Method of forming a photoresist pattern on a semiconductor...

Details Method of forming a photoresist pattern on a semiconductor... Method of forming a photoresist pattern on a semiconductor...

2000-04-27

2001-04-10

Le, Vu A. (Department: 2824)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

C438S636000, C438S152000

Reexamination Certificate

active

06214637

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method of forming, on a semiconductor substrate, a photoresist pattern used for etching a highly reflective layer.
2. Description of the Related Art
As the integration and performance of semiconductor devices continues to increase, a higher level of technology is required to form the fine patterns necessary to produce such highly integrated and high performance semiconductor devices. The fine patterns of semiconductor devices are generally formed through a photolithography process. However, during photolithography, light reflected to a photoresist layer from a layer disposed beneath the photoresist layer causes the following problems.
First, it is difficult to produce a fine line width because a ripple is generated in the profile of the photoresist pattern due to a standing wave generated by the interference of light waves propagating in the photoresist layer. Although the ripple is removed during post-exposure baking, the photoresist pattern is undercut or is deformed so as to have the shape of a tail.
Second, although constant exposure energy is used, a swing effect occurs in which the amount of light absorbed by the photoresist layer varies according to the thickness of the photoresist layer. The swing effect also occurs due to the interference of light waves in the photoresist layer. The swing effect makes it difficult to produce a fine line width within a required range.
Third, notching or bridging is produced in the photoresist pattern by light reflecting from the region of a step in an underlayer, i.e., a layer produced beneath the photoresist pattern during the manufacture of the semiconductor device.
FIGS. 1 and 2
illustrate a conventional manufacturing process in which these problems are likely to arise.
Referring first to
FIG. 1
, an underlayer
52
having a step difference is formed on a semiconductor substrate
50
. A highly reflective layer
54
having a high refractive index, such as a transparent insulating film, is formed on the underlayer
52
. A photoresist layer
56
is coated on the highly reflective layer
54
. Light
62
produced by exposure equipment (not shown) is passed through a mask
60
, having a light blocking layer
58
, in order to irradiate selected portions of the photoresist layer
56
.
Referring now to
FIG. 2
, after the photoresist layer
56
is exposed through the process shown in
FIG. 1
, the photoresist layer
56
is developed to form photoresist patterns
64
and
66
. The photoresist pattern
64
formed over a region of the underlayer
52
in which there is no step difference has a fine line width that is relatively uniform. However, the photoresist pattern
66
formed from that part of the photoresist layer
56
overlying the step difference in the underlayer
52
has a deformed line width pattern. This deformation is produced due to the interference of light waves
62
irradiating the highly reflective layer
54
. When the deformation becomes severe, a notching or bridging defect, which is a critical defect in the fine line width pattern, is produced.
A conventional process has employed an anti-reflective coating (ARC) to combat these problems.
FIG. 3
illustrates a conventional method of manufacturing a semiconductor device using such an anti-reflective coating (ARC).
In
FIG. 3
, reference numeral
68
denotes an ARC formed between the photoresist layer
56
and the highly reflective layer
54
. In this case, the light reflected from the underlayer
54
and the ARC
68
to the photoresist layer
56
consists of the light ê ;
1
, reflected from the interface between the ARC
68
and the photoresist layer
56
, and the light ê ;
2
, reflected from the interface between the highly reflective layer
54
and the ARC
68
. The ARC can reduce the amount of reflected light ê ;
1
+ê ;
2
reaching the photoresist layer
56
by ensuring that the phase difference between ê ;
1
and ê ;
2
is 180° so as to give rise to destructive interference, or by absorbing almost all of the reflected light ê ;
1
or ê ;
2
. In the former case the ARC is referred to as an interference type of ARC and in the latter case as an absorption type of ARC. A hybrid type of ARC having some of the characteristics of an interference type of ARC and an absorption type of ARC has also been developed.
The forming of such ARCs by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of hydrocarbon and helium has been disclosed in U.S. Pat. No. 5,569,501 issuing on Oct. 29, 1996 and entitled “Diamond-like Carbon Films Form Hydrocarbon Helium Plasma”. In the PECVD method, an amorphous carbon layer is formed by controlling the temperature only under the substrate in a plasma chamber. However, this process is problematic in that the helium used as a carrier gas damages the anti-reflective coating during the generation of plasma or otherwise acts to limit the quality of the anti-reflective coating which can be produced.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of forming a photoresist pattern, having a fine uniform line width that is free of bridging or notching, on a semiconductor substrate on which a stepped highly reflective layer has been formed.
To achieve this object, the method includes a step of forming an antireflective coating (ARC) using only a hydrocarbon based gas on the highly reflective layer. The hydrocarbon based gas is preferably methane, ethane, propane, butane, acetylene, propene, or n-butane gas. The photoresist pattern is then formed on the ARC.
Another object of the present invention is to provide such a method of forming a photoresist pattern, in which the anti-reflective coating (ARC) has excellent etching selectivity, is economical to produce, and can be easily removed once the photoresist pattern has been formed.
To achieve this object, the ARC is formed by plasma enhanced chemical vapor deposition (PECVD), during which the temperature on and under the substrate is controlled. In this case, an amorphous carbon ARC layer is produced from the hydrocarbon based gas. The amorphous carbon film preferably has a refractive index of 1.2 to 2.5, and an extinction coefficient of 0.2 to 0.8.
The semiconductor substrate is preferably a single crystal silicon substrate, an SOI substrate, an SOS substrate, or a gallium arsenide substrate. The highly reflective layer is typically formed of W, WSi
x
, TiSi
x
, Al, or an Al alloy.
To assist the ARC in preventing excessive light from reflecting to the photoresist from the highly reflective layer, an insulating film can be interposed between the highly reflective layer and the photoresist. The insulating film may be formed between the highly reflective layer and the ARC or between the photoresist and the ARC. The insulating film is preferably formed of polysilicon oxide, thermally grown silicon oxide, or SiON.
The method of the present invention may also include a step of adding at least one additive selected from the group consisting of oxygen, tin, lead, silicon, fluorine, and chlorine to the amorphous carbon film. The density of the ARC is preferably increased by subjecting the ARC to an annealing process, or a plasma process, an E-beam process, and a curing process.
According to the present invention, once the photoresist pattern is formed, the ARC and the highly reflective layer can be etched using the photoresist pattern as a mask. The photoresist pattern and the ARC can be simultaneously removed from the resultant because the ARC is of an organic material.
The ARC is preferably formed to a thickness of 150 to 10,000 Å. A mixture of oxygen and argon gases is preferably used for etching the ARC. The highly reflective layer may be sequentially or simultaneously removed with the ARC.
According to the present invention, using only a hydrocarbon based gas in forming the ARC keeps the manufacturing costs low compared to when using several thin film forming

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