Full-angle oblique incidence dark field illumination system and method

Abstract

The invention belongs to the technical field of wafer defect detection, and particularly relates to a full-angle oblique incidence dark field illumination system and method which can be suitable for dark field wafer defect detection. According to the invention, the annular light beam is generated by utilizing the characteristics of the axicon, a reflecting shell sleeve is designed for the objective lens behind the annular light beam according to the characteristics of the annular light, and the annular light beam is finally reflected to the surface of a sample to be detected at a certain angle after passing through the shell sleeve; the characteristic that the axicon lens can generate annular light is ingeniously combined, the axicon lens is combined with the shell sleeve to finally form full-angle oblique incidence dark field illumination, compared with single-light-source oblique incidence illumination in a traditional dark field defect detection system, the full-angle oblique incidence dark field defect detection system has the advantages that the oblique incidence angle is controllable, meanwhile, full-angle illumination is achieved, and the detection efficiency is improved. And the effect similar to multi-light-source irradiation is achieved. The method is simple in principle and lower in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of wafer defect detection, and in particular, relates to a dark field illumination system and method with full-angle oblique incidence. Background Art

[0002] With the rapid development of semiconductor manufacturing technology, the requirements for the detection of wafer surface defect sizes are becoming higher and higher. At present, there are two main ways to detect wafer defects, bright field defect detection technology and dark field defect detection technology. Bright field defect detection technology is to form an image by collecting reflected light or transmitted light from the surface to be tested; dark field defect detection technology is a non-contact optical detection technology that detects defects by collecting scattered signals from the surface of the sample to be tested. Compared with bright field illumination detection, this technology has the advantages of high contrast, high precision, low background noise, non-destructive detection, etc. due to its dark field illumination characteristics, and is widely used in the field of wafer defect detection.

[0003] However, for the current mainstream dark field defect detection systems, both domestic and foreign countries use the method of allowing the light source to independently and obliquely incident on the wafer to be tested at a certain angle to complete the dark field illumination. This means that the illumination light source is a single light source, and the current detection system can only achieve this goal with the help of a reflector or manually adjust the position of the laser light source. For the dark field defect detection system, there is a certain range requirement for the incident angle of the oblique incident illumination light. An incident angle that is too large or too small will result in poor detection results. The current system cannot accurately control the oblique incident light, and often requires the addition of multiple beam splitters and reflectors to achieve the purpose of oblique incidence. At the same time, a single light source will only be sensitive to defects in certain directions, so the detection effect is poor. Summary of the invention

[0004] In order to overcome the problem of oblique incident illumination light in existing dark field defect detection systems, single light source illumination, the illumination angle cannot be accurately controlled, and the light beam requires multiple optical elements such as beam splitters and reflectors to realize dark field oblique incident illumination, the present invention proposes an objective lens system composed of an axicon lens and a curved surface to realize a dark field objective lens capable of dark field illumination. This objective lens is different from the traditional dark field objective lens purchased on the market. It is only different from the bright field objective lens in terms of entrance and exit pupils. Instead, it forms an annular light through an axicon lens, and then uses a metal shell sleeve with a local (reflection area) coating on the surface to realize dark field illumination, thereby eliminating the need to place a laser light source on the side and manually adjust it to realize specific oblique incident light. The present invention cleverly combines the characteristics of the axicon lens that can generate annular light, and by combining it with the shell sleeve, it finally forms dark field illumination with full-angle oblique incidence. Compared with the oblique incident illumination of a single light source in the traditional dark field defect detection system, the invention not only realizes the controllable oblique incident angle, but also realizes full-angle illumination, achieving an effect similar to that of multi-light source illumination. The principle of the present invention is simple and the cost is lower. The technical solution adopted by the present invention is as follows:

[0005] The present invention provides a dark field illumination system with full-angle oblique incidence, which comprises an axicon lens, a camera CCD, an objective lens, an objective lens housing and a sample to be measured; the axicon lens, the camera CCD, the objective lens and the sample to be measured are arranged along the light propagation direction; the objective lens housing comprises a housing body and a reflector, which is arranged outside the objective lens and presents a two-stage open cylindrical structure as a whole; the distance between the objective lens housing and the objective lens is controlled so that the inner diameter of the annular light generated by the axicon lens is larger than the diameter of the objective lens; based on the fact that the radial size of the annular light formed by the light beam passing through the axicon lens increases with the increase of the propagation distance, the side wall of the housing body is arranged along the light propagation direction The inner diameter is gradually increased by tilting in the same trend, and its inner diameter is larger than the inner diameter of the ring light so that the ring light can just pass through the objective lens shell without obvious interference, and at the same time, it is prevented that the light beam is absorbed by the material or multiple reflections that change the light path after the ring light enters the objective lens shell are avoided. The reflector is arranged at the end of the body; when working, the Gaussian light beam passes through the axicon lens to form a ring light, and the ring light passes through the shell outside the objective lens to form an oblique incident light beam, and the reflected light is reflected by the reflector to the surface of the sample to be tested and then enters the camera CCD to complete the collection of scattered light, so as to realize the oblique incident illumination of the dark field detection system. In the present invention, the reflector is a plane reflector or a curved reflector.

[0006] In the present invention, a coating is provided on the inner surface of the reflector.

[0007] In the present invention, the transmittance function of the axicon lens is:

[0008]

[0009] Where λ is the wavelength of the light source, n is the refractive index of the axicon lens, β is the angle between the outgoing light and the normal of the cone surface, and R is the beam radius.

[0010] In the present invention, the slope k of the reflector satisfies the following relationship:

[0011]

[0012] Among them: (m1,n1), (m2,n2) are the coordinates of point A and point B respectively, is the angle between the emitted annular light and the Z axis; point A is the connection point between the shell body and the reflector, point B is the convergence point formed on the surface of the sample to be measured after the light beam is reflected by the reflector, and the distance between point A and point B is the working distance of the objective lens. is the angle between the emitted annular light and the Z axis.

[0013] The present invention also provides a full-angle oblique-incident dark-field illumination method for the above-mentioned system, in which a Gaussian light beam passes through an axicon lens to form an annular light beam, and the annular light passes through an objective lens shell outside the objective lens to form an oblique-incident light beam, and the reflected light is reflected by a reflector to the surface of a sample to be tested and then enters a camera CCD to complete the collection of scattered light, thereby realizing oblique-incident illumination of a dark-field detection system.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] According to the characteristics of the axicon lens, the present invention selects a Gaussian light beam of a required wavelength to form an annular light through the axicon lens, and the annular light forms an oblique incident light beam through the objective lens shell outside the objective lens, and the reflected light enters the CCD through the reflector to complete the collection of scattered light. This method improves the controllability of the incident angle of the oblique incident light beam, and cleverly uses the axicon lens to form annular light, realizing accurate dark field illumination at a low cost.

[0016] Compared with the lighting method in the traditional dark-field defect detection system, the method proposed in the present invention provides a new idea for regulating the incident light. By designing the shell layer, the lighting is cleverly combined with the objective lens. This design can be used on the objective lens to realize a truly dark-field lighting objective lens.

[0017] Compared with a single illumination light source in a traditional dark field defect detection system, the present invention realizes full-angle illumination, making defects in all directions easier to detect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The objective lens system for dark field illumination of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0019] Figure 1 It is a schematic diagram of the dark field illumination system with full-angle oblique incidence of the present invention.

[0020] Figure 2 for Figure 1 Schematic diagram of the principle of forming ring light by axial aconic lens.

[0021] Figure 3 This is a schematic diagram of the reflective part principle of the invention.

[0022] Figure 4 Three views of the objective lens housing for dark field illumination and a cross-sectional view of the reflective portion of the invention.

[0023] Numbers in the figure: 1-axis conical lens, 2-annular light, 3-camera CCD, 4-objective lens housing, 5-objective lens, 6-reflector, 7-oblique incident dark field illumination light, 8-scattered light, 9-Gaussian beam, 10-light intensity distribution after passing through the axis conical lens, 11-annular light at different distances. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example 1

[0026] In order to realize full-angle oblique-incident dark-field illumination in a dark-field defect detection system, the present invention uses the principle of an axicon lens to form annular light, and designs a shell on this basis.

[0027] Figure 2 It is a schematic diagram of the principle of the axicon lens 1 forming the ring light 2. After the Gaussian beam passes through the axicon lens 1, the transmittance function of the axicon lens 1 is In the formula, λ is the wavelength of the light source, n is the refractive index of the axicon lens 1, β is the angle between the output light and the normal of the cone surface, and R is the beam radius. Figure 2 As shown, at this time, the Gaussian beam will become a ring light, and the radius of the ring light 2 increases with the increase of the propagation distance. The ring light situation at different distances is shown in 11, and the light intensity distribution after passing through the axicon lens is shown in 10. Figure 2 .

[0028] like Figure 1 As shown, the present invention provides a dark field illumination system with full-angle oblique incidence, which comprises an axicon lens 1, a camera CCD 3 (Charge-Coupled Device), an objective lens 5, an objective lens housing 4 and a sample to be measured; the axicon lens 1, the camera CCD 3, the objective lens 5 and the sample to be measured are arranged along the light propagation direction; the objective lens housing 4 comprises a housing body and a reflector 6, the objective lens housing 4 is arranged outside the objective lens 5, and the whole is a two-stage open cylindrical structure; the distance between the objective lens housing 4 and the objective lens 5 is strictly controlled so that the inner diameter of the annular light 2 generated by the axicon lens 1 is larger than the diameter of the objective lens; based on the fact that the radial size of the annular light 2 formed by the light beam passing through the axicon lens 1 increases with the increase of the propagation distance, the side wall of the housing body is inclined in the same trend along the light propagation direction to realize the gradual increase of the inner diameter, and its inner diameter is larger than the inner diameter of the annular light 2, and its inner diameter should be larger than the inner diameter of the annular light so that the annular light can just pass through the housing without generating obvious interference, and at the same time, it is avoided that the light beam is absorbed by the material or generates complex reflection after entering the housing, and the reflector 6 is arranged at the end of the housing body. During operation, the Gaussian beam 9 forms a ring light 2 through the axicon lens 1, and the ring light 2 forms an obliquely incident dark field illumination light 7 through the objective lens housing 4 outside the objective lens 5. The reflected light is reflected to the surface of the sample to be tested through the reflector 6 and then enters the camera CCD 3 to complete the collection of scattered light 8, thereby realizing the oblique incident illumination of the dark field detection system. The objective lens housing 4 and the reflector 6 are the key parts of the entire housing. In order to make the ring light finally illuminate the sample to be tested in an oblique incident manner, the reflector 6 is set as a coated reflector.

[0029] The specific calculation of the reflector function of the reflector 6 is as follows:

[0030] like Figure 3 Here we use the principle of geometric construction method when the incident light When incident on the reflecting surface, the vector of the reflected light is recorded as According to the law of reflection, the normal vector of the reflection surface follows the following formula: According to the principle that the angle of incidence is equal to the angle of reflection, we know that the vectors satisfy

[0031] Converting this formula into geometric calculations means making the angles between the incident light and the reflected light and the normal of the reflector the same. By this principle, the slope k of the reflector is finally obtained to satisfy the following relationship:

[0032]

[0033] For details of the above parameters, please refer to Figure 3 , where point A (m1, n1) is the connection point between the main body of the housing and the reflective part, point B (m2, n2) is the convergence point formed on the surface to be measured after the light beam is reflected by the reflector 6, and the distance between point A and point B is the working distance of the objective lens. is the angle between the emitted annular light and the Z axis. Based on the above derivation, we calculate the corresponding path length of the annular light beam propagating along the objective lens 5 after entering from points C and D, determine the range AD of its annular diffusion in this process, and ensure that AD is parallel to the diffusion slope, thereby determining the coordinates of point A (m1, n1). At the same time, the coordinates of point B (m2, n2) are selected as a point on the working distance plane of the objective lens (in this embodiment, the point on the z-axis on the working distance plane of the objective lens is selected). According to the law of refraction and the co-cone angle α, the angle is calculated. Finally, according to the obtained point A (m1, n1) and point B (m2, n2) and The specific parameter k of the final reflector can be calculated.

[0034] Based on the above analysis, we can finally design Figure 4 The objective lens housing 4. The reflector 6 can be set as a curve or a straight line according to the requirements of the convergence point B. By calculating the coordinates of point A (m1, n1) and point B (m2, n2), and the angle between the emitted annular light 2 and the Z axis The geometric parameter k of the reflector can be clearly derived. This parameter determines the inclination angle of the shell side wall and its matching degree with the propagation direction of the ring light 2, ensuring that the light beam will not be distorted due to multiple reflections or absorption, and finally realizing the full-angle oblique incident dark field illumination in the dark field defect detection device, so that the oblique incident light at any angle is no longer a single light source, but irradiated in the form of ring light, thereby providing guarantee for the efficient optical performance of the system.

[0035] As described above, the present invention utilizes an axicon lens 1 to form an annular light 2 and adds a designed reflective shell behind the annular light 2. The oblique incident angle and position of the reflected light are finally determined by calculation, and the shape of the shell is determined to achieve dark field illumination with full-angle oblique incidence. In the system composed of the axicon lens 1 and the objective lens shell 4, the distance between the two can be changed according to the diameter of the selected objective lens 5. The reflective shell designed by the present invention changes its size according to the size difference of the objective lens 5, so the present invention is applicable to all dark field objective lenses. The shape of the reflective part of the reflective shell designed by the present invention can be linear, curved or other shapes. The shape and angle of the reflective part can be adjusted in the shell to control the light beam to be incident on the sample to be measured at a specific angle.

Claims

1. A dark field illumination system with full-angle oblique incidence, characterized in that: The invention comprises an axicon lens, a camera CCD, an objective lens, an objective lens housing and a sample to be measured; the axicon lens, the camera CCD, the objective lens and the sample to be measured are arranged along the light propagation direction; the objective lens housing comprises a housing body and a reflector, which is arranged outside the objective lens and presents a two-stage open cylindrical structure as a whole; the distance between the objective lens housing and the objective lens is controlled so that the inner diameter of the annular light generated by the axicon lens is larger than the diameter of the objective lens; based on the fact that the radial size of the annular light formed by the light beam passing through the axicon lens increases with the increase of the propagation distance, the side wall of the housing body is inclined in the same trend along the light propagation direction to realize the inner diameter of the annular light generated by the axicon lens. The inner diameter of the ring light is gradually increased, and its inner diameter is larger than the inner diameter of the ring light, so that the ring light can just pass through the objective lens shell without obvious interference, and at the same time, it is prevented that the light beam is absorbed by the material or produces multiple reflections that change the light path after the ring light enters the objective lens shell. The reflector is arranged at the end of the body; when working, the Gaussian light beam passes through the axicon lens to form a ring light, and the ring light passes through the shell outside the objective lens to form an oblique incident light beam, and the reflected light is reflected by the reflector to the surface of the sample to be tested and then enters the camera CCD to complete the collection of the scattered light, thereby realizing the oblique incident illumination of the dark field detection system.

2. The full-angle oblique-incidence dark-field illumination system according to claim 1, characterized in that: The reflector is a plane reflector or a curved reflector.

3. The dark field illumination system with full-angle oblique incidence according to claim 1, characterized in that: The inner surface of the reflector is provided with a coating.

4. The dark field illumination system with full-angle oblique incidence according to claim 1, characterized in that: The transmittance function of the axicon lens is: Where λ is the wavelength of the light source, n is the refractive index of the axicon lens, β is the angle between the outgoing light and the normal of the cone surface, and R is the beam radius.

5. The dark field illumination system with full-angle oblique incidence according to claim 1, characterized in that: The slope k of the reflector determines the inclination angle of the side wall of the objective lens housing and its matching degree with the propagation direction of the annular light. The slope k of the reflector satisfies the following relationship: Where: (m1, n1), (m2, n2) are the coordinates of point A and point B respectively. Point A is the connection point between the shell body and the reflector. Point B is the convergence point formed on the surface of the sample to be measured after the light beam is reflected by the reflector. The distance between point A and point B is the working distance of the objective lens. is the angle between the emitted annular light and the Z axis.

6. A dark field illumination method with full-angle oblique incidence based on the system of claim 1, characterized in that: The Gaussian light beam passes through the axicon lens to form a ring light, and the ring light passes through the objective lens shell outside the objective lens to form an oblique incident light beam. The reflected light is reflected by the reflector to the surface of the sample to be tested and then enters the camera CCD to complete the collection of the scattered light, realizing the oblique incident illumination of the dark field detection system.

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