JP4226515B2 - Manufacturing method of semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a ridge-type stripe structure suitable as a semiconductor laser.

  A semiconductor laser as a light emitting element often employs a ridge waveguide structure having a striped ridge portion. In recent years, it is common to use an “off substrate” in order to improve the characteristics of the semiconductor laser, and to fabricate the semiconductor laser on the off substrate. Here, the off-substrate is a substrate surface having a cubic crystal structure (especially a zinc-blende type in the case of a III-V compound semiconductor) whose normal is from the (100) plane, for example, in the [111] direction (or [ 1-1-1] direction) (refer to FIG. 1 (a) and FIG. 1 (b)).

  When a semiconductor laser is manufactured using an off-substrate, it is necessary to form a laser resonator so that the substrate off-direction and the stripe direction in which the ridge portion extends are perpendicular to each other in order to reduce the mirror loss of light. is there. It is known that by using such an off-substrate, it is possible to shorten the wavelength of the oscillation laser light, lower the threshold current, and improve the temperature characteristics (see, for example, Patent Document 1).

FIG. 2 is a diagram for explaining a part of a manufacturing process example of a conventional semiconductor laser having a ridge waveguide structure. For example, an n-type cladding layer 2 is formed on an n-type GaAs substrate 1 having an off angle. An n-type light guide layer 3, an MQW layer 4, a p-type light guide layer 5, a p-type cladding layer 6, an etching stopper layer 7, a p-type cladding layer 8, and a p-type GaAs contact layer 9 are sequentially stacked to form a p-type GaAs contact. A p-type contact electrode 11 covered with a dry etching mask 10 such as SiO _{2 is formed} on the surface of the layer 9 (FIG. 2A).

Next, the region not covered with the dry etching mask 10 is dry-etched from the surface side of the p-type GaAs contact layer 9 to leave only the desired thickness of the p-type cladding layer 8 and have an end surface perpendicular to the surface of the substrate 1. Striped ridges are formed (FIG. 2B). Here, it is preferable to make the p-type cladding layer 8 left by etching as thin as possible. Further, wet etching is performed to remove the damage layer on the ridge end face introduced in the dry etching process and to control the distance t from the bottom of the ridge to the top surface of the MQW layer 4. By this wet etching, the p-type cladding layer 8 provided on the etching stopper layer 7 is removed except for the ridge portion (FIG. 2C). The composition of the wet etching solution used here is, for example, HCl: H ₂ 0 = 1: 5, and the etching time is 2 minutes. Further, the p-type GaAs contact layer 9 remains without being etched due to the selectivity of the etchant.

  When such a ridge portion is provided, current is injected into the MQW layer 4 which is an active layer through the ridge portion of the p-type cladding layer 8, so that the current is concentrated in the MQW layer 4 immediately below the ridge portion. Carriers can be effectively confined in the quantum well in the region. The carriers confined in the quantum well generate light having a wavelength corresponding to the band gap, and this light is also confined in the quantum well region of the MQW layer 4 immediately below the ridge, and a transverse mode for laser oscillation is obtained. As well as being stabilized, the threshold current can be reduced.

  In order to enhance such an effect, it is generally preferable that the shape of the ridge end face is highly perpendicular to the surface of the substrate 1 and the symmetry of both side end faces is high. However, due to crystallographic etching anisotropy when the p-type cladding layer 8 is wet-etched, the etching rate of a specific crystal surface is increased and the end surface is inclined, so that the perpendicularity to the surface of the substrate 1 is lowered and both The symmetry of the side end faces also deteriorates. If the end faces of both sides of the ridge are asymmetric, the current tends to spread in the direction of the end face where the slope of the ridge portion is loose, the light emitting area is also left-right asymmetric, and the light emission density distribution is also left-right asymmetric. There arises a problem that it is difficult to obtain a single transverse mode required for use. Further, a kink as shown in FIG. 3 occurs in the current-light output characteristics (see, for example, Patent Document 2).

  In order to suppress the occurrence of such kinks, it is effective to narrow the ridge width. However, when the ridge width is narrowed with the symmetry of the ridge end face being low, the cross-sectional SEM image is shown in FIG. As a result, the width of the top of the ridge (W in FIG. 2C) becomes narrow, which makes it difficult to stably form electrodes on the top of the ridge and increases the device resistance. Therefore, in order to obtain a high light output while suppressing the occurrence of kinks in a semiconductor laser having a ridge-type stripe structure, it is necessary to simultaneously realize both the narrowing of the ridge width and the improvement of the symmetry of the ridge shape. .

  Further, the optical output (kink generation output) at the drive current at which kinks are generated depends greatly on the distance from the bottom of the ridge to the active layer (t in FIG. 2C). Therefore, in order to control the kink generation output, it is essential to strictly control the distance t. For this reason, an etching stopper layer 7 for stopping the wet etching is provided, and a wet etching solution having such a property that the etching stops at the etching stopper layer 7 is selected.

However, when the ridge portion of such a semiconductor laser is wet-etched to remove the damaged layers on both end surfaces of the ridge portion, there is a problem that the asymmetry described above appears and good laser characteristics cannot be obtained.
Japanese Patent Laid-Open No. 11-340585 JP 2002-151790 A JP-A-6-216462

  In this way, when wet etching is performed on the ridge when manufacturing a semiconductor laser with a ridge-type stripe structure, the shape of both side end faces becomes asymmetrical, increasing the light output while suppressing the occurrence of kinks There is a problem that it is difficult to plan.

  The present invention has been made in view of such problems, and the object of the present invention is to enable wet etching in a state where the ridge end face shape after dry etching is generally maintained, thereby reducing the ridge width. An object of the present invention is to achieve both improvement of the symmetry of the ridge shape at the same time and obtain a high light output while suppressing the occurrence of kinks in the semiconductor laser having the ridge type stripe structure.

According to a fourth aspect of the present invention, there is provided an active layer provided on a compound semiconductor substrate having an off angle in a [111] direction or a [1-1-1] direction from a (100) crystal plane ; A method of manufacturing a semiconductor device, comprising: an etching stopper layer provided; and a striped ridge portion made of AlGaInP provided in contact with the etching stopper layer, wherein the formation of the ridge portion A step of performing wet etching to expose the etching stopper layers on both sides, and the wet etching is performed with an etching solution of a hydrogen fluoride-containing solution, thereby forming the end surfaces of the ridge portion symmetrically. It is characterized by

Invention according to claim 2, in the manufacturing method of a semiconductor device according to claim 4, wherein the hydrogen fluoride-containing solution, characterized in that a mixed solution of NH 4 _F and HF, claim 3 The method of manufacturing a semiconductor device according to claim 1 or 2 , wherein the hydrofluoric acid concentration of the hydrogen fluoride-containing solution is 4% or more and 50% or less.

According to a fourth aspect of the present invention, in the method for manufacturing a semiconductor device according to the first to third aspects, the extending direction of the stripe is a direction perpendicular to the off-angle direction of the substrate. And

According to a fifth aspect of the present invention, in the method of manufacturing a semiconductor device according to any one of the first to fourth aspects, the etching is performed on the ridge portion formed in advance by dry etching. Features.

The invention of claim 6 is a method of manufacturing a semiconductor device according to any one of claims 1 to 5, wherein the ridge portion, GaInP, GaAs, AlGaAs, or to any of the etching stopper layer of GaInAsP It is provided.

According to a seventh aspect of the present invention, in the method for manufacturing a semiconductor device according to any one of the first to sixth aspects, the off angle of the substrate is 10 degrees or less.

  Since the present invention enables wet etching with the ridge end face shape generally maintained after dry etching, both ridge width narrowing and ridge shape symmetry improvement can be realized simultaneously. Thus, it is possible to obtain a high light output while suppressing the occurrence of kinks in the semiconductor laser having the ridge type stripe structure.

  The present invention relates to wet ridge portions when manufacturing an optical semiconductor device having a ridge-type stripe structure on a compound semiconductor substrate having an off angle in the [111] direction or [1-1-1] direction from the (100) plane. This is an etching method. Here, the semiconductor device of the present invention is applied as a light emitting element having a wavelength in the visible region, and the off angle of the substrate is 10 degrees or less. Although there is no particular limitation on the stripe extending direction, a direction perpendicular to the substrate off direction is selected when a laser resonator is formed.

Conventionally, hydrochloric acid diluted with water (HCl: H ₂ O = 1: 5) is mainly used in wet etching of the ridge portion formed on the off-substrate as described above, whereas the present invention Then, as an etchant, a solution containing hydrogen fluoride (HF), a bromine-containing solution, or buffered hydrofluoric acid (mixed solution of NH ₄ F and HF: BHF) is used. When both side end faces of the ridge portion are etched using such an etchant, even when a semiconductor device such as a semiconductor laser is manufactured using an off-substrate, a specific crystal plane is obtained from crystallographic etching anisotropy. The tendency that the etching rate increases and the symmetry of both side end faces deteriorates is greatly improved. Therefore, wet etching can be performed in a state where the ridge end face shape after dry etching is generally maintained, and both narrowing of the ridge width and improvement of symmetry of the ridge shape can be realized simultaneously.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  In this embodiment, a solution containing a relatively high concentration of hydrofluoric acid is used as an etchant.

  FIG. 5 is a diagram for explaining a part of a manufacturing process example of a semiconductor laser having a ridge waveguide structure according to the present invention. Here, steps up to wet etching of the ridge portion are illustrated. In the following description, it is assumed that the substrate is GaAs, the cladding layer for forming the ridge stripe is AlGaInP, and the etching stopper layer is GaInP.

  First, an n-type cladding layer 102, an n-type light guide layer 103, an MQW layer 104, a p-type light guide layer 105, a p-type are formed on the main surface of a GaAs substrate 101 having an off-angle (here, an n-type substrate). The clad layer 106, the etching stopper layer 107, the p-type clad layer 108, and the p-type GaAs contact layer 109 are sequentially laminated, and the p-type contact electrode 111 covered with the dry etching mask 110 is formed on the surface of the p-type GaAs contact layer 109. (FIG. 5A). As the dry etching mask 110, a photoresist film or the like can be used in addition to an insulating film such as a silicon oxide film or a silicon nitride film.

  When the dry etching mask 110 is formed of a silicon oxide film, the mask is removed in the etching process when a hydrofluoric acid solution is used as an etchant in a wet etching process described later. There is an advantage that a removal process is not required.

Next, the region not covered with the dry etching mask 110 is dry-etched from the surface side of the p-type GaAs contact layer 109 to leave only the desired thickness of the p-type cladding layer 108 and have an end surface perpendicular to the surface of the substrate 101. Striped ridges are formed (FIG. 5B). The dry etching conditions in this case are, for example, supplied at a flow rate of chlorine (Cl ₂ ) gas of 15 sccm and argon (Ar) gas of 5 sccm, a gas pressure of 0.5 Pa, and a substrate temperature of 200 ° C.

  Further, in order to remove the damaged layer at the ridge end face introduced in the dry etching process and control the distance t from the bottom of the ridge to the top surface of the MQW layer 104, wet etching is performed using an etchant of a hydrofluoric acid solution.

  The etchant used in this example has a hydrofluoric acid concentration of 50% and an etching time of 5 minutes. This is because, in addition to the maximum value of the hydrofluoric acid concentration of a commercially available semiconductor grade hydrofluoric acid solution (aqueous solution) being 50%, if an etchant having a hydrofluoric acid concentration exceeding 50% is used, other than the end face formation of the ridge portion This is because the inconvenience in the process becomes large.

  That is, although the effect of the present invention can be obtained even if the concentration of hydrofluoric acid is increased from 50%, impurities are more easily dissolved from the chemical container as the concentration of hydrofluoric acid is increased. It is necessary to form with a high purity polyethylene or Teflon (registered trademark) material. On the other hand, since the boiling point of anhydrous hydrofluoric acid is 20 ° C., if a solution having a hydrofluoric acid concentration exceeding 50% is used, the internal pressure of the container at room temperature becomes considerably high, and high-purity polyethylene or Teflon (registered) A container formed with a trademark) cannot be used. For this reason, the hydrofluoric acid concentration is 50% in this embodiment.

  By performing such wet etching, the p-type cladding layer 108 provided on the etching stopper layer 107 is removed except for the ridge portion, and left and right symmetry is maintained while maintaining perpendicularity to the main surface of the substrate 101. A good ridge shape can be obtained (FIG. 5C). Further, the wet etching is stopped at the GaInP etching stopper layer 107, and the distance t from the bottom of the ridge to the MQW layer 4 is also strictly controlled. Even in the case of this etchant, the p-type GaAs contact layer 109 remains without being etched due to its selectivity. However, when the dry etching mask 110 is formed with a silicon oxide film, this mask is removed with hydrofluoric acid. Will be.

  FIG. 6 is a cross-sectional SEM image for explaining the ridge shape after the wet etching of this example. As shown in this SEM image, the damaged layer can be removed while maintaining the shape after dry etching by wet etching the ridge end surface of AlGaInP using a relatively high concentration hydrofluoric acid solution as an etchant. Therefore, it is possible to simultaneously realize both the narrowing of the ridge width and the improvement of the symmetry of the ridge shape, and to obtain a high light output while suppressing the occurrence of kinks in the semiconductor laser having the ridge type stripe structure.

Since the hydrogen fluoride-containing solution and the bromine-containing solution are stopped by the etching stopper layer 107 provided immediately below the p-type cladding layer 108 , the distance t from the bottom surface of the ridge portion to the top surface of the MQW layer 104 can be strictly controlled. Thus, the generation of kinks can be suppressed. Note that GaAs, AlGaAs, GaInAsP, or the like may be used as the etching stopper layer 107.

  In the present embodiment, the case where the dry etching and the wet etching are performed twice has been described. However, when the height of the ridge portion may be relatively low, the dry etching is omitted and only the wet etching is performed. It may be.

  It has been confirmed that the effect of improving the symmetry of the ridge shape can be obtained with an etchant having a hydrofluoric acid concentration of up to 4% in a hydrofluoric acid solution.

  FIG. 7 is a cross-sectional SEM image for explaining the ridge shape after wet etching the ridge end face using a 4% hydrofluoric acid solution as an etchant. When the concentration of hydrofluoric acid is low, the etching rate is lowered and wet etching is performed. Although the time required is long, the damaged layer can be removed while maintaining the shape after dry etching.

  Patent Document 3 discloses a method using hydrofluoric acid as an etchant for forming a ridge portion of a III-V group compound semiconductor. In this method, hydrofluoric acid is used as an etchant when forming a ridge in an AlGaAs or AlGaInP layer. As a result, the ridge portion has a reverse mesa shape, that is, a shape in which the area increases in the stacking direction, or the ridge portion The object is to form the side surface in a shape perpendicular to the substrate.

  However, the effect of the technique disclosed in Patent Document 3 is not realized simply by using hydrofluoric acid as an etchant, but the composition (mixed crystal ratio) of a layer (cladding layer) for forming a ridge is changed in the stacking direction. It is premised on changing to. In other words, the essence of the effect manifestation of the etching method disclosed in Patent Document 3 is that the mixed crystal ratio of the cladding layer is changed in the stacking direction, and the etching rate that changes in accordance with the mixed crystal ratio is utilized. It can be said that the shape of the end face of the part is formed. Therefore, the basis for selecting hydrofluoric acid as an etchant is that the solution can maintain the dependency of the etching rate on the mixed crystal ratio.

  The method disclosed in Patent Document 3 is effective for a ridge formed on a so-called just substrate (substrate having no off angle). On the other hand, the present invention suppresses the dependence of the etching rate on the plane orientation as much as possible in order to solve the problem that the shape of the end faces of both sides of the ridge is asymmetric because the substrate on which the ridge is formed is an off-substrate. Fluoric acid is selected as a possible etchant.

  As described above, the etching method described in Patent Document 3 is different in concept and application object from the present invention, and the present invention is directed from the (100) to the [111] direction or [1-1-1]. This is the first technique for realizing an end face perpendicular to the substrate surface by using a hydrofluoric acid solution for etching a ridge portion formed on a substrate having an off angle in the direction.

In etching the ridge portion, a solution containing bromine may be used as the etchant instead of the hydrofluoric acid solution. In this case, the mixing ratio of bromine (Br): hydrobromic acid (HBr): water (H ₂ O) is, for example, 2 cc: 34 cc: 276 cc. In the case of an etchant having this composition ratio, a ridge shape substantially equivalent to the cross-sectional SEM image shown in FIG. 6 can be obtained by etching for 25 seconds at room temperature (24 ° C.).

  In this embodiment, a buffered hydrofluoric acid solution (BHF) is used as an etchant in place of the hydrofluoric acid solution or bromine-containing solution when etching the ridge portion.

  FIG. 8 is a cross-sectional SEM image of the ridge portion etched with BHF. Also in this case, the asymmetry of both side end faces that appears when a hydrochloric acid-based etchant is used does not appear, and a ridge shape with good symmetry can be obtained. However, when BHF is used, the etching rate is extremely reduced as compared with the above two etchants. Therefore, in order to remove a damaged layer during dry etching, etching at room temperature (24 ° C.) takes about 30 minutes. Need time.

  According to the present invention, since wet etching with the ridge end face shape generally maintained after dry etching is made possible, both ridge width narrowing and ridge shape symmetry improvement can be realized simultaneously. This makes it possible to obtain a high light output while suppressing the occurrence of kinks in a semiconductor laser having a ridge-type stripe structure.

It is a figure for demonstrating the plane orientation relationship of a cubic crystal structure. It is a figure for demonstrating a part of manufacturing process example of the semiconductor laser of the conventional ridge waveguide type structure. It is a figure for demonstrating the mode of generation | occurrence | production of a kink. It is a cross-sectional SEM image for demonstrating the ridge shape after the wet etching using a chlorine-type etchant. It is a figure for demonstrating a part of manufacturing example of the semiconductor laser of the ridge waveguide type structure of this invention. It is a cross-sectional SEM image for demonstrating the ridge shape after the wet etching using a hydrofluoric acid solution. It is a cross-sectional SEM image for demonstrating the ridge shape after wet etching using the solution of hydrofluoric acid concentration 4%. It is a cross-sectional SEM image of the ridge part etched by BHF.

Explanation of symbols

1, 101 Substrate 2, 102 n-type cladding layer 3, 103 n-type light guide layer 4, 104 MQW layer 5, 105 p-type light guide layer 6, 106 p-type cladding layer 7, 107 Etching stopper layer 8, 108 p-type Cladding layer 9, 109 p-type GaAs contact layer 10, 110 Dry etching mask 11, 111 p-type contact electrode

Claims (7)

(100) an active layer provided on a compound semiconductor substrate having an off angle in a [111] direction or a [1-1-1] direction from a crystal plane, an etching stopper layer provided on the active layer, A method of manufacturing a semiconductor device having a stripe-shaped ridge portion made of AlGaInP provided in contact with an etching stopper layer,
The formation of the ridge portion includes a step of performing wet etching to expose the etching stopper layers on both sides of the ridge portion, and the wet etching is performed with an etching solution of a hydrogen fluoride-containing solution. A method of manufacturing a semiconductor device, wherein the end faces of the portions are formed symmetrically. The method of manufacturing a semiconductor device according to claim 1 , wherein the hydrogen fluoride-containing solution is a mixed solution of NH ₄ F and HF. Hydrofluoric acid concentration of the hydrogen fluoride-containing solution, a method of manufacturing a semiconductor device according to claim 1 or 2, characterized in that 50% or less at more than 4%. The extending direction of the stripe, the method of manufacturing a semiconductor device according to any one of claims 1 to 3, characterized in that the off-axis directions perpendicular to the direction of the substrate. The etching method of manufacturing a semiconductor device according to any one of claims 1 to 4, characterized in that to be applied to the ridge portion formed in advance by dry etching. The ridge portion, GaInP, GaAs, AlGaAs or any of the method of manufacturing a semiconductor device according to any one of claims 1 to 5, characterized in that provided on the etching stopper layer of GaInAsP,. The off angle of the substrate, method of manufacturing a semiconductor device according to any one of claims 1 to 6, characterized in that more than 10 degrees.

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