JP2009049201A - Manufacturing method of semiconductor laser device - Google Patents

Abstract

A method of manufacturing a semiconductor laser device capable of sufficiently removing an oxide film on the surface of a mesa and improving laser characteristics and reliability.
A p-type InP cladding layer, an AlGaInAs lower optical confinement layer, an AlGaInAs-MQW active layer, an n-type AlGaInAs upper optical confinement layer, and an n-type InP clad layer are formed on a p-type InP substrate. A semiconductor multilayer structure is formed. Next, wet etching is performed using the SiO ₂ film as a mask to form a mesa in the semiconductor stacked structure. Next, the surface of the mesa is cleaned using hydrogen plasma. Next, a p-type InP buried layer 17 is formed so as to cover the surface of the mesa. Then, an n-type InP current blocking layer 18, a p-type InP buried layer 19 and an n-type InP buried layer 20 are formed on the p-type InP buried layer 17 to bury the periphery of the mesa.
[Selection] Figure 7

Description

  The present invention relates to a method of manufacturing a semiconductor laser device in which a mesa is formed by etching a semiconductor laminated structure having an active layer made of a semiconductor material containing Al, and the periphery of the mesa is buried with a buried layer, and in particular, oxidation of the surface of the mesa The present invention relates to a method of manufacturing a semiconductor laser device that can sufficiently remove a film and improve laser characteristics and reliability.

  In the semiconductor laser device, it is necessary to narrow the current path in order to efficiently supply current to the active layer. Therefore, in many semiconductor lasers, a semiconductor stacked structure having an active layer is formed, and then a mesa is formed using a fine pattern transfer technique and an etching technique to a dielectric film, thereby limiting the current flowing region. The path is narrowed. At this time, an embedded structure in which the periphery of the mesa is covered with a semiconductor is formed from the viewpoint of protection of the active layer exposed on the surface of the mesa, heat dissipation, parasitic capacitance of the element, and the like (for example, see Patent Document 1). ).

  FIG. 13 is a cross-sectional view showing a semiconductor laser device in which the periphery of a mesa having a semiconductor laminated structure having an active layer is buried with an n / p / n / p type semiconductor layer. On the p-type InP substrate 11, a p-type InP cladding layer 12, an AlGaInAs lower optical confinement layer 13, an AlGaInAs-MQW active layer 14, an n-type AlGaInAs optical confinement layer 15, and an n-type InP clad layer 16 are grown in order. A mesa having a laminated semiconductor structure is formed. Then, the periphery of the mesa is buried by a p-type InP buried layer 17, n-type InP current blocking layer 18, p-type InP burying layer 19, and n-type InP burying layer 20. On top of this, an n-type InP contact layer 21, an n-type InGaAs contact layer 22, and an n-type InP cap layer 23 are formed.

  Here, the surface of the mesa needs to be covered with the p-type InP buried layer 17. This is because when the n-type InP current blocking layer 18 is in contact with the mesa, a current flows from the mesa to the buried layer, and the current cannot be confined in the active layer 14.

JP 05-136526 A

  The active layer 14 made of a semiconductor material containing Al is exposed to the atmosphere on the surface of the mesa and the surface is oxidized. Since In atoms migrate on such an oxide layer, the p-type InP buried layer 17 is hardly epitaxially grown. Therefore, the growth starts to cover the active layer 14 after the semiconductor layer below the active layer 14 is completely buried.

  For this reason, as shown in FIG. 14, the n-type InP current blocking layer 18 is in contact with the mesa, and the reactive current path 24 through which current flows from the mesa to the buried layer is formed. In addition, oxygen and impurities at the interface also cause crystal defects. As a result, there is a problem that characteristics and reliability deteriorate.

  When a semiconductor laminated structure having an active layer made of a semiconductor material containing Al as described above is etched to form a mesa and the periphery of this mesa is filled with a buried layer, the level allowed for general regrowth is exceeded. It is also necessary to reduce the oxide layer on the surface of the mesa.

  There are a method of removing the oxide layer on the surface of the mesa with HCl gas before the burying growth, and a method of enhancing the effect of removing the oxide film by setting the temperature during etching with the HCl gas to 450 ° C. or lower. However, these methods alone could not sufficiently remove the oxide film on the surface of the mesa.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to sufficiently remove an oxide film on the surface of the mesa to improve laser characteristics and reliability. The manufacturing method is obtained.

  The method of manufacturing a semiconductor laser device according to the present invention, on a substrate, forming a semiconductor multilayer structure having an active layer comprising a semiconductor material containing Al, and forming a mesa by etching a semiconductor laminated structure, comprising a step of cleaning the surface of the mesa by using a hydrogen plasma, and forming a buried layer so as to cover the surface of the mesa after the surface of the mesa is cleaned. Other features of the present invention will become apparent below.

  According to the present invention, it is possible to sufficiently remove the oxide film on the surface of the mesa and improve the laser characteristics and reliability.

Embodiment 1 FIG.
A method for manufacturing a semiconductor laser device according to the first embodiment of the present invention will be described below with reference to the flowchart of FIG.

First, as shown in FIG. 2, on a p-type InP substrate 11, a p-type InP cladding layer 12, an AlGaInAs lower light confinement layer 13, an AlGaInAs-MQW active layer 14, an n-type AlGaInAs upper light confinement layer 15, n -type InP cladding layer 16, is grown sequentially by using a MOVPE (Metalorganic Vapor Phase Epitaxy), a semiconductor material containing _{Al Al x Ga y in 1-} x-y As (0 <x <1,0 <y < A semiconductor multilayer structure having an active layer of 1) is formed (step S1).

Next, the wafer is taken out from the MOVPE apparatus, and as shown in FIG. 3, a SiO ₂ film is formed on the wafer, and a SiO ₂ mask 25 is produced using photolithography and transfer technology. Then, wet etching is performed using this as a mask to form a mesa in the semiconductor multilayer structure as shown in FIG. 4 (step S2). Moreover, in order to remove the organic substance and oxide which remain | survive on the surface of a mesa, the process by a solution is performed (step S3).

Next, the mesa-formed wafer is placed in the MOVPE apparatus again, and the mesa is embedded and grown. However, in wet etching, solution processing, and wafer transfer, the mesa surface is exposed to the atmosphere and oxidized. The Therefore, hydrogen plasma is introduced into the apparatus before the burying growth, and the surface of the mesa is cleaned using this hydrogen plasma (step S4). Note that an additional surface treatment may be performed using a gas having an etching effect such as HCl, TBCl, or CCl ₄ .

  Here, a MOVPE apparatus having a hydrogen plasma generation mechanism is used to perform the hydrogen plasma treatment. Thereby, after performing a hydrogen plasma process, the crystal growth by MOVPE can be performed, without exposing to air | atmosphere.

  FIG. 5 is a cross-sectional view showing an example of an MOVPE apparatus having a hydrogen plasma generation mechanism. A susceptor 33 on which a wafer 32 is mounted is provided in the MOVPE reaction furnace 31. The MOVPE reactor 31 is integrated with an ECR (electron cyclotron resonance) plasma generation mechanism 34. The ECR plasma generation mechanism 34 introduces microwaves into the MOVPE reactor 31 to generate hydrogen plasma.

  FIG. 6 is a cross-sectional view showing another example of an MOVPE apparatus having a hydrogen plasma generation mechanism. An antenna 35 is inserted in the MOVPE reactor 31. An RF current flows from the RF power source 36 to the antenna 35. Thereby, ICP (Inductively Coupled Plasma) plasma is generated in the MOVPE reactor 31.

  Next, as shown in FIG. 7, a p-type InP buried layer 17 is formed by MOVPE so as to cover the surface of the mesa. Then, an n-type InP current blocking layer 18, a p-type InP buried layer 19, and an n-type InP buried layer 20 are formed by MOVPE on the p-type InP buried layer 17, and the periphery of the mesa is buried (step S5). . Thereby, an FSBH (Facet Selected Buried Hetero-structure) structure is formed.

  Next, as shown in FIG. 8, the wafer is taken out of the MOVPE apparatus, and the mask 25 is removed by etching. Thereafter, the wafer is again placed in the MOVPE apparatus, and an n-type InP contact layer 21, an n-type InGaAs contact layer 22, and an n-type InP cap layer 23 are formed. Through the above manufacturing process, a semiconductor laser device having an n / p / n / p buried structure is manufactured.

  As described above, in this embodiment, the surface of the mesa is cleaned using hydrogen plasma. Since hydrogen plasma has a strong reducing action and physical etching action, the oxide film on the surface of the mesa can be sufficiently removed.

  Further, the crystal plane orientation exposed on the surface of the mesa is not the (100) plane, and the (100) plane is different because the atomic arrangement on the outermost surface and the strength of bonding with oxygen are different from the (100) plane. It is considered that the removal effect of the oxide film is different as compared with the surface cleaning. On the other hand, the oxide film on the surface of the mesa can be sufficiently removed by performing the above-described cleaning.

  Therefore, since the n-type InP current blocking layer 18 can be grown without contacting the mesa, it is possible to prevent the formation of a reactive current path through which current flows from the mesa to the buried layer. Further, impurities at the interface between the mesa and the buried layer are reduced, and the crystallinity of the buried layer can be improved. Therefore, laser characteristics and reliability can be improved.

  The present invention is not limited to n / p / n / p type buried growth, but can be applied to all kinds of buried growth. Further, the present invention can be applied to embedded growth of a mesa having a semiconductor stacked structure composed of any semiconductor material such as InP, AlGaInAs, InGaAs, InGaAsP, AlInAs, AlGaAs, GaAs, AlGaInP, InGaP, AlGaN, GaN, and InGaN. . Further, the present invention can be applied not only to semiconductor lasers but also to the production of all semiconductor elements such as modulators and light receiving elements.

Embodiment 2. FIG.
In the present embodiment, after performing the hydrogen plasma treatment, as shown in FIG. 9, the p-type InP first buried layer 17a (first buried layer) is grown at a growth temperature Tg_p1 (the first buried layer) so as to cover the surface of the mesa. 1 growth temperature). Next, on the p-type InP first buried layer 17a, a p-type InP second buried layer 17b, an n-type InP current blocking layer 18, a p-type InP buried layer 19 and an n-type InP buried layer 20 (first 2 buried layers) is formed at the growth temperature Tg_p2 (second growth temperature) to embed the periphery of the mesa. Other steps are the same as those in the first embodiment.

  Here, FIG. 10 is a diagram schematically showing the growth temperature at the time of buried growth and the time transition of growth of each layer in the second embodiment. As illustrated, the growth temperature Tg_p1 of the p-type InP first buried layer 17a is lower than the growth temperature Tg_p2 of the p-type InP second buried layer 17b (Tg_p1 <Tg_p2). Further, the growth temperature of the layers other than the p-type InP first buried layer 17a is preferably 600 to 630 ° C. which is optimal for InP growth by the MOVPE method in terms of crystal quality.

  Since the growth temperature Tg_p1 of the p-type InP first buried layer 17a in contact with the mesa is thus low, the migration of the growth species on the surface of the mesa is suppressed, and the mesa surface is the p-type InP first buried layer 17a. Covered. As a result, the n-type InP current blocking layer 18 can be grown without contacting the mesa, thereby preventing the generation of a reactive current path.

  Although the p-type InP buried layer is divided into the p-type InP first buried layer 17a and the p-type InP second buried layer 17b in the first embodiment, it may be divided into n. At this time, the growth temperature Tg_p1 of the p-type InP buried first layer is lower than the growth temperature Tg_pm of the p-type InP buried mth layer (1 <m <= n).

  In the first embodiment, the growth is interrupted between the p-type InP first buried layer 17a and the p-type InP second buried layer 17b, and the growth temperature of the buried growth is gradually changed from Tg_p1 to Tg_p2. Although the growth is performed, the growth temperature is continuously increased from Tg_p1 to Tg_p2 while performing the growth from the p-type InP first buried layer 17a to the p-type InP second buried layer 17b without performing the growth interruption. May be.

  Further, the growth temperature optimum for the growth of the semiconductor material is 600 to 630 ° C. for InP, InGaAsP and InGaAs, 600 to 750 ° C. for AlGaInAs and AlInAs, 650 to 750 ° C. for AlGaAs, GaAs, AlGaInP and InGaP, AlGaN, GaN is 1000 to 1100 ° C, and InGaN is 700 to 800 ° C. When these materials are used as the buried layer, it is desirable that the first buried layer has a temperature lower than the optimum growth temperature.

Embodiment 3 FIG.
In the present embodiment, in the step of cleaning the surface of the mesa, the second surface is cleaned after the surface of the mesa is cleaned using hydrogen plasma at the first surface cleaning temperature Tcl_1 (first cleaning step). The surface of the mesa is cleaned using hydrogen plasma at the cleaning temperature Tcl_2 (second cleaning step). Other steps are the same as those in the first embodiment.

  FIG. 11 is a diagram schematically showing the growth temperature at the time of burying growth and the time transition of the growth of each layer in the third embodiment of the present invention. As illustrated, the first surface cleaning temperature Tcl_1 is lower than Tc, and the second surface cleaning temperature Tcl_2 is higher than Tc. However, Tc is a critical temperature at which the oxide layer on the side surface of the mesa changes to a strong one. By performing the cleaning at a temperature lower than Tc in this way, the bond with O is cut, and then the cleaning is performed at a temperature higher than Tc, thereby increasing the vapor pressure of Cl compound and O compound remaining on the surface. The effect of removing the oxide layer is increased.

  FIG. 12 shows XPS analysis results showing changes in the bonding state between O and Al when AlInAs is heated to various temperatures. At a temperature lower than 450 ° C., O is a hydroxyl group, and at a temperature higher than 560 ° C., only O is bonded to Al and forms a stronger bond. From this, it can be seen that the Tc is about 450 ° C.

  In the third embodiment, the surface cleaning at Tc or higher is performed once after the surface cleaning at Tc or lower. However, this may be performed at three or more temperatures. Further, the supply of hydrogen plasma is interrupted when the temperature is changed, but the temperature may be changed without interrupting the gas supply.

  In addition, if the material of the active layer is different, the temperature Tc at which the bond with O is strengthened is different, and the Cl and O compounds remaining on the surface are also different, so the optimum cleaning temperature is selected depending on the semiconductor material constituting the device There is a need to.

2 is a flowchart of a method for manufacturing the semiconductor laser element according to the first embodiment of the present invention. It is sectional drawing for demonstrating the manufacturing method of the semiconductor laser element which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the semiconductor laser element which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the semiconductor laser element which concerns on Embodiment 1 of this invention. It is sectional drawing which shows an example of the MOVPE apparatus with a hydrogen plasma generation mechanism. It is sectional drawing which shows the other example of the MOVPE apparatus with a hydrogen plasma generation mechanism. An antenna 35 is inserted in the MOVPE reactor 31. It is sectional drawing for demonstrating the manufacturing method of the semiconductor laser element which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the semiconductor laser element which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the semiconductor laser element concerning Embodiment 2 of this invention. It is the figure which showed typically the growth time at the time of the embedding growth in Embodiment 2 of this invention, and the time transition of the growth of each layer. It is the figure which showed typically the growth time at the time of the embedding growth in Embodiment 3 of this invention, and the time transition of the growth of each layer. It is an XPS analysis result which shows the change of the bonding state of O and Al when AlInAs is heated to each temperature. It is sectional drawing which shows the semiconductor laser element which embed | buried the circumference | surroundings of the mesa of the semiconductor laminated structure with an active layer with the embedding layer which consists of a n / p / n / p type semiconductor. It is sectional drawing which shows the conventional semiconductor laser element in which the reactive current path | route into which an electric current flows from a mesa to a buried layer was formed.

Explanation of symbols

11 p-type InP substrate (substrate)
12 p-type InP cladding layer (semiconductor laminated structure)
13 AlGaInAs lower light confinement layer (semiconductor laminated structure)
14 AlGaInAs-MQW active layer (semiconductor laminated structure)
15 n-type AlGaInAs optical confinement layer (semiconductor laminated structure)
16 n-type InP cladding layer (semiconductor laminated structure)
17 p-type InP buried layer (buried layer)
17a p-type InP first buried layer (first buried layer)
17b p-type InP second buried layer (second buried layer)
18 n-type InP current blocking layer (buried layer) (second buried layer)
19 p-type InP buried layer (buried layer) (second buried layer)
20 n-type InP buried layer (buried layer) (second buried layer)

Claims (4)

Forming a semiconductor multilayer structure having an active layer made of a semiconductor material containing Al on a substrate;
Etching the semiconductor multilayer structure to form a mesa;
Cleaning the surface of the mesa with hydrogen plasma;
And a step of forming a buried layer so as to cover the surface of the mesa after cleaning the surface of the mesa.   2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the buried layer is formed by a MOVPE method. The step of forming the buried layer includes
Forming a first buried layer at a first growth temperature so as to cover the surface of the mesa;
Forming a second buried layer on the first buried layer at a second growth temperature higher than the first growth temperature and embedding the periphery of the mesa. A method for producing a semiconductor laser device according to 1 or 2. The step of cleaning the surface of the mesa
A first cleaning step of cleaning the side surface of the mesa using the hydrogen plasma at a temperature lower than a critical temperature at which the oxide layer on the side surface of the mesa changes to a solid one;
The second cleaning step of cleaning the side surface of the mesa using the hydrogen plasma at a temperature higher than the critical temperature after the first cleaning step. The method for manufacturing a semiconductor laser device according to any one of the above.

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