Patent Application
20060269847
1. Field of the Invention
The embodiments of the invention generally relate to semiconductor device processing, and more particularly, to the use of pellicles to protect photoresist masks and/or reticles during semiconductor device processing.
2. Description of the Related Art
A pellicle is a protective structure that is applied to a photoresist mask or a reticle. Ideally, a pellicle covers the photoresist mask or reticle and prevents contaminants from reaching the underlying mask surface. Thus, a properly placed pellicle can help in reducing the occurrence of wafer defects during clean room stepper focus or printing processing.
As photolithography processes for the fabrication of semiconductor devices continue to scale to the sub 100 nm regime, it is desirable to reduce the exposure wavelength from 193 nm to 157 nm and below in order to provide a capability for enhanced resolution and depth of focus process latitude. However, there may be technical problems associated with a migration to a 157 nm exposure wavelength due to the strong absorbance of many commonly used optical materials at this wavelength. For example, it is often desirable to substitute CaF2 optical materials for the typically used silicon dioxide materials for lens fabrication. Thus, new polymers for photoresist masks should be developed to provide sufficient transparency, and new pellicle materials should be developed due to possible degradation and film thickness changes of conventional pellicle materials upon irradiation at 157 nm.
Some conventional solutions propose that a “hard” pellicle of silicon dioxide be used as a replacement for the typical conventional organic polymer type of pellicle material for 157 nm lithography. Unfortunately, this thick quartz pellicle typically functions as an optical element in the exposure system due to its greater thickness than other conventional pellicles, and is generally fabricated and mounted to the mask blank to precise tolerance values in order to avoid degradation of the aerial image during printing. Typical pellicle mounting procedures use a thick layer of a glue-like adhesive which is generally not well controlled (i.e., the thickness varies across the mask), such that the tolerance values required for mounting the hard pellicle cannot generally be attained.
A major challenge in the use of pellicles has been the mounting of the pellicle frame to the mask itself since the integrated structure is ideally extremely flat, parallel, and configured without local distortions. As mentioned, using standard adhesives or gaskets has thus far proven generally inadequate to meet the stringent specifications necessary due to stress-induced distortions and the inability to maintain tolerances for the various materials involved. Therefore, there remains a need for a new technique of bonding a pellicle to a pellicle frame and bonding a pellicle frame to a photoresist mask or reticle, which overcomes the limitations of the conventional approaches.
In view of the foregoing, an embodiment of the invention provides an apparatus for attaching a pellicle to a mask for use in optical lithography comprising a lithographic mask; a pellicle ring; and a binding layer having a thickness of less than 100 nanometers between the pellicle ring and the lithographic mask. In one embodiment, the binding layer comprises a graded oxide layer. In another embodiment, the binding layer comprises an anodic oxide layer. In still another embodiment, the binding layer comprises a polymer having a material composition capable of being vapor deposited, wherein the polymer comprises a maleic anhydride polymer. In yet another embodiment, the binding layer comprises a polymer having a uniform material composition. Another embodiment provides that the binding layer comprises a polymer having a material composition capable of being reactive with a bonding agent. Furthermore, the pellicle ring comprises a pellicle; a pellicle frame; and a binding layer having a thickness of less than 100 nanometers between the pellicle and the pellicle frame.
Another embodiment of the invention provides a reticle comprising an outer surface; a pellicle ring; and a binding layer having a thickness of less than 100 nanometers between the outer surface and the pellicle ring. In one embodiment, the binding layer comprises a graded oxide layer. In another embodiment, the binding layer comprises an anodic oxide layer. Preferably, the binding layer comprises a polymer having a material composition capable of being vapor deposited, wherein the polymer may comprise a maleic anhydride polymer. Furthermore, the binding layer preferably comprises a uniform thickness. Additionally, in one embodiment the binding layer may comprise a polymer having a material composition capable of being reactive with a bonding agent. Moreover, the pellicle ring may comprise a pellicle; a pellicle frame; and a binding layer having a thickness of less than 100 nanometers between the pellicle and the pellicle frame.
Another aspect of the invention provides a method for attaching a pellicle to a mask for use in optical lithography, wherein the method comprises applying a binding layer having a thickness of less than 100 nanometers on each of a pellicle ring and a lithographic mask; and attaching the pellicle ring to the lithographic mask. In one embodiment, the binding layer comprises a graded oxide layer. In another embodiment, the binding layer comprises an anodic oxide layer. In still another embodiment, the binding layer comprises a polymer having a material composition capable of being vapor deposited, wherein the polymer comprises a maleic anhydride polymer. In yet another embodiment, the binding layer comprises a polymer having a uniform material composition. Another embodiment provides that the binding layer comprises a polymer having a material composition capable of being reactive with a bonding agent. The method further comprises applying heat to the binding layer during the attaching of the pellicle ring to the lithographic mask. Additionally, the pellicle ring comprises a pellicle and a pellicle frame, wherein the method further comprises applying a binding layer having a thickness of less than 100 nanometers between the pellicle and the pellicle frame.
Still another aspect of the invention provides a method for attaching a pellicle to a mask for use in optical lithography, wherein the method comprises doping a pellicle ring with a cation material; attaching the pellicle ring to a metal lithographic mask; heating the pellicle ring; applying an electrical bias to the pellicle ring; and forming an oxide at an interface between the attached pellicle ring and metal lithographic mask, wherein the cation material may comprise sodium. Furthermore, in one embodiment, the method further comprises clamping the pellicle ring to the metal lithographic mask.
The embodiments of the invention provide a method and a structure for creating a bond between a pellicle frame and a mask, and between the pellicle and the pellicle frame, which can achieve the tolerance values required for the mounting of the hard pellicle to the mask blank with high uniformity for 157 nm lithography. Specifically, the embodiments of the invention achieves this by using a thin nanolayer of binding material such as a nanoglue or adhesive, which can be uniformly vapor deposited in a highly controlled manner to create very uniform adhesive thicknesses on the bonding areas across the mask. Furthermore, an alternative embodiment of the invention provides a technique of joining the mask and pellicle frame without any intermediate material. Specifically, the second embodiment utilizes anodic bonding which generally grows a mutual graded-oxide at the interface of two appropriate materials (i.e., sodium and silicon and/or sodium and chromium) in intimate contact with one another and processed accordingly.
These and other aspects of the embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments of the invention and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments of the invention without departing from the spirit thereof, and the embodiments of the invention include all such modifications.
The embodiments of the invention will be better understood from the following detailed description with reference to the drawings, in which:
FIGS. 10(A) and 10(B) illustrate schematic diagrams of alternate processing steps, which may be used according to the first or second embodiments of the invention;
The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments of the invention may be practiced and to further enable those of skill in the art to practice the embodiments of the invention. Accordingly, the examples should not be construed as limiting the scope of the embodiments of the invention.
As mentioned, there remains a need for a new technique of bonding a pellicle to a pellicle frame and bonding a pellicle frame to a photoresist mask or reticle, which overcomes the limitations of the conventional approaches. The embodiments of the invention achieve this by providing a method and a structure for creating a bond between a pellicle frame and a mask frame, and between the pellicle and the pellicle frame, which can achieve the tolerance values required for the mounting of the hard pellicle to the mask blank with high uniformity for 157 nm lithography. Referring now to the drawings and more particularly to
A first embodiment is shown in
Specifically, as shown in
Next, as illustrated in
The maleic anhydride polymer 30 is deposited using a plasma jet vapor deposition tool. Preferably, the maleic anhydride polymer film 30 is activated for adhesion by contacting it with a methanol solution of amine dendrimer 35 at approximately 25° C. for 30-60 minutes. In this regard, a vapor of maleic anhydride at 3-10 torr is provided and a carrier gas of argon may be used if desired to dilute the reagent. The vapor is passed through a plasma jet nozzle, creating a jet spray of plasma-excited maleic anhydride monomer in a narrow beam of 0.2-2.0 mm.
This beam of reagent is then guided across the surface of the patterned photomask 25 in the desired area(s) to bind the pellicle ring 5 to the photomask 25. The substrate temperature is preferably 25° C. during film deposition. After treatment with the amine dendrimer solution, the substrate 20, mask 25, and pellicle ring 5 are rinsed with methanol and placed together for bonding. Then, when the pellicle frame 15 with the attached maleic anhydride polymer 30 and amine dendrimer 35 is brought into contact with the maleic anhydride polymer 30 on the mask 25, heat is applied thereon to dry/cure the maleic anhydride polymer 30, as shown in
Preferably, the bonding process is carried out at approximately 120° C. for approximately 1-10 hours to complete the adhesive formation process. Thereafter, the maleic anhydride polymer 30 is fully cured thereby bonding the pellicle ring 5 to the mask 25. The thickness of the resulting adhesive binding layer 60, shown in
The use of the plasma jet spray tool to deposit the maleic anhydride polymer 30 allows the resulting adhesive layer 60 to be selectively formed in areas of the mask 25 and pellicle frame 15 where the bonding occurs. Accordingly, it would be undesirable to form the adhesive layer 60 in other areas of the mask blank 25 or pellicle frame 15 as it would interfere with the formation of the aerial image during the printing process. Furthermore, general types of plasma deposition equipment would not be useful for this process due to the lack of an ability to precisely control the areas of adhesive deposition.
In a second embodiment, shown in
Additionally, as shown in
Again, with reference to
The oxide 70 grows with the side effect of joining the two materials (doped/heated sodium on the pellicle frame 15 and the metal mask 25). The interface 18 in microscopic profile looks like a graded oxide meaning there is a gradient of oxide character as you move from one surface being bonded through the depth of the oxide 70 toward the other surface. The bond is hermetic, irreversible, and quite mechanically strong.
In one embodiment, as further illustrated in FIGS. 10(A) and 10(B), a maleic anhydride polymer 30 is activated with an amine (not shown in FIGS. 10(A) and 10(B)) and is vapor deposited on each of the pellicle 10 and pellicle frame 15, and upon heating, are joined together, thereby attaching the pellicle 10 to the pellicle frame 15. Alternatively, with regard to the first embodiment, the maleic anhydride polymer 30 may be vapor deposited to both ends of the pellicle frame 15 and to the pellicle 10 during one processing step, thereby further saving processing time.
Another aspect of the invention is illustrated in the flowcharts of FIGS. 11(A) and 11(B), which include descriptions which refer to components provided in
The embodiments of the invention provide a method and a structure for creating a bond between a pellicle frame 15 and a mask 25, and between the pellicle 10 and the pellicle frame 15, which can achieve the tolerance values required for the mounting of the hard pellicle 10 to the mask blank 25 with high uniformity for 157 nm lithography. Specifically, the embodiments of the invention achieves this by using a thin nanolayer of binding material 60 such as a nanoglue or adhesive, which can be uniformly vapor deposited in a highly controlled manner to create very uniform adhesive thicknesses on the bonding areas across the mask 25. Furthermore, an alternative embodiment of the invention provides a technique of joining the mask 25 and pellicle frame 15 without any intermediate material. Specifically, the second embodiment utilizes anodic bonding which generally grows a mutual graded-oxide 70 at the interface 18 of two appropriate materials (i.e., sodium and silicon and/or sodium and chromium) in intimate contact with one another and processed accordingly.
The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments of the invention have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments of the invention can be practiced with modification within the spirit and scope of the appended claims.
