CN1019855B - The Moire fringe method of testing and the device of minute surface flatness - Google Patents

Abstract

The Moire fringe method of testing and the device of minute surface flatness are characterized in allowing grating and minute surface proximity ground configured in parallel, plunder to penetrate formula ground and observe superimposed between grating and its virtual image grating in minute surface and the Moire fringe of formation.The device that utilizes the present invention to design, it has area source, grating measuring platform, and imaging system.Can be put in the supporting-point of grating measuring platform to the silicon chip of semiconductor industry, mask plate and domestic refrigerator compressor valve plate etc., or on the face, allow it be in free laying state, observe it contact the face type flatness of a side with supporting-point.Precision can reach micron order.

Description

The Moire fringe method of testing and the device of minute surface flatness

The invention belongs in the physics profile measurement with the optical means is the profile metering method and the device of feature.

More's contour measurement was seen in reported in literature in 1970 (consults [1] D.M.Meadows:Applied Optics, Volg, No.4, (1970), 942), its notable attribute is only to be applicable to that the surface has the object of enough diffuse reflection performances, need take some supplementary meanss to increase the diffuse reflection performance of testee in some occasion, detects effect to improve.

For the higher mirror article of reflectivity, adopt general More's profilometry can't observe More's profile striped.In Experiments of Machanics, though also being arranged, the report of reflection Moire technique (consults [2] Reinhold Ritter:Applied Engineering Vol21, NO.4, (1982) 663.[3] R.Ritter et:Experimental Mechanics, Vol23, NO.4(1983) 165.) but all be to be test specimen with flat minute surface, in order to measuring the slope variation before and after the test piece deformation, rather than directly obtain its contour shape.

The testing flatness of high precision minute surface all is being to utilize the optical interference principle traditionally, in recent years along with the development of Moire technique.Also useful grating detects the technology of mirror plane and (consults [4] W.Jaerisch and G.Makosch:Applied Optics, Vol17, NO.5, (1978) 740.[5] J.Motycka:Ex-perimental Mechanics, Vol15, NO.7, (1975) 279.) but this class technology is all based on principle of interference, so used optical element all needs to reach the precision of optical wavelength level in the instrument, and needs the heavy caliber colimated light system.The instrument of making will seem comparatively complicated and cost an arm and a leg.

The invention provides a kind of simple and effective method, only need the special plane grating of a suitable precision, just can in common optics processing, see the method for Newton ring, directly detect the planarity of minute surface.Select different raster densities for use and plunder and penetrate viewing angle and can adjust sensitivity easily, to be adapted to measure other test specimen of different accuracy level.Utilize the device of this method design, can the light and thin flat minute surfaces such as valve block in the silicon chip of semiconductor industry, mask plate and the domestic refrigerator compressor be put on the grating supporting-point, allow it be in free laying state, observe it contact the face type flatness of the whole audience of a side with supporting-point.

Description of drawings:

Fig. 1 is the optical schematic diagram of minute surface More consistency profiles.Light source S ₂And milky (or coloured) glass M ₁Form area source, light source S ₃With diffuse reflection surface M ₂The another kind of pattern of forming area source.S ₁It is used pointolite in general More's consistency profiles.E is imaging object lens or observer's eyes.G is a grating.W is tested minute surface.G ¹Be the virtual image grating of grating G in minute surface W when observing by the E point.M is the observed point on the minute surface, l ₂Be the normal of this point, l ₁Be the light that shines observation point E by this point, l ₃Be the light that m is ordered that incides by area source.

Fig. 2 penetrates formula minute surface More consistency profiles and observes optical schematic diagram when tilting flat minute surface with plunderring.The E point is an observation point.G is a grating.W is tested minute surface.M is on the tested minute surface a bit.l ₂Be the normal of this point, l ₁Be the light that shines observation point E by this point, l ₃Be the light of ordering by the directive m that area source comes.

Fig. 3 is the optical schematic diagram when tilting forward and back flat minute surface with general minute surface More consistency profiles observation.Wherein E is an observation point.G is a grating.W is tested minute surface.M is the point on the tested minute surface.l ₁Be the light that shines observation point by this point, l ₂Be the normal of this point,

l ₃Be the light that m is ordered that incides by area source.

Fig. 4 is the minute surface testing flatness device that utilizes this method designed.Light source [1] and milky (or coloured) glass [3] are formed area source.Light source [2] and diffuse reflection surface [4] are formed the another kind of pattern of area source.[5] be the grating that the test minute surface is used.[6], [8] are catoptrons.[7] be the imaging object lens.[9] be imaging screen.[10] be test specimen.Take down object lens [7], imaging screen [9] is made into watch window, the tester can be from [9] the minute surface More profile striped of its face type error of reflection on Direct observation test specimen surface inwards.

Theoretical foundation of the present invention is, grating and minute surface proximity ground configured in parallel are utilized superimposed between the virtual image grating in minute surface of grating and it and the minute surface More profile striped that produces.

Common More's consistency profiles is by pointolite S ₁, photographic field lens E and grating G three form (Fig. 1).When test specimen W is not a diffuse reflector but when having the minute surface of high reflectance, by pointolite S ₁The irradiate light of sending is behind grating G, and the surface of minute surface test specimen W can not form the grating shade, just can't see common More's profile striped yet.

The virtual image C that grating G is arranged in minute surface W shown in Figure 1 ¹, modulated by the surface configuration of minute surface W and the shape of this virtual image is inevitable, so at observed G of E point and G ¹In the superimposed formed Moire fringe, must comprise the contour shape information of minute surface W.In order to observe grating G and virtual image G by observation point E ¹Between the formed Moire fringe that is superimposed with each other, every bit must have this point of incident ray directive that meets reflection law accordingly on the minute surface when reflexing to observation point E, promptly needs an area source, as light source S among Fig. 1 ₂And milky (or coloured) glass M ₁The area source of forming, or light source S ₃With diffuse reflection surface M ₂The area source of being formed.

From observation point E, certain 1 A on the grating ₃Virtual image position in minute surface is by reflection law decision (Fig. 1), so the particular location of minute surface More profile striped (by the Moire fringe that is formed by stacking between grating grid line and its virtual image grid line in minute surface) should be found the solution with reflection law on minute surface contour surface pointwise ground.

In Fig. 1, set up coordinate system.Allow XOY plane and grid stroke planes overlapping, and the direction of vertical grid line is decided to be X-axis, the vertical paper of the Y-axis parallel and going out with grid line, the Z axle is by observation point E.The equation of grating planar is:

Z＝0……（1）

Line l on the minute surface between any 1 m and the observation point E ₁Be the emergent ray of this point, make the normal direction l that m is ordered on the minute surface ₂, allow incident angle and emergence angle equate to make incident ray l ₃l ₁And l ₃Respectively by the A on the grating face ₁And A ₃Point is obtained their value X on the parameter of Building X ₁And X ₃, the Moire fringe level of ordering at the viewed m of E point time N=(X then ₃-X ₁)/P.Here P is the pitch of grating.

Reflection ray l ₁Through 1 m(X on the minute surface _m, Y _m, Z _m) and observation point E(O, O, L), l ₁Straight-line equation be

$\frac{X}{X_m}=\frac{Y}{Y_m}=\frac{\mathrm{Z\; -\; L}}{Z_m\mathrm{-\; L}}{\mathrm{=\; t}}_1\mathrm{\dots \dots (2)}$

If tested curved surface is F(X, Y, Z)=0, then the directional derivative that m is ordered on this curved surface be (

),

And

, get final product the m normal equation of ordering

The emergent ray l of measured point m ₁With normal l ₂Write as vector respectively

₁And unit vector Form, promptly

If incident ray l ₃Vector be N ₃=C ₃I+C ₂J+C ₃K is according to the vector reflection law

,

Promptly

C ₁＝a ₁-2b ₁（a ₁b ₁+a ₂b ₂+a ₃b ₃）

C ₂＝a ₂-2b ₂（a ₁b ₁+a ₂b ₂+a ₃b ₃）

C ₃＝a ₃-2b ₃（a ₁b ₁+a ₂b ₂+a ₃b ₃）

Use following formula and ask N ₃Direction number C the time must be noted that, here because of N ₃And N ₁Direction is opposite, so determining ⁰ ₂Direction the time, must make N ⁰ ₂And N ₁The direction contrary.

Vector N ₃Same by 1 m(X on the minute surface _m, Y _m, Z _m), can try to achieve l ₃Straight-line equation

$\frac{{\mathrm{X\; -\; X}}_m}{C_1}=\frac{{\mathrm{Y\; -\; Y}}_m}{C_2}=\frac{{\mathrm{Z\; -\; <figure-callout\; id="3"\; label="Z\; m\; C"\; filenames="87104789\_DRIMG2.png"\; state="\{\{state\}\}">Z\; </figure-callout>}}_m}{C_{}}{\mathrm{=<figure-callout\; id="3"\; label="t"\; filenames="87104789\_DRIMG2.png"\; state="\{\{state\}\}">t</figure-callout>}}_3\mathrm{\dots \dots (4)}$

Lian Lieshi (1) and (2) can get emergent ray l ₁Intersection point A with benchmark grating planar (Z=0) ₁(X ₁, Y ₁, Z ₁).In like manner, Lian Lieshi (1) and (4) can get the intersection point A of incident ray and grating planar ₃(X ₃, Y ₃, Z ₃).According to the principle of the ordinal number equation of Moire fringe, the Moire fringe of N level time is

（X ₃-X ₁）＝NP……（5）

Here P is the pitch of grating.

According to above-mentioned theory, can extrapolate the mathematic(al) representation of the minute surface More profile striped of any known type minute surface:

As the flat minute surface that tilts of Fig. 2 shape, the angle between it and grating planar is α, and the distance of observation point E and Z between centers is d, and the distance between the grating face is L.The minute surface More profile striped of this class minute surface is cluster and the parallel straight line of Y-axis (being grating grid line direction), and the Moire fringe ordinal number of counting from oblique minute surface and grating intersection point (being set origin of coordinate) is the X-axis coordinate values X of N _NCalculating formula be

Z in the formula _NIt is the Z axle bed scale value of 1 m on the N level time pairing minute surface profile of striped.

Flat minute surface W that tilts forward and back among Fig. 3 and the angle between the grating planar G are α, and the distance between observation point E and grating face is L, and the formed minute surface More of this oblique minute surface profile striped is the cluster curve, and its Y-axis and X-axis are respectively the asymptotic lines of this curve family.Can get according to aforesaid reckoning principle equally, from X(or Y) the Moire fringe ordinal number counted of axle is the coordinate values X of the striped of N _NAnd Y _NRelational expression as follows:

The invention is characterized in to plunder and penetrate the superimposed and minute surface More profile striped that forms between formula ground observation grating and its virtual image grating in minute surface.With regard to the concrete condition of Fig. 2 shape, promptly the d value obtains big and the L value is selected lessly.In order to detect the minute surface flatness, always make the parallel placement of test specimen with grating planar, promptly the α angle is always minimum.With limiting case α=0, formula (6) can be reduced to

（d+X _N）＝（Z _N-L）NP/2Z _N

Consider concrete condition Z _N＜＜L, d+X again _N=D(sees Fig. 2), following formula can be similar to and be write as

D＝-LNP/2Z _N

In the following formula because Z _NThe value direction is opposite with the Building Z parameter, so Z during actual operation _NShould be with the negative value substitution, resulting D value still be illustrated in figure 2 as on the occasion of.If a is the gap between flat minute surface and grating planar, do not consider the coordinate direction, then following formula can be rewritten as again

D＝LNP/2a……（8）

Here L is the vertical range between observation point E and the grating G.P is a grating pitch, and N is counted the Moire fringe ordinal number from the intersection point between observation point E and grating face.At this moment the P/2a-LNP/2a=LP/2a of the Moire fringe width ω of Xing Chenging=L(N+1).

Gap between grating and minute surface becomes a by a ⁷The time, then the fringe position that m is ordered on the minute surface has moved on to D ¹=LNP/2a ¹The place, move apart from △ D=D ¹-D(a/a ¹-1).If the ratio ε of the amount of movement △ D of Moire fringe and Moire fringe width ω=△ D/ ω is referred to as sensitivity, then

ε＝△D/ω＝2D·△a/LP……（9）

What more than analyze is to be example with the flat minute surface that tilts, and the result who is calculated out by (6) formula in inclined angle alpha → 0 o'clock illustrate that gap a slightly changes, and striped is marked direction and had obvious displacement in the Building X.The flat minute surface (Fig. 3) that following surface analysis tilts forward and back, gap a changes and the stripe displacement situation that causes when inclined angle alpha is very little.

As can be seen from Figure 3, the Y in (7) formula _Nt _gα=Z _N, be the distance-gap between minute surface profile and the grating planar.Abbreviation (7) formula gets

${\mathrm{LX}}_N\mathrm{=\; NP\; (}\frac{L^2{\mathrm{cos\; 2a\; -LZ}}_N{\sin }^2{\mathrm{a\; -\; Z}}^2{}_N}{{\mathrm{2Z}}_N{\cos }^{2}a})$

Z in the following formula ² _N＜＜L ²Cos2 α can get behind the abbreviation that omit and further

$Z_N=\frac{\mathrm{LNP\; cos\; 2a}}{{\mathrm{(2X}}_N{\mathrm{+\; NPt}}_g{}^2{\mathrm{a)\; cos}}^{2}a}\mathrm{————(10)}$

Flat minute surface is described if tilt as shown in Figure 3, but inclined angle alpha is very little, and employing is plunderred when penetrating the formula observation, then at X again _NWhat see in the big zone will be a rule and the perpendicular straight line of grating grid line direction.The profile gap Z that striped presented _NN is directly proportional with fringe order.

In sum, actual face type error is not necessarily just only in the run-off the straight of X-axis (or Y-axis) direction, so the minute surface More profile striped of different shape can occur when concrete test.The size that can judge the type error of appearing according to the vergence direction and the spacing of striped is plunderred when penetrating viewing angle the moving direction of striped according to change and can be differentiated the concavo-convex of face type error.

The noncontact (or point, face contact) that utilizes the designed device of this method can be advantageously used in the thin-walled minute surface is measured.It is characterized in that

Have area source [1]～[4] as shown in Figure 4, grating measuring platform [5] and imaging interpreting system [6]～[9].The surface to be measured of test specimen is contacted towards grating and with the supporting of grating measuring platform, go up at imaging screen [9] and just can see the test specimen lip-deep face shape error that striped was reflected to be measured with non-benchmark parallel lines feature.

Area source in Fig. 4 device can be milky (or coloured) glass [3] of ordinary light source [1] (incandescent lamp, fluorescent light etc. all can) and transmission-type, under some gap situation, adopts coloured diffuse transmission light source can improve the sharpness of striped; Area source also can adopt ordinary light source [2] and the uniform diffuse reflector [4] among Fig. 4.[5] be grating, [6], [8] are catoptrons, and [7] are immaging lens, and [9] are imaging and observation screen, and [10] are test specimens, and [11] are shadow shields.Take down imaging screen [9], behind imaging object lens [7], dispose an eyepiece group that has graticule again and promptly constitute visual type observation.Take down imaging object lens [7] imaging screen [9] is changed into the form that watch window is promptly formed usefulness eyes Direct observation, structure will be the simplest.

Must be provided with one on the grating measuring platform [5] and keep the device of constant clearance, promptly set up the gap reference between a grating grid line face and test specimen surface with test specimen surface.Its form has following several, can use under the different situations.

1. on the grating measuring platform [5] in Fig. 4, the grid line of grating faces down, can be coated with the last layer reflectance coating in the zone to be measured of its grating (putting test specimen to be measured zone) outer rim (this no-raster grid line) on glass, at this moment promptly with the thickness of the basic body of Grating glass sheet as gap reference.

2. on the grating measuring platform [5] in Fig. 4, the grid line of grating can glue the glass sheet of lastblock uniform thickness towards last on the grating grid line face, and is coated with the last layer reflective film in its regional outer rim to be measured, at this moment promptly with the glass sheet of the uniform thickness that is stained with as gap reference.

3. on the grating measuring platform [5] in Fig. 4, the grid line of grating can be stained with the supporting fritter of three uniform thickness towards last in the zone to be measured of grating grid line face.Test specimen directly is put on these the three supporting fritters, and the thickness of supporting fritter is promptly as gap reference.

4. on the grating measuring platform [5] in Fig. 4, the grid line of grating is towards last, can settle three fine-tuning and can lock support lugs in the to be measured regional outer end of grating grid line face, test specimen directly is put in these three supportings, and micro-adjusting mechanism can guarantee still can adjust to behind the supporting abrasion gap standard of requirement.

In the above in four kinds of gap standards, 1,2 two kind of grating be put on the test desk [5], at this moment on imaging screen [9] (or graticule of eyepiece), the cluster striped parallel with grid line will occur in the zone that was coated with reflectance coating of Grating glass, this promptly is a calibration benchmark of measuring the error of test specimen

During as gap reference, can depict the parallel lines of cluster as measuring basis with above-mentioned 3,4 two kind of method on imaging screen [9] (or graticule of eyepiece), it can calculate by ω=LP/2a, also can be with drawing after the optical flat practical measurement.

Method provided by the present invention had both kept the device of More's consistency profiles simple, advantages such as sensitivity is easily transferred, low price, and the range of application of having widened More's consistency profiles again makes it to be used to measure minute surface.Observe minute surface More profile striped and improved measuring accuracy with plunderring the formula of penetrating, make it in the light path that does not need interference system, save under the prerequisite of the desired a series of high-precision optical elements of interference system, can reach micron-sized precision, satisfy and measured the accuracy requirement of semiconductor industry silicon chip and refrigerator with the mirror plane of compressor valve plate etc.Particularly in the occasion of face type error near 0.01 millimeter, utilize interferometry often too much to seem inconvenient because of interference fringe, and always can design the instrument of corresponding sensitivity with this law, make it on the test specimen surface, to present suitable fringe number and be convenient to interpretation.

Claims (5)

1, a kind of Moire fringe measuring method of the Measuring Object surface profile discrepancy in elevation is characterized in that allowing grating and minute surface proximity ground configured in parallel, plunders the minute surface More profile striped of penetrating superimposed between formula ground observation grating and its virtual image grating in minute surface and producing.

2, a kind of device that utilizes the Moire fringe measuring method of the Measuring Object surface profile discrepancy in elevation is characterized in that it has area source, grating measuring platform and imaging system.

3, a kind of device that utilizes the Moire fringe measuring method of the Measuring Object surface profile discrepancy in elevation according to claim 2 is characterized in that said area source is the common light source [1] and milky (or coloured) glass [3] of transmission; Or ordinary light source [2] and diffuse reflection surface [4].

4, a kind of device that utilizes the Moire fringe measuring method of the Measuring Object surface profile discrepancy in elevation according to claim 2 is characterized in that the to be measured regional outer rim of said grating measuring platform at its grating, and a side of no-raster grid line is coated with the last layer reflective film; Or in a side of grating grid line the glass of sticking one deck uniform thickness, the to be measured regional outer rim at this glass is coated with the last layer reflective film then; Or on the zone to be measured of grating grid line the supporting fritter of three uniform thickness; Or settle three fine-tuning and can lock support lugs in the to be measured regional outer end of grating grid line face.

5, a kind of device that utilizes the Moire fringe measuring method of the Measuring Object surface profile discrepancy in elevation according to claim 2, it is characterized in that said imaging system, its imaging screen [9] (or eyepiece graticule) is gone up and is delineated the cluster parallel lines that have as measuring basis.

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