Method for definitively polishing Wolter-I type optical mandrel

Abstract

The invention discloses a method for definitively polishing a Wolter-I type optical mandrel. The method comprises the following steps of: (1) determining removal height and a ball diameter of a polishing ball; (2) determining a radius of a contact area and calculating contact pressure; (3) determining a Preston coefficient; (4) calculating movement track of the ball center of the polishing ball and dwell time at each polishing point; (5) writing numerical-control processing program, realizing control on movement track of an elastic ball body polishing tool, and controlling dwell time t, at thepolishing point, of the elastic ball body polishing tool according to a numerical-control delay instruction; and (6) attaching polishing cloth on the surface of the elastic ball body polishing tool,and selecting a proper polishing solution to polish the surface of the mandrel according to pre-calculated polishing parameters. The polishing method disclosed by the invention can integrate the spherical polishing tool into turning processing equipment, realizes once completing of mandrel turning and polishing processing, and improves mandrel processing precision and processing efficiency.

Description

technical field [0001] The invention belongs to the technical field of optics and precision manufacturing, and relates to a polishing method for a Wolter-I type optical mandrel, in particular to a method for deterministically polishing a Wolter-I type optical mandrel by using an elastic spherical polishing tool. Background technique [0002] The next-generation lithography machine will use extreme ultraviolet light (EUV: Extreme Ultraviolet) with a preferred wavelength of 13.5nm as the light source. This short-wavelength light needs to be collected by a dedicated high-efficiency optical mirror. The structure of the mirror is usually based on X The Wolter-I design form of grazing incidence optical design. The Wolter-I reflector is composed of two coaxial confocal axisymmetric aspheric surfaces, and the steepness (or aspect ratio) of the aspheric surfaces is usually large. Due to the technical difficulty of directly processing the concave steep axisymmetric aspheric surface, ...

AI Technical Summary

Problems solved by technology

[0005] Although ion beam polishing technology can provide higher material removal rate and very good repeatability, there are no problems such as tool wear and edge effects, it can well correct long space wavelength errors, and produce super good surfaces, but it does not Polishing materials are highly selective, and the ion beam source must operate in a vacuum, which may generate high temperatures on the workpiece surface, so commonly used diamond turning materials, such as non-ferrous metals and plastics including electroless nickel-phosphorus alloys, are not suitable ion beam polishing

[0006] The advantages of magnetorheological and magnetic jet polishing technology are certainty and high material removal rate, which are mainly used for polishing refractive optical elements such as glass or crystal materials, and magnetic jet polishing technology can solve the high-precision precision of steep concave surfaces and deep cavities. However, the commercially available polishing fluid is mainly used to polish optical glass, and it is difficult to achieve an excellent roughness after polishing the electroless nickel-phosphorus alloy surface

[0007] Fluid jet polishing technology can reasonably select the appropriate proportion of abrasive and mixed liquid according to different polishing objects, and there is no tool wear and edge effect, and it will not damage the surface contour shape while removing diamond turning marks. It can polish glass and Many materials such as nickel, but the polishing efficiency is low, and there may be problems such as unintentional detachment of grains from the substrate and contamination of the surface by abrasive particles embedded in the substrate

[0008] The precessive balloon polishing technology is an active control, which is different from the "simple rotation" of traditional balloon polishing. In this method, the surface tangent direction used to calculate the swirling plane of the spherical tool is allowed to rotate around the center of the polishing point, with relatively High removal efficiency and good polishing effect, but the airbag needs to precess and rotate in addition to its rotation, and the contact pressure of the polishing point needs to be adjusted by controlling the air pressure in the airbag, and the polishing control process is more complicated

In addition, the structure of the airbag polishing system is relatively complicated, and sometimes the phenomenon of airbag instability and interference between the tool posture and the mold surface may occur, which is not easy to be integrated on the ultra-precision turning machine tool to realize the one-time completion of the ultra-precision turning and polishing process

[0009] To sum up, it is difficult to polish the mandrel surface of Wolter-Ⅰ electroless nickel-phosphorus alloy with high precision, and the special ultra-precision deterministic polishing equipment is very expensive, and the method suitable for high-precision polishing of the surface of electroless nickel-phosphorus alloy is relatively poor. few

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