JP3395224B2 - Thin film forming method and apparatus, and optical component - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to so-called PVD (Physical Vapor Deposit) such as vacuum deposition and sputtering.
(abbreviation of ion) method, a thin film forming method and an apparatus used therefor, and an optical component manufactured by the thin film forming method .

[0002]

2. Description of the Related Art Generally, the surface of optical components such as lenses and mirrors is coated with a thin film for the purpose of adjusting reflectance and improving surface strength. This type of thin film is usually formed by a thin film forming method such as vacuum deposition or sputtering. As a means for controlling the film thickness distribution, a method of rotating the substrate to be film-formed and covering its surface with a mask is used. It has been known. An example thereof is shown in FIG. The illustrated example shows a lens 10 placed in a vacuum chamber (not shown).
In the state where a part of the surface 100a of 0 is covered with the mask 101, the lens 100 is relatively rotated around the optical axis O with respect to the mask 101, and the evaporation material of the thin film material coming from an evaporation source (not shown) is moved to the lens. The film is formed on the surface 100a of 100 by being incident on it in parallel with the optical axis O (direction orthogonal to the paper surface). In this method, the film thickness at the position separated from the optical axis O by the distance r is determined by the radial width r · ω (r) of the mask 101 at the same position.
By appropriately changing the contour shape of No. 1, the film thickness distribution can be arbitrarily controlled.

[0003]

In recent years, diffraction of optical instruments
The wavelength is 10 to 200 to increase the limit resolution.Å
Of an optical system using soft X-rays of about (angstrom)
R & D is actively carried out. In this X-ray optical system
Can use conventional optical components for visible light and ultraviolet light.
Flaws, especially those with a multilayer film formed for X-rays
Is required. This X-ray multilayer film has visible wavelengths
The cycle length of the film is extremely short because it is 1 to 2 orders of magnitude shorter than light and ultraviolet light.
Very small and very little reflection of X-rays on each layer of the film
Therefore, the number of layers is several tens to several hundreds.
different. Due to this feature, the reflection on the multilayer film for X-rays is
Shows the characteristics close to the Bragg diffraction of crystal, and the following Bragg equation
The wavelength of X-ray, the incident angle, and the
A peak appears in the reflectance only in a narrow range centered on the cycle length.
Be done. X-ray wavelength, incident angle and cycle length of multilayer film
If any one of them goes out of the allowable range, X-rays will be totally reflected.
However, the allowable range is narrowed in inverse proportion to the number of stacked multilayer films.
Become

[Equation 1] Here, d is the cycle length of the multilayer film, ν is the incident angle measured from the reflecting surface, λ is the wavelength of the X-ray, and n is an integer. In this specification, unless otherwise specified, the angle of the incident light measured from the reflecting surface, that is, the angle formed by the reflecting surface and the incident light is referred to as the incident angle.

When a multilayer mirror having a concave mirror or a convex mirror coated with a multilayer film for X-rays is used in a monochromatic X-ray reflection optical system, the incident angle of the X-ray becomes smaller toward the peripheral portion of the mirror. Therefore, the cycle length of the multilayer film that satisfies the Bragg equation becomes longer toward the periphery of the mirror. That is, the film thickness increases toward the periphery of the mirror. If such a film thickness distribution is to be obtained by the film thickness control method shown in FIG. 8, the allowable error range of the cycle length of the multilayer film becomes narrow due to the large number of laminated X-ray multilayer films. In addition, since the mask profile shape determines the film thickness distribution, the mask dimensional error tolerance is narrow, and the mask mounting error tolerance is narrow, so it is possible to obtain a film thickness distribution with satisfactory accuracy. It was rare and unsuitable as a method for forming a multilayer film for X-ray.

The present invention is directed to a thin film forming method capable of improving the accuracy of film thickness distribution more than ever before, an apparatus used for the method, and
An object of the present invention is to provide an optical component manufactured by the method for forming a thin film .

[0006]

With reference to FIG. 1, in the method of the present invention, the substrate 1 having a spherical surface is centered on a rotation axis CL which is inclined at a constant angle from the direction in which the evaporation material E is flying. By achieving relative rotation with respect to the evaporation source 2 and covering a part of the surface 1a of the substrate 1 with the mask member 3 which is held at a fixed position with respect to the evaporation source 2, the above-described object is achieved. Further, in the apparatus of the present invention, relative rotation means for rotating the substrate 1 having the spherical surface relative to the evaporation source 2 about the rotation axis CL inclined at a constant angle α from the flying direction of the evaporation material E, and the substrate. By providing the mask member 3 which is held at a fixed position with respect to the evaporation source 2 and relatively covers a part of the surface 1a of the substrate 1 during relative rotation of 1, the above-described object is achieved. At this time, the angle α is set by the holder tilting device 12, which is an angle changing means, so that the thin film has a predetermined film thickness distribution. Furthermore, the invention of claim 3 is an optical component manufactured by the thin film forming method of claim 1.

[0007]

When the thin film is coated on the substrate of the convex mirror or concave mirror used in the X-ray optical system, as shown in FIG.
It is expected that the film thickness distribution will be changed by inclining the rotation axis CL with respect to the direction in which the evaporation material E is flying (the direction of the arrow in the drawing) while rotating the rotation axis CL around the rotation axis CL. Below, the film thickness distribution when the rotation axis of the substrate having a spherical concave surface is inclined will be calculated.

As shown in FIG. 3, two vectors A and B are taken in a three-axis orthogonal coordinate system in which the center of curvature of the surface of the substrate is the origin and the rotation axis of the substrate is the z axis. The vector A is a unit vector representing the incident direction of the vaporized substance and is taken in the xz plane. It is considered that the evaporated material E flies in the direction of the vector A while maintaining a uniform density distribution. The angle formed by the vector A and the z axis (the rotation axis of the substrate) is α. The vector B is a vector indicating an arbitrary minute area on the spherical surface from the center of the sphere, and faces the normal direction of the spherical surface. The projection length of the vector B on the xy plane is r, the angle formed with the x axis is β, and the radius of the sphere is R. Under the above conditions, the vectors A and B have the following formula 2
It is represented by.

[Equation 2] Assuming that the angle formed by the vectors A and B, that is, the inclination of the minute area defined by the vector B with respect to the flying direction of the evaporation material is θ, the film thickness d (r;
α, β) is proportional to cos θ, so

[Equation 3] Becomes If the substrate is rotating at a constant velocity around the z axis,
Formula 3 is integrated with respect to β by 0 to 2π,

[Equation 4] Becomes

That is, if the rotation axis of the substrate is tilted only with respect to the flying direction of the evaporation material, the film thickness d as a whole becomes larger than that in the case where the rotation axis and the flying direction of the evaporation material match (α = 0). However, the film thickness decreases as the angle φ formed by the normal line at each position on the surface of the substrate and the rotation axis of the substrate increases, and the film rotates thicker in the vicinity of the rotation axis. Only thin films can be obtained that are thinned in the periphery away from the axis. Although the spherical surface is considered to be concave in FIG. 3,
It can be easily confirmed that the formula 4 is exactly the same for the convex surface.

From the above, it has been found that the film thickness distribution cannot be arbitrarily controlled only by inclining the rotation axis of the substrate with respect to the direction in which the evaporation material comes in. However, the inventor here finds that when a part of the surface of the substrate is covered with a mask member while inclining the rotation axis of the substrate from the flying direction of the evaporation material, the film thickness distribution may change according to the inclination angle of the rotation axis. I noticed. This will be described below.

For example, as shown in FIG. 1, consider a case where the mask member 3 having a half-moon shaped opening 3a covers the upper half (upper side of FIG. 1) of the substrate 1 whose surface 1a is a spherical convex surface. . The same applies when the lower half of the concave surface is covered. When Equation 4 is integrated with respect to β in the range of −π / 2 to π / 2,

[Equation 5] When standardized to be 1 when r = 0,

[Equation 6] In addition to the term that decreases in proportion to cosφ of the first term, the term that increases in proportion to sinφ is added to the second term. Therefore, cos when the mask member 3 is not provided
A more uniform film thickness distribution than φ can be obtained. The ratio of the second term to the first term changes depending on tan α. That is, the film thickness distribution can be controlled using the inclination angle α of the rotation axis CL of the substrate 1 as a parameter. If the parameter that can control the film thickness distribution increases, the mask member 3
The influence of the shape dimension error and the mounting error of the mask member 3 on the accuracy of the film thickness distribution becomes relatively smaller than that of the conventional example which depends only on the above, and the allowable range for the accuracy and the mounting position of the mask member 3 is expanded accordingly. To do. If the allowable range of the shape error of the mask member 3 is expanded, it becomes possible to simplify the shape of the mask member 3 and share the mask member 3 among a plurality of types of substrates.

In the above description, the case where the half of the spherical substrate 1 is covered with the mask member 3 has been described for the sake of simplicity, but the shape of the mask member 3 is not limited to the illustrated example. For example, as shown in FIG. 4, a mask member 4 having a fan-shaped opening 4a may be used. In the film thickness distribution in this case, the integration range of Expression 4 is changed to β1 to β2. That is,

[Equation 7] If β1 = −β2,

[Equation 8] The ratio of the second term to the first term when β2 is changed is

[Equation 9] Changes in proportion to. This expression is 1 when β2 is 0, and monotonically decreases as β2 increases, and becomes 0 when β2 is π. This means that the narrower the angle of the fan-shaped opening 4a, the greater the effect of tilting the substrate appears.

Although the case where the surface of the substrate is spherical has been described above, the present invention is also effective for substrates having an aspherical surface such as a paraboloid of revolution, a ellipsoid of revolution, and a hyperboloid of revolution. The film thickness distribution in these cases can be easily obtained by changing a part of the calculation already described. Although a spherical surface having a radius R centered on the origin is considered in FIG. 3, when considering a quadratic curved surface that contacts such spherical surface in the limit where the x and y coordinates are sufficiently small, this curved surface is given by the following equation.

[Equation 10] Here, R is the radius of curvature of the curved surface at x = y = 0. κ is a parameter representing the shape of the quadric surface as follows. κ <0: hyperboloid of revolution κ = 0: paraboloid of revolution 0 <κ <1: spheroid rotated about the minor axis κ = 1: spherical κ> 1: spheroid rotated about the major axis

In the case of a spherical surface, the position vector B of each point on the curved surface matches the normal vector of the curved surface at that position, but they do not match on a general quadric surface. Therefore, considering the normal vector N again, the vector N is given by the following equation from the slope dz / dr of the tangent of the curved surface (where r ² = x ² + y ² ).

[Equation 11] For example, in the case of a paraboloid of revolution, vector B and vector N
Is as follows.

[Equation 12]

By obtaining the vector N as described above, replacing the vector B in the equation 3 with the vector N, and performing subsequent calculations, the film thickness distribution in the case of the aspherical surface can be calculated in the same manner as in the case of the spherical surface.

In the above, the evaporation source 2 and the mask member 3 are fixed, and the substrate 1 is rotated about the rotation axis CL which is inclined by a constant angle α with respect to the flying direction of the evaporation material E, but these operations are performed. It is relative, and the same effect can be obtained by moving the evaporation source 2 side. FIG. 5A shows the evaporation source 2 provided so as to be movable in a plane orthogonal to the rotation axis CL of the substrate 1. The position of the evaporation source 2 is adjusted so that the rotation axis CL of the rotation direction CL with respect to the flying direction of the evaporation material E is changed. After setting the tilt angle to the desired value,
While rotating the substrate 1 about its rotation axis CL,
The mask member 3 is fixed to the evaporation source 2 to obtain the same relative movement as in FIG. Further, in the example of FIG. 5B, while the substrate 1 is fixed, the evaporation source 2 is swung along a circle having a predetermined radius centered on the rotation axis CL, and the mask member is synchronized with the evaporation source 2. 3 is rotated about the rotation axis CL to obtain the same relative movement as in FIG. Although the substrate 1 and the mask member 3 are drawn in a flat plate shape in FIG.
The surface of is a concave or convex curved surface described above, and the mask member 3 is also appropriately inclined according to the curvature of the surface of the substrate 1.

[0017]

EXAMPLE An example in which the present invention is applied to an ion beam sputtering apparatus to form a multilayer film mirror for soft X-rays will be described below with reference to FIGS. 6 and 7. First, the outline of the apparatus used in this embodiment will be described with reference to FIG. In the figure, 10 is a holder that holds the substrate 1 by a plurality of claws 10a that engage with the outer peripheral edge of the surface 1a of the substrate 1, and 11 is an actuator (not shown) such as a motor that rotates the holder 10 around the rotation axis CL. A holder rotating device 12 is a holder tilting device that rotates a housing 11a of the holder rotating device 11 around a shaft 12a by an actuator (not shown) such as a motor. A mask bracket 13 is attached to the front side end of the housing 11 a of the holder rotating device 11. The mask bracket 13 receives the outer peripheral portion of the mask member 3 in the slit 13 a at the tip thereof and holds the mask member 3 in a state of facing the surface 1 a of the substrate 1 mounted on the holder 10.

Below the holder 10, an evaporator supply device 14 is provided.
Is provided. The vaporizer supply device 14 collides an ion beam extracted from an ion source (not shown) with a target TG made of a thin film material to generate a vaporized substance E of the thin film material. The target TG is a horizontal moving mechanism (not shown). Is movable in the horizontal direction (direction of arrow Y1 in FIG. 6). The holder 10, the holder rotating device 11, the holder tilting device 12, the mask bracket 13, and the target TG are housed in a chamber (not shown) connected to a vacuum pump.

In the above apparatus, the substrate 1 is placed on the holder 10.
Is mounted so that its center coincides with the rotation axis CL, and the holder tilting device 12 rotates the holder 10 and the holder rotating device 11 around the shaft 12a by a predetermined angle to adjust the tilt of the rotation axis CL. , Target TG
The horizontal position of was adjusted to set the inclination angle α of the rotation axis CL of the holder 10 to 25 ° with respect to the flying direction of the evaporated material E.
The substrate 1 is made of synthetic quartz and has an outer diameter of 16 mm and a radius of curvature of 50.
It was a convex spherical mirror of mm. This substrate 1 is one of the Schwarzschild mirrors composed of two spherical mirrors.
Due to the difference in the incident angle of the line depending on the location, as shown by the broken line in FIG. 7, a film thickness distribution is required in which the central part of the mirror is thin and the peripheral part is thick.

After adjusting the inclination of the rotation axis CL, the surface 1a of the substrate 1 is covered with a mask member 3 equivalent to that shown in FIG.
While covering the upper half (on the left side of the rotation axis CL in FIG. 6) of the chamber and evacuating the chamber 1 while rotating the substrate 1 around the rotation axis CL by the holder rotation device 11,
An ion beam was made to collide with the target TG to generate an evaporated material E, and a thin film was formed. This thin film is formed repeatedly for two kinds of thin film materials by exchanging the target TG every time one of the two kinds of thin films is formed to have a constant thickness. A carbon thin film and 50 layers were alternately formed so that the cycle length of the film was 22.5 Å at the center of the substrate 1.

The distribution of the period length of the multilayer film obtained by the above operation is shown by white circles in FIG. The deviation from the required film thickness distribution could be suppressed within 0.2 Å (within 1% of the cycle length of the central part). When the conventional method of controlling the film thickness with only the mask shown in FIG. 8 was tried on the substrate 1 having the same shape as the above, a reproducible film thickness distribution could not be obtained. A Schwarzschild mirror is constructed by using the multilayer film mirror prepared according to this embodiment, and K of carbon is used.
An experiment was performed to obtain a magnified image of the mesh using α characteristic X-rays (wavelength 45 Å ), and a reflection image with uniform brightness was obtained over the entire area. This indicates that the film cycle length is within the allowable range determined by the Bragg equation over the entire surface of the multilayer film mirror.

In the present embodiment, the mask member 3 similar to that shown in FIG. 1 covers the upper half of the surface 1a of the substrate 1 (the side on which the incident angle with respect to the evaporated material E becomes smaller) to cover the film on the peripheral portion of the substrate 1. Although the thickness is increased, the present invention is not limited to such an aspect. Contrary to FIG. 7, when a thick film thickness in the central portion and a thin film thickness in the peripheral portion are required, the mask member 3 is attached to the opposite side in the example of FIG. 6 to evaporate the lower half of the convex spherical surface, that is, the substrate surface 1a. It suffices to cover the side on which the incident angle on the object E is large.

In the correspondence between the above embodiment and the claims,
The rotation axis CL of the holder 10 is the rotation axis of relative rotation of the substrate with respect to the evaporation source, and the holder 10, the holder rotation device 11,
The holder tilting device 12 and the horizontal moving mechanism of the target TG form a relative rotating unit, and the target TG forms an evaporation source. However, the present invention is not limited to such an embodiment. For example, when a thin film is formed by vacuum vapor deposition, a thin film material serving as an evaporation source is put into a crucible to generate an evaporate by resistance heating or electron beam heating. Alternatively, Knudsen cell may be used. Even in the case of sputtering, not only an example of collision with an ion beam but also direct current or high frequency current may be applied to the target to generate glow discharge.

The present invention is not limited to the manufacture of a multilayer mirror for X-rays, but can be applied to the formation of a thin film of an optical system for other wavelength regions such as visible light and ultraviolet light. Besides, it can be applied to all fields in which the film thickness distribution needs to be controlled with high accuracy.

[0025]

As described above, according to the thin film forming method of the present invention, the film thickness distribution can be controlled not only by the shape and mounting position of the mask member but also by the inclination of the rotation axis of the substrate. The influence of the shape error and mounting position error on the film thickness distribution is smaller than the conventional example in which the film thickness distribution is determined only by the mask member, and the film thickness distribution can be managed with higher accuracy than before and the mask member The allowable range of error related to shape and mounting position is expanded. The shape of the mask member can be simplified in accordance with the expansion of the allowable range for the shape of the mask member, and the mask member can be commonly used for a plurality of types of substrates. According to the thin film forming apparatus of the present invention, it is possible to easily form a thin film having a high film thickness distribution accuracy by performing the above-described thin film forming method. In addition, the optical of the present invention
The component has a highly accurate controlled film thickness distribution.

[Brief description of drawings]

1A and 1B are diagrams for explaining a thin film forming method according to the present invention, in which FIG. 1A is a diagram showing a state of a substrate and its surroundings viewed from a side of the substrate, and FIG. 1B is an arrow in FIG. The figure which shows the state seen from the Ib direction.

FIG. 2 is a diagram showing a state in which the rotation axis of the substrate is tilted from the flying direction of the evaporation material.

FIG. 3 is a diagram showing a coordinate system for calculating a film thickness distribution.

FIG. 4 is a view showing an example in which a mask member is changed from FIG.
(A) is a figure which shows the state which looked at a board | substrate and its periphery from the side of a board | substrate, (b) is a figure which shows the state seen from the arrow IVb direction of the same figure (a).

FIG. 5 is a diagram showing another example of FIG. 1, in which (a) is a diagram showing a case where the evaporation source is moved in a plane orthogonal to the rotation axis;
FIG. 6B is a diagram showing a case where the evaporation source and the mask are rotated in synchronization around the rotation axis.

FIG. 6 is a diagram showing a main part of a thin film forming apparatus used in Examples.

FIG. 7 is a diagram showing a relationship between a film thickness distribution formed in the example and an ideal film thickness distribution.

FIG. 8 is a diagram for explaining a conventional film thickness control method.

[Explanation of symbols]

1 substrate 1a Substrate surface 2 evaporation sources 3,4 Mask member 10 holder 11 Holder rotation device 12 Holder tilting device 13 Mask bracket 14 Evaporated matter supply device CL substrate rotation axis E evaporation TG target

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Claims (3)

(57) [Claims] 1. An evaporation material of a thin film material coming from an evaporation source is treated as a spherical surface, a paraboloid of revolution, or an ellipsoid of revolution formed on a substrate.
And a thin film forming method for forming a thin film by adhering to a curved surface having a rotation axis such as a hyperboloid of rotation , the rotation axis is tilted at a constant angle from the flying direction of the evaporation material.
The substrate is inclined, the substrate is rotated relative to the evaporation source about the rotation axis, and a part of the curved surface is covered by a mask member held at a fixed position with respect to the evaporation source. Thin film forming method. 2. The evaporation material of the thin film material coming from the evaporation source is converted into a spherical surface, a paraboloid of revolution, or an ellipsoid of revolution formed on the substrate.
And a thin film forming apparatus for forming a thin film by adhering to a curved surface having a rotation axis such as a rotating hyperboloid, the rotation axis is tilted at a constant angle from the flying direction of the vaporized material.
Is oblique, relative rotation means for relatively rotating with respect to the evaporation source said substrate about the axis of rotation, an angle changing means for changing the inclination angle of the rotation axis, to the evaporation source during the relative rotation of the substrate On the other hand, a mask member that is held at a fixed position and covers a part of the curved surface is set, and the tilt angle is set so as to obtain a predetermined film thickness distribution.
Thin film forming apparatus and forming a thin film by. 3. An optical component manufactured by the thin film forming method according to claim 1.