CN101898324A - Method for polishing ion beam with high-gradient mirror surface - Google Patents

Abstract

The invention discloses a method for polishing an ion beam with a high-gradient mirror surface. The method comprises the following steps of: (1) measuring incidence angles theta of all points on the mirror surface; (2) confirming a compensation factor K of each point according to a model; (3) measuring an initial surface error E of a workpiece by utilizing interferometry; (4) compensating the E according to the K to acquire a compensation surface error E'; (5) acquiring a removal function R of an ion beam in the vertical incidence of the mirror surface through removal function experiment; (6) confirming residence time distribution T and generating a numerical control code according to E' and R; (7) processing by utilizing a generating device of the removal function and the generated numerical control code, enabling the ion beam to enter the mirror surface along a direction parallel to the optical axis direction of the workpiece in processing and trimming the mirror surface through a triaxiality linkage system; and (8) repeating the steps until the trimming result satisfies the requirement of surface convergence accuracy. The method of the invention has the advantages of simple operation, good stability, high processing accuracy, strong controllability, low requirement for equipment, and the like in processing the high-gradient mirror surface.

Description

The method for polishing ion beam of high-gradient mirror surface

Technical field

The present invention relates to the optical element processing technique field, relate in particular to a kind of method for polishing ion beam of high-gradient mirror surface.

Background technology

Along with development of modern science, the particularly rapid lifting of Aero-Space and armament systems performance, the optical system that is applied to various fields is more and more higher to the requirement of the precision of key components and parts and contour structures.This type of crucial optical component has the characteristic of high steepness usually, can reduce the weight and volume of system, simplifies the structure of system, simultaneously the combination property of lifting and optimization system.The lithographic objective of the hemisphere harmonic oscillator in the hemispherical resonant gyro, the spheroid rotor in the electrostatically sus pended gyroscope instrument and ball bowl and litho machine etc. for example, the core component of the optical system of numerous precision instruments and equipment all is the optical element that adopts high accuracy, high steepness.

The development trend of current international microlithography technology shows that the numerical aperture of object lens mostly is high steepness greatly from the axle mirror greater than 0.60, and it is 0.07 μ m～0.25 μ m that its characteristic size requires; And the requirement on machining accuracy of electrostatically sus pended gyroscope rotor of new generation and ball bowl and hemisphere harmonic oscillator rises to 0.1 μ m～0.01 μ m magnitude, and they all are the sphere or the hemisphere face part of high steepness.The repeatability of the machining accuracy of traditional handicraft, efficient and processing has been difficult to satisfy the batch demand of most advanced and sophisticated equipment and technology, becomes the key factor of its performance of restriction and development.

Ion beam polishing is the material that the physical sputtering effect that takes place when utilizing the ion beam bombardment optical mirror plane of ion gun emission is removed optical element surface, be to transmit kinetic energy by particle encounter optical mirror plane to realize with certain energy, the machining accuracy that has nanometer scale is a kind of high certainty, high stability and non-contacting process technology.Method for polishing ion beam has overcome the shortcomings such as edge effect, tool wear and pressure load in traditional polishing processing, has higher processing convergency factor, usually all as last procedure of high-precision optical part processing.

Since ion beam polishing technology relative complex, and cost is higher relatively, and the unit that conducts a research at present is relative with company less.The CN101261511A Chinese patent literature discloses the control method of face shape convergence precision in a kind of ion beam polishing process, it has specifically been introduced by the residence time in the polishing processing is controlled, and can realize the control of opposite shape convergence precision in the ion beam polishing process.At " based on the low steepness optical mirror surface face shape error ion beam correction residence time algorithm of Bayesian principle " (mechanical engineering journal, 2009,11 (45)) proposed a kind of face shape control technology rapidly and efficiently in the literary composition again, it can realize the low accurate correction of the flank shape of gradient mirror surface certainty.

Yet, because some technical barriers of the limitation of the above-mentioned processing mode that adopts or intrinsic existence make it be difficult to be applicable to the polishing processing of high-steepness optical part.This mainly be because the material removal amount E of one process (x, y) equal to remove function R (x, y) with residence time T (its discrete equation can be represented to become for x, convolution y):

$E(x,y)=\underset{i=0}{\mathrm{\Σ}}\underset{j=0}{\mathrm{\Σ}}R(x-x_i,y-y_j)T(x_i,y_j)\mathrm{\Δx\Δy}---\left(1\right)$

To accurately find the solution residence time according to the matrix equation of following formula (1), the face shape error E that represents with two-dimensional coordinate that need at first guarantee to measure ₀(measuring process can not produce distortion of projection for x, the positional information that y) can actual response minute surface each point and the material removal amount of expectation, and the removal function in the process need keep consistency and stability; But for the optical mirror plane of high steepness, error value E ₀(x, y) pairing coordinate points is three-dimensional coordinate (x, y, z) projection in the x-y coordinate plane, it has lost positional information, has produced the problem of distortion of projection, directly utilizes formula (1) can not satisfy the requirement that the high accuracy high-steepness optical part efficiently polishes processing.

At present, Shang Weiyou can effectively solve the processing technology of existing above-mentioned technical problem in the high-gradient mirror surface processing.In order to improve machining accuracy to high-steepness optical part, often need to regulate ionogenic attitude according to the minute surface curved surface profile, the control of residence time and accurate Calculation are also comparatively difficult, and, usually need to adopt the polishing system more than four that high-steepness optical part is processed, its difficulty of processing is big, the processing cost height.

Summary of the invention

Technical problem to be solved by this invention is to overcome the deficiencies in the prior art, provides a kind of residence time to calculate the method for polishing ion beam of simple, good stability, machining accuracy height, controllability high-gradient mirror surface strong, low for equipment requirements.

For solving the problems of the technologies described above, the technical scheme that the present invention proposes is a kind of method for polishing ion beam of high-gradient mirror surface, may further comprise the steps:

(1) measuring and calculating incidence angle: get a polished workpiece with high-gradient mirror surface, in plane, set up the X-Y rectangular coordinate system perpendicular to the workpiece optical axis, according to the surface equation z=h of high-gradient mirror surface (x, y), the angle of measuring and calculating minute surface each point normal and vertical incidence ion beam, i.e. incidence angle θ;

(2) determine that penalty coefficient distributes: according to model P (x, y)=(1/n) Y ₀(θ) (xcos θ y) (also can directly remove the experimental result of speed) to cos θ f according to relative material under the situation of not setting up model as yet, determine the corresponding penalty coefficient K of each processing stand of polished workpiece, is designated as K (θ);

(3) measure initial face shape error: utilize interferometric method to measure the primary face shape error E of described polished workpiece, be designated as E (x, y);

(4) compensate initial face shape error: distributing according to the penalty coefficient of determining in the step (2) compensates described primary face shape error E, is compensated face shape error E ', and E '=E (x, y)/K _Ij(θ);

(5) obtain to remove function: the removal function R when testing acquisition ion beam vertical incidence same material minute surface by removing function (x, y);

(6) determine residence time distribution T: according to the complementary area shape error E of determining in the step (4) ' and step (5) in the removal function R (x of acquisition, y), utilize the residence time algorithm when having the processing plane mirror now to determine residence time distribution T and generate numerical control code;

(7) ion beam polishing processing: utilize the generating means of described removal function and the residence time numerical control code of generation that described polished workpiece is carried out ion beam polishing processing, process intermediate ion bundle is along being parallel to workpiece optical axis direction vertical incidence minute surface, and the three-shaft linkage system (need not to use the linked system more than four) by described removal function generator carries out correction of the flank shape to minute surface;

(8) iteration polishing processing: repeat the technical process of above-mentioned steps (1)～step (7), satisfy the requirement of face shape convergence precision, process finishing until the correction of the flank shape result of step (7).

The basic principle of the technique scheme that the present invention proposes is: utilize the material removal characteristic of ion beam polishing at first the face shape error of high-gradient mirror surface to be compensated, improve the calculation method of residence time in the computer control shaping surface principle (CCOS) according to this, make ion beam under the condition of out of plumb beam incident optical minute surface, use linear three-shaft linkage system can realize high accuracy certainty processing high steepness optical mirror surface; And, since residence time resolve step and processing plane mirror the time method for solving basic identical, this makes processing method of the present invention and process equipment and prior art have very strong versatility, has reduced the improvement cost and newly-increased input of material conditions such as equipment, software greatly.

More particularly, the material of the ion beam polishing of technical solution of the present invention utilization is removed characteristic and is meant based on the physical sputtering theory, set up the theoretical model of removing function, analyze and remove function shape and remove the Changing Pattern of speed, utilize laboratory facilities that the accuracy and the reliability of theoretical model and Changing Pattern are verified again with incidence angle θ; According to the achievement after the checking, the influence factor that dynamic removal function is found the solution residence time is introduced in the existing convolution formula then, improved the solving model of residence time in the computer control shaping surface principle according to this; Because the solving model of residence time is improved and is optimized, therefore under the situation of ion beam out of plumb beam incident optical minute surface, be that process intermediate ion bundle is all the time along under the situation that is parallel to optical axis direction processing minute surface, all can realize polishing processing to high-gradient mirror surface, and need all not make ion beam vertical incidence optical mirror plane at each resident processing stand, so just subtracted requirement greatly to the digital control polishing machine tool universal driving shaft, only need linear three-shaft linkage system (three universal driving shafts of X-Y-Z) to get final product, process equipment does not also need to use rotating shaft, and then reduced the cost of digital control polishing machine tool, reduced control requirement to digital control polishing machine tool, compare with the linked system more than four, its reliability is also higher.

By above-mentioned basic principle as seen, in the technique scheme primary face shape error E compensated and be meant: remove the Changing Pattern of characteristic with incidence angle θ according to material, utilize this Changing Pattern that the primary face shape error E that interferometry obtains is compensated, to eliminate the adverse effect of distortion of projection in process intermediate ion bundle out of plumb incident minute surface and the measurement to determining that residence time distributes and caused, and this compensation process comes down to the discrete convolution formula of current material removal amount is improved, and it is as follows that this convolution formula is carried out improved theoretical foundation:

1, as shown in Figure 1, set up the X-Y-Z coordinate system earlier, and make rectangular coordinate plane that X-Y establishes perpendicular to the workpiece optical axis, the minute surface equation of polished like this workpiece can be expressed as z=h (x, y), make ion beam edge be parallel to optical axis direction incident minute surface, when residing in A ' (x with Gaussian distribution _i, y _i, z _i) when putting, ion beam is to the arbitrfary point B ' (x in the zone of action (being the round territory at diameter d place) ₀, y ₀, z ₀) the unit interval material removal amount be designated as R _θ, wherein θ is the incidence angle of ion beam at arbitrfary point B '; Yet when calculating residence time, reside in the corresponding subpoint A of A ' (x _i, y _i) the removal function R (x is y) to the corresponding subpoint B of B ' (x ₀, y ₀) material removal amount can be designated as R ₀Therefore, actual removal amount there are differences with the removal amount of theory, need remove speed to it and compensate; Because the minute surface in the ion beam zone of action is identical with removing the distortion of projection of function in the rectangular coordinate plane that X-Y establishes, so need not to carry out the compensation of area, for the ease of the characteristic of research removal function R, we introduce relative material and remove velocity coefficient K _Ij, that is:

$K_{\mathrm{ij}}=\frac{R_{\mathrm{\θ}}}{R_0}---\left(2\right)$

In the following formula (2), R _θ=R _θ(x ₀-x _i, y ₀-y _i), R ₀=R ₀(x ₀-x _i, y ₀-y _i);

Therefore, removing function R can be expressed as at the material removal rate of each processing stand B '

R _θ＝R ₀K _ij (3)

With the material removal amount that can obtain in following formula (3) the substitution formula (1) in the actual process, that is:

$E_f(x,y)=\underset{i=0}{\mathrm{\Σ}}\underset{j=0}{\mathrm{\Σ}}{K}_{\mathrm{ij}}R(x-x_i,y-y_j)T(x_i,y_j)\mathrm{\Δx\Δy}---\left(4\right)$

Because the Matrix Solving of formula (4) is comparatively complicated, we can be according to the COEFFICIENT K in the material removal characteristic cancelling (4) of ion beam _Ij,, and utilize method, program and the equipment that has the processing plane mirror now as far as possible with the simplification solution procedure.

2, ion beam polishing processing method is to utilize the ion sputtering effect that the material that optical mirror plane carries out the atom magnitude is removed, existing correlative study is derived the etch rate of arbitrary surfaces under the bombardment of ion beam oblique incidence optical material on according to Sigmund sputtering theory basis, and serve as the theoretical model that the removal function is set up on the basis with it:

P(x，y)＝(1/n)Y ₀(θ)cosθf(xcosθ，y) (5)

In the formula (5), f is a beam current density, and θ is an incidence angle, Y _OSputtering yield during (θ) for the oblique incidence level crossing, n are the nuclear energy in the solid per unit volume.Can know that from formula (5) etch rate is the function of incidence angle θ unitary variant, and can be compensated coefficient under the constant condition of technological parameter:

K(θ)＝Y ₀(θ)cosθ/Y ₀(0) (6)

We can obtain in view of the above: when ion beam during along parallel optical axis direction processing minute surface, incidence angle θ is only relevant with the coordinate of processing stand B ', and promptly for a certain definite processing stand B ', relative material is removed velocity coefficient K _Ij(θ) be definite value, and irrelevant with dwell point A '; So, formula (4) can be converted into:

$E_f(x,y)=K_{\mathrm{ij}}\left(\mathrm{\θ}\right)\underset{i=0}{\mathrm{\Σ}}\underset{j=0}{\mathrm{\Σ}}R(x-x_i,y-y_j)T(x_i,y_j)\mathrm{\Δx\Δy}---\left(7\right)$

In order to make the material removal amount E in the actual process _f(x, y) with the expectation material removal amount E (x, y) identical, E is arranged so _f(x, y)=E (x, y), that is:

$E^{\′}(x,y)=\underset{i=0}{\mathrm{\Σ}}\underset{j=0}{\mathrm{\Σ}}R(x-x_i,y-y_j)T(x_i,y_j)\mathrm{\Δx\Δy}=E(x,y)/K_{\mathrm{ij}}\left(\mathrm{\θ}\right)---\left(8\right)$

Wherein, (x y) is the face shape error after the compensation to E '.

By formula (8) as seen, use the method for parallel optical axis direction processing minute surface, can eliminate of the influence of dynamic removal function by the mode of compensation face shape error to residence time, and the face shape after the utilization compensation, still can use the program step when finding the solution processing plane originally to carry out the calculating of residence time.

For accuracy and the reliability of verifying the above-mentioned theory basis, we have carried out following experiment:

Experiment 1 is to be object with six quartzy facet mirrors, make its tilt respectively 10 °～60 ° (are θ=10 °, 20 °, 30 °, 40 °, 50 °, 60 °), the mounting means of this level crossing as shown in Figure 3, single-point bombardment obtains the removal spot of different incidence angles then.In the experimentation, the beam voltage of 1200eV has been processed 3min facing to each piece level crossing, the spot that can obtain by processing as shown in Figure 4 like this, utilize the face shape of processing front and back sample mirror to do the poor removal function that obtains as shown in Figure 5, the relative material that can obtain experiment 1 is as shown in Figure 2 in view of the above removed rate curve (empirical curve).And, under the situation of the technological parameter that experiment 1 is determined, obtain the theoretical curve (i.e. the theoretical curve of determining by formula (5)) of relative material removal speed as shown in Figure 2 to remove the theoretical model of function.As seen, experiment 1 is that the theoretical curve of theoretical model derivation can access the support of empirical curve as seen from Figure 2 based on the removal function that is interrupted incidence angle.

Testing 2 can utilize the line sweep method to process a protruding spherical mirror (high-gradient mirror surface), add man-hour with the bus of constant range along the mistake lens, at the uniform velocity etching obtains material removal amount (referring to Figure 13), and draw the continuous phase obtain as shown in Figure 6 to the material removal rate empirical curve, and to remove the theoretical model of function, under the situation of the technological parameters that experiment 2 is determined, obtain as shown in Figure 6 continuous phase to the theoretical curve of material removal rate.As seen, experiment 2 is based near the removal function of continuous incidence angle, and the theoretical curve of theoretical model derivation can access the support of empirical curve equally as seen from Figure 6.

Comprehensive above experiment 1 and experiment 2 can be known; the relative peak that theory analysis obtains is removed rate curve and experiment value matches; therefore when the high-steepness optical part of different bores of processing and radius of curvature; need not to experimentize at every turn and obtain to remove accordingly rate curve; directly the theoretical curve that uses the above-mentioned theory modeling to obtain has feasibility and practicality equally; reduce workload, improved efficient.

Compared with prior art, the invention has the advantages that:

1, the present invention proposes a kind of method for polishing ion beam of the high-gradient mirror surface based on face shape error compensation, by lead-in surface shape compensation of error coefficient, and adopt elder generation to compensate face shape error, on the face shape error basis after the compensation, determine the distribution of residence time again, carry out follow-up ion beam polishing processing at last, it has effectively realized the polishing of high-gradient mirror surface ion beam certainty, has solved a difficult problem that exists in the high-steepness optical part polishing.

2, in the method for polishing ion beam of the present invention, the ion beam incident direction is parallel to the optical axis direction of workpiece all the time, add man-hour at minute surface to workpiece, only the linear three-shaft linkage ion beam polishing of need system just can realize the polishing processing to high-gradient mirror surface, compare with existing polishing system more than four, its operation control is more simple, and is lower to the requirement of process equipment, the cost input of process equipment reduces, and can improve the controllability and the reliability of ion beam polishing system simultaneously;

3, the method for polishing ion beam of high-gradient mirror surface of the present invention is by compensating face shape error, optimized the numerical control operating of the definite and ion beam polishing of follow-up residence time distribution greatly, this processing step, operation sequence that makes the ion beam polishing of existing high-gradient mirror surface process is simplified greatly, make the versatility of level crossing ion beam polishing process strengthen greatly, this haves laid a good foundation for the processing of complicated optical work from now on, also save human and financial resources greatly, reduced the technology cost.

Description of drawings

Fig. 1 adds the theory analysis schematic diagram in man-hour in optical axis direction incident for ion beam parallel.

Fig. 2 verifies the reference diagram of relative peak removal speed theoretical curve feasibility in the principle of the invention down for being interrupted the incidence angle experiment condition.

Fig. 3 is for being interrupted experiment sample mirror mounting means schematic diagram in the incidence angle experiment.

Fig. 4 is for being interrupted the removal spot figure that obtains after the incidence angle experiment processing.

Fig. 5 is for being interrupted the removal function distribution map under the different incidence angles of incidence angle experiment processing back.

Fig. 6 is a reference diagram of verifying relative peak removal speed theoretical curve feasibility in the principle of the invention under the continuous incidence angle experiment condition.

Fig. 7 is the penalty coefficient distribution map of each processing stand in the embodiment of the invention.

Fig. 8 is the primary face shape figure of the high-gradient mirror surface to be processed that records in the embodiment of the invention.

Fig. 9 is the complementary area shape figure after the high-gradient mirror surface compensation to be processed in the embodiment of the invention.

Figure 10 is the face shape figure of iteration polishing processed workpiece in the embodiment of the invention.

Figure 11 is the distribution map of the removal function in the embodiment of the invention.

Figure 12 is the distribution map of the residence time in the embodiment of the invention.

Figure 13 is the material removal amount distribution map under the continuous incidence angle experiment condition.

The specific embodiment

Below with reference to the drawings and specific embodiments the present invention is described in further details.

Embodiment

A kind of method for polishing ion beam of high-gradient mirror surface of the present invention may further comprise the steps:

(1) measures incidence angle: get a polished workpiece with high-gradient mirror surface, this polished workpiece is that a vertex curvature radius is that 16mm, bore are the protruding spherical mirror of 21.3mm, maximum incident angle is 41.7 °, its f numerical value is 0.75, in plane, set up the X-Y rectangular coordinate system perpendicular to the workpiece optical axis, according to the surface equation z=h of high-gradient mirror surface (x, y), calculate the angle of each processing stand normal of minute surface and vertical incidence ion beam, i.e. incidence angle θ;

(2) determine that penalty coefficient distributes: according to model P (x, y)=(1/n) Y ₀(θ) cos θ f (xcos θ, y) penalty coefficient of determining polished each processing stand of workpiece is K, is designated as K (θ), the distribution of penalty coefficient K (θ) value of each processing stand is (K (θ)=Y as shown in Figure 7 ₀(θ) cos θ/Y ₀(0));

(3) measure initial face shape error: utilize interferometric method to measure the primary face shape error E of the polished workpiece of present embodiment, be designated as E (x, y), the face shape of this polished workpiece is schemed as shown in Figure 8;

(4) compensate initial face shape error: distributing according to the penalty coefficient of determining in the step (2) compensates primary face shape error E, is compensated face shape error E ', and the face shape figure after its compensation as shown in Figure 9;

(5) to remove function: by removing the removal function R of function experiment when obtaining the polished workpiece minute surface of ion beam vertical incidence that present embodiment selects for use, this distribution map of removing function R as shown in figure 11;

(6) determine residence time distribution T: according to the complementary area shape error E of determining in the step (4) ' and step (5) in the removal function R that obtains, utilize the residence time computational methods when having the processing plane mirror now to determine residence time distribution T and generate numerical control code; The distribution map of this residence time as shown in figure 12;

(7) ion beam polishing processing: utilize the residence time numerical control code of described removal function generator and generation to treat polishing workpiece and carry out ion beam polishing processing, process intermediate ion bundle is along being parallel to workpiece optical axis direction vertical incidence minute surface, and the three-shaft linkage system (need not to use the linked system more than four) by described removal function generator carries out correction of the flank shape to minute surface;

(8) iteration polishing processing: repeat the technical process twice of above-mentioned steps (1)～step (7), satisfy the process finishing that requires of face shape convergence precision until the correction of the flank shape result of step (7).After the present embodiment correction of the flank shape machined, the face shape of workpiece was schemed as shown in figure 10.

In the present embodiment, process altogether the time spent for twice and have only 9min, but total convergency factor has but reached 2.24.In the short period of time, realized the high accuracy processing of high-gradient mirror surface, removed the high point of error effectively, surface figure accuracy is improved, and the convergence effect is more obvious.

The above only is a preferred implementation of the present invention, and protection scope of the present invention is not limited to the foregoing description.

Claims (1)

1. the method for polishing ion beam of a high-gradient mirror surface may further comprise the steps:

(1) measuring and calculating incidence angle: get a polished workpiece with high-gradient mirror surface, in plane, set up the X-Y rectangular coordinate system perpendicular to the workpiece optical axis, according to the surface equation z=h of high-gradient mirror surface (x, y), the angle of measuring and calculating minute surface each point normal and vertical incidence ion beam, i.e. incidence angle θ;

(2) determine that penalty coefficient distributes: according to model P (x, y)=(1/n) Y ₀(θ) (xcos θ y), determines the corresponding penalty coefficient K of each processing stand of polished workpiece to cos θ f, is designated as K (θ);

(3) measure initial face shape error: utilize interferometric method to measure the primary face shape error E of described polished workpiece, be designated as E (x, y);

(4) compensate initial face shape error: distributing according to the penalty coefficient of determining in the step (2) compensates described primary face shape error E, is compensated face shape error E ', and E '=E (x, y)/K _Ij(θ);

(5) obtain to remove function: the removal function R when testing acquisition ion beam vertical incidence same material minute surface by removing function (x, y);

(6) determine residence time distribution T: according to the complementary area shape error E of determining in the step (4) ' and step (5) in the removal function R (x of acquisition, y), utilize the residence time algorithm when having the processing plane mirror now to determine residence time distribution T and generate numerical control code;

(7) ion beam polishing processing: utilize the generating means of described removal function and the residence time numerical control code of generation that described polished workpiece is carried out ion beam polishing processing, process intermediate ion bundle is along being parallel to workpiece optical axis direction vertical incidence minute surface, and the three-shaft linkage system by described removal function generator carries out correction of the flank shape to minute surface;

(8) iteration polishing processing: repeat the technical process of above-mentioned steps (1)～step (7), satisfy the requirement of face shape convergence precision, process finishing until the correction of the flank shape result of step (7).

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