Patent Application
20080318139
This application claims the priority, under 35 U.S.C. § 119, of copending German Application No. 10 2007 028 800.1, filed Jun. 22, 2007, which designated the United States and was not published in English; the prior application is herewith incorporated by reference herein in its entirety.
Embodiments of the invention relate to photomasks used, for example, for fabricating semiconductor integrated circuits and to methods of manufacturing a photomask. For mask technologies like extreme ultraviolet lithography (EUVL), as well as improved optical lithography platforms, for example, double patterning or hyper NA immersion lithography, an absorber layer is patterned through a resist mask. The resolution that may be achieved depends mainly on the required resist thickness as well as on the type of resist. A thin resist layer is needed to achieve a high resolution. On the other hand, the resist pattern is consumed during the pattern transfer from the resist layer into the absorber layer such that the resist must be sufficiently thick.
With regard to EUV lithography, the absorber pattern usually reflects radiation that is used during an optical inspection of the absorber pattern. Therefore, the absorber layer is usually coated with an anti-reflective layer, the reflectivity of which, at the inspection wavelength, is lower than that of the absorber layer. The anti-reflective layer enhances the contrast during a subsequent mask inspection. In general, anti-reflective layers are resistant versus typical etch processes transferring a resist pattern into the absorber layer.
In addition, transparent photomasks as usually used for DUV and UV lithography use chromium containing layers to form opaque areas on the mask. Patterning of chromium containing layers requires typically oxygen-based etch processes to form a volatile chromium compound, for example, CrO2Cl2. Oxygen-based etch processes, however, show usually an isotropic component influencing the pattern size (line width) in the mask pattern.
U.S. Pat. No. 6,720,118 B2 to Yan et al. discloses an EUV mask absorber stack that comprises an absorber layer based on a metal nitride, for example, titanium or tantalum nitride, and an anti-reflective layer covering the absorber layer and containing another tantalum or titanium compound containing one or more non-metals like fluorine (F), oxygen (O), argon (Ar), carbon (C), hydrogen (H), nitrogen (N), germanium (Ge) and boron (B).
A need exists for photomasks with high efficient absorber layers that have a short absorption length at the exposure wavelength and that may be patterned with high resolution and further for a method of patterning photomasks comprising such a high efficient absorber layer and an anti-reflective layer.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a mask blank, including an absorber layer being absorbent at an exposure wavelength and being reflective at an inspection wavelength, the inspection wavelength being greater than the exposure wavelength, an anti-reflective layer disposed over the absorber layer and being low-reflective at the inspection wavelength, and a hard mask layer disposed over the anti-reflective layer, the hard mask layer having constituents with an atomic number less than or equal to 41.
A mask blank according to an embodiment of the invention comprises an absorber layer that is absorbent at an exposure wavelength and that is reflective at an inspection wavelength, wherein the exposure wavelength is used in a lithography process to transfer patterns from a photomask into, for example, a semiconductor wafer. The exposure wavelength may be, for example, 13.5 nm. The inspection wavelength is that of a typical optical defect detection tool and is greater than the exposure wavelength, for example, 193 nm, 196 nm or 248 nm.
An anti-reflective layer is disposed over the absorber layer, the anti-reflective layer being low-reflective at the inspection wavelength. The anti-reflective layer may be disposed directly on the absorber layer. Further, a hard mask layer is disposed over the anti-reflective layer. The hard mask layer may be disposed directly on the anti-reflective layer to have the hard mask layer be in contact with the anti-reflective layer. In accordance with other embodiments, a further layer may be disposed between the hard mask layer and the anti-reflective layer. None of the constituents of the hard mask layer has an effective atomic number greater than 41. By selecting a suitable material for the hard mask layer and a suitable etch process, a first etch selectivity S1=R(HM)/R(Res) between the material of the hard mask layer having an etch rate R(HM) and a resist disposed above the hard mask layer for patterning the hard mask and having an etch rate R(Res) is greater than a second etch selectivity S2, with S2=R(AR)/R(Res) between the material of the anti-reflective layer having an etch rate R(AR) and the resist.
Thus, a resist layer used for patterning the mask blank may be thinner than without hard mask. Further, due to the low atomic number of the constituents of the hard mask layer, electron back scattering during electron beam writing of the resist layer disposed over the hard mask layer is reduced.
In accordance with another feature of the invention, a resist layer may cover the hard mask layer. The hard mask layer may have an etch rate in a fluorine- or chlorine-based etch process that is not smaller than that of the anti-reflective layer to facilitate the application of thin resist layers that are thinner than, for example, 160 nm.
In accordance with a further feature of the invention, the hard mask layer may be soluble in a HF solution to avoid, during removal of hard mask residuals, damaging of the absorber layer, the anti-reflective layer, or the underlayer.
In accordance with an added feature of the invention, each main constituent of the hard mask layer may have an atomic number of 24 or less, for example, 6, to reduce electron back scattering effects during electron beam exposure or exposure with any charged particles. The term main constituent or constituent here and in the following does not include contaminations due to process imperfectness.
In accordance with an additional feature of the invention, the hard mask layer may contain silicon and oxygen, for example, the hard mask layer may be a silicon dioxide layer or a silicon oxynitride layer that show high etch resistance in fluorine-based etch processes. According to another embodiment, the hard mask layer may comprise or consist of chromium or carbon. The mask blank may be that of an EUVL mask with a capped or non-capped multi-layer reflector disposed below the absorber layer or a transparent mask with a carrier substrate supporting the absorber layer, the carrier substrate being transparent at an exposure wavelength of at least 193 nm. In an embodiment, the inspection wavelength can go up to but not exceed 800 nm.
In accordance with yet another feature of the invention, the absorber layer comprises a transition metal nitride, the transition metal forming one of a volatile fluorine compound and a volatile chlorine compound.
With the objects of the invention in view, there is also provided a photomask including a carrier substrate that is transparent at an exposure wavelength and an absorber layer that is opaque at the exposure wavelength and that is reflective at an inspection wavelength, the inspection wavelength being greater than the exposure wavelength. An anti-reflective layer disposed over the absorber layer is less reflective than the absorber layer at the inspection wavelength. As the anti-reflective layer shows lower reflectivity at the inspection wavelength than, for example, a chromium-based layer, a photomask according to this embodiment shows increased contrast during defect detection.
In accordance with yet a further feature of the invention, a hard mask layer may be disposed over the anti-reflective layer, none of the constituents of the hard mask layer having an atomic number greater than 41. The same hard mask layer configuration may be also used for EUVL masks. As a consequence, transparent masks and the reflective mask may be patterned using the same or substantially the same etch chemistry.
In accordance with yet an added feature of the invention, there is provided a carrier substrate disposed below the absorber layer and transparent at an exposure wavelength that is at least 100 nanometers.
In accordance with yet an additional feature of the invention, a resist layer may cover the hard mask layer and/or a phase shift layer may be disposed between the carrier substrate and the absorber layer.
In accordance with again another feature of the invention, the anti-reflective layer and the absorber layer are patterned to form an absorber pattern comprising absorber structures, wherein between the absorber structures sections of an underlayer, for example, the carrier substrate, are exposed.
With the objects of the invention in view, there is also provided a method of manufacturing a photomask, wherein a mask blank is provided that includes an anti-reflective layer disposed over an absorber layer and a hard mask layer disposed over, for example, directly on the anti-reflective layer. The hard mask layer is patterned to form a hard mask and the pattern of the hard mask is transferred into the anti-reflective layer. Then, the pattern of the anti-reflective layer is transferred into the absorber layer so that sections of an underlayer, for example, a carrier substrate, are exposed. The hard mask layer may be patterned by transferring a resist mask pattern into the hard mask layer. The resist mask may be thin, for example, about 100 nm or less so that the resist may be patterned at a high resolution. Residuals of the resist mask may be stripped before the pattern of the anti-reflective layer is transferred into the absorber layer so that the stripping of resist residuals may not damage an underlayer beneath the absorber layer.
In accordance with again a further mode of the invention, the hard mask residuals may be stripped through a wet-etch process after the anti-reflective layer is patterned.
In accordance with a concomitant mode of the invention, the hard mask layer patterning step is carried out by transferring a resist mask pattern into the hard mask layer and residuals of the resist mask pattern are stripped before transferring the pattern of the anti-reflective layer into the absorber layer.
Although the invention is illustrated and described herein as embodied in a mask blank, a photomask, and a method for manufacturing a photomask, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Additionally, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention.
Other features that are considered as characteristic for the invention are set forth in the appended claims. As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. The figures of the drawings are not drawn to scale.
Before the present invention is disclosed and described, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms “a” or “an”, as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e., open language). The term “coupled,” as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
As used herein, the term “about” or “approximately” applies to all numeric values, whether or not explicitly indicated. These terms generally refer to a range of numbers that one of skill in the art would consider equivalent to the recited values (i.e., having the same function or result). In many instances these terms may include numbers that are rounded to the nearest significant figure.
Features and advantages of embodiments of the invention will be apparent from the following description of the drawings. The drawings are not necessarily to scale. Emphasis is placed upon illustrating the principles.
Herein various embodiment of the present invention are described. In many of the different embodiments, features are similar. Therefore, to avoid redundancy, repetitive description of these similar features may not be made in some circumstances. It shall be understood, however, that description of a first-appearing feature applies to the later described similar feature and each respective description, therefore, is to be incorporated therein without such repetition.
In the figures of the drawings, unless stated otherwise, identical reference symbols denote identical parts.
Referring now to the figures of the drawings in detail and first, particularly to
The base section 110 supports the absorber stack 120. The absorber stack 120 may be in contact with the capping layer 118. According to another embodiment, a buffer layer may be disposed between the absorber stack 120 and the base section 110. The absorber stack 120 comprises an absorber layer 122 and an anti-reflective layer 124. The absorber layer 120 may be based on a metal nitride, for example, a transition metal nitride like tantalum or titanium nitride and may have a thickness of about 10 nm to about 90 nm. The absorber layer 122 is absorbent at a first wavelength that corresponds to the exposure wavelength, where the absorbance at the exposure wavelength may be greater than 50%. The absorber layer 122 is typically reflective at a second wavelength, at which the photomask is inspected after patterning. Typically, the reflectance is greater than 40% at typical inspection wavelengths of, for example, 193 nm, 198 nm, 248 nm, 257 nm, 266 nm, 365 nm, or 488 nm. Even greater inspection wavelengths are possible, wherein shorter wavelengths stand for better resolution. Further, mask alignment tools are based on optical pattern detection operating in the visible light wavelength regime.
The absorber stack 120 comprises further an anti-reflective layer 124. The anti-reflective layer 124 is disposed over the absorber layer 122 and is less reflective at the inspection wavelength than the absorber layer 122. The reflectance is typically less than 12% at the respective inspection wavelength. The anti-reflective layer 124 may be based on a metal nitride, for example, a transition metal nitride such as titanium or tantalum nitride, and may further comprise one or more further components selected from a group comprising chlorine, fluorine, argon, hydrogen, or oxygen. The anti-reflective layer 124 may be formed by treating the absorber layer 122 in an ambient containing the further component or precursors of them. According to another embodiment, the anti-reflective layer may be a silicon nitride (Si3N4) layer.
The EUV mask blank 100 further comprises a hard mask layer 130, the heaviest constituent having an atomic number of less than 42. The hard mask layer 130 is disposed over the anti-reflective layer 124 and may be in contact with the same. The hard mask layer 130 may have an etch rate of less than 1 nm per second in a fluorine-based dry etch process. For example the atomic number of the heaviest constituent may be less than 25, for example, 24 or 14. According to another embodiment, the atomic number of the heaviest constituent may be less than 14. The thickness of the hard mask layer 130 may be, for example, about 10 to about 30 nm. The hard mask layer 130 may be a silicon oxide layer, for example, a silicon dioxide layer, a silicon oxynitride layer, a carbon layer, or a germanium- and/or aluminum- or chromium-based layer.
The hard mask layer 130 may be patterned using a thin resist layer 130. The thickness of the resist layer 130 may be less than 200 nm, for example about 100 nm, and less than the typical resist thickness required for patterning a typical absorber stack without a hard mask. The thin resist layer facilitates a high-resolution pattern process of the resist layer. Using a fluorine-based dry etch process, a hard mask layer 130 with a thickness of less than 30 nm may be sufficient for breaking through even for high etch-resistant anti-reflective layers 124. The low atomic numbers of the constituents of the hard mask layer 130 reduce electron back scattering during patterning of the resist layer through electron beam writing. The hard mask layer 130 may further protect the anti-reflective layer 124 during a following etch of the absorber layer 122. A degradation of the reflectance of the anti-reflective layer 124, which may deteriorate its reflectance performance during inspection and/or optical pattern recognition, may be avoided. Steep sidewall angles and minimal corner rounding may be achieved. Different anti-reflective layers of different photomask types may be etched using the same hard mask.
The mask blank 200 as illustrated in
A hard mask layer 230 with a thickness of 10 to 30 nm is disposed over the absorber stack 220. The absorber/hard mask layer configuration 220/230 may be the same as for the EUVL mask of
With regard to
The hard mask layer 430 is disposed over the anti-reflective layer 424, for example, directly on the anti-reflective layer 424, and may have an etch rate of less than 1 nm per second in a fluorine-based etch process. The atomic number of the heaviest constituent of the hard mask layer 430 is less than that of molybdenum, for example, 24, or less, for example 6. The hard mask layer 430 may contain or consist of, for example, silicon oxide, silicon oxynitride, a germanium compound, carbon, or chromium. For example, a 10 nm thick chromium hard mask may be sufficiently etch resistive to pattern a TaN-based absorber stack, which is about 40 nm to about 90 nm thick. In accordance with another embodiment, another layer may be provided between the hard mask layer 430 and the anti-reflective layer 424.
The mask blank 400 further includes a resist layer comprising, for example, a chemically amplified electron beam resist, which is about 60 to about 200 nm thick, for example, 130 nm. If the mask blank 400 is supplied without resist layer, at first a resist layer may be deposited upon the hard mask layer 430. The resist layer may be patterned using an electron beam writer or another tool using any kind of charged particles. Due to the low atomic number of the constituents of the hard mask layer 430, electron scattering is reduced compared to a molybdenum or tantalum containing underlayer. As reflected electrons may expose sections of the electron beam resist outside the write track, a fogging effect resulting from the backscattering electrons may be reduced.
Referring to
As shown in
Referring to
According to a further embodiment, to which
Referring to
In the result, the patterning process and the absorber stack/hard mask configuration may be applied to reflective EUV masks as well as for transparent binary and phase shift masks. The hard mask is at least partially consumed during the etch of the absorber stack 420.
With regard to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 028 800.1 | Jun 2007 | DE | national |
