JPH03245005A - Measuring method for film thickness - Google Patents

Abstract

PURPOSE:To measure the thickness of a coating film for fiber without contact by projecting luminous flux on the surface of the optical fiber coated with a thin film, and measuring the intensity of the light reflected from the thin film. CONSTITUTION:Emitted light Pi from a light source 10 such as an He-Ne laser is magnified through a lens (1) 11 and a lens (2) 12 and inputted into an optical fiber 24 wherein glass fiber is coated with a pyrolytic carbon film. Then, the image of reflected light Pr from the fiber 24 is formed on a detector 14 through a lens (3) 13. The intensity is detected with an Si photodiode 15 and the like and measured as a voltage fluctuation with a voltmeter 17 through an amplifier 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring film thickness, and more particularly to a method for measuring the thickness of a thin film with metallic luster coated on the outer periphery of an optical fiber.

[Prior Art 3] A quartz-based optical fiber has a drawback (called fatigue) that if it is left under tensile stress, it will break after a long period of time (called fatigue).

To prevent this fatigue, there is a method to prevent the growth of scratches by keeping the surface energy of the core in a high state at all times. Specifically, as shown in FIG. 2, for example, the outer periphery of a fiber 20 having a core 21 made of doped silica and a cladding 22 made of silica is coated with pyrolytic carbon, which is difficult for moisture to pass through.
A coated fiber 24 is coated with a film 23 (hereinafter referred to as carbon film) (also referred to as pyrolytic carbon) by the CVD method to prevent moisture from adsorbing onto the surface of the optical fiber. A film like this carbon film that adheres closely to the substrate (in this case, the optical fiber) and is difficult for gas to pass through is called a hermetic coating.

The fiber 24 produced by this method has the desirable property that the carbon film 23 is hardly permeable to moisture. It is known that this property varies greatly depending on the film thickness. However, if the film thickness is made thicker with emphasis placed on impermeability to H7 and water, more by-products will adhere to the reaction tube during manufacturing, and the bare fibers will come into contact with this, resulting in a decrease in initial strength and longer length. There was a problem in that it was not possible to continue manufacturing for hours.

Therefore, the coating thickness of the carbon film must be controlled to an appropriate thickness during manufacturing. However, in order to measure the carbon coating thickness of 200 to 1000, which is considered to be practically preferable for fibers, FE-8EM, AES
This required a complicated method, and there was a desire for a means that could be easily checked during manufacturing.

As a means for non-destructively measuring the carbon coating thickness of 01 □m or less, the present inventors have already published patent application No. 180 of 1999.
In the specification of the application as 157M, the electrical resistance value is 111 in total.
We propose a method for measuring carbon film thickness by 1. For example, as shown in FIG. 4(a), the resistance value is measured by using a fiber 41 coated with pyrolithic carbon with metal guides 42 and 43 made of lino bronze as contact points (44 is a contact point). not just a guide),
Alternatively, as shown in FIG. 4(b), the resistance value is measured using a liquid metal 45 such as mercury in the tie 46, 47 as a contact point.

[Problems to be Solved by the Invention] However, since the method of measuring the electrical resistance value described above is a contact measurement method, it is necessary to consider the risk of deterioration of the mechanical strength of the fiber due to the measurement. It was hoped that a method could be developed.

In view of the current situation, the purpose of the present invention is to enable non-contact and accurate measurement of the thickness of coating films with metallic luster, such as carbon thin films coated on the outer periphery of optical fibers, and to enable online measurement in the optical fiber manufacturing process. The objective is to provide a new method for measuring film thickness.

[Means for Solving the Problems] The present invention achieves the above object by measuring the P&coating thickness of a coated optical fiber in a non-contact manner by optical means.

That is, the present invention provides a method for determining the thickness of a thin film with metallic luster that coats the outer periphery of an optical fiber. Provided is a film thickness measuring method characterized by determining film thickness by measuring intensity.

Hereinafter, a detailed explanation will be given with reference to the drawings.
) is a schematic explanatory diagram of the measurement system 18 of the present invention, in which the emitted light Pi from the light source 10, such as a He-Ne laser, is transmitted through the lens (1) 11. The light is magnified by the lens (2) 12 and enters the optical fiber 24, which is a glass fiber 20 coated with a birolytic carbon film 23. The reflected light Pr from the coated optical fiber 24 is reflected by the lens (3) 1
3 forms an image on a detector 14, and its power (intensity) is detected by, for example, a Si photodiode 15, passes through an amplifier 16, and is measured as a voltage fluctuation by a voltmeter 17.

When the measurement system 18 of the present invention is used in an optical fiber manufacturing process, a carbon coating 23 is formed on a bare optical fiber 20 drawn by melting and heating a preform 1 in a drawing furnace 2, as shown in FIG. The carbon-coated fiber 24 is placed between a bilolithic coating reaction tube 3 and a die 4 for coating the outer periphery of the carbon-coated fiber 24 with resin. In the current manufacturing method, the fiber 24 passing through this position cannot avoid vibration of less than 1 mm. Therefore, even if the optical fiber 24 vibrates by about 1 mm, the intensity fluctuation of the reflected light can be ignored, so that the luminous flux after passing through the lens (2) 12 is 5 mmφ~]Qmm.
It is desirable that it is φ. Furthermore, it is necessary to provide an optical system so that even if the fiber vibrates by about 1 mm, the image does not come out from the light receiving surface. In addition, in FIG. 3, 4 is a heater, 6 is a resin curing means, and 7 is a winder.

The angle formed by the light source 10 - coated fiber 24 - detector 14 is preferably 10 to 90' because the more acute the angle, the greater the change in scattered light intensity with respect to the change in film thickness.

[Function] During the course of research into the present invention, the present inventors conducted the following studies.

(2) As shown in FIG. 1(b), samples were prepared in which birolytic carbon 23 was deposited on a slide glass 19 to a film thickness of 200, 400, and 600 layers.

■ Figure 1 (b
), light of intensity Pi is incident at an incident angle of 300, the intensity of transmitted light Pt and reflected light Pr is measured, and the transmittance (P
L/Pi) and reflectance (Pr/Pi) were determined.

The results were as shown in the table below.

In other words, there is a correlation between the film thickness and the intensity of reflected light. This experiment revealed that not only transmittance but also reflectance can be used as a means of measuring film thickness.

For small-diameter samples such as optical fibers, the measurement of transmitted light requires 31! This is difficult because some light passes through the rays and enters the detector directly. On the other hand, reflected light measurement according to the present invention does not have the above-mentioned difficulties, and therefore can be easily and accurately measured.

Specifically, a correlation curve (standard curve) between the intensity of reflected light reflected by a thin film and the film thickness is determined in advance, and the film thickness can be determined from this curve.

The measurement method of the present invention is applicable not only to a carbon film but also to a hermetic coat with metallic luster provided on the surface of the low optical fiber, such as Al1. In, Au.

It is similarly effective for measuring the coating film thickness of Ti, AL Sn, etc.

The film thickness range that can be measured by the present invention is determined by the fact that the measurable depth is theoretically determined by the depth at which electromagnetic waves penetrate into the film based on the relationship between the dielectric constant of the coating (1) and the wavelength of the light source. . (film thickness and penetration depth), the reflected light intensity changes depending on the film thickness. According to the experiments of the present inventors, C, A12
．． In, Au, Ti.

Regardless of the material such as Ag or Sn, it is possible to measure up to a film thickness range of approximately 1/3 of the wavelength of the light source used.

For example, a He-Ne laser (wavelength 633 nm) is used as a light source.
), all films made of any material will have a thickness of 200 nm.
I was able to measure up to

In addition to the above-mentioned HeNe laser, light sources used in the present invention include, for example, He-Cd laser, Ar laser, and LED.
Red lamps, halogen lamps, tungsten lamps, etc. can be used.

"Example" Film thickness measurement was carried out using the reflected light intensity of the present invention in the arrangement shown in Example Figure 3.The film thickness of the carbon foot was adjusted according to the raw material concentration and estimated from the electrical resistance value.Used in this example The light source was a He-N e laser with a wavelength of 0.633 am [2
mW, manufactured by NEC Corporation, GLG-5300], luminous flux of incident light 10 mmφ, light source fiber detector [Si photodiode, manufactured by Atoppan Test Co., Ltd., TQ8210
power meter] is 30'. Figure 1 (d
), when the raw material flow rate for carbon coating was changed, the carbon film thickness was 32 nm and 28 nm.
, 23 nm.

14 nm, S nm, and Q nm, and the power (n W ) of the light irradiated on the detector and the corresponding output (m V ) were as shown in FIG. 1(d). When the relationship between the carbon film thickness (nm) and the repulsive light power (voltage/mV) was determined, it was as shown in FIG. 1(c). From the same figure, it can be seen that the film thickness can be measured based on the intensity of reflected light, and that the present invention can also be used to measure even a drawing line with a positional vibration of about 1 mm.

The above description has been made using the measurement of the thickness of a carbon coating as an example, but the measurement method of the present invention is equally effective for measuring the thickness of a hermetic coat with metallic luster provided on the surface of other optical fibers. there were.

[Effects of the Invention] By using an optical system, the present invention makes it possible to measure the coating film thickness of a fiber in a non-contact manner, and eliminates the risk of deterioration in the strength of the optical fiber due to measurement.

In addition, since it is now possible to measure the coating film thickness online during manufacturing, the measurement results obtained can be immediately fed back to the coating conditions and continue manufacturing by, for example, adjusting the amount of raw material supplied. Appropriate coated optical fibers can be manufactured.

The present invention is particularly advantageous when applied to carbon-coated fibers and other hermetically coated fibers with metallic luster.

[Brief explanation of drawings]

FIGS. 1(a) to 1(c) are schematic diagrams for explaining the measurement method of the present invention, in which FIG. 1(a) shows the configuration of the present invention, and FIG. (c) is a diagram showing the relationship between the carbon thin film thickness and reflected light intensity obtained in the example of the present invention, and (d) is a diagram explaining the experiment of the raw material gas in the example of the present invention. Various film thicknesses (
3 is a chart showing the results of in-line measurement of reflected light intensity over time while forming a carbon film (estimated from electrical resistance value). Figure 2 is a cross-sectional view of an optical fiber with a thin film coating, Figure 3 is a line diagram when the present invention is applied to the manufacturing process, and Figures 4 (a) and (b) are schematic explanatory diagrams of the conventional measurement method. It's so hot. In the figure, 1. Preform, 2. Drawing furnace, 31 reaction tubes, 4
: Heater 5. Dice, 6: Resin curing means, 7: Winder, IO9 light source, 11-13; Lens, 14. Detector,
16. amplifier, 17. Electrometer, 204. fiber 23
．． Pyrolithinok carbon film, 24: carbon coated fiber.

Claims (1)

[Claims] (1) A method for measuring the thickness of a thin film with metallic luster that coats the outer periphery of an optical fiber, by irradiating the surface of the thin film-coated optical fiber with a light beam and measuring the intensity of the light reflected by the thin film. A film thickness measurement method characterized by determining film thickness.