Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-08-03
2001-09-04
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06284416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photo mask for exposure process and used for manufacturing semiconductor devices and also relates to a method for manufacturing the same.
2. Description of the Prior Art
A conventional photo mask used for photo-lithography processes, a part of the manufacturing process of semiconductor devices, is so constructed that it is made by forming a certain pattern layer of a thin film layer (a light shielding member) of a metal such as chromium on a glass substrate made of a material such as silica having high tranmittances for an illuminating light of an exposure wavelength. This metal thin film layer is formed on a surface of the substrate by sputtering or evaporation coating, with the thickness enough to almost completely shut off the illuminating light. Further, after a resist layer is laminated, a desired circuit pattern is transferred by a contact or proximity exposure of a master mask or using a direct-write process, and then an undesired portion of the pattern is removed by a process such as etching, etc. thereby obtaining a finished product.
That is, in the conventional photo mask, the circuit pattern is constructed with a transparent portion having the transmittance of 90% or more and the light shielding portion of almost 0% transmittance.
As a photo mask for enhancing the contrast of a projected image, Japanese Patent laid-open No. 62-50811, for example, discloses a so-called phase-shifting mask in which dielectric thin films, called phase shifters, are deposited on a specified part of the transparent portions to give a phase difference about &pgr; radian between light beams passed through the transparent portions adjoining each other. In this phase-shifting mask, the phase of a transmitted light is controlled by the phase shifter, and the phases of the transmitted light beams passed through the adjoining transparent portions are opposed with each other to enhance the contrast of the image.
However, even if the above problem can be solved by the conventional phase-shifting mask, it is necessary to form the phase-shifters selectively on the specified positions of the transparent portions after the usual mask process has been made, with the result the manufacturing process becomes complex thereby causing a defect and high cost.
Moreover, in the conventional photo mask, if the pattern formed on the photo mask is coarse in comparison with the resolution of a projecting lens of an exposure apparatus, the distribution of light intensity of the image formed by a projecting lens has a slight increase of the intensity near the center of each dark portion (corresponding to the light shielding portion of the photo mask) of the pattern image. Therefore, if the positive resist is used for object to be projected, the resist on the dark central portion of the pattern image is also exposed, especially when the large exposure amount is applied, and thus, a concave pattern might be formed on the central portion after the resist is developed.
In addition, as for a mask shown in
FIG. 16
in which phase shifters
210
are deposited on the specified portions of the pattern formed with a light shielding layer
208
on a mask substrate
201
, it is often required to control the intensity of each transmission light passing through a portion attached with the phase shifter
210
and another portion without the phase shifter respectively. Especially, in the phase-shifting masks of edge enhancement type (having an auxiliary pattern) and light shielding effect enhancement type, the line width of the opening (a portion deposited with the phase shifter
210
) in the light shielding layer
208
should be narrow, as shown in
FIG. 17
, in order to limit an amount of transmission light passing through the opening of the light shielding layer
208
. However, if the life width of the opening of the shielding layer
208
is too narrow, the opening will not have a predetermined line width or certain separation at the mask process, and therefore it is difficult to obtain the mask suitable for use.
SUMMARY OF THE INVENTION
The pre sent invention has been made in view of the above described circumstances and it is the primary object of the present invention to provide a photo mask and an exposure method using the same for enhancing the contrast of a pattern image.
Another object of the invention is to provide an easy method to manufacture a photo mask for forming a pattern image of high contrast.
In accordance with one aspect of the present invention, there is provided a photo mask for transferring a predetermined pattern to a photosensitive substrate by using an illuminating light, comprising a transparent portion having a transparence for the illuminating light and a half-transparent portion having a predetermined transmittance for the illuminating light, said transparent portion and said half-transparent portion having a material and/or thickness so determined as to produce a phase difference of 2nR or (2n+1)n radian (n denotes an integer) between the phases of light beams passing through said transparent portion and said half-transparent portion.
In order to enhance the contrast of the pattern image according to the present invention, the mask pattern is constructed with the half-transparent portion having a predetermined transmittance for an illuminated light instead of the light shielding portion, and the pattern image is formed by using interference effect between transmitted lights respectively passing through the transparent portion and the half-transparent portion.
In this case, determining the transmittance of the half-transparent portion within the range from 1 to 15%, as to the positive resist, the resist pattern (convex portion) is prevented from decreasing in its film thickness at the developing, and as to the negative resist, the resist layer is prevented from remaining at the position corresponding to the half-transparent portion after the developing. At this point, the above described transmittance is so determined as not to decrease the film thickness for the positive resist, and not to remain with the resist layer for the negative resist, by all means, based on the exposure light intensity on the mask, the optical characteristics (aberrations) of the projection optical system and the type of the resist. Therefore, the transmittance of the half-transparent portion is not limited to the range from 1 to 15%; and, if the film thickness is not decreased, the transmittance may be selected more than 15% under the certain exposure condition.
Moreover, if the half-transparent portion is constructed with multilayer films stacked with at least two kinds of thin films such as a metal thin film and a dielectric film, a desired transmittance value may be obtained by optimizing each condition (film thickness) of the dielectric and metal thin films. And, in the similar way, it is possible to provide the transmitted light passed through the half-transparent portion with a desired phase difference (2nn or (2n+1)n ) to the transmitted light passed through the transparent portion. Further, if the half-transparent portion is constructed with the multilayer films, to make each film thickness optimum, it is possible to easily control the tranmittance and phase difference. In this case, if an antireflection film is deposited outside the metal thin film which constructs the transparent portion, the reflectivity of the metal thin film pattern on the photo mask is decreased, and multilayer reflection between a wafer and the photo mask is prevented, thereby advantageously enhancing the contrast of the image.
The above described metal thin film and dielectric film can be deposited in layers on a mask substrate and then processed to form a pattern in a time. Thus, the manufacturing process is substantially the same as that of conventional photo masks consisting of transparent portions and light shielding portions, and not so complex as that of the conventional phase-shifting masks.
And, if the half transparent portion is con
Hirukawa Shigeru
Magome Nobutaka
Shiraishi Naomasa
Nikon Corporation
Rosasco S.
Staas & Halsey , LLP
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