EUV mask or reticle having reduced reflections

Details EUV mask or reticle having reduced reflections EUV mask or reticle having reduced reflections

2001-05-02

2003-07-15

Rosasco, S. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Radiation modifying product or process of making

Radiation mask

C378S035000

Reexamination Certificate

active

06593037

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to integrated circuit (IC) fabrication equipment. More particularly, the present invention relates to an extreme ultraviolet (EUV) mask or reticle used in IC fabrication.
BACKGROUND OF THE INVENTION
Integrated circuit (IC) fabrication often utilizes a mask or reticle to form an image or pattern on one or more layers comprising a semiconductor wafer. Radiation is provided through or reflected off the mask or reticle to form the image on the semiconductor wafer. The wafer is correspondingly positioned to receive the radiation transmitted through or reflected off the mask or reticle. The radiation can be light at a wavelength in the ultraviolet (UV), vacuum ultraviolet (VUV), deep ultraviolet (DUV), or extreme ultraviolet (EUV) range. The radiation can also be a particle beam such as an x-ray beam, an electron beam, etc.
Typically, the image on the mask or reticle is projected and patterned onto a layer of photoresist material disposed on the wafer. The areas of the photoresist material upon which radiation is incident undergo a photochemical change to become suitably removable or fixed in a subsequent development process. In turn, the patterned photoresist material is used to define doping regions, deposition regions, etching regions, and/or other structures comprising the IC.
Radiation or lithographic wavelengths in the EUV range are being considered for next-generation lithography. EUV lithography utilizes radiation at a wavelength in the range of approximately 5 to 70 nanometer (nm) (e.g., 13.4 nm). EUV lithography requires, among others, the use of a mask or reticle specifically configured for lithographically patterning at EUV wavelengths, and is commonly referred to as an EUV mask or reticle. Unlike conventional masks or reticles which project a pattern onto the photoresist material by selective transmission of the exposure radiation, EUV masks or reticles project the pattern onto the photoresist material by selective reflection of the exposure radiation. For this reason, EUV masks or reticles are also referred to as reflective or reflective medium masks or reticles. The radiation at an EUV wavelength is reflected off the EUV mask or reticle in accordance with a pattern provided thereon and this reflected radiation is configured by components such as an EUV lens assembly before being projected onto the photoresist material.
In
FIG. 1
, a cross-sectional view of a portion of an EUV mask or reticle
10
is shown. EUV mask
10
includes a substrate
12
, a multilayer
14
, a barrier or buffer layer
16
, an absorptive layer
18
, and a feature
20
. Multilayer
14
is disposed above substrate
12
, barrier layer
16
is disposed over multilayer
14
, and absorptive layer
18
is disposed over barrier layer
16
.
Substrate
12
is typically a low-thermal expansion material (LTEM), such as glass. Multilayer
14
is configured to reflect radiation in the EUV wavelength range. Multilayer
14
is comprised of a plurality of films, such as 20 to 40 molybdenum-beryllium (Mo—Be) film pairs or molybdenum-silicon (Mo—Si) film pairs. The material comprising barrier layer
16
is selected to have different etch characteristics than at least absorptive layer
18
. For example, barrier layer
16
can be a silicon dioxide material.
Absorptive layer
18
includes a metallic material, such as chromium. The portion of absorptive layer
18
shown in
FIG. 1
comprises feature
20
. Feature
20
forms a part of the pattern or image for EUV mask
10
and may also be used to etch layer
16
.
Ideally, EUV mask
10
is configured to selectively reflect or absorb radiation at an EUV wavelength incident thereon to project a pattern onto the wafer. In particular, the exposed areas of multilayer
14
, such as, areas
22
, reflect radiation while the remaining areas of multilayer
14
, such as, area
24
, are covered by absorptive layer
18
to be non-reflective. Presently, however, all of the materials considered for absorptive layer
18
cause a certain amount of reflection. Moreover, as shown in
FIG. 2
, when a reflected ray
26
(from the top surface of absorptive layer
18
) and a reflected ray
28
(from the bottom surface of absorptive layer
18
) are in phase with each other, they are additive such that not only is absorptive layer
18
reflective, rather than preventing reflections, but reflections therefrom may be quite strong in intensity. In extreme cases, absorptive layer
18
can act as reflective areas of EUV mask
10
(similar to areas
22
of multilayer
14
) rather than being absorbing or non-reflective areas. Hence, the pattern projected onto the wafer (i.e., the pattern defined by the reflections from EUV mask
10
) may not be the desired pattern (i.e., the pattern as defined by the exposed areas of multilayer
14
and absorptive layer
18
). Alternatively, the pattern projected onto the wafer may suffer from low image contrast.
Thus, there is a need for an EUV mask configured to provide improved image contrast. There is a further need for an EUV mask having an absorptive layer of conventional material that provides reduced reflectance.
SUMMARY OF THE INVENTION
One exemplary embodiment relates to a reflective mask or reticle. The mask or reticle includes an absorptive layer configured to reduce a reflection of a lithographic radiation having a wavelength shorter than in a deep ultraviolet (DUV) range by destructive interference.
Another exemplary embodiment relates to a reflective mask or reticle. The mask or reticle includes an absorptive layer. The mask or reticle further includes an anti-reflective coating (ARC) layer disposed over the absorptive layer. The ARC layer is configured to reduce a reflection of a lithographic radiation having a wavelength shorter than in a deep ultraviolet (DUV) range from the absorptive layer by destructive interference.
Still another exemplary embodiment relates to a method for reducing an absorptive layer reflection from an absorptive layer of a reflective mask or reticle. The reduction of the absorptive layer reflection is during lithography at a wavelength shorter than in a deep ultraviolet (DUV) range. The method includes generating an another reflection. The method further includes canceling the absorptive layer reflection using the another reflection.


REFERENCES:
patent: 6187484 (2001-02-01), Glass et al.
patent: 6395433 (2002-05-01), Smith
patent: 2002/0122989 (2002-09-01), Sterns et al.
Pei-yang Yan et al., “EUV Mask Absorber Characterization and Selection,” Photomask and Next-Generation Lithography Mask Technology VII, Proceedings of SPIE, vol. 4066 (2000), pp. 116-123.

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