JP2009052998A - Multilayer-film reflecting mirror, multilayer-film reflecting mask and extreme ultraviolet exposure system using them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer-film reflecting mirror which can improve the reflectance without having to increase the number of layers in a multilayer film. <P>SOLUTION: The multilayer-film reflecting mirror, where Mo-Si pair layers, having a main Mo layer made of Mo and an Si layer mainly made of Si, are stacked alternately on a base material, is such that the thickness of the Mo layer in the n-th Mo-Si pair layer from the first Mo-Si pair layer on the base material is set with the thickness set equal to that of the Si layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer film reflecting mirror, a multilayer film reflecting mask, and an EUV exposure apparatus using them, which are used in a lithography process using EUV light near 13 nm.

  In recent years, with the miniaturization of semiconductor integrated circuits, in order to improve the resolution of the optical system achieved by the diffraction limit of light, EUV light (wavelength near 13 nm) is used instead of conventional ultraviolet rays (wavelength near 13 nm). An exposure technique using EUV (Extreme Ultra Violet) has been developed. Lithography technology using such EUV light is expected to enable exposure with a pattern size of about 5 to 70 nm.

  In lithography technology, the shorter the wavelength of light used, the higher the resolution, but as the wavelength becomes shorter, the absorptance of an optical product such as a lens increases, and the refraction optical system cannot perform reduced projection. That is, since the refractive index of the substance in the wavelength region near 13 nm is close to 1, the transmission refractive optical element cannot be used as in the prior art, and the reflective optical element is used. Therefore, the mask used in the exposure apparatus is also a normal reflection type optical element from the viewpoint of ensuring transmittance. At this time, in order to achieve a high reflectance in each optical element, a multilayer reflective film formed by alternately laminating a large number of substances having a high refractive index and a substance having a low refractive index in the used wavelength range on the substrate. It is common to use.

As an optical element using such a multilayer reflective film, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-140147) discloses alternating layers of Mo and Si as main components on the substrate surface. A multilayer film reflector comprising a Mo / Si multilayer film having a structure in which a diffusion prevention layer is formed on a layer containing Si as a main component, wherein the diffusion prevention layer comprises the Si A multilayer film reflector is disclosed, which is composed of atoms having a shared valence radius of 80% or more of the radius of the largest sphere that enters the interatomic void of the layer containing as a main component.
JP 2007-140147 A

  By the way, in the conventional multilayer mirror, a Mo layer having a thickness of 2.8 nm containing Mo as a main component and a Si layer having a thickness of 4.2 nm containing Si as a main component are periodically and alternately paired 40 pairs. In general, a total of 80 layers were used. Even when such a multilayer film reflecting mirror is formed, both Mo and Si have an absorption coefficient for EUV light, so the reflectance in an ideal 40 pair layer is about 71%. In an exposure apparatus using a multilayer film reflecting mirror and a multilayer film reflecting mask having a reflectance of 71%, the amount of light that can be finally used for exposure on the wafer is about 10% of that of the light source.

  Therefore, it is required to improve the reflectivity of the multilayer film reflecting mirror and the multilayer film reflecting mask as much as possible. It is recognized that increasing the number of pairs of multilayer films improves the reflectivity, but in order to increase the number of pairs, it is necessary to increase the number of processes for further forming the Mo layer and the Si layer. However, as the number of multilayer film formation processes increases, the possibility of defects due to foreign matters and voids increases, as well as the cost problem, so the reflection by increasing the number of layers in the multilayer film There was a problem that the rate improvement was limited.

  The present invention is to solve the above-mentioned problems, and the invention according to claim 1 is a Mo-- comprising a Mo layer containing Mo as a main component and a Si layer containing Si as a main component on a substrate. A multilayer mirror in which Si pair layers are alternately provided, and the thickness of the Mo layer and the thickness of the Si layer from the first Mo-Si pair layer to the nth Mo-Si pair layer immediately above the substrate Are set to be equal to each other.

  The invention according to claim 2 is the multilayer mirror according to claim 1, wherein the number of all Mo—Si pair layers provided on the substrate is 40, and 9 ≦ n ≦ 18. It is characterized by that.

  The invention according to claim 3 is the multilayer film reflector according to claim 1, wherein the number of all Mo—Si pair layers provided on the substrate is 40, and n = 14. Features.

  According to a fourth aspect of the present invention, a Mo—Si pair layer composed of a Mo layer containing Mo as a main component and a Si layer containing Si as a main component is alternately provided on a base material. A multilayer film reflective mask provided with an absorption layer on the substrate, wherein the thickness of the Mo layer and the thickness of the Si layer in the first to Mo-Si pair layers immediately above the substrate are equal to each other. It is set so that it may become.

  The invention according to claim 5 is the multilayer film reflective mask according to claim 1, wherein the number of all Mo—Si pair layers provided on the substrate is 40, and 9 ≦ n ≦ 18. It is characterized by that.

  The invention according to claim 6 is the multilayer film reflective mask according to claim 1, wherein the number of all Mo—Si pair layers provided on the substrate is 40 and n = 14. Features.

  The invention according to claim 7 is an EUV exposure characterized by using either the multilayer reflector according to claims 1 to 3 or the multilayer reflector according to claims 4 to 6. apparatus.

  According to the multilayer mirror, the multilayer reflective mask, and the EUV exposure apparatus using the multilayer mirror according to the embodiment of the present invention, it becomes possible to improve the reflectance without increasing the number of layers of the multilayer film. An efficient exposure process can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a view schematically showing an EUV exposure apparatus using a multilayer film reflecting mirror and a multilayer film reflecting mask according to an embodiment of the present invention. In FIG. 1, 10 is an EUV light source, 11 is a multilayer film reflecting mask, 12 and 13 are multilayer film reflecting mirrors, and 14 is a wafer.

  As the EUV light source 10, for example, a laser plasma light source is used. This irradiates the target material in the vacuum vessel with high-intensity pulsed laser light to generate high-temperature plasma. For example, EUV light having a wavelength of about 13 nm is emitted from the plasma. As the target material, a metal film, a gas jet, a droplet, or the like is used. In order to increase the average intensity of the emitted EU V light, the repetition frequency of the pulse laser should be high. The repetition frequency is usually several kHz.

  The multilayer film reflective mask 11 is a reflective mask, on which a circuit pattern to be transferred is formed, and is supported and driven by a mask stage (not shown). Diffracted light emitted from the multilayer film reflecting mask 11 is reflected by a projection optical system including the multilayer film reflecting mirrors 12 and 13 and projected onto the wafer 14 that is the object to be processed.

  The wafer 14 is a substrate such as a semiconductor, and is configured to be chucked on a wafer stage (not shown) and movable in the XYZ directions.

  The projection optical system of the EUV exposure apparatus uses a plurality of multilayer film reflecting mirrors 12 and 13 (multilayer film mirrors) to reduce and project the pattern on the surface of the multilayer film reflection mask 11 onto the wafer 14 arranged on the image plane. . The number of the multilayer mirrors 12 and 13 is two in this embodiment, but a necessary number can be provided as appropriate.

  Next, the multilayer film reflecting mirror 12 according to the embodiment of the present invention will be described. FIG. 2 is a diagram schematically showing a multilayer-film reflective mirror according to the embodiment of the present invention. In FIG. 2, 100 is an ultra-low expansion substrate, 101 is a Mo layer having a thickness of 3.5 nm, 102 is a Si layer having a thickness of 3.5 nm, 111 is a Mo layer having a thickness of 2.8 nm, and 112 is a thickness of 4 .2 nm Si layer, 201 is a first Mo—Si pair layer, 202 is a second Mo—Si pair layer,... 240 is a 40th Mo—Si pair layer.

  FIG. 2 is a cross-sectional view of the multilayer mirror 12. As shown in FIG. 2, the multilayer reflector 12 includes a layer (Mo layer) containing molybdenum (Mo) as a main component and silicon (Mo layer) on the surface of the substrate of the ultra-low expansion substrate 100 polished into a highly accurate shape. In this structure, the Mo—Si pair layers of Si (main layer) (Si layer) are alternately and periodically formed.

  The multilayer mirror 12 is formed with a first Mo—Si pair layer 201, a second Mo—Si pair layer 202, a third Mo—Si pair layer 203, and a 40th Mo—Si pair layer 240 in order from the substrate of the ultra-low expansion substrate 100. However, in the first Mo—Si pair layer 201 to the 14th Mo—Si pair layer 214, the thickness of the Mo layer 101 is 3.5 nm, the thickness of the Si layer 102 is 3.5 nm, and the Mo layer 101 and Si layer 102 are formed to be equal.

  On the other hand, in the 15th Mo-Si pair layer 215 to the 16th Mo-Si pair layer 216, the thickness of the Mo layer 111 is 2.8 nm, the thickness of the Si layer 112 is 4.2 nm, and Mo The film is formed so that the thickness of the layer 111 is smaller than the thickness of the Si layer 112.

  In any of the first to forty Mo-Si pair layers, (Mo layer 101 thickness) + (Si layer thickness) = (1/2 of the wavelength of EUV light). ing.

  In the present embodiment, in the first Mo—Si pair layer 201 to the 14th Mo—Si pair layer 214 immediately above the substrate of the ultra-low expansion base material 100, the thickness of the Mo layer 101 and the thickness of the Si layer 102 are set equal. The present invention is not necessarily limited to this, and in the first Mo-Si pair layer 201 to the nMo-Si pair layer immediately above the substrate of the ultra-low expansion substrate 100, the thickness of the Mo layer 101 is equal to the thickness of the Si layer 102. Can be set. Here, when the total number of Mo—Si pair layers is 40, it is preferable to take a value of n = 9 to n = 18. The reason will be described below.

  FIG. 3 is a diagram showing the relationship between the number of Mo—Si pair layers in which the thickness of the Mo layer and the thickness of the Si layer are equal and the reflectance. In FIG. 3, the horizontal axis is the number n of Mo—Si pair layers from the top of the ultra-low expansion substrate 100 where (Mo layer thickness) = (Si layer thickness), and the vertical axis is the reflectance. It is shown. Note that the multilayer mirror 12 in FIG. 3 has a total number of Mo—Si pair layers of 40. As shown in FIG. 3, a good reflectance can be obtained when 9 ≦ n ≦ 18, and the best reflectance can be obtained particularly when n = 14.

  According to the configuration as described above, it is possible to improve the reflectance without increasing the number of Mo—Si pair layers only by controlling the thickness of the Mo layer and the thickness of the Si layer. According to the EUV exposure apparatus using the mirrors 12 and 13, an efficient exposure process can be realized in lithography.

  Next, the multilayer reflective mask according to the embodiment of the present invention will be described. FIG. 4 is a diagram schematically showing a multilayer reflective mask 11 according to the embodiment of the present invention. In FIG. 4, 100 is an ultra-low expansion substrate, 101 is a Mo layer having a thickness of 3.5 nm, 102 is a Si layer having a thickness of 3.5 nm, 111 is a Mo layer having a thickness of 2.8 nm, and 112 is a thickness of 4 .2 nm Si layer, 201 is a first Mo—Si pair layer, 202 is a second Mo—Si pair layer,... 240 is a 40th Mo—Si pair layer. The above configuration is the same as that of the multilayer reflector 12 described above.

  The multilayer reflective mask 11 is different from the multilayer reflective mirror 12 in that a buffer layer 301 and an absorption layer 300 are formed on the uppermost Mo—Si pair layer.

The buffer layer 301 provided on the uppermost Mo—Si pair layer of the multilayer reflective mask 11 is, for example, Ru or SiO ₂ , and the absorption layer 300 is Ta, Cr, Ti, Nb, or a compound thereof. . These buffer layer 301 and absorption layer 300 are formed in a circuit pattern to be transferred, and are configured to absorb EUV light.

  The multilayer reflective mask 11 having the above configuration can be expected to have the same characteristics as the multilayer reflective mirror described in FIG. And according to such a multilayer-film reflective mask 11, the reflectance can be improved without increasing the number of Mo—Si pair layers only by controlling the thickness of the Mo layer and the thickness of the Si layer. The EUV exposure apparatus using the multilayer film reflective mask 11 can realize an efficient exposure process in lithography.

It is a figure which shows typically the EUV exposure apparatus using the multilayer film reflective mirror and multilayer film reflective mask which concern on embodiment of this invention. It is a figure which shows typically the multilayer-film reflective mirror which concerns on embodiment of this invention. It is a figure which shows the relationship between the number of Mo-Si pair layers in which the thickness of Mo layer and the thickness of Si layer are equal, and a reflectance. It is a figure which shows typically the multilayer film reflective mask which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... EUV light source, 11 ... Multilayer reflective mask, 12, 13 ... Multilayer reflective mirror, 14 ... Wafer, 100 .. Ultra low expansion substrate, 101, 111 ... Mo layer 102, 112 ... Si layer, 300 ... absorbing layer, 301 ... buffer layer

Claims (7)

A multilayer reflector in which Mo-Si pair layers composed of Mo layers mainly composed of Mo and Si layers mainly composed of Si are alternately provided on a base material,
Multilayer film reflection characterized in that the thickness of the Mo layer and the thickness of the Si layer in the first to Mo-Si pair layers immediately above the base material are set to be equal to each other. mirror. The multilayer mirror according to claim 1, wherein the number of all Mo—Si pair layers provided on the substrate is 40 and 9 ≦ n ≦ 18. The multilayer mirror according to claim 1, wherein the number of all Mo-Si pair layers provided on the substrate is 40, and n = 14. A multilayer reflective mask in which a Mo-Si pair layer composed of a Mo layer containing Mo as a main component and a Si layer containing Si as a main component is alternately provided on the substrate, and an absorption layer is provided on the Mo-Si pair layer. Because
Multilayer film reflection characterized in that the thickness of the Mo layer and the thickness of the Si layer in the first to Moth-Si pair layers immediately above the base material are set to be equal to each other. mask. 2. The multilayer reflective mask according to claim 1, wherein the number of all Mo—Si pair layers provided on the substrate is 40 and 9 ≦ n ≦ 18. 2. The multilayer reflective mask according to claim 1, wherein the number of all Mo—Si pair layers provided on the substrate is 40 and n = 14. An EUV exposure apparatus using the multilayer film reflecting mirror according to any one of claims 1 to 3 or the multilayer film reflecting mask according to any one of claims 4 to 6.

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