JPH09148676A - Semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve purity of insulator, and prevent generation of damage due to heat, by forming at least one of resonator end surface of a semiconductor laser, from first insulator containing silicon and nitrogen as constituent elements, and second insulator on the first insulator. SOLUTION: A semiconductor laser 107 cut out from a wafer into the state of a bar is so set in an ECR equipment that the end surface of the semiconductor laser 107 is irradiated with ECR plasma 106, and further a solid Si 104 of high purity is set as a target. While nitrogen gas 108 and argon gas 110 are introduced, the ECR plasma 106 is generated. Si and N are ionized and a uniform flat SiN film is formed. Oxygen gas and argon gas 110 are introduced and an SiO2 film is formed. The SiN film can be formed by the ECR plasma 106 at a low temperature, so that generation of damage due to stress can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and its manufacturing method.

[0002]

2. Description of the Related Art Silicon nitride (hereinafter referred to as SiN) is frequently used in the manufacturing process of semiconductor devices. Particularly in semiconductor lasers, it is used as an end face reflection film or an end face passivation film.

Conventionally, the SiN film has been deposited using a magnetron sputtering device. Using SiN as the target,
Argon was used as the plasma gas. The magnetron sputtering apparatus is inexpensive and easy to handle, but the target SiN is a compound and therefore the purity is not so high. As a result, the deposited SiN film cannot be obtained with high purity.

Further, since the SiN film is deposited between the discharge electrodes of plasma, the substrate itself to be deposited is sputtered,
As a result, the plasma was greatly damaged and its use was limited.

There is also a method of depositing the SiN film by the CVD method. As the supply gas, a silicon compound gas such as SiH4 and Si2F6 and a gas containing N such as NH3 and N2 are used. Thermal CVD
In the method, the reaction is accelerated by heating the substrate with the above-mentioned supply gas to deposit the SiN film. The temperature at that time is 500 ℃ ~ 1000
° C. Therefore, it was difficult to use it for a substrate having low heat resistance. Further, the difference between the deposition temperature and the room temperature is large, and a large stress is generated in the substrate due to the difference in the coefficient of thermal expansion.

A plasma CVD method is disclosed in Japanese Patent Laid-Open No. 61-99677.
There is one such as that shown in the publication. The plasma discharge accelerates the reaction of the supply gas to deposit the SiN film. Therefore, the SiN film can be deposited at a relatively low temperature, but since the SiN film is deposited between the discharge electrodes of the plasma, plasma damage is large and the application is limited.

[0007]

As described above, the conventional SiN
For the deposition of the film, according to the magnetron sputtering device, the purity of the target is not very high, a high-purity SiN film cannot be obtained, and plasma damage occurs during the deposition.
There is that. In addition, the thermal CVD method requires high temperature deposition, which causes a large stress on the substrate, and the plasma CVD method causes plasma damage.

Therefore, an object of the present invention is to provide a semiconductor laser having a high-purity silicon nitride film deposited at a low temperature and a method for manufacturing the same.

[0009]

In order to achieve the above object, the method for producing a SiN film of the present invention uses ECR plasma. High-purity solid Si and nitrogen gas are used as the raw materials.

Further, the method for producing the SiN film is applied to the coating of the cavity end face of the semiconductor light emitting device such as a semiconductor laser.

The method for producing a SiN film according to the present invention is capable of depositing a SiN film at a relatively low temperature (200 ° C. or less), an action of depositing a SiN film without damaging the substrate, and a high-purity SiN film. It has the function of depositing a film. As a result, a SiN film with less stress can be deposited, a SiN film can be deposited without deteriorating the electrical characteristics of the electrodes of the semiconductor element, and a SiN film can be deposited without degrading the optical characteristics of the light emitting portion of the semiconductor element. It can be deposited, and a dense SiN film can be deposited.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.

(Embodiment 1) ECR (Elect
ron Cyclotron Resonance) plasma is used. The reaction formula is Si (solid) + N2 → SiN.

Solid Si is used as a raw material of Si. The reason for this is that a high purity one (six nine (6N)) is easily available, and a high purity SiN film can be deposited.

1N solid Si is set in the ECR apparatus of FIG. 1 as a target, and ECR plasma is generated while introducing nitrogen gas (flow rate 13 sccm) and argon gas (flow rate 13 sccm). The temperature at this time is room temperature. The use of ECR plasma has a high ionization rate of Si and N and enables efficient deposition of SiN film. When the flatness of the deposited SiN film was examined, it was extremely flat as shown in FIG. Since ECR plasma has a strong directivity and reactive species are supplied perpendicularly to the substrate, SiN can be uniformly deposited to obtain a flat SiN film. Further, since the ECR plasma is less damaged and does not sputter the deposited SiN film, the flatness as deposited can be maintained.

FIG. 3 shows the SiN deposition method and the refractive index of the SiN film. The presence of impurities such as hydrogen in the SiN film reduces the compactness and lowers the refractive index. With the ECR method, a refractive index similar to that of thermal CVD can be obtained at a low deposition temperature, and a dense film with few impurities can be deposited.

FIG. 4 is a diagram showing the relationship between the deposition temperature of the SiN film and the stress applied to the substrate by the SiN thin film at room temperature. The stress of the SiN film deposited at low temperature is small. Since the SiN film can be deposited at a low temperature by the ECR method, the SiN film with less stress can be obtained.

As described above, since high-purity solid Si is used in the production of the SiN film using ECR plasma, naturally, high-purity Si is used.
Not only can N film be deposited, it does not require deposition at high temperature unlike thermal CVD method, and it can be used for substrates with low heat resistance. It can be deposited at low temperature, so there is little stress, and it is flat and of high quality. Things are obtained.

Further, since a reaction gas such as SiH4 or Si2F6 is not used, a high-purity SiN film can be deposited without an intermediate product such as a Si compound, and particles are hardly generated in the deposition chamber.

Further, the ECR method is low in damage and has a high activation rate of nitrogen plasma, so that the growth rate is large,
SiN film can be deposited efficiently.

(Second Embodiment) Si described in the first embodiment
An embodiment in which an N film is applied to coating the end face of a semiconductor laser will be described.

In the apparatus shown in FIG. 1, a semiconductor laser cut out from a wafer into a bar state is installed so that plasma is irradiated to the end surface. As shown in FIG. 5, a SiN film is deposited on the end face of the laser as a front coat under the conditions described in the first embodiment, for example, by 809Å. Next, for example, oxygen gas (flow rate 13
sccm) and argon gas (flow rate 13 sccm) are introduced to remove the SiO2 film.
1172Å Accumulate. Oxidation of the laser facet is prevented by the SiN film and SiO2 film, and the facet reflection film is formed.

A SiN film is deposited on the first layer as described above,
Fig. 7 shows the reflectance when the SiO2 film is deposited as the second layer. If the 809 Å of the first layer of SiN film is deposited, the reflectance will increase.
It becomes less than 0.1% and laser oscillation becomes difficult. In addition, if the film thickness of the SiN film is deviated from 809Å, it can be set to an arbitrary value within the range of 27% or less, but in this case, the reflectivity changes greatly with a slight deviation of the film thickness, and This causes a large change in the characteristics and causes a decrease in yield. In order to prevent this, a two-layer structure is used, and the coating of the end face with good reproducibility is realized by using it in a wide range where a value close to the desired reflectance can be taken (part 701 in FIG. 7).

The reason for depositing the SiN film as the first layer of the front coat is that it has a higher thermal conductivity than the SiO2 film and is excellent in heat dissipation and can prevent an increase in the operating current of the device. If a SiO2 film is used for the first layer, mutual diffusion occurs at the interface between the laser chip and the SiO2 film, and the device deteriorates.
N film is good.

Further, in depositing the SiN film, the laser end face is less damaged, and the optical output is not deteriorated due to the damage.

The rear coat is formed by combining films so that the reflectance is optimum. Figure 6 shows the change over time in the operating current of a semiconductor laser with a constant optical output. S deposited by ECR method
The one using the iN film has less damage to the end face and does not deteriorate due to the deposition of the SiN film. As a result, the change over time is small and reliability is high. Furthermore, the deposited SiN film is flat, and the reflectance at the end face of the laser can be accurately controlled.

The second layer is SiON instead of SiO2 film.
A film may be used. The SiON film is deposited by introducing nitrogen gas, oxygen gas and argon gas. By changing the flow rate ratio of nitrogen gas and oxygen gas, the refractive index of 1.45 ~
Can be changed in 2.1. As a result, the front coat can be adjusted to the optimum reflectance.

[0028]

As described above, according to the present invention, SiN having low temperature, high purity, no damage to the substrate and high flatness is obtained.
The film can be easily deposited.

Further, when the SiN film produced by the ECR method is used for the end face of the semiconductor laser, oxidation of the end face is prevented, and since the thermal conductivity is good, a highly reliable semiconductor laser with stable operating current can be realized. You can

[Brief description of the drawings]

FIG. 1 is a structural sectional view of an ECR plasma device using a solid source.

FIG. 2 (a) is a characteristic diagram showing the roughness of the film when ECR plasma is used, and (b) is a characteristic diagram showing the roughness of the film when magnetron sputtering is used.

FIG. 3 is a diagram showing the deposition method and the refractive index of the SiN film.

FIG. 4 is a diagram showing the relationship between the deposition temperature of the SiN film and the stress applied to the substrate.

FIG. 5 is a diagram showing a configuration of an end face coat.

FIG. 6 is a diagram showing a change with time of an operating current at a constant optical output.

FIG. 7 is a diagram showing reflectance when a two-layer film is used.

[Explanation of symbols]

 101 magnetron 102 plasma generation chamber 103 electromagnet coil 104 Si target 105 RF power supply 106 ECR plasma 107 sample 108 thin film deposition chamber 109 nitrogen gas 110 argon gas 201 SiN film 202 substrate 203 SiN film 204 substrate 501 SiN film 502 SiO2 film 503 front coat 504 Rear coat 505 Laser light 701 End coat end

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhito Kumabuchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (14)

[Claims] 1. A semiconductor laser comprising a semiconductor substrate, an active layer formed on the semiconductor substrate, and a pair of clad layers sandwiching the active layer, wherein at least an end facet of a cavity of the semiconductor laser is provided. A semiconductor laser, one of which is formed of a first insulator containing silicon and nitrogen as constituent elements and a second insulator deposited on the first insulator. 2. The semiconductor laser according to claim 1, wherein
A semiconductor laser, wherein a refractive index of the first insulator is larger than a refractive index of the second insulator. 3. The semiconductor laser according to claim 1, wherein:
A semiconductor laser, wherein the first insulator is SiN. 4. The semiconductor laser according to claim 1, wherein
A semiconductor laser, wherein the first insulator is SiON. 5. The semiconductor laser according to claim 1, wherein
A semiconductor laser, wherein the second insulator is SiO 2. 6. The semiconductor laser according to claim 1, wherein
A semiconductor laser, wherein the second insulator is SiON. 7. A semiconductor laser characterized in that an insulator containing silicon and nitrogen as constituent elements is deposited on at least one of the cavity end faces of the semiconductor laser by using solid silicon and electron cyclotron resonance plasma. 8. The semiconductor laser according to claim 7, wherein
A semiconductor laser, wherein the insulator is SiN. 9. The semiconductor laser according to claim 7, wherein
A semiconductor laser, wherein the insulator is SiON. 10. A step of depositing a first insulator containing silicon and nitrogen as constituent elements on at least one of the cavity end faces of a semiconductor laser by using solid silicon and electron cyclotron resonance plasma. And a step of depositing a second insulating material on the insulating material. 11. The method of manufacturing a semiconductor laser according to claim 10, wherein the first insulator is SiN. 12. The method of manufacturing a semiconductor laser according to claim 10, wherein the first insulator is SiON. 13. The method of manufacturing a semiconductor laser according to claim 10, wherein the second insulator is SiO2. 14. The method of manufacturing a semiconductor laser according to claim 10, wherein the second insulator is SiON.