CN103076162A - Device for measuring period of sub-wavelength grating - Google Patents

Abstract

The invention discloses a device for measuring the period of a sub-wavelength grating. The device for measuring the period of the sub-wavelength grating consists of a standard grating and a metal-medium multilayer film, wherein the metal-medium multilayer film is formed by arranging a plurality of medium layers and a plurality of metal layers at intervals; the upper layer of the medium layers is located below the standard grating, and the bottom layer of the metal layers is located above the standard grating; linearly-polarized incident light with an electric field direction which is vertical with a direction of the standard grating irradiates to the standard grating; the standard grating generates multistage diffracted waves with high space frequency, and is used for filtering through the metal-medium multilayer film; the filtered diffracted waves and grating difference frequency to be measured form long-period interference fringes capable of being observed; and finally, the interference fringes are observed and measured, and the grating period to be measured can be determined.

Description

The measuring element in a kind of sub-wave length grating cycle

Technical field

The present invention relates to the method for testing in a kind of novel sub-wave length grating cycle, concrete principle is based on metal-dielectric multilayer film filtering characteristic, carries the interference fringe of sub-wave length grating information to be measured by observation and determines the grating cycle.

Background technology

Along with miniaturization and the integrated degree of electronic devices and components are more and more higher, nanoscale science and technology has caused people's extensive concern, has huge application prospect in fields such as medical treatment detection, national defense and military.Wherein diffraction limit becomes restriction and directly utilizes one of principal element of optical instrument observation microtexture, and the wave vector of part carrying object information exists with the form of evanescent wave, on the surface of object, can't be participated in the far field imaging by local.In a series of solution, by to the lining by line scan of microtexture, realize the imaging of Surface Structures pattern based on the atomic force microscope of probe structure; Also be that scanning by body structure surface is to observe the optical characteristics on surface based on the SNOM microscope of fibre-optical probe in addition.But above formation method all needs the lining by line scan of object, and real-time is relatively poor, and process means is complicated, and cost costliness etc. are unfavorable for the system integration.

Summary of the invention

The objective of the invention is the deficiency that exists for prior art, the method for testing in a kind of sub-wave length grating cycle based on the metal-dielectric multi-layer film structure is provided.The method has not only been simplified process means, has more increased design flexibility, real-time, has very strong practical value.

For realizing described purpose, the measuring element in a kind of sub-wave length grating cycle of the present invention is characterized in that: be comprised of master grating and metal medium multilayer film, the metal-dielectric multilayer film is separately placement by multilayered medium layer and multiple layer metal layer; The upper strata of dielectric layer is positioned at the below of master grating, the bottom of metal level is positioned at grating to be measured top, the linear polarization incident illumination of direction of an electric field and master grating perpendicular direction is mapped on the master grating, master grating produces the multistage diffracted wave that carries high spatial frequency, and by the filtering of metal medium multilayer film; Filter transmitted wave and grating difference frequency to be measured and form the long period interference fringe that to observe; Observe at last and measure interference fringe and determine the grating cycle to be measured.

Technical solution of the present invention is:

The characteristics that the present invention compared with prior art has are: on the basis of the super diffraction transmittability of metal-dielectric multi-layer film structure, utilize the Spatial Filtering Effect of multilayer film, the high spatial frequency diffracted wave of master grating structure generation is carried out filtering.Then observe and measure the interference fringe that produces through ripple and grating difference frequency to be measured, finish the detection for the treatment of the photometry grid cycle.With respect to common super image device, the method has not only been simplified process means, has more increased design flexibility, real-time, has very strong practical value.

Description of drawings

Fig. 1 is the embodiment of the invention test sectional view in designed sub-wave length grating cycle;

Fig. 2 is the embodiment of the invention test vertical view in designed sub-wave length grating cycle;

Fig. 3 is the metal-dielectric multi-layer film structure spatial filtering curve in the embodiment of the invention test in designed sub-wave length grating cycle;

Fig. 4 is the interference fringe analogous diagram of the test in designed sub-wave length grating cycle of the embodiment of the invention;

The interference fringe lab diagram of the test in designed sub-wave length grating cycle of embodiment of the invention during Fig. 5.

Embodiment

The below elaborates to embodiments of the invention, and the present embodiment is implemented under take technical solution of the present invention as prerequisite, provided detailed embodiment and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

See also Fig. 1, Fig. 1 and Fig. 2 are the test structure figure in sub-wave length grating cycle of the present invention.As shown in Figure 2, the present invention is comprised of master grating 1 and metal medium multilayer film, and the metal medium multilayer film is separately placement by multilayered medium layer 2 and multiple layer metal layer 3; The upper strata of dielectric layer 2 is positioned at the below of master grating 1, the bottom of metal level 3 is positioned at grating to be measured 4 tops, the linear polarization incident illumination of direction of an electric field and master grating perpendicular direction is mapped on the master grating 1, master grating 1 produces the multistage diffracted wave that carries high spatial frequency, and by the filtering of metal medium multilayer film; Filter transmitted wave and grating to be measured 4 difference frequencies and form the long period interference fringe that to observe; Observe at last and measure interference fringe and determine 4 cycles of grating to be measured.

Wherein, master grating 1 is consistent with grating 4 arragement directions to be measured.

Wherein, described metal medium multi-layer film structure has the evanescent wave transmittability.

Wherein, under service band, utilize metal medium multilayer film selectivity see through+n and-diffraction light of the master grating 1 of n level time, n be master grating 1 excite the order of diffraction time.

Wherein, the thickness of every layer of metal film 3 is chosen in 10 nanometers to 100 nanometers, and material is a kind of in can metal gold, silver, copper or the aluminium of excitating surface plasma.

The concrete steps of the embodiment of the invention are as follows:

Step 1: operation wavelength is elected 532 nanometers as, and incident light polarization state is elected the direction of an electric field linear polarization pattern vertical with grating orientation as.

Step 2: master grating 1 and grating to be measured 4 materials are selected respectively cadmium and the silicon of high index of refraction.

Step 3: master grating 1 and 4 cycles of grating to be measured are selected respectively 400 nanometers and 210 nanometers.

Step 4: after incident light incided master grating 1, the high frequency spatial diffracted wave of generation can be determined by following formula:

$k_x=k_0\sin \mathrm{\θ}+\frac{2\mathrm{\π}}{T_{\mathrm{up}}}n,(n=0,\±1,\±2,...)---\left(1\right)$

K wherein ₀Be free space wave vector, T _UpBe the cycle of master grating 1, θ is incident light and the angle of vertical normal, is that 0, n is the order of diffraction time during normal incidence.According to step 1, step 3, be 1.33n * k through exciting the spatial frequency that produces behind the grating ₀

Step 5: the dielectric layer in the preiodic type multi-layer film structure is chosen as silicon dioxide, and metal level is chosen as silver.

Step 6: the thickness of the dielectric layer in the preiodic type multi-layer film structure is chosen as 20 nanometers, and the thickness of metal level is chosen as 30 nanometers.

Step 7: for the preiodic type silver of step 5, step 6 design-silicon dioxide multi-layer film structure, its optical transfer function (Optical Transfer Functions, OTF) can be calculated by the rigorous coupled wave theory, as shown in Figure 3.The first rank and the 3rd rank diffracted wave frequency are respectively 1.33 * k ₀With 3.99 * k ₀, be transmission to pass through the metal-dielectric multi-layer film structure.Second-order diffracted wave frequency 2.66 * k is only arranged ₀Can produce transmission.

Step 8: form interference fringe through the frequency after the multilayer film filtration and grating to be measured 4 difference frequencies, wherein the relation of Filter frequency, 4 cycles of grating to be measured and fringe period satisfies following formula:

$T_{\mathrm{down}}=\frac{T_{\mathrm{interference}}\×T_{\mathrm{up}}}{n\×T_{\mathrm{interference}}-T_{\mathrm{up}}}---\left(2\right)$

T wherein _DownBe 4 cycles of grating to be measured, T _DownBe the cycle of master grating 1, T _InterferenceBe final observation fringe period.The cycle that can be obtained final interference fringe by Fig. 4 is 4.2 microns, with formula 2 to coincideing, be 20 times of cycles 210 nanometer of grating 1 to be measured.

Designed the actual experiment sample according to above-mentioned parameter, incident wavelength is selected 532 nanometers, the cycle of master grating 1 is 400 nanometers, grating 4 to be measured is 201 nanometers, and single silver thickness is 20 nanometers, and the individual layer silicon dioxide thickness is 30 nanometers, observing the long period interference fringe through charge coupled device CCD is 29.98 microns, as shown in Figure 5, be 150 times of grating 4 to be measured, experimental result has further been verified emulation and theoretical accuracy.The method has not only been simplified process means, and has increased design flexibility, real-time.

The above; only be the embodiment among the present invention, but protection scope of the present invention is not limited to this, anyly is familiar with the people of this technology in the disclosed technical scope of the present invention; conversion or the replacement expected can be understood, all of the present invention comprising within the scope should be encompassed in.

Claims (6)

1. the measuring element in a sub-wave length grating cycle is characterized in that: be comprised of master grating and metal medium multilayer film, the metal-dielectric multilayer film is to place separately by multilayered medium layer and multiple layer metal layer; The upper strata of dielectric layer is positioned at the below of master grating, the bottom of metal level is positioned at grating to be measured top, the linear polarization incident illumination of direction of an electric field and master grating perpendicular direction is mapped on the master grating, master grating produces the multistage diffracted wave that carries high spatial frequency, and by the filtering of metal medium multilayer film; Filter transmitted wave and grating difference frequency to be measured and form the long period interference fringe that to observe; Observe at last and measure interference fringe and determine the grating cycle to be measured.

2. the measuring element in sub-wave length grating cycle according to claim 1 is characterized in that, master grating is consistent with grating arragement direction to be measured.

3. the measuring element in sub-wave length grating cycle according to claim 1 is characterized in that, described metal medium multi-layer film structure has the evanescent wave transmittability.

4. the measuring element in sub-wave length grating cycle according to claim 1 is characterized in that, under service band, utilize metal medium multilayer film selectivity see through+n and-the master grating diffraction light of n level time, n be master grating excite the order of diffraction time.

5. the measuring element in sub-wave length grating cycle according to claim 1 is characterized in that, the thickness of every layer of metal film is chosen in 10 nanometers to 100 nanometers, and material is a kind of in can metal gold, silver, copper or the aluminium of excitating surface plasma.

6. the measuring element in sub-wave length grating cycle according to claim 1 is characterized in that, the test period of grating to be measured is:

$T_{\mathrm{down}}=\frac{T_{\mathrm{interference}}\×T_{\mathrm{up}}}{n\×T_{\mathrm{interference}}-T_{\mathrm{up}}}$

T wherein _DownBe grating to be measured cycle, T _UpBe master grating cycle, T _InterferenceBe final observation fringe period, n be master grating excite the order of diffraction time.

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