JPH11283959A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clean a surface which is contaminated after dry etching by including a wet etching process with ammonium sulfide solution and a dry etching process with a reaction gas containing fluorocarbon between a process for forming a channel and a process for performing embedding growth. SOLUTION: On an n-type InP substrate 2, an n-type InP buffer layer 4, an undoped multi-quantum well active layer 5, a p-type InP clad layer 6, and a p-type InGaAs contact layer 7 are successively formed by the organic metal vapor growth method. Then, an SiO2 stripe 1 is formed by the thermal CVD method and is introduced into an etching treatment apparatus, and a groove with a micron step shape is formed by dry etching due to a reaction gas containing fluorocarbon. Then, from such a wafer, an In oxide is eliminated through wet etching due to ammonium sulfide solution, a semi-insulating InP current narrow layer 8 is embedded, a p-side electrode 9 is formed, and an n-side electrode 10 is formed on the rear surface of the substrate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compound semiconductor device,
It belongs to the technical field of optical applied systems.

[0002]

2. Description of the Related Art A technique for forming a current confinement or optical confinement structure by embedding a groove portion formed by dry-etching a compound semiconductor with a semiconductor is a technique for manufacturing various compound semiconductor devices such as a semiconductor laser and an optical modulator. It is used for Here, as an example, a case in which this technique is applied to forming an optical waveguide of a semiconductor laser will be described.

In a wavelength division multiplexing transmission type optical fiber communication system which has recently been introduced, a semiconductor laser whose oscillation wavelength is controlled with high accuracy is required as a light source. The variation in the oscillation wavelength of the semiconductor laser is mainly caused by the variation in the width of the active layer (corresponding to the mesa width). Control was difficult.

On the other hand, a mesa forming technique by dry etching capable of transferring a mask pattern onto a substrate with high accuracy has been actively studied. The conventional dry etching technology for compound semiconductors is systematically and described in detail in "Integrated Circuit Process Technology Series Semiconductor Dry Etching Technology, edited by Wei Tokuyama, Sangyo Tosho Co., Ltd."

As described in detail in the above document,
As a dry etching method for InP-based materials suitable for optical fiber communication, etching using a hydrocarbon-based gas is widely used.

[0006] The mechanism by which InP is etched in the plasma of a hydrocarbon-based gas is mainly that methane radicals adsorbed on the surface react with In atoms by obtaining the energy of ion bombardment, resulting in In (CH ₃ ) ₂ and In (CH). _{3) 3} and generating and desorbing hydrogen radicals and P atoms adsorbed on the surface due to desorption to react to PH _3. However, the rate of desorption of the reaction product is PH ₃ which is a gas at normal temperature.
Is faster than methylated In, the etched surface becomes In-rich, and when exposed to air after the etching, the In-rich layer is oxidized to form In oxide.

In the subsequent process, the side portions of the mesa are buried and grown with a semi-insulating semiconductor or the like to form a current and light confinement structure. If the buried growth is performed with the oxide remaining, the mesa is grown. The oxygen atoms remaining at the interface between the buried layer and n
Since it is a type impurity, it causes a leak current and significantly degrades the performance of the semiconductor laser. Also, if regrowth is performed on a surface contaminated with oxygen, many crystal defects are formed at the regrowth interface, and the regrowth interface becomes a non-radiative recombination center, which significantly affects the static characteristics and reliability of the semiconductor laser.

For this reason, a step of removing the In oxide is required, and wet etching with an ammonium sulfide solution has conventionally been performed. Further, in this ammonium sulfide treatment, sulfur atoms remain on the semiconductor surface after the treatment.
Since it is a type impurity, it forms a leak path at the interface and degrades the device characteristics. To remove this, wet etching treatment with concentrated sulfuric acid has been performed. As a conventional example, a mesa formed by reactive ion etching with methane gas is subjected to an ammonium sulfide treatment and a concentrated sulfuric acid treatment, and then buried and grown by a metal organic chemical vapor deposition method to form a waveguide. The characteristic is "PR
OCEEDINGS OF THE 1997 INTERNATIONAL CONFERENCE ON
INDIUMPHOSPHIDE AND RELATED MATERIALS, pp. 614-617 ''
Has been reported to.

[0009]

SUMMARY OF THE INVENTION The above prior arts include:
The concentrated sulfuric acid treatment, which has been performed to remove sulfur remaining on the semiconductor surface during the ammonium sulfide treatment, etches not only sulfur but also InP-based materials. There is a problem that high-precision transferability is impaired.

A first object of the present invention is to provide a means for cleaning a contaminated surface after dry etching without impairing the controllability of processing dimensions. A second object of the present invention is to provide a semiconductor device manufactured by using the method for manufacturing a semiconductor device of the present invention. A third object of the present invention is to provide a semiconductor laser manufactured by using the semiconductor device manufacturing method of the present invention. A fourth object of the present invention is to provide an optical module equipped with the semiconductor laser of the present invention. A fifth object of the present invention is to provide an optical application system such as an optical transmission system or an optical information processing system equipped with the semiconductor laser of the present invention.

[0011]

SUMMARY OF THE INVENTION A first object of the present invention is to:
A step of forming a semiconductor multilayer film on a semiconductor substrate; a step of forming a mask pattern on the semiconductor multilayer film to form a groove by dry etching; and a step of burying and growing a semiconductor in the groove. In the manufacturing method,
It is achieved by including a wet etching step using an ammonium sulfide solution and a dry etching step using a reaction gas containing at least fluorocarbon between the step of forming the groove and the step of burying and growing.
Further, this is achieved when the fluorocarbon is CF ₄ or C ₂ F ₆ .

[0012] Further, this is achieved by the mask pattern being made of SiO ₂ or Si ₃ N ₄ . Further, the present invention is achieved when the semiconductor substrate is a compound semiconductor. In addition, this is achieved when the semiconductor multilayer film includes a mixed crystal semiconductor layer. Further, the present invention is achieved by the semiconductor multilayer film including a light-emitting active layer as a component.

Further, a second object of the present invention is achieved by providing a semiconductor device characterized by being manufactured using the method of manufacturing a semiconductor device of the present invention. Further, a third object of the present invention is achieved by providing a semiconductor laser characterized by being manufactured using the method of manufacturing a semiconductor device of the present invention. Further, a fourth object of the present invention is achieved by providing an optical module characterized by mounting the semiconductor laser of the present invention. Also,
A fifth object of the present invention is attained by providing an optical application system such as an optical transmission system or an optical information processing system, characterized by mounting the semiconductor laser of the present invention.

In the present invention, CF ₄ or C _{4 is} used to remove sulfur remaining on the semiconductor surface after the ammonium sulfide treatment.
Performing dry treatment by plasma of a fluorocarbon gas such as ₂ F _6. Sulfur adhering to the surface reacts with fluorine radicals in the fluorocarbon gas plasma to generate SF _{6 and the} like and is desorbed, so that the sulfur adhering to the surface can be removed without etching the semiconductor.

[0015]

(Embodiment 1) First, the first embodiment of the present invention will be described.
Will be described in detail with reference to FIG. An n-type InP buffer layer (thickness of 0.3 μm), an undoped multiple quantum well active layer 5 and a p-type InP cladding layer (thickness of 2.0 μm) are formed on the n-type InP substrate 2 by metal organic chemical vapor deposition. )
6, a p-type InGaAs contact layer (0.2 micron in thickness) 7 was formed sequentially. The multiple quantum well active layer 5 is composed of In
Five GaAs well layers (60 nm thick) were formed of InGaAs.
It is sandwiched between six P barrier layers (thickness: 100 nm, composition wavelength: 1.15 microns). Next, an SiO ₂ film having a thickness of 300 nm was formed by a thermal CVD method, and an SiO ₂ stripe 1 having a width of 1.5 μm was formed by using a usual lithography technique (FIG. 1A).

Next, the wafer is loaded on the cathode electrode of an etching apparatus having a parallel plate electrode structure, and a mixed gas of ethane, hydrogen and oxygen, 50 sccm (mixing ratio: 4: 10: 1), is introduced into the etching apparatus. Then, at a gas pressure of 80 mT, a high-frequency power 300
By supplying W and causing glow discharge, reactive ion etching was performed to form a step of 3 μm on the substrate (FIG. 1B). Since the etched surface immediately after the etching becomes In-rich, when exposed to air, an In oxide is formed.

Next, at a liquid temperature of 40 under a halogen lamp,
The In oxide was removed by immersion in an ammonium sulfide solution for 10 minutes. Subsequently, in order to remove sulfur atoms remaining on the surface after the ammonium sulfide treatment, an ordinary plasma etching apparatus having a quartz cylindrical bell jar was used, and a CF ₄ gas of 100 sccm and a gas pressure of 200 m were used.
Plasma etching was performed for 1 minute under the conditions of T and RF power of 200 W.

In this treatment, unlike the conventionally used concentrated sulfuric acid treatment, the semiconductor is not etched, so that a clean surface can be obtained without impairing the controllability of the processing dimensions. Then, it is carried into the metal organic chemical vapor deposition furnace, and the growth temperature is 600
A phosphine gas, trimethylindium, ferrocene, and methyl chloride were introduced at a temperature of ° C. to grow an Fe-doped semi-insulating InP current confinement layer (thickness: 3 μm) 8 (FIG. 1C). Compound semiconductors such as InP are SiO ₂
Since it does not grow on the stripe, the semiconductor exposed surface is selectively buried by the InP layer. However, a semiconductor may be precipitated in an amorphous or polycrystalline state on the SiO ₂ stripe. However, such a precipitation can be suppressed by adding a small amount of methyl chloride as in this embodiment, and the embedded surface can be suppressed. Can be made flat.

After the buried growth, the SiO ₂ stripe 1 was removed with diluted hydrofluoric acid to form a p-side electrode 9, the back surface of the substrate was thinned by polishing, and an n-side electrode 10 was formed on the back surface (FIG. 1 (d)). )). Finally, by dividing and cleaving, a semiconductor laser having an emission wavelength of 1.55 μm was manufactured.

The fabricated laser device has a threshold current of 10 mA and an oscillation efficiency of 0 at room temperature under continuous conditions, reflecting that there is no leak current component generated when oxygen atoms and sulfur atoms remain at the buried interface. High efficiency with low threshold of .45 W / A was obtained. Also, 50 ° C, 5mW
As a result of conducting a constant light output energization test at 200 ° C., 200,000 hours were obtained as the estimated life, reflecting the absence of crystal defects at the embedded interface. In addition, reflecting the high processing dimension controllability of the present invention, the oscillation wavelength yield was as high as 95%, and the device could be manufactured at low cost.

In this embodiment, the case where the present invention is applied to a 1.55 μm band semiconductor laser has been described.
It is also applicable to semiconductor lasers in the m band and other wavelength bands. In this embodiment, the case where the plasma etching is used has been described. However, the same effect can be obtained by using the downflow etching. Further, in this embodiment, the case where SiO ₂ is used as the mask material has been described, but other materials such as Si ₃ N ₄ may be used. In this embodiment, the case where the present invention is applied to a semiconductor laser has been described. However, the present invention can be applied to another compound semiconductor device such as an optical modulator. Further, in the present embodiment, an example using CF ₄ gas has been described. However, C ₂ F ₆ and CH
F ₃ or a mixed gas thereof may be used.

(Embodiment 2) Next, a second embodiment will be described in detail with reference to FIG. FIG. 2 shows a wavelength of 1.3 μm using the present invention.
This is an example of fabricating an m-band distributed feedback semiconductor laser.

As shown in FIG. 2A, an n-type (100)
N-type In on the InP substrate 2 by metal organic chemical vapor deposition.
P buffer layer 1.0 μm15, n-type InGaAsP lower guide layer (composition wavelength 1.10 μm) 0.05 μm, 5 periods of multiple quantum well layer (6.0% thick 1% compression strained InGa
AsP (composition wavelength: 1.37 μm) well layer, 10 nm thick I
nGaAsP (composition wavelength 1.10 μm) barrier layer), InG
aAsP (composition wavelength 1.10 μm) Upper light guide layer 0.0
An active layer 16 of 5 μm, a first p-type InP cladding layer 0.1 μm 17 and an undoped InGaAsP (composition wavelength 1.15 μm) diffraction grating supply layer 0.05 μm 18 are sequentially formed. The emission wavelength of the multiple quantum well active layer 16 is about 1.3.
1 μm.

Next, the period 241 is determined by the electron beam drawing method.
After forming a diffraction grating resist pattern 4 having a phase inversion at the center of the device in nm and carrying the same into an ECR plasma etching apparatus, the conditions are as follows: methane gas 10 sccm, hydrogen gas 30 sccm, gas pressure 2 mT, microwave power 1000 W, RF bias 50 V. Etch. As a result, FIG.
As shown in (b), a diffraction grating 20 having a period of 241 nm and a phase inverted at the center of the device is formed on the entire surface of the substrate.

The depth of the diffraction grating is set to about 100 nm, so that the diffraction grating penetrates the diffraction grating supply layer 18 and reaches the first p-type InP clad layer 17. Since the etched surface immediately after the etching becomes In-rich, if it is exposed to air, I
An n-oxide is formed. Next, an oxygen ashing treatment was performed to remove the resist mask and the hydrocarbon polymer generated on the resist during the etching. Subsequently, by immersing in an ammonium sulfide solution at a liquid temperature of 20 ° C. for 20 minutes, the In oxide was removed. Further, in order to remove sulfur atoms bonded to the surface after the ammonium sulfide treatment, an ordinary down-flow etching device of a microwave discharge system is used, and CF ₄ gas is set at 100 sccm and gas pressure is set at 20 sccm.
Downflow etching was performed for 1 minute under the conditions of 0 mT and microwave power of 1000 W.

In this treatment, unlike the conventionally used concentrated sulfuric acid treatment, the semiconductor is not etched, so that a clean surface could be obtained without impairing the controllability of the processing dimensions. After that, it is carried into a crystal growth furnace, and the second p-type InP cladding layer 1.7 μm 21 and the high concentration p
A type InGaAs cap layer 0.2 μm 22 is sequentially formed (FIG. 2C).

Subsequently, after processing into a buried laser structure having a width of about 1.5 μm or a ridge waveguide laser structure having a width of about 2.2 μm, an upper electrode 23 and a lower electrode 24 are formed. As shown in FIG. 2 (d), after a device having a device length of 400 μm is cut out by a cleavage step, a low reflection film 25 having a reflectance of about 1% is formed on both end surfaces of the device by a known method.

In the fabricated 1.3 μm band distributed feedback semiconductor laser device, no crystal defects are generated at the regrowth interface.
Reflecting that there is no reactive current component due to non-radiative recombination generated when there is a defect, the threshold current is 10 mA, the oscillation efficiency is 0.45 W / A, and the threshold is low and high at room temperature and continuous conditions. Efficient characteristics were obtained. Also, at 50 ° C,
As a result of conducting a constant light output energization test at 5 mW, the estimated lifetime was 2 as a reflection of a high-quality crystal structure without crystal defects.
0,000 hours were obtained.

The spectrum shape when a forward bias is applied below the oscillation threshold is shown (FIG. 2E). A typical spectrum in which the oscillation dominant mode appears at the center of the stop band reflecting the phase shift type diffraction grating was obtained.
In addition, the reproducibility and single mode selectivity of the phase shift type diffraction grating fabrication are extremely high, reflecting the excellent processing dimension controllability of the present invention.
A stable single mode operation of dB or more has been realized with a high production yield of 95% or more.

This structure is not only used in the 1.3 μm band but also in the 1.55 μm band.
The present invention is also applicable to distributed feedback semiconductor lasers in the m band and other wavelength bands. Further, in the present embodiment, the method of the present invention was used as a surface cleaning treatment after dry etching of a hydrocarbon-based gas, but the method of the present invention was used for cleaning the surface after other dry etching treatments such as a chlorine-based gas. The same effect has been confirmed by using. In this example, the present invention was applied to a semiconductor device of an InGaAsP-based material, but the same effect was confirmed when applied to a semiconductor device of another material such as AlGaInAs.

(Embodiment 3) Next, a third embodiment will be described in detail with reference to FIG. FIG. 3 shows an optical lens 28 and a photodiode 2 for monitoring the rear end face light output after mounting the distributed feedback semiconductor laser 26 of the second embodiment on a heat sink 27.
FIG. 2 is a structural diagram of an optical transmission module in which an optical fiber 9 and an optical fiber 30 are integrated. Threshold current 1 at room temperature and continuous conditions
The oscillation efficiency was 0.20 W / A at 0 mA.

The estimated lifetime was 200,000 hours, reflecting the crystal structure of the present invention having few crystal defects. Even at a high temperature of 85 ° C., good oscillation characteristics such as a threshold current of 25 mA and an oscillation efficiency of 0.13 W / A were obtained. Also,
Reflecting the excellent processing dimension controllability of the present invention, a stable single mode operation with a submode suppression ratio of 40 dB or more was realized at a high production yield of 95% or more even at a high temperature of 85 ° C.

(Embodiment 4) Next, a fourth embodiment will be described in detail with reference to FIG. FIG. 4 illustrates a trunk optical communication system using the transmission module 31 according to the third embodiment. Transmission device 3
2 has a transmission module 31 and a drive system 33 for driving the module 31. The optical signal from the module 31 passes through the fiber 34 and is detected by the light receiving unit 36 in the receiving device 35. According to the optical communication system according to the present embodiment, non-repeater optical transmission over 100 km can be easily realized.

[0034]

According to the present invention, a contaminated surface after dry etching can be cleaned without impairing controllability of processing dimensions. The use of the present invention is effective in reducing the cost by improving the performance and reliability of the compound semiconductor device and improving the production yield.

[Brief description of the drawings]

FIG. 1 is a sectional view illustrating a manufacturing process of a semiconductor device according to a first embodiment of the present invention.

FIGS. 2A and 2B are a cross-sectional view illustrating a manufacturing process of a semiconductor device according to a second embodiment of the present invention and a light-emitting characteristic diagram of a laser element.

FIG. 3 is a partial cross-sectional perspective view of an optical transmission module according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a trunk optical communication system according to a fourth embodiment of the present invention.

[Explanation of symbols]

1. SiO ₂ mask, 2. InP substrate, 4. n-type InP
Buffer layer, 5 ... undoped multiple quantum well active layer, 6 ...
p-type InP cladding layer, 7 ... p-type InGaAs contact layer, 8 ... Fe-doped semi-insulating InP current confinement layer, 9 ...
p-side electrode, 10 n-side electrode, 15 n-type InP buffer layer, 16 multi-quantum well active layer, 17 first p-type InP
Cladding layer, 18 undoped InGaAsP diffraction grating supply layer, 20 diffraction grating, 21 second p-type InP cladding layer, 22 p-type InGaAs cap layer, 23 upper electrode, 24 lower electrode, 25 low reflection film, 26: distributed feedback semiconductor laser, 27: heat sink, 28: optical lens, 29: photodiode, 30: optical fiber, 3
1 ... Transmission module, 32 ... Transmission device, 33 ... Drive system,
34: optical fiber, 35: receiving device, 36: light receiving unit.

Claims (12)

[Claims] 1. A step of forming a semiconductor multilayer film on a semiconductor substrate, a step of forming a mask pattern on the semiconductor multilayer film and forming a groove by dry etching, and a step of burying and growing a semiconductor in the groove. A method of manufacturing a semiconductor device having a method, comprising a step of wet etching with an ammonium sulfide solution and a step of dry etching with a reaction gas containing at least fluorocarbon between the step of forming the groove and the step of burying and growing. A method for manufacturing a semiconductor device, comprising: 2. The method of manufacturing a semiconductor device according to claim 1, wherein said fluorocarbon is CF ₄ . 3. The method of manufacturing a semiconductor device according to claim 1, wherein said fluorocarbon is C ₂ F ₆ . 4. The method of manufacturing a semiconductor device according to claim 1, wherein said mask pattern is made of Si.
A method for manufacturing a semiconductor device comprising O ₂ . 5. The method of manufacturing a semiconductor device according to claim 1, wherein said mask pattern is made of Si.
Method of manufacturing a semiconductor device characterized by comprising the ₃ N _4. 6. The method for manufacturing a semiconductor device according to claim 1, wherein said semiconductor substrate is a compound semiconductor. 7. The method for manufacturing a semiconductor device according to claim 1, wherein said semiconductor multilayer film includes a mixed crystal semiconductor layer. 8. The method for manufacturing a semiconductor device according to claim 1, wherein said semiconductor multilayer film includes an active layer for generating light as a component. 9. A semiconductor device manufactured by using the method of manufacturing a semiconductor device according to claim 1. 10. A semiconductor laser manufactured by using the method of manufacturing a semiconductor device according to claim 1. 11. An optical module comprising the semiconductor laser according to claim 10. 12. An optical application system comprising the semiconductor laser according to claim 10.