Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-07-18
2002-05-14
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06387573
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 same.
2. Description of the Related Art
Semiconductor devices are manufactured by sequentially depositing a variety of material layers on a substrate (wafer) and patterning (etching) the material in accordance with a preselected layout pattern. The patterning step involves photolithography and etching, which are collectively referred to as just photolithography. Referring to
FIG. 1
, the photolithography sequence typically is as follows: a photoresist layer (not shown) is deposited on a predetermined material layer (not shown), and a photo mask having opaque patterns
12
, which block light transmission on a transparent substrate
10
, is placed over the photoresist layer. When light of a selected wavelength
14
is applied to the photo mask, the mask patterns are transferred onto the photoresist layer, forming exposed portions and shielded portions in the photoresist layer. Once exposed, the photoresist layer is developed in a solution that selectively dissolves the exposed portions or shielded portions to create a photoresist pattern. The photoresist pattern is typically used as an etching mask to etch the underlying material film, resulting in a transfer of the photoresist pattern to the material film.
In the strict sense of the word, the term “photo mask” is termed a mask, which has a pattern substantially equal in size to that of the photoresist pattern formed by exposure. Meanwhile, a photo mask for use in reduction projection exposure, which has a pattern several times larger than that in the photoresist layer formed by exposure, is termed a reticle. Hereinafter, the term “mask” will be used for any mask used in photolithography for the sake of convenience.
As the integration density of semiconductor devices continues to increase, linewidth of material layer patterns becomes narrow. Accordingly, it may become difficult to fabricate a desired pattern having a narrow linewidth using a conventional mask as shown in FIG.
1
. If a mask having a fine linewidth is used, a sharp intensity difference of light, as shown in
FIG. 1
, at the boundary between opaque portions
18
and transmissive portions
16
, is not ensured due to diffraction of light.
To avoid this problem, light having a short wavelength, for example, 248 nm or 193 nm, which barely causes diffraction, is used as an exposure light source. However, as linewidths become even finer, the use of the exposure light source having a short wavelength is no longer a satisfactory solution with respect to the problem of the unclear boundary between the opaque and transmissive portions. For this reason, a phase shift mask has been produced that causes destructive interference at the boundary between the transmissive portions
16
and the opaque portions
18
based on a light interference phenomenon.
The phase shift mask shown in
FIG. 2
, which is an attenuated (also referred to as half-tone) phase shift mask, includes a transparent substrate
20
and a phase shifter pattern
22
formed of a phase shifter material. The phase shifter material may be CrO, CrF, MoSiOn, SiN, or spin-on-glass (SOG). Although not shown, the phase shift mask is classified as a mask having a phase shifter pattern formed with SOG on or below opaque patterns, and a substrate-etch type mask in which the phase of light is varied by etching a transparent substrate to have a predetermined depth, instead of using a phase shifter material, to vary the transmission length of light.
The principle of a common phase shift mask will now be described with reference to FIG.
2
. Light passed through transmissive portions
26
has a phase and amplitude as indicated by a dashed line
30
of the upper graph in FIG.
2
. Light passed through phase shift portions
28
is phase shifted by 180° and has a phase and amplitude as indicated by a dashed line
32
of the same graph. Finally, light at the surface of the photoresist layer has a phase and amplitude as indicated by a solid line
34
of the same graph. Also, light intensity at the surface of the photoresist layer, which has passed through the transmissive portions
26
and the phase shifting portions
28
, is as shown in the lower graph of FIG.
2
. Compared with the upper graph in
FIG. 1
, light intensity difference at the boundary between the transmissive portions
26
and the phase shifting portions
28
of the phase shift mask in
FIG. 2
is more distinct than that at the boundary between the transmissive portions
16
and the opaque portions
18
in FIG.
1
.
However, as shown in the lower graph in
FIG. 2
illustrating the light intensity, a secondary peak
36
, which is called a “side-lobe”, occurs in the phase shifting portions
28
. The occurrence of the side-lobe
36
is inevitable as long as the phase shifter pattern
22
is not completely opaque. Also, when the size of the side-lobe is greater than a reference value, an undesired pattern may be formed in the developed photoresist pattern. For this reason, an opaque pattern may be employed on the center of the phase shifter pattern
22
. However, it is difficult to apply this technique to a phase shifter pattern having a narrow width. Alternatively, a phase shifter material having a low transmissivity (for example, 5-10%) can be used for the purpose of reducing the side-lobe
36
. However, the use of phase shifter material having the low transmissivity degrades the effect of the phase shift mask. As can be seen from the upper graph in
FIG. 2
, as the transmissivity of phase shifter material increases, the amplitude
32
of the light passed through the phase shifting portions
28
increases and the effect of destructive interference at the boundary between the transmissive portions
26
and the phase shifting portions
28
is enhanced, resulting in a more distinct boundary between the transmissive portions
26
and the phase shifting portions
28
.
On the other hand, the problem with the side-lobe is closely associated with the performance of photoresist. In particular, when a photoresist layer is exposed to light having a higher intensity (energy) than a reference value, the exposed portions on the photoresist layer are dissolved and removed in a developer solution to afford photoresist patterns. However, when the performance of photoresist is so good (i.e., the reference value is considerably high) that it is not dissolved in a developer solution (i.e., when photoresist shows a higher contrast) even at a considerable side-lobe intensity, a phase shifter material having a higher transmissivity (for example, about 40%) can be used to enhance the efficiency of a phase shift mask. A need exists for a phase shift mask formed of a phase shifter material having a high transmissivity.
SUMMARY OF THE INVENTION
To meet the above need, it is a first object of the present invention to provide a phase shifter material having a relatively high transmissivity with respect to a short wavelength of exposure light.
A second object of the present invention is to provide a phase shifter material which shows transmissivity with respect to inspection light having a longer wavelength than exposure light, such that inspection with the inspection light is possible, and shows a higher transmissivity with respect to the exposure light.
A third object of the present invention is to provide a phase shift mask formed using the phase shifter material.
A fourth object of the present invention is to provide a method for manufacturing the phase shift mask.
The first and second objects may be achieved by a phase shifter material comprising chromium (Cr), aluminum (Al), oxygen (O) and nitrogen (N).
The third object may be achieved by a phase shift mask according to the present invention, which comprises: a transparent substrate and a phase shifting layer formed of a material including chromium (Cr), aluminum (Al), oxygen (O) and nitrogen (N) on the transparent substrate. The phase shifting layer is preferably semitransparent to a predetermined wav
Kim Eun-ah
No Kwang-soo
Park Jo-Hyun
LandOfFree
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