JPH10223990A - Manufacture of semiconductor optical element, semiconductor optical element manufactured by it, and optical applied system using the element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the residual damages on the surface of a semiconductor and side faces of a waveguide by dividing an etching process into a dry etching process involving ion irradiation and a successive dry etching process involving no ion irradiation. SOLUTION: Steps are formed on the surface of a substrate 1 by reactive ion etching. When the steps are formed on the surface of the substrate 1, damaged layers 7 are formed on the surface of the substrate 1 and side faces of the steps due to shocks from ions. After this first process, radical etching is successively performed by causing glow discharge from a mixed gas of methane and hydrogen. When the radical etching is performed, the substrate 1 is not damaged and the damaged layers 7 formed during the reactive ion etching can be removed, because no shock is given to the substrate 1 from ions. Therefore, the residual damages on the surface of the substrate 1 and side walls of a waveguide can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a technical field of a semiconductor optical device, a method of manufacturing the same, an optical module equipped with the semiconductor optical device, and an optical application system.

[0002]

2. Description of the Related Art As one of the methods for manufacturing a semiconductor device, a technique of forming a waveguide structure of a compound semiconductor by etching is used for various waveguide optical devices such as a semiconductor laser and an optical modulator. The wet etching has long been used for the etching of compound semiconductors. However, in recent years, there has been an increasing demand for improving the processing dimension uniformity within the wafer surface, and research on dry etching technology has been advanced. Known examples of an optical element using an optical waveguide using dry etching include:
For example, a reliability test result of an Fe-doped InP embedded semiconductor laser having an optical waveguide formed by reactive ion etching of a hydrocarbon-based gas was reported in the 1995 IEICE General Conference C-345.

[0003]

The above conventional dry etching technique has the following problems.

The reason why mask pattern dimensions can be transferred to a substrate with high precision by reactive ion etching or reactive ion beam etching is due to the vertical anisotropy due to the effect of ion bombardment. However, ion bombardment simultaneously causes damage to the substrate surface and the waveguide side. In high-speed electronic devices and semiconductor lasers, etching of an electrically active layer and an optically active layer is the center, respectively. Therefore, damage that occurs at the time of etching has a serious adverse effect on the reliability of device characteristics and life. For example, as disclosed in the above document, when an optical waveguide of a semiconductor laser is formed by reactive ion etching of a hydrocarbon-based gas, an element during an energization test is affected by a damaged layer on the side of the active layer due to ion bombardment. It is known that deterioration progresses faster.
In order to remove this damaged layer, conventionally, a method of adding wet etching after dry etching has been adopted. However, the addition of wet etching significantly impaired the uniformity of the pattern dimensions within the wafer surface.

A first object of the present invention is to provide a method for manufacturing a waveguide type semiconductor optical device having a small amount of residual damage layer on a semiconductor surface and a side surface of a waveguide and having high reliability. A second object of the present invention is to provide a semiconductor optical device manufactured by using the manufacturing method of the present invention. A third object of the present invention is to provide an optical module on which the semiconductor optical device of the present invention is mounted. A fourth 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 optical device of the present invention.

[0006]

The first object of the present invention is to provide a method of manufacturing a semiconductor device (for example, an optical element) in which a step is formed in a semiconductor substrate or a semiconductor laminated structure by an etching step. Dry etching step (hereinafter referred to as a first step) and a subsequent dry etching step without ion irradiation (hereinafter referred to as a second step).
This is achieved by the method for manufacturing a semiconductor device according to the present invention, comprising: The etching step of the present invention is often applied to a semiconductor laminated structure in which a single layer or a plurality of layers of semiconductor films are stacked on a semiconductor substrate (main surface of the substrate) by epitaxial growth or the like. However, for simplicity,
In this section, the term semiconductor substrate includes the semiconductor multilayer structure (that is, the upper surface of the semiconductor substrate also means the growth surface of the semiconductor multilayer structure).

In the above-mentioned first step, the upper surface of the semiconductor substrate is masked even if a mask pattern is previously formed on the upper surface of the semiconductor substrate (the upper surface is partially masked) and then the upper surface of the substrate is irradiated with ions. A technique of selectively irradiating a focused ion beam to a region to be etched without using a focused ion beam may be employed. In the former technique, a semiconductor substrate surface on which a mask pattern is formed is opposed to plasma, and ions present in the plasma are applied to the substrate surface via an ion sheath formed between the substrate surface and the plasma. Irradiation dry process can be adopted.

The above-mentioned second step employs etching by neutral particles (uncharged particles) as a dry process without ion irradiation. As the neutral particles, it is desirable to employ particles or atoms excited by discharge (for example, plasma), light irradiation, or heating. One of the excited neutral particles is a radical, which is generated by exciting atoms or molecules by plasma or light irradiation, and is highly reactive. As a neutral particle etching method other than radicals, for example, there is a hot molecular beam etching method in which a gas is supplied to a surface to be processed of a semiconductor substrate by a nozzle and the nozzle is heated.

A desirable example of the case where radicals are formed by plasma is a method in which high-frequency power is applied to a parallel plate-type electrode (a device in which two plate-like electrodes are arranged so that their surfaces face each other). A dry process of processing an object to be processed with the plasma is used, a semiconductor substrate having a mask pattern formed on one of the parallel plate electrodes is disposed, and the reactivity of the first step is determined using the electrode as a cathode. Ion etching and radical etching in the second step are performed on the semiconductor substrate using the electrode as an anode. The parallel plate type electrode is also called a plasma processing apparatus or a plasma etching apparatus, and the electrode on which the semiconductor substrate is arranged is formed in a shape suitable for holding a workpiece, for example, in a trapezoidal shape. As an example of supplying radicals by light irradiation, there is a method in which the semiconductor substrate is arranged in a housing, a gas for generating radicals is introduced into the housing, and the gas is irradiated with light. The light irradiation to the gas is desirably closer to the processing surface of the semiconductor substrate.

The dry etching step (first step) involving ion irradiation and the subsequent dry etching step (second step) without ion irradiation are performed continuously in the same etching apparatus or are performed in the atmosphere. It is desirable that the etching be performed in another etching apparatus without passing through an atmosphere from the viewpoint of preventing oxidation of the semiconductor surface exposed by the etching in the first step and adhesion of foreign substances. In the case of adopting the latter method, a combined processing apparatus in which the processing apparatus of the first step and the processing apparatus of the second step are combined by a housing provided with a semiconductor substrate transfer device, or a processing apparatus of the first step A means for transferring the semiconductor substrate from the housing to the second-stage processing device under reduced pressure after transferring the semiconductor substrate to a confidential housing under reduced pressure and carrying this housing to the second-stage processing device. Good.

The second object of the present invention is achieved by manufacturing a semiconductor optical device by using the manufacturing method of the present invention described above. Further, a third object of the present invention is to manufacture an optical module on which the semiconductor device is mounted, and a fourth object of the present invention is to provide an optical transmission system, an optical information processing system, Each is achieved by manufacturing an optical application system such as an optical switch.

Next, the operation of the method for manufacturing a semiconductor device according to the present invention will be described.

In the etching step of the present invention, the mask pattern is transferred to the substrate by anisotropic dry etching accompanied by ion bombardment to form irregularities (for example, a ridge-type waveguide of an optical device) on the upper surface of the semiconductor substrate. A step of removing the damaged layer generated by the impact by etching with neutral particles substantially without ion irradiation is added. here,
The anisotropic dry etching accompanied by ion bombardment is, for example, reactive ion etching or reactive ion beam etching. This process has a high etching rate and is excellent in processing control. The etching with neutral particles may be any process in which neutral particles dominantly act as an etchant, and one example is radical etching. Etching by neutral particles is inferior to dry etching accompanied by ion bombardment at an etching rate, but isotropic, that is, can etch the region to be etched almost uniformly, and around the etching region (for example, the surface exposed by etching). This has the advantage that damage to the device is extremely small.

In the case of radical etching,
Since there is no ion bombardment, for example, in the manufacture of a semiconductor optical device having a ridge-type waveguide, it is possible to remove a damaged side wall of the waveguide and a damaged layer on the semiconductor surface caused by ion etching. That is, although the radical etching has a disadvantage that the etching rate is low, the advantage of the above-mentioned low damage etching is emphasized in consideration of the thickness of the damaged layer to be etched by this. In radical etching, etching by radicals is required to be dominant, and even if a small amount of ions or electrons fly from the radical supply source to the waveguide side wall or the semiconductor surface, it is sufficient that damage due to this is sufficiently removed by radical etching. . As described above, in the present invention, by performing the second step of performing fine finishing after the first step of performing rough processing,
This is for manufacturing a high-quality semiconductor device.

Further, in the damage layer removing step by radical etching (the second step), the processing dimension uniformity in the wafer surface is higher than the damage layer removing step by wet etching. Can be kept sufficiently low. As a result, it is possible to perform etching with low damage and excellent in-plane uniformity of processing dimensions.

Furthermore, in the above-described method in which the potential of the semiconductor substrate holding member (electrode) with respect to the plasma is changed between the first step and the second step by using the above-mentioned plasma processing apparatus, the etching process can be performed at a higher speed and more efficiently. Thus, the through-put of semiconductor device manufacturing is dramatically improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to Examples 1 to 3, which will be specifically described with reference to FIGS.

Embodiment 1 First, a first embodiment of the present invention will be described in detail with reference to FIG. FIG. 1 shows a chip stage of a semiconductor optical device, that is, a state in which individual devices (chips) are cut out from a semiconductor wafer in order to facilitate description of a manufacturing process according to the present invention. However, in actual semiconductor device production, the steps from FIG. 1A to FIG.
That is, it should be noted that the process is often performed in a state where a plurality of devices are formed on a semiconductor wafer (before each device is separated).

First, an n-type InP buffer layer (thickness: 0.3 μm) 2, an undoped multiple quantum well active layer 3, and a p-type InP cladding layer (thickness: 2.0 μm) are formed on an n-type InP substrate 1 by metal organic chemical vapor deposition. μ
m) 4 and a p-type InGaAs cap layer (thickness 0.2 μm) 5 were sequentially formed. The multiple quantum well active layer 3 is an InGaAs well layer (thickness 60 n
m) 5 layers, InGaAsP barrier layer (thickness 100 nm, composition wavelength 1.15μ
m) It is sandwiched between 6 layers. After crystal growth, normal thermal CVD
By using the law and the lithography technology SiO ₂ stripe (thickness: 0.3
μm, 1.5 μm in width) 6 (FIG. 1 (a)).

After placing this sample on the lower electrode of an etching apparatus having a parallel plate type electrode structure, a mixed gas of methane and hydrogen is introduced, and high-frequency power is supplied using the lower electrode as a cathode to cause glow discharge. Performs normal reactive ion etching. This etching apparatus is also called a plasma etching apparatus, and its schematic diagram is shown in FIG.

Referring now to FIG. 4, a description will be given of a plasma etching apparatus 30 according to the manufacturing process of this embodiment. The plasma etching apparatus has an exhaust pipe 29 connected to the casing and an exhaust device (not shown), and an exhaust pipe 29 for exhausting the interior of the casing.
Pipes 32 and 33 for supplying gas into the housing, a pair of plate electrodes 34 and 35 forming a parallel plate electrode, a support member 36 electrically connected to the electrodes, and an electrical connection between the support member and the housing 31. A high-frequency power supply 38 for applying a high-frequency electric field to the plate-like electrode (lower electrode) 34 and a DC power supply 39 for controlling the potential of the plate-like electrode (upper electrode) 35 are provided. The plate-shaped electrode 34 is configured to fix a workpiece, and the jig 28 is provided on a surface facing the other plate-shaped electrode 35. Incidentally, FIG. 4 shows that the semiconductor laminated structure corresponding to FIG. 1A formed at the wafer stage is fixed to the plate electrode 34 as the workpiece 40 (the upper surface of the SiO ₂ stripe 6 in FIG. 1A). Is a plate electrode
35).

The above-mentioned methane gas and hydrogen gas are supplied to the pipes 32, 3
In step 3, they are separately introduced, mixed in the housing 31, and exhausted from the exhaust pipe 29 to the outside of the housing 31 (arrows in the figure indicate gas flows in the housing). When the methane-hydrogen mixed gas is glow-discharged in the housing 31, the gas supply speed to the housing 31 and the gas exhaust speed from the housing 31 are in a reduced pressure state in the housing 31, that is, methane and hydrogen which are leaner than the atmospheric pressure. It is adjusted so as to have a mixed gas atmosphere. The pressure in the housing 31 is desirably 10 Torr or less. For gas supply, one of the pipes 32 and 33 may be closed and a mixed gas of methane and hydrogen may be introduced from the other.

The high frequency power supply 38 is of a crystal oscillator type that generates high frequency power of 13.56 MHz. On the other hand, the lower electrode 34
Is used as a cathode, the potential V ₊ of the upper electrode 35 (where V ₊ >
0) connects a switch to the power supply on the right side in the DC power supply 39, and −V _RF to + V _RF (where V _RF >
0) is controlled so as to maintain the relationship of V ₊ > V _{RF with} respect to the voltage oscillation of 0).

The above-mentioned conditions for setting the pressure in the casing and the electrode potential are in view of the present embodiment using glow discharge plasma. However, in the case where the plasma is formed by a non-polar discharge or an arc discharge under atmospheric pressure. Each condition including the electrode configuration can be appropriately changed. Glow discharge is also generated by a DC electric field, but it is desirable to employ a high-frequency electric field in practical terms. The frequency of the high-frequency electric field for glow discharge generation is
It is not limited to 13.56 MHz, and a desired effect can be obtained even if, for example, 27.12 MHz or 40 MHz is adopted.

Returning again to the description of the manufacturing process of this embodiment. By the above-mentioned reactive ion etching, 3μ
m steps were formed. When a step was formed on the substrate, a damaged layer 7 of about 0.1 μm was formed on the surface of the substrate and the side wall of the step by ion bombardment (FIG. 1 (b)). The processing steps from FIG. 1A to FIG. 1B are the first steps of the present invention.

Subsequent to the first step, radical etching was performed by supplying high frequency power using the lower electrode on which the sample was placed as an anode to cause glow discharge of a mixed gas of methane and hydrogen. Since radical etching does not involve ion bombardment, it was possible to remove a damaged layer of about 0.1 μm generated during reactive ion etching without damaging the substrate (FIG. 1 (c)). From this Figure 1 (b)
The processing step leading to (c) is the second step of the present invention.

It should be noted in the second step, the potential of the upper electrode 35 to the lower electrode 34 and the anode V _- (where, V _- <0) is connecting the switch to the left of the power in the DC power supply device 39, a high frequency power source 38 Is controlled so as to maintain the relationship of V ₋ <−V _{RF with} respect to the voltage oscillation of. In reality, the lower electrode 34
It is desirable to consider the potential of the plasma 41 with respect to the surface (plasma potential) ΔV (where ΔV> 0). In this case, based on ΔV measured by a probe or the like,
V _- may be set to _- - [Delta] V <V so as to keep the -V _RF becomes relevant.

After the second step, the polymer deposited on the SiO ₂ stripe 6 during the etching was removed by oxygen plasma ashing, and the resultant was carried into a metal organic chemical vapor deposition furnace. Next, a phosphine gas, trimethylindium, ferrocene, and methyl chloride were introduced at a growth temperature of 600 ° C. to grow a Fe-doped semi-insulating InP current confinement layer (growth thickness: 3 μm) 8 (FIG. 1D). .

Since a compound semiconductor such as InP does not grow on the SiO ₂ 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, but 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 buried growth, S
The iO ₂ stripe was removed with diluted hydrofluoric acid to form a p-side electrode 9, and the back surface of the substrate was thinned by polishing.
0 was formed (FIG. 1 (e)). Finally, by dividing and cleaving, a semiconductor laser having an emission wavelength of 1.55 μm was manufactured.

The fabricated laser device has no damage layer on the side of the active layer and has a small threshold current at room temperature under continuous conditions, reflecting a small reactive current component due to non-radiative recombination generated when damage occurs. A low threshold current value of 10 mA and an oscillation efficiency of 0.45 W / A and high efficiency characteristics were obtained. Also, 50 ℃,
As a result of conducting a constant light output current test at 5 mW, an estimated lifetime of 200,000 hours was obtained, reflecting a high-quality crystal structure without a damaged layer. In this embodiment, the case where the present invention is applied to a semiconductor laser in the 1.55 μm band is described, but the present invention is also applicable to a semiconductor laser in the 1.3 μm band and other wavelength bands.

The same effect was confirmed when the present invention was applied not only to semiconductor lasers but also to other semiconductor optical devices such as optical modulators and photodiodes. In this embodiment, the dry etching step with ion irradiation and the radical etching step without ion irradiation are performed continuously in the same etching apparatus. However, a separate processing chamber is provided as a radical etching chamber. It goes without saying that you can go there.

In the above-described manufacturing process, not only the uniformity of the processing dimensions at the individual element level but also the uniformity of the processing dimensions at the wafer level among a plurality of elements formed on the same wafer (uniformity within the wafer surface) Sex) also improved.

<Embodiment 2> Next, a second embodiment will be described in detail with reference to FIG. FIG. 2 is a structural diagram of an optical transmission module in which an optical lens 13, a photodiode 14 for monitoring the optical output of a rear end face, and an optical fiber 15 are integrated after mounting the semiconductor laser 11 of Example 1 on a heat sink 12. . room temperature,
Under continuous conditions, threshold current is 10mA, oscillation efficiency is 0.20W / A
Met. In addition, reflecting the manufacturing process with less damage to the semiconductor, the threshold current is 25 mA even at a high temperature of 85 ° C.
The oscillation efficiency was 0.13W / A and good oscillation characteristics were obtained.

<Embodiment 3> Next, a third embodiment will be described in detail with reference to FIG. FIG. 3 illustrates a transmission module according to the second embodiment.
This is a trunk optical communication system using the No. 16. The transmission device 17 has a transmission module 16 and a drive system 18 for driving the module. An optical signal from the module 16 passes through the fiber 19 and is detected by the light receiving unit 21 in the receiving device 20. According to the optical communication system of this embodiment, repeaterless optical transmission over 100 km can be easily realized. This is based on the fact that the chirping is significantly reduced, which also results in significantly reduced signal degradation due to fiber dispersion.

[0035]

According to the present invention, it is possible to realize a semiconductor waveguide structure having low damage and excellent in-wafer uniformity of processing dimensions by an easy method. The use of the present invention not only dramatically improves the performance of a semiconductor optical device, but also has the effect of extending the life of an optical module and an optical application system equipped with this device.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a third embodiment of the present invention.

FIG. 4 is a schematic diagram of an etching apparatus used in Embodiment 1 of the present invention.

[Explanation of symbols]

1 ... n-type InP semiconductor substrate, 2 ... n-type InP buffer layer, 3 ... multi-quantum well active layer, 4 ... p-type InP cladding layer, 5 ... p-type InGaAs
Cap layer, 6 ... SiO ₂ stripe, 7 ... damaged layer, 8 ... Fe doped semi-insulating InP current blocking layer, 9 ... p-side electrode, 10 ... n-side electrode, 11 ... semiconductor laser, 12 ... heat sink, 13 ... optical Lens, 14 photodiode, 15 optical fiber, 16 transmitting module, 17 transmitting device, 18 driving system, 19 optical fiber, 20 receiving device, 21 light receiving unit.

Claims (6)

[Claims] In a method of manufacturing a semiconductor optical device, wherein a mask pattern is formed on a semiconductor substrate in advance and then a step is formed on the semiconductor substrate by an etching step, the etching step includes a dry etching step involving ion irradiation and a subsequent step. A method for manufacturing a semiconductor optical device, comprising a dry etching step without ion irradiation. 2. The method of manufacturing a semiconductor optical device according to claim 1, wherein the dry etching step with ion irradiation and the subsequent dry etching step without ion irradiation are continuously performed in the same etching apparatus. A method for manufacturing a semiconductor optical device, wherein the method is performed or performed in another etching processing apparatus without passing through an air atmosphere. 3. The method of manufacturing a semiconductor optical device according to claim 1, wherein said dry etching step involving ion irradiation comprises applying said mask pattern on a cathode side electrode of a parallel plate type electrode to which high-frequency power is applied. The reactive ion etching performed by arranging the formed semiconductor substrate, and the dry etching step without ion irradiation is performed on the parallel plate type electrode with the electrode on which the semiconductor substrate on which the mask pattern is formed is disposed as the anode side. A method of manufacturing a semiconductor optical device, which is radical etching performed by applying high-frequency power. 4. A semiconductor optical device manufactured by using the method for manufacturing a semiconductor optical device according to claim 1. 5. An optical module comprising the semiconductor optical device according to claim 4. 6. An optical application system comprising the semiconductor optical device according to claim 4.