JP4591686B2 - Multilayer reflector - Google Patents

Description

  The present invention is a multilayer suitable for use in an EUV exposure apparatus (also referred to as an extreme ultraviolet exposure apparatus, and in the present specification and claims, refers to an exposure apparatus using ultraviolet light having a wavelength of less than 15 nm). The present invention relates to a film reflecting mirror and an EUV exposure apparatus having the multilayer film reflecting mirror.

  In recent years, with the miniaturization of semiconductor integrated circuits, EUV light having a shorter wavelength (11 to 14 nm) is used in place of conventional ultraviolet rays in order to improve the resolving power of an optical system limited by the diffraction limit of light. Projection lithography techniques have been developed (see, for example, D. Tichenor, et al, SPIE 2437 (1995) 292: Non-Patent Document 1). 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 having a wavelength of about 190 nm.

  A complex refractive index n of a substance in a wavelength region of EUV light is represented by n = 1−δ−ik (i is a complex symbol). The imaginary part k of the refractive index represents absorption of ultrashort ultraviolet rays. Since δk is much smaller than 1, the refractive index in this region is very close to 1. Further, since k is a large value, the absorption rate is increased. Accordingly, a transmission / refraction type optical element such as a conventional lens cannot be used, and an optical system utilizing reflection is used.

  An outline of the EUV exposure apparatus is shown in FIG. The EUV light 32 emitted from the EUV light source 31 enters the illumination optical system 33, becomes a substantially parallel light beam via a concave mirror 34 that acts as a collimator mirror, and enters an optical integrator 35 including a pair of fly-eye mirrors 35a and 35b. Incident.

  Thus, a substantial surface light source having a predetermined shape is formed in the vicinity of the reflecting surface of the second fly's eye mirror 35b, that is, in the vicinity of the exit surface of the optical integrator 35. Light from a substantial surface light source is deflected by the plane mirror 36 and then forms an elongated arc-shaped illumination area on the mask M (the aperture plate for forming the arc-shaped illumination area is not shown). ing). The light from the pattern of the illuminated mask M forms an image of the mask pattern on the wafer W via the projection optical system PL composed of a plurality of mirrors (six mirrors M1 to M6 in FIG. 8 exemplarily). .

  An optical system using such a mirror cannot use paraxial rays for projection exposure, and therefore has a ring-shaped projection exposure field in order to correct the entire aberration as uniform. . In such a ring-shaped projection exposure field, a chip of about 30 mm square cannot be exposed at a time, so that exposure is performed by synchronously scanning the reticle and wafer.

  As a reflector used in such an EUV exposure apparatus, a multilayer film is formed on a substrate, and a multilayer film reflector that obtains a high reflectivity by superimposing a large number of weak reflected lights at the interface in phase. Is commonly used.

  In the wavelength region near 13.4 nm, when a Mo / Si multilayer film in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked is used, a reflectance of 67.5% can be obtained at normal incidence. In the wavelength region near 11.3 nm, when a Mo / Be multilayer film in which Mo layers and beryllium (Be) layers are alternately stacked is used, a reflectivity of 70.2% can be obtained at normal incidence (for example, C.I. Montcalm, “Proceedings of SPIE”, 1998, 3331, p. 42: see Non-Patent Document 2.

JP 11-312638 A JP 2000-56099 A D. Tichenor, et al, SPIE 2437 (1995) 292 C. Montcalm, “Proceedings of SPIE”, 1998, 3331, p.42

  What is generally used as the EUV light source 31 is one that irradiates a target material with laser light as excitation light, converts the target material into plasma, and uses EUV light (exposure light) generated at that time. . Such an EUV light source is described in, for example, (Patent Document 2).

  In an exposure apparatus having a structure using laser plasma as means for generating exposure light, laser light (for example, any of wavelengths 10600 nm, 1064 nm, 532 nm, and 266 nm) is used as excitation light in the same optical path as the generated exposure light. Reach each optical element (mirror etc.).

  At this time, a part of the reached laser light is absorbed by each optical element and induces a shape change due to thermal expansion, resulting in an adverse effect on the imaging performance. In particular, in an exposure apparatus that uses EUV light as exposure light, since each optical element is held in a vacuum, heat exchange via gas is not performed, and the temperature of the element rises more remarkably. In order to avoid such a phenomenon, the prior art has prevented the temperature of each optical element from rising by means such as suppressing the output of laser light.

  However, in a lithography process using an exposure apparatus, if the laser light output is suppressed, the exposure time becomes longer, leading to a decrease in throughput.

  The present invention has been made in view of such circumstances, and is a multilayer film reflection that is unnecessary for exposure and can absorb excitation light that causes thermal expansion of a reflecting mirror that constitutes a projection optical system. It is an object to provide a mirror and an EUV exposure apparatus using the mirror.

A first means for solving the above-described problem is a multilayer film reflector used in an exposure apparatus that excites exposure light with excitation light and performs exposure with the exposure light, and is obliquely incident on the exposure light and has a reflectance of 50% or more corners than 15 °, the have a reflectance of 50% or less with respect to the excitation light, the multilayer film, distribution in the exposure light reflection portion and the substrate side arranged on the surface side a multilayer reflection film, characterized in that have a anti-reflective portion of the excitation light.

  Since this means has a high reflectance with respect to the exposure light, the exposure light can be transmitted to the downstream optical system with a low loss rate. In addition, since the pumping light has a low reflectance, the pumping light transmitted to the downstream optical system is greatly reduced, and the amount of thermal deformation of the downstream optical system by the pumping light can be kept small. it can.

  In this means, the exposure light having a short wavelength is reflected by the exposure light reflecting portion arranged on the surface side. On the other hand, since the excitation light having a long wavelength passes through the exposure light reflection portion and reaches the absorption prevention portion of the excitation light and is absorbed, reflection of the excitation light can be suppressed to a small value.

Second means for solving the above problems, a first hand stage, it is characterized in that the exposure light is less EUV light wavelength 15 nm.

  An exposure apparatus that uses EUV light having a wavelength of 15 nm or less performs exposure of a particularly fine pattern, and since it is necessary to suppress thermal deformation of the optical system, it is particularly effective to use this means.

A third means for solving the problem is the first means or the second means , wherein the excitation light is laser light having a wavelength of 150 nm or more.

  In the case where the excitation light is laser light having a wavelength of 150 nm or more, the rate of occurrence of thermal deformation becomes particularly large when absorbed by the optical system. Therefore, it is particularly effective to use this means.

A fourth means for solving the above-mentioned problems is an EUV exposure apparatus characterized by including a multilayer mirror in any one of the first to third means.

  In this means, since the excitation light entering the projection optical system can be kept small, the thermal deformation of the projection optical system can be reduced, so that accurate exposure transfer can be performed.

  According to the present invention, it is possible to provide a multilayer-film reflective mirror that can absorb excitation light that is unnecessary for exposure and that causes thermal expansion of the reflective mirror constituting the projection optical system.

Examples of the present invention will be described below. FIG. 1 is a diagram showing the configuration of a multilayer-film reflective mirror (planar mirror) that is an embodiment of the present invention. As shown in FIG. 1, an excitation light antireflection film 2 is formed on a substrate 1 made of quartz, and an exposure light reflection film 3 is formed thereon.
Example 1
Plasma was excited by YAG laser light (excitation light) with a wavelength of 1064 nm, and a multilayer mirror was manufactured when EUV light with a wavelength of 13.5 nm was used as exposure light. In this multilayer reflector, the incident light is designed to be incident at an oblique incident angle of 13.5 °.

The excitation light antireflection film 2 has a six-layer film structure of Mo (107 nm), SiO ₂ (402 nm), Si (11 nm), Mo (6 nm), Si (87 nm), and SiO ₂ (177 nm) in this order from the substrate 1 side. The exposure light reflecting film 3 has a two-layer structure of Mo (8 nm) and Si (3 nm) in order from the substrate 1 side.

  As a comparative example, a multilayer film reflecting mirror was fabricated in which only an exposure light reflecting film having a two-layer structure of Mo (66 nm) and Si (11 nm) was formed on the substrate from the substrate side.

  FIG. 2 shows the angle dependence of the reflectance with respect to the exposure light (wavelength 13.5 nm) of the multilayer mirror of Example 1, and FIG. 3 shows the spectral reflectance with respect to the excitation light (wavelength 1064 nm) of this multilayer mirror. Show. On the other hand, FIG. 4 shows the spectral reflectance of excitation light (wavelength 1064 nm) in the multilayer mirror of the comparative example.

From FIG. 2, it can be seen that the reflectance of the exposure light at an oblique incident angle of 13.5 ° of this multilayer mirror is sufficiently high at about 74%. When the oblique incident angle is 17.5 ° or less, the reflectance is 50% or more. Further, comparing FIG. 3 with FIG. 4, the reflectance of the excitation light having a wavelength of 1064 nm is about 24% in the case of the multilayer reflector of Example 1, and about 64% in the case of the multilayer reflector of the comparative example. It can be seen that the multilayer mirror of the present embodiment is reduced to almost 1/3 of the conventional multilayer mirror.
(Example 2)
Plasma was excited by a laser beam (excitation light) having a wavelength of 266 nm, and a multilayer mirror was manufactured when EUV light having a wavelength of 13.5 nm was used as exposure light. In this multilayer reflector, the incident light is designed to be incident at an oblique incident angle of 13.5 °.

The excitation light reflection preventing film 2 has a four-layer film structure of HfO ₂ (33 nm), SiO ₂ (4 nm), and MgF ₂ (66 nm) in this order from the substrate 1 side. It has a two-layer structure of Mo (5 nm) and Si (2 nm) in order from the first side.

  As a comparative example, a multilayer film reflecting mirror was fabricated in which only an exposure light reflecting film having a two-layer structure of Mo (66 nm) and Si (11 nm) was formed on the substrate from the substrate side.

  FIG. 5 shows the angle dependence of the reflectance with respect to the exposure light (wavelength 13.5 nm) of the multilayer mirror of Example 1, and FIG. 6 shows the spectral reflectance with respect to the excitation light (wavelength 266 nm) of this multilayer mirror. Show. On the other hand, FIG. 7 shows the spectral reflectance of the excitation light (wavelength 266 nm) in the multilayer mirror of the comparative example.

From FIG. 5, it can be seen that the reflectance of the exposure light at an oblique incident angle of 13.5 ° of this multilayer mirror is sufficiently high at about 60%. When the oblique incident angle is 15 ° or less, the reflectance is 50% or more. Further, comparing FIG. 6 with FIG. 7, the reflectance of the excitation light having a wavelength of 266 nm is about 40% in the case of the multilayer reflector of Example 2 and about 63% in the case of the multilayer reflector of the comparative example. It can be seen that the multilayer mirror of Example 2 is lowered to about 2/3 of the conventional multilayer mirror.
(Embodiment of the Invention)
The EUV exposure apparatus according to the embodiment of the present invention is basically the same as the configuration of the conventional EUV exposure apparatus shown in FIG. 8, but in the present embodiment, the plane mirror 36 is used as the plane mirror 36 according to the present invention. A multilayer reflector is used. Thus, by using the multilayer film reflecting mirror of the present invention as a reflecting mirror in an illumination optical system that does not require relatively high accuracy, exposure that enters the reflecting mirror (M1 to M6) of the projection optical system that requires high accuracy is possible. Light can be reduced, and thermal deformation of the mirrors of the projection optical system can be kept small. Therefore, a decrease in exposure accuracy can be suppressed.

It is the schematic which shows the structure of the multilayer film reflective mirror which concerns on the Example of this invention. It is the schematic which shows the reflectance with respect to the exposure light of the multilayer film reflective mirror which concerns on 1st Example of this invention. It is the schematic which shows the reflectance with respect to the excitation light of the multilayer film reflective mirror which concerns on 1st Example of this invention. It is the schematic which shows the reflectance with respect to the excitation light of the multilayer film reflective mirror of a comparative example. It is the schematic which shows the reflectance with respect to the exposure light of the multilayer film reflective mirror which concerns on 2nd Example of this invention. It is the schematic which shows the reflectance with respect to the excitation light of the multilayer film reflective mirror which concerns on 2nd Example of this invention. It is the schematic which shows the reflectance with respect to the excitation light of the multilayer film reflective mirror of a comparative example. It is a figure which shows the outline | summary of an EUV exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Excitation light reflection prevention film, 3 ... Exposure light reflection film

Claims (4)

A multilayer film reflector used in an exposure apparatus that excites exposure light with excitation light and performs exposure with the exposure light, and has a reflectance of 50% or more at an oblique incident angle of 15 ° or less with respect to the exposure light. together, characterized in that the have a reflectance of 50% or less with respect to the excitation light, the multilayer film is to have a anti-reflection portion of excitation light arranged in the exposure light reflection portion and the substrate side arranged on the surface side A multilayer reflective film. 2. The multilayer film according to claim 1 , wherein the exposure light is EUV light having a wavelength of 15 nm or less. Multilayer reflection film according to claim 1 or 2, wherein the excitation light is laser light of a wavelength equal to or more than 150 nm. EUV exposure apparatus characterized by having a multilayer reflector according to any one of claims 1 to 3.

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