CN100541113C - Sub nano grade double frequency laser interferometer signal subdivision system - Google Patents

Abstract

Sub nano grade double frequency laser interferometer signal subdivision system, comprise measuring-signal and reference signal pre-process circuit, the numeral phase discriminator, master clock signal generation circuit, the phase shifter group, counting circuit, counter group and arithmetic processing circuit, measurement and reference signal pre-process circuit are finished the Photoelectric Detection of measuring-signal and reference signal respectively, amplify, after filtering and the shaping, after being output as two-way square wave digital signal, send into digital phase discriminator and carry out phase demodulation, the rising edge of numeral phase discriminator output signal drives major clock generation circuit clocking, and driving counting circuit counting, the phase shifter group is carried out accurate phase shift to the clock signal that major clock generation circuit produces, and actuation counter batch total number; The negative edge of numeral phase discriminator output signal is as the stop control signal of counting circuit sum counter group; The result draws final segmentation result after sending into the arithmetic processing circuit computing.The present invention makes the measuring accuracy of two-frequency laser interferometer reach Subnano-class, has the characteristics of high precision, high reliability.

Description

Sub nano grade double frequency laser interferometer signal subdivision system

Technical field

The present invention is a kind of signal subdivision system of Subnano-class, is applied in the double-frequency laser interferometry system, can be widely used in VLSI (very large scale integrated circuit) process equipment, precision machine tool etc. at aspects such as linear movement measuring, error correction and controls.

Background technology

China lags behind developed country in the VLSI (very large scale integrated circuit) field of making always, one of them major reason is exactly the backwardness of China's lithographic equipment development level, and the critical bottleneck that the restriction lithographic equipment improves is exactly the high precision measuring system that does not have independent development.Two-frequency laser interferometer is laser one of the most successful application in metering field, is the length measuring instrument of tool authority in the lithographic equipment, is the indispensable survey instrument of precision optical machinery industry.In theory, signal is not segmented, then measuring accuracy can only reach 1/2nd of laser source wavelength, and this precision does not all reach the resolving power requirement in a lot of application scenarios, especially in the measuring system of lithographic equipment.And to improve measuring accuracy, and then must signal be segmented, therefore segmenting functional module is the core ingredient that two-frequency laser interferometer improves resolution.Traditional divided method based on phaselocked loop is subject to the translational speed of electron device and measurement target, and also is subject to counter based on the digital phase demodulation divided method of filling out pulse, and is therefore very limited to the raising of precision.

Summary of the invention

Technology of the present invention is dealt with problems: overcome the deficiencies in the prior art, provide a kind of subdivision accuracy high sub nano grade double frequency laser interferometer signal subdivision system.

Technical solution of the present invention is: sub nano grade double frequency laser interferometer signal subdivision system, comprise the measuring-signal pre-process circuit, the reference signal pre-process circuit, the numeral phase discriminator, master clock signal generation circuit, the phase shifter group, counting circuit, counter group and arithmetic processing circuit, measuring-signal pre-process circuit and reference signal pre-process circuit are finished the Photoelectric Detection of measuring-signal and reference signal respectively, amplify, after filtering and the shaping, after being output as two-way square wave digital signal, send into digital phase discriminator and carry out phase demodulation, output has the digital pulse signal of certain width, the rising edge of numeral phase discriminator output signal drives major clock generation circuit clocking, and driving counting circuit counting, the phase shifter group is carried out accurate phase shift to the clock signal that major clock generation circuit produces, and actuation counter batch total number; The negative edge of numeral phase discriminator output signal is as the stop control signal of counting circuit sum counter group; After counting finished, the result drew final segmentation result after sending into the arithmetic processing circuit computing.

Principle of the present invention: the present invention has introduced the phase shifter group of being made up of K phase shifter, and the clock of master clock generator output is carried out phase shift and the actuation counter group is counted.The numeral phase discriminator carries out phase demodulation to measuring-signal and reference signal, be output as the digit pulse of certain width, the counter group is counted under the control of phase demodulation output, because the effect of phase shifter, difference will inevitably appear in the output of counter group, promptly from some counters of counter group, its counting output can be different with the output of all counters before this counter.If write down the position of this counter, and just can obtain segmenting the result by the processing of arithmetic processing circuit.If the counting of counting circuit is output as N ₁, and the position that begins the counter of occurrence count output difference in the counter group at first is that (0≤n≤K) then obtains segmenting result's (non-integer segment count) and is n: ε=(N ₁-1) * K+n.

The present invention's advantage compared with prior art is: the present invention has higher subdivision accuracy, and more stable and reliable.Traditional can only reach one tens or several percent of optical maser wavelength based on its subdivision accuracy of the divided method of filling out pulse, because the introducing of phase shifter group, make subdivision accuracy on based on the basis of the divided method of filling out pulse, to improve K doubly, thereby improved subdivision accuracy widely, made the present invention can satisfy the requirement that high-accuracy manufacture field is used.In addition, the present invention adopts high-speed digital circuit to realize having higher stability and reliability than traditional subdivision system.

Description of drawings

Fig. 1 is a system architecture synoptic diagram of the present invention;

Fig. 2 is the measuring-signal pre-service structural representation among Fig. 1;

Fig. 3 is the phase shifter group structural representation among Fig. 1;

Fig. 4 is the counter group structural representation among Fig. 1.

Embodiment

As shown in Figure 1, the embodiment of the invention is made up of measuring-signal pre-process circuit 1, reference signal pre-process circuit 2, digital phase discriminator 3, master clock signal generation circuit 4, phase shifter group 5, counting circuit 6, counter group 7 and arithmetic processing circuit 8, after measuring-signal pre-process circuit 1 and reference signal pre-process circuit 2 are finished Photoelectric Detection, amplification, filtering and the shaping of measuring-signal and reference signal respectively, after being output as two-way square wave digital signal, send into digital phase discriminator 3 and carry out phase demodulation, be output as the digital pulse signal of certain width.The rising edge of numeral phase discriminator 3 output signals drives major clock generation circuit 4 clockings, and driving counting circuit 6 countings, 5 pairs of major clock generations of phase shifter group circuit, 4 clockings carry out accurate phase shift, and actuation counter group 7 countings, the negative edge of digital phase discriminator 3 output signals is as the stop control signal of counter 6 sum counter groups 7.After counting finished, the result drew final segmentation result after sending into arithmetic processing circuit 8 computings.

Segmentation measuring accuracy computing formula:

$\mathrm{resolution}=\frac{f_{\mathrm{laser}}}{f_1\·(k+1)}\·\frac{\mathrm{\λ}}{N}$

Wherein: f _LaserBe signal frequency, f ₁Be the clock frequency of major clock generation circuit 4 outputs, K is the phase shift factor, and N is the optical frequency-doubling number.F in the embodiment of the invention _LaserBe 2.5MHZ, f ₁Be 80MHZ, K is 15, N=2, and then final precision is λ/1024 (0.6nm).K generally elects 2 as ⁿ-1 (n is a positive integer); N generally is taken as 2 by the structural design decision of two-frequency laser interferometer.

As shown in Figure 2, measuring-signal pre-process circuit 1 is by photoelectric switching circuit 11, operational amplification circuit 12, filtering circuit 13, shaping circuit 14 is formed, photoelectric switching circuit 11 receives the light signal of instrument output and converts thereof into electric signal, the effect of operational amplification circuit 12 is that photoelectric switching circuit 11 output electric signal are amplified, make it satisfy the subsequent conditioning circuit processing requirements, the effect of filtering circuit 13 is the high frequency noises in the filtered signal, and the effect of shaping circuit 14 is the digital pulse signals that the sinusoidal signal of filtering circuit 13 outputs are shaped as suitable digital device processing.Reference signal pre-process circuit 2 is similar to the above-mentioned structure and the course of work.

That numeral phase discriminator 3 adopts is the high speed 3 attitude ECL phase frequency detector chip MC100EP140DG of An Meisen semiconductor company.

Master clock signal generation circuit 4 is a high accurate clock signal generation circuit, employing be the NB4N441MNR2G of An Meisen semiconductor company, its t _Jitter(Typ)=3.5 (ps).

As shown in Figure 3, the accurate phase shifter group of phase shifter group 5 high precision, error≤2%.It by phase shifter 51, phase shifter 52, phase shifter 53 and phase shifter 5K altogether K transposer form.The characteristic of each phase shifter is all identical, and effect is to make input signal move particular phases output, actuation counter group 7 countings.

As shown in Figure 4, counter group 7 by counter 71, counter 72, counter 73 and counter 7K altogether K counter form.The characteristic of each counter is all identical, and effect is that 5 corresponding transposer outputs are counted to the phase shifter group.

Arithmetic processing circuit 8 is made up of the EPM240 chip of altera corp, and major function is the segmentation value that goes out the non-integer segment count of measurement result according to the position calculation that counting in the output of major clock counter and the counter group begins to occur difference.

Claims (1)

1, sub nano grade double frequency laser interferometer signal subdivision system, it is characterized in that: comprise measuring-signal pre-process circuit (1), reference signal pre-process circuit (2), digital phase discriminator (3), master clock signal generation circuit (4), phase shifter group (5), counting circuit (6), counter group (7) and arithmetic processing circuit (8), described phase shifter group (5) is formed by K all identical phase shifter serial connection of characteristic, and described counter group (7) is made up of K all identical counter of characteristic; Measuring-signal pre-process circuit (1) and reference signal pre-process circuit (2) are finished the Photoelectric Detection of measuring-signal and reference signal respectively, amplify, after filtering and the shaping, after being output as two-way square wave digital signal, send into digital phase discriminator (3) and carry out phase demodulation, output has the digital pulse signal of certain width, the rising edge of numeral phase discriminator (3) output signal drives major clock generation circuit (4) clocking, and driving counting circuit (6) counting, phase shifter group (5) is carried out accurate phase shift to the clock signal that major clock generation circuit (4) produces, and actuation counter group (7) counting; The negative edge of numeral phase discriminator (3) output signal is as the stop control signal of counting circuit (6) sum counter group (7); After counting finished, the result drew final segmentation result after sending into arithmetic processing circuit (8) computing.

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