Compound right-angle prism for a two-beam interference system and optical system thereof

Abstract

The utility model discloses a kind of composite right-angle prism for double-beam interference system and its optical system, the composite right-angle prism is plated split beam / beam combining film by the cementing surface of two prisms, and reflection film and antireflection film are plated in bevel surface partition, replace the function of multiple discrete optical elements in traditional system. Thus, the effect of simplifying optical path structure, enhancing system stability is achieved. The interferometer can utilize the ±1 order light of grating diffraction to combine in prism and interfere, realize high-precision, anti-interference measurement of grating period;Through optical path reverse operation, interference field can also be formed on substrate surface for interference lithography. The utility model integrates precision measurement and micro-nano machining function, with the advantages of compact structure, good stability, high precision and multiple functions.

Description

Technical Field

[0001] This utility model relates to the field of optical precision measurement and interferometric detection technology, specifically a composite right-angle prism for a dual-beam interferometric system and its optical system and applications. It is applicable to fields such as semiconductor manufacturing, photolithography, MEMS (microelectromechanical systems) and high-precision optical component detection, and is especially suitable for high-precision, non-contact measurement of the period and phase information of high-density gratings. Background Technology

[0002] With the increasingly widespread application of nanoscale precision large-scale displacement measurement technology in high-precision measurement and processing, high-density diffraction grating rulers have attracted widespread attention. Their superior stability compared to laser interferometers makes them a potential replacement for laser interferometers in many atmospheric applications. The grating period, as a crucial indicator, directly determines the accuracy of high-density diffraction grating rulers due to its calibration measurement error; therefore, it is extremely important for high-density diffraction grating rulers. Grating period measurement methods can be divided into contact and non-contact methods. Contact methods, such as probe profilometers and atomic force microscopes (AFM), while achieving sub-nanometer resolution, suffer from slow measurement speed, easy sample damage, and sensitivity to environmental vibrations, limiting their application in industrial settings. Non-contact measurement methods mainly include scanning electron microscopy (SEM), diffraction methods, white light interferometers, long-range profilometers, and interferometric scanning methods. Scanning electron microscopy (SEM) requires operation in a vacuum environment, resulting in high cost and low efficiency. Diffraction methods are suitable for local relative measurements of gratings. White light interferometers and long-range profilometers offer advantages such as nanometer-level resolution, fast measurement speed, and non-destructive testing. However, their measurement accuracy and on-site integration are limited when dealing with steep slope structures, low-reflectivity surfaces, or large-sized samples. Interferometric scanning, based on the principle of two-beam interference and combined with a high-precision motion stage, can achieve high-precision measurement of large-size grating periods. However, existing interferometric scanning techniques still have many shortcomings.

[0003] The following is an analysis of some patents that employ the above technologies.

[0004] Patent CN107966213B, "A measuring device, method, and calibration method for measuring the period of a diffraction grating," measures the grating period using scale lines. While the device is simple, it is not suitable for measuring large-size gratings. Patent CN110907140A, "A measuring device and method for measuring the period of a grating," uses a camera to capture interference patterns, but this has limitations when measuring high-density gratings. Patent CN120102094A, "A device and method for measuring the period and incident angle of a grating," uses diffraction, suitable for measuring local grating periods but not for measuring the absolute value of the grating period or large-size gratings. Patent CN115597511B, "A grating pitch measuring device and method," uses interferometric scanning to measure the grating period, but it involves discrete optical paths, is relatively complex, and costly. Furthermore, it is susceptible to environmental factors such as temperature, humidity, and vibration. Therefore, there is an urgent need for a high-precision interferometric measuring device with a compact structure, stable optical path, suitable for measuring the absolute value of the period of high-density gratings, and easily integrated into industrial settings. Summary of the Invention

[0005] To overcome the problems of complex structure, poor anti-interference ability, limited applicability and high cost in the existing grating period measurement technology, this utility model proposes a prism grating compound interferometer, which uses grating diffraction to generate +1 and -1 order diffracted light, and combines the two beams through a prism. The output beam contains the phase information and period information of the diffraction grating, realizing high-precision, high-efficiency and non-contact absolute measurement of the grating period.

[0006] The technical solution of this utility model is as follows:

[0007] A compound right-angle prism for a two-beam interference system, characterized in that it comprises: a first right-angle prism and a second right-angle prism;

[0008] The first right-angle prism and the second right-angle prism have the same geometric dimensions and optical materials, and are bonded together by one of their respective right-angle faces to form an internal bonding surface.

[0009] The upper half of the inclined surface of the first right-angle prism and the second right-angle prism is used as a transmission surface and can be coated with an anti-reflection film. The lower half of the inclined surface is used as a reflection surface and can be coated with a total reflection film. When the incident light on the inclined surface meets the total reflection condition, the inclined surface does not need to be coated and can be a smooth surface.

[0010] Furthermore, a beam-splitting film is coated on the adhesive surface, and the beam-splitting film is either a beam-splitting film or a beam-combining film.

[0011] Furthermore, the total reflection film is a metal reflective film or a dielectric broadband high reflective film.

[0012] Furthermore, the antireflective film is a single-wavelength antireflective film or a broadband antireflective film for a specific operating wavelength.

[0013] Furthermore, the optical material includes K9 glass, fused silica, or optical crystal.

[0014] Second, this utility model also provides an optical system, characterized in that it includes: a composite right-angle prism as described above; a light source for providing an incident light beam; and a detection element; wherein the composite right-angle prism is configured to receive the incident light from the light source and guide it to the detection element.

[0015] Furthermore, the optical system is an interferometer, an interference lithography device, an optical sensor, or a wavefront detector.

[0016] Third, this utility model also provides a method for beam manipulation using the above-mentioned composite right-angle prism, characterized by including the following steps:

[0017] The first beam and the second beam are incident from the short right-angled surfaces of the first right-angle prism and the second right-angle prism, respectively, which are coated with anti-reflection films.

[0018] The first beam and the second beam are reflected inside the composite right-angle prism via the reflecting surface of the inclined surface;

[0019] The reflected first beam and second beam are guided to the internal adhesive surface to achieve the combination or separation of the first beam and the second beam.

[0020] Fourth, a method for generating an interference field using the aforementioned composite right-angle prism, characterized by comprising the following steps:

[0021] An incident beam of light is incident from the transmission surface region of the hypotenuse of the composite right-angle prism.

[0022] The incident beam is split at the internal cemented surface to form a first sub-beam and a second sub-beam.

[0023] The first sub-beam and the second sub-beam are respectively guided to the reflective surface areas of the inclined surfaces of the first right-angle prism and the second right-angle prism for reflection;

[0024] The reflected first sub-beam and second sub-beam are emitted from the right-angled surfaces of the first and second right-angled prisms, respectively, which are coated with anti-reflection films, and form an interference field in the external space; the fringe period in the interference field corresponds to the different angles at which the incident beam is incident from the transmission surface region of the inclined surface of the composite right-angled prism.

[0025] Compared with existing technologies, this technology has the following advantages:

[0026] 1) This invention integrates the incident, reflection, and beam splitting / combining functions of a light beam into a composite right-angle prism with a specially designed film system. This reduces the number of optical components, the assembly difficulty of the system, and the overall size, and lowers the system error introduced by the assembly and adjustment errors of multiple components. At the same time, the integrated structure enhances the mechanical and thermal stability of the system, making it more resistant to environmental vibrations and temperature drift.

[0027] 2) On the same optical surface of the prism's hypotenuse, a reflective region (lower half) and a transmission region (upper half) are fabricated using a coating technique. This allows the optical surface to function as either a "reflector" or a "transmission window" depending on the incident position of the beam, thus enabling flexible control of the optical path and reuse of system functions. The same hardware platform can switch between "detection" and "exposure" modes without altering the optical path structure, achieving a functional conversion from high-precision grating period measurement to high-quality grating mask fabrication. Simultaneously, by adjusting the angle between the laser beam incident on the upper half of the hypotenuse of the second right-angle prism, different periodic interference fringes can be obtained on a photoresist-coated substrate surface, thereby fabricating grating masks with multiple periods.

[0028] 3) Utilizing the symmetry of the composite prism, the generated +1st and -1st order diffracted beams are guided into its interior, making the optical paths of the two interference beams nearly perfectly symmetrical and largely overlapping in space. This method ensures that the influence of environmental factors (such as vibration, airflow, and temperature fluctuations) on the two beams manifests as highly consistent common-mode noise. In subsequent interference signals, this common-mode noise is largely canceled out, thereby extracting a phase difference signal with a high signal-to-noise ratio, ultimately achieving sub-nanometer level high-precision and high-repeatability measurements. Attached Figure Description

[0029] Figure 1 This utility model discloses a schematic diagram of the prism geometry of a prism grating composite interferometer.

[0030] Figure 2 : A schematic diagram of the working mode of the prism grating compound interferometer embodiment 1 for grating period measurement;

[0031] Figure 3 A schematic diagram of the working mode of the prism grating composite interferometer of this utility model in interference lithography, as shown in Embodiment 2. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0033] Please see Figure 1 , Figure 1 This is a schematic diagram of the prism geometry of a prism grating compound interferometer according to this utility model. As shown in the figure, a compound right-angle prism for a two-beam interferometer system includes: a first right-angle prism and a second right-angle prism; the first right-angle prism and the second right-angle prism have the same geometric dimensions and optical materials, and are bonded together by one of their respective right-angle faces to form an internal bonding surface. The upper half of the inclined surface of the first right-angle prism and the second right-angle prism serves as a transmission surface, coated with an anti-reflection film, and the lower half of the inclined surface serves as a reflection surface, coated with a total reflection film. When the incident light on the inclined surface meets the total internal reflection condition, the inclined surface does not need to be coated and can be a smooth surface. A beam-splitting film is coated on the bonding surface, which is a beam-splitting film or a beam-combining film. The total reflection film is a metal reflective film or a dielectric broadband high-reflection film. The anti-reflection film is a single-wavelength anti-reflection film or a broadband anti-reflection film for a specific working wavelength. The optical materials include K9 glass, fused silica, or optical crystals.

[0034] Example 1

[0035] Please see Figure 2 This embodiment demonstrates the working mode of the prism grating compound interferometer of this invention for grating period measurement. For example... Figure 1 As shown, the system includes a laser source 1, a first right-angle prism 2, a second right-angle prism 3, a reflector 4, a grating 5, a photodetector, and a data acquisition and processing module 6. The first right-angle prism 2 and the second right-angle prism 3 have the same geometric dimensions and optical materials. They are bonded together by one of their respective right-angle faces to form an internal bonding surface 8, which is coated with a beam-combining / beam-splitting film. The short right-angle sides 9-1 and 9-2 of both right-angle prisms 2 and 3 are coated with anti-reflection films to ensure a high transmittance of incident light >99.5%. The upper half 10-1 of the hypotenuse of the first right-angle prism 2 and the upper half 10-2 of the hypotenuse of the second right-angle prism 3 serve as transmission surfaces and can be coated with anti-reflection films. The lower half 7-1 of the hypotenuse of the first right-angle prism 2 and the lower half 7-2 of the hypotenuse of the second right-angle prism 3 serve as reflection surfaces and can be coated with total reflection films. The hypotenuses of the two right-angle prisms can be partitioned using photolithography masking technology. When the incident light on the hypotenuse surface meets the condition of total internal reflection, the hypotenuse surface does not need to be coated and can be smooth.

[0036] The laser beam emitted from the laser source 1 illuminates the reflector 4. After being reflected by the reflector 4, it is incident perpendicularly onto the diffraction grating 5 under test, generating two diffracted beams, the +1st and -1st orders. The +1st order diffracted beam is incident through the short side 9-1 of the first right-angle prism 2, passes through the antireflection coating, and is transmitted to the lower half of its hypotenuse 7-1. After being reflected by the total reflection coating, it is incident on the central cemented surface 8. Simultaneously, the -1st order diffracted beam is incident through the short side 9-2 of the second right-angle prism 3, and after being reflected by the lower half of its hypotenuse 7-2, it is also incident on the cemented surface 8.

[0037] On the cemented surface 8, the light beam from the first right-angle prism 2 is transmitted through the beam-splitting film, while the light beam from the second right-angle prism 3 is reflected, thus combining the two beams and producing interference. The combined interference light is transmitted through the upper half 10-2 anti-reflection film on the hypotenuse of the second right-angle prism 3 and is detected, collected, and processed by the photodetector and data acquisition and processing module 6. During measurement, the grating 5 under test is mounted on a nanometer-precision piezoelectric displacement stage (not shown in the figure). The photodetector and data acquisition and processing module 6 controls the data acquisition card to synchronously send control signals, driving the displacement stage to precisely scan the grating along its grating lines perpendicular to the direction of the grating, while simultaneously acquiring the intensity changes of the interference signal output by the photodetector at a high sampling rate. The acquired interference signal exhibits a sinusoidal variation. The photodetector and data acquisition and processing module 6 processes the acquired discrete data points to calculate the grating displacement corresponding to one complete cycle of the interference signal. This displacement is numerically equal to the absolute period of the grating under test.

[0038] Example 2

[0039] Please see Figure 3 This embodiment demonstrates the working mode of using the prism grating composite interferometer of this utility model for interference lithography.

[0040] Remove the diffraction grating 5 to be tested and install the photoresist substrate to be exposed in its original position.

[0041] A laser light source 1 emits a beam that is transmitted into the right-angle prism 3 through the upper half 10-2 of the hypotenuse. Inside the prism, the beam travels to the central splitting / combining surface 8, where it is split into two beams: one beam is reflected back into the second right-angle prism 3, and the other is transmitted into the first right-angle prism 2. The two beams then propagate to the total internal reflection films 7-1 and 7-2 on the lower half of the hypotenuse of the first and second right-angle prisms 2 and 3, respectively. After reflection, they exit through the anti-reflection films 9-1 and 9-2 on the short right-angle sides of the first and second right-angle prisms 2 and 3, respectively. The two emitted laser beams meet in space, forming alternating bright and dark, periodically stable interference fringes on the photoresist-coated substrate surface. After exposure for a certain time, the substrate undergoes standard development processing, resulting in a high-quality grating mask on the substrate surface. By adjusting the angle between the laser beam emitted from the laser source 1 and the surface of the upper half 10-2 of the hypotenuse of the second right-angle prism 3, corresponding interference fringes of different periods can be obtained on the substrate surface coated with photoresist, thereby creating grating masks with multiple periods.

[0042] The above embodiments are preferred embodiments of the present utility model, but the embodiments of the present utility model are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present utility model shall be considered equivalent substitutions and shall be included within the protection scope of the present utility model.

Claims

1. A compound right-angle prism for a two-beam interference system, characterized in that, include: The first right-angle prism and the second right-angle prism; The first right-angle prism and the second right-angle prism have the same geometric dimensions and optical materials. They are bonded together by one of their respective right-angle faces to form an internal bonding surface. The upper half of the inclined surface of the first right-angle prism and the second right-angle prism is used as a transmission surface and can be coated with an anti-reflection film. The lower half of the inclined surface is used as a reflection surface and can be coated with a total reflection film. When the incident light on the inclined surface meets the total reflection condition, the inclined surface does not need to be coated and can be a smooth surface.

2. The compound right-angle prism for a two-beam interference system according to claim 1, characterized in that, A beam-splitting film is coated on the adhesive surface, and the beam-splitting film is either a beam-splitting film or a beam-combining film.

3. The compound right-angle prism for a two-beam interference system according to claim 1, characterized in that, The total reflection film is a metal reflective film or a dielectric broadband high reflective film.

4. The compound right-angle prism for a two-beam interference system according to claim 1, characterized in that, The antireflective coating is a single-wavelength antireflective coating or a broadband antireflective coating for a specific operating wavelength.

5. The compound right-angle prism for a two-beam interference system according to claim 1, characterized in that, The optical materials include K9 glass, fused silica, or optical crystals.

6. An optical system, characterized in that, include: The composite right-angle prism as described in any one of claims 1 to 5; A light source, used to provide an incident beam of light; and a detection element; wherein the composite right-angle prism is configured to receive incident light from the light source and guide it to the detection element.

7. The optical system according to claim 6, characterized in that, The optical system is an interferometer, an interference lithography device, an optical sensor, or a wavefront detector.

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