Focusing measurement system and lithographic apparatus

Abstract

This invention provides a focusing measurement system and a photolithography apparatus. The focusing measurement system includes: a light source module for providing a short-wavelength illumination beam; a projection module for illuminating a target surface with the illumination beam and forming a reflected beam; and a detection unit for detecting the reflected beam to generate an electrical signal. The projection module includes a trapezoidal coupling prism, with the illumination beam perpendicularly incident on and exiting the trapezoidal coupling prism. The trapezoidal coupling prism has two inclined surfaces with trapezoidal sides, serving as the incident and exit surfaces of the illumination beam, respectively. By using a trapezoidal coupling prism and ensuring that the illumination beam is perpendicularly incident on and exiting the trapezoidal coupling prism, this invention enables the focusing measurement system to satisfy the Scheimpflug condition and solve the chromatic aberration problem that occurs in the optical path of short-wavelength illumination beams.

Description

Technical Field

[0001] This invention relates to the field of photolithography technology, and in particular to a focusing measurement system and photolithography equipment. Background Technology

[0002] With the booming development of the electronics industry, the application of integrated circuits is becoming increasingly widespread, leading to a greater demand for high-precision manufacturing. Photolithography equipment is the most critical piece of equipment in all stages of integrated circuit production. Photolithography technology is the foundation of large-scale integrated circuit manufacturing and has become a core driving force for the development of integrated circuits. Its main function is to image the pattern on a photomask onto a silicon wafer through exposure. Because photosensitive photoresist is coated on the surface of the silicon wafer, when the pattern on the photomask is imaged onto the silicon wafer, the photoresist at the corresponding location undergoes a photochemical reaction, thereby retaining the pattern on the photomask on the silicon wafer surface.

[0003] In photolithography equipment, an automatic focusing and measurement system is essential to precisely position the silicon wafer at the designated exposure location. Several different technical solutions exist for implementing this system. In a focusing and measurement system based on intensity modulation, a scanning mirror typically performs high-speed reciprocating simple harmonic motion. This causes the marker image generated by the fixed slit marking unit to produce a dynamic measurement signal on the detector unit. By analyzing and processing this dynamic measurement signal, the position of the high signal-to-noise ratio spot can be obtained, leading to the height value of the silicon wafer. Based on this height value, the wafer support mechanism is adjusted until the silicon wafer is positioned at the optimal focal plane.

[0004] However, in the above technical solution, the focusing measurement system uses a wide-band visible and near-infrared light source, such as a halogen lamp with a spectrum covering 500nm to 900nm. This automatic focusing measurement system determines the height information of the silicon wafer by measuring the reflection of the light beam from the outermost layer of the silicon wafer after various process layers and photoresist are deposited. Since the projected light beam passes through the photoresist on the surface of the silicon wafer to reach the process layer below the top surface, the position of the emitted light beam on the silicon wafer surface will be shifted, i.e., the "Guess-Hansen shift" physical effect. This effect is related to the polarization state, wavelength, incident angle of the projected light beam, and process layer information such as thickness and its deviation, refractive index, etc., which will cause process adaptability errors in the measurement results of the focusing measurement system.

[0005] Using shorter wavelength light sources, such as those in the 200nm–400nm range, can suppress process adaptability errors to some extent. However, in traditional transmissive optical structures, the transmittance of most materials is low when using shorter wavelengths, making it difficult to suppress chromatic aberration using only a limited number of materials with higher transmittance. Especially when short-wavelength beams exit the coupling prism at large angles, the beam travels from an optically denser medium to an optically less dense medium. Because the refractive index of the coupling prism material changes more with wavelength in the short-wavelength band than in the visible and near-infrared bands, a larger dispersion angle is generated, leading to severe chromatic aberration problems in subsequent optical paths.

[0006] Currently, focusing measurement systems using short wavelengths generally employ reflective optical paths. However, the structure of focusing measurement systems using reflective optical paths can only achieve an optical system where the mark surface is perpendicular to the optical axis. That is, it cannot achieve an optical path where the mark surface is tilted and conjugate with the silicon wafer surface, thus satisfying the Scheimpflug condition.

[0007] Therefore, how to overcome the shortcomings of the aforementioned prior technologies and enable the focusing measurement system to both meet the Scheimpflug conditions and solve the chromatic aberration problem that occurs in the optical path of short-wavelength illumination beams is an urgent problem to be solved. Summary of the Invention

[0008] The purpose of this invention is to provide a focusing measurement system and a photolithography device to solve the problem of chromatic aberration in the optical path of short-wavelength illumination beams, while satisfying the Scheimpflug condition.

[0009] To achieve the above and other related objectives, the present invention provides a focusing measurement system, comprising:

[0010] Light source module, used to provide illumination beams in the short wavelength band;

[0011] A projection module is used to direct the illumination beam onto the target surface and form a reflected beam.

[0012] A detection unit is used to detect the reflected light beam to generate an electrical signal;

[0013] The projection module includes a trapezoidal coupling prism, the illumination beam is perpendicularly incident on and exits the trapezoidal coupling prism, and the trapezoidal coupling prism has two inclined surfaces with trapezoidal sides, which serve as the incident surface and exit surface of the illumination beam, respectively.

[0014] Optionally, in the focusing measurement system, the projection module further includes a projection marking unit, which is disposed inside the trapezoidal coupling prism. After the illumination beam is perpendicularly incident on the trapezoidal coupling prism, it passes through the projection marking unit to obtain a beam with a marked image.

[0015] Optionally, in the focusing measurement system, the projection marking unit includes a marking plate, which is prepared by etching the desired marking pattern on a quartz glass plated with chromium or aluminum. When the illumination beam shines on the marking pattern area of ​​the marking plate and is reflected, it carries the marking signal to form a beam with a marking image. When the illumination beam shines on the non-marking pattern area of ​​the marking plate and is transmitted, it forms a stray light beam. The inclined surfaces of the two trapezoidal sides are located on the same side of the marking plate.

[0016] Optionally, in the focusing measurement system, the projection marking unit includes a marking plate, which is prepared by etching the desired marking pattern on a quartz glass plated with chromium or aluminum. When the illumination beam shines on the marking pattern area of ​​the marking plate, it carries the marking signal and forms a beam with a marking image. When the illumination beam shines on the non-marking pattern area of ​​the marking plate, it reflects and forms a stray light beam. The inclined surfaces of the two trapezoidal sides are arranged on both sides of the marking plate.

[0017] Optionally, in the aforementioned focusing measurement system, the trapezoidal coupling prism is made of one of the following materials: natural quartz, quartz glass, and calcium fluoride.

[0018] Optionally, in the focusing measurement system, the projection module further includes a projection imaging optical path module, and the projection imaging optical path module includes a total internal reflection optical structure using three coaxial mirrors.

[0019] Optionally, in the focusing measurement system, the projection imaging optical path module includes a primary reflector, a scanning reflector, and a secondary reflector, and the illumination beam passes through the primary reflector, secondary reflector, scanning reflector, secondary reflector, and primary reflector in that order.

[0020] Optionally, in the focusing measurement system, the projection imaging optical path module further includes several directional reflectors, and the illumination beams passing through the main reflector, scanning reflector, and secondary reflector illuminate the directional reflectors.

[0021] Optionally, in the focusing measurement system, the target surface includes a silicon wafer.

[0022] Optionally, in the focusing measurement system, the detection unit includes:

[0023] The detection imaging optical path module collects and adjusts the reflected beam from the target surface;

[0024] The detection coupling prism module and the detection marker unit ensure that the reflected beam that has not deviated passes through exactly, while blocking the reflected beam that has deviated.

[0025] The relay optical path module organizes the reflected light beams that pass through;

[0026] The detector module collects the processed reflected beam to generate an electrical signal.

[0027] Optionally, in the focusing measurement system, the short wavelength band ranges from 200 nm to 500 nm.

[0028] Optionally, in the focusing measurement system, the light source module includes a light source and an illumination optical path module, wherein the light source emits an illumination beam in the short wavelength band, and the illumination beam illuminates the projection module through the illumination optical path module.

[0029] Optionally, in the focusing measurement system, the light source includes a xenon lamp.

[0030] To achieve the above and other related objectives, the present invention also provides a photolithography apparatus, including the focusing measurement system described above.

[0031] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0032] This invention employs a trapezoidal coupling prism, and ensures that the illumination beam is incident on and exits the trapezoidal coupling prism perpendicularly. This suppresses chromatic aberration caused when a short-wavelength illumination beam exits the coupling prism at a large angle. Simultaneously, it enables the focusing measurement system to meet the Scheimpflug condition, thereby improving measurement sensitivity. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a focusing measurement system;

[0034] Figure 2 It is a spectral curve of a visible and near-infrared light source in the range of 500nm to 900nm;

[0035] Figure 3 It refers to the process variation of a 500nm to 900nm visible and near-infrared light source;

[0036] Figure 4 It is a spectral curve of a short-wavelength ultraviolet light source in the range of 200nm to 400nm;

[0037] Figure 5 It refers to the process variation of a short-wavelength ultraviolet light source in the range of 200nm to 400nm;

[0038] Figure 6 This is a schematic diagram of another focusing measurement system;

[0039] Figure 7 yes Figure 1 A schematic diagram of the output dispersion angle of the coupling prism in the focusing measurement system.

[0040] Figure 8 This is a schematic diagram of the focusing measurement system according to an embodiment of the present invention;

[0041] Figure 9 This is a left-side cross-sectional view of a projection coupling prism module according to an embodiment of the present invention;

[0042] Figure 10 This is a schematic diagram of the structure of a marking unit according to an embodiment of the present invention;

[0043] Figure 11 This is a left-side cross-sectional view of another projection coupling prism module according to an embodiment of the present invention;

[0044] Figure 12 This is a schematic diagram of the structure of another marking unit according to an embodiment of the present invention. Detailed Implementation

[0045] The focusing measurement system and photolithography equipment proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0046] See Figure 1 This paper illustrates a focusing measurement system 1 that satisfies the Scheimpflug condition in the visible and near-infrared operating band. It employs a single-sided scanning mirror reciprocating motion for light intensity modulation. The light source 101 of the focusing measurement system 1 provides a broadband, pre-collimated illumination beam. This illumination beam is projected onto a projection coupling prism module 103a and a projection marking unit 103b via an illumination optical path module 102. The marking surface of the projection marking unit 103b serves as the aperture of the illumination optical path module 102 and the object plane of the projection imaging optical path module. Through the obstruction of the projection mark, a marking image corresponding to the mark shape is formed; that is, the illumination beam forms a marking image beam after passing through the projection marking unit 103b. The projection marking unit 103b can be tilted relative to the optical axis to form an tilted marking image, and it irradiates the silicon wafer surface at a large incident angle, obeying the Scheimpflug condition. The tilt angle α of the object plane and the tilt angle b of the image plane, along with the magnification m of the projection imaging unit, must satisfy Equation 1: tanb = mtana.

[0047] The projection imaging optical path module's front group 104a and rear group 104c are used to adjust the aforementioned marker image beam. They can be composed of one or more refractive transmission mirrors, which may include, but are not limited to, wedges, parallel plates, aspherical transmission mirrors, freeform transmission mirrors, and other optical devices with special adjustment functions. The scanning reflector 104b reciprocates at high speed within a certain angle range, causing the angle of the reflected beam (i.e., the marker image beam) to oscillate according to a certain pattern. The beam reflected from the scanning reflector 104b and the rear group 104c is irradiated onto the target surface 105 to be measured via the first steering reflector 104d. The adjusted marker image is projected onto the surface of the target surface 105 whose surface shape is measured by the focusing measurement system 1. If there are uneven areas on the surface, the marker image projected at these areas will not be reflected at the optimal focal plane of the focusing measurement system 1, resulting in a positional shift in the reflected image. The target surface 105 can be a silicon wafer or other surfaces requiring surface shape measurement in precision machining processes.

[0048] The focusing measurement system 1 includes a detection imaging optical path module comprising a second steering mirror 106d, a front group 106c of the detection imaging optical path, a secondary mirror 106b, and a rear group 106a of the detection imaging optical path. The detection imaging optical path module collects and adjusts the reflected beam from the target surface 105.

[0049] The focusing measurement system 1 includes a detection coupling prism module 107a and a detection marker unit 107b. The shape and position distribution of the markers in the detection marker unit 107b correspond to those in the projection marker unit 103b under certain magnification conditions. This allows the marker image that has not shifted to pass through precisely, while blocking the marker image that has shifted. The light beam that can pass through the detection marker unit 107b forms a secondary marker image. After adjustment by the relay optical path module 108, the secondary marker image is used by the detector module 109 to acquire the signal.

[0050] The process adaptability measurement error of the focusing measurement system 1, namely the height measurement error ASD caused by the "Guess-Hansen displacement" physical effect in the direction perpendicular to the target surface, and its mean value. The mathematical expression is:

[0051] Equation 2 is:

[0052] Equation 3 is:

[0053] Where λ is the wavelength; I is the light intensity; and θ is the incident angle of the light beam onto the target surface. The reflectivity of S-polarized light with wavelength λ and incident angle θ on the target surface; λ i -λj θ represents the wavelength range covered by the light source system of the focusing measurement system. i -θ j This indicates the range of incident angles of a wide beam of light incident on the target surface.

[0054] Figure 2 The image shows the visible and near-infrared spectrum curves provided by the broadband halogen lamp used in the light source module of the focusing measurement system 1. The curves showing the variation of process error with photoresist film thickness for four common substrates in typical process layers, obtained from simulations based on equations two and three, are shown below. Figure 3 As shown, the maximum process adaptability error at this time is generated when copper (Cu) is used as the substrate, with a fluctuation range of approximately -110nm to 160nm and a fluctuation amount of 270nm.

[0055] Figure 4 This is the ultraviolet spectrum curve provided by the xenon lamp source used in the light source module of the focusing measurement system 1. The curves showing the variation of process error with photoresist film thickness for four common substrates in typical process layers, obtained from simulations based on equations two and three, are shown below. Figure 5 As shown, the maximum process adaptability error at this time is generated when copper (Cu) is used as the substrate, with a fluctuation range of approximately -8nm to 15nm and a fluctuation amount of 23nm.

[0056] The comparison of the above-mentioned changes in process adaptability error shows that using an ultraviolet spectral light source to provide illumination in the focusing measurement system can effectively reduce the process adaptability error of the measurement.

[0057] See Figure 6 A short-wavelength focusing measurement system 2 is provided. The light source 201 of the focusing measurement system 2 provides an illumination beam in the ultraviolet spectral band. The illumination beam is projected onto a projection mark unit 203 via an illumination optical path module 202, and a mark image corresponding to the mark shape is formed by the obstruction of the projection mark. The first reflecting mirror 204a, second reflecting mirror 204b, third reflecting mirror 204c, and fourth reflecting mirror 204d of the projection imaging optical path module are used to adjust the mark image beam. The beam reflected from the fourth reflecting mirror 204d illuminates the target surface 205 to be measured. The target surface 205 can be a silicon wafer or other surfaces requiring surface shape measurement in precision machining processes. The detection imaging optical path module includes a fifth reflecting mirror 206a, a sixth reflecting mirror 206b, a seventh reflecting mirror 206c, and an eighth reflecting mirror 206d. The detection imaging optical path module collects and adjusts the reflected image of the target surface 105 (i.e., the beam reflected from the target surface 205). The beam of light passing through the detection marker unit 207 is a secondary marker image. After being adjusted by the relay optical path module 208, the secondary marker image is used by the detector module 209 to collect the signal.

[0058] Figure 6 The focusing measurement system 2 described above uses a reflective imaging optical path to eliminate chromatic aberration and reduce the fluctuation of process adaptability error. However, the projection mark unit and the target surface, and the detection mark unit and the target surface of the focusing measurement system 2 do not satisfy the Scheimpflug condition. The relationship between the measured mark offset Δy and the vertical offset Δz of the target surface can be described by Equation 4:

[0059] Δy1=2*sinθ*Δz.

[0060] Where θ is the angle of incidence of the light beam onto the target surface.

[0061] And for Figure 1 The relationship between the measured mark offset Δy and the vertical offset Δz of the target surface in a focusing measurement system that satisfies the Scheimpflug condition can be described by Equation 5:

[0062] Δy2=2*tanθ*Δz.

[0063] The angle θ is generally a large angle, such as 70° to 86°. In this case, Δy2 is significantly greater than Δy1, indicating that the focusing measurement system that meets the Scheimpflug condition is more sensitive to the measurement of the target surface offset.

[0064] To achieve both higher process adaptability and better sensitivity, the focusing measurement system needs to be suitable for short-wavelength operating bands and imaging optical paths using Scheimpflug conditions.

[0065] Figure 1 In the focusing measurement system based on light intensity modulation, when using a visible or near-infrared spectral light source, the imaging optical path design allows for the selection of dozens to hundreds of optical glass materials with different refractive indices and Abbe numbers. Specific combinations can effectively suppress chromatic aberration. However, when using a short-wavelength ultraviolet spectral band, the imaging optical path design is limited to a few materials with high internal transmittance, such as natural quartz, quartz glass, and calcium fluoride. This results in limited chromatic aberration suppression capabilities, necessitating the design of a more sophisticated system. Figure 6 It employs a reflective imaging optical path.

[0066] and Figure 1 The projection coupling prism module 103a of the focusing measurement system 1 causes the light beam to exit from the optically denser medium to the optically less dense medium at a relatively large angle. Since different wavelengths of light beams have different refractive indices in the coupling prism material, this results in different exit angles and thus a dispersion angle γ. Please refer to [link to relevant documentation]. Figure 7The emission angle is positively correlated with the refractive index difference of the coupling prism material at different wavelengths, and the refractive index difference of the coupling prism material is significantly greater in the ultraviolet spectral band than in the visible and near-infrared bands. Table 1 shows the corresponding relationship between the refractive index difference of different wavelengths in the coupling prism material.

[0067] Table 1:

[0068]

[0069] The formula for the exit dispersion angle of the coupling prism can be described as Equation Six:

[0070] γ=β j -β i =arcsin(n j sinθ)-arcsin(n i sinθ.

[0071] Where β i β j The angle of refraction, n, represents the angle of refraction when different wavelengths exit the coupling prism and enter the air at the same angle. i n j Representing different wavelengths λ i , λ j The refractive index in the coupling prism. Taking the refractive index data in Table 1 as an example, if we take 40°, the dispersion angle of the 500nm–900nm visible and near-infrared beam exiting the coupling prism into the air is 1.1°, and the dispersion angle of the 200nm–400nm short-wavelength ultraviolet beam exiting the coupling prism into the air is 7.5°. Therefore, when the refractive index difference of the material in the short-wavelength band increases, the ultraviolet beam exiting the coupling prism at a large angle will produce a large dispersion angle γ, causing a chromatic aberration problem that is difficult to correct.

[0072] Therefore, in the prior art, focusing measurement systems that satisfy the Scheimpflug condition, such as Figure 1 The focusing measurement system 1 in the text has problems such as large color difference and large fluctuations in process adaptability error; while a focusing measurement system that can effectively reduce the fluctuations in process adaptability error, for example... Figure 6 The focusing measurement system 2 in the middle cannot meet the Scheimpflug conditions, and the measurement sensitivity is low.

[0073] To address the above problems, this invention proposes a focusing measurement system 3 that satisfies the Scheimpflug condition in the short-wavelength operating band while suppressing chromatic aberration. Please refer to [link / reference]. Figure 8 .

[0074] The focusing measurement system 3 includes:

[0075] Light source module, used to provide illumination beams in the short wavelength band;

[0076] A projection module is used to direct the illumination beam onto the target surface and form a reflected beam.

[0077] A detection unit is used to detect the reflected light beam to generate an electrical signal;

[0078] The projection module is equipped with a projection coupling prism module 303a, and the projection coupling prism module adopts a trapezoidal coupling prism. The illumination beam is perpendicularly incident on and exits the trapezoidal coupling prism.

[0079] The light source module includes a light source 301 and an illumination optical path module 302. The light source 301 is a broadband light source, with a wavelength range covering the ultraviolet, visible, and near-infrared bands. Further, the light source 301 is a short-wavelength light source, and the short-wavelength band includes the ultraviolet spectrum and short-wavelength bands in the visible light spectrum, with a range of 200nm to 500nm. Even further, the light source 301 is preferably a xenon lamp light source, providing an illumination beam in the ultraviolet spectrum band for the system.

[0080] The illumination optical path module 302 includes several lenses and may also include filters, such as two lenses and a filter located between the two lenses. The filter filters the light emitted from the light source 301 into light in the 200nm to 500nm wavelength range. The illumination beam provided by the light source 301 illuminates the projection module through the illumination optical path module 302.

[0081] The projection module includes a projection coupling prism module 303a, which employs a trapezoidal coupling prism and serves as a chromatic aberration suppression device. (See reference...) Figure 9 By designing the trapezoidal inclined side angle, the main light beam of the illumination beam is incident on and out of the trapezoidal coupling prism in a direction perpendicular to the glass surface of the trapezoidal coupling prism, i.e., the incident angle is 0°. The main beams of different wavelengths are also emitted from the trapezoidal coupling prism at 0°, i.e., the angles θ and β in Equation 6 are both 0°. This effectively suppresses the dispersion angle γ of the large-angle output coupling prism, thereby effectively solving the chromatic aberration problem.

[0082] The projection module also includes a projection marking unit 303b, which is disposed inside the projection coupling prism module 303a, so that the illumination beam obtains a beam with a marked image after passing through the projection coupling prism module 303a. Furthermore, the projection marking unit can be tilted relative to the incident illumination beam, i.e., it can be tilted relative to the optical axis, so that the focusing measurement system satisfies the Scheimpflug condition.

[0083] The projection coupling prism module 303a preferably has eight faces, more preferably six side faces and two bottom faces. The six side faces are preferably rectangular, and the two bottom faces are preferably hexagonal, but not limited thereto. The hexagon includes four right-angled sides and two hypotenuses (i.e., two trapezoidal hypotenuses). The incident and exit surfaces of the illumination beam are respectively the inclined surfaces of the two trapezoidal hypotenuses, i.e., the side faces corresponding to the two trapezoidal hypotenuses. The material of the trapezoidal coupling prism is preferably one of natural quartz, quartz glass, and calcium fluoride, but not limited thereto.

[0084] See Figure 9 and Figure 10 The projection marking unit includes a marking plate, which is prepared by etching the desired marking pattern onto a quartz glass plated with chromium or aluminum. When the illumination beam L0 shines on the marking pattern area of ​​the marking plate and is reflected, it carries the marking signal, forming a beam L1 with a marking image. When the illumination beam L0 shines on the non-marking pattern area of ​​the marking plate and is transmitted, it forms a stray light beam L2. In this design, the inclined surfaces of the two trapezoidal sides are both located on the same side of the marking plate.

[0085] See Figure 11 and Figure 12 The projection coupling prism module 303a and projection marking unit 303b also have another structure. After the illumination beam is incident perpendicularly to the inclined surface of the trapezoidal hypotenuse of the trapezoidal coupling prism, the signal light passes through the chrome-plated or aluminum marking plate and exits from the lower layer of quartz glass. To suppress chromatic aberration, the exit surface of the lower layer of quartz glass is designed as an inclined surface of the trapezoidal hypotenuse, allowing the main ray of the signal light transmitted through the marking surface to exit perpendicularly to the quartz glass surface. This causes the ineffective stray light reflected from the marking plate to exit from the side of the upper layer of quartz glass. In this case, if the same marking image as in the previous embodiment is required, the marking area on the chrome or aluminum surface needs to be a hollowed-out surface, such as... Figure 12 As shown, with Figure 10 The marking surfaces are basically complementary. That is, the marking plate in this embodiment can be prepared by etching the desired marking pattern onto quartz glass with a chromium or aluminum plating. When the illumination beam L0 shines on the marking pattern area of ​​the marking plate, it carries the marking signal and forms a beam L1 with a marking image; when the illumination beam L0 shines on the non-marking pattern area of ​​the marking plate, it reflects and forms a stray light beam L2. In this design, the inclined surfaces of the two trapezoidal sides are both located on both sides of the marking plate.

[0086] The projection module also includes a projection imaging optical path module, which is a total internal reflection optical structure using three coaxial mirrors. The three coaxial mirrors are a primary mirror 304a, a scanning mirror 304b, and a secondary mirror 304c. The illumination beam passes through the primary mirror 304a, secondary mirror 304c, scanning mirror 304b, secondary mirror 304c, and primary mirror 304a in that order.

[0087] The projection imaging optical path module also includes several directional mirrors, such as a first directional mirror 304d and a second directional mirror 304e. Illumination beams passing through the main mirror 304a, scanning mirror 304b, and secondary mirror 304c illuminate the directional mirrors, meaning the illumination beams sequentially pass through the first directional mirror 304d and the second directional mirror 304e to illuminate the target surface 305. Since the mirror surfaces do not produce chromatic aberration, the projection imaging optical path can effectively solve the problem of chromatic aberration suppression difficulties caused by the limited types of selectable optical materials in short-wavelength optical paths.

[0088] The target surface 305 can be a silicon wafer surface or another surface that requires surface shape measurement in precision machining processes. When the illumination beam shines on the target surface 305, it will be reflected, producing a reflected beam with a marked image.

[0089] The detection unit includes:

[0090] The detection imaging optical path module collects and adjusts the reflected beam from the target surface;

[0091] The detection coupling prism module 307a and the detection marker unit 307b allow the unbiased reflected beam to pass through precisely, while blocking the biased reflected beam.

[0092] The relay optical path module 308 organizes the reflected beams that pass through;

[0093] Detector module 309 collects the processed reflected beam to generate an electrical signal.

[0094] Continue reading Figure 8 The detection imaging optical path module has a similar structure to the projection imaging optical path module, and its function is to collect and adjust the reflected light beam from the target surface. The detection imaging optical path module is a total internal reflection optical structure using three coaxial mirrors.

[0095] The detection imaging optical path module also includes several directional reflectors, such as the third directional reflector 306d and the fourth directional reflector 306e. The reflected light beam formed from the target surface 305 illuminates the fourth directional reflector 306e and the third directional reflector 306d, that is, the reflected light beam sequentially passes through the fourth directional reflector 306e and the third directional reflector 306d to illuminate the three coaxial reflectors.

[0096] The three coaxial reflectors are a second primary reflector 306a, a second reflector 306b, and a third reflector 306c. The reflected light beam passing through the steering reflector passes in the following order: second primary reflector 306a, third reflector 306c, second reflector 306b, third reflector 306c, and second primary reflector 306a. The second reflector 306b does not have high-speed motion capability.

[0097] The detection coupling prism module 307a can be a conventional prism, and the detection marker unit 307b is disposed inside the conventional prism. The detection marker unit 307b allows the reflected beam with the marked image to pass through without deviation, while blocking the reflected beam with the marked image that has deviated. The beam that can pass through the detection marker unit 307b is a secondary marker image. After being adjusted by the relay optical path module 308, the secondary marker image is used by the detector module 309 to acquire the signal.

[0098] This invention, by employing a trapezoidal coupling prism and ensuring that the illumination beam is incident and exiting the prism perpendicularly, can suppress chromatic aberration generated when a short-wavelength illumination beam exits the trapezoidal coupling prism at a large angle. Simultaneously, it allows the focusing measurement system to satisfy the Scheimpflug condition. A focusing measurement system satisfying the Scheimpflug condition is more sensitive to the measurement of target surface offset; that is, employing the Scheimpflug condition in a short-wavelength focusing system based on intensity modulation can improve measurement sensitivity. Furthermore, this invention increases the engineering feasibility of focusing measurement systems using the Scheimpflug condition at short wavelengths.

[0099] Furthermore, this invention employs a total internal reflection optical structure with three coaxial mirrors in the projection imaging optical path module and the detection imaging optical path module of the focusing measurement system. This retains the scanning mirror unit required for light intensity modulation in existing transmissive systems, and also eliminates chromatic aberration when the limited selection of transmissive optical materials in the short wavelength band makes it impossible to combine them to eliminate chromatic aberration. Moreover, it enables the realization of a short-wavelength focusing measurement system based on the principle of light intensity modulation, effectively reducing the fluctuation of process adaptability error in the focusing measurement system.

[0100] In addition, the present invention also provides a photolithography apparatus, which includes the focusing measurement system described above. During the process of precisely bringing the silicon wafer to the designated exposure position, the photolithography apparatus satisfies the Scheimpflug condition and solves the chromatic aberration problem that occurs in the optical path of short-wavelength illumination beams.

[0101] Furthermore, it is understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the scope of protection of the present invention.

[0102] Furthermore, it should be understood that the invention is not limited to the specific methods, compounds, materials, manufacturing techniques, uses, and applications described herein, which can vary. It should also be understood that the terminology described herein is used only to describe particular embodiments and not to limit the scope of the invention. It must be noted that the singular forms “a,” “an,” and “the” used herein and in the appended claims include plural bases unless the context clearly indicates otherwise. Thus, for example, a reference to “a step” means a reference to one or more steps, and may include secondary steps. All conjunctions used should be understood in the broadest sense. Therefore, the word “or” should be understood to have the definition of logical “or” rather than logical “exclusive”, unless the context clearly indicates otherwise. Structures described herein will be understood to also refer to functional equivalents of that structure. Language that can be interpreted as approximate should be understood in that way unless the context clearly indicates otherwise.

Claims

1. A focusing measurement system, characterized in that, include: Light source module, used to provide illumination beams in the short wavelength band; A projection module is used to direct the illumination beam onto the target surface and form a reflected beam. A detection unit is used to detect the reflected light beam to generate an electrical signal; The projection module includes a trapezoidal coupling prism, the illumination beam is perpendicularly incident on and exits the trapezoidal coupling prism, and the trapezoidal coupling prism has two inclined surfaces with trapezoidal hypotenuses, which serve as the incident surface and exit surface of the illumination beam, respectively. The projection module further includes a projection marking unit, which is disposed inside the trapezoidal coupling prism. After the illumination beam is perpendicularly incident on the trapezoidal coupling prism, it passes through the projection marking unit to obtain a beam with a marked image.

2. The focusing measurement system as described in claim 1, characterized in that, The projection marking unit includes a marking plate, which is prepared by etching the desired marking pattern on a quartz glass plated with chromium or aluminum. When the illumination beam shines on the marking pattern area of ​​the marking plate and is reflected, it carries the marking signal and forms a beam with a marking image. When the illumination beam shines on the non-marking pattern area of ​​the marking plate and is transmitted, it forms a stray light beam. The inclined surfaces of the two trapezoidal sides are located on the same side of the marking plate.

3. The focusing measurement system as described in claim 1, characterized in that, The projection marking unit includes a marking plate, which is prepared by etching the desired marking pattern on a quartz glass plated with chromium or aluminum. When the illumination beam shines on the marking pattern area of ​​the marking plate, it carries the marking signal and forms a beam with a marking image. When the illumination beam shines on the non-marking pattern area of ​​the marking plate, it forms a stray light beam. The inclined surfaces of the two trapezoidal sides are arranged on both sides of the marking plate.

4. The focusing measurement system as described in claim 1, characterized in that, The trapezoidal coupling prism is made of one of the following materials: natural quartz, quartz glass, and calcium fluoride.

5. The focusing measurement system as described in claim 1, characterized in that, The projection module also includes a projection imaging optical path module, and the projection imaging optical path module includes a total internal reflection optical structure using three coaxial mirrors.

6. The focusing measurement system as described in claim 5, characterized in that, The projection imaging optical path module includes a primary reflector, a scanning reflector, and a secondary reflector, and the illumination beam passes through the primary reflector, secondary reflector, scanning reflector, secondary reflector, and primary reflector in that order.

7. The focusing measurement system as described in claim 6, characterized in that, The projection imaging optical path module also includes several steering mirrors, and the illumination beams passing through the main mirror, scanning mirror and secondary mirror illuminate the steering mirrors.

8. The focusing measurement system as described in claim 1, characterized in that, The target surface includes the silicon wafer surface.

9. The focusing measurement system as described in claim 1, characterized in that, The detection unit includes: The detection imaging optical path module collects and adjusts the reflected beam from the target surface; The detection coupling prism module and the detection marker unit ensure that the reflected beam that has not deviated passes through exactly, while blocking the reflected beam that has deviated. The relay optical path module organizes the reflected light beams that pass through; The detector module collects the processed reflected beam to generate an electrical signal.

10. The focusing measurement system as described in claim 1, characterized in that, The short wavelength band ranges from 200nm to 500nm.

11. The focusing measurement system as described in claim 1, characterized in that, The light source module includes a light source and an illumination optical path module. The light source emits a short-wavelength illumination beam, and the illumination beam is irradiated onto the projection module via the illumination optical path module.

12. The focusing measurement system as described in claim 11, characterized in that, The light source includes a xenon lamp.

13. A photolithography apparatus, characterized in that, The focusing measurement system includes any one of claims 1 to 12.

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