JPH11160510A5 - - Google Patents

Description

[Document name] Statement

[Title of invention] Manufacturing method of multi-stage stepped element or mold for manufacturing said element [Claims]
1. A method for fabricating a multi-step stepped element or a mold for fabricating said element by multiple lithography steps, comprising:
forming a first mask pattern on a substrate using a first material, and etching the substrate using the first mask pattern;
forming a second mask pattern using a second material using the pattern of the first mask;
partially removing at least one of the patterns of the first and second masks to form a pattern of a third mask;
Etching the substrate using the pattern of the third mask;
1. A method for producing a multi-stage stepped element or a mold for producing said element, comprising:
[Claim 2] A method for manufacturing a multi-stage stepped element or a mold for producing said element, as described in claim 1, characterized in that the process of forming the pattern of the second mask includes a process of filling, with the second material, recesses in the substrate created by the process of etching the substrate using the pattern of the first mask.
[Claim 3] A method for manufacturing a multi-stage stepped element or a mold for producing said element as described in claim 1 or 2, characterized in that the substrate is a light-transmitting material, the first mask is a light-shielding material, and the process of forming a pattern of the second mask includes a process of irradiating light from the back surface of the substrate through the substrate onto the second material.
4. The method for manufacturing a multi-step stepped element or a mold for manufacturing said element according to claim 3, wherein the second material is a negative resist, and the negative resist is exposed to light from the back surface of the substrate.
5. The method for manufacturing a multi-stepped element or a mold for manufacturing said element according to claim 4, further comprising the step of irradiating the surface of said substrate with light to expose said negative resist.
6. A diffractive optical element manufactured by the manufacturing method according to any one of claims 1 to 5.
7. A diffractive optical element manufactured using a mold manufactured by the manufacturing method according to any one of claims 1 to 5. Description:
8. An optical system comprising the diffractive optical element according to claim 6. Description:
9. An exposure apparatus comprising the optical system according to claim 8. Description:
Detailed Description of the Invention
[0001]
[Technical Field to which the Invention Belongs]
The present invention relates to a method for manufacturing a multi-stepped element having a stepped cross section formed by a lithography process , or a mold for manufacturing such an element.
[0002]
2. Description of the Related Art
Conventionally, as a method for manufacturing a diffractive optical element, which is a binary optics, a technique of forming a resist into a stepped shape by controlling the dose of an electron beam and using this as a diffraction pattern as is has been disclosed in the Journal of the Institute of Electronics and Communication Engineers (c) J66-CP85-91, January 1983, Japanese Patent Laid-Open Nos. 62-265601 and 62-42102, etc.
[0003]
Furthermore, Japanese Patent Laid-Open Publication No. 61-137101 discloses a technique in which two or more types of films, each having etching resistance, are stacked to a desired thickness, and are etched sequentially from the top layer to form a staircase structure, which is then used as a mold for a diffractive optical element. Japanese Patent Laid-Open Publication Nos. 61-44628 and 6-160610 disclose techniques in which resist is formed by aligning each step, and this is used as an etching mask to form a staircase structure, which is then used as a mold for a diffractive optical element.
[0004]
Furthermore, Japanese Patent Laid-Open Publication No. 8-15510 discloses a technique in which an etching stopper layer and a transparent layer are stacked one layer at a time on a substrate, and alignment, exposure, and etching are performed to directly form a staircase structure, thereby forming a diffractive optical element.
[0005]
Furthermore, Japanese Patent Laid-Open No. 6-26339 and U.S. Patent Publication No. 2,554,600 disclose a technique for forming a staircase structure directly on a substrate using resist as an etching mask to form a diffractive optical element, and for performing alignment after each resist patterning. Japanese Patent Laid-Open No. 7-72319 discloses a technique for forming a staircase structure by performing alignment using resist as an etching mask.
[0006]
Figure 32 shows a cross-sectional view of the manufacturing process for an eight-stage diffractive optical element. In step (1) of Figure 32, resist is dropped onto a clean substrate 1, spin-coated to form a thin film of approximately 1 μm, and baked to form a resist film 2. In step (2) of Figure 32, the substrate 1 is loaded into an exposure device capable of exposing the finest diffraction pattern, and exposure is performed by irradiating the resist film 2 with exposure light L, to which the resist film 2 is sensitive, using a reticle 3 corresponding to the desired diffraction pattern as a mask. If a positive resist is used, the area exposed to the exposure light L becomes soluble in a developer, forming a resist pattern 4 of the desired dimensions, as shown in step (3) of Figure 32. In step (4) of Figure 32, the substrate 1 is loaded into a reactive ion etching device or ion beam etching device capable of anisotropic etching, and the patterned resist pattern 4 is used as an etching mask to etch the substrate 1 to a predetermined depth for a predetermined time. The resist pattern 4 is then removed, yielding a substrate 1 with a two-step pattern 5 formed thereon, as shown in step (5) of Figure 32.
[0007]
Again, as in step (1), a resist film 6 is formed on the substrate 1 and the substrate is loaded into an exposure tool, and in step (6) of Fig. 32, a reticle 7 having a pattern with twice the pitch of the diffraction pattern 3 is used as a mask, and alignment is performed with the alignment precision of the exposure tool relative to the pattern formed up to step (5). Then, in step (7) of Fig. 32, the resist film 6 is exposed and developed to form a resist pattern 8. Next, dry etching is performed as in step (4) to remove the resist pattern 8, and a pattern 9 having four steps is formed as shown in step (8) of Fig. 32.
[0008]
Furthermore, after forming a resist film 10 on the substrate 1 again in the same manner as in step (1), in step (9) of Fig. 32, a reticle 11 having a pattern four times as synchronous as the diffraction pattern 3 is used as a mask to form a resist pattern 12 in step (10) of Fig. 32 in the same manner as in step (7), and after dry etching, the resist pattern 12 is removed to form a diffractive optical element having a pattern 13 with eight steps, as shown in step (11) of Fig. 32. Then, anti-reflection films are formed by sputtering or vapor deposition on both sides of the substrate 1 on which the diffractive optical elements have been formed.
[0009]
In this way, diffractive optical elements or molds with stepped cross sections are manufactured using lithography processes and film-forming techniques based on exposure and etching techniques used in semiconductor manufacturing. The optical performance of these diffractive optical elements is achieved by the stepped unevenness formed on the substrate, and the diffraction efficiency is determined by the shape of the unevenness formed, i.e., the depth, width, cross-sectional shape, etc. of the steps.
[0010]
When manufacturing a diffractive optical element having a multi-step shape by sequentially using such double-pitch masks, provided that no alignment or dimensional errors occur, it is possible to form an ideal eight-step shape A, for example, using three masks 17a to 17c as shown in Figure 33.
[0011]
[Problem to be solved by the invention]
However, in the above-described embodiment, in a manufacturing technique using multiple masks, alignment errors significantly degrade diffraction efficiency, and furthermore, such shape errors, once formed, are impossible to reproduce, resulting in increased costs. In reality, it is impossible to completely eliminate these alignment errors and dimensional errors. For example, as shown in Figure 34, if the alignment of masks 17a to 17c is misaligned by the amounts indicated by r1 and r2, a diffractive optical element with a shape B different from ideal shape A is formed. This significantly reduces optical performance such as diffraction efficiency, and if dimensional errors occur in each layer, the deterioration of optical performance is further exacerbated.
[0012]
For example, if an ideal eight-step shape as shown in shape A is formed using quartz as the substrate, with a minimum line width of 0.35 μm, a step height d of 61 nm, and a wavelength of 248 nm, the theoretical diffraction efficiency excluding loss due to reflection is 95%. On the other hand, if the alignment error r1 between masks 17a and 17b is 80 nm and the alignment error r2 between masks 17a and 17c is 30 nm, the diffraction efficiency excluding reflection will be 80%, a decrease of 15%, and similar results have been confirmed in actual measurements and simulations.
[0013]
Furthermore, to form a multi-stage diffractive optical element using a similar method, a resist process involving multiple exposures and developments is performed, and a 16-step stepped diffractive optical element can be manufactured, for example, using quartz as the substrate, with a minimum line width of 0.35 μm, a step height of 30.5 nm, and a wavelength of 248 nm. In the case of an ideal 16-step shape, the theoretical diffraction efficiency excluding loss due to reflection is 99%, but if alignment errors are included, the diffraction efficiency will be significantly lower than that of an 8-step shape.
[0014]
As described above, in practice, it is extremely difficult to control the dimensions and alignment of the resist pattern, and reproducibility cannot be achieved. As a result, the width of the steps may become wider or narrower, and grooves or protrusions that do not exist in an ideal staircase shape may be formed, resulting in a significant deterioration in the optical performance of the diffractive optical element.
[0015]
In addition, in the case of electron beam lithography, alignment errors are eliminated, but the amount of lithography required is so large that sufficient throughput cannot be obtained in terms of production.
[0016]
Furthermore, in the case of glass generally used in diffractive optical elements, the etching rate is slow and the etching rates of the resist and glass are similar, so if you try to obtain a diffraction pattern with deep steps, you need to form a thick resist.If the resist is too thick, reaction products generated by etching in the deep parts of the grooves will not be able to escape, which will deteriorate the cross-sectional shape and damage the rectangular shape of the side walls.
[0017]
An object of the present invention is to provide a method for manufacturing a multi-step stepped element or a mold for manufacturing such an element, which allows for stable production of a high-precision diffractive optical element in a short time at low cost.
[0018]
[Means for solving the problem]
The technical features of the method for manufacturing a multi-step stepped element or a mold for manufacturing such an element according to the present invention for achieving the above-mentioned object are that the method is a method for manufacturing a multi-step stepped element or a mold for manufacturing such an element by multiple lithography processes, and is characterized by comprising the steps of: forming a first mask pattern on a substrate using a first material and etching the substrate using the first mask pattern; forming a second mask pattern using a second material using the first mask pattern; partially removing at least one of the first and second mask patterns to form a third mask pattern; and etching the substrate using the third mask pattern.
[0019]
[Embodiments of the Invention]
The present invention will be described in detail based on the embodiments shown in FIGS.
1 shows cross-sectional views of the manufacturing process of the diffractive optical element of the first embodiment. In step (1) of Fig. 1, a 100 nm thick chromium film 22 made of a light-shielding first material is formed as a first mask on a quartz substrate 21 made of a light-transmitting material by sputtering, and a resist pattern 23 having a diffraction pattern with a reference period is then formed. After that, the chromium film 22 is removed using an etching solution made of a mixture of ceric ammonium nitrate, perchloric acid, and water.
[0020]
In step (2) of Figure 1, the quartz substrate 21 is etched to a predetermined depth by reactive ion etching (RIE) using a mixed gas of _CF4 and hydrogen, forming recesses 24. In step (3) of Figure 1, an aluminum film 25, a second material, is formed as a second mask using electron beam evaporation to a thickness that is consistent with the surface of the remaining chromium film 22, filling the recesses 24. Next, in step (4) of Figure 1, the resist pattern 23 and the aluminum film 25 thereon are simultaneously removed by lift-off. Through these steps, a diffraction pattern with a reference period is formed in a two-stage structure, and the surface of the quartz substrate 21 is covered by the adjacent chromium film 22 and aluminum film 25, thereby defining the position and dimensions of the pattern.
[0021]
Next, in step (5) of Fig. 1, a resist pattern 26 is formed, and the predetermined chromium film 27 is removed with an etching solution, and then in step (6) of Fig. 1, the resist pattern 26 is removed using the same etching solution as in step (1). Furthermore, in step (7) of Fig. 1, a resist pattern 28 is formed, and the predetermined aluminum film 29 adjacent to the chromium film 27 removed in step (6) is removed with an etching solution consisting of a mixture of phosphoric acid, nitric acid, acetic acid, and water, and then the resist pattern 28 is removed in step (8) of Fig. 1.
[0022]
In step (9) of Fig. 1, the chromium film 22 of the first mask and the aluminum film 25 of the second mask are partially removed, and the remaining portions serve as an etching mask, or third mask. The quartz substrate 21 is then etched to a predetermined depth by the same RIE method as in step (2), a self-alignment method that does not require alignment. Finally, in step (10) of Fig. 1, the chromium film 22 is removed using the same etching solution as in step (1), and the aluminum film 25 is removed using the same etching solution as in step (6). In this way, a diffractive optical element having a highly accurate four-step structure is realized, free of grooves or protrusions due to alignment errors or pattern dimensional errors.
[0023]
2 shows cross-sectional views of the manufacturing process of a diffractive optical element by photo-CVD (photo-assisted chemical vapor deposition) according to the second embodiment. In step (1) of Fig. 2, a chromium film 32 is formed on a quartz substrate 31 by sputtering to a thickness of 100 nm as a first mask, and a resist pattern 33 having a diffraction pattern with a reference period is then formed. The chromium film 32 not forming the resist pattern 33 is then removed using an etching solution consisting of a mixture of ceric ammonium nitrate, perchloric acid, and water.
[0024]
2, the quartz substrate 31 is etched to a predetermined depth by RIE using a mixed gas of _CF4 and hydrogen to form recesses 34, and the resist pattern 33 is then removed. In step (3) of Fig. 2, an aluminum oxide film 35, which is the second material, is formed as a second mask using a KrF laser beam with a wavelength of 248 nm and a mixed gas of Al(CH3)3 and nitrogen peroxide while irradiating the rear surface of the quartz substrate 31 with exposure light L, filling the recesses 34.
[0025]
Through the steps up to this point, a diffraction pattern with a reference period is formed in a two-stage structure, and the surface of the quartz substrate 31 is covered with the adjacent chromium film 32 and aluminum oxide film 35, thereby defining the position and dimensions of the pattern. Note that the photo-CVD method using light irradiation from the backside is a self-aligning method that allows hole filling in one step, making it simpler than other methods.
[0026]
2, a predetermined resist pattern 36 is formed, and in step (5) of Fig. 2, the chromium film 37 not forming the resist pattern 36 is removed with the same etching solution as in step (1), and then the resist pattern 36 is removed. Furthermore, in step (6) of Fig. 2, a resist pattern 38 is formed, and the predetermined aluminum oxide film 39 adjacent to the chromium film 32 removed in step (5) of the aluminum oxide film 35 is removed with a phosphoric acid-based etching solution, and then the resist pattern 38 is removed in step (7) of Fig. 2.
[0027]
Next, in step (8) of FIG. 2, the remaining chromium film 32 and aluminum oxide film 35 are used as a third mask to etch the quartz substrate 31 by the same RIE method as in step (2), and then the chromium film 32 is removed with the same etching solution as in step (1), and the aluminum oxide film 35 is removed with the same etching solution as in step (7).As a result, as shown in step (9) of FIG. 2, a diffractive optical element having a high-precision four-step staircase structure, which is free from grooves or protrusions due to alignment errors or pattern dimensional errors, can be realized by the self-alignment method.
[0028]
The photo-CVD method used here can be implemented by combining a quartz substrate 31 that transmits assist light with a deposition material, and other combinations include a quartz substrate 31 with titanium oxide or boron nitride, etc. Also, by using a laminated film of chromium and chromium oxide as the first mask in this embodiment and an aluminum film as the material for the aluminum oxide film 35 in step (3), a diffractive optical element having a highly accurate four-step staircase structure can be realized using a selective deposition method.
[0029]
FIG. 3 shows cross-sectional views of a third embodiment of a manufacturing process for a diffractive optical element using a CMP (chemical mechanical polishing) or etch-back method. In step (1) of FIG. 3, a 200-nm-thick chromium film 42 is formed on a quartz substrate 41 by sputtering as a first mask. A resist pattern 43 having a diffraction pattern with a reference period is then formed. The chromium film 42 is then removed by RIE using a mixture of carbon tetrachloride and oxygen. In step (2) of FIG. 3, the resist pattern 43 is removed, and the quartz substrate 41 is then etched to a predetermined depth by RIE using a _CHF3 -based gas. In step (3) of FIG. 3, an aluminum film 44 is formed as a second mask to a thickness of approximately 500 nm by electron beam evaporation. In step (4) of FIG. 3, the aluminum film 44 is then removed by a damascene process using CMP or an etch-back process using an etching solution until the surface of the remaining chromium film 42 is exposed.
[0030]
The slurry and processing liquid used in the CMP method are aluminum oxide-based and ammonium hydroxide-based, respectively, and the etching liquid used in the etch-back method is a mixture of phosphoric acid, nitric acid, acetic acid, and water. Through the steps up to this point, a diffraction pattern with a reference period is formed in a two-stage structure on the quartz substrate 41, and the surface of the quartz substrate 41 is covered with adjacent chromium films 42 and aluminum films 44.
[0031]
Next, in step (5) of Fig. 3, a resist pattern 45 is formed in a predetermined position. Then, in step (6) of Fig. 3, the chromium film 46 where the resist pattern 45 is not formed is removed using an etching solution containing a mixture of ceric ammonium nitrate, perchloric acid, and water, and then the resist pattern 45 is removed. Furthermore, in step (7) of Fig. 3, a resist pattern 47 is formed, and the predetermined aluminum film 48 adjacent to the chromium film 46 removed in step (6) is removed using the same etching solution as in step (4). Finally, in step (8) of Fig. 3, the resist pattern 47 is removed. In step (9) of Fig. 3, the remaining chromium film 42 and aluminum film 44 are used as a third mask to etch the quartz substrate 41 by the same RIE method as in step (2), forming recesses 49. Through these steps, a diffraction pattern with a reference period is formed on the quartz substrate 41 in a four-stage structure.
[0032]
Next, in step (10) of Fig. 3, an aluminum film 50 is formed to a thickness of about 100 nm, as in step (3), and then, in step (11) of Fig. 3, the recesses 49 formed in step (9) are filled by the damascene method, and the aluminum film 50 is removed in the same manner as in step (4). Subsequently, in step (12) of Fig. 3, a resist pattern 51 is formed in a predetermined position, and in step (13) of Fig. 3, the chromium film 52 without the resist pattern 51 is removed with an etching solution. Furthermore, in step (14) of Fig. 3, a resist pattern 53 is formed, and in step (15) of Fig. 3, the aluminum films 44 and 50 are removed, and in step (16) of Fig. 3, the resist pattern 53 is removed.
[0033]
3, the quartz substrate 41 is etched by RIE similar to that in step (2) using the remaining chromium film 42 and aluminum films 44 and 50 as a mask. Finally, in step (18) in FIG. 3, the remaining chromium film 42 is removed with the same etching solution as in step (1), and the aluminum films 44 and 50 are removed with the same etching solution as in step (4).
[0034]
In this way, a diffractive optical element having a highly accurate eight-step structure without grooves or protrusions due to alignment errors or pattern dimensional errors can be realized by the self-alignment method. Note that the exposure light L for forming the pattern in the first to third embodiments is not limited to ultraviolet or far ultraviolet light, but may also be an electron beam, X-ray, or other exposure technology.
[0035]
Furthermore, the materials of the substrates 21 and 41 in the first and third embodiments are appropriately selected depending on the intended use of the mold, such as a transmission type or a reflection type. However, the two materials of the substrate (the material to be etched) and the first and second masks must have completely different etching rates and etching conditions in the etching method used, and a selectivity must be obtained. Furthermore, the etching method for the chromium film and aluminum film is not limited to wet etching, and dry etching methods such as sputter etching and ion beam etching may also be used. Furthermore, the film formation method for the first and second masks in the first and third embodiments may also be vacuum deposition, sputtering, ion beam sputtering, ion plating, CVD, electron beam etching, etc.
[0036]
FIG. 4 shows a cross-sectional view of a reflective diffractive optical element according to the fourth embodiment. A chromium layer 62, an aluminum layer 63, and a quartz layer 64 are deposited as reflective films on a substrate 61 having a multi-step staircase structure, as fabricated in the first to third embodiments, by electron beam evaporation or other methods. The chromium layer 62 functions to improve adhesion to the substrate 61, the aluminum layer 63 functions as a reflective film, and the quartz layer 64 functions as a protective film. Silicon or quartz is used as the substrate material, and the first and second masks are appropriately selected to have high selectivity. The material and layer structure of the reflective film layer are selected to fully utilize the functions of each layer depending on the wavelength and environment used. In this way, a reflective diffractive optical element having a high-precision four- or eight-step staircase structure, free of grooves or protrusions due to alignment errors or pattern dimensional errors, can be realized.
[0037]
5 shows a cross-sectional view of a diffractive optical element according to the fifth embodiment. A substrate 65 having a multi-step staircase structure, as produced in any of the first to third embodiments, is used as a mold to produce a replica of a diffractive optical element 66 using a duplication technique such as the ZP method or injection method using a photocurable resin. In this way, a diffractive optical element having a high-precision four- or eight-step staircase structure can be realized, free of grooves or protrusions due to alignment errors or pattern dimensional errors.
[0038]
6 shows the configuration of a projection optical system having a diffractive optical element. The diffractive optical element 72 of this embodiment is incorporated into a group of ordinary spherical or aspherical lenses 71, and an anti-reflection coating is formed on the surface of the ordinary lens group 71.
[0039]
The diffractive optical element 72 corrects various aberrations such as chromatic aberration and Seidel's five aberrations in cooperation with the normal lens group 71. Such projection optical systems are used in various cameras, interchangeable lenses attached to single-lens reflex cameras, office machines such as copying machines, projection exposure apparatuses used in the manufacture of liquid crystal panels, and projection exposure apparatuses used in the manufacture of semiconductor chips such as ICs and LSIs.
[0040]
7 shows the configuration of a projection exposure apparatus, which includes an illumination optical system 73 that supplies exposure light, a mask 74 that is illuminated by the illumination optical system 73, a projection optical system 75 that projects an image of a device pattern formed on the mask 74, and a glass or silicon substrate 76 that is coated with a resist pattern. The illumination optical system 73 and the projection optical system 75 incorporate a diffractive optical element according to this embodiment, and the surfaces of the lenses that make up the illumination optical system 73 and the projection optical system 75 are coated with anti-reflection coatings.
[0041]
Exposure light from an illumination optical system 73 illuminates a mask 74 , and a device pattern image formed on the mask 74 is projected onto a glass substrate or a silicon substrate 76 by a projection optical system 75 .
[0042]
8 and 9 show cross-sectional views of the manufacturing process for a diffractive optical element using a technique for exposing a negative resist to light by backside exposure according to the sixth embodiment. First, in step (1) of FIG. 8, a 100-nm-thick chromium film 82 is formed on a quartz substrate 81 by sputtering. To improve patterning resolution, a 20-30-nm anti-reflection coating such as chromium oxide is formed on the chromium film 82. In step (2) of FIG. 8, a photoresist is applied to the quartz substrate 81, and a first resist pattern 83 is formed with line and space widths of 0.35 μm. Next, using a parallel-plate RIE system, for example, the chromium film 82 is etched using chlorine gas or a mixture of chlorine gas and oxygen, with the resist pattern 83 serving as a first mask. Next, in step (3) of FIG. 8, the resist pattern 83 is stripped using oxygen ashing or a stripping solution. The pattern of the chromium film 82 defines all step positions through the following steps.
[0043]
In step (4) of Figure 8, using the pattern of the chromium film 82 as a mask, the quartz substrate 81 is etched to 61 nm in 5 minutes using, for example, a parallel-plate RIE apparatus with a mixed gas of _CF4 and hydrogen under the following etching conditions: _CF4 flow rate 20 ^cm3 /min, hydrogen flow rate 3 ^cm3 /min, pressure 4 Pa, and RF power 60 W. Next, a photoresist is applied to the substrate 81 to form a second resist pattern 84. The alignment accuracy at this time is sufficient to be half the line width of the pattern of the chromium film 82, and can be achieved with a conventional exposure apparatus. This can be applied to all patterning steps from the second onwards, including other embodiments.
[0044]
Next, in step (5) of Fig. 8, the quartz substrate 81 is etched by 61 nm using the pattern of the chromium film 82 and the resist pattern 84 as a mask. After the resist 84 is stripped in step (6) of Fig. 8, photoresist is applied again to form a third resist pattern 85. Then, in step (7) of Fig. 8, the quartz substrate 81 is etched by 61 nm using the chromium film 82 and the resist pattern 85 as a mask. After the resist 85 is stripped, photoresist is applied again to form a fourth resist pattern 86.
[0045]
In step (8) of Fig. 8, the quartz substrate 81 is etched by 61 nm using the resist pattern 86 and the pattern of the chromium film 82 as a mask. Next, in step (9) of Fig. 8, a negative resist is applied, exposed from the backside, and developed, leaving a resist pattern 87 as a second mask only in areas where there is no chromium pattern, as shown in step (10) of Fig. 8. At this time, the chromium pattern itself serves as a contact mask for the negative resist exposure, allowing for perfectly accurate alignment.
[0046]
Next, a photoresist is applied thereon, forming a fifth resist 88, as shown in step (11) of Figure 8. In step (12) of Figure 8, the chromium film in the areas not covered by the resist patterns 87 and 88 is removed by etching, for example, using a mixture of cerium ammonium nitrate, perchloric acid, and water. Furthermore, in step (13) of Figure 9, using the resists 87 and 88 as a third mask, the quartz substrate 81 is etched 366 nm in 30 minutes using the same RIE equipment and etching gas as in step (3) under the same etching conditions. In step (14) of Figure 9, the resist patterns 87 and 88 are removed by ashing, and then a negative resist is applied and exposed from the backside. In step (15) of Figure 9, this is developed, leaving a resist pattern 89 only in the areas where the chromium patterns were not present.
[0047]
In step (16) of Figure 9, photoresist is applied thereon to form a sixth resist 90. In step (17) of Figure 9, the chromium film in the areas not covered by the resist patterns 89, 90 is removed by etching using the same mixed solution as in step (12). Next, in step (18) of Figure 9, using the resists 89, 90 as a mask, the same RIE equipment and etching gas as in step (3) are used to etch the quartz substrate 81 to a depth of 244 nm under the same etching conditions as in step (3) for an etching time of 20 minutes. In step (19) of Figure 9, the resist patterns 89, 90 are removed by ashing. In step (20) of Figure 9, a negative resist is applied and exposed from the backside and developed, leaving a resist pattern 91 only in the areas where the chromium patterns were not present, as shown in step (21) of Figure 9.
[0048]
Next, photoresist is applied thereon to form a seventh photoresist 92. In step (22) of Figure 9, the portions of the chromium film not covered by the resist patterns 91 and 92 are removed by etching using the same mixed solution as in step (12). In step (23) of Figure 9, using the negative resists 91 and 92 as a mask, the quartz substrate 81 is etched 122 nm in 10 minutes using the same RIE equipment and etching gas as in step (3) under the same etching conditions as in step (3). Next, in step (24) of Figure 9, the resist patterns 91 and 92 are removed by ashing. The pattern of the chromium film 82 is etched using the same mixed solution as in step (12), completing an eight-stage diffractive optical element or a mold for fabricating diffractive optical elements, as shown in step (25) of Figure 9.
[0049]
The diffraction efficiency of the completed diffractive optical element, which had a minimum line width of 0.35 μm and a step height of 61 nm, was measured at a wavelength of 248 nm. The diffraction efficiency, excluding losses due to reflection, was found to be 93%, a 2% decrease from the theoretical value. The main cause of this 2% decrease in diffraction efficiency was the line width error of the initial chrome pattern.
[0050]
10 and 11 are cross-sectional views showing the steps of manufacturing the diffractive optical element of the seventh embodiment. Steps (1) to (3) in Fig. 10 are similar to steps (1) to (3) in Fig. 9 of the sixth embodiment, and a first resist pattern 83 is formed to complete the chrome pattern.
[0051]
In step (4) of Fig. 10, photoresist is applied to the quartz substrate 81, and a second resist pattern 93 is formed. Next, in step (5) of Fig. 10, the quartz substrate 81 is etched by 366 nm using the resist pattern 93 and the pattern of the chromium film 82 as a mask. In step (6) of Fig. 10, the resist 93 is stripped, and then photoresist is applied again, and a third resist pattern 94 is formed. In step (7) of Fig. 10, the quartz substrate 81 is etched by 244 nm using the resist pattern 94 and the pattern of the chromium film 82 as a mask. Next, the photoresist 94 is stripped, and then photoresist is applied again, and a fourth resist pattern 95 is formed.
[0052]
In step (8) of Figure 10, the quartz substrate 81 is etched by 122 nm using the resist pattern 95 and the pattern of the chromium film 82 as a mask. In step (9) of Figure 10, the resist 95 is removed, and then a polyimide film 96 is applied to the entire surface by spin coating to a thickness of approximately 1 μm. Next, the polyimide film 96 is etched back by oxygen plasma ashing until the surface of the pattern of the chromium film 82 is exposed. In step (10) of Figure 10, a resist pattern is applied, and a resist pattern 97 of a fifth second mask is formed by lithography. In step (11) of Figure 10, the chromium film not covered by the resist pattern 97 and the polyimide film 96 is removed by etching using, for example, a mixture of cerium ammonium nitrate, perchloric acid, and water. In step (12) of FIG. 10, using the resist pattern 97 and polyimide film 96 as a third mask, the quartz substrate 81 is etched to a depth of 366 nm in 30 minutes using a parallel plate type RIE apparatus with a mixed gas of _CF4 and hydrogen under etching conditions of, for example, a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of 3 ^cm3 /min, a pressure of 4 Pa, and an RF power of 60 W.
[0053]
In step (13) of Fig. 11, after the resist pattern 97 and polyimide film 96 are peeled off, a polyimide film 98 is applied to the entire surface by spin coating to a thickness of about 1 µm. In step (14) of Fig. 11, the polyimide film 98 is etched back by oxygen plasma ashing until the surface of the pattern of the chromium film 82 is exposed. Next, in step (15) of Fig. 11, a resist pattern is applied, and a sixth resist pattern 99 is formed by lithography. In step (16) of Fig. 11, the portions of the chromium film 2 not covered by the resist pattern 99 and polyimide film 98 are removed by etching using the same mixed solution as in step (11).
[0054]
In step (17) of Figure 11, using the resist pattern 99 and polyimide film 98 as a mask, the quartz substrate 81 is etched 244 nm in 20 minutes using the same RIE equipment and etching gas as in step (12) under the same etching conditions. In step (18) of Figure 11, the resist pattern 99 and polyimide film 98 are stripped. Thereafter, in step (19) of Figure 11, a polyimide film 100 is applied to the entire surface by spin coating to a thickness of approximately 1 μm. In step (20) of Figure 11, the polyimide film 100 is etched back by oxygen plasma ashing until the surface of the pattern of the chromium film 82 is exposed. Next, in step (21) of Figure 11, a resist pattern is applied, and a seventh resist pattern 101 is formed by lithography.
[0055]
Next, in step (22) of Fig. 11, the chromium film 102 in the portions not covered by the resist pattern 101 and the polyimide film 100 is removed by etching using the same mixed solution as in step (11). In step (23) of Fig. 11, the quartz substrate 81 is etched 122 nm in 10 minutes using the same RIE apparatus and etching gas as in step (12) under the same etching conditions as in step (12). In step (24) of Fig. 11, the resist pattern 101 and the polyimide film 100 are removed by ashing. The pattern of the chromium film 82 is etched using the same mixed solution as in step (11), completing an eight-stage diffractive optical element or a mold for fabricating a diffractive optical element, as shown in step (25) of Fig. 11.
[0056]
Figures 12 and 13 show cross-sectional views of the manufacturing process for a diffractive optical element using photo-CVD according to the eighth embodiment. In step (1) of Figure 12, a chromium film 102 is first formed on a quartz substrate 81 by sputtering to a thickness of 100 nm, followed by a chromium oxide film 103 of 20 to 30 nm. This chromium oxide layer reduces reflection of the exposure light L by the quartz substrate 81, improving patterning accuracy. In step (2) of Figure 12, a photoresist is applied to the substrate 81, and a first resist pattern 104 is formed with line and space widths of 0.35 μm. Next, using the resist pattern 104 as a first mask, the chromium film 102 and the chromium oxide film 103 are etched using chlorine gas or a mixture of chlorine gas and oxygen in a parallel-plate RIE apparatus. Next, the resist 104 is stripped, completing the chromium oxide/chromium pattern shown in step (3) of Figure 12. This chromium oxide/chromium pattern defines the locations of all steps through the process described below.
[0057]
In step (4) of Figure 12, using the pattern of the chromium film 102 and the chromium oxide film 103 as a mask, the quartz substrate ₈₁ is etched 61 nm in 5 minutes using, for example, a parallel-plate RIE apparatus with a mixed gas of CF4 and hydrogen under etching conditions of, for example, a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of 3 ^cm3 /min, a pressure of 4 Pa, and an RF power of 60 W. Photoresist is applied to the substrate 81, and a second resist pattern 105 is formed. Subsequently, in step (5) of Figure 12, the quartz substrate 81 is etched 366 nm using the patterns of the resist pattern 105, chromium film 102, and chromium oxide film 103 as a mask. In step (6) of Figure 12, the photoresist 105 is stripped, and then a photoresist is applied again to form a third resist pattern 106.
[0058]
In step (7) of Fig. 12, the quartz substrate 81 is etched by 244 nm using the patterns of the resist pattern 106, chromium film 102, and chromium oxide film 103 as a mask. Next, in step (8) of Fig. 12, the photoresist 106 is stripped, and then photoresist is applied again to form a fourth resist pattern 107. Then, the quartz substrate 81 is etched by 122 nm using the patterns of the resist pattern 107, chromium film 102, and chromium oxide film 103 as a mask. Next, in step (9) of Fig. 12, the resist pattern 107 is removed by oxygen plasma ashing or with a stripping solution.
[0059]
In step (10) of Figure 12, the substrate in the state of step (9) is exposed from the backside to ultraviolet light, e.g., KrF laser light, in _Al2 ( _CH3 ) ₆ gas. This allows a 100-20 nm thick aluminum film 108 to be formed as a second mask only in the non-patterned areas of the chromium film 102 and chromium oxide film 103. At this time, an aluminum film 109 is also deposited on the backside. In step (11) of Figure 12, a resist pattern film 110 is applied thereon, and then the aluminum film 109 on the backside is removed with a mixture of phosphoric acid, nitric acid, acetic acid, and water. In step (12) of Figure 12, after removing the resist pattern 110, a photoresist is applied thereon, exposed, and developed to form a fifth resist 111.
[0060]
12, the chromium film 102 and the chromium oxide film 103 that are not covered by the resist pattern 111 and the aluminum film 108 are removed by etching. In step (14) of Fig. 12, the resist pattern 111 and the aluminum film 108 are used as a third mask, and the quartz substrate 81 is etched 366 nm in 30 minutes using the same RIE equipment, etching gas, and etching conditions as in step (4).
[0061]
In step (15) of Figure 13, the resist pattern 111 is removed by ashing or with a stripping solution, and the aluminum film 108 is etched and removed using the same mixture as in step (11). The substrate is then exposed from the backside to ultraviolet light, e.g., KrF laser light, in _Al2 ( _CH3 ) ₆ gas. In this manner, a 20-30 nm thick aluminum film 112 is formed only in the non-patterned areas of the chromium film 102 and chromium oxide film 103. At this time, an aluminum film 113 is also deposited on the backside. In step (16) of Figure 13, a resist pattern film 114 is applied thereon, and the aluminum film 113 on the backside is then removed using the same mixture as in step (11). In step (17) of Figure 13, the resist pattern film 114 is removed, and a photoresist is applied thereon, exposed, and developed to form a sixth resist 115.
[0062]
In step (18) of Fig. 13, the chromium film 102 and chromium oxide film 103 in the portions not covered by the resist pattern 115 and the aluminum film 112 are removed by etching, for example, using a mixture of cerium ammonium nitrate, perchloric acid, and water. Next, in step (19) of Fig. 13, using the resist pattern 115 and the aluminum film 112 as a mask, the quartz substrate 81 is etched 244 nm in 20 minutes using the same RIE equipment, etching gas, and etching conditions as in step (4). The resist pattern 115 is removed by ashing or with a stripping solution, and the aluminum film 112 is removed by etching with the same mixture as in step (11), resulting in the state shown in step (20) of Fig. 13.
[0063]
The quartz substrate 81 is exposed from the backside to ultraviolet light, e.g., KrF laser light, in _Al2 ( _CH3 ) ₆ gas. In this way, as shown in step (21) of Figure 13, an aluminum film 116 is formed to a thickness of 10 to 20 nm only in the non-patterned areas of the chromium film 102 and chromium oxide film 103. At this time, an aluminum film 117 is also deposited on the backside. In step (22) of Figure 13, a resist pattern film 118 is applied thereon, and then the aluminum film 117 on the backside is removed with the same mixed solution as in step (11). In step (23) of Figure 13, after the resist pattern film 118 is removed, a photoresist is applied thereon, exposed, and developed to form a seventh resist pattern 119.
[0064]
In step (24) of Figure 13, the chromium film 102 and chromium oxide film 103 in the portions not covered by the resist pattern 119 and aluminum film 116 are removed by etching using the same mixed solution as in step (18). In step (25) of Figure 13, using the resist pattern 119 and aluminum film 116 as a mask, the quartz substrate 81 is etched 122 nm in 10 minutes using the same RIE etching gas and etching conditions as in step (4). In step (26) of Figure 13, the resist pattern film 119 is removed by ashing or with a stripping solution, and the aluminum film 116 is etched and removed with the same mixed solution as in step (11). In step (27) of Figure 13, the chromium film 102 and chromium oxide film 103 are etched using the same mixed solution as in step (18), completing an eight-stage diffractive optical element or a mold for fabricating a diffractive optical element.
[0065]
The diffraction efficiency of the completed diffractive optical element, which had a minimum line width of 0.35 μm and a step height of 61 nm, was measured at a wavelength of 248 nm. The diffraction efficiency, excluding reflection losses, was 93%, a 2% decrease from the theoretical value. The main causes of this 2% decrease in diffraction efficiency were line width errors in the initial chrome pattern and poor reproducibility of the etching.
[0066]
14 and 15 show cross-sectional views of the manufacturing process of a diffractive optical element using aluminum by the damascene method according to the ninth embodiment. As in the sixth embodiment, in step (1) of Fig. 14, photoresist is applied to a quartz substrate 81, in step (2) of Fig. 14, a first resist pattern 83 is formed by photolithography, and in step (3) of Fig. 14, a chromium film 82 is etched using the resist pattern 83 as a first mask.
[0067]
Next, in step (4) of Figure 14, the quartz substrate 81 is etched by 61 nm using the pattern of the chromium film 82 as a mask. Furthermore, photoresist is applied to the quartz substrate 81, and a second resist pattern 120 is formed by photolithography. In step (5) of Figure 14, the quartz substrate 81 is etched by 366 nm using the resist pattern 120 and the pattern of the chromium film 82 as a mask. In step (6) of Figure 14, the photoresist 120 is stripped, and then photoresist is applied again, and a third resist pattern 121 is formed by photolithography. In step (7) of Figure 14, the quartz substrate 81 is etched by 244 nm using the resist pattern 121 and the pattern of the chromium film 82 as a mask. Next, the photoresist 121 is stripped, and then photoresist is applied again, and a fourth resist pattern 122 is formed.
[0068]
In step (8) of Figure 14, the quartz substrate 81 is etched 122 nm using the resist pattern 122 and the pattern of the chromium film 82 as a mask. The resist pattern 122 is then removed by oxygen plasma ashing or a stripping solution. In step (9) of Figure 14, an aluminum film 123 is formed to a thickness of 1.5 μm by sputtering. Then, using a cerium oxide abrasive with a particle size of 5/100 μm and a urethane sheet abrasive cloth, the aluminum film 123, which serves as the second mask , is polished on a lapping machine at 30 rpm and 50 g/ ^cm² until the surface of the chromium film 82 is exposed, resulting in the state shown in step (10) of Figure 14. In step (11) of Figure 14, a photoresist is applied thereon, exposed, and developed to form a fifth resist 124. In step (12) of FIG. 14, the pattern of the chromium film 102 in the portion not covered by the resist pattern 124 and the aluminum film 123 is removed by etching using, for example, a mixture of cerium ammonium nitrate, perchloric acid and water.
[0069]
In step (13) of Figure 14, using the resist pattern 124 and aluminum film 123 as a third mask, the quartz substrate 81 is etched 366 nm in 30 minutes using a parallel-plate RIE apparatus with a mixed gas of _CF4 and hydrogen, for example, under etching conditions of a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of 3 ^cm3 /min, a pressure of 4 Pa, and an RF power of 60 W. In step (14) of Figure 15, after removing the resist pattern film 124 and aluminum film 123, an aluminum film 125 is formed to a thickness of 1.5 μm by sputtering. Next, using the same lapping machine and under the same conditions as in step (9), the aluminum film 125 is polished until the surface of the chromium film 82 is exposed, resulting in the state shown in step (15) of Figure 15. In step (16) of Figure 15, a photoresist is applied thereon, exposed, and developed to form a fifth photoresist 126.
[0070]
In step (17) of Fig. 15, the chromium film 82 in the portions not covered by the resist pattern film 126 and the aluminum film 125 is removed by etching using the same mixed solution as in step (11). In step (18) of Fig. 15, using the resist pattern film 126 and the aluminum film 125 as a mask, the quartz substrate 81 is etched by 244 nm in 20 minutes using the same RIE equipment and etching gases as in step (13) under the same etching conditions.
[0071]
Next, the resist pattern film 126 is removed by ashing or with a stripping solution, and the aluminum film 125 is removed by etching with a mixture of phosphoric acid, nitric acid, acetic acid, and water, resulting in the state shown in step (19) of Figure 15. Next, in step (20) of Figure 15, an aluminum film 127 is formed to a thickness of 1.5 μm by sputtering. Using the same lapping machine and under the same conditions as in step (9), the aluminum film 127 is polished until the surface of the chromium film 82 is exposed, resulting in the state shown in step (21) of Figure 15. In step (22) of Figure 15, a photoresist is applied thereon, exposed, and developed to form a sixth resist 128.
[0072]
In step (23) of Figure 15, the chromium film 102 in the portions not covered by the resist pattern 48 and the aluminum film 127 is removed using the same mixed solution as in step (11). Next, in step (24) of Figure 15, using the resist pattern 48 and the aluminum film 127 as a mask, the quartz substrate 81 is etched 122 nm in 10 minutes using the same RIE equipment, etching gas, and etching conditions as in step (13). Next, the resist pattern 48 is removed by ashing or with a stripping solution, and the aluminum film 127 is etched and removed with the same mixed solution as in step (19), resulting in the state shown in step (25) of Figure 15. In step (26) of Figure 15, the chromium film 102 is etched using the same mixed solution as in step (11), completing an eight-stage diffractive optical element or a mold for fabricating a diffractive optical element.
[0073]
The diffraction efficiency of the completed diffractive optical element, which had a minimum line width of 0.35 μm and a step height of 61 nm, was measured at a wavelength of 248 nm. The diffraction efficiency, excluding losses due to reflection, was found to be 93%, a 2% decrease from the theoretical value. The main causes of this 2% decrease in diffraction efficiency were line width errors in the initial chrome pattern and poor reproducibility of the etching.
[0074]
Fig. 16 shows a cross-sectional view of a reflective step-like diffractive optical element according to Example 10. A 100 nm thick aluminum film 129 is formed by sputtering on a step-like substrate such as that shown in Figs. 8 and 9 produced by the method of Example 6, a step-like substrate such as that shown in Figs. 10 and 11 produced by the method of Example 7, a step-like substrate such as that shown in Figs. 12 and 13 produced by the method of Example 8, or a step-like substrate such as that shown in Figs. 14 and 15 produced by the method of Example 9, to complete a reflective step-like diffractive optical element as shown in Fig. 16.
[0075]
The diffraction efficiency of this completed diffractive optical element, which had a minimum line width of 0.35 μm and a step height of 30.5 nm, was measured at a wavelength of 248 nm and found to be 91%, a 4% decrease from the theoretical value. The main causes of this 4% decrease in diffraction efficiency were line width errors in the initial chrome pattern, poor reproducibility of the etching, and rounding of the step shape due to sputtering.
[0076]
Figures 17, 18, and 19 show cross-sectional views of the manufacturing process for the diffractive optical element of the eleventh embodiment. Steps (1) to (24) in Figures 17 and 18 are exactly the same as steps (1) to (24) in Figures 8 and 9 of the first embodiment, except for the etching thickness and etching time, so only the differences will be listed below and a detailed explanation will be omitted.
[0077]
In step (3) of FIG. 17, the quartz substrate 81 is etched by 30.5 μm for 2.5 minutes using the pattern of the chromium film 82 as a mask.
[0078]
In step (13) of FIG. 17, the quartz substrate 81 is etched by 183 μm for 15 minutes using the resist patterns 87 and 88 as a mask.
[0079]
In step (18) of FIG. 18, the quartz substrate 81 is etched by 122 μm for 10 minutes using the resist patterns 89 and 90 as a mask.
[0080]
In step (24) of FIG. 18, the quartz substrate 81 is etched by 61 μm for 5 minutes using the resist patterns 91 and 92 as a mask.
[0081]
Under the above conditions, a technique of backside exposure of a negative resist is used to form a substrate 81 in the state shown in step (24) of Fig. 18. It should be noted that instead of the backside exposure technique, other techniques such as the damascene method using aluminum, the etch-back method, and the photo-CVD method using backside illumination can also be used without any problems.
[0082]
In step (25) of Figure 19, an aluminum film 130 is formed to a thickness of 1.5 µm by sputtering. Next, the aluminum film 130 is polished by the damascene method, for example, using cerium oxide abrasives with a particle size of 5/100 µm and a urethane sheet polishing cloth on a lapping machine under polishing conditions of 30 rpm and 50 g/ ^cm² until the surface of the chromium film 82 is exposed, resulting in the state shown in step (26) of Figure 19. Note that instead of the damascene method using aluminum, techniques such as backside exposure of a negative resist, etch-back, and backside photo-CVD may also be used. In step (27) of Figure 19, a photoresist is applied thereon, exposed, and developed to form a seventh resist pattern 131.
[0083]
In step (28) of Fig. 19, the chromium film 82 in the portions not covered by the resist pattern 131 and the aluminum film 130 is removed by etching using, for example, a mixture of cerium ammonium nitrate, perchloric acid, and water. In step (29) of Fig. 19, a photoresist is applied thereon, exposed to light, and developed to form an eighth resist pattern 132. Next, from this state, the aluminum film 130 in the portions not covered by the resist pattern 132 is removed by etching using a mixture of phosphoric acid, nitric acid, acetic acid, and water, resulting in the state shown in step (30) of Fig. 19.
[0084]
In step (31) of Figure 19, the photoresist 132 is removed using a stripper or oxygen plasma ashing. In step (32) of Figure 19, the chromium film 82 and aluminum film 130 are used as a mask to etch the quartz substrate 81 by 244 nm in 20 minutes using, for example, a parallel-plate RIE apparatus and a mixed gas of _CF4 and hydrogen, under etching conditions of, for example, a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of 3 ^cm3 /min, a pressure of 4 Pa, and an RF power of 60 W. Next, the aluminum film 130 is etched and removed using the same mixed liquid as in step (30), resulting in the state shown in step (33) of Figure 19. Subsequently, the chromium film 82 is etched and removed using the same mixed liquid as in step (28), completing the 16-step diffractive optical element shown in step (34) of Figure 19.
[0085]
The diffraction efficiency of the completed diffractive optical element, which had a minimum line width of 0.35 μm and a step height of 30.5 nm, was measured at a wavelength of 248 nm. The diffraction efficiency, excluding losses due to reflection, was 97%, a 2% decrease in diffraction efficiency compared to the theoretical value. The main causes of this 2% decrease in diffraction efficiency were errors in the line width of the initial chrome pattern and in the etching depth.
[0086]
Figures 20 and 21 show cross-sectional views of the manufacturing process of the diffractive optical element of the twelfth embodiment. A 100 nm thick chromium film 82 is formed by sputtering on a quartz substrate 81 shown in step (1) of Figure 20, resulting in the state shown in step (2) of Figure 20. Photoresist is applied to this quartz substrate 81, and a first resist pattern is formed by photolithography, with line and space widths of 0.35 μm. Next, using the resist pattern as a mask, the chromium film 82 is etched using a parallel-plate RIE apparatus and chlorine gas or a mixture of chlorine gas and oxygen. Next, the photoresist is stripped, completing the first mask pattern of the chromium film 82 as shown in step (3) of Figure 20. The pattern of this chromium film 82 defines the positions of all steps through the following steps.
[0087]
In step (4) of Figure 20, the quartz substrate 81 is etched by 61 nm using the pattern of the chromium film 82 as a mask, for example, using a parallel-plate RIE apparatus and a mixed gas of _CF4 and hydrogen under etching conditions of a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of 3 ^cm3 /min, a pressure of 4 Pa, and an RF power of 60 W for 5 minutes. Subsequently, in step (5) of Figure 20, a photoresist is applied to the quartz substrate 81, and a second resist pattern 133 is formed by photolithography. In step (6) of Figure 20, the quartz substrate 81 is etched by 122 nm using the resist pattern 133 and the pattern of the chromium film 82 as a mask. Next, the resist pattern 133 is stripped, resulting in the state shown in step (7) of Figure 20.
[0088]
Next, in step (8) of Figure 20, an aluminum film 134 is formed to a thickness of 1.5 μm by sputtering. The aluminum film 134, which serves as the second mask, is polished using, for example, a cerium oxide abrasive with a particle size of 5/100 μm and a urethane sheet polishing cloth on a lapping machine at 30 rpm and 50 g/ ^cm² until the surface of the chromium film 82 is exposed, resulting in the state shown in step (9) of Figure 20. Next, in step (10) of Figure 20, a photoresist is applied thereon, exposed, and developed to form a fifth photoresist pattern 135. Subsequently, in step (11) of Figure 20, the chromium 16 not covered by the resist pattern 135 and the aluminum film 134 is removed by etching using, for example, a mixture of cerium ammonium nitrate, perchloric acid, and water.
[0089]
20, using the resist pattern 135 and aluminum film 134 as a third mask, the quartz substrate 81 is etched 122 nm in 10 minutes using the same RIE equipment and etching gas under the same etching conditions as in step (4). Subsequently, the resist pattern 135 is removed using a stripping solution or plasma ashing, and the aluminum film 134 is etched and removed using a mixture of phosphoric acid, nitric acid, acetic acid, and water, resulting in the state shown in step (13) of FIG.
[0090]
Next, the quartz substrate 81 in the state of step (13) is exposed from the backside to ultraviolet light, e.g., a KrF laser, in _Al2 ( _CH3 ) ₆ gas and oxygen gas. In this manner, an aluminum oxide film 136 is formed to a thickness of 500 nm only in the areas where the chromium film 82 is not present, and an aluminum oxide film 136 is also deposited on the backside. If the aluminum oxide film 136 on the backside is not required, the surface can be covered with resist and then removed with phosphoric acid, as shown in step (14) of Figure 20. In step (15) of Figure 21, a photoresist 137 is applied. In step (16) of Figure 21, a fifth resist pattern 138 is formed by exposure and development.
[0091]
In step (17) of Fig. 21, the aluminum oxide film 136 in the portion not covered by the resist pattern 138 is removed with phosphoric acid. In step (18) of Fig. 21, the resist pattern 138 is removed with a remover or plasma ashing, and in step (19) of Fig. 21, a photoresist 139 is applied. Next, in step (20) of Fig. 21, a resist pattern 140 is formed by photolithography. In step (21) of Fig. 21, the chromium film 82 in the portion not covered by the resist pattern 140 is removed by etching using the same mixed solution as in step (11). Next, the resist pattern 140 is stripped, resulting in the state shown in step (22) of Fig. 21.
[0092]
In step (23) of Fig. 21, the chromium film 82 and aluminum oxide film 136 are masked, and the quartz substrate 81 is etched to a depth of 244 nm using the same RIE apparatus and _CF4 /hydrogen gas mixture as in step (4) under the same etching conditions for 20 minutes. In step (24) of Fig. 21, the aluminum oxide film 136 is etched with phosphoric acid, and finally the chromium film 82 is removed by etching using, for example, the same mixed solution as in step (11), completing the step-like diffractive optical element as shown in step (25) of Fig. 21.
[0093]
The diffraction efficiency of the completed diffractive optical element, with a minimum line width of 0.35 μm and a step height of 61 nm, was measured at a wavelength of 248 nm. The diffraction efficiency, excluding reflection losses, was 91%, a 4% decrease from the theoretical value. The main causes of this 2% decrease in diffraction efficiency were line width errors in the initial chrome pattern and poor reproducibility of the etching. The diffracted light efficiency of a diffractive optical element fabricated in the conventional example was 76%, demonstrating the effectiveness of the present invention.
[0094]
Fig. 22 shows cross-sectional views of the manufacturing process of a resin stepped diffractive optical element according to the thirteenth embodiment. The stepped substrate according to the sixth embodiment shown in Figs. 8 and 9, the stepped substrate according to the seventh embodiment shown in Figs. 10 and 11, the stepped substrate according to the eighth embodiment shown in Figs. 12 and 13, or the stepped substrate according to the ninth embodiment shown in Figs. 14 and 15 is used as a mold.
[0095]
First, in step (1) of Fig. 22, a reactive curing resin 152, such as an acrylic or epoxy ultraviolet curing resin or a thermosetting resin, is dropped from a syringe 150 onto a glass substrate 151. Next, as shown in steps (2) and (3) of Fig. 22, a stepped substrate mold 153 is pressed onto the resin 152 to form a replica layer 154. Before pressing the stepped substrate mold 153, which will serve as the mold, onto the resin 152, a release agent is applied to the surface of the stepped substrate mold 153 as needed.
[0096]
Next, in the case of ultraviolet-curable resin, ultraviolet light is applied from the stepped substrate mold 153 side to harden the resin. In the case of thermosetting resin, the resin is hardened by heat treatment. Then, when the stepped substrate mold 153 is peeled off, a stepped diffractive optical element 155 is completed as shown in step (4) of Figure 22.
[0097]
The diffraction efficiency of the completed diffractive optical element, which had a minimum line width of 0.35 μm and a step height of 120 nm, was measured at a wavelength of 500 nm and found to be 90%, a 5% decrease from the theoretical value. The main causes of this 5% decrease in diffraction efficiency were line width errors in the initial chrome pattern, poor reproducibility of the etching, and shrinkage of the resin 147.
[0098]
23, 24, and 25 show cross-sectional views of the manufacturing process for the stepped diffractive optical element of the fourteenth embodiment. First, in step (1) of Fig. 23, a chromium film 162 is formed to a thickness of 100 nm by sputtering on a quartz substrate 161. In addition, an anti-reflection film such as a chromium oxide film having a thickness of 20 to 30 nm may be provided on the chromium film 162 to improve the resolution of patterning.
[0099]
In step (2) of Figure 23, photoresist is applied to the quartz substrate 161 to form a first resist pattern 163. The line and space widths at this time are both 0.35 μm. Subsequently, in step (3) of Figure 23, the chromium film 162 is etched using the resist pattern 163 as a mask. This etching is performed using, for example, a parallel plate type RIE device, and the etching gas used is, for example, chlorine gas or a mixture of chlorine gas and oxygen. Next, the resist pattern 163 is stripped using oxygen ashing or a stripping solution. The positions of all steps are then defined by the chromium film 162 through the following steps.
[0100]
23, the quartz substrate 161 is etched to a depth of 61 nm using the pattern of the chromium film 162 as a first mask. For example, a parallel-plate RIE apparatus is used for this etching, and a mixed gas of _CF4 and hydrogen is used as the etching gas. The etching conditions are, for example, a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of 3 ^cm3 /min, a pressure of 4 Pa, an RF power of 60 W, and an etching time of 5 minutes.
[0101]
Next, in step (5) of Figure 23, photoresist is applied to the quartz substrate 161, and a second resist pattern 164 is formed. The alignment accuracy at this time only needs to be half the line width of the pattern formed by the chrome film 162, a value that can be achieved without fail with a normal exposure device. This applies to all patterning from the second onwards, including the other examples below. Next, in step (6) of Figure 23, the quartz substrate 161 is etched 61 nm using the resist pattern 164 and chrome film 162 as a mask.
[0102]
In step (7) of Fig. 23, the photoresist pattern 164 is peeled off. Next, in step (8) of Fig. 23, a negative resist is applied and exposed from the backside. When this is developed, as shown in step (9) of Fig. 23, a resist pattern 165 can be left as a second mask only in the areas where the chrome film 162 is not present. At this time, the chrome film 162 itself serves as a contact mask for the exposure of the negative resist, ensuring perfectly accurate alignment.
[0103]
Next, in step (10) of Fig. 24, photoresist is applied thereon to form a fifth photoresist pattern 166. In step (11) of Fig. 24, the portions of the chromium film 162 not covered by the resists 166 and 165 are removed by etching. For example, a mixture of cerium ammonium nitrate, perchloric acid, and water is used for this etching.
[0104]
24, the quartz substrate 161 is etched to a depth of 122 nm using the resist 166 and the resist 165 as a third mask. For example, a parallel plate type RIE apparatus is used for the etching, and a mixed gas of _CF4 and hydrogen is used as the etching gas. The etching conditions are, for example, a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of ^{3 cm3} /min, a pressure of 4 Pa, an RF power of 60 W, and an etching time of 30 minutes.
[0105]
In step (13) of Fig. 24, the resists 166 and 165 are removed by ashing. In step (14) of Fig. 24, photoresist is applied thereon, and a photoresist pattern 167 is formed by photolithography. In step (15) of Fig. 24, the substrate 161 is etched by 244 nm using the chromium film 162 and pattern 167 as a mask.
[0106]
Next, a negative resist is applied and exposed from the back, and then developed, leaving a resist pattern 168 only in the areas where the chromium film 162 is not present, as shown in step (16) of Figure 25. Photoresist is applied on top of this, and a photoresist pattern 169 is formed by photolithography in step (17) of Figure 25. In step (18) of Figure 25, the chromium film 162 in the areas not covered by the patterns 169 and 168 is removed by etching. A mixture of cerium ammonium nitrate, perchloric acid, and water, for example, is used for this etching.
[0107]
In step (19) of Fig. 25, the quartz substrate 161 is etched by 244 nm using the patterns 169 and 168 as a mask, and in step (20) of Fig. 25, the patterns 169 and 168 are removed by ashing.
[0108]
In step (21) of Figure 25, the chromium film 162 is etched to complete an eight-stage diffractive optical element or a mold for fabricating a diffractive optical element. For this etching, a mixture of cerium ammonium nitrate, perchloric acid, and water is used, for example. The diffractive optical element fabricated in this manner is free from alignment errors and has high diffraction efficiency.
[0109]
Figures 26, 27, and 28 show a fifteenth embodiment. In step (1) of Figure 26, a chromium film 172 is formed on a quartz substrate 171 by sputtering to a thickness of 100 nm. To improve patterning resolution, a 20-30 nm anti-reflection film, such as a chromium oxide film, can be formed on the chromium film 172. Photoresist is applied to the quartz substrate 171, and a first resist pattern is formed. The line and space widths are both 0.35 μm. Next, the chromium film 172 is etched using the resist pattern as a mask. This etching is performed using, for example, a parallel-plate RIE apparatus, and the etching gas used is, for example, chlorine gas or a mixture of chlorine gas and oxygen. The resist pattern is then stripped using oxygen ashing or a stripping solution. The chromium film 172, the first mask , is then used to define the positions of all steps through the following steps.
[0110]
In step (2) of Figure 26, photoresist is applied to the quartz substrate 171, and a resist pattern 173 is formed. Next, using the pattern of the chromium film 172 and the resist pattern 173 as a mask, the quartz substrate 171 is etched to a depth of 61 nm. For example, a parallel plate type RIE apparatus is used for this etching, and a mixed gas of _CF4 and hydrogen is used as the etching gas. The etching conditions are, for example, a _CF4 flow rate of 20 ^cm3 /min, a hydrogen flow rate of 3 ^cm3 /min, a pressure of 4 Pa, an RF power of 60 W, and an etching time of 5 minutes. The alignment accuracy required for this step is only half the line width of the chromium film 172, a value that can be achieved without fail with a normal exposure apparatus.
[0111]
In step (3) of Fig. 26, a photoresist is applied to the quartz substrate 171 to form a resist pattern 174. Subsequently, the quartz substrate 171 is etched by 183 nm using the resist pattern 174 and the chromium film 172 as a mask. In step (4) of Fig. 26, the resist pattern 174 is peeled off, and in step (5) of Fig. 26, a negative resist 175 is applied.
[0112]
In step (6) of FIG. 26, when the quartz substrate 171 is exposed from the back side, the chromium film 172 serves as a contact mask, and a latent image portion 176 is formed in the negative resist 175.
[0113]
In step (7) of Fig. 27, when the desired portion is covered with a reticle 177 and exposed to light, a negative resist pattern 178 of the second mask, which is a latent image portion, is formed on the portion of the chromium film 172 where it is to remain, and when this is developed, the state shown in step (8) of Fig. 27 is obtained. In step (9) of Fig. 27, the chromium film 172 in the portion not covered by the resist pattern 178 is removed by etching. For example, a mixture of cerium ammonium nitrate, perchloric acid, and water is used for this etching.
[0114]
27, the quartz substrate 171 is etched by 122 nm using the negative resist pattern 178 as a third mask using, for example, a parallel plate type RIE device and, for example, a mixed gas of _CF4 and hydrogen as the etching gas.
[0115]
In step (11) of Fig. 27, the resist pattern 178 is removed by ashing. In step (12) of Fig. 27, photoresist is applied thereon, and a photoresist pattern 179 is formed by photolithography. In step (13) of Fig. 27, the substrate 171 is etched by 244 nm using the chromium film 172 and pattern 179 as a mask.
[0116]
In step (14) of Fig. 28, a negative resist 180 is applied and exposed from the back, so that the chromium film 172 serves as a contact mask, and a resist pattern 181, which is a latent image portion, is formed in the negative resist 180. In step (15) of Fig. 28, a desired portion is covered with a reticle 182 and exposed to light, forming a latent image portion 183 on the portion of the chromium film 172 where it should remain, and developing this results in the state shown in step (16) of Fig. 28. In step (16) of Fig. 28, the chromium film 172 in the portion not covered by the latent image portion 183 is removed by etching. For this etching, a mixture of cerium ammonium nitrate, perchloric acid, and water, for example, is used.
[0117]
In step (17) of Fig. 28, the quartz substrate 171 is etched by 244 nm using the chromium film 172 and resist pattern 181 as a mask, and in step (18) of Fig. 28, the pattern 181 and latent image portion 183 are removed by ashing.
[0118]
28, the chromium film 172 is etched to complete an eight-stage diffractive optical element or a mold for fabricating a diffractive optical element. For this etching, a mixture of cerium ammonium nitrate, perchloric acid, and water is used, for example.
[0119]
29 shows the configuration of a stepper, which is a semiconductor exposure apparatus according to the 16th embodiment. Arranged from above are an illumination optical system 200 with a wavelength of 248 nm, a reticle 201, an imaging optical system 202, and a stage 203 on which a semiconductor substrate W is placed. A diffractive optical element D fabricated by the method of the first embodiment is incorporated into the imaging optical system 202 in order to reduce chromatic aberration and provide an aspherical effect.
[0120]
In this stepper, an illumination optical system 200 irradiates a reticle 201 with i-line or ultraviolet light such as KrF, and an imaging optical system 202 transfers the pattern drawn on the reticle 201 to a semiconductor substrate W on a stage 203 at a reduction ratio of 1/5.
[0121]
Fig. 30 is a perspective view of diffractive optical element D, and Fig. 31 shows a cross-sectional view of its cross-sectional shape. This diffractive optical element D has the same optical function as a convex lens, and is a four-step diffractive optical element with a step height of 61 nm, a width of 0.35 µm on the outermost periphery, and a diameter of 120 mm.
[0122]
Light incident on the stepped diffractive optical element D is mainly split into 1st-, 9th-, and 17th-order diffracted light beams that pass through the element D. Of these, only the 1st-order light beam is involved in image formation, accounting for 93% of the incident light. The remaining few percent are 9th- and 17th-order light beams, but because the 9th- and 17th-order light beams are far apart in diffraction order from the 1st-order light beam required for image formation, these beams are directed outside the imaging optical system and do not have a significant effect on image formation.
[0123]
Therefore, when a conventional eight-stage diffractive optical element is used, which is manufactured under the same conditions (step height of 61 nm, width of one step on the outermost periphery of 0.35 μm, diameter of 120 mm) using three masks 17 a to 17 c as shown in FIG. 32 and described as the prior art, strong third-order and other diffracted light occurs between the first-order and ninth-order diffracted light, causing unnecessary light to form a pseudo pattern on the image plane and degrading image performance. However, this problem can be avoided by using an eight-stage diffractive optical element under the same conditions as in this embodiment.
[0124]
[Effects of the Invention]
As described above, in the method for manufacturing a multi-step stepped element or a mold for manufacturing such an element according to the present invention, the positions of all steps are determined by the pattern of the first mask formed in the initial lithography process, so that an accurate pattern can be formed on the substrate without misalignment.
[Brief explanation of the drawings]
Figure 1
1A to 1C are cross-sectional views illustrating a manufacturing process of the first embodiment.
Figure 2
10A to 10C are cross-sectional views showing the manufacturing process of the second embodiment.
Figure 3
10A to 10C are cross-sectional views showing the manufacturing process of the third embodiment.
Figure 4
FIG. 10 is a cross-sectional view of a reflective diffractive optical element according to a fourth embodiment.
Figure 5
FIG. 10 is a cross-sectional view of a diffractive optical element according to a fifth embodiment.
Figure 6
FIG. 2 is a diagram illustrating the configuration of a projection optical system.
Figure 7
FIG. 1 is a diagram illustrating the configuration of a projection exposure apparatus.
Figure 8
13A to 13C are cross-sectional views showing the manufacturing process of the sixth embodiment.
Figure 9
13A to 13C are cross-sectional views showing the manufacturing process of the sixth embodiment.
Figure 10
13A to 13C are cross-sectional views showing the manufacturing process of the seventh embodiment.
Figure 11
13A to 13C are cross-sectional views showing the manufacturing process of the seventh embodiment.
Figure 12
13A to 13C are cross-sectional views showing the manufacturing process of the eighth embodiment.
Figure 13
13A to 13C are cross-sectional views showing the manufacturing process of the eighth embodiment.
FIG. 14
13A to 13C are cross-sectional views showing the manufacturing process of the ninth embodiment.
Figure 15
13A to 13C are cross-sectional views showing the manufacturing process of the ninth embodiment.
FIG. 16
FIG. 22 is a cross-sectional view of a reflective diffractive optical element according to a tenth embodiment.
FIG. 17
19A to 19C are cross-sectional views showing the manufacturing process of the eleventh embodiment.
FIG. 18
19A to 19C are cross-sectional views showing the manufacturing process of the eleventh embodiment.
FIG. 19
19A to 19C are cross-sectional views showing the manufacturing process of the eleventh embodiment.
Figure 20
12A to 12C are cross-sectional views showing the manufacturing process of the twelfth embodiment.
Figure 21
12A to 12C are cross-sectional views showing the manufacturing process of the twelfth embodiment.
Figure 22
13A to 13C are cross-sectional views showing the manufacturing process of the thirteenth embodiment.
Figure 23
20A to 20C are cross-sectional views showing the manufacturing process of the fourteenth embodiment.
FIG. 24
20A to 20C are cross-sectional views showing the manufacturing process of the fourteenth embodiment.
Figure 25
20A to 20C are cross-sectional views showing the manufacturing process of the fourteenth embodiment.
FIG. 26
20A to 20C are cross-sectional views showing the manufacturing process of the fifteenth embodiment.
FIG. 27
20A to 20C are cross-sectional views showing the manufacturing process of the fifteenth embodiment.
FIG. 28
20A to 20C are cross-sectional views showing the manufacturing process of the fifteenth embodiment.
FIG. 29
FIG. 20 is a configuration diagram of a stepper according to a sixteenth embodiment.
Figure 30
FIG. 1 is a perspective view of a stepped diffractive optical element.
FIG. 31
FIG. 2 is a cross-sectional view of a step-like diffractive optical element.
FIG. 32
10A to 10C are cross-sectional views of a conventional manufacturing process.
FIG. 33
FIG. 10 is an explanatory diagram of the relationship between a staircase shape and a mask.
FIG. 34
FIG. 10 is an explanatory diagram of the relationship between a staircase shape and a mask.
[Explanation of symbols]
21, 31, 41, 81, 161, 171 Quartz substrate
22, 27, 32, 37, 42, 46, 52, 82, 102, 162, 172 Chromium film 25, 29, 44, 48, 50, 108, 109, 112, 113, 116, 117, 123, 125, 127, 130, 134, 136 Aluminum film 35, 39 Aluminum oxide film 71 Lens group 72, 155, D Diffractive optical element 73, 160 Illumination optical system 75 Photography optical system 96, 98, 100 Polyimide film 103 Chromium oxide film 150 Syringe 151 Glass substrate 152 Reaction curing resin 201 Reticle 202 Imaging optical system