposed a method of applying a photoresist to a substrate after a nitrogen-free substance (for example, an SiO film prepared through use of the plasma CVD technique) has been deposited on the surface of an anti-reflection film (Japanese Patent Application Laid-Open No. 189441/1998). However, the test conducted by the inventors has shown that occurrence of rounded corners cannot be prevented by means of depositing an SiO film on an anti-reflection film.
In a case where an anti-reflection film, which is made of SiO
X
N
Y
or SiN
Y
, is deposited on a substrate at a temperature of, for example, less than 400° C., by means of the plasma CVD technique, the resultant anti-reflection film contains a large amount of hydrogen atoms. If the device fabrication process is carried out while the anti-reflection film containing a large amount of hydrogen atoms is left in the semiconductor device, hydrogen contained in the anti-reflection film desorbs from the film and spreads in interconnections, which are made of amorphous silicon or copper, or an interlayer film, such as a BPSG, as the wafer undergoes various baking steps to be carried out during the course of the fabrication process. Spreading of hydrogen involves degradation of interconnections or an interlayer film, which in turn deteriorates the reliability of a semiconductor device.
For instance, in the case of the step shown in
FIG. 4
, the step of depositing the anti-reflection film
7
is followed by a step of
Arai Hiroki
Okabe Ichiro
Duda Kathleen
Foley & Lardner
Semiconductor Leading Edge Technologies Inc.
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