Phase shift mask and phase shift mask blank

Details Phase shift mask and phase shift mask blank Phase shift mask and phase shift mask blank

1998-12-17

2002-01-01

Nguyen, Nam (Department: 1753)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

C204S192150, C204S192220, C204S192230

Reexamination Certificate

active

06335124

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase shift mask for use in the exposure and transfer of a fine pattern and a phase shift mask blank or the like as its parent material. More particularly, the present invention relates to a halftone phase shift mask and a halftone phase shift mask blank or the like.
2. Description of the Related Art
In the art of DRAM (Dynamic Random Access Memory), the trend toward high integration beginning with 1 Mbit has gone so far as to establish a system for the mass production of 64 Mbit and 256 Mbit DRAM's at present. This technological innovation witnessed a tendency toward the use of ultrahigh voltage mercury vapor lamp emitting light having a shorter wavelength, i.e., i-ray (365 nm) instead of g-ray (436 nm), as an exposing light source. The reduction of the wavelength of exposing light is being still considered for further integration. In ordinary photolithographic process, however, the reduction of the wavelength of exposing light causes the reduction of the depth of a focus while improving the resolution. This not only increases the burden on the design of the exposing light system but also remarkably deteriorates the stability of the process, giving an adverse effect on the yield of the product.
A phase shift process is one of ultrahigh resolution pattern transfer processes effective for the solution to the foregoing problems. In the phase shift process, as a mask for use in the transfer of a fine pattern there is used a phase shift mask.
A phase shift mask comprises, e.g., a phase shifter portion having a pattern portion formed on the mask and a non-pattern portion (exposed portion of the substrate) free of phase shifter. The phase of light transmitted by the two portions are shifted by about 180° so that the two light components interfere with each other at the pattern interface to exert an effect of enhancing the contrast of the transferred image. Further, the use of the phase shift process makes it possible to increase the depth of a focus for the necessary resolution. Accordingly, the enhancement of resolution and the expansion of applicability of process can be accomplished at the same time even if light having the same wavelength is used as compared with the conventional transfer process using an ordinary mask having an ordinary light-shielding pattern made of chromium film or the like.
Practically speaking, phase shift masks can be roughly divided into two groups, i.e., completely transparent type (Shibuya-Revenson type) phase shift mask and halftone phase shift mask. In the former type of phase shift mask, the light transmittance of the phase shifter portion is the same as that of the non-pattern portion (exposed portion of the substrate). This mask is almost transparent to the wavelength of the exposing light and thus is generally said to be effective for the transfer of a line-and-space pattern. On the other hand, in the latter type of phase shift mask, the light transmittance of the phase shifter portion is from several percents to scores of percents of that of the non-pattern portion (exposed portion of the substrate). This phase shift mask is said to be effective for the preparation of contact hole or lone pattern in the process for the production of semiconductors.
FIG. 1
is a diagram illustrating the basic structure of a halftone phase shift mask blank.
FIG. 2
is a diagram illustrating the basic structure of a halftone phase shift mask. The description of anti-reflection layer or etching stop layer which may be used in lithographic process will be omitted.
The halftone phase shift mask blank comprises a semitransparent film (halftone phase shifter layer)
2
formed on a transparent substrate
1
. The halftone phase shift mask comprises a phase shifter portion
3
having a pattern portion formed on the mask and a non-pattern portion (exposed portion of the substrate)
4
free of phase shifter. The phase shifter portion
3
acts as a phase shifter capable of shifting the phase of exposing light transmitted by the neighborhood of its edge while being capable of substantially shielding the exposing light from the resist formed on the substrate.
Among these halftone phase shift masks is a single layer-type halftone phase shift mask which is simple enough in structure to produce. Examples of such a single layer-type halftone phase shift mask include those having a phase shifter made of a chromium material such as CrO
x
, CrN, CrO
x
N
y
and Cr
x
ON
y
C
2
as described in JP-A-5-127361 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”), those having a phase shifter made of an MoSi material such as MoSiO and MoSiON as described in JP-A-6-332152, and those having a phase shifter made of an SiN or SiO material as described in JP-A-7-261370.
The recent years have witnessed the reduction of the wavelength of exposing light used in the art as well as the trend for more use of halftone phase shift mask. There has recently been a tendency toward the use of krypton fluoride (KrF) exima laser beam (248 nm), which has a wavelength shorter than i-ray. Further, the use of argon fluoride (ArF) exima laser beam (193 nm) or argon chloride (ArCl) exima laser beam (175 nm), which has a wavelength even shorter than i-ray, has been proposed.
With the reduction of the wavelength of exposing light, the corresponding phase shift mask and phase shift mask blank must meet an important requirement, i.e., control over optical coefficients such as transmittance and refractive index in the wavelength of exposing light used. Most substances show remarkably great light absorption in a wavelength range shorter than 250 nm unlike in the wavelength range of from visible light to near ultraviolet. Thus, it is difficult to control the light transmittance of substances to a desired value in this short wavelength range. Thus, a halftone phase shift mask for i-ray cannot be normally used as a halftone phase shift mask for the exposing light having a wavelength range shorter than 250 nm as it is. Referring to the predetermination of the transmittance of the halftone type phase shifter, it is preferred that the transmittance of exposing light can be controlled to a range of from 3 to 20% when the phase shifter has a thickness at which the phase of exposing light can be shifted by a predetermined angle in the case of halftone phase shift mask, though depending on the sensitivity of the resist to be used in the transfer of a pattern or the patterning process.
Another problem is that even if the foregoing basic requirements such as transmittance and refractive index in the wavelength of exposing light can be satisfied to cope with the reduction of the wavelength of exposing light, the transmittance, if it is high with respect to the wavelength of testing light (e.g., 364 nm, 488 nm, 633 nm), cannot be examined, making it impossible to put the mask into practical use. Therefore, it is required that the transmittance of the mask with respect to the wavelength of testing light can be controlled to a desired value to put the mask into practical use.
Further, a halftone phase shift mask and a halftone phase shift mask blank as a parent material from which it is prepared must satisfy some requirements besides the foregoing requirements, i.e., inertness to irradiation with exima laser used (light resistance), chemical durability at cleaning process indispensable for mask process (chemical resistance), minimization of microdefects in the blank that remarkably deteriorate the mask quality (low defect density).
More particularly, the reduction of the wavelength of exposing light is also accompanied by the increase in the density of energy applied per unit time. In this respect, the layer material from which the phase shifter layer is formed must satisfy requirements that it doesn't impair the function of phase shift mask even when damaged by irradiation with light of higher energy. The term “damage” as used herein is meant to indicate change in optical properties (e.g., refracti

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