Phase shift mask and method of manufacture

Details Phase shift mask and method of manufacture Phase shift mask and method of manufacture

2001-02-23

2003-02-04

Rosasco, S. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

Reexamination Certificate

active

06514642

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase shift mask and a method of manufacturing the phase shift mask. More particularly, the invention relates both to a novel phase shift mask having sufficient transmittance as well as durability, and thus stability over time, to irradiation by short-wavelength, high-energy light such as ArF excimer laser light and F
2
laser light, and also to a method for manufacturing such phase shift masks.
2. Prior Art
The shifter material used in halftone phase shift masks is often composed primarily of molybdenum silicide, although chromium oxide-based materials are also used.
As shown in
FIG. 5
, which is incorporated in and constitutes part of the specification, a halftone phase shift mask is comprised of a quartz substrate
32
on which there is provided a shifter
34
which changes the phase of the light. The mask improves resolution by utilizing an interference effect between light that passes through the shifter
34
and undergoes a change of phase, and light that does not pass through the shifter
34
and does not undergo a change of phase.
The trends toward higher processing speeds and a higher level of integration in large-scale integration (LSI) chips have created a need for a smaller pattern rule in semiconductor devices. The photomasks used to form those finer patterns must likewise be produced to a smaller feature size.
Efforts are being made to develop phase shift masks which meet these criteria. However, further reduction in the minimum feature size on the masks will require lowering the wavelength of exposure light emitted by the light source used during mask fabrication from the i-line wavelength (365 nm) to that of KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), and eventually F
2
laser light (157 nm).
This is because, in lithography, the resolution is proportional to the wavelength of the exposure light, as indicated by the Rayleigh formula:
R=k&lgr;/NA.
In the formula, R is the resolution, k is the process coefficient, &lgr; is the wavelength, and NA is the numerical aperture of the lens.
However, the molybdenum silicide-based shifter films which are most commonly used today have such a large absorption coefficient that very little, if any, short-wavelength light in the ArF excimer laser light (193 nm) and F
2
laser light (157 nm) regions passes through. Hence, these films are unsuitable for use together with such shorter wavelength exposure light sources.
In the case of chromium-based shifter films, those composed solely of chromium metal have very little transmittance for the simple fact that they are metal. Even if the chromium metal has oxygen, nitrogen or carbon added to it, a transmittance sufficient for use as a phase shifter material in a short-wavelength region of 193 nm or less, such as a transmittance of 3 to 40%, has been difficult to achieve.
Moreover, because short-wavelength light of 193 nm or less has a much higher energy than 365 nm or 248 nm light, like the mask substrate and the lens optics, the phase shifter material is subject to deterioration over time. A need is thus felt for the development of a material capable of enduring high-energy irradiation.
At the same time, the phase shifter material must be capable of effecting a 180 degree shift in the phase of light that passes through the shifter layer relative to light that does not pass through. Bearing in mind the topography of the shifter layer pattern, by forming the shifter film to a thickness D, defined as
D=&lgr;/
2(
n−
1)  (1),
from a material having a high refractive index, a 180-degree phase shift can be achieved at a small film thickness, or step, on the substrate. In the above formula, D is the shifter film thickness for generating a 180-degree phase shift, n is the refractive index of the shifter material, and &lgr; is the wavelength of the transmitted light.
However, prior-art chromium-based and molybdenum silicide-based shifter materials cannot provide a high refractive index at shorter exposure light wavelengths (i.e., wavelengths of 193 nm or less). Hence, they must have a large film thickness, and achieve a phase shift of 180 degrees only with difficulty.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide phase shift masks which resolve the above drawbacks of prior-art halftone phase shift masks and make it possible to fabricate semiconductor integrated circuits having a smaller minimum feature size and a higher degree of integration. Another object of the invention is to provide a method of manufacturing such phase shift masks.
An additional object of the invention is to provide a phase shifter material which has good durability to small-wavelength, high-energy irradiation such as ArF excimer laser light and F
2
laser light, and thus undergoes little deterioration over time
A further object of the invention is to provide phase shift masks which, by employing a shifter material endowed with a relatively high refractive index to short-wavelength exposure light having a wavelength of 193 nm or less and minimizing the topography of the master pattern surface at which the exposure beam is focused, are capable of a 180-degree change of phase, and can improve the profile shape at the time of exposure. A still further object of the invention is to provide a method of manufacturing such phase shift masks.
The inventor has found that by using molybdenum metal or molybdenum silicide as the target and SiF
2
as the reactive gas, or by using chromium metal or chromium silicide as the target and SiF
2
as the reactive gas, it is possible to form a high-performance fluorine-doped molybdenum silicide film or fluorine-doped chromium silicide film which shifts the phase of exposure light passing through it by 180±5 degrees and has a transmittance to short wavelengths of 193 nm or less of 3 to 40%, properties that cannot both be achieved with the chromium-based and molybdenum silicide-based shifter materials used to date. This discovery has made it possible to effectively resolve the problems inherent in prior-art halftone phase shift masks, enabling phase shift masks to be provided which are capable of further reducing the minimum feature size and increasing the level of integration in semiconductor integrated circuits.
Accordingly, in a first aspect, the invention provides a phase shift mask comprising an exposure light-transmitting substrate and a second light-transmitting region on the substrate, which second light-transmitting region functions as a phase shifter and is made of a fluorine-doped molybdenum silicide film formed by a sputtering technique that uses molybdenum metal as the target and SiF
2
as the reactive gas.
In a second aspect, the invention provides a phase shift mask comprising an exposure light-transmitting substrate and a second light-transmitting region on the substrate, which second light-transmitting region functions as a phase shifter and is made of a fluorine-doped molybdenum silicide film formed by a sputtering technique that uses molybdenum silicide as the target and SiF
2
as the reactive gas.
In a third aspect, the invention provides a phase shift mask comprising an exposure light-transmitting substrate and a second light-transmitting region on the substrate, which second light-transmitting region functions as a phase shifter and is made of a fluorine-doped chromium silicide film formed by a sputtering technique that uses chromium metal as the target and SiF
2
as the reactive gas.
In a fourth aspect, the invention provides a phase shift mask comprising an exposure light-transmitting substrate and a second light-transmitting region on the substrate, which second light-transmitting region functions as a phase shifter and is made of a fluorine-doped chromium silicide film formed by a sputtering technique that uses chromium silicide as the target and SiF
2
as the reactive gas.
In the phase shift mask of the above first, second, third or fourth aspect of the invention, the phase shif

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