Laser detection system for observing particles or defects of non-transparent sample

Abstract

The invention relates to a laser detection system for observing particles or defects of a non-transparent sample, and belongs to the technical field of laser measuring instruments. Through the combination of the light receiving lens comprising the two light transmitting holes and the symmetrically arranged conical holes, the excitation light source, the light collimation system and the reflecting mirror, on one hand, a laser focusing beam can irradiate and focus the surface of a sample through the two conical holes, and the situation that laser enters the lens and influences weak scattered light signals is avoided; on the other hand, a normal incident excitation light beam can be converged on the surface of the sample through a reflecting mirror and a light receiving lens in sequence, particles or defects on the sample are excited through the excitation light, refracted light is generated, the refracted light is reflected for four times in the light receiving lens through the light receiving lens of a special structure and then is emitted and converged, and a light collimation system is arranged for capturing; therefore, the length of the whole light path system is effectively shortened, the problems of large equipment size and complex structure are solved, and meanwhile, large-numerical-aperture light energy collection can be realized.

Description

Technical Field

[0001] The present invention relates to a laser detection system for observing particulate matter or defects of non-transparent samples, belonging to the technical field of laser measuring instruments. Background Art

[0002] When a tiny object (such as particulate matter or defects on the surface of a sample) is irradiated by light, its scattered light is emitted in all directions in space. The smaller the size of the object, the lower the scattered energy, and the wider the angular distribution of the scattered energy, hereinafter referred to as wide-channel scattered light. For a scattered light collection system, it is necessary to collect as much wide-channel scattered light as possible to collect sufficient scattered signals of tiny objects for measuring and identifying the characteristics of tiny objects or other information of interest.

[0003] In the prior art, an optical energy collection device with a large light collection range (i.e., a large numerical aperture NA) is often used to collect scattered light energy. For example, in CN119804392A and CN110426326A, an ellipsoidal mirror is used to collect light energy. However, the amount of light energy collected by the ellipsoidal mirror is closely related to the distance between the two foci of the ellipsoid. The longer the distance, the larger the collection angle can be. The structure designed in this way is inevitably large, making the device structure complex, which is not conducive to the installation and debugging of the device, stability, and cost control.

[0004] In addition, for example, in CN118732248A and CN119620341A, a two-folded optical path is used to shorten the overall length, and the folded mirror group for collecting light energy is composed of 3 separate optical elements, which also makes the device structure complex and is not conducive to the installation and debugging of the device, stability, and cost control.

[0005] Therefore, in view of the above problems, there is an urgent need to find a laser measurement and detection device that can collect as much excitation light energy as possible and simplify the volume structure of the device. Summary of the Invention

[0006] In view of the above problems, the present invention provides a laser detection system for observing particulate matter or defects of non-transparent samples, comprising:

[0007] An excitation light source capable of emitting a laser focused beam;

[0008] The light collecting lens has two optically surfaces arranged oppositely, which are S1 surface and S2 surface respectively; wherein, the S1 surface has a curvature and is provided with a first light transmitting hole at the central position, and a reflective film is plated outside the first light transmitting hole; the S2 surface is a plane and is provided with a second light transmitting hole at the central position, and a reflective film is also plated outside the second light transmitting hole; the light collecting lens is respectively provided with a first tapered hole and a second tapered hole which are symmetrically arranged and penetrate through the light collecting lens on both sides of the optical axis, and the large-diameter ends of the first tapered hole and the second tapered hole are opened on the side surface of the light collecting lens;

[0009] The light collimation system has a positive optical power and is arranged on the extension line of the optical axis of the light collecting lens;

[0010] A reflecting mirror with an inclination angle of 45 degrees is arranged between the light collecting lens and the light collimation system;

[0011] A sample is arranged on the side where the S2 surface of the light collecting lens is located. An obliquely incident excitation light beam generated by an excitation light source passes through the first tapered hole and penetrates the light collecting lens to irradiate the sample, and then passes through the second tapered hole and exits the light collecting lens after being reflected by the sample; another normally incident excitation light beam is incident on the reflecting mirror in a direction perpendicular to the optical axis, and after being reflected by the reflecting mirror, the normally incident excitation light beam passes through the light collecting lens and converges on the surface of the sample, so that the particulate matters or defects on the sample are excited to generate scattered light. The scattered light can enter the light collecting lens through the second light transmitting hole and is reflected four times between the two optically surfaces of the light collecting lens and then exits from the first light transmitting hole. The emitted light rays will converge at a convergence point F2 on the optical axis outside the light collecting lens, and the convergence point coincides with the focus of the light collimation system. The emitted light rays will emit parallel light rays after passing through the light collimation system.

[0012] Further, the scattered light can enter the light collecting lens through the second light transmitting hole at a scattering angle of α to β, wherein the minimum scattering angle α = 5°, and the maximum scattering angle β = 71.8°.

[0013] Further, the scattered light is sequentially reflected on the S1 surface and the S2 surface in the light collecting lens as r1, r2, r3, r4 in sequence, where r1 and r3 are on the S1 surface, and r2 and r4 are on the S2 surface, that is, the scattered light is reflected four times in the light collecting lens and then exits from the first light transmitting hole.

[0014] Further, the relationship between the diameter D1 of the first light transmitting hole and the diameter D2 of the second light transmitting hole is 0.8 ≤ D1 / D2 ≤ 1.2.

[0015] Further, the relationship between the diameter D3 of the light collecting lens and the diameter D1 of the first light transmitting hole and the diameter D2 of the second light transmitting hole is D1 / D3 ≤ 1 / 3, D2 / D3 ≤ 1 / 3.

[0016] Further, among the four reflections of the light entering the light collecting lens from the S2 surface at the minimum scattering angle α, the distance L2 between the fourth reflection point r4b and the optical axis O of the light collecting lens is L2 > 0.5 * D2; when the light enters the light collecting lens from the S2 surface at the maximum scattering angle β, the distance L1 between the transmission position from the S1 surface after the fourth reflection and the optical axis O of the light collecting lens is L1 < 0.5 * D1.

[0017] Further, a negative lens is also provided between the light collecting lens and the reflector. The negative lens can reduce the convergence angle of the outgoing light rays emitted from the light collecting lens and converge them at a convergence point F3 on the optical axis outside the light collecting lens, and the convergence point coincides with the focus of the light collimation system, thereby reducing the image-side NA value; a through hole for the normally incident excitation beam to pass through is provided at the center of the negative lens.

[0018] Further, the diameter of the negative lens is Df, and the diameter of the through hole is Dt, and Dt / Df ≤ 0.5.

[0019] Advantages of the present invention:

[0020] By combining a light collecting lens including two light-transmitting holes and symmetrically arranged tapered holes with an excitation light source, a light collimation system, and a reflector, on the one hand, the laser focused beam can irradiate and focus on the sample surface through the two tapered holes, avoiding the laser from entering the lens and affecting the signal of the weak scattered light. On the other hand, the normally incident excitation beam can pass through the reflector and the light collecting lens in sequence and converge on the sample surface, forming excitations in two directions, namely oblique and forward. The refracted light generated by the excitation of the particulate matter or defects on the sample by the excitation light is reflected four times in the light collecting lens with a special structure and then emitted and converged, and is captured by the light collimation system. Therefore, the overall optical path system length is effectively shortened, solving the problems of large equipment volume and complex structure, and at the same time, it can achieve the collection of light energy with a large numerical aperture. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the overall structure (without a negative lens) of Embodiment 1 of the present invention.

[0022] Figure 2 It is a schematic diagram of the overall structure (with a negative lens) of Embodiment 2 of the present invention.

[0023] Figure 3 It is a schematic diagram of the structure of the light collecting lens of the present invention.

[0024] Figure 4 It is a spot diagram of the light rays of Embodiment 1 of the present invention converged by the light collecting lens.

[0025] Figure 5 It is a spot diagram of the light rays of Embodiment 2 of the present invention converged by the light collecting lens.

[0026] In the figure, 1 is the normal incident excitation light beam; 2 is the light collecting lens; 3 is the light collimation system; 4 is the mirror; 5 is the sample; 6 is the oblique incident excitation light beam; 7 is the negative lens; 2A is the first conical hole; 2B is the second conical hole. Specific embodiments

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] In the present invention, unless otherwise clearly defined and limited, the terms "connected", "connected", and "fixed" shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the present invention, the "first" and "second" are only used to distinguish the same type of components / parts in different positions or with different features, and have no other limiting meanings; the "upper" refers to the direction in which each component deviates from the ground, and the "lower" refers to the direction in which each component is away from the ground.

[0030] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being "above", "above", and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "below", "below", and "under" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0031] Embodiment 1

[0032] As Figure 1 shown, the present invention provides a laser detection system for observing particulate matter or defects of non-transparent samples, including an excitation light source, a light collecting lens, a light collimation system, etc. The sample 5 is selected as a silicon wafer, where:

[0033] The excitation light source 1 is a light source component capable of emitting a laser focused light beam. InFigure 1 In the example, the emitted light is a vertically incident excitation light beam from bottom to top;

[0034] The light receiving lens 2 has two optical surfaces arranged opposite to each other. The two optical surfaces are the S1 surface and the S2 surface respectively. Among them, the S1 surface has a curvature (aspherical surface) and is provided with a first light-transmitting hole at the center position. A reflective film is plated outside the first light-transmitting hole. The S2 surface is a plane and is provided with a second light-transmitting hole at the center position. A reflective film is also plated outside the second light-transmitting hole. The light receiving lens is provided with symmetrically arranged first tapered holes 2A and second tapered holes 2B that penetrate the light receiving lens on both sides of the optical axis. The large-diameter ends of the first tapered holes 2A and the second tapered holes 2B are opened on the side surface of the light receiving lens 2. The obliquely incident excitation light beam 6 can pass through the first tapered hole 2A and penetrate the entire light receiving lens 2 to reach the surface of the sample 5 on the S2 surface side. After being reflected by the surface of the sample 5, it is then emitted from the light receiving lens 2 through the second tapered hole 2B;

[0035] Preferably, the diameter D1 of the first light-transmitting hole is 12 mm, and the diameter D2 of the second light-transmitting hole is 14 mm. The diameter D3 of the light receiving lens is 58 mm, the thickness is 22.926 mm, and the working wavelength is 0.266 um.

[0036] The specific parameters of the light receiving lens 2 are shown in Table 1:

[0037] Table 1

[0038]

[0039] The light collimation system has a positive optical power and is arranged on the extension line of the optical axis of the light receiving lens 2. It can collect and converge light from the left end and emit parallel light from the right end to achieve the light collimation effect, so as to facilitate the subsequent use of various optical elements to process and analyze the collected signals;

[0040] On the one hand, the sample 5 is arranged on the side where the S2 surface of the light receiving lens is located. The obliquely incident excitation light beam 6 passes through the first tapered hole 2A and passes through the light receiving lens 2 to irradiate the sample. After being reflected by the sample, it is then emitted from the light receiving lens 2 through the second tapered hole 2B, avoiding the laser from entering the light receiving lens 2 and affecting the signal of the weak scattered light.

[0041] On the other hand, in this embodiment, a downwardly inclined mirror 4 with an inclination angle of 45 degrees is provided between the light collecting lens 2 and the light collimating system 3; another normal incident excitation beam 1 is incident on the mirror from bottom to top in a direction perpendicular to the optical axis. After being reflected by the mirror, the normal incident excitation beam passes through the light collecting lens and converges on the surface of the sample 5, so that the particulate matter or defects on the sample 5 are excited to generate scattered light. The scattered light can enter the light collecting lens 2 through the second light transmission hole and be reflected four times between the two optical surfaces of the light collecting lens 2 and then exit from the first light transmission hole. The emitted light rays will converge at a convergence point F2 on the optical axis outside the light collecting lens 2 and the convergence point coincides with the focus of the light collimating system 3. The emitted light rays will emit parallel light rays after passing through the light collimating system 3, which is conducive to subsequent processing and analysis of the collected signals using various optical elements.

[0042] Further, as Figure 3 shown, the scattered light can enter the light collecting lens 2 through the second light transmission hole at a scattering angle of α to β, where the minimum scattering angle α = 23°, and the maximum scattering angle β = 71.8°. The scattered light is sequentially reflected at r1, r2, r3, and r4 on the S1 surface and the S2 surface in the light collecting lens 2, where r1 and r3 are on the S1 surface, and r2 and r4 are on the S2 surface, that is, the scattered light is reflected four times in the light collecting lens 2 and then exits from the first light transmission hole, thereby effectively shortening the overall optical path system length.

[0043] Further, in the four reflections of the scattered light entering the light collecting lens 2 from the S2 surface at the minimum scattering angle α, the distance L2 from the fourth reflection point r4b to the optical axis O of the light collecting lens is 6.3 mm; when the scattered light enters the light collecting lens 2 from the S2 surface at the maximum scattering angle β, the distance from the transmission position on the S1 surface after the fourth reflection to the optical axis O of the light collecting lens is L2 = 6.3 mm.

[0044] The light rays with scattering angles between α and β are all collected by the light collecting lens 2 and finally basically converge at a point F2 on the optical axis O outside the light collecting lens. As Figure 4 shown, the RMS radius of the converging light spot is 0.403 um, and the focusing effect is good.

[0045] Embodiment 2

[0046] On the basis of the structure of Embodiment 1, a negative lens 7 is provided between the light collecting lens 2 and the mirror 4. As Figure 2 shown, the negative lens 7 can reduce the converging angle of the emitted light rays from the light collecting lens 2 and converge them at a convergence point F3 on the optical axis outside the light collecting lens 2, and the convergence point coincides with the focus of the light collimating system 3, thereby reducing the image-side NA value. The NA of the light collimating system 3 only needs to be greater than 0.28 to collect all the light rays; a through hole for the normal incident excitation beam to pass through is provided at the center of the negative lens 7.

[0047] Different from Embodiment 1, the relevant parameters of the light collecting lens in this embodiment are adjusted: the diameter D1 of the first light transmitting hole is 16 mm, and the diameter D2 of the second light transmitting hole is 14.7 mm. The diameter D3 of the light collecting lens is 70 mm, the thickness is 28.82 mm, and the working wavelength is 0.266 um. For the specific parameters of the light collecting lens 2, please refer to Table 2:

[0048] Table 2

[0049]

[0050] Further, the distance between the light collecting lens 2 and the negative lens 7 is 2 mm. Preferably, the diameter of the negative lens 7 is Df, the diameter of the through hole is Dt, and Dt / Df ≤ 0.5. For the specific parameters of the negative lens 7, please refer to Table 3:

[0051] Table 3

[0052]

[0053] Further, in the four reflections of the light entering the light collecting lens from the S2 plane with the minimum scattering angle α, the distance L2 from the fourth reflection point r4b to the optical axis O of the light collecting lens is 6.8 mm; when the light enters the light collecting lens from the S2 plane with the maximum scattering angle β, the transmission position of the light from the S1 plane after the fourth reflection is at a distance L1 = 5.8 mm from the optical axis O of the light collecting lens.

[0054] On the one hand, a sample 5 is arranged on the side of the light collecting lens where the S2 plane is located. The obliquely incident excitation beam 6 passes through the first conical hole 2A to irradiate the sample through the light collecting lens, and after being reflected by the sample, it exits the light collecting lens 2 through the second conical hole 2B, avoiding the laser from entering the light collecting lens 2 and affecting the signal of the weak scattered light.

[0055] On the other hand, another normally incident excitation beam 1 is incident on the mirror 4 from bottom to top in a direction perpendicular to the optical axis. After being reflected by the mirror 4, the normally incident excitation beam sequentially passes through the through hole of the negative lens 7, the first light transmitting hole and the second light transmitting hole of the light collecting lens 2 and converges on the surface of the sample 5, so that the particulate matter or defects on the sample 5 are excited to generate scattered light. The scattered light can enter the light collecting lens 2 through the second light transmitting hole and undergo four reflections between the two optical surfaces of the light collecting lens 2 and then exit from the first light transmitting hole. The emitted light rays will converge at a convergence point F3 on the optical axis outside the light collecting lens 2, and the convergence point coincides with the focus of the light collimation system 3. The emitted light rays will emit parallel light rays after passing through the light collimation system 3, which is conducive to subsequent processing and analysis of the collected signals using various optical elements.

[0056] Similarly, as Figure 3As shown, the scattered light can still enter the light-receiving lens 2 through the second light-transmitting hole at a scattering angle of α to β, where the minimum scattering angle α = 18° and the maximum scattering angle β = 71.8°. The scattered light is sequentially reflected on the S1 surface and the S2 surface in the light-receiving lens 2 for r1, r2, r3, and r4 in sequence, where r1 and r3 are on the S1 surface, and r2 and r4 are on the S2 surface. That is, after the scattered light is reflected four times in the light-receiving lens 2, it exits from the first light-transmitting hole, thereby effectively shortening the overall length of the optical path system.

[0057] Light rays with scattering angles between α and β are all collected by the light-receiving lens 2 and finally basically converge at a point F2 on the optical axis O outside the light-receiving lens, as Figure 5 shown. The RMS radius of the converging light spot is 0.07 um, and the focusing effect is good.

[0058] Embodiment 3

[0059] According to actual requirements, the laser detection system of Embodiment 1 or Embodiment 2 can be reasonably selected for sample defect detection and measurement. The specific method is as follows:

[0060] Step 1: Place the surface of the sample 5 to be detected at the focal point on one side of the light-receiving lens 2, and use the normally incident excitation beam 1 to emit towards the mirror 4. After reflection, it passes through the light-receiving lens 2 (or sequentially passes through the negative lens 7 and the light-receiving lens 2) and is focused on the surface of the sample 5 to be detected; alternatively, the obliquely incident excitation beam 6 can also be used to focus on the sample through the first conical hole 2A.

[0061] Step 2: Move the sample 5 along a certain path. For example, for a circular sample, move spirally outward starting from the center of the sample, or for a square sample, move along a "bow" - shaped path.

[0062] Step 3: During the movement, if there are particles or defects on the surface of the sample, the incident laser will be scattered. The smaller the size of the particles or defects, the wider the angular distribution of the scattered light energy. This scattered light energy enters the light-receiving lens with a large numerical aperture through the second light-transmitting hole, is collected and enters the inside of the lens, and after 4 reflections between the S1 surface and the S2 surface before and after the lens, it passes through the first light-transmitting hole and exits the light-receiving lens 2, and converges at a converging point F2 or F3 on the optical axis outside the light-receiving lens 2.

[0063] Step 4: After the light passes through the point F2 or F3, it enters the light collimation system 3 and will exit in a collimated state.

[0064] Step 5: Since the light beam collimated and emitted by the light collimation system 3 is parallel light, there is sufficient space to place various optical devices for various processes. For example, a filter can be used to obtain the wavelength of interest, a polarizer can be used to obtain the light with the polarization state of interest, etc. Finally, these light beams are incident on the photoelectric conversion device to be converted into electrical signals. The presence or absence, strength, corresponding wavelength, and appearance time of the electrical signals are used to characterize the presence or absence, size, composition, position, etc. of the particulate matter, realizing the detection of particulate matter or defects in a laser manner.

[0065] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A laser detection system for observing particulate matter or defects in non-transparent samples, characterized in that, Including: An excitation light source capable of emitting excitation light beams in any direction; A light collecting lens having two optically surfaces disposed opposite to each other, the two optically surfaces being S1 surface and S2 surface respectively; wherein, the S1 surface has a curvature and is provided with a first light transmission hole at the central position, and a reflective film is plated outside the first light transmission hole; the S2 surface is a plane and is provided with a second light transmission hole at the central position, and a reflective film is also plated outside the second light transmission hole; the light collecting lens is provided with a first tapered hole and a second tapered hole which are symmetrically arranged on both sides of the optical axis and penetrate through the light collecting lens, and the large-diameter ends of the first tapered hole and the second tapered hole are opened on the side surface of the light collecting lens; A light collimation system having a positive focal power and disposed on the extension line of the optical axis of the light collecting lens; A reflecting mirror with an inclination angle of 45 degrees is disposed between the light collecting lens and the light collimation system; A sample is disposed on the side where the S2 surface of the light collecting lens is located. An obliquely incident excitation light beam generated by the excitation light source passes through the first tapered hole and penetrates through the light collecting lens to irradiate the sample, and after being reflected by the sample, it passes through the second tapered hole and exits the light collecting lens; another perpendicularly incident excitation light beam is incident on the reflecting mirror in a direction perpendicular to the optical axis, and after being reflected by the reflecting mirror, the perpendicularly incident excitation light beam passes through the light collecting lens and converges on the surface of the sample, so that the particulate matter or defects on the sample are excited to generate scattered light. The scattered light can enter the light collecting lens through the second light transmission hole and be reflected four times between the two optically surfaces of the light collecting lens and then exit from the first light transmission hole. The emitted light rays will converge at a convergence point F2 on the optical axis outside the light collecting lens, and the convergence point coincides with the focal point of the light collimation system. The emitted light rays will emit parallel light rays after passing through the light collimation system.

2. The laser detection system according to claim 1, wherein The scattered light can enter the light collecting lens through the second light transmission hole at a scattering angle of α to β, where the minimum scattering angle α = 5°, and the maximum scattering angle β = 71.8°.

3. The laser detection system according to claim 2, wherein The scattered light is sequentially reflected at the S1 surface and the S2 surface in the light collecting lens as r1, r2, r3, r4 in sequence, where r1 and r3 are at the S1 surface, and r2 and r4 are at the S2 surface, that is, the scattered light is reflected four times in the light collecting lens and then exits from the first light transmission hole.

4. The laser detection system according to claim 3, wherein The relationship between the diameter D1 of the first light transmission hole and the diameter D2 of the second light transmission hole is 0.8 ≤ D1 / D2 ≤ 1.2; the relationship between the diameter D3 of the light collecting lens and the diameter D1 of the first light transmission hole and the diameter D2 of the second light transmission hole is D1 / D3 ≤ 1 / 3, D2 / D3 ≤ 1 / 3.

5. The laser detection system according to claim 4, characterized in that, In the four reflections of the scattered light entering the light collecting lens from the S2 surface at the minimum scattering angle α, the distance L2 from the fourth reflection point r4b to the optical axis O of the light collecting lens is L2 > 0.5 * D2; when the scattered light enters the light collecting lens from the S2 surface at the maximum scattering angle β, the distance L1 from the transmission position on the S1 surface after the fourth reflection to the optical axis O of the light collecting lens is L1 < 0.5 * D1.

6. The laser detection system according to claim 5, wherein A negative lens is further disposed between the light collecting lens and the reflector. The negative lens can reduce the convergence angle of the outgoing light rays emitted from the light collecting lens and converge them at a convergence point F3 on the optical axis outside the light collecting lens, and the convergence point coincides with the focus of the light collimation system, thereby reducing the image-side NA value. A through hole for the normally incident excitation light beam to pass through is provided at the center of the negative lens.

7. The laser detection system according to claim 6, characterized in that, The diameter of the negative lens is Df, the diameter of the through hole is Dt, and Dt / Df ≤ 0.5.

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