A method for processing a Faraday rotator to improve its face type

Abstract

This invention relates to a processing method for improving the surface shape of Faraday rotator wafers. By obtaining the inherent warpage curvature T and warpage direction of a wafer of specific size and material, a curved base mold with a preset curvature is prepared, and a curved surface mold is used in conjunction with it for co-processing into a disc. The working surface curvature of the disc mold is consistent with but opposite in direction to the working surface curvature of the base mold. The wafer to be processed is fixed to the curved working surface of the disc mold using a uniform array of optical wax and pre-deformation. After disc formation, it is precisely fitted with the base mold and ground. After removal from the disc, the natural warpage tendency of the wafer cancels out the pre-deformation, resulting in a flat wafer. Therefore, this invention achieves a single-surface deformation of ≤2λ for ultra-thin Faraday rotator wafers with a diameter-to-thickness ratio ≥30:1, effectively improving the product yield.

Description

Technical Field

[0001] This invention relates to the field of crystal growth and processing technology, and specifically to a processing method for improving Faraday rotation foliation. Background Technology

[0002] Faraday rotators are optical functional components that utilize the Faraday effect. They are primarily used in laser systems such as optical isolators and optical circulators. Their surface accuracy directly determines the isolator's core performance characteristics, such as isolation and insertion loss, and is crucial to the stability of optical communication systems. With the rapid development of the AI ​​industry and the continuous expansion of cloud computing, big data centers, and computing power centers, the global data volume is growing exponentially, significantly increasing the production volume and technological iteration speed of optical communication devices. The market's requirements for the precision of optical communication devices are also rising accordingly. As a core component of optical communication devices, optical isolators are placed between the light source and other optical transmission components. They allow only light directed towards the optical transmission components to pass through in the forward direction, selectively blocking reflected light directed towards the light source to prevent reflected light from interfering with the stability of the light source. Currently, the common specifications for Faraday rotators are 11mm × 11mm × 0.35mm, with a diameter-to-thickness ratio as high as 30:1. They are typical ultra-thin optical wafers, and their processing generally employs the traditional "cutting-grinding-polishing" process.

[0003] Traditional processing employs the classical planar polishing method, using a flat glass base mold and upper disk mold. The wafer is fixed into a disk using optical wax before grinding and polishing. This process has the following fundamental drawbacks: Faraday rotators develop inherent residual stress distributions during liquid-phase epitaxial growth and dicing, manifesting as initial slight warping. The grinding process of ultrathin Faraday rotators involves continuous thickness reduction: from an initial thickness of approximately 0.6-0.8 mm after dicing, grinding and polishing reduce the final thickness to 0.4 mm, a reduction rate of 40% or more. As the thickness decreases and stiffness diminishes, the internal "springiness" of the wafer increases, but the planar constraint of the substrate prevents its release. At the start of processing, the wafer's deformation, i.e., the surface area PV value, is generally below 0.5λ (λ=632.8 nm). After processing, once the constraint (bottom plate) is released, the stored stress is released instantaneously, causing a violent surface area rebound, with deformation generally reaching 3-5λ, far exceeding the acceptable threshold of ≤2λ.

[0004] Existing technologies can only passively alleviate deformation by adjusting the hardness of the wax and fine-tuning the pressure, but cannot fundamentally solve the stress release problem, and the pass rate has long hovered around 60%.

[0005] Chinese patent CN119260587A discloses a method for processing high-quality cadmium zinc telluride (CZD) wafers. This method first involves chemically etching the wafer to remove stress from the damaged layers on both sides. Next, a diamond grinding wheel is used to grind the growth surface of the wafer. After grinding, the wafer is re-fixed and then polished. Finally, chemical polishing is performed. This method utilizes the stress from the damaged layers generated during grinding and polishing to "neutralize" the edge collapse phenomenon during chemical polishing, aiming to improve the surface shape control level in CZD wafer production. However, the stress source is a side effect of the processing, characterized by being uncontrollable, uneven, and strongly correlated with the amount of material removed, thus representing a passive compensation. It still cannot solve the global surface warping problem caused by intrinsic residual stress in the crystal. Summary of the Invention

[0006] The purpose of this invention is to provide a processing method for improving the surface shape of Faraday rotators, which can solve the problem that the existing planar polishing process cannot be adapted to ultra-thin Faraday rotators and that the surface shape deformation exceeds the standard. It has the advantages of reducing the deformation of Faraday rotators, improving their surface shape accuracy, and increasing their pass rate.

[0007] To achieve the above objectives, the solution of the present invention is: A processing method for improving the Faraday rotation plane shape includes the following steps: S1. Obtain the inherent warpage curvature T and warpage direction of a wafer of a specific size and material: Prepare several test wafers with the same size and material as the wafer to be processed. Polish each test wafer on both sides of the plane and measure the warp sagitta (to be converted into the inherent warp curvature T) and warp direction of the test wafer after processing. S2. Prepare a surface polishing mold based on the inherent warpage curvature T and warpage direction: Prepare a curved surface plate mold and a curved surface bottom mold. The width of the curved surface bottom mold is greater than or equal to the width of the curved surface plate mold * 3. Set the curved working surface of the plate mold on the curved surface to have a curvature of R1 = -T, with the direction opposite to the warping direction. Set the curved working surface of the bottom mold to have a curvature of R2 = +T, with the direction the same as the warping direction. S3. Use a double-sided asynchronous processing method to process wafers in batches: S31. Perform surface cleaning pretreatment on the wafer; S32. The first surface of the wafer is polished using a planar polishing mold; S33. Use a curved surface polishing mold to perform curved surface polishing on the second surface of the wafer: S331, Second surface mounting: Prepare the curved surface mounting mold prepared in step S2, and arrange several wafers with the first surface processed in an array at intervals on the curved working surface of the curved surface mounting mold; use photoresist to mount the wafer, and use protective paint to face and fix the first surface of the wafer processed onto the curved working surface of the curved surface mounting film, forcing the wafer to generate an elastic pre-deformation that is completely opposite to the inherent warp T. S332, Second Surface Polishing: Install the curved bottom mold prepared in step S2 onto the worktable of the polishing equipment, and fix the upper curved top mold prepared on the positioning fixture so that the concave and convex surfaces of the curved bottom mold and the upper curved top mold are opposite each other, so that the concave working surface of the curved bottom mold contacts the second surface of the wafer protrusion on the upper curved top mold, and control the distance between the working surface of the curved bottom mold and the wafer on the upper curved top mold to be ≤2μm; so that the wafer is attached to the curved bottom mold; adopt a three-stage progressive polishing: first rough polishing, then semi-fine polishing, and finally fine polishing. During the polishing process, the abrasive particle size decreases step by step, and the pressure decreases step by step; S333, Second Side Lower Plate: After processing is completed, the bonding constraint between the wafer and the plate mold on the curved surface is released. The wafer rebounds under the action of inherent residual stress and cancels out the pre-deformation, finally obtaining a finished wafer with polished surfaces on both sides and overall flatness.

[0008] Furthermore, in step S1, a number of wafers to be tested are processed into finished products of the target thickness using a traditional planar polishing process; the warp height and warp direction of each finished product after double-sided planar processing are measured using a laser interferometer, and the average warp height S0 is calculated. According to the formulas radius of curvature = (1 / 2 inner diameter of the wafer) / sinθ, tanθ = height / (1 / 2 inner diameter of the wafer), it is converted into the inherent warp curvature T.

[0009] Furthermore, the traditional planar polishing process includes: for the first surface polishing, an optical wax plate is used for fixing; for the second surface polishing, a gloss adhesive plate is used, and a gloss adhesive protective varnish is applied; the optical wax ratio is hard wax: soft wax = 3:1; both surfaces are first rough polished for 30 minutes, with a polyurethane or 20,000-grit grinding wheel, a polishing pressure of 70N, and a rotation speed of 200r / min; then fine polished for 45 minutes, with an asphalt grinding surface, a polishing pressure of 50N, and a rotation speed of 80r / min; the polishing fluid used is as follows: for rough polishing, a diamond powder solution with a particle size of 5μm is used, and for fine polishing, a colloidal SiO2 solution with a particle size of 0.25μm is used.

[0010] Furthermore, in step S32, the planar polishing process includes the following steps: S321, First Surface Mounting: Prepare a flat upper platen mold for the flat polishing mold. Apply a 0.01mm-0.05mm thick layer of optical wax as an adhesive evenly to the working surface of the flat upper platen mold. Arrange the wafers to be processed on the optical wax applied to the working surface of the flat upper platen mold, with the first surface of the wafers to be processed away from the upper platen mold. The array adopts a ring array, and the spacing between adjacent wafers is controlled within 1mm-2mm to retain the polishing liquid inflow channel. Place the flat upper platen mold with the arranged wafers into an oven for curing, so that the wafers are rigidly bonded to the flat upper platen mold by the wax. S322, First-side polishing: Install the disc mold on the flat surface of the disc into the positioning fixture, and use the polishing equipment worktable to perform three-stage progressive polishing: first rough polishing, then semi-fine polishing, and finally fine polishing, with the abrasive particle size decreasing step by step and the pressure decreasing step by step; thoroughly clean between each stage, while the pressure gradually decreases as the particle size decreases. S323, First side lower plate: After the first side is polished, the upper plate mold is removed and the optical wax is heated to soften it. The wafer after the first side is polished is taken out, cleaned, and the wafer after the first side is polished is obtained.

[0011] Furthermore, the three-stage progressive polishing includes the following steps: The first stage is rough polishing. The abrasive used is diamond powder with a diameter of 4μm-8μm. The grinding surface is a 20,000-mesh grinding wheel with a pressure of 50N-80N, a rotation speed of 200r / min-300r / min, and a time of 25min-50min. The second stage is semi-fine polishing. The abrasive used is 1μm-2μm diamond powder, the polishing surface is polyurethane, the pressure is 30N-50N, the rotation speed is 100r / min-150r / min, and the time is 20min-50min. The third stage is fine polishing. The abrasive used is 0.25μm-0.5μm SiO2 liquid, the polishing surface is asphalt, the pressure is 10N-30N, the rotation speed is 20r / min-50r / min, and the time is 40min-90min.

[0012] Furthermore, the dimensions of the wafer to be processed are 11mm × 11mm × 0.62mm; the inherent warpage curvature T = -885m, and the warpage direction is concave upwards; the wafer thickness after the first surface is processed is 0.524mm-0.525mm; the thickness of the finished wafer is 0.355mm-0.356mm.

[0013] Furthermore, the ratio of the amount of surface polishing to the amount of curved surface polishing is 1:1.

[0014] Furthermore, in step S331, the array is a ring array, and the spacing between adjacent wafers is controlled within the range of 1mm-2mm. By adopting the above technical solution, this invention discovers that wafers of specific sizes and materials exhibit unidirectional warping and natural warping with a certain warping curvature after planar polishing. Therefore, based on this, the inherent warping curvature and warping direction of the wafer were experimentally obtained. Then, a curved surface polishing mold was creatively prepared based on this inherent warping curvature. Using a bottom mold and an upper mold with working surfaces of specific curvature, a pre-deformation in opposite directions is actively applied to the wafer. As processing progresses and the thickness decreases, the natural warping trend of the wafer gradually emerges, precisely offsetting the pre-deformation. When the thickness reaches the target value, the pre-deformation and natural warping reach equilibrium, and the wafer presents a flat state after being placed on the upper mold.

[0015] This allows for precise and controllable control of the disc shape, thereby keeping the deformation of the ultra-thin Faraday rotator within acceptable limits, improving product surface accuracy, and increasing product qualification rate.

[0016] The wafers prepared by the method of this invention have an aspect ratio ≥30:1; the PV value of the wafer surface after processing is ≤2λ, and the surface roughness Ra is ≤0.5nm. The product qualification rate is ≥99%. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the principle of the present invention; Figure 2 This is a schematic diagram illustrating the processing variations of the wafer according to the present invention; Figure 3 This is a schematic diagram of the bottom mold and the upper mold of the present invention; Figure 4 This is a graph showing the relationship between the thickness of the wafer product and the average warpage height according to the present invention. Figure 5 This is a top view of the upper plate mold after it has been installed according to the present invention; Labeling explanation: Curved top mold 1, curved bottom mold 2, wafer 3. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Example 1: like Figures 1 to 5 The processing method for improving the Faraday rotation surface shape according to this embodiment includes the following steps: S1. Obtain the inherent warpage curvature T and warpage direction of a wafer of a specific size and material. Prepare several test wafers with the same size and material as the wafer to be processed. Perform double-sided planar polishing on each test wafer. Measure the inherent warpage height S0 and warpage direction of the test wafer after planar processing (data for each material and size needs to be accumulated and measured). Specifically, 20 Faraday rotation wafers of the same batch as the wafers to be processed, each with a specification of 11mm×11mm×0.62mm, were selected as test wafers. The test wafers were processed into finished products with a target thickness of 0.355mm using traditional planar polishing technology. The first side was fixed with optical wax, and the second side was protected with a protective varnish. The ratio of optical wax was 3:1 (hard wax: soft wax). The optical wax could be paraffin wax and rosin, etc. The protective varnish could be common lacquer, etc. Both sides were first rough polished for 30 minutes with polyurethane or a 20,000-grit grinding wheel, polishing pressure 70N, and rotation speed 200r / min. Then, they were fine polished for 45 minutes with asphalt, polishing pressure 50N, and rotation speed 80r / min. The polishing fluid could be as follows: diamond powder solution with a particle size of 5μm for rough polishing and colloidal SiO2 with a particle size of 0.25μm for fine polishing.

[0020] The warpage height of each finished wafer after double-sided planar processing was measured using a ZYGO laser interferometer. The average warpage height after planar processing was calculated to be S0 = -5.4λ, where λ = 632.8 nm, with the direction being concave upwards (center concave, edge up). According to the formulas: radius of curvature = (half the inner diameter of the wafer) / sinθ, tanθ = warpage height / (half the inner diameter of the wafer), and half the inner diameter of the wafer = 5.5 cm, the average warpage height S0 was converted to the inherent warpage curvature of the wafer T = 5.5 cm / sin[arctan(-5.4λ / 5.5 cm) ≈ -885 m, with the warpage direction being concave upwards (see [reference]). Figure 1 ).

[0021] In the above-mentioned traditional planar polishing process experiment, the data obtained by tracking and detecting the wafer at different processing stages are shown in the table below:

[0022] From the above table and Figure 4 It can be seen that as the thickness decreases, the warping increases monotonically, and the warping direction is highly consistent: the center is concave and the edges around the perimeter are raised.

[0023] Based on this principle, in the initial stage of the second-side processing (when the thickness and rigidity are still sufficient), this invention actively applies a pre-deformation in opposite directions to the wafer by designing a bottom mold and an upper mold with working surfaces of specific curvature. As processing progresses and the thickness decreases, the wafer's natural warping tendency gradually emerges, precisely offsetting the pre-deformation. When the thickness reaches the target value, the pre-deformation and natural warping reach equilibrium, and the wafer presents a flat state after being placed on the lower plate. This allows for precise and controllable plate shape, thereby controlling the deformation of the ultrathin Faraday rotator within the allowable range, improving product surface accuracy, and increasing product yield. Details are provided in subsequent steps.

[0024] S2. Prepare a surface polishing mold based on the inherent warpage curvature T and warpage direction. See Figure 3 Prepare a curved surface plate mold 1 and a curved surface bottom mold 2. The width of the curved surface bottom mold is greater than or equal to the width of the curved surface plate mold * 3. Since the inherent warping curvature T = -885m and the warping direction is concave upward, the curved surface working surface of the plate mold 1 is set as a convex working surface with curvature R1 = -T = 885m and direction convex. Then, the curved surface working surface of the bottom mold 2 is set as a curved surface working surface with curvature R2 = +T = -885m and direction concave, so as to match the plate mold 1 on the curved surface. S3. Batch processing of wafers is performed using a double-sided asynchronous processing method. S31. Perform surface cleaning pretreatment on the wafer. The pretreatment is a conventional method and may include the following steps: a. ultrasonic cleaning (deionized water + neutral cleaning agent, 5 min); b. dehydration with anhydrous ethanol (2 min); c. nitrogen drying; d. plasma activation treatment (Ar / O2=4:1, 50W, 30s).

[0025] S32. Perform conventional planar processing on the first surface of the wafer using a planar polishing mold. S321, First surface, upper plate (plane) The first surface mounting process includes the following steps: preparing a planar upper platen mold for a planar polishing mold, wherein the working surface of the planar upper platen mold is a normal plane with a PV value of 1μm; uniformly coating the working surface of the planar upper platen mold with an optical wax of 0.01mm-0.05mm thickness as an adhesive; and arranging the wafers to be processed in an array on the optical wax applied to the working surface of the planar upper platen mold, such that the first surface of the wafer to be processed is far away from the upper platen mold. The array can be a ring array or other array method, and the spacing between adjacent wafers can be controlled within 1mm-2mm, while retaining a channel for the polishing slurry to flow in. Place the wafer-mounted mold (with the wafer already attached) on the flat surface into an oven and cure at 90°C for 35 minutes with a cooling rate of ≤2°C / min. The wafer is rigidly bonded to the mold by the wax. S322, First surface polishing (normal planar constraint grinding and polishing) Install the prepared disc mold onto the processing station, and use it in conjunction with the polishing equipment's worktable for a three-stage progressive polishing process: The first stage is rough polishing, using 5μm diamond powder as the abrasive, a 20,000-grit grinding wheel, a pressure of 70N, a rotation speed of 200r / min, and a time of 25min, with the wafer thickness controlled between 0.537mm and 0.539mm; (rapidly reducing dimensions). The second stage is semi-finish polishing, using 1μm diamond powder as the abrasive, polyurethane as the polishing surface, with a pressure of 50N, a rotation speed of 100r / min, and a time of 20min. The wafer thickness is controlled between 0.527mm and 0.529mm. (This polishes away scratches caused by twice the amount of 5μm diamond powder). The third stage is fine polishing. The abrasive used is 0.25μm SiO2 liquid, the polishing surface is asphalt, the pressure is 10N, the rotation speed is 30r / min, and the time is 40min. The wafer thickness is controlled at 0.524mm-0.525mm. (This removes scratches caused by twice the amount of 1μm diamond powder). Furthermore, thorough cleaning between each stage prevents large particles from causing scratches. At the same time, the pressure is gradually reduced as the particle size decreases, minimizing stress introduction during the fine polishing stage.

[0026] S323, First side lower plate After the first side is polished, the mold on the flat surface is removed and heated to 100°C to soften the wax layer. The wafer after the first side is polished is then taken out and cleaned in sequence with anhydrous ethanol, adhesive remover, and deionized water to obtain the wafer after the first side is polished. The thickness of the wafer after the first side is processed is 0.524mm-0.525mm.

[0027] S33. Process the second surface of the wafer using a curved surface polishing mold. S331, Second surface up (curved surface); The curved disk mold 1 prepared in step S2; See Figure 5 The second surface mounting step is basically the same as the first surface mounting step S321. The main difference is that the planar mounting mold is replaced by a curved mounting mold 1 with a convex working surface. At the same time, instead of optical wax as an adhesive, photoresist is used for mounting. The wafers are arranged in an array, and then photoresist protective varnish is used to fix the first surface of the wafer to the curved mounting film. The wafer 3 is rigidly bonded to the mounting mold by the photoresist protective varnish, which forces the wafer to produce an elastic pre-deformation that is completely opposite to the inherent warpage T.

[0028] S332, Second surface polishing (curved surface constraint polishing): Install the curved bottom mold 2 prepared in step S2 onto the worktable of the polishing equipment, and fix the upper curved top mold 1 prepared on the positioning fixture so that the concave and convex surfaces of the curved bottom mold 2 and the upper curved top mold 1 are opposite each other, and control the distance between the working surface of the curved bottom mold 2 and the wafer on the upper curved top mold 1 to be ≤2μm.

[0029] Control the curved bottom mold 2 to slowly rotate and press down, so that the concave working surface of the curved bottom mold 2 contacts the second surface of the wafer protrusion on the curved upper mold 1.

[0030] At this point, the two surfaces of the wafer are attached to two different curved surfaces, which have the same curvature but opposite directions.

[0031] Next, a three-stage progressive polishing process is employed: The first stage is rough polishing, using 5μm diamond powder as the abrasive, a 20,000-grit grinding wheel, a pressure of 70N, a rotation speed of 200r / min, and a time of 25min. The wafer thickness is controlled between 0.369mm and 0.370mm (rapidly reducing dimensions). The second stage is semi-fine polishing, using 1μm diamond powder as the abrasive, polyurethane as the polishing surface, with a pressure of 30N, a rotation speed of 100r / min, and a time of 30min. The wafer thickness is controlled between 0.358mm and 0.359mm; (to remove scratches caused by twice the amount of 5μm diamond powder). The third stage is fine polishing, using 0.25μm SiO2 liquid as the abrasive, asphalt as the polishing surface, with a pressure of 10N, a rotation speed of 20r / min, and a time of 50min. The wafer thickness is controlled at 0.355mm-0.356mm. (This polishes away scratches caused by twice the amount of 1μm diamond powder). The rest is basically the same as the first surface polishing; Grinding and polishing are performed under the constraints of curved surface geometry. Since the wafer is completely bonded to the curved base mold 2 with the same curvature, the normal stress during the processing is minimal.

[0032] S333, the second lower plate, is basically the same as S323; after processing is completed and the bonding constraints are released, the wafer springs back under the action of inherent residual stress and cancels out the pre-deformation (see...). Figure 2 ).

[0033] The processing ratio of planar grinding and polishing to curved grinding and polishing in this invention is 1:1. Furthermore, by precisely controlling the curvature of the curved polishing mold to match the inherent warping curvature, the residual deformation Δ after springback is reduced to 0, ultimately resulting in a finished wafer with a size of 11mm×11mm×thickness of 0.355mm-0.356mm that is polished on both sides and is flat overall.

[0034] After polishing and inspecting 20 wafers using the above method, the following results were obtained: PV value of surface shape: 0.82λ-1.34λ, average 1.07λ; surface roughness Ra of each finished wafer: 0.32-0.48nm, average 0.41nm, which meets the process requirement of ≤2λ.

[0035] The present invention proposes a two-sided asynchronous collaborative processing technology that uses normal planar polishing on the first side and curved surface polishing on the second side.

[0036] Two sets of curved surface polishing molds with opposite curvatures are used to achieve separate release and balance of stress on the two surfaces. The specific principle is shown in the table below.

[0037]

[0038] Double-sided asynchronous processing offers the following advantages: 1. Avoid stress superposition caused by simultaneous pressure on both sides; 2. Curved surfaces release inherent residual stress and reduce unidirectional deformation; 3. Finally, a flat wafer with completely released stress is obtained.

[0039] The differences between this technology and existing double-sided grinding technology are shown in the table below.

[0040]

[0041] Meanwhile, in order to achieve optical-grade surface quality (roughness Ra≤0.5nm), the above-mentioned method of the present invention also proposes a three-stage progressive polishing process.

[0042] Under the constraint of curved surface, the surface roughness is gradually reduced through a three-stage process of rough polishing → semi-fine polishing → fine polishing, while avoiding stress concentration caused by curved surface constraint.

[0043] Process parameters:

[0044] Comparative Example 1 (Traditional flat surface process + three-stage polishing) Using a flat glass bottom mold and a flat glass top mold, with wafers of the same specifications, the same optical wax ratio (hard wax: soft wax = 3:1), and the same method of applying optical adhesive to the plate, and the aforementioned three-stage polishing (rough polishing + semi-fine polishing + fine polishing): Inspection was performed on 20 Faraday rotation wafers (11mm × 11mm × 0.62mm) after processing. a. PV value of surface type: 1.75λ-2.21λ, average 1.92λ b. Permissible tolerance for 4 pieces (20%) with PV values ​​exceeding 2λ c. Pass rate 80% Comparative Example 2 (proving the criticality of curvature matching) Take wafers from the same batch and use curved polishing molds with curvatures of 530m (overcompensated, with a sagitta of about 9.0λ for the same size, which is about 1.7 times the inherent warp sagitta) and 2000m (undercompensated, with a corresponding pre-deformation sagitta of about 2.4λ for the same size, which is much smaller than the inherent warp sagitta of the wafer, indicating insufficient compensation) to process them according to the same steps as in Example 1, and obtain the data in the table below.

[0045]

[0046] As can be seen from the table above, the curvature of the curved bottom mold 2 and the curved top mold 1 must be precisely matched with the inherent warpage curvature T of the wafer.

[0047] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, equivalent changes and modifications without departing from the principle of the present invention should still fall within the scope of protection of the present invention.

[0048] In the description of the embodiments of this application, it should be understood that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship that the product of this application is usually placed in when in use, or the orientation or positional relationship that is commonly understood by those skilled in the art. It is only for the convenience of describing this application and simplifying the description, and is not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this application.

Claims

1. A method for processing a Faraday rotator to improve the facet shape, characterized by, Includes the following steps: S1. Obtain the inherent warpage curvature T and warpage direction of a wafer of a specific size and material: Prepare several test wafers with the same size and material as the wafers to be processed. Polish each test wafer on both sides of the plane. Measure and calculate the inherent warpage curvature T and warpage direction of the test wafers after processing. S2. Prepare a surface polishing mold based on the inherent warpage curvature T and warpage direction: Prepare a curved surface plate mold and a curved surface bottom mold. The width of the curved surface bottom mold is greater than or equal to the width of the curved surface plate mold multiplied by 3. Set the curvature of the curved surface plate mold to R1=-T, with the direction opposite to the warping direction. Set the curvature of the curved surface bottom mold to R2=+T, with the direction the same as the warping direction. S3. Use a double-sided asynchronous processing method to process wafers in batches: S31. Perform surface cleaning pretreatment on the wafer; S32. The first surface of the wafer is polished using a planar polishing mold; S33. Use a curved surface polishing mold to perform curved surface polishing on the second surface of the wafer: S331, Second surface mounting: Prepare the curved surface mounting mold prepared in step S2, and arrange several wafers with the first surface processed in an array at intervals on the curved working surface of the curved surface mounting mold; use photoresist to mount the wafer, and use protective paint to face and fix the first surface of the wafer processed onto the curved working surface of the curved surface mounting film, forcing the wafer to generate an elastic pre-deformation that is completely opposite to the inherent warp T. S332, Second Surface Polishing: Install the curved bottom mold prepared in step S2 onto the worktable of the polishing equipment, and fix the upper curved top mold prepared on the positioning fixture so that the concave and convex surfaces of the curved bottom mold and the upper curved top mold are opposite each other, so that the concave working surface of the curved bottom mold contacts the second surface of the wafer protrusion on the upper curved top mold, and control the distance between the working surface of the curved bottom mold and the wafer on the upper curved top mold to be ≤2μm; so that the wafer is attached to the curved bottom mold; adopt a three-stage progressive polishing: first rough polishing, then semi-fine polishing, and finally fine polishing. During the polishing process, the abrasive particle size decreases step by step, and the pressure decreases step by step; S333, Second Side Lower Plate: After processing is completed, the bonding constraint between the wafer and the plate mold on the curved surface is released. The wafer rebounds under the action of inherent residual stress and cancels out the pre-deformation, finally obtaining a finished wafer with polished surfaces on both sides and overall flatness.

2. The method of claim 1, wherein the Faraday rotator is a planar Faraday rotator. In step S1, several wafers to be tested are processed into finished products of the target thickness using a traditional planar polishing process. The warp height and warp direction of each finished product after double-sided planar processing are measured using a laser interferometer, and the average warp height S0 is calculated. According to the formulas radius of curvature = 1 / 2 inner diameter of wafer / sinθ, tanθ = height / 1 / 2 inner diameter of wafer, the average warp height S0 is converted into the inherent warp curvature T.

3. A method of processing a Faraday optical rotator face type improvement according to claim 1 or 2, characterized in that, The traditional planar polishing process includes: for the first surface polishing, an optical wax plate is used for fixing; for the second surface polishing, a gloss adhesive plate is used, and a gloss adhesive protective varnish is applied; the optical wax ratio is hard wax: soft wax = 3:1; both surfaces are first rough polished for 30 minutes, with a polyurethane or 20,000-grit grinding wheel, a polishing pressure of 70N, and a rotation speed of 200r / min; then fine polished for 45 minutes, with an asphalt grinding wheel, a polishing pressure of 50N, and a rotation speed of 80r / min; the polishing fluid used is as follows: for rough polishing, a diamond powder solution with a particle size of 5μm is used, and for fine polishing, a colloidal SiO2 with a particle size of 0.25μm is used.

4. The method of claim 1, wherein the Faraday rotator is a planar Faraday rotator. In step S32, the planar polishing process includes the following steps: S321, First Surface Mounting: Prepare a flat upper platen mold for the flat polishing mold. Apply a 0.01mm-0.05mm thick layer of optical wax as an adhesive evenly to the working surface of the flat upper platen mold. Arrange the wafers to be processed on the optical wax applied to the working surface of the flat upper platen mold, with the first surface of the wafers to be processed away from the upper platen mold. The array adopts a ring array, and the spacing between adjacent wafers is controlled within 1mm-2mm to retain the polishing liquid inflow channel. Place the flat upper platen mold with the arranged wafers into an oven for curing, so that the wafers are rigidly bonded to the flat upper platen mold by the wax. S322, First-side polishing: Install the disc mold on the flat surface of the disc into the positioning fixture, and use the polishing equipment worktable to perform three-stage progressive polishing: first rough polishing, then semi-fine polishing, and finally fine polishing, with the abrasive particle size decreasing step by step and the pressure decreasing step by step; thoroughly clean between each stage, while the pressure gradually decreases as the particle size decreases. S323, First side lower plate: After the first side is polished, the upper plate mold is removed and the optical wax is heated to soften it. The wafer after the first side is polished is taken out, cleaned, and the wafer after the first side is polished is obtained.

5. A processing method for improving the Faraday rotation surface shape according to claim 1 or 4, characterized in that, The three-stage progressive polishing includes the following steps: The first stage is rough polishing. The abrasive used is diamond powder with a diameter of 4μm-8μm. The grinding surface is a 20,000-mesh grinding wheel with a pressure of 50N-80N, a rotation speed of 200r / min-300r / min, and a time of 25min-50min. The second stage is semi-fine polishing. The abrasive used is 1μm-2μm diamond powder, the polishing surface is polyurethane, the pressure is 30N-50N, the rotation speed is 100r / min-150r / min, and the time is 20min-50min. The third stage is fine polishing. The abrasive used is 0.25μm-0.5μm SiO2 liquid, the polishing surface is asphalt, the pressure is 10N-30N, the rotation speed is 20r / min-50r / min, and the time is 40min-90min.

6. The processing method for improving the Faraday rotation surface shape according to claim 1, characterized in that, The dimensions of the wafer to be processed are 11mm × 11mm × 0.62mm; the inherent warpage curvature T = -885m, and the warpage direction is concave upwards; the wafer thickness after the first surface is processed is 0.524mm-0.525mm; the thickness of the finished wafer is 0.355mm-0.356mm.

7. The processing method for improving the Faraday rotation surface shape according to claim 1, characterized in that, The ratio of the amount of surface polishing to the amount of curved surface polishing is 1:

1.

8. The processing method for improving the Faraday rotation surface shape according to claim 1, characterized in that, The array in step S331 is a ring array, and the spacing between adjacent wafers is controlled within the range of 1mm-2mm.

Images