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

2000-06-09

2002-05-28

Rosasco, S. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

C428S432000

Reexamination Certificate

active

06395434

ABSTRACT:

REFERENCE TO RELATED APPLICATION
This application claims the priority right under Paris Convention of Japanese Patent Application No. Hei 11-165902 filed on Jun. 11, 1999, the entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase shift mask for use in performing exposure, and transfer on a fine pattern and a phase shift mask blank as the mother material of the mask, particularly to a halftone phase shift mask and a phase shift mask blank.
2. Description of the Related-Art
For the high integration of DRAM starting with 1 Mbit, in these days, the mass production system of 64 Mbit. 256 Mbit DRAM has been established. In this technical innovation, an exposure light source has been shortened in wavelength from g ray (436 nm) to i ray (365 nm) of an ultrahigh pressure mercury lamp. Still at present, the reduction of the exposure wavelength has been studied aiming at higher integration. However, in the usual photolithography method, when the exposure wavelength is shortened, the resolution is improved, but the focus depth is decreased. This causes a problem that the burden on the design of the optical exposure system is increased, the process stability is remarkably deteriorated and that the product yield is adversely affected.
A phase shift method is one of ultra-resolution pattern transfer methods effective for the problem. In the phase shift method, a phase shift mask is used as a mask for transferring a fine pattern.
The phase shift mask is constituted, for example, of a phase shifter part forming a pattern part on the mask, and a non-pattern part (substrate exposure part) in which no phase shifter is present. By shifting the phase of a light transmitted through both part by about 180°, mutual light interference is caused in a pattern boundary part, and this enhances the contrast of a transferred image. Furthermore, by using the phase shift method, the focus depth can be increased to obtain a necessary resolution. As compared with a transfer process using the ordinary mask provided with a usual light screen pattern of a chromium film, and the like, even when the same wavelength light is used, the resolution can be improved and additionally the process applicability can be enlarged.
The phase shift mask is roughly classified into a complete transmission type (Shibuya/Levenson type) phase shift mask and a halftone phase shift mask for practical use in accordance with the light transmission properties of the phase shifter part. In the former, the transmittance of the phase shifter part is equal to that of the non-pattern part (substrate exposure part), the mask is substantially transparent to the exposure wavelength, and it is said that the mask is generally effective for a line and space transfer. On the other hand, for the latter, the transmittance of the phase shifter part is of the order of several percentages to several tens of percentages of that of the non-pattern part (substrate exposure part), and it is said that the mask is effective for forming a contact hole or an isolated pattern in a semiconductor manufacture process.
FIG. 1
shows the basic structure of a halftone phase shift mask blank, and FIG.
2
. shows the basic structure of a halftone phase shift mask. Additionally, the description of a reflection preventive layer, an etching stop layer, and the like for use in the lithography process is omitted.
The halftone phase shift mask blank is constituted by forming a semitransparent film (halftone phase shifter film)
2
on a transparent substrate
1
. Moreover, the halftone phase shift mask is constituted of a phase shifter part
3
forming a pattern part on the mask, and a non-pattern part (substrate exposure part)
4
in which no phase shifter is present. Here, the phase shifter part
3
shifts the phase of the exposure light transmitted in the vicinity of an edge to fulfill the function as the phase shifter, and performs a light screen function for substantially intercepting the exposure light with respect to a resist on a transfer substrate.
The halftone phase shift mask includes a single-layer halftone phase shift mask which is simplified in structure and which is easily manufactured. Examples of the single-layer halftone phase shift mask include: a mask comprising a phase shifter formed of chromium-based materials such as CrO
x
, CrN, CrO
x
N
y
, Cr
x
ON
y
C
z
as described in Japanese Patent Application Laid-Open No. 127361/1993; a mask comprising a phase shifter formed of MoSi-based materials such as MoSiO and MoSiOn as described in Japanese Patent Application Laid-Open No. 332152/1994; and a mask comprising a phase shifter formed of SiN or SiO-based materials as described in Japanese Patent Application Laid-Open No. 261370/1995.
In recent years, with the shortening of the exposure wavelength, the halftone phase shift mask has been increasingly used, and a krypton fluoride (KrF) excimer laser light (248 nm) has been used as a light shorter in wavelength than the i ray. Moreover, the use of an argon fluoride (ArF) excimer laser light (193 rnm) or a fluorine dimer (F
2
) excimer laser light (157 nm) as a shorter wavelength light is also proposed.
With the shortening of the exposure wavelength, in the corresponding phase shift mask and phase shift mask blank, the control of transmittance, refractive index and other optical coefficients in the exposure wavelength for use becomes important. Different from visible to near ultraviolet areas, in the area with the wavelength shorter than 250 nm, since the degree of light absorption remarkably increases in many substances, it is difficult to control and obtain a desired transmittance. Therefore, the halftone phase shift mask for the i ray cannot usually be used as it is, as the halftone phase shift mask for the exposure light shorter than 250 nm. The transmittance in the halftone phase shifter is set depending on the sensitivity of the resist for use in the pattern transfer and the patterning process but, for example, in the halftone phase shift mask, it is preferable to control the transmittance of the exposure light in a range of 3% to 20% in the film thickness of the phase shifter for shifting the phase of the exposure light by a predetermined angle.
Moreover, even if the basic prescribed properties such as the transmittance and refractive index in the exposure wavelength are satisfied with the shortening of the exposure wavelength, no test can be performed with a high transmittance for the wavelength of test light (e.g., 364 nm, 488 nm, 633 nm), which is not suitable for practical use. Therefore, for the practical use, the transmittance is requested to be controlled to a desired value with respect to the wavelength of the test light.
Furthermore, in addition to the above-described properties, the halftone phase shift mask and the halftone phase shift mask blank as the mother material for forming the mask are requested to be stable against excimer laser irradiation for use (light-resistant), chemically durable in a cleaning process essential for the mask process (chemical-resistant) and to minimize micro defects in the blank which remarkably deteriorate the mask quality (low defect density).
Specifically, the shortening of the exposure wavelength also means that the density of the energy radiated per unit time increases. To cope with this, the film material for forming a phase shifter layer is requested not to deteriorate the function as the phase shift mask by damages caused by the high-energy irradiation. Here, the damages mean the change in optical properties (refractive index, transmittance, and the like) of the shifter film and the generation of color defects by the irradiation, film thickness changes, film quality deterioration, and the like. For example, when the excimer laser with the wavelength in a deep ultraviolet area is radiated, in-film substances are excited by a double photon process, this is said to cause changes in film optical properties and film quality, but details are not clarified. In any ca

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