JPH0325123Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a film thickness monitoring device that uses laser light.

2. Description of the Related Art Film thickness monitoring devices that utilize laser light interference have been put into practical use in thin film growth devices such as vacuum evaporation and sputtering optical evaporation. In this device, as the thin film grows, the laser light periodically exhibits strength and weakness due to interference, and the thickness of the thin film is measured from the period using the following equation.

Here, Δd is the film thickness per period, n is the refractive index,
λ is the wavelength of the laser beam, and θ is the angle of incidence.

This device can be used satisfactorily for simply monitoring film thickness. However, due to the instability of the output intensity of commonly used small He-Ne laser devices, it is not possible to obtain even information regarding film quality (surface roughness, crack formation). Therefore, the present applicant has developed a film film that eliminates the instability of the output intensity of the laser device by dividing the signal light intensity by the reference light intensity, and observes the decrease in interference light due to surface roughness, cracks, etc. during film formation. Previous applications have been made for devices that can simultaneously monitor thickness. however,
In a typical film forming apparatus as shown in FIG. 1, signal light (interference light) is often extracted to the outside by an optical system inside the bell gear. In Figure 1, 1 is a vacuum bell gear, 2 is a thin film being formed, 3 is an evaporated material, 4 and 5 are reflecting mirrors, 6 is a window, and 7 is He-Ne
a laser device, 8 a photodetector for detecting reference light, 9 a differential amplifier circuit for amplifying its output, 10
11 is a differential amplifier circuit for amplifying the output of the photodetector for detecting signal light; 12 is a division circuit 12 for dividing the output of the differential amplifier circuit 11 by the output of the differential amplifier circuit 9; 13 is a recorder for recording the output of the divider circuit 12;

In the illustrated device, the signal light is reflected several times by the reflecting mirror, so that the laser light incident without polarization is polarized and output. On the other hand, the reference light remains almost unpolarized. However, even if the beam output of the laser device is held constant, a certain amount of "fluctuation" occurs when looking at the single polarization component, and in order to compensate for the fluctuations caused by this fluctuation, the conventional device described above Then, the signal light intensity is divided by the reference light intensity. However, since the reference light is unpolarized light, that is, it contains a plurality of polarized light components, the fluctuations of each component cancel each other out and hardly change over time. Therefore, in the configuration shown in FIG. 1, the above division is not performed accurately, and fluctuations in the signal light cannot be corrected.

Therefore, the purpose of the present invention is to divide the beam emitted from the laser generator into two parts, use one as a reference beam and the other as a signal beam, and increase the intensity of the signal beam reflected by the film being formed. Provided is a film thickness monitoring device that detects film thickness from the quotient obtained by dividing by the intensity of a reference light, in which the above division is performed accurately and information on film quality regarding surface roughness, cracking, etc. can also be obtained. An object of the present invention is to provide a film thickness monitoring device that enables the following.

In order to achieve the above object, the film thickness monitoring device according to the present invention has a linear polarizing plate at the beam exit of the laser generator.

Hereinafter, the present invention will be explained in more detail using examples with reference to the drawings, but these are merely illustrative and it is understood that various modifications and improvements may be made without going beyond the scope of the present invention. Of course.

FIG. 2 is a block diagram showing the configuration of the film thickness monitoring device according to the present invention. Reference numbers common to those in FIG. 1 in the figure represent the same parts as in FIG.
4 is a linear polarizing plate.

Generally, unpolarized laser light becomes a single linearly polarized laser light when reflected by a reflecting mirror inside the bell gear. Therefore, a linearly polarizing plate 14 provided at the exit of the laser generator 7 is used to convert the output laser beam into a linearly polarized laser beam that matches the optical system (combination of reflecting mirrors) of the device. By doing so, the signal light and the reference light have the same time fluctuation, allowing accurate division, and making it possible to monitor not only the thickness of the film being formed, but also the quality of the film.

Using a linearly polarized laser device with stable output eliminates the need for a divider circuit and a linear polarizer due to the instability of the output of the laser light, but such a device is very expensive. By using the film thickness monitoring device according to the present invention, performance equivalent to this can be obtained at a considerably lower cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the structure of a conventional film thickness monitoring device, and FIG. 2 is a block diagram showing the structure of a film thickness monitoring device according to the present invention. 1... Vacuum bell gear, 2... Thin film being formed, 3
...evaporated matter, 4,5...reflector, 6...window, 7...
...He-Ne laser device, 8,10...photodetector,
9, 11...differential amplifier circuit, 12...divider circuit,
13...Recorder, 14...Polarizing plate.

Claims (1)

[Scope of utility model registration request] The beam emitted from the laser generator is divided into two, one is used as a reference beam and the other is used as a signal beam, and the intensity of the signal beam reflected by the film being formed is divided by the intensity of the reference beam. A film thickness monitoring device for detecting film thickness from the obtained quotient, characterized in that the film thickness monitoring device has a linear polarizing plate at the exit of the beam of the laser generator.