Technological method for removing rainbow lines on surface of monocrystalline silicon optical element

Abstract

The invention discloses a process method for removing rainbow lines on the surface of a monocrystalline silicon optical element, which comprises the following steps of: S1, detecting the surface shape and smoothness of the monocrystalline silicon optical element after previous ultraprecise single-point turning, and measuring the surface roughness of the monocrystalline silicon optical element; s2, if only the rainbow lines exist on the surface of the monocrystalline silicon optical element, the whole surface of the monocrystalline silicon optical element is swept at a constant speed through magneto-rheological polishing, and the surface of the monocrystalline silicon optical element is polished and conformal; s3, detecting the smoothness of the surface of the monocrystalline silicon optical element; if the rainbow lines exist, the step S2 is repeated until the rainbow lines cannot be detected; and S4, detecting the surface shape of the processed monocrystalline silicon optical element, and measuring the surface roughness of the monocrystalline silicon optical element. The method has the advantages of being simple in principle, high in machining precision, high in automation degree and the like, shape preserving is achieved, rainbow lines are eliminated, the repairing or scrapping problem caused by the appearance problem in previous machining is reduced, and the method is suitable for batch production of ultra-precise optical products.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-precision optical element polishing and processing, and particularly relates to a process method for removing rainbow patterns from the surface of a single-crystal silicon optical element. Background Art

[0002] At present, with the change of market demand, optical systems are evolving more and more towards ultra-precision, complexity, and integration. Since the ultra-precision single-point diamond turning technology can quickly and efficiently produce a batch of ultra-precision complex curved surface optical elements, the ultra-precision single-point diamond turning technology plays an important role in manufacturing complex curved surface optical elements. However, when turning large-aperture or difficult-to-machine hard materials, due to continuous tool wear, there will be a rainbow-colored halo on the surface after turning, which is called "rainbow pattern", greatly affecting the subsequent use of the mirror surface. Therefore, how to eliminate the rainbow stripes on the mirror surface after single-point diamond turning has become an urgent technical problem to be solved in the ultra-precision processing of complex optical elements. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to solve the problem of "rainbow pattern" on the mirror surface after ultra-precision single-point diamond turning, and provide a process method for removing rainbow patterns from the surface of a single-crystal silicon optical element with simple principle, convenient operation and wide application range. At the same time, it also provides a solution to the problems such as unqualified mirror surface finish and loss of hand-polished surface shape after the previous process.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0005] A process method for removing rainbow patterns from the surface of a single-crystal silicon optical element, comprising the following steps:

[0006] Step S1, detecting the surface shape and finish of the single-crystal silicon optical element after the previous ultra-precision single-point diamond turning, and measuring the surface roughness of the single-crystal silicon optical element;

[0007] Step S2, if only rainbow patterns exist on the surface of the single-crystal silicon optical element, using magnetorheological polishing to uniformly sweep across the entire surface of the single-crystal silicon optical element to polish and maintain the shape of the single-crystal silicon optical element surface;

[0008] Step S3, detecting the finish of the single-crystal silicon optical element surface; if rainbow patterns exist, repeat Step S2 until the rainbow patterns cannot be detected;

[0009] Step S4, detecting the surface shape of the single-crystal silicon optical element after processing, and measuring the surface roughness of the single-crystal silicon optical element.

[0010] As a further improvement of the present invention, in the step S2, the process parameters of magnetorheological polishing for conformal shaping are as follows: the ribbon indentation is 0.25 - 0.35 mm, the polishing wheel rotation speed is 170 - 210 rad / min, the viscosity is 175 - 185 mPa·s, the flow rate is 55 - 65 L / H, the feed rate is F500 - 600 mm / min, and the polishing fluid is silicon magnetorheological fluid.

[0011] As a further improvement of the present invention, in the step S1, after the previous ultra-precision single-point turning process, the mirror surface shape of the single-crystalline silicon optical element is measured using a DUI profiler, and the surface finish of the single-crystalline silicon optical element is detected using a detection standard light source in a black box environment to confirm whether there are any other patterns on the mirror surface of the single-crystalline silicon optical element other than rainbow patterns. If there are other patterns, it will return to the previous process for treatment.

[0012] As a further improvement of the present invention, in the steps S1 and S4, the surface roughness of the single-crystalline silicon optical element is detected using a white light interferometer.

[0013] As a further improvement of the present invention, in the step S3, the surface finish of the single-crystalline silicon optical element is detected using a detection standard light source in a black box environment until the rainbow patterns cannot be detected under the detection light source.

[0014] Compared with the prior art, the advantages of the present invention are as follows:

[0015] The process method for removing rainbow patterns on the surface of the single-crystalline silicon optical element of the present invention utilizes the characteristics of magnetorheological polishing, such as high processing accuracy, stable removal function, good controllability, excellent processed surface quality, small processing residual stress, almost no surface and subsurface damage, and outstanding processing ability for workpieces with a large diameter-thickness ratio and low hardness. Also, because magnetorheological polishing relies on the shear force between the ribbon and the workpiece for polishing, it realizes the fine repair of the surface finish while hardly losing its surface shape accuracy, removes the rainbow patterns, and achieves conformal shaping. Thus, it reduces the rework or scrap problems caused by appearance issues in the previous processing. The method of the present invention can achieve ultra-precision processing of single-crystalline silicon with different apertures and different surfaces, with almost no loss of processed surface shape accuracy, belongs to a process design that is easy to produce high added-value products, and is suitable for small-batch production in the field of ultra-precision polishing processing. Description of the Drawings

[0016] Figure 1 It is a process flow diagram for removing rainbow patterns on the surface of the single-crystalline silicon optical element in the specific embodiment 1 of the present invention.

[0017] Figure 2 It is a schematic diagram of the surface of the single-crystalline silicon optical element before magnetorheological polishing for conformal shaping in the specific embodiment 1 of the present invention;

[0018] Figure 3Schematic diagram of the surface of a single-crystalline silicon optical element after conformal magnetic rheological polishing in Specific Embodiment 1 of the present invention;

[0019] Figure 4 Schematic diagram of the surface shape result of a single-crystalline silicon optical element after single-point turning in the previous process in Specific Embodiment 1 of the present invention;

[0020] Figure 5 Schematic diagram of the surface shape result of a single-crystalline silicon optical element after using the new process of uniform and smooth magnetic rheological polishing in Specific Embodiment 1 of the present invention;

[0021] Figure 6 Schematic diagram of the surface shape detection result of a single-crystalline silicon optical element after hand grinding and polishing in Comparative Example 1;

[0022] Figure 7 Schematic diagram of the surface shape detection result of a single-crystalline silicon optical element after small grinding head polishing in Comparative Example 2; Specific Embodiments

[0023] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0024] In the description of the present invention, it should be understood that the terms "side part", "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation of the present invention.

[0025] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0026] Embodiment 1

[0027] The processing object of this embodiment is an off-axis aspherical single-crystalline silicon optical element with a diameter of D16mm (effective aperture D14mm) and a vertex curvature radius of 50 ± 0.02mm. The required surface accuracy target is RMS less than 15.82nm (λ / 40), where the quadratic coefficient K = -1 ± 0.005. The surface of the single-crystalline silicon optical element before processing is as Figure 2 shown.

[0028] As Figure 1 shown, the process method for removing rainbow lines from the surface of the single-crystalline silicon optical element of the present invention includes the following steps:

[0029] Step S1: Detect the surface shape and surface finish of the single-crystalline silicon optical element after the previous ultra-precision single-point turning process, and measure the surface roughness of the single-crystalline silicon optical element. Specifically, use a DUI profiler to measure the mirror surface shape of the single-crystalline silicon optical element, and use a detection standard light source to detect the surface finish of the single-crystalline silicon optical element in a black box environment to confirm whether there are other lines on the mirror surface of the single-crystalline silicon optical element except for rainbow lines. If there are other lines, return to the previous process for treatment. Use a white light interferometer to detect the mirror surface roughness of the single-crystalline silicon optical element.

[0030] Step S2: If there are only rainbow lines on the surface of the single-crystalline silicon optical element, use magnetorheological polishing to sweep uniformly across the entire surface of the single-crystalline silicon optical element to polish and maintain the shape of the single-crystalline silicon optical element. Specifically, the process parameters for magnetorheological polishing to maintain the shape are: ribbon depression 0.3mm, polishing wheel rotation speed 180rad / min, viscosity 180mPa·s, flow rate 60L / H, feed speed F600mm / min, and polishing fluid is silicon magnetorheological fluid.

[0031] Step S3: Use a detection standard light source to detect the surface finish of the single-crystalline silicon optical element in a black box environment; if there are rainbow lines, repeat Step S2 until the rainbow lines cannot be detected.

[0032] Step S4: Use a DUI profiler to measure the mirror surface shape of the single-crystalline silicon optical element, and use a white light interferometer to detect the mirror surface roughness of the single-crystalline silicon optical element. As Figure 5 shown, after using the new magnetorheological polishing uniform smoothing process, the PV of the single-crystalline silicon optical surface is 125.914nm, the RMS is 14.174nm, and the surface shape accuracy changes slightly. Due to the improvement of the surface quality of the silicon mirror, the surface shape distribution changes slightly, but the change amount is small and still within the qualified range.

[0033] The surface of the single-crystalline silicon optical element after processing is as Figure 3 shown. After magnetorheological polishing to maintain the shape, the rainbow lines disappear, the surface quality of the single-crystalline silicon optical element is good, and the surface shape does not change significantly. As Figure 4As shown, the PV of the surface of the monocrystalline silicon optical element after single-point turning is 82.81 nm, and the RMS is 12.425 nm, indicating that the processed monocrystalline silicon optical element still meets the design requirements.

[0034] In this embodiment, the surface finish of the monocrystalline silicon optical element is controlled through a polishing process route. Since magnetorheological polishing hardly changes the shape and size of the element, and its uniform scanning trajectory has almost no influence on the surface shape, it not only removes the rainbow pattern but also realizes shape preservation, thereby reducing the rework or scrapping problems caused by appearance problems in the previous processing, and is suitable for mass production of ultra-precision optical products.

[0035] Comparative Example 1

[0036] The processing method of this comparative example is substantially the same as that of Example 1, except that: the magnetorheological polishing shape preservation method is not used, and the hand polishing method is used, that is, both hands are used to dip a polishing cloth in a 50% concentration silica suspension polishing liquid to perform hand polishing on the area with rainbow patterns on the mirror surface. It includes the following steps:

[0037] Step 1: Detect the surface shape and finish of the monocrystalline silicon optical element after the previous ultra-precision single-point turning, and use a white light interferometer to measure its surface roughness;

[0038] Step 2: After confirming that only obvious rainbow patterns exist on the mirror body surface, use the hand polishing method to process the mirror body surface;

[0039] Step 3: Detect the finish of the monocrystalline silicon optical element until the rainbow pattern cannot be detected under the detection light source;

[0040] Step 4: Detect the surface shape of the monocrystalline silicon optical element after processing, and use a white light interferometer to measure its surface roughness.

[0041] The surface shape detection results of the monocrystalline silicon optical element after manual polishing are as Figure 6 shown. After hand polishing and repair, the PV of the monocrystalline silicon optical surface is 285.509 nm, and the RMS is 35.454 nm. The change in surface shape accuracy is very large. Although the surface quality of the silicon mirror is improved, the surface shape accuracy becomes worse, and it is necessary to return to other processes to improve the surface shape accuracy, increasing the processing cost. It can be seen that due to the complex control process of the hand polishing method, there are many coupling factors, and it is quite dependent on manual processing experience. Therefore, after using the hand polishing method, the surface shape of the monocrystalline silicon optical element changes greatly.

[0042] Comparative Example 2

[0043] The processing method of this comparative example is substantially the same as that of Example 1, except that: the magnetorheological polishing shape preservation method is not used, and a small grinding head polishing method is used to remove the rainbow pattern. It includes the following steps:

[0044] Step 1: Detect the surface shape and surface finish of the monocrystalline silicon optical element after the previous ultra-precision single-point turning process, and measure its surface roughness using a white light interferometer;

[0045] Step 2: After confirming that there are only obvious rainbow patterns on the surface of the mirror body, use a small grinding head to polish and smooth the surface of the mirror body. The process parameters of the small grinding head polishing and shaping are a pressure of 0.05 Mpa, use a silicon dioxide suspension polishing liquid with a concentration of 50% for polishing, and the feed rate is F 600 mm / min;

[0046] Step 3: Detect the surface finish of the monocrystalline silicon optical element until the rainbow patterns cannot be detected under the detection light source;

[0047] Step 4: Detect the surface shape of the monocrystalline silicon optical element after processing, and measure its surface roughness using a white light interferometer.

[0048] The surface shape detection results of the monocrystalline silicon optical element after small grinding head polishing are as Figure 7 shown. After small grinding head polishing, the PV of the monocrystalline silicon optical surface is 270.909 nm, and the RMS is 31.565 nm. The change in surface shape accuracy is relatively large. Although the surface quality of the silicon mirror has been improved, the surface shape accuracy has deteriorated, and it is necessary to return to other processes to improve the surface shape accuracy, increasing the processing cost. It can be seen that the change in the surface shape of the monocrystalline silicon optical element after small grinding head polishing is slightly smaller than that of the hand polishing method, but compared with the magnetorheological polishing method, the change in the surface shape of the monocrystalline silicon optical element is still relatively large.

[0049] The above is only the preferred implementation mode of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art of this technology, several improvements and refinements made without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A process for removing rainbow patterns from the surface of a single-crystal silicon optical element, characterized in that: The following steps are involved: Step S1, detecting the surface shape and smoothness of the single-crystal silicon optical element after the previous ultra-precision single-point lathe processing, and measuring the surface roughness of the single-crystal silicon optical element; Step S2: If only rainbow lines exist on the surface of the single-crystal silicon optical element, magnetorheological polishing is used to uniformly sweep across the entire surface of the single-crystal silicon optical element to polish the surface of the single-crystal silicon optical element in a conformal manner; Step S3, detecting the surface finish of the single crystal silicon optical element; if rainbow lines exist, repeating step S2 until the rainbow lines cannot be detected; Step S4, detecting the surface shape of the processed single crystal silicon optical element, and measuring the surface roughness of the single crystal silicon optical element.

2. The process for removing rainbow streaks from the surface of a single crystal silicon optical element according to claim 1, characterized in that: In step S2, the process parameters of magnetorheological polishing conformal are: ribbon pressing depth 0.25-0.35 mm, polishing wheel speed 170-210 rad / min, viscosity 175-185 mPa·s, flow rate 55-65 L / H, feed speed F500-600 mm / min, and the polishing liquid is silicon magnetorheological fluid.

3. The process for removing rainbow streaks from the surface of a single crystal silicon optical element according to claim 2, characterized in that: In step S1, after the front-end ultra-precision single-point turning processing, the mirror surface shape of the single-crystal silicon optical element is measured using a DUI profilometer, and the surface finish of the single-crystal silicon optical element is detected using a detection standard light source in a black box environment to confirm whether the mirror surface of the single-crystal silicon optical element has other lines except rainbow lines. If other lines exist, return to the front-end process for processing.

4. The process for removing rainbow streaks from the surface of a single crystal silicon optical element according to claim 3, characterized in that: In the step S1 and step S4, a white light interferometer is used to detect the mirror roughness of the single crystal silicon optical element.

5. The process for removing rainbow patterns from the surface of a single crystal silicon optical element according to claim 3, characterized in that: In the step S3, the smoothness of the single crystal silicon optical element is detected using a detection standard light source in a black box environment until the rainbow pattern cannot be detected under the detection light source.

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