CN1945202A - Laser confocal feedback micro measuring device - Google Patents

Abstract

The present invention relates to topographic measurement, and is especially micro topographic measurement technology for discrete surface of low reflectivity sample. The measuring device includes single longitudinal mode microchip laser, lens and spectroscope in the laser emitting path, lens and laser detector in the reflecting path, frequency shifter and confocal feedback module in the transmitted light path, sinusoidal signal emitting source, signal modulating circuit, orthogonal phase-sensitive detector and reference signal generator circuit. The present invention may be used in the topographic measurement of both continuous surface and discrete surface.

Description

Laser confocal feedback micro measuring device

Technical field

The invention belongs to the topography measurement technical field, the discontinuous surface microscopic topographic that is specially adapted to low reflectivity sample is measured.

Background technology

Along with the fast development of micro fabrication, micro element has become a research focus of scientific research field, as MEMS device and micro-optical device research etc.; Corresponding therewith, the topography measurement instrument of micro element is faced with bigger demand at present.Have based on the optical morphology measuring method of optical interference phase measurement principle and can trace to the source, be used widely to length standard and the high advantage of resolution.But there are some shortcomings in the optical morphology method of past based on phase measurement.The conventional phase measuring method requires the testing sample surface to have certain reflectivity and surface smoothness, and reaching enough signal to noise ratio (S/N ratio)s, so the measuring surface form of low reflectivity sample becomes difficulty; And the stray reflected of some transparent sample different aspects can produce undesired signal influences phase measurement accuracy.The measurement range of phase measurement method generally all limits in the half wavelength scope, yet a lot of sample surfaces include discontinuous of step and micropore etc., and when bench height or hole depth surpassed half optical wavelength, the phase measurement method just can not be carried out.These problems have all limited the application based on the optical morphology measuring method of phase measurement.

1963, King found to work as an external mirror first with CO ₂When resonator cavity is returned in the part output optically-coupled of laser instrument, the athletic meeting of catoptron causes the modulation of laser output power, is similar to traditional two-beam interference phenomenon, and promptly a striped moves corresponding catoptron and moves optical maser wavelength half, this is the laser feedback phenomenon, also claims the self-mixed interference phenomenon.

Fig. 1 is the light feedback displacement measurement mechanism based on micro-slice laser of people such as French researchist Eric Lacot at 053824 page of report of Physical Review A the 70th volume.The principle of work of this system is: as shown in Figure 1, micro-slice laser 1 output single longitudinal mode laser behind lens 2 collimations, projects spectroscope 3; The transmitted light of process spectroscope 3 is by behind the frequency shifter 4, optical frequency is offset with respect to optical frequency in the laser chamber (ω), the driving signal frequency (Ω/2) that export in source 8 takes place in the sinusoidal signal that side-play amount equals frequency shifter 4, promptly becomes (ω+Ω/2) by frequency shifter 4 back laser frequencies; After this, laser passes through attenuator 12 again, is projected on the object under test 6 by lens 2; Part reflected light returns micro-slice laser 1 along original light path again, forms the light feedback; Because reflected light passes through frequency shifter 4 once more in return course, therefore, laser frequency is changed to (ω+Ω) when returning micro-slice laser 1; The feedback photoconduction of process shift frequency Ω causes laser optical power and is modulated, and modulating frequency is Ω, phase place and feedback outer cavity long correlation; The emergent light of micro-slice laser 1 converges on the photodetector 7 through spectroscope 3 reflection back scioptics 2, obtains reflecting the electric signal of laser power modulation, pass through signal conditioning circuit 10 again after, form measuring-signal.Sinusoidal signal is exported the sinusoidal signal that one tunnel frequency is Ω, amplitude stabilization, as the reference signal after the electric signal process reference signal generative circuit 9 of source 8 outputs takes place.Measuring-signal and reference signal are sent into quadrature phase-sensitive detector (PSD) 11 simultaneously, get final product the phase change information of measuring light power modulation signal, thereby obtain the displacement of object under test.This displacement measurement method based on light feedback phase measurement has two advantages: faint reflected light can produce the power modulation of certain amplitude, and then the reflectivity of testing sample and surface quality can be very low; The heterodyne phase measuring method can realize high-resolution phase measurement, and displacement resolution is better than 10nm in the experiment.But above-mentioned light feedback phase measurement method is subjected to the restriction of half-wavelength measurement range equally when being used for measuring surface form, therefore is restricted when discontinuous surfaces such as measurement step; And it is vulnerable to the influence from the stray reflected of sample different aspects equally when measuring low reflectivity sample, influence phase measurement accuracy.

Cofocus scanning is imaged on and is proposed by Minsky last century, owing to its characteristic with chromatography is generally paid attention to.Fig. 2 is common reflection-type confocal microscopic system synoptic diagram.The light that light source 21 sends is focused on the pin hole 23 by lens 22, by behind the pin hole from spectroscope 24 transmissions, converge on the measured object 25 by lens 22.Suppose that measured object 25 is desirable fully-reflected planes, it axially scans along lens 22.When object during in the focal plane, reflected light is focused on the pin hole 26 accurately, and this moment, detector 27 received a large amount of incident light energy.If reflecting surface is removed (dotted line Fig. 2) from the focal plane, then reflected light is focused on certain position of pin hole 26 fronts, this moment, the light intensity signal that receives of detector 27 weakened greatly, and promptly the signal that produces on point probe of out of focus face increases rapidly with defocusing amount and reduces.Further investigation shows that confocal microscope system not only can be suppressed to the weak parasitic light in the picture, and under identical image-forming condition, its lateral resolution is 1.4 times of common microscopic system, and has three-dimensional chromatography imaging function.Confocal microscopy has been applied to the measuring surface form field, and its advantage is to survey the variation of surperficial absolute position to be measured.But the axial resolution of simple confocal topography measurement method is because the influence of source noise and power excursion is restricted; And, the light intensity that point probe receives change and the object under test displacement between have certain non-linearly, the precision of topography measurement is restricted.

Summary of the invention

The purpose of this invention is to provide a kind of new topography measurement device, it has merged the high light feedback sensitivity of micro-slice laser, the high resolving power of heterodyne system light feedback phase measurement and the advantages such as Absolute position measurement of confocal system, solved in the past merely shortcoming based on the optical morphology measuring method of phase measurement or confocal method, can realize the high resolving power topography measurement on various reflectivity surface, especially can carry out the high resolving power measurement on the difficult discontinuous surface of low reflectivity sample of finishing of optical morphology measuring method in the past.

Figure 3 shows that measuring principle block diagram of the present invention.For micro-slice laser, when feedback light with respect to the frequency shift amount of endovenous laser during near the relaxation oscillation frequency of laser instrument, faint feedback light just can cause the laser optical power modulation of certain amplitude; Owing to adopted confocal smooth feedback light path, the height relief on testing sample surface affects feedback light intensity and phase place simultaneously, therefore also affects the amplitude and the phase place of laser power modulation; Detect the amplitude and the phase place of this laser power modulation simultaneously by the heterodyne measurement method, wherein, the half-wave that amplitude information is used for sample surfaces two point height differences several judgement of growing up, phase information is used for the half-wavelength decimal of this difference in height and measures; At last, grow up number and decimal information of comprehensive half-wave obtains on the sample surfaces 2 difference in height.Like this, the present invention has possessed advantages such as high sensitivity, wide range and high resolving power simultaneously, can satisfy the requirement of the discontinuous surface measurement of low reflectivity sample.

Measuring principle of the present invention is specific as follows:

The light field E (t) of single longitudinal mode laser in microchip output is:

E(t)＝E ₀exp[i(ωt+φ ₀)]，(1)

In the formula, the implication of each variable is: E ₀For light field becomes amplitude slowly, ω is a laser frequency, φ ₀Initial phase for shoot laser.

At exocoel, behind the outgoing light field E process shift frequency device (the shift frequency amount is Ω/2), to sample, after being reflected by sample, part light, turns back to laserresonator again once more by the shift frequency device through lens projects, form feedback light.Therefore, feedback light light field is:

E _inj(t)＝KE(t-τ)exp(iΩt)exp[-i(ω+Ω/2)τ]，(2)

In the formula, the implication of each variable is: K is a light feedback coefficient; τ is the time delay of feedback light at exocoel, and it is by the long decision of outer cavity.

The category-B laser instrument rate equation of considering the feedback influence of light is:

$\frac{\mathrm{dN}}{\mathrm{dt}}=\mathrm{\γ}(N_0-N)-\mathrm{BN}{\left|E\right|}^2,---\left(3\right)$

$\frac{\mathrm{dE}\left(t\right)}{\mathrm{dt}}=[i({\mathrm{\ω}}_c-\mathrm{\ω})+\frac{1}{2}(\mathrm{BN}-{\mathrm{\γ}}_c)]E\left(t\right)+{\mathrm{\γ}}_c{E}_{\mathrm{inj}}\left(t\right)$

In the formula, the implication of each variable is: N and N ₀Be respectively actual inverted population of laser instrument and small-signal inverted population; γ is the rate of decay of inverted population; γ _cRate of decay for light field in the chamber; B is einstein's stimulated radiation coefficient; ω _cBe respectively resonator cavity resonance frequency and practical laser frequency with ω.

Can be obtained by formula (3), the laser output power that the feedback of shift frequency light causes is modulated to relatively:

$\frac{\mathrm{\ΔP}}{P_s}=2K{\mathrm{\γ}}_c\frac{{({\mathrm{\η}}^2{\mathrm{\γ}}^2+{\mathrm{\Ω}}^2)}^{1/2}}{[{\mathrm{\η}}^2{\mathrm{\γ}}^2{\mathrm{\Ω}}^2+{({{\mathrm{\ω}}_R}^2-{\mathrm{\Ω}}^2)}^2{]}^{1/2}}\cos (\mathrm{\Ωt}-\mathrm{\ω\τ}+{\mathrm{\φ}}_s),---\left(4\right)$

In the formula, Δ P is the laser power modulation signal; P _sBe steady-state output power; η is the ratio of actual pump power and threshold pump power; ω _R=[(η-1) γ γ _c] ^1/2, be the relaxation oscillation frequency of micro-slice laser; φ _sFor additive phase and the ω τ that fixes has nothing to do.

According to formula (4), as the frequency shift amount Ω=ω of feedback light at exocoel _RThe time, it is maximum that the power modulation amplitude that it causes reaches:

$\frac{\mathrm{\ΔP}}{P_s}\≈\frac{2K}{\mathrm{\η}}\frac{{\mathrm{\γ}}_c}{\mathrm{\γ}};$ For micro-slice laser, γ _c/ γ can reach 10 ⁶Magnitude.This is equivalent to an amplification greatly to light feedback COEFFICIENT K; Therefore, when feedback light at the frequency shift amount of exocoel during near the relaxation oscillation frequency, micro-slice laser can show very high feedback luminous sensitivity, can be applicable to the occasion of Feebleness Light Signal Examining, and this also is the basis that the present invention can measure the low reflectivity sample surface topography.

According to formula (4), the phase=Ω t-ω τ+φ of luminous power modulation signal _s, wherein, (ω τ) directly reflected the long variation of outer cavity; The shift frequency amount Ω of feedback light realizes by frequency shifter, therefore, can obtain one road reference electrical signal E by the signal source that drives frequency shifter _r(t)=E _R0Cos (Ω t); With power modulation signal delta P and reference signal E _rSend into the quadrature phase-sensitive detector (PSD) simultaneously and carry out the heterodyne phase demodulation, variation that just can Measurement Phase item ω τ.In topography measurement, promptly corresponding to the height relief of sample surfaces, therefore, the present invention can realize the high resolving power measurement of surface topography by light feedback phase measurement method in the variation of outer cavity length.When phase measurement resolution is 1 when spending, the resolution of topography measurement reaches 1.5nm.

Yet simple light feedback phase measurement method also requires the height change of discontinuous pattern must be in the half wavelength scope when being used for measuring surface form, and this has limited its range of application.Light feedback phase measurement and confocal smooth Feedback Technology are merged in the present invention, utilize the Absolute position measurement ability of confocal system to carry out half-wave several the determining of growing up when discontinuous topography measurement, thereby have expanded the measurement capability of light feedback phase measurement greatly.

Fig. 4 is confocal smooth feedback principle schematic.Imagination sample 45 is an ideally-reflecting face, and the output light of micro-slice laser 41 converges at pin hole 43 places through lens 42, by converging on sample 45 surfaces through object lens 44 behind the pin hole 43.When sample 45 surfaces are positioned at object lens 44 focus places, have a large amount of reflected light and can pass through pin hole 43, form feedback light; When sample surfaces departs from the focal plane (dotted line among Fig. 4) of object lens 44, then most of light can not pass through pin hole 43 in the reflected light, and the feedback light intensity can weaken greatly.Therefore, in confocal smooth feedback system, finished the function of finite aperture light source and finite aperture detector simultaneously by single pin hole 43.Theoretical derivation shows that in confocal smooth feedback system, the defocusing amount u of light feedback COEFFICIENT K and sample surfaces satisfies

${\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="A20061011408800151.png"\; state="\{\{state\}\}">K</figure-callout>}}^2\&Proportional;[\frac{\sin (u/2)}{(u/2)}{]}^2.---\left(5\right)$

Can obtain the profile that concerns of laser power modulation amplitude A and defocusing amount u according to formula (4) and (5), as shown in Figure 5.If sample surfaces is arranged in the approximately linear zone a of Fig. 5 curve, then can utilize the variation of amplitude A roughly to assess the residing absolute position of sample surfaces.By the aperture of pin hole 43 and the enlargement ratio of object lens 44 among adjusting Fig. 4, can change width and the slope of the interval a of approximately linear of Fig. 5 curve.Select suitable parameters, make that the variation of the power modulation amplitude A that records can be differentiated when the absolute position of sample surfaces variation half wavelength, half-wave several judgement of growing up when amplitude A just can be used for topography measurement like this.Like this, the present invention can solve the restriction that SPA sudden phase anomalies in the feedback phase measurement method of delustering can not surpass the half-wavelength scope.The power modulation amplitude A can be passed through power modulation signal delta P and reference electrical signal E _rSend into simultaneously in the quadrature phase-sensitive detector (PSD) and obtain.

Finally, in the microcosmic surface topography measurement, the present invention uses half-wave that amplitude information A that the quadrature phase-sensitive detector (PSD) records carries out two point height difference Δ h on the sample surfaces the determining of several n of growing up, and is applied in 2 phase differential ( that record ₁- ₂) determine the half-wavelength decimal of difference in height, concrete calculating as shown in Equation (6):

In the formula, λ is a micro-slice laser output Wavelength of Laser.

The invention is characterized in, contain:

The micro-slice laser (1) of output single longitudinal mode, the output single longitudinal mode laser;

Lens (2) and spectroscope (3) are placed on this laser instrument transmitting terminal axis successively;

Frequency shifter (4) is acousto-optic frequency shifters, is placed on the transmitted light path of spectroscope (3), and the skew of Ω/2 takes place with respect to optical frequency ω in the laser chamber frequency of the laser of frequency shifter (4) output;

Confocal feedback module (5) is placed on the transmitted light path of frequency shifter (4) altogether, and this module (5) comprises lens (71), pin hole (72), lens (73) and the microcobjective of placing successively (74), wherein

Lens (71) converge at the transmitted light of frequency shifter (4) output on the pin hole (72),

Pin hole (72), transmitted light by pin hole (72) is collimated into parallel beam by lens (73), this parallel beam is focused on the surface of sample (6) by microcobjective (74), after being reflected by sample (6), part laser enters described confocal feedback module (5) altogether once more, pin hole (72) is in as confocal system in the pointolite, play the effect of point probe again, make and increase and weaken rapidly with the surperficial out of focus value of sample (6) by the described intensity of reflected light that is total to confocal feedback module (5), thereby cause the feedback light intensity to reduce, with the variation of the surperficial absolute position of assessment sample (6);

Another lens (2) and photodetector (7) are placed on the reflected light path of spectroscope (3) successively;

Source (8) takes place in sinusoidal signal, and output terminal links to each other with the input end of frequency shifter (4), and output frequency is the electric signal of Ω/2;

Reference signal generation circuit (9), the frequency in input end and described sinusoidal signal generation source (8) are that the electrical signal of Ω/2 links to each other;

Signal conditioning circuit (10), input end links to each other with the output terminal of described photodetector (7);

Quadrature phase-sensitive detector (PSD) (11), two input ends link to each other with the output terminal of described reference signal generation circuit (9) and signal conditioning circuit (10) respectively, demodulate the amplitude and the phase place of luminous power modulation signal simultaneously, so that in the topography measurement process, realize the grow up measurement of number and half-wavelength decimal of the half-wave of difference in height between last 2 of sample (6) surface successively respectively, draw the difference in height between surperficial last 2 of the sample (6) in view of the above;

Wherein, forming frequency when the reflected light of sample (6) generation passes through frequency shifter (4) once more is the feedback light of ω+Ω, modulates the Output optical power of described micro-slice laser (1) with the modulating frequency of Ω.

Lens (71), pin hole (72) and lens (73) in the described altogether confocal feedback module (5) are common optical axis, be positioned at successively under the described lens (2) with described spectroscope (3) on.

The present invention has following characteristics and good result:

Because micro-slice laser has very high light feedback sensitivity, the present invention is specially adapted to the sample topography of antiradar reflectivity or surface quality difference and measures.

The present invention has incorporated common confocal feedback module in micro-slice laser light feedback phase measuring system, make the intensity of light feedback produce significant change with the defocusing amount of sample surfaces is different, thereby the absolute position that can be used to assess sample surfaces changes, the several judgement of growing up of the half-wave when utilizing this information to carry out discontinuous measuring surface form.Therefore, compare with simple light feedback phase measurement method, the present invention can be applied to continuous surface simultaneously and have the discontinuous measuring surface form that suddenlys change greater than the half-wavelength pattern.

The present invention is owing to adopted common confocal feedback module, grow up in several decision problems having solved half-wave, system has also possessed the function of chromatography, the phase measurement error that the remaining reflected light of out of focus aspect causes in the time of can avoiding low reflectivity sample to measure, this also is the advantage that the present invention is different from existing topography measurement method.

Description of drawings

Fig. 1 is a micro-slice laser light feedback displacement measurement mechanism schematic diagram;

Fig. 2 is the confocal microscopic imaging schematic diagram;

Fig. 3 is a measuring principle block diagram of the present invention;

Fig. 4 is a confocal smooth feedback principle schematic of the present invention;

Fig. 5 is that laser power modulation amplitude A of the present invention and sample surfaces defocusing amount u concern synoptic diagram;

Fig. 6 is embodiment 1 structural drawing of laser confocal feedback micro measuring device of the present invention;

Fig. 7 is the example structure figure of confocal feedback module 5 altogether of the present invention;

Fig. 8 is embodiment 2 structural drawing of laser confocal feedback micro measuring device of the present invention;

Fig. 9 is one group of preliminary surveying result of embodiments of the invention.

Embodiment

The embodiment of laser confocal feedback micro measuring device of the present invention is described below in conjunction with accompanying drawing.

The structure of the embodiment of the invention 1 comprises as shown in Figure 6:

Export the micro-slice laser 1 of single longitudinal mode, and be placed on lens 2 and spectroscope 3 on this laser instrument transmitting terminal axis successively; Be placed on the frequency shifter 4 on spectroscope 3 transmitted light paths and be total to confocal feedback module 5; Be placed on lens 2 and photodetector 7 on spectroscope 3 reflected light paths; Source 8 takes place in sinusoidal signal, and its output terminal links to each other with the input end of frequency shifter 4 and reference signal generation circuit 9 simultaneously; Signal condition module 10, its input end links to each other with photodetector 7; Quadrature phase-sensitive detector (PSD) 11, its two input ends link to each other with the output terminal of reference signal generation circuit 9 and signal condition module 10 respectively.

The structure of the embodiment of described altogether confocal feedback module 5 comprises as shown in Figure 7: the lens 71 of Fang Zhiing, pin hole 72, lens 73 and microcobjective 74 successively.

The concrete principle of confocal laser feedback topography measurement device of present embodiment is as follows:

As shown in Figure 6, micro-slice laser 1 output single longitudinal mode laser behind lens 2 collimations, is divided into two bundles by spectroscope 3.The transmitted light of process spectroscope 3 is by behind the frequency shifter 4, skew has taken place with respect to optical frequency in the laser chamber (ω) in the frequency of laser, the electric signal frequency (Ω/2) of source 8 outputs takes place in the sinusoidal signal that side-play amount equals to drive frequency shifter 4, promptly becomes (ω+Ω/2) by frequency shifter 4 back laser frequencies.Behind frequency shifter 4, laser enters common confocal feedback module 5 (adopting embodiment shown in Figure 7), converge on the pin hole 72 by the lens 71 that are total in the confocal feedback module 5, expand into parallel beam by pin hole 72 backs by lens 73, parallel beam is focused on the surface of sample 6 by microcobjective 74.Part laser enters common confocal feedback module 5 after by sample 6 surface reflections once more.Pin hole 72 is brought into play the effect of pointolite and point probe in the confocal system simultaneously, the intensity of reflected light that makes it possible to by light feedback module 5 increases and weakens rapidly with the defocusing amount on sample 6 surfaces, thereby cause the feedback light intensity to reduce, the absolute position that therefrom can assess sample 6 surfaces changes.Pass through frequency shifter 4 once more by the sample reflected light that is total to confocal feedback module 5, frequency becomes (ω+Ω), return micro-slice laser 1 through spectroscope 3 and lens 2 again, formation feedback light; The feedback photoconduction causes laser optical power and is modulated, and modulating frequency is Ω, phase place and feedback outer cavity long correlation, and modulation amplitude is relevant with the feedback light intensity.The emergent light of micro-slice laser 1 converges on the photodetector 7 through spectroscope 3 reflection back scioptics 2, obtains reflecting the electric signal of laser power modulation, pass through signal conditioning circuit 10 again after, form measuring-signal.Sinusoidal signal is exported the sinusoidal signal that one tunnel frequency is Ω, amplitude stabilization, as the reference signal after the electric signal process reference signal generative circuit 9 of source 8 outputs takes place.Measuring-signal and reference signal are sent into quadrature phase-sensitive detector (PSD) 11 simultaneously, and it demodulates the amplitude and the phase place of power modulation signal simultaneously.Utilize the amplitude information of power modulation in the topography measurement process, to realize several the determining of growing up of the half-wave of two point height differences on the sample surfaces; Utilize the phase information of power modulation to carry out the half-wavelength decimal measurement of two point height differences on the sample surfaces; At last, grow up number and decimal information of comprehensive half-wave obtains on the sample surfaces 2 difference in height.

The structure of the embodiment of the invention 2 comprises as shown in Figure 8:

Export the micro-slice laser 1 of single longitudinal mode, and be placed on the lens 2 on this laser instrument transmitting terminal axis; Be positioned over lens 71, pin hole 72 and lens 73 in the described confocal feedback module 5 altogether under the lens 2 successively; Be placed on the spectroscope 3 under the lens 73; Be placed on frequency shifter 4 and microcobjective 74 on spectroscope 3 transmitted light paths; Be placed on lens 2 and photodetector 7 on spectroscope 3 reflected light paths; Source 8 takes place in sinusoidal signal, and its output terminal links to each other with the input end of frequency shifter 4 and reference signal generation circuit 9 simultaneously; Signal condition module 10, its input end links to each other with photodetector 7; Quadrature phase-sensitive detector (PSD) 11, its two input ends link to each other with the output terminal of reference signal generation circuit 9 and signal condition module 10 respectively.

Embodiment 2 is with the difference that embodiment 1 compares, and lens 71, pin hole 72 and the lens 73 in the described confocal feedback module 5 altogether are positioned under the described lens 2 and on the described spectroscope 3 successively; Like this, in light path is regulated, can avoid the pin hole place to produce the stray reflected of process shift frequency, reduce light path and regulate difficulty.

With embodiment 1 is that example specifies topography measurement method of the present invention, and concrete measuring process is as follows:

1) single longitudinal mode laser of micro-slice laser 1 output through lens 2 collimations, successively by frequency shifter 4 and confocal feedback module 5 altogether, is focused on the surface of sample 6 after spectroscope 3 transmissions; Part laser by sample 6 surface reflections after, by altogether confocal feedback module 5, frequency shifter 4, spectroscope 3 and lens 2, return micro-slice laser 1 once more, form feedback light; The feedback photoconduction causes laser optical power and is modulated, and modulating frequency is Ω, the chamber long correlation of phase place and feedback exocoel, and modulation amplitude is relevant with the feedback light intensity;

2) emergent light of micro-slice laser 1 converges on the photodetector 7 through spectroscope 3 reflection back scioptics 2, obtains reflecting the electric signal of laser power modulation, pass through signal conditioning circuit 10 again after, form measuring-signal;

3) after the electric signal process reference signal generative circuit 9 of source 8 outputs took place sinusoidal signal, exporting one tunnel frequency was the sinusoidal signal of Ω, amplitude stabilization, as the reference signal.

4) measuring-signal and reference signal are sent into quadrature phase-sensitive detector (PSD) 11 simultaneously, it demodulates the amplitude and the phase place of laser power modulation signal simultaneously; Utilize the variation of power modulation amplitude in topography measurement, to realize several the determining of growing up of the half-wave of two point height differences on the sample surfaces; Utilize the variation of power modulation phase place to carry out the half-wavelength decimal measurement of two point height differences on the sample surfaces; At last, grow up number and the decimal information processing of comprehensive half-wave obtains on the sample surfaces 2 difference in height.

The present invention has had both the high light feedback sensitivity of micro-slice laser, the high resolving power of heterodyne system light feedback phase measurement and the advantages such as Absolute position measurement of confocal system, estimate that longitudinal frame of the present invention is better than 10nm, the height that can survey the sudden change pattern is greater than 10 μ m, and can measure the pattern of low reflectivity sample.

The model of the main devices of embodiments of the invention and parameter:

Micro-slice laser 1 is the microplate Nd:YAG laser instrument of diode-end-pumped, and it exports single longitudinal mode laser; Frequency shifter 4 adopts acousto-optic frequency shifters; Altogether confocal feedback module 5 adopts embodiment shown in Figure 7, and wherein, the aperture of pin hole 72 is 100 μ m, microcobjective 74 be enlargement ratio 15 *, the object lens of numerical aperture 0.30; Photodetector 7 is a photodiode; Quadrature phase-sensitive detector (PSD) 11 adopts the two-phase lock-in amplifier.

For testing the feasibility of this measurement mechanism, (model: P762) tentatively demarcate this measurement mechanism, the nonlinearity erron of this micropositioner in 100 μ m stroke range is less than 5nm with the servo-controlled micropositioner of capacitance displacement sensor that has of German PI company., as measuring object it is fixed on the micropositioner with an aluminium workpiece that passes through milling, along with the micropositioner motion.Micropositioner moves 20 μ m, and Fig. 9 is one group of measurement result of test experiments.Horizontal ordinate is the displacement of targets that the built-in capacitance displacement sensor of micropositioner records, and the ordinate left side is the result after this measurement mechanism phase measurement is converted into displacement of targets, and ordinate the right is the result of this measurement mechanism amplitude measurement.This result shows that this measurement mechanism can realize high sensitivity, high resolving power topography measurement, and the amplitude information that records can be realized half-wave several judgement of growing up.

Claims (2)

1. a laser confocal feedback micro measuring device is characterized in that, contains:

The micro-slice laser (1) of output single longitudinal mode, the output single longitudinal mode laser;

Lens (2) and spectroscope (3) are placed on this laser instrument transmitting terminal axis successively;

Frequency shifter (4) is acousto-optic frequency shifters, is placed on the transmitted light path of spectroscope (3), and the skew of Ω/2 takes place with respect to optical frequency ω in the laser chamber frequency of the laser of frequency shifter (4) output;

Confocal feedback module (5) is placed on the transmitted light path of frequency shifter (4) altogether, and this module (5) comprises lens (71), pin hole (72), lens (73) and the microcobjective of placing successively (74), wherein

Lens (71) converge at the transmitted light of frequency shifter (4) output on the pin hole (72),

Pin hole (72), transmitted light by pin hole (72) is collimated into parallel beam by lens (73), this parallel beam is focused on the surface of sample (6) by microcobjective (74), after being reflected by sample (6), part laser enters described confocal feedback module (5) altogether once more, pin hole (72) is in as confocal system in the pointolite, play the effect of point probe again, make and increase and weaken rapidly with the surperficial out of focus value of sample (6) by the described intensity of reflected light that is total to confocal feedback module (5), thereby cause the feedback light intensity to reduce, with the variation of the surperficial absolute position of assessment sample (6);

Another lens (2) and photodetector (7) are placed on the reflected light path of spectroscope (3) successively;

Source (8) takes place in sinusoidal signal, and output terminal links to each other with the input end of frequency shifter (4), and output frequency is the electric signal of Ω/2;

Reference signal generation circuit (9), the frequency in input end and described sinusoidal signal generation source (8) are that the electrical signal of Ω/2 links to each other;

Signal conditioning circuit (10), input end links to each other with the output terminal of described photodetector (7);

Quadrature phase-sensitive detector (PSD) (11), two input ends link to each other with the output terminal of described reference signal generation circuit (9) and signal conditioning circuit (10) respectively, demodulate the amplitude and the phase place of luminous power modulation signal simultaneously, so that in the topography measurement process, realize the grow up measurement of number and half-wavelength decimal of the half-wave of difference in height between last 2 of sample (6) surface successively respectively, draw the difference in height between surperficial last 2 of the sample (6) in view of the above;

Wherein, forming frequency when the reflected light of sample (6) generation passes through frequency shifter (4) once more is the feedback light of ω+Ω, modulates the Output optical power of described micro-slice laser (1) with the modulating frequency of Ω.

2. laser confocal feedback micro measuring device according to claim 1 is characterized in that:

Lens (71), pin hole (72) and lens (73) in the described altogether confocal feedback module (5) are common optical axis, be positioned at successively under the described lens (2) with described spectroscope (3) on.

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