CZ299672B6 - Method of measuring thickness of non-stationary thin layers and optical thickness gauge - Google Patents

Abstract

The proposed method of measuring thickness of both non-stationary thin transparent and non-transparent layers (7, 13) is characterized in that a narrow light pencil (2) is projected under an angle of incidence {alpha} onto both, a layer (7, 13) to be measured and a light diffuser (6) thereof to which the investigated layer (7, 13) is applied. At the same time, at least two light lines (8, 9) being generated and spaced apart by a distance (L) are recorded by an optical microscope (10) and/or by CCD camera (12). Thickness of both transparent and non-transparent layer (7, 13) under investigation is then determined either by computation of the distance (L) being measured or by readout on a calibrated scale of the optical microscope (10) eyepiece (11). There is also disclosed an optical thickness gauge for measuring non-stationary thin transparent and non-transparent layers (7, 13), the thickness gauge comprising an optical projection system (16) formed by a monochromatic and/or white light emitting light source, a condenser (3), a collimator (4), a micrometrically adjustable slit (5), and an optical microscope (10). The collimator (4) optical axis (17) forms with a layer (7, 13) sample perpendicular an {alpha} angle of incidence wherein the optical microscope (10) is situated in the axis of the layer (7, 13) sample perpendicular, the layer (7, 13) sample is situated on the optical diffuser (6), wherein the optical microscope (10) is provided with an eyepiece (11) with reticule (15), and/or a scanning CCD camera (12).

Description

(57) Annotation.

The method of measuring the thickness of the non-stationary thin transparent and non-transparent layers (7, 13) consists in this. that a light beam (2) is projected at an angle of incidence (u) on the measured layer (7, 13) as well as on its light diffusion (or) (6) on which it is / is being coated. ) and formed at least two light lines (X.9) at a distance (I) are registered by an optical microscope (10) or by a CCD camera (12). As measured by the optical microscope (11) calibrated eyepiece scale (10), the thickness of both the transparent and non-transparent investigated layers (7, 13) is determined.

The optical thickness gauge for measuring non-stationary transparent and non-transparent thin films (7, 13) consists of an optical projection system (16) comprising a light source emitting monochromatic and / or white light, a condenser (3) and a coltmalor (4) and a micromelectrically adjustable slot. 5), and an optical microscope (10). The optical axis (17) of the collimator (4) forms an angle of incidence (α) with the normal of the sample layer (7, 13), the optical microscope (10) being positioned along the axis of the normal of the sample layer (7, 13). located on the optical child / ore (6). and is provided with a crosshair eyepiece (11) and / or a CCD camera (12).

Method of thickness measurement of non-stationary thin films and optical thickness gauge

Technical field

The invention relates to the measurement of the thicknesses of very thin non-stationary transparent and non-transparent layers, in particular using optical measuring methods.

BACKGROUND OF THE INVENTION

Knowledge of the time dependence of thickness d (t) is critical in determining the rate of polymerization, shaping, volatilization of volatiles and in the analysis of other chemical and photochemical reactions. At present, the measurement of very thin films with a thickness d (t)> 10 pm is based on the magnetic-induction method, the eddy current method, or ultrasonic and calotest measurements. Usually these are already cured layers, the thickness of which is independent of time. In the case of wet non-stationary layers, the method of indirect weighing of the layer is often used in the evaporation of solvents. The viscous substance to be examined is evenly spread on a slide and weighed on an analytical balance. Knowing the bulk density and total surface area of the layer, the resulting layer thickness d (t) can be easily calculated. This implies that it is an integral method that de facto determines the mean value of the layer thickness.

There are optical methods based on light absorption by the layer, on the interference of monochromatic light, spectrometric methods. based on d i fraction of light, ellipsometric methods based on elliptic polarization of light and methods based on polarization of light by reflection (Brewster's polarization angle).

For example, WO 94P28376 relates to an apparatus and method for measuring the thickness of a thin film ¹ . The time modulation of emitted plasma or reflected laser radiation from which it can be measured is measured

3 »determine the thickness of the thin film. Modulation is caused by radiation interference on a thin film. In this way, the thickness of the opaque layer cannot be determined. The device is complicated.

JP 62293103 uses a refraction of light on a thin layer at an incidence angle equal to the Brevvster angle. The sweeping substrate sweeps the beam across the surface sensor. In this way, the thickness of the opaque layer cannot be measured.

SUMMARY OF THE INVENTION

These disadvantages are overcome by a method of measuring the thickness of thin, non-stationary transparent layers on the basis of the optical properties of the layer which according to the invention consists in projecting a narrow light beam at an angle of incidence on the measured layer and its optically diffuser. The light beam passes through the measured transparent layer and refracts depending on its refractive index n 'and then impinges on the surface of the optical diffuser on which. the measured layer is applied to form a modulated line, and secondly, the light beam strikes the surface of the optical diffuser in the place without the measured layer and forms a reference line therein, the distance between the modulated line and the reference line being registered by an optical microscope and / or CCD camera of the measured layer and from the measured distance value, the thickness of the non-stationary transparent thin layer is determined either by calculation according to the formula tg (a) -sin (a) / sin ² (a)

Where d (t) is the thickness of the thin non-stationary transparent layer.

L (t) is the distance between the light reference line and the modulated line, o. Is the angle of incidence of the light beam, n '(t) and n are the refractive indices of the layer and the air.

or directly by reading on a calibrated optical microscope eyepiece scale.

The above-mentioned disadvantages further obviate the method of measuring the thickness of thin non-stationary non-transparent layers, based on the optical properties of the layer, which according to the invention consists in this. that the measured non-transparent layer and its optical diffuser, on which the measured layer is applied, project a narrow light beam at an angle of incidence [alpha], the light beam impinges on the upper surface of the measured non-transparent layer and creates a modulated line; Optical diffuser in the place without measured non-transparent layer and here creates a reference line, where the distance between the modulated line and the reference line is registered by an optical microscope and / or CCD camera placed perpendicular to the scrub layer. by calculation according to the formula d (i) - where d (t) is the thickness of the thin non-stationary non-transparent layer,

L (t) is the distance between the light reference line (and the modulated line), tx is the angle of incidence of the light beam, or directly by reading on a calibrated optical microscope eyepiece scale.

The present invention further provides an optical thickness gauge for measuring non-stationary transparent and non-transparent thin films consisting of an optical projection system comprising a light source emitting monochromatic and / or white light, a condenser and collimator and a micrometrically adjustable slit, and an optical microscope In that the optical axis of the collimator forms an angle of incidence α with the normal of the sample layer, the optical microscope is positioned in the normal of the sample and the sample layer disposed on the optical diffuser and is provided with a crosshair eyepiece and / or scanning CCD camera.

Preferably, the light source is a laser diode. The scale of the measuring eyepiece is calibrated for a given 'angle of incidence α' and the matte examined! in the air of the viscose of interest, one scale being for the transparent layer and the other for the non-transparent layer being examined.

The optical thickness gauge uses a light cut method to measure the thickness of non-stationary thin films. The narrow light beam is projected by the collimator at an angle of incidence and onto the investigated layer as well as its light-reflecting diffuser on which the investigated layer is applied. This creates two light trails - lines, spaced apart by a distance L, which is registered by a microscope or CCD camera. L of the measured value I., it is possible to precisely determine the thickness of the examined non-transparent and transparent layer d (t).

The advantage of monochromatic laser radiation is perfect focusing of light and sharpness of light lines edges. This eliminates the chromatic aberration of the optical projection system, which facilitates and increases measurement accuracy.

5o Another advantage is eg evaluation of CCD camera acquired images at a later time stage and the fact that it is a direct method of measuring the thickness of the investigated layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an optical thickness gauge arrangement.

with

Fig. 2c shows a reference line and a modular line on the surface of the opaque layer.

Fig. 3 shows a reference line and a modular line after passing light through a transparent layer.

Fig. 4 shows the thickness of the freshly coated layer and after drying.

FIG. 5 shows a scale eyepiece.

DETAILED DESCRIPTION OF THE INVENTION

The method of measuring the thickness of the non-stationary thin films utilizes the light sectioning method and the measurement of the distance L of at least two light lines, the reference line 8 and the modulated line 9, cut by cut.

Figure 1 shows the optical thickness gauge of non-stationary thin films. It consists of optical projection system J6 and optical microscope PO, which is a stereoscopic microscope. The optical projection system 16 consists of a light source 1 emitting a monochromatic

2? and / or white light, and furthermore a condenser 3 and a collimator 4 and a micrometrically adjustable slots 5. wherein the optical axis 17 of the collimator 4 forms an angle of incidence β with the normal of the sample layer 7, the optical microscope 10 is equipped with a crosshair eyepiece. camera JJ.

The light source 1 is a laser diode whose light monochromatic beam 2 is focussed by the condenser 3 into the focus of the collimator 4. The parallel resulting light beam 2 from the collimator 4 passes through a micrometrically adjustable slit 5 and then projected at incidence angle and onto the solid light diffuser 6 7. The advantage of monochromatic laser radiation is perfect focusing of light and sharpness of light lines edges

- reference line 8 and modulated line 9. This eliminates the chromatic aberration of the optical projection system 16, which facilitates and increases the measurement accuracy,

On the white plate of the light diffuser 6, the tiansparial layer 7 to be examined is spread with viscous liquid for a given thickness. Light beam 2 of monochromatic light of which

4 <> width is determined by the micrometric adjustment of the slot 5, at the same time illuminates the surface of the diffuser 6 without layer 7 and layer 7. Due to the oblique illumination two light lines of the reference line 8 and modulated line 9 arise. the measured layer 7 as shown in FIG. 1 and 3. At time t = 0, the thickness d _{() of the} just spread layer 7 will be the largest and, after curing or drying, the smallest cL. see FIG. 4. The same applies to the distance L of the reference line 8 and the modulated line 9,

The optical thickness gauge for measuring the thickness of the non-stationary thin layers according to the invention can measure the thickness of the layers 11. 7 non-transparent and transparent. Fig. 2 shows the formation of a modulated line 9 at the point of impact on the sample surface of the opaque layer 11 and the reference line 8

5o at the point of impact on the surface of the diffuser 6 at a point without layer 11.

In the first case, the light modulated line 9 is displayed on the surface of the opaque layer 11, in the second case after light has passed through the layer 7 on the surface of the light diffuser 6. The distances L between the reference line 8 and the modulated line 9 are measured by an optical microscope 11.

5? eyepiece JJ. with a crosshair and a scale 15. The scale division 11, see Fig. 5, can be designed for

-3C.7. 299672 B6 given the angle of incidence α and for refractive indices n 'of the investigated layers. In the second light channel of the stereoscopic microscope 11 can be included a CCD camera f2, which allows to record images of light reference line 8 and modulated line 9, taken at intervals of time on the hard disk of an untreated computer. As a result, the measurement is permanently documented and at the next stage for further evaluation.

The geometric ratios of the reference line 8 and the modulated line 9 under illumination of the opaque layer 13 are shown in FIG. 2. The 1-lor modulated line 9 and the lower reference line 8 are the point of impact of the light diffuser 6. When viewed perpendicularly there will be a distance between them which is determined by

Ld) ~ ddig (a).

from which the thickness of the layer d (t) is calculated.

In the case of the transparent layer 7, the fracture law applies and for the distance of the reference line 8 and the modulated line 9 the following relation applies:

tg (a) -sinfa).

n '(t)

- sin ² (a) where a is the angle of incidence of the light beam, dd) is the layer thickness, n'd) are the refractive indices of the air and the measured layer 7. If the refractive index n '(o) of the wet layer and the refractive index The reference values 8 and the modulated lines 9 increase at a given thickness of the layer 7 with increasing incidence angle α. Suitable values of incidence angle α lie in the range of 45 to 65 °. because at 25 angles, much of the light reflects from the dielectric interface. The intensity of the light entering the layer 7 then rapidly decreases and the image of the light slit will be less contrasting. The calculation can be shown that the thickness of the transparent layer 7 having a refractive index ^of n = 15 is approximately equal to d - 2L for a = 45 ° and d - L for a - 60 °.

In the case of mouse applicability, he invented ezia

The method of measuring the thickness of non-stationary thin transparent and non-transparent layers and the optical thickness gauge will find application in determining the polymerization rate. chemical reactions, curing and drying of paints and wherever it is necessary to determine the layer thickness above 10 gm. Stationary, time-independent thicknesses can also be determined from the principle of the measured method.

Claims (7)

PATENT CLAIMS 1. Method for measuring the thickness of thin, non-stationary transparent layers (7) based on the optical properties of the layer (7). characterized in that both the measured layer (7) and its optical diffuser (6) are scanned. on which the measured layer (7) is applied, projects a narrow light beam (2) at an incidence angle (a), the light beam (2) passes through the measured transparent layer (7) and breaks depending on its refractive index n 'and later impinges on the surface of the optical diffuser (6) on which the measured layer (7) is applied and forms a modulated line (9), and on the other hand the light beam (2) impinges on the surface of the optical diffuser (6) and here forms a reference line (8), wherein the distance (L) between the modulated line (9) and the reference line (8) is registered by an optical microscope (10) and / or a CCD camera (12) positioned perpendicular to the plane of the measured layer (7). ) and from the measured distance value (1), the thickness of the non-stationary transparent thin 15 layers (7) find out below the range (s) -L (t) tg (a) -sin (a) / - sin ² (a) where d (t) is the thickness of the thin non-stationary transparent layer (7), 2o L (t) is the distance between the light reference line (8) and the modulated line (9), and is the angle of incidence of the light beam (2), n '(t) and n are the refractive indices of the layer and air. or directly by reading on a calibrated eyepiece scale (11) of the optical microscope (10). ? () Method for measuring the thickness of thin non-stationary non-transparent layers (13), based on the optical properties of the layer (13), characterized by. 2. The method according to claim 1, characterized in that the measured non-transparent layer (13) and its optical diffuser (6) are applied. on which the measured layer (13) is applied, projects a narrow light beam (2) at an angle of incidence (a), the light beam (2) falls on the upper surface of the measured non-transparent layer (13) and forms a modulated line (9); the light beam (2) impinges on the surface of the optical diffuser (6) at a location without the measured non-transparent layer (13) and forms a reference line (8) there, the distance (L) between the modulated line (9) and the reference line (8) being registered an optical microscope (10) and / or a CCD camera (12) positioned perpendicularly Layer of the measured layer (13) a .. Xtó ,,. Λ k J-. i - J - I '! I \ li ^w -Ί IIV1V1IV IIUUIIUIV in zxjaici halí LIUILNI ΚΛ IICS LIUILI íl Ii 11 f transparent films (13) are detected either by calculation according to the formula ί / μ / - L (i) igits. where d (t) is the thickness of the thin non-stationary non-transparent layer (13), Ψ) L (t) is the distance between the light reference line (8) and the modulated line (9). and is the angle of incidence of the light beam (2), or directly by reading on the calibrated eyepiece scale (11) of the optical microscope (10). 45 An optical pressure gauge for measuring non-stationary transparent and non-transparent thin films of a composite / optical projection system (16) consisting of a light source emitting monochromatic and / or white light, a condenser (3) and a collimator (16) 4) and micrometry with an adjustable slit (5), and an optical microscope (10). characterized by. that the optical axis (17) of the collimator (4) forms an angle of incidence with the normal of the sample layer (7, 13) - 5 CZ 299672 B6 (a). an optical microscope (10) is positioned along the normal line of the sample layer (7, 13) located on the optical diffuser (6) and is provided with a eyepiece (11) with a crosshair (15) and / or a CCD camera (12). 5. The optical thickness gauge of claim 4, wherein the light source (0) is a laser diode. Optical thickness gauge according to claims 4 and 5, characterized in that. The measuring eyepiece (11) is provided with two scales (15) calibrated for a given angle of incidence (a) and the material of the measured layer (7, 13) in units of thickness of the measured layer (7, 13), one scale (15) being transparent layers (7) and a second for non-transparent layers (13). Optical thickness gauge according to claims 4 and 5, characterized in that the optical microscope (10) is a stereoscopic microscope or a binocular microscope or a monocular microscope. skop.