JPH11329918A - Soft x-ray projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft X-ray projection aligner by which high resolution and high throughput can be attained compatibly. SOLUTION: A bundle of rays radiated from an X-ray source 1 is condensed by a lighting optical system having two X-ray multilayer film mirrors 2, 3 and illuminates a reflection mask 5 mounted on a mask stage 4. The bundle of rays reflected on the reflection mask 5 passes through a projection optical system, constituted of four X-ray multilayer film mirrors 6 to 9 and reaches onto a wafer 11 mounted on a wafer stage 10. The projection optical system reduces the image of a circuit pattern formed on the reflection mask 5 to one- fourth and transfers on the wafer 11. A mirror comprising a mirror 18 having very large thermal deformation, a metal substrate, a thin film of amorphous materials which is formed on the substrate and its surface is polished optically smoothly, a multilayer film which is formed on the thin film and which reflects X-rays having a predetermined wavelength is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a soft X-ray projection exposure apparatus used for manufacturing semiconductor devices and the like.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of semiconductor integrated circuit elements, X-rays having shorter wavelengths have been used in place of conventional ultraviolet rays in order to improve the resolution of an optical system limited by the diffraction limit of light. Projection lithography technology has been developed. An X-ray projection exposure apparatus used in this technique mainly includes an X-ray source, an illumination optical system, a mask, an imaging optical system, a wafer stage, and the like.

As an X-ray source, a radiation light source or a laser plasma X-ray source is used. The illumination optical system includes an oblique incidence mirror, a multilayer mirror, and a filter that reflects or transmits only X-rays of a predetermined wavelength, and illuminates the mask with X-rays of a desired wavelength. The mask includes a transmission mask and a reflection mask. The transmissive mask is formed by forming a pattern on a thin membrane made of a substance that transmits X-rays well by providing a substance that absorbs X-rays in a predetermined shape.

On the other hand, a reflection type mask is formed by forming a pattern having a low reflectivity in a predetermined shape on a multilayer film which reflects X-rays, for example. The pattern formed on such a mask is imaged on a photoresist-coated wafer by a projection imaging optical system composed of a plurality of multilayer mirrors and transferred to the photoresist. Since the X-rays are absorbed by the atmosphere and attenuated, all the optical paths are maintained at a predetermined degree of vacuum.

[0005] In the X-ray wavelength region, no transparent substance exists and the reflectance on the substance surface is very low, so that ordinary optical elements such as lenses and mirrors cannot be used. Therefore, the optical system for X-rays uses an oblique incidence mirror that reflects the X-rays incident on the reflecting surface from an oblique direction by using total reflection, or interference by matching the phases of the reflected light at each interface of the multilayer film. It is composed of a multilayer mirror or the like that obtains a high reflectance by the effect.

Since the oblique incidence optical system has a large aberration, it is impossible to obtain a diffraction-limited resolution. On the other hand, a multilayer mirror can reflect X-rays vertically, and can constitute a diffraction-limited X-ray optical system. Therefore, soft X
The image forming optical system of the line projection exposure apparatus is all composed of a multilayer mirror.

In such an X-ray multilayer mirror, when a multilayer film composed of molybdenum and silicon is used on the long wavelength side of the L absorption edge (12.3 nm) of silicon, absorption by silicon is reduced, so that the highest reflection is obtained. However, at a wavelength of 13 to 15 nm, it is about 70% regardless of the incident angle. 30% at normal incidence on the shorter wavelength side than the L absorption edge of silicon
Almost no multilayer film having the above-mentioned reflectance has been developed. As a substrate material of the multilayer mirror, a glass material such as quartz, which has a high shape accuracy and can be processed with a small surface roughness, is used.

[0008]

In the above X-ray projection exposure apparatus, a practical throughput (for example, 8
In order to obtain about 30 wafers per hour on an inch wafer), X-rays of a certain intensity (for example, about 10 [mW / cm ² ]) are applied to the surface of the multilayer mirror constituting the imaging optical system. Need to be irradiated. On the other hand, as described above, the reflectivity of the multilayer mirror is at most about 70%, and the rest is absorbed, transmitted, and scattered without being reflected by the multilayer film. The loss due to scattering is small, and the X-rays transmitted through the multilayer film are almost completely absorbed by the mirror substrate.

That is, X not reflected by the multilayer mirror
Most of the lines are absorbed by the multilayer mirror and their energy is converted to heat. This heat raises the temperature of the multilayer mirror and causes thermal deformation.

Generally, in order to obtain a diffraction-limited resolution with an optical system, it is necessary to reduce the shape error of mirrors and lenses constituting the optical system sufficiently compared with the wavelength of light used. In an optical system using X-rays, the allowable range of the shape error becomes narrower than that in an optical system using visible light or ultraviolet light by the shorter wavelength. In this case, the thermal deformation of the multilayer mirror due to the above-mentioned X-ray irradiation has a great effect on the imaging characteristics of the multilayer mirror, and there is a possibility that the designed resolution may not be obtained.

To prevent such thermal deformation from affecting the imaging characteristics, the mirror is cooled from the back surface of the substrate, but there is a problem that a sufficient effect cannot be obtained. (Because the X-ray optical system is used in a vacuum, there is almost no heat radiation from the mirror surface.)

Therefore, in order to prevent the influence of thermal deformation on the imaging characteristics, there is no other way than to suppress the intensity of the X-rays incident on the mirror, so that the throughput of the soft X-ray projection exposure apparatus using the mirror decreases. There was a problem of doing.
That is, the conventional mirror has a problem that it is impossible to achieve both high resolution and high throughput of the soft X-ray projection exposure apparatus.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a soft X-ray projection exposure apparatus capable of achieving both high resolution and high throughput.

[0014]

According to a first aspect of the present invention, a metal mirror is used for a part or all of a mirror constituting an illumination optical system or a projection optical system. The mirror is formed on a metal substrate, a thin film of an amorphous material having a surface optically polished and formed on the surface of the metal substrate, and an X-ray of a predetermined wavelength formed on the surface of the thin film. A soft X-ray projection exposure apparatus (Claim 1) characterized by having a reflective multilayer film.

Here, "the surface is polished to be optically smooth" means that at least 80% of the reflectance on a completely flat surface.
It means that it is polished so as to have the above-mentioned reflectance.

In the present means, the mirror used for a part or all of the mirrors constituting the illumination optical system or the projection optical system transfers heat generated by X-rays incident on the mirror to a cooling device provided on the back surface of the mirror. In order to escape efficiently,
A metallic substrate (including an alloy substrate) is used as the substrate. Therefore, a shape error caused by thermal deformation is reduced. Also, the metal substrate is easy to process, and therefore,
A shape error at the time of manufacturing can be reduced.

However, it is difficult to reduce the surface roughness of a metal substrate. Therefore, if a multilayer film that reflects X-rays of a predetermined wavelength is formed directly on the metal substrate, the reflectance will be low. It cannot be used as a mirror for a soft X-ray projection exposure apparatus aimed at by the present invention. Therefore, in the mirror of this means, an amorphous substance whose surface is polished optically smooth is formed on these substrates. Since the amorphous material can be polished on the surface smoothly, a multilayer film reflecting X-rays of a predetermined wavelength is formed on the polished surface,
By using it as a reflecting surface, a mirror having high reflectivity can be obtained, and the object of the present invention can be achieved.

That is, such a mirror can reduce the shape error and the surface roughness, and can suppress the thermal deformation due to the irradiation light sufficiently small. In the present means, since such a mirror is used for a part or all of the mirrors constituting the projection optical system, strong X-rays can be used, and both high resolution and high throughput can be achieved. Can be.

A second means for solving the above-mentioned problem is:
In the first means, the thermal conductivity of the metal substrate constituting the metal mirror is η [W / m · K], and the linear expansion coefficient is α.
[1 / K], the heat flux from the beam or X-ray to the mirror is Q [W /
m ² ], and when the average thickness of the mirror is d [m], α · Q · d ² / (2η) ≦ 10 ⁻⁹ [m] (1) is satisfied (claim) Item 2).

Equation (1) indicates that the deformation of the mirror due to thermal deformation is 1n
It is an expression that means that it is smaller than m. Equation (1) will be described with reference to FIG. Since the actual deformation of the mirror varies greatly depending on the dimensions and shape of the mirror, calculation by the finite element method or the like is necessary to calculate the mirror deformation accurately. Approximate values shall be calculated.

FIG. 3 shows the thermal deformation Δx [x] when the back surface of a mirror having a thickness of d [m] (assumed to be flat for simplicity) is kept at a constant temperature T [K] and the surface is irradiated with X-rays. m] and a steady heat flux Q [W / m ² ] on a part of the substrate surface.
Elongation (or shrinkage) Δ in the direction (x direction) perpendicular to the substrate at the input portion when (the energy of the irradiated X-rays absorbed by the substrate without being reflected) is applied.
Consider x.

Here, the heat conduction in the horizontal direction is not considered and is simplified. At this time, FIG.
As shown in (b), since a uniform temperature gradient is generated in the x direction, the temperature at the position x (temperature difference from the heat bath) T (x)
T (x) = Qx / η (2) where η [W / m · K] is the heat transfer coefficient.

The elongation Δ (δx) of the thin layer (thickness δx) in the substrate is given by Δ (δx) = α · T (x) · δx (3) Here, α is the coefficient of thermal expansion (linear expansion coefficient [1 / K]) of the substrate material.

Therefore, the extension Δx of the entire substrate is

[0025]

(Equation 1) Becomes

Therefore, if the expression (1) is satisfied, the deformation (extension) of the mirror due to thermal deformation falls within 1 nm or less.
A mirror of sufficient accuracy can be obtained as a mirror of a projection exposure apparatus using lines.

A third means for solving the above-mentioned problem is as follows.
The first means, wherein the metal substrate constituting the metal mirror is an invar-type alloy (Claim 3).

Since the Invar type alloy is a metal having a particularly low coefficient of thermal expansion, a mirror having a small thermal deformation can be obtained by using this as a metal substrate of the mirror.

A fourth means for solving the above-mentioned problem is:
The first means, wherein the metal substrate constituting the metal mirror is aluminum, copper, beryllium, silver, gold, or an alloy containing at least one of these materials ( Claim 4).

These metals have a thermal conductivity of 200 [W / m · K].
This is a preferable material from the viewpoint of heat dissipation.

A fifth means for solving the above problem is as follows.
In any one of the first to fourth means, a surface roughness of an amorphous material constituting the metal mirror is set to 0.5 nm (rms) or less. (Claim 5).

As will be described later, by setting the surface roughness of the amorphous substance to 0.5 nm (rms) or less, the reflectivity with respect to practical X-rays is 80% or more of the reflectivity on a perfectly flat surface. Having a reflectivity of In addition, since the surface roughness of the amorphous material is 0.5 nm (rms) or less, the unevenness of the multilayer film formed thereon is substantially the same,
An optically flat reflector can be obtained.

A sixth means for solving the above-mentioned problem is as follows.
In any one of the first to fifth means, the amorphous substance constituting the metal mirror or a main component of the amorphous substance is nickel or a nickel alloy. (Claim 6).

The nickel alloy can be easily formed on a metal or alloy substrate by plating, and the surface roughness can be reduced to about 0.4 nm (rms) by processing. It is preferable to employ it as a crystalline substance.

A seventh means for solving the above-mentioned problem is as follows.
In any one of the first means to the fifth means, the amorphous material constituting the metal mirror is made of silicon oxide, silicon carbide, PSG (Phospho Silicate Glass), silicon nitride, silicon, carbon or The present invention is characterized by comprising any one of a group consisting of substances containing these as a main component (claim 7).

In these materials, the surface roughness is 0.4 n
m (rms), so that it is preferable to employ the amorphous substance. These substances are
It can be formed by a thin film forming technique such as ordinary vacuum deposition, sputtering, ion plating, and CVD (Chemical Vapor Deposition).

[0037]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention. In FIG. 1, 1 is an X-ray source, 2 and 3 are X-ray multilayer mirrors (illumination system), 4 is a mask stage, 5
Is a reflection mask, 6 to 9 are X-ray multilayer mirrors (projection system),
Reference numeral 10 denotes a wafer stage, and 11 denotes a wafer.

As the X-ray source 1, a laser plasma light source is used. The luminous flux emitted from the X-ray source 1 includes two X-rays.
Is condensed by an illumination optical system composed of linear multilayer mirrors 2 and 3,
The reflection mask 5 held on the mask stage 4 is illuminated. The light beam reflected by the reflection mask 5 passes through a projection optical system composed of four X-ray multilayer mirrors 6 to 9 and reaches a wafer 11 held on a wafer stage 10. The projection optical system transfers an image obtained by reducing the circuit pattern formed on the reflection mask 5 to １ ／ on the wafer 11.

The X-ray multilayer mirrors 2, 3, 6 to 9 and the reflection mask 5 constituting the illumination system and the projection system have a wavelength of 13 nm.
A molybdenum (Mo) / silicon (Si) multilayer film that reflects nearby soft X-rays is used.

The reflectivity of the X-ray multilayer mirror is about 70%, and the remaining 30% is absorbed by the mirror and becomes heat. Each time the X-ray intensity is reflected by the X-ray multilayer mirror, the intensity of the X-rays decreases by the loss due to absorption. Therefore, the intensity of the X-rays incident on the respective X-ray multilayer mirrors is higher in the mirror closer to the X-ray source 11 on the upstream side. To release the absorbed heat,
Each mirror is cooled by means such as water cooling.

Four mirrors 6 to 9 constituting a projection optical system
Are all rotationally symmetric about the optical axis l. The mirror 8 is arranged on the optical axis l, and the effective diameter of the mirror 8 serves as a stop of the projection optical system. Since the mirror 8 is located downstream (third of four images) in the projection system,
Although the X-ray intensity is not so strong, the X-ray irradiation area per unit area is the largest among the four mirrors constituting the projection system because the X-ray irradiation area is small.

Therefore, a mirror made of a metal and a thin film of an amorphous material formed on the surface of the substrate and having an optically polished surface are provided on the mirror 8 having the largest heat load in the projection system. A mirror formed on the surface of the thin film and having a multilayer film for reflecting X-rays of a predetermined wavelength is used.

In particular, the intensity of the X-rays incident on the X-ray multilayer mirrors 2 and 3 of the illumination system disposed immediately after the X-ray source 1 is large, and this becomes a thermal load, which causes deformation of the mirrors and deterioration of the multilayer film. Cause. Therefore, it is preferable to use a mirror which is a feature of the present invention for these mirrors.
Which of the mirrors is a feature that is a feature of the present invention can be appropriately selected and determined.

Hereinafter, an embodiment of a mirror which is a feature of the present invention will be described. FIG. 2 is a diagram showing an example of an embodiment of a mirror according to the present invention. In FIG.
Is a metal substrate, 22 is an amorphous thin film, and 23 is a multilayer film. An amorphous thin film 2 is formed on a metal substrate 1, and a multilayer film 23 for reflecting X-rays of a predetermined wavelength is formed thereon.

The metal substrate 21 may be made of an alloy, and preferably has a high thermal conductivity and a low coefficient of thermal expansion. However, generally, metals and alloys have a large coefficient of thermal expansion.
In an ordinary soft X-ray projection exposure apparatus, the thermal conductivity is preferably 200 [W / m · K] or more in order to suppress the thermal deformation to 1 nm or less. As a substrate material with a thermal conductivity of 200 [W / m · K] or more, aluminum, which has a very large thermal conductivity,
There are copper, beryllium, silver, gold, or alloys containing at least one of these materials.

Using the Rayleigh condition that the wavefront aberration of the optical system is within one-fourth of the wavelength, the shape accuracy per mirror constituting the optical system is (λ / 4 × 1/2) × 1 / N ^1/2 ... (4). Here, n is the number of mirrors constituting the optical system, and the reason why n is multiplied is that it is a reflection system.

According to equation (5), for example, when an optical system composed of four mirrors is used at a wavelength of 13 nm, the shape error (permissible shape error) allowed for one mirror is 0.81.
nm.

The thermal conductivity of fused silica (SiO ₂ ), which is widely used for a refractive optical system of a projection exposure apparatus using ultraviolet light, is 1.38 [W / m · K], and the thermal expansion coefficient is 0.5 × 10 ^−6. [1 / K]. Here, the heat flux Q input to the substrate is 10 [mW / c
m ² ]. In order to ensure a practical exposure area size in an X-ray projection exposure apparatus, the diameter of the mirror needs to be about 50 mm. In order to maintain the shape of the mirror with high precision, the thickness is generally required to be about one quarter of the diameter, and the thickness d of the substrate is set to about 12.5 mm.

When these numerical values are substituted into equation (1), the thermal deformation of the fused quartz is calculated to be 2.83 nm. Thus, when fused quartz is used for the substrate, the thermal deformation amount is a large value far from the allowable error of 0.81 nm,
An X-ray optical system constituted by a mirror using fused quartz as a substrate cannot obtain a diffraction-limited resolution.

Therefore, as the substrate, it is preferable to use the above-mentioned metallic substrate, but it is particularly preferable to use an Invar type alloy having a low coefficient of thermal expansion.

An Invar type alloy is known as a material having a remarkably small coefficient of thermal expansion due to the influence of magnetostriction. Invar type alloys include Fe-Ni alloy, Fe-Ni-Co alloy, Fe-Co-Cr
Alloy, Fe-Pt alloy, Fe-Pd alloy, Zr-Nb-Fe alloy, Cr-Fe-Sn
Alloy, Mn-Ge-Fe alloy, Fe-B amorphous alloy and Fe-Ni-Zr amorphous alloy. Hereinafter, the Invar type alloy is referred to as Invar. Invar has a thermal conductivity of 12.9 [W / m · K] and a thermal expansion coefficient of 0.01 × 10 ⁻⁶ . When the thermal deformation of the invar is calculated from this numerical value by the equation (1), the thermal deformation is 0.097 nm, which can be suppressed sufficiently smaller than the allowable shape error.

However, in general, fine grain boundaries are present in metal, and it is difficult to polish the surface to a smooth surface of the order of nanometers. Alan G. Mic
hette's Optical Systems for X Rays (1986 Plenum
Press, New York) on page 74 describes the surface roughness that can be obtained by polishing for substances that are candidates for mirror materials for X-rays. According to this, the rms value (root mean square value) of the minimum surface roughness obtained for each material is the smallest, 0.4 nm, for fused silica and SiC produced by the CVD (Chemical Vapor Deposition) method. These materials are
Since it is an amorphous substance having no fine structure, a smooth surface can be obtained.

However, in the case of metal Invar,
It can only be processed to a surface roughness of about 2.8 nm (rms). Other metals can be processed only to a surface roughness equal to or less than these.

The surface roughness required for the substrate of the multilayer mirror for X-rays can be calculated by the following equation. R / R ₀ = exp {− (4πσ sin θ / λ) ² } (5) where R ₀ : reflectance when there is no surface roughness R: reflectance when there is scattering loss due to surface roughness σ: surface RMS value of roughness λ: wavelength of X-ray θ: oblique incidence angle Here, when λ = 13 nm, θ = 90 ° (normal incidence), the value of R / R ₀ with respect to surface roughness σ is shown in FIG. Shown in

As is apparent from this figure, the surface roughness is 0.4 n
If m (rms) SiC or fused quartz is used for the substrate of the multilayer mirror, it is possible to obtain a reflectance close to 90% in an ideal case where there is no roughness, but the surface roughness is about 2.8 nm (rms). When used for a substrate, X-rays are not reflected at all.

Therefore, the present inventors have conducted intensive studies and found that if an amorphous material layer capable of reducing the surface roughness is formed on the surface of a metal such as Invar having a small thermal deformation, the thermal deformation and the surface roughness can be reduced. In each case, it has been found that a sufficiently small mirror substrate can be manufactured.

That is, as shown in FIG. 2, a thin film layer of an amorphous substance (for example, an amorphous thin film layer of a nickel alloy or an amorphous thin film layer mainly containing a nickel alloy) is formed on a metal such as Invar. ) To form an optically flat surface by processing (eg, cutting, grinding, polishing) the surface, and further forming an X-ray reflection multilayer film on the processed amorphous material thin film layer. By using a multilayer mirror, a mirror having both sufficiently small thermal deformation and low surface roughness can be manufactured.

Since such a metal mirror has a small thermal deformation and excellent heat radiation, the projection optical property formed by using the metal mirror has an optical characteristic even when irradiated with strong soft X-rays. There is no deterioration. Therefore, a soft X-ray projection exposure apparatus having a projection system using a metal mirror can realize a higher throughput than before.

As is apparent from FIG. 3, if the surface roughness (rms) of the thin film layer of the amorphous substance is set to 0.5 nm or less, the decrease in reflectance can be suppressed to 20% or less. preferable. When the surface roughness exceeds this, the reflectance sharply decreases.

According to the book of Michette, the surface roughness of nickel formed by electroless plating is 1.1 nm. However, SiC or fused silica has been developed due to recent advances in processing (for example, cutting, grinding, polishing). Processing with a small surface roughness comparable to that of. Therefore, in this embodiment, an amorphous thin film layer of a nickel alloy or an amorphous thin film layer containing a nickel alloy as a main component is employed as the thin film layer of the amorphous substance. Since the surface roughness of these amorphous thin film layers can be set to 0.4 nm (rms) as described above, FIG.
As can be seen from the figure, the decrease in the reflectance of the multilayer mirror due to the surface roughness is within 10%, and a sufficiently high reflectance can be obtained.

Silicon oxide (SiO ₂ ), silicon carbide (SiC) or the like can be used as the thin film layer of the amorphous substance. According to the book of Michette, since the surface roughness of SiO ₂ , SiC, etc. can be 0.4 nm (rms), as can be seen from FIG.
%, And a mirror having sufficiently high reflectance can be obtained.

Amorphous thin films such as SiO ₂ and SiC can be formed by ordinary vacuum evaporation, sputtering, ion plating, CVD, etc.
(Chemical Vapor Deposition) or the like. When forming a thin film on a metal substrate such as Invar, if the substrate temperature at the time of film formation is too high, it is not preferable because oxidation or crystallization of the surface of the metal substrate causes an increase in surface roughness. Film formation at room temperature is possible by vacuum evaporation, sputtering or ion plating. In the case of using CVD, it is preferable to use plasma CVD or optical CVD which can form a film at a low temperature from room temperature to about 300 ° C., instead of thermal CVD formed at a high temperature of 1000 ° C. or higher.

The material of the amorphous thin film formed on the surface of the metal substrate is not particularly limited as long as the material can polish the surface smoothly. Since the thickness is as thin as several μm,
It is not restricted by the thermal conductivity and thermal expansion coefficient. For example, in addition to the nickel alloy, silicon oxide (SiO ₂ ), and silicon carbide (SiC), PSG (Phospho Silicate Glas
s), silicon nitride (Si ₃ N ₄ ), silicon (Si), carbon (C), and the like.

As is apparent from the equation (1), the deformation amount Δx is proportional to α (thermal expansion coefficient) / η (thermal conductivity).
Therefore, in order to reduce the thermal deformation, it is also effective to use a metal having a large thermal conductivity as described above in addition to a metal having a small thermal expansion coefficient such as Invar.

For fused quartz, α / η is 3.62 × 10 ⁻⁷ [m / W]
It is. Since the coefficient of thermal expansion of aluminum is 25 × 10 ⁻⁶ / K and the thermal conductivity is 237 [W / m · K], α / η is 1.05 × 10 ⁻⁷ [m /
W]. Since the coefficient of thermal expansion of copper is 16.6 × 10 ⁻⁶ / K and the thermal conductivity is 401 [W / m · K], α / η is 4.14 × 10 ⁻⁸ [m / W]. Since the thermal expansion coefficient of beryllium is 12 × 10 ⁻⁶ / K and the thermal conductivity is 201 [W / m · K], α / η is 5.95 × 10 ⁻⁸ [m / W]. The coefficient of thermal expansion of silver is 19 × 10 ^-6 / K, and the thermal conductivity is 429 [W /
m · K], α / η is 4.43 × 10 ⁻⁸ . Since the thermal expansion coefficient of gold is 14.2 × 10 ⁻⁶ / K and the thermal conductivity is 318 [W / m · K], α
/ Η is 4.47 × 10 ⁻⁸ [m / W].

As described above, when metals such as aluminum, copper, silver, beryllium, and gold are used, the value of α (thermal expansion coefficient) / η (thermal conductivity) becomes 1 /
The deformation amount can be reduced to 3 to 1/9, and therefore, the deformation amount Δx can be suppressed accordingly. In a metal having a general thermal expansion coefficient, the thermal conductivity is 200 [W /
By using a material having a value of m · K or more, the amount of deformation of the mirror can be suppressed to 1 nm or less.

[0067]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the mirror according to the present invention will be described in more detail.

Example 1 An amorphous thin film of a nickel alloy (Ni 90 wt% -P 10 wt%) was formed on the surface of Invar by electroless plating, and the surface was processed (cut, ground, polished) to obtain the required surface. The surface of the processed amorphous thin film is made rough, and an X-ray reflective multilayer film is formed on the thin film to have a diameter of 50 mm and a radius of curvature of 50.
An X-ray multilayer mirror having a thickness of 0 mm and a center thickness of 12.5 mm was manufactured. The manufacturing steps will be described in order with reference to FIG.

First, the Invar material was cut to a diameter of 50.
mm, a center thickness of 12 mm, a concave surface having a curvature radius of 500 mm on the front surface, and a flat back surface made of Invar.

Then, the surface of the substrate (the surface on which the thin film is to be formed) is finished to a mirror surface with a surface roughness of 10 nm (rms) or less by electrolytic polishing, and then the surface is electrolessly plated with a nickel alloy (Ni90 wt% -P10 wt% ) Amorphous thin film 2
2 was formed to a thickness of 500 μm.

Next, the surface of the amorphous thin film 22 was ground and polished to smooth the surface until the surface roughness became 0.4 nm (rms). Thus, a substrate for an X-ray mirror having the amorphous thin film 22 made of a nickel alloy formed on the Invar substrate 21 was manufactured.

Finally, a cycle length of molybdenum (Mo) and silicon (Si) is formed by ion beam sputtering.
An X-ray reflective multilayer film 23 of 6.7 nm and 50 layers was formed on the surface of the substrate to complete an X-ray multilayer mirror.

If the rear surface of the multilayer mirror is cooled and maintained at a constant temperature, even if a heat flux of 10 [mW / cm ² ] is incident on the entire surface or a part thereof, the thermal deformation is 0.1 nm or less. Thus, a diffraction-limited optical system using X-rays having a wavelength of 13 nm can be configured.

Therefore, this reflecting mirror was adopted as the mirror 8 having the largest heat load in the projection system of the soft X-ray projection exposure apparatus shown in FIG. Under a condition to obtain a throughput of 30 sheets / hour, the X-ray intensity incident on the mirror 8 is about 30 [mW / c
m ² ]. Approximately 9% [mW / cm ² ] of 30% of the X-rays incident on the mirror 18 is absorbed and becomes a heat load, but the thermal deformation is 0.1%.
nm or less, and was sufficiently usable as a mirror for a high-throughput soft X-ray projection projection exposure apparatus using X-rays having a wavelength of 13 nm.

(Example 2) An amorphous thin film of silicon oxide (SiO ₂ ) was formed on the surface of Invar by sputtering.
The surface is processed (cut, ground, polished) to the required surface roughness, and an X-ray reflective multilayer film is formed on the surface of the processed amorphous thin film to have a diameter of 50 mm, a radius of curvature of 500 mm, and a center thickness of 1 mm.
A 2 mm X-ray multilayer mirror was manufactured. The manufacturing steps will be described in order with reference to FIG.

First, the Invar material was cut to a diameter of 50.
mm, a center thickness of 12 mm, a concave surface having a curvature radius of 500 mm on the front surface, and a flat back surface made of Invar. Then, the substrate surface (the surface on which the thin film is formed) is finished to a mirror surface having a surface roughness of 10 nm (rms) or less by electrolytic polishing, and then an amorphous thin film 22 made of SiO _{2 is} formed on the surface by high-frequency magnetron sputtering. It was formed to have a thickness of 5 μm.

Next, the surface of the amorphous thin film 22 was ground and polished to smooth the surface until the surface roughness became 0.4 nm (rms). In this way, the SiO ₂ substrate 1
A substrate for an X-ray mirror on which an amorphous thin film 22 made of was formed.

Finally, a cycle length of molybdenum (Mo) and silicon (Si) is formed by ion beam sputtering.
An X-ray reflective multilayer film 23 of 6.7 nm and 50 layers was formed on the surface of the substrate to complete an X-ray multilayer mirror.

If the rear surface of the multilayer mirror is cooled and maintained at a constant temperature, even if a heat flux of 10 [mW / cm ² ] is incident on the entire surface or a part thereof, the thermal deformation is 0.1 nm or less. Thus, a diffraction-limited optical system using X-rays having a wavelength of 13 nm can be configured.

Therefore, this reflecting mirror was adopted as the mirror 8 having the largest heat load in the projection system of the soft X-ray projection projection exposure apparatus shown in FIG. Under a condition to obtain a throughput of 30 sheets / hour, the X-ray intensity incident on the mirror 8 is about 30 [mW / c
m ² ]. Approximately 9% [mW / cm ² ] of 30% of the X-rays incident on the mirror 18 is absorbed and becomes a heat load, but the thermal deformation is 0.1%.
nm or less, and was sufficiently usable as a mirror for a high-throughput soft X-ray projection projection exposure apparatus using X-rays having a wavelength of 13 nm.

(Embodiment 3) Plasma C is applied to the surface of the invar.
An amorphous thin film of silicon carbide (SiC) is formed by VD, and the surface is processed (cut, ground, polished) to a required surface roughness, and an X-ray reflective multilayer film is formed on the surface of the processed amorphous thin film. Forming, diameter 50mm, radius of curvature 500mm, center thickness 12m
m x-ray multilayer mirrors were manufactured. The manufacturing steps will be described in order with reference to FIG.

First, the invar material was cut to a diameter of 50.
mm, a center thickness of 12 mm, a concave surface having a curvature radius of 500 mm on the front surface, and a flat back surface made of Invar. Then, the surface of the substrate (the surface on which the thin film is formed) is finished to a mirror surface with a surface roughness of 10 nm (rms) or less by electrolytic polishing, and then the surface is formed from SiC by plasma CVD using SiCl ₄ and CH ₄ gas as raw materials. The amorphous thin film 22 was formed to have a thickness of 50 μm.

Next, the surface of the amorphous thin film 22 was ground and polished to smooth the surface until the surface roughness became 0.4 nm (rms). In this way, the SiC is placed on the Invar substrate 21.
A substrate for an X-ray mirror on which an amorphous thin film 22 made of was formed.

Finally, an X-ray reflective multilayer film 23 composed of molybdenum (Mo) and silicon (Si) and having a cycle length of 6.7 nm and 50 layers is formed on the surface of the substrate by high-frequency magnetron sputtering. Completed the mirror.

If the rear surface of the multilayer mirror is cooled and maintained at a constant temperature, even if a heat flux of 10 [mW / cm ² ] is incident on the entire surface or a part thereof, the thermal deformation is 0.1 nm or less. Thus, a diffraction-limited optical system using X-rays having a wavelength of 13 nm can be configured.

Therefore, this reflecting mirror was adopted as the mirror 8 having the largest heat load in the projection system of the soft X-ray projection exposure apparatus shown in FIG. Under a condition to obtain a throughput of 30 sheets / hour, the X-ray intensity incident on the mirror 8 is about 30 [mW / c
m ² ]. Approximately 9% [mW / cm ² ] of 30% of the X-rays incident on the mirror 18 is absorbed and becomes a heat load, but the thermal deformation is 0.1%.
nm or less, and was sufficiently usable as a mirror for a high-throughput soft X-ray projection projection exposure apparatus using X-rays having a wavelength of 13 nm.

[0087]

As described above, in the soft X-ray projection exposure apparatus according to the present invention, the projection optical system has a small shape error and a small surface roughness, and has a thermal deformation caused by irradiation light such as X-rays. Is used, the imaging characteristics are not degraded due to thermal deformation even when strong soft X-rays are irradiated to increase the throughput. Therefore, the soft X-ray projection exposure apparatus according to the present invention can achieve both high resolution and high throughput.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of an embodiment of a mirror according to the present invention.

FIG. 3 is a diagram illustrating thermal deformation of a substrate constituting a mirror.

FIG. 4 is a diagram showing a difference in reflectance of a multilayer mirror due to the surface roughness of a substrate constituting a mirror.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray source 2, 3 X-ray multilayer mirror (illumination system) 4 Mask stage 5 Reflection mask 6-9 X-ray multilayer mirror (projection system) 10 Wafer stage 11 Wafer 21 Metal substrate 22 Amorphous thin film 23 X Line reflective multilayer film

Claims (7)

[Claims] 1. A metal mirror is used for a part or all of a mirror constituting an illumination optical system or a projection optical system, and the metal mirror is formed on a metal substrate and a surface of the metal substrate, A soft X having a thin film of an amorphous substance whose surface is polished optically smooth, and a multilayer film formed on the surface of the thin film and reflecting X-rays of a predetermined wavelength.
Line projection exposure equipment. 2. The metal substrate constituting the metal mirror has a thermal conductivity of η [W / m · K], a linear expansion coefficient of α [1 / K], and a heat flux from light rays or X-rays to the mirror. When Q is [W / m ² ] and the average thickness of the mirror is d [m], α · Q · d ² / (2η) ≦ 10 ⁻⁹ [m] is satisfied. 2. The soft X-ray projection exposure apparatus according to 1. 3. The soft X-ray projection exposure apparatus according to claim 1, wherein the metal substrate constituting the metal mirror is an invar alloy. 4. The method according to claim 1, wherein the metal substrate constituting the metal mirror is aluminum, copper, beryllium, silver, gold or an alloy containing at least one of these materials. Soft X-ray projection exposure apparatus. 5. The semiconductor device according to claim 1, wherein the surface roughness of the amorphous material constituting the metal mirror is 0.5 nm (rms) or less. The soft X-ray projection exposure apparatus as described in the above. 6. The amorphous material or a main component of the amorphous material constituting the metal mirror is nickel or a nickel alloy. Item 4. The soft X-ray projection exposure apparatus according to item 1. 7. The amorphous material constituting the metal mirror is made of silicon oxide, silicon carbide, PSG (Phospho Silicate G).
6. The semiconductor device according to claim 1, comprising one of the group consisting of: silicon), silicon nitride, silicon, carbon, and a substance containing these as main components.
Item 4. The soft X-ray projection exposure apparatus according to item 1.