JPH06175057A - Optical scanning device - Google Patents

Abstract

PURPOSE:To improve throughput without making the diameter of a beam spot large or to make the diameter of a beam spot small without lowering throughput. CONSTITUTION:In a scanning optical device scanning a surface to be examined 20 by condensing a luminous flux on the surface to be examined 20, a reflection type scanning means 15 having a rectangular reflection surface 15a is arranged at the condensing position of condensing optical systems 12-14 linearly condensing the luminous flux from a light source means 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device for scanning a surface to be inspected with condensed light.

[0002]

2. Description of the Related Art Conventionally, for example, a scanning optical device shown in FIG. 9 has been known as a scanning optical device for performing an apparatus on a surface to be inspected by means of condensed light. In this scanning optical device, the light source 91
The parallel light beam from the negative lens 92 and the sex lens
The beam diameter is expanded by the beam expander 92,93 consisting of 93 and the optical axis of the beam expander 92,93.
It reaches the vibrating mirror 95 as a parallel beam along the Ax ₄ . Then, the parallel beam is deflected by the vibrating mirror 95 and forms a beam spot on the scanning object 99 on the surface 20 to be inspected via the scanning lens 97.

The vibrating mirror 95 is provided so as to be able to vibrate in the direction of the arrow in the drawing about the vibration center axis Ax ₆ .
With the vibration of the vibrating mirror 95, the deflection direction of the parallel beam incident on the scanning lens 97 changes, and the scanning line on the surface 20 to be inspected
The beam spot is scanned along 99.

[0004]

However, in the conventional scanning optical device as described above, in order to reduce the spot size of the scanning beam on the surface to be inspected, it is necessary to increase the numerical aperture (NA) of the scanning lens. was there. At this time,
Since it is necessary to increase the diameter of the parallel beam incident on the vibrating mirror, the vibrating mirror has been enlarged.

Here, when the size of the vibrating mirror becomes large, the moment of inertia of the vibrating mirror becomes large, so that it becomes difficult to speed up the vibration cycle of the vibrating mirror to shorten the time required for scanning, and the throughput decreases. Problems arise.
Therefore, a first object of the present invention is to provide a scanning optical device capable of reducing the beam spot diameter without reducing the throughput, and to improve the throughput without increasing the beam spot diameter. A second object is to provide a scanning optical device that can be improved.

[0006]

In order to achieve the above object, a scanning optical device according to the present invention has the following configuration. For example, as shown in FIG. 1, a scanning optical device that collects a light beam on a surface to be inspected (20) and scans the surface to be inspected by this light beam includes a light source means (11) for supplying a light beam and a light source means. A condensing optical system (12 to 14) that condenses the luminous flux of
The reflection type scanning unit (15) is disposed at the position where the light beam is condensed by the light condensing optical system and reflects the light beam to scan. The reflection type scanning unit has a rectangular reflection surface (15a). Is configured as follows.

In the present invention, the locus of the light beam scanned on the surface to be inspected is referred to as a "scanning line", and the direction along this scanning line is the "scanning direction" and the light beam reflected by the vibrating mirror is referred to as "scanning direction". A surface including the chief ray and the scanning line is referred to as a "scanning surface". The direction perpendicular to this scanning plane is called the "sub-scanning direction". In the optical path from the light source means to the vibrating mirror, the direction in the scanning plane orthogonal to the optical axis of the condensing optical system is referred to as "scanning direction", and the optical axis direction of the condensing optical system is orthogonal to the scanning direction. The direction is referred to as the “sub-scanning direction”.

[0008]

As described above, in the present invention, the light beam is condensed into a linear shape on the reflection surface of the reflection type scanning means. Therefore, the numerical aperture of the scanning optical system can be increased without increasing the width (length in the sub-scanning direction) of the reflecting surface.
At this time, since the width of the reflecting surface does not widen, the moment of inertia of the reflection type scanning means does not increase. This makes it possible to reduce the spot size on the surface to be inspected without lowering the throughput.

The scanning optical means according to the present invention can significantly reduce the moment of inertia of the reflection type scanning means without reducing the numerical aperture of the scanning optical system. Thereby, the throughput can be improved without increasing the beam spot diameter on the surface to be inspected.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention. In FIG. 1, the scanning direction is the scanning direction of the light beam focused on the surface to be inspected, and scanning is performed within the surface to be inspected. The direction orthogonal to the direction is the sub-scanning direction. In the scanning optical device according to the present invention, as shown in FIG. 1, since the optical path through which the light beam travels is bent by the vibrating mirror 15, the light source 11, the condensing optical systems 12 to 14, and the vibrating mirror 15 are arranged. In the optical path of the condensing optical system 12 to 14, the scanning direction is the direction in the scanning plane orthogonal to the optical axis Ax _{1 of the} condensing optical system 12 to 14
The direction perpendicular to Ax ₁ and the scanning direction is the sub-scanning direction.

First, the scanning optical device of this embodiment will be described with reference to FIGS. Here, FIG. 2 is an optical path diagram showing a state in which an optical path is developed when the scanning optical device of FIG. 1 is viewed from the sub-scanning direction, and FIG. 3 is a scanning optical device of FIG. 1 viewed from the scanning direction. It is an optical-path figure which expands and shows the optical path at the time. First, in FIG. 1, a cylindrical negative lens 12 having a negative refracting power in the scanning direction is sequentially provided along the optical path in which the light beam travels in the light beam emission direction of the light source 11 for supplying the light beam.
And a condensing optical system 12 to 14 including a cylindrical positive lens 13 having a positive refractive power in the scanning direction and a cylindrical positive lens 14 having a positive refractive power in the sub-scanning direction. This condensing optical system 12 to 14 is a reflection surface of the vibrating mirror 15 for the light beam from the light source 11.
The light is focused so as to form a focal line extending in the scanning direction on 15a. In the reflection direction of the vibrating mirror 15, a scanning lens 17 having a projection method of fθ and a cylindrical positive lens 18 having a positive refractive power in the sub-scanning direction are arranged as a scanning optical system.

The optical path of the scanning optical device of the present invention will be described below with reference to FIGS. First, in FIG. 2, the beam diameter of the light beam from the light source 11 passes through the cylindrical negative lens 12 and the cylindrical positive lens 13 and is expanded in the scanning direction. As shown in FIG. 3, this light beam is focused on the reflecting surface 15a of the vibrating mirror 15 via the cylindrical positive lens 14. At this time, the reflective surface
A linear focal line extending in the scanning direction is formed on 15a. Then, the linearly condensed light beam is reflected by the reflecting surface 14a.
It is deflected by, is condensed by the scanning lens 17, and reaches the cylindrical positive lens 18. Here, the light beam that has passed through the scanning lens 17 is in a convergent light beam state in the scanning direction, and the light beam that has passed through the cylindrical positive lens 18 is in a convergent light beam state in the sub-scanning direction as well. The beam spot is formed by converging on one point on the upper scanning line 19.

Then, returning to FIG. 1, the vibrating mirror 15 has an axis Ax.
_It is swingably provided about ₃ as a central axis, and is configured to vibrate at a constant velocity (constant angular velocity) by a drive unit (not shown). Here, the projection method of the scanning lens 17 is
Let 1/2 be the scanning range on the scanning line 19 (image height) be y, the focal length of the scanning lens 17 be f, and the incident angle (half angle of view) of the light beam with respect to the optical axis Ax ₂ of the scanning lens 17 be ω. Then, y = f · ω (1) Therefore, on the surface 20 to be inspected, the beam spot is scanned at a constant velocity in the scanning direction by the constant velocity vibration of the vibrating mirror 15. The vibration of the vibrating mirror 15 is not limited to the constant velocity vibration with a constant angular velocity, and may be a simple vibration.

In the present invention, the condensing optical system 12-
A focal line extending in the scanning direction is formed on the vibrating mirror 15 by the vibrating mirror 15, and the vibrating mirror 15 has a rectangular shape extending in the scanning direction. The shape of the vibrating mirror 15 is shown in FIG.
Will be described with reference to. First, FIG. 4 is an optical path diagram showing the optical path when the focal line is formed on the vibrating mirror 15 by the cylindrical positive lens 14, as viewed from the sub-scanning direction. In FIG. 4, the reference position 43a is The light beam 40 incident along the optical axis Ax ₁ of the condensing optical system 12 to 14 is scanned by the vibrating mirror 15.
This is the position of the vibrating mirror 15 when reflected along the optical axis Ax _{2 of} 17. Further, as indicated by a broken line in the figure, the state in which the vibrating mirror 15 is rotated from the reference position 43a by half the half angle of view of the scanning lens 17 is defined as a position 43b. Then, the normal vibration mirror 15 located at the reference position 43a N _15, and the angle between the optical axis Ax ₁ and the normal N ₁₅ and the incident angle θ of the light beam.

Here, the irradiation region 41 of the light beam 40 formed when the vibrating mirror 15 is located at the position 43b has a shape that spreads in a coma shape with increasing distance from the optical axis Ax ₁ , as shown by the diagonal lines in FIG. Becomes The length a _{0 of the} irradiation area 41 in the scanning direction and the width b _{0 of the} sub-scanning direction are set so that the vibrating mirror 15 is positioned.
Maximum when located at 15b. Therefore, the length in the scanning direction and the width in the sub-scanning direction of the vibrating mirror 15 may be at least a ₀ and b ₀ described above.

Below, the length a _{0 in the} scanning direction and the width b _{0 in the} sub-scanning direction are obtained. In order to simplify the description, the cross-sectional shape of the light beam between the cylindrical positive lens 13 and the cylindrical positive lens 14 is a rectangle circumscribing an actual elliptical shape. As shown in FIG. 6, when a light beam having a rectangular cross-section is applied to the vibrating mirror 15 located at the position 43b, the reflecting surface 15a of the vibrating mirror 15 is symmetrical with respect to the vibration center axis Ax ₃ as indicated by the diagonal lines. Two isosceles triangular light beam irradiation regions 42 are formed.

Then, returning to FIG. 4, the angle formed by the focal line 44 formed by the light beam 40 and the vibrating mirror 15 located at the position 43b is θ +.
ω / 2. Where the diameter of the light beam 40 in the scanning direction is φ
_If the length is ₁ , the length a ₀ of the vibrating mirror 15 in the scanning direction is represented by a ₀ = φ ₁ / cos (θ + ω / 2) (2). Then, the optical axis Ax of the vibrating mirror 15 at the position 43b is
_The length L _{43 b} along _one direction is L _43b = φ ₁ · tan (θ + ω / 2) (3) as shown in the figure.

Further, as shown in FIG. 7 in which the vibrating mirror 15 located at the position 43b is viewed from the scanning direction, the width b ₀ of the vibrating mirror 15 along the vibration center axis Ax ₃ direction is as shown in the figure, b ₀ = L _43b · tan α (4) and the numerical aperture of the cylindrical positive lens 14 in the sub-scanning direction is NA ₁₄
Then, since NA ₁₄ = tan α is a sufficiently good approximation, the width b ₀ of the vibrating mirror 15 in the scanning direction is represented by b ₀ = φ ₁ · tan (θ + ω / 2) · NA ₁₄ (5) Be done.

Here, the moment of inertia I of the vibrating mirror 15
_If the surface density of the vibrating mirror 15 is ρ (g / cm ² ), then ₁₅ is I ₁₅ = 1/12 · ρa ₀ ³ b ₀ (6). On the other hand, consider the moment of inertia in the conventional scanning optical device shown in FIG. Here, in FIG. 10, which shows the optical path of the light beam 100 emitted from the beam expanders 92 and 93 in the state of parallel light flux to reach the scanning lens 17 after being reflected by the vibrating mirror 95, the beam expander is shown in FIG.
The position where the light beam 100 incident along the optical axis Ax _{4 of} 92, 93 is reflected by the vibrating mirror 95 and is reflected along the optical axis Ax ₅ of the scanning lens 17 is the reference position 93a of the vibrating mirror 95. . Then, the position where the vibrating mirror 95 is rotated from the reference position 93a by half the half angle of view ω of the scanning lens 17 is defined as a position 93b.
As shown in FIG. 11, which shows the irradiation region 96 on the vibrating mirror 95 when the position 95 is located at the position 43b, the irradiation region 96 has an elliptical shape extending in the scanning direction. Here, if the diameter of the light beam 100 with which the vibrating mirror 95 is irradiated is φ ₂ , the length b ₁ of the vibrating mirror 95 in the sub-scanning direction is φ ₂ , which is the length along the scanning direction of the vibrating mirror 95. a ₁ is represented by a ₁ = φ ₂ / cos (θ + ω / 2) (7) When the surface density of the vibrating mirror 95 is ρ (g / cm ² ), the moment of inertia I ₉₅ of the vibrating mirror ₉₅ is expressed as I ₉₅ = 1/12 · ρa ₁ ³ b ₁ (8) It

Here, in order to prevent the moment of inertia I ₁₅ of the vibrating mirror 15 of this embodiment from increasing more than the moment of inertia I ₉₅ of the vibrating mirror 95 of the conventional scanning optical apparatus, I ₉₅ ≧ I ₁₅ (9) ) Is satisfied, and therefore, 1/12 · ρa ₁ ³ b ₁ ≧ 1/12 · ρa ₀ ³ b ₀ (10).

From the above conditional expression, the length a ₀ of the vibrating mirror 15 in the scanning direction is a ₀ ≦ {NA ₁₄ · tan (θ + ω / 2)} ⁻¹ / ⁴ · a ₁ (11) It is desirable to be satisfied. Here, the length a ₀ is (1
When the value is out of the range of the equation (1), the moment of inertia I ₁₅ of the vibrating mirror 15 increases, which is not preferable. And (11)
From the formula, under the condition that the moment of inertia is not increased as compared with the conventional one, the numerical aperture NA ₁₇ of the scanning lens ₁₇ is [NA ₁₄
tan (θ + ω / 2)] ^−1/4 times larger. As a result, the beam spot size on the surface 20 to be inspected can be reduced to [NA ₁₄ · tan (θ + ω / 2)] ^1/4 times.

For example, in consideration of the effective area of the vibrating mirror, when the focal length f of the scanning lens is 230 mm and the F number is 1:14, the diameter of the beam spot on the surface 20 to be inspected is reduced by about twice. be able to. Now, when the numerical aperture NA ₁₇ of the scanning lens ₁₇ is increased as described above,
As the beam spot is scanned on the surface 20 to be inspected, the diameter of the beam spot may change, and the scanning on the surface to be inspected may be inaccurate. Hereinafter, this will be described with reference to FIG.

In FIG. 8, when the vibrating mirror 15 is located at the reference position 43a, the light beam 40 from the condensing optical systems 12 to 14 is directed to the optical axis Ax ₂ of the scanning lens 17 by the vibrating mirror 15. Is reflected along. At this time, a focal line 44 is formed at the position of the axis Ax ₃ of the vibrating mirror 15 as shown by the broken line in the figure. Then, the focal line 44 becomes an image 44a of the focal line due to the reflection of the vibrating mirror 15 located at the reference position 43a. Here, the image 44a of the focal line,
The center position of the scanning line 19 (the position where the scanning line 19 and the optical axis Ax ₂ intersect) has a conjugate relationship by the scanning optical systems 17 and 18 including the scanning lens 17 and the cylindrical lens 18.

When the vibrating mirror 15 moves in the direction of the arrow in the figure, the focal line 44 becomes an image 44b of the focal line due to the reflection of the vibrating mirror 15. The image 44b of the focal line deviates from the position conjugate with the scanning line 19 by δ. As a result, the size of the surface to be inspected 20 in the sub-scanning direction changes as the beam spot is scanned. Here, in order not to change the beam spot diameter on the surface 20 to be inspected, it is desirable that the numerical aperture NA ₁₄ of the cylindrical positive lens 14 in the sub scanning direction satisfies the following condition.

NA ₁₄ ≤ (φ _S / 2ky) ^1/2 , 0.6 ≤ k ≤ 1.0 (12) where NA _{14 is} the numerical aperture on the exit side of the cylindrical positive lens 14, φ _{S is the} surface to be inspected Beam spot diameter, y: 1/2 of the scanning range of the beam on the surface to be inspected, k: constant.

The conditional expression (12) will be described in detail below. Assuming that the numerical aperture of the scanning lens 17 is NA ₁₇ and the numerical aperture of the scanning lens 17 is f, the radius of the light beam reaching the scanning lens 17 in the scanning direction is represented by f · NA ₁₇ . When the half angle of view ω is not so large, the product of this radius and the half angle of view becomes the conjugate shift δ. That is, the conjugate shift δ is represented by δ = f · NA ₁₇ · ω (13)

In order to ignore the conjugate shift δ, it is sufficient that the conjugate shift is within the range of the focal depth of the focusing optical systems 12-14. Here, when the numerical aperture on the exit side of the cylindrical positive lens 14 in the scanning direction is NA ₁₄ , if the conjugate deviation δ satisfies δ ≦ λ / (2NA ₁₄ ² ) (14), the cylindrical positive lens It fits within the depth of focus of 14.

The diameter φ _S of the beam spot on the surface to be inspected is φ _S = k · λ /, where k is a constant (0.6 ≦ k ≦ 1.0) and the wavelength of the beam is λ. NA ₁₇ (15) Here, this constant k is a constant determined by the degree of beam deviation in the scanning lens 17.

Then, the conditional expression (12) is calculated by the conditional expression (1) and the conditional expressions (13) to (15). Here, the cylindrical positive lens 14 is conditional expression (12).
If the above condition is satisfied, the beam spot diameter on the surface 20 to be inspected becomes constant, and accurate scanning can be realized even when the numerical aperture NA ₁₇ of the scanning lens ₁₇ is extremely large.

Next, the moment of inertia I ₁₅ of the vibrating mirror 15 when the diameter of the beam spot formed on the surface 20 to be inspected is constant will be considered. Here, the diameter φ _S of the beam spot on the surface to be inspected 20 is calculated by the conditional expression (15) from the scanning lens.
The numerical aperture NA of ₁₇ determines this numerical aperture NA.
₁₇ is determined by the diameter of the light beam incident on the scanning lens 17. That is, when the diameter of the beam spot by the scanning optical device of the present embodiment is made equal to φ _S equal to the diameter of the beam spot by the conventional scanning optical device shown in FIG. 9, the beam diameter φ ₂ shown in FIG. The diameter φ ₁ of the light beam in the sub-scanning direction shown in FIG. 4 may be made equal. As a result, the diameter φ _S of the beam spot on the surface 20 to be inspected becomes constant.

The length a _{0 in the} scanning direction and the width b _{0 in the} sub-scanning direction of the vibrating mirror 15 preferably satisfy the following conditions. a ₀ ≧ φ ₁ / [cos (θ + ω / 2)] (16) b ₀ ≧ φ ₁ · tan (θ + ω / 2) · NA ₁₄ (17) where φ _{1 is} from the cylindrical positive lens 14. The diameter of the light beam in the scanning direction, θ: the incident angle of the light beam incident on the vibrating mirror 15, ω: the half angle of view of the scanning lens 17, NA ₁₄ : the numerical aperture on the exit side of the cylindrical positive lens 14.

When the length a _{0 in the} scanning direction and the width b _{0 in the} sub-scanning direction of the vibrating mirror 15 are below the lower limits of the above equations (16) and (17), the cylindrical positive lens 14 outputs When the light beam is deflected by the vibrating mirror 15, a light amount loss occurs, which is not preferable. The length a _{0 in the} scanning direction and the width b _{0 in the} sub-scanning direction of the vibrating mirror 15 are calculated from the above equations (7) and (10) as follows: a ₀ ³ b ₀ ≦ φ ₂ ⁴ / cos ³ (θ + ω / 2) It is desirable to satisfy (18).

Here, when the length a _{0 in the} scanning direction and the width b _{0 in the} sub-scanning direction of the vibrating mirror 15 deviate from the ranges of the equations (18) and (17), the moment of inertia of the vibrating mirror 15 increases. Therefore, it is not preferable. When the vibrating mirror 15 satisfies the above expressions (14) and (15), the conventional vibrating mirror 95
The ratio of the moment of inertia I ₁₅ of the vibrating mirror 15 of the relative moment of inertia _{I 95, I 95 / I 15} = (1/12 · ρa 1 3 b 1) / (1/12 · ρa 0 3 b 0) = {tan (Θ + ω / 2) · NA ₁₄ } ^-1 (19) That is, when the numerical aperture of the scanning lens 17 is constant, the moment of inertia of the vibrating mirror 15 can be reduced by {tan (θ + ω / 2) · NA ₁₄ } ⁻¹ times as compared with the conventional one. This makes it possible to significantly increase the vibration speed of the vibrating mirror 15 and improve the scanning speed of the beam spot scanning on the surface 20 to be detected.

Further, in this embodiment, the line image formed on the reflecting surface 15a of the vibrating mirror 15 and the position where the beam spot is formed on the surface 20 to be inspected have a conjugate relationship in the sub-scanning direction. Has become. Therefore, for example, as shown by the broken line in FIG. 3, a state in which the reflecting surface 15a is tilted (axis Ax ₃
And the optical axis Ax ₁ of the condensing optical systems 12 to 14 are not perpendicular to each other, the light beam passing through the reflecting surface 15a is condensed at one point on the scanning line 19. As a result, even if the vibrating mirror 15 is tilted, accurate scanning can be performed without changing the beam spot diameter.

The shape of the vibrating mirror 15 as the reflection type scanning means is not limited to a rectangular shape, but an elliptical shape having a major axis in the linear direction of a linearly condensed light beam, or a linear direction in this linear direction. It goes without saying that it may be an oval shape having long sides.

[0036]

As described above, in the scanning optical device according to the present invention, the beam spot diameter on the surface to be inspected can be reduced without reducing the throughput.
Further, in the scanning optical device according to the present invention, since the beam spot scanning can be speeded up without increasing the beam spot diameter on the surface to be inspected, the throughput can be improved.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an embodiment of a scanning optical device according to the present invention.

2 is an optical path diagram showing an optical path when the scanning optical device of FIG. 1 is viewed from a sub-scanning direction.

3 is an optical path diagram showing an optical path when the scanning optical device of FIG. 1 is viewed from a scanning direction.

FIG. 4 is an enlarged optical path diagram showing an optical path near a vibrating mirror of the scanning optical device of FIG.

FIG. 5 is a plan view showing the shape of a light beam with which a vibrating mirror is irradiated.

FIG. 6 is a plan view showing the shape of a vibrating mirror when a light beam having a rectangular cross section is irradiated onto the vibrating mirror.

FIG. 7 is an optical path diagram when an optical path of a light beam focused on a vibrating mirror is viewed from a scanning direction.

FIG. 8 is an optical path diagram when an optical path of a light beam by a vibrating mirror is viewed from a sub scanning direction.

FIG. 9 is a diagram schematically showing a conventional scanning optical device.

10 is an enlarged view showing an optical path near a vibrating mirror of the scanning optical device of FIG.

11 is a plan view showing the shape of a light beam with which the vibrating mirror of the scanning optical device of FIG. 9 is irradiated.

[Explanation of symbols]

 11… Light source, 14… Cylindrical positive lens, 15… Vibrating mirror, 17… Scan lens, 20… Test surface,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Kimura 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon Corporation

Claims (1)

[Claims] 1. A scanning optical device for condensing a light beam on a surface to be inspected and scanning the surface to be inspected by the light beam thus condensed; light source means for supplying the light beam; and light beam from the light source means. A condensing optical system for linearly condensing the light beam, and a reflection type scanning unit arranged at a condensing position of the light beam by the light condensing optical system for reflecting and scanning the light beam. The scanning optical device, wherein the means has a rectangular reflecting surface.