JPS6219683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film thickness control device for forming a dielectric film used for purposes such as an optical antireflection film, and particularly to a film thickness control device for forming a dielectric film used for purposes such as an optical antireflection film. The present invention relates to a thickness control device.

In the semiconductor device manufacturing process, the process of depositing and forming dielectric films and oxide films is generally performed frequently and is indispensable. Particularly in recent years, by applying SiO ₂ or the like as a passivation film to the reflective surface of a semiconductor laser diode, deterioration of the reflective surface is suppressed and the life of the device is significantly improved, and practical use is about to begin. However, if the thickness of the passivation film of a semiconductor laser diode is not controlled within several percent, the oscillation threshold will increase due to a change in reflectance, which will adversely affect various characteristics of the semiconductor laser diode.

In spite of this, in the past, for example, in the sputtering method, the reproducibility of the film thickness was extremely poor because control was performed empirically based only on the sputtering time. This was because the dielectric film was formed under high temperature conditions and the electromagnetic interference caused by the high frequency power source was large, making it impossible to apply conventional mechanical and electrical film thickness measurement methods.

An object of the present invention is to solve the above-mentioned problems and provide a new film thickness control device that can easily control film thickness.

In the present invention, in the process of forming a dielectric thin film,
The film thickness is continuously monitored. That is, in an apparatus for forming a dielectric thin film, fibers that are not subject to electromagnetic interference due to high temperatures and high frequencies during formation are installed on both sides of a substrate whose refractive index is higher than that of the dielectric thin film, and the fibers are passed through the substrate and the dielectric thin film. The amount of light is
The thickness of the dielectric thin film is controlled by the detection.

According to the present invention, a base material having a refractive index higher than that of the dielectric thin film is installed in a dielectric thin film forming apparatus at a position where the same film thickness is formed on the sample and is to be used as a monitor.
A fiber is placed as an introduction part or a light receiving part for the incident light at a distance that does not interfere with the formation of the dielectric thin film on the surface to which the base material is attached, and the adhesion substance is not allowed to adhere to the tip surface of the fiber that serves as the introduction part. Attach a cover to prevent this. In addition, it is possible to provide a light-receiving section or a light-emitting section for transmitted light, in which a fiber is arranged through a condensing lens, on the non-adhesive side of the substrate, and to introduce and receive the incident light outside the forming apparatus. A film thickness control device with characteristics can be obtained.

The present invention will be described below with reference to the drawings.

The principle of the device of the invention is illustrated in FIG. In FIG. 1, n ₀ is the refractive index of vacuum, n is the refractive index of the dielectric thin film, and ns is the refractive index of the substrate. It is known from light receiving textbooks that when the thin film 11 is formed on a thick substrate 10, the reflectance repeats minimum and maximum every λ/4n (λ is the wavelength of light) of the thickness of the thin film. (Figure 2a). In Figure 2, n ₀ = 1, n = 1.48
(SiO ₂ ), ns = 3.37 (GaP). From the above, as shown in FIG.
As shown in Figure b, a change in light output is detected.
By continuously monitoring this change, the film thickness during the formation process can be known and the film thickness can be easily controlled. In particular, positions at integral multiples of λ/4n are easy to control because they are the maximum and minimum transmittance positions. The difference between the maximum and minimum values is the refractive index ns of the substrate 10
The larger the difference between and the refractive index n of the dielectric thin film 11,
Furthermore, the closer the angle of incidence of light to the substrate 10 and the dielectric thin film 11 is perpendicular, the greater it is. Generally, the larger the difference, the easier it is to control the film thickness.

As described above, by employing the present invention, highly accurate film thickness control can be achieved with high reliability, and the yield in the device manufacturing process can be greatly increased.

Next, an embodiment in which the film thickness control device of the present invention is applied to passivation of the reflective surface of a semiconductor laser diode using the SiO ₂ sputtering method will be described with reference to the drawings, with the non-adhesive surface side as the light emitting side.

As shown in FIG. 1, inside the sputtering device 19, the height of the surface of the substrate is the same as the height of the surface of the coated substrate (reflecting surface of the semiconductor laser) 18.
A fiber 12 for receiving transmitted light is installed with a base 10 and a cover 15 is attached to the base 10 in a position that does not interfere with the adhesion to the base 10 to prevent the adhesion substance 11 from wrapping around and adhering to the fiber tip surface.
Set up. Next, a fiber 14 for introducing incident light is installed on the non-attached side of the substrate 10 via a condensing lens 13. Both fibers 12 and 14 have their optical axes adjusted. Both fibers 12 and 14 are taken out of the vacuum chamber of the sputtering device with sufficient sealing. In order to receive incident light, a light emitting diode or laser diode 17 with a constant wavelength of, for example, 8300 Å is installed, and a photodiode 16 is installed on the light receiving side. With the above arrangement, a film thickness control device is constructed that is completely free from electromagnetic interference due to temperature and high frequency waves during the sputtering process.

In the process of forming a thin film for passivation using the sputtering method, as shown in FIG.
As the dielectric thin film 11 (SiO ₂ ) is deposited thereon, the reflectance decreases and the amount of transmitted light increases. Film thickness is λ/
At 4n, that is, d≈1400 Å, the reflectance becomes minimum and the transmitted light becomes maximum. Subsequently, the transmitted light decreases and returns to the point of initial light output, ie, the initial reflectance without film deposition. This point has a film thickness of λ/2n, and d≈2800 Å, indicating that the passivation film is reflectively coated on the reflective surface of the semiconductor laser. That is, the oscillation threshold and differential quantum efficiency become the same as before passivation.

As described above, by implementing the present invention, it becomes possible to easily form a protective film of any thickness while continuously monitoring the formation process of the protective film. That is, the passivation process becomes highly reliable and productivity is improved.

The device of the present invention can be widely applied to controlling the thickness of transparent dielectric thin films, and can also be applied to quaternary compound semiconductor lasers such as InGaAsP by appropriate combinations of refractive indexes. Various methods can be used for vacuum sealing between the fiber and the thin film forming apparatus, such as using a fiber connector. Further, the fibers are not of small diameter for optical communication, but it is also convenient to use large diameter fibers or fiber bundles for adjusting the optical axis.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the structure of the film thickness control device of the present invention;
FIG. 2 is a characteristic diagram showing changes in reflectance and transmitted light as the film thickness d increases. DESCRIPTION OF SYMBOLS 10... Base for monitoring, 11... Dielectric thin film, 12... Light receiving fiber, 13... Condensing lens for introducing incident light, 14... Fiber introducing incident light, 15... Cover, 16... Photo Diode, 17... Light emitting diode or laser diode, 18... Coated substrate, 19... Sputtering device.

Claims (1)

[Claims] 1. On the dielectric film adhesion surface side of a film thickness monitoring substrate material placed in a dielectric film forming apparatus and having a refractive index higher than that of the deposited dielectric film material, a layer is placed on the tip surface at a position that does not interfere with the formation of adhesion to the substrate. A fiber to which an adhesion prevention cover is attached is arranged, and the tip end surface of another fiber is arranged on the non-adhesive side of the base, and a condenser lens is arranged between the base and both fibers on one or both sides. , and a film thickness control device comprising a light emitting section and a light receiving section outside the dielectric film forming device via both the fibers.