Surface scattered light collecting system

Abstract

The surface scattered light collecting system is divided into a wide-channel scattered light path and a narrow-channel scattered light path, a rear wide-channel scattered light negative-focal-power lens group is arranged on the wide-channel scattered light path to correct aberration, and the resolution of a wide-channel scattered light focal plane is improved. Besides, a second reflecting mirror is movably arranged on a narrow channel light path reflected by the first reflecting mirror, and the second reflecting mirror reflects a focal plane of the narrow channel light to an imaging system, so that imaging observation of a target object is realized, debugging and mounting of an optical system are facilitated, and actual morphology of large-size particles or other flaws can be manually observed.

Description

Technical Field

[0001] The present invention relates to the field of wafer measurement technology, and in particular to a surface scattered light collection system. Background Art

[0002] At present, wafer surface defect detection often uses laser scanning of high-speed rotating wafers. If the laser spot encounters a surface defect, scattered light will occur and be emitted in all directions in space. When the surface defect is a particle, the smaller the particle size, the lower the scattering energy. For example, when the defect radius r satisfies 2πr / λ<0.3 (where λ is the wavelength of the incident light), it manifests as Rayleigh scattering, and the scattered light energy tends to be concentrated in the direction of the incident light and the opposite direction symmetrical to the normal line of the wafer surface, which is called wide-channel scattered light. For the scattered light collection system, it is necessary to collect as much wide-channel scattered light as possible to collect enough light energy to identify tiny particles or other defects of similar size. To this end, the optical collection system is required to have a large light collection angle, that is, a large numerical aperture (Na). When the particle size is large, the scattered light intensity is large, and the spatial distribution tends to be asymmetric, usually concentrated in the direction of the normal line of the wafer surface, which is called narrow-channel scattered light.

[0003] The prior art sets up optical components to collect wide channel scattered light and narrow channel scattered light separately, and identifies the type of surface defect detected by comparing the ratio of the two signal intensities with the size of the threshold. However, to achieve a high focusing resolution of wide and narrow channel scattered light with a numerical aperture of more than 0.9 in the same focal plane requires a relatively complex optical structure, and the imaging resolution affects the accuracy of defect detection. In addition, the existing optical detection systems in this field cannot conveniently achieve the simultaneous acquisition of optical signals and detection target surface images, making it difficult to determine the actual situation of the target surface during installation and debugging or actual detection.

[0004] Therefore, how to design parameters of simple optical components to improve the resolution of the focal plane of wide-channel scattered light and narrow-channel scattered light, and how to conveniently realize the confirmation of optical signals and their corresponding images are technical problems that need to be solved in this field. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a surface scattered light collection system, which improves the resolution of the focal planes of wide channel scattered light and narrow channel scattered light through the combination of a positive optical focal power lens group and a negative optical focal power lens group and the separation of wide and narrow scattered light channels, thereby improving the detection sensitivity, and at the same time adds an imaging module to realize target position image observation.

[0006] In order to achieve the above-mentioned purpose, the surface scattered light collection system of the present invention comprises a positive optical power front lens group, a rear wide channel scattered light negative optical power lens group, a wide channel scattered light detector, a first reflector and a narrow channel scattered light detector; the first reflector is located between the positive optical power front lens group and the rear wide channel scattered light negative optical power lens group. Among them, the narrow channel scattered light is separated from the wide channel scattered light by the positive optical power front lens group and the first reflector, and is collected by the narrow channel scattered light detector. Since the wide channel collects large-angle light and has large aberrations, a rear wide channel scattered light negative optical power lens group is additionally arranged on the optical path of the wide channel scattered light to correct the aberration, so as to achieve the purpose of improving the focal plane resolution of the wide channel scattered light.

[0007] Another purpose of the present invention is to facilitate manual real-time observation of the wafer surface morphology. During the installation and debugging of the detection equipment, it is necessary to identify whether the wafer rotation center is concentric with the optical collection system. At this time, it is necessary to observe the wafer surface morphology, which requires an independent optical system for debugging, and the debugging process is complicated. In addition, in some detection processes, it is hoped that the actual morphology of particles or other defects can be observed, such as large-sized particles or scratches.

[0008] In order to achieve the above-mentioned purpose, the surface scattered light collection system of the present invention also includes a second reflector and an imaging system, wherein the second reflector is movably arranged on the optical path of the narrow channel light reflected by the first reflector, and the narrow channel light is reflected again by the second reflector, so that the focal plane of the light beam is reflected to the imaging system, thereby realizing the imaging observation of the target object; if the second reflector is moved away from the optical path of the narrow channel light, the focal plane of the light beam falls on the narrow channel scattered light detector, thereby realizing the detection of the narrow channel scattered light. Preferably, the above-mentioned imaging system selects a separate array photoelectric detector, such as a CCD or CMOS camera, or selects an imaging system composed of an optical imaging lens with a certain magnification and an array photoelectric detector.

[0009] The technical effects of the present invention are as follows: The surface scattered light collection system of the present invention is divided into a wide channel scattered light path and a narrow channel scattered light path. A rear wide channel scattered light negative focal lens group is arranged on the wide channel scattered light path to correct aberration, thereby improving the resolution of the wide channel scattered light focal plane.

[0010] A second reflector is movably arranged on the optical path of the narrow channel light reflected by the first reflector. The second reflector reflects the focal plane of the narrow channel light to the imaging system, thereby realizing imaging observation of the target object, facilitating the debugging and installation of the optical system and manual observation of the actual morphology of large-sized particles or other defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1It is a schematic diagram of the structure of the surface scattered light collection system of Example 1.

[0012] Figure 2 This is the MTF curve of the wide channel scattered light focal plane imaging resolution in Example 1.

[0013] Figure 3 This is the MTF curve of the focal plane imaging resolution of narrow channel scattered light in Example 1.

[0014] Figure 4 It is a schematic diagram of the structure of the surface scattered light collection system of Example 2.

[0015] Figure 5 This is the resolution MTF curve of wide channel scattered light focal plane imaging in Example 2.

[0016] Figure 6 This is the MTF curve of the narrow channel scattered light focal plane imaging resolution in Example 2. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0018] A surface scattered light collection system, comprising a positive focal power front lens group G 1 , rear wide channel scattered light negative focal lens group G 2 , wide channel scattered light detector D w , the first reflector M 1 , narrow channel scattered light detector D n and the second reflector M 2 .

[0019] Among them, the focal length of the positive power front lens group is f 前 Satisfy 10mm≤f 前 ≤70mm, working distance WD satisfies 3mm≤WD≤10mm, numerical aperture is 0.9; focal length f of rear wide channel scattered light negative focal lens group 后 Satisfy -50mm≤f 后 ≤-100mm; the optical spacing L between the positive focal power front lens group and the rear wide channel scattered light negative focal power lens group satisfies 30mm≤L≤100mm.

[0020] The first reflector M 1 Placed in the positive power front lens group G 1 With the rear wide channel scattered light negative focal lens group G 2 Between, positive focal length front lens group G 1 The optical axis passes through the first reflector M 1The center of the lens is 45° from the front lens group G with positive focal length. 1 The emitted light beam is partially reflected by the first reflector M 1 Reflection, the reflected light beam is equivalent to the positive focal length of the front lens group G 1 Na 窄 Satisfy 0.15≤Na 窄 ≤0.65, this part of the light is the narrow channel scattered light; the rest is not reflected by the first reflector M 1 Since the reflected light is the light at the edge of the beam, it corresponds to the wide channel scattered light. After it enters the wide channel scattered light path, the negative optical focal length lens group G 2 , forming a focal plane on the wide channel scattered light detector D w The detection of wide channel scattered light is realized. 1 And the rear wide channel scattered light negative focal lens group G 2 The combined optical system has a magnification M for the wafer surface, where M satisfies 10≤M≤30.

[0021] Second reflector M 2 The angle between the second reflector M and the light is 45°. 2 When placed on the optical path, the narrow channel light is reflected by the second reflector M 2 Reflected again, the focal plane of the light beam is reflected to the imaging system IM, realizing the imaging observation of the target object; if the second reflector M 2 When it is moved away from the narrow channel light path, the focal plane of the light beam falls on the narrow channel scattered light detector D n The detection of scattered light in a narrow channel is realized.

[0022] Furthermore, pinholes are provided at the focal planes of the wide channel and narrow channel beams, and the pinhole diameter D p Meet 0.05mm≤D p ≤2mm, distance L between pinhole and wide and narrow channel scattered light detector p Satisfy 1mm≤L p ≤20mm.

[0023] Embodiment 1 See also Figure 1 , a surface scattered light collection system, positive focal power front lens group G 1 It is composed of 4 lenses, with a numerical aperture Na of 0.9 and a focal length f 前 =27.24mm, working distance WD=5mm, incident light wavelength is 266nm, field of view range is ±0.1mm, rear wide channel scattered light negative focal lens group G 2 It consists of 2 lenses with a focal length of f 后 =-55mm, positive focal length front lens group G 1With the rear wide channel scattered light negative focal lens group G 2 The optical distance L is 41.67 mm, and the magnification M of the optical system composed of the two is 20 times.

[0024] The specific parameters of the above lens group are shown in Table 1 and Table 2: Table 1 Positive power front lens group G 1 And the rear wide channel scattered light negative focal lens group G 2 parameter

[0025] Table 2 Aspheric parameters of lens L1

[0026] The first reflector M 1 Set in the positive power front lens group G 1 With the rear wide channel scattered light negative focal lens group G 2 Between, from the positive focal power front lens group G 1 The emitted light beam is partially reflected by the first reflector M 1 The other part is reflected by the first reflector M 1 Peripheral radiation to the rear wide channel scattered light negative focal lens group G 2 , after the wide channel scattered light negative focal lens group G 2 After refraction, the light beam is focused to form a focal plane. The MTF curve of imaging resolution on the focal plane is shown in Figure 2 Among them, the top one is the diffraction limit MTF curve, and the other curves are the imaging resolution MTF curves of different target objects. It can be seen from the figure that the system resolution effect is better and is sufficient to meet the pinhole detection.

[0027] There is a pinhole at the focal plane of the wide channel scattered light, and a wide channel scattered light detector D is placed at a distance of Lp=20mm from the pinhole. w The light in the middle of the focal plane passes through the pinhole and reaches the wide channel scattered light detector D w A wide channel scattered photoelectric signal is formed.

[0028] The positive power front lens group G 1 The first reflector M 1 The reflected light beam corresponds to the positive power front lens group G 1 The object numerical aperture Na 窄 is 0.36. 1 A movable second reflector M is provided on the optical path of the reflected light. 2 , when the second reflector M 2When placed on the optical path, this part of the light is reflected again, so that the focal plane of the light beam is reflected to the imaging system IM. The imaging resolution MTF curve on the focal plane is shown in Figure 3 As can be seen from the figure, the MTF is close to the diffraction limit and the imaging effect is excellent. The imaging system IM is a CCD camera, which realizes the imaging observation of the target object, facilitates the debugging and installation of the optical system and the manual observation of the actual morphology of large-sized particles or other defects; when the second reflector M 2 When removed from the optical path, the beam falls on the narrow channel scattered light detector D n A narrow channel scatters the photoelectric signal.

[0029] There is a pinhole at the focal plane of the narrow channel scattered light, and a narrow channel scattered light detector D is placed 20 mm away from the pinhole. n The light in the middle of the focal plane passes through the pinhole and reaches the narrow channel scattered light detector D w A narrow channel scatters the photoelectric signal.

[0030] Embodiment 2 See also Figure 4 , a surface scattered light collection system, which is different from the first embodiment in that the positive focal power front lens group G 1 It is composed of 5 lenses, with a numerical aperture Na of 0.9 and a focal length f 前 =48.47mm, working distance WD=9mm, incident light wavelength is 266nm, field of view range is ±0.15mm, rear wide channel scattered light negative focal lens group G 2 Consists of 1 lens, focal length f 后 =-59.69mm, positive focal length front lens group G 1 With the rear wide channel scattered light negative focal lens group G 2 The optical distance L is 85mm, and the magnification M of the optical system composed of the two is 25 times.

[0031] The specific parameters of the above lens group are shown in Table 3 and Table 4: Table 3 Positive power front lens group G 1 And the rear wide channel scattered light negative focal lens group G 2 parameter

[0032] Table 4 Aspheric parameters of lens L1

[0033] The first reflector M 1 Set in the positive power front lens group G 1 With the rear wide channel scattered light negative focal lens group G2 Between, from the positive focal power front lens group G 1 The emitted light beam is partially reflected by the first reflector M 1 The other part is reflected by the first reflector M 1 Peripheral radiation to the rear wide channel scattered light negative focal lens group G 2 , after the wide channel scattered light negative focal lens group G 2 After refraction, the light beam is focused to form a focal plane. The MTF curve of imaging resolution on the focal plane is shown in Figure 5 As can be seen from the figure, this system has a better resolution effect and can meet the requirements of pinhole detection.

[0034] There is a pinhole P at the focal plane of the wide channel scattered light w , with the pinhole P w A wide channel scattered light detector D is placed at a distance of 30 mm from Lp. w The light in the middle of the focal plane passes through the pinhole and reaches the wide channel scattered light detector D w A wide channel scattered photoelectric signal is formed.

[0035] The positive power front lens group G 1 The first reflector M 1 The reflected light beam corresponds to the positive power front lens group G 1 The object numerical aperture Na 窄 is 0.25. 1 A movable second reflector M is provided on the optical path of the reflected light. 2 , when the second reflector M 2 When placed on the optical path, this part of the light is reflected again, so that the focal plane of the light beam is reflected to the imaging system IM. The imaging resolution MTF curve on the focal plane is shown in Figure 6 As can be seen from the figure, the MTF is close to the diffraction limit and the imaging effect is excellent. The imaging system IM is composed of a microscope objective and a CCD camera, which realizes the imaging observation of the target object, facilitates the debugging and installation of the optical system and the manual observation of the actual morphology of large-sized particles or other defects; when the second reflector M 2 When removed from the optical path, the beam falls on the narrow channel scattered light detector D n A narrow channel scatters the photoelectric signal.

[0036] There is a pinhole P at the focal plane of the scattered light in the narrow channel n , with the pinhole P n A narrow channel scattered light detector D is placed at a distance of 30 mm. n The light in the middle of the focal plane passes through the pinhole and reaches the narrow channel scattered light detector D w A narrow channel scatters the photoelectric signal.

[0037] The above describes in detail the basic principles, main features and advantages of the present invention in the field under investigation, and describes in detail some examples of use. Finally, it should be noted that the examples cited above are only used to explain this patent and are not used to limit the present invention. Although we have described the present invention in detail with reference to the examples, technicians in this field can still modify the examples and schemes described, or replace the relevant technical parts. Therefore, any modifications and equivalent replacements made within the spirit and principles of the present invention are within the scope of protection of the claims of the patent of this invention.

Claims

1. A surface scattered light collection system, comprising a positive power front lens group, a rear wide channel scattered light negative power lens group, a wide channel scattered light detector, a first reflector and a narrow channel scattered light detector; A positive power front lens group, a first reflector, a rear wide channel scattered light negative power lens group and a wide channel scattered light detector are sequentially arranged along the optical axis of the positive power front lens group; the first reflector is arranged obliquely relative to the optical axis of the positive power front lens group, and reflects the narrow channel scattered light collected by the positive power front lens group to the narrow channel scattered light detector; The wide channel scattered light collected by the positive optical power front lens group is focused by the rear wide channel scattered light negative optical power lens group onto the wide channel scattered light detector.

2. A surface scattered light collection system as claimed in claim 1, characterized in that: The focal length f of the positive power front lens group 前 :10mm≤f 前 ≤70mm; the focal length f of the rear wide channel scattered light negative focal lens group 后 :-50mm≤f 后 ≤-100mm; the optical spacing L between the positive focal power front lens group and the rear wide channel scattered light negative focal power lens group: 30mm≤L≤100mm.

3. A surface scattered light collection system as claimed in claim 2, characterized in that: The working distance WD of the positive focal power front lens group is 3mm≤WD≤10mm, and the numerical aperture is greater than or equal to 0.9; the narrow channel scattered light is equivalent to the numerical aperture Na of the positive focal power front lens group 窄 :0.15≤Na 窄 ≤0.

65.

4. A surface scattered light collection system as claimed in claim 2, characterized in that: A pinhole is provided at the focal plane of the wide channel scattered light and the narrow channel scattered light, and the pinhole diameter D p :0.05mm≤D p ≤2mm, the distance L between the pinhole and the wide channel scattered light detector and the narrow channel scattered light detector p :1mm≤L p ≤20mm.

5. A surface scattered light collection system as claimed in claim 1, characterized in that: The combined optical system of the positive focal power front lens group and the wide channel scattered light negative focal power rear lens group has a magnification M of 10≤M≤30 for the detected surface.

6. A surface scattered light collection system as claimed in claim 1, characterized in that: It also includes a second reflector and an imaging system, wherein the second reflector is movably located between the first reflector and the narrow channel scattered light detector; when the second reflector moves to the narrow channel scattered light path, the narrow channel scattered light is reflected by the second reflector to the imaging system.

Images