Method of manufacturing semiconductor device

What is provided here are: a step of forming a first semiconductor layer on a base member; a step of forming a mask on the first semiconductor layer; a step of etching the first semiconductor layer by using the mask, to thereby form a semiconductor structure; a step of forming a second semiconductor layer in a region abutting on a side surface of the semiconductor structure, said second semiconductor layer having a convex portion abutting to the mask; a convex-portion removing step of removing the convex portion by supplying an etching gas thereto; and a regrown-layer forming step of supplying a material gas onto the semiconductor structure and the second semiconductor layer, to thereby form a regrown layer; wherein the convex-portion removing step and the regrown-layer forming step are executed in a same manufacturing apparatus.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a semiconductor device.

BACKGROUND ART

When a semiconductor device is to be manufactured, partial etching using an insulative-film mask and regrowth processing are performed in many cases. For example, in the case of manufacturing a semiconductor laser having a mesa structure, using a stripe-shaped insulative-film mask, etching is applied to a semiconductor layer stacked on a substrate, to thereby form the mesa structure; semi-insulative burying layers are grown on both sides of the mesa structure; the mask is removed; and then a cladding layer and a contact layer are regrown on the mesa structure and the burying layers.

When a semiconductor laser is manufactured according to the above method, the volume of the burying layer in the vicinity of the mask becomes large due to selective growth effect, resulting in creation of a convex portion on its surface after removal of the mask. If the cladding layer and the contact layer are grown on such a surface structure having locally different heights, because of differences in growth rate between the respective plane orientations, dislocations will be propagated. As a result, pits are produced in the surface of the semiconductor laser, thus causing poor appearance, abnormal etching at a later etching step, and the like.

As a means for solving this problem, a method is known in which the cladding layer is regrown after the convex portion is removed by wet etching (for example, Patent Document 1).

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, in the case where the convex portion is removed by wet etching, because the manufacturing apparatus used in the wet etching step is different to that used in the following regrowth step of the cladding layer, the necessity arises that the thus-partially manufactured semiconductor device is exposed to the atmosphere after that wet etching. In that case, the surface cannot be kept in a clean state.

This invention has been made to solve the foregoing problem, and an object thereof is to provide a method of manufacturing a semiconductor device by which a semiconductor layer can be regrown on the surface in a clean state.

Means for Solving the Problems

A method of manufacturing a semiconductor device according to the invention comprises: a step of forming a first semiconductor layer on a base member; a step of forming a mask on the first semiconductor layer; a step of etching the first semiconductor layer by using the mask, to thereby form a semiconductor structure; a step of forming a second semiconductor layer in a region abutting on a side surface of the semiconductor structure, said second semiconductor layer having a convex portion abutting to the mask; a convex-portion removing step of removing the convex portion by supplying an etching gas thereto; and a regrown-layer forming step of supplying a material gas onto the semiconductor structure and the second semiconductor layer, to thereby form a regrown layer; wherein the convex-portion removing step and the regrown-layer forming step are executed in a same manufacturing apparatus.

Effect of the Invention

When the manufacturing method of this invention is used, since the removal of the convex portion and the following regrowth of the semiconductor layer are executed in a same manufacturing apparatus, it is possible to manufacture a semiconductor device in which a semiconductor layer has been regrown on the surface in a clean state.

MODES FOR CARRYING OUT THE INVENTION

A method of manufacturing a semiconductor laser according to Embodiment 1 will be described. InFIGS. 2 to 3for use in the description, laser light is emitted from the semiconductor laser in a direction perpendicular to the paper.

First, as shown inFIG. 2A, on an n-type InP substrate10serving as a base member, an n-type InP cladding layer12, an InGaAsP active layer14and a first p-type InP cladding layer16are epitaxially grown successively. Then, as shown inFIG. 2B, an SiO2film is deposited and photo-etching using a resist pattern is applied thereto, to thereby form a stripe-shaped SiO2mask18. Then, as shown inFIG. 2C, RIE (Reactive Ion Etching) as dry etching is applied so as to etch the portions uncovered by the SiO2mask18up to an intermediate position in the n-type InP cladding layer12, to thereby form a mesa structure20. Then, as shown inFIG. 2D, in each of regions abutting on side surfaces of the mesa structure20, a semi-insulative InP burying layer26is grown. The InP burying layer26functions as a current blocking layer. For the reason to be described later, a convex portion28is formed on a surface of each InP burying layer26in the vicinity of the SiO2mask18. Then, using hydrofluoric acid, the SiO2mask18is removed to thereby achieve a structure ofFIG. 3A.

The reason why the convex portion28is formed on the surface of the InP burying layer26is that crystal growth is promoted in the vicinity of the SiO2mask18. The material supplied onto the surface of the mask will flow on the surface of the mask to the right and left sides, to contribute the growth of the InP burying layer26in the vicinity of the mask. Accordingly, the crystal growth in the vicinity of the mask is faster than that at another area, so that the convex portion28is formed.

After the formation of the structure ofFIG. 3A, as shown inFIG. 3B, the convex portion28is removed by etching using an HCl gas. Hereinafter, this step is referred to as a convex-portion removing step.

The scheme by which the convex portion28is removed is as follows. According to the etching using an HCL gas, there is an etching-rate dependence on crystal plane orientation, so that an etching rate at (111) B plane is higher than that at (001) plane. InFIG. 4A, the convex portion28, an arrow A indicating a direction perpendicular to (001) plane and arrows B1, B2each indicating a direction perpendicular to (111) B plane, are drawn. When the etching is started from the state ofFIG. 4A, the convex portion becomes smaller with the progress of the etching as shown inFIG. 4B, so that the convex portion is finally removed as shown inFIG. 4C.

After the removal of the convex portion, under the condition that the thus-partially manufactured semiconductor laser is not taken out from the manufacturing apparatus, a second p-type InP cladding layer30is regrown thereon in such a manner that the supply of the HCl gas is stopped but a TMI (trimethyl indium) gas as a material gas is flowed, to thereby achieve a structure shown inFIG. 3C. Hereinafter, this step is referred to as a regrown-layer forming step. Further, a p-type InGaAs contact layer32is grown thereon, so that a basic crystalline structure for the semiconductor laser shown inFIG. 3Dis achieved.

InFIG. 1, the gas supply conditions are shown. In the convex-portion removing step, the removal of the convex portion is executed by the supply of the HCl gas. In the following regrown-layer forming step, the supply of the HCl gas is stopped but the TMI gas is supplied, so that the second p-type InP cladding layer30is regrown. Note that the reason that PH3(phosphine) is supplied before the removal of the convex portion and during heating-up of the inside of the manufacturing apparatus, is to prevent the element P from getting away from the InP burying layer26.

When a semiconductor laser is manufactured using the manufacturing method according to Embodiment 1, the convex-portion-removed InP burying layer26is obtained. Accordingly, the second p-type InP cladding layer30and the p-type InGaAs contact layer32can be grown flat. If the convex portion is remaining and the second p-type InP cladding layer30and the p-type InGaAs contact layer32are grown thereon, because of differences in growth rate between the respective plane orientations, dislocations will be propagated. As a result, pits are produced in the surface of the semiconductor laser, thus causing poor appearance, abnormal etching at a later etching step, and the like. In contrast, when the manufacturing method according to Embodiment 1 is used, a semiconductor laser without such troubles as described above is achieved.

Further, since the convex-portion removing step and the regrown-layer forming step are successively executed in the same manufacturing apparatus, the surfaces of the InP burying layers26and the mesa structure20, after the removal of the convex portion, are not exposed to the atmosphere. Thus, while these surfaces are kept in a clean state, the second p-type InP cladding layer30can be grown thereon.

Further, in comparison with a case where the removal of the convex portion is executed by wet etching, the number of manufacturing steps can be reduced.

A method of manufacturing a semiconductor laser according to Embodiment 2 will be described. Here, its steps similar to those in the manufacturing method according to Embodiment 1 will not be detailed, so that description will be made mainly on the difference from Embodiment 1. With respect also to an effect to be created, description will be made mainly on the difference from Embodiment 1.

Gas supply conditions in the manufacturing method according to Embodiment 2 are shown inFIG. 5. The difference from Embodiment 1 resides in that the supply of the HCl gas is continued even in the regrown-layer forming step.

In the manufacturing method according to Embodiment 2, since the HCl gas is supplied even in the regrown-layer forming step, if the convex portion could not completely be removed after the completion of the convex-portion removing step, such a convex portion will be removed in the following regrown-layer forming step.

A method of manufacturing a semiconductor laser according to Embodiment 3 will be described. Here, its steps similar to those in the manufacturing method according to Embodiment 1 will not be detailed, so that description will be made mainly on the difference from Embodiment 1. With respect also to an effect to be created, description will be made mainly on the difference from Embodiment 1.

Gas supply conditions in the manufacturing method according to Embodiment 3 are shown inFIG. 6. The difference from Embodiment 1 resides in that the TMI gas is supplied even in the convex-portion removing step. The HCl gas has a capability of etching a (001) plane surface, so that, when the HCl gas and the TMI gas are flowed concurrently, whether the (001) plane surface is actually etched or grown is determined depending on terms and conditions, such as, supply amounts of these gases, a temperature, a pressure and the like. Even if the (001) plane surface is etched, the etching rate is lower than in the case of Embodiment 1 and thus the etched amount at this surface decreases, so that the time taken for the formation of the second p-type InP cladding layer30in the following regrown-layer forming step will be reduced. On the other hand, when the (001) plane surface is grown, such a time reduction effect is enhanced.

A method of manufacturing a semiconductor laser according to Embodiment 4 will be described. Here, its steps similar to those in the manufacturing method according to Embodiment 1 will not be detailed, so that description will be made mainly on the difference from Embodiment 1. With respect also to an effect to be created, description will be made mainly on the difference from Embodiment 1.

Gas supply conditions in the manufacturing method according to Embodiment 4 are shown inFIG. 7. The difference from Embodiment 1 resides in that the TMI gas is supplied even in the convex-portion removing step and the HCl gas is supplied even in the regrown-layer forming step. InFIG. 7, although the convex-portion removing step and the regrown-layer forming step are shown as individual different steps, these steps may be regarded collectively as a single step, or may be regarded as different steps provided with a difference in condition, such as a gas flow rate or the like, between these steps.

In the manufacturing method according to Embodiment 4, using the HCl gas, the convex portion is removed in the convex-portion removing step and the regrown-layer forming step, so that an effect due to removal of the convex portion is ensured.

Further, since the TMI gas is supplied concurrently with the removal of the convex portion, the time taken for these steps can be reduced.

A method of manufacturing a semiconductor laser according to Embodiment 5 will be described. Here, its steps similar to those in the manufacturing method according to Embodiment 3 will not be detailed, so that description will be made mainly on the difference from Embodiment 3. With respect also to an effect to be created, description will be made mainly on the difference from Embodiment 3.

Gas supply conditions in the manufacturing method according to Embodiment 5 are shown inFIG. 8. The difference from Embodiment 3 resides in that the flow rate of the TMI gas in the convex-portion removing step is lower than that in the regrown-layer forming step. Besides, the flow rate of the TMI gas in the convex-portion removing step is set so that the growth rate of the (001) plane surface and the etching rate of the (001) plane surface by the HCl gas, are nearly equal to each other. This makes it possible to remove only the convex portion almost without changing the height of the (001) plane surface. Accordingly, it is possible to maximize the removal effect of impurities on the boundary face. The reason is as follows. When the etching rate is low, crystals are grown before removal of the impurities, so that the boundary face remains dirty. Contrarily, when the etching rate is high, the other supplied material or an impurity adhering to the inside of the furnace will be reacted with the HCl gas to become easier to adhere to the surface. Thus, when the height of the (001) plane surface is unchanged, the removal effect of impurities on the boundary face becomes maximum.

A method of manufacturing a semiconductor laser according to Embodiment 6 will be described. Here, its steps similar to those in the manufacturing method according to Embodiment 4 will not be detailed, so that description will be made mainly on the difference from Embodiment 4. With respect also to an effect to be created, description will be made mainly on the difference from Embodiment 4.

Gas supply conditions in the manufacturing method according to Embodiment 6 are shown inFIG. 9. The difference from Embodiment 4 resides in that the flow rate of the TMI gas in the convex-portion removing step is lower than that in the regrown-layer forming step. Besides, the flow rate of the TMI gas in the convex-portion removing step is set so that the growth rate of the (001) plane surface and the etching rate of the (001) plane surface by the HCl gas, are nearly equal to each other. This makes it possible to remove only the convex portion almost without changing the height of the (001) plane surface. Accordingly, it is possible to maximize the removal effect of impurities on the boundary face.

A method of manufacturing an EML (Electro-absorption Modulator integrated Laser-diode) according to Embodiment 7 will be described. InFIGS. 10 and 11for use in the description, laser light is emitted from the EML toward the left side of the paper. The EML is configured with: a DFB (Distributed FeedBack) portion for generating laser light; and an EA (Electro-Absorption) portion for controlling whether to emit externally or shut off the generated laser light.

First, as shown inFIG. 10A, an n-type InP cladding layer52is epitaxially grown on an n-type InP substrate50. The n-type InP substrate50with the n-type InP cladding layer52stacked thereon is referred to as a base member. Then, an InGaAsP active layer54and a first p-type InP cladding layer56are epitaxially grown successively. Then, as shown inFIG. 10B, an SiO2film is deposited and photo-etching using a resist pattern is applied thereto, to thereby form a stripe-shaped SiO2mask58. Then, as shown inFIG. 10C, RIE as dry etching is applied so as to etch the portion uncovered by the SiO2mask58up to the lower side of the InGaAsP active layer54, to thereby form a DFB structure60. Then, as shown inFIG. 10D, in a region abutting on a side surface of the DFB structure60, an InGaAsP core layer62and a second p-type InP cladding layer64are grown. The InGaAsP core layer62and the second p-type InP cladding layer64are referred collectively to as an EA structure66. On this occasion, a convex portion68is formed on a surface of the EA structure66in the vicinity of the SiO2mask58, in a manner as stated in the description of Embodiment 1. Then, using hydrofluoric acid, the SiO2mask58is removed to thereby achieve a structure ofFIG. 11A.

After the formation of the structure ofFIG. 11A, as shown inFIG. 11B, the convex portion68is removed by etching using an HCl gas. The reason why the convex portion is removed is as stated in the description of Embodiment 1.

After the removal of the convex portion, under the condition that the thus-partially manufactured EML is not taken out from the manufacturing apparatus, a p-type InGaAs contact layer72is regrown thereon in such a manner that the supply of the HCl gas is stopped but a TMI gas as a material gas is flowed, to thereby achieve a structure shown inFIG. 11C. The gas supply conditions at this time are similar to those inFIG. 1. InFIG. 11C, the right side is a DFB portion74and the left side is an EA portion76. Although a basic crystalline structure for the EML is thereafter completed through additional multiple steps, these steps are already known and thus will not be described here.

When an EML is manufactured using the manufacturing method according to Embodiment 7, the convex-portion-removed EA structure66is obtained, so that the effect stated in the description of Embodiment 1 will be achieved.

Further, the surfaces of the EA structure66and the DFB structure60, after the removal of the convex portion, are not exposed to the atmosphere, so that the effect stated in the description of Embodiment 1 will be achieved.

In the foregoing description, the DFB structure60is firstly formed and thereafter the EA structure66is formed; however, it is allowed that the EA structure is firstly formed and thereafter the DFB structure is formed. In that case, although a convex portion is formed on the surface of the DFB structure, when the convex portion is removed as described above, an effect similar to that previously described will be achieved.

Further, the gas supply methods described in relation to Embodiments 2 to 6 may each be applied to the method of manufacturing an EML according to Embodiment 7. In these cases, respective effects already described in relation to Embodiments 2 to 6 will be achieved.

It is noted that, in the description of Embodiments 1 to 7, an HCl gas is used as an etching gas; however, another halogen-based etching gas may be used. Specific examples thereof include gases of Cl2, CCl4, CBr4, CCl3Br, TBCl (Tertiarybutyl chloride) and the like.

Further, in the description of Embodiments 1 to 7, manufacturing methods of a semiconductor laser or an EML are described; however, this invention may be applied to a structure other than these devices if it is to be manufactured through execution of etching using a selection mask and regrowth processing.

DESCRIPTION OF REFERENCE NUMERALS and SIGNS