JPH0378276A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve reproducibility and element properties by burying a light wave guide path with II-VI compound semiconductor and etching the semiconduc tor with the aid of specific reactive gas. CONSTITUTION:An n-GaAs buffer layer 2, an n-Al0.5Ga0.5 clad layer 3, an Al0.15 Ga0.85As active layer 4, a p-Al0.5Ga0.5As clad layer 5, and a p-GaAs contact layer 6 are stacked in order on an n-GaAs substrate 1 so as to form a substrate in DH structure. The surface is etched to the middle of the layer 6 with the resist 7 as a mask so as to form a rib. A ZnSe film 8 is grown thereon so as to bury the rib. A resist mask 9 having an opening is formed, and the ZnSe film 8 on the rib is etched off by RIBE. For the reactive gas at that time, a mixture gas, which includes inert gas of 1-90% by volume ratio, is used. Thence, a P-type electrode 10 and an N-type electrode 11 are formed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a semiconductor laser.

[Prior art] Zinc selenide (ZnSe), zinc sulfide (ZeS), etc.
and ■-■ group compound semiconductors consisting of these mixed crystals,
It has features that other material systems do not have, such as a wide forbidden band, high specific resistance, and low refractive index. Taking advantage of these features, Zn5e thin films, for example, can be used as current confinement layers and optical confinement layers in AlGaAs semiconductor laser devices. It is used as. FIG. 2 shows a cross-sectional view of the structure of an AlGaAs semiconductor laser device embedded with a Zn5e thin film layer, which was published by Iwano et al. in the Proceedings of the Japan Society of Applied Physics (Spring 1988, 28p-ZH-8). A Zn5e thin film layer 8 is formed so as to embed a rib-shaped optical waveguide (hereinafter abbreviated as rib). Further, the upper surface of the rib is exposed in a stripe shape without forming a Zn5e thin film layer to form an electrode. When it is desired to selectively form a Zn5e thin film layer on a semiconductor substrate as in this structure, in the conventional technology, first a II-VI layer is formed on the entire surface of the semiconductor substrate.
Group compound semiconductors are laminated, and then a portion of the II-VI group compound semiconductor to be removed is removed by wet etching or dry etching using a photoresist or the like as a mask in a photolithography process.

In wet etching technology, the etching solution mainly used is hydroxide (IJ) aqueous solution,
Examples include hydrochloric acid and a mixed solution of nitric acid-hydrochloric acid and water.

On the other hand, dry etching technology uses parallel plate electrodes.
Ion etching (IE) with inert gas such as r, C
12, reactive ion etching (RIE) using a reactive gas such as BCIs, and reactive ion beam etching (RIBE).

[Problem to be solved by the invention] However, the n-vt by the above-mentioned wet etching technology
Processing of group compound semiconductors has the following problems.

A problem with wet etching technology in general is that it suffers from poor reproducibility. A constant etching rate cannot be obtained unless the temperature, composition of the etching solution, etc. are controlled very strictly. For example, according to the prior art, m-
When Zn5e, which is an n-vt group compound semiconductor, is formed on a GaAs substrate, which is a V group compound semiconductor, and the Zn5e is removed using an etching solution of nitric acid-hydrochloric acid and water, GaAs is also etched by the nitric acid-hydrochloric acid and water etching solution. Therefore, if the etching rate cannot be controlled, the GaAs substrate will also be etched, making it extremely difficult to remove only Zn5e.

Further, when etching is performed using an aqueous NaOH solution, there is a problem in that the surface morphology is extremely deteriorated.

On the other hand, in ion etching technology using an inert gas such as Ar, etching progresses by physical sputtering, and in order to bring the etching rate to a level suitable for manufacturing semiconductor laser devices, it is necessary to increase the plasma discharge power. , which causes great damage to the semiconductor layer and greatly deteriorates the characteristics of the semiconductor laser. In addition, since there is not a large difference in etching speed depending on the material in principle,
It becomes necessary to make the mask thicker, which causes a decrease in yield. Furthermore, compared to the aforementioned ion etching, the RIE method using a reactive gas such as BCIs also has the added factor of advancing etching due to a chemical reaction, so although the damage to the semiconductor layer is reduced, it is not within an acceptable range. Also, the cleanliness of the plasma is low (there are problems with contamination, such as carbon adhering to the semiconductor layer during etching).

Further, this conventional technique has the problem that abnormal discharge tends to occur and the reproducibility of the etching rate is poor. Furthermore, the aforementioned carbon adhesion also affects etching rate fluctuations. In order to control the etching rate with good reproducibility, it is necessary to stabilize the plasma, and mixing an inert gas such as Ar is effective for this purpose. However, if the mixing ratio of the inert gas is too large, there are problems such as damage to the semiconductor layer, so it is necessary to optimize the mixing ratio of the inert gas.

Therefore, the present invention aims to solve these problems, and its purpose is to provide II-
The present invention provides a method for manufacturing a semiconductor laser embedded in a group VI compound semiconductor.

[Means for Solving the Problems] A method for manufacturing a semiconductor laser of the present invention includes a step of forming a rib-shaped optical waveguide made of a laminated structure of m-v group compound semiconductors, and forming the optical waveguide with a layered structure of II-VI group compound semiconductors. In a semiconductor laser manufacturing method including a step of embedding a semiconductor and a step of etching the aforementioned ■-■ group compound semiconductor by a reactive ion beam etching method using microwave excitation of a reactive gas-ECR plasma, the etching gas contains at least a halogen element. and an inert gas, and the pressure of the etching gas is 5X.
The input power of the microwave is in the range of 10-3 Pa or more and 10 Pa or less, and the input power of the microwave is LOW or more and 1000 Pa or less.
The voltage for extracting the ion beam to the sample is in the range of 10 V or more and 1000 V or less, and the temperature during etching of the sample is in the range of 0° C. or more and 350° C. or less. It is characterized by a range.

[Example] As an example of the present invention, a rib formed on the top of a double heterojunction (DH) was buried with a Zn5e thin film layer, and Zn5e-embedded AlG was used for current confinement and optical confinement.
A part of the manufacturing process of an aAs semiconductor laser device will be explained.

FIGS. 1(a) to 1(e) illustrate the present invention in detail, and are schematic cross-sectional views of a substrate during the manufacturing process of an element. (
100) on the n-type GaAs substrate plate 1 with a plane orientation of 0. 5μ
m-thick n-type GaAs buffer layer 2.1.5 μm-thick n
Type A 1 e, sG a @, sA s cladding layer 3.
0.1 μm thick non-doped A I 11.1 G a
s, ssA sActive layer 4.1.5 μm thick p-type A 1
e, sG a s, sA s cladding layer 5.0.5μm
A substrate having a DH structure in which thick p-type GaAs contact layers 6 are sequentially laminated is prepared. (FIG. 1(a)) Next, using an etching mask such as a resist 7, the surface of the DH substrate is etched to the middle of the p-type rad layer 6 to form ribs. (Figure 1(b)) A typical rib shape has a width of 5 μm at the top and 3.5 μm at the bottom.
The height is 1. It is 5 μm. Next, a Zn5e thin film 8 is epitaxially grown to bury this rib. Epitaxial growth is performed using metal organic chemical vapor deposition (MOCV).
D method) etc. (FIG. 1(C)) Next, in order to remove the Zn5e8 on the ribs by etching, a resist mask 9 having an opening on the rib-shaped optical waveguide is formed. Here, etching is performed using reactive ion beam etching method (
RIBE). The etching apparatus used in the present invention will be explained below. FIG. 3 shows a schematic cross-sectional view of the configuration of the reactive ion beam etching apparatus used in this example. Since a gas containing a highly reactive halogen element is used, the apparatus has a sample preparation chamber 12 and an etching chamber 13.
The etching chamber 13 is kept in a high vacuum state at all times. 14
is an electron-cyclotron resonance (ECR) plasma chamber, which is surrounded by a cylindrical donut-shaped fill 15 for generating a magnetic field. 16 is a microwave waveguide, in which electrons ionized and generated by microwaves repeatedly collide with gas while performing cyclotron motion due to an axially symmetrical magnetic field. This rotation period matches the microwave frequency, for example 2.45 GHz, when the magnetic field strength is, for example, 875 Gauss, and the electronic system resonantly absorbs the microwave energy. Therefore, the discharge can be sustained even at low gas pressures, high plasma density can be obtained, and the reactive gas can be used for a long time. Furthermore, the electrons and ions are focused at the center due to the high electrolytic distribution at the center, so the sputtering effect of the ions on the side walls of the plasma chamber is small, resulting in highly clean plasma. ECR
Ions generated in the plasma chamber 14 are accelerated by the mesh-like extraction electrode section 17 and irradiated onto the sample 18. The sample holder 20 can be heated and cooled, and can maintain the sample temperature from -20°C to 500°C.

In this example, a mixed gas of pure chlorine gas and argon gas was used as the etching gas. The mixing ratio of argon gas was 25% by volume, and etching was performed under the conditions of a gas pressure of 0.1 Pa, a microwave input power of 200 W, and an extraction voltage of 400 V. The etching rate of Zn5e at this time was 700 A/min, and the etching rate of Zn5e (approximately 2 μm
) is at a sufficiently practical level for etching. Figure 4 (
a) and (b) are Z before etching (Fig. 4(a)) and after etching (Fig. 4(b)) under the above etching conditions.
This is a comparison of the photoluminescence of n5e thin films. The ratio of the intensity due to band edge emission to the intensity due to deep level emission remains about 50 both before and after etching, and there is almost no damage due to etching, and RIBH does not deteriorate the device characteristics. Further, by mixing argon gas, abnormal plasma discharge did not occur and the reproducibility of the etching rate was stable between batches at ±2% (±7% in the case of pure chlorine gas). Also, the adhesion of carbon and chlorine on the semiconductor surface has been drastically reduced. This is because carbon and chlorine adhering to the etched surface are removed by the sputtering effect of argon ions, and reactive etching progresses.

A cross-sectional view after etching is completed is shown in FIG. 1(d).

FIG. 1(e) is a cross-sectional view of a semiconductor laser device obtained by removing the etching mask after RIBE, forming a P-type electrode 10 and an N-type electrode 11, and folding the resultant layer.

Since the Zn5e layer has high resistance (10MΩ・cm), P
The current injected from the mold electrode 10 flows concentratedly in the ribs,
The Zn5e layer 8 serves as a complete current confinement layer.

The semiconductor laser manufactured according to the present invention has less variation in the threshold current of continuous oscillation at room temperature between elements and has a lower threshold current than that manufactured by the conventional wet etching method. Regarding the lifetime characteristics of the device, similar to the threshold current results, the present invention achieved longer lifetime characteristics with less variation than the conventional method.

Good etching conditions for II-VI group compound semiconductors in manufacturing semiconductor lasers are as follows.

First, regarding the proportion of inert gas in the etching gas,
The greater the proportion of inert gas, the greater the sputtering effect of inert gas ions. This sputtering effect has the effect of removing substances adhering to the etching surface, such as carbon, reactive gas, or reaction products between the reactive gas and the etching material, which inhibit the progress of etching or make it non-uniform. Furthermore, it also contributes to stabilizing the plasma, but if the proportion of inert gas becomes too large, etching due to the sputtering effect becomes dominant, resulting in a decrease in the etching rate and
Problems such as increased damage to the semiconductor layer arise. An appropriate mixing ratio of the inert gas is 1% or more and 90% or less by volume.

Regarding gas pressure, the higher the pressure, the faster the etching rate. - As an example, Table 1 shows a microwave input power of 200 W and an extraction voltage of 400 V.

Gas pressure (Pa) when using a mixed gas of pure chlorine gas and argon gas (mixing ratio of argon gas is 25% by volume)
) of Zn5e at room temperature (A
/min). The range with good practicality and controllability is 5X1
It is from 0-3 Pa to 10 Pa.

Regarding the input power of the microwave, the higher the power, the higher the etching speed. However, if the etching thickness is unnecessarily thick (if this happens, the plasma temperature will rise, causing thermal deformation of the electrode, and the substrate temperature will rise due to radiant heat, making temperature control difficult and making it impossible to control the etching rate.Table 2
For this, a mixed gas of pure chlorine gas and argon gas (mixing ratio of argon gas is 40% by volume) is used, and the microwave incident output when the gas pressure is 0°2 Pa and the extraction voltage is 300 V (in the table) The etching rate (A/min) of 2nSe at room temperature is shown relative to the incident power (unit W). The range with good practicality and controllability is 10 W or more and 1000 W or less.

Regarding the extraction voltage, the higher the voltage, the higher the etching rate; however, if the voltage is too high, physical sputtering will become stronger, causing great damage to the semiconductor layer. Table 3 uses a mixed gas of pure chlorine gas and argon gas (the mixing ratio of argon gas is 50% by volume), and the gas pressure is 0.
, 2 Pa, shows the etching rate of Zn5e at room temperature (R1 unit A/min in the table) with respect to the extraction voltage (H1 unit V in the table) when the microwave incident output is 100 W. Moreover, the inside of the table shows the degree of damage to the semiconductor layer. The range that has good practicality and controllability and does not damage the semiconductor layer is 10 V or more and 1000 V or less.

Table 1 Regarding temperature, the higher the temperature, the faster the etching rate. Table 4 uses a mixed gas of pure chlorine gas and argon gas (the mixing ratio of argon gas is 10% by volume), the gas pressure is 0.1 Pa, the microwave incident power is 100 W,
Shows the etching rate (A/min) of Zn5e against temperature ("C) when the extraction voltage is 300V. Practicality,
The range with good controllability is from 0°C to 350°C.

Although a specific II-VI group compound semiconductor was taken up in the above embodiments, the application of the present invention is not limited to this range. That is, the present invention provides
It can also be applied to a thin film formed by a combination of a group compound and a group compound such as Ss Se or Tes O. In addition, the semiconductor laser according to the present invention includes laser materials other than AlGaAs,
For example, the present invention can be similarly applied to InGaAsP-based and InGaP-based materials. In addition, the structure of the semiconductor laser is not limited to the one based on the three-layer waveguide shown in the example, but also the LOC structure in which a light guide layer is provided adjacent to one side of the active layer, and the LOC structure in which a light guide layer is provided adjacent to one side of the active layer. The present invention can be similarly applied to an SCH structure in which a light guide layer is provided adjacently, and a GRIN-3CH structure in which the refractive index and forbidden band width of these light guide layers are distributed in the film thickness direction. . Furthermore, it is also effective for those whose active layer has a quantum well structure. Further, in the embodiment, a similar effect can be obtained even in a structure in which the conductivity types of each layer are all reversed (a structure in which p is replaced with n and n is replaced with p). Also, we explained about a mixed gas of pure chlorine gas and argon gas as an etching gas in the RIBE process, but BC is a reactive gas.
Is, Br2, CFa, etc. (all containing halogen elements, rare gases such as He5Ne as inert gases, N
It is valid even for 2nd place.

[Effects of the Invention] The method for manufacturing a semiconductor laser of the present invention has the following special effects of the invention, and makes it possible to manufacture a semiconductor laser that fully utilizes the characteristics of II-VI group compound semiconductors. .

(1) RIBE removal process of II-Ml group compound semiconductor
By mixing an inert gas with the reactive gas in the RIBE process and further regulating the mixing ratio of the inert gas, control of the removal of the II-VI group compound semiconductor on the ribs is greatly improved. Semiconductor lasers can be manufactured with good reproducibility.

(2) Since the mixing ratio of inert gas is specified, RIBH
Since this does not damage the compound semiconductor layer, the characteristics of the semiconductor laser are not impaired at all.

(3) Since the II-VI group compound semiconductor is etched by a dry process, the controllability and reproducibility are much better than the conventional wet process.

(4) There is no deterioration or destruction of the device due to the etching solution seeping into the device, which is a problem especially in wet etching of n-vt group compound semiconductors.

(5) By mixing inert gas with reactive gas,
Contamination caused by carbon, chlorine, etc. on the semiconductor surface can be removed, and a decrease in yield in subsequent processes can be prevented.

[Brief explanation of drawings]

FIGS. 1(a) to 1(e) are process cross-sectional views of a semiconductor laser illustrating a first embodiment of the present invention. FIG. 2 is a cross-sectional view of the structure of a semiconductor laser manufactured by a conventional method. FIG. 3 is a schematic cross-sectional view of the structure of an etching apparatus used in an embodiment of the present invention. FIGS. 4(1m) and 4(b) are diagrams showing the 7 otoluminescence of the Zn5e thin film before (FIG. 4(a)) and after (FIG. 4(b)) RIBE. n-type GaAs substrate n! ! ! ! GaAs buffer layer n-type A 1 s, sGa s, sAs craft layer A
1 m, +sG a e, ssA s active layer p-type A
1 e, sG a a, sA s cladding layer p-type GaA
s Contact layer photoresist Zn5e buried layer photoresist O 11 2 3 4 5 6 7 8 9 0 ・P-type ohmic electrode ・N-type ohmic electrode ・Sample preparation chamber ・Etching chamber ・ECR plasma generation chamber ・Electromagnet ・Microwave waveguide・Extraction electrode・sample・gate valve fort sample holder and above

Claims (5)

[Claims] (1) Forming a rib-shaped optical waveguide made of a laminated structure of III-V compound semiconductors, and converting the optical waveguide into II-V
A semiconductor laser comprising a step of embedding a group I compound semiconductor, and a step of etching the group II-VI compound semiconductor by a reactive ion beam etching method using microwave excitation-ECR plasma of a mixed gas of a reactive gas and an inert gas. A method for manufacturing a semiconductor laser, characterized in that the proportion of inert gas in the mixed gas is 1% or more and 90% or less by volume. (2) Claim 1 characterized in that the etching pressure is in the range of 5×10^-^3Pa to 10Pa.
A method of manufacturing the semiconductor laser described above. (3) The incident power of the microwave is 10W or more and 1000
2. The method for manufacturing a semiconductor laser according to claim 1, wherein the range is W or less. (4) The method of manufacturing a semiconductor laser according to claim 1, wherein a voltage for extracting the ion beam to the sample is in a range of 10 V or more and 1000 V or less. (5) The temperature during etching of the sample is 0°C or higher and 350°C.
2. The method of manufacturing a semiconductor laser according to claim 1, wherein the temperature is below .degree.