SU1746213A1 - Method of monitoring film thickness during deposition process - Google Patents

Abstract

The invention relates to optical instrumentation and is intended for non-destructive testing of layer thicknesses in the manufacture of coatings on optical parts. The purpose of the invention is to improve the accuracy of film application. The sample is irradiated with a beam from a source with a wavelength I, and the phase shift between the P and S components of the radiation reflected from the sample is measured. Here, the wavelength I and the irradiation angle of the sample are chosen from the condition where d is the predetermined thickness of the coating film; , 2 „.. - coefficient; Vn2 -, where n is the refractive index of the film material. The application of the film is stopped when the Kth ratio of the phase difference of the radiation source, reflected from the sample before the film is applied and during its application, is reached. 1 il.

Description

The invention relates to optical instrumentation and is intended for non-destructive testing of layer thicknesses in the manufacture of coatings on optical parts.

Methods are known for controlling the thickness of layers during their deposition on a substrate, which consists in that monochromatic radiation is directed to a coated substrate and according to the degree of its interaction with the substrate and the film, to achieve an extreme value of the radiation intensity, the thickness of the applied film is achieved.

The known methods do not allow to apply a film of the required thickness,

The closest in technical essence to the present invention is a method in which monochromatic linearly polarized radiation is directed at an angle other than zero to the substrate before film deposition and the phase and amplitude anisotropy of the reflected radiation is recorded during the deposition process.

The disadvantage is the low accuracy of the film with the required thickness.

The aim of the invention is to improve the accuracy of film application.

To this end, with a known method of controlling the film thickness during its application, which means that before and during the deposition of the film, the test sample is illuminated with linearly polarized radiation with a wavelength H at an angle p and the phase shift between РVJ o

with

and S-components of the reflected radiation and determine the moment when the deposition of a film of a given thickness ceases, the radiation wavelength A, and the sample angle p are selected from the condition where

2,3 n-score

4Vn - sin

the refraction of the film material and the time of the cessation of film deposition are determined by the time the Kth ratio of the phase difference between the P and S components of the radiation is achieved before and during film nanogenesis

When linearly polarized radiation with wavelength A is incident on a clean surface of a sample made of a material whose absorption coefficient is close to zero, the angle / reflected radiation will also be linearly polarized, since the phase difference between the P and S components of the reflected radiation is k angles of incidence ppp or 0 at angles where ppp is the Brewster angle for the primed material

When a layer of a substance is deposited on the sample surface, the refractive index of which is different from that of the sample material and the absorption coefficient is close to zero, the incident linearly polarized monochromatic radiation upon reflection is converted in general case i by elliptically polarized radiation, i The S component of the reflected radiation is not equal to n (or 0), the degree of ellipticity and the direction of the higher axis of the ellipse being determined by the optical thickness of the layer of matter

The parameters of elliptical polarization of the reflected radiation can be determined from the equation describing the reflection coefficient / e of linearly polarized radiation with a wavelength H incident at an angle p on the layer of the environment substance.

"KYA roip + e- e- Wp

tg

1 + her T01GI2

1 + (3lroiSM2s rois

where roiP and P2P are the Fresnel reflection coefficients for the P-radiation composites relating respectively to the boundaries between the environment and the c / ioeiv substance and the layer of the substance and the control sample,

sois and H2S are the Fresnel reflection coefficients for the S-component of the radiation, respectively, corresponding to the same interfaces as gsr, P2P, the refractive index of the layer of matter,

i - imaginary unit

An analysis of this equation shows that during the deposition of a substance onto the surface of an about 0 g -RJ substance reflected from the ganosis of the polarized polarized phase shift between the P- and S-components of the reflected radiation becomes zero (if ipd) or n (ppp) t e 5 phase shift for a clean substrate when optical thickness is one hundred red quarters long Hbl

Therefore, the essence of the invention is LJ th i to control the process on 0 Hr ijiit inc ° | the required thickness x / do not lvl with such a length And radiation h angle tpet3 fall, at which the required float d would be a multiple of A / 4

e where K - factor of multiplicity 5 /

equal i 1 2 and process

 l - sin f

  1 and the film should be stopped at the moment of do- 1, r o rc “dy K and the multiplicity of the shift ratio 4j-c i ii chen / - o-encho on the substrate to O 1 i pp-nki and in its application

14

At any value of the ratio of just 2, the phase shift between the component ami and reflected radiation will be equal to the same value as when it is active on the film at the bottom of the substrate.

The drawing shows the scheme of the device that implements the proposed method.

0The device contains a source 1 vacuum chamber 2 with windows 3 and 4 turn-: oo mirror 5, phase shift recorder 6 second rotary mirror 7 and svefofilotr 8

5 Radiation of war of length A from source S 1 through window 3 of vacuum chamber 2 after reflection from rotating mirror 5 contacts the substrate 9, on which it is not necessary to apply a layer of substance 10 with a reflection of the required thickness after reflection from the substrate 9 mirror 7 through the eye l. Ko 4 of the vacuum chamber 2 on the phase shift recorder 6 The angle of incidence p of 5 beams on the substrate 9 can be changed by changing the distance between the turning mirrors 5 and 7 when they are simultaneously rotated across their axes. The wavelength of the radiation is set, for example, by the light filter 8 installed directly after source 1,

The invention is operable in a wide range of wavelengths (from ultraviolet to infrared), which determines, respectively, the ability to control film thicknesses of a wide range of substances.

Claims (1)

The invention The method of controlling the thickness of the film during its application, which consists in the fact that before and during the deposition of the film the controlled sample is illuminated with linearly polarized radiation with a wavelength H at an angle p, the phase shift is measured 0 between the P- and S-components of the reflected radiation and determine the moment of stopping the deposition of a film of a given thickness d, characterized in that, in order to improve the accuracy of film deposition, the radiation wavelength H and angle (p of sample illumination are chosen from the condition where, 2, 3, ...; d0 A / (4Vn2 - slnfy); n is the refractive index of the film material, and the moment when the film is stopped applying is determined by the moment the K-th brevity reaches the equality of the phase shift between the P and S components of the radiation before and in film application process.