Scan optical system and optical processor

Abstract

To provide a scan optical system capable of reducing chromatic aberration of light with wavelengths each belonging to a prescribed wavelength range and differing from each other.SOLUTION: A scan optical system includes an fθ lens for converging light on a scanned surface. The fθ lens includes a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power, which are arranged side by side in order from a mirror side. The first lens group includes a first positive lens with convex optical incident side and a first negative lens with concave optical emission side, which are arranged side by side in order from the mirror side. The second lens group includes a second negative lens which is biconcave lens, and a second positive lens which is biconvex lens and has a convex optical incident side attached to optical emission side of the second negative lens, which are arranged side by side in order from the mirror side.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a scanning optical system including a mirror, a drive source for displacing the mirror, and an fθ lens for focusing light reflected by the mirror on a surface to be scanned, and an optical processing device equipped with a light source and the scanning optical system. [Background technology]

[0002] In semiconductor manufacturing processes, optical processing devices are used to perform desired processing using light having a predetermined single wavelength. For example, an optical processing device is known that can measure the thickness of a thin film formed on a workpiece such as a semiconductor wafer by using a laser beam with a wavelength that is absorbed by a light-absorbing agent contained in the thin film (see, for example, Patent Document 1). Also known are optical processing devices that can process the workpiece by using a laser beam that causes ablation in the workpiece or alters its material.

[0003] In optical processing devices, a scanning optical system including a mirror, a drive source for displacing the mirror, and an fθ lens for focusing light reflected by the mirror on the surface to be scanned is generally used (see, for example, Patent Document 2). When light having a predetermined single wavelength is focused by the scanning optical system and irradiated onto the workpiece, processing in the optical processing device (for example, measuring the thickness of a thin film or processing the workpiece) can be performed with high accuracy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-104532 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-102623 Summary of the Invention [Problem to be solved by the invention]

[0005] Processing in optical processing equipment can be performed using light beams with different wavelengths, each of which belongs to a predetermined wavelength range. For example, the thickness of a thin film can be measured based on the spectrum of non-monochromatic light reflected and interfered by the front and back surfaces of the film, i.e., using spectral interferometry. Furthermore, a workpiece can be processed by selectively irradiating it with one of two or more laser beams with different wavelengths depending on the material, etc.

[0006] However, when a common scanning optical system is used to focus non-single wavelength light or laser beams of two or more different wavelengths on a surface to be scanned, large chromatic aberration may occur, making it difficult to perform processing in the optical processing device with high accuracy. In view of this, an object of the present invention is to provide a scanning optical system that can reduce chromatic aberration of light having different wavelengths each belonging to a predetermined wavelength range, and an optical processing device that can perform desired processing with high accuracy. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a scanning optical system including: mirrors for reflecting light beams each belonging to a predetermined wavelength range and having mutually different wavelengths; a drive source for displacing the mirrors so that the light beams reflected by the mirrors are deflected within a predetermined angle range; and an fθ lens for focusing the light beams reflected by the mirrors on a surface to be scanned, the fθ lens including a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, which are arranged in order from the mirror side. and a fourth lens group having positive refractive power, wherein the first lens group has a first positive lens having a convex surface on the light incident side and a first negative lens having a concave surface on the light exit side, which are arranged in order from the mirror side; and the second lens group has a second negative lens which is a biconcave lens, and a second positive lens which is a biconvex lens and has its convex surface on the light incident side cemented to the concave surface of the second negative lens on the light exit side, which are arranged in order from the mirror side.

[0008] Furthermore, in the scanning optical system of the present invention, when the composite focal length of the fθ lens to the d-line having a wavelength of 587.6 nm is F, the composite focal length of the first lens group to the d-line is F1, the composite focal length of the second lens group to the d-line is F2, the composite focal length of the third lens group to the d-line is F3, and the composite focal length of the fourth lens group to the d-line is F4, it is preferable that all of the following formulas (1) to (4) are satisfied:

number

number

number

number

[0009] In the scanning optical system of the present invention, for example, the light exit side surface of the first positive lens and the light incident side surface of the first negative lens may be cemented together, and the third lens group may include, arranged in order from the mirror side, a third negative lens having a concave surface on the light incident side and a third positive lens having a convex surface on the light exit side and whose light incident side surface is cemented to the light exit side surface of the third negative lens. Alternatively, in the scanning optical system of the present invention, the first positive lens and the first negative lens may be arranged so as to be spaced apart, and the third lens group may include, arranged in order from the mirror side, a third negative lens having a concave surface on the light incident side and a third positive lens having a convex surface on the light exit side and whose light incident side surface is cemented to the light exit side surface of the third negative lens. Furthermore, in the scanning optical system of the present invention, the fourth lens group may include a plurality of positive lenses. Alternatively, in the scanning optical system of the present invention, the surface of the first positive lens on the light exit side and the surface of the first negative lens on the light incident side may be cemented together, and the third lens group may have a positive meniscus lens whose light incident side is concave.

[0010] According to another aspect of the present invention, there is provided an optical processing device including a scanning optical system including a light source for emitting light beams each having a wavelength that is different from each other and that belong to a predetermined wavelength range, a mirror for reflecting the light beams, a drive source for displacing the mirror so that the light beams reflected by the mirror are deflected within a predetermined angle range, and an fθ lens for focusing the light beams reflected by the mirror on a surface to be scanned, wherein the fθ lens includes a first lens group having a positive refractive power and a second lens group having a negative refractive power, which are arranged in order from the mirror side. Provided is an optical processing device comprising a second lens group, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, wherein the first lens group has a first positive lens with a convex surface on the light incident side and a first negative lens with a concave surface on the light exit side, which are arranged in order from the mirror side; and the second lens group has a second negative lens which is a biconcave lens, and a second positive lens which is a biconvex lens and has its convex surface on the light incident side bonded to the concave surface of the second negative lens on the light exit side, which are arranged in order from the mirror side.

[0011] The optical processing device of the present invention may further include, for example, a photoelectric converter and a controller to which an electrical signal is input from the photoelectric converter, wherein the light source emits non-single wavelength light belonging to the wavelength range, the non-single wavelength light is focused by the scanning optical system and irradiated onto a thin film located on the scanned surface, the photoelectric converter outputs an electrical signal indicating the spectrum of the non-single wavelength light reflected and interfered at each of the front and back surfaces of the thin film, and the controller may identify the thickness of the thin film based on the electrical signal. Alternatively, the optical processing device of the present invention may further include a controller, wherein the light source has a first oscillator for emitting a first laser beam of a first wavelength belonging to the wavelength range, and a second oscillator for emitting a second laser beam of a second wavelength belonging to the wavelength range and different from the first wavelength, and each of the first laser beam and the second laser beam is focused by the scanning optical system and irradiated onto a workpiece located on the scanned surface, and the controller may control the first oscillator and the second oscillator so that either the first laser beam or the second laser beam is selectively irradiated onto the workpiece. [Effects of the Invention]

[0012] In the present invention, the first lens group of the fθ lens has a first positive lens and a first negative lens, and the second lens group has a second negative lens and a second positive lens. In this case, it is possible to reduce the axial chromatic aberration (chromatic aberration on the optical axis) of the fθ lens compared to when the first lens group of the fθ lens is composed of a single positive lens and / or the second lens group is composed of a single negative lens.

[0013] In the present invention, the concave surface on the light exit side of the second negative lens and the convex surface on the light entrance side of the second positive lens are cemented together, which makes it possible to reduce the lateral chromatic aberration of the fθ lens (chromatic aberration in a plane that is perpendicular to the optical axis, has a wavelength within a predetermined wavelength range, and passes through a focal point that is roughly common to light deflected within a predetermined angle range) compared to when the two surfaces are separated.

[0014] Furthermore, the optical processing device of the present invention includes the scanning optical system of the present invention, and therefore, in this optical processing device, the chromatic aberration of light beams each belonging to a predetermined wavelength range and having mutually different wavelengths can be reduced, so that the desired processing can be performed with high precision. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of an optical processing device. [Figure 2] FIG. 2 is a diagram schematically illustrating another example of an optical processing device. [Figure 3] FIG. 3 is a diagram showing a schematic configuration of an fθ lens. [Figure 4] FIG. 4A is a diagram schematically showing an fθ lens according to a first embodiment, and FIG. 4B is a diagram schematically showing an fθ lens according to a second embodiment. [Figure 5] FIG. 5A is a diagram schematically showing an fθ lens according to a third embodiment, and FIG. 5B is a diagram schematically showing an fθ lens according to a fourth embodiment. [Figure 6] FIG. 6A is a diagram schematically showing an fθ lens according to a fifth embodiment, and FIG. 6B is a diagram schematically showing an fθ lens according to a sixth embodiment. [Figure 7] FIG. 7A is a diagram schematically showing an fθ lens according to a seventh embodiment, and FIG. 7B is a diagram schematically showing an fθ lens according to an eighth embodiment. [Figure 8] FIG. 8A is a diagram showing a ninth embodiment of an fθ lens, and FIG. 8B is a diagram showing a tenth embodiment of an fθ lens. DETAILED DESCRIPTION OF THE INVENTION

[0016]

[0023] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a diagram schematically illustrating an example of an optical processing device equipped with a scanning optical system. In short, the optical processing device 14 shown in Fig. 1 is a thickness measurement device capable of measuring the thickness of a thin film 13 formed on a workpiece 11 such as a semiconductor wafer by using light focused by a scanning optical system 12.

[0017] Specifically, the optical processing device 14 includes a light source 16 capable of emitting non-single wavelength light within a predetermined wavelength range. The path of this light is simply indicated by a dashed line in Fig. 1. The light emitted from the light source 16 passes through a half mirror 18 and enters the scanning optical system 12.

[0018] In the optical processing device 14, a scanning optical system 12 is used to irradiate a thin film 13 located on the surface to be scanned with focused light. The configuration of the scanning optical system 12 will be described in detail later. The light irradiated onto the thin film 13 is reflected and interferes on both the front surface (upper surface) and the back surface (lower surface). In FIG. 1, the path of the light reflected and interfered in this way (hereinafter also simply referred to as "interference light") is indicated by a dashed line.

[0019] The interference light passes through the scanning optical system 12 and is reflected by the half mirror 18. The interference light reflected by the half mirror 18 is then supplied to the photoelectric converter 20. The photoelectric converter 20 includes a photoelectric conversion element such as a photodiode, and outputs an electrical signal indicating the spectrum of the interference light.

[0020] The electrical signal output from the photoelectric converter 20 is input to the controller 22. The controller 22 includes a processor and a memory, and determines the thickness of the thin film based on the electrical signal. The processor is configured, for example, by a CPU (Central Processing Unit). The memory is configured, for example, by a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory), and a non-volatile memory such as an SSD (Solid State Drive) (NAND flash memory) or an HDD (Hard Disk Drive) (magnetic storage device).

[0021] Fig. 2 is a diagram schematically illustrating another example of an optical processing device. In short, the optical processing device 24 shown in Fig. 2 is a laser processing device that uses light (specifically, a laser beam) focused by a scanning optical system 12 to cause ablation in the workpiece 11 or to alter the material thereof.

[0022] The optical processing device 24 has, as the light source 26, a first oscillator 26a for emitting a first laser beam of a first wavelength and a second oscillator 26b for emitting a second laser beam of a second wavelength different from the first wavelength. In Fig. 2, the path of the first laser beam is simply indicated by a dashed line, and the path of the second laser beam is simply indicated by a broken line.

[0023] The first laser beam of the first wavelength is, for example, a laser beam with a wavelength that is absorbed by the workpiece 11, and is intended to cause ablation in the workpiece 11. The second laser beam of the second wavelength is, for example, a laser beam with a wavelength that is transmitted through the workpiece 11, and is intended to alter the material of the workpiece 11. When the material of the workpiece 11 is silicon or the like, the first wavelength is set to 355 nm, and the second wavelength is set to 1080 nm, for example.

[0024] The first laser beam and the second laser beam are each incident on a dichroic mirror 28, which has a high transmittance for light of the first wavelength and a high reflectance for light of the second wavelength. Then, the first laser beam transmitted through the dichroic mirror 28 and the second laser beam reflected thereby are each incident on the scanning optical system 12. In the optical processing device 24, the scanning optical system 12 is used to irradiate the workpiece 11 located on the surface to be scanned with the focused first laser beam and second laser beam.

[0025] The first oscillator 26a and the second oscillator 26b are controlled by a controller 30. The controller 30 includes a configuration similar to that of the controller 22 shown in Fig. 1, and controls the first oscillator 26a and the second oscillator 26b so that the workpiece 11 is selectively irradiated with either the first laser beam or the second laser beam.

[0026] The scanning optical system 12 provided in the optical processing devices 14, 24 includes a mirror 32. The mirror 32 is for reflecting light beams each belonging to a predetermined wavelength range and having mutually different wavelengths, specifically, light beams emitted from the light source 16, or the first laser beam emitted from the first oscillator 26a or the second laser beam emitted from the second oscillator 26b.

[0027] The mirror 32 is also connected to a driving source 34. The driving source 34 displaces the mirror 32 so that the light reflected by the mirror 32 is deflected within a predetermined angular range. Note that, as the mirror 32 and the driving source 34, for example, a galvanometer scanner, a polygon scanner, or a MEMS (Micro-Electro Mechanical Systems) scanner can be used.

[0028] The light reflected by the mirror 32 is then focused on the surface to be scanned by the fθ lens 36. Figure 3 is a diagram schematically showing the configuration of the fθ lens 36. In Figure 3, the left side of the page is the mirror 32 side, and the light travels from left to right on the page. In Figure 3, the optical axis of the fθ lens 36 is indicated by a solid line extending in the left-right direction on the page.

[0029] The fθ lens 36 has, arranged in order from the mirror 32 side, a first lens group 38 having positive refractive power, a second lens group 40 having negative refractive power, a third lens group 42 having positive refractive power, and a fourth lens group 44 having positive refractive power.

[0030] The first lens group 38 has a first positive lens with a convex surface on the light incident side and a first negative lens with a concave surface on the light exit side, which are arranged in order from the mirror 32 side. Note that the first positive lens can be a biconvex lens, a plano-convex lens, or a convex meniscus lens.

[0031] However, it is preferable that the first positive lens is a biconvex lens from the viewpoint of reducing spherical aberration caused by the first lens group 38. Furthermore, a biconcave lens, a plano-concave lens, or a concave meniscus lens can be used as the first negative lens.

[0032] The second lens group 40 includes a second negative lens 40a, which is a biconcave lens, and a second positive lens 40b, which is a biconvex lens and has its convex surface on the light incident side bonded to the concave surface on the light exit side of the second negative lens 40a, which are arranged in order from the mirror 32 side.

[0033] In the scanning optical system 12, the first lens group 38 of the fθ lens 36 has a first positive lens and a first negative lens, and the second lens group 40 has a second negative lens 40a and a second positive lens 40b. In this case, it is possible to reduce the axial chromatic aberration of the fθ lens 36 compared to when the first lens group 38 of the fθ lens 36 is composed of a single positive lens and / or the second lens group 40 is composed of a single negative lens.

[0034] In the scanning optical system 12, the concave surface on the light exit side of the second negative lens 40a and the convex surface on the light entrance side of the second positive lens 40b are cemented together. In this case, it is possible to reduce the chromatic aberration of magnification of the fθ lens 36 compared to when the two surfaces are separated. Furthermore, by cementing the two surfaces together, it is possible to suppress light reflection that occurs on at least one of the surfaces and to reduce the astigmatism of the fθ lens 36. [Example]

[0035] Below, we will explain Examples 1 to 10 of the fθ lens 36 designed to reduce chromatic aberration. The design values ​​for each of Examples 1 to 10 are as shown in Tables 1 and 2 below. [Table 1] [Table 2]

[0036] In addition, each column (excluding the leftmost column) of the row with "Total System" written in the leftmost column shows the composite focal length (mm) of the total system (i.e., the fθ lens 36) for light with a wavelength of 587.6 nm (d-line). Furthermore, each column (excluding the leftmost column) of the row with "1st Group" written in the leftmost column shows the composite focal length (mm) of the first lens group 38 for the d-line. Similarly, each column (excluding the leftmost column) of the row with any of "2nd Group" to "4th Group" written in the leftmost column shows the composite focal length (mm) of either the second lens group 40, the third lens group 42, or the fourth lens group 44 for the d-line.

[0037] The design values ​​of each of Examples 1 to 10 can also be expressed as shown in Tables 3 and 4 below. [Table 3] [Table 4]

[0038] In the columns (excluding the leftmost column) of the rows where "Group 1 / Entire System" is described in the leftmost column, values obtained by dividing the combined focal length (mm) of the first lens group 38 with respect to the d-line by the combined focal length (mm) of the entire system are shown. Similarly, in the columns (excluding the leftmost column) of the rows where "Group 2 / Entire System" to "Group 4 / Entire System" are described in the leftmost column, values obtained by dividing any one of the second lens group 40, the third lens group 42, or the fourth lens group 44 with respect to the d-line by the focal length (mm) of the entire system are shown.

[0039] That is, each of Examples 1 to 10 was set to satisfy all of the following mathematical formulas (1) to (4) when the combined focal length of the entire system with respect to the d-line is F, the combined focal length of the first lens group 38 with respect to the d-line is F1, the combined focal length of the second lens group 40 with respect to the d-line is F2, the combined focal length of the third lens group 42 with respect to the d-line is F3, and the combined focal length of the fourth lens group with respect to the d-line is F4.

Number

Number

Number

Number

[0040] In addition, if the fθ lens 36 is designed such that 0 < F1 / F ≤ 0.9, the aberration caused by the first lens group 38 becomes large, and it becomes difficult to correct it with the second lens group 40, the third lens group 42, and the fourth lens group 44. Therefore, it is important that the fθ lens 36 is designed to satisfy 0.9 < F1 / F (see the above mathematical formula (1)).

[0041] Also, if the fθ lens 36 is designed such that F2 / F ≤ -2.7, the chromatic aberration of magnification caused by the second lens group 40 becomes large, and it becomes difficult to correct it with the third lens group 42 and the fourth lens group 44. Further, if the fθ lens 36 is designed such that -0.6 ≤ F2 / F < 0, the astigmatism and field curvature aberration in the second lens group 40 are overcorrected. Therefore, it is important that the fθ lens 36 is designed to satisfy -2.7 < F2 / F < -0.6 (see the above formula (2)).

[0042] Also, if the fθ lens 36 is designed such that 0 < F4 / F ≤ 0.8 or 1.5 ≤ F4 / F, there may be a possibility that it becomes difficult to accurately measure the thickness of the thin film 13 in the optical processing device 14. Specifically, in this case, since the angle formed by the traveling direction of the light irradiated on the thin film 13 and the thickness direction of the thin film 13 becomes large, that is, since the telecentricity deteriorates, it becomes difficult for the above interference light to reach the photoelectric converter 20. Therefore, it is important that the fθ lens 36 provided in the scanning optical system 12 included in the optical processing device 14 is designed to satisfy 0.8 < F2 / F < 1.5 (see the above formula (4)).

[0043] And in each of Examples 1 to 10 of the fθ lens 36 designed to satisfy all of the formulas (1) to (4), it was possible to focus light having wavelengths belonging to a predetermined wavelength range to substantially the same focus, that is, to substantially eliminate the axial chromatic aberration. Note that each of Examples 1 to 7 was evaluated using light having wavelengths of 500 nm to 1000 nm. Also, each of Examples 8 to 10 was evaluated using light having wavelengths of 1000 nm to 1100 nm.

[0044] Furthermore, in each of Examples 1 to 10 of the fθ lens 36 designed to satisfy all of the formulas (1) to (4), it was possible to reduce the lateral chromatic aberration of light having a wavelength within a predetermined wavelength range and deflected within a predetermined angle range to less than ±20 μm. Each of Examples 1 to 7 was evaluated by deflecting light with a wavelength of 500 nm to 1000 nm within a range of 30° (±15°). Each of Examples 8 to 10 was evaluated by deflecting light with a wavelength of 1000 nm to 1100 nm within a range of 38.2° (±19.2°).

[0045] Furthermore, in each of Examples 1 to 10 of the fθ lens 36 designed to satisfy all of the formulas (1) to (4), it was possible to keep the spherical aberration to less than ±0.5 mm and the field curvature aberration to less than ±0.5 mm.

[0046] 4(A) and 4(B), 5(A) and 5(B), 6(A) and 6(B), 7(A) and 7(B), and 8(A) and 8(B) are diagrams each showing a specific configuration of an fθ lens 36 according to Examples 1 to 10. In the diagrams showing Examples 1 to 10, the left side of the paper is the mirror 32 side, and light travels from left to right on the paper, as in FIG. 3. In addition, in the diagrams showing Examples 1 to 10, the optical axis of the fθ lens 36 is indicated by a solid line extending in the left-right direction on the paper.

[0047] In Example 1 of the fθ lens 36 shown in Figure 4(A), the first lens group 38 is composed of a biconvex lens 38a and a biconcave lens 38b, the second lens group 40 is composed of a biconcave lens 40c and a biconvex lens 40d, the third lens group 42 is composed of a biconcave lens 42a and a biconvex lens 42b, and the fourth lens group 44 is composed of a biconvex lens 44a.

[0048] The design values ​​of the seven lenses 38a, 38b, 40c, 40d, 42a, 42b, and 44a that constitute the fθ lens 36 according to the first embodiment are as shown in Table 5 below. [Table 5]

[0049] The top row labeled "Surface Number" lists the numbers assigned to the reflective surface of mirror 32 that reflects the light emitted from light source 16 or the first or second laser beam, and to two surfaces on the incident and exit sides of each of seven lenses 38a, 38b, 40c, 40d, 42a, 42b, and 44a (i.e., a total of 14 surfaces) in order from the mirror 32 side. When two consecutive numbers are listed in this row, it indicates that the surface assigned with the even number (the exit-side surface of any of the seven lenses 38a, 38b, 40c, 40d, 42a, 42b, and 44a) and the surface assigned with the odd number (the incident-side surface of any of the seven lenses 38a, 38b, 40c, 40d, 42a, 42b, and 44a) are bonded together.

[0050] Furthermore, the column with "radius of curvature" at the top quantitatively shows the shape of the surface (hereinafter referred to as "the surface") with the "surface number" in the same row. Specifically, the absolute value of the numerical value in each column indicates the radius of curvature (mm) of the surface. Furthermore, if this numerical value is positive, it indicates that the surface is convex toward the mirror 32, and if it is negative, it indicates that the surface is concave toward the mirror 32. Note that the surface with "0" as the "surface number" (i.e., the reflective surface of the mirror 32) is flat, and therefore its "radius of curvature" is shown as "∞."

[0051] The topmost column of the column labeled "Surface Spacing" indicates the distance (mm) on the optical axis between the surface in question and the surface assigned a "surface number" obtained by adding 1 to the "surface number" assigned to the surface in question. Furthermore, the bottommost column of this column indicates the distance between the surface in question (specifically, the exit-side surface of biconvex lens 44a) and the focal point.

[0052] In addition, the column with "Refractive Index (Nd)" at the top shows the refractive index for the d-line of the lens (hereinafter referred to as "the lens") that includes the incident-side surface to which the "surface number" in the same row is assigned. In addition, the column with "Abbe Number (νd)" at the top shows the Abbe number for the d-line of the lens.

[0053] In addition to the effects achieved by satisfying all of the formulas (1) to (4), the first embodiment of the fθ lens 36 also achieves the following effect: Specifically, the surface of the first lens group 38 located closest to the light exit side and the surface of the second lens group 40 located closest to the light entrance side are both concave surfaces, which makes it possible to correct chromatic aberration of magnification, curvature of field, and astigmatism caused by the first lens group 38.

[0054] Furthermore, by making the surface of the third lens group 42 closest to the light incident side a concave surface and the surface of the third lens group 42 closest to the light exit side a convex surface, it is possible to correct curvature of field aberration caused by the first lens group 38 and the second lens group 40. Furthermore, by cementing together the concave surface on the light exit side of the biconcave lens 42a of the third lens group 42 and the convex surface on the light incident side of the biconvex lens 42b, it is possible to correct chromatic aberration of magnification caused by the first lens group 38 and the second lens group 40.

[0055] In Example 2 of the fθ lens 36 shown in Figure 4(B), the first lens group 38 is composed of a biconvex lens 38c and a biconcave lens 38d, the second lens group 40 is composed of a biconcave lens 40e and a biconvex lens 40f, the third lens group 42 is composed of a biconcave lens 42c and a biconvex lens 42d, and the fourth lens group 44 is composed of a biconvex lens 44b.

[0056] The design values ​​of the seven lenses 38c, 38d, 40e, 40f, 42c, 42d, and 44b constituting the fθ lens 36 according to the second embodiment are as shown in Table 6 below. [Table 6]

[0057] The numerical values ​​shown in each column of Table 6 are the same as those shown in each column of Table 5, and therefore will not be described further. The fθ lens 36 of Example 2 achieves the same effects as those of Example 1, as well as the effects achieved by satisfying all of the formulas (1) to (4).

[0058] In Example 3 of the fθ lens 36 shown in Figure 5(A), the first lens group 38 is formed by a biconvex lens 38e and a biconcave lens 38f, the second lens group 40 is formed by a biconcave lens 40g and a biconvex lens 40h, the third lens group 42 is formed by a biconcave lens 42e and a biconvex lens 42f, and the fourth lens group 44 is formed by a biconvex lens 44c and a biconvex lens 44d.

[0059] The design values ​​of the eight lenses 38e, 38f, 40g, 40h, 42e, 42f, 44c, and 44d constituting the fθ lens 36 according to the third embodiment are as shown in Table 7 below. [Table 7]

[0060] Note that the numerical values ​​shown in each column of Table 7 are the same as those shown in each column of Table 5, and therefore a description thereof will be omitted. Example 3 of the fθ lens 36 achieves the following effect in addition to the effect achieved by satisfying all of the formulas (1) to (4) and the same effect as Example 1. Specifically, by forming the fourth lens group 44 with two biconvex lenses 44c and 44d, it is possible to improve telecentricity compared to when the fourth lens group 44 is formed with one biconvex lens 44a or one biconvex lens 44b.

[0061] In Example 4 of the fθ lens 36 shown in Figure 5(B), the first lens group 38 is composed of a biconvex lens 38g and a biconcave lens 38h, the second lens group 40 is composed of a biconcave lens 40i and a biconvex lens 40j, the third lens group 42 is composed of a biconcave lens 42g and a biconvex lens 42h, and the fourth lens group 44 is composed of a biconvex lens 44e.

[0062] The design values ​​of the seven lenses 38g, 38h, 40i, 40j, 42g, 42h, and 44e that constitute the fθ lens 36 according to the fourth embodiment are as shown in Table 8 below. [Table 8]

[0063] The numerical values ​​shown in each column of Table 8 are the same as those shown in each column of Table 5, and therefore will not be described further. The fθ lens 36 of Example 4 achieves the same effects as those of Example 1, as well as the effects achieved by satisfying all of the formulas (1) to (4).

[0064] In Example 5 of the fθ lens 36 shown in Figure 6(A), the first lens group 38 is composed of a biconvex lens 38i and a concave meniscus lens (negative meniscus lens) 38j, the second lens group 40 is composed of a biconcave lens 40k and a biconvex lens 40l, the third lens group 42 is composed of a biconcave lens 42i and a biconvex lens 42j, and the fourth lens group 44 is composed of a biconvex lens 44f.

[0065] The design values ​​of the seven lenses 38i, 38j, 40k, 40l, 42i, 42j, and 44f constituting the fθ lens 36 in Example 5 are as shown in Table 9 below. [Table 9]

[0066] The numerical values ​​shown in each column of Table 9 are the same as those shown in each column of Table 5, and therefore their explanation will be omitted. The fθ lens 36 of Example 5 achieves the same effects as those of Example 1, as well as the effects achieved by satisfying all of the formulas (1) to (4).

[0067] In Example 6 of the fθ lens 36 shown in Figure 6(B), the first lens group 38 is composed of a biconvex lens 38k and a biconcave lens 38l, the second lens group 40 is composed of a biconcave lens 40m and a biconvex lens 40n, the third lens group 42 is composed of a biconcave lens 42k and a biconvex lens 42l, and the fourth lens group 44 is composed of a biconvex lens 44g.

[0068] The design values ​​of the seven lenses 38k, 38l, 40m, 40n, 42k, 42l, and 44g that make up the f-theta lens 36 of Example 6 are as shown in Table 10 below. [Table 10]

[0069] The numerical values ​​shown in each column of Table 10 are the same as those shown in each column of Table 5, and therefore will not be described further. The fθ lens 36 of Example 6 achieves the same effects as those of Example 1, as well as the effects achieved by satisfying all of the formulas (1) to (4).

[0070] In Example 7 of the fθ lens 36 shown in Figure 7(A), the first lens group 38 is composed of a biconvex lens 38m and a biconcave lens 38n, the second lens group 40 is composed of a biconcave lens 40o and a biconvex lens 40p, the third lens group 42 is composed of a biconcave lens 42m and a biconvex lens 42n, and the fourth lens group 44 is composed of a biconvex lens 44h.

[0071] The design values ​​of the seven lenses 38m, 38n, 40o, 40p, 42m, 42n, and 44h that constitute the fθ lens 36 of Example 7 are as shown in Table 11 below. [Table 11]

[0072] The numerical values ​​shown in each column of Table 11 are the same as those shown in each column of Table 5, and therefore will not be described further. The fθ lens 36 of Example 7 achieves the same effects as those of Example 1, as well as the effects achieved by satisfying all of the formulas (1) to (4).

[0073] In Example 8 of the fθ lens 36 shown in Figure 7(B), the first lens group 38 is formed by a biconvex lens 38o and a biconcave lens 38p, the second lens group 40 is formed by a biconcave lens 40q and a biconvex lens 40r, the third lens group 42 is formed by a biconcave lens 42o and a biconvex lens 42p, and the fourth lens group 44 is formed by a biconvex lens 44i and a biconvex lens 44j.

[0074] The design values ​​of the eight lenses 38o, 38p, 40q, 40r, 42o, 42p, 44i, and 44j that constitute the fθ lens 36 in Example 8 are as shown in Table 12 below. [Table 12]

[0075] The numerical values ​​shown in each column of Table 12 are the same as those shown in each column of Table 5, and therefore their explanation will be omitted. The fθ lens 36 of Example 8 achieves the same effects as those of Example 3, as well as the effects achieved by satisfying all of the formulas (1) to (4).

[0076] In Example 9 of the fθ lens 36 shown in Figure 8(A), the first lens group 38 is formed by a biconvex lens 38q and a biconcave lens 38r, the second lens group 40 is formed by a biconcave lens 40s and a biconvex lens 40t, the third lens group 42 is formed by a biconcave lens 42q and a biconvex lens 42r, and the fourth lens group 44 is formed by a biconvex lens 44k.

[0077] The design values ​​of the seven lenses 38q, 38r, 40s, 40t, 42q, 42r, and 44k that constitute the f-theta lens 36 in Example 9 are as shown in Table 13 below. [Table 13]

[0078] The numerical values ​​shown in each column of Table 13 are the same as those shown in each column of Table 5, and therefore their explanation will be omitted. The fθ lens 36 of Example 9 achieves the same effects as those of Example 1, as well as the effects achieved by satisfying all of the formulas (1) to (4).

[0079] In the tenth embodiment of the fθ lens 36 shown in Figure 8(B), the first lens group 38 is composed of a biconvex lens 38s and a biconcave lens 38t, the second lens group 40 is composed of a biconcave lens 40u and a biconvex lens 40v, the third lens group 42 is composed of a convex meniscus lens (positive meniscus lens) 42s, and the fourth lens group 44 is composed of a biconvex lens 44l.

[0080] The design values ​​of the six lenses 38s, 38t, 40u, 40v, 42s, and 44l that make up the fθ lens 36 according to the tenth embodiment are as shown in Table 14 below. [Table 14]

[0081] The numerical values ​​shown in each column of Table 14 are the same as those shown in each column of Table 5, and therefore their explanation will be omitted. The fθ lens 36 of Example 10 exhibits the following effects in addition to the effects achieved by satisfying all of the formulas (1) to (4).

[0082] Specifically, by making the surface of the first lens group 38 closest to the light exit side and the surface of the second lens group 40 closest to the light entrance side both concave, it is possible to correct chromatic aberration of magnification, curvature of field, and astigmatism caused by the first lens group 38. Furthermore, by making the surface of the third lens group 42 closest to the light entrance side concave and the surface of the third lens group 42 closest to the light exit side convex, it is possible to correct curvature of field caused by the first lens group 38 and the second lens group 40.

[0083] Note that, since the fθ lens 36 of Example 10 is used to focus light belonging to a relatively narrow wavelength range (specifically, 1000 nm to 1100 nm), it is expected that the chromatic aberration of magnification caused by the first lens group 38 and the second lens group 40 will be relatively small. Therefore, in Example 10, even if the third lens group 42 is configured by a single convex meniscus lens 42s instead of two lenses cemented together (for example, the biconcave lens 42a and biconvex lens 42b of Example 1), the chromatic aberration of magnification is unlikely to become large.

[0084] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0085] 11: Workpiece 12: Scanning optical system 13: Thin film 14: Optical processing device (thickness measurement device) 16:Light source 18: Half mirror 20: Photoelectric converter 22: Controller 24: Optical processing equipment (laser processing equipment) 26: Light source (26a: first oscillator, 26b: second oscillator) 28:Dichroic mirror 30: Scanning optical system 30: Controller 32: Mirror 34: Power source 36: fθ lens 38: First lens group (38a: biconvex lens, 38b: biconcave lens) (38c: biconvex lens, 38d: biconcave lens) (38e: biconvex lens, 38f: biconcave lens) (38g: biconvex lens, 38h: biconcave lens) (38i: biconvex lens, 38j: concave meniscus lens (negative meniscus lens)) (38k: biconvex lens, 38l: biconcave lens) (38m: biconvex lens, 38n: biconcave lens) (38o: biconvex lens, 38p: biconcave lens) (38q: biconvex lens, 38r: biconcave lens) (38s: biconvex lens, 38t: biconcave lens) 40: Second lens group (40a: second negative lens, 40b: second positive lens) (40c: biconcave lens, 40d: biconvex lens) (40e: biconcave lens, 40f: biconvex lens) (40g: biconcave lens, 40h: biconvex lens) (40i: biconcave lens, 40j: biconvex lens) (40k: biconcave lens, 40l: biconvex lens) (40m: biconcave lens, 40n: biconvex lens) (40o: biconcave lens, 40p: biconvex lens) (40q: biconcave lens, 40r: biconvex lens) (40s: biconcave lens, 40t: biconvex lens) (40u: biconcave lens, 40v: biconvex lens) 42: Third lens group (42a: biconcave lens, 42b: biconvex lens) (42c: biconcave lens, 42d: biconvex lens) (42e: biconcave lens, 42f: biconvex lens) (42g: biconcave lens, 42h: biconvex lens) (42i: biconcave lens, 42j: biconvex lens) (42k: biconcave lens, 42l: biconvex lens) (42m: biconcave lens, 42n: biconvex lens) (42o: biconcave lens, 42p: biconvex lens) (42q: biconcave lens, 42r: biconvex lens) (42s: Convex meniscus lens (positive meniscus lens)) 44: 4th lens group (44a: biconvex lens) (44b: biconvex lens) (44c: biconvex lens, 44d: biconvex lens) (44e: biconvex lens) (44f: biconvex lens) (44g: biconvex lens) (44h: biconvex lens) (44i: biconvex lens, 44j: biconvex lens) (44k: biconvex lens) (44l: biconvex lens)

Claims

1. A scanning optical system including: mirrors for reflecting light beams each belonging to a predetermined wavelength range and having mutually different wavelengths; a drive source for displacing the mirrors so that the light beams reflected by the mirrors are deflected within a predetermined angle range; and an fθ lens for focusing the light beams reflected by the mirrors on a surface to be scanned, The fθ lens is composed of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, which are arranged in this order from the mirror side, the first lens group includes a first positive lens having a convex surface on the light incident side and a first negative lens having a concave surface on the light exit side, the first positive lens being arranged in order from the mirror side; The second lens group is a scanning optical system having, arranged in order from the mirror side, a second negative lens which is a biconcave lens, and a second positive lens which is a biconvex lens and has its convex surface on the light incident side cemented to the concave surface of the second negative lens on the light exit side.

2. 2. The scanning optical system according to claim 1, wherein when a composite focal length of the fθ lens to a d-line having a wavelength of 587.6 nm is F, a composite focal length of the first lens group to the d-line is F1, a composite focal length of the second lens group to the d-line is F2, a composite focal length of the third lens group to the d-line is F3, and a composite focal length of the fourth lens group to the d-line is F4, all of the following mathematical expressions (1) to (4) are satisfied: [Equation 1] [Equation 2] [Equation 3] [Equation 4]

3. a surface of the first positive lens on the light exit side and a surface of the first negative lens on the light incident side are cemented together, 3. The scanning optical system according to claim 2, wherein the third lens group includes, arranged in order from the mirror side, a third negative lens having a concave surface on the light incident side, and a third positive lens having a convex surface on the light exit side, the light incident side surface being bonded to the light exit side surface of the third negative lens.

4. the first positive lens and the first negative lens are disposed so as to be spaced apart from each other, 3. The scanning optical system according to claim 2, wherein the third lens group includes, arranged in order from the mirror side, a third negative lens having a concave surface on the light incident side, and a third positive lens having a convex surface on the light exit side, the light incident side surface being bonded to the light exit side surface of the third negative lens.

5. 5. The scanning optical system according to claim 2, wherein the fourth lens group comprises a plurality of positive lenses.

6. a surface of the first positive lens on the light exit side and a surface of the first negative lens on the light incident side are cemented together, 3. The scanning optical system according to claim 2, wherein the third lens group has a positive meniscus lens having a concave surface on the light incident side.

7. light sources for emitting light beams each having a wavelength different from each other and each belonging to a predetermined wavelength range; an optical processing device comprising a scanning optical system including a mirror for reflecting the light, a drive source for displacing the mirror so that the light reflected by the mirror is deflected within a predetermined angle range, and an fθ lens for focusing the light reflected by the mirror on a surface to be scanned, The fθ lens is composed of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, which are arranged in this order from the mirror side, the first lens group includes a first positive lens having a convex surface on the light incident side and a first negative lens having a concave surface on the light exit side, the first positive lens being arranged in order from the mirror side; The second lens group is an optical processing device having, arranged in order from the mirror side, a second negative lens which is a biconcave lens, and a second positive lens which is a biconvex lens and has its convex surface on the light incident side bonded to the concave surface on the light exit side of the second negative lens.

8. Further comprising a photoelectric converter and a controller to which an electrical signal is input from the photoelectric converter, the light source emits light of a non-single wavelength that falls within the wavelength range; the non-single wavelength light is focused by the scanning optical system and irradiated onto a thin film located on the scanned surface; the photoelectric converter outputs the electrical signal indicative of the spectrum of the non-monochromatic light reflected and interfered at the front and back surfaces of the thin film; The optical processing device of claim 7 , wherein the controller determines the thickness of the thin film based on the electrical signal.

9. Further comprising a controller; The light source is a first oscillator for emitting a first laser beam having a first wavelength within the wavelength range; a second oscillator for emitting a second laser beam having a second wavelength that is within the wavelength range and different from the first wavelength; the first laser beam and the second laser beam are each focused by the scanning optical system and irradiated onto a workpiece located on the scanned surface; 8. The optical processing apparatus according to claim 7, wherein the controller controls the first oscillator and the second oscillator so that either the first laser beam or the second laser beam is selectively irradiated onto the workpiece.

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