JPH098406A - Reflection preventing film forming method - Google Patents

Abstract

PURPOSE: To measure the reflection factor of 1% or smaller by a method wherein a reflection preventing film is simultaneously deposited on a P-type InP board besides the sample to be deposited on the reaction preventing film. CONSTITUTION: A sample support 21 is provided when bar-like semiconductor lasers are fixed to a jig, the bar-like semiconductor lasers are arranged with their edge faces facing upward. A P-type InP board 23 is mounted adjacent to the semiconductor lasers 22, and the bar-like semiconductor lasers 22 are fixed by the plate spring 24 supported by a plate spring support 25. As the absorption of light originated in IVBA is large, the coefficient absorption of the P-type InP board 23 is larger by one order of magnitude or more than the N-type or a semi-insulating InP board. Accordingly, the residual reflection from the backside of the board is absorved into the board and residual reflection is not generated, and the reflection factor of 1% or smaller can be measured easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an antireflection film provided on an end face of a semiconductor device used for optical communication, optical information processing and the like.

[0002]

2. Description of the Related Art In recent years, an antireflection film is formed on an end face of a semiconductor device such as a semiconductor laser to manufacture a semiconductor optical amplifier,
The characteristics of semiconductor lasers are being improved. Since such an antireflection film generally requires a reflectance of 1% or less, the technical development is to easily measure the reflectance in addition to the means for measuring the refractive index and the film thickness of the formed antireflection film. Means that can do it are indispensable.

Conventionally, as a method of knowing the reflectance of a formed film, a monitor substrate is placed in the immediate vicinity of a sample on which an antireflection film is deposited, and the film is simultaneously deposited on both the sample and the monitor substrate. There is a method of measuring the reflectance of the monitor substrate.
As the monitor substrate, an n-type InP substrate or an anti-insulating InP substrate, which has a refractive index close to that of a waveguide of a semiconductor device and has high versatility, has been used.

[0004]

However, the above n
The present inventors have found that in a type InP substrate or an anti-insulating InP substrate, residual reflection from the back surface is about 1%. That is, it was found that the above-mentioned conventional method can measure the reflectance of several percent, but cannot measure the reflectance of 1% or less.

Therefore, there is no choice but to use a known method of measuring the internal gain of a semiconductor laser having an antireflection film formed thereon and calculating the reflectance of the antireflection film from the ripple of spontaneous emission light. (NAOlsson, "Lightwave systems with
optical amplifiers ", J. Lightwave Technol., vol.LT-
7, pp.1071-1082,1989) However, this known method is complicated because the calculated reflectance is accurate but a semiconductor laser and an optical system for measuring internal gain are required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned conventional techniques and provide a means for easily measuring a reflectance of 1% or less.

[0007]

In order to achieve the above object, the present invention provides a method of forming an antireflection film on a semiconductor device, wherein the film is simultaneously deposited on a p-type InP substrate in addition to the film deposition sample. Deposit.

[0008]

[Function] The p-type InP substrate is IVBA (absorption between valence bands)
Since the light absorption due to is large, the absorption coefficient is one digit or more larger than that of the n-type or anti-insulating InP substrate. Therefore, according to the present invention, since the residual reflection from the back surface of the substrate is absorbed in the substrate and the residual reflection does not occur, the reflectance of 1% or less can be easily measured.

The operation of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a sectional view when the antireflection film 11 is provided on the substrate 10 and light is vertically incident on the substrate.
Part of the incident light 12 is reflected from the substrate surface (reflected light 14 from the substrate surface). The remaining light not reflected on the substrate surface travels in the substrate 10, is reflected on the back surface of the substrate 10, travels in the substrate 10 again, and returns to the incident side (residual reflected light 13 from the back surface of the substrate). .

The incident light intensity is 1, and the reflected light intensity from the substrate surface is R. Residual reflected light intensity from backside of substrate r
Is expressed as follows.

[0012]

[Equation 1]

(R _b : reflectance of the back surface of the substrate, α: absorption coefficient of the substrate, L: thickness of the substrate) Since the reflectance of the entire substrate is R + r, R can be obtained from the measurement of the reflectance by R >> r is required.

Then, next, r of the InP substrate is obtained, and R>
Clarify whether the relation of> r is satisfied.

R: Approximately 1%.

R _b : It is about 2.5% (measured value at a wavelength of 1.5 μm) because the back surface of a commercially available substrate is roughly scattered.

Α: The absorption coefficient at room temperature at a wavelength of 1.5 μm is as follows. n-type InP substrate (impurity concentration 5X
10 ¹⁸ / cm ³ ) is 7.5 / cm (OKKim WAB
onner, "Infrared reflectance and absorption of n-ty
pe InP ", Journal of Electronec Materials, vol.12, pp.
827-836,1983). It is known that the anti-insulating InP substrate also has almost the same absorption coefficient. On the other hand, the absorption coefficient of the p-type InP substrate (impurity concentration 5 × 10 ¹⁸ / cm ³ ) is 130.
/ Cm, which is more than an order of magnitude higher than n-type or anti-insulating properties (HCCasey, Jr and PLCarter, "Variation of
intervalence band absorption with hole concentrati
on in p-type InP ", Appl.Phys.Lett.vol.44, pp.82-83,1
984).

L: The thickness of a commercially available substrate is usually 450 μm
(0.045 cm).

R: Substituting the above parameters into Equation 1, 1.3% (n-type or anti-insulating) and 0.00
002% (p-type) is obtained.

That is, in the case of an n-type or anti-insulating InP substrate, R to r, and the reflectance R from the substrate surface (reflectance of the antireflection film) cannot be obtained from the reflectance measurement of the entire substrate.

On the other hand, the p-type InP substrate satisfies R >> r, and the reflectance R from the substrate surface (reflectance of the antireflection film) R can be obtained by measuring the reflectance of the entire substrate. . That is, as shown in FIG. 1, the p-InP substrate 1
When the antireflection film 2 is provided on the upper surface, a part of the incident light 3 becomes the reflected light 5 from the front surface of the substrate and the remaining light 4 toward the rear surface of the substrate.
Are all absorbed.

[0022]

EXAMPLE An example of the present invention will be described below with reference to the case where an antireflection film is formed on the end face of a semiconductor laser having an oscillation wavelength of 1.5 μm.

FIG. 3 shows a method of fixing the bar-shaped semiconductor laser to the jig. A sample support 21 is provided on the jig body 20, and the bar-shaped semiconductor lasers 22 are arranged side by side with the end face upward. Adjacent to the p-type InP substrate (Zn doping concentration 5
X10 ¹⁸ / cm ³ ) 23 was placed, and the bar-shaped semiconductor laser 22 was fixed by the plate spring 24 supported by the plate spring support 25.

FIG. 4 shows a method of fixing the jig to the chamber of the EB vapor deposition apparatus. The jig 32 shown in FIG.
It was fixed downward to the inner rotating dome 31. Rotating dome 3
1 rotates about the axis shown by the one-dot chain line in the figure, and a uniform film can be deposited. The chamber 30 was evacuated by the exhaust pipe 34, and a TiO ₂ film and then a SiO ₂ film were deposited for a predetermined time under a predetermined substrate temperature and oxygen partial pressure. 33 is an evaporation source.

FIG. 6 shows a reflectance measuring system for a p-type InP substrate. The light emitted from the white light source 40 enters the spectroscope 43 through the chopper 41 and the short wavelength cut filter 42. A slit 44 is provided at the entrance and exit of the spectroscope 43 for adjusting the resolution.
Is provided. The light emitted from the slit 44 on the exit side is
50:50 beam splitter 46 through lens 45
As a result, half is reflected (upper part of the drawing) and half is transmitted (right part of the drawing). The light reflected by the beam splitter 46 is p
Upon hitting the InP substrate 47, the reflected light passes through the beam splitter 46, is received by the light receiver 48, and the output is amplified by the lock-in amplifier 49.

FIG. 7 shows the reflectance of the p-type InP substrate on which the antireflection film has been deposited, which was measured using the above measurement system. The deposited antireflection film is a TiO ₂ / SiO ₂ 2 layer film which has an antireflection condition at a wavelength of 1.5 μm. In the figure, n-type InP
The reflectance of the sample in which the same antireflection film is deposited on the substrate is also shown. Deposited n-type InP at wavelength of 1.5 μm
In the substrate, the residual reflection from the back surface of the substrate was superposed and was a little over 1%, whereas in the p-type InP substrate, the residual reflection was absorbed and removed to 0.4%, which was less than 1%. It was found that the reflectance can be easily measured.

In the above embodiment, p-type InP is used.
Although the substrate is used by being fixed to the jig itself, the present invention is not limited to this. For example, as shown in FIG.
The p-type InP substrate 35 is provided in the vicinity of the jig 32 on which the sample to be deposited is fixed, the semiconductor laser 36 irradiates light of a predetermined wavelength, and the light receiver 37 receives the reflected light from the p-type InP substrate 35. You may take a structure. In this case, the film thickness can be controlled by utilizing the fact that the reflected light intensity changes with the change of the deposited film thickness, and the reproducibility can be improved.

[0028]

According to the present invention, the reflectance of 1% or less can be easily measured.

[0029]

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a diagram showing the operation of the present invention.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a diagram showing an embodiment of the present invention.

FIG. 5 is a diagram showing an embodiment of the present invention.

FIG. 6 is a diagram showing a reflectance measurement system of an antireflection film according to the present invention.

FIG. 7 is a graph showing the reflectance of the antireflection film according to the present invention.

[Explanation of symbols]

1 ... p-InP substrate, 2 ... antireflection film, 3 ...
-Incoming light, 4 ... Light directed to the back surface of the substrate, 5 ... Reflected light from the front surface of the substrate, 10 ... Substrate, 11 ... Antireflection film, 12 ... Incident light, 13 ... Reflected light from substrate back surface, 14 ... Reflected light from substrate surface, 20 ... Jig body, 21 ... Sample support, 22 ... Bar-shaped semiconductor laser, 23 ... p-InP Substrate, 24 ... Leaf spring, 25 ... Leaf spring support, 30 ... Chamber, 31
... Rotary dome, 32 ... Jig for fixing sample, 3
3 ... Evaporation source, 34 ... Exhaust pipe, 35 ... P-type I
nP substrate, 36 ... Semiconductor laser, 37 ... Photoreceiver, 40 ... White light source, 41 ... Chopper, 42.
..Short wavelength cut filters, 43 ... Spectrometers, 44.
..Slits, 45 ... Lenses, 46 ... 50: 5
0 beam splitter, 47 ... p-type InP substrate, 48
... Receiver, 49 ... Lock-in amplifier.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mari Koizumi 1-280 Higashi Koikeku, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Hiroaki Inoue 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Center

Claims (2)

[Claims] 1. A method for forming an antireflection film on a semiconductor device, which comprises simultaneously depositing the film on a p-type InP substrate in addition to the film deposition sample. 2. Irradiating the p-type InP substrate with laser light,
The method for forming an antireflection film according to claim 1, wherein the film thickness is controlled by utilizing the change in the reflected light intensity.