Method of making X-ray mask structure

Abstract: A method of making an X-ray mask structure having an X-ray absorber in a desired pattern on the surface of a support film held by a frame comprises the step of patterning the X-ray absorber, including a drawing step that utlizes charged particles, and the step of thereafter providing the frame with a magnetic member. The frame and the support film are each comprised of a non-magnetic material.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of making a mask structure (or structural body) used in X-ray lithography. More particularly, it relates to a method of making an X-ray mask structure that can be fixed to the apparatus body by magnetic chucking. Related Background Art Various methods have been hitherto employed as lithographic processing for electronic devices such as IC and LSI. In particular, X-ray lithography is based on properties inherent in X-rays, as exemplified by high transmittance (or low absorbance) and short wavelength. It has a number of advantages when compared with conventional lithographic methods that utilize visible light or ultraviolet light, and has attracted notices as a promising method for submicroscopic lithography. Mask structures used in the X-ray lithography are commonly prepared in the following way. First, a thin film (a support film) comprising a material having a high X-ray transmittance is formed on a holding frame for holding said film, and thereafter an X-ray absorber, such as Au, Ta and W formed into patterns corresponding to a shape to be transformed, is formed on said film. Because of use of soft x-rays of about 0.5 to 2 nm in the X-ray lithography, X-rays may be so greatly attenuated in the atmosphere that exposure is required to be operated in vacuum or in low-pressure helium. Now, as a method of fitting the X-ray mask structure to an apparatus body in such X-ray lithography, a magnetic chucking method has been proposed in which a magnetic force is utilized in place of vacuum attraction, as disclosed in Japanese Patent Application Laid-Open No. 60-68340. When, however, the material of the holding frame is made of a magnetic material as proposed in the Japanese Patent Application No. 60-68340, a force based on the Lorentz force is exerted on moving electric-charged particles (electrons) because of its residual magnetic flux (density) to cause misregistration from the given position, bringing about the problem that the position accuracy in drawing X-ray absorber patterns and the measurement accuracy in carrying our quality inspection on X-ray mask structures are extremely lowered. In the above proposal, the magnetic material such as metals, constituting at least a part of the holding frame, is apt to rust, often bringing about the problem that the rust causes warpage in parallelism when the mask structure is fixed to the apparatus body. A further X-ray mask comprising a holding frame formed of a magnetic material or a holding frame formed of a non-magnetic material and having a permanent magnet embedded into the groove of the frame is known from the Patent Abstracts of Japan vol. 11, no. 324 (P-628) (2771) 22 October 1987, & JP-A-62 109053 (CANON INC) 20 May 1987. The disadvantages discussed above for the Japanese Patent Application laid open no. 60-68340 also hold for this X-ray mask. SUMMARY OF THE INVENTION Accordingly, the object of the present invention is to provide an improved method of making an-X-ray mask structure of the Kind defined by the precharacterizing features of claim 1 to which the magnetic chucking can be applied under reduced-pressure or vacuum exposure conditions and that can remarkably improve position accuracy. The above object is attained by the characterizing features of claim 1. Advantageous developments of the invention are given by the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A to 1G, 2A to 2F and 3A to 3F are all schematic crosss sections of X-ray mask structures, to illustrate working examples of the present invention; Figs. 4 and 5 are schematic cross sections to illustrate the constitution of X-ray mask structures obtained in the present invention; and Figs. 6A to 6G are schematic cross sections of an X-ray mask structure, to illustrate a comparative example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail by giving preferred embodiments based on the examples illustrated in the drawings. All films conventionally used as support films can be used as the support film used in the X-ray mask structure obtained according to the present invention, as exemplified by inorganic films of single materials such as beryllium (Be), titanium (Ti), silicon (Si) and boron (B) or compounds of any of these, and organic films of polyimide, polyamide, polyester and Poly(para-xylylene), or composite films of these. These support films are X-ray transparent and may preferably have a thickness of from 0.5 to 5 µm in the case of the inorganic films and from 1 to 20 µm in the case of the organic films so that the transmittance of X-rays can be made as high as possible. In forming these support films, hitherto known methods can be employed. For example, as schematically illustrated in Figs. 1A to 1G and 2A to 2F, a support film 12 as described above is formed on a silicon wafer (holding frame) 11 (Fig. 1A). Subsequently a protective film 13 (a silicon nitride film or the like) for eching is provided on part of the back surface thereof, and then the silicon wafer 11 is etched with an aqueous 30 wt % potassium hydroxide solution. As a result, the support film 12 held on the holding frame 11 is formed (Fig. 1B). As shown in Figs. 2A to 2F, a support film 22 may be tensioned, and thus fixed by adhesion on a holding frame 21, using an adhesive 28. The holding frame 21 may be made of any materials including ceramics and low-expansion glass, so long as they are non-magnetic materials (Fig. 2A). The adhesive 28 may be an adhesive having an adhesive force by which the tensioned support film 22 may not be removed, and there may be used, for example, epoxy resin or rubber adhesives. Any X-ray absorbers used in conventional X-ray mask structures can be used as an X-ray absorber 16 or 26 formed on the above support film 12 or 22, without any particular limitations, including thin films (with a thickness of, for example, from 0.5 to 1 µm in approximation) of materials commonly having a high density as exemplified by gold, platinum, tungsten, copper, tantalum, and compounds containing these. In forming such an X-ray absorber 16 or 26, a plating electrode layer 14 or 24 is previously provided (Fig. 1C, Fig. 2B). Metals such as Cu and Au are used as materials for the electrode layer 14 or 24. A resist layer 15 or 25 is provided further thereon in a single layer or multiple layers. Thereafter, the resist layer 15 or 25 is subjected to patterning according to an electron-beam drawing method (Fig. 1D, Fig. 2C). Subsequently, the surface of the electrode layer 14 or 24 is placed with Au for the X-ray absorber 16 or 26 in accordance with the resist pattern (Fig. 1E, Fig. 2D). Thereafter, the resist layer 15 or 25 and successively the electrode layer 14 or 24 other than the absorber 16 or 26 comprising Au provided by plating are removed from the support film 12 or 22 (Fig. 1F, Fig. 2E.). On the X-ray mask structure having been passed through the above procedure, the pattern accuracy is commonly examined using an Electron Beam Metrogy System and a Laser Interferometric X-Y Measuring Machine Model 2I. In the present invention, a reinforcement member 17 the whole or a part of which is comprised of a magnetic material is further fixed on the above X-ray mask structure, using an adhesive 18 (Fig. 1G), or a magnetic member 27 is embedded in a recession made in the holding frame 21 and fixed therein using an adhesive 28′ (Fig. 2F). Such a reinforcement member 17 or magnetic member 27 oomprises a magnetic material such as iron, cobalt, nickel, or an alloy or compound of any of these, and all of conventionally known magnetic members can be used. The reinforcement member 17 may comprise the magnetic material as the whole, or it may be a combination of a non-magnetic material such as glass or ceramics with the above magnetic material. The shape of the reinforcement member may be the same as the holding frame or of similar figure thereto, and there are no particular limitations so long as it is the shape capable of holding the holding frame. The fixing to the holding frame 11 may be carried out by any fixing means such as press fitting, screw fitting, screwed stopper, and adhesion using the adhesive 18. However, taking account of the strain, stability, etc. of the magnetic member when fixed, it is preferred to use the adhesive 18, which is an adhesive causing less constriction when set up, as exemplified by epoxy resin rubber, acrylic resin and polyimide resin adhesives. The magnetic member 27 may be fixed to the holding frame 21 by any fixing means such as press fitting, screw fitting, screwed stopper, and adhesion using the adhesive 28'. In the case of the fixing of the member 27 by adhesion, the fixing is preferred to be carried out using the epoxy resin, rubber, acrylic resin, polyimide resin, etc. The preparation method of the present invention is characterized in that, in forming the mask support described above, the reinforcement member 17 which is a magnetic member or the magnetic member 27 is fixed on the holding frame 11 or 21 after the formation of and inspection on the X-ray absorber pattern 16 or 26 has been completed. In other words, if the the mask pattern 16 is formed after the fixing of the reinforcement member 17, a slight residual magnetic field ascribable to the magnetic member causes the deflection of the direction of electron beams and ion beams used in patterning, but the fixing of the reinforcement member 17 which is a magnetic member or the magnetic member 27 after the patterning has been completed as in the present invention can eliminate such a difficulty. One face (the face or side used for chucking) of the magnetic member used in the present invention may be abraded to have a surface roughness of not more than 0.2 µm and a flatness of not more than 2 µm, whereby the gap to the mask chuck of the exposure apparatus side can be reduced and the chucking by magnetic force can be made firmer. The magnetic member used in the present invention is a magnetic member having the possibility of rusting as exemplified by iron, nickel, cobalt, or alloys thereof. Rust proofing for these magnetic members may be carried out by forming a coating film of resin coating composition commonly available. However, such resin coating film, because of its insufficiency in hardness, strength, wear resistance, etc., is liable to lower the accuracy of the mask structure or is required to be formed with a large thickness because of its insufficiency in hardness, strength, wear resistance, etc., so that there is a possibility of lowering the magnetic characteristics of the magnetic member. Hence, preferred rust proofing is to apply a coating using ceramics such as TiN, SiC, Si₃N₄, Al₂O₃ and TiC, or to apply metal plating such as Kanigen plating of nickel. These ceramics coating or metal plating enable low-temperature coating, and hence the resulting coating can be free from deformation of the magnetic member due to heat shock. It also can be free from pinholes. Furthermore it is hard, and has excellent wear resistance. Thus, a thin film with a thickness of, for example, from 0.1 to 5 µm in approximation can achieve a sufficient rust proofing effect. Since such a thin film can be enough, it also may not occur that the magnetic characteristics of the magnetic member is lowered. A thickness less than 0.1 µm, of the thin film may result in a poorness in respect of its strength such as wear resistance, and a thickness more than 5 µm may lower the magnetic charactaristics. EXAMPLES The present invention will be described below in further detail by giving Examples. Example 1 A first example of the present invention will be described with reference to Fig. 1. On the silicon wafer 11, a support film 12 comprising SiN (thickness: 2 µm) and an etching protective film 13 were formed by an LP-CVD process. The etching protective film 13 was subjected to patterning in the desired back-etched form. The silicon wafer 11 was further back etched for several hours in a 30 wt.% KOH solution (70°C). On the support film 12, the plating electrode 14 was provided by resistive heating deposition of Cr and Au, successively. OEBR-1000 (trade name; Tokyo Ohka Kogyo Co., Ltd.) was further coated as an electron-beam resist 15 with a thickness of 1 µm. In an electron-beam drawing apparatus MEBES-III (trade name; manufactured by Perkin Elmer Co.), a resist pattern was formed under conditions of an accelerating voltage of 20 KV and a beam current of 100 nA. Using a gold-plating solution Neutronex 309 (trade name; a product of EEJA Co.), gold-plating was carried out to form a gold absorber pattern 16 (0.8 µm thick), and then the resist 15 was peeled. The electrode metal 14 was also removed by dry etching. The accuracy of the absorber pattern 16 was inspected using the Electron Beam Metrogy System [S-6000 (trade name; manufactured by Hitachi Ltd.) and the Laser Interferometric X-Y Measuring Machine Model 2I [Lampus A2 (trade name; manufactured by Nikon Co.)]. As a result, it was possible to form an absorber pattern of 0.25 µm L/S corresponding to 256M DRAM with a position accuracy of 0.1 µm. To the resulting mask structure, a reinforcement member 17 comprised of a magnetic member martensite stainless steel (SUS403) was adhered using an epoxy adhesive EP007 (trade name; a product of Cemedine Co., Ltd.). Used as the reinforcement member 17 was the one previously processed to have a flatness of 1 µm and a surface roughness of 0.1 µm on the side which was not adhered to the holding frame 11, and subjected to rust proofing by further providing a SiN film (0.5 µm) on the surface. Example 2 A second example of the present invention will be described with reference to Figs. 2A to 2F. Riverceram SNB-10 (trade name; manufactured by Kawasaki Steel Corporation) was used as the holding frame 21. Kapton film (thickness: 7.8 µm; trade name; a product of Toray Industries, Inc.) was used as the support film, and adhered on the holding frame 21, using as the adhesive 28 a rubber adhesive G-10 (trade name; a product of Konishi Co., Ltd.). On the support film 22, the plating electrode 24 was provided by resistive heating deposition of Cr and Au, successively. A multi-layer resist (three layers) was further provided as the resist 25. The multi-layer resist was constituted of a lower layer comprising a novolac resin, an intermediate layer comprising SiO₂ and an upper layer comprising an electron-beam resist OEBR-1000 trade name; Tokyo Ohka Kogyo Co., Ltd.). In an electron-beam drawing apparatus EBM-130/40P (trade name; manufactured by Toshiba Machine Co., Ltd.), the electron-beam resist on the upper laver of the multi-layer resist was subjected to patterning under conditions of an accelerating voltage of 20 KV and a beam current of 200 nA. In a dry etching apparatus, the intermediate layer and the lower layer were further etched using CF₄ gas and 0₂ gas, respectively. The resist pattern 25 was thus formed. Using a gold-plating solution Neutronex 309 (trade name: a product of EEJA Co.), gold-plating was carried out to form a gold absorber pattern 16 (0.8 µm thick), and then the resist 25 was removed. The electrode metal 24 was also removed by dry etching. The accuracy of the absorber pattern 16 was inspected using the Electron Beam Metrogy System S-6000 (trade name; manufactured by Hitachi Ltd.) and the Laser Interferometric X-Y Mesuring Machine Model 2I Lampus A2 (trade name; manufactured by Nikon Co.). As a result, it was possible to form an absorber pattern of 0.5 µm L/s corresponding to 16M DRAM with a position accuracy of 0.15 µm. To the resulting mask structure, a magnetic member 27 comprised of a magnetic member ferrite stainless steel (SUS430) was fixed by adhesion using an epoxy adhesive 3500 (trade name; a product of Alfa Giken Co.). Used as the magnetic member 27 was the one previously processed so as to have a flatness of 2.0 µm and a surface roughness of 0.2 µm on its side which was not adhered to the holding frame 21, and subjected to rust proofing by further applying nickel-plating of 0.8 µm thick on the surface. Example 3 A third example of the present invention will be described with reference to Figs. 3A to 3F. On a silicon wafer 31, a support film 32 comprising SiC (thickness: 2 µm) and an etching protective film 33 were formed by sputtering. The etching protective film 33 was subjected to patterning in the desired back-etched form. On the support film 32, Ta as an absorber 36 was deposited by sputtering to give a thickness of 0.8 µm, and a multi-layer resist (two layers) was provided thereon as a resist 35. The multi-layer resist was constituted of a lower layer comprising SiO₂ and an upper layer comprising an electron-beam resist RE-5000P (trade name; a product of Hitachi Chemical Co., Ltd.). In an electron-beam drawing apparatus MEBES-III (trade name; manufactured by Perkin Elmer Co.), the electron-beam resist on the upper layer was subjected to patterning under conditions of an accelerating voltage of 20 KV and a beam current of 100 nA. Then the lower layer Si0₂ was subjected to dry etching using a mixed gas of CF₄ and H₂ to form a resist pattern 35. In a dry etching apparatus, Ta was further etched using CBrF₃ gas. An absorber pattern 36 was thus formed. The silicon wafer 11 was subjected to back etching in a 30 wt.% KOH solution (70°C). The same inspection as Example 1 was carried out. As a result, it was possible to form an absorber pattern of 0.35 µm L/S corresponding to 64M DRAM with a position accuracy of 0.1 µm. To the resulting mask structure, a reinforcement member 37 comprised of a magnetic member martensite stainless steel (SUS403) was adhered using an epoxy adhesive EP007 (trade name; a product of Cemedine Co., Ltd.). A terrace was formed on the face of the reinforcement member 37 coming into contact with the holding frame 31, a part of the holding frame was embedded in the reinforcement member 37, and then the member 37 and the frame 31 were fixed each other by adhesion at the corner formed by the side face of the holding frame 31 and the top face of the reinforcement member 37 (as shown in Fig. 3F). Employment of this fixing means requires no adhesive 38 at the interface between the holding frame 31 and reinforcement member 37, thus bringing about the advantage that no warpage in the flatness and parallelism of the whole mask is caused. Used as the reinforcement member 37 was the one previously processed so as to have a flatness of 1 µm and a surface roughness of 0.1 µm on its side which was not adhered to the holding frame, and subjected to rust proofing by further providing a TiN film (0.4 µm) on the surface. Example 4 Another example of the present invention will be described with reference to Fig. 4. First, a BN-polyimide composite support film 42 with a thickness ratio of 1:1 and a total thickness of 2 µm was formed on a silicon wafer (holding frame) 41 in the same manner as Example 1. On the resulting support film 42, a plating electrode 44 was provided by continuous resistance heat deposition of Cr and Au. OEBR-1000 (trade name; Tokyo Ohka Kogyo Co., Ltd.) was further coated as an electron-beam resist 15 with a thickness of 1 µm. In an electron beam drawing apparatus MEBES-III (trade name; manufactured by Perkin Elmer Co.), a resist pattern was formed under conditions of an accelerating voltage of 20 KV and a beam current of 100 nA. Using a gold-plating solution Neutronex 309 (trade name; a product of EEJA Co.), gold-plating was carried out to form a gold absorber pattern 46 (0.8 µm thick). The electrode metal 44 from which the resist was removed was also removed by dry etching. To the resulting mask structure, a reinforcement member 47 was adhered using an acrylic adhesive 48, Type No. G5510 (trade name; a product of Denka Co., Ltd.). The above reinforcement member 47 comprises a non-magnetic material such as Pyrex glass, a low-expansion glass, or quartz glass. The accuracy of the absorber pattern 46 was inspected using the Electron Beam Metrogy System S-6000 (trade name; manufactured by Hitachi Ltd.) and the Laser Interferometric X-Y Measuring Machine Model 2I Lampus A2 (trade name; manufactured by Nikon Co.). As a result, it was possible to form an absorber pattern of 0.25 µm L/S corresponding to 256M DRAM with a position accuracy ot 0.1 µm. On the bottom surface of the reinforcement member 47, a magnetic member 47′ was formed by electroless Ni-plating and thereafter electrolytic Co-Ni-plating. As rust proofing, Ni-plating was further applied thereon. In the film formation of tbe magnetic member 47′, vacuum deposition or the like may be used. The holding frame 41 and reinforcement member 47 had substantially the same shapes as those in Example 1, and the face of the reinforcement member 47 which was nor adhered to the holding frame 41 had been processed so as to have a flatness of 1 µm and a surface roughness of 0.1 µm. Example 5 Another example of the present invention will be described with reference to Fig. 5. First, a support film 52 made of AlN with a thickness of 2 µm was formed on a silicone wafer (holding frame) 51 in the same manner as Example 1. On the resulting support film 52, W as an absorber 56 was deposited by sputtering to give a thickness of 0.8 µm, and a multi-layer resist (two layers) was further provided thereon as a resist. The multi-layer resist was constituted of a lower layer comprising polyimide resin and an upper layer comprising a Si-containing electron-beam resist SNR (trade name; a product of Toyo Soda Manufacturing Co., Ltd.). In an electron-beam drawing apparatus EBM-130/40P (trade name; manufactured by Toshiba Machine Co. Ltd.), the electron-beam resist on the upper layer was subjected to patterning under conditions of an accelerating voltage of 20 KV and a beam current of 200 nA. Then the lower layer was subjected to dry etching using an O₂ gas to form a resist pattern. W was further etched using SF₆ gas. An absorber pattern 56 was thus formed. To the resulting mask structure, a reinforcement member 57 was fixed by adhesion using an epoxy adhesive Type No. 3500 (trade name; a product of Alfa Giken Co.). The reinforcement member 57 was comprised of ceramics SHAPAL M (trade name; a product of Tokuyama Soda Co., Ltd.). The accuracy of the absorber pattern 56 was inspected using the Electron Beam Metrogy System S-6000 (trade name: manufactured by Hitachi Ltd.) and the Laser Interferometric X-Y Measuring Machine Model 2I Lampus A2 (trade name; manufactured by Nikon Co.). As a result, it was possible to form an absorber pattern of 0.15 µm L/S corresponding to 16M DRAM with a position accuracy of 0.15 µm. In a recession made in the bottom surface of the reinforcement member 57, a ring-shaped magnetic member 57′ comprising ferrite stainless steel (SUS430) was fixed by adhesion using an adhesive 58′. The ring-shaped magnetic member 57′ was previously processed so as to have a flatness of 1 µm and a surface roughness of 0.08 µm on its side which was not adhered to the reinforcing member 57, and subjected to rust proofing by further applying SiN with a thickness of 0.4 µm on its surface. Comparative Example Preparation steps of a comparative example of the present invention will be shown with reference to Figs. 6A to 6G. In the same manner as Example 1, a support film 62 and etching protective film 63 are formed on a silicon wafer 61, and then the silicon wafer 61 was subjected to back etching. What was different from Example 1 was that a reinforcement member 67 which was a magnetic member was fixed by adhesion using an adhesive 68 at the stage as shown in Fig. 6C. Thereafter in the same manner as Example 1, a plating electrode 64 and a resist 65 were provided. Then, in an electron-beam drawing apparatus MEBES-III (trade name; manufactured by Perkin Elmer Co.), the resist pattern 65 was formed under conditions of an accelerating voltage of 20 KV and a beam current of 100 nA, where the position accuracy of the resist pattern 65 was inspected using a light wave interference coordinate meter Lampus A2 (trade name; manufactured by Nikon Co.). As a result, as large as 10 µm misregistration of the resist pattern occurred at some places because of the inhomogeneous distribution of the magnetic field. Using a gold-plating step in the same manner as Example 1, an absorber pattern 66 was formed. Then, in the Electron Beam Metrogy System S-6000 (trade name; manufactured by Hitachi Ltd.), the accuracy of the absorber pattern 66 was observed at an accelerating voltage of 1 KV. As a result, there was a difference of 47 µm at maximum in pattern position mesurement between the results obtained by the Electron Beam Metrogy System and those by the Laser Interferometric X-Y Measuring Machine Model 2I Lampus A2. As having been described in the above, according to the present invention, an X-ray absorber pattern can be formed on the support film with a good position accuracy. Similar effects can be seen when charged particles such as focused ion beams used in mask modificaton or the like are used. One face (the face used for chucking) of the magnetic member used in the present invention is abraded to have a surface roughness of not more than 0.2 µm and a flatness of not more than 2 µm, so that the gap to the mask chuck of the exposure apparatus side can be reduced and the chucking by magnetic force can be made firmer. The rust proofing previously carried out on the magnetic member can eliminate the problems of warpage in the parallelism of the resulting mask structure, and dusting.

Claims: A method of making an X-ray mask structure having an X-ray absorber in a desired pattern on the surface of a support film held by a frame, the latter being provided with a magnetic member, characterized in that, whenever the X-ray absorber is patterned by using an electron beam drawing step, the frame and support film are produced from non-magnetic material and after patterning of the X-ray absorber, the frame is provided with the magnetic member. The method according to claim 1, wherein the frame and the magnetic member are joined together. The method according to claim 1, wherein a reinforcement member, at least a portion of which comprises a magnetic member, is joined to the frame. The method according to claim 2 or 3, wherein the magnetic member is embedded in a recession of the frame or of the reinforcement member, respectively. The method according to any one of claims 1 to 4, further comprising a step of inspecting the accuracy of absorber patterns including a measuring step that utilizes an electron beam, wherein the inspecting step is performed before the magnetic member is applied to the frame or reinforcement member, respectively. The method according to any one of claims 1 to 5, wherein an X-ray transparent film is used as the support film. The method according to any one of claims 1 to 6, wherein the surface of the magnetic member is subjected to rust proofing. The method according to any one of claims 1 to 7, wherein the magnetic member is subjected to abrasion processing to have a surface roughness of not more than 0.2 µm at its free surface. The method according to any one of claims 2 to 8, wherein the reinforcement member is formed in a shape similar to the frame. The method according to any one of claims 2 to 9, wherein the frame is adhered to the reinforcement member.

Inventors: CHIBA KEIKO, FUKUDA YASUAKI, MIYACHI TAKESHI, CHIBA, KEIKO, FUKUDA, YASUAKI, MIYACHI, TAKESHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1989
Main classification: G03F1
IPC codes: G03F1