CN102607435B - Device and method for measuring thickness of optical film by adopting double-slit interference method - Google Patents

Abstract

The invention relates to a device for measuring the thickness of an optical film and method for realizing the same, in particular to a device and method for measuring the thickness of an optical film by adopting the double-slit interference method, aiming to solve the problem of low measurement precision of the existing method for measuring the thickness of the optical film. The device is characterized in that a polarized light beam ejected vertically to a light barrier covers a first slit and second slit on the light barrier, the polarized light beam is transmitted by the optical film to be measured and ejected by the first slit so that a first polarized light is formed, the polarized light beam is transmitted by the optical film to be measured and ejected by the second slit so that a second polarized light is formed, the first polarized light and the second polarized light are both ejected on the detection surface of a CCD (charge-coupled device) detector, and interference fringes are formed, wherein the detection surface of the CCD detector is parallel to the light barrier. The method comprises the following steps: taking any one section of interference fringes to match with the light intensity formula to obtain the optical path difference caused by the optical film to be measured, thereby obtaining the thickness of the optical film to be measured.

Description

The device that utilizes two-slit interference method to measure optical film thickness is realized the method for measuring optical film thickness

Technical field

The present invention relates to a kind of device and method of measuring optical film thickness.

Background technology

Along with the widespread use of thin film technique and photoelectric device, optical thin film has been widely used in dual-use device production.Optical thin film is as a kind of phase that is independent of the existence of body material, the electrical and optical properties that has many uniquenesses, when these character depend on optical thin film manufacture craft, also closely related with optical film thickness, thus thickness measure for the optics of optical thin film material, the research of electrical properties is very important.

Film thickness is one of key parameter during film design and technique are manufactured, fast development along with photoelectric technology and microelectric technique, the application of film is more and more wider, various thickness only have hundreds of even the single or multiple lift function film of tens nanometer become the focus of present material research, making accurately to measure film thickness becomes the hot issue in thin film technique research field.Therefore, accurately determine that thickness and optical constant are significant for the character of research film.

Interference of light metrological testing technology be take wavelength as measurement unit, is a kind of generally acknowledged high-precision measuring measuring technology.Much precision measurement work is all that the method with the interference of light realizes.What interferometer was exported is a width interferogram, by mathematics physics model, interferogram can be associated with multiple measured parameter, thereby realize, measures relevant physical parameter.Phase shift interference art is incorporated into digital phase-shifting technique technology in interferometry technology and grows up, and is widely used in recent years.

At present measuring method is mainly divided into triangulation and phase measurement: the simplest triangulation system is to be irradiated to testee surface from light source transmitting light beam, by the position of imaging sem observation reflection light point, thereby calculates the displacement of object point; Due to incident and a triangle of reflected light formation, so be called triangulation; Phase measurement is to adopt the reflection of incident light testee upper and lower surface, when meeting certain requirements, reflected light just there will be interference fringe, the depth information of body surface will be modulated with position mutually to the amplitude of striped, adopt certain algorithm the phase place of carrying object depth information can be changed to demodulation out, thereby obtain the thickness information of object.

Triangulation device is simple, be suitable for measuring the non-cpntact measurement of roughness of machining surface, but measuring accuracy is lower.Phase measurement measuring accuracy is enough high, but installs relative complex.

Summary of the invention

The present invention is in order to solve the low problem of measuring accuracy of the method for existing optical film thickness, thereby a kind of device and method that utilizes two-slit interference method to measure optical film thickness is provided.

Utilize two-slit interference method to measure the device of optical film thickness, it comprises light barrier and ccd detector; On light barrier, have a slit and No. two slits; Optical thin film to be measured covers and is fixed on the plane of incidence of a slit;

Vertical incidence covers a slit and No. two slits on light barrier to the light beam of light barrier, and this light beam forms the first bundle polarized light through optical thin film transmission to be measured and through a slit outgoing; No. two slit outgoing of this light beam form the second bundle polarized light;

The first bundle polarized light and the second bundle polarized light are all incident on the test surface of ccd detector, and form interference fringe, and test surface and the light barrier of ccd detector are parallel to each other.

A slit and No. two slits are parallel to each other, and the longitudinal cross-section of the longitudinal cross-section of a slit and No. two slits is positioned on same perpendicular.

The two-slit interference method that utilizes based on said apparatus is measured the method for optical film thickness, and it is realized by following steps:

In step 1, the interference fringe that forms on test surface at ccd detector at the first bundle polarized light and the second bundle polarized light, appoint and get one section of interference fringe and formula:

$I\left(P\right)=\frac{c^2{E}^2}{{r_1}^2}+\frac{E^2}{{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA0000147503660000011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}^2}+\frac{{2\mathrm{<figure-callout\; id="2"\; label="cE"\; filenames="HDA0000147503660000011.png"\; state="\{\{state\}\}">cE</figure-callout>}}^2\cos [k(r_1+r_2)+\mathrm{\&delta;}]}{r_1{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA0000147503660000011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}$

Carry out matching, obtain the optical path difference δ that optical thin film to be measured causes;

In formula: I (P) is the dry light intensity of penetrating striped that the first bundle polarized light and the second bundle polarized light form at the some P place of ccd detector; r ₁for the exit facet of a slit on the light barrier distance to some P, and r ₁=D/cos β; D is the distance of light barrier and ccd detector; β is r ₁with z axle clamp angle;

R ₂for No. two slits on light barrier exit facet to P point distance, and r ₂=D/cos θ; θ is r ₂with z axle clamp angle;

C is the uptake of optical thin film to be measured to polarized light; E is the amplitude of polarized light; K is wave vector;

Step 2, according to formula:

$L=\frac{\left|\mathrm{\&delta;}\right|}{k(n-n_0)}$

Obtain the thickness L of optical thin film to be measured; Complete the measurement of the thickness for the treatment of photometry film;

In formula: n is refractive index, the n of polarized light in optical thin film to be measured ₀for polarized light refractive index in a vacuum.

Beneficial effect: measurement mechanism of the present invention is simple in structure, the precision of measuring optical film thickness is high, and can not destroy testing sample.

Accompanying drawing explanation

Fig. 1 is the structural representation of apparatus of the present invention; Fig. 2 be in the present invention except parameter δ in the situation of all the other parameter constants, interference light intensity is with the variation schematic diagram of x.

Embodiment

Embodiment one, in conjunction with Fig. 1, this embodiment is described, utilizes two-slit interference method to measure the device of optical film thickness, it comprises light barrier 2 and ccd detector 3; On light barrier 2, have a slit 21 and No. two slits 22; Optical thin film 1 to be measured covers and is fixed on the plane of incidence of a slit 21;

Vertical incidence covers a slit 21 and No. two slits 22 on light barrier 2 to the light beam of light barrier 2, and this light beam forms the first bundle polarized light through optical thin film 1 transmission to be measured and through slit 21 outgoing; 22 outgoing of No. two slits of this light beam form the second bundle polarized light;

The first bundle polarized light and the second bundle polarized light are all incident on the test surface of ccd detector 3, and form interference fringe, and the test surface of ccd detector 3 and light barrier 2 are parallel to each other.

Present embodiment can be measured the thickness of transparent material to be measured when known incident optical wavelength and refractive index of transparent materials by the side-play amount of interference fringe and mark center, the absorption of transparent material is on measuring without impact.

In present embodiment, be particularly suitable for being less than the optical film thickness measurement of incident wavelength.

The difference that utilizes two-slit interference method to measure the device of optical film thickness described in embodiment two, this embodiment and embodiment one is, a slit 21 and No. two slits 22 are parallel to each other, and the longitudinal cross-section of the longitudinal cross-section of a slit 21 and No. two slits 22 is positioned on same perpendicular.

Embodiment three, the two-slit interference method that utilizes based on embodiment one are measured the method for optical film thickness, and it is realized by following steps:

Step 1, in the first bundle polarized light and the second interference fringe of forming on the test surface of ccd detector 3 of bundle polarized light, appoint and get one section of interference fringe and formula:

$I\left(P\right)=\frac{c^2{E}^2}{{r_1}^2}+\frac{E^2}{{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA0000147503660000011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}^2}+\frac{{2\mathrm{<figure-callout\; id="2"\; label="cE"\; filenames="HDA0000147503660000011.png"\; state="\{\{state\}\}">cE</figure-callout>}}^2\cos [k(r_1+r_2)+\mathrm{\&delta;}]}{r_1{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA0000147503660000011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}$

Carry out matching, obtain the optical path difference δ that optical thin film 1 to be measured causes;

In formula: I (P) is the dry light intensity of penetrating striped that the first bundle polarized light and the second bundle polarized light form at the some P place of ccd detector 3; r ₁for the exit facet of a slit 21 on light barrier 2 distance to some P, and r ₁=D/cos β; D is the distance of light barrier and ccd detector 3; β is r ₁with z axle clamp angle;

R ₂for No. two slits on light barrier 2 exit facet to P point distance, and r ₂=D/cos θ; θ is r ₂with z axle clamp angle;

C is the uptake of 1 pair of polarized light of optical thin film to be measured; E is the amplitude of polarized light; K is wave vector;

Step 2, according to formula:

$L=\frac{\left|\mathrm{\&delta;}\right|}{k(n-n_0)}$

Obtain the thickness L of optical thin film 1 to be measured; Complete the measurement of the thickness for the treatment of photometry film 1;

In formula: n is refractive index, the n of polarized light in optical thin film 1 to be measured ₀for polarized light refractive index in a vacuum.

Present embodiment has high measuring accuracy, is applicable to not destroying in the situation of sample measuring tiny sampler.

Principle: optical thin film 1 to be measured is positioned over to the upper slit outside of light barrier 2, optical thin film to be measured is in the xy in xyz space plane, then along optical path direction successively fixed barriers 2 and ccd detector 3; Equally distributed y direction linearly polarized light vertical incidence light barrier 2, incident light at ccd detector 3 interference imagings, forms interference fringe through two slits on light barrier 2; Because the slit width on light barrier 2 is very little, emergent light can be thought the spherical wave that point source sends; Because incident light is y direction linearly polarized light, in the communication process of light, electric field direction of vibration is identical all the time, on CCD, P point light intensity is the relevant superposition that the spherical wave of two slit outgoing on light barrier 2 is ordered at P so, and then according to the theoretical thickness that obtains optical thin film 1 to be measured that calculates of interference of light.

Fig. 2 is parameter δ for a change, the light distribution that theoretical calculating receives; Other parameter remains unchanged, and only changes δ value, and δ respectively value is 0 °, 10 ° and 20 °; The visible variation with δ value, moving horizontally appears in interference fringe, and δ value is larger, and conoscope image translational movement is larger.Can calculate according to this shift value the thickness of optical thin film to be measured.According to the method, film to be measured affects measuring nothing the absorption of incident light.

In above-mentioned implementation process, the position of each parts, slit separation can change, and on the basis of technical solution of the present invention, indivedual parts is improved and equivalents, should not get rid of outside protection scope of the present invention.

Claims (2)

1. the device that utilizes two-slit interference method to measure optical film thickness is realized the method for measuring optical film thickness, utilizes two-slit interference method to measure the device of optical film thickness, and it comprises light barrier (2) and ccd detector (3); On light barrier (2), have a slit (21) and No. two slits (22); Optical thin film to be measured (1) covers and is fixed on the plane of incidence of a slit (21);

Vertical incidence covers a slit (21) and No. two slits (22) on light barrier (2) to the light beam of light barrier (2), and this light beam forms the first bundle polarized light through optical thin film to be measured (1) transmission and through a slit (21) outgoing; This light beam forms the second bundle polarized light through No. two slits (22) outgoing;

The first bundle polarized light and the second bundle polarized light are all incident on the test surface of ccd detector (3), and form interference fringe, and the test surface of ccd detector (3) and light barrier (2) are parallel to each other;

It is characterized in that, the method is realized by following steps:

Step 1, in the first bundle polarized light and the second interference fringe of forming on the test surface of ccd detector (3) of bundle polarized light, appoint and get one section of interference fringe and formula:

$I\left(P\right)=\frac{c^2{E}^2}{{r_1}^2}+\frac{E^2}{{r_2}^2}+\frac{{2\mathrm{cE}}^2\cos [k(r_1+r_2)+\mathrm{\&delta;}]}{r_1{r}_2}$

Carry out matching, obtain the optical path difference δ that optical thin film to be measured (1) causes;

In formula: I (P) is the dry light intensity of penetrating striped that the first bundle polarized light and the second bundle polarized light form at the some P place of ccd detector (3); r ₁for the exit facet of the upper slit of light barrier (2) (21) distance to some P, and r ₁=D/cos β; D is the distance of light barrier and ccd detector (3); β is r ₁with z axle clamp angle;

R ₂for the exit facet of No. two slits on light barrier (2) is to P point distance, and r ₂=D/cos θ; θ is r ₂with z axle clamp angle;

C is the uptake of optical thin film to be measured (1) to polarized light; E is the amplitude of polarized light; K is wave vector;

Step 2, according to formula:

$L=\frac{\left|\mathrm{\&delta;}\right|}{k(n-n_0)}$

Obtain the thickness L of optical thin film to be measured (1); Complete the measurement of the thickness for the treatment of photometry film (1);

In formula: n is the refractive index of polarized light in optical thin film to be measured (1); n ₀for polarized light refractive index in a vacuum.

2. the device of two-slit interference method measurement optical film thickness that utilizes according to claim 1 is realized the method for measuring optical film thickness, it is characterized in that: a slit (21) and No. two slits (22) are parallel to each other, and the longitudinal cross-section of the longitudinal cross-section of a slit (21) and No. two slits (22) is positioned on same perpendicular.

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