Method of automatically forming a rim phase shifting mask

Details Method of automatically forming a rim phase shifting mask Method of automatically forming a rim phase shifting mask

1998-11-13

2001-09-18

Rosasco, S. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

Reexamination Certificate

active

06291112

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to semiconductor fabrication technologies, and more particularly to a phase-shifting mask (PSM) for use in photolithography in semiconductor fabrication processes. PSM can eliminate ghost lines that would otherwise occur due to side-lobe effect in the resulted pattern definition.
2. Description of the Related Art
In semiconductor fabrication, photolithography is an important and indispensable technique which is used to transfer circuit layout patterns by means of a mask onto predefined locations on a semiconductor wafer. Many processes in semiconductor fabrications, such as etching and ion plantation, require the use of photolithography. In a photolithography process, resolution and depth of focus (DOF) are two major checkpoints used to appraise the quality of the pattern definition. A high level of integration requires a high resolution of pattern definition since the feature size is very small To increase the resolution, a laser source with a very short wavelength, such as a krypton (Kr) deep ultra-violet laser with a wavelength of 2,480 Å (angstrom), is used as the exposure light in the photolithography process. The use of a short-wavelength exposure light, however, will result in a shallow DOF. To allow high resolution and good DOF, one solution is to use the so-called phase-shifting mask (PSM).
Fundamentally, a PSM is formed by adding phase shifter layers onto a conventional mask in order to cause destructive interference to the light passing through the PSM such that the contrast and resolution of the resulting pattern definition can be increased. One benefit of the PSM is that it can increase the resolution of pattern definition without having to change the wavelength of the exposure light.
FIGS. 1A-1C
are schematic, cross-sectional diagrams used to depict three different conventional PSM structures.
FIG. 1A
shows a typical PSM, which includes a quartz substrate
10
, a plurality of chromium (Cr) layers
12
coated over the quartz substrate
10
to serve as the blinding portions of the PSM and a shifter layer
14
that can cause a phase shift to the light passing through it so as to enhance the resolution of the resulting pattern definition from the PSM.
FIG. 1B
shows a conventional rim PSM, which includes a quartz substrate
10
and a plurality of Cr layers
12
coated over the quartz substrate
10
. Each Cr layer
12
is covered by a shifter layer
16
that can cause a phase shift to the light passing through it so as to enhance the resolution of the resulting pattern definition from the PSM.
FIG. 1C
shows a variation of the rim PSM, which differs from the rim PSM of
FIG. 1B
only in that here the shifter layers
16
are layered beneath the Cr layers
12
.
In the foregoing PSM structures respectively shown in
FIGS. 1A-1C
, the shifting layer is formed from MoSi
z
O
x
N
y
or SiO
x
N
y
. One drawback to these conventional PSM structures is that they all require two etching steps, one for defining the Cr layers and the other for defining the shifter layers. The overall fabrication process is therefore quite complex in procedural steps, which makes the manufacturing cost considerably high. Furthermore, the pattern of a shifting layer and the pattern of a Cr layer are designed by hand. Fabrication time is therefore long and mistakes are easily made in the process.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method of automatically forming a rim phase shifting mask for use in photolithography in semiconductor fabrication, which can form patterns of Cr layers and of phase shifting layers automatically using an original file from a circuit design. The method of forming a rim PSM reduces fabricating time and prevents mistakes from being incorporated into the design.
In accordance with the foregoing and other objectives of the present invention, a method of automatically forming a rim PSM is provided. A mask medium comprising a quartz substrate, a phase shifting layer and a Cr film is provided. A first pattern comprising a conventional, original pattern as a blinding layer and assist features around the conventional circuit pattern is designed. A portion of a Cr film and a portion of a phase shifting layer under the Cr film are removed with the first pattern. The removed portion of the Cr film and the removed portion of the phase shifting layer are in the assist feature positions. A second pattern comprising the conventional circuit pattern and a half of the assist feature is designed. A portion of the Cr film in the position other than that of the second pattern is removed. The conventional circuit pattern formed by the mask medium is defined as the blinding layer. The area of the assist features only comprises a quartz substrate that light can pass through. The other area of the mask medium wherein the phase shifting layer remains is defined as the phase-shifting portion of the PSM.


REFERENCES:
patent: 5306585 (1994-04-01), Okamoto
patent: 5827623 (1998-10-01), Ishida et al.

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