CN102297725B - Device and method for detecting reference spherical wave deviation in visible point diffraction interferometer - Google Patents

Abstract

The invention discloses a device and a method for detecting reference spherical wave deviation in a visible point diffraction interferometer and belongs to the field of reference spherical wave ultra-high precision detection methods. The limitation of a Hartmann wavefront sensor on wavefront micro-deviation detection is overcome so that the wavefront high-precision detection can be realized. A light path comprises an incidence convergent light wave, a grating, a small pore plate with three circular holes along an orthogonal direction and a charge coupled device. The output end of the charge coupled device is connected to a computer. After being diffracted through the grating, the incidence convergent light wave is divided into a plurality of diffraction orders; +/-1 order of diffraction light respectively passes through two small holes; after the light is diffracted by the small holes, approximately ideal spherical waves are generated; two spherical waves are subjected to shear interference; an interference image is recorded on a CCD (Charge Coupled Device) detector; and after the interference image is collected, the diffraction wavefront deviation can be obtained. According to the device and method disclosed by the invention, the diffraction wavefront high-precision detection is realized by performing the shear interface of the spherical waves generated through double-hole diffraction in a visible light band.

Description

Reference sphere ground roll error measuring means and method in the visible point of light diffraction interferometer

Technical field

The invention belongs to reference sphere ground roll superhigh precision detection method field, promptly adopt the method for the reference sphere ground roll deviation that interferometer test hole diffraction goes out.

Background technology

Comprise several aspheric surfaces in the extreme ultraviolet photolithographic projection objective, each aspheric polishing precision must reach 0.2nm RMS～0.3nm RMS.General commercial fizeau interferometer or Tai Man-Green's interferometer is owing to receive the restriction of reference element; Its accuracy of detection can't satisfy the requirement that this superhigh precision detects task far away; Point-diffraction interferometer (PDI) produces the reference sphere ground roll through little diffraction by aperture; Can realize the detection of superhigh precision, the accuracy of detection that PDI can reach depends primarily on the quality of reference sphere ground roll.In the reality, how going to detect the deviation that is bordering on desirable reference sphere ground roll that is gone out by circular hole diffraction is the thing of a difficulty, and therefore, reference sphere ground roll deviation detecting method has very big actual value in the development visible point of light diffraction interferometer.

Usually adopt Hartmann wave front sensor to measure wavefront deviation, but its precision is very limited, can't satisfy the requirement that reference sphere ground roll deviation detects in the visible point of light diffraction interferometer at all.Formerly technological [1] (referring to: Appl.Opt.Vol.38; No.35; P7252-7263,1999) change square window into small sircle hole in the null check that the extreme ultraviolet photolithographic projection objective system wave aberration of describing in detects, thereby realize the diffraction of extreme ultraviolet light wave through diplopore; But the spacing of its diplopore is fixed, and the distance between the diplopore equals original hole and the distance between the window.The present invention then through the size that different diplopore spacings changes shearing displacement is set, obtains the corrugated deviation of visible light situation under different shearing displacements, thereby realizes that high-precision wavefront deviation detects.Formerly technological [2] (referring to: Rev.Sci.Instrum.; Vol.79, No.033107,2008) adopt the generation of optical taper diffraction to be bordering on desirable spherical wave; Realize two shear interferences between the spherical wave through adjusting two angles between the optical fiber; For the situation that produces the reference sphere ground roll through little diffraction by aperture, the present invention adopts two diffraction by apertures to produce and is bordering on desirable spherical wave, thereby realizes shear interference.The present invention proposes to carry out the check of aperture diffraction wavefront deviation through the lateral shearing interference of diplopore at visible light wave range.Owing to the desirable spherical wave that is bordering on of aperture diffraction generation, its deviation is less, and the detection that directly carry out wavefront deviation is very difficult, can realize the high Precision Detection of wavefront little deviation through lateral shearing interference.

Summary of the invention

The detection method that the purpose of this invention is to provide reference sphere ground roll deviation in a kind of visible point of light diffraction interferometer.The mode of this method employing lateral shear detects the deviation of wavefront, has overcome Hartmann wave front sensor to the restriction that the wavefront little deviation detects, and can realize the high Precision Detection of wavefront.

Technical conceive of the present invention is to adjust shearing displacement through changing two distances between the circular hole, carries out the shearing of directions X and Y direction through the distribution at the direction layout aperture of two quadratures, thereby realizes the shear interference of two light waves.Lateral shearing interference is effective ways of realizing the wavefront high Precision Detection, obtains differentiated wavefront through interferogram, obtains original wavefront through wavefront reconstruction, finally tries to achieve wavefront deviation.

Technical solution of the present invention is following:

Reference sphere ground roll error measuring means in the visible point of light diffraction interferometer; It is characterized in that; This device includes: grating, one have the aperture plate of three circular holes, ccd detector, computing machine along orthogonal directions, and described aperture plate is between grating and ccd detector; Described grating makes the convergence light wave generation diffraction through it, and diffraction light interferes stack behind the aperture plate diffraction, and on ccd detector, notes interferogram; Described computing machine is gathered the interferogram of being noted through signal wire from ccd detector.

The line of centres that three circular holes that described aperture plate is opened along orthogonal directions are respectively hole one, hole two, three, three circular holes in hole constitutes the isosceles right triangle with summit, Kong Yiwei right angle.

The detection method of reference sphere ground roll deviation is characterized in that in the visible point of light diffraction interferometer, and this method comprises the following steps:

1. assemble light wave and shine on the grating, generate 0 grade, ± 1 grade, ± 2 grades of diffraction lights that increase progressively according to rank, utilize aperture plate only let ± hole of 1 order diffraction light transmission horizontal direction one and hole three; Diffraction takes place; Produce two spherical waves, the interference fringe of utilizing two spherical waves of ccd detector record to interfere stack to produce, this interference fringe is the lateral shearing interference figure along directions X; Utilize this interferogram of computer acquisition, obtain the differentiated wavefront of diffracted wave forward position directions X thus;

2. rotating grating is taked the mode 1. identical with step, utilizes aperture plate let ± hole of 1 order diffraction light transmission vertical direction one and hole two, obtains the lateral shearing interference figure along the Y direction, obtains the differentiated wavefront of diffracted wave forward position Y direction thus;

3. carry out wavefront reconstruction according to the differentiated wavefront of directions X and the differentiated wavefront of Y direction, obtain original reference diffraction wavefront, through calculating the preceding deviate of diffracted wave;

4. change aperture plate, change the distance between the aperture, repeating step 1. to step 3., obtain the lateral shearing interference figure of different shearing displacements, and then obtain before the original diffracted wave and deviate;

Average before the diffracted wave of 5. step being tried to achieve under the different shearing displacements in 4., obtain deviate before the final diffracted wave, accomplish the detection method of reference sphere ground roll deviation in the visible point of light diffraction interferometer.

Beneficial effect of the present invention is following:

1, at visible light wave range, the spherical wave that produces through the diplopore diffraction carries out shear interference, thereby realizes the high Precision Detection before the diffracted wave;

2, through changing the size that two distances between the aperture change shearing displacement;

3,, thereby realize the shear interference of directions X and Y direction through distribution at the direction layout aperture of two quadratures.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention is further specified.

Fig. 1 is reference sphere ground roll deviation detecting method principle schematic in the visible point of light diffraction interferometer of the present invention.

Fig. 2 is the structural representation of aperture plate of the present invention.

Fig. 3 is the schematic layout pattern of aperture in the aperture plate of the present invention.

Among the figure: 1 is that convergence light wave, 2 is that grating, 3 is that aperture plate, 4 is that spherical wave, 5 is that ccd detector, 6 is that computing machine, 7 is that substrate of glass, 8 is that metallic chromium layer, 9 is that hole two, 10 is that hole one, 11 is hole three.

Embodiment

As shown in Figure 1; Comprise in the reference sphere ground roll error measuring means in the visible point of light diffraction interferometer of the present invention: grating 2, one have the aperture plate 3 of three circular holes, ccd detector 5, computing machine 6 along orthogonal directions, and described aperture plate 3 is between grating 2 and ccd detector 5; Described grating 2 makes the convergence light wave 1 through it that diffraction take place, and diffraction light interferes stack behind aperture plate 3 diffraction, and on ccd detector 5, notes interferogram; Described computing machine 6 is gathered the interferogram of being noted through signal wire from ccd detector 5.

Like Fig. 2, shown in Figure 3, substrate of glass 7, crome metal (Cr) layer 8; Three circular holes: hole 1, hole 29 and hole 3 11, hole 1 is positioned at the central authorities of aperture plate; Hole 29 be positioned at hole 1 directly over, hole 3 11 is positioned at the right in hole 1, the line of centres in three holes constitutes isosceles right triangle.

Concrete detection method of the present invention is following:

Assembling light wave 1 shines on the grating 2; Through grating 2 diffraction, generate 0 grade, ± 1 grade, ± 2 grades ... Diffraction light, aperture plate 3 is positioned on the focal plane of assembling light wave 1; Aperture plate 3 has three holes; In reality, hole 1 and hole 29 are used for the lateral shearing interference of Y direction, and hole 1 and hole 3 11 are used for the lateral shearing interference of directions X.Let earlier ± 1 order diffraction light is respectively through hole 1 and hole 3 11; The inferior diffraction light of other grade is blocked by the lightproof part of aperture plate; Incident light produces spherical wave behind hole 1 and hole 3 11 diffraction, two spherical waves are interfered stack, on ccd detector 5, obtain interference fringe; Computing machine 6 collects interferogram, and what interferogram reflected is the differentiated wavefront before the actual diffracted wave.Obtain the lateral shearing interference figure of directions X.Rotating grating then; Let ± 1 order diffraction light is respectively through hole 1 and hole 39, and the inferior diffraction light of other grade is blocked by the lightproof part of aperture plate, and incident light produces spherical wave behind hole 1 and hole 39 diffraction; Two spherical waves are interfered stack; On ccd detector 5, obtain interference fringe, computing machine 6 collects interferogram, and what interferogram reflected is the differentiated wavefront before the actual diffracted wave.Obtain the lateral shearing interference figure of Y direction.

If the distance at X, Y direction aperture center is respectively S and T, the shear interference equation is arranged then

$\begin{array}{cc}\mathrm{\Δ}{W}_S=W(x+S,y)-W(x,y)=\underset{n=0}{\overset{k-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{n}{\mathrm{\Σ}}}{C}_{\mathrm{nm}}{x}^m{y}^{n-m}& \left(1a\right)\\ \mathrm{\Δ}{W}_T=W(x,y+T)-W(x,y)=\underset{n=0}{\overset{k-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{n}{\mathrm{\Σ}}}{D}_{\mathrm{nm}}{x}^m{y}^{n-m}& \left(1b\right)\end{array}$

Coefficient C wherein _NmAnd D _NmFor

$\begin{array}{cc}{C}_{\mathrm{nm}}=\underset{j=1}{\overset{k-n}{\mathrm{\Σ}}}\left(\begin{array}{c}j+m\\ j\end{array}\right)S^j{B}_{j+n,j+m}& \left(2a\right)\\ D_{\mathrm{nm}}=\underset{j=1}{\overset{k-n}{\mathrm{\Σ}}}\left(\begin{array}{c}j+n-m\\ j\end{array}\right)T^j{B}_{j+n,m}& \left(2b\right)\end{array}$

(its expression formula does W in the formula for x, y) the original wavefront to be checked of expression

$W(x,y)=\underset{n=0}{\overset{k}{\mathrm{\Σ}}}\underset{m=0}{\overset{n}{\mathrm{\Σ}}}{B}_{\mathrm{nm}}{x}^m{y}^{n-m}---\left(3\right)$

W (x+S, y), W (x, the wavefront after y+T) expression is sheared along X, Y direction, Δ W _SWith Δ W _TPromptly be by the information that obtains on the lateral shear interferograms.Can try to achieve coefficient C by lateral shear interferograms and equation (1) _NmAnd D _Nm, (x y), calculates the preceding deviation of diffracted wave then can to try to achieve the preceding W of original diffracted wave by equation (2) again.

Change shearing displacement, repeat above operation, (x y) and deviation, through the deviation of trying to achieve under three different shearing displacement situation, makes even and all promptly get the preceding final deviate of original diffracted wave can to try to achieve W before the original diffracted wave again.

Claims (1)

1. the detection method of reference sphere ground roll deviation in the visible point of light diffraction interferometer; Wherein, Reference sphere ground roll error measuring means include in the visible point of light diffraction interferometer: a grating (2), one have aperture plate (3), a ccd detector (5), the computing machine (6) of three circular holes along orthogonal directions, and described aperture plate (3) is positioned between grating (2) and the ccd detector (5); Three circular holes that described aperture plate (3) is opened along orthogonal directions are respectively hole one (10), hole two (9), hole three (11), and it is the isosceles right triangle on summit, right angle that the line of centres of three circular holes constitutes with hole one (10); This method comprises the following steps:

1. assembling light wave (1) shines on the grating (2); Generate 0 grade, ± 1 grade, ± 2 grades of diffraction lights that increase progressively according to rank; Utilize aperture plate (3) only let ± hole one (10) and the hole three (11) of 1 order diffraction light transmission horizontal direction, diffraction takes place, produce two spherical waves (4); The interference fringe of utilizing ccd detector (5) two spherical waves of record (4) to interfere stack to produce; This interference fringe is the lateral shearing interference figure along directions X, utilizes computing machine (6) to gather this interferogram, obtains the differentiated wavefront of diffracted wave forward position directions X thus;

2. rotating grating (2) is taked the mode 1. identical with step, utilizes aperture plate (3) let ± hole one (10) and the hole two (9) of 1 order diffraction light transmission vertical direction, obtains the lateral shearing interference figure along the Y direction, obtains the differentiated wavefront of diffracted wave forward position Y direction thus;

3. carry out wavefront reconstruction according to the differentiated wavefront of directions X and the differentiated wavefront of Y direction, obtain original reference diffraction wavefront, through calculating the preceding deviate of diffracted wave;

4. change aperture plate (3), change the distance between the aperture, repeating step 1. to step 3., obtain the lateral shearing interference figure of different shearing displacements, and then obtain before the original diffracted wave and deviate;

Average before the diffracted wave of 5. step being tried to achieve under the different shearing displacements in 4., obtain deviate before the final diffracted wave, accomplish the detection method of reference sphere ground roll deviation in the visible point of light diffraction interferometer.

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