JP4144301B2 - MULTILAYER REFLECTOR, REFLECTIVE MASK, EXPOSURE APPARATUS AND REFLECTIVE MASK MANUFACTURING METHOD - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer reflector used in an X-ray apparatus such as an X-ray telescope, an X-ray laser, an X-ray reflectometer, and an X-ray analyzer. In particular, the present invention relates to a multilayer film reflecting mirror used in a reflective mask, a wavelength filter, a two-color reflecting mirror and the like used in an X-ray exposure apparatus. Furthermore, the present invention relates to an X-ray exposure apparatus using the reflective mask.
[0002]
[Prior art]
In recent years, with the miniaturization of semiconductor integrated circuits, in order to improve the resolving power of an optical system limited by the diffraction limit of light, X-rays having a shorter wavelength (11 to 14 nm) are used instead of conventional ultraviolet rays. Projection lithography techniques have been developed (see, for example, D. Tichenor, et al., SPIE 2437 (1995) 292). This technique is recently called EUV (Extreme UltraViolet) lithography, and is expected as a technique capable of obtaining a resolution of 70 nm or less, which cannot be realized by conventional optical lithography using light with a wavelength of 190 nm.
[0003]
The complex refractive index n of the substance in the X-ray wavelength region is represented by n = 1−δ−ik (δ, k: complex number). The imaginary part k of this refractive index represents X-ray absorption. Since δ and k are much smaller than 1, the refractive index in this region is very close to 1. Therefore, conventional optical elements such as lenses cannot be used, and an optical system utilizing reflection is used. In the case of an oblique incidence optical system that reflects X-rays incident on the reflecting surface obliquely using total reflection, the incident angle is smaller (nearly perpendicular) than the total reflection critical angle θc (about 20 ° or less at a wavelength of 10 nm). Then, the reflectance is very small. Here, the incident angle indicates an angle formed by the normal of the incident surface and the optical axis of the incident light.
[0004]
Therefore, a large number of reflecting surfaces (several tens to several hundreds in one example) are provided by laminating materials having as high an amplitude reflectance as possible on the interface, and each layer is based on the optical interference theory so that the phases of the reflected waves are matched. A multilayer reflector with the thickness adjusted is used. The multilayer reflector is formed by alternately laminating a material having a large difference between the refractive index in the X-ray wavelength region to be used and a vacuum refractive index (= 1) and a material having a small difference on the substrate. Is done. As a material for the multilayer film, a material using a combination of tungsten / carbon, molybdenum / carbon and the like is known, and is formed by a thin film forming technique such as sputtering, vacuum deposition, or CVD.
Note that the multilayer mirror can also reflect X-rays incident perpendicularly, so that an optical system with less aberration than the oblique incidence optical system using total reflection can be configured.
[0005]
In addition, the multilayer film reflector has Bragg's formula so that the phases of the reflected waves are in phase; 2 d sin θ = nλ (d: period length of the multilayer film, θ: oblique incident angle, π / 2−incident angle, λ: X-ray When satisfying (wavelength), it has a wavelength dependency that strongly reflects X-rays, and therefore it is necessary to select each factor so as to satisfy this equation.
[0006]
When molybdenum (Mo) / silicon (Si) is used as the multilayer film, it is known that a high reflectance is exhibited on the long wavelength side of the L absorption edge of silicon having a wavelength of 12.6 nm. Therefore, a multilayer film reflecting mirror having a high reflectance of 60% or more at a direct incidence (incident angle of 0 °) near a wavelength of 13 nm can be produced relatively easily. Such a reflector using a Mo / Si multilayer film is also applied to a reduction projection lithography technique using soft X-rays called EUVL (Extreme Ultraviolet Lithography).
[0007]
[Problems to be solved by the invention]
FIG. 11 is a cross-sectional view schematically showing the structure of a reflective mask used in conventional EUVL lithography.
In the reflective mask 80, an absorber layer 85 is provided on the Mo / Si multilayer film 83 formed on the substrate 81. The absorber layer 85 is made of a material that absorbs soft X-rays without reflecting them. Then, by patterning the absorber layer 85, a region 87 (bright portion) where the Mo / Si layer is exposed and a region 89 (dark portion) where the absorber layer 85 exists are provided, and contrast is reflected in the reflection of soft X-rays. A mask pattern is added. A buffer layer may be provided between the Mo / Si multilayer 83 and the absorber layer 85 in some cases.
[0008]
The absorber layer 85 is made of tantalum (Ta) as an example. When the thickness of this layer is about 60 nm or less, the contrast between the bright part 87 and the dark part 89 is about 100. In addition, tantalum nitride (TaN), chromium (Cr), nickel (Ni), or the like can be used as the material of the absorber layer 55.
[0009]
In such a mask, the thickness of the absorber layer 85 is usually 50 nm to several hundred nm. On the other hand, in the mask pattern, when the reduced exposure is performed 4 times, the width of the mask pattern is 200 nm in a 50 nm pattern on the wafer. Thus, the thickness of the absorber layer 85 is approximately the same as the width of the mask pattern, and when soft X-rays are exposed at oblique incidence, the shadow of the absorber layer affects the width of the mask pattern.
Further, since the absorber layer 85 itself has a thickness comparable to the thickness of the multilayer film (about 340 nm), there is a concern about deformation of the mask due to the internal stress.
[0010]
The present invention has been made in view of the above problems, and is a multilayer reflector reflecting mask capable of obtaining a high contrast mask pattern without providing a thick absorber layer on the multilayer film, a method for manufacturing the same, and a method for manufacturing the same An object is to provide an exposure apparatus and the like. It is another object of the present invention to provide a multilayer film reflecting mirror that can be applied to a wavelength filter having wavelength selectivity and a two-color reflecting mirror.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the multilayer-film reflective mirror of the present invention includes a first layer made of a material having a large difference between a refractive index in a soft X-ray region and a refractive index in a vacuum and a second layer made of a small material. In the multilayer film reflector alternately laminated on the substrate, the first layer in the layer structure located in the middle of the periodic layer structure of the first layer and the second layer of the multilayer film or the The thickness of any one of the second layers is changed with respect to other layer structures.
[0012]
In the present invention, the sum of the thickness of the layer whose thickness is changed with respect to another layer structure and the thickness of the layer above or below the layer is the optical path length with respect to the wavelength of the soft X-ray used. It is preferable to have a difference of 20% or more with respect to ½ of the wavelength of the soft X-ray when converted into.
[0013]
With such a structure, a change occurs in the reflectance curve indicating the relationship between the wavelength and the reflectance in the multilayer mirror. That is, if the thickness of one layer of the intermediate layer pair is changed with respect to the other layer pair, a trough may occur in the reflectance. Furthermore, depending on the layer sequence (position on the multilayer film) of the layer whose thickness is to be changed and the thickness to be changed, the wavelength at which this reflectance becomes a trough may be shifted. Therefore, by appropriately selecting this stratigraphy and thickness, it is possible to use the wavelength at which the reflectance trough is generated, the wavelength position where the reflectance is a trough, and the peaks on both sides of the trough are generated. It is possible to provide a multilayer-film reflective mirror having a filtering effect with respect to any wavelength.
[0014]
For example, for a light source that has a bright line at two adjacent wavelengths, only one wavelength is reflected, and the other is a wavelength filter that is to be cut, or two colors that have almost the same reflectivity for two adjacent wavelengths. Applicable to multilayer films.
[0015]
In the present invention, the main component of the first layer is molybdenum (Mo) or molybdenum silicide (MoSi). ₂ And the main component of the second layer is preferably silicon (Si).
A multilayer mirror that is inexpensive, excellent in durability, and in which the phase of the reflected wavefront is aligned can be obtained.
[0016]
In the present invention, it is preferable that the layer for changing the thickness is the second layer.
[0017]
The reflective mask of the present invention is a reflective mask in which a pattern to be transferred is formed on a sensitive substrate, and is a first layer made of a material having a large difference between a refractive index in a soft X-ray region and a refractive index in a vacuum. And a second layer made of a small substance are made of a multilayer film alternately laminated on a substrate, and a periodic layer made up of the first layer and the second layer at the portion of the multilayer film corresponding to the pattern A thickness of any one of the first layer and the second layer in the layer structure located in the middle of the structure is changed with respect to another layer structure.
[0018]
A contrast mask pattern can be obtained only by changing the film thickness of one layer in the multilayer film in the pattern portion. The change in the film thickness is very small compared to the case where the absorber layer is provided, so that the shadow generated during the oblique exposure does not greatly affect the pattern. Further, it is not necessary to provide a new absorption layer in the mask pattern, and the structures of the bright part and the dark part are almost the same, so that the influence of the stress of the absorption layer itself is eliminated.
[0019]
An exposure apparatus of the present invention includes an X-ray light source that generates X-rays, an illumination optical system that guides X-rays from the X-ray light source to a mask, a projection optical system that guides X-rays from the mask to a sensitive substrate, An exposure apparatus having a reflective mask provided with a pattern to be transferred to a sensitive substrate, the reflective mask comprising a material having a large difference between a refractive index in a soft X-ray region and a refractive index in a vacuum. 1 layer and a second layer made of a small substance are composed of a multilayer film alternately laminated on a substrate, and the multilayer film corresponding to the pattern is a periodic layer composed of the first layer and the second layer. The thickness of any one of the first layer and the second layer in the layer structure located in the middle of the layer structure is changed with respect to another layer structure.
It is possible to provide an exposure apparatus that prevents deterioration of pattern accuracy due to shadows on the absorber layer and internal stress exerted by the absorber layer.
[0020]
The reflective mask manufacturing method of the present invention is a method of manufacturing the reflective mask according to claim 7, wherein the first layer and the second layer are alternately stacked on the substrate by a plurality of layer pairs. Forming a resist pattern having the same pattern as the pattern on the second layer of the uppermost layer, etching the second layer of the uppermost layer by a predetermined depth using the resist pattern as a mask, and a resist pattern And a step of alternately stacking a plurality of layer pairs of the first layer and the second layer on the second uppermost layer.
[0021]
The other reflective mask manufacturing method of this invention is a method of manufacturing the reflective mask of Claim 7, Comprising: The process of laminating | stacking a 1st layer and a 2nd layer only by several layer pairs on a board | substrate alternately Forming a first layer on the second uppermost layer, forming a resist pattern having the same pattern as the pattern on the first layer, and forming a first pattern on the entire surface including the resist pattern. A step of forming two layers with a first thickness; a step of removing a resist pattern; and a step of forming a second layer with a second thickness on the entire surface including the second layer as the uppermost layer. The total thickness of the first thickness and the second thickness is the same as the second layer having a periodic layer structure.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, it demonstrates, referring drawings.
First, an outline of the X-ray exposure apparatus will be described with reference to FIG.
FIG. 2 is a view showing the overall configuration of an X-ray exposure apparatus equipped with the reflective mask of FIG.
This X-ray exposure apparatus is a projection exposure apparatus that performs an exposure operation by a step-and-scan method using light in a soft X-ray region (hereinafter referred to as EUV light) near a wavelength of 13 nm as illumination light for exposure.
[0023]
A laser light source 103 is disposed at the most upstream part of the X-ray exposure apparatus 100. The laser light source 103 has a function of supplying laser light having a wavelength in the infrared region to the visible region, and uses, for example, a YAG laser or an excimer laser excited by a semiconductor laser. The laser light emitted from the laser light source 103 is condensed by the condensing optical system 105 and reaches the laser plasma light source 107 disposed below. The laser plasma light source 107 can efficiently generate X-rays having a wavelength in the vicinity of 13 nm.
[0024]
The laser plasma light source 107 is provided with a nozzle (not shown) and ejects xenon gas. The ejected xenon gas receives a laser beam with high illuminance at the laser plasma light source 107. Xenon gas becomes high temperature by the energy of laser light with high illuminance, is excited to a plasma state, and emits EUV light when transitioning to a low potential state. Since EUV light has a low transmittance to the atmosphere, its optical path is covered with a chamber (vacuum chamber) 109 to block outside air. Note that since debris is generated from a nozzle that emits xenon gas, the chamber 109 needs to be arranged separately from the other chambers.
[0025]
On the upper part of the laser plasma light source 107, a rotating paraboloid reflecting mirror 111 coated with a Mo / Si multilayer film is arranged. The X-rays radiated from the laser plasma light source 107 are incident on the parabolic reflector 111, and only the X-rays having a wavelength of about 13 nm are reflected in parallel toward the lower side of the exposure apparatus 100.
[0026]
Below the rotary parabolic reflecting mirror 111, a visible light cut X-ray transmission filter 113 made of Be (beryllium) having a thickness of 0.15 nm is disposed. Of the X-rays reflected by the parabolic reflector 111, only the desired 13 nm X-rays pass through the transmission filter 113. The vicinity of the transmission filter 113 is covered with a chamber 115 to block outside air.
[0027]
An exposure chamber 133 is installed below the transmission filter 113. An illumination optical system 117 is disposed below the transmission filter 113 in the exposure chamber 133. The illumination optical system 117 is composed of a condenser-type reflection mirror, a fly-eye optical-system reflection mirror, and the like. The X-ray input from the transmission filter 113 is shaped into an arc and irradiated toward the left in the figure. To do.
[0028]
An X-ray reflecting mirror 119 is disposed on the left side of the drawing of the illumination optical system 117. The X-ray reflecting mirror 119 is a circular rotary parabolic mirror having a concave reflecting surface 119a on the right side of the drawing, and is held vertically by a holding member. The X-ray reflecting mirror 119 is made of a quartz substrate on which the reflecting surface 119a is processed with high accuracy. On the reflective surface 119a, a multilayer film of Mo and Si having a high reflectance of X-rays having a wavelength of 13 nm is formed. When X-rays having a wavelength of 10 to 15 nm are used, materials such as Ru (ruthenium) and Rh (rhodium), Si, Be (beryllium), B _Four A multilayer film combined with a substance such as C (carbon tetraboride) may be used.
[0029]
On the right side of the figure of the X-ray reflecting mirror 119, an optical path bending reflecting mirror 121 is disposed obliquely. Above the optical path bending reflecting mirror 121, a reflective mask 123 (details will be described later) is horizontally disposed so that the reflecting surface faces downward. The X-rays emitted from the illumination optical system 117 are reflected and collected by the X-ray reflecting mirror 119 and then reach the reflecting surface of the reflective mask 123 via the optical path bending reflecting mirror 121.
[0030]
A reflective film made of a multilayer film is also formed on the reflective surface of the reflective mask 123. A mask pattern corresponding to the pattern to be transferred to the wafer 129 is formed on the reflective film. The reflective mask 123 is fixed to the mask stage 125 shown in the upper part thereof. The mask stage 125 is movable at least in the Y direction, and sequentially irradiates the mask 123 with the X-rays reflected by the optical path bending reflecting mirror 121.
[0031]
Below the reflective mask 123, a projection optical system 127 and a wafer 129 are arranged in this order. The projection optical system 127 includes a plurality of reflecting mirrors and the like, reduces the X-ray reflected by the reflective mask 123 to a predetermined reduction magnification (for example, ¼), and forms an image on the wafer 129. The wafer 129 is fixed to the wafer stage 131 movable in the XYZ directions by suction or the like.
[0032]
The exposure chamber 33 is provided with a preliminary exhaust chamber (load lock chamber) via a gate valve. A vacuum pump (both not shown) is connected to the preliminary exhaust chamber, and the preliminary exhaust chamber is evacuated by the operation of the vacuum pump.
[0033]
When performing the exposure operation, the illumination optical system 117 irradiates the reflective surface of the reflective mask 123 with EUV light. At that time, the reflective mask 123 and the wafer 129 are relatively synchronously scanned with the projection optical system 127 at a predetermined speed ratio determined by the reduction magnification of the projection optical system. As a result, the entire circuit pattern of the reflective mask 123 is transferred to each of a plurality of shot areas on the wafer 129 by a step-and-scan method. The chip of the wafer 129 is, for example, 25 × 25 mm square, and an 0.07 μmL / S IC pattern can be exposed on the resist.
[0034]
Next, the structure of the reflective mask according to the embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a side sectional view for explaining an example of the structure of a reflective mask according to an embodiment of the present invention. The reflective mask 23 described above has the same structure as the reflective mask 10.
This reflective mask 10 is obtained by forming a Mo / Si multilayer film 13 on a substrate 11. The Mo layer 15 has a thickness of 2.38 nm, and the Si layer 17 has a thickness of 4.5 nm. A pair of the Mo layer and the Si layer is referred to as a single layer pair 16, and the multilayer film 13 is formed by stacking 50 Mo / Si layers. Then, the thickness of the 15th pair of Si layers 17-15 from the top of the region to be the dark portion 19 of the mask is different from the thickness (α) of other Si layers of 4.5 nm by a predetermined difference (β, this example Is 1.85 nm (= α−β) minus 2.65 nm. On the other hand, the thickness α of the 15th layer Si layer 17-15 from the top of the bright portion 21 remains 4.5 nm. For this reason, the dark part 19 of the mask is recessed from the bright part 21 on the surface of the reflective mask 10.
[0035]
Hereinafter, the characteristics of the multilayer film will be described.
The multilayer mirror has a reflection peak at a predetermined wavelength depending on the thickness of the stacked Mo layer and Si layer according to the Bragg equation described above. As an example, when 50 layer pairs (total 100 layers) of a Mo layer having a thickness of 2.38 nm and a Si layer having a thickness of 4.5 nm are stacked, the theoretical reflectance is 72.1% at a wavelength of 13.5 nm. It becomes.
[0036]
Here, when the thickness of the Si layer of one layer pair is changed in each layer pair of the multilayer film, the inventors have found that the reflectance curve indicating the relationship between the wavelength and the reflectance changes. I found it.
FIG. 3 is a side sectional view schematically showing the structure of a multilayer film in which the thickness of the Si layer of one layer pair is changed.
This multilayer film 30 is obtained by forming a Mo / Si multilayer film 33 on a substrate 31. The Mo / Si multilayer film 33 is formed by stacking 50 pairs of layers (total 100 layers) of a Mo layer 35 having a thickness of 2.38 nm and a Si layer 37 having a thickness of 4.5 nm. Only the counter Si layer 37-15 has a thickness changed from 4.5 nm to 1.85 nm.
[0037]
FIG. 4 is a graph showing the relationship between the reflectance and wavelength of the multilayer film of FIG. The vertical axis represents reflectance (%), and the horizontal axis represents wavelength (nm). A solid line in the graph indicates the multilayer film of FIG. 3 (thickness of the 15th pair of Si layers is changed), and a broken line indicates a normal multilayer film (thickness of which is not changed).
As indicated by the broken line, the one that does not change the thickness of the Si layer has a maximum reflectance of 72.1% near the wavelength of 13.5 nm. In the case where the thickness of the Si layer in FIG. 3 is changed, as shown by the solid line, the entire peak becomes thick and the reflectance becomes a trough at the wavelength of 13.5 nm. A peak appears around .75 nm. The reflectance at a wavelength of 13.5 nm is 0.017%.
Thus, it can be seen that when the thickness of the Si layer of the layer pair at a predetermined position is changed, a reflectance valley appears in the reflectance curve.
[0038]
Next, the position of the layer pair for changing the thickness of the Si layer was changed, and the relationship between the reflectance of the valley and the position of the layer pair was obtained.
FIG. 5 is a graph showing the relationship between the reflectance of the valley and the position of the layer pair when the position of the layer pair whose thickness is changed is changed. The vertical axis represents the reflectance of the portion where the reflectance curve becomes a valley, and the horizontal axis represents the position from above the layer pair.
When the Si layer whose thickness is changed from 4.5 nm to 1.85 nm is changed in order from the top of the multilayer film in FIG. 3, the trough is changed even if the thickness of the Si layer from the top to the sixth layer is changed. Does not appear, but valleys begin to appear from the 7th layer. Then, the deeper the position of the layer pair that changes the thickness, the lower the reflectance of the wavelength that becomes the trough, the smallest at the 15th layer pair from the top, and then gradually increases up to the 20th layer pair. The wavelength of the portion where the valley appears is around 13.5 nm.
Thus, it can be seen that when the thickness of the Si layer of the 15th layer from the top is changed, the reflectance of the valley is the lowest.
[0039]
Next, the amount of change in the thickness of the Si layer was changed to obtain the relationship between the reflectance and the wavelength.
FIG. 6 is a graph showing the relationship between the reflectance and the wavelength when the thickness of the 15th pair of Si layers is changed. The vertical axis represents the reflectance, and the horizontal axis represents the wavelength. The solid line in the graph indicates that the thickness of the Si layer is 1.7 nm, the broken line is 1.8 nm, the alternate long and short dash line is 1.85 nm, the alternate long and two short dashes line is 1.9 nm, and the dotted line is 2.0 nm.
As can be seen from the graph, when the thickness of the Si layer of the 15th layer from the top is changed stepwise from 1.7 nm to 2.0 nm, the portion where the reflectance becomes a valley shifts to the long wavelength side, The intensity balance of the peaks on both sides also changes.
[0040]
Here, the sum of the thickness of the modified Si layer (in this example 1.85 nm) and the thickness of the Mo layer above or below this layer (2.38 nm) (4.23 nm) is used. When converted to the optical path length with respect to the soft X-ray wavelength, it is preferable that there is a difference of 20% or more with respect to 1/2 (6.75 nm) of the soft X-ray wavelength (13.5 nm).
[0041]
As shown in FIG. 1, the reflective mask 10 of the present invention has 50 layers of a Mo film 15 having a thickness of 2.38 nm and a Si film 17 having a thickness of 4.5 nm on a substrate 11 as described above. In the stacked structure, the thickness of the 15th layer Si layer 17-15 from the top of the region to be the dark portion 19 of the mask is 1.85 nm. Therefore, from the results of FIGS. 3 to 6, in the dark part 19 where the thickness of the 15th layer Si layer 17-15 from the top is 1.85 nm, reflection at a wavelength of 13.5 nm as shown in FIG. The rate is 0.017%. On the other hand, the reflectance at 13.5 nm of the other portion (bright portion 21) where the thickness of the Si layer is not changed is 72.1%, and the reflectance ratio is 4000 or more.
[0042]
Therefore, when this reflective mask 10 is applied to EUV lithography using Li (lithium) vapor as a light source, since Li has an emission line at a wavelength of 13.5 nm, a portion corresponding to the bright portion 21 of the mask is completely ( If a multilayer film is formed (without changing the thickness), and the thickness of the 15th pair of Si layers 17-15 from the top corresponding to the dark portion 19 is changed to 1.85 nm, a contrast of 4000 is obtained.
[0043]
Next, the manufacturing method of this reflective mask is demonstrated.
First, 35 pairs of a 2.38 nm thick Mo layer and a 4.5 nm thick Si layer are formed on a substrate. Next, a Mo layer having a thickness of 2.38 nm is formed on the surface of the uppermost Si layer of the formed layer. Then, a Si layer is laminated to a thickness of 4.5 nm, a resist is applied thereon, and the mask pattern is exposed. Thereafter, the uppermost Si layer is uniformly removed by 2.65 nm using an etching technique such as RIE. Then, the resist is removed, and 14 pairs of 2.38 nm thick Mo layer and 4.5 nm thick Si layer are stacked by vertical film formation.
As a result, a multilayer film in which the thickness of the 15th layer Si layer from the top of only the pattern portion is changed to 1.85 nm is formed.
[0044]
Alternatively, 35 pairs of a Mo layer with a thickness of 2.38 nm and a Si layer with a thickness of 4.5 nm are formed on a substrate. Next, a Mo layer having a thickness of 2.38 nm is formed on the uppermost Si layer of the formed layer. And a resist is apply | coated on this Mo layer and the pattern of a mask is exposed. Next, the Si layer is uniformly laminated by vertical film formation by 2.65 nm. Here, the resist is removed, and 14 pairs of a 1.85 nm thick Si layer, a 2.38 nm thick Mo layer, and a 4.5 nm thick Si layer are stacked on the entire surface.
As a result, a multilayer film in which the thickness of the 15th layer Si layer from the top of only the pattern portion is changed to 1.85 nm is formed.
[0045]
In the reflective mask 10 manufactured by such a method, the reflectance of the bright part 21 was 63% and the reflectance of the dark part 19 was 0.06%. Therefore, the contrast is about 1000, and a high contrast can be obtained. Further, since the bright part 21 protrudes from the dark part 19 on the mask surface, the difference in height between the bright part 21 and the dark part 19 has little influence on the pattern accuracy. Moreover, this difference is about 2.65 nm (= 4.5-1.85), which is very small compared to the thickness of the conventional absorber layer of 50 nm to several hundred nm. In addition, since another substance is not used as the absorber layer, the light portion and the dark portion have almost the same structure, and no stress is generated in the absorber layer itself.
[0046]
FIG. 7 is a side sectional view for explaining the structure of a reflective mask according to another embodiment of the present invention.
The reflective mask 40 has a Mo / Si multilayer film 43 formed on a substrate 41. The Mo layer 45 has a thickness of 2.38 nm, the Si layer 47 has a thickness of 4.5 nm, and 50 pairs of Mo / Si layers are stacked. The thickness of the Si layer 47-15, which is the 15th layer from the top of the region that becomes the dark portion 49 of the mask, is 7.15 nm. The thickness (α) of the other Si layer is set to 4.5 nm, and the changed thickness (β) of 2.65 nm of the 15th pair of Si layers from the top in the reflective mask of FIG. The added thickness (= α + β). Accordingly, the dark portion 49 of the mask protrudes from the bright portion 51 on the surface of the reflective mask 40.
[0047]
The reflective mask 40 of this example has the same thickness on the multilayer film as that of the reflective mask of FIG. 1, but the thickness is increased by adding the same changed thickness. Also in this reflective mask, the same effect as that of the reflective mask of FIG. 1 can be obtained. The reflective mask of this example has a structure in which the dark portion 49 protrudes from the bright portion 51. However, as described above, the difference in height is very small, and shadows due to oblique incidence do not have a significant effect.
[0048]
Next, the multilayer film for wavelength filters according to the embodiment of the present invention will be described.
The multilayer film for wavelength filter is used for a reflecting mirror having a role of a filter for monochromatization. This wavelength filter reflects a 13 nm light to be used and cuts a weak peak light of 13.2 nm against a light beam having a spectrum mainly caused by oxygen atoms irradiated from a laser plasma X-ray source. Used for.
This multilayer film has substantially the same configuration as the multilayer mirror in FIG. 3, and is a multilayer film in which 50 pairs of a 2.5 nm thick Mo layer and a 4.5 nm thick Si layer are stacked on a substrate. The thickness of the 15th pair of Si layers from the top is changed to 1.9 nm.
[0049]
Conventionally, when a filter that needs to reflect only 13.0 nm and cut 13.2 nm is required for a light source having bright lines at two wavelengths close to 13.0 nm and 13.2 nm, an ordinary Mo / Si multilayer film Is used, the wavelength of 13.0 nm can be reflected. However, since the half-value width of the reflectance curve in this portion is wide, the wavelength of 13.2 nm is also reflected. Therefore, MoSi with low reflectivity but narrow half-value width ₂ A wavelength selective mirror (incident at 15 °) is provided using a / Si (molybdenum silicide / silicon) multilayer film.
[0050]
FIG. 8 is a graph showing the relationship between the wavelength and the reflectance of the multilayer film used in the reflection mirror / wavelength filter. The vertical axis represents the reflectance, and the horizontal axis represents the wavelength. The solid line in the graph is the multilayer film according to the present invention, and the broken line is the conventional MoSi. ₂ / Si multilayer film is shown. MoSi ₂ / Si multilayer is MoSi ₂ It consists of 100 pairs of layers and Si layers.
As can be seen from the graph, MoSi ₂ As shown by the broken line, the reflectance of the / Si multilayer film has a theoretical reflectance of about 48% at 13.0 nm and a reflectance of about 3% at 13.2 nm. On the other hand, in the multilayer film of the present invention in which the thickness of the Si layer corresponding to the 15th layer from the top is changed, as shown by the solid line, it has a reflectivity of about 63% at 13.0 nm and 1% at 13.2 nm. The following reflectance is obtained.
[0051]
Therefore, it is possible to provide a reflection mirror that improves the reflectance at a desired wavelength of 13.0 nm as compared with the conventional one and reduces the loss of light amount.
[0052]
Next, the structure of the multilayer film for a two-color reflector according to the embodiment of the present invention will be described.
The dichroic reflector is a reflector having a peak reflectance with respect to two adjacent wavelengths.
This multilayer film has substantially the same configuration as the multilayer film reflector in FIG. 3, and is a multilayer film in which 50 pairs of a 2.4 nm thick Mo layer and a 4.5 nm thick Si layer are stacked from above. The Si layer of the fifteenth layer is changed to a thickness of 1.25 nm.
[0053]
FIG. 9 is a graph showing the relationship between the wavelength and the reflectance of the multilayer film for a two-color reflector of the present invention. The vertical axis represents the reflectance, and the horizontal axis represents the wavelength. The solid line in the graph indicates the multilayer film according to the present invention.
From this graph, a trough occurs in the reflectance when the wavelength is 13.45 nm, and the reflectance at this time is 0.04%. In addition, the two peaks on both sides of the valley are 13.23 nm on the short wavelength side and the reflectance is 61%, the reflectance on the long wavelength side is 13.72 nm and the reflectance is 61%, and the reflectances of the peaks on both sides are almost equal.
[0054]
Therefore, it is possible to form a two-color multilayer film having a high peak reflectance with respect to two wavelengths separated by only 0.5 nm. Note that in a conventional multilayer film, a characteristic having an even reflectance peak at both wavelengths cannot be obtained by simply overlapping a structure having a peak at 13.23 nm and a structure having a peak at 13.72 nm.
[0055]
Next, it was determined how much the reflectance was reduced at the portion where the reflectance becomes a valley.
The multilayer film is a multilayer film in which 50 layers of a 2.4 nm thick Mo layer and a 4.5 nm thick Si layer are stacked on a substrate, and the 15th pair of Si layers having a thickness of 1. The wavelength was changed to 685 nm.
FIG. 10 is a graph showing the relationship between the wavelength of the multilayer film and the reflectance. The vertical axis represents the reflectance, and the horizontal axis represents the wavelength. A solid line indicates the multilayer film in the figure, and a dotted line indicates the multilayer film in which the thickness of the Si layer is not changed.
As shown in the graph, this multilayer film has a reflectance of 0.000000001017%, which is almost zero, at a wavelength of 13.5159 nm. Further, in the multilayer film in which the thickness of the Si layer is not changed, as shown by the dotted line, the reflectance at the wavelength of 13.5159 nm is 72.0%, so that the contrast is nearly 10 digits.
[0056]
(Example 1)
A multilayer film in which 50 pairs of 2.5 nm thick Mo layer and 4.5 nm thick Si layer are stacked on the substrate, and the thickness of the 15th pair of Si layers from the top is changed to 1.9 nm. The multilayer film was used as a wavelength filter. This wavelength filter reflects 13nm light to be used and cuts the weak peak light of 13.2nm against the light beam with the spectrum mainly caused by oxygen atoms irradiated from the laser plasma X-ray source. It is.
This multilayer film had a reflectivity of about 58% at a wavelength of 13 nm, and a reflectivity of 0.7% or less at 13.2 nm. Therefore, the purity of the light source can be improved, and the purity of the spectrum is about 99%.
On the other hand, MoSi ₂ When a wavelength selective mirror (15 ° incidence) was provided using a / Si (molybdenum silicide / silicon) multilayer film, the reflectance at a wavelength of 13 nm was 35%, and the reflectance was about 2% at 13.2 nm. For this reason, the purity of the light source was lowered, and the purity of the spectrum was about 94%.
[0057]
(Example 2)
A multi-layer film in which 50 pairs of Mo layers with a thickness of 2.4 nm and Si layers with a thickness of 4.5 nm are stacked on a substrate, and the Si layer of the 15th pair from the top is changed to a thickness of 1.25 nm. The multilayer film was used as a multilayer film for a two-color reflector.
The reflectivity has two valleys, and the two peaks on both sides of the valley are 13.23 nm on the short wavelength side and 54% reflectivity, 13.72 nm on the long wavelength side and 55% reflectivity. The reflectivity was almost equal.
[0058]
【The invention's effect】
As is apparent from the above description, according to the present invention, one of the pairs constituting the multilayer film has a thickness different from that of the other layer pairs by changing the thickness of the other layer in which the periodic structure is defined. The reflection characteristics of the film can be changed. By utilizing this characteristic, it is possible to configure a filter or a two-color reflecting mirror that cuts a specific wavelength, and a reflective mask using the effect. In particular, when applied to a reflective mask, a sufficient contrast can be given to the pattern with a slight difference in film thickness without providing a thick absorber layer as in the prior art.
[Brief description of the drawings]
FIG. 1 is a side sectional view for explaining an example of a structure of a reflective mask according to an embodiment of the present invention.
2 is a view showing an overall configuration of an X-ray exposure apparatus equipped with the reflective mask of FIG.
FIG. 3 is a side sectional view schematically showing the structure of a multilayer film in which the thickness of the Si layer of one layer pair is changed.
4 is a graph showing the relationship between the reflectance and wavelength of the multilayer film of FIG.
FIG. 5 is a graph showing the relationship between the reflectance of a valley and the position of a layer pair when the position of a layer pair whose thickness is changed is changed.
FIG. 6 is a graph showing the relationship between reflectance and wavelength when the thickness of the 15th pair of Si layers is changed.
FIG. 7 is a side sectional view for explaining the structure of a reflective mask according to another embodiment of the present invention.
FIG. 8 is a graph showing the relationship between the wavelength and the reflectance of a multilayer film used in a reflection mirror / wavelength filter.
FIG. 9 is a graph showing the relationship between the wavelength and the reflectance of the multilayer film for a two-color reflector of the present invention.
FIG. 10 is a graph showing the relationship between the wavelength and reflectance of a multilayer film.
FIG. 11 is a cross-sectional view schematically showing the structure of a reflective mask used in conventional EUVL lithography.
[Explanation of symbols]
10 Reflective mask 11 Substrate
13 Mo / Si multilayer film 15 Mo layer
16 layers vs. 17 Si layers
19 Dark part 21 Bright part

Claims (10)

In a multilayer reflector in which a first layer made of a material having a large difference between a refractive index in a soft X-ray region and a refractive index in a vacuum and a second layer made of a small material are alternately stacked on a substrate,
The thickness of any one of the first layer or the second layer in the layer structure located in the middle of the periodic layer structure composed of the first layer and the second layer of the multilayer film is changed to another thickness. A multilayer-film reflective mirror characterized in that the layer structure is changed. The sum of the thickness of the layer whose thickness is changed with respect to another layer structure and the thickness of the layer above or below the layer is converted into the optical path length with respect to the wavelength of the soft X-ray used. 2. The multilayer film reflecting mirror according to claim 1, wherein the multilayer film reflecting mirror has a difference of 20% or more with respect to 1/2 of the wavelength of soft X-rays. 3. The multilayer mirror according to claim 1, wherein the main component of the first layer is molybdenum (Mo). 4. The multilayer mirror according to claim 1, wherein the main component of the first layer is molybdenum silicide (MoSi ₂ ). The multilayer film reflector according to claim 1, wherein a main component of the second layer is silicon (Si). The multilayer reflector according to claim 1, wherein the layer for changing the thickness is the second layer. A reflective mask on which a pattern to be transferred to a sensitive substrate is formed,
A multilayer film in which a first layer made of a material having a large difference between a refractive index in a soft X-ray region and a refractive index in a vacuum and a second layer made of a small material are alternately laminated on a substrate;
Either the first layer or the second layer in the layer structure located in the middle of the periodic layer structure composed of the first layer and the second layer in the portion of the multilayer film corresponding to the pattern A reflective mask, wherein the thickness of one layer is changed with respect to another layer structure. In an exposure apparatus having an X-ray light source that generates X-rays, an illumination optical system that guides X-rays from the X-ray light source to a mask, and a projection optical system that guides X-rays from the mask to a sensitive substrate,
It has a reflective mask with a pattern to be transferred to the sensitive substrate,
This reflective mask is a multilayer film in which a first layer made of a material having a large difference between a refractive index in a soft X-ray region and a refractive index in a vacuum and a second layer made of a small material are alternately stacked on a substrate. Become
Either the first layer or the second layer in the layer structure located in the middle of the periodic layer structure composed of the first layer and the second layer in the portion of the multilayer film corresponding to the pattern An exposure apparatus characterized in that the thickness of one layer is changed with respect to another layer structure. A method for manufacturing the reflective mask according to claim 7, comprising:
Laminating only a plurality of layer pairs alternately on the substrate with the first layer and the second layer;
Forming a resist pattern comprising the same pattern as the pattern on the second uppermost layer;
Etching the uppermost second layer by a predetermined depth using the resist pattern as a mask;
Removing the resist pattern;
And a step of alternately laminating a plurality of layer pairs of the first layer and the second layer on the second uppermost layer. A method for manufacturing the reflective mask according to claim 7, comprising:
Laminating only a plurality of layer pairs alternately on the substrate with the first layer and the second layer;
Forming a first layer on the second uppermost layer;
Forming a resist pattern having the same pattern as the pattern on the first layer;
Forming a second layer with a first thickness on the entire surface including the resist pattern;
Removing the resist pattern;
Forming a second layer with a second thickness on the entire surface including the second uppermost layer;
Comprising
A method of manufacturing a reflective mask, wherein the total thickness of the first thickness and the second thickness is the same as that of the second layer having a periodic layer structure.

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