A multi-band ultraviolet optical lens

Abstract

The invention discloses a multi-band ultraviolet optical lens, and relates to the technical field of ultraviolet optical lenses. The invention comprises a reflector, a window mirror is arranged on the left side of the reflector, a lens group one is arranged on the left side of the window mirror, a lens group two is arranged on the left side of the lens group one, a lens group three is arranged on the left side of the lens group two, a lens group four is arranged on the left side of the lens group three, and a stop is arranged between the lens group three and the lens group four. The invention adopts the design concept of high numerical aperture ultraviolet objective lens, adopts single wavelength achromatic design means, and utilizes focusing method to realize the optical architecture of high numerical aperture and achromatic ultraviolet lens in two bands of 193nm and 248nm. It has the advantages of strong versatility, excellent lens optical performance, and good adaptability to ultraviolet wavelength, and has broad application prospects, and utilizes the dispersion difference between fused quartz and calcium fluoride materials as a means of achromatic aberration.

Description

Technical Field

[0001] The invention relates to the technical field of ultraviolet optical lenses, and in particular to a multi-band ultraviolet optical lens. Background Art

[0002] Due to its short wavelength, UV lenses are suitable for industrial applications of high-resolution imaging, and their applications in the fields of lithography exposure and semiconductor defect detection are growing. Combined with high numerical aperture technology, the application of UV lasers in lithography, imaging detection, and optical processing is becoming increasingly mature.

[0003] At present, there are few mature UV lenses on the market, and the numerical aperture of such lenses is generally low. However, applications such as lithography, semiconductor defect detection, and microscopic imaging have very stringent requirements on the numerical aperture of UV lenses. In addition, current UV lenses are usually designed for a certain band, and have poor versatility for commonly used UV wavelengths (such as 193nm, 248nm, etc.). For different UV band lasers, different UV lenses are required to achieve related applications. In addition, for UV pulse lasers, due to their short pulse width and wide spectrum broadening, the achromatic ability of conventional lenses is insufficient, which limits the development of UV optics. Therefore, a multi-band, high numerical aperture, and high-performance UV lens is needed to meet the demand for UV band objective lenses in the semiconductor field. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a multi-band ultraviolet optical lens.

[0005] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0006] A multi-band ultraviolet optical lens comprises a reflector, a window mirror is arranged on the left side of the reflector, a lens group 1 is arranged on the left side of the window mirror, a lens group 2 is arranged on the left side of the lens group 1, a lens group 3 is arranged on the left side of the lens group 2, a lens group 4 is arranged on the left side of the lens group 3, and a stop is arranged between the lens group 3 and the lens group 4;

[0007] The lens group 1 is composed of two optical lenses, which are used to correct spherical aberration, coma and part of astigmatism, and convert the incident parallel laser into a divergent light beam. The focal length range of the lens group 1 is: -40mm <f1<-30mm;

[0008] The lens group 2 is composed of four optical lenses, which are used to correct spherical aberration and most chromatic aberrations. The focal length range of the lens group 2 is: 90mm <f2<110mm;

[0009] The lens group 3 is composed of seven optical lenses, which are used to correct chromatic aberration, astigmatism and field curvature. The focal length range of the lens group 3 is: 15mm <f3<24mm;

[0010] The lens group 4 is composed of five optical lenses, which are used to correct spherical aberration, chromatic aberration, and field area, so that laser beams incident at different angles can achieve micron-level spot convergence along the laser propagation direction. The focal length range of the lens group 4 is: 9mm <f4<18mm。

[0011] Furthermore, the material of the second lens group is composed of two pieces of fused quartz and two pieces of calcium fluoride material.

[0012] Furthermore, the lens group three is made of a combination of fused quartz and calcium fluoride.

[0013] Furthermore, the lens group four is made of a combination of fused quartz and calcium fluoride.

[0014] Furthermore, the reflecting mirror, the window mirror, the lens group one, the lens group two, the lens group three, the aperture and the lens group four are installed on the designed lens barrel structure through centering assembly.

[0015] The beneficial effects of the present invention are as follows:

[0016] 1. The present invention adopts the design concept of high numerical aperture ultraviolet objective lens, adopts single wavelength achromatic design means, and uses focusing method to realize the optical structure of high numerical aperture and achromatic ultraviolet lens in two bands of 193nm and 248nm. It has the advantages of strong versatility, excellent lens optical performance, good ultraviolet wavelength adaptability, and has broad application prospects.

[0017] 2. The present invention adopts ultraviolet highly transparent materials such as fused quartz (SiO2) and calcium fluoride (CaF2) as optical materials, and uses the dispersion difference between fused quartz and calcium fluoride materials as a means of achromatization; multiple groups of lenses are used to control the wave aberration of the final imaging of the ultraviolet lens, and the focusing method is adopted to achieve lens imaging of the two bands of 193nm and 248nm by changing the distance between the lens groups. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0019] Figure 2 It is a schematic diagram of the overall light refraction of the present invention;

[0020] Figure 3 This is a schematic diagram of the structure of a lens assembly of the present invention;

[0021] Figure 4 It is a schematic diagram of light refraction of a lens assembly of the present invention;

[0022] Figure 5 is a schematic diagram of the structure of the second lens group of the present invention;

[0023] Figure 6 is a schematic diagram of the refraction of two light rays in the lens group of the present invention;

[0024] Figure 7 Schematic diagram of the third structure of the lens group of the present invention;

[0025] Figure 8 is a schematic diagram of the refraction of three light rays of the lens assembly of the present invention;

[0026] Fig. 9 1 is a schematic diagram of the structure of the lens group 4 of the present invention;

[0027] Fig.10 Schematic diagram of the refraction of four rays of light in the lens assembly of the present invention;

[0028] Fig.11 Schematic diagram of the RMS wavefront difference (193 / 248nm) of the lens of the present invention;

[0029] Fig.12 Schematic diagram of the convergence point diagram (193nm) of the lens of the present invention;

[0030] Fig.13 It is a schematic diagram of the convergence point diagram (248nm) of the lens of the present invention.

[0031] Figure numerals: 1, lens group one; 2, lens group two; 3, lens group three; 4, lens group four; 5, aperture; 6, window mirror; 7, reflecting mirror. DETAILED DESCRIPTION

[0032] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0033] Embodiment 1, as Figure 1-Figure 13 As shown, a multi-band ultraviolet optical lens comprises a reflector 7, a window mirror 6 is arranged on the left side of the reflector 7, a lens group 1 is arranged on the left side of the window mirror 6, a lens group 2 2 is arranged on the left side of the lens group 1, a lens group 3 3 is arranged on the left side of the lens group 2 2, a lens group 4 4 is arranged on the left side of the lens group 3 3, and an aperture is arranged between the lens group 3 3 and the lens group 4 4;

[0034] The light is reflected by the reflector 7 to the window mirror 6, then passes through the window mirror 6, and then enters the lens group 1 in parallel. The lens group 1 is composed of two optical lenses, which are used to correct spherical aberration, coma and part of astigmatism, and convert the incident parallel laser into a divergent beam, providing a design basis for the subsequent improvement of the numerical aperture. The focal length range of the lens group 1 is: -40mm <f1<-30mm;

[0035] Lens group 2 is composed of four optical lenses. Lens group 2 receives the divergent light beam from lens group 1 and switches the two bands of 193nm and 248nm by changing the distance between lens group 2 and lens group 3. This part mainly corrects spherical aberration and most chromatic aberration. The focal length range of lens group 2 is 90mm. <f2<110mm;

[0036] Lens group three 3 is composed of seven optical lenses. Lens group three 3 receives the divergent light beam from lens group two 2 and converts it into a parallel light beam. The light beams of each field of view converge at the aperture 5. This part mainly corrects chromatic aberration, astigmatism and field curvature. The focal length range of lens group three 3 is: 15mm <f3<24mm;

[0037] The aperture 5 is mainly composed of a mechanical structure, which is a circular ring with a cutting edge, which plays a role in limiting the solid angle of the incident light beam, while shielding most of the off-axis stray light, thereby improving the optical performance of the lens;

[0038] Lens group 4 is composed of five optical lenses, which are mainly used to correct spherical aberration, chromatic aberration, and field area, so that the laser beams incident at different angles through the aperture 5 can achieve micron-level spot convergence along the laser propagation direction. The focal length range of lens group 4 is: 9mm <f4<18mm;

[0039] pass Figure 11-13 It can be seen that the imaging quality of the lens at 193nm and 248nm is good, and the focused light spots of different fields of view all meet the micron level requirements; the present invention has the advantages of strong versatility, wide coverage band, and good imaging effect; the single-wavelength achromatic design can meet the requirements of optical instruments for spectrum broadening of ultraviolet femtosecond lasers, and the designed lens has the advantages of compact structure, small size, high precision, etc.; the present invention has been experimentally tested, and the tested lens has achieved a spot size better than 10 microns. It should be noted that Fig.11 The three lines in the middle are, from top to bottom, the RMS wavefront difference of 193nm, the RMS wavefront difference of the polyhedron, and the RMS wavefront difference of 248nm.

[0040] The high numerical aperture ultraviolet lens designed in the present invention has an operating band of 193nm and 248nm (typical excimer laser wavelengths are 193nm and 248nm), is suitable for mainstream ultraviolet laser equipment on the market, has a numerical aperture NA of 0.95, a lens focal length of 8.5mm, a working distance of 2.8mm to 3.2mm (depending on the input laser wavelength), and an adaptable bandwidth range of ±1nm for each typical wavelength value (for example, if the laser wavelength is 193nm, it can work within the range of 193nm±1nm), meeting the laser working requirements of the conventional femtosecond pulse width order; the imaging quality design value of the lens in each band reaches the quality of the diffraction limit, which can ensure the imaging quality of the ultraviolet lens.

[0041] There are 18 lenses in four lens groups. The curvature radius ranges of the surfaces of these lenses and the spacing between the surfaces are shown in Table 1 below (the order of the surfaces is from right to left, i.e. Figure 1 The rightmost surface is surface 1, and the leftmost surface is surface 36):

[0042] Table 1: Lens curvature radius and surface spacing

[0043]

[0044] Embodiment 2, based on the above embodiment, further includes that the lens group 2 is made of a combination of two pieces of fused quartz and two pieces of calcium fluoride.

[0045] Furthermore, lens group three 3 adopts a combination of fused quartz and calcium fluoride.

[0046] Furthermore, lens group 4 uses a combination of fused quartz and calcium fluoride.

[0047] The present invention uses fused quartz and calcium fluoride as raw materials, and realizes ultraviolet lenses of 193nm and 248nm with a numerical aperture of 0.95 through the combined action of multiple groups of lenses, and realizes the working requirements of femtosecond lasers through achromatic design.

[0048] Embodiment three, based on the above embodiment, further includes: a reflector 7, a window mirror 6, a lens group 1 1, a lens group 2 2, a lens group 3 3, an aperture 5 and a lens group 4 4 are assembled through centering and installed on a designed lens barrel structure, which is easy to install and adjust.

[0049] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-band ultraviolet optical lens, comprising a reflector (7), characterized in that: A window mirror (6) is arranged on the left side of the reflector (7), a lens group 1 (1) is arranged on the left side of the window mirror (6), a lens group 2 (2) is arranged on the left side of the lens group 1 (1), a lens group 3 (3) is arranged on the left side of the lens group 2 (2), a lens group 4 (4) is arranged on the left side of the lens group 3 (3), and an aperture (5) is arranged between the lens group 3 (3) and the lens group 4 (4); The lens group one (1) is composed of two optical lenses, which are used to correct spherical aberration, coma and part of astigmatism, and convert the incident parallel laser into a divergent light beam. The focal length range of the lens group one (1) is: -40mm <f1<-30mm; The lens group 2 (2) is composed of four optical lenses, which are used to correct spherical aberration and most chromatic aberrations. The focal length range of the lens group 2 (2) is: 90mm <f2<110mm; The lens group three (3) is composed of seven optical lenses, which are used to correct chromatic aberration, astigmatism and field curvature. The focal length range of the lens group three (3) is: 15mm <f3<24mm; The lens group four (4) is composed of five optical lenses, which are used to correct spherical aberration, chromatic aberration, and field area, so that laser beams incident at different angles can achieve micron-level spot convergence along the laser propagation direction. The focal length range of the lens group four (4) is: 9mm <f4<18mm。 2. The multi-band ultraviolet optical lens according to claim 1, characterized in that: The lens group 2 (2) is made of a combination of two pieces of fused quartz and two pieces of calcium fluoride.

3. The multi-band ultraviolet optical lens according to claim 1, characterized in that: The lens group three (3) is made of a combination of fused quartz and calcium fluoride.

4. The multi-band ultraviolet optical lens according to claim 1, characterized in that: The lens group four (4) is made of a combination of fused quartz and calcium fluoride.

5. The multi-band ultraviolet optical lens according to claim 1, characterized in that: The reflecting mirror (7), the window mirror (6), the lens group one (1), the lens group two (2), the lens group three (3), the diaphragm (5) and the lens group four (4) are mounted on the designed lens barrel structure through centering assembly.

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