JPH0719820A - Optical film thickness monitor - Google Patents

Abstract

PURPOSE:To provide an optical film thickness monitor which can monitor film forming state accurately without any influence such as optical changes in a film formation chamber. CONSTITUTION:A light emitted from a light source 1 is divided into two fluxes of light, and one flux of light is made to transmit a sample in a film formation chamber 6, while the other flux of light is made to transmit simply in the film formation chamber, then the two fluxes of light are discriminated and received by the same light receiver 8. When a detection signal of the latter is R, a detection signal of the light which transmits a film formation substrate 7 within the chamber 6 is S, and a detection signal of light quantity at the time when the two fluxes of light are shielded just before they are made incident to the chamber 6 is D, the following formula is obtained; F(t)=(S-D)/(R-D). According to the measuring value F(t), the film thickness in the film formation chamber is observed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film thickness monitor for observing the film thickness of a film forming apparatus by injecting two light beams into the film forming chamber.

[0002]

2. Description of the Related Art A film forming method on a substrate by vacuum vapor deposition, cathode sputtering, etc., is used as an optical measuring method of the film thickness, in which the reflectance or transmittance of the film surface due to mutual interference of reflected light from both front and back surfaces of the film. There is a method to detect the change of. In the conventional optical film thickness monitor, there are both a case of measuring with a single light beam and a case of measuring with two light beams. In the case of measuring with a single light flux without splitting the light flux, it is theoretically impossible to exclude the influence of the brightness change of the light source and the influence of the optical change in the deposition chamber from the measured value. There was a big problem in terms of accuracy. Therefore, the double beam method of splitting a light flux into two light fluxes is also used in the related art. In the conventional double beam method, the sample light is applied to the film formation substrate in the film formation chamber, but the reference light is a fiber or the like. Since it is only passed through the outside of the film formation chamber by using the optical system, even if the influence of the change in the brightness of the light source can be eliminated, the If the amount of light incident on the light receiving element changes due to changes in the optical axis, the effect cannot be removed from the measured value. Therefore, there is a problem that the film thickness cannot be accurately measured.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical film thickness monitor capable of accurately monitoring a film forming state without being affected by an optical change in a film forming chamber.

[0004]

As an optical film thickness monitor, a sector mirror that divides light from a light source into transmitted light, reflected light, and light shielding in time series, and a film of the reflected light and the transmitted light are formed. A means for transmitting the chamber and a means for separately receiving the reflected light, the transmitted light, and the light at the time of blocking in the same light receiver are provided, and the detection signal of the light simply transmitted through the film forming chamber is R, When the detection signal of the light transmitted through the film formation substrate is S and the detection signal of the light from the film formation chamber when the light is shielded is D, a measured value F (t) = (SD) / (RD) The film thickness in the film forming chamber was observed by F (t). In the above device, the frequency ν of two-beam classification is set higher than the frequency ν ₀ of the disturbance (vibration) with respect to the device.

[0005]

Operation: The sector mirror splits the light from the light source into two light beams and the time when the light is shielded, and divides the light beams into three in time series. (Light) S and light that has simply passed through the deposition chamber (reference light)
When R and the photodetector output D when the light is shielded are detected by the same photodetector, the signal D is a detection signal of the light generated in the film forming chamber, and an optical change in the film forming chamber or a change in the received light amount due to vibration does not occur. The same effect is applied to any detection signal. Since the monitor of the film formation state is grasped by the change in the transmittance of the film formation substrate, the film formation chamber when F (t) = (SD) / (RD) is used as the measurement value for the monitor. Considering the influence of the change of the optical axis due to the emission / absorption of light and the vibration (where S is the detection signal intensity of S light,
Let R be the detection signal intensity of the R light and D be the detection signal intensity of the D light. ), F when a light emission phenomenon occurs in the film forming chamber
As for the influence on (t), as the change of the detection signal of each light, the increase β of the light amount due to the emission increases in all the detection signals, so that F (t) = [(S + β) − (D + β)] /
[(R + β)-(D + β)] = (SD) / (RD)
It can be seen that the measured value F (t) is not affected by the light emission phenomenon. Next, if there is a shift in the optical axis due to absorption or vibration, that is, if the absorbance in the deposition chamber changes or if the amount of received light decreases due to the optical axis shift, the change in the absorbance is The detection signal of each light is reduced at a constant rate. That is, assuming that the absorptance in the film forming chamber becomes α times, the total signal intensity also becomes α times, and the amount of received light due to the optical axis shift is also reduced when the frequency of two light beam separation is sufficiently higher than the vibration frequency. Since the signal reduction rate is the same for the sample light and the reference light, if the reduction rate is α as in the above case, the total signal intensity will be α times, and the measured value F
(T) is F (t) = (αS−αD) / (αR−αD)
= Α (SD) / α (RD) = (SD) / (R-
Therefore, it can be seen that the measurement value F (t) is not affected by the light absorption phenomenon or the optical axis shift. As described above, the light of the same light source is divided into two light fluxes and light shields in time series, and the detection signals of the three lights are arithmetically processed to monitor and monitor the effects of light emission and absorption in the film formation chamber. Can be removed from the measured value.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block diagram of an optical system of an embodiment of the present invention. Reference numeral 1 is a light source, and 2 is a sector mirror that splits the light from the light source 1 into two light beams, the details of which are shown in FIG. The sector mirror 2 has a circular mask 2A provided with a fan-shaped window 2C, and a fan-shaped rotating mirror 2B is mounted on the window 2C. The window 2C has a fan angle of 60 °, and the rotating mirror 2B also has a fan angle of 60 °. Therefore, the mask 2A also has a fan angle of 60 °, and the sector mirror 2 is rotated so that the light from the light source 1 is emitted. Is split into light that passes through the window 2C of the sector mirror 2, light that is reflected by the rotating mirror 2B, and light that is shielded by the mask 2A. The light passing through the window 2C of the sector mirror 2 is reflected by the mirror 3, transmitted through the film formation substrate 7 installed in the film formation chamber 6, reflected by the sector mirror 5, and received by the light receiver 8. . The light reflected by the rotating mirror 2B of the sector mirror 2 is reflected by the mirror 4, passes through the inside of the film forming chamber 6, and is reflected by the sector mirror 5.
The light passes through the window 5C and is received by the light receiver 8. As for the details of the sector mirror 5, as shown in FIG. 3, the size of the window 5C is 60 °, which is the same as that of the sector mirror 2, but the size of the rotating mirror 5B is twice as large as 120 °. ,
There is no portion corresponding to the mask 2A. By rotating the sector mirror 5 and the sector mirror 2 in synchronization so that the rotating mirror 2B of the sector mirror 2 and the window 5C of the sector mirror 5 are on the respective measurement optical paths at the same time,
The light reflected by the sector mirror 2 is reflected by the sector mirror 5.
The light which has passed through the window 5C of the sector mirror 2 and passed through the window 2C of the sector mirror 2 is reflected by the sector mirror 5 and enters the photodetector 8, and even when the mask 2A of the sector mirror 2 is on the optical path. The period in which the rotating mirror 5C of 5 is on the optical path is obtained, and the light receiver 8 obtains a signal as shown in FIG. The dark optical signal D in FIG. 4 is the output signal of the light receiver 8 when the mask 2A of the sector mirror 2 and the rotating mirror 5C of the sector mirror 5 are both on the optical path, and the light from the light source 1 is This is a signal that represents the amount of light that has not entered the film forming chamber 6, that is, the amount of light that is generated within the film forming chamber itself. Such light is light emitted from a heat source during vacuum deposition or glow discharge light during cathode sputtering. The sample optical signal S in FIG. 4 is a signal representing the amount of light from the light source 1 that has passed through the film formation substrate 7 in the film formation chamber 6. The reference light signal R in FIG. 4 is a signal that represents the amount of light from the light source 1 that has passed through the film formation chamber 6. In the signal processing system 9, the three detection signals S, R,
From D, F (t) = (S−D) / (R−D) ………… (1) The measured value F (t) is obtained by the formula (1), and the value of F (t) Membrane condition is monitored. This F (t) represents the absorptance of the film formation substrate 7.

In the film forming chamber 6 of this optical system, when the absorptivity increases due to the influence of gas or the like, or when the amount of received light decreases at a constant rate due to optical axis deviation due to vibration, that is, the signal intensity is α ( Even if it becomes 0 <α <1) times, F (t) = (αS−αD) / (αR−αD) = (S−
D) / (RD), and the measured value F (t) does not change. Further, when some kind of light emission phenomenon occurs, that is, when the signal intensity uniformly increases by β, the above formula (1) is expressed by F (t) = [(S + β) − (D + β)] / [(R + β)
− (D + β)] = (SD) / (RD), and similarly, the measured value F (t) does not change. Thus, even if an optical change due to light emission, light absorption, optical axis shift, or the like occurs in the film forming chamber, the measured value F (t) is not affected. In this configuration, when one of the two sector mirrors is a half mirror and the remaining sector mirrors take the form of FIG. 2, it is further shown in FIG.
As shown in the modified embodiment, both of them are half mirrors 12,
Needless to say, even when the chopper 10 having the structure shown in FIG. 6 is combined as 15, the effect is the same although the signal strength is reduced.

[0008]

According to the present invention, even if an optical change due to light emission, light absorption, optical axis shift or the like occurs in the film forming chamber, the measured value F (t) is not affected. With this, the accuracy of the measured value is further increased, and the film formation state can be monitored more accurately. Since the sector mirror can be rotated at a high speed by a vacuum system rotary pump, the influence of vacuum system vibration can be easily eliminated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system according to an embodiment of the present invention.

FIG. 2 is a plan view of the sector mirror 2 of the above embodiment.

FIG. 3 is a plan view of the sector mirror 5 of the above embodiment.

FIG. 4 is a detection signal diagram of the above embodiment.

[Explanation of symbols]

 1 Light Source 2 Sector Mirror 3 Mirror 4 Mirror 5 Sector Mirror 6 Film Forming Chamber 7 Film Forming Substrate 8 Photo Receiver 9 Processing System

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[Procedure amendment]

[Submission date] September 4, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system according to an embodiment of the present invention.

FIG. 2 is a plan view of the sector mirror 2 of the above embodiment.

FIG. 3 is a plan view of the sector mirror 5 of the above embodiment.

FIG. 4 is a detection signal diagram of the above embodiment.

FIG. 5 is an optical system configuration diagram of a modified example of the present invention.

FIG. 6 is a plan view of the chopper 10 of the above embodiment.

[Explanation of reference numerals] 1 light source 2 sector mirror 3 mirror 4 mirror 5 sector mirror 6 film forming chamber 7 film forming substrate 8 light receiver 9 processing system

Claims (1)

[Claims] 1. A means for splitting light from a light source into two light fluxes,
Means for allowing the two light beams to enter the film forming chamber, one light beam passing through the sample and the film forming chamber, and the other light beam simply passing through the film forming chamber; And a means for separately receiving the light in the room into the same light receiver,
Let R be the detection signal of the light that has simply passed through the film formation chamber, S be the detection signal of the light that has passed through the film formation substrate inside the film formation chamber, and D be the detection signal of the light inside the film formation chamber when the light is blocked. t) = (S−D) / (R−D) An optical film thickness monitor characterized by observing the film thickness in the film forming chamber by a measured value F (t).