SU1346945A1 - Device for checking thickness of film in course of applying it on large optical component - Google Patents

Abstract

The invention can be used to control the thickness of an optical film during its application to a large-sized optical part. The aim of the invention is to increase the accuracy of control of the film thickness by eliminating the image displacement of the radiation source on the entrance slit of the monomator during rotation of the monitored part. Radiation from source 1 using condenser-litter 2 and mirror 17 is projected onto the surface of the test piece 12, then the image of the source from the surface of the test piece is transferred to the entrance slit of the monochromator 7 that forms radiation with a given wavelength ((. The spectrally extracted radiation is directed to the receiving and recording unit 8, where the radiation is converted into an electrical signal proportional to the transmittance of the coated part. The spectral transmittance of the monitored part with a coating at the output of the receiving-recording unit is judged on the thickness of the applied film. When the specified value is reached, the film is stopped on the monitored part. 1 Ill. (L 4: a 4 SP

Description

The invention relates to a measuring technique and can be used to control optical coatings applied by deposition of substances in a vacuum, to create large mirrors, beam splitters and other optical elements.

The purpose of the invention is to increase the accuracy of controlling the thickness of optical coatings applied to a rotating large part by eliminating the effect of displacement of the image of the radiation source on the entrance slit of the monochromator caused by the wedge and face beats of the rotating controlled part.

The drawing shows a diagram of the device.

The device contains a source of 1 radiation, a condenser 2, a diaphragm 3 forming an optical system including a mirror lens 4 and a flat mirror 5, an angular reflector 6, a monochromator 7 located behind the reflector 6 on the optical axis of the forming optical system, receiving and recording block (PRB) 8, carriage 9, drive 10 carriage, block

11 controls and settings. The input of the control unit and settings is connected to the receiver-recording unit 8.

The angular reflector 6 is mounted on a carriage 9 mounted for movement along an arrow S parallel to the bisector of the angle of the reflector 6.

In addition, the diagram shows a large-sized optical component 12, a vacuum chamber 13, in which i a controlled optical component is installed, electron-beam evaporators 14, photometric windows 15 and 16 of the vacuum chamber and a flat mirror 17.

The device works as follows.

Pre-configure the device, ensuring the design of the image of the radiation source from the surface of the test piece.

12 to the input circuit of the monochromator 7 by moving the carriage 9 with the corners of the reflector 6 along the direction S. The value of the magnitude of the displacement s S is determined by the expression

l i. m

AS

dv v

.2

346945

where v

ten

15

20

thirty

40

m 55

45

60

increase factor of the forming optical system (V "1);

uL is the magnitude of the linear compensation for the source image at the entrance slit of the monochromator.

At the stage of work corresponding to the setting, the evaporators 14 of the chamber 13 are turned off, v.6. the coating is not applied, the monochromator 7 is set to a predetermined wavelength. I .

The monitored part is driven into rotation.

In connection with the inevitable wedge-shaped shape and the beating of the large-sized optical component 12 during its rotation, the electrical signal taken from the receiving-recording unit 8 contains, along with a constant variable component. The latter has a frequency determined by the period of rotation of the optical part 12. 25 The variable component reaches the minimum value when the image A of the part 12 is projected onto the entrance slit of the monochromator 7. The beam offset relative to the entrance slit of the monochromator is thus excluded, resulting in a minimal instability of the reference and most sensitive, 1

The device is prepared for deposition of a monitored film 35 automatically by the control and adjustment unit 11, to which a photoelectric signal is fed from the receiving-recording unit 8. The control unit 11 generates a signal to the carriage movement actuator 10, allowing the carriage 9 to move with an angular reflector 6 .

After tuning is completed, the details of the 12 substances forming the coating layers are deposited on the surface A.

The coating is made by deposition in the vacuum chamber 13 on the surface A of a large-sized part 12 of the controlled films constituting the coating. The substances forming the films alternately evaporate from the evaporators 14. The deposition process of each film ceases when it reaches the required thickness, which corresponds to the calculated value of the spectral coefficient the transmission (R) of the surface A with the applied coating.

In the control, the condenser 2 and the flat mirror 17 create an image of the radiation source 1 on the surface A of the part 12. The flow passed by the part 12 with a controlled film, the lens 4 and the mirror 5, the forming optical system, as well as the angular reflector 6, is directed to the monochromator entrance slit 7

From the total radiant flux that enters the entrance slit of the monochromator, it selects radiation with a given wavelength (A), which is sent to the receiving unit 8. Receiving and recording unit 8 converts the radiation into an electrical signal proportional to the transmittance T (L ) 1 surface A. The signal goes to two outputs. The control and adjustment unit 11 is connected to one of them, and a reading device (not shown) and an actuator, which stops the deposition of the substance forming the controlled film, when the specified value T (D) is reached, is connected to the other.

The elimination of the effect of the movement of the rays on the optical elements on the accuracy of control is excluded by choosing the dimensions of the diaphragm 3 in the process of preparing the device for operation. The luminous size d of the diaphragm 3 is determined from the condition

K. d. - (p-1) (2- +

) D

..- bp

de K. - coefficient that accounts for the change in the size of the beam cross section during the passage of the rays from the diaphragm 3 to the i-ro element;

d; - the light size of the i-th optical element located between the part 12 and PRB 8;

H, - is the effective optical path from the surface A of the part 12 to the i-ro element;

D, h, n, 0

diameter, thickness, refractive index and wedge shape

VNIIti Order 5112/40. Circulation 676

Subscription

Random polygons pr-tie, Uzhgorod, st. Project, 4

large-sized optical parts 12, respectively;

YN - face beating parts 12.

The deviation of the beam path caused by the wedge shape and the beating of the rotating large-sized part does not lead to a shift of the image of the radiation source at the entrance slit of the monochromator. This eliminates the main cause of the error in controlling the transmission of film thicknesses during application.

At the same time, the device achieves an increase in the average energy level recorded during the monitoring time, which is provided by an optical circuit that allows, at all possible sizes and positions of the large-sized part, to best collect the radiant flux at the entrance slit of the monochromator and, therefore, into the receive register. block, which in turn leads to an increase in the signal-to-noise ratio, i.e. to increase the stability of the reference and control accuracy.

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five

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five

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Claims (1)

Invention Formula A device for controlling the thickness of a film during its deposition on a large-sized optical component by deposition of substances in a vacuum, containing a radiation source and a condenser located on one side of the monitored part, forming an optical system, a monochromator and a receiving-recording unit, is located. The parts on the other side, which are characterized by the fact that, in order to increase the accuracy of control, it is equipped with an angle mirror located between the monochromator and the forming (optical system, the carriage} on which the angle mirror is located, can be moved along the bisector the angle of the angle mirror, the carriage movement actuator, the control and adjustment unit, the input of which is electrically connected to the receiver-recording unit, and the output with the carriage drive, and the diaphragm installed between the source and ondensor. Subscription