JP6164620B2 - Oxidizer - Google Patents

Description

  The present invention relates to an oxidation apparatus, and more particularly to an oxidation apparatus for producing a surface emitting laser.

  The surface emitting laser (Vertical Cavity Surface Emitting Laser: VCSEL) is an important key device in the future optoelectronic field such as optical fiber communication, high-speed optical LAN, optical disk, laser printer, optical interconnect, and the like.

In the surface emitting laser, for example, an n-type reflective film is provided on a semiconductor substrate, and an n-type spacer layer, a p-type active layer, and a p-type spacer layer are sequentially stacked thereon. A current confinement layer is provided on the p-type spacer layer, and a p-type reflective film is provided thereon. The current confinement layer is formed, for example, so that a layer formed of AlAs is oxidized from the surroundings to form Al ₂ O ₃ that does not flow current, and current flows (constricts) only in the AlAs region remaining in the center ( For example, refer nonpatent literature 1).

  Since the area of the AlAs layer left unoxidized in the current confinement layer, that is, the degree of oxidation of the current confinement layer greatly affects the performance of the surface emitting laser, high controllability is required for the oxidation of the AlAs layer. Is done. For this reason, for example, the oxidation apparatus includes a microscope, and in the process of oxidizing the AlAs layer, the oxidation amount is monitored using the microscope to control the oxidation amount (see, for example, Patent Document 1), and the substrate temperature is more accurately controlled. And the amount of oxidation has been controlled accurately (see, for example, Patent Document 2).

JP 2006-228811 A JP 2006-40943 A

Jpn. J. Appl. Phys. Vol. 39 (2000) pp. 3468-3469

  In a conventional oxidation apparatus, a substrate holder on which a wafer on which a plurality of surface emitting lasers are formed is placed on a heating stage containing a heater, and water vapor is introduced into the oxidation apparatus to oxidize the AlAs layer. However, the amount of oxidation of the AlAs layer differs between the surface emitting lasers, and the device characteristics vary. This tendency was particularly remarkable as the wafer diameter increased.

  When the cause was examined, when the wafer was heated with a heater, the wafer warped, and a portion that contacted the substrate holder and a portion that did not contact were generated, and the heat conduction from the substrate holder to the wafer varied depending on the location, and the wafer temperature varied. It was found that the amount of oxidation varies depending on the conditions. In particular, the influence of the warpage of the wafer was more noticeable as the diameter of the wafer increased.

  Further, in the conventional oxidation apparatus, the heat of the heater in the heating stage is transferred to the wafer by heat conduction in a state where the relative positional relationship between the heating stage and the wafer is fixed. I also found that the temperature fluctuated.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an oxidation apparatus that prevents variations in oxidation within a wafer depending on wafer warpage and heater shape in a thermal oxidation process.

One aspect of the present invention is an oxidation apparatus for forming a current confinement layer of a surface emitting laser,
A sealable chamber;
A supply for supplying water vapor into the chamber;
A wafer holding unit that is rotatably provided on the bottom of the chamber and holds a wafer having a front surface and a back surface;
A rotation mechanism for rotating the wafer holder;
A heating unit disposed in a non-contact manner with the wafer between the wafer holding unit and the bottom of the chamber,
The wafer holding part includes an upper surface part provided with an opening part, a side wall part that supports the upper surface part on the bottom part of the chamber, and a flange part that holds the wafer in the opening part so that the back surface of the wafer is exposed, An oxidation apparatus characterized in that a wafer is heated from the back surface by a heating unit.

According to another aspect of the present invention, there is provided a method for manufacturing a current confinement layer of a surface emitting laser using the oxidation apparatus,
Preparing a wafer having a surface formed with a mesa portion of a surface emitting laser including a conductive layer sandwiched between upper and lower semiconductor layers;
Holding the wafer in the opening of the wafer holder;
Introducing water vapor from the supply unit into the chamber;
Rotating the wafer holder using a rotation mechanism;
The heating unit is used to heat the wafer from the back side, hold the wafer at the thermal oxidation temperature, oxidize the conductive layer from the surroundings, and consist of the conductive layer left in the center and the oxidized layer formed around the conductive layer Forming a current confinement layer;
And a stop step of stopping the oxidation of the conductive layer by lowering the temperature of the wafer.

  As described above, in the oxidation apparatus according to the present invention, the temperature of the wafer during thermal oxidation can be made uniform by heating the wafer with radiant heat while rotating the wafer with respect to the heater. Uniform oxidation is possible. In particular, when used for oxidizing the current confinement element of a surface emitting laser, a surface emitting laser having uniform characteristics within the wafer can be obtained.

It is the schematic of the oxidation apparatus concerning embodiment of this invention. It is sectional drawing of the heating mechanism contained in the oxidation apparatus concerning embodiment of this invention. It is a partial top view of the wafer holding part used for the oxidation apparatus concerning embodiment of this invention. It is a fragmentary sectional view at the time of seeing FIG. 3a in an AA direction. It is an example of the surface emitting laser which formed the current confinement layer using the oxidation apparatus concerning embodiment of this invention. It is a top view of a surface emitting laser. It is a side view of a surface emitting laser. It is a top view of the wafer in which the mesa part of the surface emitting laser was formed. It is a partial top view of the other wafer holding part used for the oxidation apparatus concerning embodiment of this invention. It is a fragmentary sectional view at the time of seeing Drawing 7a in a BB direction. It is a fragmentary sectional view of the other wafer holding part used for the oxidation apparatus concerning embodiment of this invention.

  FIG. 1 is a schematic view of an oxidizer according to an embodiment of the present invention, the whole being represented by 100. The oxidizer 100 includes a chamber 12 made of, for example, stainless steel. An exhaust port 66 is provided in the chamber 12, and the exhaust port 66 is connected to a vacuum pump 86 through a valve 84. A vacuum pump 86 can be used to evacuate the interior 14 of the chamber 12.

  The bottom portion 16 of the chamber 12 is provided with a heating mechanism represented as a whole by 50. The heating mechanism 50 includes a wafer holding unit 20 that holds the wafer 10, a heating unit 40, and a cover unit 30 provided so as to cover the heating unit 40.

The inside of the cover portion 30 can be sealed, and the inside can be exhausted through the exhaust air intake port 68 or can be filled with N ₂ gas.

  A rotation mechanism 36 including a motor 32 is provided below the bottom 16 of the chamber 12. The rotation mechanism 36 is connected to the wafer holding unit 20 and rotates it. The wafer holding unit 20 rotates the wafer holding unit 20 on the bottom 16 with the central axis of the wafer 10 as a substantially rotational center.

A nozzle 62 is provided in the chamber 12. The nozzle 62 is connected to water vapor 72 and N ₂ gas via valves 70 and 76. As a result, water vapor is supplied into the chamber 12 through the nozzle 62.

Further, the chamber 12 is provided with a cooling nozzle 64 and connected to a low-temperature N ₂ gas 82 via a valve 80. Thereby, the low-temperature N ₂ gas for cooling is supplied to the inside 14 of the chamber 12 via the cooling nozzle 64.

  FIG. 2 is a cross-sectional view of the heating mechanism 50 included in the oxidation apparatus 100. The wafer holding unit 20 of the heating mechanism 50 includes a side wall part 24 and an upper surface part 22 on which the wafer 10 is placed. The side wall portion 24 is made of, for example, stainless steel, nickel alloy (trade name: Inconel), or carbon, and the upper surface portion 22 is made of a material having heat resistance such as quartz or alumina and having low thermal conductivity.

  For example, a bearing (not shown) is provided between the bottom 16 of the chamber 12 and the side wall 24 of the wafer holder 20 so that the wafer holder 20 is rotated on the bottom 16 by the rotation mechanism 36. It has become.

  A heating unit 40 and a cover unit 30 that covers the heating unit 40 are provided between the wafer holding unit 20 and the bottom 16 of the chamber 12. The heating unit 40 has a structure in which a heating plate 42 in which a heater 44 is embedded is supported on the bottom 16 by support legs 46. For example, a sheath heater (nichrome wire) is used for the heater 44, and a metal having high thermal conductivity such as copper is used for the heating plate 42. Instead of such an embedded heater, a heater made of carbon, metal, or the like may be used in an exposed state.

  The cover portion 30 is made of, for example, quartz, and is sealed between the bottom portion 16 of the chamber 12 and can be sealed. Radiant heat emitted from the heating unit 40 passes through the cover unit 30 and heats the wafer 10 from the back surface. A reflector that reflects heat released downward from the heating unit 40 may be provided between the heating unit 40 and the bottom 16.

As described above, the inside of the cover 30 can be evacuated through the exhaust air inlet 68 or can be filled with N ₂ gas. Thereby, even when water vapor is introduced into the interior 14 of the chamber 12, the heating unit 40 does not come into contact with the water vapor, so that deterioration of the heater 44 due to oxidation can be prevented. The cover 30 may be omitted if it is an oxidation resistant heater such as an embedded heater.

  3A is a partial top view of the wafer holding unit 20, and FIG. 3B is a partial cross-sectional view of FIG. 3A when viewed in the AA direction.

  The upper surface portion 22 of the wafer holding unit 20 has an opening 22a. The opening 22a is slightly larger than the wafer 10 to be oxidized, and a flange 22b protruding inward is provided on the side surface below the opening 22a. The wafer 10 is supported in the opening 22a while being supported around the back surface by the flange 22b. In FIG. 3b, the flange portion 22b is a projection provided in an annular shape around the opening 22a, but may be partially provided as long as the wafer 10 can be supported.

  FIG. 4 is an example of a surface emitting laser in which a current confinement layer is oxidized using the oxidation apparatus 100 according to the embodiment of the present invention. The surface emitting laser has an n-type reflective film (Distributed Bragg Reflector: DBR) on a substrate such as GaAs. The n-type reflective film has, for example, an AlGaAs / GaAs superlattice structure.

  An n-type spacer layer, an active layer, and a p-type spacer layer are sequentially stacked on the n-type reflective film. The n-type and p-type spacer layers are made of, for example, AlGaAs, and the active layer is made of, for example, a quantum well structure of GaAs / InGaAs / GaAs.

A current confinement layer is provided on the p-type spacer layer. The current confinement layer is made of, for example, an AlAs layer that is oxidized to form an Al _x O _y (typically Al ₂ O ₃ ) layer.

  A p-type reflective film is provided on the current confinement layer. The p-type reflective film has, for example, an AlGaAs / GaAs superlattice structure, similar to the n-type reflective film.

  An n electrode and a p electrode are formed below the GaAs substrate and above the p-type reflective film, respectively. The n electrode is made of, for example, AuGe / Au, and the p electrode is made of, for example, Au / Zn / Au. As can be seen from FIG. 4, the portion above the n-type reflective film has a mesa structure.

  In the surface emitting laser, when a current is passed between the n electrode and the p electrode, the current passes (is narrowed) only in the AlAs region of the current confinement layer. As a result, since current flows only in a part of the active layer, it is possible to control the oscillation of the transverse mode and reduce the threshold current. The light emitted from the active layer laser oscillates between the p-type reflection film and the n-type reflection film, and finally exits from the upper part as a light output.

FIG. 5a is a top view of the surface emitting laser 10a, but the portion above the current confinement layer is omitted for easy understanding. The dimensions of the semiconductor laser are, for example, in FIG. 5A, d ₁ is 100 μm, d ₂ is 30 μm, d ₃ is 10 μm, d ₄ is 10 μm, and the AlAs layer is oxidized from the surroundings to form an Al _x O _y layer. In addition, it is necessary to control the oxidation amount with high accuracy. As shown in the side view of FIG. 5b, the oxidation of the AlAs layer proceeds in the horizontal direction (arrow direction in FIG. 5b) from the side surface of the AlAs layer exposed in the water vapor atmosphere.

FIG. 6 is a top view of the GaAs (100) wafer 10 on which 25 (5 × 5) surface emitting lasers 10a are formed. In the surface emitting laser manufacturing process, each layer from the p-type reflective film to the n-type reflective film is deposited on the GaAs substrate by using, for example, a CVD method, and then each layer is etched to the GaAs substrate by etching using a mask. To a mesa structure (FIG. 5b). In this state, the wafer is put in the oxidizer 100, the AlAs layer is oxidized from the lateral direction to form an Al _x O _y layer around it, and a current confinement layer is formed.

As shown in FIG. 6, since the AlAs layers of the plurality of surface emitting lasers 10a formed on the wafer 10 are oxidized at the same time, and the oxidation depth (distance d ₄ shown in FIG. 5) is also as thin as about 10 μm, In order to obtain the surface emitting laser 10a having uniform characteristics, it is necessary to uniformly oxidize the AlAs layer within the surface of the wafer 10. In the top view of FIG. 6, the surface emitting laser 10a is square, but may be other shapes such as a circle.

  In the oxidation apparatus 100 according to the embodiment of the present invention, the wafer 10 is heated by radiant heat from the heater 44 of the heating unit 40. For this reason, even if the wafer 10 becomes hot and warps, the temperature distribution of the wafer 10 is not affected. That is, as in the conventional method, when a wafer holder is placed on a heating stage and the wafer is heated using heat conduction from the heating stage, if the wafer is warped by heat, the heat conduction However, since the temperature distribution in the wafer becomes non-uniform, the oxidation apparatus 100 heats the wafer not by heat conduction but by radiation, so that variations in wafer temperature caused by warpage of the wafer can be prevented.

  Further, in the oxidation apparatus 100 according to the embodiment of the present invention, the wafer holding unit 20 rotates, and the wafer 10 changes while the relative position of the wafer 10 changes with respect to the heater 44 of the heating unit 40 (while the wafer 10 rotates). Is heated. For this reason, variation in temperature within the wafer surface depending on the arrangement of the heaters 44 can be prevented.

  As a result, the amount of oxidation in the surface of the wafer 10 becomes uniform, there is no variation in the characteristics of the surface emitting laser in the wafer, and the yield of the manufacturing process is greatly improved.

  The thermal oxidation conditions in the oxidation process can be arbitrarily set according to the size of the surface emitting laser and the degree of thermal oxidation. The thermal oxidation temperature is preferably set, for example, between 400 ° C and 500 ° C.

  Further, for example, an observation window may be provided in the ceiling portion of the oxidation apparatus 100, and the wafer 10 inside the chamber 12 may be observed using a microscope or the like to adjust the oxidation amount.

  FIG. 7A is a partial top view of another wafer holding unit 120 used in the oxidation apparatus 100 according to the embodiment of the present invention, and FIG. 7B is a partial cross-sectional view when FIG. 7A is viewed in the BB direction. It is. 7A and 7B, the same reference numerals as those in FIGS. 3A and 3B indicate the same or corresponding portions.

  In the wafer holding unit 120, a cylindrical spacer 26 is provided on the flange 22b provided in the opening 22a, and the wafer 10 is placed thereon. The spacer 26 is made of, for example, quartz.

  By providing a plurality of cylindrical spacers 26 in this way, the contact area between the wafer holding unit 120 and the wafer 10 can be reduced, heat transfer from the wafer 10 to the wafer holding unit 120 due to heat conduction can be reduced, The temperature in the wafer 10 can be made more uniform.

  In FIG. 7a, the spacers 26 are provided at three locations, but the number of the spacers 26 is not limited to this. Further, in FIG. 7a, the spacer 26 is provided on the collar portion 22b provided in an annular shape around the opening 22a. However, the collar portion 22b may be partially provided and the spacer 26 may be provided thereon. Absent.

  FIG. 8 is a partial cross-sectional view of another wafer holding unit 220 used in the oxidation apparatus 100 according to the embodiment of the present invention. In FIG. 8, the same reference numerals as those in FIGS. 3a and 3b indicate the same or corresponding portions.

  In the wafer holding part 220, an annular spacer 28 is provided on the flange part 22b provided in the opening part 22a, and the wafer 10 is placed thereon. The spacer 28 is made of, for example, quartz.

  By providing the annular spacer 28 in this manner, the contact area between the wafer holding unit 220 and the wafer 10 can be reduced, heat transfer from the wafer 10 to the wafer holding unit 220 due to heat conduction can be reduced, and the wafer 10 can be reduced. The temperature inside can be made more uniform.

  In the embodiment of the present invention, the oxidation of the AlAs layer of the current confinement layer of the surface emitting laser has been described. However, the oxidation apparatus 100 can be applied to other thermal oxidation processes such as a surface oxide film to achieve more uniform oxidation. A membrane can be obtained.

10 wafer 12 chamber 14 inside 16 bottom 20 wafer holder 30 cover portion 32 motor 36 rotary mechanism 40 heating unit 62 nozzle 64 cooling nozzle 66 exhaust port 68 exhaust air inlet 72 steam 78 N ₂ gas 82 cold _{N 2} gas 86 vacuum pump 94 N ₂ gas 96 vacuum pump 100 oxidizer

Claims (6)

An oxidation apparatus for forming a current confinement layer of a surface emitting laser,
A sealable chamber;
A supply section for supplying water vapor into the chamber;
A wafer holding unit which is rotatably provided on the bottom of the chamber and holds a wafer having a front surface and a back surface;
A rotation mechanism for rotating the wafer holder;
A heating unit disposed in a non-contact manner with the wafer between the wafer holding unit and the bottom of the chamber;
The wafer holding unit holds the wafer in the opening so that an upper surface provided with an opening, a side wall for supporting the upper surface on the bottom of the chamber, and a back surface of the wafer are exposed. Including the buttocks ,
The oxidation apparatus characterized in that the wafer is heated from the back surface by the heating unit while the wafer holding unit rotates relative to the heating unit.   The oxidation apparatus according to claim 1, wherein the heating unit is covered with a sealable cover provided between the heating unit and the wafer holding unit.   3. The oxidation apparatus according to claim 1, wherein the flange is an annular protrusion provided along a side surface of the opening and extending inward from the side surface. 4.   The oxidizer according to any one of claims 1 to 3, wherein a plurality of spacers in contact with the back surface of the wafer are provided on the flange.   The oxidizer according to any one of claims 1 to 3, wherein an annular spacer that contacts the back surface of the wafer is provided on the flange. An oxidation apparatus for forming a current confinement layer of a surface emitting laser,
A sealable chamber;
A supply section for supplying water vapor into the chamber;
A wafer holding unit which is rotatably provided on the bottom of the chamber and holds a wafer having a front surface and a back surface;
A rotation mechanism for rotating the wafer holder;
A heating unit disposed in a non-contact manner with the wafer between the wafer holding unit and the bottom of the chamber;
The wafer holding unit holds the wafer in the opening so that an upper surface provided with an opening, a side wall for supporting the upper surface on the bottom of the chamber, and a back surface of the wafer are exposed. Including the buttocks,
The wafer holder is heated from the back surface by the heating unit while rotating relative to the heating unit,
The heating unit is covered with a sealable cover unit provided between the heating unit and the wafer holding unit,
A spacer that contacts the back surface of the wafer is provided on the flange,
At least one of the upper surface portion of the wafer holding portion, the cover portion, and the spacer is made of quartz.

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